Immunoblot studies of the acid-labile subunit (ALS) in biological fluids, normal human serum and in children with GH deficiency and GH receptor deficiency before and after long-term therapy with GH or IGF-I respectively

Endocrine and cellular physiology and pathology of the insulin-like growth factor acid-labile subunit

The acid-labile subunit (ALS) of the insulin-like growth factor (IGF) binding protein (IGFBP) complex, encoded in humans by IGFALS, has a vital role in regulating the endocrine transport and bioavailability of IGF-1 and IGF-2. Accordingly, ALS has a considerable influence on postnatal growth and metabolism. ALS is a leucine-rich glycoprotein that forms high-affinity ternary complexes with IGFBP-3 or IGFBP-5 when they are occupied by either IGF-1 or IGF-2. These complexes constitute a stable reservoir of circulating IGFs, blocking the potentially hypoglycaemic activity of unbound IGFs. ALS is primarily synthesized by hepatocytes and its expression is lower in non-hepatic tissues. ALS synthesis is strongly induced by growth hormone and suppressed by IL-1β, thus potentially serving as a marker of growth hormone secretion and/or activity and of inflammation. IGFALS mutations in humans and Igfals deletion in mice cause modest growth retardation and pubertal delay, accompanied by decreased osteogenesis and enhanced adipogenesis. In hepatocellular carcinoma, IGFALS is described as a tumour suppressor; however, its contribution to other cancers is not well delineated. This Review addresses the endocrine physiology and pathology of ALS, discusses the latest cell and proteomic studies that suggest emerging cellular roles for ALS and outlines its involvement in other disease states.

Normal range for acid-labile subunit in paediatric patients in Spain and its association with age, sex, pubertal stage and other growth factors

INTRODUCTION

The acid-labile subunit (ALS) plays an important role in the endocrine effects of insulin-like growth factors (IGFs) on target tissues. Historically, it has attracted limited attention. The aim of our study was to describe the normal range of ALS in healthy children and its association with other growth factors.

PATIENTS AND METHODS

We designed a cross-sectional descriptive study. We collected data on age, height, body mass index, gestational age, anthropometry at birth and serum levels of ALS, IGF1 and IGFBP3 in healthy children aged 2-15 years with a normal height. The levels of ALS, IGF1 and IGFBP3 were measured by ELISA. We fitted GAMLSS normalization models to standardize the variables.

RESULTS

Samples were collected from 446 children. In prepubertal children, the levels of ALS, IGF1 and IGFBP3 were positively correlated in both sexes and with age (P < .01). We found significant differences in the levels of ALS, IGF1 and IGFBP3 and the IGF1/IGFBP3 molar ratio between the sexes and higher levels in pubertal boys (P < .01). We generated normal probability plots for each sex for each of the components of the ternary complex and for the IGF1/IGFBP3 and IGFBP3/ALS molar ratios. In addition, we extracted equations from the models for the calculation of z-scores for age and sex.

CONCLUSIONS

This study may contribute age- and sex-specific reference values for IGF1, IGFBP3 and ALS levels and IGF1/IGFBP3 and IGFBP3/ALS ratios in Spanish children and suggests an association between age, sex, and pubertal stage.

Growth hormone receptor-deficient pigs resemble the pathophysiology of human Laron syndrome and reveal altered activation of signaling cascades in the liver

OBJECTIVE

Laron syndrome (LS) is a rare, autosomal recessive disorder in humans caused by loss-of-function mutations of the growth hormone receptor (GHR) gene. To establish a large animal model for LS, pigs with GHR knockout (KO) mutations were generated and characterized.

METHODS

CRISPR/Cas9 technology was applied to mutate exon 3 of the GHR gene in porcine zygotes. Two heterozygous founder sows with a 1-bp or 7-bp insertion in GHR exon 3 were obtained, and their heterozygous F1 offspring were intercrossed to produce GHR-KO, heterozygous GHR mutant, and wild-type pigs. Since the latter two groups were not significantly different in any parameter investigated, they were pooled as the GHR expressing control group. The characterization program included body and organ growth, body composition, endocrine and clinical-chemical parameters, as well as signaling studies in liver tissue.

