Endothelin-1 mediates cardiac mast cell degranulation, matrix metalloproteinase activation, and myocardial remodeling in rats

The endothelin axis and gelatinase activity in alveolar macrophages after brain-stem death injury: a pilot study

BACKGROUND

Endothelin-1 (ET-1) is a potent vasoconstricting mitogen that has been implicated in the development of primary graft dysfunction. Increased activity of matrix metalloproteinases (MMPs), specifically MMP-2 and -9, has been associated with tissue damage in acute lung injury and after lung transplantation. Using a validated model of brain-stem death (BSD), we aimed to determine whether alveolar macrophage up-regulation in the pulmonary system is an early feature of BSD injury and if expression levels of ET-1, endothelin A receptors (ET(A)R) and endothelin B receptors (ET(B)R), as well as MMP-2 and -9, are increased in comparison to sham controls.

METHODS

Six control and 8 experimental Wistar-Kyoto rats had a balloon catheter inserted into their subdural space. In the experimental group the balloon was inflated for 4 hours. Lung specimens were immunohistochemically labeled with CD68, ET-1, ET(A)R, ET(B)R, MMP-2 and MMP-9, and 10 fields per slide were assessed.

RESULTS

The ratio of alveolar macrophages to polymorphonuclear neutrophils was significantly greater in the BSD group than in controls (9 +/- 4.1 vs 3 +/- 0.5, p = 0.004) and adventitial macrophages increased in BSD lung parenchyma (p < 0.0001). ET-1, ET(A)R and ET(B)R levels were elevated in the experimental group (27.6 +/- 5.7 vs 7 +/- 2.3, 36.1 +/- 4.6 vs 17.7 +/- 2.6 and 60 +/- 7.1 vs 19.8 +/- 3.7, p < 0.0001 inclusive). BSD expression of MMP-2 and MMP-9 was double that of controls (14.9 +/- 3.4 vs 30.7 +/- 3.4 and 14.2 +/- 2.2 vs 37 +/- 3.6, respectively, p < 0.0001 inclusive).

CONCLUSIONS

Alveolar macrophages are rapidly recruited after BSD and may affect peri-operative lung function via increased expression of ET-1, ET(A)R, ET(B)R, MMP-2 and MMP-9.

Elevated plasma endothelin-1 and pulmonary arterial pressure in children exposed to air pollution

BACKGROUND

Controlled exposures of animals and humans to particulate matter (PM) or ozone air pollution cause an increase in plasma levels of endothelin-1, a potent vasoconstrictor that regulates pulmonary arterial pressure.

OBJECTIVES

The primary objective of this field study was to determine whether Mexico City children, who are chronically exposed to levels of PM and O(3) that exceed the United States air quality standards, have elevated plasma endothelin-1 levels and pulmonary arterial pressures.

METHODS

We conducted a study of 81 children, 7.9 +/- 1.3 years of age, lifelong residents of either northeast (n = 19) or southwest (n = 40) Mexico City or Polotitlán (n = 22), a control city with PM and O(3) levels below the U.S. air quality standards. Clinical histories, physical examinations, and complete blood counts were done. Plasma endothelin-1 concentrations were determined by immunoassay, and pulmonary arterial pressures were measured by Doppler echocardiography.

RESULTS

Mexico City children had higher plasma endothelin-1 concentrations compared with controls (p < 0.001). Mean pulmonary arterial pressure was elevated in children from both northeast (p < 0.001) and southwest (p < 0.05) Mexico City compared with controls. Endothelin-1 levels in Mexico City children were positively correlated with daily outdoor hours (p = 0.012), and 7-day cumulative levels of PM air pollution < 2.5 mum in aerodynamic diameter (PM(2.5)) before endothelin-1 measurement (p = 0.03).

CONCLUSIONS

Chronic exposure of children to PM(2.5) is associated with increased levels of circulating endothelin-1 and elevated mean pulmonary arterial pressure.

