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

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.

Role of LRP5/6/GSK-3β/β-catenin in the differences in exenatide- and insulin-promoted T2D osteogenesis and osteomodulation

BACKGROUND AND PURPOSE

Insulin and exenatide are two hypoglycaemic agents that exhibit different osteogenic effects. This study compared the differences between exenatide and insulin in osseointegration in a rat model of Type 2 diabetes (T2D) and explored the mechanisms promoting osteogenesis in this model of T2D.

EXPERIMENTAL APPROACH

In vivo, micro-CT was used to detect differences in the peri-implant bone microstructure in vivo. Histology, dual-fluorescent labelling, immunofluorescence and immunohistochemistry were used to detect differences in tissue, cell and protein expression around the implants. In vitro, RT-PCR and western blotting were used to measure the expression of osteogenesis- and Wnt signalling-related genes and proteins in bone marrow mesenchymal stromal cells (BMSCs) from rats with T2D (TBMSCs) after PBS, insulin and exenatide treatment. RT-PCR was used to detect the expression of Wnt bypass cascade reactions under Wnt inactivation.

KEY RESULTS

Micro-CT and section staining showed exenatide extensively promoted peri-implant osseointegration. Both in vivo and in vitro experiments showed exenatide substantially increased the expression of osteogenesis-related and activated the LRP5/6/GSK-3β/β-catenin-related Wnt pathway. Furthermore, exenatide suppressed expression of Bmpr1a to inhibit lipogenesis and promoted expression of Btrc to suppress inflammation.

CONCLUSION AND IMPLICATIONS

Compared to insulin, exenatide significantly improved osteogenesis in T2D rats and TBMSCs. In addition to its dependence on LRP5/6/GSK-3β/β-catenin signalling for osteogenic differentiation, exenatide-mediated osteomodulation also involves inhibition of inflammation and adipogenesis by BMPR1A and β-TrCP, respectively.

Research Progress on the Mechanism of the SFRP-Mediated Wnt Signalling Pathway Involved in Bone Metabolism in Osteoporosis

Osteoporosis (OP) is a metabolic bone disease linked to an elevated fracture risk, primarily stemming from disruptions in bone metabolism. Present clinical treatments for OP merely alleviate symptoms. Hence, there exists a pressing need to identify novel targets for the clinical treatment of OP. Research indicates that the Wnt signalling pathway is modulated by serum-secreted frizzled-related protein 5 (SFRP5), potentially serving as a pivotal regulator in bone metabolism disorders. Moreover, studies confirm elevated SFRP5 expression in OP, with SFRP5 overexpression leading to the downregulation of Wnt and β-catenin proteins in the Wnt signalling pathway, as well as the expression of osteogenesis-related marker molecules such as RUNX2, ALP, and OPN. Conversely, the opposite has been reported when SFRP5 is knocked out, suggesting that SFRP5 may be a key factor involved in the regulation of bone metabolism via the Wnt signalling axis. However, the molecular mechanisms underlying the action of SFRP5-induced OP have yet to be comprehensively elucidated. This review focusses on the molecular structure and function of SFRP5 and the potential molecular mechanisms of the SFRP5-mediated Wnt signalling pathway involved in bone metabolism in OP, providing reasonable evidence for the targeted therapy of SFRP5 for the prevention and treatment of OP.

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.

Narrative Review of Effects of Glucagon-Like Peptide-1 Receptor Agonists on Bone Health in People Living with Obesity

Glucagon-like peptide-1 Receptor agonists (GLP-1Ras) such as liraglutide and semaglutide have been recently approved as medications for chronic weight management in people living with obesity (PwO); GLP-1 may enhance bone metabolism and improve bone quality. However, the effects of GLP-1Ras on skeletal health remain to be determined and that's the purpose of this narrative review. Nevertheless, bone consequences of intentional weight loss interventions in PwO are well known: (i) significant weight loss induced by caloric restriction and bariatric surgery results in accelerated bone turnover and bone loss, and (ii) unlike caloric restriction interventions, PwO experience a substantial deterioration in bone microarchitecture and strength associated with an increased risk of fracture after bariatric surgery especially malabsorptive procedures. Liraglutide seems to have a positive effect on bone material properties despite significant weight loss in several rodent models. However, most of positive effects on bone mineral density and microarchitecture were observed at concentration much higher than approved for obesity care in humans. No data have been reported in preclinical models with semaglutide. The current evidence of the effects of GLP-1Ra on bone health in PwO is limited. Indeed, studies on the use of GLP-1Ra mostly included patients with diabetes who were administered a dose used in this condition, did not have adequate bone parameters as primary endpoints, and had short follow-up periods. Further studies are needed to investigate the bone impact of GLP-1Ra, dual- and triple-receptor agonists for GLP-1, glucose-dependent insulin releasing polypeptide (GIP), and glucagon in PwO.

Liraglutide attenuates palmitate-induced apoptosis via PKA/β-catenin/Bcl-2/Bax pathway in MC3T3-E1 cells

Liraglutide (LRG), one agonist of glucagon-like peptide-1 receptor (GLP1R), has multiple lipid-lowering effects in type 2 diabetes mellitus, however, studies on the role of LRG in saturated fatty acid-induced bone loss are limited. Therefore, our aim was to investigate whether LRG reduces palmitate (PA)-induced apoptosis and whether the mechanism involves PKA/β-catenin/Bcl-2/Bax in osteoblastic MC3T3-E1 cells. MC3T3-E1 cells were treated with different concentrations of PA, LRG, or pretreated with Exendin 9-39 and H89, cell viability, intracellular reactive oxygen species (ROS), cAMP levels, apoptosis and the expression of protein kinase A (PKA) and phosphorylation of PKA (p-PKA), β-catenin and phosphorylation of β-catenin (Ser675)(p-β-catenin), GLP1R, cleaved-capase 3, Bcl2-Associated X Protein (Bax) and B-cell lymphoma-2 (Bcl-2) along with expression of Osteoprotegerin (OPG) and receptor activator of nuclear factor-κB ligand (RANKL) were evaluated. PA treatment inhibited cell proliferation and cAMP levels, elevated intracellular ROS levels and promoted apoptosis, increased protein expressions of RANKL, Bax and cleaved-caspase3, meanwhile decreased protein expression of OPG and Bcl-2 in a dose-dependent manner. LRG inverted PA-induced apoptosis, increased cAMP levels, promoted expression of p-PKA, p-β-catenin (Ser675) and reversed these gene expressions via increasing GLP1R expression. Pretreatment of the cells with Exendin 9-39 and H89 partially eradicated the protective effect of LRG on PA-induced apoptosis and gene expressions. Therefore, these findings indicated that LRG attenuates PA-induced apoptosis possibly by GLP1R-mediated PKA/β-catenin/Bcl-2/Bax pathway in MC3T3-E1 cells. Our results point to LRG as a new strategy to attenuate bone loss associated with high fat diet beyond its lipid-lowering actions. LRG inhibits PA-mediated apoptosis via GLP1R-mediated PKA/β-catenin/Bcl-2/ Bax pathway, while possibly enhances PA-inhibited differentiation by regulating the expression of OPG and RANKL.

