GLP-1 infusion reduces IGFBP-1 serum level in humans

GLP-1 Receptor Agonists Induce Growth Hormone Secretion in Healthy Volunteers

INTRODUCTION

Growth hormone (GH) is an essential regulator of growth, body composition and fuel metabolism and, consequently, GH secretion is under the feedback control of numerous nutritional and endocrine mediators. Glucagon-like peptide 1 receptor agonists (GLP-1RAs) have been shown to exert pleiotropic effects, including stimulation of the activity of the hypothalamic-pituitary-adrenal axis. As GLP-1RAs exert multiple metabolic effects, we hypothesised that they may also affect the secretion of GH and examined the effect of a short-acting and a long-acting GLP-1 RA on GH secretion.

METHODS

This is a post hoc analysis of data from clinical trials. Two separate single-group open-label clinical trials were carried out in the ambulatory care setting with a duration of 1 and 21 days, respectively. Healthy adult male and female volunteers with no chronic illnesses or use of daily medicines were recruited for the study. The two interventions were: study 1, single dose of 10 µg exenatide administered subcutaneously (s.c.); study 2, 0.6 mg liraglutide administered s.c. once daily for 21 days.

RESULTS

Administration of a single dose of exenatide (study 1) caused a clear increase in GH levels, peaking between 60 and 120 min post-administration. There was also a small but statistically significant decrease in luteinising hormone and testosterone levels 120 min after exenatide dosing. Administration of the long-acting GLP-1RA liraglutide daily for 21 days (study 2) elicited an increase in GH levels with no change in insulin-like growth factor-1 (IGF-1) concentrations after 3 weeks of treatment.

CONCLUSIONS

The results show that the administration of GLP-1RAs may elicit an increase in growth hormone levels. GLP-1 signalling may be a novel mechanism of regulation of GH secretion. This finding needs to be replicated in the placebo-controlled trial.

CLINICAL TRIAL REGISTRATION NUMBERS

NCT02089256 and NCT03160261.

Sitagliptin Decreases Visceral Fat and Blood Glucose in Women With Polycystic Ovarian Syndrome

CONTEXT

Women with polycystic ovarian syndrome (PCOS) have decreased growth hormone (GH), which can result in increased visceral adiposity (VAT) and impaired vascular function. GH-releasing hormone, a dipeptidyl peptidase-4 (DPP4) substrate, stimulates GH secretion.

OBJECTIVE

We tested the hypothesis that DPP4 inhibition increases GH and improves glucose levels and vascular function in women with PCOS.

METHODS

Eighteen women with PCOS participated in a double-blind, crossover study. They received sitagliptin either 100 mg or placebo daily for 1 month, with crossover treatments separated by an 8-week washout. During each treatment, women underwent a 75-gram oral glucose tolerance test (OGTT) and assessments of vascular function and body composition. Overnight GH secretion was assessed via venous sampling every 10 minutes for 12 hours and analyzed using an automated deconvolution algorithm.

RESULTS

During OGTT, sitagliptin increased glucagon-like peptide-1 (P < 0.001), early insulin secretion (from mean [± SD] insulinogenic index 1.9 ± 1.2 to 3.2 ± 3.1; P = 0.02), and decreased peak glucose (mean -17.2 mg/dL [95% CI, -27.7 to -6.6]; P < 0.01). At 1 month, sitagliptin decreased VAT (from 1141.9 ± 700.7 to 1055.1 ± 710.1 g; P = 0.02) but did not affect vascular function. Sitagliptin increased GH half-life (from 13.9 ± 3.6 to 17.0 ± 6.8 min, N = 16; P = 0.04) and interpulse interval (from 53.2 ± 20.0 to 77.3 ± 38.2 min, N = 16; P < 0.05) but did not increase mean overnight GH (P = 0.92 vs placebo).

CONCLUSIONS

Sitagliptin decreased the maximal glucose response to OGTT and VAT. Sitagliptin did not increase overnight GH but increased GH half-life and the interpulse interval.

CLINICAL TRIAL REGISTRATION

This study was registered at www.clinicaltrials.gov as NCT02122380 prior to enrollment of the first participant.

