RxPG News : Tuberculosis

PA-824 : Promising new drug for TB

Sat, 29 Nov 2008 03:43:17 PST

( from http://www.rxpgnews.com ) An international team of biochemists has discovered how an experimental drug unleashes its destructive force inside the bacteria that cause tuberculosis (TB). The finding could help scientists develop ways to treat dormant TB infections, and suggests a strategy for drug development against other bacteria as well.

A report describing the research, led by Clifton E. Barry, III, Ph.D., of the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, is published in the Nov. 28 issue of Science. Dr. Barry's collaborators included scientists from NIAID and from the Novartis Institute for Tropical Diseases in Singapore.

One-third of the world's population is infected with Mycobacterium tuberculosis (M. tb), the bacteria that cause TB. "Currently, there are no drugs available that specifically target latent tuberculosis infections in which bacteria are present but are not actively dividing," notes NIAID Director Anthony S. Fauci, M.D. "Dr. Barry and his colleagues have now given us a detailed picture of how the candidate TB drug PA-824 is metabolized inside Mycobacterium tuberculosis. Their discovery is a promising step towards developing effective drugs against latent TB as well as other bacteria."

Previously, Dr. Barry and his collaborators found that M. tb mutants lacking a specific bacterial enzyme were resistant to PA-824, but at that time, they did not know the function of the enzyme.

"It took several years, but at last we were able to recreate in the test tube what happens inside mycobacterial cells when the bacterial enzyme, which we named Ddn, and a second bacterial component called a cofactor, interact with PA-824," says Dr. Barry. The key event in PA-824 metabolism, they found, is the production of nitric oxide (NO) gas. "This highly reactive molecule," he adds, "is akin to a bomb blast that kills the bacteria from within."

NO gas is produced naturally by certain immune system cells after they engulf M. tb or other bacteria. This is one way that people with healthy immune systems can contain M. tb infection. However, this natural immune response is not always enough to completely rid the body of TB bacteria. In essence, PA-824 performs similarly to the NO-producing immune cells--but the drug's effect is more specific and triggered only after it enters the bacteria.

The non-dividing M. tb bacteria characteristic of latent TB infections are walled off by immune cells that aggregate around the bacteria to form a body called a granuloma. Oxygen levels are low inside granulomas. In their latest research, the scientists observed that NO-generation during PA-824 metabolism is greatest when oxygen levels are low. This observation suggests how PA-824 may work against non-dividing M. tb.

PA-824 was originally designed to work best under aerobic, or oxygenated, conditions. With this new understanding of how the bacterial enzyme and cofactor act on PA-824 under low-oxygen conditions, Dr. Barry says, scientists can design drugs with a chemical structure similar to PA-824 but optimize them from the start to behave best under low-oxygen conditions. This work is already proceeding in the laboratory at NIAID and in partnership with collaborators from the Novartis Institute for Tropical Diseases in Singapore as well as with scientists from the Genomics Institute of the Novartis Research Foundation in San Diego.

Because humans have neither the bacterial cofactor nor any enzymes equivalent to Ddn, PA-824 has no effect on human cells. Conversely, many bacteria have enzymes in the same family as Ddn. Thus, says Dr. Barry, it is possible to envision new kinds of NO-generating drugs designed to interact with enzymes associated with other disease-causing bacteria as well.

Drug resistent TB deadlier, more common than suspected

Tue, 11 Nov 2008 13:59:29 PST

( from http://www.rxpgnews.com ) Washington, Nov 6 - 'Exclusively drug-resistant tuberculosis' or XDR-TB is a menacing public health problem that is even deadlier and more common than suspected.

XDR-TB patients are four times as likely to fail treatment and three times more likely to die than patients with other forms of multi-drug-resistant tuberculosis -, according to a recent study.

Researchers directly compared XDR-TB patients with those having MDR-TB to determine the differences in treatment outcomes and long-term survival rates.

Researchers also found that MDR-TB was 'a major threat to public health,' representing 2.7 percent of new TB cases in South Korea in 2004, up from 1.6 percent in 1994.

Since its public appearance in 2006, XDR-TB rekindled an urgent interest in preventing, fighting and containing TB. But little was known about how this variant changed the face of combating TB on all fronts.

'Treatment outcomes [of XDR-TB] have varied among studies, and data on long-term survival are still scarce,' wrote Tae Sun Shim, an associate professor at Asan Medical Centre, Seoul, South Korea, and a principal investigator of the study.

This 'is the largest report that we know of that compares patients with XDR-TB with other patients with MDR-TB to determine the impact of XDR-TB on treatment outcomes and long-term survival in mostly HIV-negative patients with MDR-TB.'

The study reviewed the medical records of more than 1,400 patients in South Korea with MDR-TB - from all national hospitals, Korean National TB Association chest clinics and select university hospitals.

Researchers found that patients with XDR-TB were significantly older than MDR-TB patients, were more likely to have a history of treatment with second-line TB drugs, and more likely to have a history of being treated for TB two or more times.

Perhaps the biggest public health threat associated with XDR-TB, however, is not its virulence, but the lack of information and treatment options that medical authorities have on which to draw, according to a release of the American Thoracic Society.

The collective dearth of knowledge was likened by Giovanni Battista Migliori, Morgan Richardson and Christopher Lange, co-authors of the accompanying editorial, to the proverbial blind men trying to describe an elephant - too big a task to accomplish with too little information.

The results were published in a November issue of the American Journal of Respiratory and Critical Care Medicine.

Diabetes mellitus increases risk of TB

Tue, 15 Jul 2008 01:02:07 PST

( from http://www.rxpgnews.com ) People with diabetes mellitus are at increased risk of developing active tuberculosis (TB), according to an analysis published in PLoS Medicine.

Searching for research over the past four decades containing data on the relationship between diabetes and TB, Christie Jeon and Megan Murray of the Harvard School of Public Health identified 13 studies involving more than 1.7 million participants, including 17,698 cases of TB. Combining the data from cohort studies in particular, the researchers calculated that diabetes increases the risk of active TB by about a factor of three.

A three-fold increased risk suggests that diabetes may already be responsible for more than 10% of TB cases in India and China. If these findings are replicated in other countries, global TB control might benefit from special attention to people with diabetes when identifying and treating latent TB. Increased efforts to diagnose and treat diabetes might also decrease the global burden of TB, which kills about 1.6 million people each year.

XDR TB in South Africa traced to lack of drug susceptibility testing

Mon, 22 Oct 2007 03:59:37 PST

( from http://www.rxpgnews.com ) In South Africa, the 2001 implementation of the World Health Organization�s anti-tuberculosis program may have inadvertently helped to create a new strain of extensively drug-resistant tuberculosis (XDR TB). In a new study published in the December 1 issue of Clinical Infectious Diseases, currently available online, researchers tracked the developing drug resistance of one particular strain of Mycobacterium tuberculosis over 12 years. They found that at the time of the 2001 adoption of the DOT+ strategy for multi-drug resistant strains, the strain was already resistant to one or more of the drugs mandated by that strategy, thus allowing the strain to survive and develop resistance to additional drugs.

�The spread of a highly transmissible strain of drug-resistant tuberculosis has been facilitated by applying standard treatment regimens for susceptible and multi-drug resistant tuberculosis in the absence of drug resistance surveillance,� said one of the authors, A. Willem Sturm, MD, of the University of KwaZulu-Natal�s Nelson R. Mandela School of Medicine in South Africa. �Public health programs for the treatment and control of infectious diseases need to be supported by drug resistance surveillance programs.�

Like all bacteria, M. tuberculosis can evolve and develop resistance to the drugs that have historically killed them. The strategy that has been used to limit the development of drug-resistant TB is to treat the patient with multiple drugs so that if one drug is ineffective, then the others will ensure the elimination of the bacteria.

Drug-resistant M. tuberculosis develops when tuberculosis patients cannot or do not comply with the medication regimen. A second line of drugs has been used to treat those infected with drug-resistant TB. This second-line medication regimen was adopted in South Africa in 2001 to treat drug-resistant TB.

Unfortunately, at least one strain of M. tuberculosis in South Africa had already developed resistance to one or more of these second-line drugs by the time they were introduced. Drug susceptibility tests would have warned doctors that the standard second-line regimen was unlikely to help the patient but was likely to lead to additional drug-resistance, but these tests were not performed or were not available. Indeed, the reduced efficacy of the regimen allowed the strain to survive and, over time, develop resistances to other drugs.

