RxPG News : Prion Diseases

Prions transmitted through inhalation

Fri, 14 Jan 2011 22:20:29 PST

( from http://www.rxpgnews.com ) Airborne prions are also infectious and can induce mad cow disease or Creutzfeldt-Jakob disorder. This is the surprising conclusion of researchers at the University of Zurich, the University Hospital Zurich and the University of Tübingen. They recommend precautionary measures for scientific labs, slaughterhouses and animal feed plants.

The prion is the infectious agent that caused the epidemic of mad cow disease, also termed bovine spongiform encephalopathy (BSE), and claimed the life of over 280,000 cows in the past decades. Transmission of BSE to humans, e.g. by ingesting food derived from BSE-infected cows, causes variant Creutzfeldt-Jakob disease which is characterized by a progressive and invariably lethal break-down of brain cells.

It is known that prions can be transmitted through contaminated surgical instruments and, more rarely, through blood transfusions. The consumption of food products made from BSE-infected cows can also induce the disease that is responsible for the death of almost 300 people. However, prions are not generally considered to be airborne – in contrast to many viruses including influenza and chicken pox.

Prof. Adriano Aguzzi's team of scientists at the universities of Zurich and Tübingen and the University Hospital Zurich have now challenged the notion that airborne prions are innocuous. In a study, mice were housed in special inhalation chambers and exposed to aerosols containing prions. Unexpectedly, it was found that inhalation of prion-tainted aerosols induced disease with frightening efficiency. Just a single minute of exposure to the aerosols was sufficient to infect 100% of the mice, according to Prof. Aguzzi who published the findings in the Open-Access-Journal "PLoS Pathogens." The longer expo-sure lasted, the shorter the time of incubation in the recipient mice and the sooner clinical signs of a prion disease occurred. Prof. Aguzzi says the findings are entirely unexpected and appear to contra-dict the widely held view that prions are not airborne.
The prions appear to transfer from the airways and colonize the brain directly because immune sys-tem defects – known to prevent the passage of prions from the digestive tract to the brain – did not prevent infection.

Protecting humans and animals
Precautionary measures against prion infections in scientific laboratories, slaughterhouses and animal feed plants do not typically include stringent protection against aerosols. The new findings suggest that it may be advisable to reconsider regulations in light of a possible airborne transmission of prions. Prof. Aguzzi recommends precautionary measures to minimize the risk of a prion infection in humans and animals. He does, however, emphasize that the findings stem from the production of aerosols in laboratory conditions and that Creutzfeldt-Jakob patients do not exhale prions.

Prions' physical properties lead to different physiological effects

Thu, 29 Jun 2006 02:24:00 PST

( from http://www.rxpgnews.com ) Brittleness is often seen as a sign of fragility. But in the case of infectious proteins called prions, brittleness makes for a tougher, more menacing pathogen. Howard Hughes Medical Institute researcher have discovered that brittle prion particles break more readily into new "seeds," which spread infection much more quickly.

The discovery boosts basic understanding of prion infections, and could provide scientists with new ideas for designing drugs that discourage or prevent prion seeding, said the study's senior author Jonathan Weissman, a Howard Hughes Medical Institute investigator at the University of California, San Francisco (UCSF).

The scientists studied yeast prions, which are similar to mammalian prions in that they act as infectious proteins. In recent years, mammalian prions have gained increasing notoriety for their roles in such fatal brain-destroying human diseases as Creutzfeldt-Jakob disease and kuru, and in the animal diseases, bovine spongiform encephalopathy ("mad cow" disease) and scrapie.

Yeast and mammalian prions are proteins that transmit their unique characteristics via interactions in which an abnormally shaped prion protein influences a normal protein to assume an abnormal shape. In mammalian prion infections, these abnormal shapes trigger protein clumping that can kill brain cells. In yeast cells, the insoluble prion protein is not deadly; it merely alters a cell's metabolism. Prions propagate themselves by division of the insoluble clumps to create "seeds" that can continue to grow by causing aggregation of more proteins.

In earlier studies, Weissman and his colleagues had discovered that the same prion can exist in different strains and have different infectious properties. These strains arise from different misfoldings of the prion protein that result in different conformations. A similar strain phenomenon has been described for mammalian prions. More generally, even in noninfectious diseases involving protein misfolding, like Alzheimer's and Parkinson's diseases, the same protein can misfold into more than one shape with some forms being toxic and others benign. However, Weissman said, it was not understood how different conformations cause different physiological effects.

