Association of urine α1-microglobulin with kidney function decline and mortality in HIV-infected women

Urine Epidermal Growth Factor and Kidney Function Decline in Middle-Aged Adults

Rationale & Objective

The diagnosis and prognostication of chronic kidney disease (CKD) largely rely on glomerular measures that may not reflect tubular damage. We investigated the associations of urine kidney tubule biomarkers with estimated glomerular filtration rate (eGFR) change among middle-aged adults, when chronic diseases typically emerge.

Study Design

An observational cohort study.

Setting & Participants

A total of 1,145 participants of the Coronary Artery Risk Development in Young Adults (CARDIA) study without CKD, hypertension, or cardiovascular disease at the year 20 visit.

Exposures

Seven different biomarkers of tubular health: urine epidermal growth factor (EGF), alpha-1-microglobulin (α1m), interleukin-18, kidney injury molecule-1, monocyte chemoattractant protein-1, uromodulin, and chitinase-3-like protein 1.

Outcomes

Ten-year eGFR change and incident reduced eGFR (new onset of eGFR < 60 mL/min/1.73 m2).

Analytical Approach

We examined associations of tubular health biomarkers with 10-year eGFR change and incident reduced eGFR with linear mixed models and interval-censored proportional hazards regression models, respectively. Both minimally and fully adjusted models were controlled for urine creatinine levels.

Results

The mean age of participants was 44.8 ± 3.7 years, with 39% African American and 56% female. The average 10-year change in eGFR was -18.6 mL/min/1.73 m2 (95% CI, -19.4 to -17.8). In contrast to the other tubular biomarkers, which showed conflicting results, EGF demonstrated strong, consistent associations with both kidney outcomes. Each 1-standard deviation (SD) higher EGF was associated with a 2.37 mL/min/1.73 m2 (95% CI, 0.64-4.10) smaller 10-year decrease in eGFR and a 42% (95% CI, 4%-64%) lower risk of incident reduced eGFR in the fully adjusted model.

Limitations

Observational design, measurements of eGFR were done only at 5-year intervals during follow-up.

Conclusions

In middle-aged, community-dwelling adults without hypertension, cardiovascular disease or CKD, higher urine EGF concentrations are associated with slower eGFR decline, whereas other kidney tubule biomarkers lacked a consistent association with kidney function decline.

Urine Biomarkers of Kidney Tubule Health and Risk of Incident CKD in Persons Without Diabetes: The ARIC, MESA, and REGARDS Studies

Rationale & Objective

Tubulointerstitial damage is a feature of early chronic kidney disease (CKD), but current clinical tests capture it poorly. Urine biomarkers of tubulointerstitial health may identify risk of CKD.

Study Design

Prospective cohort (Atherosclerosis Risk in Communities [ARIC]) and case-cohort (Multi-Ethnic Study of Atherosclerosis [MESA] and Reasons for Geographic and Racial Differences in Stroke [REGARDS]).

Setting & Participants

Adults with estimated glomerular filtration rate (eGFR) ≥60 mL/min/1.73 m2 and without diabetes in the ARIC, REGARDS, and MESA studies.

Exposures

Baseline urine monocyte chemoattractant protein-1 (MCP-1), alpha-1-microglobulin (α1m), kidney injury molecule-1, epidermal growth factor, and chitinase-3-like protein 1.

Outcome

Incident CKD or end-stage kidney disease.

Analytical Approach

Multivariable Cox proportional hazards regression for each cohort; meta-analysis of results from all 3 cohorts.

Results

872 ARIC participants (444 cases of incident CKD), 636 MESA participants (158 cases), and 924 REGARDS participants (488 cases) were sampled. Across cohorts, mean age ranged from 60 ± 10 to 63 ± 8 years, and baseline eGFR ranged from 88 ± 13 to 91 ± 14 mL/min/1.73 m2. In ARIC, higher concentrations of urine MCP-1, α1m, and kidney injury molecule-1 were associated with incident CKD. In MESA, higher concentration of urine MCP-1 and lower concentration of epidermal growth factor were each associated with incident CKD. In REGARDS, none of the biomarkers were associated with incident CKD. In meta-analysis of all 3 cohorts, each 2-fold increase α1m concentration was associated with incident CKD (HR, 1.19; 95% CI, 1.08-1.31).

Limitations

Observational design susceptible to confounding; competing risks during long follow-up period; meta-analysis limited to 3 cohorts.

Conclusions

In 3 combined cohorts of adults without prevalent CKD or diabetes, higher urine α1m concentration was independently associated with incident CKD. 4 biomarkers were associated with incident CKD in at least 1 of the cohorts when analyzed individually. Kidney tubule health markers might inform CKD risk independent of eGFR and albuminuria.

Association of high vibration perception threshold with reduced renal function in patients with type 2 diabetes

Objective

To investigate the correlation between vibration sensory threshold (VPT) and renal function, including glomerulus and renal tubule, in patients with type 2 diabetes mellitus (T2DM).

Methods

A total of 1274 patients with T2DM who were enrolled in the Department of Endocrinology of the First Affiliated Hospital of Fujian Medical University between January 2017 and June 2020 were included. Patients were grouped according to VPT levels and divided into three groups, including the normal VPT group (VPT<15V), the mild-moderate elevated VPT group (VPT15~25V), and the severely elevated VPT group (VPT≥25 V). Linear correlation analysis was used to analyze the correlation between VPT and renal functions, including glomerulus markers urine microalbumin (MA) and urinary immunoglobulin G (U-IgG), and renal tubule marker α1-microglobulin (α1-MG). Chronic kidney disease (CKD) was defined according to Kidney Disease Improving Global Outcomes (KDIGO) criteria. The binary logistic regression of the relation between VPT and CKD, eGFR<60 ml/min, and UACR >30 mg/g were expressed.

Results

In the mild-moderate and severely elevated VPT group, injury biomarkers of glomerulus (MA and U-IgG), renal tubule (α1-MG), and the incidence of CKD, eGFR<60 ml/min, and UACR > 30 mg/g were gradually increased compared with the normal VPT group. Furthermore, patients with diabetes and severely elevated VPT had significantly higher levels of MA (β=197.54, p=0.042) and α1-MG (β=11.69, p=0.023) compared to those with normal VPT. Also, patients with mild-moderate elevated VPT demonstrate significantly higher levels of MA (β=229.02, p=0.005). Patients in mild-moderate elevated VPT group (OR=1.463, 95% CI 1.005-2.127; OR=1.816, 95% CI 1.212-2.721) and severely elevated VPT group (OR=1.704, 95% CI 1.113-2.611; OR=2.027, 95% CI 1.248-3.294) are at a higher incidence of CKD and elevated levels of UACR>30mg/g compared to those in the VPT normal group. Moreover, the incidence of positive Upro was notably higher in the severely elevated VPT group (OR=1.738, 95% CI 1.182-2.556). However, this phenomenon was not observed in the incidence of eGFR <60 ml/min.

Conclusion

A higher VPT is positively associated with the incidence of CKD in patients with T2DM, particularly with elevated UACR. VPT may serve as a marker for glomerulus and renal tubule injury.

Mediation analysis of chronic kidney disease risk factors using kidney biomarkers in women living with HIV

OBJECTIVE

Novel urinary biomarkers reflecting kidney tubule health are associated with chronic kidney disease (CKD) risk in persons living with HIV. However, it is unknown whether these biomarkers provide mechanistic insight into the associations between clinical risk factors for CKD and subsequent CKD risk.

METHODS

Among 636 women living with HIV in the Women's Interagency HIV Study with estimated glomerular filtration rate (eGFR) >60 ml/min/1.73 m 2 , we used a counterfactual approach to causal mediation analysis to evaluate the extent to which systolic blood pressure (SBP), diastolic blood pressure (DBP), hemoglobin a1c (Hba1c) and serum albumin associations with incident CKD were mediated by eight urine proteins. These biomarkers reflect proximal tubular reabsorptive dysfunction (α1-microglobulin [a1m], β2-microglobulin, trefoil factor 3); tubular injury (interleukin 18 [IL-18], kidney injury molecule 1 [KIM-1]); kidney repair (epidermal growth factor); tubular reserve (uromodulin); and glomerular injury (urinary albumin). Incident CKD was defined as eGFR <60 ml/min/1.73 m 2 measured at two consecutive 6-month visits with an average annual eGFR decline ≥3% per year.

RESULTS

During a median follow-up of 7 years, 11% developed CKD. Urinary albumin and KIM-1 mediated 32% (95% CI: 13.4%, 76.6%) and 23% (6.9%, 60.7%) of the association between SBP and incident CKD, respectively; and 19% (5.1%, 42.3%) and 22% (8.1%, 45.7%) of the association between DBP and incident CKD, respectively. Urinary albumin, α1m, and IL-18 were significant mediators of the association between Hba1c and incident CKD. None of the eight biomarkers mediated the association between serum albumin and incident CKD.

CONCLUSIONS

Among women living with HIV, several urinary biomarkers reflecting distinct dimensions of kidney health may partially explain the associations between SBP, DBP, and Hba1c and subsequent CKD risk.

Association of urine biomarkers of kidney health with subclinical cardiovascular disease among men with and without HIV

OBJECTIVE

The aim of this study was to determine whether urine biomarkers of kidney health are associated with subclinical cardiovascular disease among men with and without HIV.

DESIGN

A cross-sectional study within the Multicenter AIDS Cohort Study (MACS) among 504 men with and without HIV infection who underwent cardiac computed tomography scans and had urine biomarkers measured within the preceding 2 years.

METHODS

Our primary predictors were four urine biomarkers of endothelial (albuminuria), proximal tubule dysfunction (alpha-1-microglobulin [A1 M] and injury (kidney injury molecule-1 [KIM-1]) and tubulointerstitial fibrosis (pro-collagen-III N-terminal peptide [PIIINP]). These were evaluated for association with coronary artery calcium (CAC) prevalence, CAC extent, total plaque score, and total segment stenosis using multivariable regression.

