Growth hormone replacement therapy in adults with growth hormone deficiency improves maximal oxygen consumption independently of dosing regimen or physical activity

Treatment of adult growth hormone deficiency with human recombinant growth hormone: an update on current evidence and critical review of advantages and pitfalls

Adult-onset growth-hormone (GH) deficiency (GHD) is a rare disorder, which most commonly results from pituitary or peripituitary tumors and their treatment, and is characterized by alterations in body composition, carbohydrate and lipid metabolism, bone mineral density, cardiovascular risk profile and quality of life, all of which may contribute to an increased morbidity and mortality. Since recombinant human GH (rhGH) became available in 1985, several studies have provided evidence of its beneficial effects, despite the potential risk of developing adverse effects, and much clinical experience has been accumulated. However, in adults, the precise therapeutic role of GH replacement therapy and the individual response to it remains highly variable and is still a matter of debate. In this article, we present a critical review of the available evidence on rhGH replacement therapy in GHD adults, emphasizing the pitfalls clinicians encounter in the diagnosis of GHD and monitoring of rhGH replacement therapy. We will cover all the relevant aspects regarding the potential usefulness of GH treatment, including the hot topic of mortality.

Effects of Growth Hormone Replacement on Peripheral Muscle and Exercise Capacity in Severe Growth Hormone Deficiency

OBJECTIVE

The aim of this study is to evaluate the effect of growth hormone therapy (rGH) on mitochondrial function on peripheral muscle and to correlate with exercise capacity in subjects with severe adult growth hormone deficiency (GHD).

DESIGN

Six months, double-blind, randomized, crossover, placebo-controlled trial of subcutaneous rGH in 17 patients with GHD.

MEASUREMENTS

Quadriceps muscle biopsies were obtained at baseline, 3 months, and 6 months to measure succinate dehydrogenase (SDH) to assess mitochondrial activity. Exercise capacity was measured with cardiopulmonary exercise testing. Lipids, glycemic parameters, and body fat levels were also measured.

RESULTS

Serum insulin-like growth factor 1 (IGF1) levels reduced fat mass by 3.2% (p < 0.05) and normalized with rGH in the active phase (p < 0.005). Patients showed an increase in SDH (p < 0.01) from base line that differed between placebo and rGH therapy treatment groups (p < 0.05): those treated by rGH followed by placebo showed a significant increase in SDH (p < 0.001) followed by a decrease, with a significant between group difference at the end of 6 months (p < 0.05). No significant improvements or correlation with exercise capacity was found.

CONCLUSION

Short-term rGH for 3 months normalized IGF1 levels, reduced fat mass, and had a significant effect on mitochondrial function, but exercise capacity was unchanged.

CLINICAL TRIAL REGISTRATION

Number ISRCTN94165486.

Growth Hormone Improves Cardiopulmonary Capacity and Body Composition in Children With Growth Hormone Deficiency

CONTEXT

Growth hormone deficiency (GHD) in children may be associated with early cardiovascular risk factors and alterations in left ventricular (LV) structure and function; data on cardiopulmonary functional capacity are lacking.

OBJECTIVES

Aim of the study was to evaluate the effect of GHD and growth hormone (GH) therapy on cardiopulmonary functional capacity, left and right cardiac structure and function, and body composition in children and adolescents.

DESIGN

Prospective, case-control study.

PATIENTS AND METHODS

Twenty-one untrained GHD children (11.3 ± 0.8 years) underwent cardiopulmonary exercise testing, echocardiography and dual-energy x-ray absorptiometry, before and after 12 months of GH therapy. Twenty-one controls matched for sex, pubertal status, body mass index, and physical activity (PA) were evaluated at baseline and after 1 year.

