Effects of GH in women with abdominal adiposity: a 6-month randomized, double-blind, placebo-controlled trial

in European Journal of Endocrinology
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  • 1 Department of Radiology, Neuroendocrine Unit, Biostatistics Center, Maine Medical Center Research Institute, Cardiology Division, Department of Medicine, Children's Hospital, Vanderbilt University

Objective

Abdominal adiposity is associated with increased cardiovascular risk and decreased GH secretion. The objective of our study was to determine the effects of GH on body composition and cardiovascular risk markers in abdominally obese women.

Materials and methods

In this randomized, double-blind, placebo-controlled study, 79 obese premenopausal women received GH vs placebo for 6 months. Primary endpoints were i) total abdominal (total abdominal adipose tissue, TAT) fat by computed tomography (CT) (body composition) and ii) high-sensitivity C-reactive protein (hsCRP) (cardiovascular risk marker). Body composition was assessed by CT, dual-energy X-ray absorptiometry, and proton MR spectroscopy. Serum cardiovascular risk markers, carotid intima-media thickness, and endothelial function were measured.

Results

Mean 6-month GH dose was 1.7±0.1 mg/day, resulting in a mean IGF1 SDS increase from −1.7±0.08 to −0.1±0.3 in the GH group. GH administration decreased TAT and hsCRP compared with placebo. In addition, it increased thigh muscle mass and lean body mass and decreased subcutaneous abdominal and trunk fat, tissue plasminogen activator, apoB, and apoB/low-density lipoprotein compared with placebo. Visceral adipose tissue (VAT) decreased and intramyocellular lipid increased within the GH group. Six-month change in IGF1 levels was negatively associated with 6-month decrease in TAT and VAT. One subject had a 2 h glucose >200 mg/ml at 3 months; four subjects, three of whom were randomized to GH, had 2 h glucose levels >200 mg/ml at the end of the study.

Conclusion

GH administration in abdominally obese premenopausal women exerts beneficial effects on body composition and cardiovascular risk markers but is associated with a decrease in glucose tolerance in a minority of women.

Abstract

Objective

Abdominal adiposity is associated with increased cardiovascular risk and decreased GH secretion. The objective of our study was to determine the effects of GH on body composition and cardiovascular risk markers in abdominally obese women.

Materials and methods

In this randomized, double-blind, placebo-controlled study, 79 obese premenopausal women received GH vs placebo for 6 months. Primary endpoints were i) total abdominal (total abdominal adipose tissue, TAT) fat by computed tomography (CT) (body composition) and ii) high-sensitivity C-reactive protein (hsCRP) (cardiovascular risk marker). Body composition was assessed by CT, dual-energy X-ray absorptiometry, and proton MR spectroscopy. Serum cardiovascular risk markers, carotid intima-media thickness, and endothelial function were measured.

Results

Mean 6-month GH dose was 1.7±0.1 mg/day, resulting in a mean IGF1 SDS increase from −1.7±0.08 to −0.1±0.3 in the GH group. GH administration decreased TAT and hsCRP compared with placebo. In addition, it increased thigh muscle mass and lean body mass and decreased subcutaneous abdominal and trunk fat, tissue plasminogen activator, apoB, and apoB/low-density lipoprotein compared with placebo. Visceral adipose tissue (VAT) decreased and intramyocellular lipid increased within the GH group. Six-month change in IGF1 levels was negatively associated with 6-month decrease in TAT and VAT. One subject had a 2 h glucose >200 mg/ml at 3 months; four subjects, three of whom were randomized to GH, had 2 h glucose levels >200 mg/ml at the end of the study.

Conclusion

GH administration in abdominally obese premenopausal women exerts beneficial effects on body composition and cardiovascular risk markers but is associated with a decrease in glucose tolerance in a minority of women.

Introduction

Abdominal adiposity is associated with a marked increase in coronary heart disease and increased inflammatory cardiovascular markers, including high-sensitivity C-reactive protein (hsCRP) and carotid artery wall thickening (1, 2). In women with increased abdominal adiposity, physiological GH secretion is impaired and peak stimulated GH response is decreased (3, 4). GH plays a role in modulating body composition, and GH deficiency in women with hypopituitarism is associated with increased body fat, including visceral adiposity, and decreased lean body mass (5). Visceral adiposity has also been shown to be a major determinant of GH secretion in nonobese adults (6). GH is also a mediator of atherogenesis. GH has cytokine-like effects and its administration results in decreased hsCRP levels in patients with pituitary disorders and GH deficiency (7, 8). GH also increases low-density lipoprotein (LDL) receptor activity and affects the expression of key enzymes involved in intracellular cholesterol metabolism in the liver (9). Moreover, we have reported an independent inverse association between GH and intramyocellular lipid (IMCL), a marker of insulin resistance, and intrahepatic fat in obese women, suggesting that low GH contributes to insulin resistance through effects on skeletal muscle and intrahepatic lipids (IHLs) (10).

IGF1, an important modulator of body composition, is secreted by the liver and other organs in response to GH. As IGF1 is an important determinant of body composition, particularly critical for the maintenance of muscle mass (11), reduced levels in obese premenopausal women may exert deleterious effects on body composition. Although the effects of GH administration to decrease visceral adiposity, increase muscle mass, and improve cardiovascular risk markers, including hsCRP, are well established in patients with GH deficiency due to hypothalamic/pituitary disorders (7, 8, 12), few studies have been performed administering low-dose GH in otherwise healthy obese subjects (13, 14, 15, 16). Administration of low-dose GH to obese men (14, 15) and postmenopausal women (13) resulted in decreased visceral fat mass and improved lipid profiles, suggesting a possible beneficial effect of GH in healthy subjects with visceral obesity. However, no studies have been performed on the effects of GH on cardiovascular risk factors, including inflammatory markers, and detailed measures of body composition, focusing on premenopausal women with abdominal obesity. Given the strong association between abdominal obesity and cardiovascular disease, we investigated the effects of GH-induced changes on body composition, lipid profile, inflammatory markers, and glucose metabolism in order to enhance our understanding of the effects of low endogenous GH in obese premenopausal women.

