Exendin-4 increases bone mineral density in type 2 diabetic OLETF rats potentially through the down-regulation of SOST/sclerostin in osteocytes

Risk factors for bone fractures in type 2 diabetes and the impact of once-weekly exenatide: insights from an EXSCEL post-hoc analysis

AIMS

We investigated bone fracture predictors in people with T2D enrolled in the EXenatide Study of Cardiovascular Event Lowering (EXSCEL) and evaluated the effects of once-weekly exenatide (EQW) on incident bone fractures.

METHODS

EXSCEL randomised 14,752 people to EQW 2 mg or placebo with a median follow-up of 3.2 years. In this post-hoc analysis, baseline features associated with incident bone fractures were evaluated with multivariable Cox proportional hazard regression models, accounting for age and sex as confounders. Incidence rates were compared between study arms, and time-to-event analyses performed using Cox-proportional hazard models.

RESULTS

The primary outcome occurred in 168 (1.1 %) participants. The presence of neuropathy at baseline was associated with a 50 % higher risk (hazard ratio [HR] 1.50, 95 % confidence interval [CI] 1.10-2.05, P = 0.010) of incident bone fractures, while taking metformin at baseline was associated with a 47 % lower risk (HR 0.53, 95 %CI 0.39-0.73, P < 0.001). Incidence rates of bone fractures were similar in the EQW group and in the placebo group (HR 1.11, 95 %CI 0.82-1.51, P = 0.49).

CONCLUSIONS

Bone fractures in people with T2D occur more frequently in those with diabetic neuropathy, but less frequently in those taking metformin. No evidence was seen of any impact of EQW treatment on bone fractures.

The effect of antidiabetic drugs on bone metabolism: a concise review

Diabetes mellitus (DM) is a complex metabolic disorder characterized by chronic hyperglycemia, which derives from either insufficient insulin production [type 1 diabetes mellitus (T1DM)] or both impaired insulin sensitivity along with inadequate insulin production [type 2 diabetes mellitus (T2DM)] and affects millions of people worldwide. In addition to the adverse effects of DM on classical target organs and tissues, skeletal health can also be adversely affected. There is considerable evidence linking DM with osteoporosis. The fracture risk in patients with DM differs upon the type of diabetes, and it appears to be related to the type of anti-diabetic treatment. Antidiabetic drugs may have various effects on bone health. Most of them have neutral or even favorable effects on bone metabolism with the exception of thiazolidinediones (TZDs). Some studies suggest that TZDs may have negative impact on bone health by decreasing bone formation and increasing the fracture risk. There are also limited studies linking the use of canagliflozin, a Sodium-glucose contransporter-2 inhibitor (SGLT2i), with increased fracture risk. On the other hand, therapies that are based on incretin effect, like Dipeptidyl peptidase-4 inhibitors (DPP-4i) and Glucagon-like peptide-1 receptor agonizts (GLP-1RAs) might have positive effects on bone health by promoting bone formation. Herein we review the impact of antidiabetic drugs on bone health, highlighting the potential benefits and risks associated with these medications in an attempt to contribute to the development of personalized treatment strategies for individuals with DM.

Perioperative Glucagon-Like Peptide-1 Agonist Use and Rates of Pseudarthrosis After Single-Level Lumbar Fusion: A Large Retrospective Cohort Study

BACKGROUND AND OBJECTIVE

Pseudarthrosis is a common surgical complication after arthrodesis and is associated with poor clinical outcomes. The association between glucagon-like peptide-1 (GLP-1) agonist use and pseudarthrosis is yet to be explored. This study aims to examine the association of GLP-1 agonists with rates of pseudarthrosis in patients undergoing single-level lumbar fusion.

METHODS

This national multicenter cohort study used data spanning from June 19, 2010, to June 19, 2024, from the global health network TriNetX. One-to-one propensity score matching for age, sex, race, comorbidities, body mass index, and A1c was conducted to balance cohorts. The rates of pseudarthrosis were then assessed within the 6-month, 1-year, and 2-year postsurgical follow-up periods.

RESULTS

A total of 37 147 patients who underwent single-level lumbar fusion (mean [SD] age, 59.3 [13.5] years; 47.7% men and 52.3% women) were enrolled in the study. Among these, 712 individuals (1.9%) were identified as GLP-1 agonist users. After propensity score matching, there were 709 patients in each cohort. Patients who took a GLP-1 agonist had lower odds of developing pseudarthrosis 6 months [odds ratio (OR): 0.70, 95% CI: 0.51-0.96], 1 year [OR: 0.68, 95% CI: 0.50-0.91], and 2 years (OR: 0.68, 95% CI: 0.50-0.91) after a posterior lumbar interbody fusion/transforaminal lumbar interbody fusion procedure.

CONCLUSION

In this cohort study, patients who were prescribed GLP-1 agonists in the perioperative period had reduced rates of pseudarthrosis compared with patients without GLP-1 agonist prescriptions. These findings suggest a potential therapeutic benefit of GLP-1 agonists in enhancing spinal fusion outcomes and warrant further prospective studies to confirm these results and explore the underlying mechanisms.

Fracture events associated with GLP-1 receptor agonists in FDA adverse events reporting system

AIMS

Diabetes patients are at a higher risk of fractures, and glucagon-like peptide-1 receptor agonists (GLP-1RAs) have been suggested to positively impact on bone metabolism. We aim to provide a comprehensive assessment of fracture events associated with GLP-1RAs based on pharmacovigilance data.

METHODS

In this study, fracture-related adverse events (AEs) associated with GLP-1RAs and other commonly used glucose-lowering drugs were identified from Food and Drug Administration Adverse Event Reporting System (FAERS) database (2004-2022). The reporting odds ratio (ROR) and adjusted ROR (adj. ROR) were used to compare the reporting of fracture-related AEs associated with insulin, GLP-1RAs, and Non GLP-1RAs, in patients with diabetes through two scenarios. This involved separately comparing each glucose-lowering drug to all other medications used in diabetic patients and reiterating after excluding insulin cases.

RESULTS

A total of 490,107 AE reports for patients with diabetes were identified and 98, 625 of them were for GLP-1RAs. Among all diabetes drugs, GLP-1RAs had the lowest reporting of any fracture-related AEs [adj. ROR = 0.44 (0.40-0.47)], consistent across osteoporotic fracture [adj. ROR = 0.39 (0.34-0.45)] and hip fracture [adj. ROR = 0.34 (0.28-0.41)]. Among GLP-1RA agents, albiglutide was associated with the lowest adj. ROR [0.11 (0.05-0.21)] for any fracture-related AEs. After excluded all insulin reports, GLP-1RAs retained a significantly lower adj. ROR towards any fracture [adj. ROR = 0.45 (0.40-0.50)], osteoporotic fracture [adj. ROR = 0.44 (0.37-0.52)], and hip fracture [adj. ROR = 0.43 (0.33-0.54)].

CONCLUSION

In a real-world pharmacovigilance setting, GLP-1RAs were associated with lower reporting of fracture-related AEs, indicating the protective effect of GLP-1RAs against fractures.

Glucagon-like peptide-1 receptor agonists in neoplastic diseases

Glucagon-like peptide-1 receptor agonist (GLP-1RA), a novel hypoglycemic agent for the treatment of type 2 diabetes, has well-known effects such as lowering blood sugar, ameliorating inflammation, reducing weight, and lowering blood lipids. It has also been shown that it can influence the proliferation and survival of cells and has a certain effect on the prognosis of some neoplastic diseases. In this study, the potential effects of GLP-1RAs on the occurrence and development of tumors were reviewed to provide new ideas for the prevention and treatment of tumors in patients.

