Glimepiride induces proliferation and differentiation of rat osteoblasts via the PI3-kinase/Akt pathway

Arctiin attenuates iron overload‑induced osteoporosis by regulating the PI3K/Akt pathway

Iron overload is a prevalent pathological factor observed among elderly individuals and those with specific hematological disorders, and is frequently associated with an elevated incidence of osteoporosis. Although arctiin (ARC) has been shown to possess antioxidant properties and the ability to mitigate bone degeneration, its mechanism of action in the treatment of iron overload‑induced osteoporosis (IOOP) remains incompletely understood. To explore the potential molecular mechanisms underlying the effects of ARC, the MC3T3‑E1 cell osteoblast cell line was used. Cell Counting Kit was used to assess MC3T3‑E1 cell viability. Alkaline phosphatase staining and alizarin red staining were assessed for osteogenic differentiation. Calcein AM assay was used to assess intracellular iron concentration. In addition, intracellular levels of reactive oxygen species (ROS), lipid peroxides, mitochondrial ROS, apoptosis rate and mitochondrial membrane potential changes in MC3T3‑E1 cells were examined using flow cytometry and corresponding fluorescent dyes. The relationship between ARC and the PI3K/Akt pathway was then explored by western blotting and immunofluorescence. In addition, the effects of ARC on IOOP was verified using an iron overload mouse model. Immunohistochemistry was performed to evaluate expression of osteogenesis‑related proteins. Micro-CT and H&E were used to analyze bone microstructural parameters and histomorphometric indices in the bone tissue. Notably, ARC treatment reversed the decreased viability and increased apoptosis in MC3T3‑E1 cells originally induced by ferric ammonium citrate, whilst promoting the formation of mineralized bone nodules in MC3T3‑E1 cells. Furthermore, iron overload induced a decrease in the mitochondrial membrane potential, augmented lipid peroxidation and increased the accumulation of ROS in MC3T3‑E1 cells. ARC not only positively regulated the anti‑apoptotic and osteogenic capabilities of these cells via modulation of the PI3K/Akt pathway, but also exhibited antioxidant properties by reducing oxidative stress. In vivo experiments confirmed that ARC improved bone microarchitecture and biochemical parameters in a mouse model of iron overload. In conclusion, ARC exhibits potential as a therapeutic agent for IOOP by modulating the PI3K/Akt pathway, and via its anti‑apoptotic, antioxidant and osteogenic properties.

Glipizide Alleviates Periodontitis Pathogenicity via Inhibition of Angiogenesis, Osteoclastogenesis and M1/M2 Macrophage Ratio in Periodontal Tissue

New consensus indicates type 2 diabetes mellitus (T2DM) and periodontitis as comorbidity and may share common pathways of disease progression. Sulfonylureas have been reported to improve the periodontal status in periodontitis patients. Glipizide, a sulfonylurea widely used in the treatment of T2DM, has also been reported to inhibit inflammation and angiogenesis. The effect of glipizide on the pathogenicity of periodontitis, however, has not been studied. We developed ligature-induced periodontitis in mice and treated them with different concentrations of glipizide and then analyzed the level of periodontal tissue inflammation, alveolar bone resorption, and osteoclast differentiation. Inflammatory cell infiltration and angiogenesis were analyzed using immunohistochemistry, RT-qPCR, and ELISA. Transwell assay and Western bolt analyzed macrophage migration and polarization. 16S rRNA sequencing analyzed the effect of glipizide on the oral microbial flora. mRNA sequencing of bone marrow-derived macrophages (BMMs) stimulated by P. gingivalis lipopolysaccharide (Pg-LPS) after treatment with glipizide was analyzed. Glipizide decreases alveolar bone resorption, periodontal tissue degradation, and the number of osteoclasts in periodontal tissue affected by periodontitis (PAPT). Glipizide-treated periodontitis mice showed reduced micro-vessel density and leukocyte/macrophage infiltration in PAPT. Glipizide significantly inhibited osteoclast differentiation in vitro experiments. Glipizide treatment did not affect the oral microbiome of periodontitis mice. mRNA sequencing and KEGG analysis showed that glipizide activated PI3K/AKT signaling in LPS-stimulated BMMs. Glipizide inhibited the LPS-induced migration of BMMs but promoted M2/M1 macrophage ratio in LPS-induced BMMs via activation of PI3K/AKT signaling. In conclusion, glipizide inhibits angiogenesis, macrophage inflammatory phenotype, and osteoclastogenesis to alleviate periodontitis pathogenicity suggesting its' possible application in the treatment of periodontitis and diabetes comorbidity.