RESULTS

GHR-KO pigs lacked GHR and had markedly reduced serum insulin-like growth factor 1 (IGF1) levels and reduced IGF-binding protein 3 (IGFBP3) activity but increased IGFBP2 levels. Serum GH concentrations were significantly elevated compared with control pigs. GHR-KO pigs had a normal birth weight. Growth retardation became significant at the age of five weeks. At the age of six months, the body weight of GHR-KO pigs was reduced by 60% compared with controls. Most organ weights of GHR-KO pigs were reduced proportionally to body weight. However, the weights of liver, kidneys, and heart were disproportionately reduced, while the relative brain weight was almost doubled. GHR-KO pigs had a markedly increased percentage of total body fat relative to body weight and displayed transient juvenile hypoglycemia along with decreased serum triglyceride and cholesterol levels. Analysis of insulin receptor related signaling in the liver of adult fasted pigs revealed increased phosphorylation of IRS1 and PI3K. In agreement with the loss of GHR, phosphorylation of STAT5 was significantly reduced. In contrast, phosphorylation of JAK2 was significantly increased, possibly due to the increased serum leptin levels and increased hepatic leptin receptor expression and activation in GHR-KO pigs. In addition, increased mTOR phosphorylation was observed in GHR-KO liver samples, and phosphorylation studies of downstream substrates suggested the activation of mainly mTOR complex 2.

CONCLUSION

GHR-KO pigs resemble the pathophysiology of LS and are an interesting model for mechanistic studies and treatment trials.

IGF-1, IGFBP-3 and ALS in adult patients with chronic kidney disease

BACKGROUND

Insulin-like growth factor I (IGF-1) is for the most part bound in a ternary complex with IGF-binding protein-3 (IGFBP-3) and acid-labile subunit (ALS). This ternary complex is a storage form of IGF-1 in blood and passes not through the renal glomerulus. Little information is available in regard to the components of the ternary complex in adult renal disease.

OBJECTIVE

To investigate levels of serum IGF-1, IGFBP-3 and ALS in relation to renal function and extent of proteinuria.

DESIGN AND PATIENTS

We measured IGF-1, IGFBP-3 and ALS concentrations in 137 patients who were investigated due to proteinuria and/or haematuria and/or renal impairment. The patients received renal biopsies and the histological diagnosis was documented. Urinary albumin excretion and relevant clinical parameter were evaluated.

RESULTS

IGF-1 showed a highly positive correlation to IGFBP-3 and ALS, and the latter to IGFBP-3. IGF-1, IGFBP-3 and ALS decreased with increasing age. IGF-1 and IGFBP-3 showed no significant change depending on the creatinine clearance. However, ALS decreased with decreasing renal function. In patients with heavy proteinuria ALS levels, but not IGF-1 and IGFBP-3 levels, decreased significantly. Patients with chronic ischaemic renal damage and diabetic glomerulopathy showed higher IGF-1 and IGFBP-3 levels compared to patients with thin glomerular basement membrane disease despite their older age.

CONCLUSIONS

IGF-1 and IGFBP-3 levels seem to be independent of renal function and severity of proteinuria. However, ALS levels are altered in renal failure and nephrotic syndrome, which may be due to increased renal loss or diminished hepatic production or both.

