Accumulation of 7α-hydroxycholesterol in liver tissue of patients with cholesterol gallstones

Patients with cholesterol gallstones have a reduced pool of bile acids. This study was undertaken to clarify the mechanism by which bile acid biosynthesis does not increase to supranormal levels to cause a reexpansion of the pool. We investigated the first two steps of the bile acid biosynthesis pathway by assaying the activities of cholesterol 7α-hydroxylase, the rate-limiting enzyme in this pathway, and 3β-hydroxy-Δ⁵-C₂₇-steroid dehydrogenase/isomerase, and by measuring the concentrations of 7α-hydroxycholesterol and 7α-hydroxy-4-cholesten-3-one in liver specimens from ten patients with cholesterol gallstones and ten gallstone-free controls. In the patients with gallstones, cholesterol 7α-hydroxylase activity, 3β-hydroxy-Δ⁵-C₂₇ dehydrogenase/isomerase activity, and hepatic 7α-hydroxy-4-cholesten-3-one concentration did not significantly different from levels in controls, but hepatic 7α-hydroxycholesterol concentration was more than twofold that of controls (12.9 ± 2.6 vs 5.3 ±1.2 nmol/g liver, P<0.01). The concentration of 7α-hydroxycholesterol positively correlated with the ratio of cholesterol 7α-hydroxylase activity to 3β-hydroxy-Δ⁵-C₂₇ dehydrogenase/isomerase activity (r=0.93;P<0.005) in the gallstone-free controls. In contrast, this correlation disappeared in the patients with gallstones. These results suggest a derangement of the normal 7α-hydroxycholesterol metabolism in the patients with gallstones. The reason for the accumulation of 7α-hydroxycholesterol remains unclear; however, it is possible that, in patients with cholesterol gallstones, the accumulated 7α-hydroxycholesterol causes inappropriate suppression of cholesterol 7α-hydroxylase activity by product inhibition.