The effect of AY-9944 on yeast sterol and sterol ester metabolism

The effects of the hypocholesterolemic drug AY-9944 (trans-1,4-bis(2-chlorobenzylaminoethyl)cyclohexane dihydrochloride) at two concentrations (10(-4) M and 5 X 10(-4) M) on the synthesis of sterols and sterol esters by Saccharomyces cerevisiae were investigated. Although growth was not markedly affected by the drug, there was a decrease in the free sterol to sterol ester ratio with increased drug concentration. A concomitant increase in the saturated fatty acids esterified to sterol relative to the unsaturated fatty acids was also noted in response to increased drug concentration. Ergosterol accounted for 94.7% of the free sterol in the control culture and for 87.8% of the 5 X 10(-4) M drug-treated culture, respectively. However, in the sterol ester fraction, the ergosterol content decreased from a value of 45.1% in the control culture to 2.4% in the 5 X 10(-4) M AY-9944 treated culture. The sterol ester fraction simultaneously showed increased levels of the delta 8 sterol, fecosterol, in response to increased drug concentration from a 7.4% control value to 57.4% in the 5 X 10(-4) M drug-treated culture. The accumulation of the delta 8 sterol suggests that the site of action of the drug is probably at the delta 8 to delta 7 isomerase step in the biosynthesis of ergosterol. The fact that ergosterol is retained as the major free sterol suggests a biological advantage to the retention of this particular sterol. In addition, the near normal growth in the presence of the drug, in spite of the occurrence of an altered sterol ester profile, indicates that the composition of the sterol ester fraction is not as critical as the free sterol fraction.