Advancing Prion Science Guidance for the National Prion Research Program: Interim Report (2003) / Chapter Skim
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4. Research Recommendations for TSE Diagnostics
4. Research Recommendations for TSE Diagnostics
Pages 63-82
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From page 63... ...
Laboratory tests designed to detect prions directly are unable to identify less than 1 IU. Infectivity studies with animal bioassay models are among the most sensitive methods for demonstrating the presence of the PrPSc infectious agent, albeit indirectly.
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From page 64... ...
When coupled with sensitive methods for detection of a reagent bound to a target, such as those that rely upon upconversion of phosphors with negligible natural background fluorescence or those mentioned below, a number of approaches offer significant potential. In general, researchers need to leverage novel and fast-breaking developments in biotechnology for example, rapid advances in proteomics and mass spectrometry that enable highthroughput, precise characterization of proteins if significant breakthroughs in prion detection are to be achieved.
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From page 65... ...
Physics-Based Methods Within the past two decades, numerous detection methods based on physical phenomena have also been devised. They include evanescent-wave methods (such as those based on surface plasmon resonance)
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From page 66... ...
This requirement can be addressed by a variety of approaches. Conclusions Regarding Reagents and Detection Methods In broad terms, the present limitations to prion detection lie not in the lack of methods but in the paucity of antibody and other recognition molecules specific for prion species, strain, and allelic variants and for the infectious conformation.
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From page 67... ...
This may lead not only to better diagnostics but also to better therapeutic and prophylactic strategies. SURROGATE MARKERS AND SIGNATURES OF PRION DISEASE Diagnostic approaches based on detection of indirect disease markers have a long and checkered history.
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From page 68... ...
Pattern recognition algorithms fall into two groups: those that discover classes of disease (or genes) , such as clustering and selforganizing maps, and those that predict different classes of elements from predefined signatures, such as support vector machines and f-test algorithms (for example, diagonal linear discriminant analysis)
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From page 69... ...
This kind of approach, however, must rely on rigorous evaluation with well-chosen control samples and on predictions obtained from the results of tests with sets of test samples. Recommendation: Identify surrogate markers or signatures for the detection of prions or prion diseases.
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From page 70... ...
Multiphoton microscopy uses near-infrared light, which penetrates more deeply than visible or UV light and which permits imaging of microscopic structures within the cortex of the living animal at an extraordinarily high resolution with no apparent deleterious effects. To visualize p-amyloid deposits in living transgenic mice with Alzheimer's disease, researchers used multiphoton microscopy with locally applied fluorescently labeled antibody against ,8-amyloid or systemically administered fluorescent derivatives of chemicals that bind to p-amyloid, such as thioflavine A and Congo red (Bacskai et al., 2001; Christie et al., 2001; Klunk et al., 2002~.
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From page 71... ...
The most critical areas of basic prion research include solving the structure of PrPSc and relating the structure to prion strain differences (Box 4-1~; determining endogenous and exogenous mechanisms of prion replication (Box 4-2~; elucidating prion epidemiology and natural history (Box 4-3~; clarifying the pathways and pathogenic mechanisms used by prions (Box 4-4~; and elucidating the physiological function of prpc (Box 4-5)
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From page 72... ...
Defining the structural differences between PrP isoforms might enable scientists to synthesize a PrPSc-specific antibody probe or aptamer, opening the door to a TSE diagnostic tool. Antibody probes are increasingly used to detect infectious agents in tissue, but their application to prion detection is limited because no independently validated antibody binds exclusively to PrPSc without prior digestion of PrPC.
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From page 73... ...
These ancillary or chaperoning factors could serve as surrogate markers for prion detection and as drug targets for TSE therapeutics and prophylaxes. Therefore, it is critical that NPRP fund research designed to identify the molecules that facilitate PrPSc formation and accumulation in vivo.
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From page 74... ...
Researchers, clinicians, and public health officials must know which tissues are infectious and when, the mechanisms by which the infectious agent enters and disseminates in the body and then invades the brain, what causes cellular toxicity (priors, prions plus another molecular species, or a totally different molecular entity) , the mechanisms by which the toxic events in TSEs lead to cellular dysfunction and clinical symptomatology, how the infectious agent spreads from host to host, and host determinants of susceptibility to infection.
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At the same time, what investigators learn about the pathogenesis of one prion disease will yield information relevant to the understanding of other prion diseases. The study of TSEs should not be limited to mammalian species.
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From page 76... ...
was that prions can be advantageous to the prion host (Coustou et al., 1997~. Drosophila and Caenorhabditis elegans have also proved to be superb models for the study of a variety of cellular and molecular processes and should be exploited to study prion diseases.
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From page 77... ...
In an ongoing experiment, Nora Hunter and colleagues at the United Kingdom's Institute for Animal Health recently demonstrated for the first time that healthy sheep can become infected with prions through transfusion of blood from BSE agent-infected sheep (Hunter et al., 2002~. In a study funded by the European Union, scientists at the German Primate Center in Gottingen are performing transmission studies with rhesus monkeys to elucidate the pathogenesis of TSE in lymphoid tissue (Personal communication, A
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From page 78... ...
Recommendation: Fund basic research to elucidate the structural features of priors, the molecular mechanisms of prion replication, the mechanisms of TSE pathogenesis, the epidemiology and natural history of TSEs, and the physiological function of PrPC. REFERENCES Alizadeh AA, Eisen MB, Davis RE, Ma C, Lossos IS, Rosenwald A, Boldrick JC, Sabet H
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From page 79... ...
2001. Growth arrest of individual senile plaques in a model of Alzheimer's disease observed by in vivo multiphoton microscopy.
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2002. Imaging Abeta plaques in living transgenic mice with multiphoton microscopy and methoxy-X04, a systemically administered Congo red derivative.
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1995. Scrapie prions selectively modify the stress response in neuroblastoma cells.
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1998. Preliminary observations on the pathogenesis of experimental bovine spongiform encephalopathy (BSE)
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