Ferric ion could facilitate osteoclast differentiation and bone resorption through the production of reactive oxygen species

The Roles of DMT1 in Inflammatory and Degenerative Diseases

Iron homeostasis is critical for multiple physiological and pathological processes. DMT1, a core iron transporter, is expressed in almost all cells and organs and altered in response to various conditions, whereas, there is few reviews focusing on DMT1 in diseases associated with aberrant iron metabolism. Based on available knowledge, this review described a full view of DMT1 and summarized the roles of DMT1 and DMT1-mediated iron metabolism in the onset and development of inflammatory and degenerative diseases. This review also provided an overview of DMT1-related treatment in these disorders, highlighting its therapeutic potential in chronic inflammatory and degenerative diseases.

Melatonin Supplementation Alleviates Bone Mineral Density Decline and Circulating Oxidative Stress in Iron-Overloaded Thalassemia Patients

Thalassemia patients often exhibit low bone mineral density (BMD). The iron overload associated with thalassemia elevates oxidative stress levels, leading to reduced BMD. Melatonin improves BMD in postmenopausal osteopenia, however, its effect on BMD in thalassemia patients with iron overload has not been investigated. A randomized controlled study was conducted at Hematology Clinic, Faculty of Medicine, Chiang Mai University. Thalassemia patients with osteopenia and iron overloaded condition, as indicated by BMD Z-score <-2 at l-spine, femoral neck, or total hip, and serum ferritin level > 500 μg/L were recruited in this study. Patients were randomized to receive either melatonin 20 mg/day or placebo at bedtime for 12 months. BMD was re-evaluated 12 months after interventions. Bone turnover markers (BTM), malondialdehyde (MDA as an oxidative stress marker), and pain scores were assessed at baseline, 6, and 12 months. The outcomes, including BMD, BTM, MDA, and pain scores, were evaluated in all patients. Forty-one thalassemia patients (18 males) were enrolled in the study and randomly assigned to either the melatonin group (n = 21) or the placebo group (n = 20). Characteristics of patients were not differences between groups. Mean age was 30.8 ± 6.2 years old. Thirty-three patients (80.4%) were transfusion-dependent patients. At 12 months, mean BMD at l-spine in melatonin group was not significantly different from placebo group (p = 0.069). However, l-spine BMD at 12 months in the melatonin group was significantly greater than baseline (p = 0.029). Serum levels of P1NP and MDA were significantly reduced at 6 months compared to baseline following melatonin treatment. The melatonin group experienced a notable decrease in back pain scores after 12 months compared to the initial measurements. 20 mg daily melatonin supplementation for 12 months alleviated l-spine BMD loss in iron-overloaded thalassemia with low BMD. Melatonin also significantly reduced circulating oxidative stress and mitigated back pain in these patients.

Hepcidin knockout exacerbates hindlimb unloading-induced bone loss in mice through inhibiting osteoblastic differentiation

BACKGROUND

An oligopeptide hepcidin is encoded by the human HAMP gene (Hamp in mice). Its deficiency can result in iron overload, while excess may lead to iron deficiency. Hepcidin knockout mice exhibited iron accumulation in multiple tissues, accompanied by degeneration of bone microarchitecture and reduced biomechanical properties. Astronauts who are exposed to weightlessness during prolonged spaceflight experience bone loss. After space missions, an interrelation exists between iron stores and bone mineral density (BMD). Bone loss in mice due to unloading is linked to iron excess and involves hepcidin. The potential role of hepcidin in unloading-induced bone loss remains unclear.

METHODS

Our study conducted relevant experiments using hepcidin knockout mice and their primary osteoblasts as the research subjects. We used the hindlimb unloading (HLU) model and the random positioning machine (RPM) system to simulate weightlessness in vivo and in vitro.

RESULTS

HLU mice exhibited reduced hepcidin levels in the serum and liver. Hepcidin knockout further diminished BMD and bone mineral content (BMC) in the femurs of HLU mice. Similarly, the bone volume fraction (BV/TV) and connectivity density (Conn.Dn) followed this downward trend, whereas trabecular separation (Tb.Sp) showed an inverse pattern. Moreover, hepcidin knockout decreased the ultimate load and elastic modulus in the tibias of HLU mice. Hepcidin knockout decreased PINP levels in the serum, a commonly used marker for bone formation, alongside elevated iron levels in the serum, liver, and bone of HLU mice. We also found higher serum MDA and SOD levels in these mice. In vitro, experimental data indicated that hepcidin knockout suppresses the osteoblastic differentiation capacity under RPM conditions. Additionally, this condition upregulates SOST protein levels and downregulates LRP6 and β-catenin protein levels in osteoblasts.

CONCLUSION

Hepcidin knockout exacerbates bone loss in HLU mice, most likely due to reduced osteoblastic activity.

Facile Synthesis of N-Doped CDs from Ridge Gourd Seeds for the Sensitive Detection of Fe3+ Ions

This study reports the synthesis of nitrogen-doped carbon dots (N-CDs) from ridge gourd seeds via a hydrothermal process. The optical and physicochemical properties of the synthesized N-CDs were characterized using various techniques, including UV-Visible, fluorescence (FL), FT-IR, X-ray diffractometer (XRD), TEM, and XPS. The resulting N-CDs had an average size of 4.72 ± 0.2 nm, high monodispersity, and a quantum yield of 11.8%, which is related to efficient light emission. These N-CDs were highly dispersible in water and exhibited excitation-independent FL at varying excitation wavelengths. They showed excellent stability under diverse conditions, such as variations in pH, high ionic strengths, and prolonged light exposure, which enhances their use in potential applications. As FL probes, the N-CDs demonstrated the selective and sensitive detection of Fe3+ ions, with a significant FL quenching response. A strong linear correlation (R2 = 0.9899) was observed for Fe3+ concentrations in the range of 0-20 µM, with a detection limit of 67.3 nM. Notably, the FL quenching could be reversed by adding EDTA, which is a chelating agent for Fe3+, indicating the potential for reversible sensing applications. The biocompatibility of the N-CDs was assessed via an MTT assay on HCT 116 cells, which revealed low cytotoxicity (94.3 ± 1.8% viability at 75 µg/mL). These findings suggest that N-CDs are safe for in biological applications and hold great promise for use in biosensing, bioimaging, and environmental monitoring.

The mechanism of action of indole-3-propionic acid on bone metabolism

Indole-3-propionic acid (IPA), a metabolite produced by gut microbiota through tryptophan metabolism, has recently been identified as playing a pivotal role in bone metabolism. IPA promotes osteoblast differentiation by upregulating mitochondrial transcription factor A (Tfam), contributing to increased bone density and supporting bone repair. Simultaneously, it inhibits the formation and activity of osteoclasts, reducing bone resorption, possibly through modulation of the nuclear factor-κB (NF-κB) pathway and downregulation of osteoclast-associated factors, thereby maintaining bone structural integrity. Additionally, IPA provides indirect protection to bone health by regulating host immune responses and inflammation via activation of receptors such as the Aryl hydrocarbon Receptor (AhR) and the Pregnane X Receptor (PXR). This review summarizes the roles and signaling pathways of IPA in bone metabolism and its impact on various bone metabolic disorders. Furthermore, we discuss the therapeutic potential and limitations of IPA in treating bone metabolic diseases, aiming to offer novel strategies for clinical management.

Depletion of macrophages and osteoclast precursors mitigates iron overload-mediated bone loss

Iron is an essential element for physiological cellular processes, but is toxic in excess. Iron overload diseases are commonly associated with low bone mass. Increased bone resorption by osteoclasts as well as decreased bone formation by osteoblasts have been implicated in bone loss under iron overload conditions. However, the exact contribution of individual cell types has not yet been formally tested. In this study, we aimed to investigate the role of osteoclast precursors in iron overload-induced bone loss. To that end, we used clodronate liposomes to deplete phagocytic cells (including macrophages and osteoclast precursors) in male C57BL/6J mice that were exposed to ferric derisomaltose. Bone microarchitecture and bone turnover were assessed after 4 weeks. The application of clodronate resulted in the efficient depletion of circulating myeloid-lineage cells by about 70%. Depletion of osteoclast precursors mitigated iron overload-induced trabecular bone loss at the lumbar vertebrae and distal femur. While clodronate treatment led to a profound inhibition of bone turnover in control mice, it significantly reduced osteoclast numbers in iron-treated mice without further impacting the bone formation rate or serum PINP levels. Our observations suggest that even though bone formation is markedly suppressed by iron overload, osteoclasts also play a key role in iron overload-induced bone loss and highlight them as potential therapeutic targets.

