The effects of MAPK inhibitors on pyrogallol-treated Calu-6 lung cancer cells in relation to cell growth, reactive oxygen species and glutathione

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.

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.

Antitumor Effect of Pyrogallol via miR-134 Mediated S Phase Arrest and Inhibition of PI3K/AKT/Skp2/cMyc Signaling in Hepatocellular Carcinoma

Though Pyrogallol, one of the natural polyphenols, was known to have anti-inflammatory and antitumor effects in breast and colon cancers, the underlying antitumor mechanisms of Pyrogallol, still remain unclear so far. Here, the antitumor mechanisms of Pyrogallol were elucidated in Hep3B and Huh7 hepatocellular carcinoma cells (HCCs). Pyrogallol showed significant cytotoxicity and reduced the number of colonies in Hep3B and Huh7 cells. Interestingly, Pyrogallol induced S-phase arrest and attenuated the protein expression of CyclinD1, Cyclin E, Cyclin A, c-Myc, S-phase kinase-associated protein 2 (Skp2), p-AKT, PI3K, increased the protein expression of p27, and also reduced the fluorescent expression of Cyclin E in Hep3B and Huh7 cells. Furthermore, Pyrogallol disturbed the interaction between Skp2, p27, and c-Myc in Huh7 cells. Notably, Pyrogallol upregulated miRNA levels of miR-134, and conversely, miR-134 inhibition rescued the decreased expression levels of c-Myc, Cyclin E, and Cyclin D1 and increased the expression of p27 by Pyrogallol in Huh7 cells. Taken together, our findings provide insight that Pyrogallol exerts antitumor effects in HCCs via miR-134 activation-mediated S-phase arrest and inhibition of PI3K/AKT/Skp2/cMyc signaling as a potent anticancer candidate.

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.

Gallic acid-induced lung cancer cell death is related to glutathione depletion as well as reactive oxygen species increase

Gallic acid (GA) widely distributed in plants and foods has its various biological effects. Here, we investigated the anti-cancer effects of GA on Calu-6 and A549 lung cancer cells in relation to reactive oxygen species (ROS) and glutathione (GSH). GA dose-dependently decreased the growth of Calu-6 and A549 cells with an IC(50) of approximately 10-50 microM and 100-200 microM GA at 24h, respectively. GA also induced cell death in lung cancer cells, which was accompanied by the loss of mitochondrial membrane potential (MMP; DeltaPsi(m)). The percents of MMP (DeltaPsi(m)) loss and death cells were lower in A549 cells than Calu-6 cells. GA increased ROS levels including O(2)(-) in lung cancer cells at 24h and also GSH depleted cell numbers at this time. N-acetyl-cysteine (NAC; a well-known antioxidant) intensified growth inhibition and death in GA-treated lung cancer cells. NAC changed ROS levels and increased GSH depletion in these cells. Vitamin C significantly attenuated cell death, ROS levels and GSH depletion in GA-treated lung cancer cells. L-buthionine sulfoximine (BSO; an inhibitor of GSH synthesis) slightly enhanced growth inhibition and death in GA-treated lung cancer cells and also mildly increased ROS levels and GSH depletion in these cells. In conclusion, GA inhibited the growth of lung cancer cells. GA-induced lung cancer cell death was related to GSH depletion as well as ROS level changes.