We hypothesized that GH treatment for 6 months would result in a reduction in total abdominal adipose tissue and hsCRP levels (primary endpoints) in premenopausal women with relative GH and IGF1 deficiency due to abdominal obesity. We also hypothesized that both visceral and subcutaneous adipose tissue (SAT) depots would decrease and muscle mass would increase with GH administration. We also explored the effects on other cardiovascular risk markers. In addition, we hypothesized that although acute GH administration would increase glucose intolerance, chronic GH administration would result in normalization of measures of glucose tolerance due to an increase in muscle mass and a decrease in IMCL and IHL concentrations.

Materials and methods

The study was approved by the institutional review board of Partners HealthCare, Inc. and was Health Insurance Portability and Accountability Act compliant. Written informed consent was obtained from all subjects before conducting any study procedures.

Subjects

Subjects were recruited from the community through advertisements. Inclusion criteria were 18–45 years, female, eumenorrhic, body mass index (BMI) ≥25 kg/m2, waist circumference >88 cm (17, 18), IGF1 level within the lowest two quartiles for age, stable weight (defined as weight loss or weight gain ≤5 pounds in the preceding 3 months), and willingness to maintain current activity level and diet for the duration of the study. Exclusion criteria included smoking, pregnancy or breastfeeding, hypothalamic or pituitary disorders, presence of diabetes mellitus or other chronic illnesses, use of estrogen or glucocorticoid, use of statins, antihypertensives, or regular use of aspirin.

One-hundred and fifty-four obese premenopausal women were screened for participation in the double-blind, placebo-controlled trial. Eighty subjects met the inclusion criteria and enrolled in the study; one subject was discontinued due to a positive pregnancy test at the baseline visit before any procedures were performed or study medication was dispensed. Seventy-nine subjects completed the baseline visit, 72 subjects completed the 3-week visit, 68 subjects completed the 6-week visit, 66 subjects completed the 9-week visit, 59 subjects completed the 3-month visit, and 50 subjects completed the 6-month visit.

Nineteen subjects withdrew for personal reasons and eight for medical causes (breast lump discovered before initiation of study medication, goiter (placebo group), cervical human papilloma virus, cancer (placebo group), breast calcifications noted on mammogram, 2 h oral glucose tolerance test (OGTT) glucose >200 mg/dl (11.1 mmol/l) (n=1 pretreatment and n=1 after initiation of study medication), and rash). One subject was discontinued due to oral contraceptive initiation and one due to IV access issues. Eleven dropouts had been randomized to GH and 18 to placebo (Fig. 1). Dropouts were replaced with additional study subjects to achieve the predetermined completers (n=50) at 6 months. Baseline clinical characteristics and body composition have been previously reported on a subset of these study subjects (4, 10, 19, 20, 21, 22, 23), but no longitudinal data have been previously published.

Figure 1
Figure 1

Flow diagram of randomized trial of GH vs placebo according to CONSORT guidelines.

Citation: European Journal of Endocrinology 166, 4; 10.1530/EJE-11-1068

Protocol

The study was a 6-month, double-blind, randomized, placebo-controlled trial performed in the Massachusetts General Hospital General Clinical Research Center.

Baseline IGF1 and cardiovascular risk markers were drawn after an overnight fast, followed by a 75 g, 2 h OGTT. Computed tomography (CT) at the level of the 4th lumbar vertebra (L4) and mid-thigh and dual-energy X-ray absorptiometry (DXA) were performed to assess body composition, and bioelectric impedance analysis (BIA) was performed to assess total body water. Proton magnetic resonance spectroscopy (1H-MRS) of soleus muscle and liver was performed to determine IMCL and IHL. A GHRH-arginine stimulation test was performed in a subset of patients (n=39) as described previously (4); testing was discontinued when GHRH became unavailable in the USA. After baseline evaluation, subjects were randomized to receive daily s.c. recombinant human GH (Genentech, Inc., South San Francisco, CA, USA) or placebo, which was identical in appearance to the GH, for 6 months. Randomization was performed by the Massachusetts General Hospital research pharmacy to maintain double blinding. Starting GH dose was 4 μg/kg per day. Subjects were asked to inject the study medication before bed.

Follow-up visits were performed at 3 weeks, 6 weeks, 9 weeks, 3 months, and 6 months after baseline testing. GH doses were adjusted based on IGF1 levels at all visits, by a physician not involved in the study, using an algorithm based on pretreatment IGF1 level and an IGF1 level target in the upper normal age appropriate range. Participants in the placebo group were adjusted to sham dose to maintain study subject and investigator blinding to randomization assignment. Body composition with CT and 1H-MRS and cardiovascular endpoints were measured at baseline, 6 weeks, and 6 months. DXA was performed at baseline, 3 months, and 6 months. OGTTs were performed at baseline, 6 weeks, 3 months, and 6 months.

