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.

KEY POINTS: Higher plasma and urine kidney injury molecule-1, urine monocyte chemoattractant protein-1, and lower urine alpha-1-microglobulin were associated with left ventricular hypertrophy, even after adjustment for confounders. Biomarkers of tubular injury, dysfunction, and inflammation may indicate the severity of kidney pathology and are associated with left ventricular hypertrophy. BACKGROUND: Left ventricular hypertrophy (LVH) is common in children with CKD and is associated with an increased risk of cardiovascular disease and mortality. We have shown that several plasma and urine biomarkers are associated with increased risk of CKD progression. As CKD is associated with LVH, we sought to investigate the association between the biomarkers and LVH. METHODS: In the CKD in Children Cohort Study, children aged 6 months to 16 years with an eGFR of 30–90 ml/min per 1.73 m2 were enrolled at 54 centers in the United States and Canada. We measured plasma biomarkers kidney injury molecule-1 (KIM-1), tumor necrosis factor receptor-1, tumor necrosis factor receptor-2, soluble urokinase-type plasminogen activator receptor and urine KIM-1, monocyte chemoattractant protein-1 (MCP-1), YKL-40, alpha-1-microglobulin (alpha-1m), and epidermal growth factor in stored plasma and urine collected 5 months after enrollment. Echocardiograms were performed 1 year after enrollment. We assessed the cross-sectional association between the log2 biomarker levels and LVH (left ventricular mass index greater than or equal to the 95th percentile) using a Poisson regression model, adjusted for age, sex, race, body mass index, hypertension, glomerular diagnosis, urine protein-to-creatinine ratio, and eGFR at study entry. RESULTS: Among the 504 children, LVH prevalence was 12% (n=59) 1 year after enrollment. In a multivariable-adjusted model, higher plasma and urine KIM-1 and urine MCP-1 concentrations were associated with a higher prevalence of LVH (plasma KIM-1 prevalence ratio [PR] per log2: 1.27, 95% confidence interval [CI], 1.02 to 1.58; urine KIM-1 PR: 1.21, 95% CI, 1.11 to 1.48; and urine MCP-1 PR: 1.18, 95% CI, 1.04 to 1.34). After multivariable adjustment for covariates, lower urine alpha-1m was also associated with a higher prevalence of LVH (PR: 0.90, 95% CI, 0.82 to 0.99). CONCLUSIONS: Higher plasma and urine KIM-1, urine MCP-1, and lower urine alpha-1m were each associated with LVH prevalence in children with CKD. These biomarkers may better inform risk and help elucidate the pathophysiology of LVH in pediatric CKD.

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.

We evaluated the cross-sectional associations of N-terminal pro-B-type natriuretic peptide (NT-proBNP) with cardiac structural and functional abnormalities in a cohort of patients with chronic kidney disease without clinical heart failure, the Chronic Renal Insufficiency Cohort (n = 3,232). The associations of NT-proBNP with echocardiographically determined left ventricular (LV) mass and LV systolic and diastolic function were evaluated using multivariate logistic and linear regression models. Reclassification of participants' predicted risk of LV hypertrophy (LVH), systolic and diastolic dysfunction was performed using a category-free net reclassification improvement index that compared a clinical model with and without NT-proBNP. The median NT-proBNP was 126.6 pg/ml (interquartile range 55.5 to 303.7). The greatest quartile of NT-proBNP was associated with a nearly threefold odds of LVH (odds ratio 2.7, 95% confidence interval [CI] 1.8 to 4.0) and LV systolic dysfunction (odds ratio 2.7, 95% CI 1.7 to 4.5) and a twofold odds of diastolic dysfunction (odds ratio 2.0, 95% CI 1.3 to 2.9) in the fully adjusted models. When evaluated alone as a screening test, NT-proBNP functioned modestly for the detection of LVH (area under the curve 0.66) and LV systolic dysfunction (area under the curve 0.62) and poorly for the detection of diastolic dysfunction (area under the curve 0.51). However, when added to the clinical model, NT-proBNP significantly reclassified participants' likelihood of having LVH (net reclassification improvement 0.14, 95% CI 0.13-0.15; p <0.001) and LV systolic dysfunction (net reclassification improvement 0.28, 95% CI 0.27 to 0.30; p <0.001) but not diastolic dysfunction (net reclassification improvement 0.10, 95% CI 0.10 to 0.11; p = 0.07). In conclusion, in this large chronic kidney disease cohort without heart failure, NT-proBNP had strong associations with prevalent LVH and LV systolic dysfunction.

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.

Background

Serum β-trace protein (BTP) and β2-microglobulin (B2M) are independently associated with end-stage renal disease (ESRD) and mortality in the general population and high-risk groups with diabetes or advanced chronic kidney disease (CKD). Less is known about their associations with outcomes and predictive ability in adults with moderate CKD.

Study design

Prospective cohort study.

Setting & participants

3,613 adults from the CRIC (Chronic Renal Insufficiency Cohort) Study (45% women; mean age, 57.9 years; 41.0% non-Hispanic black; 51.9% with diabetes).

Predictors

BTP and B2M levels with a reciprocal transformation to reflect their associations with filtration, creatinine-based estimated glomerular filtration rate (eGFRcr), measured GFR, and a 4-marker composite score combining BTP, B2M, creatinine, and cystatin C levels. Predictors were standardized as z scores for comparisons across filtration markers.

Outcomes

ESRD, all-cause mortality, and new-onset cardiovascular disease.

Results

During a 6-year median follow-up, 755 (21%) participants developed ESRD, 653 died, and 292 developed new-onset cardiovascular disease. BTP, B2M, and the 4-marker composite score were independent predictors of ESRD and all-cause mortality, and B2M and the 4-marker composite score of cardiovascular events, after multivariable adjustment. These associations were stronger than those observed for eGFRcr (P vs eGFRcr≤0.02). The 4-marker composite score led to improvements in C statistic and 2.5-year risk reclassification beyond eGFRcr for all outcomes.

Limitations

Filtration markers measured at one time point; measured GFR available in subset of cohort.

Conclusions

BTP and B2M levels may contribute additional risk information beyond eGFRcr, and the use of multiple markers may improve risk prediction beyond this well-established marker of kidney function among persons with moderate CKD.

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.

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.