Bone metabolism and circulating IGF-I and IGFBPs in dexamethasone-treated preterm infants

Quantitative ultrasound measurements in premature infants at 1 year of age: the effects of antenatal administered corticosteroids

The aim of this study was to evaluate the effects of antenatally administered glucocorticoids on bone status of preterm infants at 1 year corrected age. The study population consisted of 32 preterm infants with a gestational age of 24-34 weeks. The infants were divided into two groups according to antenatal exposure to corticosteroids. Quantitative ultrasound (QUS) assessment of bone was performed in the study infants at the corrected age of 1 year. Blood levels of carboxy-terminal propeptide of type I procollagen (PICP) and carboxy-terminal telopeptide of type I collagen (ICTP) were measured at birth and at 1 year corrected age. Levels of PICP and ICTP were significantly lower at birth in corticosteroid-exposed neonates (P < 0.05). At corrected age of 12 months ICTP levels remained significantly lower in corticosteroid-exposed infants, but we found no significant difference in levels of the bone-formation marker PICP between corticosteroid-exposed and nonexposed infants. In the majority of participant preterm infants bone speed of sound (SOS) was within age-adjusted normal values of full-term infants. There was no significant difference in bone SOS between exposed and nonexposed infants at corrected age of 12 months. There was no correlation between SOS and levels of bone markers. The results of our study indicate that, despite the suppression of fetal bone turnover at birth in corticosteroid-exposed infants, antenatal glucocorticoid treatment seems to have no long-term impact on bone status of preterm infants assessed by QUS complementary to measurement of bone-turnover markers at 1 year corrected age.

Bone development of suckling piglets after prenatal, neonatal or perinatal treatment with dexamethasone

In mammals, the release from growth-inhibiting conditions results in catch-up growth. To investigate animal evidence for whether prenatal dexamethasone (DEX) treatment leads to the development of growth restriction especially reduced mineralization of skeleton, and release from it leads to the phenomenon of catch-up, piglets were prenatally exposed to DEX (3.0 mg/sow per day(-2)) during the last 24 days of prenatal life and tested further in two different ways: discontinued at birth and continued administration of DEX (0.5 mg/kg day(-2)) to piglets through 30 days of neonatal life. Using dual energy X-ray absorptiometry methods, bone mineral density (BMD) and bone mineral content (BMC) were measured. The three-point bending test was applied to determine the mechanical properties of the bones. Furthermore, geometric properties of the bones were assessed. Serum concentration of osteocalcin (OC) was determined. Histomorphological analysis of the ribs was also performed. The consequences of neonate DEX treatment and in utero DEX exposure were reflected in a dramatic decrease of BMD, BMC and blood serum OC concentration and geometric parameters of piglets' bones. Prenatal action of DEX during the last 24 days of pregnancy resulted in continued neonatal modification of bone tissues, thus diminishing bone quality, and negatively influenced structural development and mechanical properties, finally increasing the risk of fractures of ribs and limb bones. Prenatal DEX treatment limited to the last 24 days of foetal life did not reduce the term birth weight and the growth of suckling piglets followed up to 30 days of neonatal life, and catch-up in bone mineralization did not occur.

The prolonged effect of repeated maternal glucocorticoid exposure on the maternal and fetal leptin/insulin-like growth factor axis in Papio species

BACKGROUND

Maternal obesity represents a risk factor for pregnancy-related complications. Glucocorticoids are known to promote obesity in adults.

METHODS

We evaluated maternal and fetal metabolic changes during and after 3 weekly courses of betamethasone administered to pregnant baboons (Papio subspecies) at doses equivalent to those given to pregnant women.

RESULTS

Betamethasone administration during the second half of pregnancy increased maternal weight but neither maternal food intake nor fetal weight, as assessed at the end of gestation. Betamethasone increased maternal serum glucose concentration, the ratio of insulin-like growth factor-I and insulin-like growth factor binding protein-3, and serum leptin during treatment (normalized by 17, 35, and 45 days posttreatment, respectively, for each parameter). Maternal and fetal serum leptin concentrations did not differ between groups at the end of gestation.

CONCLUSION

Prolonged maternal hyperleptinemia caused by betamethasone administration in the second half of gestation did not change fetal metabolic parameters measured and placental leptin distribution at the end of gestation.

