By: Ashleigh Hampton, MSc
December 5, 2011

Previous reports of resveratrol have suggested that resveratrol undergoes extensive metabolism, thus resulting in a low bioavailability of the parent compound (As reviewed by Walle, 2011). The recently published clinical evidence presented here provides some insight into the mechanism by which resveratrol elicits its antioxidant potential in vivo. Recently, resveratrol had been observed to elicit beneficial effects in both healthy individuals and in type 2 diabetics.

Ghanim et al. (2011) provided 10 healthy individuals with a Polygonum cuspidatum extract in combination with a muscadine grape extract or a matching placebo control and evaluated the effects on inflammation and oxidative stress. The Polygonum/grape blend contained 100 mg resveratrol and 75 mg grape polyphenols per single dose. After an overnight fast, subjects were provided with a high fat, high carbohydrate meal on its own, or the same high fat, high carbohydrate meal following treatment with the test supplement. Consumption of the high fat, high carbohydrate meal in combination with the test supplement was associated with a significant increase in the binding activity of transcription factor, NF-E2 related factor 2 (Nrf-2) when compared to control (meal only) and baseline activity levels. Nrf-2 elicits its effect by binding to an antioxidant response element within the promoter of various genes to facilitate the transcription of potent antioxidant proteins. Thus, this study provides insight into the mechanism of action by which resveratrol and grape polyphenols elicit their antioxidant effects.

Ghanim et al. (2011) also observed a beneficial effect following the administration of the test supplement prior to consuming the high fat, high carbohydrate meal. Inflammation was decreased as indicated by a steady decrease in plasma lipopolysaccharide (LPS) concentrations following the consumption of the high fat, high carbohydrate meal. Alternatively, in the group which consumed the high fat, high carbohydrate meal only, a steady increase in plasma LPS concentrations was observed and found to be significantly different when compared to the test group. These findings suggest that resveratrol supplementation when combined with grape polyphenols is associated with increased endogenous antioxidant status and decreased inflammation following ingestion of a high fat, high carbohydrate meal.

In a separate randomized, placebo-controlled clinical trial, Brasnyo et al. (2011) investigated the effects of 10 mg of a natural resveratrol isolate daily in 19 males diagnosed with type 2 diabetes. Following 4 weeks of treatment with oral resveratrol, the researchers observed a significant decrease in the interstitial glucose concentration and time to maximum plasma glucose concentration, following consumption of a test meal, when compared with both placebo and baseline controls. It is important to note that there was no significant difference in insulin levels among any of the treatment groups after 4 weeks of supplementation. However, a significant increase in the phosphorylation of platelet-derived protein kinase b (Akt) was observed in the resveratrol-treated group when compared to the placebo control. Akt phosphorylation is believed to be the initial step in insulin signalling. Thus, the results of the study provide insight into the physiological mechanism associated with insulin resistance and suggest that resveratrol may be responsible for the activation of the insulin signalling pathway.

In summary, these recently published clinical trials confirm that resveratrol is a potent antioxidant and warrant further clinical trials to be conducted to fully assess the benefits of the phytochemical.

References:

Brasnyó P, Molnár GA, Mohás M, Markó L, Laczy B, Cseh J, Mikolás E, Szijártó IA, Mérei A, Halmai R, Mészáros LG, Sümegi B, Wittmann I. Resveratrol improves insulin sensitivity, reduces oxidative stress and activates the Akt pathway in type 2 diabetic patients. Br J Nutr. 2011 Aug;106(3):383-9.

Ghanim H, Sia CL, Korzeniewski K, Lohano T, Abuaysheh S, Marumganti A, Chaudhuri A, Dandona P. A resveratrol and polyphenol preparation suppresses oxidative and inflammatory stress response to a high-fat, high-carbohydrate meal. J Clin Endocrinol Metab. 2011 May;96(5):1409-14.

Walle T. Bioavailability of resveratrol. Ann N Y Acad Sci. 2011 Jan;1215:9-15.

doi: 10.1111/j.1749-6632.2010.05842.x. Review.

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