Metabolism of a disulfiram metabolite, S-Methyl N,N-diethyldithiocarbamate, by flavin monooxygenase in human renal microsomes

S-Methyl N,N-diethyldithiocarbamate (MeDDC), a metabolite of the alcohol deterrent disulfiram, is converted to MeDDC sulfine and then S-methyl N,N-diethylthiocarbamate sulfoxide, the proposed active metabolite in vivo. Several isoforms of CYP450 and to a lesser extent flavin monooxygenase (FMO) metabolize MeDDC in the liver. The human kidney contains FMO1 and several isoforms of CYP450, including members of the CYP3A, CYP4A, CYP2B, and CYP4F subfamilies. In this study the metabolism of MeDDC by the human kidney was examined, and the enzymes responsible for this metabolism were determined. MeDDC was incubated with human renal microsomes from five donors or with insect microsomes containing human FMO1, CYP4A11, CYP3A4, CYP3A5, or CYP2B6. MeDDC sulfine was formed at 5 μM MeDDC by renal microsomes at a rate of 210 ± 50 pmol/min/mg of microsomal protein (mean ± S.D., n = 5) and by FMO1 at 7.6 ± 0.2 nmol/min/nmol (n = 3). Oxidation of 5 μM MeDDC was negligible by all CYP450 tested (≤0.03 nmol/min/nmol). Inhibition of FMO by methimazole or heat diminished MeDDC sulfine formation 75 to 89% in renal microsomes. Inhibition of CYP450 in renal microsomes by N-benzylimidazole or antibody to the CYP450 NADPH reductase had no effect on MeDDC sulfine production. Benzydamine N-oxidation, a probe for FMO activity, correlated with MeDDC sulfine formation in renal microsomes (r = 0.951, p = 0.013). The K_M values for MeDDC sulfine formation by renal microsomes and recombinant human FMO1 were 11 and 15 μM, respectively. These results demonstrate a role for the kidney and FMO1 in the metabolism of MeDDC in humans.