Scientists devise accelerated method to determine infectious prion strains
May 29, 2009Current tests to identify specific strains of infectious prions, which cause a range of transmissible diseases (such as mad cow) in animals and humans, can take anywhere from six months to a year to yield results - a time-lag that may put human populations at risk.
Now, a group of scientists from The Scripps Research Institute's Florida campus have developed a new method that cuts this critical time lag by several months.
The new research was published in the open-access journal PLoS ONE on May 29, 2009.
"Because some prion strains are pathogenic for humans and some are not, it's vital that we know the difference when we find them in the field and when we study them in the laboratory," said Corinne Lasmézas, a professor in the Department of Infectology at Scripps Florida who led the study. "Currently, the identification process for mouse-adapted strains takes between six and eight months and can take as long as a year, depending on the strain. Our accelerated method reduces that time to around four months."
The new method for distinguishing among various strains combines a transgenic mouse model with a rapid and sensitive cell-based procedure, the Cell Panel Assay developed by Scripps Florida's Charles Weissmann (chair of the Department of Infectology) and Sukhvir Mahal (senior staff scientist), also investigators on the new study.
"There are about 20 prion strains known in mouse models," Lasmézas said. "We still don't understand what determines the difference among strains even though it's very important, especially for any potential therapeutic development. Our new method should help quicken the pace of research."
The Mysteries of Prions
Prion diseases, also called spongiform encephalopathies, are a group of closely related, fatal neurodegenerative disorders that affect mammals, including cows, sheep, and deer, as well as humans. Different strains of the infectious agent, called a prion, cause mad cow disease, chronic wasting disease, and different forms of scrapie and human Creutzfeldt-Jacob disease.
Mad cow disease has had devastating consequences for bovine livestock populations, particularly in Europe, and for humans who have consumed contaminated beef products.
To date, there have been more than 200 recorded human fatalities worldwide due to mad cow disease. Creutzfeldt-Jacob disease, a low-incidence but always fatal disease, affects humans in all countries.
Prions consist mainly or entirely of an abnormal form of a normal cellular protein. They multiply by converting their normal counterparts into a likeness of themselves, which may aggregate to form deposits called amyloid. Accumulation of different kinds of amyloid plays a role in a wide range of neurodegenerative diseases, including Alzheimer's and Parkinson's diseases.
Currently, different varieties of prion strains are identified in mouse models according to incubation time, clinical symptoms, and localization of brain lesions.
Accelerated Incubation
In the new test developed by Lasmézas and Weissmann, a transgenic mouse line called Tga20 plays an important role, because it succumbs rapidly to prion disease.
"The prions primarily target the brainstem and the thalamus of this transgenic mouse, explaining why these animals have a shorter incubation time than their normal counterparts," Lasmézas said. "The prion aggregates also don't spread evenly to other brain regions, and their distribution is characteristic for different strains."
Importantly, the brain tissue can be subjected to the Cell Panel Assay, which unlike the current histological method, doesn't require time intensive examination of brain lesions and can be completed within two weeks, Lasmézas added. The test has been partially automated.
Development of the method provided the scientists with the opportunity to make the observation that there was, in some brain regions, little relationship between the amount of abnormal prion protein deposition and the amount of normal prion protein. This was something of a surprise, Lasmézas said, but not totally unexpected.
"We and others believe that the prion protein may not be the sole player in these diseases," she said. "Perhaps there is a co-factor, or perhaps the protein structure differs somewhat from one brain region to the next. We don't know. Just like we don't really know the reason for the different behavior of the various prion strains—is this cause or effect? Our new method should help accelerate the process of discovery."
More information: The first authors of the study, "Prion Strain Discrimination Based on Rapid in Vivo Amplification and Analysis by the Cell Panel Assay," are Yervand E. Karapetyan and Paula Saá of The Scripps Research Institute. Other authors include Sukhvir P. Mahal, Gian Franco Sferrazza, Alexandra Sherman and Nicole Salčs, also of Scripps Research. For more information, see http://dx.plos.org/10.1371/journal.pone.0005730 .
