Serum GH-binding Protein Levels Research Articles

Associations of GHR, IGF-1 and IGFBP-3 expression in adipose tissue cells with obesity-related alterations in corresponding circulating levels and adipose tissue function in children

Components of the growth hormone (GH) axis, such as insulin-like growth factor-1 (IGF-1), IGF-1 binding protein-3 (IGFBP-3), GH receptor (GHR) and GH-binding protein (GHBP) regulate growth and metabolic pathways. Using our Leipzig Adipose Tissue (AT) Childhood Cohort and Leipzig Atherobesity Childhood Cohort (n=306), we asked if serum levels of these factors are altered with overweight/obesity and if this is related to gene expression of these factors in AT cells and/or increased fat mass in childhood obesity. Furthermore, we hypothesized that gene expression of GHR, IGF-1 and IGFBP-3 in AT is associated with overweight/obesity and AT function in children. Serum GHBP levels were increased in children with overweight/obesity throughout childhood, while for IGF-1 levels and the IGF-1/IGFBP-3 molar ratio this obesity-related elevation was only detectable until early puberty. Circulating levels did not correlate with gene expression of these factors in AT cells, which was decreased with overweight/obesity. Independent from body mass index, gene expression of GHR, IGF-1 and IGFBP-3 in AT cells was related to parameters of AT dysfunction, such as adipocyte hypertrophy, and increased insulin levels. Serum GHBP was associated with the percentage of liver fat and transaminase levels. We conclude that the obesity-related elevations in serum GHBP and IGF-1 are unlikely to be caused by increased subcutaneous AT mass and elevations in serum GHBP are more closely related to liver status in children. The diminished gene expression of these factors in AT cells with childhood obesity may contribute to early AT dysfunction and a deterioration of the metabolic state.

A Novel GHR Intronic Variant, c.266+83G>T, Activates a Cryptic 5′ Splice Site Causing Severe GHR Deficiency and Classical GH Insensitivity Syndrome

Background/Aims: Mutations in the human growth hormone receptor gene (GHR) are the most common cause of growth hormone insensitivity (GHI) syndrome and insulin-like growth factor (IGF-1) deficiency. The extracellular domain of GHR (encoded by exons 2-7 of the GHR gene) can be proteolytically cleaved to circulate as GH-binding protein (GHBP). Methods: We evaluated the cause of classical GHI (Laron) phenotypes in 3 siblings. Results: Two brothers (aged 16.5 and 14.9 years) and their half-brother (aged 11.3 years) presented with extreme short stature (height standard deviation score, SDS, of -7.05, -6.34 and -8.02, respectively). The parents were consanguineous and of normal stature. Serum GHBP levels of probands were undetectable and circulating IGF-1 and IGF-binding protein-3 were abnormally low, but GH concentrations were elevated. Molecular analysis of the GHR gene revealed homozygous deletion of exon 3, a common polymorphism, and a novel c.266+83G>T variant within intron 4 which generated a 5′ donor splice site. Splicing events from this cryptic 5′ donor site resulted in retention of 81 intronic nucleotides in the GHR mRNA. Long-term rhIGF-1 therapy combined with leuprolide depot increased height by +2 to +3 SDS. Conclusion: The c.266+83G>T is the second intronic GHR mutation identified that activates a cryptic 5′ donor splice site. The abnormal splicing event led to early protein termination and undetectable serum GHBP concentrations.

Circulating Growth Hormone Binding Protein Levels and Mononuclear Cell Growth Hormone Receptor Expression in Uremia

Resistance to growth hormone (GH) in end-stage renal disease (ESRD) causes growth retardation and muscle wasting. In humans, circulating GH binding protein (GHBP), the extracellular domain of the GH receptor that is shed into the circulation and is believed to reflect tissue GH receptor levels, is reduced in uremia and suggests that cellular GH receptor levels are correspondingly reduced. If true, this could be a cause of GH resistance. We set out to establish whether serum GHBP levels reflect cellular GH receptor levels and whether changes in serum GHBP levels are related to nutritional or inflammatory status. GH receptor protein expression in peripheral blood mononuclear cells (PBMC) from 21 ESRD and 14 normal subjects were analyzed by fluorochrome flow cytometry. The GH receptor density and percent total PBMCs expressing the GH receptor were similar in the 2 groups, and there was no difference in percent GH receptor positive T or B cells or monocytes. In contrast, serum GHBP levels were 80% lower in ESRD. GHBP levels did not correlate with serum albumin, body mass index, or muscle mass but seemed to be partly related to the log serum C-reactive protein levels. Serum GHBP levels are markedly reduced in ESRD; this seems to occur independent of nutritional status and may in part be caused by inflammation. Because GH receptor expression on PBMC of ESRD and control subjects was similar, our findings argue against a reduction in GH receptor as a cause of GH resistance and the use of serum GHBP levels as a reliable marker of specific tissue GH receptor levels.

