Preparation of soluble infectious samples from scrapie-infected brain: a new tool to study the clearance of transmissible spongiform encephalopathy agents during plasma fractionation

Characterization of the 263K-derived microsomal fraction: a source of prions for nanofiltration validation studies

BACKGROUND

The manufacturing processes of plasma products include steps that can remove prions. The efficacy of these steps is measured in validation studies using animal brain-derived prion materials called spikes. Because the nature of the prion agent in blood is not known, the relevance of these spikes, particularly with steps that are based on retention mechanisms such as nanofiltration, is important to investigate.

STUDY DESIGN AND METHODS

The aggregation and sizes of PrPres assemblies of microsomal fractions (MFs) extracted from 263K-infected hamster brains were analyzed using velocity gradients. The separated gradient fractions were either inoculated to Tg7 mice expressing hamster-PrPc to measure infectivity or used in Protein Misfolding Cyclic Amplification for measuring seeding activity. The collected data allowed for reanalyzing results from previous nanofiltration validation studies.

RESULTS

A significant portion of MFs was found to be composed of small PrPres assemblies, estimated to have a size ≤24 mers (~22-528 kDa), and to contain a minimum of 20% of total prion infectivity. With this data we could calculate reductions of 4.10 log (15 N), 2.53 log (35 N), and 1.77 log (35 N) from validation studies specifically for these small PrPres objects.

CONCLUSION

Our gradient data provided evidence that nanofilters can remove the majority of the smallest PrPres entities within microsomes spikes, estimated to be in a size below 24 mers, giving insight about the fact that, in our conditions, size exclusion may not be the only mechanism for retention nanofiltration.

Prion assemblies: structural heterogeneity, mechanisms of formation, and role in species barrier

Prions are proteinaceous pathogens responsible for a wide range of neurodegenerative diseases in animal and human. Prions are formed from misfolded, ß-sheet rich, and aggregated conformers (PrPSc) of the host-encoded prion protein (PrPC). Prion replication stems from the capacity of PrPSc to self-replicate by templating PrPC conversion and polymerization. The question then arises about the molecular mechanisms of prion replication, host invasion, and capacity to contaminate other species. Studying these mechanisms has gained in recent years further complexity with evidence that PrPSc is a pleiomorphic protein. There is indeed compelling evidence for PrPSc structural heterogeneity at different scales: (i) within prion susceptible host populations with the existence of different strains with specific biological features due to different PrPSc conformers, (ii) within a single infected host with the co-propagation of different strains, and (iii) within a single strain with evidence for co-propagation of PrPSc assemblies differing in their secondary to quaternary structure. This review summarizes current knowledge of prion assembly heterogeneity, potential mechanisms of formation during the replication process, and importance when crossing the species barrier.

Analysis of the Glycosylation Profile of Disease-Associated Water-Soluble Prion Protein Using Lectins

The disease-associated water-soluble form of hamster prion protein (ws-PrP^Sc) has recently been found to be less stable than classical PrP^Sc. Since the stability of PrP to degradation correlates with its glycosylation level, the aim of this study was to investigate whether there are differences between the glycosylation of ws-PrP^Sc and classical PrP^Sc of hamster which might account for the ws-PrP^Sc minor stability compared with that of the classical PrP^Sc. Thus, ws-PrP and classical PrP were captured from noninfected or scrapie-infected hamster brain homogenate [high-speed supernatant (S^HS) and high-speed pellet (P^HS)] and blood plasma by anti-PrP antibodies (3F4 and 6H4) and subjected to screening for glycans by lectins under denaturing or nondenaturing procedures in a sandwich lectin-ELISA. Glycans have been found in minor quantities and differently exposed on ws-PrP^Sc from S^HS and plasma compared with classical PrP^Sc from P^HS. These differences have been shown to be potentially responsible for the instability of ws-PrP^Sc. Treatment of infected blood with GdnHCl significantly (P<0.01) increased the detection of ws-PrP^Sc in ELISA, reflecting an increase in its stability, and showed efficacy in removing high-abundance proteins in silver-stained gels. This increase in ws-PrP^Sc stability is due to an interaction of GdnHCl not only with high-abundance proteins but also with the ws-PrP^Sc glycosylation with particular regard to the mannose sugar. Analysis of lectins immunoreactivity toward total proteins from plasma collected before and at different time points after infection revealed that mannose might exert a stabilizing effect toward all of hamster blood glycoproteins, regardless of scrapie infection. Since low levels of ws-PrP^Sc/soluble-infectivity have been estimated both in blood and brain of hamster, this glycosylation-related instability may have negatively influenced the propensity of ws-PrP^C to convert to ws-PrP^Sc both in blood and the brain. Therefore, PrP^C glycosylation characteristics may provide a tool for the determination risk of prion transmissibility.

