Sodium-hydrogen exchange inhibition by cariporide to reduce the risk of ischemic cardiac events in patients undergoing coronary artery bypass grafting: results of the EXPEDITION study

A recombinant human neuregulin-1 peptide improves preservation of the rodent heart after prolonged hypothermic storage

BACKGROUND

Donor hearts are subjected to ischemia-reperfusion injury during transplantation. Recombinant human neuregulin (rhNRG)-1 peptide attenuates myocardial injury in various animal models of cardiomyopathy. Supplementing the organ-storage solution, Celsior (C), with glyceryl trinitrate (GTN) and cariporide improves cardiac preservation after hypothermic storage. We hypothesized that the addition of rhNRG-1 to C would improve cardiac preservation after hypothermic storage and provide incremental benefit in combination with GTN and cariporide.

METHODS

An isolated working rat heart model was used. To assess the effect of rhNRG-1, hearts were stored for 6 hr at 4°C in C ± rhNRG-1 (14 nM). To assess the effect of using a combination of prosurvival kinase activators on cardiac preservation, the ischemic storage time was extended to 10 hr and hearts stored in C ± rhNRG-1 (14 nM) ± GTN (0.1 mg/mL) ± Cariporide (10 μM). Hearts were subsequently reperfused, cardiac function remeasured, and tissue collected for protein analysis and immunohistochemistry. Optimal timing of rhNRG-1 administration was also assessed.

RESULTS

rhNRG-1 supplemented C improved functional recovery after 6 hr of storage (cardiac output recovery [mean ± SEM]: control 1.4% ± 0.6%; rhNRG-1+C 21.1% ± 7.9%; P<0.05). After 10-hr storage, no improvement in functional recovery was observed with rhNRG-1, GTN, or cariporide alone; however, GTN combined with cariporide did improve recovery (P<0.01), which was further enhanced by the addition of rhNRG-1 (P<0.01). Functional improvements were accompanied by increased phosphorylation of Akt, ERK1/2, STAT3, and GSK-3β and reduced cleaved caspase-3 (P<0.01).

CONCLUSIONS

rhNRG-1 given together with other activators of prosurvival pathways improves preservation of the rat heart and shows promise for increasing the cold-ischemic life of donor hearts in transplantation.

Disruption of chronic cariporide treatment abrogates myocardial ion homeostasis during acute ischemia reperfusion

Cariporide, an Na/H exchanger inhibitor, is a drug with cardioprotective properties. However, chronic treatment with cariporide may modify the protein phenotype of the cardiomyocytes. Disruption of the equilibrium between a cariporide-modified phenotype and the supply of cariporide could be deleterious. The aim of this study was to test the effects of this equilibrium rupture (EqR) on cardiac function at baseline and acute ischemia reperfusion. Rats were chronically treated with cariporide (2.5 mg·kg·d) or with placebo for 21 days, after which isolated Langendorff-mode heart perfusion experiments utilized cariporide-free buffer. During this type of perfusion, the drug is rapidly cleared from the cellular environment. After 30 minutes of stabilization, the hearts were subjected to global zero-flow ischemia (25 minutes) followed by reperfusion (45 minutes). Measures of mechanical function, oxygen consumption, lactate plus pyruvate, CO2 and proton release into the coronary effluent were determined. The gene and protein expression of proton extruders was also evaluated. Chronic cariporide administration followed by EqR reduced the expression of the Na/H exchanger, increased the expression of the HCO3 or Na exchanger, decreased monocarboxylate/H carrier expression, reduced the lactate plus pyruvate release but did not change the glucose oxidation rate and mechanical function compared with baseline conditions. The resulting low glycolytic rate was associated with a stronger contracture during ischemia. During reperfusion, the early release of acidic forms was higher and redirected toward the use of the Na/H and HCO3 /Na exchangers to the detriment of the safe monocarboxylate/H carrier. Both phenomena were assumed to increase the Na uptake and activate the Na/Ca exchanger, resulting in Na and Ca overload and further cellular damage. This explains the impaired recovery of the contractile function observed in the EqR group during reperfusion. In conclusion, although cariporide is usually cardioprotective, a disruption of its chronic treatment followed by an ischemia/reperfusion event can become deleterious.

Resuscitation after prolonged cardiac arrest: effects of cardiopulmonary bypass and sodium-hydrogen exchange inhibition on myocardial and neurological recovery

OBJECTIVE

To determine if cardiopulmonary bypass (CPB), together with inhibition of the sodium-hydrogen exchanger (NHE), limits myocardial and neurological injury and improves recovery after prolonged (unwitnessed) cardiac arrest (CA), as NHE inhibition improved recovery after deep hypothermic circulatory arrest.

METHODS

Twenty-seven pigs (31-39 kg) underwent 15 min of prolonged (no-flow) CA followed by 10 min of cardiopulmonary resuscitation-advanced life support (CPR-ALS). Subjects with restoration of spontaneous circulation (ROSC) during CPR-ALS received either no drug (n=6) or an inhibitor of the NHE (HOE-642; n=5). In the 16 unsuccessfully resuscitated animals, peripheral normothermic CPB was instituted, and either no drug (n=9) or similar HOE-642 (n=7) therapy started. Hemodynamic data, a species-specific neurological deficit score (0=normal to 500=brain death), and mortality were recorded at 24h, and biochemical variables of organ injury measured.

