Comparison of estimated GFR using cystatin C versus creatinine in pediatric kidney transplant recipients.

BACKGROUND: An accurate, rapid estimate of glomerular filtration rate (GFR) in kidney transplant patients affords early detection of transplant deterioration and timely intervention. This study compared the performance of serum creatinine (Cr) and cystatin C (CysC)-based GFR equations to measured GFR (mGFR) using iohexol among pediatric kidney transplant recipients. METHODS: CysC, Cr, and mGFR were obtained from 45 kidney transplant patients, 1-18 years old. Cr- and CysC-estimated GFR (eGFR) was compared against mGFR using the Cr-based (Bedside Schwartz, U25-Cr), CysC-based (Gentian CysC, CAPA, U25-CysC), and Cr-CysC combination (CKiD Cr-CysC, U25 Cr-CysC) equations in terms of bias, precision, and accuracy. Bland-Altman plots assessed the agreement between eGFR and mGFR. Secondary analyses evaluated the formulas in patients with biopsy-proven histological changes, and K/DOQI CKD staging. RESULTS: Bias was small with Gentian CysC (0.1 ml/min/1.73 m2); 88.9% and 37.8% of U25-CysC estimations were within 30% and 10% of mGFR, respectively. In subjects with histological changes on biopsy, Gentian CysC had a small bias and U25-CysC were more accurate-both with 83.3% of and 41.7% of estimates within 30% and 10% mGFR, respectively. Precision was better with U25-CysC, CKiD Cr-CysC, and U25 Cr-CysC. Bland-Altman plots showed the Bedside Schwartz, Gentian CysC, CAPA, and U25-CysC tend to overestimate GFR when > 100 ml/min/1.72 m2. CAPA misclassified CKD stage the least (whole cohort 24.4%, histological changes on biopsy 33.3%). CONCLUSIONS: In this small cohort, CysC-based equations with or without Cr may have better bias, precision, and accuracy in predicting GFR.

Base (HCO3-/CO32-) Transport Properties of SLC4 Proteins: New Insights in Acid-Base Kidney Physiology.

H+ or base transporters and channels in the mammalian genome play important roles in the maintenance of numerous cellular biochemical and physiologic processes throughout the body. Among the known base transporters, those within the SLC4 and SLC26 gene families are involved in cell, transepithelial, and whole organ function. Whether the functional properties of these transporters involve HCO3-, CO32-, or HCO3-/CO32- stimulated H+ (or OH-) transport has not received widespread attention in the literature. Accordingly, "bicarbonate" is the term typically used in most textbooks without greater specificity. Moreover, clinicians and physiologists have historically focused on the blood HCO3- concentration as the base term in the Henderson-Hasselbalch equation in the analysis of clinical acid-base abnormalities, thus, bicarbonate has been assumed to be the species reabsorbed along the nephron as required to maintain the blood [HCO3-] at approximately 25 mM. However, accumulating data in the literature suggest that carbonate, rather than bicarbonate, is the species absorbed across the proximal tubule basolateral membrane, whereas in the collecting duct, bicarbonate is indeed transported. Various experimental approaches leading to this new concept are herein reviewed.

Development of an adaptive clinical web-based prediction tool for kidney replacement therapy in children with chronic kidney disease.

Clinicians need improved prediction models to estimate time to kidney replacement therapy (KRT) for children with chronic kidney disease (CKD). Here, we aimed to develop and validate a prediction tool based on common clinical variables for time to KRT in children using statistical learning methods and design a corresponding online calculator for clinical use. Among 890 children with CKD in the Chronic Kidney Disease in Children (CKiD) study, 172 variables related to sociodemographics, kidney/cardiovascular health, and therapy use, including longitudinal changes over one year were evaluated as candidate predictors in a random survival forest for time to KRT. An elementary model was specified with diagnosis, estimated glomerular filtration rate and proteinuria as predictors and then random survival forest identified nine additional candidate predictors for further evaluation. Best subset selection using these nine additional candidate predictors yielded an enriched model additionally based on blood pressure, change in estimated glomerular filtration rate over one year, anemia, albumin, chloride and bicarbonate. Four additional partially enriched models were constructed for clinical situations with incomplete data. Models performed well in cross-validation, and the elementary model was then externally validated using data from a European pediatric CKD cohort. A corresponding user-friendly online tool was developed for clinicians. Thus, our clinical prediction tool for time to KRT in children was developed in a large, representative pediatric CKD cohort with an exhaustive evaluation of potential predictors and supervised statistical learning methods. While our models performed well internally and externally, further external validation of enriched models is needed.

