Lionelle Nugon-Baudon

Comparative study of the fermentative characteristics of inulin and different types of fibre in rats inoculated with a human whole faecal flora

It is known that the physico-chemical characteristics of fibre modify their fermentation characteristics in the colon. Previously we showed the varying effects of inulin and different types of fibre on the hepatic and intestinal xenobiotic-metabolizing enzymes (XME) in initially germ-free rats inoculated with a human, methanogenic, whole-faecal flora (Roland et al. 1994). The aim of the present work was to assess whether or not these effects could be related to differences in production of fermentation metabolites (gases excreted in vivo and caecal metabolites) due to the different compositions of fibre. The different types of fibres were analysed with regard to their solubility and their composition of neutral monomers and uronic acids. Inulin was totally soluble, carrot (Daucus carota), cocoa (Theobroma cacao) and wheat bran were partially soluble; pea (Pisum sativum) and oat were nearly totally insoluble. Uronic acids were found mostly in carrot and cocoa fibre. Glucose was present as the main neutral monomer in each fibre type. Xylose was found also in wheat bran, pea and oat fibres, and arabinose was found in wheat bran. Inulin consumption led to high levels of H2 production but no CH4 production, to a 4-fold greater caecal concentration of butyrate than with the other fibres and to a decrease in caecal pH. Conversely, rats fed on carrot or cocoa fibre produced a large amount of CH4 but no H2 and generated a different profile of short-chain fatty acids (SCFA). The lowest amounts of gases and SCFA were found in rats fed on wheat bran, pea and oat fibre. We observed a relationship between the caecal concentration of SCFA and the activity of hepatic glutathione-S-transferase (EC 2.5.1.18) but no direct link was shown between the other XME and the fermentation profile.

Rape-seed meal toxicity in gnotobiotic rats : influence of a whole human faecal flora or single human strains of Escherichia coli and Bacteroides vulgatus

Gnotobiotic growing rats harbouring either a whole human faecal flora or single human strains of Escherichia coli (EM0) or Bacteroides vulgatus (BV8H1) were fed for 7 weeks on semi-synthetic diets in which the protein source was either soya-bean meal (SM) or rape-seed meal (RM). For each bacterial status the RM-diet group was compared with the control group fed on the SM diet. The association of human faecal flora with the RM diet was responsible for reduced feed intake and reduced weight gain, an enlargement of the liver and thyroid and a decrease in both thyroxine and triiodothyronine plasma levels. The association of the B. vulgatus BV8H1 strain with the RM diet reproduced all these effects, except that triiodothyronine plasma levels were not significantly modified. Rats inoculated with the E. coli EM0 strain and fed on the RM diet exhibited a goitre and lowered thyroxine and triiodothyronine plasma levels. These results show that the human intestinal microflora may be involved in glucosinolate metabolism when cruciferous vegetables are consumed by man. The specificity of the symptoms observed according to the rat bacterial status supports the hypothesis that bacteria yield specific toxic glucosinolate derivatives according to their enzymic potential.

Glucosinolates and Glucosinolate Derivatives: Implications for Protection Against Chemical Carcinogenesis

CONTENTS G L U CO S I N 0 LAT ES : OCCURRENCE AND METABOLIC FATE . G L U C O S I N O L A T E S I N T H E P L A N T . GENESIS O F G L U C O S I N O L A T E D E R I V A T I V E S . Enzymic hydrolysis and autolysis in cruciferous vegetables . Bacterial metabolism of glucosinolates . . F R O M T H E P L A N T T O T H E D I E T : I N F L U E N C E O F F O O D P R O C E S S I N G A N D D I E T A R Y H A B I T S . . TOXICITY OF GLUCOSINOLATES AND GLUCOSINOLATE

The human colonic microflora influences the alterations of xenobiotic-metabolizing enzymes by catechins in male F344 rats

