Chronic kidney disease associated cardiomyopathy: recent advances and future perspectives.

PURPOSE OF REVIEW: Cardiomyopathy in chronic kidney disease (CKD) is a complex condition with multiple triggers and poor prognosis. This review provides an overview of recent advances in CKD-associated cardiomyopathy, with a focus on pathophysiology, newly discovered biomarkers and potential therapeutic targets. RECENT FINDINGS: CKD is associated with a specific pattern of myocardial hypertrophy and fibrosis, resulting in diastolic and systolic dysfunction, and often triggered by nonatherosclerotic processes. Novel biomarkers, including amino-terminal type III procollagen peptide (PIIINP), carboxy-terminal type I procollagen peptide (PICP), FGF23, marinobufagenin, and several miRNAs, show promise for early detection and risk stratification. Treatment options for CKD-associated cardiomyopathy are limited. Sodium glucose cotransporter-2 inhibitors have been shown to reduce left ventricle hypertrophy and improve ejection fraction in individuals with diabetes and mild CKD, and are currently under investigation for more advanced stages of CKD. In hemodialysis patients calcimimetic etelcalcetide resulted in a significant reduction in left ventricular mass. SUMMARY: CKD-associated cardiomyopathy is a common and severe complication in CKD. The identification of novel biomarkers may lead to future therapeutic targets. Randomized clinical trials in individuals with more advanced CKD would be well posed to expand treatment options for this debilitating condition.

Association of urine and plasma ADMA with atherosclerotic risk in DKD cardiovascular disease risk in diabetic kidney disease: findings from the Chronic Renal Insufficiency Cohort (CRIC) study.

BACKGROUND: Chronic kidney disease (CKD) is associated with atherosclerotic cardiovascular disease (ASCVD) risk, especially among those with diabetes. Altered metabolism of solutes that accumulate in CKD [asymmetric dimethylarginine (ADMA), symmetric dimethylarginine (SDMA) and trimethylamine N-oxide (TMAO)] may reflect pathways linking CKD with ASCVD. METHODS: This case-cohort study included Chronic Renal Insufficiency Cohort participants with baseline diabetes, estimated glomerular filtration rate <60 mL/min/1.73 m2, and without prior history for each outcome. The primary outcome was incident ASCVD (time to first myocardial infarction, stroke or peripheral artery disease event) and secondary outcome was incident heart failure. The subcohort comprised randomly selected participants meeting entry criteria. Plasma and urine ADMA, SDMA and TMAO concentrations were determined by liquid chromatography-tandem mass spectrometry. Associations of uremic solute plasma concentrations and urinary fractional excretions with outcomes were evaluated by weighted multivariable Cox regression models, adjusted for confounding covariables. RESULTS: Higher plasma ADMA concentrations (per standard deviation) were associated with ASCVD risk [hazard ratio (HR) 1.30, 95% confidence interval (CI) 1.01-1.68]. Lower fractional excretion of ADMA (per standard deviation) was associated with ASCVD risk (HR 1.42, 95% CI 1.07-1.89). The lowest quartile of ADMA fractional excretion was associated with greater ASCVD risk (HR 2.25, 95% CI 1.08-4.69) compared with the highest quartile. Plasma SDMA and TMAO concentration and fractional excretion were not associated with ASCVD. Neither plasma nor fractional excretion of ADMA, SDMA and TMAO were associated with incident heart failure. CONCLUSION: These data suggest that decreased kidney excretion of ADMA leads to increased plasma concentrations and ASCVD risk.

Association of Uremic Solutes With Cardiovascular Death in Diabetic Kidney Disease.

