Bioassays and Inactivation of Prions

Research advances in the diagnosis of infectious disease by aptasensor technology

Infectious diseases remain a major challenge to public health. The accurate and timely detection of pathogens responsible for these diseases is essential for controlling their spread, supporting clinical diagnosis, and enabling the application of appropriate therapies. Traditionally, the antibody-based assay has been the primary method for pathogen detection. However, recent advancements in aptamer-based technologies have initiated a transformative shift in diagnostic approaches. Aptamer-based sensors (aptasensors) are characterized by lower production costs and greater flexibility, making them compatible with various detection techniques. This broad applicability facilitates multifaceted, high-throughput applications, significantly improving the capacity to monitor and detect infectious diseases. In this review, we introduce the pathogenic mechanisms and characteristics of pathogens, provide an overview of recent advancements in the development of aptasensors for pathogen detection and highlight their versatility in identifying various infectious disease pathogens, including viruses, bacteria, parasites and other microorganisms. We systematically categorize aptasensors according to their detection mechanisms, including colorimetry, fluorescence, chemiluminescence, surface-enhanced Raman spectroscopy (SERS), surface plasmon resonance (SPR), electrochemistry and incorporation of field-effect transistors (FETs). We further demonstrate how these platforms leverage pathogen-specific biological features to achieve ultrasensitive and rapid diagnostics. Further optimization and validation of aptasensor platforms are anticipated to accelerate their clinical translation and industrialization. Advancing these innovative technologies will be crucial to meeting the growing demand for rapid, accurate and reliable pathogen detection across diverse clinical and environmental conditions, ultimately strengthening the ability to respond effectively to infectious disease threats.

Amyloidogenesis: What Do We Know So Far?

The study of protein aggregation, and amyloidosis in particular, has gained considerable interest in recent times. Several neurodegenerative diseases, such as Alzheimer's (AD) and Parkinson's (PD) show a characteristic buildup of proteinaceous aggregates in several organs, especially the brain. Despite the enormous upsurge in research articles in this arena, it would not be incorrect to say that we still lack a crystal-clear idea surrounding these notorious aggregates. In this review, we attempt to present a holistic picture on protein aggregation and amyloids in particular. Using a chronological order of discoveries, we present the case of amyloids right from the onset of their discovery, various biophysical techniques, including analysis of the structure, the mechanisms and kinetics of the formation of amyloids. We have discussed important questions on whether aggregation and amyloidosis are restricted to a subset of specific proteins or more broadly influenced by the biophysiochemical and cellular environment. The therapeutic strategies and the significant failure rate of drugs in clinical trials pertaining to these neurodegenerative diseases have been also discussed at length. At a time when the COVID-19 pandemic has hit the globe hard, the review also discusses the plausibility of the far-reaching consequences posed by the virus, such as triggering early onset of amyloidosis. Finally, the application(s) of amyloids as useful biomaterials has also been discussed briefly in this review.

Impairment of Neuronal Mitochondrial Quality Control in Prion-Induced Neurodegeneration

Mitochondrial dynamics continually maintain cell survival and bioenergetics through mitochondrial quality control processes (fission, fusion, and mitophagy). Aberrant mitochondrial quality control has been implicated in the pathogenic mechanism of various human diseases, including cancer, cardiac dysfunction, and neurological disorders, such as Alzheimer’s disease, Parkinson’s disease, and prion disease. However, the mitochondrial dysfunction-mediated neuropathological mechanisms in prion disease are still uncertain. Here, we used both in vitro and in vivo scrapie-infected models to investigate the involvement of mitochondrial quality control in prion pathogenesis. We found that scrapie infection led to the induction of mitochondrial reactive oxygen species (mtROS) and the loss of mitochondrial membrane potential (ΔΨm), resulting in enhanced phosphorylation of dynamin-related protein 1 (Drp1) at Ser616 and its subsequent translocation to the mitochondria, which was followed by excessive mitophagy. We also confirmed decreased expression levels of mitochondrial oxidative phosphorylation (OXPHOS) complexes and reduced ATP production by scrapie infection. In addition, scrapie-infection-induced aberrant mitochondrial fission and mitophagy led to increased apoptotic signaling, as evidenced by caspase 3 activation and poly (ADP-ribose) polymerase cleavage. These results suggest that scrapie infection induced mitochondrial dysfunction via impaired mitochondrial quality control processes followed by neuronal cell death, which may have an important role in the neuropathogenesis of prion diseases.

