US: Mad cow & related neurological diseases likely due to virus not prions
Refer Feminist Researchin a scientific world besotted with prion theories:
Manuelidis, Laura, Sklaviadis, Theodoros and Manuelidis, Elias E. Evidence suggesting that PrP is not the infectious agent in Creutzfeldt-Jakob disease. European Molecular Biology Organization Journal 1987; 6: 341-347.
Manuelidis, Laura, Murdoch, Geoffrey and Manuelidis, Elias E. Potential involvement of retroviral elements in human dementias. In: Novel Infectious Agents and the Central Nervous System, Ciba Foundation Symposium 135 Chichester, U.K.: John Wiley & Sons, 1988, p 117-134.
What if rogue proteins aren't to blame for vCJD...
VIRUSES, not prions, may be at the root of diseases such as scrapie, BSE and vCJD.
The widely accepted theory of what causes these so-called "transmissible spongiform encephalopathies" (TSEs), such as mad cow disease, is that deformed proteins called prions corrupt other brain proteins, eventually clogging and destroying brain cells. But this theory has never been proved completely.
Laura Manuelidis of Yale University has insisted for years that virus-like particles observed in TSE-infected brains may be the culprits, but since such brains are degenerating, the particles have been dismissed as general debris.
However, when Manuelidis studied the particles in cultures of neural cells infected with two particular strains of scrapie and CJD, she found they contained particles that had clustered in regular arrays, as viruses do in cells - and no apparent prions (Proceedings of the National Academy of Sciences, vol 104, p 1965). Cells with more particles were better at infecting other cell cultures, while boosting prions did not appear to increase their infectiousness or particle numbers. Agents that disrupt viruses stopped the cells infecting other cultures.
However, leading prion researcher Adriano Aguzzi of the University Hospital of Zurich in Switzerland says Manuelidis won't prove her case without isolating the proposed virus and showing it causes TSE. She should also test other strains for these particles and see if her infected cultures cause TSE in animals, he says.
From issue 2591 of New Scientist magazine, 17 February 2007, page 17
Though challenging the accepted theory of the causes of mad cow disease may seem like madness itself, a team of researchers from the Yale School of Medicine has announced potentially groundbreaking findings concerning the origins of the disease.
Yale School of Medicine professor Dr. Laura Manuelidis, the head of neuropathology at the school, and her team of researchers recently published a report in the Proceedings of the National Academy of Sciences asserting that a virus, rather than prion proteins, is the cause of mad cow disease in animals and Creutzfeldt-Jakob disease in humans. These spongiform encephalopathies of the brain have traditionally been thought to be caused by prions abnormal proteins that convert healthy proteins to the disease state. But the new study suggests prions may simply be part of the late stages of the diseases, not part of the causes.
Transmissible spongiform encephalopathies affect the brains and nervous systems of victims, including sheep, deer and humans. The term ”spongiform” comes from the fact that the infection causes neurons to die, leaving tiny holes in the brain so that it eventually resembles a sponge. Humans afflicted with the incurable degenerative disease show memory and personality changes and sometimes problems with movement. Mad cow, the cattle version of the disease, has achieved infamy because the infectious agent in cows appears to be the cause of vCJD, a variant form of CJD in humans.
The research team’s goal was to try to identify viral particles in infected cells. They infected cell lines with either scrapie (a sheep disease related to mad cow) or CJD agents and found virus-like particles that did not contain prion protein. An abundance of these particles was related to high levels of infectivity, which was not true of the presence of prion proteins.
“People hypothesize that prion proteins are infectious, but they’re probably part of the disease, not the infectious agent itself,” Manuelidis said.
The virus-like particles had been found by other researchers but were largely ignored. They were first identified in 1968 in synaptic regions of scrapie-infected brain and later found in many other animals with different TSEs. But Manuelidis said that researchers apparently forgot about them once the prion hypothesis became dominant.
“I had totally forgotten about them, too,” she said. “But after we found the 25-nanometer particles, I went home and remembered I’ve seen these before. I went back to the old journals from the ’70s and there they were.”
Manuelidis said part of the reason for the neglect of the virus-like particles is that in previous studies, they were always found in degenerating brain tissue, so it was impossible for scientists to draw accurate conclusions about them. What allowed her to collect relevant experimental data was the fact that her team observed the particles in highly infectious tissue culture cells.