RATIONALE & OBJECTIVE: Cardiovascular disease (CVD) is a major cause of mortality among people with diabetic kidney disease (DKD). The pathophysiology is inadequately explained by traditional CVD risk factors. The uremic solutes trimethylamine-N-oxide (TMAO) and asymmetric and symmetric dimethylarginine (ADMA, SDMA) have been linked to CVD in kidney failure with replacement therapy (KFRT), but data are limited in populations with diabetes and less severe kidney disease. STUDY DESIGN: Observational cohort. SETTINGS & PARTICIPANTS: Random subcohort of 555 REGARDS (Reasons for Geographic and Racial Differences in Stroke) study participants with diabetes and estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m2 at study entry. EXPOSURE: ADMA, SDMA, and TMAO assayed by liquid chromatography-mass spectrometry in plasma and urine. OUTCOME: Cardiovascular mortality (primary outcome); all-cause mortality and incident KFRT (secondary outcomes). ANALYTICAL APPROACH: Plasma concentrations and ratios of urine to plasma concentrations of ADMA, SDMA, and TMAO were tested for association with outcomes. Adjusted Cox regression models were fitted and hazard ratios of outcomes calculated per standard deviation and per doubling, and as interquartile comparisons. RESULTS: The mean baseline eGFR was 44 mL/min/1.73 m2. Cardiovascular death, overall mortality, and KFRT occurred in 120, 285, and 89 participants, respectively, during a mean 6.2 years of follow-up. Higher plasma ADMA and SDMA (HRs of 1.20 and 1.28 per 1-SD greater concentration), and lower ratios of urine to plasma concentrations of ADMA, SDMA, and TMAO (HRs per halving of 1.53, 1.69, and 1.38) were associated with cardiovascular mortality. Higher plasma concentrations of ADMA, SDMA, and TMAO (HRs of 1.31, 1.42, and 1.13 per 1-SD greater concentration) and lower urine to plasma ratios of ADMA, SDMA, and TMAO (HRs per halving of 1.34, 1.37, and 1.26) were associated with all-cause mortality. Higher plasma ADMA and SDMA were associated with incident KFRT by categorical comparisons (HRs of 2.75 and 2.96, comparing quartile 4 to quartile 1), but not in continuous analyses. LIMITATIONS: Single cohort, restricted to patients with diabetes and eGFR < 60 mL/min/1.73 m2, potential residual confounding by GFR, no dietary information. CONCLUSIONS: Higher plasma concentrations and lower ratios of urine to plasma concentrations of uremic solutes were independently associated with cardiovascular and all-cause mortality in DKD. Associations of ratios of urine to plasma concentrations with mortality suggest a connection between renal uremic solute clearance and CVD pathogenesis.

Urine Biomarkers of Kidney Tubule Health, Injury, and Inflammation are Associated with Progression of CKD in Children.

BACKGROUND: Novel urine biomarkers may improve identification of children at greater risk of rapid kidney function decline, and elucidate the pathophysiology of CKD progression. METHODS: We investigated the relationship between urine biomarkers of kidney tubular health (EGF and α-1 microglobulin), tubular injury (kidney injury molecule-1; KIM-1), and inflammation (monocyte chemoattractant protein-1 [MCP-1] and YKL-40) and CKD progression. The prospective CKD in Children Study enrolled children aged 6 months to 16 years with an eGFR of 30-90ml/min per 1.73m2. Urine biomarkers were assayed a median of 5 months [IQR: 4-7] after study enrollment. We indexed the biomarker to urine creatinine by dividing the urine biomarker concentration by the urine creatinine concentration to account for the concentration of the urine. The primary outcome was CKD progression (a composite of a 50% decline in eGFR or kidney failure) during the follow-up period. RESULTS: Overall, 252 of 665 children (38%) reached the composite outcome over a median follow-up of 6.5 years. After adjustment for covariates, children with urine EGF concentrations in the lowest quartile were at a seven-fold higher risk of CKD progression versus those with concentrations in the highest quartile (fully adjusted hazard ratio [aHR], 7.1; 95% confidence interval [95% CI], 3.9 to 20.0). Children with urine KIM-1, MCP-1, and α-1 microglobulin concentrations in the highest quartile were also at significantly higher risk of CKD progression versus those with biomarker concentrations in the lowest quartile. Addition of the five biomarkers to a clinical model increased the discrimination and reclassification for CKD progression. CONCLUSIONS: After multivariable adjustment, a lower urine EGF concentration and higher urine KIM-1, MCP-1, and α-1 microglobulin concentrations were each associated with CKD progression in children.

Association of Multiple Plasma Biomarker Concentrations with Progression of Prevalent Diabetic Kidney Disease: Findings from the Chronic Renal Insufficiency Cohort (CRIC) Study.

