Hepatic HMGCoA reductase in human cholelithiasis: effects of chenodeoxycholic and ursodeoxycholic acids*

Abstract. To study further the role of hepatic cholesterol synthesis in patients with gallstones, the activity of the rate-limiting step in cholesterbgenesis, hydroxy-methyl glutaryl co-enzyme A reductase (HMGCoAR), was measured in operative wedge liver biopsies from ten patients with untreated cholesterol gallstones, six with pigment stones and ten controls. Hepatic HMGCoAR was also measured in six patients with cholesterol-rich gallstones treated for 1–24 months with 14-6-18-6 mg chenodeoxycholic acid (CDCA) kg^-1 day^-1, in two patients with radiolucent pigment stones treated with 17-3 and 17-7 mg CDCA kg^-1 day^-1 and in ten other patients with cholesterol-rich stones given 4–5-7-2 mg ursodeoxycholic acid kg^-1 day^-1 for 1–6 months. HMGCoAR activity was also related to the free and esterified cholesterol content of both hepatic homogenates and the microsomal fractions. Compared with the controls (HMGCoAR activity 14-6±1 6 (SEM) pmole mg microsomal protein^-1 min^-1), the mean activity in untreated cholesterol cholelithiasis was 32 2 ±2-0 (P < 0–001), but was near normal in patients with pigment stones (16-2 + 1 5). In cholesterol gallstone patients, chenodeoxycholic acid treatment reduced the mean enzyme activity by 51% compared with the untreated gallstone group (P < 0001) and in smaller doses, ursodeoxycholic acid therapy lowered it by 40% (P < 0001) but in the two patients with pigment stones, CDCA did not seem to affect HMGCoAR activity. Despite this four-fold variation in enzyme activity, there were no significant differences in mean free or esterified cholesterol concentrations in whole liver homogenates or in the microsomal fraction from any of the patient groups. Presented in part at the European Society for Clinical Investigation, Rotterdam, April 1978 (Maton P.N. & Dowling R.H (1978) Eur J Clin Invest 8, 329 (abstract)) and at the V International Bile Acid Meeting, Freiburg, June 1978 (Maton P.N. & Dowling R.H. (1978) in: Biological Effects of Bile Acids (ed. by G. Paumgartner, A. Stiehl and W. Gerok), pp. 91–98. MTP Press, Lancaster).