RESULTS

Of the 504 participants, 384 were men with HIV (MWH) and 120 were men without HIV. In models adjusted for sociodemographic factors, cardiovascular disease risk factors, eGFR, and HIV-related factors, each two-fold higher concentration of albuminuria was associated with a greater extent of CAC (1.35-fold higher, 95% confidence interval 1.11-1.65), and segment stenosis (1.08-fold greater, 95% confidence interval 1.01-1.16). Associations were similar between MWH and men without HIV in stratified analyses. The third quartile of A1 M showed an association with greater CAC extent, total plaque score, and total segment stenosis, compared with the lowest quartile.

CONCLUSION

Worse endothelial and proximal tubule dysfunction, as reflected by higher urine albumin and A1 M, were associated with greater CAC extent and coronary artery stenosis.

A novel multiplex biomarker panel for profiling human acute and chronic kidney disease

Acute and chronic kidney disease continues to confer significant morbidity and mortality in the clinical setting. Despite high prevalence of these conditions, few validated biomarkers exist to predict kidney dysfunction. In this study, we utilized a novel kidney multiplex panel to measure 21 proteins in plasma and urine to characterize the spectrum of biomarker profiles in kidney disease. Blood and urine samples were obtained from age-/sex-matched healthy control subjects (HC), critically-ill COVID-19 patients with acute kidney injury (AKI), and patients with chronic or end-stage kidney disease (CKD/ESKD). Biomarkers were measured with a kidney multiplex panel, and results analyzed with conventional statistics and machine learning. Correlations were examined between biomarkers and patient clinical and laboratory variables. Median AKI subject age was 65.5 (IQR 58.5-73.0) and median CKD/ESKD age was 65.0 (IQR 50.0-71.5). Of the CKD/ESKD patients, 76.1% were on hemodialysis, 14.3% of patients had kidney transplant, and 9.5% had CKD without kidney replacement therapy. In plasma, 19 proteins were significantly different in titer between the HC versus AKI versus CKD/ESKD groups, while NAG and RBP4 were unchanged. TIMP-1 (PPV 1.0, NPV 1.0), best distinguished AKI from HC, and TFF3 (PPV 0.99, NPV 0.89) best distinguished CKD/ESKD from HC. In urine, 18 proteins were significantly different between groups except Calbindin, Osteopontin and TIMP-1. Osteoactivin (PPV 0.95, NPV 0.95) best distinguished AKI from HC, and β2-microglobulin (PPV 0.96, NPV 0.78) best distinguished CKD/ESKD from HC. A variety of correlations were noted between patient variables and either plasma or urine biomarkers. Using a novel kidney multiplex biomarker panel, together with conventional statistics and machine learning, we identified unique biomarker profiles in the plasma and urine of patients with AKI and CKD/ESKD. We demonstrated correlations between biomarker profiles and patient clinical variables. Our exploratory study provides biomarker data for future hypothesis driven research on kidney disease.

Ambulatory urine biomarkers associations with acute kidney injury and hospitalization in people with HIV

BACKGROUND

People with HIV (PWH) generally have worse ambulatory levels of kidney injury biomarkers and excess risk of acute kidney injury (AKI) compared to persons without HIV. We evaluated whether ambulatory measures of subclinical kidney injury among PWH are associated with subsequent AKI.

METHODS

In the Predictors of Acute Renal Injury Study (PARIS), which enrolled 468 PWH from April 2016 to August 2019, we measured 10 urine biomarkers of kidney health (albumin, a1m, b2M, NGAL, IL18, KIM-1, EGF, UMOD, MCP-1, YKL40) at baseline and annually during follow-up. Using multivariable Cox regression models, we evaluated baseline and time-updated biomarker associations with the primary outcome of AKI (≥0.3 mg/dl or ≥1.5-times increase in serum creatinine from baseline) and secondary outcome of all-cause hospitalization.

RESULTS

At baseline, the mean age was 53 years old, and 45% self-identified as female. In time-updated models adjusting for sociodemographic factors, comorbidities, albuminuria, estimated glomerular filtration rate, and HIV-associated factors, higher KIM-1 [hazard ratio (HR) = 1.30 per twofold higher; 95% confidence interval (CI) 1.03-1.63] and NGAL concentrations (HR = 1.24, 95% CI 1.06-1.44) were associated with higher risk of hospitalized AKI. Additionally, in multivariable, time-updated models, higher levels of KIM-1 (HR = 1.19, 95% CI 1.00, 1.41), NGAL (HR = 1.13, 95% CI 1.01-1.26), and MCP-1 (HR = 1.20, 95% CI 1.00, 1.45) were associated with higher risk of hospitalization.

CONCLUSIONS

Urine biomarkers of kidney tubular injury, such as KIM-1 and NGAL, are strongly associated with AKI among PWH, and may hold potential for risk stratification of future AKI.

Protein Biomarkers in Chronic Kidney Disease in Children-What Do We Know So Far?

Chronic kidney disease (CKD) in children is a major concern of medical care and public health as it is related to high morbidity and mortality due to progression to end-stage kidney disease (ESKD). It is essential to identify patients with a risk of developing CKD to implement therapeutic interventions. Unfortunately, conventional markers of CKD, such as serum creatinine, glomerular filtration rate (GFR) and proteinuria, have many limitations in serving as an early and specific diagnostic tool for this condition. Despite the above, they are still the most frequently utilized as we do not have better. Studies from the last decade identified multiple CKD blood and urine protein biomarkers but mostly assessed the adult population. This article outlines some recent achievements and new perspectives in finding a set of protein biomarkers that might improve our ability to prognose CKD progression in children, monitor the response to treatment, or even become a potential therapeutic target.

Association of Kidney Tubule Biomarkers With Cardiac Structure and Function in the Multiethnic Study of Atherosclerosis

Markers of glomerular disease, estimated glomerular filtration rate (eGFR) and albuminuria, are associated with cardiac structural abnormalities and incident cardiovascular disease (CVD). We aimed to determine whether biomarkers of kidney tubule injury, function, and systemic inflammation are associated with cardiac structural abnormalities. Among 393 Multi-Ethnic Study of Atherosclerosis participants without diabetes, CVD, or chronic kidney disease, we assessed the association of 12 biomarkers of kidney tubule injury, function, and systemic inflammation with the left ventricular mass/volume ratio (LVmvr) and left ventricular ejection fraction (LVEF) on cardiac magnetic resonance imaging using linear regression. The average age was 60 ± 10 years; 48% were men; mean eGFR was 96±16 ml/min/1.73 m2; mean LVmvr was 0.93±0.18 g/ml, and mean LVEF was 62±6%. Each twofold greater concentration of plasma soluble urokinase plasminogen activator receptor was associated with a 0.04 g/ml (95% confidence interval [CI] 0.01 to 0.08 g/ml) higher LVmvr and 2.1% (95% CI 0.6 to 3.5%) lower LVEF, independent of risk factors for CVD, eGFR, and albuminuria. Each twofold greater plasma monocyte chemoattractant protein 1 was associated with higher LVmvr with a similar coefficient to that of plasma soluble urokinase plasminogen activator receptor. Each twofold greater concentration of plasma chitinase-3-like protein 1 and urine alpha-1-microglobulin was associated with a 1.1% (95% CI 0.4 to 1.7%) and 1.2% (95% CI 0.2 to 2.2%) lower LVEF, respectively. In conclusion, abnormal kidney tubule health may lead to cardiac dysfunction above and beyond eGFR and albuminuria.

HIV at 40: kidney disease in HIV treatment, prevention, and cure

Four decades after the first cases of HIV were reported, kidney disease remains an important comorbidity in people with HIV (PWH). Both HIV-associated nephropathy and immune complex kidney disease were recognized as complications of HIV infection in the early years before treatment was available. Although the introduction of effective antiretroviral therapy in the late 1990s resulted in dramatic improvements in survival and health in PWH, several commonly used antiretroviral agents have been associated with kidney injury. HIV infection and treatment may also promote the progression of comorbid chronic kidney disease due to traditional risk factors such as diabetes, and HIV is one of the strongest "second hits" for the high-risk APOL1 genotype. Unique considerations in the management of chronic kidney disease in PWH are largely related to the need for lifelong antiretroviral therapy, with potential for toxicity, drug-drug interactions, and polypharmacy. PWH who develop progressive chronic kidney disease are candidates for all modalities of kidney replacement therapy, including kidney transplantation, and at some centers, PWH may be candidates to serve as donors for recipients with HIV. Transplantation of kidney allografts from donors with HIV also offers a unique opportunity to study viral dynamics in the kidney, with implications for kidney health and for research toward HIV cure. In addition, HIV-transgenic animal models have provided important insights into kidney disease pathogenesis beyond HIV, and experience with HIV and HIV-related kidney disease has provided important lessons for future pandemics.

Diabetic Proteinuria Revisited: Updated Physiologic Perspectives

Albuminuria, a hallmark of diabetic nephropathy, reflects not only injury and dysfunction of the filtration apparatus, but is also affected by altered glomerular hemodynamics and hyperfiltration, as well as by the inability of renal tubular cells to fully retrieve filtered albumin. Albuminuria further plays a role in the progression of diabetic nephropathy, and the suppression of glomerular albumin leak is a key factor in its prevention. Although microalbuminuria is a classic manifestation of diabetic nephropathy, often progressing to macroalbuminuria or overt proteinuria over time, it does not always precede renal function loss in diabetes. The various components leading to diabetic albuminuria and their associations are herein reviewed, and the physiologic rationale and efficacy of therapeutic interventions that reduce glomerular hyperfiltration and proteinuria are discussed. With these perspectives, we propose that these measures should be initiated early, before microalbuminuria develops, as substantial renal injury may already be present in the absence of proteinuria. We further advocate that the inhibition of the renin–angiotensin axis or of sodium–glucose co-transport likely permits the administration of a normal recommended or even high-protein diet, highly desirable for sarcopenic diabetic patients.

