Mechanisms underlying the long-term and withdrawal effects of denosumab therapy on bone

Lysosomal biogenesis and function in osteoclasts: a comprehensive review

Lysosomes serve as catabolic centers and signaling hubs in cells, regulating a multitude of cellular processes such as intracellular environment homeostasis, macromolecule degradation, intracellular vesicle trafficking and autophagy. Alterations in lysosomal level and function are crucial for cellular adaptation to external stimuli, with lysosome dysfunction being implicated in the pathogenesis of numerous diseases. Osteoclasts (OCs), as multinucleated cells responsible for bone resorption and maintaining bone homeostasis, have a complex relationship with lysosomes that is not fully understood. Dysregulated function of OCs can disrupt bone homeostasis leading to the development of various bone disorders. The regulation of OC differentiation and bone resorption for the treatment of bone disease have received considerable attention in recent years, yet the role and regulation of lysosomes in OCs, as well as the potential therapeutic implications of intervening in lysosomal biologic behavior for the treatment of bone diseases, remain relatively understudied. This review aims to elucidate the mechanisms involved in lysosomal biogenesis and to discuss the functions of lysosomes in OCs, specifically in relation to differentiation, bone resorption, and autophagy. Finally, we explore the potential therapeutic implication of targeting lysosomes in the treatment of bone metabolic disorders.

Regorafenib Attenuates Osteoclasts Differentiation by Inhibiting the NF-κB, NFAT, ERK, and p38 Signaling Pathways

Osteolytic diseases such as osteoporosis and neoplastic bone metastases are caused by the excessive activation of osteoclasts. Inhibiting the excessive activation of osteoclasts is a crucial strategy for treating osteolytic diseases. This study investigated the roles and mechanisms of regorafenib, a tyrosine kinase inhibitor, on osteoclasts and osteolytic diseases. We first identified the potential targets and mechanisms of regorafenib on osteoclast-related osteolytic diseases using network pharmacological analysis and molecular docking techniques. Then, we verified its role and mechanism on osteoclasts via cellular and animal experiments. Network pharmacology analysis identified 89 common targets shared by regorafenib and osteoclast-related osteolytic diseases. Enrichment analysis suggested that regorafenib may act on osteoclast-related osteolytic diseases by modulating targets such as AKT1, CASP3, MMP9, and MAPK3, regulating biological processes such as cell proliferation, apoptosis, and phosphorylation regulation, and influencing signaling pathways such as MAPK, PI3K/AKT, and osteoclast differentiation. The molecular docking results indicated that regorafenib and AKT1, CASP3, MMP9, MAPK3, and MAPK14 were stably docked. Cell experiments demonstrated that regorafenib significantly inhibited osteoclast differentiation and bone resorption in RAW 264.7 cells and bone marrow macrophages in a dose-dependent manner, with up to 50% reduction at 800 nM concentration without exhibiting cytotoxic effects. Furthermore, Western blot and RT-qPCR results demonstrated that regorafenib inhibited osteoclast differentiation by blocking the transduction of RANKL-induced NF-κB, p38, ERK, and NFAT signaling pathways. In vivo studies using an ovariectomized mouse model showed that regorafenib significantly improved bone volume fraction (BV/TV), bone surface to total volume (BS/TV), and number of trabeculae (TB.N), as well as reduced trabecular separation (Tb.Sp) compared to the OVX groups (P < 0.05). TRAcP staining results revealed a reduction in the number of osteoclasts with regorafenib treatment (P < 0.01). These results indicate that regorafenib exerts its protective effects against osteoclast-related osteolytic disease by inhibiting the RANKL-induced NF-κB, NFAT, ERK, and p38 signaling pathways. This study proves that regorafenib may serve as a potential therapeutic agent for osteoclast-related osteolytic diseases.

Jaw osteoporosis: Challenges to oral health and emerging perspectives of treatment

Osteoporosis is a prevalent bone metabolic disease that poses a significant challenge to global human health. Jaw osteoporosis, characterized by microstructural damage of the jaw resulting from various factors, is one of the common manifestations of this condition. Recent studies have demonstrated that jaw osteoporosis has multifaceted effects on oral health and can negatively impact conditions such as periodontitis, oral implantation, orthodontic treatment, and wound healing. However, there are still some limitations in the conventional treatment of osteoporosis. For instance, while bisphosphonates can enhance bone quality, they may also lead to osteonecrosis of the jaw, which poses a potential safety hazard in oral diagnosis and treatment. In recent years, considerable attention has been focused on improving the pathological condition of jaw osteoporosis. Treatment strategies such as gut microbial regulation, extracellular vesicles, molecular targeted therapy, herbal medicine, mechanical stimulation are expected to enhance efficacy and minimize adverse reactions. Therefore, understanding these effects and exploring novel treatments for jaw osteoporosis may provide new insights for oral health maintenance and disease treatment. This article reviews the impact of jaw osteoporosis on oral health and describes the limitations associated with current methods. It also discusses emerging perspectives on treatment, offering a comprehensive overview of the challenges and future directions in managing jaw osteoporosis.

