Molecular Modulation of Osteoblasts and Osteoclasts in Type 2 Diabetes

miRNA-seq analysis of high glucose induced osteoblasts provides insight into the mechanism underlying diabetic osteoporosis

The present study aims to explore the etiology of Diabetic osteoporosis (DOP), a chronic complication associated with diabetes mellitus. Specifically, the research seeks to identify potential miRNA biomarkers of DOP and investigated role in regulating osteoblasts. To achieve this, an animal model of DOP was established through the administration of a high-sugar and high-fat diet, and then injection of streptozotocin. Bone microarchitecture and histopathology analysis were analyzed. Rat calvarial osteoblasts (ROBs) were stimulated with high glucose (HG). MiRNA profiles of the stimulated osteoblasts were compared to control osteoblasts using sequencing. Proliferation and mineralization abilities were assessed using MTT assay, alkaline phosphatase, and alizarin red staining. Expression levels of OGN, Runx2, and ALP were determined through qRT-PCR and Western blot. MiRNA-sequencing results revealed increased miRNA-702-5p levels. Luciferase reporter gene was utilized to study the correlation between miR-702-5p and OGN. High glucose impaired cell proliferation and mineralization in vitro by inhibiting OGN, Runx2, and ALP expressions. Interference with miR-702-5p decreased OGN, Runx2, and ALP levels, which were restored by OGN overexpression. Additionally, downregulation of OGN and Runx2 in DOP rat femurs was confirmed. Therefore, the miRNA-702-5p/OGN/Runx2 signaling axis may play a role in DOP, and could be diagnostic biomarker and therapeutic target for not only DOP but also other forms of osteoporosis.

Osteogenic effect and mechanism of IL-10 in diabetic rat jaw defect mode

OBJECTIVE

The aim of this study was to investigate the effect of IL-10 on the phenotype polarization of macrophages and osteogenesis in diabetes mellitus type 2 (T2DM) rat jaw defects.

METHODS

Lipopolysaccharide (LPS) and interleukin-10 (IL-10) were chosen to induce the polarization of macrophages. In vitro assessment included wound-healing assay, western blotting, and alizarin red staining after co-culture of the bone marrow-derived mesenchymal stem cells (BMSCs) and induced macrophages. For in vivo study, IL-10 was loaded on GelMA-Heparin and applied to bone defects of the alveolar ridge in diabetic rats, while Bio-Oss Collagen, simple GelMA-Heparin, and blank control groups were set for contrast experiment. The mandibles of rats were processed for micro-computed tomography, histology, and immunohistochemistry 1 week and 4 weeks after the operation.

RESULTS

IL-10 induced expression of arginase 1, TGF-β1, EGR2, and Mannose Receptor (CD206), whereas LPS induced expression of iNOS, TNF-α, IL-6, CD80. The BMSCs co-cultured with macrophages induced by IL-10 showed increased migration, osteogenic differentiation, and mineralization in vitro. Notably, the IL-10-laden GelMA-Heparin group showed quicker new bone formation and a higher M2/M1 ratio of macrophages in the jawbone defect area compared with the control groups.

CONCLUSIONS

IL-10 can stably induce macrophages to M2 type, thereby influencing BMSCs and improving the osteogenesis of jaw bone defects.

Alkaline Water Mitigates Bone Loss in Streptozotocin-Induced Type II Diabetic Rats

Background A decline in bone mineral density is a defining feature of osteoporosis, which is a prevalent bone complication associated with diabetes. This study aims to shed light on the protective effect of Zamzam water (ZW), a famous alkaline water, on diabetes-induced osteoporosis. Methodology Of a total of 40 male rats, 10 male rats each were divided into the following four groups: group I (normal control rats), group II (ZW group), group III (diabetic rats), and group IV (DM + ZW). Anteroposterior and lateral X-rays were taken of the rats in each group before the end of the experiment. The study assessed serum levels of inflammatory markers including interleukin 6, interleukin-1 beta, and tumor necrosis factor-alpha; bone formation markers including osteocalcin (OC); alkaline phosphatase (ALP); and bone resorption markers including the N-terminal telopeptide of collagen type I (NTX-1), bone deoxypyridinoline (DPD), and tartrate-resistant acid phosphatase 5b (TRAP-5b). Results Rats with diabetes who consumed ZW exhibited a significant (p < 0.001) increase in OC and ALP bone formation markers and a decrease in NTX-1, DPD, and TRAP-5b bone resorption markers, with improvements in the X-ray image of the vertebral column at the L6 vertebra level. Conclusions ZW improved diabetes-induced osteoporosis in rats by enhancing osteoblastic activity and downregulating osteoclastic activity.

Autophagy, a double-edged sword for oral tissue regeneration

BACKGROUND

Oral health is of fundamental importance to maintain systemic health in humans. Stem cell-based oral tissue regeneration is a promising strategy to achieve the recovery of impaired oral tissue. As a highly conserved process of lysosomal degradation, autophagy induction regulates stem cell function physiologically and pathologically. Autophagy activation can serve as a cytoprotective mechanism in stressful environments, while insufficient or over-activation may also lead to cell function dysregulation and cell death.

AIM OF REVIEW

This review focuses on the effects of autophagy on stem cell function and oral tissue regeneration, with particular emphasis on diverse roles of autophagy in different oral tissues, including periodontal tissue, bone tissue, dentin pulp tissue, oral mucosa, salivary gland, maxillofacial muscle, temporomandibular joint, etc. Additionally, this review introduces the molecular mechanisms involved in autophagy during the regeneration of different parts of oral tissue, and how autophagy can be regulated by small molecule drugs, biomaterials, exosomes/RNAs or other specific treatments. Finally, this review discusses new perspectives for autophagy manipulation and oral tissue regeneration.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Overall, this review emphasizes the contribution of autophagy to oral tissue regeneration and highlights the possible approaches for regulating autophagy to promote the regeneration of human oral tissue.

Traditional Chinese medicine in osteoporosis: from pathogenesis to potential activity

Osteoporosis characterized by decreased bone density and mass, is a systemic bone disease with the destruction of microstructure and increase in fragility. Osteoporosis is attributed to multiple causes, including aging, inflammation, diabetes mellitus, and other factors induced by the adverse effects of medications. Without treatment, osteoporosis will further progress and bring great trouble to human life. Due to the various causes, the treatment of osteoporosis is mainly aimed at improving bone metabolism, inhibiting bone resorption, and promoting bone formation. Although the currently approved drugs can reduce the risk of fragility fractures in individuals, a single drug has limitations in terms of safety and effectiveness. By contrast, traditional Chinese medicine (TCM), a characteristic discipline in China, including syndrome differentiation, Chinese medicine prescription, and active ingredients, shows unique advantages in the treatment of osteoporosis and has received attention all over the world. Therefore, this review summarized the pathogenic factors, pathogenesis, therapy limitations, and advantages of TCM, aiming at providing new ideas for the prevention and treatment of OP.

Estudio del efecto del tratamiento con fármacos antidiabéticos sobre el metabolismo óseo

Objetivos

La prevalencia de la diabetes mellitus tipo 2 (DMT2) está aumentando de forma exponencial en todo el mundo, habiéndose comprobado que estos pacientes tienen mayor riesgo de presentar fracturas óseas, con respecto a la población sana, por lo que resulta de gran relevancia el conocimiento del efecto de los fármacos antidiabéticos sobre el metabolismo óseo.

Métodos

Estudio estadístico descriptivo, retrospectivo, de 106 pacientes en tratamiento con seis grupos de fármacos antidiabéticos: insulina, inhibidores de dipeptidilpeptidasa 4 (iDPP4), agonistas del receptor del péptido similar al glucagón tipo 1 (arGLP1), sulfonilureas, inhibidores del cotransportador de sodio-glucosa tipo 2 (iSGLT2) y pioglitazona, en los que se determinaron osteocalcina (OC), fosfatasa alcalina ósea (FAO) y telopéptido C-terminal del colágeno tipo 1 o beta-crosslaps (β-CTx).

Resultados

Se encontraron concentraciones más elevadas de β-CTx en los pacientes tratados con pioglitazona que en los tratados con iDPP4 (p=0,035), iSGLT2 (p=0,020) y con arGLP1 (p<0,001), siendo los pacientes tratados con arGLP1 los que presentaron las concentraciones más bajas de β-CTx.