The effect of different patterns of growth hormone administration on the IGF axis and somatic and skeletal growth of the dwarf rat

Normal childhood growth is determined by ultradian and infradian variations in GH secretion, yet GH treatment of children with short stature is restricted to daily fixed doses. We have used GH-deficient dwarf rats to determine whether variable GH dose regimens promote growth more effectively than fixed doses. Animals were treated with saline or 4.2 mg of recombinant bovine GH given as 1) 700 microg/wk in 100 microg/day doses, 2) alternating weekly doses of 966 (138 microg/day) or 434 microg (62 microg/day), or 3) 700 microg/wk in randomized daily doses (5-250 microg/day). Body weight and length were measured weekly. Femur and tibia lengths and internal organ, fat pad, and muscle weights were recorded at the end of the study (6 wk); blood was collected for IGF axis measurements. GH promoted femur [F(3,60) = 14.67, P < 0.05], tibia [F(3,60) = 14.90, P < 0.05], muscle [F(3,60) = 10.37, P < 0.05], and organ growth [liver: F(3,60) = 9.30, P < 0.05; kidney: F(3,60) = 2.82, P < 0.05] and an increase in serum IGF-I [F(3,60) = 9.18, P < 0.05] and IGFBP-3 [F(3,60) = 6.70, P < 0.05] levels. IGF-I levels correlated with final weight (r = 0.45, P < 0.05) and length (r = 0.284, P < 0.05) in the whole cohort, but within each group, growth parameters correlated with serum IGF-I only in animals treated with random GH doses. The variable regimens promoted femur length (P < 0.05) and muscle (P < 0.05) and kidney (P < 0.05) weight more effectively than treatment with the fixed regimen. This study demonstrates that aspects of growth are improved following introduction of infradian variation to GH treatment in a GH-deficient model. The data suggest that varying the pattern of GH doses administered to children may enhance growth performance without increasing the overall GH dose.

The insulin-like growth factor-1 binding protein acid-labile subunit alters mesenchymal stromal cell fate

Age-related osteoporosis is accompanied by an increase in marrow adiposity and a reduction in serum insulin-like growth factor-1 (IGF-1) and the binding proteins that stabilize IGF-1. To determine the relationship between these proteins and bone marrow adiposity, we evaluated the adipogenic potential of marrow-derived mesenchymal stromal cells (MSCs) from mice with decreased serum IGF-1 due to knockdown of IGF-1 production by the liver or knock-out of the binding proteins. We employed 10-16-week-old, liver-specific IGF-1-deficient, IGFBP-3 knock-out (BP3KO) and acid-labile subunit knock-out (ALSKO) mice. We found that expression of the late adipocyte differentiation marker peroxisome proliferator-activated receptor gamma was increased in marrow isolated from ALSKO mice. When induced with adipogenic media, MSC cultures from ALSKO mice revealed a significantly greater number of differentiated adipocytes compared with controls. MSCs from ALSKO mice also exhibited decreased alkaline-phosphatase positive colony size in cultures that were stimulated with osteoblast differentiation media. These osteoblast-like cells from ALSKO mice failed to induce osteoclastogenesis of control cells in co-culture assays, indicating that impairment of IGF-1 complex formation with ALS in bone marrow alters cell fate, leading to increased adipogenesis.

The effect of laparoscopy on the IGF system in patients diagnosed with acute cholecystitis

OBJECTIVE

IGFs and IGF binding proteins in the circulation are subject to modulation by a number of catabolic states including inflammation, trauma and surgery. We sought to determine the impact of laparoscopy on the IGF system in patients diagnosed with acute cholecystitis.

DESIGN

The components of the IGF system, cortisol, glucose and insulin concentration in both the serum and urine of patients were compared to those from a healthy group of subjects. An additional comparison was made between pre- and post-laparoscopically assisted patients.

PATIENTS

Thirty patients diagnosed with acute cholecystitis and 81 matched controls were included in the study.

MEASUREMENTS

Radioimmunoassays were used to determine the IGF-I, IGF-II, insulin and cortisol concentrations. The concentration of IGFBP-3 was measured using an immunoradiometric assay. The GOD-PAP method was used to determine the glucose concentration. Gel filtration chromatography was performed to calculate the IGF binary/ternary complex ratio. The amount of sialic acid in IGFBP-3 was determined by affinity chromatography. The presence of IGFBPs in serum was determined by both immunoblotting and ligandblotting.

