Metabolism of cholate, 7 beta-hydroxy- and 12 beta-hydroxy-isocholates in the rat

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.

Transport, metabolism, and effect of chronic feeding of lagodeoxycholic acid. A new, natural bile acid

Ursodeoxycholic acid, the 7 beta-hydroxy epimer of chenodeoxycholic acid, is more hydrophilic and less hepatotoxic than chenodeoxycholic acid. Because "lagodeoxycholic acid," the 12 beta-hydroxy epimer of deoxycholic acid, is also more hydrophilic than deoxycholic acid, it was hypothesized that it should also be less hepatotoxic than deoxycholic acid. To test this, lagodeoxycholic acid was synthesized, and its transport and metabolism were examined in the rat, rabbit, and hamster. The taurine conjugate of lagodeoxycholic acid was moderately well transported by the perfused rat ileum (Tmax = 2 mumol/min.kg). In rats and hamsters with biliary fistulas, the taurine conjugate of lagodeoxycholic acid was well transported by the liver with a Tmax greater than 20 mumol/min.kg; for the taurine conjugate of deoxycholic acid, doses infused at a rate greater than 2.5 mumol/min.kg are known to cause cholestasis and death. Hepatic biotransformation of lagodeoxycholic acid in the rabbit was limited to conjugation with glycine; in the hamster, lagodeoxycholic acid was conjugated with glycine or taurine; in addition, 7-hydroxylation occurred to a slight extent (approximately 10%). When lagodeoxycholic acid was instilled in the rabbit colon, it was absorbed as such although within hours it was progressively epimerized by bacteria to deoxycholic acid. When injected intravenously and allowed to circulate enterohepatically, lagodeoxycholic acid was largely epimerized to deoxycholic acid in 24 hours. Surgical creation of a distal ileostomy abolished epimerization in the rabbit, indicating that exposure to colonic bacterial enzymes was required for the epimerization. Lagodeoxycholic acid was administered for 3 weeks at a dose of 180 mumol/day (0.1% by weight of a chow diet; 2-4 times the endogenous bile acid synthesis rate); other groups received identical doses of deoxycholic acid (hamster) or cholyltaurine, a known precursor of deoxycholic acid (rabbit). After 3 weeks of lagodeoxycholic acid ingestion, liver test results and liver appearance were normal. The total bile acid pool expanded by 37% in the rabbit, lagodeoxycholic acid composing 10% of biliary bile acids. In the hamster, the total bile acid pool was expanded by 95%, lagodeoxycholic acid composing 22% of biliary bile acids; biliary lipid secretion remained unchanged. Tracer studies indicated that the fractional turnover rate of lagodeoxycholic acid was high (157%/day, rabbit; 116%/day, hamster) because of its rapid epimerization to deoxycholic acid in the colon. These studies indicate that lagodeoxycholic acid, the more hydrophilic epimer of deoxycholic acid, is transported and metabolized as other dihydroxy bile acids but is much less toxic than deoxycholic acid.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Effects of feeding ursocholic acid to germfree rats

Germfree rats were fed 24-14C-ursocholic acid (UC) mixed into the diets for 10 days. The bile was then drained by cannulation for 6 hours to collect the bile salt pool. No biotransformation of the labelled UC occurred and it constituted approximately equal to 75% of an enlarged bile salt pool. Less phospholipid and cholesterol were secreted into the bile per mumol bile salt compared to normal rats. The critical micellar concentration (CMC) of the bile was determined by equilibrium dialysis and found to be increased. Faecal excretion of labelled triolein added to the diet was unaffected by feeding ursocholic acid. Excretion of 14C-octadecane and 14C-cholesterol increased significantly under the same conditions. Ursocholic acid feeding thus resulted in a selective malabsorption of octadecane and cholesterol.