Chronic blockade of endothelin A and B receptors using macitentan in experimental renovascular disease

With a Little Help From My Friends: the Role of the Renal Collateral Circulation in Atherosclerotic Renovascular Disease

The collateral circulation can adapt to bypass major arteries with limited flow and serves a crucial protective role in coronary, cerebral, and peripheral arterial disease. Emerging evidence indicates that the renal collateral circulation can similarly adapt and thereby limit kidney ischemia in atherosclerotic renovascular disease. These adaptations predominantly include recruitment of preexisting microvessels for arteriogenesis, with de novo vessel formation playing a limited role. Yet, adaptations of the renal collateral circulation in renovascular disease are often insufficient to fully compensate for the limited flow within an obstructed renal artery and may be hampered by the severity of obstruction or patient comorbidities. Experimental strategies have attempted to circumvent limitations of collateral formation and improve the prognosis of patients with various ischemic vascular territories. These have included pharmacological approaches such as endothelial growth factors, renin-angiotensin-aldosterone system blockade, and If-channel-blockers, as well as interventions like preconditioning, exercise, enhanced external counter-pulsation, and low-energy shock-wave therapy. However, few of these strategies have been implemented in atherosclerotic renovascular disease. This review summarizes current understanding regarding the development of renal collateral circulation in atherosclerotic renovascular disease. Studies are needed to apply lessons learned in other vascular beds in the setting of atherosclerotic renovascular disease to develop new treatment regimens for this patient group.

Intrarenal Renin Angiotensin System Imbalance During Postnatal Life Is Associated With Increased Microvascular Density in the Mature Kidney

Environmental stress during early life is an important factor that affects the postnatal renal development. We have previously shown that male rats exposed to maternal separation (MatSep), a model of early life stress, are normotensive but display a sex-specific reduced renal function and exacerbated angiotensin II (AngII)-mediated vascular responses as adults. Since optimal AngII levels during postnatal life are required for normal maturation of the kidney, this study was designed to investigate both short- and long-term effect of MatSep on (1) the renal vascular architecture and function, (2) the intrarenal renin-angiotensin system (RAS) components status, and (3) the genome-wide expression of genes in isolated renal vasculature. Renal tissue and plasma were collected from male rats at different postnatal days (P) for intrarenal RAS components mRNA and protein expression measurements at P2, 6, 10, 14, 21, and 90 and microCT analysis at P21 and 90. Although with similar body weight and renal mass trajectories from P2 to P90, MatSep rats displayed decreased renal filtration capacity at P90, while increased microvascular density at both P21 and P90 (p < 0.05). MatSep increased renal expression of renin, and angiotensin type 1 (AT1) and type 2 (AT2) receptors (p < 0.05), but reduced ACE2 mRNA expression and activity from P2-14 compared to controls. However, intrarenal levels of AngII peptide were reduced (p < 0.05) possible due to the increased degradation to AngIII by aminopeptidase A. In isolated renal vasculature from neonates, Enriched Biological Pathways functional clusters (EBPfc) from genes changed by MatSep reported to modulate extracellular structure organization, inflammation, and pro-angiogenic transcription factors. Our data suggest that male neonates exposed to MatSep could display permanent changes in the renal microvascular architecture in response to intrarenal RAS imbalance in the context of the atypical upregulation of angiogenic factors.

Molecular targeting of renal inflammation using drug delivery technology to inhibit NF-κB improves renal recovery in chronic kidney disease

