Parameters in 7-alpha-dehydroxylation of bile acids by anaerobic lactobacilli

Bile Acids Activated Receptors in Inflammatory Bowel Disease

Once known exclusively for their role in nutrients absorption, bile acids have emerged as signaling molecules, generated from cholesterol breakdown, acting on several immune cells by activating a variety of receptors including the G protein-coupled bile acid receptor 1 (GPABR1 or TGR5), the Farnesoid-X-receptor (FXR) and, as recently discovered, the retinoid-related orphan receptors (ROR)γt. GPBAR1, FXR, and RORγt are highly expressed in cells of the innate and adaptive immune system (i.e., dendritic cells (DCs), macrophages, innate lymphoid 3 cells (ILC3s), and T helper 17 (Th17) lymphocytes) and plays an important role in regulating intestinal and liver immunity, highlighting a role for various bile acid species in regulating immune responses to intestinal microbial antigens. While primary bile acids are generated from the cholesterol breakdown secondary bile acids, the GPBAR1 ligands, and oxo-bile acids derivatives, the RORγt ligands, are generated by the intestinal microbiota, highlighting the potential of these bile acids in mediating the chemical communication between the intestinal microbiota and the host. Changes in intestinal microbiota, dysbiosis, alter the composition of the bile acid pool, promoting the activation of the immune system and development of chronic inflammation. In this review, we focus on the molecular mechanisms by which an altered bile acid signaling promotes intestinal inflammation.

Bile Acid Signaling in Inflammatory Bowel Diseases

Bile acids are a group of chemically different steroids generated at the host/microbial interface. Indeed, while primary bile acids are the end-product of cholesterol breakdown in the host liver, secondary bile acids are the products of microbial metabolism. Primary and secondary bile acids along with their oxo derivatives have been identified as signaling molecules acting on a family of cell membrane and nuclear receptors collectively known as "bile acid-activated receptors." Members of this group of receptors are highly expressed throughout the gastrointestinal tract and mediate the bilateral communications of the intestinal microbiota with the host immune system. The expression and function of bile acid-activated receptors FXR, GPBAR1, PXR, VDR, and RORγt are highly dependent on the structure of the intestinal microbiota and negatively regulated by intestinal inflammation. Studies from gene ablated mice have demonstrated that FXR and GPBAR1 are essential to maintain a tolerogenic phenotype in the intestine, and their ablation promotes the polarization of intestinal T cells and macrophages toward a pro-inflammatory phenotype. RORγt inhibition by oxo-bile acids is essential to constrain Th17 polarization of intestinal lymphocytes. Gene-wide association studies and functional characterizations suggest a potential role for impaired bile acid signaling in development inflammatory bowel diseases (IBD). In this review, we will focus on how bile acids and their receptors mediate communications of intestinal microbiota with the intestinal immune system, describing dynamic changes of bile acid metabolism in IBD and the potential therapeutic application of targeting bile acid signaling in these disorders.

In vitro and in vivo characterization of Clostridium scindens bile acid transformations

The human gut hosts trillions of microorganisms that exert a profound influence on human biology. Gut bacteria communicate with their host by secreting small molecules that can signal to distant organs in the body. Bile acids are one class of these signaling molecules, synthesized by the host and chemically transformed by the gut microbiota. Among bile acid metabolizers, bile acid 7-dehydroxylating bacteria are commensals of particular importance as they carry out the 7-dehydroxylation of liver-derived primary bile acids to 7-dehydroxylated bile acids. The latter represents a major fraction of the secondary bile acid pool. The microbiology of this group of gut microorganisms is understudied and warrants more attention. Here, we detail the bile acid transformations carried out by the 7-dehydroxylating bacterium Clostridium scindens in vitro and in vivo. In vitro, C. scindens exhibits not only 7α-dehydroxylating capabilities but also, the ability to oxidize other hydroxyl groups and reduce ketone groups in primary and secondary bile acids. This study revealed 12-oxolithocholic acid as a major transient product in the 7α-dehydroxylation of cholic acid. Furthermore, the in vivo study included complementing a gnotobiotic mouse line (devoid of the ability to 7-dehydroxylate bile acids) with C. scindens and investigating its colonization dynamics and bile acid transformations. Using NanoSIMS (Nanoscale Secondary Ion Mass Spectrometry), we demonstrate that the large intestine constitutes a niche for C. scindens, where it efficiently 7-dehydroxylates cholic acid to deoxycholic acid. Overall, this work reveals a novel transient species during 7-dehydroxylation as well as provides direct evidence for the colonization and growth of 7-dehydroxylating bacteria in the large intestine.