Trajectories of eGFR after kidney transplantation according to trajectories of eGFR prior to kidney replacement therapies in children with chronic kidney disease.

BACKGROUND: In children with chronic kidney disease (CKD), certain risk factors are associated with faster eGFR decline and earlier kidney failure. Whether these factors have lingering effects on post-transplant eGFR trajectory remains unclear. We characterized pre- and post-transplant eGFR trajectories in pediatric kidney transplant recipients by their pre-kidney replacement therapy (KRT) risk factors. METHODS: We studied eGFR trajectories before KRT initiation and after transplantation among Chronic Kidney Disease in Children (CKiD) Study participants. We used mixed-effects models to compare pre-KRT versus post-transplant eGFR trajectories within individual participants by 7 pre-KRT risk factors: glomerular/non-glomerular etiology, race, preemptive transplant, proteinuria, albuminuria, and systolic/diastolic blood pressure (SBP/DBP). RESULTS: We analyzed 1602 pre-KRT and 592 post-transplant eGFR measurements from 246 transplant recipients. Mean annual eGFR decline was decreased from 18.0% pre-KRT (95%CI, 16.1-19.8) to 5.0% post-transplant (95%CI, 3.3-6.7). All 7 pre-KRT risk factors showed strong associations with faster pre-KRT eGFR decline, but not with post-transplant eGFR decline; only albuminuria, high SBP, and high DBP reached statistical significance with notably attenuated associations. In our multivariable model of the pre-KRT risk factors, post-transplant eGFR decline was more rapid only when albuminuria and high SBP were both present. CONCLUSIONS: eGFR decline substantially slows down after transplant even among children with rapidly progressing forms of CKD. Nonetheless, those who had albuminuria and high SBP before KRT might continue to show faster eGFR decline after transplant, specifically when both risk factors were present. This subgroup might benefit from intensive pre-transplant management for at least one of the two risk factors. A higher resolution version of the Graphical abstract is available as Supplementary information.

Application of GFR estimating equations to children with normal, near-normal, or discordant GFR.

BACKGROUND: The objective was to determine the extent that eGFR formulas correspond to measured plasma iohexol clearance (iGFR) in children with normal or near normal kidney function, particularly how different eGFR formulas yield discordant results. METHODS: iGFR from 2 (iGFR-2pt) and 4 (iGFR-4pt) time points along with creatinine and/or cystatin C-based eGFR were measured in children with mild CKD, stages 1-2. eGFR was calculated using 6 equations: 3 under 25 (U25) formulas from the Chronic Kidney Disease in Children (CKiD) study, the full age-combined cystatin C (cysC) and creatinine spectrum (FAS-combined), the European Kidney Function Consortium (EKFC-creatinine) equation, and the Chronic Kidney Disease Epidemiology Collaboration (CKD-epi) cysC-based equation. RESULTS: Twenty-nine children were included, of which 22 had discordant creatinine vs. cystatin C-based eGFR by ≥ 15mL/min/1.73 m2. Overall, the FAS-combined had the least bias, while the U25 most accurately identified children with an eGFR < 90 mL/min/1.73 m2. When Cr-eGFR was ≥ 15 mL/min higher than CysC-eGFR, the U25 creatinine eGFR was closest to iGFR-4pt. When CysC eGFR was higher, the U25-combined was closest to iGFR-4pt. CONCLUSION: The formulas that most closely approximated the measured GFR varied depending on the pattern of discordant eGFR results. Based on the results, we recommend using the CKiD U25-combined formula to screen for children with a low GFR. Either the CKiD U25-combined or FAS-combined would be recommended for changes in eGFR longitudinally. However, because all formulas were discordant from the iGFR-4pt in over a third of participants, further refinement of pediatric eGFR formulas is needed at the normal/near-normal range. A higher resolution version of the Graphical abstract is available as Supplementary information.

