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1.  Age and the Association of Kidney Measures with Mortality and End-Stage Renal Disease 
Context
Chronic kidney disease (CKD) is prevalent in older individuals, but the risk implications of low estimated glomerular filtration rate (eGFR) and high albuminuria across the full age range are controversial.
Objective
To evaluate possible effect modification (interaction) of age on the association of estimated GFR and albuminuria with clinical risk examining both relative and absolute risk.
Design, Setting, Participants
We investigated 2,051,244 participants from 33 general population or high-risk (of vascular disease) cohorts and 13 CKD cohorts from Asia, Australesia, Europe, and North/South America conducted during 1972–2011 with mean follow-up time of 5.8 years (range 0–31 years).
Main Outcome Measures
Hazard ratios (HRs) of mortality and end-stage renal disease (ESRD) according to eGFR and albuminuria were meta-analyzed across age categories after adjusting for sex, race, cardiovascular disease, diabetes, systolic blood pressure, cholestserol, body mass index, and smoking. Absolute risks were estimated using HRs and average incidence rates.
Results
Mortality (112,325 deaths) and ESRD (8,411 events) risk were higher at lower eGFR and higher albuminuria in every age category. In general/high-risk cohorts, relative mortality risk for reduced eGFR decreased with increasing age: e.g., adjusted HRs (95% CI) at eGFR 45 vs. 80 ml/min/1.73m2 were 3.50 (2.55–4.81), 2.21 (2.02–2.41), 1.59 (1.42–1.77), and 1.35 (1.23–1.48) in age categories 18–54, 55–64, 65–74 and 75+ years, respectively (P-values for age interaction <0.05). Absolute risk differences for the same comparisons were higher at older age (9.0 [95% CI, 6.0–12.8], 12.2 [10.3–14.3], 13.3 [9.0–18.6], and 27.2 [13.5–45.5] excess deaths per 1,000 person-years, respectively). For increased albuminuria, reduction of relative risk with increasing age were less evident, while differences in absolute risk were higher in the older age categories (7.5 [95% CI, 4.3–11.9], 12.2 [7.9–17.6], 22.7 [15.3–31.6], and 34.3 [19.5–52.4] excess deaths per 1,000 person-years, respectively by age category, at ACR 300 mg/g compared to 10 mg/g). In CKD cohorts, adjusted relative hazards of mortality did not decrease with age. In all cohorts, ESRD relative risks and absolute risk differences at lower eGFR or higher albuminuria were comparable across age categories.
Conclusions
Both low eGFR and high albuminuria were independently associated with mortality and ESRD regardless of age across a wide range of populations. Mortality showed lower relative risk but higher absolute risks differences at older age.
doi:10.1001/jama.2012.16817
PMCID: PMC3936348  PMID: 23111824
2.  Impact on cardiovascular risk follow-up from a shift to the CKD-EPI formula for eGFR reporting: a cross-sectional population-based primary care study 
BMJ Open  2013;3(9):e003631.
Objective
To assess the impact on cardiovascular risk factor management in primary care by the introduction of chronic kidney disease epidemiological collaboration (CKD-EPI) for estimated-glomerular filtration rate (eGFR) reporting.
Design and setting
Cross-sectional study of routine healthcare provision in 47 primary care practices in The Netherlands with Modification of Diet and Renal Disease Study eGFR reporting.
Methods
eGFR values were recalculated using CKD-EPI in patients with available creatine tests. Patients reclassified from CKD stage 3a to CKD stage 2 eGFR range were compared to those who remained in stage 3a for differences in demographic variables, blood pressure, comorbidity, medication usage and laboratory results.
Results
Among the 60 673 adult patients (37% of adult population) with creatine values, applying the CKD-EPI equation resulted in a 16% net reduction in patients with CKD stage 3 or worse. Patients reclassified from stage 3a to 2 had lower systolic blood pressure (139.7 vs 143.3 mm Hg p<0.0001), higher diastolic blood pressure (81.5 vs 78.4 mm Hg p<0.0001) and higher cholesterol (5.4 vs 5.1 mmol/L p<0.0001) compared to those who remained in stage 3a. Of those reclassified out of a CKD diagnosis 463 (32%) had no comorbidities that would qualify for annual CVD risk factor assessment and 20 (12% of those with sufficient data) had a EuroSCORE CVD risk >20% within 10 years.
Conclusions
Use of the CKD-EPI equation will result in many patients being removed from CKD registers and the associated follow-up. Current risk factor assessment in this group may be lacking from routine data and some patients within this group are at an increased risk for cardiovascular events.
doi:10.1136/bmjopen-2013-003631
PMCID: PMC3787480  PMID: 24071463
Primary Care; Chronic Renal Failure < Nephrology; Risk Management < Health Services Administration & Management
3.  Uremic Toxins Inhibit Transport by Breast Cancer Resistance Protein and Multidrug Resistance Protein 4 at Clinically Relevant Concentrations 
PLoS ONE  2011;6(4):e18438.