The authors recorded the development of resistance to seven drugs in just over a decade in one strain of M. tuberculosis. There are very few treatment options for patients infected with XDR TB. For the most part, patients are given drugs that had been used to treat tuberculosis but which were abandoned when today�s first-line drugs became available. The older drugs were abandoned because they were less effective or more toxic.

The authors call for an increased use of drug resistance surveillance programs to help forestall the development of drug-resistance in M. tuberculosis.

Vitamin D supplements may offer cheap and effective immune system boost against TB

Tue, 15 May 2007 19:13:46 PST

( from http://www.rxpgnews.com ) Scientists have shown that a single 2.5mg dose of vitamin D may be enough to boost the immune system to fight against tuberculosis (TB) and similar bacteria for at least 6 weeks. Their findings came from a study that identified an extraordinarily high incidence of vitamin D deficiency amongst those communities in London most at risk from the disease, which kills around two million people each year.

The research, funded by the Wellcome Trust, the Department of Environmental Health at Newham Council and Newham University Hospital NHS Trust Respiratory Research Fund, is published online in the American Journal of Respiratory and Critical Care Medicine.

Whilst a diet of oily fish can provide some vitamin D, the main source of the body's vitamin D comes from exposing the skin to sunlight. In Britain, however, the amount of sunlight is usually insufficient to make vitamin D in the skin between October and April, and much of the population becomes deficient during the winter and spring.

Researchers from Queen Mary's School of Medicine and Dentistry, London, and the Wellcome Trust Centre for Research in Clinical Tropical Medicine, Imperial College London, studied patients at Newham University Hospital and Northwick Park Hospital in London who had been exposed to TB. They found that over 90% of such patients had a vitamin D deficiency.

Vitamin D was used to treat TB in the pre-antibiotic era, when special sanatoria were built in sunny locations, such as the Swiss Alps. But until now, no study has evaluated the effect of vitamin D supplementation on immunity to mycobacteria, the family of bacteria that cause TB.

The researchers performed a randomised control trial on a group of volunteers who were given either a 2.5mg supplement or a placebo. Samples of the volunteers' blood were then tested in Dr Robert Wilkinson's Wellcome Trust-funded laboratory at Imperial College, to see whether the supplement affected the immune system's ability to withstand infection by mycobacteria.

"We found that a single large dose of vitamin D was sufficient to enhance a person's immunity to the bacteria," says Dr Adrian Martineau from Imperial College London, who co-ordinated the study. "This is very significant given the high levels of vitamin D deficiency in people at the highest risk of TB infection, and shows that a simple, cheap supplement could make a significant impact on the health of people most at risk from the disease."

According to the Health Protection Agency, the incidence of TB in the UK is increasing, with around 8,000 new cases a year. Cases in the UK are predominantly confined to the major cities and about 40 per cent of all cases are in London. TB is also a major global problem: an estimated one-third of the world's population â nearly two billion people â are infected. Nine million people a year develop the active disease worldwide, which kills two million each year.

"Most cases of TB in London arise from people who have already become infected with the bacteria but in whom it lies latent," says Professor Chris Griffiths from Queen Mary's School of Medicine and Dentistry. "Our results indicate that vitamin D supplementation may prevent reactivation of latent TB. Identifying people with latent TB and providing supplements could be an important strategy for tackling the disease."

Treatment is both very cheap â about 60p per dose or 10p per week â and safe. Vitamin D supplements could be prescribed for patients with or at risk of latent TB through GP surgeries.

Dr Martineau points out: "Our work adds to the growing evidence that vitamin D may have a wide range of important health benefits, including preventing falls and fractures and reducing risk of cancer and diabetes, as well as boosting the immune system against infection. Population-wide supplementation needs to be considered by public health planners."

"Milk and orange juice could be fortified with vitamin D, as in the US and Canada," he says. "At present only margarine is supplemented in the UK, and recent studies show that this is not an effective way to prevent vitamin D deficiency."

Tuberculin skin tests not sensitive in detecting latent TB

Thu, 15 Mar 2007 05:45:58 PST

( from http://www.rxpgnews.com ) Two new interferon-gamma blood test assays to detect latent tuberculosis infection (LTBI) showed customers were exposed to a supermarket employee in Holland who had smear-positive tuberculosis, while traditional tuberculin skin tests (TST) did not, according to a large contact study.

Results from these tests were published in the second issue for March 2007 of the American Journal of Respiratory and Critical Care Medicine, published by the American Thoracic Society.

Ailko Bossink, M.D., Ph.D., of the Department of Pulmonology at Diakonessenhuis Utrecht in The Netherlands, and eight associates recruited 785 supermarket customers who had not received BCG vaccine against tuberculosis, the immunizing agent prepared from Calmette-Guéren bacillus. TST results are not accurate in those vaccinated with BCG.

All individuals in the study cohort were recruited from over 20,000 customers who had shopped at the supermarket for more than 10 months. Many had numerous contacts with the infected employee, who had been contagious since February 2004. The large-scale contact investigation began in January 2005.

"One-third of the worlds population is believed to harbor latent TB infection, or LTBI," said Dr. Bossink. "Approximately 5 to 15 percent of immunocompetent persons with LTBI will develop TB disease. In countries with a low-incidence of TB, the tracing and targeted treatment of individuals with LTBI constitutes the major pillar of TB control. "

For the study, researchers selected 469 customers randomly on the day that their TST was administered and 316 with a TST result of more than 0 mm.

TSTs are based on a skin reaction to injection, scratching or puncturing the skin with a purified protein derivative of tuberculosis bacterium. Swelling and redness indicate a positive result.

In the new blood tests, two interferon-gamma release assays (IGRAs) measure response to an antigen highly specific for Mycobacterium tuberculosis. One of the blood tests, QuantiFERON-TB Gold, has received approval from the U.S. Food and Drug Administration for use in the United States. The other has been approved for use in Europe.

"Among the 785 study participants, TST results were associated with age, whereas positive interferon-gamma blood test assay results were significantly associated with cumulative shopping time," said Dr. Bossink. "TST results were not associated with any measure of exposure to the index case in the supermarket."

The researchers noted that positive TST responses largely reflected delayed type hypersensitivity due to remote infection with M. tuberculosis acquired before the source case at the supermarket became infectious.

Among the 759 shoppers who had valid results from both interferon-gamma blood assay, slightly over 80 percent (608) were concordant negative with both blood tests, while 72 were concordant positive and 79 were discordant. Overall agreement between the two tests was 89.6 percent.

"Although the interferon-gamma blood tests are now considered more specific and show a better correlation with exposure than TST, it has not been demonstrated whether they provide a valid basis for therapeutic decisions regarding treatment," said Dr. Bossink. "The risk of TB disease in the presence of a positive test result had not been established."

"Notably, positive interferon-gamma blood assays were observed in a significant proportion of recently exposed contacts with a negative TST result," he added. "The clinical significance of this finding merits further study if the blood tests are to replace the TST and be used for therapeutic decisions."

In an editorial on the research in the same issue of the journal, Madhukar Pai, M.D., Ph.D., and Dick Menzies, M.D., M.Sc., of McGill University in Montreal, Canada, wrote:

"The key question is whether the two new IGRAs are better than the TST in predicting the development of TB disease, and thus identifying persons who will benefit most from latent TB infection (LTBI) therapy. There is abundant evidence, from numerous large-scale cohorts and randomized trials, regarding the prognosis of untreated persons with positive TST results; this remains the greatest advantage of the TST."

"What is urgently needed is similar longitudinal studies of cohorts who have been tested with IGRA (ideally both IGRAs) and the TST," they continued. "However, in almost all low-incidence, high-income countries, it would be ethically impossible not to treat persons with evidence of LTBI. Moreover, in high-incidence countries, where treatment of LTBI is not the current standard of care, it would seem unethical to test for a condition without plans to offer appropriate treatment."

"However, this should not be a problem. Almost everyone would agree that individuals with concordant positive TST and IGRA are likely to have LTBI and they will never inform the question as to which test predicts active TB better. Thus, such patients can and should be managed appropriately. However, individuals with discordant results (TST+/IGRA- or vice versa) will be informative regarding the risk of development of active disease without treatment. In addition, because the clinical interpretation, and therefore management is unclear for persons with such discordant results, equipoise exists. Therefore, close observation without treatment is reasonable and ethical."

Emergence of highly drug-resistant tuberculosis strains requires urgent action

Fri, 15 Sep 2006 18:10:37 PST

( from http://www.rxpgnews.com ) New forms of highly drug-resistant tuberculosis are emerging and action must be taken soon before they become widespread globally, says an editorial in this week's BMJ.

