A quantitative study of normal nephrogenesis in the human fetus: its implication in the natural history of kidney changes due to low obstructive uropathies

Assessment of nephron number and single-nephron glomerular filtration rate in a clinical setting

Total nephron counts vary widely between individuals and may affect susceptibility to certain diseases, including hypertension and chronic kidney disease. Detailed analyses of whole kidneys collected from autopsy patients remain the only method for accurately counting nephrons in humans, with no equivalent option in living subjects. Current technological advances have enabled estimations of nephron numbers in vivo, particularly the use of total nephron number and whole-kidney glomerular filtration rate to estimate the mean single-nephron glomerular filtration rate. The use of this method would allow physicians to detect dynamic changes in filtration function at the single-nephron level rather than to simply count the number of nephrons that appear to be functioning. Currently available methods for estimating total nephron number in clinical practice have the potential to overcome limitations associated with autopsy analyses and may therefore pave the way for new therapeutic interventions and improved clinical outcomes.

Cohort profile: the Dutch famine birth cohort (DFBC)- a prospective birth cohort study in the Netherlands

PURPOSE

The Dutch famine birth cohort study was set up to investigate the effects of acute maternal undernutrition of the 1944-1945 Dutch famine during the specific stages of gestation on later health, with a particular focus on chronic cardiovascular and metabolic diseases, ageing and mental health.

PARTICIPANTS

The Dutch famine birth cohort consists of 2414 singletons born alive and at term in the Wilhelmina Gasthuis in Amsterdam around the time of the Dutch famine (1943-1947) whose birth records have been kept. The cohort has been traced and studied since 1994, when the first data collection started. The cohort has been interviewed and physically examined in several waves of data collection since that time, allowing repeated measures of a wide range of phenotypic information as well as the collection of biological samples (blood, urine, buccal swabs), functional testing (of heart, lungs, kidney, HPA axis) and imaging of the brain (MRI) and vasculature (ultrasound). Additionally, genetic and epigenetic information was collected. Through linkage with registries, mortality and morbidity information of the entire cohort has been obtained.

FINDINGS TO DATE

Prenatal famine exposure had lasting consequences for health in later life. The effects of famine depended on its timing during the gestation and the organs and tissues developing at that time, with most effects after exposure to famine in early gestation. The effects of famine were widespread and affected the structure and function of many organs and tissues, resulted in altered behaviour and increased risks of chronic degenerative diseases and increased mortality. The effects of famine were independent of size at birth, which suggests that programming may occur without altering size at birth.

FUTURE PLANS

As the cohort ages, we will be assessing the effects of prenatal undernutrition on (brain) ageing, cognitive decline and dementia, as well as overall morbidity and mortality.

REGISTRATION

The Dutch famine birth cohort is not linked to a clinical trial.

Fetal Physiologically Based Pharmacokinetic Models: Systems Information on the Growth and Composition of Fetal Organs

BACKGROUND

The growth of fetal organs is a dynamic process involving considerable changes in the anatomical and physiological parameters that can alter fetal exposure to xenobiotics in utero. Physiologically based pharmacokinetic models can be used to predict the fetal exposure as time-varying parameters can easily be incorporated.

OBJECTIVE

The objective of this study was to collate, analyse and integrate the available time-varying parameters needed for the physiologically based pharmacokinetic modelling of xenobiotic kinetics in a fetal population.

METHODS

We performed a comprehensive literature search on the physiological development of fetal organs. Data were carefully assessed, integrated and a meta-analysis was performed to establish growth trends with fetal age and weight. Algorithms and models were generated to describe the growth of these parameter values as functions of age and/or weight.

RESULTS

Fetal physiologically based pharmacokinetic parameters, including the size of the heart, liver, brain, kidneys, lungs, spleen, muscles, pancreas, skin, bones, adrenal and thyroid glands, thymus, gut and gonads were quantified as a function of fetal age and weight. Variability around the means of these parameters at different fetal ages was also reported. The growth of the investigated parameters was not consistent (with respect to direction and monotonicity).

CONCLUSION

Despite the limitations identified in the availability of some values, the data presented in this article provide a unique resource for age-dependent organ size and composition parameters needed for fetal physiologically based pharmacokinetic modelling. This will facilitate the application of physiologically based pharmacokinetic models during drug development and in the risk assessment of environmental chemicals and following maternally administered drugs or unintended exposure to environmental toxicants in this population.

Exposure to famine in early life and chronic kidney diseases in adulthood

Objective

Chronic kidney disease (CKD) is an increasing contributor to the global disease burden. Previous findings indicated that exposure to famine in early life was associated with various metabolic diseases and urinary protein levels. We aimed to assess whether the exposure to China’s Great Famine 1959–1962 during fetal or childhood period was associated with glomerular filtration rate (GFR) and risk of CKD (eGFR<60 mL/min per 1.73 m²) in adulthood.

