Endothelin-1 increases glomerular permeability and inflammation independent of blood pressure in the rat

Sex-Specific Differences in Kidney Function and Blood Pressure Regulation

Premenopausal women generally exhibit lower blood pressure and a lower prevalence of hypertension than men of the same age, but these differences reverse postmenopause due to estrogen withdrawal. Sexual dimorphism has been described in different components of kidney physiology and pathophysiology, including the renin-angiotensin-aldosterone system, endothelin system, and tubular transporters. This review explores the sex-specific differences in kidney function and blood pressure regulation. Understanding these differences provides insights into potential therapeutic targets for managing hypertension and kidney diseases, considering the patient's sex and hormonal status.

Mechanism of protective actions of sparsentan in the kidney: lessons from studies in models of chronic kidney disease

Simultaneous inhibition of angiotensin II AT1 and endothelin ETA receptors has emerged as a promising approach for treatment of chronic progressive kidney disease. This therapeutic approach has been advanced by the introduction of sparsentan, the first dual AT1 and ETA receptor antagonist. Sparsentan is a single molecule with high affinity for both receptors. It is US Food and Drug Administration approved for immunoglobulin A nephropathy (IgAN) and is currently being developed as a treatment for rare kidney diseases, such as focal segmental glomerulosclerosis. Clinical studies have demonstrated the efficacy and safety of sparsentan in these conditions. In parallel with clinical development, studies have been conducted to elucidate the mechanisms of action of sparsentan and its position in the context of published evidence characterizing the nephroprotective effects of dual ETA and AT1 receptor inhibition. This review summarizes this evidence, documenting beneficial anti-inflammatory, antifibrotic, and hemodynamic actions of sparsentan in the kidney and protective actions in glomerular endothelial cells, mesangial cells, the tubulointerstitium, and podocytes, thus providing the rationale for the use of sparsentan as therapy for focal segmental glomerulosclerosis and IgAN and suggesting potential benefits in other renal diseases, such as Alport syndrome.

Sparsentan: the first and only non-immunosuppressive therapy for the reduction of proteinuria in IgA nephropathy

INTRODUCTION

IgA nephropathy is one of the most common forms of glomerular disease. Patients with persistent proteinuria are at increased risk of progression to kidney failure. There is a significant need for safe and effective therapies to lower proteinuria in these patients. Sparsentan is a non-immunosuppressive agent that acts as a dual angiotensin and endothelin receptor antagonist. It lowers proteinuria in experimental models of glomerular disease and in affected patients.

AREAS COVERED

This review covers the immunological and non-immunological actions of sparsentan in glomerular disease. It reviews the clinical trials that evaluated the impact of the drug in pediatric and adult patients with IgA nephropathy. It places the use of sparsentan in an overall treatment paradigm for the full spectrum of patients with IgA nephropathy including nonspecific renoprotective agents such as inhibitors of the renin-angiotensin-aldosterone axis and SGLT2 transporter and immunosuppressive drugs. The review represents a search of the current literature about the effect of the drug on normal physiology and the pathogenesis of IgA nephropathy.

EXPERT OPINION

The safety, tolerability, and therapeutic efficacy of sparsentan have been demonstrated in long-term studies of patients with primary glomerular diseases extending over 5 years. The evidence in support of a beneficial treatment effect of sparsentan is stronger in IgAN than in FSGS. It is anticipated that sparsentan will supplant the use of ACEI or ARB as the first-line therapy to reduce proteinuria prior to the implementation of immunosuppressive agents in patients with IgA nephropathy. It may be combined with other renoprotective drugs like SGLT2 inhibitors. Practice guidelines are needed to promote safe and effective use of this new drug by nephrologists caring for patients with IgAN in all clinical settings.

Population pharmacokinetic analysis of sparsentan in healthy volunteers and patients with focal segmental glomerulosclerosis

Sparsentan is a single-molecule dual endothelin angiotensin receptor antagonist (DEARA) currently under investigation as a treatment for focal segmental glomerulosclerosis (FSGS) and IgA nephropathy (IgAN). A population pharmacokinetic (PK) analysis was performed to characterize the PKs of sparsentan and to evaluate the impact of FSGS disease characteristics and co-medications as covariates on sparsentan PKs. Blood samples were collected from 236 healthy volunteers, 16 subjects with hepatic impairment, and 194 primary and genetic FSGS patients enrolled in nine studies ranging from phase I to phase III. Sparsentan plasma concentrations were determined using validated liquid chromatography-tandem mass spectrometry with a lower limit of quantitation of 2 ng/mL. Modeling was conducted with the first-order conditional estimation with η-ϵ interaction (FOCE-1) method in NONMEM. A total of 20 covariates were tested using a univariate forward addition and stepwise backward elimination analysis with significance level of p < 0.01 and p < 0.001, respectively. A two-compartment model with first-order absorption and an absorption lag time with proportional plus additive residual error (2 ng/mL) described sparsentan PKs. A 32% increase of clearance due to CYP3A auto-induction occurred at steady-state. Covariates retained in the final model included formulation, cytochrome P450 (CYP) 3A4 inhibitor co-administration, sex, race, creatinine clearance, and serum alkaline phosphatase. Moderate and strong CYP3A4 inhibitors comedications increased area under the concentration-time curve by 31.4% and 191.3%, respectively. This population PK model of sparsentan suggests that dose adjustments may be warranted for patients taking moderate and strong CYP3A4 inhibitors concomitantly, but other covariates analyzed may not require dose adjustments.

Role of Inflammation in Progression of Chronic Kidney Disease in Type 2 Diabetes Mellitus: Clinical Implications

Progression of chronic kidney disease in type 2 diabetes has been understood conventionally as a consequence of intraglomerular hemodynamic changes and aberrant metabolic pathways. However, an increasing body of experimental evidence has highlighted the role of inflammatory response in the progression of diabetic kidney disease. Macrophage polarization in response to specific microenvironmental stimuli affects the pathology of diabetic kidneys. The diabetic milieu also up-regulates inflammatory cytokines, chemokines, and adhesion molecules, and promotes inflammatory signal transduction pathways, including inflammasomes. Therefore, from a reverse translational perspective, modulation of the inflammatory response may be the driving force of the renoprotective effects of renin-angiotensin system inhibitors, sodium-glucose cotransporter-2 inhibitors, and mineralocorticoid receptor antagonists, all of which have been shown to slow disease progression. Currently, many agents that target the inflammation in the kidneys directly are evaluated in clinical trials. This article discusses recent clinical and experimental milestones in drug development for diabetic kidney disease with a perspective on inflammation in the kidneys. Such insights may enable a targeted approach to discovering novel drugs against chronic kidney disease in type 2 diabetes.

RhoA/ROCK inhibition attenuates endothelin-1-induced elevated glomerular permeability to albumin, inflammation, and fibrosis

Endothelin-1 (ET-1) contributes to the development of kidney diseases. However, the underlying molecular mechanism is largely undefined. Here we sought to investigate the potential role of ET-1 receptors, ET_A and ET_B in the regulation of increased glomerular permeability and underlying signaling pathways post-ET-1 infusion. Male Sprague-Dawley rats were infused with ET-1 (2 pmol/kg per minute, i.v.) for four weeks, and the effect on glomerular permeability to albumin (P_alb) and albuminuria was measured. The selective ROCK-1/2 inhibitor, Y-27632, was administered to a separate group of rats to determine its effect on ET-1-induced P_alb and albuminuria. The role of ET_A and ET_B receptors in regulating RhoA/ROCK activity was determined by incubating isolated glomeruli from normal rats with ET-1 and with selective ET_A and ET_B receptor antagonists. ET-1 infusion for four weeks significantly elevated P_alb and albuminuria. Y-27632 significantly reduced the elevation of P_alb and albuminuria. The activities of both RhoA and ROCK-1/2 were increased by ET-1 infusion. Selective ET_B receptor antagonism had no effect on the elevated activity of both RhoA and ROCK-1/2 enzymes. Selective ET_A receptor and combined ET_A/ET_B receptors blockade restored the activity of RhoA and ROCK-1/2 to normal levels. In addition, chronic ET-1 infusion increased the levels of glomerular inflammatory and fibrotic markers. These effects were all attenuated in rats following ROCK-1/2 inhibition. These observations suggest that ET-1 contributes to increased albuminuria, inflammation, and fibrosis by modulating the activity of the ET_A-RhoA/ROCK-1/2 pathway. Selective ET_A receptor blockade may represent a potential therapeutic strategy to limit glomerular injury and albuminuria in kidney disease.