Early life factors predict abnormal growth and bone accretion at prepuberty in former premature infants with/without neonatal dexamethasone exposure

Growth, bone, and body composition were studied at prepuberty in former very low birth weight (VLBW) infants who received dexamethasone (DEX) for bronchopulmonary dysplasia (BPD) compared with VLBW infants without DEX and term-born infants (TERM) to identify early life risk factors for later low bone mass. Children (56 girls/63 boys, 5-10 y) previously studied in neonatal life were recruited into three groups: VLBW + DEX, VLBW - DEX, and TERM children. Anthropometry and whole body bone, fat, and lean mass were measured. At prepuberty, the average height and weight for VLBW + DEX group were significantly lower than that for VLBW - DEX and TERM. Both VLBW groups had lower bone mass even adjusted for height and lean mass than TERM children and lower lean mass both total and adjusted for height. Z-scores for whole body bone mineral content below -1.5 occurred in 27.9% of VLBW + DEX children. The key factors for low bone mass were earlier gestational age and having BPD with DEX in neonatal life. In former VLBW infants, growth and bone mass attainment before puberty can be predicted from early life variables. VLBW + DEX children may be protected from overweight, but are at risk for short stature and low bone mass.

Peak bone mass after exposure to antenatal betamethasone and prematurity: follow-up of a randomized controlled trial

Small birth size is associated with reduced adult bone mass. We determined if antenatal betamethasone exposure, birth weight, or prematurity affects peak bone mass in 174 adults. Antenatal betamethasone exposure did not. Lower birth weight and prematurity predicted reduced adult height. Slower fetal growth rather than prematurity predicted lower bone mass, but this lower bone mass was appropriate for reduced adult height.

INTRODUCTION

Small size at birth is reported to be associated with lower bone mass in adulthood. However, previous studies have not distinguished the relative contributions of length of gestation and fetal growth to size at birth. Fetal exposure to excess glucocorticoids has been proposed as a core mechanism underlying the associations between birth size and later disease risk. Antenatal glucocorticoids are given to pregnant women at risk for preterm delivery for the prevention of neonatal respiratory distress syndrome in their infants. We determined the relationship of antenatal exposure to betamethasone, birth weight, and prematurity to peak bone mass and femoral geometry in the adult survivors of the first randomized trial of antenatal glucocorticoids.

MATERIALS AND METHODS

We studied 174 young adults (mean age, 31 years) whose mothers participated in a randomized trial of antenatal betamethasone. Mothers received two doses of intramuscular betamethasone or placebo 24 h apart. Two thirds of participants were born preterm (<37 weeks gestation). We measured indices of bone mass and size and derived estimates of volumetric density and bone geometry from DXA assessments of the lumbar spine, femur, and total body.

RESULTS

There were no differences between betamethasone-exposed and placebo-exposed groups in any of the lumbar spine, femur, or total body DXA measures. There was no effect of antenatal betamethasone on adult height, although leg length was increased relative to trunk length (p = 0.002). A lighter birth weight (p <or = 0.001) and lower gestational age (p = 0.013) were associated with shorter stature (height Z scores) at age 31 years. Prematurity had no effect on peak bone mass or femoral geometry. However, lower birth weight, independent of gestational age, was associated with lower later bone mass (p < 0.001 for lumbar spine and total body, p = 0.003 for femoral neck BMC). These effects on bone mass were related to bone size and not to estimates of volumetric density. In the femur, lower birth weight, independent of gestational age, was associated with narrowing of the upper shaft and narrow neck regions.

CONCLUSIONS

Antenatal betamethasone exposure does not affect peak bone mass or femoral geometry in adulthood. Birth weight and prematurity predict adult height, but it is slower fetal growth, rather than prematurity, that predicts lower peak bone mass. The lower peak bone mass in those born small is appropriate for their adult height.

Does Insulin-Like Growth Factor 1 Contribute in Red Blood Cell Transfusions to the Pathogenesis of Retinopathy of Prematurity during Retinal Neovascularization?

