Accelerated maturation and abnormal morphology in the preterm neonatal kidney

Postnatal renal tubule development: roles of tubular flow and flux

PURPOSE OF REVIEW

Postnatal renal tubule development is critical to adult kidney function. Several postnatal changes regulate the differentiation and proliferation of renal tubular cells. Here, we review the literature and our efforts on thick ascending limb (TAL) development in Bartter syndrome (BS).

RECENT FINDINGS

Glomerular filtrate quickly increases after birth, imposing fluid shear stress and circumferential stretch on immature renal tubules. Recent studies showed that kidney organoids under flow (superfusion) have better development of tubular structures and the expression of cilia and solute transporters. These effects are likely mediated by mechanosensors, such as cilia and the piezo1 channel. Improved renal oxygenation and sodium pump-dependent active transport can stimulate mitochondrial respiration and biogenesis. The functional coupling between transport and mitochondria ensures ATP supply for energy-demanding reactions in tubular cells, including cell cycle progression and proliferation. We recently discovered that postnatal renal medulla maturation and TAL elongation are impaired in Clc-k2-deficient BS mice. Primary cultured Clc-k2-deficient TAL cells have G1-S transition and proliferation delay. These developmental defects could be part of the early pathogenesis of BS and worsen the phenotype.

SUMMARY

Understanding how tubular flow and transepithelial ion fluxes regulate renal tubule development may improve the treatment of congenital renal tubulopathies.

Perinatal risk factors of renal outcome in former extremely low birth weight neonates

Former Extremely Low Birthweight (ELBW) neonates suffer from adverse renal and cardiovascular outcomes later in life. Less is known about additional perinatal risk factors for these adverse outcomes which we have investigated in this study. We compared renal outcome between ELBW children and controls, to find perinatal risk factors for poorer renal outcome and to unveil associations between kidney function and blood pressure. This study included 93 former ELBW children and 87 healthy controls with a mean age of 11 years at assessment. We measured cystatin C-based estimated glomerular filtration rate (eGFR) and blood pressure. Blood pressure and eGFR levels were compared between cases and controls. We subsequently investigated perinatal risk factors for adverse outcome amongst ELBW children. ELBW children have significantly higher blood pressure (mean SBP percentile 75th vs. 47th, p <0.001) and lower mean eGFR (94 vs. 107 ml/min/1.73 m2, p = 0.005) compared to the control group. Elevated blood pressure did not correlate with perinatal characteristics and none of them had microalbuminuria. ELBW children with eGFR <90 ml/min/1.73 m2 were ventilated longer (17 vs. 9 days, p = 0.006), more frequently male (OR = 3.33, p = 0.055) and tended to suffer more from intraventricular hemorrhage (40% vs. 15.8%, p = 0.056). There was no association between blood pressure and kidney dysfunction.

CONCLUSIONS

Understanding risk profiles for unfavorable outcomes may help to identify children at increased risk for kidney dysfunction. Poorer eGFR was associated with longer ventilation, male sex, and intra-ventricular hemorrhage but not with blood pressure. This knowledge can lead to safer neonatal therapeutic regimens for ELBW infants, a more intensive follow-up and earlier treatment initiation for children at highest risk.

WHAT IS KNOWN

• Extremely Low Birthweight (ELBW) neonates suffer later in life from adverse renal and cardiovascular outcomes. • Perinatal risk factors that further predict the individual risk for adverse outcomes are not well known.

WHAT IS NEW

• Poorer eGFR in adolescence was associated with male sex, longer ventilation and intra-ventricular hemorrhage at birth but not with blood pressure. • Former ELBW infants had higher blood pressures compared to controls, but no microalbuminuria. • This knowledge can lead to potential precision medicine, safer neonatal therapeutic regimens for ELBW infants, a more intensive follow-up and earlier treatment initiation for children at highest risk.

ADVANCE: a biomedical informatics approach to investigate acute kidney injury in infants

BACKGROUND

Acute kidney injury (AKI) occurs in up to half of infants admitted to the neonatal intensive care unit (NICU) and is associated with increased risks of death and more days of mechanical ventilation, hospitalization, and vasopressor drug support. Our objective was to build a granular relational database to study the impact that AKI has on infants admitted to Level-IV NICUs.

METHODS

A relational database was created by linking data from the Children's Hospitals Neonatal Database with AKI-focused data from electronic health records from 9 centers.

RESULTS

The current cohort consists of 24,870 infants with a median (IQR) gestational age of birth of 37 weeks (32 weeks, 39 weeks), and a median birth weight of 2.720 kg (1.750 kg, 3.310 kg). There was a male predominance with 14,214 (57%) males. In all, 2434 (9.8%) of the mothers were of Hispanic ethnicity. The maternal race breakdown of the cohort was as follows: 741 (3.0%) Asian, 5911 (24%) Black, and 14,945 (60%) White. Overall mortality was 5.8%.

CONCLUSION

The ADVANCE relational database is an innovative research tool to rigorously study the epidemiology of AKI in a large national cohort of infants admitted to Level-IV NICUs involved in the Children's Hospital Neonatal Consortium.

IMPACT

We used a biomedical informatics approach to build a relational database to study acute kidney injury in infants. We highlight our methodology linking Children's Hospital Neonatal Consortium and electronic health record data from nine neonatal intensive care units. The ADVANCE relational database is a granular and innovative research tool to study risk factors and in-hospital outcomes of acute kidney injury and mortality in a vulnerable patient population.

Neonatal hyperoxia exposure leads to developmental programming of cardiovascular and renal disease in adult rats

Premature infants are often exposed to hyperoxia. However, there is limited data regarding the mechanistic underpinnings linking neonatal hyperoxia exposure and its contribution to cardio-renal dysfunction in adults born preterm. Our objective was to determine whether neonatal hyperoxia induces systemic vascular stiffness and cardio-renal dysfunction in adulthood. Newborn rats were randomly assigned to room air (RA) or hyperoxia (85% O2) from postnatal day 1 to 14, then recovered in RA until 1 year of life. Arterial stiffness, cardio-renal histomorphometry, and fibrosis in the aorta, heart, and kidney were assessed. RNA-sequencing (RNA-seq) of the aorta and kidney was also done. Adult rats exposed to neonatal hyperoxia had increased aortic and mesenteric artery stiffness as demonstrated by wire and pressure myography. They also had cardiomyocyte hypertrophy, glomerulomegaly, and tubular injury. Hyperoxia exposure altered the transcriptome profile associated with fibrosis and matrix remodeling in the aorta and kidney. There was also increased TGF-β1 levels and fibrosis in the aorta, left ventricle, and kidney. In conclusion, neonatal hyperoxia exposure was associated with systemic vascular and cardio-renal alterations in 1-year-old rats. Further studies to determine how targeted therapies could reprogram cardio-renal injury after neonatal hyperoxia exposure are indicated.

Plasma D-asparagine and the D/L-serine ratio reflect chronic kidney diseases in children regardless of physique

Biomarkers that accurately reflect renal function are essential in management of chronic kidney diseases (CKD). However, in children, age/physique and medication often alter established renal biomarkers. We studied whether amino acid enantiomers in body fluids correlate with renal function and whether they are influenced by physique or steroid medication during development. We conducted a prospective study of children 2 to 18 years old with and without CKD. We analyzed associations of serine/asparagine enantiomers in body fluids with major biochemical parameters as well as physique. To study consequences of kidney dysfunction and steroids on serine/asparagine enantiomers, we generated juvenile mice with uninephrectomy, ischemic reperfusion injury, or dexamethasone treatment. We obtained samples from 27 children, of which 12 had CKD due to congenital (n = 7) and perinatal (n = 5) causes. Plasma D-asparagine and the D/L-serine ratio had robust, positive linear associations with serum creatinine and cystatin C, and detected CKD with high sensitivity and specificity, uninfluenced by body size or biochemical parameters. In the animal study, kidney dysfunction increased plasma D-asparagine and the D/L-serine ratio, but dexamethasone treatment did not. Thus, plasma D-asparagine and the D/L-serine ratio can be useful markers for renal function in children.

Familial focal segmental glomerulosclerosis with Alport-like glomerular basement changes caused by paired box protein 2 gene variant

Paired box protein 2 (PAX2) gene variant causes renal coloboma syndrome (MIM#120330). Further, they are associated with focal segmental glomerulosclerosis and characterized by basement membrane changes similar to Alport syndrome.Herein, we report an 8-year-old boy who presented with proteinuria and decreased renal function. His paternal uncle has focal segmental glomerulosclerosis and renal failure, and his paternal grandmother has renal failure and is receiving peritoneal dialysis. Further, his father has stage 2 chronic kidney disease. At 3 years of age, his serum creatinine-estimated glomerular filtration rate was 40-50 mL/min/1.73 m2. At 8 years of age, his renal function further decreased and he had proteinuria (urinary protein/Cr 3.39 g/g Cr). Renal histopathology showed oligonephronia and focal segmental glomerulosclerosis. A partial basket-weave pattern, similar to Alport syndrome, was also observed on a transmission electron microscope, and low-vacuum scanning electron microscopy revealed coarse meshwork changes in the glomerular basement membrane. Genetic analysis revealed a PAX2 heterozygous variant (NM_003987.4:c.959C  >  G), a nonsense variant in which the serine at position 320 changes to a stop codon, in our patient and his father. PAX2 is a transcription factor that is important for the podocyte variant. However, podocytes with PAX2 gene variants may cause abnormal basement membrane production and repair, thereby resulting in Alport-like changes.

