H(2)O(2)-induced Ca(2+) overload in NRVM involves ERK1/2 MAP kinases: role for an NHE-1-dependent pathway

Acylated ghrelin protection inhibits apoptosis in the remote myocardium post-myocardial infarction by inhibiting calcineurin and activating ARC

This study investigated if acylated ghrelin (AG) could inhibit myocardial infarction (MI)-induced apoptosis in the left ventricles (LV) of male rats and tested if this protection involves modulating ARC anti-apoptotic protein. Rats (n = 12/group) were assigned as a sham-operated, a sham + AG (100 µg/kg, 2x/d, S.C.), MI, and MI + AG. With no antioxidant activity or expression of FAS, AG inhibited caspase-3, 8, and 9 and decreased cytosolic/mitochondrial levels of cytochrome-c, Bax, Bad, and Bad-BCL-2 complex in the LVs of the sham-operated and MI-treated rats. Concomitantly, AG preserved the mitochondria structure, decreased mtPTP, and enhanced state-3 respiration in the LVs of both treated groups. These effects were associated with increased mitochondrial levels of ARC and a reduction in the activity of calcineurin. Overall, AG suppresses MI-induced ventricular apoptosis by inhibition of calcineurin, activation of ARC, and preserving mitochondria integrity.

Requirement of Na+/H+ Exchanger NHE1 for Vasopressin-Induced Osteogenic Signaling and Calcification in Human Aortic Smooth Muscle Cells

BACKGROUND/AIMS

Vasopressin is a powerful stimulator of vascular calcification, augmenting osteogenic signaling in vascular smooth muscle cells (VSMCs) including upregulation of transcription factors such as core-binding factor α-1 (CBFA1), msh homeobox 2 (MSX2), and SRY-Box 9 (SOX9), as well as of tissue-nonspecific alkaline phosphatase (ALPL). Vasopressin-induced osteogenic signaling and calcification require the serum- and glucocorticoid-inducible kinase 1 (SGK1). Known effects of SGK1 include upregulation of Na+/H+ exchanger 1 (NHE1). NHE1 further participates in the regulation of reactive oxygen species (ROS). NHE1 has been shown to participate in the orchestration of bone mineralization. The present study, thus, explored whether vasopressin modifies NHE1 expression and ROS generation, as well as whether pharmacological inhibition of NHE1 disrupts vasopressin-induced osteogenic signaling and calcification in VSMCs.

METHODS

Human aortic smooth muscle cells (HAoSMCs) were treated with vasopressin in the absence or presence of SGK1 silencing, SGK1 inhibitor GSK-650394, and NHE1 blocker cariporide. Transcript levels were determined by using quantitative real-time polymerase chain reaction, protein abundance by Western blotting, ROS generation with 2',7'-dichlorofluorescein diacetate fluorescence, and ALP activity and calcium content by using colorimetric assays.

RESULTS

Vasopressin significantly enhanced the NHE1 transcript and protein levels in HAoSMCs, effects significantly blunted by SGK1 inhibition with GSK-650394 or SGK1 silencing. Vasopressin increased ROS accumulation, an effect significantly blocked by the NHE1 inhibitor cariporide. Vasopressin further significantly increased osteogenic markers CBFA1, MSX2, SOX9, and ALPL transcript levels, as well as ALP activity and calcium content in HAoSMCs, all effects significantly blunted by SGK1 silencing or in the presence of GSK-650394 or cariporide.

CONCLUSION

Vasopressin stimulates NHE1 expression and ROS generation, an effect dependent on SGK1 and required for vasopressin-induced stimulation of osteogenic signaling and calcification of VSMCs.

PDE5 inhibition improves cardiac morphology and function in SHR by reducing NHE1 activity: Repurposing Sildenafil for the treatment of hypertensive cardiac hypertrophy

Previously, we have shown that an increased cGMP-activated protein Kinase (PKG) activity after phosphodiesterase 5 (PDE5) inhibition by Sildenafil (SIL), leads to myocardial Na+/H+ exchanger (NHE1) inhibition preserving its basal homeostatic function. Since NHE1 is hyperactive in the hypertrophied myocardium of spontaneous hypertensive rats (SHR), while its inhibition was shown to prevent and revert this pathology, the current study was aimed to evaluate the potential antihypertrophic effect of SIL on adult SHR myocardium. We initially tested the inhibitory capability of SIL on NHE1 in isolated cardiomyocytes of SHR by comparing H+ efflux during the recovery from an acid load. After confirmed that effect, eight-month-old SHR were chronically treated for one month with SIL through drinking water. Compared to their littermate controls, SIL-treated rats presented a decreased NHE1 activity, which correlated with a reduction in its phosphorylation level assigned to activation of a PKG-p38 MAP kinase-PP2A signaling pathway. Moreover, treated animals showed a decreased oxidative stress that appears to be a consequence of a decreased mitochondrial NHE1 phosphorylation. Treated SHR showed a significant reduction in the pro-hypertrophic phosphatase calcineurin, despite slight tendency to decrease hypertrophy was detected. When SIL treatment was prolonged to three months, a significant decrease in myocardial hypertrophy and interstitial fibrosis that correlated with a lower myocardial stiffness was observed. In conclusion, the current study provides evidence concerning the ability of SIL to revert established cardiac hypertrophy in SHR, a clinically relevant animal model that resembles human essential hypertension.

Structural and Functional Changes in the Na+/H+ Exchanger Isoform 1, Induced by Erk1/2 Phosphorylation

The human Na⁺/H⁺ exchanger isoform 1 (NHE1) is a plasma membrane transport protein that plays an important role in pH regulation in mammalian cells. Because of the generation of protons by intermediary metabolism as well as the negative membrane potential, protons accumulate within the cytosol. Extracellular signal-regulated kinase (ERK)-mediated regulation of NHE1 is important in several human pathologies including in the myocardium in heart disease, as well as in breast cancer as a trigger for growth and metastasis. NHE1 has a N-terminal, a 500 amino acid membrane domain, and a C-terminal 315 amino acid cytosolic domain. The C-terminal domain regulates the membrane domain and its effects on transport are modified by protein binding and phosphorylation. Here, we discuss the physiological regulation of NHE1 by ERK, with an emphasis on the critical effects on structure and function. ERK binds directly to the cytosolic domain at specific binding domains. ERK also phosphorylates NHE1 directly at multiple sites, which enhance NHE1 activity with subsequent downstream physiological effects. The NHE1 cytosolic regulatory tail possesses both ordered and disordered regions, and the disordered regions are stabilized by ERK-mediated phosphorylation at a phosphorylation motif. Overall, ERK pathway mediated phosphorylation modulates the NHE1 tail, and affects the activity, structure, and function of this membrane protein.

The slow force response to stretch: Controversy and contradictions

When exposed to an abrupt stretch, cardiac muscle exhibits biphasic active force enhancement. The initial, instantaneous, force enhancement is well explained by the Frank-Starling mechanism. However, the cellular mechanisms associated with the second, slower phase remain contentious. This review explores hypotheses regarding this "slow force response" with the intention of clarifying some apparent contradictions in the literature. The review is partitioned into three sections. The first section considers pathways that modify the intracellular calcium handling to address the role of the sarcoplasmic reticulum in the mechanism underlying the slow force response. The second section focuses on extracellular calcium fluxes and explores the identity and contribution of the stretch-activated, non-specific, cation channels as well as signalling cascades associated with G-protein coupled receptors. The final section introduces promising candidates for the mechanosensor(s) responsible for detecting the stretch perturbation.

