Lactulose ingestion increases faecal bifidobacterial counts: a randomised double-blind study in healthy humans

OBJECTIVE

Faecal bifidobacteria and lactobacilli, perceived as exerting health-promoting properties, may be increased by ingestion of high-dose lactulose in humans. The effects of low and well-tolerated doses of lactulose are not well known. The aim of the study was to assess the effects of prolonged low-dose lactulose administration on faecal bifidobacteria and selected metabolic indexes potentially involved in colonic carcinogenesis.

SUBJECTS AND METHODS

In all, 16 healthy volunteers were included in this controlled, randomised, double-blind, parallel group trial. Participants ingested lactulose or placebo (sucrose) at a dose of 5 g b.i.d. for 6 weeks. Stools were regularly collected at baseline (d0), and after 3 (d21) and 6 (d42) weeks of sugar ingestion. Tolerance was evaluated using a daily chart.

RESULTS

Faecal bifidobacterial counts were higher in lactulose than in sucrose group (P=0.03). Lactulose ingestion led to a significant increase in faecal bifidobacteria counts from d0 to d21 and d42 ((m+/-s.e.m.) 8.25+/-0.53, 8.96+/-0.40 and 9.54+/-0.28 log colony-forming units/g wet wt (CFU/g), respectively (P=0.048)). Placebo ingestion did not lead to any faecal bifidobacterial count change. Total anaerobes, Lactobacillus and pH were not significantly changed throughout the study in the two groups. Neither faecal bile acids nor neutral sterols were modified by lactulose. Excess flatus was more common in the lactulose group (P=0.03), but was very mild. Bloating and borborygmi did not differ between both the groups.

CONCLUSIONS

A measure of 10 g lactulose/day increases faecal bifidobacterial counts, and lactulose fulfils the criteria requested to be considered as a prebiotic.

Prospective, randomized, parallel-group trial to evaluate the effects of lactulose and polyethylene glycol-4000 on colonic flora in chronic idiopathic constipation

BACKGROUND

Although lactulose and polyethylene glycol are osmotic laxatives widely used in the treatment of chronic constipation, no study has been conducted to compare their actions on the colonic bacterial ecosystem, which has an important influence on host health.

AIM

To assess the effects of lactulose and polyethylene glycol on the composition and metabolic indices of the faecal flora in patients with chronic idiopathic constipation.

METHODS

Sixty-five patients with chronic idiopathic constipation were included in this controlled, multi-centre, randomized, parallel-group study. Participants received lactulose (Duphalac) or polyethylene glycol-4000 (Forlax) powders for the first week at a fixed dosage at night (20 g/day); in the second week, patients were given the option to vary the dose according to efficacy and tolerance (10-30 g/day); for the last 2 weeks, treatment was administered at a fixed dosage based on the results of the second week (10-30 g/day). Stools were recovered for bacteriological analysis at days -1, 21 and 28.

RESULTS

Clinical efficacy and tolerance were similar with both treatments. In the lactulose group, an increase in faecal bifidobacteria counts (P = 0.04) and beta-galactosidase activity (P < 0.001) was observed from day -1 to day 28, whereas, in the polyethylene glycol group, there was a decrease in total short-chain fatty acids (P = 0.02), butyrate (P = 0.04), acetate (P = 0.02) and faecal bacterial mass (P = 0.001). No differences were observed in stools with regard to the following parameters: counts of Lactobacillus, clostridial spores, Bacteroides and enterobacteria, pH, biliary acids and neutral sterol concentrations.

CONCLUSIONS

Both lactulose and polyethylene glycol are efficacious and well tolerated. However, although lactulose can be considered as a pre-biotic in constipated patients, polyethylene glycol produces signs of decreased colonic fermentation in the stool.

Cholesterol, bile acid, and lipoprotein metabolism in two strains of hamster, one resistant, the other sensitive (LPN) to sucrose-induced cholelithiasis

A comprehensive study of cholesterol, bile acid, and lipoprotein metabolism was undertaken in two strains of hamster that differed markedly in their response to a sucrose-rich/low fat diet. Under basal conditions, hamsters from the LPN strain differed from Janvier hamsters by a lower cholesterolemia, a higher postprandial insulinemia, a more active cholesterogenesis in both liver [3- to 4-fold higher 3-hydroxy 3-methylglutaryl coenzyme A reductase (HMG-CoAR) activity and mRNA] and small intestine, and a lower hepatic acyl-coenzyme A:cholesterol acyltransferase activity. Cholesterol saturation indices in the gallbladder bile were similar for both strains, but the lipid concentration was 2-fold higher in LPN than in Janvier hamsters. LPN hamsters had a lower capacity to transform cholesterol into bile acids, shown by the smaller fraction of endogenous cholesterol converted into bile acids prior to fecal excretion (0.34 vs. 0.77). In LPN hamsters, the activities of cholesterol 7alpha-hydroxylase (C7OHase) and sterol 27-hydroxylase (S27OHase), the two rate-limiting enzymes of bile acid synthesis, were disproportionably lower (by 2-fold) to that of HMG-CoAR. When fed a sucrose-rich diet, plasma lipids increased, dietary cholesterol absorption improved, hepatic activities of HMG-CoA reductase, C7Ohase, and S27OHase were reduced, and intestinal S27OHase was inhibited in both strains. Despite a similar increase in the biliary hydrophobicity index due to the bile acid enrichment in chenodeoxycholic acid and derivatives, only LPN hamsters had an increased lithogenic index and developed cholesterol gallstones (75% incidence), whereas Janvier hamsters formed pigment gallstones (79% incidence). These studies indicate that LPN hamsters have a genetic predisposition to sucrose-induced cholesterol gallstone formation related to differences in cholesterol and bile acid metabolism.