Biomarkers of Kidney Tubule Disease and Risk of End-Stage Kidney Disease in Persons With Diabetes and CKD

Introduction

Tubulointerstitial damage in diabetes and chronic kidney disease (CKD) is poorly captured by estimated glomerular filtration rate (eGFR) and albuminuria. Urine biomarkers of kidney health may better elucidate disease progression in persons with diabetes and CKD.

Methods

Per case-cohort design, we randomly selected a subcohort of 560 study participants of the REasons for Geographic And Racial Differences in Stroke (REGARDS) study from 1092 adults with diabetes and baseline eGFR <60 ml/min per 1.73 m2 and registered a total of 161 end-stage kidney disease (ESKD) cases (n = 93 from the subcohort; n = 68 from outside the subcohort) during 4.3 ± 2.7 years mean follow-up. We measured urine biomarkers of kidney tubule injury (kidney injury molecule-1 [KIM-1]), inflammation and fibrosis (monocyte chemoattractant protein-1 [MCP-1]), repair (chitinase-3-like protein 1 [YKL-40]), and tubule function, including reabsorption (alpha-1-microglobulin [α1m]) and synthetic capacity (epidermal growth factor [EGF] and uromodulin [UMOD]). Weighted Cox regression models estimated ESKD risk adjusting for demographics, ESKD risk factors, and baseline eGFR and urine albumin. Least absolute shrinkage and selection operator (LASSO) regression identified a subset of biomarkers most strongly associated with ESKD.

Results

At baseline, subcohort participants had mean age of 70 ± 9 years, mean eGFR of 40 ±13 ml/min per 1.73 m2, and median urine albumin-to-creatinine ratio of 33 (interquartile range 10-213) mg/g. Adjusting for baseline eGFR and albuminuria, each 2-fold higher urine KIM-1 (hazard ratio = 1.43 [95% CI: 1.17-1.75]), α1m (hazard ratio = 1.47 [1.19-1.82]), and MCP-1 (hazard ratio = 1.27 [1.06-1.53]) were independently associated with ESKD. LASSO retained KIM-1 and α1m for associations with ESKD.

Conclusion

Among adults with diabetes and eGFR <60 ml/min per 1.73 m2, higher urine KIM-1, α1m, and MCP-1 are independently associated with incident ESKD, providing insight into kidney disease progression in persons with diabetes and CKD.

The Promise of Tubule Biomarkers in Kidney Disease: A Review

For over 70 years, serum creatinine has remained the primary index for detection and monitoring of kidney disease. Tubulointerstitial damage and fibrosis are highly prognostic for subsequent kidney failure in biopsy studies, yet this pathology is invisible to the clinician in the absence of a biopsy. Recent discovery of biomarkers that reflect distinct aspects of kidney tubule disease have led to investigations of whether these markers can provide additional information on risk of chronic kidney disease (CKD) progression and associated adverse clinical end points, above and beyond estimated glomerular filtration rate and albuminuria. These biomarkers can be loosely grouped into those that mark tubule cell injury (eg, kidney injury molecule 1, monocyte chemoattractant protein 1) and those that mark tubule cell dysfunction (eg, α1-microglobulin, uromodulin). These kidney tubule biomarkers provide new opportunities to monitor response to therapeutics used to treat CKD patients. In this review, we describe results from some unique contributions in this area and discuss the current challenges and requirements in the field to bring these markers to clinical practice. We advocate for a broader assessment of kidney health that moves beyond a focus on the glomerulus, and we highlight how such tools can improve diagnostic accuracy and earlier assessment of therapeutic efficacy or harm in CKD patients.

Urine Alpha-1-Microglobulin Levels and Acute Kidney Injury, Mortality, and Cardiovascular Events following Cardiac Surgery

INTRODUCTION

Urine alpha-1-microglobulin (Uα1m) elevations signal proximal tubule dysfunction. In ambulatory settings, higher Uα1m is associated with acute kidney injury (AKI), progressive chronic kidney disease (CKD), cardiovascular (CV) events, and mortality. We investigated the associations of pre- and postoperative Uα1m concentrations with adverse outcomes after cardiac surgery.

METHODS

In 1,464 adults undergoing cardiac surgery in the prospective multicenter Translational Research Investigating Biomarker Endpoints for Acute Kidney Injury (TRIBE-AKI) cohort, we measured the pre-and postoperative Uα1m concentrations and calculated the changes from pre- to postoperative concentrations. Outcomes were postoperative AKI during index hospitalization and longitudinal risks for CKD incidence and progression, CV events, and all-cause mortality after discharge. We analyzed Uα1m continuously and categorically by tertiles using multivariable logistic regression and Cox proportional hazards regression adjusted for demographics, surgery characteristics, comorbidities, baseline estimated glomerular filtration rate, urine albumin, and urine creatinine.

RESULTS

There were 230 AKI events during cardiac surgery hospitalization; during median 6.7 years of follow-up, there were 212 cases of incident CKD, 54 cases of CKD progression, 269 CV events, and 459 deaths. Each 2-fold higher concentration of preoperative Uα1m was independently associated with AKI (adjusted odds ratio [aOR] = 1.36, 95% confidence interval 1.14-1.62), CKD progression (adjusted hazard ratio [aHR] = 1.46, 1.04-2.05), and all-cause mortality (aHR = 1.19, 1.06-1.33) but not with incident CKD (aHR = 1.21, 0.96-1.51) or CV events (aHR = 1.01, 0.86-1.19). Postoperative Uα1m was not associated with AKI (aOR per 2-fold higher = 1.07, 0.93-1.22), CKD incidence (aHR = 0.90, 0.79-1.03) or progression (aHR = 0.79, 0.56-1.11), CV events (aHR = 1.06, 0.94-1.19), and mortality (aHR = 1.01, 0.92-1.11).

CONCLUSION

Preoperative Uα1m concentrations may identify patients at high risk of AKI and other adverse events after cardiac surgery, but postoperative Uα1m concentrations do not appear to be informative.

Plasma and Urine Biomarkers of CKD: A Review of Findings in the CKiD Study

Serum creatinine and level of proteinuria, as biomarkers of chronic kidney disease (CKD) progression, inadequately explain the variability of glomerular filtration rate decline, and are late markers of glomerular filtration rate decline. Recent studies have identified plasma and urine biomarkers at higher levels in children with CKD and also associate independently with CKD progression, even after adjustment for serum creatinine and proteinuria. These novel biomarkers represent diverse biologic pathways of tubular injury, tubular dysfunction, inflammation, and tubular health, and can be used as a liquid biopsy to better characterize CKD in children. In this review, we highlight the biomarker findings from the Chronic Kidney Disease in Children cohort, a large longitudinal study of children with CKD, and compare results with those from other pediatric CKD cohorts. The biomarkers in focus in this review include plasma kidney injury molecule-1, monocyte chemoattractant protein-1, fibroblast growth factor-23, tumor necrosis factor receptor-1, tumor necrosis factor receptor-2, soluble urokinase plasminogen activator receptor, and chitinase-3-like protein 1, as well as urine epidermal growth factor, α-1 microglobulin, kidney injury molecule-1, monocyte chemoattractant protein-1, and chitinase-3-like protein 1. Blood and urine biomarkers improve our ability to prognosticate CKD progression and may improve our understanding of CKD pathophysiology. Further research is required to establish how these biomarkers can be used in the clinical setting to improve the clinical management of CKD.

Associations of CKD risk factors and longitudinal changes in urine biomarkers of kidney tubules among women living with HIV

BACKGROUND

Novel urine biomarkers have enabled the characterization of kidney tubular dysfunction and injury among persons living with HIV, a population at an increased risk of kidney disease. Even though several urine biomarkers predict progressive kidney function decline, antiretroviral toxicity, and mortality in the setting of HIV infection, the relationships among the risk factors for chronic kidney disease (CKD) and urine biomarkers are unclear.

METHODS

We assessed traditional and infection-related CKD risk factors and measured 14 urine biomarkers at baseline and at follow-up among women living with HIV in the Women's Interagency Health Study (WIHS). We then used simultaneously adjusted multivariable linear regression models to evaluate the associations of CKD risk factors with longitudinal changes in biomarker levels.

RESULTS

Of the 647 women living with HIV in this analysis, the majority (67%) were Black, the median age was 45 years and median follow-up time was 2.5 years. Each traditional and infection-related CKD risk factor was associated with a unique set of changes in urine biomarkers. For example, baseline hemoglobin a1c was associated with worse tubular injury (higher interleukin [IL]-18), proximal tubular reabsorptive dysfunction (higher α1-microglobulin), tubular reserve (lower uromodulin) and immune response to injury (higher chitinase-3-like protein-1 [YKL-40]). Furthermore, increasing hemoglobin a1c at follow-up was associated with further worsening of tubular injury (higher kidney injury molecule-1 [KIM-1] and IL-18), as well as higher YKL-40. HCV co-infection was associated with worsening proximal tubular reabsorptive dysfunction (higher β2-microglobulin [β2m]), and higher YKL-40, whereas HIV viremia was associated with worsening markers of tubular and glomerular injury (higher KIM-1 and albuminuria, respectively).

CONCLUSIONS

CKD risk factors are associated with unique patterns of biomarker changes among women living with HIV, suggesting that serial measurements of multiple biomarkers may help in detecting and monitoring kidney disease in this setting.

Kidney tubule health scores and their associations with incident CKD in women living with HIV

OBJECTIVES

Individual kidney tubule biomarkers are associated with chronic kidney disease (CKD) risk in people living with HIV (PLWH). Whether a combination of kidney biomarkers can be integrated into informative summary scores for PLWH is unknown.

METHODS

We measured eight urine biomarkers of kidney tubule health at two visits over a 3-year period in 647 women living with HIV in the Women's Interagency Health Study. We integrated biomarkers into factor scores using exploratory factor analysis. We evaluated associations between CKD risk factors and factor scores, and used generalized estimating equations to determine associations between factor scores and risk of incident CKD.

