Endothelin-1 and the kidney: new perspectives and recent findings

Metabolic acidosis in chronic kidney disease: mere consequence or also culprit?

Metabolic acidosis is a frequent complication in non-transplant chronic kidney disease (CKD) and after kidney transplantation. It occurs when net endogenous acid production exceeds net acid excretion. While nephron loss with reduced ammoniagenesis is the main cause of acid retention in non-transplant CKD patients, additional pathophysiological mechanisms are likely inflicted in kidney transplant recipients. Functional tubular damage by calcineurin inhibitors seems to play a key role causing renal tubular acidosis. Notably, experimental and clinical studies over the past decades have provided evidence that metabolic acidosis may not only be a consequence of CKD but also a driver of disease. In metabolic acidosis, activation of hormonal systems and the complement system resulting in fibrosis have been described. Further studies of changes in renal metabolism will likely contribute to a deeper understanding of the pathophysiology of metabolic acidosis in CKD. While alkali supplementation in case of reduced serum bicarbonate < 22 mmol/l has been endorsed by CKD guidelines for many years to slow renal functional decline, among other considerations, beneficial effects and thresholds for treatment have lately been under intense debate. This review article discusses this topic in light of the most recent results of trials assessing the efficacy of dietary and pharmacological interventions in CKD and kidney transplant patients.

An Update on Current Therapeutic Options in IgA Nephropathy

Immunoglobulin A nephropathy (IgAN) remains the leading cause of primary glomerular disease worldwide. Outcomes are poor with high rates of progressive chronic kidney disease and kidney failure, which contributes to global healthcare costs. Although this disease entity has been described, there were no disease-specific treatments until recently, with the current standard of care focusing on optimal supportive measures including lifestyle modifications and optimization of the renin-angiotensin-aldosterone blockade. However, with significant advances in the understanding of the pathogenesis of IgAN in the past decade, and the acceptance of surrogate outcomes for accelerated drug approval, there have been many new investigational agents tested to target this disease. As these agents become available, we envision a multi-pronged treatment strategy that simultaneously targets the consequences of ongoing nephron loss, stopping any glomerular inflammation, inhibiting pro-fibrotic signals in the glomerulus and tubulo-interstitium, and inhibiting the production of pathogenic IgA molecules. This review is an update on a previous review published in 2021, and we aim to summarize the developments and updates in therapeutic strategies in IgAN and highlight the promising discoveries that are likely to add to our armamentarium.

ET-traps: Potential therapeutics for preeclampsia

Elevated endothelin-1 (ET-1) has been implicated in several diseases including preeclampsia, where it causes the induction of hypertension, oxidative stress, endoplasmic reticulum stress, microvascular dysfunction and tissue damage in different organs. ET-traps are Fc-fusion proteins with a design based on the physiological receptors of ET-1. This paper discusses the potential use of ET-traps as a therapeutic for preeclampsia. ET-traps potently bind and sequester pathologically elevated ET-1 to significantly reduce different markers of pathology to non-disease levels with no toxicity.

Biomarkers related to gas embolism: Gas score, pathology, and gene expression in a gas bubble disease model

Fish exposed to water supersaturated with dissolved gas experience gas embolism similar to decompression sickness (DCS), known as gas bubble disease (GBD) in fish. GBD has been postulated as an alternative to traditional mammals' models on DCS. Gas embolism can cause mechanical and biochemical damage, generating pathophysiological responses. Increased expression of biomarkers of cell damage such as the heat shock protein (HSP) family, endothelin 1 (ET-1) or intercellular adhesion molecule 1 (ICAM-1) has been observed, being a possible target for further studies of gas embolism. The GBD model consisted of exposing fish to supersaturation in water with approximately 170% total dissolved gas (TDG) for 18 hours, producing severe gas embolism. This diagnosis was confirmed by a complete histopathological exam and the gas score method. HSP70 showed a statistically significant upregulation compared to the control in all the studied organs (p <0.02). Gills and heart showed upregulation of HSP90 with statistical significance (p = 0.015 and p = 0.02, respectively). In addition, HSP70 gene expression in gills was positively correlated with gas score (p = 0.033). These results suggest that gas embolism modify the expression of different biomarkers, with HSP70 being shown as a strong marker of this process. Furthermore, gas score is a useful tool to study the abundance of gas bubbles, although individual variability always remains present. These results support the validity of the GBD model in fish to study gas embolism in diseases such as DCS.

A Systematic Review of Aminaphtone from Pathophysiology to Clinical Applications: Focus on New Rheumatological Acquisitions

Aminaphtone is a chemical drug that has been used for more than thirty years to treat a variety of vascular disorders, with good clinical results and a satisfying safety profile. In the last two decades, multiple clinical studies have reported the efficacy of the drug in different clinical scenarios of altered microvascular reactivity, describing the downregulation of adhesion molecules (i.e., VCAM, ICAM, Selectins), vasoconstrictor peptides (i.e., Endothelin-1), and pro-inflammatory cytokine expression (i.e., IL-6, IL-10, VEGF, TGF-beta) by Aminaphtone. In this review, we summarize the current knowledge concerning Aminaphtone, with particular attention to rheumatological conditions in which microvascular disfunction plays a pivotal role, such as Raynaud's phenomenon and systemic sclerosis. These latter conditions may represent a promising field of application for Aminaphtone, due to the growing pre-clinical, clinical, and instrumental reports of efficacy. However, randomized, double-blind, placebo-controlled clinical trials are lacking and are desirable.

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.

Protease-activated receptors in kidney diseases: A comprehensive review of pathological roles, therapeutic outcomes and challenges

Studies have demonstrated that protease-activated receptors (PARs) with four subtypes (PAR1-4) are mainly expressed in the renal epithelial, endothelial, and podocyte cells. Some endogenous and urinary proteases, namely thrombin, trypsin, urokinase, and kallikrein released during diseased conditions, are responsible for activating different subtypes of PARs. Each PAR receptor subtype is involved in kidney disease of distinct aetiology. PAR1 and PAR2 have shown differential therapeutic outcomes in rodent models of type-1 and type-2 diabetic kidney diseases due to the distinct etiological basis of each disease type, however such findings need to be confirmed in other diabetic renal injury models. PAR1 and PAR2 blockers have been observed to abolish drug-induced nephrotoxicity in rodents by suppressing tubular inflammation and fibrosis and preventing mitochondrial dysfunction. Notably, PAR2 inhibition improved autophagy and prevented fibrosis, inflammation, and remodeling in the urethral obstruction model. Only the PAR1/4 subtypes have emerged as a therapeutic target for treating experimentally induced nephrotic syndrome, where their respective antibodies attenuated the podocyte apoptosis induced upon thrombin activation. Strikingly PAR2 and PAR4 subtypes involvement has been tested in sepsis-induced acute kidney injury (AKI) and renal ischemia-reperfusion injury models. Thus, more studies are required to delineate the role of other subtypes in the sepsis-AKI model. Evidence suggests that PARs regulate oxidative, inflammatory stress, immune cell activation, fibrosis, autophagic flux, and apoptosis during kidney diseases.

Sparsentan in patients with IgA nephropathy: a prespecified interim analysis from a randomised, double-blind, active-controlled clinical trial

BACKGROUND

Sparsentan is a novel, non-immunosuppressive, single-molecule, dual endothelin and angiotensin receptor antagonist being examined in an ongoing phase 3 trial in adults with IgA nephropathy. We report the prespecified interim analysis of the primary proteinuria efficacy endpoint, and safety.

