Ras Signaling Pathway in the Chemopreventive Action of Different Ratios of Fish Oil and Corn Oil in Experimentally Induced Colon Carcinogenesis

Abstract

Dietary factors play a significant role in colon cancer. The essential polyunsaturated fatty acids (PUFAs), n-3 PUFAs, and n-6 PUFAs exert inverse effect on cancer. This study was designed to understand the mechanism of chemopreventive action of different ratios of fish oil (FO) and corn oil (CO) in colon carcinoma. Wistar rats were divided into 3 groups: Group 1 received purified diet whereas Groups 2 and 3 received modified diet with FO:CO (1:1) and FO:CO (2.5:1), respectively. The groups were further subdivided into controls receiving ethylenediamine-tetra acetic-acid and treated groups received dimethylhydrazine-dihydrochloride (DMH)/wk for 4 wk. Animals sacrificed 48 h after last injection constituted initiation phase and that sacrificed after 16 wk constituted post-initiation phase. Differential effect of different ratios of FO and CO was analyzed in isolated colonocytes. In both phases, DMH treatment showed an increase in pan Ras, Raf, MEK1/2, extracellular signal regulated kinase (Erk)1/2, and c-fos levels. Akt levels were increased in post-initiation phase only. Treatment with FO + CO (1:1) + DMH decreased pan Ras, MEK1/2 and Erk1/2 levels in post-initiation phase whereas Raf and c-fos were decreased in both phases. Treatment with FO + CO (2.5:1) + DMH decreased Ras, Raf, MEK1/2, Erk1/2, and c-fos levels in both phases. Akt was decreased in post-initiation phase only. The chemo-preventive action of FO and CO may be mediated by time- and dose-dependent effect.

ACKNOWLEDGMENTS

This work was supported by a grant from the Indian Council of Medical Research (Immuno/18/11/27/2008-ECD-I). The authors would like to acknowledge the Council of Scientific Research as Ms. Shevali Kansal is SRF-CSIR. The authors would also like to acknowledge Mrs. Sandhya, Senior Technician, CSIC Department, Postgraduate Institute of Medical Education and Research, Chandigarh, for doing flowcytometric estimations.