Hyperkalemia in pediatric chronic kidney disease.

BACKGROUND: While hyperkalemia is well described in adult chronic kidney disease (CKD), large studies evaluating potassium trends and risk factors for hyperkalemia in pediatric CKD are lacking. This study aimed to characterize hyperkalemia prevalence and risk factors in pediatric CKD. METHODS: Cross-sectional analysis of Chronic Kidney Disease in Children (CKiD) study data evaluated median potassium levels and percentage of visits with hyperkalemia (K ≥5.5 mmoL/L) in relation to demographics, CKD stage, etiology, proteinuria, and acid-base status. Multiple logistic regression was used to identify risk factors for hyperkalemia. RESULTS: One thousand and fifty CKiD participants with 5183 visits were included (mean age 13.1 years, 62.7% male, 32.9% self-identifying as African American or Hispanic). A percentage of 76.6% had non-glomerular disease, 18.7% had CKD stage 4/5, 25.8% had low CO2, and 54.2% were receiving ACEi/ARB therapy. Unadjusted analysis identified a median serum potassium level of 4.5 mmol/L (IQR 4.1-5.0, p <0.001) and hyperkalemia in 6.6% of participants with CKD stage 4/5. Hyperkalemia was present in 14.3% of visits with CKD stage 4/5 and glomerular disease. Hyperkalemia was associated with low CO2 (OR 7.72, 95%CI 3.05-19.54), CKD stage 4/5 (OR 9.17, 95%CI 4.02-20.89), and use of ACEi/ARB therapy (OR 2.14, 95%CI 1.36-3.37). Those with non-glomerular disease were less frequently hyperkalemic (OR 0.52, 95%CI 0.34-0.80). Age, sex, and race/ethnicity were not associated with hyperkalemia. CONCLUSIONS: Hyperkalemia was observed more frequently in children with advanced stage CKD, glomerular disease, low CO2, and ACEi/ARB use. These data can help clinicians identify high-risk patients who may benefit from earlier initiation of potassium-lowering therapies. A higher resolution version of the Graphical abstract is available as Supplementary information.

Longitudinal changes in uric acid concentration and their relationship with chronic kidney disease progression in children and adolescents.

BACKGROUND: Elevated serum uric acid concentration is a risk factor for CKD progression. Its change over time and association with CKD etiology and concomitant changes in estimated glomerular filtration rate (eGFR) in children and adolescents are unknown. METHODS: Longitudinal study of 153 children/adolescents with glomerular (G) and 540 with non-glomerular (NG) etiology from the CKD in Children (CKiD) study. Baseline serum uric acid, change in uric acid and eGFR over time, CKD etiology, and comorbidities were monitored. Adjusted linear mixed-effects regression models quantified the relationship between within-person changes in uric acid and concurrent within-person changes in eGFR. RESULTS: Participants with stable uric acid over follow-up had CKD progression which became worse for increased baseline uric acid (average annual percentage changes in eGFR were - 1.4%, - 7.7%, and - 14.7% in those with G CKD with baseline uric acid < 5.5 mg/dL, 5.5 - 7.5 mg/dL, and > 7.5 mg/dL, respectively; these changes were - 1.4%, - 4.1%, and - 8.6% in NG CKD). Each 1 mg/dL increase in uric acid over follow-up was independently associated with significant concomitant eGFR decreases of - 5.7% (95%CI - 8.4 to - 3.0%) (G) and - 5.1% (95%CI - 6.3 to - 4.0%) (NG) for those with baseline uric acid < 5.5 mg/dL and - 4.3% (95%CI - 6.8 to - 1.6%) (G) and - 3.3% (95%CI - 4.1 to - 2.6%) (NG) with baseline uric acid between 5.5 and 7.5 mg/dL. CONCLUSIONS: Higher uric acid levels and increases in uric acid over time are risk factors for more severe progression of CKD in children and adolescents. A higher resolution version of the Graphical abstract is available as Supplementary information.

