Gastrointestinal tract is the second largest organ in the body that mainly functions in nutrients and minerals intake through the intestinal barrier. Intestinal permeability maintains the circulation of minerals and nutrients from digested foods. Life and all the metabolic processes depend either directly or indirectly on proper functioning of GI tract. Compromised intestinal permeability and related disorders are common among all the patients with inflammatory bowel disease (IBD), which is a collective term of inflammatory diseases including Crohn’s disease and ulcerative colitis. Many synthetic drugs are currently in use to treat IBD such as 5-aminosalicylic acid corticosteroids. However, they all have some drawbacks as long-term use result in many complications. These problems encourage us to look out for alternative medicine. Numerous in vitro and in vivo experiments showed that the plant-derived secondary metabolites including phenolic compounds, glucosinolates, alkaloids, terpenoids, oligosaccharides, and quinones could reduce permeability, ameliorate-related dysfunctions with promising results. In addition, many of them could modulate enzymatic activity, suppress the inflammatory transcriptional factors, ease oxidative stress, and reduce pro-inflammatory cytokines secretion. In this review, we summarized the phytochemicals, which were proven potent in treating increased intestinal permeability and related complication along with their mechanism of action.

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-κβ, IL-6, and TNF-α mRNA expression). Our findings provide evidence that AE could upregulate tight junction protein expression, probably acting via the reduction of oxidative stress and inflammation.

Epigallocatechin‐3‐gallate (EGCG) is a major bioactive compound in tea polyphenol extract. After ingestion, EGCG reaches the intestine and may commence anti‐inflammation in the intestinal organ. Thus, in this paper, the anti‐inflammatory effect of EGCG was studied using lipopolysaccharide (LPS)‐induced inflammation in RAW 264.7 cells. LPS induction instigated morphological deformation extensively which was normalized by EGCG. In LPS‐induced macrophage cells, EGCG was found to lower cellular nitric oxide (32% of LPS group) and intercellular ROS level (45.4% of LPS group). It also suppressed the expression of IL‐1β (LPS 132.6 ± 14.6, EGCG 10.67 ± 3.65), IL‐6 (LPS 2994.44 ± 178.5, EGCG 408.33 ± 52.34), TNF‐α (LPS 27.11 ± 2.84, EGCG 1.22 ± 0.03), and iNOS (LPS 40.45 ± 11.17, EGCG 10.24 ± 0.89). The GO function analysis identified that these differential genes involved 24 biological processes, 18 molecular functions, and 19 cellular component‐related processes. KEGG pathway enrichment analysis revealed that LPS significantly affects NF‐κB, TNF, and TLR signaling pathways. Western blotting revealed that EGCG diminished P‐IκB/IκB ratio by 75% and p‐p65/p65 by 50% compared to the LPS group. Finally, Arg‐1 and CD‐206 mRNA expression were determined by RT‐PCR, which was consistent with the RNA‐Seq result. These findings indicate that EGCG exerts an anti‐inflammatory effect by reducing NO and ROS production, suppressing TLR4 protein expression, and inhibiting IκB and p65 phosphorylation.