Glucagon-like peptide-1(GLP-1) receptor agonists: potential to reduce fracture risk in diabetic patients?

Microbiota-bone axis in ageing-related bone diseases

Bone homeostasis in physiology depends on the balance between bone formation and resorption, and in pathology, this homeostasis is susceptible to disruption by different influences, especially under ageing condition. Gut microbiota has been recognized as a crucial factor in regulating host health. Numerous studies have demonstrated a significant association between gut microbiota and bone metabolism through host-microbiota crosstalk, and gut microbiota is even an important factor in the pathogenesis of bone metabolism-related diseases that cannot be ignored. This review explores the interplay between gut microbiota and bone metabolism, focusing on the roles of gut microbiota in bone ageing and aging-related bone diseases, including osteoporosis, fragility fracture repair, osteoarthritis, and spinal degeneration from different perspectives. The impact of gut microbiota on bone metabolism during aging through modification of endocrinology system, immune system and gut microbiota metabolites are summarized, facilitating a better grasp of the pathogenesis of aging-related bone metabolic diseases. This review offers innovative insights into targeting the gut microbiota for the treatment of bone ageing-related diseases as a clinical therapeutic strategy.

Effect of gut hormones on bone metabolism and their possible mechanisms in the treatment of osteoporosis

Bone is a highly dynamic organ that changes with the daily circadian rhythm. During the day, bone resorption is suppressed due to eating, while it increases at night. This circadian rhythm of the skeleton is regulated by gut hormones. Until now, gut hormones that have been found to affect skeletal homeostasis include glucagon-like peptide-1 (GLP-1), glucagon-like peptide-2 (GLP-2), glucose-dependent insulinotropic polypeptide (GIP), and peptide YY (PYY), which exerts its effects by binding to its cognate receptors (GLP-1R, GLP-2R, GIPR, and Y1R). Several studies have shown that GLP-1, GLP-2, and GIP all inhibit bone resorption, while GIP also promotes bone formation. Notably, PYY has a strong bone resorption-promoting effect. In addition, gut microbiota (GM) plays an important role in maintaining bone homeostasis. This review outlines the roles of GLP-1, GLP-2, GIP, and PYY in bone metabolism and discusses the roles of gut hormones and the GM in regulating bone homeostasis and their potential mechanisms.

The effects of exenatide and insulin glargine treatments on bone turnover markers and bone mineral density in postmenopausal patients with type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) related bone fracture. The effects of glucagon-like peptide-1 receptor analogs for the treatment of T2DM on bone are controversial in human studies. This study aimed to compare the effects of GLP-1 receptor analogs exenatide and insulin glargine treatment on bone turnover marker levels and bone mineral density (BMD) in postmenopausal female patients with T2DM. Thirty female patients with T2DM who were naive to insulin and incretin-based treatments, with spontaneous postmenopause, were randomized to exenatide or insulin glargine arms and were followed up for 24 weeks. BMD was evaluated using dual-energy X-ray absorptiometry and bone turnover markers by serum enzyme-linked immunosorbent assay. The body mass index significantly decreased in the exenatide group compared to the glargine group (P < .001). Receptor activator of nuclear factor kappa-B (RANK) and RANK ligand (RANKL) levels were significantly decreased with exenatide treatment (P = .009 and P = .015, respectively). Osteoprotegerin (OPG) level significantly increased with exenatide treatment (P = .02). OPG, RANK, RANKL levels did not change with insulin glargine treatment. No statistically significant difference was found between the pre- and posttreatment BMD, alkaline phosphatase, bone-specific alkaline phosphatase, and type 1 crosslinked N-telopeptide levels in both treatment arms. Despite significant weight loss with exenatide treatment, BMD did not decrease, OPG increased, and the resorption markers of RANK and RANKL decreased, which may reflect early antiresorptive effects of exenatide via the OPG/RANK/RANKL pathway.

The mechanism of palmatine-mediated intestinal flora and host metabolism intervention in OA-OP comorbidity rats

Background

ErXian decoction is a Chinese herbal compound that can prevent and control the course of osteoarthritis (OA) and osteoporosis (OP). OP and OA are two age-related diseases that often coexist in elderly individuals, and both are associated with dysregulation of the gut microbiome. In the initial study, Palmatine (PAL) was obtained by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and network pharmacological screening techniques, followed by 16S rRNA sequencing and serum metabolomics of intestinal contents, to explore the mechanism of PAL in the treatment of OA and OP.

Methods

The rats selected for this study were randomly divided into three groups: a sham group, an OA-OP group and a PAL group. The sham group was intragastrically administered normal saline solution, and the PLA group was treated with PAL for 56 days. Through microcomputed tomography (micro-CT), ELISA, 16S rRNA gene sequencing and non-targeted metabonomics research, we explored the potential mechanism of intestinal microbiota and serum metabolites in PAL treatment of OA-OP rats.

Results

Palmatine significantly repair bone microarchitecture of rat femur in OA-OP rats and improved cartilage damage. The analysis of intestinal microflora showed that PAL could also improve the intestinal microflora disorder of OA-OP rats. For example, the abundance of Firmicutes, Bacteroidota, Actinobacteria, Lactobacillus, unclassified_f_Lachnospiraceae, norank_f_Muribaculaceae, Lactobacillaceae, Lachnospiraceae and Muribaculaceae increased after PAL intervention. In addition, the results of metabolomics data analysis showed that PAL also change the metabolic status of OA-OP rats. After PAL intervention, metabolites such as 5-methoxytryptophol, 2-methoxy acetaminophen sulfate, beta-tyrosine, indole-3-carboxylic acid-O-sulfate and cyclodopa glucoside increased. Association analysis of metabolomics and gut microbiota (GM) showed that the communication of multiple flora and different metabolites played an important role in OP and OA.