The insulin-like growth factor-I receptor stimulating activity (IRSA) in health and disease

Determination of true IGF-I bioactivity in serum and other biological fluids is still a substantial challenge. The IGF-IR Kinase Receptor Activation assay (IGF-IR KIRA assay) is a novel tool to asses IGF-IR stimulating activity (IRSA) and has opened a new era in studying the IGF system. In this paper we discuss many studies showing that measuring IRSA by the IGF-IR KIRA assay often provides fundamentally different information about the IGF system than the commonly used total IGF-I immunoassays. With the IGF-IR KIRA assay phosphorylation of tyrosine residues of the IGF-IR is used as read out to quantify IRSA in unknown (serum) samples. The IGF-IR KIRA assay gives information about net overall effects of circulating IGF-I, IGF-II, IGFBPs and IGFBP-proteases on IGF-IR activation and seems especially superior to immunoreactive total IGF-I in monitoring therapeutic interventions. Although the IRSA as measured by the IGF-IR KIRA assay probably more closely reflects true bioactive IGF-I than measurements of total IGF-I in serum, the IGF-IR KIRA assay in its current form does not give information about all the post-receptor intracellular events mediated by the IGF-IR. Interestingly, in several conditions in health and disease IRSA measured by the IGF-IR KIRA assay is considerably higher in interstitial fluid and ascites than in serum. This suggests that both the paracrine (local) and endocrine (circulating) IRSA should be measured to get a complete picture about the role of the IGF system in health and disease.

The IGF system in patients with type 2 diabetes: associations with markers of cardiovascular target organ damage

OBJECTIVE

Perturbations in the insulin-like growth factor (IGF) system may contribute to the accelerated cardiovascular disease (CVD) that occurs in patients with type 2 diabetes (T2D). However, it remains unknown whether the IGF system is also involved in the development of early, subclinical CVD. We characterised the IGF system in T2D patients and matched controls and examined the associations with markers of subclinical target organ damage.

METHODS

The study included 99 patients with recently diagnosed T2D and 99 age- and sex-matched controls. IGF-1 and IGFBP-1 to -4 were measured by immunoassays, as were pregnancy-associated plasma protein-A (PAPP-A) and the PAPP-A-generated N-terminal (NT) and C-terminal (CT) IGFBP-4 fragments, which are novel CVD risk markers. Arterial stiffness was evaluated by carotid-femoral pulse wave velocity (PWV). Cerebral white matter lesions (WMLs) and carotid artery remodelling were determined by MRI.

RESULTS

After multivariate adjustments, patients with T2D had lower concentrations of IGFBP-2, IGFBP-4, NT- and CT-IGFBP-4, when compared with controls. IGFBP-2 was inversely correlated to PWV in all subjects in multivariate analysis (P < 0.05), and IGFBP-3 was inversely associated with severity of WMLs (P < 0.05). The NT-IGFBP-4 fragment was associated with the degree of carotid artery remodelling among all subjects (regression coefficient (95% CI): 2.95 (0.70, 5.16), P = 0.011). Levels of NT- and CT-IGFBP-4 were reduced in T2D patients receiving metformin compared to those in controls and patients not receiving metformin.

CONCLUSIONS

Even in recently diagnosed and well-controlled T2D patients, IGF protein levels are altered and associated with CVD risk factors.

Improved glycemic control due to sitagliptin is not related to cortisol or the surrogate marker IGFBP-1 for hepatic insulin sensitivity

IMPORTANCE

Elevated cortisol levels and dysregulated insulin-like growth factor binding protein-1 (IGFBP-1; a marker of hepatic insulin sensitivity) are both related to insulin resistance and glucose abnormalities. It is unknown whether improvement in these parameters is related to improved glucose metabolism during treatment with sitagliptin.

OBJECTIVE

To determine whether improved insulin sensitivity and beta-cell function during treatment with sitagliptin is related to lower cortisol levels and/or improved regulation of IGFBP-1 in patients with recent acute coronary syndrome (ACS) and newly discovered glucose abnormalities.

DESIGN

Samples were taken from The BEta-cell function in Glucose abnormalities and Acute Myocardial Infarction (BEGAMI) trial, a double-blinded, placebo-controlled randomized clinical trial on the efficacy and safety of sitagliptin for patients with ACS and newly discovered glucose abnormalities.

