Activation of TRPM2 and TRPV1 Channels in Dorsal Root Ganglion by NADPH Oxidase and Protein Kinase C Molecular Pathways: a Patch Clamp Study

The efficacy and safety of a fixed-dose combination of apocynin and paeonol, APPA, in symptomatic knee OA: A double-blind, randomized, placebo-controlled, clinical trial

OBJECTIVE

Apocynin (AP) and paeonol (PA) are low molecular weight phenolic compounds with a broad array of anti-inflammatory and immunoregulatory effects. This study assessed of a fixed-dose combination of APPA in people with symptomatic knee osteoarthritis (OA).

METHODS

A multi-center, randomized, placebo-controlled, double-blind phase 2a trial enrolled participants with radiographic knee OA (Kellgren-Lawrence, KL, grades 2-3) and pain ≥40/100 on WOMAC pain subscale, and evaluated the efficacy and safety of oral APPA over a 28-day period. APPA 800 mg or matching placebo was administered twice daily in a 1:1 ratio. Post-hoc analyses explored the response to APPA in sub-groups with more severe pain and structural severity.

RESULTS

The two groups were comparable at baseline; 152 subjects were enrolled and 148 completed the trial. There was no statistically significant difference between groups with respect to the primary outcome, WOMAC pain (mean difference between groups was -0.89, 95% CI: -5.62, 3.84, p = 0.71), nor WOMAC function or WOMAC total. However, predefined subgroup analyses of subjects with symptoms compatible with nociplastic/neuropathic pain features showed a statistically significant effect of APPA compared to placebo. Adverse events (mainly gastrointestinal) were mild to moderate.

CONCLUSION

Treatment with APPA 800 mg twice daily for 28 days in subjects with symptomatic knee OA was not associated with significant symptom improvement compared to placebo. The treatment was well-tolerated and safe. While the study was not powered for such analysis, pre-planned subgroup analyses showed a significant effect of APPA in subjects with nociplastic pain/severe OA, indicating that further research in the effects of APPA in appropriate patients is warranted.

Silver nanoparticles stimulate 5-Fluorouracil-induced colorectal cancer cells to kill through the upregulation TRPV1-mediated calcium signaling pathways

The involvement of the TRP vanilloid 1 (TRPV1) cation channel on the 5-Fluorouracil (5-FU)-caused Ca2+ signals through the activation of the apoptotic signaling pathway and stimulating the mitochondrial Ca2+ and Zn2+ accumulation-induced reactive oxygen species (ROS) productions in several cancer cells, except the colorectal cancer (HT-29) cell line, was recently reported. I aimed to investigate the action of silver nanoparticles (SiNPs) and 5-FU incubations through the activation of TRPV1 on ROS, apoptosis, and cell death in the HT-29 cell line. The cells were divided into four groups: control, SiNP (100 µM for 48 h), 5-FU (25 μM for 24 h), and 5-FU + SiNP. SiNP treatment through TRPV1 activation (via capsaicin) stimulated the oxidant and apoptotic actions of 5-FU in the cells, whereas they were diminished in the cells by the TRPV1 antagonist (capsazepine) treatment. The apoptotic and cell death actions of 5-FU were determined by increasing the propidium iodide/Hoechst rate, caspase-3, -8, and -9 activations, mitochondrial membrane depolarization, lipid peroxidation, and ROS, but decreasing the glutathione and glutathione peroxidase. The increase of cytosolic free Ca2+ and Zn2+ into mitochondria via the stimulation of TRPV1 current density increased oxidant and apoptotic properties of 5-FU in the cells. For the therapy of HT-29 tumor cells, I found that the combination of SiNPs and 5-FU was synergistic via TRPV1 activation.

Transient receptor potential melastatin 2 is involved in trinitrobenzene sulfonic acid-induced acute and chronic colitis-associated fibrosis progression in mice

Crohn's disease, a chronic and recurrent gastrointestinal disease, frequently causes intestinal fibrosis. Transient receptor potential melastatin 2 (TRPM2), a non-selective cation channel, is activated by reactive oxygen species. This study investigated the role of TRPM2 in acute colitis and chronic colitis-associated fibrosis progression. Acute colitis and chronic colitis-associated fibrosis were induced in TRPM2-deficient (TRPM2KO) and wild-type (WT) mice through single and repeated intrarectal injections of 2,4,6-trinitrobenzene sulfonic acid (TNBS). Bone marrow-derived macrophages (BMDMs) from WT and TRPM2KO mice were stimulated using H2O2. In WT mice, a single TNBS injection induced acute colitis with upregulated inflammatory cytokines/chemokines and Th1/Th17-related cytokines, while repeated TNBS injections induced chronic colitis-associated fibrosis with upregulation of fibrogenic factors and Th2-related cytokines. Acute colitis and chronic colitis-associated fibrosis with cytokines/chemokine upregulation and fibrogenic factors were considerably suppressed in TRPM2KO mice. Treating BMDMs with H2O2 increased cytokine/chemokine expression and JNK, ERK, and p38 phosphorylation; however, these responses were significantly less in TRPM2KO than in WT mice. These findings suggest that TRPM2 contributes to acute colitis progression via Th1/Th17-mediated immune responses. Furthermore, TRPM2 may be directly involved in colitis-associated fibrosis induction, likely due to the regulation of Th2/TGF-β1-mediated fibrogenesis in addition to a consequence of acute colitis progression.

Human neutrophil Fc gamma receptors: different buttons for different responses

Neutrophils are fundamental cells in host defense. These leukocytes are quickly recruited from the blood to sites of infection or tissue damage. At these sites, neutrophils initiate several innate immune responses, including phagocytosis, production of reactive oxygen species, degranulation to release proteases and other antimicrobial compounds, production of inflammatory mediators, and formation of neutrophil extracellular traps. In addition to their role in innate immunity, neutrophils are now recognized as cells that also regulate adaptive immunity, via interaction with dendritic cells and lymphocytes. Neutrophils also respond to adaptive immunity by interacting with antibody molecules. Indeed, antibody molecules allow neutrophils to have antigen-specific responses. Neutrophils express different receptors for antibodies. The receptors for immunoglobulin G molecules are known as Fcγ receptors. Upon Fcγ receptor aggregation on the cell membrane, these receptors trigger distinct signal transduction cascades that activate particular cellular responses. In this review, we describe the major Fcγ receptors expressed on human neutrophils and discuss how each Fcγ receptor activates a choice of signaling pathways to stimulate particular neutrophil responses.