Endothelin Receptor Antagonists in Kidney Disease

Endothelin (ET) is found to be increased in kidney disease secondary to hyperglycaemia, hypertension, acidosis, and the presence of insulin or proinflammatory cytokines. In this context, ET, via the endothelin receptor type A (ET_A) activation, causes sustained vasoconstriction of the afferent arterioles that produces deleterious effects such as hyperfiltration, podocyte damage, proteinuria and, eventually, GFR decline. Therefore, endothelin receptor antagonists (ERAs) have been proposed as a therapeutic strategy to reduce proteinuria and slow the progression of kidney disease. Preclinical and clinical evidence has revealed that the administration of ERAs reduces kidney fibrosis, inflammation and proteinuria. Currently, the efficacy of many ERAs to treat kidney disease is being tested in randomized controlled trials; however, some of these, such as avosentan and atrasentan, were not commercialized due to the adverse events related to their use. Therefore, to take advantage of the protective properties of the ERAs, the use of ET_A receptor-specific antagonists and/or combining them with sodium-glucose cotransporter 2 inhibitors (SGLT2i) has been proposed to prevent oedemas, the main ERAs-related deleterious effect. The use of a dual angiotensin-II type 1/endothelin receptor blocker (sparsentan) is also being evaluated to treat kidney disease. Here, we reviewed the main ERAs developed and the preclinical and clinical evidence of their kidney-protective effects. Additionally, we provided an overview of new strategies that have been proposed to integrate ERAs in kidney disease treatment.

Thalidomide modulates renal inflammation induced by brain death experimental model

BACKGROUND

Brain death (BD) is characterized by a complex inflammatory response, resulting in dysfunction of potentially transplantable organs. This process is modulated by cytokines, which amplify graft immunogenicity. We have investigated the inflammatory response in an animal model of BD and analyzed the effects of thalidomide, a drug with powerful immunomodulatory properties.

METHODS

BD was induced in male Lewis rats. We studied three groups: Control (sham-operated rats) (n = 6), BD (rats subjected to brain death) (n = 6) and BD + Thalid (BD rats treated with one dose of thalidomide (200 mg/Kg), administered by gavage) (n = 6). Six hours after BD, serum levels of urea and creatinine, as well as systemic and renal tissue protein levels of TNF-α and IL-6, were analyzed. We also determined the mRNA expression of ET-1, and macrophage infiltration by immunohistochemistry.

RESULTS

BD induced a striking inflammatory status, demonstrated by a significant increase of plasma cytokines: TNF-α (2.8 ± 4.3 pg/mL [BD] vs. 9.4 ± 2.8 pg/mL [Control]), and IL-6 (6219.5 ± 1380.6 pg/mL [BD] vs. 1854.7 ± 822.6 pg/mL [Control]), and in the renal tissue: TNF-α (2.5 ± 0.3 relative expression [BD] vs. 1.0 ± 0.4 relative expression [Control]; p < 0.05), and IL-6 (4.0 ± 0.4 relative expression [BD] vs. 1.0 ± 0.3 relative expression [Control]; p < 0.05). Moreover, BD increased macrophages infiltration (2.47 ± 0.07 cells/field [BD] vs. 1.20 ± 0.05 cells/field [Control]; p < 0.05), and ET-1 gene expression (2.5 ± 0.3 relative expression [BD] vs. 1.0 ± 0.2 relative expression [Control]; p < 0.05). In addition, we have observed deterioration in renal function, characterized by an increase of urea (194.7 ± 25.0 mg/dL [BD] vs. 108.0 ± 14.2 mg/dL [Control]; p < 0.05) and creatinine (1.4 ± 0.04 mg/dL [BD] vs. 1.0 ± 0.07 mg/dL [Control]; p < 0.05) levels. Thalidomide administration significantly reduced plasma cytokines: TNF-α (5.1 ± 1.4 pg/mL [BD + Thalid] vs. BD; p < 0.05), and IL-6 (1056.5 ± 488.3 pg/mL [BD + Thalid] vs. BD; p < 0.05), as well as in the renal tissue: TNF-α (1.5 ± 0.2 relative expression [BD + Thalid] vs. BD; p < 0.05), and IL-6 (2.1 ± 0.3 relative expression [BD + Thalid] vs. BD; p < 0.05). Thalidomide treatment also induced a significant decrease in the expression of ET-1 (1.4 ± 0.3 relative expression [BD + Thalid] vs. BD; p < 0.05), and macrophages infiltration (1.17 ± 0.06 cells/field [BD + Thalid] vs. BD; p < 0.05). Also thalidomide prevented kidney function failure by reduced urea (148.3 ± 4.4 mg/dL [BD + Thalid] vs. BD; p < 0.05), and creatinine (1.1 ± 0.14 mg/dL [BD + Thalid] vs. BD; p < 0.05).

CONCLUSIONS

The immunomodulatory properties of thalidomide were effective in decreasing systemic and local immunologic response, leading to diminished renal damage, as reflected in the decrease of urea and creatinine levels. These results suggest that use of thalidomide may represent a potential strategy for treating in BD kidney organ donors.

Endothelin-1 down-regulated vascular endothelial growth factor A is involved in trichloroethene-induced kidney injury

The mechanism of kidney injury in occupational medicamentosa-like dermatitis due to trichloroethylene exposure is not well understood. This study aimed to investigate the role of endothelin-1 (ET-1)/vascular endothelial-derived growth factor-A (VEGF-A) in trichloroethylene (TCE)-induced renal injury. Forty BALB/c female mice were used in this study to build the TCE-sensitization mouse model. Transmission electron microscopic observation, histological examination, periodic acid-Schiff staining, serum urea nitrogen, creatinine, and urinary total protein levels were used to reflect renal injury. Glypican1, syndecan1, ET-1 and VEGF-A protein levels were measured by western blot. Serum ET-1 level was also measured. Tumor necrosis factor alpha (TNF-α) and vascular cell adhesion molecule-1 (VCAM-1) were detected by immunohistochemistry. The results showed that TCE-sensitized mouse kidneys were damaged and accompanied by increased serum ET-1. After treatment with CGS 35066, the inhibitor of endothelin converting enzyme-1 (ECE-1), kidney ET-1, TNF-α and VCAM-1 levels decreased, and renal function improved in TCE+CGS 35066–sensitized positive mice. In addition, kidney VEGF-A, glomerular endothelial cell glypican1 and syndecan1 levels increased, and endothelial cell damage was alleviated after treatment with CGS 35066. The results suggest that inhibiting ECE-1 could alleviate glomerular endothelial cell injury by inhibiting ET-1 expression, thus promoting endothelial cell repair by upregulating VEGF-A.

Bevacizumab Increases Endothelin-1 Production via Forkhead Box Protein O1 in Human Glomerular Microvascular Endothelial Cells In Vitro

Molecular mechanisms underlying the nephrotoxicity associated with bevacizumab are unclear. Endothelin-1 (ET-1) is involved in podocyte injury and proteinuria, and its level increases in most cases of kidney disorders. Forkhead box protein O1 (FoxO1), a transcription factor, is a major determinant of ET-1 promoter activation and is regulated by protein kinase B (Akt) phosphorylation-dependent nuclear exclusion. We evaluated the effect of bevacizumab on ET-1 production in human glomerular microvascular endothelial cells (hGECs). We analyzed the changes in the mRNA and protein levels of ET-1 in hGECs treated with bevacizumab using real-time reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay. Changes in the protein levels and phosphorylation status of Akt and FoxO1 in hGECs treated with bevacizumab were analyzed by western blotting. After cell lysis, FoxO1 protein was isolated from the cytoplasmic and nuclear fractions. We also investigated the effects of AS1842856 (a FoxO1 inhibitor) on bevacizumab-induced ET-1 production. Bevacizumab significantly and dose-dependently increased the mRNA and protein levels of ET-1 in hGECs (p < 0.05). Bevacizumab treatment also led to a decrease in phosphorylated Akt protein levels. Inhibition of Akt activity by LY294002 promoted ET-1 production. Bevacizumab also induced an increase in FoxO1 protein levels in the nucleus. Inhibition of FoxO1 activity by AS1842856 resulted in decreased ET-1 levels in bevacizumab-treated hGECs. ET-1 axis activation, Akt inactivation, and FoxO1 nuclear localization are the molecular mechanisms underlying bevacizumab-induced nephrotoxicity. Therefore, inhibition of renal ET-1 production could be a promising approach to protect against or treat bevacizumab-induced nephrotoxicity.

