Predictors of Atrasentan-Associated Fluid Retention and Change in Albuminuria in Patients with Diabetic Nephropathy

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.

Targeting the Endothelin A Receptor in IgA Nephropathy

Immunoglobulin A nephropathy (IgAN) is the most common primary glomerulonephritis worldwide and carries a substantial risk of kidney failure. New agency-approved therapies, either specifically for IgAN or for chronic kidney disease (CKD) in general, hold out hope for mitigating renal deterioration in patients with IgAN. The latest addition to this therapeutic armamentarium targets the endothelin-A receptor (ETAR). Activation of ETAR on multiple renal cell types elicits a host of pathophysiological effects, including vasoconstriction, cell proliferation, inflammation, apoptosis, and fibrosis. Blockade of ETAR is renoprotective in experimental models of IgAN and reduces proteinuria in patients with IgAN. This review discusses the evidence supporting the use of ETAR blockade in IgAN as well as addressing the potential role for this class of agents among the current and emerging therapies for treating this disorder.

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.

Therapeutic mechanism and clinical application of Chinese herbal medicine against diabetic kidney disease

Diabetic kidney disease (DKD) is the major complications of type 1 and 2 diabetes, and is the predominant cause of chronic kidney disease and end-stage renal disease. The treatment of DKD normally consists of controlling blood glucose and improving kidney function. The blockade of renin-angiotensin-aldosterone system and the inhibition of sodium glucose cotransporter 2 (SGLT2) have become the first-line therapy of DKD, but such treatments have been difficult to effectively block continuous kidney function decline, eventually resulting in kidney failure and cardiovascular comorbidities. The complex mechanism of DKD highlights the importance of multiple therapeutic targets in treatment. Chinese herbal medicine (active compound, extract and formula) synergistically improves metabolism regulation, suppresses oxidative stress and inflammation, inhibits mitochondrial dysfunction, and regulates gut microbiota and related metabolism via modulating GLP-receptor, SGLT2, Sirt1/AMPK, AGE/RAGE, NF-κB, Nrf2, NLRP3, PGC-1α, and PINK1/Parkin pathways. Clinical trials prove the reliable evidences for Chinese herbal medicine against DKD, but more efforts are still needed to ensure the efficacy and safety of Chinese herbal medicine. Additionally, the ideal combined therapy of Chinese herbal medicine and conventional medicine normally yields more favorable benefits on DKD treatment, laying the foundation for novel strategies to treat DKD.

Novel strategies in nephrology: what to expect from the future?

Chronic kidney disease (CKD) will become the fifth global case of death by 2040. Its largest impact is on premature mortality but the number of persons with kidney failure requiring renal replacement therapy (RRT) is also increasing dramatically. Current RRT is suboptimal due to the shortage of kidney donors and dismal outcomes associated with both hemodialysis and peritoneal dialysis. Kidney care needs a revolution. In this review, we provide an update on emerging knowledge and technologies that will allow an earlier diagnosis of CKD, addressing the current so-called blind spot (e.g. imaging and biomarkers), and improve renal replacement therapies (wearable artificial kidneys, xenotransplantation, stem cell-derived therapies, bioengineered and bio-artificial kidneys).

The Effect of Atrasentan on Kidney and Heart Failure Outcomes by Baseline Albuminuria and Kidney Function: A Post Hoc Analysis of the SONAR Randomized Trial

BACKGROUND AND OBJECTIVES

Atrasentan reduces the risk of kidney failure but increases the risk of edema and, possibly, heart failure. Patients with severe CKD may obtain greater absolute kidney benefits from atrasentan but may also be at higher risk of heart failure. We assessed relative and absolute effects of atrasentan on kidney and heart failure events according to baseline eGFR and urinary albumin-creatinine ratio (UACR) in a post hoc analysis of the Study of Diabetic Nephropathy with Atrasentan (SONAR) trial.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The effect of atrasentan versus placebo in 3668 patients with type 2 diabetes and CKD with elevated albuminuria was examined in the SONAR trial. We used Cox proportional hazards regression analysis to study effects on the primary kidney outcome (composite of doubling of serum creatinine, kidney failure, or kidney death) and heart failure hospitalization across subgroups of eGFR (<30, ≥30-45, and ≥45 ml/min per 1.73 m²) and UACR (<1000, ≥1000-3000, and ≥3000 mg/g).

