Effect of oestrogen status on serum levels of growth hormone-binding protein and insulin-like growth factor-I in non-pregnant and pregnant women

Assessment of quality of life on 4-year growth hormone therapy in Japanese patients with adult growth hormone deficiency: A post-marketing, multicenter, observational study

OBJECTIVE

Improvement of quality of life (QOL) by growth hormone (GH) therapy was not demonstrated in Japanese adult growth hormone deficiency (AGHD) patients by either the QOL Assessment of Growth Hormone Deficiency in Adults or the Questions on Life Satisfaction-Hypopituitarism, which are widely used to evaluate QOL in Western AGHD patients. We therefore evaluated QOL in Japanese AGHD patients receiving recombinant GH, Norditropin® (Novo Nordisk A/S, Denmark), using the newly developed Adult Hypopituitarism Questionnaire (AHQ).

DESIGN

This multicenter, non-interventional, observational study in Japanese patients with severe AGHD was conducted from 1 October 2009 to 30 September 2014. Patients with severe AGHD already receiving somatropin and somatropin-naïve patients were included. GH therapy (Norditropin®) was initiated as injections of 0.021mg/kg/week divided into 6-7 doses/week, and was adjusted according to clinical responses. Demographic/clinical data were obtained from medical records or by patient recall. QOL was assessed using the AHQ at baseline; 3, 6, and 12months; and annually up to 4years.

RESULTS

Of 387 registered patients, 161 were eligible for QOL analysis. AHQ scores significantly improved after 3months of treatment. Improvements in the psycho-social and physical domains were statistically significant throughout the 4-year study period. Although the GH dose was increased in females such that insulin-like growth factor-1 levels reached those of males, QOL improvements in females did not reach those of males. Despite the greater GH dose in child-onset patients, limited QOL improvements were observed in child-onset vs adult-onset cases.

CONCLUSIONS

Four-year GH treatment in Japanese AGHD patients elicits sustained improvement in QOL as assessed by AHQ scores.

A summary of the influence of exogenous estrogen administration across the lifespan on the GH/IGF-1 axis and implications for bone health

Bone growth, development, and remodeling are modulated by numerous circulating hormones. Throughout the lifespan, the extent to which each of the hormones impacts bone differs. Understanding the independent and combined impact of these hormones on controlling bone remodeling allows for the development of more informed decision making regarding pharmacology, specifically the use of hormonal medication, at all ages. Endocrine control of bone health in women is largely dictated by the growth hormone (GH)/insulin-like growth factor-1 (IGF-1) axis and the hypothalamic-pituitary-ovarian (HPO) axis. Growth hormone, secreted from the pituitary gland, stimulates cells in almost every tissue to secrete IGF-1, although the majority of circulating IGF-1 is produced hepatically. Indeed, systemic IGF-1 concentrations have been found to be correlated with bone mineral density (BMD) in both pre- and post-menopausal women and is often used as a marker of bone formation. Sex steroids produced by the ovaries, namely estradiol, mediate bone resorption through binding to estrogen receptors on osteoclasts and osteoblasts. Specifically, by increasing osteoclast apoptosis and decreasing osteoblast apoptosis, adequate estrogen levels prevent excessive bone resorption, which helps to explain the rapid decline in bone mass that occurs with the menopausal decrease in estrogen production. Though there are documented correlations between endogenous estrogen concentrations and GH/IGF-1 dynamics, this relationship changes across the lifespan as sex-steroid dynamics fluctuate and, possibly, as tissue responsiveness to GH stimulation decreases. Aside from the known role of endogenous sex steroids on bone health, the impact of exogenous estrogen administration is of interest, as exogenous formulations further modulate GH and IGF-1 production. However, the effect and extent of GH and IGF-1 modulation seems to be largely dependent on age at administration and route of administration. Specifically, premenopausal women using combined oral contraceptive therapy (COC), post-menopausal women taking oral hormone therapy (HT), and both pre- and post-menopausal women using a transdermal form of estrogen therapy (COC or HT) demonstrate disparate GH/IGF-1 responses to exogenous estrogen. This review serves to summarize what is currently known regarding the influence of exogenous estrogen administration across the lifespan on the GH/IGF-1 axis and implications for bone health.