Total Absence of Functional Acid Labile Subunit, Resulting in Severe Insulin-Like Growth Factor Deficiency and Moderate Growth Failure

Primary IGF deficiency (IGFD) describes the condition in which serum concentrations of IGF-I are low in the face of normal to elevated GH production. Because IGF-I, which circulates as part of a ternary complex with IGF binding protein (IGFBP)-3 and acid-labile subunit (ALS), mediates the growth-promoting effects of GH, IGFD is associated with severe growth failure in humans. We investigated a case of IGFD in which serum IGF-I and IGFBP-3 were abnormally low, yet growth failure was modest (-2.1 sd score at 15.5 yr of age). The young male subject, from a consanguineous pedigree, had a postnatal growth profile consistently below the third percentile. The subject had a normal fasting GH level of 3.7 muU/ml and normal serum GH binding protein level (1258 pmol/liter; normal range 431-1892 pmol/liter), but serum IGF-I and IGFBP-3 were profoundly reduced (-5.8 and -7.2 sd score, respectively, at age 12.3 yr), even through puberty. A novel homozygous missense mutation was subsequently identified in the ALS gene, which resulted in severe deficiency of serum ALS (undetectable). ALS is critical for maintaining normal serum concentrations of IGF-I and IGFBP-3, most likely by prolonging the half-lives of both proteins. ALS deficiency can be associated with moderate growth failure, but in this patient, the onset and progression of puberty appear to be normal. Altogether the results support a modest role for the ternary complex in the regulation of stature.

Growth of children with β-thalassemia major

Hypertransfusion and regular chelation therapy have allowed improved survival in patients with thalassemia major (TM). Despite medical advances, growth failure and hypogonadism remain significant clinical problems in these patients in adolescence. Disproportionate truncal shortening which is common especially among adolescents with thalassemia, is due to platyspondyly resulting from a combination of factors like hemosiderosis, desferrioxamine toxicity or deficiency of trace elements. Although growth hormone (GH) deficiency and GH neurosecretory dysfunction have been described in TM patients, most short TM patients have normal GH reserve. The low serum IGF-1 and IGFBP-3 concentrations in TM patients despite having normal GH reserve and serum GH binding protein levels suggest that a state of secondary GH insensitivity exists. The pubertal growth spurt may be impaired in TM patients going through spontaneous or induced puberty and may have a negative effect on final adult height. GH therapy in dosages ranging from 0.5-1.0 IU/kg/wk has resulted in a significant improvement in growth velocity in short TM children without any adverse effects on skeletal maturation, blood pressure, glucose tolerance and serum lipids. There is limited evidence that GH treatment can result in an improved final adult height in short TM children. Careful and regular clinical and biochemical monitoring should be preformed on these patients while they are treated with GH.

Growth hormone binding protein, insulin-like growth factor-I and short stature in two pygmy populations from the Philippines.

The molecular basis and biochemical mediators of genetic growth propensity and adult height achievement in the general population are largely unknown. Pygmies represent one extreme of the height spectrum that may provide important clues regarding this issue. Previous studies in pygmies from Africa and Papua-New Guinea have shown decreased serum levels of growth hormone binding protein (GHBP), the circulating ectodomain of the growth hormone receptor (GHR). By inference, a similar limitation in tissue GHR expression has been assumed to be responsible for the partial growth hormone (GH) resistance observed in African pygmies. It is not clear how generalizable this concept is to other populations. To address this question, we studied two pygmy populations from the Philippines (Aeta and Mamanwa people) that are unrelated to the African pygmies. Serum GHBP and IGF-I levels were significantly decreased in both pygmy populations, compared to normal-statured Philippino controls. The results, together with previous observations in African and New Guinean pygmies, indicate that short stature is associated with low serum GHBP levels in pygmy populations of diverse origins and in different parts of the world. This strengthens the tentative postulate that the GHBP/GHR system plays an important role in the genetic and perhaps nutritional determination of adult stature in humans. Molecular genetic studies of the GHR gene in various pygmy populations may shed further light on the mystery of pygmy short stature.

Anthropometric parameters and their relationship to serum growth hormone-binding protein and leptin levels in children with acute lymphoblastic leukemia: a prospective study.