RESULTS

Atrasentan reduced the relative risk of the primary kidney outcome (hazard ratio, 0.71; 95% confidence interval, 0.58 to 0.88) consistently across all subgroups of baseline eGFR and UACR (all P interaction >0.21). Patients in the highest UACR and lowest eGFR subgroups, in whom rates of the primary kidney outcome were highest, showed the largest absolute benefit (all P interaction <0.01). The risk of heart failure hospitalization was higher in the atrasentan group (hazard ratio, 1.39; 95% confidence interval, 0.97 to 1.99) and was consistent across subgroups, with no evidence that relative or absolute risks differed across eGFR or UACR subgroups (all P interaction >0.09).

CONCLUSIONS

Atrasentan reduced the relative risk of the primary kidney outcome consistently across baseline UACR and eGFR subgroups. The absolute risk reduction was greater among patients in the lowest eGFR and highest albuminuria category who were at highest baseline risk. Conversely, the relative and absolute risks of heart failure hospitalization were similar across baseline UACR and eGFR subgroups.Clinical Trial registry name and registration number: Study of Diabetic Nephropathy with Atrasentan (SONAR), NCT01858532.

Endothelin Receptor Antagonists as a Potential Treatment of Diabetic Nephropathy: A Systematic Review

Diabetic nephropathy is becoming a more predominant cause of end-stage renal disease, as the prevalence of diabetes mellitus worldwide is on the rise. In this systematic review, we aimed to define the role of endothelin receptor antagonists, in the prevention and treatment of diabetic nephropathy, in addition to determining their safety. For this review, PubMed, Google Scholar, and Cochrane Library databases, in addition to ClinicalTrials.gov, were searched for publications in the last 20 years. We included 14 studies, seven randomized control trials, and seven post hoc analyses in this paper. Atrasentan decreased albuminuria, reduced blood pressure, and improved lipid profiles with more manageable fluid overload-related adverse events than avosentan and bosentan. Overall, endothelin receptor antagonists, in combination with renin-angiotensin-aldosterone system inhibitors, effectively reduce albuminuria and prevent the progression of diabetic kidney disease. However, more extensive clinical trials still need to be conducted to confirm these relationships and to learn more about the specific factors affecting their efficacy in individual patients.

Endothelin receptor antagonism improves glucose handling, dyslipidemia, and adipose tissue inflammation in obese mice

Endothelin-1 (ET-1) is elevated in patients with obesity; however, its contribution to the pathophysiology related to obesity is not fully understood. We hypothesized that high ET-1 levels cause dyslipidemia, inflammation, and insulin resistance within the adipose tissue of obese mice. To test this hypothesis, male C57BL/6J mice were fed either normal diet (NMD) or high-fat diet (HFD) for 8 weeks followed by 2 weeks of treatment with either vehicle, atrasentan (ETA receptor antagonist, 10 mg/kg/day) or bosentan (ETA/ETB receptor antagonist, 100 mg/kg/day). Atrasentan and bosentan lowered circulating non-esterified free fatty acids and triglycerides seen in HFD mice, while atrasentan-treated mice had significantly lower liver triglycerides compared with non-treated HFD mice. ET-1 receptor blockade significantly improved insulin tolerance compared with insulin-resistant HFD mice and lowered expression of genes in epididymal white adipose tissue (eWAT) associated with insulin resistance and inflammation. Flow cytometric analyses of eWAT indicated that HFD mice had significantly higher percentages of both CD4+ and CD8+ T cells compared with NMD mice, which was attenuated by treatment with atrasentan or bosentan. Atrasentan treatment also abolished the decrease in eosinophils seen in HFD mice. Taken together, these data indicate that ETA and ETA/ETB receptor blockade improves peripheral glucose homeostasis, dyslipidemia and liver triglycerides, and also attenuates the pro-inflammatory immune profile in eWAT of mice fed HFD. These data suggest a potential use for ETA and ETA/ETB receptor blockers in the treatment of obesity-associated dyslipidemia and insulin resistance.

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.

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.

Inter-individual variability in atrasentan exposure partly explains variability in kidney protection and fluid retention responses: A post hoc analysis of the SONAR trial

AIM

To evaluate whether atrasentan plasma exposure explains between-patient variability in urinary albumin-to-creatinine ratio (UACR) response, a surrogate for kidney protection, and B-type natriuretic peptide (BNP) response, a surrogate for fluid expansion.

