Antioxidant activities of curcumin and combinations of this curcuminoid with other phytochemicals.

Biomedical investigations of curcumin (and curcuminoids) have provided evidence of a wide range of molecular and cellular activities, most related to redox reactions and signal transduction. The main goal of the present study was to compare antioxidant activities of curcumin with those of resveratrol, a polyphenol present in some dietary plants such as Vitis vinifera (L.) and Arachis hypogaea (L.) and many other, non-dietary plants. Combinations of the two were also examined for potential synergism in a heme-enhanced oxidation reaction. Curcumin exhibited antioxidant effects at all time points (1-5 min; 10 microM), e.g., 30.5 +/- 11.9% (SEM) oxidation relative to controls without phytochemicals (p < 0.01) at 3 min, a time chosen for comparisons. The same concentration of resveratrol exhibited about half of curcumin's activity. Curcumin and resveratrol together (5 microM each) resulted in a synergistic antioxidant effect: 15.5 +/- 1.7% greater than an average of individual activities. This synergy was significantly greater (p < 0.05; about 4-fold) than that of curcumin together with the flavonol quercetin. In conclusion, curcumin is a potent antioxidant in a reaction that may be relevant to in vivo toxicity. In relation to two other well-known antioxidants, curcumin shows significantly greater synergism with resveratrol than with quercetin.