Development and application of criteria for classification of hydrolysed proteins in the framework of feed safety

In the view of a circular economy, there is an increasing need for (re-)using animal by-products that have a wide range of applications and sufficient safety. Hydrolysates of animal proteins (HPs) are frequently used as feed ingredients. Nevertheless, clear criteria for legal use and methods for monitoring feed applications are not available. Here, a range of methods have been used and evaluated for characterizing a set of 26 samples of hydrolysed proteins, 'hydrolysed' feather meals and processed animal proteins (PAPs), with verification based on an additional set of eight samples. Methods included determination of ash content, sediment (mineral fraction) content, protein content, species identity, solubility, protein solubility, size exclusion chromatography and polyacrylamide gel electrophoresis (SDS-PAGE). After a comparison of results obtained with water and SDS, water was chosen as the solvent for environmental and occupational reasons. Typical HP samples have a protein content higher than 60%, a solubility exceeding 50% and a virtual absence of a mineral fraction. The first discrimination between HPs and PAPs could be based on the absence or presence, respectively, of a mineral fraction. An approach for HP characterization is designed using a Hydrolysation Index (HI) based on the fraction of peptides smaller than 10 kDa, the solubility of the sample and the fraction of soluble proteins. A simplified version (HI_s), exclusively based on the fraction of peptides smaller than 10 kDa and the solubility of the sample, shows a trend among the samples highly comparable to HI. Values for HI and HI_s exceeding 60% would characterise HPs. Feather meals, which are heat treated instead of treatment by a chemical process of hydrolysation, range among the PAPs and should not be indicated as "hydrolysed." The HI_s can be used as an easy parameter for classifying HPs and for legal enforcement.

Prion potentiation after life-long dormancy in mice devoid of PrP

Prions are neurotropic pathogens composed of misfolded assemblies of the host-encoded prion protein PrP^C which replicate by recruitment and conversion of further PrP^C by an autocatalytic seeding polymerization process. While it has long been shown that mouse-adapted prions cannot replicate and are rapidly cleared in transgenic PrP^0/0 mice invalidated for PrP^C, these experiments have not been done with other prions, including from natural resources, and more sensitive methods to detect prion biological activity. Using transgenic mice expressing human PrP to bioassay prion infectivity and RT-QuIC cell-free assay to measure prion seeding activity, we report that prions responsible for the most prevalent form of sporadic Creutzfeldt-Jakob disease in human (MM1-sCJD) can persist indefinitely in the brain of intra-cerebrally inoculated PrP^0/0 mice. While low levels of seeding activity were measured by RT-QuIC in the brain of the challenged PrP^0/0 mice, the bio-indicator humanized mice succumbed at a high attack rate, suggesting relatively high levels of persistent infectivity. Remarkably, these humanized mice succumbed with delayed kinetics as compared to MM1-sCJD prions directly inoculated at low doses, including the limiting one. Yet, the disease that did occur in the humanized mice on primary and subsequent back-passage from PrP^0/0 mice shared the neuropathological and molecular characteristics of MM1-sCJD prions, suggesting no apparent strain evolution during lifelong dormancy in PrP^0/0 brain. Thus, MM1-sCJD prions can persist for the entire life in PrP^0/0 brain with potential disease potentiation on retrotransmission to susceptible hosts. These findings highlight the capacity of prions to persist and rejuvenate in non-replicative environments, interrogate on the type of prion assemblies at work and alert on the risk of indefinite prion persistence with PrP-lowering therapeutic strategies.

EFSA Panel on Biological Hazards (BIOHAZ), Koutsoumanis K, Allende A, Bolton D, Bover‐Cid S, Chemaly M, Davies R, De Cesare A, Herman L, Hilbert F, Lindqvist R, Nauta M, Peixe L, Ru G, Simmons M, Skandamis P, Suffredini E, Fernández Escámez P, Spiropoulos J, Iulietto MF, Ortiz‐Peláez A, Alvarez‐Ordóñez A. Evaluation of the application for new alternative biodiesel production process for rendered fat including Category 1 animal by-products (BDI-RepCat® process, AT)