The role of endothelin II type A receptor (ETAR) in transplant injury

PURPOSE OF REVIEW

Antibody-mediated rejection is the leading cause of deterioration of graft function and graft loss after kidney transplantation. Recent studies have reported an increasing role of non-HLA antibodies in the humoral injury after kidney transplantation. We decided to present the influence of non-HLA antibodies - anti-endothelin II type A receptor (ETAR) on a transplanted kidney and characterize the significance of their receptor.

RECENT FINDINGS

The role of non-HLA antibodies is still uncertain. Many studies suggest that the presence of non-HLA antibodies, including anti-ETAR antibodies, is among the risk factors for antibody-mediated rejection, graft injury, and graft loss. The discovery of new antigen targets and antibodies, which participate in the humoral response, has provided a significantly better understanding of the mechanism of antibody-mediated rejection after organ transplantation.

SUMMARY

Endothelin and its receptors play an important role in physiology and pathophysiology after solid organ transplantation. ETAR and antibodies against ETAR may participate in humoral rejection and graft damage. The measurement of anti-ETAR antibodies may identify patients with an increased risk of rejection and even loss of a transplanted organ. Expression of ETAR detected in biopsy of transplant could become an additional tool used to better understand humoral activity. More research is needed to address many questions about non-HLA directed rejection and graft damage.

Novel HIF-1-target gene isthmin1 contributes to hypoxia-induced hyperpermeability of pulmonary microvascular endothelial cells monolayers

Hypoxia-induced pulmonary microvascular endothelial cell (PMVEC) monolayers hyperpermeability is vital for vascular leakage, which participates in vascular diseases, such as acute lung injury (ALI) and high-altitude pulmonary edema (HAPE). We previously observed that PMVEC permeability was markedly elevated in hypoxia when cocultured with primary type II alveolar epithelial cells (AECII) in which isthmin1 (ISM1) was highly upregulated. However, whether the upregulation of ISM1 plays a role in hypoxia-induced PMVEC hyperpermeability is unclear. In this study, we assessed the role of AECII-derived ISM1 in hypoxia-induced PMVEC hyperpermeability with an AECII/PMVEC coculture system and uncovered the underlying mechanism whereby hypoxia stimulates ISM1 gene expression. We found that ISM1 gene expression was upregulated in cultured AECII cells exposed to hypoxia (3% O2) and that AECII-derived ISM1 participated in hypoxia-induced hyperpermeability of PMVEC monolayers, as small interference RNA (siRNA)-mediated knockdown of ISM1 in AECII markedly attenuated the increase in PMVEC permeability in coculture system under hypoxia. In addition, we confirmed that ISM1 was regulated by hypoxia-inducible factor-1α (HIF1α) according to the evidence that silencing of HIF1α inhibited the hypoxia-mediated upregulation of ISM1. Mechanismly, overexpression of HIF1α transcriptionally activated ISM1 gene expression by directly binding to the conserved regulatory elements upstream of the ism1 locus. We identified a novel HIF-1-target gene ISM1, which involves in hyperpermeability of pulmonary microvascular endothelial cell monolayers under hypoxia. Our in vitro cell experiments implied that the upregulated ISM1 derived from alveolar epithelium might be a vital modulator in hypoxia-induced endothelial hyperpermeability and thereby implicates with hypoxic pulmonary-related diseases.

Selective ETA vs. dual ETA/B receptor blockade for the prevention of sunitinib-induced hypertension and albuminuria in WKY rats

AIMS

Although effective in preventing tumour growth, angiogenesis inhibitors cause off-target effects including cardiovascular toxicity and renal injury, most likely via endothelin (ET)-1 up-regulation. ET-1 via stimulation of the ETA receptor has pro-hypertensive actions whereas stimulation of the ETB receptor can elicit both pro- or anti-hypertensive effects. In this study, our aim was to determine the efficacy of selective ETA vs. dual ETA/B receptor blockade for the prevention of angiogenesis inhibitor-induced hypertension and albuminuria.

METHODS AND RESULTS

Male Wistar Kyoto (WKY) rats were treated with vehicle, sunitinib (angiogenesis inhibitor; 14 mg/kg/day) alone or in combination with macitentan (ETA/B receptor antagonist; 30 mg/kg/day) or sitaxentan (selective ETA receptor antagonist; 30 or 100 mg/kg/day) for 8 days. Compared with vehicle, sunitinib treatment caused a rapid and sustained increase in mean arterial pressure of ∼25 mmHg. Co-treatment with macitentan or sitaxentan abolished the pressor response to sunitinib. Sunitinib did not induce endothelial dysfunction. However, it was associated with increased aortic, mesenteric, and renal oxidative stress, an effect that was absent in mesenteric arteries of the macitentan and sitaxentan co-treated groups. Albuminuria was greater in the sunitinib- than vehicle-treated group. Co-treatment with sitaxentan, but not macitentan, prevented this increase in albuminuria. Sunitinib treatment increased circulating and urinary prostacyclin levels and had no effect on thromboxane levels. These increases in prostacyclin were blunted by co-treatment with sitaxentan.

CONCLUSIONS

Our results demonstrate that both selective ETA and dual ETA/B receptor antagonism prevents sunitinib-induced hypertension, whereas sunitinib-induced albuminuria was only prevented by selective ETA receptor antagonism. In addition, our results uncover a role for prostacyclin in the development of these effects. In conclusion, selective ETA receptor antagonism is sufficient for the prevention of sunitinib-induced hypertension and renal injury.

The glomerular filtration barrier: a structural target for novel kidney therapies

Loss of normal kidney function affects more than 10% of the population and contributes to morbidity and mortality. Kidney diseases are currently treated with immunosuppressive agents, antihypertensives and diuretics with partial but limited success. Most kidney disease is characterized by breakdown of the glomerular filtration barrier (GFB). Specialized podocyte cells maintain the GFB, and structure-function experiments and studies of intercellular communication between the podocytes and other GFB cells, combined with advances from genetics and genomics, have laid the groundwork for a new generation of therapies that directly intervene at the GFB. These include inhibitors of apolipoprotein L1 (APOL1), short transient receptor potential channels (TRPCs), soluble fms-like tyrosine kinase 1 (sFLT1; also known as soluble vascular endothelial growth factor receptor 1), roundabout homologue 2 (ROBO2), endothelin receptor A, soluble urokinase plasminogen activator surface receptor (suPAR) and substrate intermediates for coenzyme Q10 (CoQ₁₀). These molecular targets converge on two key components of GFB biology: mitochondrial function and the actin-myosin contractile machinery. This Review discusses therapies and developments focused on maintaining GFB integrity, and the emerging questions in this evolving field.

Simulations of Glomerular Shear and Hoop Stresses in Diabetes, Hypertension, and Reduced Renal Mass using a Network Model of a Rat Glomerulus

A novel anatomically accurate model of rat glomerular filtration is used to quantify shear stresses on the glomerular capillary endothelium and hoop stresses on the glomerular capillary walls. Plasma, erythrocyte volume, and plasma protein mass are distributed at network nodes using pressure differentials calculated taking into account volume loss to filtration, improving on previous models which only took into account blood apparent viscosity in calculating pressures throughout the network. Filtration is found to be heterogeneously distributed throughout the glomerular capillary network and is determined by concentration of plasma proteins and surface area of the filtering capillary segments. Hoop stress is primarily concentrated near the afferent arteriole, whereas shear stress is concentrated near the efferent arteriole. Using parameters from glomerular micropuncture studies, conditions of diabetes mellitus (DM), 5/6‐Nephrectomy (5/6‐Nx), and Angiotensin II‐induced hypertension (HTN) are simulated and compared to their own internal controls to assess the changes in mechanical stresses. Hoop stress is increased in all three conditions, while shear stress is increased in 5/6‐Nx, decreased in HTN, and maintained at control levels in DM by the hypertrophic response of the glomerular capillaries. The results indicate that these alterations in mechanical stresses and the consequent release of cytokines by or injury of the glomerular cells may play a significant role in the progression of glomerulopathy in these disease conditions.

Towards Better Drug Repositioning: Targeted Immunoinflammatory Therapy for Diabetic Nephropathy

Diabetic nephropathy (DN) is one of the most common and important microvascular complications of diabetes mellitus (DM). The main clinical features of DN are proteinuria and a progressive decline in renal function, which are associated with structural and functional changes in the kidney. The pathogenesis of DN is multifactorial, including genetic, metabolic, and haemodynamic factors, which can trigger a sequence of events. Controlling metabolic risks such as hyperglycaemia, hypertension, and dyslipidaemia is not enough to slow the progression of DN. Recent studies emphasized immunoinflammation as a critical pathogenic factor in the progression of DN. Therefore, targeting inflammation is considered a potential and novel treatment strategy for DN. In this review, we will briefly introduce the inflammatory process of DN and discuss the anti-inflammatory effects of antidiabetic drugs when treating DN.