Conclusion

Palmatine can improve cartilage degeneration and bone loss in OA-OP rats. The evidence we provided supports the idea that PAL improves OA-OP by altering GM and serum metabolites. In addition, the application of GM and serum metabolomics correlation analysis provides a new strategy for uncovering the mechanism of herbal treatment for bone diseases.

Treatment of Diabetes and Osteoporosis—A Reciprocal Risk?

Diabetes mellitus is a metabolic and systematic disorder that requires individualized therapy. The disease leads to various consequences, resulting in the destruction of tissues and organs. The aforementioned outcomes also include bone mineral disorders, caused by medications as well as diet therapy and physical activity. Some drugs may have a beneficial effect on both bone mineral density and the risk of fractures. Nevertheless, the impact of other medications remains unknown. Focusing on pharmacotherapy in diabetes may prevent bone mineral disorders and influence both the treatment and quality of life in patients suffering from diabetes mellitus. On the other hand, anti-osteoporosis drugs, such as antiresorptive or anabolic drugs, as well as drugs with a mixed mechanism of action, may affect carbohydrate metabolism, particularly in patients with diabetes. Therefore, the treatment of diabetes as well as osteoporosis prevention are vital for this group of patients.

Positive association of glucagon with bone turnover markers in type 2 diabetes: A cross-sectional study

AIMS

The osteo-metabolic changes in type 2 diabetes (T2D) patients are intricate and have not been fully revealed. It is not clear whether glucagon is entirely harmful in the pathogenesis of diabetes or a possible endocrine counter-regulation mechanism to reverse some abnormal bone metabolism. This study aimed to investigate the association between glucagon and bone turnover markers (BTMs) in T2D patients.

METHODS

A total of 3984 T2D participants were involved in a cross-sectional study in Shanghai, China. Serum glucagon was measured to elucidate its associations with intact N-terminal propeptide of type I collagen (P1NP), osteocalcin (OC), and β-C-terminal telopeptide (β-CTX). Glucagon was detected with a radioimmunoassay. Propeptide of type I collagen, OC, and β-CTX were detected using chemiluminescence. The diagnosis of T2D was based on American Diabetes Association criteria.

RESULTS

The concentration of glucagon was positively correlated with two BTMs [OC-β: 0.034, 95% CI: 0.004, 0.051, p = 0.024; CTX-β: 0.035, 95% CI: 0.004, 0.062, p = 0.024]. The result of P1NP was [P1NP-regression coefficient (β): 0.027, 95% CI: -0.003, 0.049, p = 0.083]. In the glucagon tertiles, P for trend of the BTMs is [P1NP: 0.031; OC: 0.038; CTX: 0.020], respectively.

CONCLUSIONS

Glucagon had a positive effect on bone metabolism. The concentrations of the three BTMs increased as glucagon concentrations rose. This implied that glucagon might speed up skeletal remodelling, accelerate osteogenesis, and promote the formation of mature bone tissue. At the same time, the osteoclastic process was also accelerated, providing raw materials for osteogenesis to preserve the dynamic balance. In view of the successful use of single-molecule as well as dual/triple agonists, it would be feasible to develop a preparation that would reduce osteoporosis in diabetic patients.

The Impact of GLP1 Agonists on Bone Metabolism: A Systematic Review

Background and Objectives: The association between diabetes mellitus and increased risk of bone fractures has led to the investigation of the impact of antidiabetic drugs on bone metabolism. Glucagon-like peptide-1 receptor agonists (GLP1RAs) are a relatively novel and promising class of anti-hyperglycemic drugs. In addition to their blood glucose lowering action, GLP1RAs seem to have additional pleiotropic properties such as a beneficial skeletal effect; although the underlying mechanisms are not completely understood. The present systematic review summarizes current evidence about GLP1RAs and their effects on bone metabolism and fracture. Methods: An extensive literature search was conducted based on electronic databases namely, PubMed, Google Scholar and Cochrane Central Register of Controlled Trials (CENTRAL) through October 2019 to January 2020 for articles related to bone mineral density, diabetes mellitus and GLP1RAs. We included articles published in English. Finally, we included four randomized controlled trials, three meta-analyses, a case-control study and a population-based cohort analysis. Results: Based on the articles included, the animal studies indicated the salutary skeletal effects of GLP1RAs in opposition to what has been commonly observed in human studies, showing that these agents have no impact on bone mineral density (BMD) and the turnover markers. Moreover, it was demonstrated that GLP1 was not associated with fracture risk as compared to other anti-hyperglycemic drugs. Conclusions: Findings from this systematic review have demonstrated the neutral impact of GLP1RAs on BMD. Moreover, further double-blind randomized controlled trials are needed to draw more meaningful and significant conclusions on the efficacy of GLP1RAs on BMD.