The first randomized controlled trial in pediatric nephrology: the history of the International Study of Kidney Disease in Children (ISKDC).

The International Study of Kidney Disease in Children (ISKDC), begun in 1966, conducted the first international collaborative randomized blinded controlled trial in pediatric nephrology and one of the first in either pediatrics or nephrology. For this trial, the ISKDC developed the criteria, such as those for response and relapse, used today to describe the clinical course of the nephrotic syndrome, and the trial generated the nephropathologic terminology and criteria which largely remain the current standards. Over an approximately 20-year span, the ISKDC followed the natural history and evaluated the therapeutic effectiveness of therapies in over 500 children with the nephrotic syndrome from three continents. It published 14 peer-reviewed studies and several reports and commentaries, many of which helped create current standards of practice for therapy of childhood nephrotic syndrome and consequently remain highly cited today. The ISKDC continues to be an important model for subsequent collaborative studies and was the impetus for the development of regional and national pediatric nephrology societies leading to the recognition and growth of pediatric nephrology as a separate subspecialty. A higher resolution version of the Graphical abstract is available as Supplementary information.

Reduced kidney function and hypertension in adolescents with low birth weight, NHANES 1999-2016.

BACKGROUND: Chronic kidney disease (CKD) is a major health problem, and the risk of CKD and hypertension in children born low birth weight (LBW) is under-recognized. We hypothesized that children born with LBW would have a higher prevalence of reduced kidney function and hypertension. METHODS: Using the National Health and Nutrition Examination Survey (NHANES), we conducted a cross-sectional study to evaluate whether LBW (< 2500 g), very low birth weight (VLBW < 1500 g), and large birth weight (BW) (> 4000 g) were associated with kidney disease using 4 different estimating equations. We used the Counahan-Barratt, updated Schwartz, CKiD-U25, and full age spectrum creatinine-based GFR estimating equations to evaluate associations between a history of LBW/VLBW/large BW and reduced kidney function (eGFR < 90 mL/min/1.73 m2) in children. We also assessed blood pressure (BP) using the old and new pediatric hypertension guidelines. RESULTS: Our analysis included 6336 children (age 12-15 years) in NHANES representing over 13 million US individuals. Using the updated Schwartz, the prevalence of reduced kidney function was 30.1% (25.2-35.6) for children born with LBW compared to 22.4% (20.5-24.3) in children with normal BW. Equations yielded different estimates of prevalence of reduced kidney function in LBW from 21.5% for Counahan-Barratt to 35.4% for CKiD-U25. Compared to those with normal BW, participants with LBW and VLBW had a 7.2 and 10.3% higher prevalence of elevated BP and a 2.4 and 14.6% higher prevalence of hypertension, respectively. CONCLUSIONS: Children born with LBW are at higher risk of reduced kidney function and hypertension than previously described. A higher resolution version of the Graphical abstract is available as Supplementary information.

Maturation of GFR in Term-Born Neonates: An Individual Participant Data Meta-Analysis.

