Hyperglycemia potentiates collagen-induced platelet activation through mitochondrial superoxide overproduction

Alteration of platelet function contributes to microthrombus formation and may play an important role in the pathogenesis of diabetic micro- and macro angiopathies, However, the molecular mechanism for platelet dysfunction obs erved in patients with diabetes has not been fully elucidated. In this stud y, the direct effects of hyperglycemia on platelet function in vitro were i nvestigated. Hyperglycemia increased reactive oxygen species generation in human platelets, and this effect was additive with that of collagen. Thenoy ltrifluoroacetone (TTFA), an inhibitor of mitochondrial electron transport chain complex II, and carbonyl cyanide m-chlorophenylhydrazone (CCCP), an u ncoupler of oxidative phosphorylation, completely prevented the effects of hyperglycemia, suggesting that reactive oxygen species arise from the mitoc hondrial electron transport chain. Hyperglycemia potentiated both platelet aggregation and the subsequent release of platelet-derived growth factor AB induced by a nonaggregating subthreshold concentration of collagen, which were also completely inhibited by TTFA or CCCP, Furthermore, hyperglycemia was found to inhibit protein tyrosine phosphatase (PTP) activity and increa se phosphorylation of the tyrosine kinase Syk in platelets exposed to colla gen. Hyperglycemia-induced PTP inhibition and Syk phosphorylation were foun d to be completely prevented by TTFA, CCCP, or Mn(III)tetrakis (4-benzoic a cid) porphyrin, a stable cell-permeable superoxide dismutase mimetic, These results suggest that hyperglycemia-induced mitochondrial superoxide genera tion may play an important role in platelet dysfunction observed in patient s with diabetes.