Showing papers by "Sushrut S. Waikar published in 2019"

The single-cell transcriptomic landscape of early human diabetic nephropathy

Abstract: Diabetic nephropathy is characterized by damage to both the glomerulus and tubulointerstitium, but relatively little is known about accompanying cell-specific changes in gene expression. We performed unbiased single-nucleus RNA sequencing (snRNA-seq) on cryopreserved human diabetic kidney samples to generate 23,980 single-nucleus transcriptomes from 3 control and 3 early diabetic nephropathy samples. All major cell types of the kidney were represented in the final dataset. Side-by-side comparison demonstrated cell-type–specific changes in gene expression that are important for ion transport, angiogenesis, and immune cell activation. In particular, we show that the diabetic thick ascending limb, late distal convoluted tubule, and principal cells all adopt a gene expression signature consistent with increased potassium secretion, including alterations in Na+/K+-ATPase, WNK1, mineralocorticoid receptor, and NEDD4L expression, as well as decreased paracellular calcium and magnesium reabsorption. We also identify strong angiogenic signatures in glomerular cell types, proximal convoluted tubule, distal convoluted tubule, and principal cells. Taken together, these results suggest that increased potassium secretion and angiogenic signaling represent early kidney responses in human diabetic nephropathy.

Complex inter-relationship of body mass index, gender and serum creatinine on survival: exploring the obesity paradox in melanoma patients treated with checkpoint inhibition

Abstract: A male gender driven obesity paradox (improved survival for overweight/obese patients compared to normal weight) was recently shown in melanoma in the context of checkpoint inhibition (anti-PD-1/anti-CTLA4 monotherapy) in a pooled meta-analysis. We characterized the relationship of Body Mass Index (BMI) with survival and explored gender-based interactions with surrogates of body composition/malnutrition in the context of PD-1 blockade as monotherapy or in combination with ipilimumab in a real-world setting. Advanced melanoma patients who received at least one dose of pembrolizumab, nivolumab, or nivolumab plus ipilimumab (combination) from June 2014 to September 2016 were included in this retrospective cohort study (N = 139). Overall Survival (OS) and Progression Free Survival (PFS) were the main outcomes. Analysis was performed using Random Survival Forests (RSF)/ multivariable Cox Proportional-Hazards models. Overweight/Class-I (25- < 35 kg/m2) obese patients had a significantly lower risk of mortality (adjusted-HR:0.26; 95%CI:0.1–0.71; p-value = 0.008) and progressive disease (adjusted-HR:0.43; 95%CI:0.19–0.95; p-value:0.038) compared to normal-weight (18.5- < 25 kg/m2). Class II/III obesity (compared to normal-weight) had an adjusted HR of 0.42 (95%CI: 0.1–1.77; p-value: 0.238) for OS and 1 (95%CI:0.34–2.94; p-value:0.991) for PFS. Exploration of interactions for OS showed that the association was predominantly driven by males (adjusted-HRmales:0.11; 95%CI:0.03–0.4; adjusted-HRfemales: 0.56; 95%CI:0.16–1.89; p-valueinteraction:0.044); the association was not seen in patients with serum creatinine< 0.9 mg/dL (adjusted-HR:0.43; 95%CI:0.15–1.24; p-valueinteraction:0.020), who were predominantly females. These observations were made in both the anti-PD-1 monotherapy (n = 79) and combination therapy (anti-PD-1/CTLA-4, n = 60) cohorts. The findings support the existence of an “obesity paradox” restricted to overweight/Class-I obesity in the real-world setting; the association was driven predominantly by males who largely had higher serum creatinine levels, a surrogate for skeletal muscle mass in the setting of metastatic disease. These observations suggest that sarcopenia (low skeletal muscle mass) or direct measures of body mass composition may be more suitable predictors of survival in melanoma patients treated with PD-1 blockade (monotherapy/combination).

