Hyperglycemia Potentiates Collagen-Induced Platelet Activation Through Mitochondrial Superoxide Overproduction
- Department of Medicine, Diabetes Research Center, Albert Einstein College of Medicine, Bronx, New York
Abstract
Alteration of platelet function contributes to microthrombus formation and may play an important role in the pathogenesis of diabetic micro- and macroangiopathies. However, the molecular mechanism for platelet dysfunction observed in patients with diabetes has not been fully elucidated. In this study, the direct effects of hyperglycemia on platelet function in vitro were investigated. Hyperglycemia increased reactive oxygen species generation in human platelets, and this effect was additive with that of collagen. Thenoyltrifluoroacetone (TTFA), an inhibitor of mitochondrial electron transport chain complex II, and carbonyl cyanide m-chlorophenylhydrazone (CCCP), an uncoupler of oxidative phosphorylation, completely prevented the effects of hyperglycemia, suggesting that reactive oxygen species arise from the mitochondrial 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 increase phosphorylation of the tyrosine kinase Syk in platelets exposed to collagen. Hyperglycemia-induced PTP inhibition and Syk phosphorylation were found to be completely prevented by TTFA, CCCP, or Mn(III)tetrakis (4-benzoic acid) porphyrin, a stable cell-permeable superoxide dismutase mimetic. These results suggest that hyperglycemia-induced mitochondrial superoxide generation may play an important role in platelet dysfunction observed in patients with diabetes.
Footnotes
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Address correspondence and reprint requests to Dr. Michael Brownlee, Department of Medicine, Diabetes Research Center, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461; E-mail: brownlee{at}aecom.yu.edu.
Received for publication 11 September 2000 and accepted in revised form 26 February 2001.
CCCP, carbonyl cyanide m-chlorophenylhydrazone; ELISA, enzyme-linked immunosorbent assay; MnTBAP, Mn(III)tetrakis (4-benzoic acid) porphyrin; PDGF-AB, platelet-derived growth factor-AB; PLCγ2, phospholipase Cγ2; PMSF, phenylmethylsulfonyl fluoride; PRP, platelet-rich plasma; PTP, protein tyrosine phosphatase; ROS, reactive oxygen species; TTFA, thenoyltrifluoroacetone.
