In vitro peroxynitrite scavenging activity of diarylheptanoids from Curcuma longa

Peroxynitrite is a cytotoxic intermediate produced by the reaction between the superoxide anion (O(2)) and nitric oxide (NO). The aim of this study was to investigate the scavenging effects of Curcuma longa L. on authentic peroxynitrite, and further studies are planned that will attempt to identify the active principles from the active fractions. The methanolic extract of C. longa showed 50% scavenging activity (IC(50)) at concentration of 1.7 +/- 0.08 micro g/ml, and was thus fractionated with several solvents. The peroxynitrite scavenging activity potential of the individual fraction was in the order of ethyl acetate > dichloromethane > water fraction. The ethyl acetate soluble fraction exhibiting strong scavenging activity was further purified by repeated silica gel column chromatography. Peroxynitrite scavenging diarylheptanoids, curcumin I (1), curcumin II (2), and curcumin III (3) were isolated as active principles. Compounds 1-3 showed the peroxynitrite scavenging activities with IC(50) values of 4.0 +/- 0.04, 6.4 +/- 0.30, and 29.7 +/- 1.29 micro M, respectively. Penicillamine as positive control exhibited IC(50) value of 2.38 +/- 0.34 micro M. The structure-activity relationship of diarylheptanoids on peroxynitrite was also discussed.