Polysaccharide from seeds of Plantago asiatica L. increases short-chain fatty acid production and fecal moisture along with lowering pH in mouse colon

Mice (20.0 ± 2.0 g, n = 48 per group) were given 30 days oral administration of polysaccharide from Plantago asiatica L. seeds at the dose of 0.4 g/kg body weight by gavage to investigate the effects of the polysaccharide on mouse colon. Results showed that the concentrations of total short-chain fatty acids (SCFA), acetic, propionic, and n-butyric acids in mouse colonic content of polysaccharide treated group were all significantly higher than that of control group (water) (p < 0.05). In addition, moisture of mouse colonic content of polysaccharide treated group was also notably higher than that of the control group (p < 0.05) indicating the intake of polysaccharide from P. asiatica L. resulted in a stronger water-holding capacity for colonic content throughout the experimental period. Furthermore, a decreased pH (from 7.5 ± 0.1 to 7.2 ± 0.1) was observed in mouse colon of the polysaccharide treated group compared with the control group (pH from 7.5 ± 0.1 to 7.5 ± 0.1). These results suggested that the intake of the polysaccharide from P. asiatica L. might be beneficial for the colon health.

Purification and Characterization of Conjugated Bile Salt Hydrolase from Bifidobacterium longum BB536

Bifidobacterium species deconjugate taurocholic, taurodeoxycholic, taurochenodeoxycholic, glycocholic, glycodeoxycholic, and glycochenodeoxycholic acids. The enzyme level increases in the growth phase. No increase in activity is observed for the cytoplasmic enzyme after addition of conjugated bile acids to a stationary-phase culture. Conjugated bile salt hydrolase (BSH) was purified from Bifidobacterium longum BB536. Its apparent molecular mass in denaturing polyacrylamide gel electrophoresis was ca. 40,000 Da. The intact enzyme had a relative molecular weight of ca. 250,000 as determined by gel filtration chromatography, suggesting that the native BSH of B. longum is probably a hexamer. The purified enzyme is active towards both glycine and taurine conjugates of cholate, deoxycholate, and chenodeoxycholate. The pH optimum is in the range of 5.5 to 6.5. A loss of BSH activity is observed after incubation at temperatures higher than 42(deg)C; at 60(deg)C, 50% of the BSH activity is lost. The importance of free sulfhydryl groups at the enzyme active center is suggested. For B. longum BB536, no significant difference in the initial rate of deconjugation and enzymatic efficiency appears between bile salts. The enzymatic efficiency is higher for B. longum BB536 than for other genera. In this paper, a new method which permits a display of BSH activity directly on polyacrylamide gels is described; this method confirms the molecular weight obtained for B. longum BB536 BSH.

Effect of clindamycin given alone or with Lactobacillus delbrueckii and Streptococcus thermophilus on 7alpha-dehydroxylation of bile acids in rats

OBJECTIVES: To evaluate the influence of clindamycin, given alone or with Lactobacillus delbrueckii and Streptococcus thermophilus to conventional rats, on 7alpha-dehydroxylation of cholic acid to deoxycholic acid. METHODS: The presence of deoxycholic acid was determined by gas-liquid chromatography. The fecal concentration of clindamycin was determined on PDM antibiotic sensitivity medium. Colony-forming units of L. delbrueckii and S. thermophilus were counted on lactic acid bacteria agar, and their ability to deconjugate was determined by thin-layer chromatography. RESULTS: Clindamycin significantly reduced the formation of deoxycholic acid, while the administration of lactobacilli-streptococci at the same time significantly reduced the effect of the antibiotic (p<0.05). CONCLUSIONS: Clindamycin reduced the formation of deoxycholic acid in rats and this effect was diminished by concomitant administration of L. delbrueckii and S. thermophilus. As the given microbes could not 7alpha-dehydroxylate, it seems reasonable to assume that they stimulate microbial species already present in the intestine.

