The phosphorylation status of insulin-like growth factor-binding protein-1 in prepubertal obese children

OBJECTIVE: We measured the total and nonphosphorylated insulin-like growth factor-binding protein (IGFBP)-1 concentrations in obese children to determine the effect of obesity on the status of IGFBP-1 phosphorylation. We also measured the serum levels of insulin, total and free IGF-I, and IGFBP-3 to investigate their relationships to the IGFBP-1 phosphorylation status in obese subjects. SUBJECTS AND METHODS: Nineteen prepubertal obese and 15 age-matched control children were included in the study. The serum levels of total and nonphosphorylated IGFBP-1 were determined by noncompetitive RIAs. RESULTS: The serum levels of total and nonphosphorylated IGFBP-1 were significantly lower in the obese group (48.7+/-5.6 microgram/l, P<0.001 and 11.1+/-1.9 microgram/l, P<0.01 respectively) than in the controls (86.7+/-9.0 microgram/l and 28.8+/-6.2 microgram/l respectively). However, the ratio of nonphosphorylated IGFBP-1 to total IGFBP-1 did not differ significantly between the obese and control groups. The circulating free IGF-I level was significantly higher in the obese children than in the controls (P<0.05), while the serum levels of insulin, total IGF-I and IGFBP-3 were not significantly different between the two groups. A stepwise regression analysis of the combined group revealed that only the total IGFBP-1 level was an independent predictor of the free IGF-I concentration (P<0.001). CONCLUSION: The present study shows that both total and nonphosphorylated IGFBP-1 concentrations are decreased in obese children and the increased free IGF-I level in obese children is related to the reduced total IGFBP-1 level, but unrelated to the change in the IGFBP-1 phosphorylation status.     

Combining insulin-like growth factor-I and mean spontaneous nighttime growth hormone levels for the diagnosis of growth hormone deficiency.

There is no gold standard for the diagnosis of GH deficiency. Recent data show that spontaneous GH levels may lack sensitivity, and that GH stimulation tests lack specificity as currently performed. Serum insulin-like growth factor-I (IGF-I) measurements lack both sensitivity and specificity. Some of these problems may be explained by nutritional effects. In children, overnutrition decreases GH and increases IGF-I, while undernutrition decreases IGF-I and increases GH. To overcome these difficulties and improve diagnostic accuracy, we combined mean spontaneous nighttime GH levels with IGF-I levels in a statistically based bivariate model. On a two-dimensional plot of mean spontaneous nighttime GH level (in SD units) vs. IGF-I level (in SD units), we defined a new variable, S (sum) score, where S = (1/square root of 2) x (nighttime mean GH SD+IGF-I SD). While IGF-I (SD) and the mean spontaneous nighttime GH (SD) showed a significant correlation with body mass index, the S score was independent of body mass. We, therefore, used the S score to define a new test for GH deficiency. A child failed this bivariate test if his S score was less than -2 SD. We applied this model to 47 normal children and 48 short or slowly growing children (all prepubertal). We measured spontaneous nighttime GH levels and IGF-I levels in all children. In addition, the short children underwent 3 GH stimulation tests. Forty-six of the 47 normal children passed the bivariate test for GH sufficiency. Twenty-three of the 48 short or slowly growing children failed the bivariate test, whereas only 11 children had an abnormally low mean spontaneous nighttime GH measurement alone. Sixteen of 23 children who were GH deficient by the bivariate test were also GH deficient by the stimulation tests. In summary, the bivariate test for GH deficiency appears 1) to be independent of body mass, unlike either IGF-I or GH individually; 2) to identify more children than the mean spontaneous nighttime GH level alone; and 3) to be highly specific in the normal population, unlike stimulation tests.     

