Affiliations: Department of Pharmaceutical and Biomedical Sciences,
Nutraceutical Research Laboratories, University of Georgia, Athens, GA,
USA | Department of Foods and Nutrition, Nutraceutical
Research Laboratories, University of Georgia Athens, GA, USA
Note: [] Address for correspondence: Dr. Phillip Greenspan, University
of Georgia, College of Pharmacy, Athens, GA 30602, USA. Tel.: +1 706 542 5410;
Fax: +1 706 542 3398; E-mail: [email protected]
Abstract: The formation of advanced glycation end products (AGEs) leading to
protein glycation and cross-linking is associated with the pathogenesis of
diabetic complications. The inhibition of protein glycation by phenolic and
flavonoid antioxidants demonstrates that the process is mediated, in part, by
oxidative processes. In this study, the effects of seed and skin extracts of
the muscadine grape on AGEs formation were examined. Seeds and skins were
extracted (10% w/v) with 50% ethanol and incubated at
37°C with a solution containing 250 mM fructose and
10 mg/ml albumin. After 72 h, fluorescence was measured at the wavelength pair
of 370 and 440 nm as an index of the formation of AGEs. Both seed and skin
extracts were found to be efficacious inhibitors of AGE formation. A 1:300
dilution of the seed extract decreased fluorescence by approximately 65%,
whereas muscadine grape skin extract produced a 40% lowering. This
difference correlates with the greater antioxidant activity found in muscadine
seeds in comparison to skins, however, on a mass basis, the inhibitory
activities of the seeds and skins were found to be nearly equivalent. Gallic
acid, catechin and epicatechin, the three major polyphenols in the seeds, all
significantly decreased the AGE product related fluorescence at a concentration
of 50 μM. Neither muscadine seed extract nor skin extract
inhibited the methylglyoxal-mediated glycation of albumin. These results
suggest that consumption of the muscadine grape may have some benefit in
altering the progression of diabetic complications.
