Effects of feeding ursocholic acid to germfree rats

Bile but not chyle lipoprotein is an important source of arachidonic acid for the rat small intestine

Arachidonic acid (AA) functions as a structural component, eicosanoid precursor and surface material for chylomicron production in the gastrointestinal tract. The origin of this AA is poorly characterized. [3H]AA labelled chylomicrons and [14C]AA albumin-FFA were injected intravenously into biliary diverted rats and controls. Radioactivity in tissue lipids was measured after different time intervals. Output of 3H and 14C in bile was 8% of the injected dose during 24 h. Radioactivity of the upper small intestine but not of colon and stomach increased with time. Bile drain reduced the recovered amounts of radioactivity in upper small intestine by 75% after 24 h. In stomach and colon 3H/g tissue was 16-20 fold lower than in liver after 24 h. Recovery of 3H in liver was higher than of 14C. In liver 3H/g tissue was 15-40 fold higher than in stomach and colon after 10-60 min. Equilibration between AA pools of liver and other organs was not complete after 96 h. Biliary phospholipid is an important source of AA for the small intestine.

Metabolism of ursocholic acid in humans: conversion of ursocholic acid to deoxycholic acid

To study the metabolism of ursocholic acid, control subjects were injected with radiolabeled cholic and ursocholic acids before and after 1 wk of 900 mg/day oral ursocholic acid. Daily samples of bile were obtained, and biliary bile acids were extracted and purified to determine bile acid kinetics. During ursocholic acid therapy ursocholic acid became the principal bile acid (35% +/- 3% of total bile acids, mean +/- S.E.M.), and the percentage of biliary cholic and chenodeoxycholic acids decreased (p less than 0.05). Cholic acid production fell from 190 +/- 15 mg/day to 135 +/- 20 mg/day (p = 0.078). The total bile acid pool was increased twofold (p less than 0.05), whereas the deoxycholic acid pool was enlarged from 440 +/- 170 mg to 1,175 +/- 90 mg (p less than 0.02). As much as 28% of the fed ursocholic acid was excreted in the urine, 85% as the free acid and 15% as the glycine conjugate. During treatment, ursocholic acid became the source for 69% +/- 11% of biliary deoxycholic acid. The time course of the deoxycholic acid specific activity was modeled as a single pool precursor-product system with a variable time delay for the C-7-dehydroxylation of cholic and ursocholic acids (mean delay 0.86 +/- 0.11 days, p less than 0.001 vs. zero delay). Most of this delay probably arises from a slow process of bacterial C-7-dehydroxylation within the colon. These results demonstrate that during ursocholic acid therapy the synthesis of primary bile acids continues whereas the formation of secondary bile acids is greatly increased.

Differential effects of ursodeoxycholic acid and ursocholic acid on the formation of biliary cholesterol crystals in mice

The preventive effect of 3 alpha, 7 beta, 12 alpha-trihydroxy-5 beta-cholanoic acid (ursocholic acid) and ursodeoxycholic acid on the formation of biliary cholesterol crystals was studied in mice. Cholesterol crystals developed with 80% incidence after feeding for five weeks a lithogenic diet containing 0.5% cholesterol and 0.25% sodium cholate. When 0.25% ursocholic acid or ursodeoxycholic acid was added to the lithogenic diet, the incidence as well as the grade (severity) of the gallstones were reduced. Plasma and liver cholesterol levels were decreased by ursodeoxycholic acid but not by ursocholic acid. Gallbladder cholesterol and phospholipid levels were decreased by both bile acids. The biliary bile acid level was decreased by ursocholic acid but not by ursodeoxycholic acid. After feeding ursocholic acid, its level in the bile was about 25% and the levels of cholic acid and beta-muricholic acid decreased. Fecal sterol excretion was not changed by ursocholic acid, but was increased by ursodeoxycholic acid. After feeding ursocholic acid, fecal excretion of deoxycholic acid, cholic acid, and ursocholic acid increased. No differences were found between mice, with or without gallstones, in plasma and liver cholesterol levels, biliary phospholipid and bile acid levels, fecal sterol and bile acid levels, and biliary and fecal bile acid composition. The results suggest that the lower incidence of crystal formation after treatment with ursocholic acid is probably by a different mechanism than with ursodeoxycholic acid. In the mouse model, ursodeoxycholic acid exerts its effect at least partially, by decreasing cholesterol absorption. Ursocholic acid is well absorbed and excreted into bile and transformed into deoxycholic acid by the intestinal microflora in mice.

Effect of chronic ursocholic acid administration on bile lipid composition and bile acid pool size in gallstone patients

We assessed the effect of chronic (4-6 weeks) administration of ursocholic acid (UCA) (15 mg/kg/day), a natural bile acid with poor detergent capacity, on biliary lipid composition of gallbladder bile (n = 26) and bile acid pool size (n = 5) in gallstone patients. During treatment the biliary molar percentage UCA increased from trace values to 28% (p less than 0.001). This effect was accompanied by an increase in molar percentage deoxycholic acid from 16% to 33% (p less than 0.001). Total bile acid pool size remained unchanged during UCA administration; cholic acid and chenodeoxycholic acid pool sizes decreased from 1.0 to 0.6 mmol (p less than 0.05) and from 1.6 to 0.9 mmol (p less than 0.05), respectively. The molar percentage cholesterol of gallbladder bile decreased from 9.8% to 7.0% (p less than 0.001) during UCA, but bile remained supersaturated with cholesterol in 21 patients. The weak effect on biliary lipid composition and the increase of potentially toxic deoxycholic acid in bile suggest that UCA is unlikely to replace ursodeoxycholic and chenodeoxycholic acid for medical treatment of gallstones.

Defective bile acid amidation: predicted features of a new inborn error of metabolism

Biochemical and clinical features are predicted for an as yet unreported inborn error of metabolism, in which bile acids cannot be conjugated with glycine or taurine. Unconjugated cholic acid will be secreted into bile, be absorbed from the intestine, and become the predominant bile acid in bile and plasma. Other bile acids will be esterified with glucuronate and secreted into bile, but undergo little enterohepatic circulation. Cholestasis will not be present; the bile acid pool will be diminished and lipid absorption, especially that of fat-soluble vitamins, will be impaired. A secretory diarrhoea may occur, caused by increased bile acid concentrations in the colon. Awareness of this possible syndrome should aid in its identification; oral administration of bile acids conjugated with glycine or taurine should correct the metabolic and clinical abnormalities.