Association of Urinary Oxalate Excretion With the Risk of Chronic Kidney Disease Progression

Abstract: Importance Oxalate is a potentially toxic terminal metabolite that is eliminated primarily by the kidneys. Oxalate nephropathy is a well-known complication of rare genetic disorders and enteric hyperoxaluria, but oxalate has not been investigated as a potential contributor to more common forms of chronic kidney disease (CKD). Objective To assess whether urinary oxalate excretion is a risk factor for more rapid progression of CKD toward kidney failure. Design, Setting, and Participants This prospective cohort study assessed 3123 participants with stages 2 to 4 CKD who enrolled in the Chronic Renal Insufficiency Cohort study from June 1, 2003, to September 30, 2008. Data analysis was performed from October 24, 2017, to June 17, 2018. Exposures Twenty-four–hour urinary oxalate excretion. Main Outcomes and Measures A 50% decline in estimated glomerular filtration rate (eGFR) and end-stage renal disease (ESRD). Results This study included 3123 participants (mean [SD] age, 59.1 [10.6] years; 1414 [45.3%] female; 1423 [45.6%] white). Mean (SD) eGFR at the time of 24-hour urine collection was 42.9 (16.8) mL/min/1.73 m2. Median urinary excretion of oxalate was 18.6 mg/24 hours (interquartile range [IQR], 12.9-25.7 mg/24 hours) and was correlated inversely with eGFR (r = −0.13,P Conclusions and Relevance Higher 24-hour urinary oxalate excretion may be a risk factor for CKD progression and ESRD in individuals with CKD stages 2 to 4.

Iron, Hepcidin, and Death in Human AKI

Abstract: Background Iron is a key mediator of AKI in animal models, but data on circulating iron parameters in human AKI are limited. Methods We examined results from the ARF Trial Network study to assess the association of plasma catalytic iron, total iron, transferrin, ferritin, free hemoglobin, and hepcidin with 60-day mortality. Participants included critically ill patients with AKI requiring RRT who were enrolled in the study. Results Of the 807 study participants, 409 (51%) died by day 60. In both unadjusted and multivariable adjusted models, higher plasma concentrations of catalytic iron were associated with a significantly greater risk of death, as were lower concentrations of hepcidin. After adjusting for other factors, patients with catalytic iron levels in the highest quintile versus the lowest quintile had a 4.06-fold increased risk of death, and patients with hepcidin levels in the lowest quintile versus the highest quintile of hepcidin had a 3.87-fold increased risk of death. These findings were consistent across multiple subgroups. Other iron markers were also associated with death, but the magnitude of the association was greatest for catalytic iron and hepcidin. Higher plasma concentrations of catalytic iron and lower concentrations of hepcidin are each independently associated with mortality in critically ill patients with AKI requiring RRT. Conclusions These findings suggest that plasma concentrations of catalytic iron and hepcidin may be useful prognostic markers in patients with AKI. Studies are needed to determine whether strategies to reduce catalytic iron or increase hepcidin might be beneficial in this patient population.

The Single Cell Transcriptomic Landscape of Early Human Diabetic Nephropathy

Abstract: Diabetic nephropathy is characterized by damage to both the glomerulus and tubulointerstitium, but relatively little is known about accompanying cell-specific changes in gene expression. We performed unbiased single nucleus RNA sequencing (snRNAseq) on cryopreserved human diabetic kidney samples to generate 23,980 single nucleus transcriptomes from three control and three early diabetic nephropathy samples. All major cell types of the kidney were represented in the final dataset. Side by side comparison demonstrated cell-type-specific changes in gene expression that are important for ion transport, angiogenesis, and immune cell activation. In particular, we show that the diabetic loop of Henle, late distal convoluted tubule, and principal cells all adopt a gene expression signature consistent with increased potassium secretion, including alterations in Na-K+-ATPase, WNK1, mineralocorticoid receptor and NEDD4L expression, as well as decreased paracellular calcium and magnesium reabsorption. We also identify strong angiogenic signatures in glomerular cell types, proximal convoluted tubule, distal convoluted tubule and principal cells. Taken together, these results suggest that increased potassium secretion and angiogenic signaling represent early kidney responses in human diabetic nephropathy. Significance Statement Single nucleus RNA sequencing revealed gene expression changes in early diabetic nephropathy that promote urinary potassium secretion and decreased calcium and magnesium reabsorption. Multiple cell types exhibited angiogenic signatures, which may represent early signs of aberrant angiogenesis. These alterations may help to identify biomarkers for disease progression or signaling pathways amenable to early intervention.