The aim of this study was to follow auxological parameters and their relationship to serum growth hormone-binding protein (GHBP) and leptin levels in children with acute lymphoblastic leukemia (ALL). In total, 26 prepubertal children with ALL were studied. We report these data at the time of the clinical diagnosis (n=26) and at 6 (n=21), 12 (n=21), 18 (n=21), 24 (n=20), 30 (n=16) and 36 months (n=16) after beginning treatment. Serum GHBP levels decreased during the first 18 months and returned to normal when therapy was withdrawn. Height SDS increased at 24 months after diagnosis. Weight and the upper arm circumference had increased 6 months after chemotherapy withdrawal, whereas tricipital and subscapular skinfolds had increased both at 6 months after diagnosis and 6 months after therapy had stopped. Therefore, the tendency to become overweight is both an early and a late side-effect of anti-leukemia therapy. A significant positive correlation was found between serum leptin levels and every nutritional anthropometric parameter, with body mass index having the best relationship. However, serum GHBP levels were only correlated with BMI at the end of the study. No correlation was found between leptin and GHBP. In children with ALL, linear growth is compromised during the acute phase of their illness and therapy; this is probably secondary to a state of partial and transient GH insensitivity. These patients tend to become obese after therapy withdrawal, with leptin being an excellent nutritional marker.

Clinical review 112: Does serum growth hormone (GH) binding protein reflect human GH receptor function?

Previous observations raised the possibility that circulating GH-binding protein (GHBP) may serve as a useful index for tissue GH receptor (GHR) responsiveness in humans. Indeed, there are many examples to indicate that across a wide scope of comparative studies, ontogenic data, experimental systems, physiological conditions, nutritional states, and diseases there is a close relationship between the concentration of GHR and the level of serum GHBP. In the present review, we discuss various aspects that might affect differentially cellular GHR and circulating GHBP, based on species and tissue divergence, regulation of cell-surface GHR turnover, GHR cleavage mechanism, GHR mRNA splicing, and GH insensitivity (GHI) syndrome patients with normal or high serum GHBP levels. Most previous experimental data were collected through comparative analysis of human GHBP against GHR and GHBP determinations in animal models. Yet, GHBPs possess species-specific properties, and the mechanism for their generation and regulation display evolutionary divergence. Another important aspect is tissue divergence, in terms of GHR regulation and its cleavage to GHBP. Although GHBP is generated mainly from the liver GHR, many other tissues express GHRs and probably also contribute to the total GHBP level. Human GHBP is generated by proteolytic cleavage of GHR at the cell-surface and, thus, occupancy or modulation of GHR turnover/internalization would impact the level of cell-surface GHR that are available for proteolysis. An additional degree of complexity arises from recent reports, implicating a protein kinase C-regulated metalloprotease activity in GHBP generation. This suggests that the proteolytic system, which controls the specific cleavage mechanism and switch between GHR proteolysis and GHBP shedding, is a regulated process. Finally, differential splicing regulation to the full-length, active human GHR (hGHR) and the inactive truncated hGHRtr isoform messenger RNA transcripts might regulate both the production of GHBP and GHR bioactivity, as hGHRtr generates large amounts of GHBP but has a dominant negative effect on GH signaling. Several clinical GH-resistant conditions, such as liver cirrhosis, renal insufficiency, insulin-dependent diabetes mellitus, hypothyroidism, malnutrition, or critical illness are associated with reduced GHBP levels. However, this is not universally true, as in other conditions (e.g. early childhood, acromegaly) decreased GHBP levels are not associated with GHI. Divergence between serum GHBP and insulin-like growth factor I, such as which occur during puberty or obesity, also questions whether GHBP levels reflect GHR function. Even in patients with GHI syndrome, serum GHBP cannot be relied on to detect all GHR mutations. The correct assessment of GHR expression and GH functionality in an individual patient will require, in parallel to measurements of serum GHBP, additional detailed diagnostic screening of the entire GH-insulin-like growth factor I axis.