The Potential Regulatory Role of Ferroptosis in Orthodontically Induced Inflammatory Root Resorption

People, in increasing numbers, are seeking orthodontic treatment to correct malocclusion, while some of them are suffering from orthodontically induced inflammatory root resorption (OIIRR). Recent evidence suggests that the immune-inflammatory response occurring during bone remodeling may be responsible for OIIRR. Ferroptosis, a new type of programmed cell death (PCD), has been found to have a close interrelation with inflammation during disease progression. While ferroptosis has been extensively studied in bone-related diseases, its role in OIIRR is poorly understood. Considering that the tooth root shares a lot of similar characteristics with bone, it is reasonable to hypothesize that ferroptosis contributes to the development of OIIRR. Nevertheless, direct evidence supporting this theory is currently lacking. In this review, we introduced ferroptosis and elucidated the mechanisms underlying orthodontic tooth movement (OTM) and OIIRR, with a special focus on the pivotal role inflammation plays in these processes. Additionally, we covered recent research exploring the connections between inflammation and ferroptosis. Lastly, we emphasized the important regulatory function of ferroptosis in bone homeostasis. Further investigations are required to clarify the modulation mechanisms of ferroptosis in OIIRR and to develop novel and potential therapeutic strategies for the management of OIIRR.

Advances in the study of ferroptosis and its relationship to autoimmune diseases

Ferroptosis represents a novel mode of programmed cell death characterized by the intracellular accumulation of iron and lipid peroxidation, culminating in oxidative stress and subsequent cell demise. Mounting evidence demonstrates that ferroptosis contributes significantly to the onset and progression of diverse pathological conditions and diseases, including infections, neurodegenerative disorders, tissue ischemia-reperfusion injury, and immune dysregulation. Recent investigations have underscored the pivotal role of ferroptosis in the pathogenesis of rheumatoid arthritis, ulcerative colitis, systemic lupus erythematosus, and asthma. This review provides a comprehensive overview of the current understanding of the regulatory mechanisms governing ferroptosis, particularly its interplay with iron, lipid, and amino acid metabolism. Furthermore, we explore the implications of ferroptosis in autoimmune diseases and deliberate on its potential as a promising therapeutic target for diverse autoimmune disorders.

Antioxidative effects of N-acetylcysteine in patients with β-thalassemia: A quick review on clinical trials

Background and Aims

Several studies have highlighted the potent antioxidant properties of N-acetyl cysteine (NAC). This review aimed to assess the impact of NAC on oxidative stress biomarkers in patients with β-thalassemia.

Methods

The review included articles published before 2024 that investigated the effects of NAC on oxidative stress in individuals with β-thalassemia. A comprehensive search was conducted across various databases, including Scopus, PubMed, Web of Science, Trip, and CENTRAL. Only English-language clinical trials were considered for inclusion in this review. Besides, the number needed to treat (NNT) was calculated based on the included studies.

Results

Ninety-nine articles were retrieved from electronic databases, and after a thorough review, eight articles were selected for comprehensive text analysis. The highest dose of NAC administered was 10 mg/kg/day (equivalent to 600 mg/day) over a period of 3-6 months. All the studies assessing the impact of NAC on oxidative stress indicators in β-thalassemia patients demonstrated positive effects during the 3-month follow-up period. Most estimated NNTs fell into 1-5, suggesting significant clinical therapeutic value in this context.

Conclusion

The current potency of NAC alone appears to be effective in ameliorating oxidative stress in patients with β-thalassemia major. While a 3-month duration seems adequate to demonstrate the antioxidant properties of NAC in this population, larger and well-designed clinical trials are warranted. Current clinical evidence possesses a high risk of bias.

Cell life-or-death events in osteoporosis: All roads lead to mitochondrial dynamics

Mitochondria exhibit heterogeneous shapes and networks within and among cell types and tissues, also in normal or osteoporotic bone tissues with complex cell types. This dynamic characteristic is determined by the high plasticity provided by mitochondrial dynamics and is stemmed from responding to the survival and functional requirements of various bone cells in a specific microenvironments. In contrast, mitochondrial dysfunction, induced by dysregulation of mitochondrial dynamics, may act as a trigger of cell death signals, including common apoptosis and other forms of programmed cell death (PCD). These PCD processes consisting of tightly structured cascade gene expression events, can further influence the bone remodeling by facilitating the death of various bone cells. Mitochondrial dynamics, therefore, drive the bone cells to stand at the crossroads of life and death by integrating external signals and altering metabolism, shape, and signal-response properties of mitochondria. This implies that targeting mitochondrial dynamics displays significant potential in treatment of osteoporosis. Considerable effort has been made in osteoporosis to emphasize the parallel roles of mitochondria in regulating energy metabolism, calcium signal transduction, oxidative stress, inflammation, and cell death. However, the emerging field of mitochondrial dynamics-related PCD is not well understood. Herein, to bridge the gap, we outline the latest knowledge on mitochondrial dynamics regulating bone cell life or death during normal bone remodeling and osteoporosis.

Iron and bones: effects of iron overload, deficiency and anemia treatments on bone

Iron is a vital trace element and exerts opposing effects on bone in both iron overload and iron deficiency situations. Remarkably, iron supplementation through intravenous infusion in patients with iron deficiency can also have detrimental effects on bone in special cases. The diverse mechanisms underlying these effects and their manifestations contribute to the complexity of this relationship. Iron overload impacts both bone resorption and formation, accelerating bone resorption while reducing bone formation. These effects primarily result from the direct action of reactive oxygen species (ROS), which influence the proliferation, differentiation, and activity of both osteoclasts and osteoblasts differently. This imbalance favors osteoclasts and inhibits the osteoblasts. Simultaneously, multiple pathways, including bone morphogenic proteins, RANK ligand, and others, contribute to these actions, leading to a reduction in bone mass and an increased susceptibility to fractures. In contrast, iron deficiency induces low bone turnover due to energy and co-factor deficiency, both of which require iron. Anemia increases the risk of fractures in both men and women. This effect occurs at various levels, reducing muscular performance and, on the bone-specific level, decreasing bone mineral density. Crucially, anemia increases the synthesis of the phosphaturic hormone iFGF23, which is subsequently inactivated by cleavage under physiological conditions. Thus, iFGF23 levels and phosphate excretion are not increased. However, in specific cases where anemia has to be managed with intravenous iron treatment, constituents-particularly maltoses-of the iron infusion suppress the cleavage of iFGF23. As a result, patients can experience severe phosphate wasting and, consequently, hypophosphatemic osteomalacia. This condition is often overlooked in clinical practice and is often caused by ferric carboxymaltose. Ending iron infusions or changing the agent, along with phosphate and vitamin D supplementation, can be effective in addressing this issue.

The role of N-acetylcysteine in osteogenic microenvironment for bone tissue engineering

Bone defect is a common clinical symptom which can arise from various causes. Currently, bone tissue engineering has demonstrated positive therapeutic effects for bone defect repair by using seeding cells such as mesenchymal stem cells and precursor cells. N-acetylcysteine (NAC) is a stable, safe and highly bioavailable antioxidant that shows promising prospects in bone tissue engineering due to the ability to attenuate oxidative stress and enhance the osteogenic potential and immune regulatory function of cells. This review systematically introduces the antioxidant mechanism of NAC, analyzes the advancements in NAC-related research involving mesenchymal stem cells, precursor cells, innate immune cells and animal models, discusses its function using the classic oral microenvironment as an example, and places particular emphasis on the innovative applications of NAC-modified tissue engineering biomaterials. Finally, current limitations and future prospects are proposed, with the aim of providing inspiration for targeted readers in the field.

Effects of dietary iron deficiency or overload on bone: Dietary details matter

PURPOSE

Bone is susceptible to fluctuations in iron homeostasis, as both iron deficiency and overload are linked to poor bone strength in humans. In mice, however, inconsistent results have been reported, likely due to different diet setups or genetic backgrounds. Here, we assessed the effect of different high and low iron diets on bone in six inbred mouse strains (C57BL/6J, A/J, BALB/cJ, AKR/J, C3H/HeJ, and DBA/2J).

