Creutzfeldt-Jakob disease used to be an affliction of the elderly, revealing its devastating mental and physical symptoms after the age of 55. Now, in Britain and France, the so-called new variant Creutzfeldt-Jakob disease (nvCJD) strikes its victims in their teens or young adulthood.
As of Feb. 4, the body count in Britain had reached 106 dead of nvCJD, plus eight still living with the malady. Another three deaths have occurred in France, and one in Ireland. There is no treatment or cure for CJD, which usually causes death within one calendar year. (See BioWorld Today, July 25,2001, p. 1.)
CJD is a unique ailment, caused by prions. Prions (proteinaceous infectious particles) are unique pathogens, containing amino acids but neither DNA nor RNA. Non-infectious prion particles, dubbed PrPC, perch on the surface of mammalian cells function unknown. Unlike intruding viruses, bacteria, protozoans and fungi, these cellular prions propagate their own infectivity. The PrPC protein becomes lethal when some of the spirals in a portion of its molecules lose their normal conformation and flatten into beta sheets. Once this conversion takes place, the now-infectious prion, dubbed PrPSc, contacts many normal PrPC proteins and flattens their spirals as well.
The “Sc” in PrPSc, its new, contagious form, stands for “scrapie” a prion disease of sheep. It denotes their demented urge to scrape their itchy necks against trees or fences. Dementia is the hallmark of both human and animal prion diseases. It shows up as Swiss-cheese-like vacuoles in their brains. Similarly, cattle in Britain have bovine spongiform encephalopathy (BSE) which led in the 1990s to wholesale slaughter of British herds to prevent spread of the epizootic.
Because of this neural focus, prions have always been construed as attackers of brain tissue. That long-standing assumption changed March 19, 2002 the date of a paper in the current Proceedings of the National Academy of Sciences (PNAS). It bears the cryptic title: “Prions in skeletal muscle.” The article’s senior author is neurologist Stanley Prusiner at the University of California at San Francisco, who discovered prions in 1982. Its lead author is neurologist Patrick Bosque, now practicing at the University of Colorado-affiliated Denver Health Medical Center.
Muscle Harbors High Prion Protein Titers
“Our core finding,” Bosque told BioWorld Today, “was that skeletal muscle is relatively efficient at propagating prions. When we looked at the skeletal muscle in mice infected with scrapie, we found surprisingly high prion titers.
“We also developed transgenic mice,” he went on, “which showed that muscles are relatively good at propagating prions, whereas liver is poor. Also,” he continued, “different muscles seemed to accumulate different levels of prion the highest being in the mouse’s hind limbs.”
Another PNAS co-author, immunologist and molecular biologist Guiseppe Legname, told BioWorld Today: “Researching why prion infection occurs on certain regions of muscle tissue is one side of our efforts. The other side is screening. What we need now is to screen livestock cows, sheep to see if similar findings can be obtained with these animals.
“This has implications for diagnostics,” Legname observed, “because if we validate this study in other animals, we could find a region of the animal’s muscles and do biopsies while it is still alive to determine if it’s infected or not. Until now, unfortunately, you have to kill the animal, and do this assessment post-mortem on brain tissue. It will be true of human patients as well.
“We are well equipped for doing this screening,” he said. “Prusiner’s lab has established a very sensitive and high-throughput prion assay Conformation Immunoassay that we carried out last year for the European Union. The InPro Biotechnology company was set up by Prusiner just to handle large numbers of such samples.”
Richard Murdock is InPro’s president and CEO. “Our company was formed in January 2001,” he told BioWorld Today. “It’s in South San Francisco. InPro,” he explained, stands for “Infectious Proteins.” “Its job is to take all of the intellectual property that has been developed in the Prusiner labs at UC/SF, which we have licensed, and commercialize it. We think our Conformation Immunoassay is the most sensitive and specific test currently available for postmortem BSE.
“Right now the company is focusing on three areas,” Murdock recounted. “The first is obviously diagnostics. BSE testing post-mortem in cattle, and now also in sheep, has become a major issue in Europe, with all the EC countries mandating prion testing of all slaughtered animals.Today it’s post-mortem testing, basically brain tissue. Clearly, we are looking very hard right now at next-generation tests, which would be muscle tissue and also blood.
“In addition to the immunoassay,” Murdock went on, “Prusiner’s lab has developed strains of transgenic mice for bioassays, which is Gold Standard for prion testing. InPro has access to all of those transgenic mice, a lot of which we will be using for validation studies and other types of screening. Another thing we’re working on, which the Prusiner lab has patented, is disinfectant for prions. It’s a very nontoxic, noncaustic disinfectant. The problem with prions is that they’re almost bullet-proof. This is a very different approach to disinfectant, which we hope to manufacture and market.”
Deer, Elk Have Prion Wasting Disease
“The last things we’re going to be developing,” Murdock observed, “are therapeutic products to treat prion diseases. With their burden of amyloid plaques, neurodegenerative diseases such as Alzheimer’s and Parkinson’s look very similar to prion diseases. It’s going to take a while before any of these products will be commercialized, but we have a major R&D effort ongoing in therapeutic products to treat these diseases as well.”
Bosque made the point that although no human or animal prion diseases have erupted in the U.S. as yet, “In this country we have the unique problem of chronic wasting disease [CWD] in deer which is the cervine form of prion disease. Deer in certain Rocky Mountain regions are fairly highly infected with prions. Sometimes 15 percent or more of the wild deer in a herd have been found to be infected with CWD. They are generally found in the corner where Colorado, Nebraska and Wyoming border together. But maybe eight months ago, people were screening in Wisconsin 1,000 miles away and in the last hunting season there they found three white-tail deer with CWD. That’s very disturbing,” he said, “because elk and venison are sold in stores. We don’t know if CWD can be transferred to humans.”