Improvement of renal dysfunction in rats with chronic heart failure after myocardial infarction by treatment with the endothelin A receptor antagonist, LU 135252

Edema formation in congestive heart failure and the underlying mechanisms

Congestive heart failure (HF) is a complex disease state characterized by impaired ventricular function and insufficient peripheral blood supply. The resultant reduced blood flow characterizing HF promotes activation of neurohormonal systems which leads to fluid retention, often exhibited as pulmonary congestion, peripheral edema, dyspnea, and fatigue. Despite intensive research, the exact mechanisms underlying edema formation in HF are poorly characterized. However, the unique relationship between the heart and the kidneys plays a central role in this phenomenon. Specifically, the interplay between the heart and the kidneys in HF involves multiple interdependent mechanisms, including hemodynamic alterations resulting in insufficient peripheral and renal perfusion which can lead to renal tubule hypoxia. Furthermore, HF is characterized by activation of neurohormonal factors including renin-angiotensin-aldosterone system (RAAS), sympathetic nervous system (SNS), endothelin-1 (ET-1), and anti-diuretic hormone (ADH) due to reduced cardiac output (CO) and renal perfusion. Persistent activation of these systems results in deleterious effects on both the kidneys and the heart, including sodium and water retention, vasoconstriction, increased central venous pressure (CVP), which is associated with renal venous hypertension/congestion along with increased intra-abdominal pressure (IAP). The latter was shown to reduce renal blood flow (RBF), leading to a decline in the glomerular filtration rate (GFR). Besides the activation of the above-mentioned vasoconstrictor/anti-natriuretic neurohormonal systems, HF is associated with exceptionally elevated levels of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP). However, the supremacy of the deleterious neurohormonal systems over the beneficial natriuretic peptides (NP) in HF is evident by persistent sodium and water retention and cardiac remodeling. Many mechanisms have been suggested to explain this phenomenon which seems to be multifactorial and play a major role in the development of renal hyporesponsiveness to NPs and cardiac remodeling. This review focuses on the mechanisms underlying the development of edema in HF with reduced ejection fraction and refers to the therapeutic maneuvers applied today to overcome abnormal salt/water balance characterizing HF.

A Clinically Relevant Functional Model of Type-2 Cardio-Renal Syndrome with Paraventricular Changes consequent to Chronic Ischaemic Heart Failure

Cardiorenal syndrome, de novo renal pathology arising secondary to cardiac insufficiency, is clinically recognised but poorly characterised. This study establishes and characterises a valid model representative of Type 2 cardiorenal syndrome. Extensive permanent left ventricular infarction, induced by ligation of the left anterior descending coronary artery in Lewis rats, was confirmed by plasma cardiac troponin I, histology and cardiac haemodynamics. Renal function and morphology was assessed 90-days post-ligation when heart failure had developed. The involvement of the paraventricular nucleus was investigated using markers of inflammation, apoptosis, reactive oxygen species and of angiotensin II involvement. An extensive left ventricular infarct was confirmed following coronary artery ligation, resulting in increased left ventricular weight and compromised left ventricular diastolic function and developed pressure. Glomerular filtration was significantly decreased, fractional excretion of sodium and caspase activities were increased and basement membrane thickening, indicating glomerulosclerosis, was evident. Interestingly, angiotensin II receptor I expression and reactive oxygen species levels in the hypothalamic paraventricular nucleus remained significantly increased at 90-days post-coronary artery ligation, suggesting that these hypothalamic changes may represent a novel, valuable pharmacological target. This model provides conclusive morphological, biochemical and functional evidence of renal injury consequent to heart failure, truly representative of Type-2 cardiorenal syndrome.

Patients with hypertensive responses to exercise or dobutamine stress testing differ in resting hypertensive phenotype

Little is known of the importance of echocardiographic measures of resting systemic vascular resistance (SVR), cardiac output, and diastolic function in the development of a hypertensive response during dobutamine stress echocardiography. We performed a retrospective review of 325 subjects who underwent stress echocardiography and a resting echocardiogram on the same day. Logistical regressions were performed to determine associations between hypertensive response to each type of stress test and clinical and hemodynamic measurements obtained by transthoracic echocardiography. Patients with a hypertensive response to dobutamine or exercise stress modalities had Stage 1 hypertension. Those with a hypertensive response to dobutamine had a significantly elevated SVR and a lower cardiac output compared to those with a hypertensive response to exercise or a nonhypertensive response to dobutamine. An SVR ≥2000 dynes × sec/cm⁵ showed excellent discrimination between patients who did and did not have a hypertensive response to dobutamine (c = 0.80). A hypertensive response to both stress modalities showed an association with measures of diastolic dysfunction. The hemodynamic and echocardiographic phenotypes of individuals with a hypertensive response to exercise differ from those with a hypertensive response to dobutamine. Further work is necessary to understand and guide antihypertensive therapy when a hypertensive response to stress testing is discovered and to inform choice of stress modality when resting hypertension is present.