Body composition evaluation

Fat mass and fat-free mass were measured by DXA (Hologic QDR-4500; Hologic, Inc., Waltham, MA, USA) at baseline, 3 months, and 6 months (precision error of 1.7% for fat mass and 2.4% for fat-free mass). Each subject underwent single-slice CT of the abdomen at the level of L4, and 52 subjects underwent additional single-slice CT of the left mid-thigh at baseline, 6 weeks, and 6 months as described previously (19) (coefficient of variation (CV) <1% for fat and muscle area). Abdominal SAT, visceral adipose tissue (VAT), and total adipose tissue (TAT) areas and thigh muscle cross-sectional areas were determined. BIA was used to measure total body water (precision <3%) using Bioelectrical Analyzer model BIA 101 (RJL Systems, Clinton Township, MI, USA) and standard protocol at baseline, 6 weeks, and 6 months (24). Resting energy expenditure (REE) was calculated from substrate oxidation rates obtained by indirect calorimetry (Vmax29N Sensor Medics, Viasys Healthcare, Loma Linda, CA, USA) after an overnight fast (25) at baseline, 3 months, and 6 months. 1H-MRS of calf muscle and liver was performed in 42 subjects using a 3.0 Tesla MRI system (Siemens Trio; Siemens Medical Systems, Erlangen, Germany) following an overnight fast at baseline, 6 weeks, and 6 months. 1H-MRS of soleus muscle and liver (CV=6% for intramuscular and 8% for intrahepatic fat) was performed as described previously (20, 21). All body composition analyses were performed by study personnel blinded to the randomization assignment.

Cardiovascular risk factor analysis

Real-time serum IGF1 for GH dose adjustment was measured using an Immulite 2000 automated immunoanalyzer (Diagnostic Products Corp., Los Angeles, CA, USA), by a solid-phase enzyme-labeled chemiluminescent immunometric assay, with a CV <5%. Serum IGF1 levels were batched and run after study completion for correlational analyses by IDS-iSYS Multi-Discipline Automated Analyser (Immunodiagnostic Systems, Inc., Fountain Hills, AZ, USA) with CV≤2%. GH levels were measured using an immunoradiometric assay kit (Diagnostic Systems Laboratories, Inc., Webster, TX, USA), with a minimum detection limit of 0.01 ng/ml and CV<6%. hsCRP, fibrinogen, and apolipoprotein B were measured by latex particle-enhanced immunoturbidimetric assay on an Hitachi 911 analyzer (Roche Diagnostics) with CV<6%. Tissue plasminogen activator (tPA) was measured using a ELISA assay (American Diagnostica, Greenwich, CT, USA) with CV<6%. Insulin was measured using an RIA kit (Linco, Research, Inc., St Charles, MO, USA). Homeostasis model assessment-insulin resistance (HOMA-IR) was calculated as insulin (mIU/ml)×glucose (mM/l)/22.5.

Carotid intima-media thickness (IMT) was measured at baseline and at 6 months by a single cardiologist, blinded to treatment randomization, as described previously (CV=4.7%) (26).

A fingertip peripheral arterial tonometry (PAT) device (Endo-PAT2000; Itamar Medical, Caesarea, Israel) was used to measure endothelial function in 40 subjects, and reactive hyperemic index (RHI) was calculated (27).

Compliance

To test for compliance of GH administration, 6-month and 3-month blood samples from all subjects in the GH group who completed the 6-month visit (n=28) and 6-week blood samples from subjects who dropped out between the 6-week and the 3-month visits (n=7) were analyzed for the presence of 22 kDa hGH, which becomes predominant after administration of rhGH, using specific sandwich-type immunoassays as described previously (28) with improved monoclonal antibodies (29).

Physical activity

Subjects were asked to refrain from modifying their exercise levels throughout the duration of the study. Level of activity, including exercise, was assessed using the Paffenbarger questionnaire, a self-administered questionnaire that measures current levels of activity. The Modified Activity Questionnaire (MAQ) assesses activity level over the past year and was used to investigate whether women who have a higher chronic basal activity level would experience greater or lesser effects of GH administration than sedentary women.

Statistical analysis

The primary body composition endpoint was TAT and the primary cardiovascular risk marker endpoint was hsCRP. The study was powered based on a study by Sesmilo et al. (8). With 25 evaluable study subjects in each study arm, we had >90% power for detecting a difference of 1.68 in hsCRP at a two-sided 0.05 significance level, assuming a s.d. of the difference from baseline of 1.79.

The data were analyzed using repeated measures ANOVA with the treatment difference at 6 months as the primary contrast of interest (SAS Proc Mixed, SAS Institute, Cary, NC, USA). This analysis included all data collected on all study subjects irrespective of whether the subject completed the 6 months of follow-up and follows the Institute of Medicine suggestion for analysis of data with missing observations (http://books.nap.edu/openbook.php?record_id=12955). Outliers above or below 1.5 times the interquartile range are excluded by quantile analysis. A secondary analysis including outlying observations is reported when the results differed. Within-group treatment effects were assessed using paired t-tests. Univariate regression models were constructed to determine hormonal and body composition predictors of endpoints studied, and Spearman ρ are reported. Multivariate models were constructed using standard least squares regression modeling to control for baseline age, IGF1 level, and BMI. Statistical significance was defined as a two-tailed P<0.05.

Results

Baseline characteristics

Baseline characteristics are presented in Table 1. Thirty-nine subjects were randomized to receive GH and 40 subjects to receive placebo. Both groups were of comparable age, IGF1 levels, BMI, body composition, and cardiovascular risk marker levels, and there was no significant difference in any baseline parameter between the groups at baseline. Subjects ranged in age from 21 to 45 years, with a mean age of 36±0.8 years. Subjects ranged in BMI from 25 to 50 kg/m2, with a mean of 35±0.6 kg/m2. There was no difference between completers and dropouts in any baseline characteristics, including age, BMI, body composition parameters, cardiovascular risk markers, and IGF1. There was no difference in REE at baseline, 3 months, or 6 months between the groups (P=0.9). Baseline physical activity determined using the Paffenbarger questionnaire was similar in both groups and remained unchanged during the study (P=0.4–0.6). However, women in the GH group had lower baseline activity levels as determined by MAQ compared with controls (12.0±1.5 vs 18.6±2.2, P=0.03).