BACKGROUND: Although diabetic kidney disease is the leading cause of ESKD in the United States, identifying those patients who progress to ESKD is difficult. Efforts are under way to determine if plasma biomarkers can help identify these high-risk individuals. METHODS: In our case-cohort study of 894 Chronic Renal Insufficiency Cohort Study participants with diabetes and an eGFR of <60 ml/min per 1.73 m2 at baseline, participants were randomly selected for the subcohort; cases were those patients who developed progressive diabetic kidney disease (ESKD or 40% eGFR decline). Using a multiplex system, we assayed plasma biomarkers related to tubular injury, inflammation, and fibrosis (KIM-1, TNFR-1, TNFR-2, MCP-1, suPAR, and YKL-40). Weighted Cox regression models related biomarkers to progression of diabetic kidney disease, and mixed-effects models estimated biomarker relationships with rate of eGFR change. RESULTS: Median follow-up was 8.7 years. Higher concentrations of KIM-1, TNFR-1, TNFR-2, MCP-1, suPAR, and YKL-40 were each associated with a greater risk of progression of diabetic kidney disease, even after adjustment for established clinical risk factors. After accounting for competing biomarkers, KIM-1, TNFR-2, and YKL-40 remained associated with progression of diabetic kidney disease; TNFR-2 had the highest risk (adjusted hazard ratio, 1.61; 95% CI, 1.15 to 2.26). KIM-1, TNFR-1, TNFR-2, and YKL-40 were associated with rate of eGFR decline. CONCLUSIONS: Higher plasma levels of KIM-1, TNFR-1, TNFR-2, MCP-1, suPAR, and YKL-40 were associated with increased risk of progression of diabetic kidney disease; TNFR-2 had the highest risk after accounting for the other biomarkers. These findings validate previous literature on TNFR-1, TNFR-2, and KIM-1 in patients with prevalent CKD and provide new insights into the influence of suPAR and YKL-40 as plasma biomarkers that require validation.

Plasma Biomarkers of Tubular Injury and Inflammation Are Associated with CKD Progression in Children.

BACKGROUND: After accounting for known risk factors for CKD progression in children, clinical outcomes among children with CKD still vary substantially. Biomarkers of tubular injury (such as KIM-1), repair (such as YKL-40), or inflammation (such as MCP-1, suPAR, TNF receptor-1 [TNFR-1], and TNFR-2) may identify children with CKD at risk for GFR decline. METHODS: We investigated whether plasma KIM-1, YKL-40, MCP-1, suPAR, TNFR-1, and TNFR-2 are associated with GFR decline in children with CKD and in subgroups defined by glomerular versus nonglomerular cause of CKD. We studied participants of the prospective CKiD Cohort Study which enrolled children with an eGFR of 30-90 ml/min per 1.73 m2 and then assessed eGFR annually. Biomarkers were measured in plasma collected 5 months after study enrollment. The primary endpoint was CKD progression, defined as a composite of a 50% decline in eGFR or incident ESKD. RESULTS: Of the 651 children evaluated (median age 11 years; median baseline eGFR of 53 ml/min per 1.73 m2), 195 (30%) had a glomerular cause of CKD. Over a median follow-up of 5.7 years, 223 children (34%) experienced CKD progression to the composite endpoint. After multivariable adjustment, children with a plasma KIM-1, TNFR-1, or TNFR-2 concentration in the highest quartile were at significantly higher risk of CKD progression compared with children with a concentration for the respective biomarker in the lowest quartile (a 4-fold higher risk for KIM-1 and TNFR-1 and a 2-fold higher risk for TNFR-2). Plasma MCP-1, suPAR, and YKL-40 were not independently associated with progression. When stratified by glomerular versus nonglomerular etiology of CKD, effect estimates did not differ significantly. CONCLUSIONS: Higher plasma KIM-1, TNFR-1, and TNFR-2 are independently associated with CKD progression in children.

Incident Type 2 Diabetes Among Individuals With CKD: Findings From the Chronic Renal Insufficiency Cohort (CRIC) Study.

RATIONALE & OBJECTIVE: Few studies have examined incident type 2 diabetes mellitus (T2DM) in chronic kidney disease (CKD). Our objective was to examine rates of and risk factors for T2DM in CKD, using several alternative measures of glycemic control. STUDY DESIGN: Prospective cohort study. SETTING & PARTICIPANTS: 1,713 participants with reduced glomerular filtration rates and without diabetes at baseline, enrolled in the Chronic Renal Insufficiency Cohort (CRIC) Study. PREDICTORS: Measures of kidney function and damage, fasting blood glucose, hemoglobin A1c (HbA1c), HOMA-IR (homeostatic model assessment of insulin resistance), demographics, family history of diabetes mellitus (DM), smoking status, medication use, systolic blood pressure, triglyceride level, high-density lipoprotein cholesterol level, body mass index, and physical activity. OUTCOME: Incident T2DM (defined as fasting blood glucose ≥ 126mg/dL or prescription of insulin or oral hypoglycemic agents). ANALYTICAL APPROACH: Concordance between fasting blood glucose and HbA1c levels was assessed using κ. Cause-specific hazards modeling, treating death and end-stage kidney disease as competing events, was used to predict incident T2DM. RESULTS: Overall T2DM incidence rate was 17.81 cases/1,000 person-years. Concordance between fasting blood glucose and HbA1c levels was low (κ for categorical versions of fasting blood glucose and HbA1c = 13%). Unadjusted associations of measures of kidney function and damage with incident T2DM were nonsignificant (P ≥ 0.4). In multivariable models, T2DM was significantly associated with fasting blood glucose level (P = 0.002) and family history of DM (P = 0.03). The adjusted association of HOMA-IR with T2DM was comparable to that of fasting blood glucose level; the association of HbA1c level was nonsignificant (P ≥ 0.1). Harrell's C for the models ranged from 0.62 to 0.68. LIMITATIONS: Limited number of outcome events; predictors limited to measures taken at baseline. CONCLUSIONS: The T2DM incidence rate among individuals with CKD is markedly higher than in the general population, supporting the need for greater vigilance in this population. Measures of glycemic control and family history of DM were independently associated with incident T2DM.