Insulin-like growth factor-1 effects on kidney development in preterm piglets

BACKGROUND

Preterm birth disrupts fetal kidney development, potentially leading to postnatal acute kidney injury. Preterm infants are deficient in insulin-like growth factor 1 (IGF-1), a growth factor that stimulates organ development. By utilizing a preterm pig model, this study investigated whether IGF-1 supplementation enhances preterm kidney maturation.

METHODS

Cesarean-delivered preterm pigs were treated systemically IGF-1 or vehicle control for 5, 9 or 19 days after birth. Blood, urine, and kidney tissue were collected for biochemical, histological and gene expression analyses. Age-matched term-born pigs were sacrificed at similar postnatal ages and served as the reference group.

RESULTS

Compared with term pigs, preterm pigs exhibited impaired kidney maturation, as indicated by analyses of renal morphology, histopathology, and inflammatory and injury markers. Supplementation with IGF-1 reduced signs of kidney immaturity, particularly in the first week of life, as indicated by improved morphology, upregulated expression of key developmental genes, reduced severity and incidence of microscopic lesions, and decreased levels of inflammatory and injury markers. No association was seen between the symptoms of necrotizing enterocolitis and kidney defects.

CONCLUSION

Preterm birth in pigs impairs kidney maturation and exogenous IGF-1 treatment partially reverses this impairment. Early IGF-1 supplementation could support the development of preterm kidneys.

IMPACT

Preterm birth may disrupt kidney development in newborns, potentially leading to morphological changes, injury, and inflammation. Preterm pigs have previously been used as models for preterm infants, but not for kidney development. IGF-1 supplementation promotes kidney maturation and alleviates renal impairments in the first week of life in preterm pigs. IGF-1 may hold potential as a supportive therapy for preterm infants sensitive to acute kidney injury.

Nephrotic Syndrome Throughout Childhood: Diagnosing Podocytopathies From the Womb to the Dorm

The etiologies of podocyte dysfunction that lead to pediatric nephrotic syndrome (NS) are vast and vary with age at presentation. The discovery of numerous novel genetic podocytopathies and the evolution of diagnostic technologies has transformed the investigation of steroid-resistant NS while simultaneously promoting the replacement of traditional morphology-based disease classifications with a mechanistic approach. Podocytopathies associated with primary and secondary steroid-resistant NS manifest as diffuse mesangial sclerosis, minimal change disease, focal segmental glomerulosclerosis, and collapsing glomerulopathy. Molecular testing, once an ancillary option, has become a vital component of the clinical investigation and when paired with kidney biopsy findings, provides data that can optimize treatment and prognosis. This review focuses on the causes including selected monogenic defects, clinical phenotypes, histopathologic findings, and age-appropriate differential diagnoses of nephrotic syndrome in the pediatric population with an emphasis on podocytopathies.

Podocyte involvement in the pathogenesis of preterm-related long-term chronic kidney disease

With the continuous advancement of neonatal intensive care technology, the survival rate of preterm infants is gradually increasing. However, this improvement in survival is accompanied by long-term prognostic implications in various systems. In the field of renal diseases, current epidemiological data indicate that preterm birth is a significant risk factor for the development of long-term chronic kidney disease (CKD). This not only imposes an economic burden on patients families but also severely impacts their quality of life. Understanding the underlying mechanisms involved in this process could offer potential strategies for early prevention and management of CKD. Although the nephron number hypothesis is currently widely accepted as a mechanism, there has been limited exploration regarding podocytes - one of the most important structures within nephrons - in relation to long-term CKD associated with preterm birth. Therefore, this review aims to summarize current knowledge on how prematurity influences CKD development overall, while specifically focusing on our current understanding of podocytes in relation to prematurity.

When will the Glomerular Filtration Rate in Former Preterm Neonates Catch up with Their Term Peers?

AIMS

Whether and when glomerular filtration rate (GFR) in preterms catches up with term peers is unknown. This study aims to develop a GFR maturation model for (pre)term-born individuals from birth to 18 years of age. Secondarily, the function is applied to data of different renally excreted drugs.

METHODS

We combined published inulin clearance values and serum creatinine (Scr) concentrations in (pre)term born individuals throughout childhood. Inulin clearance was assumed to be equal to GFR, and Scr to reflect creatinine synthesis rate/GFR. We developed a GFR function consisting of GFRbirth (GFR at birth), and an Emax model dependent on PNA (with GFRmax, PNA50 (PNA at which half ofGFR max is reached) and Hill coefficient). The final GFR model was applied to predict gentamicin, tobramycin and vancomycin concentrations.

RESULT

In the GFR model, GFRbirth varied with birthweight linearly while in the PNA-based Emax equation, GA was the best covariate for PNA50, and current weight for GFRmax. The final model showed that for a child born at 26 weeks GA, absolute GFR is 18%, 63%, 80%, 92% and 96% of the GFR of a child born at 40 weeks GA at 1 month, 6 months, 1 year, 3 years and 12 years, respectively. PopPK models with the GFR maturation equations predicted concentrations of renally cleared antibiotics across (pre)term-born neonates until 18 years well.

CONCLUSIONS

GFR of preterm individuals catches up with term peers at around three years of age, implying reduced dosages of renally cleared drugs should be considered below this age.

Impact of preterm birth on kidney health and development

Preterm birth, defined as birth before the gestational age of 37 weeks, affects 11% of the newborns worldwide. While extensive research has focused on the immediate complications associated with prematurity, emerging evidence suggests a link between prematurity and the development of kidney disease later in life. It has been demonstrated that the normal course of kidney development is interrupted in infants born prematurely, causing an overall decrease in functional nephrons. Yet, the pathogenesis leading to the alterations in kidney development and the subsequent pathophysiological consequences causing kidney disease on the long-term are incompletely understood. In the present review, we discuss the current knowledge on nephrogenesis and how this process is affected in prematurity. We further discuss the epidemiological evidence and experimental data demonstrating the increased risk of kidney disease in these individuals and highlight important knowledge gaps. Importantly, understanding the intricate interplay between prematurity, abnormal kidney development, and the long-term risk of kidney disease is crucial for implementing effective preventive and therapeutic strategies.

Advances in pediatric acute kidney injury pathobiology: a report from the 26th Acute Disease Quality Initiative (ADQI) conference

BACKGROUND

In the past decade, there have been substantial advances in our understanding of the pathobiology of pediatric acute kidney injury (AKI). In particular, animal models and studies focused on the relationship between kidney development, nephron number, and kidney health have identified a number of heterogeneous pathophysiologies underlying AKI. Despite this progress, gaps remain in our understanding of the pathobiology of pediatric AKI.

METHODS

During the 26th Acute Disease Quality Initiative (ADQI) Consensus conference, a multidisciplinary group of experts discussed the evidence and used a modified Delphi process to achieve consensus on recommendations for opportunities to advance translational research in pediatric AKI. The current state of research understanding as well as gaps and opportunities for advancement in research was discussed, and recommendations were summarized.

RESULTS

Consensus was reached that to improve translational pediatric AKI advancements, diverse teams spanning pre-clinical to epidemiological scientists must work in concert together and that results must be shared with the community we serve with patient involvement. Public and private research support and meaningful partnerships with adult research efforts are required. Particular focus is warranted to investigate the pediatric nuances of AKI, including the effect of development as a biological variable on AKI incidence, severity, and outcomes.

CONCLUSIONS

Although AKI is common and associated with significant morbidity, the biologic basis of the disease spectrum throughout varying nephron developmental stages remains poorly understood. An incomplete understanding of factors contributing to kidney health, the diverse pathobiologies underlying AKI in children, and the historically siloed approach to research limit advances in the field. The recommendations outlined herein identify gaps and outline a strategic approach to advance the field of pediatric AKI via multidisciplinary translational research.

Early postnatal nutrition and renal consequences in preterm infants

Perinatal nutritional factors may lead to decreased nephron endowment, decreased kidney function, and long-term development of chronic kidney disease and non-communicable diseases. At the same time, optimal postnatal nutrition and catch-up growth are associated with better neurodevelopmental outcomes in preterm infants. Therefore, nutritional management of preterm infants is a major challenge for neonatologists. In this context, the Section of Nutrition, Gastroenterology and Metabolism reviewed the current knowledge on nutritional issues related to kidney function. This narrative review discusses the clinical impact of early postnatal nutrition on long-term kidney function. In preterm infants, data are largely lacking to determine the extent to which early nutrition contributes to nephrogenesis and nephron endowment. However, some nutritional principles may help clinicians better protect the developing kidney in preterm infants. IMPACT: Clinical data show that preterm infants are an emerging population at high risk for chronic kidney disease. Both undernutrition and overnutrition can alter long-term kidney function. In preterm infants, data are largely lacking to determine the extent to which early postnatal nutrition contributes to nephrogenesis, nephron endowment and increased risk for chronic kidney disease. Some nutritional principles may help clinicians better protect the developing kidney in preterm infants: avoiding extrauterine growth restriction; providing adequate protein and caloric intakes; limiting exposure to high and prolonged hyperglycaemia; avoiding micronutrient deficiencies and maintaining acid-base and electrolyte balance.