Renin: at the heart of the mast cell

Cardiac mast cells proliferate in cardiovascular diseases. In myocardial ischemia, mast cell mediators contribute to coronary vasoconstriction, arrhythmias, leukocyte recruitment, and tissue injury and repair. Arrhythmic dysfunction, coronary vasoconstriction, and contractile failure are also characteristic of cardiac anaphylaxis. In coronary atherosclerosis, mast cell mediators facilitate cholesterol accumulation and plaque destabilization. In cardiac failure, mast cell chymase causes myocyte apoptosis and fibroblast proliferation, leading to ventricular dysfunction. Chymase and tryptase also contribute to fibrosis in cardiomyopathies and myocarditis. In addition, mast cell tumor necrosis factor-alpha promotes myocardial remodeling. Cardiac remodeling and hypertrophy in end-stage hypertension are also induced by mast cell mediators and proteases. We recently discovered that cardiac mast cells contain and release renin, which initiates local angiotensin formation. Angiotensin causes coronary vasoconstriction, arrhythmias, fibrosis, apoptosis, and endothelin release, all demonstrated mechanisms of mast-cell-associated cardiac disease. The effects of angiotensin are further amplified by the release of norepinephrine from cardiac sympathetic nerves. Our discovery of renin in cardiac mast cells and its release in pathophysiological conditions uncovers an important new pathway in the development of mast-cell-associated heart diseases. Several steps in this novel pathway may constitute future therapeutic targets.

Response of cardiac mast cells to atrial natriuretic peptide

Previously, our laboratory demonstrated that cardiac mast cell degranulation induces adverse ventricular remodeling in response to chronic volume overload. The purpose of this study was to investigate whether atrial natriuretic peptide (ANP), which is known to be elevated in chronic volume overload, causes cardiac mast cell degranulation. Relative to control, ANP induced significant histamine release from peritoneal mast cells, whereas isolated cardiac mast cells were not responsive. Infusion of ANP (225 pg/ml) into blood-perfused isolated rat hearts produced minimal activation of cardiac mast cells, similar to that seen in the control group. ANP also did not increase matrix metalloproteinase-2 activity, reduce collagen volume fraction, or alter diastolic or systolic cardiac function compared with saline-treated controls. In a subsequent study to evaluate the effects of natriuretic peptide receptor antagonism on volume overload-induced ventricular remodeling, anantin was administered to rats with an aortocaval fistula. Comparable increases of myocardial MMP-2 activity in treated and untreated rats with an aortocaval fistula were associated with equivalent decreases in ventricular collagen (P < 0.05 vs. sham-operated controls). Cardiac functional parameters and left ventricular hypertrophy were unaffected by anantin. We conclude that ANP is not a cardiac mast cell secretagogue and is not responsible for the cardiac mast cell-mediated adverse ventricular remodeling in response to volume overload.

Pitavastatin improves cardiac function and survival in association with suppression of the myocardial endothelin system in a rat model of hypertensive heart failure

Statin therapy may be associated with lower mortality in patients with heart failure, but the underlying mechanism of such an association is unknown. We have evaluated the effects of pitavastatin on cardiac function and survival in a rat model of hypertensive heart failure and investigated the molecular mechanism of the observed effects. Dahl salt-sensitive rats fed with high-salt diet from 7 weeks of age developed compensatory left ventricular hypertrophy at 12 weeks and heart failure at 19 weeks. Dahl salt-sensitive rats were treated with either vehicle or pitavastatin (0.3 mg/kg per day) from 7 or 12 weeks. Both early-onset and late-onset pitavastatin treatment reduced left ventricular fibrosis, improved cardiac function, and increased the survival rate apparent at 19 weeks. The increases in the expression levels of hypertrophic, profibrotic, and metalloproteinase genes as well as in gelatinase activities in the heart induced by the high-salt diet were suppressed by pitavastatin treatment. Furthermore, the level of cardiac endothelin-1 was increased in association with the development of heart failure in a manner sensitive to treatment with pitavastatin. Both early and late pitavastatin treatment thus improved cardiac function and survival, with modulation of extracellular matrix remodeling and endothelin-1 signaling possibly contributing to these beneficial effects.