BACKGROUND

Red blood cell (RBC) transfusions are associated with the development of retinopathy of prematurity (ROP). During the period of retinal neovascularization a rise of insulin-like growth factor 1 (IGF-1) may trigger rapid growth of new blood vessels.

OBJECTIVES

To study endocrine factors in RBC transfusions that might be of importance for ROP.

METHODS

IGF-1, IGF-2 and their binding proteins 1-3 (IGFBP-1-3) were determined by radioimmunoassays in 7 very-low-birthweight (VLBW) infants with ROP >or= stage 2 receiving a RBC transfusion, in 10 controls (VLBW infants with ROP <or= stage 1, no transfusion), in supernatants of 7 RBCs and of 5 washed RBCs (WRBC).

RESULTS

IGF-1 (mean +/- SD) in infants with ROP was 20.0 +/- 4.2 microg/l, in controls 35.9 +/- 15.2 microg/l (Mann-Whitney U test, p = 0.030). IGF-1 in RBC was 12.88 +/- 5.03 microg/l and in WRBC 0.45 +/- 0.74 microg/l (average of the three-course washing procedure). IGF-2 in infants with ROP was 485.67 +/- 158.73 microg/l, in controls 389.9 +/- 102.8 microg/l (not significant), in RBC 109.50 +/- 117.89 microg/l, in WRBC 61.07 +/- 30.0 microg/l. Except for IGFBP-3 other IGFBPs were barely or not detectable in RBC or WRBC.

CONCLUSIONS

Considering lower IGF-1 concentrations in preterm infants than in adults (factor 20), the IGF-1 in RBC transfusions is equivalent to a single dose of 1 microg/kg IGF-1 (5-10% of the adult dose with proved metabolic responses). Endocrinological relationships between the donor's load and the acceptor's individual features are a new aspect of potential side effects of RBC transfusions. Further research is necessary to clarify the share of the described IGF administration on the development of ROP.

Thyroid hormone, but not parathyroid hormone, partially restores glucocorticoid-induced growth retardation

Growth retardation is a serious side effect of long-term glucocorticoid (GC) treatment. In order to prevent or diminish this deleterious effect, a combination therapy including growth hormone (GH), a stimulator of bone growth, is often recommended. Parathyroid hormone (PTH) and thyroid hormone (T(4)) are important hormonal regulators of bone growth, and might also be helpful anabolic agents for counteracting the negative effects of GCs. Therefore, we studied the interaction of GCs in combination with a single dose of either PTH or T(4) on GC-induced growth retardation. Dexamethasone (Dex) treatment of mice for four weeks induced a significant growth inhibition of body length and weight and weights of several organs. PTH or T(4) alone did not affect the normal growth pattern. However, T(4) could partially restore the Dex-induced growth inhibition, whereas PTH could not. Although PTH did not affect total body growth, it did affect the height of the proliferative zone, which could be counteracted by Dex. This contrasts with T(4) treatment alone or in combination with Dex, which both resulted in a disturbed morphology of the growth plate. IGF-I mRNA, one of the mediators of longitudinal bone growth, was present in proliferative and hypertrophic chondrocytes. However, its expression was not affected by any of the treatments. In conclusion, T(4) but not PTH can partially counteract the effects of Dex on general body growth, with possible implications for future treatments of GC-induced growth retardation. Additionally, both T(4) and PTH, alone or in combination with Dex, have differential effects on the morphology of the growth plate.

Effect of dexamethasone treatment on serum GH, IGF-I, and the binding proteins IGFBP-1 and -3 in ventilated very preterm infants

