Transmissible Spongiform Encephalopathy Diseases Research Articles

Characterization and polyanion-binding properties of purified recombinant prion protein

Certain polysulphated polyanions have been shown to have prophylactic effects on the progression of transmissible spongiform encephalopathy disease, presumably because they bind to prion protein (PrP). Until now, the difficulty of obtaining large quantities of native PrP has precluded detailed studies of these interactions. We have over-expressed murine recombinant PrP (recPrP), lacking its glycophosphoinositol membrane anchor, in modified mammalian cells. Milligram quantities of secreted, soluble and partially glycosylated protein were purified under non-denaturing conditions and the identities of mature-length aglycosyl recPrP and two cleavage fragments were determined by electrospray MS. Binding was assessed by surface plasmon resonance techniques using both direct and competitive ligand-binding approaches. recPrP binding to immobilized polyanions was enhanced by divalent metal ions. Polyanion binding was strong and showed complex association and dissociation kinetics that were consistent with ligand-directed recPrP aggregation. The differences in the binding strengths of recPrP to pentosan polysulphate and to other sulphated polyanions were found to parallel their in vivo anti-scrapie and in vitro anti-scrapie-specific PrP formation potencies. When recPrP was immobilized by capture on metal-ion chelates it was found, contrary to expectation, that the addition of polyanions promoted the dissociation of the protein.

Mad cow and related diseases: Challenges for waste management

AbstractMad cow disease and related transmissible spongiform encephalopathy diseases (TSEs) in both animals and humans have received worldwide attention. Interestingly, the issue of managing biohazardous wastes, for which TSE agents are an issue, has received little attention by environmental professionals. The burial of wastes associated with mad cow and related diseases may eventually lead to unusual challenges for remediation professionals. The core challenge is that medical researchers have confirmed the incredible difficulty in destroying TSE infectious agents or pathogens, generally called prions. Risk reduction is certainly possible with treatment technologies, but complete elimination of risk by reliable and verifiable destruction of all TSE agents is probably infeasible. Proving the efficacy of any waste treatment method for TSE‐infected wastes is not practical because there is no commercially available test for TSE pathogens (although one is expected soon) and in only a few cases is there a reasonable surrogate approach. These circumstances have contributed to some biohazardous waste managers discounting the TSE issue. The goal of this article is to more thoroughly analyze available information and various risks to identify useful implications for alternative waste management technologies. A number of prudent actions can be taken in recognition of the TSE problem, including more careful assessment of treatment technologies, avoiding any reuse or recycling of waste treatment residues, using air pollution control systems to avoid releases of materials possibly containing infectious agents, and using wastewater pretreatment prior to sewer disposal.

A Review of the BSE Epidemic in British Cattle

ABSTRACT Bovine spongiform encephalopathy (BSE) was first diagnosed in British cattle in 1986. The infectious agents of transmissible spongiform encephalopathy (TSE) diseases are believed to be infectious proteins or prions. They can remain infectious despite exposures to disinfectants, autoclaving, radiation, and ultraviolet light. TSEs affect animals as well as humans and are characterized by progressively severe psychomotor dysfunction and long incubation periods. As of August 27, 1999, 175,404 cases of BSE have been confirmed in Great Britain with 1,787 additional confirmed cases in Northern Ireland (as of August 31, 1999). Mathematical and statistical analyses of the BSE epidemic data suggest that the incidence of BSE in Great Britain and Northern Ireland will continue its rapid decline. Evidence relating to maternal and horizontal transmission of BSE is discussed. Public concern remains focused on the probable link between BSE infection in cattle and a new variant of Creutzfeldt‐Jakob Disease (vCJD) in humans, another TSE. Given the long and variable incubation periods associated with TSEs, and a possible genetic component, the eventual magnitude of this human epidemic remains uncertain.

Species-independent inhibition of abnormal prion protein (PrP) formation by a peptide containing a conserved PrP sequence.

