Noninvasive Antemortem Detection of Retinal Prions by a Fluorescent Tracer.

BACKGROUND: Neurodegenerative diseases are widespread yet challenging to diagnose and stage antemortem. As an extension of the central nervous system, the eye harbors retina ganglion cells vulnerable to degeneration, and visual symptoms are often an early manifestation of neurodegenerative disease. OBJECTIVE: Here we test whether prion protein aggregates could be detected in the eyes of live mice using an amyloid-binding fluorescent probe and high-resolution retinal microscopy. METHODS: We performed retinal imaging on an experimental mouse model of prion-associated cerebral amyloid angiopathy in a longitudinal study. An amyloid-binding fluorophore was intravenously administered, and retinal imaging was performed at timepoints corresponding to early, mid-, and terminal prion disease. Retinal amyloid deposits were quantified and compared to the amyloid load in the brain. RESULTS: We report that by early prion disease (50% timepoint), discrete fluorescent foci appeared adjacent to the optic disc. By later timepoints, the fluorescent foci surrounded the optic disc and tracked along retinal vasculature. CONCLUSION: The progression of perivascular amyloid can be directly monitored in the eye by live imaging, illustrating the utility of this technology for diagnosing and monitoring the progression of cerebral amyloid angiopathy.

Synthesis and Characterization of Hydroxyethylamino- and Pyridyl-Substituted 2-Vinyl Chromone Derivatives for Detection of Cerebral Abnormal Prion Protein Deposits.

Prion diseases are fatal neurodegenerative diseases characterized by the deposition of abnormal prion protein aggregates (PrPSc) in the brain. In this study, we developed hydroxyethylamino-substituted styrylchromone (SC) and 2-(2-(pyridin-3-yl)vinyl)-4H-chromen-4-one (VPC) derivatives for single-photon emission computed tomography (SPECT) imaging of PrPSc deposits in the brain. The binding affinity of these compounds was evaluated using recombinant mouse prion protein (rMoPrP) aggregates, which resulted in the inhibition constant (Ki) value of 61.5 and 88.0 nM for hydroxyethyl derivative, (E)-2-(4-((2-hydroxyethyl)amino)styryl)-6-iodo-4H-chromen-4-one (SC-NHEtOH) and (E)-2-(4-((2-hydroxyethyl)(methyl)amino)styryl)-6-iodo-4H-chromen-4-one (SC-NMeEtOH), respectively. However, none of the VPC derivatives showed binding affinity for the rMoPrP aggregates. Fluorescent imaging demonstrated that the accumulation pattern of SC-NHEtOH matched with the presence of PrPSc in the brain slices from mouse-adapted bovine spongiform encephalopathy-infected mice. A biodistribution study of normal mice indicated low initial brain uptake of [125I]SC-NHEtOH (0.88% injected dose/g (% ID/g) at 2 min) despite favorable washout from the brain (0.26% ID/g, at 180 min) was displayed. [125I]SC-NHEtOH exhibited binding affinities to both artificial prion aggregates as well as prion deposits in the brain. However, significant improvement in the binding affinity for PrPSc and blood-brain barrier permeability is necessary for the development of successful in vivo imaging probes for the detection of cerebral PrPSc in the brain.

The importance of ongoing international surveillance for Creutzfeldt-Jakob disease.

Creutzfeldt-Jakob disease (CJD) is a rapidly progressive, fatal and transmissible neurodegenerative disease associated with the accumulation of misfolded prion protein in the CNS. International CJD surveillance programmes have been active since the emergence, in the mid-1990s, of variant CJD (vCJD), a disease linked to bovine spongiform encephalopathy. Control measures have now successfully contained bovine spongiform encephalopathy and the incidence of vCJD has declined, leading to questions about the requirement for ongoing surveillance. However, several lines of evidence have raised concerns that further cases of vCJD could emerge as a result of prolonged incubation and/or secondary transmission. Emerging evidence from peripheral tissue distribution studies employing high-sensitivity assays suggests that all forms of human prion disease carry a theoretical risk of iatrogenic transmission. Finally, emerging diseases, such as chronic wasting disease and camel prion disease, pose further risks to public health. In this Review, we provide an up-to-date overview of the transmission of prion diseases in human populations and argue that CJD surveillance remains vital both from a public health perspective and to support essential research into disease pathophysiology, enhanced diagnostic tests and much-needed treatments.

Clinical diagnosis of human prion disease.

