Modulation of non-steroidal anti-inflammatory drug-induced, ER stress-mediated apoptosis in Caco-2 cells by different polyphenolic antioxidants: a mechanistic study

Abstract

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.

Epigallocatechin-3-Gallate Reduces Cd-Induced Developmental Toxicity of Bodysize in Caenorhabditis elegans via the PEK-1/eIF-2α/ATF-4 Pathway

“…PERK (PEK-1 in C. elegans), the second ER stress sensor, is an ER transmembrane protein [27]. In a cellular model, EGCG inhibited the expression of the ER stress marker ATF4 in trabecular meshwork cells treated with Tm [39], suppressed the increase in p-PERK/p-eIF-2α/ATF-4 expression levels in Caco-2 cells treated with Tm and thapsigargin [40], and decreased the expression of p-PERK in high-glucose-induced podocytes [41]. Our study shows that RNAi targeting pek-1 abolishes the inhibitory effect of EGCG on Cd-induced ER stress in the nematode head (Figure 5A,B).…”

The roles of epigallocatechin gallate in the tumor microenvironment, metabolic reprogramming, and immunotherapy

“…Relevant evidence has revealed the transcriptional programs of these transporters are largely regulated by HIF-1α, ATF4, and Myc ( 198 , 199 ). Indeed, it has been observed that EGCG can markedly reduce the expression of these transcription factors in tumors ( 16 , 200 , 201 ). Given that, we speculate EGCG may downregulate the expression levels of the abovementioned glutamine receptors, but direct experimental results are still needed to confirm our hypothesis.…”

Predicting molecular mechanism of silymarin-potentiated diclofenac toxicity: Insight from in silico molecular docking

“…Its notable adverse effect has been related to gastrointestinal damage which, in part, occurs from its inhibition against mitochondrial complex I activity and production of stress-induced apoptotic cell death [1] , [2] , [3] . Recently, we demonstrated that some natural antioxidants with ability to suppress endoplasmic reticulum (ER) stress such as epigallocatechin, quercetin and rutin could prevent diclofenac-induced apoptosis in Caco-2 cell, which is a widely accepted cell model for intestinal absorption, as well as in intestinal rat tissue [4] , [5] . Their “key” protective mechanisms involve inhibition of PERK-CHOP ER sensor activation, and maintaining mitochondrial permeability and function [4] .…”

“…On the other hand, certain antioxidants such as phyllanthin and silymarin increased diclofenac toxicity in Caco-2 cells through suppression of survival responses and/ or increase of apoptosis [5] . For example, the potentiation effect of phyllanthin was caused by downregulating the expression of p-Nrf-2/HO-1 proteins, activating PERK-CHOP proteins, disrupting mitochondrial membrane permeability (MMP), and inducing apoptosis [4] . Silymarin, a known hepatoprotective compound in milk thistle, enhanced apoptosis of diclofenac-treated Caco-2 cells possible through MMP disruption without generating ER stress [5] .…”