Iron homeostasis in osteoporosis and its clinical implications

A systematic review on the impact of nutrition and possible supplementation on the deficiency of vitamin complexes, iron, omega-3-fatty acids, and lycopene in relation to increased morbidity in women after menopause

A balanced and healthy diet during the menopausal transition and after menopause is crucial for women to reduce the risk for morbidities and chronic diseases due to deficiency of essential nutrients.

PURPOSE

The objective of this study was to conduct a systematic review of studies that analyzed the impact of vitamin and nutrient deficiencies in postmenopausal women in relation to increased morbidities and chronic conditions.

METHODS

Observational studies were searched in the databases PubMed, UpToDate, and Google Scholar.

RESULTS

We searched 122 studies, of which 90 were included in our analysis. The meta-analysis of the data could not be performed because of the heterogeneity of the statistical methods in the included studies. In our study, we focused on the aspects of vitamin B6, vitamin B12, vitamin D, iron, omega-3-fatty acids, and lycopene, belonging to the family of carotenoids. Postmenopausal women with deficiencies of these nutrients are more vulnerable to comorbidities such as cardiovascular and cerebrovascular events, metabolic diseases, osteoporosis, obesity, cancer and neurodegenerative diseases such as Parkinson's disease, Alzheimer's disease, depression, cognitive decline, dementia, and stroke. We concluded that women after menopause tend to have a greater probability of suffering from deficiencies in various vitamins and nutrients, and consequently have an increased risk of developing morbidities and chronic diseases.

CONCLUSION

In conclusion, maintaining optimum serum levels of nutrients and vitamins, either through a balanced and healthy diet consuming fresh fruits, vegetables, and fats or by taking appropriate supplementation, is essential in maintaining optimal health-related quality of life and reducing the risk for women during the menopausal transition and after menopause. Nevertheless, more recent studies need to be assessed to formulate adequate recommendations to achieve positive clinical outcomes.

Iron status and sarcopenia-related traits: a bi-directional Mendelian randomization study

Although serum iron status and sarcopenia are closely linked, the presence of comprehensive evidence to establish a causal relationship between them remains insufficient. The objective of this study is to employ Mendelian randomization techniques to clarify the association between serum iron status and sarcopenia. We conducted a bi-directional Mendelian randomization (MR) analysis to investigate the potential causal relationship between iron status and sarcopenia. MR analyses were performed using inverse variance weighted (IVW), MR-Egger, and weighted median methods. Additionally, sensitivity analyses were conducted to verify the reliability of the causal association results. Then, we harvested a combination of SNPs as an integrated proxy for iron status to perform a MVMR analysis based on IVW MVMR model. UVMR analyses based on IVW method identified causal effect of ferritin on appendicular lean mass (ALM, β = - 0.051, 95% CI - 0.072, - 0.031, p = 7.325 × 10-07). Sensitivity analyses did not detect pleiotropic effects or result fluctuation by outlying SNPs in the effect estimates of four iron status on sarcopenia-related traits. After adjusting for PA, the analysis still revealed that each standard deviation higher genetically predicted ferritin was associated with lower ALM (β = - 0.054, 95% CI - 0.092, - 0.015, p = 0.006). Further, MVMR analyses determined a predominant role of ferritin (β = - 0.068, 95% CI - 0.12, - 0.017, p = 9.658 × 10-03) in the associations of iron status with ALM. Our study revealed a causal association between serum iron status and sarcopenia, with ferritin playing a key role in this relationship. These findings contribute to our understanding of the complex interplay between iron metabolism and muscle health.

Identification of osteoporosis ferroptosis-related markers and potential therapeutic compounds based on bioinformatics methods and molecular docking technology

RESEARCH BACKGROUND AND PURPOSE

Osteoporosis (OP) is one of the most common bone diseases worldwide, characterized by low bone mineral density and susceptibility to pathological fractures, especially in postmenopausal women and elderly men. Ferroptosis is one of the newly discovered forms of cell death regulated by genes in recent years. Many studies have shown that ferroptosis is closely related to many diseases. However, there are few studies on ferroptosis in osteoporosis, and the mechanism of ferroptosis in osteoporosis is still unclear. This study aims to identify biomarkers related to osteoporosis ferroptosis from the GEO (Gene Expression Omnibus) database through bioinformatics technology, and to mine potential therapeutic small molecule compounds through molecular docking technology, trying to provide a basis for the diagnosis and treatment of osteoporosis in the future.

MATERIALS AND METHODS

We downloaded the ferroptosis-related gene set from the FerrDb database ( http://www.zhounan.org/ferrdb/index.html ), downloaded the data sets GSE56815 and GSE7429 from the GEO database, and used the R software "limma" package to screen differentially expressed genes (DEGs) from GSE56815, and intersected with the ferroptosis gene set to obtain ferroptosis-related DEGs. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis were performed by the R software "clusterProfiler" package. The random forest model was further screened to obtain essential ferroptosis genes. R software "corrplot" package was used for correlation analysis of essential ferroptosis genes, and the Wilcox test was used for significance analysis. The lncRNA-miRNA-mRNA-TF regulatory network was constructed using Cytoscape software. The least absolute shrinkage and selection operator (LASSO) was used to construct a disease diagnosis model, and a Receiver operating characteristic (ROC) curve was drawn to evaluate the diagnostic performance, and then GSE7429 was used to verify the reliability of the diagnosis model. Molecular docking technology was used to screen potential small molecule compounds from the Drugbank database. Finally, a rat osteoporosis model was constructed, and peripheral blood mononuclear cells were extracted for qRT-PCR detection to verify the mRNA expression levels of crucial ferroptosis genes.

RESULT

Six DEGs related to ferroptosis were initially screened out. GO function and KEGG pathway enrichment analysis showed that ferroptosis-related DEGs were mainly enriched in signaling pathways such as maintenance of iron ion homeostasis, copper ion binding function, and ferroptosis. The random forest model identified five key ferroptosis genes, including CP, FLT3, HAMP, HMOX1, and SLC2A3. Gene correlation analysis found a relatively low correlation between these five key ferroptosis genes. The lncRNA-miRNA-mRNA-TF regulatory network shows that BAZ1B and STAT3 may also be potential molecules. The ROC curve of the disease diagnosis model shows that the model has a good diagnostic performance. Molecular docking technology screened out three small molecule compounds, including NADH, Midostaurin, and Nintedanib small molecule compounds. qRT-PCR detection confirmed the differential expression of CP, FLT3, HAMP, HMOX1 and SLC2A3 between OP and normal control group.

CONCLUSION

This study identified five key ferroptosis genes (CP, FLT3, HAMP, HMOX1, and SLC2A3), they were most likely related to OP ferroptosis. In addition, we found that the small molecule compounds of NADH, Midostaurin, and Nintedanib had good docking scores with these five key ferroptosis genes. These findings may provide new clues for the early diagnosis and treatment of osteoporosis in the future.

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.

The Therapeutic Effect of Natural Compounds on Osteoporosis through Ferroptosis

Ferroptosis is a newly discovered non-apoptotic cell death whose key is lipid peroxidation. It has been reported that ferroptosis is involved in the occurrence and development of tumors and nervous system and musculoskeletal diseases. Cellular ferroptosis contributes to the imbalance of bone homeostasis and is involved in the development of osteoporosis; however, the detailed mechanism of which is still unclear though it may provide a new direction for anti-osteoporosis. The current drugs used in the treatment of osteoporosis, such as bisphosphonates and teriparatide, have many side effects, increasing people's search for natural compounds to treat osteoporosis. This review paper briefly summarizes the current research regarding the mechanisms of ferroptosis and natural anti-osteoporosis compounds targeting its pathway.