Conclusiones

El tipo de tratamiento antidiabético recibido en pacientes que padecen DMT2 puede afectar el remodelado óseo. En nuestro estudio los pacientes que fueron tratados con pioglitazona mostraron las concentraciones más elevadas de β-CTx con respecto al resto de grupos de fármacos, lo cual parece indicar la conveniencia de evitar estos fármacos, sobre todo en mujeres postmenopáusicas con DMT2. Los fármacos arGLP1 presentaron los valores más bajos de β-CTx, por lo que podrían ejercer un efecto beneficioso sobre el metabolismo óseo.

Effects of antidiabetic drugs on bone metabolism

Objectives

The prevalence of diabetes mellitus type 2 (DMT2) is increasing exponentially worldwide. DMT2 patients have been found to be at a higher risk for bone fractures than the healthy population. Hence, improving our understanding of the impact of antidiabetic drugs on bone metabolism is crucial.

Methods

A descriptive, retrospective study involving 106 patients receiving six groups of antidiabetic drugs: insulin; dipeptidylpeptidase four inhibitors (DPP4i); glucagon-like peptide type 1 receptor agonists (GLP1ra); sulfonylureas; sodium-glucose cotransporter two inhibitors (SGLT2i); and pioglitazone, in which osteocalcin (OC), bone alkaline phosphatase (BAP) and C-terminal telopeptide of collagen type 1 or beta-crosslaps (β-CTx) were determined.

Results

β-CTx concentrations were higher in the patients treated with pioglitazone, as compared to patients treated with DPP4i (p=0.035), SGLT2i (p=0.020) or GLP1ra (p<0.001). The lowest β-CTx concentrations were observed in the patients treated with GLP1ra.

Conclusions

Bone remodeling is influenced by the type of antidiabetic drug administered to DMT2 patients. In our study, the patients who received pioglitazone showed higher β-CTx concentrations, as compared to patients treated with other types of antidiabetic drugs. This finding highlights the convenience of avoiding these drugs, especially in postmenopausal women with DMT2. GLP1ra drugs were associated with the lowest β-CTx concentrations, which suggests that these agents could exert beneficial effects on bone metabolism.

The association between type 2 diabetes mellitus/prediabetes status and femoral neck bone mineral density in old adults

BACKGROUND

The prevalence of both type 2 diabetes mellitus (T2DM) and osteoporosis has been increasing among older individuals, with these two health conditions often coexisting. Our aim in this study was to evaluate the association between T2DM status and bone mineral density (BMD) of the femoral neck among older adults in the United States.

METHODS

This was a retrospective analysis of the data from 5695 adults, 60-80 years of age. The data were obtained from the National Health and Nutrition Examination Survey, for the following years: 2005-2006, 2007-2008, 2009-2010, 2013-2014, and 2017-2018. Weighted multivariable regression analyses, with subgroup analyses as appropriate, were performed to identify an association between T2DM/prediabetes status and femoral BMD and mediating factors.

RESULTS

There was a significant positive association between T2DM/prediabetes status and femoral neck BMD among older women, but not men, after adjusting for body mass index (BMI). On subgroup analysis, stratified by BMI, the significant positive association was retained for T2DM women with a BMI of 25-29.9 kg/m2 (β, 0.030; 95% CI, 0.007-0.052) or ≥30 kg/m2 (β, 0.029; 95% CI, 0.007-0.05), and for prediabetes women with a BMI of 25-29.9 kg/m2 (β, 0.016; 95% CI, 0.001-0.030).

CONCLUSIONS

The association between a positive T2DM/prediabetes status and femoral neck BMD differed by sex among older individuals, with the association being further modulated by BMI. For women with a BMI of 25-29.9 kg/m2 or ≥30 kg/m2, T2DM was associated with a significantly higher femoral neck BMD, compared to the non-diabetes group.

Effect of Liraglutide on Osteoporosis in a Rat Model of Type 2 Diabetes Mellitus: A Histological, Immunohistochemical, and Biochemical Study

Diabetic osteoporosis (DOP) is a diabetic complication associated with a significant disability rate. Liraglutide, a glucagon-like peptide-1 receptor agonist, is a promising and innovative drug for type 2 diabetes mellitus (T2DM), with potential therapeutic implications for bone disorders. This investigation examined the impact of liraglutide on osteoporosis in rats with T2DM and studied the influence of vitamin D receptor Bsm1 polymorphism on liraglutide-induced outcomes. Thirty rats were divided into control, T2DM induced by a combination of a high-fat diet and 25 mg/kg streptozotocin, and T2DM-liraglutide (T2DM treated with 0.4 mg/kg/day liraglutide) groups. After 8 weeks of liraglutide treatment, femurs and blood samples were obtained from all rats for subsequent investigations. Diabetes induced a remarkable rise in the serum levels of receptor activator of nuclear factor kappa B ligand (RANKL) and C-telopeptide of type I collagen (CTX-1) associated with a remarkable decline in osteocalcin and osteoprotegerin (OPG). Impaired bone architecture was also demonstrated by light and scanning electron microscopic study. The immune expression of OPG was down-regulated, while RANKL was up-regulated. Interestingly, the administration of liraglutide ameliorated the previous changes induced by diabetes mellitus. In conclusion, liraglutide can prevent DOP, mostly due to liraglutide's ability to increase bone growth, while inhibiting bone resorption.

Metformin reverses impaired osteogenesis due to hyperglycemia-induced neutrophil extracellular traps formation

Diabetic patients suffer from delayed fracture healing and impaired osteogenic function, but the underlying pathophysiological mechanisms are not fully understood. Neutrophil extracellular traps (NETs) formed by neutrophils in high glucose microenvironments affect the healing of wounds and other tissues. Some evidence supports that NETs may inhibit osteogenic processes in the microenvironment through sustained inflammatory activation. In this study, we observed that high glucose-induced NETs led to sustained inflammatory activation of macrophages. Pro-inflammatory NETs inhibited the osteogenic function of osteoblasts in vitro. A bone defect healing model based on diabetic rat animal models confirmed that bone healing was impaired in a high glucose environment, but this process could be reversed by DNase I, a NETs clearance agent. More importantly, the classic hypoglycemic drug metformin had a similar antagonistic effect as DNase I and could reverse the inhibitory effect of NETs on osteogenesis in a high-glucose environment. In summary, we found that NETs formation induced by high glucose microenvironment is a potential cause of osteogenic dysfunction in diabetic patients, and metformin can reverse this osteogenic disadvantage.

Overexpression of SENP3 promotes PPAR-γ transcription through the increase of HIF-1α stability via SUMO2/3 and participates in molecular mechanisms of osteoporosis

Patients with type II diabetes are exposed to a high risk of osteoporosis. The present study sought to exploit the detailed mechanisms of the SENP3/HIF-1α/PPAR-γ axis in osteoporosis. A rat model of type II diabetic osteoporosis was established, followed by the isolation of bone marrow mononuclear macrophages (BMMs). Gain- and loss-of-function assays were conducted in rat models and BMMs from rat models, followed by the evaluation of SENP3, HIF-1α, and PPAR-γ expression and detection of osteoclast differentiation-related indexes. Next, the SUMOylated modification of HIF-1α and the regulation of SENP3 on SUMOylated modification level of HIF-1α were assessed using immunoprecipitation, and the binding of HIF-1α to the PPARγ promoter was identified with ChIP and dual-luciferase reporter assays. SENP3 and HIF-1α expression was down-regulated in tissues of type II diabetes-induced osteoporotic rats and BMMs, with high SUMOylated modification levels of HIF-1α. Mechanically, HIF-1α was modified by SUMO2/3. SENP3 suppressed SUMOylated modification of HIF-1α and enhanced HIF-1α stability. HIF-1α bound to the PPAR-γ promoter and facilitated PPAR-γ transcription. SENP3 overexpression restrained osteoblast differentiation in type II diabetes-induced osteoporotic rats and BMMs from rat models. SENP3 knockdown facilitated osteoclast differentiation in type II diabetes-induced osteoporotic rats and BMMs from rat models, which was neutralized by further HIF-1α overexpression. To sum up, SENP3 overexpression restrained osteoclast differentiation in type II diabetic osteoporosis by increasing HIF-1α stability and expression and thus promoting PPAR-γ expression via de-SUMOylation, which might expand the understanding of the mechanisms of type II diabetes combined with osteoporosis.