Effects of simvastatin on hepatic cholesterol metabolism, bile lithogenicity and bile acid hydrophobicity in patients with gallstones

BACKGROUND AND AIMS

There is limited information available on the effects of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors on hepatic and biliary cholesterol metabolism in patients with gallstones. The aims of this study were to determine the effect of simvastatin on the regulatory elements of cholesterol metabolism that determine the concentrations of cholesterol in plasma and bile.

METHODS

Thirty-one gallstone patients were enrolled in the study; 17 were treated with 20 mg simvastatin daily for 3 weeks prior to cholecystectomy and 14 served as controls. Samples of blood, liver, gall-bladder bile and bile from the common bile duct (CBD) were collected and analysed.

RESULTS

The plasma cholesterol (-30%), triacylglycerol (-23%) and low-density lipoprotein (LDL) cholesterol (-42%) concentrations were significantly lowered by simvastatin treatment, as was the plasma lathosterol: cholesterol (-70%), which reflects whole-body cholesterol synthesis. Despite these changes, the hepatic LDL receptor protein and LDL receptor activity in circulating mononuclear cells were similar in both groups. There were no differences in the plasma phytosterol: cholesterol, which reflects the intestinal cholesterol absorption capacity or in the activity of hepatic acyl-coenzyme A: cholesterol acyltransferase. There were however, lower cholesterol concentrations in CBD (-68%) and gall bladder (-41%) bile, and decreased lithogenic (-47%) and bile acid hydrophobicity (-22%) indices of CBD bile in the simvastatin group.

CONCLUSIONS

These data indicate that simvastatin reduced plasma and biliary cholesterol levels primarily by reducing cholesterol synthesis. The reduction in CBD bile lithogenicity and bile acid hydrophobicity by simvastatin suggests that this agent may be useful for people who have early stages of cholesterol gallstone development and in whom a choleretic effect is required.

Cholesterol crystallization in gall-bladder bile of pigs given cholesterol-beta-cyclodextrin-enriched diets with either casein or soyabean concentrate as protein sources

Cholesterol precipitation from supersaturated bile is the earliest and determinant step in the formation of cholesterol gallstones, which is thought to be diet-dependent. Bile composition, appearance and growth of cholesterol crystals were studied in fresh gall-bladder biles from pigs adapted to four different protein-containing diets over 3 weeks: 160 g dietary protein/kg as casein (C16; n 6), or as soyabean-protein concentrate (S16; n 6), or a mixture of both protein sources (casein-soyabean protein, 70:30, w/w) (CS16; n 6), or 320 g of the mixed protein/kg (CS32; n 6). Moreover, all four diets contained 3 g cholesterol/kg and 50 g beta-cyclodextrin/kg as modifiers of bile composition towards cholesterol pro-crystallization. Cholesterol precipitation was most active after the high-protein diet, CS32, and the casein diet, C16, and lowest after the soyabean-protein diet, S16. It was intermediate after the mixed diet, CS16, but still much lower than in the former two groups. These diet-induced variations were suggested to be mediated through modifications in the biliary profile of bile acids, whereas all other biliary constituents studied were essentially unchanged. The fasting level of plasma cholesterol was lowest in both 160 g protein/kg diets containing soyabean protein (S16 and CS16), highest for the high-protein diet CS32, and intermediate for the C16 diet. These results should encourage clinical studies on the effect of soyabean protein, or other vegetable proteins, for primary or recurrence prevention of cholelithiasis at its earliest stage.

Antilithiasic effect of beta-cyclodextrin in LPN hamster: comparison with cholestyramine

Beta-Cyclodextrin (BCD), a cyclic oligosaccharide that binds cholesterol and bile acids in vitro, has been previously shown to be an effective plasma cholesterol lowering agent in hamsters and domestic pigs. This study examined the effects of BCD as compared with cholestyramine on cholesterol and bile acid metabolism in the LPN hamster model model for cholesterol gallstones. The incidence of cholesterol gallstones was 65% in LPN hamsters fed the lithogenic diet, but decreased linearly with increasing amounts of BCD in the diet to be nil at a dose of 10% BCD. In gallbladder bile, cholesterol, phospholipid and chenodeoxycholate concentrations, hydrophobic and lithogenic indices were all significantly decreased by 10% BCD. Increases in bile acid synthesis (+110%), sterol 27-hydroxylase activity (+106%), and biliary cholate secretion (+140%) were also observed, whereas the biliary secretion of chenodeoxycholate decreased (-43%). The fecal output of chenodeoxycholate and cholate (plus derivatives) was increased by +147 and +64%, respectively, suggesting that BCD reduced the chenodeoxycholate intestinal absorption preferentially. Dietary cholestyramine decreased biliary bile acid concentration and secretion, but dramatically increased the fecal excretion of chenodeoxycholate and cholate plus their derivatives (+328 and +1940%, respectively). In contrast to BCD, the resin increased the lithogenic index in bile, induced black gallstones in 34% of hamsters, and stimulated markedly the activities of HMG-CoA reductase (+670%), sterol 27-hydroxylase (+310%), and cholesterol 7alpha-hydroxylase (+390%). Thus, beta-cyclodextrin (BCD) prevented cholesterol gallstone formation by decreasing specifically the reabsorption of chenodeoxycholate, stimulating its biosynthesis and favoring its fecal elimination. BCD had a milder effect on lipid metabolism than cholestyramine and does not predispose animals to black gallstones as cholestyramine does in this animal model.