The authors say that urgent action is needed to implement effective tuberculosis control strategies, especially in countries where tuberculosis control practices have been inadequate.

Research is also needed to assess the extent of the spread of these highly drug resistant strains of tuberculosis worldwide and improved means of diagnosis of tuberculosis and early detection of drug resistance are urgently required, they add.

Among 536 cases of tuberculosis confirmed at a rural hospital in South Africa earlier this year, 41% were multi-drug resistant and of those, 24% met the exact definition of being extensively drug resistant tuberculosis (also referred to as XDR tuberculosis). Such tuberculosis is almost untreatable.

All patients in this outbreak who were tested were HIV positive and 52 of the 53 died after an average of 25 days.

Strains of extensively drug resistant tuberculosis have also been noted in Europe, Asia and North and South America. It appears that there are several strains of this tuberculosis.

Author Dr Stephen Lawn, senior lecturer in infectious and tropical diseases at the University of Cape Town, South Africa, says that drug resistance to tuberculosis results largely from poorly managed care and control of the disease.

Poor prescribing practices, low drug quality (or erratic supply) and poor adherence to drugs can all contribute to this resistance to drugs. Where HIV rates are high, this allows particularly rapid spread of the disease within hospital settings and the community.

Dr Lawn says several responses to this problem are required including urgent assessment of the scale of the problem and an increase in laboratory capacity.

"Detection rates for cases of tuberculosis need to be improved, highlighting the need for a new diagnostic test," he writes. "Technologies that can determine the presence of drug-resistance at the point of care are needed as are new drug treatments."

Treating populations infected with HIV and latent TB could speed the emergence of drug-resistant TB

Tue, 18 Apr 2006 14:27:37 PST

( from http://www.rxpgnews.com ) In 2005, 46 regional Ministers of Health in Africa declared that a dramatic rise in tuberculosis (TB) cases was cause for emergency. In some African countries, annual TB case notifications have increased as much as four-fold over the past 15 years. The main culprit? The emergence of HIV. When individuals are infected with both HIV and TB, they are more likely to progress from latent TB infection to active TB.

To combat the problem, the World Health Organization currently recommends that as part of HIV/AIDS programs, patients infected with both HIV and TB be treated with isoniazid, an antimicrobial, as a preventive therapy to reduce the risk that TB will progress from latent infection to active disease. However, researchers from the Harvard School of Public Health (HSPH) and a team of collaborators believe that strategy has flaws. Their findings appear in the advance online edition of the May 2, 2006 issue of Proceedings of the National Academy of Sciences.

The researchers, led by Ted Cohen, doctoral student at HSPH, and senior author Megan Murray, Assistant Professor of Epidemiology, developed a mathematical model to describe the projected impact of isoniazid preventive therapy (IPT) programs on the transmission dynamics of drug-resistant TB in areas where community-wide preventive therapy may be used as a strategy to control TB. They concluded that the implementation of IPT targeted to people co-infected with HIV and TB may also have the perverse effect of speeding the emergence of drug-resistant TB.

"We're not saying isoniazid preventive therapy policies are ill-advised," said Cohen. "But we think they need to be coupled with an understanding that large-scale IPT programs should be ready to diagnose and treat individuals with drug-resistant TB as part of the programs."

Solution to TB epidemic may lie in protective Heme oxygenase 1 protein

Wed, 22 Mar 2006 07:59:37 PST

( from http://www.rxpgnews.com ) Most Americans think of tuberculosis as a disease of the past, but with HIV and drug-resistant strains fueling epidemics in India and Africa, TB kills someone every six seconds across the world.

Now University of Florida and Indian scientists suspect they are on the path to solving a piece of the puzzle. The researchers are studying a protective protein they believe may boost bacteria-battling defenses, protecting against TB and giving infected patients an easier recovery.

Alcohol consumption likely reduces the amount of this protective protein, called heme oxygenase 1, weakening the body's defenses against TB, said Veena Antony, M.D., a UF professor of pulmonary medicine and division chief of pulmonary and critical care medicine for the College of Medicine. The researchers hope to pinpoint the role of alcoholism in the global epidemic by studying a population of HIV- and tuberculosis-infected patients in India. The researchers are collecting data for the National Institutes of Health-funded project and hope to have answers within two to three years, Antony said.

The epidemic may be more prevalent in resource-poor countries like India right now, but with immigrants unknowingly carrying bacteria that cause TB into the United States each year, this crisis could spread to American soil if left untended, Antony warns.

"We cannot build walls high enough to keep these organisms out," she said. "In the U.S., we cannot afford to grow complacent about TB. This is a disease that appears in many forms, many guises. We will never be able to eradicate it from the U.S. unless we eradicate it from the world."

The increasing number of multidrug-resistant strains of TB makes the disease even more troublesome, Antony says. The only currently approved treatment for TB requires patients to go to a clinic every day for up to nine months, and people often do not complete the full course of therapy, breeding new bacteria that are immune to the drugs. There is currently no way to treat large populations infected with drug-resistant strains of the disease, Antony said. The drug-resistant organism is one of several the federal government lists as a potential bioterrorism threat.

But the combination of HIV and TB currently poses the biggest problem globally. Patients with HIV are more apt to develop tuberculosis after they have contracted bacteria that cause TB, said Amy Davidow, Ph.D., an associate professor of preventive medicine and community health at the University of Medicine and Dentistry of New Jersey.

"The rule of thumb is if you have been infected (with TB) and are otherwise healthy, there is a 5 to 10 percent chance you will (ever) develop active disease," Davidow said. "The immune system keeps the infection in check so it never develops. HIV depresses the immune system, so certain infections (such as TB) can become active."

Tuberculosis can affect any organ in the body but causes more problems in the lungs, resulting in painful coughing and respiratory problems. Coupled with HIV, the two diseases form a deadly one-two punch that could be just as dangerous to the public as it is to the HIV- and TB-infected patient. Because TB develops more quickly in a person with HIV, the organism is more prevalent in the body and may spread more easily to other people, other research has shown.

"In resource-poor societies there is a meeting of HIV and tuberculosis, so that one disease is fueling the other disease," Antony said. "That is true in Africa. That is true in India where the HIV epidemic is just beginning to explode.

"Because of this concern, we believe we have to find novel ways of killing the organism. We have shown that heme oxygenase 1 is effective in boosting the cell's ability to protect itself."

In India, outbreaks of HIV and TB have erupted along highways where truck drivers often solicit prostitutes, Antony said. Doctors at the Post Graduate Institute of Medical Education and Research in India treat many of these patients, which is one of the reasons why UF researchers chose to collaborate with them for this research project, Antony said.

UF researchers also hope to initiate an international training program with PGIMER, allowing Indian researchers to come to Florida to learn sophisticated techniques and giving UF trainees firsthand experience in dealing with the epidemic there.

"One single patient with tuberculosis can infect hundreds of people," Antony said. "One-third of the world's population is infected with the organism that causes tuberculosis. We're going out into the field to meet the disease head-on and try to find answers."

Explaining Why People of African Descent Are More Vulnerable to TB

Sat, 25 Feb 2006 10:05:37 PST

( from http://www.rxpgnews.com ) A team of scientists has identified a cellular mechanism that may help explain the puzzle of why people of African descent are more susceptible to tuberculosis infection and why, once infected, they develop more severe states of the disease than whites. The team includes researchers from University of California, Los Angeles (UCLA), and Harvard School of Public Health (HSPH).

Approximately eight million people worldwide are infected with TB annually, with an estimated two million people dying from the lung disease each year. TB is caused by the pathogen Mycobacterium tuberculosis, but infection does not automatically result in full-blown disease. In the U.S., minority and foreign-born populations have significantly higher rates of TB than the overall U.S. average, according to the Centers for Disease Control and Prevention. In 2004, African Americans had TB case rates that were eight times higher than whites.

Scientists have understood that mice -- a frequently used animal model in experiments -- combat microbes such as TB by producing nitric oxide in scavenger cells of the immune system known as macrophages. However, this mechanism is not prominent in humans, and the mechanism by which human macrophages kill the tubercle bacillus has remained an additional puzzle. Innate immunity is the rapid immune response of host scavenger cells to recognition of certain patterns of molecules found on pathogens, which has been retained in evolution from fruit flies to humans. A set of receptors on macrophages in humans called Toll-like receptors contribute to innate immune responses. The researchers describe a novel pathway used by human macrophages that may be critical to resisting infection with certain pathogens and that turns out to be critically dependent on vitamin D. This description provides a different way to think about how human immune systems battle pathogens in general.

