Unmet needs of biochemical biomarkers for human prion diseases.

Although the development of aggregation assays has noticeably improved the accuracy of the clinical diagnosis of prion diseases, research on biomarkers remains vital. The major challenges to overcome are non-invasive sampling and the exploration of new biomarkers that may predict the onset or reflect disease progression. This will become extremely important in the near future, when new therapeutics are clinically evaluated and eventually become available for treatment. This article aims to provide an overview of the achievements of biomarker research in human prion diseases, addresses unmet needs in the field, and points out future perspectives.

Novel method for classification of prion diseases by detecting PrPres signal patterns from formalin-fixed paraffin-embedded samples.

Prion disease is an infectious and fatal neurodegenerative disease. Western blotting (WB)-based identification of proteinase K (PK)-resistant prion protein (PrPres) is considered a definitive diagnosis of prion diseases. In this study, we aimed to detect PrPres using formalin-fixed paraffin-embedded (FFPE) specimens from cases of sporadic Creutzfeldt-Jakob disease (sCJD), Gerstmann-Sträussler-Scheinker disease (GSS), glycosylphosphatidylinositol-anchorless prion disease (GPIALP), and V180I CJD. FFPE samples were prepared after formic acid treatment to inactivate infectivity. After deparaffinization, PK digestion was performed, and the protein was extracted. In sCJD, a pronounced PrPres signal was observed, with antibodies specific for type 1 and type 2 PrPres exhibited a strong or weak signals depending on the case. Histological examination of serial sections revealed that the histological changes were compatible with the biochemical characteristics. In GSS and GPIALP, prion protein core-specific antibodies presented as PrPres bands at 8-9 kDa and smear bands, respectively. However, an antibody specific for the C-terminus presented as smears in GSS, with no PrPres detected in GPIALP. It was difficult to detect PrPres in V180I CJD. Collectively, our findings demonstrate the possibility of detecting PrPres in FFPE and classifying the prion disease types. This approach facilitates histopathological and biochemical evaluation in the same sample and is safe owing to the inactivation of infectivity. Therefore, it may be valuable for the diagnosis and research of prion diseases.

Infectious Diseases of the Brain and Spine: Parasitic and Other Atypical Transmissible Diseases.

Atypical infections of the brain and spine caused by parasites occur in immunocompetent and immunosuppressed hosts, related to exposure and more prevalently in endemic regions. In the United States, the most common parasitic infections that lead to central nervous system manifestations include cysticercosis, echinococcosis, and toxoplasmosis, with toxoplasmosis being the most common opportunistic infection affecting patients with advanced HIV/AIDS. Another rare but devastating transmittable disease is prion disease, which causes rapidly progressive spongiform encephalopathies. Familiarity and understanding of various infectious agents are a crucial aspect of diagnostic neuroradiology, and recognition of unique features can aid timely diagnosis and treatment.

[Clinical characteristics and diagnostics of human spongiform encephalopathies: an update]. / Klinik und Diagnostik humaner spongiformer Enzephalopathien: ein Update.

Human spongiform encephalopathies are rare transmissible neurodegenerative diseases of the brain and the nervous system that are caused by misfolding of the physiological prion protein into a pathological form and its deposition in the central nervous system (CNS). Prion diseases include Creutzfeldt-Jakob disease (CJD, sporadic or familial), Gerstmann-Straussler-Scheinker syndrome (GSS) and fatal familial insomnia (FFI). Prion diseases can be differentiated into three etiological categories: spontaneous (sporadic CJD), inherited (familial CJD, FFI, and GSS) and acquired (variant CJD and iatrogenic CJD). Most cases occur sporadically. Prion diseases can lead to a variety of neurological symptoms and always have an inevitably fatal course. Cerebrospinal fluid analysis and magnetic resonance imaging (MRI) play a crucial role in the diagnostics of prion diseases and may facilitate an early and reliable clinical diagnosis. A causal treatment or specific therapeutic agents are not yet available. In general, a palliative therapeutic concept is indicated.

Detection limitations of prion seeding activities in blood samples from patients with sporadic prion disease.

