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

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.

Evaluation of IGF1/IGFBP3 Molar Ratio as an Effective Tool for Assessing the Safety of Growth Hormone Therapy in Small-for-gestational-age, Growth Hormone-Deficient and Prader-Willi Children

OBJECTIVE

IGF1 concentration is the most widely used parameter for the monitoring and therapeutic adaptation of recombinant human growth hormone (rGH) treatment. However, more than half the variation of the therapeutic response is accounted for by variability in the serum concentrations of IGF1 and IGFBP3. We therefore compared the use of IGF1/IGFBP3 molar ratio with that of IGF1 concentration alone.

METHODS

We selected 92 children on rGH for this study and assigned them to three groups on the basis of growth deficiency etiology: small for gestational age (SGA), GH deficiency (GHD) and Prader-Willi syndrome (PWS). Plasma IGF1 and IGFBP3 concentrations and their molar ratio were determined.

RESULTS

Before rGH treatment, mean IGF1/IGFBP3 molar ratio in the SGA, GHD and PWS groups was 0.14±0.04, 0.07±0.01 and 0.12±0.02, respectively. After the initiation of rGH treatment, these averages were 0.19±0.07, 0.20±0.08 and 0.19±0.09, within the normal range for most children, even at puberty and despite some significant increases in serum IGF1 levels.

CONCLUSION

We consider IGF1/IGFBP3 molar ratio to be a useful additional parameter for assessing therapeutic safety in patients on rGH, and for maintaning the values within the normal range for age and pubertal stage.

Biomarkers of GH action in children and adults

Growth hormone (GH) and IGF-I levels in serum are used as biomarkers in the diagnosis and management of GH-related disorders but have not been subject to structured validation. Auxological parameters in children and changes in body composition in adults, as well as metabolic parameters and patient related outcomes are used as clinical and surrogate endpoints. New treatment options, such as long acting GH and GH antagonists, require reevaluation of the currently used biochemical biomarkers. This article will review biomarkers, surrogate endpoints and clinical endpoints related to GH treatment in children and adults as well as in acromegaly.

Growth hormone (GH) dose-dependent IGF-I response relates to pubertal height gain

BACKGROUND

Responsiveness to GH treatment can be estimated by both growth and ∆IGF-I. The primary aim of the present study was to investigate if mimicking the physiological increase during puberty in GH secretion, by using a higher GH dose could lead to pubertal IGFs in short children with low GH secretion. The secondary aim was to explore the relationship between IGF-I, IGFBP-3 and the IGF-I/IGFBP-3 ratio and gain in height.

METHODS

A multicentre, randomized, clinical trial (TRN88-177) in 104 children (90 boys), who had received GH 33 μg/kg/day during at least 1 prepubertal year. They were followed from GH start to adult height (mean, 7.5 years; range, 4.6-10.7). At onset of puberty, children were randomized into three groups, to receive 67 μg/kg/day (GH(67)) given once (GH(67x1); n = 30) or divided into two daily injection (GH(33x2); n = 36), or to remain on a single 33 μg/kg/day dose (GH(33x1); n = 38). The outcome measures were change and obtained mean on-treatment IGF-I(SDS), IGFBP3(SDS) and IGF-I/IGFBP3 ratio(SDS) during prepuberty and puberty. These variables were assessed in relation to prepubertal, pubertal and total gain in heightSDS.

RESULTS

Mean prepubertal increases 1 year after GH start were: 2.1 IGF-I(SDS), 0.6 IGFBP3(SDS) and 1.5 IGF-I/IGFBP3ratio(SDS). A significant positive correlation was found between prepubertal ∆IGFs and both prepubertal and total gain in height(SDS). During puberty changes in IGFs were GH dose-dependent: mean pubertal level of IGF-I(SDS) was higher in GH(67) vs GH(33) (p = 0.031). First year pubertal ∆IGF-I(SDS) was significantly higher in the GH(67)vs GH(33) group (0.5 vs -0.1, respectively, p = 0.007), as well as ∆IGF-I(SDS) to the pubertal mean level (0.2 vs -0.2, p = 0.028). In multivariate analyses, the prepubertal increase in '∆IGF-I(SDS) from GH start' and the 'GH dose-dependent pubertal ∆IGF-I(SDS)' were the most important variables for explaining variation in prepubertal (21 %), pubertal (26 %) and total (28 %) gain in height(SDS).

TRIAL REGISTRATION

TRN 88-177, not applicable 1988.

CONCLUSION

The dose-dependent change in IGFs was related to a dose-dependent pubertal gain in height(SDS). The attempt to mimic normal physiology by giving a higher GH dose during puberty was associated with both an increase in IGF-I and a dose-dependent gain in height(SDS).

Transcriptional response of peripheral blood mononuclear cells to recombinant human growth hormone in a routine four-days IGF-I generation test

BACKGROUND

There are very few laboratory markers which reflect the biological sensitivity of children to recombinant human growth hormone (rhGH) treatment. Genome-wide transcriptional changes in peripheral blood mononuclear cells (PBMC) have been widely used as functional readout for different pharmacological stimuli.

OBJECTIVE

To characterize transcriptional changes in PBMC induced by rhGH during a routine short-term IGF-I generation test (IGFGT) in children with growth disorders.

MATERIALS AND METHODS

Blood was obtained for IGF-I determination and RNA-preparation from PBMC of 12 children before and after 4days treatment with 30μgrhGH/kg body weight/day s.c. Transcriptional changes were assessed by cDNA-microarrays in the first six children. Selected genes were validated in all 12 cases by RT-qPCR.

