Gliadin induced oxidative stress and altered cellular responses in human intestinal cells: An in-vitro study to understand the cross-talk between the transcription factor Nrf-2 and multifunctional APE1 enzyme.

The present study examined the wheat protein gliadin-induced oxidative and nitrosative stress and its downstream responses in human intestinal HCT-116 and HT-29 cells. The beneficial role of dietary phytochemical curcumin and role of multifunctional enzyme Apurinic/aprymidinic endonuclease 1 (APE1) a major player involved in the base excision repair (BER)-pathway in gliadin intolerant intestinal HCT-116 and HT-29 cell lines were evaluated as an in vitro model study. The cultured cells were exposed to gliadin protein, H2 O2 , and curcumin followed by the assessment of oxidative stress and the consequences were measured using spectrophotometric, PCR, flow cytometer, Western blotting, confocal microscopy, and other methods. Results demonstrate that a 3 h pretreatment of curcumin, followed by the treatment of gliadin protein for 24 h time period protected both the HCT-116 and HT-29 cells via: (i) decreasing the ROS/RNS, restoring the mitochondrial transmembrane potential; (ii) re-establishing the cellular antioxidant defense system (superoxide dismutase, catalase, and GSH); (iii) enhancing the functions of APE1 viz. endonuclease activity and redox activation of transcription factor Nrf-2, the later binds with the antioxidant response elements (ARE) and activates downstream targets involved in cell survival. The cross-talk between APE1 and Nrf-2 was also established using immunofluorescence imaging and co-immunoprecipitation assays. In conclusion, gliadin protein induces oxidative/nitrosative stress, mitochondrial dysfunction and it damages cellular biomolecules in the intestinal cells. Hence it can be attributed to the tissue damage and disease pathogenesis in wheat intolerance-associated intestinal diseases. The gliadin-induced stress and its consequences are significantly reduced by the pretreatment of curcumin via BER-pathway and ARE-pathway; which is evident through the interaction between these two essential proteins. Hence suggesting for the intervention of curcumin and other natural dietary phytochemicals-based disease management and treatment of gliadin intolerance associated intestinal diseases like celiac disease.