Beyond the somatopause: growth hormone deficiency in adults over the age of 60 years

Cell non-autonomous regulation of cerebrovascular aging processes by the somatotropic axis

Age-related cerebrovascular pathologies, ranging from cerebromicrovascular functional and structural alterations to large vessel atherosclerosis, promote the genesis of vascular cognitive impairment and dementia (VCID) and exacerbate Alzheimer's disease. Recent advances in geroscience, including results from studies on heterochronic parabiosis models, reinforce the hypothesis that cell non-autonomous mechanisms play a key role in regulating cerebrovascular aging processes. Growth hormone (GH) and insulin-like growth factor 1 (IGF-1) exert multifaceted vasoprotective effects and production of both hormones is significantly reduced in aging. This brief overview focuses on the role of age-related GH/IGF-1 deficiency in the development of cerebrovascular pathologies and VCID. It explores the mechanistic links among alterations in the somatotropic axis, specific macrovascular and microvascular pathologies (including capillary rarefaction, microhemorrhages, impaired endothelial regulation of cerebral blood flow, disruption of the blood brain barrier, decreased neurovascular coupling, and atherogenesis) and cognitive impairment. Improved understanding of cell non-autonomous mechanisms of vascular aging is crucial to identify targets for intervention to promote cerebrovascular and brain health in older adults.

Effects of GH on the Aging Process in Several Organs: Mechanisms of Action

In order to investigate the possible beneficial effects of GH administration on the aging process, 24-month-old rats of both sexes and 10-month-old SAMP8 mice were used. Male rats showed increased fat content and decreased lean body mass together with enhanced vasoconstriction and reduced vasodilation of their aortic rings compared to young adult animals. Chronic GH treatment for 10 weeks increased lean body mass and reduced fat weight together with inducing an enhancement of the vasodilatory response by increasing eNOS and a reduction of the constrictory responses. Old SAMP8 male mice also showed insulin resistance together with a decrease in insulin production by the endocrine pancreas and a reduced expression of differentiation parameters. GH treatment decreased plasma levels and increased pancreatic production of insulin and restored differentiation parameters in these animals. Ovariectomy plus low calcium diet in rabbits induced osteoporosis Titanium implants inserted into these rabbit tibiae showed after one month lesser bone to implant (BIC) surface and bone mineral density (BMD). Local application of GH in the surgical opening was able to increase BIC in the osteoporotic group. The hippocampus of old rats showed a reduction in the number of neurons and also in neurogenesis compared to young ones, together with an increase of caspases and a reduction of Bcl-2. GH treatment was able to enhance significantly only the total number of neurons. In conclusion, GH treatment was able to show beneficial effects in old animals on all the different organs and metabolic functions studied.

Impact of Long-Term Growth Hormone Replacement Therapy on Metabolic and Cardiovascular Parameters in Adult Growth Hormone Deficiency: Comparison Between Adult and Elderly Patients

Growth hormone deficiency (GHD) in adults is due to a reduced growth hormone (GH) secretion by the anterior pituitary gland which leads to a well-known syndrome characterized by decreased cognitive function and quality of life (QoL), decreased bone mineral density (BMD), increased central adiposity with a reduction in lean body mass, decreased exercise tolerance, hyperlipidemia and increased predisposition to atherogenesis. Considering some similar features between aging and GHD, it was thought that the relative GH insufficiency of the elderly person could make an important contribution to the fragility of elderly. GH stimulation tests are able to differentiate GHD in elderly patients (EGHD) from the physiological reduction of GH secretion that occurs with aging. Although there is no evidence that rhGH replacement therapy increases the risk of developing Diabetes Mellitus (DM), reducing insulin sensitivity and inducing cardiac hypertrophy, long-term monitoring is, however, also mandatory in terms of glucose metabolism and cardiovascular measurements. In our experience comparing the impact of seven years of rhGH treatment on metabolic and cardiovascular parameters in GHD patients divided in two groups [adult (AGHD) and elderly (EGHD) GHD patients], effects on body composition are evident especially in AGHD, but not in EGHD patients. The improvements in lipid profile were sustained in all groups of patients, and they had a lower prevalence of dyslipidemia than the general population. The effects on glucose metabolism were conflicting, but approximately unchanged. The risk of DM type 2 is, however, probably increased in obese GHD adults with impaired glucose homeostasis at baseline, but the prevalence of DM in GHD is like that of the general population. The increases in glucose levels, BMI, and SBP in GHD negatively affected the prevalence of Metabolic Syndrome (MS) in the long term, especially in AGHD patients. Our results are in accordance to other long-term studies in which the effects on body composition and lipid profile are prominent.