During chronic kidney disease (CKD), there is a progressive accumulation of toxic solutes due to inadequate renal clearance. Here, the interaction between uremic toxins and two important efflux pumps, viz. multidrug resistance protein 4 (MRP4) and breast cancer resistance protein (BCRP) was investigated. Membrane vesicles isolated from MRP4- or BCRP-overexpressing human embryonic kidney cells were used to study the impact of uremic toxins on substrate specific uptake. Furthermore, the concentrations of various uremic toxins were determined in plasma of CKD patients using high performance liquid chromatography and liquid chromatography/tandem mass spectrometry. Our results show that hippuric acid, indoxyl sulfate and kynurenic acid inhibit MRP4-mediated [3H]-methotrexate ([3H]-MTX) uptake (calculated Ki values: 2.5 mM, 1 mM, 25 µM, respectively) and BCRP-mediated [3H]-estrone sulfate ([3H]-E1S) uptake (Ki values: 4 mM, 500 µM and 50 µM, respectively), whereas indole-3-acetic acid and phenylacetic acid reduce [3H]-MTX uptake by MRP4 only (Ki value: 2 mM and IC50 value: 7 mM, respectively). In contrast, p-cresol, p-toluenesulfonic acid, putrescine, oxalate and quinolinic acid did not alter transport mediated by MRP4 or BCRP. In addition, our results show that hippuric acid, indole-3-acetic acid, indoxyl sulfate, kynurenic acid and phenylacetic acid accumulate in plasma of end-stage CKD patients with mean concentrations of 160 µM, 4 µM, 129 µM, 1 µM and 18 µM, respectively. Moreover, calculated Ki values are below the maximal plasma concentrations of the tested toxins. In conclusion, this study shows that several uremic toxins inhibit active transport by MRP4 and BCRP at clinically relevant concentrations.
doi:10.1371/journal.pone.0018438
PMCID: PMC3070735  PMID: 21483698
5.  Optimized Metabolomic Approach to Identify Uremic Solutes in Plasma of Stage 3–4 Chronic Kidney Disease Patients 
PLoS ONE  2013;8(8):e71199.
Background
Chronic kidney disease (CKD) is characterized by the progressive accumulation of various potential toxic solutes. Furthermore, uremic plasma is a complex mixture hampering accurate determination of uremic toxin levels and the identification of novel uremic solutes.
Methods
In this study, we applied 1H-nuclear magnetic resonance (NMR) spectroscopy, following three distinct deproteinization strategies, to determine differences in the plasma metabolic status of stage 3–4 CKD patients and healthy controls. Moreover, the human renal proximal tubule cell line (ciPTEC) was used to study the influence of newly indentified uremic solutes on renal phenotype and functionality.
Results
Protein removal via ultrafiltration and acetonitrile precipitation are complementary techniques and both are required to obtain a clear metabolome profile. This new approach, revealed that a total of 14 metabolites were elevated in uremic plasma. In addition to confirming the retention of several previously identified uremic toxins, including p-cresyl sulphate, two novel uremic retentions solutes were detected, namely dimethyl sulphone (DMSO2) and 2-hydroxyisobutyric acid (2-HIBA). Our results show that these metabolites accumulate in non-dialysis CKD patients from 9±7 µM (control) to 51±29 µM and from 7 (0–9) µM (control) to 32±15 µM, respectively. Furthermore, exposure of ciPTEC to clinically relevant concentrations of both solutes resulted in an increased protein expression of the mesenchymal marker vimentin with more than 10% (p<0.05). Moreover, the loss of epithelial characteristics significantly correlated with a loss of glucuronidation activity (Pearson r = −0.63; p<0.05). In addition, both solutes did not affect cell viability nor mitochondrial activity.
Conclusions
This study demonstrates the importance of sample preparation techniques in the identification of uremic retention solutes using 1H-NMR spectroscopy, and provide insight into the negative impact of DMSO2 and 2-HIBA on ciPTEC, which could aid in understanding the progressive nature of renal disease.
doi:10.1371/journal.pone.0071199
PMCID: PMC3732267  PMID: 23936492
6.  Hepcidin-25 in Chronic Hemodialysis Patients Is Related to Residual Kidney Function and Not to Treatment with Erythropoiesis Stimulating Agents 
PLoS ONE  2012;7(7):e39783.
Hepcidin-25, the bioactive form of hepcidin, is a key regulator of iron homeostasis as it induces internalization and degradation of ferroportin, a cellular iron exporter on enterocytes, macrophages and hepatocytes. Hepcidin levels are increased in chronic hemodialysis (HD) patients, but as of yet, limited information on factors associated with hepcidin-25 in these patients is available. In the current cross-sectional study, potential patient-, laboratory- and treatment-related determinants of serum hepcidin-20 and -25, were assessed in a large cohort of stable, prevalent HD patients. Baseline data from 405 patients (62% male; age 63.7±13.9 [mean SD]) enrolled in the CONvective TRAnsport STudy (CONTRAST; NCT00205556) were studied. Predialysis hepcidin concentrations were measured centrally with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Patient-, laboratory- and treatment related characteristics were entered in a backward multivariable linear regression model. Hepcidin-25 levels were independently and positively associated with ferritin (p<0.001), hsCRP (p<0.001) and the presence of diabetes (p = 0.02) and inversely with the estimated glomerular filtration rate (p = 0.01), absolute reticulocyte count (p = 0.02) and soluble transferrin receptor (p<0.001). Men had lower hepcidin-25 levels as compared to women (p = 0.03). Hepcidin-25 was not associated with the maintenance dose of erythropoiesis stimulating agents (ESA) or iron therapy. In conclusion, in the currently studied cohort of chronic HD patients, hepcidin-25 was a marker for iron stores and erythropoiesis and was associated with inflammation. Furthermore, hepcidin-25 levels were influenced by residual kidney function. Hepcidin-25 did not reflect ESA or iron dose in chronic stable HD patients on maintenance therapy. These results suggest that hepcidin is involved in the pathophysiological pathway of renal anemia and iron availability in these patients, but challenges its function as a clinical parameter for ESA resistance.
doi:10.1371/journal.pone.0039783
PMCID: PMC3396629  PMID: 22808058

Results 1-6 (6)