Ion Channel Genes in Painful Neuropathies

Neuropathic pain (NP) is a typical symptom of peripheral nerve disorders, including painful neuropathy. The biological mechanisms that control ion channels are important for many cell activities and are also therapeutic targets. Disruption of the cellular mechanisms that govern ion channel activity can contribute to pain pathophysiology. The voltage-gated sodium channel (VGSC) is the most researched ion channel in terms of NP; however, VGSC impairment is detected in only <20% of painful neuropathy patients. Here, we discuss the potential role of the other peripheral ion channels involved in sensory signaling (transient receptor potential cation channels), neuronal excitation regulation (potassium channels), involuntary action potential generation (hyperpolarization-activated cyclic nucleotide-gated channels), thermal pain (anoctamins), pH modulation (acid sensing ion channels), and neurotransmitter release (calcium channels) related to pain and their prospective role as therapeutic targets for painful neuropathy.

Alpha-lipoic acid modulates the diabetes mellitus-mediated neuropathic pain via inhibition of the TRPV1 channel, apoptosis, and oxidative stress in rats

Diabetes mellitus (DM) is a chronic syndrome involving neuropathic pain. Increased oxidative stress in DM is assumed to increase free reactive oxygen radicals (ROS) and causes diabetic damage. The sciatic nerve (ScN) and dorsal root ganglion (DRG) both contain high levels of the TRPV1 channel, which is triggered by capsaicin and ROSs and results in increased Ca²⁺ entry into the neurons. Alpha-lipoic acid (ALA) is considered an important part of the antioxidant system. To better characterize the protective effects of ALA on the DM-induced neuronal through TRPV1 modulation, we investigated the role of ALA on DM-induced neuropathic pain, oxidative ScN, and DRG damage in diabetic rats. Forty adult Wistar albino female rats were divided into four groups as control, ALA (50 mg/kg for 14 days), streptozotocin (STZ and 45 mg/kg and single dose), and STZ + ALA. Rats were used for the pain tests. After obtaining the DRGs and ScN, they were used for plate reader, patch-clamp, and laser confocal microscope analyses. We observed the modulator role of ALA on the thresholds of mechanical withdrawal pain (von Frey test) and hot sensitivity pain (hot plate test) in the STZ + ALA group. The treatment of ALA decreased STZ-induced increase of TRPV1 current densities, intracellular free Ca²⁺ concentrations (Fura-2 and Fluo - 3/AM), ROS, caspase 3, caspase 9, mitochondrial membrane potential, and apoptosis values in the ScN and DRG neurons, although its treatment induced the increase of cell viability and body weight gain. The treatment of ALA acted a neuroprotective role on the TRPV1 channel stimulation-mediated Ca²⁺ influx, neuropathic pain, and neuronal damage in diabetic rats. The neuroprotective role of ALA treatment can be explained by its modulating the TRPV1 channel activity, intracellular Ca²⁺ increase-induced oxidative stress, and apoptosis.

Emerging Nonpharmacologic Interventions to Treat Diabetic Peripheral Neuropathy

Significance: Diabetic peripheral neuropathy (DPN), a complication of metabolic syndrome, type I and type II diabetes, leads to sensory changes that include slow nerve conduction, nerve degeneration, loss of sensation, pain, and gate disturbances. These complications remain largely untreatable, although tight glycemic control can prevent neuropathy progression. Nonpharmacologic approaches remain the most impactful to date, but additional advances in treatment approaches are needed. Recent Advances: This review highlights several emerging interventions, including a focus on dietary interventions and physical activity, that continue to show promise for treating DPN. We provide an overview of our current understanding of how exercise can improve aspects of DPN. We also highlight new studies in which a ketogenic diet has been used as an intervention to prevent and reverse DPN. Critical Issues: Both exercise and consuming a ketogenic diet induce systemic and cellular changes that collectively improve complications associated with DPN. Both interventions may involve similar signaling pathways and benefits but also impact DPN through unique mechanisms. Future Directions: These lifestyle interventions are critically important as personalized medicine approaches will likely be needed to identify specific subsets of neuropathy symptoms and deficits in patients, and determine the most impactful treatment. Overall, these two interventions have the potential to provide meaningful relief for patients with DPN and provide new avenues to identify new therapeutic targets.

TRPV1 stimulation increased oxidative neurotoxicity and apoptosis in the glia cell membrane but not in the perinuclear area: An evidence of TRPV1 subtype

Glia are essential neurons of the immune system in the central nervous system. The effective mission of glia depends on their activation, release of cytokines, and oxidative cleaning of debris material from neuronal cells. Accumulating evidence indicates that microglia activation-induced oxidative stress via the activation Ca2+ permeable TRPV1 channel has an essential role in the pathophysiology of neurodegenerative diseases. However, there is scarce information on the cytosolic localization of TRPV1 and the induction of oxidative cytotoxicity in the glia. Hence, we investigated the interactions between cytosolic TRPV1 expression levels and oxidative neurotoxicity in the BV2, C8-D1A, N9 glia, and DBTRG glioblastoma cells. We observed TRPV1 expression in the perinuclear area but not in the cell membrane in the BV2, C8-D1A, and N9 cells. Hence, we observed no activation of TRPV1 on the increase of mitochondrial free reactive oxygen species (mROS) and apoptosis in the cells after the capsaicin stimulation. However, we observed TRPV1 channel expression in the positive control (DBTRG) cell membranes. Hence, the Ca2+ influx, TRPV1 current density, apoptosis, and mROS levels were increased in the DBTRG cells after the capsaicin stimulation, although their levels were diminished by the treatment of the TRPV1 blocker (capsazepine). In conclusion, the presence of TRPV1 in the cell membrane of DBTRG cells induced excessive generation of mROS and apoptosis actions, although the presence of TRPV1 in the perinuclear area did not cause the actions. It seems that there is a subtype of TRPV1 in the perinuclear area, and it is not activated by the capsaicin.

