Flavonoids are functional constituents of many fruits and vegetables. Some flavonoids have antidiabetic properties because they improve altered glucose and oxidative metabolisms of diabetic states. Procyanidins are flavonoids with an oligomeric structure, and it has been shown that they can improve the pathological oxidative state of a diabetic situation. To evaluate their effects on glucose metabolism, we administered an extract of grape seed procyanidins (PE) orally to streptozotocin-induced diabetic rats. This had an antihyperglycemic effect, which was significantly increased if PE administration was accompanied by a low insulin dose. The antihyperglycemic effect of PE may be partially due to the insulinomimetic activity of procyanidins on insulin-sensitive cell lines. PE stimulated glucose uptake in L6E9 myotubes and 3T3-L1 adipocytes in a dose-dependent manner. Like insulin action, the effect of PE on glucose uptake was sensitive to wortmannin, an inhibitor of phosphoinositol 3-kinase and to SB203580, an inhibitor of p38 MAPK. PE action also stimulated glucose transporter-4 translocation to the plasma membrane. In summary, procyanidins have insulin-like effects in insulin-sensitive cells that could help to explain their antihyperglycemic effect in vivo. These effects must be added to their antioxidant activity to explain why they can improve diabetic situations.
In the present paper, we report the effect of a grape seed procyanidin extract (GSPE) on antioxidant enzyme systems (AOEs). Gene expression was tested using the hepatocarcinoma cell line HepG2 by exposing it to several GSPE doses between 0 and 100 mg/L for 24 h. We evaluated mRNA expression and enzyme activity levels using real time RT-PCR and spectrophotometry. The results suggested a transcriptional GSPE regulation of glutathione related enzymes caused by an increase both in mRNA and in enzyme activity levels overall at 15 mg/L. We also assessed the GSPE effect on AOEs in cells submitted to oxidative stress. Under oxidative conditions (1 mM H(2)O(2), 1 h), we found a decrease in GSH content and an increase in MDA, and we suggested a posttranslational regulation of GPx/GR mRNAs and a transcriptional enhancement of GST mRNA. The GSPE pretreatment (15 mg/L, 23 h) before HepG2 submission to H(2)O(2) (1 mM, 1 h) showed an increase of the mRNA of GPx/GR with respect to the H(2)O(2) group, whereas the GSH content was similar to the control group. However, the GPx/GR enzyme activities were not increased. We hypothesize that GSPE probably improves the cellular redox status via glutathione synthesis pathways instead of regulation of the GPx and/or GR activities protecting against oxidative damage.
Grape seed proanthocyanidin extract (GSPE) modulates several parameters involved in metabolic syndrome. GSPE is a mixture of compounds, some which are rapidly absorbed, while others remain in the lumen where they might have effects that are translated to the whole organism. Our aim was to decipher if the 8-day treatment of GSPE, previously shown to reduce food intake, induces changes in the microbiota and enterohormone secretion. The ratio of Firmicutes : Bacteroidetes was lower in the microbiota of GSPE-treated rats compared to controls, and differences in several taxonomic families and genera were observed. Such modulation led to a reduction in cecal butyrate content. GSPE also increased plasma glucagon-like-peptide-1 (GLP-1). Gallic acid did not induce major changes in the microbiota profile nor in GLP-1 secretion. Correlations between several microbiota taxa and plasma triacylglycerol, adiposity, and enterohormones were observed. Modulation of microbiota may be one of the mechanism by which GSPE impacts metabolic health.
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