AN ALTERNATIVE MECHANISM FOR THE INHIBITION OF CHOLESTEROL-BIOSYNTHESIS IN HEPG2 CELLS BY N-[(1,5,9)-TRIMETHYLDECYL]-4-ALPHA, 10-DIMETHYL-8-AZA-TRANS-DECAL-3-BETA-OL (MDL 28,815)

Compounds that block hepatic cholesterol biosynthesis and secretion ma y be useful hypocholesterolemic agents. cyl]-4alpha,10-dimethyl-8-aza- trans-decal-3beta-ol (MDL 28,81 5) has been shown to block cholesterol biosynthesis in 3T3 fibroblasts and it causes cellular accumulation o f squalene 2,3-epoxide and squalene 2,3:23,24-diepoxide (squalene epox ides), which suggests that it inhibits 2,3-oxidosualene cyclase. The p urpose of the present report was to determine whether MDL 28,815 acts only at the level of 2,3-oxidosqualene cyclase or whether other enzyme s in the cholesterol biosynthetic pathway are affected. HepG2 cells, g rown in lipoprotein-deficient serum, were incubated with MDL 28,815 an d C-14-acetate to radiolabel cholesterol and the intermediates in the cholesterol biosynthetic pathway. Blockade of cholesterol biosynthesis by MDL 28,815 in these cells was associated with the accumulation of two metabolites, one of which was 5alpha-cholest-8-en-30-ol. The other metabolite was identified by a combination of ultraviolet spectrometr y, gas chromatography, mass spectroscopy and analytical high-performan ce liquid chromatography as 5alpha-cholest-8,14-dien-3beta-ol. Maximal blockade of cholesterol biosynthesis was associated with the accumula tion of these two metabolites and, in particular, 5alpha-cholest-8,14- dien-3beta-ol, rather than with squalene epoxides. These results sugge st that MDL 28,815 blocks cholesterol biosynthesis primarily by the in hibition of sterol-DELTA14-2,3-reductase, and possibly sterol-DELTA8-e ne isomerase, rather than 2,3-oxidosqualene cyclase.