METHODS

PROTECT is an international, randomised, double-blind, active-controlled study, being conducted in 134 clinical practice sites in 18 countries. The study examines sparsentan versus irbesartan in adults (aged ≥18 years) with biopsy-proven IgA nephropathy and proteinuria of 1·0 g/day or higher despite maximised renin-angiotensin system inhibitor treatment for at least 12 weeks. Participants were randomly assigned in a 1:1 ratio to receive sparsentan 400 mg once daily or irbesartan 300 mg once daily, stratified by estimated glomerular filtration rate at screening (30 to <60 mL/min per 1·73 m² and ≥60 mL/min per 1·73 m²) and urine protein excretion at screening (≤1·75 g/day and >1·75 g/day). The primary efficacy endpoint was change from baseline to week 36 in urine protein-creatinine ratio based on a 24-h urine sample, assessed using mixed model repeated measures. Treatment-emergent adverse events (TEAEs) were safety endpoints. All endpoints were examined in all participants who received at least one dose of randomised treatment. The study is ongoing and is registered with ClinicalTrials.gov, NCT03762850.

FINDINGS

Between Dec 20, 2018, and May 26, 2021, 404 participants were randomly assigned to sparsentan (n=202) or irbesartan (n=202) and received treatment. At week 36, the geometric least squares mean percent change from baseline in urine protein-creatinine ratio was statistically significantly greater in the sparsentan group (-49·8%) than the irbesartan group (-15·1%), resulting in a between-group relative reduction of 41% (least squares mean ratio=0·59; 95% CI 0·51-0·69; p<0·0001). TEAEs with sparsentan were similar to irbesartan. There were no cases of severe oedema, heart failure, hepatotoxicity, or oedema-related discontinuations. Bodyweight changes from baseline were not different between the sparsentan and irbesartan groups.

INTERPRETATION

Once-daily treatment with sparsentan produced meaningful reduction in proteinuria compared with irbesartan in adults with IgA nephropathy. Safety of sparsentan was similar to irbesartan. Future analyses after completion of the 2-year double-blind period will show whether these beneficial effects translate into a long-term nephroprotective potential of sparsentan.

FUNDING

Travere Therapeutics.

Nephroprotective effects of honokiol in a high-fat diet-streptozotocin rat model of diabetic nephropathy

AIMS

Diabetic nephropathy (DN) is the foremost basis of end-stage kidney failure implicating endoplasmic reticulum (ER) stress and dysregulation of Rho kinase/Rock pathway. Magnolia plants are used in traditional medicine systems in Southeast Asia owing to bioactive phytoconstituents. Earlier, honokiol (Hon) exhibited therapeutic potential in experimental models of metabolic, renal, and brain disorders. In the present study, we evaluated potential of Hon against DN and possible molecular mechanisms.

MAIN METHODS

In the existing experiments, high-fat diet (HFD) (17 weeks) and streptozotocin (STZ) (40 mg/kg once) induced DN rats were orally treated with Hon (25, 50, 100 mg/kg) or metformin (150 mg/kg) for 8 weeks.

KEY FINDINGS

Hon attenuated albuminuria, blood biomarkers (e.g., urea nitrogen, glucose, C-reactive protein, and creatinine) and ameliorated lipid profile, electrolytes levels (Na⁺/K⁺), and creatinine clearance against DN. Hon significantly decreased renal oxidative stress and inflammatory biomarkers against DN. Histomorphometry and microscopic analysis revealed nephroprotective effects of Hon marked by a decrease in leukocyte infiltration, renal tissue damage, and urine sediments. RT-qPCR showed that Hon treatment attenuated mRNA expression of transforming growth factor-β1 (TGF-β1), endothelin-1 (ET-1), ER stress markers (GRP78, CHOP, ATF4, and TRB3), and Rock 1/2 in DN rats. Data from ELISA supported a decrease in levels of TGF-β1, ET-1, ER stress markers, and Rock1/2 by Hon.

SIGNIFICANCE

Hon attenuated hyperglycemia, redox imbalance, and inflammation and improved renal functions in rats. Hon alleviates DN pathogenesis possibly by attenuating ER stress and Rock pathway.

The circadian clock protein PER1 is important in maintaining endothelin axis regulation in Dahl salt-sensitive rats

Endothelin-1 (ET-1) is a peptide hormone that acts on its receptors to regulate sodium handling in the kidney's collecting duct. Dysregulation of the endothelin axis is associated with various diseases, including salt-sensitive hypertension and chronic kidney disease. Previously, our lab has shown that the circadian clock gene PER1 regulates ET-1 levels in mice. However, the regulation of ET-1 by PER1 has never been investigated in rats. Therefore, we used a novel model where knockout of Per1 was performed in Dahl salt-sensitive rat background (SS Per1 -/-) to test a hypothesis that PER1 regulates the ET-1 axis in this model. Here, we show increased renal ET-1 peptide levels and altered endothelin axis gene expression in several tissues, including the kidney, adrenal glands, and liver in SS Per1 -/- compared with control SS rats. Edn1 antisense lncRNA Edn1-AS, which has previously been suggested to be regulated by PER1, was also altered in SS Per1 -/- rats compared with control SS rats. These data further support the hypothesis that PER1 is a negative regulator of Edn1 and is important in the regulation of the endothelin axis in a tissue-specific manner.

Endothelin type A receptor blockade increases renoprotection in congestive heart failure combined with chronic kidney disease: Studies in 5/6 nephrectomized rats with aorto-caval fistula

BACKGROUND

Association of congestive heart failure (CHF) and chronic kidney disease (CKD) worsens the patient's prognosis and results in poor survival rate. The aim of this study was to examine if addition of endothelin type A (ET_A) receptor antagonist to the angiotensin-converting enzyme inhibitor (ACEi) will bring additional beneficial effects in experimental rats.

METHODS

CKD was induced by 5/6 renal mass reduction (5/6 NX) and CHF was elicited by volume overload achieved by creation of aorto-caval fistula (ACF). The follow-up was 24 weeks after the first intervention (5/6 NX). The treatment regimens were initiated 6 weeks after 5/6 NX and 2 weeks after ACF creation.

RESULTS

The final survival in untreated group was 15%. The treatment with ET_A receptor antagonist alone or ACEi alone and the combined treatment improved the survival rate to 64%, 71% and 75%, respectively, however, the difference between the combination and either single treatment regimen was not significant. The combined treatment exerted best renoprotection, causing additional reduction in albuminuria and reducing renal glomerular and tubulointerstitial injury as compared with ACE inhibition alone.

CONCLUSIONS

Our results show that treatment with ET_A receptor antagonist attenuates the CKD- and CHF-related mortality, and addition of ET_A receptor antagonist to the standard blockade of RAS by ACEi exhibits additional renoprotective actions.

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.

Renal blood flow and oxygenation

Our kidneys receive about one-fifth of the cardiac output at rest and have a low oxygen extraction ratio, but may sustain, under some conditions, hypoxic injuries that might lead to chronic kidney disease. This is due to large regional variations in renal blood flow and oxygenation, which are the prerequisite for some and the consequence of other kidney functions. The concurrent operation of these functions is reliant on a multitude of neuro-hormonal signaling cascades and feedback loops that also include the regulation of renal blood flow and tissue oxygenation. Starting with open questions on regulatory processes and disease mechanisms, we review herein the literature on renal blood flow and oxygenation. We assess the current understanding of renal blood flow regulation, reasons for disparities in oxygen delivery and consumption, and the consequences of disbalance between O₂ delivery, consumption, and removal. We further consider methods for measuring and computing blood velocity, flow rate, oxygen partial pressure, and related parameters and point out how limitations of these methods constitute important hurdles in this area of research. We conclude that to obtain an integrated understanding of the relation between renal function and renal blood flow and oxygenation, combined experimental and computational modeling studies will be needed.

