The potential protective roles of zinc, selenium and glutathione on hypoxia-induced TRPM2 channel activation in transfected HEK293 cells

Ca2+ Signalling and Hypoxia/Acidic Tumour Microenvironment Interplay in Tumour Progression

Solid tumours are characterised by an altered microenvironment (TME) from the physicochemical point of view, displaying a highly hypoxic and acidic interstitial fluid. Hypoxia results from uncontrolled proliferation, aberrant vascularization and altered cancer cell metabolism. Tumour cellular apparatus adapts to hypoxia by altering its metabolism and behaviour, increasing its migratory and metastatic abilities by the acquisition of a mesenchymal phenotype and selection of aggressive tumour cell clones. Extracellular acidosis is considered a cancer hallmark, acting as a driver of cancer aggressiveness by promoting tumour metastasis and chemoresistance via the selection of more aggressive cell phenotypes, although the underlying mechanism is still not clear. In this context, Ca²⁺ channels represent good target candidates due to their ability to integrate signals from the TME. Ca²⁺ channels are pH and hypoxia sensors and alterations in Ca²⁺ homeostasis in cancer progression and vascularization have been extensively reported. In the present review, we present an up-to-date and critical view on Ca²⁺ permeable ion channels, with a major focus on TRPs, SOCs and PIEZO channels, which are modulated by tumour hypoxia and acidosis, as well as the consequent role of the altered Ca²⁺ signals on cancer progression hallmarks. We believe that a deeper comprehension of the Ca²⁺ signalling and acidic pH/hypoxia interplay will break new ground for the discovery of alternative and attractive therapeutic targets.

Response of TRPM2 Channel to Hypercapnic Acidosis and Role of Zn, Se, and GSH

Hypercapnia can increase the production of reactive oxygen species (ROS) by inducing oxidative stress in cells. Transient receptor potential melastatin 2 (TRPM2) channel activation that is realized by ROS plays a critical role in the cellular mechanism. It was shown that antioxidants such as zinc (Zn), selenium (Se), and glutathione (GSH) can partake in the structures of enzymes and create a protective effect against oxidative stress. This study revealed the relationship between TRPM2 channel and hypercapnia, and the interaction of zinc, selenium, and glutathione. In our study, normoxia, hypercapnia, hypercapnia + Zn, hypercapnia + Se, and hypercapnia + GSH were created, in transfected HEK293 cells. The cells were exposed to normoxia or hypercapnia gasses in two different times (30 min and 60 min), while Zn, Se, and GSH were applied to the cells in the other groups before being exposed to the gas mixtures. The statistical evaluation showed a significant increase in lipid peroxidation (LPO) level and lactate dehydrogenase (LDH)% in the hypercapnia 30 min and 60 min groups, compared to the normoxia 30 min and 60 min groups, and an increase in LPO level and LDH% in the hypercapnia groups that Zn, Se, and GSH were applied. It was determined that in comparison with the normoxia 30 min and 60 min groups, the amount of inward Ca⁺² current across TRPM2 channels and mean current density increased in the groups that were exposed to hypercapnia for 30 min and 60 min, while the same values significantly decreased in the hypercapnia groups that Zn, Se, and GSH were applied. Also, it was shown that oxidative stress rose as the duration of hypercapnia exposure increased. It was concluded that hypercapnia increased oxidative stress and caused cellular membrane damage, while the addition of Zn, Se, and GSH could protect the cell membrane from these damaging effects.

