Indomethacin stimulation of lipid peroxidation and chemiluminescense in rat liver microsomes

Peroxidation of endogenous lipid by rat liver microsomes, coupled with oxidation of reduced nicotinamide adenine dinucleotide phosphate (NADPH) and measured as thiobarbituric acid reactive materials, is markedly stimulated in the presence of indomethacin [1-(p-chlorobenzyl)-5-methoxy-2-methyl-3-indole acetic acid] (0.1–1.0 mM). Concurrently, indomethacin enhances the lipolysis of membrane phospholipid containing arachidonic acid but has no effect on the rate of O₂ uptake in these samples. The system generates a rapidly developed chemiluminescense (CL), the intensity and rate of development of which are related to indomethacin concentration. The microsomal CL generated in the presence of indomethacin is distinct from the previously reported CL in that the time required for maximum intensity development is a matter of seconds (20–180) rather than hours. The enhanced CL is believed to be due to an energy transfer reaction whereby a high energy species transfers energy to the indomethacin molecule, which, in turn, decays via chemiluminescense. An enhanced chemiluminescense was also observed when indomethacin was added to a lipoxidase system and superoxide generating system (xanthine oxidase). Based on inhibitor studies, the rapidly developed chemiluminescense of the microsomal system requires cytochrome P-450 in addition to NADPH and coordinated iron ions. The results indicate that the CL is related to neither hydroxyl free radical nor superoxide anion formation.