Role of endothelins in septic, cardiogenic, and hemorrhagic shock

New directions for sepsis and septic shock research

BACKGROUND

Septic shock is a frequent complication in intensive care unit that can result in multiple organ failure and death. In addition, recent data suggested that severe sepsis and septic shock represent an economic burden. Therefore, septic shock is an important public health problem.

METHOD

In this review, we will focus on the recent evidences concerning the stages of septic shock, the complex macrocirculation and microcirculation relationship, and the importance of those evidences for future resuscitation goals and therapeutic strategies during late septic shock.

RESULT

Recently, two stages of septic shock are suggested. In early stage, hypovolemia is the main contributing factor. During this stage, macrocirculatory and microcirculatory changes run parallel, and fluid resuscitation seems to be effective in restoring the hemodynamic parameters. Late stage of septic shock is characterized by complex microcirculation and macrocirculation relationship.

CONCLUSIONS

Although early goal-directed therapy is a stepwise approach in the treatment of septic shock, tissue perfusion remains an important factor that contributes to septic shock outcome. Because appropriate monitoring of tissue perfusion is a matter of debt, the ideal therapeutic strategy remains a controversial issue that needs further investigations.

Evaluation of the serum levels of soluble IL-2 receptor and endothelin-1 in children with Crimean-Congo hemorrhagic fever

We aimed to assess the association between serum levels of soluble IL-2 receptor (sIL-2r) and endothelin-1 and severe infection in children with Crimean-Congo hemorrhagic fever (CCHF). Fifty-two patients under 18 years of age with a laboratory- confirmed diagnosis of CCHF and 38 healthy controls were enrolled in the study. Patients were classified into two groups based on disease severity (severe group and non-severe group). The sIL-2r and endothelin-1 levels were observed to be significantly higher in patients with severe CCHF compared with those with non-severe CCHF and the control group (p < 0.05). In addition, those with non-severe CCHF were also found to have a significantly higher sIL-2r level relative to the control group (p < 0.001). Although there was a positive correlation between sIL-2r and endothelin-1 levels, serum levels of both sIL-2r and endothelin-1 were negatively correlated with the platelets count. In children with CCHF, serum levels of sIL-2r and endothelin-1 were increased, and this increase is related to the severity of the disease. In this study, we concluded through prognosis that serum levels of sIL-2r and endothelin-1 might be related, and that hemophagocytic lymphohistiocytosis and endothelial injury might contribute to a pathogenesis of the disease.

Postmortem diagnosis of acute myocardial infarction in patients with acute respiratory failure: demographics, etiologic and pulmonary histologic analysis

OBJECTIVES

Acute respiratory failure is present in 5% of patients with acute myocardial infarction and is responsible for 20% to 30% of the fatal post-acute myocardial infarction. The role of inflammation associated with pulmonary edema as a cause of acute respiratory failure post-acute myocardial infarction remains to be determined. We aimed to describe the demographics, etiologic data and histological pulmonary findings obtained through autopsies of patients who died during the period from 1990 to 2008 due to acute respiratory failure with no diagnosis of acute myocardial infarction during life.

METHODS

This study considers 4,223 autopsies of patients who died of acute respiratory failure that was not preceded by any particular diagnosis while they were alive. The diagnosis of acute myocardial infarction was given in 218 (4.63%) patients. The age, sex and major associated diseases were recorded for each patient. Pulmonary histopathology was categorized as follows: diffuse alveolar damage, pulmonary edema, alveolar hemorrhage and lymphoplasmacytic interstitial pneumonia. The odds ratio of acute myocardial infarction associated with specific histopathology was determined by logistic regression.

RESULTS

In total, 147 men were included in the study. The mean age at the time of death was 64 years. Pulmonary histopathology revealed pulmonary edema as well as the presence of diffuse alveolar damage in 72.9% of patients. Bacterial bronchopneumonia was present in 11.9% of patients, systemic arterial hypertension in 10.1% and dilated cardiomyopathy in 6.9%. A multivariate analysis demonstrated a significant positive association between acute myocardial infarction with diffuse alveolar damage and pulmonary edema.

