Abstract
BackgroundThe potential of ascorbic acid and two botanical decoctions, green tea and cat's claw, to limit cell death in response to oxidants were evaluated in vitro.MethodsCultured human gastric epithelial cells (AGS) or murine small intestinal epithelial cells (IEC-18) were exposed to oxidants – DPPH (3 μM), H2O2 (50 μM), peroxynitrite (300 μM) – followed by incubation for 24 hours, with antioxidants (10 μg/ml) administered as a 1 hour pretreatment. Cell number (MTT assay) and death via apoptosis or necrosis (ELISA, LDH release) was determined. The direct interactions between antioxidants and DPPH (100 μM) or H2O2 (50 μM) were evaluated by spectroscopy.ResultsThe decoctions did not interact with H2O2, but quenched DPPH although less effectively than vitamin C. In contrast, vitamin C was significantly less effective in protecting human gastric epithelial cells (AGS) from apoptosis induced by DPPH, peroxynitrite and H2O2 (P < 0.001). Green tea and cat's claw were equally protective against peroxynitrite and H2O2, but green tea was more effective than cat's claw in reducing DPPH-induced apoptosis (P < 0.01). Necrotic cell death was marginally evident at these low concentrations of peroxynitrite and H2O2, and was attenuated both by cat's claw and green tea (P < 0.01). In IEC-18 cells, all antioxidants were equally effective as anti-apoptotic agents.ConclusionsThese results indicate that dietary antioxidants can limit epithelial cell death in response to oxidant stress. In the case of green tea and cat's claw, the cytoprotective response exceed their inherent ability to interact with the injurious oxidant, suggestive of actions on intracellular pathways regulating cell death.
Highlights
Epithelial apoptosis in the gastro-intestinal tract is normally restricted to superficial cells but in pathological states of inflammation or infection, apoptotic cell death can be far more expansive
Despite the knowledge that apoptosis is increased in gut inflammation, either from idiopathic causes like inflammatory bowel disease [8,9] or associated with infections like H. pylori[13], little has been done to examine the effects of antioxidants on epithelial cell death
We have previously demonstrated an excessive degree of apoptosis in patients with gastritis induced by H. pylori, and that the degree of apoptosis could be reduced by dietary supplementation with vitamin C, irrespective of whether the infection was cleared or not [13]
Summary
Epithelial apoptosis in the gastro-intestinal tract is normally restricted to superficial cells but in pathological states of inflammation or infection, apoptotic cell death can be far more expansive. Depending on the agonist or eliciting milieu, apoptotic cell death is accompanied by the activation of various cell death pathways including caspases, ceramide, altered gene expression, mitochondrial dysfunction and consumption of ATP e.g., with DNA repair, that result in histone-associated DNA fragmentation [8,9]. We have previously demonstrated an excessive degree of apoptosis in patients with gastritis induced by H. pylori, and that the degree of apoptosis could be reduced by dietary supplementation with vitamin C, irrespective of whether the infection was cleared or not [13] This observation was suggestive that dietary antioxidants could limit the gut pathology by limiting cell death mechanisms. The potential of ascorbic acid and two botanical decoctions, green tea and cat's claw, to limit cell death in response to oxidants were evaluated in vitro
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