Effects of Glucagon-Like Peptide-1 Receptor Agonist on Bone Mineral Density and Bone Turnover Markers: A Meta-Analysis

AIMS

Glucagon-like peptide-1 receptor agonist (GLP-1RA) may promote bone formation, but conversely, they could also weaken bones due to the reduction in mechanical load associated with weight loss. However, the clinical effects in humans have not been clearly demonstrated. This meta-analysis aimed to evaluate whether GLP-1RAs affect BMD and bone turnover markers.

MATERIAL AND METHODS

PubMed, Embase, and Scopus were searched on June 13, 2024. The eligibility criteria were: (1) human studies, (2) receiving a GLP-1RA for more than 4 weeks, (3) an untreated control group or a placebo group, (4) reporting of at least one BMD or bone turnover marker, and (5) an RCT design. The risk of bias was assessed using the Cochrane risk of bias 2 tool. Fixed- or random-effects meta-analysis was performed according to heterogeneity.

RESULTS

Seven studies were included in the meta-analysis. GLP-1RAs did not significantly change BMD in the femoral neck (mean difference [MD], 0.01 g/cm2; 95% CI, -0.01-0.04 g/cm2), in the total hip (MD, -0.01 g/cm2; 95% CI, -0.02-0.01 g/cm2), and in the lumbar spine (MD, 0 g/cm2; 95% CI, -0.02-0.02 g/cm2). C-terminal telopeptide of type 1 collagen (CTX), a bone resorption marker, significantly increased after GLP-1RA treatment (MD, 0.04 μg/L; 95% CI, 0.01-0.07 μg/L). GLP-1RAs did not significantly change bone formation markers such as procollagen type 1 N-terminal propeptide, bone-specific alkaline phosphatase, osteocalcin.

CONCLUSIONS

GLP-1RA did not affect BMD and bone formation markers. However, GLP-1RAs led to a significant increase in CTX.

Bone Fragility in Diabetes and its Management: A Narrative Review

Bone fragility is a serious yet under-recognised complication of diabetes mellitus (DM) that is associated with significant morbidity and mortality. Multiple complex pathophysiological mechanisms mediating bone fragility amongst DM patients have been proposed and identified. Fracture risk in both type 1 diabetes (T1D) and type 2 diabetes (T2D) continues to be understated and underestimated by conventional risk assessment tools, posing an additional challenge to the identification of at-risk patients who may benefit from earlier intervention or preventive strategies. Over the years, an increasing body of evidence has demonstrated the efficacy of osteo-pharmacological agents in managing skeletal fragility in DM. This review seeks to elaborate on the risk of bone fragility in DM, the underlying pathogenesis and skeletal alterations, the approach to fracture risk assessment in DM, management strategies and therapeutic options.

Beyond Glycemic Control: GLP-1 Receptor Agonists and Their Impact on Calcium Homeostasis in Real-World Patients

Background/Objectives: The effect of glucagon-like peptide-1 receptor (GLP-1R) agonists on calcium homeostasis is poorly understood. This study aimed to investigate the association between GLP-1R agonist use and the risk of hypocalcemia and/or hypercalcemia, as well as other clinical outcomes. Methods: A retrospective cohort study used de-identified patient data from the TriNetX Global Collaborative Network, including 15,655 adult patients prescribed GLP-1R agonists and 15,655 propensity-matched controls. Outcomes included hypocalcemia, hypercalcemia, emergency visits, hospitalizations, cardiovascular events, and all-cause mortality. Results: GLP-1R agonist use was associated with a reduced risk of hypocalcemia (2.7% vs. 5.5%, RR 0.49, 95% CI: 0.44-0.55) but an increased risk of hypercalcemia (2.3% vs. 1.1%, RR 2.02, 95% CI: 1.69-2.42). The effect on hypocalcemia was most pronounced during the first six months of treatment. Among individual agents, tirzepatide showed the most pronounced effect, reducing hypocalcemia risk by 63% while increasing hypercalcemia risk by 85%. Semaglutide demonstrated similar effects, while dulaglutide and liraglutide showed modest effects. Furthermore, GLP-1R agonist use was associated with reduced risks of emergency visits (RR 0.57, 95% CI: 0.54-0.60), hospitalizations (RR 0.40, 95% CI: 0.36-0.44), cardiovascular events, and all-cause mortality (HR 0.27, 95% CI: 0.21-0.36). Conclusions: GLP-1R agonists exhibit a complex influence on calcium homeostasis, reducing hypocalcemia risk while increasing hypercalcemia risk. Beyond calcium regulation, these medications significantly reduce healthcare utilization, improve cardiovascular outcomes, and decrease mortality. Further research is needed to elucidate the mechanisms behind the differential effects of individual GLP-1R agonists, particularly tirzepatide, to optimize personalized treatment approaches and long-term safety.

Gut hormone analogues and skeletal health in diabetes and obesity: Evidence from preclinical models

Diabetes mellitus and obesity are rapidly growing worldwide. Aside from metabolic disturbances, these two disorders also affect bone with a higher prevalence of bone fractures. In the last decade, a growing body of evidence suggested that several gut hormones, including ghrelin, gastrin, glucose-dependent insulinotropic polypeptide (GIP), glucagon, and glucagon-like peptide-1 and 2 (GLP-1 and GLP-2, respectively) may affect bone physiology. Several gut hormone analogues have been developed for the treatment of type 2 diabetes and obesity, and could represent a new alternative in the therapeutic arsenal against bone fragility. In the present review, a summary of the physiological roles of these gut hormones and their analogues is presented at the cellular level but also in several preclinical models of bone fragility disorders including type 2 diabetes mellitus, especially on bone mineral density, microarchitecture and bone material properties. The present review also summarizes the impact of GLP-1 receptor agonists approved for the treatment of type 2 diabetes mellitus and the more recent dual or triple analogue on bone physiology and strength.

Gut hormones and bone homeostasis: potential therapeutic implications

Bone resorption follows a circadian rhythm, with a marked reduction in circulating markers of resorption (such as carboxy-terminal telopeptide region of collagen type I in serum) in the postprandial period. Several gut hormones, including glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide 1 (GLP1) and GLP2, have been linked to this effect in humans and rodent models. These hormones are secreted from enteroendocrine cells in the gastrointestinal tract in response to a variety of stimuli and effect a wide range of physiological processes within and outside the gut. Single GLP1, dual GLP1-GIP or GLP1-glucagon and triple GLP1-GIP-glucagon receptor agonists have been developed for the treatment of type 2 diabetes mellitus and obesity. In addition, single GIP, GLP1 and GLP2 analogues have been investigated in preclinical studies as novel therapeutics to improve bone strength in bone fragility disorders. Dual GIP-GLP2 analogues have been developed that show therapeutic promise for bone fragility in preclinical studies and seem to exert considerable activity at the bone material level. This Review summarizes the evidence of the action of gut hormones on bone homeostasis and physiology.

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.

Enhanced bone regeneration via endochondral ossification using Exendin-4-modified mesenchymal stem cells

Nonunions and delayed unions pose significant challenges in orthopedic treatment, with current therapies often proving inadequate. Bone tissue engineering (BTE), particularly through endochondral ossification (ECO), emerges as a promising strategy for addressing critical bone defects. This study introduces mesenchymal stem cells overexpressing Exendin-4 (MSC-E4), designed to modulate bone remodeling via their autocrine and paracrine functions. We established a type I collagen (Col-I) sponge-based in vitro model that effectively recapitulates the ECO pathway. MSC-E4 demonstrated superior chondrogenic and hypertrophic differentiation and enhanced the ECO cell fate in single-cell sequencing analysis. Furthermore, MSC-E4 encapsulated in microscaffold, effectively facilitated bone regeneration in a rat calvarial defect model, underscoring its potential as a therapeutic agent for bone regeneration. Our findings advocate for MSC-E4 within a BTE framework as a novel and potent approach for treating significant bone defects, leveraging the intrinsic ECO process.

