Effects of Benzo(a)pyrene on the Expression of Heat Shock Proteins, Pro-inflammatory Cytokines and Antioxidant Enzymes in Hepatic Tumors Induced by Rat Hepatoma N1-S1 Cells

Benzo(a)pyrene (BaP) is a polycyclic aromatic hydrocarbon (PAH) that is easily introduced to humans via consumption of grilled or smoked meat. BaP causes harmful oxidative effects on cell development, growth and survival through an increase in membrane lipid peroxidation, oxidative DNA damage and mutagenesis. Therefore, the present study was conducted to evaluate the synergistic effects of BaP on oxidative stress in hepatic tumors. In this study, we established a hepatic tumor model by injecting rat hepatoma N1-S1 cells into healthy rats. Changes in the abundance of heat shock proteins (HSPs), antioxidant enzymes and pro-inflammatory cytokines were then investigated by western blot analysis. In addition, we examined changes in oxidative stress levels. Injection of N1-S1 cells or concomitant injection of BaP and N1-S1 cells resulted in the formation of hepatic tumors at the injection site. Evaluation of rat plasma reveals that hepatic tumors induced by BaP and N1-S1 cells expresses higher levels of Hsp27, superoxide dismutase (SOD), and tumor necrosis factor-alpha (TNF-alpha) when compared to those induced by N1-S1 cells only. The collective results of this study suggest that BaP exerts synergistic effects on the expression of HSP, cytokines and antioxidant enzymes in hepatic tumors induced by rat hepatoma N1-S1 cells.

Involvement of mitogen-activated protein kinases and p21Waf1 in hydroxyurea-induced G1 arrest and senescence of McA-RH7777 rat hepatoma cell line

Hydroxyurea is commonly used to treat hematologic disorders and some type of solid tumors, but the mechanism for its therapeutic effect is not clearly known. In this study, we examined the effect of hydroxyurea on rat hepatoma McA-RH7777 cells, specifically, on the role of mitogen-activated protein (MAP) kinase signal transduction pathways and p21Waf1, p27Kip1 and p53. Rat hepatoma McA-RH7777 cells treated with hydroxyurea for 7 days, caused the inhibition of cell growth in a dose-dependent manner. But, this growth inhibition was not caused by necrosis or apoptosis but instead was associated with cell senescence-like change as evidenced by senescence associated-beta-galactosidase staining, and cells arrest at G1 phase of cell cycle. Phosphorylation of MAP kinases, such as ERK, JNK, and p38, was found to be decreased after treatment of cells with hydroxyurea. But, the expression of p21Waf1 was increased, while p27Kip1 and p53 were not detected in hydroxyurea treated rat hepatoma cells. Hydroxyurea treatment induced G1 arrest and a senescence-like changes in rat hepatoma McA-RH7777 cells may be the likely results of signal disruption of MAP kinases (ERK, JNK, and p38 MAP kinase) and p21Waf1 over-expression.