Inducing cholesterol precipitation from pig bile with beta-cyclodextrin and cholesterol dietary supplementation

BACKGROUND/METHODS

In this study, pigs fed for 3 weeks a well-balanced semi-purified diet enriched with 0.3% cholesterol and 0, 5 or 10% beta-cyclodextrin were proposed as new animal donors of gallbladder bile exhibiting different rates of cholesterol crystallization, in order to gain insight into the early mechanisms underlying cholesterol precipitation in vivo. The appearance and growth of cholesterol crystals were monitored in the incubated freshly collected gallbladder biles through light microscopy and concomitant time-sequential determination of crystallized cholesterol concentration, and interpreted in terms of the composition of the bile.

RESULTS

Although the concentration of total lipids and proteins and the relative proportions of bile acids, phospholipids, and cholesterol remained unchanged under beta-cyclodextrin, the cholesterol crystallization increased in the following order: 0<<10<5% beta-cyclodextrin. Concomitantly, the proportion of chenodeoxycholic acid in bile, and the hydrophobicity index of the biliary bile acid mixture increased in the following order: 0<5<10% beta-cyclodextrin (the same as reported elsewhere for the decrease in the antinucleating ApoA1), while sn-2 arachidonoyl biliary lecithins were specifically increased with 5% beta-cyclodextrin in the diet.

CONCLUSIONS

We hypothesized that lecithin molecular species may be the determinant factor in modulating high cholesterol crystallization rates in biles otherwise enriched with hydrophobic bile acids.

Reduced cholesterol absorption in hamsters by crilvastatin, a new 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor

Crilvastatin, a new drug from the pyrrolidone family, has been previously shown to inhibit the activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase, in vitro and in vivo, to reduce the absorption of dietary cholesterol and to stimulate the activity of cholesterol 7 alpha-hydroxylase in the rat. The aim of this study was to evaluate the effects of crilvastatin on cholesterol and bile acid metabolism in the hamster. In hamsters fed on a lithogenic diet for 8 weeks, crilvastatin treatment (200 mg/day per kg body weight) did not change plasma lipid levels, failed to improve bile parameters and did not prevent gallstone formation. In hamsters fed on a basal cholesterol-rich (0.2%) diet for 8 weeks, crilvastatin at the same dose reduced the cholesterol level in the plasma by 20%, with a decrease of both low-density and high-density lipoprotein cholesterol. The drug did not significantly stimulate the biliary secretion of bile acids but significantly decreased the activity of acyl coenzyme A:cholesterol acyltransferase in the small intestine by 64%. This effect was enhanced when cholestyramine, a bile acid-sequestering resin, was given in combination with crilvastatin. Crilvastatin alone did not change the activity of cholesterol 7 alpha-hydroxylase in the liver, despite the marked reduction in both hepatic cholesterogenesis and intestinal absorption of dietary cholesterol (the absorption coefficient was 44 +/- 2% in treated hamsters vs. 61 +/- 7% in controls).

Hypocholesterolemic action of beta-cyclodextrin and its effects on cholesterol metabolism in pigs fed a cholesterol-enriched diet

To examine the effects of beta-cyclodextrin (BCD), a non-absorbable carbohydrate, on lipid metabolism, growing pigs were fed a 0.3% cholesterol-enriched diet for 4 weeks or this diet containing 5% or 10% BCD. Pigs fed a basal diet without added cholesterol or BCD were used as controls. The cholesterol-rich diet induced hypercholesterolemia (1.75 vs. 0.84 g/l plasma) due to increased LDL concentration, delayed the plasma clearance of vitamin A, enhanced liver cholesterol storage, lowered the hepatic activities of LDL-receptors (by 47%) and HMG-CoA reductase (by 62%), stimulated cholesterol 7alpha-hydroxylase (x3), and accelerated the fecal output of neutral sterols (x4). Addition of BCD to the cholesterol-rich diet prevented the elevation of plasma cholesterol due to dietary cholesterol excess. Moreover, BCD produced a dose-dependent effect in reducing liver cholesterol storage, stimulating hepatic cholesterogenesis, increasing the proportion of primary bile acids in bile and in feces, and the fecal loss of neutral sterols and bile acids. Pigs receiving 10% BCD thus differed markedly from controls, especially for HMG-CoA reductase and cholesterol 7alpha-hydroxylase hepatic activities (x5), and fecal output of total bile acids (x3) and hyocholic acid (x20), and their overall cholesterol synthesis was higher (+50%), despite the abundant dietary cholesterol. Owing to the property of BCD to bind cholesterol and bile acids in vitro, these results suggest that this resistant carbohydrate accelerates body cholesterol turnover by reducing cholesterol absorption, increasing cholesterol and bile acid synthesis, and altering the action of the intestinal microflora.

Effect of two levels of transgalactosylated oligosaccharide intake in rats associated with human faecal microflora on bacterial glycolytic activity, end-products of fermentation and bacterial steroid transformation

The effects of two levels of transgalactosylated oligosaccharide (TOS) intake on bacterial glycolytic activity, end products of fermentation and bacterial steroid transformation were studied in rats associated with a human faecal flora. Rats were fed a human-type diet containing 0, 5 or 10% TOS. Caecal pH decrease correlated with the amount of TOS in the diet. Intake of the TOS diet induced a decrease in blood cholesterol and a strong increase in beta-galactosidase activity in the hindgut. TOS fermentation led to production of hydrogen and short chain fatty acids, whereas ammonia and branched-chain fatty acids were decreased. A diet containing 10% TOS increased caecal lactic acid concentrations and reduced beta-glucuronidase activities and steroid transformation.