Effects of glucagon‑like peptide‑1 receptor agonists on fracture healing in a rat osteoporotic model

Osteoporosis is a common disease characterized by reduced bone mass, microstructural deterioration, fragility and consequent fragility fractures and is particularly prevalent among the elderly population. Although glucagon-like peptide-1 receptor agonists (GLP-1 RAs) have positive effects on bones, their role in the prevention of osteoporotic fractures remains to be elucidated. The present study assigned female Sprague Dawley rats with osteoporotic fractures into variectomized osteoporosis (OVX), OVX + liraglutide (LIRA) (50 µg/kg/day subcutaneous LIRA) and control groups. At 3 and 6 weeks postoperatively, X-ray, tartrate-resistant acid phosphatase (TRAP) staining, histological and biomechanical assays and assessment of femoral bone mineral density (BMD) were performed. Compared with the OVX group, GLP-1 RA treatment improved the formation of calluses and osseous union. TRAP staining showed significantly fewer osteoclasts in the OVX + LIRA group compared with the OVX group. In the osteoporotically fractured rats, LIRA improved bone strength at the femoral diaphysis, stiffness, ultimate load and femoral trabecular BMD Compared with the OVX group. GLP-1 RA treatment inhibited osteoclast formation and improved trabecular bone architecture and mass in osteoporotic fracture model rats, leading to improved biomechanical strength. GLP-1 RAs may be used as novel anti-osteoporotic fracture agents.

Bone resorption and incretin hormones following glucose ingestion in healthy emerging adults

Background

Studies in adults indicate that macronutrient ingestion yields an acute anti-resorptive effect on bone, reflected by decreases in C-terminal telopeptide (CTX), a biomarker of bone resorption, and that gut-derived incretin hormones, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1), facilitate this response. There remain knowledge gaps relating to other biomarkers of bone turnover, and whether gut-bone cross-talk is operative during the years surrounding peak bone strength attainment. This study first, describes changes in bone resorption during oral glucose tolerance testing (OGTT), and second, tests relationships between changes in incretins and bone biomarkers during OGTT and bone micro-structure.

Methods

We conducted a cross-sectional study in 10 healthy emerging adults ages 18-25 years. During a multi-sample 2-hour 75 g OGTT, glucose, insulin, GIP, GLP-1, CTX, bone-specific alkaline phosphatase (BSAP), osteocalcin, osteoprotegerin (OPG), receptor activator of nuclear factor kappa-β ligand (RANKL), sclerostin, and parathyroid hormone (PTH) were assayed at mins 0, 30, 60, and 120. Incremental areas under the curve (iAUC) were computed from mins 0-30 and mins 0-120. Tibia bone micro-structure was assessed using second generation high resolution peripheral quantitative computed tomography.

Results

During OGTT, glucose, insulin, GIP, and GLP-1 increased significantly. CTX at min 30, 60, and 120 was significantly lower than min 0, with a maximum decrease of about 53 % by min 120. Glucose-iAUC_0-30 inversely correlated with CTX-iAUC_0-120 (rho = -0.91, P < 0.001), and GLP-1-iAUC_0-30 positively correlated with BSAP-iAUC_0-120 (rho = 0.83, P = 0.005), RANKL-iAUC_0-120 (rho = 0.86, P = 0.007), and cortical volumetric bone mineral density (rho = 0.93, P < 0.001).

Conclusions

Glucose ingestion yields an anti-resorptive effect on bone metabolism during the years surrounding peak bone strength. Cross-talk between the gut and bone during this pivotal life stage requires further attention.

Endocrine Functions of Sclerostin

Sclerostin, the product of the SOST gene has primarily been studied for its profound impact on bone mass. By interacting with LRP5 and LRP6, the glycoprotein suppresses the propagation of Wnt signals to β-catenin and thereby suppresses new bone formation. In this review, we discuss emerging data which suggest that sclerostin also acts outside the skeleton to influence metabolism. In humans, serum sclerostin levels are associated with body mass index and indices of metabolic function. Likewise, genetic mouse models of Sost gene deficiency indicate sclerostin influences adipocyte development and insulin signaling. These data raise the possibility that sclerostin neutralization may be effective at treating two epidemic conditions: osteoporosis and obesity.

[Diagnosis and management of patients with diabetes and co-existing osteoporosis (Update 2023) : Common guideline of the Austrian Society for Bone and Mineral Research and the Austrian Diabetes Society]

Fragility fractures are increasingly recognized as a complication of both type 1 and type 2 diabetes, with fracture risk that increases with disease duration and poor glycemic control. The identification and management of fracture risk in these patients remains challenging. This manuscript explores the clinical characteristics of bone fragility in adults with diabetes and highlights recent studies that have evaluated areal bone mineral density (BMD), bone microstructure and material properties, biochemical markers, and fracture prediction algorithms (FRAX) in these patients. It further reviews the impact of diabetes drugs on bone tissue as well as the efficacy of osteoporosis treatments in this population. An algorithm for the identification and management of diabetic patients at increased fracture risk is proposed.

Effects of Incretin Pathway Elements on Bone Properties

Introduction The effects of incretin-based drugs, such as receptor agonists of glucagon-like peptide-1 and inhibitors of dipeptidyl peptidase-4, on bone metabolism are not completely clear yet. The aim of this study is to compare the effects of glucagon-like peptide-1 and inhibitors of dipeptidyl peptidase-4 on the bone to see how different elements of the incretin pathway affect bone quality in terms of biomechanical properties, bone turnover, and mineral properties. Materials and methods Forty 10-week-old Wistar rats were divided into four groups: a control group, a control diabetic group, a diabetic group treated with sitagliptin, and a diabetic group treated with exenatide. Type 2 diabetes was simulated by dietary manipulation in addition to low-dose streptozotocin, and then two different incretin-based drugs were administered. The rats were sacrificed after five weeks of therapeutic treatment. Their serum was analyzed with the enzyme-linked immunosorbent assay (ELISA) method for basic bone turnover markers, and their right femur was subjected to a three-point bending test. Finally, Hematoxylin & Eosin staining, in addition to Raman spectroscopy, were employed to access the collagen and mineral properties of the bone. Results Both incretin-based drugs reduced osteoclast function; however, they were not able to restore osteoblastic function to normal. The net effect on bone strength was surprising: bone elasticity was restored by the antidiabetic treatment, but bone strength deteriorated. Exenatide had a slightly more pronounced effect, which, although not significant, points to the direction that dipeptidyl peptidase-4 (DPP4) may be a linking factor between reduced osteoclastic function and reduced bone formation, as suggested by the literature. Conclusion DPP4 receptors seem to be one of the links between reduced osteoclast function and reduced bone remodeling, so DPP4 inhibition can be more detrimental to the bone than glucagon-like peptide-1 (GLP-1) receptor agonists.

Exendin-4 regulates the MAPK and WNT signaling pathways to alleviate the osteogenic inhibition of periodontal ligament stem cells in a high glucose environment

Diabetes mellitus (DM) increases the destruction of periodontal tissue and impairs osteogenesis differentiation. Exendin-4 (Ex-4), a glucagon-like peptide-1 (GLP-1) analogue, can be used for treating DM and promotes bone regeneration. The aim of this study was to explore the effect and mechanism of Ex-4 on improving the osteogenesis of periodontal ligament stem cells (PDLSCs) in a high glucose environment. Alkaline phosphatase staining and alizarin red staining were used to detect the osteogenic differentiation of PDLSCs. The results showed that 10 nM Ex-4 could reduce the osteogenesis inhibition of PDLSCs induced by high glucose. RT-PCR and western blot results showed that Ex-4 increased the osteogenesis-related gene expression of ALP, Runx2, and Osx, and upregulated the phosphorylation of P38, JNK, and ERK1/2; the peak effect was observed in the range 0.5-1.0 h. Mitogen-activated protein kinase (MAPK) inhibitors PD98059, SB203580, and SP600125 blocked the effects of Ex-4 on MAPK activation and decreased the expression of ALP, Runx2, and Osx in PDLSCs. Moreover, after Ex-4 treatment, the total β-catenin, p-GSK3β, LEF, and Runx2 protein levels increased under normal or high glucose environments. In conclusion, our results indicated that Ex-4 regulates the MAPK and WNT signaling pathways to alleviate the osteogenic inhibition of PDLSCs in a high glucose environment.

