Update on estrogens and the skeleton

Oral Therapeutics Post Menopausal Osteoporosis

Osteoporosis affects a significant number of postmenopausal women in the United States. Screening is performed using clinical assessments and bone mineral density scans via dual x-ray absorptiometry. Oral therapy is indicated to prevent pathologic fractures in those deemed at increased risk following screening. Bisphosphonates including alendronate, ibandronate, and risedronate are currently first-line oral therapeutics in fracture prevention following the diagnosis of osteoporosis. Hormonal therapies include estrogen-containing therapies, selective estrogen receptor modulators, and other compounds that mimic the effects of estrogen such as tibolone. Lifestyle modifications such as supplementation and physical activity may also contribute to the prevention of osteoporosis and are used as adjuncts to therapy following diagnosis. These therapeutics are limited primarily by their adverse effects. Treatment regimens should be tailored based on significant risk factors demonstrated by patients, adverse effects, and clinical response to treatment. The most severe risk factors relevant to pharmacological selection involve hormone replacement therapies, where concern for venous thrombosis, coronary artery disease, breast, and uterine cancer exist. Bisphosphonates are most commonly associated with gastrointestinal discomfort which may be mitigated with proper administration. Although adverse effects exist, these medications have proven to be efficacious in the prevention of vertebral and non-vertebral fractures in post-menopausal women. Fracture risk should be weighed against the risk of adverse events associated with each of the regimens, with clinical judgment dictating the treatment approach centered around patient goals and experiences.

Early zoledronate treatment inhibits subchondral bone microstructural changes in skeletally-mature, ACL-transected canine knees

Anterior cruciate ligament (ACL) tear leads to post-traumatic osteoarthritis (PTOA), a significant clinical burden worldwide that currently has no cure. Recent studies suggest a role of subchondral bone adaptations in the development of PTOA. Particularly, microstructural changes in the rod-and-plate microstructure of subchondral bone may precede and contribute to OA progression. In this study, we quantified microstructural changes in subchondral trabecular rods and plates after ACL-transection for the first time in the well-established preclinical canine model of PTOA and investigated the therapeutic potentials of a bisphosphonate (zoledronate) and NSAID treatment (meloxicam). Unilateral hindlimb ACL transection was performed on skeletally-mature (2-year-old, N = 20) and juvenile (10-month-old, N = 20) male beagles. Animals were assigned to 4 groups (N = 5): ACLT, un-operated control, ACLT with zoledronate, and ACLT with meloxicam treatment. Subchondral bone microstructure was evaluated by micro-computed tomography and cartilage integrity was evaluated histologically. We found that ACL-induced subchondral bone changes depended on skeletal maturity of animals. In mature animals, significant loss of trabecular plates that resulted in reduced PR ratio occurred at Month 1 and persisted until Month 8. Zoledronate treatment prevented trabecular plate loss while meloxicam treatment did not. Whether cartilage degeneration is also attenuated warrants further investigation. In juvenile animals that have not reached skeletal maturity, transient changes in trabecular plate and rod microstructure occurred at Month 3 but not Month 9. Neither zoledronate nor meloxicam treatment attenuated bone microstructural changes or cartilage damages. Findings from this study suggest that early inhibition of bone resorption by bisphosphonate after injury may be a promising therapeutic approach to prevent alterations in subchondral bone microstructure associated with PTOA. Our results further demonstrate that pathogenesis of PTOA may differ between adolescent and adult patients and therefore require distinct management strategies.

Transition of young adults with metabolic bone diseases to adult care

As more accurate diagnostic tools and targeted therapies become increasingly available for pediatric metabolic bone diseases, affected children have a better prognosis and significantly longer lifespan. With this potential for fulfilling lives as adults comes the need for dedicated transition and intentional care of these patients as adults. Much work has gone into improving the transitions of medically fragile children into adulthood, encompassing endocrinologic conditions like type 1 diabetes mellitus and congenital adrenal hyperplasia. However, there are gaps in the literature regarding similar guidance concerning metabolic bone conditions. This article intends to provide a brief review of research and guidelines for transitions of care more generally, followed by a more detailed treatment of bone disorders specifically. Considerations for such transitions include final adult height, fertility, fetal risk, heritability, and access to appropriately identified specialists. A nutrient-dense diet, optimal mobility, and adequate vitamin D stores are protective factors for these conditions. Primary bone disorders include hypophosphatasia, X-linked hypophosphatemic rickets, and osteogenesis imperfecta. Metabolic bone disease can also develop secondarily as a sequela of such diverse exposures as hypogonadism, a history of eating disorder, and cancer treatment. This article synthesizes research by experts of these specific disorders to describe what is known in this field of transition medicine for metabolic bone diseases as well as unanswered questions. The long-term objective is to develop and implement strategies for successful transitions for all patients affected by these various conditions.

