OPG/RANK/RANKL signaling axis in patients with type I diabetes: Associations with parathormone and vitamin D

Epimedin B protects against bone loss and inflammation in diabetic osteoporosis rats by regulating OPG/RANKL pathway

BACKGROUND

Diabetes is a common disease contributing to osteoporosis. Epimedin B (EB), a major ingredient of Herba Epimedii, has been found to be effective in preventing osteoporosis in mice. However, the potential of EB to ameliorate diabetic osteoporosis (DOP) remains elusive. In this study, our goal is to investigate the functions and underlying mechanisms of EB in the progression of DOP.

METHODS

A DOP rat model was established via a high-fat diet combined with intraperitoneal injection of streptozotocin (STZ). DOP rats were daily administered with EB or vehicle via intragastric administration for 8 weeks. Body weights and blood glucose levels were measured every 4 weeks during the drug administration period. Blood samples and femoral tissues were collected for further analysis. Bone parameters and bone histopathological changes were detected. Bone formation and resorption markers as well as inflammatory factors were detected using enzyme-linked immunosorbent assay kits. Reverse-transcription quantitative polymerase chain reaction and western blotting were conducted to measure the expression of osteoprotegerin (OPG) and Rev-Erbα, receptor activator of NF-κB ligand (RANKL).

RESULTS

EB improved weight loss and lowered blood glucose of DOP rats. EB promoted the formation of bone trabeculae and altered several bone microstructure parameters in DOP rats. EB ameliorated improved bone structure, restored histological abnormalities of femoral bone, and reduced the number of bone marrow adipocytes in DOP rats. EB inhibited excessive bone resorption and inflammation and increased bone formation in DOP rats. EB regulated the OPG/RANKL axis in DOP rats.

CONCLUSION

EB attenuates STZ-induced DOP in rats by maintaining the balance between bone formation and resorption and inhibiting inflammation through regulating the OPG/RANKL axis.

Association between osteocalcin and residual β-cell function in children and adolescents newly diagnosed with type 1 diabetes: a pivotal study

PURPOSE

This pivotal study aimed to evaluate circulating levels of bone remodeling markers in children and adolescents at the onset of type 1 diabetes (T1D). Additionally, we assessed their correlation with glucose control, residual β-cell function, and the severity of presentation.

METHODS

In this single-center cross-sectional study, we recruited children and adolescents newly diagnosed with T1D at our tertiary-care Diabetes Centre. Anamnestic, anthropometric, clinical, and biochemical data at T1D diagnosis were collected. Basal and stimulated C-peptide levels were assessed, along with the following bone remodeling biomarkers: osteocalcin (OC), alkaline phosphatase (ALP), parathormone (PTH), 25-OH Vitamin D (25OH-D), and the C-terminal cross-linked telopeptide of type 1 collagen (CTX).

RESULTS

We enrolled 29 individuals newly diagnosed with T1D, with a slight male prevalence (51.7%). The mean age was 8.4 ± 3.7 years. A positive correlation between OC and stimulated C-peptide (R = 0.538; p = 0.026) and between PTH and serum HCO3- (R = 0.544; p = 0.025) was found. No other correlations between bone remodeling biomarkers and clinical variables were detected.

CONCLUSION

Our data showed a positive correlation between OC levels and residual β-cell function in children and adolescents at T1D presentation. Further longitudinal studies evaluating OC levels in pediatric subjects with T1D are needed to better understand the complex interaction between bone and glucose metabolisms.

Extra-osseous Roles of the RANK-RANKL-OPG Axis with a Focus on Skeletal Muscle

PURPOSE OF REVIEW

This review aims to consolidate recent observations regarding extra-osseous roles of the RANK-RANKL-OPG axis, primarily within skeletal muscle.

