Pyrogallol-induced As4.1 juxtaglomerular cell death is attenuated by MAPK inhibitors via preventing GSH depletion

Propyl gallate induces human pulmonary fibroblast cell death through the regulation of Bax and caspase-3

Propyl gallate (PG) has been found to exert an inhibitory effect on the growth of different cell types, including lung cancer cells. However, little is known about the cytotoxicological effects of PG specifically on normal primary lung cells. The current study examined the cellular effects and cell death resulting from PG treatment in human pulmonary fibroblast (HPF) cells. DNA flow cytometry results demonstrated that PG (100-1,600 μM) had a significant impact on the cell cycle, leading to G1 phase arrest. Notably, 1,600 μM PG slightly increased the number of sub-G1 cells. Additionally, PG (400-1,600 μM) resulted in the initiation of cell death, a process that coincided with a loss of mitochondrial membrane potential (MMP; ΔΨm). This loss of MMP (ΔΨm) was evaluated using a FACS cytometer. In PG-treated HPF cells, inhibitors targeting pan-caspase, caspase-3, caspase-8, and caspase-9 showed no significant impact on the quantity of annexin V-positive and MMP (ΔΨm) loss cells. The administration of siRNA targeting Bax or caspase-3 demonstrated a significant attenuation of PG-induced cell death in HPF cells. However, the use of siRNAs targeting p53, Bcl-2, or caspase-8 did not exhibit any notable effect on cell death. Furthermore, none of the tested MAPK inhibitors, including MEK, c-Jun N-terminal kinase (JNK), and p38, showed any impact on PG-induced cell death or the loss of MMP (ΔΨm) in HPF cells. In conclusion, PG induces G1 phase arrest of the cell cycle and cell death in HPF cells through apoptosis and/or necrosis. The observed HPF cell death is mediated by the modulation of Bax and caspase-3. These findings offer insights into the cytotoxic and molecular effects of PG on normal HPF cells.

Imbalanced GSH/ROS and sequential cell death

Reactive oxygen species (ROS) are produced in cells during metabolic processes. Excessive intracellular ROS may react with large biomolecules, such as DNA, RNA, proteins, and small biomolecules, that is, glutathione (GSH) and unsaturated fatty acids. GSH has physiological functions, including free radical scavenging, anti-oxidation, and electrophile elimination. The disruption of ROS/GSH balance results in the deleterious oxidation and chemical modification of biomacromolecules, which eventually leads to cell-cycle arrest and proliferation inhibition, and even induces cell death. Imbalanced ROS/GSH may result from a direct increase of ROS, consumption of GSH, intracellular oxidoreductase interference, or thioredoxin activity reduction. Some chemicals including arsenic trioxide (ATO), pyrogallol (PG), and carbobenzoxy-Leu-Leu-leucinal (MG132) could also disrupt the balance of GSH and ROS. This article reviews the occurrence and consequences of the imbalance between GSH and ROS and introduces factors responsible for the disruption of cellular ROS and GSH balance, resulting in cell death. "GSH" and "ROS" were used as keywords to search the relevant literaturess.

Enhanced cell death effects of MAP kinase inhibitors in propyl gallate-treated lung cancer cells are related to increased ROS levels and GSH depletion

Propyl gallate (PG) has an anti-growth effect in lung cancer cells. The present study investigated the effects of mitogen-activated protein kinase (MAPK; MEK, JNK, and p38) inhibitors on PG-treated Calu-6 and A549 lung cancer cells in relation to cell death as well as reactive oxygen species (ROS) and glutathione (GSH) levels. PG induced cell death in both Calu-6 and A549 lung cancer cells at 24 h, which was accompanied by loss of mitochondrial membrane potential (MMP; ΔΨ_m). All of the tested MAPK inhibitors increased cell death in both PG-treated lung cancer cell lines. In particular, MEK inhibitor strongly enhanced cell death and MMP (ΔΨ_m) loss in PG-treated Calu-6 cells and p38 inhibitor had the same effects in A549 cells as well. PG increased ROS levels and caused GSH depletion in both cell lines at 24 h. MAPK inhibitors increased O₂^•- levels and GSH depletion in PG-treated Calu-6 cells, and JNK and p38 inhibitors increased ROS levels and GSH depletion in PG-treated A549 cells. In conclusion, MAPK inhibitors increased cell death in PG-treated Calu-6 and A549 lung cancer cells. Enhanced cell death and GSH depletion in Calu-6 cells caused by the MEK inhibitor were related to increased O₂^•- levels, and the effects of the p38 inhibitor in A549 cells were correlated with increased general ROS levels.

