Role of B vitamins on Oxidative Stress and Apoptotic Proteins Expression in Experimental Colon Cancer Model

Abstract

BackgroundAzoxymethane is a potent carcinogenic agent commonly used to induce colon cancer and oxidative stress in rats. The endoplasmic reticulum (ER) stress response, represents an adaptive mechanism to support cellular survival in response to adverse microenvironment conditions by accumulating misfolded proteins and leading to apoptosis of cells. GRP78 has the potency of (potential to) inhibiting apoptosis by blocking BAX activity and thereby switching off intrinsic apoptotic pathway. Clinical studies continue to stress that oxidative stress (GRP78) is mediated B‐vitamins (folate and B12) deficiencies, oxidative and hyper homocysteinemia. However, it is relatively unknown how B vitamins affect oxidative stress on colon cancer tissue.ObjectiveTo study the expression of GRP78 and apoptotic proteins on azoxymethane(AOM) induced colon cancer using B vitamins and also to see any ultrastructure changes using Electron Microscopy.MethodsAzoxymethane (AOM)‐induced colon cancer model was used in Sprague‐Dawley rats were randomly divided into groups. The control group fed a basal diet with no AOM injection; the AOM‐treated group fed a basal diet with AOM intraperitoneal injections, whereas the other experimental groups received daily doses of folate or vitamin B12 supplementation in the presence or absence of AOM injection. Another 6 groups of rats were tested for the potential synergistic effects of both folate and vitamin B12 supplementation. All animals continuously fed ad‐libitumuntil 16 weeks, then all rats were sacrificed and the colon tissues were examined for the immunohistochemical and ultrastructural changes. Briefly, 2–3mm of colon tissue sections were stored in glutaraldehyde and from these semithin and ultrathin sections were cut and viewed to delineate the cellular organelles architecture in a transmission electron microscope (TEM). Paraffin blocks were cut and the expression of GRP78, Bcl2 and Bax was observed under a light microscope using Immunohistochemistry (IHC) technique.ResultsThere was over expression of GRP78 , Bcl2 and Bax proteins on IHC in colon cancer tissues treated with B vitamins however their expression was dose dependent. There were also ultrastructure changes in the cell organelles with dilation of endoplasmic reticulum and increase in the number of mitochondria. This is consistent with our earlier finding that early exposure to AOM causes morphological changes in the colonic mucosa of the assayed groups.ConclusionVitamin B12 and folate play a protective role against oxidative stress at both the cellular and protein levels and might ameliorate the metabolic stress on colon cells caused by cancer. Overexpression of GRP78 and the role of B vitamins will help in future to study the UPR components for understanding the cellular mechanisms involved in cancer progression.Support or Funding InformationSQU Institutional Fund