Early and Pre-Clinical Detection of Prion Seeding Activity in Cerebrospinal Fluid of Goats using Real-Time Quaking-Induced Conversion Assay

Conventional and State-of-the-Art Detection Methods of Bovine Spongiform Encephalopathy (BSE)

Bovine spongiform encephalopathy (BSE) is a fatal neurodegenerative disease that belongs to a group of diseases known as transmissible spongiform encephalopathies (TSEs). It is believed that the infectious agent responsible for prion diseases is abnormally folded prion protein (PrP^Sc), which derives from a normal cellular protein (PrP^C), which is a cell surface glycoprotein predominantly expressed in neurons. There are three different types of BSE, the classical BSE (C-type) strain and two atypical strains (H-type and L-type). BSE is primarily a disease of cattle; however, sheep and goats also can be infected with BSE strains and develop a disease clinically and pathogenically indistinguishable from scrapie. Therefore, TSE cases in cattle and small ruminants require discriminatory testing to determine whether the TSE is BSE or scrapie and to discriminate classical BSE from the atypical H- or L-type strains. Many methods have been developed for the detection of BSE and have been reported in numerous studies. Detection of BSE is mainly based on the identification of characteristic lesions or detection of the PrP^Sc in the brain, often by use of their partial proteinase K resistance properties. The objective of this paper was to summarize the currently available methods, highlight their diagnostic performance, and emphasize the advantages and drawbacks of the application of individual tests.

Standardization of Data Analysis for RT-QuIC-Based Detection of Chronic Wasting Disease

Chronic wasting disease (CWD) is a disease affecting cervids and is caused by prions accumulating as pathogenic fibrils in lymphoid tissue and the central nervous system. Approaches for detecting CWD prions historically relied on antibody-based assays. However, recent advancements in protein amplification technology provided the foundation for a new class of CWD diagnostic tools. In particular, real-time quaking-induced conversion (RT-QuIC) has rapidly become a feasible option for CWD diagnosis. Despite its increased usage for CWD-focused research, there lacks a consensus regarding the interpretation of RT-QuIC data for diagnostic purposes. It is imperative then to identify a standardized and replicable method for determining CWD status from RT-QuIC data. Here, we assessed variables that could impact RT-QuIC results and explored the use of maxpoint ratios (maximumRFU/backgroundRFU) to improve the consistency of RT-QuIC analysis. We examined a variety of statistical analyses to retrospectively analyze CWD status based on RT-QuIC and ELISA results from 668 white-tailed deer lymph nodes. Our results revealed an MPR threshold of 2.0 for determining the rate of amyloid formation, and MPR analysis showed excellent agreement with independent ELISA results. These findings suggest that the use of MPR is a statistically viable option for normalizing between RT-QuIC experiments and defining CWD status.

Animal Models of Neurodegenerative Disease: Recent Advances in Fly Highlight Innovative Approaches to Drug Discovery

Neurodegenerative diseases represent a formidable challenge to global health. As advances in other areas of medicine grant healthy living into later decades of life, aging diseases such as Alzheimer's disease (AD) and other neurodegenerative disorders can diminish the quality of these additional years, owed largely to the lack of efficacious treatments and the absence of durable cures. Alzheimer's disease prevalence is predicted to more than double in the next 30 years, affecting nearly 15 million Americans, with AD-associated costs exceeding $1 billion by 2050. Delaying onset of AD and other neurodegenerative diseases is critical to improving the quality of life for patients and reducing the burden of disease on caregivers and healthcare systems. Significant progress has been made to model disease pathogenesis and identify points of therapeutic intervention. While some researchers have contributed to our understanding of the proteins and pathways that drive biological dysfunction in disease using in vitro and in vivo models, others have provided mathematical, biophysical, and computational technologies to identify potential therapeutic compounds using in silico modeling. The most exciting phase of the drug discovery process is now: by applying a target-directed approach that leverages the strengths of multiple techniques and validates lead hits using Drosophila as an animal model of disease, we are on the fast-track to identifying novel therapeutics to restore health to those impacted by neurodegenerative disease.

