SummaryThe purpose of this study was to investigate the relationship between hypercholesterolemia and superoxide anion production.Experimental studies demonstrated that hypercholesterolemia is associated with enhanced cellular superoxide anion (O2
−) production. Aim of the study was to assess whether the same phenomenon occurs in humans.Lipid profile and platelet O2
− production were measured in 28 patients with hypercholesterolemia, compared with 25 age- and sexmatched healthy subjects, and in 21 out of the 28 patients after 8-week treatment with 10 mg/day atorvastatin (a HMGCoA reductase inhibitor). In order to assess the mechanism by which LDL cholesterol interferes with platelet production of O2
−, human platelets were incubated with LDL cholesterol in the presence of either an inhibitor of the phospholipaseA2 enzyme, AACOCF3, or an inhibitor of NADH/NADPH oxidases, DPI.O2
− platelet generation was significantly higher (p <0.001) and significantly related to LDL cholesterol (p < 0.001 ) in patients as compared to controls. 8-week treatment with 10 mg/day atorvastatin significantly reduced both LDL cholesterol and O2
− platelet production. This effect was partially related to the cholesterol-lowering, in that three days of treatment with atorvastatin significantly decreased platelet O2
− production, while no significant change in LDL-cholesterol levels was observed. Platelets incubated with LDL cholesterol showed O2
− release by atorvastatin is partially related to cholesterol lowering effect, suggesting that other mechanisms could be responsible for the antioxidant activity of the drug.