A new alternative method for the production of biodiesel from rendered fat, including animal by-product (ABP) Category 1 tallow, was evaluated. The method consists of a conversion phase, based on esterification and transesterification in a single step (at temperature ≥ 200°C, pressure ≥ 70 bar with a retention time ≥ 15 min), using MgO as a catalyst and in the presence of methanol (10-15%), followed by vacuum distillation (at ≥ 150°C, ≤ 10 mbar) of the end-product, biodiesel and the co-product, glycerine. Prions (PrPS c), which are abnormal isoforms of the prion protein, were considered by the applicant to be the most resistant hazard. In accordance with previous EFSA Opinions and current expert evaluation, a reduction in prion infectivity, or detectable PrPS c, of at least 6 log10 should be achieved for the process to be considered equivalent to the processing method laid down in the Regulation (EU) No 142/2011. Published data from an experimental replication of the conversion step of the biodiesel production process under consideration were provided, which showed an at least 6 log10 reduction in detectable PrPS c, by Western blot, in tallow that had been spiked with murine and human prion strains. In addition, it was demonstrated that the presence of methanol does not affect the recovery or detection of PrPS c from a biodiesel substrate. Based on scientific literature, the vacuum distillation step has been shown to be capable of achieving an additional 3 log10 reduction in PrPS c. Therefore, the proposed alternative method is considered to be at least equivalent to the processing method laid down in the legislation for the production of biodiesel from raw materials including Category 1 ABP.

Autoclave treatment of the classical scrapie agent US No. 13-7 and experimental inoculation to susceptible VRQ/ARQ sheep via the oral route results in decreased transmission efficiency

Scrapie, a prion disease of sheep, is highly resistant to conventional deactivation. Numerous methods to deactivate scrapie have been tested in laboratory animal models, and adequate autoclave treatment can reduce or remove the infectivity of some classical scrapie strains depending on the heating parameters used. In this study, we autoclaved brain homogenate from a sheep with US scrapie strain 13–7 for 30 minutes at 121°C. Genetically susceptible VRQ/ARQ sheep were orally inoculated with 3 grams of the autoclaved brain homogenate. For comparison, a second group of sheep was inoculated with a non-autoclaved brain homogenate. Rectal biopsies were used to assess antemortem scrapie disease progression throughout the study. Five out of ten (5/10) sheep that received autoclaved inoculum ultimately developed scrapie after an experimental endpoint of 72 months. These sheep had a mean incubation period of 26.99 months. Two out of five (2/5) positive sheep had detectable PrP^Sc in antemortem rectal biopsies, and two (2/5) other sheep had PrP^Sc in postmortem rectal tissue. A single sheep (1/5) was positive for scrapie in the CNS, small intestine, and retropharyngeal lymph node but had negative rectal tissue. All of the sheep (10/10) that received non-autoclaved inoculum developed scrapie with a mean incubation period of 20.2 months and had positive rectal biopsies at the earliest timepoint (14.7 months post-inoculation). These results demonstrate that sheep are orally susceptible to US derived classical scrapie strain 13–7 after autoclave treatment at 121°C for 30 minutes. Differences in incubation periods and time interval to first positive rectal biopsies indicate a partial reduction in infectivity titers for the autoclaved inoculum group.

Improving the Predictive Value of Prion Inactivation Validation Methods to Minimize the Risks of Iatrogenic Transmission With Medical Instruments

Prions are pathogenic infectious agents responsible for fatal, incurable neurodegenerative diseases in animals and humans. Prions are composed exclusively of an aggregated and misfolded form (PrP^Sc) of the cellular prion protein (PrP^C). During the propagation of the disease, PrP^Sc recruits and misfolds PrP^C into further PrP^Sc. In human, iatrogenic prion transmission has occurred with incompletely sterilized medical material because of the unusual resistance of prions to inactivation. Most commercial prion disinfectants validated against the historical, well-characterized laboratory strain of 263K hamster prions were recently shown to be ineffective against variant Creutzfeldt-Jakob disease human prions. These observations and previous reports support the view that any inactivation method must be validated against the prions for which they are intended to be used. Strain-specific variations in PrP^Sc physico-chemical properties and conformation are likely to explain the strain-specific efficacy of inactivation methods. Animal bioassays have long been used as gold standards to validate prion inactivation methods, by measuring reduction of prion infectivity. Cell-free assays such as the real-time quaking-induced conversion (RT-QuIC) assay and the protein misfolding cyclic amplification (PMCA) assay have emerged as attractive alternatives. They exploit the seeding capacities of PrP^Sc to exponentially amplify minute amounts of prions in biospecimens. European and certain national medicine agencies recently implemented their guidelines for prion inactivation of non-disposable medical material; they encourage or request the use of human prions and cell-free assays to improve the predictive value of the validation methods. In this review, we discuss the methodological and technical issues regarding the choice of (i) the cell-free assay, (ii) the human prion strain type, (iii) the prion-containing biological material. We also introduce a new optimized substrate for high-throughput PMCA amplification of human prions bound on steel wires, as translational model for prion-contaminated instruments.