Development of an electronic health record-based chronic kidney disease registry to promote population health management.

Abstract: Electronic health record (EHR) based chronic kidney disease (CKD) registries are central to population health strategies to improve CKD care. In 2015, Partners Healthcare System (PHS), encompassing multiple academic and community hospitals and outpatient care facilities in Massachusetts, developed an EHR-based CKD registry to identify opportunities for quality improvement, defined as improvement on both process measures and outcomes measures associated with clinical care. Patients are included in the registry based on the following criteria: 1) two estimated glomerular filtration rate (eGFR) results 300 mg protein/g creatinine on either urine total protein/creatinine ratio or urine albumin/creatinine ratio; or 3) an EHR problem list diagnosis of end stage renal disease (ESRD). The registry categorizes patients by CKD stage and includes rates of annual testing for eGFR and proteinuria, blood pressure control, use of angiotensin converting enzyme inhibitors (ACE-Is) or angiotensin receptor blockers (ARBs), nephrotoxic medication use, hepatitis B virus (HBV) immunization, vascular access placement, transplant status, CKD progression risk; number of outpatient nephrology visits, and hospitalizations. The CKD registry includes 60,503 patients and has revealed several opportunities for care improvement including 1) annual proteinuria testing performed for 17% (stage 3) and 31% (stage 4) of patients; 2) ACE-I/ARB used in 41% (stage 3) and 46% (stage 4) of patients; 3) nephrotoxic medications used among 23% of stage 4 patients; and 4) 89% of stage 4 patients lack HBV immunity. For advanced CKD patients there are opportunities to improve vascular access placement, transplant referrals and outpatient nephrology contact. A CKD registry can identify modifiable care gaps across the spectrum of CKD care and enable population health strategy implementation. No linkage to Social Security Death Master File or US Renal Data System (USRDS) databases limits our ability to track mortality and progression to ESRD.

Proximal Tubule-Derived Amphiregulin Amplifies and Integrates Profibrotic EGF Receptor Signals in Kidney Fibrosis.

Abstract: Background Sustained activation of EGF receptor (EGFR) in proximal tubule cells is a hallmark of progressive kidney fibrosis after AKI and in CKD. However, the molecular mechanisms and particular EGFR ligands involved are unknown. Methods We studied EGFR activation in proximal tubule cells and primary tubular cells isolated from injured kidneys in vitro. To determine in vivo the role of amphiregulin, a low-affinity EGFR ligand that is highly upregulated with injury, we used ischemia-reperfusion injury or unilateral ureteral obstruction in mice with proximal tubule cell-specific knockout of amphiregulin. We also injected soluble amphiregulin into knockout mice with proximal tubule cell-specific deletion of amphiregulin's releasing enzyme, the transmembrane cell-surface metalloprotease, a disintegrin and metalloprotease-17 (ADAM17), and into ADAM17 hypomorphic mice. Results Yes-associated protein 1 (YAP1)-dependent upregulation of amphiregulin transcript and protein amplifies amphiregulin signaling in a positive feedback loop. YAP1 also integrates signals of other moderately injury-upregulated, low-affinity EGFR ligands (epiregulin, epigen, TGFα), which also require soluble amphiregulin and YAP1 to induce sustained EGFR activation in proximal tubule cells in vitro. In vivo, soluble amphiregulin injection sufficed to reverse protection from fibrosis after ischemia-reperfusion injury in ADAM17 hypomorphic mice; injected soluble amphiregulin also reversed the corresponding protective proximal tubule cell phenotype in injured proximal tubule cell-specific ADAM17 knockout mice. Moreover, the finding that proximal tubule cell-specific amphiregulin knockout mice were protected from fibrosis after ischemia-reperfusion injury or unilateral ureteral obstruction demonstrates that amphiregulin was necessary for the development of fibrosis. Conclusions Our results identify amphiregulin as a key player in injury-induced kidney fibrosis and suggest therapeutic or diagnostic applications of soluble amphiregulin in kidney disease.