Selected musculoskeletal disorders in patients with thyroid dysfunction, diabetes, and obesity

Many medical conditions affect the skeletal system and constitute independent risk factors for fractures. The action of thyroid hormones is necessary to maintain adequate development, mineralization, and bone strength. Untreated hyperthyroidism can lead to a decrease in bone mineral density (BMD), osteoporosis, and pathological fractures. In hypothyroidism, the changes in the quality of bone structure lead to an increase in the frequency of fractures. Excessive body weight negatively impacts fracture risk, increases the risk of osteoarthritis and accelerates the development of rheumatoid arthritis and osteoporosis. Type 1 and type 2 diabetes are associated with an increased risk of bone fractures despite different etiopathogenesis due to the duration of the disease and the pro-inflammatory state, the incorporation of advanced glycation end products (AGEs) into the bone matrix, and microvascular disorders. This study summarizes the current literature on the influence of thyroid dysfunction, obesity, and diabetes on the skeletal system.

The Synergistic Effect of Zuogui Pill and Eldecalcitol on Improving Bone Mass and Osteogenesis in Type 2 Diabetic Osteoporosis

Background and Objectives: The incidence of diabetic osteoporosis, an important complication of diabetes mellitus, is increasing gradually. This study investigated the combined effect of the Zuogui pill (ZGP) and eldecalcitol (ED-71), a novel vitamin D analog, on type 2 diabetic osteoporosis (T2DOP) and explored their action mechanism. Materials and Methods: Blood glucose levels were routinely monitored in db/db mice while inducing T2DOP. We used hematoxylin and eosin staining, Masson staining, micro-computed tomography, and serum biochemical analysis to evaluate changes in the bone mass and blood calcium and phosphate levels of mice. Immunohistochemical staining was performed to assess the osteoblast and osteoclast statuses. The MC3T3-E1 cell line was cultured in vitro under a high glucose concentration and induced to undergo osteogenic differentiation. Quantitative real-time polymerase chain reaction, Western blot, immunofluorescence, ALP, and alizarin red staining were carried out to detect osteogenic differentiation and PI3K-AKT signaling pathway activity. Results: ZGP and ED-71 led to a dramatic decrease in blood glucose levels and an increase in bone mass in the db/db mice. The effect was strongest when both were used together. ZGP combined with ED-71 promoted osteoblast activity and inhibited osteoclast activity in the trabecular bone region. The in vitro results revealed that ZGP and ED-71 synergistically promoted osteogenic differentiation and activated the PI3K-AKT signaling pathway. The PI3K inhibitor LY294002 or AKT inhibitor ARQ092 altered the synergistic action of both on osteogenic differentiation. Conclusions: The combined use of ZGP and ED-71 reduced blood glucose levels in diabetic mice and promoted osteogenic differentiation through the PI3K-AKT signaling pathway, resulting in improved bone mass. Our study suggests that the abovementioned combination constitutes an effective treatment for T2DOP.

Abnormal Decrease of Macrophage ALKBH5 Expression Causes Abnormal Polarization and Inhibits Osteoblast Differentiation

Peri-implant tissue inflammation is an inflammatory injury that occurs in the soft and hard tissues surrounding the implant and is the main cause of short- or long-term failure of implant prosthetic restorations, which is compounded by bone loss and bone destruction in the alveolar bone of diabetes patients with peri-implantitis. However, the mechanisms underlying the persistence of diabetic peri-implantitis, as well as the essential connections and key molecules that regulate its start and progression, remain unknown. In this study, we discovered that M1 macrophage polarization was abnormally enhanced in diabetic peri-implantitis and influenced the osteogenic differentiation of mesenchymal stem cells. RNA sequencing revealed that ALKBH5 expression was abnormally reduced in diabetic peri-implantitis. Further mechanism study showed that ALKBH5 and its mediated m6A can influence osteogenic differentiation, which in turn influences the persistence of diabetic peri-implantitis. Our findings present a new mechanism for the suppression of osteoblast development in diabetic peri-implantitis and a new treatment strategy to promote anabolism by inhibiting ALKBH5.

Glucose uptake and distribution across the human skeleton using state-of-the-art total-body PET/CT

A growing number of studies have demonstrated that the skeleton is an endocrine organ that is involved in glucose metabolism and plays a significant role in human glucose homeostasis. However, there is still a limited understanding of the in vivo glucose uptake and distribution across the human skeleton. To address this issue, we aimed to elucidate the detailed profile of glucose uptake across the skeleton using a total-body positron emission tomography (PET) scanner. A total of 41 healthy participants were recruited. Two of them received a 1-hour dynamic total-body ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) PET scan, and all of them received a 10-minute static total-body ¹⁸F-FDG PET scan. The net influx rate (K_i) and standardized uptake value normalized by lean body mass (SUL) were calculated as indicators of glucose uptake from the dynamic and static PET data, respectively. The results showed that the vertebrae, hip bone and skull had relatively high K_i and SUL values compared with metabolic organs such as the liver. Both the K_i and SUL were higher in the epiphyseal, metaphyseal and cortical regions of long bones. Moreover, trends associated with age and overweight with glucose uptake (SUL_max and SUL_mean) in bones were uncovered. Overall, these results indicate that the skeleton is a site with significant glucose uptake, and skeletal glucose uptake can be affected by age and dysregulated metabolism.

Oxidative stress: A common pathological state in a high-risk population for osteoporosis

Osteoporosis is becoming a major concern in the field of public health. The process of bone loss is insidious and does not directly induce obvious symptoms. Complications indicate an irreversible decrease in bone mass. The high-risk populations of osteoporosis, including postmenopausal women, elderly men, diabetic patients and obese individuals need regular bone mineral density testing and appropriate preventive treatment. However, the primary changes in these populations are different, increasing the difficulty of effective treatment of osteoporosis. Determining the core pathogenesis of osteoporosis helps improve the efficiency and efficacy of treatment among these populations. Oxidative stress is a common pathological state secondary to estrogen deficiency, aging, hyperglycemia and hyperlipemia. In this review, we divided oxidative stress into the direct effect of reactive oxygen species (ROS) and the reduction of antioxidant enzyme activity to discuss their roles in the development of osteoporosis. ROS initiated mitochondrial apoptotic signaling and suppressed osteogenic marker expression to weaken osteogenesis. MAPK and NF-κB signaling pathways mediated the positive effect of ROS on osteoclast differentiation. Antioxidant enzymes not only eliminate the negative effects of ROS, but also directly participate in the regulation of bone metabolism. Additionally, we also described the roles of proinflammatory factors and HIF-1α under the pathophysiological changes of inflammation and hypoxia, which provided a supplement of oxidative stress-induced osteoporosis. In conclusion, our review showed that oxidative stress was a common pathological state in a high-risk population for osteoporosis. Targeted oxidative stress treatment would greatly optimize the therapeutic schedule of various osteoporosis treatments.

Reduced High-Density Lipoprotein Cholesterol Is an Independent Determinant of Altered Bone Quality in Women with Type 2 Diabetes

Type 2 diabetes mellitus (T2DM) is associated with an increased fracture risk. Our study aimed to explore differences in bone alterations between T2DM women and controls and to assess clinical predictors of bone impairment in T2DM. For this observational case control study, we recruited 126 T2DM female patients and 117 non-diabetic, age- and BMI-comparable women, who underwent clinical examination, routine biochemistry and dual-energy X-ray absorptiometry (DXA) scans for bone mineral density (BMD) and trabecular bone score (TBS) assessment-derived indexes. These were correlated to metabolic parameters, such as glycemic control and lipid profile, by bivariate analyses, and significant variables were entered in multivariate adjusted models to detect independent determinants of altered bone status in diabetes. The T2DM patients were less represented in the normal bone category compared with controls (5% vs. 12%; p = 0.04); T2DM was associated with low TBS (OR: 2.47, C.I. 95%: 1.19–5.16, p = 0.016) in a regression model adjusted for age, menopausal status and BMI. In women with T2DM, TBS directly correlated with plasma high-density lipoprotein cholesterol (HDL-c) (p = 0.029) and vitamin D (p = 0.017) levels. An inverse association was observed with menopausal status (p < 0.001), metabolic syndrome (p = 0.014), BMI (p = 0.005), and waist circumference (p < 0.001). In the multivariate regression analysis, lower HDL-c represented the main predictor of altered bone quality in T2DM, regardless of age, menopausal status, BMI, waist circumference, statin treatment, physical activity, and vitamin D (p = 0.029; R2 = 0.47), which likely underlies common pathways between metabolic disease and bone health in diabetes.

