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.

The Genetic Architecture of Kidney Disease

The kidney is subject to a wide range of abnormalities, many of which have a significant hereditable component. Next generation sequencing is increasingly bringing the genetic drivers of Mendelian disease into focus at the base pair level, whereas inexpensive genotyping arrays have surveyed hundreds of thousands of individuals to identify common variants that predispose to kidney dysfunction. In this first article in a CJASN series on kidney genomics, we review how both rare and common variants contribute to kidney disease, explore how evolution may influence the genetic variants that affect kidney function, consider how genetic information is and will be used in the clinic, and identify some of the most important future directions for kidney disease research. Forthcoming articles in the series will elaborate on many of these themes.

Systems Biology and Kidney Disease

The kidney is a complex organ responsible for maintaining multiple aspects of homeostasis in the human body. The combination of distinct, yet interrelated, molecular functions across different cell types make the delineation of factors associated with loss or decline in kidney function challenging. Consequently, there has been a paucity of new diagnostic markers and treatment options becoming available to clinicians and patients in managing kidney diseases. A systems biology approach to understanding the kidney leverages recent advances in computational technology and methods to integrate diverse sets of data. It has the potential to unravel the interplay of multiple genes, proteins, and molecular mechanisms that drive key functions in kidney health and disease. The emergence of large, detailed, multilevel biologic and clinical data from national databases, cohort studies, and trials now provide the critical pieces needed for meaningful application of systems biology approaches in nephrology. The purpose of this review is to provide an overview of the current state in the evolution of the field. Recent successes of systems biology to identify targeted therapies linked to mechanistic biomarkers in the kidney are described to emphasize the relevance to clinical care and the outlook for improving outcomes for patients with kidney diseases.

Computational Fluid Dynamic Modeling of Urethral Strictures

PURPOSE

Computational fluid dynamics have paradigm shifting potential in understanding the physiological flow of fluids in the human body. This translational branch of engineering has already made an important clinical impact on the study of cardiovascular disease. We evaluated the feasibility and applicability of computational fluid dynamics to model urine flow.

MATERIALS AND METHODS

We prepared a computational fluid dynamics model using an idealized male genitourinary system. We created 16 hypothetical urethral stricture scenarios as a test bed. Standard parameters of urine such as pressure, temperature and viscosity were applied as well as typical assumptions germane to fluid dynamic modeling. We used ABAQUS/CAE 6.14 (Dassault Systèmes®) with a direct unsymmetrical solver with standard (FC3D8) 3D brick 8Node elements for model generation.

RESULTS

The average flow rate in urethral stricture disease as measured by our model was 5.97 ml per second (IQR 2.2-10.9). The model predicted a flow rate of 2.88 ml per second for a single 5Fr stricture in the mid bulbar urethra when assuming all other variables constant. The model demonstrated that increasing stricture diameter and bladder pressure strongly impacted urine flow while stricture location and length, and the sequence of multiple strictures had a weaker impact.

CONCLUSIONS

We successfully created a computational fluid dynamics model of an idealized male urethra with varied types of urethral strictures. The resultant flow rates were consistent with the literature. The accuracy of modeling increasing bladder pressure should be improved by future iterations. This technology has vast research and clinical potential.

The Effect of Bladder Filling Rate on the Voiding Behavior of Patients with Overactive Bladder

PURPOSE

Many self-help guides advise patients that spreading fluid intake throughout the day can reduce overactive bladder symptoms. However, although animal studies suggest a link between a faster filling rate and increased afferent nerve firing, to our knowledge the relationship between the filling rate and bladder sensation has not been examined in humans. The aim of this study was to investigate the effect of bladder volume and the bladder filling rate on the bladder sensation and voiding patterns of patients with overactive bladder.

MATERIALS AND METHODS

A control group of 40 female volunteers were recruited by open advertisement. A further 24 female patients with overactive bladder were recruited from the urology outpatient department. Each participant completed the UDI-6 (Urinary Distress Inventory, Short Form), the IIQ-7 (Incontinence Impact Questionnaire, Short Form) and a 3-day sensation related bladder diary.

RESULTS

The proportion of urgent voids in the control group increased with increasing voided volume and bladder filling rates (each p ≤0.001). The proportion of urgent voids in patients with overactive bladder also increased with increasing voided volume and bladder filling rates (p = 0.004 and 0.013, respectively). On regression analysis the rate of bladder filling was an independent predictor of urgent voids in patients with overactive bladder but not in the control group. Patients with overactive bladder were less tolerant of higher bladder filling rates, and experienced most grades of bladder sensation at lower voided volumes and filling rates than the control group.

