Feedback regulation of bile acid synthesis in primary human hepatocytes: evidence that CDCA is the strongest inhibitor.

Primary human hepatocytes were used to elucidate the effect of individual bile acids on bile acid formation in human liver. Hepatocytes were treated with free as well as glycine-conjugated bile acids. Bile acid formation and messenger RNA (mRNA) levels of key enzymes and the nuclear receptor short heterodimer partner (SHP) were measured after 24 hours. Glycochenodeoxycholic acid (GCDCA; 100 micromol/L) significantly decreased formation of cholic acid (CA) to 44% +/- 4% of controls and glycodeoxycholic acid (GDCA) decreased formation of CA to 67% +/- 11% of controls. Glycoursodeoxycholic acid (GUDCA; 100 micromol/L) had no effect. GDCA or glycocholic acid (GCA) had no significant effect on chenodeoxycholic acid (CDCA) synthesis. Free bile acids had a similar effect as glycine-conjugated bile acids. Addition of GCDCA, GDCA, and GCA (100 micromol/L) markedly decreased cholesterol 7alpha-hydroxylase (CYP7A1) mRNA levels to 2% +/- 1%, 2% +/- 1%, and 29% +/- 11% of controls, respectively, whereas GUDCA had no effect. Addition of GDCA and GCDCA (100 micromol/L) significantly decreased sterol 12alpha-hydroxylase (CYP8B1) mRNA levels to 48% +/- 5% and 61% +/- 4% of controls, respectively, whereas GCA and GUDCA had no effect. Addition of GCDCA and GDCA (100 micromol/L) significantly decreased sterol 27-hydroxylase (CYP27A1) mRNA levels to 59% +/- 3% and 60% +/- 7% of controls, respectively, whereas GUDCA and GCA had no significant effect. Addition of both GCDCA and GDCA markedly increased the mRNA levels of SHP to 298% +/- 43% and 273% +/- 30% of controls, respectively. In conclusion, glycine-conjugated and free bile acids suppress bile acid synthesis and mRNA levels of CYP7A1 in the order CDCA > DCA > CA > UDCA. mRNA levels of CYP8B1 and CYP27A1 are suppressed to a much lower degree than CYP7A1.