Protective mechanisms of polyphenols against NSAIDs-induced intestinal cell death in Caco-2 cells

Abstract

Indomethacin (INDO) and diclofenac (DIC) cause intestinal cell death through reactive oxygen species (ROS), endoplasmic reticulum stress (ER stress) and mitochondrial dysfunction. This study investigated the cytoprotective effects of certain natural polyphenolic antioxidants against INDO- and DIC-mediated Caco-2 cell death as well as underlying mechanisms. In this study, caffeic acid (CAF), curcumin (CUR), epigallocatechin gallate (EGCG), gallic acid (GAL), hypophyllanthin (HYPO), naringenin (NAR), phyllanthin (PHY), piperine (PIP), quercetin (QUE), rutin (RUT) and silymarin (SLY) were able to decrease ROS production in Caco-2 cells treated with INDO and DIC. However, only EGCG, QUE and RUT (100 µM) could prevent INDO- and DIC-mediated cytotoxicity after 72-h treatment. Their cytoprotective action could be related to suppression of CHOP expression, Bax/Bcl-2 ratios and loss of mitochondria membrane permeability (MMP). Further study on the cytoprotective effect of EGCG demonstrated that its underlying mechanism involved with suppressions of p-PERK/p-eIF-2α/ATF-4/CHOP and p-IRE-1α/p-JNK1/2 expressions. Another two polyphenols CAF and NAR (100 µM) protected Caco-2 toxicity from INDO treatment, but not DIC treatment. Moreover, the effect of NAR involved with suppression of Bax/Bcl-2 mRNA ratios and loss in MMP. Apparently, NAR did not affect CHOP expression. A group of polyphenols including CUR (50 µM), GAL (100 µM), HYPO (10 µM), PHY (10 µM), PIP (10 µM) and SLY (100 µM) had no effects on INDO-/DIC-induced Caco-2 cytotoxicity. Instead, CUR, NAR, PHY, PIP and SLY enhanced cytotoxicity caused by DIC exposure. Further study on the potentiation effect of PHY suggested that this compound suppressed survival p-Nrf-2/HO-1 expression in DIC-treated cells, leading to increased activation of PERK/CHOP pathway and apoptosis. Taken together, the cytoprotective capabilities of polyphenols against INDO-/DIC-induced Caco-2 apoptosis might be involved with suppressions of the specific ER stress signaling pathways, but not the direct ROS scavenging mechanism.