YiQiFuMai Powder Injection Attenuates Coronary Artery Ligation-Induced Heart Failure Through Improving Mitochondrial Function via Regulating ROS Generation and CaMKII Signaling Pathways

The YiQiFuMai powder injection (YQFM), a traditional Chinese medicine (TCM) prescription re-developed based on Sheng-Mai-San, is widely applied for the treatment of cardiovascular diseases. However, its potential molecular mechanism remains obscure. The present study was designed to observe the effects of YQFM and underlying mechanisms on coronary artery ligation (CAL)-induced heart failure (HF) and cell hypoxia of 24 h oxygen-glucose deprivation (OGD) in neonatal rat ventricular myocytes (NRVMs). HF was induced by permanent CAL for 2 weeks in ICR mice. The results demonstrated that YQFM significantly attenuated CAL-induced HF via improving the cardiac function, cardiac systolic function, cardiac structure impairment, cardiac histological features and fibrosis. YQFM markedly attenuated mitochondrial dysfunction through improving mitochondrial morphology, increasing mitochondria membrane potential (Δψm), mitochondrial ROS generation and expression of Mitofusin-2 (Mfn2), meanwhile, decreasing phosphorylation of dynamin-related protein 1 (p-Drp1). Mechanistically, YQFM could significantly decrease the expression of isoforms of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunit NADPH oxidase 2 (NOX2), p67^phox and NADPH oxidase 4 (NOX4), ultimately reducing reactive oxygen species (ROS) generation. In addition, YQFM could down-regulate expression of calcium voltage-gated channel subunit α1C (CACNA1C) and phosphorylation of calmodulin dependent protein kinase II (p-CaMKII). These results suggest that YQFM ameliorates mitochondrial function in HF mice, partially through inhibiting ROS generation and CaMKII signaling pathways. Therefore, the present study provided scientific evidence for the underlying mechanism of YQFM.

Heat Failure Phenotypes Induced by Knockdown of DAPIT in Zebrafish: A New Insight into Mechanism of Dilated Cardiomyopathy

The pathogenesis of heart failure associated with dilated cardiomyopathy (DCM) may result in part from adenosine triphosphate (ATP) dysregulation in the myocardium. Under these conditions, diabetes-associated protein in insulin-sensitive tissue (DAPIT), which is encoded by the upregulated during skeletal muscle growth 5 (USMG5) gene, plays a crucial role in energy production by mitochondrial ATP synthase. To determine whether USMG5 is related to the development of heart failure, we performed clinical and experimental studies. Microarray analysis showed that the expression levels of USMG5 were positively correlated with those of natriuretic peptide precursor A in the human failed myocardium. When endogenous z-usmg5 in zebrafish was disrupted using morpholino (MO) oligonucleotides, the pericardial sac and atrial areas were larger and ventricular fractional shortening was reduced compared to in the control MO group. The expression levels of natriuretic peptides were upregulated in the z-usmg5 MO group compared to in controls. Further, microarray analysis revealed that genes in the calcium signalling pathway were downregulated in the z-usmg5 MO group. These results demonstrate that DAPIT plays a crucial role in the development of heart failure associated with DCM and thus may be a therapeutic target for heart failure.

Acute Exposure to Cigarette Smoking Followed by Myocardial Infarction Aggravates Renal Damage in an In Vivo Mouse Model

Cigarette smoking (S) is a risk factor for progressive chronic kidney disease, renal dysfunction, and renal failure. In this study, the effect of smoking on kidney function was investigated in a mouse model of myocardial infarction (MI) using 4 groups: control (C), smoking (S), MI, and S+MI. Histological analysis of S+MI group showed alterations in kidney structure including swelling of the proximal convoluted tubules (PCTs), thinning of the epithelial lining, focal loss of the brush border of PCTs, and patchy glomerular retraction. Molecular analysis revealed that nephrin expression was significantly reduced in the S+MI group, whereas sodium-hydrogen exchanger-1 (NHE-1) was significantly increased, suggesting altered glomerular filtration and kidney functions. Moreover, S+MI group, but not S alone, showed a significant increase in the expression of connective tissue growth factor (CTGF) and fibrotic proteins fibronectin (FN) and α-smooth muscle actin (SMA), in comparison to controls, in addition to a significant increase in mRNA levels of IL-6 and TNF-α inflammatory markers. Finally, reactive oxygen species (ROS) production was significantly accentuated in S+MI group concomitant with a significant increase in NOX-4 protein levels. In conclusion, smoking aggravates murine acute renal damage caused by MI at the structural and molecular levels by exacerbating renal dysfunction.

Protective effect of reduced glutathione C60 derivative against hydrogen peroxide-induced apoptosis in HEK 293T cells

Hydrogen peroxide (H2O2) and free radicals cause oxidative stress, which induces cellular injuries, metabolic dysfunction, and even cell death in various clinical abnormalities. Fullerene (C60) is critical for scavenging oxygen free radicals originated from cell metabolism, and reduced glutathione (GSH) is another important endogenous antioxidant. In this study, a novel water-soluble reduced glutathione fullerene derivative (C60-GSH) was successfully synthesized, and its beneficial roles in protecting against H2O2-induced oxidative stress and apoptosis in cultured HEK 293T cells were investigated. Fourier Transform infrared spectroscopy and (1)H nuclear magnetic resonance were used to confirm the chemical structure of C60-GSH. Our results demonstrated that C60-GSH prevented the reactive oxygen species (ROS)-mediated cell damage. Additionally, C60-GSH pretreatment significantly attenuated H2O2-induced superoxide dismutase (SOD) consumption and malondialdehyde (MDA) elevation. Furthermore, C60-GSH inhibited intracellular calcium mobilization, and subsequent cell apoptosis via bcl-2/bax-caspase-3 signaling pathway induced by H2O2 stimulation in HEK 293T cells. Importantly, these protective effects of C60-GSH were superior to those of GSH. In conclusion, these results suggested that C60-GSH has potential to protect against H2O2-induced cell apoptosis by scavenging free radicals and maintaining intracellular calcium homeostasis without evident toxicity.

The cardiac electrogenic sodium/bicarbonate cotransporter (NBCe1) is activated by aldosterone through the G protein-coupled receptor 30 (GPR 30)

The sodium/bicarbonate cotransporter (NBC) transports extracellular Na⁺ and HCO₃^- into the cytoplasm upon intracellular acidosis, restoring the acidic pH_i to near neutral values. Two different NBC isoforms have been described in the heart, the electroneutral NBCn1 (1Na⁺:1HCO₃^-) and the electrogenic NBCe1 (1Na⁺:2HCO₃^-). Certain non-genomic effects of aldosterone (Ald) were due to an orphan G protein-couple receptor 30 (GPR30). We have recently demonstrated that Ald activates GPR30 in adult rat ventricular myocytes, which transactivates the epidermal growth factor receptor (EGFR) and in turn triggers a reactive oxygen species (ROS)- and PI3K/AKT-dependent pathway, leading to the stimulation of NBC. The aim of this study was to investigate the NBC isoform involved in the Ald/GPR30-induced NBC activation. Using specific NBCe1 inhibitory antibodies (a-L3) we demonstrated that Ald does not affect NBCn1 activity. Ald was able to increase NBCe1 activity recorded in isolation. Using immunofluorescence and confocal microscopy analysis we showed in this work that both NBCe1 and GPR30 are localized in t-tubules. In conclusion, we have demonstrated that NBCe1 is the NBC isoform activated by Ald in the heart.

Role of MIF in myocardial ischaemia and infarction: insight from recent clinical and experimental findings

First discovered in 1966 as an inflammatory cytokine, MIF (macrophage migration inhibitory factor) has been extensively studied for its pivotal role in a variety of inflammatory diseases, including rheumatoid arthritis and atherosclerosis. Although initial studies over a decade ago reported increases in circulating MIF levels following acute MI (myocardial infarction), the dynamic changes in MIF and its pathophysiological significance following MI have been unknown until recently. In the present review, we summarize recent experimental and clinical studies examining the diverse functions of MIF across the spectrum of acute MI from brief ischaemia to post-infarct healing. Following an acute ischaemic insult, MIF is rapidly released from jeopardized cardiomyocytes, followed by a persistent MIF production and release from activated immune cells, resulting in a sustained increase in circulating levels of MIF. Recent studies have documented two distinct actions of MIF following acute MI. In the supra-acute phase of ischaemia, MIF mediates cardioprotection via several distinct mechanisms, including metabolic activation, apoptosis suppression and antioxidative stress. In prolonged myocardial ischaemia, however, MIF promotes inflammatory responses with largely detrimental effects on cardiac function and remodelling. The pro-inflammatory properties of MIF are complex and involve MIF derived from cardiac and immune cells contributing sequentially to the innate immune response evoked by MI. Emerging evidence on the role of MIF in myocardial ischaemia and infarction highlights a significant potential for the clinical use of MIF agonists or antagonists and as a unique cardiac biomarker.

