The influence of antioxidants on thrombotic risk factors in healthy population

Oxidative damage has been suggested to play a key role in the pathogenesis of atherosclerosis and other cardiovascular disease. Increased free radical production induced by oxidative stress can oxidise low density lipoproteins, activates platelets, induces endothelial dysfunction and disturbs glucose transport by consuming endogenous antioxidants. Using a combination, of in vitro and in vivo experimental models, the primary aims of the studies undertaken for this thesis were to examine whether different antioxidants could negate risk factors leading to thrombosis, atherosclerosis and other cardiovascular diseases. The studies utilised the mechanisms involved in platelet activity and glucose uptake by skeletal muscle myotubes.<br><br>The first study determined if olive leaf extract would attenuate platelet activity in healthy human subjects. Blood samples (n=11) were treated with five different concentrations of extract of Olea europaea L. leaves ranging from 5.4 μg/mL to 54 μg/mL. A significant reduction in platelet activity 54 μg/mL (p<0.001) and ATP release from platelets (p=0.02) was observed with μg/mL olive leaf extract. <br><br>The next crossover study compared the effect of exercise and antioxidant supplementation on platelet function between trained and sedentary individuals. An acute bout of 1 hour exercise (sub maximal cycling at 70% of VO2max) was used to induce oxidative stress in 8 trained and 8 sedentary male subjects, before and after one week supplementation with 236 mg/day of cocoa polyphenols. Baseline platelet count and ATP release increased significantly (p<0.05) after exercise in all subjects. Baseline platelet numbers in the trained were higher than in the sedentary ((235±37 vs. 208235±34 x109/L,p<0.05), whereas platelet activation in trained subjects was lower than sedentary individuals (51±6 vs. 59±5%, p<0.05). Seven days of cocoa polyphenol supplementation did not change platelet activity compared to the placebo group. <br><br>The third study determined the effect of 5 weeks of either 100mg/day γ- Tocopherol (n=14), 200mg/d γ-Tocopherol (n=13) or placebo (n=12) on platelet function, lipid profile and the inflammatory marker C-reactive protein. Blood γ -tocopherol concentrations increased significantly (p<0.05) relative to dose. Both doses attenuated platelet activation (p<0.05). LDL cholesterol, platelet aggregation and mean platelet volume were decreased by 100mg/d γ-tocopherol (all p<0.05). <br><br>The final study determined the effect of glucose oxidase induced oxidative stress and gamma-tocopherol treatment on glucose transport and insulin signalling in cultured rat L6 muscle cells. One hour treatment with 100 mU/mL glucose oxidase significantly decreased glucose uptake both with and without 100nM insulin stimulation (p<0.05). Pre-treatment with 100μM and 200μM gamma-tocopherol partially protected cells from the effect of glucose oxidase, whereas 200μM gamma-tocopherol restored both basal and insulin stimulated glucose transport to control levels. Glucose oxidase-induced oxidative stress did not impair basal or insulin stimulated phosphorylation of Akt or AS160, but 200μM gamma-tocopherol improved insulin-stimulated phosphorylation of these proteins.<br><br>In summary, the results from the studies undertaken for this thesis provide evidence that antioxidant supplementation maintains normal platelet function, exerts a positive effect on blood lipid profile and improves glucose uptake in normal healthy asymptomatic population as well as under conditions of induced oxidative stress. Antioxidants including foods rich in cocoa, olive and gamma tocopherol have the potential to combat oxidative stress induced risk factors leading to cardiovascular diseases.<br><br>