GH Replacement in the Elderly: Is It Worth It?

Growth hormone (GH), once the age of linear growth is completed, continues to play a fundamental role for the human body. In adulthood, GH contributes to regulate muscle, cardiovascular and bone metabolism. The same happens in old age, although there is less data on the effect of GH in the elderly. Regardless the age of onset, a reduced quality of life (QoL), an increased cardiovascular risk and an accelerated age-related decline in physical strength have been demonstrated in the elderly with GH deficiency (EGHD). In adults with GH deficiency (AGHD), recent studies suggest a role of GH replacement therapy (GHrt) in improving lean/fat mass ratio, blood pressure, lipid profile, bone metabolism and QoL. Despite these recent studies, there is still a lack of randomized controlled trials proving these positive effects in EGHD. Moreover, the lack of a long-term positive outcome on mortality, and the cost of GHrt could often impact on treatment decision-making and lead to postpone or avoid the prescription. The aim of this mini-review is to summarize the available data on GHrt in EGHD, in order to highlight its weaknesses and strengths and to provide directions to clinicians that will help in the management of this specific set of patients.

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

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

Effects of gender, body weight, and blood glucose dynamics on the growth hormone response to the glucagon stimulation test in patients with pituitary disease

OBJECTIVE

Body weight blunts the growth hormone (GH) response to provocative stimuli. The appropriate GH cut-off to confirm GH deficiency in obese and overweight patients undergoing the glucagon stimulation test (GST) has recently been questioned. We hypothesized that the peak GH would be inversely related to the nadir blood glucose (BG) after glucagon and that this may be a mechanism influencing peak GH in overweight patients. This retrospective study examined effects of gender, body weight, and BG dynamics on GH response to GST in patients evaluated in our Pituitary Center.

DESIGN

Adult patients who underwent GST from September 2009-2014 were included. Continuous variable comparisons were analyzed using the Mann-Whitney U-test and categorical data by Fisher's Exact Test. Spearman correlation was used to determine associations between continuous variables.

RESULTS

42 patients (N=28, 66.7% female) had sufficient data for analysis. Obese patients (N=26) had a reduced GH response, summarized as GH area under the curve (AUC) (p=0.03 vs. non-obese patients) and higher BG during GST, summarized as AUC (p<0.01 vs. non-obese patients). Obese women (N=19), in particular, stimulated lower (p=0.03 vs. non-obese women) and had a higher nadir BG (p=0.03 vs. non-obese women). While weight correlated with extent (rs=0.35; p=0.02) and timing (rs=0.31; p=0.05) of nadir BG reached, there was no significant correlation between BG dynamics and the GH response in the total population (N=42). Ten patients (7 with pan anterior hypopituitarism, defined as 3 anterior pituitary deficiencies) had a peak GH≤0.1ng/mL during GST. When these subjects with a negligible peak GH response were excluded from the analysis, weight was associated with GH AUC (rs=-0.45; p=0.01), peak GH response (rs=-0.42; p=0.02) and nadir BG (rs=0.48; p<0.01). Furthermore, the nadir BG achieved during GST was inversely related to GH AUC (rs=-0.38; p=0.03) and peak GH (rs=-0.37; p=0.04) such that patients (N=32) with higher nadir BG had lower peak GH in response to glucagon.

CONCLUSIONS

Obese patients, particularly women, do not respond as robustly to glucagon stimulation. These data suggest that there exists an altered BG profile during GST in obese individuals, and that a less robust hypoglycemic stimulus may contribute to an impaired GH response. We suggest measuring BG levels during glucagon stimulation testing to assist with clinical interpretation of GH dynamics. The diagnostic accuracy of the GST in patients with known disorders in glucose metabolism and those taking anti-diabetic medications deserves further study.