Recent insights in the paracrine modulation of cardiomyocyte contractility by cardiac endothelial cells

The cardiac endothelium is formed by a continuous monolayer of cells that line the cavity of the heart (endocardial endothelial cells (EECs)) and the luminal surface of the myocardial blood vessels (intramyocardial capillary endothelial cells (IMCEs)). EECs and IMCEs can exercise substantial control over the contractility of cardiomyocytes by releasing various factors such as nitric oxide (NO) via a constitutive endothelial NO-synthase (eNOS), endothelin-1, prostaglandins, angiotensin II, peptide growth factors, and neuregulin-1. The purpose of the present paper is actually to shortly review recent new information concerning cardiomyocytes as effectors of endothelium paracrine signaling, focusing particularly on contractile function. The modes of action and the regulatory paracrine role of the main mediators delivered by cardiac endothelial cells upon cardiac contractility identified in cardiomyocytes are complex and not fully described. Thus, careful evaluation of new therapeutic approaches is required targeting important physiological signaling pathways, some of which have been until recently considered as deleterious, like reactive oxygen species. Future works in the field of cardiac endothelial cells and cardiac function will help to better understand the implication of these mediators in cardiac physiopathology.

Modulation of the cardiac sodium/bicarbonate cotransporter by the renin angiotensin aldosterone system: pathophysiological consequences

The sodium/bicarbonate cotransporter (NBC) is one of the major alkalinizing mechanisms in the cardiomyocytes. It has been demonstrated the existence of at least two functional isoforms, one that promotes the co-influx of 1 molecule of Na⁺ per 1 molecule of HCO⁻₃ (electroneutral isoform; NBCn1) and the other one that generates the co-influx of 1 molecule of Na⁺ per 2 molecules of HCO⁻₃ (electrogenic isoform; NBCe1). Both isoforms are important to maintain intracellular pH (pH_i) and sodium concentration ([Na⁺]_i). In addition, NBCe1 generates an anionic repolarizing current that modulates the action potential duration (APD). The renin-angiotensin-aldosterone system (RAAS) is implicated in the modulation of almost all physiological cardiac functions and is also involved in the development and progression of cardiac diseases. It was reported that angiotensin II (Ang II) exhibits an opposite effect on NBC isoforms: it activates NBCn1 and inhibits NBCe1. The activation of NBCn1 leads to an increase in pH_i and [Na⁺]_i, which indirectly, due to the stimulation of reverse mode of the Na⁺/Ca²⁺ exchanger (NCX), conduces to an increase in the intracellular Ca²⁺ concentration. On the other hand, the inhibition of NBCe1 generates an APD prolongation, potentially representing a risk of arrhythmias. In the last years, the potentially altered NBC function in pathological scenarios, as cardiac hypertrophy and ischemia-reperfusion, has raised increasing interest among investigators. This review attempts to draw the attention on the relevant regulation of NBC activity by RAAS, since it modulates pH_i and [Na⁺]_i, which are involved in the development of cardiac hypertrophy, the damage produced by ischemia-reperfusion and the generation of arrhythmic events, suggesting a potential role of NBC in cardiac diseases.

N-n-butyl haloperidol iodide inhibits H2O2-induced Na+/Ca2+-exchanger activation via the Na+/H+ exchanger in rat ventricular myocytes

N-n-butyl haloperidol iodide (F2), a novel compound, has shown palliative effects in myocardial ischemia/reperfusion (I/R) injury. In this study, we investigated the effects of F2 on the extracellular signal-regulated kinase kinase (MEK)/extracellular signal-regulated kinase (ERK)/Na(+)/H(+) exchanger (NHE)/Na(+)/Ca(2+) exchanger (NCX) signal-transduction pathway involved in H2O2-induced Ca(2+) overload, in order to probe the underlying molecular mechanism by which F2 antagonizes myocardial I/R injury. Acute exposure of rat cardiac myocytes to 100 μM H2O2 increased both NHE and NCX activities, as well as levels of phosphorylated MEK and ERK. The H2O2-induced increase in NCX current (I NCX) was nearly completely inhibited by the MEK inhibitor U0126 (1,4-diamino-2,3-dicyano-1,4-bis[o-aminophenylmercapto] butadiene), but only partly by the NHE inhibitor 5-(N,N-dimethyl)-amiloride (DMA), indicating the I NCX increase was primarily mediated by the MEK/mitogen-activated protein kinase (MAPK) pathway, and partially through activation of NHE. F2 attenuated the H2O2-induced I NCX increase in a concentration-dependent manner. To determine whether pathway inhibition was H2O2-specific, we examined the ability of F2 to inhibit MEK/ERK activation by epidermal growth factor (EGF), and NHE activation by angiotensin II. F2 not only inhibited H2O2-induced and EGF-induced MEK/ERK activation, but also completely blocked both H2O2-induced and angiotensin II-induced increases in NHE activity, suggesting that F2 directly inhibits MEK/ERK and NHE activation. These results show that F2 exerts multiple inhibitions on the signal-transduction pathway involved in H2O2-induced I NCX increase, providing an additional mechanism for F2 alleviating intracellular Ca(2+) overload to protect against myocardial I/R injury.

Endogenous endothelin 1 mediates angiotensin II-induced hypertrophy in electrically paced cardiac myocytes through EGFR transactivation, reactive oxygen species and NHE-1

Emerging evidence supports a key role for endothelin-1 (ET-1) and the transactivation of the epidermal growth factor receptor (EGFR) in angiotensin II (Ang II) action. We aim to determine the potential role played by endogenous ET-1, EGFR transactivation and redox-dependent sodium hydrogen exchanger-1 (NHE-1) activation in the hypertrophic response to Ang II of cardiac myocytes. Electrically paced adult cat cardiomyocytes were placed in culture and stimulated with 1 nmol l(-1) Ang II or 5 nmol l(-1) ET-1. Ang II increased ~45 % cell surface area (CSA) and ~37 % [(3)H]-phenylalanine incorporation, effects that were blocked not only by losartan (Los) but also by BQ123 (AT1 and ETA receptor antagonists, respectively). Moreover, Ang II significantly increased ET-1 messenger RNA (mRNA) expression. ET-1 similarly increased myocyte CSA and protein synthesis, actions prevented by the reactive oxygen species scavenger MPG or the NHE-1 inhibitor cariporide (carip). ET-1 increased the phosphorylation of the redox-sensitive ERK1/2-p90(RSK) kinases, main activators of the NHE-1. This effect was prevented by MPG and the antagonist of EGFR, AG1478. Ang II, ET-1 and EGF increased myocardial superoxide production (187 ± 9 %, 149 ± 8 % and 163.7 ± 6 % of control, respectively) and AG1478 inhibited these effects. Interestingly, Los inhibited only Ang II whilst BQ123 cancelled both Ang II and ET-1 actions, supporting the sequential and unidirectional activation of AT1, ETA and EGFR. Based on the present evidence, we propose that endogenous ET-1 mediates the hypertrophic response to Ang II by a mechanism that involves EGFR transactivation and redox-dependent activation of the ERK1/2-p90(RSK) and NHE-1 in adult cardiomyocytes.

Exercise alters the regulation of myocardial Na(+)/H(+) exchanger-1 activity

The myocardial Na(+)/H(+) exchanger-1 (NHE1) plays a major role in regulation of intracellular pH, and its upregulation has been implicated in increased ischemia-reperfusion injury and other pathologies. Hydrogen peroxide (H2O2) increases NHE1 activity acutely via ERK1/2 signaling. Chronic strenuous exercise upregulates NHE1 in skeletal muscle, but we hypothesize this will not occur in the heart, because exercise creates a cardioprotective phenotype. NHE1 activity and its regulation by H2O2 were examined at physiological pH using isolated cardiomyocytes from female Sprague-Dawley rats exercised on a treadmill for 5 wk (E; n = 11). Compared with sedentary (S; n = 15), E displayed increases (P < 0.05) in heart-to-body weight ratio (6.8%) and plantaris mitochondria content (89%). NHE1 activity (acid efflux rate following an acid load) was 209% greater in E (0.65 ± 0.12 vs. 2.01 ± 0.29 fmol/min). The difference was attributed primarily to greater cell volume (22.2 ± 0.6 vs. 34.3 ± 1.1 pl) and intracellular pH-buffering capacity (33.94 ± 1.59 vs. 65.82 ± 5.20 mM/pH unit) of E myocytes. H2O2 stimulation (100 μM) raised NHE1 activity significantly less in E (45%) than S (167%); however, activity remained 185% greater in E. ERK1/2 inhibition abrogated the increases. H2O2-stimulated ERK1/2 phosphorylation levels normalized to total ERK1/2 were similar between groups. Content of NHE1 and activities of H2O2 scavengers were also similar. We observed that intracellular pH-buffering capacity differences between groups became progressively less with declining pH, which may be an exercise-induced cardioprotective adaptation to lower NHE1 activity during certain pathological situations. We conclude that strenuous endurance exercise increases myocardial NHE1 activity at physiological pH, which would likely enhance cardiac performance under physiological conditions.

