ABSTRACT
CONTENTS 10.1 Introduction ............................................................................................. 256
10.1.1 How Is a Normal Protein Converted to a TSE Agent? ...... 257 10.1.2 From Food to Brain .................................................................. 258 10.1.3 Species Barrier Phenomenon .................................................. 259 10.1.4 Animal TSEs as Zoonoses ....................................................... 259
10.2 Current Methods in Prion Detection ................................................... 260 10.2.1 Needs for an Ultra-Sensitive Method for Prion
Detection..................................................................................... 260 10.2.2 In Vitro Assays for Prion Detection....................................... 262
10.2.2.1 Histopathological Study ......................................... 262 10.2.2.2 Western Blot-Based Tests ....................................... 262 10.2.2.3 ELISA-Based Tests ................................................... 262 10.2.2.4 BSE and Scrapie Discriminatory Test................... 263 10.2.2.5 Conformational Assays........................................... 264 10.2.2.6 Spectroscopic Techniques: Multispectral
Ultraviolet Fluoroscopy .......................................... 266 10.2.2.7 Prion Concentration and Specific Ligands .......... 266
10.2.3 Amplification Assays for Prion Detection............................ 268 10.2.3.1 In Vitro Amplification............................................. 268 10.2.3.2 In Vivo Amplification ............................................. 271
10.3 Concluding Remarks.............................................................................. 273 Acknowledgments ............................................................................................. 275 References ........................................................................................................... 275
Prion diseases or transmissible spongiform encephalopathies (TSEs) are a group of fatal, transmissible neurodegenerative diseases affecting humans and animals (Table 10.1). They are usually characterized by the presence of protease-resistant prion protein (PrPres), an abnormal, protease-resistant isoform of the normal host cell surface protein1 denoted PrPC. No amino acid sequence or posttranslational differences have been detected between PrPC
and its pathological form, PrPSc. The conversion of PrPC into PrPSc involves a conformational change, whereby the a-helical content diminishes and the amount of b-sheet increases.2 Depending on how they arise, TSEs can be classified as sporadic, hereditary, or infectious; most have been experimentally transmitted and, with some exceptions, the presence of PrPres is related to their infectivity.1,3-5 The etiology of spontaneous and familial TSE has been only described in humans and includes the Creutzfeldt-Jakob disease (CJD), the Gertsmann-Strau¨ssler-Scheinker syndrome, and fatal familial insomnia.6-12
It is generally accepted that misfolding of the cellular prion protein (PrPC) leads to the build up in the brain of an insoluble, pathologic PrP isoform (PrPSc). PrPSc aggregation and accumulation in the brain produce spongiform brain degeneration (vacuolization), neuronal death, astrocytosis, and microglial proliferation.2 Clinically, the disease is manifested mainly by rapidly progressive dementia, visual and motor impairments, and inexorable death.