Materials and methods

SPECT-China was a population-based observational study in 2014–2015. Totally, 5124 women were included from SPECT-China study. Based on the birth year, they were divided into fetal-exposed (1959–1962), childhood-exposed (1949–1958), adolescence/young adult-exposed (1921–1948), and non-exposed (1963–1974, reference). The estimated glomerular filtration rate (eGFR) was calculated according to the Chronic Kidney Disease Epidemiology Collaboration equation. CKD was defined as eGFR less than 60 mL/min per 1.73 m².

Results

Compared with the non-exposed, fetal exposure to famine was significantly associated with lower eGFR (B −1.47, 95%CI −2.81, −1.13) and greater risk of having CKD (OR 2.85, 95%CI 1.25, 6.50) in the crude model adjusting age. Further adjustments for demographic variables, body mass index, diabetes, and blood pressure did not qualitatively change the association (eGFR B −1.35, 95%CI −2.67, −0.04; CKD OR 2.42, 95%CI 1.05, 5.58). This association was not found in childhood-exposed and adolescence/young adult-exposed individuals.

Conclusions

Prenatal exposure to famine may have long-term effects on declined GFR and the development of CKD in humans. thus, fetal stage may be an important time window to prevent CKD in later life.

Mast Cells and MCPT4 Chymase Promote Renal Impairment after Partial Ureteral Obstruction

Obstructive nephropathy constitutes a major cause of pediatric renal progressive disease. The mechanisms leading to disease progression are still poorly understood. Kidney fibrotic lesions are reproduced using a model of partial unilateral ureteral obstruction (pUUO) in newborn mice. Based on data showing significant mast cell (MC) infiltration in patients, we investigated the role of MC and murine MCPT4, a MC-released chymase, in pUUO using MC- (W^sh/sh), MCPT4-deficient (Mcpt4^−/−), and wild-type (WT) mice. Measurement of kidney length and volume by magnetic resonance imaging (MRI) as well as postmortem kidney weight revealed hypotrophy of operated right kidneys (RKs) and compensatory hypertrophy of left kidneys. Differences between kidneys were major for WT, minimal for W^sh/sh, and intermediate for Mcpt4^−/− mice. Fibrosis development was focal and increased only in WT-obstructed kidneys. No differences were noticed for local inflammatory responses, but serum CCL2 was significantly higher in WT versus Mcpt4^−/− and W^sh/sh mice. Alpha-smooth muscle actin (αSMA) expression, a marker of epithelial–mesenchymal transition (EMT), was high in WT, minimal for W^sh/sh, and intermediate for Mcpt4^−/− RK. Supernatants of activated MC induced αSMA in co-culture experiments with proximal tubular epithelial cells. Our results support a role of MC in EMT and parenchyma lesions after pUUO involving, at least partly, MCPT4 chymase. They confirm the importance of morphologic impairment evaluation by MRI in pUUO.

Postembryonic Nephrogenesis and Persistence of Six2-Expressing Nephron Progenitor Cells in the Reptilian Kidney

New nephron formation (nephrogenesis) ceases in mammals around birth and is completely absent in adults. In contrast, postembryonic nephrogenesis is well documented in the mesonephric kidneys of fishes and amphibians. The transient mesonephros in reptiles (including birds) and mammals is replaced by the metanephros during embryogenesis. Thus, one may speculate that postembryonic nephrogenesis is restricted to the mesonephric kidney. Previous reports have suggested the metanephros of non-avian reptiles (hereafter reptiles) may continually form nephrons throughout life. We investigated the presence of adult nephrogenesis in reptiles by examining adult kidneys from several species including Trachemys scripta, Chrysemys picta, Boa constrictor, Tupinambis tegu, Anolis carolinensis, and Alligator mississipiensis among others. We found that all major reptilian groups (Testudines, Crocodylia, and Squamates) showed the presence of adult nephrogenesis. The total amount of nephrogenesis varied greatly between species with turtles displaying the highest density of nephrogenesis. In contrast, we were unable to detect adult nephrogenesis in monotremes, and in the iguanid A. carolinensis. Nephron progenitor cells express the transcription factor Six2, which in mammals, becomes downregulated as the progenitor cell population is exhausted and nephrogenesis ends. Using the alligator as a model, we were able to detect Six2-positive cap mesenchyme cells in the adult kidney, which spatially correlated with areas of nephrogenesis. These results suggest that the metanephric kidney of reptiles has maintained the ability to continually grow new nephrons during postembryonic life, a process lost early in mammalian evolution, likely due to the persistence of a Six2-expressing progenitor cell population.

Elevated levels of protein in urine in adulthood after exposure to the Chinese famine of 1959-61 during gestation and the early postnatal period

BACKGROUND

Animal models have suggested that undernutrition during gestation and the early postnatal period may adversely affect kidney development and compromise renal function. As a natural experiment, famines provide an opportunity to test such potential effects in humans. We assessed whether exposure to the Chinese famine of 1959-1961 during gestation and early postnatal life was associated with the levels of proteinuria among female adults three decades after exposure to the famine.

