Vertebral marrow fat fraction is associated with circulating RANKL in postmenopausal females.

Objective: To investigate the relationship between circulating receptor activator of nuclear factor-kappa B ligand (RANKL) levels and marrow adipose tissue in postmenopausal females. Methods: A total of 164 postmenopausal females were included in the study. Serum levels of osteoprotegerin (OPG) and RANKL were measured using ELISA kits. Body composition and bone mineral density (BMD) were assessed using dual-energy X-ray absorptiometry. Complex-based chemical shift imaging-based MRI was employed to evaluate the vertebral marrow proton density fat fraction (PDFF). A multivariate linear regression model was utilized to analyze the predictive effects of PDFF and BMD on circulating levels of OPG and RANKL. Results: Simple regression analysis showed significant associations among the marrow PDFF, BMD at either site, serum RANKL, and the RANKL/OPG ratio. In multivariate linear regression models, marrow PDFF was found to have a positive correlation (ß = 3.15, 95% CI 2.60 to 3.70) and BMD had negative correlations (ß = -0.200, 95% CI -0.348 to -0.051 for vertebral BMD; ß = -0.383, 95% CI -0.589 to -0.177 for total hip BMD; and ß =-0.393, 95% CI -0.598 to -0.188 for femoral neck BMD, all p < 0.01) with circulating soluble RANKL levels after adjusting for age, body mass index, physical activity, total fat mass, android/gynoid ratio, and lean mass. Similar results were observed for the RANKL/OPG ratio. Additionally, multivariate linear regression analyses revealed that marrow PDFF was a significant independent contributor of circulating soluble RANKL (ß = 1.34, 95% CI 1.10 to 1.58, p < 0.001) after further controlling for BMD. However, marrow PDFF or BMD had no associations with circulating levels of OPG after adjusting for all potential confounders mentioned above. Conclusions: Vertebral marrow fat fraction is independently associated with circulating soluble RANKL levels in postmenopausal females.

Interactions of the Osteokines, Glucose/Insulin System and Vascular Risk Networks in Patients With Newly Diagnosed Type 2 Diabetes (VNDS 15).

BACKGROUND AND AIM: Bone as an endocrine organ regulates metabolic processes independently of mineral metabolism through the production/release of proteins collectively named 'osteokines'. Relevant connections were reported between the insulin/glucose system, calcification of the atherosclerotic plaque, and several osteokines. We aimed to test the hypothesis that the osteokine network could be involved in beta-cell function, insulin sensitivity, and vascular damage in a cohort of people with newly diagnosed type 2 diabetes (T2D). SUBJECTS AND METHODS: In 794 drug-naive, GADA-negative, newly-diagnosed T2D patients (mean ± SD age: 59 ± 9.8 years; BMI: 29.3 ± 5.3 kg/m2; HbA1c: 6.6 ± 1.3%) we assessed: plasma concentration of osteocalcin (OCN), osteopontin (OPN), RANKL, and its putative decoy receptor osteoprotegerin (OPG); insulin sensitivity (SI) by hyperinsulinemic euglycemic clamp; beta cell function (BCF), estimated by OGTT minimal modelling and expressed as derivative (DC) and proportional (PC) control. Echo-doppler of carotid and lower limb arteries were also performed in 708 and 701 subjects, respectively. RESULTS: OCN, RANKL and OPG were significantly associated with PC (p < 0.02); OCN was positively related to DC (p = 0.018). OPG was associated with lower IS (p < 0.001). Finally, the higher RANKL levels, the greater was the severity of atherosclerosis in common carotid artery (p < 0.001). Increased OPG and OPN concentrations were related to subclinical atherosclerosis in peripheral arteries of lower limbs (p = 0.023 and p = 0.047, respectively). CONCLUSION: These data suggest that, in patients with newly diagnosed T2D, the osteokine network crosstalks with the glucose/insulin system and may play a role in modulating the atherosclerotic process.

Denosumab stimulates spermatogenesis in infertile men with preserved Sertoli cell capacity.

