Platelets have a crucial role in the maintenance of normal haemostasis, and perturbations of this system can lead to pathological thrombus formation and vascular occlusion, resulting in stroke, myocardial infarction and unstable angina. ADP released from damaged vessels and red blood cells induces platelet aggregation through activation of the integrin GPIIb-IIIa and subsequent binding of fibrinogen. ADP is also secreted from platelets on activation, providing positive feedback that potentiates the actions of many platelet activators. ADP mediates platelet aggregation through its action on two G-protein-coupled receptor subtypes. The P2Y1 receptor couples to Gq and mobilizes intracellular calcium ions to mediate platelet shape change and aggregation. The second ADP receptor required for aggregation (variously called P2Y(ADP), P2Y(AC), P2Ycyc or P2T(AC)) is coupled to the inhibition of adenylyl cyclase through Gi. The molecular identity of the Gi-linked receptor is still elusive, even though it is the target of efficacious antithrombotic agents, such as ticlopidine and clopidogrel and AR-C66096 (ref. 9). Here we describe the cloning of this receptor, designated P2Y12, and provide evidence that a patient with a bleeding disorder has a defect in this gene. Cloning of the P2Y12 receptor should facilitate the development of better antiplatelet agents to treat cardiovascular diseases.

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The critical role for ADP in arterial thrombogenesis was established by the clinical success of P2Y12 antagonists, currently used at doses that block 40–50% of the P2Y12 on platelets. This study was designed to determine the role of P2Y12 in platelet thrombosis and how its complete absence affects the thrombotic process. P2Y12-null mice were generated by a gene-targeting strategy. Using an in vivo mesenteric artery injury model and real-time continuous analysis of the thrombotic process, we observed that the time for appearance of first thrombus was delayed and that only small, unstable thrombi formed in P2Y12–/– mice without reaching occlusive size, in the absence of aspirin. Platelet adhesion to vWF was impaired in P2Y12–/– platelets. While adhesion to fibrinogen and collagen appeared normal, the platelets in thrombi from P2Y12–/– mice on collagen were less dense and less activated than their WT counterparts. P2Y12–/– platelet activation was also reduced in response to ADP or a PAR-4–activating peptide. Thus, P2Y12 is involved in several key steps of thrombosis: platelet adhesion/activation, thrombus growth, and stability. The data suggest that more aggressive strategies of P2Y12 antagonism will be antithrombotic without the requirement of aspirin cotherapy and may provide benefits even to the aspirin-nonresponder population

Background-This study was designed to determine whether (1) P2Y 12 antagonism synergizes with other antithrombotics and (2) anticoagulants (thrombin inhibitors) affect the antithrombotic activity elicited by P2Y 12 antagonism. Methods and Results-Thrombosis was achieved by perfusion of human and murine blood through type III collagencoated capillaries at arterial shear rate. CT50547, a direct-acting P2Y 12 antagonist, inhibited thrombosis in PPACK-but not heparin-anticoagulated human blood. In contrast, CT50547 inhibited thrombosis in aspirin-treated individuals independently of the anticoagulant. Thrombin and TXA 2 also synergized with P2Y 12 in the absence of anticoagulation, because combined treatment of aspirin or C921-78 (a factor Xa inhibitor) with CT50547 or 2-MeSAMP (a P2Y 12 antagonist) inhibited the thrombotic process, whereas all treatments failed to inhibit thrombosis when used individually. Synergism was also observed ex vivo when P2Y 12 -deficient (P2Y 12 Ϫ/Ϫ ) mice were administered aspirin or coagulation inhibitors (C921-78 and bivalirudin). Finally, using intravital microscopy, we found that both C921-78 and bivalirudin abrogated the thrombotic process in P2Y 12 ϩ/Ϫ mice, whereas each showed only partial efficacy in P2Y 12 ϩ/ϩ animals. Conclusions-Our study indicates that (1)

Forty-three cases of peripheral neuropathy (PN) have been reported in the literature with a proven mitochondria (mt) DNA mutation, and 21 had a peripheral nerve biopsy (PNB). We studied 8 patients, 1 of whom had severe sensory PN, 3 mild PN, and 4 subclinical PN. Nerve biopsy was performed in every case; all patients showed axonal degeneration and 4 showed features of primary myelin damage. In addition, there were 2 crystalline-like inclusions in the Schwann cell cytoplasm of a patient with MERRF, and 1 in a patient with multiple deletions on the mtDNA. There are 11 cases of PNB in the literature with axonal lesions, 5 with demyelination, and 4 with mixed lesions. One PNB was not modified. A few crystalline-like inclusions were seen in 1 case of MERRF. Such inclusions were first reported in the Schwann cell cytoplasm of unmyelinated fibers in a patient with Refsum disease and were considered to be modified mitochondria. However, their mitochondrial origin remains debatable.