Unexpected prion phenotypes in experimentally transfused animals: predictive models for humans?

The recently reevaluated high prevalence of healthy carriers (1/2,000 in UK) of variant Creutzfeldt-Jakob Disease (v-CJD), whose blood might be infectious, suggests that the evolution of this prion disease might not be under full control as expected. After experimental transfusion of macaques and conventional mice with blood derived from v-CJD exposed (human and animal) individuals, we confirmed in these both models the transmissibility of v-CJD, but we also observed unexpected neurological syndromes transmissible by transfusion: despite their prion etiology confirmed through transmission experiments, these original cases would escape classical prion diagnosis, notably in the absence of detectable abnormal PrP with current techniques. It is noteworthy that macaques developed an original, yet undescribed myelopathic syndrome associating demyelination and pseudo-necrotic lesions of spinal cord, brainstem and optical tract without affecting encephalon, which is rather evocative of spinal cord disease than prion disease in human medicine. These observations strongly suggest that the spectrum of human prion diseases may extend the current field restricted to the phenotypes associated to protease-resistant PrP, and may notably include spinal cord diseases.

Experimental transfusion of variant CJD-infected blood reveals previously uncharacterised prion disorder in mice and macaque

Exposure of human populations to bovine spongiform encephalopathy through contaminated food has resulted in <250 cases of variant Creutzfeldt-Jakob disease (vCJD). However, more than 99% of vCJD infections could have remained silent suggesting a long-term risk of secondary transmission particularly through blood. Here, we present experimental evidence that transfusion in mice and non-human primates of blood products from symptomatic and non-symptomatic infected donors induces not only vCJD, but also a different class of neurological impairments. These impairments can all be retransmitted to mice with a pathognomonic accumulation of abnormal prion protein, thus expanding the spectrum of known prion diseases. Our findings suggest that the intravenous route promotes propagation of masked prion variants according to different mechanisms involved in peripheral replication.

Transmission of Soluble and Insoluble α-Synuclein to Mice

The neurodegenerative synucleinopathies, which include Parkinson disease, multiple-system atrophy, and Lewy body disease, are characterized by the presence of abundant neuronal inclusions called Lewy bodies and Lewy neurites. These disorders remain incurable, and a greater understanding of the pathologic processes is needed for effective treatment strategies to be developed. Recent data suggest that pathogenic misfolding of the presynaptic protein, α-synuclein (α-syn), and subsequent aggregation and accumulation are fundamental to the disease process. It is hypothesized that the misfolded isoform is able to induce misfolding of normal endogenous α-syn, much like what occurs in the prion diseases. Recent work highlighting the seeding effect of pathogenic α-syn has largely focused on the detergent-insoluble species of the protein. In this study, we performed intracerebral inoculations of the sarkosyl-insoluble or sarkosyl-soluble fractions of human Lewy body disease brain homogenate and show that both fractions induce CNS pathology in mice at 4 months after injection. Disease-associated deposits accumulated both near and distal to the site of the injection, suggesting a cell-to-cell spread via recruitment of α-syn. These results provide further insight into the prion-like mechanisms of α-syn and suggest that disease-associated α-syn is not homogeneous within a single patient but might exist in both soluble and insoluble isoforms.

