The level of bioavailable growth hormone (GH) after the first GH injection predicts the first year's growth response in GH-deficient children

Broad variability in pharmacokinetics of GH following rhGH injections in children

OBJECTIVE

Daily subcutaneous self-injection of GH is used worldwide to treat short stature in childhood; longitudinal data on the impact of this regimen on GH-uptake are lacking.

DESIGN

Children with/without GH-deficiency participating in clinical trials were followed prospectively (≤8 times). Blood was sampled pre-GH-injection (dose GH³³/GH⁶⁷ μg/kg) and either every 30 min thereafter for 24 h (Experimental-setting; 59 GH-curves/15 children); or every 2 h thereafter for 16 h (Clinical-setting; 429 GH-curves/117 children). Pharmacokinetics were estimated by time T_max (h) of maximal GH-concentration (C_max, mU/L) and area under the curve for 16 h (AUC, mU/L ∗ h).

RESULTS

In the Clinical-setting, median C_max was 71 mU/L and AUC was 534 mU/L ∗ h, with coefficients of variation for intra-individual variation of 39% and 36%, respectively, and inter-individual variation of 44% and 42%, respectively. 43% of C_max and AUC variability was explained by GH-dose and proxies for injection depth (baseline GH-level, GH_peakwidth, BMI_SDS). In the Experimental- versus Clinical-setting, 85% and 40% of GH-curves, respectively, reached zero-levels within 24 h. A longer duration was found following a more superficial GH-injection. Spontaneous GH-peaks were identified already 6 h after the GH-injection in about half of the curves of both GHD and non-GHD patients.

CONCLUSION

Very broad intra-individual and inter-individual variability was found. A high GH-peak will optimize growth effects; the highest C_max was found after a deep injection of GH at the higher dose and concentration. In as many as 60% of the children, GH remained detectable in serum after 24 h; a constant GH-level will promote IGF-I and metabolic effects.

Dynamic response of C-type natriuretic peptide and its aminoterminal propeptide (NTproCNP) to growth hormone treatment in children with short stature

OBJECTIVE

C-type natriuretic peptide (CNP) and its aminoterminal propeptide (NTproCNP) are potential biomarkers of recombinant human growth hormone (rhGH) efficacy. The objective of this study was to describe the pharmacodynamics of plasma CNP and NTproCNP levels in response to rhGH treatment and to identify the optimal time of sampling after starting rhGH.

DESIGN

This was a prospective, observational study. Subjects were treated with rhGH for 1 year, with blood sampled at regular intervals.

PATIENTS

Eighteen prepubertal children, eight with low levels of GH on biochemical testing and ten with idiopathic short stature, completed the study.

MEASUREMENTS

Blood levels of CNP, NTproCNP, GH, insulin-like growth factor-I, leptin and bone-specific alkaline phosphatase were measured. Anthropometrics were obtained.

RESULTS

Plasma levels of both CNP and NTproCNP reached peak levels 7-28 days after starting rhGH treatment and then declined to intermediate levels through the first year. Plasma NTproCNP levels after 14 days trended towards a correlation with height velocity after 6 and 12 months of treatment. Unexpectedly, serum GH levels measured 2 and 28 days after starting rhGH correlated strongly with height velocity after 6 and 12 months of treatment.

CONCLUSIONS

This study identified 14 days after starting rhGH treatment as the optimal time for assessing CNP and NTproCNP levels as biomarkers of rhGH efficacy. Additionally, we identified GH levels as a potential biomarker. Larger, prospective studies are now needed to test the clinical utility of these biomarkers.

Inhaled growth hormone (GH) compared with subcutaneous GH in children with GH deficiency: pharmacokinetics, pharmacodynamics, and safety

BACKGROUND

Delivery of GH via inhalation is a potential alternative to injection. Previous studies of inhaled GH in adults have demonstrated safety and tolerability.

OBJECTIVE

We sought to assess safety and tolerability of inhaled GH in children and to estimate relative bioavailability and biopotency between inhaled GH and sc GH.

DESIGN/METHODS

This pediatric multicenter, randomized, double-blind, placebo-controlled, crossover trial had two 7-d treatment phases. Patients received inhaled GH and sc GH in the alternate phase. Placebo was administered by the route opposite from active drug. GH and IGF-I levels were measured at multiple time points. Pharmacokinetics were assessed using noncompartmental methods.

RESULTS

Twenty-two GH-deficient children aged 6-16 yr were treated. Absorption of GH appeared to be faster after inhalation with maximum serum concentrations measured at 1-4 h compared with 2-8 h for sc GH. Mean relative bioavailability for inhaled GH was 3.5% (90% confidence interval 2.7-4.4%). Mean relative biopotency, based on IGF-I response, was 5.5% (confidence interval 5.2-5.8%). Similar dose-dependent increases in mean serum GH area under the curve and IGF-I changes from baseline were seen after inhaled and sc GH doses. Inhaled GH was well tolerated and preferred to injection. No significant changes in pulmonary function tests were seen.