METHODS

Type 2 diabetic patients with chronic kidney disease (n = 4775) received 0.75 mg atrasentan for 6 weeks in the active run-in period. Individual area under the concentration-time-curve (AUC) was estimated using a population pharmacokinetic model. The association between atrasentan AUC, other clinical characteristics, and UACR and BNP response, was estimated using linear regression.

RESULTS

The median atrasentan AUC was 43.8 ng.h/mL with a large variation among patients (2.5th-97.5th percentiles [P]: 12.6 to 197.5 ng.h/mL). Median UACR change at the end of enrichment was -36.0% and median BNP change was 8.7%, which also varied among patients (UACR, 2.5th-97.5th P: -76.2% to 44.5%; BNP, 2.5th-97.5th P: -71.5% to 300.0%). In the multivariable analysis, higher atrasentan AUC was associated with greater UACR reduction (4.88% per doubling in ng.h/mL [95% confidence interval {CI}: 6.21% to 3.52%], P < .01) and greater BNP increase (3.08% per doubling in ng.h/mL [95% CI: 1.12% to 4.11%], P < .01) independent of estimated glomerular filtration rate, haemoglobin or BNP. Caucasian patients compared with black patients had greater UACR reduction (7.06% [95% CI: 1.38% to 13.07%]) and also greater BNP increase (8.75% [95% CI: 1.65% to 15.35%]). UACR response was not associated with BNP response (r = 0.06).

CONCLUSION

Atrasentan plasma exposure varied among individual patients and partially explained between-patient variability in efficacy and safety response.

Efficacy and safety of endothelin receptor antagonists in type 2 diabetic kidney disease: A systematic review and meta-analysis of randomized controlled trials

AIM

To analyse the efficacy and safety of endothelin receptor antagonists for people with diabetic kidney disease.

METHODS

Randomized controlled trials comparing endothelin receptor antagonists with placebo in people with diabetic kidney disease were identified through PubMed, Embase and the Cochrane Library. We used a random-effect model to calculate the mean difference or risk ratio with the 95% CI.

RESULTS

Seven studies with a total of 4730 participants were included. Overall, endothelin receptor antagonists significantly reduced albuminuria compared with placebo (standardized mean difference -0.48, 95% CI -0.64 to -0.33). Atrasentan, in particular, effectively reduced albuminuria (standardized mean difference -0.58, 95% CI -1.00 to -0.17) and the risk of composite renal endpoints (risk ratio 0.65; 95% CI 0.49 to 0.88), with insignificant change in the rate of congestive heart failure (risk ratio 1.40, 95% CI 0.76 to 2.56) and mortality (risk ratio 1.11, 95% CI 0.77 to 1.61). In contrast, although avosentan reduced albuminuria (standardized mean difference -0.47, 95% CI -0.57 to -0.36) and the risk of composite renal endpoints (risk ratio 0.63, 95% CI 0.42 to 0.94), it was associated with a significant increase in congestive heart failure risk (risk ratio 2.61, 95% CI 1.36 to 5.00) and an insignificant increase in mortality risk (risk ratio 1.50, 95% CI 0.81, 2.78). No significant change in efficacy or safety outcomes with bosentan was detected. Dose-response analysis indicated that 0.75 mg/day atrasentan is expected to be optimal for renoprotection, with maximal albuminuria reduction and minimal fluid retention events.

CONCLUSIONS

Among the endothelin receptor antagonists, atrasentan and avosentan, but not bosentan, are effective for renoprotection in people with diabetic kidney disease. Compared with other types and doses, atrasentan 0.75 mg/day is the most promising, with maximal albuminuria reduction and minimal fluid retention. Vigilant monitoring of congestive heart failure risk is needed in future clinical practice. (PROSPERO registration no. CRD42020169840).