Circadian Control of Sodium and Blood Pressure Regulation

The attention for the control of dietary risk factors involved in the development of hypertension, includes a large effort on dietary salt restrictions. Ample studies show the beneficial role of limiting dietary sodium as a lifestyle modification in the prevention and management of essential hypertension. Not until the past decade or so have studies more specifically investigated diurnal variations in renal electrolyte excretion, which led us to the hypothesis that timing of salt intake may impact cardiovascular health and blood pressure regulation. Cell autonomous molecular clocks as the name implies, function independently to maintain optimum functional rhythmicity in the face of environmental stressors such that cellular homeostasis is maintained at all times. Our understanding of mechanisms influencing diurnal patterns of sodium excretion and blood pressure has expanded with the discovery of the circadian clock genes. In this review, we discuss what is known about circadian regulation of renal sodium handling machinery and its influence on blood pressure regulation, with timing of sodium intake as a potential modulator of the kidney clock.

Renal fibrosis due to multiple cisplatin treatment is exacerbated by kinin B1 receptor antagonism

Cisplatin is a widely used chemotherapeutic drug, but its side effects are a major limiting factor. Nephrotoxicity occurs in one third of patients undergoing cisplatin treatment. The acute tubular injury caused by cisplatin often leads to a defective repair process, which translates into chronic renal disorders. In this way, cisplatin affects tubular cells, and maladaptive tubules regeneration will ultimately result in tubulointerstitial fibrosis. Kinins are well known for being important peptides in the regulation of inflammatory stimuli, and kinin B1 receptor deficiency and antagonism have been shown to be beneficial against acute cisplatin nephrotoxicity. This study aimed to analyze the effects of kinin B1 receptor deletion and antagonism against repeated cisplatin-induced chronic renal dysfunction and fibrosis. Both the deletion and the antagonism of B1 receptor exacerbated cisplatin-induced chronic renal dysfunction. Moreover, the inhibition of B1 receptor increased tubular injury and tubulointerstitial fibrosis after repeated treatment with cisplatin. The balance between M1/M2 macrophage polarization plays an important role in renal fibrosis. Kinin B1 receptor antagonism had no impact on M1 markers when compared to cisplatin. However, YM1, an M2 marker and an important molecule for the wound healing process, was decreased in mice treated with kinin B1 receptor antagonist, compared to cisplatin alone. Endothelin-1 levels were also increased in mice with B1 receptor inhibition. This study showed that kinin B1 receptor inhibition exacerbated cisplatin-induced chronic renal dysfunction and fibrosis, associated with reduced YM1 M2 marker expression, thus possibly affecting the wound healing process.

Circulating endothelin-1 levels are positively associated with chronic kidney disease in women but not in men: a longitudinal study in the Vara-Skövde cohort

Background

The vasoconstricting peptide endothelin-1 (ET-1) is associated with endothelial dysfunction. The aim of this paper was to investigate whether circulating ET-1 levels predicts chronic kidney disease (CKD) in a prospective population study.

Methods

In 2002–2005, 2816 participants (30–74 years) were randomly selected from two municipalities in South-Western Sweden and followed up in a representative sample of 1327 individuals after 10 years. Endothelin-1 levels were assessed at baseline. Outcome was defined as CKD stage 3 or above based on eGFR < 60 mL/min/1.73m². Those 1314 participants with successful analysis of ET-1 were further analyzed using binary logistic regression.

Results

At follow-up, 51 (8%) men and 47 (7,8%) women had CKD stage 3 and above. Based on levels of ET-1 the population was divided into quintiles showing that women in the highest quintile (n = 132) had a significantly increased risk of developing CKD during the follow up period (OR = 2.54, 95% CI:1.19–5.45, p = 0.02) compared with the other quintiles (1–4). The association was borderline significant after adjusted for age, current smoking, alcohol consumption, hypertension, diabetes, BMI, high- sensitive CRP and LDL-cholesterol (OR = 2.25, 95% CI:0.97–5.24, p = 0.06). No significant differences were observed between quintiles of ET-1 and development of CKD in men (NS).

Conclusions

High levels of ET-1 are associated with development of CKD in women.

Renal biomarkers of acute kidney injury in response to increasing intermittent hypoxia episodes in the neonatal rat

BACKGROUND

We tested the hypotheses that: 1) early exposure to increasing episodes of clinically relevant intermittent hypoxia (IH) is detrimental to the developing kidneys; and 2) there is a critical number of daily IH episodes which will result in irreparable renal damage that may involve angiotensin (Ang) II and endothelin (ET)-1.

METHODS

At birth (P0), neonatal rat pups were exposed to brief IH episodes from the first day of life (P0) to P7 or from P0-P14. Pups were either euthanized immediately or placed in room air (RA) until P21. RA littermates served as controls. Kidneys were harvested at P7, P14, and P21 for histopathology; angiotensin converting enzyme (ACE), ACE-2, ET-1, big ET-1, and malondialdehyde (MDA) levels; immunoreactivity of ACE, ACE-2, ET-1, ET-2, ET receptors (ETAR, ETBR), and hypoxia inducible factor (HIF)1α; and apoptosis (TUNEL stain).

RESULTS

Histopathology showed increased renal damage with 8-12 IH episodes/day, and was associated with Ang II, ACE, HIF1α, and apoptosis. ACE-2 was not expressed at P7, and minimally increased at P14. However, a robust ACE-2 response was seen during recovery with maximum levels noted in the groups recovering from 8 IH episodes/day. ET-1, big ET-1, ETAR, ETBR, and MDA increased with increasing levels of neonatal IH.

CONCLUSIONS

Chronic neonatal IH causes severe damage to the developing kidney with associated elevations in vasoconstrictors, suggesting hypertension, particularly with 8 neonatal IH episodes. ACE-2 is not activated in early postnatal life, and this may contribute to IH-induced vasoconstriction. Therapeutic targeting of ACE and ET-1 may help decrease the risk for kidney injury in the developing neonate to prevent and/or treat neonatal acute kidney injury and/or chronic kidney disease.

Endothelin-1 and Parameters of Systolic Blood Pressure in Hemodialysis

BACKGROUND

Hypertension is common in hemodialysis (HD) patients. Increased blood pressure (BP) variability, particularly higher and lower extremes, is associated with adverse outcomes. We explored the association of endothelin-1 (ET-1), a potent vasoconstrictor, with different BP parameters (pre-HD, intra-HD, and post-HD) during HD in a contemporary patient cohort.

METHODS

This study uses the DaVita Biorepository, a longitudinal prospective cohort study with quarterly collection of clinical data and biospecimens. Unadjusted and adjusted linear mixed effects regression models were fit to determine association of pre-HD ET-1 (log-transformed and quartiles) with HD-related systolic BP (SBP) parameters (pre-HD, nadir intra-HD, and post-HD). As ET-1 was measured at baseline, analyses were restricted to 1 year of follow-up.

