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Experimental dietary studies of human colorectal carcinogenesis are usually based on the AIN-76A diet, which is dissimilar to human food in source, preparation, and content. The aims of this study were to examine the feasibility of preparing and feeding rats the diet of a specific human population at risk for colorectal neoplasia and to determine whether changes in the colonic morphology and metabolic contents would differ from those resulting from a standard rat diet. The mean daily food intake composition of a previously evaluated adenoma patient case-control study was used for the "human adenoma" (HA) experimental diet. Foods were prepared as for usual human consumption and processed by dehydration to the physical characteristics of an animal diet. Sixty-four female Sprague-Dawley rats were randomized and fed ad libitum the HA or the AIN-76A diet. Every eight weeks, eight rats from each group were sacrificed, and the colons and contents were examined. Analysis of the prepared food showed no significant deleterious changes; food intake and weight gain were similar in both groups. Compared with the controls, the colonic contents of rats fed the HA diet contained significantly less calcium, concentrations of neutral sterols, total lipids, and cholic and deoxycholic acids were increased, and there were no colonic histological changes other than significant epithelial hyperproliferation. This initial study demonstrated that the HA diet can be successfully processed for feeding to experimental animals and is acceptable and adequate for growth but induces significant metabolic and hyperproliferative changes in the rat colon. This dietary model may be useful for studies of human food, narrowing the gap between animal experimentation and human nutritional research.

Hepatitis C virus (HCV) in highly infectious sera has been shown to be predominantly associated with low-density lipoproteins. To determine whether the association is specific to low-density lipoproteins (LDL) or very low-density lipoproteins (VLDL), we fractionated HCV-containing plasma by a column chromatographic procedure known to separate these classes. Hepatitis C virus RNA detected by polymerase chain reaction (PCR) was associated primarily with the very low-density (VLDL) fraction. However, it could not be ruled out that virus-associated LDL may have eluted with this fraction. Hepatitis C virus virions isolated from sera having sufficient titre for visualization by electron microscopy are generally coated with antiviral antibodies, therefore we utilized the lipid association to isolate antibody-free virions. Very low-density lipoproteins were isolated by ultracentrifugal flotation and then treated with deoxycholate to release the virions. These were then isolated in a highly purified form by centrifugation in a sucrose gradient. The 1.10-1.11 g ml-1 region of the gradients contained 60-70 nm particles. Particles with similar surface structure but having a diameter of only 30-40 nm constituted about 30% of the total. The latter may represent defective interfering particles. The identity of both small and large particles with HCV virions and associated particles was confirmed by their trapping on grids by an anti-HCV E2 monoclonal antibody, and by their aggregation by rabbit antiserum to an amino-terminal peptide of E1. Thus, both E1 and E2 epitopes are displayed on the surface of intact HCV virions.

Background & Aims: Because ursodeoxycholate has been shown to act as a tumor-suppressive agent in the colon, the absorption and metabolism of its sulfate conjugates were examined in rats to show that sulfation would facilitate the site-specific delivery of ursodeoxycholate to the colon., Methods: Bile acids were measured in intestinal contents, feces, urine, plasma, and liver tissue after oral administration of ursodeoxycholate and its C-3, C-7, and C-3,7 sulfate derivatives., Results: Ursodeoxycholate was found in the jejunum after administration of all bile acids, but the mass was greatest for ursodeoxycholic acid administration. In the colon, lithocholic acid, normally found in negligible amounts, became the major bile acid after ursodeoxycholate administration. In contrast, reductions in mass and proportions of lithocholate and deoxycholate occurred after administering the C-7 sulfates. The fecal lithocholate/deoxycholate ratio, a risk marker for colon cancer, increased markedly after administration of ursodeoxycholate and its C-3 sulfate, but did not change after administering the C-7 sulfates. Unlike ursodeoxycholate or its C-3 sulfate, which increased liver concentrations of lithocholate and ursodeoxycholate, the C-7 sulfates had the opposite effect, which was consistent with poor absorption., Conclusions: Sulfation of ursodeoxycholate, specifically at the C-7 position, protects the molecule from bacterial degradation and inhibits its intestinal absorption, thereby facilitating delivery to the colon.

Little is known about the effects of biliary deoxycholic acid on the partitioning of biliary cholesterol between vesicles and micelles and on the rate of nucleation of cholesterol microcrystals, key steps in gallstone formation. Therefore, 43 samples of fresh gallbladder bile were obtained from a heterogeneous group of patients with and without stones. Univariate and multivariate analyses were then applied to determine the inter-relationships between biliary cholesterol saturation, total lipid concentration, and bile acid species and (1) the distribution of biliary cholesterol between vesicles and micelles and (2) the cholesterol microcrystal nucleation time. The percentage of deoxycholic acid in bile was shown to be linearly related to the cholesterol saturation index (r = .54; P < .001), the vesicular cholesterol:phospholipid molar ratio (r = .53; P < .001), and the molar concentration of cholesterol in the vesicles (r = .59; P < .001). The mean proportion of biliary deoxycholic acid conjugates was also greater in patients with rapid nucleation times (23.4 +/- SEM 1.1%) than in those with slow nucleation times (17.3 +/- 1.9%; P < .05). As total bile lipid concentration increased, the proportion of total biliary cholesterol in vesicles decreased (r = .53; P < .001), whereas the molar concentration of vesicular cholesterol increased (r = .42, P < .01). The cholesterol saturation indices, total bile lipid concentration, and proportion of biliary deoxycholate were independent determinants of the molar concentration of cholesterol in vesicles. We conclude that relative increases in the percentage of deoxycholic acid and in bile lipid concentration, favor the partitioning of cholesterol into vesicles. In turn, this leads to an increase in the vesicular cholesterol:phospholipid molar ratio and thus to a decrease in the cholesterol microcrystal nucleation time.

The aim of this paper is to point out that: 1) CDCA and DCA increase the polarity of cell membranes and cause the release of cholesterol and phospholipid from the membranes; 2) the extent of this damage is inversely correlated with the cholesterol content of the membrane investigated; 3) UDCA, TUDCA and GUDCA decrease membrane polarity; 4) they prevent membrane damage when added prior to CDCA or DCA; 5) UDCA appears to be incorporated into the apolar domain of the membrane, TUDCA, GUDCA into the interface; 6) UDCA decreases HLA class I expression on hepatocyte membranes; 7) CDCA induces GLDH-release from liver mitochondria and increases mitochondrial membrane polarity and mobility; and 8) UDCA reduces the release of GLDH from mitochondria caused by CDCA.