Noopept Attenuates Diabetes-Mediated Neuropathic Pain and Oxidative Hippocampal Neurotoxicity via Inhibition of TRPV1 Channel in Rats

Neuropathic pain and oxidative neurotoxicity are two adverse main actions of diabetes mellitus (DM). The expression levels of calcium ion (Ca²⁺) permeable TRPV1 channels are high in the dorsal root ganglion (DRGs) and hippocampus (HIPPO). TRPV1 is activated by capsaicin and reactive free oxygen radicals (fROS) to mediate peripheral neuropathy and neurotoxicity. Noopept (NP) acted several protective antioxidant actions against oxidative neurotoxicity. As DM is known to increase the levels of fROS, the protective roles of antioxidant NP were evaluated on the DM-mediated neurotoxicity and neuropathic pain via the modulation of TRPV1 in rats. Thirty-six rats were equally divided into control, NP, DM (streptozotocin, STZ), and STZ + NP groups. A decrease on the STZ-mediated increase of neuropathic pain (via the analyses of Von Frey and hot plate) and blood glucose level was observed by the treatment of NP. A protective role of NP via downregulation of TRPV1 activity on the STZ-induced increase of apoptosis, mitochondrial fROS, lipid peroxidation, caspase -3 (CASP-3), caspase -9 (CASP-9), TRPV1 current density, glutathione (GSH), cytosolic free Zn²⁺, and Ca²⁺ concentrations in the DRGs and HIPPO was also observed. The STZ-mediated decrease of glutathione peroxidase, GSH, vitamin E, and β-carotene concentrations in the brain cortex, erythrocyte, liver, kidney, and plasma was also attenuated by the treatment of NP. The STZ-mediated increase of TRPV1, CASP-3, and CASP-9 expressions was decreased in the DRGs and HIPPO by the treatment of NP. In conclusion, the treatment of NP induced protective effects against STZ-induced adverse peripheral pain and HIPPO oxidative neurotoxicity. These effects might attribute to the potent antioxidant property of NP.

The Antibody Receptor Fc Gamma Receptor IIIb Induces Calcium Entry via Transient Receptor Potential Melastatin 2 in Human Neutrophils

Human neutrophils express two unique antibody receptors for IgG, the FcγRIIa and the FcγRIIIb. FcγRIIa contains an immunoreceptor tyrosine-based activation motif (ITAM) sequence within its cytoplasmic tail, which is important for initiating signaling. In contrast, FcγRIIIb is a glycosylphosphatidylinositol (GPI)-linked receptor with no cytoplasmic tail. Although, the initial signaling mechanism for FcγRIIIb remains unknown, it is clear that both receptors are capable of initiating distinct neutrophil cellular functions. For example, FcγRIIa is known to induce an increase in L-selectin expression and efficient phagocytosis, while FcγRIIIb does not promote these responses. In contrast, FcγRIIIb has been reported to induce actin polymerization, activation of β1 integrins, and formation of neutrophils extracellular traps (NET) much more efficiently than FcγRIIa. Another function where these receptors seem to act differently is the increase of cytoplasmic calcium concentration. It has been known for a long time that FcγRIIa induces production of inositol triphosphate (IP₃) to release calcium from intracellular stores, while FcγRIIIb does not use this phospholipid. Thus, the mechanism for FcγRIIIb-mediated calcium rise remains unknown. Transient Receptor Potential Melastatin 2 (TRPM2) is a calcium permeable channel expressed in many cell types including vascular smooth cells, endothelial cells and leukocytes. TRPM2 can be activated by protein kinase C (PKC) and by oxidative stress. Because we previously found that FcγRIIIb stimulation leading to NET formation involves PKC activation and reactive oxygen species (ROS) production, in this report we explored whether TRPM2 is activated via FcγRIIIb and mediates calcium rise in human neutrophils. Calcium rise was monitored after Fcγ receptors were stimulated by specific monoclonal antibodies in Fura-2-loaded neutrophils. The bacterial peptide fMLF and FcγRIIa induced a calcium rise coming initially from internal pools. In contrast, FcγRIIIb caused a calcium rise by inducing calcium entry from the extracellular medium. In addition, in the presence of 2-aminoethoxydiphenyl borate (2-APB) or of clotrimazole, two inhibitors of TRPM2, FcγRIIIb-induced calcium rise was blocked. fMLF- or FcγRIIa-induced calcium rise was not affected by these inhibitors. These data suggest for the first time that FcγRIIIb aggregation activates TRPM2, to induce an increase in cytoplasmic calcium concentration through calcium internalization in human neutrophils.

Deletion of Mitochondrial Translocator Protein (TSPO) Gene Decreases Oxidative Retinal Pigment Epithelial Cell Death via Modulation of TRPM2 Channel

Simple Summary

18 kDa mitochondrial translocator protein (TSPO) is a mitochondria protein of the cellular outer membrane in the mitochondria of several cells, including ARPE19 is TSPO. Accumulating evince indicates that the presence of TSPO participated the modulations of Ca²⁺ homeostasis and mitochondrial free reactive oxygen species (fROS) generation. The deletion of TSPO gene provides to study the action of TSPO on the levels of apoptosis, ADP-ribose (ADPR), mitochondria-fROS (Mito-fROS), and apoptosis via the stimulation of Ca²⁺ permeable channels in the models of cell culture. The stimulations of oxidative stress and ADPR induce the activation of TRPM2 in the ARPE19. For clarifying the involvement of TSPO in retinal human diseases, we used the ARPE19 human cell culture model. The current results demonstrated that the deletion of TSPO induces the regulation of TRPM2 in the TSPO gene knockout ARPE19 (ARPE19-KO) In fact, the present results show that the presence of TSPO increased the upregulations of apoptosis and mitochondria oxidative cytotoxicity values via stimulation of TRPM2 in the ARPE19. Nevertheless, the blockages of PARP-1 (PJ34 and DPQ) and TRPM2 (2APB and ACA) downregulated the values of cell death and oxidative cytotoxicity in the ARPE19. In summary, present results clearly demonstrate that the deletion of TSPO decreases mitochondrial oxidative cytotoxicity-mediated cell death via the modulation of TRPM2 in the ARPE19.

