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

• Published in: Free radical research 2004-05, Vol.38 (5), p.487-494
• Main Authors: Sakurai, Kazushi, Sasabe, Hiroyuki, koga, Toshihisa, Konishi, Tetsuya
• Format: Article
• Language: English
• Subjects: 3-Hydroxylated rebamipide; Alanine - analogs & derivatives; Alanine - pharmacology; Anti-Ulcer Agents - pharmacology; Chromatography, High Pressure Liquid; Chromatography, Liquid; Cyclic N-Oxides - metabolism; Electron Spin Resonance Spectroscopy; Free Radical Scavengers - pharmacology; Glutathione - metabolism; Hydrogen Peroxide - metabolism; Hydroxyl Radical - chemistry; Hydroxyl Radical - metabolism; Hydroxylation - drug effects; Hydroxylation - radiation effects; LC-MS/MS; Magnetic Resonance Spectroscopy; Mass Spectrometry; Molecular Structure; NMR; OH scavenger; Quinolones - pharmacology; Rebamipide; Spin Labels; Ultraviolet Rays; UVB/HO
• ISSN: 1071-5762; 1029-2470
• DOI: 10.1080/1071576042000209808

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.