As part of the studies published in Nature, the researchers created a mathematical model that enabled them to describe the growth and replication of prions according to the physical properties of the prion protein. To validate that model in yeast, they then created in a test tube, infectious forms of the prion protein in three different conformations and introduced them into yeast cells. They then correlated the strength of infectivity of each prion with its physical properties and compared their results to those predicted by their mathematical model.

According to Weissman, the researchers found that the slowest-growing conformation seemed to have the strongest effect in producing protein aggregates inside cells. "But we knew from our model that growth was only half of the equation," said Weissman. "The other key feature was how easy it was to break up the prion and create new seeds, and this propensity to seed could be an important determinant of the prion's physiological impact. And that is what we found experimentally -- that the slower growth of that conformation was more than compensated for by an increased brittleness that promotes fragmentation."

According to Weissman, the importance of a prion's brittleness, or "frangibility," to its physiological effects has both basic research and clinical implications. "Investigators trying to develop synthetic prions as a research model for mammalian prions have had a very hard time getting a high degree of activity," he said. "Part of the reason may be that they were trying to create forms that were very stable. But that might have been exactly the wrong thing to do, because prions that are too stable may be the ones that are not very infectious because the aggregates are hard to break up.

"And from a therapeutic point of view, our findings suggest that effective treatment strategies for prion diseases might aim at stabilizing prion aggregates. By preventing the aggregates from being broken up to smaller seeds, their propagation can be reduced. In contrast, most such strategies now aim at preventing the proteins from forming in the first place," he said.

In future studies, Weissman and his colleagues plan to expand their analytical model to describe in more detail how prions' physical properties lead to different physiological effects. They also plan more detailed analyses to examine how the molecular structure of a prion protein gives rise to its physical properties.

Seven UK cases of Creutzfeldt-Jakob disease associated with transplanted human tissue

Thu, 20 Apr 2006 16:50:00 PST

( from http://www.rxpgnews.com ) Seven cases of Creutzfeldt-Jakob disease (CJD) associated with transplanted human tissue have occurred in the UK over a period of 33 years, reveals a study published ahead of print in the Journal of Neurology Neurosurgery and Psychiatry.

The seven cases of the fatal neurodegenerative disease were reported to the UK CJD surveillance system.

This monitors all cases of CJD arising sporadically, genetically, and as a result of infection from contaminated food products (variant form) or surgery (iatrogenic).

The seven cases reported between 1970 and 2003 were the result of inadvertent transmission via transplanted human dura mater.

Dura mater is the outermost, toughest, and most fibrous of the three membranes covering the brain and spinal cord. It is used in cranial and spinal surgical repair, and in various other procedures, such as the reinforcement of tendons and ligaments.

CJD arose between four and 15 years after surgery, and was traced to one particular supplier in six of the seven cases. In the remaining case, the source was traced to pig tissue, and is believed to be the first such case in the world.

The authors emphasise that transmission of CJD though the use of transplanted human dura mater is rare. Only 164 such cases have been identified around the globe, and most of these were treated with the product identified as the primary source in the UK cases.

The risk to patients in the UK is unknown, say the authors, but research from Australia puts the risk as high as 1 in 500 for those treated between 1973 and 2003.

In Japan, where some 20,000 human mater dura grafts are performed every year, the risk is put at between 1 in 1000 and 1 in 2000.

More stringent selection criteria and better disinfection techniques introduced since 1987 may help to reduce the numbers of future cases arising from surgical transplants, suggest the authors.

First Successful Blood Test for 'Mad Cow' Disease Prions

Mon, 29 Aug 2005 23:22:00 PST

( from http://www.rxpgnews.com ) Researchers at the University of Texas Medical Branch at Galveston (UTMB) have found a way to detect in blood the malformed proteins that cause "mad cow disease," the first time such "prions" have been detected biochemically in blood.