Advances of long non-coding RNAs in osteoclast differentiation and osteoporosis

INTRODUCTION

Osteoclasts, which are responsible for bone resorption, are specialized multinucleated cells generated from monocyte/macrophage progenitor cells or hematopoietic stem cells (HSCs). Physiological bone remodeling can become pathological, such as osteoporosis, when osteoclastogenesis is out of balance. Thousands of long noncoding RNAs (lncRNAs) influence important molecular and biological processes. Recent research has revealed gene expression regulation function that numerous lncRNAs regulate nuclear domain organization, genome stability. Furthermore, the research of lncRNAs has substantial clinical implications for the treatment of existing and new diseases.

AREAS COVERED

In this review, we gather the most recent research on lncRNAs and their potential for basic research and clinical applications in osteoclast and osteoporosis. We also discuss the findings here in order to fully understand the role of lncRNAs in osteoclast differentiation and osteoporosis, as well as to provide a solid basis for future research exploring associated mechanisms and treatments.

EXPERT OPINION

LncRNA has been considered as an important role in the regulation of osteoclast differentiation and osteoporosis. It is exciting to investigate pathophysiological processes in osteoporosis and the therapeutic potential of lncRNAs. We hope that this review will offer promising prospects for the development of precision and individualized approaches to treatment.

Oroxylin A suppresses breast cancer-induced osteoclastogenesis and osteolysis as a natural RON inhibitor

BACKGROUND

Malignant breast cancer cells trigger the over-activation of osteoclast precursor cells, leading to bone loss and severe pain. Targeted inhibition of osteoclast differentiation has emerged as an important strategy for treating bone syndromes induced by breast cancer.

PURPOSE

The objective is to discover natural osteoclast inhibitor to treat osteoclastogenesis and bone destruction induced by breast cancer, and clarify the specific mechanisms.

METHODS

Recepteur d'origine Nantais (RON) protein was employed to search the natural osteoclast inhibitor for breast cancer-induced osteoclastogenesis by molecular docking, molecular dynamics simulation and cellular thermal shift assay (CETSA). In the in vitro experiment, breast cancer MDA-MB-231 cell-conditioned medium (MDA-MB-231 CM) was used to induce osteoclastogenesis in murine bone marrow-derived macrophages (BMMs), aiming to elucidate the effects and mechanisms of the natural osteoclast inhibitor. In the in vivo model, MDA-MB-231 cells was injected into the mouse tibia to evaluate the therapeutic effect of drug on breast cancer-induced bone destruction.

RESULTS

We discovered a significant increase in the expression of RON during MDA-MB-231 CM-induced osteoclast differentiation in vitro. Molecular docking analysis found that oroxylin A (OA), a flavonoid derived from the Chinese medicine Scutellaria baicalensis Georgi, showed binding ability with RON, while its impact and mechanism on breast cancer-induced osteoclastogenesis and osteolysis remains unclear. Molecular dynamics simulation and CETSA further revealed that OA bound directly to the RON protein, and it also decreased RON expression in breast cancer CM-induced osteoclastogenesis. Correspondingly, OA suppressed the MDA-MB-231 CM-induced osteoclastogenesis and bone resorption in vitro. The downstream signals of RON including Src and NFATc1, as well as the osteoclast-specific genes, were downregulated by OA. Of interesting, the suppressive effect of OA on osteoclastogenesis induced by MDA-MB-231 CM was abolished after RON was knocked down by the specific RON-siRNA, this further confirmed that OA showed inhibitory effects on osteoclasts through targeting RON. In addition, we found that OA attenuated MDA-MB-231 cell-induced osteolysis and reduced the number of osteoclasts in vivo.

CONCLUSION

Our results indicate that OA acts as a natural RON inhibitor to suppress breast cancer-induced osteoclastogenesis and osteolysis. This provides new strategy for treating breast cancer-induced bone destruction and related syndromes.

