Sodium ion/hydrogen ion exchange inhibition: a new pharmacologic approach to myocardial ischemia and reperfusion injury

(Patho-)Physiology of Na+/H+ Exchangers (NHEs) in the Digestive System

Na⁺/H⁺ exchangers (NHEs) are expressed in virtually all human tissues and organs. Two major tasks of those NHE isoforms that are located in plasma membranes are cell volume control by Na⁺-uptake and cellular pH regulation by H⁺-extrusion. Several NHEs, particularly NHE 1–4 and 8, are involved in the pathogenesis of diseases of the digestive system such as inflammatory bowel disease (ulcerative colitis, Crohn’s disease) and gastric and colorectal tumorigenesis. In the present review, we describe the physiological purposes, possible malfunctions and pathophysiological effects of the different NHE isoforms along the alimentary canal from esophagus to colon, including pancreas, liver and gallbladder. Particular attention is paid to the functions of NHEs in injury repair and to the role of NHE1 in Barrett’s esophagus. The impact of NHEs on gut microbiota and intestinal mucosal integrity is also dealt with. As the hitherto existing findings are not always consistent, sometimes even controversial, they are compared and critically discussed.

The Role of Sodium in Diabetic Cardiomyopathy

Cardiovascular complications are the major cause of mortality and morbidity in diabetic patients. The changes in myocardial structure and function associated with diabetes are collectively called diabetic cardiomyopathy. Numerous molecular mechanisms have been proposed that could contribute to the development of diabetic cardiomyopathy and have been studied in various animal models of type 1 or type 2 diabetes. The current review focuses on the role of sodium (Na⁺) in diabetic cardiomyopathy and provides unique data on the linkage between Na⁺ flux and energy metabolism, studied with non-invasive ²³Na, and ³¹P-NMR spectroscopy, polarography, and mass spectroscopy. ²³Na NMR studies allow determination of the intracellular and extracellular Na⁺ pools by splitting the total Na⁺ peak into two resonances after the addition of a shift reagent to the perfusate. Using this technology, we found that intracellular Na⁺ is approximately two times higher in diabetic cardiomyocytes than in control possibly due to combined changes in the activity of Na⁺–K⁺ pump, Na⁺/H⁺ exchanger 1 (NHE1) and Na⁺-glucose cotransporter. We hypothesized that the increase in Na⁺ activates the mitochondrial membrane Na⁺/Ca²⁺ exchanger, which leads to a loss of intramitochondrial Ca²⁺, with a subsequent alteration in mitochondrial bioenergetics and function. Using isolated mitochondria, we showed that the addition of Na⁺ (1–10 mM) led to a dose-dependent decrease in oxidative phosphorylation and that this effect was reversed by providing extramitochondrial Ca²⁺ or by inhibiting the mitochondrial Na⁺/Ca²⁺ exchanger with diltiazem. Similar experiments with ³¹P-NMR in isolated superfused mitochondria embedded in agarose beads showed that Na⁺ (3–30 mM) led to significantly decreased ATP levels and that this effect was stronger in diabetic rats. These data suggest that in diabetic cardiomyocytes, increased Na⁺ leads to abnormalities in oxidative phosphorylation and a subsequent decrease in ATP levels. In support of these data, using ³¹P-NMR, we showed that the baseline β-ATP and phosphocreatine (PCr) were lower in diabetic cardiomyocytes than in control, suggesting that diabetic cardiomyocytes have depressed bioenergetic function. Thus, both altered intracellular Na⁺ levels and bioenergetics and their interactions may significantly contribute to the pathology of diabetic cardiomyopathy.

Cardioprotective effect of atorvastatin alone or in combination with remote ischemic preconditioning on the biochemical changes induced by ischemic/reperfusion injury in a mutual prospective study with a clinical and experimental animal arm

BACKGROUND

Atorvastatin and remote ischemic preconditioning (RIPC) have beneficial cardiovascular protective effects. The aim of the study was to investigate possible effect of this drug alone and in combination with RIPC on the biochemical changes induced by ischemic/reperfusion injury (I/R) in a combined study with a clinical and experimental animal arm.

METHODS

Thirty consecutive patients undergoing elective percutaneous coronary intervention (PCI) were divided into three groups (10 each): group I (control group without any preconditioning), group II (patients who were maintained on atorvastatin (80mg/day) for one month before PCI), and group III (similar to group II but PCI was preceded by RIPC). On the other hand, sixty adult male New Zealand white rabbits were divided into 6 groups (10 each): group I (control), group II (sham), group III (I/R as 30min ischemia followed by 120min reperfusion), group IV (regular atorvastatin 10mg/kg for 40days orally followed by I/R), group V (I/R preceded by RIPC) and group VI (similar to group IV but I/R was preceded by RIPC). Tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), nitric oxide (NO), troponin I (cTnI), creatine kinase MB (CK-MB) and C-reactive protein (CRP) were measured in blood for all study groups.

RESULTS

Clinical and experimental parts showed that groups with RIPC combined with atorvastatin pre-treatment showed a synergistic protective effect against I/R injury as evidenced by significant reduction (P<0.001) in the levels of TNF-α, cTnI (in patients) and IL-6, CK-MB and CRP (in rabbits) while the level of NO was significantly (P<0.001) increased compared with other groups.

CONCLUSIONS

Pretreatment with atorvastatin combined with RIPC can exert a synergistic cardioprotective effects by reducing the possible biochemical changes related to ischemic reperfusion injury.

Advances in treatment strategies for ischemia reperfusion injury

INTRODUCTION

Ischemia-reperfusion injury (IRI) involves a complex sequence of events and limits the outcome of various surgical interventions. Clinical trials, based on the data of experimental models, aim to prove whether a pharmacological or technical approach could be suitable to provide a beneficial effect in humans. Due to the complexity of IRI, few pharmacological treatments have been investigated in clinical Phase III.

AREAS COVERED

In this review we report clinical trials that test specific drugs in clinical trials of organ transplantation. These studies form part of Phase II trials and examine the administration of caspase inhibitors, P-selectin antagonist or an antioxidant component in order to attenuate cold IRI during transplantation. Moreover, we provide a brief description of drugs tested on trials of different clinical situations associated to IRI, such as the coronary artery bypass graft surgery and percutaneous coronary intervention.

EXPERT OPINION

Future clinical trials could be centered on the application of techniques suitable for organs with increased vulnerability toward IRI. Furthermore, the standardization of reliable biomarkers and a careful estimation of the impact of high risk factors may be the key in order to achieve a more critical evaluation of the obtained results.

The RSK Inhibitor BIX02565 Limits Cardiac Ischemia/Reperfusion Injury

AIMS

During ischemia/reperfusion (I/R), ribosomal S6 kinase (RSK) activates Na(+)/H(+) exchanger 1 (NHE1) by phosphorylating NHE1 at serine 703 (pS703-NHE1), which promotes cardiomyocyte death and injury. Pharmacologic inhibition of NHE1 effectively protects animal hearts from I/R. However, clinical trials using NHE1 inhibitors failed to show benefit in patients with acute myocardial infarction (MI). One possible explanation is those inhibitors block both agonist-stimulated activity (increasing I/R injury) and basal NHE1 activity (necessary for cell survival). We previously showed that dominant-negative RSK (DN-RSK) selectively blocked agonist-stimulated NHE1 activity. Therefore, we hypothesized that a novel RSK inhibitor (BIX02565) would blunt agonist-stimulated NHE1 and protect hearts from I/R.

METHODS AND RESULTS

Serum/angiotensin II-stimulated pS703-NHE1 was significantly decreased by BIX02565 in cultured cells. Intracellular pH recovery assay showed that BIX02565 selectively inhibited serum-stimulated NHE1 activity. Ischemia/reperfusion decreased left ventricular-developed pressure (LVDP; inhibited) to 8.7% of the basal level in non-transgenic littermate control (NLC) mouse hearts, which was significantly improved (44.6%) by BIX02565. Similar protection was observed in vehicle-treated, cardiac-specific DN-RSK-Tg mice (43%). No additional protective effect was seen in BIX02565-treated DN-RSK-Tg hearts. BIX02565 also improved LVDP in cardiac-specific wild-type (WT)-RSK-Tg mouse hearts (7.4%-40.9%, P < .01). Finally, Western Blotting results confirmed DN-RSK and BIX02565 significantly decreased I/R-induced pS703-NHE1.

