Nephrogenesis and the development of renal disease

Kidney development in the first year of life in small-for-gestational-age preterm infants

BACKGROUND

Small-for-gestational-age (SGA) infants have been reported to have a significantly reduced number of nephrons that could be a risk factor for development of hypertension later in life.

OBJECTIVE

To evaluate kidney size prospectively in relation to other anthropometric parameters during the first year of life in SGA babies.

MATERIALS AND METHODS

The babies in the study were 31-36 weeks' gestational age (GA) at birth and were matched with control preterm infants of similar GA, but appropriate for gestational age (AGA). The SGA infants were further classified as symmetrical and asymmetrical according to the anthropometric parameters.

RESULTS

The total number of measurements in symmetrical SGA preterm infants was 324, in asymmetrical SGA preterm infants 295, and in AGA infants 536. In symmetrical SGA preterm infants (31-36 weeks' GA) mean kidney length (+/- SD) of 56+/-4 mm was significantly different from the controls (58.9+/-4.6 mm) up to 6 months' chronological age (P < 0.05). In the asymmetrical SGA preterm infants, mean kidney length (45.3+/-4.0 mm) was significantly different from the controls (48.2+/-4.4 mm) up to 40 weeks' corrected age. At 1 year chronological age, all preterm infants (symmetrical and asymmetrical SGA and AGA) had similar mean kidney length (61.6+/-4.6, 62.8+/-4.3, and 62.3+/-4.0 mm, respectively). The ratio of kidney length to crown-to-heel length was similar in all preterm groups.

CONCLUSIONS

Kidney length in preterm SGA infants (symmetrical and asymmetrical) follows closely the other auxological parameters during the first year of life.

Morphologic changes suggesting abnormal renal differentiation in congenital nephrotic syndrome

Retrograde differentiation (or dedifferentiation) has recently been proposed as a pathogenetic mechanism involved also in various renal diseases. Here we studied whether evidence of these mechanisms can be found in the kidneys of patients with congenital nephrotic syndrome of the Finnish type (CNF). These patients show isolated massive proteinuria but no primary symptoms from any other organ systems. For the analysis we used antibody markers of early (fibronectin, stem cell factor, Wilms' tumor gene product, cytokeratin) and later (laminin, midgestation and kidney, heparin binding growth-associated molecule) stages of nephron differentiation as well as for apoptosis (acridine orange staining), rescue from apoptosis (anti-Bcl-2 antibodies) and cell proliferation (antibodies to proliferating cell nuclear antigen). In the peritubular spaces atypically organized areas were found which appeared positive with markers of low stages of differentiation, but neither abnormal cell proliferation nor activation of the apoptotic pathway could be detected. As morphologic signs of abnormal tissue organization, we found clusters of tightly compacted and large glomeruli corresponding to the size of two to three normal glomeruli. However, all individual glomerular cell compartments (mesangial, endothelial, visceral epithelial cells) appeared balanced in relative cell numbers. Together these results may indicate abnormal early mesenchymoepithelial tissue interaction leading to excessive and poorly organized formation of glomeruli. This could be causally related also to the serious functional immaturity of CNF kidneys presented as isolated proteinuria.

Acute renal failure in the newborn: incidence and outcome

OBJECTIVE

To describe an experience from a developing country of newborn renal disease particularly those without advanced neonatal care.

METHODOLOGY

Prospective evaluation from a referral hospital, North-East of Nigeria between 1 July 1990 and 30 June 1994. Babies admitted for any morbidities who were diagnosed as being in acute renal failure (ARF) during the study period (non-oliguric inclusive). Onset of ARF; day on which oliguria or anuria detected, or serum urea first exceeded 10 mmol/L. Urine output quantitated from carefully bagged urine and suprapubic bladder aspiration, and venous blood regularly obtained for serum electrolytes, urea and creatinine. Fractional excretion of sodium (FE(Na)) and renal failure index (RFI) were determined on some babies.

RESULTS

Forty-three neonates (M:F; 3.3:1) with ARF, the majority (27) of whom were out-born, and 14, 26 and three were preterm, full-term and post term, respectively. Encountered incidence was 3.9/1000 live births with a high prevalence rate; 34.5/1000 admissions. A significantly greater incidence was seen in the latter half of study; 10.7 vs 53.7/1000, P < 0.05. Early ARF occurrence (aged; 0-5 days) in 33 (77%) of babies. The aetiology was comprised of perinatal asphyxia, sepsis, obstructive uropathy and miscellaneous in 53.4%, 32.6%, 9.3% and 4.7%, respectively. Twenty-two (51.2%) deaths occurred; however, the exact causes were indeterminable. Fractional excretion of sodium (FE(Na)) and renal failure index (RFI) were of < 1.75% and < or = 2.0, respectively, significantly differentiated sepsis (intrinsic) from perinatal asphyxial (pre-renal) ARF; P < 0.01. No case of persistent renal failure occurred.

CONCLUSION

Our FE(Na) value (although less than reported in previous literature from affluent societies) remained sensitive (along with RFI) in differentiating aetiological group of ARF. Our data and medical management outcome, despite absence of level-III care, support the need for good resuscitation, careful monitoring and constant re-evaluation. The effect of salbutamol on hyperkalaemia is emphasized.

Analysis of fetal and neonatal urine using proton nuclear magnetic resonance spectroscopy

AIM

To use high field proton nuclear magnetic resonance spectroscopy (1H NMR) to characterise the low molecular weight metabolite composition of neonatal and fetal urine in relation to gestational age and perinatal outcome.

METHODS

The first urine passed by two neonatal groups, six full term and five preterm infants with normal renal function, was analysed by 1H NMR and compared with fetal urine from 14 cases with obstructive uropathy.

