GENERATION OF INTRACELLULAR ACTIVE OXYGENS IN MOUSE FM3A CELLS BY 3‐HYDROXYAMINO‐1‐METHYL‐5H‐PYRIDO[4,3‐b]INDOLE, THE ACTIVATED TRP‐P‐2

Mouse FM3A cells in culture were treated with a reactive metabolite of 3‐amino‐1‐methyl‐5H‐pyrido[4,3‐b]indole (Trp‐P‐2), 3‐hydroxyamino‐1‐methyl ‐ 5H ‐ pyrido[4,3 ‐b]indole (Trp ‐ P ‐ 2‐ (NHOH)). When the treated cells, which were judged as viable on the basis of trypan‐blue exclusion, were subjected to nitroblue tetrazolium staining, formazan was formed inside the cells, a fact suggesting the intracellular presence of superoxide. No formazan formation was detected on treatment of the cells with Trp‐P‐2. Single‐strand breaks in the cellular DNA took place during this treatment with Trp‐P‐2(NHOH). Since Trp‐P‐2(NHOH) in solution generates superoxide anion accompanying its oxidative degradation, we conclude that the Trp‐P‐2(NHOH) treatment produces intracellular active oxygens that can damage DNA.