EFFECTS OF EXERCISE AND GROWTH HORMONE-RELEASING PEPTIDE-6 ON GROWTH HORMONE-BINDING PROTEIN

1090 Assuming that circulating high affinity growth hormone-binding protein (GHBP) reflects tissue GH-receptor activation, we hypothesize that acute massive increases in serum GH stimulate the proteolytic cleavage of the extracellular part of the GH-receptor and subsequently, increases circulating GHBP. Aim of this study was to investigate whether serum GHBP levels increase following acute massive increments of GH, induced by the combined administration of exercise plus the potent GH secretagogue GH Releasing Peptide-6 (EX+GHRP-6). In six healthy, male subjects (age: 22.4±2.8 yr; BMI: 22.8±2.5 kg/m2; V̇O2max: 65.2±6.3 ml/kg/min; mean±SD) responses of serum GH (IRMA) and GHBP (FPLC gel chromatography) were analysed. EX was performed on a cycle ergometer with a stepwisely increased workload protocol with a duration of 20 min up to exhaustion. Blood was sampled at the start of the test (t=0) and 25, 60, 90 and 120 min therafter. GHRP-6 (100 μg,iv) was administered immediately before t=0. In addition, control experiments were performed with EX alone and GHRP-6 alone. GH values (median and (range) after EX+GHRP-6 increased from 0.4 (0.1-9.8) mU/l at t=0, to 145 (99-357) at t=25 (Kruskal-Wallis test, p<0.001), whereas at t=120 the value was 35 (8-180), still above baseline level. This response appeared to be synergistic, as compared to the arithmetic sum of the responses to EX alone and GHRP-6 alone. Taking into account interference of high GH levels (>300 mU/l) with the GHBP assay, the baseline GHBP level (915 (850-1125) pmol/l) showed no significant change during the test period (p=0.13). These results indicate that acute massive increases in serum GH levels do not influence circulating GHBP. Thus, proteolytic cleavage of the extracellular part of the GH-receptor seems to be independent of acute changes in the GH secretory status. The unchanged circulating level of GHBP is in line with the observation that acute exercise, resulting in GH increments upto about 100 mU/l, does not alter circulating GHBP levels.

Functional characterization of truncated growth hormone (GH) receptor-(1-277) causing partial GH insensitivity syndrome with high GH-binding protein.

We have previously reported a novel heterozygous donor splice site mutation in intron 9 of the GH receptor (GHR) gene in Japanese siblings who showed partial GH insensitivity and high serum GH-binding protein (GHBP) levels. This mutation caused the splicing abnormality and produced the truncated GHR consisting of 277 amino acids (GHR-277), which lacked most of the intracellular domain of GHR, including both boxes 1 and 2. In this study, we have characterized the function of GHR-277 expression in COS-7 and CHO cells in vitro. Scatchard analysis revealed that GHR-277 possessed approximately 1.5 times higher affinity to GH and twice the number of binding sites compared to wild-type full-length GHR (GHR-fl). The GHBP level in culture medium of GHR-277-expressing cells was approximately 3 times higher than that in GHR-fl-expressing cells. Interestingly, the ligand-induced internalization of GHR-277 was significantly reduced compared with that of GHR-fl. Moreover, in GH-induced tyrosine phosphorylation of signal transducer and activator of transcription-5 (STAT5), GHR-277 exerted a dominant negative effect when GHR-277 and GHR-fl were cotransfected. These in vitro data would well explain the clinical characteristics in our patients showing high serum GHBP levels and development of short stature despite a heterozygous mutation of the GHR gene.

Serum growth hormone (GH) binding protein, IGF-I and IGFBP-3 in patients with beta-thalassaemia major and the effect of GH treatment.

Levels of IGFI have been shown to be low in transfusion-dependent thalassaemia and there is preliminary evidence to suggest that this may be reversed by GH treatment. In this further study we have evaluated serum growth hormone (GH) binding protein (GHBP), IGF-I and IGFBP-3 in patients with beta-thalassaemia major and the effects of GH treatment on these various parameters. Fifty-six transfusion dependent patients with beta-thalassaemia major without GH deficiency between 2 and 20 years of age were studied. Thirteen non-GH deficient patients with heights of -1.5 SD or more were treated with GH at a dose of 0.14 IU/kg/day subcutaneously for 1 year. Serum GHBP, IGF-I and IGFBP-3 were measured in all the patients. In the 13 patients treated with GH, these serum parameters were measured before and after 3, 6 and 12 months of treatment. The mean serum GHBP concentrations were normal in both prepubertal and pubertal children but the serum IGF-I and IGFBP-3 concentrations were low throughout childhood and adolescence. There was a significant correlation between serum IGF-I and IGFBP-3 concentrations (r = 0.79; P = 0.0001) but there was no correlation between the height SDS of the patients with serum GHBP, IGF-I or IGFBP-3 levels. GH treatment in the 13 patients resulted in significant growth acceleration associated with a significant rise in the serum IGF-I and IGFBP-3 and a significant fall in serum GHBP concentrations. The low serum concentrations of IGF-I and IGFBP-3 in the presence of normal GH reserve and serum GHBP concentrations in patients with beta-thalassaemia suggest a state of partial GH insensitivity at the post-receptor level. This partial GH insensitivity state can be overcome by supraphysiological doses of exogenous GH. The lack of correlation of IGF-I, IGFBP-3 and GHBP with height SDS of the patients imply that the growth failure commonly observed in patients with beta-thalassaemia major may not be specifically related to dysregulation of the GH-IGF-I axis. GH therapy resulted in significant increase in serum IGF-I and IGFBP-3 but a significant fall in GHBP.

