Hydrogen peroxide induces intracellular calcium overload by activation of a non-selective cation channel in an insulin-secreting cell line

Cell death induced by acute renal injury: a perspective on the contributions of accidental and programmed cell death

The involvement of cell death in acute kidney injury (AKI) is linked to multiple factors including energy depletion, electrolyte imbalance, reactive oxygen species, inflammation, mitochondrial dysfunction, and activation of several cell death pathway components. Since our review in 2003, discussing the relative contributions of apoptosis and necrosis, several other forms of cell death have been identified and are shown to contribute to AKI. Currently, these various forms of cell death can be fundamentally divided into accidental cell death and regulated or programmed cell death based on functional aspects. Several death initiator and effector molecules switch molecules that may act as signaling components triggering either death or protective mechanisms or alternate cell death pathways have been identified as part of the machinery. Intriguingly, several of these cell death pathways share components and signaling pathways suggesting complementary or compensatory functions. Thus, defining the cross talk between distinct cell death pathways and identifying the unique molecular effectors for each type of cell death may be required to develop novel strategies to prevent cell death. Furthermore, depending on the multiple forms of cell death simultaneously induced in different AKI settings, strategies for combination therapies that block multiple cell death pathways need to be developed to completely prevent injury, cell death, and renal function. This review highlights the various cell death pathways, cross talk, and interactions between different cell death modalities in AKI.

Endothelial cells promote smooth muscle cell resilience to H2 O2 -induced cell death in mouse cerebral arteries

AIM

Brain injury produces reactive oxygen species (ROS). However, little is known of how acute oxidative stress affects cell survival in the cerebral vascular supply. We hypothesized that endothelial cells (ECs) are more resilient to H₂ O₂ and protect vascular smooth muscle cells (SMCs) during acute oxidative stress.

METHODS

Mouse posterior cerebral arteries (PCAs; diameter, ~80 µm) were exposed to H₂ O₂ (200 µM, 50 min, 37°C). Nuclear staining identified dead and live cells of intact and endothelium-disrupted vessels. SMC [Ca²⁺ ]_i was assessed with Fura-2 fluorescence, and superoxide production was assessed by dihydroethidium and MitoSOX fluorescence.

RESULTS

In response to H₂ O₂ : SMC death (21%) exceeded EC death (5%) and increased following endothelial disruption (to 48%) with a corresponding increase in SMC Ca²⁺ entry through transient receptor potential (TRP) channels. Whereas pharmacological inhibition of TRPV4 channels prevented SMC death and reduced Ca²⁺ entry for intact vessels, both remained elevated following endothelial disruption. In contrast, pharmacological inhibition or genetic deletion of TRPC3 prevented SMC death and attenuated Ca²⁺ entry for both intact and endothelium-disrupted vessels. Inhibiting gap junctions increased EC death (to 22%) while SMC death and [Ca²⁺ ]_i responses were attenuated by inhibiting nitric oxide synthesis or scavenging superoxide/peroxynitrite. Inhibiting NADPH oxidases also prevented SMC Ca²⁺ entry and death. H₂ O₂ increased mitochondrial ROS production while scavenging mitochondria-derived superoxide prevented SMC death but not Ca²⁺ entry.

CONCLUSIONS

During acute exposure of cerebral arteries to acute oxidative stress, ECs are more resilient than SMCs and the endothelium may protect SMCs by reducing Ca²⁺ entry through TRPC3 channels.

Antioxidant Properties of Hydrogen Gas Attenuates Oxidative Stress in Airway Epithelial Cells

Oxidative stress plays a crucial role in the development of airway diseases. Recently, hydrogen (H₂) gas has been explored for its antioxidant properties. This study investigated the role of H₂ gas in oxidative stress-induced alveolar and bronchial airway injury, where A549 and NCI-H292 cells were stimulated with hydrogen peroxide (H₂O₂) and lipopolysaccharide (LPS) in vitro. Results show that time-dependent administration of 2% H₂ gas recovered the cells from oxidative stress. Various indicators including reactive oxygen species (ROS), nitric oxide (NO), antioxidant enzymes (catalase, glutathione peroxidase), intracellular calcium, and mitogen-activated protein kinase (MAPK) signaling pathway were examined to analyze the redox profile. The viability of A549 and NCI-H292 cells and the activity of antioxidant enzymes were reduced following induction by H₂O₂ and LPS but were later recovered using H₂ gas. Additionally, the levels of oxidative stress markers, including ROS and NO, were elevated upon induction but were attenuated after treatment with H₂ gas. Furthermore, H₂ gas suppressed oxidative stress-induced MAPK activation and maintained calcium homeostasis. This study suggests that H₂ gas can rescue airway epithelial cells from H₂O₂ and LPS-induced oxidative stress and may be a potential intervention for airway diseases.

Metabolomic Profiling of Mango (Mangifera indica Linn) Leaf Extract and Its Intestinal Protective Effect and Antioxidant Activity in Different Biological Models

Mangifera indica Linn popularly known as mango is used in folk medicine to treat gastrointestinal disorders. The aim of this study was to identify the metabolomic composition of lyophilized extract of mango leaf (MIE), to evaluate the antioxidant activity on several oxidative stress systems (DPPH, FRAP, TBARS, and ABTS), the spasmolytic and antispasmodic activity, and intestinal protective effect on oxidative stress induced by H₂O₂ in rat ileum. Twenty-nine metabolites were identified and characterized based on their ultra-high-performance liquid chromatography (UHPLC) high-resolution orbitrap mass spectrometry, these include: benzophenone derivatives, xanthones, phenolic acids, fatty acids, flavonoids and procyanidins. Extract demonstrated a high antioxidant activity in in-vitro assays. MIE relaxed (p < 0.001) intestinal segments of rat pre-contracted with acetylcholine (ACh) (10⁻⁵ M). Pre-incubation of intestinal segments with 100 µg/mL MIE significantly reduced (p < 0.001) the contraction to H₂O₂. Similar effects were observed with mangiferin and quercetin (10⁻⁵ M; p < 0.05) but not for gallic acid. Chronic treatment of rats with MIE (50 mg/kg) for 28 days significantly reduced (p < 0.001) the H₂O₂-induced contractions. MIE exhibited a strong antioxidant activity, spasmolytic and antispasmodic activity, which could contribute to its use as an alternative for the management of several intestinal diseases related to oxidative stress.

TRPM2 channel-mediated cell death: An important mechanism linking oxidative stress-inducing pathological factors to associated pathological conditions

Oxidative stress resulting from the accumulation of high levels of reactive oxygen species is a salient feature of, and a well-recognised pathological factor for, diverse pathologies. One common mechanism for oxidative stress damage is via the disruption of intracellular ion homeostasis to induce cell death. TRPM2 is a non-selective Ca2+-permeable cation channel with a wide distribution throughout the body and is highly sensitive to activation by oxidative stress. Recent studies have collected abundant evidence to show its important role in mediating cell death induced by miscellaneous oxidative stress-inducing pathological factors, both endogenous and exogenous, including ischemia/reperfusion and the neurotoxicants amyloid-β peptides and MPTP/MPP+ that cause neuronal demise in the brain, myocardial ischemia/reperfusion, proinflammatory mediators that disrupt endothelial function, diabetogenic agent streptozotocin and diabetes risk factor free fatty acids that induce loss of pancreatic β-cells, bile acids that damage pancreatic acinar cells, renal ischemia/reperfusion and albuminuria that are detrimental to kidney cells, acetaminophen that triggers hepatocyte death, and nanoparticles that injure pericytes. Studies have also shed light on the signalling mechanisms by which these pathological factors activate the TRPM2 channel to alter intracellular ion homeostasis leading to aberrant initiation of various cell death pathways. TRPM2-mediated cell death thus emerges as an important mechanism in the pathogenesis of conditions including ischemic stroke, neurodegenerative diseases, cardiovascular diseases, diabetes, pancreatitis, chronic kidney disease, liver damage and neurovascular injury. These findings raise the exciting perspective of targeting the TRPM2 channel as a novel therapeutic strategy to treat such oxidative stress-associated diseases.