The research team found that when Toll-like receptors in humans are stimulated by specific molecules of the tubercle bacillus, vitamin D receptors and an enzyme called Cyp27B1, which converts the vitamin from an inactive form to an active form, are dramatically increased. The result of this dual activation is the cleavage of a preexistent protein to a small peptide called cathelicidin, which can kill TB bacilli in the test tube. One of the interesting aspects of this mechanism is that production of vitamin D in humans is dependent on exposure to UV light, generally sunlight, and may not have evolved in mice since they are nocturnal animals.

"These studies began with a very basic exploration of differences in gene expression in two related human white blood cell types known to be involved in host responses to infection, and concluded by revealing a new and potentially important human mechanism for killing intracellular pathogens, said Philip Liu, postdoctoral scholar in the Department of Immunology and Molecular Genetics at the David Geffen School of Medicine at UCLA and co-lead author of the paper.

African Americans have significantly lower levels of vitamin D in their blood serum than whites because higher levels of melanin -- the pigment that provides color to skin absorbs UV light and reduces African Americans' ability to produce vitamin D. When the macrophages were stimulated by molecules of the tubercle bacillus that trigger Toll-like receptors, the research team found that cells cultured in serum provided by African Americans produced 63 percent less of the microbe-killing cathelicin than when cultured in serum from whites. Supplementing the serum from African Americans with vitamin D precursor to a range found in serum samples from whites boosted the induction of cathelicidin.

Scientists have long known that African Americans have less vitamin D than whites and that they are more vulnerable to TB. This study helps to resolve two of the puzzles of tuberculosis, the differences between mice and human antibacterial mechanisms, and the susceptibility of people of African and possibly Asian descent to tuberculosis. The researchers suggest a need for clinical trials to investigate the effect of vitamin D supplementation.

Our results indicate that we have much yet to learn about human immune responses to infections. They also emphasize the importance of vitamin D in human immune responses, and suggest that it is now important to learn how much vitamin D is optimal for innate immunity, and how that can best be achieved through diet or supplementation, said the senior investigator of these studies, Dr. Robert Modlin, Klein Professor of Dermatology and Professor of Microbiology, Immunology and Molecular Genetics at the David Geffen School of Medicine at UCLA.

Tuberculosis is a devastating disease that strikes vulnerable populations particularly hard," said immunologist Barry R. Bloom, Dean of the Faculty at HSPH and a co-author of the paper. "This study provides a new mechanism for innate immunity in humans and demonstrates how variations in vitamin D synthesis may make individuals susceptible to TB infection. It is exciting to consider the possibility that innate immunity to tuberculosis and other infections in vulnerable populations might be enhanced by providing a simple vitamin that would cost only pennies a day.

Indian Scientists Identify Key Genes in Tuberculosis Infection

Sat, 04 Feb 2006 23:38:37 PST

( from http://www.rxpgnews.com ) Scientists in India, led by a Howard Hughes Medical Institute (HHMI) international research scholar, have identified five key genes that enable Mycobacterium tuberculosis to acquire the iron it needs to sustain growth and promote infection.

Using microarray data, the available literature, and intuition, Gokhale's group identified the location of the four genes that produce the lipid tail after observing that the expression of the genes significantly increased in response to low iron concentrations. The gene required for the synthesis of the siderophore core, called mbt-1, functions the same way, so Gokhale's team named the new locus mbt-2 and the new genes mbtK, mbtL, mbtM, and mbtN.

Now that the major siderophore genes and their functions have been defined, understanding the biosynthetic pathway provides an opportunity to develop small-molecule inhibitors with the potential for developing anti-tuberculosis drugs, said Gokhale. Since the mbt-1 genes are also conserved across many bacterial families, the mbt genes appear to be ideal antibacterial targets for treating tuberculosis and other bacterial infections, he said.

Targeting genes within this cluster represents a good strategy for preventing tuberculosis and other mycobacterial infections, said Rajesh S. Gokhale, an HHMI international research scholar at the National Institute of Immunology in New Delhi, India, and lead investigator on the study. Because some of these genes are conserved across a number of related bacterial families, they are promising targets for drugs to treat TB and other bacterial diseases.

The tuberculosis bacterium, which infects more than one third of the world's inhabitants, is a leading cause of death and disease worldwide.

Gokhale and colleagues report their findings in early online publication January 30, 2006, in the Proceedings of the National Academy of Sciences.

When M. tuberculosis infects humans, it takes up residence in immune cells called macrophages. To survive in this harsh environment, mycobacteria, like many other types of bacteria, need iron to carry out life-sustaining functions, such as creating proteins and synthesizing nucleotides to form DNA. However, free iron is not easily found in an intracellular environment. To obtain this rare element, most bacteria manufacture and secrete chemical compounds called siderophores that scavenge iron from the environment.

Researchers discovered siderophoreschemical compounds used by bacteria to scavenge iron from their cellular environmentwell over 50 years ago, but the genes involved in adding the long-chain lipid anchor that enables M. tuberculosis to do so more efficiently, remained a mystery until now.

Dr. Gokhale holds the position of Scientist at the National Institute of Immunology in New Delhi, India. He received his Ph.D. in 1996 from the Indian Institute of Science and worked as a postdoctoral fellow in the Chemical Engineering Department of Stanford University from 1996 to 1999. In 2001, he received a Wellcome Trust International Senior Research Fellowship; in 2003, he received the B. M. Birla Science Prize. (Photo: Aseema R. Gokhale)

Mycobacteria have evolved siderophores with lipid-chain tails that enable them to exploit the macrophage's lipid-trafficking system to capture iron more efficiently. Instead of using siderophores that diffuse freely, mycobacteria anchor their siderophores to lipid membranes by means of a long fatty acid tail. After these siderophores bind to iron within the macrophage, the lipid tail makes the iron sticky enough to permit delivery to the very compartment in macrophages where the mycobacteria are lurking.

PA-824 holds promise for shortening the TB treatment regimen

Tue, 27 Dec 2005 16:53:38 PST

( from http://www.rxpgnews.com ) Scientists from the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, have determined how a promising drug candidate attacks the bacterium that causes tuberculosis (TB). Published online this week in Proceedings of the National Academy of Sciences, the finding may help scientists optimize the drug candidate, PA-824, which targets Mycobacterium tuberculosis (M. tb).

"PA-824, now in early stage clinical trials, holds promise for shortening the TB treatment regimen, which is currently cumbersome and lengthy," says NIAID Director Anthony S. Fauci, M.D. "This new finding will allow a streamlined approach for making improved versions of the drug."

"Previously, we were flying blind in trying to optimize PA-824 in a rational way because we didn't know which M. tb protein was the target of PA-824's action," says NIAID scientist Clifton Barry, III, Ph.D., who headed the research team.

In preclinical testing, PA-824 showed evidence of being effective against both actively dividing and slow-growing M. tb, giving rise to optimism that the compound may be useful in treating both active and latent TB. (For information about the first clinical trial of PA-824, see June 14, 2005, NIAID press release: http://www3.niaid.nih.gov/news/newsreleases/2005/tb_pa_824.htm.)

PA-824 must be chemically activated in the bacterium before it exerts its anti-tubercular effect, notes Dr. Barry. Earlier research had sketched out the first few steps in this process, but Dr. Barry and his colleagues wanted to pinpoint the precise protein that binds PA-824 and transforms it into a lethal molecule for TB.

The scientists approached the problem indirectly by searching for M. tb mutants that resisted the killing power of PA-824. The team confirmed previous research suggesting that resistance usually occurs when M. tb lacks components called FGD1 and F420, neither of which interacts directly with the drug.

Next, the investigators screened for PA-824-resistant M. tb that retained sensitivity to a close relative of PA-824. Within this subgroup of PA-824-resistant bacteria, the team identified those mutant strains with FGD1 and F420. The investigators reasoned that resistance to PA-824 in mutants possessing FGD1 and F420 must be due to a mutation in the M. tb protein that directly interacts with PA-824.

But determining exactly which of M. tb's thousands of proteins was changed in these mutants proved difficult, says Dr. Barry. Conventional genetic techniques for comparing normal and mutant strains of M. tb failed, so the team turned to a specially modified microarray-based technique, called comparative genome sequencing, developed by NimbleGen Systems, Inc. (Madison, WI). This was the first time the technique has been used to identify a protein involved in TB drug resistance, notes Dr. Barry.