Table 1

Baseline characteristics. Data presented as mean±s.e.m. Conversion to SI units: IGF1 (ng/ml)×0.131 for nmol/l.

GH group (n=39)Placebo group (n=40)P
Age (years)35.7±1.136.1±1.10.8
BMI (kg/m2)34.8±0.834.9±0.90.9
Peak stimulated  GH (ng/ml)13.9±1.911.5±2.10.4
IGF1 (ng/ml)137.9±8.1130.4±7.40.5
IGF1 SDS−1.7±0.1−1.8±0.10.4

The mean GH dose for the GH treatment group at 6 weeks was 0.5±0.02 mg/day and at 6 months 1.7±0.1 mg/day. These doses resulted in a mean IGF1 level of 212.3±12.2 ng/ml (27.9±1.6 nmol/l) and mean IGF1 SDS of −0.7±0.2 at 6 weeks and mean IGF1 level of 265.1±23.0 ng/ml (34.7±3.0 nmol/l) and a mean IGF1 z-score of −0.1±0.3 at 6 months (P<0.0001 compared with placebo) (Fig. 2).

Figure 2
Figure 2

IGF1 levels (A) and IGF1 SDS (B) of subjects randomized to GH. Open diamonds represent mean values. Conversion to SI units: IGF1 (ng/ml)×0.131 for nmol/l.

Citation: European Journal of Endocrinology 166, 4; 10.1530/EJE-11-1068

Effects of GH administration on body composition

Body composition parameters at baseline, 6 weeks, and 6 months are summarized in Table 2. There was a decrease in abdominal TAT (primary endpoint), as measured by CT, compared with placebo. SAT also decreased in the GH group compared with placebo group. There were three outliers for change in abdominal TAT: one in the placebo group, and two in the treatment group. When data from these individuals were included in the analysis, the difference between the groups was no longer significant. Within the GH group, there was a significant decrease in VAT (P=0.03) at 6 months. A CT image at the level of L4 pretreatment and at 6 months in a subject who received GH is shown in Fig. 3. There was an increase in thigh muscle area, as measured by CT, in the GH group compared with placebo group. There was a decrease in trunk fat measured by DXA in the GH group compared with placebo group. There was no significant change in total body fat, as measured by DXA, between the GH and the placebo groups. There was a significant increase in lean mass measured by DXA in the GH group compared with placebo group. Within the GH group, IMCL increased at 6 months (P=0.04), but this change was not significant compared with placebo group. There was no significant change in IHLs between the GH and the placebo groups. There was no significant change in weight and BMI in the GH group over the treatment period compared with the placebo group. Total body water did not change between GH and placebo over the treatment period (P=0.7).

Table 2

Body composition in premenopausal women with abdominal obesity treated with GH vs placebo for 6 months. Data are presented as mean±s.e.m.

VariableTreatmentBaseline (n=79) (GH, n=39 Placebo, n=40)6 Weeks (n=68) (GH, n=35 Placebo, n=33)6 Months (n=50) (GH, n=28 Placebo, n=22)P value within groupP value between groupsa
Abdominal TAT (cm2)  (primary endpoint)GH571.0±23.0592.1±35.1538.8±33.30.040.04
Placebo591.1±30.6579.4±36.8591.0±36.30.5
Abdominal SAT (cm2) GH466.2±19.8481.1±29.2441.4±27.20.070.02
Placebo475.3±24.7472.1±30.6474.5±29.60.6
VAT (cm2)GH105.0±7.7111.0±11.197.0±8.30.030.6
Placebo116.0±8.9106.6±10.8116.8±13.60.3
Thigh muscle (cm2)GH145.4±4.0144.0±4.0147.7±4.70.20.01
Placebo142.7±4.3142.0±4.4136.9±3.70.1
Total body fat (kg)bGH39.2±1.537.2±1.536.7±1.40.090.1
Placebo40.1±1.741.8±2.342.3±2.50.7
Trunk fat (kg)bGH18.8±0.818.0±0.817.3±0.70.030.04
Placebo18.8±0.919.0±1.318.9±1.50.9
Total lean mass (kg)bGH52.1±1.153.8±1.254.0±1.20.00090.04
Placebo52.2±1.051.7 (1.1)51.6±1.30.8
IMCL-SOL (AU)GH667.5±65.0734.8±89.7764.9±106.80.040.2
Placebo661.2±67.4710.0±63.3752.6±89.40.9
Intrahepatic lipids (%)GH9.0±2.39.8±3.06.6±1.70.30.7
Placebo7.2±2.48.7±3.09.9±4.10.8

AU, arbitrary units.

P value (0–6 months) determined by repeated measures ANOVA.

DXA was performed at baseline, 3 months, and 6 months.

Figure 3
Figure 3

Abdominal CT at the level of L4 in a study subject before (A) and after (B) 6 months of GH administration showing reduction of abdominal fat (dark gray areas).

Citation: European Journal of Endocrinology 166, 4; 10.1530/EJE-11-1068

Effects of GH on cardiovascular risk markers

Cardiovascular risk makers at baseline, 6 weeks, and 6 months are summarized in Table 3. There was a significant decrease in hsCRP (primary endpoint) in the GH group compared with placebo group (Fig. 4). Nine subjects in the GH group experienced a decrease in hsCRP cardiovascular risk quintile (by one to four quintiles), and one experienced an increase (by two quintiles). In the placebo group, five subjects experienced an increase and three a decrease (each by one quintile only).