Abstract

The current results indicated the possible protective actions of 18 kDa mitochondrial translocator protein (TSPO) deletion on TRPM2 stimulation, mitochondrial free ROS (Mito-fROS) and apoptotic harmful actions in the cells of adult retinal pigment epithelial19 (ARPE19). There was a direct relationship between TSPO and the disease of age-related macular degeneration. The nature of TSPO implicates upregulation of Mito-fROS and apoptosis via the activation of Ca²⁺ channels in ARPE19, although deletion of TSPO gene downregulates the activation. The decrease of oxidative cytotoxicity and apoptosis might induce in TSPO gene deleted cells by the inhibition of Mito-fROS and PARP-1 activation-induced TRPM2 cation channel activation. The ARPE19 cells were divided into two main groups as TSPO expressing (ARPE19) and non-expressing cells (ARPE19-KO). The levels of caspase -3 (Casp -3), caspase -9 (Casp -9), apoptosis, Mito-fROS, TRPM2 current and intracellular free Ca²⁺ were upregulated in the ARPE19 by the stimulations of H₂O₂ and ADP-ribose, although their levels were downregulated in the cells by the modulators of PARP-1 (DPQ and PJ34), TRPM2 (ACA and 2APB) and glutathione. However, the H₂O₂ and ADP-ribose-mediated increases were not observed in the ARPE19-KO. The expression levels of Bax, Casp -3, Casp -9 and PARP-1 were higher in the ARPE19 group as compared to the ARPE19-KO group. In summary, current results confirmed that TRPM2-mediated cell death and oxidative cytotoxicity in the ARPE19 cells were occurred by the presence of TSPO. The deletion of TSPO may be considered as a therapeutic way to TRPM2 activation-mediated retinal oxidative injury.

Melatonin and Selenium Suppress Docetaxel-Induced TRPV1 Activation, Neuropathic Pain and Oxidative Neurotoxicity in Mice

Docetaxel (DT) has been reported to positive therapeutic actions in the treatment of glioblastoma, breast tumors, and prostate cancers. However, it can also induce peripheral neuropathic pain and neurotoxicity as adverse effects. Expression level of TRPV1 cation channel is high in dorsal root ganglion (DRG), and its activation via capsaicin and reactive oxygen species (ROS) mediates peripheral neuropathic pain in mice. As cancer is known to increase the levels of ROS, the protective roles of melatonin (MT) and selenium (Se) were evaluated on the TRPV1-mediated neurotoxicity and pain in the DT-treated mice. Mice and TRPV1 expressing SH-SY5Y cells were equally divided into control, MT, Se, DT, DT+MT, and DT+Se groups. In the results of pain tests in the mice, we observed a decrease in DT-mediated mechanical and heat neuropathic pain by MT and Se. The results of plate reader assay and laser confocal microscopy image analyses indicated a protective role of MT and Se on the DT-induced increase of mitochondrial ROS, cytosolic ROS, apoptosis, lipid peroxidation, intracellular free Zn²⁺, Ca²⁺, and caspase-3 and -9 levels in the DRG and SH-SY5Y cells. MT and Se modulated DT-induced decreases of total antioxidant status, reduced glutathione and glutathione peroxidase in the DRG. However, the effects of DT were not observed in the non-TRPV1 expressing SH-SY5Y cells. Hence, MT and Se mediated protective effects against DT-induced adverse peripheral oxidative neurotoxicity and peripheral pain. These effects may be attributed to potent antioxidant properties of MT and Se.

The protective role of selenium against dental amalgam-induced intracellular oxidative toxicity through the TRPV1 channel in DBTRG glioblastoma cells

OBJECTIVE

The exposure to mercury (Hg) from dental amalgams is a suspected causative factor in neurological diseases. This study investigated the toxic effects of two different amalgam compositions related to Hg and the protective effects of selenium against the toxic effects of Hg through the TRPV1 channel in the human DBTRG glioblastoma cell line.

METHODOLOGY

Six groups of the cells were organized. Analyses of cell viability, apoptosis, caspase 3 and caspase 9 activities, mitochondrial membrane depolarization, reactive oxygen species (ROS) production, and Western Blotting for protein expression levels were performed.

RESULTS

Cell viability values were lower in amalgam with high copper (HCu) and low copper (LCu) groups independently of time but were increased by selenium and capsazepine (p<0.001 and p<0.05). Conversely, apoptosis rates, caspase 3 and caspase 9 expression, ROS formation, mitochondrial membrane depolarization, and protein expression levels were higher in the HCu and LCu groups but were decreased by selenium (p<0.001 and p<0.05).

CONCLUSIONS

Selenium combined with an amalgam of either HCu or LCu decreases the toxic effects created by Hg in human DBTRG glioblastoma cells.

Selenium prevents interferon-gamma induced activation of TRPM2 channel and inhibits inflammation, mitochondrial oxidative stress, and apoptosis in microglia