CONCLUSIONS

For the first time, we demonstrated that in autopsies of patients with acute respiratory failure as the cause of death, 5% were diagnosed with acute myocardial infarction. Pulmonary histology revealed a significant inflammatory response, which has not previously been reported.

Endothelin-1 attenuates the hemodynamic response to exogenous epinephrine in a porcine ischemic ventricular fibrillation cardiac arrest model

Endothelin-1 (ET-1) increases in the ischemically induced ventricular fibrillation (VF) swine model of cardiac arrest and affects outcome by potentially attenuating the hemodynamic response to epinephrine. Fifty-one swine underwent percutaneous left anterior descending occlusion. Seven minutes postonset of ischemic VF, cardiopulmonary resuscitation (CPR) was initiated. If VF persisted after 3 shocks, 1 mg of epinephrine was given. ET-1 (collected at baseline and every 5 min until VF onset) was assayed with ELISA. Bayesian multivariate logistic regression analysis compared peak ET-1 levels with the binary outcome of a positive coronary perfusion pressure response of >20 mmHg following epinephrine. Sixteen animals (31%) failed to achieve a positive response. Restoration of spontaneous circulation (ROSC) was observed in 1/16 (6.3%) of epinephrine nonresponders and 20/35 (57.1%) of epinephrine responders (P = 0.0006). The median peak ET-1 level was 2.71 pg/mL [interquartile range (IQR) 1.06-4.40] in nonresponders and 1.69 pg/mL (IQR 0.99-2.35) in responders. ET-1 levels were inversely associated with epinephrine response with a median posterior odds ratio (OR) of a coronary perfusion pressure response of 0.72 (95% confidence interval [CI] 0.48-1.06) for each one-unit increase in ET-1 and a probability that the associated OR is <1 of 0.95. Peak ET-1 levels predict a lack of a hemodynamic response to epinephrine during treatment of cardiac arrest during ischemic VF.

Plasma endothelin-1 level at the onset of ischemic ventricular fibrillation predicts resuscitation outcome

BACKGROUND

Endogenous vasopressors, including endothelin-1 (ET-1), have been shown to be elevated in patients following resuscitation from out-of-hospital cardiac arrest and are likely a physiologic response to global ischaemia. The importance of ET-1 in the setting of arrest and resuscitation has not been established. Prior work has demonstrated that ET-1 increases significantly after coronary occlusion. The purpose of this study was to assess changes in ET-1 following induction of ischaemia and VF.

METHODS

VF was induced in 30 anesthetized and instrumented swine by balloon occlusion of the LAD. Blood was collected from the right atrium at baseline and at 5 min intervals following LAD occlusion until VF occurred. After 7 min of VF, resuscitation was attempted in accordance with guidelines. ET-1 and matrix metalloproteinase-9 (MMP-9), a measure of infarct size, were measured using ELISA.

RESULTS

ET-1 and MMP-9 levels increased significantly from baseline within 20 min of occlusion of the LAD. Animals that could not be resuscitated had a higher ET-1 (p=0.031) at VF onset but similar ischaemia time (time to VF) and MMP-9, reflecting infarct size. An ET-1 level >4 pg/ml had a likelihood ratio of 4 for predicting resuscitation failure.

CONCLUSIONS

Elevated levels of ET-1 during acute ischaemia predict resuscitation failure independent of the time to VF. This finding may be due to the known effect of ET-1 on coronary vascular resistance or ventricular compliance, resulting in early ischemic contracture.

