Indomethacin inactivates gastric peroxidase to induce reactive-oxygen-mediated gastric mucosal injury and curcumin protects it by preventing peroxidase inactivation and scavenging reactive oxygen

Abstract

We have investigated the mechanism of indomethacin-induced gastric ulcer caused by reactive oxygen species (ROS) and the gastroprotective effect of curcumin thereon. Curcumin dose-dependently blocks indomethacin-induced gastric lesions, showing 82% protection at 25 mg/kg. Indomethacin-induced oxidative damage by ROS as shown by increased lipid peroxidation and thiol depletion is almost completely blocked by curcumin. Indomethacin causes nearly fivefold increase in hydroxyl radical (radical dotOH) and significant inactivation of gastric mucosal peroxidase to elevate endogenous H₂O₂ and H₂O₂-derived radical dotOH, which is prevented by curcumin. In vitro studies indicate that indomethacin inactivates peroxidase irreversibly only in presence of H₂O₂ by acting as a suicidal substrate. 5,5-Dimethyl-pyrroline-N-oxide (DMPO) protects the peroxidase, indicating involvement of indomethacin radical in the inactivation. Indomethacin radical was also detected in the peroxidase–indomethacin–H₂O₂ system as DMPO adduct (a^N = 15 G, a_β^H = 16 G) by electron spin resonance spectroscopy. Curcumin protects the peroxidase in a concentration-dependent manner and consumes H₂O₂ for its oxidation as a suitable substrate of the peroxidase, thereby blocking indomethacin oxidation. Curcumin can also scavenge radical dotOH in vitro. We suggest that curcumin protects gastric damage by efficient removal of H₂O₂ and H₂O₂ -derived radical dotOH by preventing peroxidase inactivation by indomethacin.