RESULTS

At baseline, GHD patients showed reduced LV mass (LVM; 63.32 ± 7.80 vs 80.44 ± 26.29 g/m2, P = 0.006), peak oxygen consumption (VO2peak; 22.92 ± 4.80 vs 27.48 ± 6.71 mL/Kg/min, P = 0.02), peak workload (80.62 ± 29.32 vs 103.76 ± 36.20 W, P = 0.02), and O2 pulse (4.93 ± 1.30 vs 7.67 ± 2.93 mL/beat, P = 0.0003), compared with controls. GHD patients also exhibited lower lean body mass (LBM 65.36 ± 7.84% vs 76.13 ± 8.23%, P < 0.001), and higher fat mass (FM 30.84 ± 7.92% vs 22.19 ± 8.18%, P = 0.001) than controls. GH therapy resulted in a significant increase of LVM (72.01 ± 15.88, P = 0.03), VO2peak (26.80 ± 4.97; P = 0.01), peak workload (103.67 ± 32.24, P = 0.001), O2 pulse (6.64 ± 1.68, P = 0.0007), and LBM (75.36 ± 7.59%, P = 0.0001), with a reduction in FM (22.62 ± 7.73%, P = 0.001). No difference was found in either left or right ventricular function.

CONCLUSION

Our results suggest that cardiac structure, body composition and cardiopulmonary functional capacity are impaired in children with untreated GHD and can be restored after short-term GH replacement therapy.

Functional Changes after Recombinant Human Growth Hormone Replacement in Patients with Chronic Traumatic Brain Injury and Abnormal Growth Hormone Secretion

We explored the effects of recombinant human growth hormone (rhGH) replacement on physical and cognitive functioning in subjects with a moderate-to-severe traumatic brain injury (TBI) with abnormal growth hormone (GH) secretion. Fifteen individuals who sustained a TBI at least 12 months prior to study enrollment were identified as having abnormal GH secretion by glucagon stimulation testing (maximum GH response less than 8 ng/mL). Peak cardiorespiratory capacity, body composition, and muscle force testing were assessed at baseline and one year after rhGH replacement. Additionally, standardized neuropsychological tests that assess memory, processing speed, and cognitive flexibility, as well as self-report inventories related to depression and fatigue, were administered at baseline and 1 year after rhGH replacement. Comparison tests were performed with proper post hoc analyses. All analyses were carried out at α < 0.05. Peak O₂ consumption, peak oxygen pulse (estimate of cardiac stroke volume), and peak ventilation all significantly increased (p < 0.05). Maximal isometric and isokinetic force production were not altered. Skeletal muscle fatigue did not change but the perceptual rating of fatigue was reduced by ∼25% (p = 0.06). Cognitive performance did not change significantly over time, whereas self-reported symptoms related to depression and fatigue significantly improved. The observed changes suggest that rhGH replacement has a positive impact on cardiorespiratory fitness and a positive impact on perceptual fatigue in survivors of TBI with altered GH secretion.

Cellular bioenergetics as a target for obesity therapy

Obesity develops when energy intake exceeds energy expenditure. Although most current obesity therapies are focused on reducing calorific intake, recent data suggest that increasing cellular energy expenditure (bioenergetics) may be an attractive alternative approach. This is especially true for adaptive thermogenesis - the physiological process whereby energy is dissipated in mitochondria of brown fat and skeletal muscle in the form of heat in response to external stimuli. There have been significant recent advances in identifying the factors that control the development and function of these tissues, and in techniques to measure brown fat in human adults. In this article, we integrate these developments in relation to the classical understandings of cellular bioenergetics to explore the potential for developing novel anti-obesity therapies that target cellular energy expenditure.

Growth hormone receptor antagonist treatment reduces exercise performance in young males

CONTEXT

The effects of GH on exercise performance remain unclear.

OBJECTIVE

The aim of the study was to examine the effects of GH receptor (GHR) antagonist treatment on exercise performance.

DESIGN

Subjects were treated with the GHR antagonist pegvisomant or placebo for 16 d. After the treatment period, they exercised to determine exercise performance and hormonal and metabolic responses.

PARTICIPANTS

Twenty healthy males participated in the study.