Polymorphisms in the glucagon-like peptide-1 receptor gene and their interactions on the risk of osteoporosis in postmenopausal Chinese women

Postmenopausal osteoporosis (PMOP) is a prevalent form of primary osteoporosis, affecting over 40% of postmenopausal women. Previous studies have suggested a potential association between single nucleotide polymorphisms (SNPs) in glucagon-like peptide-1 receptor (GLP-1R) and PMOP in postmenopausal Chinese women. However, available evidence remains inconclusive. Therefore, this study aimed to investigate the possible association between GLP-1R SNPs and PMOP in Han Chinese women. Thus, we conducted a case-control study with 152 postmenopausal Han Chinese women aged 45-80 years, including 76 women with osteoporosis and 76 without osteoporosis. Seven SNPs of the GLP-1R were obtained from the National Center of Biotechnology Information and Genome Variation Server. We employed three genetic models to assess the association between GLP-1R genetic variants and osteoporosis in postmenopausal women, while also investigating SNP-SNP and SNP-environment interactions with the risk of PMOP. In this study, we selected seven GLP-1R SNPs (rs1042044, rs2268641, rs10305492, rs6923761, rs1126476, rs2268657, and rs2295006). Of these, the minor allele A of rs1042044 was significantly associated with an increased risk of PMOP. Genetic model analysis revealed that individuals carrying the A allele of rs1042044 had a higher risk of developing osteoporosis in the dominant model (P = 0.029, OR = 2.76, 95%CI: 1.09-6.99). Furthermore, a multiplicative interaction was found between rs1042044 and rs2268641 that was associated with osteoporosis in postmenopausal women (Pinteraction = 0.034). Importantly, this association remained independent of age, menopausal duration, family history of osteoporosis, and body mass index. However, no significant relationship was observed between GLP-1R haplotypes and PMOP. In conclusion, this study suggests a close association between the A allele on the GLP-1R rs1042044 and an increased risk of PMOP. Furthermore, this risk was significantly augmented by an SNP-SNP interaction with rs2268641. These results provide new scientific insights into the development of personalized prevention strategies and treatment approaches for PMOP.

Effects of Incretin Therapy on Skeletal Health in Type 2 Diabetes-A Systematic Review

Diabetes poses a significant risk to bone health, with Type 1 diabetes (T1D) having a more detrimental impact than Type 2 diabetes (T2D). The group of hormones known as incretins, which includes gastric inhibitory peptide (GIP) and glucagon-like peptide 1 (GLP-1), play a role in regulating bowel function and insulin secretion during feeding. GLP-1 receptor agonists (GLP-1 RAs) are emerging as the primary treatment choice in T2D, particularly when atherosclerotic cardiovascular disease is present. Dipeptidyl peptidase 4 inhibitors (DPP-4is), although less potent than GLP-1 RAs, can also be used. Additionally, GLP-1 RAs, either alone or in combination with GIP, may be employed to address overweight and obesity. Since feeding influences bone turnover, a relationship has been established between incretins and bone health. To explore this relationship, we conducted a systematic literature review following the PRISMA guidelines. While some studies on cells and animals have suggested positive effects of incretins on bone cells, turnover, and bone density, human studies have yielded either no or limited and conflicting results regarding their impact on bone mineral density (BMD) and fracture risk. The effect on fracture risk may vary depending on the choice of comparison drug and the duration of follow-up, which was often limited in several studies. Nevertheless, GLP-1 RAs may hold promise for people with T2D who have multiple fracture risk factors and poor metabolic control. Furthermore, a potential new area of interest is the use of GLP-1 RAs in fracture prevention among overweight and obese people. Based on this systematic review, existing evidence remains insufficient to support a positive or a superior effect on bone health to reduce fracture risk in people with T2D. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

mTOR Signaling Pathway in Bone Diseases Associated with Hyperglycemia

The interplay between bone and glucose metabolism has highlighted hyperglycemia as a potential risk factor for bone diseases. With the increasing prevalence of diabetes mellitus worldwide and its subsequent socioeconomic burden, there is a pressing need to develop a better understanding of the molecular mechanisms involved in hyperglycemia-mediated bone metabolism. The mammalian target of rapamycin (mTOR) is a serine/threonine protein kinase that senses extracellular and intracellular signals to regulate numerous biological processes, including cell growth, proliferation, and differentiation. As mounting evidence suggests the involvement of mTOR in diabetic bone disease, we provide a comprehensive review of its effects on bone diseases associated with hyperglycemia. This review summarizes key findings from basic and clinical studies regarding mTOR's roles in regulating bone formation, bone resorption, inflammatory responses, and bone vascularity in hyperglycemia. It also provides valuable insights into future research directions aimed at developing mTOR-targeted therapies for combating diabetic bone diseases.

RANKL inhibition: a new target of treating diabetes mellitus?

