Pierre Besançon

Polymeric grape seed tannins prevent plasma cholesterol changes in high-cholesterol-fed rats

Abstract The objective of this study was to determine the effect of grape seed tannins in either monomeric or polymeric form on plasma cholesterol in rats. These tannins were supplemented at a level of 2% of the diet of high-cholesterol-fed Sprague Dawley rats for 9 weeks; the diets were compared with a diet without tannins (control diet) and with a standard diet. Rats fed diets containing 1% cholesterol showed an increase in total and low-density lipoprotein plasma cholesterol and a decrease in plasma high-density lipoprotein. These changes were prevented by the addition of 2% polymeric grape tannins but not by monomeric tannins. Similarly, liver weight, liver lipids and total liver cholesterol were increased by dietary cholesterol and these increases were largely inhibited by the tannin polymers but not the monomers. The polymers significantly increased the faecal excretion of lipids and cholesterol. In conclusion, we have shown that polymeric grape seed tannins exert a hypocholesterolaemic effect in high-cholesterol-fed rats.

Antioxidant effects of dietary polymeric grape seed tannins in tissues of rats fed a high cholesterol-vitamin E-deficient diet

Effects of dietary monomeric and polymeric grape seed tannins on the activity of antioxidant enzymes, total glutathione and level of lipid peroxidation in various tissues were investigated in rats fed a high cholesterol diet poor in vitamin E. They were compared with those in rats receiving a high cholesterol-vitamin E-sufficient diet without addition of tannins. Four groups of rats were studied for 10 weeks: Group 1, sufficient vitamin E diet; Group 2, deficient vitamin E diet; Group 3, deficient vitamin E diet + monomeric tannins (71 mg/kg); Group 4, deficient vitamin E diet + polymeric tannins (71 mg/kg). Compared with a normal vitamin E diet (Group 1), aortic, cardiac, hepatic, intestinal, muscular and renal catalase, glutathione peroxidase and superoxide dismutase activities were significantly lower in rats receiving the deficient vitamin E diet (Group 2); polymeric tannins (Group 4), but not monomeric tannins, were able to restore all these enzymic activities. In all tissues and in blood, total glutathione concentration, which was significantly lowered by vitamin E deficiency, was brought to the normal level only with polymeric tannins. Furthermore, the lipid peroxidation in plasma and tissues was significantly reduced in the presence of supplemented polymeric tannins as much as in the presence of vitamin E. It is therefore likely that polymeric grape seed tannins function as antioxidants in vivo, negating the effects of the oxidative stress induced by both vitamin E deficiency and atherogenic diet.

Hydrogen Peroxide Generation in Caco-2 Cell Culture Medium by Addition of Phenolic Compounds: Effect of Ascorbic Acid

Phenolic compounds have recently attracted special attention due to their beneficial health effects; their intestinal absorption and bioavailability need, therefore, to be investigated and Caco-2 cell culture model appeared as a promising tool. We have shown herein that the addition of a grape seed extract (GSE) to Dulbeccos modified Eagles medium (DMEM) used for Caco-2 cell culture leads to a substantial loss of catechin, epicatechin and B2 and B3 dimers from GSE in the medium after 24 h and to a production of hydrogen peroxide (H2O2). When 1420 microM ascorbic acid is added to the DMEM, such H2O2 production was prevented. This hydrogen peroxide generation substantially involves inorganic salts from the DMEM. We recommend that ascorbic acid be added to circumvent such a risk.

Effects of dietary grape seed tannins on rat cecal fermentation and colonic bacterial enzymes

Abstract In rats, the effects of a 12-wk supplementation of a purified diet with 71 mg/kg monomeric or polymeric grape seed tannins were explored on cecal fermentation and colonic bacterial enzymes. Weight gain was affected by addition of polymers to the diet. There was a significant increment of volatile fatty acids (VFA) pool and a pH decrease in the cecal contents of rats fed polymeric tannins, compared to controls. When expressed per gram of nitrogen content, the concentrations of all colonic fecal bacterial enzyme activities tested (β-glucosidase, β-glucuronidase, mucinase and nitroreductase) were decreased, due to a dilution effect. In these experimental conditions, monomeric tannins exhibited neither beneficial nor detrimental effect. On the other hand, these results show that although at a low dietary level equivalent of a daily amount of 0.5 L red wine, polymeric grape seed tannins exert a beneficial cecal metabolic and colonic protective effect.

Oxidation of methionine residues of food proteins and nutritional availability of protein-bound methionine sulphoxide

Abstract The extent of oxidation of methionine residues has been determined in food proteins submitted to various oxidative treatments. The nutritional value of oxidised casein, in which 98% of the methionine residues were converted to the corresponding sulphoxide, was assessed both by proteolysis in vitro and on rats. The nutritional availability of residues of methionine sulphoxide appears to be only slightly inferior to that of methionyl residues.

