exenatide and Osteoporosis

The present brief review looks at the evidence on the role of GLP-1 and its agonists in osteopenia and osteoporosis in type 2 diabetes (T2DM). There is accumulating data to suggest a favourable effect of GLP-1 on bone metabolism. However, most data is from experimental studies, while clinical confirmation is still inadequate. Moreover, little is known on the precise mechanisms underlying these effects. Therefore, we need randomised clinical trials in T2DM patients to learn more on the action of GLP-1 on bone metabolism and its potential clinical implications.

Topics: Bone and Bones; Bone Diseases, Metabolic; Calcitonin; Diabetes Mellitus, Type 2; Exenatide; Female; Glucagon-Like Peptide 1; Glucagon-Like Peptide-1 Receptor; Humans; Male; Osteoporosis; Peptides; Receptors, Glucagon; Treatment Outcome; Venoms

Glucagon-like peptide 1 (GLP-1) plays an important role in regulating bone remodeling, and GLP-1 receptor agonist shows a positive relationship with osteoblast activity. However, GLP-1 receptor is not found in osteoblast, and the mechanism of GLP-1 receptor agonist on regulating bone remodeling is unclear. Here, we show that the GLP-1 receptor agonist exendin-4 (Ex-4) promoted bone formation and increased bone mass and quality in a rat unloading-induced bone loss model. These functions were accompanied by an increase in osteoblast number and serum bone formation markers, while the adipocyte number was decreased. Furthermore, GLP-1 receptor was detected in bone marrow stromal cells (BMSCs), but not in osteoblast. Activation of GLP-1 receptor by Ex-4 promoted the osteogenic differentiation and inhibited BMSC adipogenic differentiation through regulating PKA/β-catenin and PKA/PI3K/AKT/GSK3β signaling. These findings reveal that GLP-1 receptor regulates BMSC osteogenic differentiation and provide a molecular basis for therapeutic potential of GLP-1 against osteoporosis.

Topics: Active Transport, Cell Nucleus; Animals; beta Catenin; Bone and Bones; Bone Density; Cell Differentiation; Cell Nucleus; Exenatide; Glucagon-Like Peptide-1 Receptor; Immunoblotting; Male; Mesenchymal Stem Cells; Microscopy, Confocal; Osteoblasts; Osteogenesis; Osteoporosis; Peptides; Rats, Sprague-Dawley; Reverse Transcriptase Polymerase Chain Reaction; RNA Interference; Signal Transduction; Venoms

Some anti-diabetic therapies can have adverse effects on bone health and increase fracture risk. In this study, we tested the skeletal effects of chronic administration of two Glucagon-like peptide-1 receptor agonists (GLP-1RA), increasingly used for type 2 diabetes treatment, in a model of osteoporosis associated bone loss and examined the expression and activation of GLP-1R in bone cells. Mice were ovariectomised (OVX) to induce bone loss and four weeks later they were treated with Liraglutide (LIR) 0.3mg/kg/day, Exenatide (Ex-4) 10 μg/kg/day or saline for four weeks. Mice were injected with calcein and alizarin red prior to euthanasia, to label bone-mineralising surfaces. Tibial micro-architecture was determined by micro-CT and bone formation and resorption parameters measured by histomorphometric analysis. Serum was collected to measure calcitonin and sclerostin levels, inhibitors of bone resorption and formation, respectively. GLP-1R mRNA and protein expression were evaluated in the bone, bone marrow and bone cells using RT-PCR and immunohistochemistry. Primary osteoclasts and osteoblasts were cultured to evaluate the effect of GLP-1RA on bone resorption and formation in vitro. GLP-1RA significantly increased trabecular bone mass, connectivity and structure parameters but had no effect on cortical bone. There was no effect of GLP-1RA on bone formation in vivo but an increase in osteoclast number and osteoclast surfaces was observed with Ex-4. GLP-1R was expressed in bone marrow cells, primary osteoclasts and osteoblasts and in late osteocytic cell line. Both Ex-4 and LIR stimulated osteoclastic differentiation in vitro but slightly reduced the area resorbed per osteoclast. They had no effect on bone nodule formation in vitro. Serum calcitonin levels were increased and sclerostin levels decreased by Ex-4 but not by LIR. Thus, GLP-1RA can have beneficial effects on bone and the expression of GLP-1R in bone cells may imply that these effects are exerted directly on the tissue.

