Resuscitation with Na+/H+exchanger inhibitor in traumatic haemorrhagic shock: Cardiopulmonary performance, oxygen transport and tissue inflammation

The role of CD44, hyaluronan and NHE1 in cardiac remodeling

Cardiac remodeling, characterized by excessive extracellular matrix (ECM) remodeling, predisposes the heart to failure if left unresolved. Understanding the signaling mechanisms involved in excessive extracellular matrix (ECM) remodeling is necessary to identify the means to regress the development of cardiac remodeling and heart failure. Recently, hyaluronan (HA), a ubiquitously expressed glycosaminoglycan in the ECM, was shown to participate in tissue fibrosis and myofibroblast proliferation through interacting with its ubiquitously expressed cell-surface receptor, CD44. CD44 is a multifunctional transmembrane glycoprotein that serves as a cell-surface receptor for a number of ECM proteins. The mechanism by which the interaction between CD44-HA contributes to ECM and cardiac remodeling remains unknown. A previous study performed on a non-cardiac model showed that CD44-HA enhances Na⁺/H⁺ exchanger isoform-1 (NHE1) activity, causing ECM remodeling, HA metabolism and tumor invasion. Interestingly, NHE1 has been demonstrated to be involved in cardiac remodeling and myocardial fibrosis. In addition, it has previously been demonstrated that CD44 is upregulated in transgenic mouse hearts expressing active NHE-1. The role of CD44, HA and NHE1 and the cellular interplay of these factors in the ECM and cardiac remodeling is the focus of this review.

Role of epithelial ion transports in inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic inflammatory disorder with a complex pathogenesis. Diarrhea is a highly prevalent and often debilitating symptom of IBD patients that results, at least in part, from an intestinal hydroelectrolytic imbalance. Evidence suggests that reduced electrolyte absorption is more relevant than increased secretion to this disequilibrium. This systematic review analyses and integrates the current evidence on the roles of epithelial Na(+)-K(+)-ATPase (NKA), Na(+)/H(+) exchangers (NHEs), epithelial Na(+) channels (ENaC), and K(+) channels (KC) in IBD-associated diarrhea. NKA is the key driving force of the transepithelial ionic transport and its activity is decreased in IBD. In addition, the downregulation of apical NHE and ENaC and the upregulation of apical large-conductance KC all contribute to the IBD-associated diarrhea by lowering sodium absorption and/or increasing potassium secretion.

Role of NHE1 in the cellular dysfunction of acute metabolic acidosis

BACKGROUND

Metabolic acidosis is associated with impaired cellular function. This has been attributed to the accompanying reduction in intracellular and interstitial pH of the myocardium. Recent studies suggest that activation of the cellular Na(+)-H(+) exchanger NHE1 might contribute to myocardial dysfunction. This review examines the experimental evidence which supports the role of NHE1 in the genesis of acidosis-induced cellular dysfunction, the benefits of its inhibition, and the type of acidosis that might benefit from therapy.

SUMMARY

Information was obtained by searching MEDLINE for articles published between 1969 and 2013 using the terms: NHE1, metabolic acidosis, lactic acidosis, ischemia-reperfusion, shock, resuscitation, high anion gap acidosis, and non-gap acidosis. Each article was also reviewed for additional suitable references. Nineteen manuscripts published between 2002 and 2013 assessed the impact of inhibition of NHE1 on cellular function. They revealed that NHE1 is activated with metabolic acidosis associated with hypoxia, hypoperfusion, hemorrhagic shock, and sepsis. This was associated with a rise in cellular sodium and calcium and cardiac dysfunction including reduced contractility and a predisposition to cardiac arrhythmias. Inhibition of NHE1 with specific inhibitors improved cardiac function, reduced blood and tissue levels of proinflammatory cytokines, and decreased mortality. Key Message: These results suggest that use of inhibitors of NHE1 might be worthwhile in the treatment of some types of acute metabolic acidosis, specifically the lactic acidosis associated with hypoxia, hemorrhagic shock, and cardiac arrest. Its potential role in the treatment of other forms of acute metabolic acidosis remains to be determined.

Sabiporide reduces ischemia-induced arrhythmias and myocardial infarction and attenuates ERK phosphorylation and iNOS induction in rats

The aim of the present study was to investigate the effects of sabiporide, a potent and selective NHE1 inhibitor, on myocardial ischemia-induced arrhythmias and myocardial infarction and the possible pathways related to the cardioprotection afforded by sabiporide treatment. Anesthetized rats were subjected to myocardial ischemia via left main coronary artery occlusion for 30 minutes, followed by 2 hours of reperfusion. Administration of sabiporide (0.01–3.0 mg/kg) prior to coronary artery occlusion dose-dependently reduced ischemia-induced arrhythmias and infarct size with an ED50 value of 0.14 mg/kg. Administration of sabiporide (1.0 mg/kg) prior to reperfusion also reduced infarct size by 38.6%. The reduction in infarct size was accompanied by a decrease in circulating levels of creatine phosphokinase and troponin I. In addition, sabiporide (1.0 mg/kg) given prior to coronary artery occlusion or immediately before reperfusion significantly reduced phosphorylation of the extracellular signal-regulated kinase (ERK1/2) and the expression of the inducible nitric oxide synthase (iNOS) following myocardial ischemia-reperfusion. This study demonstrates that sabiporide is a potent and effective cardioprotective agent during myocardial ischemia and reperfusion, by reducing serious ventricular arrhythmias and myocardial infarct size. The cardioprotection afforded by sabiporide is attributed in part to inhibition of ERK1/2 phosphorylation and suppression of iNOS expression.

Mechanisms of the beneficial effect of NHE1 inhibitor in traumatic hemorrhage: inhibition of inflammatory pathways

This study evaluated the effects of sodium-hydrogen exchanger (NHE1) inhibition on enhancing fluid resuscitation outcomes in traumatic hemorrhagic shock, and examined the mechanisms related to NHE1 inhibitor-induced protection and recovery from hemorrhagic shock. Traumatic hemorrhage was modeled in anesthetized pigs by producing tibia fractures followed by hemorrhage of 25 ml/kg for 20 min, and then a 4mm hepatic arterial tear with surgical repair after 20 min. Animals then underwent low volume fluid resuscitation with either hextend (n=6) or 3mg/kg BIIB513 (NHE1 inhibitor)+hextend (n=6). The experiment was terminated 6h after the beginning of resuscitation. In association with traumatic hemorrhagic shock, there was a decrease in cardiac index, stimulation of the inflammatory response, myocardial, liver and kidney injury. The administration of the NHE1 inhibitor at the time of resuscitation attenuated shock-resuscitation-induced myocardial hypercontracture and resulted in a significant increase in stroke volume index, compared to vehicle-treated controls. NHE1 inhibition also reduced the inflammatory response, and lessened myocardial, liver and kidney injury. In addition, NHE1 inhibition reduced NF-κB activation and iNOS expression, and attenuated of ERK1/2 phosphorylation. Results from the present study indicate that NHE1 inhibition prevents multiple organ injury by attenuating shock-resuscitation-induced myocardial hypercontracture and by inhibiting NF-κB activation and neutrophil infiltration, reducing iNOS expression and ERK1/2 phosphorylation, thereby, reducing systemic inflammation and thus multi-organ injury.