Human Nephrogenesis can Persist Beyond 40 Postnatal Days in Preterm Infants

Introduction

Human nephrogenesis is typically completed by 36 weeks gestation; however, it is impacted by preterm birth. Early studies suggested that nephrogenesis persisted for ≤40 postnatal days in preterm infants. However, the postmenstrual age (PMA) of the preterm infants who survived >40 days was uncertain. In this study, we sought to reexamine postnatal kidney development in preterm infants surviving >40 days.

Methods

Human kidney samples were obtained from an institutional biobank. Samples were considered controls if survival was ≤4 days after birth with PMA of 30 to ≤36 weeks. Kidneys from preterm neonates with postnatal survival >40 days and PMA of 30 to ≤36 weeks were compared to controls. We counted glomerular generations, measured nephrogenic zone widths (NZW), and performed immunofluorescence (IF) with SIX1 and RET. We compared kidney weights and quantified the cross-sectional area of proximal (lotus tetragonolobus lectin [LTL], SL22A2), distal (SLC12A3, KCNJ10), and glomerular (nephrin) markers using IF.

Results

Seven preterm infants surviving >40 days and 8 controls were analyzed. Four of 7 preterm infants had histologic and molecular evidence of nephrogenesis. Cessation of nephrogenesis in preterm infants occurred 2 weeks earlier than PMA-matched controls with attenuated expression of both SIX1 and RET. We found increased kidney weight-to-body weight ratio, increased distal tubular cross-sectional staining in the superficial nephrons, and distal tubular hypertrophy and hyperplasia in the preterm infant kidneys.

Conclusion

Our study supports that nephrogenesis in preterm infants persists longer than previously thought with evidence of early nephron stress, placing importance on the neonatal environment.

Modeling Developmental Changes in Caffeine Clearance Considering Differences between Pre- and Postnatal Period

Taguchi et al. reported that postmenstrual age (PMA) is a promising factor in describing and understanding the developmental change of caffeine (CAF) clearance. The aim of the present study was to quantify how developmental changes occur and to determine the effect of the length of the gestational period on CAF clearance. We performed a nonlinear mixed effect model (NONMEM) analysis and evaluated the fit of six models. A total of 115 samples were obtained from 52 patients with a mean age of 34.3 ± 18.2 d. The median values of gestational age (GA) and postnatal age (PNA) were 196 and 31 d, respectively. Serum CAF levels corrected for dose per body surface area (BSA) (C/D ratioBSA) were dependent on PMA rather than PNA, which supports the findings of a previous study. NONMEM analysis provided the following final model of oral clearance: CL/F = 0.00603∙WT∙∙0.877GA ≤ 196 L/h. This model takes into account developmental changes during prenatal and postnatal periods separately. The model successfully described the variation in clearance of CAF. Our findings suggest that the dosage of CAF in preterm infants should be determined based not only on body weight (WT) but also on both PNA and GA.

Ultra-High Temperature Treatment of Liquid Infant Formula, Systemic Immunity, and Kidney Development in Preterm Neonates

SCOPE

Ready-to-feed liquid infant formulas (IFs) are increasingly being used for newborn preterm infants when human milk is unavailable. However, sterilization of liquid IFs by ultra-high temperature (UHT) introduces Maillard reaction products (MRPs) that may negatively affect systemic immune and kidney development.

METHODS AND RESULTS

UHT-treated IF without and with prolonged storage (SUHT) are tested against pasteurized IF (PAST) in newborn preterm pigs as a model for preterm infants. After 5 days, blood leukocytes, markers of systemic immunity and inflammation, kidney structure and function are evaluated. No consistent differences between UHT and PAST pigs are observed. However, SUHT increases plasma TNFα and IL-6 and reduces neutrophils and in vitro response to LPS. In SUHT pigs, the immature kidneys show minor upregulation of gene expressions related to inflammation (RAGE, MPO, MMP9) and oxidative stress (CAT, GLO1), together with glomerular mesangial expansion and cell injury. The increased inflammatory status in SUHT pigs appears unrelated to systemic levels of MRPs.

CONCLUSION

SUHT feeding may impair systemic immunity and affect kidney development in preterm newborns. The systemic effects may be induced by local gut inflammatory effects of MRPs. Optimal processing and length of storage are critical for UHT-treated liquid IFs for preterm infants.

Intrauterine life to adulthood: a potential risk factor for chronic kidney disease

Multiple risk factors for chronic kidney disease (CKD), one of the major causes of morbidity and mortality in the adult population globally, have been identified, including older age, male gender, family history, smoking, diabetes mellitus, hypertension, ischaemic heart diseases and various medications. Preterm delivery, affecting >10% of the newborns in the USA, is a global concern with increasing incidence in recent decades. Preterm birth has been linked to multiple medical comorbidities such as diabetes mellitus, hypertension and cardiovascular diseases, while its association with CKD has recently been investigated. Prematurity and intrauterine growth restriction (IUGR) have been associated with an increased risk for CKD, specific histopathological examination findings and CKD-associated risk factors such as diabetes mellitus, hypertension and dyslipidaemia. In this narrative review, our aim is to evaluate and summarize the association between the risk for CKD and prematurity, low birthweight and IUGR along with potential underlying pathophysiological mechanisms.

Installation of the developing nephron in the fetal human kidney during advanced pregnancy

BACKGROUND

The kidneys of preterm and low birth weight babies reflect vulnerability, since several noxae can evoke the termination of nephron formation. This again leads to oligonephropathy with severe consequences for health in the later life. While the clinical parameters have been intensely investigated, only little is known about the initial traces left by the noxae. For the fetal human kidney, solely the lack of basophilic S-shaped bodies and the reduction in width of the nephrogenic zone were registered. It is not known in how far also the involved progenitor cells, the earlier nephron stages, the collecting duct (CD) ampullae, and the local interstitium are collaterally harmed.

AIM

The interstitium at the forming nephron is heterogeneously structured. Thereby, it fulfills quite different mastering and integrative tasks. Since data dealing with the installation of a nephron is not available, the microanatomical features were recorded.

RESULTS

The microscopic specimens show that the installation of the transient stages of nephron anlage is not synchronized. Instead, it is controlled within a nephrogenic compartment of the nephrogenic zone. It starts near the renal capsule by positioning the nephrogenic niche so that the nephrogenic progenitor cells face the epithelial progenitor cell at the tip of a CD ampulla. Then, the induced nephrogenic progenitor cells assimilate in the pretubular aggregate. While its medial part remains opposite the head of the CD ampulla, at its proximal end, the primitive renal vesicle is formed. Only a part of it separates to stick to the section border between the head and conus of the CD ampulla. This marks the link with the future connecting tubule at the distal pole of the extending renal vesicle. Meanwhile, the proximal pole is mounted next to the connecting tubule of an earlier developed nephron. The resulting two-point mounting serves a common elongation of the conus at the CD ampulla and the medial aspect of the comma-shaped body. In the S-shaped body, it supports to defoliate the arising glomerulus and to link it with the perforating radiate artery at its deep lateral aspect.

CONCLUSIONS

The investigation depicts that the installation is an interactive process between the stages of nephron anlage and its structural neighbors. A special meaning has the interjacent interstitium. It is vital for the positioning, shaping, and physiological integration. Due to its special location, this is mainly exposed to noxae.

Characterizing post-branching nephrogenesis in the neonatal rabbit

Human nephrogenesis ends prior to birth in term infants (34-36 week gestation), with most (60%) nephrons forming in late gestation in two post-branching nephrogenesis (PBN) periods: arcading and lateral branch nephrogenesis. Preterm infants, however, must execute PBN postnatally. Extreme prematurity is associated with low nephron counts. Identifying additional model(s) that undergo PBN postnatally will help support postnatal PBN in preterm infants. The rabbit exhibits longer postnatal nephrogenesis than the mouse but whether it forms nephrons through PBN has not been determined. We performed morphologic and immunohistological assessments of rabbit nephrogenesis from birth (post-conceptual day 31 or 32) to PC49 using H&E and antibodies against SIX1, SIX2, WT1, ZO-1, and JAG1 in the postnatal period. We performed 3D rendering of the nephrogenic niche to assess for PBN, and supplemented the staining with RNAScope to map the expression of Six1, Six2 (nephron progenitors, NPC), and Ret (ureteric bud tip) transcripts to determine the nephrogenic niche postnatal lifespan. Unlike the mouse, rabbit SIX2 disappeared from NPC before SIX1, resembling the human niche. Active nephrogenesis as defined by the presence of SIX1 + naïve NPC/tip population persisted only until PC35-36 (3-5 postnatal days). 3D morphologic assessments of the cortical nephrons identified an elongated tubule with attached glomeruli extending below the UB tip, consistent with PBN arcades, but not with lateral branch nephrogenesis. We conclude that the rabbit shows morphologic and molecular evidence of PBN arcades continuing postnatally for a shorter period than previously thought. The rabbit is the first non-primate expressing SIX1 in the progenitor population. Our findings suggest that studies of arcading in postnatal nephrogenic niche should be performed within the first 5 days of life in the rabbit.