Regulation of the cardiac sodium/bicarbonate cotransporter by angiotensin II: potential Contribution to structural, ionic and electrophysiological myocardial remodelling

The sodium/ bicarbonate cotransporter (NBC) is, with the Na⁺/H⁺ exchanger (NHE), an important alkalinizing mechanism that maintains cellular intracellular pH (pHi). In the heart exists at least three isoforms of NBC, one that promotes the co-influx of 1 molecule of Na⁺ per 1molecule of HCO₃^-(electroneutral isoform; nNBC) and two others that generates the co-influx of 1 molecule of Na⁺ per 2 molecules of HCO₃^- (electrogenic isoforms; eNBC). In addition, the eNBC generates an anionic repolarizing current that modulate the cardiac action potential (CAP), adding to such isoforms the relevance to modulate the electrophysiological function of the heart. Angiotensin II (Ang II) is one of the main hormones that regulate cardiac physiology. The alkalinizing mechanisms (NHE and NBC) are stimulated by Ang II, increasing pHi and intracellular Na⁺ concentration, which indirectly, due to the stimulation of the Na⁺/Ca²⁺ exchanger (NCX) operating in the reverse form, leads to an increase in the intracellular Ca²⁺ concentration. Interestingly, it has been shown that Ang II exhibits an opposite effect on NBC isoforms: it activates the nNBC and inhibits the eNBC. This inhibition generates a CAP prolongation, which could directly increase the intracellular Ca²⁺ concentration. The regulation of the intracellular Na⁺ and Ca²⁺ concentrations is crucial for the cardiac cellular physiology, but these ions are also involved in the development of cardiac hypertrophy and the damage produced by ischemia-reperfusion, suggesting a potential role of NBC in cardiac diseases.

Mitochondrial NHE1: a newly identified target to prevent heart disease

Mitochondrial damage has been associated with early steps of cardiac dysfunction in heart subjected to ischemic stress, oxidative stress and hypertrophy. A common feature for the mitochondrial deterioration is the loss of the mitochondrial membrane potential (ΔΨ m) with the concomitant irreversible opening of the mitochondrial permeability transition pore (MPTP) which follows the mitochondrial Ca²⁺ overload, and the subsequent mitochondrial swelling. We have recently characterized the expression of the Na⁺/H⁺ exchanger 1 (mNHE1) in mitochondrial membranes. This surprising observation provided a unique target for the prevention of the Ca²⁺-induced MPTP opening, based on the inhibition of the NHE1 m. In this line, inhibition of NHE1 m activity and/or reduction of NHE1 m expression decreased the Ca²⁺-induced mitochondrial swelling and the release of reactive oxygen species (ROS) in isolated cardiac mitochondria and preserved the ΔΨ m in isolated cardiomyocytes. Mitochondrial NHE1 thus represents a novel target to prevent cardiac disease, opening new avenues for future research.

Mitochondrial reactive oxygen species (ROS) as signaling molecules of intracellular pathways triggered by the cardiac renin-angiotensin II-aldosterone system (RAAS)

Mitochondria represent major sources of basal reactive oxygen species (ROS) production of the cardiomyocyte. The role of ROS as signaling molecules that mediate different intracellular pathways has gained increasing interest among physiologists in the last years. In our lab, we have been studying the participation of mitochondrial ROS in the intracellular pathways triggered by the renin-angiotensin II-aldosterone system (RAAS) in the myocardium during the past few years. We have demonstrated that acute activation of cardiac RAAS induces mitochondrial ATP-dependent potassium channel (mitoK_ATP) opening with the consequent enhanced production of mitochondrial ROS. These oxidant molecules, in turn, activate membrane transporters, as sodium/hydrogen exchanger (NHE-1) and sodium/bicarbonate cotransporter (NBC) via the stimulation of the ROS-sensitive MAPK cascade. The stimulation of such effectors leads to an increase in cardiac contractility. In addition, it is feasible to suggest that a sustained enhanced production of mitochondrial ROS induced by chronic cardiac RAAS, and hence, chronic NHE-1 and NBC stimulation, would also result in the development of cardiac hypertrophy.

Mitochondrial K+ channels are involved in ischemic postconditioning in rat hearts

The mitochondrial calcium-activated potassium channel (mitoK(Ca)) and the mitochondrial ATP-sensitive potassium channel (mitoK(ATP)) are both involved in cardiac preconditioning. Here, we examined whether these two channels are also involved in ischemic or pharmacological postconditioning. Using Langendorff perfusion, rat hearts were made hypoxic for 45 min and then reoxygenated for 30 min. Ischemic postconditioning (IPT) was achieved through application of 3 cycles of 10 s of reperfusion and 10 s of ischemia before reoxygenation, with and without paxilline (Pax; a mitoK(Ca) blocker) or 5-hydroxydecanoate (5-HD; a mitoK(ATP) blocker). Pharmacological postconditioning was carried out for 5 min at the onset of reoxygenation using NS1619 (a mitoK(Ca) opener) or diazoxide (Dia; a mitoK(ATP) opener). Pax and 5-HD abolished IPT-induced cardioprotection from reoxygenation injury, whereas administration of NS1619 or Dia significantly improved cardiac contractile activity and reduced aspartate aminotransferase (an index of myocyte injury) release following reoxygenation. In addition, isolated rat myocytes were loaded with tetramethylrhodamine methyl ester (TMRE; fluorescent mitochondrial membrane potential indicator) and 2',7'-dichlorofluorescein [DCFH; fluorescent reactive oxygen species (ROS) indicator] or Fluo-4-acetoxymethyl ester (Fluo-4-AM; fluorescent calcium indicator). When TMRE-loaded myocytes were laser illuminated, the DCFH and Fluo-4 fluorescence increased, and TMRE fluorescence decreased. These effects were significantly inhibited by NS1619 and Dia. We therefore conclude that IPT may protect the heart through activation of mitoK(ATP) and mitoK(Ca) channels, and that opening of these channels at the onset of reoxygenation protects the heart from reoxygenation injury, most likely by reducing excess generation of ROS and the resultant Ca(2+) overload.

Mineralocorticoid receptor activation is crucial in the signalling pathway leading to the Anrep effect

The increase in myocardial reactive oxygen species after epidermal growth factor receptor transactivation is a crucial step in the autocrine/paracrine angiotensin II/endothelin receptor activation leading to the slow force response to stretch (SFR). Since experimental evidence suggests a link between angiotensin II or its AT1 receptor and the mineralocorticoid receptor (MR), and MR transactivates the epidermal growth factor receptor, we thought to determine whether MR activation participates in the SFR development in rat myocardium. We show here that MR activation is necessary to promote reactive oxygen species formation by a physiological concentration of angiotensin II (1 nmol l(-1)), since an increase in superoxide anion formation of ~50% of basal was suppressed by blocking MR with spironolactone or eplerenone. This effect was also suppressed by blocking AT1, endothelin (type A) or epidermal growth factor receptors, by inhibiting NADPH oxydase or by targeting mitochondria, and was unaffected by glucocorticoid receptor inhibition. All interventions except AT1 receptor blockade blunted the increase in superoxide anion promoted by an equipotent dose of endothelin-1 (1 nmol l(-1)) confirming that endothelin receptors activation is downstream of AT1. Similarly, an increase in superoxide anion promoted by an equipotent dose of aldosterone (10 nmol l(-1)) was blocked by spironolactone or eplerenone, by preventing epidermal growth factor receptor transactivation, but not by inhibiting glucocorticoid receptors or protein synthesis, suggesting non-genomic MR effects. Combination of aldosterone plus endothelin-1 did not increase superoxide anion formation more than each agonist separately. We found that aldosterone increased phosphorylation of the redox-sensitive kinases ERK1/2-p90RSK and the NHE-1, effects that were eliminated by eplerenone or by preventing epidermal growth factor receptor transactivation. Finally, we provide evidence that the SFR is suppressed by MR blockade, by preventing epidermal growth factor receptor transactivation or by scavenging reactive oxygen species, but it is unaffected by glucocorticoid receptor blockade or protein synthesis inhibition. Our results suggest that MR activation is a necessary step in the stretch-triggered reactive oxygen species-mediated activation of redox-sensitive kinases upstream NHE-1.

