Genotoxic alterations in murine hepatocytes after short- and long-term exposure to N-nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, NNK, a component in tobacco cigarette smoke
There are over 7,000 components in cigarette smoke, 70 of which are considered genotoxic and carcinogenic. N-Nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is one of these components. When treated with NNK at concentrations of as low as 0.1 nM, breast and lung cells are known to acquire malignant properties. The liver plays an important role in toxin metabolization, yet little is known about the cytotoxic effects of NNK on hepatocytes. Therefore, we assessed the effects of NNK on immortalized murine hepatocytes (AML12 cell line) using a repeated exposure approach. AML12 cells were subjected to either short- (single exposure for up to 72 h) or long-term (cumulative exposure for 90 days) testing, at various NNK concentrations (0.1, 10, and 1000 nM). DNA damage was analyzed using the comet assay, a gold-standard technique to assess DNA strand breaks in eukaryotic cells. The cells subjected to short-term exposure had a significantly increased proliferation rate in the 0.1 and 10 nM groups when compared to controls. Furthermore, the cells from the 10 nM group exhibited increased migration rate after cumulative exposure to NNK. The clastogenic effect of NNK increased in a concentration-dependent manner up to 10 nM. We conclude that NNK is genotoxic and significantly alters cell viability and migration, contributing to malignant transformation of hepatocytes.