Progression of multiple vertebral fractures after denosumab discontinuation under treatment with romosozumab. A case-report

INTRODUCTION

Denosumab (Dmab) is widely used for the treatment of post-menopausal osteoporosis. Its discontinuation is sometimes accompanied by multiple vertebral fractures. Romosozumab (Rmab) has not been tested for its ability to prevent the rebound phenomenon.

CASE PRESENTATION

We present the case of a 68-year-old female patient with post-menopausal osteoporosis under treatment with Rmab who presented with multiple vertebral fractures after denosumab discontinuation. The addition of Rmab did not prevent new-onset rebound-associated vertebral fractures. The patient discontinued Rmab and Dmab was re-initiated. After six months, no new vertebral fractures occurred, bone mineral density increased and bone turnover markers remained suppressed.

DISCUSSION

Our clinical case illustrates the ineffectiveness of Rmab to prevent the multiple vertebral fracture cascade attributable to discontinuation of Dmab. We believe that treatment with Rmab might not be enough to prevent this phenomenon. Treatment with Dmab or possibly combination treatment with Dmab and Rmab could be another treatment option.

Three-year effect of bisphosphonates on bone mineral density after denosumab withdrawal: observations from a real-world study

Data on long-term treatment regimens for preventing bone mineral density (BMD) loss that occurs after denosumab (Dmab) withdrawal are scarce. Our aim was to evaluate the long-term changes (12-36 months) in BMD and bone turnover markers in a group of postmenopausal women who had been treated with Dmab and received subsequent treatment with bisphosphonates. Secondary objectives were to evaluate factors associated with BMD loss, to compare the BMD change in patients who received oral vs intravenous bisphosphonates, and to assess the frequency of fragility fractures after Dmab discontinuation. The clinical data of 54 patients, 26 of whom had clinical and DXA assessments at 36 months, were analyzed. After 12 months, the mean LS BMD had decreased by 2.8% (±5.0), FN BMD by 1.9% (±5.8), and TH BMD by 1.9% (±3.7). After 36 months, LS BMD had decreased by 3.7% (±6.7), FN BMD by 2.5% (±7.1), and TH BMD by 3.6% (±5.2). C-terminal cross-linked telopeptide of type I collagen significantly increased during the first 12 months after Dmab withdrawal but then decreased at 36 months. BMD loss at 12 months was higher in patients with more than 30 months of Dmab treatment, but this difference was only statistically significant at FN (-3.3% vs -0.3%, P = .252 at LS, -3.3% vs 0.3%, P = .033 at FN, and -2.1% vs 0.9, P = .091 at TH). There were no statistically significant differences regarding the change in BMD at 12 and 36 months between oral and intravenous treatment. Seven patients suffered incidental vertebral fractures (clinical vertebral fractures: n = 6, morphometric fractures: n = 1) three of which were multiple. None of these patients were treated following international or institutional guidelines or recommendations. In summary, our study suggests that bisphosphonates can help maintain BMD for 36 months after Dmab discontinuation.

Zoledronate after denosumab discontinuation: Is repeated administrations more effective than single infusion?

BACKGROUND

After Denosumab (Dmab) discontinuation C-terminal telopeptide (CTX) levels increase, bone mineral density (BMD) decreases and multiple vertebral fractures (FX) may occur with relevant impact on women's health. A sequential therapy with bisphosphonates is recommended and the European Calcified Tissue Society (ECTS) proposed repeated zoledronate (ZOL) administrations in patients with persistently high CTX levels, although the efficacy of this schedule is unknown. In this retrospective study we describe BMD changes and FX rate in 52 patients managed according to the ECTS recommendations.

METHODS

We measured CTX levels and administered ZOL after one month from Dmab withdrawal (t0). After 6 months (t1), we administered a second ZOL infusion, if CTX levels were ≥280 ng/L. BMD changes and FX rate were assessed on average after 17 months from Dmab withdrawal.

RESULTS

75% of patients repeated ZOL infusion. In this group spine BMD declined significantly (-5.5 ± 5.6%), while it remained stable in the group with CTX levels <280 ng/L (-0.1 ± 5.5%, p = 0.008). All fractured patients (9.6%) had received >5 Dmab injections and two ZOL infusions. The BMD worsening after Dmab withdrawal was associated with CTX t1 (OR 2.9, IQR 1.3-6.6, p = 0.009) and spine BMD gain during Dmab therapy corrected for the number of Dmab injections (OR 3.0, IQR 1.2-7.2, p = 0.014). A CTX level at t1 > 212 ng/L had 100% sensitivity in predicting the BMD loss.

