Growth restriction at birth and kidney function during childhood

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.

Is small for gestational age status independently correlated with body composition during childhood?

This study aims to examine if small for gestation age (SGA) status is correlated with alterations in body composition at prepuberty, independently of other factors, comparing SGA-born children with appropriate for gestational age (AGA)-born children. We examined anthropometrics, waist circumference, body mass index (BMI), six skinfold thickness, and body composition using the method of bioelectrical impedance in 636 children aged 7 to 10 years. We also considered age, gender, birth mode, mother's age, prepregnancy weight, weight gain during pregnancy, social status, parental BMI, type of feeding, and daily exercise. We examined 636 children at a mean age of 9 years: 106 SGA-born and 530 AGA-born children. SGA as compared to AGA-born children had a lower BMI z-score (0.26 ± 0.89 kg/cm² vs 0.46 ± 0.84 kg/cm², p < 0.050) and a lower lean mass, although that was not statistically significant (24.0 ± 6.6 kg vs 25.6 ± 6.4 kg, p < 0.100). SGA-born children presented no difference in waist circumference or fat mass in comparison to children born AGA. Logistic regression analysis revealed a strong independent negative association between SGA status and BMI (beta =  - 2.33, OR = 0.70 p = 0.019) and SGA status and lean mass (beta =  - 2.43, OR = 0.95 p = 0.010).  Conclusion: Our findings suggest that SGA-born children had a lower BMI as compared to AGA-born subjects, whereas SGA status was negatively associated with BMI and lean mass. What is Known: • Deviant birth weight for gestation has been associated with an increased risk of childhood adiposity. • Evidence remains scarce on whether small for gestational age status affects body composition and obesity later in childhood. What is New: • Among school-aged children, small for gestational age subjects had a lower body mass index as compared to appropriate for gestational age counterparts, whereas small for gestational age status was negatively associated with body mass index and lean mass. • A meticulous observation is needed during childhood in children born with deviant birth weight.

Renal function in short-statured children born small for gestational age and treated with growth hormone

BACKGROUND

Children born small for gestational age (SGA), particularly when associated with an extremely low birthweight (ELBW), have a higher risk of renal dysfunction. Growth hormone (GH) treatment is used to treat short-statured children born SGA; however, its effects on renal function remain elusive, especially in those born SGA with ELBW.

METHODS

Short-statured children born SGA (N = 42) were included. Subjects were subdivided into two groups based on their birthweight: the ELBW group (N = 15) with a birthweight of <1,000 g, and the non-ELBW group (N = 27) with birthweights ranging between 1,000 and 2,500 g. The creatinine-based estimated glomerular filtration rates (eGFR) before (pre-eGFR) and 5 years after GH treatment (post-eGFR) were compared. Correlations between eGFR, anthropometric, or birth parameters, and cumulative GH dose were evaluated using Spearman's rank correlation coefficient.

RESULTS

The ELBW group had a lower pre- and post-eGFR than the non-ELBW group. Five-year GH treatment did not significantly reduce eGFR in either group. Post-eGFR was positively associated with gestational week and birthweight. However, the cumulative GH dose was not correlated with pre-eGFR, post-eGFR, or percentage change in eGFR (%ΔeGFR). The change in bodyweight standard deviation score during GH treatment was positively correlated with %ΔeGFR in the ELBW group.

CONCLUSIONS

The current results indicated that GH treatment was unlikely a risk for the reduction in eGFR in short-statured children born SGA. However, eGFR should be carefully monitored, especially in those born SGA with ELBW because these subjects had lower eGFR than non-ELBW subjects.

Are low birth weight children predisposed to renal loss of carnitine?

