Objectives Indomethacin (INDO) and diclofenac (DIC) can induce intestinal cell death through induction of oxidative stress‐mediated ER stress and mitochondrial dysfunction. This study investigated the cytoprotective potential of 11 polyphenols, namely 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) against these two NSAIDs in Caco‐2 cells. Methods Reactive oxygen species (ROS) production was determined with fluorescence spectroscopy using specific probes (DHE, DCFH‐DA, HPF). Cell viability and mitochondrial function were assessed by MTT and TMRE assays. The mRNA levels of Bax, Bcl‐2 and CHOP proteins were determined by quantitative real‐time polymerase chain reaction technique. Key findings All test polyphenols reduced NSAIDs‐mediated ROS production. Only EGCG, QUE and RUT protected INDO‐/DIC‐induced cell death. These three polyphenols suppressed Bax/Bcl‐2 mRNA ratio, CHOP up‐regulation and MMP disruption in NSAIDs‐treated cells. CAF and NAR prevented cytotoxicity from INDO, but not DIC. The cytoprotective effect of NAR, but not CAF, involved alteration of Bax/Bcl‐2 mRNA ratio or MMP disruption, but not CHOP transcription. Conclusion The cytoprotective activity of polyphenols against NSAIDs‐induced toxicity stemmed from either suppression of CHOP‐related ER and mitochondria stresses or other CHOP‐independent pathways, but not from the intrinsic ROS scavenging capacity.

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Objectives The study compared the protective effects against indomethacin-induced GI ulceration of chlorogenic acid with quercetin in rats. Methods Rats were orally given chlorogenic acid or quercetin (100 mg/kg; 5 days), followed by indomethacin (40 mg/kg; single dose). After 24 h, GI tissues were assessed for histopathological damages, then analysed by ELISA and western blot methods. Cell viability was measured in vitro by MTT assay. Key findings Unlike quercetin, chlorogenic acid could not prevent gastric ulcers in indomethacin-treated rats. The levels of gastric prostaglandin E2 (PGE2) and Bax/Bcl-2 ratio in the chlorogenic acid-treated group were not different from those receiving indomethacin alone. Nevertheless, both compounds alleviated jejunum ulcers through suppression of PERK/eIF-2/ATF-4/CHOP-related endoplasmic reticulum (ER) stress and decrease Bax/Bcl-2 ratio. Moreover, at 100 µM, they abolished the cytotoxicity of tunicamycin (an ER stress inducer) in gastric (AGS) and intestinal (Caco-2) cells. In silico docking studies suggested that both compounds could interact with key amino acid residues in the ­catalytic domain of PERK. Conclusion Chlorogenic acid and quercetin exerted comparable protective effects against indomethacin-induced intestinal ulcer through suppression of ER stress-mediated apoptosis but, unlike quercetin, chlorogenic acid offered no protection against gastric ulceration due to its ­inability to increase PGE2 production.

Objectives Direct scavenging of reactive oxygen species could not prevent ER stress-associated cytotoxicity of indomethacin or diclofenac in Caco-2 cells. This study investigated the effects of three polyphenolic antioxidants epigallocatechin gallate (EGCG), phyllanthin and hypophyllathin in non-steroidal anti-inflammatory drug-induced Caco-2 apoptosis. Methods Cells were treated with ER stressors (indomethacin, diclofenac, tunicamycin or thapsigargin) and the polyphenols for up to 72 h. Cell viability, apoptosis and mitochondrial function were monitored by MTT, Hoechst 33342 and TMRE assays, respectively. Protein expression was measured by Western blot analysis. Key findings Epigallocatechin gallate suppressed increases in p-PERK/p-eIF-2a/ ATF-4/CHOP and p-IRE-1a/p-JNK1/2 expression levels in the cells treated with any of the ER stressors, leading to inhibition of apoptosis. In contrast, phyllanthin increased apoptosis in the cells subsequently exposed to either diclofenac, tunicamycin or thapsigargin, but not in the indomethacin-treated cells. The potentiation effect of phyllanthin seen with the three ER stressors was related to suppression of survival p-Nrf-2/HO-1 expression, resulting in increased activation of the eIF-2a/ATF-4/CHOP pathway. On the other hand, hypophyllanthin had no significant effect on the ER stressor-induced apoptosis. Conclusion Epigallocatechin gallate, phyllanthin and hypophyllanthin displayed different effects in the ER stress-mediated apoptosis, depending upon their interaction with the specific unfolded protein response signalling.