The metabolic consequences of slow colonic transit

Intestinal transit has a substantial influence on the enterohepatic circulation of bile acids and steroid hormones, on colonic pH, and on short chain fatty acid concentrations in the distal colon. Slow transit is likely to favor disease processes that are related to over-efficient enterohepatic recirculation and to lack of short chain fatty acid in the distal colon. These include gallstones, large bowel cancer, and possibly breast cancer. The best-documented influence of slow colonic transit is on bile acid metabolism. Slowing colonic transit increases deoxycholate and raises cholesterol saturation of bile, making gallstone formation more likely. In this review, we also examine the evidence that slow colonic transit may be important in the etiology of large bowel and breast cancer. There is a lack of data pertaining to the relationship between colonic transit and diseases such as colon and breast cancer. Should slow colonic transit prove to be a significant factor in the etiology of such diseases, then the health of the population might benefit from dietary and lifestyle changes that speed up intestinal transit.

Bifidobacteria and probiotic effects: action of Bifidobacterium species on conjugated bile salts

The effect of six different conjugated bile salts (two trihydroxyconjugated bile salts: tauro and glycocholic acids; and four dihydroxyconjugated bile salts: tauro- and glycochenodeoxycholic, tauro- and glycodeoxycholic acids) on eight bifidobacteria strains were studied. A strong growth-inhibitory effect was observed (80% at 0.95 mM) for each bile salt and strain. This phenomenon was explained by the production of deconjugated bile salt during bifidobacteria growth. The deconjugation phenomenon was concurrent with biomass production, and deconjugated bile salts were the sole compound produced during bifidobacteria biotransformation. In resting cell experiments, differences appeared between the strains and the kind of bile salts, particularly concerning taurocholic acid. The Bifidobacterium longum strains were the most efficient among the bacteria tested.

Determination of enzyme activity by high-performance liquid chromatography

The application of high-performance liquid chromatography (HPLC) in the study of enzymatic reactions is reviewed. The rationale for using HPLC is given and whether the components of the reaction mixture should be derivatized prior to or after HPLC. An alphabetical list of enzymes assayed by HPLC is given. Substrate and product are included as well the derivatization reagent, detection method and biological matrix. Specific examples of these assays in a complex biological matrix viz. faeces are given. Future prospects are the detection of new enzymes using synthetic substrates and implementation of mass spectrometry to elucidate enzyme specificities.

Colonic mucosal pH in humans

Mucosal pH was measured at specific anatomic segments within the colon using a flexible pH probe in patients prepared for colonoscopy. The data revealed similar pH measurements along the length of the colon, irrespective of the presence or absence of colorectal neoplasia. Patients exhibited a relatively acidic right colon; a more alkaline transverse, left, and sigmoid colon; and a relatively acidic rectum. There were no apparent gender- or age-related effects on colonic mucosal pH.

Comparison of fermentation reactions in different regions of the human colon

Colonic contents were obtained from two human sudden-death victims within 3 h of death. One of the subjects (1) was methanogenic, the other (2) was a non-CH4 producer. Measurements of bacterial fermentation products showed that in both individuals short-chain fatty acids, lactate and ethanol concentrations were highest in the caecum and ascending colon. In contrast, products of protein fermentation, such as ammonia, branched chain fatty acids and phenolic compounds, progressively increased from the right to the left colon, as did the pH of gut contents. In Subject 1, cell population densities of methanogenic bacteria (MB) increased distally through the gut and methanogenic activity was lower in the right (0.78-1.18 mumol CH4 produced/h/g dry wt contents) than in the left colon (1.34 mumol CH4 produced/h/g dry wt contents). Methane production rates did not correlate with MB numbers. Sulphate-reducing bacteria (SRB) were not found and dissimilatory sulphate reduction was not detected in any region of the colon. Methanogenic bacteria did not occur in subject 2, but high numbers of SRB were present throughout the gut (ca 10(9)/g dry wt contents). Sulphate reduction rates were maximal in the ascending and transverse colons (0.24 and 0.22 mumol 35SO4(2-) reduced/h/g dry wt contents, respectively). Short-chain fatty acid production by caecal contents was up to eight-fold higher than contents from the sigmoid/rectum. These findings demonstrate significant differences in fermentation reactions in different regions of the large gut.