METHODS

We measured famine intensity using the cohort size shrinkage index and we constructed a difference-in-difference model to compare the levels of proteinuria, measured with a dipstick test of random urine specimens, among Chinese women (n = 70 543) whose exposure status to the famine varied across birth cohorts (born before, during or after the famine) and counties of residence with different degrees of famine intensity.

RESULTS

Famine exposure was associated with a greater risk [odds ratio (OR) = 1.54; 95% confidence interval (CI): 1.04, 2.28; P = 0.029) of having higher level of proteinuria among women born during the famine years (1959-61) compared with the unexposed post famine-born cohort (1964-65) in rural samples. No association was observed among urban samples. Results were robust to adjustment for covariates.

CONCLUSIONS

Severe undernutrition during gestation and the early postnatal period may have long-term effects on levels of proteinuria in humans, but the effect sizes may be small.

Proteinuria in aging rats due to low-protein diet during mid-gestation

Nephrogenesis in the rat starts mid-gestation and continues into lactation. Maternal low protein (LP) intake leads to renal injury in rats and associates with mild renal injury in humans. We hypothesized that LP during early nephrogenesis or throughout gestation would induce more renal injury in rat offspring than when LP was only present before nephrogenesis. Pregnant rats were fed LP diet (9% casein) at early gestation (LPE, day 0-7), mid (LPM, day 8-14), late (LPL, day 15-22) or throughout gestation (LPA, day 0-22) and compared to controls on 18% casein diet. Offspring were studied at 18 months. Renal injury was assessed by 24 h proteinuria, plasma urea, antioxidant enzyme activities, and apoptosis (Bax/Bcl2). Proteinuria was higher in LPM males and LPE and LPM females. In LPM males glutathione peroxidase activity was lower, while in LPE males catalase activity was higher. Antioxidants were not much affected in females. Bax expression was higher in LPM males and females, while Bcl2 expression was higher in LPA females. Thus even before nephrogenesis (day 0-7), LP impacted on renal integrity in adult life, while LP during a later phase (day 15-22) or throughout gestation had less effect. In summary, for aging rat kidney LP poses the greatest threat when restricted to early nephrogenesis.

Quantitative analysis of renal vascularization in fetuses with urinary tract obstruction by three-dimensional power-Doppler

OBJECTIVE

To evaluate the applicability of 3-dimensional evaluation of renal vascularization for predicting postnatal renal function in fetuses with suspected urinary obstruction.

STUDY DESIGN

Fetuses were evaluated by 3-dimensional power-Doppler histogram, and vascular indices were estimated. Depth between the probe and the renal cortex was also evaluated. Postnatal follow-up was obtained in all cases and the main outcome was renal impairment.

RESULTS

Twenty-three fetuses with urinary dilatation (cases) and 73 with normal renal morphology (controls) were included in the current study. Five (21.7%) cases developed renal impairment. Vascularization index and vascularization and flow index were significantly lower in fetuses that developed renal impairment compared with those with normal renal function (P = .009 and P = .036, respectively). The 3 vascular indexes correlated with depth. Percentage of depth-corrected vascularization index and vascularization flow index were lower in fetuses developing postnatal renal failure.

CONCLUSION

Fetal renal vascularity (vascularization index and vascularization and flow index) was significantly lower in fetuses that developed renal impairment.

Uncharted waters: nephrogenesis and renal regeneration in fish and mammals

The major functions of the vertebrate kidney are the removal of metabolic waste and the balance of salt and water. These roles are fulfilled by nephrons, which generally comprise a blood filter (glomerulus) attached to an epithelial tubule. The number of nephrons in the mammalian kidney is set at the end of kidney organogenesis in the late fetal or neonatal period. Subsequent increases in nephron size and functionality then occur during postnatal growth to match increases in body mass/fluid. Because of this strategy of renal development, injuries or birth defects that reduce nephron number lead to a permanent nephron deficit and increase the risk of kidney disease. In contrast to mammals, fish kidneys continue to add nephrons throughout their lifespan. In response to renal injury, fish increase the rate of nephrogenesis, effectively replacing lost nephrons and maintaining their nephron endowment. A better understanding of the remarkable nephrogenic abilities of fish kidneys may lead to innovative ways to restore nephrogenesis in the adult mammalian kidney. This review examines our current understanding of nephrogenesis in mammals and fish and explores possible explanations for why fish, but not mammals, utilize a perpetual nephrogenesis strategy to grow and maintain their kidneys.

The optimal dose of Adriamycin to create a viable rat model potentially applicable to congenital obstructive uropathy

PURPOSE

The Adriamycin rat model is an established model for different organ anomalies including congenital obstructive uropathy. In the current study, we carried out a dose-response analysis to find out the optimal dose of Adriamycin to create a viable rat model of obstructive uropathy.

METHODS

Thirty time-mated Sprague-Dawley rats were divided into 5 groups including 1 control group and 4 different treatment groups. The 4 Adriamycin dosage regimens investigated in this study were 1.25, 1.5, 1.75, and 2 mg/(kg d). Experimental rats (n = 24) were injected intraperitoneally with different doses of Adriamycin on gestational days 7 to 9 (6 rats in each group). Control rats (n = 6) were injected with an equivalent volume of saline on the same days. Viable term fetuses were harvested on gestational day 21 by cesarean delivery and dissected under a dissecting microscope. Serial transverse sections from urinary tract system were obtained for histological examination.