Aim: The plasma homeostasis of both free and esterified carnitines is mostly regulated by renal tubular reabsorption, which may be disturbed in low birth weight children. The aim of study was to check whether disturbances in excretion of l-carnitine (LC) and its main ester, acetyl-carnitine (ALC), may be the result of renal dysfunction in low birth weight children (LBW).Methods: This study included 59 LBW children (2165 g [1490-2440]) and 22 children with normal birth weight as a reference group (3500 g [3275-3650]). Subjects were divided into three groups: 0-3 months, 4-12 months and over 1 year at the time of testing. Urinary levels of carnitine were measured spectrophotometrically.Results: The urine excretion of Free LC, Free LC/cr, Total LC and Total LC/cr. Were significantly higher in 0-3 and 4-12-month old LBW infants study groups when compared to the reference groups. We found statistically significant higher urine excretion of ALC and ALC/cr. in all age groups of LBW infants compared to the reference group. There was a negative correlation between birth weight and free LC/cr. (r= -0.3, p < .05), Total LC/cr. (r= -0.34, p < .05), and ALC/cr. (r= -39, p < .05), and in the children >12-month-old strong negative correlation between eGFR and free LC/cr. (r= -0.6, p < .05), Total LC/cr. (r= -0.61, p < .05), ALC/cr. (r= -0.61, p < .05.)Conclusion: Higher urine excretion of both LC and ALC and its negative correlation with birth weight and eGFR may reflect some degree of renal dysfunction in LBW infants.

Long-term renal tubular damage in intrauterine growth-restricted rats

BACKGROUND

Intrauterine growth restriction (IUGR) has been shown to be associated with increased risk of renal disease or hypertension in later life. Glomerular dysfunction, however, has mainly been reported, and limited information is available to link IUGR with renal tubular damage. The aim of this study was therefore to investigate urinary markers of tubular damage in a rat model of IUGR induced by bilateral uterine artery ligation.

METHODS

Pregnant Sprague-Dawley rats underwent bilateral uterine artery ligation, while the control group underwent sham surgery.

RESULTS

Birthweight was reduced, and urinary β2-microglobulin (β2-MG)-, cystatin C (Cys-C)-, and calbindin-to-creatinine ratios were significantly higher at weeks 4 and 8 in the IUGR group compared with the control group. These urinary markers were not significantly different at week 16 between the two groups. Increased excretion of urinary β2-MG, Cys-C, and calbindin was observed in IUGR rats at ≥8 weeks of age.

CONCLUSION

Children born with IUGR are at increased risk for renal tubular damage.

Longitudinal analysis of serum cystatin C for estimating the glomerular filtration rate in preterm infants

BACKGROUND

Cystatin C (Cys-C) is a more sensitive marker of renal function than creatinine (Cre) in pediatric and adult populations. However, the reference values of serum Cys-C for estimating glomerular filtration rates (eGFRs) in premature infants during the first year of life have not been sufficiently studied.

METHODS

In this prospective study, 481 blood samples were collected from 261 preterm infants with uncomplicated clinical courses during their first year of life. Infants were divided into three groups according to gestational age at birth: 27-30 weeks, 31-33 weeks, and 34-36 weeks. Serum Cys-C and Cre levels were measured at 6-30 days, 3-5 months, 7-9 months, and 12-14 months after birth and the eGFR was calculated using two previously published equations.

RESULTS

The median serum Cys-C levels were 1.776, 1.248, 1.037, and 0.960 mg/L at the first, second, third, and fourth measurement time-point, respectively, with the value significantly decreasing with age up to 12-14 months. Cys-C levels were independent of gestational age and gender. In contrast to Cys-C, serum Cre values declined rapidly up to 3-5 months, then remained constant up to 12-14 months. Using the Cys-C-based equation, the eGFR significantly increased with increasing age until approximately 1 year after birth; however, no such trend was noted using the equation based on Cys-C + Cre.

CONCLUSIONS

Reference ranges for Cys-C in premature infants decline gradually over the first year after birth. Cys-C appears to be a more reliable marker than Cre for estimating GFR in preterm infants.

Leptin in pregnancy and development: a contributor to adulthood disease?