Involvement of Cytokines in the Pathogenesis of Salt and Water Imbalance in Congestive Heart Failure

Congestive heart failure (CHF) has become a major medical problem in the western world with high morbidity and mortality rates. CHF adversely affects several systems, mainly the kidneys and the lungs. While the involvement of the renin-angiotensin-aldosterone system and the sympathetic nervous system in the progression of cardiovascular, pulmonary, and renal dysfunction in experimental and clinical CHF is well established, the importance of pro-inflammatory mediators in the pathogenesis of this clinical setting is still evolving. In this context, CHF is associated with overexpression of pro-inflammatory cytokines, such as tumor necrosis factor-α, interleukin (IL)-1, and IL-6, which are activated in response to environmental injury. This family of cytokines has been implicated in the deterioration of CHF, where it plays an important role in initiating and integrating homeostatic responses both at the myocardium and circulatory levels. We and others showed that angiotensin II decreased the ability of the lungs to clear edema and enhanced the fibrosis process via phosphorylation of the mitogen-activated protein kinases p38 and p42/44, which are generally involved in cellular responses to pro-inflammatory cytokines. Literature data also indicate the involvement of these effectors in modulating ion channel activity. It has been reported that in heart failure due to mitral stenosis; there were varying degrees of vascular and other associated parenchymal changes such as edema and fibrosis. In this review, we will discuss the effects of cytokines and other inflammatory mediators on the kidneys and the lungs in heart failure; especially their role in renal and alveolar ion channels activity and fluid balance.

Cardiorenal syndrome: acute kidney injury secondary to cardiovascular disease and role of protein-bound uraemic toxins

Cardiovascular disease (CVD) and kidney disease are closely interrelated. Disease of one organ can induce dysfunction of the other, ultimately leading to failure of both. Clinical awareness of synergistic adverse clinical outcomes in patients with coexisting CVD and kidney disease or 'cardiorenal syndrome (CRS)' has existed. Renal dysfunction, even mild, is a strong independent predictor for poor prognosis in CVD patients. Developing therapeutic interventions targeting acute kidney injury (AKI) has been limited due mainly to lack of effective tools to accurately detect AKI in a timely manner. Neutrophil gelatinase-associated lipocalin and kidney injury molecule-1 have been recently demonstrated to be potential candidate biomarkers in patients undergoing cardiac surgery. However, further validation of AKI biomarkers is needed in other CVD settings, especially acute decompensated heart failure and acute myocardial infarction where AKI commonly occurs. The other concern with regard to understanding the pathogenesis of renal complications in CVD is that mechanistically oriented studies have been relatively rare. Pre-clininal studies have shown that activation of renal inflammation-fibrosis processes, probably triggered by haemodynamic derangement, underlies CVD-associated renal dysfunction. On the other hand, it is postulated that there still are missing links in the heart-kidney connection in CRS patients who have significant renal dysfunction. At present, non-dialysable protein-bound uraemic toxins (PBUTs) appear to be the main focus in this regard. Evidence of the causal role of PBUTs in CRS has been increasingly demonstrated, mainly focusing on indoxyl sulfate (IS) and p-cresyl sulfate (pCS). Both IS and pCS are derived from colonic microbiotic metabolism of dietary amino acids, and hence the colon has become a target of treatment in addition to efforts to improve dialysis techniques for better removal of PBUTs. Novel therapy targeting the site of toxin production has led to new prospects in early intervention for predialysis patients with chronic kidney disease.