RESULTS

The concentrations of circulating IGF-I, IGF-II and IGFBP-3 were significantly reduced in pre-operative patients compared to healthy subjects. No further reductions were observed post-laparoscopy. Immunoblotting and ligandblotting demonstrated a decreased amount of IGFBP-3 in both pre- and post-operative patients compared to healthy subjects. Increased levels of IGFBP-2 and IGFBP-1 were observed in pre-operative patients compared to healthy subjects, but laparoscopy did not cause further elevation. No alteration in the IGF binary/ternary complex ratio was witnessed between any of the study groups. A significant increase in the sialic acid content of IGFBP-3 was seen in both patient groups when compared to healthy subjects. The level of urinary cortisol was significantly increased in post-operative patients, whereas the urinary IGF-I concentration was decreased compared to healthy subjects.

CONCLUSIONS

Our results indicate that acute cholecystitis causes several significant changes in the circulating IGF system. Laparoscopy, however, does not aggravate such changes, but elevates urinary cortisol.

Pharmacodynamic considerations with recombinant human insulin-like growth factor-I in children

AIM

To report effects of weight-based recombinant human insulin-like growth factor-I (rhIGF-I) on IGF axis parameters in children with hyperinsulinism.

METHODS

Open label trial with subcutaneous rhIGF-I (40 microg/kg/dose). Patients studied were children (1 month to 11 years) with diffuse hyperinsulinism (n = 7). Serial serum IGF and insulin-like growth factor binding protein (IGFBP) concentrations were measured by RIA and analyzed by linear Pearson regression.

RESULTS

Following the initial rhIGF-I dose, total insulin-like growth factor-I (IGF-I) rose by 56% at 30 min (p < 0.01) and 85% at 120 min (p < 0.02). Serum IGF-II, IGFBP-2, and IGFBP-3 levels did not change. Peak serum IGF-I levels within 12 h of the initial rhIGF-I dose were 167-700 mg/ml. The variable peak IGF-I response is attributable in part to IGFBP-3 differences across this pediatric age range. Models of rhIGF-I dosing based upon body surface area (BSA) or initial IGFBP-3 resulted in predictable peak serum IGF-I levels (r = 0.78; p < 0.03). Recalculating rhIGF-I dosing based upon the BSA . IGFBP-3 product correlated closely with peak IGF-I level (r = 0.85; p < 0.007).

CONCLUSIONS

Weight-based IGF-I dosing in this cohort resulted in variable IGF-I levels. Considering BSA and serum IGFBP-3 concentration in children is appropriate for subcutaneous IGF-I administration. A combination of these values may yield predictable individualization of rhIGF-I dosing.