TRPM2 Non-Selective Cation Channels in Liver Injury Mediated by Reactive Oxygen Species

TRPM2 channels admit Ca²⁺ and Na⁺ across the plasma membrane and release Ca²⁺ and Zn²⁺ from lysosomes. Channel activation is initiated by reactive oxygen species (ROS), leading to a subsequent increase in ADP-ribose and the binding of ADP-ribose to an allosteric site in the cytosolic NUDT9 homology domain. In many animal cell types, Ca²⁺ entry via TRPM2 channels mediates ROS-initiated cell injury and death. The aim of this review is to summarise the current knowledge of the roles of TRPM2 and Ca²⁺ in the initiation and progression of chronic liver diseases and acute liver injury. Studies to date provide evidence that TRPM2-mediated Ca²⁺ entry contributes to drug-induced liver toxicity, ischemia–reperfusion injury, and the progression of non-alcoholic fatty liver disease to cirrhosis, fibrosis, and hepatocellular carcinoma. Of particular current interest are the steps involved in the activation of TRPM2 in hepatocytes following an increase in ROS, the downstream pathways activated by the resultant increase in intracellular Ca²⁺, and the chronology of these events. An apparent contradiction exists between these roles of TRPM2 and the role identified for ROS-activated TRPM2 in heart muscle and in some other cell types in promoting Ca²⁺-activated mitochondrial ATP synthesis and cell survival. Inhibition of TRPM2 by curcumin and other “natural” compounds offers an attractive strategy for inhibiting ROS-induced liver cell injury. In conclusion, while it has been established that ROS-initiated activation of TRPM2 contributes to both acute and chronic liver injury, considerable further research is needed to elucidate the mechanisms involved, and the conditions under which pharmacological inhibition of TRPM2 can be an effective clinical strategy to reduce ROS-initiated liver injury.

Involvement of TRPM2 Channel on Hypoxia-Induced Oxidative Injury, Inflammation, and Cell Death in Retinal Pigment Epithelial Cells: Modulator Action of Selenium Nanoparticles

Hypoxia (HYPX) in several eye diseases such as glaucoma and diabetic retinopathy causes oxidative cell death and inflammation. TRPM2 cation channel is activated by HYPX-induced ADP-ribose (ADPR) and oxidative stress. The protective role of selenium via inhibition of TRPM2 on the HYPX-induced oxidative cytotoxicity and inflammation values in the human kidney cell line was recently reported. However, the protective role of selenium nanoparticles (SeNP) on the values in the retinal pigment epithelial (ARPE-19) cells has not been clarified yet. In the current study, we investigated two subjects. First, we investigated the involvement of TRPM2 channel on the HYPX-induced oxidative injury, inflammation, and apoptosis in the ARPE-19 cells. Second, we investigated the protective role of SeNP via inhibition of TRPM2 channel on the HYPX-induced oxidative injury and apoptosis in the ARPE-19 cells. For the aims, the ARPE-19 cells were divided into four main groups as follows: Control (Ctr), SeNP (2.5 μg/ml for 24 h), HYPX (200 μM CoCl₂ for 24 h), and HYPX+SeNP. The TRPM2 current density and Ca²⁺ fluorescence intensity with an increase of mitochondrial membrane depolarization and oxygen free radical (OFR) generations were increased in the ARPE-19 cells by the treatment of HYPX. There was no increase of Ca²⁺ fluorescence intensity in the pre-treated cells with PARP-1 inhibitors (DPQ and PJ34) or in the presence of Ca²⁺-free extracellular buffer. When HYPX-induced TRPM2 activity was treated by SeNP and TRPM2 (2-APB and ACA) blockers, the increases of OFR generation, cytokine (TNF-α and IL-1β) levels, TRPM2, and PARP-1 expressions were restored. In conclusion, the exposure of HYPX caused mitochondrial oxidative cell cytotoxicity and cell death via TRPM2-mediated Ca²⁺ signaling and may provide an avenue for treating HYPX-induced retinal diseases associated with the excessive OFR and Ca²⁺ influx.