RESULTS

Serum IGF-I rose in all patients except one (p<0.0001), confirming biological response to rhGH. Unsupervised microarray data analysis in the first six children revealed 313 transcripts with abundant transcriptional changes but considerable inter-individual variability of response patterns. Many patients showed a large cluster of up-regulated genes, including EGR1, EGR2, FOS and to a lesser extent STAT2 and 5b. Exemplarily, EGR1, EGR2 and FOS data were independently reproduced by RT-qPCR. Gene ontology analysis revealed that pathways involved in cell proliferation and immune functions were significantly over represented.

CONCLUSION

The IGFGT is a suitable method for measuring reproducible and biologically conclusive transcriptional changes in PBMC. As our unsupervised data analysis strategy exposed a considerable inter-individual variability of response profiles a search for molecules of diagnostic and even prognostic value needs to be based on large long-term studies.

Partial growth hormone deficiency and changed bone quality and mass in type I trichorhinophalangeal syndrome

The trichorhinophalangeal syndromes (TRPSs) are syndromes due to haploinsufficiency of genes in the chromosome 8q24.12 region. Type I TRPS is characterized by typical facial features including sparse, brittle and fine hair, bulbous nose, and a long philtrum, as well as skeletal abnormalities. Growth retardation is a feature frequently found in these patients, who commonly are of short stature; however, only one case with growth hormone deficiency has been described in a TRPS patient and that patient had type II TRPS. Skeletal morphological abnormalities have been studied, but investigation of bone metabolism and quality in this kind of patients are not available. In this report we describe two cases of type I TRPS with partial growth hormone deficiency and significant bone mass and quality impairment, which was unresponsive to GH treatment.

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.

Effects of dose and gender on the growth and growth factor response to GH in GH-deficient children: implications for efficacy and safety

We evaluated the dose-response effects of GH on the growth and growth factor levels of GH-deficient patients. One hundred eleven short (-3.0 +/- 0.9 height SD score), prepubertal GH-deficient children were randomized to receive low- (L; 0.025 mg/kg per day), medium- (M; 0.05 mg/kg per day), or high- (H; 0.1 mg/kg per day) dose GH. One hundred four children completed the 2-yr study. At 2 yr, the three groups displayed increases in height SD scores of 1.4 +/- 0.1 for L, 2.2 +/- 0.1 for M, and 2.3 +/- 0.1 for H (P < 0.001 relative to L, P = NS relative to M). The serum levels of IGF-I and IGF binding protein-3 during treatment also demonstrated dependency on the GH dose and were independently correlated with the increase in height SD scores attained. Bone age advancement, the occurrence of puberty, fasting glucose, and hemoglobin A1c did not change during therapy, but fasting insulin levels rose in a dose-dependent manner. Surprisingly, the GH dose-response curve for both auxological and biochemical parameters differed between prepubertal females (n = 33) and males (n = 71). Males had a linear GH dose response, whereas females had an apparent plateau of both linear growth and IGF-I SD score responses at 0.05 mg/kg per day. In this large, randomized, 2-yr study, we observed a dose-response effect of GH on growth and serum growth factor levels and a prepubertal gender difference in GH sensitivity. These results suggest that the efficacy and theoretical safety of GH therapy can be optimized by modulating the GH dose in a gender-specific manner, based on the growth response and serum growth factor levels.

Stimulation of the 150-kilodalton insulin-like growth factor-binding protein-3 ternary complex by continuous and pulsatile patterns of growth hormone (GH) administration in GH-deficient patients

In the circulation insulin-like growth factor I (IGF-I), IGF-binding protein 3 (IGFBP-3), and the acid-labile subunit (ALS) form a 150-kDa ternary complex that is of importance for the regulation of IGF-I bioactivity. GH administration is known to increase each of the single components of the ternary complex, and in GH-deficient rats formation of the 150-kDa complex is induced more by continuous than by pulsatile GH patterns. The aim of the present studies was to study the effects of the GH administration pattern on the formation of the 150-kDa ternary complex in humans. A fixed total GH dose (2 IU/m2-24 h) was administered iv randomly as 1) continuous infusion or 2) eight bolus injections to five GH-deficient patients over a period of 24 h. GH administration significantly increased serum IGF-I and IGFBP-3 levels and the IGF-I/IGFBP-3 ratio. IGF-I levels increased most pronouncedly after continuous administration (P < 0.01). Serum ALS levels increased significantly (both P < 0.005) from 94+/-21 to 180+/-29 (infusion) and from 85+/-17 to 155+/-17 nmol/L (pulses). Employment of neutral size exclusion chromatography enabled separation of IGFBP-3 in ternary complex and noncomplex-bound fractions. IGFBP-3 in the ternary complex increased significantly after GH administration [by 44% (P = 0.048) during infusion and by 62% (P = 0.004) during bolus]. The noncomplex-associated IGFBP-3 fraction, however, did not increase significantly after GH administration (P = NS). Finally, formation of the ternary complex was unaffected by the pattern of GH delivery. In conclusion, short-term GH administration increased all components of the 150-kDa ternary complex. Higher levels of IGF-I after constant GH exposure could indicate an increased bound fraction. However, the GH pattern did not influence the induction of the ternary complex itself. Continuous and intermittent GH patterns may be clinically equally effective during long-term GH therapy, as judged by levels of the components of the ternary complex.