Gastrointestinal intraluminal pH in normal subjects and those with colorectal adenoma or carcinoma

Recent evidence suggests that the production of colorectal carcinogens is facilitated when the pH of the colonic contents is alkaline. It follows that the colonic intraluminal pH of patients with colorectal neoplasms should be higher than in normal subjects. Gastrointestinal pH has been measured in 30 patients with colorectal cancer and 37 patients with benign colorectal adenomas (using a pH sensitive radiotelemetry capsule). These values have been compared with those recorded in 66 normal subjects. No differences in gastrointestinal pH were found and the results did not support the hypothesis that colonic pH plays a role in the aetiology of colorectal neoplasia.

Inhibition of secondary bile acid formation in the large intestine by lactulose in healthy subjects of two different age groups

Secondary bile acids have been implicated in colonic carcinogenesis. Transformation of primary into secondary bile acids (7 alpha-dehydroxylation) in the large bowel is a pH-dependent process. Inhibition of this reaction could be achieved by lowering colonic pH. We, therefore, studied the effects of lactulose (a non-absorbable disaccharide), which is capable of acidifying colonic contents, on secondary bile acid metabolism. Because this metabolism is age dependent, lactulose was given (0.3 g kg-1 twice daily for 12 weeks) to nine middle-aged (age 31-54 years; mean 45.7) and ten elderly subjects (age 56-81 years; mean 66.4). Twice before, and after 6 and 12 weeks' lactulose administration, biliary and faecal bile acids, whole gut transit time, faecal weight and dry weight, and faecal pH were recorded. The concentration of (iso)lithocholic and deoxycholic acid in faeces was higher in elderly subjects (P less than 0.05) but the excretion was comparable. After lactulose the concentration and excretion of the major secondary bile acids decreased. The primary bile acid fraction rose from 5% before, to more than 20% after, lactulose (P less than 0.05). Faecal weight increased and faecal dry weight decreased, resulting in a higher faecal water output during lactulose. Whole gut transit time did not change. The faecal pH dropped after 6 (P less than 0.05) and further after 12 weeks' lactulose (P less than 0.05). The percentage deoxycholic acid in bile was higher, and cholic acid lower, in elderly subjects (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Short chain fatty acids in human large intestine, portal, hepatic and venous blood

Evidence for the occurrence of microbial breakdown of carbohydrate in the human colon has been sought by measuring short chain fatty acid (SCFA) concentrations in the contents of all regions of the large intestine and in portal, hepatic and peripheral venous blood obtained at autopsy of sudden death victims within four hours of death. Total SCFA concentration (mmol/kg) was low in the terminal ileum at 13 +/- 6 but high in all regions of the colon ranging from 131 +/- 9 in the caecum to 80 +/- 11 in the descending colon. The presence of branched chain fatty acids was also noted. A significant trend from high to low concentrations was found on passing distally from caecum to descending colon. pH also changed with region from 5.6 +/- 0.2 in the caecum to 6.6 +/- 0.1 in the descending colon. pH and SCFA concentrations were inversely related. Total SCFA (mumol/l) in blood was, portal 375 +/- 70, hepatic 148 +/- 42 and peripheral 79 +/- 22. In all samples acetate was the principal anion but molar ratios of the three principal SCFA changed on going from colonic contents to portal blood to hepatic vein indicating greater uptake of butyrate by the colonic epithelium and propionate by the liver. These data indicate that substantial carbohydrate, and possibly protein, fermentation is occurring in the human large intestine, principally in the caecum and ascending colon and that the large bowel may have a greater role to play in digestion than has previously been ascribed to it.

Total parenteral nutrition and the function of the intestinal microflora in Crohn's disease

The effect of total parenteral nutrition (TPN) on the following six intestinal microflora-associated characteristics (MACs) was studied in patients with Crohn's disease: faecal tryptic activity (FTA), formation of coprostanol, urobilinogen, and deoxycholic acid, and degradation of mucin and beta-aspartylglycine. The FTA showed high levels before TPN, in accordance with previous findings, and decreased during TPN. Formation of coprostanol, urobilinogen, and deoxycholic acid was reduced in some patients, whereas no changes were found in the mucin and beta-aspartylglycine degradation.

