Evaluation of urinary PrPSc as a diagnostic test for sporadic, variant, and familial CJD

Clinical Use of Improved Diagnostic Testing for Detection of Prion Disease

Prion diseases are difficult to recognize as many symptoms are shared among other neurologic pathologies and the full spectra of symptoms usually do not appear until late in the disease course. Additionally, many commonly used laboratory markers are non-specific to prion disease. The recent introduction of second-generation real time quaking induced conversion (RT-QuIC) has revolutionized pre-mortem diagnosis of prion disease due to its extremely high sensitivity and specificity. However, RT-QuIC does not provide prognostic data and has decreased diagnostic accuracy in some rarer, atypical prion diseases. The objective of this review is to provide an overview of the current clinical utility of fluid-based biomarkers, neurodiagnostic testing, and brain imaging in the diagnosis of prion disease and to suggest guidelines for their clinical use, with a focus on rarer prion diseases with atypical features. Recent advancements in laboratory-based testing and imaging criteria have shown improved diagnostic accuracy and prognostic potential in prion disease, but because these diagnostic tests are not sensitive in some prion disease subtypes and diagnostic test sensitivities are unknown in the event that CWD transmits to humans, it is important to continue investigations into the clinical utility of various testing modalities.

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.

PMCA Applications for Prion Detection in Peripheral Tissues of Patients with Variant Creutzfeldt-Jakob Disease

Prion diseases are neurodegenerative and invariably fatal conditions that affect humans and animals. In particular, Creutzfeldt-Jakob disease (CJD) and bovine spongiform encephalopathy (BSE) are paradigmatic forms of human and animal prion diseases, respectively. Human exposure to BSE through contaminated food caused the appearance of the new variant form of CJD (vCJD). These diseases are caused by an abnormal prion protein named PrP^Sc (or prion), which accumulates in the brain and leads to the onset of the disease. Their definite diagnosis can be formulated only at post-mortem after biochemical and neuropathological identification of PrP^Sc. Thanks to the advent of an innovative technique named protein misfolding cyclic amplification (PMCA), traces of PrP^Sc, undetectable with the standard diagnostic techniques, were found in peripheral tissues of patients with vCJD, even at preclinical stages. The technology is currently being used in specialized laboratories and can be exploited for helping physicians in formulating an early and definite diagnosis of vCJD using peripheral tissues. However, this assay is currently unable to detect prions associated with the sporadic CJD (sCJD) forms, which are more frequent than vCJD. This review will focus on the most recent advances and applications of PMCA in the field of vCJD and other human prion disease diagnosis.

Ultra-efficient Amplification of Abnormal Prion Protein by Modified Protein Misfolding Cyclic Amplification with Electric Current

Prion diseases are clinically diagnosed and confirmed upon post-mortem histopathological examination of brain tissue. The only reliable molecular marker for prion diseases is abnormal prion protein (PrPSc), a pathologically conformed prion protein that primarily accumulates in the central nervous system and to a lesser extent in lymphoreticular tissues. However, the use of PrPSc as a marker for preclinical diagnoses is limited because the concentration of PrPSc in easily accessible body fluids is extremely low. Hence, one of the most promising approaches would be the development of an efficient in vitro amplification method for PrPSc. Indeed, protein misfolding cyclic amplification (PMCA) has become an important diagnostic tool for prion diseases. Here, we first describe a new superior PMCA device that employs electricity (referred to as ePMCA) to amplify PrPSc. The ePMCA device markedly improved the detection limit for PrPSc by amplifying trace amounts of pathogenic prion protein by applying electricity to improve PMCA. To increase the cavitation of sonication, a glass sample tube was used, and the upper side of the horn was shaped such that it had a curved cross-section. The ePMCA device enabled PrPSc to be amplified even from a sample seeded with 10–28-fold diluted 263K scrapie-infected brain homogenates with recombinant hamster prion protein (rHaPrP). In addition, the efficiency of prion amplification was best when 50 mM HEPES and 1% Triton X-100 were used as a PMCA conversion buffer in the various conditions that we applied. These results indicate that ePMCA would be very valuable for the rapid and specific diagnosis of human prion diseases and, thus, may provide a practically improved method for antemortem diagnoses using the body fluids of patients and animals with prion disease.

