New diagnostic tests for prion diseases

Enhanced Creutzfeldt-Jakob disease surveillance in the older population: Assessment of a protocol for screening brain tissue donations for prion disease

Human prion diseases, including Creutzfeldt-Jakob disease (CJD), occur in sporadic, genetic, and acquired forms. Variant Creutzfeldt-Jakob disease (vCJD) first reported in 1996 in the United Kingdom (UK), resulted from contamination of food with bovine spongiform encephalopathy. There is a concern that UK national surveillance mechanisms might miss some CJD cases (including vCJD), particularly in the older population where other neurodegenerative disorders are more prevalent. We developed a highly sensitive protocol for analysing autopsy brain tissue for the misfolded prion protein (PrPSc ) associated with prion disease, which could be used to screen for prion disease in the elderly. Brain tissue samples from 331 donors to the Edinburgh Brain and Tissue Bank (EBTB), from 2005 to 2022, were analysed, using immunohistochemical analysis on fixed tissue, and five biochemical tests on frozen specimens from six brain regions, based on different principles for detecting PrPSc . An algorithm was established for classifying the biochemical results. To test the effectiveness of the protocol, several neuropathologically confirmed prion disease controls, including vCJD, were included and blinded in the study cohort. On unblinding, all the positive control cases had been correctly identified. No other cases tested positive; our analysis uncovered no overlooked prion disease cases. Our algorithm for classifying cases was effective for handling anomalous biochemical results. An overall analysis suggested that a reduced biochemical protocol employing only three of the five tests on only two brain tissue regions gave sufficient sensitivity and specificity. We conclude that this protocol may be useful as a UK-wide screening programme for human prion disease in selected brains from autopsies in the elderly. Further improvements to the protocol were suggested by enhancements of the in vitro conversion assays made during the course of this study.

Heterologous aggregates promote de novo prion appearance via more than one mechanism

Prions are self-perpetuating conformational variants of particular proteins. In yeast, prions cause heritable phenotypic traits. Most known yeast prions contain a glutamine (Q)/asparagine (N)-rich region in their prion domains. [PSI⁺], the prion form of Sup35, appears de novo at dramatically enhanced rates following transient overproduction of Sup35 in the presence of [PIN⁺], the prion form of Rnq1. Here, we establish the temporal de novo appearance of Sup35 aggregates during such overexpression in relation to other cellular proteins. Fluorescently-labeled Sup35 initially forms one or a few dots when overexpressed in [PIN⁺] cells. One of the dots is perivacuolar, colocalizes with the aggregated Rnq1 dot and grows into peripheral rings/lines, some of which also colocalize with Rnq1. Sup35 dots that are not near the vacuole do not always colocalize with Rnq1 and disappear by the time rings start to grow. Bimolecular fluorescence complementation failed to detect any interaction between Sup35-VN and Rnq1-VC in [PSI⁺][PIN⁺] cells. In contrast, all Sup35 aggregates, whether newly induced or in established [PSI⁺], completely colocalize with the molecular chaperones Hsp104, Sis1, Ssa1 and eukaryotic release factor Sup45. In the absence of [PIN⁺], overexpressed aggregating proteins such as the Q/N-rich Pin4C or the non-Q/N-rich Mod5 can also promote the de novo appearance of [PSI⁺]. Similar to Rnq1, overexpressed Pin4C transiently colocalizes with newly appearing Sup35 aggregates. However, no interaction was detected between Mod5 and Sup35 during [PSI⁺] induction in the absence of [PIN⁺]. While the colocalization of Sup35 and aggregates of Rnq1 or Pin4C are consistent with the model that the heterologous aggregates cross-seed the de novo appearance of [PSI⁺], the lack of interaction between Mod5 and Sup35 leaves open the possibility of other mechanisms. We also show that Hsp104 is required in the de novo appearance of [PSI⁺] aggregates in a [PIN⁺]-independent pathway.

Certain proteins can misfold into β-sheet-rich, self-seeding aggregates. Such proteins appear to be associated with neurodegenerative diseases such as prion, Alzheimer's and Parkinson's. Yeast prions also misfold into self-seeding aggregates and provide a good model to study how these rogue polymers first appear. De novo prion appearance can be made very frequent in yeast by transient overexpression of the prion protein in the presence of heterologous prions or prion-like aggregates. Here, we show that the aggregates of one such newly induced prion are initially formed in a dot-like structure near the vacuole. These dots then grow into rings at the periphery of the cell prior to becoming smaller rings surrounding the vacuole and maturing into the characteristic heritable prion tiny dots found throughout the cytoplasm. We found considerable colocalization of two heterologous prion/prion-like aggregates with the newly appearing prion protein aggregates, which is consistent with the prevalent model that existing prion aggregates can cross-seed the de novo aggregation of a heterologous prion protein. However, we failed to find any physical interaction between another heterologous aggregating protein and the newly appearing prion aggregates it stimulated to appear, which is inconsistent with cross-seeding.

