Contribution of cytochrome P450s to MEOS (microsomal ethanol-oxidizing system): a specific and sensitive assay of MEOS activity by HPLC with fluorescence labeling.

The contribution of cytochrome P450s to MEOS (microsomal ethanol-oxidizing system) in rat hepatic microsomes was studied with a modified assay method for MEOS activity. Acetaldehyde produced by MEOS was converted into the fluorescent derivative with cyclohexane-1,3-dione and analyzed by HPLC with a fluorescence detector. Acetaldehyde production by hepatic microsomes of rats treated with ethanol was higher by 75% than that by control rats. Ethanol oxidation activity of eight forms of P450 was investigated in a reconstituted system. CYP1A2 and CYP2E1 had high rates of acetaldehyde formation. The Km value of CYP2E1 for ethanol oxidation was 9.48 mM, similar to that of hepatic microsomes from rats treated with ethanol. The Km value of CYP1A2 was higher than that of CYP2E1, indicating the CYP1A2 with lower affinity for ethanol compared with CYP2E1. From the results of an inhibition study with antibodies, CYP2E1 was found to be a main contributor to MEOS induced by ethanol in rats, but CYP1A2 was considered to play an important role for MEOS when CYP2E1 was not induced. These results present the possibility that CYP1A2 and CYP2E1 contribute to MEOS activity.