RESULTS

CPR-ALS restored ROSC in 41% (11/27) of animals, but was unsuccessful in 59% (16/27) that required CPB. Without CPB, HOE-642 increased cardiac index and decreased vascular resistance; with CPB, HOE-642 caused higher pump flows (3.4±0.6 l min(-1)m(-2) vs 2.5±0.7 l min(-1)m(-2); p<0.001) and higher post-arrest cardiac index; but animals required more vasopressors (p=0.019) from drug-induced vasodilation. No differences between biochemical markers of oxidative and organ injury and overall 24-h mortality (20%) were found between groups. Neurological score was improved at 24h compared with 4h only after HOE-642 treatment with (150±34 vs 220±43; p=0.003) or without CPB (162±39 vs 238±48; p≤0.001), but failed to reach statistical difference with respect to the untreated group.

CONCLUSIONS

CPB is an effective resuscitative tool to treat prolonged CA but there is limited improvement of neurological function. NHE inhibition augments cardiac and neurological function, but its effect was less pronounced than in other studies.

KATP channel blocker does not abolish the protective effect of Na+/H+ exchange 1 inhibition against ischaemia/reperfusion in aged myocardium

BACKGROUND AND OBJECTIVE

Ageing is associated with an increase in myocardial susceptibility to ischaemia/reperfusion (I/R) injury. Na+/H+ exchange (NHE) inhibition and anaesthetic preconditioning (APC) are shown to protect myocardium from I/R injury. We set out to investigate whether NHE inhibition can induce protection against I/R injury and whether KATP channel inhibition can enhance this effect in aged rat myocardium.

METHODS

Hearts from 24-month-old rats were assigned to four groups: control group; APC group perfused with 2.5% sevoflurane before ischaemia; HOE group perfused with (3-methylsulfonyl-4-piperidinobenzoyl) guanidine methanesulfonate (HOE-694) prior to ischaemia; and HOE+5HD group perfused with both HOE and 5-hydroxydecanoic acid before ischaemia. We measured intracellular Na+ and Ca++ to quantitate the severity of myocardial injury.

RESULTS

Both intracellular Na+ and Ca++ were significantly increased at the end of ischaemia and both were attenuated by NHE inhibition. Intracellular Na+ was 134 +/- 12 mEq kg(-1) dry weight in control group and 55 +/- 7 in HOE group (P < 0.05). Intracellular Ca++ was 1764 +/- 142 nmol l(-1) in control group and 694 +/- 213 in HOE group (P < 0.05). Infarct size was measured at 28 +/- 4% in control group vs. 17 +/- 2% in HOE group (P < 0.05). High-energy phosphates and myocardial function were better preserved in HOE group compared with control (P < 0.05). The beneficial effect of HOE on myocardial preservation was not blocked by 5HD nor were there any differences between APC and control groups.

CONCLUSION

NHE inhibition was effective in protecting myocardium from I/R injury in aged rats, whereas APC was not. 5HD failed to block the protective effect of NHE inhibition.

Contribution of delayed intracellular pH recovery to ischemic postconditioning protection

Ischemic postconditioning (PoCo) has been proven to be a feasible approach to attenuate reperfusion injury and enhance myocardial salvage in patients with acute myocardial infarction, but its mechanisms have not been completely elucidated yet. Recent studies demonstrate that PoCo may delay the recovery of intracellular pH during initial reperfusion, and that its ability to limit infarct size critically depends on this effect. Prolongation of postischemic intracellular acidosis inhibits hypercontracture, mitochondrial permeability transition, calpain-mediated proteolysis, and gap junction-mediated spread of injury during the first minutes of reflow. This role of prolonged acidosis does not exclude the participation of other pathways in PoCo-induced cardioprotection. On the contrary, it may allow these pathways to act by preventing immediate reperfusion-induced cell death. Moreover, the existence of interactions between intracellular acidosis and endogenous protection signaling cannot be excluded and needs to be investigated. The role of prolonged acidosis in PoCo cardioprotection has important implications in the design of optimal PoCo protocols and in the translation of cardioprotective strategies to patients with on-going myocardial infarction receiving coronary reperfusion.

Silencing of cardiac mitochondrial NHE1 prevents mitochondrial permeability transition pore opening

Inhibition of Na(+)/H(+) exchanger 1 (NHE1) reduces cardiac ischemia-reperfusion (I/R) injury and also cardiac hypertrophy and failure. Although the mechanisms underlying these NHE1-mediated effects suggest delay of mitochondrial permeability transition pore (MPTP) opening, and reduction of mitochondrial-derived superoxide production, the possibility of NHE1 blockade targeting mitochondria has been incompletely explored. A short-hairpin RNA sequence mediating specific knock down of NHE1 expression was incorporated into a lentiviral vector (shRNA-NHE1) and transduced in the rat myocardium. NHE1 expression of mitochondrial lysates revealed that shRNA-NHE1 transductions reduced mitochondrial NHE1 (mNHE1) by ∼60%, supporting the expression of NHE1 in mitochondria membranes. Electron microscopy studies corroborate the presence of NHE1 in heart mitochondria. Immunostaining of rat cardiomyocytes also suggests colocalization of NHE1 with the mitochondrial marker cytochrome c oxidase. To examine the functional role of mNHE1, mitochondrial suspensions were exposed to increasing concentrations of CaCl(2) to induce MPTP opening and consequently mitochondrial swelling. shRNA-NHE1 transduction reduced CaCl(2)-induced mitochondrial swelling by 64 ± 4%. Whereas the NHE1 inhibitor HOE-642 (10 μM) decreased mitochondrial Ca(2+)-induced swelling in rats transduced with nonsilencing RNAi (37 ± 6%), no additional HOE-642 effects were detected in mitochondria from rats transduced with shRNA-NHE1. We have characterized the expression and function of NHE1 in rat heart mitochondria. Because mitochondria from rats injected with shRNA-NHE1 present a high threshold for MPTP formation, the beneficial effects of NHE1 inhibition in I/R resulting from mitochondrial targeting should be considered.