Ca2+ entry into the cell may be an early event in the pathophysiology of bile salt-induced gastric mucosal injury. The aim of this study was to characterize the rise in cytosolic free Ca2+ associated with bile salt injury and its association with cell injury and death. Rabbit gastric mucosal cells were preloaded with the Ca2+ indicator fura 2-acetoxymethyl ester (fura 2-AM) for 20 min at 37 degrees C and then exposed to graded concentrations of the bile salt deoxycholate (DC). Cytosolic free Ca2+ concentration ([Ca2+]i) was estimated by spectrofluorometry. The resting [Ca2+]i in gastric cells was 177 +/- 15 nM (n = 6). When cells were subjected to 0.5 mM DC, there was a time-dependent rise in [Ca2+]i. An increase in [Ca2+]i was observed within 2 min, at which time [Ca2+]i rose from 177 +/- 15 to 480 +/- 30 nM. The maximal increase in [Ca2+]i was observed after 20 min of exposure to 0.5 mM DC (639 +/- 49 nM), and [Ca2+]i remained unchanged for at least 2 h. The increase in [Ca2+]i depended on the concentration of DC. The minimum effective dose of DC was 0.2 mM, with which [Ca2+]i was increased by 1.6-fold (from 177 to 285 nM). At 0.5 mM DC also caused a rise in 45Ca2+ influx into the cells and reduced the viability of gastric cells from 96% to 58% at 2 h. The DC-induced rise in cytosolic free Ca2+ depended on the presence of extracellular Ca2+. In the absence of extracellular Ca2+ there was no rise in cytosolic Ca2+ and gastric cells were protected from cell death caused by DC. The DC-induced cell death was reduced from 26% to 10% and from 37% to 16% at 60 and 90 min, respectively, by removal of extracellular Ca2+. The association of DC with gastric cells was not altered by removing extracellular Ca2+. This suggests decreased DC-induced injury in the absence of extracellular Ca2+ is due to the protection from cellular hypercalcemia rather than some other mechanism related to reduced binding and/or association of DC to gastric cells. These experiments show that rising [Ca2+]i appears to be an early pathophysiological event in bile salt-induced cellular injury and that extracellular Ca2+ is critical to produce this effect.

A total of 100 nonobese and normolipidemic subjects (29 control subjects, 49 patients with cholesterol stones [CSs], and 22 patients with brown pigment stones) were studied to elucidate the pathogenetic contributions of deoxycholate (DC) to supersaturated bile formation with special reference to de novo syntheses of cholesterol and bile acids in the liver. A higher proportion of DC was observed in gallbladder bile from patients with CSs (CSs; 21.7 +/- 1.4%, mean +/- SEM, vs. control subjects; 10.2 +/- 0.9%). Cholesterol saturation in bile was elevated parallel to the increase of DC (r = .48; P = .0002), irrespective of the existence of stones. In a comparison between the 52 subjects with increased DC in bile (> 10% of biliary bile acids) and the 20 subjects without the increase (< 10%), the molar percentage of cholesterol in bile was significantly higher in the former (9.4 +/- 0.5%) than in the latter (6.7 +/- 0.4%) (P < .001). Consistent with the decrease in steady-state level of low-density lipoprotein (LDL) receptor-messenger RNA (mRNA), the catalytic activity and mRNA level of microsomal hepatic 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, the rate-limiting enzyme for de novo cholesterol synthesis, were significantly lower in the former (2.9 +/- 0.3 pmol/min/mg protein) than in the latter (5.1 +/- 0.6) (P < .0001). Biliary molar percentage of bile acids was significantly lower in the former (69.8 +/- 1.1%) than in the latter (75.2 +/- 1.5%) (P < .01). However, contrary to expectations, the catalytic activity and mRNA level of cholesterol 7 alpha-hydroxylase, the rate-limiting enzyme for bile acid synthesis, were significantly higher in the former (5.8 +/- 0.4 pmol/min/mg protein) than in the latter (3.7 +/- 0.6) (P < .01). The magnitude of the impaired gallbladder emptying (control subjects; 78.4 +/- 4% vs. CSs; 58 +/- 3%; P < .0005) together with the prolonged small intestinal transit (control subjects; 126 +/- 9 minutes vs. CSs; 198 +/- 9 minutes; P < .01) correlated significantly with the increased percentage of DC in bile. It is concluded that in cholesterol gallstone disease an increase of DC in bile, linked to an impaired gallbladder emptying together with a prolonged small intestinal transit, may play a significant role in downregulating de novo cholesterol synthesis but not bile acid synthesis in the liver.(ABSTRACT TRUNCATED AT 400 WORDS)

Comparative studies between different patient groups have suggested that cholecystectomy enhances bacterial dehydroxylation of the primary bile acid cholic acid (CA) to the secondary bile acid deoxycholic acid (DCA). DCA may exert a cocarcinogenic effect on the colonic mucosa. In a short-term follow-up study on nine female patients we found no alterations of the CA or DCA pools after cholecystectomy. However, in the long term, cholecystectomy could promote changes of the intestinal bacterial flora and thereby lead to enhanced conversion of CA to DCA, causing an expansion of the DCA pool size and a reduction of the CA pool size. To test this hypothesis, pool sizes, fractional turnover rates (FTR), and synthesis or input rates of CA, chenodeoxycholic acid (CDCA) and DCA were determined in 12 female patients before and again 5 to 8 years after cholecystectomy. In the long term, pool size and synthesis rate of CA had not changed and DCA pool size had expanded by only 7.5% (not significant [NS]). DCA input increased by 32% (NS) but was balanced by an increase in FTR of 36%. Pool size (-17%) and synthesis rate (-5%) of CDCA were not significantly diminished. Overall, the sizes of the total bile acid pool (-6%, NS; 50 +/- 8 vs. 53 +/- 13 mumol/kg) and the pool fractions of CA (44.7 +/- 10.3% vs. 42.8 +/- 7.6%) and DCA (25.5 +/- 14.1% vs. 23.6 +/- 9.3%) remained similar. In conclusion, cholecystectomy causes no changes in bile acid pool composition and thus has no adverse effects on bile acid metabolism in the long term.

Nine normolipidemic young men consumed a constant diet for 2 mo into which oat bran was incorporated during the second month so that we might test the hypotheses that oats lower serum cholesterol concentrations by decreasing bile acid and fat absorption and increasing bile acid synthesis. Bile acid kinetics were determined by measuring the 13C enrichment of serum cholic and chenodeoxycholic acids. Oat bran consumption decreased serum cholesterol levels (p < 0.01) and cholic acid pool size (p < 0.05). Deoxycholic acid pool size (p < 0.01) and the synthesis and fractional turnover rates of both primary bile acids (p < 0.05) increased. Total bile acid pool size did not change. Fecal excretion of total bile acids, the two secondary bile acids and fat increased significantly. The results demonstrate that oat bran lowers serum cholesterol levels in part by altering bile acid metabolism. In addition, the substantial increase in the proportion of the total bile acid pool that was deoxycholic acid is consistent with the hypothesis that oat bran also decreases cholesterol synthesis.

In order to establish the position of conjugation of bile acids with glucose or N-acetylglucosamine, glucosides of chenodeoxycholic and hyodeoxycholic acids and of 13C-labeled cholic, lithocholic, chenodeoxycholic, hyodeoxycholic, and ursodeoxycholic acids, and N-acetylglucosaminides of ursodeoxycholic, isoursodeoxycholic, 3-dehydro-ursodeoxycholic, and ursodeoxycholylglycine were synthesized in vitro. The conjugates were purified by anion-exchange chromatography and reversed-phase HLPC and were analyzed by gas chromatography-mass spectrometry. The glucosides of chenodeoxycholic and hyodeoxycholic acids were also analyzed after periodate and chronic acid oxidation. All conjugates were analyzed by fast atom bombardment mass spectrometry with collision-induced dissociation. Glucose conjugation was shown to occur at C-3 in all bile acid glucosides studied. In contrast, the selective N-acetylglucosaminidation of 7 beta-hydroxy bile acids was shown to occur at the 7 beta-position.