Type 2 diabetes and bone fragility in children and adults

Type 2 diabetes (T2D) is a global epidemic disease. The prevalence of T2D in adolescents and young adults is increasing alarmingly. The mechanisms leading to T2D in young people are similar to those in older patients. However, the severity of onset, reduced insulin sensitivity and defective insulin secretion can be different in subjects who develop the disease at a younger age. T2D is associated with different complications, including bone fragility with consequent susceptibility to fractures. The purpose of this systematic review was to describe T2D bone fragility together with all the possible involved pathways. Numerous studies have reported that patients with T2D show preserved, or even increased, bone mineral density compared with controls. This apparent paradox can be explained by the altered bone quality with increased cortical bone porosity and compr-omised mechanical properties. Furthermore, reduced bone turnover has been described in T2D with reduced markers of bone formation and resorption. These findings prompted different researchers to highlight the mechanisms leading to bone fragility, and numerous critical altered pathways have been identified and studied. In detail, we focused our attention on the role of microvascular disease, advanced glycation end products, the senescence pathway, the Wnt/β-catenin pathway, the osteoprotegerin/receptor-activator of nuclear factor kappa B ligand, osteonectin and fibroblast growth factor 23. The understanding of type 2 myeloid bone fragility is an important issue as it could suggest possible interventions for the prevention of poor bone quality in T2D and/or how to target these pathways when bone disease is clearly evident.

Risk of fracture caused by anti-diabetic drugs in individuals with type 2 diabetes: A network meta-analysis

AIMS

Diabetes is associated with increased risk of fracture. This study aims to evaluate the correlation between anti-diabetic agents and fracture risk in patients with type 2 diabetes.

METHODS

Literature research was conducted using PubMed, Embase, and ClinicalTrials.gov. Search-term included "type 2 diabetes," "fracture," "randomized controlled trial," and seven kinds of anti-diabetic agents. Random-effect models established fractures in the follow-up period as the primary outcome. A network meta-analysis was performed to compare available treatments within a single Bayesian analytical framework.

RESULTS

A total of 191,361 patients were included in 161 studies, with 2916 fractures. DPP-4i (risk ratio [RR] 1.76 [95 % confidence interval (CI) 1.21-2.55]), SGLT-2i (RR 1.5 [95 % CI 1.05-2.16]) and placebo (RR 1.44 [95 % CI 1.04-1.98]) increased fracture risk when compared to GLP1-RA. GLP1-RA (RR 0.5 [95 % CI 0.31-0.79]) and SU (RR 0.56 [95 % CI 0.41-0.77]) provided greater protection against fracture than TZD. DPP-4i increased fracture risk when compared to SU (RR 1.55 [95 % CI 1.08-2.22]), and was comparable in effect to TZD.

CONCLUSIONS

GLP1-RA offered better protection against fracture than placebo. Insulin and SU had effects comparable with GLP1-RA. SU offered greater protection against fractures than TZD and DPP-4i. SGLT-2i increased risk of fracture when compared to GLP1-RA.

Glucagon-like peptide-1 attenuates diabetes-associated osteoporosis in ZDF rat, possibly through the RAGE pathway

Background

Diabetes-associated osteoporosis are partly caused by accumulation of advanced glycation endproducts (AGEs). Glucagon-like peptide-1 (GLP-1) has been shown to regulate bone turnover. Here we explore whether GLP-1 receptor agonist (GLP1RA) can have a beneficial effect on bone in diabetes by ameliorating AGEs.

Methods

In the present study, we evaluated the effects of the GLP-1 receptor agonist liraglutide, insulin and dipeptidyl peptidase-4 inhibitor saxagliptin on Zucker diabetic fatty rats. Meanwhile, we observed the effect of GLP-1 on AGEs-mediated osteoblast proliferation and differentiation and the signal pathway.

Results

Liraglutide prevented the deterioration of trabecular microarchitecture and enhanced bone strength. Moreover, it increased serum Alpl, Ocn and P1NP levels and decreased serum CTX. In vitro we confirmed that GLP-1 could attenuate AGEs-mediated damage in osteogenic proliferation and differentiation. Besides, GLP-1 down-regulated the ROS that caused by AGEs and the mRNA and protein expression of Rage .

Conclusions

Altogether, our findings suggest that GLP-1 receptor agonist promotes osteoblastogenesis and suppresses bone resorption on obese type 2 diabetic rats to a certain degree. The mechanism of these effects may be partly mediated by AGEs-RAGE-ROS pathway via the interaction with GLP-1 receptor.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-022-05396-5.

Osteoimmunology in Periodontitis: Local Proteins and Compounds to Alleviate Periodontitis

Periodontitis is one of the most common oral diseases resulting in gingival inflammation and tooth loss. Growing evidence indicates that it results from dysbiosis of the oral microbiome, which interferes with the host immune system, leading to bone destruction. Immune cells activate periodontal ligament cells to express the receptor activator of nuclear factor kappa-B (NF-κB) ligand (RANKL) and promote osteoclast activity. Osteocytes have active roles in periodontitis progression in the bone matrix. Local proteins are involved in bone regeneration through functional immunological plasticity. Here, we discuss the current knowledge of cellular and molecular mechanisms in periodontitis, the roles of local proteins, and promising synthetic compounds generating a periodontal regeneration effect. It is anticipated that this may lead to a better perception of periodontitis pathophysiology.

Construction and performance of exendin-4-loaded chitosan-PLGA microspheres for enhancing implant osseointegration in type 2 diabetic rats

The updating and optimization of drug delivery systems is critical for better in vivo behaviors of drugs, as well as for improving impaired implant osseointegration in diabetes. Numerous studies have reported the benefits of exendin-4 on diabetic bone, with the potential to enhance osseointegration in diabetes. To construct an appropriate sustained-release system of exendin-4 targeting implant osseointegration in diabetes, this study fabricated exendin-4-loaded microspheres using poly(lactic-co-glycolic acid) (PLGA) and chitosan. The morphology, size, encapsulation efficiency, and drug release behavior of microspheres were investigated. The bioactivity of drug-loaded microspheres on cell proliferation and osteogenic differentiation of diabetic BMSCs was investigated to examine the pharmacologic action of exendin-4 loaded into chitosan-PLGA microspheres. Further, the influence of microspheres on osseointegration was evaluated using type 2 diabetes mellitus (T2DM) rat implant model. After 4 weeks, the samples were evaluated by radiological and histological analysis. The results of in vitro experiments showed that the prepared exendin-4-loaded chitosan-PLGA microspheres have good properties as a drug delivery system, and the chitosan could improve the encapsulation efficiency and drug release of PLGA microspheres. In addition, exendin-4-loaded microspheres could enhance the proliferation and osteogenic differentiation of diabetic BMSCs. The results of in vivo experiments showed the exendin-4-loaded microspheres significantly improved the impaired osseointegration and bone formation around implants in T2DM rats without affecting blood glucose levels. Thus, the local application of exendin-4-loaded chitosan-PLGA microspheres might be a promising therapeutic strategy for improving the efficacy of dental implants in T2DM individuals.

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.