Endothelin Receptor Antagonists: Status Quo and Future Perspectives for Targeted Therapy

The endothelin axis, recognized for its vasoconstrictive action, plays a central role in the pathology of pulmonary arterial hypertension (PAH). Treatment with approved endothelin receptor antagonists (ERAs), such as bosentan, ambrisentan, or macitentan, slow down PAH progression and relieves symptoms. Several findings have indicated that endothelin is further involved in the pathogenesis of certain other diseases, making ERAs potentially beneficial in the treatment of various conditions. In addition to PAH, this review summarizes the use and perspectives of ERAs in cancer, renal disease, fibrotic disorders, systemic scleroderma, vasospasm, and pain management. Bosentan has proven to be effective in systemic sclerosis PAH and in decreasing the development of vasospasm-related digital ulcers. The selective ERA clazosentan has been shown to be effective in preventing cerebral vasospasm and delaying ischemic neurological deficits and new infarcts. Furthermore, in the SONAR (Study Of Diabetic Nephropathy With Atrasentan) trial, the selective ERA atrasentan reduced the risk of renal events in patients with diabetes and chronic kidney disease. These data suggest atrasentan as a new therapy in the treatment of diabetic nephropathy and possibly other renal diseases. Preclinical studies regarding heart failure, cancer, and fibrotic diseases have demonstrated promising effects, but clinical trials have not yet produced measurable results. Nevertheless, the potential benefits of ERAs may not be fully realized.

Endothelin: 30 Years From Discovery to Therapy

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

Baseline characteristics and enrichment results from the SONAR trial

AIM

The SONAR trial uses an enrichment design based on the individual response to the selective endothelin receptor antagonist atrasentan on efficacy (the degree of the individual response in the urinary albumin-to-creatinine ratio [UACR]) and safety/tolerability (signs of sodium retention and acute increases in serum creatinine) to assess the effects of this agent on major renal outcomes. The patient population and enrichment results are described here.

METHODS

Patients with type 2 diabetes with an estimated glomerular filtration rate (eGFR) within 25 to 75 mL/min/1.73 m² and UACR between 300 and 5000 mg/g were enrolled. After a run-in period, eligible patients received 0.75 mg/d of atrasentan for 6 weeks. A total of 2648 responder patients in whom UACR decreased by ≥30% compared to baseline were enrolled, as were 1020 non-responders with a UACR decrease of <30%. Patients who experienced a weight gain of >3 kg and in whom brain natriuretic peptide exceeded ≥300 pg/mL, or who experienced an increase in serum creatinine >20% (0.5 mg/dL), were not randomized.

RESULTS

Baseline characteristics were similar for atrasentan responders and non-responders. Upon entry to the study, median UACR was 802 mg/g in responders and 920 mg/g in non-responders. After 6 weeks of treatment with atrasentan, the UACR change in responders was -48.8% (95% CI, -49.8% to -47.9%) and in non-responders was -1.2% (95% CI, -6.4% to 3.9%). Changes in other renal risk markers were similar between responders and non-responders except for a marginally greater reduction in systolic blood pressure and eGFR in responders.

CONCLUSIONS

The enrichment period has successfully identified a population with a profound UACR reduction without clinical signs of sodium retention in whom a large atrasentan effect on clinically important renal outcomes is possible. The SONAR trial aims to establish whether atrasentan confers renal protection.

Deleting Death and Dialysis: Conservative Care of Cardio-Vascular Risk and Kidney Function Loss in Chronic Kidney Disease (CKD)

The uremic syndrome, which is the clinical expression of chronic kidney disease (CKD), is a complex amalgam of accelerated aging and organ dysfunctions, whereby cardio-vascular disease plays a capital role. In this narrative review, we offer a summary of the current conservative (medical) treatment options for cardio-vascular and overall morbidity and mortality risk in CKD. Since the progression of CKD is also associated with a higher cardio-vascular risk, we summarize the interventions that may prevent the progression of CKD as well. We pay attention to established therapies, as well as to novel promising options. Approaches that have been considered are not limited to pharmacological approaches but take into account lifestyle measures and diet as well. We took as many randomized controlled hard endpoint outcome trials as possible into account, although observational studies and post hoc analyses were included where appropriate. We also considered health economic aspects. Based on this information, we constructed comprehensive tables summarizing the available therapeutic options and the number and kind of studies (controlled or not, contradictory outcomes or not) with regard to each approach. Our review underscores the scarcity of well-designed large controlled trials in CKD. Nevertheless, based on the controlled and observational data, a therapeutic algorithm can be developed for this complex and multifactorial condition. It is likely that interventions should be aimed at targeting several modifiable factors simultaneously.