In the present paper, we have aimed at studying the variations in the metabolism of bile acids occurring during an hepatocarcinogenic process induced in male Wistar Rats by the biphasic protocol of Solt and Farber. Bile acids concentrations was measured in the liver. The most significant changes have been observed 5 weeks after the beginning of the treatment, it means one week after the selection treatment consisting in 2-acetylaminofluorene administration: the increase in cholic acid, and of its intestinal metabolite, deoxycholic acid, and of alpha- and beta- muricholic acids, are likely to be a consequence of an acute effect of 2-acetylaminofluorene. To test for the putative implication of liver bile acids modifications in the selection effect of 2-acetylaminofluorene, diethyl-nitrosamine-pretreated rats were fed a diet containing 1% lithocholic acid, a treatment that induces essentially the same qualitative changes in liver bile acids, as 2-acetylaminofluorene does: no selection effect of lithocholic acid could be demonstrated. These results suggest that changes in bile acid metabolism occurring early in hepatocarcinogenesis are more likely to be secondary than causative events. The same conclusion comes from the results obtained later on in the process, where there is only a high increase in liver cholic acid and deoxycholic acid concentrations.

Monospecific polyclonal antibodies were raised against a variable amino-terminal domain (amino acids 14-150) of a human liver form of UDP-glucuronosyl-transferase conjugating bile acids, UGT2B4 (Jackson, M. R., McCarthy, L. R., Harding, D., Wilson, S., Coughtrie, M. W., and Burchell, B. (1987) Biochem. J. 242, 581-588), expressed as a fusion protein in Escherichia coli. The antibodies were able to recognize the protein, stably expressed in a genetically engineered eukaryotic V79 cell line, against which they were directed. The specificity of these antibodies allowed their use for analyzing the substrate specificity of this isoform in human liver, as well as for determining its contribution to the total hepatic and extra-hepatic glucuronidation of hyodeoxycholic acid. Western blot analysis of microsomal proteins demonstrated the presence of UGT2B4 exclusively in human liver and not in human kidney. In human liver microsomes, the antibodies were able to inhibit and precipitate up to 90% of the total hyodeoxycholic acid 6-O-glucuronidation activity, but had no effect on activities toward several other substrates, such as phenols, bilirubin, or other bile acids, especially hyocholic acid and the steroids 4-hydroxyesterone and estriol. Moreover, Western blot analysis and immunoinhibition studies of human liver microsomes from healthy patients and from patients presenting liver diseases revealed a good correlation between the glucuronidation rate of hyodeoxycholic acid and the UGT2B4 expression level. The absence of immunoinhibition of hyodeoxycholic acid conjugation with UDP sugars other than UDP-glucuronic acid suggests the involvement of different enzymatic systems in the glucosidation and xylosylation of hyodeoxycholic acid. Altogether, the results provided strong evidence for the specific and predominant involvement of UGT2B4 in the 6-O-glucuronidation of this bile acid via a UDP-glucuronic acid-dependent mechanism.

We have developed a method to accurately and reproducibly determine the total activity of cytochrome oxidase (CO) in rat brain tissue homogenates. Previously, accurate measurements have been difficult to obtain because detergents, which are needed to disrupt membranes and unmask CO, also inhibit the enzyme by solubilizing certain phospholipids required for rapid turnover. We compared various methods of sample preparation, and found that maximal CO activity in homogenates could be obtained using specific concentrations of detergents. The range of optimal detergent concentrations was relatively narrow, as CO activity fell sharply with small deviations from the optimum. Of 5 detergents tested, deoxycholate stimulated CO maximally over the widest range of concentrations. In deoxycholate-treated homogenate samples, the calculated CO turnover number was about 480 s-1, indicating that overall enzyme activity was maximal or near maximal, and therefore that the total content of CO was probably detected. This method was reproducible with large or small samples (e.g., < 1 mg tissue), and should be applicable to studies of neural tissue in general.

Fecal bile acid excretion is one of the two major routes by which cholesterol is eliminated from the body, fecal cholesterol being the other. During their enterohepatic circulation, bile acids are secreted into the duodenum, pass down the jejunum and into the ileum where more than 95% is reabsorbed by the gut. Bile acids that escape reabsorption in the small intestine are metabolized by microorganisms in the large intestine. The major routes of metabolism are reported to be deconjugation, dehydroxylation, especially at the 7 alpha-hydroxy position, and dehydrogenation of the hydroxyl moieties. There are also some reports that saponifiable metabolites containing mostly deoxycholic acid form a major component of the bile acids found in human feces. We have identified a novel metabolite of cholic acid, 3 alpha-hydroxy polydeoxycholate, in both human and hamster feces that is the major constituent of these saponifiable metabolites. Furthermore, we have shown in hamsters that the animals that excreted more bile acid were excreting the additional bile acid as polydeoxycholate. As expected, there was a negative correlation between bile acid excretion in the feces and plasma cholesterol concentrations in these animals. We speculate that polydeoxycholate is formed in the lower gut of both humans and hamsters and that, by its formation, bile acid will be sequestered in an insoluble form, thus inhibiting its reabsorption by the gut. This process may help to reduce plasma cholesterol concentrations and coronary heart disease in humans.

The purification and the characterization of functional human liver UDP-glucuronosyltransferase 2B4 produced as a Staphylococcus aureus protein A fusion protein in E. coli are described. The purified fusion protein was able to catalyze the glucuronidation of hyodeoxycholic acid, the major substrate described for this isoform to date. The effects of the amount and the nature of the phospholipids upon reconstitution into phospholipid micelles were investigated. Apparent determined Km values for hyodeoxycholic acid and UDP-glucuronic acid were 0.55 and 0.43 mM, respectively. Moreover, photoaffinity labelling of the fusion protein with a photoactivatable analog of UDP-glucuronic acid strongly suggested that this recombinant protein exhibited similar binding properties as the microsomal protein, which emphasizes its use for further structural analyses.

We have developed a partially inbred substrain of New Zealand white rabbits (CRT/mlo) that are resistant to the hypercholesterolemia that accompanies cholesterol feeding to normal rabbits. The plasma cholesterol concentration of normal rabbits increases dramatically from about 30 mg/dl to > 300 mg/dl after they are fed a 0.1% cholesterol-enriched diet for 3-4 months. Cholesterol-fed CRT/mlo animals, however, maintain a cholesterol level of about 30 mg/dl during the entire cholesterol feeding period. In addition to the low plasma cholesterol level, measurements of cellular cholesterol indicate that the hepatic cholesterol content of the cholesterol-fed resistant rabbit remains markedly lower than it does in normal animals fed the same diet. The only mechanism for removal of significant quantities of cholesterol carbon from the body is via the fecal excretion of cholesterol, neutral sterol metabolites, and bile acids. In comparison to the basal, low-cholesterol diet, we observed that cholesterol-fed resistant rabbits had increased excretion of lithocholic acid, while excretion of this bile acid by cholesterol-fed normal rabbit remained similar to basal diet levels. Deoxycholic acid excretion, the other main bile acid excreted in the feces of rabbits, was decreased in response to cholesterol challenge in animals with either resistant or normal phenotypes, but the decrease was significantly less in the resistant rabbits. Thus, the resistant rabbits excreted relatively more lithocholic and deoxycholic acid than did the cholesterol-fed normal rabbit. The difference in bile acid excretion was also manifest by a higher than normal level of cholesterol 7 alpha-hydroxylase activity and cholesterol 7 alpha-hydroxylase mRNA in the livers from resistant versus normal rabbits. As cholesterol 7 alpha-hydroxylase is the putative rate-limiting step of bile acid synthesis, we believe that the increased excretion of bile acids by resistant animals is due, at least in part, to increased levels of cholesterol 7 alpha-hydroxylase expression.

