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Articles in PresS, published online ahead of print September 5, 2002
Am J Physiol Heart Circ Physiol, 10.1152/ajpheart.00249.2002
Submitted on March 20, 2002
Accepted on August 5, 2002
1 Dipartimento di Medicina Sperimentale e Patologia, Universita di Roma, Rome, Italy
2 Dipartimento di Medicina Interna, Universita di Roma Tor Vergata, Rome, Italy
3 Istituto di Chirurgia Toracica e Cardiovascolare, Universita di Siena, Siena, Italy
* To whom correspondence should be addressed. E-mail: francesco.violi{at}uniroma1.it.
Carnitine is a physiological cellular constituent that favours intracellular fatty acid transport. Its role on platelet function and oxygen free radicals has not been fully investigated. The aim of the study was to seek if carnitine interferes with arachidonic acid metabolism and in turn with platelet function. Carnitine (10-50 µM) was able to inhibit dose-dependently the incorporation of arachidonic acid into platelet phospholipids and the release of arachidonic acid elicited by platelet agonists. Incubation of platelets with carnitine dose-dependently inhibited collagen induced platelet aggregation (-54% with 50 µM carnitine, p<0.005), thromboxane A2 formation (-77% with 50 µM carnitine, p<0.005) and calcium mobilization (-80% with 50 µM carnitine, p<0.005) but didn't affect phospholipase A2 activation. Furthermore Carnitine inhibited platelet O2- formation elicited by arachidonic acid and collagen. In order to explore the underlying mechanism arachidonic acid-stimulated platelets were incubated with NADPH; this study showed an enhanced platelet O2- formation suggesting a role for NADPH oxidase in arachidonic acid-mediated platelet O2- production. Incubation of platelets with carnitine significantly reduced AA-mediated NADPH oxidase activation(-60% with 50 µM carnitine, p<0.01). As protein kinase C has a role in enhancing oxidative stress via activation of NADPH oxidase we investigated if carnitine inhibited protein kinase C activation and demonstrated that 50 µM carnitine inhibited its substrate (p47 KD) phosphorylation. This study shows that carnitine inhibits arachidonic acid accumulation into platelet phospholipids and in turn platelet function and arachidonic acid release elicited by platelet agonists.
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