A Novel, Reliable and Highly Versatile Method to Evaluate Different Prion Decontamination Procedures

Transmissible spongiform encephalopathies (TSEs) are a group of invariably fatal neurodegenerative disorders. The causal agent is an aberrantly folded isoform (PrP^Sc or prion) of the endogenous prion protein (PrP^C) which is neurotoxic and amyloidogenic and induces misfolding of its physiological counterpart. The intrinsic physical characteristics of these infectious proteinaceous pathogens makes them highly resistant to the vast majority of physicochemical decontamination procedures used typically for standard disinfection. This means prions are highly persistent in contaminated tissues, the environment (surfaces) and, of great concern, on medical and surgical instruments. Traditionally, decontamination procedures for prions are tested on natural isolates coming from the brain of infected individuals with an associated high heterogeneity resulting in highly variable results. Using our novel ability to produce highly infectious recombinant prions in vitro we adapted the system to enable recovery of infectious prions from contaminated materials. This method is easy to perform and, importantly, results in highly reproducible propagation in vitro. It exploits the adherence of infectious prion protein to beads of different materials allowing accurate and repeatable assessment of the efficacy of disinfectants of differing physicochemical natures to eliminate infectious prions. This method is technically easy, requires only a small shaker and a standard biochemical technique and could be performed in any laboratory.

Quantifying the Role of Lysine in Prion Replication by Nano-LC Mass Spectrometry and Bioassay

Prions propagate by a template driven process, inducing the normal cellular isoform (PrP^C) to adopt the prion (PrP^Sc) conformation. In PrP^C, the positions of lysines are highly conserved and strongly influence prion propagation. In this study, covalent modification was used to quantitate the role of lysines in the PrP^Sc template that drives prion replication. The ε-amino group of lysines in the PrP^Sc (hamster-adapted scrapie Sc237) template was acetylated by either acetic anhydride (Ac₂O) or the N-hydroxysuccinimide ester of acetic acid (Ac-NHS). The extent of lysine acetylation in PrP^Sc was quantitated by mass spectrometry or Western blot-based analysis. Identical samples were bioassayed to quantitate the loss of infectivity associated with lysine acetylation. The reduction of infectivity at the highest reagent concentration was approximately 90% (∼10-fold). Ten of the eleven prion lysines were acetylated to a greater extent (25−400-fold) than the observed loss of infectivity. Only one lysine, at position 220 (K₂₂₀), had a reactivity that is consistent with the loss of infectivity. Although lysines are highly conserved and play a crucial role in converting PrP^C into the PrP^Sc conformation, once that conformation is adopted, the lysines present in the PrP^Sc template play only a limited role in prion replication. In principle, this approach could be used to clarify the role of other amino acids in the replication of prions and other prion-like protein misfolding diseases.

Invited Review: The role of prion-like mechanisms in neurodegenerative diseases

The prototype of transmissible neurodegenerative proteinopathies is prion diseases, characterized by aggregation of abnormally folded conformers of the native prion protein. A wealth of mechanisms has been proposed to explain the conformational conversion from physiological protein into misfolded, pathological form, mode of toxicity, propagation from cell-to-cell and regional spread. There is increasing evidence that other neurodegenerative diseases, most notably Alzheimer's disease (Aβ and tau), Parkinson's disease (α-synuclein), frontotemporal dementia (TDP43, tau or FUS) and motor neurone disease (TDP43), exhibit at least some of the misfolded prion protein properties. In this review, we will discuss to what extent each of the properties of misfolded prion protein is known to occur for Aβ, tau, α-synuclein and TDP43, with particular focus on self-propagation through seeding, conformational strains, selective cellular and regional vulnerability, stability and resistance to inactivation, oligomers, toxicity and summarize the most recent literature on transmissibility of neurodegenerative disorders.

