Bile lipid alterations in taurine-depleted monkeys

Abstract

Newborn cebus and cynomolgus monkeys, differing in their inherent taurine-glycine conjugation of bile acids, were fed taurine-free soy protein infant formula (Isomil) with or without added taurine (500 mg/kg dry diet). After 5 months, monkeys were anesthetized, their enterohepatic circulation interrupted, and their bile pool drained for 4.5 h. Bile acid conjugation, total bile acid pool size, biliary lipid composition, and theoretical maximal cholesterol solubility in bile were determined. Taurine depletion in cebus monkey, an obligate taurine conjugator (97%), did not reduce bile acid conjugation with taurine, or did it alter bile acid pool size, biliary lipid composition, or theoretical maximal cholesterol solubility in bile. Conversely, taurine depletion in cynomolgus, a species normally conjugating with some glycine (15 to 20%), significantly reduced conjugation of taurine with bile acids from 84 to 64%, essentially doubling that of glycine from 16 to 36%. Furthermore, theoretical maximal cholesterol solubility in cynomolgus bile improved significantly as a result of taurine depletion. This improvement was associated with increased percentage distribution of biliary phospholipid from 17 to 33%, in turn reflecting an increase in the taurochenodeoxycholate to taurocholate ratio from 0.7 to 2.9. Concomitant increase in biliary cholesterol concentration associated with increased glycine conjugation precluded any changes in the percent saturation of bile which remained constant at 130% for both dietary groups of cynomolgus. Taurochenodeoxycholate uniquely conserved taurine in the face of body taurine depletion. Taurine availability thus potentially has a substantial influence on bile acid characteristics and cholesterol solubility in a glycine conjugating primate.