Pharmacologic inhibition of mast cell degranulation prevents left ventricular remodeling induced by chronic volume overload in rats

BACKGROUND

Left ventricular (LV) hypertrophy and dilation are important compensatory responses to chronic volume overload; however, the mechanisms responsible for this LV remodeling have not been well characterized. Previous observations that the number of myocardial mast cells are increased in congestive heart failure (CHF) suggested the hypothesis that mast cells might be involved in the ventricular remodeling induced by a chronic volume overload.

METHODS AND RESULTS

Accordingly, the intent of this study was to determine the contribution of mast cells to LV remodeling, dysfunction, and morbidity/mortality secondary to CHF in the infrarenal aortocaval fistula model of sustained volume overload. To this end, LV end-diastolic pressure, size, and function (ie, isovolumetric pressure-volume relations in the blood-perfused isolated heart) were assessed in both nedocromil sodium treated and untreated rats at 8 weeks after fistula and compared with age-matched controls. Nedocromil, a mast cell-stabilizing drug, effectively prevented the LV dilation and decreased contractility seen in the untreated fistula group in a dose-dependent fashion, resulting in a significant reduction in the incidence of morbidity/mortality from CHF.

CONCLUSION

The ability of mast cell stabilization to prevent ventricular dilation induced by chronic volume overload identifies a key role for mast cells in the regulation of myocardial remodeling.

Vitamin D in chronic kidney disease: A systemic role for selective vitamin D receptor activation

Hyperparathyroidism occurs in most patients during the progression of chronic kidney disease (CKD) and one of its initiating events, reduced serum levels of 1,25-dihydroxyvitamin D, results from a decrease in renal 1alpha hydroxylase activity, which converts 25-hydroxyvitamin D to its activated form. The combination of persistently high parathyroid hormone (PTH) and low 1,25-dihydroxyvitamin D is associated with bone loss, cardiovascular disease, immune suppression and increased mortality in patients with end-stage kidney failure. Recent studies in dialysis patients suggest that paricalcitol, a selective activator of the vitamin D receptor (VDR), is associated with a more favorable efficacy to side effect profile than calcitriol, with less morbidity and better survival. One hypothesis derived from such studies suggests that systemic activation of VDRs may have direct effects on the cardiovascular system to decrease mortality in CKD. Although current guidelines for regulating serum calcium, phosphate and PTH recommend specific interventions at the various stages of CKD to prevent or postpone irreversible parathyroid disease and decrease cardiovascular morbidity and mortality, emerging data suggest that vitamin D therapy may prolong survival in this patient population by mechanisms that are independent of calcium, phosphate and PTH. It is suggested that a re-evaluation of current treatment recommendations is needed and that future research should focus on mechanisms that distinguish potential tissue specific benefits of selective VDR activators in patients with CKD.

Kounis syndrome (allergic angina and allergic myocardial infarction): a natural paradigm?

Inflammatory mediators including histamine, neutral proteases, arachidonic acid products, platelet activating factor and a variety of cytokines and chemokines are increased in blood or urine in both allergic episodes and acute coronary syndromes. The release of mediators during allergic insults has been incriminated to induce coronary artery spasm and/or atheromatous plaque erosion or rupture. A common pathway between allergic and non-allergic coronary syndromes seems to exist. Today, there is evidence that mast cells not only enter the culprit region before plaque erosion or rupture but they release their contents before an actual coronary episode. Kounis syndrome is the concurrence of acute coronary syndromes with conditions associated with mast cell activation including allergic or hypersensitivity and anaphylactic or anaphylactoid insults. It is caused by inflammatory mediators released through mast cell activation. Kounis syndrome, as consequence, of the above pathophysiologic association is regarded as nature's own experiment and magnificent natural paradigm showing novel way in an effort to prevent acute coronary syndromes. Drugs and natural molecules which stabilize mast cell membrane and monoclonal antibodies that protect mast cell surface could emerge as novel therapeutic modalities capable to prevent acute coronary and cerebrovascular events.

