Effect of Mammalian Tissues on Mutagenicity of Several N-Nitroso Compounds ¹

Supernatant fractions from different organs of rat and beef origin were tested for their effect on the mutagenic activity of N-methyl-N'-nitro-N-Nitrosoguanidine (MNNG), using Salmonella typhimurium tester strain (TA 1535). At equal protein concentrations their effects were quite different. Both beef and rat liver supernatant fluids (1.7 - 3.4 mg of protein per plate) completely inhibited the mutagenic action of MNNG (5 μg per 0.1 ml of cell culture) while that of the heart showed partial inactivation. Under similar conditions, beef kidney and rat seminal vesicle fractions had no effect on MNNG-induced mutagenesis. The antimutagenic property of the liver supernatant fluid was unaffected by mild heat treatment (70°C for 30 min) but completely destroyed by boiling for 10 min. Liver supernatant fluids also had a lethal effect on the tester strain. The antibacterial agent was separated from the antimutagenic property by dialysis. The dialyzate fraction had no lethal effect, but still remained active in inhibiting mutagenesis. To test whether the action of liver supernatatnt fluid was specific for MNNG alone, several other carcinogens belonging to the N-nitroso groups, methyl methane sulfonate (MMS), ethyl methane sulfonate (EMS) and l-nitrosopyrrolidine (NO-Pyr), were tested. Among various tissue fractions tested only the liver supernatant fluids drastically reduced the mutagenic activity of MMS (500 μg/plate), EMS (10⁴ μg/plate) and NO-Pyr (10⁴ μM/plate).