A quinoxaline-based compound ameliorates bone loss in ovariectomized mice

DMB (6,7-dichloro-2-methylsulfonyl-3-Ntert-butylaminoquinoxaline) is a quinoxaline-based compound that has been investigated as a glucagon-like peptide-1 receptor (GLP-1R) agonist. To clarify anti-osteoporosis effect of DMB, an osteoporotic mice model was established by ovariectomy (OVX) operation. The OVX mice were given intraperitoneally DMB, exendin-4 (EX-4), or 17β-estradiol (E₂) for two months. Then bone mass and structure, and bone morphometric parameters were examined by micro-CT. Weight gain and food consumption, bone turnover markers, and biomechanical strength of the femur were tested, and bone histomorphometry was analyzed. The food intake and weight gain was obviously reduced by E₂ or EX-4, but not DMB. However, DMB or EX-4 treatment obviously inhibited skeletal deterioration and enhanced bone strength. The improvement involved in the increased osteoblast number and level of bone formation markers, and reduced osteoclasts number and level of bone resorption markers. In addition, DMB was found to stimulate osteoblastogenesis-related marker gene expression. These results demonstrated that DMB ameliorated bone loss mainly via induction of bone formation, which suggests that the small molecule compound might be applied to the management of postmenopausal osteoporosis.

Effects of Incretin-Related Diabetes Drugs on Bone Formation and Bone Resorption

Patients with type 2 diabetes have an increased risk of fracture compared to the general population. Glucose absorption is accelerated by incretin hormones, which induce insulin secretion from the pancreas. The level of the incretin hormone, glucagon-like peptide-1 (GLP-1), shows an immediate postprandial increase, and the circulating level of intact GLP-1 is reduced rapidly by dipeptidyl peptidase-4 (DPP-4)-mediated inactivation. Therefore, GLP-1 receptor agonists and DPP-4 inhibitors are effective in the treatment of type 2 diabetes. However, these incretin-related diabetic agents have been reported to affect bone metabolism, including bone formation and resorption. These agents enhance the expression of bone markers, and have been applied to improve bone quality and bone density. In addition, they have been reported to suppress chronic inflammation and reduce the levels of inflammatory cytokine expression. Previously, we reported that these incretin-related agents inhibited both the expression of inflammatory cytokines and inflammation-induced bone resorption. This review presents an overview of current knowledge regarding the effects of incretin-related diabetes drugs on osteoblast differentiation and bone formation as well as osteoclast differentiation and bone resorption. The mechanisms by which incretin-related diabetes drugs regulate bone formation and bone resorption are also discussed.

Exendin-4, a glucagon-like peptide receptor agonist, facilitates osteoblast differentiation via connexin43

PURPOSE

To investigate whether exendin-4 (Ex-4), a glucagon-like peptide 1 receptor (GLP-1R) agonist, affects connexin 43 (Cx43) expression in osteoblasts, and determine the specific mechanism underlying Cx43 modulation by Ex-4.

METHODS

Osteoblast-like MC3T3-E1 cells were treated with Ex-4 with or without GLP-1R antagonist. We assessed Cx43 expression using RT-PCR, western blotting, and confocal microscopy; visualized intercellular communication using Lucifer yellow dye transfer assay; evaluated osteoblast differentiation using alkaline phosphatase and Alizarin red S (ARS) staining. Cx43 silencing or overexpression was investigated via RNA-interference or adenovirus infection. The mechanism underlying Cx43 regulation by Ex-4 was determined via treatment with either Src kinase inhibitor, KX2-391, Akt activator, sc79, or inhibitor, LY294002.

RESULTS

Ex-4 treatment enhanced Cx43 expression and gap junctional intercellular communication in MC3T3-E1 cells. GLP-1R antagonist pretreatment abrogated the induction of Cx43 expression. Cx43 silencing significantly decreased ARS staining intensity in Ex-4-treated cells, whereas overexpression enhanced cell differentiation. Treatment with KX2-391 reduced both the Ex-4-induced increase of Cx43 expression and p-Akt protein levels. sc79 upregulated Cx43 expression, while LY294002 attenuated Cx43 upregulation by Ex-4.

CONCLUSIONS

Induced Cx43 expression in osteoblasts via the Src-Akt signaling pathway illustrates the underlying mechanism for promoting osteoblast differentiation by Ex-4.

Exendin-4 promotes bone formation in diabetic states via HDAC1-Wnt/β-catenin axis

Exendin-4 has been found to have hypoglycemic effect and prevent bone loss in diabetic patients, but its mechanism of preventing bone loss is still unclear. In this study, high-fat diet combined with streptozotocin was used to establish type 2 diabetes mellitus (T2DM) mice, and bone marrow mesenchyme stem cells (BMSCs) were isolated for osteogenic induction in vitro. Alizarin red staining and ALP activity detection were used to observe the effect of exendin-4 on osteogenic differentiation of BMSCs. Western blot was used to detect the proteins expression in BMSCs. In vivo, the effects of exendin-4 treatment on body weight, blood glucose, bone density and bone quality of T2DM mice were observed by treatment with exendin-4. The results showed that exendin-4 promoted osteogenic differentiation of T2DM derived BMSCs, down-regulated histone deacetylase 1 (HDAC1) and p-β-Catenin proteins expression, and up-regulated Wnt3, β-Catenin and runt-related transcription factor 2 (Runx 2) proteins expression. In vivo, exendin-4 effectively suppressed the blood glucose and increased body weight of T2DM mice, and significantly improved bone density and bone quality of the right tibia. Interestingly, by over-expression of HDAC1 in BMSCs, the effect of exendin-4 on promoting osteogenic differentiation of BMSCs was attenuated, and the regulation of Wnt3a, β-Catenin, p-β-Catenin or Runx2 proteins were reversed. By injecting adenovirus containing HDAC1 into the right tibia of mice, the effect of exendin-4 on bone density and bone quality of T2DM mice was significantly attenuated. All above results suggest that the HDAC1-Wnt/β-Catenin signal axis is involved in the anti-diabetic bone loss effect of exendin-4, and HDAC1 may be the target of exendin-4.

[Gly²]-GLP-2, But Not Glucagon or [D-Ala²]-GLP-1, Controls Collagen Crosslinking in Murine Osteoblast Cultures

Bone tissue is organized at the molecular level to resist fracture with the minimum of bone material. This implies that several modifications of the extracellular matrix, including enzymatic collagen crosslinking, take place. We previously highlighted the role of several gut hormones in enhancing collagen maturity and bone strength. The present study investigated the effect of proglucagon-derived peptides on osteoblast-mediated collagen post-processing. Briefly, MC3T3-E1 murine osteoblasts were cultured in the presence of glucagon (GCG), [D-Ala²]-glucagon-like peptide-1 ([D-Ala²]-GLP-1), and [Gly²]-glucagon-like peptide-2 ([Gly²]-GLP-2). Gut hormone receptor expression at the mRNA and protein levels were investigated by qPCR and Western blot. Extent of collagen postprocessing was examined by Fourier transform infrared microspectroscopy. GCG and GLP-1 receptors were not evidenced in osteoblast cells at the mRNA and protein levels. However, it is not clear whether the known GLP-2 receptor is expressed. Nevertheless, administration of [Gly²]-GLP-2, but not GCG or [D-Ala²]-GLP-1, led to a dose-dependent increase in collagen maturity and an acceleration of collagen post-processing. This mechanism was dependent on adenylyl cyclase activation. In conclusion, the present study highlighted a direct effect of [Gly²]-GLP-2 to enhance collagen post-processing and crosslinking maturation in murine osteoblast cultures. Whether this effect is translatable to human osteoblasts remains to be elucidated.

Update on: effects of anti-diabetic drugs on bone metabolism

INTRODUCTION

Preclinical, clinical, and population-based studies have provided evidence that anti-diabetic drugs affect bone metabolism and may affect the risk of fracture in diabetic patients.

AREAS COVERED

An overview of the skeletal effects of anti-diabetic drugs used in type 2 diabetes is provided. Searches on AdisInsight, PubMed, and Medline databases were conducted up to 1^st July 2020. The latest evidence from randomized clinical trials and population-based studies on the skeletal safety of the most recent drugs (DPP-4i, GLP-1RA, and SGLT-2i) is provided.

