Catherine Besson

Effect of propionate on fatty acid and cholesterol synthesis and on acetate metabolism in isolated rat hepatocytes

In the present study the actual role of propionic acid in the control of fatty acid and cholesterol synthesis was investigated in isolated liver cells from fed rats maintained in the presence of near-physiological concentrations of glucose, glutamine and acetate. Using 3H2O for lipid labelling, propionate appears as an effective inhibitor of fatty acid synthesis and to a lesser extent of cholesterol synthesis, even at the lowest concentration used (0.6 mmol/l). Butyrate is a potent activator of both synthetic pathways, and the activating effect was not counteracted by propionate. Using 1-[14C]acetate, it was observed that propionate at a moderate concentration, or 1 mmol oleate/l, are both very effective inhibitors of 14C incorporation into fatty acid and cholesterol. This incorporation was drastically inhibited when propionate and oleate were present together in the incubation medium. The net utilization of acetate by rat hepatocytes was impaired by propionate, in contrast to oleate. 1-[14C]butyrate was utilized at a high rate for fatty acid synthesis, but to a lesser extent for cholesterol synthesis; both processes were unaffected by propionate. Intracellular citrate concentration was not markedly depressed by propionate, whereas it was strongly elevated by butyrate. In conclusion, propionate may represent an effective inhibitor of lipid synthesis when acetate is a major source of acetyl-CoA, a situation which is encountered with diets rich in readily-fermentable fibres. The present findings also suggest that propionate may be effective at concentrations close to values measured in vivo in the portal vein.

Part of quercetin absorbed in the small intestine is conjugated and further secreted in the intestinal lumen

Rutin and quercetin absorption and metabolism were investigated in rats after in situ perfusion of jejunum plus ileum (15 nmol/min). In contrast to rutin, a high proportion of quercetin (two-thirds) disappeared during perfusion, reflecting extensive transfer into the intestinal wall. Net quercetin absorption was not complete (2.1 nmol/min), inasmuch as 52% were reexcreted in the lumen as conjugated derivatives (7.7 nmol/min). Enterohepatic recycling contribution of flavonoids was excluded by catheterization of the biliary duct before perfusion. After a 30-min perfusion period, 0.71 microM of quercetin equivalents were detected in plasma, reflecting a significant absorption from the small intestine. The differential hydrolysis of effluent samples by glucuronidase and/or sulfatase indicates that the conjugated forms released in the lumen were 1) glucuronidated derivatives of quercetin and of its methoxylated forms (64%) and 2) sulfated form of quercetin (36%). In vitro quercetin glucuronides synthetized using jejunal and ileal microsomal fractions were similar to those recovered in the effluent of perfusion. These data suggest that glucuronidation and sulfatation take place in intestinal cells, whereas no glucurono-sulfoconjugates could be detected in the effluent. The present work shows that a rapid quercetin absorption in the small intestine is very effective together with its active conjugation in intestinal cells.

Catechin reduces atherosclerotic lesion development in apo E-deficient mice: A transcriptomic study

Much experimental evidence supports a protective role of dietary flavonoids against cardiovascular diseases. The aim of the present study was to investigate the anti-atherosclerotic effects of catechin supplemented in the diet of apoE deficient mice at a low nutritional level and to explore the mechanisms of action by a transcriptomic approach. After 6 weeks of supplementation, atherosclerotic lesions were assessed by histomorphometry and several markers of lipid, inflammation and oxidative stress status were evaluated. Analysis of the global gene expression in the aorta was carried out using pangenomic arrays. Catechin supplementation reduced the mean atherosclerotic lesion area by 32% but had no effect on total cholesterol and triacylglycerol levels in the plasma and the liver. The plasma antioxidant capacity (FRAP) and inflammatory status (serum amyloid A) were unchanged. The expression of 450 genes was significantly modified by catechin supplementation. Some of the most significantly down-regulated genes included genes coding for adhesion molecules such as CD34 and PSGL-1 known to play a key role in leukocyte adhesion to the endothelium. Other genes involved in energy metabolism, lipid metabolism and lipids trafficking such as FABP4, LPL and SCARA5 were down-regulated and may contribute to the atheroprotective effect of catechin. This work shows that transcriptomic allows characterizing the biological effects of low doses of flavonoids where common markers were not significantly affected.

Quercetin exerts a preferential cytotoxic effect on active dividing colon carcinoma HT29 and Caco-2 cells

The effect of the naturally occurring flavonol, quercetin, was investigated on cell growth and metabolism of two human carcinoma cell lines, HT29 and Caco-2 cells, both during the exponentially growing phase and after confluence. Our results show clearly that, after a 48-h period of treatment, quercetin (in the range of concentration from 15 microM to 120 microM) exerted a preferential cytotoxic effect on active proliferating cells. This effect was dose dependent and was accompanied by a simultaneous inhibition of lactate release and a dramatic decrease of total cellular ATP content. In contrast, in confluent cells, quercetin failed to affect cell viability or lactate release, but led nevertheless to a depletion of cellular ATP level. In conclusion, the cytotoxicity of quercetin is markedly higher in actively growing cells in comparison with confluent cells.