CONCLUSIONS

The bladder filling rate appears to influence the intervoiding interval and the sensation associated with each void in patients with overactive bladder. Advising patients to lower the bladder filling rate should help reduce urinary frequency, urgency and urge incontinence.

A Multicenter Cohort Study of Histologic Findings and Long-Term Outcomes of Kidney Disease in Women Who Have Been Pregnant

BACKGROUND AND OBJECTIVES

For many women pregnancy is the first contact with health services, thus providing an opportunity to identify renal disease. This study compares causes and long-term renal outcomes of biopsy-proven renal disease identified during pregnancy or within 1 year postpartum, with nonpregnant women.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Native renal biopsies (1997-2012), in women of childbearing age (16 to <50 years), from 21 hospitals were studied. The pregnancy-related diagnosis group included those women with abnormal urinalysis/raised creatinine identified during pregnancy or within 1 year postpartum. Pregnancy-related and control biopsies were matched for age and ethnicity (black versus nonblack).

RESULTS

One hundred and seventy-three pregnancy-related biopsies (19 antenatal, 154 postpregnancy) were identified and matched with 1000 controls. FSGS was more common in pregnancy-related biopsies (32.4%) than controls (9.7%) (P<0.001) but there were no differences in Columbia classification. Women with a pregnancy-related diagnosis were younger (32.1 versus 34.2 years; P=0.004) and more likely to be black (26.0% versus 13.3%; P<0.001) than controls, although there were no differences in ethnicities in women with FSGS. The pregnancy-related group (excluding antenatal biopsies) was more likely to have a decline in Chronic Kidney Disease Epidemiology Collaboration eGFR in the follow-up period than the control group (odds ratio, 1.67; 95% confidence interval, 1.03 to 2.71; P=0.04), and this decline appeared to be more rapid (-1.33 versus -0.56 ml/min per 1.73 m2 per year, respectively; P=0.045). However, there were no differences between groups in those who required RRT or who died.

CONCLUSIONS

Pregnancy is an opportunity to detect kidney disease. FSGS is more common in women who have been pregnant than in controls, and disease identified in pregnancy or within 1 year postpartum is more likely to show a subsequent decline in renal function. Further work is required to determine whether pregnancy initiates, exacerbates, or reveals renal disease.

Risk factors for progression or improvement of lower urinary tract symptoms in a prospective cohort of men

PURPOSE

We determined the metabolic, lifestyle and physical factors associated with progression or improvement of storage and voiding lower urinary tract symptoms in a population based cohort of men.

MATERIALS AND METHODS

After the exclusion of men with prostate or bladder cancer and/or surgery from the study, progression and improvement of storage and voiding lower urinary tract symptoms was assessed using the AUA-SI (American Urological Association symptom index) in 780 men, age 35 to 80 years at baseline, who attended 5-year followup clinics.

RESULTS

Storage and voiding lower urinary tract symptoms progressed in 39.8% (308) and 32.3% (250) of men, and improved in 33.1% (256) and 23.4% (181), respectively. In final adjusted regression models greater bother and physical activity at baseline predicted improvement in storage and voiding lower urinary tract symptoms, while greater income, high-density lipoprotein cholesterol and lower triglycerides predicted improvement of storage lower urinary tract symptoms only. Being widowed, higher plasma estradiol and depression at baseline predicted the progression of storage and voiding lower urinary tract symptoms, while greater abdominal fat mass and obstructive sleep apnea risk predicted the progression of storage lower urinary tract symptoms only. Older age, lower high-density lipoprotein cholesterol, testosterone, income, previous benign prostatic hyperplasia and erectile dysfunction at baseline predicted the progression of voiding lower urinary tract symptoms only. The initiation or continued use of α-blockers or anticholinergics (storage lower urinary tract symptoms), and 5α-reductase inhibitors (voiding lower urinary tract symptoms), were associated with symptom improvement.

CONCLUSIONS

Lower urinary tract symptoms may progress or remit. Even accounting for medication use, progression may be associated with modifiable disease, or metabolic or behavioral factors, which are also risk factors for type 2 diabetes and cardiovascular disease. These factors should be looked for and managed.