The Risk of Prion Infection through Bovine Grafting Materials

BACKGROUND

Bovine-derived grafting materials are frequently used in a variety of bone augmentation techniques. The aim of this paper is to assess the unique safety issue of bovine-derived grafting materials that is rarely addressed in dental literature: risk of bovine spongiform encephalopathy (BSE).

METHODS

The validity of the current BSE diagnostic methods, surveillance and epidemiological trends in affected countries, and BSE infectivity in bovine bone before and after manufacturing processing were reviewed and analyzed.

RESULTS

Prion screening has significant limits. Humans are not safe from the infection of prion disease of other species. Prions can and do break the species barrier. There is evidence there may be tens of thousands of infectious carriers in the western countries alone. This raises concern about the potential for perpetuation of infection via medical procedures.

CONCLUSION

The limited ability to screen prions within the animal genome, along with a long latency period to manifestation of the disease (1 to over 50 years) in infected patients, provides a framework for discussing posible long-term risks of the xenografts that are used so extensively in dentistry. We suggest abolishing the use of bovine bone.

Detection of water-soluble disease-associated PrP species in blood and brain of scrapie-infected hamster

The high-speed supernatant (S(HS)) of scrapie-infected hamster brain homogenate contains a soluble infectivity similar to that of the plasma that escapes leukodepletion and can transmit prion infection. This recent finding highlights the fact that soluble prion infectivity could be relevant for prion disease propagation and progression. PrP(Sc) is essential in prion disease pathogenesis, but little to nothing is known about the PrP(Sc) species that may be associated with this form of prion infectivity. Scrapie-infected hamster plasma and S(HS) were subjected to biochemical analysis, and the results demonstrate for the first time that soluble infectivity is associated with a water-soluble PrP(Sc) species with substantially different properties from classical PrP(Sc), the concentration of which seems to correlate with the magnitude and efficiency of the soluble infectivity. Such characteristics suggest that this species might represent the soluble prion agent itself or its vehicle, highlighting the need to adequately revise the strategies involved in prion removal, diagnosis, and therapy.

Mutant PrPCJD prevails over wild-type PrPCJD in the brain of V210I and R208H genetic Creutzfeldt-Jakob disease patients

Creutzfeldt-Jakob disease (CJD) is a neurodegenerative disorder characterized by the deposition of the pathological conformer (PrP(CJD)) of the host encoded cellular prion protein (PrP(C)). In genetic CJD associated with V210I or R208H PrP substitutions, the pathogenic role of mutant residues is still poorly understood. To understand how V210I or R208H PrP mutations facilitate the development of the disease, we determined by mass spectrometry the quantitative ratio of mutant/wild-type PrP(CJD) allotypes in brains from affected subjects. We found that the mutant PrP(CJD) allotypes moderately exceeds of 2- or 3-fold the amount of the wild-type counterpart suggesting that these mutations mainly exert their pathogenic effect on the onset of the pathogenic cascade. Different mechanisms can be hypothesized to explain the pathogenic role of mutant residues: V210I and R208H substitutions can increase the concentration of PrP(C) and the probability to form insoluble aggregates, or they may facilitate the formation of pathological intermediates, or, alternatively, they may increase the affinity for ligands that are involved in the initial phases of PrP(CJD) formation and aggregation. Whatever the mechanism, the enrichment found for the mutated PrP(CJD) species indicates that these altered structures are more prone, with respect to the non-mutated ones, to be captured in the polymerization process either at the onset or during the development of the disease.