Table 3

Cardiovascular risk markers in premenopausal women with abdominal obesity treated with GH vs placebo for 6 months. Data are presented as mean±s.e.m. Conversion to SI units: hsCRP (mg/l)×9.524 for nmol/l, fibrinogen (mg/dl)×0.0294 for μmol/l, triglycerides (mg/dl)×0.0113 for mmol/l, cholesterol (total, HDL, and LDL) (mg/dl)×0.0259 for mmol/l.

VariableTreatmentBaseline (n=79) (GH, n=39 Placebo, n=40)6 Weeks (n=68) (GH, n=35 Placebo, n=33)6 Months (n=50) (GH, n=28 Placebo, n=22)P value within groupP value between groupsa
hsCRP (mg/l)  (primary endpoint)GH2.8±0.42.6±0.41.5±0.20.020.002
Placebo2.5±0.62.0±0.32.2±0.40.9
Fibrinogen (mg/dl)GH476.1±15.3473.7±14.6458.4±18.80.40.07
Placebo481.5±14.7496.7±14.8513.5±26.30.09
tPA (ng/ml)GH6.7±1.17.2±1.35.7±1.30.60.03
Placebo7.7±1.56.9±1.311.2±3.20.5
Triglycerides (mg/dl)GH102.6±8.5105.0±9.4100.3±8.91.00.7
Placebo96.1±8.0103.2±9.0101.9±14.30.6
Total cholesterol (mg/dl)GH180.9±5.5175.1±5.1169.2±5.10.020.7
Placebo176.8±6.3180.8±6.0176.4±6.20.4
HDL-cholesterol (mg/dl)GH50.9±1.649.8±2.151.7±2.20.70.9
Placebo47.2±1.949.2±2.847.9±3.30.9
LDL-cholesterol (mg/dl)GH109.6±4.7104.3±4.697.4±5.00.021.0
Placebo110.5±5.6109.3±4.7108.2±6.00.1
Apolipoprotein B (mg/dl)GH88.6±3.686.2±3.478.0±3.90.010.04
Placebo86.8±4.690.0±4.295.2±4.80.4
Apolipoprotein B/LDLGH0.82±0.020.82±0.020.81±0.020.70.006
Placebo0.79±0.030.88±0.070.90±0.040.02
Mean carotid IMT (mm)bGH0.62±0.020.62±0.030.40.1
Placebo0.59±0.010.61±0.020.2
RHIbGH2.2±0.12.4±0.10.30.6
Placebo2.1±0.12.0±0.20.9

tPA, tissue plasminogen activator; IMT, intima-media thickness; RHI, reactive hyperemic index.

P value (0–6 months) determined by repeated measures ANOVA.

Measured only at baseline and 6 months.

Figure 4
Figure 4

Mean (±s.e.m.) change in hsCRP over 6 months of GH administration vs placebo. *P<0.05 vs placebo. Conversion to SI units: hsCRP (mg/l)×9.524 for nmol/l.

Citation: European Journal of Endocrinology 166, 4; 10.1530/EJE-11-1068

Apolipoprotein B and the apolipoprotein B/LDL ratio decreased in the GH group compared with placebo group. tPA decreased in the GH group compared with placebo group. There was a trend in decrease in fibrinogen in the GH group compared with placebo group. LDL- and total cholesterol decreased within the GH group (P=0.02). There was no significant change in carotid IMT and RHI between the groups.

Effects of GH on glucose tolerance

Measures of glucose tolerance at baseline, 6 weeks, and 6 months are summarized in Table 4. No subjects had fasting glucose levels ≥126 mg/dl (6.99 mmol/l) at any point during the study. Fasting glucose and 2 h glucose levels increased in the GH group compared with placebo group. Three subjects experienced increases in their fasting glucose levels from <100 mg/dl (5.55 mmol/l) to >100 mg/dl at 6 months. All three subjects had been randomized to GH. Seven subjects experienced increases in their 2-h glucose levels from <140 mg/dl (7.77 mmol/l) to >140 mg/dl at 6 months, five of whom had been randomized to receive GH and two to the placebo group. Baseline fasting glucose predicted 6-month change in 2-h glucose within the GH group (r=0.48, P=0.01; Fig. 5), suggesting that subjects with higher fasting pretreatment glucose were more likely to experience decreases in glucose tolerance with GH administration. Baseline fasting glucose correlated with 6-month fasting glucose (r=0.68, P=0.0001), and baseline 2-h glucose correlated with 6-month 2-h glucose (r=0.66, P=0.002). There was no association between GH dose or increase in IGF1 levels and change in any measure of glucose tolerance. One subject was discontinued from the study at 3 months secondary to a 2-h glucose >200 mg/ml (11.1 mmol/l), a prespecified drop criterion. Four subjects had 2-h glucose levels >200 mg/ml at 6 months, one of whom was receiving placebo.

Table 4

Measures of glucose tolerance in premenopausal women with abdominal obesity treated with GH vs placebo for 6 months. Data are presented as mean±s.e.m. Conversion to SI units: glucose (mg/l)×0.0555 for mmol/l.

VariableTreatmentBaseline (n=79) (GH, n=39 Placebo, n=40)6 Weeks (n=68) (GH, n=35 Placebo, n=33)6 Months (n=50) (GH, n=28 Placebo, n=22)P value within groupP value between groupsa
Fasting glucose (mg/dl)GH87.5±1.292.4±1.490.5±2.10.050.03
Placebo85.7±1.287.2±1.484.9±1.40.9
2 h Glucose (mg/dl)GH122.9±4.7127.6 (5.8)140.6 (7.7)0.0070.04
Placebo118.9±4.7111.4 (4.8)125.9 (7.7)0.9
HOMA-IRGH1.7±0.22.2±0.32.2±0.30.20.07
Placebo1.6±0.21.8±0.31.5±0.80.3

HOMA-IR, homeostasis model assessment-insulin resistance.

