Effects of α-tocopherol (Vitamin E) on the Ultrastructure of Human Platelets In Vitro

Washed human platelets were incubated with increasing concentrations of α-tocopherol. Spontaneous aggregation was induced by tocopherol (0.5 mM or above). Aggregation was inhibited by ethylenediaminetetraacetate and platelet activation was reduced by prostaglandin E(1). Using electron microscopy, it was confirmed that tocopherol caused platelet disruption to some extent and the released components may have generated aggregation. These effects were not observed in platelet-rich plasma. Spontaneous activation was not observed when the concentration of tocopherol was 0.03 mM or lower. Concentrations of tocopherol between 0.075 mM and 0.0075 mM had inhibiting influences on activation of washed platelets by thrombin. Tocopherol (between 0.1 mM and 0.005 mM) changed activation of washed platelets by cationized ferritin in that it facilitated the first phase of aggregation but reduced the second phase in an indirect proportional manner. The results show that the effects of tocopherol in washed platelet preparations are not comparable to those observed in plasma and that the platelet membrane must be regarded as a crucial target for vitamin E.