Target organ cross talk in cardiorenal syndrome: animal models

The combination of chronic kidney disease (CKD) and heart failure (HF) is associated with an adverse prognosis. Although clinical studies hint at a specific bidirectional interaction between HF and CKD, insight into the pathogenesis of cardiorenal syndrome (CRS) remains limited. We review available evidence on cardiorenal interactions from animal models of CKD and HF and discuss several studies that employed a "double-hit" model to research organ cross talk between the heart and kidneys. Regarding cardiac changes in CKD models, parameters of cardiac remodeling are equivocal and cardiac systolic function generally remains preserved. Structural changes include hypertrophy, fibrosis, and microvasculopathy. In models of HF, data on renal pathology are mostly limited to functional hemodynamic changes. Most double-hit models were unable to show that combined renal and cardiac injury induces additive damage to both organs, perhaps because of the short study duration or absence of organ failure. Because of this lack of "dual-failure" models, we have developed two rat models of combined CKD and HF in which renal dysfunction induced by a subtotal nephrectomy preceded cardiac dysfunction. Cardiac dysfunction was induced either functionally by nitric oxide depletion or structurally by myocardial infarction. In both models, we found that cardiac remodeling and failure were worse in CKD rats compared with controls undergoing the same cardiac insult. Variables of renal damage, like glomerulosclerosis and proteinuria, were also further worsened by combined cardiorenal injury. These studies show that target organ cross talk does occur in CRS. These models may be useful for interventional studies in rats.

Subtotal nephrectomy plus coronary ligation leads to more pronounced damage in both organs than either nephrectomy or coronary ligation

Coexistence of chronic kidney disease (CKD) and heart failure (HF) in humans is associated with poor outcome. We hypothesized that preexistent CKD worsens cardiac outcome after myocardial infarction, and conversely that ensuing HF worsens progression of CKD. Subtotally nephrectomized (SNX) or sham-operated (CON) rats were subjected to coronary ligation (CL) or sham surgery in week 9 to realize four groups: CON, SNX, CON + CL, and SNX + CL. Blood pressure and renal function were measured in weeks 8, 11, 13, and 15. In week 16, cardiac hemodynamics and end-organ damage were assessed. Blood pressure was significantly lower in SNX + CL vs. SNX. Despite this, glomerulosclerosis was more severe in SNX + CL vs. SNX. Two weeks after CL, SNX + CL had more cardiac dilatation compared with CON + CL (end-diastolic volume index: 0.28 ± 0.04 vs. 0.19 ± 0.03 ml/100 g body wt; mean ± SD, P < 0.001), although infarct size was similar. During follow-up in SNX + CL, ejection fraction declined. Mortality was only observed in SNX + CL (2 out of 9). In SNX + CL, end-diastolic pressure (18 ± 4 mmHg) and tau (29 ± 9 ms), the time constant of active relaxation, were significantly higher compared with SNX (13 ± 3 mmHg, 20 ± 4 ms; P < 0.01) and CON + CL (11 ± 5 mmHg, 17 ± 2 ms; P < 0.01). The diameter of small arterioles in the myocardium was significantly decreased in SNX + CL vs. CON + CL (P < 0.01). Urinary excretion of NO metabolites was significantly lower in SNX + CL compared with both CL and SNX. This study demonstrates the existence of more heart and more kidney damage in a new model of combined CKD and HF than in the individual models. Such enhanced damage appears to be separate from systemic hemodynamic changes. Reduced nitric oxide availability may have played a role in both worsened glomerulosclerosis and cardiac diastolic function and appears to be a connector in the cardiorenal syndrome.

Endothelins: Pathophysiology and treatment implications in chronic heart failure

Less than 20 years after its discovery, endothelin is recognized as playing a central role in the pathogenesis of chronic heart failure. Endothelin is not only one of the most potent known vasoconstrictors; it also has multiple other actions. It mediates pathologic hypertrophy and fibrosis of both ventricular and vascular tissues, it potentiates the effects of other neurohormones, and it acts as a proarrhythmic. Endothelin receptor antagonists have been developed to investigate the hypothesis that these adverse effects could be prevented, and experimental studies showed promise in this regard. Clinical studies have confirmed the ability of these new agents to improve hemodynamics, but beneficial effects on clinical outcomes have been more difficult to demonstrate. Further analysis of the data from these trials, as well as other ongoing studies, may provide insight into these disparate findings and guidance for future investigations.

Double transgenic mice with type 1 diabetes mellitus develop somatic, metabolic and vascular disorders

The double transgenic mice (dTg) were obtained by mating: (i) transgenic mice expressing the hemagglutinin of influenza virus under the insulin promoter with (ii) transgenic mice expressing specific T lymphocytes with receptor for the immunodominant epitope of the same virus. In this study we show that dTg mice developed type 1 diabetes mellitus associated with hyperglycemia, low level of plasma insulin, glucosuria, weight loss and approximately 90% mortality (at 3 months biological age). The membrane of red blood cells was more sensitive to osmotic shock in diabetic mice, compared to non-diabetic mice, assessing systemic oxidative stress. Both vasoconstriction and vasorelaxation of the renal arteries decreased significantly in diabetic mice (compared to the control group of non-diabetic mice) related to the phenotypic change of endothelium and smooth muscle cells within the artery wall. This animal model, may be used in developing various strategies to study pancreatic beta-cell function, as well as for a better metabolic control conducting to a reduced risk of vascular complications.