RESULTS

Factor analysis identified two unique factor scores: a tubule reabsorption score comprising alpha-1-microglobulin, beta-2-microglobulin and trefoil factor-3; and a tubule injury score comprising interleukin-18 and kidney injury molecule-1. We modelled the two factor scores in combination with urine epidermal growth factor (EGF) and urine albumin. Predominantly HIV-related CKD risk factors were independently associated with worsening tubule reabsorption scores and tubule injury scores. During a median follow-up of 7 years, 9.7% (63/647) developed CKD. In multivariable time-updated models that adjusted for other factor scores and biomarkers simultaneously, higher tubule reabsorption scores [risk ratio (RR) = 1.27, 95% confidence interval (CI): 1.01-1.59 per 1 SD higher time-updated score], higher tubule injury scores (RR = 1.36, 95% CI: 1.05-1.76), lower urine EGF (RR = 0.75, 95% CI: 0.64-0.87), and higher urine albumin (RR = 1.20, 95% CI: 1.02-1.40) were jointly associated with risk of incident CKD.

CONCLUSIONS

We identified two novel and distinct dimensions of kidney tubule health that appear to quantify informative metrics of CKD risk in PLWH.

Urine Biomarkers of Kidney Tubule Health and Incident CKD Stage 3 in Women Living With HIV: A Repeated Measures Study

Rationale & Objective

Single measurements of urinary biomarkers reflecting kidney tubule health are associated with chronic kidney disease (CKD) risk in HIV infection, but the prognostic value of repeat measurements over time is unknown.

Study Design

Cohort study.

Setting & Participants

647 women living with HIV infection enrolled in the Women’s Interagency Health Study.

Exposures

14 urinary biomarkers of kidney tubule health measured at 2 visits over a 3-year period.

Outcome

Incident CKD, defined as estimated glomerular filtration rate (eGFR) < 60 mL/min/1.73 m² at two 6-month visits and an average eGFR decline ≥ 3% per year.

Analytical Approach

We used multivariable generalized estimating equations adjusting for CKD risk factors to evaluate baseline, time-updated, and change-over-time biomarker associations with incident CKD. We compared CKD discrimination between models with and without a parsimoniously selected set of biomarkers.

Results

During a median 7 years of follow-up, 9.7% (63/647) developed CKD. In multivariable-adjusted analyses, 3 of 14 baseline biomarkers associated with incident CKD. In contrast, 10 of 14 time-updated biomarkers and 9 of 14 biomarkers modeled as change over time associated with incident CKD. Urinary epidermal growth factor (EGF), α₁-microglobulin (A1M), and albumin were selected using penalized regression methods. In the time-updated model, lower urinary EGF (risk ratio [RR] per 2-fold higher time-updated biomarker levels, 0.69; 95% CI, 0.58-0.81), higher urinary A1M (RR, 1.47; 95% CI, 1.25-1.73), and higher urinary albumin excretion (RR, 1.21; 95% CI, 1.03-1.42) were jointly associated with increased risk for CKD. Compared with a base model (C statistic, 0.75), CKD discrimination improved after adding urinary EGF, A1M, and albumin values across baseline (C = 0.81), time-updated (C = 0.83), and change-over-time (C = 0.83) models (P < 0.01 for all).

Limitations

Observational design, incident CKD definition limited to eGFR.

Conclusions

Repeat urinary biomarker measurements for kidney tubule health have stronger associations with incident CKD compared with baseline measurements and moderately improve CKD discrimination in women living with HIV infection.

Kidney Diseases: The Age of Molecular Markers

Kidney diseases are conditions that increase the morbidity and mortality of those afflicted. Diagnosis of these conditions is based on parameters such as the glomerular filtration rate (GFR), measurement of serum and urinary creatinine levels and equations derived from these measurements (Wasung, Chawla, Madero. Clin Chim Acta 438:350-357, 2015). However, serum creatinine as a marker for measuring renal dysfunction has its limitations since it is altered in several other physiological situations, such as in patients with muscle loss, after intense physical exercise or in people on a high protein diet (Riley, Powers, Welch. Res Q Exerc Sport 52(3):339-347, 1981; Juraschek, Appel, Anderson, Miller. Am J Kidney Dis 61(4):547-554, 2013). Besides the fact that serum creatinine is a marker that indicates glomerular damage, it is necessary the discovery of new biomarkers that reflect not only glomerular damage but also tubular impairment. Recent advances in Molecular Biology have led to the generation or identification of new biomarkers for kidney diseases such as: Acute Kidney Failure (AKI), chronic kidney disease (CKD), nephritis or nephrotic syndrome. There are recent markers that have been used to aid in diagnosis and have been shown to be more sensitive and specific than classical markers, such as neutrophil gelatinase associated lipocalin (NGAL) or kidney injury molecule-1 (KIM-1) (Wasung, Chawla, Madero. Clin Chim Acta 438:350-357, 2015; George, Gounden. Adv Clin Chem 88:91-119, 2019; Han, Bailly, Abichandani, Thadhani, Bonventre. Kidney Int 62(1):237-244, 2002; Fontanilla, Han. Expert Opin Med Diagn 5(2):161-173, 2011). However, early diagnostic biomarkers are still necessary to assist the intervention and monitor of the progression of these conditions.

HCV cirrhotic patients treated with direct-acting antivirals: Detection of tubular dysfunction and resolution after viral clearance

BACKGROUND/AIMS

Hepatitis C virus (HCV) has been identified in tubular epithelial cells of infected patients; however, the presence of tubular dysfunction, which is a risk factor for chronic kidney disease (CKD), has never been examined in vivo. The present prospective longitudinal study aimed to estimate the prevalence of tubular dysfunction alone or with glomerular damage and its evolution after HCV clearance in cirrhotic patients.

METHODS

One hundred and thirty-five consecutive Child-Pugh A cirrhotic patients were evaluated before antiviral treatment and 6 months after the end of therapy. Tubular dysfunction was evaluated by urinary alpha1-microglobulin to creatinine ratio (α1-MCR), and glomerular damage was assessed by urinary albumin to creatinine ratio (ACR).

RESULTS

Almost all the patients (93.3%) showed a normal or mildly decreased e-GFR (KDIGO-G1/G2-categories). Tubular dysfunction was found in 23.7% (32/135) of patients, co-occurring with glomerular damage in 37.5% (12/32) of cases, while glomerular damage was found in 16.3% (22/135) of patients. In multiple logistic regression, glomerular damage and the concomitant presence of diabetes and hypertension were the only predictors significantly associated with tubular dysfunction. After HCV clearance, patients experienced a significant reduction of α1-MCR levels (21.0 vs 10.5 μg/mg, P = .009) and tubular dysfunction resolved in 57.1% of subjects.

CONCLUSIONS

Tubular dysfunction is an unrecognized feature of HCV-related kidney disease in cirrhotic patients and its presence should be primarily investigated in subjects with glomerular damage, diabetes and hypertension, despite normal e-GFR. Tubular dysfunction resolves in the majority of cases after HCV clearance; however, it may persist after antiviral treatment and further studies should evaluate its long-term impact on kidney function.

Prevalence of tubulopathy and association with renal function loss in HIV-infected patients

BACKGROUND

The incidence of chronic kidney disease (CKD) is 10 times higher in human immunodeficiency virus (HIV)-infected patients than in the general population. We explored the prevalence and determinants of proximal tubular dysfunction (PTD) in HIV-infected individuals, and assessed the impact of the tubulopathy on the estimated glomerular filtration rate (eGFR) outcome.

METHODS

A cohort study was performed on 694 outpatients followed in a French centre to analyse the prevalence of PTD, the diagnosis performance of screening tools and the associated factors. eGFR was prospectively evaluated to analyse the predictive value of the tubulopathy on eGFR decrease.

RESULTS

At inclusion, 14% of the patients presented with PTD and 5% with CKD. No individual tubular marker, including non-glomerular proteinuria, glycosuria dipstick or hypophosphataemia, registered sufficient performance to identify PTD. We found a significant interaction between tenofovir disoproxil fumarate exposure and ethnicity (P = 0.03) for tubulopathy risk. Tenofovir disoproxil fumarate exposure was associated with PTD in non-Africans [adjusted odds ratio (aOR) = 4.71, P < 10-3], but not in patients of sub-Saharan African origin (aOR = 1.17, P = 0.73). Among the 601 patients followed during a median of 4.3 years, 13% experienced an accelerated eGFR decline. Unlike microalbuminuria and glomerular proteinuria, tubulopathy was not associated with accelerated eGFR decline.

CONCLUSION

PTD is not rare in HIV-infected individuals but is less frequent in sub-Saharan African patients and is associated with tenofovir disoproxil fumarate exposure only in non-Africans. Its diagnosis requires multiple biochemical testing and it is not associated with an accelerated eGFR decline.

The utility of kidney injury molecule-1 as an early biomarker of kidney injury in people living with HIV

There are increasing reports of antiretroviral therapy (ART) drug-related kidney dysfunction. Traditional markers of kidney dysfunction such as urine protein/creatinine ratio and estimated glomerular filtration rate (eGFR) have thus far proven ineffective at detecting some sub-clinical forms of ART-related kidney injury. This is a cross-sectional examination of 114 people living with HIV (PLWH), either naïve (N =104) or treatment experienced (N =10). Urinary kidney injury molecule-1 (KIM-1 ng/mg) thresholds were estimated using electrochemiluminescent assays from stored urine samples and normalised for urinary creatinine excretion (KIM-1/Cr). Correlation coefficients and predictors of kidney tubular injury were compared and derived for both adjusted and unadjusted urinary KIM-1/CR (ng/mg). In PLWH (both ART-naïve and treatment experienced) had a higher baseline unadjusted and adjusted median (≥3.7 ng/mg) and upper tertile (≥6.25 ng/mg) urinary KIM-1/Cr levels compared to either non-normal volunteers (0.39 ng/mg) or those with acute kidney injury in the general population (0.57 ng/mg). When upper tertile KIM-1/Cr (≥6.25 ng/mg) was utilised as a marker of kidney injury, eGFR (ml/min/1.73 m²), white Caucasian ethnicity, and protease inhibitor exposure were significantly associated with increased risk of kidney injury in multivariate analyses (odds ratio 0.91, confidence interval [CI] 0.68–0.98, P = 0.02; odds ratio 8.9, CI 1.6–48.6, p = 0.01; and odds ratio 0.05, CI 0.03–0.9, p =0.04, respectively). We found a significant degree of sub-clinical kidney injury (high unadjusted and adjusted KIM-1/Cr) in PLWH with normal kidney function (eGFR ≥60 ml/min/1.73 m²). We also found a higher baseline KIM-1/Cr (ng/mg) in our study cohort than reported both in normal volunteers and patients with kidney injury in the general population.