As other xenobiotics, polyphenols are metabolized both by the endogenous detoxication system and the gut microflora. We hypothesized that the presence of a gut microflora may account for the effect of catechins on phase I and II xenobiotic-metabolizing enzymes and that the human bacterial metabolites may be different from those of a rodent gut microflora. Therefore, the effects of 2% (+)-catechin or 2% (-)-epicatechin were studied in germ free (GF) rats and rats inoculated with the flora of a human volunteer (HFA). In addition, the catechins were administered in ethanol as a vehicle. In the liver, (+)-catechin or (-)-epicatechin decreased the total amount of CYP450 in both GF and HFA rats while the isoenzyme CYP2E1 decreased. In GF rats only, CYP2C11 increased when compared to the rats treated with the vehicle alone. (+)-catechin increased the specific activity of UGT-chloramphenicol in GF rats only and that of cytosolic glutathion-S-transferase (GST) in HFA rats only. In the intestine, (+)-catechin and (-)-epicatechin increased the specific activity of UGT-4-methylumbelliferone in both GF and HFA rats and that of UGT- chloramphenicol in HFA rats only. In conclusion, the presence of a human flora in rats is able to modify the inducing effect of catechins on the UGT and GST activities suggesting the involvement of bacterial metabolites. The alterations on CYP 450 are independent of the presence of a human gut flora.

Modulation of the biological effects of glucosinolates by inulin and oat fibre in gnotobiotic rats inoculated with a human whole faecal flora

The influence of dietary fibre on the biological effects of glucosinolates was investigated in gnotobiotic rats harbouring a human whole faecal flora. Animals were fed for 6 wk with diets containing 12% rapeseed meal (RSM) supplemented or not supplemented with 10% inulin (INL) or oat fibre. Both fibre types enhanced the liver hypertrophy due to RSM to equal extents, but had different effects on the other glucosinolate-related toxic effects. INL partially restored a normal thyroid hormone status whereas kidney weight, goitre and growth deficit were increased on exposure to the diet containing oat fibre. Oat fibre and, to a lesser extent, INL modulated the alterations of digestive xenobiotic-metabolizing enzymes (XME) induced by RSM. They counter-balanced the induction of hepatic cytochrome P-450 and lessened the induction of uridine diphosphate-glucuronosyltransferase in the liver but did not modify depletion of its activity in the small intestine. On the other hand, they enhanced the induction of glutathione S-transferase in the liver and the large intestine but not in the small intestine. These findings give new evidence that the biological effects of naturally occurring non-nutrient compounds are closely dependent on the composition of the diet. Two mechanisms are proposed to explain the different influence of INL and oat fibre on RSM toxicity. Their different fermentative characteristics could lead to a modulation of the bacterial metabolism of glucosinolates in the caecum. Alternatively, their own action on the digestive XME could modify the subsequent metabolism of bacterial glucosinolate derivatives.

Effects of the bacterial status of rats on the changes in some liver cytochrome P450 (EC 1.14.14.1) apoproteins consequent to a glucosinolate-rich diet

The aim of the present work was to investigate the influence of the intestinal microflora on the changes in hepatic cytochrome P450 apoproteins induced by dietary glucosinolates. Ten rats harbouring a conventional digestive microflora were offered either a diet containing 390 g myrosinase-free rapeseed meal/kg (n 5) or a control diet devoid of glucosinolates (n 5). A similar trial was performed using germ-free rats. After 4 weeks of exposure to the dietary regimens, animals were slaughtered and their livers removed for preparation of microsomes and analysis of cytochrome P450 (EC 1.14.14.1). The glucosinolate-rich diet decreased the concentration of total cytochrome P450 in conventional rats only (-34%). The bacterial status did not modify the concentration of apoproteins CYP1A2 and CYP2B1/B2, but greatly decreased the concentration of the male constitutive isoform CYP2C11 (-53 and -45% respectively in conventional and germ-free rats). Germ-free rats fed on the glucosinolate-rich diet had a greater concentration of CYP3A (+139%) and a lower concentration of CYP2E1 (-32%) than their counterparts fed on the control diet. However, these differences were absent in conventional animals. On the whole, the influence of the intestinal microflora on the changes in hepatic cytochrome P450 due to the consumption of cruciferous vegetables is very complex and obviously involves different mechanisms according to the apoprotein.