The effects of bran and starchy endosperm fractions of oat and rye on faecal weight and on biliary and faecal bile acids were studied in Syrian golden hamsters (Mesocricetus auratus). The animals fed on diets supplemented with steam-flaked oat bran, oat bran or rye bran had higher wet and dry weights of faeces compared with the animals fed on the fibre-free or low-fibre endosperm diets. A higher mean percentage of biliary cholic acid and a lower mean percentage of chenodeoxycholic and lithocholic (LCA) acids was observed in the bran-supplemented dietary groups. Animals fed on the bran-supplemented diets had increased daily faecal excretion of both total saponifiable and total free bile acids compared with the animals fed on fibre-free or endosperm-supplemented diets. The mean percentage of total saponifiable bile acids in the faeces was higher, and that of free bile acids lower in the animals fed on bran-supplemented diets. A significantly lower concentration of faecal free LCA was observed in the animals fed on the rye-bran diet. Both bran and endosperm diets reduced the faecal LCA:deoxycholic acid compared with the fibre-free diet, but the bran diets had a more pronounced effect than endosperm diets.

Two active site-directed photoaffinity analogs, 5-[beta-32P]azido-UDP-glucuronic acid and 5-[beta-32P]azido-UDP-glucose, were used for the characterization of UDP-sugar-utilizing enzymes in human liver microsomes. Both compounds were recognized by human microsomal proteins: major photolabeled bands of 50-56 kDa were detected. Both photoincorporations were competitively decreased by increasing concentrations of either UDP-Glc or UDP-GlcUA, indicating a high affinity for both nucleotides. The patterns of photoaffinity labeling in the 50-56-kDa range by the two probes were significantly different, indicating the presence of different UDP-GlcUA- and UDP-Glc-specific enzymes of similar molecular mass. The presence of a UDP-Glc-dependent transferase was confirmed by the identification of an enzymatic activity catalyzing the formation of glucosides of the 6 alpha-hydroxylated bile acid hyodeoxycholic acid (3 alpha, 6 alpha-diOH (HDCA)) in the presence of UDP-Glc. The specific activity of 1.5-3.2 nmol/min/mg of protein was similar to that of 6 alpha-glucuronidation of HDCA. The apparent Km for UDP-Glc estimated with HDCA was 280 microM, and the formation of HDCA glucosides was strongly inhibited by UDP-GlcUA (apparent Ki = 7 microM). Evidence is presented that HDCA-specific UDP-glucuronosyltransferase (clone UGT2B4) expressed in V79 cells is not involved in glucosidation of HDCA and is not photolabeled with 5-[beta-32P]azido-UDP-Glc. Rigorous structure identification of the biosynthetic product proved that HDCA was glucosidated at the 6-position. Thus, this UDP-Glc-dependent activity catalyzing the biosynthesis of 6-O-glucosides of 6 alpha-hydroxylated bile acids represents a new pathway in the metabolism of these bile acids.

Dietary factors have been shown to affect excretion of fecapentaenes, potent mutagens present in human feces. Apart from effects of the diet on the bacterial synthesis of fecapentaenes in the bowel, fecapentaene excretion is likely to be indirectly influenced by the composition of the bowel contents, in particular fecapentaene-binding or -solubilizing factors. In the present study, interactions between dietary fiber and fecapentaene-12 (FP-12), as well as the effects of bile acids and calcium on the solubility of FP-12 in aqueous solutions, have been investigated in vitro. The results demonstrated that FP-12 may strongly adsorb to fiber, as indicated by reduced concentrations in the aqueous PBS phase when increasing amounts of fiber are added. This fecapentaene-binding capacity of fiber may explain the positive correlations that have previously been found between excreted fecapentaene concentrations and fiber consumption in human population studies. Further, it was found that at concentrations physiologically occurring in feces, both cholic and deoxycholic acid as well as mixtures of bile acids may increase the aqueous solubility of FP-12. This solubilizing effect of bile acids can be reduced by adding calcium at physiological concentrations of 2.5 mg/ml. It is hypothesized that high dietary fiber intake may increase fecapentaene excretion as a result of this fecapentaene fiber adsorption, which in turn may result in diminished exposure of the human bowel epithelium to these putative initiators of colorectal cancer. In contrast, high concentrations of fecal bile acids may act as fecapentaene-solubilizing factors which increase fecapentaene bioavailability, thereby possibly resulting in increased risk for colorectal cancer.

Ursodeoxycholic acid has been proposed for the treatment of primary biliary cirrhosis. The aim of this study was to evaluate the effect of ursodeoxycholic acid administration on bile acid metabolism in patients with early-stage primary biliary cirrhosis. Biliary bile acid composition, primary bile acid pool sizes, synthesis, and fractional turnover rate were measured before and after four weeks of ursodeoxycholic acid administration (600 mg/day) in nine patients with biopsy-proven primary biliary cirrhosis (stages I-III). Molar percentages of chenodeoxycholic, cholic, and deoxycholic acids in bile were significantly decreased by ursodeoxycholic acid administration, while its biliary concentration increased to 34.2% at the end of the same four-week period. The cholic and chenodeoxycholic acid pools decreased, although not significantly, while the deoxycholic acid pool was reduced by 60% (from 0.7 +/- 0.12 to 0.29 +/- 0.07 mmol, P < 0.002). Primary bile acid synthesis was slightly increased, and fractional turnover rate was significantly increased. The conversion rate of cholic to deoxycholic acid was measured and found to be significantly increased (P < 0.05) after ursodeoxycholic acid administration; however, serum levels of both free and conjugated deoxycholic acid were significantly decreased (from 23.2 +/- 9.7 to 3.8 +/- 1.9 mumol/liter, P < 0.001). We conclude that in patients with primary biliary cirrhosis, ursodeoxycholic acid administration replaces endogenous bile acids in the enterohepatic circulation by increasing bile acid fractional turnover rate without significant increments of their hepatic synthesis.