Emerging research has highlighted the importance of leptin in fetal growth and development independent of its essential role in the maintenance of hunger and satiety through the modulation of neuropeptide Y and proopiomelanocortin neurons. Alterations in maternal-placental-fetal leptin exchange may modify the development of the fetus and contribute to the increased risk of developing disease in adulthood. In addition, leptin also plays an important role in reproductive functions, with plasma leptin concentrations rising in pregnant women, peaking during the third trimester. Elevated plasma leptin concentrations occur at the completion of organogenesis, and research in animal models has demonstrated that leptin is involved in the development and maturation of a number of organs, including the heart, brain, kidneys, and pancreas. Elevated maternal plasma leptin is associated with maternal obesity, and reduced fetal plasma leptin is correlated with intrauterine growth restriction. Alterations in plasma leptin during development may be associated with an increased risk of developing a number of adulthood diseases, including cardiovascular, metabolic, and renal diseases via altered fetal development and organogenesis. Importantly, research has shown that leptin antagonism after birth significantly reduces maturation of numerous organs. Conversely, restoration of the leptin deficiency after birth in growth-restricted animals restores the offspring's body weight and improves organogenesis. Therefore, leptin appears to play a major role in organogenesis, which may adversely affect the risk of developing a number of diseases in adulthood. Therefore, greater understanding of the role of leptin during development may assist in the prevention and treatment of a number of disease states that occur in adulthood.

Low birthweight and risk of albuminuria in living kidney donors

Low birthweight is linked to hypertension, chronic kidney disease and even end-stage renal disease. We hypothesized that living kidney donors born with lower birthweight may be at increased risk of hypertension, albuminuria, or reduced GFR beyond what is typical following uninephrectomy. Two hundred fifty-seven living kidney donors who donated at the University of Minnesota between 1967 and 2005 underwent iohexol GFR and urinary albumin excretion measurements. Predictors of iohexol GFR <60 mL/min/1.73 m(2), albuminuria, and hypertension were examined using logistic regression. Predictors examined include age at GFR measurement, time since donation, BMI, gender, serum creatinine level (at donation and GFR measurement), systolic and diastolic blood pressure, race, and birthweight. The latter was obtained through self-report and verified through birth certificates and family members. Older age, higher BMI, and time from donation were associated with reduced GFR. Older age and higher BMI were also associated with hypertension. Birthweight was not associated with GFR <60 mL/min/1.73 m(2): OR=0.70, 95% CI (0.28, 1.74), p = 0.45 or hypertension: OR=0.92, 95% CI (0.46, 1.84), p = 0.82 but was associated with albuminuria: OR=0.37, 95% CI (0.15, 0.92), p = 0.03. These data further strengthen the link between low birthweight and potential adverse renal outcomes.

Sex differences in the developmental programming of hypertension

Experimental models of developmental programming provide proof of concept and support Barker's original findings that link birthweight and blood pressure. Many experimental models of developmental insult demonstrate a sex difference with male offspring exhibiting a higher blood pressure in young adulthood relative to their age-matched female counterparts. It is well recognized that men exhibit a higher blood pressure relative to age-matched women prior to menopause. Yet, whether this sex difference is noted in individuals born with low birthweight is not clear. Sex differences in the developmental programming of blood pressure may originate from innate sex-specific differences in expression of the renin angiotensin system that occur in response to adverse influences during early life. Sex differences in the developmental programming of blood pressure may also involve the influence of the hormonal milieu on regulatory systems key to the long-term control of blood pressure such as the renin angiotensin system in adulthood. In addition, the sex difference in blood pressure in offspring exposed to a developmental insult may involve innate sex differences in oxidative status or the endothelin system or may be influenced by age-dependent changes in the developmental programming of cardiovascular risk factors such as adiposity. Therefore, this review will highlight findings from different experimental models to provide the current state of knowledge related to the mechanisms that contribute to the aetiology of sex differences in the developmental programming of blood pressure and hypertension.