The discovery, reported in an article scheduled to appear online in Nature Medicine Aug. 28, is expected to lead to a much more effective detection method for the infectious proteins responsible for brain-destroying disorders, such as bovine spongiform encephalopathy (BSE) in cattle and variant Creutzfeldt-Jakob disease (vCJD) in humans. The blood test would make it much easier to keep BSE-infected beef out of the human food supply, ensure that blood transfusions and organ transplants do not transmit vCJD, and give researchers their first chance to figure out how many people may be incubating the disease.

"The concentration of infectious prion protein in blood is far too small to be detected by the methods used to detect it in the brain, but we know it's still enough to spread the disease," said UTMB neurology professor Claudio Soto, senior author of the Nature Medicine paper. "The key to our success was developing a technique that would amplify the quantity of this protein more than 10 million-fold, raising it to a detectable level."

Soto and the paper's other authors, UTMB assistant professor of neurology Joaquin Castilla and research assistant Paula Saá, applied a method they call protein misfolding cyclic amplification (PMCA) to blood samples taken from 18 prion-infected hamsters that had developed clinical symptoms of prion disease. PMCA uses sound waves to vastly accelerate the process that prions use to convert normal proteins to misshapen infectious forms.

Successive rounds of PMCA led to the discovery of prions in the blood of 16 of the 18 infected hamsters. No prions were found in blood samples that were taken from 12 healthy control hamsters and subjected to the same treatment.

"Since the original publication of a paper on our PMCA technology, we've spent four years optimizing and automating this process to get to this point," Soto said. "The next step, which we're currently working on, will be detecting prions in the blood of animals before they develop clinical symptoms and applying the technology to human blood samples."

Tests for infectious prions in cattle and human blood are badly needed. Because current tests require post-slaughter brain tissue for analysis, in the United States only cattle already showing clinical symptoms of BSE (so-called "downer cows") are tested for the disorder. This is true even though vCJD potentially can be transmitted by animals not yet showing symptoms of the disease. (Only two cases of BSE have been found in American cows so far.) And although British BSE cases have been in decline since 1992, scientists believe the British BSE epidemic of the 1980s could have exposed millions of people in the UK and Europe to infectious prions. The extent of the vCJD epidemic is yet unknown. So far the disease has killed around 180 people worldwide, but numbers could reach thousands or even hundreds of thousands in the coming decades. Prions have also been shown to be transmissible through blood transfusions and organ transplants.

"Who knows what the real situation is in cattle in the United States? And with people, we could be sitting on a time bomb, because the incubation period of this disease in humans can be up to 40 years," Soto said. "That's why a blood test is so important. We need to know the extent of the problem, we need to make sure that beef and the human blood supply are safe, and we need early diagnosis so that when scientists develop a therapy we can intervene before clinical symptoms appear--by then, it's too late."

Variant prion protein causes infection but no symptoms

Fri, 03 Jun 2005 16:40:00 PST

( from http://www.rxpgnews.com ) Abnormal prion proteins are little understood disease agents involved in causing horrific brain-wasting diseases such as Creutzfeldt-Jacob disease in people, mad cow disease in cattle and chronic wasting disease in deer and elk. Now, new research suggests that a variant form of abnormal prion protein--one lacking an "anchor" into the cell membrane--may be unable to signal cells to start the lethal disease process, according to scientists at the Rocky Mountain Laboratories (RML), part of the National Institute of Allergy and Infectious Diseases (NIAID) of the National Institutes of Health.

"This work provides novel insights into how prion and other neurodegenerative diseases develop and it provides tantalizing clues as to how we might delay or even prevent such diseases by preventing certain cellular interactions," notes NIAID Director Anthony S. Fauci, M.D. A paper describing the research was released online today by the journal Science. RML virologist Bruce Chesebro, M.D., directed the project. Other key co-authors from the Hamilton, MT, RML laboratory include Richard Race, D.V.M., and Gerald Baron, Ph.D. Their collaborators included Michael Oldstone, M.D., and Matthew Trifilo, Ph.D., of The Scripps Research Institute in La Jolla, CA, and Eliezer Masliah, M.D., of the University of California, San Diego (UCSD).