Serum concentrations of insulin, insulin-like growth factor(IGF)-I, IGF binding protein (IGFBP)-1 and -3 and growth hormone binding protein in obese children: fasting IGFBP-1 is suppressed in normoinsulinaemic obese children.

Simple obesity is characterized by normal or accelerated growth in the presence of reduced serum levels of GH, whereas its detailed mechanism remains unknown. We, therefore, evaluated interrelationships among serum levels of insulin, IFG-I, IGF binding protein (IGFBP)-1 and -3 and growth hormone binding protein (GHBP) in prepubertal obese children. Prepubertal 20 obese children and 20 age-matched control children were included in the study. Serum levels of insulin, IGF-I and IGFBP-3 in obese children did not differ from those in controls. The serum level of IGFBP-1 was significantly lower in obese children (22.1 +/- 18.4 micrograms/l, P < 0.001) than in control children (76.0 +/- 62.9 micrograms/l). No relationship was found between the serum levels of insulin and IGF-I, IGFBP-1, or IGFBP-3 in obese subjects. The serum level of GHBP in obese children was significantly elevated as compared with that in controls and was positively correlated with body mass index (BMI). No relationship was found between the serum levels of GHBP and IGF-I in obese subjects. The present study showed for the first time that the fasting IGFBP-1 level was suppressed in prepubertal obese children with fasting normoinsulinaemia. We speculate that the hyperinsulinaemia which cannot be detected in the fasting state may have suppressed hepatic production of IGFBP-1. Alternatively, the reduced IGFBP-1 is likely to be a compensatory response to impaired insulin sensitivity. Thus, the IGFBP-1 level may be a useful predictor for the early identification in the development of insulin resistance in prepubertal obese children.

Increased serum GHBP levels in obese pubertal children and adolescents: relationship to body composition, leptin and indicators of metabolic disturbances.

The serum concentration of the high-affinity growth hormone-binding protein (GHBP) is increased in obesity but the mechanisms are poorly understood. This study assessed the physiological mechanisms involved in the regulation of GHBP in adiposity. We tested a number of obesity specific parameters for their association with GHBP. In this study, 199 normal or overweight children and adolescents (101 boys, 98 girls, aged (mean +/- s.d.): 13.7 +/- 2.3 y) underwent an anthropometric evaluation (circumference measurements and bioimpedance analysis) combined with blood withdrawal for the measurement of insulin-like growth factor-I (IGF-I), insulin, leptin and GHBP (by specific RIA), uric acid, triglycerides and cholesterol. By linear regression analysis GHBP correlated significantly (P < 0.001) with percent body fat mass (r = 0.71), waist (r = 0.73) and hip (r = 0.69) circumference, weight (r = 0.61) waist hip ratio (WHR) (r = 0.54), as well as with the serum concentrations of leptin (r = 0.64), uric acid (r = 0.54), insulin (r = 0.45), LDL-cholesterol (r = 0.43), cholesterol (r =0.33), LDL/HDL ratio (r = 0.47), triglycerides (r = 0.30) and with height standard deviations scores (SDS) (r = 0.23). Age, gender and pubertal stage had no impact on GHBP. In a multiple regression analysis containing age and gender, as well as the anthropometric variables, percent fat mass and waist circumference, as independent variables, associations between GHBP and leptin (P < 0.001), cholesterol (P < 0.01), LDL-cholesterol (P = 0.01), LDL/HDL ratio (P = 0.02), triglycerides (P = 0.01) remained significant. In a final model using the stepwise analysis involving age, gender and all the independent predictors of GHBP, waist circumference (P < 0.001), accounted for 49.5% of the 60.0% total variability in GHBP, while the implication of leptin (P < 0.001), age (P < 0.01) and cholesterol (P < 0.05) increased the predicted variability for 7.5%, 1.9%, and 1.0%, respectively. Serum GHBP was significantly reduced in a subgroup of 104 overweight or obese patients during a diet-induced weight loss programme, the coefficient of correlation between GHBP and leptin after (r = 0.45, P < 0.001) and before weight reduction (r = 0.41, P < 0.001) were comparable. Waist circumference, an indicator of abdominal body fat mass, is a major determinant of GHBP levels during childhood, while leptin may be one candidate for a signal linking adipocytes to the growth hormone receptor related GHBP release. Additionally, elevated serum levels of GHBP may reflect metabolic disturbances of adiposity.

