Effects of GH and insulin-like growth factor-I on body composition

Beyond Menstrual Dysfunction: Does Altered Endocrine Function Caused by Problematic Low Energy Availability Impair Health and Sports Performance in Female Athletes?

Low energy availability, particularly when problematic (i.e., prolonged and/or severe), has numerous negative consequences for health and sports performance as characterized in relative energy deficiency in sport. These consequences may be driven by disturbances in endocrine function, although scientific evidence clearly linking endocrine dysfunction to decreased sports performance and blunted or diminished training adaptations is limited. We describe how low energy availability-induced changes in sex hormones manifest as menstrual dysfunction and accompanying hormonal dysfunction in other endocrine axes that lead to adverse health outcomes, including negative bone health, impaired metabolic activity, undesired outcomes for body composition, altered immune response, problematic cardiovascular outcomes, iron deficiency, as well as impaired endurance performance and force production, all of which ultimately may influence athlete health and performance. Where identifiable menstrual dysfunction indicates hypothalamic-pituitary-ovarian axis dysfunction, concomitant disturbances in other hormonal axes and their impact on the athlete's health and sports performance must be recognized as well. Given that the margin between podium positions and "losing" in competitive sports can be very small, several important questions regarding low energy availability, endocrinology, and the mechanisms behind impaired training adaptations and sports performance have yet to be explored.

Serum afamin and its implications in adult growth hormone deficiency: a prospective GH-withdrawal study

Introduction

Adult growth hormone deficiency (AGHD) is associated with a high prevalence of metabolic syndrome (MS), which contributes to the unfavorable cardiovascular risk profile in these patients. Insulin like growth factor-1 (IGF-1) is a widely used biomarker, however it does not always reflect the cardiometabolic risk and has a poor relationship with clinical efficacy endpoints. Consequently, there is an unmet need for biomarkers to monitor responses to GH-replacement. Afamin is a hormone-like glycoprotein, expressed in the liver. Higher afamin levels are strongly associated with MS and insulin resistance (IR). Although both MS and IR are very common in AGHD, afamin has not been investigated in these patients.

Purpose

To investigate afamin as a potential biomarker in patients with AGHD.

Materials and methods

Participants included 20 AGHD patients (11 GH-substituted and 9 GH-unsubstituted) and 37 healthy controls. Subjects underwent routine laboratory examinations, anthropometric measurements, body composition analysis using multi-frequency bioelectrical impedance analysis (InBody720) and measurement of serum afamin concentrations. In GH-substituted subjects, GH-substitution was withdrawn for 2 months. Measurements were carried out right before GH-withdrawal, at the end of the 2-month withdrawal period, and 1 month after reinstituting GH-replacement therapy (GHRT).

Results

GH-unsubstituted patients demonstrated higher afamin levels compared to controls (p=0.03). Afamin positively correlated with skeletal muscle mass, bone mineral content, total body water, extracellular- and intracellular water content, insulin (all, p<0.01), HOMA-IR (p=0.01) and C-peptide (p=0.03) levels in AGHD but not in healthy controls. In GH-substituted patients 2-month of GH-withdrawal caused significant changes in body composition, including decreased fat-free mass, skeletal muscle mass, total body water, and intracellular water content (all, p<0.01); but these changes almost fully recovered 1 month after reinstituting GHRT. Unexpectedly, afamin levels decreased after GH-withdrawal (p=0.03) and increased with reinstitution (p<0.01). Changes of afamin levels during GH-withdrawal positively correlated with changes of HOMA-IR (r=0.80; p<0.01) and changes of insulin (r=0.71; p=0.02).

Conclusion

Higher afamin levels in unsubstituted AGHD patients might indicate severe metabolic dysregulation. Significant changes accompanying GH-withdrawal and reinstitution, along with strong correlations with measures of IR, suggest that afamin could be a promising biomarker to monitor GHRT-associated changes of insulin sensitivity.

Prevalence of refractoriness when testing growth hormone levels in children

OBJECTIVE

Late night spontaneous growth hormone (GH) pulses may influence the pituitary GH response to provocation tests. We evaluated GH response during arginine-insulin-tolerance test (AITT) after a GH peak during a short spontaneous nocturnal profile (SSNP) in children with short stature or low growth velocity.