RESULTS

One hundred thirty-three viable fetuses were recovered from Adriamycin-treated rats, and 50 were from rats in the control group. There were no resorptions in the control group; however, 52 resorptions were recorded in Adriamycin groups. The rates of hydronephrosis and resorptions were 60% and 0%, 80.5% and 5.8%, 100% and 17.3%, and 100% and 76.9% at doses of 1.25, 1.50, 1.75, and 2 mg/(kg d), respectively. Histologic examination of the kidneys in the treated groups showed a significant decrease in renal parenchyma compared with the control group.

CONCLUSIONS

The dosage of 1.5 mg/(kg d) of Adriamycin yielded the highest number of viable hydronephrotic fetuses. At this dose, urinary abnormalities are milder; but the highest number of viable fetuses is provided, which is necessary to create a reproducible and viable animal model.

Mechanisms of renal injury and progression of renal disease in congenital obstructive nephropathy

Congenital obstructive nephropathy accounts for the greatest fraction of chronic kidney disease in children. Genetic and nongenetic factors responsible for the lesions are largely unidentified, and attention has been focused on minimizing obstructive renal injury and optimizing long-term outcomes. The cellular and molecular events responsible for obstructive injury to the developing kidney have been elucidated from animal models. These have revealed nephron loss through cellular phenotypic transition and cell death, leading to the formation of atubular glomeruli and tubular atrophy. Altered renal expression of growth factors and cytokines, including angiotensin, transforming growth factor-beta, and adhesion molecules, modulate cell death by apoptosis or phenotypic transition of glomerular, tubular, and vascular cells. Mediators of cellular injury include hypoxia, ischemia, and reactive oxygen species, while fibroblasts undergo myofibroblast transformation with increased deposition of extracellular matrix. Progression of the lesions involves interstitial inflammation and interstitial fibrosis, both of which impair growth of the obstructed kidney and result in compensatory growth of the contralateral kidney. The long-term outcome depends on timing and severity of the obstruction and its relief, minimizing ongoing injury, and enhancing remodeling. Advances will depend on new biomarkers to evaluate the severity of obstruction, to determine therapy, and to follow the evolution of lesions.

Congenital urinary tract obstruction

Congenital urinary tract obstruction is a heterogenous condition with a varying natural history. Accurate diagnosis within the late-first and second trimesters allows for counselling of the parents and planning of multi-disciplinary care for the pregnancy and newborn. Antenatal investigations to predict postnatal renal function are of varying accuracy. However, some factors have been shown to be predictive of poor outcome in terms of renal function at birth and infancy. There is the possibility of in-utero intervention in these fetuses.

Histochemical and immunohistochemical study of the glomerular development in human fetuses

Few studies exist that establish the normal morphological patterns of glomerular development, though this is one of the organs that continues to evolve morphologically during the postnatal period up to 4 weeks after birth. In our study one kidney from each autopsy of a total of 86 autopsies was analyzed [15 weeks to 40 weeks of gestational age (GA)]. We examined the variation in the nephrogenic zone thickness, the area and diameter of the glomerular tuft, the area and diameter of the glomerular capsule, and the immunohistochemical markers, anti-CD31 and anti-CD34 antibodies, which accompany the development of the glomerular microvasculature. Periodic acid-methenamine silver (PAMS) stain was used for the morphological and morphometrical analyses, and it was particularly useful in fetuses in which autolysis had occurred. The length of the nephrogenic zone (NZ) decreased with the increase of the GA (P < 0.001) according to the formula: GA = 36.5 - (0.05 x length of NZ). The areas of the Bowman capsule (P < 0.0001), the capillary tuft (P < 0.0001), and the capillary tuft diameter (P = 0.00393) of the intermediary glomeruli increased with the advance of GA, with a positive significant correlation. The same parameters of the juxtamedullary and superficial glomeruli had no correlation with the advance of GA. The cells of the primary structures in the "S" shape of the primitive nephrons were negative for CD31 and CD34. Staining for both antibodies was found, for all GAs, in the endothelial cells of the mature glomeruli tuft and in the renal interstitial vessels. The data obtained in this work contribute to the evaluation of renal maturity in autopsied fetuses and are particularly important in fetuses when autolysis has occurred, to which the parameters used in this study can also be applied. The establishment of normal morphometric and immunohistochemical parameters for the evaluation of renal maturity increases the diagnostic precision of renal pathological alterations in aborted material and perinatal autopsy.

