Cell cycle arrest at these checkpoints AG-014699 research buy prevents DNA replication and mitosis in the presence of

DNA damage. For this reason, no dose-response effect could be observed. The inactivation of these cell cycle checkpoints results in genomic instability, which is closely associated with cell transformation and tumorigenesis. It is widely accepted that the mutagenic action of nitrosamines is mediated via their immediate metabolic product (Verna et al., 1996). The metabolism of NDEA in vivo results in the formation of electrophilic reactive intermediates, free radicals, and associated oxidative stress ( Parke, 1987 and Shiota et al., 2002), which are in turn able to alkylate lipids, proteins, and genetic materials. Among its many effects as a potent tumor promoting agent, PB can cause oxidative damage to livers in response to the induction of certain cytochrome P450 enzymes ( Imaoka et al., 2004).

Wastl et al. (1998) demonstrate in preneoplastic and neoplastic INCB024360 mouse liver lesions that PB is a potent inducer of CYP2A5, and is likewise involved in NDEA metabolism, suggesting that it may play an important role in the development of liver cancer and may be used as a marker for spontaneous and NDEA-induced mouse liver foci. In the present work we did not investigate the effects on mouse CYP2A5 (an ortholog of human CYP2A6). Several genetic models of carcinogenesis indicate that progression to carcinoma involves the activation of proto-oncogenes and an additional event involving the deletion or inactivation of a suppressor gene ( Osanai et al., 1997).

The described mechanisms of proto-oncogene Smoothened activation include point mutations and gross DNA rearrangements, such as translocations and gene amplification ( Slenman and Sager, 1987 and Sargent et al., 1996). In the present study an increasing number of dicentric chromosomes was observed for both treatments, especially involving the largest chromosomes. This might suggest that the ras proto-oncogene, located on chromosome 1, is involved in the carcinogenic process ( Sargent et al., 1996). NDEA was also found to induce more CYP2B2 than CYP2B1, but when PB was used as a CYP inducer, the levels of CYP2B1 were higher than those of CYP2B2. The results obtained for the phenobarbital-induction of CYP2B1 and CYP2B2 mRNAs in cultured rat hepatocytes reflect the situation found in vivo, in that CYP2B1 mRNAs are more inducible than CYP2B2. The same was already described for Valproate, an anti-epileptic drug ( Rogiers et al., 1995). Measurements of cell viability are very important when the objective is RNA expression, since a decrease in the number of cells can be problematic for down-regulated genes. Another problem correlated to cytotoxic effects is the decrease in the micronucleus index, and the absence of any dose-response, as related before.