Rationale and protocol of the Study Of diabetic Nephropathy with AtRasentan (SONAR) trial: A clinical trial design novel to diabetic nephropathy

AIMS

Individuals with diabetes and chronic kidney disease (CKD) are at high risk for renal events. Recent trials of novel treatments have been negative, possibly because of variability in response to treatment of the target risk factor. Atrasentan is a selective endothelin A receptor antagonist that reduces urinary albumin-to-creatinine ratio (UACR), with a large variability between patients. We are assessing its effect on renal outcomes in the Study Of diabetic Nephropathy with AtRasentan (SONAR; NCT01858532) with an enrichment design (>30% lowering of albuminuria) to select patients most likely to benefit.

MATERIALS AND METHODS

SONAR is a randomized, double-blind, placebo-controlled trial with approximately 3500 participants who have stage 2-4 CKD and macroalbuminuria and are receiving a maximum tolerated dose of a renin-angiotensin system inhibitor.

RESULTS

After 6 weeks of exposure to atrasentan 0.75 mg once daily (enrichment period), participants with ≥30% UACR decrease and no tolerability issues (responders) were randomly assigned to placebo or atrasentan 0.75 mg/day. The responder group will be used for primary efficacy and safety analyses. Approximately 1000 participants with <30% UACR reduction (non-responders) were also randomized to placebo or atrasentan. The primary endpoint is a composite of a sustained doubling of serum creatinine or end-stage renal disease. The original power calculation indicated that a total of 425 primary renal events in the responder group provides 90% power to detect a 27% reduction in relative risk (alpha level of .05).

CONCLUSION

SONAR aims to determine whether atrasentan added to guideline-recommended therapies safely reduces the risk of CKD progression and delays the onset of end-stage renal disease in patients with type 2 diabetes and nephropathy. SONAR also aims to establish whether the enrichment of patients based on their initial "surrogate" response to atrasentan will deliver a trial design in accord with personalized treatment of diabetic kidney disease.

Endothelin A receptor antagonists in diabetic kidney disease

PURPOSE OF REVIEW

Despite optimal therapy of diabetic nephropathy with agents blocking the renin-angiotensin-aldosterone system, the residual risk of nephropathy progression to end-stage renal disease (ESRD) remains high. The purpose of this review is to discuss the potential role of endothelin antagonism as a therapeutic tool to reduce residual proteinuria and delay kidney injury progression among patients with diabetic nephropathy.

RECENT FINDINGS

Preclinical studies have shown that endothelin receptor antagonists (ERAs) exert proteinuria lowering and nephroprotective actions in experimental models of diabetic nephropathy. ERAs reduce proteinuria in phase 2 trials that included therapy with renin-angiotensin-aldosterone system blockers. Safety of these agents and protection from ESRD needs to be demonstrated in phase 3 trials. Excess risk of fluid retention and heart failure risk remains.

SUMMARY

The hypothesis that the antiproteinuric effect of endothelin antagonism may be translated into a slower progression of diabetic nephropathy to ESRD is investigated in ongoing randomized trials assessing 'hard' renal endpoints. ERAs may represent a promising tool toward renoprotection in diabetic nephropathy by individualizing therapy and mitigating the risk of heart failure, if these trials are positive.

Novel therapies for diabetic kidney disease

Over the past 30 years there have been many complementary therapies developed to achieve glycemic control and have an impact on cardiovascular outcomes, as well as reduce the risk of microvascular disease. The 2 most notable new entries have been the sodium-glucose cotransporter 2 (SGLT2) inhibitors and the glucagon-like peptide-1 (GLP-1) agonists. Both these classes of agents have demonstrated reductions in cardiovascular event rates as well as reductions in blood pressure and weight. Moreover, while both have demonstrated a benefit in slowing nephropathy progression, the SGLT2 inhibitors appear to have a significantly greater effect compared with the GLP-1 agents. There is an ongoing trial specifically powered for renal disease progression, CREDENCE (Evaluation of the Effects of Canagliflozin on Renal and Cardiovascular Outcomes in Participants With Diabetic Nephropathy). Additionally, there are 2 other classes of agents being tested to slow nephropathy progression, a selective endothelin-1 receptor antagonist, atrasantan, in the SONAR (Study of Diabetic Nephropathy With Atrasentan) trial and a nonsteroidal mineralocorticoid receptor antagonist, finerenone, in the FIDELIO (Efficacy and Safety of Finerenone in Subjects With Type 2 Diabetes Mellitus) trial. These and other studies are discussed.

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.