BACKGROUND: The evidence from individual studies to support the maturational pattern of GFR in healthy, term-born neonates is inconclusive. We performed an individual participant data (IPD) meta-analysis of reported measured GFR (mGFR) data, aiming to establish neonatal GFR reference values. Furthermore, we aimed to optimize neonatal creatinine-based GFR estimations. METHODS: We identified studies reporting mGFR measured by exogenous markers or creatinine clearance (CrCL) in healthy, term-born neonates. The relationship between postnatal age and clearance was investigated using cubic splines with generalized additive linear mixed models. From our reference values, we estimated an updated coefficient for the Schwartz equation (eGFR [ml/min per 1.73 m2]=(k×height [cm])/serum creatinine [mg/dl]). RESULTS: Forty-eight out of 1521 screened articles reported mGFR in healthy, term-born neonates, and 978 mGFR values from 881 neonates were analyzed. IPD were available for 367 neonates, and the other 514 neonates were represented by 41 aggregated data points as means/medians per group. GFR doubled in the first 5 days after birth, from 19.6 (95% CI, 14.7 to 24.6) to 40.6 (95% CI, 36.7 to 44.5) ml/min per 1.73 m2, and then increased more gradually to 59.4 (95% CI, 45.9 to 72.9) ml/min per 1.73 m2 by 4 weeks of age. A coefficient of 0.31 to estimate GFR best fitted the data. CONCLUSIONS: These reference values for healthy, term-born neonates show a biphasic increase in GFR, with the largest increase between days 1 and 5. Together with the re-examined Schwartz equation, this can help identify altered GFR in term-born neonates. To enable widespread implementation of our proposed eGFR equation, validation in a large cohort of neonates is required.

Using Serum Cystatin C to Predict Acute Kidney Injury Following Infant Cardiac Surgery.

Acute kidney injury (AKI) following cardiopulmonary bypass (CPB) is associated with increased morbidity and mortality. Serum Cystatin C (CysC) is a novel biomarker synthesized by all nucleated cells that may act as an early indicator of AKI following infant CPB. Prospective observational study of infants (< 1 year) requiring CPB during cardiac surgery. CysC was measured at baseline and 12, 24, 48, and 72 h following CPB initiation. Each post-op percent difference in CysC (e.g. %CysC12h) from baseline was calculated. Clinical variables along with urine output (UOP) and serum creatinine (SCr) were followed. Subjects were divided into two groups: AKI and non-AKI based upon the Kidney Disease Improving Global Outcomes (KDIGO) classification. AKI occurred in 41.9% (18) of the 43 infants enrolled. Patient demographics and baseline CysC levels were similar between groups. CysC levels were 0.97 ± 0.28 mg/L over the study period, and directly correlated with SCr (R = 0.71, p < 0.0001). Although absolute CysC levels were not significant between groups, the %CysC12h was significantly greater in the AKI group (AKI: - 16% ± 22% vs. Non-AKI - 28% ± 9% mg/L; p = 0.003). However, multivariate analysis demonstrated that a lower UOP (Odds Ratio:0.298; 95% CI 0.073, 0.850; p = 0.02) but not %CysC12h was independently associated with AKI. Despite a significant difference in the %CysC12h, only UOP was independently associated with AKI. Larger studies of a more homogenous population are needed to understand these results and to explore the variability in this biomarker seen across institutions.

Self-reported Race, Serum Creatinine, Cystatin C, and GFR in Children and Young Adults With Pediatric Kidney Diseases: A Report From the Chronic Kidney Disease in Children (CKiD) Study.