Erythrocytosis is associated with intradialytic hypotension: a case series.

BACKGROUND: For patients with end stage renal disease undergoing hemodialysis, erythrocytosis occurs rarely. Erythrocytosis increases the risk of thrombosis, which is a common complication in hemodialysis patients. The risk of thrombosis may also be increased by hypotension. The purpose of our report is to examine the relationship between intradialytic hypotension and erythrocytosis. CASE PRESENTATION: We present a series of five patients with end stage renal disease and erythrocytosis (peak hemoglobin range 15.2-18.5 g/dL). All were erythropoiesis-stimulating agent naïve and non-smokers. Prior to developing erythrocytosis, each patient developed recurring episodes of intradialytic hypotension over several months. A statistically significant inverse correlation was observed between nadir intradialytic systolic blood pressure and hemoglobin concentration. In the index case, midodrine treatment resulted in resolution of the hypotension and erythrocytosis. Most of the patients had multiple acquired renal cysts, which is a potential source of erythropoietin. Four of the five cases developed arteriovenous dialysis access or deep venous thrombosis. CONCLUSIONS: An association between intradialytic hypotension and erythrocytosis was observed in five cases. We postulate that chronic intermittent hypotension and renal ischemia may lead to erythropoietin secretion, and this cascade could represent a newly recognized cause of secondary erythrocytosis.

Kidney Proximal Tubule Lipoapoptosis Is Regulated by Fatty Acid Transporter-2 (FATP2).

Albuminuria and tubular atrophy are among the highest risks for CKD progression to ESRD. A parsimonious mechanism involves leakage of albumin-bound nonesterified fatty acids (NEFAs) across the damaged glomerular filtration barrier and subsequent reabsorption by the downstream proximal tubule, causing lipoapoptosis. We sought to identify the apical proximal tubule transporter that mediates NEFA uptake and cytotoxicity. We observed transporter-mediated uptake of fluorescently labeled NEFA in cultured proximal tubule cells and microperfused rat proximal tubules, with greater uptake from the apical surface than from the basolateral surface. Protein and mRNA expression analyses revealed that kidney proximal tubules express transmembrane fatty acid transporter-2 (FATP2), encoded by Slc27a2, but not the other candidate transporters CD36 and free fatty acid receptor 1. Kidney FATP2 localized exclusively to proximal tubule epithelial cells along the apical but not the basolateral membrane. Treatment of mice with lipidated albumin to induce proteinuria caused a decrease in the proportion of tubular epithelial cells and an increase in the proportion of interstitial space in kidneys from wild-type but not Slc27a2-/- mice. Ex vivo microperfusion and in vitro experiments with NEFA-bound albumin at concentrations that mimic apical proximal tubule exposure during glomerular injury revealed significantly reduced NEFA uptake and palmitate-induced apoptosis in microperfused Slc27a2-/- proximal tubules and Slc27a2-/- or FATP2 shRNA-treated proximal tubule cell lines compared with wild-type or scrambled oligonucleotide-treated cells, respectively. We conclude that FATP2 is a major apical proximal tubule NEFA transporter that regulates lipoapoptosis and may be an amenable target for the prevention of CKD progression.

Genome-Wide Association and Trans-ethnic Meta-Analysis for Advanced Diabetic Kidney Disease: Family Investigation of Nephropathy and Diabetes (FIND).