Effects of fructo-oligosaccharides ingestion on fecal bifidobacteria and selected metabolic indexes of colon carcinogenesis in healthy humans

Fructo-oligosaccharides (FOS) are a mixture of oligosaccharides consisting of glucose linked to fructose units. They are not digested in the human small intestine but fermented in the colon, where they could specifically promote the growth of some species of the indigenous microflora, especially bifidobacteria. We assessed in healthy humans the effects of FOS ingestion in fecal bifidobacteria and selected metabolic indexes potentially involved in colonic carcinogenesis. Twenty volunteers randomly divided into two groups were studied for three consecutive 12-day periods. During the ingestion period, they received 12.5 g/day FOS or placebo (saccharose) in three oral doses. Stools were regularly collected and analyzed. FOS ingestion led to an increase in fecal bifidobacterial counts [7.9 +/- 0.5 to 9.1 +/- 0.3 (SE) log colony-forming units/g wet wt, p < 0.01] and beta-fructosidase activity (9.6 +/- 1.9 to 13.8 +/- 1.9 IU/g dry wt, p < 0.01). In contrast, FOS ingestion had no significant effect on fecal total anaerobes, pH, the activities of nitroreductase, azoreductase, and beta-glucuronidase, and the concentrations of bile acids and neutral sterols. We conclude that ingestion of FOS, at a clinically tolerated dose of 12.5 g/day, led to an increase in colonic bifidobacteria. This effect was not associated in healthy humans with beneficial changes in various factors potentially involved in the pathogenesis of colonic cancer.

Antilithiasic and hypocholesterolemic effects of diets containing autoclaved amylomaize starch in hamster

The prevention of cholelithiasis by dietary manipulation was investigated in hamsters receiving a fat-free lithogenic (L) diet or this diet in which sucrose was replaced by 12 (group AS12), 36 (group AS36), 48 (group AS48), or 72.5% (group AS72.5) of autoclaved amylomaize starch for seven weeks. All hamsters (6/6) had cholesterol gallstones in groups L and AS12, while only 3/6 hamsters in group AS36 had gallstones. None were present in groups AS48 and AS72.5. Except in group AS12, biliary cholesterol level and lithogenic index (LI) decreased significantly in hamsters receiving amylomaize starch. Plasma cholesterol concentration was reduced by 31 and 54%, respectively, in groups AS48 and AS72.5 as compared to group L. The concentration of esterified cholesterol in the liver was also reduced significantly in all groups receiving amylomaize starch. Hepatic cholesterogenesis was decreased by 74 and 65%, respectively, in groups AS48 and AS72.5 as compared to group L. The transformation of cholesterol to bile acids was increased in group AS72.5 (+152%) as compared to L, while fecal cholesterol excretion was strongly lowered (-31%). Amylomaize starch reduced the microbial transformation of cholesterol to coprosterol and epicoprosterol, and in group AS72.5 it decreased the degradation of cholic acid. Thus, this autoclaved amylomaize starch, which could be used in human nutrition, prevents cholelithiasis and lowers cholesterolemia.

Evidence for the absence of participation of the microbial flora in the hypocholesterolemic effect of guar gum in gnotobiotic rats

Germ-free (GF) and heteroxenic (Hx) rats were given a hypocholesterolemic diet (Hyper) with or without 5% guar gum (GG) for 4 weeks. The GF and Hx rats fed GG diets showed a lower hepatic and plasmatic cholesterol level when compared with Hyper groups. This reduction of cholesterolemia was due to a decrease in the chylomicron + very low density lipoprotein (VLDL) fraction. The caecal and portal concentrations of propionate were 30% higher in Hx rats fed the GG diet than in Hx rats fed the Hyper diet. These results exclude the participation of the intestinal microflora in the hypocholesterolemic effect of GG, and show that guar gum nullifies the effect of the hypocholesterolemic diet in the GF rats.

Interaction of beta-cyclodextrin with bile acids and their competition with vitamins A and D3 as determined by 1H-NMR spectrometry

The interaction of beta-cyclodextrin (beta-CD) with four bile acids, cholic, taurocholic, chenodeoxycholic and lithocholic, was demonstrated by proton-NMR spectroscopy. Lithocholic and chenodeoxycholic acids exhibit a stronger affinity for beta-CD than cholic and taurocholic acids. The affinity of bile acids for beta-CD increases in relation to their hydrophobicity. The competition between these bile acids and the lipophilic vitamins A and D3 in the formation of beta-CD inclusion complexes was studied. These vitamins compete with cholic and taurocholic acids whereas they do not with lithocholic and chenodeoxycholic acids. In the latter case all of the beta-CD present was consumed by the bile acids with the vitamins remaining free in the medium. The affinity of vitamins A and D3 for beta-CD is lower than that of the bile acids. Therefore, when lithocholic or chenodeoxycholic acids are present, the formation of beta-CD inclusion complexes with the vitamins does not occur. The results of this study suggest that depletion of lipophilic vitamins will not occur upon ingestion of beta-CD, thus providing further support for the safety and suitability of beta-CD as an ingredient in foods and orally administered drugs.