Using the NimbleGen technique, which effectively re-sequences the entire genome of the bacterium, the scientists quickly pinpointed the protein altered in the PA-824-resistant mutant strains of M. tb. In the past, such a complete genome comparison might have taken many months of work; this new technology enables scientists to zero in on the specific genetic difference between mutant and normal bacterial strains in just days, says Dr. Barry.

The scientists found a total of four PA-824-resistant mutant strains: two lacked the newly described M. tb protein altogether, while the remaining two mutants evidently acquired resistance to PA-824 through a mutation that made the protein unable to bind to the drug, Dr. Barry says.

With the discovery of the specific protein that interacts with PA-824, Dr. Barry and colleagues, including researchers at the Novartis Institute for Tropical Diseases in Singapore, have information they can use to produce improved PA-824 relatives and accelerate the pace of new TB drug development.

DC-SIGN expressing alveolar macrophages are preferentially targeted by M. tuberculosis

Tue, 15 Nov 2005 19:20:38 PST

( from http://www.rxpgnews.com ) C-type lectins are carbohydrate-binding cell surface molecules with a wide range of biological functions, many of which are related to immunity. Despite its name, dendritic cell specific intercellular adhesion molecule-3 grabbing nonintegrin (DC-SIGN) is not only expressed on dendritic cells but also on specialized macrophages in the placenta and lung. A number of pathogens are known to interact with DC-SIGN, and some (including HIV) seem to have evolved to derive advantages from these interactions.

Recent in vitro studies have shown that DC-SIGN can interact with Mycobacterium tuberculosis through a lipoglycan (a molecule composed of sugars and fatty acids) on the mycobacterial envelope called lipoarabinomannan (LAM). Trying to understand the role of DC-SIGN in tuberculosis (TB), Ludovic Tailleux and colleagues have focused on the interaction between M. tuberculosis and DC-SIGNâexpressing cells in the lungs of human patients.

The researchers studied a total of 74 individuals, including 40 with TB, 11 with sarcoidosis, 14 with asthma, and nine control participants without active lung infection or inflammation. All patients underwent bronchoalveolar lavage (BAL), a procedure that yields cells and proteins from the lower respiratory tract. The researchers then examined BAL cell populations after staining for various cell-surface markers by flow cytometry, and found that, in individuals without TB, very few alveolar macrophages (an average of 3%) expressed DC-SIGN. In contrast, an average of 30% (and up to 70%) of macrophages from patients with TB expressed the lectin.

Tailleux and colleagues then incubated alveolar macrophages from a patient without TB ex vivo with M. tuberculosis, which resulted in infection of a subset of the cells. When the researchers examined DC-SIGN expression, they found that both infected and noninfected (bystander) cells in the population started to express DC-SIGN. The effect on bystander cells suggests that soluble factors from the microbe and/or the infected cells can induce DC-SIGN expression. Further functional ex vivo studies with cells from human patients indicated that DC-SIGN expression renders alveolar macrophages more susceptible to infection.

The authors propose a scenario where complement receptors mediate most of the initial infection of alveolar macrophages in a naÃ¯ve host, and whereâonce the infection is establishedâDC-SIGNâexpressing alveolar macrophages become preferential target cells for M. tuberculosis. Future work will be focused on identifying the soluble factors involved, and on determining whether DC-SIGN induction is an essential part of TB pathogenesis.

Tuberculosis Still a Risk for Patients on Anti-retrovirals

Sat, 12 Nov 2005 19:57:38 PST

( from http://www.rxpgnews.com ) People taking highly active antiretroviral therapy (HAART) for HIV infection remain susceptible to tuberculosis, though the risk is lower than for HIV-infected patients not on HAART, according to an article in the Dec. 15 issue of Clinical Infectious Diseases, now available online.

Opportunistic infections such as tuberculosis (TB) can be fatal for immunocompromised patients. HAART not only reduces the viral load of HIV, but it also often helps to keep other infections such as TB under control. In fact, previous studies indicate that HAART can reduce the risk of TB in HIV patients by 70 to 90 percent. Although HIV-infected people living in industrialized nations are at lower risk of TB than those living in resource-poor countries, it continues to be a significant problem for HIV-infected people everywhere.

A group of European and American researchers followed patients with HIV for three years after they began HAART. The rate of tuberculosis was highest within the first three months of therapy, but declined after longer HAART exposure. Patients risk of developing tuberculosis more than doubled if HAART did not successfully control their HIV. Patients were also more likely to develop TB if they were more immunodeficient when they started taking HAART.

HIV-infected patients from industrialized nations might develop TB if they were exposed to the tuberculosis organism in the past, especially for those emigrating from resource-poor countries. Their weakened immune status can allow reactivation of latent TB infection, according to lead author Enrico Girardi, MD, of the Istituto Nazionale per le Malattie Infettive Lazzaro Spallanzani in Rome.

But they dont necessarily have to leave the country to contract TB. HIV-infected American and European patients who are exposed to someone with tuberculosis, for example in a hospital setting, are at increased risk of acquiring tuberculosis infection and of developing active tuberculosis within a short time, usually six months to one year, Dr. Girardi said.

Since TB is a potentially deadly opportunistic infection for patients with HIV, doctors need to be aware of the risk and take certain precautionary measures. HIV-infected patients, even when treated with HAART, remain at increased risk of developing tuberculosis, Dr. Girardi said. Thus, physicians caring for patients with HIV should continue to screen for and to treat latent tuberculosis infection in their patients, even if they have minor levels of immune suppression or are successfully treated with HAART. Health care settings should also maintain strict control measures to prevent the spread of tuberculosis to patients being treated for HIV, Dr. Girardi added.

In an accompanying editorial commentary, Stephen D. Lawn, MRCP, MD, and Robin Wood, MBChB, of the Desmond Tutu HIV Centre in South Africa indicated similar findings (unpublished) related to patients immunological response to HAART and subsequent development of TB. The commentary concludes that HIV-infected patients risk for infection with TB remains elevated among those receiving treatment in both high- and low-income countries.

Evolutionary history of tuberculosis is shaped by human migration patterns

Wed, 28 Sep 2005 08:03:38 PST

( from http://www.rxpgnews.com ) Genghis Khan and his troops may have unwittingly used more than just brute military force to conquer entire nations and to establish the infamous Mongolian empire. A report in the October issue of Genome Research suggests that Genghis Khan's invasions spanning the continent of Asia during the 13th century may have been a primary vehicle for the dissemination of one of the world's most deadly diseases: tuberculosis.

In this study, a team of scientists led by Dr. Igor Mokrousov from St. Petersburg's Pasteur Institute demonstrated that the evolutionary history of the causative agent of tuberculosis (TB) has been shaped by human migration patterns.

The researchers examined the genetic signatures of over 300 strains of Mycobacterium tuberculosis, rod-shaped bacteria that, when airborne, infect the pulmonary systems of vulnerable individuals and give rise to clinical TB. The World Health Organization (WHO) estimates that TB kills 5,000 people worldwide every day, or approximately 2 million people each year. The pathogen is rapidly spreading and evolving multi-drug resistant strains in susceptible regions such as Africa. Interestingly, a strong gender bias in TB infection is reported globally each year; a 70% excess of male TB cases is typical.

"M. tuberculosis also has a remarkable ability to persist in the human host as a latent, asymptomatic form," explains Mokrousov. "This is probably what permitted M. tuberculosis to co-exist with humans during pre-industrialized times, when the primary mode of transmission was within families or households where there was significant physical contact." Today, approximately one-third of the world's population are carriers of latent TB.

Mokrousov's team hypothesized that, given the strong gender bias of TB infectivity and the likely family-based mode of TB transmission during pre-industrialized times, M. tuberculosis dissemination has reflected the unidirectional inheritance of the paternally transmitted human Y chromosome. To test this hypothesis, the authors compared the genetic profiles of a common form of M. tuberculosis, called the Beijing genotype, with known patterns of prehistoric and recent human migrations, as well as with global patterns of Y-chromosome variation. Strikingly, they observed that over the past 60,000-100,000 years, the dispersal and evolution of M. tuberculosis appears to have precisely ebbed and flowed according to human migration patterns.

The authors describe how the Beijing genotype of M. tuberculosis originated in a specific human population called the K-M9 in central Asia approximately 30,000-40,000 years ago following a second "out of Africa" migration event. The bacteria and its human host then disseminated northeast into Siberia between 20,000-30,000 years ago and throughout eastern Asia between 4,000-10,000 years ago. More recently, the Beijing genotype of M. tuberculosis was introduced into northern Eurasia, perhaps by Genghis Khan himself during the 1200's, and into South Africa, possibly through sea trade contacts with Indonesia or China during the last 300 years.