Sperm production depends on proper Sertoli-germ cell interaction, and we hypothesized that receptor activator of nuclear factor κB ligand (RANKL) activity in Sertoli cells may influence spermatogenesis. Treatment with the RANKL inhibitor denosumab, normally used to treat osteoporosis, increased testicular weight, inhibin B, and germ cell proliferation in ex vivo testis cultures and in vivo in a humanized RANKL mouse. The effect on germ cell proliferation was positively associated with baseline serum concentrations of anti-müllerian hormone (AMH). In accordance, denosumab increased germ cell proliferation in ex vivo human testis cultures with low/moderate but not severe impairment of Sertoli cell function. In a placebo-controlled randomized clinical trial, denosumab had no effect on semen quality but increased sperm concentration in a subgroup of infertile men with serum AMH ≥38 pmol/L at baseline. In conclusion, high serum AMH may increase the probability of a beneficial response to denosumab treatment in infertile men, thus suggesting a possible venue for precision medicine in male infertility.

Pdk3's role in RANKL-induced osteoclast differentiation: insights from a bone marrow macrophage model.

Background: Osteoporosis (OP) is a chronic disease characterized by decreased bone mass, loss of skeletal structural integrity and increased susceptibility to fracture. Available studies have shown that the pyruvate dehydrogenase kinase (PDK) family is associated with osteoclastogenesis and bone loss, but the specific role of Pdk3 in bone pathology has not been systematically investigated. Methods: A cell OP model was established in receptor activator for nuclear factor-κB Ligand (RANKL)-induced bone marrow macrophages (BMMs). Hereafter, the expression levels of Pdk3 and osteoclastogenesis feature genes including nuclear factor of activated T cells 1 (Nfatc1), Cathepsin K (Ctsk), osteoclast associated Ig-like receptor (Oscar) in BMMs-derived osteoclasts were examined based on real-time quantitative PCR and western blotting methods. Further, the phosphorylation of ERK, P65 and JAK/STAT and their correlation was Pdk3 was gauged. In particular, changes in the activity of these signaling pathways were observed by silencing experiments of the Pdk3 gene (using small interfering RNA). Finally, the effects of Pdk3 gene silencing on signaling pathway activity, osteoclastogenesis, and related inflammatory and apoptotic indicators were observed by transfection with PDK3-specific siRNA. Results: Following RANKL exposure, the levels of Pdk3 and osteoclastogenesis feature genes were all elevated, and a positive correlation between Pdk3 and osteoclastogenesis feature genes was seen. Meanwhile, ERK, P65 and JAK/STAT phosphorylation was increased by RANKL, and Pdk3 was confirmed to be positively correlated with the phosphorylation of ERK, P65 and JAK/STAT. Additionally, in RANKL-exposed osteoclasts, Pdk3 knockdown diminished the phosphorylation of ERK, P65 and JAK/STAT, reduced the expressions of osteoclastogenesis feature genes. Importantly, knockdown of Pdk3 also reduced the expression of inflammatory cytokines and resulted in elevated levels of Bax and Casp3 expression, as well as downregulation of Bcl2 expression. Conclusion: This study reveals for the first time the role of Pdk3 in RANKL-induced osteoclastogenesis and OP. These findings provide a foundation for future studies on the role of Pdk3 in other bone diseases and provide new ideas for the development of OP therapeutics targeting Pdk3.

Evaluation of Functional Components of Lactobacillus plantarum AR495 on Ovariectomy-Induced Osteoporosis in Mice And RAW264.7 Cells.

Osteoporosis is a disease characterized by abnormal bone metabolism, where bone resorption outpaces bone formation. In this study, we investigated the key functional components of Lactobacillus plantarum AR495 in mitigating ovariectomy (OVX)-induced osteoporosis in mice. The results indicated that both Lactobacillus plantarum AR495 and its fermentation broth significantly reduced urinary calcium and deoxypyridinoline (DPD) levels in the mice. These interventions inhibited bone resorption and improved trabecular bone architecture by modulating the nuclear factor κB (RANK)/RANK ligand (RANKL)/osteoprotegerin (OPG) signaling pathway. Additionally, the L. plantarum AR495 and fermentation broth groups inhibited the RANKL/TRAF-6 and TLR4/MYD88 pathways, leading to enhanced bone metabolism, improved intestinal barrier function, and reduced intestinal inflammation. In vitro experiments revealed that AR495 fermentation supernatant fractions larger than 100 kDa and those between 50-100 kDa significantly decreased the activity of the osteoclast marker TRAP, regulated the expression of the TLR4/MYD88 pathway, and inhibited osteoclast formation, thereby alleviating the OVX-induced osteoporosis phenotype. These findings suggest that these components may be primary functional elements of L. plantarum AR495 in the treatment of osteoporosis.

