E. Sacquet

Effects of some poorly digestible carbohydrates on bile acid bacterial transformations in the rat

The effects of ingestion of poorly digestible carbohydrates on bacterial transformations of cholic acid and beta-muricholic acid were studied in rats fed on increasing levels of lactose, lactulose, amylomaize or potato starches. Each level was given for 3 weeks and, at the end of each dietary treatment, bile acid faecal composition was analysed and a group of six rats was killed every 4 h during 24 h to determine the amounts of fermented carbohydrate and fermentation characteristics (caecal pH, volatile fatty acids (VFA) and lactic acid concentrations). Fermentation of carbohydrates decreased caecal pH and enhanced caecal VFA and lactic acid concentrations. Irrespective of the poorly digestible carbohydrate, the variation of bacterial transformation always occurred in the same way: the bacterial transformation of beta-muricholic acid into hyodeoxycholic acid was the first to disappear, while omega-muricholic acid formation increased; second, cholic acid transformation decreased and finally all bile acid transformations were strongly affected. There was a significant correlation between bile acid transfer and the minimal caecal pH in vivo. This effect of pH was similar in vitro. To determine whether the levels of bacteria which transformed bile acids were modified, rats fed on the highest amounts of poorly digestible carbohydrates were introduced into isolators and carbohydrate feeding was stopped. Caecal pH recovered its initial value but bile acid transformations remained changed, suggesting that the intestinal microflora were modified by ingestion of fermentable carbohydrates.

β-Muricholic acid; potentiometric and cholesterol-dissolving properties

Abstract Some physicochemical properties of β-niuricholic acid (3α,6β,7β-trihydroxyβ-cholanic acid), a major bile acid biosynthesized by rat liver, were determined and compared to those of ursodeoxycholic and chenodeoxycholic acids. From potentiometric studies, the following characteristics of β-muricholic acid were shown: a low monomer solubility (13 μM), a high equilibrium precipitation pH (7.92 for 30 mM solution), an apparent critical micellar concentration of 4 mM, and a very low micellar capacity of the bile salt to dissolve the protonated bile acid. Sodium β-muricholate solution (30 mM) poorly solubilized cholesterol, as indicated by a bile salt/cholesterol molar ratio of 1430, whereas saturation ratios obtained with chenodeoxycholate and ursoseoxycholate were 24 and 384, respectively. Sodium β-muricholate (30 mM)/phosphatidylcholine/cholesterol mixtures contained non-micellar aggregates from very low cholesterol concentrations. At physiological phosphatidylcholine concentrations, sodium β-muricholate (100 mM) dissolved cholesterol crystals via essentially lamellar liquid-crystal formation. These solubilizing properties might have important physiological relevance to the dissolution of cholesterol gallstones in man.

Glucuronidation of bile acids in human liver, intestine and kidney: An in vitro study on hyodeoxycholic acid

The activities of UDP-glucuronyl transferase(s) in homogenates and microsomal preparations of human liver, kidney and intestine were tested with hyodeoxycholic acid (HDC). The various kinetic parameters of the UDC-glucuronidation were determined from time course experiments. In both liver and kidney preparations, HDC underwent a very active metabolic transformation: liver Km = 78 μM, Vmax = 3.3 nmol·min −1mg −1 protein; kidney Km = 186 μM, Vmax = 9.9 nmol·min −1.mg −1 protein. To our knowledge this is the first observation of both an extensive and comparable bile acid glucuronidation occurring in renal and hepatic tissues.The activities of UDP‐glucuronyl transferase(s) in homogenates and microsomal preparations of human liver, kidney and intestine were tested with hyodeoxycholic acid (HDC). The various kinetic parameters of the UDC‐glucuronidation were determined from time course experiments. In both liver and kidney preparations, HDC underwent a very active metabolic transformation: liver Km = 78 μM, Vmax = 3.3 nmol·min −1mg −1 protein; kidney Km = 186 μM, Vmax = 9.9 nmol·min −1.mg −1 protein. To our knowledge this is the first observation of both an extensive and comparable bile acid glucuronidation occurring in renal and hepatic tissues.

Metabolism of β-muricholic acid in man

Abstract Labeled β-muricholic acid was obtained from germfree rats given [24- 14 C]-chenodeoxycholic acid. It was crystallized with the same unlabeled bile acid extracted from germfree rat pooled biles. Five patients fitted with a T-tube after cholecystectomy were given orally 100 mg of the bile acid. Metabolites of β-muricholic acid in bile, urine and feces were studied. Glyco- and tauro-β-muricholic acid were the only metabolites detected in bile. The urinary bile acid pattern was complex and included free, glyco- and sulfoconjugated β-muricholic acid, but no glucuronide was observed. Analysis of fecal bile acid showed very few metabolites: the 3β-epimer was identified; the 6β- and 7β-hydroxyls were apparently not transformed by human intestinal microflora.

Measurement of fecal bile acid excretion in gnotobiotic rats: Comparison of gas-liquid chromatography and [4-14c] cholesterol isotopic equilibrium

Gas-liquid chromatography (G.L.C.) and the method of [4(-14C)] cholesterol isotopic equilibrium (C.I.E.) were used to determine the fecal bile acid excretion in gnotobiotic rats. The same samples were submitted to both methods. In these conditions, it was observed that the fecal bile acid excretions determined by G.L.C. were 38% of lower than when determined by C.I.E. In thin-layer chromatographic analyses (T.L.C.) of the bile acid extracts obtained from rats in which a [4(-14C)] cholesterol isotopic equilibrium was established, 33 to 35% of the radioactivity of this fraction was not observed in the rat primary bile acids. No bile acids could be observed in G.L.C. made with eluates obtained from the T.L.C. areas containing this radioactivity. It therefore appears that the difference observed in the results obtained by G.L.C. and C.I.E. is due to the fact that chemical species which are not measured by the former method can be determined by the latter one. T.L.C. analyses of bile acid extracts from axenic rats in which either a [26(-14C)] cholesterol or a [2,4(-3H)] cholic acid and [24(-14C)] chenodeoxycholic acid equilibrium were established, lead to the conclusion that the chemical composition of these undetermined substances is complex: part of these substances comes from the transformation of bile acids; another part is made of molecules which maintain the 26(-14C) of cholesterol.