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.

A GLP-1 Receptor Agonist Inhibits Aldosterone Release in Healthy Volunteers

Glucagon-like peptide 1 receptor agonists (GLP-1 RAs) are antidiabetic drugs with effects beyond antihyperglycemic action. The aim of the study was to examine whether a single dose of exenatide could be used as a stimulation test for the pituitary-adrenal axis. We carried out a single-group, open-label pilot clinical trial in an ambulatory setting. Ten healthy volunteers of both sexes with body weight>65 kg and age between 18-50 years were recruited. After fasting for 12 hours the subjects received 10 μg of exenatide solution subcutaneously. Blood samples were taken before the administration of exenatide and up to 150 minutes thereafter. The primary outcome was the maximal level of cortisol after the administration of exenatide. Single administration of exenatide 10 μg resulted in a modest increase in ACTH and cortisol levels, as compared to untreated values, and a decrease in blood glucose levels. Remarkably, a robust suppression of both renin and aldosterone levels occurred. We showed that acute administration of exenatide in a full therapeutic dose modestly stimulates the hypothalamic-pituitary-adrenal axis but inhibits the renin-aldosterone system. Further research is warranted to confirm this finding in the placebo-controlled study.

Tolerance Does Not Develop Toward Liraglutide's Glucose-Lowering Effect

CONTEXT

Glucagon-like peptide-1 receptor agonists are popular antidiabetic drugs with potent glucose-lowering effects and low risk of hypoglycemia. Animal experiments and human data indicate that tolerance develops toward at least some of their effects (e.g., gastric motility). Whether tolerance develops toward the glucose-lowering effect of glucagon-like peptide-1 receptor agonists has never been formally tested.

OBJECTIVE

The objective of this pilot study was to test the hypothesis whether tolerance develops toward glucagon-like peptide-1 receptor agonists' glucose-lowering effect in chronic use.

DESIGN, SETTING, PARTICIPANTS, AND INTERVENTION

We conducted a single group, open-label clinical trial. Ten healthy volunteers were treated with 0.6 mg liraglutide once daily subcutaneously for 21 days. The drug's effect was quantified by serial graded glucose infusion tests, with glucose and c-peptide measured every 20 minutes and insulin secretion rate calculated.

MAIN OUTCOME MEASURE

The primary outcome was a change in the dose-response relationship between calculated insulin secretion rate and blood glucose level after acute and chronic administration of liraglutide.

RESULTS

Liraglutide clearly decreased the glucose values during the graded glucose infusion test and robustly enhanced insulin secretion. For all parameters, chronic liraglutide was as effective as acute treatment in human subjects.

CONCLUSIONS

We conclude that our results largely refute the hypothesis of tolerance development with prolonged liraglutide use in healthy nonobese humans.

Liraglutide Treatment May Affect Renin and Aldosterone Release

Nowadays, GLP-1 receptor agonists are widely used as effective and safe antidiabetic medications. In addition to glucose-dependent insulin secretion, their effects reach beyond glucose control. Previously, it has been shown that acute administration of GLP-1 receptor agonists increases circulating glucocorticoid and mineralocorticoid levels in both humans and rodents. So far, no studies have reported the effects of chronic administration of GLP-1 receptor agonists on the hypothalamic-pituitary-adrenal axis in humans. The aim of the current study was to examine the effects of acute and chronic treatment with the GLP-1 receptor agonist liraglutide on adrenal function in humans. Ten healthy volunteers were recruited into a single group open-label clinical trial. Each participant was tested for baseline levels, and after acute and chronic treatment with 0.6 mg liraglutide daily. A graded glucose infusion test was performed 3 times. We found that aldosterone tended to be suppressed (albeit not statistically different) after acute administration of liraglutide, and increased after chronic dosing; the difference was statistically significant when compared between acute and chronic dosing. Changes in aldosterone levels followed the changes in renin concentrations and the aldosterone-to-renin ratio remained stable. No statistically significant differences were observed in ACTH or cortisol levels. In conclusion, we have shown that a low dose of GLP-1 receptor agonist may interfere with renin and aldosterone release. Further studies in a larger patient sample and with higher doses of GLP-1 receptor agonists are warranted to corroborate this finding. The study protocol was registered at clinical.trials.gov (NCT02089256) and EU Clinical Trial Register (2014-000238-43).