Large-scale prion protein genotyping in Canadian caribou populations and potential impact on chronic wasting disease susceptibility

Polymorphisms within the prion protein gene (Prnp) are an intrinsic factor that can modulate chronic wasting disease (CWD) pathogenesis in cervids. Although wild European reindeer (Rangifer tarandus tarandus) were infected with CWD, as yet there have been no reports of the disease in North American caribou (R. tarandus spp.). Previous Prnp genotyping studies on approximately 200 caribou revealed single nucleotide polymorphisms (SNPs) at codons 2 (V/M), 129 (G/S), 138 (S/N), 146 (N/n) and 169 (V/M). The impact of these polymorphisms on CWD transmission is mostly unknown, except for codon 138. Reindeer carrying at least one allele encoding for asparagine (138NN or 138SN) are less susceptible to clinical CWD upon infection by natural routes, with the majority of prions limited to extraneural tissues. We sequenced the Prnp coding region of two caribou subspecies (n = 986) from British Columbia, Saskatchewan, Yukon, Nunavut and the Northwest Territories, to identify SNPs and their frequencies. Genotype frequencies at codon 138 differed significantly between barren-ground (R. t. groenlandicus) and woodland (R. t. caribou) caribou when we excluded the Chinchaga herd (p < .05). We also found new variants at codons 153 (Y/F) and 242 (P/L). Our findings show that the 138N allele is rare among caribou in areas with higher risk of contact with CWD-infected species. As both subspecies are classified as Threatened and play significant roles in North American Indigenous culture, history, food security and the economy, determining frequencies of Prnp genotypes associated with susceptibility to CWD is important for future wildlife management measures.

Potential of Microfluidics and Lab-on-Chip Platforms to Improve Understanding of "prion-like" Protein Assembly and Behavior

Human aging is accompanied by a relevant increase in age-associated chronic pathologies, including neurodegenerative and metabolic diseases. The appearance and evolution of numerous neurodegenerative diseases is paralleled by the appearance of intracellular and extracellular accumulation of misfolded proteins in affected brains. In addition, recent evidence suggests that most of these amyloid proteins can behave and propagate among neural cells similarly to infective prions. In order to improve understanding of the seeding and spreading processes of these "prion-like" amyloids, microfluidics and 3D lab-on-chip approaches have been developed as highly valuable tools. These techniques allow us to monitor changes in cellular and molecular processes responsible for amyloid seeding and cell spreading and their parallel effects in neural physiology. Their compatibility with new optical and biochemical techniques and their relative availability have increased interest in them and in their use in numerous laboratories. In addition, recent advances in stem cell research in combination with microfluidic platforms have opened new humanized in vitro models for myriad neurodegenerative diseases affecting different cellular targets of the vascular, muscular, and nervous systems, and glial cells. These new platforms help reduce the use of animal experimentation. They are more reproducible and represent a potential alternative to classical approaches to understanding neurodegeneration. In this review, we summarize recent progress in neurobiological research in "prion-like" protein using microfluidic and 3D lab-on-chip approaches. These approaches are driven by various fields, including chemistry, biochemistry, and cell biology, and they serve to facilitate the development of more precise human brain models for basic mechanistic studies of cell-to-cell interactions and drug discovery.

Virulent Pseudomonas aeruginosa infection converts antimicrobial amyloids into cytotoxic prions

Pseudomonas aeruginosa infection elicits the production of cytotoxic amyloids from lung endothelium, yet molecular mechanisms of host‐pathogen interaction that underlie the amyloid production are not well understood. We examined the importance of type III secretion system (T3SS) effectors in the production of cytotoxic amyloids. P aeruginosa possessing a functional T3SS and effectors induced the production and release of cytotoxic amyloids from lung endothelium, including beta amyloid, and tau. T3SS effector intoxication was sufficient to generate cytotoxic amyloid release, yet intoxication with exoenzyme Y (ExoY) alone or together with exoenzymes S and T (ExoS/T/Y) generated the most virulent amyloids. Infection with lab and clinical strains engendered cytotoxic amyloids that were capable of being propagated in endothelial cell culture and passed to naïve cells, indicative of a prion strain. Conversely, T3SS‐incompetent P aeruginosa infection produced non‐cytotoxic amyloids with antimicrobial properties. These findings provide evidence that (1) endothelial intoxication with ExoY is sufficient to elicit self‐propagating amyloid cytotoxins during infection, (2) pulmonary endothelium contributes to innate immunity by generating antimicrobial amyloids in response to bacterial infection, and (3) ExoY contributes to the virulence arsenal of P aeruginosa through the subversion of endothelial amyloid host‐defense to promote a lung endothelial‐derived cytotoxic proteinopathy.