Apple favourably affects parameters of cholesterol metabolism and of anti-oxidative protection in cholesterol-fed rats

Abstract The effects of apples on lipid metabolism were studied on 40 male Wistar rats adapted to semi-purified diets containing 0.3% cholesterol. In the experimental ‘apple’ diet, a part of starch (15%) was replaced by lyophilized apple (Gala variety). In the control diet, 13% of carbohydrate was replaced by a mixture of fructose/glucose/saccharose to match the sugar supply from the apples. The lipid source was corn oil and the dietary supply of vitamin E was reduced to 1/3 of the recommended value. The rats were sampled after 21 days adaptation. The fibre supply of the apple diet was notably low (about 2%); nevertheless, there was a slight but significant cholesterol-lowering effect in plasma, as well as in liver where cholesterol esters accumulate with cholesterol diets. The lipoprotein profile was markedly altered in apple-fed rats: a reduction of cholesterol in the triglyceride rich lipoprotein (TGRLP) fraction, together with a rise in the HDL fraction; hence there was a favourable effect in a cardiovascular protection perspective. This was paralleled by effects of the apple on cholesterol apparent absorption, which was markedly depressed, whereas bile acid digestive balance was unaffected. In parallel, there was a positive effect of the apple diet on parameters of oxidative stress prevention: higher FRAP plasma levels than in controls, together with a reduced MDA excretion in urine. In conclusion, the present work indicates that a moderate supply of dessert apples elicits interesting effects on lipid and peroxidation parameters.

A Liquid Chromatography−Quadrupole Time-of-Flight (LC−QTOF)-based Metabolomic Approach Reveals New Metabolic Effects of Catechin in Rats Fed High-Fat Diets

Unbalanced diets generate oxidative stress commonly associated with the development of diabetes, atherosclerosis, obesity and cancer. Dietary flavonoids have antioxidant properties and may limit this stress and reduce the risk of these diseases. We used a metabolomic approach to study the influence of catechin, a common flavonoid naturally occurring in various fruits, wine or chocolate, on the metabolic changes induced by hyperlipidemic diets. Male Wistar rats ( n = 8/group) were fed during 6 weeks normolipidemic (5% w/w) or hyperlipidemic (15 and 25%) diets with or without catechin supplementation (0.2% w/w). Urines were collected at days 17 and 38 and analyzed by reverse-phase liquid chromatography-mass spectrometry (LC-QTOF). Hyperlipidic diets led to a significant increase of oxidative stress in liver and aorta, upon which catechin had no effect. Multivariate analyses (PCA and PLS-DA) of the urine fingerprints allowed discrimination of the different diets. Variables were then classified according to their dependence on lipid and catechin intake (ANOVA). Nine variables were identified as catechin metabolites of tissular or microbial origin. Around 1000 variables were significantly affected by the lipid content of the diet, and 76 were fully reversed by catechin supplementation. Four variables showing an increase in urinary excretion in rats fed the high-fat diets were identified as deoxycytidine, nicotinic acid, dihydroxyquinoline and pipecolinic acid. After catechin supplementation, the excretion of nicotinic acid was fully restored to the level found in the rats fed the low-fat diet. The physiological significance of these metabolic changes is discussed.

Cholesterol-lowering effects of guar gum: Changes in bile acid pools and intestinal reabsorption

Soluble fibers such as guar gum (GG) may exert cholesterol-lowering effects. It is generally accepted that bile acid (BA) reabsorption in portal blood is reduced, thus limiting the capacity of BA to down-regulate liver cholesterol 7α-hydroxylase, the rate-limiting enzyme of BA synthesis. In the present work, rats were adapted to fiber-free (FF) or 5% GG diets (supplemented or not with 0.25% cholesterol), to investigate various aspects of enterohepatic BA cycling. GG in the diet at a level of 5% elicited a significant lowering of plasma cholesterol during the absorptive period, in cholesterol-free (−13%) or 0.25% cholesterol (−20%) diet conditions. In rats adapted to the GG diets, the small intestinal and cecal BA pools and the ileal vein-artery difference for BA were markedly enhanced; reabsorption in the cecal vein was also enhanced in these rats. [14C]Taurocholate absorption, determined in perfused ileal segments, was not significantly different in rats adapted to the FF or GG diet, suggesting that a greater flux of BA in the ileum might support a greater ileal BA reabsorption in rats adapted to the GG diet. In contrast, capacities for [14C]cholate absorption from the cecum at pH 6.5 were higher in rats adapted to the GG diet than to the FF diet. Acidification of the bulk medium in isolated cecum (from pH 7.1 down to pH 6.5 or 5.8) or addition of 100 mM volatile fatty acids was also found to stimulate cecal [14C]cholate absorption. These factors could contribute to accelerated cecal BA absorption in rats fed the GG diet. The effects of GG on steroid fecal excretion thus appear to accompany a greater intestinal BA absorption and portal flux to the liver. These results suggest that some mechanisms invoked to explain cholesterol-lowering effect of fibers should be reconsidered.

