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CLINICAL STUDY |
Section of Endocrinology, The National Hospital, Oslo, Norway, 1 The Norwegian University of Sport and PE, Oslo, Norway 2 Medical Department, Section of Endocrinology, St Olavs Hospital, Trondheim University Hospital, Trondheim, Norway, 3 Department of Endocrinology, Aker University Hospital, Oslo, Norway 4 Capturo AS, Kjeller, Norway 5 Scandinavian Clinical Research AS, Kjeller, Norway and the 6 Department of Endocrinology, University Hospital Malmø University Hospital, Malmø, Sweden
(Correspondence should be addressed to J Bollerslev, Section of Endocrinology, Department of Medicine, National University Hospital, N-0027 Oslo, Norway; Email: jens.bollerslev{at}klinmed.uio.no)
| Abstract |
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| Introduction |
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GH replacement therapy in adult-onset GHD (AO-GHD) increases lean body mass (LBM) (10) and muscle mass (9, 14), even at low doses. However, its effect on muscle strength has been controversial. In smaller, relatively short-term studies, GH therapy had no significant effect on muscle strength despite an increase in muscle mass (14, 15). In long-term (
2 years), open-label studies, age- and sex-specific increases, and normalization of muscle mass and strength were found with treatment (16, 17).
A limited number of placebo-controlled studies have assessed the effect of GH replacement therapy on exercise and endurance capacity (Table 1
) (14, 15, 1827). In three studies in adults with GHD, a significant increase in endurance capacity (i.e. work performed) was reported with high doses of GH (14, 23, 26). In a prospective, open-label study using a lower GH dose (median, 5.05.3 µg/kg per day), treatment for 12 months demonstrated a significant improvement in cardiac performance and in exercise endurance capacity (9). To date, no controlled study has investigated the effect of a low, physiologic dose of GH therapy on maximal oxygen uptake (vo2max) and endurance capacity in patients with AO-GHD.
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The aim of the present study was to investigate the effects and potential benefits of physiologic GH replacement therapy on exercise endurance capacity, muscle strength, vo2max, body composition, lipid profile, and QOL in GH-naive patients with AO-GHD.
| Subjects and methods |
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Fifty-five subjects (31 men and 24 women; mean age, 49 years (range, 2662 years)) who had had severe AO-GHD for at least 2 years (mean duration, 4.0 (range, 0.312.4 years)) and who had never been treated with GH were randomly assigned to treatment with GH replacement therapy or placebo. Severe GHD was defined as a peak GH response to a stimulation test (insulin tolerance test with a nadir glucose level
2.2 mmol/l) less than 3 µg/l. All subjects with multiple pituitary insufficiencies received stable doses of substitution therapy with other hormones for at least 6 months before study entry. Computed tomography or magnetic resonance imaging of the pituitary had been performed within 1 year before the inclusion of each subject in the study.
Primary diagnosis for most subjects (37/55; 67%) was pituitary adenoma; most subjects were treated with surgery alone (27/37; 73%) or with a combination of surgery and irradiation (7/37; 19%). One patient (1/37; 3%) was treated with irradiation only, and the other two patients (2/37; 5.4%) were treated with other therapies. Primary diagnosis was craniopharyngioma (7/55; 13%) or parasellar tumor or meningioma (3/55; 5%) for the other additional subjects; two subjects had cystic tumor of unknown origin. Four subjects acquired hypopituitarism in adulthood from Sheehan syndrome and two subjects had idiopathic hypopituitarism. Of the total study population, most subjects (53/55; 96%) had multiple pituitary deficiencies and only two had isolated GHD. Of the 24 women in the study, 15 underwent estrogen replacement therapy. Six women were considered post-menopausal and did not undergo estrogen replacement therapy, the remaining women were evaluated as eugonadal and no patient received dehydroepiandrosterone. Of the 31 men, 22 received testosterone substitution and the remaining were considered to be eugonadal.