Microglia as the primary immune cells of brain act protective effects against injuries and infections in the central nervous system. Inflammation via excessive Ca²⁺ influx and oxygen radical species (ROS) generation is a known factor in many neurodegenerative disorders. Importantly, the Ca²⁺ permeable TRPM2 channel is activated by oxidative stress. Thus, TRPM2 could provide the excessive Ca²⁺ influx in the microglia. Although TRPM2 expression level is high in inflammatory cells, the interplay between mouse microglia and TRPM2 channel during inflammation is not fully identified. Thus, it is important to understand the mechanisms and factors involved in order to enhance neuronal regeneration and repair. The data presented here indicate that TRPM2 channels were activated in microglia cells by interferon-gamma (IFNγ). The IFNγ treatment further increased apoptosis (early and late) and cytokine productions (TNF-α, IL-1β, and IL-6) which were due to increased lipid peroxidation and ROS generations as well as increased activations of caspase -3 (Casp-3) and - 9 (Casp-9). However, selenium treatment diminished activations of TRPM2, cytokine, Casp-3, and Casp-9, and levels of lipid peroxidation and mitochondrial ROS production in the microglia that were treated with IFNγ. Moreover, addition of either PARP1 inhibitors (PJ34 or DPQ) or TRPM2 blockers (2-APB or ACA) potentiated the modulator effects of selenium. These results clearly suggest that IFNγ leads to TRPM2 activation in microglia cells; whereas, selenium prevents IFNγ-mediated TRPM2 activation and cytokine generation. Together the interplay between IFNγ released from microglia cells is importance in brain inflammation and may affect oxidative cytotoxicity in the microglia. Graphical abstract Summary of pathways involved in IFNγ-induced TRPM2 activation and microglia death through excessive reactive oxygen species (ROS): Modulator role of selenium (Se). The IFNγ causes the microglia activation. Nudix box domain of TRPM2 is sensitive to ROS. The ROS induces DNA damage and ADPR-ribose (ADPR) production in the nucleus via PARP1 enzyme activation. ADPR and ROS-induced TRPM2 activation stimulates excessive Ca²⁺ influx. ROS are produced in the mitochondria through the increase of free cytosolic Ca²⁺ (via TRPM2 activation) by the IFNγ treatment, although they are diminished by the TRPM2 channel blocker (ACA and 2-APB) and PARP1 inhibitor treatments. The main mechanism in the cell death and inflammatory effects of IFNγ is mediated by stimulation of ROS-mediated caspase (caspase -3 and - 9) activations and cytokine production (TNF-α, IL-1β, and IL-6) via TRPM2 activation, respectively. The apoptotic, inflammatory, and oxidant actions of IFNγ are modulated through TRPM2 inhibition by the Se treatment.

Glutathione depletion induces oxidative injury and apoptosis via TRPM2 channel activation in renal collecting duct cells

Oxidative stress (OS)-induced glutathione (GSH) depletion plays an essential role in several kidney diseases such as chronic kidney disease and nephrotoxicity. The OS-dependent activation of TRPM2 cation channel in several neurons and cells were modulated by the concentration of intracellular GSH. However, the effects of GSH alteration on TRPM2 activation, OS, and apoptosis in the cortical collecting duct (mpkCCD_c14) cells still remain elusive. We investigated the effects of GSH supplementation on OS-induced TRPM2 activation, mitochondrial oxidative stress, and apoptosis in the human embryonic kidney 293 (HEK293) and mpkCCD_c14 cells treated with buthionine-sulfoximine (BSO), a GSH synthase inhibitor. The HEK293 and mpkCCD_c14 cells were divided into five groups as control, GSH (10 mM for 2 h), BSO (0.5 mM for 6 h), BSO + GSH, and BSO + TRPM2 channel blockers. Apoptosis, cell death, mitochondrial OS, caspase -3, caspase -9, cytosolic free Zn²⁺, and Ca²⁺ concentrations were increased in the BSO group of the TRPM2 expressing mpkCCD_c14 cells, although they were diminished by the treatments of GSH, PARP-1 inhibitors (PJ34 and DPQ), and TRPM2 blockers (ACA and 2-APB). The BSO-induced decreases in the levels of cell viability and cytosolic GSH were increased by the treatments of GSH, ACA, and 2-APB. However, the effects of BSO and GSH were not observed in the non-TRPM2 expressing HEK293 cells. Current results show that maintaining GSH homeostasis is not only important for quenching OS in the cortical collecting duct cells but equally critical to modulate TRPM2 activation. Thus, suppressing apoptosis and mitochondrial OS responses elicited by oxidant action of GSH depletion.

Repeated Administration of Baclofen Modulates TRPV-1 Channel Expression by PKC Pathway in Dorsal Root Ganglia of Spinal Cord in a Morphine Tolerance Model of Rats

Background:

Tolerance and dependence to anti-nociceptive effect of morphine restricted its use. Nowadays co-administration of morphine and other drugs suggests diminishing this tolerance. Baclofen is one of the drugs that may be beneficial in the attenuation of tolerance to morphine. Studies have shown that changes in TRPV-1 expression during administration of morphine have a pivotal role in developing morphine tolerance. Therefore, the effect of baclofen on TRPV-1 expression during chronic administration of morphine was investigated in this study.

Methods:

A total of 48 rats were divided into four groups of control, morphine single injection, morphine tolerance, and morphine tolerance + baclofen. To induce morphine tolerance in rats, animals received 10 mg/kg of i.p. morphine sulfate once a day for 10 days. In the treatment group, baclofen (0.5 mg/kg) was injected for 10 days, before morphine injection. Finally, to evaluate baclofen treatment on morphine analgesia and hyperalgesia, thermal hyperalgesia and formalin test were used. TRPV-1 and PKC expression and protein production in DRG of spinal cord were then evaluated by real-time PCR and Western blot.

Results:

In baclofen treatment group, thermal hyperalgesia and formalin test improved in comparison with morphine tolerance group. In morphine tolerance group, both TRPV-1/PKC gene expression and protein levels increased in comparison with the control group. However, following the baclofen treatment, the TRPV-1 and PKC levels decreased.

Conclusion:

Baclofen can enhance anti-nociceptive effect of morphine by modulating TRPV-1 channel and PKC activity.

Morphine Induces Apoptosis, Inflammation, and Mitochondrial Oxidative Stress via Activation of TRPM2 Channel and Nitric Oxide Signaling Pathways in the Hippocampus

Morphine as an opioid is an important drug in the treatment of moderate to severe pain. Several stress factors via generation of nitric oxide (NO) and oxidative stress (OS) are responsible for the adverse effects of morphine-induced analgesia, addiction, and antinociceptive tolerance, including altered Ca²⁺ concentration, inflammation, OS, and release of apoptotic factors. TRPM2 is a Ca²⁺-permeable cation channel and it is activated by OS and NO. Hence, adverse effect of morphine addiction may occur via the OS and NO-induced TRPM2 activation. Because of the unclear etiology of morphine-induced adverse effects in the hippocampus, investigating the involvement of TRPM2 and NO synthetase (NOS) activations in the treatment of morphine-induced OS, apoptosis, and neuroinflammation is a major challenge. The hippocampal neuron of TRPM2 wild-type (TRPM2-WT) and knockout (TRPM2-KO) mice were divided into control, morphine, NOS inhibitor (L-NAME) + morphine, and TRPM2 channel blockers (ACA and 2-APB) + morphine. The morphine-induced increases of apoptosis, neuron death, OS, lipid peroxidation, caspase-3 and caspase-9, neuroinflammatory cytokines (IL-1β, TNF-α, IL-6), and Ca²⁺ levels in the hippocampal neuron of TRPM2-WT mouse were decreased by the L-NAME, ACA, and 2-APB treatments, although cell viability, neuron count, and reduced glutathione and glutathione peroxidase levels were increased by the treatments. However, the effects of morphine were not observed in the hippocampus of TRPM2-KO mice. Taken together, our data show that neurodegeneration adverse effects of morphine were induced by activation of TRPM2, and excessive generations of NO and OS. Thus, inhibition of TRPM2 may modulate morphine-induced neurodegeneration in the hippocampus.