SETTING

Cardiology departments (cardiac ICU and outpatient clinic) in two hospitals in Stockholm, Sweden.

PARTICIPANTS

Subjects hospitalized (or recently hospitalized) for ACS, in whom an oral glucose tolerance test revealed previously unknown glucose abnormalities.

INTERVENTIONS

Subjects were randomized to sitagliptin 100mg once daily (n=34) or placebo (n=37) for twelve weeks. Oral glucose tolerance test (OGTT) and randomization occurred after stabilization median 7 days after ACS.

MAIN OUTCOMES AND MEASURES

Fasting serum cortisol and IGFBP-1 were analyzed before OGTT, around 8a.m., and after at 10a.m. The latter time point was chosen as the spread in cortisol levels around is small then, allowing improved chances to detect differences between groups.

RESULTS

Glucose tolerance and insulin sensitivity improved in both groups, while HbA1c and indices of β-cell function improved only in the sitagliptin group as reported previously. Both groups displayed decreased cortisol levels around 10a.m. (from 338±21 to 278±14 nmol/L, p=0.038, in the sitagliptin group; from 343±17 to 302±15 nmol/L, p=0.017, in the placebo group), and improved correlation between fasting log-IGFBP-1 and insulin.

CONCLUSIONS AND RELEVANCE

These findings suggest that a stress-related elevation in cortisol may have negative impact on glucose tolerance in patients with recent ACS. However, improved glycemic control with sitagliptin does not appear to be related to changes in cortisol levels or hepatic insulin sensitivity as assessed by IGFBP-1.

Differential effects of low birthweight and intrauterine growth restriction on umbilical cord blood insulin-like growth factor concentrations

OBJECTIVE

Alterations in the growth hormone-insulin-like growth factor (IGF) axis have been considered as a causal factor for intrauterine growth restriction (IUGR) and for the increased risk of metabolic disease in later life. We compared members of the IGF axis in umbilical cord blood between IUGR neonates, small for gestational age without foetal restriction (SGA) and appropriate for gestational age (AGA) neonates.

DESIGN

Prospective controlled multicenter study.

PATIENTS

Sixteen ultrasound-proven IUGR, 8 SGA and 40 AGA neonates.

MEASUREMENTS

Concentrations of total IGF-I and total IGF-II by immunoassays, bioactive IGF by cell-based bioassay and IGFBP-I in mixed venous and arterial umbilical cord blood samples at birth. Auxological parameters at birth.

RESULTS

IGF-I concentrations in IUGR [17·7 μg/l (CI 13·8;21·6)] were clearly below those in AGA [48·3 μg/l (CI 43·7;52·9)] and SGA neonates [36·0 μg/l (CI 26·6;45·4)]. IGF-II levels were significantly reduced in IUGR [201·4 μg/l (CI 190·2;212·6)] compared to AGA neonates [231·2 μg/l (CI 220·6;241·9)]. A trend for lower IGF-II concentrations was observed in IUGR when compared to SGA neonates [232·0 μg/l (CI 207·2;256·8)]. These differences could not be explained by confounding. For IGFBP-1, a trend towards higher values in IUGR was observed.

CONCLUSIONS

Low IGF-I cord blood concentrations in hypotrophic neonates after IUGR might not only result from low birthweight per se, but also reflect prenatal placental environment. Alterations of the IGF axis could be in the causal pathway of IUGR and thus constitute a potential surrogate marker for IUGR in the assessment of foetal programming.

Cell-based assays for IGF-I bioactivity measurement: overview, limitations and current trends

Insulin-like growth factor-I (IGF-I) is an important growth promoting protein that is involved in numerous cellular responses and multiple biological systems. Although the molecular structure, function and recombinant production of IGF-I in various hosts have been the subject of much researches over the recent past, methods to determine the bioactivity of this protein have not been fully explored. Several assays have traditionally been used to measure IGF-I bioactivity, but have not become a routine laboratory practice due to the high cost involved and technical problems. Thus, there is still a need for a rapid, technically simple and accurate assay to determine IGF-I bioactivity. This review highlights the various cell-based assays currently commercially available for measuring the bioactivity of IGF-I along with their limitations. This is aimed at presenting the modern-day IGF researcher with a holistic overview of the current trends and future prospects regarding IGF-I bioactivity determinations.