ANTIOXIDANT ACTIVITY OF CURCUMIN: A COMPARISON WITH RESVERATROL IN A HEME-ENHANCED OXIDATION REACTION

Preparations of the turmeric (Curcuma longa Linn.; family: Zingiberaceae) rhizome have been used medicinally and as spices for millennia in several Asian countries. Some of the medicinal properties are attributed to curcumin (diferuloylmethane), a major polyphenolic component (~5-10% of dry weight) of the rhizomes. Biomedical investigations of curcumin (and curcuminoids) have provided evidence for 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 (3,5,4’-trihydroxystilbene), a polyphenol present in many non-dietary plants (e.g. Polygonium genus) and a few dietary ones such as grapes and peanuts. Combinations of the two were also examined for potential synergism. The methods involved a heme-enhanced N,N,N’,N’-tetramethyl p-phenylenediamine-based oxidation reaction. Polyphenols were tested at 10 microM (5 microM each for combinations) over time periods of 1-5 min. Results: Curcumin exhibited a statistically significant antioxidant effect at all time points, e.g., 30.5 ± 11.9% (s.e.m.) relative to controls without phytochemicals (p < 0.01) at 3 min, a time chosen for comparisons. Resveratrol was significantly less potent (p < 0.05), about half of curcumin’s activity. Curcumin and resveratrol together 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 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.