Granny Smith apple procyanidin extract upregulates tight junction protein expression and modulates oxidative stress and inflammation in lipopolysaccharide-induced Caco-2 cells

The present work is undertaken to characterize a Granny Smith apple procyanidin extract (AE) and investigate the beneficial effect of the AE in the intestine in vitro. Each AE was characterized via LC-ESI-MS. Caco-2 cells were used to study the preventive actions of the AE against the downregulation of tight junction protein expression, oxidative stress and inflammation induced by lipopolysaccharides (LPS). Phenolic compounds present in the AE, including chlorogenic acid, catechin, epicatechin, proanthocyanidin dimers, and proanthocyanidin trimers, were characterized. The expression of the tight junction protein, including occludin and zona occludens (ZO)-1, increased significantly in LPS + AE treated Caco-2 cells, compared to LPS induced Caco-2 cells. Proanthocyanidin dimers had the most potent effect on increasing tight junction protein expression. The addition of LPS to Caco-2 cells induced oxidative stress and inflammation. However, incubation with proanthocyanidin dimers prevented LPS-mediated oxidative stress, including the increase of SOD, HO-1, CAT, and GSH-Px mRNA expression, and counteracted LPS-mediated inflammation as evidenced by the down-regulation of inflammatory markers (NF-, IL-6, and TNF- mRNA expression). Our findings provide evidence that AE could upregulate tight junction protein expression, probably acting via the reduction of oxidative stress and inflammation.