A comprehensive review on environmental pollutants and osteoporosis: Insights into molecular pathways

A significant problem that has an impact on community wellbeing is environmental pollution. Environmental pollution due to air, water, or soil pollutants might pose a severe risk to global health, necessitating intense scientific effort. Osteoporosis is a common chronic condition with substantial clinical implications on mortality, morbidity, and quality of life. It is closely linked to bone fractures. Worldwide, osteoporosis affects around 200 million people, and every year, there are almost 9 million fractures. There is evidence that certain environmental factors may increase the risk of osteoporosis in addition to traditional risk factors. It is crucial to understand the molecular mechanisms at play because there is a connection between osteoporosis and exposure to environmental pollutants such as heavy metals, air pollutants, endocrine disruptors, metal ions and trace elements. Hence, in this scoping review, we explore potential explanations for the link between pollutants and bone deterioration through deep insights into molecular pathways. Understanding and recognizing these pollutants as modifiable risk factors for osteoporosis would possibly help to enhance environmental policy thereby aiding in the improvement of bone health and improving patient quality of life.

Arctiin attenuates iron overload‑induced osteoporosis by regulating the PI3K/Akt pathway

Iron overload is a prevalent pathological factor observed among elderly individuals and those with specific hematological disorders, and is frequently associated with an elevated incidence of osteoporosis. Although arctiin (ARC) has been shown to possess antioxidant properties and the ability to mitigate bone degeneration, its mechanism of action in the treatment of iron overload‑induced osteoporosis (IOOP) remains incompletely understood. To explore the potential molecular mechanisms underlying the effects of ARC, the MC3T3‑E1 cell osteoblast cell line was used. Cell Counting Kit was used to assess MC3T3‑E1 cell viability. Alkaline phosphatase staining and alizarin red staining were assessed for osteogenic differentiation. Calcein AM assay was used to assess intracellular iron concentration. In addition, intracellular levels of reactive oxygen species (ROS), lipid peroxides, mitochondrial ROS, apoptosis rate and mitochondrial membrane potential changes in MC3T3‑E1 cells were examined using flow cytometry and corresponding fluorescent dyes. The relationship between ARC and the PI3K/Akt pathway was then explored by western blotting and immunofluorescence. In addition, the effects of ARC on IOOP was verified using an iron overload mouse model. Immunohistochemistry was performed to evaluate expression of osteogenesis‑related proteins. Micro-CT and H&E were used to analyze bone microstructural parameters and histomorphometric indices in the bone tissue. Notably, ARC treatment reversed the decreased viability and increased apoptosis in MC3T3‑E1 cells originally induced by ferric ammonium citrate, whilst promoting the formation of mineralized bone nodules in MC3T3‑E1 cells. Furthermore, iron overload induced a decrease in the mitochondrial membrane potential, augmented lipid peroxidation and increased the accumulation of ROS in MC3T3‑E1 cells. ARC not only positively regulated the anti‑apoptotic and osteogenic capabilities of these cells via modulation of the PI3K/Akt pathway, but also exhibited antioxidant properties by reducing oxidative stress. In vivo experiments confirmed that ARC improved bone microarchitecture and biochemical parameters in a mouse model of iron overload. In conclusion, ARC exhibits potential as a therapeutic agent for IOOP by modulating the PI3K/Akt pathway, and via its anti‑apoptotic, antioxidant and osteogenic properties.

Calcium-Deficit Diet Improves Iron Content in Ovariectomized Rats

In women, menopause is associated with disorders related to calcium and iron content, which may increase the risk of osteoporosis. This study aimed to determine the effect of calcium deficiency on the iron content in ovariectomized rats. This study included 30 3-month-old female rats, which were divided into three groups: group C (n = 10)-control group fed the standard diet; group O-ovariectomized rats fed the standard diet; and group D-ovariectomized rats fed the calcium-deficit diet. After 3 months of experimental intervention, the weight of the rats was measured, and blood and tissue samples were collected. Morphological parameters were analyzed in whole blood, and serum levels of leptin, estrogen and C-reactive protein, and total antioxidant status were determined. The iron content was measured in tissues, and histological analysis was performed in the femur. The results obtained demonstrated that ovariectomy significantly decreased the iron content in bones, hair, spleen, liver, and kidneys. The calcium-deficit diet increased the iron content in tissues and the hemoglobin level in ovariectomized rats and also enhanced the number of osteoblasts in bones compared with the O group. In conclusion, calcium deficiency improved the iron content in ovariectomized rats in this 12-week study.

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.

Iron metabolism and ferroptosis in diabetic bone loss: from mechanism to therapy

Osteoporosis, one of the most serious and common complications of diabetes, has affected the quality of life of a large number of people in recent years. Although there are many studies on the mechanism of diabetic osteoporosis, the information is still limited and there is no consensus. Recently, researchers have proven that osteoporosis induced by diabetes mellitus may be connected to an abnormal iron metabolism and ferroptosis inside cells under high glucose situations. However, there are no comprehensive reviews reported. Understanding these mechanisms has important implications for the development and treatment of diabetic osteoporosis. Therefore, this review elaborates on the changes in bones under high glucose conditions, the consequences of an elevated glucose microenvironment on the associated cells, the impact of high glucose conditions on the iron metabolism of the associated cells, and the signaling pathways of the cells that may contribute to diabetic bone loss in the presence of an abnormal iron metabolism. Lastly, we also elucidate and discuss the therapeutic targets of diabetic bone loss with relevant medications which provides some inspiration for its cure.

The impact of soy products, isoflavones, and Lactobacillus acidophilus on iron status and morphological parameters in healthy female rats

BACKGROUND

Isoflavones and probiotics are two major factors involved in bone health. Osteoporosis and disturbances in iron (Fe) levels are common health problems in aging women. This study aimed to analyze how soybean products, daidzein, genistein, and Lactobacillus acidophilus (LA) affect Fe status and blood morphological parameters in healthy female rats.

METHODS

A total of 48 Wistar rats aged 3 months were randomly divided into six groups. The control group (K) received a standard diet (AIN 93 M). The remaining five groups received a standard diet supplemented with the following: tempeh flour (TP); soy flour (RS); daidzein and genistein (DG); Lactobacillus acidophilus DSM20079 (LA); as well as a combination of daidzein, genistein, and L. acidophilus DSM20079 (DGLA). After 8 weeks of intervention, blood samples of the rats were collected for morphological analysis, whereas tissue samples were collected and kept at -80 °C until Fe analysis. Red blood cells, hemoglobin, hematocrit, mean corpuscular volume (MCV), mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, platelets (PLTs), red cell distribution width, white blood cells, neutrophils (NEUT), lymphocytes (LYM), monocytes, eosinophils (EOS), and basophils were measured for blood morphological analysis. Fe concentrations were determined using flame atomic spectrometry. For statistical analysis, an ANOVA test for significance at the 5 % level was used. The relationship between tissue Fe levels and blood morphological parameters was determined using Pearson's correlation.

RESULTS

Although no significant differences were observed in the Fe content between all diets, the TP group showed significantly higher levels of NEUT and lower levels of LYM than the control group. Compared with the DG and DGLA groups, the TP group showed a dramatically higher PLT level. In addition, the RS group showed significantly higher Fe concentrations in the spleen compared with the standard diet. Compared with the DG, LA, and DGLA groups, the RS group also showed significantly higher Fe concentrations in the liver. Compared with the TP, DG, LA, and DGLA groups, the RS group showed dramatically higher Fe concentrations in the femur. Pearson's correlations between blood morphological parameters and Fe levels in tissues were observed, especially a negative correlation between the Fe level in the femur and the NEUT concentration (-0.465) and a strong positive correlation between the Fe level in the femur and the LYM concentration (0.533).

CONCLUSION

Soybean flour was found to increase Fe levels in rats, whereas tempeh may alter anti-inflammatory blood parameters. Isoflavones and probiotics did not affect Fe status in healthy female rats.

Quercetin protects against iron overload-induced osteoporosis through activating the Nrf2/HO-1 pathway

AIMS

Eucommia is the tree bark of Eucommia japonica, family Eucommiaceae. In traditional Chinese medicine, Eucommia is often used to treat osteoporosis. Quercetin (QUE), a major flavonoid extract of Eucommia japonica, has been reported to have anti-osteoporosis effects. However, there are no studies reporting the mechanism of QUE in the treatment of iron overload-induced osteoporosis. This study set out to investigate the therapeutic effects of QUE against iron overload-induced bone loss and its potential molecular mechanisms.

