| Summary: | Natural and synthetic saponins inhibit cholesterol absorption and reduce plasma cholesterol levels in experimental animals and are therefore of potential pharmacologic utility in the treatment of hypercholesterolemia. To determine the effects of this class of compounds on cholesterol absorption and metabolism, we evaluated the effects of the synthetic saponin, beta-tigogenin cellobioside (tiqueside; CP-88818), on male golden Syrian hamsters. When administered as either a single oral bolus or as a dietary supplement for up to 2 weeks, tiqueside inhibited cholesterol absorption in a dose-dependent manner in both the presence and absence of dietary cholesterol. Administration of tiqueside to chow-fed hamsters as a 0.2% dietary supplement (150 mg/kg per day) for 4 days resulted in a 68% decrease in intestinal cholesterol absorption with no change in either bile absorption or cholesterol 7 alpha-hydroxylase activity, suggesting that tiqueside inhibits cholesterol absorption without interfering with enterohepatic bile acid recirculation. Under these conditions, hepatic cholesterol levels were also reduced in a dose-dependent manner. Hepatic cholesterol reduction was highly correlated with cholesterol absorption inhibition, and induced compensatory increases in both hepatic HMG-CoA reductase activity and hepatic low density lipoprotein (LDL) receptor levels. Compensatory increases in intestinal HMG-CoA reductase activity were also noted after tiqueside administration, and are consistent with a luminal mechanism for tiqueside action. As a consequence of these changes to cholesterol metabolism, tiqueside administration induced plasma cholesterol reductions that were highly correlated with both hepatic cholesterol reduction and cholesterol absorption inhibition. Tiqueside also produced comparable plasma cholesterol lowering in a variety of other species fed either cholesterol-free diets (hamster, rat, mouse, dog) or cholesterol-containing diets (hamster, rat, rabbit, mouse, cynomolgus monkey, rhesus monkey, SEA quail) indicating the ubiquity of tiqueside action. For all species evaluated except the dog, the reduction in plasma cholesterol was due primarily to a reduction in circulating non-HDL cholesterol levels with little or no change in HDL cholesterol levels. Taken together, these results indicate that inhibition of cholesterol absorption by tiqueside produces profound effects on cholesterol metabolism without affecting bile acid metabolism, and that these changes lead to reductions primarily in plasma non-HDL cholesterol concentrations. The synthetic saponin, tiqueside, may thus represent a prototypical form of therapy for the treatment of hypercholesterolemia.
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