Neuroprotective and Antioxidant Activity of Arachidonoyl Choline, Its Bis-Quaternized Analogues and Other Acylcholines

The antioxidant activity and protective effect in the toxicity model of H₂O₂ were studied for arachidonic (AA-CHOL), docosahexaenoic (DHA-CHOL), linoleic (Ln-CHOL), and oleic (Ol-CHOL) fatty acids, as well as arachidonoyl dicholine (AA-diCHOL) and O-arachidonoyl bistetramethylaminoisopropanol (ABTAP). AA-CHOL, DHA-CHOL and Ln-CHOL provided a 20% increase in cell survival. AA-CHOL, AA-diCHOL, Ol-CHOL, and ABTAP had a radical-scavenging effect in the ABTS test, approximately equal to the activity of a standard radical scavenger Trolox.

Molecular Biology of Escherichia Coli Shiga Toxins' Effects on Mammalian Cells

Shiga toxins (Stxs), syn. Vero(cyto)toxins, are potent bacterial exotoxins and the principal virulence factor of enterohemorrhagic Escherichia coli (EHEC), a subset of Shiga toxin-producing E. coli (STEC). EHEC strains, e.g., strains of serovars O157:H7 and O104:H4, may cause individual cases as well as large outbreaks of life-threatening diseases in humans. Stxs primarily exert a ribotoxic activity in the eukaryotic target cells of the mammalian host resulting in rapid protein synthesis inhibition and cell death. Damage of endothelial cells in the kidneys and the central nervous system by Stxs is central in the pathogenesis of hemolytic uremic syndrome (HUS) in humans and edema disease in pigs. Probably even more important, the toxins also are capable of modulating a plethora of essential cellular functions, which eventually disturb intercellular communication. The review aims at providing a comprehensive overview of the current knowledge of the time course and the consecutive steps of Stx/cell interactions at the molecular level. Intervention measures deduced from an in-depth understanding of this molecular interplay may foster our basic understanding of cellular biology and microbial pathogenesis and pave the way to the creation of host-directed active compounds to mitigate the pathological conditions of STEC infections in the mammalian body.

Molecular Regulations and Functions of the Transient Receptor Potential Channels of the Islets of Langerhans and Insulinoma Cells

Insulin secretion from the β-cells of the islets of Langerhans is triggered mainly by nutrients such as glucose, and incretin hormones such as glucagon-like peptide-1 (GLP-1). The mechanisms of the stimulus-secretion coupling involve the participation of the key enzymes that metabolize the nutrients, and numerous ion channels that mediate the electrical activity. Several members of the transient receptor potential (TRP) channels participate in the processes that mediate the electrical activities and Ca²⁺ oscillations in these cells. Human β-cells express TRPC1, TRPM2, TRPM3, TRPM4, TRPM7, TRPP1, TRPML1, and TRPML3 channels. Some of these channels have been reported to mediate background depolarizing currents, store-operated Ca²⁺ entry (SOCE), electrical activity, Ca²⁺ oscillations, gene transcription, cell-death, and insulin secretion in response to stimulation by glucose and GLP1. Different channels of the TRP family are regulated by one or more of the following mechanisms: activation of G protein-coupled receptors, the filling state of the endoplasmic reticulum Ca²⁺ store, heat, oxidative stress, or some second messengers. This review briefly compiles our current knowledge about the molecular mechanisms of regulations, and functions of the TRP channels in the β-cells, the α-cells, and some insulinoma cell lines.

Can Mesenchymal Stem Cells Act Multipotential in Traumatic Brain Injury?

Traumatic brain injury (TBI), a leading cause of morbidity and mortality throughout the world, will probably become the third cause of death in the world by the year 2020. Lack of effective treatments approved for TBI is a major health problem. TBI is a heterogeneous disease due to the different mechanisms of injury. Therefore, it requires combination therapies or multipotential therapy that can affect multiple targets. In recent years, mesenchymal stem cells (MSCs) transplantation has considered one of the most promising therapeutic strategies to repair of brain injuries including TBI. In these studies, it has been shown that MSCs can migrate to the site of injury and differentiate into the cells secreting growth factors and anti-inflammatory cytokines. The reduction in brain edema, neuroinflammation, microglia accumulation, apoptosis, ischemia, the improvement of motor and cognitive function, and the enhancement in neurogenesis, angiogenesis, and neural stem cells survival, proliferation, and differentiation have been indicated in these studies. However, translation of MSCs research in TBI into a clinical setting will require additional preclinical trials.

Hydrogen Peroxide Gates a Voltage-Dependent Cation Current in Aplysia Neuroendocrine Cells

Nonselective cation channels promote persistent spiking in many neurons from a diversity of animals. In the hermaphroditic marine-snail, Aplysia californica, synaptic input to the neuroendocrine bag cell neurons triggers various cation channels, causing an ∼30 min afterdischarge of action potentials and the secretion of egg-laying hormone. During the afterdischarge, protein kinase C is also activated, which in turn elevates hydrogen peroxide (H₂O₂), likely by stimulating nicotinamide adenine dinucleotide phosphate oxidase. The present study investigated whether H₂O₂ regulates cation channels to drive the afterdischarge. In single, cultured bag cell neurons, H₂O₂ elicited a prolonged, concentration- and voltage-dependent inward current, associated with an increase in membrane conductance and a reversal potential of ∼+30 mV. Compared with normal saline, the presence of Ca²⁺-free, Na⁺-free, or Na⁺/Ca²⁺-free extracellular saline, lowered the current amplitude and left-shifted the reversal potential, consistent with a nonselective cationic conductance. Preventing H₂O₂ reduction with the glutathione peroxidase inhibitor, mercaptosuccinate, enhanced the H₂O₂-induced current, while boosting glutathione production with its precursor, N-acetylcysteine, or adding the reducing agent, dithiothreitol, lessened the response. Moreover, the current generated by the alkylating agent, N-ethylmaleimide, occluded the effect of H₂O₂ The H₂O₂-induced current was inhibited by tetrodotoxin as well as the cation channel blockers, 9-phenanthrol and clotrimazole. In current-clamp, H₂O₂ stimulated burst firing, but this was attenuated or prevented altogether by the channel blockers. Finally, H₂O₂ evoked an afterdischarge from whole bag cell neuron clusters recorded ex vivo by sharp-electrode. H₂O₂ may regulate a cation channel to influence long-term changes in activity and ultimately reproduction.SIGNIFICANCE STATEMENT Hydrogen peroxide (H₂O₂) is often studied in a pathological context, such as ischemia or inflammation. However, H₂O₂ also physiologically modulates synaptic transmission and gates certain transient receptor potential channels. That stated, the effect of H₂O₂ on neuronal excitability remains less well defined. Here, we examine how H₂O₂ influences Aplysia bag cell neurons, which elicit ovulation by releasing hormones during an afterdischarge. These neuroendocrine cells are uniquely identifiable and amenable to recording as individual cultured neurons or a cluster from the nervous system. In both culture and the cluster, H₂O₂ evokes prolonged, afterdischarge-like bursting by gating a nonselective voltage-dependent cationic current. Thus, H₂O₂, which is generated in response to afterdischarge-associated second messengers, may prompt the firing necessary for hormone secretion and procreation.