Oxidative stress and heart failure in altered thyroid States

Increased or reduced action of thyroid hormone on certain molecular pathways in the heart and vasculature causes relevant cardiovascular derangements. It is well established that hyperthyroidism induces a hyperdynamic cardiovascular state, which is associated with a faster heart rate, enhanced left ventricular systolic and diastolic function whereas hypothyroidism is characterized by the opposite changes. Hyperthyroidism and hypothyroidism represent opposite clinical conditions, albeit not mirror images. Recent experimental and clinical studies have suggested the involvement of ROS tissue damage under altered thyroid status. Altered-thyroid state-linked changes in heart modify their susceptibility to oxidants and the extent of the oxidative damage they suffer following oxidative challenge. Chronic increase in the cellular levels of ROS can lead to a catastrophic cycle of DNA damage, mitochondrial dysfunction, further ROS generation and cellular injury. Thus, these cellular events might play an important role in the development and progression of myocardial remodeling and heart failure in altered thyroid states (hypo- and hyper-thyroidism). The present review aims at elucidating the various signaling pathways mediated via ROS and their modulation under altered thyroid state and the possibility of antioxidant therapy.

Protective effects of early hypoxic post-conditioning in cultured cortical neurons

PRIMARY OBJECTIVE

Recent evidence suggests that delayed hypoxic post-conditioning is neuroprotective. The aim of the present study was to test whether early post-conditioning applied immediately after hypoxia could protect cultured neurons from hypoxia/reoxygenation (H/R)-induced injuries.

METHODS

Primary cortical neuronal culture depleted of microglia was exposed to H/R. Post-conditioning started immediately after hypoxia and consisted of three cycles of 15-minutes of reoxygenation and 15-minutes of hypoxia. Cell viability assay was performed using Cell Counting Kit-8 (CCK-8). Apoptosis was evaluated by Hoechst 33258 staining, FITC-Annexin V/PI double staining and Western blot assay (testing the cleaved caspase-3 expression). Reactive oxygen species (ROS), intracellular Ca(2+) and mitochondrial membrane potential (MMP) were examined using confocal laser-scanning microscopy.

MAIN RESULTS

H/R significantly reduced cell viability and increased neuronal apoptosis and necrosis. Furthermore, the expression of cleaved caspase-3, ROS production and intracellular Ca(2+) were increased. MMP was attenuated. Injuries induced by H/R were substantially attenuated by early hypoxic post-conditioning. Changes in cleaved caspase-3 expression, ROS production, intracellular Ca(2+) level and MMP in response to H/R were significantly decreased by the post-conditioning.

CONCLUSIONS

The findings demonstrated that early hypoxic post-conditioning could protect neurons against H/R-induced injuries independent of microglial cells, possibly by inhibiting ROS over-production and intracellular Ca(2+) accumulation and maintaining MMP.

Regulation of blood pressure and salt homeostasis by endothelin

Endothelin (ET) peptides and their receptors are intimately involved in the physiological control of systemic blood pressure and body Na homeostasis, exerting these effects through alterations in a host of circulating and local factors. Hormonal systems affected by ET include natriuretic peptides, aldosterone, catecholamines, and angiotensin. ET also directly regulates cardiac output, central and peripheral nervous system activity, renal Na and water excretion, systemic vascular resistance, and venous capacitance. ET regulation of these systems is often complex, sometimes involving opposing actions depending on which receptor isoform is activated, which cells are affected, and what other prevailing factors exist. A detailed understanding of this system is important; disordered regulation of the ET system is strongly associated with hypertension and dysregulated extracellular fluid volume homeostasis. In addition, ET receptor antagonists are being increasingly used for the treatment of a variety of diseases; while demonstrating benefit, these agents also have adverse effects on fluid retention that may substantially limit their clinical utility. This review provides a detailed analysis of how the ET system is involved in the control of blood pressure and Na homeostasis, focusing primarily on physiological regulation with some discussion of the role of the ET system in hypertension.

Ocimum gratissimum Aqueous Extract Protects H9c2 Myocardiac Cells from H(2)O(2)-Induced Cell Apoptosis through Akt Signalling

Increased cell death of cardiomyocyte by oxidative stress is known to cause dysfunction of the heart. O. gratissimum is one of the more well-known medicinal plants among the Ocimum species and widely used in treatment of inflammatory diseases. In this study, we hypothesized that aqueous extract of O. gratissimum leaf (OGE) may protect myocardiac cell H9c2 from oxidative injury by hydrogen peroxide (H₂O₂). Our results revealed that OGE pretreatment dose-dependently protects H9c2 cells from cell death when exposed to H₂O₂. Additionally, DNA condensation induced by H₂O₂ was also reduced by OGE pretreatment, suggesting that Ocimum gratissimum extract may attenuate H₂O₂-induced chromosome damage. Further investigation showed that OGE pretreatment inhibited H₂O₂-induced activation of caspase-3 and caspase-9, as well as H₂O₂-induced upregulation of proapoptotic Apaf-1 and the release of cytosolic cytochrome c, but has little effect on the activation of caspase-8. Additionally, OGE pretreatment significantly upregulated Bcl-2 expression and Akt phosphorylation, and slightly affected the phosphorylation of mitogen-activated protein kinases including p38 MAPK and JNK. Taken together, our findings revealed that Ocimum gratissimum extract effectively inhibited the mitochondrial pathway and upregulated Bcl-2 expression, which may be important in protecting H9c2 cells from H₂O₂-induced cell death.

Sustained intracellular acidosis activates the myocardial Na(+)/H(+) exchanger independent of amino acid Ser(703) and p90(rsk)

The mammalian Na(+)/H(+) exchanger isoform 1 (NHE1) is a ubiquitously expressed pH-regulatory membrane protein that functions in the myocardium and other tissues. It is an important mediator of the myocardial damage that occurs after ischemia-reperfusion injury and is implicated in heart hypertrophy. Regulation of NHE1 has been proposed as a therapeutic target for cardioprotection. We therefore examined mechanisms of control of NHE1 in the myocardium. Several different amino acids have been implicated as a being critical to NHE1 regulation in a number of tissues including Ser(703), Ser(770), and Ser(771). In the myocardium, NHE1 is activated in response to a variety of stimuli including activation by an ERK-dependent sustained intracellular acidosis. In this study, we determined whether Ser(703) and p90(rsk) activity are critical in activation of NHE1 by sustained intracellular acidosis. In vitro phosphorylation of NHE1 C-terminal fusion proteins determined that ERK-dependent phosphorylation of the cytoplasmic region was not dependent on Ser(703); however, phosphorylation by p90(rsk) required Ser(703). A Ser703Ala mutation decreased basal NHE1 activity in CHO cells but not in cardiomyocytes. NHE1 with a Ser703Ala mutation was activated in response to sustained intracellular acidosis in CHO cells. In addition, sustained intracellular acidosis also activated the Ser703Ala mutant protein in isolated cardiomyocytes and phosphorylation levels were also increased by acidosis. The presence of a dominant-negative p90(rsk) kinase also did not prevent activation and phosphorylation of NHE1 by sustained intracellular acidosis in isolated cardiomyocytes. We conclude that Ser(703) and p90(rsk) are not required for activation by sustained intracellular acidosis and that p90(rsk) phosphorylation of Ser(703) is independent of this type of activation.