Accumulating evidence demonstrates the link between glucose and bone metabolism. The receptor activator of nuclear factor-kB ligand (RANKL)/the receptor activator of NF-κB (RANK)/osteoprotegerin (OPG) axis is an essential signaling axis maintaining the balance between bone resorption and bone formation. In recent years, it has been found that RANKL and RANK are distributed not only in bone but also in the liver, muscle, adipose tissue, pancreas, and other tissues that may influence glucose metabolism. Some scholars have suggested that the blockage of the RANKL signaling may protect islet β-cell function and prevent diabetes; simultaneously, there also exist different views that RANKL can improve insulin resistance through inducing the beige adipocyte differentiation and increase energy expenditure. Currently, the results of the regulatory effect on glucose metabolism of RANKL remain conflicting. Denosumab (Dmab), a fully human monoclonal antibody that can bind to RANKL and prevent osteoclast formation, is a commonly used antiosteoporosis drug. Recent basic studies have found that Dmab seems to regulate glucose homeostasis and β-cell function in humanized mice or in vitro human β-cell models. Besides, some clinical data have also reported the glucometabolic effects of Dmab, however, with limited and inconsistent results. This review mainly describes the impact of the RANKL signaling pathway on glucose metabolism and summarizes clinical evidence that links Dmab and DM to seek a new therapeutic strategy for diabetes.

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.

GLP-1 receptor agonist as a modulator of innate immunity

Glucagon-like peptide-1 (GLP-1) is a 30-amino acid hormone secreted by L cells in the distal ileum, colon, and pancreatic α cells, which participates in blood sugar regulation by promoting insulin release, reducing glucagon levels, delaying gastric emptying, increasing satiety, and reducing appetite. GLP-1 specifically binds to the glucagon-like peptide-1 receptor (GLP-1R) in the body, directly stimulating the secretion of insulin by pancreatic β-cells, promoting proliferation and differentiation, and inhibiting cell apoptosis, thereby exerting a glycemic lowering effect. The glycemic regulating effect of GLP-1 and its analogues has been well studied in human and murine models in the circumstance of many diseases. Recent studies found that GLP-1 is able to modulate innate immune response in a number of inflammatory diseases. In the present review, we summarize the research progression of GLP-1 and its analogues in immunomodulation and related signal pathways.

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.

Transfer RNAs-derived small RNAs and their application potential in multiple diseases

The role of tRNAs is best known as adapter components of translational machinery. According to the central dogma of molecular biology, DNA is transcribed to RNA and in turn is translated into proteins, in which tRNA outstands by its role of the cellular courier. Recent studies have led to the revision of the canonical function of transfer RNAs (tRNAs), which indicates that tRNAs also serve as a source for short non-coding RNAs called tRNA-derived small RNAs (tsRNAs). tsRNAs play key roles in cellular processes by modulating complicated regulatory networks beyond translation and are widely involved in multiple diseases. Herein, the biogenesis and classification of tsRNAs were firstly clarified. tsRNAs are generated from pre-tRNAs or mature tRNAs and are classified into tRNA-derived fragments (tRFs) and tRNA halves (tiRNA). The tRFs include five types according to the incision loci: tRF-1, tRF-2, tRF-3, tRF-5 and i-tRF which contain 3′ tiRNA and 5′ tiRNA. The functions of tsRNAs and their regulation mechanisms involved in disease processes are systematically summarized as well. The mechanisms can elaborate on the specific regulation of tsRNAs. In conclusion, the current research suggests that tsRNAs are promising targets for modulating pathological processes, such as breast cancer, ischemic stroke, respiratory syncytial virus, osteoporosis and so on, and maintain vital clinical implications in diagnosis and therapeutics of various diseases.

Network pharmacology and molecular docking approach to elucidate the mechanisms of Liuwei Dihuang pill in diabetic osteoporosis

Background

Diabetic osteoporosis (DOP) is one of the chronic complications of diabetes mellitus, but without a standardized treatment plan till now. Liuwei Dihuang pill (LDP) has gradually exerted a remarkable effect on DOP in recent years; its specific mechanism is not clear yet.

Methods

We adopted network pharmacology approaches, including multi-database search, pharmacokinetic screening, network construction analysis, gene ontology enrichment analysis, Kyoto Encyclopedia of Genes and Genomes pathway analysis and molecular docking to elaborate the active components, signaling pathways and potential mechanisms of LDP in the treatment of DOP.

Results

Twenty-seven active ingredients and 55 related disease targets have been found through integrated network pharmacology. Functional enrichment analysis shows that five key active ingredients, including beta-sitosterol, stigmasterol, diosgenin, tetrahydroalstonine, and kadsurenone, may give full scope to insulin secretion estrogen-level raising and angiogenesis in biological process through the pivotal targets. In addition, the underlying effect of PI3K/AKT/FOXO and VEGF pathways is also suggested in the treatment.

Conclusion

Based on systematic network pharmacology methods, we predicted the basic pharmacological effects and potential mechanisms of LDP in the treatment of DOP, revealing that LDP may treat DOP through multiple targets and multiple signaling pathways, which provide evidence for the further study of pharmacological mechanism and broader clinical thinking.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13018-022-03194-2.

The therapeutic potential of GLP-1 receptor biased agonism

Glucagon-like peptide-1 (GLP-1) receptor agonists are effective treatments for type 2 diabetes as they stimulate insulin release and promote weight loss through appetite suppression. Their main side effect is nausea. All approved GLP-1 agonists are full agonists across multiple signalling pathways. However, selective engagement with specific intracellular effectors, or biased agonism, has been touted as a means to improve GLP-1 agonists therapeutic efficacy. In this review, I critically examine how GLP-1 receptor-mediated intracellular signalling is linked to physiological responses and discuss the implications of recent studies investigating the metabolic effects of biased GLP-1 agonists. Overall, there is little conclusive evidence that beneficial and adverse effects of GLP-1 agonists are attributable to distinct, nonoverlapping signalling pathways. Instead, G protein-biased GLP-1 agonists appear to achieve enhanced anti-hyperglycaemic efficacy by avoiding GLP-1 receptor desensitisation and downregulation, partly via reduced β-arrestin recruitment. This effect seemingly applies more to insulin release than to appetite regulation and nausea, possible reasons for which are discussed. At present, most evidence derives from cellular and animal studies, and more human data are required to determine whether this approach represents a genuine therapeutic advance. LINKED ARTICLES: This article is part of a themed issue on GLP1 receptor ligands (BJP 75th Anniversary). To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.4/issuetoc.