Pathogenic mutations within the hydrophobic domain of the prion protein lead to the formation of protease-sensitive prion species with increased lethality

Prion diseases are a group of fatal and incurable neurodegenerative diseases affecting both humans and animals. The principal mechanism of these diseases involves the misfolding the host-encoded cellular prion protein, PrP(C), into the disease-associated isoform, PrP(Sc). Familial forms of human prion disease include those associated with the mutations G114V and A117V, which lie in the hydrophobic domain of PrP. Here we have studied the murine homologues (G113V and A116V) of these mutations using cell-based and animal models of prion infection. Under normal circumstances, the mutant forms of PrP(C) share similar processing, cellular localization, and physicochemical properties with wild-type mouse PrP (MoPrP). However, upon exposure of susceptible cell lines expressing these mutants to infectious prions, very low levels of protease-resistant aggregated PrP(Sc) are formed. Subsequent mouse bioassay revealed high levels of infectivity present in these cells. Thus, these mutations appear to limit the formation of aggregated PrP(Sc), giving rise to the accumulation of a relatively soluble, protease sensitive, prion species that is highly neurotoxic. Given that these mutations lie next to the glycine-rich region of PrP that can abrogate prion infection, these findings provide further support for small, protease-sensitive prion species having a significant role in the progression of prion disease and that the hydrophobic domain is an important determinant of PrP conversion.

IMPORTANCE

Prion diseases are transmissible neurodegenerative diseases associated with an infectious agent called a prion. Prions are comprised of an abnormally folded form of the prion protein (PrP) that is normally resistant to enzymes called proteases. In humans, prion disease can occur in individuals who inherited mutations in the prion protein gene. Here we have studied the effects of two of these mutations and show that they influence the properties of the prions that can be formed. We show that the mutants make highly infectious prions that are more sensitive to protease treatment. This study highlights a certain region of the prion protein as being involved in this effect and demonstrates that prions are not always resistant to protease treatment.

Quaternary structure of pathological prion protein as a determining factor of strain-specific prion replication dynamics

Prions are proteinaceous infectious agents responsible for fatal neurodegenerative diseases in animals and humans. They are essentially composed of PrP(Sc), an aggregated, misfolded conformer of the ubiquitously expressed host-encoded prion protein (PrP(C)). Stable variations in PrP(Sc) conformation are assumed to encode the phenotypically tangible prion strains diversity. However the direct contribution of PrP(Sc) quaternary structure to the strain biological information remains mostly unknown. Applying a sedimentation velocity fractionation technique to a panel of ovine prion strains, classified as fast and slow according to their incubation time in ovine PrP transgenic mice, has previously led to the observation that the relationship between prion infectivity and PrP(Sc) quaternary structure was not univocal. For the fast strains specifically, infectivity sedimented slowly and segregated from the bulk of proteinase-K resistant PrP(Sc). To carefully separate the respective contributions of size and density to this hydrodynamic behavior, we performed sedimentation at the equilibrium and varied the solubilization conditions. The density profile of prion infectivity and proteinase-K resistant PrP(Sc) tended to overlap whatever the strain, fast or slow, leaving only size as the main responsible factor for the specific velocity properties of the fast strain most infectious component. We further show that this velocity-isolable population of discrete assemblies perfectly resists limited proteolysis and that its templating activity, as assessed by protein misfolding cyclic amplification outcompetes by several orders of magnitude that of the bulk of larger size PrP(Sc) aggregates. Together, the tight correlation between small size, conversion efficiency and duration of disease establishes PrP(Sc) quaternary structure as a determining factor of prion replication dynamics. For certain strains, a subset of PrP assemblies appears to be the best template for prion replication. This has important implications for fundamental studies on prions.

Assessment of prion reduction filters in decreasing infectivity of ultracentrifuged 263K scrapie-infected brain homogenates in "spiked" human blood and red blood cells

BACKGROUND

The safety of red blood cells (RBCs) is of concern because of the occurrence of four transfusion-transmitted variant Creutzfeldt-Jakob disease (vCJD) cases in the United Kingdom. The absence of validated screening tests requires the use of procedures to remove prions from blood to minimize the risk of transmission. These procedures must be validated using infectious prions in a form that is as close as possible to one in blood.

STUDY DESIGN AND METHODS

Units of human whole blood (WB) and RBCs were spiked with high-speed supernatants of 263K scrapie-infected hamster brain homogenates. Spiked samples were leukoreduced and then passed through prion-removing filters (Pall Corporation). In another experiment, RBCs from 263K scrapie-infected hamsters were treated as above, and residual infectivity was measured by bioassay.