EXPERT OPINION

Diabetic patients present with a higher risk of fracture for a given bone mineral density suggesting a role of bone quality in the etiology of diabetic fracture. Bone quality is difficult to assess in human clinical practice and the use of preclinical models provides valuable information on diabetic bone alterations. As several links have been established between bone and energy homeostasis, it is interesting to study the safety of anti-diabetic drugs on the skeleton. So far, evidence for the newest molecules suggests a neutral fracture risk, but further studies, especially in different types of patient populations (patients at risk or with history of cardiovascular disease, renal impairment, neuropathy) are required to fully appreciate this matter.

Impact of diabetes mellitus simulations on bone cell behavior through in vitro models

Diabetes mellitus (DM) is related to impaired bone healing and an increased risk of bone fractures. While it is recognized that osteogenic differentiation and the function of osteoblasts are suppressed in DM, the influence of DM on osteoclasts is still unclear. Hyperglycemia and inflammatory environment are the hallmark of DM that causes dysregulation of various pro-inflammatory cytokines and alternated gene expression in periodontal ligament cells, osteoblasts, osteocytes, osteoclasts, and osteoclast precursors. A methodological review on conceptual and practical implications of in vitro study models is used for DM simulation on bone cells. Several major databases were screened to find literature related to the study objective. Published literature within last 20 years that used in vitro DM-simulated models to study how DM affects the cellular behavior of bone cells were selected for this review. Studies utilizing high glucose and serum acquired from diabetic animals are the mainly used methods to simulate the diabetic condition. The combination with various simulating factors such as lipopolysaccharide (LPS), hydrogen peroxide (H₂O₂), and advanced glycation end products (AGEs) have been reported in diabetic situations in vitro, as well. Through screening procedure, it was evident DM-simulated conditions exerted negative impact on bone-related cells. However, inconsistent results were found among different reported studies, which could be due to variation in culture conditions, concentrations of the stimulating factors and cell lineage, etc. This manuscript has concisely reviewed currently existing DM-simulated in vitro models and provides valuable insights of detailed components in simulating DM conditions in vitro. Studies using DM-simulated microenvironment revealed that in vitro simulation negatively impacted periodontal ligament cells, osteoblasts, osteocytes, osteoclasts, and osteoclast precursors. Contrarily, studies also indicated beneficial influence on bone-related cells when such conditions are reversed.

Dapagliflozin and Liraglutide Therapies Rapidly Enhanced Bone Material Properties and Matrix Biomechanics at Bone Formation Site in a Type 2 Diabetic Mouse Model

The aim of this study is to compare head-to-head the effects of dapagliflozin and liraglutide on bone strength and bone material properties in a pre-clinical model of diabetes-obesity. Combined low-dose streptozotocin and high fat feeding were employed in mice to promote obesity, insulin resistance, and hyperglycaemia. Mice were administered daily for 28 days with saline vehicle, 1 mg/kg dapagliflozin or 25 nmol/kg liraglutide. Bone strength was assessed by three-point bending and nanoindentation. Bone material properties were investigated by Fourier transform infrared microspectroscopy/imaging. Although diabetic controls presented with dramatic reductions in mechanical strength, no deterioration of bone microarchitecture was apparent. At the tissue level, significant alterations in phosphate/amide ratio, carbonate/phosphate ratio, tissue water content, crystal size index, collagen maturity and collagen glycation were observed and linked to alteration of matrix biomechanics. Dapagliflozin and liraglutide failed to improve bone strength by 3-point bending or bone microarchitecture during the 28-day-treatment period. At bone formation site, dapagliflozin enhanced phosphate/amide ratio, mineral maturity, and reduced tissue water content, crystal size index, and collagen glycation. Liraglutide had significant effects on phosphate/amide ratio, tissue water content, crystal size index, mature collagen crosslinks, collagen maturity, and collagen glycation. At bone formation site, both drugs modulated matrix biomechanics. This study highlighted that these two molecules are effective in improving bone material properties and modulating matrix biomechanics at bone formation site. This study also highlighted that the resulting effects on bone material properties are not identical between dapagliflozin and liraglutide and not only mediated by lower blood glucose.

GLP-1 inhibits PKCβ2 phosphorylation to improve the osteogenic differentiation potential of hPDLSCs in the AGE microenvironment

BACKGROUND AND OBJECTIVE

Advanced glycation end products (AGEs) have been hypothesized as the etiologic factors of diabetic periodontitis. The discovery of incretins (including GLP-1 and GIP) provides a novel therapy for the treatment of diabetes. Recent reports have shown that glucagon-like peptide-1 (GLP-1) is an important modulator of bone growth and remodeling. The aim of this study was to clarify the mechanism of how GLP-1 weakens/inhibits the effect of AGEs in hPDLSCs (human periodontal ligament stem cells).

MATERIALS AND METHODS

The hPDLSCs were cultured under simulated conditions of osteogenic culture, AGEs, AGEs + GLP-1, AGEs + GLP-1 + PMA and AGEs + GLP-1 + LY333531. The phenomenon and related mechanism of cell osteogenesis under different microenvironments were evaluated by Alizarin red staining, ALP staining and quantitative activity measurement, RT-qPCR, western blotting and immunofluorescence staining.

RESULTS

RT-qPCR showed that AGEs negatively regulated the expression of osteogenic differentiation markers (ALP, BSP, OPN, and Runx2); in contrast, GLP-1 increased the expression of these markers. Furthermore, the expression of RAGE and pPKCβ (PKC phosphorylation) in the AGE group was upregulated, while the expression of RAGE and pPKCβ was decreased in the GLP-1 group compared with the AGE group.

CONCLUSIONS

AGEs impaired the osteogenic potential of hPDLSCs via PKCβ2. Our phenomenon showed that GLP-1 could reverse the function of AGEs on osteogenic potential. In addition, the mechanism of GLP-1 weakens/inhibits the effect of AGEs in hPDLSCs, possibly by inhibiting PKCβ2 phosphorylation.

Pathophysiology and Management of Type 2 Diabetes Mellitus Bone Fragility

Individuals with type 2 diabetes mellitus (T2DM) have an increased risk of bone fragility fractures compared to nondiabetic subjects. This increased fracture risk may occur despite normal or even increased values of bone mineral density (BMD), and poor bone quality is suggested to contribute to skeletal fragility in this population. These concepts explain why the only evaluation of BMD could not be considered an adequate tool for evaluating the risk of fracture in the individual T2DM patient. Unfortunately, nowadays, the bone quality could not be reliably evaluated in the routine clinical practice. On the other hand, getting further insight on the pathogenesis of T2DM-related bone fragility could consent to ameliorate both the detection of the patients at risk for fracture and their appropriate treatment. The pathophysiological mechanisms underlying the increased risk of fragility fractures in a T2DM population are complex. Indeed, in T2DM, bone health is negatively affected by several factors, such as inflammatory cytokines, muscle-derived hormones, incretins, hydrogen sulfide (H2S) production and cortisol secretion, peripheral activation, and sensitivity. All these factors may alter bone formation and resorption, collagen formation, and bone marrow adiposity, ultimately leading to reduced bone strength. Additional factors such as hypoglycemia and the consequent increased propensity for falls and the direct effects on bone and mineral metabolism of certain antidiabetic medications may contribute to the increased fracture risk in this population. The purpose of this review is to summarize the literature evidence that faces the pathophysiological mechanisms underlying bone fragility in T2DM patients.

Identification of a prolonged action molecular GLP-1R agonist for the treatment of femoral defects

Poly-GLP-1 promotes angiogenesis to accelerate bone formationviaBMSC differentiation and M2 polarization.