The Multiple Biological Functions of Dipeptidyl Peptidase-4 in Bone Metabolism

Dipeptidyl peptidase-4 (DPP4) is a ubiquitously occurring protease involved in various physiological and pathological processes ranging from glucose homeostasis, immunoregulation, inflammation to tumorigenesis. Recently, the benefits of DPP4 inhibitors as novel hypoglycemic agents on bone metabolism have attracted extensive attraction in many studies, indicating that DPP4 inhibitors may regulate bone homeostasis. The effects of DPP4 on bone metabolism are still unclear. This paper thoroughly reviews the potential mechanisms of DPP4 for interaction with adipokines, bone cells, bone immune cells, and cytokines in skeleton system. This literature review shows that the increased DPP4 activity may indirectly promote bone resorption and inhibit bone formation, increasing the risk of osteoporosis. Thus, bone metabolic balance can be improved by decreasing DPP4 activities. The substantial evidence collected and analyzed in this review supports this implication.

Challenges to Improve Bone Healing Under Diabetic Conditions

Diabetes mellitus (DM) can affect bone metabolism and the bone microenvironment, resulting in impaired bone healing. The mechanisms include oxidative stress, inflammation, the production of advanced glycation end products (AGEs), etc. Improving bone healing in diabetic patients has important clinical significance in promoting fracture healing and improving bone integration. In this paper, we reviewed the methods of improving bone healing under diabetic conditions, including drug therapy, biochemical cues, hyperbaric oxygen, ultrasound, laser and pulsed electromagnetic fields, although most studies are in preclinical stages. Meanwhile, we also pointed out some shortcomings and challenges, hoping to provide a potential therapeutic strategy for accelerating bone healing in patients with diabetes.

Curculigoside Ameliorates Bone Loss by Influencing Mesenchymal Stem Cell Fate in Aging Mice

Senile osteoporosis is characterized by increased bone loss and fat accumulation in marrow. Curculigoside (CCG) is the major bioactive component of Curculigo orchioides, which has been used as anti-osteoporosis therapy for elder patients since antiquity. We aimed to investigate the underlying mechanisms by which CCG regulated the bone-fat balance in marrow of aging mice. In our study, CCG treatment was identified to interfere with the stem cell lineage commitment both in vivo and in vitro. In vivo, CCG promoted the transcriptional co-activator with PDZ-binding motif (TAZ) expression to reverse age-related bone loss and marrow adiposity. In vitro, proper concentration of CCG upregulated TAZ expression to increase osteogenesis and decrease adipogenesis of bone marrow mesenchymal stem cells (BMSCs). This regulating effect was discounted by TAZ knockdown or the use of MEK-ERK pathway inhibitor, UO126. Above all, our study confirmed the rescuing effects of CCG on the differential shift from adipogenesis to osteogenesis of BMSCs in aging mice and provided a scientific basis for the clinical use of CCG in senile osteoporosis.

Metabolomic biomarkers of low BMD: a systematic review

Due to the metabolic nature of osteoporosis, this study was conducted to identify metabolomic studies investigating the metabolic profile of low bone mineral density (BMD) and osteoporosis. A comprehensive systematic literature search was conducted through PubMed, Web of Science, Scopus, and Embase databases up to April 08, 2020, to identify observational studies with cross-sectional or case-control designs investigating the metabolic profile of low BMD in adults using biofluid specimen via metabolomic platform. The quality assessment panel specified for the "omics"-based diagnostic research (QUADOMICS) tool was used to estimate the methodologic quality of the included studies. Ten untargeted and one targeted approach metabolomic studies investigating biomarkers in different biofluids through mass spectrometry or nuclear magnetic resonance platforms were included in the systematic review. Some metabolite panels, rather than individual metabolites, showed promising results in differentiating low BMD from normal. Candidate metabolites were of different categories including amino acids, followed by lipids and carbohydrates. Besides, certain pathways were suggested by some of the studies to be involved. This systematic review suggested that metabolic profiling could improve the diagnosis of low BMD. Despite valuable findings attained from each of these studies, there was great heterogeneity regarding the ethnicity and age of participants, samples, and the metabolomic platform. Further longitudinal studies are needed to validate the results and confirm the predictive role of metabolic profile on low BMD and fracture. It is also mandatory to address and minimize the heterogeneity in future studies by using reliable quantitative methods. Summary: Due to the metabolic nature of osteoporosis, researchers have considered metabolomic studies recently. This systematic review showed that metabolic profiling including different categories of metabolites could improve the diagnosis of low BMD. However, great heterogeneity was observed and it is mandatory to address and minimize the heterogeneity in future studies.

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.

The Impact of Glucagon-Like Peptide 1 Receptor Agonists on Bone Metabolism and Its Possible Mechanisms in Osteoporosis Treatment

Diabetes mellitus and osteoporosis are closely related and have complex influencing factors. The impact of anti-diabetic drugs on bone metabolism has received more and more attention. Type 2 diabetes mellitus (T2DM) would lead to bone fragility, high risk of fracture, poor bone repair and other bone-related diseases. Furthermore, hypoglycemic drugs used to treat T2DM may have notable detrimental effects on bones. Thus, the clinically therapeutic strategy for T2DM should not only effectively control the patient's glucose levels, but also minimize the complications of bone metabolism diseases. Glucagon-like peptide-1 receptor agonists (GLP-1RAs) are novel and promising drug for the treatment of T2DM. Some studies have found that GLP-1RAs may play an anti-osteoporotic effect by controlling blood sugar levels, promoting bone formation and inhibiting bone resorption. However, in clinical practice, the specific effects of GLP-1RA on fracture risk and osteoporosis have not been clearly defined and evidenced. This review summarizes the current research findings by which GLP-1RAs treatment of diabetic osteoporosis, postmenopausal osteoporosis and glucocorticoid-induced osteoporosis and describes possible mechanisms, such as GLP-1R/MAPK signaling pathway, GLP-1R/PI3K/AKT signaling pathway and Wnt/β-catenin pathway, that are associated with GLP-1RAs and osteoporosis. The specific role and related mechanisms of GLP-1RAs in the bone metabolism of patients with different types of osteoporosis need to be further explored and clarified.

