[Mechanisms of hepatocyte multinucleation in rats exposed to N-nitrosodimethylamine]

Mechanisms of hepatocyte multinucleation were investigated in rats exposed to N-nitrosodimethylamine (NDMA).Using immunohistochemical reaction to y-tubulin it was established that the number of cells containing three and more centrosomes increased in 48 h after NDMA injection. It was shown that formation of extra-centrosomes in hepatocytes was enhanced by oxidative stress induced by cytochromes P450 superfamily in the course of NDMA metabolism. NDMA administration led to a sharp increase in cytochrome P450 content in the liver, especially in 24 and 48 h (3.3 and 2.8 times respectively) after NDMA injection. Extensive staining of cytoplasm in the centrolobular hepatocytes was revealed by immunohistochemical reaction to cytochrome P450 2E1 in 24 and 48 h after the NDMA injection. Malone dialdehyde (the derivative of lipid peroxidation) was shown to increase 1.1-2.0 times, whereas catalase activity as of the antioxidative agent reduced to 1.1-1.3 times in that time. In 72-120 h after NDMA treatment, the number of cells with three or more centrosomes, the intensity of cytoplasmic staining, cytochrome P450 and malone dialdehyde contents in the liver were shown to decrease, whereas catalase activity increased. In 48 h after treatment, binucleated hepatocytes with various 3H-thymidine distribution in nuclei appeared in NDMA-treated cell populations evidencing of asynchronous DNA synthesis. Immunohistochemical reaction against Ki-67 proliferation marker revealed asynchronous nuclear proliferation activity in binucleated cells spreading not only to S-phase, but also to other phases of cell cycle, and namely G1, G2 and M. Thus, main mechanisms of hepatocyte multinucleation under NDMA exposure are accounted for hyperamplification of centrosomes as a consequence of oxidative stress and for asynchronous DNA synthesis in the nuclei of binucleate hepatocyte followed by asynchronous acytokinetic mitosis.