Medical Research: What are the main findings of the study?
Dr. Soto: In this study we describe for the first time the highly sensitive detection of prions in human urine, specifically in samples from patients affected by the variant form of Creutzfeldt-Jakob disease (vCJD), which is the disease produced by infection with prions associated with bovine spongiform encephalopathy, also known as mad cow disease. For detection we used the protein misfolding cyclic amplification (PMCA) technique which amplifies the amount of abnormal prion protein in a cyclical manner conceptually analogous to the polymerize chain reaction. We detected prions in 13 of the 14 vCJD cases analyzed, and the only negative was a sample coming from a patient under treatment with a experimental drug injected directly into the brain. No false positive were observed in the more than 200 cases analyzed. The concentration of abnormal prion protein in urine was estimated at 1×10^-16 g/ml, or 3×10^-21 moles/ml, which extrapolates to ~40-100 particles per ml of urine.
Medical Research: What should clinicians and patients take away from your report?
Dr. Soto: The detection of prions in urine may be utilized as a non-invasive diagnostic test for vCJD, and also uncovers a possible risk related with the use of urinary-derived products as well as the collection and disposal of urine from vCJD patients. Annually, more than 300,000 women in the United States and Canada are prescribed urine-derived gonadotropins for infertility. Importantly, using advanced proteomic methods it has been shown that peptide fragments from the normal prion protein are a frequent contaminant that co-purifies with various commercially available urine-derived gonadotropins. Fortunately, no cases of human prion disease have been recognized to date due to the use of urinary gonadotropins.56 However, considering that urine collection systems pool the urine of thousands of donors, proteins get largely concentrated during the purification procedure, the intra-muscular route of administration by which these materials are injected is an efficient route of prion transmission and normally the users of these hormones are young females, it seem prudent to apply precautionary measures to urinary derived products.
Medical Research: What recommendations do you have for future research as a result of this study?
Dr. Soto: The development of methods for high sensitive and specific detection of prions is of utmost importance to minimize further spreading of this fatal disease. This is a challenging task, because prions are likely circulating at very low quantities in peripheral tissues and fluids and because prion diseases have a long clinically-silent incubation period in which infected individuals may unknowingly transmit the disease. Development and implementation of a large scale program to screen individuals, tissues and fluids at risk of infection requires ultra-sensitive detection of prions in easily accessible samples, such as blood or urine. Future research should be done to validate this test for commercial use on diagnosis of vCJD, which would require regulatory approval. Also, it would be interesting to perform a large scale study in countries at high risk of vCJD (UK, France, etc) to estimate the hidden prevalence of vCJD infection in healthy carriers. This would enable to have an idea how many people may develop the disease in the future. Another avenue for future research will be to expand the principles of PMCA to detect abnormal proteins associated to other neurodegenerative diseases, including the highly prevalent Alzheimer‘s and Parkinson‘s diseases. We already have promising results in the application of our technique for the sensitive and specific detection of these diseases.