MATERIALS AND METHODS

In vitro, MC3T3-E1 cells were used to study the effects of QUE on osteogenic differentiation, anti-apoptosis and anti-oxidative stress damage in an iron overload environment (FAC 200 μM). In vivo, we constructed an iron overload mouse model by injecting iron dextrose intraperitoneally and assessed the osteoprotective effects of QUE by Micro-CT and histological analysis.

KEY FINDINGS

In vitro, we found that QUE increased the ALP activity of MC3T3-E1 cells in iron overload environment, promoted the formation of bone mineralized nodules and upregulated the expression of Runx2 and Osterix. In addition, QUE was able to reduce FAC-induced apoptosis and ROS production, down-regulated the expression of Caspase3 and Bax, and up-regulated the expression of Bcl-2. In further studies, we found that QUE activated the Nrf2/HO-1 signaling pathway and attenuated FAC-induced oxidative stress damage. The results of the in vivo study showed that QUE was able to reduce iron deposition induced by iron dextrose and attenuate bone loss.

SIGNIFICANCE

Our results suggested that QUE protects against iron overload-induced osteoporosis by activating the Nrf2/HO-1 signaling pathway.

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.

Influence of prazosin on systemic iron levels and the associated iron metabolic alterations in spontaneously hypertensive rats

The relationship between cardiovascular diseases and iron disorders has gained increasing attention; however, the effects of hypotensive drugs on iron metabolic alterations in hypertension are not well understood. The purpose of this study was to investigate iron metabolic changes after prazosin treatment of spontaneously hypertensive rats (SHRs) and Wistar–Kyoto (WKY) rats. Our second objective was to examine the effects of hypertension and anti‐hypertensive drugs on bone formation and resorption. SHRs and WKY rats were randomized into either prazosin‐treated groups (WKY + PZ and SHR + PZ) or untreated groups (WKY and SHR). After 7 days of intragastric prazosin administration, the rats were sacrificed for analysis; blood samples and organs (the duodenum, liver, kidneys, spleen, and femur) were collected. Both WKY + PZ and SHR groups exhibited iron deficiency in the serum and liver. Prazosin increased the iron levels in the bone tissue of SHRs. Prazosin stimulated the expression of hepcidin mRNA in the liver of SHRs and inhibited the expression of this iron‐regulatory hormone in WKY rats. FPN1 expression in the duodenum was increased significantly in SHRs, however markedly decreased after prazosin treatment. The expression of TLR4 and Ctsk was enhanced in the bone tissue of SHRs, whereas CLC‐7 expression was inhibited. Both hypotension and hypertension can lead to iron deficiency. Treatment with prazosin restored iron homeostasis in SHRs. The inverse impacts of prazosin on hepatic hepcidin expression in SHRs versus WKY rats indicates differing iron regulatory mechanisms between hypertensive and normal animals. The osteoclast activity was found to be enhanced in SHRs. Further study is needed to address whether the changes in osteoblast and osteoclast activity in SHRs correlates with the effects on iron metabolism.

Canagliflozin mitigates ferroptosis and ameliorates heart failure in rats with preserved ejection fraction

Recently, hypoglycemic drugs belonging to sodium-glucose cotransporter 2 inhibitors (SGLT2i) have generated significant interest due to their clear cardiovascular benefits for heart failure with preserved ejection fraction (HFpEF) since there are no effective drugs that may improve clinical outcomes for these patients over a prolonged period. But, the underlying mechanisms remain unclear, particularly its effects on ferroptosis, a newly defined mechanism of iron-dependent non-apoptotic cell death during heart failure (HF). Here, with proteomics, we demonstrated that ferroptosis might be a key mechanism in a rat model of high-salt diet-induced HFpEF, characterized by iron overloading and lipid peroxidation, which was blocked following treatment with canagliflozin. Data are available via ProteomeXchange with identifier PXD029031. The ferroptosis was evaluated with the levels of acyl-CoA synthetase long-chain family member 4, glutathione peroxidase 4, ferritin heavy chain 1, transferrin receptor, Ferroportin 1, iron, glutathione, malondialdehyde, and 4-hydroxy-trans-2-nonenal. These findings highlight the fact that targeting ferroptosis may serve as a cardioprotective strategy for HFpEF prevention and suggest that canagliflozin may exert its cardiovascular benefits partly via its mitigation of ferroptosis.

Association Between Serum Iron Status and Muscle Mass in Adults: Results From NHANES 2015–2018

Background

Iron deficiency or overload may contribute to complications associated with diseases, but the link between iron status and skeletal muscle disorder is poorly understood. This study aimed to investigate the relationship between serum iron status, reflected by serum ferritin concentration, and muscle mass in U.S. adults.

Methods

We utilized data from National Health and Nutrition Examination Survey (NHANES) 2015-2018 for analysis. Data on serum ferritin, appendicular skeletal muscle mass (ASM), body mass index (BMI) and confounding factors were extracted and analyzed. Multivariate linear regression analyses and smooth curve fittings were employed to investigate the association between serum ferritin and muscle mass. Subgroup analysis based on iron status, age, gender and race were performed.

Results

A total of 2,078 participants were included, and divided into iron deficiency (n = 225), normal iron status (n = 1,366), and iron overload (n = 487) groups. Participants with iron overload had significantly lower ASM and appendicular skeletal muscle index (ASMI) (ASM: 19.329 ± 4.879, ASMI: 0.709 ± 0.138) compared to those with iron deficiency (ASM: 22.660 ± 6.789, ASMI: 0.803 ± 0.206) and normal iron status (ASM: 22.235 ± 6.167, ASMI: 0.807 ± 0.201). The serum ferritin was negatively linked with muscle mass after adjusting for potential confounders (β = −0.0001, 95% CI: −0.0001, −0.0000). When stratified by iron status, the trend test between them remained significant (P for trend: 0.008). Furthermore, subgroup analysis identified a stronger association in men (β = −0.0001, 95% CI: −0.0002, −0.0001), age ≥ 40 years (β = −0.0001, 95% CI: −0.0002, −0.0000), non-Hispanic black (β = −0.0002, 95% CI: −0.0003, −0.0001) and other races (β = −0.0002, 95% CI: −0.0003, −0.0000).

Conclusions

Our study revealed an inverse relationship between serum iron status and muscle mass in adults. This finding improves our understanding of the impact of serum iron status on muscle mass, and sheds new light on the prevention and treatment of muscle loss.

Systemic Literature Review on Multilevel Analysis of Radiation Effects on Bone Microarchitecture

Introduction

Modern radiation therapy has become an effective method to treat and monitor tumour growth in cancer patients. It has proved to be a successful way to minimise mortality rates. However, the adverse effects of radiation have been historical evidence in the clinical environment involving diminishing the quality and density of bone and causing fragility fracture to the bone in the long run. This systematic review was aimed at identifying and evaluating the effects of irradiation on morphology and mechanical properties of murine model bone in previous publications.

Methods

A systematic literature review was undertaken following the Preferred Reporting Items for Systemic Reviews and Meta-analysis (PRISMA) guidelines. A comprehensive literature search was performed using Scopus, Web of Science, and Science Direct databases (English only studies published between 2015 and 2020). The selected studies were evaluated according to three criteria: (1) criteria for study sample selection; (2) criteria for methodological procedures; and (3) criteria for detection and evaluation.

Results

The initial search strategy identified 1408 related studies, 8 of were included based on inclusion and exclusion criteria. This review revealed an association between bone destruction and the magnitude of time and dose postirradiation. We agreed that the effect of radiation on bone morphology and strength primarily is a later stage event but noticeable in both low (1 Gy) and high dose (30 Gy) radiation. Trabecular and cortical bone microstructures were significantly altered at irradiation and contralateral sites. Besides, the mechanical strength was significantly impacted in both shorter and longer periods.

Conclusion

Overall, the radiotherapy altered bone microstructures and substantially decreases bone mechanical properties. The alteration was related to quantity and the activity of the osteoblast and osteoclast. Early detection of those most at risk for radiation-induced bone alterations could lead to better prophylactic intervention decisions.

