Summary Platelets play a central role in thrombosis, hemostasis, and inflammation. We show that activated platelets release inorganic polyphosphate (polyP), a polymer of 60-100 phosphate residues that directly bound to and activated the plasma protease factor XII. PolyP-driven factor XII-activation triggered release of the inflammatory mediator bradykinin by plasma kallikrein-mediated kininogen processing. PolyP increased vascular permeability and induced fluid extravasation in skin microvessels of mice. Mice deficient in factor XII or bradykinin receptors were resistant to polyP-induced leakage. PolyP initiated clotting of plasma via the contact pathway. Ablation of intrinsic coagulation pathway proteases factor XII and factor XI protected mice from polyP-triggered lethal pulmonary embolism. Targeting polyP with phosphatases interfered with procoagulant activity of activated platelets and blocked platelet-induced thrombosis in mice. Infusion of polyP restored defective plasma clotting of Hermansky-Pudlak Syndrome patients, which lack platelet polyP. The data identify polyP as a new class of mediator having fundamental roles in platelet-driven proinflammatory and procoagulant disorders.

Abstract-In the present study, we examined the expression of regulators of bone formation and osteoclastogenesis in human atherosclerosis because accumulating evidence suggests that atherosclerotic calcification shares features with bone calcification. The most striking finding of this study was the constitutive immunoreactivity of matrix Gla protein, osteocalcin, and bone sialoprotein in nondiseased aortas and the absence of bone morphogenetic protein (BMP)-2, BMP-4, osteopontin, and osteonectin in nondiseased aortas and early atherosclerotic lesions. When atherosclerotic plaques demonstrated calcification or bone formation, BMP-2, BMP-4, osteopontin, and osteonectin were upregulated. Interestingly, this upregulation was associated with a sustained immunoreactivity of matrix Gla protein, osteocalcin, and bone sialoprotein. The 2 modulators of osteoclastogenesis (osteoprotegerin [OPG] and its ligand, OPGL) were present in the nondiseased vessel wall and in early atherosclerotic lesions. In advanced calcified lesions, OPG was present in bone structures, whereas OPGL was only present in the extracellular matrix surrounding calcium deposits. The observed expression patterns suggest a tight regulation of the expression of bone matrix regulatory proteins during human atherogenesis. The expression pattern of both OPG and OPGL during atherogenesis might suggest a regulatory role of these proteins not only in osteoclastogenesis but also in atherosclerotic calcification. (Arterioscler Thromb Vasc Biol.

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The lag time, ETP and peak height of thrombin generation depend on the levels of multiple coagulation factors and inhibitors. The specific assay determinants vary with the experimental conditions.

Arterial calcification (AC) is generally regarded as an independent risk factor for cardiovascular morbidity and mortality. Matrix Gla protein (MGP) is a potent inhibitor of AC, and its activity depends on vitamin K (VK). In rats, inactivation of MGP by treatment with the vitamin K antagonist warfarin leads to rapid calcification of the arteries. Here, we investigated whether preformed AC can be regressed by a VK-rich diet. Rats received a calcification-inducing diet containing both VK and warfarin (W&K). During a second 6-week period, animals were randomly assigned to receive either W&K (3.0 mg/g and 1.5 mg/g, subsequently), a diet containing a normal (5 g/g) or high (100 g/g) amount of VK (either K 1 or K 2 ). Increased aortic calcium concentration was observed in the group that continued to receive W&K and also in the group changed to the normal dose of VK and AC progressed. Both the VK-rich diets decreased the arterial calcium content by some 50%. In addition, arterial distensibility was restored by the VK-rich diet. Using MGP antibodies, local VK deficiency was demonstrated at sites of calcification. This is the first study in rats demonstrating that AC and the resulting decreased arterial distensibility are reversible by high-VK intake. IntroductionArterial calcification is an important independent risk factor for the development of atherosclerosis, myocardial infarction, stroke, and renal disease. 1,2 Patients with manifest arterial calcification have an unfavorable prognosis compared with patients with no or mild calcification. 3,4 Therefore, the prevention or reversal of arterial calcification may lead to improved patient outcomes.For a long time it has been thought that calcification was a passive process and the end stage of cardiovascular disease. During the past 10 years, however, it has become clear that several osteoregulatory proteins, both stimulatory and inhibitory, are involved in the calcification of vascular tissue. [5][6][7][8] One of the strongest in vivo inhibitors of arterial calcification is matrix Gla protein (MGP). MGP was first discovered in bone, 9 but it is mainly produced by vascular smooth muscle cells and chondrocytes. Its function became clear in MGP-deficient mice, 10 which died within 6 to 8 weeks after birth as a result of rupture of the large arteries. Histochemical evaluation demonstrated complete calcification of the elastic fibers in the arterial vessels and a phenotypic change of smooth muscle cells into chondrocytes. MGP acts by direct inhibition of calcium crystal formation and regulates bone morphogenetic protein-2, a growth factor responsible for osteogenic differentiation. [11][12][13] Murshed et al 14 demonstrated that restoration of MGP exclusively in the vascular smooth muscle cells of the MGP-null mice completely rescued the vascular calcification phenotype. For this effect the MGP needed to be ␥-carboxylated because mutating the Gla residues into aspartic acid residues led to the synthesis of nonfunctional MGP and to the death of all animals.Vitamin K is an e...