Human prion disease may present in a non-specific way and is often diagnosed at a relatively late stage of the illness. Until recently, clinical diagnosis has been supported by tests that are mostly non-specific and, sometimes, insensitive. Recent laboratory developments have led to a variety of tests that rely on a disease-specific mechanism. One test, the CSF RT-QuIC (Real-Time Quaking-Induced Conversion) test is very sensitive and specific for sporadic CJD and is now used in routine clinical practice. Other tests, based on other tissues, including blood and urine, have been developed and potentially could improve both clinical diagnostic accuracy and lead to earlier diagnosis. While there are yet no proven treatments for prion disease, any treatment to be developed will almost certainly require earlier diagnosis if therapeutic success is to be realized.

Diagnostic Accuracy of Prion Disease Biomarkers in Iatrogenic Creutzfeldt-Jakob Disease.

Human prion diseases are classified into sporadic, genetic, and acquired forms. Within this last group, iatrogenic Creutzfeldt-Jakob disease (iCJD) is caused by human-to-human transmission through surgical and medical procedures. After reaching an incidence peak in the 1990s, it is believed that the iCJD historical period is probably coming to an end, thanks to lessons learnt from past infection sources that promoted new prion prevention and decontamination protocols. At this point, we sought to characterise the biomarker profile of iCJD and compare it to that of sporadic CJD (sCJD) for determining the value of available diagnostic tools in promptly recognising iCJD cases. To that end, we collected 23 iCJD samples from seven national CJD surveillance centres and analysed the electroencephalogram and neuroimaging data together with a panel of seven CSF biomarkers: 14-3-3, total tau, phosphorylated/total tau ratio, alpha-synuclein, neurofilament light, YKL-40, and real-time quaking induced conversion of prion protein. Using the cut-off values established for sCJD, we found the sensitivities of these biomarkers for iCJD to be similar to those described for sCJD. Given the limited relevant information on this issue to date, the present study validates the use of current sCJD biomarkers for the diagnosis of future iCJD cases.

Prion disease diagnosis using subject-specific imaging biomarkers within a multi-kernel Gaussian process.

Prion diseases are a group of rare neurodegenerative conditions characterised by a high rate of progression and highly heterogeneous phenotypes. Whilst the most common form of prion disease occurs sporadically (sporadic Creutzfeldt-Jakob disease, sCJD), other forms are caused by prion protein gene mutations, or exposure to prions in the diet or by medical procedures, such us surgeries. To date, there are no accurate quantitative imaging biomarkers that can be used to predict the future clinical diagnosis of a healthy subject, or to quantify the progression of symptoms over time. Besides, CJD is commonly mistaken for other forms of dementia. Due to the heterogeneity of phenotypes and the lack of a consistent geometrical pattern of disease progression, the approaches used to study other types of neurodegenerative diseases are not satisfactory to capture the progression of human form of prion disease. In this paper, using a tailored framework, we aim to classify and stratify patients with prion disease, according to the severity of their illness. The framework is initialised with the extraction of subject-specific imaging biomarkers. The extracted biomakers are then combined with genetic and demographic information within a Gaussian Process classifier, used to calculate the probability of a subject to be diagnosed with prion disease in the next year. We evaluate the effectiveness of the proposed method in a cohort of patients with inherited and sporadic forms of prion disease. The model has shown to be effective in the prediction of both inherited CJD (92% of accuracy) and sporadic CJD (95% of accuracy). However the model has shown to be less effective when used to stratify the different stages of the disease, in which the average accuracy is 85%, whilst the recall is 59%. Finally, our framework was extended as a differential diagnosis tool to identify both forms of CJD among another neurodegenerative disease. In summary we have developed a novel method for prion disease diagnosis and prediction of clinical onset using multiple sources of features, which may have use in other disorders with heterogeneous imaging features.

Prion Disease.

Prion diseases are a phenotypically diverse set of disorders characterized by protease-resistant abnormally shaped proteins known as prions. There are three main groups of prion diseases, termed sporadic (Creutzfeldt-Jakob disease [CJD], sporadic fatal insomnia, and variably protease-sensitive prionopathy), genetic (genetic CJD, fatal familial insomnia, and Gerstmann-Straussler-Scheinker syndrome), and acquired (kuru, variant CJD, and iatrogenic CJD). This article will review the pathophysiology, genetics, clinical presentations, and diagnostic challenges in patients with prion disease. Case discussions, images, and tables will be used to highlight important characteristics of prion disease and prion mimics.

Development of Radioiodinated Benzofuran Derivatives for in Vivo Imaging of Prion Deposits in the Brain.