The Na+/Ca2+ exchanger-mediated Ca2+ influx triggers nitric oxide-induced cytotoxicity in cultured astrocytes

Nitric oxide (NO) is involved in many pathological conditions including neurodegenerative disorders. We have previously found that sodium nitroprusside (SNP), an NO donor, stimulates mitogen-activated protein kinases (MAPKs) such as extracellular signal-regulating kinase (ERK), c-jun N-terminal protein kinase (JNK) and p38 MAPK, leading to caspase-independent apoptosis in cultured astrocytes. In view of the previous observation that NO stimulates the activity of the Na(+)/Ca(2+) exchanger (NCX), this study examines the involvement of NCX in cytotoxicity. The specific NCX inhibitor SEA0400 blocked SNP-induced phosphorylation of ERK, JNK and p38 MAPK, and decrease in cell viability. SNP-induced phosphorylation of ERK, JNK and p38 MAPK was blocked by removal of external Ca(2+), and SNP treatment caused an increase in (45)Ca(2+) influx. This increase in (45)Ca(2+) influx was blocked by SEA0400, but not the Ca(2+) channel blocker nifedipine. In addition, SNP-induced (45)Ca(2+) influx and cytotoxicity were reduced in NCX1-deficient cells which were transfected with NCX1 siRNA. Inhibitors of intracellular Ca(2+)-dependent proteins such as calpain and calmodulin blocked SNP-induced ERK phosphorylation and decrease in cell viability. Furthermore, the guanylate cyclase inhibitor LY83583 and the cGMP-dependent protein kinase inhibitor KT5823 blocked SNP-induced cytotoxicity. These findings suggest that NCX-mediated Ca(2+) influx triggers SNP-induced apoptosis in astrocytes, which may be mediated by a cGMP-dependent pathway.

Neuroprotectin D1 induces dephosphorylation of Bcl-xL in a PP2A-dependent manner during oxidative stress and promotes retinal pigment epithelial cell survival

Retinal pigment epithelial (RPE) cell integrity is critical for the survival of photoreceptor cells. Bcl-x(L) is a major anti-apoptotic Bcl-2 protein required for RPE cell survival, and phosphorylation of Bcl-x(L) at residue Ser-62 renders this protein pro-apoptotic. In this study, we identify serine/threonine protein phosphatase 2A (PP2A) as a key regulator of Bcl-x(L) phosphorylation at residue Ser-62 in ARPE-19 cells, a spontaneously arising RPE cell line in which Bcl-x(L) is highly expressed. We found that either PP2A inhibitor okadaic acid or depletion of catalytic subunit alpha of PP2A (PP2A/Calpha) by small interfering RNA enhanced Bcl-x(L) phosphorylation when activated with hydrogen peroxide and tumor necrosis factor alpha-induced oxidative stress. Disruption of PP2A/Calpha exacerbated oxidative stress-induced apoptosis. PP2A/Calpha colocalized and interacted with S62Bcl-x(L) in cells stressed with H(2)O(2)/tumor necrosis factor alpha. By contrast, the omega-3 fatty acid docosahexaenoic acid derivative, neuroprotectin D1 (NPD1), a potent activator of survival signaling, down-regulated oxidative stress-induced phosphorylation of Bcl-x(L) by increasing protein phosphatase activity. NPD1 also attenuated the oxidative stress-induced apoptosis by knockdown of PP2A/Calpha and increased the association of PP2A/Calpha with S62Bcl-x(L) as well as total Bcl-x(L). NPD1 also enhanced the heterodimerization of Bcl-x(L) with its counterpart, pro-apoptotic protein Bax. Thus, NPD1 modulates the activation of this Bcl-2 family protein by dephosphorylating in a PP2A-dependent manner, suggesting a coordinated, NPD1-mediated regulation of cell survival in response to oxidative stress.

The Anrep effect requires transactivation of the epidermal growth factor receptor

Myocardial stretch elicits a biphasic contractile response: the Frank-Starling mechanism followed by the slow force response (SFR) or Anrep effect. In this study we hypothesized that the SFR depends on epidermal growth factor receptor (EGFR) transactivation after the myocardial stretch-induced angiotensin II (Ang II)/endothelin (ET) release. Experiments were performed in isolated cat papillary muscles stretched from 92 to 98% of the length at which maximal twitch force was developed (L(max)). The SFR was 123 +/- 1% of the immediate rapid phase (n = 6, P < 0.05) and was blunted by preventing EGFR transactivation with the Src-kinase inhibitor PP1 (99 +/- 2%, n = 4), matrix metalloproteinase inhibitor MMPI (108 +/- 4%, n = 11), the EGFR blocker AG1478 (98 +/- 2%, n = 6) or the mitochondrial transition pore blocker clyclosporine (99 +/- 3%, n = 6). Stretch increased ERK1/2 phosphorylation by 196 +/- 17% of control (n = 7, P < 0.05), an effect that was prevented by PP1 (124 +/- 22%, n = 7) and AG1478 (131 +/- 17%, n = 4). In myocardial slices, Ang II (which enhances ET mRNA) or endothelin-1 (ET-1)-induced increase in O(2)() production (146 +/- 14%, n = 9, and 191 +/- 17%, n = 13, of control, respectively, P < 0.05) was cancelled by AG1478 (94 +/- 5%, n = 12, and 98 +/- 15%, n = 8, respectively) or PP1 (100 +/- 4%, n = 6, and 99 +/- 8%, n = 3, respectively). EGF increased O(2)() production by 149 +/- 4% of control (n = 9, P < 0.05), an effect cancelled by inhibiting NADPH oxidase with apocynin (110 +/- 6% n = 7), mKATP channels with 5-hydroxydecanoic acid (5-HD; 105 +/- 5%, n = 8), the respiratory chain with rotenone (110 +/- 7%, n = 7) or the mitochondrial permeability transition pore with cyclosporine (111 +/- 10%, n = 6). EGF increased ERK1/2 phosphorylation (136 +/- 8% of control, n = 9, P < 0.05), which was blunted by 5-HD (97 +/- 5%, n = 4), suggesting that ERK1/2 activation is downstream of mitochondrial oxidative stress. Finally, stretch increased Ser703 Na(+)/H(+) exchanger-1 (NHE-1) phosphorylation by 172 +/- 24% of control (n = 4, P < 0.05), an effect that was cancelled by AG1478 (94 +/- 17%, n = 4). In conclusion, our data show for the first time that EGFR transactivation is crucial in the chain of events leading to the Anrep effect.

The role of signalling molecules on actin glutathionylation and protein carbonylation induced by cadmium in haemocytes of mussel Mytilus galloprovincialis (Lmk)

This study investigated the role of Na(+)/H(+) exchanger (NHE) and signalling molecules, such as cAMP, PKC, PI 3-kinase, and immune defence enzymes, NADPH oxidase and nitric oxide synthase, in the induction of protein glutathionylation and carbonylation in cadmium-treated haemocytes of mussel Mytilus galloprovincialis. Glutathionylation was detected by western blot analysis and showed actin as its main target. A significant increase of both actin glutathionylation and protein carbonylation, were observed in haemocytes exposed to micromolar concentration of cadmium chloride (5 micromol l(-1)). Cadmium seems to cause actin polymerization that may lead to its increased glutathionylation, probably to protect it from cadmium-induced oxidative stress. It is therefore possible that polymerization of actin plays a signalling role in the induction of both glutathionylation and carbonylation processes. NHE seems to play a regulatory role in the induction of oxidative damage and actin glutathionylation, since its inhibition by 2 micromol l(-1) cariporide, significantly diminished cadmium effects in each case. Similarly, attenuation of cadmium effects were observed in cells pre-treated with either 11 micromol l(-1) GF-109203X, a potent inhibitor of PKC, 50 nmol l(-1) wortmannin, an inhibitor of PI 3-kinase, 0.01 mmol l(-1) forskolin, an adenylyl cyclase activator, 10 micromol l(-1) DPI, a NADPH oxidase inhibitor, or 10 micromol l(-1) L-NAME, a nitric oxide synthase inhibitor, suggesting a possible role of PKC, PI 3-kinase and cAMP, as well as NADPH oxidase and nitric oxide synthase in the enhancement of cadmium effects on both actin glutathionylation and protein carbonylation.

The antioxidant, taurine reduced lipopolysaccharide (LPS)-induced generation of ROS, and activation of MAPKs and Bax in cultured pneumocytes

Lipopolysaccharide (LPS) can cause damage to the epithelia of the respiratory tract. However, taurine can protect the lung tissue from such oxidant-induced inflammation. This study examined the effects of a LPS treatment on the intracellular calcium levels ([Ca(2+)]i) as well as the specific mechanisms of LPS-induced cell death in pneumocytes. In addition, the effects of taurine on the LPS-induced increase in the accumulation of reactive oxygen species (ROS) in pneumocytes were investigated. The [Ca(2+)]i in cultured pneumocytes was determined using microfluorescence techniques. The level of activation of the mitogen-activated protein kinases (MAPKs) and Bax protein were measured by Western blotting. LPS at 10 and 100 ng/ml induced cell death and decreased the viability of MRC-5 cells. Moreover, the intracellular Ca(2+) and ROS levels were increased by LPS. The LPS treatment led to the phosphorylation of ERK1/2, JNK and the activation of Bax. A pretreatment with 20 mM taurine reduced the LPS-induced production of ROS and MARK activity. These results show that a LPS treatment induces cell death in MRC-5 cells by increasing the intracellular ROS and Ca(2+) levels. The increase in the intracellular level of ROS promotes MAPKs activation and Bax translocation. Overall, LPS induces lung cell death by activating MAPKs. Furthermore, taurine decreased the LPS-induced generation of ROS and activation of MAPK and Bax.

