Inhibition of cholesteryl ester deposition in macrophages by calcium entry blockers: an effect dissociable from calcium entry blockade

Abstract

The effects of calcium entry blockers on stimulated cholesteryl [3H]-oleate deposition in cultured macrophages were characterized in order to elucidate mechanisms underlying possible antiatherosclerotic effects. Stimulation of intracellular cholesteryl [3H]-oleate deposition was initiated by incubation of macrophages with beta-very low density lipoproteins (beta-VLDL). Nifedipine (Class I) markedly reduced cholesteryl [3H]-oleate deposition at all concentrations tested. However, Bay K 8644, a dihydropyridine which is known to stimulate calcium entry, also reduced cholesteryl [3H]-oleate deposition with a similar potency to nifedipine. The effects of three Class II calcium entry blockers were evaluated: verapamil, methoxyverapamil, and diltiazem. Verapamil inhibited cholesteryl [3H]-oleate deposition in a concentration-dependent manner. Similarly, methoxyverapamil reduced cholesteryl [3H]-oleate deposition in a concentration-dependent manner although the reduction was not as great as that produced by verapamil. In contrast, diltiazem at any concentration tested did not inhibit cholesteryl [3H]-oleate deposition. Flunarizine (a Class III calcium entry blocker) produced a modest stimulation of cholesteryl [3H]-oleate deposition at the lowest concentration used (10(-7)M) but marked depression at the highest concentration (10(-5)M). The results indicate calcium entry blockers may exert protective effects on the development of atherosclerosis in animal models of diet-induced hyperlipidaemia by inhibiting intracellular cholesteryl ester deposition, but this effect may not be related to their calcium entry-blocking effects.