BACKGROUND: Human prion diseases (HPDs) are fatal neurodegenerative disorders characterized by abnormal prion proteins (PrPSc). However, the detection of prion seeding activity in patients with high sensitivity remains challenging. Even though real-time quaking-induced conversion (RT-QuIC) assay is suitable for detecting prion seeding activity in a variety of specimens, it shows lower accuracy when whole blood, blood plasma, and blood-contaminated tissue samples are used. In this study, we developed a novel technology for the in vitro amplification of abnormal prion proteins in HPD to the end of enabling their detection with high sensitivity known as the enhanced quaking-induced conversion (eQuIC) assay. METHODS: Three antibodies were used to develop the novel eQUIC method. Thereafter, SD50 seed activity was analyzed using brain tissue samples from patients with prion disease using the conventional RT-QUIC assay and the novel eQUIC assay. In addition, blood samples from six patients with solitary prion disease were analyzed using the novel eQuIC assay. RESULTS: The eQuIC assay, involving the use of three types of human monoclonal antibodies, showed approximately 1000-fold higher sensitivity than the original RT-QuIC assay. However, when this assay was used to analyze blood samples from six patients with sporadic human prion disease, no prion activity was detected. CONCLUSION: The detection of prion seeding activity in blood samples from patients with sporadic prion disease remains challenging. Thus, the development of alternative methods other than RT-QuIC and eQuIC will be necessary for future research.

Detection of prions in matching post-mortem skin and cerebrospinal fluid samples using second-generation real-time quaking-induced conversion assay.

Real-time quaking-induced conversion assay (RT-QuIC) exploits templating activity of pathogenic prion protein for ultrasensitive detection of prions. We have utilized second generation RT-QuIC assay to analyze matching post-mortem cerebrospinal fluid and skin samples of 38 prion disease patients and of 30 deceased neurological controls. The analysis of cerebrospinal fluid samples led to 100% sensitivity and 100% specificity, but some samples had to be diluted before the analysis to alleviate the effect of present RT-QuIC inhibitors. The analysis of the corresponding skin samples provided 89.5% sensitivity and 100% specificity. The median seeding dose present in the skin was one order of magnitude higher than in the cerebrospinal fluid, despite the overall fluorescent signal of the skin samples was comparatively lower. Our data support the use of post-mortem cerebrospinal fluid for confirmation of prion disease diagnosis and encourage further studies of the potential of skin biopsy samples for intra-vitam prion diseases´ diagnostics.

Creutzfeldt-Jakob disease and other prion diseases.

Prion diseases share common clinical and pathological characteristics such as spongiform neuronal degeneration and deposition of an abnormal form of a host-derived protein, termed prion protein. The characteristic features of prion diseases are long incubation times, short clinical courses, extreme resistance of the transmissible agent to degradation and lack of nucleic acid involvement. Sporadic and genetic forms of prion diseases occur worldwide, of which genetic forms are associated with mutations in PRNP. Human to human transmission of these diseases has occurred due to iatrogenic exposure, and zoonotic forms of prion diseases are linked to bovine disease. Significant progress has been made in the diagnosis of these disorders. Clinical tools for diagnosis comprise brain imaging and cerebrospinal fluid tests. Aggregation assays for detection of the abnormally folded prion protein have a clear potential to diagnose the disease in peripherally accessible biofluids. After decades of therapeutic nihilism, new treatment strategies and clinical trials are on the horizon. Although prion diseases are relatively rare disorders, understanding their pathogenesis and mechanisms of prion protein misfolding has significantly enhanced the field in research of neurodegenerative diseases.

Large-scale validation of skin prion seeding activity as a biomarker for diagnosis of prion diseases.