The growth hormone and insulin-like growth factor 1 axis in heart failure

Experimental data suggests that growth hormone and IGF-1 have beneficial effects on myocardial function in animal models of heart failure. Preliminary evidence suggests an abnormality in the growth hormone-IGF-1 axis in heart failure with relative growth hormone resistance. Beneficial effects of growth hormone and IGF-1 include vasodilatation, stimulation of cardiac hypertrophy, increase in calcium sensitivity of cardiac myofilaments and prevention of apoptosis. Recently, cardiac cachexia has been shown to be a powerful negative predictive factor in heart failure. Cachectic patients have higher angiotensin II levels. In the rat there is an important interaction between the renin-angiotensin system and IGF-1. Thus, angiotensin II infusion causes weight loss in part through a catabolic effect. This effect results from increased protein degradation. Angiotensin II reduces circulating and skeletal muscle IGF-1 but increases IGF-1 and the IGF-IR expression in cardiac muscle. Preliminary data suggest a potential beneficial effect of growth hormone in heart failure. Further trials are necessary to test the potential beneficial effect of growth hormone and/or IGF-1 in heart failure.     

Alterations in the oxidant-antioxidant status in prepubertal children with growth hormone deficiency: effect of growth hormone replacement therapy

OBJECTIVE: Growth hormone deficiency (GHD) in adults is associated with increased oxidative stress determined by the underlying GH-IGF-1 axis alterations. Despite GHD being a common diagnosis in children with short stature, no data on the oxidant/antioxidant status are available in this age group. This study was designed to detect differences in oxidative stress parameters between prepubertal GH-deficient children and healthy controls. Furthermore, the effect of 12 months of conventional GH replacement (rGH) on oxidant-antioxidant status was evaluated in the GHD group only. PATIENTS: Ten (nine males and one female) prepubertal children (mean age 9.1 +/- 1.3 years) with GHD were recruited and matched for sex and age (9.2 +/- 1.9 years) with 20 healthy controls (18 males and two females). MEASUREMENTS: At study entry, lag phase, an index of susceptibility of low density lipoprotein (LDL) to in vitro oxidation, malondialdehyde (MDA) and vitamin E were measured in all subjects. These parameters were also evaluated in GH-deficient children after 12 months of rGH treatment. RESULTS: The lag phase was significantly decreased in GH-deficient children compared to healthy controls (15.50 +/- 7.4 vs. 43.00 +/- 9.2 min; P = 0.0007), while MDA was significantly increased (1.33 +/- 0.38 vs. 0.46 +/- 0.10 nmol/mg; P = 0.0006). Vitamin E levels were significantly decreased (22.44 +/- 9.57 vs. 35.38 +/- 16.49 micromol/l; P = 0.001). IGF-1 and IGFBP-3 correlated directly to lag phase (r = 0.48; P = 0.01; r = 0.63, P = 0.002, respectively) and to vitamin E (r = 0.59, P = 0.003; r = 0.58, P = 0.006, respectively). By contrast, IGF-1 and IGFBP-3 correlated indirectly to MDA (r = -0.47, P = 0.01; r =-0.65, P = 0.002, respectively). After 1 year of rGH therapy, lag phase (39.32 +/- 15.24 min; P = 0.005) and vitamin E (34.9 +/- 7.7 micromol/l; P = 0.005) increased significantly, while MDA decreased significantly (0.71 +/- 0.42 nmol/mg; P = 0.005), reaching normal levels. CONCLUSIONS: These data show that children with GHD have substantially increased oxidative stress parameters compared to healthy controls and demonstrate a normalization of these parameters after 1 year of rGH therapy.     

The insulin-like growth factor-I response to growth hormone is increased in prepubertal children with obesity and tall stature

CONTEXT: Children with obesity [body mass index (BMI) > +2 sd score (SDS)] and children with constitutional tall stature [CTS; height > +2 SDS)] have normal-high serum IGF-I levels, associated with a low and broad range of GH secretion, respectively. This suggests increased sensitivity to GH, whereas children with idiopathic short stature (ISS; height < -2 SDS) are believed to have decreased GH sensitivity. OBJECTIVE, DESIGN, AND MAIN OUTCOME MEASURE: To compare the responsiveness to GH in 62 prepubertal children (43 females, 19 males) with obesity, CTS, or ISS and 26 controls (15 females, 11 males; height and BMI -2 to +2 SDS), we used an IGF-I generation test and studied the IGF-I concentration 24 h after a single injection of GH (2 mg/m2). PATIENTS: Twenty patients with obesity, 20 with CTS, 22 with ISS, and 26 controls were studied. The mean age was 8.3 +/- 2.9 yr, with no difference in age or gender between groups. RESULTS: Compared with controls, the mean IGF-I increment was 80% higher in obese children and 36% higher in tall children (P < 0.05 obese or tall vs. control children; P = 0.05 obese vs. tall children). Conversely, the IGF-I increment was similar in short compared with control children, despite a mean baseline IGF-I 62% lower in short children (P < 0.05 vs. controls). In all groups, the IGF-I increment was correlated with the BMI SDS or the fat mass percentage (r = 0.51-0.58, P < 0.05). CONCLUSION: Obese children tend to have greater GH responsiveness than tall children, and both have greater GH responsiveness than controls. GH responsiveness was similar in controls and short children, despite a lower baseline IGF-I in short children. Whether the differences in the IGF-I response to GH between these children reflect differences in the respective anabolic (growth promotion) and metabolic (i.e. insulin action modulation) roles of circulating IGF-I is unknown.     