Chronic partial ureteral obstruction and the developing kidney

Although congenital urinary tract obstruction is a common disorder, its pathophysiology remains poorly understood and clinical practice is controversial. Animal models have been used to elucidate the mechanisms responsible for obstructive nephropathy, and the models reveal that renal growth and function are impaired in proportion to the severity and duration of obstruction. Ureteral obstruction in the neonatal rat or mouse leads to activation of the renin-angiotensin system, renal infiltration by macrophages, and tubular apoptosis. Nephrons are lost by glomerular sclerosis and the formation of atubular glomeruli, and progressive injury leads to tubular atrophy and interstitial fibrosis. Recovery following release of obstruction depends on the timing, severity, and duration of obstruction. Growth factors and cytokines are produced by the hydronephrotic kidney, including MCP-1 and TGF-beta1, which are excreted in urine and can serve as biomarkers of renal injury. Because MRI can be used to monitor renal morphology, blood flow, and filtration rate, its use might supplant current imaging modalities (ultrasonography and diuretic renography), which have significant drawbacks. Combined use of MRI and new urinary biomarkers should improve our understanding of human congenital obstructive nephropathy and should lead to new approaches to evaluation and management of this challenging group of patients.

Growth patterns of the heart and kidney suggest inter-organ collaboration in facultative fetal growth

Maternal smoking during pregnancy has been associated with a number of negative sequelae among offspring, including elevated postnatal blood pressure. While animal studies have described organ level alterations with smoke exposure, human data have been more limited. Thirty-four healthy maternal/fetal pairs (24 nonsmokers, 10 smokers) participated in a longitudinal growth study from the thirteenth week of pregnancy to document fetal kidney and heart growth trajectories and morphology. Curve fitting followed by a mixed model for repeated measures identified significantly different growth patterns in kidney width, thickness, length, and volume growth with exposure: the smoke-exposed fetal kidney was wide and thick compared to the unexposed kidney during the second and early third trimester, declining to proportionately thin kidneys for length and width subsequently. Cardiac growth in width and volume followed a reverse pattern: a surge in cardiac volume occurred after 30 weeks with acceleration in cardiac width, resulting in a heart that was wide for length and for fetal weight. Smoke exposure altered fetal growth in size and timing of the heart and kidneys during midgestation, with changes in organ morphology suggesting compensatory growth. These are the first data providing anatomical evidence of altered renal/cardiac volume relationships that may provide a mechanism to previously reported sequelae of in utero smoke exposure. They suggest that cell-level adaptive responses to hypoxia and/or chemical insults are operative and illustrate the importance of longitudinal ultrasound to directly assess the organ-level growth response of the human fetus to a prenatal stress, in lieu of relying on birth outcome measures.

Ontogeny of the VATER kidney in a rat model

By exposing rat fetuses to adriamycin prenatally, a rat model of VATER association has been created. Absence of the fetal bladder is prominent and the kidneys show features of chronic obstruction with hydronephrosis/hydroureter, loss of parenchyma, fewer glomeruli, and less differentiation. The aim of this study was to elucidate this rat model, to determine exactly when the changes in the kidneys develop, hopefully thereby to expand our understanding of congenital obstructive uropathy. Timed-pregnant Sprague-Dawley rats were injected intraperitoneally with adriamycin on days 6-9 of gestation. The control group received saline. Fetuses were recovered on gestational days (GDs) 20, 19, 18, 17, 16, 15, 14, 12, and 10 (total, 120 control, 121 treated). Macroscopic features were determined. Serial sections were then taken and stained with hematoxylin and eosin. Comparisons were made under light microscopy. The metanephric kidney first became apparent at GD12. The development of the control and treated kidneys appeared similar till GD18. Beyond this day, the treated kidneys exhibited increasing degrees of distension of Bowman's capsule, ducts, and subsequently pelvis and ureter. There were fewer levels of glomeruli, which were also less differentiated. Less differentiation was also noted in the medulla, and with time this became thin in comparison to the control kidneys. By GD20, the renal pelvis was grossly dilated with a blunted papilla, and the renal parenchyma was thin. Prenatal exposure of rat fetuses to adriamycin results in kidneys that are chronically obstructed, as the majority of the fetuses show absence of the bladder. Absence of renal dysmorphology until GD18, when urine is first produced, suggests strongly that the effect of adriamycin on the kidney is indirect, via agenesis of the bladder and secondary to backpressure from early urine production. This is a unique, simple, and reliable model of fetal obstructive uropathy and will be very useful to facilitate further investigation into its pathophysiology and to explore new treatment options.

Microalbuminuria in adults after prenatal exposure to the Dutch famine

Maternal undernutrition during gestation is associated with an increase in cardiovascular risk factors in the offspring in adult life. The effect of famine exposure during different stages of gestation on adult microalbuminuria (MA) was studied. MA was measured in 724 people, aged 48 to 53, who were born as term singletons in a university hospital in Amsterdam, the Netherlands, around the time of the Dutch famine 1944 to 1945. Twelve percent of people who were exposed to famine in mid gestation had MA (defined as albumin/creatinine ratio >/=2.5) compared with 7% of those who were not prenatally exposed to famine (odds ratio 2.1; 95% confidence interval 1.0 to 4.3). Correcting for BP, diabetes, and other influences that affect MA did not attenuate this association (adjusted odds ratio 3.2; 95% confidence interval 1.4 to 7.7). The effect of famine was independent of size at birth. Midgestation is a period of rapid increase in nephron number, which is critical in determining nephron endowment at birth. Fetal undernutrition may lead to lower nephron endowment with consequent MA in adult life.