Accelerated Aging and the Life Course of Individuals Born Preterm

Individuals born preterm have shorter lifespans and elevated rates of chronic illness that contribute to mortality risk when compared to individuals born at term. Emerging evidence suggests that individuals born preterm or of low birthweight also exhibit physiologic and cellular biomarkers of accelerated aging. It is unclear whether, and to what extent, accelerated aging contributes to a higher risk of chronic illness and mortality among individuals born preterm. Here, we review accelerated aging phenotypes in adults born preterm and biological pathways that appear to contribute to accelerated aging. We highlight biomarkers of accelerated aging and various resiliency factors, including both pharmacologic and non-pharmacologic factors, that might buffer the propensity for accelerated aging among individuals born preterm.

Preceding risks and mortality outcomes of different neonatal acute kidney injury in preterm infants

BACKGROUND

The aim of the study was to examine preceding risks and mortality outcomes of oliguric and non-oliguric acute kidney injury (AKI) in very preterm infants.

METHODS

Infants born ≤30 weeks' gestation were included. AKI was diagnosed based on neonatal Kidney Disease: Improving Global Outcomes criteria and was classified as oliguric and non-oliguric according to the urine-output criteria. We used modified Poisson and Cox proportional-hazards models for statistical comparisons.

RESULTS

Of 865 enrolled infants (gestational age 27.2 ± 2.2 weeks and birth weight 983 ± 288 gm), 204 (23.6%) developed AKI. Before AKI, the oliguric AKI group had significantly higher prevalence of small-for-gestational age (p = 0.008), lower 5-min Apgar score (p = 0.009) and acidosis (p = 0.009) on admission, and hypotension (p = 0.008) and sepsis (p = 0.001) during admission than the non-oliguric AKI group. Oliguric (adjusted risk ratio 3.58, 95% CI 2.33-5.51; adjusted hazard ratio 4.93, 95% CI 3.14-7.72) instead of non-oliguric AKI had significantly higher mortality risks than no AKI. Oliguric AKI showed significantly higher mortality risks than non-oliguric AKI, irrespective of serum creatinine and severity of AKI.

CONCLUSIONS

Categorizing AKI as oliguric and non-oliguric was crucial because of the distinct preceding risks and mortality outcomes of these two types of AKI in very preterm neonates.

IMPACT

The differences of the underlying risks and prognosis between oliguric and non-oliguric AKI in very preterm infants remain unclear. We found that oliguric AKI, but not non-oliguric AKI, carries higher mortality risks than infants without AKI. Oliguric AKI possessed higher mortality risks than non-oliguric AKI, irrespective of concomitant serum creatinine elevation and severe AKI. Oliguric AKI is more associated with prenatal small-for-the-gestational age and perinatal and postnatal adverse events, while non-oliguric AKI is associated with nephrotoxins exposures. Our finding highlighted the importance of oliguric AKI and is helpful in developing future protocol in neonatal critical care.

The association of low birthweight and prematurity on outcomes in children and adults with nephrotic syndrome-a NEPTUNE cohort study

BACKGROUND

In single-center studies, both preterm birth and low birth weight (LBW) are associated with worse outcomes in childhood nephrotic syndrome. Using the Nephrotic Syndrome Study Network (NEPTUNE) observational cohort, we tested the hypothesis that in patients with nephrotic syndrome, hypertension, proteinuria status, and disease progression would be more prevalent and more severe in subjects with LBW and prematurity singly or in combination (LBW/prematurity).

METHODS

Three hundred fifty-nine adults and children with focal segmental glomerulosclerosis (FSGS) or minimal change disease (MCD) and available birth history were included. Estimated glomerular filtration rate (eGFR) decline and remission status were primary outcomes, and secondary outcomes were kidney histopathology, kidney gene expression, and urinary biomarkers. Logistic regression was used to identify associations with LBW/prematurity and these outcomes.

RESULTS

We did not find an association between LBW/prematurity and remission of proteinuria. However, LBW/prematurity was associated with greater decline in eGFR. This decline in eGFR was partially explained by the association of LBW/prematurity with APOL1 high-risk alleles, but the association remained after adjustment. There were no differences in kidney histopathology or gene expression in the LBW/prematurity group compared to normal birth weight/term birth.

CONCLUSION

LBW and premature babies who develop nephrotic syndrome have a more rapid decline in kidney function. We did not identify clinical or laboratory features that distinguished the groups. Additional studies in larger groups are needed to fully ascertain the effects of (LBW) and prematurity alone or in combination on kidney function in the setting of nephrotic syndrome.

Diagnosis and management of mineral and bone disorders in infants with CKD: clinical practice points from the ESPN CKD-MBD and Dialysis working groups and the Pediatric Renal Nutrition Taskforce

BACKGROUND

Infants with chronic kidney disease (CKD) form a vulnerable population who are highly prone to mineral and bone disorders (MBD) including biochemical abnormalities, growth retardation, bone deformities, and fractures. We present a position paper on the diagnosis and management of CKD-MBD in infants based on available evidence and the opinion of experts from the European Society for Paediatric Nephrology (ESPN) CKD-MBD and Dialysis working groups and the Pediatric Renal Nutrition Taskforce.

METHODS

PICO (Patient, Intervention, Comparator, Outcomes) questions were generated, and relevant literature searches performed covering a population of infants below 2 years of age with CKD stages 2-5 or on dialysis. Clinical practice points (CPPs) were developed and leveled using the American Academy of Pediatrics grading matrix. A Delphi consensus approach was followed.

RESULTS

We present 34 CPPs for diagnosis and management of CKD-MBD in infants, including dietary control of calcium and phosphate, and medications to prevent and treat CKD-MBD (native and active vitamin D, calcium supplementation, phosphate binders).

CONCLUSION

As there are few high-quality studies in this field, the strength of most statements is weak to moderate, and may need to be adapted to individual patient needs by the treating physician. Research recommendations to study key outcome measures in this unique population are suggested. A higher resolution version of the Graphical abstract is available as Supplementary information.

The Urinary Concentration of Trefoil Factor 3 (TFF3) in the Term and Preterm Neonates

BACKGROUND

Distinguishing between a pathologic state and renal development is important in neonatology. Because the assessment of serum creatinine in neonates is not reliable, better biomarkers are needed. Trefoil factor 3 (TFF3) is proposed as a biomarker of kidney injury. The study aimed to assess its urinary concentration in healthy term and stable preterm neonates.

MATERIAL AND METHODS

The study included 80 term and 20 preterm neonates born in the Department of Perinatology of the University Clinical Hospital in Bialystok. Urine was obtained from the term neonates on the 1st day of life and from the preterm neonates on the 1st, 8th, 15th and 22nd day of life. The urinary concentration of TFF3 was determined using a commercially available immunoassay and was normalized for the urinary creatinine concentration (cr.).

RESULTS

The values of TFF3/cr. were higher in the preterm than in the term neonates (p < 0.05) (median (Q1-Q3): 1486.85 (614.92-3559.18) and 317.29 (68.07-671.40) ng/mg cr.). They did not differ in the subsequent days of the preterm neonates' lives. The ROC curve for TFF3/cr. in the preterm and term neonates showed AUC = 0.751 (cut-off value = 1684.25 ng/mg cr.).

CONCLUSIONS

Prematurity is associated with higher urinary excretion of TFF3. Male gender is associated with an increased urinary TFF3 excretion in term neonates.

Blood pressure and cardiovascular risk in relation to birth weight and urinary sodium: an individual-participant meta-analysis of European family-based population studies

BACKGROUND

Although the relation of salt intake with blood pressure (BP) is linear, it is U-shaped for mortality and cardiovascular disease (CVD). This individual-participant meta-analysis explored whether the relation of hypertension, death or CVD with 24-h urinary sodium excretion (UVNA) or sodium-to-potassium (UNAK) ratio was modified by birth weight.

METHODS

Families were randomly enrolled in the Flemish Study on Genes, Environment and Health Outcomes (1985-2004) and the European Project on Genes in Hypertension (1999-2001). Categories of birth weight, UVNA and UNAK (≤2500, >2500-4000, >4000 g; <2.3, 2.3-4.6 and >4.6 g; and <1, 1-2, >2, respectively) were coded using deviation-from-mean coding and analyzed by Kaplan-Meier survival functions and linear and Cox regression.

RESULTS

The study population was subdivided into the Outcome ( n  = 1945), Hypertension ( n  = 1460) and Blood Pressure cohorts ( n  = 1039) to analyze the incidence of mortality and cardiovascular endpoints, hypertension and BP changes as function of UVNA changes. The prevalence of low/medium/high birth weight in the Outcome cohort was 5.8/84.5/9.7%. Over 16.7 years (median), rates were 4.9, 8 and 27.1% for mortality, CVD and hypertension, respectively, but were not associated with birth weight. Multivariable-adjusted hazard ratios were not significant for any endpoint in any of the birth weight, UVNA and UNAK strata. Adult body weight tracked with birth weight ( P  < 0.0001). The partial r in the low-birth-weight group associating changes from baseline to follow-up in UVNA and SBP was 0.68 ( P  = 0.023) but not significant in other birth weight groups.