Definitive diagnosis of sporadic Creutzfeldt-Jakob disease (sCJD) relies on the examination of brain tissues for the pathological prion protein (PrPSc). Our previous study revealed that PrPSc-seeding activity (PrPSc-SA) is detectable in skin of sCJD patients by an ultrasensitive PrPSc seed amplification assay (PrPSc-SAA) known as real-time quaking-induced conversion (RT-QuIC). A total of 875 skin samples were collected from 2 cohorts (1 and 2) at autopsy from 2-3 body areas of 339 cases with neuropathologically confirmed prion diseases and non-sCJD controls. The skin samples were analyzed for PrPSc-SA by RT-QuIC assay. The results were compared with demographic information, clinical manifestations, cerebrospinal fluid (CSF) PrPSc-SA, other laboratory tests, subtypes of prion diseases defined by the methionine (M) or valine (V) polymorphism at residue 129 of PrP, PrPSc types (#1 or #2), and gene mutations in deceased patients. RT-QuIC assays of the cohort #1 by two independent laboratories gave 87.3% or 91.3% sensitivity and 94.7% or 100% specificity, respectively. The cohort #2 showed sensitivity of 89.4% and specificity of 95.5%. RT-QuIC of CSF available from 212 cases gave 89.7% sensitivity and 94.1% specificity. The sensitivity of skin RT-QuIC was subtype dependent, being highest in sCJDVV1-2 subtype, followed by VV2, MV1-2, MV1, MV2, MM1, MM1-2, MM2, and VV1. The skin area next to the ear gave highest sensitivity, followed by lower back and apex of the head. Although no difference in brain PrPSc-SA was detected between the cases with false negative and true positive skin RT-QuIC results, the disease duration was significantly longer with the false negatives [12.0 ± 13.3 (months, SD) vs. 6.5 ± 6.4, p < 0.001]. Our study validates skin PrPSc-SA as a biomarker for the detection of prion diseases, which is influenced by the PrPSc types, PRNP 129 polymorphisms, dermatome sampled, and disease duration.

Quantitative analysis of prion disease using an AI-powered digital pathology framework.

Prion disease is a fatal neurodegenerative disorder characterized by accumulation of an abnormal prion protein (PrPSc) in the central nervous system. To identify PrPSc aggregates for diagnostic purposes, pathologists use immunohistochemical staining of prion protein antibodies on tissue samples. With digital pathology, artificial intelligence can now analyze stained slides. In this study, we developed an automated pipeline for the identification of PrPSc aggregates in tissue samples from the cerebellar and occipital cortex. To the best of our knowledge, this is the first framework to evaluate PrPSc deposition in digital images. We used two strategies: a deep learning segmentation approach using a vision transformer, and a machine learning classification approach with traditional classifiers. Our method was developed and tested on 64 whole slide images from 41 patients definitively diagnosed with prion disease. The results of our study demonstrated that our proposed framework can accurately classify WSIs from a blind test set. Moreover, it can quantify PrPSc distribution and localization throughout the brain. This could potentially be extended to evaluate protein expression in other neurodegenerative diseases like Alzheimer's and Parkinson's. Overall, our pipeline highlights the potential of AI-assisted pathology to provide valuable insights, leading to improved diagnostic accuracy and efficiency.

The advances in the early and accurate diagnosis of Creutzfeldt-Jakob disease and other prion diseases: where are we today?

INTRODUCTION: Before the introduction of MRI diffusion-weighted images (DWI), the diagnosis of Creutzfeldt-Jakob disease (CJD) relied upon nonspecific findings including clinical symptoms, EEG abnormalities, and elevated levels of cerebrospinal fluid 14-3-3 protein. Subsequently, the use of DWI has improved diagnostic accuracy, but it sometimes remains difficult to differentiate CJD from encephalitis, epilepsy, and other dementing disorders. The revised diagnostic criteria include real-time quaking-induced conversion (RT-QuIC), detecting small amounts of CJD-specific prion protein, and clinically sensitive DWI. Combining these techniques has further improved diagnostic accuracy, enabling earlier diagnosis. AREAS COVERED: Herein, the authors review the recent advances in diagnostic methods and revised diagnostic criteria for sporadic CJD. They also discuss other prion diseases, such as variant CJD and chronic wasting disease, where the emergence of new types is a concern. EXPERT OPINION: Despite improvements in diagnostic methods and criteria, some subtypes of prion disease are still difficult to diagnose, and even the diagnosis using the most innovative RT-QuIC test remains a challenge in terms of accuracy and standardization. However, these revised criteria can be adapted to the emergence of new types of prion diseases. It is essential to continue careful surveillance and update information on the latest prion disease phenotypes.

Creutzfeldt-Jakob disease surveillance in Australia: update to 31 December 2022.

