Barker, Brenner, and babies--early environment and renal disease in adulthood

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.

Renal agenesis and unilateral nephrectomy: what are the risks of living with a single kidney?

The long-term outlook for patients with unilateral renal agenesis or following unilateral nephrectomy in childhood is controversial. Animal studies suggest that the resultant compensatory increase in glomerular filtration might lead to progressive damage to the remaining renal tissue and may generate hypertension. Human studies addressing these concerns are limited in number and are difficult to interpret because they are small, retrospective, or cross sectional with significant variations in duration and completeness of follow-up. The published studies suggest that renal function remains stable for several decades in the majority of subjects. The clinical significance of mild-grade proteinuria and hypertension seen in some patients is unknown. Longitudinal studies are needed to understand the long-term effect and significance of the several pathophysiological changes observed in the solitary kidney.

Consequences of Intrauterine Growth Restriction for the Kidney

Low birth weight due to intrauterine growth restriction is associated with various diseases in adulthood, such as hypertension, cardiovascular disease, insulin resistance and end-stage renal disease. The purpose of this review is to describe the effects of intrauterine growth restriction on the kidney. Nephrogenesis requires a fine balance of many factors that can be disturbed by intrauterine growth restriction, leading to a low nephron endowment. The compensatory hyperfiltration in the remaining nephrons results in glomerular and systemic hypertension. Hyperfiltration is attributed to several factors, including the renin-angiotensin system (RAS), insulin-like growth factor (IGF-I) and nitric oxide. Data from human and animal studies are presented, and suggest a faltering IGF-I and an inhibited RAS in intrauterine growth restriction. Hyperfiltration makes the kidney more vulnerable during additional kidney disease, and is associated with glomerular damage and kidney failure in the long run. Animal studies have provided a possible therapy with blockage of the RAS at an early stage in order to prevent the compensatory glomerular hyperfiltration, but this is far from being applicable to humans. Research is needed to further unravel the effect of intrauterine growth restriction on the kidney.

Intrauterine growth restriction increases blood pressure and central pulse pressure measured with telemetry in aging rats

OBJECTIVES

Intrauterine growth restriction (IUGR) is associated with a higher risk of hypertension in adulthood. In Western countries, IUGR is based on uteroplacental dysfunction. We hypothesize that aging augments the increased baseline blood pressure after IUGR and alters the cardiovascular response to acute stress.

METHODS

To evaluate blood pressure during aging in the rat, we used a model of uteroplacental dysfunction (bilateral uterine artery ligation). Blood pressure was measured in male offspring at the ages of 6, 9, and 12 months using telemetry, allowing for unstressed measurements in conscious animals. At 6 and 12 months of age, cardiovascular data were obtained during acute olfactory stress induced by ammonia and subsequent recovery.

RESULTS

Rats born after IUGR had lower birth weights (4.6 versus 6.5 g, P < 0.001) and did not completely catch up in weight by 12 months of age (519 versus 567 g, P < 0.01). Systolic blood pressure was significantly higher in IUGR animals at all ages. Pulse pressure (PP) was identical in both groups at the age of 6 months. However, PP increased in the IUGR group with increasing age, unlike the control group, and was significantly higher at 9 and 12 months of age. At the age of 12 months, there was a highly significant negative correlation between birth weight and PP (r = -0.82, P < 0.001). IUGR rats reached a higher peak in systolic blood pressure during stress, and showed a longer period for the raised heart rate to recover after stress.

CONCLUSIONS

IUGR is associated with raised baseline blood pressure, an increasing PP with age, and an altered stress response.

Association of birth weight with cardiovascular parameters in adult rats during baseline and stressed conditions

Low birth weight (LBW) due to intrauterine growth restriction (IUGR) in humans is associated with increased blood pressure (BP) in adulthood. In Western countries, IUGR is based on uteroplacental dysfunction. We used an animal model of uteroplacental dysfunction to evaluate this correlation. We hypothesize that IUGR increases baseline BP and alters the BP response to acute stress, which may explain BP differences in previous studies using stressful methods to obtain BP. IUGR was induced by bilateral uterine artery ligation in pregnant Wistar rats according to a modified method of Wigglesworth. BP was measured in the offspring using telemetry, allowing for unstressed measurements in conscious animals. Cardiovascular data were obtained at the age of 12 wk during baseline and acute olfactory stress induced by an ammonia gauze. Rats born after IUGR had a lower birth weight versus controls and did not completely catch up in weight. At baseline, systolic BP (SBP), mean arterial pressure (MAP), and pulse pressure (PP) were elevated in IUGR rats versus controls, by 8, 6, and 5 mm Hg, respectively. There was a strong negative correlation between birth weight and SBP and between birth weight and PP. During acute stress, there was a tendency to reach a higher peak in SBP and to need a longer period to recover in IUGR animals. We conclude that IUGR is associated with increased baseline BP.

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.

A life course approach to cognitive reserve: A model for cognitive aging and development?

The concept of reserve in neuroscience maintains that there are aspects of brain structure and function that can buffer the effects of neuropathology such that the greater the reserve, the more severe the pathology must be to cause functional impairment. This article provides a concise overview of structural and functional approaches to reserve and shows how reserve may be conceived as the sum of its lifetime input. In this context, reserve therefore provides an empirical yet general model of cognitive aging and development.