Multiple endocrine abnormalities of the growth hormone and insulin-like growth factor axis in prepubertal children with exogenous obesity: effect of short- and long-term weight reduction.

We have studied the GH-insulin-like growth factor (IGF) axis in prepubertal children with exogenous obesity at the time of clinical diagnosis and at two time points during weight reduction on a calorie-restricted diet. Spontaneous GH secretion, IGF-I, free IGF-I (fIGF-I), IGF-II, their binding proteins (IGFBP-1, IGFBP-2, and IGFBP-3), and GH-binding protein (GHBP) values at the time of clinical diagnosis (n = 65), after a 25% decrease in the body mass index (BMI) expressed as the SD score (BMI SD score; n = 29), and after a diminution of at least 50% of the initial BMI SD score (n = 9) are reported. GH secretion was significantly reduced at diagnosis, and after a decrease of at least 25% in the initial BMI SD score, it returned to normal in all patients. Total IGF-I levels were not significantly different from those in controls at any point. In contrast, fIGF-1 and IGF-II levels were significantly increased, both at diagnosis and after BMI SD score reduction. Obese patients were hyperinsulinemic at diagnosis and remained so even after a 50% reduction of their BMI SD score. Serum IGFBP-1 and IGFBP-2 levels were significantly decreased at diagnosis and at the two points studied during weight reduction. Serum IGFBP-3 and GHBP levels were increased significantly at diagnosis and returned to normal levels after a reduction in the BMI SD score. A positive correlation between serum GHBP levels and BMI was found in both controls and obese patients. Serum IGFBP-3 levels correlated positively with IGF-I, fIGF-I, and IGF-II in all groups, but these correlations were weaker in the obese patients at diagnosis. IGFBP-2 correlated significantly with IGF-II only in the obese group at diagnosis (r = -0.760; P < 0.0001), but with fIGF-I in all groups. IGFBP-1 was negatively correlated with IGF-I and fIGF-I in all groups. In conclusion, the GH-IGF axis is dramatically altered in patients with exogenous obesity. However, most changes in the peripheral IGF system appear to be independent of the modifications in GH secretion. In addition, in contrast to current thought, not all of the observed abnormalities are reversed with a significant reduction in the BMI SD score.

Multiple endocrine abnormalities of the growth hormone and insulin-like growth factor axis in patients with anorexia nervosa: effect of short- and long-term weight recuperation.

We have studied the GH-insulin-like growth factor (IGF) axis in patients with anorexia nervosa at the time of diagnosis and at two points during weight recuperation. We report their spontaneous GH secretion and IGF-I, free IGF-I (fIGF-I), IGF-II, the IGF-binding proteins (IGFBP-1, IGFBP-2, and IGFBP-3), and GH-binding protein (GHBP) levels at the time of the clinical diagnosis (n = 50) and after recuperation of between 6-8% (n = 42) and 10% or less of the initial weight (n = 20). Two distinct groups were seen, those who significantly hypersecreted GH and those whose GH secretion was reduced significantly. After recuperation of 10% or more of their initial weight, all patients had a normal GH pattern. Independently of GH secretory dynamics, IGF-1, IGFBP-3, and GHBP serum levels were all significantly decreased at diagnosis, and only GHBP returned to normal after weight recuperation. Serum IGFBP-1 and IGFBP-2 levels were significantly increased at the time of diagnosis and decreased after weight recuperation. The body mass index (BMI) correlated positively with fIGF-I levels and negatively with IGFBP-1 and IGFBP-2 levels, but only after weight recuperation in all cases. Contrary to what is seen in normal individuals, no correlation was found between BMI and serum GHBP levels in anorexia nervosa patients. Serum IGFBP-2 levels had a strong negative correlation with fIGF-I, IGF-II, and the sum of IGF-I and IGF-II, but only at the time of diagnosis. In conclusion, the GH-IGF axis is dramatically altered in patients with anorexia nervosa. Changes in the peripheral IGF system however, appear to be independent of modifications in GH secretion and, in contrast to current thought, not all of the observed abnormalities are rapidly reversed with weight recuperation.