RESULTS

Among 769 participants, mean age was 52 years, 42% were females, and 41% were Black. Mean pre-HD SBP was 152 (±28) mm Hg and mean ET-1 concentration was 2.3 (±1.2) ng/ml. In fully adjusted models, each unit increase in SD of log-transformed ET-1 was associated with a 2.7 (95% confidence interval [CI] 1.5, 4.0) mm Hg higher pre-SBP; 1.6 (95% CI 0.9, 2.3) mm Hg higher nadir SBP; and 2.0 (95% CI 1.1, 2.9) mm Hg higher post-SBP. Each SD increase in log-transformed ET-1 was associated with 21% higher odds of experiencing intradialytic hypertension (odds ratio 1.21; 95% CI 1.10-1.34).

CONCLUSIONS

Higher baseline ET-1 levels are independently associated with higher SBP and higher odds of intradialytic hypertension. These results highlight a potential role for ET-1 in BP control in HD patients and raise the possibility of ET-1 antagonism as a therapeutic target.

micro-RNA-486-5p protects against kidney ischemic injury and modifies the apoptotic transcriptome in proximal tubules

Acute kidney injury (AKI) carries high morbidity and mortality, and effective treatments are lacking. Preclinical models support involvement of micro-RNAs (miRs) in AKI pathogenesis, although effects on the kidney transcriptome are unclear. We previously showed that injection of cord blood endothelial colony forming cell-derived exosomes, enriched in miR-486-5p, prevented ischemic AKI in mice. To further define this, we studied direct effects of miR-486-5p in mice with kidney ischemia-reperfusion injury. RNA-Seq was used to compare the impact of miR-486-5p and exosomes on the transcriptome of proximal tubules and kidney endothelial cells 24 hours after ischemia-reperfusion. In mice with AKI, injection of miR-486-5p mimic increased its levels in proximal tubules and endothelial cells, and improved plasma creatinine, histological injury, neutrophil infiltration, and apoptosis. Additionally, miR-486-5p inhibited expression of its target phosphatase and tensin homolog, and activated protein kinase B. In proximal tubules, miR-486-5p or exosomes reduced expression of genes associated with ischemic injury and the tumor necrosis factor (TNF) pathway, and altered distinct apoptotic genes. In endothelial cells, genes associated with metabolic processes were altered by miR-486-5p or exosomes, although TNF pathway genes were not affected. Thus, our results suggest that miR-486-5p may have therapeutic potential in AKI.

Preoperative Serum GDF-15, Endothelin-1 Levels, and Intraoperative Factors as Short-Term Operative Risks for Patients Undergoing Cardiovascular Surgery

Objectives: The Society of Thoracic Surgeons (STS) risk score is widely used for the risk assessment of cardiac surgery. Serum biomarkers such as growth differentiation factor-15 (GDF-15) and endothelin-1 (ET-1) are also used to evaluate risk. We investigated the relationships between preoperative serum GDF-15, ET-1 levels, and intraoperative factors and short-term operative risks including acute kidney injury (AKI) for patients undergoing cardiovascular surgery. Methods: In total, 145 patients were included in this study (92 males and 53 females, age 68.4 ± 13.2 years). The preoperative STS score was determined, and the serum GDF-15 and ET-1 levels were measured by ELISA. These were related to postoperative risks, including AKI, defined according to the Acute Kidney Injury Network (AKIN) classification criteria. Results: AKI developed in 23% of patients. The GDF-15 and ET-1 levels correlated with the STS score. The STS score and GDF-15 and ET-1 levels all correlated with preoperative eGFR, Alb, Hb, and BNP levels; perioperative data (urine output); ICU stay period; and postoperative admission days. Patients with AKI had longer circulatory pulmonary bypass (CPB) time, and male patients with AKI had higher ET-1 levels than those without AKI. In multivariable logistic regression analysis, the preoperative ET-1 level and CPB time were the independent determinants of AKI, even adjusted by age, sex, and BMI. The preoperative GDF-15 level, CPB time, and RCC transfusion were independent determinants of 30-day mortality plus morbidity. Conclusion: Preoperative GDF-15 and ET-1 levels as well as intraoperative factors such as CPB time may be helpful to identify short-term operative risks for patients undergoing cardiovascular surgery.

Endothelin antagonism and sodium glucose Co-transporter 2 inhibition. A potential combination therapeutic strategy for COVID-19

The novel coronavirus 2019 (COVID-19) infection caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a global pandemic that requires a multi-faceted approach to tackle this unprecedent health crisis. Therapeutics to treat COVID-19 are an integral part of any such management strategy and there is a substantial unmet need for treatments for individuals most at risk of severe disease. This perspective review provides rationale of a combined therapeutic regimen of selective endothelin-A (ET-A) receptor antagonism and sodium glucose co-transporter-2 (SGLT-2) inhibition to treat COVID-19. Endothelin is a potent vasoconstrictor with pro-inflammatory and atherosclerotic effects. It is upregulated in a number of conditions including acute respiratory distress syndrome and cardiovascular disease. Endothelin mediates vasocontractility via endothelin (ET-A and ET-B) receptors on vascular smooth muscle cells (VSMCs). ET-B receptors regulate endothelin clearance and are present on endothelial cells, where in contrast to their role on VSMCs, mediate vasodilation. Therefore, selective endothelin-A (ET-A) receptor inhibition is likely the optimal approach to attenuate the injurious effects of endothelin and may reduce ventilation-perfusion mismatch and pulmonary inflammation, whilst improving pulmonary haemodynamics and oxygenation. SGLT-2 inhibition may dampen inflammatory cytokines, reduce hyperglycaemia if present, improve endothelial function, cardiovascular haemodynamics and cellular bioenergetics. This combination therapeutic approach may therefore have beneficial effects to mitigate both the pulmonary, metabolic and cardiorenal manifestations of COVID-19. Given these drug classes include medicines licensed to treat heart failure, diabetes and pulmonary hypertension respectively, information regarding their safety profile is established. Randomised controlled clinical trials are the best way to determine efficacy and safety of these medicines in COVID-19.

HDAC2 targeting stabilizes the CoREST complex in renal tubular cells and protects against renal ischemia/reperfusion injury

Histone/protein deacetylases (HDAC) 1 and 2 are typically viewed as structurally and functionally similar enzymes present within various co-regulatory complexes. We tested differential effects of these isoforms in renal ischemia reperfusion injury (IRI) using inducible knockout mice and found no significant change in ischemic tolerance with HDAC1 deletion, but mitigation of ischemic injury with HDAC2 deletion. Restriction of HDAC2 deletion to the kidney via transplantation or PAX8-controlled proximal renal tubule-specific Cre resulted in renal IRI protection. Pharmacologic inhibition of HDAC2 increased histone acetylation in the kidney but did not extend renal protection. Protein analysis demonstrated increased HDAC1-associated CoREST protein in HDAC2-/- versus WT cells, suggesting that in the absence of HDAC2, increased CoREST complex occupancy of HDAC1 can stabilize this complex. In vivo administration of a CoREST inhibitor exacerbated renal injury in WT mice and eliminated the benefit of HDAC2 deletion. Gene expression analysis of endothelin showed decreased endothelin levels in HDAC2 deletion. These data demonstrate that contrasting effects of HDAC1 and 2 on CoREST complex stability within renal tubules can affect outcomes of renal IRI and implicate endothelin as a potential downstream mediator.