Effect of type 2 diabetes medications on fracture risk

Type 2 diabetes, one of the most frequent chronic diseases, has an important effect on bone metabolism, with most studies reporting an increased prevalence of fractures in these patients despite an apparently increased bone mineral density. Most probable explanation is an alteration of bone structure/quality with increased fragility but the different diabetes medications influence the risk of fracture. While metformin and incretin-based therapies are safe, thiazolidinediones and canagliflozin (sodium-glucose cotransporter-2 inhibitor) negatively impact bone metabolism and should be avoided in subjects at increased risk of fractures. Insulin and sulphonylureas are generally safe but can increase the risk of hypoglycemia and falls with subsequent traumatic fractures. Their combination should be avoided, especially in elderly subjects.

A Pilot Study Showing Acute Inhibitory Effect of GLP-1 on the Bone Resorption Marker CTX in Humans

Bones have been suggested to be a target for glucagon-like peptide -1 (GLP-1); however, studies of the effects on human bones so far have given diverging results. We hypothesized that GLP-1, together with glucagon-like peptide-2 and glucose-dependent insulinotropic polypeptide, plays a role in the gut-bone axis. We examined the acute effect of three GLP-1 receptor ligands [GLP-1 (7-36)amide, GLP-1 (9-36)amide, and exenatide] on markers of bone remodeling. Eight healthy, normal-weight participants, with a mean age of 24.3 years, were studied for 4 days in a double-blinded, randomized clinical trial. Blood was collected before and after s.c. injection of GLP-1 (7-36)amide (1.5 nmol/kg), GLP-1 (9-36)amide (1.5 nmol/kg), exenatide (2.4 nmol/subject), or saline. Plasma was analyzed for bone markers and for osteoprotegerin (OPG), PTH, and IGF-1 levels. All ligands were tested in vitro for their cAMP-inducing activity on the human GLP-1 receptor. GLP-1 (7-36)amide decreased CTX-levels, compared with placebo (area under the curve [AUC] ±SD 0 to 120 min = -2143 ± 1294 % × min versus -883 ± 1557 % × min; p < 0.05). No difference was observed between placebo and GLP-1 (9-36)amide, or between placebo and exenatide, although exenatide had a similar potency as GLP-1 (7-36)amide for cAMP formation in vitro (EC₅₀ of 0.093 and 0.054 nmol/L). However, exenatide reached maximum plasma concentration at 90 min versus 15 min for GLP-1 (7-36)amide, and plasma CTX was significantly decreased during the second hour of the study after exenatide injections compared with placebo (AUC ±SD -463.1 ± 218 % × min and -136 ± 91 % × min; p < 0.05). There was no effect of the injections on bone formation markers (P1NP and osteocalcin) or on OPG, PTH and IGF-1 levels. In conclusion, we show that GLP-1 receptor agonists, but not the primary metabolite GLP-1 (9-36)amide, decrease bone resorption, and suggest that GLP-1 may be part of the gut-bone axis. © 2019 The Authors. JBMR Plus is published by Wiley Periodicals, Inc. on behalf of the American Society for Bone and Mineral Research.

The effects of resistance training on bone mineral density and bone quality in type 2 diabetic rats

Resistance training (RT) has been known to be effective in maintaining and improving bone strength, which is based on bone mineral density (BMD) and bone quality. However, it is not clear whether RT is effective in improving bone strength in patients with type-2 diabetes mellitus (T2DM), who have a high risk of fracture. Therefore, we tested the effects of a 6-week RT regimen using percutaneous electrical stimulation in T2DM model rats, male Otsuka Long-Evans Tokushima Fatty (OLETF), and its control, Long-Evans Tokushima Otsuka (LETO). After 6 weeks of RT, tibial BMD in RT legs was significantly higher than that in control (CON) legs in both groups. In diaphyseal cortical bone, bone area/tissue area, and cortical thickness was significantly increased in RT legs compared with CON legs in both groups. Cortical porosity was highly observed in OLETF compared with LETO, but RT improved cortical porosity in both groups. Interestingly, trabecular number, trabecular thickness and trabecular space as well as BMD and bone volume/tissue volume in proximal tibial metaphyseal trabecular bone were significantly improved in RT legs compared with CON legs in both groups. In contrast, connectivity density and structural model index were not affected by RT. These results indicate that the 6-week RT regimen effectively increased BMD and improved bone quality in T2DM model rats as well as control rats. Therefore, RT may have the potential to improve bone strength and reduce fracture risk, even in patients with T2DM.

Update on the impact of type 2 diabetes mellitus on bone metabolism and material properties

The prevalence of type 2 diabetes mellitus (T2DM) is increasing worldwide, especially as a result of our aging society, high caloric intake and sedentary lifestyle. Besides the well-known complications of T2DM on the cardiovascular system, the eyes, kidneys and nerves, bone strength is also impaired in diabetic patients. Patients with T2DM have a 40-70% increased risk for fractures, despite having a normal to increased bone mineral density, suggesting that other factors besides bone quantity must account for increased bone fragility. This review summarizes the current knowledge on the complex effects of T2DM on bone including effects on bone cells, bone material properties and other endocrine systems that subsequently affect bone, discusses the effects of T2DM medications on bone and concludes with a model identifying factors that may contribute to poor bone quality and increased bone fragility in T2DM.

Gut Hormones and Their Effect on Bone Metabolism. Potential Drug Therapies in Future Osteoporosis Treatment

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.

Diabetes pharmacotherapy and effects on the musculoskeletal system

Persons with type 1 or type 2 diabetes have a significantly higher fracture risk than age-matched persons without diabetes, attributed to disease-specific deficits in the microarchitecture and material properties of bone tissue. Therefore, independent effects of diabetes drugs on skeletal integrity are vitally important. Studies of incretin-based therapies have shown divergent effects of different agents on fracture risk, including detrimental, beneficial, and neutral effects. The sulfonylurea class of drugs, owing to its hypoglycemic potential, is thought to amplify the risk of fall-related fractures, particularly in the elderly. Other agents such as the biguanides may, in fact, be osteo-anabolic. In contrast, despite similarly expected anabolic properties of insulin, data suggests that insulin pharmacotherapy itself, particularly in type 2 diabetes, may be a risk factor for fracture, negatively associated with determinants of bone quality and bone strength. Finally, sodium-dependent glucose co-transporter 2 inhibitors have been associated with an increased risk of atypical fractures in select populations, and possibly with an increase in lower extremity amputation with specific SGLT2I drugs. The role of skeletal muscle, as a potential mediator and determinant of bone quality, is also a relevant area of exploration. Currently, data regarding the impact of glucose lowering medications on diabetes-related muscle atrophy is more limited, although preclinical studies suggest that various hypoglycemic agents may have either aggravating (sulfonylureas, glinides) or repairing (thiazolidinediones, biguanides, incretins) effects on skeletal muscle atrophy, thereby influencing bone quality. Hence, the therapeutic efficacy of each hypoglycemic agent must also be evaluated in light of its impact, alone or in combination, on musculoskeletal health, when determining an individualized treatment approach. Moreover, the effect of newer medications (potentially seeking expanded clinical indication into the pediatric age range) on the growing skeleton is largely unknown. Herein, we review the available literature regarding effects of diabetes pharmacotherapy, by drug class and/or by clinical indication, on the musculoskeletal health of persons with diabetes.