Long-Term Survival in Human Epidermal Growth Factor Receptor 2-Positive Bone-Only Metastatic Breast Cancer: Trastuzumab, Denosumab, and Potential Synergistic Effects.

Breast cancer is the second most common cancer worldwide. There are four main subtypes of breast cancer, one of which involves positivity for human epidermal growth factor receptor 2 (HER2). Here, we present a case series of unusually long survival in three patients with HER2-positive metastatic breast cancer. All cases involved post-menopausal women with bone-only metastases undergoing treatment with the HER2-targeted therapy trastuzumab and the receptor activator of nuclear factor kappa-Β ligand (RANK-L) inhibitor denosumab. Our three patients survived for 17, 13, and 11 years, respectively, from the time of metastasis. The patients who survived for 17 and 13 years both presented with metastatic disease at diagnosis, while the patient who survived for 11 years with metastatic disease was known to have non-metastatic breast cancer for four years prior. We also report the development of foot fractures from minor trauma, as low as walking, despite a bone density reported as normal in the patient with 17 years of treatment. These unusually long survival times and the unusual location of the fractures are questioned to be secondary to the long duration of treatment with HER2-targeted therapy and RANK-L inhibitor therapy. Our case series is the first to describe the use of trastuzumab and denosumab in HER2-positive metastatic breast cancer. All three reported cases had no clinical or radiographic disease progression at the time of reporting. Furthermore, our case of survival for 17 years represents the longest survival time reported yet, raising the possibility of a synergistic relationship between RANK-L inhibitors and HER2-targeted therapy in the long-term control of HER2-positive metastatic breast cancer. This manuscript discusses evidence from primary studies on HER2 and receptor activator of nuclear factor kappa-Β (RANK) signalling and drug responses and hypothesizes on possible mechanisms of synergism. Given that treatment of HER2-positive breast cancer has historically not involved RANK-L inhibition, this study may outline future areas of research in improving treatment algorithms, especially for bone-only metastatic disease.

A real-world disproportionality analysis of FDA adverse event reporting system (FAERS) events for denosumab.

Background: Denosumab is authorized to treat several diseases, including cancer and bone disorders. Nevertheless, its use in clinical practice has been affected by safety concerns. The work retrospectively investigated adverse events (AEs) of denosumab to better understand toxicities. Methods: The FAERS data base data from Q1 of 2010 to Q3 of 2023 was chosen. The definition of Medical Dictionary for Regulatory Activities (MedDRA) was dependent on preferred terms (PTs) and system organ class (SOCs). Following the removal of duplicate reports, a disproportionality analysis was conducted to identify safety signals through the calculation of reporting odds ratios (ROR). Results: During the reporting period, 130611 denosumab-related cases were identified; 670 pTs with a substantial disproportionality were retained. The connective and musculoskeletal tissue disorders, poisoning, injury, and procedural complications, as well as medical and surgical procedures, were among the important SOCs that satisfied the criteria. Reports at PT levels including off-label use, death, osteonecrosis of the jaw, arthralgia, and pain in extremities were determined. Severe consequences in terms of life-threatening injuries and death accounted for 841 and 19704 cases, respectively of the reported cases. Conclusion: These findings underscore the critical importance of pharmacovigilance and are consistent with established clinical observations. Notably, osteonecrosis of the jaw, arthralgia, pain in extremities, back pain, myalgia, and bone pain were identified as the most prevalent risk signals associated with denosumab.

Cementocyte-derived extracellular vesicles regulate osteoclastogenesis and osteoblastogenesis.