Small-molecule theranostic probes: a promising future in neurodegenerative diseases

Prion diseases are fatal neurodegenerative illnesses, which include Creutzfeldt-Jakob disease in humans and scrapie, chronic wasting disease, and bovine spongiform encephalopathy in animals. They are caused by unconventional infectious agents consisting primarily of misfolded, aggregated, β -sheet-rich isoforms, denoted prions, of the physiological cellular prion protein (PrP(C)). Many lines of evidence suggest that prions (PrP(Sc)) act both as a template for this conversion and as a neurotoxic agent causing neuronal dysfunction and cell death. As such, PrP(Sc) may be considered as both a neuropathological hallmark of the disease and a therapeutic target. Several diagnostic imaging probes have been developed to monitor cerebral amyloid lesions in patients with neurodegenerative disorders (such as Alzheimer's disease, Parkinson's disease, and prion disease). Examples of these probes are Congo red, thioflavin T, and their derivatives. We synthesized a series of styryl derivatives, denoted theranostics, and studied their therapeutic and/or diagnostic potentials. Here we review the salient traits of these small molecules that are able to detect and modulate aggregated forms of several proteins involved in protein misfolding diseases. We then highlight the importance of further studies for their practical implications in therapy and diagnostics.

Update on human prion disease

The recognition that variant Creutzfeldt-Jakob disease (vCJD) is caused by the same prion strain as bovine spongiform encephalopathy in cattle has dramatically highlighted the need for a precise understanding of the molecular biology of human prion diseases. Detailed clinical, pathological and molecular data from a large number of human prion disease patients indicate that phenotypic diversity in human prion disease relates in part to the propagation of disease-related PrP isoforms with distinct physicochemical properties. Incubation periods of prion infection in humans can exceed 50 years and therefore it will be some years before the extent of any human vCJD epidemic can be predicted with confidence.

Microdissection: a method developed to investigate mechanisms involved in transmissible spongiform encephalopathy pathogenesis

Background

The transmissible spongiform encephalopathies (TSEs) are a group of neurodegenerative diseases affecting both human and animals. The neuroanatomical changes which occur in the central nervous system (CNS) of TSE infected animals include vacuolation, gliosis, neuronal loss and the deposition of a disease specific protein, PrP^Sc. Experimental murine models of scrapie, a TSE of sheep, have revealed that pathology may be confined to specific brain areas with targeting of particular neuronal subsets depending on route of injection and scrapie isolate.

To assess the biochemical changes which are taking place in these targeted areas it was necessary to develop a reliable sampling procedure (microdissection) which could be used for a variety of tests such as western blotting and magnetic resonance spectroscopy.

Methods

The method described is for the microdissection of murine brains. To assess the usefulness of this dissection technique for producing similar sample types for analysis by various down-stream biochemical techniques, the areas dissected were analysed for PrP^Sc by western blotting and compared to immunocytochemical (ICC) techniques.

Results

Results show that the method generates samples yielding a consistent protein content which can be analysed for PrP^Sc. The areas in which PrP^Sc is found by western blotting compares well with localisation visualised by immunocytochemistry.

Conclusion

The microdisssection method described can be used to generate samples suitable for a range of biochemical techniques. Using these samples a range of assays can be carried out which will help to elucidate the molecular and cellular mechanisms underlying TSE pathogenesis. The method would also be useful for any study requiring the investigation of discrete areas within the murine brain.

Molecular classification of sporadic Creutzfeldt-Jakob disease

According to the protein-only hypothesis of prion propagation, an abnormal isoform (designated PrP(Sc)) of the cellular prion protein (PrP(C)) is the principal or sole component of transmissible prions. However, the existence of multiple prion strains has been difficult to accommodate within this hypothesis. We have previously reported the identification of four types of human PrP(Sc) associated with sporadic and acquired human prion diseases. These PrP(Sc) types are distinguished by differing molecular mass of fragments following limited proteinase K digestion and by differing ratios of di-, mono- and unglycosylated PrP(Sc). That these discrete biochemical features of PrP(Sc) are serially transmissible to human PrP in transgenic mice following experimental transmission suggests that they may be responsible for encoding prion strain diversity. Here we present detailed clinical, pathological and molecular data from a large number of sporadic Creutzfeldt-Jakob disease (CJD) cases. We show that PrP(Sc) types are associated with codon 129 status, duration of illness and neuropathological phenotype. A novel PrP(Sc) type is presented, illustrating further heterogeneity in CJD, and suggesting that further molecular subtypes of CJD may exist at lower frequencies. A molecular classification of sporadic CJD is proposed.