Pyrogallol induces oxidative stress defects in the fission yeast S. pombe

Apart from the beneficial roles of pyrogallol in industries, it also tends to produce free radicals that trigger apoptosis in human cells. In this study, we checked the toxic effect of pyrogallol in fission yeast S. pombe cells. We observed that the wild type and wat1/pop3 delete cells were unable to grow on plates containing pyrogallol in a dose-dependent manner. Furthermore, the wat1/pop3 delete cells exhibit higher sensitivity against pyrogallol as compared to wild type cells suggesting that the pyrogallol induces oxidative stress. The exposure to pyrogallol also leads to the production of ROS and affects the sporulation in S. pombe.

Inhibition of suicidal erythrocyte death by pyrogallol

Pyrogallol, a polyphenolic component of Acacia nilotica has previously been reported to induce apoptosis of diverse cell types. Pyrogallol is in part effective by influencing gene expression and by interference with mitochondrial function. Despite lack of nuclei and mitochondria, erythrocytes may undergo eryptosis, a suicidal death apparent from phosphatidylserine translocation to the erythrocyte surface and cell shrinkage. Eryptosis is triggered by glucose depletion, by oxidation, by hyperosmotic cell shrinkage and by excessive Ca²⁺ entry. As enhanced eryptosis is a common cause of anemia, uncovering inhibitors and stimulators of eryptosis may, both, be of clinical interest. Here we tested, whether eryptosis of human erythrocytes is modified by pyrogallol. Utilizing flow cytometry, phosphatidylserine abundance at the cell surface was estimated from annexin-V-binding and cell volume from forward scatter. Prior to determinations erythrocytes were incubated with or without glucose, without or with added oxidant tert-butyl-hydroperoxide (t-BOOH, 0.5 mM), without or with added hyperosmotic sucrose (550 mM) or without or with added Ca²⁺ ionophore ionomycin (1 µM). Treatment of erythrocytes with pyrogallol (2-8 µM) was without significant effect on annexin-V-binding and forward scatter. Glucose deprivation, t-BOOH, sucrose and ionomycin, each, triggered annexin-V-binding and decreased forward scatter. Pyrogallol significantly blunted the effects on annexin-V-binding but not on forward scatter. Pyrogallol thus blunts phosphatidylserine translocation in erythrocytes exposed to glucose depletion, oxidative stress, hyperosmotic shock and excessive Ca²⁺ entry.

Treatment with a JNK inhibitor increases, whereas treatment with a p38 inhibitor decreases, H2O2-induced calf pulmonary arterial endothelial cell death

Oxidative stress induces apoptosis in endothelial cells (ECs). Reactive oxygen species (ROS) promote cell death by regulating the activity of various mitogen-activated protein kinases (MAPKs) in ECs. The present study investigated the effects of MAPK inhibitors on cell survival and glutathione (GSH) levels upon H₂O₂ treatment in calf pulmonary artery ECs (CPAECs). H₂O₂ treatment inhibited the growth and induced the death of CPAECs, as well as causing GSH depletion and the loss of mitochondrial membrane potential (MMP). While treatment with the MEK or JNK inhibitor impaired the growth of H₂O₂-treated CPAECs, treatment with the p38 inhibitor attenuated this inhibition of growth. Additionally, JNK inhibitor treatment increased the proportion of sub-G₁ phase cells in H₂O₂-treated CPAECs and further decreased the MMP. However, treatment with a p38 inhibitor reversed the effects of H₂O₂ treatment on cell growth and the MMP. Similarly, JNK inhibitor treatment further increased, whereas p38 inhibitor treatment decreased, the proportion of GSH-depleted cells in H₂O₂-treated CPAECs. Each of the MAPK inhibitors affected cell survival, and ROS or GSH levels differently in H₂O₂-untreated, control CPAECs. The data suggest that the exposure of CPAECs to H₂O₂ caused the cell growth inhibition and cell death through GSH depletion. Furthermore, JNK inhibitor treatment further enhanced, whereas p38 inhibitors attenuated, these effects. Thus, the results of the present study suggest a specific protective role for the p38 inhibitor, and not the JNK inhibitor, against H₂O₂-induced cell growth inhibition and cell death.

