Effects Of PhIP On Oxidative Stress And Oncogene, Tumor Suppressor Genes Expression In Colons From Rats And Protective Role Of SBT Oil

Heterocyclic amines (HCAs) are a kind of organic amine compounds formed by pyrolysis process under high temperature in food and environment. Presently more than 20 kinds of HCAs have been identified. 2-amino-l-methyl-6-phenylimidazo [4,5-b] pyridine (PhIP) is one of the main compositions of the HCAs chemicals. Many studies have demonstrated that HCAs possess mutagenicity and carcinogenicity, and they are closely related to colorectal cancer, breast cancer and so on. However, PhIP-induced colon injury and the protective effects of anti-oxidants are not very clear. Oxidative damage, activation of proto-oncogene and inactivation of tumor suppressor gene may lead to cell damage and cell abnormal proliferation, which may be the important mechanism for the initiation of colon cancer. Additionally, studies have shown that seabuckthorn (SBT) seed oil may exert an antioxidative role. Therefore, oxidative damage effects and expressions of proto-oncogenes and tumor suppressor genes in rat colons induced by PhIP were investigated to explore the injury effect and molecular mechanism of colonic carcinogenesis by PhIP in this study. Also, the protective effects of SBT against the colonic oxidative damage were studied.Using Wistar male rats as experimental animals, oxidative damage effects and expressions of proto-oncogenes and tumor suppressor genes in rat colons after exposure to different concentrations of PhIP were measured by using biochemical analysis, real time qRT-PCR, western blotting to indicate injury of colonic tissue in rats. Moreover, the protective effects of SBT against PhIP-induced colonic oxidative damage were studied. The indexes of lipid preoxidation were chosen as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) activities and malondialdehyde (MDA) contents; the indexes of protein oxidative damage were protein carbonyl (PCO) contents and DNA-protein crosslinks (DPC) coefficients, c-fos and c-jun were representative genes of proto-oncogenes while p16 and Rb were representative genes of tumor suppressor genes.The experimental results show:PhIP significantly reduced SOD, CAT,GPx activities in colon tissues of rats, and increased the content of MDA in a dose-dependent manner (P< 0.05). Compared with the control group, such effects were significant at the higher concentrations of PhIP (10 mg/kg and 15 mg/kg b.w., P< 0.05). PhIP with different doses significantly increased PCO contents and DPC coefficients compared with the control groups (P< 0.05, or P< 0.01), showing a dose-dependent manner with the elevated concentrations. In addition, PhIP elevated proto-oncogene c-fos and c-jun gene mRNA and protein expressions and suppressed tumor suppressor gene p16 and Rb gene expressions in a dose-dependent manner (P< 0.05). Also, the combined actions of SBT oil and PhIP significantly increased the antioxidant indices, decreased MDA and PCO contents as well as DPC cross-linking rates compared with the PhIP exposure group.The results show that PhIP could induce oxidative damage on rat colon tissue, cause the abnormal expressions of proto-oncogenes and tumor suppressor gene. The combined effects of PhIP and SBT seed oil can suppress oxidative damage in colons of rats, suggesting the protective roles of SBT seed oil. These data may not only provide some experimental evidences for clarifying the toxicological effects of PhIP on colons of rats, but also address the protective roles of SBT seed oil against colon oxidative damage, which may have significant meanings for prevent human from harmful substances and protect human health.