Characterization and Optimization of the Novel Transient Receptor Potential Melastatin 2 Antagonist tatM2NX

Transient receptor potential melastatin 2 (TRPM2) is a calcium-permeable channel activated by adenosine diphosphate ribose metabolites and oxidative stress. TRPM2 contributes to neuronal injury in the brain caused by stroke and cardiac arrest among other diseases including pain, inflammation, and cancer. However, the lack of specific inhibitors hinders the study of TRPM2 in brain pathophysiology. Here, we present the design of a novel TRPM2 antagonist, tatM2NX, which prevents ligand binding and TRPM2 activation. We used mutagenesis of tatM2NX to determine the structure-activity relationship and antagonistic mechanism on TRPM2 using whole-cell patch clamp and Calcium imaging in human embryonic kidney 293 cells with stable human TRPM2 expression. We show that tatM2NX inhibits over 90% of TRPM2 channel currents at concentrations as low as 2 μM. Moreover, tatM2NX is a potent antagonist with an IC₅₀ of 396 nM. Our results from tatM2NX mutagenesis indicate that specific residues within the tatM2NX C terminus are required to confer antagonism on TRPM2. Therefore, the peptide tatM2NX represents a new tool for the study of TRPM2 function in cell biology and enhances our understanding of TRPM2 in disease. SIGNIFICANCE STATEMENT: TatM2NX is a potent TRPM2 channel antagonist with the potential for clinical benefit in neurological diseases. This study characterizes interactions of tatM2NX with TRPM2 and the mechanism of action using structure-activity analysis.

Activation of a Ca2+-dependent cation conductance with properties of TRPM2 by reactive oxygen species in lens epithelial cells

Ion channels are crucial for maintenance of ion homeostasis and transparency of the lens. The lens epithelium is the metabolically and electrophysiologically active cell type providing nutrients, ions and water to the lens fiber cells. Ca2+-dependent non-selective ion channels seem to play an important role for ion homeostasis. The aim of the study was to identify and characterize Ca2+- and reactive oxygen species (ROS)-dependent non-selective cation channels in human lens epithelial cells. RT-PCR revealed gene expression of the Ca2+-activated non-selective cation channels TRPC3, TRPM2, TRPM4 and Ano6 in both primary lens epithelial cells and the cell line HLE-B3, whereas TRPM5 mRNA was only found in HLE-B3 cells. Using whole-cell patch-clamp technique, ionomycin evoked non-selective cation currents with linear current-voltage relationship in both cell types. The current was decreased by flufenamic acid (FFA), 2-APB, 9-phenanthrol and miconazole, but insensitive to DIDS, ruthenium red, and intracellularly applied spermine. H2O2 evoked a comparable current, abolished by FFA. TRPM2 protein expression in HLE-B3 cells was confirmed by means of immunocytochemistry and western blot. In summary, we conclude that lens epithelial cells functionally express Ca2+- and H2O2-activated non-selective cation channels with properties of TRPM2.

Study on Chemical Profile and Neuroprotective Activity of Myrica rubra Leaf Extract

The chemical profile of Myrica rubra (a native species in China) leaf extract was investigated by UPLC-PDA-HRMS, and the neuroprotective activity of two characteristic constituents, myricanol and myricetrin, was evaluated with N2a cells using H₂O₂-inducedoxidative challenge through a series of methods, e.g., MTT assay, ROS assay and [Ca2+]i assay. Among the 188 constituents detected in the extract of Myrica rubra leaf, 116 were identified definitely or tentatively by the comprehensive utilization of precise molecular weight and abundant multistage fragmentation information obtained by quadrupole orbitrap mass spectrometry. In addition, 14 potential new compounds were reported for the first time. This work established an example for the research of microconstituents in a complex analyte and revealed that suppression of H₂O₂-induced cytotoxicity in N2a cells was achieved by the pretreatment with myricanol. The evidence suggested myricanol may potentially serve as a remedy for prevention and therapy of neurodegenerative diseases induced by oxidative stress.

The overexpressed functional transient receptor potential channel TRPM2 in oral squamous cell carcinoma

TRPM2, one member of the transient receptor potential (TRP) protein super-family, is a Ca²⁺-permeable channel that is activated by oxidative stress and confers susceptibility to cell death. In the human tongue specimens of carcinoma and the tongue carcinoma SCC cell lines, we observed the enhanced expression of TRPM2. By means of the whole-cell electrophysiological recording, the ADPR-induced currents mediated by TRPM2 were recorded in cultured SCC9 cells. Moreover, after H₂O₂ treatment for 24 hours, the apoptotic number of SCC9 cells was significantly increased. However, the selectively knocked-down TRPM2 with the small interfering RNA technique inhibited the survival and migration of the SCC9 cancer cells, which was independent of the p53-p21 pathway, since the expression of p21 was enhanced after TRPM2 knockdown. Furthermore, the sub-cellular localization of TRPM2 was remarkably different between cancerous and non-cancerous cells. A significant amount of the TRPM2 proteins were located in the nuclei in cancer cells. All these data suggest that TRPM2 is essential for the survival and migration of SCC cancer cells and may be a potential target for the selective treatment of tongue cancer.

Specific combinations of ion channel inhibitors reduce excessive Ca2+ influx as a consequence of oxidative stress and increase neuronal and glial cell viability in vitro

Combinations of Ca²⁺ channel inhibitors have been proposed as an effective means to prevent excess Ca²⁺ flux and death of neurons and glia following neurotrauma in vivo. However, it is not yet known if beneficial outcomes such as improved viability have been due to direct effects on intracellular Ca²⁺ concentrations. Here, the effects of combinations of Lomerizine (Lom), 2,3-dioxo-7-(1H-imidazol-1-yl)6-nitro-1,2,3,4-tetrahydro-1-quinoxalinyl]acetic acid monohydrate (YM872), 3,5-dimethyl-1-adamantanamine (memantine (Mem)) and/or adenosine 5'-triphosphate periodate oxidized sodium salt (oxATP) to block voltage-gated Ca²⁺ channels, Ca²⁺ permeable α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, NMDA receptors and purinergic P2X₇ receptors (P2X₇R) respectively, on Ca²⁺ concentration and viability of rat primary mixed cortical (MC) cultures exposed to hydrogen peroxide (H₂O₂) insult, were assessed. The contribution of ryanodine-sensitive intracellular stores to intracellular Ca²⁺ concentration was also assessed. Live cell calcium imaging revealed that a 30min H₂O₂ insult induced a slow increase in intracellular Ca²⁺, in part from intracellular sources, associated with loss of cell viability by 6h. Most combinations of inhibitors that included oxATP significantly decreased Ca²⁺ influx and increased cell viability when administered simultaneously with H₂O₂. However, reductions in intracellular Ca²⁺ concentration were not always linked to improved cell viability. Examination of the density of specific cell subpopulations demonstrated that most combinations of inhibitors that included oxATP preserved NG2+ non-oligodendroglial cells, but preservation of astrocytes and neurons required additional inhibitors. Olig2⁺ oligodendroglia and ED-1⁺ activated microglia/macrophages were not preserved by any of the inhibitor combinations. These data indicate that following H₂O₂ insult, limiting intracellular Ca²⁺ entry via P2X₇R is generally associated with increased cell viability. Protection of NG2+ non-oligodendroglial cells by Ca²⁺ channel inhibitor combinations may contribute to observed beneficial outcomes in vivo.