The TRPM2 Ion Channel Regulates Inflammatory Functions of Neutrophils During Listeria monocytogenes Infection

During infection, phagocytic cells pursue homeostasis in the host via multiple mechanisms that control microbial invasion. Neutrophils respond to infection by exerting a variety of cellular processes, including chemotaxis, activation, phagocytosis, degranulation and the generation of reactive oxygen species (ROS). Calcium (Ca²⁺) signaling and the activation of specific Ca²⁺ channels are required for most antimicrobial effector functions of neutrophils. The transient receptor potential melastatin-2 (TRPM2) cation channel has been proposed to play important roles in modulating Ca²⁺ mobilization and oxidative stress in neutrophils. In the present study, we use a mouse model of Listeria monocytogenes infection to define the role of TRPM2 in the regulation of neutrophils' functions during infection. We show that the susceptibility of Trpm2^−/− mice to L. monocytogenes infection is characterized by increased migration rates of neutrophils and monocytes to the liver and spleen in the first 24 h. During the acute phase of L. monocytogenes infection, Trpm2^−/− mice developed septic shock, characterized by increased serum levels of TNF-α, IL-6, and IL-10. Furthermore, in vivo depletion of neutrophils demonstrated a critical role of these immune cells in regulating acute inflammation in Trpm2^−/− infected mice. Gene expression and inflammatory cytokine analyses of infected tissues further confirmed the hyperinflammatory profile of Trpm2^−/− neutrophils. Finally, the increased inflammatory properties of Trpm2^−/− neutrophils correlated with the dysregulated cytoplasmic concentration of Ca²⁺ and potentiated membrane depolarization, in response to L. monocytogenes. In conclusion, our findings suggest that the TRPM2 channel plays critical functional roles in regulating the inflammatory properties of neutrophils and preventing tissue damage during Listeria infection.

Resveratrol Enhances Apoptotic and Oxidant Effects of Paclitaxel through TRPM2 Channel Activation in DBTRG Glioblastoma Cells

Numerous studies have reported a strong association between increased production of reactive oxygen species (ROS) and the pathobiology of several diseases, and cancer in particular. Therefore, manipulation of cellular oxidative stress levels represents an important therapeutic target. Recently, resveratrol (RESV), a naturally occurring phytochemical, has been shown to sensitize several cell lines to the anticancer effects of other chemotherapeutic agents, including paclitaxel (PAX). However, the molecular mechanisms of action of RESV through oxidative sensitive TRPM2 channel activation remain unclear. The aim of this study was to evaluate the effect of combination therapy of RESV and PAX on activation of TRPM2 in DBTRG glioblastoma cells. DBTRG cells were divided into four treatment groups: control, RESV (50 μM), PAX (50 μM), and PAX + RESV for 24 hours. Our data shows that markers for apoptosis, mitochondrial membrane depolarization and mitochondrial function, intracellular steady-state ROS levels, caspase 3 activity, TRPM2 current density, and Ca²⁺ florescence intensity were significantly increased in DBTRG cells following treatment with PAX and RESV, respectively, although cell viability was also decreased by these treatments. These biochemical markers were further increased to favor the anticancer effects of PAX in DBTRG cells in combination with RESV. The PAX and RESV-mediated increase in current density and Ca²⁺ florescence intensity was decreased with a TRPM2 blocker. This suggests that for this combination therapy to have a substantial effect on apoptosis and cell viability, the TRPM2 channel must be stimulated.

Developmental Axon Degeneration Requires TRPV1-Dependent Ca2+ Influx

Development of the nervous system relies on a balance between axon and dendrite growth and subsequent pruning and degeneration. The developmental degeneration of dorsal root ganglion (DRG) sensory axons has been well studied in part because it can be readily modeled by removing the trophic support by nerve growth factor (NGF) in vitro. We have recently reported that axonal fragmentation induced by NGF withdrawal is dependent on Ca²⁺, and here, we address the mechanism of Ca²⁺ entry required for developmental axon degeneration of mouse embryonic DRG neurons. Our results show that the transient receptor potential vanilloid family member 1 (TRPV1) cation channel plays a critical role mediating Ca²⁺ influx in DRG axons withdrawn from NGF. We further demonstrate that TRPV1 activation is dependent on reactive oxygen species (ROS) generation that is driven through protein kinase C (PKC) and NADPH oxidase (NOX)-dependent pathways that become active upon NGF withdrawal. These findings demonstrate novel mechanistic links between NGF deprivation, PKC activation, ROS generation, and TRPV1-dependent Ca²⁺ influx in sensory axon degeneration.