The metabolism and time-courses of urinary and fecal excretions of murideoxycholic acid (MDCA; 3 alpha,6 beta-dihydroxy-5 beta-cholanoic acid), a 6 beta-hydroxylated bile acid, was investigated in man. The study was carried out in two groups of subjects. Six cholecystectomized patients fitted with a cystic duct drain ingested 100 mg of a tracer dose of 3H-MDCA. Time-course of radioactivity in plasma was then followed for an 8-h period. Biliary, urinary and fecal excretions of radioactivity were measured for a 5-day period and excreted MDCA metabolites were identified. Five lithiasic patients with intact enterohepatic circulation ingested 500 mg of the same tracer dose of 3H-MDCA. Radioactivity in plasma was followed for a 49-h period and urinary and fecal excretions of radioactivity were measured daily for 7 days. In the first group, the excretion of the radioactivity by the three routes (bile+urine+feces) reached 97.8 +/- 1.5% of the ingested dose but dropped to 75 +/- 8.3% (urine+feces) in patients in the second group. In cholecystectomized patients, the estimation of intestinal MDCA absorption was dependent on cystic duct drain flow rate and gave values ranging from 20% to 87%. The biological half-life of MDCA in lithiasic patients averaged 3.4 +/- 0.7 days. Radioactivity appeared in the plasma in the first hour and reached a maximum 6 and 3 h after the beginning of the experiment in group I and II respectively. In the second group, another peak of radioactivity in plasma was observed just after breakfast.(ABSTRACT TRUNCATED AT 250 WORDS)

Arachidonic acid (AA) activates brain protein kinase C (PKC) in a specific manner, and which differs from that of diacylglycerol (DG)-mediated PKC activation in cofactor Ca2+ and phosphatidylserine (PtdSer) requirements. We presently report that characteristics of AA-mediated activation are heterogenous, and are dependent upon the concentrations of AA. Highly sensitive PKC activation (HS) occurring at concentrations of 20 microM AA can be distinguished from less sensitive PKC activation (LS) requiring concentrations of at least 160 microM AA, on the basis of the effects of phorbol ester TPA or DG, phosphatidylcholine (PtdCho) and sodium deoxycholate (DOC). TPA, like DG suppressed the HS reaction whereas it enhanced the LS reaction. PtdCho, a phospholipid which does not affect DG-mediated activation, also prevented the HS reaction without affecting the LS reaction. This latter was inhibited at 100 microM DOC, a concentration which slightly stimulated the HS reaction. The substrate specificity was also different in the two reactions: the preferential substrate for PKC in HS was histone type VII-S, while it was histone type V-S in LS. Both reactions were similarly affected by PtdSer. In 0.1 mM CaCl2, PtdSer stimulated AA-mediated activation without evoking additive responses while this phospholipid prevented this activation in 0.5 mM EGTA, suggesting that AA and PtdSer bind PKC on the same or related sites. Together these results provide evidence for the existence of different modes of AA-mediated PKC activation with unique characteristics which presumably involve two different binding sites for AA on the same molecule and/or different PKC isoforms.

Metabolism of cholic acid, chenodeoxycholic acid, ursodeoxycholic acid, and deoxycholic acid by the grown cells of the bacterium Alcaligenes recti suspended in water was studied. Each isolated metabolite was characterized by the application of various spectroscopic methods. Cholic acid, chenodeoxycholic acid, ursodeoxycholic acid, and deoxycholic acid yielded methylated derivatives 3 alpha-methoxy-7 alpha, 12 alpha-dihydroxy-5 beta-cholanoic acid, 3 alpha-methoxy-7 alpha-hydroxy-5 beta-cholanoic acid, 3 alpha-methoxy-7 beta-hydroxy-5 beta-cholanoic acid, and 3 alpha-methoxy-12 alpha-hydroxy-5 beta-cholanoic acid, respectively. In addition, cholic acid furnished 7 alpha, 12 alpha-dihydroxy-3-oxochol-4-en-24-oic acid; chenodeoxycholic acid gave 7 alpha-hydroxy-3-oxo-5 beta-cholanoic acid and 7 alpha-hydroxy-3-oxochol-4-en-24-oic acid while ursodeoxycholic acid yielded 7 beta-hydroxy-3-oxochol-4-en-24-oic acid and 3-oxochola-4,6-dien-24-oic acid. The formation of various metabolites showed that two competitive enzymic reactions, i.e., selective methylation of the 3 alpha-hydroxy group and dehydrogenation in the A/B rings, were operative. The methylation process was found to be enzymic involving an S-adenosyl-L-methionine (AdoMet)-dependent methyl transferase, and this reaction appeared to be inhibitory to the process of degradation of the ring system. In the other reaction sequence, degradation of the ring system was initiated by dehydrogenation of the 3 alpha-hydroxy group. A 7 beta-dehydratase activity producing the delta 6 double bond was also noticeable in the metabolism of ursodeoxycholic acid.

We treated 6 patients with Stage II primary biliary cirrhosis with cholic acid (CA) 10 mg.kg-1 per day for 3 months and then with the same dose of ursodeoxycholic acid (UDCA). A matching group of 6 patients was observed for 3 months without any therapy. Liver function tests and serum and stool bile acids were investigated before, during and at the end of CA and UDCA therapy. The results of liver function tests deteriorated after 6-8 weeks of CA therapy and the changes were correlated (r = 0.92) with an increase in alpha-dihydroxy-bile acids (chenodeoxycholic acid and deoxycholic acid) in the serum. The 24 h excretion of DCA in 24 h faeces was markedly increased. Ursodeoxycholic acid treatment improved liver function tests; after 4 weeks glutamate dehydrogenase (GLDH) had decreased. After 8-12 weeks of therapy ursodeoxycholic acid had increased to 50-60% of the total serum bile acids whereas the more apolar bile acids were significantly decreased. No changes in liver function tests or bile acid metabolism were found in the untreated group. Since CA and UDCA are non-toxic in man, this trial indicates that the apolar bile acids chenodeoxycholic acid and deoxycholic acid may be responsible for the deterioration of liver function in primary biliary cirrhosis. However, the therapeutic effect of UDCA cannot be explained merely by the decrease in alpha-dihydroxy-bile acids in the serum, since the laboratory results had improved prior to the decrease in the serum apolar bile acids.

The aim of this study was to define whether N-acetylglucosaminidation is a selective conjugation pathway of structurally related bile acids in humans. The following bile acids released enzymatically from N-acetylglucosaminides were identified: 3 alpha,7 beta-dihydroxy-5 beta-cholanoic (ursodeoxycholic), 3 beta, 7 beta-dihydroxy-5 beta-cholanoic (isoursodeoxycholic), 3 beta,7 beta-dihydroxy-5 alpha-cholanoic (alloisoursodeoxycholic), 3 beta,7 beta-dihydroxy-5-cholenoic, 3 alpha,7 beta,12 alpha-trihydroxy-5 beta-cholanoic, and 3 alpha,6 alpha,7 beta-trihydroxy-5 beta-cholanoic acids. The selectivity of conjugation was studied by administration of 0.5 g ursodeoxycholic (UDCA) or hyodeoxycholic (HDCA) acids, labeled with 13C, to patients with extrahepatic cholestasis, and of 0.5 g of 13C-labeled chenodeoxycholic acid (CDCA) to patients with extra- or intrahepatic cholestasis. After administration of [24-13C]-CDCA, labeled glucosides, and the glucuronide of CDCA were excreted in similar amounts. Labeled N-acetylglucosaminides of UDCA and isoUDCA were also formed. When [24-13C]-UDCA was given, 13C-label was detected in the N-acetylglucosaminide, the glucosides, and the glucuronide of UDCA, and in the N-acetylglucosaminide of isoUDCA. In the patient studied, 32% of the total UDCA excreted in urine was conjugated with N-acetylglucosamine. In contrast, 96% of the excreted amount of [24-13C]HDCA was glucuronidated, and 13C-labeled glucosides but no N-acetylglucosaminide were detected. The selectivity of N-acetylglucosaminidation towards bile acids containing a 7 beta-hydroxyl group was confirmed in vitro using human liver and kidney microsomes and uridine diphosphate glucose (UDP)-N-acetylglucosamine. These studies show that N-acetylglucosaminidation is a selective conjugation pathway for 7 beta-hydroxylated bile acids.