CONCLUSION

The RSK plays a crucial role in I/R-induced activation of NHE1 and cardiac injury. The RSK inhibition may provide an alternative target for patients with MI.

Effect of citrate phosphate dextrose solution on reperfusion injury in coronary artery bypass surgical patients undergoing cardiopulmonary bypass

INTRODUCTION

Reperfusion injury is one of the most common phenomena associated with coronary artery bypass graft (CABG) .The mechanism of ischemia and reperfusion injury is not known precisely, but may be free radicals and other activated oxygen metabolites have an important role in tissue damage following reperfusion injury. This study was to evaluation of citrate solution effects on oxidative stress and cardiac function and Cardiac enzymes in patient's candidate to CABG.

METHODS

In Double blind clinical trial study in Tabriz University of medical science, 50 patients candidate to CABG randomly divided in two groups and matched together according to sex, age and NYHA class. In intervention group after surgery and before the opening of the aortic clamping solution warm blood containing citrate phosphate dextrose (CPD; 3cc/100cc), value (100cc/min/m2BSA) for three minutes was administered. In control group, only pure blood administered. Oxidative stress markers measured in five stages and cardiac enzymes measured in three stages of surgery.

RESULTS

Mean age 62.3±9.1 years including 30(60%) men and 20(40%) women. Ejection fractions between two groups were not significant before and after treatment. Administration of CPD was not significant effects on cardiac enzyme. Measurement of oxidative stress in different time were not different in malonil dialdehyde, superoxide dismutase and GPx but total antioxidant status were improved after intervention in compared with control group (p<0.001).

CONCLUSION

Results showed that CPD were positive effects of increasing in total antioxidant status after CABG, but in reduction of other oxidative markers were unlabeled.

Adenosine triphosphate depletion by cyanide results in a Na(+)-dependent Mg(2+) extrusion from liver cells

Addition of NaCN to isolated hepatocytes results in a marked and rapid decrease in cellular adenosine triphosphate (ATP) content, and in the extrusion of a sizable amount of cellular Mg(2+). This extrusion starts after a 10-minute lag phase and reaches a maximum of 35 to 40 nmol Mg(2+) per milligram protein within 60 minutes from the addition of CN(-). A quantitatively similar Mg(2+) extrusion is also observed after the addition of the mitochondrial uncoupler carbonyl cyanide p-trifluoromethoxy-phenylhydrazone but not that of the glycolysis inhibitor iodoacetate. The Mg(2+) extrusion is completely inhibited by the removal of extracellular Na(+) or the addition of imipramine, quinidine, or glibenclamide, whereas it persists after the removal of extracellular Ca(2+) or K(+), or the addition of amiloride. An acidic extracellular pH or the removal of extracellular HCO₃⁻ inhibits the cyanide-induced Mg(2+) extrusion by at least 80%. Taken together, these data suggest that the decrease in cellular adenosine triphosphate content removes a major Mg(2+) complexing agent from the hepatocyte and results in an extrusion of hepatic Mg(2+) exclusively through a Na(+)-dependent exchange mechanism modulated by acidic changes in extracellular pH.

A Real-Time Screening Assay for GIRK1/4 Channel Blockers

The cardiac acetylcholine-activated K+ channel (IK,Ach) represents a novel target for drug therapy in the treatment of atrial fibrillation (AF). This channel is a member of the G-protein-coupled inward rectifier K+ (GIRK) channel superfamily and is composed of the GIRK1/4 (Kir3.1 and Kir3.4) subunits. The goal of this study was to develop a cell-based screening assay for identifying new blockers of the GIRK1/4 channel. The mouse atrial HL-1 cell line, expressing the GIRK1/4 channel, was plated in 96-well plate format, loaded with the fluorescent membrane potential-sensitive dye bis-(1,3-dibutylbarbituric acid) trimethine oxonol (DiBAC4(3)) and measured using a fluorescent imaging plate reader (FLIPR). Application of the muscarinic agonist carbachol to the cells caused a rapid, time-dependent decrease in the fluorescent signal, indicative of K+ efflux through the GIRK1/4 channel (carbachol vs. control solution, Z′ factor = 0.5-0.6). The GIRK1/4 channel fluorescent signal was blocked by BaCl2 and enhanced by increasing the driving force for K+ across the cell membrane. To test the utility of the assay for screening GIRK1/4 channel blockers, cells were treated with a small compound library of Na+ and K+ channel modulators. Analogues of amiloride and propafenone were identified as channel blockers at concentrations less than 1 µM. Thus, the GIRK1/4 channel assay may be used in the development of new and selective agents for treating AF.

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.

Treatment of lactic acidosis: appropriate confusion

BACKGROUND

Lactic acidosis (LA) is common in hospitalized patients and is associated with poor clinical outcomes. There have been major recent advances in our understanding of lactate generation and physiology. However, treatment of LA is an area of controversy and uncertainty, and the use of agents to raise pH is not clearly beneficial.

AIM AND METHODS

We reviewed animal and human studies on the pathogenesis, impact, and treatment of LA, published in the English language and available through the PubMed/MEDLINE database. Our aim was to clarify the physiology of the generation of LA, its impact on outcomes, and the different treatment modalities available. We also examined relevant data regarding LA induced by medications commonly prescribed by hospitalists: biguanides, nucleoside analog reverse-transcriptase inhibitors (NRTIs), linezolid, and lorazepam.

RESULTS/CONCLUSIONS

Lactic acid is a marker of tissue ischemia but it also may accumulate without tissue hypoperfusion. In the latter circumstance, lactic acid accumulation may be an adaptive mechanism-a novel possibility quite in contrast to the traditional view of lactic acid as only a marker of tissue ischemia. Studies on the treatment of LA with sodium bicarbonate or other buffers fail to show consistent clinical benefit. Severe acidemia in the setting of LA is a particularly poorly studied area. In the settings of medication-induced LA, optimal treatment, apart from prompt cessation of the offending agent, is still unclear.

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.

Hydrogen peroxide mobilizes Ca2+ through two distinct mechanisms in rat hepatocytes

AIM

Hydrogen peroxide (H2O2) is produced during liver transplantation. Ischemia/reperfusion induces oxidation and causes intracellular Ca2+ overload, which harms liver cells. Our goal was to determine the precise mechanisms of these processes.

METHODS

Hepatocytes were extracted from rats. Intracellular Ca2+ concentrations ([Ca2+](i)), inner mitochondrial membrane potentials and NAD(P)H levels were measured using fluorescence imaging. Phospholipase C (PLC) activity was detected using exogenous PIP2. ATP concentrations were measured using the luciferin-luciferase method. Patch-clamp recordings were performed to evaluate membrane currents.

RESULTS

H2O2 increased intracellular Ca2+ concentrations ([Ca2+](i)) across two kinetic phases. A low concentration (400 micromol/L) of H2O2 induced a sustained elevation of [Ca2+](i) that was reversed by removing extracellular Ca2+. H2O2 increased membrane currents consistent with intracellular ATP concentrations. The non-selective ATP-sensitive cation channel blocker amiloride inhibited H2O2-induced membrane current increases and [Ca2+](i) elevation. A high concentration (1 mmol/L)of H2O2 induced an additional transient elevation of [Ca2+](i), which was abolished by the specific PLC blocker U73122 but was not eliminated by removal of extracellular Ca2+. PLC activity was increased by 1 mmol/L H2O2 but not by 400 micromol/L H2O2.