Long-term culture and functionality of pancreatic islets monitored using microelectrode arrays

Extracellular recording of the electrical activity of pancreatic islets permits long-term measurements of beta-cell function and reveals oxidant-induced damage and rescue.

The involvement of PI3K-mediated and L-VGCC-gated transient Ca2+ influx in 17β-estradiol-mediated protection of retinal cells from H2O2-induced apoptosis with Ca2+ overload

Intracellular calcium concentration ([Ca²⁺]_i) plays an important role in regulating most cellular processes, including apoptosis and survival, but its alterations are different and complicated under diverse conditions. In this study, we focused on the [Ca²⁺]_i and its control mechanisms in process of hydrogen peroxide (H₂O₂)-induced apoptosis of primary cultured Sprague-Dawley (SD) rat retinal cells and 17β-estradiol (βE2) anti-apoptosis. Fluo-3AM was used as a Ca²⁺ indicator to detect [Ca²⁺]_i through fluorescence-activated cell sorting (FACS), cell viability was assayed using MTT assay, and apoptosis was marked by Hoechst 33342 and annexin V/Propidium Iodide staining. Besides, PI3K activity was detected by Western blotting. Results showed: a) 100 μM H₂O₂-induced retinal cell apoptosis occurred at 4 h after H₂O₂ stress and increased in a time-dependent manner, but [Ca²⁺]_i increased earlier at 2 h, sustained to 12 h, and then recovered at 24 h after H₂O₂ stress; b) 10 μM βE2 treatment for 0.5-24 hrs increased cell viability by transiently increasing [Ca²⁺]_i, which appeared only at 0.5 h after βE2 application; c) increased [Ca²⁺]_i under 100 µM H₂O₂ treatment for 2 hrs or 10 µM βE2 treatment for 0.5 hrs was, at least partly, due to extracellular Ca²⁺ stores; d) importantly, the transiently increased [Ca²⁺]_i induced by 10 µM βE2 treatment for 0.5 hrs was mediated by the phosphatidylinositol-3-kinase (PI3K) and gated by the L-type voltage-gated Ca²⁺ channels (L-VGCC), but the increased [Ca²⁺]_i induced by 100 µM H₂O₂ treatment for 2 hrs was not affected; and e) pretreatment with 10 µM βE2 for 0.5 hrs effectively protected retinal cells from apoptosis induced by 100 µM H₂O₂, which was also associated with its transient [Ca²⁺]_i increase through L-VGCC and PI3K pathway. These findings will lead to better understanding of the mechanisms of βE2-mediated retinal protection and to exploration of the novel therapeutic strategies for retina degeneration.

Androgen and PARP-1 regulation of TRPM2 channels after ischemic injury

The calcium-permeable transient receptor potential M2 (TRPM2) ion channel was recently demonstrated to have a sexually dimorphic contribution to ischemic brain injury, with inhibition or knockdown of the channel protecting male brain preferentially. We tested the hypothesis that androgen signaling is required for this male-specific cell-death pathway. Additionally, we tested the hypothesis that differential activation of the enzyme poly (ADP-ribose) polymerase-1 (PARP-1) is responsible for male-specific TRPM2 channel activation and neuronal injury. We observed that administration of the TRPM2 inhibitor clotrimazole (CTZ) 2 hours after onset of ischemia reduced infarct volume in male mice and that protection from ischemic damage by CTZ was abolished by removal of testicular androgens (castration; CAST) and rescued by androgen replacement. Male PARP-1 knockout mice had reduced ischemic damage compared with WT mice and inhibition of TRPM2 with CTZ failed to reduce infarct size. Lastly, we observed that ischemia increased PARP activity in the peri-infarct region of male mice to a greater extent than female mice and the difference was abolished in CAST male mice. Data presented in the current study indicate that TRPM2-mediated neuronal death in the male brain requires intact androgen signaling and PARP-1 activity.

Oxidative stress-modulated TRPM ion channels in cell dysfunction and pathological conditions in humans

The transient receptor potential melastatin (TRPM) protein family is an extensive group of ion channels expressed in several types of mammalian cells. Many studies have shown that these channels are crucial for performing several physiological functions. Additionally, a large body of evidence indicates that these channels are also involved in numerous human diseases, known as channelopathies. A characteristic event frequently observed during pathological states is the raising in intracellular oxidative agents over reducing molecules, shifting the redox balance and inducing oxidative stress. In particular, three members of the TRPM subfamily, TRPM2, TRPM4 and TRPM7, share the remarkable feature that their activities are modulated by oxidative stress. Because of the increase in oxidative stress, these TRPM channels function aberrantly, promoting the onset and development of diseases. Increases, absences, or modifications in the function of these redox-modulated TRPM channels are associated with cell dysfunction and human pathologies. Therefore, the effect of oxidative stress on ion channels becomes an essential part of the pathogenic mechanism. Thus, oxidative stress-modulated ion channels are more susceptible to generating pathological states than oxidant-independent channels. This review examines the most relevant findings regarding the participation of the oxidative stress-modulated TRPM ion channels, TRPM2, TRPM4, and TRPM7, in human diseases. In addition, the potential roles of these channels as therapeutic tools and targets for drug design are discussed.

H2O2-induced endothelial NO production contributes to vascular cell apoptosis and increased permeability in rat venules

Although elevated levels of H(2)O(2) have been implicated to play important roles in the pathogenesis of various cardiovascular diseases, the underlying mechanisms remain unclear. This study aims to examine the effect of H(2)O(2) on endothelial nitric oxide (NO) production in intact venules, and elucidate the role and mechanisms of NO in H(2)O(2)-induced increases in microvessel permeability. Experiments were conducted on individually perfused rat mesenteric venules. Microvessel permeability was determined by measuring hydraulic conductivity (Lp), and endothelial [Ca(2+)](i) was measured on fura-2-loaded vessels. Perfusion of H(2)O(2) (10 μM) caused a delayed and progressively increased endothelial [Ca(2+)](i) and Lp, a pattern different from inflammatory mediator-induced immediate and transient response. Under the same experimental conditions, measuring endothelial NO via DAF-2 and the spatial detection of cell apoptosis by fluorescent markers revealed that H(2)O(2) induced two phases of NO production followed by caspase activation, intracellular Ca(2+) accumulation, and vascular cell apoptosis. The initial NO production was correlated with increased endothelial NO synthase (eNOS) Ser(1177) phosphorylation in the absence of elevated endothelial [Ca(2+)](i), whereas the second phase of NO depended on increased [Ca(2+)](i) and was associated with Thr(495) dephosphorylation without increased Ser(1177) phosphorylation. Inhibition of NOS prevented H(2)O(2)-induced caspase activation, cell apoptosis, and increases in endothelial [Ca(2+)](i) and Lp. Our results indicate that H(2)O(2) at micromolar concentration is able to induce a large magnitude of NO in intact venules, causing caspase activation-mediated endothelial Ca(2+) accumulation, cell apoptosis, and increases in permeability. The mechanisms revealed from intact microvessels may contribute to the pathogenesis of oxidant-related cardiovascular diseases.