Iron metabolism and ferroptosis in diabetic bone loss: from mechanism to therapy

Osteoporosis, one of the most serious and common complications of diabetes, has affected the quality of life of a large number of people in recent years. Although there are many studies on the mechanism of diabetic osteoporosis, the information is still limited and there is no consensus. Recently, researchers have proven that osteoporosis induced by diabetes mellitus may be connected to an abnormal iron metabolism and ferroptosis inside cells under high glucose situations. However, there are no comprehensive reviews reported. Understanding these mechanisms has important implications for the development and treatment of diabetic osteoporosis. Therefore, this review elaborates on the changes in bones under high glucose conditions, the consequences of an elevated glucose microenvironment on the associated cells, the impact of high glucose conditions on the iron metabolism of the associated cells, and the signaling pathways of the cells that may contribute to diabetic bone loss in the presence of an abnormal iron metabolism. Lastly, we also elucidate and discuss the therapeutic targets of diabetic bone loss with relevant medications which provides some inspiration for its cure.

A narrative review of diabetic bone disease: Characteristics, pathogenesis, and treatment

Recently, the increasing prevalence of diabetes mellitus has made it a major chronic illness which poses a substantial threat to human health. The prevalence of osteoporosis among patients with diabetes mellitus has grown considerably. Diabetic bone disease is a secondary osteoporosis induced by diabetes mellitus. Patients with diabetic bone disease exhibit variable degrees of bone loss, low bone mineral density, bone microarchitecture degradation, and increased bone fragility with continued diabetes mellitus, increasing their risk of fracture and impairing their ability to heal after fractures. At present, there is extensive research interest in diabetic bone disease and many significant outcomes have been reported. However, there are no comprehensive review is reported. This review elaborates on diabetic bone disease in the aspects of characteristics, pathogenesis, and treatment.

Involvement of PI3K/Akt signaling pathway in promoting osteogenesis on titanium implant surfaces modified with novel non-thermal atmospheric plasma

Non-thermal atmospheric plasma (NTAP) modification to induce a hydrophilic titanium (Ti) surface with less carbon contamination, has been demonstrated to boost the osteogenic responses. In this study, we investigated the underlying bone formation mechanism of NTAP-Ti, and the involvement of PI3K/Akt signaling pathway in regulating osteogenic activities on NTAP-Ti surfaces. NTAP was employed for Ti activation, and PI3K inhibitor, LY294002, was applied to the suppression of PI3K/Akt pathway. We systematically and quantitatively detected the cell morphology, attachment, proliferation, osteogenic differentiation and mineralization of MC3T3-E1 mouse preosteoblasts, and molecular expressions involved in osteogenesis and PI3K/Akt signaling pathway in vivo and in vitro. A descent in osteoblast proliferation on Ti surfaces in relation to LY294002. Alkaline phosphatase (ALP) activity, as well as matrix mineralization, was mitigated by PI3K inhibitor in NTAP-Ti. Likewise, the expression levels of osteogenesis-related genes [ALP, osteocalcin (Ocn), osteopontin (Opn) and runt-related transcription factor 2 (Runx2)] on NTAP-Ti were notably attenuated by LY294002, as confirmed by the results of osteogenesis-related proteins (ALP, and Runx2) expression analysis. In addition, the expression of PI3K/Akt signal pathway proteins further verified the inhibition of LY294002 on Ti surfaces modified by NTAP. Collectively, the PI3K/Akt signal pathway was involved in the amelioration of osteogenesis induced by NTAP modification. NTAP treatment for Ti activation is promising in augmented osteogenic potential through the activation of PI3K/Akt signal pathway.

Conditional knockout of the PDK-1 gene in osteoblasts affects osteoblast differentiation and bone formation

Osteoblasts are the main functional cells of bone formation, and they are responsible for the synthesis, secretion, and mineralization of the bone matrix. Phosphatidylinositol-3-kinase/Akt is an important signaling pathway involved in the regulation of cell proliferation, death, and survival. Some studies have shown that 3-phosphoinositide-dependent protein kinase-1 (PDK-1) plays an important role in the phosphorylation of Akt. In the present study, an osteocalcin (OCN) promoter-driven Cre-LoxP system was established to specifically delete the PDK-1 gene in osteoblasts. It was found that the size and weight of PDK-1 conditional gene knockout (cKO) mice were significantly reduced. von Kossa staining and microcomputed tomography showed that the trabecular thickness, trabecular number, and bone volume were significantly decreased, whereas trabecular separation was increased, as compared with wide-type littermates, which were characterized by a decreased bone mass. A model of distal femoral defect was established, and it was found that cKO mice delayed bone defect repair. In osteoblasts derived from PDK-1 cKO mice, the alkaline phosphatase (ALP) secretion and ability of calcium mineralization were significantly decreased, and the expressions of osteoblast-related proteins, runt-related transcription factor 2, OCN, and ALP were also clearly decreased. Moreover, the phosphorylation level of Akt and downstream factor GSK3β and their response to insulin-like growth factor-1 (IGF-1) decreased clearly. Therefore, we believe that PDK-1 plays a very important role in osteoblast differentiation and bone formation by regulating the PDK-1/Akt/GSK3β signaling pathway.