Heat or gamma irradiation sterilization affects the hypocholesterolemic effect of guar gum in axenic and heteroxenic rats

1. Twenty-two axenic (germfree) or thirty heteroxenic (axenic colonized with human flora) 2.5-3.5 months old female Fisher rats were fed for four weeks either a hypercholesterolemic (HYPER) diet or a HYPER diet containing 5% guar gum (GG) sterilized by heat or by gamma irradiation. 2. Axenic rats fed the irradiated GG diet had higher cholesterolemia than their counterparts fed an autoclaved diet (4.50 vs 2.29 mmol/l), whereas the method of sterilization had no effect on plasma cholesterol in axenic HYPER or heteroxenic animals (7.35 vs 6.51 mg/dl). 3. The levels of hepatic esterified cholesterol were higher in heteroxenic animals fed the irradiated GG diet than in their counterparts fed the autoclaved GG diet (5.65 vs 3.57 mmol/g tissue). 4. The composition of volatile fatty acids in the cecal content of heteroxenic rats was dependent on the method of sterilization regardless of the presence of fiber: the levels of butyrate were 2.88 and 0.85 mumol/g for rats fed the autoclaved and irradiated diets, respectively. 5. Gamma irradiation abolished the cholesterol-lowering effect of guar gum, whereas sterilization by heat preserved this effect. 6. The hypocholesterolemic effect of guar was reduced by gamma irradiation sterilization and was probably mediated by qualitative changes in the intestinal microflora which interfered with bile acid absorption.

Hypolipidemic effects of beta-cyclodextrin in the hamster and in the genetically hypercholesterolemic Rico rat

The effect of increasing amounts of a cyclic oligosaccharide, beta-cyclodextrin (BCD), included in the diet on plasma cholesterol and triglycerides, was investigated in two animal models, namely in male genetically hypercholesterolemic Rico rats and in male Syrian hamsters. The distribution of bile acids in the gastrointestinal tract and in the feces of hamsters was also determined. In the Rico rats and hamsters, plasma cholesterol and triglycerides decreased linearly with increasing doses of BCD. In these two species, 20% BCD as compared to control diet lowered cholesterolemia (-35%) and triglyceridemia (-70%). In the hamster, the BCD diet caused a marked decrease in cholesterol and triglycerides in chylomicrons and very low density lipoprotein, and in high density lipoproteins cholesterol. Composition and amounts of bile acids were modified in the gastrointestinal tract of hamsters receiving 10% BCD as compared to the control group. The total bile acid content of the gallbladder of treated hamsters was fourfold higher than in the control group, and the bile contained a large amount of hydrophilic bile acids. This trend was also observed in the small intestine, in which percentages and total quantities of cholic plus deoxycholic acids (cholic pathway) were higher than those of chenodeoxycholic plus ursodeoxycholic plus lithocholic acids (chenodeoxycholic pathway). The bile acid contents of the cecum and colon of treated hamsters were 2.7-fold higher than those of control animals, but the bile acid composition was similar in the two groups of hamsters.(ABSTRACT TRUNCATED AT 250 WORDS)

Intestinal mucosal morphometry and ileal epithelial renewal in conventional and germ-free rats fed an amylomaize starch diet

Intestinal mucosal morphometry and ileal epithelial renewal were studied in conventional (CV) and germ-free (GF) rats fed either poorly digestible amylomaize or normal maize starch diets. Intestinal morphometry and position of labelled enterocytes were studied at various times after tritiated thymidine injection. With amylomaize starch diet, no difference was observed in the size of crypts (C), villi (V) and C + V between duodenum and jejunum both in CV and GF rats. In the ileum, however, values were significantly lower than those in the duodenum and jejunum. Furthermore, the presence of the microbial flora led to higher values when compared with GF values. Despite the morphological modifications in the ileum, no significant difference was detected in the labelled cell positions and epithelial renewal time between CV and GF values. This suggests that the resistant part of amylomaize starch was responsible for the modification in mucosal morphometry and the longer ileal epithelium renewal time in CV rats which then becomes similar to that in GF rats.

Biodynamics of cholesterol and bile acids in the lithiasic hamster

By using the isotopic equilibrium method in the young male Syrian hamster, the rates of cholesterol turnover processes, i.e. dietary cholesterol absorption, cholesterol synthesis, cholesterol excretion in the faeces and urine and cholesterol transformation into bile acids, were determined in the hamster receiving a control (C) or a lithogenic diet (L) for 7 weeks. At the end of this period the gall bladder of all animals in group L contained cholesterol gallstones. The coefficient of dietary cholesterol absorption was reduced by 26%, cholesterol synthesis and cholesterol faecal excretion were twofold higher in group L than in group C. Bile acid content in the small intestine was diminished in group L, but bile acid composition was similar in the two groups. The increase in cholesterogenesis in lithiasic animals essentially took place in the liver. Bile acid biosynthesis did not significantly differ in the two groups, but represented only 35% of total cholesterol input (dietary absorption + internal secretion) in group L v. 52% in group C. Thus, in the lithiasic hamster, hepatic synthesis of cholesterol and bile acids are not coupled. The molar percentage of cholesterol in bile was twofold higher in group L than in group C but those of bile acids and of phospholipids were not modified. In the lithiasic hamster the specific activity of biliary cholesterol was similar to that in plasma and liver. Consequently, biliary cholesterol does not derive directly from cholesterol newly synthesized in the liver but from hepatic cholesterol rapidly exchangeable with plasma cholesterol.

