Cholestyramine treatment of type IIa hypercholesterolaemia normalizes platelet reactivity against prostacyclin.

The effect of lowering total plasma and low density lipoprotein (LDL) cholesterol in heterozygous familial hypercholesterolaemia type IIa (FH) on platelet function, thromboxane (TX) formation and platelet sensitivity against iloprost, a stable prostacyclin mimetic, was studied in platelet-rich plasma ex vivo. Seven FH patients were treated with cholestyramine (12 g day 1) for 8-11 months and were compared with eight untreated FH patients and 11 healthy control subjects. In comparison with platelets from healthy controls, platelets from untreated FH patients exhibited a significantly increased aggregation response and TX formation, and a reduced reactivity against inhibition of platelet aggregation by prostacyclin. Treatment with cholestyramine for 8-11 months resulted in a 21% reduction in total serum and LDL-cholesterol. This was not accompanied by any change in platelet hyperreactivity or TX formation. However, cholestyramine treatment normalized the platelet reactivity of FH patients against iloprost, being no more different from healthy controls. It is concluded that reduction in plasma cholesterol by cholestyramine results in normalization of the reduced platelet sensitivity against prostacyclin. This might contribute to beneficial effects of cholestyramine treatment in preventing thromboembolic complications of atherosclerosis.