Background/purpose: Cementum shares many properties with bone; however, in contrast to bone, it is not innervated or vascularized and has a limited capacity for remodeling. Osteocytes located in the lacunae-canalicular system of bone tissue play a central role in bone remodeling by communicating with osteoblasts and osteoclasts. Although cementocytes are present in cellular cementum and are morphologically similar to osteocytes, it remains unclear whether they are involved in the dynamic functional regulation of metabolism in cementum. The present study focused on the extracellular vesicles (EVs) secreted by cementocytes and examined their effects on osteoclasts and osteoblasts. Materials and methods: EVs were extracted from the mouse cementocyte cell line, IDG-CM6. The effects of EVs on recombinant RANKL-induced osteoclastogenesis and recombinant Bone morphogenetic protein (BMP)-2-mediated osteoblastogenesis were investigated using the mouse osteoclast progenitor cell line, RAW264.7 and mouse pre-osteoblast cell line, MC3T3-E1, respectively. Results: EVs enhanced the formation of tartrate-resistant acid phosphatase activity-positive cells. Real-time PCR revealed that EVs up-regulated the expression of osteoclast-related genes. On the other hand, the cell culture supernatant of cementocytes significantly inhibited the differentiation of osteoclasts. Regarding osteoblastogenesis, EVs suppressed the expression of alkaline phosphatase, bone sialoprotein, and osteocalcin induced by recombinant BMP-2 at the gene and protein levels. Conclusion: A network of cementocytes, osteoblasts, and osteoclasts may exist in cellular cementum, which suggests the involvement of cementocytes in dynamic metabolism of cementum through EVs.

Cardenolides; calotropin and gomphogenin from Calotropis procera (Aiton) mitigate bone turnover in ovariectomized osteoporotic rats: Targeting RANKL/OPG axis and estrogen receptor-alpha.

The present study aimed to examine the effect of Calotropis procera (Aiton) and its major cardenolides; calotropin and gomphogenin on ovariectomy-induced osteoporosis in rats. Osteoporotic rats were orally treated with C. procera alcoholic extract (100 mg/kg), calotropin (CLT; 100 µg/kg) and gomphogenin (GPG; 100 µg/kg) for 14 consecutive days. Bone resorption/formation biomarkers; bone specific alkaline phosphatase (BALP), osteoprotegerin (OPG) and nuclear factor-κß ligand (RANKL) as well as serum calcium and phosphorus were assessed 24 h after last doses of treatments. Serum levels of estradiol (E2) and catalase were also measured. Oral treatment with C. procera extract, CLT and GPG caused E2 restoration to normal level with a marked regulation in the RANKL/OPG axis. Serum phosphorus and calcium were up-leveled whereas BALP was downregulated. Histopathological examination, bone histomorphometric analysis and immunohistochemical staining for osteopontin (OPN) inspection further emphasized the aforementioned outcomes. The results revealed the superiority of CLT and to a lesser extent GPG osteoporotic effect over C. procera extract. Molecular docking of the two compounds on ER-α and RANKL/OPG complex showed noteworthy binding affinities which also confirmed the supremacy of CLT due to the additional hydrogen bonding of the hydroxyl groups of the sugar moiety with RANKL/OPG complex. Finally, it is concluded that CLT and GPG from C. procera hinder bone turnover by decreasing osteoclastic bone cells activity and increasing calcium mineralization thus suppressing bone remodeling and preventing bone infirmity in OVX osteoporotic rats directly via binding to RANKL/OPG complex and ER-α and indirectly through elevating level of E2.

The Impact of Modern Bone Markers in Multiple Myeloma: Prospective Analyses Pre and Post-First Line Treatment.