Drawing on experimental concepts first developed at RML a decade ago, the research team exposed two groups of 6-week-old mice to different strains of the agent that causes scrapie, a brain-wasting disease of sheep. Within 150 days of being inoculated with the natural form of scrapie prion protein, all 70 mice in the control group showed visible signs of infection: twitching, emaciation and poor coordination. In contrast, the scientists observed 128 transgenic mice--those engineered to produce prion protein without a glycophosphoinositol (GPI) cell membrane anchor--for 500 to 600 days and saw no signs of scrapie disease. Subsequent electron microscopic examinations at UCSD, however, confirmed that they produced amyloid fibrils, an abnormal form of prion protein, and that they even had brain lesions. More remarkably, according to Dr. Chesebro, the diseased brain tissue resembled that found in Alzheimer's disease rather than in scrapie.

Chesebro mentions two theories as to why the transgenic mice did not show symptoms of illness despite being infected:

The host cell might require the GPI anchor to receive the "toxic signal" from the abnormal prion protein
The plaques might be less toxic than the non-plaque form of prion protein clumps

In either case, more time might be required to produce disease due to the reduced toxicity, Dr. Chesebro says.

"There was so much about this research that surprised us and gave us ideas to pursue," says Dr. Chesebro. "First, the mice didn't get sick. That's very significant. Second, the dense accumulations of scrapie plaque in the brain resembled the plaque seen in Alzheimer's, but it wasn't toxic," which might support more recent concepts about plaque in Alzheimer's patients. "Previously, most researchers thought plaques were the toxic component of Alzheimer's that kills neurons, and many treatments focus on removing the plaques. But what if the plaques are inert, as they were in this research? What if only small clumps are toxic?"

If this hypothesis proves correct, Dr. Chesebro says, the ongoing research could eventually alter scientists' views on preventing prion diseases, shifting emphasis away from stopping the production of prion protein clumps and toward preventing interactions with prion protein anchored to cells, or learning to direct abnormal prion protein accumulations to specific parts of the brain where they will not produce symptoms.

"Abnormal prion protein by itself may not be rapidly lethal--in these mice it wasn't," Dr. Chesebro says.

First mucosal prion vaccine tested in mice

Fri, 13 May 2005 20:08:00 PST

( from http://www.rxpgnews.com ) NYU School of Medicine scientists have created the first active vaccine that can significantly delay and possibly prevent the onset of a brain disease in mice that is similar to mad cow disease. The new findings, published online this week in the journal Neuroscience, could provide a platform for the development of a vaccine to prevent a group of fatal brain diseases caused by unusual infectious particles called prions.

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First mucosal prion vaccine
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The NYU study is also the first to use a mucosal prion vaccine, given by mouth rather than through the skin, which localizes the initial immune response to the gut and mainly stimulates an antibody response, says Dr. Wisniewski. "By giving our vaccine orally, we're stimulating an immune response mainly in the digestive tract," he explains. "Thus, harmful prions in contaminated food will be destroyed in the gut and will not reach other organs in the body." Because the research was conducted in normal mice, the NYU researchers say it will be easier to apply in animals in the wild, which are at risk for developing prion disease.

Prion disease is contracted when an animal eats the body parts of other animals contaminated with prions. What makes these infectious particles unusual is that they are proteins that have the same amino acid composition as equivalent proteins occurring naturally in the body. But the prions turn deadly by changing shape. These "misfolded" proteins tend to aggregate in toxic, cell-killing clumps. As an infection takes hold, prion proteins invade brain tissue and force normal proteins to adopt their configuration. In time, the diseased animal develops dementia, loses control of its limbs, and eventually dies.

There are no treatments for prion-related diseases, and prions can easily infect the body because they do not elicit any immune response.

To create a vaccine that could rally the immune system of mice, the NYU researchers designed a vaccine in which scrapie prions were attached to a genetically modified strain of Salmonella. This bacterium is also used in several animal vaccines and in human vaccines for cholera and typhoid fever. Among mice vaccinated prior to prion exposure, approximately 30% remained alive and symptom-free for 500 days, according to the study. By comparison, mice that didn't receive the vaccine survived only an average of 185 days, and all were dead by 300 days.

The NYU scientists are in the process of redesigning the vaccine for deer and cattle. After choosing the appropriate bacteria for each vaccine, they must genetically modify it to carry the prion protein. "These technical issues are not major hurdles," says Dr. Wisniewski. "Developing a marketable vaccine for livestock is something that is very achievable."
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Although no cure for these diseases -- which include scrapie, mad cow disease, and chronic wasting disease -- is on the horizon, many research groups in both the United States and Europe are working on prion vaccines. But the NYU study is important because it breaks new ground in demonstrating that active immunization can protect a significant percentage of animals from developing symptoms of prion disease, explains Thomas Wisniewski, M.D., Professor of Neurology, Pathology, and Psychiatry, and the lead author of the study.