Developmental renal pathology: its past, present, and future

Congenital anomalies of the kidney and urinary tract are responsible for approximately 40% of cases of childhood end-stage renal failure in the United States. This article describes the spectrum of developmental renal lesions in children (including renal agenesis, dysplasias, hereditary hydronephrosis, autosomal recessive and dominant polycystic kidneys, vesicoureteral reflux, diabetic embryopathy, some teratogenic drugs affecting renal development, and syndromes associated with renal dysplasias). The article quotes some historic references that established the foundation for further studies; reviews the embryology, pathology, postnatal renal development, and its possible consequences of renal function; as well as recent advances in fetal ultrasonography and molecular biology with some novel treatment and diagnostic modalities. Finally, an attempt is made to predict several future avenues in pharmacogenetics that are being built currently and that will allow a better prognosis for many children with congenital renal conditions.

Perinatal obstructive nephropathy

Significant advances have been made recently in elucidating the cellular consequences of urinary tract obstruction during renal development. Urinary tract obstruction impairs growth and maturation of the kidney, and can also cause renal maldevelopment. This includes a reduction in the number of nephrons, tubular atrophy, and progressive interstitial fibrosis. Apoptosis (programmed cell death) accounts for much of the loss of tubular epithelial cells. Factors contributing to apoptosis include stretching of cells in dilated tubules, altered renal production of growth factors, and infiltration of the renal interstitium by macrophages. Two major controversies remain regarding the surgical management of congenital obstructive nephropathy: first, which fetuses with bladder outlet obstruction should undergo prenatal intervention, and second, which infants should undergo early pyeloplasty for ureteropelvic junction obstruction? Even after successful surgery for congential obstructive nephropathy, all patients should be followed for hypertension, proteinuria, or renal deterioration.

Prenatal intervention for urinary obstruction and myelomeningocele

Widespread use of ultrasonography has resulted in an increase in the recognition of fetal hydronephrosis. The enthusiasm that accompanied early interventions has been tempered by the experience and results obtained over the past 2 decades. The goal has remained the same: to identify patients with serious prenatal obstruction and to identify those which may benefit from intervention. Myelomeningocele remains a devastating congenital anomaly. Fetal and experimental studies suggested that patients with myelomeningocele could benefit from prenatal intervention. Advances in technology and perinatal management have made intervention for more complex malformations such as myelomeningocele possible. This article will review current knowledge and will detail rational management for the management of prenatal hydronephrosis. The current state of antenatal myelomeningocele repair and the urologic implications will be described as well.

Early release of neonatal ureteral obstruction preserves renal function

The incidence of congenital hydronephrosis is approximately 1% and is often associated with renal insufficiency. It is unknown whether early release is essential to prevent deterioration of renal function. Rats were subjected to partial unilateral ureteral obstruction (PUUO) on postnatal day 2. The obstruction was left in place or released after 1 or 4 wk. Renal blood flow (RBF) and kidney size were measured sequentially over 24 wk using MRI. In rats in which the obstruction was left in place, RBF of the obstructed kidney was progressively reduced to 0.92 +/- 0.17 vs. 1.79 +/- 0.12 ml.min(-1).100 g body wt(-1) (P < 0.05) after 24 wk. Similarly, glomerular filtration rate of the obstructed kidney was severely reduced at 24 wk: 172 +/- 36 vs. 306 +/- 42 microl.min(-1).100 g body wt(-1) (P < 0.05). These changes were preceded by development of severe hydronephrosis and obstructive nephropathy with a reduction in total protein content: 45 +/- 3 vs. 58 +/- 4 mg/kidney. Moreover, nonreleased PUUO caused a marked natriuresis (0.32 +/- 0.07 vs. 0.11 +/- 0.02 micromol.min(-1).100 g body wt(-1), P < 0.05) and impaired solute free water reabsorption (0.47 +/- 0.16 vs. 2.71 +/- 0.67 microl.min(-1).100 g body wt(-1), P < 0.05), consistent with a significant downregulation of Na-K-ATPase to 62 +/- 7%, aquaporin-1 to 53 +/- 3%, and aquaporin-3 to 53 +/- 7% of sham levels. Release after 1 wk completely prevented development of hydronephrosis, reduction in RBF and glomerular filtration rate, and downregulation of renal transport proteins, whereas release after 4 wk had no effect. These results suggest that early release of neonatal obstruction provides dramatically better protection of renal function than release of obstruction after the maturation process is completed.

Recovery from release of ureteral obstruction in the rat: relationship to nephrogenesis

BACKGROUND

Obstructive nephropathy is a major cause of renal insufficiency in infants and children. Despite release of unilateral ureteral obstruction (UUO) in the first five days of life in the rat, renal growth is impaired, while glomerular filtration rate (GFR) is preserved at one month, but decreases markedly by one year. To test the hypothesis that renal recovery from UUO depends on the stage of nephrogenesis at the time of relief of obstruction, renal recovery from relief of five days UUO following completion of nephrogenesis (days 14 to 19) was compared with UUO during nephrogenesis (days 1 to 5).