RECENT FINDINGS

Preclinical efforts to decipher a common signalling pathway that links the synchronous decline in bone and muscle health in ageing and disease disclosed a potential role of the RANK-RANKL-OPG axis in skeletal muscle. Evidence suggests RANKL inhibition benefits skeletal muscle function, mass, fibre-type switching, calcium homeostasis and reduces fall incidence. However, there still exists ambiguity regarding the exact mechanistic actions and subsequent functional improvements. Other potential RANK-RANKL-OPG extra-osseous roles include regulation of neural-inflammation and glucose metabolism. Growing evidence suggests the RANK-RANKL-OPG axis may play a regulatory role in extra-osseous tissues, especially in skeletal muscle. Targeting RANKL may be a novel therapy in ameliorating loss of muscle mass and function. More research is warranted to determine the causality of the RANK-RANKL-OPG axis in extra-osseous tissues, especially those affected by aging.

Cardiometabolic Effects of Denosumab in Premenopausal Women With Breast Cancer Receiving Estradiol Suppression: RCT

CONTEXT

Menopause is associated with changes in musculoskeletal, body composition, and metabolic parameters that may be amplified in premenopausal women receiving estradiol suppression for breast cancer. Denosumab offsets deleterious skeletal effects of estradiol suppression and has been reported to have effects on body composition and metabolic parameters in preclinical and observational studies, but evidence from double-blind randomized controlled trials is limited.

OBJECTIVE

To assess the effect of denosumab on body composition and metabolic parameters.

METHODS

In a prespecified secondary analysis of a 12-month randomized, double-blind, placebo-controlled trial, 68 premenopausal women with breast cancer initiating ovarian function suppression and aromatase inhibition were randomized to denosumab 60-mg or placebo administered at baseline and 6 months. Outcome measures were total and regional fat and lean mass (DXA), body mass index (BMI), waist and hip circumference, fasting glucose, HOMA-IR, and lipid profile. Using a mixed model, between-group mean adjusted differences over time are reported.

RESULTS

Over 12 months, relative to placebo, android and gynoid fat mass decreased in the denosumab group (-266 g [95% CI -453 to -79], P = .02, and -452 g [-783 to -122], P = .03, respectively). Total fat mass and waist circumference were lower in the denosumab group but not significantly (-1792 g [-3346 to -240], P = .08 and (- 3.77 cm [-6.76 to -0.79], P = .06, respectively). No significant treatment effects were detected in lean mass, BMI, hip circumference, fasting glucose, HOMA-IR, or lipid profile.

CONCLUSION

In premenopausal women receiving estradiol suppression, denosumab decreases some measures of fat mass with no detectable effects on other measures of body composition or metabolic parameters.

RANKL/RANK is required for cytokine-induced beta cell death; osteoprotegerin, a RANKL inhibitor, reverses rodent type 1 diabetes

Treatment for type 1 diabetes (T1D) requires stimulation of functional β cell regeneration and survival under stress. Previously, we showed that inhibition of the RANKL/RANK [receptor activator of nuclear factor kappa Β (NF-κB) ligand] pathway, by osteoprotegerin and the anti-osteoporotic drug denosumab, induces rodent and human β cell proliferation. We demonstrate that the RANK pathway mediates cytokine-induced rodent and human β cell death through RANK-TRAF6 interaction and induction of NF-κB activation. Osteoprotegerin and denosumab protected β cells against this cytotoxicity. In human immune cells, osteoprotegerin and denosumab reduce proinflammatory cytokines in activated T-cells by inhibiting RANKL-induced activation of monocytes. In vivo, osteoprotegerin reversed recent-onset T1D in nonobese diabetic/Ltj mice, reduced insulitis, improved glucose homeostasis, and increased plasma insulin, β cell proliferation, and mass in these mice. Serum from T1D subjects induced human β cell death and dysfunction, but not α cell death. Osteoprotegerin and denosumab reduced T1D serum-induced β cell cytotoxicity and dysfunction. Inhibiting RANKL/RANK could have therapeutic potential.