AVE4454B--a novel sodium-hydrogen exchanger isoform-1 inhibitor--compared less effective than cariporide for resuscitation from cardiac arrest

We compared the efficacy of the novel sodium-hydrogen exchanger (NHE-1) inhibitor AVE4454B with cariporide for resuscitation from ventricular fibrillation (VF) assessing the effects on left ventricular myocardial distensibility during chest compression, myocardial function after the return of spontaneous circulation, and survival. Three groups of 10 rats each were subjected to 10 min of untreated VF and resuscitation attempted by providing chest compression for up to 8 min with the depth of compression adjusted to attain an aortic diastolic pressure between 26 and 28 mmHg (to secure a coronary perfusion pressure above 20 mmHg) followed by electrical shocks. Rats received AVE4454B (1 mg/kg), cariporide (1 mg/kg), or vehicle control immediately before chest compression. We observed that NHE-1 inhibition (NHEI) preserved left ventricular myocardial distensibility during chest compression evidenced by less depth of compression required to attain the target aortic diastolic pressure corresponding to (mean ± standard deviation) 14.1 ± 1.1 mm in the AVE4454B group (P < 0.001 versus control), 15.0 ± 1.4 mm in the cariporide group (P < 0.01 versus control), and 17.0 ± 1.2 mm in controls. When the depth of compression was related to the coronary perfusion pressure generated-an index of left ventricular distensibility-only the cariporide group attained statistical significance. Postresuscitation, both compounds ameliorated myocardial dysfunction evidenced by lesser reductions in mean aortic pressure and the maximal rate of left ventricular pressure increase as well as earlier normalization of left ventricular end-diastolic pressure increases. This effect was associated with improved survival corresponding to 55% in the AVE4454B group (not significant) and 70% in the cariporide group (P < 0.01 versus control by Gehan-Breslow analysis) at 240 min postresuscitation. An inverse correlation was found between plasma cytochrome c and indices of left ventricular function at 240 min postresuscitation suggesting that NHEI exerts beneficial effects in part by attenuating mitochondrial injury. We conclude that cariporide is more effective than AVE4454B for resuscitation from cardiac arrest given its more prominent effect on preserving left ventricular myocardial distensibility and promoting survival.

Critical role of the STAT3 pathway in the cardioprotective efficacy of zoniporide in a model of myocardial preservation - the rat isolated working heart

BACKGROUND AND PURPOSE

Ischemia-reperfusion injury plays an important role in the development of primary allograft failure after heart transplantation. Inhibition of the Na+/H+ exchanger is one of the most promising therapeutic strategies for treating ischemia-reperfusion injury. Here we have characterized the cardioprotective efficacy of zoniporide and the underlying mechanisms in a model of myocardial preservation using rat isolated working hearts.

EXPERIMENTAL APPROACH

Rat isolated hearts subjected to 6 h hypothermic (1-4°C) storage followed by 45 min reperfusion at 37°C were treated with zoniporide at different concentrations and timing. Recovery of cardiac function, levels of total and phosphorylated protein kinase B, extracellular signal-regulated kinase 1/2, glycogen synthase kinase-3β and STAT3 as well as cleaved caspase 3 were measured at the end of reperfusion. Lactate dehydrogenase release into coronary effluent before and post-storage was also measured.

KEY RESULTS

Zoniporide concentration-dependently improved recovery of cardiac function after reperfusion. The functional recovery induced by zoniporide was accompanied by up-regulation of p-extracellular signal-regulated kinase 1/2 and p-STAT3, and by reduction in lactate dehydrogenase release and cleaved caspase 3. There were no significant differences in any of the above indices when zoniporide was administered before, during or after ischemia. The STAT3 inhibitor, stattic, abolished zoniporide-induced improvements in functional recovery and up-regulation of p-STAT3 after reperfusion.

CONCLUSIONS AND IMPLICATIONS

Zoniporide is a potent cardioprotective agent and activation of STAT3 plays a critical role in the cardioprotective action of zoniporide. This agent shows promise as a supplement to storage solutions to improve preservation of donor hearts.

Inhibiting the Na+/H+ exchanger reduces reperfusion injury: a small animal MRI study

We used magnetic resonance imaging (MRI) to assess the efficacy of Na+/H+ exchanger isoform 1 (NHE-1) inhibition following cerebral ischemia. Transient focal cerebral ischemia was induced in wild-type controls (NHE-1(+/+)), NHE-1 genetic knockdown mice (NHE-1(+/-)), and NHE-1(+/+) mice treated with the selective NHE-1 inhibitor HOE642. Diffusion weighted imaging (DWI) revealed a brain lesion as early as 1 hour following reperfusion and illustrated significant protection in NHE-1(+/-) mice (16.2 +/- 7.9 mm3 in NHE-1(+/-) mice vs. 47.5 +/- 16.6 mm3 in NHE-1(+/+) mice). Knockdown of NHE-1 showed significantly smaller infarct at 72 hours on T2 imaging (21.2 +/- 12.6 mm3 in NHE-1(+/-) mice vs. 64.6 +/- 2.5 mm3 in NHE-1(+/+) mice). Administration of HOE642 prior to reperfusion or during early reperfusion reduced ischemic damage. Thus, high resolution T2 images can be used for consistent and precise calculation of lesion volumes, while changes of DWI are a sensitive early marker of ischemic injury. The results of this study demonstrate the therapeutic potential for inhibition of NHE-1 in treating cerebral ischemia.

