Curcumin utilizes the anti-inflammatory response pathway to protect the intestine against bacterial invasion

Abstract

Background/objectives: Curcumin, a major component of the Curcuma species, contains antioxidant and anti-inflammatory properties. Although it was found to induce apoptosis in cancer cells, the functional role of curcumin as well as its molecular mechanism in anti-inflammatory response, particularly in intestinal cells, has been less investigated. The intestine epithelial barrier is the first barrier and the most important location for the substrate coming from the lumen of the gut.

Subjects/methods: We administered curcumin treatment in the human intestinal epithelial cell lines, T84 and Caco-2. We examined endoplasmic reticulum (ER) stress response by thapsigargin, qPCR of XBP1 and BiP, electrophysiology by wild-type cholera toxin in the cells.

Results: In this study, we showed that curcumin treatment reduces ER stress and thereby decreases inflammatory response in human intestinal epithelial cells. In addition, curcumin confers protection without damaging the membrane tight junction or actin skeleton change in intestine epithelial cells. Therefore, curcumin treatment protects the gut from bacterial invasion via reduction of ER stress and anti-inflammatory response in intestinal epithelial cells.

Conclusions: Taken together, our data demonstrate the important role of curcumin in protecting the intestine by modulating ER stress and inflammatory response post intoxication.

Keywords: Anti-inflammatory response; Bacteria; Curcumin; Intestine; NF-κB.

Fig. 1. Effect of curcumin showed reduction of ER stress in human intestinal epithelial cells.

Polarized human intestinal epithelia cell lines T84 (A and B) and Caco-2 (C and D) were treated with thapsigargin apically for 4 hours following 24 hour pretreatment with different concentrations of curcumin as indicated. RNA was extracted and hallmark of ER stress, BiP mRNA level was measured by qRT-PCR. The fold change of the thapsigargin treated group was normalized by curcumin treatment only (B and D) to eliminate basal difference from each concentration of curcumin. Open bars represent negative controls. Thaps: Thapsigargin, Data are expressed as mean ± SEM. ^*P < 0.05 by ANOVA (A and B), t-test (C and D).

Fig. 2. Effect of curcumin on IRE1α activation in human intestinal epithelial cells.

Polarized human intestinal epithelia cell lines T84 (A and B) and Caco-2 (C) were treated with thapsigargin apically for 4 hours following 24 hour pretreatment with different concentrations of curcumin as indicated. mRNA was extracted and spliced form of XBP1 mRNA level (XBP1s), downstream target gene of IRE1α, was measured by qRT-PCR. The fold change of the thapsigargin treated group was normalized by curcumin treatment only (B) to eliminate basal difference from each concentration of curcumin. Open bars represent negative controls.

Fig. 3. Effect of curcumin on the defense mechanism against bacterial invasion in human intestinal epithelial cells.

Polarized human intestinal epithelia cell lines T84 (A and B) and Caco-2 (C and D) were treated with either thapsigargin for 4 hours (A) or 3 nM wild-type cholera toxin for 24 hours (B, C, and D) apically following 24 hour pretreatment with different concentrations of curcumin as indicated. RNA was extracted and the inflammatory response marker, IL-8 mRNA expression and ER stress marker, BiP mRNA expression level measured by qRT-PCR. Open bars represent negative controls. Thaps: Thapsigargin, Data are expressed as mean ± SEM. ^*P < 0.05 by ANOVA.

Fig. 4. Curcumin treatment displayed no change of the epithelial junction in human intestinal epithelial cells after intoxication.

(A) Polarized human intestinal epithelia cell line T84 cells were treated with 40 nM wild-type Cholera Toxin apically for 24 hours, respectively, following 24 hour pretreatment with 1 uM curcumin. The cells were fixed and stained with anti-ZO-1 antibody (green color for tight junction), anti-Phalloidin antibody (red color for actin skeleton), and DRAQ5 (blue color for nucleus). There was no change of the tight junction by curcumin. Arrows indicate the epithelial junction. (B) Proposed role of curcumin in anti-inflammatory response. wt CT: wild-type cholera toxins.