Toxicokinetics and in vivo genotoxicity after single dose oral gavage and intravenous administration of N-Nitrosonornicotine in Sprague Dawley rats

N-Nitrosonornicotine (NNN) is a tobacco specific nitrosamine (TSNA) and a known human carcinogen. NNN is mutagenic in bacterial mutation assay. The dose response and a correlation between its exposure and genotoxic mode of action is not well characterized. In this study, we evaluated the toxicokinetics (TK) of NNN via oral gavage (PO) and intravenous (IV) administration. In addition, genotoxicity assays, such as comet assay and micronucleus assay were conducted using different tissues as a toxicodynamic endpoints. The genotoxicity of NNN in the select target organs of toxicity in vivo was studied in rats following NNN exposure. A single dose of 0.24 μg/kg, 2.4 μg/kg, or 24 μg/kg of NNN (mixture of 70 % R and 30 % S) and 0.9 % saline (vehicle control) was acutely administered in male Sprague-Dawley (SD) rats (9–10 weeks age) via PO and IV administrations. Plasma, urine, and tissue specimens were collected at designated timepoints and analyzed for levels of NNN and its major metabolites, (R, S)-Nornicotine (NN) and N′-nitrosonornicotine-1-N-oxide (NNN-N-Oxide); and DNA from various tissues were evaluated for the genotoxic potential of NNN using in vivo alkaline comet assay. Following IV administration, tail migration increased compared to that of the vehicle control in peripheral blood, bronchoalveolar lavage (BAL), liver, kidney, and bone marrow. These increases were mostly dose dependent. Similar changes were seen for tail moments in peripheral blood lymphocytes (PBLs), BAL, and liver. Similarly to the IV administration, tail migration showed treatment related effects following PO administration. Tail migration in liver, kidney, duodenum, bone marrow, and BAL showed statistically significant increase in length compared to that of the vehicle control. TK data analysis indicated that NNN was rapidly absorbed and metabolized to NNN-N-Oxide after NNN administration via the two routes as shown by the short half-life (T_1/2 = 1.25–2.5 h). While NNN concentration was not quantifiable in plasma at low dose, systemic exposure as indicated by C_max and AUC was found to be increased in a dose proportional manner between the mid and high NNN exposure groups in the plasma samples following the PO and IV administration. Similarly, urinary excretions of NNN showed a dose proportional increase between the mid and high NNN after PO and IV administrations. Overall, the results suggest that the different tissue-specific genotoxic profiles are mainly due to the different effective doses of NNN resulting from the route of administration. First pass metabolism may play a role in enhancing NNN genotoxicity via the PO route as indicated by positive comet assay results from different target organs of toxicity.