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.

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.

An update on therapies for the treatment of diabetes-induced osteoporosis

Introduction: Currently, 424 million people aged between 20 and 79 years worldwide are diabetic. More than 25% of adults aged over 65 years in North America have Type 2 diabetes mellitus (DM). Diabetes-induced osteoporosis (DM-OS) is caused by chronic hyperglycemia, advanced glycated end products and oxidative stress. The increase in the prevalence of DM-OS has prompted researchers to develop new biological therapies for the management of DM-OS. Areas covered: This review covered the current and novel biological agents used in the management of DM-OS. Data were retrieved from PubMed, Scopus, American Diabetes Association and International Osteoporosis Foundation websites, and ClinicalTrials.gov. The keywords for the search included: DM, osteoporosis, and management. Expert opinion: Several biological molecules have been examined in order to find efficient drugs for the treatment of DM-OS. These biological agents include anti-osteoporosis drugs: net anabolics (parathyroid hormone/analogs, androgens, calcilytics, anti-sclerostin antibody), net anti-resorptive osteoporosis drugs (calcitonin, estrogen, selective estrogen receptor modulators, bisphosphonates, RANKL antibody) and anti-diabetic drugs (alpha glucosidase inhibitors, sulfonylureas, biguanides, meglitinides, thiazolidinediones, GLP-1 receptor agonists, dipeptidylpeptidase-4 inhibitors, sodium glucose co-transporter-2 inhibitors, insulin). Biological medications that effectively decrease hyperglycemia and, at the same time, maintain bone health would be an ideal drug/drug combination for the treatment of DM-OS.

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.

Dexamethasone induces osteoblast apoptosis through ROS-PI3K/AKT/GSK3β signaling pathway

BACKGROUND

Osteoblasts play important roles in the process of osteogenesis and prevention of osteonecrosis. Dexamethasone (Dex), a type of glucocorticoids (GCs), induces apoptosis of osteoblasts and leads to the occurrence of non-traumatic osteonecrosis. This study aimed to explore the effects of phosphatidylinositol 3-kinase/Protein kinase 3 (PI3K/AKT) and glycogen synthase kinase 3β (GSK3β) on Dex-induced osteoblasts apoptosis.

METHODS

Viabilities, proliferation, and apoptosis of primary osteoblasts and pre-osteoblast MC3T3-E1 cells after Dex treatment were detected using cell counting kit-8 (CCK-8) assay, 5-bromo-2'-deoxyuridine (BrdU) incorporation assay, FITC-Annexin V/PI staining and western blotting, respectively. 2',7'-Dichlorodihydrofluorescein diacetate (DCFH-DA) staining was performed to measure the intracellular reactive oxygen species (ROS) levels after Dex treatment. N-acetyl-l-cysteine (NAC) was used as ROS scavenger in this research. The expressions of PI3K/AKT and GSK3β in osteoblasts and MC3T3-E1 cells after Dex treatment were analyzed using western blotting and qRT-PCR, respectively. Then the effects of GSK3β knockdown on Dex-induced apoptosis of osteoblasts were explored. Alkaline phosphatase (ALP) activity assay was used to detect the role of Dex in regulating ALP activity.

RESULTS

Dex remarkably inhibited proliferation and induced apoptosis of osteoblasts and MC3T3-E1 cells. Dex potentially attenuated the osteoblast differentiation. The intracellular ROS levels were significantly increased after Dex treatment. Dex suppressed the activation of PI3K/AKT pathway in osteoblasts and MC3T3-E1 cells by down-regulating the expressions of p-PI3K and p-AKT. The expressions of GSK3β in osteoblasts and MC3T3-E1 cells were obviously up-regulated after Dex treatment. Knockdown of GSK3β alleviated Dex-induced osteoblast and MC3T3-E1 cell apoptosis by decreasing the expressions of Bax, cleaved-caspase 3, cleaved-caspase 9 and increasing the expression of Bcl-2.

CONCLUSION

Our research verified that Dex induced osteoblasts apoptosis by ROS-PI3K/AKT/GSK3β signaling pathway.