The vaccines that provide active immunization are made, in part, from proteins found on disease-causing organisms. In response to these proteins, the animal's immune system produces antibodies that will destroy them any time they appear in the body. Most vaccines in use today provide such active immunization.

The prion vaccine developed at NYU would most likely first be used to protect livestock, since most prion infections occur in animals and are thought to be transmitted orally, explains Dr. Wisniewski. The version of prion disease that affects humans usually occurs spontaneously, and only rarely as a result of eating contaminated meat.

"The potential use for a prion vaccine in humans is still theoretical," says Dr. Wisniewski. "But if, for example, there is ever a more significant outbreak of chronic wasting disease and if this disease were found to be transmissible to humans, then we would need a vaccine like this to protect people in hunting areas."

Currently, an outbreak of chronic wasting disease is occurring in some Western states, and the disease's geographic range is expanding. Two cases in wild deer have recently been reported for the first time in New York State, according to the New York State Department of Environmental Conservation.

Blocking apoptosis fails to stop prion damage in mouse brains

Thu, 23 Dec 2004 13:07:00 PST

( from http://www.rxpgnews.com ) Researchers knew that prions, the misfolded proteins that cause mad cow disease and other brain disorders, were killing off a class of important brain cells in a transgenic mouse model. But when they found a way to rescue those cells, they were astonished to discover the mice still became sick.

Now they believe previous efforts to find the beginnings of the mouse disorder may have been focused on the wrong part of the brain cell and are plotting new directions for research.

In a study that appears in the Jan. 1 issue of the Proceedings of the National Academy of Sciences, scientists report evidence that clinical symptoms in the mice are produced by damage to synapses, the areas where nerve cell branches come together for communication.

"This could have important therapeutic implications," says senior author David Harris, M.D, Ph.D, professor of cell biology and physiology at Washington University School of Medicine in St. Louis. "There's a great deal of effort being put into developing treatments for neurodegenerative disorders that would inhibit neuron death. Our results suggest that if we just prevent cell death without doing something to maintain the functionality of the synapse, patients may still get sick."

Harris notes that the findings also link prion diseases, which are relatively rare, to more common neurodegenerative disorders like Alzheimer's disease, where recent evidence has also elevated the importance of damage to synapses.

Because of the bizarre methods by which prions spread and cause disease, they have only recently gained widespread acceptance as the source of several disorders that rapidly devastate the brains of humans, cows, deer and sheep.

In these disorders, the most infamous of which is mad cow disease, copies of a normal brain protein, PrP, fold themselves into abnormal shapes, dramatically altering the proteins' properties. Genetic mutations can increase chances that copies of the PrP protein will misfold into the prion form. Proximity to prions also can increase the chances that normally folded copies of PrP will misfold and become prions.

Human prion disorders can be caused by inherited mutations, through contamination during a medical procedure or, in very rare instances, from consumption of infected animals. In addition, some "spontaneous" cases of human prion disease currently can't be tracked to any genetic or environmental cause. Human prion disorders have no treatment and are fatal in months to several years.

Harris has created nearly 50 genetically modified lines of mice to study prion diseases. The mouse model that he and his colleagues used for the most recent study has a mutation in PrP that causes it to misfold, leading to difficulty in movement and other symptoms similar to those seen in human prion diseases.

Scientists previously found that the mouse mutation kills off a class of brain cells known as cerebellar granule neurons. They form an important part of the structure of the cerebellum, an area in the back of the brain involved in motor coordination and other functions.

"The die-off is very dramatic--it's massive and occurs at roughly the same time among all the granule neurons, and it leads to visible shrinkage of the cerebellum," Harris says. "That had us thinking these cellular deaths had to be related to the onset of symptoms."

To further understand what was happening, Harris began to look into proteins involved in a cellular suicide process called apoptosis. He became interested in a protein called Bax that other scientists had previously identified as a trigger of apoptosis in central nervous system cells.

