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

Targeting endothelin signaling in podocyte injury and diabetic nephropathy-diabetic kidney disease

Despite advances in diabetes management, there is an urgent need for novel therapeutic strategies since the current treatments remain insufficient in halting the progression of diabetic nephropathy-diabetic kidney disease (DN-DKD). This review is mainly addressed on the pivotal role of endothelin-1 in the pathophysiology of DN, with a specific focus on its effects on podocytes and the glomerular filtration barrier. Endothelin-1 promotes mesangial cell proliferation, sclerosis, and direct podocyte injury via the activation of endothelin type A and B receptors, that drive the progression of glomerulosclerosis in DN-DKD. Endothelin receptor antagonists, including drugs like atrasentan and sparsentan, have demonstrated nephroprotective effects in experimental models by reducing proteinuria and podocyte injury. The therapeutic potential to slow the progression of DN to end-stage kidney disease (ESKD) of these endothelin receptor antagonists in clinical practice is currently under evaluation. However, fluid retention and increased risk of heart failure associated with endothelin receptor antagonists need careful consideration. This review aims to provide an in-depth analysis of the pathophysiological role of endothelin and the emerging therapeutic implications of targeting this pathway in DN-DKD and discusses efficacy, safety, and the possibility of combining the new generation of endothelin receptor antagonists with the standard treatment of CKD and DN-DKD.

Endothelin receptor antagonists in diabetic and non-diabetic chronic kidney disease

Chronic kidney disease (CKD) is one of the major causes of morbidity and mortality, affecting >800 million persons globally. While we still lack efficient, targeted therapies addressing the major underlying pathophysiologic processes in CKD, findings of several recent trials have brought about a shifting landscape of promising therapies. The endothelin system has been implicated in the pathophysiology of CKD and endothelin receptor antagonists are one class of drugs for which we have increasing evidence of efficacy in these patients. In this review we summarize the most recent findings on the safety and efficacy of endothelin receptor antagonists in diabetic and non-diabetic CKD, future directions of research and upcoming treatments.

Efficacy and safety of zibotentan and dapagliflozin in patients with chronic kidney disease: study design and baseline characteristics of the ZENITH-CKD trial

BACKGROUND

Sodium-glucose co-transporter 2 inhibitors (SGLT2is) are part of the standard of care for patients with chronic kidney disease (CKD), both with and without type 2 diabetes. Endothelin A (ETA) receptor antagonists have also been shown to slow progression of CKD. Differing mechanisms of action of SGLT2 and ETA receptor antagonists may enhance efficacy. We outline a study to evaluate the effect of combination zibotentan/dapagliflozin versus dapagliflozin alone on albuminuria and estimated glomerular filtration rate (eGFR).

METHODS

We are conducting a double-blind, active-controlled, Phase 2b study to evaluate the efficacy and safety of ETA receptor antagonist zibotentan and SGLT2i dapagliflozin in a planned 415 adults with CKD (Zibotentan and Dapagliflozin for the Treatment of CKD; ZENITH-CKD). Participants are being randomized (1:2:2) to zibotentan 0.25 mg/dapagliflozin 10 mg once daily (QD), zibotentan 1.5 mg/dapagliflozin 10 mg QD and dapagliflozin 10 mg QD alone, for 12 weeks followed by a 2-week off-treatment wash-out period. The primary endpoint is the change in log-transformed urinary albumin-to-creatinine ratio (UACR) from baseline to Week 12. Other outcomes include change in blood pressure from baseline to Week 12 and change in eGFR the study. The incidence of adverse events will be monitored. Study protocol-defined events of special interest include changes in fluid-related measures (weight gain or B-type natriuretic peptide).

RESULTS

A total of 447 patients were randomized and received treatment in placebo/dapagliflozin (n = 177), zibotentan 0.25 mg/dapagliflozin (n = 91) and zibotentan 1.5 mg/dapagliflozin (n =  179). The mean age was 62.8 years, 30.9% were female and 68.2% were white. At baseline, the mean eGFR of the enrolled population was 46.7 mL/min/1.73 m2 and the geometric mean UACR was 538.3 mg/g.

CONCLUSION

This study evaluates the UACR-lowering efficacy and safety of zibotentan with dapagliflozin as a potential new treatment for CKD. The study will provide information about an effective and safe zibotentan dose to be further investigated in a Phase 3 clinical outcome trial.

CLINICAL TRIAL REGISTRATION NUMBER

NCT04724837.

