Indomethacin added to rat liver microsomes in vitro resulted in the denaturation of cytochrome P-450 to cytochrome P-420. This was NADPH independent, appeared to be non-enzyme mediated, did not involve free radicals or lipid peroxidation and was prevented by glycerol, butylated hydroxytoluene or SKF-525A. Indomethacin in vitro also caused a loss of cytochrome b5, NADH-cytochrome b5 reductase, NADPH-cytochrome c reductase and epoxide hydrolase activities, but an activation of UDP-glucuronyltransferase. Amongst a total of 22 non-steroidal anti-inflammatory drugs and derivatives there was a highly significant correlation between the extent of their denaturation of cytochrome P-450 and their surfactant potency. The results suggest that the denaturation of cytochrome P-450 by certain non-steroidal anti-inflammatory drugs was due to a detergent-like, membrane-perturbing action of the drugs and that in most cases the denaturation also involved a specific effect of a p-chlorophenyl moiety of the drug.
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