ELAV-like RNA binding protein 1 regulates osteogenesis in diabetic osteoporosis: Involvement of divalent metal transporter 1

Diabetic osteoporosis (DOP) is a complication of diabetes mellitus (DM) and occurs due to alterations in bone metabolism under hyperglycemic condition. ELAV-like RNA binding protein 1 (ELAVL1) is abnormally up-regulated in diabetes-related diseases. Bioinformatics prediction indicates that divalent metal transporter 1 (DMT1) is a potential target of ELAVL1. To explore the role of ELAVL1 and the involvement of ELAVL1/DMT1 axis in DOP, we established a mouse model of DM by administration of high-fat diet and intraperitoneal injection with streptozotocin (STZ). The expression of ELAVL1 and DMT1 was increased in the bone tissues of DM mice. Knockdown of ELAVL1 reduced iron level and oxidative stress, promoted osteogensis, and prevented bone mass loss, thus mitigating DOP in DM mice. In vitro, mouse pre-osteoblast MC3T3-E1 cells were treated with high glucose (25 mM) and ferric ammonium citrate (FAC, 200 μM). The inhibitory effects of ELAVL1 knockdown on iron accumulation and oxidative stress were evidenced in MC3T3-E1 cells. Knockdown of ELAVL1 enhanced osteoblast viability, differentiation and mineralization. Notably, the expression of DMT1 was positively correlated with that of ELAVL1 in vivo and in vitro. Overexpression of DMT1 abolished the effect of ELAVL1 knockdown on the behaviors of MC3T3-E1 cells, suggesting that ELAVL1 might function through regulating DMT1. In conclusion, knockdown of ELAVL1 likely alleviated DOP by inhibiting iron overload and oxidative stress and promoting osteogenesis, and DMT1 might be involved in this process. These findings provide insights into the pathogenesis of DOP and suggest a potential therapeutic target for DOP treatment.

Advances in pathogenesis and therapeutic strategies for osteoporosis

Osteoporosis, is the most common bone disorder worldwide characterized by low bone mineral density, leaving affected bones vulnerable to fracture. Bone homeostasis depends on the precise balance between bone resorption by osteoclasts and bone matrix formation by mesenchymal lineage osteoblasts, and involves a series of complex and highly regulated steps. Bone homeostasis will be disrupted when the speed of bone resorption is faster than bone formation. Based on various regulatory mechanisms of bone homeostasis, a series of drugs targeting osteoporosis have emerged in clinical practice, including bisphosphonates, selective estrogen receptor modulators, calcitonin, molecular-targeted drugs and so on. However, many drugs have major adverse effects or are unsuitable for long-term use. Therefore, it is very urgent to find more effective therapeutic drugs based on the new pathogenesis of osteoporosis. In this review, we summarize novel mechanisms involved in the pathological process of osteoporosis, including the roles of gut microbiome, autophagy, iron balance and cellular senescence. Based on the above pathological mechanism, we found promising drugs for osteoporosis treatment, such as: probiotics, alpha-ketoglutarate, senolytics and hydrogen sulfide. This new finding may provide an important basis for elucidating the complex pathological mechanisms of osteoporosis and provide promising drugs for clinical osteoporosis treatment.

Deciphering core proteins of osteoporosis with iron accumulation by proteomics in human bone

Iron accumulation is an independent risk factor for postmenopausal osteoporosis, but mechanistic studies of this phenomenon are still focusing on molecular and genetic researches in model animal. Osteoporosis with iron accumulation is a distinct endocrine disease with complicated pathogenesis regulated by several proteins. However, the comprehensive proteome-wide analysis of human bone is lacking. Using multiplex quantitative tandem mass tag-based proteomics, we detected 2900 and quantified 1150 proteins from bone of 10 postmenopausal patients undergoing hip replacement. Comparing with non-osteoporosis patients, a total of 75 differentially expressed proteins were identified, comprising 53 downregulated proteins and 22 upregulated proteins. These proteins primarily affect oxidoreductase activity, GTPase activity, GTP binding, and neural nucleus development, were mainly enriched in neural, angiogenesis and energy-related pathways, and formed complex regulatory networks with strong interconnections. We ultimately identified 4 core proteins (GSTP1, LAMP2, COPB1, RAB5B) that were significantly differentially expressed in the bone of osteoporosis patients with iron accumulation, and validated the changed protein level in the serum of the medical examination population. Our systemic analysis uncovers molecular insights for revealing underlying mechanism and clinical therapeutics in osteoporosis with iron accumulation.

No genetic causal association between iron status and osteoporosis: A two-sample Mendelian randomization

OBJECTIVE

To explore the genetic causal association between osteoporosis (OP) and iron status through Mendelian randomization (MR).

METHODS

Publicly available genome-wide association study (GWAS) summary data were used for MR analysis with four iron status-related indicators (ferritin, iron, total iron binding capacity, and transferrin saturation) as exposures and three different types of OP (OP, OP with pathological fracture, and postmenopausal OP with pathological fracture) as outcomes. The inverse-variance weighted (IVW) method was used to analyze the genetic causal association between the four indicators of iron status and OP. The heterogeneity of MR results was determined using IVW and MR-Egger methods. The pleiotropy of MR results was determined using MR-Egger regression. A leave-one-SNP-out test was performed to determine whether the MR results were affected by a single nucleotide polymorphism (SNP). The weighted median method was conducted to further validate our results.

RESULTS

Based on IVW, MR-Egger and weighted median models, we found no causal association between iron status (ferritin, iron, total iron binding capacity, or transferrin saturation) and OP (P_beta > 0.05 in all models). IVW and MR-Egger analysis of OP with pathological fracture and iron status indicators showed no potential genetic causal association (P_beta> 0.05 in the two analyses). The results of the weighted median were consistent with those of IVW (P_beta> 0.05 in all analyses). There was no potential genetic causal association between iron status and postmenopausal OP with pathological fracture based on serum iron (P_beta>0.05 in all models). No heterogeneity or horizontal pleiotropy was found in any of the analyses. None of the leave-one-out tests in the analyses found any SNP that could affect the results of MR.

CONCLUSION

Our results demonstrate that there is no genetic causal association between OP and iron status, but the effects of other factors were not excluded.

Ferroptosis and Its Potential Role in Metabolic Diseases: A Curse or Revitalization?

Ferroptosis is classified as an iron-dependent form of regulated cell death (RCD) attributed to the accumulation of lipid hydroperoxides and redox imbalance. In recent years, accumulating researches have suggested that ferroptosis may play a vital role in the development of diverse metabolic diseases, for example, diabetes and its complications (e.g., diabetic nephropathy, diabetic cardiomyopathy, diabetic myocardial ischemia/reperfusion injury and atherosclerosis [AS]), metabolic bone disease and adrenal injury. However, the specific physiopathological mechanism and precise therapeutic effect is still not clear. In this review, we summarized recent advances about the development of ferroptosis, focused on its potential character as the therapeutic target in metabolic diseases, and put forward our insights on this topic, largely to offer some help to forecast further directions.

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.

Therapeutic potential of iron chelators on osteoporosis and their cellular mechanisms

Iron is an essential trace element in the metabolism of almost all living organisms. Iron overload can disrupt bone homeostasis by significant inhibition of osteogenic differentiation and stimulation of osteoclastogenesis, consequently leading to osteoporosis. Iron accumulation is also involved in the osteoporosis induced by multiple factors, such as estrogen deficiency, ionizing radiation, and mechanical unloading. Iron chelators are first developed for treating iron overloaded disorders. However, growing evidence suggests that iron chelators can be potentially used for the treatment of bone loss. In this review, we focus on the therapeutic effects of iron chelators on bone loss. Iron chelators have therapeutic effects not only on iron overload induced osteoporosis, but also on osteoporosis induced by estrogen deficiency, ionizing radiation, and mechanical unloading, and in Alzheimer's disease-associated osteoporotic deficits. Iron chelators differently affect the cellular behaviors of bone cells. For osteoblast lineage cells (bone mesenchymal stem cells and osteoblasts), iron chelation stimulates osteogenic differentiation. Conversely, iron chelation significantly inhibits osteoclast differentiation. These different responses may be associated with the different needs of iron during differentiation. Fibroblast growth factor 23, angiogenesis, and antioxidant capability are also involved in the osteoprotective effects of iron chelators.