Developmental programming of hypertension and kidney disease

A growing body of evidence supports the concept that changes in the intrauterine milieu during "sensitive" periods of embryonic development or in infant diet after birth affect the developing individual, resulting in general health alterations later in life. This phenomenon is referred to as "developmental programming" or "developmental origins of health and disease." The risk of developing late-onset diseases such as hypertension, chronic kidney disease (CKD), obesity or type 2 diabetes is increased in infants born prematurely at <37 weeks of gestation or in low birth weight (LBW) infants weighing <2,500 g at birth. Both genetic and environmental events contribute to the programming of subsequent risks of CKD and hypertension in premature or LBW individuals. A number of observations suggest that susceptibility to subsequent CKD and hypertension in premature or LBW infants is mediated, at least in part, by reduced nephron endowment. The major factors influencing in utero environment that are associated with a low final nephron number include uteroplacental insufficiency, maternal low-protein diet, hyperglycemia, vitamin A deficiency, exposure to or interruption of endogenous glucocorticoids, and ethanol exposure. This paper discusses the effect of premature birth, LBW, intrauterine milieu, and infant feeding on the development of hypertension and renal disease in later life as well as examines the role of the kidney in developmental programming of hypertension and CKD.

Increased albuminuria in 4-year-old preterm-born children with normal height

OBJECTIVE

To determine risk factors for high blood pressure (BP), increased markers of glomerulosclerosis, and tubular dysfunction in 4-year-old preterm-born children.

STUDY DESIGN

The study group was a longitudinal cohort of 119 children with BP, albuminuria, and β2 microglobulin measurements obtained during the neonatal period and at age 4 years.

RESULTS

Systolic BP was >95(th) percentile in 15 (12.6%) of the children at age 4 years and lower in those born small for gestational age compared with those born appropriate for gestational age. Preterm-born 4-year-olds with height <-1 SD had lower systolic and diastolic BP, and 14.4% of the 4-year-olds had albuminuria. Albuminuria was less prevalent in the 4-year-olds with height <-1 SD than in those with height ≥-1 SD (6.8% vs 19.3%; P=.04). Mean albuminuria level was 1.0±0.7 mg/mmol in 4-year-olds with height <-1 SD and 1.4±1.3 mg/mmol in those with height ≥-1 SD. In multivariate analysis, albuminuria level was increased by 0.4±0.2 mg/mmol in preterm-born children with normal height at age 4, and by 0.5±0.2 mg/mmol in females, after adjustment for gestational age, sex, neonatal morbidity, and intrauterine growth restriction. These results were unchanged after adjustment for body mass index.

CONCLUSION

Normal height at age 4 years may be associated with an increased risk for glomerulosclerosis in preterm-born children.

Childhood Growth and Adult Hypertension in a Population of High Birth Weight

Low birth weight has consistently been associated with increased adult blood pressure. The relative importance of childhood growth is, however, less well established. This study examined sex-specific associations between childhood growth and adult blood pressure in 2120 subjects born from 1921 to 1935 in Reykjavik who were recruited into a longitudinal study in 1967–1991. Size at birth and growth at regular intervals between 8 and 13 years were collected from national archives. Hypertensive males did not differ from normotensive males at birth but were increasingly taller and of higher body mass index between 8 and 13 years. No differences in adult height were observed between hypertensive and normotensive males. For boys, growth-velocity (change in growth per year) for body mass index and height between 8 to 13 years was positively associated ( P <0.05) with adult blood pressure. The association for body mass index-velocity was fully accounted for by concurrent body size, whereas height-velocity was independent of birth weight and concurrent body size. Males in the highest compared with the lowest tertile in the height-velocity distribution had 66% increased risks of hypertension (95% CI: 15% to 139% increased risks of hypertension) corresponding with 5.0 mm Hg increase (95% CI: 1.5 to 8.5 mm Hg increase) and 3.1 mm Hg increase (95% CI: 1.1 to 5.0 mm Hg increase) in systolic and diastolic blood pressures, respectively. Hypertensive females weighed less at birth but did not differ markedly from normotensive girls between 8 and 13 years, and no association was observed for growth-velocity. In conclusion, rapid linear growth between 8 and 13 years predicts elevated adult blood pressure in boys. This association is likely to reflect relatively early onset of puberty among hypertensive males.