Endothelin-targeted new treatments for proteinuric and inflammatory glomerular diseases: focus on the added value to anti-renin-angiotensin system inhibition

Chronic kidney disease (CKD) is the main cause of end-stage renal disease worldwide arising as a frequent complication of diabetes, obesity, and hypertension. Current therapeutic options, mainly based of inhibition of the renin-angiotensin system (RAS), provide imperfect renoprotection if started at an advanced phase of the disease, and treatments that show or even reverse the progression of CKD are needed. The endothelin (ET) system contributes to the normal renal physiology; however, robust evidence suggests a key role of ET-1 and its cognate receptors, in the progression of CKD. The effectiveness of ET receptor antagonists in ameliorating renal hemodynamics and fibrosis has been largely demonstrated in different experimental models. A significant antiproteinuric effect of ET receptor antagonists has been found in diabetic and non-diabetic CKD patients even on top of RAS blockade, and emerging evidence from ongoing clinical trials highlights their beneficial effects on a wide range of kidney disorders.

Novel therapeutic agents for the treatment of diabetic kidney disease

INTRODUCTION

Diabetic kidney disease (DKD) involves multifaceted pathophysiology which increases the risk of cardiorenal events and mortality. Conventional therapy is limited to renin-angiotensin aldosterone system inhibition and management of hyperglycemia and hypertension. Recent clinical trials have demonstrated promising nephroprotective effects of antihyperglycemic agents thus modifying guideline treatment recommendations for type 2 diabetic patients with chronic kidney disease.

AREAS OF COVERED

Relevant studies and clinical trials were searched via PubMed and clinicaltrials.gov through August 2020. Authors offer an update on clinical evidence regarding nephroprotective effects and side effects of sodium-glucose-cotransporter-2 (SGLT2) inhibitors, glucagon-like-peptide-1 (GLP1) agonists and dipeptidylpeptidase-4 (DPP4) inhibitors. They discuss the potential benefits of novel therapy targeting DKD pathogenic processes including inflammation, oxidative stress, fibrosis, and vasoconstriction shown in early phases of clinical trials and offer an opinion on key challenges and directions for future progress.

EXPERT OPINION

SGLT2 inhibitors are the most promising agents for DKD and improving cardiorenal outcomes. Mineralocorticoid-receptor antagonists and janus kinase inhibitors are also promising investigational therapies that target oxidative stress, nitric oxide synthesis, and inflammation. Novel therapeutic targets and the identification of clinically useful biomarkers may provide future therapies that detect early stages of DKD enabling a slower kidney function decline.

A novel role for myeloid endothelin-B receptors in hypertension

AIMS

Hypertension is common. Recent data suggest that macrophages (Mφ) contribute to, and protect from, hypertension. Endothelin-1 (ET-1) is the most potent endogenous vasoconstrictor with additional pro-inflammatory properties. We investigated the role of the ET system in experimental and clinical hypertension by modifying Mφ number and phenotype.

METHODS AND RESULTS

In vitro, Mφ ET receptor function was explored using pharmacological, gene silencing, and knockout approaches. Using the CD11b-DTR mouse and novel mice with myeloid cell-specific endothelin-B (ETB) receptor deficiency (LysMETB-/-), we explored the effects of modifying Mφ number and phenotype on the hypertensive effects of ET-1, angiotensin II (ANG II), a model that is ET-1 dependent, and salt. In patients with small vessel vasculitis, the impacts of Mφ depleting and non-depleting therapies on blood pressure (BP) and endothelial function were examined. Mouse and human Mφ expressed both endothelin-A and ETB receptors and displayed chemokinesis to ET-1. However, stimulation of Mφ with exogenous ET-1 did not polarize Mφ phenotype. Interestingly, both mouse and human Mφ cleared ET-1 through ETB receptor mediated, and dynamin-dependent, endocytosis. Mφ depletion resulted in an augmented chronic hypertensive response to both ET-1 and salt. LysMETB-/- mice displayed an exaggerated hypertensive response to both ET-1 and ANG II. Finally, in patients who received Mφ depleting immunotherapy BP was higher and endothelial function worse than in those receiving non-depleting therapies.

CONCLUSION

Mφ and ET-1 may play an important role in BP control and potentially have a critical role as a therapeutic target in hypertension.

Plasma Endothelin-1 and Risk of Death and Hospitalization in Patients Undergoing Maintenance Hemodialysis

BACKGROUND AND OBJECTIVES

Endothelin-1 is a potent endothelium-derived vasoconstrictor peptide implicated in the pathogenesis of hypertension, congestive heart failure, and inflammation, all of which are critical pathophysiologic features of CKD.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

To test the hypothesis that plasma endothelin-1 levels are associated with increased risks of mortality and hospitalization in patients with chronic kidney failure, we measured plasma endothelin-1 levels in a prospective cohort of 794 individuals receiving maintenance hemodialysis. The primary outcomes were time to death and time to hospitalization.

RESULTS

The median plasma endothelin-1 level was 2.02 (interquartile range, 1.57-2.71) pg/ml. During a median follow-up period of 28 (interquartile range, 21-29) months, 253 individuals (32%) died and 643 individuals (81%) were hospitalized at least once. In multivariable models adjusted for demographic, clinical, and laboratory variables, individuals in the highest quartile of plasma endothelin-1 had a 2.44-fold higher risk of death (hazard ratio, 2.44; 95% confidence interval, 1.61 to 3.70) and a 1.54-fold higher risk of hospitalization (hazard ratio, 1.54; 95% confidence interval, 1.19 to 1.99) compared with individuals in the lowest quartile. The Harrell C-statistic of the fully adjusted model increased from 0.73 to 0.74 after addition of natural log-transformed plasma endothelin-1 (P<0.001) for all-cause mortality, and increased from 0.608 to 0.614 after addition of natural log-transformed plasma endothelin-1 (P=0.002) for hospitalization.

CONCLUSIONS

Higher plasma endothelin-1 is associated with adverse clinical events in patients receiving hemodialysis independent of previously described risk factors.

PODCAST

This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2020_05_15_CJN11130919.mp3.

Inhibition of RAGE by FPS-ZM1 alleviates renal injury in spontaneously hypertensive rats

The current study was designed to examine the protection of RAGE-specific inhibitor FPS-ZM1 against renal injury in spontaneously hypertensive rats (SHR) and investigate the underlying mechanism. The adult male SHR were treated with FPS-ZM1 via oral gavages for 12 weeks, and age-matched male Wistar-Kyoto rats (WKY) were used as control. Treatment of SHR with FPS-ZM1 slightly reduced blood pressure, and significantly improved baroreflex sensitivity in SHR. Treatment of SHR with FPS-ZM1 improved renal function, evidenced by increased glomerular filtration rate and renal blood flow, and reduced plasma creatinine, blood urea nitrogen and urine albumin excretion rate. Histology results revealed that treatment of SHR with FPS-ZM1 alleviated renal injury and reduced tubulointerstitial fibrosis. Treatment of SHR with FPS-ZM1 suppressed activation of NF-κB and reduced expression of pro-inflammatory cytokines including Tnf, Il6, and Il1b. Treatment of SHR with FPS-ZM1 abated oxidative stress and downregulated mRNA levels of components of NADPH oxidase (Nox) including Cyba, Nox1, Nox2, Nox4 and Ncf1 in kidneys. In addition, treatment of SHR with FPS-ZM1 reduced renal AngII levels, downregulated mRNA expression of Ace and upregulated expression of Agtr2. In conclusion, treatment with FPS-ZM1 alleviated hypertension-related renal dysfunction, possibly by suppressing NF-κB-mediated inflammation, abating Nox-mediated oxidative stress, and improving local renal renin-angiotensin system (RAS).

Renal Autocrine and Paracrine Signaling: A Story of Self-protection

Autocrine and paracrine signaling in the kidney adds an extra level of diversity and complexity to renal physiology. The extensive scientific production on the topic precludes easy understanding of the fundamental purpose of the vast number of molecules and systems that influence the renal function. This systematic review provides the broader pen strokes for a collected image of renal paracrine signaling. First, we recapitulate the essence of each paracrine system one by one. Thereafter the single components are merged into an overarching physiological concept. The presented survey shows that despite the diversity in the web of paracrine factors, the collected effect on renal function may not be complicated after all. In essence, paracrine activation provides an intelligent system that perceives minor perturbations and reacts with a coordinated and integrated tissue response that relieves the work load from the renal epithelia and favors diuresis and natriuresis. We suggest that the overall function of paracrine signaling is reno-protection and argue that renal paracrine signaling and self-regulation are two sides of the same coin. Thus local paracrine signaling is an intrinsic function of the kidney, and the overall renal effect of changes in blood pressure, volume load, and systemic hormones will always be tinted by its paracrine status.