"The population structure of M. tuberculosis appears to have been shaped by the demographic history of its human carrier," explains Mokrousov, "but this is the opposite of what William McNeill suggested in 1976 in his famous book Plagues and Peoples, where he so popularly described how the growth and spread of infectious diseases such as the Black Death have influenced human history."

Mokrousov feels that these observations have important implications for tracing the evolutionary history of microorganisms. "The timing of hallmark changes in bacterial genomes within the last 100,000 years may be inferred from comparison with relevant human migrations," he says.

TB vaccines will fail in developing countries

Sun, 04 Sep 2005 09:37:38 PST

( from http://www.rxpgnews.com ) Tuberculosis (TB) vaccines currently on trial at a cost of hundreds of millions of dollars will fail to protect populations living close to the Equator, warns a review published in Nature Reviews Immunology . Scientists from UCL (University College London) warn that vaccines designed in the developed world do not take into account differences in immune systems across the globe. They recommend greater use of negative vaccination' in drug design, to prevent the West from developing TB vaccines destined to fail in Asia, Africa and Latin America, where an effective vaccine is most needed.

As described in the review, funded by the British Lung Foundation, the UCL team has explored variations in immune responses to TB bacteria and has found that in developing countries, the bacteria trigger a corrupted response which converts the body's protective system into a harmful one.

In the northern hemisphere, the immune system typically protects the body from TB via Th1 cells which lead the immune response. However, for populations living close to the Equator, UCL scientists have found that this response becomes immunopathological because of the simultaneous activation of inappropriate response mechanisms. This not only prevents the body from eliminating the bacteria, but also causes bacteria-rich lung cavities to form, which enable the infection to spread further.

The UCL scientists warn that TB vaccines currently on trial are typically designed to boost the Th1 cell response, which in principle works in Europe or northern parts of USA . However, for the vaccine to work successfully in equatorial countries, it would need to suppress the inappropriate response mechanisms that cause immunopathology rather than increase Th1 cells. The UCL team recommends more intelligent use of negative vaccination', which involves the use of vaccines that suppress damaging immune responses.

Professor Graham Rook, of the UCL Centre for Infectious Diseases and International Health, says: It is already known that the BCG vaccine works in the northern hemisphere but not close to the Equator, where countries within 30 degrees latitude of the Equator have the greatest failure rates. Yet vaccine design continues to ignore crucial differences in immune systems between populations.

We are not saying that funding for TB vaccination in developing countries should be stopped quite the contrary, given that TB kills between 2 and 3 million people every year. But we are concerned that the BCG vaccine is failing these countries and that TB vaccines currently on trial are likely to go the same way.

What we are arguing for is negative vaccination', where a vaccine is designed to reduce rather than increase its target mechanism. We believe this method will work for TB vaccination in equatorial countries, where it would appear that some steps in the body's immune response need to be dampened down or switched off. This approach might also work for other problematic infections such as HIV, and would certainly be worth exploring.

The irony is that variations in the immune system are intensely studied when it comes to seeking explanations for the increases in chronic inflammatory disorders such as allergies or inflammatory bowel disease in wealthy countries, but few people think about the significance of the differences in relation to the problems of poor countries and vaccine development.

Increased vaccine efficacy against tuberculosis of recombinant Mycobacterium bovis listeriolysin secreting BCG mutants

Fri, 19 Aug 2005 13:42:38 PST

( from http://www.rxpgnews.com ) Tuberculosis remains a major global health threat. Although more than 3 billion doses of the BCG vaccine have been administered to fight tuberculosis, the ability of the BCG vaccine to protect adults is very limited, as is its efficacy against newly emerging isolates.

In a study appearing online on August 18 in advance of print publication of the September 1 issue of the Journal of Clinical Investigation, Stefan Kaufmann and colleagues from the Max Planck Institute devise a strategy to boost the immunogenicity of BCG and describe a novel vaccine strain with high efficacy against tuberculosis. The researchers engineer a BCG strain that secretes the listeriolysin protein, which punches holes in the membranes of phagosomes where M. tuberculosis is located, allowing better T cell-mediated immunity. Because listeriolysin works optimally at a pH of 5.8, the researchers also deleted the urease C gene of BCG, which normally plays a role in pH neutralization of the phagosome. The lack of urease C allows phagosomal acidification and provides an ideal pH environment for listeriolysin.

The new BCG vaccine strain protects mice against tuberculosis significantly better than the parental BCG. Superior protection is not only induced against the laboratory strain of M. tuberculosis but also against a clinical isolate of the Beijing/W family, a straing of tuberculosis that is spreading all over the world, is drug-resistant, and is responsible for the most threatening disease outbreaks.

Ancient origins of tuberculosis-causing bacteria

Fri, 19 Aug 2005 13:34:38 PST

( from http://www.rxpgnews.com ) Researchers have long considered tuberculosis, a bacterial respiratory disease that kills 3 million people each year, a relatively recent human affliction. But a new study in PLoS Pathogens suggests that the disease and the pathogens responsible are much older than previously thought.

"Our results change the current paradigm of the recent origin of tuberculosis," says Veronique Vincent, senior author of the study and researcher at Institut Pasteur, Paris, France. These results may have important future implications for improving diagnosis and treatment of the disease.

Most tuberculosis cases are caused by Mycobacterium tuberculosis and its close relatives. However, some tuberculosis patients from East Africa are infected with unusual bacterial strains that form colonies that appear physically different from M. tuberculosis. Using genetic data from the different strains, Vincent and her colleagues discovered that the ancestors of these bacterial strains were also the progenitors of M. tuberculosis.

These results suggest that M. tuberculosis and related strains recently emerged from a much more ancient bacterial species than previously thought, possibly as old as 3 million years, Vincent says. "Tuberculosis could thus be much older than the plague, typhoid fever, or malaria, and might have affected early hominids," and its expansion to the rest of the world may have coincided with the waves of human migration out of Africa.

Flaws Detected in TB Screening in HIV Patients

Thu, 16 Jun 2005 17:56:38 PST

( from http://www.rxpgnews.com ) New findings from a Dartmouth Medical School collaboration in Tanzania may alter assumptions about the diagnosis of tuberculosis in HIV-infected people, and prompt a major change in way TB testing is routinely done in the developing world.

Writing in the journal, "Clinical Infectious Diseases," researchers found that while the co-existence of HIV and TB is well-known, traditional screening methods for TB are allowing significant number of cases of subclinical, active tuberculosis to go undetected. In apparent response to the these findings, the international physicians' group, Médecins Sans Frontières (Doctors Without Borders), has recommended that all HIV/AIDS patients receive the more sensitive and accurate TB culture test used in the Tanzania research project.

This latest research was reported by investigators in the DARDAR Health Study, a collaboration between Dartmouth Medical School and the Muhimbili University College of Health Sciences in Dar Es Salaam, Tanzania. C. Fordham von Reyn, MD, Chief of the Section of Infectious Disease and International Health at Dartmouth-Hitchcock Medical Center, is the leader of the DARDAR project and author of the new study with Lillian Mtei MD, and other colleagues in Tanzania.

"Our study team found that when we used the same comprehensive diagnostic approach to tuberculosis available in industrialized countries 15% of HIV-infected patients in Tanzania had previously unrecognized active tuberculosis," von Reyn said. "These findings emphasize the importance of improving the availability of TB diagnostic tests in the developing world."

In the developing world, TB is the leading cause of death among people with HIV infection. Thus, diagnosis and proper treatment of TB is a critical component of HIV treatment in these regions. Unfortunately, HIV infection can actually make TB more difficult to diagnose, creating additional challenges for health workers.

The DARDAR team, working from their clinic in Tanzania, tested HIV-positive subjects with traditional skin testing for TB and physical exams, followed by chest x-rays and microscopic examination of sputum samples. They then preformed cultures of these samples, incubating them in a controlled lab environment a procedure used widely in the industrialized countries, but typically not available or recommended in resource poor countries . In 10 cases sputum culture was the only positive test. These patients with "subclinical" tuberculosis denied symptoms when they were first examined and had normal chest x-rays.

"Previously undiagnosed tuberculosis was common, often asymptomatic, and difficult to detect on the basis of a single evaluation," the authors reported. In addition the authors noted that the HIV-infected patients with subclinical tuberculosis had a much better prognosis than previously observed, perhaps due to earlier diagnosis and treatment. Failure to diagnose an subclinical case of active TB and treat with standard multiple drug treatment could result in improper single drug treatment for latent TB, which has the potential to induce TB drug resistance.