Serum Metabolomic Alterations Associated with Proteinuria in CKD.

Abstract: Background and objectives Data are scarce on blood metabolite associations with proteinuria, a strong risk factor for adverse kidney outcomes. We sought to investigate associations of proteinuria with serum metabolites identified using untargeted profiling in populations with CKD. Design, setting, participants, & measurements Using stored serum samples from the African American Study of Kidney Disease and Hypertension (AASK; n=962) and the Modification of Diet in Renal Disease (MDRD) study (n=620), two rigorously conducted clinical trials with per-protocol measures of 24-hour proteinuria and GFR, we evaluated cross-sectional associations between urine protein-to-creatinine ratio and 637 known, nondrug metabolites, adjusting for key clinical covariables. Metabolites significantly associated with proteinuria were tested for associations with CKD progression. Results In the AASK and the MDRD study, respectively, the median urine protein-to-creatinine ratio was 80 (interquartile range [IQR], 28–359) and 188 (IQR, 54–894) mg/g, mean age was 56 and 52 years, 39% and 38% were women, 100% and 7% were black, and median measured GFR was 48 (IQR, 35–57) and 28 (IQR, 18–39) ml/min per 1.73 m2. Linear regression identified 66 serum metabolites associated with proteinuria in one or both studies after Bonferroni correction (P Conclusions We identified 58 serum metabolites with cross-sectional associations with proteinuria, some of which were also associated with CKD progression. Podcast This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2019_02_07_CJASNPodcast_19_03_.mp3

Variability of Two Metabolomic Platforms in CKD

Abstract: Background and objectives Nontargeted metabolomics can measure thousands of low-molecular-weight biochemicals, but important gaps limit its utility for biomarker discovery in CKD. These include the need to characterize technical and intraperson analyte variation, to pool data across platforms, and to outline analyte relationships with eGFR. Design, setting, participants, & measurements Plasma samples from 49 individuals with CKD (eGFR Results The Metabolon platform reported 837 known metabolites and 483 unnamed compounds (selected from 44,953 unknown ion features). The Broad Institute platform reported 594 known metabolites and 26,106 unknown ion features. Median coefficients of variation (CVs) across blind replicates were 14.6% (Metabolon) and 6.3% (Broad Institute) for known metabolites, and 18.9% for (Metabolon) unnamed compounds and 24.5% for (Broad Institute) unknown ion features. Median CVs for day-to-day variability were 29.0% (Metabolon) and 24.9% (Broad Institute) for known metabolites, and 41.8% for (Metabolon) unnamed compounds and 40.9% for (Broad Institute) unknown ion features. A total of 381 known metabolites were shared across platforms (median correlation 0.89). Many metabolites were negatively correlated with eGFR at P Conclusions Nontargeted metabolomics quantifies >1000 analytes with low technical CVs, and agreement for overlapping metabolites across two leading platforms is excellent. Many metabolites demonstrate substantial intraperson variation and correlation with eGFR.

Urinary oxalate as a potential mediator of kidney disease in diabetes mellitus and obesity.

