Effects of ursodeoxycholate and other bile salts on levels of rat intestinal alkaline sphingomyelinase: a potential implication in tumorigenesis.

Previous studies showed that bile salts had a promoting effect on colon cancer development and this effect was inhibited by ursodeoxycholate (UDC). We recently found that both human colorectal adenomas and carcinomas were associated with a specific decrease in alkaline sphingomyelinase activity. In this work, we compared the effects of ursodeoxycholate and other bile salts on the levels of rat intestinal alkaline sphingomyelinase both in the intestinal loops and after oral administration. Bile salts at different concentrations were injected into intestinal loops and the dissociation of alkaline sphingomyelinase from the mucosa was assayed. We found that bile salts, including taurocholate, taurodeoxycholate, glycocholate, glycochenodeoxycholate, and 3-(3-cholamidopropyl dimethylammonio)-1-propanesulonate (CHAPS), dose dependently dissociated alkaline sphingomyelinase from the intestinal mucosa. UDC alone did not dissociate the enzyme but significantly inhibited the dissociation caused by other bile salts and CHAPS. Feeding rats with 0.3% (w/w) taurocholate for four days decreased peak activity of intestinal alkaline sphingomyelinase by 39% and total activity in the intestine by 20% and increased the output of the enzyme in the feces. In contrast, feeding 0.3% (w/w) UDC for four days increased the peak activity of alkaline sphingomyelinase in the small intestine by 87% and the activity in the colon by 187%. The total activity of alkaline sphingomyelinase was increased by 80% and the output of the enzyme in the feces was only slightly increased by UDC administration. The changes in alkaline phosphatase after feeding taurocholate and UDC were much smaller. Our results indicate that UDC and other bile salts have different effects on the levels of alkaline sphingomyelinase, which may be implicated in their different influences on cancer development reported previously.