Mechanism of antimutagenic action of (+)-catechin against the plant-activated aromatic amine 4-nitro-o-phenylenediamine.

Aromatic amines are activated into mutagens by both animal and plant systems. For plant-activated aromatic amines an important step in this process involves peroxidase enzymes. 4-nitro-o-phenylenediamine (NOP) is a well known direct-acting mutagen that can be enhanced in mutagenic potency by intact plant cells and also by isolated peroxidase enzymes. This activation process is inhibited by several different chemical agents including potassium cyanide (KCn), a known peroxidase inhibitor, and (+)-catechin. In our laboratory both KCn and (+)-catechin inhibited peroxidase-mediated NOP activation into a Salmonella mutagen. However, while KCn demonstrated strong peroxidase enzyme inhibition (as measured biochemically), (+)-catechin showed only minimal inhibition of peroxidase. Experiments comparing NOP direct and plant-activated mutagenic activity to different Salmonella strains (in the presence and absence of (+)-catechin) suggest that (+)-catechin may inhibit the mutagenic process by limiting O-acetyltransferase (OAT) activity in Salmonella. OAT activity in Salmonella is a required process for mutations to be induced following treatment with NOP and other aromatic amines.