Abstract: Purpose of review Hyperoxaluria can cause kidney disease through multiple mechanisms, including tubular obstruction from calcium oxalate crystals, sterile inflammation, and tubular epithelial cell injury. Hyperoxaluria is also observed in individuals with diabetes mellitus and obesity, which are in turn risk factors for chronic kidney disease (CKD). Whether hyperoxaluria is a potential mediator of increased risk of CKD in diabetes mellitus and obesity is unknown. Recent findings Individuals with diabetes have increased levels of plasma glyoxal (a protein glycation product) and glyoxylate, both of which are precursors for oxalate. Increased gut absorption of oxalate in obesity may be because of obesity-associated inflammation. A recent study in individuals with CKD found that higher 24 h urinary oxalate excretion was independently associated with increased risk of kidney disease progression, especially in individuals with diabetes and obesity. Summary Both diabetes mellitus and obesity are associated with higher urinary oxalate excretion through distinct mechanisms. Hyperoxaluria could be a mechanism by which kidney disease develops in individuals with diabetes mellitus or obesity and could also contribute to progressive loss of renal function. Future research on pharmacologic or dietary measures to limit oxalate absorption or generation are required to test whether lowering urinary oxalate excretion is beneficial in preventing kidney disease development and progression in diabetes mellitus and obesity.

When to stop renal replacement therapy in anticipation of renal recovery in AKI: The need for consensus guidelines.

Abstract: There is wide variation in clinical practice regarding timing of discontinuation of renal replacement therapy (RRT) in patients with acute kidney injury (AKI). Prolonged, unnecessary RRT treatment can contribute to length of stay, overall hospital costs, and risk of complications associated with RRT. In addition, prolonged RRT can paradoxically lengthen the time for which the patient remains dialysis-dependent. Well-designed, randomized clinical trials have utilized varied discontinuation criteria specifically related to urine output and creatinine clearance, which impedes the comparison of outcomes from such studies. Other observational studies have attempted to assess the sensitivity and specificity of various criteria for discontinuation of RRT. Whether diuretics influence renal recovery has not been fully elucidated as well. In this article, we propose a starting framework for RRT discontinuation criteria to guide clinicians and clinical researchers. We emphasize the importance of frequent clinical assessment while considering discontinuation of RRT for AKI patients with a creatinine clearance >15 mL/min on a timed urine collection and/or a urine output >400 mL/24 h without diuretics, or >2000 mL/24 h with diuretics. We also discuss newer biomarkers, methods of GFR estimation, and imaging techniques that may play a greater role in the future. Clinical trials objectively comparing the success of RRT discontinuation criteria will be required to provide high-quality evidence for our proposed guidelines.

Nephrologists’ emotional burden regarding decision-making about dialysis initiation in older adults: a qualitative study

Abstract: Conservative management, an approach to treating end-stage kidney disease without dialysis, while generally associated with shorter life expectancy than treatment with dialysis, is associated with fewer hospitalizations, better functional status and, potentially, better quality of life. Conservative management is a well-established treatment approach in a number of Western countries, including the United Kingdom (U.K.). In contrast, despite clinical practice guidelines in the United States (U.S.) recommending that nephrologists discuss all treatment options, including conservative management, with stage 4 and 5 chronic kidney disease patients, studies suggest that this rarely occurs. Therefore, we explored U.S. nephrologists’ approaches to decision-making about dialysis and perspectives on conservative management among older adults. We conducted a qualitative research study. We interviewed 20 nephrologists – 15 from academic centers and 5 from community practices – utilizing a semi-structured interview guide containing open-ended questions. Interview transcripts were analyzed using grounded thematic analysis in which codes were generated inductively and iteratively modified, and themes were identified. Transcripts were coded independently by two investigators, and interviews were conducted until thematic saturation. Twenty nephrologists (85% white, 75% male, mean age 50) participated in interviews. We found that decision-making about dialysis initiation in older adults can create emotional burden for nephrologists. We identified four themes that reflected factors that contribute to this emotional burden including nephrologists’ perspectives that: 1) uncertainty exists about how a patient will do on dialysis, 2) the alternative to dialysis is death, 3) confronting death is difficult, and 4) patients do not regret initiating dialysis. Three themes revealed different decision-making strategies that nephrologists use to reduce this emotional burden: 1) convincing patients to “just do it” (i.e. dialysis), 2) shifting the decision-making responsibility to patients, and 3) utilizing time-limited trials of dialysis. A decision not to start dialysis and instead pursue conservative management can be emotionally burdensome for nephrologists for a number of reasons including clinical uncertainty about prognosis on dialysis and discomfort with death. Nephrologists’ attempts to reduce this burden may be reflected in different decision-making styles – paternalistic, informed, and shared decision-making. Shared decision-making may relieve some of the emotional burden while preserving patient-centered care.

