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As a result of screening, several isoflavans were identified to be antagonists of cholesterol ester transfer protein (CETP) activity. The present study evaluates CGS 25159, a synthetic isoflavan, as a putative inhibitor of CETP activity of human and hamster plasma. Determined by [3]CE transfer from HDL to VLDL + LDL fraction or by fluorescent-CE transfer assay, CGS 25159 inhibited CETP in both human plasma bottom fraction (d = 1.21 g/ml) and in plasma from Golden Syrian Hamsters with an IC50 < 10 microM. The compound also inhibited (IC 50 approximately equal to 15 microM) the reciprocal transfer of triglycerides in the incubated whole plasma from normal and hyperlipidemic hamsters. When orally administered to normolipidemic hamsters, CGS 25159 (10 mg/kg, 4 days) reduced plasma transfer activity by 35-60%. Treatment with CGS 25159 (10 and 30 mg/kg, p.o.) resulted in dose dependent and time dependent changes in CETP activity. After two weeks of treatment at 10 mg/kg, the changes in VLDL + LDL cholesterol, total triglycerides and HDL cholesterol were -22 +/- 4.6*, -23 +/- 7.5 and +10 +/- 2.8%, respectively. The corresponding changes at 30 mg/kg were -28 +/- 5.5*, -38 +/- 6.8* and +29 +/-4.4.*%, (*, P, 0.05; mean +/- S.E.M., n = 6). A single spin gradient density ultracentrifugation of plasma lipoproteins and treated animals showed an increase in HDL cholesterol and a redistribution to larger HDL particles. These data support the contention that pharmacological down regulation of CETP activity could result in favorable changes in lipoprotein profile.

The ansamycins are structurally novel hypolipidemic agents derived from rifampicin, but lacking antibacterial activity. Oral or intravenous administration resulted in rapid lowering of plasma cholesterol in rats, hamsters, guinea pigs and dogs. In the chow-fed rat, three related compounds (CGP 43371, CGS 23810 and CGS 24565) exhibited ED50 values of 13.7, 3.1 and 0.18 mg/kg, respectively. A feature common to the lipid lowering documented in these four species was the concomitant reduction of low density lipoprotein (LDL) and high density lipoprotein (HDL) cholesterol. In the chow-fed rat, however, apolipoprotein AI (apo AI) levels were much less affected than were those of HDL cholesterol. CGP 43371 at 3 and 10 mg/kg, lowered HDL cholesterol by 20% and 39%, respectively, whereas plasma apo AI was reduced by only 1% and 12%. Similarly, in lipoprotein fractions separated by ultracentrifugation, apo AI was unchanged in the d = 1.019-1.21 g/ml fraction after treatment with 3 or 10 mg/kg of CGP 43371, but HDL cholesterol was reduced 12% and 26% in this fraction at the two dose levels. Plasma and lipoprotein apo B levels, on the other hand, were reduced to a level equivalent to that of the reduction in cholesterol. The ansamycins thus represent a new structural series which may possess a novel mechanism of action as well, involving differential effects on HDL cholesterol and protein.