TRPM2 channel activation following in vitro ischemia contributes to male hippocampal cell death

Hippocampal CA1 neurons are particularly sensitive to ischemic damage, such as experienced following cardiac arrest and cardiopulmonary resuscitation. In recent years transient receptor potential M2 (TRPM2) channels have been identified as mediators of ischemic damage. We previously demonstrated that neuroprotective strategies targeting TRPM2 channels preferentially protect male cortical neurons from ischemic injury both in vitro and in vivo. It is important to determine the role of TRPM2 in ischemic injury of hippocampal neurons as this population of neurons are particularly sensitive to ischemic injury and are therapeutic targets. Here we report significantly decreased neuronal cell death following in vitro ischemia preferentially in male hippocampal neurons using TRPM2 inhibitors or knockdown of TRPM2 expression. Electrophysiological characterization of sex-stratified cultures shows similar levels of functional TRPM2 channel expression in male and female hippocampal neurons under basal conditions. In contrast, recordings made during reperfusion following in vitro ischemia revealed that TRPM2 channels are activated only in male neurons, resulting in rapid and complete depolarization. These findings provide strong evidence for TRPM2 as a target for protection against cerebral ischemia in male brain and helps define a molecular cell death pathway that is differentially engaged in male and female neurons.

Hypoxic Pulmonary Vasoconstriction

It has been known for more than 60 years, and suspected for over 100, that alveolar hypoxia causes pulmonary vasoconstriction by means of mechanisms local to the lung. For the last 20 years, it has been clear that the essential sensor, transduction, and effector mechanisms responsible for hypoxic pulmonary vasoconstriction (HPV) reside in the pulmonary arterial smooth muscle cell. The main focus of this review is the cellular and molecular work performed to clarify these intrinsic mechanisms and to determine how they are facilitated and inhibited by the extrinsic influences of other cells. Because the interaction of intrinsic and extrinsic mechanisms is likely to shape expression of HPV in vivo, we relate results obtained in cells to HPV in more intact preparations, such as intact and isolated lungs and isolated pulmonary vessels. Finally, we evaluate evidence regarding the contribution of HPV to the physiological and pathophysiological processes involved in the transition from fetal to neonatal life, pulmonary gas exchange, high-altitude pulmonary edema, and pulmonary hypertension. Although understanding of HPV has advanced significantly, major areas of ignorance and uncertainty await resolution.

Sex differences in neuroprotection provided by inhibition of TRPM2 channels following experimental stroke

The calcium-permeable transient receptor potential M2 (TRPM2) ion channel is activated following oxidative stress and has been implicated in ischemic damage; however, little experimental evidence exists linking TRPM2 channel activation to damage following cerebral ischemia. We directly assessed the involvement of TRPM2 channels in ischemic brain injury using pharmacological inhibitors and short-hairpin RNA (shRNA)-mediated knockdown of TRPM2 expression. Each of the four TRPM2 inhibitors tested provided significant protection to male neurons following in vitro ischemia (oxygen-glucose deprivation, OGD), while having no effect in female neurons. Similarly, TRPM2 knockdown by TRPM2 shRNA resulted in significantly reduced neuronal cell death following OGD only in male neurons. The TRPM2 inhibitor clotrimazole reduced infarct volume in male mice, while having no effect on female infarct volume. Finally, intrastriatal injection of lentivirus expressing shRNA against TRPM2 resulted in significantly smaller striatal infarcts only in male mice following middle cerebral artery occlusion, having no significant effect in female mice. Data presented in the current study demonstrate that TRPM2 inhibition and knockdown preferentially protects male neurons and brain against ischemia in vitro and in vivo, indicating that TRPM2 inhibitors may provide a new therapeutic approach to the treatment of stroke in men.

Neuroprotective effects of 2-cyclopropylimino-3-methyl-1,3-thiazoline hydrochloride against oxidative stress

Oxidative stress, glutamate excitotoxicity, and inflammation are the important pathological mechanisms in neurodegenerative diseases. Recently, we reported that 2-cyclopropylimino-3-methyl-1,3-thiazoline hydrochloride protects rat glial cells against glutamate-induced excitotoxicity. In this study, we report the effects of 2-cyclopropylimino-3-methyl-1,3-thiazoline hydrochloride on primary cultured cortical astrocytes after exposure to hydrogen peroxide (H₂O₂). Pretreatment of cells with 2-cyclopropylimino-3-methyl-1,3-thiazoline hydrochloride prior to H₂O₂ exposure attenuated the H₂O₂-induced reductions in cell survival and superoxide dismutase, catalase, glutathione, and glutathione peroxidase activities. It also reduced H₂O₂-induced increases in reactive oxygen species levels, malondialdehyde content, and production of nitric oxide. These effects were all concentration-dependent. Our results suggest that 2-cyclopropylimino-3-methyl-1,3-thiazoline hydrochloride protects against oxidative stress.

The chemopreventive effect of dimethylthiourea against carmustine-induced myelotoxicity in rats

The possible chemopreventive role of dimethylthiourea (DMTU) against carmustine (1,3-bis(2-chloroethyl)-1-nitrosourea, BCNU)-induced myelotoxicity was assessed through evaluation of apoptosis, lipid peroxidation, glutathione (GSH) content and some antioxidant enzymes activities in bone marrow cells of rats. Thirty-six rats were randomly classified into four groups. The first group was injected i.p. with ethanol and served as a control. The second group was treated with BCNU. The third group was given DMTU, while the fourth group was co-administered with DMTU prior to BCNU administration. BCNU treatment in a single dose of 30 mg/kg significantly decreased the normal counts of RBCs, WBCs and platelets as well as hemoglobin level. In addition, BCNU exhibited marked apoptotic effect associated with significant alterations in the oxidative cascade parameters. Treatment of animals with DMTU in a single dose of 500 mg/kg 1h before BCNU injection, followed by 125 mg/kg twice daily for 5 consecutive days significantly mitigated the induced changes in the hematological parameters. The induced alterations in the oxidant and antioxidant parameters as well as apoptosis were also improved. Conclusively, DMTU treatment exhibited marked chemopreventive effect against BCNU-induced myelotoxicity; an effect which may be partially attributed to its inherently antioxidant potential.

TRPM2: a multifunctional ion channel for calcium signalling

The transient potential receptor melastatin-2 (TRPM2) channel has emerged as an important Ca(2+) signalling mechanism in a variety of cells, contributing to cellular functions that include cytokine production, insulin release, cell motility and cell death. Its ability to respond to reactive oxygen species has made TRPM2 a potential therapeutic target for chronic inflammation, neurodegenerative diseases, and oxidative stress-related pathologies. TRPM2 is a non-selective, calcium (Ca(2+))-permeable cation channel of the melastatin-related transient receptor potential (TRPM) ion channel subfamily. It is activated by intracellular adenosine diphosphate ribose (ADPR) through a diphosphoribose hydrolase domain in its C-terminus and regulated through a variety of factors, including synergistic facilitation by [Ca(2+)](i), cyclic ADPR, H(2)O(2), NAADP, and negative feedback regulation by AMP and permeating protons (pH). In addition to its role mediating Ca(2+) influx into the cells, TRPM2 can also function as a lysosomal Ca(2+) release channel, contributing to cell death. The physiological and pathophysiological context of ROS-mediated events makes TRPM2 a promising target for the development of therapeutic tools of inflammatory and degenerative diseases.

TRPM2 channel properties, functions and therapeutic potentials

IMPORTANCE OF THE FIELD

Oxidative stress, through production of reactive oxygen species, triggers disturbance in intracellular calcium [Ca(2+)](i) homeostasis, which has been identified as an important causative factor in the pathogenesis of numerous inflammatory, cardiovascular and neurodegenerative diseases.

