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

Management of Growth Disorders in Puberty: GH, GnRHa, and Aromatase Inhibitors: A Clinical Review

Pubertal children with significant growth retardation represent a considerable therapeutic challenge. In growth hormone (GH) deficiency, and in those without identifiable pathologies (idiopathic short stature), the impact of using GH is significantly hindered by the relentless tempo of bone age acceleration caused by sex steroids, limiting time available for growth. Estrogen principally modulates epiphyseal fusion in females and males. GH production rates and growth velocity more than double during puberty, and high-dose GH use has shown dose-dependent increases in linear growth, but also can raise insulin-like growth factor I concentrations supraphysiologically, and increase treatment costs. Gonadotropin-releasing hormone analogs (GnRHas) suppress physiologic puberty, and when used in combination with GH can meaningfully increase height potential in males and females while rendering adolescents temporarily hypogonadal at a critical time in development. Aromatase inhibitors (AIs) block androgen to estrogen conversion, slowing down growth plate fusion, while allowing normal virilization in males and stimulating longitudinal bone growth via androgen receptor effects on the growth plate. Here, we review the physiology of pubertal growth, estrogen and androgen action on the epiphyses, and the therapeutic impact of GH, alone and in combination with GnRHa and with AIs. The pharmacology of potent oral AIs, and pivotal work on their efficacy and safety in children is also reviewed. Time-limited use of AIs is a viable alternative to promote growth in pubertal males, particularly combined with GH. Use of targeted growth-promoting therapies in adolescence must consider the impact of sex steroids on growth plate fusion, and treatment should be individualized.

Differential Diagnosis of the Short IGF-I-Deficient Child with Apparently Normal Growth Hormone Secretion

The current differential diagnosis for a short child with low insulin-like growth factor I (IGF-I) and a normal growth hormone (GH) peak in a GH stimulation test (GHST), after exclusion of acquired causes, includes the following disorders: (1) a decreased spontaneous GH secretion in contrast to a normal stimulated GH peak ("GH neurosecretory dysfunction," GHND) and (2) genetic conditions with a normal GH sensitivity (e.g., pathogenic variants of GH1 or GHSR) and (3) GH insensitivity (GHI). We present a critical appraisal of the concept of GHND and the role of 12- or 24-h GH profiles in the selection of children for GH treatment. The mean 24-h GH concentration in healthy children overlaps with that in those with GH deficiency, indicating that the previously proposed cutoff limit (3.0-3.2 μg/L) is too high. The main advantage of performing a GH profile is that it prevents about 20% of false-positive test results of the GHST, while it also detects a low spontaneous GH secretion in children who would be considered GH sufficient based on a stimulation test. However, due to a considerable burden for patients and the health budget, GH profiles are only used in few centres. Regarding genetic causes, there is good evidence of the existence of Kowarski syndrome (due to GH1 variants) but less on the role of GHSR variants. Several genetic causes of (partial) GHI are known (GHR, STAT5B, STAT3, IGF1, IGFALS defects, and Noonan and 3M syndromes), some responding positively to GH therapy. In the final section, we speculate on hypothetical causes.

Cell and Cell-Free Therapies to Counteract Human Premature and Physiological Aging: MSCs Come to Light

The progressive loss of the regenerative potential of tissues is one of the most obvious consequences of aging, driven by altered intercellular communication, cell senescence and niche-specific stem cell exhaustion, among other drivers. Mesenchymal tissues, such as bone, cartilage and fat, which originate from mesenchymal stem cell (MSC) differentiation, are especially affected by aging. Senescent MSCs show limited proliferative capacity and impairment in key defining features: their multipotent differentiation and secretory abilities, leading to diminished function and deleterious consequences for tissue homeostasis. In the past few years, several interventions to improve human healthspan by counteracting the cellular and molecular consequences of aging have moved closer to the clinic. Taking into account the MSC exhaustion occurring in aging, advanced therapies based on the potential use of young allogeneic MSCs and derivatives, such as extracellular vesicles (EVs), are gaining attention. Based on encouraging pre-clinical and clinical data, this review assesses the strong potential of MSC-based (cell and cell-free) therapies to counteract age-related consequences in both physiological and premature aging scenarios. We also discuss the mechanisms of action of these therapies and the possibility of enhancing their clinical potential by exposing MSCs to niche-relevant signals.