Study design
Three centers in Norway participated in this prospective, double-blind, randomized, crossover study. An independent ethics committee approved the study protocol, and written informed consent was obtained from all subjects. Subjects underwent treatment with either recombinant human GH therapy (Genotropin; Pfizer Inc, New York, NY, USA) or placebo in a crossover fashion. Each treatment period lasted 9 months, with a 4-month washout interval between periods.
GH replacement therapy was dosed individually to maintain serum insulin-like growth factor-I (IGF-I) concentrations between the mean±1 S.D. of the sex-and age-related reference range. GH therapy was initiated at a dose of 0.4 IU/day for men and at 0.8 IU/day for women. Dose adjustments were made in increments of 0.4 IU/day every 4 weeks (maximum dose, 2.0 IU/day (men) and 2.8 IU/day (women)) based on IGF-I concentrations and the absence of adverse effects. A physician who was not blinded to the study and who was not participating in subject care guided all dose adjustments, including dose adjustment for subjects receiving placebo. Patients given placebo received the same adjustments as a given parallel patient receiving active treatment.
At the beginning and end of each treatment period, the following parameters were assessed: exercise capacity, muscle strength, body weight, body composition, physical examination findings, and QOL. Fasting blood samples were obtained and analyzed for IGF-I concentration, glucose, glucosylated hemoglobin (HbA1c) insulin concentrations, and lipid profiles. Adverse effects and vital signs were recorded at each of the monthly visits in each treatment period, including baseline visits (ten visits per treatment period). vo2max, muscle strength, and QOL tests were performed before baseline (pretest) to familiarize subjects with these procedures.
Physical exercise capacity, muscle strength, and body composition
Exercise tests and muscle strength were conducted in the subjects from the centers in Oslo, (n = 28 for vo2max and n = 35 for muscle strength) at a single location by one of the investigators (J H). vo2max and time to exhaustion were determined by treadmill walking or running using a stepwise incremental protocol. The exercise test was started at a relatively low intensity to provide a warm-up period; the speed or incline was then increased at 2-min intervals until subjects reached volitional exhaustion. The initial workload was chosen individually according to the pretest, so that the continuous exercizing phase lasted from 8 to 12 min. The work intensity increment was fixed for every subject and was chosen so it equaled approximately 1 metabolic equivalent (3.5 ml/(kg x min)). Heart rate (Siemens SC6000; Siemens Nederland N.V., Hague, The Netherlands), ratings of perceived exertion (29), and ergospirometric values (Oxicon; Erich Jaeger GmbH, Hoechberg, Germany) were registered at the last minute before exhaustion. Blood from the fingertip was taken 1 and 3 min after exhaustion and analyzed for lactate concentrations (YSI 1500 Sport; Yellow Spring Instruments, OH, USA), and the maximal value was registered. Knee extension strength was tested in voluntary isokinetic knee extensions at 60°/s using a Cybex 6000 dynamometer (Lumex, Ronkonkoma, NY, USA). The range of motion was set to a knee angle of 9020° from full extension. Subjects performed four warm-up contractions followed by three maximal contractions (30). Dominant leg peak torque was used to measure knee extensor muscle strength.
Total body composition was measured by dual-energy X-ray absorptiometry as body fat mass (BFM) and LBM. The two centers in Oslo used Lunar DPX-L, software version 1.31 (Lunar Corp., Madison, WI, USA). The center in Trondheim used the Hologic QDR-4500 (Waltham, MA, USA) in dual-beam mode. Total body imaging was performed and analyzed by one person at each center, as previously described (31).
QOL assessments
The primary questionnaire was the sum score of the Hopkins Symptom Checklist-58 (HSCL-58) (32). The range of scores possible on the HSCL-58 questionnaire was 58232, with low scores indicating better QOL. The generic questionnaire (short form-36 general health survey; SF-36) (33) where higher scores indicate better QOL was also performed. Results of the baseline SF-36 questionnaire were compared with normative Norwegian data (34). Another QOL instrument used was the assessment of growth hormone deficiency in adults (AGHDA) (35).
