Pediatric Renal Ontogeny and Applications in Drug Development

The clinical applications of renal ontogeny mainly include renal function evaluation and optimal dosing of renally eliminated drugs in pediatric patients, which rely on pharmacometric models and/or bedside estimated glomerular filtration rate equations. However, these applications in drug development are based on an understanding of renal function development, especially when considering premature infants, and the renal biomarkers that can be used for renal function assessment. This review provides a general overview on (1) renal function development, (2) the biomarkers that are used to assess renal function, and (3) the practical application of this knowledge to drug dosing for renally eliminated drugs during pediatric development. While pharmacometric approaches for estimating renal function during development have improved considerably, the number of drug development programs that have studied premature infants is small and suggests that caution should be taken in estimating doses for renally eliminated drugs during periods of rapid change in renal function.

Variables of interest to predict glomerular filtration rate in preterm newborns in the first days of life

BACKGROUND

Measurement of neonatal renal function is challenging, and accurate, easy-to-use markers to estimate glomerular filtration rate (eGFR) are lacking. This study aimed to evaluate principal determinants of GFR in neonates and develop a predictive equation.

METHODS

GFR was measured, using single injection inulin clearance, at median day 3 of life in 48 newborns. Associations of clearance with height, gestational age, weight, creatinine, and cystatin C were explored and a multivariable model to estimate GFR developed. We also evaluated preexisting GFR equations (Schwartz, Zappitelli, combined Zappitelli).

RESULTS

Forty-four clearances were measured, 36 very preterm neonates (28-32 weeks); 5 extremely preterm (< 28 weeks), and 3 term newborns. No patient presented acute renal insufficiency. Median inulin clearance in preterm infants was 18.83 ml/min/1.73 m² (IQ 15.29; 24.99). Inulin clearance correlated with weight (ρ 0.74), gestational age (ρ 0.72), height (ρ 0.49), and creatinine (ρ - 0.42), but not cystatin C. In the multivariable model, predicted GFR equation was 2.32* (weight (g))^0.64/(creatinine (mcmol/l))^0.62. Mean error in predicting clearance was - 0.8 ml/min/1.73 m² (- 3.0-1.4) ranging from - 14.9 to 13.3 ml/min/1.73 m². Mean prediction error with Zappitelli and combined Zappitelli equations were 28.5 ml/min/1.73 m² (95% CI 24.6-32.3) and 28.3 ml/min/1.73 m² (95% CI 24.9-31.7), respectively, and 2 ml/min/1.73 m² (95% CI - 0.6-4.6) for Schwartz equation.

CONCLUSIONS

Weight and gestational age are crucial determinants of GFR in neonates. The Zappitelli models were not validated in our population. Our predictive model and Schwartz models performed better. Our model should be evaluated in another preterm population, particularly in those presenting renal insufficiency.

The role of urinary NGAL and serum cystatin C in assessing the severity of ureteropelvic junction obstruction in infants

BACKGROUND

The ideal management of ureteropelvic junction obstruction (UPJO) remains debatable. This prospective case-control study aimed to investigate if urinary levels of Neutrophil Gelatinase-Associated Lipocalin (NGAL) and serum levels of cystatin C could distinguish surgical from non-surgical cases of UPJO and if they could detect earlier impairment of renal function.

METHODS

Biomarkers were measured in the following age-matched groups: (a) 22 infants with surgical UPJO, at initial diagnosis and 12 months postoperatively (groups A1 and A2, respectively); (b) 19 infants with non-surgical UPJO (group B); and (c) 17 controls (group C). Based on serum cystatin C levels, estimated glomerular filtration rate (eGFR) was calculated.

RESULTS

Urinary NGAL (uNGAL) was significantly higher in group A1 vs. group A2 (p = 0.02) and in group A1 vs. group C (p = 0.03), whereas there was no statistically significant difference between groups A2 and C (p = 0.77). Likewise, cystatin C levels were significantly higher in group A1 vs. group A2 and in group A1 vs. group C (p = 0.004 and p = 0.02, respectively), but no statistically significant difference between groups A2 and C (p = 0.82). uNGAL and serum cystatin C did not differ between groups B and A, nor did they differ between groups B and C. Cystatin C levels and eGFR of group A1 were significantly higher than those of group A2 and group C (p = 0.0001 and p = 0.02, respectively).

CONCLUSION

It seems that NGAL and cystatin C are able to distinguish patients who were treated surgically from healthy controls, and their levels appear to improve significantly following surgery.