Metabolism and effects on biliary lipid secretion of murocholic acid in the hamster

The metabolism of murocholic acid (MC), a 6 beta-hydroxylated bile acid, was investigated after intravenous (i.v.), intraduodenal (i.d.) or intragastric (i.g.) administration to bile fistula hamsters. The effects on biliary cholesterol and phospholipid secretion were measured during intravenous infusions of increasing doses of [3H]MC. At an infusion rate of 0.1 or 1 mumol.min-1.kg-1, the hepatic uptake was effective. More than 90% of the dose was recovered in bile within 4 h. A bolus injection of 500 micrograms of [3H]MC in the duodenum led to a rapid and efficient biliary secretion of radioactivity. Increasing i.v. infused doses of MC had no effect on bile flow or biliary cholesterol output compared to the controls. Phospholipid secretion was significantly reduced (0.113 mumol.min-1.kg-1 versus 0.238 mumol.min-1.kg-1 in in controls per mumol.min-1.kg-1 of excreted bile acids) as MC progressively replaced the endogenous bile acid pool in bile. After i.v. and i.d. administration, MC was secreted in bile as glyco and tauro conjugates without additional hepatic hydroxylation, sulfation or glucuronidation. The i.g. ingestion of MC followed by the faecal analysis of metabolites showed the formation of hyodeoxycholic acid and 3 alpha-OH-6-oxo-5 beta-cholan-24-oic acid. An equivalent experiment with hyodeoxycholic acid gave MC and the same oxo bile acid. We concluded that MC is metabolized by the hamster liver as an endogenous bile acid, which undergoes intestinal bacterial transformation into a 6-oxo derivative and is then reduced into hyodeoxycholic acid. This process is completely reversible.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of chronic glucagon administration on cholesterol and bile acid metabolism

Male adult Wistar rats received daily, at 9 a.m. and 5 p.m., 10 micrograms of Zn-protamine glucagon for 21 days by subcutaneous injections. The blood glucose level was not significantly modified. Cholesterol and triacylglycerol levels were decreased by 40 and 70% in plasma but not in the liver. The rates of cholesterol turnover processes were determined in vivo with an isotope balance method. Internal secretion of cholesterol (13.8 +/- 0.5 mg/day per rat in control rats and 22.4 +/- 0.9 mg/day per rat in glucagon-treated rats) and cholesterol transformation into bile acids were strikingly increased by chronic administration of glucagon. Biliary secretion rates of bile acids measured by a wash-out method were increased by 139%, while the intestinal bile acid pool was not changed. The enterohepatic cycle number was increased from five per day in control rats to nine per day in glucagon-treated rats. An increased turnover rate of the exchangeable cholesterol would explain the hypocholesterolemic effect of glucagon.

Metabolism of beta-muricholic acid in man

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

Increase in the ileal absorption rate of sodium taurocholate in germ-free or conventional rats given an amylomaize-starch diet

Twenty germ-free and twenty conventional male Fischer 344 rats, 3 months old, were fed ad lib. diets based either on normal or on amylomaize starch for 1 month. The absorption rate of sodium taurocholate, 25 mmol/l, was determined in vivo in jejunal or ileal segments. Each determination included five rats. Jejunal absorption rate was not modified either by the amylomaize-based diet or by the digestive microflora. Ileal absorption rate was slightly higher in germ-free than in conventional rats. Ileal absorption rate was largely increased by the amylomaize-based diet. This increase was slightly larger in germ-free rats than in conventional rats. It is suggested that dietary amylomaize starch has an action on the active absorption process of bile acid.

Dietary fiber and cholesterol and bile acid metabolism in axenic (germfree) and holoxenic (conventional) rats. III. Effect of non-sterilized pectin

Axenic (germfree) and holoxenic (conventional) rats were given a pectin-containing diet (5%) or a pectin-free diet. The diet was not sterilized and the axenic state was maintained by the addition of antibiotics. Pectin modified little or not at all the quantity of bile acids in the small intestine, fecal bile acid excretion and fecal elimination of the sum of cholesterol and bile acids. It similarly decreased the concentration of liver cholesterol and the amount of bile acids in the cecum and large intestine of both germfree and conventional rats. Pectin decreased the absorption coefficient of dietary cholesterol and its plasma concentration and increased fecal cholesterol elimination in conventional rats but not in germfree animals. The data imply that some of the actions of pectin depend on the presence of the intestinal flora but the exact nature of this relationship is unclear.

Effect of wheat bran upon gastro-intestinal transit in germ-free and conventional rats

Germ-free and conventional rats were fed a semi-synthetic diet including 10% wheat bran for 1 month. They were compared to similar rats fed the same diet without bran. Transit of polyethylene glycol (PEG) 4000 was studied in giving the marker either in saline or in the diet. The presence of a bacterial flora was found to accelerate small intestine transit and total transit. The ingestion of solid food slowed gastric emptying but had little effect on small intestine transit. Wheat bran slowed gastric emptying of PEG in most of the experimental groups. It had no significant effect on small intestine transit except in germ-free rats having received the marker in solid food. It accelerated total transit in germ-free and conventional rats. The results suggest that bran mainly exerts its action in the hindgut. The role of microflora in this action of bran is discussed.