Exenatide Is an Effective Antihyperglycaemic Agent in a Mouse Model of Wolfram Syndrome 1

Wolfram syndrome 1 is a very rare monogenic disease resulting in a complex of disorders including diabetes mellitus. Up to now, insulin has been used to treat these patients. Some of the monogenic forms of diabetes respond preferentially to sulphonylurea preparations. The aim of the current study was to elucidate whether exenatide, a GLP-1 receptor agonist, and glipizide, a sulphonylurea, are effective in a mouse model of Wolfram syndrome 1. Wolframin-deficient mice were used to test the effect of insulin secretagogues. Wolframin-deficient mice had nearly normal fasting glucose levels but developed hyperglycaemia after glucose challenge. Exenatide in a dose of 10 μg/kg lowered the blood glucose level in both wild-type and wolframin-deficient mice when administered during a nonfasted state and during the intraperitoneal glucose tolerance test. Glipizide (0.6 or 2 mg/kg) was not able to reduce the glucose level in wolframin-deficient animals. In contrast to other groups, wolframin-deficient mice had a lower insulin-to-glucose ratio during the intraperitoneal glucose tolerance test, indicating impaired insulin secretion. Exenatide increased the insulin-to-glucose ratio irrespective of genotype, demonstrating the ability to correct the impaired insulin secretion caused by wolframin deficiency. We conclude that GLP-1 agonists may have potential in the treatment of Wolfram syndrome-related diabetes.

A DNA helicase required for maintenance of the functional mitochondrial genome in Saccharomyces cerevisiae

A novel DNA helicase, a homolog of several prokaryotic helicases, including Escherichia coli Rep and UvrD proteins, is encoded by the Saccharomyces cerevisiae nuclear genome open reading frame YOL095c on the chromosome XV. Our data demonstrate that the helicase is localized in the yeast mitochondria and is loosely associated with the mitochondrial inner membrane during biochemical fractionation. The sequence of the C-terminal end of the 80-kDa helicase protein is similar to a typical N-terminal mitochondrial targeting signal; deletions and point mutations in this region abolish transport of the protein into mitochondria. The C-terminal signal sequence of the helicase targets a heterologous carrier protein into mitochondria in vivo. The purified recombinant protein can unwind duplex DNA molecules in an ATP-dependent manner. The helicase is required for the maintenance of the functional ([rho(+)]) mitochondrial genome on both fermentable and nonfermentable carbon sources. However, the helicase is not essential for the maintenance of several defective ([rho(-)]) mitochondrial genomes. We also demonstrate that the helicase is not required for transcription in mitochondria.

Effect of bovine papillomavirus E2 protein-specific monoclonal antibodies on papillomavirus DNA replication

The bovine papillomavirus type 1 (BPV-1) E2 protein is the master regulator of papillomavirus replication and transcription. We have raised a panel of monoclonal antibodies (MAbs) against the BPV-1 E2 protein and used them to probe the structure and function of the protein. Five MAbs reacted with linear epitopes, and four MAbs recognized conformation-dependent epitopes which mapped within the C-terminal DNA-binding and dimerization domain. MAb 1E2 was able to recognize the replication- and transactivation-defective but not the competent conformation of the transactivation domain of the E2 protein. MAb 5H4 prevented efficiently the formation of E2-DNA as well as E2-dependent E1-E2-origin complexes and also dissociated preformed complexes in a concentration-dependent manner. Cotransfection of several MAbs with the BPV-1 minimal origin plasmid pUCAlu into CHO4.15 cells resulted in a dose-dependent inhibition of replication. Inhibition of replication by MAb 5H4 and the Fab' fragment of 5H4 correlated with their ability to dissociate the E2 protein from the DNA. MAb 3F12 and MAbs 1H10 and 1E4, directed against the hinge region, were also capable of inhibiting BPV-1 origin replication in CHO4.15 cells. However, the Fab' fragments of 1H10 and 3F12 had no effect in the transient replication assay. These data suggest that MAbs directed against the hinge region sterically hinder the inter- or intramolecular interactions required for the replication activity of the E2 protein.

Binding of the E1 and E2 proteins to the origin of replication of bovine papillomavirus

DNA replication of bovine papillomavirus (BPV) requires two viral proteins encoded from the E1 and E2 open reading frames. E1 and E2 are sequence-specific DNA binding proteins that bind to their cognate binding sites in the BPV origin of replication (ori). The E1 and E2 proteins can interact physically with each other, and this interaction results in cooperative binding when binding sites for both proteins are present. We have analyzed the binding of E1 to the ori in the absence and presence of E2, using DNase I footprint analysis, gel mobility shift assays, and interference analysis. We have also generated a large number of point mutations in the E1 binding site and tested them for binding of E1 as well as for activity in DNA replication. Our results demonstrate that E1 binds to the ori in different forms in the absence and presence of E2 and that E2 has both a quantitative and a qualitative effect on the binding of E1. Our results also suggest that the ori contains multiple overlapping individual E1 recognition sequences which together constitute the E1 binding site and that different subsets of these recognition sequences are used for binding of E1 in the presence and absence of E2.