Source: The Scripps Research Institute (news : web)
Dec 04, 2007 |
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However, also SARS and now swine flu: some diseases grab the headlines. But thousands of people worldwide suffer from very rare conditions, many of which few people have ever heard of. There is question; why these animal related diseases are worldwide well known when only hundreds of people worldwide suffer...? I think that these diseases are interesting for media - politics- economists because their eradication is very expensive . However, also very interesting for some science- specialists ! See one example; human mad cow disease or variant CJD. After more than ten years prevalence of variant CJD agent in Britain remains uncertain. WHY? Because mad cow disease (BSE) is only believed to be linked to the rare but fatal brain-wasting human variant Creutzfeldt-Jakob disease (vCJD); see the number of cases of variant Creutzfeldt-Jakob disease (vCJD) in the United Kingdom has decreased since 2000 to zero level in 2009 (http://www.cjd.ed...es.htm). However, in 2004, a study of 13,000 appendix and tonsil samples revealed that thousands of people may be unknowingly harbouring vCJD and raising concerns over the possible extent of vCJD transmission via blood transfusions in the United Kingdom. So the prion protein infection from transmissible BSE is then thought to travel to the brain via peripheral nerves, perhaps with assistance from the lymphoreticular system. However, in 2007 scientists find connection between nerve cells and immune system. They have made visible an astounding number of contacts between immune and nerve cells. These include some of the most important immune cell types, such as B-lymphocytes, T-lymphocytes and dendric cells - all of which form connections to the nerves (http://www.news-m...=21792).
In addition, the link between vCJD, BSE and scrapie has been widely accepted although never proved. Two groups of eminent British scientists argued in 2001 over whether the "infectious agent" in BSE would kill 136,000 Britons or only a few thousand. And what is the reality- where is the truth, seven years later? The 1st vCJD cases were observed in 1995, and the peak number of deaths was 28 in the year 2000, followed by 20 in 2001, 17 in 2002, 18 in 2003, 9 in 2004, 5 in 2005, 5 in 2006, 5 in 2007, and only one in 2008.
There will be no epidemic of the human form of mad cow disease in Britain, despite fears that the worst is yet to come, an expert said. We are "highly unlikely" to see a resurgence in the fatal brain condition, according to Professor Bob Will, director of the National CJD Surveillance Unit, who was speaking at a medical conference in Edinburgh (PRION, September 2007) (http://theherald....c_of_vcj d_in_uk_highly_unlikely.php). So these findings (2008/ 2009) act in concert with Dr VENTERS theory (The epidemic that never was) published in 2001 (http://www.bmj.co...17/858).
Also according to the research; mad cow disease (BSE) can not be "infectious disease ". Why? Authors in Journal of Pathology (March, 2006) found that prion proteins implicated in the development of transmissible spongiform encephalopathies, such as vCJD, may be markers for disease rather than the infectious agents. So, under laboratory circumstances prion-protein can be absorbed across the gut, it also shows that this is unlikely to occur in real life (http://www3.inter...STRACT).
So according to my opinion, there is nutritional and not infectious (BSE- vCJD) way. For example see; Canada discovered its 16th case of mad cow disease (May 15, 2009). WHY? I think and believe that in Canada, there are not respected the recommendations about the dietary protein requirements in dairy cows. So on the other hand see my conclusions about the reasons of the BSE incidence decrease;
1. Increase of magnesium in mineral feed supplement (by 160%) for dairy cattle at the beginning of 1990s (see later; a fundamental %u201Cinitial decrease%u201D of BSE incidence in the United Kingdom). For example see well known Czech experiment (December 1989);
%u201EEvaluation of a new mineral feed supplement used in feeding young breeding cattle in the winter season%u201D (http://www.ncbi.n...stract). However, the official scientific statement about the 5-years incubation period of the BSE in the UK is different. It is based on the feed ban of meat and bone meal (1988) and the BSE incidence decrease after 1993.
2. The research during 1990s resulted to decrease of protein content in dairy rations; see the comparison of the NRC (1989 and 2001); Recommendations about lower protein intake in dairy cows as a %u201Ephenomenon%u201C at the 2001/2002 period; and later steady %u201Cfinal decrease%u201D of BSE incidence; in European states with high producing dairy cows, especially.
The proof about these conclusions; My advice is following concerning to obtain the proof about the "BSE not infectious disease": The BSE disease was tested in dairy cows, see "nutritional experiment" performed in England; published in Veterinary Record (MOORBY et al., 2000) and in Journal of Dairy Science ( DEWHURST et al., 2000; MOORBY et al., 2000).
So there is necessary to repeat their nutritional experiment (investigate under %u201Etypical%u201C western European conditions from 1980s- 1990s) according to these authors; by using ryegrass forage heavily of %u201Enitrogen and potassium fertilized%u201C, and keeping the level of 20% crude protein in dry matter of dairy ration (using protein concentrate- with soya bean meal); during a minimum of six months! I am sure that the BSE will be developed in a minimum of 13 % experimental animals. Why? Because in their trial, also 13% ; six from the 47 experimental of dairy cows developed clinical signs of BSE; after six month incubation period; without meat and bone meal feeding, however with a high protein concentrate feeding. In connection with the protein surplus, ruminants are predominant about the Mg- deficiency, so BSE can be involved. See these relationships, according to my recent presentation at 29th World Veterinary Congress in Vancouver; Neurodegenerative Diseases and Schizophrenia as a Hyper or Hypofunction of the NMDA Receptors (http://www.bse-ex...es.pdf).