GH Responsiveness in Children With Noonan Syndrome Compared to Turner Syndrome

BACKGROUND

Despite different genetic background, Noonan syndrome (NS) shares similar phenotype features to Turner syndrome (TS) such as short stature, webbed neck and congenital heart defects. TS is an entity with decreased growth hormone (GH) responsiveness. Whether this is found in NS is debated.

METHODS

Data were retrieved from combined intervention studies including 25 children diagnosed with NS, 40 diagnosed with TS, and 45 control children (all prepubertal). NS-children and TS-girls were rhGH treated after investigation of the GH/IGFI-axis. GH was measured with poly- and monoclonal antibodies; 24hGH-profile pattern analysed by PULSAR. The NS-children were randomly assigned to Norditropin^® 33 or 66 μg/kg/day, and TS-girls were consecutively treated with Genotropin^® 33 or 66 μg/kg/day.

RESULTS

Higher PULSAR-estimates of 24h-profiles were found in both NS-children and TS-girls compared to controls: Polyclonal GH_max24h-profile (Mean ± SD) was higher in both groups (44 ± 23mU/L, p<0.01 in NS; 51 ± 47, p<0.001 in TS; compared to 30 ± 23 mU/L in controls) as was GH-baseline (1.4 ± 0.6 mU/L in NS; 2.4 ± 2.4 mU/L in TS, p<0.01 for both, compared to 1.1 ± 1.2 mU/L in controls). Pre-treatment IGFI_SDS was 2.2 lower in NS-children (-1.7 ± 1.3) compared to TS-girls (0.6 ± 1.8, p<0.0001). GH_max, IGFI/IGFBP3-ratio_SDS, and chronological age at start of GH accounted for 59% of the variance in first-year growth response in NS.

CONCLUSION

Both prepubertal NS-children and TS-girls had a high GH secretion, but low IGFI/IGFBP3 levels only in NS-children. Both groups presented a broad individual response. NS-children showed higher response in IGFI and growth, pointing to higher responsiveness to GH treatment than TS-girls.

The cytoskeleton as a modulator of tension driven axon elongation

Throughout development, neurons are capable of integrating external and internal signals leading to the morphological changes required for neuronal polarization and axon growth. The first phase of axon elongation occurs during neuronal polarization. At this stage, membrane remodeling and cytoskeleton dynamics are crucial for the growth cone to advance and guide axon elongation. When a target is recognized, the growth cone collapses to form the presynaptic terminal. Once a synapse is established, the growth of the organism results in an increased distance between the neuronal cell bodies and their targets. In this second phase of axon elongation, growth cone-independent molecular mechanisms and cytoskeleton changes must occur to enable axon growth to accompany the increase in body size. While the field has mainly focused on growth-cone mediated axon elongation during development, tension driven axon growth remains largely unexplored. In this review, we will discuss in a critical perspective the current knowledge on the mechanisms guiding axon growth following synaptogenesis, with a particular focus on the putative role played by the axonal cytoskeleton.

GH Dose Reduction Maintains Normal Prepubertal Height Velocity After Initial Catch-Up Growth in Short Children

CONTEXT

GH responsiveness guides GH dosing during the catch-up growth (CUG) period; however, little is known regarding GH dosing during the prepubertal maintenance treatment period.

OBJECTIVE

To evaluate whether SD score (SDS) channel parallel growth with normal height velocity can be maintained after CUG by reducing the GH dose by 50% in children receiving doses individualized according to estimated GH responsiveness during the catch-up period.

DESIGN AND SETTINGS

Prepubertal children (n = 98; 72 boys) receiving GH during CUG (GH deficient, n = 33; non-GH deficient, n = 65), were randomized after 2 to 3 years to either a 50% reduced individualized dose (GHRID; n = 27; 20 boys) or unchanged individualized dose (GHUID; n = 38; 27 boys). Another 33 children (25 boys) continued a standard weight-based dose [43 µg/kg/d (GHFIX)].

MAIN OUTCOME MEASURES

The primary endpoint was the proportion of children with ΔheightSDS within ±0.3 at 1 year after GH dose reduction compared with two control groups: GHUID and GHFIX. The hypothesis was that heightSDS could be maintained within ±0.3 with a reduced individualized GH dose.