METHODS

Rats underwent UUO or sham operation at one day of age, with relief five days later. In additional groups of neonatal rats, the operation was at 14 days, with relief at 19 days. Three months later, blood pressure, GFR, urine flow, sodium and potassium excretion, and kidney weight were measured. In addition, the number of glomeruli, glomerular maturation, glomerular diameter, tubular atrophy, and interstitial fibrosis were determined in each kidney. The effects of five-day UUO on number of glomeruli was determined also in adult rats one month following relief of obstruction.

RESULTS

Three months following relief of UUO during days 14 to 19, renal growth was decreased by 50%, compared to a 30% reduction following relief of UUO during days 1 to 5 (P < 0.05). The number of glomeruli was reduced by approximately 50% regardless of the timing of UUO, but glomerular size was reduced only in rats with UUO from days 14 to 19. Blood pressure and tubular atrophy were increased, and GFR, urine flow, sodium and potassium excretion were decreased in the postobstructed kidney of both neonatal groups. In the adult rat, the five-day UUO did not result in a decrease in the number of glomeruli.

CONCLUSIONS

In the period immediately following nephrogenesis, the kidney is particularly susceptible to long-term injury from temporary UUO. This suggests that a delay in relief of significant ureteral obstruction should be avoided if diagnosed in the perinatal or neonatal period.

Recovery after relief of fetal urinary obstruction: morphological, functional and molecular aspects

The effects of obstruction [urinary tract obstruction (UTO)] and relief on renal development were examined in an experimental model in the fetal lamb. Bladder outlet obstruction was performed at 60 days of gestation; relief was performed by vesicoamniotic shunting at 90 days of gestation. Studies were carried out in obstructed (OF60; n = 11), shunted (SF; n = 5), and control fetuses (CF; n = 11) at 120 days of gestation. Fetal UTO produced either hydronephrosis (64%) or dysplasia (36%); dysplasia was always associated with a reduction in the number of glomeruli [950 +/- 99 (dysplasia) vs. 1,852 +/- 249 (CF) glomeruli/section]. Obstructed fetuses had lower creatinine clearance [0.76 +/- 0.41 (OF60) vs. 0.96 +/- 0.21 (CF) ml x min(-1) x kg(-1)], higher sodium fractional excretion [17.2 +/- 20.3 (OF60) vs. 2.4 +/- 3.7% (CF)], and higher urinary concentration [80 +/- 30 (OF60) vs. 43 +/- 22 (CF) micromol/l] than controls. In SF, the number of glomeruli was increased at 120 days of gestation (1,643 +/- 106 glomeruli/section) compared with nondiverted fetuses (1,379 +/- 502 glomeruli/section), and the temporal pattern of PAX2, disrupted after obstruction, was restored. In conclusion, early fetal UTO leads to either renal hydronephrosis with normal glomerular development or dysplasia with a decreased number of glomeruli; in utero urine diversion performed before the end of nephrogenesis may allow a reversal of the glomerulogenesis arrest observed.

Congenital reflux nephropathy: a follow-up of 108 cases diagnosed perinatally

OBJECTIVE

To determine: (i) the proportion of vesicoureteric reflux (VUR) associated with congenital renal damage and whether it can be severe enough to cause renal impairment from birth: (ii) to evaluate the distribution of males and females affected; and (iii) to describe the course of congenital damage in the first years of life.

PATIENTS AND METHODS

A total of 108 children (76 male and 32 female, M:F 2.3:1), whose VUR was diagnosed before any infection, were followed from birth for a mean (range) of 4.3 (1-10) years. Renal damage was defined by serum creatinine concentration, creatinine clearance and renal imaging (ultrasonography and renal scintigraphy) performed within the first month of life and periodically thereafter.

RESULTS

Of the 108 children, 58 had bilateral and 50 unilateral reflux (total number of refluxing units, 166). High-grade VUR (grade > or = 4) was found in 96 (58%) refluxing renal units (RRUs). Males had a prevalence of bilateral severe (> or = grade 4) reflux (M:F 5.2:1), while in those wit unilateral VUR, the M:F ration was 1.5:1. At birth, mild to moderate damage was present in 56 (36%) RRUs and only associated with VUR of grade > or = 3. Bilateral reflux of grade > or = 4 was associated with congenital moderate/severe renal failure in nine neonates (seven males). In infants with grade > or = 4 VUR who underwent surgical correction, VUR resolved in 92% of cases. In infants with VUR of grade > or = 4 followed medically, the reflux spontaneously resolved in 42% and ameliorated in 16% after 18 months. Serial renal scans during the follow-up showed no progression of renal damage.

CONCLUSIONS

VUR diagnosed at birth on prenatal ultrasonography is associated with congenital damage, with males affected more often than females. The damage involves both kidneys in a consistent proportion and is an important cause of chronic renal impairment from birth. It does not progress in the first years of life if infections are prevented. It is suggested that males with this condition may constitute a major group at risk of developing chronic renal failure in later life.