Improvement of cognitive function, glucose and lipid homeostasis and serum osteocalcin levels by liraglutide in diabetic rats

BACKGROUND

Glucose and lipid abnormalities, oxidative stress (OXS) and reduced brain-derived neurotrophic factor (BDNF) are involved in cognitive dysfunction in diabetes. Glucagon like peptide 1 (GLP1) receptors modulate glucose and lipid metabolism, cognitive function and serum osteocalcin. On the other hand, osteocalcin modulates cognitive function and glucose and lipid metabolism. This study investigated whether the GLP 1 agonist liraglutide improves cognitive function via modulation of serum osteocalcin and glucose and lipid metabolism.

METHODS

Effects of 4 weeks liraglutide treatment (100 µg/Kg/d and 300 µg/Kg/d) on changes in cognitive function and bone homeostasis, induced by high fat diet/low-dose streptozotocin (HFD-STZ), were determined in rats. Cognitive function was assessed using Morris water maze (MWM) test. Serum and bone biochemical parameters were determined.

RESULTS

Liraglutide dose-dependently improved cognitive function in diabetic rats (reduced escape latency, and increased time spent in target quadrant in MWM test, compared to diabetic control). Glucose and lipid abnormalities and the associated changes in serum BDNF and oxidative stress makers were improved. Serum BDNF and glutathione were significantly increased, whereas malondialdehyde level was reduced. Serum osteocalcin was significantly increased and correlated with improvement in cognitive dysfunction. Serum and bone receptor activator of nuclear factor κB ligand (RANKL)/osteoprotegerin ratios were significantly reduced by liraglutide treatment.

CONCLUSION

Improvement of cognitive dysfunction by liraglutide involves modulation of glucose and lipid metabolism and serum osteocalcin. GLP1 agonists may provide an alternative metabolic approach for cognitive dysfunction in diabetes.

Liraglutide Protects Nucleus Pulposus Cells Against High-Glucose Induced Apoptosis by Activating PI3K/Akt/ mTOR/Caspase-3 and PI3K/Akt/GSK3β/Caspase-3 Signaling Pathways

Background and Objective: Diabetes mellitus (DM) is reportedly a significant risk factor for intervertebral disc degeneration (IDD). Incretin system and particularly glucagon-like peptide 1 (GLP-1) because of its glucose-lowering effects has become an important target in therapeutic strategies of type 2 diabetes (T2D). Liraglutide is a GLP-1 receptor (GLP-1R) agonist with glucoregulatory and insulinotropic functions as well as regulatory functions on cell proliferation, differentiation, and apoptosis. However, little is known on the roles and signaling pathways of apoptosis protecting effects of liraglutide in IDD. This study aimed to investigate the potential protective effects of liraglutide against high glucose-induced apoptosis of nucleus pulposus cells (NPCs) and the possible involved signaling pathways.

Methods: The human NPCs were incubated with 100 nM liraglutide alone or in combination with LY294002 (PI3K inhibitor), rapamycin (mTOR inhibitor), and SB216763 (GSK3β inhibitor) in a high glucose culture for 48 h. The four groups were assessed further for apoptosis and genes expressions. The apoptotic effect was evaluated by flow cytometry and further confirmed by cell death detection enzyme-linked immunoassay plus (ELISAPLUS). The gene and protein expression levels were assessed by quantitative real-time polymerase chain reaction (qRT-PCR) and Western blotting techniques. The results were comparatively assessed between the four groups.

Results: The results confirmed the presence of GLP-1R in the NPCs indicating that liraglutide inhibited the high glucose-induced apoptosis, which was blocked by silencing GLP-1R with siRNA. Moreover, liraglutide stimulated the phosphorylation of Akt, mTOR and GSK3β. Treatment with LY294002 significantly increased the apoptosis of NPCs and reduced the levels of their downstream substrates (p-AKT, p-mTOR, and p-GSK3β). Further assessments revealed that activation of mTOR and GSK3β was almost completely inhibited by rapamycin and SB216763, respectively, which significantly increased the caspase-3 levels.

Conclusion: Liraglutide could protect NPCs against high glucose-induced apoptosis by activating the PI3K/AKT/mTOR/caspase-3 and PI3K/AKT/GSK3β/caspase-3 signaling pathways.

Methylation-mediated down-regulation of microRNA-497-195 cluster confers osteogenic differentiation in ossification of the posterior longitudinal ligament of the spine via ADORA2A

Aberrant expression of microRNAs (miRNAs) has been associated with spinal ossification of the posterior longitudinal ligament (OPLL). Our initial bioinformatic analysis identified differentially expressed ADORA2A in OPLL and its regulatory miRNAs miR-497 and miR-195. Hence, this study was conducted to clarify the functional relevance of miR-497-195 cluster in OPLL, which may implicate in Adenosine A2A (ADORA2A). PLL tissues were collected from OPLL and non-OPLL patients, followed by quantification of miR-497, miR-195 and ADORA2A expression. The expression of miR-497, miR-195 and/or ADORA2A was altered in posterior longitudinal ligament (PLL) cells, which then were stimulated with cyclic mechanical stress (CMS). We validated that ADORA2A was expressed highly, while miR-497 and miR-195 were down-regulated in PLL tissues of OPLL patients. miR-195 and miR-497 expression in CMS-treated PLL cells was restored by a demethylation reagent 5-aza-2'-deoxycytidine (AZA). Moreover, expression of miR-195 and miR-497 was decreased by promoting promoter CpG island methylation. ADORA2A was verified as the target of miR-195 and miR-497. Overexpression of miR-195 and miR-497 diminished expression of osteogenic factors in PLL cells by inactivating the cAMP/PKA signaling pathway via down-regulation of ADORA2A. Collectively, miR-497-195 cluster augments osteogenic differentiation of PLL cells by inhibiting ADORA2A-dependent cAMP/PKA signaling pathway.