Selenium Enhances the Apoptotic Efficacy of Docetaxel Through Activation of TRPM2 Channel in DBTRG Glioblastoma Cells

The rate of mitosis of cancer cells is significantly higher than normal primary cells with increased metabolic needs, which in turn enhances the generation of reactive oxygen species (ROS) production. Higher ROS production is known to increase cancer cell dependence on ROS scavenging systems to counteract the increased ROS. Therapeutic options which selectively modulate the levels of intracellular ROS in cancers are likely candidates for drug discovery. Docetaxel (DTX) has demonstrated antitumor activity in preclinical and clinical studies. It is thought that DTX induces cell death through excessive ROS production and increased Ca²⁺ entry. The Ca²⁺ permeable TRPM2 channel is activated by ROS. Selenium (Se) has been previously used to stimulate apoptosis for the treatment of glioblastoma cells resistant to DTX. However, the potential mechanism(s) of the additive effect of DTX on TRPM2 channels in cancer cells remains unclear. The aim of this study was to evaluate the effect of combination therapy of DTX and Se on activation of TRPM2 in DBTRG glioblastoma cells. DBTRG cells were divided into four treatment groups: control, DTX (10 nM for 10 h), Se (1 μM for 10 h), and DTX+Se. Our study showed that apoptosis (Annexin V and propidium iodide), mitochondrial membrane depolarization (JC1), and ROS production levels were increased in DBTRG cells following treatment with Se and DTX respectively. Cell number and viability, and the levels of apoptosis, JC1, ROS, and [Ca²⁺]_i, induced by DTX, were further increased following addition of Se. We also observed an additive increase in the activation of the NAD-dependent DNA repair enzyme poly (ADP-ribose) polymerase-1 (PARP-1) activity, which was accompanied by a decline in its essential substrate NAD⁺. As well, the Se- and DTX-induced increases in intracellular Ca²⁺ florescence intensity were decreased following treatment with the TRPM2 antagonist N-(p-amylcinnamoyl) anthranilic acid (ACA). Therefore, combination therapy with Se and DTX may represent an effective strategy for the treatment of glioblastoma cells and may be associated with TRPM2-mediated increases in oxidative stress and [Ca²⁺]_i.

Calorie restriction protects against apoptosis, mitochondrial oxidative stress and increased calcium signaling through inhibition of TRPV1 channel in the hippocampus and dorsal root ganglion of rats

The TRPV1 channel is activated in neurons by capsaicin, oxidative stress, acidic pH and heat factors, and these factors are attenuated by the antioxidant role of calorie restriction (CR). Hence, we investigated the hypothesis that the antioxidant roles of CR and food frequency (FF) may modulate TRPV1 activity and apoptosis through inhibition of mitochondrial oxidative stress in hippocampal (HIPPON) and dorsal root ganglion neurons (DRGN). We investigated the contribution of FF and CR to neuronal injury and apoptosis through inhibition of TRPV1 in rats. We assigned rats to control, FF and FF + CR groups. A fixed amount of food ad libitum was supplemented to the control and FF groups for 20 weeks, respectively. FF + CR group were fed the same amount of food as the control group but with 20% less calories during the same period. In major results, TRPV1 currents, intracellular Ca²⁺ levels, apoptosis, reactive oxygen species, mitochondrial depolarization, PARP-1 expression, caspase 3 and 9 activity and expression values were found to be increased in the HIPPON and DRGN following FF treatment, and these effects were decreased following FF + CR treatment. The FF-induced decrease in cell viability of HIPPO and DRGN, and vitamin E concentration of brain, glutathione peroxidase, vitamin A, and β-carotene values of the HIPPO, DRGN, plasma, liver and kidney were increased by FF + DR treatment, although lipid peroxidation levels in the same samples were decreased. In conclusion, CR reduces FF-induced increase of oxidative stress, apoptosis and Ca²⁺ entry through TRPV1 in the HIPPON and DRGN. Our findings may be relevant to the etiology and treatment of obesity following CR treatment.

Long term exposure to cell phone frequencies (900 and 1800 MHz) induces apoptosis, mitochondrial oxidative stress and TRPV1 channel activation in the hippocampus and dorsal root ganglion of rats

Mobile phone providers use electromagnetic radiation (EMR) with frequencies ranging from 900 to 1800 MHz. The increasing use of mobile phones has been accompanied by several potentially pathological consequences, such as neurological diseases related to hippocampal (HIPPON) and dorsal root ganglion neuron (DRGN). The TRPV1 channel is activated different stimuli, including CapN, high temperature and oxidative stress. We investigated the contribution TRPV1 to mitochondrial oxidative stress and apoptosis in HIPPON and DRGN following long term exposure to 900 and 1800 MHz in a rat model. Twenty-four adult rats were equally divided into the following groups: (1) control, (2) 900 MHz, and (3) 1800 MHz exposure. Each experimental group was exposed to EMR for 60 min/ 5 days of the week during the one year. The 900 and 1800 MHz EMR exposure induced increases in TRPV1 currents, intracellular free calcium influx (Ca²⁺), reactive oxygen species (ROS) production, mitochondrial membrane depolarization (JC-1), apoptosis, and caspase 3 and 9 activities in the HIPPON and DRGN. These deleterious processes were further increased in the 1800 MHz experimental group compared to the 900 MHz exposure group. In conclusion, mitochondrial oxidative stress, programmed cell death and Ca²⁺ entry pathway through TRPV1 activation in the HIPPON and DRGN of rats were increased in the rat model following exposure to 900 and 1800 MHz cell frequencies. Our results suggest that exposure to 900 and 1800 MHz EMR may induce a dose-associated, TRPV1-mediated stress response.

The early signaling pathway of live yeast cell derivative in THP-1 monocytes

Live yeast cell derivative (LYCD) is a medicinal yeast extract that has been used in the treatment of burns, wounds and hemorrhoids for over 70 years. It has been shown to enhance the closure of skin wounds in diabetic mice by increasing inflammation, angiogenesis, formation of granulation tissue and epithelial migration. An active fraction of LYCD has been identified as a mixture of peptides ranging in size from 5 kDA to 17 kDA. Despite its widespread use over many years, understanding of the mechanism by which LYCD acts to effect tissue repair responses is very limited. In this study, we have used a human monocyte-derived cell line, THP-1, as a representative of the inflammatory component of the wound healing process. We have identified two of the earliest responses to LYCD as an increase in cytoplasmic free calcium ([Ca2+]i) and the transcripts for c-fos. We have found that the increase in [Ca2+]i is both necessary and sufficient to account for the LYCD-induced elevation of c-fos. Furthermore, we have shown that the signaling pathway by which LYCD elevates [Ca2+]i involves both mobilization of Ca2+ from intracellular stores and influx of Ca2+ from the extracellular medium. Mobilization of store Ca2+ occurs first via activation of phospholipase C and this is followed by influx through activation of store operated calcium channels. These results constitute the first delineation of the early steps of the LYCD signaling pathway.