Short chain fatty acids in human large intestine, portal, hepatic and venous blood

Evidence for the occurrence of microbial breakdown of carbohydrate in the human colon has been sought by measuring short chain fatty acid (SCFA) concentrations in the contents of all regions of the large intestine and in portal, hepatic and peripheral venous blood obtained at autopsy of sudden death victims within four hours of death. Total SCFA concentration (mmol/kg) was low in the terminal ileum at 13 +/- 6 but high in all regions of the colon ranging from 131 +/- 9 in the caecum to 80 +/- 11 in the descending colon. The presence of branched chain fatty acids was also noted. A significant trend from high to low concentrations was found on passing distally from caecum to descending colon. pH also changed with region from 5.6 +/- 0.2 in the caecum to 6.6 +/- 0.1 in the descending colon. pH and SCFA concentrations were inversely related. Total SCFA (mumol/l) in blood was, portal 375 +/- 70, hepatic 148 +/- 42 and peripheral 79 +/- 22. In all samples acetate was the principal anion but molar ratios of the three principal SCFA changed on going from colonic contents to portal blood to hepatic vein indicating greater uptake of butyrate by the colonic epithelium and propionate by the liver. These data indicate that substantial carbohydrate, and possibly protein, fermentation is occurring in the human large intestine, principally in the caecum and ascending colon and that the large bowel may have a greater role to play in digestion than has previously been ascribed to it.

Effect of long term lactulose ingestion on secondary bile salt metabolism in man: potential protective effect of lactulose in colonic carcinogenesis

This study investigated whether colonic absorption of secondary bile acids, especially deoxycholate in patients with adenomas could be decreased by oral lactulose. Bile acid metabolism was studied using bile sampling and 14C-deoxycholate kinetics in patients with colonic adenomatous polyps before and after four and 12 weeks of lactulose, 60 g/day. The results indicate that lactulose decreased the deoxycholate pool size from a mean of 22.0 (SD: +/- 13.8) to 14.3 (+/- 7.6) mumol/kg (p less than 0.025). Deoxycholate absorption fell from 3.8 (+/- 2.3) to 2.9 (+/- 1.4 mumol/kg/d (ns). The biliary bile acid composition decreased significantly in deoxycholate after four and 12 weeks with a rise in primary bile acids. There was a highly significant correlation between the %-change in DCA input and the %-change in DCA pool size (r = 0.89). Intestinal transit measured by the pellet method (4.1 +/- 1.9 to 2.4 +/- 0.6 day; p less than 0.01) and faecal pH decreased, while stool frequency and weight rose significantly. Significant correlations between the %-change in gut transit time and the %-change in DCA pool size or %-change in DCA input were absent. The results show that it is possible to lower colonic secondary bile acid absorption by long term lactulose feeding. This effect can be mediated by accelerated transit and the acidification of the colonic contents.

In vivo studies with fibre components

There are few studies in man examining the in vivo effects of dietary fibre on bile acid metabolism but divergent results have been recorded depending on the amount and type of fibre eaten. Studies in which the fibre components pectin, cellulose, and lignin were fed to normal volunteers for four weeks have been reported. The highly fermentable component pectin is associated with increased secondary bile acid formation in contrast to the partially fermentable component cellulose in which the opposite occurs. Lignin has no effect on bile acid metabolism. No component significantly alters biliary lipids. Since ordinary diets contain a mixture of different fibres the net effect will depend on the relative amounts of each. Significant changes in bile acid metabolism and biliary lipids in the longer term (greater than 4 weeks) however, are not precluded by the results of these short term studies.

7 alpha-Dehydroxylation of bile acids by resting cells of a Eubacterium lentum-like intestinal anaerobe, strain c-25

7 alpha-Dehydroxylation of cholic acid and chenodeoxycholic acid by whole cells of strain c-25, a Eubacterium lentum-like intestinal anaerobe, was studied. 7 alpha-Dehydroxylase activity was observed only in whole cells grown in the presence of the primary bile acid (cholic acid or chenodeoxycholic acid). Chenodeoxycholic acid was twice as effective as cholic acid as an inducer. Although cells grown in the presence of chenodeoxycholic acid had no significant substrate specificity for the two primary bile acids, cells grown in the presence of cholic acid showed two times greater activity against cholic acid than chenodeoxycholic acid. Exposure of cell suspensions to atmospheric oxygen resulted in little loss of the 7 alpha-dehydroxylase activity. The induced enzyme had an optimal pH range of 7.3 to 7.7. Although adding flavin mononucleotide to the growth medium significantly increased the 7 alpha-dehydroxylation of bile acids without an increase in cell growth, inhibition of the enzyme activity was observed in the resting cell system when flavin mononucleotide was included in the reaction mixture.