Pooled Analysis of Multiple Crossover Trials To Optimize Individual Therapy Response to Renin-Angiotensin-Aldosterone System Intervention

BACKGROUND AND OBJECTIVES

In the treatment of CKD, individual patients show a wide variation in their response to many drugs, including renin-angiotensin-aldosterone system inhibitors (RAASi). To investigate whether therapy resistance to RAASi can be overcome by uptitrating the dose of drug, changing the mode of intervention (with drugs from similar or different classes), or lowering dietary sodium intake, we meta-analyzed individual responses to different modes of interventions.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Randomized crossover trials were analyzed to assess correlation of individual responses to RAASi and nonsteroidal anti-inflammatory drugs (NSAIDs; n=395 patients). Included studies compared the antialbuminuric effect of uptitrating the dose of RAASi (n=10 studies) and NSAIDs (n=1), changing within the same class of RAASi (e.g., angiotensin-converting enzyme inhibition to angiotensin receptor blockers; n=5) or NSAIDs (n=1), changing from RAASi to NSAIDs (n=2), and changing from high to low sodium intake (n=5). A two-stage meta-analysis was conducted: Deming regression was conducted in each study to assess correlations in response, and individual study results were then meta-analyzed.

RESULTS

The albuminuria response to one dose of RAASi or NSAIDs positively correlated with the response to a higher dose of the same drug (r=0.72; 95% confidence interval [95% CI], 0.66 to 0.78), changes within the same class of RAASi or NSAIDs (r=0.54; 95% CI, 0.35 to 0.68), changes between RAASi and NSAIDs (r=0.44; 95% CI, 0.16 to 0.66), and changes from high to moderately low salt intake (r=0.36; 95% CI, 0.22 to 0.48). Results were similar when the individual systolic BP and potassium responses were analyzed, and were consistent in patients with and without diabetes.

CONCLUSIONS

Individuals who show a poor response to one dose or type of RAASi also show a poor response to higher doses, other types of RAASi or NSAIDs, or a reduction in dietary salt intake. Whether other drugs or drug combinations targeting pathways beyond the renin-angiotensin-aldosterone system and prostaglandins would improve the individual poor response requires further study.

Sparstolonin B prevents lumbar intervertebral disc degeneration through toll like receptor 4, NADPH oxidase activation and the protein kinase B signaling pathway

Intervertebral disc degeneration (IVDD) is the most common pathogeny of lumbago. It is the pathological basis for a series of spinal degenerative diseases. For a long time, the diagnosis and treatment of lumbago have rendered difficult, since the pathogeny has not been identified. Therefore, the present study aimed to investigate the protective effect of Sparstolonin B in preventing lumbar intervertebral disc degeneration, and explored its potential mechanism in rats. Firstly, Sparstolonin B effectively reduced the histological score of disc degeneration and increased endplate porosity of L2 superior endplates in a lumbar IVDD rat model. Sparstolonin B significantly inhibited the IVDD‑induced inflammatory factors tumor necrosis factor‑α, interleukin (IL)‑1β and IL‑6, oxidative stress factors (malondialdehyde), and superoxide dismutase and caspase‑3/9 activities. Treatment with Sparstolonin B significantly suppressed toll‑like receptor 4 (TLR4), myeloid differentiation primary response protein 88 (MyD88) and nuclear factor (NF)‑κB protein expression, inhibited NAPDH oxidase 2 protein expression and induced phosphoinositide 3‑kinase and phosphorylated protein kinase B protein expression in the IVDD rat model. These results demonstrated that Sparstolonin B prevents lumbar IVDD‑induced inflammation, oxidative stress and apoptosis through TLR4/MyD88/NF‑κB, NADPH oxidase activation and the phosphoinositide 3‑kinase/protein kinase B signaling pathway. These results implicate Sparstolonin B for use as a therapeutic agent for IVDD in clinical applications.

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).

Comparison of exposure response relationship of atrasentan between North American and Asian populations

AIMS

The selective endothelin (ET) A receptor antagonist atrasentan has been shown to lower albuminuria in North American and Asian patients with type 2 diabetes and nephropathy. As drug responses to many drugs may differ between North American and Asian populations, we assessed the influence of geographical region on the albuminuria and fluid retention response to atrasentan.