The acute administration of either amiloride or captopril does not prevent endothelial dysfunction induced by ischemia and reperfusion in the human forearm vasculature

Animal studies have demonstrated the ability of both sodium–hydrogen exchange inhibitors and angiotensin-converting enzyme inhibitors to reduce infarct size and preserve postischemic ventricular function following ischemia and reperfusion (IR) injury. Whether these interventions can also prevent IR-induced impairment of endothelial function in humans has not been investigated. We performed 2 separate double-blind, placebo-controlled, crossover studies. In the first study, 10 healthy volunteers were randomized to receive oral amiloride (10 mg) or a placebo. In a separate study, another group of volunteers (n = 10) was randomized to receive oral captopril (50 mg) or a placebo. At the time of the peak hemodynamic effect of the drug (3 and 1.5 h after administration of amiloride and captopril, respectively), endothelium-dependent, flow-mediated dilatation of the radial artery was measured before and after IR. IR significantly blunted flow-mediated dilatation in all groups (placebo: pre-IR: 6.8% ± 0.7%; post-IR: 2.9% ± 0.9%; P < 0.01; amiloride: pre-IR: 5.9% ± 0.6%; post-IR: 2.1% ± 1.3%; P = 0.01; captopril: pre-IR: 6.0% ± 0.5%; post-IR: 2.0% ± 0.6%; P < 0.01). In humans, neither 10 mg of oral amiloride nor 50 mg of oral captopril was able to provide protection against IR-induced endothelial dysfunction in the peripheral vasculature.

Involvement of signaling molecules on na/h exchanger-1 activity in human monocytes

Background:

Sodium/hydrogen exchanger-1 (NHE-1) contributes to maintaining intracellular pH (pHi). We assessed the effect of glucose, insulin, leptin and adrenaline on NHE-1 activity in human monocytes in vitro. These cells play a role in atherogenesis and disturbances in the hormones evaluated are associated with obesity and diabetes.

Methods and Results:

Monocytes were isolated from 16 healthy obese and 10 lean healthy subjects. NHE-1 activity was estimated by measuring pHi with a fluorescent dye. pHi was assessed pre- and post-incubation with glucose, insulin, leptin and adrenaline. Experiments were repeated after adding a NHE-1 inhibitor (cariporide) or an inhibitor of protein kinase C (PKC), nitric oxide synthase (NOS), nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, phosphoinositide 3-kinases (PI3K) or actin polymerization. Within the whole study population, glucose enhanced NHE-1 activity by a processes involving PKC, NOS, PI3K and actin polymerization (p = 0.0006 to 0.01). Insulin-mediated activation of NHE-1 (p = <0.0001 to 0.02) required the classical isoforms of PKC, NOS, NADPH oxidase and PI3K. Leptin increased NHE-1 activity (p = 0.0004 to 0.04) through the involvement of PKC and actin polymerization. Adrenaline activated NHE-1 (p = <0.0001 to 0.01) by a process involving the classical isoforms of PKC, NOS and actin polymerization. There were also some differences in responses when lean and obese subjects were compared. Incubation with cariporide attenuated the observed increase in NHE-1 activity.

Conclusions:

Selective inhibition of NHE-1 in monocytes could become a target for drug action in atherosclerotic vascular disease.

Translating novel strategies for cardioprotection: the Hatter Workshop Recommendations

Ischemic heart disease (IHD) is the leading cause of death worldwide. Novel cardioprotective strategies are therefore required to improve clinical outcomes in patients with IHD. Although a large number of novel cardioprotective strategies have been discovered in the research laboratory, their translation to the clinical setting has been largely disappointing. The reason for this failure can be attributed to a number of factors including the inadequacy of the animal ischemia–reperfusion injury models used in the preclinical cardioprotection studies and the inappropriate design and execution of the clinical cardioprotection studies. This important issue was the main topic of discussion of the UCL-Hatter Cardiovascular Institute 6th International Cardioprotection Workshop, the outcome of which has been published in this article as the “Hatter Workshop Recommendations”. These have been proposed to provide guidance on the design and execution of both preclinical and clinical cardioprotection studies in order to facilitate the translation of future novel cardioprotective strategies for patient benefit.

Pathogenesis of myocardial ischemia-reperfusion injury and rationale for therapy

Since the initial description of the phenomenon by Jennings et al 50 years ago, our understanding of the underlying mechanisms of reperfusion injury has grown significantly. Its pathogenesis reflects the confluence of multiple pathways, including ion channels, reactive oxygen species, inflammation, and endothelial dysfunction. The purposes of this review are to examine the current state of understanding of ischemia-reperfusion injury, as well as to highlight recent interventions aimed at this heretofore elusive target. In conclusion, despite its complexity our ongoing efforts to mitigate this form of injury should not be deterred, because nearly 2 million patients annually undergo either spontaneous (in the form of acute myocardial infarction) or iatrogenic (in the context of cardioplegic arrest) ischemia-reperfusion.