Minimal change nephrotic syndrome in children with intrauterine growth retardation

It has been well established that intrauterine growth retardation (IUGR) is associated with greater morbidity and mortality rates during perinatal and adult life. The aim of this study is to clarify whether IUGR, defined as a birth weight less than the 10th percentile for gestational age, influences the clinical course of minimal change nephrotic syndrome (MCNS) in children. The study included 50 children aged 1 to 13 years at the onset of MCNS. The diagnosis of MCNS was confirmed by renal biopsy in 25 children (50%). Eight children (16%) had IUGR at birth. Comparisons between children with and without IUGR showed significant differences in mean number of relapses (13.0 +/- 3.5 versus 3.4 +/- 3.0 relapses; P < 0.0001) and relapse rates (relapses per year, 1.6 +/- 0.3 versus 0.5 +/- 0.4; P < 0.0001). We also observed a greater incidence of steroid dependence (100% versus 21.4%; P < 0.001) in children with than without IUGR. In addition, children with IUGR underwent treatment with cytotoxic agents and cyclosporine more frequently than those without IUGR. There was a significantly greater incidence of complications and concomitant diseases of nephrotic syndrome in children with IUGR; results show that MCNS in children with IUGR had a more unfavorable course and outcome. It is important for clinicians to be aware that IUGR may help in the early identification of children at greater risk for frequent relapses and the development of steroid dependence and/or steroid resistance. More aggressive therapy may be indicated for these children.

Determinants of albuminuria in people with Type 2 diabetes mellitus

This study sought to identify determinants of albuminuria in people with Type 2 diabetes. In 335 primary care patients, we assessed albumin-creatinine ratio (ACR) in two 24-h urine samples, and its cross-sectional associations with protein and alcohol intake, cigarette smoking, body weight and height, glycosuria, blood pressure, hypoglycaemic and antihypertensive treatment, gender, age, age at diagnosis, diabetes duration, family history of diabetes and cardiovascular diseases, ethnic origin, and education. The prevalence of micro- or macro-albuminuria (ACR> or =2.0 mg/mmol) was 33%. Among these patients, compared to those with normo-albuminuria, there were more men, protein intake (g/kg) estimated from urinary urea as well as systolic blood pressure and glycosuria were higher, there were more smokers, men were shorter, and a family history of diabetes was less prevalent (all P<0.05). In linear and logistic regression (n=270) albuminuria was independently associated (P<0.05 unless indicated otherwise) with systolic blood pressure (OR(10 mmHg)=1.32), smoking (OR(ex/never)=2.36, OR(current/never)=4.89), glycosuria (OR(> or =7/<1 g/l)=2.41), gender (OR(men/women)=2.50), age in men (OR(10 year)=1.60) (P<0.10) and, inversely, in women (OR(10 year)=0.63) (P>0.10). On aggregation, the modifiable determinants systolic blood pressure, smoking and glycosuria explained 12% of the variation in albuminuria. These factors thus are, although to a moderate extent only, potential determinants of albuminuria. We also observed an independent, inverse association with body height (OR(0.10 m)=0.47). This is in line with the hypothesis that development in utero or during early life influences kidney function in later life.

Unfavorable course of minimal change nephrotic syndrome in children with intrauterine growth retardation

BACKGROUND

Intrauterine growth retardation (IUGR) is associated with higher morbidity and mortality not only in perinatal life but also in later life. The purpose of our study was to determine whether IUGR has any effect on the course of minimal change nephrotic syndrome (MCNS) in children.

METHODS

Forty children who were between 1 and 16 years old at the onset of MCNS, who have been followed for at least three years and for whom we were able to obtain birth weights and gestational ages, were included. The diagnosis of MCNS was predicted on the basis of clinical and laboratory features, and in 11 children (27.5%) the diagnosis was confirmed by renal biopsy. IUGR was defined as birth weight below the tenth percentile for gestational age.

RESULTS

Five children (12.5%) had signs of IUGR at birth. In children with IUGR, we observed a higher mean number of relapses (10.4 vs. 3.3, P < 0.001) and a higher incidence of steroid dependency (80% vs. 21%, P < 0.02) than in children without IUGR. Other differences between children with and those without IUGR included more frequent treatment with cytotoxic agents and cyclosporine, and a higher incidence of renal biopsy in children with IUGR.

CONCLUSION

Our study demonstrated an unfavorable course of MCNS in children with IUGR. IUGR could therefore enable early identification of those children who are at risk of becoming frequent relapsers and of developing steroid dependency. This, however, should be confirmed in a larger number of patients.

Developmental renal physiology of the low birth weight pre-term newborn

PURPOSE

The remarkable growth of the kidney and the rapid changes in renal function in the second half of gestation and early postnatal period are discussed.

MATERIALS AND METHODS

Adaptation to the extrauterine environment involves immediate postnatal natriuresis that is prolonged in the pre-term neonate, followed by the sodium retention necessary for growth. Glomerular filtration rate increases throughout the postnatal period, and it is modulated by the renin-angiotensin system and prostaglandins. Because of this, the fetus and neonate are particularly susceptible to renal injury following the administration of angiotensin converting enzyme inhibitors or nonsteroidal anti-inflammatory drugs. Renal tubular function in the neonate is characterized by reduced renal concentration and acidification ability, which can be further compromised by obstructive uropathy. Urine calcium excretion is high in the neonate, which can be aggravated by calciuric drugs, such as furosemide and glucocorticoids.

RESULTS

Reduced renal mass results in compensatory renal growth even in the fetus, a response that could prove maladaptive later in life through excessive glomerular hyperfiltration and progressive interstitial fibrosis.

CONCLUSIONS

These factors underscore the importance of attempting to maximize functional renal mass in the neonate or infant with renal impairment of any etiology.