Liraglutide suppresses production of extracellular matrix proteins and ameliorates renal injury of diabetic nephropathy by enhancing Wnt/β-catenin signaling

The Wnt/β-catenin signaling pathway is involved in production of the extracellular matrix (ECM) by mesangial cells (MCs). Recent studies by us and others have demonstrated that glucagon-like peptide-1 receptor agonists (GLP-1RAs) have protective effects against diabetic nephropathy. The purpose of the present study was to investigate whether the Wnt/β-catenin signaling in MCs contributes to GLP-1RA-induced inhibition of ECM accumulation and mitigation of glomerular injury in diabetic nephropathy. In cultured human mesangial cells, liraglutide (a GLP-1RA) treatment significantly reduced high glucose (HG)-stimulated production of fibronectin, collagen type IV, and α-smooth muscle actin, and the liraglutide effects were significantly attenuated by XAV-939, a selective inhibitor of Wnt/β-catenin signaling. Furthermore, HG treatment significantly decreased protein abundance of Wnt4, Wnt5a, phospho-glycogen synthase kinase-3β, and β-catenin. These HG effects on Wnt/β-catenin signaling proteins were significantly blunted by liraglutide treatment. For in vivo experiments, we administered liraglutide (200 μg·kg^-1·12 h^-1) by subcutaneous injection to streptozocin-induced type 1 diabetic rats for 8 wk. Administration of liraglutide significantly improved elevated blood urine nitrogen, serum creatinine, and urinary albumin excretion rate and alleviated renal hypertrophy, mesangial expansion, and glomerular fibrosis in type 1 diabetic rats, whereas blood glucose level and body weight did not have significant changes. Consistent with the in vitro experiments, liraglutide treatment significantly reduced the diabetes-induced increases in glomerular fibronectin, collagen type IV, and α-smooth muscle actin and decreases in glomerular Wnt/β-catenin signaling proteins. These results suggest that liraglutide alleviated glomerular ECM accumulation and renal injury in diabetic nephropathy by enhancing Wnt/β-catenin signaling.

Liraglutide, a glucagon-like peptide-1 receptor agonist, suppresses osteoclastogenesis through the inhibition of NF-κB and MAPK pathways via GLP-1R

Bone disorders such as osteoporosis, Paget's disease of the bone, osteogenesis imperfecta, are caused by the uncoordinated action of osteoclasts and osteoblasts. Inhibiting osteoclastogenesis and suppressing the resorptive function of osteoclasts might become a gold standard strategy for treating this kind of disease. Glucagon-like peptide-1 (GLP-1) and its receptor agonist have been reported to have protective effects on bone. Little is known about the effect of GLP-1 on osteoclasts. Therefore, we investigated the effects of liraglutide, a GLP-1 receptor agonist, on murine bone marrow-derived macrophage (BMM) and RAW264.7 preosteoclast differentiation and explored the potential cellular basis of its action. In this study, we confirmed the presence of GLP-1 receptor (GLP-1R) on BMMs and RAW264.7 cells and demonstrated that GLP-1R might be important for osteoclastogenesis by increasing the expression of osteoclastogenic biomarkers after GLP-1R knockdown. In addition, we found that liraglutide treatment of both BMMs and RAW264.7 cells could inhibit osteoclast formation and bone resorption. Mechanistically, Western blotting and RT-PCR showed that liraglutide inhibited the NF-κB and MAPK signalling pathways, ultimately inhibiting the expression of nuclear factor of activated T cells (NFATc1). In addition, knocking down GLP-1R reversed the inhibitory effect of liraglutide on NF-κB/MAPK-NFATc1. Overall, these results indicated a potential therapeutic effect of liraglutide on bone disorders.

Bone resorption is unchanged by liraglutide in type 2 diabetes patients: A randomised controlled trial

BACKGROUND

Liraglutide, a glucagon-like peptide-1 receptor agonist, has well known beneficial effects on glucose metabolism, and animal studies indicate that liraglutide also affects bone turnover by decreasing bone resorption. The primary objective of the study was to investigate the effect of liraglutide on bone turnover in patients with T2D.

METHODS

The study was a randomized, double-blinded, clinical trial. Sixty participants with T2D were randomized to treatment with liraglutide 1.8 mg daily or placebo for 26 weeks. The primary endpoint was change in p-collagen I cross-linked C-terminal telopeptide (p-CTX).

RESULTS

P-CTX increased in patients treated with liraglutide by 0.07 (0.03; 0.10) μg/L (p < 0.001) and in patients treated with placebo by 0.03 (0.00; 0.06) μg/L (p = 0.04), however, changes were not different between the groups (p = 0.16). Weight decreased in patients treated with liraglutide from baseline to week four (p < 0.001) and remained stable thereafter. P-procollagen type 1 N-terminal propeptide (P1NP) decreased in patients treated with liraglutide from baseline to week four (p < 0.01), increased between weeks 4 and 13 (p = 0.03), and remained elevated thereafter. Weight and p-P1NP did not change in patients treated with placebo. Hip bone mineral density (BMD) decreased in placebo treated patients from baseline to end of study, whereas no changes were seen in patients treated with liraglutide (p = 0.01 difference between groups).

CONCLUSION

Liraglutide treatment for 26 weeks did not affect bone resorption and preserved hip BMD despite weight loss in patients with T2D, suggesting that liraglutide has some antiresorptive effect.

Association between bile acid metabolism and bone mineral density in postmenopausal women

OBJECTIVES

Previous studies have not shown any correlation between bile acid metabolism and bone mineral density (BMD) in women with postmenopausal osteoporosis. Thus, the current study evaluated the association between bile acid levels as well as BMD and bone turnover marker levels in this group of women.

METHODS

This single-center cross-sectional study included 150 postmenopausal Chinese women. According to BMD, the participants were divided into three groups: osteoporosis group, osteopenia group, and healthy control group. Serum bile acid, fibroblast growth factor 19 (FGF19), and bone turnover biomarker levels were assessed. Moreover, the concentrations of parathyroid hormone, 25-hydroxy vitamin D [25(OH)D], procollagen type I N-peptide (P1NP), and beta-CrossLaps of type I collagen containing cross-linked C-terminal telopeptide (β-CTX) were evaluated. The BMD of the lumbar spine and proximal femur were examined via dual-energy X-ray absorptiometry.

RESULTS

The serum total bile acid levels in the osteoporosis and osteopenia groups (5.28±1.56 and 5.31±1.56 umol/L, respectively) were significantly lower than that in the healthy control group (6.33±2.04 umol/L; p=0.002 and 0.018, respectively). Serum bile acid level was positively associated with the BMD of the lumbar spine, femoral neck, and total hip. However, it negatively correlated with β-CTX concentration. Moreover, no correlation was observed between bile acid and P1NP levels, and the levels of the other biomarkers that were measured did not differ between the groups.