Growth hormone binding protein - physiological and analytical aspects

A significant proportion of total circulating growth hormone (GH) is bound to a high affinity growth hormone binding protein (GHBP). Several low affinity binding proteins have also been described. Significant differences between species exist with respect to origin and regulation of GHBP, but generally it resembles the extracellular domain of the GH receptor. Concentrations are associated with GH status, body composition and other factors. Although the clinical relevance of GHBP is not fully understood it is suggested that concentrations indirectly reflect GH receptor status. This is supported by cases of Laron's syndrome where a molecular defect in the extracellular domain of the GH receptor is associated with low or unmeasurable GHBP concentrations. Methods to measure GHBP have evolved from chromatographic, activity based procedures to direct immunoassays. In clinical practice, measurement of GHBP can be helpful to differentiate between GH deficiency and GH insensitivity, particularly if GHBP is absent.

Aspects of placental growth hormone physiology

Placental growth hormone (PGH) has been known for 20 years. Nevertheless, its physiology is far from understood. In this review, basal aspects of PGH physiology are summarised and put in relation to the highly homologous pituitary growth hormone (GH). During normal pregnancy, PGH progressively replaces GH and reach maximum serum concentrations in the third trimester. A close relationship to insulin-like growth factor (IGF)-I and -II levels is observed. Furthermore, PGH levels are positively associated to fetal growth. The potential importance of growth hormone receptors and binding protein for PGH effects is discussed. Finally, the review outlines current knowledge of PGH in pathological pregnancies.

Physiology and pathophysiology of growth hormone-binding protein: methodological and clinical aspects

Circulating GH is partly bound to a high-affinity binding protein (GHBP), which in humans is derived from cleavage of the extracellular domain of the GH receptor. The precise biological function GHBP is unknown, although a regulation of GH bioactivity appears plausible. GHBP levels are determined by GH secretory status, body composition, age, and sex hormones, but the cause-effect relationships remain unclarified. In addition to the possible in vivo significance of GHBP, the interaction between GH and GHBP has methodological implications for both GH and GHBP assays. The present review concentrates on methodological aspects of GHBP measurements, GHBP levels in certain clinical conditions with a special emphasis on disturbances in the GH-IGF axis, and discusses the possible relationship between plasma GHBP and GH receptor status in peripheral tissues.

Dehydroepiandrosterone supplementation in women with adrenal failure: impact on twenty-four hour GH secretion and IGF-related parameters

OBJECTIVE

In women, GH secretion is strongly influenced by oestrogen status, whereas the role of androgens is unclear. We, therefore, examined GH secretory dynamics during low vs. normalized androgen levels in women with adrenal failure.

PATIENTS

Ten females with adrenal failure (AF), mean age of 42 years (range 22-54 years).

DESIGN

The effects of 8 days of oral dehydroepiandrosterone (DHEA; 50 mg/day) were studied in a double-blind placebo-controlled, cross-over design. A control group of healthy women was studied once without any treatment.

MEASUREMENTS

Before and after each treatment period, blood was sampled for measurement of androgens, IGF-I, IGFBP-3 and GHBP. A 24-h GH profile with measurements every 20 min was performed at the end of each period.

