N–nitrosodiethylamine cytochrome P450 induction and cytotoxicity evaluation in primary cultures of rat hepatocytes

The primary routes of potential human exposure to N-nitrosodiethylamine (NDEA) are ingestion, inhalation, and dermal contact. Air, diet and smoking contribute to potential human exposure at levels of a few μg of NDEA/day. Potential exposure depends on the ability of the nitrosamines to migrate from the product into the body. The first step in the metabolic degradation of NDEA by cytochrome oxidase (CYPs) enzymes is the introduction of a hydroxyl group and in human esophage and liver CYP2A3 and CYP2E1 participate on this metabolism. Measuring cytotoxicity in female rat primary hepatocytes cultures, were used to understand the CYP induction and metabolization correlated with low NDEA concentrations. We observed that NDEA at different concentrations in the absence of CYPs inducers, was able to induce CYP2B1, CYP2B2, CYP2E1, CYP3A1 and CYP4A3. A positive NDEA synergistic effect on the levels of mRNA, was observed in the presence of pyrazole (300 μM) for CYP2B1 and CYP2B2 and for pregnenolone 16-α carbonitrile (0.15 μM) for CYP2E1. Negative NDEA synergistic effects were observed for ethanol (0.3%) for CYP3A1, pyrazol (300 μM) for CYP2A1 and CYP2E1, and phenobarbital (1 mM) for CYP2A1. These facts are extremally important once that these metabolites can be directly related to the primary DNA lesions. We consider that studies to elucidate the biological factors that determine the shape of the dose-response curve are crucial for lowdose extrapolations of risk.