Influence of diabetes on tissue healing in orthopaedic injuries

Diabetes is a group of metabolic diseases characterized by hyperglycaemia resulting from the defective action or secretion of insulin. Chronic hyperglycaemia can lead to the damage, dysfunction and failure of various organs. In the context of complications of healing and orthopaedic rehabilitation, vascular (microangiopathy) and nerve (neuropathy) disorders deserve particular attention. About 12% of the patients admitted to orthopaedic departments have diabetes. Studies indicate that there is an indisputable link between diabetes and: an increased risk of fractures, the difficult healing of injuries of bones, ligaments and musculotendinous. It appears that one of the main reasons for this is non-enzymatic glycosylation (glycation) of collagen molecules, a phenomenon observed in the elderly and diabetic populations, as it leads to the formation of advanced glycation end products (AGEs). Collagen is one of the major connective tissue components, and is therefore part of ligaments, tendons and bones. AGEs affect the weakening of its structure and biomechanical properties, and thus also affects the weakening of the structure and properties of the above-mentioned tissues. The aim of the study is to undertake an overview of the current knowledge of the impact of diabetes on the risk of some injuries and subsequent healing and rehabilitation of patients following orthopaedic injuries.

Molecular Modulation of Osteoblasts and Osteoclasts in Type 2 Diabetes

Diabetes is a common disease affecting majority of populations worldwide. Since 1980, there has been an increase in the number of people diagnosed as prediabetic and diabetic. Diabetes is characterized by high levels of circulating glucose and leads to most microvascular and macrovascular complications such as retinopathy, nephropathy, neuropathy, stroke, and myocardial infarction. Bone marrow vascular disruption and increased adiposity are also linked to various complications in type II diabetes mellitus. In addition to these complications, type 2 diabetic patients also have fragile bones caused by faulty mineralization mainly due to increased adiposity among diabetic patients that affects both osteoblast and osteoclast functions. Other factors that increase fracture risk in diabetic patients are increased oxidative stress, inflammation, and drugs administered to diabetic patients. This review reports the modulation of different pathways that affect bone metabolism in diabetic conditions.

The effects of dipeptidyl peptidase-4 inhibitors on bone fracture among patients with type 2 diabetes mellitus: A network meta-analysis of randomized controlled trials

Aim

The association between dipeptidyl peptidase-4 inhibitors (DPP-4is), a class of anti-diabetes, and bone fracture in patients with type 2 diabetes mellitus (T2DM) is unknown. This meta-analysis aimed to systematically evaluate the effects of DPP-4is on bone fracture in T2DM patients.

Methods

We searched the Cochrane Library, Embase, Medline and ClinicalTrials.gov from inception through April 28th, 2016 to identify randomized controlled trials (RCTs) that compared DPP-4is with placebo or other anti-diabetes in T2DM patients. RCTs lasting more than 12 weeks and having data on bone fracture were included. We conducted random-effects meta-analysis to estimate odds ratios (ORs) and their 95% confidence intervals (CIs), and network meta-analysis (NMA) to supplement direct comparisons. Predictive interval plot and node-splitting method were used to evaluate the heterogeneity and inconsistency for NMA, while the funnel plot was applied to explore publication bias. Besides, study quality was assessed according to Cochrane risk of bias tool.

Results

We identified 75 RCTs with a total of 70,207 patients and 11 treatments: interventions included 5 DPP-4is (alogliptin, linagliptin, saxagliptin, sitagliptin, vildagliptin), while controls included placebo and 5 other anti-diabetes (sulfonylureas, glucagon-like peptide-1 receptor agonists, metformin, thiazolidinediones, sodium-glucose co-transporter 2 inhibitors). In the NMA, the risk of fracture for alogliptin tended to decrease when versus placebo (OR, 0.51; 95% CI, 0.29 to 0.88). Besides, aloglitpin had a lower risk compared with linagliptin (OR, 0.45; 95% CI, 0.20 to 0.99) and saxagliption (OR, 0.46; 95%CI, 0.25 to 0.84); the risk was higher with saxagliptin when versus sitagliptin (OR, 1.90; 95% CI, 1.04 to 3.47) and sulfonylureas (OR, 1.98; 95% CI, 1.06 to 3.71). In the direct pairwise meta-analysis, alogliptin was associated with a non-significant tendency to reduction of bone fracture compared with placebo (OR, 0.54; 95% CI, 0.29 to 1.01). Ranking probability analysis indicated alogliptin decreased the risk of bone fracture most with a probability of 76.3%.

