Phenolic compounds (PCs) are considered to possess anti-inflammatory properties and therefore were proposed as an alternative natural approach to prevent or treat chronic inflammatory diseases. However their effects are not fully understood, particularly at the intestinal level. To further understand their mode of action at the molecular level during intestinal inflammation, an in vitro model of inflamed human intestinal epithelium was established. Different representative dietary PCs, i.e. resveratrol, ellagic and ferulic acids, curcumin, quercetin, chrysin, (-)-epigallocatechin-3-gallate (EGCG) and genistein, were selected. To mimic intestinal inflammation, differentiated Caco-2 cells cultivated in bicameral inserts, in a serum-free medium, were treated with a cocktail of pro-inflammatory substances: interleukin (IL)-1β, tumor necrosis factor-α, interferon-γ and lipopolysaccharides. The inflammatory state was characterized by a leaky epithelial barrier (attenuation of the transepithelial electrical resistance) and by an over-expression at the mRNA and protein levels for pro-inflammatory markers, i.e. IL-6, IL-8 and monocyte chemoattractant protein-1 (MCP-1), quantified by ELISA and by gene expression analysis using a low-density array allowing the evaluation of expression level for 46 genes relevant of the intestinal inflammation and functional metabolism. Treatment with PCs, used at a realistic intestinal concentration, did not affect cell permeability. In inflamed cells, the incubation with genistein reduced the IL-6 and MCP-1 overproduction, to ca. 50% of the control, whereas EGCG provoked a decrease in the IL-6 and IL-8 over-secretion, by 50 and 60%, respectively. This occurred for both flavonoids without any concomitant inhibition of the corresponding mRNA expression. All the PCs generated a specific gene expression profile, with genistein the most efficient in the downregulation of the expression, or over-expression, of inflammatory genes notably those linked to the arachidonic metabolism pathway. In conclusion, this study provides evidence that genistein and EGCG downregulate the inflammatory response in inflamed intestinal epithelial cells by a pathway implicating largely a post-transcriptional regulatory mechanism.
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