The degradation of cholic acid by Pseudomonas sp. N.C.I.B. 10590 under anaerobic conditions

The bacterial degradation of cholic acid under anaerobic conditions by Pseudomonas sp. N.C.I.B. 10590 was studied. The major unsaturated neutral compound was identified as 12 beta-hydroxyandrosta-4,6-diene-3,17-dione, and the major unsaturated acidic metabolite was identified as 12 alpha-hydroxy-3-oxochola-4,6-dien-24-oic acid. Eight minor unsaturated metabolites were isolated and evidence is given for the following structures: 12 alpha-hydroxyandrosta-4,6-diene-3,17-dione, 12 beta,17 beta-dihydroxyandrosta-4,6-dien-3-one, 12 beta-hydroxyandrosta-1,4,6-triene-3,17-dione, 12 beta,17 beta-dihydroxyandrosta-1,4,6-trien-3-one, 12 beta-hydroxyandrosta-1,4,6-triene-3,17-dione, 12 beta,17 beta-dihydroxyandrosta-1,4,6-trien-3-one, 12 alpha-hydroxyandrosta-1,4-diene-3,17-dione, 3-hydroxy-9,10-secoandrosta-1,3,5(10)-triene-9,17-dione, 3,12-dioxochola-4,6-dien-24-oic acid and 12 alpha-hydroxy-3-oxopregna-4,6-diene-20-carboxylic acid. In addition, a major saturated neutral compound was isolated and identified as 3 beta,12 beta-dihydroxy-5 beta-androstan-17-one, and the only saturated acidic metabolite was 7 alpha,12 alpha-dihydroxy-3-oxo-5 beta-cholan-24-oic acid. Nine minor saturated neutral compounds were also isolated, and evidence is presented for the following structures: 12 beta-hydroxy-5 beta-androstane-3,17-dione, 12 alpha-hydroxy-5 beta-androstane-3,17-dione, 3 beta,12 alpha-dihydroxy-5 beta-androstan-17-one, 3 alpha,12 beta-androstan-17-one, 3 alpha,12 alpha-dihydroxy-5 beta-androstan-17-one, 5 beta-androstane-3 beta,12 beta,17 beta-triol, 5 beta-androstane-3 beta,12 alpha,17 beta-triol, 5 beta-androstane-3 alpha,12 beta,17 beta-triol and 5 beta-androstane-3 alpha,12 alpha,17 beta-triol. The induction of 7 alpha-dehydroxylase and 12 alpha-dehydroxylase enzymes is discussed, together with the significance of dehydrogenation and ring fission under anaerobic conditions.

The biotransformation of hyodeoxycholic acid by Pseudomonas sp. NCIB 10590 under anaerobic conditions

The bacterial degradation of hyodeoxycholic acid under anaerobic conditions was studied. The major acidic product has been identified as 6 alpha-hydroxy-3-oxochol-4-ene-24-oic acid whilst the major neutral product has been identified as 6 alpha-hydroxyandrosta-1,4-diene-3,17-dione. The minor acidic products were 3,6-dioxochola-1,4-diene-24-oic acid, 3-oxochol-5-ene-24-oic acid, 3-oxochol-4-ene-24-oic acid, 3-oxochola-1,4-diene-24-oic acid and 6 alpha-hydroxy-3-oxochola-1,4-diene-24-oic acid and the minor neutral products were androst-4-ene-3,17-dione, androst-4-ene-3,6,17-trione, androsta-1,4-diene-3,6,17-trione, androsta-1,4-diene-3,17-dione, 17 beta-hydroxyandrosta-1,4-diene-3-one and 6 alpha-hydroxyandrost-4-ene-3,17-dione. Evidence is presented which suggests that under aerobic conditions, one pathway of hyodeoxycholic acid metabolism exists whilst under anaerobic conditions an extra biotransformation pathway becomes operative involving the induction of a 6 alpha-dehydroxylase enzyme. A biochemical pathway of hyodeoxycholic acid metabolism by bacteria under anaerobic conditions is discussed incorporating a scheme involving such an enzyme.