Inflammation is a major determinant for the progression of chronic kidney disease (CKD). NF-κB is a master transcription factor upregulated in CKD that promotes inflammation and regulates apoptosis and vascular remodeling. We aimed to modulate this pathway for CKD therapy in a swine model of CKD using a peptide inhibitor of the NF-κB p50 subunit (p50i) fused to a protein carrier [elastin-like polypeptide (ELP)] and equipped with a cell-penetrating peptide (SynB1). We hypothesized that intrarenal SynB1-ELP-p50i therapy would inhibit NF-κB-driven inflammation and induce renal recovery. CKD was induced in 14 pigs. After 6 wk, pigs received single intrarenal SynB1-ELP-p50i therapy (10 mg/kg) or placebo (n = 7 each). Renal hemodynamics were quantified in vivo using multidetector computed tomography before and 8 wk after treatment. Pigs were then euthanized. Ex vivo experiments were performed to quantify renal activation of NF-κB, expression of downstream mediators of NF-κB signaling, renal microvascular density, inflammation, and fibrosis. Fourteen weeks of CKD stimulated NF-κB signaling and downstream mediators (e.g., TNF-α, monocyte chemoattractant protein-1, and IL-6) accompanying loss of renal function, inflammation, fibrosis, and microvascular rarefaction versus controls. All of these were improved after SynB1-ELP-p50i therapy, accompanied by reduced circulating inflammatory cytokines as well, which were evident up to 8 wk after treatment. Current treatments for CKD are largely ineffective. Our study shows the feasibility of a new treatment to induce renal recovery by offsetting inflammation at a molecular level. It also supports the therapeutic potential of targeted inhibition of the NF-κB pathway using novel drug delivery technology in a translational model of CKD.

Assessment of Inflammation in Pulmonary Artery Hypertension by 68Ga-Mannosylated Human Serum Albumin

Rationale: Diagnosis and monitoring of patients with pulmonary artery hypertension (PAH) is currently difficult.Objectives: We aimed to develop a noninvasive imaging modality for PAH that tracks the infiltration of macrophages into the pulmonary vasculature, using a positron emission tomography (PET) agent, ⁶⁸Ga-2-(p-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) mannosylated human serum albumin (MSA), that targets the mannose receptor (MR).Methods: We induced PAH in rats by monocrotaline injection. Tissue analysis, echocardiography, and ⁶⁸Ga-NOTA-MSA PET were performed weekly in rats after monocrotaline injection and in those treated with either sildenafil or macitentan. The translational potential of ⁶⁸Ga-NOTA-MSA PET was explored in patients with PAH.Measurements and Main Results: Gene sets related to macrophages were significantly enriched on whole transcriptome sequencing of the lung tissue in PAH rats. Serial PET images of PAH rats demonstrated increasing uptake of ⁶⁸Ga-NOTA-MSA in the lung by time that corresponded with the MR-positive macrophage recruitment observed in immunohistochemistry. In sildenafil- or macitentan-treated PAH rats, the infiltration of MR-positive macrophages by histology and the uptake of ⁶⁸Ga-NOTA-MSA on PET was significantly lower than that of the PAH-only group. The pulmonary uptake of ⁶⁸Ga-NOTA-MSA was significantly higher in patients with PAH than normal subjects (P = 0.009) or than those with pulmonary hypertension by left heart disease (P = 0.019) (n = 5 per group).Conclusions: ⁶⁸Ga-NOTA-MSA PET can help diagnose PAH and monitor the inflammatory status by imaging the degree of macrophage infiltration into the lung. These observations suggest that ⁶⁸Ga-NOTA-MSA PET has the potential to be used as a novel noninvasive diagnostic and monitoring tool of PAH.

Cellular inflammation in pulmonary hypertension: Detailed analysis of lung and right ventricular tissue, circulating immune cells and effects of a dual endothelin receptor antagonist

