A comparative study: Dietary grape extracts, derived dietary supplements and the effect of tannins on antioxidant, anticancer, and anti-inflammatory activity

The antioxidant, anti-cancer, and anti-inflammatory activities of extracts of red wine, grape juice, whole grapes, grape seeds, grape skins, and GSKE extracts were compared. A portion of each extract was detannified, and both unprocessed and detannified extracts were separated into ten fractions by flash chromatography. Antioxidant activity was assessed spectrophotometrically by measuring the reduction of the 2,2-diphenyl-1-picrylhydrazyl radical. Fractions with antioxidant activity were re-assayed over a range of concentrations to obtain effective concentration (EC50) values for scavenging the DPPH radical, and by thin-layer chromatograpy. Strong antioxidant activity was associated with all the extracts. For red wine and grapes, the presence of tannins was strongly linked to the antioxidant activity. The grape extracts were examined for anti-cancer activity using alamarBlue as an indicator of cell viability. The extracts were not cytotoxic to Jurkat and L929 cancer cells and did not protect Jurkat cells from killing by tumor necrosis factor (TNF). However, several pure compounds—resveratrol, ellagic acid and gallic acid known to be present in red wine—did significantly protect these cells against TNF killing. Although these compounds protected Jurkat cells against TNF, they were not present in sufficient quantities in the extracts to protect the cells. Extracts were screened for anti-inflammatory activity using luciferase reporter gene-transfected JB-6 cells that were either unstimulated or stimulated with trypsin. Unprocessed red wine contained inhibitors of NF-kappa-B transcription. Transcription was inhibited by grape constituents in unstimulated cells, but was stimulated in cells treated with trypsin. Although both inhibitory and stimulatory fractions were present in grape seeds and grape skin, the crude extract of grape seeds did not affect NF-kappa-B transcription. Transcription in the cells was stimulated by several GSKE fractions but not by the crude extract. Further research may confirm that grape extracts are capable of significant biological health effects.