Innate immunity in diabetic kidney disease

Increasing evidence suggests that renal inflammation contributes to the pathogenesis and progression of diabetic kidney disease (DKD) and that anti-inflammatory therapies might have renoprotective effects in DKD. Immune cells and resident renal cells that activate innate immunity have critical roles in triggering and sustaining inflammation in this setting. Evidence from clinical and experimental studies suggests that several innate immune pathways have potential roles in the pathogenesis and progression of DKD. Toll-like receptors detect endogenous danger-associated molecular patterns generated during diabetes and induce a sterile tubulointerstitial inflammatory response via the NF-κB signalling pathway. The NLRP3 inflammasome links sensing of metabolic stress in the diabetic kidney to activation of pro-inflammatory cascades via the induction of IL-1β and IL-18. The kallikrein-kinin system promotes inflammatory processes via the generation of bradykinins and the activation of bradykinin receptors, and activation of protease-activated receptors on kidney cells by coagulation enzymes contributes to renal inflammation and fibrosis in DKD. In addition, hyperglycaemia leads to protein glycation and activation of the complement cascade via recognition of glycated proteins by mannan-binding lectin and/or dysfunction of glycated complement regulatory proteins. Data from preclinical studies suggest that targeting these innate immune pathways could lead to novel therapies for DKD.

Podocyte NLRP3 Inflammasome Activation and Formation by Adipokine Visfatin

BACKGROUND/AIMS

NLRP3 inflammasome activation has been reported to be an early mechanism responsible for glomerular inflammation and injury in obese mice. However, the precise mechanism of obesity-induced NLRP3 inflammasome activation remains unknown. The present study explored whether adipokine visfatin mediates obesity-induced NLRP3 inflammasome activation and consequent podocyte injury.

METHODS

Inflammasome formation and immunofluorescence expressions were quantified by confocal microscopy. Caspase-activity, IL-1β production and VEGF concentrations were measured by ELISA.

RESULTS

Confocal microscopic analysis showed that visfatin treatment increased the colocalization of Nlrp3 with Asc or Nlrp3 with caspase-1 in podocytes indicating the formation of NLRP3 inflammasomes. This visfatin-induced NLRP3 inflammasome formation was abolished by pretreatment of podocytes with Asc siRNA. Correspondingly, visfatin treatment significantly increased the caspase-1 activity and IL-1β production in podocytes, which was significantly attenuated by Asc siRNA transfection. Further RT-PCR and confocal microscopic analysis demonstrated that visfatin treatment significantly decreased the podocin expression (podocyte damage). Podocytes pretreatment with Asc siRNA or caspase-1 inhibitor, WEHD attenuated this visfatin-induced podocin reduction. Furthermore, Asc siRNA transfection was found to preserve podocyte morphology by maintaining the distinct arrangement of F-actin fibers normally lost in response to visfatin. It also prevented podocyte dysfunction by restoring visfatin-induced suppression of VEGF production and secretion.

CONCLUSION

Visfatin induces NLRP3 inflammasome activation in podocytes and thereby resulting in podocyte injury.

Impact of ET-1 and sex in glomerular hyperfiltration in humanized sickle cell mice

Hyperfiltration, highly prevalent early in sickle cell disease (SCD), is in part driven by an increase in ultrafiltration coefficient (K_f). The increase in K_f may be due to enlarged filtration surface area and/or increased glomerular permeability (P_alb). Previous studies have demonstrated that endothelin-1 (ET-1) contributes to P_alb changes in models of diabetes and SCD. Thus, we performed longitudinal studies of renal function to determine the relationship between ET-1 and glomerular size and P_alb that may contribute to hyperfiltration in humanized sickle cell (HbSS) and control (HbAA) mice at 8-32 weeks of age. HbSS mice were characterized by significant increases in plasma and glomerular ET-1 expression in both sexes although this increase was significantly greater in males. HbSS glomeruli of both males and females presented with a progressive and significant increase in glomerular size, volume, and K_f During the onset of hyperfiltration, plasma and glomerular ET-1 expression were associated with a greater increase in glomerular size and K_f in HbSS mice, regardless of sex. The pattern of P_alb augmentation during the hyperfiltration was also associated with an increase in glomerular ET-1 expression, in both male and female HbSS mice. However, the increase in P_alb was significantly greater in males and delayed in time in females. Additionally, selective endothelin A receptor (ET_A) antagonist prevented hyperfiltration in HbSS, regardless of sex. These results suggest that marked sex disparity in glomerular hyperfiltration may be driven, in part, by ET-1-dependent ultra-structural changes in filtration barrier components contributing to glomerular hyperfiltration in HbSS mice.

Childhood adversity and mechanistic links to hypertension risk in adulthood

Adverse childhood experiences (ACEs), defined as traumatic events in childhood that range from various forms of abuse to household challenges and dysfunction, have devastating consequences on adult health. Epidemiological studies in humans and animal models of early life stress (ELS) have revealed a strong association and insight into the mechanistic link between ACEs and increased risk of cardiovascular disease (CVD). This review focuses on the mechanistic links of ACEs in humans and ELS in mice and rats to vasoactive factors and immune mediators associated with CVD and hypertension risk, as well as sex differences in these phenomena. Major topics of discussion in this review are as follows: (a) epidemiological associations between ACEs and CVD risk focusing on hypertension, (b) evidence for association of ACE exposures to immune-mediated and/or vasoactive pathways, (c) rodent models of ELS-induced hypertension risk, (d) proinflammatory mediators and vasoactive factors as mechanisms of ELS-induced hypertension risk. We also provide some overall conclusions and directions of further research. LINKED ARTICLES: This article is part of a themed section on Immune Targets in Hypertension. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.12/issuetoc.

Endothelial factors in the pathogenesis and treatment of chronic kidney disease Part I: General mechanisms: a joint consensus statement from the European Society of Hypertension Working Group on Endothelin and Endothelial Factors and The Japanese Society of Hypertension

: Kidney damage is a common consequence of arterial hypertension, but is also a cause of atherogenesis. Dysfunction and/or harm of the endothelium in glomeruli and tubular interstitium damage the function of these structures and translates into dynamic changes of filtration fraction, with progressive reduction in glomerular filtration rate, expansion of extracellular fluid volume, abnormal ion balance, and hypoxia, ultimately leading to chronic kidney disease. Considering the key role played by endothelial dysfunction in chronic kidney disease, the Working Group on Endothelin and Endothelial Factors of the European Society of Hypertension and the Japanese Society of Hypertension have critically reviewed available knowledge on the mechanisms underlying endothelial cell injury. This resulted into two articles: in the first, we herein examine the mechanisms by which endothelial factors induce vascular remodeling and the role of different players, including endothelin-1, the renin-angiotensin-aldosterone system and their interactions, and of oxidative stress; in the second, we discuss the role of endothelial dysfunction in the major disease conditions that affect the kidney.

ETA receptor activation contributes to T cell accumulation in the kidney following ischemia-reperfusion injury

Renal ischemia-reperfusion (IR) injury and acute kidney injury (AKI) increase the risk of developing hypertension, with T cells suspected as a possible mechanistic link. Endothelin promotes renal T cell infiltration in several diseases, predominantly via the ETA receptor, but its contribution to renal T cell infiltration following renal IR injury is poorly understood. To test whether ETA receptor activation promotes T cell infiltration of the kidney following IR injury, male C57BL/6 mice were treated with the ETA receptor antagonist ABT-627 or vehicle, commencing 2 days prior to unilateral renal IR injury. Mice were sacrificed at 24 h or 10 days post-IR for assessment of the initial renal injury and subsequent infiltration of T cells. Vehicle and ABT-627-treated mice displayed significant upregulation of endothelin-1 (ET-1) in the IR compared to contralateral kidney at both 24 h and 10 days post-IR (P < 0.001). Renal CD3+ T cell numbers were increased in the IR compared to contralateral kidneys at 10 days, but ABT-627-treated mice displayed a 35% reduction in this effect in the outer medulla (P < 0.05 vs. vehicle) and a nonsignificant 23% reduction in the cortex compared to vehicle-treated mice. Whether specific T cell subsets were affected awaits confirmation by flow cytometry, but outer medullary expression of the T helper 17 transcription factor RORγt was reduced by ABT-627 (P = 0.06). These data indicate that ET-1 acting via the ETA receptor contributes to renal T cell infiltration post-IR injury. This may have important implications for immune system-mediated long-term consequences of AKI, an area which awaits further investigation.