Related or not? Development of spontaneous Creutzfeldt-Jakob disease in a patient with chronic, well-controlled HIV: A case report and review of the literature

Background:

We report a novel case of a rare disease: spontaneous Creutzfeldt–Jakob disease in a patient with well-controlled HIV. We explore the relationship between spontaneous Creutzfeldt–Jakob disease and HIV.

Case report:

A 66-year-old man with long-standing, well-controlled HIV infection presented with 3 months of progressive, subacute neurocognitive decline. His symptoms included conceptual apraxia, apathy, memory impairment, and gait disturbance, and were initially attributed to depressive “pseudo-dementia.” Unfortunately, the patient’s symptoms rapidly progressed and he ultimately succumbed to his illness. Autopsy confirmed the clinical diagnosis of spontaneous Creutzfeldt–Jakob disease.

Discussion:

This case highlights spontaneous Creutzfeldt–Jakob disease as a rare terminal illness in the setting of well-controlled chronic HIV. To our knowledge, this is the first report of a patient with chronic and previously well-controlled HIV infection dying from a prion disease. Despite the very different epidemiology and pathophysiology of HIV and spontaneous Creutzfeldt–Jakob disease, this case does raise questions of whether certain host genetic factors could predispose to both conditions, albeit currently, there is no clear causal link between HIV and spontaneous Creutzfeldt–Jakob disease.

Quantitative Real-Time Quaking-Induced Conversion Allows Monitoring of Disease-Modifying Therapy in the Urine of Prion-Infected Mice

Prion diseases are fatal neurodegenerative diseases characterized by accumulation of the pathogenic prion protein PrP in the brain. We established quantitative real-time quaking-induced conversion for the measurement of minute amounts of PrP in body fluids such as urine. Using this approach, we monitored the efficacy of antiprion therapy by quantifying the seeding activity of PrP from the brain and urine of mice after prion infection. We found that the aggregation inhibitor anle138b decreased the levels of PrP in the brain and urine. Importantly, variations of PrP levels in the urine closely corresponded to those in the brain. Our findings indicate that quantification of urinary PrP enables measurement of prion disease progression in body fluids and can substitute for immunodetection in brain tissue. We expect PrP quantification biologic fluids (such as urine and cerebrospinal fluid) with quantitative real-time quaking-induced conversion to emerge as a valuable noninvasive diagnostic tool for monitoring disease progression and the efficacy of therapeutic approaches in animal studies and human clinical trials of prion diseases. Moreover, highly sensitive methods for quantifying pathologic aggregate seeds might provide novel molecular biomarkers for other neurodegenerative diseases that may involve prion-like mechanisms (protein aggregation and spreading), such as Alzheimer disease and Parkinson disease.

Assessing prion infectivity of human urine in sporadic Creutzfeldt-Jakob disease

Prion diseases are neurodegenerative conditions associated with a misfolded and infectious protein, scrapie prion protein (PrP(Sc)). PrP(Sc) propagate prion diseases within and between species and thus pose risks to public health. Prion infectivity or PrP(Sc) presence has been demonstrated in urine of experimentally infected animals, but there are no recent studies of urine from patients with Creutzfeldt-Jakob disease (CJD). We performed bioassays in transgenic mice expressing human PrP to assess prion infectivity in urine from patients affected by a common subtype of sporadic CJD, sCJDMM1. We tested raw urine and 100-fold concentrated and dialyzed urine and assessed the sensitivity of the bioassay along with the effect of concentration and dialysis on prion infectivity. Intracerebral inoculation of transgenic mice with urine from 3 sCJDMM1 patients failed to demonstrate prion disease transmission, indicating that prion infectivity in urine from sCJDMM1 patients is either not present or is <0.38 infectious units/mL.