CONCLUSIONS

H2O2 mobilizes Ca2+ through two distinct mechanisms. In one, 400 micromol/L H2O2-induced sustained [Ca2+](i) elevation is mediated via a Ca2+ influx mechanism, under which H2O2 impairs mitochondrial function via oxidative stress,reduces intracellular ATP production, and in turn opens ATP-sensitive, non-specific cation channels, leading to Ca2+ influx.In contrast, 1 mmol/L H2O2-induced transient elevation of [Ca2+](i) is mediated via activation of the PLC signaling pathway and subsequently, by mobilization of Ca2+ from intracellular Ca2+ stores.

Electrospun fibers of acid-labile biodegradable polymers containing ortho ester groups for controlled release of paracetamol

The local delivery and controllable release profiles make electrospun ultrafine fibers as potential implantable drug carriers and functional coatings of medical devices. There are few attempts to form acid-labile electrospun fibers, whose release behaviors respond to the local environment and fiber characteristics. In the current study a novel strategy was presented to synthesize biodegradable pH-sensitive polymers containing ortho ester groups. The acid-labile segments were synthesized through reacting 3,9-dimethylene-2,4,8,10-tetraoxaspiro [5.5] undecane with 1,10-decanediol or poly(ethylene glycol), which were further copolymerized with D,L-lactide to obtain triblock copolymers. Biodegradable acid-labile polymers were electrospun with the encapsulation of paracetamol as a model drug. In vitro release study showed that the total amount of drug released from acid-labile polymeric fibers was accelerated after incubation into acid buffer solutions, and the amount of initial burst release and sustained release rate were significantly higher for matrix polymers with hydrophilic acid-labile segments. In vitro degradation study indicated that the electrospun fibers containing acid-labile segments were stable in neutral buffer solution, but the molecular weight reduction of matrix polymers, the morphological changes and mass loss of fibrous mats were significantly enhanced under acid circumstances.

Sheddable coatings for long-circulating nanoparticles

Nanoparticles, such as liposomes, polymeric micelles, lipoplexes and polyplexes are frequently studied as targeted drug carrier systems. The ability of these particles to circulate in the bloodstream for a prolonged period of time is often a prerequisite for successful targeted delivery. To achieve this, hydrophilic ‘stealth’ polymers, such as poly(ethylene glycol) (PEG), are used as coating materials. Such polymers shield the particle surface and thereby reduce opsonization by blood proteins and uptake by macrophages of the mononuclear phagocyte system. Yet, after localizing in the pathological site, nanoparticles should deliver their contents in an efficient manner to achieve a sufficient therapeutic response. The polymer coating, however, may hinder drug release and target cell interaction and can therefore be an obstacle in the realization of the therapeutic response. Attempts have been made to enhance the therapeutic efficacy of sterically stabilized nanoparticles by means of shedding, i.e. a loss of the coating after arrival at the target site. Such an ‘unmasking’ process may facilitate drug release and/or target cell interaction processes. This review presents an overview of the literature regarding different shedding strategies that have been investigated for the preparation of sterically stabilized nanoparticulates. Detach mechanisms and stimuli that have been used are described.

Effect of Diuretic Therapy on Exercise Capacity in Patients With Chronic Angina and Preserved Left Ventricular Function

AIM

This study was designed to determine whether therapy with a diuretic has antianginal effects in patients with stable angina who are already treated with a traditional antianginal regimen.

METHODS AND RESULTS

Forty patients with chronic stable angina and normal left ventricular function were randomized in a double-blind, placebo-controlled study. Background antianginal therapy included beta blockers (n = 27), calcium channel antagonists (n = 18), and long-acting nitrates (n = 24). Of the patients 30% had diabetes and 75% had a history of hypertension. Patients were treated with a diuretic (hydrochlorothiazide 25 mg plus amiloride 5 mg) or placebo for 21 days. All patients underwent a treadmill exercise test before randomization and at day 21. The primary end point was the change in treadmill walking time until moderate angina. Diuretic therapy was associated with an increase in treadmill walking time of 63 +/- 17 seconds versus 19 +/- 9 seconds in the placebo group (P = 0.026) and reduced ST-segment depression (0.6 +/- 0.2 mm versus 0.1 +/- 0.2 mm (P = 0.03). There was a 25% increase in walking time in 8 patients (40%) treated with diuretic versus 1 patient (5%) in the placebo group (P = 0.02). The increases did not depend on changes in blood pressure or heart rate.

CONCLUSION

Therapy with hydrochlorothiazide plus amiloride has potent antianginal effects in patients with stable angina and preserved left ventricular function under treatment with standard antianginal therapy. Because most of the study patients had a history of hypertension the extrapolation of these findings to patients who did not have hypertension requires further investigation.

Calcium signaling phenomena in heart diseases: a perspective

Ca(2+) is a major intracellular messenger and nature has evolved multiple mechanisms to regulate free intracellular (Ca(2+))(i) level in situ. The Ca(2+) signal inducing contraction in cardiac muscle originates from two sources. Ca(2+) enters the cell through voltage dependent Ca(2+) channels. This Ca(2+) binds to and activates Ca(2+) release channels (ryanodine receptors) of the sarcoplasmic reticulum (SR) through a Ca(2+) induced Ca(2+) release (CICR) process. Entry of Ca(2+) with each contraction requires an equal amount of Ca(2+) extrusion within a single heartbeat to maintain Ca(2+) homeostasis and to ensure relaxation. Cardiac Ca(2+) extrusion mechanisms are mainly contributed by Na(+)/Ca(2+) exchanger and ATP dependent Ca(2+) pump (Ca(2+)-ATPase). These transport systems are important determinants of (Ca(2+))(i) level and cardiac contractility. Altered intracellular Ca(2+) handling importantly contributes to impaired contractility in heart failure. Chronic hyperactivity of the beta-adrenergic signaling pathway results in PKA-hyperphosphorylation of the cardiac RyR/intracellular Ca(2+) release channels. Numerous signaling molecules have been implicated in the development of hypertrophy and failure, including the beta-adrenergic receptor, protein kinase C, Gq, and the down stream effectors such as mitogen activated protein kinases pathways, and the Ca(2+) regulated phosphatase calcineurin. A number of signaling pathways have now been identified that may be key regulators of changes in myocardial structure and function in response to mutations in structural components of the cardiomyocytes. Myocardial structure and signal transduction are now merging into a common field of research that will lead to a more complete understanding of the molecular mechanisms that underlie heart diseases. Recent progress in molecular cardiology makes it possible to envision a new therapeutic approach to heart failure (HF), targeting key molecules involved in intracellular Ca(2+) handling such as RyR, SERCA2a, and PLN. Controlling these molecular functions by different agents have been found to be beneficial in some experimental conditions.

Use of base in the treatment of acute severe organic acidosis by nephrologists and critical care physicians: results of an online survey

BACKGROUND

Acute severe metabolic acidosis associated with lactic acidosis or ketoacidosis can have severe detrimental effects on organ function, and might contribute to mortality. A general consensus exists that elimination of the cause of the acidosis is essential for treatment, but there is controversy concerning the use of base for the treatment of these disorders. Some physicians advocate administration of base when the acidosis is severe to prevent a decrease in cardiac output, whereas others oppose administration of base even when the acidosis is severe given the potential compromise of cardiac function. Nephrologists and critical care specialists are often the physicians developing recommendations for the treatment of severe acid-base disorders.

METHODS

A short online survey of 20 questions was developed to assess the approach to the treatment of acute metabolic acidosis of program directors of fellowship programs and experts from the specialties of critical care and nephrology.

RESULTS

Although there was variability among individual physicians from both specialties, a larger percentage of nephrologists than critical care physicians queried recommended administration of base for the treatment of lactic acidosis (86% vs 67%) and ketoacidosis (60% vs 28%). Also, critical care physicians in general used a lower level of blood pH when deciding when to initiate treatment. Of the physicians who gave base, most utilized sodium bicarbonate as the form of base given.

