Influence of apple polyphenols on the intestinal barrier in a colonic cell model

Apples (Malus spp., Rosaceae) and apple-derived foods contain polyphenols that are associated with various desirable health attributes. Amongst other effects, in vivo studies with rodent models have shown that these substances can help to prevent and aid the treatment of intestinal inflammation and other lesions linked to reductions in intestinal barrier function (and thus adverse effects on the status of tight junctions, TJs). In the study presented here we investigated effects of apple polyphenols and their intestinal degradation products on the TJ status (as indicated by the transepithelial resistance, TER), and the mRNA levels of TJ-associated genes (using quantitative real-time PCR) in T84 colon carcinoma cell line monolayers. T84 monolayers were preincubated with sodium caprate (C10) to obtain a model system with decreased barrier function. Polyphenols and their intestinal degradation products significantly increased the TER during 4 h incubations both with and without C10 treatment in comparison to controls. The transcription analyses revealed that polyphenols influenced the transcript levels of all of the tested genes encoding TJ-associated genes. Using physiological concentrations up to 5.7-fold increasing mRNA levels were achieved. Further, apple-specific dihydrochalcones strongly affected both the TER and the expression of tight junction-relevant genes. Generally, apple polyphenols and their intestinal metabolites appeared to enhance the epithelial barrier functions in the T84 colonic cell monolayer model, indicating that consumption of apples and apple-derived foods may have positive effects on the intestinal barrier in healthy humans and may play an important role in the prevention of inflammatory bowel diseases (IBDs)