Roles of Genetic Predisposition in the Sex Bias of Pulmonary Pathophysiology, as a Function of Estrogens : Sex Matters in the Prevalence of Lung Diseases

In addition to studies focused on estrogen mediation of sex-different regulation of systemic circulations, there is now increasing clinical relevance and research interests in the pulmonary circulation, in terms of sex differences in the morbidity and mortality of lung diseases such as inherent-, allergic- and inflammatory-based events. Thus, female predisposition to pulmonary artery hypertension (PAH) is an inevitable topic. To better understand the nature of sexual differentiation in the pulmonary circulation, and how heritable factors, in vivo- and/or in vitro-altered estrogen circumstances and changes in the live environment work in concert to discern the sex bias, this chapter reviews pulmonary events characterized by sex-different features, concomitant with exploration of how alterations of genetic expression and estrogen metabolisms trigger the female-predominant pathological signaling. We address the following: PAH (Sect.7.2) is characterized as an estrogenic promotion of its incidence (Sect. 7.2.2), as a function of specific germline mutations, and as an estrogen-elicited protection of its prognosis (Sect.7.2.1). More detail is provided to introduce a less recognized gene of Ephx2 that encodes soluble epoxide hydrolase (sEH) to degrade epoxyeicosatrienic acids (EETs). As a susceptible target of estrogen, Ephx2/sEH expression is downregulated by an estrogen-dependent epigenetic mechanism. Increases in pulmonary EETs then evoke a potentiation of PAH generation, but mitigation of its progression, a phenomenon similar to the estrogen-paradox regulation of PAH. Additionally, the female susceptibility to chronic obstructive pulmonary diseases (Sect. 7.3) and asthma (Sect.7.4), but less preference to COVID-19 (Sect. 7.5), and roles of estrogen in their pathogeneses are briefly discussed.

SGLT2 Inhibitors and Other Novel Therapeutics in the Management of Diabetic Kidney Disease

Over the past 40 years there has been a steady rise in the number of people with chronic kidney disease due mainly to a significant increase in the number of people with diabetic kidney disease (DKD). Current treatments (blood pressure control, blood sugar control, and renin-angiotensin-aldosterone system inhibitors) have had a significant impact on slowing progression of DKD. But the continued rise illustrates that there is a great need for new medications. Recently, a number of potentially reno-protective medicines have been studied. In this review, these new medications are discussed with respect to both their reported benefits and possible risks.

Contribution of Th17 cells to tissue injury in hypertension

PURPOSE OF REVIEW

Hypertension has been demonstrated to be a chief contributor to morbidity and mortality throughout the world. Although the cause of hypertension is multifactorial, emerging evidence, obtained in experimental studies, as well as observational studies in humans, points to the role of inflammation and immunity. Many aspects of immune function have now been implicated in hypertension and end-organ injury; this review will focus upon the recently-described role of Th17 cells in this pathophysiological response.

RECENT FINDINGS

Studies in animal models and human genetic studies point to a role in the adaptive immune system as playing a contributory role in hypertension and renal tissue damage. Th17 cells, which produce the cytokine IL17, are strongly pro-inflammatory cells, which may contribute to tissue damage if expressed in chronic disease conditions. The activity of these cells may be enhanced by physiological factors associated with hypertension such as dietary salt or Ang II. This activity may culminate in the increased sodium retaining activity and exacerbation of inflammation and renal fibrosis via multiple cellular mechanisms.

SUMMARY

Th17 cells are a distinct component of the adaptive immune system that may strongly enhance pathways leading to increased sodium reabsorption, elevated vascular tone and end-organ damage. Moreover, this pathway may lend itself towards specific targeting for treatment of kidney disease and hypertension.

Endothelin XVI

Although 31 years have passed since the discovery of endothelin, that pioneering report, and the subsequent flood of influential studies elucidating its molecular and clinical details, have since paved the way for thousands of publications. They showed the promise of endothelin and the vast amount of work that remains to be done to fully unleash the potential this peptide possesses, both as a key physiological regulator and as a therapeutic target. Endothelin conferences and their proceedings have served as a host for many of these breakthrough studies, and in keeping with this fine tradition, Endothelin XVI will host novel research articles presented at the Sixteenth International Conference on Endothelin (ET-16) as its proceedings. On September 22-25, 2019, ET-16 was held at Kobe Port Oasis, Kobe, Japan, where numerous important discoveries were presented to the scientific community for the first time, many of which are compiled and published in this special issue. As the Editors of this special issue that comprises in-depth reviews, insightful editorials, and numerous original research articles discussing findings from various biomedical fields, we are extremely proud to present Endothelin XVI. We sincerely hope for the continued growth of this field for the benefit of the patients and the advancement of biomedical science.

Local renal complement activation mediates immune kidney injury by inducing endothelin-1 signalling and inflammation in trichloroethylene-sensitised mice

Trichloroethylene (TCE) is a widely used industrial solvent that causes trichloroethylene hypersensitivity syndrome (THS) with multi-system damage, including kidney injury. Clinical studies have shown that the complement system is important for TCE-induced kidney injury. Our previous study found excessive deposition of complement C3, mainly on the glomerulus, indicating that local renal complement is activated after TCE sensitisation. However, whether local renal complement activation mediates TCE-induced immune kidney injury and the underlying mechanisms remain unknown. Therefore, we established a TCE percutaneous sensitisation BALB/c mouse model to explore the mechanisms by pretreating with or without the complement activation antagonist, cathepsin L inhibitor (CatLi). As expected, more C3 and C3a were detected mainly on glomerulus of TCE positive sensitisation (TCE⁺) mice. Renal dysfunction and pathological damage were also clearly observed in TCE⁺ mice. Moreover, the mRNA and protein expression of ET-1 increased significantly with local renal complement activation after TCE sensitisation, leading to cytokines release and inflammation. In addition, activation of p38MAPK and NF-κBp65 pathways were detected in kidneys of TCE⁺ mice, and CatLi pretreatment decreased these changes through complement activation antagonisation. Our research uncovered a novel role of local renal complement activation during immune kidney injury after TCE sensitisation through induction of ET-1 signalling and inflammation.

Metformin Preconditioning and Postconditioning to Reduce Ischemia Reperfusion Injury in an Isolated Ex Vivo Rat and Porcine Kidney Normothermic Machine Perfusion Model

Metformin may act renoprotective prior to kidney transplantation by reducing ischemia-reperfusion injury (IRI). This study examined whether metformin preconditioning and postconditioning during ex vivo normothermic machine perfusion (NMP) of rat and porcine kidneys affect IRI. In the rat study, saline or 300 mg/kg metformin was administered orally twice on the day before nephrectomy. After 15 minutes of warm ischemia, kidneys were preserved with static cold storage for 24 hours. Thereafter, 90 minutes of NMP was performed with the addition of saline or metformin (30 or 300 mg/L). In the porcine study, after 30 minutes of warm ischemia, kidneys were preserved for 3 hours with oxygenated hypothermic machine perfusion. Subsequently, increasing doses of metformin were added during 4 hours of NMP. Metformin preconditioning of rat kidneys led to decreased injury perfusate biomarkers and reduced proteinuria. Postconditioning of rat kidneys resulted, dose-dependently, in less tubular cell necrosis and vacuolation. Heat shock protein 70 expression was increased in metformin-treated porcine kidneys. In all studies, creatinine clearance was not affected. In conclusion, both metformin preconditioning and postconditioning can be done safely and improved rat and porcine kidney quality. Because the effects are minor, it is unknown which strategy might result in improved organ quality after transplantation.

Endothelin-1 rs9296344 associates with the susceptibility of childhood primary nephrotic syndrome

BACKGROUND

Recently, the rs5370 single nucleotide polymorphisms (SNPs) of Endothelin-1 (EDN1) showed association with the susceptibility of childhood primary nephrotic syndrome (CPNS). This study aims to investigate potential relationships between other EDN1 SNPs and CPNS.