RT-QuIC detection of pathological prion protein in subclinical goats following experimental oral transmission of L-type BSE

Objective

The spread of bovine spongiform encephalopathy (BSE) agent to small ruminants is still a major issue in the surveillance of transmissible spongiform encephalopathies (TSEs). L-type bovine spongiform encephalopathy (L-BSE) is an atypical form of BSE with an unknown zoonotic potential that is transmissible to cattle and small ruminants. Our current knowledge of bovine atypical prion strains in sheep and goat relies only on experimental transmission studies by intracranial inoculation. To assess oral susceptibility of goats to L-BSE, we orally inoculated five goats with cattle L-BSE brain homogenates and investigated pathogenic prion protein (PrP^sc) distribution by an ultrasensitive in vitro conversion assay known as Real-Time Quaking Induced Conversion (RT-QuIC).

Results

Despite a prolonged observation period of 80 months, all these animals and the uninfected controls did not develop clinical signs referable to TSEs and tested negative by standard diagnostics. Otherwise, RT-QuIC analysis showed seeding activity in five out of five examined brain samples. PrP^sc accumulation was also detected in spinal cord and lymphoreticular system. These results indicate that caprine species are susceptible to L-BSE by oral transmission and that ultrasensitive prion tests deserve consideration to improve the potential of current surveillance systems against otherwise undetectable forms of animal prion infections.

COVID-19-associated encephalitis or Creutzfeldt-Jakob disease: a case report

Background: Accurate diagnosis and management of patients with rapidly progressive dementia may be challenging during the COVID-19 pandemic, which has negatively influenced the diagnostic performances, medical resource allocation and routine care for all non-COVID-19 diseases. Case Presentation: We herein present a case of a 57‐year‐old male with rapidly progressive cognitive decline, headache, diplopia, myalgia, unsteady gait, aggression, depression, insomnia, hallucinations and delusions of persecution. COVID-19-associated encephalitis was briefly considered as a differential diagnosis. However, this hypothesis was rejected upon further investigation. A final diagnosis of sporadic Creutzfeldt–Jakob disease was made. Conclusion: A timely and accurate diagnosis of Creutzfeldt–Jakob disease gives patients and their families the chance to receive a good standard of healthcare and avoid extensive evaluations for other conditions.

Preclinical Detection of Alpha-Synuclein Seeding Activity in the Colon of a Transgenic Mouse Model of Synucleinopathy by RT-QuIC

In synucleinopathies such as Parkinson’s disease (PD) and dementia with Lewy body (DLB), pathological alpha-synuclein (α-syn) aggregates are found in the gastrointestinal (GI) tract as well as in the brain. In this study, using real-time quaking-induced conversion (RT-QuIC), we investigated the presence of α-syn seeding activity in the brain and colon tissue of G2-3 transgenic mice expressing human A53T α-syn. Here we show that pathological α-syn aggregates with seeding activity were present in the colon of G2-3 mice as early as 3 months old, which is in the presymptomatic stage prior to the observation of any neurological abnormalities. In contrast, α-syn seeding activity was not detectable in 3 month-old mouse brains and only identified at 6 months of age in one of three mice. In the symptomatic stage of 12 months of age, RT-QuIC seeding activity was consistently detectable in both the brain and colon of G2-3 mice. Our results indicate that the RT-QuIC assay can presymptomatically detect pathological α-syn aggregates in the colon of G2-3 mice several months prior to their detection in brain tissue.

[Problems of ante mortem diagnostics of prion diseases]

The review presents the state-of-the-art on the problem of diagnosis of prion diseases (PD) in humans and animals with a brief description of their etiology and pathogenesis. We pointed out that understanding the nature of the etio logical agent of PD determined their zoonotic potential and led to the development of highly specific immunological diagnostic methods aimed at identifying the infectious isoform of prion protein (PrPd) as the only marker of the disease. In this regard, we briefly summarize the results of studies, including our own, concerning the conversion of normal prion protein molecules (PrPc) to PrPd, the production of monoclonal antibodies and their application as immunodiagnostic reagents for the post-mortem detection of PrPd in various formats of immunoassay. We also emphasize the issues related to the development of methods for ante mortem diagnostics of PD. In this regard, a method for amplifying amino acid sequences using quacking-induced conversion of PrPc to PrPd in real time (RTQuIC) described in details. The results of recent studies on the assessment of the sensitivity, specificity and reproducibility of this method, carried out in various laboratories around the world, are presented. The data obtained indicate that RT-QuIC is currently the most promising laboratory assay for detecting PrPd in biological material at the preclinical stage of the disease. The significant contribution of US scientists to the introduction of this method into clinical practice on the model of diagnosis of chronic wasting disease of wild Cervidae (CWD) is noted. The possible further spread of CWD in the population of moose and deer in the territories bordering with Russia, as well as the established fact of alimentary transmission of CWD to macaques, indicate the threat of the appearance of PD in our country. In conclusion, the importance of developing new hypersensitive and/or selective components of known methods for PrPd identification from the point of view of assessing the risks of creating artificial infectious prion proteins in vivo or in vitro, primarily new pathogenic isoforms ("strains") and synthetic prions, was outlined.