Multiple myeloma, the disease characterized by the malignant proliferation of plasma cells that invades the bone marrow, produces osteolytic lesions and secretes monoclonal proteins. Several biomarkers have been shown to represent important tools in the pathogenesis of myeloma and offer insights into bone degradation and formation. The objectives of this current study were to assess the associations of modern biomarkers (TNF-α: tumor necrosis factor; IFN: Interferon; FreeRANKL: Free Receptor Activator for Nuclear Factor kappa B Ligand; RANKL: Receptor Activator for Nuclear Factor kappa B Ligand, Beta crosslaps, IL-6: Interleukin 6) with osteolytic lesions status after first-line treatment and to evaluate the correlations between modern and classical biomarkers (LDH: Lactate Dehydrogenase; VSH: Erythrocyte Sedimentation Rate; Hgb: Hemoglobin, Calcium, Albumin, B2microglobulin) stratified by osteolytic lesions status. A total of 35 patients diagnosed with multiple myeloma divided into two groups according to the osteolytic bone lesions, were studied: (1) unchanged status of osteolytic lesions and (2) changed status of osteolytic lesions. After fist-line treatment, we found a significant difference in Albumin (p = 0.0029) and Calcium levels (p = 0.0304), patients with a changed status in osteolytic lesions having higher values of Albumin and Calcium compared to those without changes in status of osteolytic lesions. After first-line treatment, decreased IL-6 values were significantly correlated with elevated values of Albumin (ρ = -0.96, p = 0.0005) in the patients with changed status of osteolytic lesions. Post-treatment values of IFN showed a significant positive correlation with Hemoglobin (ρ = 0.47, p = 0.0124), IL-6 (ρ = 0.55, p = 0.0026) and TNF-alpha values (ρ = 0.54, p = 0.0029). The results obtained from patients with unmodified lytic lesions identified a significant correlation between the biomarkers IL-6, Free RANKL, and IFN-beta with the classical marker LDH. This association highlights the involvement of these markers in promoting bone destruction and the development of osteolytic lesions.

Serum proinflammatory cytokines, receptor activator of nuclear factor kappa-Β ligand (RANKL), osteoprotegerin (OPG) and RANKL/OPG ratio in mild and severe COVID-19.

INTRODUCTION: Osteoporosis, a systemic skeletal disease, is characterized by a quantitative and qualitative, and progressive decrease in bone mass, which is related to inflammation. Since a cytokine storm is triggered in Coronavirus disease 2019 (COVID-19), this study aims to evaluate pro-inflammatory cytokines (TNF-α, IL-1ß), Receptor activator of nuclear factor-κB ligand (RANKL)/serum osteoprotegerin (OPG) ratio, and their relationship in mild and severe COVID-19. METHODS: This study was performed on 48 adult patients (18 mild, 18 severe COVID-19, and 12 healthy subjects as a control group). Serum OPG, RANKL, TNF-α, IL-1ß, 25-OH vitamin D, and ALKp were measured by ELISA and colorimetric assay. RESULTS: COVID-19 patients had a significant increase in RANKL, and RANKL/OPG in mild and severe form (p < 0.001) while OPG decreased significantly in severe form compared to healthy controls (p < 0.05). Inflammatory cytokines (TNF-α and IL-1ß) increased in both groups of patients whereas Alkaline phosphatase (ALKp) increased only in severe patients (p < 0.001). Both groups had 25-OH vitamin D deficiency in comparison to healthy ones (p < 0.001). Pearson's correlation coefficient was performed to determine the relationship between RANKL, OPG, ALKp, and 25-OH vitamin D with TNF-α and IL-1ß in mild and severe COVID-19, which was statistically significant. CONCLUSION: Serum RANKL/OPG ratio was elevated in COVID-19 individuals and is assumed to be a risk factor for BMD reduction and osteoporosis in these patients. Correlations between IL-1ß, TNF-α, ALKp, 25-OH vitamin D, OPG, RANKL, and RANKL/OPG ratio offered the potential role of these proinflammatory markers in the mechanism of osteoporosis in COVID-19 patients.

RANK in cancer-associated fibroblasts: A valuable prognostic determinant for metastasis in early-stage breast cancer patients.