The Role of Depletion of Gut Microbiota in Osteoporosis and Osteoarthritis: A Narrative Review

Osteoporosis and osteoarthritis are common diseases in an aging society, are considered metabolic diseases, and affect the quality of life of older adults. In addition, the gut microbiome is considered an additional organ to regulate bone metabolism. In the past decade, people have been studying the relationship between gut microbiota and bone metabolism. The role and mechanism of the gut microbiota in regulating bone metabolism is very important to improve the development of osteoporosis and osteoarthritis. Depletion of the gut microbiota as a method of studying the role of the gut microbiota was provided strategies to enhance the role of the gut microbiota in regulating osteoporosis and osteoarthritis. In this review, we discuss how depletion of the gut microbiota affects osteoporosis and osteoarthritis.

Lessons from bariatric surgery: Can increased GLP-1 enhance vascular repair during cardiometabolic-based chronic disease?

Type 2 diabetes (T2D) and obesity represent entangled pandemics that accelerate the development of cardiovascular disease (CVD). Given the immense burden of CVD in society, non-invasive prevention and treatment strategies to promote cardiovascular health are desperately needed. During T2D and obesity, chronic dysglycemia and abnormal adiposity result in systemic oxidative stress and inflammation that deplete the vascular regenerative cell reservoir in the bone marrow that impairs blood vessel repair and exacerbates the penetrance of CVD co-morbidities. This novel translational paradigm, termed 'regenerative cell exhaustion' (RCE), can be detected as the depletion and dysfunction of hematopoietic and endothelial progenitor cell lineages in the peripheral blood of individuals with established T2D and/or obesity. The reversal of vascular RCE has been observed after administration of the sodium-glucose cotransporter-2 inhibitor (SGLT2i), empagliflozin, or after bariatric surgery for severe obesity. In this review, we explore emerging evidence that links improved dysglycemia to a reduction in systemic oxidative stress and recovery of circulating pro-vascular progenitor cell content required for blood vessel repair. Given that bariatric surgery consistently increases systemic glucagon-like-peptide 1 (GLP-1) release, we also focus on evidence that the use of GLP-1 receptor agonists (GLP-1RA) during obesity may act to inhibit the progression of systemic dysglycemia and adiposity, and indirectly reduce inflammation and oxidative stress, thereby limiting the impact of RCE. Therefore, therapeutic intervention with currently-available GLP-1RA may provide a less-invasive modality to reverse RCE, bolster vascular repair mechanisms, and improve cardiometabolic risk in individuals living with T2D and obesity.

The enteroendocrine-osseous axis in patients with long-term type 1 diabetes mellitus

INTRODUCTION

The relationship between the gut and skeleton is increasingly recognized as a component of the regulation of carbohydrate metabolism. The aim of our study was to assess the relationship between bone mineral density (BMD), incretin hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1), intestinotrophic peptide glucagon-like peptide-2 (GLP-2) and osteocalcin isoforms in patients with long-term type 1 diabetes (T1D) when compared to healthy controls.

METHODS

Eighty two patients with long term T1D, treated in the Department of Metabolic Diseases and 53 healthy controls were recruited to the study. Long term disease duration was defined as lasting for more than 10 years. The control group was selected among age- and sex-matched healthy people. Fasting blood samples were collected to measure levels of incretin hormones (GLP-1, GLP-2, GIP), two forms of osteocalcin (uncarboxylated (ucOC), and carboxylated (cOC)), and additional biochemical parameters associated with glucose and bone metabolism (HbA1c, calcium, phosphorus, 25(OH)D3, PTH).

RESULTS

Patients with T1D had higher BMI than in controls (p = 0.02). There was no difference in BMD at the lumbar spine and the femoral neck between patients with long-term T1D and healthy ones. Z-score values in both groups were within normal ranges. The level of GIP was significantly higher in T1D patients (p = 0.0002) in comparison to the healthy ones. The levels of GLP-1 and GLP-2 did not differ between T1D patients and controls. In the T1D group, strong, positive associations were found between serum levels of GLP-1 and cOC (r = 0.546, p < 0.001) and between GLP-1 and total OC (r = 0.51, p < 0.001), also after adjusting for BMI (p < 0.001 and p < 0.001, respectively). Significant positive associations were also found between serum levels of GLP-2 and cOC (r = 0.27, p = 0.013) and between GLP-2 and total OC (r = 0.25, p = 0.018), also in a multivariate regression (p = 0.009, p = 0,175, respectively). Moreover, in T1D patients, GLP-1 correlated positively with the femoral neck BMD (g/cm²) (r = 0.265, p = 0.016) and this association was statistically significant after adjusting for BMI (p = 0.011). These correlations were not present in the control group. The only significant correlation observed in the control group was between OC and BMD of the neck (p = 0.049 for neck BMD g/cm², and p = 0.041 for neck Z-score).

CONCLUSIONS

Our data suggests an effect of gut hormones on bone in long-term T1D, which could be associated with OC activity, however we did not find a direct connection with glucose metabolism. GLP-1 could have a possible, protective role on bone mineral density in patients with T1D. The data from our study suggests that gut hormones could be considered as a new link in the skeleton - pancreatic endocrine loop in patients with T1D.

Association of Sodium-Glucose Cotransporter-2 Inhibitors With Fracture Risk in Older Adults With Type 2 Diabetes

IMPORTANCE

Whether sodium-glucose cotransporter-2 inhibitors (SGLT-2i) are associated with an increased risk of fractures in older adults with type 2 diabetes (T2D) outside of clinical trials remains unknown.