Insulin-like growth factors in childhood-onset Gaucher disease

There is a high prevalence of growth retardation in children with type 1 Gaucher disease. The cause of this poor growth is not yet known; however, studies have shown acceleration of growth with enzyme replacement therapy (ERT). IGF are recognized as important determinants of somatic growth. It has been proven that chronic diseases with liver involvement might cause IGF deficiency. The aim of this study was to assess the IGF system in patients with childhood-onset Gaucher disease, before and after ERT, and its association with other clinical and analytical parameters. Twenty-two patients with type I Gaucher disease were included. The diagnosis was established before 14 y of age in all patients. Baseline determinations of total IGF-I, free IGF-I, and IGF binding protein 3 (IGFBP-3) were obtained in 19 patients before starting ERT at a mean age of 13.8 +/- 11.2 y. A Spearman test was performed to establish the association with other clinical and analytical parameters. In a group of 13 patients receiving IGF, changes were evaluated during the initial 2 y of treatment. A Wilcoxon test was performed for the statistical analysis. Total IGF-I, free IGF-I, and IGFBP-3 were expressed as SD scores (SDS). We found low levels of IGF and its binding proteins before ERT. A significant association was found between the total IGF-I SDS before treatment and the age-adjusted severity score index: r = -0.62, p < 0.05. Total IGF-I and IGFBP-3 SDS correlated negatively with the presence of the L444P mutation (r = -0.53 and -0.5, respectively, p < 0.05). Height SDS correlated with total IGF-I and IGFBP-3 SDS in eight children (r = 0.84 and 0.78, respectively, p < 0.05). Total IGF-I SDS increased from -1.8 +/- 0.8 to -0.8 +/- 1.4 (p = 0.005) and free IGF-I increased from -1.2 +/- 1 to 1.1 +/- 2.1 after 12 +/- 6.8 mo (p = 0.011) of ERT. IGFBP-3 SDS increased from -1.3 +/- 0.6 to -0.2 +/- 1.2 (p = 0.012) after 12 +/- 4.5 mo of ERT. Type 1 Gaucher disease is associated with low levels of IGF and its binding proteins, which could be a consequence of liver involvement. Total IGF-I deficiency is associated with the severity of the illness. Growth retardation in pediatric patients with Gaucher disease is related to the alterations in IGF axis. Total IGF-I and IGFBP-3 are the two parameters that better correlate with height before treatment. ERT results in significant increase of total IGF-I, free IGF-I, and IGFBP-3 during the first year of treatment.

Monoclonal anti-acid-labile subunit oligopeptide antibodies and their use in a two-site immunoassay for ALS measurement in humans

Quantification of the acid-labile subunit (ALS) has to date been restricted to immunoassays utilizing polyclonal antibodies. By immunization with N-terminal and C-terminal specific ALS oligopeptides, we generated monoclonal antibodies (mAbs) that target ALS-specific sequences outside the nonspecific leucine-rich repeats in the ALS molecule. For mAb selection, a special screening method was developed. Monoclonal antibody 5C9, which targets the N-terminus of ALS, is immobilized and the anti-ALS mAb 7H3, directed against the C-terminus, is biotinylated and used as tracer Ab. Due to the extreme pH-lability of ALS, changes in immunorecognition of ALS were investigated after acidification for protein unfolding in different pH ranges and in a time-dependent manner. It was determined that acidification of the serum samples to pH 2.7 for 30 min, followed by neutralization and dilution to 1:100 was the optimal acid-neutralization method. For standardization purposes, a serum pool derived from healthy volunteers was assigned the value 1 U/ml ALS. The sandwich assay has a working range with a linear dose-response curve in a log/log system between 0.005 and 10 U/ml. ALS levels in seven acromegalic patients ranged from 2.0 to 4.2 U/ml, and in 12 untreated growth hormone deficient patients from 0.036 to 0.986 U/ml (mean=0.45 U/ml). After 12 months of growth hormone therapy, ALS levels increased significantly to 1.18+/-0.45 U/ml (mean+/-SD; p<0.0006). The increase ranged from 0.48 to 1.4 U/ml. The change in ALS with growth hormone (GH) therapy correlated closer with the change in IGF-I (r=0.798, p=0.0057; Spearman rank correlation) than with the change in insulin-like growth factor binding protein (IGFBP3; r=0.549, p=0.057). This specific sandwich assay for the measurement of ALS provides a potentially valuable indicator of growth hormone secretory status. With this mAb-based immunofluorometric assay, the nonspecific detection of other proteins containing leucine-rich repeat sequences can be excluded.

