👤 Maria Saur Svane

Enhanced secretion of glucagon-like peptide 1 (GLP-1) seems to be essential for improved postprandial β-cell function after Roux-en-Y gastric bypass (RYGB) but is less studied after sleeve gastrectomy (SG). Moreover, the role of the other major incretin hormone, glucose-dependent insulinotropic polypeptide (GIP), is relatively unexplored after bariatric surgery. We studied the effects of separate and combined GLP-1 receptor (GLP-1R) and GIP receptor (GIPR) blockade during mixed-meal tests in unoperated (CON), SG-operated, and RYGB-operated people with no history of diabetes. Postprandial GLP-1 concentrations were highest after RYGB but also higher after SG compared with CON. In contrast, postprandial GIP concentrations were lowest after RYGB. The effect of GLP-1R versus GIPR blockade differed between groups. GLP-1R blockade reduced β-cell glucose sensitivity and increased or tended to increase postprandial glucose responses in the surgical groups but had no effect in CON. GIPR blockade reduced β-cell glucose sensitivity and increased or tended to increase postprandial glucose responses in the CON and SG groups but had no effect in the RYGB group. Our results support that GIP is the most important incretin hormone in unoperated people, whereas GLP-1 and GIP are equally important after SG, and GLP-1 is the most important incretin hormone after RYGB. Show less

The intestinal hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-2 (GLP-2) are key regulators of postprandial bone turnover in humans. We hypothesized that GIP and GLP-2 co-administration would provide stronger effect on bone turnover than administration of the hormones separately, and tested this using subcutaneous injections of GIP and GLP-2 alone or in combination in humans. Guided by these findings, we designed series of GIPR-GLP-2R co-agonists as template for new osteoporosis treatment. The clinical experiment was a randomized cross-over design including 10 healthy men administered subcutaneous injections of GIP and GLP-2 alone or in combination. The GIPR-GLP-2R co-agonists were characterized in terms of binding and activation profiles on human and rodent GIP and GLP-2 receptors, and their pharmacokinetic (PK) profiles were improved by dipeptidyl peptidase-4 protection and site-directed lipidation. Co-administration of GIP and GLP-2 in humans resulted in an additive reduction in bone resorption superior to each hormone individually. The GIPR-GLP-2R co-agonists, designed by combining regions of importance for cognate receptor activation, obtained similar efficacies as the two native hormones and nanomolar potencies on both human receptors. The PK-improved co-agonists maintained receptor activity along with their prolonged half-lives. Finally, we found that the GIPR-GLP-2R co-agonists optimized toward the human receptors for bone remodeling are not feasible for use in rodent models. The successful development of potent and efficacious GIPR-GLP-2R co-agonists, combined with the improved effect on bone metabolism in humans by co-administration, support these co-agonists as a future osteoporosis treatment. Show less

Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-2 (GLP-2) are gut hormones secreted postprandially. In healthy humans, both hormones decrease bone resorption accompanied by a rapid reduction in parathyroid hormone (PTH). The aim of this study was to investigate whether the changes in bone turnover after meal intake and after GIP- and GLP-2 injections, respectively, are mediated via a reduction in PTH secretion. This was tested in female patients with hypoparathyroidism given a standardized liquid mixed-meal test (n = 7) followed by a peptide injection test (n = 4) using a randomized crossover design. We observed that the meal- and GIP- but not the GLP-2-induced changes in bone turnover markers were preserved in the patients with hypoparathyroidism. To understand the underlying mechanisms, we examined the expression of the GIP receptor (GIPR) and the GLP-2 receptor (GLP-2R) in human osteoblasts and osteoclasts as well as in parathyroid tissue. The GIPR was expressed in both human osteoclasts and osteoblasts, whereas the GLP-2R was absent or only weakly expressed in osteoclasts. Furthermore, both GIPR and GLP-2R were expressed in parathyroid tissue. Our findings suggest that the GIP-induced effect on bone turnover may be mediated directly via GIPR expressed in osteoblasts and osteoclasts and that this may occur independent of PTH. In contrast, the effect of GLP-2 on bone turnover seems to depend on changes in PTH and may be mediated through GLP-2R in the parathyroid gland. © 2021 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR). Show less

Glucagon-like peptide-2 (GLP-2) and glucose-dependent insulinotropic polypeptide (GIP) both inhibit bone resorption in humans but the underlying mechanisms are poorly understood. In vitro, GLP-2 activates the GIP-receptor (GIPR). Based on in vitro studies, we hypothesized that the antiresorptive effect of GLP-2 was mediated through the GIPR. This was tested using the selective GIPR-antagonist GIP(3-30)NH The study was a randomized, single-blinded, placebo-controlled, crossover study conducted at Hvidovre University Hospital, Denmark. Eight healthy young men were included and studied on four study days: GIP (200 μg), GLP-2 (800 μg), GIP(3-30)NH CTX (mean ± SEM) significantly decreased after both GIP (to 55.3 ± 6.3% of baseline at t = 90 min) and GLP-2 (to 60.5 ± 5.0% of baseline at t = 180 min). The maximal reduction in CTX after GIP(3-30)NH GIPR antagonism did not inhibit the GLP-2-induced reduction in bone resorption (CTX) in healthy young men. In contrast to GLP-2, GIP increased P1NP despite decreasing CTX indicating an uncoupling of bone resorption from formation. Thus, GLP-2 and GIP seem to exert separate effects on bone turnover in humans. ClinicalTrials.gov (NCT03159741). Show less

Bone homeostasis displays a circadian rhythm with increased resorption during the night time as compared to day time, a difference that seems-at least partly-to be caused by food intake during the day. Thus, ingestion of a meal results in a decrease in bone resorption, but people suffering from short bowel syndrome lack this response. Gut hormones, released in response to a meal, contribute to this link between the gut and bone metabolism. The responsible hormones appear to include glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1), known as incretin hormones due to their role in regulating glucose homeostasis by enhancing insulin release in response to food intake. They interact with their cognate receptors (GIPR and GLP-1R), which are both members of the class B G protein-coupled receptors (GPCRs), and already recognized as targets for treatment of metabolic diseases, such as type 2 diabetes mellitus (T2DM) and obesity. Glucagon-like peptide-2 (GLP-2), secreted concomitantly with GLP-1, acting via another class B receptor (GLP-2R), is also part of this gut-bone axis. Several studies, including human studies, have indicated that these three hormones inhibit bone resorption and, moreover, that GIP increases bone formation. Another hormone, peptide YY (PYY), is also secreted from the enteroendocrine L-cells (together with GLP-1 and GLP-2), and acts mainly via interaction with the class A GPCR NPY-R2. PYY is best known for its effect on appetite regulation, but recent studies have also shown an effect of PYY on bone metabolism. The aim of this review is to summarize the current knowledge of the actions of GIP, GLP-1, GLP-2, and PYY on bone metabolism, and to discuss future therapies targeting these receptors for the treatment of osteoporosis. Show less