OBJECTIVE

To examine the association of incident fracture among older adults with T2D with initiating an SGLT-2i compared with initiating a dipeptidyl peptidase 4 inhibitor (DPP-4i) or a glucagon-like peptide 1 receptor agonist (GLP-1RA).

DESIGN, SETTING, AND PARTICIPANTS

This is a population-based, new-user cohort study including older adults (aged ≥65 years) with T2D enrolled in Medicare fee-for-service from April 2013 to December 2017. Data analysis was performed from October 2020 to April 2021.

EXPOSURES

New users of an SGLT-2i, DPP-4i, or GLP-1RA without a previous fracture were matched in a 1:1:1 ratio using 3-way propensity score matching.

MAIN OUTCOMES AND MEASURES

The primary outcome was a composite end point of nontraumatic pelvic fracture, hip fracture requiring surgery, or humerus, radius, or ulna fracture requiring intervention within 30 days. After 3-way 1:1:1 propensity score matching, multivariable Cox proportional hazards regression models were used to generate hazard ratios (HRs) for SGLT-2i compared with DPP-4i and GLP-1RA and Kaplan-Meier curves to visualize fracture risk over time across groups.

RESULTS

Of 466 933 new initiators of study drugs, 62 454 patients were new SGLT-2i users. After 3-way matching, 45 889 (73%) new SGLT-2i users were matched to new users of DPP-4i and GLP-1RA, yielding a cohort of 137 667 patients (mean [SD] age, 72 [5] years; 64 126 men [47%]) matched 1:1:1 for analyses. There was no difference in the risk of fracture in SGLT-2i users compared with DPP-4i users (HR, 0.90; 95% CI, 0.73-1.11) or GLP-1RA users (HR, 1.00; 95% CI, 0.80-1.25). Results were consistent across categories of sex, frailty (nonfrail, prefrail, and frail), age (<75 and ≥75 years), and insulin use (baseline users and nonusers).

CONCLUSIONS AND RELEVANCE

In this nationwide Medicare cohort, initiating an SGLT-2i was not associated with an increased risk of fracture in older adults with T2D compared with initiating a DPP-4i or GLP-1RA, with consistent results across categories of frailty, age, and insulin use. These findings add to the evidence base evaluating the potential risks associated with SGLT-2i use for older adults outside of randomized clinical trials.

Effects of GLP-1 Receptor Agonists on Bone Mineral Density in Patients with Type 2 Diabetes Mellitus: A 52-Week Clinical Study

Introduction

Hypoglycemic drugs affect the bone quality and the risk of fractures in patients with type 2 diabetes mellitus (T2DM). We aimed to investigate the effects of glucagon-like peptide-1 receptor agonists (GLP-1RAs) and insulin on bone mineral density (BMD) in T2DM.

Methods

In this single-blinded study, a total of 65 patients with T2DM were randomly assigned into four groups for 52 weeks: the exenatide group (n = 19), dulaglutide group (n = 19), insulin glargine group (n = 10), and placebo (n = 17). General clinical data were collected, and BMD was measured by dual-energy X-ray absorptiometry.

Results

Compared with baseline, the glycosylated hemoglobin (HbA1c) decreased significantly in the exenatide (8.11 ± 0.24% vs. 7.40 ± 0.16%, P = 0.007), dulaglutide (8.77 ± 0.37% vs. 7.06 ± 0.28%, P < 0.001), and insulin glargine (8.57 ± 0.24% vs. 7.23 ± 0.25%, P < 0.001) groups after treatment. In the exenatide group, the BMD of the total hip increased. In the dulaglutide group, only the BMD of the femoral neck decreased (P = 0.027), but the magnitude of decrease was less than that in the placebo group; the BMD of L1-L4, femoral neck, and total hip decreased significantly (P < 0.05) in the placebo group, while in the insulin glargine group, the BMD of L2, L4, and L1-4 increased (P < 0.05). Compared with the placebo group, the BMD of the femoral neck and total hip in the exenatide group and the insulin glargine group were increased significantly (P < 0.05); compared with the exenatide group, the BMD of L4 in the insulin glargine group was also increased (P = 0.001).

Conclusions

Compared with the placebo, GLP-1RAs demonstrated an increase of BMD at multiple sites of the body after treatment, which may not exacerbate the consequences of bone fragility. Therefore, GLP-1RAs might be considered for patients with T2DM. This trial is registered with ClinicalTrials.gov NCT01648582.

GLP-1 promotes osteogenic differentiation of human ADSCs via the Wnt/GSK-3β/β-catenin pathway

Glucagon-like peptide-1 (GLP-1) analogues are promising anti-diabetic drugs which had been shown to have beneficial effects on bone metabolism in clinical practice, but the molecular mechanism remains unclear. In this study, we evaluated whether GLP-1 can affect the "intestine-fat-bone axis" via the Wnt/GSK-3β/β-catenin pathway. We established a diabetic mouse model and then treated mice with GLP-1 analogue liraglutide. The results showed that after liraglutide treatment, glucose tolerance and insulin tolerance were significantly improved in diabetic mice as expected. Moreover, osteogenic markers such as collagenⅠ, Runx2 and OCN were upregulated; and the adipogenic differentiation markers C/EBP-α and PPAR-γ were downregulated, these results indicated that liraglutide could ameliorate the osteogenic metabolism in diabetic mice. In the cell model, human ADSCs (hADSCs) were cultured and induced to undergo osteogenic and adipogenic differentiation under high glucose conditions in vitro and then treated with GLP-1. The results showed that GLP-1 repressed the induction of adipocyte differentiation biomarkers and the secretion of GSK-3β in a dose-dependent manner. In addition, GLP-1 enhanced the expression of osteoblastogenic biomarkers, such as OCN, Runx2 and collagenⅠ, and promoted osteoblastic mineralization. These effects were substantially suppressed by the Wnt signal recombinant human DKK-1 or activated by Wnt pathway agonist LiCl. Silencing of GSK-3β showed that the levels of β-catenin, GSK-3β and Runx2 were significantly increased by 2.46-, 2.05-, 4.44-fold after GLP-1 treatment compared to that observed in the GSK-3β lentiviral group, respectively. We conclude that GLP-1 promotes the osteogenic differentiation of hADSCs via the Wnt/GSK-3β/β-catenin pathway.