RESULTS

The overall removal of infectivity by the filters from prion-spiked WB and RBCs was approximately two orders of magnitude. No infectivity was detected in filtered hamster RBCs endogenously infected with scrapie.

CONCLUSION

The use of prion-removing filters may help to reduce the risk of transfusion-transmitted vCJD. To avoid overestimation of prion removal efficiency in validation studies, it may be more appropriate to use supernates from ultracentrifugation of scrapie-infected hamster brain homogenate rather than the current standard brain homogenates.

Enzymatic formulation capable of degrading scrapie prion under mild digestion conditions

The prion agent is notoriously resistant to common proteases and conventional sterilisation procedures. The current methods known to destroy prion infectivity such as incineration, alkaline and thermal hydrolysis are harsh, destructive, environmentally polluting and potentially hazardous, thus limit their applications for decontamination of delicate medical and laboratory devices, remediation of prion contaminated environment and for processing animal by-products including specified risk materials and carcases. Therefore, an environmentally friendly, non-destructive enzymatic degradation approach is highly desirable. A feather-degrading Bacillus licheniformis N22 keratinase has been isolated which degraded scrapie prion to undetectable level of PrP^Sc signals as determined by Western Blot analysis. Prion infectivity was verified by ex vivo cell-based assay. An enzymatic formulation combining N22 keratinase and biosurfactant derived from Pseudomonas aeruginosa degraded PrP^Sc at 65°C in 10 min to undetectable level -. A time-course degradation analysis carried out at 50°C over 2 h revealed the progressive attenuation of PrP^Sc intensity. Test of residual infectivity by standard cell culture assay confirmed that the enzymatic formulation reduced PrP^Sc infectivity to undetectable levels as compared to cells challenged with untreated standard scrapie sheep prion (SSBP/1) (p-value = 0.008 at 95% confidence interval). This novel enzymatic formulation has significant potential application for prion decontamination in various environmentally friendly systems under mild treatment conditions.

Role of proteomics in understanding prion infection

Transmissible spongiform encephalopathies or prion diseases are fatal neurodegenerative pathologies characterized by the autocatalytic misfolding and polymerization of a cellular glycoprotein (cellular prion protein [PrP(C)]) that accumulates in the CNS and leads to neurodegeneration. The detailed mechanics of PrP(C) conversion to its pathological isoform (PrP(TSE)) are unclear but one or more exogenous factors are likely involved in the process of PrP misfolding. In the last 20 years, proteomic investigations have identified several endogenous proteins that interact with PrP(C), PrP(TSE) or both, which are possibly involved in the prion pathogenetic process. However, current approaches have not yet produced convincing conclusions on the biological value of such PrP interactors. Future advancements in the comprehension of the molecular pathogenesis of prion diseases, in experimental techniques and in data analysis procedures, together with a boost in more productive international collaborations, are therefore needed to improve the understanding on the role of PrP interactors. Finally, the advancement of 'omics' techniques in prion diseases will contribute to the development of novel diagnostic tests and effective drugs.

Risk of prion disease transmission through bovine-derived bone substitutes: a systematic review

BACKGROUND

Despite the causal association between variant Creutzfeldt - Jakob disease and bovine spongiform encephalopathy (BSE), bovine origin graft materials are widely used during dental surgical procedures. The aim of this study was to assess the risk of BSE transmission through anorganic bovine bone substitutes.

METHODS

Electronic database of MEDLINE was searched to identify relevant studies regarding our focused questions, presence of BSE prion infectivity in raw bovine bone, BSE prion inactivation by bone substitute manufacturing process, protein contents in anorganic bovine bone substitutes, and validity of current BSE diagnostic methods. Search terms yielded 1,704 titles. After title/abstract screening and duplicates removal, 36 full-text articles were screened for inclusion.