P value (0–6 months) determined by repeated measures ANOVA.

Figure 5
Figure 5

Regression analysis of baseline fasting glucose on 6-month change in 2 h glucose within the GH group. Baseline fasting glucose predicted 2 h glucose after 6 months of GH administration. Conversion to SI units: glucose (mg/l)×0.0555 for mmol/l.

Citation: European Journal of Endocrinology 166, 4; 10.1530/EJE-11-1068

Predictors of response within the group that received GH

Six-month change in IGF1 levels was associated with 6-month decrease in TAT (r=−0.42, P=0.03) and VAT (r=−0.56, P=0.002) (Fig. 6), which remained significant after controlling for baseline age and BMI (P=0.002 and P=0.009 respectively), suggesting that those subjects experiencing the greatest increases in IGF1 levels with GH administration experienced the greatest decreases in total and visceral abdominal fat. There was a trend of an association between 6-month increase in IGF1 and 6-month decrease in hsCRP (r=−0.44, P=0.08). GH dose at 6 weeks correlated with the 6-week changes in TAT (r=−0.50, P=0.05) and SAT (r=−0.50, P=0.04). There were also trends toward significant associations between GH dose at 6 weeks and the 6-month change in thigh muscle area (r=0.50, P=0.05), TAT (r=−0.40, P=0.06), SAT (r=−0.30, P=0.08), and VAT (r=−0.34, P=0.07). The GH dose at 6 months was inversely associated with the 6-month change in fibrinogen (r=−0.42, P=0.03).

Figure 6
Figure 6

Regression analysis of 6-month change in IGF1 on 6-month change in VAT within the GH group; 6-month change in IGF1 predicted 6-month change in VAT.

Citation: European Journal of Endocrinology 166, 4; 10.1530/EJE-11-1068

Neither baseline or prior level of activity, baseline peak GH after stimulation with GHRH, nor baseline IGF1 levels predicted 6-month change in body composition, cardiovascular risk markers, or glucose tolerance.

Compliance

Blood samples from 3-month and 6-month visits of subjects in the GH group who completed the 6-month visit demonstrated 22 kDa hGH, indicating rhGH presence in both the blood samples in 13 cases (46%) and in either the 3-month or the 6-month sample in 12 cases (43%), implying intermittent rhGH use, while in three cases (11%), no 22 kDa hGH could be detected in either sample. For the subjects who dropped out between 6 weeks and 3 months (n=7), 22 kDa hGH was detected in two cases (29%).

Side effects

There was no significant difference between the GH and the placebo groups in reported incidences of mild edema (GH group: 53.6%, placebo: 45.5%; P=0.8), mild joint discomfort (GH group: 53.6%, placebo: 31.8%; P=0.2), muscle aches (GH group: 17.9%, placebo: 13.6%; P=1), nasal congestion (GH group: 25.0%, placebo: 22.7%; P=1), back pain (GH group: 10.7%, placebo: 22.7%; P=0.3), headache (GH group: 35.7%, placebo: 36.4%; P=1), or intermittent mild hand paresthesias (GH group: 50.0%, placebo: 22.7%; P=0.08). There was one serious unrelated adverse event: development of cancer in a study subject who was receiving placebo. No other serious related or unrelated adverse events occurred during this study.

Discussion

This is the first study to demonstrate that GH treatment in abdominally obese premenopausal women exerts beneficial effects on body composition and markers of cardiovascular risk. Specifically, we show that GH treatment for 6 months, at doses that increased the mean IGF1 approximately to the mean for age (mean IGF1 SDS in the GH group=−0.1), decreases abdominal fat and increases muscle mass. In addition, it decreases hsCRP, tPA, apolipoprotein B, and apolipoprotein B/LDL ratio – a measure of LDL atherogenicity. However, it is also associated with a small decrease in glucose tolerance in a subset of women, particularly those with higher pretreatment fasting glucose levels.

Our study demonstrated a decrease in total abdominal and abdominal subcutaneous fat and decrease in trunk fat with GH treatment in premenopausal women with visceral adiposity. VAT decreased compared with baseline in women randomized to receive GH, and an inverse association between the increase in IGF1 level and decrease in VAT in women receiving GH suggests that the effect was dose dependent. Importantly, we also observed an increase in muscle mass. As decreased GH secretion is an independent risk factor for increased abdominal obesity and cardiovascular risk (30, 31), we hypothesized that GH treatment would result in beneficial alterations in body composition and improvements in cardiovascular risk markers in women with visceral adiposity. These data suggest a beneficial GH-mediated modification in body composition in obese women of reproductive age.

