Further characterisation of the prion protein molecular types detectable in the NIBSC Creutzfeldt–Jakob disease brain reference materials

Improving the Predictive Value of Prion Inactivation Validation Methods to Minimize the Risks of Iatrogenic Transmission With Medical Instruments

Prions are pathogenic infectious agents responsible for fatal, incurable neurodegenerative diseases in animals and humans. Prions are composed exclusively of an aggregated and misfolded form (PrP^Sc) of the cellular prion protein (PrP^C). During the propagation of the disease, PrP^Sc recruits and misfolds PrP^C into further PrP^Sc. In human, iatrogenic prion transmission has occurred with incompletely sterilized medical material because of the unusual resistance of prions to inactivation. Most commercial prion disinfectants validated against the historical, well-characterized laboratory strain of 263K hamster prions were recently shown to be ineffective against variant Creutzfeldt-Jakob disease human prions. These observations and previous reports support the view that any inactivation method must be validated against the prions for which they are intended to be used. Strain-specific variations in PrP^Sc physico-chemical properties and conformation are likely to explain the strain-specific efficacy of inactivation methods. Animal bioassays have long been used as gold standards to validate prion inactivation methods, by measuring reduction of prion infectivity. Cell-free assays such as the real-time quaking-induced conversion (RT-QuIC) assay and the protein misfolding cyclic amplification (PMCA) assay have emerged as attractive alternatives. They exploit the seeding capacities of PrP^Sc to exponentially amplify minute amounts of prions in biospecimens. European and certain national medicine agencies recently implemented their guidelines for prion inactivation of non-disposable medical material; they encourage or request the use of human prions and cell-free assays to improve the predictive value of the validation methods. In this review, we discuss the methodological and technical issues regarding the choice of (i) the cell-free assay, (ii) the human prion strain type, (iii) the prion-containing biological material. We also introduce a new optimized substrate for high-throughput PMCA amplification of human prions bound on steel wires, as translational model for prion-contaminated instruments.

Both murine host and inoculum modulate expression of experimental variant Creutzfeldt-Jakob disease

Transmissible spongiform encephalopathies (TSEs) are infections that are experimentally transmissible to laboratory animals. TSE agents (prions) can be serially passaged in the same animal species. The susceptibility of mice to infection with specific TSE agents can be unpredictable and must be established empirically. We challenged wild-type C57BL/6 and RIIIS/J mice and transgenic mice overexpressing bovine prion protein (TgBo110) with a human brain infected with variant Creutzfeldt-Jakob disease (vCJD) agent and pooled brains of macaques experimentally infected with human vCJD agent (first-passage macaque vCJD). The human vCJD brain yielded a wide range of infectivity titres in different mouse models; TgBo110 mice were the most sensitive. In contrast, infectivity titres of macaque vCJD brain were similar in all three murine models. The brains of RIIIS/J mice infected with both human and macaque vCJD had mild or no vacuolation, while infected C57BL/6 and TgBo110 mice had spongiform degeneration with vacuolation. Abnormal prion protein (PrP^TSE) extracted from the brains of vCJD-infected TgBo110 mice displayed different glycosylation profiles and had greater resistance to denaturation by guanidine hydrochloride than PrP^TSE from infected wild-type mice or from either inoculum. Those histopathological features of TSE and physical properties of PrP^TSE in mice with experimental vCJD were intrinsic to the host, even though we also observed differences between wild-type mice infected with either agent, suggesting a modulatory effect of the inoculum. This study compared three widely used mouse models infected with two different vCJD inocula. The results show that the host plays a major role in manifestations of experimental TSEs.

Review: Creutzfeldt-Jakob disease: prion protein type, disease phenotype and agent strain

The human transmissible spongiform encephalopathies or human prion diseases are one of the most intensively investigated groups of rare human neurodegenerative conditions. They are generally held to be unique in terms of their complex epidemiology and phenotypic variability, but they may also serve as a paradigm with which other more common protein misfolding disorders might be compared and contrasted. The clinico-pathological phenotype of human prion diseases appears to depend on a complex interaction between the prion protein genotype of the affected individual and the physico-chemical properties of the neurotoxic and transmissible agent, thought to comprise of misfolded prion protein. A major focus of research in recent years has been to define the phenotypic heterogeneity of the recognized human prion diseases, correlate this with molecular-genetic features and then determine whether this molecular-genetic classification of human prion disease defines the biological properties of the agent as determined by animal transmission studies. This review seeks to survey the field as it currently stands, summarize what has been learned, and explore what remains to be investigated in order to obtain a more complete scientific understanding of prion diseases and to protect public health.