BACKGROUND: The molecular system of receptor activator of nuclear factor kappa-ß (RANK) and its ligand (RANKL) plays a role in a variety of physiological and pathological processes. These encompass the regulation of bone metabolism, mammary gland development, immune function, as well as their involvement and tumorigenesis. Nevertheless, limited knowledge exists regarding their function within the tumor microenvironment. METHODS AND RESULTS: We explored the significance of RANK expression in cancer-associated fibroblasts (CAFs) as a prognostic biomarker in early breast cancer patients (BCPs) by immunohistochemistry. Results reveal a significant correlation between high RANK expression in CAFs and an increased risk of metastasis (p= 0.006), shorter metastasis-free survival (MFS) [p= 0.007, OR (95%CI) = 2.290 (1.259-4.156)], and lower overall survival (OS) [p= 0.004, OR (95%CI) = 2.469 (1.343-4.541)]. Upon analyzing the phenotype of CD34(-) CAFs isolated from primary tumors in BCPs, we observed co-expression of RANK with CD105 marker by immunofluorescence and flow cytometry, characteristic of mesenchymal stem/stromal cells (MSCs), suggesting the possible cellular origin. Also RANKL-RANK system increase the OCT-4, SOX-2 and DKK-1 (dickkopf 1) gene expression in CD34(-) CAFs by RT-PCR. Moreover, this system plays a crucial role in the migration of these CD34(-) CAFs. CONCLUSIONS: These results support the clinical relevance of RANK in CAFs and propose its potential as a future therapeutic target in the treatment of early BCPs.

Tetrahydroberberine Prevents Ovariectomy-Induced Bone Loss by Inhibiting RANKL-Induced Osteoclastogenesis and Promoting Osteoclast Apoptosis.

Postmenopausal osteoporosis (PMOP) arises from the disruption in bone remodeling caused by estrogen deficiency, leading to a heightened susceptibility to osteoporotic fractures in aging women. Tetrahydroberberine (THB) is a chemical compound extracted from Corydalis yanhusuo, a member of the traditional Chinese medicine series "Zhejiang eight taste", possessing a variety of pharmacological functions such as lowering lipids and preventing muscle atrophy. However, the impact of THB on PMOP has not been systematically explored. In vitro experiments supported that THB suppresses osteoclast formation and resorption of bone concentration-dependently. Further experiments confirmed that these inhibitory effects of THB were related to inhibition on expressions of osteoclast-specific genes, the mitogen-activated protein kinase (MAPK) pathway, and the nuclear factor kappa-B (NF-κB) pathway and an increased apoptosis level in mature osteoclasts. Additionally, THB treatment mitigated the ovariectomy-induced bone loss and improved the skeletal microarchitecture in vivo. In conclusion, THB has such potential to improve the PMOP status.

RANKL/RANK contributes to the pathological process of type 2 diabetes mellitus through TRAF3 activation of NIK.

Diabetic osteoporosis is a complication of diabetes mellitus (DM). Denosumab (DMB) is an effective anti-osteoporotic drug functions by inhibiting NF-κB ligand receptor-activating factor (RANKL). Previous study found that osteoprotegerin (OPG) regulated ßcell homeostasis through the RNAK/RANKL pathway. The present study aimed to investigate the effect of RANKL/RANK on the pathological process of DM and the underlying mechanism. We used D-glucose-induced RINm5F cells to construct in vitro type 2 diabetes models (T2DM). A high-fat diet combined with intraperitoneal injection of streptozotocin (STZ) was used to establish a T2DM model in SD rats. The apoptosis of ß-cells was determined by TdT-mediated dUTP nick-end labeling (TUNEL) analysis. qRT-PCR and western blotting assays were used to explore the mRNA and protein expression of the TRAF3 (Tumor necrosis factor receptor-associated factor)/NIK (NF-κB-inducible kinase) pathway. Furthermore, insulin expression was detected by ELISA and immunohistochemistry assay. The islet morphology was analyzed by H&E. In vivo experiments demonstrated that sRANKL-IN-3 down-regulated insulin secretion levels by significantly ameliorating pancreatic tissue damage and mitigating apoptosis of high glucose induced ß-cells. Subsequently, sRANKL-IN-3, acting as an inhibitor of RANKL, mitigated functional decline in ß-cells induced by high glucose, mainly manifested by the low expression of PDX-1 (pancreatic duodenal homeobox 1), BETA2 (beta-2 adrenoceptors), INS-1 (insulin 1), and INS-2 (insulin 2). Mechanistic studies revealed that deletion of TRAF3 combined with sRANKL-IN-3 administration reduced the activity of NIK, NF-κB2, and RelB in RINm5F cells. In addition, our study demonstrated that inhibition of either RANKL or TRAF3 had a protective effect on high glucose induced apoptosis. Moreover, the combined action of sRANKL-IN-3 and shTRAF3 had a more pronounced inhibitory effect on high glucose-induced apoptosis. In summary, RANKL/RANK deficiency may attenuate apoptosis of ß-cells, a phenomenon associated with the TRAF3/NIK pathway. Therefore, RANKL/RANK could be regarded as a potential therapeutic strategy for DM.

