Differential effects of alpha- and gamma-tocopherol on low-density lipoprotein oxidation, superoxide activity, platelet aggregation and arterial thrombogenesis.

OBJECTIVES: This study was designed to examine the differential effects of alpha- and gamma-tocopherol on parameters of oxidation-antioxidation and thrombogenesis. BACKGROUND: Experimental studies have shown that antioxidants, such as vitamin E (alpha-tocopherol), improve atherosclerotic plaque stability and vasomotor function, and decrease platelet aggregation and tendency to thrombus formation. METHODS: Sprague Dawley rats were fed chow mixed with alpha- or gamma-tocopherol (100 mg/kg/day) for 10 days. A filter soaked in 29% FeCl3 was applied around the abdominal aorta to study the patterns of arterial thrombosis. The aortic blood flow was observed and continuously recorded using an ultrasonic Doppler flow probe. ADP-induced platelet aggregation, low-density lipoprotein oxidation induced by phorbol 12-myristate 13-acetate (PMA)-stimulated leukocytes, superoxide anion generation and superoxide dismutase (SOD) activity were also measured. RESULTS: Both alpha- and gamma-tocopherol decreased platelet aggregation and delayed time to occlusive thrombus (all p < 0.05 vs. control). Both alpha- and gamma-tocopherol decreased arterial superoxide anion generation, lipid peroxidation and LDL oxidation (all p < 0.05 vs. control), and increased endogenous SOD activity (p < 0.05). The effects of gamma-tocopherol were more potent than those of alpha-tocopherol (p < 0.05). CONCLUSIONS: This study indicates that both alpha- and gamma-tocopherol decrease platelet aggregation and delay intraarterial thrombus formation, perhaps by an increase in endogenous antioxidant activity. Gamma-tocopherol is significantly more potent than alpha-tocopherol in these effects.