Inhibition of benzo[a]pyrene-dependent mutagenesis and cytochrome P-450 reductase activity by copper complexes

The superoxide dismutase (SOD) biomimetic copper(II) (3,5-diisopropylsalicylate)2 (CuDIPS) has been previously reported to inhibit the tumorigenicity of a polycyclic aromatic hydrocarbon (PAH) requiring metabolic activation. We have used the Ames Salmonella typhimurium revertant assay to survey the effects of CuDIPS and its analogs on the metabolic activation of the PAH benzo[a]pyrene (BP) by liver homogenates. Supplementation of homogenates from normal and Aroclor 1254-treated SENCAR mice with varied concentrations of CuDIPS resulted in a dose-dependent noncompetitive inhibition of BP mutagenesis. Cytochrome P-450 reductase activity in liver homogenates and microsomal preparations was also inhibited by concentrations of CuDIPS possessing antimutagenic activity. Neither DIPS nor ZnDIPS, analogs of CuDIPS lacking SOD activity, inhibited mutagenesis or P-450 reductase activity. CuSO4, which has SOD activity, was almost as effective as CuDIPS on a molar basis in inhibiting mutagenesis and P-450 reductase activity. The inhibitory effects of CuDIPS and CuSO4 could not be attributed to their SOD activity since bovine liver superoxide dismutase, at a 100-fold excess of CuDIPS-SOD activity, had no effect on their activity. Collectively these findings suggest that the in vitro antimutagenic activity of CuDIPS is independent of its salicylate structure and is mediated through a copper-dependent but non SOD-associated inhibition of P-450 reductase activity.