Transitory stimulation of human platelet 12-lipooxygenase by vitamin E supplementation.

Human platelet lipooxygenase converts arachidonic acid to 12-hydroperoxy-eicosatetraenoic acid (12-HPETE), which is rapidly reduced by peroxidases to 12-hydroxy-eicosatetraenoic acid (12-HETE). This study was conducted to examine the effect of vitamin E supplementation on platelet 12-lipooxygenase activity. Sixteen healthy subjects were supplemented with 400 IU/day of either D-alpha-tocopherol (268 mg) or DL-alpha-tocopherol (364 mg) for 4 wk. Supplements elicited a transitory increase of lipooxygenase activity but a suppression of peroxidase activity, as indicated by increased 12-HETE production and 12-HPETE accumulation. Plasma-tocopherol concentration was double the presupplement value and remained stable during supplementation. Neither age, sex, nor isomeric form of tocopherol supplement significantly influenced the pattern of response. Results show that vitamin E exerts a differential effect on platelet lipooxygenase and peroxidase activities.