Abstract B2: Supplementation of dietary fish oil induces apoptosis through activation of PPARγ and involves inhibition of angiogenesis in colon cancer

Abstract

Abstract Introduction: Eicosapentanoic acid (EPA) and docosahexaenoic acid (DHA), the n-3 polyunsaturated fatty acids (PUFAs) enriched in fish oil, reduces proliferation and enhances apoptosis relative to n-6 PUFA treated cells. PPARγ, a member of retinoid X receptors (RXR) family, is implicated in the control of cell proliferation and apoptosis. One of the important components of Wnt pathway, β-catenin is also involved in cell proliferation. Hence, the present study was designed to understand the mechanism of action of different ratios of fish oil (FO) and corn oil (CO) in experimentally induced colon carcinoma by estimating the expression of PPARγ, apoptosis, β-catenin and VEGF. Methods: Male wistar rats were divided into following groups- Group I received purified diet while Group II and Group III received modified diet with FO:CO(1:1) and FO:CO(2.5:1) respectively for 4 weeks. After one week of purified diet, all the 3 groups were divided into two subgroups- one received the injection of ethylenediamine-tetra acetic acid intraperitoneally and another received dimethylhydrazine dihydrochloride (DMH) per week for 4 weeks (20mg/kg body weight). The animals which were killed 48 hours after the last injection constituted initiation phase whereas the remaining were kept on standard pellet diet and sacrificed on completion of 16 weeks constituted post initiation phase. The effect of different ratios of FO:CO was analyzed by estimating the expression of PPARγ in colonocytes; apoptotic/ necrotic cells by immunofluorescence; expression of β-catenin and VEGF by immunohistochemistry. Results: DMH administered animals have shown: No significant alteration in the expression of PPARγ in initiation phase whereas the expression was decreased significantly (p<0.001) in post-initiation phase.Apoptotic cells were increased significant (p<0.01) in the initiation phase whereas apoptotic cells were decreased significant in post-initiation phase (p<0.001).An increased expression of β-catenin and VEGF in both the phases. In comparison to DMH treated animals, treatment with different ratios of FO and CO have shown: A significant (p<0.001) increase in the expression of PPARγ in both the phases. However, the increase was more pronounced with FO+CO(2.5:1).A significant increase in apoptotic cells in both the phases. On treatment with FO+CO(2.5:1), cells undergoing necrosis were significantly increased as compared to FO+CO(1:1).The expression of β-catenin and VEGF were decreased in both the phases with both the ratios. Conclusion: The dose and time dependent chemopreventive effect of FO and CO may be mediated by increasing the expression of PPARγ, apoptosis and by inhibiting β-catenin and VEGF.