METHODS

Mice received a high (20,000 ppm) or low-iron diet (∼10 ppm) after weaning for 6-8 weeks. For C57BL/6J males, we used two dietary setups with similar amounts of iron, yet different nutritional compositions that were either richer ("TUD study") or poorer ("UCLA study") in minerals and vitamins. After sacrifice, liver, blood and bone parameters as well as bone turnover markers in the serum were analyzed.

RESULTS

Almost all mice on the UCLA study high iron diet had a significant decrease of cortical and trabecular bone mass accompanied by high bone resorption. Iron deficiency did not change bone microarchitecture or turnover in C57BL/6J, A/J, and DBA/2J mice, but increased trabecular bone mass in BALB/cJ, C3H/HeJ and AKR/J mice. In contrast to the UCLA study, male C57BL/6J mice in the TUD study did not display any changes in trabecular bone mass or turnover on high or low iron diet. However, cortical bone parameters were also decreased in TUD mice on the high iron diet.

CONCLUSION

Thus, these data show that cortical bone is more susceptible to iron overload than trabecular bone and highlight the importance of a nutrient-rich diet to potentially mitigate the negative effects of iron overload on bone.

Isobavachin attenuates osteoclastogenesis and periodontitis-induced bone loss by inhibiting cellular iron accumulation and mitochondrial biogenesis

As bone-resorbing cells rich in mitochondria, osteoclasts require high iron uptake to promote mitochondrial biogenesis and maintain a high-energy metabolic state for active bone resorption. Given that abnormal osteoclast formation and activation leads to imbalanced bone remodeling and osteolytic bone loss, osteoclasts may be crucial targets for treating osteolytic diseases such as periodontitis. Isobavachin (IBA), a natural flavonoid compound, has been confirmed to be an inhibitor of receptor activator of nuclear factor κB ligand (RANKL)-induced osteoclast differentiation from bone marrow-derived macrophages (BMMs). However, its effects on periodontitis-induced bone loss and the potential mechanism of its anti-osteoclastogenesis effect remain unclear. Our study demonstrated that IBA suppressed RANKL-induced osteoclastogenesis in BMMs and RAW264.7 cells and inhibited osteoclast-mediated bone resorption in vitro. Transcriptomic analysis indicated that iron homeostasis and reactive oxygen species (ROS) metabolic process were enriched among the differentially expressed genes following IBA treatment. IBA exerted its anti-osteoclastogenesis effect by inhibiting iron accumulation in osteoclasts. Mechanistically, IBA attenuated iron accumulation in RANKL-induced osteoclasts by inhibiting the mitogen-activated protein kinase (MAPK) pathway to upregulate ferroportin1 (Fpn1) expression and promote Fpn1-mediated intracellular iron efflux. We also found that IBA inhibited mitochondrial biogenesis and function, and reduced RANKL-induced ROS generation in osteoclasts. Furthermore, IBA attenuated periodontitis-induced bone loss by reducing osteoclastogenesis in vivo. Overall, these results suggest that IBA may serve as a promising therapeutic strategy for bone diseases characterized by osteoclastic bone resorption.

Comparison of the effects of high dietary iron levels on bone microarchitecture responses in the mouse strains 129/Sv and C57BL/6J

Iron is an essential nutrient for all living organisms. Both iron deficiency and excess can be harmful. Bone, a highly metabolic active organ, is particularly sensitive to fluctuations in iron levels. In this study, we investigated the effects of dietary iron overload on bone homeostasis with a specific focus on two frequently utilized mouse strains: 129/Sv and C57BL/6J. Our findings revealed that after 6 weeks on an iron-rich diet, 129/Sv mice exhibited a decrease in trabecular and cortical bone density in both vertebral and femoral bones, which was linked to reduced bone turnover. In contrast, there was no evidence of bone changes associated with iron overload in age-matched C57BL/6J mice. Interestingly, 129/Sv mice exposed to an iron-rich diet during their prenatal development were protected from iron-induced bone loss, suggesting the presence of potential adaptive mechanisms. Overall, our study underscores the critical role of genetic background in modulating the effects of iron overload on bone health. This should be considered when studying effects of iron on bone.

Redox signaling and antioxidant defense in osteoclasts

Bone remodeling is essential for the repair and replacement of damaged or aging bones. Continuous remodeling is necessary to prevent the accumulation of bone damage and to maintain bone strength and calcium balance. As bones age, the coupling mechanism between bone formation and absorption becomes dysregulated, and bone loss becomes dominant. Bone development and repair rely on interaction and communication between osteoclasts and surrounding cells. Osteoclasts are specialized cells that are accountable for bone resorption and degradation, and any abnormalities in their activity can result in notable alterations in bone structure and worsen disease symptoms. Recent findings from transgenic mouse models and bone analysis have greatly enhanced our understanding of the origin, differentiation pathway, and activation stages of osteoclasts. In this review, we explore osteoclasts and discuss the cellular and molecular events that drive their generation, focusing on intracellular oxidative and antioxidant signaling. This knowledge can help develop targeted therapies for diseases associated with osteoclast activation.

The influence of iron on bone metabolism disorders

Iron is a necessary trace element in the human body, and it participates in many physiological processes. Disorders of iron metabolism can cause lesions in many tissues and organs, including bone. Recently, iron has gained attention as an independent factor influencing bone metabolism disorders, especially the involvement of iron overload in osteoporosis. The aim of this review was to summarize the findings from clinical and animal model research regarding the involvement of iron in bone metabolism disorders and to elucidate the mechanisms behind iron overload and osteoporosis. Lastly, we aimed to describe the association between bone loss and iron overload. We believe that a reduction in iron accumulation can be used as an alternative treatment to assist in the treatment of osteoporosis, to improve bone mass, and to improve the quality of life of patients.

Prevention and treatment of osteoporosis with natural products: Regulatory mechanism based on cell ferroptosis

CONTEXT

With the development of society, the number of patients with osteoporosis is increasing. The prevention and control of osteoporosis has become a serious and urgent issue. With the continuous progress of biomedical research, ferroptosis has attracted increased attention. However, the pathophysiology and mechanisms of ferroptosis and osteoporosis still need further study. Natural products are widely used in East Asian countries for osteoporosis prevention and treatment.

OBJECTIVE

In this paper, we will discuss the basic mechanisms of ferroptosis, the relationship between ferroptosis and osteoclasts and osteoblasts, and in vitro and in vivo studies of natural products to prevent osteoporosis by interfering with ferroptosis.

METHODS

This article takes ferroptosis, natural products, osteoporosis, osteoblasts and osteoclast as key words. Retrieve literature from 2012 to 2023 indexed in databases such as PubMed Central, PubMed, Web of Science, Scopus and ISI.

RESULTS

Ferroptosis has many regulatory mechanisms, including the system XC -/GSH/GPX4, p62/Keap1/Nrf2, FSP1/NAD (P) H/CoQ10, P53/SAT1/ALOX15 axes etc. Interestingly, we found that natural products, such as Artemisinin, Biochanin A and Quercetin, can play a role in treating osteoporosis by promoting ferroptosis of osteoclast and inhibiting ferroptosis of osteoblasts.

CONCLUSIONS

Natural products have great potential to regulate OBs and OCs by mediating ferroptosis to prevent and treat osteoporosis, and it is worthwhile to explore and discover more natural products that can prevent and treat osteoporosis.

REPIN1 regulates iron metabolism and osteoblast apoptosis in osteoporosis

Osteoporosis is not well treated due to the difficulty of finding commonalities between the various types of it. Iron homeostasis is a vital component in supporting biochemical functions, and iron overload is recognized as a common risk factor for osteoporosis. In this research, we found that there is indeed evidence of iron accumulation in the bone tissue of patients with osteoporosis and REPIN1, as an origin specific DNA binding protein, may play a key role in this process. We revealed that sh-Repin1 therapy can rescue bone loss in an iron-overload-induced osteoporosis mouse model. Knockdown of Repin1 can inhibit apoptosis and enhance the resistance of osteoblasts to iron overload toxicity. REPIN1 promoted apoptosis by regulating iron metabolism in osteoblasts. Mechanistically, knockdown of Repin1 decreased the expression of Lcn2, which ameliorated the toxic effects of intracellular iron overload. The anti-iron effect of lentivirus sh-Repin1 was partially reversed or replicated by changing LCN2 expression level via si-RNA or plasmid, which indirectly verified the key regulatory role of LCN2 as a downstream target. Furthermore, the levels of BCL2 and BAX, which play a key role in the mitochondrial apoptosis pathway, were affected. In summary, based on the results of clinical specimens, animal models and in vitro experiments, for the first time, we proved the key role of REPIN1 in iron metabolism-related osteoporosis.