Prion diseases are fatal neurodegenerative disorders associated with the deposition of abnormal prion protein aggregates (PrPSc) in the brain tissue. Here, we report the development of 125I-labeled iodobenzofuran (IBF) derivatives as single photon emission computed tomography (SPECT) imaging probes to detect cerebral PrPSc deposits. We synthesized and radioiodinated several 5-IBF and 6-IBF derivatives. The IBF derivatives were evaluated as prion imaging probes using recombinant mouse prion protein (rMoPrP) aggregates and brain sections of mouse-adapted bovine spongiform encephalopathy (mBSE)-infected mice. Although all the IBF derivatives were strongly adsorbed on the rMoPrP aggregates, [125I]5-IBF-NHMe displayed the highest adsorption rate and potent binding affinity with an equilibrium dissociation constant (Kd) of 12.3 nM. Fluorescence imaging using IBF-NHMe showed clear signals of the PrPSc-positive amyloid deposits in the mBSE-infected mouse brains. Biodistribution studies in normal mice demonstrated slow uptake and clearance from the brain of 125I-IBF derivatives. Among the derivatives, [125I]6-IBF-NH2 showed the highest peak brain uptake [2.59% injected dose (ID)/g at 10 min] and good clearance (0.51% ID/g at 180 min). Although the brain distribution of IBF derivatives should still be optimized for in vivo imaging, these compounds showed prospective binding properties to PrPSc. Further chemical modification of these IBF derivatives may contribute to the discovery of clinically applicable prion imaging probes.

Co-occurrence of chronic traumatic encephalopathy and prion disease.

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease associated with repetitive traumatic brain injury (TBI). CTE is generally found in athletes participating in contact sports and military personnel exposed to explosive blasts but can also affect civilians. Clinically and pathologically, CTE overlaps with post-traumatic stress disorder (PTSD), a term mostly used in a clinical context. The histopathology of CTE is defined by the deposition of hyperphosphorylated tau protein in neurons and astrocytes preferentially with perivascular distribution and at the depths of the cortical sulci. In addition to hyperphosphorylated tau, other pathologic proteins are deposited in CTE, including amyloid ß (Aß), transactive response (TAR) DNA-binding protein 43 kDa (TDP-43) and α-synuclein. However, the coexistence of prion disease in CTE has not been observed. We report three cases of histopathologically validated CTE with co-existing sporadic prion disease. Two were identified in a cohort of 55 pathologically verified cases of CTE submitted to the CTE Center of Boston University. One was identified among brain tissues submitted to the National Prion Disease Pathology Surveillance Center of Case Western Reserve University. The histopathological phenotype and properties of the abnormal, disease-related prion protein (PrPD) of the three CTE cases were examined using lesion profile, immunohistochemistry, electrophoresis and conformational tests. Subjects with sporadic Creutzfeldt-Jakob disease (sCJD) matched for age, PrP genotype and PrPD type were used as controls. The histopathology phenotype and PrPD properties of the three CTE subjects showed no significant differences from their respective sCJD controls suggesting that recurring neurotrauma or coexisting CTE pathology did not detectably impact the prion disease phenotype and PrPD conformational characteristics. Based on the reported incidence of sporadic prion disease, the detection of two cases with sCJD in the CTE Center series of 55 CTE cases by chance alone would be highly unlikely (p = 8.93*10- 6). Nevertheless, examination of a larger cohort of CTE is required to conclusively determine whether the risk of CJD is significantly increased in patients with CTE.

Fatal familial insomnia and sporadic fatal insomnia.

Fatal familial insomnia (FFI) and sporadic fatal insomnia (sFI), or thalamic form of sporadic Creutzfeldt-Jakob disease MM2 (sCJDMM2T), are prion diseases originally named and characterized in 1992 and 1999, respectively. FFI is genetically determined and linked to a D178N mutation coupled with the M129 genotype in the prion protein gene (PRNP) at chromosome 20. sFI is a phenocopy of FFI and likely its sporadic form. Both diseases are primarily characterized by progressive sleep impairment, disturbances of autonomic nervous system, and motor signs associated with severe loss of nerve cells in medial thalamic nuclei. Both diseases harbor an abnormal disease-associated prion protein isoform, resistant to proteases with relative mass of 19 kDa identified as resPrPTSE type 2. To date at least 70 kindreds affected by FFI with 198 members and 18 unrelated carriers along with 25 typical cases of sFI have been published. The D178N-129M mutation is thought to cause FFI by destabilizing the mutated prion protein and facilitating its conversion to PrPTSE. The thalamus is the brain region first affected. A similar mechanism triggered spontaneously may underlie sFI.

In Vivo-Near Infrared Imaging of Neurodegeneration.