Diabetic kidney disease (DKD) is the most common etiology of chronic kidney disease (CKD) in the industrialized world and accounts for much of the excess mortality in patients with diabetes mellitus. Approximately 45% of U.S. patients with incident end-stage kidney disease (ESKD) have DKD. Independent of glycemic control, DKD aggregates in families and has higher incidence rates in African, Mexican, and American Indian ancestral groups relative to European populations. The Family Investigation of Nephropathy and Diabetes (FIND) performed a genome-wide association study (GWAS) contrasting 6,197 unrelated individuals with advanced DKD with healthy and diabetic individuals lacking nephropathy of European American, African American, Mexican American, or American Indian ancestry. A large-scale replication and trans-ethnic meta-analysis included 7,539 additional European American, African American and American Indian DKD cases and non-nephropathy controls. Within ethnic group meta-analysis of discovery GWAS and replication set results identified genome-wide significant evidence for association between DKD and rs12523822 on chromosome 6q25.2 in American Indians (P = 5.74x10-9). The strongest signal of association in the trans-ethnic meta-analysis was with a SNP in strong linkage disequilibrium with rs12523822 (rs955333; P = 1.31x10-8), with directionally consistent results across ethnic groups. These 6q25.2 SNPs are located between the SCAF8 and CNKSR3 genes, a region with DKD relevant changes in gene expression and an eQTL with IPCEF1, a gene co-translated with CNKSR3. Several other SNPs demonstrated suggestive evidence of association with DKD, within and across populations. These data identify a novel DKD susceptibility locus with consistent directions of effect across diverse ancestral groups and provide insight into the genetic architecture of DKD.

Urine biomarkers of tubular injury do not improve on the clinical model predicting chronic kidney disease progression.

Few investigations have evaluated the incremental usefulness of tubular injury biomarkers for improved prediction of chronic kidney disease (CKD) progression. As such, we measured urinary kidney injury molecule-1, neutrophil gelatinase-associated lipocalin, N-acetyl-ß-D-glucosaminidase and liver fatty acid binding protein under highly standardized conditions among 2466 enrollees of the prospective Chronic Renal Insufficiency Cohort Study. During 9433 person-years of follow-up, there were 581 cases of CKD progression defined as incident end-stage renal disease or halving of the estimated glomerular filtration rate. Levels of the urine injury biomarkers, normalized for urine creatinine, were strongly associated with CKD progression in unadjusted Cox proportional hazard models with hazard ratios in the range of 7 to 15 comparing the highest with the lowest quintiles. However, after controlling for the serum creatinine-based estimated glomerular filtration rate and urinary albumin/creatinine ratio, none of the normalized biomarkers was independently associated with CKD progression. None of the biomarkers improved on the high (0.89) C-statistic for the base clinical model. Thus, among patients with CKD, risk prediction with a clinical model that includes the serum creatinine-based estimated glomerular filtration rate and the urinary albumin/creatinine ratio is not improved on with the addition of renal tubular injury biomarkers.

Selecting SNPs informative for African, American Indian and European Ancestry: application to the Family Investigation of Nephropathy and Diabetes (FIND).

BACKGROUND: The presence of population structure in a sample may confound the search for important genetic loci associated with disease. Our four samples in the Family Investigation of Nephropathy and Diabetes (FIND), European Americans, Mexican Americans, African Americans, and American Indians are part of a genome- wide association study in which population structure might be particularly important. We therefore decided to study in detail one component of this, individual genetic ancestry (IGA). From SNPs present on the Affymetrix 6.0 Human SNP array, we identified 3 sets of ancestry informative markers (AIMs), each maximized for the information in one the three contrasts among ancestral populations: Europeans (HAPMAP, CEU), Africans (HAPMAP, YRI and LWK), and Native Americans (full heritage Pima Indians). We estimate IGA and present an algorithm for their standard errors, compare IGA to principal components, emphasize the importance of balancing information in the ancestry informative markers (AIMs), and test the association of IGA with diabetic nephropathy in the combined sample. RESULTS: A fixed parental allele maximum likelihood algorithm was applied to the FIND to estimate IGA in four samples: 869 American Indians; 1385 African Americans; 1451 Mexican Americans; and 826 European Americans. When the information in the AIMs is unbalanced, the estimates are incorrect with large error. Individual genetic admixture is highly correlated with principle components for capturing population structure. It takes ~700 SNPs to reduce the average standard error of individual admixture below 0.01. When the samples are combined, the resulting population structure creates associations between IGA and diabetic nephropathy. CONCLUSIONS: The identified set of AIMs, which include American Indian parental allele frequencies, may be particularly useful for estimating genetic admixture in populations from the Americas. Failure to balance information in maximum likelihood, poly-ancestry models creates biased estimates of individual admixture with large error. This also occurs when estimating IGA using the Bayesian clustering method as implemented in the program STRUCTURE. Odds ratios for the associations of IGA with disease are consistent with what is known about the incidence and prevalence of diabetic nephropathy in these populations.