Effect of the Abnormal Expression of BMP-4 in the Blood of Diabetic Patients on the Osteogenic Differentiation Potential of Alveolar BMSCs and the Rescue Effect of Metformin: A Bioinformatics-Based Study

The success rate of oral implants is lower in type 2 diabetes mellitus (T2DM) patients than in nondiabetic subjects; functional impairment of bone marrow-derived mesenchymal stem cells (BMSCs) is an important underlying cause. Many factors in the blood can act on BMSCs to regulate their biological functions and influence implant osseointegration, but which factors play important negative roles in T2DM patients is still unclear. This study is aimed at screening differentially expressed genes in the blood from T2DM and nondiabetic patients, identifying which genes impact the osteogenic differentiation potential of alveolar BMSCs in T2DM patients, exploring drug intervention regimens, and providing a basis for improving implant osseointegration. Thus, a whole-blood gene expression microarray dataset (GSE26168) of T2DM patients and nondiabetic controls was analyzed. Based on Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) results, differentially expressed genes and signaling pathways related to BMSC osteogenic differentiation were screened, and major risk genes were extracted based on the mean decrease Gini coefficient calculated using the random forest method. Bone morphogenetic protein-4 (BMP-4), with significantly low expression in T2DM blood, was identified as the most significant factor affecting BMSC osteogenic differentiation potential. Subsequently, metformin, a first-line clinical drug for T2DM treatment, was found to improve the osteogenic differentiation potential of BMSCs from T2DM patients via the BMP-4/Smad/Runx2 signaling pathway. These results demonstrate that low BMP-4 expression in the blood of T2DM patients significantly hinders the osteogenic function of BMSCs and that metformin is effective in counteracting the negative impact of BMP-4 deficiency.

Differential indication for SGLT-2 inhibitors versus GLP-1 receptor agonists in patients with established atherosclerotic heart disease or at risk for congestive heart failure

SGLT-2 inhibitors and most GLP-1 receptor agonists demonstrated cardiovascular superiority and reduction of cardiovascular and overall mortality. These results stand as a turning point in the management of diabetes, shifting the focus from controlling glucose levels to mastering the extra-glycemic effects of these new drugs. This narrative review will discuss recent CVOT with focus on SGLT-2 inhibitors and GLP-1 receptor agonists to distinguish relevant patients' characteristics as potential predictors for therapeutic efficacy. It will also examine their efficacy and safety, the differences in their cardiovascular and renal benefits, aiming to convey clinical suggestions for everyday practice.

Incretin accelerates platelet-derived growth factor-BB-induced osteoblast migration via protein kinase A: The upregulation of p38 MAP kinase

Incretins, including glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), secreted from enteroendocrine cells after food ingestion, are currently recognized to regulate glucose metabolism through insulin secretion. We previously demonstrated that platelet-derived growth factor-BB (PDGF-BB) induces the migration of osteoblast-like MC3T3-E1 cells through mitogen-activated protein (MAP) kinases, including p38 MAP kinase. In the present study, we investigated whether or not incretins affect the osteoblast migration. The PDGF-BB-induced cell migration was significantly reinforced by GLP-1, GIP or cAMP analogues in MC3T3-E1 cells and normal human osteoblasts. The upregulated migration by GLP-1 or cAMP analogues was suppressed by H89, an inhibitor of protein kinase A. The amplification by GLP-1 of migration induced by PDGF-BB was almost completely reduced by SB203580, a p38 MAP kinase inhibitor in MC3T3-E1 cells and normal human osteoblasts. In addition, GIP markedly strengthened the PDGF-BB-induced phosphorylation of p38 MAP kinase. Exendin-4, a GLP-1 analogue, induced Rho A expression and its translocation from cytoplasm to plasma membranes in osteoblasts at the epiphyseal lines of developing mouse femurs in vivo. These results strongly suggest that incretins accelerates the PDGF-BB-induced migration of osteoblasts via protein kinase A, and the up-regulation of p38 MAP kinase is involved in this acceleration. Our findings may highlight the novel potential of incretins to bone physiology and therapeutic strategy against bone repair.