Role of Iron Accumulation in Osteoporosis and the Underlying Mechanisms

Osteoporosis is prevalent in postmenopausal women. The underlying reason is mainly estrogen deficiency, but recent studies have indicated that osteoporosis is also associated with iron accumulation after menopause. It has been confirmed that some methods of decreasing iron accumulation can improve the abnormal bone metabolism associated with postmenopausal osteoporosis. However, the mechanism of iron accumulation-induced osteoporosis is still unclear. Iron accumulation may inhibit the canonical Wnt/β-catenin pathway via oxidative stress, leading to osteoporosis by decreasing bone formation and increasing bone resorption via the osteoprotegerin (OPG)/receptor activator of nuclear factor kappa-B ligand (RANKL)/receptor activator of nuclear factor kappa-B (RANK) system. In addition to oxidative stress, iron accumulation also has been reported to inhibit either osteoblastogenesis or osteoblastic function as well as to stimulate either osteoclastogenesis or osteoclastic function directly. Furthermore, serum ferritin has been widely used for the prediction of bone status, and nontraumatic measurement of iron content by magnetic resonance imaging may be a promising early indicator of postmenopausal osteoporosis.

Dietary iron intake and its impact on osteopenia/osteoporosis

BACKGROUND

Osteoporosis is a prevalent condition characterized by low bone density and increased risk of fractures, resulting in a significant healthcare burden. Previous research has suggested that serum ferritin levels may be related to the risk of developing osteoporosis. The aim of this study was to investigate the relationship between dietary iron intake and the development of osteoporosis.

METHODS

Using data from the National Health and Nutrition Examination Survey (NHANES) conducted between 2005 and 2018, a total of 11,690 adults aged over 20 were evaluated. Bone mineral density (BMD) measurements of the femoral neck and lumbar spine were used to assess osteoporosis and osteopenia. Dietary iron intake was determined using food intake interviews and the Food and Nutrient Database for Dietary Studies. Logistic regression models were applied to investigate the association between dietary iron consumption and osteopenia and osteoporosis.

RESULTS

After adjusting for sociodemographic factors, compared with those who had the first quartile (Q1) of dietary iron intake, the odds ratio (OR) for osteopenia across the quartiles of dietary iron intake levels was 0.88 (95%CI: 0.79-0.98), 0.80 (95%CI: 0.72-0.89), and 0.74 (95%CI: 0.67-0.83) for Q2, Q3, and Q4, respectively. And the OR for osteoporosis across the quartiles of dietary iron intake levels was 1.00, 0.77 (95%CI: 0.50-1.19), 0.54 (95%CI: 0.34-0.89), and 0.83 (95%CI: 0.54-1.29) for Q1, Q2, Q3, and Q4, respectively. Notably, the observed association was significant among females but not males.

CONCLUSION

The risk of osteopenia/osteoporosis in females decreases with a moderate increase in dietary iron consumption. For females to preserve bone health, moderately increasing their dietary iron intake without overindulging should be seen as a key approach. Our study provides useful insights for developing dietary strategies to prevent and manage osteoporosis in vulnerable populations.

The Role of Trace Elements and Minerals in Osteoporosis: A Review of Epidemiological and Laboratory Findings

The objective of the present study was to review recent epidemiological and clinical data on the association between selected minerals and trace elements and osteoporosis, as well as to discuss the molecular mechanisms underlying these associations. We have performed a search in the PubMed-Medline and Google Scholar databases using the MeSH terms "osteoporosis", "osteogenesis", "osteoblast", "osteoclast", and "osteocyte" in association with the names of particular trace elements and minerals through 21 March 2023. The data demonstrate that physiological and nutritional levels of trace elements and minerals promote osteogenic differentiation through the up-regulation of BMP-2 and Wnt/β-catenin signaling, as well as other pathways. miRNA and epigenetic effects were also involved in the regulation of the osteogenic effects of trace minerals. The antiresorptive effect of trace elements and minerals was associated with the inhibition of osteoclastogenesis. At the same time, the effect of trace elements and minerals on bone health appeared to be dose-dependent with low doses promoting an osteogenic effect, whereas high doses exerted opposite effects which promoted bone resorption and impaired bone formation. Concomitant with the results of the laboratory studies, several clinical trials and epidemiological studies demonstrated that supplementation with Zn, Mg, F, and Sr may improve bone quality, thus inducing antiosteoporotic effects.

The Potential Roles of Ferroptosis in Pathophysiology and Treatment of Musculoskeletal Diseases—Opportunities, Challenges, and Perspectives

Ferroptosis is different from other forms of cell death, such as apoptosis, autophagy, pyroptosis, and cuproptosis, mainly involving iron metabolism and lipid peroxidation. Ferroptosis plays an important role in various disease, such as malignant tumors, neuron-degenerative diseases, and cardiovascular diseases, and has become the focus of current research. Both iron overload and lipid peroxide accumulation contribute to the occurrence, development, and treatment of musculoskeletal diseases, such as osteoporosis, osteoarthritis, osteosarcoma, intervertebral disc degeneration, and spinal cord injury. For a better understanding of the potential roles ferroptosis may play in pathophysiology and treatment of common musculoskeletal disorders, this article briefly reviewed the relationship and possible mechanisms. Through an investigation of ferroptosis’ role in musculoskeletal diseases’ occurrence, development, and treatment, ferroptosis could offer new opportunities for clinical diagnosis and treatment.

Fighting age-related orthopedic diseases: focusing on ferroptosis

Ferroptosis, a unique type of cell death, is characterized by iron-dependent accumulation and lipid peroxidation. It is closely related to multiple biological processes, including iron metabolism, polyunsaturated fatty acid metabolism, and the biosynthesis of compounds with antioxidant activities, including glutathione. In the past 10 years, increasing evidence has indicated a potentially strong relationship between ferroptosis and the onset and progression of age-related orthopedic diseases, such as osteoporosis and osteoarthritis. Therefore, in-depth knowledge of the regulatory mechanisms of ferroptosis in age-related orthopedic diseases may help improve disease treatment and prevention. This review provides an overview of recent research on ferroptosis and its influences on bone and cartilage homeostasis. It begins with a brief overview of systemic iron metabolism and ferroptosis, particularly the potential mechanisms of ferroptosis. It presents a discussion on the role of ferroptosis in age-related orthopedic diseases, including promotion of bone loss and cartilage degradation and the inhibition of osteogenesis. Finally, it focuses on the future of targeting ferroptosis to treat age-related orthopedic diseases with the intention of inspiring further clinical research and the development of therapeutic strategies.

Identification and Validation of Potential Ferroptosis-Related Genes in Glucocorticoid-Induced Osteonecrosis of the Femoral Head

Background and Objectives. Glucocorticoid-induced osteonecrosis of the femoral head (GIONFH) is a serve complication of long-term administration of glucocorticoids. Previous experimental studies have shown that ferroptosis might be involved in the pathological process of GIONFH. The purpose of this study is to identify the ferroptosis-related genes and pathways of GIONFH by bioinformatics to further illustrate the mechanism of ferroptosis in SONFH through bioinformatics analysis. Materials and Methods. The GSE123568 mRNA expression profile dataset, including 30 GIONFH samples and 10 non-GIONFH samples, was downloaded from the Gene Expression Omnibus (GEO) database. Ferroptosis-related genes were obtained from the FerrDb database. First, differentially expressed genes (DEGs) were identified between the serum samples from GIONFH cases and those from controls. Ferroptosis-related DEGs were obtained from the intersection of ferroptosis-related genes and DEGs. Only ferroptosis DEGs were used for all analyses. Then, we conducted a Kyoto encyclopedia of genome (KEGG) and gene ontology (GO) pathway enrichment analysis. We constructed a protein-protein interaction (PPI) network to screen out hub genes. Additionally, the expression levels of the hub genes were validated in an independent dataset GSE10311. Results. A total of 27 ferroptosis-related DEGs were obtained between the peripheral blood samples of GIONFH cases and non-GIONFH controls. Then, GO, and KEGG pathway enrichment analysis revealed that ferroptosis-related DEGs were mainly enriched in the regulation of the apoptotic process, oxidation-reduction process, and cell redox homeostasis, as well as HIF-1, TNF, FoxO signaling pathways, and osteoclast differentiation. Eight hub genes, including TLR4, PTGS2, SNCA, MAPK1, CYBB, SLC2A1, TXNIP, and MAP3K5, were identified by PPI network analysis. The expression levels of TLR4, TXNIP and MAP3K5 were further validated in the dataset GSE10311. Conclusion. A total of 27 ferroptosis-related DEGs involved in GIONFH were identified via bioinformatics analysis. TLR4, TXNIP, and MAP3K5 might serve as potential biomarkers and drug targets for GIONFH.