Na/H exchange inhibition protects newborn heart from ischemia/reperfusion injury by limiting Na+-dependent Ca2+ overload

The results of the Guardian/Expedition trials demonstrate the need for more precisely controlled studies to inhibit Na/H exchange (NHE1) during ischemia/reperfusion. This is because overwhelming evidence is consistent with the hypothesis that myocardial ischemic injury results in part from increases in intracellular Na (Nai) mediated by NHE1 that in turn promote Na/Ca exchanger-mediated increases in intracellular Ca ([Ca]i) and Ca-dependent cell damage. We used a more potent and specific NHE1 inhibitor HOE 694 (HOE) to test whether inhibition of NHE1 during ischemia limits increases in Nai and [Ca]i in newborns. NMR was used to measure pHi, Nai, [Ca]i, and ATP in isolated newborn rabbit hearts. Perfusion pressure, left ventricular developed pressure, and creatine kinase were measured. HOE was added before global ischemia. Results are reported as mean +/- SE. Nai (mEq/kg dry weight) rose from 11.6 +/- 0.9 before ischemia to 114.0 +/- 16.1 at the end of ischemia and recovered to 55.2 +/- 11.8 in the control group. During ischemia and reperfusion, the corresponding values for Nai in the HOE group (63.1 +/- 8.4 and 15.9 +/- 2.5, respectively, P < 0.05) were lower than control. In the control group [Ca]i (nM/L) rose from 331 +/- 41 to 1069 +/- 71 and recovered to 814 +/- 51, whereas in the HOE group [Ca]i rose less (P < 0.05): 359 +/- 50, 607 +/- 85, and 413 +/- 40, respectively. Total creatine kinase release was significantly reduced in the HOE group. Perfusion pressure and left ventricular developed pressure also recovered significantly better in the HOE group than in the control. In conclusion, NHE1 inhibition diminishes ischemia-induced increases in Nai and therefore [Ca], and thus diminishes myocardial injury in neonatal hearts.

NA+/H+ Exchanger 1-and Aquaporin-1-Dependent Hyperosmolarity Changes Decrease Nitric Oxide Production and Induce VCAM-1 Expression in Endothelial Cells Exposed to High Glucose

Since diabetic hyperglycaemia causes hyperosmolarity, we investigated the contribution of hyperosmolarity in the proinflammatory endothelial effects of hyperglycemia, and sought to unravel the mechanisms involved. Human aortic endothelial cells (HAEC) were incubated for short-term (1–3 days) or long-term (1–2 weeks) exposures to 5.5 mmol/L glucose (normoglycemia, basal), high glucose (25 and 45 mmol/L, HG), or a hyperosmolar control (mannitol 25 and 45 mmol/L, HM), in the presence or absence of the aquaporin-1 (AQP1) inihibitor dimethylsulfoxide (DMSO), the Na+/H+ exchanger 1 (NHE-1) inihibitor cariporide (CA), the protein kinase C (PKC) inihibitor calphostin C or the PKCβ isoform inhibitor LY379196 (LY). Both short- and long-term exposures to HG and HM decreased the expression of the active, phosphorylated form of endothelial nitric oxide synthase (Ser1146-eNOS) and, in parallel, increased vascular cell adhesion molecule(VCAM)-1 protein at immunoblotting. After 24 h incubation with HG/HM, we observed a significant similar and concentration-dependent enhancement of AQP1 expression. DMSO and CA inhibited hyperosmolarity-induced VCAM-1 expressions, while increasing nitrite levels and Ser1146-eNOS expression. Gene silencing by small interfering RNA reduced the expression of AQP1, and suppressed HG- and HM-stimulated VCAM-1 expression. Calphostin C and LY blunted hyperosmolarity-induced VCAM-1 expression, while increasing the expression of Ser1146-eNOS and nitrite production. Thus HG decreases eNOS activation and induces total VCAM-1 expression in HAEC through a hyperosmolar mechanism. These effects are mediated by activation of the water channels AQP1 and NHE-1, and a PKCβ-mediated intracellular signaling pathway. Targeting osmosignaling pathways may represent a novel strategy to reduce vascular effects of hyperglycemia.

Ion channels, transporters, and pumps as targets for heart failure therapy

Congestive heart failure is a leading cause of morbidity and mortality. Congestive heart failure is marked by atrial and ventricular enlargements and reduced cardiac contractility and an association with an increased incidence of atrial and ventricular arrhythmias and sudden cardiac death. Dysfunctional ion channel function is one of the major underlying mechanisms of the reduced contractility and arrhythmias. In this review, we explore the utility of ion channels, transporters, and pumps as targets for the treatment of heart failure, focusing predominantly on the treatment for reduced contractility and arrhythmias.

Emerging drugs for acute myocardial infarction

IMPORTANCE OF THE FIELD

The present review is aimed at going over the pharmacological profile (and the clinical impact) of the emerging drugs involved in the management of patients with ST-elevation myocardial infarction (STEMI) in order to provide the cardiologists who deal with these patients in the early phase with the most recent evidence on this topic.

AREAS COVERED IN THIS REVIEW

Anticoagulant and antiplatelet drugs are the main cornerstones of therapy in the treatment of STEMI patients undergoing primary percutaneous coronary intervention (PCI). The main issues that clinicians have to deal with are represented by balancing thrombotic and bleeding risks. In tailoring therapy, variables such as age, sex and previous disease should be taken into account, as well as ongoing complications (such as acute renal failure) that could affect hemostasis. Despite the well-established clinical benefits of antiplatelet agents, questions remain, mainly surrounding potential for variable platelet response, which are strictly related to non-genetic (i.e., diet, drug-drug interaction, clinical factors such as obesity, diabetes mellitus, and inflammation) and genetic determinants.

WHAT THE READER WILL GAIN

In their daily practice, cardiologists cannot abstract from the knowledge and updating on the ongoing research fields as well as the newly developed drugs, which they should frame in the very patient in the attempt to the develop a personalized medical strategy. These include also the pharmacological option(s) in the treatment of the reperfusion injury, the metabolic aspects and the stem cell therapy. TAKE HOME MASSAGE: In our opinion, the goal of ongoing research on the pharmacological approach to STEMI patients is a personalized medical strategy that relies on critical clinicians who merge newly developed acquisitions on this topic and a more complete, systemic and critical approach to the patient.