Native nanodiscs formed by styrene maleic acid copolymer derivatives help recover infectious prion multimers bound to brain-derived lipids

Prions are lipidated proteins that interact with endogenous lipids and metal ions. They also assemble into multimers and propagate into the infectious scrapie form known as PrP^Sc The high-resolution structure of the infectious PrP^Sc state remains unknown, and its analysis largely relies on detergent-based preparations devoid of endogenous ligands. Here we designed polymers that allow isolation of endogenous membrane:protein assemblies in native nanodiscs without exposure to conventional detergents that destabilize protein structures and induce fibrillization. A set of styrene-maleic acid (SMA) polymers including a methylamine derivative facilitated gentle release of the infectious complexes for resolution of multimers, and a thiol-containing version promoted crystallization. Polymer extraction from brain homogenates from Syrian hamsters infected with Hyper prions and WT mice infected with Rocky Mountain Laboratories prions yielded infectious prion nanoparticles including oligomers and microfilaments bound to lipid vesicles. Lipid analysis revealed the brain phospholipids that associate with prion protofilaments, as well as those that are specifically enriched in prion assemblies captured by the methylamine-modified copolymer. A comparison of the infectivity of PrP^Sc attached to SMA lipid particles in mice and hamsters indicated that these amphipathic polymers offer a valuable tool for high-yield production of intact, detergent-free prions that retain in vivo activity. This native prion isolation method provides an avenue for producing relevant prion:lipid targets and potentially other proteins that form multimeric assemblies and fibrils on membranes.

Use of different RT-QuIC substrates for detecting CWD prions in the brain of Norwegian cervids

Chronic wasting disease (CWD) is a highly contagious prion disease affecting captive and free-ranging cervid populations. CWD has been detected in United States, Canada, South Korea and, most recently, in Europe (Norway, Finland and Sweden). Animals with CWD release infectious prions in the environment through saliva, urine and feces sustaining disease spreading between cervids but also potentially to other non-cervids ruminants (e.g. sheep, goats and cattle). In the light of these considerations and due to CWD unknown zoonotic potential, it is of utmost importance to follow specific surveillance programs useful to minimize disease spreading and transmission. The European community has already in place specific surveillance measures, but the traditional diagnostic tests performed on nervous or lymphoid tissues lack sensitivity. We have optimized a Real-Time Quaking-Induced Conversion (RT-QuIC) assay for detecting CWD prions with high sensitivity and specificity to try to overcome this problem. In this work, we show that bank vole prion protein (PrP) is an excellent substrate for RT-QuIC reactions, enabling the detection of trace-amounts of CWD prions, regardless of prion strain and cervid species. Beside supporting the traditional diagnostic tests, this technology could be exploited for detecting prions in peripheral tissues from live animals, possibly even at preclinical stages of the disease.

Prion-like propagation of α-synuclein in neurodegenerative diseases

Prions are defined as proteinaceous infectious particles that do not contain nucleic acids. Neuropathological investigations of post-mortem brains and recent studies of experimental transmission have suggested that amyloid-like abnormal protein aggregates, which are the defining feature of many neurodegenerative diseases, behave like prions and propagate throughout the brain. This prion-like propagation may be the underlying mechanism of onset and progression of neurodegenerative diseases, although the precise molecular mechanisms involved remain unclear. However, in vitro and in vivo experimental models of prion-like propagation using pathogenic protein seeds are well established and are extremely valuable for the exploration and evaluation of novel drugs and therapies for neurodegenerative diseases for which there is no effective treatment. In this chapter, we introduce the experimental models of prion-like propagation of α-synuclein, which is accumulated in Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy, and we describe their applications for the development of new diagnostic and therapeutic modalities. We also introduce the concept of "α-syn strains," which may underlie the pathological and clinical diversity of α-synucleinopathies.