INTERVENTION

Subjects were treated with the GHR antagonist (n = 10; 10 mg/d) or placebo (n = 10). After the treatment period, they performed a maximal oxygen uptake (VO(2 max)) test and a prolonged exercise test, consisting of 60 min of submaximal cycling followed by exercise to fatigue at 90% of VO(2 max).

MAIN OUTCOME MEASURES

VO(2 max) was measured before and after the treatment period. Hormonal and metabolic responses and time to exhaustion during prolonged exercise were determined.

RESULTS

Resting serum IGF-I concentration decreased by 20% in the GHR antagonist-treated group (P < 0.05), whereas no change was observed in the placebo group. Conversely, resting serum GH concentration was significantly higher in the treatment group compared with the placebo group (P < 0.01). VO(2 max) did not change significantly in either group after the treatment period. Time to exhaustion at 90% of VO(2 max) was significantly shorter in the treatment group (P < 0.05). No significant differences were observed between the groups in terms of changes in serum free fatty acids, glycerol, VO(2), or relative fat oxidation.

CONCLUSION

GH might be an important determinant of exercise capacity during prolonged exercise, but GHR antagonist did not alter fat metabolism during exercise.

The effect of growth hormone replacement on exercise capacity in patients with GH deficiency: a metaanalysis

CONTEXT/OBJECTIVES

GH replacement in GH-deficient adults exerts clear effects on body composition, but there is a lack of high-quality evidence concerning its functional effects, which are more clinically important. This metaanalysis was carried out to determine the effects of GH replacement on exercise performance.

DESIGN/METHODS

A Medline search and examination of reference lists of included studies and relevant review articles identified 11 studies with utilizable, robust data, involving a total of 268 patients. All included studies were randomized, double blind, placebo controlled, and of either parallel or crossover design. Information was retrieved in uniform format, with data pertaining to patient numbers, study design, GH dose, age, IGF-I levels, and the exercise variables maximal oxygen uptake and maximal power output recorded. The data were analyzed using a fixed-effects model, using continuous data measured on different scales. A summary effect measure (ds) was derived for the individual exercise parameters, whereas an overall summary effect was derived from the sum of all studies across different variables; 95% confidence intervals were calculated from the weighted variances of individual study effects.

RESULTS

GH replacement was associated with significant improvement with all studies combined (ds=+0.32, 0.08-0.56), for maximal power output (ds=+0.4, 0.06-0.74), and maximal oxygen uptake (ds=+0.34, 0.07-0.62). There was no association between age or GH dose on the degree of improvement.

CONCLUSIONS

There is strong evidence that GH replacement improves exercise performance in GH-deficient patients. This evidence should be considered when decisions are made regarding prescription of GH.

Adult-onset growth hormone deficiency: causes, complications and treatment options

PURPOSE OF REVIEW

Description of the progresses related to the complications and treatment of adult-onset growth hormone deficiency.

RECENT FINDINGS

Growth hormone deficiency in adults has gained attention as a clinical syndrome associated with increased morbidity and possibly mortality. Many studies have been conducted on the consequences of growth hormone deficiency and of its replacement, supporting its use in appropriate patients. Early studies were characterized by a high incidence of side effects due to a lack of pilot data to guide appropriate dosing. Given the wide variability in individual responsiveness to growth hormone therapy based on age, sex, and body composition, recent work has been dedicated to understanding which patients derive benefit from therapy, minimizing side effects, and ensuring cost-effectiveness.

SUMMARY

Long-term prospective trials have shown that growth hormone replacement therapy results in improvements in body composition, dyslipidemia, bone mineral density, and quality of life. The effects on endpoints such as cardiovascular morbidity and mortality and fractures are, however, not fully proven. Randomized trials that compare homogenous groups of growth hormone deficiency patients are still needed. Given the high cost of treatment, dynamic testing for growth hormone deficiency should only be performed in patients in whom there is high clinical suspicion, and therapy should be limited to those with biochemically proven growth hormone deficiency.