GH is an important mediator of inflammation and atherogenesis (4). In our 6-month, double-blind, placebo-controlled trial, GH decreased cardiovascular risk markers including hsCRP, tPA, apolipoprotein B, and apolipoprotein B/LDL ratio. The effects on hsCRP are consistent with demonstrated effects in hypopituitary men (8) and women (7). The effects on apolipoprotein B and apolipoprotein B/LDL ratio suggest that GH results in increased size of LDL particles, which have been shown to be less atherogenic than smaller, denser LDLs. Within the GH group, there was also a decrease in total and LDL-cholesterol. These findings are similar to the results of previous studies that investigated the effects of GH in hypopituitary men and women (32) and in obese men and postmenopausal women (13, 14, 15). The significance of this is that alterations in body composition, including increased abdominal adiposity, are associated with a marked increase in coronary heart disease and elevation of inflammatory cardiovascular markers, including hsCRP, and classic cardiovascular risk markers, including LDL-cholesterol and triglycerides (33). In addition, although GH administration has been clearly shown to reduce body fat, including VAT (7, 8, 12, 30), and to increase lean body mass (7, 12) in men with hypopituitarism, and a recent randomized, placebo-controlled study demonstrated effectiveness in hypopituitary women (7), other studies have shown less efficacy in women (34). There are few studies on obese subjects, in whom endogenous GH is also reduced, and none on obese women of reproductive age, in whom the hormonal milieu significantly differs from that of other groups studied. Our study is the first to isolate the effects of GH administration in women of reproductive age with obesity. A previous study administering GH to elderly women reported a significant decrease in abdominal SAT and no significant change in VAT (35), in contrast to a study that found a larger reduction in VAT compared with abdominal SAT in obese men following 12 months of low-dose GH administration (14). In contrast, Tomlinson et al. (16) did not observe a reduction in fat mass assessed by DXA in a study of obese men and women following 8 months of low-dose GH administration compared with placebo. Franco et al. (13) reported decreased VAT, increased muscle area, and decreased liver fat using CT density measurements after 12 months of GH administration in postmenopausal women. We did not observe a significant decrease in intrahepatic fat measured by 1H-MRS in the GH group compared with placebo in our study on obese premenopausal women. Whether the differences in results from these studies reflect differences in study population, study duration, GH dosing, imaging technique, or other factors is unknown.

Limitations of the study include evidence of noncompliance with GH administration; consistent rhGH administration was present in only 46%, while 42% manifested biochemical evidence of only intermittent GH administration. This may explain the apparently high dose relative to the modest increase in mean IGF1 levels within the normal range. More regular GH administration might have resulted in more significant findings. Another limitation was our high dropout rate. However, of note, we replaced dropouts to ensure our prespecified completers (n=50) at 6 months. Also, we followed the Institute of Medicine guideline for analysis of data with missing observations. There was no difference in baseline characteristics between the completers and the dropouts, and our dropout rate was commensurate with other obesity studies (36, 37). Finally, it should be noted that this is a small, physiological experiment, and clinical recommendations cannot be made based on the results.

In our study, GH administration decreased glucose tolerance in a minority of women. This suggests that relative GH deficiency in obesity may be an adaptive mechanism with regard to glucose tolerance. Whether the effects of GH administration observed in this study are clinically significant is debatable, as the absolute increases in glucose were small and few study subjects developed hyperglycemia with a 2 h glucose level over 200 mg/dl (11.1 mmol/l). Of note, higher fasting glucose levels predicted greater 6-month increases in 2 h glucose levels, suggesting that obese women with abnormal glucose tolerance may be more likely to experience this adverse effect. Acute GH administration increases insulin resistance in women with GH deficiency due to hypopituitarism, whereas chronic GH administration has been shown in some, but not all, studies to return measures of insulin resistance to normal or even result in improvements (32, 33, 38, 39, 40). It is thought that the acute worsening of insulin resistance may be secondary to GH-induced adipocyte lipolysis and lipid turnover, resulting in increased plasma free fatty acids, and the long-term improvement in insulin resistance may be mediated in part by the GH-induced decrease in VAT and increase in muscle mass (41). It should also be noted that a recent paper confirmed the reversibility of acute GH-induced insulin resistance (42). For a detailed review on GH and glucose metabolism, please see (43). In our study, the increase in insulin resistance was accompanied by an increase in IMCL within the GH group. Krag et al. (44) demonstrated an increase in IMCL using muscle biopsies following 8 days of GH administration in healthy men. We have previously reported an inverse association between GH and IMCL using 1H-MRS, independent of VAT in women with visceral obesity (10), suggesting that low GH may contribute to insulin resistance through effects on IMCL. Our data do not support our hypothesis, generated from our cross-sectional data, that normalization of glucose tolerance with chronic GH treatment would be mediated by a reduction in IMCL and hepatic lipid concentrations. Further studies are warranted to investigate the mechanisms underlying the effects of GH on glucose tolerance.

We demonstrated that GH administration in viscerally obese premenopausal women results in beneficial effects on body composition and cardiovascular risk markers. However, it was also associated with a decrease in glucose tolerance in a minority of women, suggesting a possible adaptive effect of low endogenous GH with regard to glucose tolerance in premenopausal viscerally obese women. The net effect of GH on long-term cardiovascular risk in premenopausal women with abdominal adiposity is unknown.

Declaration of interest

The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.

Funding

This work was supported in part by National Institutes of Health Grants RO1 HL-077674, UL1 RR025758, and K23 RR-23090. Only study medication and placebo were supplied by Genentech, Inc. Clinical trials registration number: NCT00131378.

Acknowledgements

The authors thank Gary Bradwin at Children's Hospital Boston for assistance with laboratory assays.

References

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  • View in gallery

    Flow diagram of randomized trial of GH vs placebo according to CONSORT guidelines.

  • View in gallery

    IGF1 levels (A) and IGF1 SDS (B) of subjects randomized to GH. Open diamonds represent mean values. Conversion to SI units: IGF1 (ng/ml)×0.131 for nmol/l.

  • View in gallery

    Abdominal CT at the level of L4 in a study subject before (A) and after (B) 6 months of GH administration showing reduction of abdominal fat (dark gray areas).

  • View in gallery

    Mean (±s.e.m.) change in hsCRP over 6 months of GH administration vs placebo. *P<0.05 vs placebo. Conversion to SI units: hsCRP (mg/l)×9.524 for nmol/l.

  • View in gallery

    Regression analysis of baseline fasting glucose on 6-month change in 2 h glucose within the GH group. Baseline fasting glucose predicted 2 h glucose after 6 months of GH administration. Conversion to SI units: glucose (mg/l)×0.0555 for mmol/l.