Bridging legal requirements and analytical methods: a review of monitoring opportunities of animal proteins in feed

Availability and safety of food ranks among the basic requirements for human beings. The importance of the food producing sector, inclusive of feed manufacturing, demands a high level of regulation and control. This paper will present and discuss the relationships in the triangle of legislation, the background of hazards with a biological nature, and opportunities for monitoring methods, most notable for prion-based diseases as primary issue. The European Union legislation for prevention of prion-based diseases since 2000 is presented and discussed. The definitions and circumscriptions of groups of species will be analysed in the view biological classification and evolutionary relationships. The state of the art of monitoring methods is presented and discussed. Methods based on visual markers (microscopy), DNA-based methods (PCR), protein-based methods (ELISA, mass spectroscopy, proteomics), near infrared oriented methods and combinations thereof are being evaluated. It is argued that the use in legislation of non-homogeneous groups of species in a biological sense will hamper the optimal design of monitoring methods. Proper definitions are considered to act as bridges between legal demands and suitable analytical methods for effective monitoring. Definitions including specified groups of species instead of single species are more effective for monitoring in a range of cases. Besides the desire of precise circumscription of animal groups targeted by legislation, processed products need well defined definitions as well. Most notable examples are blood versus blood products, and hydrolysis of several types of material. The WISE principle for harmonising the design of legislation and of analytical methods is discussed. This principle includes the elements Witful (reasonable legal principles), Indicative (clear limits between prohibition and authorisation), Societal demands (public health, environment, economy), and Enforceable (presence of suited monitoring methods) in order to promote a balanced effort for reaching the desired level of safety in the food production chain.

Potent prion-like behaviors of pathogenic α-synuclein and evaluation of inactivation methods

The concept that abnormal protein aggregates show prion-like propagation between cells has been considered to explain the onset and progression of many neurodegenerative diseases. Indeed, both synthetic amyloid-like fibrils and pathogenic proteins extracted from patients’ brains induce self-templated amplification and cell-to-cell transmission in vitro and in vivo. However, it is unclear whether exposure to exogenous prion-like proteins can potentially cause these diseases in humans. Here, we investigated in detail the prion-like seeding activities of several kinds of pathogenic α-synuclein (α-syn), including synthetic fibrils and detergent-insoluble fractions extracted from brains of patients with α-synucleinopathies. Exposure to synthetic α-syn fibrils at concentrations above 100 pg/mL caused seeded aggregation of α-syn in SH-SY5Y cells, and seeded aggregation was also observed in C57BL/6 J mice after intracerebral inoculation of at least 0.1 μg/animal. α-Syn aggregates extracted from brains of multiple system atrophy (MSA) patients showed higher seeding activity than those extracted from patients with dementia with Lewy bodies (DLB), and their potency was similar to that of synthetic α-syn fibrils. We also examined the effects of various methods that have been reported to inactivate abnormal prion proteins (PrP^Sc), including autoclaving at various temperatures, exposure to sodium dodecyl sulfate (SDS), and combined treatments. The combination of autoclaving and 1% SDS substantially reduced the seeding activities of synthetic α-syn fibrils and α-syn aggregates extracted from MSA brains. However, single treatment with 1% SDS or generally used sterilization conditions proved insufficient to prevent accumulation of pathological α-syn. In conclusion, α-syn aggregates derived from MSA patients showed a potent prion-like seeding activity, which could be efficiently reduced by combined use of SDS and autoclaving.

MSA prions exhibit remarkable stability and resistance to inactivation

In multiple system atrophy (MSA), progressive neurodegeneration results from the protein α-synuclein misfolding into a self-templating prion conformation that spreads throughout the brain. MSA prions are transmissible to transgenic (Tg) mice expressing mutated human α-synuclein (TgM83^+/-), inducing neurological disease following intracranial inoculation with brain homogenate from deceased patient samples. Noting the similarities between α-synuclein prions and PrP scrapie (PrP^Sc) prions responsible for Creutzfeldt-Jakob disease (CJD), we investigated MSA transmission under conditions known to result in PrP^Sc transmission. When peripherally exposed to MSA via the peritoneal cavity, hind leg muscle, and tongue, TgM83^+/- mice developed neurological signs accompanied by α-synuclein prions in the brain. Iatrogenic CJD, resulting from PrP^Sc prion adherence to surgical steel instruments, has been investigated by incubating steel sutures in contaminated brain homogenate before implantation into mouse brain. Mice studied using this model for MSA developed disease, whereas wire incubated in control homogenate had no effect on the animals. Notably, formalin fixation did not inactivate α-synuclein prions. Formalin-fixed MSA patient samples also transmitted disease to TgM83^+/- mice, even after incubating in fixative for 244 months. Finally, at least 10% sarkosyl was found to be the concentration necessary to partially inactivate MSA prions. These results demonstrate the robustness of α-synuclein prions to denaturation. Moreover, they establish the parallel characteristics between PrP^Sc and α-synuclein prions, arguing that clinicians should exercise caution when working with materials that might contain α-synuclein prions to prevent disease.