Endothelin receptor antagonists in heart failure: current status and future directions

Experimental evidence suggests that endothelin substantially contributes to left ventricular remodelling and progression of heart failure. Plasma endothelin (ET)-1 levels are increased in patients with heart failure, independent of the aetiology, and correlate with the severity of the disease. Furthermore, tissue endothelin levels and endothelin receptors are upregulated in myocardium from animals and humans with heart failure. In several experimental models of left ventricular remodelling and/or heart failure, treatment with nonselective ET-A and -B as well as selective ET-A antagonists exerted beneficial cardiovascular effects. In patients with heart failure, short-term studies of treatment with endothelin antagonists demonstrated an improvement of haemodynamic parameters; however, long-term treatment with these drugs did not significantly improve combined morbidity/mortality endpoints. Furthermore, in the recently completed Endothelin-A Receptor Antagonist Trial in Heart Failure (EARTH) trial in patients with chronic heart failure, the selective ET-A receptor antagonist darusentan did not significantly affect left ventricular remodelling as assessed by cardiac magnetic resonance imaging. Potential reasons for the lack of beneficial effects of long-term treatment with ET antagonists in patients with heart failure include the following. Firstly, adverse effects on left ventricular healing have been observed when endothelin antagonist therapy was introduced early after myocardial infarction in rats. Secondly, the role of the ET-B receptor in the pathophysiology of heart failure and remodelling processes has not been clearly defined. Finally, for the detection of improvement in left ventricular remodelling, a study needs to be conducted in patients with recent myocardial infarction and signs of heart failure.

Role of Protein Kinase Cδ in Endothelin-Induced Type I Collagen Expression in Cardiac Myofibroblasts Isolated from the Site of Myocardial Infarction

The role of endothelin-1 (ET) in tissue remodeling/fibrogenesis has been demonstrated in various in vitro and in vivo models. Our previous studies have revealed ET-induced expression of type I collagen in cardiac myofibroblasts (myoFb). Here we report that protein kinase Cdelta (PKCdelta) and mitogen-activated protein kinase/extracellular signal-regulated kinase-1/2 (MAPK/ERK1/2) play a role in ET-induced type I collagen expression using specific pharmacological inhibitors. The present study also reveals the expression of various isoforms of PKC including PKCalpha, PKCbetaI, PKCbetaII, PKCgamma, PKCdelta, PKCepsilon, PKCeta, and PKCzeta in cardiac myoFb. Our results from mRNA and protein studies demonstrate that calphostin-C, a PKC inhibitor, decreased the ET-induced type I collagen expression suggesting a role for the PKC pathway. Further treatment with rottlerin, a PKCdelta isoform-specific inhibitor, demonstrated attenuation of 80 to 90% of type I collagen expression induced by ET. However, Go6976 [12-(2-cyanoethyl)-6,7,12,13-tetrahydro-13-methyl-5-oxo-5H-indolo[2,3-a]pyrrolo [3,4-c]carbazole]], an inhibitor of Ca(2+)-dependent PKC isoforms (PKCalpha and PKCbetaI), showed little to no effect on ET-stimulated type I collagen expression. Furthermore, the MAPK inhibitor PD98059 (2'-amino-3'-methoxyflavone) attenuated ET-dependent activation of p44/42 MAPK (pERK1/2) and also down-regulated type I collagen expression. Similarly, rottlerin inhibited the activation of p44/42 MAPK (pERK) implicating the involvement of PKC and MAPK/ERK1/2 in ET-induced type I collagen expression. Our protein/DNA array and reverse transcription-polymerase chain reaction results from ET-treated samples showed a significant increase in Sp1 expression. PD98059 and rottlerin decreased ET-induced Sp1 expression, suggesting a possible interaction of Sp1 with PKCdelta and MAPK in ET-induced type I collagen expression in cardiac myoFb.

