The effects of taurine depletion on bile acid composition and its amino acid‐conjugation in the bile of cats

Abstract

AimThe most established effect of functional amino acid‐like compound taurine is the conjugation with bile acids. In addition, taurine ameliorates hypercholesterolemia through promotion of hepatic bile acid synthesis from cholesterol by enhancing of CYP7A1. On the other hand, the conjugations of bile acids with taurine as well as glycine and the biosynthesis of taurine are also promoted by bile acids through the nucleus farnesoid X receptor. These findings imply that there is an interactive relationship on the metabolism of taurine and bile acids. Contrary to rodents, the ability of taurine biosynthesis is very poor in humans, and therefore, the body pool of taurine in humans depends on the oral ingestion. Furthermore, the ratio of conjugation of taurine, but not glycine, with bile acids also depends on taurine ingestion. This study evaluated the influence of depletion by taurine non‐ingestion on the metabolism of bile acid in bile in cats with poor taurine‐synthesizing ability as in humans.MethodControl (N=4) and Depletion(N=6) groups of adult cats were fed the soy protein‐based diet containing 0.15% and 0% taurine, respectively, for 30 weeks. Thereafter, taurine in the serum and tissues and bile acids in the bile were measured by LC‐MS/MS system.ResultSerum taurine concentration in the Depletion group significantly decreased to one tenth compared to that in the Control group after the 2nd week, and was undetectable since the 4th week. After 30 weeks, taurine in the various tissues was depleted in the Depletion group. Over 99.5% of bile acids in the bile were conjugated with taurine in the Control group. In the Depletion group, taurine‐conjugated bile acids significantly decreased to 35.2%, and instead, unconjugated bile acids significantly increased to 62.9%. Bile acid concentration in the bile significantly decreased to approximately 40% compared to that in the Control group. Bile acid types in cats were same to those in humans. In the composition of bile acids, cholic acid (CA), deoxycholic acid (DCA), and chenodeoxycholic acids (CDCA) were 83%, 12%, and 5%, respectively, in the Control group. On the other hands, CA significantly increased to 98%, and DCA and CDCA significantly decreased to 0.6% and 1.2%, respectively, in the Depletion group.ConclusionTaurine depletion caused the decrease of taurine conjugated bile acids in the bile, and instead, the increase of unconjugated bile acids. Consequently, the level of bile acids significantly decreased and the composition has changed. These results suggested that the synthesis of bile acids in humans might be regulated by taurine ingestion through the direct effects of taurine or the state of taurine conjugation with bile acids.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.