MATERIALS AND METHODS

Two 12-week double-blind randomised controlled trials were performed with atrasentan 0.75 or 1.25 mg/d vs placebo in patients with type 2 diabetes and nephropathy. The efficacy endpoint was the percentage change in albuminuria. Bodyweight change, a proxy of fluid retention, was used as a safety endpoint. Pharmacodynamics were determined in Asians (N = 77) and North Americans (N = 134). Atrasentan plasma concentration was measured in 161 atrasentan-treated patients.

RESULTS

Mean albuminuria reduction in Asian, compared to North American, patients was, respectively, -34.4% vs -26.3% for 0.75 mg/d ( P  = .44) and -48.0% vs -28.9% for 1.25 mg/d ( P  = .035). Bodyweight gain did not differ between North American and Asian populations. Atrasentan plasma concentrations were higher in Asians compared to North Americans and correlated with albuminuria response (7.2% albuminuria reduction per doubling atrasentan concentration; P  = .024). Body surface area (β = -1.09 per m² ; P  < .001) and bilirubin, as a marker of hepatic organic anion transporter activity, (β = 0.69 per mg/dL increment; P  = .010) were independent determinants of atrasentan plasma concentration; correction by body surface area and bilirubin left no significant difference in plasma concentration between Asian and North American populations.

CONCLUSION

The higher exposure and albuminuria reduction of atrasentan in Asian patients is not associated with more fluid retention, suggesting that Asian patients are less sensitive to atrasentan-induced sodium retention.

Systematic Literature Review of DPP-4 Inhibitors in Patients with Type 2 Diabetes Mellitus and Renal Impairment

INTRODUCTION

Dipeptidyl peptidase-4 (DPP-4) inhibitors are widely used in the management of patients with type 2 diabetes mellitus (T2DM) and renal impairment (RI). A systematic literature review was performed to compare the efficacy and safety of DPP-4 inhibitors in patients with T2DM and RI.

METHODS

We searched EMBASE, MEDLINE, and the Cochrane Central Register of Controlled Trials (cut-off, June 2015) to identify ≥12-week, randomized, placebo-controlled trials on DPP-4 inhibitors in ≥50 patients with T2DM and RI. Outcomes of interest included change in glycated hemoglobin (HbA1c), overall safety, and incidence of hypoglycemic events (HEs).

RESULTS

Seven trials of ≤52-54 weeks duration were retrieved, which included one study each on vildagliptin, saxagliptin, and sitagliptin, two on linagliptin, and the remaining two were extension studies of vildagliptin and saxagliptin. Majority of patients were on insulin at baseline (53-86%), except in the sitagliptin study, where approximately 11% received insulin during the placebo-controlled phase. After 52 weeks, vildagliptin and saxagliptin reduced HbA1c levels by 0.6-0.7% (baseline 7.8-8.4%) versus placebo in the overall population. HbA1c reductions were similar at weeks 12 and 52. In the 12-week, placebo-controlled phase, sitagliptin and linagliptin reduced mean HbA1c by approximately 0.4% (baseline 7.7-8.1%) versus placebo. Rates of HEs with DPP-4 inhibitors were not significantly different versus placebo in any study. Rates of adverse events (AEs) and changes involving renal function were similar in the active- and placebo-treated groups.

CONCLUSION

These results suggest that DPP-4 inhibitors have the potential to improve glycemic control in patients with RI without increasing the risk of HEs or overall AEs.

FUNDING

Novartis Pharma AG.

Serum metabolites predict response to angiotensin II receptor blockers in patients with diabetes mellitus

Background

Individual patients show a large variability in albuminuria response to angiotensin receptor blockers (ARB). Identifying novel biomarkers that predict ARB response may help tailor therapy. We aimed to discover and validate a serum metabolite classifier that predicts albuminuria response to ARBs in patients with diabetes mellitus and micro- or macroalbuminuria.

Methods

Liquid chromatography-tandem mass spectrometry metabolomics was performed on serum samples. Data from patients with type 2 diabetes and microalbuminuria (n = 49) treated with irbesartan 300 mg/day were used for discovery. LASSO and ridge regression were performed to develop the classifier. Improvement in albuminuria response prediction was assessed by calculating differences in R² between a reference model of clinical parameters and a model with clinical parameters and the classifier. The classifier was externally validated in patients with type 1 diabetes and macroalbuminuria (n = 50) treated with losartan 100 mg/day. Molecular process analysis was performed to link metabolites to molecular mechanisms contributing to ARB response.