Cellular Senescence in Bone

Senescence is an irreversible cell-cycle arrest process induced by environmental, genetic, and epigenetic factors. An accumulation of senescent cells in bone results in age-related disorders, and one of the common problems is osteoporosis. Deciphering the basic mechanisms contributing to the chronic ailments of aging may uncover new avenues for targeted treatment. This review focuses on the mechanisms and the most relevant research advancements in skeletal cellular senescence. To identify new options for the treatment or prevention of age-related chronic diseases, researchers have targeted hallmarks of aging, including telomere attrition, genomic instability, cellular senescence, and epigenetic alterations. First, this chapter provides an overview of the fundamentals of bone tissue, the causes of skeletal involution, and the role of cellular senescence in bone and bone diseases such as osteoporosis. Next, this review will discuss the utilization of pharmacological interventions in aging tissues and, more specifically, highlight the role of senescent cells to identify the most effective and safe strategies.

Estradiol and Estrogen-like Alternative Therapies in Use: The Importance of the Selective and Non-Classical Actions

Estrogen is one of the most important female sex hormones, and is indispensable for reproduction. However, its role is much wider. Among others, due to its neuroprotective effects, estrogen protects the brain against dementia and complications of traumatic injury. Previously, it was used mainly as a therapeutic option for influencing the menstrual cycle and treating menopausal symptoms. Unfortunately, hormone replacement therapy might be associated with detrimental side effects, such as increased risk of stroke and breast cancer, raising concerns about its safety. Thus, tissue-selective and non-classical estrogen analogues have become the focus of interest. Here, we review the current knowledge about estrogen effects in a broader sense, and the possibility of using selective estrogen-receptor modulators (SERMs), selective estrogen-receptor downregulators (SERDs), phytoestrogens, and activators of non-genomic estrogen-like signaling (ANGELS) molecules as treatment.

Bone Mass and Osteoblast Activity Are Sex-Dependent in Mice Lacking the Estrogen Receptor α in Chondrocytes and Osteoblast Progenitor Cells

While estrogen receptor alpha (ERα) is known to be important for bone development and homeostasis, its exact function during osteoblast differentiation remains unclear. Conditional deletion of ERα during specific stages of osteoblast differentiation revealed different bone phenotypes, which were also shown to be sex-dependent. Since hypertrophic chondrocytes can transdifferentiate into osteoblasts and substantially contribute to long-bone development, we aimed to investigate the effects of ERα deletion in both osteoblast and chondrocytes on bone development and structure. Therefore, we generated mice in which the ERα gene was inactivated via a Runx2-driven cyclic recombinase (ERαfl/fl; Runx2Cre). We analyzed the bones of 3-month-old ERαfl/fl; Runx2Cre mice by biomechanical testing, micro-computed tomography, and cellular parameters by histology. Male ERαfl/fl; Runx2Cre mice displayed a significantly increased cortical bone mass and flexural rigidity of the femurs compared to age-matched controls with no active Cre-transgene (ERαfl/fl). By contrast, female ERαfl/fl; Runx2Cre mice exhibited significant trabecular bone loss, whereas in cortical bone periosteal and endosteal diameters were reduced. Our results indicate that the ERα in osteoblast progenitors and hypertrophic chondrocytes differentially contributes to bone mass regulation in male and female mice and improves our understanding of ERα signaling in bone cells in vivo.