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.

ROLE OF RANKL SIGNALING IN BONE HOMEOSTASIS.

RANKL and its cognate receptor RANK are crucial regulators of bone metabolism in physiological as well as in pathological conditions. Here we go through the works that unveiled the paramount role of this signaling pathway. We focus on the RANKL cytokine, whose alterations are responsible for rare and common bone diseases. We describe recent insights on the regulation of RANKL expression, which provide new hints for the pharmacological regulation of this molecule. Based on the multiple functions exerted by RANKL (within and outside the bone tissue), we advise caution regarding potential unintended consequences of its inhibition.

Interplay between bone marrow adiposity and bone resorption in RANKL-mediated modelled osteoporosis.

Bone marrow adipose tissue (BMAT) accrues in osteoporosis, whereas its contribution to the progression of bone resorption remains insufficiently understood. To understand the mechanisms that promote BMAT expansion in osteoporosis, in the present study, we performed extensive analysis of the spatiotemporal pattern of BMAT expansion during the progression of bone resorption in TgRANKL transgenic mouse models of osteoporosis expressing human RANKL (receptor activator of nuclear factor-κB ligand). Our results showed that TgRANKL mice of both sexes developed dramatically increased BMAT expansion compared to wild-type (WT) littermates, that was analogous to the levels of RANKL expression and the severity of the bone loss phenotype. BMAT was formed at close proximity to areas undergoing active bone remodelling and bone resorption, whereas bone resorption preceded BMAT development. Expression analysis in bone fractions demonstrated that BMAT constitutes a major source for RANKL production. Ex vivo analysis of isolated bone marrow stromal cells from TgRANKL mice showed an increased adipogenic differentiation capacity compared to WT, while osteoclast supernatants further exaggerated adipogenesis, supporting a critical role of the osteoclast-derived secretome in the differentiation of bone marrow adipocytes. Furthermore, the effectiveness of an antiosteoporosis treatment in BMAT development was investigated upon treatment of TgRANKL models with the bisphosphonate alendronate. Notably, alendronate effectively improved bone mass and attenuated BMAT expansion, indicating a possible involvement of osteoclasts and bone resorption in BMAT development. On the contrary, inhibition of BMAT with PPARγ antagonists (GW9662 or BADGE) effectively ameliorated BMAT expansion but failed to reverse the osteoporotic phenotype of TgRANKL mice. Overall, our data demonstrate that TgRANKL mice constitute unique genetic mouse models for investigating the pathogenic mechanisms that regulate the development and expansion of BMAT in osteolytic diseases.

Incidence and Risk Factors of Hypomagnesemia in Patients With Bone Metastasis From Solid Malignancies Treated With Denosumab: A Retrospective Chart Review.