RESULTS

For the intention-to-treat population at 1 year, 85% of the GHRIDgroup maintained ΔheightSDS within ±0.3 vs 41% in the GHUIDgroup (P = 0.0055) and 48% in the GHFIXgroup (P = 0.0047). The ΔIGF-ISDS in the GHRID group was -0.75 ± 1.0 at 3 months (P = 0.003) and -0.72 ± 1.2 at 1 year compared with the GHUID group (0.15 ± 1.2; P = 0.005) and GHFIX group (0.05 ± 1.0; P = 0.02).

CONCLUSIONS

Channel parallel growth (i.e., normal height velocity) and IGF-ISDS levels within ±2 were maintained after completed CUG using a 50% lower individualized dose than that used during the CUG period.

Children Born Small for Gestational Age: Differential Diagnosis, Molecular Genetic Evaluation, and Implications

Children born small for gestational age (SGA), defined as a birth weight and/or length below -2 SD score (SDS), comprise a heterogeneous group. The causes of SGA are multifactorial and include maternal lifestyle and obstetric factors, placental dysfunction, and numerous fetal (epi)genetic abnormalities. Short-term consequences of SGA include increased risks of hypothermia, polycythemia, and hypoglycemia. Although most SGA infants show catch-up growth by 2 years of age, ∼10% remain short. Short children born SGA are amenable to GH treatment, which increases their adult height by on average 1.25 SD. Add-on treatment with a gonadotropin-releasing hormone agonist may be considered in early pubertal children with an expected adult height below -2.5 SDS. A small birth size increases the risk of later neurodevelopmental problems and cardiometabolic diseases. GH treatment does not pose an additional risk.

Variation of bone acquisition during growth hormone treatment in children can be explained by proteomic biomarkers, bone formation markers, body composition and nutritional factors

OBJECTIVE

Growth hormone (GH) regulates both longitudinal growth and bone acquisition in children, and has profound metabolic effects. The aim was to investigate the association between proteomic biomarkers, body fat, nutrition and bone formation markers, and longitudinal growth in response to GH during the first year of treatment. The degree to which changes in these factors could explain variations in GH-dependent longitudinal growth and bone mineralization was also assessed.

METHODS

The individualized GH dose trial included 128 short prepubertal children with either normal (non-GH-deficient) or reduced levels of GH secretion (GH-deficient) (mean age ± SD, 8.6 ± 2.6 years; 90 boys), i.e., with a broad range of GH-secretion and GH-responsiveness, receiving GH treatment (mean 43 μg/kg/day). Blood samples were taken and dual-energy X-ray absorptiometry (DXA) measured at baseline and 1 year of treatment. Step-wise multiple regression models were constructed including three steps with different independent variables added at each step to explain the variance in outcome variables (height_SDS, bone mineral content (BMC) and bone mineral density (BMD). Independent variables included in Step I were previously identified proteomic markers related to GH treatment response, bone formation markers (intact PINP, bone-specific alkaline phosphatase and osteocalcin), variables at treatment start (GH dose mU/kg/day, GH maximum secretion, and difference between child's current and mid-parental height_SDS). Step II explored the added influence of body composition data (body mass index or DXA). Step III explored the added influence of serum nutritional markers and hormones.

RESULTS

Step I variables explained 71% of the variation in first year height_SDS gain, median (minimum-maximum) 0.8 (0.24-1.67); and the proportion explained rose to 73% following inclusion of step II variables and 75% following step III. Corresponding values for total body BMC were 58%, 78%, and 80%, respectively. Proportions fell by approximately 20% when BMC was adjusted for height; 33%, 57%, and 57% for steps I, II, and III, respectively. Corresponding values for total body BMD were 29%, 39%, and 45%, respectively.

CONCLUSION

For total BMC, as much as 80% of the variation during the first year of GH treatment could be explained by proteomic biomarkers, body fat, nutrition and bone formation markers, whereas for height-adjusted BMC 57% could be explained. The inclusion of information about either body composition (fat/lean mass) or nutritional markers contributed with approximately 20%. The variation in height_SDS gain could be explained to 75%. Hence, information of fat or nutrition markers was needed for explaining the variation in bone acquisition to the same magnitude as explaining the variation in height response.