IGF-I and other chemistry profiles
Biochemical analyses were performed by accredited laboratories according to standard laboratory methods. IGF-I analysis was performed using the commercial kit Immulite (Diagnostic Products Corporation, Los Angeles, CA, USA). The intra-assay coefficient of variation (C.V.) was 48% and the interassay C.V. was less than 9%. Insulin, lipids, and other chemistry measurements were performed by routine methods at Furst Laboratory, Oslo, Norway.
Statistical analyses
An analysis of covariance (ANCOVA) model that included treatment drug, center, baseline value, sex, and age was presented. Variables analyzed with ANCOVA included the sum score for exercise variables (i.e. vo2max (ml/(kg x min) and l/min) endurance time), LBM, BFM, HSCL-58, dimensions of HSCL-58 and SF-36, and sum scores of AGHDA. The difference (month 9 to month 0) was the dependent variable in the ANCOVA models. The direct effect of GH therapy compared with placebo treatment was estimated by the crossover effect, which was calculated by taking the difference between GH and placebo (month 0 to month 9 changes). Using mean values, a point estimate and a two-sided 95% confidence interval of the crossover differences were calculated. Subjects who withdrew in period 1 were excluded from analysis; those subjects participating for at least 3 months of period 2 were included. All tests performed were two sided, and the significance level was set at 5%.
| Results |
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Patient demographics and baseline characteristics for the 55 subjects enrolled in the study are summarized in Table 2
. Of those subjects enrolled, seven withdrew from the study (two during placebo treatment, three during GH treatment and two withdrew prior to the first study dose). Sufficient data were accumulated in the second treatment period to include one of the two subjects in the analysis of efficacy, resulting in a total of 49 study subjects (29 men and 20 women) who were evaluable for efficacy and safety.
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Fig. 1
illustrates IGF-I concentrations at baseline compared with age-adjusted IGF-I reference curves. Mean baseline IGF-I concentrations were significantly higher in men (95±33 vs 68±41 µg/l respectively; P < 0.04). Mean final dose of GH in women (1.8±0.8 IU/day) was approximately 50% greater than the dose used in men (1.2±0.6 IU/day; P = 0.03). Women prescribed estrogen replacement therapy (n = 15) tended to require higher doses of GH than women not prescribed estrogen (n = 9) (2.0±0.9 vs 1.6±0.3 IU/day; P < 0.05). The mean time to reach the final GH dose was 3.2 months. During treatment with GH, IGF-I concentrations increased to a similar level in men and women (217±65 and 186±70 µg/l respectively; P = not significant (NS); Fig. 1
). In two women the final dose of GH administered did not increase IGF-I to the desired level.
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vo2max increased significantly with GH treatment compared with placebo in absolute value (l/min, 6%; P = 0.01) and relative to body weight (ml/(kg x min), 9%; P = 0.004) (Fig. 2
). The crossover difference for endurance performance increased by 0.6 min in favor of GH treatment, representing a 7% increase (P = 0.07). Heart rate, ventilation rate, respiratory exchange ratio, rating of perceived exertion, and lactate concentration at exhaustion were not significantly different between the treatment periods (data not shown). Knee extensor peak torque was 178.5±62.8 Newton meters (Nm) before and 176.3±62.0 Nm after GH treatment (P = NS).
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LBM increased with GH replacement therapy compared with placebo (1.8±2.8 kg; P = 0.0001) and BFM decreased significantly (1.9±2.9 kg; P = 0.0001). Total and low-density lipoprotein cholesterol concentrations decreased by 0.50 mmol/l (P = 0.004) and 0.47 mmol/l (P = 0.0002) respectively, whereas triglycerides increased by 0.40 mmol/l (P = 0.01) during GH treatment.
QOL assessments
QOL was not impaired in most subjects, as is represented by the mean baseline values as assessed by the HSCL-58, the SF-36, and the AGHDA in Table 2
. After 9 months of GH treatment, overall QOL in subjects was not significantly different from the reported QOL in those receiving placebo. There was no sex difference in response to treatment. Assessment in patients with HSCL-58 values above the median sum score of 78 showed that there was a marked improvement in women compared with men with respect to the global score (P = 0.033) and in dimensions assessing somatization (P = 0.026), fearfulness (P = 0.003), and tension (P = 0.016). Figure 3
compares baseline SF-36 results of study patients with those of normative Norwegian data (34). Patients with AO-GHD scored lower than the referenced healthy population only in the sum scores vitality and general health.