Active hematopoiesis triggers exosomal release of PRDX2 that promotes osteoclast formation

Hematopoietic disorders, particularly hemolytic anemias, commonly lead to bone loss. We have previously reported that actively proliferating cancer cells stimulate osteoclastogenesis from late precursors in a RANKL-independent manner. We theorized that cancer cells exploit the physiological role of bone resorption to support expanding hematopoietic bone marrow and examined if hematopoietic cells can trigger osteoclastogenesis. Using phlebotomy-induced acute anemia in mice, we found strong correlation between augmented erythropoiesis and increased osteoclastogenesis. Conditioned medium (CM) from K562 erythroleukemia cells and primary mouse erythroblasts stimulated osteoclastogenesis when added to RANKL-primed precursors from mouse bone marrow or RAW264.7 cells. Using immunoblotting and mass spectrometry, PRDX2 was identified as a factor produced by erythroid cells in vitro and in vivo. PRDX2 was detected in K562-derived exosomes, and inhibiting exosomal release significantly decreased the osteoclastogenic capacity of K562 CM. Recombinant PRDX2 induced osteoclast formation from RANKL-primed primary or RAW 264.7 precursors to levels comparable to achieved with continuous RANKL treatment. Thus, increased bone marrow erythropoiesis secondary to anemia leads to upregulation of PRDX2, which is released in the exosomes and acts to induce osteoclast formation. Increased bone resorption by the osteoclasts expands bone marrow cavity, which likely plays a supporting role to increase blood cell production.

Serum hepcidin level, iron metabolism and osteoporosis in patients with rheumatoid arthritis

Hepcidin, a major regulator of iron metabolism and homeostasis, is regulated by inflammation. Recent studies have suggested that hepcidin and iron metabolism are involved in osteoporosis, and the aim of this study was to determine whether serum hepcidin levels are correlated with the degree of osteoporosis in patients with rheumatoid arthritis (RA). A total of 262 patients with RA (67.5 ± 11.4 years; 77.5% female) were enrolled. Serum iron, ferritin, and hepcidin levels were positively correlated each other. Multiple regression analyses revealed that the serum iron level was positively correlated with femoral T and Z scores, whereas the serum hepcidin level was not. Serum hepcidin level was correlated with the serum 25-hydroxy vitamin D level, which was in turn positively related to the femoral Z score. Serum hepcidin and serum iron were indirectly and directly related to osteoporosis in patients with RA.

The Effect of Abnormal Iron Metabolism on Osteoporosis

Iron is one of the important trace elements in life activities. Abnormal iron metabolism increases the incidence of many skeletal diseases, especially for osteoporosis. Iron metabolism plays a key role in the bone homeostasis. Disturbance of iron metabolism not only promotes osteoclast differentiation and apoptosis of osteoblasts but also inhibits proliferation and differentiation of osteoblasts, which eventually destroys the balance of bone remodeling. The strength and density of bone can be weakened by the disordered iron metabolism, which increases the incidence of osteoporosis. Clinically, compounds or drugs that regulate iron metabolism are used for the treatment of osteoporosis. The goal of this review summarizes the new progress on the effect of iron overload or deficiency on osteoporosis and the mechanism of disordered iron metabolism on osteoporosis. Explaining the relationship of iron metabolism with osteoporosis may provide ideas for clinical treatment and development of new drugs.

Hepcidin deficiency causes bone loss through interfering with the canonical Wnt/β-catenin pathway via Forkhead box O3a

Objective

Hepcidin deficiency is known to cause body iron accumulation and bone microarchitecture defects, but the exact underlying mechanisms of hepcidin deficiency-induced bone loss remain unclear. Our objective was to understand the molecular mechanism of hepcidin deficiency-induced bone loss.

Methods

The bone phenotypes of wild type (WT) and hepcidin knockout (Hepcidin-KO) mice were measured by microcomputed tomography. The osteoclastic marker of the bone was measured by tartrate-resistant acid phosphatase staining. The osteoblastic marker of the bone was measured by immunostaining of osteocalcin. Primary osteoblastic and osteoclastic differentiation was performed using bone marrow cells. The mature osteoclast was determined by tartrate-resistant acid phosphatase staining, pit formation assay and relative gene expression. The mature osteoblast was determined by alkaline phosphatase activity, alkaline phosphatase staining, Alizarin Red staining and relative gene expression. The protein expression of β-catenin, TCF4/TCF7L2 and Forkhead box O3a (FOXO3a) was measured by Western blot and their combination by co-immunoprecipitation. In vivo study was performed by tail vein administration of FOXO3a-RNAi using an adeno-associated virus in Hepcidin-KO mice.

Results

We found that Hepcidin-KO mice exhibited iron accumulation and bone loss compared with WT mice. The osteoclastic differentiation of bone marrow-derived macrophages from Hepcidin-KO mice was not significantly different from that of bone marrow–derived macrophages from WT mice. However, the osteoblastic differentiation of bone marrow–derived mesenchymal stem cells from Hepcidin-KO mice was obviously decreased compared with that of bone marrow–derived mesenchymal stem cells from WT mice. Furthermore, it was confirmed in this study that upon hepcidin deficiency, β-catenin, TCF4/TCF7L2 and FOXO3a expression in bone tissues was not altered, but β-catenin combination with TCF4/TCF7L2 was strongly inhibited by β-catenin combination with FOXO3a, indicating that the canonical Wnt/β-catenin pathway was affected. Tail vein administration of FOXO3a-RNAi using an adeno-associated virus in Hepcidin-KO mice resulted in bone mass recovery.

Conclusion

These findings suggested that hepcidin deficiency might cause bone loss by interfering with the canonical Wnt/β-catenin pathway via FOXO3a, and FOXO3a inhibition would be a possible approach to treat hepcidin deficiency-induced bone loss.

The translational potential of this article

Hepcidin deficiency, as well as iron accumulation, has been considered as a risk factor for osteoporosis. For this kind of osteoporosis, inhibition of FOXO3a either by neutralized antibody or AAV-mediated RNAi, represents an effective and promising method.

Iron overload threatens the growth of osteoblast cells via inhibiting the PI3K/AKT/FOXO3a/DUSP14 signaling pathway

Iron overload is a common stress in the development of cells. Growing evidence has indicated that iron overload is associated with osteoporosis. Therefore, enhancing the understanding of iron overload would benefit the development of novel approaches to the treatment of osteoporosis. The purpose of the present study was to analyze the effect of iron overload on osteoblast cells, via the MC3T3-E1 cell line, and to explore its possible underlying molecular mechanisms. Ferric ammonium citrate (FAC) was utilized to simulate iron overload conditions in vitro. FAC-induced iron overload strongly suppressed proliferation of osteoblast cells and induced apoptosis. Moreover, iron overload strongly suppressed the expression of dual-specificity phosphatase 14 (DUSP14). Additionally, overexpression of DUSP14 protected osteoblast cells from the deleterious effects of iron overload, and this protective effect was mediated by FOXO3a. Additionally, matrine rescued the function of DUSP14 in osteoblast cells. Most importantly, our analysis demonstrated the essential role of the PI3K/AKT/FOXO3a/DUSP14 signaling pathway in the defense against iron overload in osteoblast cells. Overall, our results not only elucidate deleterious effects of iron overload, but also unveil its possible signaling pathway in osteoblast cells.