CONCLUSION

This study did not substantiate its prior hypothesis but showed tracking of adult with birth weight and suggest that low birth weight increases salt sensitivity.

Associations of prematurity and low birth weight with blood pressure and kidney function in middle-aged participants of the Brazilian Longitudinal Study of Adult Health: ELSA-Brasil

BACKGROUND

An adverse intrauterine environment reflected by low birth weight (LBW) and prematurity may induce fetal programming that favors kidney dysfunction in adulthood. We examined the association of LBW and prematurity with blood pressure (BP) and kidney function markers in non-diabetic, middle-aged adults without kidney disease from the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil).

METHODS

A cross-sectional analysis of 768 subjects aged 35-54 years was conducted. Comparisons were performed according to self-reported birth weight: LBW (< 2.5 kg) or normal birth weight (2.5-4.0 kg). Associations of LBW and prematurity with BP levels and kidney function markers "(estimated glomerular filtration rate [eGFR], albumin-creatinine ratio [ACR] and serum cystatin-C) were tested by multiple linear regression using adjustments based on Directed Acyclic Graphs. Propensity score matching was applied to control imbalances.

RESULTS

Mean age of participants was 45.5 ± 4.6 years and 56.8% were female; 64 (8.3%) participants reported LBW and 39 (5.0%) prematurity. The LBW group had higher systolic (p = 0.015) and diastolic BP (p = 0.014) and ACR values (p = 0.031) and lower eGFR (p = 0.015) than the normal birth weight group, but no group difference for cystatin-C was found. The preterm group had higher mean levels of systolic and diastolic BP, but no difference in kidney function markers was evident. In a regression model adjusted for sex, skin color and family history of hypertension, both systolic and diastolic BP levels were associated with LBW, but this association disappeared after adding for prematurity, which remained associated with BP (p = 0.017). Having applied a propensity score matching, LBW was associated with ACR values (p = 0.003), but not with eGFR or BP levels.

CONCLUSION

The study findings of independent associations of prematurity with higher BP levels, and of LBW with markers of kidney function in adulthood, support that early life events may predict risk for hypertension and kidney dysfunction in adulthood. The study design precluded the inferring of causality, and prospective studies are needed to further investigate this hypothesis.

The impact of intrauterine growth restriction and prematurity on nephron endowment

In humans born at term, maximal nephron number is reached by the time nephrogenesis is completed - at approximately 36 weeks' gestation. The number of nephrons does not increase further and subsequently remains stable until loss occurs through ageing or disease. Nephron endowment is key to the functional capacity of the kidney and its resilience to disease; hence, any processes that impair kidney development in the developing fetus can have lifelong adverse consequences for renal health and, consequently, for quality and length of life. The timing of nephrogenesis underlies the vulnerability of developing human kidneys to adverse early life exposures. Indeed, exposure of the developing fetus to a suboptimal intrauterine environment during gestation - resulting in intrauterine growth restriction (IUGR) - and/or preterm birth can impede kidney development and lead to reduced nephron endowment. Furthermore, emerging research suggests that IUGR and/or preterm birth is associated with an elevated risk of chronic kidney disease in later life. The available data highlight the important role of early life development in the aetiology of kidney disease and emphasize the need to develop strategies to optimize nephron endowment in IUGR and preterm infants.

Kidney growth following preterm birth: evaluation with renal parenchyma ultrasonography

BACKGROUND

Preterm birth impairs nephrogenesis, leading to a reduced nephron endowment which is inextricably linked to hypertension and chronic kidney disease in adults. The aim of this study was to compare nephron endowment between preterm infants to that of intrauterine fetuses at the same gestational age (GA) using a novel indirect ultrasound measurement of the renal parenchymal thickness. We hypothesized that extrauterine and intrauterine renal parenchymal thickness would differ based on altered renal growth environments.

METHODS

In this observational study, appropriately grown preterm infants (birth weight of between the 5th and 95th percentile) born <32 weeks, admitted to the neonatal department were eligible to participate. Renal parenchymal thickness of the infants was measured at 32- and 37-weeks postmenstrual age (PMA). These measurements were compared to the intrauterine renal parenchymal thickness of appropriately grown fetuses (control).

RESULTS

At 32-weeks PMA, the preterm infants had a significantly thinner renal parenchyma compared to fetuses at 32-weeks GA suggesting they had less nephrons, however by 37-weeks there was no significant difference in renal parenchymal thickness.

CONCLUSIONS

We propose that the differences in the extrauterine growth of the renal parenchyma in preterm infants may be due to a reduced number of nephrons and compensatory hyperfiltration.

IMPACT

This article provides insight into the effects of prematurity on nephrogenesis by comparing extrauterine renal parenchymal growth of born preterm infants to the ideal intrauterine fetal growth. Renal parenchyma thickness measurement using ultrasonography is a novel non-invasive measurement of renal development for the determination of nephron endowment. Differences in the renal parenchymal thickness of the preterm infants may be due to a deficit in nephron number and compensatory hyperfiltration.

Hypoxia-Induced Kidney Injury in Newborn Rats

Exposure to hypoxia during the early postnatal period can have adverse effects on vital organs. Neonatal Sprague-Dawley rats housed in a hypoxic chamber were compared to those in a normoxic chamber from postnatal days 0 to 7. Arterial blood was collected to evaluate renal function and hypoxia. Kidney morphology and fibrosis were evaluated using staining methods and immunoblotting. In the kidneys of the hypoxic group, protein expressions of hypoxia-inducible factor-1 were higher than those in the normoxic group. Hypoxic rats had higher levels of hematocrit, serum creatinine, and lactate than normoxic rats. Body weight was reduced, and protein loss of kidney tissue was observed in hypoxic rats compared to normoxic rats. Histologically, hypoxic rats showed glomerular atrophy and tubular injury. Renal fibrosis with collagen fiber deposition was observed in the hypoxic group. The expression of nicotinamide adenine dinucleotide phosphate oxidases was enhanced in the kidneys of hypoxic rats. Proteins involved in apoptosis were upregulated in the kidneys of hypoxic rats. An increase in the expression of pro-inflammatory cytokines was also observed in the kidneys of hypoxic rats. Hypoxic kidney injury in neonatal rats was associated with oxidative stress, inflammation, apoptosis, and fibrosis.

Current and potential methods to assess kidney structure and morphology in term and preterm neonates

After birth, the kidney structure in neonates adapt to the functional demands of extrauterine life. Nephrogenesis is complete in the third trimester, but glomeruli, tubuli, and vasculature mature with the rapidly increasing renal blood flow and glomerular filtration. In preterm infants, nephrogenesis remains incomplete and maturation is slower and may be aberrant. This structural and functional deficit has life-long consequences: preterm born individuals are at higher risk for chronic kidney disease and arterial hypertension later in life. This review assembles the literature on existing and potential methods to visualize neonatal kidney structure and morphology and explore their potential to longitudinally document the developmental deviation after preterm birth. X-rays with and without contrast, fluoroscopy and computed tomography (CT) involve relevant ionizing radiation exposure and, apart from CT, do not provide sufficient structural details. Ultrasound has evolved into a safe and noninvasive high-resolution imaging method which is excellent for longitudinal observations. Doppler ultrasound modes can characterize and quantify blood flow to and through the kidneys. Microvascular flow imaging has opened new possibilities of visualizing previously unseen vascular structures. Recent advances in magnetic resonance imaging display renal structure and function in unprecedented detail, but are offset by the logistical challenges of the imaging procedure and limited experience with the new techniques in neonates. Kidney biopsies visualize structure histologically, but are too invasive and remain anecdotal in newborns. All the explored methods have predominantly been examined in term newborns and require further research on longitudinal structural observation in the kidneys of preterm infants.

Low nephron endowment increases susceptibility to renal stress and chronic kidney disease

Preterm birth results in low nephron endowment and increased risk of acute kidney injury (AKI) and chronic kidney disease (CKD). To understand the pathogenesis of AKI and CKD in preterm humans, we generated potentially novel mouse models with a 30%-70% reduction in nephron number by inhibiting or deleting Ret tyrosine kinase in the developing ureteric bud. These mice developed glomerular and tubular hypertrophy, followed by the transition to CKD, recapitulating the renal pathological changes seen in humans born preterm. We injected neonatal mice with gentamicin, a ubiquitous nephrotoxic exposure in preterm infants, and detected more severe proximal tubular injury in mice with low nephron number compared with controls with normal nephron number. Mice with low nephron number had reduced proliferative repair with more rapid development of CKD. Furthermore, mice had more profound inflammation with highly elevated levels of MCP-1 and CXCL10, produced in part by damaged proximal tubules. Our study directly links low nephron endowment with postnatal renal hypertrophy, which in this model is maladaptive and results in CKD. Underdeveloped kidneys are more susceptible to gentamicin-induced AKI, suggesting that AKI in the setting of low nephron number is more severe and further increases the risk of CKD in this vulnerable population.