The GLP-1 Receptor Agonist Exenatide Ameliorates Bone Composition and Tissue Material Properties in High Fat Fed Diabetic Mice

Type 2 diabetes mellitus (T2DM) has recently been recognized as a significant risk factor for bone fragility. Careful investigations of bone mechanical properties in human studies suggested possible alterations of bone composition, although this axis has poorly been investigated. The main aim of this study was to evaluate the impact of high fat diet-induced diabetes and therapy using the clinically approved GLP-1 receptor agonist, exenatide, on tissue bone mechanical properties and compositional parameters. Male mice had free access to high fat diet for 16 weeks to induce diabetes prior to commencement of the study. Exenatide was administered twice daily by i.p. injection at a dose of 25 nmol/kg for 52 days. Normal and high fat diet fed (HFD) mice injected with saline were used as controls. Bone mechanical properties was assessed at the organ level by 3-point bending and at the tissue level by nanoindentation. Bone microarchitecture was investigated by microcomputed tomography and bone composition was evaluated by Fourier transform infrared imaging. HFD mice exhibited profound alterations of bone mechanical properties at both the organ and tissue level. Collagen maturity as well as trabecular and cortical bone microarchitectures were abnormal. Administration of exenatide, led to clear ameliorations in bone mechanical properties at the organ and tissue levels by modifications of both cortical microarchitecture and bone compositional parameters (collagen maturity, mineral crystallinity, carbonate/phosphate ratio, acid phosphate content). These results bring new light on the mode of action of exenatide in bone physiology and demonstrate the value of GLP-1 mimetics in the treatment of fragility fractures in diabetes.

The bone anabolic effects of irisin are through preferential stimulation of aerobic glycolysis

Irisin, a recently identified hormone secreted by skeletal muscle in response to exercise, exhibits anabolic effects on the skeleton primarily through the stimulation of bone formation. However, the mechanism underlying the irisin-stimulated anabolic response remains largely unknown. To uncover the underlying mechanism, we biosynthesized recombinant irisin (r-irisin) using an Escherichia coli expression system and used it to treat several osteoblast cell types. Our synthesized r-irisin could promote proliferation and differentiation of osteoblasts as evidenced by enhanced expression of osteoblast-specific transcriptional factors, including Runt-related transcription factor-2 (Runx2), Oster (Osx), as well as early osteoblastic differentiation markers such as alkaline phosphatase (Alp) and collagen type I alpha 1 (Col1a1). Furthermore, we showed that the promotion of r-irisin on the proliferation and differentiation of osteoblast lineage cells are preferentially through aerobic glycolysis, as indicated by the enhanced abundance of representative enzymes such as lactate dehydrogenase A (LDHA) and pyruvate dehydrogenase kinase 1 (PDK1), together with increased lactate levels. Suppression of r-irisin-mediated aerobic glycolysis with Dichloroacetate blunted its anabolic effects. The favorite of the aerobic glycolysis after r-irisin treatment was then confirmed in primary calvarial cells by metabolic analysis using gas chromatography-mass spectrometry. Thus, our results suggest that the anabolic actions of r-irisin on the regulation of osteoblast lineage cells are preferentially through aerobic glycolysis, which may help to develop new irisin-based bone anabolic agents.

Exendin-4 relieves the inhibitory effects of high glucose on the proliferation and osteoblastic differentiation of periodontal ligament stem cells

BACKGROUND

With the impaired regenerative potential in patients with diabetes mellitus (DM), Periodontal ligament stem cells (PDLSCs) are regarded as an attractive source of stem cells for periodontal cytotherapy. Recent studies have shown that Exendin-4 (Ex-4) exerts cell-protective effects and bone remodeling ability on many types of cells. The aim of this study was to investigate whether Ex-4 alleviates the inhibition of high glucose on the proliferation and osteogenic differentiation of PDLSCs.

METHODS

PDLSCs were incubated in medium supplemented with 5.5 mM d-glucose (NG), 30 mM d-glucose (HG), NG plus Ex-4, and HG plus different concentration (1, 10, 20, 100 nM) of Ex-4 respectively. Cell proliferation was detected by CCK-8 assay and cell cycle analysis. Osteogenesis was assessed by Alizarin Red S staining and evaluation of the mRNA expression of Runx2, ALP and Osx at day 7, 14 and 21. Intracellular level of reactive oxygen species (ROS) was detected using 5-(and-6)-chloromethyl-2',7'-dichlorodihydro-fluorescein diacetate (CMH2DCF-DA).

RESULTS

The proliferation ability, mineralized nodules forming capacity and the mRNA expression of Runx2, ALP and Osx of PDLSCs in HG group were decreased, the ROS level was increased compared to NG group. With the treatment of Ex-4, the HG-inhibited proliferation ability and osteogenic differentiation ability of PDLSCs were significantly reversed, the HG-increased ROS level could be down-regulated. Moreover, Ex-4 enhanced the osteogenic differentiation of normal PDLSCs.

CONCLUSIONS

Ex-4 alleviates the inhibitory effect of HG on the proliferation and osteoblastic differentiation of PDLSCs, and has a significant enhance in the osteoblastic differentiation of normal PDLSCs, giving new insights into the possible therapeutic method of diabetic periodontitis.

The effects of diabetes therapy on bone: A clinical perspective

The effects of diabetes and diabetes therapy on bone are less known among clinicians. Traditionally, the emphasis of diabetes therapy has been on reducing cardiovascular risk by facilitating reductions in weight, blood pressure, blood sugar, systemic inflammation, and lipid levels. Now, with ample research demonstrating that patients with diabetes are more susceptible to bone fractures relative to controls, there has been a greater or renewed interest in studying the effects of diabetes therapy on bone. Interestingly, the majority of antidiabetic agents positively affect bone, but a few have detrimental effects. Specifically, although insulin has been demonstrated to be anabolic to bone, the rate of hypoglycemic episodes are increased with exogenous infusion; consequently, there is an increased fall and fracture frequency. Other agents such as thiazolidinediones have more direct negative effects on bone through transcriptional regulation. Even metabolic surgery, to a varying operation-dependent extent, exacerbates bone strength and may heighten fracture rate. The remaining diabetes agents seem to have neutral or positive effects on bone. With the increasing incidence of diabetes, it is more pertinent than ever to fully comprehend the effects of diabetes-related therapeutic modalities.

Glucagon-like Peptide-1 Receptor Agonists and Cardiovascular Events: Class Effects versus Individual Patterns

Several new glucose-lowering medications have been approved, such as dipeptidyl peptidase-4 inhibitors, glucagon-like peptide-1 receptor agonists (GLP-1RAs), and sodium glucose cotransporter-2 inhibitors. Among GLP-1RAs, lixisenatide, a short-acting drug, did not show cardiovascular (CV) benefits in patients with Type 2 diabetes mellitus (T2D) and acute coronary syndrome. Extended-release exenatide was also not significantly better for CV outcomes. By contrast, once daily liraglutide and once weekly semaglutide, both long-acting GLP-1RAs, decreased the incidence of major adverse CV events and mortality. This Review attempts to explain favorable CV results with some, but not all, GLP-1RAs, to aid in their differential prescription with the aim of further reducing the adverse CV burden of T2D.

Incretin-based therapy for the treatment of bone fragility in diabetes mellitus

Bone fractures are common comorbidities of type 2 diabetes mellitus (T2DM). Bone fracture incidence seems to develop due to increased risk of falls, poor bone quality and/or anti-diabetic medications. Previously, a relation between gut hormones and bone has been suspected. Most recent evidences suggest indeed that two gut hormones, namely glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1), may control bone remodeling and quality. The GIP receptor is expressed in bone cells and knockout of either GIP or its receptor induces severe bone quality alterations. Similar alterations are also encountered in GLP-1 receptor knock-out animals associated with abnormal osteoclast resorption. Some GLP-1 receptor agonist (GLP-1RA) have been approved for the treatment of type 2 diabetes mellitus and although clinical trials may not have been designed to investigate bone fracture, first results suggest that GLP-1RA may not exacerbate abnormal bone quality observed in T2DM. The recent design of double and triple gut hormone agonists may also represent a suitable alternative for restoring compromised bone quality observed in T2DM. However, although most of these new molecules demonstrated weight loss action, little is known on their bone safety. The present review summarizes the most recent findings on peptide-based incretin therapy and bone physiology.