Catechin and Procyanidin B2 Modulate the Expression of Tight Junction Proteins but Do Not Protect from Inflammation-Induced Changes in Permeability in Human Intestinal Cell Monolayers

Abstract

The possibility of counteracting inflammation-related barrier defects with dietary compounds such as (poly)phenols has raised much interest, but information is still scarce. We have investigated here if (+)-catechin (CAT) and procyanidin B2 (PB2), two main dietary polyphenols, protect the barrier function of intestinal cells undergoing inflammatory stress. The cell model adopted consisted of co-cultured Caco-2 and HT29-MTX cells, while inflammatory conditions were mimicked through the incubation of epithelial cells with the conditioned medium of activated macrophages (MCM). The epithelial barrier function was monitored through trans-epithelial electrical resistance (TEER), and ROS production was assessed with dichlorofluorescein, while the expression of tight-junctional proteins and signal transduction pathways were evaluated with Western blot. The results indicated that MCM produced significant oxidative stress, the activation of NF-κB and MAPK pathways, a decrease in occludin and ZO-1 expression, and an increase in claudin-7 (CL-7) expression, while TEER was markedly lowered. Neither CAT nor PB2 prevented oxidative stress, transduction pathways activation, ZO-1 suppression, or TEER decrease. However, PB2 prevented the decrease in occludin expression and both polyphenols produced a huge increase in CL-7 abundance. It is concluded that, under the conditions adopted, CAT and PB2 do not prevent inflammation-dependent impairment of the epithelial barrier function of intestinal cell monolayers. However, the two compounds modify the expression of tight-junctional proteins and, in particular, markedly increase the expression of CL-7. These insights add to a better understanding of the potential biological activity of these major dietary flavan-3-ols at intestinal level.

Health-Promoting Properties of Proanthocyanidins for Intestinal Dysfunction

“…Studies on intestinal dysfunction have employed human colon carcinoma cell lines, with Caco-2 being the most well-established and widely used model of the human intestine barrier ( [105] and Table 1). Mucus producer [106], macrophages [107], and B cell lines [108] have been employed in co-culture systems to explore the interaction between cell populations. Although there is a strong trend in the industry towards replacing animal experiments with human cell-culture based models [109,110], there are no in vitro models of the human intestine that replicate the complex interplay between cell types and the regulation of the barrier function by the mucosal innate and adaptive immunity.…”

“…Some in vitro studies have associated PACs with increased TEER and decreased transport of permeability markers in the context of barrier dysfunction [115][116][117]. The expression levels of TJ proteins (claudins, occludins, and ZOs) often correlate, but not always [106], with intestinal permeability and are also considered markers of epithelial integrity. Bitzer et al [116] found that the dextran sodium sulphate (DSS)-induced loss of barrier function in Caco-2 cells was significantly inhibited by polymeric PACs of cocoa but not by oligomers.…”

“…Moreover, a higher barrier protective activity was determined in PACs with DP ≥ 7, which were able to reduce the detrimental effect of DSS in a dose-dependent fashion [116]. Effectiveness of procyanidin B2 ameliorating dextran sodium sulphate (DSS)-induced permeability alterations was examined using a Caco-2/HT29-MTX co-culture model [106]. Although procyanidin B2-incubated cells showed increased levels of the TJ proteins claudin-7, occludin, and ZO-1, these changes did not reduce TEER loss.…”

Plant Food, Nutrition, and Human Health

“…This is of interest to further studying the bioactivity of the compounds in the extracts. Bianchi et al [ 17 ] looked at the role of key dietary flavan-3-ols, (+)-catechin and procyanidin B 2 , in protecting the barrier function of intestinal cells undergoing inflammatory stress. The authors highlighted how, under the physiological conditions adopted, these compounds did not prevent inflammation-dependent impairment of the epithelial barrier function.…”

“…The authors highlighted how, under the physiological conditions adopted, these compounds did not prevent inflammation-dependent impairment of the epithelial barrier function. Nevertheless, these flavan-3-ols modified the expression of tight-junctional proteins and, in particular, claudin-7, shedding light on the potential biological activity of these major dietary flavan-3-ols at the intestinal level [ 17 ]. Our research group, in collaboration with other teams, also assessed the capability of the main colonic metabolites of flavan-3-ols, phenyl-γ-valerolactones, to reach the brain by crossing the blood-brain barrier [ 18 ].…”