Targeting calcium transport in ischaemic heart disease

Ischaemic heart disease (IHD) is the leading cause of morbidity and mortality worldwide. While timely reperfusion of acutely ischaemic myocardium is essential for myocardial salvage, it leads to a unique type of injury known as 'myocardial ischaemia/reperfusion (I/R) injury'. Growing evidence suggests that a defect in myocardial Ca(2+) transport system with cytosolic Ca(2+) overload is a major contributor to myocardial I/R injury. Progress in molecular genetics and medicine in past years has clearly demonstrated that modulation of Ca(2+) handling pathways in IHD could be cardioprotective. The potential benefits of these strategies in limiting I/R injury are vast, and the time is right for challenging in vivo systemic work both at pre-clinical and clinical levels.

Combining cariporide with glyceryl trinitrate optimizes cardiac preservation during porcine heart transplantation

Sodium-hydrogen exchange inhibitors, such as cariporide, are potent cardioprotective agents, however, safety concerns have been raised about intravenously (i.v.) administered cariporide in humans. The aim of this study was to develop a preservation strategy that maintained cariporide's cardioprotective efficacy during heart transplantation while minimizing recipient exposure. We utilized a porcine model of orthotopic heart transplantation that incorporated donor brain death and 14 h static heart storage. Five groups were studied: control (CON), hearts stored in Celsior; CAR1, hearts stored in Celsior with donors and recipients receiving cariporide (2 mg/kg i.v.) prior to explantation and reperfusion, respectively; CAR2, hearts stored in Celsior supplemented with cariporide (10 mumol/L); GTN, hearts stored in Celsior supplemented with glyceryl trinitrate (GTN) (100 mg/L); and COMB, hearts stored in Celsior supplemented with cariporide (10 mumol/L) plus GTN (100 mg/L). A total of 5/5 CAR1 and 5/6 COMB recipients were weaned from cardiopulmonary bypass compared with 1/5 CON, 1/5 CAR2 and 0/5 GTN animals (p = 0.001). Hearts from the CAR1 and COMB groups demonstrated similar cardiac function and troponin release after transplantation. Supplementation of Celsior with cariporide plus GTN provided superior donor heart preservation to supplementation with either agent alone and equivalent preservation to that observed with systemic administration of cariporide to the donor and recipient.

Functional roles of bestrophins in ocular epithelia

There are four members of the bestrophin family of proteins in the human genome, of which two are known to be expressed in the eye. The gene BEST1 (formerly VMD2) which encodes the protein bestrophin-1 (Best1) was first identified in 1998. Mutations in this gene have now been associated with four clinically distinguishable human eye diseases, collectively referred to as "bestrophinopathies". Over the last decade, laboratories have sought to understand how Best1 mutations could result in eye diseases that range in presentation from macular degeneration to nanophthalmos. The majority of our knowledge comes from studies that have sought to understand how Best1 mutations or dysfunction could induce the classical symptoms of the most common of these diseases: Best vitelliform macular dystrophy (BVMD). BVMD is a dominant trait that is characterized electrophysiologically by a diminished electrooculogram light peak with a normal clinical electroretinogram. This together with the localization of Best1 to the retinal pigment epithelium (RPE) basolateral plasma membrane and data from heterologous expression studies, have led to the proposal that Best1 generates the light peak, and that bestrophins are a family of Ca(2+) activated Cl(-) channels (CaCCs). However, data from Best1 knock-out and knock-in mice, coupled with the recent discovery of a recessive bestrophinopathy suggest that Best1 does not generate the light peak. Recently Best2 was found to be expressed in non-pigmented epithelia in the ciliary body. However, aqueous dynamics in Best2 knock-out mice do not support a role for Best2 as a Cl(-) channel. Thus, the purported CaCC function of the bestrophins and how loss of this function relates to clinical disease needs to be reassessed. In this article, we examine data obtained from tissue-type and animal models and discuss the current state of bestrophin research, what roles Best1 and Best2 may play in ocular epithelia and ocular electrophysiology, and how perturbation of these functions may result in disease.

Na+/H+ exchanger mediates TNF-alpha-induced hepatocyte apoptosis via the calpain-dependent degradation of Bcl-xL

BACKGROUND AND AIM

It is well known that tumor necrosis factor-alpha (TNF-alpha) induces hepatocyte apoptosis and contributes to liver diseases. However, the exact mechanisms are not well understood.

METHODS

In the present study, we reported that Na(+)/H(+) exchanger (NHE) is involved in TNF-alpha-induced hepatocyte apoptosis.

RESULTS

TNF-alpha time dependently induced an increase in NHE activity in hepatocytes, but cariporide, an NHE inhibitor, blocked the TNF-alpha-induced increase of NHE activity in a dose-dependent manner. Increased NHE activity induced by TNF-alpha was associated with increased intracellular calcium (Ca(2+)(i)) concentration and calpain activity. Cariporide reversed these effects induced by TNF-alpha. In addition, TNF-alpha downregulated Bcl-xL, an anti-apoptotic protein, but not mRNA levels. The inhibition of either calpain or NHE blocked the TNF-alpha-induced decrease of the Bcl-xL protein. TNF-alpha did not change the pro-apoptotic Bax and Bak protein levels. Cariporide, calcium remover 1,2-bis (2-aminophenoxy) ethane-N,N,N0,N0-tetraacetic acid, or calpain inhibitor benzyloxycarbonyl-leucyl-leucinal attenuated TNF-alpha-induced hepatocyte apoptosis.

