Counting of single prion particles bound to a capture-antibody surface (surface-FIDA)

ArticleinVeterinary Microbiology 123(4):294-304 · September 2007with17 Reads
DOI: 10.1016/j.vetmic.2007.04.001 · Source: PubMed
Abstract
Hitherto accredited prion tests use the PK resistance of PrP(Sc), the pathogenic isoform of the prion protein, as a marker for the disease. Because of variations in the amount of disease-related aggregated PrP, which is not PK-resistant, these prion tests offer only limited sensitivity. Therefore, a prion detection method that does not rely on PK digestion would allow for the detection of both PK-resistant as well as PK-sensitive PrP(Sc). Furthermore, single particle counting is more sensitive than methods measuring an integrated signal. Our new test system is based on dual-colour fluorescence correlation spectroscopy (FCS). This method quantifies the number of protein aggregates that have been simultaneously labelled with two different antibodies using dual-colour fluorescence intensity distribution analysis (2D-FIDA). This only counts PrP aggregates, and not PrP monomers. To increase the sensitivity, PrP(Sc) was concentrated in a two-dimensional space by immobilizing it so that the antibodies could be captured on the surface of the slide (surface-FIDA). When the surface was systematically scanned, even single prion particles were detected. Using this new technique, the sensitivity to identify samples from scrapie-infected hamster as well as BSE-infected cattle can be dramatically increased in comparison with identification using FIDA in solution.
    • "The method discriminates aggregated PrP forms from monomeric PrP without the use of the proteinase K (PK) digestion step and therefore recognizes both PK-resistant and PK-sensitive PrPTSE. Surface-FIDA enabled the counting of bovine and hamster PrP aggregates in brain homogenates and in bovine cerebrospinal fluid [47]. PrP aggregates were also blind-detected in blood of scrapie-infected sheep (n = 15) with high specificity and sensitivity [46], although it remains unsettle whether the detection of PrP aggregates correlates with infectivity. "
    [Show abstract] [Hide abstract] ABSTRACT: Transmissible spongiform encephalopathy (TSE) or prion diseases are fatal rare neurodegenerative disorders affecting man and animals and caused by a transmissible infectious agent. TSE diseases are characterized by spongiform brain lesions with neuronal loss and the abnormal deposition in the CNS, and to less extent in other tissues, of an insoluble and protease resistant form of the cellular prion protein (PrP(C)), named PrP(TSE). In man, TSE diseases affect usually people over 60 years of age with no evident disease-associated risk factors. In some cases, however, TSE diseases are unequivocally linked to infectious episodes related to the use of prion-contaminated medicines, medical devices, or meat products as in the variant Creutzfeldt-Jakob disease (CJD). Clinical signs occur months or years after infection, and during this silent period PrP(TSE), the only reliable marker of infection, is not easily measurable in blood or other accessible tissues or body fluids causing public health concerns. To overcome the limit of PrP(TSE) detection, several highly sensitive assays have been developed, but attempts to apply these techniques to blood of infected hosts have been unsuccessful or not yet validated. An update on the latest advances for the detection of misfolded prion protein in body fluids is provided.
    Full-text · Article · Aug 2013
    • "Starting from the basic principle of the " sFIDA " assay [17, 18], which has been developed to detect and quantify prion protein aggregates from scrapieinfected hamster as well as BSE-infected cattle, and an earlier version of this assay adapted to detect A aggregates [20, 21], we optimized the assay to an even more sensitive and highly specific A oligomer detection and quantification assay. The details are described in the methods section and a general scheme of the procedure is shown in Fig. 1. "
    [Show abstract] [Hide abstract] ABSTRACT: Recent studies indicate that small amyloid-β peptide (Aβ) oligomers are the major toxic species responsible for development and progression of Alzheimer's disease (AD). Therefore, we suggest that the number of Aβ oligomers in body fluids is the most direct and relevant biomarker for AD. Determination of the Aβ oligomer content of cerebrospinal fluid (CSF) samples from 14 AD patients and 12 age-matched controls revealed a clear distinction between both groups. All samples of the control group showed homogenously low numbers of Aβ oligomers, while the samples of the AD group exhibited significantly higher levels of Aβ oligomers. The Aβ oligomer numbers correlated with the patients' Mini-Mental State Examination scores. This indicates that the quantity of Aβ oligomers in CSF reflects the severity of the disease and that Aβ oligomers play a crucial role in AD pathology and in turn can be used as a diagnostic biomarker.
    Article · Jan 2013
    • "It should be noted, however, that infectivity in the PBMC fraction is about one order of magnitude higher compared to blood plasma [6,7], and prions were not detected in plasma by the ELISA method reported by Terry et al. In an earlier study, we described the detection of PrP aggregates with high sensitivity in brain homogenate of BSE cattle, and in a small number of cerebrospinal fluid samples from BSE cattle [26]. According to the literature, infectivity in blood -even in symptomatic experimental hamsters -is as low as 10 infectious units per ml [33,34]. "
    [Show abstract] [Hide abstract] ABSTRACT: Prion diseases are transmissible neurodegenerative diseases affecting humans and animals. The agent of the disease is the prion consisting mainly, if not solely, of a misfolded and aggregated isoform of the host-encoded prion protein (PrP). Transmission of prions can occur naturally but also accidentally, e.g. by blood transfusion, which has raised serious concerns about blood product safety and emphasized the need for a reliable diagnostic test. In this report we present a method based on surface-FIDA (fluorescence intensity distribution analysis), that exploits the high state of molecular aggregation of PrP as an unequivocal diagnostic marker of the disease, and show that it can detect infection in blood. To prepare PrP aggregates from blood plasma we introduced a detergent and lipase treatment to separate PrP from blood lipophilic components. Prion protein aggregates were subsequently precipitated by phosphotungstic acid, immobilized on a glass surface by covalently bound capture antibodies, and finally labeled with fluorescent antibody probes. Individual PrP aggregates were visualized by laser scanning microscopy where signal intensity was proportional to aggregate size. After signal processing to remove the background from low fluorescence particles, fluorescence intensities of all remaining PrP particles were summed. We detected PrP aggregates in plasma samples from six out of ten scrapie-positive sheep with no false positives from uninfected sheep. Applying simultaneous intensity and size discrimination, ten out of ten samples from scrapie sheep could be differentiated from uninfected sheep. The implications for ante mortem diagnosis of prion diseases are discussed.
    Full-text · Article · May 2012
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