Prevention of the progression of renal injury in diabetic rodent models with preexisting renal disease with chronic endothelin A receptor blockade

The endothelin (ET) system has emerged as a therapeutic target for the treatment of diabetic nephropathy (DN). The present study examined whether chronic endothelin A (ET_A) receptor blockade with atrasentan prevents the progression of renal injury in two models of DN with preexisting renal disease that exhibit an increased renal ET-1 system compared with nondiabetic rats: streptozotocin-treated Dahl salt-sensitive (STZ-SS) and type 2 diabetic nephropathy (T2DN) rats. Nine week-old SS rats were treated with (STZ; 50 mg/kg ip) to induce diabetes. After 3 wk of diabetes, proteinuria increased to 353 ± 34 mg/day. The rats were then separated into two groups: 1) vehicle and 2) atrasentan (5 mg·kg^-1·day^-1) via drinking water. After 6 wk of treatment with atrasentan, mean arterial pressure (MAP) and proteinuria decreased by 12 and 40%, respectively, in STZ-SS rats. The degree of glomerulosclerosis and renal fibrosis was significantly reduced in the kidneys of atrasentan-treated STZ-SS rats compared with vehicle STZ-SS rats. Interestingly, treatment with atrasentan did not affect GFR but significantly increased renal blood flow by 33% and prevented the elevations in filtration fraction and renal vascular resistance by 23 and 20%, respectively, in STZ-SS rats. In contrast to the STZ-SS study, atrasentan had no effect on MAP or proteinuria in T2DN rats. However, treatment with atrasentan significantly decreased glomerular injury and renal fibrosis and prevented the decline in renal function in T2DN rats. These data indicate that chronic ET_A blockade produces advantageous changes in renal hemodynamics that slow the progression of renal disease and also reduces renal histopathology in the absence of reducing arterial pressure and proteinuria.

Early life stress induces immune priming in kidneys of adult male rats

Early life stress (ELS) in humans is associated with elevated proinflammatory markers. We hypothesized that ELS induces activation of the immune response in a rat model of ELS, maternal separation (MatSep), in adulthood. MatSep involves separating pups from the dam from postnatal day 2 to postnatal day 14 for 3 h/day. Control rats are nonseparated littermates. We determined circulating and renal immune cell numbers, renal immune cell activation markers, renal cytokine levels, and the renal inflammatory gene expression response to low-dose lipopolysaccharide (LPS) in male MatSep and control rats. We observed that MatSep did not change the percentage of gated events for circulating CD3+, CD4+, CD8+, and CD4+/Foxp3+ cells or absolute numbers of mononuclear and T cells in the circulation and kidneys; however, MatSep led to an increase in activation of renal neutrophils as well as CD44+ cells. Renal toll-like receptor 4 (TLR4) and interleukin 1 beta (IL-1β) was significantly increased in MatSep rats, specifically in the outer and inner medulla and distal nephron, respectively. Evaluation of renal inflammatory genes showed that in response to a low-dose LPS challenge (2 mg/kg iv) a total of 20 genes were significantly altered in kidneys from MatSep rats (17 genes were upregulated and 3 were downregulated), as opposed to no significant differences in gene expression in control vs. control + LPS groups. Taken together, these findings indicate that MatSep induces priming of the immune response in the kidney.

New strategies to tackle diabetic kidney disease

PURPOSE OF REVIEW

The purpose of this review is to provide an overview of recent preclinical and clinical studies, which demonstrate new insights for the treatment of diabetic kidney disease (DKD) and to outline future directions with respect to novel therapies.

RECENT FINDINGS

Positive findings with respect to new glucose-lowering agents such as sodium-dependent glucose transporter 2 inhibitors may lead to a change in the way we treat diabetic individuals with or at risk of DKD. Additional positive phase 2 clinical studies with drugs that have hemodynamic actions such as endothelin antagonists and mineralocorticoid receptor antagonists have led to larger phase 3 trials with atrasentan and finerenone, respectively, in order to address if these drugs indeed delay the development of end-stage renal disease. A number of other pathways are currently under active preclinical investigation and hopefully over the next decade will lead to promising drug candidates for subsequent clinical trials.

SUMMARY

DKD remains an area of active preclinical and clinical investigation. Positive results with some of the more promising agents should lead to strategies to reverse, attenuate or prevent DKD.

Free radical scavenging decreases endothelin-1 excretion and glomerular albumin permeability during type 1 diabetes

Increased renal endothelin-1 (ET-1) production and an ET_A receptor-dependent increase in glomerular albumin permeability (P_alb) accompany type 1 diabetes mellitus (T1D). We hypothesized that T1D-induced oxidative stress contributes to renal ET-1 production and glomerular P_alb Male rats with streptozotocin-induced T1D were provided free access to drinking water without additives (T1D rats) or containing the free radical scavenger tempol (1 mmol/L; T1D+Tempol). After 3 weeks, T1D+Tempol rats displayed lower urinary excretion of thiobarbituric acid reactive substances and glomerular superoxide production (dihydroethidium staining) compared to T1D rats. Urinary ET-1 excretion and inner medullary (but not cortical or outer medullary) prepro-ET-1 mRNA expression were lower in the T1D+Tempol group than in the T1D group. P_alb, measured as the change in volume of isolated glomeruli upon exposure to oncotic gradients of albumin, was significantly lower in the T1D+Tempol group than in the T1D group. Tempol treatment did not alter protein excretion or creatinine clearance. These data support the postulate that oxidative stress contributes to glomerular P_alb and renal ET-1 production during the early phase of type 1 diabetes.

Immune regulation of systemic hypertension, pulmonary arterial hypertension, and preeclampsia: shared disease mechanisms and translational opportunities

Systemic hypertension, preeclampsia, and pulmonary arterial hypertension (PAH) are diseases of high blood pressure in the systemic or pulmonary circulation. Beyond the well-defined contribution of more traditional pathophysiological mechanisms, such as changes in the renin-angiotensin-aldosterone system, to the development of these hypertensive disorders, there is substantial clinical evidence supporting an important role for inflammation and immunity in the pathogenesis of each of these three conditions. Over the last decade, work in small animal models, bearing targeted deficiencies in specific cytokines or immune cell subsets, has begun to clarify the immune-mediated mechanisms that drive changes in vascular structure and tone in hypertensive disease. By summarizing the clinical and experimental evidence supporting a contribution of the immune system to systemic hypertension, preeclampsia, and PAH, the current review highlights the cellular and molecular pathways that are common to all three hypertensive disorders. These mechanisms are centered on an imbalance in CD4⁺ helper T cell populations, defined by excessive Th17 responses and impaired T_reg activity, as well as the excessive activation or impairment of additional immune cell types, including macrophages, dendritic cells, CD8⁺ T cells, B cells, and natural killer cells. The identification of common immune mechanisms in systemic hypertension, preeclampsia, and PAH raises the possibility of new therapeutic strategies that target the immune component of hypertension across multiple disorders.

The Matrikine Acetylated Proline-Glycine-Proline Couples Vascular Inflammation and Acute Cardiac Rejection

The extracellular matrix (ECM) is a dynamic, bioactive structure critical to organ development, structure and function. Excessive remodeling of the ECM is a hallmark of a variety of inflammatory conditions including vascular disease. Endothelin-1 (ET1) synthesis is understood to promote cardiovascular diseases including acute cardiac transplant rejection; however, the contribution of ECM-derived chemokines (matrikines) to vascular inflammation remains poorly understood. Herein we report that the matrikine acetylated Pro-Gly-Pro (PGP) stimulates vascular inflammation through activation of endothelial CXC Chemokine Receptor 2 (CXCR2) and production of endothelin-1 both in vitro and in vivo. As a proof of hypothesis, we demonstrate that coronary PGP levels associate with both circulating endothelin-1 and acute rejection in cardiac transplant patients (sensitivity of 100% and specificity of 86%). These findings establish PGP as a novel mediator in cardiovascular disease, and implicate bioactive matrix fragments as underappreciated agents potentially active in numerous conditions propagated by progressive vascular inflammation.