Growth hormone and insulin-like growth factor regulate insulin-like growth factor-binding protein-1 in Laron type dwarfism, growth hormone deficiency and constitutional short stature.

Insulin-like growth factors (IGFs) mediate the effects of growth hormone (GH), and the insulin-like growth factor-binding proteins (IGFBPs) modulate the actions of IGFs in tissues. We studied the circulating levels of IGFBP-1 in 6 children and 9 adults with Laron type dwarfism (LTD), in 11 children and 21 adults with growth hormone deficiency (GHD), and in 8 children with constitutional short stature. Compared with the situation in healthy children, the basal serum IGFBP-1 concentration was 5.4-fold higher in LTD children, 4.1-fold higher in GHD children, and 3.8-fold higher in children with short stature (p < 0.02 vs controls in all groups). In adult patients with multiple pituitary hormone deficiency (MPHD), the IGFBP-1 concentration was 2-fold elevated, but it was normal in adult LTD patients. Intravenous (N = 10) or subcutaneous (N = 9) administration of IGF-I (75 micrograms.kg-1 and 150 micrograms.kg-1, respectively) in LTD children resulted in a rapid 50-60% fall in serum insulin (p < 0.02), a decline in blood glucose and a concomitant 40-60% rise of IGFBP-1 levels (p < 0.05). Treatment for seven days with IGF-I (150 micrograms.kg-1 x d-1) resulted in a decrease by 34% and 44% of serum IGFBP-1 level in two out of three children with LTD. After prolonged GH therapy, the IGFBP-1 level fell in GHD children by 29% (p < 0.05), in GHD adults by 52% (p < 0.02) and in children with constitutional short stature by 17% (p < 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)     

Seasonality of growth response to GH therapy in prepubertal children with idiopathic growth hormone deficiency

OBJECTIVE: Longitudinal growth of children exhibits seasonal variation. In both healthy children and in children with growth hormone (GH) deficiency (GHD) receiving GH therapy, growth rate is maximal during spring and summer. In the present study, we analyzed the growth response to GH therapy in children with GHD as a function of the season when therapy was started. SUBJECTS AND METHODS: Anthropometric measurements and biochemical analyses of GH secretion status and bone formation were longitudinally assessed in a cohort of 52 prepubertal children with GHD (14 girls, mean age 7.6 years) who were treated with a fixed dose of GH (0.025 mg/kg/day). RESULTS: Auxological assessments over the 2-year observation period revealed a significantly better growth response to GH therapy in children who started therapy between the spring and summer (group 1) compared with children who started in the autumn or winter (group 2). The difference was largest in the initial 3-month treatment period (35%; P<0.01). The initial better gain in height of group 1 was sustained during the study period. Baseline peak GH levels during stimulation tests and insuin-like growth factor-I levels did not differ between the two groups. However, group 1 had significantly higher bone resorption and formation markers, either at the start or shortly after initiation of GH treatment. This suggests that children with GHD have higher bone turnover during spring and early summer, irrespective of GH therapy. CONCLUSIONS: In summary, this study suggests that the season of GH initiation is a determinant of the initial growth response to GH replacement in prepubertal children with GHD.     