“We saw them in tissue culture cells that weren’t degenerating,” she said. “The infected cells were as healthy as the uninfected cells that had no 25-nm virus-like particles.”
The study is a work in progress, and the researchers want to conduct more experiments with tissue cultures to gather further evidence and learn more about the particles. Manuelidis said that since it is easier to work with a simplified cell system than with infected animals whose brains are degenerating, tissue culture experiments can be used to identify essential features of the infectious agent and clarify the way in which the particles invade cells. Her team will use the tissue cultures to purify the virus-like particles more completely.
“In the future, we will try to isolate the particles from tissue cultures and characterize what is in them,” she said.
The team’s specific viral particle hypothesis suggests new avenues for treatment and vaccines, Manuelidis said. If they are successful in rapidly measuring infectivity in tissue culture, they will be able to gain better understanding of possible remedies. She even pointed out that prion proteins, while not the infectious agent, are probably essential receptors for replication and growth of the TSE virus.
”The infectious agent needs prion proteins to grow,” Manuelidis said. “This means targeting the prion protein may also be a useful therapeutic step.”
Researchers at other universities pointed out that the Yale study does not definitely prove the viral hypothesis, nor does it fully disprove the prion hypothesis.
Tricia Serio, an assistant professor of molecular biology, cell biology and biochemistry at Brown University, said that while the research is intriguing, the viral hypothesis still needs to be directly proven. She also pointed out that there are many examples of protein-based phenotypes, like the one described in the prion hypothesis.
“For example, we study prions in yeast, and work from the Weissman, King, Liebman, Saupe and Wickner labs has shown that the transfer of recombinant protein produced in bacteria is sufficient to induce a heritable phenotype in yeast,” she said. ”This is direct proof of a prion mechanism for the yeast traits.”
Surachai Supattapone, associate professor of biochemistry and medicine at Dartmouth University, said that the next challenge for Dr. Manuelidis’ group will be to isolate and identify a specific virus that can cause transmissible spongiform encephalopathy. He said, however, that there is still work ahead for prion protein researchers.
“Proponents of the ‘protein only’ hypothesis which is also not proven will need to demonstrate that purified prion proteins alone can fulfill Koch’s postulates [a set of criteria for establishing a causal relationship between an infectious agent and a disease] to prove their alternative claim,” he said.
Researchers have found virus-like particles in the brain tissue of animals infected with so-called prion diseases, including the fatal human disorder Creutzfeldt-Jakob disease, a finding that calls into question a controversial theory that the diseases are caused by rogue proteins devoid of genetic material.
Although the finding does not disprove the prion theory, it provides evidence of a "very strong alternative," said lead author Laura Manuelidis, a professor of neurobiology at Yale University Medical School.
Manuelidis, whose work appears today in the Proceedings of the National Academy of Sciences, said the same slow-acting viruses most likely also cause chronic wasting disease, the fatal brain disease that has infected the wild deer herd in Wisconsin and other states.
"Everybody has been ignoring these (virus-like particles) for years," Manuelidis said. "The final proof is not in, but there is a lot of evidence (of a viral cause)."
If the virus theory were to hold up, it could lead to new ways to test for mad cow disease and chronic wasting disease.
The new research used electron microscopy to examine cell cultures from mice that were infected with scrapie, a brain disease in sheep, and Creutzfeldt-Jakob disease, a similar disorder in people. They found an abundance of small virus-like particles.
These virus-like particles were able to induce brain disease when injected into hamsters, Manuelidis said. The particles also did not bind to the antibodies of normal prion protein. That suggests they contained no prion protein and that only the virus could be the infectious agent, Manuelidis said.
The virus-like particles found in the cell cultures were small, roughly the size of the polio virus, said Sheldon Penman, a virologist and emeritus professor of biology at Massachusetts Institute of Technology.
Building a case
Penman, who submitted the Manuelidis paper to the National Academy, said he has been following her work for years as she slowly has built a case that prion diseases, known formally as transmissible spongiform encephalopathies or TSEs, are caused by a virus rather than a protein-only substance.
Penman noted that virus-like particles first were observed in TSE-infected brain tissue decades ago, but they were largely ignored as the field became focused on the prion theory.