Growing evidence suggests that inflammation is crucially involved in the pathogenesis of pulmonary hypertension (PH) and consecutive right heart failure. The present study analyzed the inflammatory response in lung and right ventricle in a rat model of PH and evaluated the effects of the dual endothelin receptor antagonist (ERA) Macitentan. PH was induced by monocrotalin (60 mg/kg body weight s.c.) in Sprague-Dawley rats (PH, n = 10) and compared to healthy controls (CON, n = 10) as well as monocrotalin-induced, macitentan-treated rats (THER, n = 10). Detection of Dendritic cells (DCs), regulatory T cells (Tregs) and others as well as RT-PCR based inflammatory gene expression analysis were performed. Circulating DCs and Tregs were quantified by flow cytometry in the rat model and in PH patients (n = 70) compared to controls (n = 52). Inflammatory cells were increased in lung and right ventricular tissue, whereas DCs and Tregs were decreased in blood. Expression of 17 genes in the lung and 20 genes in the right ventricle were relevantly (>2.0 fold) regulated in the PH group. These effects were, at least in part, attenuated in response to Macitentan treatment. In humans as well as rats, immune cells showed significant correlations to clinical, echocardiographic, and haemodynamic parameters. PH is accompanied by a distinct inflammatory response in lung and right but not left ventricular tissue attenuated by Macitentan. Correlations of circulating DCs as well as tissue resident immune cells with parameters reflecting right ventricular function raise the idea of both, promising biomarkers and novel treatment strategies.

Endothelin: 30 Years From Discovery to Therapy

Discovered in 1987 as a potent endothelial cell-derived vasoconstrictor peptide, endothelin-1 (ET-1), the predominant member of the endothelin peptide family, is now recognized as a multifunctional peptide with cytokine-like activity contributing to almost all aspects of physiology and cell function. More than 30 000 scientific articles on endothelin were published over the past 3 decades, leading to the development and subsequent regulatory approval of a new class of therapeutics-the endothelin receptor antagonists (ERAs). This article reviews the history of the discovery of endothelin and its role in genetics, physiology, and disease. Here, we summarize the main clinical trials using ERAs and discuss the role of endothelin in cardiovascular diseases such as arterial hypertension, preecclampsia, coronary atherosclerosis, myocardial infarction in the absence of obstructive coronary artery disease (MINOCA) caused by spontaneous coronary artery dissection (SCAD), Takotsubo syndrome, and heart failure. We also discuss how endothelins contributes to diabetic kidney disease and focal segmental glomerulosclerosis, pulmonary arterial hypertension, as well as cancer, immune disorders, and allograft rejection (which all involve ET_A autoantibodies), and neurological diseases. The application of ERAs, dual endothelin receptor/angiotensin receptor antagonists (DARAs), selective ET_B agonists, novel biologics such as receptor-targeting antibodies, or immunization against ET_A receptors holds the potential to slow the progression or even reverse chronic noncommunicable diseases. Future clinical studies will show whether targeting endothelin receptors can prevent or reduce disability from disease and improve clinical outcome, quality of life, and survival in patients.

Targeted VEGF (Vascular Endothelial Growth Factor) Therapy Induces Long-Term Renal Recovery in Chronic Kidney Disease via Macrophage Polarization

Chronic kidney disease (CKD) universally associates with renal microvascular rarefaction and inflammation, but whether a link exists between these 2 processes is unclear. We designed a therapeutic construct of VEGF (vascular endothelial growth factor) fused to an ELP (elastin-like polypeptide) carrier and show that it improves renal function in experimental renovascular disease. We test the hypothesis that ELP-VEGF therapy will improve CKD, and that recovery will be driven by decreasing microvascular rarefaction partly via modulation of macrophage phenotype and inflammation. CKD was induced in 14 pigs, which were observed for 14 weeks. At 6 weeks, renal blood flow and filtration were quantified using multidetector computed tomography, and then pigs received single intrarenal ELP-VEGF or placebo (n=7 each). Renal function was quantified again 4 and 8 weeks later. Pigs were euthanized and renal microvascular density, angiogenic and inflammatory markers, fibrosis, macrophage infiltration, and phenotype were quantified. Loss of renal hemodynamics in CKD was progressively recovered by ELP-VEGF therapy, accompanied by improved renal microvascular density, fibrosis, and expression of inflammatory mediators. Although renal macrophage infiltration was similar in both CKD groups, ELP-VEGF therapy distinctly shifted their phenotype from proinflammatory M1 to VEGF-expressing M2. Our study unravels potential mechanisms and feasibility of a new strategy to offset progression of CKD using drug-delivery technologies. The results indicate that renal recovery after ELP-VEGF therapy was largely driven by modulation of renal macrophages toward VEGF-expressing M2 phenotype, restoring VEGF signaling and sustaining improvement of renal function and microvascular integrity in CKD.

