Cholesterol-lowering effects of taurine through the reduction of ileal FXR signaling due to the alteration of ileal bile acid composition.

Studies using animal models of hypercholesterolemia have established that taurine reduces cholesterol levels; however, the precise mechanism underlying this cholesterol-lowering effect is unclear. This study addressed this issue by investigating whether bile acid/farnesoid X receptor (FXR) signaling is involved in taurine-mediated cholesterol-lowering effect. Fxr-null and wild-type mice were administered 2% (w/v) taurine in their drinking water and fed a control diet or control diet supplemented with 1% (w/w) cholesterol (cholesterol diet) for 10 days. Taurine intake did not significantly alter hepatic and serum total cholesterol (TC) levels and bile acid compositions of the liver and intestinal lumen in Fxr-null and wild-type mice fed the control diet. By changing to a cholesterol diet, taurine intake significantly decreased hepatic and serum cholesterol levels in wild-type mice. In contrast, it significantly decreased hepatic, not serum, cholesterol levels in Fxr-null mice. Taurine intake significantly altered the bile acid composition of the intestinal lumen in wild-type mice fed a cholesterol diet, but not in Fxr-null mice. An increase in FXR antagonistic bile acids was detected in the intestinal lumen of taurine-treated wild-type mice fed a cholesterol diet. Taurine intake reduced the ileal expression of FXR target genes fibroblast growth factor 15 (Fgf15) and small heterodimer partner (Shp). In contrast, it enhanced the hepatic expression of cholesterol 7α-hydroxylase (Cyp7a1) in wild-type mice fed a cholesterol diet, but not in Fxr-null mice. These results suggest that taurine is partially involved in cholesterol lowering by reducing the ileal FXR signaling due to the alteration of ileal bile acid composition.

Taurine attenuates hepatic steatosis in a genetic model of fatty liver disease.

Mice lacking the farnesoid X receptor (FXR) are used as a genetic model for nonalcoholic fatty liver disease because their livers exhibit hepatic steatosis and inflammation. The influence of taurine drinking on disrupted hepatic function was investigated using female Fxr-null mice. Significant decreases in the levels of hepatic damage-associated diagnostic markers, hepatic triglycerides, non-esterified fatty acids, and total bile acids were found in Fxr-null mice that had drunk water containing 0.5% taurine for four weeks. Hepatic but not serum taurine concentrations were significantly increased in these mice. The expression levels of oxidative stress-related genes (Hmox1 and Gsta1) and fatty acid synthetic genes (Acc1 and Scd1) were significantly decreased in these mice. These results suggest that drinking taurine improves hepatic steatosis and dysfunction caused by a lack of FXR.