Harris and his colleagues crossbred the mouse prion model with a line of mice where the Bax gene had been deleted. As they expected, cerebellar granule neurons survived in mice that both had the prion mutation and lacked the Bax gene.

"That's important by itself, because it tells us that Bax is involved in the cell death pathway," Harris notes. "There are other options for self-destruction that the cells could have been using, but now we know that the Bax pathway is the one to focus on."

Although the neurons survived, the clinical symptoms persisted. Microscopic examinations of the brains of mice from the original prion model had previously revealed clumps of prion protein in brain areas heavy with synapses, so researchers decided to look at the health of synapses in the new crossbred line of mice.

A test for synaptophysin, a protein found at synapses, revealed widespread loss of synapses in the new line of mice.

"The neurons were still alive, but their connections were damaged or missing," Harris says. "This discovery really has changed the way we think about future directions for our work."

According to Harris, future research will include studies of how prions damage the synapse and whether the clumps of prion protein are involved in that damage.

Mad cow prions piggyback on iron-storing proteins after surviving digestive juices

Thu, 16 Dec 2004 18:50:00 PST

( from http://www.rxpgnews.com ) A new study from the Department of Pathology at Case Western Reserve University School of Medicine shows that the infectious version of prion proteins, the main culprits behind the human form of mad cow disease or variant Creutzfeldt-Jakob Disease (vCJD), are not destroyed by digestive enzymes found in the stomach. Furthermore, the study finds that the infectious prion proteins, also known as prions, cross the normally stringent intestinal barrier by riding piggyback on ferritin, a protein normally absorbed by the intestine and abundantly present in a typical meat dish. The study appears in the Dec. 15 issue of the Journal of Neuroscience.

Prions are a modified form of normal proteins, the prion proteins, which become infectious and accumulate in the nervous system causing fatal neurodegenerative disease. Variant CJD results from eating contaminated beef products from cattle infected with mad cow disease. To date, 155 cases of confirmed and probable vCJD in the world have been reported, and it is unclear how many others are carrying the infection.

According to the study's senior author Neena Singh, M.D., Ph.D., associate professor of pathology, little is known about the mechanism by which prions cross the human intestinal barrier, which can be a particularly difficult obstacle to cross.

"The mad cow epidemic is far from over, and the continuous spread of a similar prion disease in the deer and elk population in the U.S. raises serious public health concerns," said Singh. "It is therefore essential to understand how this disease is transmitted from one species to another, especially in the case of humans where the infectious prions survive through stages of cooking and digestion."

Using brain tissues infected with the spontaneously occurring version of CJD which is also caused by prions, the researchers simulated the human digestive process by subjecting the tissue to sequential treatment with digestive fluids as found in the human intestinal tract. They then studied how the surviving prions are absorbed by the intestine using a cell model. The prions were linked with ferritin, a cellular protein that normally binds excess cellular iron to store it in a soluble, non-toxic form within the cell.

"Since ferritin shares considerable similarity between species, it may facilitate the uptake of prions from distant species by the human intestine,"said Singh."This important finding provides insight into the cellular mechanisms by which infectious prions ingested with contaminated food cross the species barrier, and provides the possibility of devising practical methods for blocking its uptake," she said. "If we can develop a method of blocking the binding of prions to ferritin, we may be able to prevent animals from getting this disease through feed, and stop the transmission to humans."

Currently, Singh's group is checking whether prions from distant species such as deer and elk can cross the human intestinal barrier.

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The study was supported by National Institutes of Health grants.

Testing Transepithelial Prion Protein Transport In Vitro

Wed, 15 Dec 2004 18:45:00 PST

( from http://www.rxpgnews.com ) The discovery of the "mad cow" variant of CreutzfeldtJakob disease (CJD) as a foodborne illness not only created a worldwide scare but also focused attention on the mechanisms of transmission of the infective agent, the scrapie prion protein (PrPSc). Mishra et al. were surprised to find PrPSc associated with ferritin, a protein clearly abundant in muscle tissue associated with food.

Ravi Shankar Mishra, Subhabrata Basu, Yaping Gu, Xiu Luo, Wen-Quan Zou, Richa Mishra, Ruliang Li, Shu G. Chen, Pierluigi Gambetti, Hisashi Fujioka, and Neena Singh