Estradiol and RSPO3 regulate vertebral trabecular bone mass independent of each other

Osteoporosis is an age-dependent serious skeletal disease that leads to great suffering for the patient and high social costs, especially as the global population reaches higher age. Decreasing estrogen levels after menopause result in a substantial bone loss and increased fracture risk, whereas estrogen treatment improves bone mass in women. RSPO3, a secreted protein that modulates WNT signaling, increases trabecular bone mass and strength in the vertebrae of mice, and is associated with trabecular density and risk of distal forearm fractures in humans. The aim of the present study was to determine if RSPO3 is involved in the bone-sparing effect of estrogens. We first observed that estradiol (E2) treatment increases RSPO3 expression in bone of ovariectomized (OVX) mice, supporting a possible role of RSPO3 in the bone-sparing effect of estrogens. As RSPO3 is mainly expressed by osteoblasts in the bone, we used a mouse model devoid of osteoblast-derived RSPO3 (Runx2-creRspo3^flox/flox mice) to determine if RSPO3 is required for the bone-sparing effect of E2 in OVX mice. We confirmed that osteoblast-specific RSPO3 inactivation results in a substantial reduction in trabecular bone mass and strength in the vertebrae. However, E2 increased vertebral trabecular bone mass and strength similarly in mice devoid of osteoblast-derived RSPO3 and control mice. Unexpectedly, osteoblast-derived RSPO3 was needed for the full estrogenic response on cortical bone thickness. In conclusion, although osteoblast-derived RSPO3 is a crucial regulator of vertebral trabecular bone, it is required for a full estrogenic effect on cortical, but not trabecular, bone in OVX mice. Thus, estradiol and RSPO3 regulate vertebral trabecular bone mass independent of each other.NEW & NOTEWORTHY Osteoblast-derived RSPO3 is known to be a crucial regulator of vertebral trabecular bone. Our new findings show that RSPO3 and estrogen regulate trabecular bone independent of each other, but that RSPO3 is necessary for a complete estrogenic effect on cortical bone.

Angiotensin Receptor Blocker is Associated with a Lower Fracture Risk: An Updated Systematic Review and Meta-Analysis

BACKGROUND

Angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) are widely used in the treatment of hypertension. Hypertension is often accompanied by osteoporosis. However, the relationship between ACEI/ARB and fractures remains controversial. The purpose of this meta-analysis was to update the potential relationship between ACEI/ARB and fractures.

METHODS

This meta-analysis was identified through PubMed, EMBASE, Cochrane Library, and Web of Science. Related studies about ACEI/ARB with the risk of fracture were published from inception to June 2022.

RESULTS

Nine qualified prospective designed studies, involving 3,649,785 subjects, were included in this analysis. Overall, the RRs of ACEI compared with the nonusers were 0.98 (95% CI: 0.88, 1.10; P < 0.001) for composite fractures and 0.96 (95% CI: 0.87, 1.05; P=0.048) for hip fractures; the RRs of ARB compared to the nonusers were 0.82 (95% CI: 0.73, 0.91; P < 0.001) for composite fractures and 0.85 (95% CI: 0.74, 0.97; P=0.028) for hip fractures. Furthermore, in the subgroup analysis, male may benefit from ARB (RR = 0.65, 95% CI: 0.49, 0.89, P=0.028), and the European may also benefit from ARB (RR = 0.86, 95% CI: 0.80, 0.93, P=0.015).

CONCLUSIONS

ACEI usage will not decrease the risk of osteoporosis fracture. On the contrary, ARB usage can decrease the risk of total fracture and hip fracture, especially for males and Europeans. Compared with ACEI, for patients at higher risk of fracture in cardiovascular diseases such as hypertension, the protective effect of ARB should be considered.

Shatavari Supplementation in Postmenopausal Women Improves Handgrip Strength and Increases Vastus lateralis Myosin Regulatory Light Chain Phosphorylation but Does Not Alter Markers of Bone Turnover