Phenylephrine and sustained acidosis activate the neonatal rat cardiomyocyte Na+/H+ exchanger through phosphorylation of amino acids Ser770 and Ser771

The mammalian Na(+)/H(+) exchanger isoform 1 (NHE1) is a ubiquitously expressed membrane protein that regulates intracellular pH in the myocardium. NHE1 is also important in mediating myocardial hypertrophy, and the blockage of NHE1 activity prevents hypertrophy and reduces ischemia-reperfusion injury in animal models. We recently demonstrated that extracellular-regulated kinase (ERK)-mediated activation of NHE1 occurs during ischemia-reperfusion of the myocardium. To understand the regulation of NHE1 in the myocardium by phosphorylation, we expressed a series of adenoviruses that express wild-type and mutant cDNA for NHE1. All exogenous cDNA for NHE1 had additional mutations [Leu(163)Phe/Gly(174)Ser], which increases NHE1 resistance to EMD-87580 (a specific blocker of NHE1) 100-fold, and allowed the measurement of exogenous NHE1 while inhibiting endogenous NHE1. By examining the effects of a series of mutations of the NHE1 cytosolic region, we determined that the amino acids Ser(770) and Ser(771) were essential for the acute activation of NHE1 activity in rat cardiomyocytes. The specific mutation of either residue prevented the rapid activation of exchanger activity by a sustained intracellular acidosis through ERK-dependent pathways. The same amino acids were critical to phenylephrine-mediated, ERK-dependent activation of NHE1 activity and increased the phosphorylation in intact rat cardiomyocytes. The results demonstrate that both sustained intracellular acidosis and phenylephrine rapidly activate the NHE1 protein in intact cardiac cells through ERK-dependent pathways that act on a common pathway mediated by amino acids Ser(770) and Ser(771) of the cytosolic tail of the protein.

Characterization of cytotoxicity induced by arsenic trioxide (a potent anti-APL drug) in rat cardiac myocytes

Arsenic, a known environmental toxicant, is ubiquitously present in the environment. Arsenic trioxide (ATO), an anti-acute promyelocytic leukemia (APL) drug, is associated with cardiac toxicity. It is reported to induce cardiac arrhythmia via altering various ion channels involved in the repolarization phase of cardiac action potential. The exact molecular mechanism of cardiovascular adverse effect due to ATO exposure has not been fully elucidated except for alteration on ion channels. To evaluate the cytotoxic effect of ATO on cardiac myocytes, primary culture of myocytes was treated with different doses (30, 60 and 90 microM) of ATO for various periods (24, 48 and 72 h). Cardiac toxicity was assessed by monitoring cell viability, mitochondrial and deoxyribonucleic acid (DNA) integrity, reactive oxygen species (ROS) generation, calcium overload and apoptosis. ATO exposure caused alteration in mitochondrial integrity, generation of ROS, calcium overload and apoptosis in cardiac cells in dose- and duration-dependent manner. There was no DNA fragmentation. Hence our results show that ATO causes apoptosis in cardiomyocytes by generation of ROS and the induction of calcium overload.

SERPINA3K prevents oxidative stress induced necrotic cell death by inhibiting calcium overload

Background

SERPINA3K, an extracellular serine proteinase inhibitor (serpin), has been shown to have decreased levels in the retinas of diabetic rats, which may contribute to diabetic retinopathy. The function of SERPINA3K in the retina has not been investigated.

Methodology/Principal Findings

The present study identified a novel function of SERPINA3K, i.e. it protects retinal cells against oxidative stress-induced cell death including retinal neuronal cells and Müller cells. Flow-cytometry showed that the protective effect of SERPINA3K on Müller cells is via reducing oxidation-induced necrosis. Measurements of intracellular calcium concentration showed that SERPINA3K prevented the intracellular calcium overload induced by H₂O₂. A similar protective effect was observed using a calcium chelator (BAPTA/AM). Further, SERPINA3K inhibited the phosphorylation of phospholipase C (PLC)-gamma1 induced by H₂O₂. Likewise, a specific PLC inhibitor showed similar protective effects on Müller cells exposed to H₂O₂. Furthermore, the protective effect of SERPINA3K was attenuated by a specific PLC activator (m-3M3FBS). Finally, in a binding assay, SERPINA3K displayed saturable and specific binding on Müller cells.

Conclusion/Significance

These results for the first time demonstrate that SERPINA3K is an endogenous serpin which protects cells from oxidative stress-induced cells death, and its protective effect is via blocking the calcium overload through the PLC pathway. The decreased retinal levels of SERPINA3K may represent a new pathogenic mechanism for the retinal Müller cell dysfunction and neuron loss in diabetes.

Amiloride inhibits hydrogen peroxide-induced Ca2+ responses in human CNS pericytes

The aims of the present study were to investigate the mechanisms of Ca(2+) signaling caused by hydrogen peroxide in CNS pericytes. In cultured human brain microvascular pericytes, cytosolic Ca(2+) concentration was measured by means of fura-2 fluorescence. Reverse transcription and polymerase chain reaction was performed to examine the expression of mRNA. Knockdown of Na(+)/H(+) exchanger (NHE) was done by transfecting the cells with specific double-strand siRNAs for NHE. Externally applied hydrogen peroxide dose-dependently (100 microM-10 mM) increased cytosolic Ca(2+) in human CNS pericytes. Cytosolic Ca(2+) remained high after wash-out of hydrogen peroxide. However, the addition of dithiothreitol rapidly reversed cytosolic Ca(2+) to the resting level. The hydrogen peroxide-induced Ca(2+) increase was not inhibited by nicardipine, Gd(3+), La(3+), or omission of external Ca(2+). Neither thapsigargin nor carbonyl cyanide 4-trifluoromethoxyphenylhydrazone attenuated the hydrogen peroxide-induced Ca(2+) rise. Amiloride and its derivatives, benzamil and hexamethylene amiloride reversed the hydrogen peroxide-induced Ca(2+) increase. Human CNS pericytes expressed acid sensing ion channel (ASIC) 1a, Na(+)/Ca(2+) exchanger (NCX) 1, Na(+)/H(+) exchanger (NHE) 1, and NHE7. However, the removal of external Na(+), treatment with KB-R 7943 and mibefradil, or knockdown of NHE1 and NHE7 did not affect the hydrogen peroxide-induced Ca(2+) increase. Hydrogen peroxide releases Ca(2+) from intracellular Ca(2+) pool via an amiloride-sensitive protein, which is controlled by oxidation of thiol group in human CNS pericytes.

Enhanced Na+/H+ exchange during ischemia and reperfusion impairs mitochondrial bioenergetics and myocardial function

Inhibition of Na+/H+ exchange (NHE) during ischemia reduces cardiac injury due to reduced reverse mode Na+/Ca2+ exchange. We hypothesized that activating NHE-1 at buffer pH 8 during ischemia increases mitochondrial oxidation, Ca2+ overload, and reactive O2 species (ROS) levels and worsens functional recovery in isolated hearts and that NHE inhibition reverses these effects. Guinea pig hearts were perfused with buffer at pH 7.4 (control) or pH 8 +/- NHE inhibitor eniporide for 10 minutes before and for 10 minutes after 35- minute ischemia and then for 110 minutes with pH 7.4 buffer alone. Mitochondrial NADH and FAD, [Ca2+], and superoxide were measured by spectrophotofluorometry. NADH and FAD were more oxidized, and cardiac function was worse throughout reperfusion after pH 8 versus pH 7.4, Ca2+ overload was greater at 10-minute reperfusion, and superoxide generation was higher at 30-minute reperfusion. The pH 7.4 and eniporide groups exhibited similar mitochondrial function, and cardiac performance was most improved after pH 7.4+eniporide. Cardiac function on reperfusion after pH 8+eniporide was better than after pH 8. Percent infarction was largest after pH 8 and smallest after pH 7.4+eniporide. Activation of NHE with pH 8 buffer and the subsequent decline in redox state with greater ROS and Ca2+ loading underlie the poor functional recovery after ischemia and reperfusion.