GFR Estimation Using ß-Trace Protein and ß2-Microglobulin in CKD.

BACKGROUND: ß-Trace protein (BTP) and ß2-microglobulin (B2M) are novel glomerular filtration markers that have stronger associations with adverse outcomes than creatinine. Comparisons of BTP and B2M to creatinine and cystatin C are limited by the absence of rigorously developed glomerular filtration rate (GFR) estimating equations for the novel markers. STUDY DESIGN: Study of diagnostic test accuracy. SETTING & PARTICIPANTS: Pooled database of 3 populations with chronic kidney disease (CKD) with mean measured GFR of 48 mL/min/1.73 m2 (N=3,551; MDRD [Modification of Diet in Renal Disease] Study, AASK [African American Study of Kidney Disease and Hypertension], and CRIC [Chronic Renal Insufficiency Cohort] Study). INDEX TESTS: GFR estimated using creatinine, cystatin C, BTP, or B2M level. REFERENCE TEST: GFR measured as the urinary clearance of iothalamate. RESULTS: For BTP and B2M, coefficients for age, sex, and race were smaller than for creatinine and were similar or smaller than for cystatin C. For B2M, coefficients for sex, age, and race were smaller than for creatinine and were similar (age and race) or smaller (sex) than for cystatin C. The final equations with BTP (BTP, age, and sex) or B2M (B2M alone) were less accurate than either the CKD-EPI (CKD Epidemiology Collaboration) creatinine or cystatin C equations. The combined BTP-B2M equation (BTP and B2M alone) had similar accuracy to the CKD-EPI creatinine or cystatin C equation. The average of the BTP-B2M equation and the CKD-EPI creatinine-cystatin C equation was not more accurate than the CKD-EPI creatinine-cystatin C equation. LIMITATIONS: No external validation population, study population was restricted to CKD, few participants older than 65 years, or nonblack nonwhite race. CONCLUSIONS: BTP and B2M are less influenced by age, sex, and race than creatinine and less influenced by race than cystatin C, but provide less accurate GFR estimates than the CKD-EPI creatinine and cystatin C equations. The CKD-EPI BTP and B2M equation provides a methodological advance for their study as filtration markers and in their associations with risk and adverse outcomes, but further study is required before clinical use.

Variants in genes belonging to the fibroblast growth factor family are associated with lower extremity amputation in non-Hispanic whites: Findings from the chronic renal insufficiency cohort study.

Diabetes is the major risk factor for nontraumatic lower extremity amputation (LEA). The role of genetic polymorphisms in predisposing diabetics to impaired wound healing leading to LEA has not been sufficiently explored. We investigated the association between a set of genes belonging to the angiogenesis/wound repair pathway with LEA in the Chronic Renal Insufficiency Cohort, a study of adults with chronic kidney disease (CKD) that includes a subgroup with diabetes. This study was performed on 3,772 Chronic Renal Insufficiency Cohort participants who were genotyped on the ITMAT-Broad-CARe array chip. A total of 1,017 single-nucleotide polymorphisms (SNPs) in 22 genes belonging to the angiogenesis/would repair pathway were investigated. LEA was determined from patient self-report. The association between genetic variants and LEA status was examined using logistic regression and additive genetic models after stratifying the cohort by race/ethnicity and diabetic status. Unadjusted analyses as well as analyses adjusted for age, sex, estimated glomerular filtration rate, body mass index, peripheral vascular disease, hemoglobin A1c, and population stratification were performed. In non-Hispanic white participants with diabetes, rs11938826 and rs1960669, both intronic SNPs in the gene basic fibroblast growth factor-2 (FGF2), were significantly associated with LEA in covariate-adjusted analysis (OR: 2.83 (95% CI: 1.73, 4.62); p-value: 0.000034; Bonferroni adjusted p-value: 0.0006) and (OR: 2.61 (95% CI: 1.48, 4.61); p-value: 0.00095; Bonferroni adjusted p-value: 0.02). In the same subgroup, rs10883688, an FGF8 SNP of unknown functional effect, was also associated with LEA (OR: 1.72 (95% Confidence Interval: 1.14, 2.6); p-value: 0.00999; Bonferroni adjusted p-value: 0.04). No statistically significant associations were identified in the other ethnic groups. In conclusion, variant/s in FGF2 and FGF8 may predispose diabetics with CKD to LEA. Dysregulation of the FGF2 gene represents an opportunity to understand further, and possibly intervene upon, mechanisms of wound healing in diabetics with CKD.