Shatavari has long been used as an Ayurvedic herb for women's health, but empirical evidence for its effectiveness has been lacking. Shatavari contains phytoestrogenic compounds that bind to the estradiol receptor. Postmenopausal estradiol deficiency contributes to sarcopenia and osteoporosis. In a randomised double-blind trial, 20 postmenopausal women (68.5 ± 6 years) ingested either placebo (N = 10) or shatavari (N = 10; 1000 mg/d, equivalent to 26,500 mg/d fresh weight shatavari) for 6 weeks. Handgrip and knee extensor strength were measured at baseline and at 6 weeks. Vastus lateralis (VL) biopsy samples were obtained. Data are presented as difference scores (Week 6-baseline, median ± interquartile range). Handgrip (but not knee extensor) strength was improved by shatavari supplementation (shatavari +0.7 ± 1.1 kg, placebo -0.4 ± 1.3 kg; p = 0.04). Myosin regulatory light chain phosphorylation, a known marker of improved myosin contractile function, was increased in VL following shatavari supplementation (immunoblotting; placebo -0.08 ± 0.5 a.u., shatavari +0.3 ± 1 arbitrary units (a.u.); p = 0.03). Shatavari increased the phosphorylation of Akt^ser473 (Akt^ser473 (placebo -0.6 ± 0.6 a.u., shatavari +0.2 ± 1.3 a.u.; p = 0.03) in VL. Shatavari supplementation did not alter plasma markers of bone turnover (P1NP, β-CTX) and stimulation of human osteoblasts with pooled sera (N = 8 per condition) from placebo and shatavari supplementation conditions did not alter cytokine or metabolic markers of osteoblast activity. Shatavari may improve muscle function and contractility via myosin conformational change and further investigation of its utility in conserving and enhancing musculoskeletal function, in larger and more diverse cohorts, is warranted.

Compromised Volumetric Bone Density and Microarchitecture in Men With Congenital Hypogonadotropic Hypogonadism

CONTEXT

Men with congenital hypogonadotropic hypogonadism (CHH) and Kallmann syndrome (KS) have both low circulating testosterone and estradiol levels. Whether bone structure is affected remains unknown.

OBJECTIVE

To characterize bone geometry, volumetric density and microarchitecture in CHH/KS.

METHODS

This cross-sectional study, conducted at a single French tertiary academic medical center, included 51 genotyped CHH/KS patients and 40 healthy volunteers. Among CHH/KS men, 98% had received testosterone and/or combined gonadotropins. High-resolution peripheral quantitative computed tomography (HR-pQCT), dual-energy x-ray absorptiometry (DXA), and measurement of serum bone markers were used to determine volumetric bone mineral density (vBMD) and cortical and trabecular microarchitecture.

RESULTS

CHH and controls did not differ for age, body mass index, and levels of vitamin D and PTH. Despite long-term hormonal treatment (10.8 ± 6.8 years), DXA showed lower areal bone mineral density (aBMD) in CHH/KS at lumbar spine, total hip, femoral neck, and distal radius. Consistent with persistently higher serum bone markers, HR-pQCT revealed lower cortical and trabecular vBMD as well as cortical thickness at the tibia and the radius. CHH/KS men had altered trabecular microarchitecture with a predominant decrease of trabecular thickness. Moreover, CHH/KS men exhibited lower cortical bone area, whereas total and trabecular areas were higher only at the tibia. Earlier treatment onset (before age 19 years) conferred a significant advantage for trabecular bone volume/tissue volume and trabecular vBMD at the tibia.

CONCLUSION

Both vBMD and bone microarchitecture remain impaired in CHH/KS men despite long-term hormonal treatment. Treatment initiation during adolescence is associated with enhanced trabecular outcomes, highlighting the importance of early diagnosis.

Comprehensive evaluation of the combined extracts of Epimedii Folium and Ligustri Lucidi Fructus for PMOP in ovariectomized rats based on MLP-ANN methods

ETHNOPHARMACOLOGICAL RELEVANCE

Kidney deficiency is the main pathogenesis of osteoporosis based on the theory of "kidney governing bones" in traditional Chinese medicine (TCM). Osteoporosis is a systemic disease; kidney deficiency influences the growth, aging and reproduction of human body, reflecting in endocrine, nerve, immunity, metabolism and other functions. Multi-target drugs composed of natural non-toxic products from kidney-reinforcing herbs, are being investigated for the treatment of osteoporosis. Therefore, it is necessary and imperative to develop an objective and comprehensive method to evaluate and compare the effects of herbs with listed drugs.

AIM OF THE STUDY

This study was designed to evaluate and compare the therapeutic effects and the underlying molecular mechanism of the combined extracts of Epimedii Folium and Ligustri Lucidi Fructus (EL) with Raloxifene hydrochloride (RH) in ovariectomy (OVX)-induced postmenopausal osteoporosis (PMOP) rats based on the multi-layer perception (MLP)-artificial neural network (ANN) model.