Results

In discovery, median change in urinary albumin excretion (UAE) was −42 % [Q1–Q3: −69 to −8]. The classifier, consisting of 21 metabolites, was significantly associated with UAE response to irbesartan (p < 0.001) and improved prediction of UAE response on top of the clinical reference model (R² increase from 0.10 to 0.70; p < 0.001). In external validation, median change in UAE was −43 % [Q1–Q35: −63 to −23]. The classifier improved prediction of UAE response to losartan (R² increase from 0.20 to 0.59; p < 0.001). Specifically ADMA impacting eNOS activity appears to be a relevant factor in ARB response.

Conclusions

A serum metabolite classifier was discovered and externally validated to significantly improve prediction of albuminuria response to ARBs in diabetes mellitus.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-0960-3) contains supplementary material, which is available to authorized users.

Stop chronic kidney disease progression: Time is approaching

Progression of chronic kidney disease (CKD) is inevitable. However, the last decade has witnessed tremendous achievements in this field. Today we are optimistic; the dream of withholding this progression is about to be realistic. The recent discoveries in the field of CKD management involved most of the individual diseases leading the patients to end-stage renal disease. Most of these advances involved patients suffering diabetic kidney disease, chronic glomerulonephritis, polycystic kidney disease, renal amyloidosis and chronic tubulointerstitial disease. The chronic systemic inflammatory status and increased oxidative stress were also investigated. This inflammatory status influences the anti-senescence Klotho gene expression. The role of Klotho in CKD progression together with its therapeutic value are explored. The role of gut as a major source of inflammation, the pathogenesis of intestinal mucosal barrier damage, the role of intestinal alkaline phosphatase and the dietary and therapeutic implications add a novel therapeutic tool to delay CKD progression.

Kidney tubules: intertubular, vascular, and glomerular cross-talk

PURPOSE OF REVIEW

The kidney mediates the excretion or conservation of water and electrolytes in the face of changing fluid and salt intake and losses. To ultrafilter and reabsorb the exact quantities of free water and salts to maintain euvolemia a range of endocrine, paracrine, and hormonal signaling systems have evolved linking the tubules, capillaries, glomeruli, arterioles, and other intrinsic cells of the kidney. Our understanding of these systems remains incomplete.

RECENT FINDINGS

Recent work has provided new insights into the workings of the communication pathways between tubular segments and the glomeruli and vasculature, with novel therapeutic agents in development. Particular progress has also been made in the visualization of tubuloglomerular feedback.

SUMMARY

The review summarizes our current understanding of pathway functions in health and disease, as well as future therapeutic options to protect the healthy and injured kidney.

Endothelin

The endothelins comprise three structurally similar 21-amino acid peptides. Endothelin-1 and -2 activate two G-protein coupled receptors, ETA and ETB, with equal affinity, whereas endothelin-3 has a lower affinity for the ETA subtype. Genes encoding the peptides are present only among vertebrates. The ligand-receptor signaling pathway is a vertebrate innovation and may reflect the evolution of endothelin-1 as the most potent vasoconstrictor in the human cardiovascular system with remarkably long lasting action. Highly selective peptide ETA and ETB antagonists and ETB agonists together with radiolabeled analogs have accurately delineated endothelin pharmacology in humans and animal models, although surprisingly no ETA agonist has been discovered. ET antagonists (bosentan, ambrisentan) have revolutionized the treatment of pulmonary arterial hypertension, with the next generation of antagonists exhibiting improved efficacy (macitentan). Clinical trials continue to explore new applications, particularly in renal failure and for reducing proteinuria in diabetic nephropathy. Translational studies suggest a potential benefit of ETB agonists in chemotherapy and neuroprotection. However, demonstrating clinical efficacy of combined inhibitors of the endothelin converting enzyme and neutral endopeptidase has proved elusive. Over 28 genetic modifications have been made to the ET system in mice through global or cell-specific knockouts, knock ins, or alterations in gene expression of endothelin ligands or their target receptors. These studies have identified key roles for the endothelin isoforms and new therapeutic targets in development, fluid-electrolyte homeostasis, and cardiovascular and neuronal function. For the future, novel pharmacological strategies are emerging via small molecule epigenetic modulators, biologicals such as ETB monoclonal antibodies and the potential of signaling pathway biased agonists and antagonists.