Lowering iron level protects against bone loss in focally irradiated and contralateral femurs through distinct mechanisms

Radiation therapy leads to increased risk of late-onset fragility and bone fracture due to the loss of bone mass. On the other hand, iron overloading causes osteoporosis by enhancing bone resorption. It has been shown that total body irradiation increases iron level, but whether the systemic bone loss is related to the changes in iron level and hepcidin regulation following bone irradiation remains unknown. To investigate the potential link between them, we first created an animal model of radiation-induced systemic bone loss by targeting the mid-shaft femur with a single 2 Gy dose of X-rays. We found that mid-shaft femur focal irradiation led to structural deterioration in the distal region of the trabecular bone with increased osteoclasts surface and expressions of bone resorption markers in both irradiated and contralateral femurs relative to non-irradiated controls. Following irradiation, reduced hepcidin activity of the liver contributed to elevated iron levels in the serum and liver. By injecting hepcidin or deferoxamine (an iron chelator) to reduce iron level, deterioration of trabecular bone microarchitecture in irradiated mice was abrogated. The ability of iron chelation to inhibit radiation-induced osteoclast differentiation was observed in vitro as well. We further showed that ionizing radiation (IR) directly stimulated osteoclast differentiation and bone resorption in bone marrow cells isolated not from contralateral femurs but from directly irradiated femurs. These results suggest that increased iron levels after focal radiation is at least one of the main reasons for systemic bone loss. Furthermore, bone loss in directly irradiated bones is not only due to the elevated iron level, but also from increased osteoclast differentiation. In contrast, the bone loss in the contralateral femurs is mainly due to the elevated iron level induced by IR alone. These novel findings provide proof-of-principle evidence for the use of iron chelation or hepcidin as therapeutic treatments for IR-induced osteoporosis.

Icariin Protects Bone Marrow Mesenchymal Stem Cells Against Iron Overload Induced Dysfunction Through Mitochondrial Fusion and Fission, PI3K/AKT/mTOR and MAPK Pathways

Iron overload has been reported to contribute to bone marrow mesenchymal stem cells (BMSCs) damage, but the precise mechanism still remains elusive. Icariin, a major bioactive monomer belonging to flavonoid glucosides isolated from Herba Epimedii, has been shown to protect cells from oxidative stress induced apoptosis. The aim of this study was to investigate whether icariin protected against iron overload induced dysfunction of BMSCs and its underlying mechanism. In this study, we found that iron overload induced by 100 μM ferric ammonium citrate (FAC) caused apoptosis of BMSCs, promoted cleaved caspase-3 and BAX protein expressions while inhibited Bcl-2 protein expression, which effects were significantly attenuated by icariin treatment. In addition, iron overload induced significant depolarization of mitochondrial membrane potential (MMP), reactive oxygen species (ROS) generation and inhibition of mitochondrial fusion/fission, which effects were also attenuated by icariin treatment. Meanwhile, we found that iron overload induced by 100 μM FAC significantly inhibited mitochondrial fission protein FIS1 and fusion protein MFN2 expressions, inhibited DRP1 and Cytochrome C protein translocation from the cytoplasm to mitochondria. Icariin at concentration of 1 μM was able to promote mitochondrial fission protein FIS1 and fusion protein MFN2 expressions, and increase DRP1 and cytochrome C protein translocation from the cytoplasm to mitochondria. Further, osteogenic differentiation and proliferation of BMSCs was significantly inhibited by iron overload, but icariin treatment rescued both osteogenic differentiation and proliferation of BMSCs. Further studies showed that icariin attenuated iron overload induced inactivation of the PI3K/AKT/mTOR pathway and activation of the ERK1/2 and JNK pathways. In summary, our study indicated that icariin was able to protect against iron overload induced dysfunction of BMSCs. These effects were potentially related to the modulation of mitochondrial fusion and fission, activation of the PI3K/AKT/mTOR pathway and inhibition of ERK1/2 and JNK pathways.

Iron Accumulation Leads to Bone Loss by Inducing Mesenchymal Stem Cell Apoptosis Through the Activation of Caspase3

Osteoporosis (OP) is a disease associated with bone loss and microstructure degradation. Recent studies have shown that iron accumulation may be a risk factor for OP. Bone marrow mesenchymal stem cells (MSCs) are multipotent cells and precursors to osteoblasts. MSCs play an important role in OP. Therefore, we evaluated the correlation between MSCs and OP in an environment of iron accumulation. Serum P1NP was decreased in iron accumulation mice. Micro-CT revealed that iron accumulation decreased bone mineral density and spatial structural parameters. Iron accumulation inhibited MSC quantity in bone marrow. However, the iron chelator deferoxamine (DFO) rescued the suppression. Iron accumulation also changed the MSC cell cycle. Iron elevated MSC cell ROS level and NOX4 protein expression. MSC apoptosis was increased, and more caspase3 was cleaved after iron intervention. Our data suggests that iron accumulation inhibits MSC quantity and induces MSC apoptosis. Bone loss from iron accumulation may correlate with the inhibition of MSCs.

Irp2 Knockout Causes Osteoporosis by Inhibition of Bone Remodeling

It has been found that iron disorder may lead to osteoporosis. However, the mechanism has been little explored. In the present study, we try to investigate the effects of iron disorder on bone metabolism using Irp2 knockout (Irp2^-/-) mice. Female Irp2^-/- mice were used in this study. Bone mineral density (BMD) was measured by Micro-CT. Serum markers for bone turnover were measured by enzyme-linked immunosorbent assay. Content of iron was measured in bone and liver tissue, and Vitamin D 25-hydroxylase (CYP2R1) content was measured in liver tissue. Relative gene expression involved in iron export and uptake, and some genes involved in activities of osteoblast and osteoclast were all measured by real-time PCR and western blot. Compared to wild-type mice, Irp2^-/- mice exhibited reduced BMD, bone iron deficiency, and hepatic iron overload. Serum levels of 25(OH)D₃ and markers for bone formation such as bone alkaline phosphatase (Balp), bone-gla-protein (BGP), and type I collagen alpha1 chain (Col I α₁) were decreased, while markers for bone resorption including cathepsin K (Ctsk) and tartrate-resistant acid phosphatase (Trap) were all significantly increased. Hepatic CYP2R1 level was decreased in Irp2^-/- mice compared with wild-type control mice. Compared to wild-type C57BL6 control mice, the expression of genes involved in osteoblast activity such as Balp, BGP, and Col I α₁ were all significantly decreased in bone tissue, while genes for osteoclast activity such as Ctsk and Trap were all markedly increased in Irp2^-/- mice at mRNA level. Genes involved in iron storage, uptake, and exporting were also measured in bone tissue. Posttranscriptionally decreased ferritin (FTL), ferroportin 1 (FPN1), and increased transferrin receptor 1 (TfR1) gene expressions have been unexpectedly found in bone tissue of Irp2^-/- mice. Irp2^-/- mice exhibit reduced bone iron content and osteoporosis. Decreased circulating 25(OH)D₃ levels promoted activity of osteoclast, while impaired activity of osteoblast may contribute to pathogenesis of osteoporosis. And, reduced bone iron content may not be totally caused by TfR1-dependent pathways.

Is Iron Accumulation a Possible Risk Factor for Sarcopenia?

Sarcopenia has a high incidence among the elderly, with significant negative effects on the quality of life. The pathogenesis of sarcopenia is complex, and many factors are involved in its development and progression. Sarcopenia might be associated with iron accumulation given that (1) age-related iron accumulation was found in the skeletal muscle, (2) excess iron could cause skeletal muscle damage or atrophy, and (3) patients with sarcopenia showed higher levels of serum ferritin. Understanding the etiology and pathogenesis of sarcopenia would help to develop new treatment and preventive methods, thereby improving the quality of life of the elderly patients.

Influence of Iron on Bone Homeostasis

Bone homeostasis is a complex process, wherein osteoclasts resorb bone and osteoblasts produce new bone tissue. For the maintenance of skeletal integrity, this sequence has to be tightly regulated and orchestrated. Iron overload as well as iron deficiency disrupt the delicate balance between bone destruction and production, via influencing osteoclast and osteoblast differentiation as well as activity. Iron overload as well as iron deficiency are accompanied by weakened bones, suggesting that balanced bone homeostasis requires optimal-not too low, not too high-iron levels. The goal of this review is to summarize our current knowledge about how imbalanced iron influence skeletal health. Better understanding of this complex process may help the development of novel therapeutic approaches to deal with the pathologic effects of altered iron levels on bone.