Molecular mechanism of mast cell mediated innate defense against endothelin and snake venom sarafotoxin

Mast cells are protective against snake venom sarafotoxins that belong to the endothelin (ET) peptide family. The molecular mechanism underlying this recently recognized innate defense pathway is unknown, but secretory granule proteases have been invoked. To specifically disrupt a single protease function without affecting expression of other proteases, we have generated a mouse mutant selectively lacking mast cell carboxypeptidase A (Mc-cpa) activity. Using this mutant, we have now identified Mc-cpa as the essential protective mast cell enzyme. Mass spectrometry of peptide substrates after cleavage by normal or mutant mast cells showed that removal of a single amino acid, the C-terminal tryptophan, from ET and sarafotoxin by Mc-cpa is the principle molecular mechanism underlying this very rapid mast cell response. Mast cell proteases can also cleave ET and sarafotoxin internally, but such “nicking” is not protective because intramolecular disulfide bridges maintain peptide function. We conclude that mast cells attack ET and sarafotoxin exactly at the structure required for toxicity, and hence sarafotoxins could not “evade” Mc-cpa's substrate specificity without loss of toxicity.

Circulating cardiovascular markers and mediators in acute illness: an update

An update is given of the circulating markers and mediators of cardiovascular dysfunction in acute illness. Some of these circulating markers reflect mediator action on the peripheral vasculature, such as endothelium-derived endothelin and nitrite/nitritate, the stable end products of nitric oxide. Other markers mainly reflect actions on the heart, such as the natriuretic peptide family, released from the heart upon dilatation, serving as a marker of congestive heart failure and potentially having negative inotropic effects. Indeed, some factors may be both markers as well as mediators of cardiovascular dysfunction of the acutely ill and bear prognostic significance. Assessing circulating levels may help refine clinical judgment of the cardiovascular derangements encountered at the bedside, together with clinical signs and hemodynamic variables. For instance, assessing natriuretic peptides in patients with pulmonary edema of unclear origin may help to diagnose congestive heart failure and cardiogenic pulmonary edema, when the pulmonary capillary wedge pressure is not measured or inconclusive. Future aligning of hemodynamic abnormalities with patterns of circulating cardiovascular markers/mediators may help to stratify patients for inclusion in studies to assess the causes, response to therapy and prognosis of cardiovascular derangements in the acutely ill.

Regulation of vasopressin secretion by ETA and ETB receptors in compartmentalized rat hypothalamo-neurohypophysial explants

The endothelins (ET) have been implicated in vasopressin (AVP) release in vivo and in vitro. The effects of ET in this system are complex, and the net AVP secretory response likely depends on a unique combination of ET isoform, ET receptor subtype, and neural locus. The purpose of these studies was to examine the role of ET receptor subtypes at hypothalamic vs. neurohypophysial sites on somatodendritic and neurohypophysial AVP secretion. Experiments were done in cultured explants of the hypothalamo-neurohypophysial system of Long Evans rats. Either the whole explant (standard) or only the hypothalamus or posterior pituitary (compartmentalized) was exposed to log dose increases (0.01-10 nM) of the agonists ET-1 (ET(A) selective), ET-3 (nonselective), or IRL-1620 (ET(B) selective) with or without selective ET(A) (BQ-123, 2-200 nM) or ET(B) (IRL-1038, 6-600 nM) receptor antagonism. In standard explants, ET-1 and ET-3 dose-dependently increased, whereas IRL-1620 decreased net AVP release. Hypothalamic ET(B) receptor activation increased both somatodendritic and neurohypophysial AVP release. At least one intervening synapse was involved, as tetrodotoxin blocked the response. Activation of ET(A) receptors at the hypothalamic level inhibited, whereas ET(A) receptor activation at the posterior pituitary stimulated, neurohypophysial AVP secretion. Antagonism of hypothalamic ET(A) receptors potentiated the stimulatory effect of ET-1 and ET-3 on neurohypophysial secretion, an effect not observed with ET(B) receptor-induced somatodendritic release of AVP. Thus the response of whole explants reflects the net result of both stimulatory and inhibitory inputs. The integration of these excitatory and inhibitory inputs endows the vasopressinergic system with greater plasticity in its response to physiological and pathophysiological states.