Conclusion

Alogliptin may be associated with a lower risk of bone fracture compared with placebo, linagliptin, or saxagliptin, while other anti-diabetes did not seem to have an association with the risk of bone fracture.

Diabetes Drug Effects on the Skeleton

Diabetes be it type 1 or type 2 is associated with an increased risk of fragility fractures. The mechanisms underlying this increased risk are just being elucidated. Anti-diabetes medications are crucial for maintaining glucose control and for preventing micro- and macrovascular complications in diabetes. However, they may modulate fracture risk in diabetes in different ways. Thiazolidinediones have demonstrated an unfavorable effect on the skeleton, while metformin and sulfonylureas may have a neutral if not beneficial effect on bone. The use of insulin has been associated with an increased risk of fragility fractures though it is not clear whether it is due to direct influence of insulin or whether it is mediated through hypoglycemia and increased falls risk. The overall effect of incretin mimetics appears to be beneficial; however, this has to be elucidated further. The bone effects of pramlintide, a synthetic analog of amylin, have not been explored fully. Finally, issues regarding bone safety of SGLT2 (sodium-dependent glucose transporter 2) inhibitors, the newest anti-diabetic medications on the market are of concern. The purpose of this review is to provide a comprehensive overview of the effect of these medications on bone metabolism and the studies exploring the risk or lack thereof of these medications on bone loss and fragility fractures.

Oral anti-diabetic drugs and fracture risk, cut to the bone: safe or dangerous? A narrative review

Fracture risk is higher in older adults with type 2 diabetes and may be influenced by treatments for diabetes. Oral anti-diabetic drugs have different effects on bone metabolism. The purpose of this review is to describe the effects of these drugs on bone metabolism and fracture risk. Osteoporosis is a progressive skeletal disorder that is characterized by compromised bone strength and increased risk of fracture. This condition has become an important global health problem, affecting approximately 200 million people worldwide. Another chronic and highly prevalent condition is diabetes mellitus, which affects more than 380 million people; both type 1 and type 2 diabetes are risk factors for fracture. Type 2 diabetes, in particular, is associated with impaired bone strength, although it is characterized by normal or elevated bone mineral density. Several therapeutic strategies are available to achieve the best outcomes in the management of diabetes mellitus but these have different effects on bone metabolism. The purpose of this narrative review is to describe the effects of oral hypoglycemic agents (metformin, sulfonylureas, thiazolidinediones, meglitinides, dipeptidyl peptidase-4 inhibitors, glucagon-like peptide-1 receptor agonists and sodium-dependent glucose transporter 2 inhibitors) on bone metabolism and on the risk of developing fragility fractures in patients with type 2 diabetes. Both diabetes and osteoporosis represent a significant burden in terms of healthcare costs and quality of life. It is very important to choose therapies for diabetes that ensure good metabolic control whilst preserving skeletal health.

Analysis of multi-site drug-protein interactions by high-performance affinity chromatography: Binding by glimepiride to normal or glycated human serum albumin

High-performance affinity chromatography (HPAC) was used in a variety of formats to examine multi-site interactions between glimepiride, a third-generation sulfonylurea drug, and normal or in vitro glycated forms of the transport protein human serum albumin (HSA). Frontal analysis revealed that glimepiride interacts with normal HSA and glycated HSA at a group of high affinity sites (association equilibrium constant, or Ka, 9.2-11.8×10(5)M(-1) at pH 7.4 and 37°C) and a group of lower affinity regions (Ka, 5.9-16×10(3)M(-1)). Zonal elution competition studies were designed and carried out in both normal- and reversed-role formats to investigate the binding by this drug at specific sites. These experiments indicated that glimepiride was interacting at both Sudlow sites I and II. Allosteric effects were also noted with R-warfarin at Sudlow site I and with tamoxifen at the tamoxifen site on HSA. The binding at Sudlow site I had a 2.1- to 2.3-fold increase in affinity in going from normal HSA to the glycated samples of HSA. There was no significant change in the affinity for glimepiride at Sudlow site II in going from normal HSA to a moderately glycated sample of HSA, but a slight decrease in affinity was seen in going to a more highly glycated HSA sample. These results demonstrated how various HPAC-based methods can be used to profile and characterize multi-site binding by a drug such as glimepiride to a protein and its modified forms. The information obtained from this study should be useful in providing a better understanding of how drug-protein binding may be affected by glycation and of how separation and analysis methods based on HPAC can be employed to study systems with complex interactions or that involve modified proteins.