Creutzfeldt-Jakob disease surveillance in Australia: update to 31 December 2022: Nationwide surveillance of Creutzfeldt-Jakob disease (CJD) and other human prion diseases is performed by the Australian National Creutzfeldt-Jakob Disease Registry (ANCJDR). National surveillance encompasses the period since 1 January 1970, with prospective surveillance occurring from 1 October 1993. Over this prospective surveillance period, considerable developments have occurred in pre-mortem diagnostics; in the delineation of new disease subtypes; and in a heightened awareness of prion diseases in healthcare settings. Surveillance practices of the ANCJDR have evolved and adapted accordingly. This report summarises the activities of the ANCJDR during 2022. Since the ANCJDR began offering diagnostic cerebrospinal fluid (CSF) 14-3-3 protein testing in Australia in September 1997, the annual number of referrals has steadily increased. In 2022, a total of 599 domestic CSF specimens were referred for diagnostic testing and 79 persons with suspected human prion disease were formally added to the national register. As of 31 December 2022, just under half of the 79 suspect case notifications (36/79) remain classified as 'incomplete'; 15 cases were classified as 'definite' and 23 as 'probable' prion disease; five cases were excluded through neuropathological examination. For 2022, fifty-five percent of all suspected human-prion-disease-related deaths in Australia underwent neuropathological examination. No cases of variant or iatrogenic CJD were identified. The SARS-CoV-2 pandemic did not affect prion disease surveillance outcomes in Australia during 2022.

Enfermedades por priones humanas. Una revisión general / Human prion diseases: An overview

Las enfermedades por priones constituyen un grupo de enfermedades neurodegenerativas, cuyo agente causal es una proteína normal del cerebro (PrP) que se agrega en una conformación anómala. La proteína anormal, conocida como prion (PrPSc), tiene la propiedad de autopropagarse, induciendo la plegadura anómala de la proteína normal PrP. Estas enfermedades se presentan de manera esporádica, por transmisión genética, o de forma adquirida por ingesta de carne contaminada con priones o por exposición iatrógena. Su diagnóstico resulta difícil. La utilización de exploraciones complementarias de alta sensibilidad y especificidad, como la resonancia magnética o la RT-QuIC, facilitan su diagnóstico. El diagnóstico definitivo se establece por el estudio histopatológico de muestras de tejidos. Actualmente, no se dispone de ningún tratamiento que modifique el curso de la enfermedad, pero su diagnóstico precoz es fundamental para planificar los cuidados del enfermo, adoptar las medidas de prevención necesarias y el consejo genético (AU)

Prion diseases are a group of neurodegenerative diseases. The disease-causing agent is a protein (PrP), that is normally produced in the nervous system, aggregated in an abnormal form. The abnormal protein, known as prion (PrPSc), is capable of self-propagation promoting the misfolding of the normal protein (PrP). These conditions can be acquired sporadically, genetically, or infectiously either by eating meat contaminated with prions or from iatrogenic exposure. The diagnosis of these diseases is often challenging. The use of highly sensitive and specific diagnostic tools, such as MRI and RT-QuIC, may aid in the diagnosis. Neuropathological examination of brain tissue ensures a definite diagnosis. At present, no treatment significantly improves the course of prion diseases; however, an early diagnosis is of paramount importance for patient care decision planning, infection control purposes, and genetic counseling (AU)

Detection of Abnormal Prion Protein by Immunohistochemistry.