Two human liver UDP-glucuronosyltransferase cDNA clones, HLUG25 [Jackson, M. R., et al. (1987) Biochem. J. 242, 581-588] and UDPGTh-2 [Ritter, J. K., et al. (1990) J. Biol. Chem. 266, 7900-7906] have previously been shown to encode isozymes active in the glucuronidation of hyodeoxycholic acid (HDCA) and certain estrogen derivatives (estriols and 3,4-catechol estrogens), respectively. Here we report that the UDPGTh-2-encoded isoform (udpgth-2) and the HLUG25-encoded isoform (udpgth-1) have parallel aglycon specificities. Following expression in COS-1 cells, each isoform metabolized three types of dihydroxy- or trihydroxy-substituted ring structures, including the 3,4-catechol estrogen (4-hydroxyestrone), estriol and 17-epiestriol, and HDCA, but the udpgth-2 isozyme is 100-fold more efficient than udpgth-1. udpgth-1 and udpgth-2 are 86% identical overall (76 differences out of 528 amino acids), including 55 differences in the first 300 amino acids of the amino terminus, a domain which confers isoform substrate specificity. The data indicate that a high level of conservation in the amino terminus is not required for the preservation of substrate selectivity. Analysis of glucuronidation activity encoded by UDPGTh-1/UDPGTh-2 chimeric cDNAs constructed at their common restriction sites, SacI (codon 297), NcoI (codon 385), and HhaI (codon 469), showed that nine amino acids between residues 385 and 469 are important for catalytic efficiency, suggesting that this region represents a domain which is critical for catalysis but distinct from that responsible for aglycon selection.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Bile salts are potent inhibitors of bovine carbonic anhydrase and human carbonic anhydrase I and human carbonic anhydrase II. To further characterize the binding of bile salts to carbonic anhydrase, rate constants for the CO2 hydration reaction in the presence of deoxycholate, cholate, glycocholate and taurocholate were determined using stop-flow experiments. Values for the Michaelis-Menton dissociation constant for bovine carbonic anhydrase, human carbonic anhydrase I and human carbonic anhydrase II were found to be 5.2, 9.2 and 13.2 mmol/L, respectively. The inhibition constant values for the various bile salts tested ranged from 0.1 to 1 mmol/L for bovine carbonic anhydrase, 1.6 to 2.4 mmol/L for human carbonic anhydrase I and 0.09 to 0.7 mmol/L for human carbonic anhydrase II. Our results suggest a mechanism of noncompetitive carbonic anhydrase inhibition for bile salts. Bile-salt binding to carbonic anhydrases as measured by scanning molecular sieve chromatography resulted in an increase in partition radius, molecular volume and surface area. The partition radius increased from 24 A to 28 A in the presence of 2.5 mmol/L sodium deoxycholate at critical micelle concentration. As determined by sedimentation equilibrium measurements, approximately 1 gm of carbonic anhydrase will bind 0.03 gm of deoxycholate, suggesting three to six binding sites for bile salt on the carbonic anhydrase molecule. The conformational changes and inhibition of carbonic anhydrases resulting from bile-salt binding may be important to the regulation of enzymatic activity in tissues along the enterohepatic circulation; by limiting bicarbonate availability this interaction may also contribute to the metabolic derangements seen in patients with cholestatic liver disease.

In order to study the glycosidic conjugation of chenodeoxycholic, hyodeoxycholic, and ursodeoxycholic acids in patients with cholestasis after oral administration of pharmacological amounts of the respective bile acids avoiding the application of radioactive tracers we synthesized [24-13C]chenodeoxycholic, [24-13C]hyodeoxycholic, and [24-13C]ursodeoxycholic acids. The reaction intermediates of the bile acid syntheses were characterized by infrared spectroscopy. Purity was confirmed using thin-layer chromatography as well as gas chromatography-mass spectrometry. The 13C atom excess of approximately 90% of the synthesized bile acids was the same as the 13C atom excess of the sodium [13C]cyanide used for the labeling reaction confirming the successful synthesis. After oral administration of 0.5 g of [24-13C]ursodeoxycholic acid to a healthy volunteer, 13C label was detected in the nonamidated and glycine- or taurine conjugated glucosides and the N-acetylglucosaminide of ursodeoxycholic acid in urine. This establishes ursodeoxycholic acid as the first bile acid so far known to undergo both of the recently described glycosidic conjugation reactions in humans.

The enzyme hyodeoxycholic-acid: UDP-glucuronosyltransferase was purified about 230-fold from a solubilized human liver microsomal preparation utilizing anion-exchange chromatography, ampholyte-displacement chromatography and UDP-hexanolamine--Sepharose affinity chromatography. The homogeneity of the final enzyme preparation was judged by two criteria: the appearance of a single band of Mr 52000 in SDS/PAGE; the elution of a single peak in reversed-phase FPLC. The isolated enzyme catalyzed the glucuronidation of the 6 alpha-hydroxy bile acids hyodeoxycholic and hyocholic acids, and of the steroid hormone estriol, with a ratio of relative reaction rates of 13:1:2.7. UDP-glucuronosyltransferase activities toward the 3 alpha-hydroxy bile acid lithocholic acid, androsterone, testosterone, bilirubin and p-nitrophenol were not detectable in the pure enzyme preparation and were shown to be separated from enzyme activity toward hyodeoxycholic acid during ampholyte-displacement chromatography and/or UDP-hexanolamine--Sepharose affinity chromatography. Two-substrate kinetic analysis of hyodeoxycholic-acid-conjugating activity gave a sequential mechanism with apparent Km values of 12 microM and 4 microM for hyodeoxycholic acid and UDP-glucuronic acid, respectively. Phospholipids were required for reconstitution of maximal activity toward hyodeoxycholic acid. Phosphatidylcholine was the most effective activator of enzyme activity.

Our aim was to examine the relationship between biliary deoxycholate and arachidonate in obese patients and the relationship of deoxycholate and arachidonate to the stimulation of biliary mucous glycoprotein among obese patients predisposed to cholesterol gallstones. Thirty-four obese patients predisposed to cholesterol gallstones by a weight-reducing diet (520 kcal/day) received placebo, ursodiol (1200 mg/day), or aspirin (1300 mg/day). Duodenal bile was collected prior to beginning the diet and at four weeks. There was no correlation between deoxycholate and arachidonate among the 34 patients before beginning the diet. With placebo, deoxycholate decreased while arachidonate and glycoprotein increased. With ursodiol, deoxycholate decreased while arachidonate decreased and glycoprotein did not change. With aspirin, there was no change in deoxycholate but a decrease in arachidonate and no change in glycoprotein. Our data do not support a role for biliary deoxycholate in the regulation of biliary arachidonate. Our data do support a role for arachidonate, but not deoxycholate, in the regulation of biliary glycoprotein during the formation of cholesterol gallstones.