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.

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.

Impact of the underlying etiology of growth hormone deficiency on serum IGF-I SDS levels during GH treatment in children

CONTEXT

Regular monitoring of serum IGF-I levels during growth hormone (GH) therapy has been recommended, for assessing treatment compliance and safety.

OBJECTIVE

To investigate serum IGF-I SDS levels during GH treatment in children with GH deficiency, and to identify potential determinants of these levels.

DESIGN, PATIENTS AND METHODS

This observational cohort study included all patients (n = 308) with childhood-onset non-acquired or acquired GH deficiency (GHD) included in the database of a single academic pediatric care center over a period of 10 years for whom at least one serum IGF-I SDS determination during GH treatment was available. These determinations had to have been carried out centrally, with the same immunoradiometric assay. Serum IGF-I SDS levels were determined as a function of sex, age and pubertal stage, according to our published normative data.

RESULTS

Over a median of 4.0 (2-5.8) years of GH treatment per patient, 995 serum IGF-I SDS determinations were recorded. In addition to BMI SDS, height SDS and GH dose (P < 0.01), etiological group (P < 0.01) had a significant effect on serum IGF-I SDS levels, with patients suffering from acquired GHD having higher serum IGF-I SDS levels than those with non-acquired GHD, whereas sex, age, pubertal stage, treatment duration, hormonal status (isolated GHD (IGHD) vs multiple pituitary hormone deficiency (MPHD)) and initial severity of GHD, had no effect.

CONCLUSIONS

These original findings have important clinical implications for long-term management and highlight the need for careful and appropriate monitoring of serum IGF-I SDS and GH dose, particularly in patients with acquired GHD, to prevent the unnecessary impact of potential comorbid conditions.

Using a spontaneous profile rather than stimulation test makes the KIGS idiopathic growth hormone deficiency model more accessible for clinicians

AIM

Children treated with a growth hormone (GH) for idiopathic growth hormone deficiency (IGHD) may be monitored with the first-year prediction model from the Pfizer International Growth Database (KIGS) using auxology, age, GH dose and the maximum GH concentration from a stimulation test (GH_max stim). We tested the hypothesis that using a 12-hour spontaneous profile (GH_max 12h) would be as accurate.

METHODS

We studied 98 prepubertal Swedish children (78 boys) aged 2-12 years enrolled in KIGS. The first-year growth was predicted using the GH_max from the GH profile and a stimulation test, and both of these were compared separately with the observed growth response.

RESULTS

The increased height observed in the first year was 0.74 standard deviation scores (SDS), and the studentised residuals for the predicted and observed growth with GH_max stim (-0.16 SDS) and GH_max 12h (-0.22) were similar. Individual predictions calculated with stimulated or spontaneous GH_max showed a significant correlation (r = 0.80).

CONCLUSION

We validated the KIGS IGHD prediction model and found that the stimulated GH_max peak can be reliably replaced by the GH_max 12h with similar accuracy. This makes the model more accessible for clinicians, who can then provide realistic expectations for the growth response during the first year of treatment.

Serum relaxin-3 hormone relationship to male delayed puberty

Puberty is the transitional period between childhood and adulthood, a process encompassing morphological, physiological and behavioural development to attain full reproductive capability. This study aimed to assess serum relaxin-3 hormone relationship with male delayed puberty. Sixty males were investigated as two equal groups: males with delayed puberty and healthy matched males as controls. They were subjected to history taking, clinical examination and estimation of serum FSH, LH, testosterone, relaxin-3 hormonal levels. The results showed that the secondary sexual characters in the patients group were at Tanner stages 1-2 and in the healthy controls at Tanner stages 3-5. The mean BMI in the patients group was significantly increased, whereas the mean levels of the span, testicular volume, serum LH, FSH, testosterone as well as relaxin-3 hormonal levels were significantly decreased compared with the healthy controls. Serum relaxin-3 levels showed significant positive correlation with the age, testis volume, span, Tanner stages, serum testosterone, FSH, LH hormones. In addition, serum relaxin-3 levels showed significant negative correlation with BMI. It is concluded that serum level of relaxin-3 hormone is an important mediator in the pathophysiological process of normal puberty being significantly decreased in males with delayed puberty.