AREAS COVERED IN THIS REVIEW

Transient receptor potential melastatin 2 (TRPM2) protein forms a Ca(2+)-permeable cationic channel that is activated in response to oxidative stress and therefore acts as a cellular redox sensor. Research over the years has substantially advanced the knowledge of expression and functional properties of the TRPM2 channel, and particularly has accumulated compelling evidence for an important role for TRPM2 channel-mediated extracellular Ca(2+) influx in several physiological and pathophysiological functions exemplified by insulin release from pancreatic beta-cells, production of pro-inflammatory cytokines from immune cells, increased endothelial permeability, microglia activation and cell death. These findings suggest therapeutic potential of the TRPM2 channel as a drug target for combating oxidative-stress-related diseases.

WHAT THE READER WILL GAIN

The current state of knowledge with respect to the TRPM2 channel properties and the roles in oxidant stress signalling and functions.

TAKE HOME MESSAGE

TRPM2 may be a novel therapeutic target for oxidative stress-related diseases.

Oxidative stress and beta-cell dysfunction

Diabetes mellitus type 1 and 2 (T1DM and T2DM) are complex multifactorial diseases. Loss of beta-cell function caused by reduced secretory capacity and enhanced apoptosis is a key event in the pathogenesis of both diabetes types. Oxidative stress induced by reactive oxygen and nitrogen species is critically involved in the impairment of beta-cell function during the development of diabetes. Because of their low antioxidant capacity, beta-cells are extremely sensitive towards oxidative stress. In beta-cells, important targets for an oxidant insult are cell metabolism and K(ATP) channels. The oxidant-evoked alterations of K(ATP) channel activity seem to be critical for oxidant-induced dysfunction because genetic ablation of K(ATP) channels attenuates the effects of oxidative stress on beta-cell function. Besides the effects on metabolism, interference of oxidants with mitochondria induces key events in apoptosis. Consequently, increasing antioxidant defence is a promising strategy to delay beta cell failure in (pre)-diabetic patients or during islet transplantation. Knock-out of K(ATP) channels has beneficial effects on oxidant-induced inhibition of insulin secretion and cell death. Interestingly, these effects can be mimicked by sulfonylureas that have been used in the treatment of T2DM for many years. Loss of functional K(ATP) channels leads to up-regulation of antioxidant enzymes, a process that depends on cytosolic Ca(2+). These observations are of great importance for clinical intervention because they show a possibility to protect beta-cells at an early stage before dramatic changes of the secretory capacity and loss of cell mass become manifest and lead to glucose intolerance or even overt diabetes.

TRPC channels and their implication in neurological diseases

Calcium is an essential intracellular messenger and serves critical cellular functions in both excitable and non-excitable cells. Most of the physiological functions in these cells are uniquely regulated by changes in cytosolic Ca2+ levels ([Ca2+](i)), which are achieved via various mechanisms. One of these mechanism(s) is activated by the release of Ca2+ from the endoplasmic reticulum (ER), followed by Ca2+ influx across the plasma membrane (PM). Activation of PM Ca2+ channel is essential for not only refilling of the ER Ca2+ stores, but is also critical for maintaining [Ca2+](i) that regulates biological functions, such as neurosecretion, sensation, long term potentiation, synaptic plasticity, gene regulation, as well as cellular growth and differentiation. Alterations in Ca2+ homeostasis have been suggested in the onset/progression of neurological diseases, such as Parkinson's, Alzheimer's, bipolar disorder, and Huntington's. Available data on transient receptor potential conical (TRPC) protein indicate that these proteins initiate Ca2+ entry pathways and are essential in maintaining cytosolic, ER, and mitochondrial Ca2+ levels. A number of biological functions have been assigned to these TRPC proteins. Silencing of TRPC1 and TRPC3 has been shown to inhibit neuronal proliferation and loss of TRPC1 is implicated in neurodegeneration. Thus, TRPC channels not only contribute towards normal physiological processes, but are also implicated in several human pathological conditions. Overall, it is suggested that these channels could be used as potential therapeutic targets for many of these neurological diseases. Thus, in this review we have focused on the functional implication of TRPC channels in neuronal cells along with the elucidation of their role in neurodegeneration.

Endoplasmic reticulum calcium release potentiates the ER stress and cell death caused by an oxidative stress in MCF-7 cells

Increase in cytosolic calcium concentration ([Ca2+](c)), release of endoplasmic reticulum (ER) calcium ([Ca2+](er)) and ER stress have been proposed to be involved in oxidative toxicity. Nevertheless, their relative involvements in the processes leading to cell death are not well defined. In this study, we investigated whether oxidative stress generated during ascorbate-driven menadione redox cycling (Asc/Men) could trigger these three events, and, if so, whether they contributed to Asc/Men cytoxicity in MCF-7 cells. Using microspectrofluorimetry, we demonstrated that Asc/Men-generated oxidative stress was associated with a slow and moderate increase in [Ca2+](c), largely preceding permeation of propidium iodide, and thus cell death. Asc/Men treatment was shown to partially deplete ER calcium stores after 90 min (decrease by 45% compared to control). This event was associated with ER stress activation, as shown by analysis of eIF2 phosphorylation and expression of the molecular chaperone GRP94. Thapsigargin (TG) was then used to study the effect of complete [Ca2+](er) emptying during the oxidative stress generated by Asc/Men. Surprisingly, the combination of TG and Asc/Men increased ER stress to a level considerably higher than that observed for either treatment alone, suggesting that [Ca2+](er) release alone is not sufficient to explain ER stress activation during oxidative stress. Finally, TG-mediated [Ca2+](er) release largely potentiated ER stress, DNA fragmentation and cell death caused by Asc/Men, supporting a role of ER stress in the process of Asc/Men cytotoxicity. Taken together, our results highlight the involvement of ER stress and [Ca2+](er) decrease in the process of oxidative stress-induced cell death in MCF-7 cells.

H2O2-induced Ca2+ influx and its inhibition by N-(p-amylcinnamoyl) anthranilic acid in the beta-cells: involvement of TRPM2 channels

Type 2 melastatin-related transient receptor potential channel (TRPM2), a member of the melastatin-related TRP (transient receptor potential) subfamily is a Ca(2+)-permeable channel activated by hydrogen peroxide (H(2)O(2)). We have investigated the role of TRPM2 channels in mediating the H(2)O(2)-induced increase in the cytoplasmic free Ca(2+) concentration ([Ca(2+)](i)) in insulin-secreting cells. In fura-2 loaded INS-1E cells, a widely used model of beta-cells, and in human beta-cells, H(2)O(2) increased [Ca(2+)](i), in the presence of 3 mM glucose, by inducing Ca(2+) influx across the plasma membrane. H(2)O(2)-induced Ca(2+) influx was not blocked by nimodipine, a blocker of the L-type voltage-gated Ca(2+) channels nor by 2-aminoethoxydiphenyl borate, a blocker of several TRP channels and store-operated channels, but it was completely blocked by N-(p-amylcinnamoyl)anthranilic acid (ACA), a potent inhibitor of TRPM2. Adenosine diphosphate phosphate ribose, a specific activator of TRPM2 channel and H(2)O(2), induced inward cation currents that were blocked by ACA. Western blot using antibodies directed to the epitopes on the N-terminal and on the C-terminal parts of TRPM2 identified the full length TRPM2 (TRPM2-L), and the C-terminally truncated TRPM2 (TRPM2-S) in human islets. We conclude that functional TRPM2 channels mediate H(2)O(2)-induced Ca(2+) entry in beta-cells, a process potently inhibited by ACA.