Epigenetic characterization of the growth hormone gene identifies SmcHD1 as a regulator of autosomal gene clusters

Regulatory elements for the mouse growth hormone (GH) gene are located distally in a putative locus control region (LCR) in addition to key elements in the promoter proximal region. The role of promoter DNA methylation for GH gene regulation is not well understood. Pit-1 is a POU transcription factor required for normal pituitary development and obligatory for GH gene expression. In mammals, Pit-1 mutations eliminate GH production resulting in a dwarf phenotype. In this study, dwarf mice illustrated that Pit-1 function was obligatory for GH promoter hypomethylation. By monitoring promoter methylation levels during developmental GH expression we found that the GH promoter became hypomethylated coincident with gene expression. We identified a promoter differentially methylated region (DMR) that was used to characterize a methylation-dependent DNA binding activity. Upon DNA affinity purification using the DMR and nuclear extracts, we identified structural maintenance of chromosomes hinge domain containing -1 (SmcHD1). To better understand the role of SmcHD1 in genome-wide gene expression, we performed microarray analysis and compared changes in gene expression upon reduced levels of SmcHD1 in human cells. Knock-down of SmcHD1 in human embryonic kidney (HEK293) cells revealed a disproportionate number of up-regulated genes were located on the X-chromosome, but also suggested regulation of genes on non-sex chromosomes. Among those, we identified several genes located in the protocadherin β cluster. In addition, we found that imprinted genes in the H19/Igf2 cluster associated with Beckwith-Wiedemann and Silver-Russell syndromes (BWS & SRS) were dysregulated. For the first time using human cells, we showed that SmcHD1 is an important regulator of imprinted and clustered genes.

Growth Hormone Deteriorates the Functional Outcome in an Experimental Model of Huntington's Disease Induced by 3-Nitropionic Acid

Background and Purpose:

Growth hormone (GH) has been frequently used to control the aging process in healthy individuals, probably due to its slowing effect on senescence-associated degeneration. Mitochondrial dysfunction is related to the aging process, and one of the chemical models of Huntington’s disease is that it can be induced by mitochondrial toxin. To investigate the potential application of GH to modify the progression of Huntington’s disease (HD), we examined whether GH can protect the functional deterioration by striatal damage induced by 3-nitropropionic acid (3NP).

Methods:

3NP (63 mg/kg/day) was delivered to Lewis rats by osmotic pumps for five consecutive days, and the rats received intraperitoneal administration of GH or vehicle (saline) throughout the experiment. Neurological deficits and body weight were monitored. A 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test was performed to further determine the mitochondrial activity in cultured N18TG2 neuroblastoma cells in vitro.

Results:

3NP-treated rats showed progressive neurologic deficits with striatal damage. Application of GH accelerated behavioral deterioration, particularly between day 3 and day 5, resulting in reduced survival outcome. The body weights of rats given 3NP were decreased, but GH did not affect such decrease compared to the non-treated control group. The effect of GH on cultured neuronal cells was a decrease in the MTT absorbance, suggesting a lower number of cells in a dose dependent pattern.

Conclusions:

Those results suggest that application of GH to a 3NP-induced experimental model of HD deteriorates the progress of functional deficits, possibly disturbing mitochondrial activities.

Effects of 3-year GH replacement therapy on bone mineral density in younger and elderly adults with adult-onset GH deficiency

OBJECTIVE

Little is known of the effects of long-term GH replacement on bone mineral content (BMC) and bone mineral density (BMD) in elderly GH-deficient (GHD) adults. DESIGN/PATIENTS/METHODS: In this prospective, single-center, open-label study, the effects of 3-year GH replacement were determined in 45 GHD patients >65 years and in 45 younger control GHD patients with a mean age of 39.5 (S.E.M. 1.1) years. All patients had adult-onset disease and both groups were comparable in terms of number of anterior pituitary hormonal deficiencies, gender, body mass index, and waist:hip ratio.

RESULTS

The mean maintenance dose of GH was 0.24 (0.02) mg/day in the elderly patients and 0.33 (0.02) mg/day in the younger GHD patients (P<0.01). The 3 years of GH replacement induced a marginal effect on total body BMC and BMD, whereas femur neck and lumbar (L2-L4) spine BMC and BMD increased in both the elderly and the younger patients. The treatment response in femur neck BMC was less marked in the elderly patients (P<0.05 vs younger group). However, this difference disappeared after correction for the lower dose of GH in the elderly patients using an analysis of covariance. There were no between-group differences in responsiveness in BMC or BMD at other skeletal locations.

CONCLUSIONS

This study shows that GH replacement increases lumbar (L2-L4) spine and femur neck BMD and BMC in younger as well as elderly GHD patients. This supports the notion that long-term GH replacement is also useful in elderly GHD patients.

