Effect of bile acids and neutral sterols on benzo[a]pyrene-induced tumorigenesis in skin of mice.

The effect of neutral sterols and bile acids were determined in the classic mouse skin tumor induction system by applying each sterol or acid with benzo[a]pyrene to the skin of Swiss mice three times per week for 60 weeks. The mice were killed 63 weeks after the experimenta was begun. Most of the chemicals had an inhibitory effect on skin tumor formation by benzo[a]pyrene. Unconjugated bile acids had higher inhibitory action than did conjugated bile acids. The inhibition decreased in the following order of acids: chenodeoxycholic, lithocholic, deoxycholic, and clinic. Within the group of conjugated acids, taurine conjugates were more effective inhibitors than were glycine conjugates. The neutral sterols cholesterol, coprostanol, and coprostanone showed relatively similar, moderate inhibitory effects.