7 alpha-Dehydroxylation of bile acids by resting cells of an unidentified, gram-positive, nonsporeforming anaerobic bacterium

Transformation of bile acids by washed whole cells of strain HD-17, an unidentified gram-positive anaerobic bacterium isolated from human feces, was studied. 7 alpha-Dehydroxylase was produced only during adaptive growth on medium containing 7 alpha-hydroxy bile acids. Both the extent of hydroxylation and the state of conjugation of the bile acids had marked effects on the induction of the enzyme, and the order of the enzyme induction was conjugated cholic acid much greater than cholic acid greater than taurochenodeoxycholic acid greater than or equal to chenodeoxycholic acid. The addition of excess glucose to the growth medium appreciably reduced the enzyme level. The induced enzyme required strict anaerobic conditions for activity and had an optimal pH range of 6.5 to 7.5. In contrast with the induction of the enzyme, the induced enzyme showed a low degree of substrate specificity between cholic acid and chenodeoxycholic acid, with some preference for the former. In addition, the organism contained 3 alpha-, 7 alpha-, and 12 alpha-hydroxysteroid dehydrogenases, and the addition of bile acids to the medium somewhat enhanced the production of the oxidoreductases. The dehydrogenations were obviously stimulated by oxygen as a terminal electron acceptor. The organism also contained bile salt hydrolase.

Cholesterol metabolism in gnotobiotic gerbils

Germfree gerbils were associated with a murine-derived hexaflora which produced only minor changes in the primary bile acid pattern of rats. These hexaflora-associated gerbils had relatively small ceca (4% of body weight) and reproduced well. Although serum cholesterol levels of both conventional and hexaflora-associated gerbils increased in response to dietary cholesterol, the hexaflora-associated gerbil showed a greater elevation in serum cholesterol than the conventional gerbil when maintained on a diet containing 0.1% cholesterol. This increase in serum cholesterol manifested itself almost totally in the very low density lipoprotein and low density lipoprotein fractions. The fecal bile acids of the hexaflora-associated gerbil were largely deconjugated, but very little further modification of either cholic or chenodeoxycholic acid had taken place. The data suggest that in the absence of elements of the intestinal microflora that can express a bile acid-modifying potential, and particularly a 7-alpha-dehydroxylating capacity, catabolism of cholesterol to bile acids is reduced, and cholesterol accumulates in the very low density and low density serum lipoprotein fractions.

Diagnosis of deep vein thrombosis using autologous indium-III-labelled platelets

Forty-eight patients who had undergone surgical reduction of a fractured neck of femur or in whom deep vein thrombosis was suspected clinically were studied by ascending phlebography and imaging after injection of autologous indium-111-labelled platelets to assess the accuracy and value of the radioisotopic technique in diagnosing deep vein thrombosis. Imaging was performed with a wide-field gammacamera linked with data display facilities. Phlebography showed thrombi in 26 out of 54 limbs examined and a thrombus in the inferior vena cava of one patient; imaging the labelled platelets showed the thrombi in 24 of the 26 limbs and the thrombus in the inferior vena cava. The accumulation of indium-111 at sites corresponding to those at which venous thrombi have been shown phlebographically indicates that this radioisotopic technique is a useful addition to methods already available for the detection of deep vein thrombosis.

Do colonic bacteria contribute to cholesterol gall-stone formation? Effects of lactulose on bile

Ten healthy middle-aged women volunteered for a study to test the effect of lactulose--a synthetic, non-absorbable disaccharide--on the colonic metabolism of bile acids and on bile lipid composition. Lactulose (60 g daily in eight cases, 39 g daily in two) was taken as a proprietary syrup for six weeks, and bile was collected by duodenal intubation before and immediately after six weeks. All subjects showed a fall in the percentage of the 7-alpha-dehydroxylated bile acid deoxycholic acid (mean 28.4 +/- SEM 3.7 to 15.6 +/- 2.4; p less than 0.002) and a rise in the percentage of the primary bile acid chenodeoxycholic acid (mean 33.2 +/- 42.9 +/- 2.9; p less than 0.001). The percentage of cholic acid rose in eight subjects but mean values did not differ significantly. Bile was initially super-saturated with cholesterol in most subjects and became less saturated with cholesterol in all but one (mean saturation index 1.40 +/- 0.11 to 1.19 +/- 0.07; p less these 0.005). These data support the theory colonic bacteria contribute to cholesterol gall-stone formation.