CONCLUSIONS

The results of this survey indicate that the decisions whether to use base for the treatment of acute severe metabolic acidosis, and under which circumstances, vary among physicians, and indicate the need for further studies to develop evidence-based guidelines for therapy.

Discovery of N-(3-{4-[(3-fluorobenzyl)oxy]phenoxy}propyl)-2-pyridin-4-ylacetamide as a potent and selective reverse NCX inhibitor

In the setting of heart failure and myocardial ischemia-reperfusion, the sodium-calcium exchanger (NCX) can lead to calcium overload, which is responsible for contractile dysfunction and arrhythmia. NCX is an attractive target for treatment in heart failure and myocardial ischemia-reperfusion. We have designed and synthesized a series of benzyloxyphenyl derivatives based on compound 3. These derivatives have been evaluated for their inhibitory activity against both the reverse and forward modes of NCX. We have discovered a novel potent and selective reverse NCX inhibitor (12) with an IC50 value of 0.085 microM against reverse NCX.

Failure and function of intracellular pH regulation in acute hypoxic-ischemic injury of astrocytes

Astrocytes can die rapidly following ischemic and traumatic injury to the CNS. Brain acid-base status has featured prominently in theories of acute astrocyte injury. Failure of astrocyte pH regulation can lead to cell loss under conditions of severe acidosis. By contrast, the function of astrocyte pH regulatory mechanisms appears to be necessary for acute cell death following the simulation of transient ischemia and reperfusion. Severe lactic acidosis, and the failure of astrocytes to regulate intracellular pH (pH(i)) have been emphasized in brain ischemia under hyperglycemic conditions. Direct measurements of astrocyte pH(i) after cardiac arrest demonstrated a mean pH(i) of 5.3 in hyperglycemic rats. In addition, both in vivo and in vitro studies of astrocytes have shown similar pH levels to be cytotoxic. Whereas astrocytes exposed to hypoxia alone may require 12-24 h to die, acidosis has been found to exacerbate and speed hypoxic loss of these cells. Recently, astrocyte cultures were exposed to hypoxic, acidic media in which the large ionic perturbations characteristic of brain ischemia were simulated. Upon return to normal saline ("reperfusion"), the majority of cells died. This injury was dependent on external Ca2+ and was prevented by inhibition of reversed Na(+)-Ca2+ exchange, blockade of Na(+)-H+ exchange, or by low pH of the reperfusion saline. These data suggested that cytotoxic elevation of [Ca2+]i occurred during reperfusion due to a sequence of activated Na(+)-H+ exchange, cytosolic Na+ loading, and resultant reversal of Na(+)-Ca2+ exchange. The significance of this reperfusion model to ischemic astrocyte injury in vivo is discussed.

Investigations on the pharmacology of the cardioprotective guanidine ME10092

The guanidine compound ME10092 (1-(3,4-dimethoxy-2-chlorobenzylideneamino)-guanidine), which possesses a strong cardioprotective effect to ischemia-reperfusion, was assessed for different pharmacological actions that may underlie its cardioprotective effect. In the living rat ME10092 decreased the blood pressure and heart rate in a dose-dependent manner. We found ME10092 to bind to alpha 1- and alpha 2-adrenoreceptors with moderate affinity (Ki values 1-4 microM), and to block adrenaline-elicited contractile responses in isolated guinea pig aortas. Our results indicate that ME10092 possesses a certain anti-oxidant profile. Thus, in a competitive manner and with low affinity it inhibited the bovine milk xanthine oxidase enzyme, as well as NAD(P)H oxidase driven oxyradical formation in membrane fractions isolated from the rat brain. By using electron paramagnetic resonance we here show that, after its systemic administration, ME10092 modulates the nitric oxide (NO) content in several tissues of the rat in a time-dependent manner. However, in vitro ME10092 inhibited the activities of nitric oxide synthases nNOS and eNOS, but not that of iNOS. Our data give evidence that the cardioprotective effect of ME10092 could be mediated through pharmacological mechanisms that include some modulation of NO production, as well as possible inhibition of radical formation during ischemia-reperfusion.

Transport of extracellular l-arginine via cationic amino acid transporter is required during in vivo endothelial nitric oxide production

In cultured endothelial cells, 70-95% of extracellular l-arginine uptake has been attributed to the cationic amino acid transporter-1 protein (CAT-1). We tested the hypothesis that extracellular l-arginine entry into endothelial cells via CAT-1 plays a crucial role in endothelial nitric oxide (NO) production during in vivo conditions. Using l-lysine, the preferred amino acid transported by CAT-1, we competitively inhibited extracellular l-arginine transport into endothelial cells during conditions of NaCl hyperosmolarity, low oxygen, and flow increase. Our prior studies indicate that each of these perturbations causes NO-dependent vasodilation. The perivascular NO concentration ([NO]) and blood flow were determined in the in vivo rat intestinal microvasculature. Suppression of extracellular l-arginine transport significantly and strongly inhibited increases in vascular [NO] and intestinal blood flow during NaCl hyperosmolarity, lowered oxygen tension, and increased flow. These results suggest that l-arginine from the extracellular space is accumulated by CAT-1. When CAT-1-mediated transport of extracellular l-arginine into endothelial cells was suppressed, the endothelial cell NO response to a wide range of physiological stimuli was strongly depressed.

Role of Na+-H+ and Na+-Ca2+ exchange in hypoxia-related acute astrocyte death

Cultured astrocytes do not succumb to hypoxia/zero glucose for up to 24 h, yet astrocyte death following injury can occur within 1 h. It was previously demonstrated that astrocyte loss can occur quickly when the gaseous and interstitial ionic changes of transient brain ischemia are simulated: After a 20-40-min exposure to hypoxic, acidic, ion-shifted Ringer (HAIR), most cells died within 30 min after return to normal saline (i.e., "reperfusion"). Astrocyte death required external Ca2+ and was blocked by KB-R7943, an inhibitor of reversed Na+-Ca2+ exchange, suggesting that injury was triggered by a rise in [Ca2+]i. In the present study, we confirmed the elevation of [Ca2+]i during reperfusion and studied the role of Na+-Ca2+ and Na+-H+ exchange in this process. Upon reperfusion, elevation of [Ca2+]i was detectable by Fura-2 and was blocked by KB-R7943. The low-affinity Ca2+ indicator Fura-FF indicated a mean [Ca2+]i rise to 4.8+/-0.4 microM. Loading astrocytes with Fura-2 provided significant protection from injury, presumably due to the high affinity of the dye for Ca2+. Injury was prevented by the Na+-H+ exchange inhibitors ethyl isopropyl amiloride or HOE-694, and the rise of [Ca2+]i at the onset of reperfusion was blocked by HOE-694. Acidic reperfusion media was also protective. These data are consistent with Na+ loading via Na+-H+ exchange, fostering reversal of Na+-Ca2+ exchange and cytotoxic elevation of [Ca2+]i. The results indicate that mechanisms involved in pH regulation may play a role in the fate of astrocytes following acute CNS injuries.

Adjunctive therapies in sepsis: An evidence-based review

OBJECTIVE

In 2003, critical care and infectious disease experts representing 11 international organizations developed management guidelines for adjunctive therapies in sepsis that would be of practical use for the bedside clinician, under the auspices of the Surviving Sepsis Campaign, an international effort to increase awareness and to improve outcome in severe sepsis.

DESIGN

The process included a modified Delphi method, a consensus conference, several subsequent smaller meetings of subgroups and key individuals, teleconferences, and electronic-based discussion among subgroups and among the entire committee.

METHODS

The modified Delphi methodology used for grading recommendations built on a 2001 publication sponsored by the International Sepsis Forum. We undertook a systematic review of the literature graded along five levels to create recommendation grades from A to E, with A being the highest grade. Pediatric considerations to contrast adult and pediatric management are in the article by Parker et al. on p. S591.