A role for astroglia in prion diseases

In this issue of JEM, Krejciova et al. (https://doi.org/10.1084/jem.20161547) report that astrocytes derived from human iPSCs can replicate human CJD prions. These observations provide a new, potentially very valuable model for studying human prions in cellula and for identifying antiprion compounds that might serve as clinical candidates. Furthermore, they add to the evidence that astrocytes may not be just innocent bystanders in prion diseases.

Ricci A, Allende A, Bolton D, Chemaly M, Davies R, Girones R, Herman L, Koutsoumanis K, Lindqvist R, Nørrung B, Robertson L, Ru G, Sanaa M, Simmons M, Skandamis P, Snary E, Speybroeck N, Ter Kuile B, Threlfall J, Wahlström H, Alvarez Ordoñez A, Griffin J, Spiropoulos J, Vanopdenbosch E, Correia S, Fernández Escámez PS. Evaluation of the Application for new alternative biodiesel production process for rendered fat of Cat 1 (BDI-RepCat process, AT)

A new alternative method for the production of biodiesel from rendered fat of all categories of animal by‐products was assessed. The process was compared to the approved biodiesel production process described in Chapter IV Section 2 D of Annex IV of Commission Regulation (EU) 142/2011. Tallow derived from Category 1 material is treated according to Method 1 from the same Regulation (133°C, 20 min, 3 bar) and subsequently mixed with 15% methanol, heated to reaction temperature (220°C) in several heat exchangers and transferred into the continuous conversion reactor by means of a high pressure pump (80 bar) for 30 min. In the conversion phase, there is an exposure to methanol in the absence of alkaline or acidic conditions. The impact of this procedure on the thermostability of transmissible spongiform encephalopathy (TSE) has not been assessed in the literature. After the reaction, the biodiesel/glycerol mixture is distilled under vacuum at a minimum temperature of 150°C and a maximum pressure of 10 mbar, which is equivalent to the distillation step in the approved biodiesel production process, for which a 3 log₁₀ reduction factor in PrP27–30 was obtained. Therefore, a similar level of TSE infectivity reduction could be expected for that phase of the method. A previous EFSA Opinion established that a reduction of 6 log₁₀ in TSE infectivity should be achieved by any proposed alternative method in order to be equivalent to the approved processing method. This level of reduction has not been shown with experimental trials run under conditions equivalent to the ones described for the RepCat process. It was not possible to conclude whether or not the level of TSE infectivity reduction in the RepCat process is at least of 6 log₁₀. Therefore, it was also not possible to conclude about the equivalence with the approved biodiesel production process.

Developing Therapeutics for PrP Prion Diseases

The prototypical PrP prion diseases are invariably fatal, and the search for agents to treat them spans more than 30 years, with limited success. However, in the last few years, the application of high-throughput screening, medicinal chemistry, and pharmacokinetic optimization has led to important advances. The PrP prion inoculation paradigm provides a robust assay for testing therapeutic efficacy, and a dozen compounds have been reported that lead to meaningful extension in survival of prion-infected mice. Here, we review the history and recent progress in the field, focusing on studies validated in animal models. Based on screens in cells infected with mouse-passaged PrP prions, orally available compounds were generated that double or even triple the survival of mice infected with the same prion strain. Unfortunately, no compounds have yet shown efficacy against human prions. Nevertheless, the speed of the recent advances brings hope that an effective therapeutic can be developed. A successful treatment for any neurodegenerative disease would be a major achievement, and the growing understanding that the more common neurodegenerative diseases, including Alzheimer's and Parkinson's, progress by an analogous prion mechanism serves to highlight the importance of antiprion therapeutics.