Conversion of the normal protease-sensitive prion protein (PrP) to its abnormal protease-resistant isoform (PrP-res) is a major feature of the pathogenesis associated with transmissible spongiform encephalopathy (TSE) diseases. In previous experiments, PrP conversion was inhibited by a peptide composed of hamster PrP residues 109 to 141, suggesting that this region of the PrP molecule plays a crucial role in the conversion process. In this study, we used PrP-res derived from animals infected with two different mouse scrapie strains and one hamster scrapie strain to investigate the species specificity of these conversion reactions. Conversion of PrP was found to be completely species specific; however, despite having three amino acid differences, peptides corresponding to the hamster and mouse PrP sequences from residues 109 to 141 inhibited both the mouse and hamster PrP conversion systems equally. Furthermore, a peptide corresponding to hamster PrP residues 119 to 136, which was identical in both mouse and hamster PrP, was able to inhibit PrP-res formation in both the mouse and hamster cell-free systems as well as in scrapie-infected mouse neuroblastoma cell cultures. Because the PrP region from 119 to 136 is very conserved in most species, this peptide may have inhibitory effects on PrP conversion in a wide variety of TSE diseases.

Survey description of down-cows and cows with progressive or non-progressive neurological signs compatible with a TSE from veterinary-client herds in 38 states

The surveillance efforts to detect a potential transmissible spongiform encephalopathy (TSE) disease in US cattle have been in place since 1990. This monitoring programme is vital to US interests as it assures the American public and foreign governments of the freedom from TSEs in the US cattle population. The objective of this study was to collect data from practicing veterinarians that would describe non-ambulatory or "downer-cows" in the US cattle population. A second objective was to estimate rates for progressive central nervous system (CNS) conditions potentially compatible with a TSE and determine if affected by regional and herd-size differences. The design of this study was to survey veterinary members of the American Association of Bovine Practitioners (AABP) and compile the data from downer cows as reported from their clients' dairy and beef herds. For non-ambulatory dairy cows with non-progressive neurological signs (NANP), 85% of cases fell into three cause categories: injury/trauma, septicaemia/toxaemia or non-responsive milk fevers. For beef cows, injury/trauma, septicaemia/toxaemia and other known CNS disorders cases accounted for the majority (76%) of NANP cows. The profile of the progressive CNS cases in dairy cattle found that other known CNS conditions, septicaemia/toxaemia, unknown CNS conditions and non-responsive milk fever to be the most frequently reported causes. In beef cattle four case categories accounted for 88.4% of the total reported causes: injury/trauma, known infectious agent, septicaemia/toxaemia and known CNS conditions. There were regional and herd-size effects on the percentages and rates for unknown cases and non-recovered, progressive CNS rates. Non-recovery rates for progressive cases were >400/106 in the south central and northeast regions. Dairy cattle in the southeast had the highest incidence of progressive and unknown CNS disorders. The same was found for beef cows in the southeast. Results of the herd-size analysis showed that dairy herds with <50 cows and beef herds with <100 cows were at the highest risk for unknown non-progressive plus unknown and total progressive cases in this study. Suggested minimum numbers of tests for surveillance were constructed to account for regional and herd-size differences.

Experimentally induced bovine spongiform encephalopathy did not transmit via goat embryos.

Goats are susceptible to experimental challenge with bovine spongiform encephalopathy (BSE). This study set out to investigate whether the transmission of BSE could occur in goats following the transfer of embryos from experimentally infected donor females into uninfected recipient females. The results showed no evidence of transmissible spongiform encephalopathy disease in any of the offspring which developed from embryos from infected donors, nor indeed in any of the recipient females used as surrogate dams. In addition, there was no indication of experimental BSE spreading as either a venereal infection to males used in mating or by maternal transmission to offspring born naturally to experimentally infected donors, although numbers were small.

