Effect of chlorogenic acid on hydroxyl radical.

Chlorogenic acid (CGA) is considered to act as an antioxidant. However, the inhibitory effects of CGA on specific radical species are not well understood. Electron spin resonance (ESR) in combination with spin trapping techniques was utilized to detect free radicals. 5,5-Dimethyl-1-pyrroline-N-oxide (DMPO) was used as a spin trapping reagent while the Fenton reaction was used as a source of hydroxyl radical (*OH). We found that CGA scavenges *OH in a dose-dependent manner. The kinetic parameters, IC50 and Vmax, for CGA scavenging of *OH were 110 and 1.27 microM/sec, respectively. The rate constant for the scavenging of *OH by CGA was 7.73 x 10(9) M(-1) sec(-1). Our studies suggest that the antioxidant properties of CGA may involve a direct scavenging effect of CGA on *OH.