METHODS

Seven SNPs (rs5370, rs10478723, rs1476046, rs1800541, rs2070698, rs2071942, and rs9296344) of the EDN1 gene were genotyped in 579 CPNS patients and 586 age-matched healthy children. Then, we analyzed potential associations of the six SNPs with susceptibility of CPNS by using rs5370 as a conditional variant in a logistic regression model. SNP-SNP interaction analysis was performed to investigate the joint effects of the seven SNPs in the pathogenesis of CPNS.

RESULTS

Independent with rs5370, only rs9296344 significantly associated (T vs C, odds ratio [OR] = 0.71, 95% confidence interval [CI] = 0.57-0.88, P = .001) with the susceptibility of CPNS. Meanwhile, no joint effect among the analyzed seven SNPs was discovered in this study.

CONCLUSIONS

This study discovered that C allele of rs9296344 on EDN1 is a novel independent risk factor for CPNS.

Pathophysiologic mechanisms in diabetic kidney disease: A focus on current and future therapeutic targets

Diabetic kidney disease (DKD) is the primary cause of chronic kidney disease around the globe and is one of the main complications in patients with type 1 and 2 diabetes. The standard treatment for DKD is drugs controlling hyperglycemia and high blood pressure. Renin angiotensin aldosterone system blockade and sodium glucose cotransporter 2 (SGLT2) inhibition have yielded promising results in DKD, but many diabetic patients on such treatments nevertheless continue to develop DKD, leading to kidney failure and cardiovascular comorbidities. New therapeutic options are urgently required. We review here the promising therapeutic avenues based on insights into the mechanisms of DKD that have recently emerged, including mineralocorticoid receptor antagonists, SGLT2 inhibitors, glucagon-like peptide-1 receptor agonist, endothelin receptor A inhibition, anti-inflammatory agents, autophagy activators and epigenetic remodelling. The involvement of several molecular mechanisms in DKD pathogenesis, together with the genetic and epigenetic variability of this condition, makes it difficult to target this heterogeneous patient population with a single drug. Personalized medicine, taking into account the genetic and mechanistic variability, may therefore improve renal and cardiovascular protection in diabetic patients with DKD.

The Role of Endothelin and Endothelin Antagonists in Chronic Kidney Disease

Background

Endothelins (ET) are a family of peptides that act as potent vasoconstrictors and pro-fibrotic growth factors. ET-1 is integral to renal and cardiovascular pathophysiology and exerts effects via autocrine, paracrine and endocrine signaling pathways tied to regulation of aldosterone, catecholamines, and angiotensin. In the kidney, ET-1 is critical to maintaining renal perfusion and controls glomerular arteriole tone and hemodynamics. It is hypothesized that ET-1 influences the progression of chronic kidney disease (CKD), and the objective of this review is to discuss the pathophysiology, and role of ET and endothelin receptor antagonists (ERAs) in CKD.

Summary

The use of ERAs in hypertensive nephropathy has the potential to decrease proteinuria, and in diabetic nephropathy has the potential to restore glycocalyx thickness, also decreasing proteinuria. Focal segmental glomerular sclerosis has no specific Food and Drug Administration-approved therapy currently, however, ERAs show promise in decreasing proteinuria and slowing tissue damage. ET-1 is a potential biomarker for autosomal dominant polycystic kidney disease progression and so it is thought that ERAs may be of some therapeutic benefit.

Key Messages

Multiple studies have shown the utility of ERAs in CKD. These agents have shown to reduce blood pressure, proteinuria, and arterial stiffness. However, more clinical trials are needed, and the results of active or recently concluded studies are eagerly awaited.

Conservation of glucagon like peptide-1 level with liraglutide and linagilptin protects the kidney against angiotensin II-induced tissue fibrosis in rats

This study tested the hypothesis that the enhancement of glucagon-like peptide-1 (GLP-1) level through either exogenous supply of GLP-1 agonist, liraglutide or prevention of endogenous GLP-1 degradation with dipeptidyl peptidease-4 inhibitor, lingaliptin ameliorates angiotensin II (Ang II)-induced renal fibrosis. Sprague-Dawley rats were randomly divided into four groups: 0.9% saline or Ang II (500 ng/kg/min) was infused with osmotic minipumps for 4 weeks, defined as sham and Ang II groups. In drug treated groups, liraglutide (0.3 mg/kg) was injected subcutaneously twice daily or linagliptin (8 mg/kg) was administered daily via oral gavage during Ang II infusion. Compared with Ang II stimulation, liraglutide or linagliptin comparatively down-regulated the protein level of the AT₁ receptor, and up-regulated the AT₂ receptor, as identified by a reduced AT₁/AT₂ ratio (all p < 0.05), consistent with less locally-expressed AT₁ receptor and enhanced AT₂ receptor in the glomerular capillaries and proximal tubules of the renal cortex. Furthermore, both drugs significantly increased the expression of GLP-1 receptor and attenuated the protein levels of TLR4, NOX4 and IL-6. The populations of macrophages and α-SMA expressing myofibroblasts decreased with treatment of liraglutide and linagliptin, in coincidence with the reduced expression of phosphor-Smad2/3, Smad4, TGFβ1, and up-regulated Smad7. Along with these modulations, renal morphology was preserved and synthesis of fibronectin/collagen I was down-regulated, as identified by small collagen-rich area in the renal cortex. These results suggest that the preservation of GLP-1 level using liraglutide or linagliptin might be considered as an add-on therapeutic option for inhibiting Ang II induced renal fibrosis and failure.

Addition of Endothelin A-Receptor Blockade Spoils the Beneficial Effect of Combined Renin-Angiotensin and Soluble Epoxide Hydrolase Inhibition: Studies on the Course of Chronic Kidney Disease in 5/6 Nephrectomized Ren-2 Transgenic Hypertensive Rats

Introduction: Previous studies in Ren-2 transgenic hypertensive rats (TGR) after 5/6 renal ablation (5/6 NX) have shown that besides pharmacological blockade of the renin-angiotensin system (RAS) also increasing kidney tissue epoxyeicosatrienoic acids (EET) levels by blocking soluble epoxide hydrolase (sEH), an enzyme responsible for degradation of EETs, and endothelin type A (ETA) receptor blockade retards chronic kidney disease (CKD) progression. This prompted us to evaluate if this progression will be alleviated by the addition of sEH inhibitor and ETA receptor antagonist to the standard complex blockade of RAS (angiotensin-converting enzyme inhibitor plus angiotensin II type 1 receptor blocker) in rats with established CKD. Methods: The treatment regimens were initiated 6 weeks after 5/6 NX in TGR, and the follow-up period was 60 weeks. Results: The addition of sEH inhibition to RAS blockade improved survival rate, further reduced albuminuria and renal glomerular and kidney tubulointerstitial injury, and attenuated the decline in creatinine clearance – all this as compared with 5/6 NX TGR treated with RAS blockade alone. Addition of ETA receptor antagonist to the combined RAS and sEH blockade not only offered no additional renoprotection but, surprisingly, also abolished the beneficial effects of adding sEH inhibitor to the RAS blockade. Conclusion: These data indicate that pharmacological strategies that combine the blockade of RAS and sEH could be a novel tool to combat the progression of CKD. Any attempts to further extend this therapeutic regimen should be made with extreme caution.