Functional characterization of 27 CYP3A4 variants on macitentan metabolism in vitro

Objective

Macitentan is a new choice for pulmonary hypertension treatment which is converted to active metabolite ACT132577 by human cytochrome P450 3A4. Human cytochrome P450 3A4 often occurred gene mutations. Gene polymorphism might cause a variety of changes of protein expression and thus give rise to metabolic difference. The aim of this study was to investigate the catalytic characteristics of 27 CYP3A4 protein variants on the metabolism of macitentan in vitro.

Method

The incubation mixtures (final volume of 200 μl in 1 m PBS) consisted of 1 pmol wild-type CYP3A4.1 or other CYP3A4 protein variants, 2.38 pmol CYP b5 and macitentan (10–600 μm) with 1 mm NADPH. All specimens were processed using same approach with acetonitrile precipitation. The metabolite of macitentan was analysed by ultra performance liquid chromatography–tandem mass spectrometry.

Key finding

Most CYP3A4 protein variants (CYP3A4.9, .11, .12, .13, .17, .20, .23, .24, .28, .29, .33, .34) exhibited a sharp decrease, meanwhile nearly one in five variants (CYP3A4.3, .4, .5, .10, .15, .16) showed a significant rise in intrinsic clearance. The relative clearance of CYP3A4 protein variants was ranged from 5.53 to 501.00%.

Conclusion

Twenty-seven CYP3A4 protein variants displayed different catalytic characteristics towards macitentan in vitro, especially CYP3A4.5, .17, .20, .23. It is important to pay more attention to the dosage of macitentan in order to get better treatment for pulmonary arterial hypertension.

A dual blocker of endothelin A/B receptors mitigates hypertension but not renal dysfunction in a rat model of chronic kidney disease and sleep apnea

Obstructive sleep apnea is characterized by recurrent episodes of pharyngeal collapse during sleep, resulting in intermittent hypoxia (IH), and is associated with a high incidence of hypertension and accelerated renal failure. In rodents, endothelin (ET)-1 contributes to IH-induced hypertension, and ET-1 levels inversely correlate with glomerular filtration rate in patients with end-stage chronic kidney disease (CKD). Therefore, we hypothesized that a dual ET receptor antagonist, macitentan (Actelion Pharmaceuticals), will attenuate and reverse hypertension and renal dysfunction in a rat model of combined IH and CKD. Male Sprague-Dawley rats received one of three diets (control, 0.2% adenine, and 0.2% adenine + 30 mg·kg^-1·day^-1 macitentan) for 2 wk followed by 2 wk of recovery diet. Rats were then exposed for 4 wk to air or IH (20 short exposures/h to 5% O₂-5% CO₂ 7 h/day during sleep). Macitentan prevented the increases in mean arterial blood pressure caused by CKD, IH, and the combination of CKD + IH. However, macitentan did not improve kidney function, fibrosis, and inflammation. After CKD was established, rats were exposed to air or IH for 2 wk, and macitentan feeding continued for 2 more wk. Macitentan reversed the hypertension in IH, CKD, and CKD + IH groups without improving renal function. Our data suggest that macitentan could be an effective antihypertensive in patients with CKD and irreversible kidney damage as a way to protect the heart, brain, and eyes from elevated arterial pressure, but it does not reverse toxin-induced tubule atrophy.

Renoprotective effects of ET(A) receptor antagonists therapy in experimental non-diabetic chronic kidney disease: Is there still hope for the future?

