Adrenochrome reaction implicates oxygen radicals in metabolism of cyclosporine A and FK-506 in rat and human liver microsomes
Ahmed, S.S.; Strobel, H.W.; Napoli, K.L.; Grevel, J.
Journal of Pharmacology and Experimental Therapeutics 265(3): 1047-1054
1993
ISSN/ISBN: 0022-3565 PMID: 7685382 Document Number: 421028
The role of oxygen radicals in the metabolism of cyclosporine A (CyA), FR900506 (FK-506) and carbon tetrachloride (CCl-4) catalyzed by the cytochrome P450 system was investigated in vitro in rat and human microsomal preparations. Varying concentrations of CyA, FK-506 and CCl-4 (100 mu-M-1.0 mM) were added to microsomal preparations, and lipid peroxidation was measured by malondialdehyde (MDA) formation as detected by the thio-barbituric acid assay. The effects of oxygen radical scavengers (superoxide dismutase (SOD) and catalase (CAT)) and an antioxidant (glutathione (GLUT)) were tested on various incubations of CyA, FK-506 and CCl-4 to assess the role of oxygen radicals in lipid peroxidation. CyA-dependent MDA formation was moderately inhibited by SOD in the rat model and increased by SOD in the human model. In both models, CAT slightly inhibited CyA-dependent MDA formation and GLUT significantly inhibited MDA formation. FK-506-dependent MDA formation, studied only in the rat model, paralleled CyA-induced MDA formation but showed greater inhibition with CAT and less inhibition with SOD or GLUT. In both models, CCl-4-dependent MDA formation was significantly inhibited by GLUT and showed no sensitivity to SOD or CAT. In addition, the adrenochrome reaction, which measures the oxidation of epinephrine to adrenochrome, was used to measure the increased oxygen radical-flux resulting from the metabolism of CyA, FK-506 and CCl-4. CyA with epinephrine showed the highest oxidative activity, followed by FK-506 and then CCl-4, which showed the least formation of adrenochrome. These results indicated a role for oxygen radicals in CyA and FK-506 metabolism.