Uric Acid and Acute Kidney Injury in the Critically Ill

Abstract: Rationale & Objective Uric acid is excreted by the kidney and accumulates in acute kidney injury (AKI). Whether higher plasma uric acid level predisposes to AKI or its complications is not known. Study Design Prospective observational cohort study. Setting & Participants 2 independent cohorts of critically ill patients: (1) 208 patients without AKI admitted to the intensive care unit (ICU) at Brigham & Women's Hospital between October 2008 and December 2016; and (2) 250 participants with AKI requiring renal replacement therapy (RRT) who had not yet initiated RRT enrolled in the Acute Renal Failure Trial Network (ATN) Study. Exposure Plasma uric acid level upon ICU admission and before RRT initiation in the ICU and ATN Study cohorts, respectively. Outcomes Incident AKI and 60-day mortality in the ICU and ATN Study cohorts, respectively. Analytical Approach Logistic regression models were used to test the association of plasma uric acid level with incident AKI and 60-day mortality. Results In the ICU cohort, median plasma uric acid level was 4.7 (interquartile range [IQR], 3.6-6.4) mg/dL, and 40 patients (19.2%) developed AKI. Higher plasma uric acid levels associated with incident AKI, but this association was confounded by serum creatinine level and was not significant after multivariable adjustment (adjusted OR per doubling of uric acid, 1.50; 95% CI, 0.80-2.81). In the ATN Study cohort, median plasma uric acid level was 11.1 (IQR, 8.6–14.2) mg/dL, and 125 participants (50.0%) died within 60 days. There was no statistically significant association between plasma uric acid levels and 60-day mortality in either unadjusted models or after multivariable adjustment for demographic, severity-of-illness, and kidney-specific covariates (adjusted OR per doubling of uric acid, 1.15; 95% CI, 0.71-1.86). Limitations Heterogeneity of ICU patients. Conclusions Plasma uric acid levels upon ICU admission or before RRT initiation are not independently associated with adverse clinical outcomes in critically ill patients.

IDEAL-ICU in Context.

Abstract: Mortality rates among critically ill patients with AKI requiring kidney replacement therapy (KRT) remain unacceptably high ([1][1]). Various therapeutic strategies have been investigated to improve outcomes in this high-risk patient population, including alterations to the intensity of KRT ([2][2

Clearance of FGF-23 during continuous renal replacement therapy.

Abstract: FGF-23 is a 32 kDa protein that is a key regulator of phosphorus and vitamin D metabolism. Emerging evidence also demonstrates that FGF-23 increases within 24 hours of acute kidney injury (AKI) and may be associated with adverse clinical outcomes. We conducted this study to evaluate FGF23 clearance during continuous veno-venous hemofiltration (CVVH) in critically ill patients with AKI. We demonstrate that plasma clearance of FGF-23 during CVVH is ∼11 mL/min and the mean sieving coefficient is 0.27 ± 0.1. Future studies will need to clarify FGF-23's role in adverse outcomes among AKI patients, and whether therapies aimed at reducing FGF-23 levels may be beneficial.