Cell death regulation: A new way for natural products to treat osteoporosis

Osteoporosis is a common metabolic bone disease that results from the imbalance of homeostasis within the bone. Intra-bone homeostasis is dependent on a precise dynamic balance between bone resorption by osteoclasts and bone formation by mesenchymal lineage osteoblasts, which comprises a series of complex and highly standardized steps. Programmed cell death (PCD) (e.g., apoptosis, autophagy, ferroptosis, pyroptosis, and necroptosis) is a cell death process that involves a cascade of gene expression events with tight structures. These events play a certain role in regulating bone metabolism by determining the fate of bone cells. Moreover, existing research has suggested that natural products derived from a wide variety of dietary components and medicinal plants modulate the PCDs based on different mechanisms, which show great potential for the prevention and treatment of osteoporosis, thus revealing the emergence of more acceptable complementary and alternative drugs with lower costs, fewer side effects and more long-term application. Accordingly, this review summarizes the common types of PCDs in the field of osteoporosis. Moreover, from the perspective of targeting PCDs, this review also discussed the roles of currently reported natural products in the treatment of osteoporosis and the involved mechanisms. Based on this, this review provides more insights into new molecular mechanisms of osteoporosis and provides a reference for developing more natural anti-osteoporosis drugs in the future.

Remarkable Plasticity of Bone Iron Homeostasis in Hibernating Daurian Ground Squirrels (Spermophilus dauricus) May Be Involved in Bone Maintenance

Iron overload is an independent risk factor for disuse osteoporosis. Hibernating animals are natural models of anti-disuse osteoporosis; however, whether iron metabolism is involved in bone adaptation and maintenance during hibernation is unclear. To investigate this question, Daurian ground squirrels (Spermophilus dauricus) (n = 5-6/group) were used to study changes in bone iron metabolism and its possible role in anti-disuse osteoporosis during hibernation. Iron content in the femur and liver first decreased in the torpor group (vs. summer group, -66.8% and -25.8%, respectively), then recovered in the post-hibernation group, suggesting remarkable plasticity of bone iron content. The expression of ferritin in the femur and hepcidin in the liver also initially decreased in the torpor group (vs. summer group, -28.5% and -38.8%, respectively), then increased in the inter-bout arousal (vs. torpor group, 126.2% and 58.4%, respectively) and post-hibernation groups (vs. torpor group, 153.1% and 27.1%, respectively). In conclusion, bone iron metabolism in hibernating Daurian ground squirrels showed remarkable plasticity, which may be a potential mechanism to avoid disuse bone loss during extended periods of inactivity. However, the specific location of iron during low-iron hibernation and the source of iron in post-hibernation recovery need to be further explored.

Nox4 promotes osteoblast differentiation through TGF-beta signal pathway

NADPH oxidase 4 (Nox4) is the main source of reactive oxygen species, which promote osteoclast formation and lead to bone loss, thereby causing osteoporosis. However, the role of Nox4 in osteoblasts during early development remains unclear. We used zebrafish to study the effect of Nox4 deletion on bone mineralization in early development. nox4-/- zebrafish showed decreased bone mineralization during early development and significantly reduced numbers of osteoblasts, osteoclasts, and chondrocytes. Transcriptome sequencing showed that the TGF-β signaling pathway was significantly disrupted in nox4-/- zebrafish. Inhibiting TGF-β signaling rescued the abnormal bone development caused by nox4 deletion and increased the number of osteoblasts. We used Saos-2 human osteosarcoma cells to confirm our results, which clarified the role of Nox4 in human osteoblasts. Our results demonstrate the mechanism of reduced bone mineralization in early development and provide a basis for the clinical treatment of osteoporosis.

Iron overload induced osteocytes apoptosis and led to bone loss in Hepcidin-/- mice through increasing sclerostin and RANKL/OPG

BACKGROUND

Numerous studies have demonstrated that iron overload is a risk factor of osteoporosis. However, there has been no systematic and in-depth studies on the effect of iron overload on osteocytes and its role in iron overload-induced bone loss. Therefore, to address this problem, we carried out in vitro and in vivo studies using MLO-Y4 osteocyte-like cells and Hepcidin^-/- mice as iron overload models.

METHODS

(1) MLO-Y4 cells were treated with ferric ammonium citrate (FAC). Intracellular reactive oxygen species (ROS) levels and apoptosis of MLO-Y4 cells were determined by flow cytometry. Western blotting was performed to evaluate the effect of FAC on the expression of sclerostin and RANKL/OPG. (2) The conditioned medium of MLO-Y4 cells after treatment with FAC was collected and used to treat pre-osteoblasts and monocytes. Alkaline phosphatase (ALP) staining and alizarin red (AR) staining were used to evaluate osteogenic differentiation capacity, and tartrate-resistant acid phosphatase (TRAP) staining was performed to demonstrate osteoclast differentiation capacity. (3) In vivo studies included a wild type mouse, Hepcidin^-/- mice, Hepcidin^-/- mice + deferoxamine (DFO), and Hepcidin^-/- mice + N-actyl-l-cysteine (NAC) group. Micro-CT was performed to evaluate the bone mineral density (BMD), bone volume, and bone micro-architecture of the mice, and three bending tests were used to assess bone strength. Histological analysis was used to detect alterations in bone turnover. TUNEL staining and scanning electron microscopy (SEM) were performed to evaluate the apoptosis and morphology of osteocytes. Immunohistochemical staining and Western blotting were used to determine alterations in sclerostin and RANKL/OPG expression levels in mice.

RESULTS

(1) FAC increased intracellular ROS and apoptosis in MLO-Y4 cells, while FAC enhanced the expression of sclerostin and RANKL/OPG in MLO-Y4 cells. (2) Conditioned medium of MLO-Y4 cells inhibited the osteogenic capacity of osteoblasts while stimulating osteoclast differentiation. (3) By increasing oxidative stress, iron overload promotes the apoptosis of osteocytes and undermines the morphology of osteocytes in Hepcidin^-/- mice, further increasing the expression levels of sclerostin and RANKL/OPG in osteocytes, which is considered to be the causative factor for reduced bone formation and enhanced bone resorption. DFO administration reduced iron levels, and NAC treatment decreased oxidative stress in Hepcidin^-/- mice. Therefore, DFO or NAC treatment rescued the decrease in BMD, bone volume, and bone strength and attenuated the deterioration of bone architecture in Hepcidin^-/- mice by attenuating the effect of iron overload on osteocytes.

CONCLUSION

Osteocyte apoptosis due to increased ROS and resultant sclerostin and RANKL/OPG expression alteration was the main reason for bone loss in Hepcidin^-/- mice. Osteocytes are the main targets for the prevention and treatment of iron overload-induced osteoporosis.

Trimethylamine-N-Oxide Promotes Osteoclast Differentiation and Bone Loss via Activating ROS-Dependent NF-κB Signaling Pathway

Trimethylamine-N-oxide (TMAO), an important gut microbiota (GM)-derived metabolite, has been shown to be abnormally increased in osteoporosis. However, the role and underlying mechanism of TMAO in regulating bone loss during osteoporosis have not been fully investigated. In the current study, we found that 100–400 μM TMAO dose-dependently enhanced TRAP-positive osteoclasts, F-actin ring formation, and resorption area on bovine bone slices and up-regulated osteoclast-related gene expression (Calcr, Traf6, Dcstamp, Acp5, C-Fos, and NFATc1). Western blotting validated that TMAO not only activated NF-κB signaling pathway but also stimulated c-Fos and NFATc1 protein expression in a dose-dependent manner. Furthermore, BAY 11-7082, an NF-κB inhibitor, pretreatment markedly suppressed TRAP-positive osteoclast formation and osteoclast-related genes under TMAO treatment. BAY 11-7082 also inhibited p-p65/p65, c-Fos, and NFATc1 protein expression promoted by TMAO. Moreover, TMAO significantly increased ROS production, which was inhibited by N-acetylcysteine (NAC), an ROS antagonist. In addition, we proved that NAC pretreatment could inhibit TMAO-promoted NF-κB activation. NAC also suppressed TRAP-positive osteoclast formation, osteoclast-related gene expression, and protein expression of c-Fos and NFATc1 under TMAO treatment. In vivo studies showed significantly decreased bone mass and increased TRAP-positive osteoclasts in TMAO-treated C57BL/6 mice. Moreover, western-blotting and immunohistochemical staining showed that TMAO administration markedly stimulated NF-κB p65 expression. Additionally, TMAO administration significantly promoted the gene and protein expression of C-Fos and NFATc1. In conclusion, TMAO could promote osteoclast differentiation and induce bone loss in mice by activating the ROS-dependent NF-κB signaling pathway.