Nephrogenesis and angiotensin II receptor subtypes gene expression in the fetal lamb

To investigate the role of angiotensin II (ANG II) in nephrogenesis, a developmental study of renal AT1 and AT2 receptor mRNA expression was performed in parallel with the quantitative and qualitative analysis of metanephros development in fetal lamb from 60 to 140 days of gestation. Both ANG II receptor subtypes were expressed early during nephrogenesis but displayed specific spatial and temporal distribution during gestation. High-AT2 mRNA expression took place in the outermost nephrogenic area and in the undifferentiated mesenchymal cells surrounding the ampulla; level of AT2 expression in this localization followed closely glomeruli proliferation rate and disappeared after nephrogenesis completion (>120 days). AT2 mRNA was also detected in the differentiated epithelial cells of macula densa of maturing glomeruli. Although most of AT1 mRNA labeling was found in the mesangial cells of maturing glomeruli, where it persisted after nephrogenesis completion, additional labeling was found in undifferentiated cells, in cells invading the inferior cleft of S-shaped bodies (80 days), and in medullar cells between tubules (120 days). Our results suggest that each receptor subtype has a specific role in renal morphogenesis, i.e., AT2 in mesenchymal proliferation or apoptosis and AT1 in vascular smooth muscle cells differentiation.

Fetal renal biopsies in obstructive uropathy: feasibility and clinical correlations--preliminary results

Final assessment on the outcome of fetal obstructive uropathy is a challenging matter. Ultrasonography, fetal urine electrolytes, and beta 2 microglobulin are postulated as being useful in many cases. For cases in which renal function remains unclear, ultrasound-guided fetal kidney biopsy may be used in order to detect histologic features distinctive of renal dysplasia. We present preliminary results aimed at studying the feasibility and possible risks. Biopsies were initially performed in 11 severely malformed fetuses, three of them with associated renal abnormalities. The success rate in obtaining renal material was 63.6 per cent with no maternal complications. In the next phase of this study, ten biopsies and urine collections were performed in fetuses with bilateral obstructive uropathy. The success rate was 50 per cent with no complications. Normal fetal renal histology was seen in 80 per cent of cases. In one case, although electrolytes were normal, a histologic diagnosis of renal dysplasia was made, showing a good correlation with outcome. In conclusion, fetal kidney biopsies for obstructive uropathy are feasible and further studies are needed to show their clinical relevance and risks.

Fetal urinary tract abnormalities. Natural history, pathophysiology, and treatment

Urologic abnormalities are commonly detected on routine obstetric sonographic examinations. The progressive nature and potential reversibility of obstructive urologic anomalies have led to interest in in utero treatment of these lesions. Over 90% of obstructive urologic lesions do not need treatment until after birth. For a select group of patients, antenatal treatment may improve postnatal renal and pulmonary function. When indicated, minimally invasive nephroamniotic or vesicoamniotic stenting is the preferred method of treatment.

Development of human fetal kidney in obstructive uropathy: correlations with ultrasonography and urine biochemistry

In utero urethral obstruction results in bilateral hydronephrosis and severe fetal and post-natal morbidity and mortality. Obstetrical management depends on the indirect evaluation of fetal renal function by ultrasonography and biochemical analysis. No direct evaluation of the severity and possible reversibility of renal lesions is available. In this paper we analyzed kidneys from 34 fetuses (14 to 37 gestational weeks) in which (1) isolated bilateral urinary tract obstruction had been detected in utero by sonography, and (2) the severity of sonographic and biochemical prognostic indicators led to the indication of termination of pregnancy or to perinatal death. Pure hydronephrosis was observed in two young fetuses [14 and 20 gestational weeks (GW)] and was associated with regressive changes in two others. In contrast, a wide spectrum of dysplastic renal lesions was present in 30 fetuses and was classified into four subgroups according to the association of dysplasia, hypoplasia and cysts. They had the following characteristics in common: (1) premature cessation of nephrogenesis assessed by the medullary ray counting method; (2) early disappearance or myofibroblastic differentiation of metanephric blastema; (3) early increase in interstitial mesenchyme with widespread expression of alpha-smooth muscle actin by mesenchymal cells; (4) frequent absence of classical criteria of dysplasia (nests of cartilage were observed in only 5 fetuses); (5) an identification, based upon the detection of alpha-smooth muscle actin expression, of the muscular phenotype of mesenchymal cells encircling primitive ducts. In conclusion, (1) the value of prognostic markers in fetuses less than 20 GW should be reconsidered; (2) after 20 GW there is a good correlation between markers predicting poor prognosis and the severity of renal lesions; (3) hypoplasia with disappearance of blastema cells, dysplasia and early interstitial fibrosis are evidence of the irreversibility of renal lesions and preclude any possibility of new nephron formation; (4) these findings suggest that most surgical in utero procedures are performed when irreversible renal lesions have developed.