Tubular Biomarkers and Chronic Kidney Disease Progression in SPRINT Participants

BACKGROUND

Kidney tubular atrophy on biopsy is a strong predictor of chronic kidney disease (CKD) progression, but tubular health is poorly quantified by traditional measures including estimated glomerular filtration rate (eGFR) and albuminuria. We hypothesized that urinary biomarkers of impaired tubule function would be associated with faster eGFR declines in persons with CKD.

METHODS

We measured baseline urine concentrations of uromodulin, β2-microglobulin (β2m), and α1-microglobulin (α1m) among 2,428 participants of the Systolic Blood Pressure Intervention Trial with an eGFR <60 mL/min/1.73 m2. We used linear mixed models to evaluate biomarker associations with annualized relative change in eGFR, stratified by randomization arm.

RESULTS

At baseline, the mean age was 73 ± 9 years and eGFR was 46 ± 11 mL/min/1.73 m2. In the standard blood pressure treatment arm, each 2-fold higher urinary uromodulin was associated with slower % annual eGFR decline (0.34 [95% CI: 0.08, 0.60]), whereas higher urinary β2m was associated with faster % annual eGFR decline (-0.10 [95% CI: -0.18, -0.02]) in multivariable-adjusted models including baseline eGFR and albuminuria. Associations were weaker and did not reach statistical significance in the intensive blood pressure treatment arm for either uromodulin (0.11 [-0.13, 0.35], p value for interaction by treatment arm = 0.045) or β2m (-0.01 [-0.08, 0.08], p value for interaction = 0.001). Urinary α1m was not independently associated with eGFR decline in the standard (0.01 [-0.22, 0.23]) or intensive (0.03 [-0.20, 0.25]) arm.

CONCLUSIONS

Among trial participants with hypertension and CKD, baseline measures of tubular function were associated with subsequent declines in kidney function, although these associations were diminished by intensive blood pressure control.

Is Tubular Dysfunction a Risk Factor for AKI?

Tubular functions are critical for homeostasis maintenance. However, tubular function markers are not typically assessed in routine clinical care. Recent research by our group has revealed that tubular dysfunction at baseline is a risk factor for subsequent acute kidney injury (AKI), independent of estimated glomerular filtration rate and albuminuria. Here, we describe the underlying hypotheses and biological insights and contrast the changes in tubule function versus injury both before and after an AKI episode.

Biomarkers of Acute and Chronic Kidney Disease

The current unidimensional paradigm of kidney disease detection is incompatible with the complexity and heterogeneity of renal pathology. The diagnosis of kidney disease has largely focused on glomerular filtration, while assessment of kidney tubular health has notably been absent. Following insult, the kidney tubular cells undergo a cascade of cellular responses that result in the production and accumulation of low-molecular-weight proteins in the urine and systemic circulation. Modern advancements in molecular analysis and proteomics have allowed the identification and quantification of these proteins as biomarkers for assessing and characterizing kidney diseases. In this review, we highlight promising biomarkers of kidney tubular health that have strong underpinnings in the pathophysiology of kidney disease. These biomarkers have been applied to various specific clinical settings from the spectrum of acute to chronic kidney diseases, demonstrating the potential to improve patient care.

Association of Statin Use With Kidney Damage and Function Among HIV-Infected Men

BACKGROUND

Chronic kidney disease (CKD) occurs commonly among HIV-infected persons. Statins may delay CKD onset and progression through their cholesterol-lowering and pleiotropic effects.

METHODS

Among 850 HIV-infected men from the Multicenter AIDS Cohort Study with stored urine samples (2009-2011), we evaluated cross-sectional associations of statin use with urine biomarkers of kidney damage [albumin-to-creatinine ratio (ACR), alpha-1-microglobulin, interleukin-18, kidney injury molecule-1, and procollagen type III N-terminal propeptide] using multivariable linear regression. We evaluated the longitudinal associations of statin use with annual change in estimated glomerular filtration rate by creatinine (eGFR) using linear mixed models, and with incident proteinuria and incident CKD (eGFR <60 mL/min/1.73 m) using Cox proportional hazards regression. We used inverse probability weighting to address potential confounding related to statin use.

RESULTS

Statin users comprised 30% of participants. In adjusted analyses, each year of cumulative statin use was associated with 4.0% higher baseline ACR levels (P = 0.05), but there was no association with baseline levels of other urine biomarkers. Statin use had no overall association with annual eGFR decline. Among participants with baseline proteinuria, statin use was modestly associated with slower annual eGFR decline compared to non-use (adjusted difference: 1.33 mL/min/1.73 m per year; 95% confidence interval: -0.07 to 2.70). Statin use was not associated with risk of incident proteinuria or incident CKD.

CONCLUSIONS

Statin use was associated with higher baseline ACR, but not with biomarkers of tubulointerstitial injury. Statin use was associated with modestly slower eGFR decline only among participants with baseline proteinuria. Although these findings may be susceptible to confounding by indication, they suggest a limited effect of statins on CKD risk among HIV-infected men.

Markers of kidney tubule function and risk of cardiovascular disease events and mortality in the SPRINT trial

AIMS

Biomarkers of kidney tubule injury, inflammation and fibrosis have been studied extensively and established as risk markers of adverse kidney and cardiovascular disease (CVD) outcomes. However, associations of markers of kidney tubular function with adverse clinical events have not been well studied, especially in persons with chronic kidney disease (CKD).

METHODS AND RESULTS

Using a sample of 2377 persons with CKD at the baseline Systolic Blood Pressure Intervention Trial (SPRINT) visit, we evaluated the association of three urine tubular function markers, alpha-1 microglobulin (α1m), beta-2 microglobulin (β2m), and uromodulin, with a composite CVD endpoint (myocardial infarction, acute coronary syndrome, stroke, acute decompensated heart failure, or death from cardiovascular causes) and mortality using Cox proportional hazards regression, adjusted for baseline estimated glomerular filtration rate (eGFR), albuminuria, and CVD risk factors. In unadjusted analysis, over a median follow-up of 3.8 years, α1m and β2m had positive associations with composite CVD events and mortality, whereas uromodulin had an inverse association with risk for both outcomes. In multivariable analysis including eGFR and albuminuria, a two-fold higher baseline concentration of α1m was associated with higher risk of CVD [hazard ratio (HR) 1.25; 95% confidence interval (CI): 1.10-1.45] and mortality (HR 1.25; 95% CI: 1.10-1.46), whereas β2m had no association with either outcome. A two-fold higher uromodulin concentration was associated with lower CVD risk (HR 0.79; 95% CI: 0.68-0.90) but not mortality (HR 0.86; 95% CI: 0.73-1.01) after adjusting for similar confounders.

CONCLUSION

Among non-diabetic persons with CKD, biomarkers of tubular function are associated with CVD events and mortality independent of glomerular function and albuminuria.

Associations of Urine Biomarkers with Kidney Function Decline in HIV-Infected and Uninfected Men

BACKGROUND

HIV-infected (HIV+) persons are at increased risk of chronic kidney disease, but serum creatinine does not detect early losses in kidney function. We hypothesized that urine biomarkers of kidney damage would be associated with subsequent changes in kidney function in a contemporary cohort of HIV+ and HIV-uninfected (HIV-) men.

METHODS

In the Multicenter AIDS Cohort Study, we measured baseline urine concentrations of 5 biomarkers from 2009 to 2011 in 860 HIV+ and 337 HIV- men: albumin, alpha-1-microglobulin (α1m), interleukin-18 (IL-18), kidney injury molecule-1 (KIM-1), and procollagen type III N-terminal propeptide (PIIINP). We evaluated associations of urine biomarker concentrations with annual changes in estimated glomerular filtration rate (eGFR) using multivariable linear mixed models adjusted for demographics, traditional kidney disease risk factors, HIV-related risk factors, and baseline eGFR.

RESULTS

Over a median follow-up of 4.8 years, the average annual eGFR decline was 1.42 mL/min/1.73 m2/year in HIV+ men and 1.22 mL/min/1.73 m2/year in HIV- men. Among HIV+ men, the highest vs. lowest tertiles of albumin (-1.78 mL/min/1.73 m2/year, 95% CI -3.47 to -0.09) and α1m (-2.43 mL/min/1.73 m2/year, 95% CI -4.14 to -0.73) were each associated with faster annual eGFR declines after multivariable adjustment. Among HIV- men, the highest vs. lowest tertile of α1m (-2.49 mL/min/1.73 m2/year, 95% CI -4.48 to -0.50) was independently associated with faster annual eGFR decline. Urine IL-18, KIM-1, and PIIINP showed no independent associations with eGFR decline, regardless of HIV serostatus.

CONCLUSIONS

Among HIV+ men, higher urine albumin and α1m are associated with subsequent declines in kidney function, independent of eGFR.