Molecular and clinical classification of human prion disease

While rare in humans, the prion diseases have become an area of intense clinical and scientific interest. The recognition that variant Creutzfeldt-Jakob disease is caused by the same prion strain as bovine spongiform encephalopathy in cattle has dramatically highlighted the need for a precise understanding of the molecular biology of human prion diseases. Detailed clinical, pathological and molecular data from a large number of human prion disease cases have shown that distinct abnormal isoforms of prion protein are associated with prion protein gene polymorphism and neuropathological phenotypes. A molecular classification of human prion diseases seems achievable through characterisation of structural differences of the infectious agent itself.

The 14-3-3 protein detectable in the cerebrospinal fluid of patients with prion-unrelated neurological diseases is expressed constitutively in neurons and glial cells in culture

The 14-3-3 protein belongs to a family of 30-kD proteins originally identified by two-dimensional analysis of brain protein extracts. Recently, the detection of the 14-3-3 protein in the cerebrospinal fluid (CSF) is utilized as a highly reliable test for the premortem diagnosis of prion diseases such as Creutzfeldt-Jakob disease. For the initial step, to clarify the biological implication of the CSF 14-3-3 protein in these diseases, its expression was investigated in neural tissues and cultures and CSF samples from patients with a variety of neurological diseases by Western blot analysis and immunocytochemistry. The constitutive expression of the 14-3-3 protein was identified in all neural and nonneural tissues examined. It was expressed in all neurons, astrocytes, oligodendrocytes, and microglia in culture with its location in both cytoplasmic and nuclear regions. The 14-3-3 protein was detected in the CSF of 8 out of 71 patients, including 1 Gerstmann-Sträussler-Scheinker disease patient and 7 patients with prion-unrelated neurological diseases, such as meningoencephalitis of viral, bacterial, or tuberculous origin, multiple sclerosis, and mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes. These results suggest that the 14-3-3 protein expressed constitutively at substantial levels in both neurons and glial cells might be released into the CSF as a disease-nonspecific consequence of the extensive brain damage and indicate that the analysis of the 14-3-3 protein in the CSF is not useful as a screening test for prion diseases.

Reuse of angioplasty catheters and risk of Creutzfeldt-Jakob disease

BACKGROUND

In 1996, the Quebec Ministry of Health and Social Services, concerned that reuse of devices contaminated with blood or blood products could cause the transmission of Creutzfeldt-Jakob disease (CJD), discontinued its practice of reusing angioplasty catheters despite the significant cost savings reuse had afforded the health care system for several years. The objective of this study was to establish whether the medical literature provides documentation of any cases in which CJD was transmitted by reused percutaneous transluminal coronary angioplasty (PTCA) equipment.

METHODS AND RESULTS

A Medline search was performed to identify previous studies that examined this issue. Key words for the search included PTCA, CJD, and material and equipment reuse. A substantial amount of effort has been spent on the study of PTCA catheter reuse in relation to the risk of infection, toxicity, and catheter breakage as well as cost. In Québec, studies by the Conseil d'Evaluation des Technologies de la Santé investigated the effectiveness of cleaning and sterilizing PTCA equipment and considered the possibility that reuse of single-use catheters, hemodialyzers, and cardiac pacemakers could spread CJD. A number of other studies found evidence that iatrogenic transmission was responsible for several cases of CJD by direct implantation in or adjacent to the central nervous system during neurosurgery. CJD was also transmitted to human beings by injection of pituitary growth hormone and to mice through cerebral inoculation of contaminated blood and urine. However, there were no documented cases of CJD occurring as a complication of PTCA equipment reuse.

CONCLUSIONS

The current literature indicates that there are no known cases of CJD attributable to the reuse of PTCA devices contaminated by blood or to the transfusion of blood or blood products. This practice is associated with a very low risk of CJD transmission. With the considerable cost savings made possible by reuse of PTCA equipment, reimplementation of this practice should be considered by health delivery systems, provided that stringent methods of cleaning and sterilization are observed.

The current status of haemoglobin-based blood substitutes

Haemoglobin-based red cell substitutes have recently passed a myriad of safety studies and are now undergoing efficacy evaluation. There are numerous potential benefits with use of these solutions: they are readily available and have a long shelf-life; do not require typing and cross-matching; are free of viral or bacterial contamination; lack the immunosuppressive effects of blood; and have a much lower viscosity than blood. One-third of the 10 million units of blood transfused in the United States each year is utilized in the emergency setting. Therefore, a safe, effective substitute for blood should have significant impact upon the way we resuscitate bleeding patients. In this article, the current status of the various haemoglobin-based red cell substitutes is reviewed.