An update on diabetes related skeletal fragility

There are several mechanisms by which diabetes could affect bone mass and strength. These mechanisms include insulin deficiency; hyperglycemia; the accumulation of advanced glycation end products that may influence collagen characteristics; marrow adiposity and bone inflammation. Furthermore, associated diabetic complications and treatment with thaizolidinediones may also increase risk of fracturing. The following article provides its readers with an update on the latest information pertaining to diabetes related bone skeletal fragility. In the authors' opinion, future studies are needed in order to clarify the impact of different aspects of diabetes metabolism, glycemic control, and specific treatments for diabetes on bone. Given that dual energy x-ray absorptiometry is a poor predictor of bone morbidity in this group of patients, there is a need to explore novel approaches for assessing bone quality. It is important that we develop a better understanding of how diabetes affects bone in order to improve our ability to protect bone health and prevent fractures in the growing population of adults with diabetes.

Type 2 diabetes mellitus and fracture risk

Increased fracture risk, traditionally associated with type 1 diabetes, has lately been of great concern in patients with type 2 diabetes. A variable increase in fracture risk has been reported, ranging from 20% to 3-fold, depending on skeletal site, diabetes duration and study design. Longer disease duration, the presence of diabetic complications, inadequate glycemic control, insulin use and increased risk for falls are all reported to increase fracture risk. Patients with type 2 diabetes display a unique skeletal phenotype with either normal or more frequently increased, bone mineral density and impaired structural and geometric properties. Recently, alterations in bone material properties seem to be the predominant defect leading to increased bone fragility. Accumulation of advanced glycation end-products and changes in collagen cross-linking along with suppression of bone turnover seem to be significant factors impairing bone strength. FRAX score has been reported to underestimate fracture risk and lumbar spine BMD is inadequate in predicting vertebral fractures. Anti-diabetic medications, apart from thiazolidinediones, appear to be safe for the skeleton, although more data are needed. Optimal strategies to reduce skeletal fragility in type 2 diabetic patients are yet to be determined.

Glimepiride promotes osteogenic differentiation in rat osteoblasts via the PI3K/Akt/eNOS pathway in a high glucose microenvironment

Our previous studies demonstrated that glimepiride enhanced the proliferation and differentiation of osteoblasts and led to activation of the PI3K/Akt pathway. Recent genetic evidence shows that endothelial nitric oxide synthase (eNOS) plays an important role in bone homeostasis. In this study, we further elucidated the roles of eNOS, PI3K and Akt in bone formation by osteoblasts induced by glimepiride in a high glucose microenvironment. We demonstrated that high glucose (16.5 mM) inhibits the osteogenic differentiation potential and proliferation of rat osteoblasts. Glimepiride activated eNOS expression in rat osteoblasts cultured with two different concentrations of glucose. High glucose-induced osteogenic differentiation was significantly enhanced by glimepiride. Down-regulation of PI3K P85 levels by treatment with LY294002 (a PI3K inhibitor) led to suppression of P-eNOS and P-AKT expression levels, which in turn resulted in inhibition of RUNX2, OCN and ALP mRNA expression in osteoblasts induced by glimepiride at both glucose concentrations. ALP activity was partially inhibited by 10 µM LY294002. Taken together, our results demonstrate that glimepiride-induced osteogenic differentiation of osteoblasts occurs via eNOS activation and is dependent on the PI3K/Akt signaling pathway in a high glucose microenvironment.

The PI3K/Akt signalling pathway may play an internal role related to abnormal condylar growth: a preliminary study

Developmental deformity of the mandible is one of the most common craniofacial malformations and is closely related to abnormal condylar growth. In this study, the role of PI3K/Akt signalling in the regulation of chondrocyte proliferation and hypertrophic differentiation in the condylar cartilage was studied. Immunohistochemical staining was used to investigate the expression of PI3K and p-Akt in the rat condyle cartilage. Rat condylar chondrocytes were cultured for the investigation of chondrocyte proliferation and hypertrophic differentiation when PI3K/Akt was inhibited. In addition, organ culture of the rat mandibular condyle was performed to evaluate the condyle cartilage growth while PI3K/Akt was inhibited. PI3K-positive cells and p-Akt-positive cells showing cytoplasmic staining were found to be present in the condylar cartilage. Reduced cell proliferation was observed in the culture of rat condylar chondrocytes when PI3K/Akt was inhibited; however, the hypertrophic differentiation level was increased. The proliferative zone thickness of condylar cartilage in the experimental group was less than that in the control group (P=0.00185), but the hypertrophic zone was greater than that in the control group (P=0.01048). PI3K/Akt signalling exerts opposite influences on chondrocyte proliferation and hypertrophic differentiation of the condylar cartilage, and these data suggest that PI3K/Akt is a potential intracellular regulation signal pathway in condylar cartilage development.