RATIONALE & OBJECTIVE: Recent reassessment of the use of race in estimated glomerular filtration rate (eGFR) in adults has instigated questions about the role of race in eGFR expressions for children. Little research has examined the associations of self-reported race with measured GFR (mGFR) adjusting for serum creatinine or cystatin C in children and young adults with chronic kidney disease (CKD). This study examined these associations and evaluated the performance of the previously published "U25" (under the age of 25 years) eGFR equations in a large cohort of children and young adults with CKD. STUDY DESIGN: Observational cohort study. SETTING & PARTICIPANTS: Participants in the Chronic Kidney Disease in Children (CKiD) study including 190 Black and 675 non-Black participants contributing 473 and 1,897 annual person-visits, respectively. EXPOSURE: Self- or parental-reported race (Black, non-Black). Adjustment for serum creatinine or cystatin C, body size, and socioeconomic status. OUTCOME: mGFR based on iohexol clearance. ANALYTICAL APPROACH: Linear regression with generalized estimating equations, stratified by age (<6, 6-12, 12-18, and ≥18 years) incorporating serum creatinine or serum cystatin C. Contrasting performance in different self-reported racial groups of the U25 eGFR equations. RESULTS: Self-reported Black race was significantly associated with 12.8% higher mGFR among children in regression models including serum creatinine. Self-reported Black race was significantly associated with 3.5% lower mGFR after adjustment for cystatin C overall but was not significant for those over 12 years. The results were similar after adjustment for body size and socioeconomic factors. The average of creatinine- and cystatin C-based U25 equations was unbiased by self-reported race groups. LIMITATIONS: Small number of children < 6 years; lean body mass was estimated. CONCLUSIONS: Differences in the creatinine-mGFR relationship by self-reported race were observed in children and young adults with CKD and were consistent with findings in adults. Smaller and opposite differences were observed for the cystatin C-mGFR relationship, especially in the younger age group. We recommend inclusion of children for future investigations of biomarkers to estimate GFR. Importantly, for GFR estimation among those under 25 years of age, the average of the new U25 creatinine and cystatin C equations without race coefficients yields unbiased estimates of mGFR.

Low variability of plant protein intake in the CKiD cohort does not demonstrate changes in estimated GFR nor electrolyte balance.

BACKGROUND: Vegetable or plant-based sources of protein may confer health benefits in children with progressive kidney disease. Our aims were to understand the effect of the proportion of vegetable protein intake on changes in estimated GFR and to understand the effect of the proportion of vegetable protein intake on serum levels of bicarbonate, phosphorus, and potassium. METHODS: Children with baseline eGFR between 30 and 90 mL/min/1.73 m2 were recruited from 59 centers across North America as part of the chronic kidney disease in children (CKiD) study. The percentage of dietary vegetable protein (VP%) was gathered from annual Food Frequency Questionnaires. We performed longitudinal linear mixed models to determine the effect of VP% on eGFR and longitudinal logistic mixed models to determine the effect of VP% on electrolyte balance (potassium, phosphorus, bicarbonate). RESULTS: Two thousand visits from 631 subjects. Across all dichotomized groups of children (sex, African American race, Hispanic ethnicity, glomerular etiology of CKD, hypertension, anemia, hyperkalemia, hyperphosphatemia, acidosis, BMI < 95th percentile), the median VP% was 32-35%. The longitudinal mixed model analysis did not show any effect of VP% on eGFR electrolyte (bicarbonate, phosphorus, and potassium) abnormalities (p > 0.1). CONCLUSIONS: A diverse cohort of children with CKD has a narrow and homogeneous intake of vegetable protein. Due to the low variability of plant-based protein in the cohort, there were no associations between the percentage of plant protein intake and changes in eGFR nor electrolyte balance. A higher resolution version of the Graphical abstract is available as Supplementary information.

Age- and sex-dependent clinical equations to estimate glomerular filtration rates in children and young adults with chronic kidney disease.

Using data (2655 observations from 928 participants) from the Chronic Kidney Disease in Children Study, we developed and internally validated new glomerular filtration rate estimating equations for clinical use in children and young adults: two forms of K × [heigh(ht) / serum creatinine(sCr)] and two forms of K × [1 / cystatin C(cysC)]. For each marker, one equation used a sex-dependent K; in the other, K is sex-and age-dependent. Glomerular filtration rate (GFR) was measured directly by plasma iohexol disappearance. The equations using ht/sCr had sex-specific constants of 41.8 for males and 37.6 for females. In the age- dependent models, K increased monotonically for children 1-18 years old and was constant for young adults 18-25 years. For males, K ranged from 35.7 for one-year-olds to 50.8 for those 18 and older. For females, the values of K ranged from 33.1 to 41.4. Constant K values for cystatin-C equations were 81.9 for males and 74.9 for females. With age-dependency, K varied non-monotonically with the highest values at age 15 for males (K of 87.2) and 12 years for females (K of 79.9). Use of an age-dependent K with ht/sCr models reduced average bias, notably in young children and young adults; age-dependent cystatin-C models produced similar agreement to using a constant K in children under 18 years, but reduced bias in young adults. These age-dependent proposed equations were evaluated alongside estimated GFRs from 11 other published equations for pediatrics and young adults. Only our proposed equations yielded non- significant bias and within 30% accuracy values greater than 85% in both the pediatric and young adult subpopulations.