Association between cord blood cystatin C levels and early mortality of neonates with congenital abnormalities of the kidney and urinary tract: a single-center, retrospective cohort study

BACKGROUND

Some fetuses with congenital abnormalities of the kidney and urinary tract (CAKUT) have severe renal dysfunction during the prenatal period that can result in oligohydramnios, pulmonary hypoplasia, and death following birth. We hypothesized that cord blood cystatin C (CysC) levels are elevated in neonates who have life-threatening pulmonary hypoplasia and oligohydramnios due to severe renal dysfunction. In this study we compared cord blood CysC levels between a non-survivor group with CAKUT and a survivor group.

METHODS

This was a single-center, retrospective cohort study conducted between January 2007 and December 2015. Eighty-seven neonates who were prenatally diagnosed with CAKUT were included in the study. Cord blood CysC and creatinine levels were compared between the survivor and non-survivor groups at discharge from hospital.

RESULTS

Of the 87 neonates enrolled in the study, 67 survived and 21 died before discharge. Median cord blood CysC levels were higher in the non-survivor group than in the survivor group (4.28 vs. 1.96 mg/L, respectively; p < 0.001). Cord blood creatinine levels were not significantly different between the two groups. In patients with oligohydramnios (n = 28), cord blood CysC levels were significantly higher in the non-survivor group than in the survivor group (4.28 vs. 2.23 mg/L, respectively; p = 0.002).

CONCLUSIONS

In this study population, cord blood CysC levels were significantly higher in the non-survivor group with CAKUT than in the survivor group. These results suggest that cord blood CysC levels may be a good marker of the severity of renal dysfunction at birth.

Serum cystatin C levels in preterm newborns in our setting: Correlation with serum creatinine and preterm pathologies

BACKGROUND

Cystatin C (CysC) is a renal function marker that is not as influenced as creatinine (Cr) by endogenous or exogenous agents, so it is therefore proposed as a marker in preterm infants.

OBJECTIVES

To determine serum CysC values in preterm infants during the first week of life, compared to Cr. To analyze alterations caused by prematurity diseases.

METHOD

The design involved a longitudinal, observational study of prospective cohorts. Groups were based on gestational age (GA): Group A (24-27 weeks), Group B (28-33 weeks), Group C (34-36 weeks). Blood samples were collected at birth, within 48-72hours and after 7 days of life.

STATISTICS

SPSS v.20 software was used. The statistical methods applied included chi-squared test and ANOVA.

RESULTS

A total of 109 preterm infants were included in the study. CysC levels were: 1.54mg/L (±0.28) at birth; 1.38mg/L (±0.36) within 48-72hours of life; 1.50mg/L (±0.31) after 7 days (p<0.05). Cr levels were: 0.64mg/dL (±0.17) at birth; 0.64mg/dL (±0.28) within 48-72hours; 0.56mg/dL (±0.19) after 7 days (P<.05). CysC values were lower in hypotensive patients and those with a respiratory disease (P<.05), and no alterations associated with other diseases were observed. There were no differences in Cr levels associated with any disease. Creatinine levels were higher in patients ≤1.500g (P<.05).

CONCLUSIONS

Serum CysC decreased within 48-72hours of life, and this decline showed significance (P<.05). The levels increased after 7 days in all 3 GA groups, and there was no difference in CysC levels among the groups. More studies in preterm infants with hypotension and respiratory disease are required. CysC is a better glomerular filtration (GF) marker in ≤1.500g preterm infants.

Cystatin C in newborns: a promising renal biomarker in search for standardization and validation

OBJECTIVE

Neonatologists still commonly use creatinine as a proxy for renal clearance, despite issues related to neonatal (patho)physiology and methodology (assay variability). Cystatin C (CysC) has been suggested to be a more reliable biomarker, but assay related differences have also been reported in children and adults. We are unaware of any review on the assay related impact on CysC reference values in newborns.

METHODS

A structured literature search was performed on published CysC values in (pre)term neonates.

RESULTS

The extensive range (>5-fold) in serum CysC observations in neonates in part relates to the fact that CysC concentrations are higher at birth with subsequent decrease and that CysC concentrations are higher in preterm compared to term neonates. The CysC assay matters while disease characteristics also affect CysC values, but not always in the predicted direction.

CONCLUSIONS

Similar to creatinine, the extensive CysC range in neonates is only in part explained by renal (patho)physiology. Its applicability in neonatal medicine can be further improved by use of assay specific reference values, adapted to neonatal renal physiology (e.g. weight, age) and should be compared to a gold standard such as inulin clearance.

