Oxidative Stress and Stress-signaling in Chemoprevention of Early Colon Cancer by Diclofenac

Abstract

Role of oxidative stress and NF-κB signalling was evaluated in the chemopreventive effects of diclofenac, a dual cycloxygenase inhibitor in 1,2-dimethylhydrazine dihydrochloride (DMH)-induced colon carcinogenesis in rat model. After a 6 week long treatment with DMH (early stage), morphological analysis revealed marked occurrence of preneoplastic features such as multiple plaque lesions (MPLs), aberrant crypts (ACs) and aberrant crypt foci (ACF) in the colonic mucosa. Histologically well characterized dysplasia and hyperplasia were also observed. Simultaneous administration of diclofenac with DMH resulted in a significant reduction of these, proving the chemopreventive efficacy of diclofenac at the chosen dose. Diclofenac only group didn’t show any prominent carcinogenic feature. The colonic mucosa showed decreased reactive oxygen species (ROS) generation, nitric oxide (NO) levels and inducible nitric oxide synthase (iNOS) expression in the DMH group. Apoptosis was quantified in the colonic mucosa by measuring caspase-1 and 3 activities and cleavage of PARP by Western blot analysis. Immunohistochemical localization of PARP was also done in colonic paraffin sections. The activities of both the caspases and cleavage of PARP decreased after DMH treatment. Also, the number of PARP positive cells was few in the DMH group, while it featured prominently in all the other groups. The expression of nuclear factor-κB (NFκB) and IκB kinase (IKK) was elevated while that of inhibitory κB (IκB) reduced after DMH treatment, as assessed both by Western blot and immunohistochemistry. Diclofenac significantly altered the modulations induced by DMH in all the studied parameters, thus confirming the role of oxidative stress and signalling in its chemopreventive action.