CONCLUSION

Serum bile acid was positively correlated with BMD and negatively correlated with bone turnover biomarkers reflecting bone absorption in postmenopausal women. Thus, bile acid may play an important role in bone metabolism.

Liraglutide Promotes Osteoblastic Differentiation in MC3T3-E1 Cells by ERK5 Pathway

Liraglutide is a glucagon-like peptide-1 analogue widely used in the treatment of type 2 diabetes mellitus. However, the effects of liraglutide on osteoblast proliferation and differentiation in MC3T3-E1 cells have not been fully elucidated. In the present study, the promoting effects of liraglutide were investigated in MC3T3-E1 cells. The results indicated that cell viability was affected following the treatment of the cells with different concentrations of liraglutide (0, 10, 100, and 1000 nM) at different time periods of culture (24, 48, and 72 h). Moreover, the activity levels of alkaline phosphatase and the number of mineralized nodules in MC3T3-E1 cells were significantly increased following treatment with 100 nM liraglutide. The mRNA and protein levels of Col-1, OPG, and OCN in MC3T3-E1 cells were also markedly increased following 100 nM liraglutide treatment compared with those of the control group. The expression levels of the ERK5 signaling pathway key proteins (MEK5, p-ERK5, ERK5, and NUR77) were increased following liraglutide treatment in MC3T3-E1 cells, and the gene expression levels of the ERK5 signaling pathway were also elevated. Moreover, the ERK5 inhibitor XMD8-92 significantly decreased the expression levels of p-ERK5 and NUR77 as well as the proliferation of osteoblasts. However, these changes could be rescued by liraglutide to some extent. Therefore, these results revealed that liraglutide may promote osteoblastic differentiation and proliferation in MC3T3-E1 cells via the activation of the ERK5 signaling pathway.

The Interplay Between Bone and Glucose Metabolism

The multiple endocrine functions of bone other than those related to mineral metabolism, such as regulation of insulin sensitivity, glucose homeostasis, and energy metabolism, have recently been discovered. In vitro and murine studies investigated the impact of several molecules derived from osteoblasts and osteocytes on glucose metabolism. In addition, the effect of glucose on bone cells suggested a mutual cross-talk between bone and glucose homeostasis. In humans, these mechanisms are the pivotal determinant of the skeletal fragility associated with both type 1 and type 2 diabetes. Metabolic abnormalities associated with diabetes, such as increase in adipose tissue, reduction of lean mass, effects of hyperglycemia per se, production of the advanced glycation end products, diabetes-associated chronic kidney disease, and perturbation of the calcium-PTH-vitamin D metabolism, are the main mechanisms involved. Finally, there have been multiple reports of antidiabetic drugs affecting the skeleton, with differences among basic and clinical research data, as well as of anti-osteoporosis medication influencing glucose metabolism. This review focuses on the aspects linking glucose and bone metabolism by offering insight into the most recent evidence in humans.

Alanyl-glutamine Heals Indomethacin-induced Gastric Ulceration in Rats Via Antisecretory and Anti-apoptotic Mechanisms

OBJECTIVES

Alanylglutamine (AG) is a dipeptide that fuels enterocytes and has a coadjuvant role during gut healing. The current study aimed to investigate the potential ulcer-healing effect of AG in indomethacin-induced gastropathy.

METHODS

Animals (n = 10 rats/group) were randomly allocated into 5 groups. Gastric ulcerated rats were administered AG, AG + dexamethasone, or pantoprazole after indomethacin exposure.

RESULTS

Comparable to pantoprazole, AG inhibited H-KATPase pump, and elevated the pH of gastric juice. Moreover, the dipeptide increased the serum/mucosal contents of glucagon-like peptide-1 (GLP-1), pS473-Akt, and cyclin-D1. On the contrary, AG abated serum tumor necrosis factor-α and gastric mucosal content of pS45-β catenin, pS9-GSK3β, pS133-CREB, pS536-NF-κB, H2O2, claudin-1, and caspase-3. The administration of dexamethasone before AG hampered its effect on almost all the measured parameters.

CONCLUSIONS

AG confers its antiulcerogenic/antisecretory potentials by repressing the proton pump to increase the gastric juice pH via boosting p-CREB, p-Akt, p-GSK-3β, and GLP-1. Also, it inhibits apoptosis through suppressing nuclear factor-kappa B/tumor necrosis factor-α/H2O2/claudin-1 cue. This trajectory contributes to loosen the tight junction priming AG-mediated GLP-1/β-catenin/cyclin-D1 that results in pronounced increase in gastric mucosa proliferation. Therefore, the crosstalk between multiple pathways orchestrates the action of AG against gastric ulceration.

Brain-derived neurotrophic factor stimulation of T-type Ca2+ channels in sensory neurons contributes to increased peripheral pain sensitivity

Although brain-derived neurotrophic factor (BDNF) is implicated in the nociceptive signaling of peripheral sensory neurons, the underlying mechanisms remain largely unknown. Here, we elucidated the effects of BDNF on the neuronal excitability of trigeminal ganglion (TG) neurons and the pain sensitivity of rats mediated by T-type Ca2+ channels. BDNF reversibly and dose-dependently enhanced T-type channel currents through the activation of tropomyosin receptor kinase B (TrkB). Antagonism of phosphatidylinositol 3-kinase (PI3K) but not of its downstream target, the kinase AKT, abolished the BDNF-induced T-type channel response. BDNF application activated p38 mitogen-activated protein kinase (MAPK), and this effect was prevented by inhibition of PI3K but not of protein kinase A (PKA). Antagonism of either PI3K or p38 MAPK prevented the BDNF-induced stimulation of PKA activity, whereas PKA inhibition blocked the BDNF-mediated increase in T-type currents. BDNF increased the rate of action potential firing in TG neurons and enhanced the pain sensitivity of rats to mechanical stimuli. Moreover, inhibition of TrkB signaling abolished the increased mechanical sensitivity in a rat model of chronic inflammatory pain, and this effect was attenuated by either T-type channel blockade or knockdown of the channel Cav3.2. Together, our findings indicate that BDNF enhances T-type currents through the stimulation of TrkB coupled to PI3K-p38-PKA signaling, thereby inducing neuronal hyperexcitability of TG neurons and pain hypersensitivity in rats.