Beta-trace protein as a marker of GFR--history, indications, and future research

OBJECTIVES

Recent findings suggest that beta-trace protein (BTP), a small molecular weight protein, is at least equal if not superior to serum creatinine as a marker of glomerular filtration rate (GFR), particularly since it is independent from height, gender, age, and muscle mass. The authors sought to summarize knowledge on BTP and its use as a marker of GFR using the most recent literature available.

DESIGN AND METHODS

The authors compiled key articles and all relevant recent literature on this topic. Physical and chemical features of the molecule are described, as well as factors that may affect its expression. The use of BTP in estimating GFR as a whole and in specific patient groups, including pregnant women, neonates and infants, children and adolescents, and patients who have undergone renal transplantation is discussed. The use of BTP as a marker for cardiovascular risk factors is also briefly addressed.

RESULTS

Although its performance in the general population is marginally inferior to cystatin C, studies have suggested that it may be superior in accurately estimating GFR in select patient groups such as pregnant women and neonates.

CONCLUSIONS

This novel marker shows promise, but further research is required to clarify findings from available data.

Serum cystatin-C as a marker of acute kidney injury in the newborn after perinatal hypoxia/asphyxia

We evaluated cystatin-C (cysC) in the umbilical blood as a predictor of acute kidney injury (AKI) after perinatal hypoxia/asphyxia compared with creatinine (Cr). One hundred full-term newborns were enrolled in the study (50 in a group affected by perinatal hypoxia/asphyxia [AS] and 50 controls). CysC and Cr were measured in blood samples from the umbilical cord at birth (cysC-umb and Cr-umb) and from a peripheral vein 3 days later (cysC-3 and Cr-3). At birth, the mean level of cysC in healthy term babies was found to be 1.39 ± 0.19 mg/L and 1.34 ± 0.21 mg/L after 3 days of life, not significantly decreased (P = 0.137). The mean of cysC in the AS group was 2.12 ± 0.53 mg/L in cord blood and 1.56 ± 0.32 g/L in day 3 blood samples, also decreased (P < 0.001) and different from the control (P < 0.001). Cr levels, determined simultaneously at birth were different (P = 0.001) between the control (62.74 ± 12.84 μmol/L) and AS (72.60 ± 15.55 μmol/L) group, significantly decreased after 3 days in both groups (P < 0.001). The receiver-operating characteristic curve analysis, comparing AS and the control group, showed area under the curve for cysC-umb, cysC-3, Cr-umb and Cr-3 (0.918; 0.698; 0.692; 0.660). The highest diagnostic accuracy was achieved with a chosen cut-off for cysC-umb of 1.67 mg/L (sensitivity of 84.0%, specificity of 90.0%) or 1.69 mg/L (sensitivity of 82.0%, specificity of 94.0%). Our results indicate serum CysC is a more sensitive marker of glomerular filtration rate than Cr in the newborns.

Measuring cystatin C to determine renal function in neonates

OBJECTIVES

The incidence of acute kidney injury in neonates is high and associated with up to a 50% mortality rate. The purpose of this review was to determine the feasibility of using serum cystatin C measurements to assist clinicians in making early and accurate diagnoses of acute kidney injury in neonates.

DATA SOURCE

We searched for the following seven key words within the PubMed database and the Cochrane Database of Systematic Reviews: cystatin C, neonates, newborn, preterm, premature, kidney failure, and kidney injury.

STUDY SELECTION

The selected studies included neonates within their study populations and were published in English. We reviewed literature published between January 1990 and May 2012.

DATA EXTRACTION

Ten studies had conducted serum cystatin C measurements in neonates.

DATA SYNTHESIS

The cystatin C level in neonates is not influenced by the maternal level and is highest at birth. In most studies, cystatin C levels on day 1 of life ranged between 1 and 2 mg/L, gradually declined during the first year and then remained relatively stable thereafter. Cystatin C levels did not differ between male and female infants, and no significant gestational age-dependent differences were found. Cystatin C levels were increased in cases of sepsis, acute kidney injury, and congenital renal abnormalities.

CONCLUSIONS

Cystatin C has all of the theoretical properties needed to be an ideal marker of renal function. It can be used to determine baseline renal function on day 1 and is increasingly being used to determine renal function in sick neonates. In the majority of studies, the day 1 cystatin C level ranged between 1 and 2 mg/L, which gradually declined in the first year of life. However, the number of available studies evaluating cystatin C in sick neonates is currently limited, and there are also no studies linking cystatin C levels in sick babies with short-term and long-term outcomes.