The findings are important because existing standards for detection of TB rely on using cough as the indication for screening, with chest x-ray as the screening method. "Our study demonstrates that neither cough nor chest radiography would have identified the 10 subjects (in the study) with subclinical tuberculosis," write the authors.

In an accompanying editorial in the same issue, Dr. David L. Cohn said the findings serve "as a reminder of the complexity of tuberculosis in HIV-infected patients in high-burden countries. This study presents a potential new challenge for the diagnosis of subtle tuberculosis in asymptomatic patients and it may have implications with regard to treatment decisions."

In the wake of the study, Médecins Sans Frontières issued an advisory from its South Africa office, urging patients to insist on the sputum culture test if traditional TB skin and X-ray tests come back negative.

Chest X rays not Effective in Determining when TB is Acquired

Thu, 09 Jun 2005 18:11:38 PST

( from http://www.rxpgnews.com ) There is little correlation between the appearance of tuberculosis on chest x-rays and how recently the disease was acquired, according to a study in the June 8 issue of JAMA, a theme issue on tuberculosis.

Co-author Neil W. Schluger, M.D., of Columbia University, New York, presented the findings of the study at a JAMA media briefing on tuberculosis at the National Press Club.

Traditionally, active tuberculosis (TB) disease has been classified as either primary or secondary, reflecting the time between initial infection with Mycobacterium tuberculosis (MTB) and the onset of clinical disease, according to background information in the article. That interval can range over many years. Primary and secondary TB are also thought to have different characteristic radiographic (x-ray) and clinical features, though these clinical observations have been based on studies conducted before the availability of molecular fingerprinting techniques for TB. Molecular (DNA) fingerprinting, also known as restriction fragment length polymorphism (RFLP) analysis is a method for comparing strains of MTB from individual patients on a genetic basis. These techniques allow comparison of patients who have recently acquired tuberculosis to those whose tuberculosis was acquired long ago.

The researchers in this study used molecular fingerprinting and conventional epidemiology to test whether recently transmitted cases have radiographic features distinct from distantly acquired infection and secondly, whether the atypical features of the radiograph in HIV-associated TB are due to recent infection or are manifestations of altered immunity in the reactivation of latent infection. The study included 546 patients treated at a New York City medical center between 1990 and 1999. Eligible patients had to have had at least 1 positive respiratory culture for Mycobacterium tuberculosis and available radiographic data.

The researchers found that in "...clinically well-defined patients with TB that the most significant independent predictor of radiographic appearance is HIV status," the authors write. "The altered radiographic appearance of pulmonary tuberculosis in HIV is due to altered immunity rather than recent acquisition of infection and progression to active disease."

Although a clustered fingerprint (a DNA fingerprint from an MTB strain from one patient which has an exact match with an MTB strain recovered from at least one other patient), representing recently acquired disease, was associated with typical radiograph, the association was lost when adjusted for HIV status.

"In summary our findings argue that the terms primary and reactivation TB are misleading when used to make inferences linking radiographic findings to epidemiologic characteristics of patients. Radiographic findings have implications regarding host immune status of patients, but whether a patient's disease is due to recently transmitted or remotely acquired infection cannot be determined from them," the authors conclude.

Blood-based TB test matches up to old skin test

Wed, 08 Jun 2005 19:45:38 PST

( from http://www.rxpgnews.com ) In a head-to-head matchup between a new blood-based tuberculosis (TB) test and the traditional tuberculin skin test, researchers from the University of California, Berkeley, and the Mahatma Gandhi Institute of Medical Sciences in India found that the two methods of detecting latent TB infection are equally good.

The results of the study, to be published in a special June 8 theme issue on tuberculosis in the Journal of the American Medical Association, mean that switching to the more expensive blood test may not be necessary for people in India.

"Our study is the first time this blood test has been evaluated in India, where TB is highly endemic," said Dr. Madhukar Pai, a post-doctoral fellow in epidemiology at UC Berkeley's School of Public Health and lead author of the paper. "It's also the largest study of its kind among health care workers, a group that is at high risk for occupational TB."

There are about 9 million new cases of TB each year, and a large proportion of the disease burden is in developing countries. Most people infected with TB contain the infection, and it remains latent. In some individuals, the infection progresses to active disease.

The tuberculin skin test, in which the skin is pricked with antigens from Mycobacterium tuberculosis, had stood alone for more than 100 years as the method for detecting latent TB infection.

However, many health professionals consider the skin test crude, said Pai, because it is unable to clearly distinguish between people who have received a vaccine against TB from those who have a true infection. Moreover, the skin test requires the patient to return three days after the skin prick so that a health worker can measure the resulting bump on the skin.

Having a test that allows health care officials to confirm a true TB infection is important because a positive test can lead to a six-month treatment of daily anti-TB drugs for the patient.

Pai said the development of a more advanced assay that uses specific TB antigens to detect levels of interferon-gamma, a protein released by the immune cells of people infected with tuberculosis, was greeted with a measure of excitement among health officials.

The test, called QuantiFERON-TB-Gold, has been approved by the U.S. Food and Drug Administration. Unlike the skin test, the interferon-gamma test requires only one visit by the patient, and its results do not rely upon the subjective interpretation of a health worker.

However, the new test requires special lab facilities, making it more expensive than the old skin test. The skin test, in turn, involves more personnel time because it requires health care workers to deal with a patient twice. "The new test may turn out to be more cost-effective in developed nations like the United States where labor costs are higher," said Pai.

For this study, researchers analyzed the results of 726 health care workers from the Mahatma Gandhi Institute, a rural hospital in Sevagram, India, that treats about 300 tuberculosis patients a year. The workers were tested with both the traditional TB skin test and the interferon-gamma assay.

About half of the workers tested positive for latent TB infection. The researchers found a high level of agreement - 81.4 percent - between the two tests. Surprisingly, previous TB vaccination had little impact on the results of either test.

Pai notes that other studies in North America and Europe have shown that the interferon-gamma test outperformed the skin test. "It's important to keep both tests on the menu so that health professionals can choose what's best for their target population," said Pai. "For high-burden, low-resource countries such as India, the skin test might still have value."

Ipr1 Gene that influences Innate Immunity to Tuberculosis

Thu, 14 Apr 2005 16:20:38 PST

( from http://www.rxpgnews.com ) Researchers from the Harvard School of Public Health studying tuberculosis resistance and susceptibility in animals have identified a gene in mice which plays a significant role in limiting the multiplication of intracellular pathogens Mycobacterium tuberculosis and Listeria monocytogenes inside host cells. The gene, Intracellular pathogen resistance 1 (Ipr1), found in the chromosome location known as sst1 (super susceptibility to tuberculosis 1), turns on a regulated cell death pathway of the bacteria-infected cells causing apoptosis and prevents catastrophic cell death, or necrosis. The findings appear in a paper in the April 7, 2005 issue of the journal Nature.

It is estimated that 8 million people are infected with tuberculosis annually with approximately 2 million of those dying from the lung disease per year. Yet only about 10 percent of people infected actually develop tuberculosis. Stress, malnutrition and other environmental factors significantly influence an individuals susceptibility to developing the disease. In addition, genetic factors have been known to play an important role in determining outcomes of tuberculosis infection in human and other mammalian hosts. However, individual host resistance genes such as Ipr1, involved in innate immunity for tuberculosis, have been difficult to pinpoint, because of a highly complex multigenic control of host immunity.

The researchers studied which genes might influence an individuals susceptibility to developing tuberculosis and found that an important genetic determinant of host resistance to tuberculosis is encoded within the region on mouse chromosome 1, which they named sst1. By identifying the Ipr1 gene within the sst1 region they believe they have uncovered a new mechanism that helps in limiting the possibility of developing M. tuberculosis, especially in the lungs.

Of interest, the Ipr1 gene also controls innate immunity to another intracellular pathogen Listeria monocytogenes, a parasitic disease transferred to humans generally from consuming infected animal products and that causes flu-like symptoms, swelling of the brain and for pregnant women potential loss of fetus. That suggests that the Ipr1 gene controls a general mechanism that protects against other intracellular pathogens besides M. tuberculosis. The researchers suggest that the human equivalent of Ipr1 might be a gene described as SP110 and may play a significant role in determining tuberculosis susceptibility in people.

