Mechanism of Hydroxyl Radical Scavenging by Rebamipide: Identification of Mono-hydroxylated Rebamipide as a Major Reaction Product

Abstract

Rebamipide, an antiulcer agent, is known as a potent hydroxyl radical (^•OH) scavenger. In the present study, we further characterized the scavenging effect of rebamipide against ^•OH generated by ultraviolet (UV) irradiation of hydrogen peroxide (H²O²), and identified the reaction products to elucidate the mechanism of the reaction. Scavenging effect of rebamipide was accessed by ESR using DMPO as a ^•OH-trapping agent after UVB exposure (305 nm) to H²O² for 1 min in the presence of rebamipide. The signal intensity of ^•OH adduct of DMPO (DMPO-OH) was markedly reduced by rebamipide in a concentration-dependent fashion as well as by dimethyl sulfoxide and glutathione as reference radical scavengers. Their second order rate constant values were 5.62 × 10¹⁰, 8.16 × 10⁹ and 1.65 × 10¹⁰ M^-1 s^-1, respectively. As the rebamipide absorption spectrum disappeared during the reaction, a new spectrum grew due to generation of rather specific reaction product. The reaction product was characterized by LC-MS/MS and NMR measurements. Finally, a hydroxylated rebamipide at the 3-position of the 2(1H)-quinolinone nucleus was newly identified as the major product exclusively formed in the reaction between rebamipide and the ^•OH generated by UVB/H²O². Specific formation of this product explained the molecular characteristics of rebamipide as a potential ^•OH scavenger.

• Rebamipide
• OH scavenger
• UVB/HO
• LC-MS/MS
• NMR
• 3-Hydroxylated rebamipide