Strategies of Macrophages to Maintain Bone Homeostasis and Promote Bone Repair: A Narrative Review

Bone homeostasis (a healthy bone mass) is regulated by maintaining a delicate balance between bone resorption and bone formation. The regulation of physiological bone remodeling by a complex system that involves multiple cells in the skeleton is closely related to bone homeostasis. Loss of bone mass or repair of bone is always accompanied by changes in bone homeostasis. However, due to the complexity of bone homeostasis, we are currently unable to identify all the mechanisms that affect bone homeostasis. To date, bone macrophages have been considered a third cellular component in addition to osteogenic spectrum cells and osteoclasts. As confirmed by co-culture models or in vivo experiments, polarized or unpolarized macrophages interact with multiple components within the bone to ensure bone homeostasis. Different macrophage phenotypes are prone to resorption and formation of bone differently. This review comprehensively summarizes the mechanisms by which macrophages regulate bone homeostasis and concludes that macrophages can control bone homeostasis from osteoclasts, mesenchymal cells, osteoblasts, osteocytes, and the blood/vasculature system. The elaboration of these mechanisms in this narrative review facilitates the development of macrophage-based strategies for the treatment of bone metabolic diseases and bone defects.

Metformin suppresses Oxidative Stress induced by High Glucose via Activation of the Nrf2/HO-1 Signaling Pathway in Type 2 Diabetic Osteoporosis

BACKGROUND

Metformin (MET) is widely used as a first-line hypoglycemic agent for the treatment of type 2 diabetes mellitus (T2DM) and was also confirmed to have a therapeutic effect on type 2 diabetic osteoporosis (T2DOP). However, the potential mechanisms of MET in the treatment of T2DOP are unclear.

OBJECTIVE

To clarify the effect of MET in T2DOP and to explore the potential mechanism of MET in the treatment of T2DOP.

METHODS

In vitro, we used MC3T3-E1 cells to study the effects of MET on osteogenic differentiation and anti-oxidative stress injury in a high glucose (Glucose 25 mM) environment. In vivo, we directly used db/db mice as a T2DOP model and assessed the osteoprotective effects of MET by Micro CT and histological analysis.

RESULTS

In vitro, we found that MET increased ALP activity in MC3T3-E1 cells in a high-glucose environment, promoted the formation of bone mineralized nodules, and upregulated the expression of the osteogenesis-related transcription factors RUNX2, Osterix, and COL1A1-related genes. In addition, MET was able to reduce high glucose-induced reactive oxygen species (ROS) production. In studies on the underlying mechanisms, we found that MET activated the Nrf2/HO-1 signaling pathway and alleviated high-glucose-induced oxidative stress injury. In vivo results showed that MET reduced bone loss and bone microarchitecture destruction in db/db mice.

CONCLUSION

Our results suggest that MET can activate the Nrf2/HO-1 signaling pathway to regulate the inhibition of osteogenic differentiation induced by high glucose thereby protecting T2DOP.

Dysfunction of macrophages leads to diabetic bone regeneration deficiency

Insufficient bone matrix formation caused by diabetic chronic inflammation can result in bone nonunion, which is perceived as a worldwide epidemic, with a substantial socioeconomic and public health burden. Macrophages in microenvironment orchestrate the inflammation and launch the process of bone remodeling and repair, but aberrant activation of macrophages can drive drastic inflammatory responses during diabetic bone regeneration. In diabetes mellitus, the proliferation of resident macrophages in bone microenvironment is limited, while enhanced myeloid differentiation of hematopoietic stem cells (HSCs) leads to increased and constant monocyte recruitment and thus macrophages shift toward the classic pro-inflammatory phenotype, which leads to the deficiency of bone regeneration. In this review, we systematically summarized the anomalous origin of macrophages under diabetic conditions. Moreover, we evaluated the deficit of pro-regeneration macrophages in the diabetic inflammatory microenvironment. Finally, we further discussed the latest developments on strategies based on targeting macrophages to promote diabetic bone regeneration. Briefly, this review aimed to provide a basis for modulating the biological functions of macrophages to accelerate bone regeneration and rescue diabetic fracture healing in the future.

Bone Metabolism Discrepancy in Type 2 Diabetes Mellitus Patients With and Without Non-Alcoholic Fatty Liver Disease

To explore the distribution of several bone metabolic indicators in type 2 diabetes patients (T2DM) with and without non-alcoholic fatty liver disease (NAFLD) and to preliminarily evaluate the relationship of bone metabolism with NAFLD in patients with T2DM. The hospitalized patients with T2DM were divided into the group of T2DM complicated with NAFLD and the group of T2DM alone according to the results of ultrasonic diagnosis. The general information and laboratory test data such as bone metabolism indexes of these patients were collected and the differences of the indexes between the 2 groups were compared. Furthermore, the independent influencing factors of NAFLD in patients with T2DM were analyzed. A total of 186 patients were included in the study. Compared with patients with T2DM only, patients with T2DM combined with NAFLD were characterized with younger age (p &lt; 0.001), higher BMI (p = 0.016), ALT (p = 0.001), TG (p = 0.005), HOMA-IR (p = 0.005), and lower HDL-C (p = 0.031). Significant discrepancy of age (OR 1.052, p = 0.001), ALT (OR 0.964, p = 0.047), HOMA-IR (OR 0.801, p = 0.005), and T-PINP (OR 1.022, p = 0.008) was found using multivariate logistic regression model. Significant discrepancy of T-PINP was found in T2DM patients with and without NAFLD. Further studies are needed to explore whether T-PINP could be used as a predictor of fatty liver disease, osteoporosis, and other related complications in patients with T2DM.

Hormone and implant osseointegration: Elaboration of the relationship among function, preclinical, and clinical practice

As clusters of peptides or steroids capable of high-efficiency information transmission, hormones have been substantiated to coordinate metabolism, growth, development, and other physiological processes, especially in bone physiology and repair metabolism. In recent years, the application of hormones for implant osseointegration has become a research hotspot. Herein, we provide a comprehensive overview of the relevant reports on endogenous hormones and their corresponding supplementary preparations to explore the association between hormones and the prognosis of implants. We also discuss the effects and mechanisms of insulin, parathyroid hormone, melatonin, vitamin D, and growth hormone on osseointegration at the molecular and body levels to provide a foothold and guide future research on the systemic conditions that affect the implantation process and expand the relative contraindications of the implant, and the pre-and post-operative precautions. This review shows that systemic hormones can regulate the osseointegration of oral implants through endogenous or exogenous drug-delivery methods.

pH-responsive cinnamaldehyde-TiO2 nanotube coating: fabrication and functions in a simulated diabetes condition

Current evidence has suggested that diabetes increases the risk of implanting failure, and therefore, appropriate surface modification of dental implants in patients with diabetes is crucial. TiO₂ nanotube (TNT) has an osteogenic nanotopography, and its osteogenic properties can be further improved by loading appropriate drugs. Cinnamaldehyde (CIN) has been proven to have osteogenic, anti-inflammatory, and anti-bacterial effects. We fabricated a pH-responsive cinnamaldehyde-TiO₂ nanotube coating (TNT-CIN) and hypothesized that this coating will exert osteogenic, anti-inflammatory, and anti-bacterial functions in a simulated diabetes condition. TNT-CIN was constructed by anodic oxidation, hydroxylation, silylation, and Schiff base reaction to bind CIN, and its surface characteristics were determined. Conditions of diabetes and diabetes with a concurrent infection were simulated using 22-mM glucose without and with 1-μg/mL lipopolysaccharide, respectively. The viability and osteogenic differentiation of bone marrow mesenchymal stem cells, polarization and secretion of macrophages, and resistance to Porphyromonas gingivalis and Streptococcus mutans were evaluated. CIN was bound to the TNT surface successfully and released better in low pH condition. TNT-CIN showed better osteogenic and anti-inflammatory effects and superior bacterial resistance than TNT in a simulated diabetes condition. These findings indicated that TNT-CIN is a promising, multifunctional surface coating for patients with diabetes needing dental implants. Graphical abstract.