Effects of chronic growth hormone and insulin-like growth factor 1 deficiency on osteoarthritis severity in rat knee joints

OBJECTIVE: To determine the effects of chronic deficiency of growth hormone (GH) and insulin-like growth factor 1 (IGF-1) on osteoarthritis (OA) severity. METHODS: Thirty-five rats were divided into 4 treatment groups at 4 weeks of age: 1 control group (normal GH/IGF-1 levels [heterozygous]) and 3 groups of dwarves with a genetic mutation that results in GH deficiency. The first dwarf group received GH for 64 weeks (GH replete) and the second received GH until 14 weeks of age, followed by saline for 50 weeks (adult-onset GH/IGF-1 deficiency [AO-GHD]). The third dwarf group received saline injections only (lifetime GH deficient [GHD]). Sections of the medial knee joint compartment were graded and measured histologically; data were summarized using factor analysis, and treatment effects were assessed using analysis of variance and adjusting for body weight. RESULTS: Terminal IGF-1 levels and body weights were significantly affected by treatment (P = 0.002 and P < 0.001, respectively). Factor analysis yielded a total of 5 factors, the first 3 of which were not significantly affected by treatment. Factor 4 (weighted by medial tibial plateau articular cartilage width and area) was significantly affected by treatment (P < 0.012), with larger values in the AO-GHD group than in the GHD group (P < 0.05). Factor 5 (weighted primarily by articular cartilage structure and loss of toluidine blue staining scores) also was significantly affected by treatment (P < 0.001), and was significantly lower (less severe lesions) in the GH replete group than in all other treatment groups (P < 0.05). Despite the presence of cartilage lesions, osteophytes and subchondral sclerosis were not observed in GH/IGF-1-deficient animals. CONCLUSION: These results indicate that chronic GH/IGF-1 deficiency causes an increased severity of articular cartilage lesions of OA without the bony lesions normally seen in this disease.     

The bone mineral density in acquired growth hormone deficiency correlates with circulating levels of insulin-like growth factor I.

Insulin-like growth factor I (IGF-I) is an important anabolic factor for osteoblasts in vitro. Low plasma levels of IGF-I have been observed in young men with osteoporosis. In the present study, we have studied bone mineral density (BMD) and the circulating levels of IGF-I and growth hormone (GH) in adults with acquired GH deficiency. BMD was determined by dual-energy x-ray absorptiometry in 17 men and 12 women (age 27-54 years). Spinal BMD was positively correlated with the plasma levels of IGF-I (r = 0.43, P = 0.019), with the median of GH values obtained by repeated sampling at night (r = 0.43, P = 0.0019), and with the peak of GH values during GHRH provocation test (r = 0.49, P = 0.039). The total BMD was positively related to plasma IGF-I and median of GH values, but not to peak GH by GHRH provocation. In a multiple regression analysis model, IGF-I, peak GH by GHRH provocation test and duration of GH deficiency explained 49% of the variation in spinal BMD. As compared to healthy controls, total, but not spinal, bone mass was lower in men with GH deficiency, but no clinical symptoms of osteoporosis were observed. The positive relationships between BMD and circulating IGF-I and other indices of GH secretion suggest that IGF-I has an endocrine effect on bone mass.     

Alcohol suppresses insulin-like growth factor-1 gene expression in prepubertal transgenic female mice overexpressing the bovine growth hormone gene

BACKGROUND: Alcohol (ALC) delays puberty in female rats and alters the development of a normal menstrual pattern in rhesus monkeys. These actions are associated with depressed serum levels of growth hormone (GH), luteinizing hormone and insulin-like growth factor-1 (IGF-1). The mechanism of this ALC-induced depression in IGF-1 is not known, however, could be due to depressed GH and, possibly, to an alteration in the hepatic GH receptor. To assess whether ALC has a direct action at the liver, we used a transgenic mouse model that overexpresses GH, allowing assessment of potential direct actions of ALC on the level of either the GH receptor or the IGF-1-synthesizing machinery within the hepatocyte. METHODS: One group of transgenic mice was fed a liquid diet containing ALC. The second group was pair-fed the companion isocaloric control liquid diet. The third group of transgenic mice was fed Lab Chow and water. The fourth group consisted of normal (nontransgenic) littermates fed Lab Chow and water. Animals received their respective diets for 5 days. Mice were killed during their late juvenile stage of development, and tissues and blood collected and frozen. RESULTS: The ALC-fed transgenic mice showed a decrease (p < 0.01) in hepatic IGF-1a and IGF-1b messenger RNA levels compared with transgenic controls, and this paralleled a decrease (p < 0.01) in serum IGF-1. ALC did not alter the circulating levels of bovine GH held constant by the promotor and did not alter mouse GH receptor protein levels as analyzed by Western blotting. CONCLUSIONS: Using this transgenic animal model that maintains circulating GH in the presence of ALC, we found that the ability of ALC to suppress prepubertal Igf1 gene expression can also occur independently of any alterations in the level of circulating GH. This direct effect on the hepatocyte is a postreceptor event because the GH receptor protein levels were not altered by ALC exposure.     