Effect of glimepiride on the skeletal system of ovariectomized and non-ovariectomized rats

BACKGROUND

Diabetes mellitus type 2 and osteoporosis are major health problem, especially in postmenopausal women. Glimepiride is a third-generation sulfonylurea derivative and is used as a first-line drug in the treatment of type 2 diabetes mellitus. The effect of this drug on bone tissue is unknown. The aim of the present study was to investigate the influence of glimepiride on the skeletal system in ovariectomized and non-ovariectomized rats.

METHODS

The experiment was conducted on 3-month-old female Wistar rats, divided into 4 groups (n=10 per group): I (NOVX)-non-ovariectomized control rats, II (NOVX+G)-non-ovariectomized rats receiving glimepiride (0.8 mg/kg po), III (OVX)-ovariectomized control rats, IV (OVX+G)-ovariectomized rats receiving glimepiride (0.8 mg/kg po). Bilateral ovariectomy was performed 7 days before the start of the experiment, under ketamine-xylazine anesthesia. Glimepiride was administered once daily for 28 days. The effect of glimepiride on the skeletal system was assessed based on macrometric parameters, histomorphometric parameters and mechanical properties of the tibial metaphysis, femoral diaphysis and femoral neck. Bone mass, mineral mass, calcium and phosphorus content, as well as serum estrogen, osteocalcin and RatLaps levels were also studied.

RESULTS

Estrogen deficiency in ovariectomized rats caused increased bone remodeling, with an intensification of bone resorption and formation, and mineralization impairment. Glimepiride in ovariectomized rats inhibited the development of changes in the skeletal system caused by estrogen deficiency, intensifying bone formation. In the presence of estrogens (in non-ovariectomized rats), glimepiride also intensified bone formation, but to a lesser extent.

CONCLUSIONS

Glimepiride, in the therapy of type 2 diabetes mellitus in postmenopausal women, may have a beneficial effect on bone remodeling and may reduce the risk of development of osteoporosis.

Omentin-1 Stimulates Human Osteoblast Proliferation through PI3K/Akt Signal Pathway

It has been presumed that adipokines deriving from adipose tissue may play important roles in bone metabolism. Omentin-1, a novel adipokine, which is selectively expressed in visceral adipose tissue, has been reported to stimulate proliferation and inhibit differentiation of mouse osteoblast. However, little information refers to the effect of omentin-1 on human osteoblast (hOB) proliferation. The current study examined the potential effects of omentin-1 on proliferation in hOB and the signal pathway involved. Omentin-1 promoted hOB proliferation in a dose-dependent manner as determined by [(3)H]thymidine incorporation. Western blot analysis revealed that omentin-1 induced activation of Akt (phosphatidylinositol-3 kinase downstream effector) and such effect was impeded by transfection of hOB with Akt-siRNA. Furthermore, LY294002 (a selective PI3K inhibitor) and HIMO (a selective Akt inhibitor) abolished the omentin-1-induced hOB proliferation. These findings indicate that omentin-1 induces hOB proliferation via the PI3K/Akt signaling pathway and suggest that osteoblast is a direct target of omentin-1.

New understanding and treatments for osteoporosis

To summarize promising areas of investigation in osteoporosis and to stimulate further research in this area, as discussed in a recent international conference. Over the recent years, there has been an improvement in the knowledge of molecular pathways involved in bone formation and resorption with the development of new drugs to treat osteoporosis. Intact parathyroid hormone, teriparatide, and anti-sclerostin monoclonal antibody are anabolic drugs, whereas denosumab and odanacatib are anti-resorptive drugs with more reversible effects as compared to bisphosphonates. Anabolic and anti-resorptive agents have different effects on bone, and research in this area includes the efficacy of combination and sequential therapies with them. New insights in the molecular pathways of bone remodeling have clarified the mechanisms responsible for skeletal fragility in several forms of secondary osteoporosis, such as that occurring in type 2 diabetes, following drug exposure and systemic inflammatory diseases. Future research is needed to address the efficacy of anti-osteoporotic drugs in these more recently recognized conditions of skeletal fragility. Osteoporosis continues to be an important field of biomedical research.