Detection of Pathognomonic Biomarker PrPSc and the Contribution of Cell Free-Amplification Techniques to the Diagnosis of Prion Diseases

Transmissible spongiform encephalopathies or prion diseases are rapidly progressive neurodegenerative diseases, the clinical manifestation of which can resemble other promptly evolving neurological maladies. Therefore, the unequivocal ante-mortem diagnosis is highly challenging and was only possible by histopathological and immunohistochemical analysis of the brain at necropsy. Although surrogate biomarkers of neurological damage have become invaluable to complement clinical data and provide more accurate diagnostics at early stages, other neurodegenerative diseases show similar alterations hindering the differential diagnosis. To solve that, the detection of the pathognomonic biomarker of disease, PrP^Sc, the aberrantly folded isoform of the prion protein, could be used. However, the amounts in easily accessible tissues or body fluids at pre-clinical or early clinical stages are extremely low for the standard detection methods. The solution comes from the recent development of in vitro prion propagation techniques, such as Protein Misfolding Cyclic Amplification (PMCA) and Real Time-Quaking Induced Conversion (RT-QuIC), which have been already applied to detect minute amounts of PrP^Sc in different matrixes and make early diagnosis of prion diseases feasible in a near future. Herein, the most relevant tissues and body fluids in which PrP^Sc has been detected in animals and humans are being reviewed, especially those in which cell-free prion propagation systems have been used with diagnostic purposes.

Quaking-induced conversion of prion protein on a thermal mixer accelerates detection in brains infected with transmissible spongiform encephalopathy agents

Detection of misfolded prion protein, PrPTSE, in biological samples is important to develop antemortem tests for transmissible spongiform encephalopathies (TSEs). The real-time quaking-induced conversion (RT-QuIC) assay detects PrPTSE but requires dedicated equipment and relatively long incubation times when applied to samples containing extremely low levels of PrPTSE. It was shown that a microplate shaker with heated top (Thermomixer-C) accelerated amplification of PrPTSE in brain suspensions of 263K scrapie and sporadic Creutzfeldt-Jakob disease (sCJD). We expanded the investigation to include TSE agents previously untested, including chronic wasting disease (CWD), macaque-adapted variant CJD (vCJD) and human vCJD, and we further characterized the assays conducted at 42°C and 55°C. PrPTSE from all brains containing the TSE agents were successfully amplified using a truncated hamster recombinant protein except for human vCJD which required truncated bank vole recombinant protein. We compared assays conducted at 42°C on Thermomixer-C, Thermomixer-R (without heated top) and on a fluorimeter used for RT-QuIC. QuIC on Thermomixer-R achieved in only 18 hours assay sensitivity similar to that of RT-QuIC read at 60 hours (or 48 hours with sCJD). QuIC on Thermomixer-C required 24 hours to complete and the endpoint titers of some TSEs were 10-fold lower than those obtained with RT-QuIC and Thermomixer-R. Conversely, at 55°C, the reactions with sCJD and CWD on Thermomixer-C achieved the same sensitivity as with RT-QuIC but in shorter times. Human vCJD samples tested at higher temperatures gave rise to high reactivity in wells containing normal control samples. Similarly, reactions on Thermomixer-R were unsuitable at 55°C. The main disadvantage of Thermomixers is that they cannot track formation of PrP fibrils in real time, a feature useful in some applications. The main advantages of Thermomixers are that they need shorter reaction times to detect PrPTSE, are easier to use, involve more robust equipment, and are relatively affordable. Improvements to QuIC using thermal mixers may help develop accessible antemortem TSE tests.