Chronic kidney disease (CKD) is a life-threatening disease arising as a frequent complication of diabetes, obesity and hypertension. Since it is typically undetected for long periods, it often progresses to end-stage renal disease. CKD is characterized by the development of progressive glomerulosclerosis, interstitial fibrosis and tubular atrophy along with a decreased glomerular filtration rate. This is associated with podocyte injury and a progressive rise in proteinuria. As endothelin-1 (ET-1) through the activation of endothelin receptor type A (ET(A)) promotes renal cell injury, inflammation, and fibrosis which finally lead to proteinuria, it is not surprising that ET(A) receptors antagonists have been proven to have beneficial renoprotective effects in both experimental and clinical studies in diabetic and non-diabetic CKD. Unfortunately, fluid retention encountered in large clinical trials in diabetic CKD led to the termination of these studies. Therefore, several advances, including the synthesis of new antagonists with enhanced pharmacological activity, the use of lower doses of ET antagonists, the addition of diuretics, plus simply searching for distinct pathological states to be treated, are promising targets for future experimental studies. In support of these approaches, our group demonstrated in adult subtotally nephrectomized Ren-2 transgenic rats that the addition of a diuretic on top of renin-angiotensin and ET(A) blockade led to a further decrease of proteinuria. This effect was independent of blood pressure which was normalized in all treated groups. Recent data in non-diabetic CKD, therefore, indicate a new potential for ET(A) antagonists, at least under certain pathological conditions.

Endothelin-1 receptor antagonists protect the kidney against the nephrotoxicity induced by cyclosporine-A in normotensive and hypertensive rats

Cyclosporin-A (CsA) is an immunosuppressant associated with acute kidney injury and chronic kidney disease. Nephrotoxicity associated with CsA involves the increase in afferent and efferent arteriole resistance, decreased renal blood flow (RBF) and glomerular filtration. The aim of this study was to evaluate the effect of Endothelin-1 (ET-1) receptor blockade with bosentan (BOS) and macitentan (MAC) antagonists on altered renal function induced by CsA in normotensive and hypertensive animals. Wistar and genetically hypertensive rats (SHR) were separated into control group, CsA group that received intraperitoneal injections of CsA (40 mg/kg) for 15 days, CsA+BOS and CsA+MAC that received CsA and BOS (5 mg/kg) or MAC (25 mg/kg) by gavage for 15 days. Plasma creatinine and urea, mean arterial pressure (MAP), RBF and renal vascular resistance (RVR), and immunohistochemistry for ET-1 in the kidney cortex were measured. CsA decreased renal function, as shown by increased creatinine and urea. There was a decrease in RBF and an increase in MAP and RVR in normotensive and hypertensive animals. These effects were partially reversed by ET-1 antagonists, especially in SHR where increased ET-1 production was observed in the kidney. Most MAC effects were similar to BOS, but BOS seemed to be better at reversing cyclosporine-induced changes in renal function in hypertensive animals. The results of this work suggested the direct participation of ET-1 in renal hemodynamics changes induced by cyclosporin in normotensive and hypertensive rats. The antagonists of ET-1 MAC and BOS reversed part of these effects.

Therapeutic potential of endothelin receptor antagonism in kidney disease

Our growing understanding of the role of the endothelin (ET) system in renal physiology and pathophysiology is from emerging studies of renal disease in animal models and humans. ET receptor antagonists reduce blood pressure and proteinuria in chronic kidney disease and cause regression of renal injury in animals. However, the therapeutic potential of ET receptor antagonism has not been fully explored and clinical studies have been largely limited to patients with diabetic nephropathy. There remains a need for more work in nondiabetic chronic kidney disease, end-stage renal disease (patients requiring maintenance dialysis and those with a functioning kidney transplant), ischemia reperfusion injury, and sickle cell disease. The current review summarizes the most recent advances in both preclinical and clinical studies of ET receptor antagonists in the field of kidney disease.