Reduced concentration of serum growth hormone (GH)-binding protein in children with chronic renal failure: correlation with GH insensitivity. The European Study Group for Nutritional Treatment of Chronic Renal Failure in Childhood. The German Study Group for Growth Hormone Treatment in Chronic Renal Failure.

Growth retardation in children with chronic renal failure (CRF) despite normal or elevated GH levels indicates a peripheral insensitivity to the action of GH. One possible molecular mechanism is a reduced density of GH receptors in GH target organs. In humans, the circulating high affinity GH binding protein (GHBP) is thought to reflect GH receptor expression, because it is derived from the extra-cellular domain of the GH receptor by proteolytic cleavage. We, therefore, analyzed serum GHBP levels by ligand-mediated immunofunctional assay in 126 children with CRF compared to reference values obtained by analysis of 773 healthy children. In 77% of CRF patients, serum GHBP concentrations were below the mean for age- and gender-matched controls. The decrease in serum GHBP levels was related to the degree of renal dysfunction. In advanced CRF (glomerular filtration rate, < 35 mL/min.1.73 m2), mean age- and gender-adjusted GHBP levels were -1.40 +/- 0.18 SD score; 36% of patients had GHBP levels below the normal range (< -2 SD score). Children with end-stage renal disease (n = 26) had the lowest GHBP levels (-2.25 +/- 0.22 SD score). Multiple linear regression analysis revealed that body mass index, rather than glomerular filtration rate, is the prevailing determinant of serum GHBP levels in CRF. GHBP levels correlated with both the spontaneous growth rate ( r = 0.44; P < 0.0001) and the growth response to GH therapy (r = 0.48; P < 0.005), indicating decreased sensitivity to both endogenous and exogenous GH. Subcutaneous GH therapy did not consistently affect serum GHBP levels after 3 months of treatment. It is suggested that low GHBP levels in children with CRF represent a quantitative tissue GH receptor deficiency as one of the molecular mechanisms of GH insensitivity.

High-affinity growth hormone binding protein, insulin-like growth factor I and insulin-like growth factor binding protein 3 in adults with growth hormone deficiency.

The high-affinity growth hormone binding protein (GHBP) circulates in human blood and represents the extracellular domain of the growth hormone (GH) receptor. The effects of GH deficiency on GHBP in adults are not clear. The aim of this study was to evaluate serum GHBP levels in adults with GH deficiency and to assess whether GHBP measurement may contribute to the diagnosis of adult GH deficiency, based on a two-step model. We measured insulin-like growth factor I (IGF-I), IGF binding protein 3 (IGFBP-3) and GHBP levels in serum samples of 36 patients with adult-onset GH deficiency. The GHBP levels were measured by FPLC size-exclusion chromatography; IGF-I and IGFBP-3 levels were measured by RIA. Serum GHBP levels were elevated above the upper limit of the 95% confidence interval in 26 patients, whereas IGF-I and IGFBP-3 levels were low in 10 patients and in 16 patients, respectively. The combination of low serum IGF-I and low IGFBP-3 levels was found in 10 patients. In nine patients, serum IGF-I levels were low, with elevated GHBP levels. Low serum IGF-I, low IGFBP-3 and elevated GHBP levels were found in five patients. Only four out of 36 patients had serum IGF-I, IGFBP-3 and GHBP levels that were within the 95% confidence interval of the control values. We conclude that adults with acquired GH deficiency have elevated GHBP levels in comparison to healthy subjects. We suggest that measurement of GHBP levels might contribute to the diagnosis of adult GH deficiency, though further research is required to study the additional value of GHBP measurements.

Serum Growth-Hormone-Binding Protein and Growth during Treatment of Children with Hyperthyroidism and Hypotyroidism