The role of nitric oxide and reactive oxygen species in the positive inotropic response to mechanical stretch in the mammalian myocardium

The endothelial nitric oxide synthase (eNOS) has been implicated in the rapid (Frank–Starling) and slow (Anrep) cardiac response to stretch. Our work and that of others have demonstrated that a neuronal nitric oxide synthase (nNOS) localized to the myocardium plays an important role in the regulation of cardiac function and calcium handling. However, the effect of nNOS on the myocardial response to stretch has yet to be investigated. Recent evidence suggests that the stretch-induced release of angiotensin II (Ang II) and endothelin 1 (ET-1) stimulates myocardial superoxide production from NADPH oxidases which, in turn, contributes to the Anrep effect. nNOS has also been shown to regulate the production of myocardial superoxide, suggesting that this isoform may influence the cardiac response to stretch or ET-1 by altering the NO-redox balance in the myocardium. Here we show that the increase in left ventricular (LV) myocyte shortening in response to the application of ET-1 (10 nM, 5 min) did not differ between nNOS^−/− mice and their wild type littermates (nNOS^+/+). Pre-incubating LV myocytes with the NADPH oxidase inhibitor, apocynin (100 μM, 30 min), reduced cell shortening in nNOS^−/− myocytes only but prevented the positive inotropic effects of ET-1 in both groups. Superoxide production (O₂⁻) was enhanced in nNOS^−/− myocytes compared to nNOS^+/+; however, this difference was abolished by pre-incubation with apocynin. There was no detectable increase in O₂⁻ production in ET-1 pre-treated LV myocytes. Inhibition of protein kinase C (chelerythrine, 1 μM) did not affect cell shortening in either group, however, protein kinase A inhibitor, PKI (2 μM), significantly reduced the positive inotropic effects of ET-1 in both nNOS^+/+ and nNOS^−/− myocytes. Taken together, our findings show that the positive inotropic effect of ET-1 in murine LV myocytes is independent of nNOS but requires NADPH oxidases and protein kinase A (PKA)-dependent signaling. These results may further our understanding of the signaling pathways involved in the myocardial inotropic response to stretch.

H2O2-induced Ca2+ influx and its inhibition by N-(p-amylcinnamoyl) anthranilic acid in the beta-cells: involvement of TRPM2 channels

Type 2 melastatin-related transient receptor potential channel (TRPM2), a member of the melastatin-related TRP (transient receptor potential) subfamily is a Ca(2+)-permeable channel activated by hydrogen peroxide (H(2)O(2)). We have investigated the role of TRPM2 channels in mediating the H(2)O(2)-induced increase in the cytoplasmic free Ca(2+) concentration ([Ca(2+)](i)) in insulin-secreting cells. In fura-2 loaded INS-1E cells, a widely used model of beta-cells, and in human beta-cells, H(2)O(2) increased [Ca(2+)](i), in the presence of 3 mM glucose, by inducing Ca(2+) influx across the plasma membrane. H(2)O(2)-induced Ca(2+) influx was not blocked by nimodipine, a blocker of the L-type voltage-gated Ca(2+) channels nor by 2-aminoethoxydiphenyl borate, a blocker of several TRP channels and store-operated channels, but it was completely blocked by N-(p-amylcinnamoyl)anthranilic acid (ACA), a potent inhibitor of TRPM2. Adenosine diphosphate phosphate ribose, a specific activator of TRPM2 channel and H(2)O(2), induced inward cation currents that were blocked by ACA. Western blot using antibodies directed to the epitopes on the N-terminal and on the C-terminal parts of TRPM2 identified the full length TRPM2 (TRPM2-L), and the C-terminally truncated TRPM2 (TRPM2-S) in human islets. We conclude that functional TRPM2 channels mediate H(2)O(2)-induced Ca(2+) entry in beta-cells, a process potently inhibited by ACA.

TRPM2 Is Elevated in the tMCAO Stroke Model, Transcriptionally Regulated, and Functionally Expressed in C13 Microglia

We report the detailed expression profile of TRPM2 mRNA within the human central nervous system (CNS) and demonstrate increased TRPM2 mRNA expression at 1 and 4 weeks following ischemic injury in the rat transient middle cerebral artery occlusion (tMCAO) stroke model. Microglial cells play a key role in pathology produced following ischemic injury in the CNS and possess TRPM2, which may contribute to stroke-related pathological responses. We show that TRPM2 mRNA is present in the human C13 microglial cell line and is reduced by antisense treatment. Activation of C13 cells by interleukin-1beta leads to a fivefold increase of TRPM2 mRNA demonstrating transcriptional regulation. To confirm mRNA distribution correlated with functional expression, we combined electrophysiology, Ca2+ imaging, and antisense approaches. C13 microglia exhibited, when stimulated with hydrogen peroxide (H2O2), increased [Ca2+]i, which was reduced by antisense treatment. Moreover, patch-clamp recordings from C13 demonstrated that increased intracellular adenosine diphosphoribose (ADPR) or extracellular H2O2 induced an inward current, consistent with activation of TRPM2. In addition we confirm the functional expression of a TRPM2-like conductance in primary microglial cultures derived from rats. Activation of TRPM2 in microglia during ischemic brain injury may mediate key aspects of microglial pathophysiological responses.

Identification and physiological activity of survival factor released from cardiomyocytes during ischaemia and reperfusion

AIMS

We carried out a screening of survival factors released from cells exposed to simulated ischaemia and reperfusion (sI/R) using the embryonic rat heart-derived cell line, H9c2 cells, and examined the physiological role of the identified factor.

METHOD AND RESULTS

The culture medium supernatant of H9c2 cells exposed to sI/R was separated by column chromatography and the fractions examined for survival activity. The protein with survival activity was identified by mass spectrometry, and its physiological role was examined in the models of ischaemia. Cell survival activity was detected in at least three fractions of the cell supernatant collected during sI/R and subjected to a series of column chromatographic steps. Among the proteins measured by mass spectrometry and western blotting, a p36 protein identified as a glycolytic enzyme, lactate dehydrogenase muscle subunit (M-LDH), showed strong survival activity. H(2)O(2)-induced intracellular calcium overload in H9c2 cells and irregular Ca(2+) transients in adult rat cardiomyocytes were both found to be inhibited by pretreatment with M-LDH. M-LDH also lowered the frequency and amplitude of early afterdepolarizations induced by H(2)O(2) in adult rat cardiomyocytes and suppressed the ischaemia-reperfusion-induced reduction of cardiac output from mouse working heart preparations. M-LDH was found to increase the phosphorylation of extracellular signal-regulated kinase1/2 (ERK1/2), which plays a role in H9c2 cell survival.

CONCLUSION

M-LDH released from cardiomyocytes after hypoxia and reoxygenation has a role in protecting the heart from oxidative stress-induced injury through an intracellular signal transduction pathway involving ERK1/2.

TRPM2

TRPM2 is a cation channel enabling influx of Na+ and Ca2+, leading to depolarization and increases in the cytosolic Ca2+ concentration ([Ca2+]i). It is widely expressed, e.g. in many neurons, blood cells and the endocrine pancreas. Channel gating is induced by ADP-ribose (ADPR) that binds to a Nudix box motif in the cytosolic C-terminus of the channel. Endogenous ADPR concentrations in leucocytes are sufficiently high to activate TRPM2 in the presence of an increased [Ca2+]i but probably not at resting [Ca2+]i. Another channel activator is oxidative stress, especially hydrogen peroxide (H2O2) that may act through ADPR after ADPR polymers have been formed by poly(ADP-ribose) polymerases (PARPs) and hydolysed by glycohydrolases. H2O2-stimulated TRPM2 channels essentially contribute to insulin secretion in pancreatic beta-cells and alloxan-induced diabetes mellitus. Inhibition of TRPM2 channels may be achieved by channel blockers such as flufenamic acid or the anti-fungal agents clotrimazole or econazole. Selective blockers of TRPM2 are not yet available; those would be valuable for a characterization of biological roles of TRPM2 in various tissues and as potential drugs directed against oxidative cell damage, reperfusion injury or leucocyte activation. Activation of TRPM2 may be prevented by anti-oxidants, PARP inhibitors and glycohydrolase inhibitors. In future, binding of ADPR to the Nudix box may be targeted. In light of the wide-spread expression and growing list of cellular functions of TRPM2, useful therapeutic applications are expected for future drugs that block TRPM2 channels or inhibit their activation.