CONCLUSIONS

In patients with uncontrolled CTX levels after Dmab withdrawal, two ZOL infusions at 6 months apart do not prevent BMD loss and FX.

Association between pharmacotherapy and secondary vertebral fracture managed with a brace in a real-world setting: A nationwide database study in Japan

AIM

This retrospective cohort study assessed the association between the incidence of secondary vertebral fracture managed with a brace (SVF) and pharmacotherapy.

METHODS

The association between the incidence of SVF and the presence, type, and medication possession ratio (MPR) of pharmacotherapy was investigated using medical insurance data acquired from the National Database of Health Insurance Claims and Specific Health Checkups of Japan.

RESULTS

The data of female patients (n = 637 303) were analyzed. The 2-year incidence of SVF was 73.5 per 10 000 patients (n = 4687). Approximately 0.73% of patients without medications and 0.74% with medications had SVF. Patients taking bisphosphonates (0.87), denosumab (0.77), and selective estrogen receptor modulators (0.88) had significantly lower standardized incidence ratios (SIRs) than patients not taking medications after the occurrence of primary fracture; meanwhile, patients taking parathyroid hormone medications had considerably higher SIRs than those not taking medications. The non-SVF group (59.1%) had a significantly higher mean MPR than the SVF group (55.5%). Patients taking denosumab in the non-SVF group (68.2%) had the highest mean MPR. The proportion of patients taking denosumab with an MPR of ≥80% in the non-SVF group was significantly higher than that in the SVF group.

CONCLUSION

Patients taking medications were at a lower risk of developing SVF than those not taking medications. Although this study did not compare the medications' SVF prevention effects, patients taking denosumab had a 0.77 SIR of SVF in Japan. The effect of pharmacotherapy on SVF prevention might be affected by the MPR of each medication. Geriatr Gerontol Int 2024; 24: 390-397.

The relationship between length of denosumab treatment for postmenopausal osteoporosis and serum TRAcP5b measured six months after the last injection

To test the hypothesis that during treatment with denosumab osteomorphs and precursors recycle to higher number of osteoclasts with time, we measured TRAcP5b in serum taken 6 months after the last injection in postmenopausal women treated for 1-10 years. Serum TRAcP5b values were not related to time of exposure to denosumab.

PURPOSE

In women with postmenopausal osteoporosis the aetiology of the observed inverse relationship between duration of denosumab (Dmab) therapy and bone loss after its discontinuation is currently unknown. In studies in mice inhibition of RANKL is associated with an increase in osteomorphs and osteoclast precursors that recycle into osteoclasts and may accumulate with time. We hypothesized that longer inhibition of RANKL by Dmab will be followed by the synchronous formation of a larger number of osteoclasts after stopping treatment. To test this hypothesis, we measured serum TRAcP5b, a marker of osteoclast numbers, in postmenopausal women treated with Dmab for different periods of time up to 10 years.

METHODS

TRAcP5b, C-terminal telopeptide of type 1 collagen (CTX) and procollagen type 1 N-terminal propeptide (P1NP) were measured at 6.0 months ± 15 days after last Dmab injection in 59 women who had received Dmab for 4.0 ± 2.3 years (range 1-10 years). Of these, 38 were treatment naïve (group 1) and 21 had received other treatments prior Dmab (group 2).

RESULTS

Duration of Dmab treatment was not related to serum TRAcP5b values or to TRAcP5b/CTX ratio either in the whole cohort or in each of the two groups separately. In contrast, serum TRAcP5b values were significantly correlated with serum CTX values (rs = 0.619; p < 0.001), but not with serum P1NP values or BMD at all skeletal sites.

CONCLUSION

Our observations indicate that serum TRAcP5b, measured at 6 months after a Dmab injection, is not a useful early marker for time-dependent increased accumulation of osteoclasts in humans and for identification of patients at risk for a higher rebound increase in bone resorption.