Tubular atrophy in the pathogenesis of chronic kidney disease progression.

The longstanding focus in chronic kidney disease (CKD) research has been on the glomerulus, which is sensible because this is where glomerular filtration occurs, and a large proportion of progressive CKD is associated with significant glomerular pathology. However, it has been known for decades that tubular atrophy is also a hallmark of CKD and that it is superior to glomerular pathology as a predictor of glomerular filtration rate decline in CKD. Nevertheless, there are vastly fewer studies that investigate the causes of tubular atrophy, and fewer still that identify potential therapeutic targets. The purpose of this review is to discuss plausible mechanisms of tubular atrophy, including tubular epithelial cell apoptosis, cell senescence, peritubular capillary rarefaction and downstream tubule ischemia, oxidative stress, atubular glomeruli, epithelial-to-mesenchymal transition, interstitial inflammation, lipotoxicity and Na(+)/H(+) exchanger-1 inactivation. Once a a better understanding of tubular atrophy (and interstitial fibrosis) pathophysiology has been obtained, it might then be possible to consider tandem glomerular and tubular therapeutic strategies, in a manner similar to cancer chemotherapy regimens, which employ multiple drugs to simultaneously target different mechanistic pathways.

Na+-H+ exchanger-1 (NHE1) regulation in kidney proximal tubule.

The ubiquitously expressed plasma membrane Na(+)-H(+) exchanger NHE1 is a 12 transmembrane-spanning protein that directs important cell functions such as homeostatic intracellular volume and pH control. The 315 amino acid cytosolic tail of NHE1 binds plasma membrane phospholipids and multiple proteins that regulate additional, ion-translocation independent functions. This review focuses on NHE1 structure/function relationships, as well as the role of NHE1 in kidney proximal tubule functions, including pH regulation, vectorial Na(+) transport, cell volume control and cell survival. The implications of these functions are particularly critical in the setting of progressive, albuminuric kidney diseases, where the accumulation of reabsorbed fatty acids leads to disruption of NHE1-membrane phospholipid interactions and tubular atrophy, which is a poor prognostic factor for progression to end stage renal disease. This review amplifies the vital role of the proximal tubule NHE1 Na(+)-H(+) exchanger as a kidney cell survival factor.

Mesangial cell αvß8-integrin regulates glomerular capillary integrity and repair.

αvß8-Integrin is most abundantly expressed in the kidney, brain, and female reproductive organs, and its cognate ligand is latent transforming growth factor (LTGF)-ß. Kidney αvß8-integrin localizes to mesangial cells, and global ß8-integrin gene (Itgb8) deletion results in embryonic lethality due to impaired placentation and cerebral hemorrhage. To circumvent the lethality and better define kidney αvß8-integrin function, Cre-lox technology was used to generate mesangial-specific Itgb8-null mice. Platelet-derived growth factor-ß receptor (PDGFBR)-Cre mice crossed with a reporter strain revealed functional Cre recombinase activity in a predicted mesangial pattern. However, mating between two different PDGFBR-Cre or Ren1(d)-Cre strains with Itgb8 (flox/-) mice consistently resulted in incomplete recombination, with no renal phenotype in mosaic offspring. Induction of a renal phenotype with Habu snake venom, a reversible mesangiolytic agent, caused exaggerated glomerular capillary microaneurysms and delayed recovery in Cre(+/-) PDGFRB (flox/-) mice compared with Cre(+/-) PDGFRB (flox/+) control mice. To establish the mechanism, in vitro experiments were conducted in Itgb8-null versus Itgb8-expressing mesangial cells and fibroblasts, which revealed ß8-integrin-regulated adhesion to Arg-Gly-Asp (RGD) peptides within a mesangial-conditioned matrix as well as ß8-integrin-dependent migration on RGD-containing LTGF-ß or vitronectin matrices. We speculate that kidney αvß8-integrin indirectly controls glomerular capillary integrity through mechanical tension generated by binding RGD peptides in the mesangial matrix, and healing after glomerular injury may be facilitated by mesangial cell migration, which is guided by transient ß8-integrin interactions with RGD ligands.

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.