Characterization of the prion protein in human urine

The presence of the prion protein (PrP) in normal human urine is controversial and currently inconclusive. This issue has taken a special relevance because prion infectivity has been demonstrated in urine of animals carrying experimental or naturally occurring prion diseases, but the actual presence and tissue origin of the infectious prion have not been determined. We used immunoprecipitation, one- and two-dimensional electrophoresis, and mass spectrometry to prove definitely the presence of PrP in human urine and its post-translational modifications. We show that urinary PrP (uPrP) is truncated mainly at residue 112 but also at other residues up to 122. This truncation makes uPrP undetectable with some commonly used antibodies to PrP. uPrP is glycosylated and carries an anchor which, at variance with that of cellular PrP, lacks the inositol-associated phospholipid moiety, indicating that uPrP is probably shed from the cell surface. The detailed characterization of uPrP reported here definitely proves the presence of PrP in human urine and will help determine the origin of prion infectivity in urine.

Excretion of transmissible spongiform encephalopathy infectivity in urine

Infectivity in hamster urine indicates a possible route of horizontal transmission of natural sheep scrapie and poses a potential risk in human urine-derived pharmaceuticals.

The route of transmission of most naturally acquired transmissible spongiform encephalopathy (TSE) infections remains speculative. To investigate urine as a potential source of TSE exposure, we used a sensitive method for detection and quantitation of TSE infectivity. Pooled urine collected from 22 hamsters showing clinical signs of 263K scrapie contained 3.8 ± 0.9 infectious doses/mL of infectivity. Titration of homogenates of kidneys and urinary bladders from the same animals gave concentrations 20,000-fold greater. Histologic and immunohistochemical examination of these same tissues showed no indications of inflammatory or other pathologic changes except for occasional deposits of disease-associated prion protein in kidneys. Although the source of TSE infectivity in urine remains unresolved, these results establish that TSE infectivity is excreted in urine and may thereby play a role in the horizontal transmission of natural TSEs. The results also indicate potential risk for TSE transmission from human urine–derived hormones and other medicines.

Transmission and detection of prions in feces

In chronic wasting disease (CWD) in cervids and in scrapie in sheep, prions appear to be transmitted horizontally. Oral exposure to prion-tainted blood, urine, saliva, and feces has been suggested as the mode of transmission of CWD and scrapie among herbivores susceptible to these prion diseases. To explore the transmission of prions through feces, uninoculated Syrian hamsters (SHas) were cohabitated with or exposed to the bedding of SHas orally infected with Sc237 prions. Incubation times of 140 days and a rate of prion infection of 80%-100% among exposed animals suggested transmission by feces, probably via coprophagy. We measured the disease-causing isoform of the prion protein (PrP(Sc)) in feces by use of the conformation-dependent immunoassay, and we titrated the irradiated feces intracerebrally in transgenic mice that overexpressed SHa prion protein (SHaPrP). Fecal samples collected from infected SHas in the first 7 days after oral challenge harbored 60 ng/g PrP(Sc) and prion titers of approximately 10(6.6) ID(50)/g. Excretion of infectious prions continued at lower levels throughout the asymptomatic phase of the incubation period, most likely by the shedding of prions from infected Peyer patches. Our findings suggest that horizontal transmission of disease among herbivores may occur through the consumption of feces or foodstuff tainted with prions from feces of CWD-infected cervids and scrapie-infected sheep.

Persistence of pathogenic prion protein during simulated wastewater treatment processes

Transmissible spongiform encephalopathies (TSEs, prion diseases) are a class of fatal neurodegenerative diseases affecting a variety of mammalian species including humans. A misfolded form of the prion protein (PrP(TSE)) is the major, if not sole, component of the infectious agent. Prions are highly resistant to degradation and to many disinfection procedures suggesting that, if prions enter wastewater treatment systems through sewers and/or septic systems (e.g., from slaughterhouses, necropsy laboratories, rural meat processors, private game dressing) or through leachate from landfills that have received TSE-contaminated material, prions could survive conventional wastewater treatment. Here, we report the results of experiments examining the partitioning and persistence of PrPTSE during simulated wastewater treatment processes including activated and mesophilic anaerobic sludge digestion. Incubation with activated sludge did not result in significant PrPTSE degradation. PrPTSE and prion infectivity partitioned strongly to activated sludge solids and are expected to enter biosolids treatment processes. A large fraction of PrPTSE survived simulated mesophilic anaerobic sludge digestion. The small reduction in recoverable PrPTSE after 20-d anaerobic sludge digestion appeared attributable to a combination of declining extractability with time and microbial degradation. Our results suggest that if prions were to enter municipal wastewater treatment systems, most would partition to activated sludge solids, survive mesophilic anaerobic digestion, and be present in treated biosolids.