RESULTS

A total of 16 studies were included in the final analysis. No eligible studies were identified regarding the efficacy of BSE prion inactivation by the treatments used for anorganic bovine bone manufacturing. BSE infectivity and PrP(Sc) , pathological prion, were detected in bovine bone marrow and serum samples. Proteins were detected in Tutoplast® (bovine), Bio-Oss®, and tibia samples treated at the similar condition for Bio-Oss deproteinization. Inconsistent results of different BSE diagnostic tests were not unusual findings (Iwata et al. 2006; Arnold et al. 2007; Murayama et al. 2010), and a study by Balkema-Buschmann and colleagues showed an apparent discrepancy between BSE infectivity and detection of PrP(27-30), the current surrogate marker for prion disease infectivity.

CONCLUSION

This review indicates that bovine-derived graft biomaterials may carry a risk of prion transmission to patients.

Comparison of nanofiltration efficacy in reducing infectivity of centrifuged versus ultracentrifuged 263K scrapie-infected brain homogenates in "spiked" albumin solutions

BACKGROUND

The safety of plasma-derived products is of concern for possible transmission of variant Creutzfeldt-Jakob disease. The absence of validated screening tests requires the use of procedures to remove or inactivate prions during the manufacture of plasma-derived products to minimize the risk of transmission. These procedures need proper validation studies based on spiking human plasma or intermediate fractions of plasma fractionation with prions in a form as close as possible to that present in blood.

STUDY DESIGN AND METHODS

Human albumin was spiked with low-speed or high-speed supernatants of 263K scrapie-infected hamster brain homogenates. Spiked albumin was then passed through a cascade of filters from 100 nm down to 20 to 15 nm. Residual infectivity was measured by bioassay.

RESULTS

The overall removal of infectivity spiked into albumin through serial nanofiltration steps was 4 to 5 logs using low-speed supernatant and 2 to 3 logs with high-speed supernatant.

CONCLUSION

These findings confirm the utility of nanofiltration in removing infectivity from plasma (or other products) spiked with scrapie brain homogenate supernatants. However, efficiency is diminished using supernatants that have been ultracentrifuged to reduce aggregated forms of the infectious agent. Thus, filtration removal data based on experiments using "standard" low-speed centrifugation supernatants might overestimate the amount of prion removal in plasma or urine-derived therapeutic products.

Recovery of small infectious PrP(res) aggregates from prion-infected cultured cells

Prion diseases are characterized by deposits of abnormal conformers of the PrP protein. Although large aggregates of proteinase K-resistant PrP (PrP(res)) are infectious, the precise relationships between aggregation state and infectivity remain to be established. In this study, we have fractionated detergent lysates from prion-infected cultured cells by differential ultracentrifugation and ultrafiltration and have characterized a previously unnoticed PrP species. This abnormal form is resistant to proteinase K digestion but, in contrast to typical aggregated PrP(res), remains in the soluble fraction at intermediate centrifugal forces and is not retained by filters of 300-kDa cutoff. Cell-based assay and inoculation to animals demonstrate that these entities are infectious. The finding that cell-derived small infectious PrP(res) aggregates can be recovered in the absence of strong in vitro denaturating treatments now gives a biological basis for investigating the role of small PrP aggregates in the pathogenicity and/or the multiplication cycle of prions.

The physical relationship between infectivity and prion protein aggregates is strain-dependent

