Benign recurrent intrahepatic cholestasis: Altered bile acid metabolism

Abstract

Altered bile acid metabolism has been claimed to play a role in the etiology of benign recurrent intrahepatic cholestasis (BRIC). Therefore, we studied bile acid metabolism in detail in 10 patients with this syndrome. Pool sizes of both primary bile acids were estimated simultaneously, using deuterated cholic acid and chenodeoxycholic acid. The pool sizes of cholic acid and chenodeoxycholic acid, expressed in micromoles per kilogram body weight, were significantly contracted in BRIC patients during a cholestasis-free period: 8.0 ± 4.2 and 11.7 ± 4.7, respectively, versus 24.1 ± 11.7 and 22.9 ± 7.8 in controls. Fractional turnover rates (per day) for cholic acid and chenodeoxycholic acid were increased: 0.70 ± 0.29 and 0.58 ± 0.27, respectively, versus 0.29 ± 0.12 and 0.23 ± 0.10 in controls. Bile acid pool composition expressed as percentages in BRIC patients was cholic acid 34 ± 17, chenodeoxycholic acid 38 ± 9, deoxycholic acid 27 ± 18, and lithocholic acid 1 ± 1, with a glycine to taurine conjugation ratio of 6.7 ± 4.9. Corresponding values for 32 controls were cholic acid 57 ± 13, chenodeoxycholic acid 29 ± 9, deoxycholic acid 14 ± 9, and lithocholic acid <1, with a glycine to taurine conjugation ratio of 2.4 ± 1.3. Fecal bile acid loss, in micromoles per kilogram body weight per day, was 11.2 ± 9.0 in BRIC patients compared with 2.8 ± 1.4 in controls. The serum 7α-hydroxycholesterol level (nanomoles per liter) was significantly increased in BRIC patients: 326 ± 179 versus 171 ± 90 in controls. These results suggest that in BRIC patients spillover of bile acids into the colon occurs, which leads to increased fecal bile acid loss and a reduced bile acid pool size. Increased serum 7α-hydroxycholesterol is probably indicative of an accelerated bile acid synthesis rate due to increased activity of cholesterol 7α-hydroxylase, the enzyme catalyzing the first step in the major pathway of bile acid synthesis. The results of our study suggest that in BRIC patients a contracted bile acid pool increases the susceptibility of the liver for cholestatic agents.