DESIGN

Using SSNP and subsequent AITT, we examined 257 children 4-18 years old (138 (53.7%) males) recruited from three hospitals. Medical records were reviewed retrospectively. Refractory children were defined as a GH peak ≥7 μg/L during SSNP but no GH peak ≥7 μg/L during AITT.

RESULTS

In total, 201/257 children had a GH peak ≥7 μg/L at SSNP and/or AITT. Of these, 21.9% were refractory. The proportion of males (p = 0.033) and body mass index (BMI) standard deviation score (SDS) (p = 0.037) were higher in the refractory group than in children with a GH peak ≥7 μg/L during AITT. The median period between last GH peak ≥7 μg/L during SSNP and GHmax at AITT was 210 (30-390) minutes. The GHmax at AITT occurred 30 min earlier for children without a peak ≥7 μg/L during the SSNP (p = 0.004). The number of refractoriness differed somewhat between the hospitals (p = 0.025).

CONCLUSIONS

Many children with short stature were refractory at testing; among them we found few clinical characteristics. Refractoriness might be influenced by some differences in procedure, but needs to be considered when evaluating GH response in children.

The Effects of 20-kDa Human Placental GH in Male and Female GH-deficient Mice: An Improved Human GH?

A rare 20K isoform of GH-V (here abbreviated as GHv) was discovered in 1998. To date, only 1 research article has characterized this isoform in vivo, observing that GHv treatment in male high-fat fed rats had several GH-like activities, but unlike GH lacked diabetogenic and lactogenic activities and failed to increase IGF-1 or body length. Therefore, the current study was conducted to further characterize the in vivo activities of GHv in a separate species and in a GH-deficient model (GH-/- mice) and with both sexes represented. GHv-treated GH-/- mice had significant increases to serum IGF-1, femur length, body length, body weight, and lean body mass and reduced body fat mass similar to mice receiving GH treatment. GH treatment increased circulating insulin levels and impaired insulin sensitivity; in contrast, both measures were unchanged in GHv-treated mice. Since GHv lacks prolactin receptor (PRLR) binding activity, we tested the ability of GH and GHv to stimulate the proliferation of human cancer cell lines and found that GHv has a decreased proliferative response in cancers with high PRLR. Our findings demonstrate that GHv can stimulate insulin-like growth factor-1 and subsequent longitudinal body growth in GH-deficient mice similar to GH, but unlike GH, GHv promoted growth without inhibiting insulin action and without promoting the growth of PRLR-positive cancers in vitro. Thus, GHv may represent improvements to current GH therapies especially for individuals at risk for metabolic syndrome or PRLR-positive cancers.

Central body fat changes in men affected by post-surgical hypogonadotropic hypogonadism undergoing testosterone replacement therapy are modulated by androgen receptor CAG polymorphism

BACKGROUND AND AIMS

Little is known about the effect of androgen receptor (AR) gene CAG repeat polymorphism in conditioning body composition changes after testosterone replacement therapy (TRT). In this study, we aimed to clarify this aspect by focussing our attention on male post-surgical hypogonadotropic hypogonadism, a condition often associated with partial or total hypopituitarism.

METHODS AND RESULTS

Fourteen men affected by post-surgical hypogonadotropic hypogonadism and undergoing several replacement hormone therapies were evaluated before and after TRT. Dual-energy X-ray absorptiometry (DEXA)-derived body composition measurements, pituitary-dependent hormones and AR gene CAG repeat polymorphism were considered. While testosterone and insulin-like growth factor-1 (IGF-1) levels increased after TRT, cortisol concentration decreased. No anthropometric or body composition parameters varied significantly, except for abdominal fat decrease. The number of CAG triplets was positively and significantly correlated with this abdominal fat decrease, while the opposite occurred between the latter and Δ-testosterone. No correlation of IGF-1 or cortisol variation (Δ-) with Δ-abdominal fat was found. At multiple linear regression, after correction for Δ-testosterone, the positive association between CAG triplet number and abdominal fat change was confirmed.

