Human arylacetamide deacetylase is responsible for deacetylation of rifamycins: rifampicin, rifabutin, and rifapentine.

Rifamycins such as rifampicin, rifabutin, and rifapentine are used for the treatment of tuberculosis and induce various drug-metabolizing enzymes. Rifamycins have been reported to be mainly deacetylated by esterase(s) expressed in human liver microsomes (HLM) to 25-deacetylrifamycins, but the responsible enzyme remained to be determined. In this study, we found that recombinant human arylacetamide deacetylase (AADAC) could efficiently deacetylate rifamycins, whereas human carboxylesterases, which are enzymes responsible for the hydrolysis of many prodrugs, showed no activity. The involvement of AADAC in the deacetylation of rifamycins in HLM was verified by the similarities of the K(m) and K(i) values and the inhibitory characteristics between recombinant AADAC and HLM. Rifamycins exhibited potent cytotoxicity to HepG2 cells, but their 25-deacetylated metabolites did not. Luciferase assay using a reporter plasmid containing CYP3A4 direct repeat 3 and everted repeat 6 motifs revealed that 25-deacetylrifamycins have lesser potency to transactivate CYP3A4 compared with the parent drugs. Supporting these results, HepG2 cells infected with a recombinant adenovirus expressing human AADAC showed low cytotoxicity and induction potency of CYP3A4 by rifamycins. In addition, CYP3A4 induction in human hepatocytes by rifamycins was increased by transfecting siRNA for human AADAC. Thus, we found that human AADAC was the enzyme responsible for the deacetylation of rifamycins and would affect the induction rate of drug-metabolizing enzymes by rifamycins and their induced hepatotoxicity.