OPG/RANK/RANKL Axis in Egyptian Children With Acute Lymphoblastic Leukemia After Maintenance Therapy: Relationship to Bone Mineral and Vitamin D Status

Policies to maximize peak bone mass in survivor's children of acute lymphoblastic leukemia (ALL) have been recognized as a priority area for research. The present study aimed to evaluate the relationship between osteoprotegerin (OPG)/receptor activator of nuclear factor kappa-B (RANK)/RANK ligand (RANKL) axis, vitamin D status, and serum magnesium in ALL survivors. Sixty ALL survivors treated with chemotherapy and 60 age and sex-matched controls were included. Vitamin D and parathyroid hormone, RANK, RANKL, and OPG levels were immunoassayed, in addition to serum calcium, phosphorus, magnesium levels, and alkaline phosphatase activity assessment. Furthermore, standard anthropometric measurement, history of fractures since treatment and clinical assessment were recorded. History of bone fractures after the start of therapy was detected in 17 ALL subjects (28.33%). Significantly lower vitamin D, magnesium, calcium, and OPG levels, meanwhile, significantly higher serum parathyroid hormone, RANK, and RANKL levels were detected in survivors compared with the control group. Vitamin D level was significantly positively correlated with magnesium, calcium, and OPG levels. Meanwhile, negatively correlated with RANK and RANKL levels. ALL survivors had a high prevalence of impaired vitamin D status, decreased Mg, and altered OPG/RANK/RANKL axis with impaired bone remodeling. The results herein may open the door for new interventional actions in ALL survivors to protect against bone resorption.

mTOR Signaling Pathway in Bone Diseases Associated with Hyperglycemia

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

RANKL inhibition: a new target of treating diabetes mellitus?

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

Non-Alcoholic Fatty Liver Disease and Bone Tissue Metabolism: Current Findings and Future Perspectives

Non-alcoholic fatty liver disease (NAFLD) is reaching epidemic proportions worldwide. Moreover, the prevalence of this liver disease is expected to increase rapidly in the near future, aligning with the rise in obesity and the aging of the population. The pathogenesis of NAFLD is considered to be complex and to include the interaction between genetic, metabolic, inflammatory, and environmental factors. It is now well documented that NAFLD is linked to the other conditions common to insulin resistance, such as abnormal lipid levels, metabolic syndrome, and type 2 diabetes mellitus. Additionally, it is considered that the insulin resistance may be one of the main mechanisms determining the disturbances in both bone tissue metabolism and skeletal muscles quality and functions in patients with NAFLD. To date, the association between NAFLD and osteoporosis has been described in several studies, though it worth noting that most of them included postmenopausal women or elderly patients and originated from Asia. However, taking into account the health and economic burdens of NAFLD, and the increasing prevalence of obesity in children and adolescents worldwide, further investigation of the relationship between osteopenia, osteoporosis and sarcopenia in NAFLD, including in young and middle-aged patients, is of great importance. In addition, this will help to justify active screening and surveillance of osteopenia and osteoporosis in patients with NAFLD. In this review, we will discuss various pathophysiological mechanisms and possible biologically active molecules that may interplay between NAFLD and bone tissue metabolism.

Assessment of biochemical bone markers of osteoporosis in children with thalassemia major

BACKGROUND

Beta thalassemia major (β-TM) is a common cause of skeletal morbidity and is associated with increased bone fracture risk, particularly in inadequately transfused children. The aim of this study was to investigate some potential biochemical markers as possible early predictors of BMD variations in children with β-TM.

METHODS

The study included 38 children with β-TM and 40 sex-age matched controls. All patients were subjected to BMD assessment by dual-energy X-ray absorptiometry (DEXA). Serum beta-crosslaps (beta-CTx), osteoprotegerin (OPG), receptor activator of nuclear factor-kappa B ligand (RANKL), urinary deoxypyridinoline (DPD) and ferritin levels were compared between the groups.

RESULTS

Serum OPG levels were significantly lower in thalassemic children than in controls. The mean ratio of RANKL/OPG was significantly higher in the thalassemic patients than in the control group. Osteoporosis was detected in 10 (3 female and 7 male) of 38 patients (26.3%) according to the femur Z score and in 6 of them (4 male and 2 female) (15.8%) according to the spine Z score.

CONCLUSIONS

Serum OPG concentrations can be used as a biochemical marker in screening patients with beta-thalassemia major for the development of osteoporosis.