Modulation of integrin receptor by polyphenols: Downstream Nrf2-Keap1/ARE and associated cross-talk mediators in cardiovascular diseases

As a group of heterodimeric and transmembrane glycoproteins, integrin receptors are widely expressed in various cell types overall the body. During cardiovascular dysfunction, integrin receptors apply inhibitory effects on the antioxidative pathways, including nuclear factor erythroid 2-related factor 2 (Nrf2)-Kelch like ECH Associated Protein 1 (Keap1)/antioxidant response element (ARE) and interconnected mediators. As such, dysregulation in integrin signaling pathways influences several aspects of cardiovascular diseases (CVDs) such as heart failure, arrhythmia, angina, hypertension, hyperlipidemia, platelet aggregation and coagulation. So, modulation of integrin pathway could trigger the downstream antioxidant pathways toward cardioprotection. Regarding the involvement of multiple aforementioned mediators in the pathogenesis of CVDs, as well as the side effects of conventional drugs, seeking for novel alternative drugs is of great importance. Accordingly, the plant kingdom could pave the road in the treatment of CVDs. Of natural entities, polyphenols are multi-target and accessible phytochemicals with promising potency and low levels of toxicity. The present study aims at providing the cardioprotective roles of integrin receptors and downstream antioxidant pathways in heart failure, arrhythmia, angina, hypertension, hyperlipidemia, platelet aggregation and coagulation. The potential role of polyphenols has been also revealed in targeting the aforementioned dysregulated signaling mediators in those CVDs.

Iron effects versus metabolic alterations in hereditary hemochromatosis driven bone loss

Hereditary hemochromatosis (HH) is a genetic disorder in which mutations affect systemic iron homeostasis. Most subtypes of HH result in low hepcidin levels and iron overload. Accumulation of iron in various tissues can lead to widespread organ damage and to various complications, including liver cirrhosis, arthritis, and diabetes. Osteoporosis is another frequent complication of HH, and the underlying mechanisms are poorly understood. Currently, it is unknown whether iron overload in HH directly damages bone or whether complications associated with HH, such as liver cirrhosis or hypogonadism, affect bone secondarily. This review summarizes current knowledge of bone metabolism in HH and highlights possible implications of metabolic dysfunction in HH-driven bone loss. We further discuss therapeutic considerations managing osteoporosis in HH.

Orthovoltage X-Rays Exhibit Increased Efficacy Compared with γ-Rays in Preclinical Irradiation

Radionuclide irradiators (137Cs and 60Co) are commonly used in preclinical studies ranging from cancer therapy to stem cell biology. Amidst concerns of radiological terrorism, there are institutional initiatives to replace radionuclide sources with lower energy X-ray sources. As researchers transition, questions remain regarding whether the biological effects of γ-rays may be recapitulated with orthovoltage X-rays because different energies may induce divergent biological effects. We therefore sought to compare the effects of orthovoltage X-rays with 1-mm Cu or Thoraeus filtration and 137Cs γ-rays using mouse models of acute radiation syndrome. Following whole-body irradiation, 30-day overall survival was assessed, and the lethal dose to provoke 50% mortality within 30-days (LD50) was calculated by logistic regression. LD50 doses were 6.7 Gy, 7.4 Gy, and 8.1 Gy with 1-mm Cu-filtered X-rays, Thoraeus-filtered X-rays, and 137Cs γ-rays, respectively. Comparison of bone marrow, spleen, and intestinal tissue from mice irradiated with equivalent doses indicated that injury was most severe with 1-mm Cu-filtered X-rays, which resulted in the greatest reduction in bone marrow cellularity, hematopoietic stem and progenitor populations, intestinal crypts, and OLFM4+ intestinal stem cells. Thoraeus-filtered X-rays provoked an intermediate phenotype, with 137Cs showing the least damage. This study reveals a dichotomy between physical dose and biological effect as researchers transition to orthovoltage X-rays. With decreasing energy, there is increasing hematopoietic and intestinal injury, necessitating dose reduction to achieve comparable biological effects.

SIGNIFICANCE

Understanding the significance of physical dose delivered using energetically different methods of radiation treatment will aid the transition from radionuclide γ-irradiators to orthovoltage X-irradiators.

Manganese, iron, copper, and selenium co-exposure and osteoporosis risk in Chinese adults

BACKGROUND & AIMS

Previous experimental studies demonstrated that either deficient or excessive trace elements, such as manganese (Mn), iron (Fe), copper (Cu) and selenium (Se), are detrimental to bone health. Epidemiologic evidence for the effect of the four trace elements on osteoporosis (OP) risk remains inadequate. This cross-sectional study aimed to examine their associations with the OP risk among Chinese adults.

METHODS

Concentrations of Mn, Fe, Cu, and Se were measured in plasma using an inductively coupled plasma mass spectrometer among 627 Chinese adults aged ≥ 50 years. Individual effect of the four elements on OP risk was analyzed by logistic regression and Bayesian Kernel Machine Regression (BKMR) models. The latter model was also adopted to examine the exposure-response relationships and joint effects of the four elements on OP risk.

RESULTS

The median Mn, Fe, Cu, and Se levels were 4.78, 1026.63, 904.55, and 105.39 μg/L, respectively, in all participants. Inverse associations of Fe and Se levels with OP risk were observed in the logistic regression model. BKMR analysis revealed a U-shape pattern for the Fe-OP association, and a reduced OP risk in response to co-exposure of the four elements above the 50th percentiles but an elevated one in response to that below the 50th percentiles. Sex discrepancy existed in the findings. No interactions were found for the four elements affecting OP risk.

CONCLUSIONS

Co-exposure to Mn, Fe, Cu, and Se was associated with improved bone density, where Fe contributed most to the beneficial effect. Further studies are needed to verify these findings and explore the underlying biological mechanism.

Osteogenic potential of calcium silicate-doped iron oxide nanoparticles versus calcium silicate for reconstruction of critical-sized mandibular defects: An experimental study in dog model

Objective

To evaluate bioactivity and osteogenic potential of calcium silicate (CS)-doped iron oxide (Fe₂O₃) nanoparticles versus pure CS in the reconstruction of induced critical-sized mandibular defects.

Design

CS-doped Fe₂O₃ was prepared; morphological and microstructure identification of nanoparticles were made. An in vivo randomised design was developed on 24 adult male dogs where four critical-sized mandibular defects were created in each dog. Bone defects were allocated into control, CS, CS-3% Fe₂O₃ and CS-10% Fe₂O₃ group. Dogs were euthanized at 1 and 3 months (12 dog/time) for histopathologic and histomorphometric evaluation.

Results

At three months, bone formation and maturation were evident where mean ± SD percent of mature bone was 2.66 ± 1.8, 9.9 ± 2.5, 22.9 ± 4.9, and 38.6 ± 8.1 in control, CS, CS-3% Fe₂O₃, and CS-10% Fe₂O₃ groups respectively. A high significant (P < 0.001) increase in area percent of mature bone was recorded in CS, CS-3% Fe₂O₃, and CS- 10% Fe₂O₃ groups compared to control group (73%, 88% and 93.3% respectively). Significant increase (P < 0.001) in area of mature bone was recorded in CS-3% Fe₂O₃ and CS-10% Fe₂O₃ groups compared to CS group. A significant increase (P < 0.001) in area of mature bone formation was detected in CS-10% Fe₂O₃ group compared to other groups.

Conclusion

CS-doped Fe₂O₃ has good osteoconductive, biocompatible properties with promoted bone regeneration. Fe₂O₃ has synergistic effect in combination with CS to promote bone formation. Increasing concentration of Fe₂O₃ nanoparticles resulted in improved osteogenesis and maturation. Results suggests that the novel CS-Fe₂O₃ alloplasts could be used for reconstruction of critical-sized bone defects.