CONCLUSIONS

In male post-surgical hypogonadotropic hypogonadism, shorter length of AR CAG repeat tract is independently associated with a more marked decrease of abdominal fat after TRT.

Liver-spleen axis, insulin-like growth factor-(IGF)-I axis and fat mass in overweight/obese females

BACKGROUND

Fat mass (FM) in overweight/obese subjects has a primary role in determining low-grade chronic inflammation and, in turn, insulin resistance (IR) and ectopic lipid storage within the liver. Obesity, aging, and FM influence the growth hormone/insulin-like growth factor (IGF)-I axis, and chronic inflammation might reduce IGF-I signaling. Altered IGF-I axis is frequently observed in patients with Hepatic steatosis (HS). We tested the hypothesis that FM, or spleen volume and C-reactive protein (CRP)--all indexes of chronic inflammation--could affect the IGF-I axis status in overweight/obese, independently of HS.

METHODS

The study population included 48 overweight/obese women (age 41 ± 13 years; BMI: 35.8 ± 5.8 kg/m2; range: 25.3-53.7), who underwent assessment of fasting plasma glucose and insulin, homeostasis model assessment of insulin resistance (HOMA), cholesterol and triglycerides, HDL-cholesterol, transaminases, high-sensitive CRP, uric acid, IGF-I, IGF binding protein (BP)-1, IGFBP-3, and IGF-I/IGFBP-3 ratio. Standard deviation score of IGF-I according to age (zSDS) were also calculated. FM was determined by bioelectrical impedance analysis. HS severity grading (score 0-4 according liver hyperechogenicity) and spleen longitudinal diameter (SLD) were evaluated by ultrasound.

RESULTS

Metabolic syndrome (MS) and HS were present in 33% and 85% of subjects, respectively. MS prevalence was 43% in subjects with increased SLD. IGF-I values, but not IGF-I zSDS, and IGF-I/IGFBP-3 ratio were significantly lower, while FM%, FPI, HOMA, ALT, CRP, were significantly higher in patients with severe HS than in those with mild HS. IGF-I zSDS (r = -0.42, r = -0.54, respectively; p < 0.05), and IGFBP-1 (r = -0.38, r = -0.42, respectively; p < 0.05) correlated negatively with HS severity and FM%. IGF-I/IGFBP-3 ratio correlated negatively with CRP, HS severity, and SLD (r = -0.30, r = -0.33, r = -0.43, respectively; p < 0.05). At multivariate analysis the best determinants of IGF-I were FM% (β = -0.49; p = 0.001) and IGFBP-1 (β = -0.32; p = 0.05), while SLD was in the IGF-I/IGFBP-3 ratio (β = -0.43; p = 0.004).

CONCLUSIONS

The present study suggests that lower IGF-I status in our study population is associated with higher FM, SLD, CRP and more severe HS.

IGF-I improved bone mineral density and body composition of weaver mutant mice

Our recent report on a parallel decrease in the body weights and serum IGF-I levels of weaver mice suggests that IGF-I's endocrine function may be impaired in neurodegenerative diseases. To further understand the overall effects of IGF-I deficiency on the postnatal growth, we measured bone mineral density (BMD), bone mineral content (BMC), lean body mass (LBM) and fat mass in male and female weaver mice and wild-type littermates on D21 (prepuberty), D45 (puberty), and D60 (postpuberty) using dual-energy X-ray absorptiometry (DEXA). In both male and female weaver mice, we found that the levels of circulating IGF-I paralleled those of BMD, BMC, and LBM, but not the fat mass. Male weaver mice have normal fat mass at all three ages studied, whereas female weaver mice showed a trend to increase their fat mass as they mature. To determine whether circulating IGF-I is a determinant of body composition, we crossbred IGF-I transgenic mice with homozygous weaver mice, which resulted in a significant increase in circulating IGF-I levels in both male and female weaver mice and normalization of their BMD, BMC and body weights. In summary, our results demonstrated that normal circulating IGF-I levels are important in maintaining BMD, BMC, and body composition in neurodegenerative diseases, such as hereditary cerebellar ataxia.