Acute Kidney Injury in Very Low Birth Weight Infants: A Major Morbidity and Mortality Risk Factor

BACKGROUND AND OBJECTIVES

Very low birth weight (VLBW) infants are at high risk of developing acute kidney injury (AKI), presumably secondary to low kidney reserves, stressful postnatal events, and drug exposures. Our study aimed to identify the prevalence, risk factors, and outcomes associated with AKI in VLBW infants.

STUDY DESIGN

Records of all VLBW infants admitted to two medical campuses between January 2019 and June 2020 were retrospectively reviewed. AKI was classified using the modified KDIGO definition to include only serum creatinine. Risk factors and composite outcomes were compared between infants with and without AKI. We evaluated the main predictors of AKI and death with forward stepwise regression analysis.

RESULTS

152 VLBW infants were enrolled. 21% of them developed AKI. Based on the multivariable analysis, the most significant predictors of AKI were the use of vasopressors, patent ductus arteriosus, and bloodstream infection. AKI had a strong and independent association with neonatal mortality.

CONCLUSIONS

AKI is common in VLBW infants and is a significant risk factor for mortality. Efforts to prevent AKI are necessary to prevent its harmful effects.

Use of Kidneys from Anencephalic Donors to Offset Organ Shortage

Background: It is well recognized that patient survival and quality of life are superior with renal transplantation than with dialysis. Organ availability is far outweighed by the large number of wait-listed patients. Additional stratagems are sought to expand the donor pool, and kidneys from anencephalic infants can be considered a source of organs, until now unexplored. We plan to assess the feasibility of using the kidneys from anencephalic infants for transplantation. Material and Methods: Information about anencephaly, the characteristics of the infant kidneys, the ethical, social and medico-legal aspects raised by the use of these kidneys, their procurement and their transplantation are reviewed. Conclusions: En bloc kidney transplants from infants can provide long-term normal renal function after an accelerated catch up growth. They are not subjected to hyperfiltration since they have a full complement of nephrons. They can be transplanted using the techniques currently available.

Preterm birth leads to a decreased number of differentiated podocytes and accelerated podocyte differentiation

Preterm birth was previously identified as a high-risk factor for the long-term development of chronic kidney disease. However, the detailed pattern of podocyte (PD) changes caused by preterm birth and the potential mechanism underlying this process have not been well clarified. In present study, a rat model of preterm birth was established by delivery of pups 2 days early and podometric methods were applied to identify the changes in PDs number caused by preterm birth. In addition, single-cell RNA sequencing (scRNA-seq) and subsequent bioinformatic analysis were performed in the preterm rat kidney to explore the possible mechanism caused by preterm birth. As results, when the kidney completely finished nephrogenesis at the age of 3 weeks, a reduction in the total number of differentiated PDs in kidney sections was detected. In addition, 20 distinct clusters and 12 different cell types were identified after scRNA-seq in preterm rats (postnatal day 2) and full-term rats (postnatal day 0). The numbers of PDs and most types of inherent kidney cells were decreased in the preterm birth model. In addition, 177 genes were upregulated while 82 genes were downregulated in the PDs of full-term rats compared with those of preterm rats. Further functional GO analysis revealed that ribosome-related genes were enriched in PDs from full-term rats, and kidney development-related genes were enriched in PDs from preterm rats. Moreover, known PD-specific and PD precursor genes were highly expressed in PDs from preterm rats, and pseudotemporal analysis showed that PDs were present earlier in preterm rats than in full-term rats. In conclusion, the present study showed that preterm birth could cause a reduction in the number of differentiated PDs and accelerate the differentiation of PDs.

Persistent high blood pressure and renal dysfunction in preterm infants during childhood

BACKGROUND

Infants born very preterm (≤32 weeks gestational age, GA) and very-low birth weight (≤1500 g; PT-VLBW) demonstrate high systolic blood pressure (SBP), renal dysfunction, and obesity at 6 months-3 years and in early adulthood. Their parallel measurement and progression during childhood is unclear.

METHODS

We reenrolled 62/120 patients originally seen at 1-3 years at 10-13 years and remeasured anthropometric indices, SBP, and serum creatinine (Cr) and cystatin C (cysC) to determine estimated glomerular filtration rate (eGFR). We selected Term-matched Controls at 10-13 years from the 2015-2016 NHANES database at a ratio of 2 Controls:1 Case (124:62).

RESULTS

Reenrolled patients were predominantly Hispanic, birth weight 1073 ± 251 g, and GA at birth 28 ± 2 weeks. At 10-13 years, 45% were classified overweight/obese, 48% had SBP ≥ 90th centile (77% considered hypertensive), and 34% had low eGFR (<90 mL min^-1 [1.73 m²]^-1). Notably, 57% of reenrolled PT-VLBW Cases had low eGFR_cysC at both 1-3 and 10-13 years, P < 0.03. Compared to Controls, Cases had four times the adjusted odds for having an elevated SBP and low eGFR_Cr despite similar proportions with overweight/obesity among Cases and Controls.

CONCLUSIONS

PT-VLBW infants seen at 1-3 years exhibit obesity, elevated SBP, and low eGFR in infancy and 10-13 years. Although the small sample size may limit conclusions, pediatricians should consider serial evaluations of PT-VLBW throughout childhood.

IMPACT

The association between preterm birth and elevated blood pressure, renal dysfunction, and obesity in young adults begins as early as 1 year and persists at 10-13 years of age. This is the first study reporting serial measurements of blood pressure, renal function, and obesity from infancy to preadolescence in children born very preterm. Fifty-seven percent of preterm 1-3 year olds have persistent low estimated glomerular filtration rate associated with hypertension at 10-13 years. Clinicians should consider serial evaluations of blood pressure, renal function, and obesity throughout infancy and childhood in all preterm births.

Changes in regional oxygen saturation of the kidney and brain of infants during hospitalization

BACKGROUND

In pre-term infants, the postnatal changes in the regional oxygen saturation (rSO₂) of the brain and kidney are unclear.

METHODS

We performed a prospective observational study. We measured the cerebral/renal rSO₂ ratio and recorded the associated clinical features of infants born at 23 to 41 weeks of gestation weekly from the early postnatal period to discharge.

RESULTS

The median cerebral/renal rSO₂ ratios (interquartile ranges) between birth and the expected date of birth were 1.13 (1.06-1.26) at 23-24 weeks (n = 7), 1.18 (1.10-1.32) at 25-26 weeks (n = 11), 1.24 (1.11-1.37) at 27-28 weeks (n = 9), 1.12 (1.05-1.19) at 29-30 weeks (n = 4), 1.11 (1.03-1.15) at 31-32 weeks (n = 5), 1.02 (0.98-1.06) at 33-34 weeks (n = 9), 0.98 (0.94-1.06) at 35-36 weeks (n = 19), and 0.95 (0.86-0.99) at 37-41 weeks of gestation (n = 22). The median cerebral/renal rSO₂ ratio did not significantly change after birth, but with increasing gestational age, the cerebral/renal rSO₂ ratio at the expected date of birth decreased (r = - 0.74, p < 0.001). Nephrotoxic drugs did not affect cerebral/renal rSO₂ at the expected date of birth, after adjustment for clinical factors.

CONCLUSIONS

Unlike in most infants born after the late pre-term period, the renal rSO₂ remained lower than the cerebral rSO₂ on the expected date of birth in infants born very pre-term.

Regulation of nephron progenitor cell lifespan and nephron endowment

Low nephron number - resulting, for example, from prematurity or developmental anomalies - is a risk factor for the development of hypertension, chronic kidney disease and kidney failure. Considerable interest therefore exists in the mechanisms that regulate nephron endowment and contribute to the premature cessation of nephrogenesis following preterm birth. The cessation of nephrogenesis in utero or shortly after birth is synchronized across multiple niches in all mammals, and is coupled with the exhaustion of nephron progenitor cells. Consequently, no nephrons are formed after the cessation of developmental nephrogenesis, and lifelong renal function therefore depends on the complement of nephrons generated during gestation. In humans, a tenfold variation in nephron endowment between individuals contributes to differences in susceptibility to kidney disease; however, the mechanisms underlying this variation are not yet clear. Salient advances in our understanding of environmental inputs, and of intrinsic molecular mechanisms that contribute to the regulation of cessation timing or nephron progenitor cell exhaustion, have the potential to inform interventions to enhance nephron endowment and improve lifelong kidney health for susceptible individuals.

Serum and urinary biomarkers to predict acute kidney injury in premature infants: a systematic review and meta-analysis of diagnostic accuracy

BACKGROUND

Premature infants are at high risk for acute kidney injury (AKI) and current diagnostic criteria are flawed. The objective of this study was to determine the diagnostic accuracy of urine and serum biomarkers not currently used in routine clinical practice to predict AKI in premature infants.