Ferroptosis as a Novel Therapeutic Target for Diabetes and Its Complications

The global diabetes epidemic and its complications are increasing, thereby posing a major threat to public health. A comprehensive understanding of diabetes mellitus (DM) and its complications is necessary for the development of effective treatments. Ferroptosis is a newly identified form of programmed cell death caused by the production of reactive oxygen species and an imbalance in iron homeostasis. Increasing evidence suggests that ferroptosis plays a pivotal role in the pathogenesis of diabetes and diabetes-related complications. In this review, we summarize the potential impact and regulatory mechanisms of ferroptosis on diabetes and its complications, as well as inhibitors of ferroptosis in diabetes and diabetic complications. Therefore, understanding the regulatory mechanisms of ferroptosis and developing drugs or agents that target ferroptosis may provide new treatment strategies for patients with diabetes.

Identification of Common Pathogenic Pathways Involved in Hemochromatosis Arthritis and Calcium Pyrophosphate Deposition Disease: a Review

OBJECTIVES

Arthritis is a common clinical manifestation of hereditary hemochromatosis (HH), and HH is one of a handful of conditions linked to calcium pyrophosphate deposition (CPPD) in joints. The connection between these two types of arthritis has not yet been fully elucidated. In light of new pathogenic pathways recently implicated in CPPD involving bone, we reviewed the literature on the etiology of hemochromatosis arthropathy (HHA) seeking shared pathogenic mechanisms.

RESULTS

Clinical observations reinforce striking similarities between HHA and CPPD even in the absence of CPP crystals. They share a similar joint distribution, low grade synovial inflammation, and generalized bone loss. Excess iron damages chondrocytes and bone cells in vitro. While direct effects of iron on cartilage are not consistently seen in animal models of HH, there is decreased osteoblast alkaline phosphatase activity, and increased osteoclastogenesis. These abnormalities are also seen in CPPD. Joint repair processes may also be impaired in both CPPD and HHA.

CONCLUSIONS

Possible shared pathogenic pathways relate more to bone and abnormal damage/repair mechanisms than direct damage to articular cartilage. While additional work is necessary to fully understand the pathogenesis of arthritis in HH and to firmly establish causal links with CPPD, this review provides some plausible hypotheses explaining the overlap of these two forms of arthritis.

Interplay Between Iron Overload and Osteoarthritis: Clinical Significance and Cellular Mechanisms

There are multiple diseases or conditions such as hereditary hemochromatosis, hemophilia, thalassemia, sickle cell disease, aging, and estrogen deficiency that can cause iron overload in the human body. These diseases or conditions are frequently associated with osteoarthritic phenotypes, such as progressive cartilage degradation, alterations in the microarchitecture and biomechanics of the subchondral bone, persistent joint inflammation, proliferative synovitis, and synovial pannus. Growing evidences suggest that the conditions of pathological iron overload are associated with these osteoarthritic phenotypes. Osteoarthritis (OA) is an important complication in patients suffering from iron overload-related diseases and conditions. This review aims to summarize the findings and observations made in the field of iron overload-related OA while conducting clinical and basic research works. OA is a whole-joint disease that affects the articular cartilage lining surfaces of bones, subchondral bones, and synovial tissues in the joint cavity. Chondrocytes, osteoclasts, osteoblasts, and synovial-derived cells are involved in the disease. In this review, we will elucidate the cellular and molecular mechanisms associated with iron overload and the negative influence that iron overload has on joint homeostasis. The promising value of interrupting the pathologic effects of iron overload is also well discussed for the development of improved therapeutics that can be used in the field of OA.

Ferroptosis: A New Regulatory Mechanism in Osteoporosis

Osteoporosis can be caused by a multitude of factors and is defined by a decrease in bone density and mass caused by the destruction of bone microstructure, resulting in increased bone brittleness. Thus, it is a systemic bone disease in which patients are prone to fracture. The role of ferroptosis in the pathogenesis of osteoporosis has become a topic of growing interest. In this review, we discuss the cell morphology, basic mechanisms of ferroptosis, the relationship between ferroptosis and osteoclasts and osteoblasts, as well as the relationship between ferroptosis and diabetic osteoporosis, steroid-induced osteoporosis, and postmenopausal osteoporosis. Emerging biomedical research has provided new insights into the roles of ferroptosis and osteoporosis, such as in cellular function, signaling pathways, drug inhibition, and gene silencing. The pathophysiology and mechanism of ferroptosis and osteoporosis need to be further studied and elucidated to broaden our understanding of iron metabolism and immune regulation. Studies using animal models of osteoporosis in vivo and cell models in vitro will help clarify the relationship between ferroptosis and osteoporosis and provide research ideas for the elucidation of new mechanisms and development of new technologies and new drugs for the treatment of osteoporosis in the future.

Iron homeostasis in arthropathies: From pathogenesis to therapeutic potential

Iron is an essential element for proper functioning of cells within mammalian organ systems; in particular, iron homeostasis is critical for joint health. Excess iron can induce oxidative stress damage, associated with the pathogenesis of iron-storage and ageing-related diseases. Therefore, iron levels in body tissues and cells must be tightly regulated. In the past decades, excess iron content within joints has been found in some patients with joint diseases including hemophilic arthropathy, hemochromatosis arthropathy, and osteoarthritis (OA). Currently, increased evidence has shown that iron accumulation is closely associated with multiple pathological changes of these arthropathies. This review summarizes system-level and intracellular regulation of iron homeostasis, and emphasizes the role of iron in synovial alterations, cartilage degeneration, and subchondral bone of several arthropathies. Of note, we discuss the potential link between iron homeostasis and OA pathogenesis. Finally, we discuss the therapeutic potential of maintaining iron homeostasis in these arthropathies.

Progress of Phototherapy Applications in the Treatment of Bone Cancer

Bone cancer including primary bone cancer and metastatic bone cancer, remains a challenge claiming millions of lives and affecting the life quality of survivors. Conventional treatments of bone cancer include wide surgical resection, radiotherapy, and chemotherapy. However, some bone cancer cells may remain or recur in the local area after resection, some are highly resistant to chemotherapy, and some are insensitive to radiotherapy. Phototherapy (PT) including photodynamic therapy (PDT) and photothermal therapy (PTT), is a clinically approved, minimally invasive, and highly selective treatment, and has been widely reported for cancer therapy. Under the irradiation of light of a specific wavelength, the photosensitizer (PS) in PDT can cause the increase of intracellular ROS and the photothermal agent (PTA) in PTT can induce photothermal conversion, leading to the tumoricidal effects. In this review, the progress of PT applications in the treatment of bone cancer has been outlined and summarized, and some envisioned challenges and future perspectives have been mentioned. This review provides the current state of the art regarding PDT and PTT in bone cancer and inspiration for future studies on PT.

Iron accumulation deteriorated bone loss in estrogen-deficient rats

Background

Postmenopausal osteoporosis is characterized by an imbalance of bone resorption exceeding bone formation, resulting in a net loss of bone mass. Whether a menopause-related excess of iron contributes to the development of postmenopausal osteoporosis has remained unresolved due to a lack of an appropriate animal model. This study aimed to explore the effects of iron accumulation in bone mass in estrogen-deficient rats.

Methods

In the present study, ovariectomy (OVX) was performed in female rats and the changes of iron metabolism and some related modulated genes were detected. Ferric ammonium citrate (FAC) was used as a donor of iron for OVX rats. Moreover, micro-CT was performed to assess the bone microarchitecture in sham group, OVX, and FAC groups. Histological detection of iron in liver was assessed by Perl’s staining. The expressions of β-CTX and osteocalcin were assessed by ELISA.

Results

It was found that serum iron decreased after OVX. It was found that the expressions of Hepcidin in liver and Fpn, DMT-1 in duodenum significantly decreased at transcriptional level in OVX group than sham group. However, no difference existed in the expression of DMT-1. Then, ferric ammonium citrate (FAC) was used as a donor of iron for OVX rats. The FAC group manifested significant iron accumulation by increased serum iron and hepatic iron content. In addition, FAC treatment accelerated bone loss and decreased BMD and biomechanics in OVX rats. Moreover, bone biomarker β-CTX rather than osteocalcin increased significantly in FAC groups than OVX group.