Comparison of bone mineral density and Fracture Risk Assessment Tool in Saudi women with and without type 2 diabetes mellitus: A cross-sectional study

OBJECTIVES

To compare the bone mineral density and the fracture risks in Saudi women with and without type 2 diabetes mellitus (T2DM).

METHODS

This cross-sectional study was carried out at Taibah Early Diagnostic Center, Al Madinah Al Munawarah, Saudi Arabia. A total of 465 women with and without T2DM aged ≥40 years who visited the center for a dual-energy X-ray absorptiometry scan between December 2020 and July 2021 were randomly selected. The 10-year probabilities of major osteoporotic fracture (MOF) and hip fracture (HF) were calculated using the Abu Dhabi Fracture Risk Assessment Tool (FRAX) with and without adjustment for T2DM. The adjustment was made by setting rheumatoid arthritis as the equivalent risk for T2DM in the FRAX. Bone mineral density values and the FRAX scores were compared between women with T2DM and non-diabetes.

RESULTS

Of 465 women, 214 had T2DM, and 251 were non-diabetics. The mean age of women was 59.42±7.9 years. There were no significant differences in mean age, menopausal status, height, weight, and body mass index between T2DM and non-diabetic women. Bone mineral density values and the unadjusted FRAX scores were comparable between the 2 groups. However, after adjusting FRAX for T2DM, the FRAX for MOF and HF became significantly higher in T2DM women (p=0.000 and p=0.004).

CONCLUSION

In Saudi women with T2DM, unadjusted FRAX underestimated the risk of MOF and HF. Type 2 diabetes mellitus should be included as one of the clinical risk factors for fracture in future versions of the FRAX score.

SIRT3 improves bone regeneration and rescues diabetic fracture healing by regulating oxidative stress

Diabetes mellitus (DM), a chronic metabolic disorder caused by uncontrolled high blood glucose levels due to insufficient insulin secretion or insulin resistance, is one of the most common metabolic diseases globally and is responsible for severe socio-economic burden. DM is associated with impaired fracture healing caused by oxidative stress induced-excessive bone resorption. Sirtuin3 (SIRT3), predominantly located in mitochondria, offers great influence on mitochondrial homeostasis, oxidative stress and immune cell function. However, the exact effect of SIRT3 on fracture healing with DM still remains to be elucidated. The present study demonstrated that SIRT3 expression was diminished in diabetic fracture healing and genetic deletion of SIRT3 increased mitochondrial oxidative stress and delayed diabetic bone healing via exacerbating the impact of DM on cartilage and osteoclast. The Honokiol (HKL) extracted from bark of magnolia trees, is a small molecular weight compound with various pharmaceutical properties by activating SIRT3. Our study proved that the SIRT3 agonist HKL could partially reverse the effect of diabetes on fracture healing, which provides a new promising approach for improving fracture healing in DM.

Lycopene Improves Bone Quality and Regulates AGE/RAGE/NF-кB Signaling Pathway in High-Fat Diet-Induced Obese Mice

Objective. This study was aimed at examining the effects of lycopene on bone metabolism in high-fat diet (HFD)- induced obese mice and to identify the potential underlying mechanisms. Methods. Mice were fed a HFD for 12 weeks and then continue with or without lycopene intervention (15 mg/kg) for additional 10 weeks. The effects of lycopene on blood glucose and lipid metabolism, as well as serum levels of total antioxidant capacity (T-AOC), superoxide dismutase (SOD), and malondialdehyde (MDA) were determined by biochemical assays. Bone histomorphological features and osteoclast activity were assessed by hematoxylin/eosin and tartrate-resistant acid phosphatase staining. Bone microstructure at the proximal tibial metaphysis and diaphysis was determined by microcomputed tomography. Tibial biomechanical strength and material profiles were measured by a three-point bending assay and Fourier transform infrared spectroscopy. Protein expressions involved in the AGE/RAGE/NF-кB signaling pathway were determined by western blot and/or immunohistochemical staining. Results. Lycopene consumption reduced body weight gain and improved blood glucose and lipid metabolism in HFD-induced obese mice. In addition, lycopene treatment preserved bone biomechanical strength, material profiles, and microarchitecture in obese mice. Moreover, these alterations were associated with an increase in serum levels of T-AOC and SOD, and a decline in serum levels of MDA, as well as a reduction of AGEs, RAGE, cathepsin K, and p-NF-кBp65 and NF-кBp65 expressions in the femurs and tibias of obese mice. Conclusion. Lycopene may improve bone quality through its antioxidant properties, which may be linked with the regulation of the AGE/RAGE/NF-кB signaling pathway in obese mice. These results suggest that lycopene consumption may be beneficial for the management of obesity-induced osteoporosis.

High glucose mediates apoptosis and osteogenesis of MSCs via downregulation of AKT-Sirt1-TWIST

BACKGROUND

Mesenchymal stem cells have been widely used in the treatment of diabetes mellitus. However, hyperglycemia associated with DM promotes cell apoptosis and affects osteogenic differentiation of MSCs in varying degrees, leading to osteoporosis in DM patients. Therefore, in this paper, the effect of high glucose on apoptosis and osteogenesis of MSCs was investigated and underlying mechanism was further determined.

METHODS AND RESULTS

Intracellular ROS levels were determined using probe DCFH-DA. MMP was detected using JC-1 staining. Cell apoptosis was detected using Annexin V-FITC/PI and Flow Cytometer. The expression of genes and protein was detected by qRT-PCR and Western blot respectively. The results showed high glucose induced MSC apoptosis but promoted its osteogenesis. Western blot analysis revealed that high glucose downregulated AKT-Sirt1-TWIST pathway. Activation of Sirt1 via SRT1720 increased TWIST expression, alleviated MSC apoptosis and promoted osteogenesis of MSCs. TWIST knockdown studies demonstrated that inhibition of TWIST intensified high glucose-induced apoptosis but promoted osteogenesis differentiation of MSCs. TWIST is likely to be a new regulator for cross talk between Sirt1 and its downstream targets.

CONCLUSION

Our data demonstrates that high glucose induces MSC apoptosis and enhances osteogenesis differentiation via downregulation of AKT-Sirt1-TWIST.

Purple Tea Water Extract Blocks RANKL-induced Osteoclastogenesis through Modulation of Akt/GSK3β and Blimp1-Irf8 Pathways

A number of studies demonstrated that some tea extracts exert inhibitory effects on osteoclastogenesis induced by receptor activator of nuclear factor κB ligand (RANKL). However, the effect of purple tea,...

Bone-kidney axis: A potential therapeutic target for diabetic nephropathy

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease (ESRD). However, its pathogenesis remains unclear, and effective prevention and treatment strategies are lacking. Recently, organ-to-organ communication has become a new focus of studies on pathogenesis. Various organs or tissues (the liver, muscle and adipose tissue) secrete a series of proteins or peptides to regulate the homeostasis of distal organs in an endocrine manner. Bone, an important part of the body, can also secrete bone-derived proteins or peptides that act on distal organs. As an organ with high metabolism, the kidney is responsible for signal and material exchange with other organs at any time through circulation. In this review, we briefly discussed bone composition and changes in bone structure and function in DN and summarized the current status of bone-derived proteins and their role in the progression of DN. We speculated that the "bone-kidney axis" is a potential target for early diagnosis and treatment of DN.

