Presumptive BSE cases with an aberrant prion protein phenotype in Switzerland, 2011: Lack of prion disease in experimentally inoculated cattle and bovine prion protein transgenic mice

Kinetics of Abnormal Prion Protein in Blood of Transgenic Mice Experimentally Infected by Multiple Routes with the Agent of Variant Creutzfeldt-Jakob Disease

Transmissible spongiform encephalopathies (TSEs) or prion diseases are characterized by the accumulation in affected tissues of the abnormal prion protein PrP^TSE. We previously demonstrated PrP^TSE in the blood of macaques experimentally infected with variant Creutzfeldt-Jakob disease (vCJD), a human TSE, months to years prior to clinical onset. That work supported the prospect of using PrP^TSE as a blood biomarker to detect vCJD and possibly other human TSEs before the onset of overt illness. However, our results also raised questions about the origin of PrP^TSE detected in blood early after inoculation and the effects of dose and route on the timing of the appearance of PrP^TSE. To investigate these questions, we inoculated vCJD-susceptible transgenic mice and non-infectable prion protein-knockout mice under inoculation conditions resembling those used in macaques, with additional controls. We assayed PrP^TSE in mouse blood using the protein misfolding cyclic amplification (PMCA) method. PrP^TSE from the inoculum cleared from the blood of all mice before 2 months post-inoculation (mpi). Mouse PrP^TSE generated de novo appeared in blood after 2 mpi. These results were consistent regardless of dose or inoculation route. We also demonstrated that a commercial ELISA-like PrP^TSE test detected and quantified PMCA products and provided a useful alternative to Western blots.

Exploration of genetic factors resulting in abnormal disease in cattle experimentally challenged with bovine spongiform encephalopathy

Since the discovery of bovine spongiform encephalopathy (BSE), researchers have orally challenged cattle with infected brain material to study various aspects of disease pathogenesis. Unlike most other pathogens, oral BSE challenge does not always result in the expected clinical presentation and pathology. In a recent study, steers were challenged orally with BSE and all developed clinical signs and were sacrificed and tested. However, despite a similar incubation and clinical presentation, one of the steers did not have detectable PrP^Sc in its brain. Samples from this animal were analysed for genetic differences as well as for the presence of in vitro PrP^Sc seeding activity or infectivity to determine the BSE status of this animal and the potential reasons that it was different. Seeding activity was detected in the brainstem of the abnormal steer but it was approximately one million times less than that found in the normal BSE positive steers. Intra-cranial challenge of bovinized transgenic mice resulted in no transmission of disease. The abnormal steer had different genetic sequences in non-coding regions of the PRNP gene but detection of similar genotypes in Canadian BSE field cases, that showed the expected brain pathology, suggested these differences may not be the primary cause of the abnormal result. Breed composition analysis showed a higher Hereford content in the abnormal steer as well as in two Canadian atypical BSE field cases and several additional abnormal experimental animals. This study could point towards a possible impact of breed composition on BSE pathogenesis.

A seven-residue deletion in PrP leads to generation of a spontaneous prion formed from C-terminal C1 fragment of PrP

Prions result from a drastic conformational change of the host-encoded cellular prion protein (PrP), leading to the formation of β-sheet-rich, insoluble, and protease-resistant self-replicating assemblies (PrP^Sc). The cellular and molecular mechanisms involved in spontaneous prion formation in sporadic and inherited human prion diseases or equivalent animal diseases are poorly understood, in part because cell models of spontaneously forming prions are currently lacking. Here, extending studies on the role of the H2 α-helix C terminus of PrP, we found that deletion of the highly conserved ¹⁹⁰HTVTTTT¹⁹⁶ segment of ovine PrP led to spontaneous prion formation in the RK13 rabbit kidney cell model. On long-term passage, the mutant cells stably produced proteinase K (PK)-resistant, insoluble, and aggregated assemblies that were infectious for naïve cells expressing either the mutant protein or other PrPs with slightly different deletions in the same area. The electrophoretic pattern of the PK-resistant core of the spontaneous prion (Δ^Spont) contained mainly C-terminal polypeptides akin to C1, the cell-surface anchored C-terminal moiety of PrP generated by natural cellular processing. RK13 cells expressing solely the Δ190-196 C1 PrP construct, in the absence of the full-length protein, were susceptible to Δ^Spont prions. Δ^Spont infection induced the conversion of the mutated C1 into a PK-resistant and infectious form perpetuating the biochemical characteristics of Δ^Spont prion. In conclusion, this work provides a unique cell-derived system generating spontaneous prions and provides evidence that the 113 C-terminal residues of PrP are sufficient for a self-propagating prion entity.

Evaluation of an alternative method for production of biodiesel from processed fats derived from Category 1, 2 and 3 animal by-products (submitted by College Proteins)

An alternative method for the production of biodiesel from processed fats derived from Category 1, 2 and 3 animal by-products was assessed. The method is based on a pre-cleaning process, acidic esterification/transesterification of tallow using 1.5% methanesulfonic acid w/w; 140°C; 5.5 bar absolute pressure (bara); 4 h, followed by fractional distillation. The application focuses on the capacity of the alternative method to inactivate prions. Given the limitations that biodiesel presents for direct measurement of prion infectivity, the BIOHAZ Panel considered, based on the outcome of previous EFSA Opinions and current expert evaluation, that a reduction of 6 log10 in detectable PrPS c signal would be necessary to consider the process at least equivalent to previously approved methods for Category 1 animal by-products. This is in addition to the inactivation achieved by the pressure sterilisation method applied before the application of any biodiesel production method. Experimental data were provided via ad hoc studies commissioned to quantify the reduction in detectable PrPS c in material spiked with scrapie hamster strain 263K, as measured by western blot, for the first two steps, with distillation assumed to provide at least an additional 3 log10 reduction, based on published data. Despite the intrinsic methodological caveats of the detection of PrPS c in laboratory studies, the BIOHAZ Panel considers that the alternative method, including the final fractional distillation, is capable of achieving the required 6 log10 reduction of the strain 263K PrPS c signal. Therefore, the method under assessment can be considered at least equivalent to the processing methods previously approved for the production of biodiesel from all categories of animal by-product raw materials. It is recommended to check the feasibility of the proposed HACCP plan by recording the main processing parameters for a certain time period under real industrial conditions.