CONCLUSION

Glycemic control (maintenance of glucose <150 mg/dL) is recommended. The beneficial effect of glycemic control appears to be related control of glucose and not the administration of insulin. Glycemic control should be combined with a nutritional protocol. The dialysis dose is important in sepsis-induced acute renal failure. Continuous hemofiltration offers easier management of fluid balance in hemodynamically unstable septic patients but in the absence of hemodynamic instability is equivalent to intermittent hemodialysis. It is uncertain whether high-volume hemofiltration improves prognosis in sepsis. Bicarbonate therapy is not recommended for the purpose of improving hemodynamics or reducing vasopressor requirements in the presence of lactic academia and pH >7.15.

The Na+/H+ exchange inhibitor: a new therapeutic approach for hepatic ischemia injury in rats

BACKGROUND

Na+/H+ exchanger (NHE) is one of the major mechanisms for restoring pH after ischemia-induced intracellular acidosis. However, activation of NHE during ischemia and reperfusion (I/R) is also involved in the paradoxical induction of cell injury. This study was designed to evaluate the effects of 5-(N-ethyl-N-isopropyl)-amiloride (EIPA), an NHE inhibitor, on hepatic I/R injury.

METHODS

Partial hepatic ischemia was induced in male Wistar rats by cross-clamping the hepatic arterial and portal venous branches to the left lateral and median lobes of the liver for 120 minutes. The caudate and right lateral lobes were removed immediately after reperfusion. The concentrations of serum enzymes and ATP levels and energy charge in the live tissue were examined after 1-hour reperfusion.

RESULT

EIPA afforded considerable protection against I/R injury, as demonstrated by decreased transaminase release and reduced histologic hepatocyte damage and increased energy charge. The 7-day survival rate was significantly improved from 15.4% to 55.6% (P <.05).

CONCLUSIONS

This study shows for the first time that NHE may play an important role in the hepatic I/R injury and that EIPA should be considered as a new therapeutic approach to prevent hepatic I/R injury.

Apoptosis versus necrosis in acute pancreatitis

Acute pancreatitis is a disease of variable severity in which some patients experience mild, self-limited attacks, whereas others manifest a severe, highly morbid, and frequently lethal attack. The events that regulate the severity of acute pancreatitis are, for the most part, unknown. It is generally believed that the earliest events in acute pancreatitis occur within acinar cells and result in acinar cell injury. Other processes, such as recruitment of inflammatory cells and generation of inflammatory mediators, are believed to occur subsequent to acinar cell injury, and these "downstream" events are believed to influence the severity of the disease. Several recently reported studies, however, have suggested that the acinar cell response to injury may, itself, be an important determinant of disease severity. In these studies, mild acute pancreatitis was found to be associated with extensive apoptotic acinar cell death, whereas severe acute pancreatitis was found to involve extensive acinar cell necrosis but very little acinar cell apoptosis. These observations led to the hypothesis that apoptosis could be a favorable response to acinar cells and that interventions that favor induction of apoptotic, as opposed to necrotic, acinar cell death might reduce the severity of an attack of acute pancreatitis. Indeed, in an experimental setting, the induction of pancreatic acinar cell apoptosis protects mice against acute pancreatitis. Little is known about the mechanism of apoptosis in the pancreatic acinar cell, although some early attempts have been made in that direction. Also, clinical relevance of these experimental studies remains to be investigated.

Cardiac-specific overexpression of fibroblast growth factor-2 protects against myocardial dysfunction and infarction in a murine model of low-flow ischemia

BACKGROUND

Preconditioning the heart before an ischemic insult has been shown to protect against contractile dysfunction, arrhythmias, and infarction. Pharmacological studies have suggested that fibroblast growth factor-2 (FGF2) is involved in cardioprotection. However, because of the number of FGFs expressed in the heart and the promiscuity of FGF ligand-receptor interactions, the specific role of FGF2 during ischemia-reperfusion injury remains unclear.

METHODS AND RESULTS

FGF2-deficient (Fgf2 knockout) mice and mice with a cardiac-specific overexpression of all 4 isoforms of human FGF2 (FGF2 transgenic [Tg]) were compared with wild-type mice to test whether endogenous FGF2 elicits cardioprotection. An ex vivo work-performing heart model of ischemia was developed in which murine hearts were subjected to 60 minutes of low-flow ischemia and 120 minutes of reperfusion. Preischemic contractile function was similar among the 3 groups. After ischemia-reperfusion, contractile function of Fgf2 knockout hearts recovered to 27% of its baseline value compared with a 63% recovery in wild-type hearts (P<0.05). In FGF2 Tg hearts, an 88% recovery of postischemic function occurred (P<0.05). Myocardial infarct size was also reduced in FGF2 Tg hearts compared with wild-type hearts (13% versus 30%, P<0.05). There was a 2-fold increase in FGF2 release from Tg hearts compared with wild-type hearts (P<0.05). No significant alterations in coronary flow or capillary density were detected in any of the groups, implying that the protective effect of FGF2 is not mediated by coronary perfusion changes.

CONCLUSIONS

These results provide evidence that endogenous FGF2 plays a significant role in the cardioprotective effect against ischemia-reperfusion injury.

The hemodynamic effects of acute myocardial ischemia and reperfusion in Clawn miniature pigs

Acute myocardial ischemia was induced by occluding the LAD in Clawn miniature pigs. Eight pigs (group 1) were subjected to 6 h ischemia and nine pigs (group 2) were subjected to 20 min ischemia, followed by reperfusion for 340 min. Three animals of the group 1 died due to ventricular fibrillation after occlusion and in group 2, four animals died due to the arrhythmia after reperfusion. Though the ischemic area of group 2 (15.6% of the ventricle) was narrower than that of group 1 (21.7%), the survival rate was lower. We supposed that ischemia-reperfusion injuries were strongly connected with the hemodynamics of group 2. Clawn miniature pigs are useful experimental animals for myocardial ischemic researches.

Cardiac effects of amiloride and of enalapril in the spontaneously hypertensive rat

OBJECTIVES

To compare the effects of the sodium-hydrogen exchange blocker, amiloride, with those of the angiotensin-converting enzyme inhibitor, enalapril, on cardiac structure and function and intracardiomyocyte calcium concentration ([Ca2+]i) and pH (pHi), in spontaneously hypertensive rats (SHRs).

METHODS

Experiments were performed in SHRs treated for 4 weeks with amiloride 7.5 mg/kg per day, enalapril 6.0 mg/kg per day or vehicle, and in Sprague-Dawley rats (SDRs). After haemodynamic measurements were taken, the heart was removed and weighed and hydroxyproline (a marker of collagen content) was assayed. In separate rats, ventricular myocytes were isolated, their size determined, and [Ca2+]i and pHi examined using fluo-3 acetoxymethyl ester and 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein tetrakis acetoxymethyl ester fluorescence, respectively.

RESULTS

Left ventricular end-diastolic pressure was increased, and the maximal rates of increase and of decrease in pressure with time in the left ventricle were decreased in SHRs compared with SDRs. Myocytes were larger and hydroxyproline was increased in the left ventricle, but not in the right ventricle of SHRs compared with SDRs. Amiloride and enalapril decreased systolic blood pressure in SHRs similarly, and improved diastolic function in these rats, enalapril more than amiloride. Both agents decreased left ventricular myocyte size to similar extents; however, whereas enalapril decreased the left ventricular hydroxyproline content, amiloride did not. Left ventricular myocytes from SHRs exhibited greater [Ca2+]i and pHi than those from SDRs; enalapril decreased [Ca2+]i more than amiloride, but amiloride decreased pHi more than enalapril.

CONCLUSIONS

In SHRs, enalapril prevents left ventricular hypertrophy, collagen deposition, diastolic dysfunction, and increases in [Ca2+]i more effectively than does amiloride. In contrast, the latter prevents the increase in pHi more effectively than enalapril, despite similar reductions in blood pressure. These findings suggest that their effects do not depend solely on blood pressure reduction.

