Changes in classic and alternative pathways of bile acid synthesis in chronic liver disease

Background: Cholesterol elimination occurs through bile acid synthesis that starts within the liver from 7\u3b1-hydroxylation or in extrahepatic tissues from 27-hydroxylation. This study was aimed at investigating in vivo these two pathways in patients with chronic liver disease. Methods: Serum concentrations of 7\u3b1- and 27-hydroxycholesterol were measured in 54 patients (29 with primary biliary cirrhosis and 25 with chronic hepatitis C) and 18 controls. The rate of oxysterol plasma appearance was calculated after intravenous infusions of deuterated 7\u3b1- and 27-hydroxycholesterol in patients (n = 8) and control subjects (n = 8) who gave consent. The expression of sterol 27-hydroxylase was evaluated in macrophages isolated from 20 subjects. Results: In patients with liver disease, the rate of plasma appearance of 7\u3b1-hydroxycholesterol was significantly reduced (1.44 \ub1 0.96 vs. 2.75 \ub1 1.43\ua0mg/hour, p = 0.03), the degree of reduction being related with the severity of the disease (p = 0.01) whereas that of 27-hydroxycholesterol was unaffected. The rate of plasma appearance of 27-hydroxycholesterol was significantly related to its serum concentrations (r = 0.54, p = 0.03) and to its release from cultured macrophages ( r = 0.85, p = 0.03). Conclusions: In liver disease 7\u3b1-hydroxylation of cholesterol seems to be impaired while 27-hydroxylation is unaffected. Serum concentrations of 27-hydroxycholesterol are useful to obtain information on the activity of this alternative pathway

A minimally invasive technique for the evaluation of the regulatory steps of the two major pathways of bile acid synthesis

Background: Bile acid synthesis accounts for more than 95% of total cholesterol catabolism per day. We have developed a minimally invasive technique in humans that quantifies the rates of plasma appearance of 7 alpha and 27-hydroxycholesterol, representing the first steps of the "classical" and "altemative" pathways of bile acid synthesis, respectively. Methods: For this purpose, during the intravenous infusion of synthetic deuterated isotoporners of 7 alpha-hydroxycholesterol and 27-hydroxycholesterol plasma samples are collected and analysed by a GC-MS based method that allows to quantify the exogenous/natural isotoporner ratio of the two sterols. From this data, the rates of plasma appearance of 7 alpha and 27-hydroxycholesterol are calculated. Results: In a group of healthy individuals steady state kinetics are obtained during a 2 h period yielding mean values of 2.0 +/- 0.8 and 3.7 +/- 0.6 mg/h for 7 alpha and 27-hydroxycholesterol, respectively. The data are consistent with findings using older techniques that require studies over several days. Conclusion: Considering that at steady state of the exogenous/natural isotopomer ratio the plasma. appearance of the two regulatory hydroxysterols are related to the rate of bile acid synthesis via the "classical" and the "altemative" pathways,respectively, the proposed method could be used to evaluate the immediate effects of different diets and drugs and other determinants on cholesterol catabolism