CONCLUSIONS

In this first pediatric trial of GH delivered by inhalation, it was well tolerated and resulted in dose-dependent increases in serum GH and IGF-I levels. This study establishes that delivery of GH via the deep lung is feasible in children.

Response to long-term growth hormone therapy in short children with reduced GH bioactivity

BACKGROUND/AIMS

The aim of the present study was to investigate whether short children with normal growth hormone (GH) immunoreactivity, but reduced bioactivity (bioinactive GH) could benefit from rhGH treatment as GH deficient (GHD) patients.

METHODS

We evaluated 12 pre-pubertal children (8 M, 4 F), with GH deficiency-like phenotype showing normal serum GH peak levels (>10 ng/ml), measured by immunofluorimetric assay (IFMA-GH), in contrast with a reduced GH bioactivity (bio-GH), evaluated using the Nb(2) cells. We also evaluated 15 age-matched GHD pre-pubertal children (11 M, 4 F) with serum GH peak <5 ng/ml. Both groups were treated with rhGH therapy at the dose of 0.23 mg/kg/week s.c.

RESULTS

Serum bio-GH/IFMA-GH ratio at peak time for each patient during the provocative test was significantly lower in bioinactive GH than in GHD children (0.29 vs. 2.05, p = 0.00001). Recombinant human GH therapy induced a significant (p < 0.001) increase in growth rate in both groups during the first 2 years. In the third year of treatment, while growth rate in GHD children is maintained, in bioinactive GH patients it decreases remaining, however higher compared to the pre-treatment one.

CONCLUSIONS

Short rhGH therapy given to selected bioinactive GH children improve growth rate and might result in greater final adult height.

High serum levels of growth hormone (GH) and insulin-like growth factor-I (IGF-I) during high-dose GH treatment in short children born small for gestational age

CONTEXT

Epidemiological studies have indicated that high serum levels of GH and IGF-I are associated with long-term risks.

OBJECTIVE

The objective of the study was to evaluate the changes in serum levels of GH during overnight profiles, IGF-I, and IGF binding protein 3 (IGFBP-3) in short small for gestational age (SGA) children during GH treatment with two doses.

PATIENTS

Thirty-six prepubertal short SGA children were the subjects of this study.

INTERVENTION

Subjects received 1 (group A) or 2 (group B) mg GH/m(2).d.

MAIN OUTCOME MEASURES

At baseline and after 6 months of GH treatment, overnight GH profiles were performed, and serum IGF-I and IGFBP-3 levels were measured.

RESULTS

After 6 months, group B had significantly higher GH levels during the profile (mean, maximum, and area under the curve above zero line) than group A (P < 0.009). In group B, maximum GH levels increased from 43.9-161 mU/liter (P < 0.0002), and in group A, from 57.2-104 mU/liter (P = 0.002). During the profile (i.e. 12 h per day), children of group B had mean GH levels of 64.4 vs. 34.8 mU/liter in group A (P = 0.001). The IGF-I and IGF-I to IGFBP-3 ratio sd scores increased significantly in both groups, but were higher in group B than A [1.5 vs. 0.2 (P = 0.002) and 1.4 vs. 0.3 (P = 0.007), respectively]. In group B, 74% of the children had IGF-I levels in the highest quintile during GH treatment compared with 19% in group A.

CONCLUSION

Our study shows that high-dose GH treatment in short SGA children results in high serum GH and IGF-I levels in most children. We recommend monitoring IGF-I levels during GH therapy to ensure that these remain within the normal range.

Growth hormone immunoreactivity does not reflect bioactivity

In childhood, the largest secretory burst of GH occurs during nighttime, and consists of a complex mixture of molecular forms of GH that are thought to have different biologic activity. Standard GH assays cannot distinguish between bioactive and biologically inactive GH isoforms. To examine this relationship, overnight GH secretion was assessed by blood sampling every 30 min in 10 short prepubertal children (7 boys and 3 girls) to evaluate both the serum concentration and the biologic activity of GH. Serum GH concentrations were measured by an immunofluorometric assay and its biologic activity by the Nb2 cell bioassay. The 12-h (2000 h to 0800 h) and 6-h (2000 h to 0200 h and 0200 h to 0800 h) GH profiles were analyzed using the Pulsar program. When GH secretory pattern was measured by immunofluorometric assay, the area under the curve above the 0 line, the mean GH concentration, and the mean height of the secretory peaks were significantly higher during the first than during the second part of the night (29.17+/-5.93 versus 16.29+/-1.87 mIU/L, p<0.05; 7.77+/-1.28 versus 4.83+/-0.33 mIU/L, p<0.05; 4.61+/-0.94 versus 2.68+/-0.27 mIU/L, p<0.05, respectively). In contrast, GH biologic activity was not significantly different during the two parts of the night. In conclusion, a dissociation between GH bioactivity and immunoreactivity is present in physiologic conditions, indicating that standard GH measurements do not provide any information on the biologic activity of the hormone. Although GH secretion is regulated by complex neuroendocrine mechanisms, the biologic activity of the hormone seems to be independent of them and is most probably regulated by peripheral mechanisms acting on its clearance or bioavailability to the target tissues.