Alterations of the hepatic xenobiotic-metabolizing enzymes by a glucosinolate-rich diet in germ-free rats: influence of a pre-induction with phenobarbital

Germ-free growing rats were fed on a glucosinolate-rich diet (rapeseed-meal-based) and compared with counterparts fed on a glucosinolate-free diet (soya-bean-meal-based), both diets being isonitrogenous and isoenergetic. For each diet half the animals received phenobarbital in drinking water as an inducer of xenobiotic-metabolizing enzymes. Some of the usual deleterious glucosinolate-linked effects, i.e. kidney hypertrophy and reduction in growth and feed intake, were followed and three of the major hepatic xenobiotic-metabolizing enzymes were investigated. Growth rate, dietary intake and kidney weight were not altered by glucosinolates in the absence of intestinal microflora, whether the animals were treated with phenobarbital or not. As far as the hepatic xenobiotic-metabolizing enzymes are concerned, the specific level of cytochrome P450 and the specific activities of glutathione-S-transferase (EC 2.5.1.18) and UDPglucuronosyltransferase (EC 2.4.1.17) remained unchanged in rats receiving the glucosinolate-rich diet compared with the control animals. Despite the low dose given, phenobarbital displayed its usual inducing effect on all three enzymes, similar whatever the diet. A previous counterpart experiment performed with conventional animals had shown that glucosinolate feeding led to large alterations of the variables herein studied, some of these modifications being hugely enhanced by a phenobarbital treatment. Therefore, the present results obtained on germ-free animals prove that alterations of the xenobiotic-metabolizing enzymes induced by glucosinolates are somehow mediated by the intestinal microflora. Furthermore, the involvement of those enzymes in glucosinolate toxicity definitely requires the presence of the intestinal microflora.

The bioavailability of α- and β-carotene is affected by gut microflora in the rat

The present study examined whether the intestinal microflora could affect the bioavailability and vitamin A activity of dietary alpha- and beta-carotene in the rat. In the first set of experiments, we used conventional, germ-free (axenic), and human-flora-associated (heteroxenic) rats. In a second series, conventional rats were treated with either an antibiotic mixture or a potent inhibitor of gastric secretion (Omeprazole). All animals were first depleted of vitamin A over 4 weeks and then were fed on a sterilized diet supplemented with 14 mg beta-carotene and 3 mg alpha-carotene/kg for 2 weeks. In both experiments, a reduction in the intestinal microflora resulted in an increased storage of beta-carotene, alpha-carotene and vitamin A in the liver. Neither the nature of the metabolism of the intestinal microflora (aerobic or anaerobic) nor treatment with omeprazole, to modify intestinal pH, induced a significant effect on the measured variables. When incubated with 15 mumol beta-carotene/l for 72 h, neither the anaerobic nor the aerobic sub-fractions obtained from rat or human faeces contributed to beta-carotene degradation or to vitamin A synthesis. These findings suggest that reduction in gut microflora results in a better utilization of alpha- and beta-carotene by rats, although bacteria do not have a direct effect on the bioavailability of these pigments.

Variations in digestive physiology of rats after short duration flights aboard the US space shuttle.

The purpose of this work was to assess the influence of microgravity on several endogenous and microbial parameters of digestive physiology. On the occasion of two Spacelab Life Sciences missions, SLS-1 (a 9-day space flight) and SLS-2 (a 14-day space flight), Sprague-Dawley rats flown aboard the US space shuttle were compared to age-matched ground-based controls. In both flights, exposure to microgravity modified cecal fermentation: concentration and profile of short-chain fatty acids were altered, whereas urea and ammonia remained unchanged. Only in SLS-1 was there an induction of intestinal glutathione-S-transferase. Additional analyses in SLS-2 showed a decrease of hepatic CYP450 and of colonic goblet cells containing neutral mucin. After a postflight recovery period equal to the mission length, only modifications of the hepatic and intestinal xenobiotic metabolizing enzymes still persisted. These findings should help to predict the alterations of digestive physiology and detoxification potential likely to occur in astronauts. Their possible influence on health is discussed.

Production d'amines in vitro et in vivo par une souche de lactobacille isolée d'un jabot de coq

Summary The chicken digestive tract is mainly colonized by bacteria belonging to the Lactobacillus genus. One of these strains (LEM-207) isolated from the crop of a cock and closely resembling L. acidophilus, was able to develop on a carbohydrate-free medium. Production of carbon dioxide and synthesis of tyramine, putrescine and cadaverine were observed in the cultures. Once implanted in the crops of germ-free chickens, strain LEM-207 led to the formation of amines. In germ-free (axenic) animals, only endogenous tyramine was detected, whereas in monoassociated chickens, we found a production of tyramine, cadaverine and putrescine. The concentrations of cadaverine and putrescine decreased with increasing acidification of the contents, whereas the level of tyramine increased (7-fold higher level than in germ-free chicken). Amine production was not detected in the c˦ca. The toxicological aspects of tyramine production in terms of the animal are discussed.