METHOD

A systematic review was performed that followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses of Diagnostic Test Accuracy Studies (PRISMA-DTA). Data were extracted on the diagnostic accuracy of AKI biomarkers using serum creatinine or urine output as the reference standard. Quality and validity were assessed using modified Standards for Reporting Diagnostic Accuracy (STARD) criteria.

RESULTS

We identified 1024 articles, with 15 studies (791 infants) eligible for inclusion. Twenty-seven biomarkers were identified including serum cystatin C and urinary neutrophil gelatinase-associated lipocalin (uNGAL), osteopontin, kidney injury molecule-1, epidermal growth factor, and protein S100-P. However, many were only reported by one study each. A meta-analysis could only be conducted on uNGAL (288 infants from 6 studies) using a hierarchical, random-effects logistic-regression model. uNGAL had a summary sensitivity of 77% (95% CI 58-89%), specificity of 76% (95% CI 57-88%) and AUC-SROC of 0.83 (95% CI 0.80-0.86) for the diagnosis of AKI. By utilising uNGAL, the post-test probability of AKI increased to 52% (95% CI 37-66%) with a positive test and decreased to 9% (95% CI 5-16%) with a negative test if the pre-test probability was 25%.

CONCLUSION

uNGAL shows promise as a diagnostically accurate biomarker for AKI in premature infants.

The interstitium at the developing nephron in the fetal kidney during advanced pregnancy - a microanatomical inventory

Background

A series of noxae can evoke the termination of nephron formation in preterm and low birth weight babies. This results in oligonephropathy with severe consequences for health in the later life. Although the clinical parameters have been extensively investigated, little is known about the initial damage. Previous pathological findings indicate the reduction in width of the nephrogenic zone and the lack of S-shaped bodies. Current morphological investigations suggest that due to the mutual patterning beside the forming nephron, also its structural neighbors, particularly the interjacent interstitium, must be affected. However, beside the findings on integrative and mastering functions, systematic microanatomical data explaining the configuration of the interstitium at the developing nephron in the fetal kidney during advanced pregnancy is not available. Therefore, this work explains the typical features.

Results

The generated data depicts that the progenitor cells, nephrogenic niche, pretubular aggregate, and mesenchymal-to-epithelial transition are restricted to the subcapsular interstitium. During the proceeding development, only the distal pole of the renal vesicles and comma- and S-shaped bodies stays in further contact with it. The respective proximal pole is positioned opposite the peritubular interstitium at the connecting tubule of an underlying but previously formed nephron. The related medial aspect faces the narrow peritubular interstitium of a collecting duct (CD) ampulla first only at its tip, then at its head, conus, and neck, and finally at the differentiating CD tubule. The lateral aspect starts at the subcapsular interstitium, but then it is positioned along the wide perivascular interstitium of the neighboring ascending perforating radiate artery. When the nephron matures, the interstitial configuration changes again.

Conclusions

The present investigation illustrates that the interstitium at the forming nephron in the fetal kidney consists of existing, transient, stage-specific, and differently far matured compartments. According to the developmental needs, it changes its shape by formation, degradation, fusion, and rebuilding.

Prevalence and Risk Factors for Kidney Disease and Elevated BP in 2-Year-Old Children Born Extremely Premature

BACKGROUND AND OBJECTIVES

Extremely low gestational age neonates born <28 weeks gestation are at risk for chronic disease. We sought to describe the prevalence of kidney outcomes by gestational age and determine risk factors for their development.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The Recombinant Erythropoietin for Protection of Infant Renal Disease (REPAIReD) study examined kidney outcomes of extremely low gestational age neonates enrolled in the Preterm Epo NeuroProtection Trial (PENUT) study. Kidney function, urine albumin, and BP were measured at 2-year (24±2 months) corrected gestational age. We compared outcomes across gestational age categories and evaluated associations between kidney-related outcomes and neonatal and maternal characteristics. The primary outcome was eGFR <90 ml/min per 1.73 m² (CKD); secondary outcomes were spot urine albumin-creatinine ratio ≥30 mg/g (albuminuria) and either systolic BP or diastolic BP >90th percentile for height, age, and sex.

RESULTS

A total of 832 survived to 2 years, and 565 (68%) had at least one outcome measured. Overall, 297 (53%) had one abnormal kidney outcome; 61 (18%) had an eGFR <90 ml/min per 1.73 m², 155 (36%) had albuminuria, 65 (22%) had elevated systolic BP, and 128 (44%) had elevated diastolic BP. Gestational age (odds ratio, 0.94; 95% confidence interval, 0.89 to 0.99), birth weight z-score (odds ratio, 0.92; 95% confidence interval, 0.85 to 0.98), and prenatal steroids (odds ratio, 1.23; 95% confidence interval, 1.08 to 1.39) were associated with an eGFR <90 ml/min per 1.73 m². An elevated systolic BP was associated with indomethacin use (odds ratio, 1.18; 95% confidence interval, 1.04 to 1.33) and Black race (odds ratio, 1.19; 95% confidence interval, 1.01 to 1.39); elevated diastolic BP was associated with male sex (odds ratio, 1.29; 95% confidence interval, 1.12 to 1.49), severe AKI (odds ratio, 1.24; 95% confidence interval, 1.04 to 1.48), and indomethacin use (odds ratio, 1.16; 95% confidence interval, 1.01 to 1.33).

CONCLUSIONS

Approximately 18% of extremely low gestational age neonates have CKD, 36% have albuminuria, 22% have an elevated systolic BP, and 44% have an elevated diastolic BP at 2 years of age. Gestational age, birthweight z-score, and prenatal steroids were associated with CKD. Male sex, Black race, indomethacin use, and severe AKI were associated with elevated BP.

PODCAST

This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2022_07_19_CJN15011121.mp3.

Neonatal hypertension: concerns within and beyond the neonatal intensive care unit

Neonatal hypertension occurs in 1%-2% of neonates in the neonatal intensive care unit (NICU) although may be underdiagnosed. Blood pressure values in premature neonates change rapidly in the first days and weeks of life which may make it more difficult to recognize abnormal blood pressure values. In addition, the proper blood pressure measurement technique must be used to ensure the accuracy of the measured values as most blood pressure devices are not manufactured specifically for this population. In premature neonates, the cause of the hypertension is most commonly related to prematurity-associated complications or management while in term neonates is more likely to be due to an underlying condition. Both oral and intravenous antihypertensive medications can be used in neonates to treat high blood pressure although none are approved for use in this population by regulatory agencies. The natural history of most neonatal hypertension is that it resolves over the first year or two of life. Of concern are the various neonatal risk factors for later cardiovascular and kidney disease that are present in most NICU graduates. Prematurity increases the risk of adulthood hypertension while intrauterine growth restriction may even lead to hypertension during childhood. From neonates through to adulthood NICU graduates, this review will cover each of these topics in more detail and highlight the aspects of blood pressure management that are established while also highlighting where knowledge gaps exist.

Preterm Birth, Kidney Function and Cardiovascular Disease in Children and Adolescents

Over recent decades, there has been a global increase in preterm birth rate, which constitutes about 11% of total births worldwide. The present review aims to summarize the current knowledge on the long-term consequences of prematurity on renal and cardiovascular development and function. Recent literature supports that prematurity, intrauterine growth restriction or low birth weight (LBW) may have an adverse impact on the development of multiple organ systems, predisposing to chronic diseases in childhood and adulthood, such as arterial hypertension and chronic kidney disease. According to human autopsy and epidemiological studies, children born preterm have a lower nephron number, decreased kidney size and, in some cases, affected renal function. The origin of hypertension in children and adults born preterm seems to be multifactorial as a result of alterations in renal, cardiac and vascular development and function. The majority of the studies report increased systolic and diastolic blood pressure (BP) in individuals born preterm compared to full term. The early prevention and detection of chronic non-communicable diseases, which start from childhood and track until adulthood in children with a history of prematurity or LBW, are important.

When the progresses in neonatology lead to severe congenital nephron deficit: is there a pilot in the NICU?

Advances in the care of neonates to the extreme limits of viability have increased the risk of severe comorbidities in surviving preemies. The respiratory and the neurodevelopmental consequences of premature birth and/or intra-uterine growth retardation have been well described. Because of the usual clinical silence of the kidney, the long-term renal consequences of low birth weight have not been as well studied. A case report illustrates the risk factors associated with low birth weight and prematurity and discusses the pathogenesis of the late consequences of the congenital nephron deficit associated with a low birth weight. Practical recommendations are given for a tight follow-up of these newly born preemies.

Impact of nephrotoxic drugs on urinary biomarkers of renal function in very preterm infants

BACKGROUND

Following preterm birth, the immature kidney is exposed to several harmful conditions, with an increased risk of renal impairment. We aimed to assess urinary biomarkers of renal function in very preterm infants during early nephrotoxic treatments.

METHODS

Infants ≤32 weeks' gestation and ≤1500 g were enrolled in this observational prospective study. Urine samples were collected on day 1(T1), 2-4(T2), 5-7(T3), 8-10(T4), 11-13(T5). The following urinary biomarkers were determined: osteopontin (uOPN), epidermal growth factor (uEGF), neutrophil gelatinase-associated lipocalin (uNGAL), cystatin C (uCysC). The infants were grouped according to their exposure to amikacin or ibuprofen during the study period and a between-group comparison of urinary biomarkers at each time point was performed.