Very preterm infants developing bronchopulmonary dysplasia frequently show a compromised growth in the neonatal period especially when steroids are given to facilitate weaning from the ventilator. The aim of this study was to evaluate the short-term effect of dexamethasone (DEXA) on the GH-IGF axis in ventilated very preterm infants developing bronchopulmonary dysplasia. We studied 10 very preterm artificially ventilated infants with bronchopulmonary dysplasia [median (range) gestational age 27.5 wk (25.9-32.0 wk), median (range) birth weight 970 g (610-2150 g)] immediately before and 2 d after the start of DEXA treatment. On both days of study, serum GH profiles were obtained, and serum IGF-I and IGF binding protein (IGFBP) -1 and -3 levels were measured. The ventilation score and the nutritional intake were calculated. Before the start of DEXA treatment, the median serum mean GH level was 12.0 microg/L (6-28.4 microg/L), whereas 2 d after the start of DEXA treatment the median serum mean GH level declined significantly to a value of 4.4 microg/L (1.7-11.9 microg/L). During DEXA treatment, mean, baseline, and maximal GH levels (Pulsar analysis) were significantly lower compared with pretreatment levels (p < 0.01, p < 0.01, and p < 0.05, respectively). Serum IGF-I and IGFBP-3 levels did not decline during DEXA. Serum IGFBP-1 levels were significantly lower compared with pretreatment levels (p < 0.01). Serum GH levels during DEXA treatment were correlated with neither the time interval between the administration of DEXA and the second GH profile nor the cumulative DEXA dose administered. Ventilation score and nutritional intake did not significantly correlate with serum GH, IGF-I, or IGFBP-1 or -3 levels, either before or after the start of DEXA. Two days of DEXA treatment in very preterm ventilated infants has a suppressive effect on serum GH levels, without an acute decline in serum IGF-I levels. A concomitant decrease in serum IGFBP-1 levels was found.

Leptin predicts bone and fat mass after accounting for the effects of diet and glucocorticoid treatment in piglets

The role of leptin in neonatal growth and bone metabolism has been investigated, but not simultaneously. The objectives of this study were to determine if leptin relates to bone mass during rapid growth; if consumption of maternal milk is related to elevated circulating concentrations of leptin resulting in higher fat mass; and if glucocorticoids result in higher fat mass and reduced bone mass due to elevated leptin. Thirty-two piglets were randomized to either a suckling or milk substitute plus either dexamethasone (DEX) or placebo injection for 15 days beginning at 5 days of age. Milk and blood samples were obtained at baseline, and after 15 days, blood was sampled again for measurement of leptin and bone biochemistry. Weight at baseline plus weight and length after 15 days were recorded, followed by measurement of whole body bone mineral content, bone area, and fat mass using dual energy x-ray absorptiometry. At baseline, plasma leptin was elevated in suckled piglets. Piglets that suckled had elevated fat mass as did those who received DEX. However, DEX resulted in suppressed weight and length, bone mass, and bone metabolism. Leptin was similar among groups after the 15 days. After accounting for body size and treatment effects, piglet plasma leptin was predictive of bone and fat mass. Leptin circulating early postnatally is linked to body composition, specifically fat and bone mass. Elevations in fat mass and reductions in bone mass observed after 15 days of DEX treatment are not related to leptin metabolism. Both human and porcine neonates share similar characteristics with respect to relationships of leptin with fat and bone mass.

Dietary long-chain polyunsaturated fatty acids minimize dexamethasone-induced reductions in arachidonic acid status but not bone mineral content in piglets

The primary objective of this study was to determine whether exogenous arachidonic acid (AA) in a supplemented formula substitute for piglets or sow milk would attenuate reductions in AA status, growth, and bone mineral content (BMC) as a result of exogenous glucocorticoid excess using dexamethasone (DEX). A secondary objective was to confirm a positive effect of exogenous AA on growth and BMC of piglets fed formula and not treated with DEX as well as to determine whether the elevation in BMC was related to greater production of prostaglandin E(2) in bone. Forty-eight 5-d-old male piglets were randomized to be suckled or receive either a standard formula or the same formula, but containing AA (0.5% wt/wt total fat) for 15 d in addition to either treatment with DEX or placebo. Piglets treated with DEX grew slower and had lower BMC of whole body, lumbar spine, and femur in addition to lower proportions of AA, but those fed standard formula had the greatest reductions. Piglets in the supplemented group weighed more than piglets fed standard formula or suckled in both the DEX and placebo groups. Suckled piglets had the highest BMC of whole body and femur compared with standard formula, and the supplemented group was intermediate for whole body but similar to suckled pigs for femur. Release of prostaglandin E(2) was elevated only with supplementation of AA. These data indicate that supplemental AA is associated with elevated whole body and femur BMC but that BMC is not enhanced during glucocorticoid treatment.