RESULTS

The mean ratios of taurine, myo-inositol, and trimethylamine-N-oxide (TMAO) to creatinine were 4.3, 10.1, and 14.1 times higher, respectively, in the preterm group when compared with those of the full term group. Fetal obstructive uropathy was characterised by glycosuria, amino and organic aciduria, regardless of gestational age (13-30 weeks).

CONCLUSIONS

Samples of the first urine passed--that is, urine produced in fetal life--by normal preterm infants are useful controls for cases of obstructive uropathy detected in the third trimester. 1H NMR will become a clinically useful tool for monitoring renal development and abnormalities in utero.

Histological features of glomerular immaturity in infants and small children with normal or altered tubular function

In children with renal tubular disorders the existence of retarded histological features of glomerular maturation has been suggested by our group. However, no valuable information is available on the frequency of histopathologically immature glomeruli in the normal kidney. For this reason we established a simple, semiquantitative definition of postnatal glomerular development: immature glomeruli (with at least half of the circumference of capillary loops densely lined with cuboidal epithelial cells), intermediate glomeruli (circumference of capillary loops lined with at least five adjoining cuboidal cells), and mature glomeruli. This definition was applied in a set of 71 normal kidneys from ages birth to 5 years. The relative frequency of the mentioned stages of glomerular maturation was strongly age dependent. In comparing the patients data with the normal findings it was possible to separate patients with the finding of disproportionately high fractions of immature glomeruli, provided the right age at biopsy is chosen. It is therefore concluded that the previous suspicion of late glomerular maturation may be validated in at least in some bioptic specimens.

Nephron segment and cell-type specific expression of gangliosides in the developing and adult kidney

Despite the increasing knowledge of the role of gangliosides in normal and diseased tissues, little is known of the presence, distribution and functions of these molecules in the kidney. In this study we analyzed the main gangliosides of isolated glomeruli and cortical, medullary and papillary fractions of the human, rat and bovine kidneys biochemically. In addition, we used immunohistochemistry to visualize the distribution of GM1/GM2, GD2, GD3 and O-acetyl GD3 gangliosides along the nephron. Furthermore, we explored the species specific expression of gangliosides by comparing those from the rat, bovine and human kidney, and studied the pattern of ganglioside expression during development. In glomeruli, cortical tubuli, medullae and papillae, a relatively simple pattern of main gangliosides was observed as revealed by thin layer chromatographic (TLC) analysis in each species studied. Furthermore, considerable changes in the glomerular gangliosides during maturation were observed, with a complex type of gangliosides predominating during the fetal age and with a preference to more simple precursors upon maturation. Interestingly, the immunohistochemical detection revealed a distinct pattern of ganglioside compartmentation to various nephron segments or cell types. These findings provide a basis for studying the role of segment- and cell type-specific gangliosides for local functions.

Genetically engineered kidneys

We review the available methods of creating genetically engineered kidneys. These include transgenic technology to introduce novel genes or delete existing genes and methods of gene transfer into the post-natal or adult kidney. The use of such technology has provided insights into renal development and growth and created new animal models of human diseases. Although some of these techniques are of potential use for introducing therapeutically useful gene products into the diseased kidney, many problems remain to be solved before this aim is attained.

Distinctive patterns of renal neoplasms containing Tamm-Horsfall protein

Sections of 114 renal neoplasms from adults, and 2 renal rhabdoid tumours from children, were examined by an indirect immunoperoxidase method using two antibodies to Tamm-Horsfall protein. Forty-five of the adult neoplasms were also examined with an antibody to proximal tubular brush border. Tamm-Horsfall protein is normally only found in the cells of the thick limb of the loop of Henle, and there are widely divergent reports on its occurrence in renal neoplasms. In the present series, Tamm-Horsfall protein was detected in parts of 31 neoplasms. Four distinctive patterns of cell contained the protein: cells with a paranuclear inclusion typical of rhabdoid tumours; 'plasma rich' cells, which were large cells with cytoplasm that was centrally dense and peripherally clear; eosinophilic cells forming one type of papillary structure; and giant cells. The areas containing Tamm-Horsfall protein did not express markers of proximal tubular brush border, and appeared white to the naked eye, rather than the yellow of typical clear cell carcinomas. Tamm-Horsfall protein can therefore be found in renal neoplasms. The four distinctive patterns of positive cells appear to represent neoplastic phenotypes of thick limb cells. This has implications for the classification of renal neoplasms and for theories of their origin.

Gentamicin administered during gestation alters glomerular basement membrane development

Gentamicin during gestation alters glomerular basement membrane development. A drug-induced nephrotoxicity was described for neonates after gentamicin was given intraperitoneally to pregnant Wistar rats; glomerular alterations and changes in permselectivity were important. We investigated the ultrastructure of the glomerular basement membrane (GBM), the arrangement of anionic sites, and the urinary proteins at two ages, with 1-day- and 12-month-old control and prenatally exposed animals. For neonates, the pattern of glomerular differentiation was similar, anionic sites were made of heparan sulfate proteoglycans, and the GBM had the same total thickness in both groups. After transplacental gentamicin exposure, the lamina densa was larger; the laminae rarae were thinner; the density of anionic sites was increased; the levels of hydroxyproline, sulfate, and hexuronic acid in the kidney were increased; and the immunoelectrophoresis of urinary proteins was abnormal. For adults, prenatal exposure to gentamicin led to altered juxta-medullary glomeruli with a larger GBM and abundant anionic sites, especially in the lamina densa, and to a protein excretion different from that of controls. Thus, gentamicin administered during pregnancy leads to permanent alterations of the GBM with modifications of both the layers and the anionic sites, possibly because of a perturbed protein metabolism. These altered glomeruli are at risk during life and could be the starting point for a kidney disease.