Acidosis induces antimicrobial peptide expression and resistance to uropathogenic E. coli infection in kidney collecting duct cells via HIF-1α.

Acute pyelonephritis is frequently associated with metabolic acidosis. We previously reported that metabolic acidosis stimulates expression of hypoxia-inducible factor (HIF)-1α-induced target genes such as stromal derived factor-1 and cathelicidin, an antimicrobial peptide. Since the collecting duct (CD) plays a pivotal role in regulating acid-base homeostasis and is the first nephron segment encountered by an ascending microbial infection, we examined the contribution of HIF-1α to innate immune responses elicited by acid loading of an M-1 immortalized mouse CD cell line. Acid loading of confluent M-1 cells was achieved by culture in pH 6.8 medium supplemented with 5-(N-ethyl-N-isopropyl)-amiloride to block Na+/H+ exchange activity for 24 h. Acid loading induced antimicrobial peptide [cathelicidin and ß-defensin (Defb2 and Defb26)] mRNA expression and M-1 cell resistance to uropathogenic Escherichia coli infection to an extent similar to that obtained by inhibition of HIF prolyl hydroxylases, which promote HIF-1α protein degradation. The effect of acid loading on M-1 cell resistance to uropathogenic E. coli infection was reduced by inhibition of HIF-1α (PX-478), and, in combination with prolyl hydroxylase inhibitors, acidosis did not confer additional resistance. Thus, metabolic stress of acidosis triggers HIF-1α-dependent innate immune responses in CD (M-1) cells. Whether pharmacological stabilization of HIF prevents or ameliorates pyelonephritis in vivo warrants further investigation.

Developmental loss, but not pharmacological suppression, of renal carbonic anhydrase 2 results in pyelonephritis susceptibility.

Carbonic anhydrase II knockout (Car2-/-) mice have depleted numbers of renal intercalated cells, which are increasingly recognized to be innate immune effectors. We compared pyelonephritis susceptibility following reciprocal renal transplantations between Car2-/- and wild-type mice. We examined the effect of pharmacological CA suppression using acetazolamide in an experimental murine model of urinary tract infection. Car2-/- versus wild-type mice were compared for differences in renal innate immunity. In our transplant scheme, mice lacking CA-II in the kidney had increased pyelonephritis risk. Mice treated with acetazolamide had lower kidney bacterial burdens at 6 h postinfection, which appeared to be due to tubular flow from diuresis because comparable results were obtained when furosemide was substituted for acetazolamide. Isolated Car2-/- kidney cells enriched for intercalated cells demonstrated altered intercalated cell innate immune gene expression, notably increased calgizzarin and insulin receptor expression. Intercalated cell number and function along with renal tubular flow are determinants of pyelonephritis risk.

Recalibration of cystatin C using standardized material in Siemens nephelometers.

BACKGROUND: Cystatin C is a key GFR biomarker. Recently, Siemens recalibrated the assay based on certified reference material ERM-DA471/IFCC. The NIH-funded longitudinal chronic kidney disease in children (CKiD) study has > 3000 cystatin C measurements based on a pre-IFCC calibrator provided by Siemens. Since cystatin C values for CKiD are now standardized to IFCC certified reference material, it is important to relate the IFCC-calibrated results to the previous values so that there are no discontinuous results. METHODS: We diluted cystatin C ERM-DA471/IFCC (5.48 mg/L) into buffer and compared results with predicted ones. We then updated the cystatin C application on our BN II nephelometer to provide results based on pre-IFCC and IFCC calibrations of CKiD specimens simultaneously. We assayed 51 previously analyzed sera and 62 fresh additional specimens. RESULTS: The predicted concentrations from the IFCC standard were consistently 17% higher than the measured values using the pre-IFCC calibration (y = 1.1686x). Similarly, the re-run and fresh sample concentrations were 17% higher via the IFCC calibration than by the pre-IFCC calibration (y = 1.168x). There was very high reliability in the measurements using the previous calibration for re-run specimens (0.99) and for 33 pristine specimens using IFCC calibration (0.99). CONCLUSIONS: We confirm the recalibration proposed by Siemens. To convert pre-IFCC results to IFCC-calibrated concentrations, the value is multiplied by 1.17. Conversely, one divides IFCC-calibrated results by 1.17 to estimate GFR via previously published pre-IFCC CKiD eGFR equations. For older adolescents, cystatin C has already been standardized and can be directly applied to the CKD-EPI equations.