The SPRINT trial suggests that markers of tubule cell function in the urine associate with risk of subsequent acute kidney injury while injury markers elevate after the injury

Urine markers can quantify tubular function including reabsorption (α-1 microglobulin [α1m]) and β-2-microglobulin [β2m]) and protein synthesis (uromodulin). Individuals with tubular dysfunction may be less able to compensate to insults than those without, despite similar estimated glomerular filtration rate (eGFR) and albuminuria. Among Systolic Blood Pressure Intervention Trial (SPRINT) participants with an eGFR under 60 ml/min/1.73m2, we measured urine markers of tubular function and injury (neutrophil gelatinase-associated lipocalin [NGAL], kidney injury molecule-1 [KIM-1], interleukin-18 [IL-18], monocyte chemoattractant protein-1, and chitinase-3-like protein [YKL-40]) at baseline. Cox models evaluated associations with subsequent acute kidney injury (AKI) risk, adjusting for clinical risk factors, baseline eGFR and albuminuria, and the tubular function and injury markers. In a random subset, we remeasured biomarkers after four years, and compared changes in biomarkers in those with and without intervening AKI. Among 2351 participants, 184 experienced AKI during 3.8 years mean follow-up. Lower uromodulin (hazard ratio per two-fold higher (0.68, 95% confidence interval [0.56, 0.83]) and higher α1m (1.20; [1.01, 1.44]) were associated with subsequent AKI, independent of eGFR and albuminuria. None of the five injury markers were associated with eventual AKI. In the random subset of 947 patients with repeated measurements, the 59 patients with intervening AKI versus without had longitudinal increases in urine NGAL, IL-19, and YKL-40 and only 1 marker of tubule function (α1m). Thus, joint evaluation of tubule function and injury provided novel insights to factors predisposing to AKI, and responses to kidney injury.

Pre-exposure Prophylaxis With Tenofovir Disoproxil Fumarate/Emtricitabine and Kidney Tubular Dysfunction in HIV-Uninfected Individuals

BACKGROUND

Pre-exposure prophylaxis (PrEP) with tenofovir disoproxil fumarate (TDF) and emtricitabine (FTC) is becoming increasingly adopted for HIV prevention. Tenofovir can cause proximal tubular damage and chronic kidney disease in HIV-infected persons, but little is known regarding its nephrotoxic potential among HIV-uninfected persons. In this study, we evaluated the effects of PrEP on urine levels of the following: α1-microglobulin (α1m), a marker of impaired tubular reabsorption; albuminuria, a measure of glomerular injury; and total proteinuria.

SETTING

The Iniciativa Profilaxis Pre-Exposicion (iPrEx) study randomized HIV-seronegative men and transgender women who have sex with men to oral TDF/FTC or placebo. The iPrEx open-label extension (iPrEx-OLE) study enrolled former PrEP trial participants to receive open-label TDF/FTC.

METHODS

A cross-sectional analysis compared urine biomarker levels by study arm in iPrEx (N = 100 treatment arm, N = 100 placebo arm). Then, urine biomarker levels were compared before and after PrEP initiation in 109 participants of iPrEx-OLE.

RESULTS

In iPrEx, there were no significant differences in urine α1m, albuminuria, or proteinuria by treatment arm. In iPrEx-OLE, after 24 weeks on PrEP, urine α1m and proteinuria increased by 21% [95% confidence interval (CI): 10 to 33] and 18% (95% CI: 8 to 28), respectively. The prevalence of detectable α1m increased from 44% to 65% (P < 0.001) and estimated glomerular filtration rate declined by 4 mL/min/1.73 m (P < 0.001). There was no significant change in albuminuria (6%; 95% CI: -7% to 20%).

CONCLUSION

PrEP with TDF/FTC was associated with a statistically significant rise in urine α1m and proteinuria after 6 months, suggesting that PrEP may result in subclinical tubule dysfunction.

Kidney disease risk factors associate with urine biomarkers concentrations in HIV-positive persons; a cross-sectional study

Background

HIV-positive persons bear an excess burden of chronic kidney disease (CKD); however, conventional methods to assess kidney health are insensitive and non-specific for detecting early kidney injury. Urinary biomarkers can detect early kidney injury, and may help mitigate the risk of overt CKD.

Methods

Cross-sectional study of HIV-positive persons in the Multicenter AIDS Cohort Study and the Women’s Interagency HIV Study. We measured levels of 14 biomarkers, capturing multiple dimensions of kidney injury. We then evaluated associations of known CKD risk factors with urine biomarkers using separate multivariable adjusted models for each biomarker.

Results

Of the 198 participants, one third were on HAART and virally suppressed. The vast majority (95%) had preserved kidney function as assessed by serum creatinine, with a median eGFR of 103 ml/min/1.73 m² (interquartile range (IQR): 88, 116). In our multivariable analyses, the associations of each CKD risk factor with urinary biomarker levels varied in magnitude. For example, HIV viral load was predominantly associated with elevations in interleukin(IL)-18, and albuminuria, while higher CD4 levels were associated with lower monocyte chemoattractant protein-1 (MCP-1) and β2-microglobulin. In contrast, older age was significantly associated with elevations in α1-microglobulin, kidney injury marker-1, clusterin, MCP-1, and chitinase-3-like protein-1 levels, as well as lower epidermal growth factor, and uromodulin levels.

Conclusions

Among HIV-positive persons, CKD risk factors are associated with unique and heterogeneous patterns of changes in urine biomarkers levels. Additional work is needed to develop parsimonious algorithms that integrate multiple biomarkers and clinical data to discern the risk of overt CKD and its progression.

Electronic supplementary material

The online version of this article (10.1186/s12882-018-1192-y) contains supplementary material, which is available to authorized users.

Effects of Intensive Blood Pressure Lowering on Kidney Tubule Injury in CKD: A Longitudinal Subgroup Analysis in SPRINT

BACKGROUND

Random assignment to the intensive systolic blood pressure (SBP) arm (<120mmHg) in the Systolic Blood Pressure Intervention Trial (SPRINT) resulted in more rapid declines in estimated glomerular filtration rates (eGFRs) than in the standard arm (SBP<140mmHg). Whether this change reflects hemodynamic effects or accelerated intrinsic kidney damage is unknown.

STUDY DESIGN

Longitudinal subgroup analysis of clinical trial participants.

SETTINGS & PARTICIPANTS

Random sample of SPRINT participants with prevalent chronic kidney disease (CKD) defined as eGFR<60mL/min/1.73m² by the CKD-EPI (CKD Epidemiology Collaboration) creatinine-cystatin C equation at baseline.

OUTCOMES & MEASUREMENTS

Urine biomarkers of tubule function (β₂-microglobulin [B2M], α₁-microglobulin [A1M]), and uromodulin), injury (interleukin 18, kidney injury molecule 1, and neutrophil gelatinase-associated lipocalin), inflammation (monocyte chemoattractant protein 1), and repair (human cartilage glycoprotein 40) at baseline, year 1, and year 4. Biomarkers were indexed to urine creatinine concentration and changes between arms were evaluated using mixed-effects linear models and an intention-to-treat approach.

RESULTS

978 SPRINT participants (519 in the intensive and 459 in the standard arm) with prevalent CKD were included. Mean age was 72±9 years and eGFR was 46.1±9.4mL/min/1.73m² at baseline. Clinical characteristics, eGFR, urinary albumin-creatinine ratio, and all 8 biomarker values were similar across arms at baseline. Compared to the standard arm, eGFR was lower by 2.9 and 3.3mL/min/1.73m² in the intensive arm at year 1 and year 4. None of the 8 tubule marker levels was higher in the intensive arm compared to the standard arm at year 1 or year 4. Two tubule function markers (B2M and A1M) were 29% (95% CI, 10%-43%) and 24% (95% CI, 10%-36%) lower at year 1 in the intensive versus standard arm, respectively.

LIMITATIONS

Exclusion of persons with diabetes, and few participants had advanced CKD.

CONCLUSIONS

Among participants with CKD in SPRINT, random assignment to the intensive SBP arm did not increase any levels of 8 urine biomarkers of tubule cell damage despite loss of eGFR. These findings support the hypothesis that eGFR declines in the intensive arm of SPRINT predominantly reflect hemodynamic changes rather than intrinsic damage to kidney tubule cells.

Urinary Biomarkers of Kidney Tubular Damage and Risk of Cardiovascular Disease and Mortality in Elders

RATIONALE & OBJECTIVE

Novel urinary biomarkers have enabled earlier detection of kidney tubular damage, but their prognostic value for adverse cardiovascular outcomes is uncertain. We hypothesized that tubular damage, measured by urine α₁-microglobulin (A1M), amino-terminal propeptide of type III procollagen (PIIINP), and neutrophil gelatinase-associated lipocalin (NGAL), would be associated with higher risks for cardiovascular events and mortality among elders.

STUDY DESIGN

Case-cohort study.

SETTING & PARTICIPANTS

This study included a randomly selected subcohort (n=502), cardiovascular disease (CVD) cases (n=245), and heart failure cases (n=220) from the Health, Aging, and Body Composition (Health ABC) Study.

PREDICTORS

Baseline urine A1M, PIIINP, and NGAL concentrations.

OUTCOMES

Incident CVD, heart failure, and all-cause mortality.

ANALYTICAL APPROACH

Cox proportional hazards models were used to evaluate biomarker associations with each outcome.

RESULTS

At baseline, mean age was 74 years and estimated glomerular filtration rate was 73mL/min/1.73m². After adjustment for demographics, estimated glomerular filtration rate, albumin-creatinine ratio, and other cardiovascular risk factors, each doubling in biomarker concentration was associated with the following adjusted HRs for CVD: A1M, 1.51 (95% CI, 1.16-1.96); PIIINP, 1.21 (95% CI, 1.00-1.46); and NGAL, 1.12 (95% CI, 1.05-1.20). There were 248 deaths in the subcohort during a median follow-up of 12.4 years. Adjusted associations of each biomarker (HR per doubling) with all-cause mortality were: A1M, 1.29 (95% CI, 1.10-1.51); PIIINP, 1.05 (95%, 0.94-1.18); and NGAL, 1.07 (95% CI, 1.02-1.12). Biomarker concentrations did not have statistically significant associations with heart failure after multivariable adjustment.

LIMITATIONS

Urine biomarkers were measured at a single time point; no validation cohort available.