Diagnosing growth hormone deficiency in adults

Adult growth hormone (GH) deficiency is a recognised syndrome associated with adverse phenotypic, metabolic, and quality-of-life features which improve in many patients when GH is substituted. The appropriate selection of patients at risk of growth hormone deficiency (GHD) is the crucial first step in arriving at a correct diagnosis. Although multiple diagnostic modalities are available including a 24-hour serum GH profile, stimulated GH levels, and insulin-like growth factor-1 (IGF-1) levels, the use of dynamic tests for GH reserves is required in most cases. This paper discusses the utility and drawbacks of the various testing modalities with reference to international guidelines. Regardless of the test chosen, clinical pitfalls including age and obesity must be taken into account. In addition, there is considerable analytical variation in the biochemical measurements of GH and IGF-1 which must be considered before making a diagnosis of GHD in adulthood.

Role of the GH/IGF-1 axis in lifespan and healthspan: lessons from animal models

Animal models are fundamentally important in our quest to understand the genetic, epigenetic, and environmental factors that contribute to human aging. In comparison to humans, relatively short-lived mammals are useful models as they allow for rapid assessment of both genetic manipulation and environmental intervention as related to longevity. These models also allow for the study of clinically relevant pathologies as a function of aging. Data associated with more distant species offers additional insight and critical consideration of the basic physiological processes and molecular mechanisms that influence lifespan. Consistently, two interventions, caloric restriction and repression of the growth hormone (GH)/insulin-like growth factor-1/insulin axis, have been shown to increase lifespan in both invertebrates and vertebrate animal model systems. Caloric restriction (CR) is a nutrition intervention that robustly extends lifespan whether it is started early or later in life. Likewise, genes involved in the GH/IGF-1 signaling pathways can lengthen lifespan in vertebrates and invertebrates, implying evolutionary conservation of the molecular mechanisms. Specifically, insulin and insulin-like growth factor-1 (IGF-1)-like signaling and its downstream intracellular signaling molecules have been shown to be associated with lifespan in fruit flies and nematodes. More recently, mammalian models with reduced growth hormone (GH) and/or IGF-1 signaling have also been shown to have extended lifespans as compared to control siblings. Importantly, this research has also shown that these genetic alterations can keep the animals healthy and disease-free for longer periods and can alleviate specific age-related pathologies similar to what is observed for CR individuals. Thus, these mutations may not only extend lifespan but may also improve healthspan, the general health and quality of life of an organism as it ages. In this review, we will provide an overview of how the manipulation of the GH/IGF axis influences lifespan, highlight the invertebrate and vertebrate animal models with altered lifespan due to modifications to the GH/IGF-1 signaling cascade or homologous pathways, and discuss the basic phenotypic characteristics and healthspan of these models.

Effect of growth hormone and estrogen administration on hepatocyte alterations in old ovariectomized female wistar rats

Aging could be due to the accumulation of oxidative damage. On the other hand, growth hormone (GH) and estrogen deficiency induce deleterious effects on different tissues, and hormonal replacement could counteract these effects. We have investigated whether GH and estrogen administration modify some parameters related to oxidative stress and inflammation in hepatocytes isolated from old ovariectomized female rats. Twenty-two month-old ovariectomized animals were divided into control rats, rats treated with GH, rats treated with estradiol, and rats treated with GH+estradiol. Two-month-old intact female rats were used as young reference group. Hepatocytes were isolated, cultured, and CO and NO release, ATP, cyclic-guanosyl monophosphate (cGMP), and lipid peroxide (LPO) content of cells, as well as phosphatidylcholine (PC)synthesis, were measured. Hepatocytes isolated from old ovariectomized rats showed a decrease in ATP content and PC synthesis compared to young rats. Age also induced an increase in LPO, NO, CO, and cGMP. Treating old rats with GH significantly increased ATP and reduced CO and cGMP levels. Estradiol administration improved all the parameters that were altered. Co-administration of GH and estrogens induced a more marked effect than estrogens alone only in cGMP content. In conclusion, administration of estrogens to old ovariectomized females seemed to prevent oxidative changes in hepatocytes, whereas the effect of GH is not so evident.