Thyroid hormone greatly influences postnatal growth in children and secretion of growth hormone (GH). To study the relation between serum GH-binding protein (GHBP), which is expressed as tissue GH-receptor concentrations and influenced by the nutritional state, thyroid hormone and growth development, we measured serum GHBP in six children with hyperthyoidism and six children with hypothyroidism using samples taken before and during treatment. Mean treatment periods of these diseases are 13 and 10 months, respectively. Mean height velocity standard deviation (SD) score decreased from 2.51 to -0.62, but was not significantly related to the treatment, in hyperthyroidism, and significantly increased from -3.02 to 5.27 due to the treatment in hypothyroidism. There was no significant difference of GHBP levels before the treatment between hyper- and hypothyroidism (mean 9.59 vs. 8.53ng/mL). In hyperthyroidism, GHBP levels decreased significantly during the treatment. In hypothyroidism, insulin-like growth factor I (IGF-I) and IGF binding protein-3 (IGFBP-3) increased, but percent overweight decreased significantly, and GHBP levels did not significantly change during the treatment.ΔGHBP was defined as the change in GHBP during treatment to examine whether or not the change in GHBP was parallel to the change in thyroid hormone. ΔGHBP showed no correlation with Δ height velocity SD score. ΔGHBP showed a significant positive correlation with ΔT4 level and negative correlation with Δpercent overweight. However, only ΔT4 was identified as an influencing factor on ΔGHBP by stepwise multiple regression analysis.The data demonstrate that the changes in serum GHBP level were influenced by the changes in T4 levels during the treatment of abnormal thyroid function. The data also show that GHBP was unrelated to height gain associated with treatment in hyperthyroidism and hypothroidism.

Insulin-like growth factor I, insulin-like growth factor binding proteins, and growth hormone binding protein in Spanish premature and full-term newborns.

The normal values of insulin-like growth factor I (IGF-I), IGF-binding proteins 1 and 3 (IGFBP-1 and IGFBP-3), and the high-affinity growth hormone binding protein (GHBP) are not well established in large series of healthy fullterm newborns. We report the normative data for IGF-I, IGFBP-I, IGFBP-3, and GHBP in 271 normal Spanish full-term newborns, born between 37 and 42 weeks of gestation, and compare these results with the same parameters studied in 39 premature infants. Furthermore, we report the relationship between results found in the normal full-term newborns and those of 252 healthy prepubertal (Tanner stage I) Spanish children. Serum GHBP, IGF-I, and IGFBP-3 levels are very low in the premature infant and show a significant increase in full-term newborns, and continue to decline during childhood (p < 0.001; analysis of variance). A positive correlation between GHBP, IGF-I, and IGFBP-3 versus gestational age was observed. In contrast, we found a negative correlation between IGFBP-I and gestational age. There is a direct relationship between the ponderal index and IGF-I and IGFBP-3. When the group of premature newborns was divided into infants born before or after 32 weeks of gestation, we found higher levels of IGF-I and IGFBP-3 (p < 0.01 and p < 0.05, respectively, by Student's test) in the group with the higher gestational age; however, the IGFBP-I level was lower in this group (p < 0.001 by Student's t test), with no differences seen in serum GHBP concentrations. The presence of IGFBPs in the premature infant suggests that they are important modulators of IGF-I action during fetal growth and development.

Detection of human growth hormone receptors on IM-9 cells and peripheral blood mononuclear cell subsets by flow cytometry: correlation with growth hormone-binding protein levels.

We have developed a method using flow cytometry to identify fluorescein-conjugated GH receptors (GHR) on IM-9 lymphocytes and circulating peripheral blood mononuclear cell subsets. Binding to IM-9 cells and peripheral blood mononuclear cells was concentration dependent and could be competitively blocked by the addition of unlabeled human GH, but not by the addition of rat or bovine GH or human insulin or PRL. Using two-color flow cytometric analysis, fluorescein-conjugated human GHR were readily detected on more than 90% of B lymphocytes and monocytes, but only variably on T lymphocytes. B Lymphocytes and monocytes had approximately 6000 GHR/cell. Using two-color flow cytometry, we identified GHR on circulating B lymphocytes in subjects with GH deficiency (n = 9), precocious puberty (n = 6), and Turner syndrome (n = 5) and in seven subjects with miscellaneous disorders, including familial short stature, bone dysplasia, Crohn disease, congenital adrenal hyperplasia, and acromegaly. The percentage of B lymphocytes expressing GHR in subjects with GH deficiency (mean +/- SD, 95 +/- 9%), precocious puberty (91 +/- 15%), and Turner syndrome (84 +/- 15%) was not different from that in normal volunteers (90 +/- 12%; n = 14). In 10 subjects, serum GH-binding protein levels were assayed simultaneously with B lymphocyte GHR. GH-binding protein was normal in all (mean, 1255 pmol/L; range, 773-1809). There was a good correlation between GHR expression on B lymphocytes and GH-binding protein levels (r = 0.75; P = 0.01). We postulate that GHR found on circulating B lymphocytes may contribute to the pool of receptors identified in serum as GH-binding proteins. Two-color flow cytometry appears to be an effective method for the detection of GHR on circulating peripheral blood mononuclear cell subsets. The evaluation of GHR on circulating B lymphocytes may prove to be a useful means of evaluating GH-GHR interactions in subjects with growth disorders.