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During active treatment, serum insulin concentrations increased by 33.7 pmol/l (P < 0.02), fasting glucose concentrations increased by 0.49 mmol/l (P = 0.02), and HbA1c increased by 0.14% (P = 0.05). There were no differences in the effect of treatment between women and men. Numbers of adverse effects, changes in vital signs, and physical examination findings were similar in both treatment periods.
| Discussion |
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Previous studies assessing the effects of GH therapy on exercise capacity in patients with GHD have been open labeled (9, 4044) or have used higher, weight-based or fixed doses of GH (14, 15, 18, 2023, 25, 26). In the present study, we attempted to reduce a possible placebo effect by using a similar individualized GH dosing regimen during each treatment period. The dose of GH was lower than used in previous controlled studies and took into account the sex-related difference in GH responsiveness in women by using a higher starting dose and allowing for a higher final dose. Using this method, we found that women treated with GH needed a dose approximately 50% greater than that administered to men to obtain the target IGF-I concentration and similar effects on body composition and lipids.
In studies of patients with GHD (41, 44, 45), GH treatment with higher doses has been associated with increases of up to 20% in exercise performance. An increase in vo2max of 79% as found in this study is likely to be clinically relevant in middle-aged patients, improving daily exercise capacity (46). Physical training per se, in the absence of GHD, typically increases vo2max by 1020%, depending on training status and genetic predisposition (46).
The improvement in endurance capacity was paralleled by a similar increase in absolute and relative vo2max. Theoretically, the increase in oxygen uptake could be explained, in part, by alterations in LBM. However, adjusting for the change in LBM did not change the results (data not shown), indicating that additional factors are likely to contribute, for instance, an increase in cardiac output (41, 44). Interestingly, physical capacity, as measured in our cohort at baseline, was not correlated with IGF-I concentrations but with baseline QOL (data not shown). Recently, in a controlled study, the potential benefit of combining an exercise program with GH replacement therapy for 3 months in ten patients with GHD was studied (19). A positive effect of training was noted, but no additive effect of GH therapy was observed, illustrating that physical fitness may influence the extent of change achieved by GH. In our study, we did not find a relation between the baseline exercise capacity and the response to GH.
Muscle strength was not improved by active treatment in this study in accordance with other investigations using GH in physiologic doses (14, 15), although some positive effect has been reported in two long-term, open-label studies (16, 17). The lack of effect in the present study is not surprising, even if muscle mass was greater (LBM, 1.8 kg) during GH therapy than with placebo because muscle strength is determined by several factors, in addition to muscle size (16). It is likely that GH therapy alone, without an adequate weight-training program, is not sufficient to produce an increase in muscle strength (15).
QOL was assessed by a variety of non-specific and disease-specific questionnaires in this study. In contrast to findings in several previous controlled and open-label studies (3, 47, 48), we were unable to demonstrate significant improvements in QOL. Several explanations are possible. Because GH has been in clinical use for several years, our population might have represented a population of patients with slight or vague symptoms (49). This is suggested by the results of the SF-36 questionnaire. Patients scored lower, but not significantly lower, for each of the separate domains compared with normative data. Only the sum scores vitality and general health were significantly reduced, substantiating the minor reduction in psychologic health in our population at baseline. In addition to patient selection, the benefit of GH therapy on QOL in early studies might have been related to higher GH dosing, either throughout the studies or during the initial phases (49).
In conclusion, physiologic and individualized GH replacement therapy aimed at normalizing IGF-I concentration in relation to age in GH-naive patients with AO-GHD was followed by significant improvements in body composition, as well as low-density lipoprotein cholesterol and exercise capacity. Treatment with GH was not associated with changes in the patients perceived QOL, probably because these patients had a good QOL at the onset of the study.
| Acknowledgements |
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| References |
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