Insulin resistance, kidney outcomes and effects of the endothelin receptor antagonist atrasentan in patients with type 2 diabetes and chronic kidney disease

BACKGROUND

Insulin resistance (IR) is a pathophysiologic hallmark of type 2 diabetes and associated with the presence of chronic kidney disease (CKD). Experimental studies suggest that endothelin-1 increases IR. We assessed the association between IR and cardio-renal outcomes and the effect of the selective endothelin receptor antagonist atrasentan on IR in patients with type 2 diabetes and CKD.

METHODS

We used data from the RADAR and SONAR trials that recruited participants with type 2 diabetes and CKD [eGFR 25-75 mL/min/1.73 m², urine albumin-to-creatinine ratio of 300-5000 mg/g]. IR was calculated using the homeostatic model assessment (HOMA-IR). The association between HOMA-IR and the pre-specified cardio-renal outcomes was assessed using multivariable Cox proportional hazards regression, and effects of atrasentan on HOMA-IR by a linear mixed effect model.

RESULTS

In the SONAR trial, each log-unit increase in HOMA-IR was associated with an increased risk of the composite cardio-renal outcome [hazard ratio 1.32 (95%CI 1.09,1.60; p = 0.004)], kidney outcome [hazard ratio 1.30 (95%CI 1.00,1.68; p-value = 0.048)], and the kidney or all-cause mortality outcome [hazard ratio 1.25 (95%CI 1.01,1.55; p-value = 0.037)]. After 12 weeks treatment in the RADAR trial (N = 123), atrasentan 0.75 mg/day and 1.25 mg/day compared to placebo reduced HOMA-IR by 19.1 (95%CI -17.4, 44.3) and 26.7% (95%CI -6.4, 49.5), respectively. In the SONAR trial (N = 1914), atrasentan 0.75 mg/day compared to placebo reduced HOMA-IR by 9.6% (95%CI 0.6, 17.9).

CONCLUSIONS

More severe IR is associated with increased risk of cardio-renal outcomes. The endothelin receptor antagonist atrasentan reduced IR.

TRIAL REGISTRATION

RADAR trial (Reducing Residual Albuminuria in Subjects With Diabetes and Nephropathy With AtRasentan): NCT01356849. SONAR trial (The Study Of Diabetic Nephropathy With AtRasentan) NCT01858532.

Organic Anion Transporter Gene Variants Associated With Plasma Exposure and Long-Term Response to Atrasentan in Patients With Diabetic Kidney Disease

Plasma exposure of the endothelin receptor antagonist atrasentan varies between individuals and is associated with nephroprotective effects and the risk of heart failure. We examined the influence of genetic polymorphisms on atrasentan plasma exposure and pharmacodynamic effects. We performed a substudy of the Study of Diabetic Nephropathy With Atrasentan (SONAR) trial which enrolled adults with type 2 diabetes and chronic kidney disease (estimated glomerular filtration rate: 25-75 mL/min/1.73 m² , and a urine albumin-to-creatinine ratio of 300-5,000 mg/g). Single nucleotide polymorphisms (SNPs) were determined for prespecified membrane transporters, metabolizing enzymes, and the endothelin-1 peptide. The associations among genotype, atrasentan plasma exposure, and the effect of atrasentan on the prespecified kidney and heart failure hospitalization (HHF) outcomes was assessed with Cox proportional hazards regression models. Of 3,668 patients randomized, 2,329 (63.5%) consented to genotype analysis. Two SNPs in the SLCO1B1 gene (rs4149056 and rs2306283), encoding the hepatic organic anion transporter 1B1 (OATP1B1), showed the strongest association with atrasentan plasma exposure. Based on their SLCO1B1 genotype, patients were classified into normal (atrasentan area under the plasma-concentration time curve from zero to infinity (AUC_0-inf ) 41.3 ng·h/mL) or slow (atrasentan AUC_0-inf 49.7 ng·h/mL, P < 0.001) OATP1B1 transporter phenotypes. Among patients with a normal OATP1B1 phenotype, the hazard ratio (HR) with atrasentan for the primary kidney and HHF outcomes were 0.61 (95% confidence interval (CI): 0.45-0.81) and 1.35 (95% CI: 0.84-2.13), respectively. In the slow transporter phenotype, HRs for kidney and HHF outcomes were 1.95 (95% CI: 0.95-4.03, P-interaction normal phenotype = 0.004), and 4.18 (95% CI: 1.37-12.7, P-interaction normal phenotype = 0.060), respectively. OATP1B1 gene polymorphisms are associated with significant between-patient variability in atrasentan plasma exposure and long-term efficacy and safety.

