Resveratrol increases glucose induced GLP-1 secretion in mice: a mechanism which contributes to the glycemic control

Abstract

Resveratrol (RSV) is a potent anti-diabetic agent when used at high doses. However, the direct targets primarily responsible for the beneficial actions of RSV remain unclear. We used a formulation that increases oral bioavailability to assess the mechanisms involved in the glucoregulatory action of RSV in high-fat diet (HFD)-fed diabetic wild type mice. Administration of RSV for 5 weeks reduced the development of glucose intolerance, and increased portal vein concentrations of both Glucagon-like peptid-1 (GLP-1) and insulin, and intestinal content of active GLP-1. This was associated with increased levels of colonic proglucagon mRNA transcripts. RSV-mediated glucoregulation required a functional GLP-1 receptor (Glp1r) as neither glucose nor insulin levels were modulated in Glp1r-/- mice. Conversely, levels of active GLP-1 and control of glycemia were further improved when the Dipeptidyl peptidase-4 (DPP-4) inhibitor sitagliptin was co-administered with RSV. In addition, RSV treatment modified gut microbiota and decreased the inflammatory status of mice. Our data suggest that RSV exerts its actions in part through modulation of the enteroendocrine axis in vivo.

Conflict of interest statement

Competing Interests: The authors have read the journal's policy and have the following conflicts: Laurent Pechere and Sylvain Barthelemy have a duality of interest with ENTERONOVA and YVERY Cosmetics, because they are employed by the above mentioned companies. Rémy Burcelin and Eric Sérée have a duality of interest with ENTERONOVA as they have a consultancy mission. This does not alter the authors' adherence to all the PLoS ONE policies on sharing data and materials.

Figures

Figure 1. RSV improves glucose tolerance in high fat-fed diabetic mice.

A) Glycemic profiles (mg/dL) of normal chow (circles), high fat diet-fed mice treated with vehicle (triangles) or RSV (squares) for five weeks and B) area under the curve for glucose (AUC); Data are presented as mean ± S.E.M, n = 8 mice per group * and *** statistically different between groups when p<0.05 and p<0.001, respectively, as analyzed by one-way ANOVA followed by Tukey test.

Figure 2. RSV increases levels of GLP-1 and Insulin.

A) Portal vein active GLP-1 concentrations (pM); B) proglucagon mRNA concentration (Relative Expression Level, REL); C) intestinal GLP-1 concentrations (pmol/g of tissue) and D) portal plasma insulin concentrations (µg/L) of normal chow (stripe bars), high fat diet-fed mice treated with vehicle (open bars) or RSV (closed bars) for five weeks. Data are presented as mean ± S.E.M, n = 8 mice per group (in fed state) *, ** and *** statistically different between groups when p<0.05, p<0.01 and p<0.001, respectively, as analyzed by one-way ANOVA followed by Tukey test.

Figure 3. The glucose control by RSV is blunted in high fat diet-fed Glp1r−/− mice.

A) Glycemic profiles (mg/dL) of high fat diet-fed Glp1r−/− mice treated with vehicle (triangles) or RSV (squares) for five weeks and B) an index of area under the curve glucose (AUC); C) proglucagon mRNA levels (Relative expression level REL) of high fat diet-fed mice treated with vehicle (open bars) and RSV (closed bars) for five weeks. D) Glycemic profiles (mg/dL) of high fat diet-fed wild type mice (high fat diet-fed mice treated with vehicule (white triangles) or RSV (white squares)) and Glp1r−/− mice (high fat diet-fed mice treated with vehicule (black triangles) or RSV (black squares)) after five weeks of treatment and E) an index of area under the curve glucose (AUC). Data are presented as mean ± S.E.M, n = 8 mice per group.

Figure 4. Co-administration of the dipeptidyl peptidase-4 inhibitor sitaglipin and RSV further improves glucose tolerance in high fat diet-fed diabetic mice.

A) Glycemic profiles (mg/dL) of high fat diet-fed diabetic mice treated with RSV (squares), or RSV plus sitagliptin (triangles) for five weeks; B) portal vein active GLP-1 concentrations (pM) and C) proglucagon mRNA levels (Relative Expression Level REL) of high at diet-fed mice treated with RSV (closed bars) and sitagliptin plus RSV (spotted bars) for five weeks. Data are presented as mean ±S.E.M, n = 8 mice per group, * and *** statistically different between groups when p<0.05 and p<0.001, respectively, as analyzed by the Student's T test.

Figure 5. RSV has a prebiotic effect on gut microbiota.

DGGE profiles generated from the caecal content of mice fed normal chow (NC), high fat diet and treated with vehicle (HFD±Veh), or RSV (HFD±RSV) for 5 weeks. Each number and profile corresponds to a different animal. The arrows denote a subset of bands, which have disappeared with the RSV treatment, were cloned and sequenced (see results for identification).

Figure 6. RSV decreases the inflammatory status in high fat-fed diabetic mice.

IL-10 mRNA levels (Relative Expression Level, REL) (A) and IL-10 protein concentration (µg/g) (B) in colon; IL-10 mRNA in liver (C) and muscle (D), TGF-β mRNA in colon (E), liver (F), muscle (G), and TNF-α mRNA in colon (H), liver (I), muscle (J) of normal chow (stripe bars), high fat diet-fed mice treated with vehicle (open bars) or RSV (closed bars) for five weeks. Data are presented as mean ± S.E.M, n = 8 mice per group (in fed state) *, ** and *** statistically different between groups when p<0.05, p<0.01 and p<0.001, respectively, as analyzed by the Student's T test (Fig. 6B) and one-way ANOVA followed by Tukey test. (Fig. 6A, C, D, E, F, G, H, I, J).