This study analyzed 3 cohorts (ARIC, MESA, and REGARDS) of adults without diabetes or prevalent chronic kidney disease (CKD) to determine the associations of 5 urinary biomarkers of kidney tubulointerstitial health with incident CKD, independent of traditional measures of kidney health. Meta-analysis of results from all 3 cohorts suggested that higher baseline levels of urine alpha-1-microglobulin were associated with incident CKD at follow-up. Results from individual cohorts suggested that in addition to alpha-1-microglobulin, monocyte chemoattractant protein-1, kidney injury molecule-1, and epidermal growth factor may also be associated with the development of CKD. These findings underscore the importance of kidney tubule interstitial health in defining risk of CKD independent of creatinine and urine albumin.

Diabetes, lower extremity amputation, loss of protective sensation, and neuronal nitric oxide synthase associated protein in the chronic renal insufficiency cohort study.

Lower extremity amputation (LEA) is a life-altering complication of diabetes. The goal of our study was to investigate the possibility that genetic variation in neuronal nitric oxide synthase associated protein (NOS1AP) is associated with LEA and diabetic peripheral neuropathy (DPN). Our work used data from the Chronic Renal Insufficiency Cohort (CRIC) study. CRIC is a multicenter investigation undertaken to pursue the relationship between chronic renal insufficiency and cardiovascular disease. We evaluated 3,040 CRIC study subjects; 1,490 individuals were African Americans and 1,550 were whites. LEA occurred in 162 (5.3%) subjects, 93 (6.2%) of African Americans and 69 (4.4%) of whites. In whites, NOS1AP single nucleotide polymorphism rs1963645 was most strongly associated with LEA (1.73 [1.23, 2.44]). In African Americans three NOS1AP single nucleotide polymorphisms were associated with LEA: rs6659759 (1.65 [1.21, 2.24]); rs16849113 (1.58 [1.16, 2.14]); rs880296 (1.54 [1.14, 2.10]). We tested a subset of 100 CRIC participants for DPN using Semmes-Weinstein filaments. DPN in those with diabetes was associated with rs1963645 (16.97 [2.38, 120.97]) in whites and rs16849113 and rs6659759 (3.62 [1.11, 11.83] and 3.02 [0.82, 11.12], respectively) in African Americans. In conclusion, this is one of the first studies to show that NOS1AP gene variants are associated with DPN and LEA.

Diabetic nephropathy in a sibling and albuminuria predict early GFR decline: a prospective cohort study.

BACKGROUND: Diabetic nephropathy is a growing clinical problem, and the cause for >40% of incident ESRD cases. Unfortunately, few modifiable risk factors are known. The objective is to examine if albuminuria and history of diabetic nephropathy (DN) in a sibling are associated with early DN progression or mortality. METHODS: In this longitudinal study of adults >18 yrs with diabetes monitored for up to 9 yrs (mean 4.6 ± 1.7 yrs), 435 subjects at high risk (DN family history) and 400 at low risk (diabetes >10 yrs, normoalbuminuria, no DN family history) for DN progression were evaluated for rate of eGFR change using the linear mixed effects model and progression to ESRD. All-cause mortality was evaluated by Kaplan-Meier analyses while controlling for baseline covariates in a Cox proportional hazards model. Covariates included baseline eGFR, age, gender, race, diabetes duration, blood pressure, hemoglobin A1c and urine albumin:creatinine ratio. Propensity score matching was used to identify high and low risk group pairs with balanced covariates. Sensitivity analyses were employed to test for residual confounding. RESULTS: Mean baseline eGFR was 74 ml/min/1.73 m2 (86% of cohort >60 ml/min/1.73 m2). Thirty high risk and no low risk subjects developed ESRD. eGFR decline was significantly greater in high compared to low risk subjects. After controlling for confounders, change in eGFR remained significantly different between groups, suggesting that DN family history independently regulates GFR progression. Mortality was also significantly greater in high versus low risk subjects, but after controlling for baseline covariates, no significant difference was observed between groups, indicating that factors other than DN family history more strongly affect mortality. Analyses of the matched pairs confirmed change in eGFR and mortality findings. Sensitivity analyses demonstrated that the eGFR results were not due to residual confounding by unmeasured covariates of a moderate effect size in the propensity matching. CONCLUSIONS: Diabetic subjects with albuminuria and family history of DN are vulnerable for early GFR decline, whereas subjects with diabetes for longer than 10 years, normoalbuminuria and negative family history, experience slower eGFR decline, and are extremely unlikely to require dialysis. Although we would not recommend that patients with low risk characteristics be neglected, scarce resources would be more sensibly devoted to vulnerable patients, such as the high risk cases in our study, and preferably prior to the onset of albuminuria or GFR decline.