Iohexol-measured glomerular filtration rate in children and adolescents with chronic kidney disease: a pilot study comparing venous and finger stick methods.

BACKGROUND: Measurement of glomerular filtration rate by iohexol disappearance (iGFR) has become a gold standard in the pediatric chronic kidney disease (CKD) population. The need for serial phlebotomy can be difficult and minimizing venipunctures would be beneficial. Furthermore, finger stick collection for dried blood spot (DBS) may be more tolerable in the pediatric population, and equivalence between these two methods may further simplify the process. METHODS: This was a cross-sectional study in children and adolescents 1 to 21 years with stages I-IV CKD. Iohexol was infused and blood drawn 10, 30, 120, and 300 min later. Blood spots on filter paper were collected by finger stick after each of the latter two blood draws. The rate of iohexol plasma disappearance was used to calculate GFR. Pearson's correlation coefficient and bias, Students t test, and Bland-Altman graphical representations were used to compare methods. RESULTS: Forty-one patients were recruited. The mean creatinine was 1.13 mg/dL (SD 0.45), the mean 4-point iGFR was 73.2 ml/min/1.73m2 (SD 27.5) and the mean 2-point iGFR was 75.6 ml/min/1.73m2 (SD 27.3). Correlation between 2-point and 4-point venous GFR was r = 0.97; p < 0.001. The correlation between the DBS and the 2-point venous GFR was r = 0.95; p < 0.001, with no significant bias. Ninety-four percent of the 2-point GFR's were within 10% of the 4-point GFR's and 80% of DBS-GFRs were within 10% of the 2-point GFR's. CONCLUSIONS: The 2-point iGFR was highly correlated and agreed well with the 4-point iGFR. The same was true for the DBS method and the 2-point venous method. DBS sampling by finger stick sampling at 2 time points after iohexol infusion gave an acceptably accurate measurement of GFR.

Cell-specific qRT-PCR of renal epithelial cells reveals a novel innate immune signature in murine collecting duct.

The urinary tract is usually culture negative despite its close proximity to microbial flora. The precise mechanism by which the kidneys and urinary tract defends against infection is not well understood. The initial kidney cells to encounter ascending pathogens are the collecting tubule cells that consist of principal cells (PCs) that express aquaporin 2 (AQP2) and intercalated cells (ICs) that express vacuolar H+-ATPase (V-ATPase, B1 subunit). We have previously shown that ICs are involved with the human renal innate immune defense. Here we generated two reporter mice, VATPase B1-cre+tdT+ mice to fluorescently label ICs and AQP2-cre+tdT+ mice to fluorescently label PCs, and then performed flow sorting to enrich PCs and ICs for analysis. Isolated ICs and PCs along with proximal tubular cells were used to measure antimicrobial peptide (AMP) mRNA expression. ICs and PCs were significantly enriched for AMPs. Isolated ICs responded to uropathogenic Escherichia coli (UPEC) challenge in vitro and had higher RNase4 gene expression than control while both ICs and PCs responded to UPEC challenge in vivo by upregulating Defb1 mRNA expression. To our knowledge, this is the first report of isolating murine collecting tubule cells and performing targeted analysis for multiple classes of AMPs.