Topics: Adaptor Proteins, Signal Transducing; Animals; Bone and Bones; Bone Resorption; Calcitonin; Diabetes Mellitus, Type 2; Disease Models, Animal; Exenatide; Female; Glucagon-Like Peptide-1 Receptor; Glycoproteins; Immunohistochemistry; Intercellular Signaling Peptides and Proteins; Liraglutide; Mice; Mice, Inbred C57BL; Osteoblasts; Osteoclasts; Osteocytes; Osteogenesis; Osteoporosis; Ovariectomy; Peptides; RNA, Messenger; Tibia; Venoms; X-Ray Microtomography

Osteoporosis mainly affects postmenopausal women and older men. Gastrointestinal hormones released after meal ingestion, such as glucose-dependent insulinotropic peptide (GIP) and glucagon-like peptide (GLP)-2, have been shown to regulate bone turnover. However, whether GLP-1, another important gastrointestinal hormone, and its analogues also have antiosteoporotic effects, especially in aged postmenopausal situation, has not been confirmed. In the present study, we evaluated the effects of the GLP-1 receptor agonist exendin-4 on ovariectomy (OVX)-induced osteoporosis in old rats. Twelve-month-old female Sprague-Dawley rats were subjected to OVX, and exendin-4 was administrated 4 weeks after the surgery and lasted for 16 weeks. Bone characters and related serum and gene biomarkers were analyzed. Sixteen weeks of treatment with exendin-4 slowed down body weight gain by decreasing fat mass and prevented the loss of bone mass in old OVX rats. Exendin-4 also enhanced bone strength and prevented the deterioration of trabecular microarchitecture. Moreover, exendin-4 decreased the urinary deoxypyridinoline (DPD)/creatinine ratio and serum C-terminal cross-linked telopeptides of type I collagen (CTX-I) and increased serum alkaline phosphatase (ALP), osteocalcin (OC), and N-terminal propeptide of type 1 procollagen (P1NP) levels, key biochemical markers of bone turnover. Interestingly, gene expression results further showed that exendin-4 not only inhibited bone resorption by increasing the osteoprotegerin (OPG)/receptor activator of NF-κB ligand (RANKL) ratio, but also promoted bone formation by increasing the expression of OC, Col1, Runx2, and ALP, which exhibited dual regulatory effects on bone turnover as compared with previous antiosteoporotic agents. In conclusion, these findings demonstrated for the first time the antiosteoporotic effects of exendin-4 in old OVX rats and that it might be a potential candidate for treatment of aged postmenopausal osteoporosis.

Topics: Alkaline Phosphatase; Amino Acids; Animals; Collagen Type I; Core Binding Factor Alpha 1 Subunit; Creatinine; Exenatide; Female; Glucagon-Like Peptide-1 Receptor; Humans; Hypoglycemic Agents; Male; Osteocalcin; Osteoporosis; Ovariectomy; Peptides; Rats; Rats, Sprague-Dawley; Receptors, Glucagon; Time Factors; Venoms

Poor control of glucose homeostasis accounts for diabetes-related bone loss. Incretins - GLP-1 and GIP - have been proposed to affect bone turnover. GLP-1, apart from its anti-diabetic and other actions, has shown to exert a bone anabolic effect in streptozotocin-induced type 2 diabetic (T2D) and fructose-induced insulin-resistant (IR) rats. Exendin-4 (Ex-4), a peptide of non-mammalian nature, is sharing with GLP-1 part of its structural sequence, and also several glucoregulatory effects in mammals in an even more efficient manner. We have explored the effect of continuous administration (3 days by osmotic pump) of Ex-4 or saline (control) on bone turnover factors and bone structure in T2D and IR rats, compared to N, and the possible interaction of Ex-4 with the Wnt signalling pathway. Blood was taken before and after treatment for plasma measurements; tibiae and femurs were collected for gene expression of bone markers (RT-PCR) and structure (microCT) analysis; we also measured the mRNA levels of LRP5 - an activator of the Wnt pathway - and those of DKK1 and sclerostin (SOST) - both blockers of LRP5 activity. Compared to N-control, plasma glucose and insulin were respectively higher and lower in T2D; osteocalcin (OC) and tartrate-resistant alkaline phosphatase 5b (TRAP5b) were lower; after Ex-4, these turnover markers were further reduced in T2D and IR, while TRAP5b increased in N. Bone OC, osteoprogeterin (OPG) and receptor activator of NF-kB ligand (RANKL) mRNA were lower in T2D and IR; Ex-4 increased OC in all groups and OPG in N and IR, reduced RANKL in N and T2D but increased it in IR; the LRP5/DKK1 and LRP5/SOST mRNA ratios were similarly decreased in T2D, but in IR, the latter ratio was reduced while the former was increased; after Ex-4, both ratios augmented in N, and that of LRP5/DKK1 tended to normalize in T2D and IR. In conclusion, Ex-4 exerts osteogenic effects in T2D and IR models, and interacts with the Wnt pathway to promote bone formation.

Topics: Animals; Blood Glucose; Bone Morphogenetic Proteins; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 2; Exenatide; Fructose; Gastric Inhibitory Polypeptide; Genetic Markers; Glucagon-Like Peptide 1; Hypoglycemic Agents; Insulin; Insulin Resistance; Intercellular Signaling Peptides and Proteins; LDL-Receptor Related Proteins; Low Density Lipoprotein Receptor-Related Protein-5; Male; Osteocalcin; Osteogenesis; Osteoporosis; Peptides; Rats; Rats, Wistar; Sweetening Agents; Venoms; Wnt Proteins