In vivo near-infrared (NIR) imaging of molecular processes at the preclinical stage promises to provide more valuable mechanistic information about pathological pathways involved in neurodegeneration. NIR imaging has the potential to improve in vivo therapeutic screening protocols by enabling noninvasive monitoring of presymptomatic responses to treatment. We have developed new NIR fluorescent contrast agents conjugated to markers of cell death, and using these agents we have identified molecular pathways associated with prion-induced neurodegeneration and determined the optimal window for meaningful therapeutic intervention in prion disease. This chapter provides a description of the synthesis and purification of our NIR cell Death (NIRD) contrast agent and the application of in vivo NIRD (iNIRD) imaging to a prion model of neurodegeneration.

Neuroradiology of human prion diseases, diagnosis and differential diagnosis.

Human transmissible spongiform encephalopathies (TSEs), or prion diseases, are invariably fatal conditions associated with a range of clinical presentations. TSEs are classified as sporadic [e.g. sporadic Creutzfeldt-Jakob disease (sCJD), which is the most frequent form], genetic (e.g. Gerstmann-Straussler-Scheinker disease, fatal familial insomnia, and inherited CJD), and acquired or infectious (e.g. Kuru, iatrogenic CJD, and variant CJD). In the past, brain imaging played a supporting role in the diagnosis of TSEs, whereas nowadays magnetic resonance imaging (MRI) plays such a prominent role that MRI findings have been included in the diagnostic criteria for sCJD. Currently, MRI is required for all patients with a clinical suspicion of TSEs. Thus, MRI semeiotics of TSEs should become part of the cultural baggage of any radiologist. The purposes of this update on the neuroradiology of CJD are to (i) review the pathophysiology and clinical presentation of TSEs, (ii) describe both typical and atypical MRI findings of CJD, and (iii) illustrate diseases mimicking CJD, underlining the MRI key findings useful in the differential diagnosis.

Development of radioiodinated acridine derivatives for in vivo imaging of prion deposits in the brain.

Prion diseases are caused by deposition of abnormal prion protein aggregates (PrPSc) in the central nervous system. This study aimed to develop in vivo imaging probes that can detect cerebral PrPSc deposits. We synthesized several quinacrine-based acridine (AC) derivatives with 2,9-substitution and radioiodinated them. The AC derivatives were evaluated as prion-imaging probes using recombinant mouse prion protein (rMoPrP) aggregates and brain sections of mouse-adapted bovine spongiform encephalopathy (mBSE)-infected mice. The distribution of these compounds in mice was also evaluated. The 2-methoxy derivative [125I]2 exhibited the highest binding affinity for rMoPrP aggregates with an equilibrium dissociation constant (Kd) value of 43.4nM. Fluorescence imaging with 2 showed clear signals at the thioflavin T (ThT)-positive amyloid deposits in the mBSE-infected mouse brain. Although a discrepancy was observed between the in vitro binding of AC derivatives to the aggregates and in vivo distribution of these compounds in the brain and we failed to identify prospective prion-imaging probes in this study, the AC derivatives may be considered a useful scaffold for the development of in vivo imaging probes. Further chemical modification of these AC derivatives may discover clinically applicable prion imaging probes.

Genetic Prion Disease Caused by PRNP Q160X Mutation Presenting with an Orbitofrontal Syndrome, Cyclic Diarrhea, and Peripheral Neuropathy.

Patients with pathogenic truncating mutations in the prion gene (PRNP) usually present with prolonged disease courses with severe neurofibrillary tangle and cerebral amyloidosis pathology, but more atypical phenotypes also occur, including those with dysautonomia and peripheral neuropathy. We describe the neurological, cognitive, neuroimaging, and electrophysiological features of a 31-year-old man presenting with an orbitofrontal syndrome, gastrointestinal symptoms, and peripheral neuropathy associated with PRNP Q160X nonsense mutation, with symptom onset at age 27. The mutation was also detected in his asymptomatic father and a symptomatic paternal cousin; several members of prior generations died from early onset dementia. This is the first report of a family affected with the nonsense PRNP mutation Q160X displaying clear autosomal dominant disease in multiple family members and reduced penetrance. This case strengthens the evidence suggesting an association between PRNP truncating mutations and prion systemic amyloidosis. PRNP gene testing should be considered in any patient with atypical dementia, especially with early onset and neuropathy, even in the absence of a family history.

Neuroanatomical correlates of prion disease progression - a 3T longitudinal voxel-based morphometry study.