RESULTS

DHEA supplementation normalized the mean circulating levels of testosterone and androgen precursors. The secretory pattern of GH was unaltered during DHEA [placebo vs. DHEA; half-life 22.83 +/- 1.24 vs. 21.45 +/- 1.19 (min), P = 0.429; pulse frequency 9.9 +/- 0.7 vs. 10.5 +/- 0.5 (/24 h), P = 0.502; total production rate 62.27 +/- 13.44 vs. 52.61 +/- 7.06 (microg/l/day), P = 0.317]. Subgroup analysis, however, indicated that DHEA treatment increased GH secretion in patients not receiving oestrogen (n = 5), whereas the opposite was observed among patients receiving exogenous oestrogen derivatives (n = 5). Compared to the control group (CON), GH half-life was longer in AF (half-life CON: 16.48 +/- 0.91, P = 0.001). The additional features of GH secretion were similar. Unexpectedly, the levels of IGF-I, IGFBP-3 and GHBP were elevated in the patients as compared to controls, without significant effects of DHEA [AF vs. CON. IGF-I: 186 +/- 20 vs. 144 +/- 7 (microg/l), P = 0.04; IGFBP-3: 5196 +/- 224 vs. 3687 +/- 212 (microg/l), P = 0.001; GHBP: 2.27 +/- 0.25 vs. 1.41 +/- 0.13 (nmol/l), P = 0.002].

CONCLUSION

(1) Short-term DHEA administration in women with adrenal failure normalizes the circulating levels of androgens without uniformly affecting the GH-IGF axis; (2) The observation that exogenous oestradiol may mask a stimulatory effect of DHEA on GH secretion merits future investigation.

Timing of onset of growth hormone deficiency is a major influence on insulin-like growth factor I status in adult life

OBJECTIVE

Several reports have suggested that IGF-I levels in patients with childhood-onset (CO) GH deficiency are lower than those observed in patients with adult-onset (AO) GH deficiency. However, these reports are unsatisfactory as there are several differences between the cohorts studied other than the timing of onset of GH deficiency; in particular, the patients were not matched for equal severity of GH deficiency. We have pursued this question further by examining the IGF-I standard deviation score (SDS) in patients with CO and AO GH deficiency, with equal degrees of severity of GH deficiency, as defined by the peak GH response to the insulin tolerance test (ITT).

PATIENTS AND MEASUREMENTS

IGF-I SDS were compared in 146 non acromegalic patients (69 male), aged 15.7-76.6 years (median 33.4 years), bone mass index (BMI) 27.8 +/- 5.8 kg/m2, with severe GH deficiency (peak GH response < 9 mU/l to insulin-induced hypoglycaemia). Patients were subdivided by timing of onset of GH deficiency and the peak GH response to the ITT (GH response < or = 1 mU/l, group 1; > 1-3 mU/l, group 2; > 3-6 mU/l, group 3; > 6-8.9 mU/l, group 4).

RESULTS

The IGF-I SDS (mean value +/- SD) in the CO group (n = 63) as a whole was significantly lower than that found in the AO group (n = 83) (-3.7 +/- 2.8 vs.-1.55 +/- 2.2, respectively; P < 0.0001). Despite this, there was no significant difference in the peak GH response to an ITT between the two cohorts (2.8 +/- 2.3 mU/l in the AO cohort and 2.6 +/- 2.2 mU/l in the CO cohort; P = 0.5). When the cohorts were subdivided by severity of GH deficiency, there remained a significant difference in IGF-I SDS in groups 1 (P < 0.0001), 2 (P = 0.05) and 3 (P < 0.05), but there was no significant difference between the AO and CO cohorts in group 4. The peak GH response to an ITT was similar in the AO and CO cohorts in all groups (P = 0.8, 0.8, 0.9 and 0.3 in groups 1-4, respectively). Although increasing severity of hypopituitarism was associated with a decline in IGF-I SDS in the CO cohort (P < 0.01), this was not the case in the AO cohort (P = 0.3).

CONCLUSION

These data support the hypothesis that there is an innate difference between adult patients with either CO or AO GH deficiency that cannot be explained solely by variation in the severity of GH deficiency. A possible explanation is that childhood GH deficiency programmes the subsequent relationship between GH and IGF-I in adult life or that the body composition changes, which are more severe in AO GH deficiency, influence IGF-I status.

