The prion protein (PrP) has a central role in the pathogenesis of transmissible spongiform encephalopathies (TSE).Creutzfeldt-Jakob disease (CJD) is a transmissible spongiform encephalopathy (TSE) with some variants (nvCJD) zoonotically linked to bovine spongiform encephalopathy.

A considerable body of data supports the model that the infectious agent (called a prion) which causes the transmissible spongiform encephalopathies is a replicating polypeptide devoid of nucleic acid. Prions are believed to propagate by changing the conformation of the normal cellular prion protein (PrPc) into an infectious isoform without altering the primary sequence. Proteins equivalent to the mature form of the wild-type mouse prion protein (residues 23-231) or with a mutation equivalent to that associated with Gerstmann-Straüssler-Scheinker disease (proline to leucine at codon 102 in human; 101 in mouse) were expressed in E. coli. The mutation did not alter the relative proteinase K susceptibility properties of the mouse prion proteins. The wild-type and mutant proteins were analyzed by circular dichroism under different pH and temperature conditions. The mutation was associated with a decrease in alpha-helical content, while the beta-sheet content of the two proteins was unchanged. This suggests the mutation, while altering the secondary structure of PrP, is not sufficient to induce proteinase K resistance and could therefore represent an intermediate isoform along the pathway toward prion formation.

Transmissible spongiform encephalopathies are characterised by the transformation of the normal cellular prion protein (PrP(C)) into an abnormal isoform (PrP(TSE)). Previous studies have shown that N-methyl-D-aspartate (NMDA) receptor antagonists can inhibit glutathione depletion and neurotoxicity induced by PrP(TSE) and a toxic prion protein peptide, PrP106-126, in vitro. NMDA receptor activation is known to increase intracellular accumulation of Ca(2+), resulting in up-regulation of arachidonic acid (AA) metabolism. This can stimulate the lipoxygenase pathways that may generate a number of potentially neurotoxic metabolites. Because of the putative relationship between AA breakdown and PrP106-126 neurotoxicity, we investigated AA metabolism in primary cerebellar granule neuron cultures treated with PrP106-126. Our studies revealed that PrP106-126 exposure for 30 min significantly up-regulated AA release from cerebellar granule neurons. PrP106-126 neurotoxicity was mediated through the 5-lipoxygenase (5-LOX) pathway, as shown by abrogation of neuronal death with the 5-LOX inhibitors quinacrine, nordihydroguaiaretic acid, and caffeic acid. These inhibitors also prevented PrP106-126-induced caspase 3 activation and annexin V binding, indicating a central role for the 5-LOX pathway in PrP106-126-mediated proapoptosis. Interestingly, inhibitors of the 12-lipoxygenase pathway had no effect on PrP106-126 neurotoxicity or proapoptosis. These studies clearly demonstrate that AA metabolism through the 5-LOX pathway is an important early event in PrP106-126 neurotoxicity and consequently may have a critical role in PrP(TSE)-mediated cell loss in vivo. If this is so, therapeutic intervention with 5-LOX inhibitors may prove beneficial in the treatment of prion disorders.

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Using rodent-adapted scrapie as a model, the studies indicated that ion exchange chromatography, as well as Cohn immunoglobulin fractionation have the potential to effectively reduce the load of TSE agents should they be present in plasma pools.

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A model system for assessment of prion inactivation/removal from chromatography gels has been established. Spiked prion infectivity does bind to DEAE Sepharose gel; however, the cleaning cycle removed infectivity to levels below that detectable by bioassay.

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