MATERIALS AND METHODS

Female SD rats were subjected to either sham surgery (n = 8) or bilateral OVX (n = 48). One week after recovering from surgery, the OVX-induced rats were randomly divided into three groups: OVX model group (n = 32, every 8 rats were killed at the end of the 5th, 9th, 11th or 13th week after OVX), EL group (treated with EL 0.35 g/kg, n = 8), and RH group (treated with RH 6.25 mg/kg, n = 8). The rats in the treatment groups were administrated once a day for 12 weeks, then sacrificed. We observed bone mass and quality, bone remodeling, the function of estrogen and TGF-β1/Smads pathway in all rats.

RESULTS

Both EL and RH could increase bone mineral density, enhance bone strength, relieve bone micro-structure degeneration, re-balance bone remodeling, regulate estrogen dysfunction, and up-regulate TGF-β1 expression. The evaluation of the MLP-ANN model showed that EL and RH had markedly anti-PMOP effects, and there was no significant difference in the comprehensive evaluation of anti-osteoporosis between the two drugs. However, RH had better effects on bone mass and quality and TGF-β1/Smads pathway than EL; EL had better effects on estrogen function than RH.

CONCLUSION

Combined extracts of Epimedii Folium and Ligustri Lucidi Fructus (EL) exhibited bone-protective effects on PMOP. The MLP-ANN method evaluated the efficacy of drugs more comprehensively, which provided a new direction for the evaluation and comparison of drugs.

Case Report: Severe Osteoporosis and Preventive Therapy in RNA Polymerase III-Related Leukodystrophy

RNA polymerase III (POLR3)-related leukodystrophy is an autosomal recessive form of leukodystrophy caused by homozygous or compound heterozygous mutations of the RNA polymerase III subunit genes, including subunit A (POLR3A). With respect to the manifestation triad, hypomyelination, hypodontia, and hypogonadotropic hypogonadism, it is also known as 4H leukodystrophy. Here, we report a 41-year-old woman of POLR3-related leukodystrophy by carrying compound heterozygous pathogenic variants of c.2554A>G (p.M852V) and c.2668G>T (p.V890F) in the POLR3A gene. She was amenorrheic and became a wheelchair user from the age of 15 years and suffered from multiple episodes of pathologic fractures, starting with a subtrochanteric fracture of the right femur after a tonic seizure at age 30 years. Head magnetic resonance imaging demonstrated hypomyelination and atrophies of the cerebellum, brainstem, and corpus callosum. Laboratory examination revealed a marked decrease of gonadotropins and estrogen, low bone density, and high bone resorption markers. Administration of anti-receptor activator of nuclear factor kappa-B ligand monoclonal antibody restored bone resorption markers to a normal level and prevented further pathological bone fractures. Our case emphasizes that osteoporosis should be recognized as a potential but serious complication in POLR3-related leukodystrophy. It may be feasible to prevent pathologic fractures by intensive osteoporosis therapy after endocrinological examinations and evaluation of bone metabolism.

Arginine site 264 in murine estrogen receptor-α is dispensable for the regulation of the skeleton

Mutation of arginine 264 in ERα has been shown to abrogate rapid membrane ERα-mediated endothelial effects. Our novel finding that mutation of R264 is dispensable for ERα-mediated skeletal effects supports the concept that R264 determines tissue specificity of ERα. Estrogen protects against bone loss but is not a suitable treatment due to adverse effects in other tissues. Therefore, increased knowledge regarding estrogen signaling in estrogen-responsive tissues is warranted to aid the development of bone-specific estrogen treatments. Estrogen receptor-α (ERα), the main mediator of estrogenic effects in bone, is widely subjected to posttranslational modifications (PTMs). In vitro studies have shown that methylation at site R260 in the human ERα affects receptor localization and intracellular signaling. The corresponding amino acid R264 in murine ERα has been shown to have a functional role in endothelium in vivo, although the methylation of R264 in the murine gene is yet to be empirically demonstrated. The aim of this study was to investigate whether R264 in ERα is involved in the regulation of the skeleton in vivo. Dual-energy X-ray absorptiometry (DEXA) analysis at 3, 6, 9, and 12 mo of age showed no differences in total body areal bone mineral density (BMD) between R264A and wild type (WT) in either female or male mice. Furthermore, analyses using computed tomography (CT) demonstrated that trabecular bone mass in tibia and vertebra and cortical thickness in tibia were similar between R264A and WT mice. In addition, R264A females displayed a normal estrogen treatment response in trabecular bone mass as well as in cortical thickness. Furthermore, uterus, thymus, and adipose tissue responded similarly in R264A and WT female mice after estrogen treatment. In conclusion, our novel finding that mutation of R264 in ERα does not affect the regulation of the skeleton, together with the known role of R264 for ERα-mediated endothelial effects, supports the concept that R264 determines tissue specificity of ERα.NEW & NOTEWORTHY Mutation of arginine 264 in ERα has been shown to abrogate rapid membrane ERα-mediated endothelial effects. Our novel finding that mutation of R264 is dispensable for ERα-mediated skeletal effects supports the concept that R264 determines tissue specificity of ERα.