Long-term magnetic resonance imaging/spectroscopy study of cariporide in a canine cardiac ischemia/reperfusion model

Using both 31P and 1H cardiac magnetic resonance techniques, it is possible to monitor the functional (ejection fraction [EF]) and biochemical (pH) status of the heart following a reperfused ischemic insult. This study assessed the effects of Na+/H+ exchange inhibition with cariporide in a closed-chest canine ischemia/reperfusion model. Dogs received 1-mg/kg cariporide treatments for 3 days after occlusion, but were monitored for 10 days. Baseline intracellular pH (+/-SEM) for the control and treated groups were 7.10 +/- 0.03 and 7.14 +/- 0.04, respectively, and dropped to 6.25 +/- 0.08 and 6.38 +/- 0.08 during occlusion. There was a significant increase in pH from occlusion to early reperfusion in the control group (P = 0.03) but, during the same time period, this increase was not seen in the cariporide group. There was a significant (P = 0.01) drug interaction in recovery of EF over the 10-day protocol. Individual time-point analysis revealed significant differences at immediate reperfusion through day 3 (73.9% +/- 2.5%, 84.5% +/- 3.1%; baseline normalized EF controls and cariporide, respectively). Neither pH nor EF measurements were significantly different between the groups at day 10. Despite early functional and metabolic benefits, infarct size, as measured at day 10, was 13.2% +/- 2.2% for the controls and 11.8% +/- 2.3% for the cariporide group (NS). Thus there were no long-term cariporide functional or biochemical benefits.

Cell death induced by acute renal injury: a perspective on the contributions of apoptosis and necrosis

In humans and experimental models of renal ischemia, tubular cells in various nephron segments undergo necrotic and/or apoptotic cell death. Various factors, including nucleotide depletion, electrolyte imbalance, reactive oxygen species, endonucleases, disruption of mitochondrial integrity, and activation of various components of the apoptotic machinery, have been implicated in renal cell vulnerability. Several approaches to limit the injury and augment the regeneration process, including nucleotide repletion, administration of growth factors, reactive oxygen species scavengers, and inhibition of inducers and executioners of cell death, proved to be effective in animal models. Nevertheless, an effective approach to limit or prevent ischemic renal injury in humans remains elusive, primarily because of an incomplete understanding of the mechanisms of cellular injury. Elucidation of cell death pathways in animal models in the setting of renal injury and extrapolation of the findings to humans will aid in the design of potential therapeutic strategies. This review evaluates our understanding of the molecular signaling events in apoptotic and necrotic cell death and the contribution of various molecular components of these pathways to renal injury.

Inflammatory response to cardiopulmonary bypass

Inflammation in cardiac surgical patients is produced by complex humoral and cellular interactions with numerous pathways including activation, generation, or expression of thrombin, complement, cytokines, neutrophils, adhesion molecules, mast cells, and multiple inflammatory mediators. Because of the redundancy of the inflammatory cascades, profound amplification occurs to produce multiorgan system dysfunction that can manifest as coagulopathy, respiratory failure, myocardial dysfunction, renal insufficiency, and neurocognitive defects. Coagulation and inflammation are also closely linked through networks of both humoral and cellular components including proteases of the clotting and fibrinolytic cascades, including tissue factor. Vascular endothelial cells also mediate inflammation and the cross talk between coagulation and inflammation. Novel antiinflammatory agents inhibit these processes by several mechanisms such as preventing proteolysis of the protease-activated receptor (aprotinin), inhibiting complement-mediated injury (pexelizumab), or inhibiting contact activation (kallikrein inhibitors). Surgery alone also activates specific hemostatic responses, activation of immune mechanisms, and inflammatory response mediated by the release of various cytokines and chemokines. Novel agents are under investigation to further improve outcomes in cardiac surgical patients.

Altered gene expression of Na+/Ca2+ exchanger isoforms NCX1, NCX2 and NCX3 in chronic ischemic rat brain

To investigate the effect of chronic global cerebral ischemia on gene expression of Na(+)/Ca(2+) exchanger isoforms NCX1, NCX2 and NCX3 in rat brain. Chronic global cerebral ischemia was induced by bilateral common carotid artery ligation (BCAL) in rats for 1 week, 2 weeks and 4 weeks, respectively. Morris water maze was applied to demonstrate the credibility of BCAL models. After BCAL for 4 weeks, there was learning and memory deficiency that the latency and distance of BCAL group were longer than those of sham group from the second trial to tenth trial in hidden platform trials. Reverse transcription-polymerase chain reaction was used to assess the gene expression of Na(+)/Ca(2+) exchanger isoforms at mRNA level in cerebral cortex and hippocampus. For NCX1, its expression was decreased by 35%, 54% and 27% of rats with BCAL for 1 week, 2 weeks and 4 weeks, respectively; For NCX2, its expression was decreased by 41%, 29% and 12% of rats with BCAL for 1 week, 2 weeks and 4 weeks, respectively; For NCX3, its expression was decreased by 29%, 27% and 12% of rats with BCAL for 1 week, 2 weeks and 4 weeks, respectively. However, in hippocampus, the expressions of NCX1 and NCX3 did not change significantly in different BCAL groups. NCX2 was increased by 60% in BCAL for 1 week only, but did not change significantly in BCAL for 2 weeks or 4 weeks. The study indicated that brain ischemia regulated gene expression levels of Na(+)/Ca(2+) exchanger isoforms especially in cerebral cortex.

Novel, non-acylguanidine-type Na(+)/H(+) exchanger inhibitors: synthesis and pharmacology of 5-tetrahydroquinolinylidene aminoguanidine derivatives

In the course of our research into new types of non-acylguanidine Na(+)/H(+) exchanger (NHE) inhibitors, we designed and synthesized aryl-fused tetrahydropyranylidene and cyclohexylidene aminoguanidine derivatives I (X = O, CH(2)), which were tested for their inhibitory effects on rat platelet NHEs. After optimization, we found that the S isomer of tetrahydroquinoline derivatives that possess a methyl group in the 4-position and a halogen or methyl group in the o-position of Ar(2) exhibited high inhibitory activity. In these compounds, (5E,7S)-[[7-(5-fluoro-2-methylphenyl)-4-methyl-7,8-dihydro-5(6H)-quinolinylidene]amino]guanidine dimethanesulfonate (18, T-162559) was found to be a potent inhibitor of both rat and human platelet NHEs, with IC(50) values of 14 and 13 nM, respectively. Furthermore, in a rat myocardial infarction model in vivo (1 h ischemia-24 h reperfusion), 18 (0.1 mg/kg, intravenously administered 5 min or 2 h before coronary occlusion) showed significant activity (33% or 23% inhibition, respectively). These results suggested that 18 may exhibit a potent and long-lasting protective activity against cardiac injuries induced by ischemia-reperfusion.

Amiloride and KB-R7943 in outward Na+ /Ca2+ exchange current in guinea pig ventricular myocytes

The reverse mode of Na+/Ca2+ exchange represents an important pathway in inducing Ca2+ overload during ischemia and reperfusion. The inhibitory effects of amiloride and KB-R7943 on Na+/Ca2+ exchange current (INa/Ca) were investigated in guinea pig ventricular myocytes. Whole-cell patch clamp techniques were used under bidirectional ionic conditions and 25 mM of Na+ in pipette solution. At +50 mV, amiloride 10, 30, and 100 microM inhibited the outward INa/Ca by 15, 23, and 41%, respectively; at -80 mV, it inhibited inward INa/Ca by 6, 15, and 23%, respectively. Its inhibitory effect on outward INa/Ca was greater than that on inward INa/Ca. At +50 mV, KB-R7943 1 and 10 microM inhibited the outward INa/Ca by 29 and 61%, respectively; at -80 mV, it inhibited inward INa/Ca by 22 and 57%, respectively. KB-R7943 inhibited both directions of the exchange current with an equal potency. The data suggest that KB-R7943 is not a selective inhibitor on reverse mode of Na+/Ca2+ exchange.

