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Etofibrate increases binding of low and high density lipoprotein to human platelets of patients with Type II hyperlipoproteinemia

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      Abstract

      Previous work suggested an influence of etofbrate, a diester of nicotinic acid and clolibric acid, on lipoprotein receptors. Besides its beneficial effects on plasma lipoprotein levels of decrease in total cholesterol, LDL-cholesterol and triglycerides and increase in HDL-cholesterol, etofibrate was shown to inhibit platelet function. In order to further evaluate platelet-lipoprotein interactions, the effects of etofibrate on plasma lipids and lipoproteins on the specific binding of normal [111In]LDL and [111In]HDL onto platelets as well as its effect on platelet function were evaluated in 8 patients affected by Type II hyperlipoproteinemia (HLP). In all patients binding was saturable and indicated high affinity binding sites capable of binding 927 ± 233 ng protein of [111In]LDL/109 platelets (Kd 12 ± 3 μg protein/ml) and 1496 ± 435 ng protein of [111In]HDL/109 platelets (Kd14 ± 3 μg protein/ml). The capacity of native LDL (HDL) to displace bound [111In] LDL ([111In] HDL) by half (IC50) amounted to 22 ± 9 μg protein/ml (26 ± 8 μg protein/ml). Following a 6-week treatment period with etofibrate (500 mg twice daily), decrease in plasma total cholesterol, LDL-cholesterol and apolipoprotein (apo) B and increase in HDL-cholesterol and apo AI was correlated to a significant (P < 0.01) increase in LDL- as well as HDL-receptor binding. The platelet binding capacity increased to 1085 ± 212 ng protein/109 platelets (Kd8 ± 3 μg protein/ml) for [111In]LDL and to 1867 ± 266 ng protein/109 platelets for [111In]HDL (Kd 11 ± 3 μg protein/ml). Platelet function studies demonstrated significantly (P < 0.01) reduced platelet aggregation in response to ADP and thromboxane formation after 6 weeks of etofibrate therapy. These findings in patients with HLP Type II indicate in vivo upregulation of specific [111In]LDL as well as [111In]HDL binding sites on human platelets associated with reduced platelet activation following etofibrate therapy.

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