Acute renal impairment characterization using diffusion magnetic resonance imaging: Validation by histology

Diffusion magnetic resonance imaging has been demonstrated to be a simple, noninvasive and accurate method for the detection of renal microstructure and microcirculation, which are closely linked to renal function. Moreover, serum endothelin-1 (ET-1) was also reported as a good indicator of early renal injury. The aim of this study was to evaluate the feasibility and capability of diffusion MRI and ET-1 to detect acute kidney injury by an operation simulating high-pressure renal pelvic perfusion, which is commonly used during ureteroscopic lithotripsy. Histological findings were used as a reference. Fourteen New Zealand rabbits in an experimental group and 14 in a control group were used in this study. Diffusion tensor imaging and intravoxel incoherent motion diffusion-weighted imaging were acquired by a 3.0 T MRI scanner. Significant corticomedullary differences were found in the values of the apparent diffusion coefficient (ADC), pure tissue diffusion, volume fraction of pseudo-diffusion (fp) and fractional anisotropy (FA) (P < 0.05 for all) in both preoperation and postoperation experimental groups. Compared with the control group, the values of cortical fp_mean , medullary ADC_mean and FA_mean decreased significantly (P < 0.05) after the operation in the experimental group. Also, the change rate of medullary ADC_mean in the experimental group was more pronounced than that in the control group (P = 0.018). No significant change was found in serum ET-1 concentration after surgery in either the experimental (P = 0.80) or control (P = 0.17) groups. In the experimental group, histological changes were observed in the medulla, while no visible change was found in the cortex. This study demonstrated the feasibility of diffusion MRI to detect the changes of renal microstructure and microcirculation in acute kidney injury, with the potential to evaluate renal function. Moreover, the sensitivity of diffusion MRI to acute kidney injury appears to be superior to that of serum ET-1.

BNP as a Major Player in the Heart-Kidney Connection

Brain natriuretic peptide (BNP) is an important biomarker for patients with heart failure, hypertension and cardiac hypertrophy. Although it is known that BNP levels are relatively higher in patients with chronic kidney disease and no heart disease, the mechanism remains unknown. Here, we review the functions and the roles of BNP in the heart-kidney interaction. In addition, we discuss the relevant molecular mechanisms that suggest BNP is protective against chronic kidney diseases and heart failure, especially in terms of the counterparts of the renin-angiotensin-aldosterone system (RAAS). The renal medulla has been reported to express depressor substances. The extract of the papillary tips from kidneys may induce the expression and secretion of BNP from cardiomyocytes. A better understanding of these processes will help accelerate pharmacological treatments for heart-kidney disease.

Sustained, delayed, and small increments in glomerular permeability to macromolecules during systemic ET-1 infusion mediated via the ETA receptor

Emerging evidence indicates that endogenous production of endothelin (ET)-1, a 21-amino acid peptide vasoconstrictor, plays an important role in proteinuric kidney disease. Previous studies in rats have shown that chronic administration of ET-1 leads to increased glomerular albumin leakage. The underlying mechanisms are, however, currently not known. Here, we used size-exclusion chromatography to measure glomerular sieving coefficients for neutral FITC-Ficoll (molecular Stokes-Einstein radius: 15-80 Å, molecular weight: 70 kDa/400 kDa) in anesthetized male Sprague-Dawley rats (n = 12) at baseline and at 5, 15, 30, and 60 min after intravenous administration of ET-1. In separate experiments, ET-1 was given together with the selective ET type A (ET_A) or ET type B (ET_B) receptor antagonists JKC-301 and BQ-788, respectively. At both 15 and 30 min postadministration, the glomerular sieving coefficient for macromolecular Ficoll (70 Å) was significantly increased to 4.4 × 10^-5 ± 0.7 × 10^-5 (P = 0.024) and 4.5 × 10^-5 ± 0.8 × 10^-5 (P = 0.007), respectively, compared with baseline (2.2 × 10^-5 ± 0.4 ×10^-5). Decreased urine production after ET-1 prevented the use of higher doses of ET-1. Data analysis using the two-pore model indicated changes in large-pore permeability after ET-1, with no changes in the small-pore pathway. Administration of ET_A blocker abrogated the permeability changes induced by ET-1 at 30 min, whereas blockade of ET_B receptors was ineffective. Mean arterial pressure was only significantly increased at 60 min, being 123 ± 4 mmHg compared with 111 ± 2 mmHg at baseline (P = 0.02). We conclude that ET-1 evoked small, delayed, and sustained increases in glomerular permeability, mediated via the ET_A receptor.

TSC1 deletion in fibroblasts alleviates lipopolysaccharide-induced acute kidney injury

Mechanistic target of rapamycin complex 1 (mTORC1) signaling is active in inflammation, but its involvement in septic acute kidney injury (AKI) has not been shown. mTORC1 activation (p-S6) in renal fibroblasts was increased in a mouse AKI model induced by 1.5 mg/kg lipopolysaccharide (LPS). Deletion of tuberous sclerosis complex 1 (TSC1), an mTORC1 negative regulator, in fibroblasts (Fibro-TSC1^-/-) inhibited the elevation of serum creatinine and blood urea nitrogen in AKI compared with that in TSC1^fl/fl control mice. Endothelin-1 (EDN1) and phospho-Jun-amino-terminal kinase (p-JNK) were up-regulated in Fibro-TSC1^-/- renal fibroblasts after LPS challenge. Rapamycin, an mTORC1 inhibitor, and bosentan, an EDN1 antagonist, eliminated the difference in renal function between TSC1^fl/fl and Fibro-TSC1^-/- mice after LPS injection. Rapamycin restored LPS-induced up-regulation of EDN1, endothelin converting enzyme-1 (ECE1), and p-JNK in TSC1-knockdown mouse embryonic fibroblasts (MEFs). SP600125, a Jun-amino-terminal kinase (JNK) inhibitor, attenuated LPS-induced enhancement of EDN1 and ECE1 in TSC1-knockdown MEFs without a change in phospho-S6 ribosomal protein (p-S6) level. The results indicate that mTORC1-JNK-dependent up-regulation of ECE1 elevated EDN1 in TSC1-knockout renal fibroblasts and contributed to improvement of renal function in Fibro-TSC1^-/- mice with LPS-induced AKI. Renal fibroblast mTORC1 plays an important role in septic AKI.

High preoperative plasma endothelin-1 levels are associated with increased acute kidney injury risk after pulmonary endarterectomy

OBJECTIVES

The only curative treatment for chronic thromboembolic pulmonary hypertension (CTEPH) is pulmonary endarterectomy (PEA). PEA requires cardiopulmonary bypass (CPB) which is associated with a high acute kidney injury (AKI) risk. Circulating endothelin-1 (ET-1) levels are elevated in CTEPH, and ET-1 plays a pivotal role in AKI. Because AKI is burdened by high morbidity and mortality, we aimed to evaluate the association between preoperative ET-1 and the risk to develop AKI in CTEPH individuals who undergo PEA. We also evaluated the association of AKI and ET-1 with kidney function and mortality at 1 year after PEA.

METHODS

In 385 consecutive patients diagnosed with CTEPH who underwent PEA at the Foundation IRCC Policlinico San Matteo (Pavia, Italy) from January 2009 to April 2015, we assessed preoperative circulating ET-1 by ELISA and identified presence of AKI based on 2012 KDIGO criteria.