A diet high in cholesterol and deficient in vitamin E induces lipid peroxidation but does not enhance antioxidant enzyme expression in rat liver

Expression of antioxidant enzymes (AOE), an important mechanism in the protection against oxidative stress, could be modified by the redox status of the cells. The aim of this project was to evaluate the role of vitamin E deficiency in association with a high-cholesterol diet in the hepatic lipid peroxidation and the expression of AOE. Two groups of 6 male rats were fed with a high-cholesterol or a high-cholesterol vitamin E-deficient diet. All animals were sacrificed at 72 days of treatment. Liver lipid peroxidation index (Malondialdehyde; MDA) and hepatic AOE were evaluated. Total liver RNA was extracted, and the steady state messenger RNA (mRNA) levels of glutathion peroxydase, manganese superoxide dismutase, Cu/Zn superoxide dismutase and catalase were examined by northern blot. After 72 days on the diet, a significant increase in the lipid peroxidation index was observed in the vitamin E deficient group (MDA : 4.45 +/- 0.29 nmol/mg protein versus 3.65 +/- 0.1 nmol/mg protein in vitamin E normal group). Despite this oxidative stress, the activities and mRNA levels of liver AOE were not significantly different in the 2 groups. These preliminary results show that chronic vitamin E deficiency associated with high cholesterol diet is able to increase lipid peroxidation without modulation of AOE expression and activity in the liver. This suggests that beneficial effects of dietary vitamin E are due to a plasma antioxidant effect or a cell mediated action, rather than to a specific modulation of cellular enzymes.

Comparative Evaluation of the Effects of Two Different Forms of Dietary Fibre (Rice Bran vs. Wheat Bran) on Rat Colonic Mucosa and Fæcal Microflora

The aim of the study was to compare the physiological consequences of two dietary fibre sources on the faecal microflora and colonic mucosal growth in rats. The studied sources, a moderately well-soluble fibre (rice bran, RB) and a less well-soluble fibre (wheat bran, WB), were included in diets of rats at a level of 10% for 3 weeks and compared with a totally fibre-deprived diet. RB significantly increased faecal water compared to the control diet (p

Effect of grape seed tannins on the activity of some rat intestinal enzyme activities.

The present study was designed to investigate the effects of grape seed tannins on rat intestinal alkaline phosphatase (AP), sucrase and dipeptidyl peptidase IV (DPP IV) activities. An experiment was performed in vivo by dietary supplementation with 2% tannins; this diet was tested on an experimental group of rats; a control group received a diet without tannins. After 31 days, tannins intake significantly decreased middle-jejunal AP from 123 to 45 mU/mg protein and sucrase activities from 310 to 195 mU/mg protein, while no significant difference appeared at the duodenal stage (p < 0.05). Ileal DPP IV activity was also significantly reduced (p < 0.05) from 190 to 110 mU/mg protein after tannin intake. Using in vitro experiments on purified brush border membranes, AP activity was found to be inhibited by grape tannins; this inhibition was prevented by the detergent Triton X-100. The addition of pancreatic-biliary (PB) juice to the incubation medium prevented or reversed the tannin-inhibited enzyme activity. The present data indicate that in the duodenal lumen, alkalinity and detergency from the PB secretion neutralized the ability of tannins to inactivate brush border hydrolase activities and suggest that enzyme inhibition took place once bile salts were reabsorbed while moving down the gut. This was confirmed by in vitro experiments where sucrase and DPP IV activities inhibited by grape seed tannins were largely recovered after the addition of PB juice to the incubation medium.

Monospecificity of the antibodies to bovine αs1-casein fragment 140-149: application to the detection of bovine milk in caprine dairy products

Comparison of the primary sequences of bovine, ovine and caprine alpha s1-casein shows a deletion of eight amino acid residues in the ovine casein region 141-148, which is identical in the bovine and caprine proteins except for a single difference in position 148 (Q or E). Polyclonal antibodies raised in rabbits against the bovine casein sequence 140-149 (QELAYFYPEL) appeared monospecific for bovine alpha s1-casein, since no antibody-antigen complex was formed with homologous ovine or caprine proteins. These antibodies remained unable to recognize the caprine sequence in the native protein even after extensive tryptic proteolysis. The lack of immunoreactivity of the antibodies against synthetic caprine alpha s1-casein peptide 138-149 (VNQELAYFYPQL) suggested that the glutamic acid residue in position 148 is essential for the antigenic character of the bovine peptide. From these observations, the use of these antibodies for the detection and quantitation of bovine milk present in ovine dairy products could be extended to caprine products.

Dietary grape seed tannins : effects on nutritional balance and on some enzymic activities along the crypt-villus axis of rat small intestine

The aim of the study was to determine the nutritional and intestinal effects of grape seed tannins. For this purpose, tannins were incorporated in diets of rats at levels of 0.2 or 2.0% for 31 days in comparison to a control diet. The animals were pair-fed. Nutritional balances were not affected by feeding 0.2% tannins. At the highest dose (2%) grape seed tannins reduced growth as well as dry matter (DM) and nitrogen (N) digestibility. In rats fed protein-free diets, 2% tannins significantly increased endogenous fecal N. Starch and fat were well digested in all groups of rats. No changes in organ weights were observed. Duodenal alkaline phosphatase activity (AP) was never affected by tannins. On the other hand, in the jejunum, along the vilus-crypt unit, a reduction of AP and sucrase appeared at the tip villus which was balanced by an enhancement of 3H-thymidine incorporation in the middle of the crypt zone, giving evidence of endogenous N loss. This study did not reveal a major toxic effect of tannins except a reduced DM and N digestibility; nevertheless tannins directly interfere with mucosal proteins, thereby stimulating the cell renewal.