Changes in markers of bone metabolism during dexamethasone treatment for chronic lung disease in preterm infants

AIM

To characterise the change in serum and urinary bone markers in the early postnatal period, and to assess the effect of systemic corticosteroid on bone metabolism in preterm infants.

METHODS

Bone formation was quantified by measurement of serum concentrations of bone specific alkaline phosphatase (BALP) and osteocalcin. Bone resorption was measured by monitoring creatinine adjusted urinary deoxypyridinoline (Dpd) concentration. Blood and urinary samples were collected from corticosteroid treated infants (n = 19) immediately before the start (T(d-pre)), three weeks after the start (T(d-end)), and two (T(d-post2)) and four weeks (T(d-post4)) after the end of the dexamethasone course. Untreated patients (n = 30) had specimens taken at week 3 (T(wk-3)), 6 (T(wk-6)), 8 (T(wk-8)), and 10 (T(wk-10)) of postnatal age.

RESULTS

Serum concentrations of BALP and osteocalcin at T(d-end) were significantly lower than pretreatment levels and the levels at the corresponding time point (T(wk-6)) of the non-treatment group. In contrast, urinary Dpd concentration at T(d-end) was not significantly decreased compared with the pretreatment level. However, it was significantly lower than the urinary Dpd concentration at T(wk-6) of the non-treatment group. The rate of increase in lower leg length was significantly higher in the non-treatment group between weeks 3 and 6 than in the corresponding period during dexamethasone treatment in the corticosteroid group.

CONCLUSION

Systemic corticosteroid causes appreciable suppression of serum BALP and osteocalcin and, to a lesser extent, urinary Dpd. The results suggest that corticosteroid inhibits bone growth mainly by decreasing bone formation.

Special nutritional needs of infants for prevention of and recovery from bronchopulmonary dysplasia

Extremely low birth weight infants who develop severe respiratory disease may have special nutrient requirements imposed by a combination of enhanced utilization of nutrients or the need for epithelial cell repair resulting from the disease process, as well as to support catch-up growth. Inositol, free fatty acids, vitamin E and vitamin A are proposed as nutrients for which infants at risk of chronic pulmonary insufficiency may have special requirements. Of these nutrients, only for vitamin A does suggestive evidence exist that high doses when given intramuscularly may reduce the incidence of death or chronic lung disease. Exogenous steroid therapy (dexamethasone), which is often used to improve pulmonary compliance in ventilated premature infants, may compromise vitamin A status and induce restricted somatic and bone mineral growth. Supplemental nutrition by means of enriched infant formulas has provided benefits in growth and bone mass accretion to infants recovering from bronchopulmonary dysplasia up to 3-mo corrected age. This growth advantage was not sustained over the subsequent 9 mo, suggesting that prolonged nutritional support is required until catch-up growth is complete. Further studies are required to delineate the needs for specific nutrients such as antioxidant vitamins and minerals or vitamin A that may play a role in preventing severe chronic lung disease in premature infants. As well, the role of supplemental nutrition (beyond the requirements of term infants) to support catch-up growth and maintenance during the critical stages of early development requires further investigation before evidence-based nutrient recommendations can be developed for this special population of infants.

Growth restriction in dexamethasone-treated preterm infants may be mediated by reduced IGF-I and IGFBP-3 plasma concentrations

OBJECTIVE

Preterm infants receiving dexamethasone for respiratory morbidity frequently suffer restricted growth. The aim of this study was to investigate the interactions between dexamethasone treatment regimen and circulating IGFBP-3 and IGF-I levels, and the associations between these variables and linear growth rate in preterm babies receiving dexamethasone for chronic lung disease of prematurity.

DESIGN

A randomised, unblinded, clinical trial of two different courses of dexamethasone: a 42-day tapering course (the long course) and a repeatable 3 day pulse course.

PATIENTS

Forty preterm infants (19 in the pulse group, 21 in the long group) with a birthweight < or = 1250 g who were ventilated at 7 days of age.

MEASUREMENTS

Lower leg length was measured thrice weekly by knemometry, and IGFBP-3 and IGF-I levels were measured prior to commencing treatment, at 14 and 42 days of treatment and at 36 weeks postmenstrual age (PMA). Interactions between variables were analysed by stepwise regression analysis and analysis of covariance (ANCOVA). Associations between variables were assessed by correlation coefficients.