Molecular and Cellular Mechanisms of Osteoporosis

Osteoporosis is a widespread systemic disease characterized by a decrease in bone mass and an imbalance of the microarchitecture of bone tissue. Experimental and clinical studies devoted to investigating the main pathogenetic mechanisms of osteoporosis revealed the important role of estrogen deficiency, inflammation, oxidative stress, cellular senescence, and epigenetic factors in the development of bone resorption due to osteoclastogenesis, and decreased mineralization of bone tissue and bone formation due to reduced function of osteoblasts caused by apoptosis and age-depended differentiation of osteoblast precursors into adipocytes. The current review was conducted to describe the basic mechanisms of the development of osteoporosis at molecular and cellular levels and to elucidate the most promising therapeutic strategies of pathogenetic therapy of osteoporosis based on articles cited in PubMed up to September 2023.

The Five-Year Effect of a Single Zoledronate Infusion on Bone Mineral Density Following Denosumab Discontinuation in Women with Postmenopausal Osteoporosis

The long-term effects of zoledronate treatment in women with postmenopausal osteoporosis who stop denosumab therapy when they become osteopenic are not known. In a prospective, randomized, controlled clinical trial we previously reported that a single intravenous infusion of zoledronate 5 mg given to such patients 6 months after the last denosumab injection effectively prevents bone loss in the majority of them for up to 3 years. The study was extended for an additional 2 years and included all 19 patients from one Trial Site of the total 27 patients originally randomized in the zoledronate arm. Baseline characteristics of this cohort treated with denosumab for 2.4 ± 0.2 years were not different from those of the whole initial cohort or from the patients who did not participate in this extension. At the end of 5 years 7 patients had become again osteoporotic requiring additional treatment, 9 remained osteopenic while 3 did not complete the study extension. Thus, more than half of the osteoporotic women who became osteopenic with denosumab treatment and stopped it, maintained the BMD gains 5 years after a single zoledronate infusion with no additional treatment. Whether these results are also applicable to patients treated with denosumab for longer periods remains to be established.

Similarities and Differences in the Management of Patients with Osteoporotic Vertebral Fractures and Those with Rebound-Associated Vertebral Fractures Following Discontinuation of Denosumab

Rebound-associated vertebral fractures (RVFx) following denosumab discontinuation are typically multiple, are commonly associated with acute sharp pain, increase the risk of imminent fractures, and are pathogenetically different from common osteoporotic vertebral fractures (VFx). A clinically relevant question is whether patients with RVFx should be managed differently from patients with osteoporotic VFx. To address this question, we performed a systematic search of the PubMed database, and we reviewed current evidence on the optimal management of patients with RVFx. For pain relief of patients with RVFx, potent analgesics, often opioids, are essential. Information on the effectiveness of braces in these patients is scarce. Vertebroplasty and kyphoplasty are strongly contraindicated as they confer a substantial risk for new VFx. Exercise may be helpful, but again evidence is lacking. In contrast to patients with osteoporotic VFx, in whom initial treatment with bone-forming agents is recommended, patients with RVFx should initiate treatment with potent antiresorptives. To summarize, patients who have sustained RVFx following denosumab discontinuation are at a very high risk for new fractures, especially VFx. The management of such patients requires a multidisciplinary approach that should not be restricted to pain relief and administration of antiosteoporotic medication, but should also include back protection, early mobilization, and appropriate exercise.

Structure-Based Discovery of Receptor Activator of Nuclear Factor-κB Ligand (RANKL)-Induced Osteoclastogenesis Inhibitors

Receptor activator of nuclear factor-κB ligand (RANKL) has been actively pursued as a therapeutic target for osteoporosis, given that RANKL is the master mediator of bone resorption as it promotes osteoclast differentiation, activity and survival. We employed a structure-based virtual screening approach comprising two stages of experimental evaluation and identified 11 commercially available compounds that displayed dose-dependent inhibition of osteoclastogenesis. Their inhibitory effects were quantified through TRAP activity at the low micromolar range (IC₅₀ < 5 μΜ), but more importantly, 3 compounds displayed very low toxicity (LC₅₀ > 100 μΜ). We also assessed the potential of an N-(1-aryl-1H-indol-5-yl)aryl-sulfonamide scaffold that was based on the structure of a hit compound, through synthesis of 30 derivatives. Their evaluation revealed 4 additional hits that inhibited osteoclastogenesis at low micromolar concentrations; however, cellular toxicity concerns preclude their further development. Taken together with the structure-activity relationships provided by the hit compounds, our study revealed potent inhibitors of RANKL-induced osteoclastogenesis of high therapeutic index, which bear diverse scaffolds that can be employed in hit-to-lead optimization for the development of therapeutics against osteolytic diseases.