Abnormal prion proteins (PrPSc) are the disease-associated isoform of cellular prion protein and diagnostic markers of transmissible spongiform encephalopathies (TSEs). These neurodegenerative diseases affect humans and several animal species and include scrapie, zoonotic bovine spongiform encephalopathy (BSE), chronic wasting disease of cervids (CWD), and the newly identified camel prion disease (CPD). Diagnosis of TSEs relies on immunodetection of PrPSc by application of both immunohistochemistry (IHC) and western immunoblot methods (WB) on encephalon tissues, namely, the brainstem (obex level). IHC is a widely used method that uses primary antibodies (monoclonal or polyclonal) against antigens of interest in cells of a tissue section. The antibody-antigen binding can be visualized by a color reaction that remains localized in the area of the tissue or cell where the antibody was targeted. As such, in prion diseases, as in other fields of research, the immunohistochemistry techniques are not solely used for diagnostic purposes but also in pathogenesis studies. Such studies involve detecting the PrPSc patterns and types from those previously described to identify the new prion strains. As BSE can infect humans, it is recommended that biosafety laboratory level-3 (BSL-3) facilities and/or practices are used to handle cattle, small ruminants, and cervid samples included in the TSE surveillance. Additionally, containment and prion-dedicated equipment are recommended, whenever possible, to limit contamination. The PrPSc IHC procedure consists of a formic acid epitope-demasking step also acting as a prion inactivation measure, as formalin-fixed and paraffin-embedded tissues used in this technique remain infectious. When interpreting the results, care must be taken to distinguish non-specific immunolabeling from target labeling. For this purpose, it is important to recognize artifacts of immunolabeling obtained in known TSE-negative control animals to differentiate those from specific PrPSc immunolabeling types, which can vary between TSE strains, host species, and prnp genotype, further described herein.

Improved Real-Time Quaking Induced Conversion for Early Diagnostics of Creutzfeldt-Jakob Disease in Denmark.

Cerebrospinal fluid-based real-time quaking-induced conversion (CSF RT-QuIC) is currently the most prominent method for early detection of sporadic Creutzfeldt-Jakob disease (sCJD), the most common prion disease. CSF RT-QuIC delivers high sensitivity (>90%) and specificity (100%), which has been demonstrated by large ring-trial studies testing probable and definitive sCJD cohorts. Following the inclusion of CSF RT-QuIC in the revised European CJD Surveillance Network diagnostic criteria for sCJD, it has become a standard diagnostic procedure in many prion disease reference or surveillance centers around the world. In this study, we present the implementation of the second-generation CSF RT-QuIC (commonly known as Improved QuIC or IQ) at the Danish Reference Center for Prion Diseases (DRCPD). The method's sensitivity and specificity were evaluated and validated by analyzing 63 CSF samples. These 63 samples were also analyzed at the National CJD Research and Surveillance Unit (NCJDRSU), based at the University of Edinburgh, UK; analysis was carried out using the first generation or previous CSF RT-QuIC method (PQ). The sensitivity and specificity of PQ during tests at the NCJDRSU were 92% and 100%, respectively. Using these 63 CSF samples, the agreement between the two RT-QuIC generations at DRCPD and NCJDRSU prion laboratories was 100%.

[Human prion diseases: An overview]. / Enfermedades por priones humanas. Una revisión general.

Prion diseases are a group of neurodegenerative diseases. The disease-causing agent is a protein (PrP), that is normally produced in the nervous system, aggregated in an abnormal form. The abnormal protein, known as prion (PrPSc), is capable of self-propagation promoting the misfolding of the normal protein (PrP). These conditions can be acquired sporadically, genetically, or infectiously either by eating meat contaminated with prions or from iatrogenic exposure. The diagnosis of these diseases is often challenging. The use of highly sensitive and specific diagnostic tools, such as MRI and RT-QuIC, may aid in the diagnosis. Neuropathological examination of brain tissue ensures a definite diagnosis. At present, no treatment significantly improves the course of prion diseases; however, an early diagnosis is of paramount importance for patient care decision planning, infection control purposes, and genetic counseling.

Real-time quaking-induced conversion assays for prions: Applying a sensitive but imperfect test in clinical practice.