Investigating the Effects of Diet-Induced Pre-Diabetes on the Functioning of Calcium-Regulating Organs in Male Sprague Dawley Rats: Effects on Selected Markers

Derangements to the functioning of calcium-regulating organs have been associated with type 2 diabetes mellitus (T2DM), a condition preceded by pre-diabetes. Type 2 diabetes has shown to promote renal calcium wastage, intestinal calcium malabsorption and increased bone resorption. However, the changes to the functioning of calcium-regulating organs in pre-diabetes are not known. Subsequently, the effects of diet-induced pre-diabetes on the functioning of calcium-regulating organs in a rat model for pre-diabetes was investigated in this study. Male Sprague Dawley rats were separated into two groups (n=6, each group): non-pre-diabetic (NPD) group and a diet-induced pre-diabetic (DIPD) group for 20 weeks. After the experimental period, postprandial glucose and HOMA-IR were analysed in addition to plasma and urinary calcium concentrations. Gene expressions of intestinal vitamin D (VDR), intestinal calbindin-D9k, renal 1-alpha hydroxylase and renal transient receptor potential vanilloid 5 (TRPV5) expressions in addition to plasma osteocalcin and urinary deoxypyridinoline concentrations were analysed at week 20. The results demonstrated significantly increased concentrations of postprandial glucose, HOMA-IR and urinary calcium in addition to unchanged plasma calcium levels in the DIPD group by comparison to NPD. Renal TRPV5, renal 1-alpha hydroxylase, intestinal VDR and intestinal calbindin-D9k expressions were increased in the DIPD group by comparison to NPD. Furthermore, plasma osteocalcin levels were increased and urine deoxypyridinoline levels were decreased in the DIPD group by comparison to NPD. These observations may suggest that calcium-regulating organs compensate for the changes to calcium homeostasis by inducing increased renal calcium reabsorption, increased intestinal calcium absorption and decreased bone resorption followed by increased bone formation.

Strontium-incorporated titanium implant surfaces treated by hydrothermal treatment enhance rapid osseointegration in diabetes: A preclinical vivo experimental study

OBJECTIVES

The aim of the current study was to explore effects of strontium-incorporated titanium implant surfaces by hydrothermal treatment on osseointegration in diabetic rats.

MATERIALS AND METHODS

The surface characteristics of SLA and SLA-Sr surfaces were detected by related instruments. Thirty-six male Sprague-Dawley rats were induced into diabetes, and thirty-six rats were normal. SLA and SLA-Sr implants were, respectively, inserted into bilateral tibial metaphysis of each rat. Percentage of bone-to-implant contact (BIC%) and percentage of bone area (BA%) were analyzed at 4 and 8 weeks after implantation. Immunohistochemistry of osteoprotegerin (OPG) and Wnt5a were conducted at 1 and 4 weeks. Gene expression levels of inflammatory cytokines and related signaling molecules in peri-implant bone tissue were detected at 3 and 7 days.

RESULTS

Strontium was uniformly distributed on SLA-Sr surfaces, and it was released in an effective concentration range. SLA-Sr surfaces showed significantly higher BIC% in diabetic rats at 4 (p < .05) and 8 weeks (p < .05). Besides, it displayed higher BIC% at 4 weeks (p < .05) in normal rats. Also, SLA-Sr surfaces upregulated expression of OPG at 4 weeks (p < .05) in diabetic rats. What's more, SLA-Sr surfaces downregulated inflammation (TNF-α, IL-1β, and IL-6; p < .01) in diabetic rats at 3 days. In addition, expression of Wnt5a and ROR2 was upregulated (p < .05) at 7 days after implantation under diabetes.

CONCLUSION

It is suggested that strontium-incorporated titanium implant surfaces by hydrothermal treatment could enhance implant osseointegration as compared with SLA implant surfaces in diabetic rats.

Correlation Between 25 Hydroxyvitamin D Levels and Nonalcoholic Fatty Liver Disease in Chinese Patients with Type 2 Diabetes Mellitus: A Cross-Sectional Study

Purpose

We aimed to analyze the serum vitamin D level in Chinese patients with type 2 diabetes mellitus (T2DM) and discuss its correlation with nonalcoholic fatty liver disease (NAFLD).

Patients and Methods

A total of 300 patients with T2DM (92 patients without NAFLD and 208 patients with NAFLD) were enrolled, and 25-hydroxyvitamin D [25-(OH)D] levels were compared between the two groups. Second, the NAFLD fibrosis score (NFS) and fatty liver index (FLI) were used to group patients with T2DM complicated by NAFLD, and the differences in serum 25-(OH)D in patients with different degrees of liver fibrosis were compared. Third, multiple regression analysis was used to analyze the independent predictors of liver fibrosis in patients with T2DM complicated by NAFLD.

Results

The level of 25-(OH)D in patients with T2DM complicated by NAFLD was significantly lower than that in patients with T2DM alone. Based on the NFS and FLI, the 25-(OH)D level of the hepatic fibrosis subgroup was significantly lower than that of the subgroup without liver fibrosis. 25-(OH)D was found to be an independent predictor of liver fibrosis in patients with T2DM complicated by NAFLD.

Conclusion

The serum 25-(OH)D level in patients with T2DM complicated by NAFLD was significantly reduced, and the 25-(OH)D level showed a gradual downward trend with the degree of liver fibrosis. Low concentrations of 25-(OH)D may be indicative of the degree of liver fibrosis in diabetic patients.

Osteoclastic activity was associated with the development of steroid-induced osteonecrosis of femoral head

This study is focussed on evaluating and comparing two mediators of osteoclast, osteoprotegerin (OPG) and nuclear factor-κB ligand (RANKL), in plasma and tissue levels in patients with steroid-induced osteonecrosis of femoral head (SIONFH). Subjects were included in this cross-sectional case-control study in 2016. Bone histomorphology, immunohistochemistry, Western blotting, OPG and RANKL plasma levels, post-hoc statistical power and receiver-operating characteristic (ROC) curves were evaluated. Eighty-six patients diagnosed with SIONFH and 51 healthy subjects were included. OPG expression levels in bone samples increased with ARCO stage, and RANKL expression levels decreased with ARCO stages. Plasma OPG and RANKL levels were significantly higher in the SIONFH group compared with the healthy control group. The plasma OPG level and ratio of OPG and RANKL were positively associated with ARCO stages and significantly higher in stages III and IV. Plasma RANKL levels were negatively associated with ARCO stage and were significantly higher in ARCO stages II and III. Plasma OPG and RANKL may represent potential biomarkers during SIONFH at different stages. Higher plasma OPG levels indicated late-stage SIONFH, and higher plasma RANKL levels indicated early stage. Our findings may provide a clue for the development of diagnostic tools and therapies for SIONFH.

Glycolipid toxicity induces osteogenic dysfunction via the TLR4/S100B pathway

Diabetes can cause bone metabolism disorders and osteoporosis. The occurrence of both diabetes mellitus and osteoporosis increases the disability and mortality of elderly individuals due to pathological fracture. Abnormal metabolism of nutrientsis considered to be one of the important mechanisms of diabetes mellitus-induced osteoporosis. This study preliminarily explored the roles of TLR4 (Toll-like receptor 4) and S100B in osteogenic dysfunction induced by glycolipid toxicity. In this study, a diabetic rat model and TLR4-knockdown diabetic rat model were used in vivo. MC3T3-E1 cells in a high glucose and palmitic acid environment were used as glycolipid toxicity cell models in vitro. We investigated the effects of TLR4 and S100B on osteogenesis by overexpression or inhibition of TLR4 and S100B in vitro. We found that when TLR4 or S100B was inhibited, ALP and OCN were significantly up-regulated and p-ERK was significantly down regulated in the glycolipid model. These results suggest that TLR4/S100B may play a role in reducing glycolipid toxicity by regulating ERK phosphorylation.

Relationship between bone turnover markers and oxidative stress in children with type 1 diabetes mellitus

BACKGROUND

Oxidative stress in children with type 1 DM (T1DM) may negatively affect the bone.

METHODS

This study included 40 children with T1DM as the patient group and 40 healthy children of matched age and sex as the control group. Plasma alkaline phosphatase, procollagen type-1 amino-terminal propeptide (P1NP), and urinary deoxypyridinoline (DPD) were measured to assess bone turnover. Glutathione, superoxide dismutase (SOD), and malondialdehyde (MDA) were measured to assess oxidative stress.

RESULTS

Patients with T1DM had a significantly lower P1NP level but a significantly higher urinary DPD level compared to the control group. Moreover, there were significantly lower glutathione and SOD levels with significantly higher MDA levels in patients with T1DM. We found a significant positive correlation between P1NP level and both glutathione and SOD levels but a significant negative correlation between P1NP and MDA in patients with T1DM. There was a significant negative correlation between DPD levels and both glutathione and SOD levels and a significant positive correlation between DPD and MDA. Moreover, glutathione was a significant predictor for both P1NP and DPD levels, while MDA was a significant predictor for P1NP levels.