Conclusions

In conclusion, no iron accumulation occurred in OVX rats. Furthermore, iron accumulation could further deteriorate osteopenia through enhanced bone resorption.

Shaping the bone through iron and iron-related proteins

Well-controlled iron levels are indispensable for health. Iron deficiency is the most common cause of anemia, whereas iron overload, either hereditary or secondary due to disorders of ineffective erythropoiesis, causes widespread organ failure. Bone is particularly sensitive to fluctuations in systemic iron levels as both iron deficiency and overload are associated with low bone mineral density and fragility. Recent studies have shown that not only iron itself, but also iron-regulatory proteins that are mutated in hereditary hemochromatosis can control bone mass. This review will summarize the current knowledge on the effects of iron on bone homeostasis and bone cell activities, and on the role of proteins that regulate iron homeostasis, i.e. hemochromatosis proteins and proteins of the bone morphogenetic protein pathway, on bone remodeling. As disorders of iron homeostasis are closely linked to bone fragility, deeper insights into common regulatory mechanisms may provide new opportunities to concurrently treat disorders affecting iron homeostasis and bone.

Agaricus bisporus-Derived Glucosamine Hydrochloride Facilitates Skeletal Injury Repair through Bmp Signaling in Zebrafish Osteoporosis Model

Glucosamine hydrochloride (GAH), one of the most basic and important derivatives of chitin, is obtained by hydrolysis of chitin in concentrated hydrochloric acid. At present, little is known about how GAH functions in skeletal development. In this report, we demonstrate that GAH, extracted from the cell wall of Agaricus bisporus, acts in a dose-dependent manner to promote not only cartilage and bone development in larvae but also caudal fin regeneration in adult fish. Furthermore, GAH treatment causes a significant increase in expression of bone-related marker genes, indicating its important role in promoting skeletal development. We show that in both larval and adult osteoporosis models induced by high iron osteogenic defects are significantly ameliorated after treatment with GAH, which regulates expression of a series of bone-related genes. Finally, we demonstrate that GAH promotes skeletal development and injury repair through bone morphogenetic protein (Bmp) signaling, and it works at the downstream of the receptor level. Taken together, our findings not only provide a strong research foundation and strategy for the screening of natural osteoporosis drugs and product development using a zebrafish model but also establish the potential for the development of Agaricus bisporus-derived GAH as a new drug for osteoporosis treatment.

Hepcidin-induced reduction in iron content and PGC-1β expression negatively regulates osteoclast differentiation to play a protective role in postmenopausal osteoporosis

As a necessary trace element, iron is involved in many physiological processes. Clinical and basic studies have found that disturbances in iron metabolism, especially iron overload, might lead to bone loss and even be involved in postmenopausal osteoporosis. Hepcidin is a key regulator of iron homeostasis. However, the exact role of hepcidin in bone metabolism and the underlying mechanism remain unknown. In this study, we found that in postmenopausal osteoporosis cohort, the concentration of hepcidin in the serum was significantly reduced and positively correlated with bone mineral density. Ovariectomized (OVX) mice were then used to construct an osteoporosis model. Hepcidin overexpression in these mice significantly improved bone mass and rescued the phenotype of bone loss. Additionally, overexpression of hepcidin in OVX mice greatly reduced the number and differentiation of osteoclasts in vivo and in vitro. This study found that overexpression of hepcidin significantly inhibited ROS production, mitochondrial biogenesis, and PGC-1β expression. These data showed that hepcidin protected osteoporosis by reducing iron levels in bone tissue, and in conjunction with PGC-1β, reduced ROS production and the number of mitochondria, thus inhibiting osteoclast differentiation and bone absorption. Hepcidin could provide new targets for the clinical treatment of postmenopausal osteoporosis.

Novel rhodamine probe for colorimetric and fluorescent detection of Fe3+ ions in aqueous media with cellular imaging

A novel rhodamine-pyridine conjugated spectroscopic probe RhP was synthesized and its X-ray single crystalline properties were revealed with tabulation. The RhP displayed a distinct pale-pink colorimetric and "turn-on" fluorescent response to Fe³⁺ in aqueous media [H₂O:DMSO (95:5, v/v)] than that of other interfering ions. During the Fe³⁺ recognition, the absorption (UV-Vis) and photoluminescence (PL) spectral studies revealed new peaks at 561 and 592 nm, respectively. The 1:1 stoichiometry and binding sites were verified by Job's plot, ESI-mass, and ¹H NMR titrations. Subsequently, LOD and binding constant for RhP + Fe³⁺ complex were estimated as 102.3 nM and 6.265 × 10⁴ M^-1 from linear fitting and Benesi-Hildebrand plots, correspondingly. Sensor reversibility of RhP + Fe³⁺ by EDTA was demonstrated by UV/PL and TRPL investigations. Moreover, the photoinduced energy transfer mechanism and band gap changes were established from the DFT interrogations. Lastly, cellular imaging studies were carried out to authenticate the real applicability of RhP in Fe³⁺ detection.

Fe3O4@GO magnetic nanocomposites protect mesenchymal stem cells and promote osteogenic differentiation of rat bone marrow mesenchymal stem cells

Fe₃O₄ nanoparticles (Fe₃O₄ NPs) are typical magnetic materials for bone tissue regeneration. However, the accompanying oxidative stress during the reaction process of Fe₃O₄ NPs and H₂O₂ in bone remodeling and disease may hinder their application. In order to reduce this side effect, we selected graphene oxide (GO) to modify Fe₃O₄ NPs. We showed that Fe₃O₄@GO magnetic nanocomposites (Fe₃O₄@GO MNCs) eliminated 30% of H₂O₂ in 3 h, and reduced the amount of ˙OH, the intermediate product of the Fenton reaction. The cellular study demonstrated that Fe₃O₄@GO MNCs reduced the cell damage caused by reactive oxygen species (ROS) and improved the activity of mesenchymal stem cells (MSCs). Moreover, when the magnetic field and bone morphogenetic protein-2 (BMP2) delivered by Fe₃O₄@GO MNCs worked together, osteogenic differentiation of MSCs in vitro was well promoted.

Iron Overload-Induced Osteocyte Apoptosis Stimulates Osteoclast Differentiation Through Increasing Osteocytic RANKL Production In Vitro

Iron overload is closely associated with osteoporosis, the potential cellular mechanism involved in decreased osteoblast differentiation and increased osteoclast formation. However, the effect of iron overload on the biological behavior in osteocytes has not been reported. This study aims to investigate the changes of osteocytic activity, apoptosis, and its regulation on osteoclastogenesis in response to iron overload. MLO-Y4 osteocyte-like cells and primary osteocytes from mice were processed with ferric ammonium citrate (FAC) and deferoxamine (DFO), the conditioned medium (CM) was harvested and co-cultured with Raw264.7 cells and bone marrow-derived macrophages (BMDMs) to induce them to differentiate into osteoclasts. Osteocyte apoptosis, osteoclast differentiation, osteocytic gene expression and protein secretion of receptor activator of nuclear factor κB ligand (RANKL) and osteoprotegerin (OPG) was examined. Excessive iron has a toxic effect on MLO-Y4 osteocyte-like cells. Increased cell apoptosis in MLO-Y4 cells and primary osteocytes was induced by iron overload. The osteoclastic formation, differentiation-related gene expression, and osteoclastic bone-resorption capability were significantly increased after treated with the CM from iron overload-exposed osteocytes. Excessive iron exposure significantly promoted the gene expression and protein secretion of the RANKL in MLO-Y4 cells. Addition of RANKL-blocking antibody completely abolished the increase of osteoclast formation and bone resorption capacity induced by the CM from osteocytes exposed to excessive iron. Moreover, the pan-caspase apoptosis inhibitor, QVD (quinolyl-valyl-O-methylaspartyl-[-2,6-difluorophenoxy]-methylketone) was used to inhibit osteocyte apoptosis. The results showed osteocyte apoptosis induced by iron overload was reduced by QVD and accompanied by the decrease of soluble RANKL (sRANKL) in supernatant. The increase of osteoclast formation and bone resorption capacity induced by the CM from osteocytes exposed to excessive iron was significantly decreased by QVD. These results indicated that iron overload-induced osteocyte apoptosis is required to regulate osteoclast differentiation by increasing osteocytic RANKL production. This study, for the first time, reveals the indirect effect of iron overload on osteoclast differentiation through regulating osteocytes.