ET-1 as a Sex-Specific Mechanism Impacting Age-Related Changes in Vascular Function

Aging is a primary risk factor for cardiovascular disease (CVD), which is the leading cause of death in developed countries. Globally, the population of adults over the age of 60 is expected to double by the year 2050. CVD prevalence and mortality rates differ between men and women as they age in part due to sex-specific mechanisms impacting the biological processes of aging. Measures of vascular function offer key insights into cardiovascular health. Changes in vascular function precede changes in CVD prevalence rates in men and women and with aging. A key mechanism underlying these changes in vascular function is the endothelin (ET) system. Studies have demonstrated sex and sex hormone effects on endothelin-1 (ET-1), and its receptors ETA and ETB. However, with aging there is a dysregulation of this system resulting in an imbalance between vasodilation and vasoconstriction. Thus, ET-1 may play a role in the sex differences observed with vascular aging. While most research has been conducted in pre-clinical animal models, we describe more recent translational data in humans showing that the ET system is an important regulator of vascular dysfunction with aging and acts through sex-specific ET receptor mechanisms. In this review, we present translational evidence (cell, tissue, animal, and human) that the ET system is a key mechanism regulating sex-specific changes in vascular function with aging, along with therapeutic interventions to reduce ET-mediated vascular dysfunction associated with aging. More knowledge on the factors responsible for the sex differences with vascular aging allow for optimized therapeutic strategies to attenuate CVD risk in the expanding aging population.

Molecular Mechanism of Induction of Bone Growth by the C-Type Natriuretic Peptide

The skeletal development process in the body occurs through sequential cellular and molecular processes called endochondral ossification. Endochondral ossification occurs in the growth plate where chondrocytes differentiate from resting, proliferative, hypertrophic to calcified zones. Natriuretic peptides (NPTs) are peptide hormones with multiple functions, including regulation of blood pressure, water-mineral balance, and many metabolic processes. NPTs secreted from the heart activate different tissues and organs, working in a paracrine or autocrine manner. One of the natriuretic peptides, C-type natriuretic peptide-, induces bone growth through several mechanisms. This review will summarize the knowledge, including the newest discoveries, of the mechanism of CNP activation in bone growth.

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 receptors in renal interstitial cells do not contribute to the development of fibrosis during experimental kidney disease

Renal interstitial fibrosis is characterized by the development of myofibroblasts, originating from resident renal and immigrating cells. Myofibroblast formation and extracellular matrix production during kidney damage are triggered by various factors. Among these, endothelins have been discussed as potential modulators of renal fibrosis. Utilizing mouse models of adenine nephropathy (AN) and unilateral ureter occlusion (UUO), this study aimed to investigate the contribution of endothelin signaling in stromal mesenchymal resident renal interstitial cells. We found in controls that adenine feeding and UUO caused marked upregulations of endothelin-1 (ET-1) gene expression in endothelial and in tubular cells and a strong upregulation of ET_A-receptor (ET_A-R) gene expression in interstitial and mesangial cells, while the gene expression of ET_B-receptor (ET_B-R) did not change. Conditional deletion of ET_A-R and ET_B-R gene expression in the FoxD1 stromal cell compartment which includes interstitial cells significantly reduced renal ET_A-R gene expression and moderately lowered renal ET_B-R gene expression. ET receptor (ET-R) deletion exerted no apparent effects on kidney development nor on kidney function. Adenine feeding and UUO led to similar increases in profibrotic and proinflammatory gene expression in control as well as in ET_A^flflET_B^flfl FoxD1^Cre+ mice (ET-Ko). In summary, our findings suggest that adenine feeding and UUO activate endothelin signaling in interstitial cells which is due to upregulated ET_A-R expression and enhanced renal ET-1 production Our data also suggest that the activation of endothelin signaling in interstitial cells has less impact for the development of experimentally induced fibrosis.

Individual Atrasentan Exposure is Associated With Long-term Kidney and Heart Failure Outcomes in Patients With Type 2 Diabetes and Chronic Kidney Disease

Atrasentan, an endothelin receptor antagonist, showed clinically significant albuminuria reduction with minimal signs of fluid retention in phase II trials. We evaluated whether plasma exposure was associated with long-term outcomes for kidney protection and heart failure in the phase III SONAR trial (n = 3668) in type 2 diabetics with chronic kidney disease. A population pharmacokinetic model was used to estimate plasma exposure of atrasentan 0.75 mg/day. Parametric time-to-event models were used to quantify the association between plasma exposure and long-term outcomes. Mean atrasentan plasma exposure was 41.4 ng.h/mL (2.5th to 97.5th P: 14.2 to 139.9). Compared with placebo, a mean atrasentan exposure translated in a hazard ratio of 0.76 (95% confidence interval (CI): 0.28-0.85) for kidney events and 1.13 (95% CI: 1.03-2.20) for heart failure events. At the mean atrasentan exposure, the kidney protective effect was larger than the increase in heart failure supporting the atrasentan 0.75 mg/day dose in this population.

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.