Glucagon-like peptide 1 and Glucagon-like peptide 2 in relation to osteoporosis in non-diabetic postmenopausal women

Osteoporosis results from an imbalance in bone remodeling, which is known to follow a circadian rhythm determined by a functional relationship between intestine and bone tissue. Specific intestinal peptides have been identified as mediators. Glucagon-like peptide 1 and glucagon-like peptide 2, have been associated with bone health. Our main objective was to determine whether postprandial plasma levels of glucagon-like peptide 1, glucagon-like peptide 2 and dipeptidyl-peptidase 4 activity, are associated with osteoporosis in non-diabetic postmenopausal women. We studied non-diabetic postmenopausal women with osteoporosis diagnosed by dual-energy X-ray absorptiometry (cases, n = 43) and age-matched (±1 yr) controls without osteoporosis or a history of osteoporotic fracture (n = 43). We measured postprandial plasma levels of glucagon-like peptide 1, glucagon-like peptide 2, and dipeptidyl-peptidase 4 activity, bone mineral density, and baseline levels of bone remodeling markers and analyzed the food intake using a food-frequency questionnaire. Postprandial glucagon-like peptide 1 values were lower (p < 0.001) in cases, μ (SEM) = 116.25 (2.68), than in controls, μ (SEM) = 126.79 (2.68). Glucagon-like peptide 1 was associated with reduced osteoporosis risk in the crude logistic regression analysis [OR (95% CI) = 0.724 (0.53-0.97), p = 0.031] and adjusted analysis [OR = 0.603 (0.38-0.94), p = 0.027]. We found no association of glucagon-like peptide 2, or dipeptidyl-peptidase 4 activity with osteoporosis. Postprandial glucagon-like peptide 1 levels are related to osteoporosis and osteoporosis risk in non-diabetic postmenopausal women. Further studies are required to verify these findings.

Gut microbiota: an overlooked factor that plays a significant role in osteoporosis

Gut microbes are known as the body’s second gene pool. Symbiotic intestinal bacteria play a major role in maintaining balance in humans. Bad eating habits, antibiotic abuse, diseases, and a poor living environment have a negative effect on intestinal flora. Abnormal intestinal microbes are prone to cause a variety of diseases, affecting life expectancy and long-term quality of life, especially in older people. Several recent studies have found a close association between intestinal microorganisms and osteoporosis. The potential mechanism of intestinal flora affecting bone formation or destruction by mediating nitric oxide, the immune and endocrine systems, and other factors is briefly described in this review. All of these factors may be responsible for the intestinal flora that causes osteoporosis. Studying the relationship between intestinal flora and bone health not only provides new ideas for studying the role of intestinal microorganism in osteoporosis, but also provides a new therapeutic direction for clinically refractory osteoporosis. Study of the relationship between intestinal microbiota and osteoporosis is important for maintaining bone health and minimizing osteoporosis.

Gut Microbiome, Probiotics and Bone: An Updated Mini Review

The gut microbiome is now considered as a large organ that has a direct effect on gastrointestinal tract, immune and endocrine system. There is no evidence that gut microbiota regulates the immune system and is responsible for bone formation and destruction. Probiotics have been shown through the gastrointestinal tract to have a positive effect on the management of the healthy bone. This article discusses the latest data available from PubMed and Scopus databases regarding gut microbiome, probiotics and bone briefly.

Fracture Risk After Initiation of Use of Canagliflozin: A Cohort Study

BACKGROUND

Sodium-glucose cotransporter-2 inhibitors promote glycosuria, resulting in possible effects on calcium, phosphate, and vitamin D homeostasis. Canagliflozin is associated with decreased bone mineral density and a potential increased risk for fracture.

OBJECTIVE

To estimate risk for nonvertebral fracture among new users of canagliflozin compared with a glucagon-like peptide-1 (GLP-1) agonist.

DESIGN

Population-based new-user cohort study.

SETTING

Two U.S. commercial health care databases providing data on more than 70 million patients from March 2013 to October 2015.

PATIENTS

Persons with type 2 diabetes who initiated use of canagliflozin were propensity score-matched in a 1:1 ratio to those initiating use of a GLP-1 agonist.

MEASUREMENTS

The primary outcome was a composite end point of humerus, forearm, pelvis, or hip fracture requiring intervention. Secondary outcomes included fractures at other sites. A fixed-effects meta-analysis that pooled results from the 2 databases provided an overall hazard ratio (HR).

RESULTS

79 964 patients initiating use of canagliflozin were identified and matched to 79 964 patients initiating use of a GLP-1 agonist. Mean age was 55 years, 48% were female, average baseline hemoglobin A1c level was 8.7%, and 27% were prescribed insulin. The rate of the primary outcome was similar for canagliflozin (2.2 events per 1000 person-years) and GLP-1 agonists (2.3 events per 1000 person-years), with an overall HR of 0.98 (95% CI, 0.75 to 1.26). Risk for pelvic, hip, humerus, radius, ulna, carpal, metacarpal, metatarsal, or ankle fracture was also similar for canagliflozin (14.5 events per 1000 person-years) and GLP-1 agonists (16.1 events per 1000 person-years) (overall HR, 0.92 [CI, 0.83 to 1.02]).

LIMITATION

Unmeasured confounding, measurement error, and low fracture rate.

CONCLUSION

In this study of middle-aged patients with type 2 diabetes and relatively low fracture risk, canagliflozin was not associated with increased risk for fracture compared with GLP-1 agonists.

PRIMARY FUNDING SOURCE

Brigham and Women's Hospital, Division of Pharmacoepidemiology and Pharmacoeconomics.