"It shows we should go back and consider that this is a viral disease," Penman said. "The idea that it's an infectious protein is ridiculous."
The new research is suggestive but not compelling, said Judd Aiken, a prion researcher at the University of Wisconsin-Madison.
It still needs to be shown that the particles have nucleic acid, Aiken said.
"The article shows there's clearly some debate," he said. "But I'm skeptical."
He said most scientists in the field accept the prion theory, although some agree that it, too, has yet to be fully proven.
If it turns out the TSEs are caused by a virus, it would have enormous implications, Aiken said. For instance, testing for disorders such as mad cow and chronic wasting disease would be much simpler and reliable, he said.
Stanley Prusiner first proposed that a rogue protein molecule devoid of nucleic acid could replicate itself and cause the family of fatal brain disorders in people and animals. This abnormally shaped protein caused disease, he said, simply by inducing another protein in the brain to mimic its deformed shape.
His revolutionary idea won the Nobel Prize in 1997, although a few researchers have remained unconvinced.
Proof is tough to find
Three years ago Frank Bastian, a professor of neuropathology at Tulane University, found bacteria known as spiroplasma in brain tissue samples from people and animals that died of TSEs, including chronic wasting disease, scrapie in sheep and Creutzfeldt-Jakob disease in people. However, no one else has duplicated his research.
So far Bastian has shown only an association between spiroplasma and TSE diseases. He has not proved that the organism causes the disease.
But evidence of the infectivity of prions also has been indirect. No one yet has been able to fully purify and isolate prions from infected brain tissue and show that they cause disease.
A spokeswoman for Prusiner, a researcher at the University of California, San Francisco School of Medicine, said he was not available to comment on the new paper because he does not do media telephone interviews.
Neurobiologist Kamel Khalili said he has seen the electron microscopy images from the new paper and the particles certainly look like viruses.
There is a large body of evidence supporting the prion theory, albeit circumstantial, he said. "We must always keep our minds open," said Khalili, chief of neuroscience at Temple University School of Medicine.
A study disputes the theory that deformed proteins are to blame for the brain disease. By Jia-Rui Chong, Times Staff Writer
Graphic Top Markets for Beef
Mad cow disease and other related brain disorders may be caused by a virus and not the weird, misshapen proteins, known as prions, that scientists think are responsible, according to a study released Monday.
Researchers reported that they found virus-like particles in mouse nerve cells infected with two brain-wasting diseases similar to mad cow disease, but found no traces of the particles in uninfected cells.
Lead author Dr. Laura Manuelidis, a neuropathologist at Yale University, said the finding suggested that prions in infected brains were the result of a viral infection and not the cause of the disease.
"We found something that people have been ignoring," Manuelidis said of the virus particles. "What we hypothesize is the simplest, most parsimonious point of view."
Several brain researchers were skeptical about Manuelidis' findings, published in the Proceedings of the National Academy of Sciences.
"It's very remarkable that we only see these particles after infection of these cells," said Bob Rohwer, director of the Molecular Neurovirology Laboratory at the Veterans Affairs Medical Center in Baltimore, who was not involved in the study. "But the evidence that they are in fact the infectious agent responsible is still highly circumstantial."
Mad cow disease, known formally as bovine spongiform encephalopathy, is a cattle disease that destroys brain tissue by causing abnormal tangles of protein fibers and creating microscopic holes in the brain.
It is part of a family of slow-developing brain diseases, including scrapie in sheep and Creutzfeldt-Jakob disease in humans. Human infection in recent years has been connected to eating infected meat. There have been dozens of fatalities over the years.
The prion theory of mad cow disease proposes that a normal protein spontaneously misfolds, starting a cascade of abnormal changes in other proteins.
In Manuelidis' previous experiments, prions did not appear until late in the progression of spongy brain diseases.
To find what appears at an earlier phase, Manuelidis' team homogenized mouse brains infected with scrapie and Creutzfeldt-Jakob disease and injected them into nerve cell cultures.
The only new objects were dense spheres that looked like small viruses, she said.
She later added a compound to spur the growth of prions about fivefold to see if that would increase the level of infection. The level did not show a significant increase, suggesting that prions were not the active agent of infection, she said.
To prove that the virus-like particles are solely responsible for the infection, Manuelidis plans to isolate the particles and see if they can start an infection when injected into healthy cells.