Modulation of cardiac mast cell-mediated extracellular matrix degradation by estrogen

There are fundamental differences between males and females with regard to susceptibility to heart disease. Although numerous animal models of heart failure have demonstrated that premenopausal females are afforded cardioprotection and, therefore, fare better in the face of cardiac disease than their male counterparts, many questions as to how this occurs still exist. Recently, we showed that 1) increased mast cell density is associated with adverse ventricular remodeling and 2) chemically induced mast cell degranulation using compound 48/80 resulted in remarkable changes in matrix metalloproteinase (MMP) activity, cardiac collagen structure, and cardiac diastolic function in normal male rats. With the known gender differences in cardiac disease in mind, we sought to examine the effects of chemically induced cardiac mast cell degranulation in isolated, blood-perfused hearts of intact female rats, ovariectomized female rats, and ovariectomized female rats treated with 17β-estradiol. In response to mast cell degranulation, no significant differences in cardiac function, MMP-2 activity, or collagen volume fraction were observed between intact female rats and ovariectomized female rats treated with estrogen. In the ovariectomized female group, a significant rightward shift in the left ventricular pressure-volume relation, accompanied by a marked 133% increase in active MMP-2 values over that in the intact female group, was noted after treatment with compound 48/80 ( P ≤ 0.05), along with a significant reduction in collagen volume fraction below control (0.46 ± 0.23 vs. 0.73 ± 0.13%, P ≤ 0.05). These findings indicate that estrogen's cardioprotective role can be partially mediated by its effects on cardiac mast cells, MMPs, and the extracellular matrix.

The effect of bosentan on matrix metalloproteinase-9 levels in patients with systemic sclerosis-induced pulmonary hypertension

OBJECTIVE

Systemic sclerosis (SSc) is an autoimmune disease that can potentially involve all tissues and organs of the human body. Based on the extent of the disease and organ involvement, different subsets of patients and organ involvement, different subsets of patients have been identified and several classifications proposed have been identified and several classifications proposed aiming to better stratify affected patients. The occurrence aiming to better stratify affected patients. The occurrence of pulmonary arterial hypertension (PAH), characterized of pulmonary arterial hypertension (PAH), characterized by altered tissue remodelling of the entire vessel wall, is the most severe complication that influences prognosis and survival. The molecular basis underlying the vascular damage is not yet known, but a family of enzymes named matrix metalloproteinases (MMPs), with a proteolytic activity towards several extra-cellular matrix (ECM) components, is likely to be involved. Recently, a dual inhibitor of endothelin-1, bosentan, has been successfully evaluated in clinical trials in PAH patients.

RESEARCH DESIGN AND METHOD

The aim of this study is to investigate the expression of MMP-2 and MMP-9 in the serum of different subsets of SSc patients, and in patients treated with bosentan. Thirty-five Caucasian patients with SSc were enrolled in the study, 12 of whom were found to have isolated PAH assessed by Doppler echocardiography. Eight patients fully met the inclusion criteria and were eligible for therapy with bosentan given at the dosage of 62.5 mg twice daily for 4 weeks followed by 125 mg twice daily for 50 weeks(15). The remaining patients (4/12) initiated bosentan therapy for a few weeks and, therefore, were considered at the baseline level only. Serum samples were analysed by gelatine zymography.

RESULTS

The results suggest that MMP-9 but not MMP-2 is differently expressed according to the degree of organ involvement. In particular, MMP-9 serum levels are significantly decreased in PAH with respect to other subsets of SSc patients. Moreover, in bosentan-treated patients, after 12 months of therapy MMP-9 significantly (p < 0.05) increased and correlated with an improved clinical outcome, as measured by the '6-minutes walking' test.

CONCLUSIONS

This is the first time that MMP-9 serum levels are reported to be down-regulated in PAH patients and up-regulated following bosentan treatment. Whether MMP-9 has a pathogenetic role in the vascular damage observed in PAH patients or it is a marker of bosentan effectiveness is not yet known. However, MMP-9 may be an important molecule that needs further investigation in SSc patients to better define its role.