Influence of acute selective endothelin-receptor-A blockade on renal hemodynamics in a rat model of chronic allograft rejection

We have recently demonstrated up-regulation of renal endothelin (ET) synthesis in a rat model of chronic renal allograft rejection. Treatment with a selective ET-A receptor antagonist improved survival and reduced functional and morphological kidney damage. However, the underlying mechanisms have not yet been elucidated, as ET exhibits both hemodynamic and inflammatory properties. Therefore, in the present study we investigated acute hemodynamic effects of the selective ET-A receptor antagonist LU 302146 (LU) on chronic renal allograft rejection in rats. Experiments were performed in the Fisher-to-Lewis model of chronic renal allograft rejection. Lewis-to-Lewis isografts served as controls. After 2, 12, and 24 weeks, hemodynamic measurements were performed on anesthetized animals. Measurement of mean arterial pressure (MAP) was performed via a catheter in the femoral artery. Renal blood flow (RBF) was measured by an ultrasonic flow probe placed around the renal transplant artery. Medulla blood flow (MBF) and cortex blood flow (CBF) were determined with laser Doppler probes. Hemodynamic response upon intravenous bolus injection of LU (50 mg/kg) was investigated. The application of LU was followed by a decline in MAP that reached statistical significance only in isografts (ISOs) after 12 weeks and allografts (ALLOs) after 24 weeks. RBF slightly decreased in all groups; however, without reaching statistical significance. MBF showed a small increase in ALLO12 and ALLO24 whereas CBF slightly decreased in all groups. Acute ET-A receptor blockade does not induce important hemodynamic effects in kidneys undergoing chronic rejection. The lack of response to ET-A receptor blockade suggests that the beneficial effect of ET receptor antagonists in this model is likely to be due to improvement of renal morphology.

Effects of aortic stenosis on renal renin, angiotensin receptor, endothelin and NOS gene expression in rats

BACKGROUND/AIMS

Published data regarding the effects of common cardiovascular diseases, i.e. aortic stenosis on renal regulation of major vasoconstrictive (renin, endothelins) and vasodilatory systems (NO) are controversial. Therefore we aimed to evaluate the effects of chronic aortic stenosis on the renal renin-angiotensin, endothelin and NO systems.

METHODS

Experimental supravalvular aortic stenosis was induced by using silver clips with a 0.6 mm internal diameter on the ascending aorta of weanling rats. Renal endothelin-1 (ET-1), endothelin-3 (ET-3), renin, AT(1a), AT(1b), eNOS, and bNOS gene expression were assessed by RNase protection assay.

RESULTS

Renal renin gene expression increased twofold in rats with aortic stenosis. In contrast, renal ET-1, ET-3, eNOS, bNOS, and AT(1a), AT(1b) gene expression were unchanged in rats with aortic stenosis.

CONCLUSION

Our study demonstrates that in rats with severe experimental supravalvular aortic stenosis only renal renin gene expression is stimulated. This contrasts with severe heart failure where endothelins and NO synthases are also upregulated. Different patterns of regulation of renal vasoactive mediators may be of importance for the extent of the renal impairment associated with aortic stenosis, and may be correlated with the severity of congestive heart failure.

Basic and therapeutic relevance of endothelin-mediated regulation

Three endothelin family peptides (endothelin-1, -2 and -3) exert an extremely potent and long-lasting vasoconstrictor action as well as other various actions through stimulating two subtypes of receptor (ETA and ETB). Vascular endothelial cells produce only endothelin-1. Although the pharmacological actions of exogenous endothelin-1 have been extensively analyzed, the physiological roles of endogenous endothelin-1 have long been obscure. Using potent and selective receptor antagonists, endothelin-1 has been demonstrated to contribute slightly to the maintenance of regional vascular tone. In gene-targeted mice, endothelin family peptides and their receptors have been shown to play an important role in the embryonic development of neural crest-derived tissues. In addition to its potent vasoconstrictor action, endothelin-1 has direct mitogenic actions on cardiovascular tissues, as well as co-mitogenic actions with a wide variety of growth factors and vasoactive substances. Endothelin-1 also promotes the synthesis and secretion of various substances including extracellular constituents. These effects of endogenous endothelin-1 would appear to be naturally concerned with the development and/or aggravation of chronic cardiovascular diseases, e.g. hypertension, pulmonary hypertension, vascular remodeling (restenosis, atherosclerosis), renal failure, and heart failure. A great many non-peptide and orally active endothelin receptor antagonists have been developed, and shown to exert excellent therapeutic effects in animal models as well as human patients with these diseases.