  • View in gallery

    Regression analysis of 6-month change in IGF1 on 6-month change in VAT within the GH group; 6-month change in IGF1 predicted 6-month change in VAT.

  • 1

    Grundy SM. Obesity, metabolic syndrome, and coronary atherosclerosis. Circulation 2002 105 26962698. doi:10.1161/01.CIR.0000020650.86137.84.

    • Search Google Scholar
    • Export Citation
  • 2

    Rexrode KM, Carey VJ, Hennekens CH, Walters EE, Colditz GA, Stampfer MJ, Willett WC, Manson JE. Abdominal adiposity and coronary heart disease in women. Journal of the American Medical Association 1998 280 18431848. doi:10.1001/jama.280.21.1843.

    • Search Google Scholar
    • Export Citation
  • 3

    Pijl H, Langendonk JG, Burggraaf J, Frolich M, Cohen AF, Veldhuis JD, Meinders AE. Altered neuroregulation of GH secretion in viscerally obese premenopausal women. Journal of Clinical Endocrinology and Metabolism 2001 86 55095515. doi:10.1210/jc.86.11.5509.

    • Search Google Scholar
    • Export Citation
  • 4

    Utz AL, Yamamoto A, Hemphill L, Miller KK. Growth hormone deficiency by growth hormone releasing hormone-arginine testing criteria predicts increased cardiovascular risk markers in normal young overweight and obese women. Journal of Clinical Endocrinology and Metabolism 2008 93 25072514. doi:10.1210/jc.2008-0169.

    • Search Google Scholar
    • Export Citation
  • 5

    Weaver JU, Monson JP, Noonan K, John WG, Edwards A, Evans KA, Cunningham J. The effect of low dose recombinant human growth hormone replacement on regional fat distribution, insulin sensitivity, and cardiovascular risk factors in hypopituitary adults. Journal of Clinical Endocrinology and Metabolism 1995 80 153159. doi:10.1210/jc.80.1.153.

    • Search Google Scholar
    • Export Citation
  • 6

    Vahl N, Jorgensen JO, Skjaerbaek C, Veldhuis JD, Orskov H, Christiansen JS. Abdominal adiposity rather than age and sex predicts mass and regularity of GH secretion in healthy adults. American Journal of Physiology 1997 272 E1108E1116.

    • Search Google Scholar
    • Export Citation
  • 7

    Beauregard C, Utz AL, Schaub AE, Nachtigall L, Biller BM, Miller KK, Klibanski A. Growth hormone decreases visceral fat and improves cardiovascular risk markers in women with hypopituitarism: a randomized, placebo-controlled study. Journal of Clinical Endocrinology and Metabolism 2008 93 20632071. doi:10.1210/jc.2007-2371.

    • Search Google Scholar
    • Export Citation
  • 8

    Sesmilo G, Biller BM, Llevadot J, Hayden D, Hanson G, Rifai N, Klibanski A. Effects of growth hormone administration on inflammatory and other cardiovascular risk markers in men with growth hormone deficiency. A randomized, controlled clinical trial. Annals of Internal Medicine 2000 133 111122.

    • Search Google Scholar
    • Export Citation
  • 9

    Rudling M, Angelin B. Loss of resistance to dietary cholesterol in the rat after hypophysectomy: importance of the presence of growth hormone for hepatic low density lipoprotein-receptor expression. PNAS 1993 90 88518855. doi:10.1073/pnas.90.19.8851.

    • Search Google Scholar
    • Export Citation
  • 10

    Bredella MA, Torriani M, Thomas BJ, Ghomi RH, Brick DJ, Gerweck AV, Miller KK. Peak growth hormone-releasing hormone-arginine-stimulated growth hormone is inversely associated with intramyocellular and intrahepatic lipid content in premenopausal women with obesity. Journal of Clinical Endocrinology and Metabolism 2009 94 39954002. doi:10.1210/jc.2009-0438.

    • Search Google Scholar
    • Export Citation
  • 11

    Rommel C, Bodine SC, Clarke BA, Rossman R, Nunez L, Stitt TN, Yancopoulos GD, Glass DJ. Mediation of IGF-1-induced skeletal myotube hypertrophy by PI(3)K/Akt/mTOR and PI(3)K/Akt/GSK3 pathways. Nature Cell Biology 2001 3 10091013. doi:10.1038/ncb1101-1009.

    • Search Google Scholar
    • Export Citation
  • 12

    Baum HB, Biller BM, Finkelstein JS, Cannistraro KB, Oppenhein DS, Schoenfeld DA, Michel TH, Wittink H, Klibanski A. Effects of physiologic growth hormone therapy on bone density and body composition in patients with adult-onset growth hormone deficiency. A randomized, placebo-controlled trial. Annals of Internal Medicine 1996 125 883890.

    • Search Google Scholar
    • Export Citation
  • 13

    Franco C, Brandberg J, Lonn L, Andersson B, Bengtsson BA, Johannsson G. Growth hormone treatment reduces abdominal visceral fat in postmenopausal women with abdominal obesity: a 12-month placebo-controlled trial. Journal of Clinical Endocrinology and Metabolism 2005 90 14661474. doi:10.1210/jc.2004-1657.

    • Search Google Scholar
    • Export Citation
  • 14

    Johannsson G, Marin P, Lonn L, Ottosson M, Stenlof K, Bjorntorp P, Sjostrom L, Bengtsson BA. Growth hormone treatment of abdominally obese men reduces abdominal fat mass, improves glucose and lipoprotein metabolism, and reduces diastolic blood pressure. Journal of Clinical Endocrinology and Metabolism 1997 82 727734. doi:10.1210/jc.82.3.727.

    • Search Google Scholar
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  • 15

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