BACKGROUND: Hypomagnesemia is associated with poor clinical outcomes in cancer patients. Patients with bone metastasis from solid malignancies receiving denosumab (Dmab) to prevent skeletal-related events often receive concurrent antineoplastic agents for cancer treatment. The incidence and risk factors of hypomagnesemia in patients receiving Dmab and the optimal frequency of monitoring serum magnesium (Mg) levels have not been studied in these patient populations. OBJECTIVE: The objective is to investigate the incidence and potential risk factors of hypomagnesemia and the optimal frequency of monitoring serum Mg levels. METHODS: A retrospective chart review identified patients with solid malignancies with bone metastases treated with Dmab at the Loma Linda University Cancer Center between January 2013 and February 2024. The incidence of hypomagnesemia was determined using the number of patients with hypomagnesemia and the total number of patients in the study. Univariate and multivariate logistic regression analyses identified risk factors for hypomagnesemia. RESULTS: Hypomagnesemia was observed in 19% (29/153) of patients, the majority of whom were on concurrent antineoplastic agents with ≥15% hypomagnesemia incidence (high-hypomagnesemic antineoplastics) or nonantineoplastic drugs with documented cases or incidence of hypomagnesemia (hypomagnesemic nonantineoplastics) in addition to high-hypomagnesemic antineoplastics. Multivariate analysis showed increased odds of developing hypomagnesemia with high-hypomagnesemic antineoplastics (odds ratio [OR]: 174.93, 95% confidence interval [CI]: 12.82 to 387.43, P < 0.001); hypomagnesemic nonantineoplastics plus high-hypomagnesemic antineoplastics (OR: 210.09, 95% CI: 11.80 to 3740.12, P < 0.001); and Mg level ≤ 0.85 prior to Dmab administration (OR: 16.79, 95% CI: 2.30 to 122.41, P = 0.005). CONCLUSION AND RELEVANCE: This study describes the incidence and potential risk factors for hypomagnesemia in patients with solid malignancies and metastatic bone disease treated with Dmab. This study's findings provide additional clinical insight into potential risk factors for hypomagnesemia and the need for more frequent serum Mg level monitoring of at-risk patients. Future prospective studies are needed to determine the exact frequencies most appropriate in monitoring serum Mg levels in this group of patients.

Identification of novel RANKL inhibitors through in silico analysis.

Receptor activator of nuclear factor-κB ligand (RANKL) is considered the principal regulator of osteoclast differentiation. Therefore, strategies interfering with the RANKL-RANK signaling pathway may effectively inhibit osteoclast differentiation and mitigate bone resorption. Consequently, RANKL has become a promising target for new drug design strategies. Despite extensive research on specific drugs and antibodies, only a few have shown efficacy in treating osteoporosis. To address this challenge, we aimed to explore new approaches for designing drugs for osteoporosis. In this study, a 3D quantitative structure-activity relationship (QSAR) pharmacophore model was built for RANKL with reference to known inhibitor IC50 values. The optimal pharmacophore model was then employed as a 3D query to screen databases for novel lead compounds. The obtained compounds were subjected to ADMET and TOPKAT analyses to predict drug pharmacokinetics and toxicity. Molecular docking and de novo evolution approaches were applied to verify the docking binding affinities of the compounds. Five candidate compounds were subjected to further in vitro analyses to assess their anti-osteoporotic effects, among which compound 4 demonstrated significant inhibitory activity, achieving an inhibitory rate of 92.6 % on osteoclastogenesis at a concentration of 10 µM. Subsequent molecular dynamics (MD) simulations to assess the stability and behavior of compound 4 and its evolved variant, ZINC00059014397_Evo, within the RANKL binding site revealed that the variant is a potential therapeutic agent for targeting osteoclasts. This study offers valuable insights for developing next generation RANKL inhibitors for osteoporosis treatments.

Electrochemical immunoplatform for the determination of multiple salivary biomarkers of oral diseases related to microbiome dysbiosis.

Several diseases of the oral cavity are related to compositional and functional shifts in the oral microbiome. The analysis of saliva is an attractive alternative for the diagnosis and prognosis of these diseases. Samples can be obtained by no invasive procedures and processing is relatively simple. However, sensitive and selective analytical methods are needed to make the diagnosis as specific as possible. In this work, four salivary biomarkers of oral diseases: interleukin-6 (IL-6), receptor activator of NF-kB ligand (RANKL), protein arginine deiminase 4 (PAD4) and the corresponding antibody (anti-PAD-4) were selected as targets for their simultaneous determination using an electrochemical immunosensing platform. Sandwich-type amperometric immunoassays were implemented using horseradish peroxidase (HRP)/H2O2/hydroquinone (HQ) for application to the analysis of saliva of six volunteers. The developed method provides excellent sensitivity, selectivity, and wide linear ranges with LOD values of 0.09 pg mL-1 (IL-6), 0.10 pg mL-1 (RANKL); 0.09 ng mL-1(PAD4) and 14.5 ng mL-1 (anti-PAD4) and allows the accurate analysis of saliva without matrix effects, using 25 µL of raw sample. The developed methodology is competitive with commercial ELISA kits available only for a single biomarker determination, while the assay for the four biomarkers can be completed in less than two hours.