Antiproliferative effects of insulin-like growth factor-binding protein-3 in mesenchymal chondrogenic cell line RCJ3.1C5.18. relationship to differentiation stage

Chondrogenesis results from a complex equilibrium between chondrocyte proliferation and differentiation. Insulin-like growth factors (IGFs) have a crucial role in chondrogenesis, but their mechanisms of action are not well defined. IGF-binding protein-3 (IGFBP-3) is the major carrier for circulating IGFs in postnatal life, and has been shown to have IGF-independent effects on proliferation of several cancer cell lines. In this study, we have evaluated the IGF-independent and -dependent effects of IGFBP-3 on chondrocyte proliferation and the relationship of these effects with chondrocyte differentiation stage. We used the RCJ3.1C5.18 nontransformed mesenchymal chondrogenic cell line, which, over 2 weeks of culture, progresses through the differentiation pathway exhibited by chondrocytes in the growth plate. We demonstrated that IGFBP-3 inhibited, in a dose-dependent manner (1-30 nm), the proliferation of chondroprogenitors and early differentiated chondrocytes, stimulated by des-(1-3)-IGF-I and longR(3)-IGF-I (IGF-I analogs with reduced affinity for IGFBP-3), and by insulin and IGF-I. In terminally differentiated chondrocytes, IGFBP-3 retained the ability to inhibit cell proliferation stimulated by IGF-I, but had no effect on cell growth stimulated by insulin, or des-(1-3)-IGF-I or longR(3)IGF-I. By monolayer affinity cross-linking, we demonstrated a specific IGFBP-3-associated cell-membrane protein of approximately 20 kDa. We determined that IGFBP-3 has an antiproliferative effect on chondrocytes and, that this effect is related to the differentiation process. In chondroprogenitors and early differentiated chondrocytes, antiproliferative effect of IGFBP-3 is mainly IGF-independent, whereas, following terminal differentiation this effect is IGF-dependent.

The acid-labile subunit of the ternary insulin-like growth factor complex in cirrhosis: relation to liver dysfunction

BACKGROUND/AIMS

In the circulation, insulin-like growth factor-I (IGF-I) is bound in a trimeric complex of 150 kDa with IGF binding protein-3 (IGFBP-3) and the acid-labile subunit (ALS). Whereas circulating IGF-I and IGFBP-3 are reported to be low in patients with chronic liver failure, the level of ALS has not been described in relation to hepatic dysfunction. The aim of the present study was therefore to measure circulating and hepatic venous concentrations of ALS in relation to hepatic function and the IGF axis.

METHODS

Twenty-five patients with cirrhosis (Child class A/B/C:5/10/10) and 30 controls with normal liver function were studied. During a haemodynamic investigation, blood samples were collected from the hepatic vein and femoral artery, and the plasma concentrations of ALS, IGF-I and IGFBP-3 were determined.

RESULTS

Hepatic venous and arterial concentrations of ALS were significantly decreased in the cirrhotic patients compared with the controls (-69% and -68%, respectively, both p<0.001). IGF-I and IGFBP-3 were similarly decreased in the cirrhotic patients (-51%,p<0.001). A significant hepatic extraction of ALS was found in the controls (6%, p<0.01) and in the cirrhotic patients (8%, p=0.08). ALS correlated significantly with indicators of liver dysfunction, including the Child-Turcotte score (r=-0.69, p<0.0001), IGF-I (r=0.82, p<0.0001) and IGFBP-3 (r=0.74, p<0.0001).

CONCLUSIONS

Circulating and hepatic venous ALS are decreased in patients with cirrhosis with significant relations to liver dysfunction and other components of the IGF complex. A small hepatic extraction was found in controls, which suggests extrahepatic production of ALS. Future studies should focus on organ-specific removal of ALS.

Growth response to rhIGF-I 80 microg/kg twice daily in children with growth hormone insensitivity syndrome: relationship to severity of clinical phenotype

BACKGROUND

rhIGF-I has been used effectively to promote growth in growth hormone insensitivity syndrome (GHIS) in doses ranging from 40 microg/kg twice daily to 150-200 microg/kg once daily. It appears that the dose of 80 microg/kg twice daily s.c. may induce an equivalent response to higher doses with less side-effects.

OBJECTIVE

To study the efficacy and safety of rhIGF-I, 80 microg/kg twice daily s.c., in children with GHIS and to analyse the relationship of growth response to severity of phenotype.