Prions are unconventional infectious agents thought to be primarily composed of PrP(Sc), a multimeric misfolded conformer of the ubiquitously expressed host-encoded prion protein (PrP(C)). They cause fatal neurodegenerative diseases in both animals and humans. The disease phenotype is not uniform within species, and stable, self-propagating variations in PrP(Sc) conformation could encode this 'strain' diversity. However, much remains to be learned about the physical relationship between the infectious agent and PrP(Sc) aggregation state, and how this varies according to the strain. We applied a sedimentation velocity technique to a panel of natural, biologically cloned strains obtained by propagation of classical and atypical sheep scrapie and BSE infectious sources in transgenic mice expressing ovine PrP. Detergent-solubilized, infected brain homogenates were used as starting material. Solubilization conditions were optimized to separate PrP(Sc) aggregates from PrP(C). The distribution of PrP(Sc) and infectivity in the gradient was determined by immunoblotting and mouse bioassay, respectively. As a general feature, a major proteinase K-resistant PrP(Sc) peak was observed in the middle part of the gradient. This population approximately corresponds to multimers of 12-30 PrP molecules, if constituted of PrP only. For two strains, infectivity peaked in a markedly different region of the gradient. This most infectious component sedimented very slowly, suggesting small size oligomers and/or low density PrP(Sc) aggregates. Extending this study to hamster prions passaged in hamster PrP transgenic mice revealed that the highly infectious, slowly sedimenting particles could be a feature of strains able to induce a rapidly lethal disease. Our findings suggest that prion infectious particles are subjected to marked strain-dependent variations, which in turn could influence the strain biological phenotype, in particular the replication dynamics.

Differential display detects host nucleic acid motifs altered in scrapie-infected brain

The transmissible spongiform encephalopathies (TSEs) including scrapie have been attributed to an infectious protein or prion. Infectivity is allied to conversion of the endogenous nucleic-acid-binding protein PrP to an infectious modified form known as PrP(sc). The protein-only theory does not easily explain the enigmatic properties of the agent including strain variation. It was previously suggested that a short nucleic acid, perhaps host-encoded, might contribute to the pathoetiology of the TSEs. No candidate host molecules that might explain transmission of strain differences have yet been put forward. Differential display is a robust technique for detecting nucleic acid differences between two populations. We applied this technique to total nucleic acid preparations from scrapie-infected and control brain. Independent RNA preparations from eight normal and eight scrapie-infected (strain 263K) hamster brains were randomly amplified and visualized in parallel. Though the nucleic acid patterns were generally identical in scrapie-infected versus control brain, some rare bands were differentially displayed. Molecular species consistently overrepresented (or underrepresented) in all eight infected brain samples versus all eight controls were excised from the display, sequenced, and assembled into contigs. Only seven ros contigs (RNAs over- or underrepresented in scrapie) emerged, representing <4 kb from the transcriptome. All contained highly stable regions of secondary structure. The most abundant scrapie-only ros sequence was homologous to a repetitive transposable element (LINE; long interspersed nuclear element). Other ros sequences identified cellular RNA 7SL, clathrin heavy chain, visinin-like protein-1, and three highly specific subregions of ribosomal RNA (ros1-3). The ribosomal ros sequences accurately corresponded to LINE; retrotransposon insertion sites in ribosomal DNA (p<0.01). These differential motifs implicate specific host RNAs in the pathoetiology of the TSEs.

Recent advances in prion chemotherapeutics

The transmissible spongiform encephalopathies are rapidly progressive and invariably fatal neurodegenerative diseases for which there are no proven efficacious treatments. Many approaches have been undertaken to find ways to prevent, halt, or reverse these prion diseases, with limited success to date. However, as both our understanding of pathogenesis and our ability to detect early disease increases, so do our potential therapeutic targets and our chances of finding effective drugs. There is increasing pressure to find effective decontaminants for blood supplies, as variant Creutzfeldt Jakob Disease (vCJD) has been shown to be transmissible by blood, and to find non-toxic preventative therapies, with ongoing cases of Bovine Spongiform Encephalopathy (BSE) and the spread of Chronic Wasting Disease (CWD). Within the realm of chemotherapeutic approaches, much research has focussed on blocking the conversion of the normal form of prion protein (PrP(c)) to its abnormal counterpart (PrP(res)). Structurally, these chemotherapeutic agents are often polyanionic or polycyclic and may directly bind PrP(c) or PrP(res), or act by redistributing, sequestering, or down-regulating PrP(c), thus preventing its conversion. There are also some polycationic compounds which proport to enhance the clearance of PrP(res). Other targets include accessory molecules such as the laminin receptor precursor which influences conversion, or cell signalling molecules which may be required for pathogenesis. Of recent interest are the possible neuroprotective effects of some drugs. Importantly, there is evidence that combining compounds may provide synergistic responses. This review provides an update on current testing methods, therapeutic targets, and promising candidates for chemical-based therapy.