Interpulse growth hormone secretion in the episodic plasma profile causes the sex reversal of cytochrome P450s in senescent male rats

Humans as well as other mammals experience an aging-related decline in drug metabolism as well as a diminution in growth hormone secretion. In the case of rats, these events are more pronounced in senescent males, whose expression of male-specific isoforms of cytochrome P450, the major drug-metabolizing enzymes and constituting approximately 60-70% of the total cytochrome P450 in male rat liver, is completely suppressed, whereas female-dependent isoforms are remarkably induced to female-like levels. Overlooked in these independently reported studies is the fact that "signals" inherent in the masculine episodic and female continuous growth hormone profiles regulate expression and/or suppression of the dozen or so sex-dependent cytochrome P450 isoforms in rat liver. Whereas previous studies identified profound reductions in the pulse amplitudes of the masculine growth hormone profile as the cause for the diminished hormone secretion during aging, pulse heights are not recognized by the cytochromes as regulatory signals. Instead, we have shown that just a nominal secretion of growth hormone during the usual growth hormone-devoid interpulse period in the masculine episodic profile can explain the complete repression of male-specific CYP2C11, CYP3A2, and CYP2A2 and induction of female-dependent CYP2C12, CYP2C6, and CYP2A1 observed in senescent male rats.

Insulin-Like growth factor I: implications in aging

According to the somatomedin model, growth hormone (GH)-dependent hepatic synthesis is responsible for maintaining circulating insulin-like growth factor (IGF)-I levels. On the other hand, the local autocrine/paracrine IGF-I expression in peripheral tissue is generally GH-independent and reflects the effects of various and tissue-specific trophic hormones. Circulating IGF-I levels undergo important age-related variations increasing at puberty and decreasing, thereafter, to low levels in the elderly. Low IGF-I levels in the elderly mainly reflect impaired somatotroph secretion but the decline in gonadal sex steroid levels, some protein and micronutrients malnutrition as well as age-dependent variations in IGF-binding proteins may also play a role in the age-related decrease in IGF-I activity. This, in turn, partially accounts for age-related changes in bones, muscles, cardiovascular system, central nervous system and the immune system. However, it is currently unclear whether treatment with exogenous IGF-I can retard or reverse age-related changes in body structure and function.

Growth hormone deficiency in elderly patients with hypothalamo-pituitary tumors

In 18 patients with hypothalamo-pituitary diseases aged over 60 years and in 18 sex, age- and BMI-matched healthy subjects, the results of plasma IGF-I and IGF-BP3 levels and the GH response to GHRH + arginine test (GHRH + ATT) were correlated to the results of body composition, serum osteocalcin (OC) and urinary cross-linked N-telopeptides of type I collagen (Ntx) and the bone mineral density (BMD). In 10 patients and 10 controls, the GH response to ITT was also evaluated. The GH response to GHRH + ATT and ITT was markedly reduced in patients compared to controls (3.1 +/- 0.7 vs. 23.2 +/- 2.3 micrograms/L, P < 0.001 and 1.1 +/- 0.3 vs. 6.4 +/- 0.8 micrograms/L, P < 0.001), so all patients were classified as GHD, though no significant difference was found in plasma IGF-I and IGF-BP3 levels between the two groups. Body composition analysis revealed a significant increase of fat mass (37.4 +/- 2.2 vs. 28.0 +/- 1.0%, P < 0.001), a significant decrease of lean mass (62.6 +/- 2.2 vs. 72.0 +/- 1.0%, P < 0.001) and total body water (45.7 +/- 1.5 vs. 52.5 +/- 1.1%, P < 0.001) in patients compared to controls. Serum OC levels were lower (1.9 +/- 0.1 vs. 4.6 +/- 0.4 micrograms/L, P < 0.001) in patients than in controls, whereas urinary Ntx levels were similar. BMD values in lumbar spine (0.81 +/- 0.02 vs. 0.90 +/- 0.02 g/cm2, P < 0.001) and femoral neck (0.70 +/- 0.02 vs. 0.82 +/- 0.02 g/cm2, P < 0.001) were significantly lower in patients than in controls. A significant inverse correlation was found between GHD duration and lumbar spine (r = -0.73, P&1t; 0.001) or femoral neck (r = -0.81, P&1t; 0.001) BMD values and a significant direct correlation was found between GH peak after GHRH + ATT and lumbar BMD (r = 0.69, p = 0.001) in GHD patients. In conclusion, GHD in patients over 60 yrs aged with a characteristic history of hypothalamus-pituitary pathology is distinct from the physiological decline in GH secretion associated with aging.