Necrotic volume increase and the early physiology of necrosis

Whether a lethally injured mammalian cell undergoes necrosis or apoptosis may be determined by the early activation of specific ion channels at the cell surface. Apoptosis requires K+ and Cl- efflux, which leads to cell shrinking, an active phenomenon termed apoptotic volume decrease (AVD). In contrast, necrosis has been shown to require Na+ influx through membrane carriers and more recently through stress-activated non-selective cation channels (NSCCs). These ubiquitous channels are kept dormant in viable cells but become activated upon exposure to free-radicals. The ensuing Na+ influx leads to cell swelling, an active response that may be termed necrotic volume increase (NVI). This review focuses on how AVD and NVI become conflicting forces at the beginning of cell injury, on the events that determine irreversibility and in particular, on the ion fluxes that decide whether a cell is to die by necrosis or by apoptosis.

Use of base in the treatment of severe acidemic states

Severe acidemia (blood pH < 7.1 to 7.2) suppresses myocardial contractility, predisposes to cardiac arrhythmias, causes venoconstriction, and can decrease total peripheral vascular resistance and blood pressure, reduce hepatic blood flow, and impair oxygen delivery. These alterations in organ function can contribute to increased morbidity and mortality. Although it seemed logical to administer sodium bicarbonate to attenuate acidemia and therefore lessen the impact on cardiac function, the routine use of bicarbonate in the treatment of the most common causes of severe acidemia, diabetic ketoacidosis, lactic acidosis, and cardiac arrest, has been an issue of great controversy. Studies of animals and patients with these disorders have reported conflicting data on the benefits of bicarbonate, showing both beneficial and detrimental effects. Alternative alkalinizing agents, tris-hydroxymethyl aminomethane and Carbicarb, have shown some promise in studies of animals and humans, and reevaluation of these buffers in the treatment of severe acidemic states seems warranted. The potential value of base therapy in the treatment of severe acidemia remains an important issue, and further studies are required to determine which patients should be administered base therapy and what base should be used.

Relationship between the neuroprotective effect of Na+/H+ exchanger inhibitor SM-20220 and the timing of its administration in a transient middle cerebral artery occlusion model of rats

The aim of this study was to determine the relationship between the neuroprotective effect of SM-20220 (N(aminoiminomethyl)-1-methyl-1H-indole-2-carboxamide methanesulfonate) and the timing of its administration in an experimental stroke model. Two hours of occlusion followed by 22 h of perfusion of the left middle cerebral artery (MCA) was performed by inserting a nylon thread into the MCA to occlude it, and pulling the thread to initiate reperfusion. Intravenous infusion of SM-20220 for 1 h reduced the infarct volume at doses of 0.2-0.8 mg/kg in a dose-dependent manner without causing changes in the systemic arterial blood pressure or blood gases, when SM-20220 administration was started 1 h after the onset of occlusion. Administration of SM-20220 at a dose of 0.4 mg/kg also reduced the edema formation induced by ischemia. In contrast, SM-20220 failed to reduce the infarction, even at 1.6 mg/kg, when administration was started 2 h after the onset of occlusion. Thus, the therapeutic time window of SM-20220 for this transient MCA occlusion model is 1 h. Daily administration of SM-20220 (0.4 mg/kg) for the 7 d following 1.5 h of middle cerebral artery occlusion reduced the infarct volume with statistical significance (p<0.05), showing that SM-20220 did not merely delay but prevented ischemic damage.

Na+/H+ exchange inhibitor SM-20220 attenuates leukocyte adhesion induced by ischemia-reperfusion

Leukocytes play a key role in ischemia-reperfusion-induced tissue injuries. It has been suggested that blocking the Na+/H+ exchanger improves ischemic injuries such as stroke. In this study, we investigated the effect of the Na+/H+ exchanger inhibitor SM-20220 (N-[aminoiminomethyl]- 1-methyl-1H-indole-2-carboxamide methanesulfonate) on leukocyte-endothelial cell interactions during ischemia-reperfusion. SM-20220 (0.3-1.0 mg/kg i.v.) given after ischemia significantly attenuated the leukocyte adhesion in the mesenteric postcapillary venules that was induced by transient superior mesenteric artery occlusion. At 60 min after reperfusion, the numbers of adherent leukocytes in groups treated with vehicle or SM-20220 (0.3 mg/kg) were 15.1+/-2.9 cells/100 microm/3 min and 3.0+/-0.7 cells/100 microm/3 min (p < 0.01), respectively. In a transient middle cerebral artery occlusion model, i.v. infusion of SM-20220 (0.4 mg/kg per hour) for 1 h, beginning 1 h after the start of occlusion, significantly reduced both the infarct size and the increase in brain myeloperoxidase activity, compared with the vehicle group (p < 0.01 and p < 0.05, respectively). In summary, this is the first evidence that the leukocyte adhesion to the endothelium that is induced by ischemia-reperfusion is attenuated by the inhibition of Na+/H+ exchanger activity in vivo. Our results suggest that Na+/H+ exchanger inhibitors may prevent ischemia-reperfusion injuries such as stroke partly through the attenuation of leukocyte-endothelial cell interactions.

Discovery of zoniporide: a potent and selective sodium-hydrogen exchanger type 1 (NHE-1) inhibitor with high aqueous solubility

Zoniporide (CP-597,396) is a potent and selective inhibitor of NHE-1, which exhibits high aqueous solubility and acceptable pharmacokinetics for intravenous administration. The discovery, synthesis, activities, and rat and dog pharmacokinetics of this compound are presented. The potency and selectivity of zoniporide may be due to the conformation that the molecule adopts due to the presence of a cyclopropyl and a 5-quinolinyl substituent on the central pyrazole ring of the molecule.

Steric stabilization of fusogenic liposomes by a low-pH sensitive PEG--diortho ester--lipid conjugate

We describe the synthesis and characterization of a pH-sensitive poly(ethylene glycol)-diortho ester-distearoyl glycerol conjugate (POD). POD was prepared by a one-step synthesis, and its acid sensitivity characterized by TLC. The conjugate was found to be stable at neutral pH for greater than 3 h but degraded completely within 1 h at pH 5. Liposomes composed of 10% of POD and 90% of a fusogenic lipid, dioleoyl phosphatidylethanolamine (DOPE) were readily prepared and remained stable for up to 12 h in neutral buffer as shown by photon correlation spectrometry and a liposome contents leakage assay. However, when POD/DOPE liposomes were incubated in acidic pH as mild as 5.5, they aggregated and released most of their contents within 30 min. The kinetics of content release from POD/DOPE liposomes consisted of two phases, a lag phase, and a burst phase. The lag phase is inversely correlated with pH and the logarithm of the length of lag phase showed a linear relationship with the buffer pH. When the POD/DOPE liposomes were incubated in 75% of fetal bovine serum at 37 degrees C, they remained as stable as traditional PEG-grafted liposomes for 12 h but released 84% of the encapsulated ANTS in the following 4 h. Upon intravenous administration into mice, liposomes composed of 10% POD and 90% DOPE were cleared from circulation by a one-compartment kinetics with a half-life of about 200 min. POD is an example for the design of a novel category of pH sensitive lipids composed of a headgroup, an acid-labile diortho ester linker and a hydrophobic tail. The uniquely fast degradation kinetics of POD at pH 5-6 and its ability to stabilize liposomes in serum make the conjugate suitable for applications for triggered drug release systems targeted to mildly acidic bio-environments such as endosomes, solid tumors, and inflammatory tissues.