CONCLUSIONS

There is an association between oxidative stress and bone turnover markers in children with T1DM.

IMPACT

Oxidative stress can negatively affect bone but the exact relationship between oxidative stress and bone turnover in T1DM has not been previously studied in pediatrics. For the best of our knowledge, our study was the first to assess the relationship between oxidative stress and bone turnover in children with T1DM. We revealed that increased oxidative stress in children and adolescents with T1DM may be involved in the impairment of bone turnover process, so treatment strategies toward better glycemic control and decreasing oxidative stress may be beneficial in preventing and treating diabetic bone disease in these children.

Genistein prevents bone loss in type 2 diabetic rats induced by streptozotocin

Background

Diabetic osteoporosis has become a severe public health problem in the aging societies. Genistein has been reported to play an important role in preventing and treating metabolic diseases via its anti-inflammatory, antioxidant, anti-estrogenic, and estrogen-like functions.

Objective

We aimed to investigate whether genistein exerts bone-protective effect on diabetic rats induced by 35 mg/kg streptozotocin (STZ) plus a 4-week high-fat diet.

Design

Sprague–Dawley rats were randomly divided into four groups: (1) control group, (2) type 2 diabetes mellitus (T2DM) model group, (3) T2DM with 10 mg/kg genistein, and (4) T2DM with 30 mg/kg genistein. After an 8-week treatment with genistein, the femurs, tibias, and blood were collected from all rats for further analysis.

Results

Genistein at 10 mg/kg showed little effect on diabetic osteoporosis, whereas genistein at 30 mg/kg significantly improved glucose and bone metabolisms compared with diabetic rats. Our results showed that 30 mg/kg genistein significantly increased bone mineral density, serum osteocalcin, and bone alkaline phosphatase. Genistein also effectively lowered fasting blood glucose, tartrate-resistant acid phosphatase 5b, tumor necrosis factor-α, interleukin-6, and numbers of adipocytes and osteoclasts. Compared with the T2DM group, protein levels of receptor activator of nuclear factor κB ligand (RANKL) and peroxisome proliferator-activated receptor-γ (PPAR-γ) were decreased, while protein levels of osteoprotegerin (OPG), β-catenin, and runt-related transcription factor 2 (Runx-2) were increased after genistein intervention.

Conclusion

Genistein could effectively improve abnormal bone metabolism in STZ-induced diabetic rats; the underlying molecular mechanisms might be related to OPG/RANKL, PPAR-γ, and β-catenin/Runx-2 pathways.

A promising biomarker of elevated galanin level in hypothalamus for osteoporosis risk in type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) and osteoporosis are two major healthcare problems worldwide. T2DM is considered to be a risk factor for osteoporosis. Interestingly, several epidemiological studies suggest that bone abnormalities associated with diabetes may differ, at least in part, from those associated with senile or post-menopausal osteoporosis. The growing prevalence that patients with T2DM simultaneously suffer from osteoporosis, puts forward the importance to discuss the relationship between both diseases, as well as to investigate correlative agents to treat them. Emerging evidences demonstrate that neuropeptide galanin is involved in the pathogenesis of T2DM and osteoporosis. Galanin via activation of central GALR2 increases insulin sensitivity as well as bone density and mass in animal models. The disorder of galanin function plays major role in development of both diseases. Importantly, galanin signaling is indispensable for ΔFosB, an AP1 antagonist, to play the bone mass-accruing effects in the ventral hypothalamic neurons of diabetic models. This review summarizes our and other recent studies to provide a new insight into the multivariate relationship among galanin, T2DM and osteoporosis, highlighting the beneficial effect of galanin on the comorbid state of both diseases. These may help us better understanding the pathogenesis of osteoporosis and T2DM and provide useful clues for further inquiry if elevated galanin level may be taken as a biomarker for both conjoint diseases, and GALR2 agonist may be taken as a novel therapeutic strategy to treat both diseases concurrently.

Progress of Mesenchymal Stem Cell-Derived Exosomes in Tissue Repair

Mesenchymal stem cells (MSCs) are a kind of adult stem cells with self-replication and multidirectional differentiation, which can differentiate into tissue-specific cells under physiological conditions, maintaining tissue self-renewal and physiological functions. They play a role in the pathological condition by lateral differentiation into tissue-specific cells, replacing damaged tissue cells by playing the role of a regenerative medicine , or repairing damaged tissues through angiogenesis, thereby, regulating immune responses, inflammatory responses, and inhibiting apoptosis. It has become an important seed cell for tissue repair and organ reconstruction, and cell therapy based on MSCs has been widely used clinically. The study found that the probability of stem cells migrating to the damaged area after transplantation or differentiating into damaged cells is very low, so the researchers believe the leading role of stem cell transplantation for tissue repair is paracrine secretion, secreting growth factors, cytokines or other components. Exosomes are biologically active small vesicles secreted by MSCs. Recent studies have shown that they can transfer functional proteins, RNA, microRNAs, and lncRNAs between cells, and greatly reduce the immune response. Under the premise of promoting proliferation and inhibition of apoptosis, they play a repair role in tissue damage, which is caused by a variety of diseases. In this paper, the biological characteristics of exosomes (MSCs-exosomes) derived from mesenchymal stem cells, intercellular transport mechanisms, and their research progress in the field of stem cell therapy are reviewed.

[Zoledronate regulates osteoclast differentiation and bone resorption in high glucose through p38 MAPK pathway]

OBJECTIVE

To investigate the effect of zoledronate (ZOL) on osteoclast differentiation and bone resorption under high glucose, and the regulation mechanism of p38 mitogen activated kinase (p38 MAPK) signaling pathway in this process.

METHODS

RAW264.7 cells were divided into four groups: low group, high group, low+ZOL group and high+ZOL group after induced into osteoclasts. Cell proliferation activity was determined by MTT assay. The migration of RAW264.7 cells were examined Optical microscopy. Immunofluorescence microscopy was used to observe the cytoskeleton and sealing zones of osteoclasts. After adding group 5: high + ZOL + SB203580 group, trap staining was used to identify the number of positive osteoclasts in each group. The number and area of resorption lacunae were observed by SEM. The mRNA and protein expression of osteoclast related factors were detected by real-time PCR and Western blotting.

RESULTS

The cells in the 5 groups showed similar proliferative activity. High glucose promoted the migration of RAW264.7 cells (P < 0.05), inhibited the clarity of cytoskeleton and the formation of sealing zones in the osteoclasts. Exposure to high glucose significantly lowered the expressions of p38 MAPK, p-p38 MAPK, NFATc1, CTSK and TRAP, and inhibited osteoclast differentiation and bone absorption (P < 0.05). Treatment with ZOL obviously suppressed the migration ability of RAW264.7 cells, further reduced the clarity of the cytoskeleton, inhibited the formation of sealing zones of the osteoclasts, lowered the expressions of p38 MAPK, p-p38 MAPK, NFATc1, CTSK, and TRAP (P < 0.05), and inhibited osteoclast differentiation and bone absorption. Treatment with SB203580 obviously inhibited osteoclast differentiation and bone resorption and the expressions of P38 MAPK, p-p38 MAPK, NFATc1, CTSK and TRAP (P < 0.05).

CONCLUSIONS

High glucose inhibits osteoclast differentiation and bone resorption. ZOL inhibits osteoclast differentiation and bone resorption in high-glucose conditions by regulating p38 MAPK pathway, which can be a new pathway for ZOL to regulate diabetic osteoporosis.

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

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

Bone Mineral Density in Diabetes Mellitus Foot Patients for Prediction of Diabetic Neuropathic Osteoarthropathic Fracture

BACKGROUND

Diabetic neuropathic osteoarthropathy (DNOAP) is known as debilitating diabetes complications. The aim of study is to compare bone mineral density (BMD) among diabetic foot and DNOAP, and investigate the impact of BMD proceeded from diabetic foot to DNOAP.