Intestinal absorption, excretion, and biotransformation of hyodeoxycholic acid in man

Five patients fitted with a biliary T-tube after cholecystectomy were given orally a tracer dose of [14C]hyodeoxycholic acid and 500 mg of the same unlabeled acid. Intestinal absorption and biotransformation, liver metabolism, bile secretion, fecal and urinary excretions of this acid or of its metabolites were studied. Hyodeoxycholic acid was well absorbed by the human intestine. It was not subjected to intestinal transformations and, particularly, did not produce a significant amount of lithocholic acid, which does not support the existence of intestinal bacterial 6 alpha-dehydroxylases. The percentage of hyodeoxycholic acid and of its metabolites recovered in bile varied from 11.5 to 31%. Two major metabolites were isolated from bile: glycohyodeoxycholic acid and hyodeoxycholic acid glucuronide. Analysis of urinary bile acids showed that a large proportion (30-84%) of the administered hyodeoxycholic acid was excreted by the kidney as a glucuronide. The large extent of both glucuronidation and urinary excretion of hyodeoxycholic acid is a unique example of bile acid metabolism and excretion in man.

Effect of amylomaize starch on cholesterol and bile acid metabolisms in germfree (axenic) and conventional (holoxenic) rats

Germfree and conventional rats were given a semi-synthetic diet containing either normal cornstarch or an amylomaize starch. The experimental groups thus formed were compared to assess the effects of these two types of starch and to determine if digestive tract microflora was involved in these effects. The presence of amylomaize starch decreased body growth in germfree and conventional rats, increasing food intake in the former and decreasing it in the latter. In conventionals, amylomaize starch decreased the apparent digestibility of the ration only slightly, while in germfrees it diminished apparent digestibility considerably. The cecal weight of germfree animals was not modified by amylomaize starch but that of conventional rats was increased fourfold. In both types of rat, amylomaize starch largely decreased the plasma concentration of cholesterol, largely increased the total amount of bile acids in the small intestine but slightly modified the fecal elimination of cholesterol and bile acids. It augmented the cholesterol concentration in the liver of germfrees and decreased it in conventionals while, on the contrary, it diminished the total amount of bile acids in the hind gut in the former and augmented it in the latter. This starch did not change bile acid deconjugation in conventional rats but considerably decreased other bacterial transformations of cholesterol and bile acids. Digestive tract microflora was undoubtedly involved in the action of amylomaize starch on cecal weight, ration digestibility, food intake, hepatic cholesterol concentration, the amount of bile acid in the hind gut and obviously in the transformation of cholesterol and bile acids. It did not play a role in the other effects of this starch: the strong decrease in the concentration of plasma cholesterol was the direct effect of amylomaize starch on rat metabolism.

Dietary fiber and cholesterol and bile acid metabolisms in axenic (germfree) and holoxenic (conventional) rats. I. -- Effect of wheat bran

Axenic (GF) and holoxenic (CV) rats were given a semi-synthetic diet containing no fiber (0) or 10 p. 100 bran (B). The GFO, GFB, CVO and CVB groups were compared to assess the action of the flora and the bran. The bran diet did not change body growth, food intake or cecal water content. It caused only a slight decrease in the digestive utilization of the diet in the holoxenic rats and a decline in cecal weight in the axenic rats. The bran diet modified unabsorbed cholesterol transit in both types of rats, and slightly altered dietary cholesterol absorption which was a little lower in axenics than in holoxenics. In the former (GF), the bran-containing diet dit not change either the plasma or the hepatic cholesterol concentration. In the latter (CV), it increased plasma cholesterol which was lower in CVO rats than in the other three groups and decreased hepatic cholesterol which was thus lower in the CVB lot than in the others. The bran diet reduced fecal cholesterol elimination in axenic and holoxenic rats. This decrease was a little higher in the latter. The digestive tract microbial flora was thus implicated in the effect of bran on those characteristics of cholesterol metabolism. The bran did not change fecal bile acid composition in the axenics. In the holoxenics, it contributed to make this composition uniform because without bran, individual compositions varied. The microbial flora thus changed many aspects of bran action on cholesterol and bile acid metabolisms. But total cholesterol and bile acid elimination was only slightly affected by those two factors.

Dietary fiber and cholesterol and bile acid metabolisms in axenic (germfree) and holoxenic (conventional) rats. II. Effect of pectin

Axenic and holoxenic rats were fed with a semi-synthetic diet containing 5 p. 100 pectin as the only fiber. Although the microbial flora of the digestive tract converted most of the bile acids in holoxenic rats, it hardly changed the other characteristics of cholesterol and bile acid metabolisms, except intestinal bile salt pools which were much larger in the axenic rats. When the pectin-containing and pectin-free diets were compared, it appeared that the former diet increased cecal weight, especially in axenic rats, but slightly modified cholesterol and bile acid metabolisms. However, the values of some characteristics of those metabolisms varied individually in the holoxenic rat fed with the pectin-containing diet, while they were very homogeneous in the other groups. This heterogeneity might result from pectin-digestive tract microbial flora interactions which would vary among individuals.

Effect of various modifications in the diet on ileal epithelium renewal in germ-free and conventional rats

Renewal of the ileal epithelium has been studied in germ-free (GF) and conventional (CV) rats fed with a semi-synthetic diet in the following forms: a) pellets sterilized by autoclaving (Pel. Au. diet); b) powder sterilized by gamma irradiation; when given to the rats, its weight in water was added to make a paste (Pa. I. diet); c) powder treated as (b) but with 10 p. 100 lactose added (L. Pa. I. diet). Ileal epithelium renewal time was similar in the GF rats fed with the Pel. Au. and Pa. I. diets. It was shorter in the CV rats fed with these two diets than in the GF rats and also in the CV rats given the Pa. I. diet than in those given the Pel. Au. diet. In GF and CV rats fed with the lactose diet, L. Pa. I., ileal epithelium renewal time was similar. These different effects were mainly due to variations in the number of cells produced in Lieberkühn's crypts. They were not related to changes in the intestinal bile salts pool caused by the different diet treatments.