Toll-like Receptor 4 Deficiency Reduces Oxidative Stress and Macrophage Mediated Inflammation in Hypertensive Kidney

Oxidative stress and inflammation are integral to hypertension-induced renal injury. A unifying feature for the two components is Toll-like receptors (TLR), which are key regulators of the innate immune system. Recent studies implicate TLR4 activation and oxidative stress in cardiovascular diseases and also as a link between inflammation and hypertension. However, its role in hypertension induced renal injury remains unexplored. In the present study, we investigated whether TLR-4 deficiency reduces Ang-II-induced renal injury and fibrosis by attenuating reactive oxygen species (ROS) production and inflammation. C3H/HeOuJ mice with normal TLR-4 and C3H/HeJ Lps-d with dysfunctional TLR4 (TLR4 deficiency) were treated without or with Ang-II. In response to Ang-II, TLR4 deficient mice had reduced renal resistive index and increased renal cortical blood flow compared to mice with normal TLR4. Further, TLR4 deficiency reduced oxidative stress and increased antioxidant capacity (MnSOD, CuSOD and Catalase activity). TLR4 deficiency was also associated with reduced inflammation (MCP-1, MIP-2, TNF-α, IL-6 and CD68), decreased accumulation of bone marrow-derived fibroblasts and TGF-β expression. Our data suggests that in C3H/HeJ Lps-d mice, deficiency of functional TLR4 reduces oxidative stress and macrophage activation to decrease TGF-β-induced extracellular matrix protein deposition in the kidney in Ang-II induced hypertension.

Association between Endothelin-1 Levels and Kidney Disease among Blacks

Endothelin-1, a marker of endothelial dysfunction, is a potent vasoconstrictor released by endothelial cells and an important regulator of renal physiology. It is not known whether elevated serum levels of endothelin-1 indicate future risk of kidney disease in the general population. In participants in the Jackson Heart Study, a community-based observational study of cardiovascular risk in black adults, we measured serum endothelin-1 level at baseline (2000-2004; n=3538). We defined incident CKD as eGFR<60 ml/min per 1.73 m² and ≥30% eGFR decline at the third visit (2009-2013) relative to baseline among those participants with baseline eGFR ≥60 ml/min per 1.73 m² At baseline, mean age was 55 years old, 37% of participants were men, and mean eGFR was 94 ml/min per 1.73 m² Over a median follow-up of 8 years, 228 (6.4%) cases of incident CKD occurred in participants. Participants with baseline endothelin-1 levels in higher quartiles had a greater incidence of CKD in the fully adjusted model (odds ratio for fourth versus first quartile, 1.81; 95% confidence interval, 1.11 to 2.96; P_trend=0.04). Endothelin-1 positively associated with all-cause mortality (hazard ratio for fourth versus first quartile, 1.64; 95% confidence interval, 1.24 to 2.16; P_trend<0.001). In conclusion, higher baseline serum endothelin-1 levels associated with incident CKD and all-cause mortality during follow-up in this general population sample of blacks.

Atrasentan for the treatment of diabetic nephropathy

INTRODUCTION

Endothelin-1 (ET-1) is the most potent vasoconstrictor, and is involved in the renal regulation of salt and water homeostasis. When produced in excess in the kidney, ET-1 promotes proteinuria and tubulointerstitial injury. There is great interest in the clinical use of endothelin receptor antagonists (ERAs) in chronic kidney disease (CKD), mainly in diabetic nephropathy (DN). Areas covered: Physiopathological actions of ET-1 on the kidney. Both dual ETAR/ET_BR (bosentan) or ET_AR specific endothelin antagonists (avosentan and atrasentan, among others), which have progressed to early clinical development, with particular emphasis on atrasentan. Expert opinion: Different phase I and II clinical trials with ERAs in DN, mostly with atrasentan, have shown that these drugs have a marked anti-proteinuric effect on residual proteinuria when administered as add-on therapy in addition to ACEi or ARAII treatment. In the past few years, a series of randomized controlled trials investigating new approaches to DN have provided negative or inconclusive data, or even were terminated due to safety concerns or lack of efficacy. Therefore, we eagerly but cautiously await the results of the ongoing SONAR trial with atrasentan in more than 4,000 patients including assessment of renal and cardiovascular hard-end points (estimated primary completion date, July 2018).

Targeting heme oxygenase-1 in early diabetic nephropathy in streptozotocin-induced diabetic rats

Diabetic nephropathy (DN) is one of the most common microvascular diabetic complications. This study was designed to evaluate the possible protective effect and underlying mechanisms of HO-1 induction in streptozotocin (STZ)-induced early DN in rats. The diabetic rats were divided into three groups: STZ-diabetic, cobalt protoporphyrin (CoPP)-treated diabetic, and zinc protoporphyrin IX (ZnPP)-treated diabetic groups. Compared to the STZ-diabetic group, CoPP-induced HO-1 upregulation improved the diabetic state and renal functional parameters, suppressed the renal proinflammatory marker, NF-κB, abrogated the elevated renal hydroxyprolin, and decreased the enhanced renal nicotinamide adenine dinucleotide phosphate oxidase activity with parallel reduction of urinary oxidative stress markers. On the contrary, treatment with ZnPP abrogated HO-1 levels, aggravated the diabetic condition with further increases in renal oxidative stress, fibrotic and inflammatory markers, and exacerbated renal dysfunction in diabetic animals. These findings suggest that the reduced diabetic renal injury upon HO-1 induction implicates the role of HO-1 induction as a potential treatment for DN.

Intravital imaging of the kidney in a rat model of salt-sensitive hypertension

Hypertension is one of the most prevalent diseases worldwide and a major risk factor for renal failure and cardiovascular disease. The role of albuminuria, a common feature of hypertension and robust predictor of cardiorenal disorders, remains incompletely understood. The goal of this study was to investigate the mechanisms leading to albuminuria in the kidney of a rat model of hypertension, the Dahl salt-sensitive (SS) rat. To determine the relative contributions of the glomerulus and proximal tubule (PT) to albuminuria, we applied intravital two-photon-based imaging to investigate the complex renal physiological changes that occur during salt-induced hypertension. Following a high-salt diet, SS rats exhibited elevated blood pressure, increased glomerular sieving of albumin (GSC_alb = 0.0686), relative permeability to albumin (+Δ16%), and impaired volume hemodynamics (-Δ14%). Serum albumin but not serum globulins or creatinine concentration was decreased (-0.54 g/dl), which was concomitant with increased filtration of albumin (3.7 vs. 0.8 g/day normal diet). Pathologically, hypertensive animals had significant tubular damage, as indicated by increased prevalence of granular casts, expansion and necrosis of PT epithelial cells (+Δ2.20 score/image), progressive augmentation of red blood cell velocity (+Δ269 µm/s) and micro vessel diameter (+Δ4.3 µm), and increased vascular injury (+Δ0.61 leakage/image). Therefore, development of salt-induced hypertension can be triggered by fast and progressive pathogenic remodeling of PT epithelia, which can be associated with changes in albumin handling. Collectively, these results indicate that both the glomerulus and the PT contribute to albuminuria, and dual treatment of glomerular filtration and albumin reabsorption may represent an effective treatment of salt-sensitive hypertension.

Long-Term Endothelin-A Receptor Antagonism Provides Robust Renal Protection in Humanized Sickle Cell Disease Mice

Sickle cell disease (SCD)-associated nephropathy is a major source of morbidity and mortality in patients because of the lack of efficacious treatments targeting renal manifestations of the disease. Here, we describe a long-term treatment strategy with the selective endothelin-A receptor (ET_A) antagonist, ambrisentan, designed to interfere with the development of nephropathy in a humanized mouse model of SCD. Ambrisentan preserved GFR at the level of nondisease controls and prevented the development of proteinuria, albuminuria, and nephrinuria. Microscopy studies demonstrated prevention of podocyte loss and structural alterations, the absence of vascular congestion, and attenuation of glomerulosclerosis in treated mice. Studies in isolated glomeruli showed that treatment reduced inflammation and oxidative stress. At the level of renal tubules, ambrisentan treatment prevented the increased excretion of urinary tubular injury biomarkers. Additionally, the treatment strategy prevented tubular brush border loss, diminished tubular iron deposition, blocked the development of interstitial fibrosis, and prevented immune cell infiltration. Furthermore, the prevention of albuminuria in treated mice was associated with preservation of cortical megalin expression. In a separate series of identical experiments, combined ET_A and ET_B receptor antagonism provided only some of the protection observed with ambrisentan, highlighting the importance of exclusively targeting the ET_A receptor in SCD. Our results demonstrate that ambrisentan treatment provides robust protection from diverse renal pathologies in SCD mice, and suggest that long-term ET_A receptor antagonism may provide a strategy for the prevention of renal complications of SCD.