MAPK inhibitors enhance cell death in pyrogallol-treated human pulmonary fibroblast cells via increasing O2•- levels

Pyrogallol (PG) induces apoptosis in lung cancer cells via the overproduction of O₂^•- and affects mitogen-activated protein kinases (MAPKs) in these cells. The aim of the present study was to elucidate the effect of PG and/or MAPK inhibitors on human pulmonary fibroblast (HPF) cell viability in relation to reactive oxygen species (ROS) and glutathione (GSH). Treatment with 50 or 100 µM PG inhibited the viability of HPF cells, and induced cell death and the loss of mitochondrial membrane potential (MMP; ΔΨ_m). In particular, treatment with 100 µM PG induced cell death via apoptosis as well as necrosis in HPF cells. PG increased mitochondrial O₂^•- levels and the number of GSH-depleted HPF cells. All the MAPK (mitogen-activated protein kinase kinase, c-Jun N-terminal kinase and p38) inhibitors enhanced the inhibition of cell viability, cell death and MMP (ΔΨ_m) loss in 100 µM PG-treated HPF cells. All the inhibitors increased the O₂•- levels in 100 µM PG-treated HPF cells, but none of the inhibitors significantly altered the PG-induced GSH depletion. In conclusion, PG treatment induced cell death via apoptosis and necrosis in HPF cells. Treatment with MAPK inhibitors slightly enhanced cell death in PG-treated HPF cells. HPF cell death induced by PG and/or MAPK inhibitors was at least partially associated with changes in O₂•- levels and GSH content. The present data provided useful information to understand PG-induced normal lung cell death in association with MAPK signaling pathways and ROS levels.

Stimulation of GSH synthesis to prevent oxidative stress-induced apoptosis by hydroxytyrosol in human retinal pigment epithelial cells: activation of Nrf2 and JNK-p62/SQSTM1 pathways

The Nrf2-Keap1 pathway is believed to be a critical regulator of the phase II defense system against oxidative stress. By activation of Nrf2, cytoprotective genes such as heme oxygenase-1 (HO-1), NAD(P)H:quinone oxidoreductase (NQO-1) and γ-glutamyl-cysteine ligase (GCL) are induced. GCL-induced glutathione (GSH) production is believed to affect redox signaling, cell proliferation and death. We here report that tert-butyl hydroperoxide (t-BHP)-induced GSH reduction led to mitochondrial membrane potential loss and apoptosis in cultured human retinal pigment epithelial cells from the ARPE-19 cell line. Hydroxytyrosol (HT), a natural phytochemical from olive leaves and oil, was found to induce phase II enzymes and GSH, thus protect t-BHP-induced mitochondrial dysfunction and apoptosis. Depletion of GSH by buthionine-[S,R]-sulfoximine enhanced t-BHP toxicity and abolished HT protection. Overexpression of Nrf2 increased GSH content and efficiently protected t-BHP-induced mitochondrial membrane potential loss. Meanwhile, HT-induced GSH enhancement and induction of Nrf2 target gene (GCLc, GCLm, HO-1, NQO-1) messenger RNA (mRNA) were inhibited by Nrf2 knockdown, suggesting that HT increases GSH through Nrf2 activation. In addition, we found that HT was able to activate the PI3/Akt and mTOR/p70S6-kinase pathways, both of which contribute to survival signaling in stressed cells. However, the effect of HT was not inhibited by the PI3K inhibitor LY294002. Rather, c-Jun N-terminal kinase (JNK) activation was found to induce p62/SQSTM1 expression, which is involved in Nrf2 activation. Our study demonstrates that Nrf2 activation induced by the JNK pathway plays an essential role in the mechanism behind HT's strengthening of the antiapoptotic actions of the endogenous antioxidant system.