Taurine ameliorates cholesterol metabolism by stimulating bile acid production in high‐cholesterol‐fed rats

Abstract

This study was designed to investigate the effects of dietary taurine on cholesterol metabolism in high-cholesterol-fed rats. Male Sprague-Dawley rats were randomly divided into two dietary groups (n = 6 in each group): a high-cholesterol diet containing 0.5% cholesterol and 0.15% sodium cholate, and a high-cholesterol diet with 5% (w/w) taurine. The experimental diets were given for 2 weeks. Taurine supplementation reduced the serum and hepatic cholesterol levels by 37% and 32%, respectively. Faecal excretion of bile acids was significantly increased in taurine-treated rats, compared with untreated rats. Biliary bile acid concentrations were also increased by taurine. Taurine supplementation increased taurine-conjugated bile acids by 61% and decreased glycine-conjugated bile acids by 53%, resulting in a significant decrease in the glycine/taurine (G/T) ratio. Among the taurine-conjugated bile acids, cholic acid and deoxycholic acid were significantly increased. In the liver, taurine supplementation increased the mRNA expression and enzymatic activity of hepatic cholesterol 7α-hydroxylase (CYP7A1), the rate-limiting enzyme for bile acid synthesis, by three- and two-fold, respectively. Taurine also decreased the enzymatic activity of acyl-CoA:cholesterol acyltransferase (ACAT) and microsomal triglyceride transfer protein (MTP). These observations suggest that taurine supplementation increases the synthesis and excretion of taurine-conjugated bile acids and stimulates the catabolism of cholesterol to bile acid by elevating the expression and activity of CYP7A1. This may reduce cholesterol esterification and lipoprotein assembly for very low density lipoprotein (VLDL) secretion, leading to reductions in the serum and hepatic cholesterol levels.

Running Head: Heat Affects Cholesterol and Bile Acid Alterations in Cholesterol and Bile Acids Metabolism in Large White Pigs during Short-Term Heat Exposure

“…Taurocholate infusion produced a marked increase both in total output and in the esterification of cholesterol [46]. Furthermore, Murakami S et al concluded that taurine supplementation increases the synthesis of TCBAs and stimulates the catabolism of cholesterol to BAs, leading to reductions in hepatic cholesterol levels [47]. Thus, increased levels of TCBAs in the liver in heat-stress pigs may promote the conversion from cholesterol to BAs and consequently increase cholesterol and triglycerides release into the systemic circulation, leading to reduced cholesterol and triglycerides levels in the liver.…”

Dietary taurine stimulates the hepatic biosynthesis of both bile acids and cholesterol in the marine teleost, tiger puffer (Takifugu rubripes)

“…Regarding the mechanisms involved in TAU actions on bile acids, cholesterol and lipids, the mammal studies have well revealed that TAU stimulated the expression of cholesterol 7α-hydroxylase (CYP7A1) (4,(15)(16)(17)(18) , the rate-limiting enzyme for bile acid synthesis, and farnesoid X receptor (FXR (nuclear receptor subfamily 1, group H, member 4, NR1H4)) activation might be involved in this process (19) . Besides, regulation of lipoproteins and the LDL receptor contributes to the effects of TAU on cholesterol metabolism (3,4,20) .…”

Cholesterol-lowing effect of taurine in HepG2 cell

“…Many in vivo studies with hypercholesterolemia rat, mouse and hamster reveal that the cholesterol-lowering effect of taurine is carried out by enhancing CYP7A1 activity or gene expression and fecal bile acid excretion [5, 6, 16, 17], while in vitro researches are few. Yanagita T et al noted that the cellular cholesterol levels decreased and synthesis of cholesterol ester was inhibited when the HepG2 cells were incubated in DMEM medium with taurine for 24 h [22].…”

“…Many studies on the hypercholesterolemia rat and mouse have revealed that taurine increases the mRNA expression and activity of CYP7A1 [5, 6, 16, 17], and the same improvement has also been observed via the in vitro experiment [7]. The in vitro studies have focused on the upregulating-effect of taurine on CYP7A1 mRNA level, but the regulatory mechanism and the changes of cellular bile acids, the products of cholesterol degradation, have not been discussed.…”