Reduced hepcidin level features osteoporosis

Osteoporosis (OP) is a common serious skeletal disorder marked by increased risk of bone fracture due to fragility. OP has been taken to be a disease linked with abnormal calcium metabolism that alone is obviously insufficient to explain the development of OP. Iron overload has been associated with the development of OP and increasing studies have suggested the association. However, direct evidence for this has not been clinically established. To this end, using the Roche biochemical autoanalyzer, we detected the concentration of iron, soluble transferrin receptor 2 (TFR2), and hepcidin, a key peptide regulating iron homeostasis, in the sera from patients with OP. It was shown that the iron and TFR2 concentration was markedly higher than that of healthy control; whereas the concentration of hepcidin was markedly lower than that in control. In addition, to pilot explore the underlying mechanism by which hepcidin was downregulated, we present that hepcidin can directly interact with TFR2 using immunoprecipitation. The present study first established the direct biochemical evidence for the involvement of hepcidin in the pathogenesis of OP, indicating that the upregulation of hepcidin could be used as a novel alternative therapeutic strategy in the management of OP.

Hydroxysafflor Yellow A Promoted Bone Mineralization and Inhibited Bone Resorption Which Reversed Glucocorticoids-Induced Osteoporosis

Glucocorticoids intake is the most common cause of secondary osteoporosis. Clinical studies have shown that 50% patients develop glucocorticoids-induced osteoporosis (GCIOP) after taking glucocorticoids for more than 6 months. Hydroxysafflor yellow A (HYA) is one main active ingredient in Carthamus tinctorius L. Previous studies have shown that HYA promoted bone marrow mesenchymal stem cells to differentiate into osteoblasts which promoted bone formation. Therefore, we speculated that HYA has a therapeutic effect on GCIOP. However, there is no in vivo evidence about the anti-GCIOP effect of HYA. In this paper, the effect of HYA (0.1, 1.0, and 10.0 μM) on bone formation in normal zebrafish was investigated firstly. Secondly, the reversal effect of HYA on GCIOP was also evaluated by zebrafish model. It is demonstrated that HYA not only promoted bone formation in normal zebrafish (compared to Control group), but also reversed glucocorticoid induced bone loss (compared to Prednisolone group) according to the intervention of HYA in upregulating the area of mineralized bones (p < 0.01), increasing cumulative optical density (p < 0.01), promoting bone formation related gene expression (AKP, Type I, Runx2, OPG, and OCN, p < 0.01), inhibiting bone resorption related gene expression (TRACP, p < 0.01), and elevating whole-body trace mineral elements (Ca, P, K, Mg, Zn, and Fe) levels (p < 0.01). In conclusion, HYA had the potential to prevent and heal GCIOP by promoting bone mineralization, osteoblasts viability, and bone collagen expression and inhibiting bone resorption.

Investigation of osteogenic responses of Fe-incorporated micro/nano-hierarchical structures on titanium surfaces

Fe incorporated micro/nano topographical titanium substrates are fabricated to synergistically regulate osteogenic responses in vitro and osseointegration in vivo.

Iron deficiency beyond erythropoiesis: should we be concerned?

OBJECTIVE

To consider the key implications of iron deficiency for biochemical and physiological functions beyond erythropoiesis.

METHODS

PubMed was searched for relevant journal articles published up to August 2017.

RESULTS

Anemia is the most well-recognized consequence of persisting iron deficiency, but various other unfavorable consequences can develop either before or concurrently with anemia. Mitochondrial function can be profoundly disturbed since iron is a cofactor for heme-containing enzymes and non-heme iron-containing enzymes in the mitochondrial electron transport chain. Biosynthesis of heme and iron-sulfur clusters in the mitochondria is inhibited, disrupting synthesis of compounds such as hemoglobin, myoglobin, cytochromes and nitric oxide synthase. The physiological consequences include fatigue, lethargy, and dyspnea; conversely, iron repletion in iron-deficient individuals has been shown to improve exercise capacity. The myocardium, with its high energy demands, is particularly at risk from the effects of iron deficiency. Randomized trials have found striking improvements in disease severity in anemic but also non-anemic chronic heart failure patients with iron deficiency after iron therapy. In vitro and pre-clinical studies have demonstrated that iron is required by numerous enzymes involved in DNA replication and repair, and for normal cell cycle regulation. Iron is also critical for immune cell growth, proliferation, and differentiation, and for specific cell-mediated effector pathways. Observational studies have shown that iron-deficient individuals have defective immune function, particularly T-cell immunity, but more evidence is required. Pre-clinical models have demonstrated abnormal myelogenesis, brain cell metabolism, neurotransmission, and hippocampal formation in iron-deficient neonates and young animals. In humans, iron deficiency anemia is associated with poorer cognitive and motor skills. However, the impact of iron deficiency without anemia is less clear.

CONCLUSION

The widespread cellular and physiological effects of iron deficiency highlight the need for early detection and treatment of iron deficiency, both to ameliorate these non-erythropoietic effects, and to avoid progression to iron deficiency anemia.

Obesity status influences the relationship among serum osteocalcin, iron stores and insulin sensitivity

BACKGROUND & AIMS

Increased iron stores significantly influence the clinical course of several chronic metabolic diseases. Recent studies have shown that iron overload decreases osteocalcin. We aimed to explore the relationship among osteocalcin, iron stores and insulin sensitivity.

METHODS

Extensive clinical and laboratory measurements, including serum ferritin, cross-linked C-telopeptide of type I collagen (CTX) and osteocalcin (OC) concentrations, were analyzed in 250 adult consecutive Caucasian men. Insulin sensitivity was evaluated through frequently sampled intravenous glucose tolerance tests with minimal model analysis.

RESULTS

Circulating serum ferritin were negatively associated with serum OC and CTX (p = 0.004 and p = 0.045 respectively). In all subjects as a whole, BMI and ferritin contributed to explain 5.2% of OC variance after controlling for age and smoking status. However, the association between OC and insulin sensitivity remained significant only in lean subjects (BMI < 25 kg/m², r = 0.468; p = 0.006) whereas the link between serum ferritin concentration and OC and CTX were significant only in overweight/obese subjects (BMI ≥ 25 kg/m², r = -0.229; p = 0.002 and r = -0.196; p = 0.008, respectively).

CONCLUSIONS

The association of circulating osteocalcin with parameters of insulin sensitivity and iron stores were dependent on obesity status. Increased iron stores could contribute to the detrimental metabolic effects of overweight and obesity on bone.

Melatonin protects bone marrow mesenchymal stem cells against iron overload-induced aberrant differentiation and senescence

Bone marrow mesenchymal stem cells (BMSCs) are an expandable population of stem cells which can differentiate into osteoblasts, chondrocytes and adipocytes. Dysfunction of BMSCs in response to pathological stimuli contributes to bone diseases. Melatonin, a hormone secreted from pineal gland, has been proved to be an important mediator in bone formation and mineralization. The aim of this study was to investigate whether melatonin protected against iron overload-induced dysfunction of BMSCs and its underlying mechanisms. Here, we found that iron overload induced by ferric ammonium citrate (FAC) caused irregularly morphological changes and markedly reduced the viability in BMSCs. Consistently, osteogenic differentiation of BMSCs was significantly inhibited by iron overload, but melatonin treatment rescued osteogenic differentiation of BMSCs. Furthermore, exposure to FAC led to the senescence in BMSCs, which was attenuated by melatonin as well. Meanwhile, melatonin was able to counter the reduction in cell proliferation by iron overload in BMSCs. In addition, protective effects of melatonin on iron overload-induced dysfunction of BMSCs were abolished by its inhibitor luzindole. Also, melatonin protected BMSCs against iron overload-induced ROS accumulation and membrane potential depolarization. Further study uncovered that melatonin inhibited the upregulation of p53, ERK and p38 protein expressions in BMSCs with iron overload. Collectively, melatonin plays a protective role in iron overload-induced osteogenic differentiation dysfunction and senescence through blocking ROS accumulation and p53/ERK/p38 activation.