Na+/H+ exchange inhibitor SM-20220 improves endothelial dysfunction induced by ischemia-reperfusion

Endothelial cells play an important role in the physiologic homeostasis of the cerebral circulation. Previously, we showed that the Na+/H+ exchanger (NHE) inhibitor SM-20220 (N-(aminoimino-methyl)-1-methyl-1H-indole-2-carboxamide methanesulfonate) improved ischemic brain injury. In this study, we investigated the effect of SM-20220 on cerebrovascular dysfunction after ischemia-reperfusion, focusing on the kinds of dysfunction that involved endothelial function. In cultured bovine brain microvascular endothelial cells (BBMCs), the IC50 value for the NHE activity of SM-20220 was 4 x 10(-8) M. SM-20220 also reduced the cell injury induced by hypoxia/aglycemia-reoxygenation in BBMCs, with statistical significance at 10(-7) M (P<0.05). Next, the effect of SM-20220 on disruption of the blood-brain barrier and cerebral blood flow were evaluated using transient middle cerebral artery (MCA) occlusion models. Intravenous infusion of SM-20220 (0.4 mg/kg per hour for 1 h) attenuated the extravasation of Evans blue, a blood-brain barrier disruption indicator, into cerebral tissue on the day after transient ischemia (P<0.05). The occlusion of the MCA decreased the cerebral blood flow in the MCA territory by about 20%, and only about 45% of the preischemic value was recovered at 1-h reperfusion. A bolus injection of SM-20220 (1 mg/kg, i.v.) improved the postischemic hypoperfusion by about 75%, without causing changes in the systemic blood pressure. These results indicate that the protective effect of NHE inhibitor on ischemic brain injury may be at least partially mediated by the prevention of endothelial dysfunction.

Pharmacokinetic/pharmacodynamic evaluation of the NHE inhibitor eniporide

The aim of this study was to investigate the pharmacokinetics and pharmacodynamics of the new cardioprotective sodium/proton exchange (NHE-1) inhibitor eniporide in humans. Eniporide was administered intravenously to healthy volunteers in doses between 2.5 and 100 mg. Concentrations of parent drug and its metabolite were measured by HPLC, and the data were analyzed by noncompartmental and compartmental pharmacokinetic methods. Platelet-swelling time was determined in each subject as a biomarker to assess pharmacodynamic activity. Eniporide showed linear pharmacokinetics with an average half-life of approximately 2 hours. The mean total body clearance was 34.4 L/h. The mean volume of distribution (Vdss) was 77.5 L, and the mean residence time was 2.3 hours. An average of 43% of the dose was recovered unchanged from urine. A pharmacokinetic two-compartment model was found suitable to provide excellent curve fits of the measured plasma concentration profiles. Plasma concentrations of the major metabolite were lower than that of the parent drug. An average of 27% of the dose was found in urine as that metabolite. The effect on platelet swelling could be well characterized by a direct Emax model. The average concentration for half-maximum effect (IC50) was 12 ng/mL. Eniporide was found to have predictable linear pharmacokinetics in the investigated dose range. Platelet-swelling time was shown to be a reproducible individual biomarker for pharmacodynamic activity, with great potential for a surrogate that predicts clinical outcome, since this effect is mediated through the same mechanism of action (NHE-1 inhibition) as the desired cardioprotective activity. Pharmacokinetic/pharmacodynamic modeling allowed a first estimate of the degree of NHE inhibition in the investigated dose range.

Effect of combined K(ATP) channel activation and Na(+)/H(+) exchange inhibition on infarct size in rabbits

We tested if combining treatment with cariporide, an Na(+)/H(+) exchange inhibitor, and diazoxide, a mitochondrial ATP-sensitive K(+) (K(ATP)) channel opener, would reduce myocardial infarct size (IS) to a greater extent than either intervention alone. Four groups of rabbits were studied (n = 10 each): cariporide (0.3 mg/kg), diazoxide (10 mg/kg), both drugs, and saline control, given 15 min before a 30-min coronary artery occlusion and 3 h reperfusion. IS in controls comprised 47 +/- 6% of the risk region. Cariporide reduced IS by 55% compared with control (21 +/- 3%), but diazoxide did not significantly reduce IS compared with controls (37 +/- 6%). Combined treatment resulted in an IS of 18 +/- 5%. Also we determined that diazoxide did not potentiate a subthreshold dose of cariporide nor did a mitochondrial K(ATP) channel blocker, 5-hydroxydecanoate (5-HD), prevent cariporide from reducing IS. Thus cariporide reduced necrosis by >50% in this model, both in the presence and absence of K(ATP) channel blockade. There was no significant difference in IS reduction between the group receiving cariporide alone and the group receiving combined treatment. Because the effect of cariporide was not blocked by 5-HD, it is unlikely that K(ATP) channels play a role as an end effector in cariporide's mechanism.

Exploring new strategies for the management of acute coronary syndromes

Patients who present today with an acute coronary syndrome face a substantially lower risk of death, recurrent myocardial infarction, or severe ischemia than patients did a decade ago. Researchers are pursuing new strategies to further improve the outcomes of patients with acute coronary syndromes. These strategies may be grouped into 3 paradigms: (1) restoration and maintenance of coronary flow at the site of culprit lesion; (2) reduction of infarct size, reperfusion injury, and postischemic dysfunction; (3) stabilization of the coronary arterial wall and its interaction with the bloodstream to reduce recurrent ischemic events. The last approach encompasses strategies to alter the underlying vascular pathophysiology that leads to plaque instability and coronary thrombosis. Investigation into each of these paradigms may yield new strategies that will be incorporated into standard clinical management of acute coronary syndromes in coming years. With so many mechanistically different approaches to the management of acute coronary syndromes, clinicians have reason for optimism that continued progress will further reduce the morbidity and mortality associated with acute coronary syndromes and the likelihood of their recurrence.

Effect of SMP-300, a new Na+/H+ exchange inhibitor, on myocardial ischemia and experimental angina models in rats

We evaluated the effects of SMP-300 (N-(aminoiminomethyl)-11-chloro-5,6,7,8-tetrahydro-8-oxo-4H-pyrrolo[3,2,1-kl][1]benzazocine-2-carboxamide monomethanesulfonate monohydrate), a newly synthesized compound, on Na+/H+ exchange activity in rat cardiomyocytes and on other ion transporters, channels and receptors. We also investigated the protective effects of SMP-300 in isolated ischemic rat hearts and rat isoproterenol- or vasopressin-induced experimental angina models. SMP-300 concentration-dependently inhibited recovery from acidosis in rat myocytes, and its IC50 for Na+/H+ exchange was 6 nM. In comparison, its IC50s for Na+/Ca2+ exchange and for the Na+ channel were >1000 nM, and those for other channels or receptors tested were >10,000 nM. In rat isolated perfused hearts, SMP-300 (10(-8)-10(-7) M), administered only at preischemia and not during reperfusion, significantly improved the postischemic recovery of cardiac function. SMP-300 (0.03-0.3 mg/kg, i.v.) or 5-(N-ethyl-N-isopropyl)-amiloride (1 mg/kg, i.v.) prevented the isoproterenol-induced ST-segment depression in the ECG of anesthetized rats, in a dose-dependent manner. SMP-300 (0.1 mg/kg, i.v.) and 5-(N-ethyl-N-isopropyl)-amiloride (1 mg/kg, i.v.) also inhibited the vasopressin-induced ST-segment depression in the ECG of anesthetized rats. This is the first report presenting the protective effect of Na+/H+ exchange inhibitors on isoproterenol- or vasopressin-induced ECG changes in rats, providing the future perspective of SMP-300, a potent Na+/H+ exchange inhibitor, as an anti-anginal drug.

Prediction of inhibition of the sodium ion-proton antiporter by benzoylguanidine derivatives from molecular structure

The use of quantitative structure-activity relationships to predict IC50 values of 113 potential Na+/H+ antiporter inhibitors is reported. Multiple linear regression and computational neural networks (CNNs) are used to develop models using a set of information-rich descriptors. The descriptors encode information about topology, geometry, electronics, and combination hybrids. A five-descriptor CNN model with root-mean-square (rms) errors of 0.278 log units for the training set and 0.377 log units for the prediction set was developed. Examination of data set subclasses showed that systematic structural variations were also well-encoded resulting in 100% accuracy of prediction trends. An experiment involving a committee of five CNNs was also performed to examine the effect of network output averaging. This showed improved results decreasing the training and cross-validation set rms error to 0.228 log units and the prediction set rms error to 0.296 log units.