Complex interplay among adiposity, insulin resistance and bone health

Obesity and osteoporosis are common public health problems. Paradoxically, while obesity is associated with higher bone density, type 2 diabetic obese individuals have an increased fracture risk. Although obesity and insulin resistance co-exist, some obese individuals remain insulin-sensitive. We suggest that the apparent paradox relating obesity, bone density and fracture risk in type 2 diabetes may be at least partly influenced by differences in bone strength and quality between insulin-resistant and insulin-sensitive obese individuals. In this review, we focus on the complex interplay between, adiposity, insulin resistance and osteoporotic fracture risk and suggest that this is an important area of study that has implications for individually tailored and targeted treatment to prevent osteoporotic fracture in obese type 2 diabetic individuals.

Insulin resistance and bone: a biological partnership

Despite a clear association between type 2 diabetes (T2D) and fracture risk, the pathogenesis of bone fragility in T2D has not been clearly elucidated. Insulin resistance is the primary defect in T2D. Insulin signalling regulates both bone formation and bone resorption, but whether insulin resistance can affect bone has not been established. On the other hand, evidence exists that bone might play a role in the regulation of glucose metabolism. This article reviews the available experimental and clinical evidence on the interplay between bone and insulin resistance. Interestingly, a bilateral relationship between bone and insulin resistance seems to exist that unites them in a biological partnership.

Liraglutide Inhibits the Apoptosis of MC3T3-E1 Cells Induced by Serum Deprivation through cAMP/PKA/β-Catenin and PI3K/AKT/GSK3β Signaling Pathways

In recent years, the interest towards the relationship between incretins and bone has been increasing. Previous studies have suggested that glucagon-like peptide-1 (GLP-1) and its receptor agonists exert beneficial anabolic influence on skeletal metabolism, such as promoting proliferation and differentiation of osteoblasts via entero-osseous-axis. However, little is known regarding the effects of GLP-1 on osteoblast apoptosis and the underlying mechanisms involved. Thus, in the present study, we investigated the effects of liraglutide, a glucagon-like peptide-1 receptor agonist, on apoptosis of murine MC3T3-E1 osteoblastic cells. We confirmed the presence of GLP-1 receptor (GLP-1R) in MC3T3-E1 cells. Our data demonstrated that liraglutide inhibited the apoptosis of osteoblastic MC3T3-E1 cells induced by serum deprivation, as detected by Annexin V/PI and Hoechst 33258 staining and ELISA assays. Moreover, liraglutide upregulated Bcl-2 expression and downregulated Bax expression and caspase-3 activity at intermediate concentration (100 nM) for maximum effect. Further study suggested that liraglutide stimulated the phosphorylation of AKT and enhanced cAMP level, along with decreased phosphorylation of GSK3β, increased β-catenin phosphorylation at Ser675 site and upregulated nuclear β-catenin content and transcriptional activity. Pretreatment of cells with the PI3K inhibitor LY294002, PKA inhibitor H89, and siRNAs GLP-1R, β-catenin abrogated the liraglutide-induced activation of cAMP, AKT, β-catenin, respectively. In conclusion, these findings illustrate that activation of GLP-1 receptor by liraglutide inhibits the apoptosis of osteoblastic MC3T3-E1 cells induced by serum deprivation through cAMP/PKA/β-catenin and PI3K/Akt/GSK3β signaling pathways.

A comparative safety review between GLP-1 receptor agonists and SGLT2 inhibitors for diabetes treatment

INTRODUCTION

Glucagon-like peptide-1 receptor agonists (GLP-1RA) and sodium glucose cotransporter 2 inhibitors (SGLT2i) are of particular interest in type 2 diabetes treatment strategies, due to their efficacy in reducing HbA1c with a low risk of hypoglycaemia, to their positive effects on body weight and blood pressure and in light of their effects on cardiovascular risk and on nephroprotection emerged from the most recent cardiovascular outcome trials. Since it is therefore very likely that GLP-1RA and SGLT2i use will become more and more common, it is more and more important to gather and discuss information about their safety profile.

AREAS COVERED

Adverse events and the safety concerns most often emerged in trials with GLP-1RA namely, exenatide long acting release (LAR), dulaglutide, liraglutide, semaglutide, lixisenatide or SGLT2i, namely empagliflozin, dapagliflozin, canagliflozin and SGLT2i with an attempt at comparing the safety profiles of molecules of these two classes.

EXPERT OPINION

GLP-1RA and SGLT2i, although each associated with different specific side effects, share a 'similar' safety profile and are both drugs relatively easy to handle. The potentially complementary mechanisms of action, the cardio and nephroprotective effects demonstrated by molecules of both classes, make these drugs potentially useful even in add on to each other.

Association Between Gut Microbiota and Bone Health: Potential Mechanisms and Prospective

CONTEXT

It has been well established that the human gut microbiome plays a critical role in the regulation of important biological processes and the mechanisms underlying numerous complex diseases. Although researchers have only recently begun to study the relationship between the gut microbiota and bone metabolism, early efforts have provided increased evidence to suggest an important association.

EVIDENCE ACQUISITION

In this study, we attempt to comprehensively summarize the relationship between the gut microbiota and bone metabolism by detailing the regulatory effects of the microbiome on various biological processes, including nutrient absorption and the intestinal mucosal barrier, immune system functionality, the gut-brain axis, and excretion of functional byproducts. In this review, we incorporate evidence from various types of studies, including observational, in vitro and in vivo animal experiments, as well as small efficacy clinic trails.