The Role of Angiotensin II in Glomerular Volume Dynamics and Podocyte Calcium Handling

Podocytes are becoming a primary focus of research efforts due to their association with progressive glomeruli damage in disease states. Loss of podocytes can occur as a result of excessive intracellular calcium influx, and we have previously shown that angiotensin II (Ang II) via canonical transient receptor potential 6 (TRPC6) channels caused increased intracellular Ca2+ flux in podocytes. We showed here with patch-clamp electrophysiology that Ang II activates TRPC channels; then using confocal calcium imaging we demonstrated that Ang II-dependent stimulation of Ca2+ influx in the podocytes is precluded by blocking either AT1 or AT2 receptors (ATRs). Application of Ang(1-7) had no effect on intracellular calcium. Ang II-induced calcium flux was decreased upon inhibition of TRPC channels with SAR7334, SKF 96365, clemizole hydrochloride and La3+, but not ML204. Using a novel 3D whole-glomerulus imaging ex vivo assay, we revealed the involvement of both ATRs in controlling glomerular permeability; additionally, using specific inhibitors and activators of TRPC6, we showed that these channels are implicated in the regulation of glomerular volume dynamics. Therefore, we provide evidence demonstrating the critical role of Ang II/TRPC6 axis in the control of glomeruli function, which is likely important for the development of glomerular diseases.

Interplay between renal endothelin and purinergic signaling systems

Alterations in extracellular fluid volume regulation and sodium balance may result in the development and maintenance of salt-dependent hypertension, a major risk factor for cardiovascular disease. Numerous pathways contribute to the regulation of sodium excretion and blood pressure, including endothelin and purinergic signaling. Increasing evidence suggests a link between purinergic receptor activation and endothelin production within the renal collecting duct as a means of promoting natriuresis. A better understanding of the relationship between these two systems, especially in regard to sodium homeostasis, will fill a significant knowledge gap and may provide novel antihypertensive treatment options. Therefore, this review focuses on the cross talk between endothelin and purinergic signaling as it relates to the renal regulation of sodium and blood pressure homeostasis.

Endothelin-1 contributes to the progression of renal injury in sickle cell disease via reactive oxygen species

BACKGROUND AND PURPOSE

Endothelin-1 (ET-1) is increased in patients with sickle cell disease and may contribute to the development of sickle cell nephropathy. The current study was designed to determine whether ET-1 acting via the ETA receptor contributes to renal injury in a mouse model of sickle cell disease.

EXPERIMENTAL APPROACH

Adult, humanized HbSS (homozygous for sickle Hb) mice had increased ET-1 mRNA expression in both the cortex and the glomeruli compared with mice heterozygous for sickle and Hb A (HbAS controls). In the renal cortex, ETA receptor mRNA expression was also elevated in HbSS (sickle) mice although ETB receptor mRNA expression was unchanged. Ligand binding assays confirmed that sickle mice had increased ETA receptors in the renal vascular tissue when compared with control mice.

KEY RESULTS

In response to PKC stimulation, reactive oxygen species production by isolated glomeruli from HbSS sickle mice was increased compared with that from HbSA controls, an effect that was prevented by 1 week in vivo treatment with the selective ETA antagonist, ABT-627. Protein and nephrin excretion were both elevated in sickle mice, effects that were also significantly attenuated by ABT-627. Finally, ETA receptor antagonism caused a significant reduction in mRNA expression of NADPH oxidase subunits, which may contribute to nephropathy in sickle cell disease.

CONCLUSIONS AND IMPLICATIONS

These data support a novel role for ET-1 in the progression of sickle nephropathy, specifically via the ETA receptor, and suggest a potential role for ETA receptor antagonism in a treatment strategy.

The heart as an extravascular target of endothelin-1 in particulate matter-induced cardiac dysfunction

Exposure to particulate matter air pollution has been causally linked to cardiovascular disease in humans. Several broad and overlapping hypotheses describing the biological mechanisms by which particulate matter exposure leads to cardiovascular disease have been explored, although linkage with specific factors or genes remains limited. These hypotheses may or may not also lead to particulate matter-induced cardiac dysfunction. Evidence pointing to autocrine/paracrine signaling systems as modulators of cardiac dysfunction has increased interest in the emerging role of endothelins as mediators of cardiac function following particulate matter exposure. Endothelin-1, a well-described small peptide expressed in the pulmonary and cardiovascular systems, is best known for its ability to constrict blood vessels, although it can also induce extravascular effects. Research on the role of endothelins in the context of air pollution has largely focused on vascular effects, with limited investigation of responses resulting from the direct effects of endothelins on cardiac tissue. This represents a significant knowledge gap in air pollution health effects research, given the abundance of endothelin receptors found on cardiac tissue and the ability of endothelin-1 to modulate cardiac contractility, heart rate, and rhythm. The plausibility of endothelin-1 as a mediator of particulate matter-induced cardiac dysfunction is further supported by the therapeutic utility of certain endothelin receptor antagonists. The present review examines the possibility that endothelin-1 release caused by exposure to PM directly modulates extravascular effects on the heart, deleteriously altering cardiac function.

The next generation of therapeutics for chronic kidney disease

Chronic kidney disease (CKD) represents a leading cause of death in the United States. There is no cure for this disease, with current treatment strategies relying on blood pressure control through blockade of the renin-angiotensin system. Such approaches only delay the development of end-stage kidney disease and can be associated with serious side effects. Recent identification of several novel mechanisms contributing to CKD development - including vascular changes, loss of podocytes and renal epithelial cells, matrix deposition, inflammation and metabolic dysregulation - has revealed new potential therapeutic approaches for CKD. This Review assesses emerging strategies and agents for CKD treatment, highlighting the associated challenges in their clinical development.

Dual inhibition of renin-angiotensin-aldosterone system and endothelin-1 in treatment of chronic kidney disease

Inhibition of the renin-angiotensin-aldosterone system (RAAS) plays a pivotal role in treatment of chronic kidney diseases (CKD). However, reversal of the course of CKD or at least long-term stabilization of renal function are often difficult to achieve, and many patients still progress to end-stage renal disease. New treatments are needed to enhance protective actions of RAAS inhibitors (RAASis), such as angiotensin-converting enzyme (ACE) inhibitors (ACEIs) or angiotensin receptor blockers (ARBs), and improve prognosis in CKD patients. Inhibition of endothelin (ET) system in combination with established RAASis may represent such an approach. There are complex interactions between both systems and similarities in their renal physiological and pathophysiological actions that provide theoretical rationale for combined inhibition. This view is supported by some experimental studies in models of both diabetic and nondiabetic CKD showing that a combination of RAASis with ET receptor antagonists (ERAs) ameliorate proteinuria, renal structural changes, and molecular markers of glomerulosclerosis, renal fibrosis, or inflammation more effectively than RAASis or ERAs alone. Practically all clinical studies exploring the effects of RAASis and ERAs combination in nephroprotection have thus far applied add-on designs, in which an ERA is added to baseline treatment with ACEIs or ARBs. These studies, conducted mostly in patients with diabetic nephropathy, have shown that ERAs effectively reduce residual proteinuria in patients with baseline RAASis treatment. Long-term studies are currently being conducted to determine whether promising antiproteinuric effects of the dual blockade will be translated in long-term nephroprotection with acceptable safety profile.

Role of the endothelin system in sexual dimorphism in cardiovascular and renal diseases

Epidemiological studies of blood pressure in men and women and in experimental animal models point to substantial sex differences in the occurrence of arterial hypertension as well as in the various manifestations of arterial hypertension, including myocardial infarction, stroke, retinopathy, chronic kidney failure, as well as hypertension-associated diseases (e.g. diabetes mellitus). Increasing evidence demonstrates that the endothelin (ET) system is a major player in the genesis of sex differences in cardiovascular and renal physiology and diseases. Sex differences in the ET system have been described in the vasculature, heart and kidney of humans and experimental animals. In the current review, we briefly describe the role of the ET system in the cardiovascular and renal systems. We also update information on sex differences at different levels of the ET system including synthesis, circulating and tissue levels, receptors, signaling pathways, ET actions, and responses to antagonists in different organs that contribute to blood pressure regulation. Knowledge of the mechanisms underlying sex differences in arterial hypertension can impact therapeutic strategies. Sex-targeted and/or sex-tailored approaches may improve treatment of cardiovascular and renal diseases.