PURPOSE: MRI has become an essential tool for prion disease diagnosis. However there exist only a few serial MRI studies of prion patients, and these mostly used whole brain summary measures or region of interest based approaches. We present here the first longitudinal voxel-based morphometry (VBM) study in prion disease. The aim of this study was to systematically characterise progressive atrophy in patients with prion disease and identify whether atrophy in specific brain structures correlates with clinical assessment. METHODS: Twenty-four prion disease patients with early stage disease (3 sporadic, 2 iatrogenic, 1 variant and 18 inherited CJD) and 25 controls were examined at 3T with a T1-weighted 3D MPRAGE sequence at multiple time-points (2-6 examinations per subject, interval range 0.1-3.2 years). Longitudinal VBM provided intra-subject and inter-subject image alignment, allowing voxel-wise comparison of progressive structural change. Clinical disease progression was assessed using the MRC Prion Disease Rating Scale. Firstly, in patients, we determined the brain regions where grey and white matter volume change between baseline and final examination correlated with the corresponding change in MRC Scale score. Secondly, in the 21/24 patients with interscan interval longer than 3 months, we identified regions where annualised rates of regional volume change in patients were different from rates in age-matched controls. Given the heterogeneity of the cohort, the regions identified reflect the common features of the different prion sub-types studied. RESULTS: In the patients there were multiple regions where volume loss significantly correlated with decreased MRC scale, partially overlapping with anatomical regions where yearly rates of volume loss were significantly greater than controls. The key anatomical areas involved included: the basal ganglia and thalamus, pons and medulla, the hippocampal formation and the superior parietal lobules. There were no areas demonstrating volume loss significantly higher in controls than patients or negative correlation between volume and MRC Scale score. CONCLUSIONS: Using 3T MRI and longitudinal VBM we have identified key anatomical regions of progressive volume loss which correlate with an established clinical disease severity index and are relevant to clinical deterioration. Localisation of the regions of progressive brain atrophy correlating most strongly with clinical decline may help to provide more targeted imaging endpoints for future clinical trials.

Quality evaluation for the surveillance system of human prion diseases in China based on the data from 2010 to 2016.

The surveillance of CJD or human prion diseases (PrDs) has been conducted for 10 y in China. To evaluate the quality of China CJD surveillance system, the collections of the clinical and epidemiological information, the sampling, the clinical examinations and laboratory tests and follow-up survey were separately analyzed based on the data from 2010 to 2015. The obtaining rates of clinical-information table, epidemiological-information table, sample inspection sheet and medical record of the referring patients from reporting units to the center of CJD surveillance maintained or reached at very high levels, being close to 100% in the past 3 y. 93.82%, 85.23%, 96.21% and 94.70% of the reported cases had the data of MRI, EEG, CSF 14-3-3 and PRNP sequencing, respectively. Follow-up surveys were conducted in about 50% cases in 2010 and 2011, 93.39% cases in 2012 and 100% cases in the last 3 y. High obtaining rates of the clinical and epidemiological data, high conducting rates of the relevant clinical examinations and laboratory tests, high performing rates of follow-up survey for every referring case reflect a good implemental capacity in China CJD surveillance system, which supplies solid basis for recognition and diagnosis of human prion diseases and guarantees good quality of China CJD surveillance system.

Metabolic patterns in prion diseases: an FDG PET voxel-based analysis.

PURPOSE: Clinical diagnosis of human prion diseases can be challenging since symptoms are common to other disorders associated with rapidly progressive dementia. In this context, (18)F-fluorodeoxyglucose (FDG) positron emission tomography (PET) might be a useful complementary tool. The aim of this study was to determine the metabolic pattern in human prion diseases, particularly sporadic Creutzfeldt-Jakob disease (sCJD), the new variant of Creutzfeldt-Jakob disease (vCJD) and fatal familial insomnia (FFI). METHODS: We retrospectively studied 17 patients with a definitive, probable or possible prion disease who underwent FDG PET in our institution. Of these patients, 12 were diagnosed as sCJD (9 definitive, 2 probable and 1 possible), 1 was diagnosed as definitive vCJD and 4 were diagnosed as definitive FFI. The hypometabolic pattern of each individual and comparisons across the groups of subjects (control subjects, sCJD and FFI) were evaluated using a voxel-based analysis. RESULTS: The sCJD group exhibited a pattern of hypometabolism that affected both subcortical (bilateral caudate, thalamus) and cortical (frontal cortex) structures, while the FFI group only presented a slight hypometabolism in the thalamus. Individual analysis demonstrated a considerable variability of metabolic patterns among patients, with the thalamus and basal ganglia the most frequently affected areas, combined in some cases with frontal and temporal hypometabolism. CONCLUSION: Patients with a prion disease exhibit a characteristic pattern of brain metabolism presentation in FDG PET imaging. Consequently, in patients with rapidly progressive cognitive impairment, the detection of these patterns in the FDG PET study could orient the diagnosis to a prion disease.