Strawberry pelargonidin glycosides are excreted in urine as intact glycosides and glucuronidated pelargonidin derivatives in rats

Anthocyanins are natural dietary pigments with a wide array of biological properties that are possibly involved in the prevention of various diseases. These properties depend on their absorption and metabolism in the body. In the present study we first examined the gastric and intestinal absorption of pelargonidin 3-glucoside (Pg 3-glc) using rat in situ models. A high proportion of Pg 3-glc was rapidly absorbed from both the stomach (23 %) and small intestine (24 %). Its metabolism was further studied by feeding rats during 8 d with a diet enriched in freeze-dried strawberries. Only low amounts of total anthocyanins were recovered in 24 h urine (0.163 (SEM 0.013) % of ingested anthocyanins; n 8). Strawberry anthocyanins were analysed in urine by HPLC-electrospray ionisation-tandem MS. Similar proportions of intact glycosides (about 53 %) and glucuronidated metabolites (about 47 %) were found. Pg 3-glc was thus glucuronidated to a larger extent than cyanidin 3-glucoside. These results highlight the influence of the aglycone structure on anthocyanin metabolism.

Effects of a diet rich in resistant starch on hepatic lipid metabolism in the rat

Abstract The aim of this study was to examine the effects of the replacement of a large part of absorbed glucose by volatile fatty acids on hepatic lipid metabolism. For this purpose, experiments were conducted in rats fed either a diet containing digestible wheat starch or amylase-resistant cornstarch. Compared with the digestible wheat starch diet, plasma insulin was lower in rats fed the resistant cornstarch diet, and the fluctuations of insulinemia during the fed/postabsorptive period were smaller. The marked reduction of hepatic lipogenesis in rats fed the resistant cornstarch diet ( −52% compared with the digestible wheat starch diet) resulted from the coordinated inhibition of all major enzymes implicated in the lipogenic pathway, except acetyl CoA synthetase activity. This suggests that volatile fatty acids, particularly acetate, constituted the major source of acetyl CoA for lipogenesis, rather than glucose. However, these modifications were not accompanied by a significant depressive effect on plasma triglycerides. In rats fed the resistant cornstarch diet, changes in lipogenesis activity were accompanied by a reduction of glycolysis as shown by the net inhibition of glucokinase and pyruvate kinase. In parallel to these modifications, with the resistant cornstarch phosphoenolpyruvate carboxykinase was markedly induced; with this diet, propionate should constitute the major gluconeogenic substrate removed by the liver. HMG CoA reductase was markedly induced in rats adapted to the resistant cornstarch diet (1.6-fold higher than with the digestible wheat starch diet); this could be related to the increased fecal bile acids excretion. A significant hypocholesterolemic effect of the resistant cornstarch diet was only observed during the postabsorptive period. In conclusion, hepatic fatty acid synthesis is tightly controlled by carbohydrate availability, but the possibility that volatile fatty acids exert specific effects on lipogenesis could not be ruled out.

Radiolabelled cyanidin 3-O-glucoside is poorly absorbed in the mouse.

Anthocyanins are natural pigments abundant in various fruits and berries that are involved in the prevention of various chronic diseases. Their low concentrations in plasma and urine are explained in part by their complex chemistry and the formation of still uncharacterised metabolites. The aim of the present study was to follow the distribution of anthocyanins in the body using 14C-labelled cyanidin 3-O-glucoside (Cy3G) fed by gavage to mice. After the administration of 22.2 kBq 14C-Cy3G (0.93 mg), radioactivity was detected in most organs tested over the following 24 h with a peak observed in inner tissues at 3 h. The major fraction of the radioactivity (44.5 %) was found in the faeces collected 24 h after ingestion. At 3 h after oral administration of 141 kBq 14C-Cy3G (4.76 mg), most of the radioactivity (87.9 % of intake) was recovered in the gastrointestinal (GI) tract, especially in the small intestine (50.7 %) and the caecum (23 %). At this time, 3.3 % of the radioactivity was detected in urine. There was minimal accumulation (0.76 %) of radioactivity in tissues outside the GI tract. Distribution of radioactivity varied among organs, with liver, gallbladder and kidneys showing the highest radioactivity. Taken as a whole, these results show that Cy3G is poorly absorbed in the mouse.