PATIENTS AND DESIGN

Eleven prepubertal children (3 females, 8 males) with GHIS; basal GH > 2.5 microg/l, IGF-I < 50 microg/l, IGFBP-3 < - 2SD; were treated with IGF-I 80 microg/kg twice daily in a multi-centre study. The baseline characteristics of these patients were as follows (mean +/- SD): age, 7.5 +/- 2.5 years (range, 2.5-11.7 years), bone age (Tanner-Whitehouse - 2 RUS), 5.2 +/- 2.4 years (range, 2.3-9.1 years), mean height SDS, - 5.6 +/- 1.6 (range, - 3.1 to - 8.1), height velocity (HV), 3.1 +/- 1.1 cm/year (range, 1.9-4.9 cm/year). Height, HV, weight, skinfold thickness, puberty stage and bone age were measured at baseline and 6 monthly for 2 years.

RESULTS

During the first 12 months of IGF-I therapy, the mean +/- SD HV was 7.7 +/- 1.6 cm/year (range, 6.1-11.2 cm/year), the mean +/- SD increase in HV was 4.7 +/- 2.1 cm/year (range, 1.7-8.8 cm/year) and the mean +/- SD progression of bone age was 1.9 +/- 1.0 years (range, 0.8-3.8 years). Pre-treatment height SDS at the start of IGF-I therapy correlated positively with pretreatment serum IGFBP-3 SDS levels (r = 0.85; P < 0.01). There was a significant inverse correlation between gain in height SDS and pre-treatment height SDS (r = - 0.76; P < 0.01). During the 2nd 12 months of therapy, mean HV was 7.0 +/- 3.4 cm/year (range 3.8-12.4) change in height SDS from 12 to 24 months was not significantly correlated with pre-treatment height SDS. Subscapular skinfold SDS decreased significantly (P < 0.05) during the study period, whereas there was no significant change in body mass index and triceps skinfold thickness SDS. Adverse events reported in the patient group included headache (2 patients), hypoglycaemia (2 patients), papilloedema (transient, 1 patient), lipohypertrophy (5 patients) and tonsillectomy/adenoidectomy (2 patients).

CONCLUSION

This study reveals that IGF-I treatment at a dose of 80 microg/kg twice daily is effective in patients with growth hormone insensitivity syndrome. During the first 12 months of therapy, there was a significant inverse relationship between growth response to IGF-I therapy and the severity of the phenotype of growth hormone insensitivity syndrome, as measured by height SDS, at the start of therapy. Patients with a more severe clinical phenotype of growth hormone insensitivity syndrome, who also had most severe IGFBP-3 deficiency, responded better than those who were more mildly affected. An analogous situation has been shown to be the case in GH-deficient patients treated with hGH.

Acute and short-term effects of growth hormone on insulin-like growth factors and their binding proteins: serum levels and hepatic messenger ribonucleic acid responses in humans

We investigated the acute (4-5 h) and short-term (5 days) effects of GH treatment on hepatic messenger RNA (mRNA) levels of the genes for the insulin-like growth factors (IGFs), insulin-like growth factor binding protein-1, -2, and -3 (IGFBPs), and the acid labile subunit (ALS), as well as serum levels of these proteins in humans. At the mRNA level, we observed an increase in IGF-1 transcription (+173%) following GH treatment in the acute group, which remained elevated in the short-term treatment group. IGFBP-2 mRNA decreased after short-term GH treatment, without changes in IGFBP-1 or -3 expression. The ALS transcript level increased after 5 days. In serum, we found increased levels of IGF-I and insulin, and decreased levels of IGF-II, in the short-term treatment group. IGFBP-1 decreased in both treatment groups, whereas IGFBP-2 was reduced after 5 days treatment. ALS increased in the short-term group. We observed increased IGFBP-3 serum levels after 5 days of GH treatment, likely due to increased formation of the ternary complex. Our results show that the metabolic effects by GH on the IGF axis are complex. In addition to a direct stimulation of IGF-I and ALS expression, GH inhibits IGFBP-1 serum levels and IGFBP-2 expression in an indirect manner, possibly facilitating enhanced IGF bioavailability to target tissues.