Childhood-onset growth hormone (GH) deficiency in adult life

Over the last decade GH replacement therapy for adults has progressed in status from research study to a mainstream clinical indication. An area ripe for further research, however, is the difference between adults who developed GHD before and after completion of growth and puberty. That differences exist, not only in aetiology, but also in phenotype and response to GH therapy is clear. However, whether these differences are intrinsic to the timing of onset of GHD, or related to secondary factors including the method of assessment or dose of GH employed is uncertain. This chapter discusses the current state of knowledge in this area and poses further questions, not only for the researcher attempting to understand the mechanisms underlying these differences, but also for the physician seeking to ameliorate the impact of GHD in patients who acquired GHD in childhood.

IGF status is altered by tamoxifen in patients with breast cancer

AIMS

An increased concentration of insulin-like growth factor 1 (IGF-1) is an independent risk factor for premenopausal breast cancer. Tamoxifen is thought initially to reduce concentrations of IGF-1 and increase concentrations of the IGF binding proteins. The aim of this study was to compare concentrations of IGF-1, IGF binding protein 1 (IGF-BP1), and IGF-BP3 in patients with breast cancer (n = 14) with those seen in control subjects (n = 23) and to assess the effect of tamoxifen on IGF status in these patients.

METHODS

Non-fasting blood samples were collected from patients with breast cancer before surgery and after nine, 18, and 27 months of tamoxifen treatment. The baseline concentrations were compared with those of age and sex matched healthy control subjects.

RESULTS

IGF-1, IGF-BP3, and IGF-BP1 concentrations were not significantly different in cases and controls. Tamoxifen treatment significantly increased IGF-BP1 after 18 and 27 months (baseline: mean, 21.6 ng/ml; SD, 16.6; 18 months: mean, 52.0 ng/ml; SD, 41.8; p = 0.019; 27 months: mean, 40.7 ng/ml; SD, 24.9; p = 0.043) and IGF-BP3 after nine, 18, and 27 months (baseline: mean, 3119 ng/ml; SD, 507; nine months: mean, 3673 ng/ml; SD, 476; p = 0.004; 18 months: mean, 3445 ng/ml; SD, 634; p = 0.034; 27 months: 3409 ng/ml; SD, 501; p = 0.043) when compared with baseline values. IGF-1 was not altered significantly from baseline at any time point. However, the IGF-1 to IGF-BP3 ratio was significantly decreased at both nine and 18 months (baseline: mean, 0.058; SD, 0.014; nine months: mean, 0.039; SD, 0.008; p = 0.033; 18 months: mean, 0.044; SD, 0.012; p = 0.01). This ratio was not significantly different from baseline at 27 months (mean, 0.054; SD, 0.01; p = 0.08).

CONCLUSIONS

Tamoxifen increases IGF-BP3 and IGF-BP1 concentrations. It also decreases the IGF-1 to IGF-BP3 ratio but this effect may be limited after long term use. Longer follow up, with larger numbers of patients, should determine when, and for how long, tamoxifen can reduce circulating IGF-1.

Effects of two oral contraceptives on plasma levels of insulin-like growth factor I (IGF-I) and growth hormone (hGH)

In 18 healthy women, the effect of two oral contraceptives (OCs) on insulin-like growth factor (IGF-I) and its binding protein-3 (IGFBP-3) and growth hormone (hGH) plasma level were studied before and after intake of either of two OC formulations over 21 days, one containing 2 mg dienogest and 0.03 mg ethinylestradiol (group A) and the other 0.125 mg levonorgestrel and 0.03 mg ethinylestradiol (group B). There was a reduction of the mean IGF-I concentration of 30% (p = 0.008) in the women receiving dienogest-containing pills and 12% (p = 0.006) in women taking the levonogestrel-containing preparation. This difference between drug groups was statistically significant (p = 0.002). A correlation between the control values and the basal-treatment difference (r = 0.945; p = 0.000) was observed only in women of group A. Between basal and treatment cycles the mean plasma levels of hGH remained unchanged in both groups tested, but the 23.5-h integrated mean hGH plasma concentrations (AUC(0-23.5h)) were significantly elevated by 36% (p = 0.016) in comparison to basal values before treatment only in women receiving the levonorgestrel-containing pills. Also, in the women who received the dienogest-containing preparation, the changes of integrated mean plasma level were inversely associated with the control values (r = -0.723; p = 0.025). Neither in group A nor in group B was the mean plasma level of IGFB-3 changed.