Effects of short-term GH supplementation and treadmill exercise training on physical performance and skeletal muscle apoptosis in old rats

Growth hormone (GH) supplementation at old age has been shown to improve body composition, although its effect on muscle performance is still debated. On the other hand, resistance training increases muscle mass and strength even when initiated at advanced age. In the present study, we investigated the effects of short-term GH supplementation and exercise training on physical performance and skeletal muscle apoptosis in aged rats. Old (28 mo) male Fischer 344 x Brown Norway rats were randomized to 4 wk of GH supplementation (300 mug subcutaneous, twice daily) or 4 wk of treadmill running or used as sedentary controls. Eight-month-old rats, sedentary or exercised, were used as young controls. Exercise training improved exercise capacity and muscle strength in old animals. In soleus muscle, age and exercise were not associated with significant changes in the extent of apoptosis. However, we detected an age-related increase of cleaved caspase-8 (+98%), cleaved caspase-3 (+136%), and apoptotic DNA fragmentation (+203%) in the extensor digitorum longus muscle of old sedentary rats, which was attenuated by exercise. GH administration neither ameliorated physical performance nor attenuated apoptosis in extensor digitorum longus and was associated with increased apoptosis in soleus muscle (+206% vs. old controls). Our findings indicate that a short-term program of exercise training started at advanced age reverses age-related skeletal muscle apoptosis and represents an effective strategy to improve physical performance. In contrast, short-term administration of GH late in life does not provide any protection against functional decline or muscle aging and may even accelerate apoptosis in slow-twitch muscles, such as the soleus.

Modulation of calmodulin gene expression as a novel mechanism for growth hormone feedback control by insulin-like growth factor in grass carp pituitary cells

Calmodulin (CaM), the Ca2+ sensor in living cells, is essential for biological functions mediated by Ca2+-dependent mechanisms. However, modulation of CaM gene expression at the pituitary level as a means to regulate pituitary hormone synthesis has not been characterized. In this study we examined the functional role of CaM in the feedback control of GH by IGF using grass carp pituitary cells as a cell model. To establish the structural identity of CaM expressed in the grass carp, a CaM cDNA, CaM-L, was isolated from the carp pituitary using 3'/5' rapid amplification of cDNA ends. The open reading frame of this cDNA encodes a 149-amino acid protein sharing the same primary structure with CaMs reported in mammals, birds, and amphibians. This CaM cDNA is phylogenetically related to the CaM I gene family, and its transcripts are ubiquitously expressed in the grass carp. In carp pituitary cells, IGF-I and IGF-II induced CaM mRNA expression with a concurrent drop in GH transcript levels. These stimulatory effects on CaM mRNA levels were not mimicked by insulin and appeared to be a direct consequence of IGF activation of CaM gene transcription without altering CaM transcript stability. CaM antagonism and inactivation of calcineurin blocked the inhibitory effects of IGF-I and IGF-II on GH gene expression, and CaM overexpression also suppressed the 5' promoter activity of the grass carp GH gene. These results, as a whole, provide evidence for the first time that IGF feedback on GH gene expression is mediated by activation of CaM gene expression at the pituitary level.

Relationships between IGF-I and Weight Z Score, BMI, Tricipital Skin-Fold Thickness, Type of Feeding in Healthy Infants in the First 5 Months of Life

AIM

To determine the concentration of insulin-like growth factor-I (IGF-I) in exclusively breast-fed (BF) and formula-fed (FF) infants in the first 5 months of life and to study the relationship between the IGF-I level and Z score for weight, body mass index (BMI) and tricipital skin-fold thickness.

METHODS

We performed a cross-sectional study in order to evaluate serum IGF-I in 97 age-matched healthy term infants: 50 FF and 47 BF.

RESULTS

FF infants showed higher values of IGF-I (38.9 +/- 12 ng/ml) when compared to BF infants (26.7 +/- 11.6 ng/ml; p < 0.05). A positive correlation was found between IGF-I values and Z score for weight (p < 0.001), BMI (p = 0.014), tricipital skin-fold thickness (p = 0.043) and age (p = 0.02).

CONCLUSION

These results show that the IGF-I serum concentration is higher in FF infants. The observed association between IGF-I and Z score for weight, BMI, tricipital skin-fold thickness confirms the effect of different infant feeding on body size.