CONCLUSIONS

Kidney tubular damage is an independent risk factor for CVD and death among elders. Future studies should investigate mechanisms by which kidney tubular damage may adversely affect cardiovascular risk.

Changes in Kidney Function Associated With Daily Tenofovir Disoproxil Fumarate/Emtricitabine for HIV Preexposure Prophylaxis Use in the United States Demonstration Project

BACKGROUND

HIV preexposure prophylaxis (PrEP) using daily oral tenofovir-disoproxil-fumarate/emtricitabine (TDF/FTC) is effective for preventing HIV acquisition, but concerns remain about its potential kidney toxicity. This study examined kidney function in individuals using PrEP in real-world clinical settings.

SETTING

Demonstration project in 2 sexually transmitted infection clinics and a community health center.

METHODS

We evaluated kidney function among men who have sex with men and transgender women taking tenofovir-disoproxil-fumarate/emtricitabine PrEP for up to 48 weeks. Serum creatinine and urine dipstick for protein were obtained at 12-week intervals. Kidney function was estimated using creatinine clearance (CrCl) (Cockcroft-Gault) and estimated glomerular filtration rate (eGFR) (CKD-EPI).

RESULTS

From October 2012 to January 2014, we enrolled 557 participants (median age 33). Mean creatinine increased from baseline to week 12 by 0.03 mg/dL (4.6%) (P < 0.0001); mean CrCl decreased by 4.8 mL/min (3.0%) (P < 0.0001). These changes remained stable through week 48 (P = 0.81, P = 0.71 respectively). There were 75/478 (15.7%) participants who developed worsening proteinuria at week 12 compared with baseline (P < 0.0001), and this percent remained stable through week 48 (P = 0.73). Twenty-five participants (5.1%) developed new-onset eGFR <70 mL/min/1.73 m; independent predictors of this outcome were age ≥40 years (OR 3.79, 95% CI: 1.43 to 10.03) and baseline eGFR <90 mL/min/1.73 m (OR 9.59, 3.69-24.94).

CONCLUSIONS

In a demonstration setting, daily tenofovir-disoproxil-fumarate/emtricitabine PrEP leads to reduced CrCl and eGFR; however, these eGFR changes are based on very small changes in serum creatinine and seem to be nonprogressive after the first 12 weeks. Future studies are needed to understand the prognostic significance of these small changes.

Association Between Urinary Alpha1-Microglobulin Levels and Nonalcoholic Fatty Liver Disease: A Cross-Sectional Study

BACKGROUND

We aimed to explore the association between urinary alpha1-microglobulin (A1M) levels and nonalcoholic fatty liver disease (NAFLD) in a Chinese population.

STUDY

We performed a cross-sectional study among 2,215 Chinese who attended their annual health examination at First Affiliated Hospital, College of Medicine, Zhejiang University. Urinary A1M-creatinine ratio and other clinical and laboratory parameters were measured.

RESULTS

A total of 20.9% of subjects fulfilled the diagnostic criteria of NAFLD. NAFLD subjects had significantly higher urinary A1M-creatinine ratios. These levels were positively associated with NAFLD prevalence. The association between A1M-creatinine ratio and NAFLD was independent of hyperglycemia status. Stepwise regression showed that urinary A1M-creatinine ratio was significantly associated with the risk for NAFLD. Urinary A1M-creatinine ratio was an independent factor predicting advanced fibrosis (FIB-4 ≥1.3) in NAFLD patients.

CONCLUSIONS

Our results showed a significant association between urinary A1M-creatinine ratio and NAFLD.

Kidney Disease in HIV: Moving beyond HIV-Associated Nephropathy

In developed countries, remarkable advances in antiretroviral therapy have transformed HIV infection into a chronic condition. As a result, HIV-associated nephropathy, the classic HIV-driven kidney lesion among individuals of African descent, has largely disappeared in these regions. However, HIV-positive blacks continue to have much higher rates of ESRD than HIV-positive whites, which could be attributed to the APOL1 renal risk variants. Additionally, HIV-positive individuals face adverse consequences beyond HIV itself, including traditional risk factors for CKD and nephrotoxic effects of antiretroviral therapy. Concerns for nephrotoxicity also extend to HIV-negative individuals using tenofovir disoproxil fumarate-based pre-exposure prophylaxis for the prevention of HIV infection. Therefore, CKD remains an important comorbid condition in the HIV-positive population and an emerging concern among HIV-negative persons receiving pre-exposure prophylaxis. With the improved longevity of HIV-positive individuals, a kidney transplant has become a viable option for many who have progressed to ESRD. Herein, we review the growing knowledge regarding the APOL1 renal risk variants in the context of HIV infection, antiretroviral therapy-related nephrotoxicity, and developments in kidney transplantation among HIV-positive individuals.

Diagnostic challenges of kidney diseases in HIV-infected patients

INTRODUCTION

Chronic kidney disease (CKD) is a prevalent comorbidity in persons living with HIV infection (PLWH) associated with an increase in cardiovascular morbidity and all-cause mortality. Furthermore, early diagnosis of CKD is difficult in PLWH. Areas covered: We reviewed the main diagnostic tools for CKD in PLWH, and discussed their strengths and limits. We performed a literature search on PubMed to identify reviews and clinical trials dealing with attractive kidney biomarkers of CKD in PLWH, with the following key words: 'HIV AND kidney', 'HIV AND Kidney biomarkers', 'CKD AND Kidney biomarkers'. Expert commentary: Currently, CKD diagnosis is based on the estimation of Glomerular Filtration Rate (GFR), and measurement of proteinuria by urine protein/creatinine ratio (uPCR). These parameters are independent and complementary predictors of outcomes. GFR estimates are lacking in accuracy in PLWH. The best GFR estimate is CKD-EPI study equation. Moreover, low-grade proteinuria is associated with an increased risk of kidney disease progression in PLWH, and guidelines derived from the general population may lack sensitivity. Different biomarkers of kidney diseases like N-acetyl beta glucosaminidase (NAG), Kidney Injury Molecule-1 (KIM-1), and Alpha-1-microglobulin may predict kidney disease progression and mortality in PLWH. Others may help clinicians detect antiretroviral-induced tubulopathy, or predict cardiovascular events. More studies are needed to validate the routine use of these types of biomarkers.

Changes in Urinary Biomarkers Over 10 Years Is Associated With Viral Suppression in a Prospective Cohort of Women Living With HIV

BACKGROUND

Urine biomarkers have helped identify persons at risk for progressing to kidney disease in the setting of HIV infection. We explored factors associated with changes in 3 urine biomarkers over 10 years among women living with HIV.

METHODS

Prospective cohort of 294 HIV-infected women from the multicenter Women's Interagency HIV Study. Predictors included HIV viral and immunological parameters, comorbid conditions, and health-related behaviors. Outcomes were patterns of changes of urine interleukin-18 (IL-18), albumin-to-creatinine ratio (ACR), and alpha-1-microglobulin (α1m) over 10 years. We used quantile regression to examine patterns of change in each urine biomarker during follow-up and multivariable analysis of variance regression to identify predictors of biomarker changes.

RESULTS

Over 10 years, the median concentrations of IL-18 declined from 120 to 64 pg/mL, α1m rose from 0.7 to 1.5 ng/mL, and ACR remained stable (9-8 mg/g). In multivariate analyses, the strongest predictors of increases in IL-18 were higher baseline body mass index, increase in waist circumference, higher follow-up HIV viral load, lower follow-up CD4 cell count, hepatitis C virus (HCV) coinfection, and higher follow-up high density lipoprotein cholesterol. Predictors of increasing concentration of α1m were lower CD4 cell counts, higher diastolic blood pressure, HCV coinfection, and smoking. Finally, determinants of ACR increases during follow-up were higher follow-up diastolic blood pressure, HCV coinfection, higher follow-up HIV viral load, and triglyceride concentration.

CONCLUSIONS

Over 10 years, HIV disease status had different associations with each urine biomarker under study. Overall, the associations with changes in each biomarker support research into their use for longitudinal monitoring of kidney health.

Urine Fibrosis Markers and Risk of Allograft Failure in Kidney Transplant Recipients: A Case-Cohort Ancillary Study of the FAVORIT Trial

BACKGROUND

Kidney tubulointerstitial fibrosis marks risk for allograft failure in kidney transplant recipients, but is poorly captured by estimated glomerular filtration rate (eGFR) or urine albumin-creatinine ratio (ACR). Whether urinary markers of tubulointerstitial fibrosis can noninvasively identify risk for allograft failure above and beyond eGFR and ACR is unknown.

STUDY DESIGN

Case-cohort study.

SETTING & PARTICIPANTS

The FAVORIT (Folic Acid for Vascular Outcome Reduction in Transplantation) Trial was a randomized double-blind trial testing vitamin therapy to lower homocysteine levels in stable kidney transplant recipients. We selected a subset of participants at random (n=491) and all individuals with allograft failure during follow-up (cases; n=257).

PREDICTOR

Using spot urine specimens from the baseline visit, we measured 4 urinary proteins known to correlate with tubulointerstitial fibrosis on biopsy (urine α1-microglobulin [A1M], monocyte chemoattractant protein 1 [MCP-1], and procollagen type III and type I amino-terminal amino pro-peptide).

OUTCOME

Death-censored allograft failure.

RESULTS

In models adjusted for demographics, chronic kidney disease risk factors, eGFR, and ACR, higher concentrations of urine A1M (HR per doubling, 1.73; 95% CI, 1.43-2.08) and MCP-1 (HR per doubling, 1.60; 95% CI, 1.32-1.93) were strongly associated with allograft failure. When additionally adjusted for concentrations of other urine fibrosis and several urine injury markers, urine A1M (HR per doubling, 1.76; 95% CI, 1.27-2.44]) and MCP-1 levels (HR per doubling, 1.49; 95% CI, 1.17-1.89) remained associated with allograft failure. Urine procollagen type III and type I levels were not associated with allograft failure.

LIMITATIONS

We lack kidney biopsy data, BK titers, and HLA antibody status.

