Neurodegenerative diseases such as Alzheimer's, Parkinson's and the transmissible spongiform encephalopathies (TSEs) are characterized by abnormal protein deposits, often with large amyloid fibrils. However, questions have arisen as to whether such fibrils or smaller subfibrillar oligomers are the prime causes of disease. Abnormal deposits in TSEs are rich in PrP(res), a protease-resistant form of the PrP protein with the ability to convert the normal, protease-sensitive form of the protein (PrP(sen)) into PrP(res) (ref. 3). TSEs can be transmitted between organisms by an enigmatic agent (prion) that contains PrP(res) (refs 4 and 5). To evaluate systematically the relationship between infectivity, converting activity and the size of various PrP(res)-containing aggregates, PrP(res) was partially disaggregated, fractionated by size and analysed by light scattering and non-denaturing gel electrophoresis. Our analyses revealed that with respect to PrP content, infectivity and converting activity peaked markedly in 17-27-nm (300-600 kDa) particles, whereas these activities were substantially lower in large fibrils and virtually absent in oligomers of < or =5 PrP molecules. These results suggest that non-fibrillar particles, with masses equivalent to 14-28 PrP molecules, are the most efficient initiators of TSE disease.

Platelet-and plasma-derived factor Va (FVa) serve essential cofactor roles in prothrombinase-catalyzed thrombin generation. Platelet-derived FV/Va, purified from Triton X-100 platelet lysates was composed of a mixture of polypeptides ranging from ϳ40 to 330 kDa, mimicking those visualized by Western blotting of platelet lysates and releasates with anti-FV antibodies. The purified, platelet-derived protein expressed significant cofactor activity such that thrombin activation led to only a 2-3-fold increase in cofactor activity yet expression of a specific activity identical to that of purified, plasma-derived FVa. Physical and functional differences between the two cofactors were identified. Purified, platelet-derived FVa was 2-3-fold more resistant to activated protein C-catalyzed inactivation than purified plasma-derived FVa on the thrombin-activated platelet surface. The heavy chain subunit of purified, plateletderived FVa contained only a fraction (ϳ10 -15%) of the intrinsic phosphoserine present in the plasma-derived FVa heavy chain and was resistant to phosphorylation at Ser 692 catalyzed by either casein kinase II or thrombin-activated platelets. MALDI-TOF mass spectrometric analyses of tryptic digests of platelet-derived FV peptides detected an intact heavy chain uniquely modified on Thr 402 with an N-acetylglucosamine or N-acetylgalactosamine, whereas Ser 692 remained unmodified. N-terminal sequencing and MALDI-TOF analyses of plateletderived FV/Va peptides identified the presence of a fulllength heavy chain subunit, as well as a light chain subunit formed by cleavage at Tyr 1543 rather than Arg 1545 accounting for the intrinsic levels of cofactor activity exhibited by native platelet-derived FVa. These collective data are the first to demonstrate physical differences between the two FV cofactor pools and support the hypothesis that, subsequent to its endocytosis by megakaryocytes, FV is modified to yield a platelet-derived cofactor distinct from its plasma counterpart.Factor Va (FVa), 1 a heterodimeric protein composed of heavy chain (105 kDa) and light chain (74 kDa) subunits, is formed by limited proteolysis of factor V (FV) (1). In normal hemostasis, FVa functions as a non-enzymatic cofactor of the prothrombinase complex, which consists of a 1:1 stoichiometric and Ca 2ϩ -dependent complex of the serine protease factor Xa and FVa, bound to the membrane of appropriately activated platelets, and catalyzes the proteolytic conversion of prothrombin to thrombin (2). When incorporated into the prothrombinase complex, the catalytic activity of factor Xa is increased by approximately 5 orders of magnitude, and FVa contributes substantially to this increase (3). Removal of FVa from the prothrombinase complex results in a 10,000-fold decrease in the rate of thrombin generation (3), the physiologic effect of which is demonstrated in the bleeding diatheses expressed by FV-deficient individuals (4 -8)Factor V circulates in two pools in whole blood. The majority (75-80%) is found in the plasma as an inactive, singl...

Inhibition of the accumulation of protease-resistant prion protein (PrP-res) is a prime strategy in the development of potential transmissible spongiform encephalopathy (TSE) therapeutics. Here we show that curcumin (diferoylmethane), a major component of the spice turmeric, potently inhibits PrP-res accumulation in scrapie agent-infected neuroblastoma cells (50% inhibitory concentration, ϳ10 nM) and partially inhibits the cell-free conversion of PrP to PrP-res. In vivo studies showed that dietary administration of curcumin had no significant effect on the onset of scrapie in hamsters. Nonetheless, other studies have shown that curcumin is nontoxic and can penetrate the brain, properties that give curcumin advantages over inhibitors previously identified as potential prophylactic and/or therapeutic anti-TSE compounds.Transmissible spongiform encephalopathies (TSE) or prion diseases are untreatable, fatal neurodegenerative diseases that include bovine spongiform encephalopathy, chronic wasting disease, scrapie, and Creutzfeldt-Jakob disease. A central event in TSE diseases is the conversion of the normal, protease-sensitive isoform of prion protein (PrP-sen or PrP C ) to an abnormal, protease-resistant form, PrP-res or PrP Sc . Numerous compounds have been identified as inhibitors of PrPres formation in scrapie agent-infected murine neuroblastoma (ScNB) cells (1-3, 5). The most potent of these inhibitors can also protect rodents against scrapie if they are administered near the time of infection (7,8,10,11,14). Unfortunately, none of these compounds are known to be both safe and effective for use in humans and animals (8, 10, 11). One therapeutic weakness of most of these compounds is likely an inability to penetrate the brain where most of the PrP-res accumulates and TSE pathogenesis occurs.Curcumin, the major component of the spice turmeric and the yellow pigment in curry powder, has several properties that make it of interest as a possible anti-TSE drug. First, its structure resembles Congo red, the most potent of the small-molecule PrP-res inhibitors that have been assayed in ScNB cells (Fig. 1) in that both are potentially planar compounds that have two aromatic rings or ring systems with conjugated linkers. Structure-activity studies have provided evidence that the potential for coplanarity of the rings and linker is important for the inhibitory potency of Congo red (6). Second, unlike Congo red, curcumin is uncharged and is thought to have at least limited bioavailability to the brain after consumption. Indeed, recent studies with a rat model of Alzheimer's disease reported that dietary curcumin reduces ␤-peptide deposition in the brain as well as associated neuropathology and cognitive deficits (9, 12). Third, curcumin has antioxidant activity, a factor that may be important given that oxidative damage is a feature in TSE neuropathogenesis (13). Fourth, humans consume curcumin in large amounts with no apparent toxicity. Toxicology studies have indicated that rodents can tolerate for a long period up to 5%...