Time dependent impact of perinatal hypoxia on growth hormone,insulin-like growth factor 1 and insulin-like growth factor binding protein-3

Hypoxic-ischemia (HI) is a widely used animal model to mimic the preterm or perinatal sublethal hypoxia, including hypoxic-ischemic encephalopathy. It causes diffuse neurodegeneration in the brain and results in mental retardation, hyperactivity, cerebral palsy, epilepsy and neuroendocrine disturbances. Herein, we examined acute and subacute correlations between neuronal degeneration and serum growth factor changes, including growth hormone (GH), insulin-like growth factor 1 (IGF-1) and insulin-like growth factor binding protein-3 (IGFBP-3) after hypoxic-ischemia (HI) in neonatal rats. In the acute phase of hypoxia, brain volume was increased significantly as compared with control animals, which was associated with reduced GH and IGF-1 secretions. Reduced neuronal survival and increased DNA fragmentation were also noticed in these animals. However, in the subacute phase of hypoxia, neuronal survival and brain volume were significantly decreased, accompanied by increased apoptotic cell death in the hippocampus and cortex. Serum GH, IGF-1, and IGFBP-3 levels were significantly reduced in the subacute phase of HI. Significant retardation in the brain and body development were noted in the subacute phase of hypoxia. Here, we provide evidence that serum levels of growth-hormone and factors were decreased in the acute and subacute phase of hypoxia, which was associated with increased DNA fragmentation and decreased neuronal survival.     

Long-term treatment with recombinant insulin-like growth factor (IGF)-I in children with severe IGF-I deficiency due to growth hormone insensitivity

CONTEXT: Children with severe IGF-I deficiency due to congenital or acquired defects in GH action have short stature that cannot be remedied by GH treatment. OBJECTIVES: The objective of the study was to examine the long-term efficacy and safety of recombinant human IGF-I (rhIGF-I) therapy for short children with severe IGF-I deficiency. DESIGN: Seventy-six children with IGF-I deficiency due to GH insensitivity were treated with rhIGF-I for up to 12 yr under a predominantly open-label design. SETTING: The study was conducted at general clinical research centers and with collaborating endocrinologists. SUBJECTS: Entry criteria included: age older than 2 yr, sd scores for height and circulating IGF-I concentration less than -2 for age and sex, and evidence of resistance to GH. INTERVENTION: rhIGF-I was administered sc in doses between 60 and 120 microg/kg twice daily. MAIN OUTCOME MEASURES: Height velocity, skeletal maturation, and adverse events were measured. RESULTS: Height velocity increased from 2.8 cm/yr on average at baseline to 8.0 cm/yr during the first year of treatment (P < 0.0001) and was dependent on the dose administered. Height velocities were lower during subsequent years but remained above baseline for up to 8 yr. The most common adverse event was hypoglycemia, which was observed both before and during therapy. It was reported by 49% of treated subjects. The next most common adverse events were injection site lipohypertrophy (32%) and tonsillar/adenoidal hypertrophy (22%). CONCLUSIONS: Treatment with rhIGF-I stimulates linear growth in children with severe IGF-I deficiency due to GH insensitivity. Adverse events are common but are rarely of sufficient severity to interrupt or modify treatment.     