Igor Kramnik, assistant professor of immunology and infectious disease at the Harvard School of Public Health and senior author of the study said, The findings are encouraging and highlight the role of genetic function in determining whether a person has a high risk of developing tuberculosis. Finding a specific gene in a mouse that has a human equivalent within a highly conserved genetic region suggests that the human equivalent may also be involved in innate immunity to the disease and may further lead to development of diagnostic tests and prevention approaches. He added, Further studies of the Ipr1 gene in a mouse model and its counterpart in humans will improve our understanding of how our immune system works during complex interactions with live, and very successful, pathogens.

Rv1347c - The Missing Enzyme for Tuberculosis Iron Scavenging Pathway

Thu, 31 Mar 2005 16:02:38 PST

( from http://www.rxpgnews.com ) Scientists have discovered that a protein that was originally believed to be involved in tuberculosis antibiotic resistance is actually a "missing enzyme" from the biosynthetic pathway for an agent used by the bacteria to scavenge iron.

Mycobacterium tuberculosis, the causative agent of tuberculosis, is responsible for more morbidity in humans than any other bacteria. The emergence of multi-drug resistant strains of M. tuberculosis has prompted the search for new drug targets and a better understanding of the mechanism of resistance in this bacterium.

Several spans of DNA in the M. tuberculosis genome have been annotated as antibiotic resistance genes due to their sequence similarity to existing antibiotic resistance genes. Dr. Edward N. Baker of the University of Auckland in New Zealand explains, "Generally the sequence of the open reading frame is compared with the sequences of genes for other proteins (most of which are from different species) in sequence databases. If a close match is found, it is assumed that the function is the same or similar."

Rv1347c is one of these annotated antibiotic resistance genes in M. tuberculosis. It encodes a putative aminoglycoside N-acetyltransferase that is thought to be involved in resistance to aminoglycoside antibiotics such as streptomycin.

"The aminoglycoside antibiotics have sugar rings with amino groups attached," explains Dr. Baker. "The N-acetyltransferase chemically modifies the sugar amino group by transferring an acetyl group to it. This inactivates the antibiotic because it can no longer fit into its target."

However, in vitro biochemical assays have failed to demonstrate aminoglycoside N-acetyltransferase activity in Rv1347c. By solving the three-dimensional structure of Rv1347c, Dr. Baker and his colleagues have discovered that the enzyme most likely plays an entirely different role in M. tuberculosis.

"What the structure showed, when combined with careful analysis of the sequence, its neighbors in the genome, and the fact that its gene was also regulated by iron, was that Rv1347c was almost certainly a "missing enzyme" from the pathway for biosynthesis of the iron scavenging agent mycobactin," recalls Dr. Baker.

"Mycobactin is a small molecule which binds iron very tightly. Bacteria synthesize it so that they can acquire the iron they need to grow it is secreted out into the external environment where it scavenges iron and then (with iron bound to it) it is taken up by the bacterium again."

Although Rv1347c is not involved in antibiotic resistance, it still remains a target for the design of new anti-TB drugs. "Enzymes that synthesize mycobactin are drug targets, because if mycobactin biosynthesis is stopped, the bacterium cannot acquire the iron that it needs for survival," explains Dr. Baker. "Importantly this seems to be true even of the bacteria that are taken up by macrophages in the lung and enter a dormant state these are the hardest to attack with drugs."

A New Biochemical Target to Attack Resistant Tuberculosis Bacteriae

Wed, 16 Mar 2005 12:54:38 PST

( from http://www.rxpgnews.com ) A worldwide health problem, tuberculosis kills more people than any other bacterial infection. The World Health Organization estimates that two billion people are infected with TB, and that two million people die each year from the disease.

However, due to multi-drug resistance and a protracted medication regimen, it is extremely difficult to treat. Hence, there is still a great deal of interest in developing new anti-tubercular drugs.

Researchers at the University of Pennsylvania School of Medicine have identified a biochemical target that could lead to a new class of antibiotics to fight TB. They report their findings in this week's online edition of the Proceedings of the National Academy of Sciences.

In a proof-of-principle study, Harvey Rubin, MD, PhD, Professor of Medicine, Division of Infectious Diseases, and colleagues were able to stop the bacteria from multiplying by inhibiting the first step in a common biochemical pathway.

This pathway is responsible for making the energy molecules all cells need to survive.

First author Edward Weinstein, an MD/PhD student, Rubin, and colleagues characterized the pathway and showed that an important enzyme in it is a key target for anti-TB agents.

The pathway, explains Rubin, is like a series of links in a chain, with enzymes facilitating reactions along the way. "We discovered that if you inhibit the very first enzyme in the chain, you inhibit everything else downstream and eventually the bacteria die," he explains.

The research group tested phenothiazine, a drug used in the past to treat schizophrenia, in cultures of Mycobacterium tuberculosis, the bacterium that causes TB. They found that phenothiazines killed the bacterium in culture and suppressed its growth in mice with acute TB infection.

While the effect on the growth of TB in mice was small, it suggested that a valid target was identified. The research group went on to show that the enzyme disabled by the phenothiazines is called type II NADH dehydrogenase and is a unique and important antimicrobial target.

"What we have now is a new target in TB," says Rubin. "We've been able to find at least the beginnings of a class of compounds that we can start working with and that we know is biochemically active against the TB bacteria in culture and in small animals."

Is it a new drug for tuberculosis? Not yet, cautions Rubin. It's premature to say that this class of drugs will cure TB, but it does represent the start of basic research towards that, he concludes.

Next steps include more investigations on inhibitors of the NADH biochemical pathway in TB, and the development of high-throughput screens to find better and safer inhibitors of type II NADH dehydrogenase.

Structure of resuscitation promoting factor (Rpf) unveiled

Mon, 28 Feb 2005 21:27:38 PST

( from http://www.rxpgnews.com ) UCL scientists have found a protein that could unlock the secret to quicker, more effective treatment of TB by waking TB bacteria in the body. Once the TB bacteria are active again, the disease becomes treatable using common drugs like antibiotics. Scientists believe that uncovering the molecular structure of this protein will lead the way to designing drugs which enable treatment of dormant and multidrug resistant TB.

In England and Wales around 400 people die each year from the disease. The top challenge for TB control in the European region is multidrug-resistant TB (MDR-TB). Eight per cent of the bacteria causing TB in patients are resistant to one or more drugs and one per cent show multidrug resistance. Left untreated, a person with infectious TB of the lungs infects around 10 to 15 people every year.

In a study published on 1st March 2005 in Nature Structural & Molecular Biology, a combined team discovered the structure of a protein known as resuscitation promoting factor (Rpf). Five versions of the Rpf protein exist in TB bacteria. The papers unveiling of the molecular structure of Rpf could be crucial to the treatment of TB in the future.

Dr John Ward, Dept of Biochemistry and Molecular Biology at UCL, said: The discovery of Rpf in the TB bacteria could allow the development of methods to wake-up all dormant bacteria in a patient allowing antibiotics to kill the bacteria and cure the disease.

TB, or not TB: that is the question does TLR signaling hold the answer?

Thu, 16 Dec 2004 18:02:38 PST

( from http://www.rxpgnews.com ) Defense against invading pathogens comes in two major forms: innate and adaptive immunity. Local barriers to infection such as the skin, and the production of stomach acid, mucous, tears, and saliva comprise what is known as innate immunity. This form of immunity is critically dependent on signaling by Toll-like receptors (TLRs) that rely heavily on an intracellular adaptor protein called myeloid differentiation factor 88 (MyD88). Acquired immunity is a form of cellular defense where foreign substances are attacked by lymphocytes and destroyed by T cells, and the adaptive immune response is also generally thought to require intact TLR-MyD88 signaling pathways.

However a study by Bernhard Ryffel and colleagues from Centre National de la Recherche Scientifique, France, in the December 15 issue of the Journal of Clinical Investigation, challenges this view and instead suggests that MyD88 may not be absolutely required for a normal adaptive immune response.

The authors used mice genetically deficient in MyD88 and subjected them to Mycobacterium tuberculosis infection. While their adaptive immune response appeared to be unaffected, markedly blunted defense by innate immune mechanisms eventually proved lethal. With the support of additional data, the authors concluded that MyD88-dependent signaling is not significantly involved in T cell activation (an adaptive immune response), but in the absence of MyD88, T cellmediated immunity is only able to provide partial protection from infection.

This study suggests that we need to reassess whether adaptive immunity is really dependent upon innate immunity, and if MyD88 is not involved in regulating the adaptive response to M. tuberculosis infection, then what is? In an accompanying commentary, Terence Doherty and Moshe Arditi from Cedars-Sinai Medical Center in Los Angeles address these and other questions that arise from this study.