The effect of GH therapy on the immunoreactive forms and distribution of IGFBP-3, IGF-I, the acid-labile subunit, and growth rate in GH-deficient children

We have previously shown that the major correlates of growth following growth hormone (GH) therapy in growth hormone-deficient (GHD) children are changes in circulating insulin-like growth factor-I (IGF-I) and IGF binding protein-3 (IGFBP-3), suggesting a synergistic interaction between IGF-I and IGFBP-3 (1). The first aim of this project was to examine the molecular forms of IGFBP-3 and the acid-labile subunit (ALS), and to assess the changes in these molecular forms during GH administration to GHD children. Plasma samples from prepubertal GHD patients, prior to therapy and during the first year of GH treatment, were subjected to Western ligand and immunoblot analysis. Densitometric analysis of Western ligand blotting (WLB) showed a 76% increase in IGFBP-3 (p = 0.02), but a 56% decrease in 36-kDa IGFBP-2 (p = 0.03) during GH therapy. Western immunoblot (WIB) analysis of IGFBP-3 revealed the presence of intact (40- to 45-kDa doublet) as well as a proteolyzed (28-kDa) form of IGFBP-3 in the serum of GHD and healthy children. Both immunoreactive forms of IGFBP-3 increased by 64% during GH therapy (intact p = 0.003; proteolyzed p = 0.0001). WIB analysis of the ALS showed an 84-to 86-kDa doublet, which increased by 41% with GH therapy (p = 0.01). The response to GH therapy, as measured by the height velocity standard deviation score (SDS) adjusted for bone age, correlated with the percent change in total IGFBP-3 (r = 0.772, p = 0.002 by WIB), intact IGFBP-3 (r = 0.845, p = 0.0005 by WLB; r = 0.541, p = 0.05 by WIB), and proteolyzed IGFBP-3 (r = 0.703, p = 0.007), as well as with the percent change in ALS (r = 0.813, p = 0.014). The second aim of this project was to assess the changes in distribution of the immunoreactive forms of IGFBP-3 and IGF-I among the ternary (ALS/IGFBP-3/IGF) complex, the binary (IGFBP-3/IGF) complex, and uncomplexed IGF during the first year of GH therapy, and to explore further the correlation with growth response to GH. Plasma samples, prior to therapy and after the first year of GH treatment, were separated by neutral size-exclusion chromatography and then subjected to IGFBP-3 immunoradiometric assay (IRMA), IGFBP-3 WIB, and IGF-I IRMA analysis. IGFBP-3 increased in both the ternary (p < 0.0001) and binary (p = 0.01) complexes, but there was a shift in the percentage of IGFBP-3 from the binary to the ternary complex during GH therapy. Both intact and proteolyzed forms of IGFBP-3 were found in both the ternary and binary complexes, but the shift occurred primarily for the proteolyzed (28-kDa) form (p = 0.001). There was a significant increase in IGF-I in the ternary (p = 0.001) and binary (p = 0.005) complexes, but not in uncomplexed IGF-I. The percentage of IGF-I in the ternary complex increased (p = 0.006), whereas the percentage of uncomplexed IGF-I decreased (p = 0.02), during GH therapy. Growth rate, assessed by the height velocity SDS for bone age, correlated best with the changes in ternary complex IGFBP-3 (r = 0.72, p = 0.01) and ternary complex IGF-I (r = 0.56, p = 0.10). In conclusion, GH treatment of GHD children results in significant increases of intact, proteolyzed, and total IGFBP-3, as well as an increase in ALS, which all correlate with the growth response to GH therapy. In addition, GH treatment results in increases in ternary complex IGFBP-3 and IGF-I, which also correlate with the response to therapy. We suggest that the formation of the ternary complex may be a determining factor in the somatic growth response.