RESULTS

In an ANCOVA, mean daily dose of dexamethasone/kg (MDDD) and treatment group both significantly influenced IGFBP-3 levels (P = 0.0009 and P = 0.017, respectively), and tended to influence IGF-I levels similarly (P = 0.098 and P = 0.07). MDDD also significantly influenced mean daily increase in lower leg length (MDILL; P < 0.01). IGFBP-3 and IGF-I levels were significantly related to MDILL (ANCOVA: P < 0.01). The correlation coefficients for IGFBP-3 and IGF-I levels and MDILL were 0.2 and 0.3 (both P < 0.0001), respectively. IGFBP-3 and IGF-I levels were highly correlated (r(2) = 0.52, P < 0.0001) and both increased significantly with increasing PMA (P < 0.0001). IGF-I levels were higher in females (P = 0.036).

CONCLUSION

This study provides evidence that the growth-restricting effects of dexamethasone may be mediated, at least in part, via suppression of the IGF axis. Both dexamethasone dose and treatment regimen influence circulating IGF-I and IGFBP-3 levels, and both are important in inducing growth restriction.

Comparative response in growth and bone status to three dexamethasone treatment regimens in infant piglets

The objectives of this study were 1) to determine whether a zenith in bone formation (indicated by circulating osteocalcin) existed at night in early life, and 2) to compare the effects of three different dexamethasone (DEX) treatment regimens on bone turnover, bone mineral content, and growth. Three DEX treatment regimens were tested in 8-d-old piglets (n = 8/group): 1) low evening dose of DEX (0.5 mg/kg/d) as 70% in the morning and 30% in the evening for 10 d; 2) tapering course of DEX (0.5, 0.3, and 0.2 mg/kg/d) as 50% in the morning and 50% in the evening for 14 d; and 3) constant dose of DEX (0.5 mg/kg/d) as 50% in the morning and 50% in the evening for 10 d. Oral water placebo groups were tested with the same time courses. At pretreatment, plasma osteocalcin was significantly higher (p < 0.05) at 0100 than at 0900 and 1700. At necropsy, measures for DEX groups were calculated as Z-scores using values from the placebo groups. The low evening DEX dose led to a significantly lower reduction in plasma osteocalcin compared with the tapered and constant dosing regimens (p < 0.05). The significant weight. reduction in the DEX group occurred at d 9 in the low evening dose regimen but at d 7 in the constant dosing regimen, compared with the placebo group. Bone mineral content Z-score was reduced similarly in all DEX-treated groups across the three dosing regimens. We conclude that a plasma osteocalcin zenith at night exists in early life. A high DEX dose in the morning and low DEX dose in the evening may partially attenuate corticosteroid-induced suppression of bone formation and growth restriction.

Factors influencing body composition of premature infants at term-adjusted age

We investigated the influence of body size at birth, feeding of mother's milk versus formula, or standard-term formula versus energy- or nutrient-enriched formula on the growth and whole body bone mineral content (BMC), lean and fat mass (using dual-energy X-ray absorptiometry) of low-birth-weight (LBW) infants to term-adjusted age. LBW infants who were appropriate for gestational age were lighter and shorter than term-born infants (n = 46) but had a higher percent fat mass (19-28% vs. 15 +/- 7%). For LBW infants fed standard formula or mother's milk after hospital discharge, the mean BMC expressed either as a function of weight (17 +/- 2, 19 +/- 2 vs. 20 +/- 2 g/kg) or length (1.1 +/- 0.2, 1.1 +/- 0.2 vs. 1.5 +/- 0.2 g/cm) was more than 1 SD below term infant values. However, infants fed a nutrient-enriched formula from hospital discharge had BMC within 1 SD below term infants. Infants who were born small, compared to appropriate for gestational age, compared to infants of similar birth weight had lower percent body fat (16 +/- 6 vs. 19 +/- 5) and lower BMC (47 +/- 3 vs. 62 +/- 5 g) at term age. Both size at birth and diet influence patterns of growth and body composition in early life in very-low-birth-weight (VLBW) infants. The long-term significance of these variable growth patterns in VLBW infants in early life requires further investigation.