The metalloprotease ADAMTS13 is assumed to regulate the functional levels of von Willebrand factor (VWF) appropriate for normal hemostasis in vivo by reducing VWF multimer size, which directly represents the thrombogenic activity of this factor. Using an in vitro perfusion chamber system, we studied the mechanisms of ADAMTS13 action during platelet thrombus formation on a collagen surface under whole blood flow conditions. Inhibition studies with a functionblocking anti-ADAMTS13 antibody, combined with immunostaining of thrombi with an anti-VWF monoclonal antibody that specifically reflects the VWFcleaving activity of ADAMTS13, provided visual evidence for a shear ratedependent action of ADAMTS13 that limits thrombus growth directly at the site of the ongoing thrombus generation process. Our results identify an exquisitely specific regulatory mechanism that prevents arterial occlusion under high shear rate conditions during mural thrombogenesis. IntroductionThe adhesive protein von Willebrand factor (VWF) plays a major role in platelet thrombogenesis, a process crucial for hemostasis. However, the excessive function of VWF is thought to increase the risk of fatal arterial thrombosis. 1,2 The thrombogenic activity of VWF is strictly dependent upon its multimeric structure, which is thought to be regulated in vivo by the metalloprotease ADAMTS13 through its cleavage of the A2 domain of the VWF subunit. 3,4 Indeed, patients with congenital deficiency of ADAMTS13 suffer repeated thrombotic complications attributed to excessive function of the ultra-large VWF (ULVWF) multimer, which is not found in normal blood circulation. [3][4][5][6] This concept was recently confirmed by knock-out mouse studies, in which ADAMTS13 Ϫ/Ϫ mice exhibited enhanced thrombogenicity in the ex vivo or in vitro experimental blood flow conditions tested. 7,8 The mechanisms by which ADAMTS13 regulates VWF remain poorly understood. However, recent studies showing that ADAMTS13 under flow conditions can rapidly cleave ULVWF secreted from and anchored to cultured endothelial cell layers 9,10 have raised the possibility that blood flow is critical in activating ADAMTS13. 11 Indeed, the VWF-cleaving activity of ADAMTS13 cannot be reproduced in vitro under static conditions unless the substrate VWF molecule is somewhat modified (eg, denatured by guanidine-HCl or urea). 3,4 Further, the question arises of whether ADAMTS13, in addition to its known action on ULVWF freshly released from endothelial cells, might also act directly at the local sites of thrombus generation to regulate thrombus growth.To address these issues, we analyzed the role and mechanisms of ADAMTS13 action in mural platelet thrombogenesis on a collagen-coated glass surface in an in vitro perfusion chamber system. Our visual evidence demonstrates that ADAMTS13 cleaves VWF and down-regulates mural thrombus growth at the site of ongoing thrombus generation in a shear rate-dependent manner under whole blood flow conditions. Methods Blood collectionThe present work was approved by the i...

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In addition to lowering cholesterol, the 3-hydroxyl-3-methylglutaryl coenzyme A reductase inhibitors (statins) have a range of pleiotropic effects that help reduce the risk of adverse cardiovascular events. We sought to understand the molecular mechanisms by which statins could exert anti-platelet actions under physiologic whole blood flow conditions. Using an in vitro perfusion chamber system, we examined the anti-platelet effects of pravastatin under whole blood flow conditions with high or low shear rates. We determined that pravastatin significantly suppressed platelet activation-dependent procoagulant activity, decreasing P-selectin membrane expression, tissue factor accumulation, and thrombin binding within platelet thrombi generated on a von Willebrand factor-surface under high shear rate conditions. These effects resulted in reductions of intra-thrombus fibrin deposition. These antithrombotic properties of pravastatin, which were comparable to those of atorvastatin, could be abrogated by mevalonate. Our experimental approach revealed a novel mechanism mediating the anti-platelet action of statins. Shear rate-dependent antithrombotic activity may explain the favourable effect of pravastatin on the reduction in cardiovascular events that typically occur in vivo under whole blood flow conditions with high shear rates.

The present data do not support the thesis that the increased plasma histamine concentration is causally related to pruritus in hemodialysis patients or that the antiallergic drug, azelastin HCL, alleviates the pruritus of dialysis patients by decreasing plasma histamine levels. The possible role of the increased tissue levels of histamine remains to be studied.

SUMMARYA controlled, double-blind study of effects of dl-alpha-tocopheryl nicotinate (vitamin E-nicotinate: EN) for relief of symptoms was perf ormed in 94 patients with hypertension and cerebral arteriosclerosis. Eighty-nine cases (44 cases treated with EN and 45 with inactive placebo) had completed this study, and remaining 5 cases were dropped out. Six capsules of EN (600mg) in the treated group and 6 capsules of inactive placebo in the placebo group were given daily for 4 weeks in all cases, and for 6 weeks in 43 cases. The following results were obtained.1) The general improvement rating was significantly greater in EN group than that in placebo group (p<0.005).2) For 5 items of subjective symptoms, the improvement rating of EN was relatively higher than that of placebo. The result of statistical analysis of them was as follows; numbness of limbs (p=0.032), dizziness (p=0.054), stiff neck (p<0.10), heavy feeling of head (p<0.10), and insomnia (p=0.025).3) The general improvement rating increased consistently as related to the time intervals following the treatment in EN group as follows; 73.7%