Patients with familial adenomatous polyposis have an excess risk for adenomas and cancers of the upper and lower gastrointestinal tract. In the upper intestine these lesions occur mainly around the ampulla of Vater and they parallel mucosal exposure to bile. In view of this finding and of evidence that bile acids play a role in colorectal carcinogenesis, biliary bile acid profiles were determined in 29 patients with familial adenomatous polyposis (12 before colectomy, 17 after colectomy) and in 28 patients without familial adenomatous polyposis (all with colons in situ). Patients with familial adenomatous polyposis had a higher total biliary bile acid concentration than the others. The bile of patients with polyposis had a greater proportion of chenodeoxycholic acid and a lower proportion of deoxycholic acid than did the bile of patients without polyposis. The ratio of chenodeoxycholic acid and its metabolite lithocholic acid to cholic acid and its metabolite deoxycholic acid, which is related to subsequent bile acid profiles in the colon, was higher in patients with polyposis. Because bile acids influence cellular proliferation, these findings may be of importance with respect to intestinal adenoma and cancer growth.

Two human liver UDP-glucuronosyltransferase cDNA clones (HLUGP1 and HLUG25) were individually inserted into the eukaryotic expression vector pKCRH2. Each recombinant plasmid was cotransfected with a SFVneo vector, thereby allowing establishment of several V79 cell lines retaining the exogenous UDP-glucuronosyltransferase cDNA after selection with G418 (Geneticin). Southern blot analysis suggested that the cDNAs were integrated into the host cell genome. Northern blot and immunoblot analyses indicated that the cDNAs were correctly transcribed and translated for the production of functional enzymes. The established recombinant V79 cell lines stably expressed the UDP-glucuronosyltransferase activities towards 1-naphthol (HLUGP1) and hyodeoxycholic acid (HLUG25) at levels 10-20-fold higher than with transient expression, and in the range found in human liver. These high levels of expression of UDP-glucuronosyltransferase activity allowed the determination of apparent kinetic constants and substrate specificities of glucuronidation in the genetically engineered cell lines. HLUG25 cDNA encoded an isoform with restricted specificity towards the 6-OH group of the bile acid hyodeoxycholic acid. The other steroids, bile acids, endobiotics, and xenobiotics tested as substrates were glucuronidated in various samples of human liver microsomes, but not by this isoenzyme. This study, allowing the expression of individual UDP-glucuronosyltransferases in heterologous cells with no endogenous transferases, offered a unique solution for the characterization of UDP-glucuronosyltransferase functional heterogeneity.

We previously reported that the 7 alpha-dehydroxylation of cholic acid appears to be carried out by a multi-step pathway in intestinal anaerobic bacteria both in vitro and in vivo. The pathway is hypothesized to involve an initial oxidation of the 3 alpha-hydroxy group and the introduction of a double bond at C4-C5 generating a 3-oxo-4-cholenoic bile acid intermediate. The loss of water generates a 3-oxo-4,6-choldienoic bile acid which is reduced (three steps) yielding deoxycholic acid. We synthesized, in radiolabel, the following putative bile acid intermediates of this pathway 7 alpha,12 alpha-dihydroxy-3-oxo-4-cholenoic acid, 7 alpha,12 alpha-dihydroxy-3-oxo-5 beta-cholanoic acid, 12 alpha-dihydroxy-3-oxo-4,6-choldienoic acid, and 12 alpha-hydroxy-3-oxo-4-cholenoic acid and showed that they could be converted to 3 alpha,12 alpha-dihydroxy-5 beta-cholanoic acid (deoxycholic acid) by whole cells or cell extracts of Eubacterium sp. VPI 12708. During studies of this pathway, we discovered the accumulation of two unidentified bile acid intermediates formed from cholic acid. These bile acids were purified by thin-layer chromatography and identified by gas-liquid chromatography-mass spectrometry as 12 alpha-hydroxy-3-oxo-5 alpha-cholanoic acid and 3 alpha,12 alpha-dihydroxy-5 alpha-cholanoic (allo-deoxycholic acid). Allo-deoxycholic acid was formed only in cell extracts prepared from bacteria induced by cholic acid, suggesting that their formation may be a branch of the cholic acid 7 alpha-dehydroxylation pathway in this bacterium.

We have studied the effect of two surfactants, one non-ionic, lauryl sucrose (LS) and the other ionic, sodium deoxycholate (DOC), on the aggregation state of amphotericin B (AmB) and its selectivity towards ergosterol and cholesterol. It is shown that the addition of these surfactants has very similar effects on the AmB micelles. Below the critical micellar concentration of the surfactants, mixed micelles with AmB are first formed as a result of the penetration of the surfactant molecules into the AmB micelles. At higher concentrations of the surfactant molecules, the micellar structure is completely destroyed and AmB is found as monomers in solution. When the concentration of the surfactant is further increased, micelles of the surfactant molecules are built up, AmB remaining in monomeric form. However, the critical micellar concentration of LS is modified by the presence of AmB in solution, while that of DOC is not affected, thereby indicating that the interactions of AmB with LS are stronger than those of DOC with AmB. We also show that both surfactants enhance the selectivity of the AmB binding to sterols at exactly the concentrations of the surfactants which induce the monomerization of the antibiotic. It is observed that the maximal selectivity is found at a concentration of the surfactants corresponding to their particular CMC in presence of the antibiotic.

An association between colorectal cancer and previous peptic ulcer surgery is reported. In a prospective screening study, 100 asymptomatic patients (80 men and 20 women) who had undergone truncal vagotomy at least 10 years previously were investigated by barium enema, colonoscopy and gallbladder ultrasonography. Control data were obtained from forensic autopsy subjects. The incidence of neoplasms greater than or equal to 1.0 cm in the vagotomized group was 14 per cent (11 adenomas, 3 carcinomas) and 3 per cent in controls (P = 0.01). Duodenal bile obtained at endoscopy from 21 vagotomized patients with normal gallbladders and from 21 control patients undergoing endoscopy was analysed by high performance liquid chromatography. The mean percentage of cholic (CA), chenodeoxycholic (CDCA), deoxycholic (DCA) and lithocholic (LCA) acids in the bile of vagotomized patients was 32.3, 45.6, 20.7 and 1.4 per cent respectively compared with 45.3, 36.2, 17.9 and 0.7 per cent respectively in controls. The increased proportions of CDCA and LCA and decreased proportions of CA in the duodenal bile of vagotomized patients were significant (P less than 0.001; P = 0.02; P = 0.007). Abnormalities in bile acid metabolism may help to explain the increased risk of colorectal neoplasia 10 years after truncal vagotomy.