CONCLUSIONS

Urine measurement of tubulointerstitial fibrosis may provide a noninvasive method to identify kidney transplant recipients at higher risk for future allograft failure, above and beyond eGFR and urine ACR.

Association of Kidney Function and Early Kidney Injury With Incident Hypertension in HIV-Infected Women

Subclinical kidney disease is associated with developing hypertension in the general population, but data are lacking among HIV-infected people. We examined associations of kidney function and injury with incident hypertension in 823 HIV-infected and 267 HIV-uninfected women in the Women's Interagency HIV Study, a multicenter, prospective cohort of HIV-infected and uninfected women in the United States. Baseline kidney biomarkers included estimated glomerular filtration rate using cystatin C, urine albumin-to-creatinine ratio, and 7 urine biomarkers of tubular injury: α-1-microglobulin, interleukin-18, kidney injury molecule-1, neutrophil gelatinase-associated lipocalin, liver fatty acid-binding protein, N-acetyl-β-d-glucosaminidase, and α1-acid-glycoprotein. We used multivariable Poisson regression to evaluate associations of kidney biomarkers with incident hypertension, defined as 2 consecutive visits of antihypertensive medication use. During a median follow-up of 9.6 years, 288 HIV-infected women (35%) developed hypertension. Among the HIV-infected women, higher urine albumin-to-creatinine ratio was independently associated with incident hypertension (relative risk =1.13 per urine albumin-to-creatinine ratio doubling, 95% confidence interval, 1.07-1.20), as was lower estimated glomerular filtration rate (relative risk =1.10 per 10 mL/min/1.73 m² lower estimated glomerular filtration rate; 95% confidence interval, 1.04-1.17). No tubular injury and dysfunction biomarkers were independently associated with incident hypertension in HIV-infected women. In contrast, among the HIV-uninfected women, urine albumin-to-creatinine ratio was not associated with incident hypertension, whereas higher urine interleukin-18, α1-acid-glycoprotein, and N-acetyl-β-d-glucosaminidase levels were significantly associated with incident hypertension. These findings suggest that early glomerular injury and kidney dysfunction may be involved in the pathogenesis of hypertension in HIV-infected people. The associations of tubular markers with hypertension in HIV-uninfected women should be validated in other studies.

Urinary Markers of Tubular Injury in HIV-Infected Patients

Renal disease is a common complication of HIV-infected patients, associated with increased risk of cardiovascular events, progression to AIDS, AIDS-defining illness, and mortality. Early and accurate identification of renal disease is therefore crucial to improve patient outcomes. The use of serum creatinine, along with proteinuria, to detect renal involvement is essentially to screen for markers of glomerular disease and may not be effective in detecting earlier stages of renal injury. Therefore, more sensitive and specific markers are needed in order to early identify HIV-infected patients at risk of renal disease. This review article summarizes some new and important urinary markers of tubular injury in HIV-infected patients and their clinical usefulness in the renal safety follow-up of TDF-treated patients.

HIV Infection, Tenofovir, and Urine α1-Microglobulin: A Cross-sectional Analysis in the Multicenter AIDS Cohort Study

BACKGROUND

Tenofovir disoproxil fumarate (TDF) can cause proximal tubular damage and chronic kidney disease in human immunodeficiency virus (HIV)-infected individuals. Urine α1-microglobulin (A1M), a low-molecular-weight protein indicative of proximal tubular dysfunction, may enable earlier detection of TDF-associated tubular toxicity.

STUDY DESIGN

Cross-sectional.

SETTING & PARTICIPANTS

883 HIV-infected and 350 -uninfected men enrolled in the Multicenter AIDS Cohort Study.

PREDICTORS

HIV infection and TDF exposure.

OUTCOME

Urine A1M level.

RESULTS

Urine A1M was detectable in 737 (83%) HIV-infected and 202 (58%) -uninfected men (P<0.001). Among HIV-infected participants, 573 (65%) were current TDF users and 112 (13%) were past TDF users. After multivariable adjustment including demographics, traditional kidney disease risk factors, and estimated glomerular filtration rate, HIV infection was associated with 136% (95% CI, 104%-173%) higher urine A1M levels and 1.5-fold (95% CI, 1.3- to 1.6-fold) prevalence of detectable A1M. When participants were stratified by TDF exposure, HIV infection was associated with higher adjusted A1M levels, by 164% (95% CI, 127%-208%) among current users, 124% (95% CI, 78%-183%) among past users, and 76% (95% CI, 45%-115%) among never users. Among HIV-infected participants, each year of cumulative TDF exposure was associated with 7.6% (95% CI, 5.4%-9.9%) higher A1M levels in fully adjusted models, a 4-fold effect size relative to advancing age (1.8% [95% CI, 0.9%-2.7%] per year). Each year since TDF treatment discontinuation was associated with 4.9% (95% CI, -9.4%--0.2%) lower A1M levels among past users.

LIMITATIONS

Results may not be generalizable to women.

CONCLUSIONS

HIV-infected men had higher urine A1M levels compared with HIV-uninfected men. Among HIV-infected men, cumulative TDF exposure was associated with incrementally higher A1M levels, whereas time since TDF treatment discontinuation was associated with progressively lower A1M levels. Urine A1M appears to be a promising biomarker for detecting and monitoring TDF-associated tubular toxicity.

Use of urine biomarker-derived clusters to predict the risk of chronic kidney disease and all-cause mortality in HIV-infected women

BACKGROUND

Although individual urine biomarkers are associated with chronic kidney disease (CKD) incidence and all-cause mortality in the setting of HIV infection, their combined utility for prediction remains unknown.

METHODS

We measured eight urine biomarkers shown previously to be associated with incident CKD and mortality risk among 902 HIV-infected women in the Women's Interagency HIV Study: N-acetyl-β-d-glucosaminidase (NAG), kidney injury molecule-1 (KIM-1), alpha-1 microglobulin (α1m), interleukin 18, neutrophil gelatinase-associated lipocalin, albumin-to-creatinine ratio, liver fatty acid-binding protein and α-1-acid-glycoprotein. A group-based cluster method classified participants into three distinct clusters using the three most distinguishing biomarkers (NAG, KIM-1 and α1m), independent of the study outcomes. We then evaluated associations of each cluster with incident CKD (estimated glomerular filtration rate <60 mL/min/1.73 m(2) by cystatin C) and all-cause mortality, adjusting for traditional and HIV-related risk factors.

RESULTS

Over 8 years of follow-up, 177 CKD events and 128 deaths occurred. The first set of clusters partitioned women into three groups, containing 301 (Cluster 1), 470 (Cluster 2) and 131 (Cluster 3) participants. The rate of CKD incidence was 13, 21 and 50% across the three clusters; mortality rates were 7.3, 13 and 34%. After multivariable adjustment, Cluster 3 remained associated with a nearly 3-fold increased risk of both CKD and mortality, relative to Cluster 1 (both P < 0.001). The addition of the multi-biomarker cluster to the multivariable model improved discrimination for CKD (c-statistic = 0.72-0.76, P = 0.0029), but only modestly for mortality (c = 0.79-0.80, P = 0.099). Clusters derived with all eight markers were no better for discrimination than the three-biomarker clusters.

CONCLUSIONS

For predicting incident CKD in HIV-infected women, clusters developed from three urine-based kidney disease biomarkers were as effective as an eight-marker panel in improving risk discrimination.

APOL1 Genotype and Glomerular and Tubular Kidney Injury in Women With HIV

BACKGROUND

APOL1 genotype is associated with advanced kidney disease in African Americans, but the pathogenic mechanisms are unclear. Here, associations of APOL1 genotype with urine biomarkers of glomerular and tubular injury and kidney function decline were evaluated.

STUDY DESIGN

Observational study.

SETTING & PARTICIPANTS

431 human immunodeficiency virus (HIV)-infected African American women enrolled in Women's Interagency HIV Study (WIHS).

PREDICTOR

APOL1 genotype.

OUTCOMES

Albumin-creatinine ratio (ACR), 4 tubular injury biomarkers (interleukin 18 [IL-18], kidney injury molecule 1 [KIM-1], neutrophil gelatinase-associated lipocalin [NGAL], and α1-microglobulin [A1M]), and kidney function estimated using the CKD-EPI cystatin C equation.

MEASUREMENTS

Participants were genotyped for APOL1 single-nucleotide polymorphisms rs73885319 (G1 allele) and rs71785313 (G2 allele). Urine biomarkers were measured using stored samples from 1999-2000. Cystatin C was measured using serum collected at baseline and 4- and 8-year follow-ups.

RESULTS

At baseline, ACRs were higher among 47 women with 2 APOL1 risk alleles versus 384 women with 0/1 risk allele (median, 24 vs 11mg/g; P<0.001). Compared with women with 0/1 risk allele, women with 2 risk alleles had 104% higher ACRs (95% CI, 29-223mg/g) and 2-fold greater risk of ACR>30 (95% CI, 1.17-3.44) mg/g after multivariable adjustment. APOL1 genotype showed little association with urine IL-18:Cr ratio, KIM-1:Cr ratio, and NGAL:Cr ratio (estimates of -5% [95% CI, -24% to 18%], -20% [95% CI, -36% to -1%], and 10% [95% CI, -26% to 64%], respectively) or detectable urine A1M (prevalence ratio, 1.13; 95% CI, 0.65-1.97) in adjusted analyses. Compared with women with 0/1 allele, women with 2 risk alleles had faster eGFR decline, by 1.2 (95% CI, 0.2 to 2.2) mL/min/1.73m(2) per year, and 1.7- and 3.4-fold greater rates of incident chronic kidney disease (95% CI, 1.1 to 2.5) and 10% annual eGFR decline (95% CI, 1.7 to 6.7), respectively, with minimal attenuation after adjustment for glomerular and tubular injury biomarker levels.

LIMITATIONS

Results may not be generalizable to men.

CONCLUSIONS

Among HIV-infected African American women, APOL1-associated kidney injury appears to localize to the glomerulus, rather than the tubules.