Strain-dependent Differences in β-Sheet Conformations of Abnormal Prion Protein

Strain diversity in the transmissible spongiform encephalopathies (TSEs) has been proposed to be determined by variations in the conformation of the abnormal, protease-resistant form of prion protein (PrP-res). We have investigated whether infection of hamsters with three TSE strains resulted in the formation of PrP-res with different conformations using limited proteinase K (PK) digestion and infrared spectroscopy. PrP-res isolated from the brains of hamsters infected with the hyper (HY), drowsy (DY), and 263K TSE strains yielded similar SDS-polyacrylamide gel electrophoresis profiles prior to PK treatment. However, after limited digestion with PK, the PrP-res from the DY strain exhibited a fragmentation pattern that was distinct from that of the other two strains. Infrared spectra of HY and 263K PrP-res each had major absorption bands in the amide I region at 1626 and 1636 cm-1 both prior to and after digestion with PK. These bands were not evident in the DY PrP-res spectra, which had a unique band at 1629-1630 cm-1 and stronger band intensity at both 1616 and 1694-1695 cm-1. Because absorbances from 1616 to 1636 cm-1 of protein infrared spectra are attributed primarily to beta-sheet structures, these findings indicate that the conformations of HY and 263K PrP-res differ from DY PrP-res at least in structural regions with beta-sheet secondary structure. These results support the hypothesis that strain-specific PrP-res conformers can self-propagate by converting the normal prion protein to the abnormal conformers that induce phenotypically distinct TSE diseases.

A dual pathway for the transmission of spongiform encephalopathy disease

The nature of the infective process in the transmissible spongiform encephalopathy (SE) diseases has been a longstanding problem — in particular, whether the causative agents are (unusual) nucleic-acid-mediated viruses, or replicating non-nucleic acid molecules such as protein. Although there is much (conflicting) evidence supporting both views, it does not seem to have been considered that many of the outstanding problems could be resolved if both mechanisms are operating — either separately or together — i.e. that there is a dual, but interconnected, pathway leading to disease development. It is suggested that this is in fact the case, and the implications are discussed.

Transmissible spongiform encephalopathies, hypotheses and food safety: An overview

The transmissible spongiform encephalopathies (TSEs) (in both humans and animals) have been reviewed with the principal focus on bovine spongiform encephalopathy (BSE), its recent outbreak amongst cattle in the UK (`mad cow disease') and its sequelae. The possible reasons for this outbreak are discussed as well as a number of hypotheses reviewed for TSEs (e.g. prions, organophosphates, etc.) and current measures attendant with food safety and surveillance taken in the European Union. It is generally accepted that the combined weight of all the evidence to date supports the conclusion that the new rare but lethal variant Creutzfeldt-Jacob Disease (vCJD) is the human counterpart of the aetiological agent BSE and that eating meat from the infected animals is probably to blame for 24 deaths (23 in the UK and one in France) to date from vCJD. Considerable evidence from biochemical, immunologic, pathologic and genetic studies strongly suggests that PrP sc is the major component of the transmissible prion particle responsible for the rare fatal brain TSE diseases.

Involvement of the immune system in TSE pathogenesis

The transmissible spongiform encephalopathies (TSEs) are continuing to attract both scientific interest and public concern. Here, Neil Mabbott and colleagues review current understanding of the peripheral pathogenesis of TSE diseases.

Molecular assessment of the potential transmissibilities of BSE and scrapie to humans.

More than a million cattle infected with bovine spongiform encephalopathy (BSE) may have entered the human food chain. Fears that BSE might transmit to man were raised when atypical cases of Creutzfeldt-Jakob disease (CJD), a human transmissible spongiform encephalopathy (TSE), emerged in the UK. In BSE and other TSE diseases, the conversion of the protease-sensitive host prion protein (PrP-sen) to a protease-resistant isoform (PrP-res) is an important event in pathogenesis. Biological aspects of TSE diseases are reflected in the specificities of in vitro PrP conversion reactions. Here we show that there is a correlation between in vitro conversion efficiencies and known transmissibilities of BSE, sheep scrapie and CJD. On this basis, we used an in vitro system to gauge the potential transmissibility of scrapie and BSE to humans. We found limited conversion of human PrP-sen to PrP-res driven by PrP-res associated with both scrapie (PrP[Sc]) and BSE (PrP[BSE]). The efficiencies of these heterologous conversion reactions were similar but much lower than those of relevant homologous conversions. Thus the inherent ability of these infectious agents of BSE and scrapie to affect humans following equivalent exposure may be finite but similarly low.