Vitamin D supplementation induces CatG-mediated CD4+ T cell inactivation and restores pancreatic β-cell function in mice with type 1 diabetes

Type 1 diabetes (T1D) is a chronic autoimmune disease accompanied by the immune-mediated destruction of pancreatic β-cells. In this study, we aimed to explore the regulatory effects of vitamin D (VD) supplementation on pancreatic β-cell function by altering the expression of bioinformatically identified cathepsin G (CatG) in T1D mice. A T1D mouse model was established in nonobese diabetic (NOD) mice, and their islets were isolated and purified. Pancreatic mononuclear cells (MNCs) were collected, from which CD4⁺ T cells were isolated. The levels of interleukin (IL)-2, IL-10, tumor necrosis factor-α (TNF-α), and interferon-γ (IFN-γ) in the supernatant of mouse pancreatic tissue homogenate were assessed using ELISA. Immunohistochemistry and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labelin (TUNEL) staining were conducted to evaluate the effects of VD supplementation on pancreatic tissues of T1D mice. The pancreatic β-cell line MIN6 was used for in vitro substantiation of findings in vivo. VD supplementation reduced glucose levels and improved glucose tolerance in T1D mice. Furthermore, VD supplementation improved pancreatic β-cell function and suppressed immunological and inflammatory reactions in the T1D mice. We documented overexpression of CatG in diabetes tissue samples, and then showed that VD supplementation normalized the islet immune microenvironment through downregulating CatG expression in T1D mice. Experiments in vitro subsequently demonstrated that VD supplementation impeded CD4⁺ T activation by downregulating CatG expression and thereby enhanced pancreatic β-cell function. Results of the present study elucidated that VD supplementation can downregulate the expression of CatG and inhibit CD4⁺ T cell activation, thereby improving β-cell function in T1D.NEW & NOTEWORTHY We report that vitamin D (VD) supplementation downregulates CatG expression and inhibits CD4⁺ T cell activation, thereby improving β-cell function in type 1 diabetes (T1D). This study deepens our understanding of the pathogenesis of T1D and clarifies molecular events underlying the alleviatory effect of VD for immunotherapy against T1D.

Role of nitric oxide in type 1 diabetes-induced osteoporosis

Type 1 diabetes (T1D)-induced osteoporosis is characterized by decreased bone mineral density, bone quality, rate of bone healing, bone formation, and increased bone resorption. Patients with T1D have a 2-7-fold higher risk of osteoporotic fracture. The mechanisms leading to increased risk of osteoporotic fracture in T1D include insulin deficiency, hyperglycemia, insulin resistance, lower insulin-like growth factor-1, hyperglycemia-induced oxidative stress, and inflammation. In addition, a higher probability of falling, kidney dysfunction, weakened vision, and neuropathy indirectly increase the risk of osteoporotic fracture in T1D patients. Decreased nitric oxide (NO) bioavailability contributes to the pathophysiology of T1D-induced osteoporotic fracture. This review discusses the role of NO in osteoblast-mediated bone formation and osteoclast-mediated bone resorption in T1D. In addition, the mechanisms involved in reduced NO bioavailability and activity in type 1 diabetic bones as well as NO-based therapy for T1D-induced osteoporosis are summarized. Available data indicates that lower NO bioavailability in diabetic bones is due to disruption of phosphatidylinositol 3‑kinase/protein kinase B/endothelial NO synthases and NO/cyclic guanosine monophosphate/protein kinase G signaling pathways. Thus, NO bioavailability may be boosted directly or indirectly by NO donors. As NO donors with NO-like effects in the bone, inorganic nitrate and nitrite can potentially be used as novel therapeutic agents for T1D-induced osteoporosis. Inorganic nitrites and nitrates can decrease the risk for osteoporotic fracture probably directly by decreasing osteoclast activity, decreasing fat accumulation in the marrow cavity, increasing osteoblast activity, and increasing bone perfusion or indirectly, by improving hyperglycemia, insulin resistance, and reducing body weight.

Osteoprotegerin expression and serum values in obese women with type 2 diabetes mellitus

BACKGROUND

Obesity and diabetes prevalence are increasing worldwide. We aimed to detect the possible association of osteoprotegerin (OPG) gene expression with visceral adiposity indices and cardiometabolic risk factors among obese women.