Bone Health in Patients With Hematopoietic Disorders of Bone Marrow Origin: Systematic Review and Meta- Analysis

Blood cell production and bone homeostasis are physically interlinked systems that exhibit active cross-talk. We examined how bone health is affected in patients with hematopoietic disorders due to abnormal proliferation of bone marrow cells. The electronic databases Medline, Embase, PubMed, BIOSIS Previews, Web of Science, and Cochrane were searched for studies presenting numerical values for trabecular bone volume or bone mineral density in control and patients with hematopoietic disorders. We identified 5 studies for beta-thalassemia, 6 for sickle cell anemia, 2 for polycythemia vera and essential thrombocythemia, 3 for chronic myelogenous leukemia, 6 for myelofibrosis, 5 for multiple myeloma, and 4 studies each for systemic mastocytosis, lymphocytic leukemia, and hemochromatosis. The effect of the disease state on bone density was significant and negative for beta-thalassemia (r = -2.00; 95% confidence interval [CI] -3.41, -0.58; p < 0.005), sickle cell anemia (-0.91; -1.36, -0.47; p < 0.00005), chronic myelogenous leukemia (-0.55; -0.88, -0.22; p < 0005), mastocytosis (-0.99; -1.16, -0.82; p < 0.00001), lymphoblastic leukemia (-0.69; -0.98, -0.40; p < 0.00001), multiple myeloma (-0.67; -0.99, -0.35; p < 0.00005), and hemochromatosis (-1.15; -1.64, -0.66; p < 0.00001). The changes were negative but not significant for polycythemia vera (-0.16; -0.38, 0.05; p = 0.069) and essential thrombocythemia (-0.33; -0.92, 0.26; p = 0.14). In myelofibrosis, disease state was associated with increased bone density (0.74; 0.12, 1.36; p < 0.05). Bone density change significantly and negatively correlated with the level of ferritin and bone marrow cellularity but not with hemoglobin or erythropoietin. Thus, independent of hematopoietic lineage, abnormal proliferation of bone marrow cells appears to be associated with bone loss. Iron metabolism may independently contribute to bone homeostasis. © 2016 American Society for Bone and Mineral Research.

The regulation of iron metabolism by hepcidin contributes to unloading-induced bone loss

Iron overload inhibits osteoblast function and promotes osteoclastogenesis. Hepcidin plays an important role in this process. The changes in iron content and the regulation of hepcidin under unloading-induced bone loss remain unknown. A hindlimb suspension model was adopted to simulate unloading-induced bone loss in mice. The results showed that iron deposition in both liver and bone was markedly increased in hindlimb unloaded mice, and was accompanied by the upregulation of osteoclast activity and downregulation of osteoblast activity. The iron chelator deferoxamine mesylate (DFO) reduced the iron content in bone and alleviated unloading-induced bone loss. The increased iron content in bone was mainly a result of the upregulation of transferrin receptor 1 (TfR1) and divalent metal transporter 1 with iron response element (DMT1+IRE), rather than changes in the iron transporter ferroportin 1 (FPN1). The hepcidin level in the liver was significantly higher, while the FPN1 level in the duodenum was substantially reduced. However, there were no changes in the FPN1 level in bone tissue. During hindlimb unloading, downregulation of hepcidin by siRNA increased iron uptake in bone and liver, which aggravated unloading-induced bone loss. In summary, these data show that unloading-induced bone loss was orchestrated by iron overload and coupled with the regulation of hepcidin by the liver.

Iron overload induced death of osteoblasts in vitro: involvement of the mitochondrial apoptotic pathway

BACKGROUND

Iron overload is recognized as a new pathogenfor osteoporosis. Various studies demonstrated that iron overload could induce apoptosis in osteoblasts and osteoporosis in vivo. However, the exact molecular mechanisms involved in the iron overload-mediated induction of apoptosis in osteoblasts has not been explored.

PURPOSE

In this study, we attempted to determine whether the mitochondrial apoptotic pathway is involved in iron-induced osteoblastic cell death and to investigate the beneficial effect of N-acetyl-cysteine (NAC) in iron-induced cytotoxicity.

METHODS

The MC3T3-E1 osteoblastic cell line was treated with various concentrations of ferric ion in the absence or presence of NAC, and intracellular iron, cell viability, reactive oxygen species, functionand morphology changes of mitochondria and mitochondrial apoptosis related key indicators were detected by commercial kits. In addition, to further explain potential mechanisms underlying iron overload-related osteoporosis, we also assessed cell viability, apoptosis, and osteogenic differentiation potential in bone marrow-derived mesenchymal stemcells(MSCs) by commercial kits.

RESULTS

Ferric ion demonstrated concentration-dependent cytotoxic effects on osteoblasts. After incubation with iron, an elevation of intracelluar labile iron levels and a concomitant over-generation of reactive oxygen species (ROS) were detected by flow cytometry in osteoblasts. Nox4 (NADPH oxidase 4), an important ROS producer, was also evaluated by western blot. Apoptosis, which was evaluated by Annexin V/propidium iodide staining, Hoechst 33258 staining, and the activation of caspase-3, was detected after exposure to iron. Iron contributed to the permeabilizatio of mitochondria, leading to the release of cytochrome C (cyto C), which, in turn, induced mitochondrial apoptosis in osteoblasts via activation of Caspase-3, up-regulation of Bax, and down-regulation of Bcl-2. NAC could reverse iron-mediated mitochondrial dysfunction and blocked the apoptotic events through inhibit the generation of ROS. In addition, iron could significantly promote apoptosis and suppress osteogenic differentiation and mineralization in bone marrow-derived MSCs.

CONCLUSIONS

These findings firstly demonstrate that the mitochondrial apoptotic pathway involved in iron-induced osteoblast apoptosis. NAC could relieved the oxidative stress and shielded osteoblasts from apoptosis casused by iron-overload. We also reveal that iron overload in bone marrow-derived MSCs results in increased apoptosis and the impairment of osteogenesis and mineralization.

Identification of human serum protein targets of Qianggu Decoction () in primary type I osteoporosis based on tandem mass tag labeling and liquid chromatography-tandem mass spectrometry technology

OBJECTIVE

To investigate the serum protein targets of Qianggu Decoction (, QGD) on treating osteoporosis by the proteomics analysis using tandem mass tag (TMT) and liquid chromatographytandem mass spectrometry (LC-MS/MS).

METHODS

Twenty serum protein samples were recruited (10 patients with primary type I osteoporosis before and after QGD treatment) and the high abundance ratios protein was removed, two serum samples were extracted and labeled with TMT reagent. Then, mass spectrometric detection, identification of differentially expressed proteins and bioinformatics analysis of differentially expressed proteins were carried out.

RESULTS

A total of 60 proteins were identified, within a 99% confidence interval, to be differentially regulated of which, 34 proteins were up-regulated and 26 proteins were down-regulated. Differentially expressed proteins analyzed by Gene Ontology (GO) annotation mainly get involved in 12 different biological processes, 7 types of cellular components, and 6 kinds of molecular functions. Angiotensinogen (AGT), stromelysin-1 (MMP3), heparanase (HPSE) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) were screened as candidate protein targets of QGD treatment, which were related to metabolic mechanism of bone remodeling and/or bone collagen of osteoporosis. By the utilization of the protein-protein interaction network analysis tool named STRING10.0, it showed that AGT, MMP3, HPSE and GAPDH were located in the key node of the protein-protein interactions network. Furthermore, AGT, MMP3, HPSE and GAPDH were found to be directly related to BMP, MAPK, Wnt, SMAD and tumor necrosis factor ligand superfamily member 11 (TNFSF11) families.

CONCLUSIONS

The proteomics analysis by using TMT combined with LC-MS/MS was a feasible method for screening the potential therapeutic targets associated with QGD treatment. It suggests that AGT, MMP3, HPSE and GAPDH may be candidate protein targets of QGD treatment which can be used as therapeutic effect monitor and early diagnosis of primary type I osteoporosis.