IN CONCLUSION

the results of the present analysis indicate that hormonal contraceptives can modulate the GH and IGF-I-axis in the reproductive age. Probably the androgenic progestogen levonorgestrel (0.125 mg/day) opposes the estrogen-induced action. In the women who took the dienogest-containing formulations (anti-androgenic progestogen-group A), the extent of individual changes (hGh and IGF-I) depends on the basal level prior to pill intake. Further studies, especially of long-term intake of OCs, are necessary to confirm these results and to assess the practical relevance for possible effects on connective tissue and bone.

Intersubject responsiveness of high-affinity growth hormone (GH)-binding protein (GHBP) to long-term GH replacement therapy

In adult growth hormone deficiency (GHD) syndrome responsiveness to GH replacement therapy is reported to vary considerably. The underlying mechanisms, however, are not well understood. The aim of this study was to investigate which baseline variables determine the reported variable intersubject responsiveness of high-affinity GH-binding protein (GHBP) to GH replacement therapy. In the setting of a double blind study over 12 months with placebo control over the first 6 months, we analyzed the interrelationship between a number of baseline variables, which vary considerably amongst subjects, and the GHBP response to GH replacement in 31 GHD adults (21 males and 10 females). The following variables were investigated: age, gender, duration of GHD, body composition, serum levels of high-affinity GHBP, insulin-like growth factor-1 (IGF-1), and IGF-binding protein-3 (IGFBP-3). The results showed that in the 6 months treated group of 16 patients (11 males, 5 females), serum IGF-1 increased from 87 ng/ml (range: 26 to 173) to 250 (range: 62 to 467) (p<0.01) and GHBP increased from 1,302 pmol/l (range: 845 to 1,m960) to 1418 (range: 941 to 2,025) (p=0.04). Both parameters showed a significant time effect (within-subjects) (p<0.001). In the 12 months treated group of 15 patients (10 males, 5 females), serum IGF-1 increased from 92 ng/ml (range: 20 to 180) to 272 (range: 45 to 491) (p<0.01), whereas GHBP did not show a significant change: from 1,186 pmol/l (range: 660 to 1,690) to 1,252 (range: 580 to 1,890) (p=0.87). Also no significant time effect (within-subjects) was observed for GHBP (p=0.06). Step-wise multiple regression analyses revealed that during the 6 months placebo period baseline GHBP explained 83% of the variance in post-placebo GHBP, whereas the variance in post-treatment GHBP could be accurately predicted (adjusted R2=0.93) from baseline GHBP and body fat mass, irrespective of the duration of GH treatment. No other baseline variables contributed independently to the GHBP response, with the exception of IGFBP-3, which showed a small, but significant contribution in females, but not in males. These findings indicate that the variable intersubject responsiveness of GHBP to GH replacement therapy is mainly due to differences in baseline body fat mass amongst adult GHD patients, and that in female patients a relatively low baseline IGFBP-3 contributes to a rise in serum GHBP after GH treatment. The clinical relevance of measuring GHBP in adult GHD patients is limited to the first screening step to diagnose GHD, because long-term GH therapy tends to restore serum GHBP to pretreatment levels.

The aromatase inhibitor letrozole in advanced breast cancer: effects on serum insulin-like growth factor (IGF)-I and IGF-binding protein-3 levels

Serum insulin-like growth factor (IGF)-I and IGF-binding protein-3 levels were measured in two groups of postmenopausal women with advanced breast cancer, who received the aromatase inhibitor letrozole 0.5 or 2.5 mg p.o. once daily. Blood samples were obtained from 15 patients in each dose group at baseline, and one and three months after starting therapy. Circulating IGF-I and IGFBP-3 concentrations were determined by means of radioimmunoassay. In both dosage groups a statistically significant increase in the IGF-I levels was observed during three months of letrozole treatment (P=0.003). In addition, the multiple testing procedure yielded in the whole patient population a significant result in the comparison between mean IGF-I values after three months of therapy and those observed at baseline (P=0.004), the estimated average increase being of 24%. No significant result was obtained in the analysis for the dose effect (P=0.077) and for the time x dose interaction (P=0.208). Circulating IGFBP-3 levels did not appear to be affected by letrozole treatment in either of the dose groups. This is the first report concerning the short-term effects of letrozole on components of the IGF system in breast cancer patients; further investigations are warranted in order to confirm these preliminary data.

