Growth and development: how safe is growth hormone therapy for children?

The Growth Hormone Receptor: Mechanism of Receptor Activation, Cell Signaling, and Physiological Aspects

The growth hormone receptor (GHR), although most well known for regulating growth, has many other important biological functions including regulating metabolism and controlling physiological processes related to the hepatobiliary, cardiovascular, renal, gastrointestinal, and reproductive systems. In addition, growth hormone signaling is an important regulator of aging and plays a significant role in cancer development. Growth hormone activates the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) signaling pathway, and recent studies have provided a new understanding of the mechanism of JAK2 activation by growth hormone binding to its receptor. JAK2 activation is required for growth hormone-mediated activation of STAT1, STAT3, and STAT5, and the negative regulation of JAK-STAT signaling comprises an important step in the control of this signaling pathway. The GHR also activates the Src family kinase signaling pathway independent of JAK2. This review covers the molecular mechanisms of GHR activation and signal transduction as well as the physiological consequences of growth hormone signaling.

Metabolic health of young adults who were born small for gestational age and treated with growth hormone, after cessation of growth hormone treatment: a 5-year longitudinal study

BACKGROUND

Growth hormone treatment reduces fat mass and insulin sensitivity and increases lean body mass. Data are only available for short-term longitudinal changes after cessation of growth hormone treatment in young adults born small for gestational age. We aimed to assess long-term changes over a 5-year period following cessation of growth hormone treatment.

METHODS

We did a longitudinal study of young adults born small for gestational age and previously treated with growth hormone. Individuals were followed up for 5 years after attainment of adult height, when growth hormone treatment was discontinued: assessments were done at cessation of growth hormone treatment and at 6 months, 2 years, and 5 years thereafter. Data 5 years after cessation of growth hormone were compared with untreated age-matched controls. We used dual-energy x-ray absorptiometry to assess body composition, and did frequently sampled intravenous glucose tolerance tests to assess insulin sensitivity, acute insulin response, and the disposition index (a measure of β-cell function). This study is registered with ISRCTN, numbers ISRCTN96883876 and ISRCTN65230311.

FINDINGS

Between April, 2004, and April, 2016, we followed up 199 young adults born small for gestational age and previously treated with growth hormone, during the 5 years after cessation of growth hormone treatment. Data at 5 years for these individuals were compared with those for 51 untreated adults born small for gestational age with short stature, 92 untreated adults born small for gestational age with spontaneous catch-up growth, and 142 adults born appropriate for gestational age and unexposed to growth hormone treatment. In young adults born small for gestational age and previously treated with growth hormone, 5 years after cessation of growth hormone treatment, there were increases in fat mass (estimated marginal mean 10·73 kg [95% CI 9·95-11·50] at cessation of treatment vs 16·12 kg [14·77-17·46] at 5 years; p<0·0001), trunk fat (5·34 kg [4·94-5·73] vs 7·86 kg [7·12-8·60]; p<0·0001), and limb fat (4·87 kg [4·49-5·25] vs 7·41 kg [6·78-8·05]; p<0·0001); furthermore, lean body mass had decreased (42·41 kg [95% CI 41·09-43·73] at cessation of treatment vs 41·42 kg [40·17-42·66] at 5 years; p=0·0013). Insulin sensitivity increased within 6 months of cessation and was sustained 5 years after treatment cessation (estimated marginal mean 4·14 mU/L [95% CI 3·79-4·53] at cessation of treatment vs 6·15 mU/L [5·21-7·24] at 5 years; p<0·0001), and acute insulin response was diminished at 6 months, which persisted at 5 year follow-up (597·63 mU/L [539·62-661·86] vs 393·69 mU/L [337·56-459·15]; p<0·0001). The disposition index was increased 6 months after treatment but values at 5 years were similar to those at cessation of treatment (2483·94 [95% CI 2233·43-2762·54] at cessation of treatment vs 2367·83 [2033·43-2757·22] at 5 years; p=0·49). 5 years after cessation of growth hormone treatment, adults born small for gestational age and previously treated with growth hormone had fat mass, insulin sensitivity, and disposition index similar to those of untreated adults born small for gestational age with short stature, but lean body mass (adjusted for sex and height) was lower (46·47 kg [44·95-48·00] in those born small for gestational age with short stature vs 44·32 kg [43·35-45·30] in those born small for gestational age and treated with growth hormone; p=0·007). In adults previously treated with growth hormone born small for gestational age, at 5 years after cessation of growth hormone treatment, compared with adults born small for gestational age with spontaneous catch-up growth and adults born appropriate for gestational age, lean body mass was lower and results from frequently sampled intravenous glucose tolerance tests were similar.

INTERPRETATION

Significant changes in body composition and insulin sensitivity were recorded 5 years after cessation of growth hormone treatment in adults born small for gestational age, reflecting a loss of pharmacological effects of growth hormone. 5 years after cessation of treatment, fat mass, insulin sensitivity, and β-cell function of previously treated adults were similar to untreated adults born small for gestational age with short stature, indicating that long-term growth hormone treatment in children born small for gestational age has no unfavourable effects on metabolic health in early adulthood.

FUNDING

Novo Nordisk Farma BV (Netherlands).

Treatment with recombinant human growth hormone during childhood is associated with increased intraocular pressure

OBJECTIVE

To evaluate the association between recombinant human growth hormone (rhGH) treatment and intraocular pressure (IOP) in children.

STUDY DESIGN

This is an observational cohort study including comparison between children treated with rhGH for at least 12 months (treatment group), matched children prior to treatment (control group), and population age-adjusted normograms of IOP. All children underwent an ocular slit lamp assessment and Goldmann applanation tonometry. Charts were reviewed for cause of therapy, peak stimulated growth hormone level prior to therapy, treatment duration, insulin-like growth factor 1, and rhGH dosage.

RESULTS

The treatment group included 55 children and the control group included 24 children. Mean age at examination was comparable at 11.4 ± 3.3 years and 10.3 ± 2.6 years, respectively (P = .13). Mean treatment duration was 37.5 ± 22.8 months and mean rhGH dose was 0.04 ± 0.01 mg/kg/d. Mean IOP was significantly increased in the treatment group compared with the control group and compared with age-matched normograms (16.09 ± 2.2 mm Hg, 13.26 ± 1.83 mm Hg and 14.6 ± 1.97 mm Hg, respectively, P < .001). IOP was positively correlated with treatment duration (r = 0.559, P < .001) and rhGH dosage (r = 0.274, P = .043).

CONCLUSION

IOP in children treated with rhGH is increased compared with a similar population without treatment and compared with healthy population normograms. IOP is associated with longer treatment duration and higher dosages.

Role of the growth hormone-IGF-1 axis in cancer

A substantial body of evidence supports a role for the growth hormone (GH)-IGF-1 axis in cancer incidence and progression. This includes epidemiological evidence relating elevated plasma IGF-1 to cancer incidence as well as a lack of cancers in GH/IGF-1 deficiency. Rodent models lacking GH or its receptor are strikingly resistant to the induction of a wide range of cancers, and treatment with the GH antagonist pegvisomant slows tumor progression. While GH receptor expression is elevated in many cancers, autocrine GH is present in several types, and overexpression of autocrine GH can induce cell transformation. While the mechanism of autocrine action is not clear, it does involve both STAT5 and STAT3 activation, and probably nuclear translocation of the GH receptor. Development of a more potent GH receptor antagonist or secretion inhibitor is warranted for cancer therapy.