Neuropathic Pain: Delving into the Oxidative Origin and the Possible Implication of Transient Receptor Potential Channels

Currently, neuropathic pain is an underestimated socioeconomic health problem affecting millions of people worldwide, which incidence may increase in the next years due to chronification of several diseases, such as cancer and diabetes. Growing evidence links neuropathic pain present in several disorders [i.e., spinal cord injury (SCI), cancer, diabetes and alcoholism] to central sensitization, as a global result of mitochondrial dysfunction induced by oxidative and nitrosative stress. Additionally, inflammatory signals and the overload in intracellular calcium ion could be also implicated in this complex network that has not yet been elucidated. Recently, calcium channels namely transient receptor potential (TRP) superfamily, including members of the subfamilies A (TRAP1), M (TRPM2 and 7), and V (TRPV1 and 4), have demonstrated to play a role in the nociception mediated by sensory neurons. Therefore, as neuropathic pain could be a consequence of the imbalance between reactive oxygen species and endogen antioxidants, antioxidant supplementation may be a treatment option. This kind of therapy would exert its beneficial action through antioxidant and immunoregulatory functions, optimizing mitochondrial function and even increasing the biogenesis of this vital organelle; on balance, antioxidant supplementation would improve the patient's quality of life. This review seeks to deepen on current knowledge about neuropathic pain, summarizing clinical conditions and probable causes, the relationship existing between oxidative stress, mitochondrial dysfunction and TRP channels activation, and scientific evidence related to antioxidant supplementation.

Nociceptive Roles of TRPM2 Ion Channel in Pathologic Pain

Pain is a protective mechanism that enables us to avoid potentially harmful environments. However, when pathologically persisted and aggravated under severely injured or inflamed conditions, pain often reduces the quality of life and thus is considered as a disease to eliminate. Inflammatory and/or neuropathic mechanisms may exaggerate interactions between damaged tissues and neural pathways for pain mediation. Similar mechanisms also promote the communication among cellular participants in synapses at spinal or higher levels, which may amplify nociceptive firing and subsequent signal transmission, deteriorating the pain sensation. In this pathology, important cellular players are afferent sensory neurons, peripheral immune cells, and spinal glial cells. Arising from damage of injury, overloaded interstitial and intracellular reactive oxygen species (ROS) and intracellular Ca²⁺ are key messengers in the development and maintenance of pathologic pain. Thus, an ROS-sensitive and Ca²⁺-permeable ion channel that is highly expressed in the participant cells might play a critical role in the pathogenesis. Transient receptor potential melastatin subtype 2 (TRPM2) is the unique molecule that satisfies all of the requirements: the sensitivity, permeability, and its expressing cells. Notable progress in delineating the role of TRPM2 in pain has been achieved during the past decade. In the present review, we summarize the important findings in the key cellular components that are involved in pathologic pain. This overview will help to understand TRPM2-mediated pain mechanisms and speculate therapeutic strategies by utilizing this updated information.

Involvement of TRPM2 and TRPV1 channels on hyperalgesia, apoptosis and oxidative stress in rat fibromyalgia model: Protective role of selenium

Fibromyalgia (FM) results in pain characterized by low selenium (Se) levels, excessive Ca2+ influx, reactive oxygen species (ROS) production, and acidic pH. TRPM2 and TRPV1 are activated by ROS and acid; nevertheless, their roles have not been elucidated in FM. Therefore, we investigated the contribution of TRPM2 and TRPV1 to pain, oxidative stress, and apoptosis in a rat model of FM and the therapeutic potential of Se. Thirty-six rats were divided into four groups: control, Se, FM, and FM + Se. The Se treatment reduced the FM-induced increase in TRPM2 and TRPV1 currents, pain intensity, intracellular free Ca2+, ROS, and mitochondrial membrane depolarization in the sciatic (SciN) and dorsal root ganglion (DRGN) neurons. Furthermore, Se treatment attenuated the FM-induced decrease in cell viability in the DRGN and SciN, glutathione peroxidase, and reduced glutathione and α-tocopherol values in the DRGN, SciN, brain, muscle, and plasma; however, lipid peroxidation levels were decreased. Se also attenuated PARP1, caspase 3, and 9 expressions in the SciN, DRGN, and muscle. In conclusion, Se treatment decreased the FM-induced increase in hyperalgesia, ROS, apoptosis, and Ca2+ entry through TRPM2 and TRPV1 in the SciN and DRGN. Our findings may be relevant to the elucidation and treatment of FM.

Inhibition of the TRPM2 and TRPV1 Channels through Hypericum perforatum in Sciatic Nerve Injury-induced Rats Demonstrates their Key Role in Apoptosis and Mitochondrial Oxidative Stress of Sciatic Nerve and Dorsal Root Ganglion

Sciatic nerve injury (SNI) results in neuropathic pain, which is characterized by the excessive Ca²⁺ entry, reactive oxygen species (ROS) and apoptosis processes although involvement of antioxidant Hypericum perforatum (HP) through TRPM2 and TRPV1 activation has not been clarified on the processes in SNI-induced rat, yet. We investigated the protective property of HP on the processes in the sciatic nerve and dorsal root ganglion neuron (DRGN) of SNI-induced rats. The rats were divided into five groups as control, sham, sham+HP, SNI, and SNI+HP. The HP groups received 30 mg/kg HP for 4 weeks after SNI induction. TRPM2 and TRPV1 channels were activated in the neurons by ADP-ribose or cumene peroxide and capsaicin, respectively. The SNI-induced TRPM2 and TRPV1 currents and intracellular free Ca²⁺ and ROS concentrations were reduced by HP, N-(p-amylcinnamoyl) anthranilic acid (ACA), and capsazepine (CapZ). SNI-induced increase in apoptosis and mitochondrial depolarization in sciatic nerve and DRGN of SNI group were decreased by HP, ACA, and CapZ treatments. PARP-1, caspase 3 and 9 expressions in the sciatic nerve, DRGN, skin, and musculus piriformis of SNI group were also attenuated by HP treatment. In conclusion, increase of mitochondrial ROS, apoptosis, and Ca²⁺ entry through inhibition of TRPM2 and TRPV1 in the sciatic nerve and DRGN neurons were decreased by HP treatment. The results may be relevant to the etiology and treatment of SNI by HP.