CONCLUSION

TNF-alpha via NHE results in hepatocyte apoptosis through the calcium/calpain/Bcl-xL pathway.

'Conditioning' the heart during surgery

Coronary heart disease (CHD) is the leading cause of death worldwide. Coronary artery bypass graft (CABG) surgery remains the procedure of choice for coronary artery revascularisation in a large number of patients with severe CHD. However, the profile of patients undergoing CABG surgery is changing with increasingly higher-risk patients being operated upon, resulting in significant morbidity and mortality in this patient group. Myocardial injury sustained during cardiac surgery, most of which can be attributed to acute myocardial ischaemia-reperfusion injury, is associated with worse short-term and long-term clinical outcomes. Clearly, new treatment strategies are required to protect the heart during cardiac surgery in terms of reducing myocardial injury and preserving left ventricular systolic function, such that clinical outcomes can be improved. 'Conditioning' the heart to harness its endogenous cardioprotective capabilities using either brief ischaemia or pharmacological agents, provides a potentially novel approach to myocardial protection during cardiac surgery, and is the subject of this review article.

HL-1 mouse cardiomyocyte injury and death after simulated ischemia and reperfusion: roles of pH, Ca2+-independent phospholipase A2, and Na+/H+ exchange

The Ca(2+)-independent phospholipase A(2) VI (iPLA(2)-VI) and the Na(+)/H(+) exchanger isoform 1 (NHE1) are highly pH-sensitive proteins that exert both protective and detrimental effects in cardiac ischemia-reperfusion. Here, we investigated the role of extracellular pH (pH(o)) in ischemia-reperfusion injury and death and in regulation and function of iPLA(2)-VI and NHE1 under these conditions. HL-1 cardiomyocytes were exposed to simulated ischemia (SI; 0.5% O(2), 8 mM K(+), and 20 mM lactate) at pH(o) 6.0 and 7.4, with or without 4 or 8 h of reperfusion (SI/R). Cytochrome c release and caspase-3 activation were reduced after acidic compared with neutral SI, whereas necrotic death, estimated as glucose-6-phosphate dehydrogenase release, was similar in the two conditions. Inhibition of iPLA(2)-VI activity by bromoenol lactone (BEL) elicited cardiomyocyte necrosis during normoxia and after acidic, yet not after neutral, SI. The isoform-selective enantiomers R- and S-BEL both mimicked the effect of racemic BEL after acidic SI. In contrast, inhibition of NHE activity by EIPA had no significant effect on necrosis after SI. Both neutral and acidic SI were associated with a reversible loss of F-actin and cortactin integrity. Inhibition of iPLA(2)-VI disrupted F-actin, cortactin, and mitochondrial integrity, whereas inhibition of NHE slightly reduced stress fiber content. iPLA(2)-VIA and NHE1 mRNA levels were reduced during SI and upregulated in a pH(o)-dependent manner during SI/R. This also affected the subcellular localization of iPLA(2)-VIA. Thus, the mode of cell death and the roles and regulation of iPLA(2)-VI and NHE1 are at least in part determined by the pH(o) during SI. In addition to having clinically relevant implications, these findings can in part explain the contradictory results obtained from previous studies of iPLA(2)-VIA and NHE1 during cardiac I/R.

Reduction of myocardial infarction by postischemic administration of the calpain inhibitor A-705253 in comparison to the Na(+)/H(+) exchange inhibitor Cariporide in isolated perfused rabbit hearts

The calpain inhibitor A-705253 and the Na(+)/H(+)-exchange inhibitor Cariporide were studied in isolated perfused rabbit hearts subjected to 60 min occlusion of the ramus interventricularis of the left coronary artery (below the origin of the first diagonal branch), followed by 120 min of reperfusion. The inhibitors were added to the perfusion fluid solely or in combination at the beginning of reperfusion. Hemodynamic monitoring and biochemical analysis of perfusion fluid from the coronary outflow were performed. Myocardial infarct size and area at risk (transiently not perfused myocardium) were determined from left ventricular slices after a special staining procedure with Evans blue and 2,3,5-triphenyltetrazolium chloride. The infarcted area (dead myocardium) was 72.7+/-4.0% of the area at risk in untreated controls, but was significantly smaller in the presence of the inhibitors. The largest effect was seen with 10(-6) m A-705253, which reduced the infarcted area to 49.2+/-4.1% of the area at risk, corresponding to a reduction of 33.6%. Cariporide at 10(-6) m reduced the infarct size to the same extent. The combination of both inhibitors, however, did not further improve cardioprotection. No statistical difference was observed between the experimental groups in coronary perfusion, left ventricular pressure, heart rate, and in the release of lactate dehydrogenase and creatin kinase from heart muscle.

Cell volume regulation: physiology and pathophysiology

Cell volume perturbation initiates a wide array of intracellular signalling cascades, leading to protective and adaptive events and, in most cases, activation of volume-regulatory osmolyte transport, water loss, and hence restoration of cell volume and cellular function. Cell volume is challenged not only under physiological conditions, e.g. following accumulation of nutrients, during epithelial absorption/secretion processes, following hormonal/autocrine stimulation, and during induction of apoptosis, but also under pathophysiological conditions, e.g. hypoxia, ischaemia and hyponatremia/hypernatremia. On the other hand, it has recently become clear that an increase or reduction in cell volume can also serve as a specific signal in the regulation of physiological processes such as transepithelial transport, cell migration, proliferation and death. Although the mechanisms by which cell volume perturbations are sensed are still far from clear, significant progress has been made with respect to the nature of the sensors, transducers and effectors that convert a change in cell volume into a physiological response. In the present review, we summarize recent major developments in the field, and emphasize the relationship between cell volume regulation and organism physiology/pathophysiology.