Oxidative stress and left ventricular remodelling after myocardial infarction

In acute myocardial infarction (MI), reactive oxygen species (ROS) are generated in the ischaemic myocardium especially after reperfusion. ROS directly injure the cell membrane and cause cell death. However, ROS also stimulate signal transduction to elaborate inflammatory cytokines, e.g. tumour necrosis factor-alpha (TNF-alpha), interleukin (IL)-1beta and -6, in the ischaemic region and surrounding myocardium as a host reaction. Inflammatory cytokines also regulate cell survival and cell death in the chain reaction with ROS. Both ROS and inflammatory cytokines are cardiodepressant mainly due to impairment of intracellular Ca(2+) homeostasis. Inflammatory cytokines stimulate apoptosis through a TNF-alpha receptor/caspase pathway, whereas Ca(2+) overload induced by extensive ROS generation causes necrosis through enhanced permeability of the mitochondrial membrane (mitochondrial permeability transition). Apoptosis signal-regulating kinase-1 (ASK1) is an ROS-sensitive, mitogen-activated protein kinase kinase kinase that is activated by many stress signals and can activate nuclear factor kappaB and other transcription factors. ASK1-deficient mice demonstrate that the ROS/ASK1 pathway is involved in necrotic as well as apoptotic cell death, indicating that ASK1 may be a therapeutic target to reduce left ventricular (LV) remodelling after MI. ROS and inflammatory cytokines activate matrix metalloproteinases which degrade extracellular matrix, causing a slippage of myofibrils and hence LV dilatation. Consequently, collagen deposition is increased and tissue repair is enhanced with myocardial fibrosis and angiogenesis. Since the extent of LV remodelling is a major predictor of prognosis of the patients with MI, the therapeutic approach to attenuating LV remodelling is critically important.

Role of Fyn and PI3K in H2O2-induced inhibition of apical Cl-/OH- exchange activity in human intestinal epithelial cells

H(2)O(2) is a highly reactive oxygen metabolite that has been implicated as an important mediator of inflammation-induced intestinal injury associated with ischaemia/reperfusion, radiation and inflammatory bowel disease. Previous studies have shown that H(2)O(2) inhibits NaCl absorption and activates Cl(-) secretion in the rat and rabbit colon. To date, however, almost no information is available with respect to its effect on the human intestinal apical anion exchanger Cl(-)/OH(-) (HCO(3)(-)). The present studies were, therefore, undertaken to examine the direct effects of H(2)O(2) on OH(-) gradient-driven DIDS (4,4'-di-isothiocyanostilbene-2,2'-disulfonate)-sensitive (36)Cl(-) uptake utilizing a post-confluent transformed human intestinal epithelial cell line, Caco-2. Our results demonstrate that H(2)O(2) (1 mM for 60 min) significantly inhibited (approx. 60%; P<0.05) Cl(-)/OH(-) exchange activity in Caco-2 cells. H(2)O(2)-mediated inhibition of Cl(-)/OH(-) exchange activity involved the Src kinase Fyn and PI3K (phosphoinositide 3-kinase)-dependent pathways. H(2)O(2) also induced phosphorylation of Fyn and p85 (the regulatory subunit of PI3K) in Caco-2 cells. Moreover, an increased association of Fyn and p85 was observed in response to H(2)O(2), resulting in the activation of the downstream target PLCgamma1 (phospholipase Cgamma1). Elevated intracellular Ca(2+) levels and PKCalpha (protein kinase Calpha) functioned as downstream effectors of H(2)O(2)-induced PLCgamma1 activation. Our results, for the first time, provide evidence for H(2)O(2)-induced Src kinase Fyn/PI3K complex association. This complex association resulted in the subsequent activation of PLCgamma1 and Ca(2+)-dependent PKCalpha, resulting in the inhibition of Cl(-)/OH(-) exchange activity. These findings suggest that H(2)O(2)-induced inhibition of the Cl(-)/OH(-) exchange process may play an important role in the pathophysiology of diarrhoea associated with inflammatory disorders, where the amount of reactive oxygen species is markedly elevated.

Na+/H+ exchanger-1 inhibitors decrease myocardial superoxide production via direct mitochondrial action

The possibility of a direct mitochondrial action of Na(+)/H(+) exchanger-1 (NHE-1) inhibitors decreasing reactive oxygen species (ROS) production was assessed in cat myocardium. Angiotensin II and endothelin-1 induced an NADPH oxidase (NOX)-dependent increase in anion superoxide (O(2)(-)) production detected by chemiluminescence. Three different NHE-1 inhibitors [cariporide, BIIB-723, and EMD-87580] with no ROS scavenger activity prevented this increase. The mitochondria appeared to be the source of the NOX-dependent ROS released by the "ROS-induced ROS release mechanism" that was blunted by the mitochondrial ATP-sensitive potassium channel blockers 5-hydroxydecanoate and glibenclamide, inhibition of complex I of the electron transport chain with rotenone, and inhibition of the permeability transition pore (MPTP) by cyclosporin A. Cariporide also prevented O(2)(-) production induced by the opening of mK(ATP) with diazoxide. Ca(2+)-induced swelling was evaluated in isolated mitochondria as an indicator of MPTP formation. Cariporide decreased mitochondrial swelling to the same extent as cyclosporin A and bongkrekic acid, confirming its direct mitochondrial action. Increased O(2)(-) production, as expected, stimulated ERK1/2 and p90 ribosomal S6 kinase phosphorylation. This was also prevented by cariporide, giving additional support to the existence of a direct mitochondrial action of NHE-1 inhibitors in preventing ROS release. In conclusion, we report a mitochondrial action of NHE-1 inhibitors that should lead us to revisit or reinterpret previous landmark observations about their beneficial effect in several cardiac diseases, such as ischemia-reperfusion injury and cardiac hypertrophy and failure. Further studies are needed to clarify the precise mechanism and site of action of these drugs in blunting MPTP formation and ROS release.

H(2)O(2)-induced left ventricular dysfunction in isolated working rat hearts is independent of calcium accumulation

Reactive oxygen species (ROS) and intracellular Ca(2+) overload play key roles in myocardial ischemia-reperfusion (IR) injury but the relationships among ROS, Ca(2+) overload and LV mechanical dysfunction remain unclear. We tested the hypothesis that H(2)O(2) impairs LV function by causing Ca(2+) overload by increasing late sodium current (I(Na)), similar to Sea Anemone Toxin II (ATX-II). Diastolic and systolic Ca(2+) concentrations (d[Ca(2+)](i) and s[Ca(2+)](i)) were measured by indo-1 fluorescence simultaneously with LV work in isolated working rat hearts. H(2)O(2) (100 microM, 30 min) increased d[Ca(2+)](i) and s[Ca(2+)](i). LV work increased transiently then declined to 32% of baseline before recovering to 70%. ATX-II (12 nM, 30 min) caused greater increases in d[Ca(2+)](i) and s[Ca(2+)](i). LV work increased transiently before declining gradually to 17%. Ouabain (80 microM) exerted similar effects to ATX-II. Late I(Na) inhibitors, lidocaine (10 microM) or R56865 (2 microM), reduced effects of ATX-II on [Ca(2+)](i) and LV function, but did not alter effects of H(2)O(2). The antioxidant, N-(2-mercaptopropionyl)glycine (MPG, 1 mM) prevented H(2)O(2)-induced LV dysfunction, but did not alter [Ca(2+)](i). Paradoxically, further increases in [Ca(2+)](i) by ATX-II or ouabain, given 10 min after H(2)O(2), improved function. The failure of late I(Na) inhibitors to prevent H(2)O(2)-induced LV dysfunction, and the ability of MPG to prevent H(2)O(2)-induced LV dysfunction independent of changes in [Ca(2+)](i) indicate that impaired contractility is not due to Ca(2+) overload. The ability of further increases in [Ca(2+)](i) to reverse H(2)O(2)-induced LV dysfunction suggests that Ca(2+) desensitization is the predominant mechanism of ROS-induced contractile dysfunction.