BACKGROUND AND PURPOSE: Real-time quaking-induced conversion (RT-QuIC) assays offer a sensitive and specific means for detection of prions, although false negative results are recognized in clinical practice. We profile the clinical, laboratory, and pathologic features associated with false negative RT-QuIC assays and extend these to frame the diagnostic approach to patients with suspected prion disease. METHODS: A total of 113 patients with probable or definite prion disease were assessed at Mayo Clinic (Rochester, MN; Jacksonville, FL; Scottsdale, AZ) or Washington University School of Medicine (Saint Louis, MO) from 2013 to 2021. RT-QuIC testing for prions was performed in cerebrospinal fluid (CSF) at the National Prion Disease Pathology Surveillance Center (Cleveland, OH). RESULTS: Initial RT-QuIC testing was negative in 13 of 113 patients (sensitivity = 88.5%). RT-QuIC negative patients were younger (median = 52.0 years vs. 66.1 years, p < 0.001). Other demographic and presenting features, and CSF cell count, protein, and glucose levels were similar in RT-QuIC negative and positive patients. Frequency of 14-3-3 positivity (4/13 vs. 77/94, p < 0.001) and median CSF total tau levels were lower in RT-QuIC negative patients (2517 vs. 4001 pg/mL, p = 0.020), and time from symptom onset to first presentation (153 vs. 47 days, p = 0.001) and symptomatic duration (710 vs. 148 days, p = 0.001) were longer. CONCLUSIONS: RT-QuIC is a sensitive yet imperfect measure necessitating incorporation of other test results when evaluating patients with suspected prion disease. Patients with negative RT-QuIC had lower markers of neuronal damage (CSF total tau and protein 14-3-3) and longer symptomatic duration of disease, suggesting that false negative RT-QuIC testing associates with a more indolent course.

Canine detection of chronic wasting disease (CWD) in laboratory and field settings.

Chronic wasting disease (CWD) is a fatal transmissible spongiform encephalopathy that affects both free-ranging and farmed cervid species, including mule deer, white-tailed deer, and elk (Odocoileus hemionus, Odocoileus virginianus, and Cervus canadensis). Due to the long incubation period and variability of clinical signs, CWD can expand and spread to new areas before they reach diagnostically detectable levels. Antemortem testing methods currently available can be difficult to obtain and to be applied to the large numbers required for adequate surveillance. However, key volatile biomarkers could be harnessed for non-invasive antemortem surveillance. Detection dogs are the most effective tool currently available for volatile detection; dogs can effectively complete wildlife surveys at rates surpassing that of humans. This study is the first to demonstrate that trained detection dogs can be used as an antemortem test for CWD. First, we trained three dogs to differentiate between CWD-positive and CWD-negative white-tailed deer faeces in a laboratory setting. Dogs spent significantly more time at the positive sample than the negative samples, suggesting that they differentiated between the positive and negative volatile signatures. We then trained the same dogs to search for CWD-positive faecal samples in a more naturalistic field setting. In the field, dogs found 8/11 CWD-positive samples and had an average false detection rate of 13%. These results suggest that dogs can be trained to differentiate CWD-positive faeces from CWD-negative faeces in both laboratory and field settings. Future studies will compare canine accuracy to other antemortem methods, as well as improved canine training methods.

Bifunctional carbazole derivatives for simultaneous therapy and fluorescence imaging in prion disease murine cell models.

Prion diseases are characterized by the self-assembly of pathogenic misfolded scrapie isoforms (PrPSc) of the cellular prion protein (PrPC). In an effort to achieve a theranostic profile, symmetrical bifunctional carbazole derivatives were designed as fluorescent rigid analogues of GN8, a pharmacological chaperone that stabilizes the native PrPC conformation and prevents its pathogenic conversion. A focused library was synthesized via a four-step route, and a representative member was confirmed to have native fluorescence, including a band in the near-infrared region. After a cytotoxicity study, compounds were tested on the RML-infected ScGT1 neuronal cell line, by monitoring the levels of protease-resistant PrPSc. Small dialkylamino groups at the ends of the molecule were found to be optimal in terms of therapeutic index, and the bis-(dimethylaminoacetamido)carbazole derivative 2b was selected for further characterization. It showed activity in two cell lines infected with the mouse-adapted RML strain (ScGT1 and ScN2a). Unlike GN8, 2b did not affect PrPC levels, which represents a potential advantage in terms of toxicity. Amyloid Seeding Assay (ASA) experiments showed the capacity of 2b to delay the aggregation of recombinant mouse PrP. Its ability to interfere with the amplification of the scrapie RML strain by Protein Misfolding Cyclic Amplification (PMCA) was shown to be higher than that of GN8, although 2b did not inhibit the amplification of human vCJD prion. Fluorescent staining of PrPSc aggregates by 2b was confirmed in living cells. 2b emerges as an initial hit compound for further medicinal chemistry optimization towards strain-independent anti-prion compounds.