These results support the participation of hydroxyl radicals in arsenic-induced
disturbances in the central nervous system. In this connection, an interesting route to produce H2O2 was explained by the oxidation of As(III) to As(V) which, under physiological conditions, results in the formation of H2O2 (a source of damaging hydroxyl radical): equation(20) H3AsO3 + H2O + O2 → H3AsO4 + H2O2 (ΔrGΘ = −40.82 kcal/mol) The above reaction is spontaneous and exergonic with an estimated standard reaction free energy change for H2O2 formation of −40.82 kcal/mol (−170.87 J/mol). In addition to ROS, arsenic exposure can also initiate the generation of RNS. Several conflicting reports concerning arsenic-induced production of NO have been published Y-27632 in vitro (Shi et al., 2004). One report concluded that there was no cadmium-induced
increase in NO generation in hepatocytes and human liver cells, which inhibited inducible NO synthase gene expression in cytokine-stimulated human liver cells and hepatocytes (Germolec et al., 1996). In another report, arsenite was found to inhibit inducible NO synthase gene expression in rat pulmonary artery smooth muscle cells (Kodavanti et al., 1996). Similarly, a third study with low levels of arsenite reported no change in intracellular concentration of Ca(II) as well as no NO generation as detected by EPR spectroscopy (Barchowsky et al., 1999). GSH is a very effective cellular antioxidant and plays an important learn more role in maintaining cellular redox status. In addition, GSH level is a good marker of oxidative stress of an organism (Halliwell and Gutteridge, 2007). Several papers have reported decreased levels of GSH
after exposure to arsenic. It was reported that following oral intake of arsenic, Astemizole the GSH concentration was significantly decreased in the liver of male Wistar rats (Maiti and Chatterjee, 2001). After 6 months exposure to arsenic, hepatic GSH and the enzymes glucose-6-phosphate dehydrogenase and GPx were significantly lowered in mice. Overall, from these studies follow that GSH possibly acts as an electron donor for the reduction of pentavalent to trivalent arsenicals and that arsenite has high affinity to GSH. The exact molecular mechanism of arsenic toxicity and carcinogenesis is still not known. Current views of molecular mechanisms of arsenic toxicity involve genetic changes, the involvement of increased oxidative stress, enhanced cell proliferation and altered gene expression. Arsenic is known to induce hypoxia signalling pathways. For example in prostate cancer cells treated with arsenite induced HIF-1alpha expression in a concentration- and time-dependent manner, whereas the level of HIF-1beta remained unaffected (Posey et al., 2008). The VEGF protein level was also elevated. ROS formation was linked with the activation of the PI3K/Akt pathway and the subsequent induction of HIF-1alpha and VEGF.