Prion protein in sheep urine

The misfolded form of cellular prion protein (PrP(C)) is the main component of the infectious agent of transmissible spongiform encephalopathies and the validated biomarker for these diseases. The expression of PrP(C) is highest in the central nervous system and has been found in peripheral tissues. Soluble PrP(C) has been detected in cerebrospinal fluid, urine, serum, milk, and seminal plasma. In this study, attempts were made to characterize prion protein in urine samples from normal and scrapie-infected sheep. Urine samples from scrapie-infected sheep and age-matched healthy sheep were collected and analyzed by Western blot following concentration. A protease K-sensitive protein band with a molecular weight of approximately 27-30 kDa was visualized after immunoblotting with anti-PrP monoclonal antibodies to a C-terminal part of PrP(C), but not after immunoblotting with monoclonal antibodies to an N-terminal epitope of PrP(C) or with secondary antibodies only. The amount of PrP(C) in the urine of 49 animals (control group: n = 16; naturally scrapie-infected group: n = 33) was estimated by comparison with known amounts of ovine recombinant PrP in the immunoblot. Background concentration of PrP(C) in urine was found to be 0-0.16 ng/ml (adjusted to the initial nonconcentrated volume of the urine samples). Seven out of 33 naturally scrapie-infected animals had an elevated level (0.3-4.7 ng/ml) of PrP(C) in urine. The origin of PrP(C) in urine and the reason for the increased level of PrP(C) in scrapie-infected sheep urine has yet to be explored.

Urinary excretion and blood level of prions in scrapie-infected hamsters

Prions, infectious agents causing transmissible spongiform encephalopathy (TSE), are composed primarily of the pathogenic form (PrP(Sc)) of the host-encoded prion protein. Although very low levels of infectivity have been detected in urine from scrapie-infected rodents, no reports of urinary PrP(Sc) have been substantiated. Studies on the dynamics of urinary PrP(Sc) during infection are needed to ensure the safety of urine-derived biopharmaceuticals and to assess the possible horizontal transmission of prion diseases. Using the protein misfolding cyclic amplification technique, a time-course study of urinary excretion and blood levels of PrP(Sc) was performed in Sc237-infected hamsters and a high rate of PrP(Sc) excretion was found during the terminal stage of the disease. Following oral administration, PrP(Sc) was present in all buffy coat samples examined; it was also present in most of the plasma samples obtained from hamsters in the symptomatic stage. PrP(Sc) was excreted in urine for a few days after oral administration; subsequently, urinary PrP(Sc) was not detected until the terminal disease stage. These results represent the first biochemical detection of PrP(Sc) in urine from TSE-infected animals.

Disease-associated prion protein is not detectable in human systemic amyloid deposits

Cerebral and cardiac amyloid deposits have been reported after scrapie infection in transgenic mice expressing variant prion protein (PrP(C)) lacking the glycophosphatidylinositol anchor. The amyloid fibril protein in the systemic amyloid deposits was not characterized, and there is no clinical or pathological association between prion diseases and systemic amyloidosis in humans. Nevertheless, in view of the potential clinical significance of these murine observations, we tested both human amyloidotic tissues and isolated amyloid fibrils for the presence of PrP(Sc), the prion protein conformation associated with transmissible spongiform encephalopathy (TSE). We also sequenced the complete prion protein gene, PRNP, in amyloidosis patients. No specific immunohistochemical staining for PrP(Sc) was obtained in the amyloidotic cardiac and other visceral tissues of patients with different types of systemic amyloidosis. No protease-resistant prion protein, PrP(res), was detectable by Western blotting of amyloid fibrils isolated from cardiac and other systemic amyloid deposits. Only the complete normal wild-type PRNP gene sequence was identified, including the usual distribution of codon 129 polymorphisms. These reassuringly negative results do not support the idea that there is any relationship of prions or TSE with human systemic amyloidosis, including cardiac amyloid deposition.