Variations of bile salt pool size and secretion rate in rats according to the modes of sterilization and preparation of a semi-synthetic diet

A semi-synthetic diet was sterilized by irradiation and given to rats as pellets, powder or paste obtained by admixing an equal amount of water. The bile salt pool increased from the first to the third treatment. That effect disappeared when the starch was replaced by sucrose or when the diet was autoclaved instead of irradiated. The bile duct secretion of bile salts varied according to the bile salt pool. Hypotheses are proposed to explain the relationship between the form of the diet and bile salt pool size and secretion.

Capsular serotypic specificity of the protection conferred on mice by Klebsiella pneumoniae ribosomal preparations

Klebsiella pneumoniae ribosomal preparations protect mice immunized by the subcutaneous route against an intraperitoneal challenge of 100 50% lethal doses. The minimal protective doses are 5 and 0.4 micrograms of proteins for preparations extracted from strains of capsular serotypes 1 and 2, respectively. This difference in protective activity is also found in bacteria killed by Formalin. The protective activity of these preparations is not diminished by their purification on sucrose gradient, which eliminates most of the membrane vesicles which are visible by electron microscopy. The use of four strains of K. pneumoniae belonging to capsular serotypes 1 and 2 allowed us to show that the immunoprotective capacity of the ribosomal preparations was specific to the capsular serotype of the origin strain. This was confirmed by experiments in which the serum of immunized mice was transferred passively. The experimental data favor the presence in the ribosomal preparation of antigens belonging to the bacterial surface and resisting elimination by ultracentrifugation on sucrose gradient. Those surface antigens (possibly capsular polysaccharide) at least play a role in the orientation of the specificity of the protection induced by the ribosomal preparations.

Measurement of fecal bile acid excretion in gnotobiotic rats: comparison of gas-liquid chromatography and [4(-14C)] cholesterol isotopic equilibrium

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

[Action of the microbial flora of the digestive tract on the biosynthesis of cholic acid in the rat (author's transl)]

Axenic and holoxenic (conventional) rats were fed a diet containing trace amounts of [2,4-3H]cholic and [24-14C]chemodeoxycholic acids. In the feces of both groups of rats, the percentage of labelled bile acids which were 3H-labelled was slightly different. In the experimental conditions used, the intestinal microflora only slightly modified the synthesis of 12alpha-hydroxylated bile acids.

[Formation of omega-muricholic acid and fecal excretion of biliary acids in rats]

Two groups of Rats which were fed the same diet, excreted fecal bile acids of different patterns: in one group, the feces contained a large amount of omega-muricholic acid and very little hydrodeoxycholic acid; in the other group the reversed composition was observed. The first group excreted more total bile acids than the second. This observation suggests that the formation of a large amount of omega-muricholic acid results in an increase in total bile acid fecal excretion.

[The effect of dietary lactose on the ileal absorption of sodium taurocholate in rats]

When Rats were fed a lactose containing diet, both the absorption rate of sodium taurocholate at the level of ileum and the contents of bile acids of the small intestine were increased. On the contrary, feeding of lactose did not modify the daily fecal excretion of bile acids. It therefore appears that dietary lactose increases the intestinal pool of bile acids by increasing their ileal absorption rate and that this effect of lactose is not subordinated to a modification of bile acid synthesis.

[Action of microbial flora of the digestive tract on the metabolism of bile acids in the rat (author's transl)]

An isotopic balance is established in rats receiving a regular feed intake of [4-14-C]cholesterol so that various chemical species of bile acids have the same specific activity. This property is used to study bile acids distribution in the rat liver, digestive tract and fecal excretion. Bile acids are separated by thin-layer chromatography, radioactivity is determined by liquid scintillation, and the mass by 3-hydroxysteroid dehydrogenase action. The resulting comparative study made between the germ-free rat (axenic rat) and the rat exposed to microbes ("holoxenic" or conventional rat) receiving a semi-synthetetic feed, shows the influence excercised on the metabolism by the microbial flora of the digestive tract. This study confirms that the axenic rat compared to its holoxenic homologue has a higher bile acids pool and a lower fecal excretion. At all levels of the digestive tract (small intestine and the whole caecum and large intestine), probably as well as in the liver, the total amount of bile acids which is observed in the axenic rat is about twice the amount observed in the holoxenic rat, but fecal excretion is decreased by 20%. Values obtained by this method are higher than those previously observed by other authors using gas-liquid chromatography or [14-C]cholic acid isotopic dilution. This study also confirms that cholic and beta-muricholic acids are the main bile acids in the axenic rat and in addition establishes that in this animal bile acids composition is complex and varies from the small intestine to the feces. Besides cholic, alpha- and beta-muricholic, chenodeoxycholic and ursodeoxycholic acids, unidentified chemical species constitute 21% of the whole in the feces. Comparing the compositions observed in axenic and holoxenic rats in this experiment, it could not be determined if the relative activity of the two pathways of bile acid biosynthesis is deeply or only slightly changed by the presence of microbial flora. This is because of a large fraction of unknown composants in the feces of the axenic rat and the extreme complexity in the feces of the holoxenic rat.