EVIDENCE SYNTHESIS

We review the various potential mechanisms of influence for the gut microbiota on the regulation of bone metabolism and discuss the importance of further examining the potential effects of the gut microbiota on the risk of osteoporosis in humans. Furthermore, we outline some useful tools/approaches for metagenomics research and present some prominent examples of metagenomics association studies in humans.

CONCLUSION

Current research efforts, although limited, clearly indicate that the gut microbiota may be implicated in bone metabolism, and therefore, further exploration of this relationship is a promising area of focus in bone health and osteoporosis research. Although most existing studies investigate this relationship using animal models, human studies are both needed and on the horizon.

Review article: effects of type 2 diabetes therapies on bone metabolism

Diabetes complications and osteoporotic fractures are two of the most important causes of morbidity and mortality in older patients, and they share many features, including genetic susceptibility, molecular mechanisms, and environmental factors. Type 2 diabetes mellitus (T2DM) compromises bone microarchitecture by inducing abnormal bone cell function and matrix structure with increased osteoblast apoptosis, diminished osteoblast differentiation, and enhanced osteoclast-mediated bone resorption. The linkage between these two chronic diseases creates a possibility that certain antidiabetic therapies may affect bone function. The treatment of T2DM has been improved in the past two decades with the development of new therapeutic drugs. Each class has a pathophysiologic target related to the regulation of the energy metabolism and insulin secretion. However, both glycemic homeostasis and bone homeostasis are under the control of common regulatory factors. This background allows the individual pharmacological targets of antidiabetic therapies to affect bone quality due to their indirect effects on bone cell differentiation and the bone remodeling process. With a greater number of diabetic patients and antidiabetic agents being launched, it is critical to highlight the consequences of this disease and its pharmacological agents on bone health and fracture risk. Currently, there is little scientific knowledge approaching the impact of most anti-diabetic treatments on bone quality and fracture risk. Thus, this review aims to explore the pros and cons of the available pharmacologic treatments for T2DM on bone mineral density and risk fractures in humans.

Liraglutide, a glucagon-like peptide-1 receptor agonist, facilitates osteogenic proliferation and differentiation in MC3T3-E1 cells through phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT), extracellular signal-related kinase (ERK)1/2, and cAMP/protein kinase A (PKA) signaling pathways involving β-catenin

Previous studies have proven that glucagon-like peptide-1 (GLP-1) and its receptor agonist exert favorable anabolic effects on skeletal metabolism. However, whether GLP-1 could directly impact osteoblast-mediated bone formation is still controversial, and the underlying molecular mechanism remains to be elucidated. Thus in this paper, we investigated the effects of liraglutide, a glucagon-like peptide-1 (GLP-1) receptor agonist, on murine MC3T3-E1 preosteoblasts proliferation and differentiation and explored the potential cellular basis. Our study confirmed the presence of GLP-1R in MC3T3-E1, and demonstrated that liraglutide promotes osteoblasts proliferation at an intermediate concentration (100nM) and time (48h), upregulated the expression of osteoblastogenic biomarkers at various stages, and stimulated osteoblastic mineralization. Liraglutide also elevated the intracellular cAMP level and phosphorylation of AKT, ERK and β-catenin simultaneously with increased nuclear β-catenin content and transcriptional activity. Pretreatment of cells with the inhibitors LY294002, PD98059, H89 and GLP-1R and β-catenin siRNA partially blocked the liraglutide-induced signaling activation and attenuated the facilitating effect of liraglutide on MC3T3-E1 cells. Collectively, liraglutide was capable of acting upon osteoblasts directly through GLP-1R by activating PI3K/AKT, ERK1/2, cAMP/PKA/β-cat-Ser675 signaling to promote bone formation via GLP-1R. Thus, GLP-1 analogues may be potential therapeutic strategy for the treatment of osteoporosis in diabetics.

Glucagon-like peptide-1(GLP-1) receptor agonists: potential to reduce fracture risk in diabetic patients?

This review summarizes current knowledge about glucagon-like peptide 1 receptor agonists (GLP-1 RA) and their effects on bone metabolism and fracture risk. Recent in vivo and in vitro experiments indicated that GLP-1 RA could improve bone metabolism. GLP-1 could affect the fat-bone axis by promoting osteogenic differentiation and inhibiting adipogenic differentiation of bone mesenchymal precursor cells (BMSCs), which express the GLP-1 receptor. GLP-1 RA may also influence the balance between osteoclasts and osteoblasts, thus leading to more bone formation and less bone resorption. Wnt/β-catenin signalling is involved in this process. Mature osteocytes, which also express the GLP-1 receptor, produce sclerostin which inhibits Wnt/β-catenin signalling by binding to low density lipoprotein receptor-related protein (LRP) 5 and preventing the binding of Wnt. GLP-1 RA also decreases the expression of sclerostin (SOST) and circulating levels of SOST. In addition, GLP-1 receptors are expressed in thyroid C cells, where GLP-1 induces calcitonin release and thus indirectly inhibits bone resorption. Furthermore, GLP-1 RA influences the osteoprotegerin(OPG)/receptor activator of nuclear factor-κB ligand (RANKL)/receptor activator of nuclear factor-κB (RANK) system by increasing OPG gene expression, and thus reverses the decreased bone mass in rats models. However, a recent meta-analysis and a cohort study did not show a significant relationship between GLP-RA use and fracture risk. Future clinical trials will be necessary to investigate thoroughly the relationship between GLP-1 RA use and fracture risk in diabetic patients.