The effect of growth hormone on the insulin-like growth factor system during fasting

The present study investigates the possible stimulatory effect of endogenous GH on IGF and IGF-binding protein (IGFBP) levels during fasting. Eight normal subjects were examined on four occasions: 1) in the basal postabsorptive state; 2) after 40 h of fasting; 3) after 40 h of fasting with somatostatin suppression of GH; and 4) after 40 h of fasting with suppression of GH and exogenous GH replacement. The two somatostatin experiments were identical in terms of hormone replacement (except for GH). Short-term fasting led to a 50% reduction in free IGF-I. The reduction in free IGF-I was paralleled by an increase in IGFBP-1, an increase in the complex formation of IGFBP-1 and IGF-I, and a modest reduction in IGFBP-3 proteolysis. GH deprivation during fasting led to a 35% reduction in total IGF-I and a 70% reduction in free IGF-I. GH replacement increased free and total IGF-I to levels similar to those observed during plain fasting and decreased IGFBP-1, however, without affecting IGFBP-1-bound IGF-I. Finally, IGFBP-3 proteolysis was slightly increased by GH replacement. In conclusion, the major new finding of the present study is that the GH hypersecretion seen during short-term fasting is not merely secondary to a reduction in IGF bioactivity.     

The intrahepatic biliary epithelium is a target of the growth hormone/insulin-like growth factor 1 axis

BACKGROUND/AIMS: We evaluated the role and mechanisms by which the GH/IGF1 axis modulates cholangiocyte proliferation. METHODS: GH-receptors (GH-R), IGF1, IGFBP3 (binding protein 3), IGF1-R and receptor substrates (IRS) were evaluated in cholangiocytes of normal or bile duct-ligated (BDL) rat livers. The effects of GH and IGF1 on proliferation of normal quiescent cholangiocytes and the transduction pathways involved were investigated. RESULTS: IGF1, GH-R, IGF1-R, IRS-1/2 were expressed in normal cholangiocytes and overexpressed in cholangiocytes proliferating after BDL which also secrete IGF1 in a higher amount than normal cells. IGFBP3, which may counter-regulate IGF1 effects, was decreased in BDL cholangiocytes. IGF1 promoted cholangiocyte proliferation in association with overexpression of p-IGF1R, IRS1, IRS-2, p-ERK1/2 and p-AKT. GH induced IGF1 expression and release in isolated cholangiocytes, and reproduced the effects of IGF1 but GH effects were abolished by IGF1-R blocking antibody, suggesting IGF1 as a mediator of GH. Finally, IGF1 and 17beta-estradiol reciprocally potentiated their proliferative effects on cholangiocytes, and by interacting at both receptor and post-receptor levels. CONCLUSIONS: Cholangiocytes respond to GH with production and release of IGF1 that modulates cell proliferation by transduction pathways involving IGF1-R, IRS1/2 and both ERK and PI3-kinase pathways. The biliary epithelium is a target of GH/IGF1 liver axis.     

Short-term changes in growth and urinary growth hormone, insulin-like growth factor-I and markers of bone turnover excretion in healthy prepubertal children.

Childhood growth is a non-linear process. To assess whether there is a biochemical correlate of non-linear growth, we have measured free pyridinoline (fPYR) and deoxypyridinoline (fDPYR) excretion in seven healthy prepubertal children, aged 6.1-7.7 years. To examine the link between short-term growth and hormone output, urinary growth hormone (uGH) and insulin-like growth factor-I (uIGF-I) were also measured. Height and weight were measured and a timed overnight urine was collected three times per week from September to July, with results expressed as a weekly change in height (Dheight(w)) or weight (Dweight(w)), and as weekly average hormone or bone marker excretion (uGH(w), uIGF-I(w), fPYR(w), fDPYR(w)). Subject specific SD scores (SDS) were derived for each variable.Dheight(w)and Dweight(w)did not correlate to uGH(w), uIGF-I(w), fPYR(w)or fDPYR(w). Dheight(w)SDS was weakly but significantly correlated to fPYR(w)SDS (r = +0.16;P<0.05) and fDPYR(w)SDS (r = +0.15;P<0.05). The percentage of high frequency (2-4 weeks) variation in uGH(w)excretion, as defined by time series analysis, was correlated with the mean uIGF-I(w)(r = +0.81;P<0.05), which in turn was significantly reduced (92 +/- 38 vs 120 +/- 47 ng;P<0.001) during periods of slow growth (Dheight(w)< 0.05 cm/week).We conclude that in normal children the amount of urinary fPYR, fDPYR, GH and IGF-I does not provide a direct biochemical correlate of growth from week to week. However good growth is associated with a relative increase in fPYR and fDPYR excretion, while poor growth is associated with reduced IGF-I excretion, which in turn is influenced by the temporal secretory pattern of GH over 2-4 weeks.