Geniposide Alleviates Glucocorticoid-Induced Inhibition of Osteogenic Differentiation in MC3T3-E1 Cells by ERK Pathway

Glucocorticoid (GC) therapy is the leading cause of secondary osteoporosis and the therapeutic and preventative drugs for GC-induced osteoporosis are limited. In this study, we investigated the protective effects of geniposide on dexamethasone (DEX)-induced osteogenic inhibition in MC3T3-E1 cells. The results showed that there was no obvious toxicity on MC3T3-E1 cells when geniposide was used at the doses ranging from 1 to 75 μM. In DEX-treated MC3T3-E1 cells, geniposide promoted the alkaline phosphatase (ALP) activity and the mineralization. In addition, geniposide also significantly increased the mRNA and protein expression of osteopontin (OPN), Runt-related transcription factor 2 (Runx2), and Osterix (Osx) in DEX-treated MC3T3-E1 cells. Furthermore, geniposide activated ERK pathway in DEX-treated MC3T3-E1 cells. The ERK activation inhibitor U0126 and glucagon-like peptide-1 (GLP-1) receptor antagonist exendin 9-39 abolished the geniposide-induced activation of ERK and inhibited the protective effect of geniposide. Taken together, our study revealed that geniposide alleviated GC-induced osteogenic suppression in MC3T3-E1 cells. The effect of geniposide was at least partially associated with activating ERK signaling pathway via GLP-1 receptor. Geniposide might be a potential therapeutic agent for GC-induced osteoporosis.

Wound Healing Potential of Spirulina Protein on CCD-986sk Cells

Wound healing is a dynamic and complex process. The proliferation and migration of dermal fibroblasts are crucial for wound healing. Recent studies have indicated that the extracts from Spirulina platensis have a positive potential for wound healing. However, its underlying mechanism is not fully understood. Our previous study showed that spirulina crude protein (SPCP) promoted the viability of human dermal fibroblast cell line (CCD-986sk cells). In this study, we further investigated the wound healing effect and corresponding mechanisms of SPCP on CCD-986sk cells. Bromodeoxyuridine (BrdU) assay showed that SPCP promoted the proliferation of CCD-986sk cells. The wound healing assay showed that SPCP promoted the migration of CCD-986sk cells. Furthermore, cell cycle analysis demonstrated that SPCP promoted CCD-986sk cells to enter S and G₂/M phases from G₀/G₁ phase. Western blot results showed that SPCP significantly upregulated the expression of cyclin D1, cyclin E, cyclin-dependent kinase 2 (Cdk2), cyclin-dependent kinase 4 (Cdk4), and cyclin-dependent kinase 6 (Cdk6), as well as inhibited the expression of CDK inhibitors p21 and p27 in CCD-986sk cells. In the meanwhile, SPCP promoted the phosphorylation and activation of phosphoinositide 3-kinase (PI3K) and protein kinase B (Akt). However, the phosphorylation of Akt was significantly blocked by PI3K inhibitor (LY294002), which in turn reduced the SPCP-induced proliferation and migration of CCD-986sk cells. Therefore, the results presenting in this study suggested that SPCP can promote the proliferation and migration of CCD-986sk cells; the PI3K/Akt signaling pathway play a positive and important role in these processes.

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.

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.

Glucagon-like peptide-1 analogue liraglutide facilitates wound healing by activating PI3K/Akt pathway in keratinocytes

AIMS

Diabetes induces various skin troubles including foot ulcer. This type of skin ulcer is refractory but the pathogenesis is not so certain. Recent study show that glucagon-like peptide-1 (GLP-1) analogues reduce foot complications with diabetes (Pérez et al., 2015), however, the role of GLP-1/GLP-1R axis is not fully understood, and clear evidence of GLP-1 to facilitate wound closure is still lacking. In this study, we investigated whether a potent GLP-1R agonist liraglutide affects wound healing process.

METHODS

The expression of GLP-1R in HaCaT cells were indentified by quantitative reverse-transcription polymerase chain reaction (qRT-PCR) and immunoblotting analysis. To assess the effect on wound closure in keratinocytes, we performed in vitro scratch assay using the IncuCyte system (Essen BioSciences, Ann Arborm MI). We applied ointment containing liraglutide on full-thickness wounds in the dorsum of female balb/c mice (n = 6) until healing. To investigate the effect on PI3K/Akt pathway, we used IncuCyte system in HaCaT treated with PI3K inhibitor and Akt inhibitor.

RESULTS

Keratinocytes expressed GLP-1R and liraglutide induced their migration. Liraglutide facilitated the wound healing in mice. Liraglutide upregulated keratinocyte migration via PI3K/Akt activation.

CONCLUSIONS

Our study suggests that liraglutide may be a potential target drug to improve skin ulcer with diabetes through its specific receptor GLP-1.

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.

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.

Exenatide Improves Bone Quality in a Murine Model of Genetically Inherited Type 2 Diabetes Mellitus

Type 2 diabetes mellitus (T2DM) is associated with skeletal complications, including an increased risk of fractures. Reduced blood supply and bone strength may contribute to this skeletal fragility. We hypothesized that long-term administration of Exenatide, a glucagon-like peptide-1 receptor agonist, would improve bone architecture and strength of T2DM mice by increasing blood flow to bone, thereby stimulating bone formation. In this study, we used a model of obesity and severe T2DM, the leptin receptor-deficient db/db mouse to assess alterations in bone quality and hindlimb blood flow and to examine the beneficial effects of 4 weeks administration of Exenatide. As expected, diabetic mice showed marked alterations in bone structure, remodeling and strength, and basal vascular tone compared with lean mice. Exenatide treatment improved trabecular bone mass and architecture by increasing bone formation rate, but only in diabetic mice. Although there was no effect on hindlimb perfusion at the end of this treatment, Exenatide administration acutely increased tibial blood flow. While Exenatide treatment did not restore the impaired bone strength, intrinsic properties of the matrix, such as collagen maturity, were improved. The effects of Exenatide on in vitro bone formation were further investigated in primary osteoblasts cultured under high-glucose conditions, showing that Exenatide reversed the impairment in bone formation induced by glucose. In conclusion, Exenatide improves trabecular bone mass by increasing bone formation and could protect against the development of skeletal complications associated with T2DM.