Na+/H+ exchange inhibitor cariporide attenuates skeletal muscle infarction when administered before ischemia or reperfusion

Administration of Na(+)/H(+) exchange isoform-1 (NHE-1) inhibitors before ischemia has been shown to attenuate myocardial infarction in several animal models of ischemia-reperfusion injury. However, controversy still exists as to the efficacy of NHE-1 inhibitors in protection of myocardial infarction when administered at the onset of reperfusion. Furthermore, the efficacy of NHE-1 inhibition in protection of skeletal muscle from infarction (necrosis) has not been studied. This information has potential clinical applications in prevention or salvage of skeletal muscle from ischemia-reperfusion injury in elective and trauma reconstructive surgery. The objective of this research project is to test our hypothesis that the NHE-1 inhibitor cariporide is effective in protection of skeletal muscle from infarction when administered at the onset of sustained ischemia or reperfusion and to study the mechanism of action of cariporide. In our studies, we observed that intravenous administration of cariporide 10 min before ischemia (1 or 3 mg/kg) or reperfusion (3 mg/kg) significantly reduced infarction in pig latissimus dorsi muscle flaps compared with the control, when these muscle flaps were subjected to 4 h of ischemia and 48 h of reperfusion (P < 0.05; n = 5 pigs/group). Both preischemic and postischemic cariporide treatment (3 mg/kg) induced a significant decrease in muscle myeloperoxidase activity and mitochondrial-free Ca(2+) content and a significant increase in muscle ATP content within 2 h of reperfusion (P < 0.05; n = 4 pigs/group). Preischemic and postischemic cariporide treatment (3 mg/kg) also significantly inhibited muscle NHE-1 protein expression within 2 h of reperfusion after 4 h of ischemia, compared with the control (P < 0.05; n = 3 pigs/group). These observations support our hypothesis that cariporide attenuates skeletal muscle infarction when administered at the onset of ischemia or reperfusion, and the mechanism involves attenuation of neutrophil accumulation and mitochondrial-free Ca(2+) overload and preservation of ATP synthesis in the early stage of reperfusion.

Paradoxical resistance to myocardial ischemia and age-related cardiomyopathy in NHE1 transgenic mice: a role for ER stress?

Sarcolemmal Na(+)/H(+) exchanger (NHE) activity, which is provided by the NHE isoform 1 (NHE1), has been implicated in ischemia/reperfusion-induced myocardial injury in animal models and humans, on the basis of studies with pharmacological NHE1 inhibitors. We generated a transgenic (TG) mouse model with cardiac-specific over-expression of NHE1 to determine whether this would be sufficient to increase myocardial susceptibility to ischemia/reperfusion-induced injury. TG mouse hearts exhibited increased sarcolemmal NHE activity and normal morphology and function. Surprisingly, they also showed reduced susceptibility to ischemia/reperfusion-induced injury, as reflected by improved functional recovery and smaller infarcts. Such protection was sustained in the presence of NHE1 inhibition with zoniporide, indicating a mechanism that is independent of sarcolemmal NHE activity. Immunoblot analysis revealed accumulation of immature NHE1 protein as well as marked upregulation of both cytoprotective (78/94 kDa glucose-regulated proteins, calreticulin, protein disulfide isomerase) and pro-apoptotic (C/EBP homologous protein) components of the endoplasmic reticulum (ER) stress response in TG myocardium. With increasing age, NHE1 TG mice exhibited increased myocyte apoptosis, developed left ventricular contractile dysfunction, underwent cardiac remodelling and died prematurely. Our findings indicate that: (1) Cardiac-specific NHE1 over-expression induces the ER stress response in mouse myocardium, which may afford protection against ischemia/reperfusion-induced injury despite increased NHE activity; (2) Ageing NHE1 TG mice exhibit myocyte apoptosis, cardiac remodelling and failure, likely as a result of sustained ER stress; (3) The pluripotent effects of the ER stress response may confound studies that are based on the chronic over-expression of complex proteins in myocardium.

Regulation of cell survival by Na+/H+ exchanger-1

Na(+)/H(+) exchanger-1 (NHE1) is a ubiquitous plasma membrane Na(+)/H(+) exchanger typically associated with maintenance of intracellular volume and pH. In addition to the NHE1 role in electroneutral Na(+)/H(+) transport, in renal tubular epithelial cells in vitro the polybasic, juxtamembrane NHE1 cytosolic tail domain acts as a scaffold, by binding with ezrin/radixin/moesin (ERM) proteins and phosphatidylinositol 4,5-bisphosphate, which initiates formation of a signaling complex that culminates in Akt activation and opposition to initial apoptotic stress. With robust apoptotic stimuli renal tubular epithelial cell NHE1 is a caspase substrate, and proteolytic cleavage may permit progression to apoptotic cell death. In vivo, genetic or pharmacological NHE1 loss of function causes renal tubule epithelial cell apoptosis and renal dysfunction following streptozotocin-induced diabetes, ureteral obstruction, and adriamycin-induced podocyte toxicity. Taken together, substantial in vivo and in vitro data demonstrate that NHE1 regulates tubular epithelial cell survival. In contrast to connotations of NHE1 as an unimportant "housekeeping" protein, this review highlights that NHE1 activity is critical for countering tubular atrophy and chronic renal disease progression.