METHODS AND RESULTS

The study enrolled 150 controls and 150 obese cases subdivided into two subgroups non-diabetic (n = 70) and 80 patients with type 2 diabetes mellitus (T2DM). Circulating OPG gene expression levels were figured out by real time PCR (Polymerase Chain Reaction). Serum OPG levels were assessed by Enzyme Linked Immunosorbent Assay. Our results explored that OPG serum levels were lower in the obese women compared to control group (p < 0.001) and obese diabetics had higher serum levels of OPG in comparison to obese non-diabetic patients (p < 0.001). Expression levels of OPG were higher in obese women than controls (p < 0.001). Moreover, the blood expression levels of OPG gene were higher in diabetic obese patients than non-diabetics. We found positive correlations between parameters of metabolic syndrome and obesity indices. After adjustment of the traditional risk factors, stepwise linear regression analysis test revealed that OPG expression levels were independently correlated with glycated hemoglobin, high-density lipoprotein-cholesterol, and waist-to-hip ratio.

CONCLUSIONS

OPG mRNA levels were associated with surrogate markers of insulin resistance in Egyptian obese women.

Mechanisms of altered bone remodeling in children with type 1 diabetes

Bone loss associated with type 1 diabetes mellitus (T1DM) begins at the onset of the disease, already in childhood, determining a lower bone mass peak and hence a greater risk of osteoporosis and fractures later in life. The mechanisms underlying diabetic bone fragility are not yet completely understood. Hyperglycemia and insulin deficiency can affect the bone cells functions, as well as the bone marrow fat, thus impairing the bone strength, geometry, and microarchitecture. Several factors, like insulin and growth hormone/insulin-like growth factor 1, can control bone marrow mesenchymal stem cell commitment, and the receptor activator of nuclear factor-κB ligand/osteoprotegerin and Wnt-b catenin pathways can impair bone turnover. Some myokines may have a key role in regulating metabolic control and improving bone mass in T1DM subjects. The aim of this review is to provide an overview of the current knowledge of the mechanisms underlying altered bone remodeling in children affected by T1DM.

Study on the morphological and metabolic changes of femur in laying hens with hypophosphatemia

Layer fatigue syndrome caused by the lack of calcium and phosphorus can cause fracture in laying hens. The effect of phosphorus deficiency on the femur of laying hens with layer fatigue syndrome has not been studied. In this study, sixty 22-week-old Roman white layers were randomly divided into control group (group C) and low phosphorus group (group P), 30 individuals in each group. The available phosphorus content of group P was 0.18%. At the age of 26, 30 and 34 weeks, the production performance, biomechanical index, protein expression, histopathological change of femur and serological index were detected. The results showed that the laying rate, egg quality and body weight of laying hens, bone density, cortical bone thickness, rigidity, flexural modulus, flexural rigidity, the maximum load of femur and expression of osteocalcin (OCN), receptor activator of nuclear factor kappa-Β (RANK) and receptor activator of nuclear factor kappa-Β ligand (RANKL) decreased of group P. The number of osteocytes was decreased, and the voids was increased. However, cell lacunae were not obvious. The levels of phosphorus, calcium and OCN were increased, and the content of estradiol (E₂), OPG and calcitonin (CT) were decreased in serum. In conclusion, the low phosphorus diet can induce layer fatigue syndrome and affect the content of OPG and E₂ in serum and the expression of OCN, OPG, RANK and RANKL in femur protein, which leads to the imbalance of bone homeostasis, the thinning of femur cortex bone and the decrease of bone density.

Osteocytes and Diabetes: Altered Function of Diabetic Osteocytes

PURPOSE OF REVIEW

Diabetes mellitus is a prevalent chronic disease affecting millions of people in the world. Bone fragility is a complication found in diabetic patients. Although osteoblasts and osteoclasts are directly affected by diabetes, herein we focus on how the diabetic state-based on hyperglycemia and accumulation of advanced glycation end products among other features-impairs osteocyte functions exerting deleterious effects on bone.

RECENT FINDINGS

In the last years, several studies described that diabetic conditions cause morphological modifications on lacunar-canalicular system, alterations on osteocyte mechanoreceptors and intracellular pathways and on osteocyte communication with other cells through the secretion of proteins such as sclerostin or RANKL. This article gives an overview of events occurring in diabetic osteocytes. In particular, mechanical responses seem to be seriously affected in these conditions, suggesting that mechanical sensibility could be a target for future research in the field.