Effects of exogenous zinc supplementation on intestinal epithelial repair in vitro

Background Substitution of zinc modulates antioxidant capabilities within t he intestinal mucosa and improves intestinal wound healing in zinc-deficien t patients with inflammatory bowel diseases. The aim of this study was to c haracterize the modulating effects of zinc on intestinal epithelial cell fu nction in vitro. Materials and methods The effects of zinc on intestinal epithelial cell mor phology were assessed by phase contrast and transmission electron microscop y using the non-transformed small intestinal epithelial cell line IEC-6. Zi nc-induced apoptosis was assessed by DNA fragmentation analysis, lactate de hydrogluase (LDH) release and flow cytometry with propidium iodine staining . Furthermore, the effects of zinc on IEC-6 cell proliferation were assesse d using a colorimetric thiazolyl blue (MTT) assay and on IEC-6 cell restitu tion using an in vitro wounding model. Results Physiological concentrations of zinc (25 mu m) did not significantl y alter the morphological appearance of IEC-6 cells. However, a 10-fold hig her dose of zinc (250 mu m) induced epithelial cell rounding, loss of adher ence and apoptotic characteristics. While physiological zinc concentrations (< 100 mu m) did not induce apoptosis, supraphysiological zinc concentrati ons (> 100 mu m) caused apoptosis. Physiological concentrations of zinc (6. 25-50 mu m) had no significant effect on intestinal epithelial cell prolife ration. In contrast, physiological concentrations of zinc (12.5-50 mu m) si gnificantly enhanced epithelial cell restitution through a transforming gro wth factor-beta (TGF beta)-independent mechanism. Simultaneous addition of TGF beta and zinc resulted in an additive stimulation of IEC-6 cell restitu tion. Conclusion Zinc may promote intestinal epithelial wound healing by enhancem ent of epithelial cell restitution, the initial step of epithelial wound he aling. Zinc supplementation may improve epithelial repair; however, excessi ve amounts of zinc may cause tissue injury and impair epithelial wound heal ing.