Prion protein in patients with renal failure

We previously found elevated levels of prion protein (PrP(C)) in the blood plasma of 16 patients with renal failure. We studied a further 20 patients with renal failure, and all had a significantly higher PrP(C) concentration than healthy normal subjects (P < 0.0001). Renal dialysis did not remove plasma PrP(C) in these patients. Because dialysis patients receive heparin during dialysis, which could potentially bind to PrP(C), the concentration of PrP(C) was measured in patients receiving heparin for cardiopulmonary bypass and was found to be similar to normal controls. We also studied several other groups with chronic illnesses and found that patients with thrombotic thrombocytopenic purpura and sickle cell anaemia had normal plasma PrP(C) levels, but that those with beta-thalassaemia had slightly elevated levels of plasma PrP(C). This suggests that the observations in renal failure were not just part of a generalized response to chronic illness or acute phase reaction. The mechanism of elevated plasma PrP(C) levels in renal disease is unknown, but this shows that plasma PrP(C) is not a specific marker of neurological disease or Creutzfeldt-Jakob disease.

Prion urine comprises a glycosaminoglycan-light chain IgG complex that can be stained by Congo red

Light chain IgG, a known amyloidotic protein, is present in the urine of prion disease affected individuals in a protease resistant form. In addition, it was shown recently that prion urine samples comprise a significant excess of glycosaminoglycans. Since amyloidotic proteins and glycosaminoglycans are the major components of amyloid aggregates, a Congo red dot blot assay was developed for detection of Creutzfeldt-Jacob disease (CJD) in urine. This assay was also positive for about 10% of patients suffering from diseases such as Alzheimer disease, cerebrovascular attacks and multiple sclerosis, but negative for healthy controls. Both glycosaminoglycans and proteins such as light chain IgG were required for the binding of Congo red to the urine fractions, as shown by the fact that Proteinase K digestion of the samples either after guanidine or after choindrotinase abolished the Congo red signal from the CJD samples.

Coincident Scrapie Infection and Nephritis Lead to Urinary Prion Excretion

Prion infectivity is typically restricted to the central nervous and lymphatic systems of infected hosts, but chronic inflammation can expand the distribution of prions. We tested whether chronic inflammatory kidney disorders would trigger excretion of prion infectivity into urine. Urinary proteins from scrapie-infected mice with lymphocytic nephritis induced scrapie upon inoculation into noninfected indicator mice. Prionuria was found in presymptomatic scrapie-infected and in sick mice, whereas neither prionuria nor urinary PrP(Sc) was detectable in prion-infected wild-type or PrP(C)-overexpressing mice, or in nephritic mice inoculated with noninfectious brain. Thus, urine may provide a vector for horizontal prion transmission, and inflammation of excretory organs may influence prion spread.

Consensus statement on the bio-safety of urinary-derived gonadotrophins with respect to Creutzfeldt–Jakob disease

Human transmissible spongiform encephalopathies (TSE) encompass a group of rare neurodegenerative diseases. In April 2004, a group of international experts and regulators met in Buenos Aires, Argentina, to review the safety and to reach consensus on the use of urinary-derived gonadotrophins with respect to TSE. Iatrogenic transmission of Creutzfeldt-Jakob Disease (CJD) from pituitary-derived gonadotrophins has been reported, no infectivity in urine has been demonstrated, and no definite cases of transmission via urine have been reported. It is currently not possible to monitor donor urine or finished product for the presence of prions. Therefore the assessment of risk has to be based on the likelihood of infection in urine, the source of the urine, and the capacity of the manufacturing process to remove any adventitious infection. Urine for the production of medicinal products should be obtained from sources that minimize the possible presence of materials derived from subjects suffering from human TSE. As no strong evidence for TSE infectivity in urine exists, it can be concluded that the risk of disease-generating prions and TSE infectivity being present in donor urine is low. Current evidence indicates that, with respect to the risk of TSE infection, urinary-derived gonadotrophins appear to be safe.