PrPTSE in muscle-associated lymphatic tissue during the preclinical stage of mice infected orally with bovine spongiform encephalopathy

The involvement of muscles in the pathogenesis of transmissible spongiform encephalopathies (TSEs) is irregular and unpredictable. We show that the TSE-specific protein (PrP(TSE)) is present in muscles of mice fed with a mouse-adapted strain of bovine spongiform encephalopathy as early as 100 days post-infection, corresponding to about one-third of the incubation period. The proportion of mice with PrP(TSE)-positive muscles and the number of muscles involved increased as infection progressed, but never attained more than a limited distribution, even at the clinical stage of disease. The appearance of PrP(TSE) in muscles during the preclinical stage of disease was probably due to the haematogenous/lymphatic spread of infectivity from the gastrointestinal tract to lymphatic tissues associated with muscles, whereas in symptomatic animals, the presence of PrP(TSE) in the nervous system, in neuromuscular junctions and in muscle fibres suggests a centrifugal spread from the central nervous system, as already observed in other TSE models.

Ultrastructures and strain comparison of under-glycosylated scrapie prion fibrils

Prions, composed primarily of misfolded, often fibrillar, polymers of prion protein, have poorly understood structures. Heavy surface glycosylation may obscure visualization of their fibrillar cores, so we purified severely under-glycosylated prion protein fibrils from scrapie-infected transgenic mice expressing anchorless prion protein. Using electron and atomic force microscopy, we obtained dimensions and morphological information about prion protein core protofilaments which variably intertwined to form scrapie fibrils. Occasional isolated protofilaments were observed, suggesting that the lateral association of protofilaments is neither essential nor invariant in prion protein polymerization. Strain comparisons suggested basic structural differences; ME7 and 22L fibrils contained thinner protofilaments, 22L fibrils preferred left-handed twists, and 22L fibril periodicities averaged 106nm per half-turn, compared with 64 and 66nm for RML and ME7 fibrils, respectively. The strains displayed overlapping fibril morphologies, providing evidence that prion fibril morphology is influenced, but not dictated, by strain-dependent differences in protofilament structure. These measurements of the amyloid core of scrapie fibrils should aid development of models of prion structure and strain determination.

Manufacture of plasma-derived products in France and measures to prevent the risk of vCJD transmission: Precautionary measures and efficacy of manufacturing processes in prion removal

The emergence of the variant Creutzfeldt-Jakob disease in the mid 1990s soon raised concerns about its possible transmission through the use of blood and plasma-derived medicinal products. A risk analysis approach was initiated by health authorities, based on updated scientific knowledge and precautionary measures were implemented in France and other countries for the management of this new possible risk. Assessment of the vCJD risk is based on epidemiology and estimates of the number of potential cases in the future, on blood infectivity data from models of transmissible spongiform encephalopathies and on data from studies of the capacity of manufacturing processes to remove the agent, should it be present in the plasma of infected donors. The transmission of vCJD by non leukocyte-depleted labile blood components has recently been confirmed. There have been no reports of cases associated with the use of plasma-derived products and the scientific data, and risk analyses for those plasma products, which are of the greatest therapeutic interest, support their safety with respect to this transmission risk. The precautionary measures applied in France and the data contributing to the risk assessment of plasma products are reviewed and updated in the present paper. The uncertainties, which remain, are also addressed and discussed, as well as the ongoing research and developments in this area.

Selection of spiking materials for studies on the clearance of agents of transmissible spongiform encephalopathy during plasma fractionation

Manufacturers of plasma derivatives are encouraged to perform product-specific investigational studies on the ability of their processes to remove prion agents. Such studies are invariably performed using spiking materials derived from infected brain tissue. However, there is little guidance available on which preparations are suitable and no consensus on the acceptability of resultant data. Further research is required to resolve this question.