Relationships between insulin-like growth hormone factor-I and estradiol in reproductive aging

OBJECTIVE

To evaluate gonadotropins, estrogen, and insulin-like growth hormone factor (IGF)-I and its binding proteins throughout the normal menstrual cycle and during aging within the reproductive life span.

DESIGN

Daily blood samples were obtained from 17 normally cycling women.

SETTING

Center for Fertility and Reproductive Medicine, Newark, New Jersey.

PARTICIPANTS

Ten women aged 19 to 34 years old and seven women aged 42 to 47 years old.

MAIN OUTCOME MEASURES

Luteinizing hormone (LH), FSH, E2, and P were assayed in daily blood samples. Early follicular, late follicular, midluteal phase, and samples taken at ovulation were also assayed for IGF-I and IGFBP-I and IGFBP-III.

RESULTS

Follicle-stimulating hormone (FSH) increased significantly with reproductive aging. IGF-I and its binding proteins did not fluctuate through the menstrual cycle. IGF-I and its binding proteins did not change over the 28-year time span studied, in the face of significantly increased circulating estradiol associated with reproductive aging.

CONCLUSION

Rising E2 may be a subtle harbinger of the perimenopause. IGF-I and its binding proteins did not decrease with cycle stage or with aging during the reproductive years, perhaps because of increased estradiol stimulation of the somatotrophic axis.

Relations between sex hormones, sex hormone binding globulin, insulin-like growth factor-I and insulin-like growth factor binding protein-1 in post-menopausal breast cancer patients

OBJECTIVE

Oestrogens, androgens and anti-endocrine drugs such as tamoxifen and aminoglutethimide influence plasma insulin-like growth factor-I (IGF-I). IGF-I, in turn, has been found to stimulate the peripheral aromatase in vitro. The aim of this study was to examine relations between sex hormones, IGF-I and insulin-like growth factor binding protein-1 (IGFBP-1) in post-menopausal women with breast cancer.

DESIGN

To measure plasma sex steroids, sex hormone binding globulin (SHBG), IGF-I, IGFBP-1, insulin and urinary oestrogen metabolites in post-menopausal women with breast cancer not receiving any endocrine therapy.

PATIENTS

Thirty-two patients had fasting blood samples obtained between 0800 and 1000 h. A sub-group of 10 patients had 24-hour urine oestrogen metabolites determined.

MEASUREMENTS

Plasma steroids and proteins were measured by radioimmunoassays. Urinary oestrogens were measured by GC-MS.

RESULTS

SHBG correlated negatively with plasma androstenedione (P < 0.001), insulin (P < 0.001), IGF-I, height and plasma oestrone sulphate (P < 0.025 for all), but positively with plasma IGFBP-1 (P < 0.025). IGFBP-1 correlated negatively with IGF-I (P < 0.001) and the testosterone/SHBG ratio (P < 0.05). Neither IGF-I nor IGFBP-1 correlated with any of the plasma or urinary sex hormones or with the oestrone/androstenedione and oestradiol/testosterone ratios. Multivariate analysis revealed plasma SHBG to correlate positively with IGFBP-1 (P = 0.029) and negatively with insulin (P = 0.031). Plasma IGFBP-1 correlated negatively with IGF-I (P < 0.0001) but not with insulin.

CONCLUSION

Our results do not suggest any influence of plasma sex steroids in physiological concentrations on IGF-I or IGFBP-1 in post-menopausal breast cancer patients, nor do they indicate IGF-I at physiological concentrations influences the ratios between plasma oestrogens and their androgen precursors.