RESULTS

Thirty-six infants were included. Urinary CysC, uOPN, and uNGAL rose significantly during ibuprofen or amikacin treatment, while no difference was observed for uEGF. After adjustment for possible influencing factors, amikacin administration was associated with higher uCysC at T1 (p = 0.007) and T2 (p = 0.016), whereas ibuprofen increased uOPN (p = 0.001) and uNGAL concentration (p = 0.009) at T3.

CONCLUSION

Nephrotoxic therapies induce molecule-specific change patterns of renal function biomarkers in treated preterm infants. Serial assessments of these biomarkers may aid to identify neonates at risk of renal impairment and to develop tailored therapeutic approaches.

IMPACT

Despite the wide use of nephrotoxic therapies in neonatal settings, little is known on their effect on renal function biomarkers in preterm infants. This study describes molecule-specific change patterns of urinary biomarkers during ibuprofen and amikacin administration, suggesting underlying pathophysiological effects on renal function. Given their low analytical costs and non-invasive collection, the urinary biomarkers investigated in this study represent a promising strategy for serial monitoring of renal function in at-risk neonates and may aid the early detection of renal function impairment at different kidney levels during nephrotoxic treatments.

Protective Effects of Hydrogen-rich Water Intake on Renal Injury in Neonatal Rats with High Oxygen Loading

Objectives

This study aimed to investigate the protective effects of hydrogen-rich water (HW) intake on renal injury in neonatal rats with high oxygen loading.

Materials

We used pregnant and newborn Sprague-Dawley rats.

Methods

Four groups were set up, with mother and newborn rats immediately after delivery as one group: RA-PW (room air and purified water), RA-HW (room air and HW), O2-PW (80% oxygen and purified water), and O2-HW (80% oxygen and HW). The newborn rats were maintained in either a normoxic (room air, 21% oxygen) or controlled hyperoxic (80% oxygen) environment from birth. Then, HW (O2-HW and RA-HW groups) or PW (O2-PW and RA-PW groups) was administered to parents of each group.

Results

The number of immature glomeruli significantly increased in the O2-PW group (exposed to hyperoxia). Conversely, the O2-HW group had significantly fewer immature glomeruli than O2-PW group. In the RT-PCR analysis of kidney tissue, α-SMA, TGF-β, and TNF-α levels were significantly higher in the O2-PW group than in the RA-PW group and significantly lower in the O2-HW group than in the O2-PW group.

Conclusions

HW intake can potentially reduce oxidative stress and prevent renal injury in neonates with high oxygen loading.

Filtering Down to Risks and Solutions: Risk Factors and Stratification After Pediatric Cardiac Surgery

Acute kidney injury after cardiac surgery (CS-AKI) is common in neonatal and pediatric populations and is a risk factor for poor outcomes, such as mortality and increased hospital resource utilization. This review presents a summary of CS-AKI risk factors, integration of biomarkers, and the need to improve risk stratification for targeting future clinical trials. To date, studies examining CS-AKI risk factors cannot be generalized easily owing to variability in patient age, surgical complexity or population, AKI definition, and center-specific practices. However, certain risk associations, such as younger age at surgery, history of prematurity, cardiopulmonary bypass time, and surgical complexity, have been identified across multiple, but not all, studies. CS-AKI appears to have different severity and duration phenotypes, and serum creatinine is limited in its ability to identify CS-AKI early and predict CS-AKI course. Treatment strategies are largely supportive, and efforts are ongoing to use biomarkers and clinical features to risk-stratify patients, which in turn may facilitate differential CS-AKI phenotyping and management with supportive care bundles, clinical decision support techniques, and modulation of modifiable risk factors.

Fluid Homeostasis and Diuretic Therapy in the Neonate

Understanding physiologic water balance and homeostasis mechanisms in the neonate is critical for clinicians in the NICU as pathologic fluid accumulation increases the risk for morbidity and mortality. In addition, once this process occurs, treatment is limited. In this review, we will cover fluid homeostasis in the neonate, explain the implications of prematurity on this process, discuss the complexity of fluid accumulation and the development of fluid overload, identify mitigation strategies, and review treatment options.

Sociodemographic determinants of chronic kidney disease in Indigenous children

Rates of chronic kidney disease (CKD) are disproportionately increased in Indigenous peoples. The focus has traditionally been on adults, as they experience the highest rates of kidney failure requiring kidney replacement therapy. The impacts of colonization, systemic racism, and sociodemographic marginalization however impact the health of Indigenous peoples across the lifespan. This review presents the social context within which Indigenous children develop and the impact relevant to kidney health across the developmental stages. In utero exposures impact nephron endowment which can manifest in glomerular hyperfiltration and sclerosis as well as an increased risk of congenital anomalies of the kidney and urinary tract. Young children are at increased risk of autoimmune conditions, secondary to infectious and environmental exposures, and are also exposed to the impacts of a Western lifestyle manifesting early onset overweight/obesity. Adolescents begin to manifest more severe metabolic complications such as type 2 diabetes. The impacts of early onset diabetes are associated with aggressive kidney complications and high rates of kidney failure in young adulthood. Finally, the key elements of successful prevention and treatment strategies are discussed including the importance of screening for asymptomatic, modifiable early disease, linked with clinical primary and tertiary care follow-up, and culturally relevant and safe care.

Prediction of glomerular filtration rate maturation across preterm and term neonates and young infants using inulin as marker

Describing glomerular filtration rate (GFR) maturation across the heterogeneous population of preterm and term neonates and infants is important to predict the clearance of renally cleared drugs. This study aims to describe the GFR maturation in (pre)term neonates and young infants (PNA < 90 days) using individual inulin clearance data (CL_inulin). To this end, published GFR maturation models were evaluated by comparing their predicted GFR with CL_inulin retrieved from literature. The best model was subsequently optimized in NONMEM V7.4.3 to better fit the CL_inulin values. Our study evaluated seven models and collected 381 individual CL_inulin values from 333 subjects with median (range) birthweight (BWb) 1880 g (580-4950), gestational age (GA) 34 weeks (25-43), current weight (CW) 1890 g (480-6200), postnatal age (PNA) 3 days (0-75), and CL_inulin 2.20 ml/min (0.43-17.90). The De Cock 2014 model (covariates: BWb and PNA) performed the best in predicting CL_inulin, followed by the Rhodin 2009 model (covariates: CW and postmenstrual age). The final optimized model shows that GFR at birth is determined by BWb, thereafter the maturation rate of GFR is dependent on PNA and GA, with a higher GA showing an overall faster maturation. To conclude, using individual CL_inulin data, we found that a model for neonatal GFR requires a distinction between prenatal maturation quantified by BWb and postnatal maturation. To capture postnatal GFR maturation in (pre)term neonates and young infants, we developed an optimized model in which PNA-related maturation was dependent on GA.

Histologic characterization and risk factors for persistent albuminuria in adolescents in a region of highly prevalent end-stage renal failure of unknown origin

Background

End-stage renal failure of unknown origin (ESRD-UO) is a public health problem in Mexico and many regions of the world. The prevalence of ESRD-UO in Aguascalientes Mexico is one of the highest worldwide, particularly in adults between 20 and 40 years of age.

Aim

To screen adolescents for chronic kidney disease (CKD), identify risk factors, and histologically characterize adolescents with persistent albuminuria (pACR).

Methodology

This is a cross-sectional, observational, and comparative study of adolescents in whom serum creatinine and the albumin creatinine ratio (ACR) were determined when screening for CKD. A clinical evaluation and risk factor survey were conducted. Patients with an abnormal ACR (≥ 30 mg/gr) or a low glomerular filtration rate (GFR) (≤75 ml/min/1.73 m2) were reevaluated and a renal ultrasound was obtained (rUS). A kidney biopsy was performed in patients with pACR.

Results

Five-hundred and thirteen (513) students were included, 19 had pACR and 494 were controls. The prevalence of pACR was 3.7% (95%CI 2.1 – 5.3). Only one patient had a decreased GRF. None of the patients with pACR had anatomical abnormalities of the urinary tract by rUS. Patients with pACR had a decreased total renal volume in comparison with the control group (150 vs 195 ml/m2, p &lt;0.01). Eighteen (18) kidney biopsies were performed, 72% had glomerulomegaly, and only one patient had mild fibrosis. Podocyte abnormalities were evident on electron microscopy: partial fusion (100%), microvillous degeneration (80%), and increased organelles (60%). Risk factors for pACR were: homestead proximity to maize crops, the use of pesticides at the father´s workplace, a family history of CKD, and blood pressure abnormalities. The body mass index and breastfeeding were protective factors.

Conclusions

The prevalence of pACR in adolescents in Aguascalientes is high, and histologic compromise is characterized by podocyte injury in the absence of fibrosis. The renal volume of pACR patients was decreased, suggesting oligonephronia. Exposure to environmental toxins such as pesticides, even prenatally, may be responsible for this pathological entity. Screening programs in adolescents by determining ACR are necessary in our milieu.