TRP channels of the pancreatic beta cell

Orchestrated ion fluctuations within pancreatic islets regulate hormone secretion and maybe essential to processes such as apoptosis. A diverse set of ion channels allows for islet cells to respond to a variety of signals and dynamically regulate hormone secretion and glucose homeostasis (reviewed by Houamed et al. 2004). This chapter focuses on transient receptor potential (TRP)-related channels found within the beta cells of the islet and reviews their roles in both insulin secretion and apoptosis.

Involvement of calcium-mediated apoptotic signals in H2O2-induced MIN6N8a cell death

Reactive oxygen species are believed to be the central mediators of beta-cell destruction that leads to type 1 and 2 diabetes, and calcium has been reported to be an important mediator of beta cell death. In the present study, the authors investigated whether Ca(2+) plays a role in hydrogen peroxide (H(2)O(2))-induced MIN6N8a mouse beta cell death. Treatment with low concentration H(2)O(2) (50 microM) was found to be sufficient to reduce MIN6N8a cell viability by 55%, largely via apoptosis. However, this H(2)O(2)-induced cell death was near completely blocked by pretreatment with BAPTA/AM (5 microM), a chelator of intracellular Ca(2+). Moreover, the intracellular calcium store channel blockers, such as, xestospongin c and ryanodine, significant protected cells from 50 microM H(2)O(2)-induced cell death and under extracellular Ca(2+)-free conditions, 50 microM H(2)O(2) elicited transient [Ca(2+)](i) increases. In addition, pharmacologic inhibitors of calpain, calcineurin, and calcium/calmodulin-dependent protein kinase II were found to have a protective effect on H(2)O(2)-induced death. Moreover, H(2)O(2)-induced apoptotic signals, such as c-JUN N-terminal kinase activation, cytochrome c release, caspase 3 activation, and poly (ADP-ribose) polymerase cleavage were all down-regulated by the intracellular Ca(2+) chelation. These findings show that [Ca(2+)](i) elevation, possibly due to release from intracellular calcium stores and the subsequent activation of Ca(2+)-mediated apoptotic signals, critically mediates low concentration H(2)O(2)-induced MIN6N8a cell death. These findings suggest that a breakdown of calcium homeostasis by low level of reactive oxygen species may be involved in beta cell destruction during diabetes development.

Reciprocal effects of glucose on the process of cell death induced by calcium ionophore or H2O2 in rat lymphocytes

We have examined the effects of glucose at high concentrations on the process of cell death induced by excessive increase in intracellular Ca(2+) concentration ([Ca(2+)](i)) or oxidative stress in rat lymphocytes. The cell death elicited by the excessive increase in [Ca(2+)](i) seemed to be induced by an activation of Ca(2+)-dependent K(+) channels because the inhibitors for Ca(2+)-dependent K(+) channels attenuated the decrease in cell viability. Glucose at 30-50mM augmented the decrease in cell viability by the excessive increase in [Ca(2+)](i). It was not specific for glucose because it was the case for sucrose or NaCl, suggesting an involvement of increased osmolarity in adverse action of glucose. On the contrary, glucose protected the cells suffering from oxidative stress induced by H(2)O(2), one of reactive oxygen species. It was also the case for fructose or sucrose, but not for NaCl. The process of cell death induced by H(2)O(2) started, being independent from the presence of glucose. Glucose delayed the process of cell death induced by H(2)O(2). Sucrose and fructose also protected the cells against oxidative stress. The reactivity of sucrose to reactive oxygen species is lower than those of glucose and fructose. The order in the reactivity cannot explain the protective action of glucose. Glucose at high concentrations exerts reciprocal actions on the process of cell death induced by the oxidative stress and excessive increase in [Ca(2+)](i).

The role of TRP channels in oxidative stress-induced cell death

The transient receptor potential (TRP) protein superfamily is a diverse group of voltage-independent calcium-permeable cation channels expressed in mammalian cells. These channels have been divided into six subfamilies, and two of them, TRPC and TRPM, have members that are widely expressed and activated by oxidative stress. TRPC3 and TRPC4 are activated by oxidants, which induce Na(+) and Ca(2+) entry into cells through mechanisms that are dependent on phospholipase C. TRPM2 is activated by oxidative stress or TNFalpha, and the mechanism involves production of ADP-ribose, which binds to an ADP-ribose binding cleft in the TRPM2 C-terminus. Treatment of HEK 293T cells expressing TRPM2 with H(2)O(2) resulted in Ca(2+) influx and increased susceptibility to cell death, whereas coexpression of the dominant negative isoform TRPM2-S suppressed H(2)O(2)-induced Ca(2+) influx, the increase in [Ca(2+)](i), and onset of apoptosis. U937-ecoR monocytic cells expressing increased levels of TRPM2 also exhibited significantly increased [Ca(2+)](i) and increased apoptosis after treatment with H(2)O(2) or TNFalpha. A dramatic increase in caspase 8, 9, 3, 7, and PARP cleavage was observed in TRPM2-expressing cells, demonstrating a downstream mechanism through which cell death is mediated. Inhibition of endogenous TRPM2 function through three approaches, depletion of TRPM2 by RNA interference, blockade of the increase in [Ca(2+)](i) through TRPM2 by calcium chelation, or expression of the dominant negative splice variant TRPM2-S protected cell viability. H(2)O(2) and amyloid beta-peptide also induced cell death in primary cultures of rat striatal cells, which endogenously express TRPM2. TRPM7 is activated by reactive oxygen species/nitrogen species, resulting in cation conductance and anoxic neuronal cell death, which is rescued by suppression of TRPM7 expression. TRPM2 and TRPM7 channels are physiologically important in oxidative stress-induced cell death.

Metabolite of SIR2 reaction modulates TRPM2 ion channel

The transient receptor potential melastatin-related channel 2 (TRPM2) is a nonselective cation channel, whose prolonged activation by oxidative and nitrative agents leads to cell death. Here, we show that the drug puromycin selectively targets TRPM2-expressing cells, leading to cell death. Our data suggest that the silent information regulator 2 (Sir2 or sirtuin) family of enzymes mediates this susceptibility to cell death. Sirtuins are protein deacetylases that regulate gene expression, apoptosis, metabolism, and aging. These NAD+-dependent enzymes catalyze a reaction in which the acetyl group from substrate is transferred to the ADP-ribose portion of NAD+ to form deacetylated product, nicotinamide, and the metabolite OAADPr, whose functions remain elusive. Using cell-based assays and RNA interference, we show that puromycin-induced cell death is greatly diminished by nicotinamide (a potent sirtuin inhibitor), and by decreased expression of sirtuins SIRT2 and SIRT3. Furthermore, we demonstrate using channel current recordings and binding assays that OAADPr directly binds to the cytoplasmic domain of TRPM2 and activates the TRPM2 channel. ADP-ribose binds TRPM2 with similarly affinity, whereas NAD+ displays almost negligible binding. These studies provide the first evidence for the potential role of sirtuin-generated OAADPr in TRPM2 channel gating.