Human prion diseases in the Netherlands (1998-2009): clinical, genetic and molecular aspects

Prion diseases are rare and fatal neurodegenerative disorders that can be sporadic, inherited or acquired by infection. Based on a national surveillance program in the Netherlands we describe here the clinical, neuropathological, genetic and molecular characteristics of 162 patients with neuropathologically confirmed prion disease over a 12-year period (1998–2009). Since 1998, there has been a relatively stable mortality of Creutzfeldt-Jakob disease (CJD) in the Netherlands, ranging from 0.63 to 1.53 per million inhabitants per annum. Genetic analysis of the codon 129 methionine/valine (M/V) polymorphism in all patients with sporadic CJD (sCJD) showed a trend for under-representation of VV cases (7.0%), compared with sCJD cohorts in other Western countries, whereas the MV genotype was relatively over-represented (22,4%). Combined PrP^Sc and histopathological typing identified all sCJD subtypes known to date, except for the VV1 subtype. In particular, a “pure" phenotype was demonstrated in 60.1% of patients, whereas a mixed phenotype was detected in 39.9% of all sCJD cases. The relative excess of MV cases was largely accounted for by a relatively high incidence of the MV 2K subtype. Genetic analysis of the prion protein gene (PRNP) was performed in 161 patients and showed a mutation in 9 of them (5.6%), including one FFI and four GSS cases. Iatrogenic CJD was a rare phenomenon (3.1%), mainly associated with dura mater grafts. Three patients were diagnosed with new variant CJD (1.9%) and one with variably protease-sensitive prionopathy (VPSPr). Post-mortem examination revealed an alternative diagnosis in 156 patients, most commonly Alzheimer's disease (21.2%) or vascular causes of dementia (19.9%). The mortality rates of sCJD in the Netherlands are similar to those in other European countries, whereas iatrogenic and genetic cases are relatively rare. The unusual incidence of the VV2 sCJD subtype compared to that reported to date in other Western countries deserves further investigation.

Phenotypic variability of sporadic human prion disease and its molecular basis: past, present, and future

Human prion diseases are rare neurodegenerative disorders related to prion protein misfolding that can occur as sporadic, familial or acquired forms. In comparison to other more common neurodegenerative disorders, prion diseases show a wider range of phenotypic variation and largely transmit to experimental animals, a feature that led to the isolation and characterization of different strains of the transmissible agent or prion with distinct biological properties. Biochemically distinct PrP(Sc) types have been demonstrated which differ in their size after proteinase cleavage, glycosylation pattern, and possibly other features related to their conformation. These PrP(Sc) types, possibly enciphering the prion strains, together with the naturally occurring polymorphism at codon 129 in the prion protein gene have a major influence on the disease phenotype. In the sporadic form, the most common but perhaps least understood form of human prion disease, there are at least six major combinations of codon 129 genotype and prion protein isotype, which are significantly related to distinctive clinical-pathological subgroups of the disease. In this review, we provide an update on the current knowledge and classification of the disease subtypes of the sporadic human prion diseases as defined by molecular features and pathological changes. Furthermore, we discuss the molecular basis of phenotypic variability taking into account the results of recent transmission studies that shed light on the extent of prion strain variation in humans.

Comparison of the level, distribution and form of disease-associated prion protein in variant and sporadic Creutzfeldt-Jakob diseased brain using conformation-dependent immunoassay and Western blot

Disease-associated prion protein (PrP(Sc)) can be distinguished from the cellular isoform (PrP(C)) by conformation-dependent immunoassay (CDI). This technique exploits the presence of an epitope, accessible in PrP(C), but only unmasked by denaturation in PrP(Sc). In this study, we investigated PrP(Sc) in different brain regions in variant and sporadic Creutzfeldt-Jakob disease (CJD) by using CDI, and directly compared the results with those obtained using the more commonly employed protease digestion and Western blotting. In general, there was good agreement between the results, although there were certain discrepancies in relative abundance when the regional distribution in variant CJD cases was considered. The results largely confirmed the previously described targeting of different brain regions by variant and sporadic CJD. Additionally, the combination of protease digestion and CDI detection demonstrated, for the first time, the presence of PrP(Sc) in variant CJD brains that is susceptible to proteolysis under standard conditions.