Objective: Cloning of the ileal apical sodium-dependent bile acid transporter (ASBT) has identified a new pharmacological target for the modulation of plasma lipoproteins. The objective of this study was to determine whether a novel, specific, minimally absorbed ASBT inhibitor (SC-435) decreases LDL cholesterol through the alteration of plasma apoB kinetics.
Methods and results: Miniature pigs were treated for 21 days with 10 mg/kg/day of SC-435 or placebo. SC-435 decreased plasma cholesterol by 9% and LDL cholesterol by 20% with no effect on other lipids. Autologous (131)I-VLDL, (125)I-LDL, and [(3)H]-leucine were injected simultaneously to determine apoB kinetics. LDL apoB concentrations decreased significantly by 10% resulting entirely from an increase in LDL-apoB fractional catabolic rate. SC-435 had no effect on either total LDL apoB production or VLDL apoB converted to LDL. SC-435 increased VLDL apoB production by 22%; however, the concentration was unchanged as a result of increased VLDL apoB direct removal. SC-435 increased hepatic mRNA and enzymatic activity for both cholesterol 7alpha-hydroxylase and HMG-CoA reductase. Hepatic LDL receptor mRNA increased significantly, whereas apoB expression was unaffected.
Conclusions: A low dose of the ASBT inhibitor, SC-435, significantly reduces plasma LDL cholesterol through enhanced LDL receptor-mediated LDL apoB clearance, secondary to increased expression of cholesterol 7alpha-hydroxylase.