Bevacizumab induces oxidative cytotoxicity and apoptosis via TRPM2 channel activation in retinal pigment epithelial cells: Protective role of glutathione

PURPOSE

Bevacizumab (BEV) is a blocker of circulating VEGF A generation. However, BEV has adverse apoptotic and cytotoxic effects via upregulation of mitochondrial reactive oxygen species (ROS) and TRPM2 activation, and downregulation of cytosolic glutathione (GSH) in neuronal cells. We investigated the possible protective effects of GSH treatment on BEV-induced oxidant and apoptotic adverse actions in the TRPM2 expressing adult retinal pigment epithelial-19 (ARPE-19) and SH-SY5Y neuronal cells.

MATERIAL AND METHODS

The ARPE-19 and SH-SY5Y cells were divided into five main groups: Control, GSH (10 mM for 2 h), BEV (0.25 mg/ml for 24 h), BEV+GSH, and BEV+TRPM2 channel blockers (ACA or 2-APB). In the SH-SY5Y cells, the Ca²⁺ analyses (Fluo-3) were performed only, although Fluo-3 and the remaining analyses were performed in the ARPE-19 cells.

RESULTS

The levels of apoptosis, cell death, mitochondrial ROS, lipid peroxidation, caspase-3, caspase-9, ADP-ribose-induced TRPM2 current density, cytosolic-free Zn²⁺, and Ca²⁺ were increased by BEV, although their levels were diminished by the treatments of GSH and TRPM2 blockers. The BEV-induced decreases of cell viability, GSH levels, and glutathione peroxidase activities were increased by the treatment of GSH. BEV-induced increase of TRPM2 expression was decreased by the treatment of GSH, although BEV-induced decrease of VEGF A expression was further decreased by the treatment of GSH.

CONCLUSION

Our data confirmed that BEV-induced mitochondrial ROS and apoptosis in the human retinal epithelial cells were modulated by GSH and TRPM2 inhibition. The treatment of GSH may be considered as a therapeutic approach to BEV-induced ARPE-19 cell injury.

Curcumin Attenuates Hypoxia-Induced Oxidative Neurotoxicity, Apoptosis, Calcium, and Zinc Ion Influxes in a Neuronal Cell Line: Involvement of TRPM2 Channel

Apoptosis/cell death and reactive oxygen species (ROS) via overload free Ca²⁺ and Zn²⁺ uptake into mitochondria are emerging as crucial events in the etiology of hypoxia (HPX)-induced neurodegenerative diseases. The neuroprotective actions of curcumin (CURC) via modulation of oxidative stress and the PARP1-dependent activated TRPM2 cation channel on the ROS generation and cell death in several neurons have been recognized. However, the molecular mechanisms underlying CURC's neuroprotection remain elusive. We investigated the role of CURC via modulation of TRPM2 on cell death and oxidative cytotoxicity in SH-SY5Y neuronal cells. The SH-SY5Y cells were divided into five groups as follows: CURC (10 µM for 24 h), HPX (200 µM CoCl₂ for 24 h), CURC + HPX, and HPX + TRPM2 blockers (2-APB-100 µM or ACA-25 µM for 30 min). In some experiments, the cells in the HPX groups were additionally incubated with PARP1 (PJ34) and Zn²⁺ (TPEN) inhibitors. The exposure of CoCl₂ induced increases of TRPM2 current density and Ca²⁺ fluorescence intensity with an increase of mitochondrial membrane depolarization and ROS generation. When HPX-induced TRPM2 activity was blocked by 2-APB and ACA, or the cells were treated with CURC, the increase of ROS generation, the expression levels of TRPM2 and PARP1 were restored. The levels of apoptosis and cell death in the cells were enriched with increases of caspase-3 and -9 activations, although they were decreased by CURC treatment. HPX-induced increase of cytosolic Zn²⁺ was attenuated by the TPEN and CURC treatments. In conclusion, CURC attenuates HPX-induced mitochondrial ROS generation, apoptosis, cell death, and TRPM2-mediated Ca²⁺ signaling and may provide an avenue for treating HPX-induced neurological diseases associated with the ROS, Ca²⁺, and Zn²⁺.