RESULTS

AKI occurred in 26.5% of the 347 patients included in the analysis, and was independently associated with preoperative ET-1 (p = 0.008), body mass index (BMI) (p = 0.022), male gender (p = 0.005) and duration of CPB (p = 0.002). At 1-year post PEA, estimated glomerular filtration rate (eGFR) significantly improved in patients who did not develop AKI [ΔeGFR 5.6 ml/min/1.73 m² (95% CI 3.6-7.6), p < 0.001] but not in those with perioperative AKI. AKI (p < 0.001), age (p < 0.001), preoperative eGFR (p < 0.001) and systemic hypertension diagnosis (p = 0.015) were independently associated with 1-year ΔeGFR. Neither perioperative AKI nor preoperative ET-1 was associated with 1-year survival.

CONCLUSION

Perioperative AKI is associated with higher preoperative circulating ET-1 and it negatively influences long-term kidney function in patients with CTEPH who undergo PEA.

The Src homology and collagen A (ShcA) adaptor protein may participate in the pathogenesis of membranous lupus nephritis

The Src homology and collagen A (ShcA) adaptor protein that binds to tyrosine kinase receptors. ShcA plays a role in insulin signaling, stress resistance and energy metabolism. The 66-kDa Src homology 2 domain-containing protein (p66shc) belongs to the ShcA family and has been associated with reactive oxygen species (ROS); increased ROS is involved in the pathology of lupus nephritis (LN). However, whether ShcA can act as a biomarker for oxidative injury in LN is unknown. This study is aimed to investigate the ShcA expression in kidney tissues from patients presenting with LN and the association between ShcA expression and clinical parameters. Renal biopsy tissues were obtained from 62 LN, 20 primary membranous nephropathy (MN) and 10 other secondary MN patients. ShcA was measured by immunofluorescence. The expression of ShcA in the membranous lupus nephritis (class V) group showed a higher trend but there were no significant differences compared with pure mesangial disease (class II) and proliferative (Class III/IV) lupus nephritis. ShcA deposits were negative in primary and other secondary MN. ShcA might act as a new biomarker and a diagnostic tool to identify membranous lupus nephritis with other MN.

Synergistic effect of renalase and chronic kidney disease on endothelin-1 in patients with coronary artery disease ‒ a cross-sectional study

Endothelin-1 (ET-1) is associated with endothelial dysfunction and vasoconstriction. Increased circulating ET-1 levels are associated with long-term cardiovascular mortality. Renalase, released from kidney, metabolizes catecholamines and regulates blood pressure. An increase in circulating renalase levels has been reported in patients with chronic kidney disease (CKD) and is associated with coronary artery disease (CAD). We hypothesized the existence of a synergistic effect of serum renalase levels and CKD on ET-1 levels in patients with CAD. We evaluated 342 non-diabetic patients with established CAD. ET-1 and renalase levels were measured in all patients after an overnight fast. Patients with CKD had higher ET-1 (1.95 ± 0.77 vs. 1.62 ± 0.76 pg/ml, P < 0.001) and renalase levels (46.8 ± 17.1 vs. 33.9 ± 9.9 ng/ml, P < 0.001) than patients without CKD. Patients with both CKD and high renalase levels (>the median of 36.2 ng/ml) exhibited the highest serum ET-1 (P value for the trend <0.001). According to multivariate linear regression analysis, the combination of high serum renalase levels with CKD was a significant risk factor for increased serum ET-1 levels (regression coefficient = 0.297, 95% confidence interval = 0.063‒0.531, P = 0.013). In conclusion, our data suggest a synergistic effect of high serum renalase levels and CKD on increases in ET-1 levels in patients with established CAD.

Antiproteinuric effect of an endothelin-1 receptor antagonist in puromycin aminonucleoside-induced nephrosis in rat

BackgroundThe pathogenesis of idiopathic nephrotic syndrome (INS) remains unclear, although recent studies suggest endothelin 1 (ET-1) and CD80 of podocytes are involved. We investigated the potential of antagonist to ET-1 receptor type A (ETRA) as therapeutic agent through the suppression of CD80 in a rat model of INS.MethodsPuromycin aminonucleoside (PAN) was injected to Wister rats to induce proteinuria: some were treated with ETRA antagonist and others were treated with 0.5% methylcellulose. Blood and tissue samples were collected. Quantitative PCR was used to determine the expression of Toll-like receptor-3 (TLR-3), nuclear factor-κB (NF-κB), CD80, talin, ETRA, and ET-1 in the kidney. To confirm the level of CD80 protein expression, immunofluorescence staining and western blot analysis of the renal tissue were performed.ResultsAmount of proteinuria in the treatment group was significantly lower than the other groups. The same-day body weight, serum creatinine values, and blood pressure were not significantly different. ETRA antagonist restores podocyte foot process effacement as well as the aberrant expression of TLR-3, nuclear factor-κB (NF-κB), and CD80 in PAN-injured kidneys.ConclusionsThe ETRA antagonist may be promising drug for INS as it showed an antiproteinuric effect. Its action was considered to be through suppression of CD80 expression on podocytes.

Acute Kidney Injury and Progression of Diabetic Kidney Disease

Diabetic kidney disease, commonly termed diabetic nephropathy (DN), is the most common cause of end-stage kidney disease (ESKD) worldwide. The characteristic histopathology of DN includes glomerular basement membrane thickening, mesangial expansion, nodular glomerular sclerosis, and tubulointerstitial fibrosis. Diabetes is associated with a number of metabolic derangements, such as reactive oxygen species overproduction, hypoxic state, mitochondrial dysfunction, and inflammation. In the past few decades, our knowledge of DN has advanced considerably although much needs to be learned. The traditional paradigm of glomerulus-centered pathophysiology has expanded to the tubule-interstitium, the immune response and inflammation. Biomarkers of proximal tubule injury have been shown to correlate with DN progression, independent of traditional glomerular injury biomarkers such as albuminuria. In this review, we summarize mechanisms of increased susceptibility to acute kidney injury in diabetes mellitus and the roles played by many kidney cell types to facilitate maladaptive responses leading to chronic and end-stage kidney disease.

The spectrum of sickle hemoglobin-related nephropathy: from sickle cell disease to sickle trait

INTRODUCTION

Renal dysfunction is among the most common complication of sickle cell disease (SCD), from hyposthenuria in children to progression to overt chronic kidney disease (CKD) in young adults. Emerging evidence now suggests that sickle hemoglobin-related nephropathy extends to individuals with sickle cell trait (SCT). Areas covered: This review will highlight the pathophysiology, epidemiology, and management recommendations for sickle hemoglobin-related nephropathy in both SCD and SCT. In addition, it will focus on the major demographic and genetic modifiers of renal disease in sickling hemoglobinopathies. Expert commentary: Studies have elucidated the course of renal disease in SCD; however, the scope and age of onset of renal dysfunction in SCT has yet to be determined. In SCD, several modifiers of renal disease - such as α-thalassemia, hemoglobin F, APOL1 and HMOX1 - have been described and provide an opportunity for a precision medicine approach to risk stratify patients who may benefit from early intervention. Extrapolating from this literature may also provide insight into the modifiers of renal disease in SCT. Further studies are needed to determine the optimal treatment for sickle hemoglobin-related nephropathy.

Role of adaptor protein p66Shc in renal pathologies

p66Shc is one of the three adaptor proteins encoded by the Shc1 gene, which are expressed in many organs, including the kidney. Recent studies shed new light on several key questions concerning the signaling mechanisms mediated by p66Shc. The central goal of this review article is to summarize recent findings on p66Shc and the role it plays in kidney physiology and pathology. This article provides a review of the various mechanisms whereby p66Shc has been shown to function within the kidney through a wide range of actions. The mitochondrial and cytoplasmic signaling of p66Shc, as it relates to production of reactive oxygen species (ROS) and renal pathologies, is further discussed.

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).