Transformation of bile acids by mixed microbial cultures from human feces and bile acid transforming activities of isolated bacterial strains

Microbiol transformation of cholic acid and chenodeoxycholic acid by anaerobic mixed cultures of human fecal microorganisms was investigated, and the results were examined in relation to the bile acid transforming activities of 75 bacterial strains isolated from the same fecal cultures. The reactions involved in the mixed cultures were dehydrogenation and dehydroxylation of the 7 alpha-hydroxy group in both primary bile acids and epimerization of the 3 alpha-hydroxy group in all metabolic bile acids. Extensive epimerization of the 7 alpha-hydroxy group of chenodeoxycholic acid yielding ursodeoxycholic acid was also demonstrated by certain fecal samples. 7 alpha-Dehydrogenase activity was widespread among the fecal isolates (88% of 16 facultative anaerobes and 51% of 59 obligate anaerobes), and 7 alpha-dehydroxylase activity was revealed in one of the isolates, and unidentified gram-positive nonsporeforming anaerobic bacterium. 3 alpha-Epimerization was effected by seven strains assigned to Eubacterium lentum, which were also active for 3 alpha- and 7 alpha-dehydrogenations. No microorganism accounting for 7 alpha-epimerization was recovered among the isolates. Splitting of conjugated bile acid was demonstrated by the majority of obligate anaerobes but the activity was rare among facultative anaerobes.

Isolation and characterization of thirteen intestinal microorganisms capable of 7 alpha-dehydroxylating bile acids

Thirteen anaerobic bacteria capable of performing the 7 alpha-dehydroxylation of both cholic acid and chenodeoxycholic acid were isolated from human feces and also from sewage. Ten organisms from heat-treated samples were species of Clostridium identical or closely related to the Clostridium bifermentans-C. sordellii group and consisted of four strains elaborating 7 alpha-dehydroxylase alone and six strains capable of catalyzing both 7 alpha-dehydrogenation and 7 alpha-dehydroxylation. The remaining three organisms, recovered from fresh human feces, were gram-positive, nonflagellated, nonsporeforming, anaerobic rods and comprised two distinct species. Strain HD-17, still unidentified, had both activities, but was unique in that it exclusively 7 alpha-dehydroxylated cholic acid while biotransforming chenodeoxycholic acid, preferably though 7 alpha-dehydrogenation. Two unclassified strains, b-8 and c-25, metabolized both acids though 7 alpha-dehydroxylation and 7 alpha-dehydrogenation. Except for strains b-8 and c-25, all of th 7 alpha-dehydroxylating bacteria split the conjugated bile acid series, and hydrolases were detected in cell-free filtrates of early stationary-phase broth cultures.

Intestinal microflora and bile acids. In vitro cholic acid transformation by mixed fecal culture of rats

In vitro cholic acid (CA) transformation by mixed fecal culture was investigated. Concentrations of glucose, peptone, and yeast extract in the medium and the initial pH of the medium markedly affected the CA transformation. Yeast extract enhanced the transformation, whereas high concentrations of glucose and peptone inhibited it. When the initial pH of the medium was below 6.5, CA was converted to 7-keto-deoxycholic acid (7KD), and formation of deoxycholic acid (DC) was not observed. In contrast, with an initial pH of 7.0, about 60% of the CA was converted to 7KD after 3 days of incubation, and then DC gradually formed after 4 days of incubation, following the disappearance of 7KD. The formation of DC in the cultured samples was paralleled in each case by disappearance of 7KD. In pure culture systems, Escherichia coli and some strains of Bacteroides formed 7KD from CA. No DC formation was observed in pure cultures of any of the strains examined.

Alteration of bile salt metabolism by dietary fibre (bran)

Feeding dietary fibre in the form of bran induced changes in bile salt metabolism in five people with intact gall bladders. There was evidence of reduced dehydroxylation of bile salts; the proportion of deoxycholate conjugates in bile was reduced and the transfer of radioactivity from labelled taurocholate to deoxycholate was decreased. These findings, which were independent of changes in intestinal transit rate, imply that bran reduced the degradation of bile salts by colonic bacteria. This property of bran accords with recent theories that fibre-depleted diets favour the degradation of bile salts in the colon. These findings may be relevant to the aetiology of large bowel cancer.