The role of hepatocytes in bile acid and cholesterol metabolism has been extensively studied. By contrast, nothing is known about the role of bile ductular epithelial cells in cholesterol and bile acid metabolism. The purpose of the current studies was to establish whether bile ductular epithelial cells synthesize cholesterol, bile acids or both and to determine whether these cells are capable of metabolizing (hydroxylating, conjugating) bile acids. Bile ductular epithelial cells were isolated from rat liver after ligation of the common bile duct for 6 to 8 wk. Bile ductular epithelial cells were essentially free (greater than 99%) of hepatocytes and were histochemically positive (greater than 80%) for gamma-glutamyl transpeptidase activity. Cholestatic hepatocytes were simultaneously isolated and characterized with regard to their ability to synthesize and metabolize bile acids. Incubation of bile ductular epithelial cells with [14C]-acetate resulted in rapid labeling of cellular cholesterol, suggesting that these cells have a complete cholesterol biosynthetic pathway. The addition of [4-14C]-cholesterol to bile ductular epithelial cells did not lead to detectable synthesis of [14C]-bile acids. [24-14C]-Cholic acid, [24-14C]-deoxycholic acid, [24-14C]-lithocholic acid and [3H]-ursodeoxycholic acid were individually added to bile ductular epithelial cells and incubated for 24 or 48 hr. Bile acid metabolites were extracted and separated by C-18 reverse-phase high-performance liquid chromatography or thin-layer chromatography. Bile ductular epithelial cells conjugated deoxycholic acid, ursodeoxycholic acid and lithocholic acid to glycine and taurine. Surprisingly, no conjugation of cholic acid was detected. Conjugated lithocholic acid was further metabolized to highly polar metabolite(s), possibly beta-muricholic acid.(ABSTRACT TRUNCATED AT 250 WORDS)

Male ExHC (exogenous hypercholesterolemic) rats were either prematurely weaned at 17 days of age or allowed to nurse until 35 days of age. The prematurely weaned rats were either fed a diet containing cholestyramine or cholestyramine-free diet until 35 days of age. Cholestyramine supplementation markedly increased fecal bile acid excretion and modified the composition. After giving a stock diet for 7 weeks, all rats received a cholesterol-enriched diet for 9 weeks. The serum cholesterol level in later time was not affected by early dietary manipulation. The activity of hepatic cholesterol 7 alpha-hydroxylase and fecal bile acid excretion at the end of the cholesterol challenge decreased in the cholestyramine-pretreated group, when compared to the normally weaned group. Fecal excretion and the ratio of the secondary (deoxycholic and lithocholic acids) to the primary (cholic and chenodeoxycholic acids) bile acids significantly decreased in the early cholestyramine-treated group. These results suggest that a modification of bile acid metabolism in early life may strongly influence the hepatic and possibly colonic bile acid metabolism in later life, when challenged with a high-cholesterol diet.

Experiments were performed using isolated mucosal cells from the rat jejunum or using the perfused jejunum in the anesthetized rat to test whether lipophilic unconjugated dihydroxy bile acids are absorbed from the proximal small intestine via the same carrier mechanism involved in the uptake of long chain fatty acids. With isolated jejunal mucosal cells, the cellular uptake rate of deoxycholic acid or chenodeoxycholic acid increased linearly with time, showed no evidence of saturation, and was not decreased by the presence of a monospecific antibody to the membrane fatty acid binding protein. In contrast, oleate uptake was saturable, was inhibited by the same antibody, but was not affected by the presence of chenodeoxycholic acid or deoxycholic acid. Bile acid uptake by isolated enterocytes occurred at one-eighth the rate of fatty acid uptake if expressed in relation to total solute concentration; if expressed in relation to monomeric concentration, initial bile acid uptake was four orders of magnitude slower than fatty acid uptake. In the isolated perfused jejunal segment, chenodeoxycholic acid and deoxycholic acid uptake was not influenced by the presence of the antibody to membrane fatty acid binding protein, whereas absorption of oleate was inhibited by more than 70%. These experiments indicate that absorption of unconjugated lipophilic dihydroxy bile acids in the rodent jejunum does not involve the carrier mediated uptake mechanism involved in the absorption of long chain fatty acids--the mechanism is likely to be passive nonionic diffusion.

Infection of the biliferous system in patients with cholelithiasis was shown to be the most frequent when the levels of cholic acid in bile were low. Physiological concentrations of cholic and deoxycholic acids have antimicrobial activity against organisms not adapted to the presence in bile. Outer drainage of the bile ducts was accompanied by an increase in the levels of cholic acid when at the background of outer decompression bacteria were eliminated from the biliferous system. In vitro studies revealed a synergistic antibacterial effect of cholic and deoxycholic acid combinations with cefazolin.

It was previously reported that in chromatophores of Rhodospirillum rubrum, reaction center, which consists of three kinds of protein (Mm, about 78K), is a small fragment of a large protein complex (PRU; photoreaction unit), which contains six other kinds of protein including light-harvesting bacteriochlorophyll protein, has Mm of about 700K and is free of phospholipid [J. Biochem. 86, 1211-1224 (1979); 94, 1815-1826 (1983(]. In the present study, the photosynthetic, cyclic electron transport system sensitive to antimycin A was effectively reconstructed by incubating 60 nM PRU (which contained 1 mol of reaction center and 2 mol of ubiquinone-10 per mol) with 300 nM each of oxidized ubiquinone-10 protein, reduced cytochrome c2 and lipoamino acid (which were all purified from Rhodospirillum rubrum) in the presence of low concentrations of cholate and deoxycholate (pH 8.0). In the light, the cytochrome was oxidized while the quinone was reduced. The oxidation and reduction each progressed rapidly at first, then slowly, reaching maxima (steady states) 1-2 min after the light had been turned on. At the steady states, 30% of the cytochrome was oxidized while 11% of the total quinone was reduced. When the light was turned off, the original oxidation-reduction states of the cytochrome and quinone were restored at rapid rates initially then at slow rates. Antimycin A stimulated the slow rates in the light-on state and depressed them in the light-off state, but did not influence the fast rates. Ubiquinone-10 protein was required for the antibiotic-sensitive, slow oxidation reactions. This indicates that the slow rates were due to cyclic electron transport. Cytochrome c2 was tightly bound to PRU at a molar ratio of 1:1. This cytochrome as well as the quinone bound to PRU was responsible for the fast rates. PRU had other sites able to bind cytochrome c2 and ubiquinone-10 protein with Km of 0.4 and 0.1 microM, respectively. Of the polar lipids tested, lipoamino acid was the most effective for reconstruction, and its effect was maximal at 300 nM, which is far below its critical micelle concentration.

Kinetic studies of cholic and chenodeoxycholic acids were carried out in three patients by simultaneous intravenous administration of appropriate pairs of (3)H- and (14)C-labeled compounds. The results obtained indicated two sources of error: chemical impurity and loss of tritium by biological exchange. Precautions are listed for use of tritiated bile acids in studies of pool sizes and turnover rates.

Relative concentrations of conjugated and sulfated bile acids in duodenal bile were measured in 5 patients before and during treatment with 0.50-0.75 g of chenodeoxycholic acid per day for 3-4 months. Lithocholic acid constituted 0.8-3.3% (mean 1.8%) of total conjugated and sulfated bile acids before and 0-5.4% (mean 2.6%) during treatment. Lithocholic acid was the predominant bile acid in the sulfate fraction in three patients and chenodeoxycholic acid in two. Sulfated bile acids constituted less than 1% of total bile acids and did not increase during treatment. Ursodeoxycholic acid, the other major metabolite of chenodeoxycholic acid, was found in higher amounts during therapy. The unsaturated bile acid 3beta-hydroxy-delta5-cholenic acid, which was found exclusively as its sulfate ester, showed a slight fall. The average G/T conjugation ratio rose from 2.2 to 4.5.