Reduced cell proliferation and neuroblast differentiation in the dentate gyrus of high fat diet-fed mice are ameliorated by metformin and glimepiride treatment

We investigated the effects of a high-fat diet (HFD) and the subsequent treatment of metformin (met) and glimepiride (glim), which are widely prescribed for type 2 diabetes, on cell proliferation and neuroblast differentiation using Ki67 and doublecortin (DCX) immunohistochemistry, respectively. Animals were fed low-fat diet (LFD) or HFD for 8 weeks. After 5 weeks of the HFD treatment, met alone or met + glim was administered orally once a day for 3 weeks. Body weight and food intake were much higher in the HFD + vehicle-treated group than the LFD-treated group. The administration of met or met + glim to the HFD-treated group resulted in a decrease in weight gain and food intake. Ki67-immunoreactive ((+)) nuclei, DCX(+) neuroblasts and brain-derived neurotrophic factor (BDNF) protein levels were markedly decreased in the dentate gyrus (DG) of the HFD + vehicle-treated group compared to the LFD-treated group. The administration of met or met + glim to the HFD-treated group prevented the reduction of Ki67(+) nuclei, DCX(+) neuroblasts, BDNF levels in the DG. The intraventricular injection of K252a (a BDNF receptor blocker) to the HFD-treated group treated met or met + glim distinctively lowered the reduction of cell proliferation and neuroblast differentiation induced by HFD. These results suggest that a HFD significantly reduces cell proliferation and neuroblast differentiation by reducing BDNF levels and these effects are ameliorated by treatment with met or met + glim.

Osteoporosis in diabetes mellitus: Possible cellular and molecular mechanisms

Osteoporosis, a global age-related health problem in both male and female elderly, insidiously deteriorates the microstructure of bone, particularly at trabecular sites, such as vertebrae, ribs and hips, culminating in fragility fractures, pain and disability. Although osteoporosis is normally associated with senescence and estrogen deficiency, diabetes mellitus (DM), especially type 1 DM, also contributes to and/or aggravates bone loss in osteoporotic patients. This topic highlight article focuses on DM-induced osteoporosis and DM/osteoporosis comorbidity, covering alterations in bone metabolism as well as factors regulating bone growth under diabetic conditions including, insulin, insulin-like growth factor-1 and angiogenesis. Cellular and molecular mechanisms of DM-related bone loss are also discussed. This information provides a foundation for the better understanding of diabetic complications and for development of early screening and prevention of osteoporosis in diabetic patients.

Mechanisms of impaired bone strength in type 1 and 2 diabetes

Diabetes and osteoporosis are common and complex disorders with an enormous health burden that can be often associated especially in middle-age and elderly individuals. Although there is raising awareness of the higher fractures rates among patients with type 1 (DM1) and 2 (DM2) diabetes, there are few data available on the pathogenetic mechanisms responsible for this increased risk. Importantly, several experimental and clinical observations suggest that bone abnormalities associated with diabetes may differ, at least in part, from those associated with senile or post-menopausal osteoporosis. This implies that specific preventive and therapeutic strategies have to be developed and tested to prevent fractures in DM1 and DM2 patients. It is also likely that shared (i.e. due to glucose-toxicity) as well as different (i.e. due to insulin levels or other hormones) mechanisms may be associated with bone fragility in DM1 and DM2. Moreover, the hypothesis of an endocrine role of the skeleton in the regulation of glucose metabolism and insulin sensitivity has been recently proposed by experimental observations. This review summarizes the recent clinical and experimental advances on glucose tolerance, bone fragility and osteoporosis associated with diabetes.

Relationship between treatments with insulin and oral hypoglycemic agents versus the presence of vertebral fractures in type 2 diabetes mellitus

Although previous studies indicated that hypoglycemic agents could affect bone metabolism, little is known about whether these agents are associated with the risks of osteoporotic fracture in Japanese patents with type 2 diabetes. We examined whether treatments of diabetes, such as insulin administration, sulfonylurea, thiazolidinedione, and metformin, were associated with the presence of vertebral fractures in 494 men and 344 postmenopausal women with type 2 diabetes. We analyzed the relationships between each treatment versus bone turnover markers, bone mineral density (BMD), and the presence of prevalent vertebral fractures. Multiple logistic regression analysis adjusted for age, duration of diabetes, body mass index, serum creatinine, serum C-peptide, and HbA(1c) showed that, in postmenopausal women, treatments with insulin administration or thiazolidinedione were significantly and positively associated with the presence of vertebral fractures [odds ratio (OR) = 2.27, P = 0.012 and OR = 3.38, P = 0.038, respectively], whereas treatment with sulfonylurea was significantly and inversely associated with vertebral fractures (OR = 0.48, P = 0.018). These relationships were still significant after additional adjustment for lumbar BMD. In contrast, no significant relationships between treatments with any agent and the presence of vertebral fractures were found in men. These findings suggest that postmenopausal women treated with insulin or thiazolidinedione have a high risk of vertebral fractures independent of age, body stature, blood glucose level, insulin secretion, or BMD whereas treatment with sulfonylurea is associated with a decreased risk.