METHODS

A DNOAP group (subgroup A and subgroup B) and control group were examined for this study. Subgroup A (n=21) were patients diagnosed with DNOAP with the development of new foot and ankle fractures, whereas subgroup B (n=4) were patients being managed with the diabetic foot before a diagnosis of DNOAP. BMD was also evaluated before the diagnosis. Control group (n=30) was diabetic foot patients without DNOAP. The demographic data, clinical and radiologic data, comorbidities, and BMD were compared for each group. And optimal BMD score was reviewed to predict fractures in neuropathic arthropathy.

RESULTS

BMD was significantly lower in DNOAP group (group A and B) compared with control group. Also neuropathic arthropathy group showed poor radiological results. After comparisons of 2 group lumbar and femur BMD was significantly different, but logistic regression analysis revealed that low femur T-score could be risk predictors of the condition. Base on the data of group B and control group, the cut-off point for predicting foot and ankle fracture-related with DNOAP was -1.65 of femur BMD.

CONCLUSIONS

Low BMD shows greater incidence in foot and ankle fracture patients associated with neuropathic arthropathy. A femur T score can be a risk predictor of diabetic neuropathic arthropathy for diabetic foot patients.

Chondroitin Sulfate Prevents STZ Induced Diabetic Osteoporosis through Decreasing Blood Glucose, AntiOxidative Stress, Anti-Inflammation and OPG/RANKL Expression Regulation

Chondroitin sulfate (CS) has antioxidative, anti-inflammatory, anti-osteoarthritic and hypoglycemic effects. However, whether it has antidiabetic osteoporosis effects has not been reported. Therefore, in this study, we established a STZ-induced diabetic rat model; CS (500 mg kg⁻¹ d⁻¹) was orally administrated for eight weeks to study its preventive effects on diabetic osteoporosis. The results showed that eight weeks of CS treatment improved the symptoms of diabetes; the CS-treated group has increased body weight, decreased water or food intake, decreased blood glucose, increased bone-mineral density, repaired bone morphology and decreased femoral osteoclasts and tibia adipocytes numbers. After CS treatment, bone histomorphometric parameters returned to normal, the levels of serum inflammatory cytokines (IL-1β, IL-6 and TNF-α) decreased significantly, serum SOD, GPX and CAT activities increased and MDA level increased. In the CS-treated group, the levels of serum ALP, CTX-1, TRACP 5b, osteocalcin and RANKL decreased and the serum RUNX 2 and OPG levels increased. Bone immunohistochemistry results showed that CS can effectively increase the expression of OPG and RUNX2 and reduce the expression of RANKL in diabetic rats. All of these indicate that CS could prevent STZ induced diabetic osteoporosis—mainly through decreasing blood glucose, antioxidative stress, anti-inflammation and regulation of OPG/RANKL expression. CS can therefore effectively prevent bone loss caused by diabetes.

Biological Factors, Metals, and Biomaterials Regulating Osteogenesis through Autophagy

Bone loss raises great concern in numerous situations, such as ageing and many diseases and in both orthopedic and dentistry fields of application, with an extensive impact on health care. Therefore, it is crucial to understand the mechanisms and the determinants that can regulate osteogenesis and ensure bone balance. Autophagy is a well conserved lysosomal degradation pathway, which is known to be highly active during differentiation and development. This review provides a revision of the literature on all the exogen factors that can modulate osteogenesis through autophagy regulation. Metal ion exposition, mechanical stimuli, and biological factors, including hormones, nutrients, and metabolic conditions, were taken into consideration for their ability to tune osteogenic differentiation through autophagy. In addition, an exhaustive overview of biomaterials, both for orthopedic and dentistry applications, enhancing osteogenesis by modulation of the autophagic process is provided as well. Already investigated conditions regulating bone regeneration via autophagy need to be better understood for finely tailoring innovative therapeutic treatments and designing novel biomaterials.

Zhibaidihuang Decoction Ameliorates Cell Oxidative Stress by Regulating the Keap1-Nrf2-ARE Signalling Pathway

Zhibaidihuang decoction (ZBDHD) is a Chinese herbal formula, which is used in Chinese traditional medicine to treat symptoms of Yinxuhuowang (Yin deficiency and high fire) syndrome. This study elucidates the mechanism of ZBDHD on oral ulcers, one Yinxuhuowang syndrome. Simultaneously, some ingredients in ZBDHD were found and identified by ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). A Ganjiangfuzirougui decoction- (GJD-) induced Yinxuhuowang syndrome SD rat model was used to demonstrate the efficiency of ZBDHD treatment. The oral mucosa of rat in the GJD group, stained with hematoxylin and eosin (H&E), showed epidermal shedding and inflammatory cell infiltration. And an alleviation efficiency of ZBDHD in GJD-induced pathological changes in the oral mucosa could be obtained. ZBDHD treatment restored the GJD-induced imbalance of metabolites, which were choline, glycocholic acid, and palmitoyl-L-carnitine (PALC). GJD stimulated the expression of NF-κB. And the overexpressed of NF-κB in mucosa of rat in the GJD group could be inhibited by ZBDHD treatment. Simultaneously, the optimal efficiency of ZBDHD treatment on the cellular ATP content, oxygen consumption rate (OCR), and superoxide dismutase (SOD) concentration was evaluated, in vitro assay. Compared to the control cells, the ATP content, OCR, and SOD activity in the ZBDHD-treated cells were significantly higher. For the mechanisms study, seven cytokines were screened with a Dual-Luciferase Reporter gene assay. In the ARE assay, the luciferase signal was stimulated significantly by ZBDHD. In cells, the transcription of nrf2, maf, and keap1, which were related to the ARE pathway, was elevated by ZBDHD treatment. Our study demonstrated that high-dose GJD could lead to Yinxuhuowang syndrome, such as oral ulcers, and the imbalance in serum metabolites. And ZBDHD can improve oral cell inflammation and the imbalance of metabolism by inhibiting NF-κB and enhancing the activity of the ARE signalling pathway to ameliorate oxidative stress in the cell. This study provides a theoretical basis for the clinical application of ZBDHD.

Hyperglycemia-Induced Aberrant Cell Proliferation; A Metabolic Challenge Mediated by Protein O-GlcNAc Modification

Chronic hyperglycemia has been associated with an increased prevalence of pathological conditions including cardiovascular disease, cancer, or various disorders of the immune system. In some cases, these associations may be traced back to a common underlying cause, but more often, hyperglycemia and the disturbance in metabolic balance directly facilitate pathological changes in the regular cellular functions. One such cellular function crucial for every living organism is cell cycle regulation/mitotic activity. Although metabolic challenges have long been recognized to influence cell proliferation, the direct impact of diabetes on cell cycle regulatory elements is a relatively uncharted territory. Among other "nutrient sensing" mechanisms, protein O-linked β-N-acetylglucosamine (O-GlcNAc) modification emerged in recent years as a major contributor to the deleterious effects of hyperglycemia. An increasing amount of evidence suggest that O-GlcNAc may significantly influence the cell cycle and cellular proliferation. In our present review, we summarize the current data available on the direct impact of metabolic changes caused by hyperglycemia in pathological conditions associated with cell cycle disorders. We also review published experimental evidence supporting the hypothesis that O-GlcNAc modification may be one of the missing links between metabolic regulation and cellular proliferation.

Rhizoma coptidis as a Potential Treatment Agent for Type 2 Diabetes Mellitus and the Underlying Mechanisms: A Review

Diabetes mellitus, especially type 2 diabetes mellitus (T2DM), has become a significant public health burden. Rhizoma coptidis (RC), known as Huang Lian, is widely used for treating diabetes in China. The bioactive compounds of RC, especially alkaloids, have the potential to suppress T2DM-induced lesions, including diabetic vascular dysfunction, diabetic heart disease, diabetic hyperlipidemia, diabetic nephropathy, diabetic encephalopathy, diabetic osteopathy, diabetic enteropathy, and diabetic retinopathy. This review summarizes the effects of RC and its bioactive compounds on T2DM and T2DM complications. Less research has been conducted on non-alkaloid fractions of RC, which may exert synergistic action with alkaloids. Moreover, we summarized the pharmacokinetic properties and structure-activity relationships of RC on T2DM with reference to extant literature and showed clearly that RC has potential therapeutic effect on T2DM.