Phosphorylation site S122 in estrogen receptor α has a tissue-dependent role in female mice

Estrogen treatment increases bone mass and reduces fat mass but is associated with adverse effects in postmenopausal women. Knowledge regarding tissue-specific estrogen signaling is important to aid the development of new tissue-specific treatments. We hypothesized that the posttranslational modification phosphorylation in estrogen receptor alpha (ERα) may modulate ERα activity in a tissue-dependent manner. Phosphorylation of site S122 in ERα has been shown in vitro to affect ERα activity, but the tissue-specific role in vivo is unknown. We herein developed and phenotyped a novel mouse model with a point mutation at the phosphorylation site 122 in ERα (S122A). Female S122A mice had increased fat mass and serum insulin levels but unchanged serum sex steroid levels, uterus weight, bone mass, thymus weight, and lymphocyte maturation compared to WT mice. In conclusion, phosphorylation site S122 in ERα has a tissue-dependent role with an impact specifically on fat mass in female mice. This study is the first to demonstrate in vivo that a phosphorylation site in a transactivation domain in a nuclear steroid receptor modulates the receptor activity in a tissue-dependent manner.

G Protein-Coupled Estrogen Receptor Mediates Cell Proliferation through the cAMP/PKA/CREB Pathway in Murine Bone Marrow Mesenchymal Stem Cells

Estrogen is an important hormone to regulate skeletal physiology via estrogen receptors. The traditional estrogen receptors are ascribed to two nuclear estrogen receptors (ERs), ERα and ERβ. Moreover, G protein-coupled estrogen receptor-1 (GPER-1) was reported as a membrane receptor for estrogen in recent years. However, whether GPER-1 regulated osteogenic cell biology on skeletal system is still unclear. GPER-1 is expressed in growth plate abundantly before puberty but decreased abruptly since the very late stage of puberty in humans. It indicates GPER-1 might play an important role in skeletal growth regulation. GPER-1 expression has been confirmed in osteoblasts, osteocytes and chondrocytes, but its expression in mesenchymal stem cells (MSCs) has not been confirmed. In this study, we hypothesized that GPER-1 is expressed in bone MSCs (BMSC) and enhances BMSC proliferation. The cultured tibiae of neonatal rat and murine BMSCs were tested in our study. GPER-1-specific agonist (G-1) and antagonist (G-15), and GPER-1 siRNA (siGPER-1) were used to evaluate the downstream signaling pathway and cell proliferation. Our results revealed BrdU-positive cell counts were higher in cultured tibiae in the G-1 group. The G-1 also enhanced the cell viability and proliferation, whereas G-15 and siGPER-1 reduced these activities. The cAMP and phosphorylation of CREB were enhanced by G-1 but inhibited by G-15. We further demonstrated that GPER-1 mediates BMSC proliferation via the cAMP/PKA/p-CREB pathway and subsequently upregulates cell cycle regulators, cyclin D1/cyclin-dependent kinase (CDK) 6 and cyclin E1/CDK2 complex. The present study is the first to report that GPER-1 mediates BMSC proliferation. This finding indicates that GPER-1 mediated signaling positively regulates BMSC proliferation and may provide novel insights into addressing estrogen-mediated bone development.

Cxcl12 Deletion in Mesenchymal Cells Increases Bone Turnover and Attenuates the Loss of Cortical Bone Caused by Estrogen Deficiency in Mice

CXCL12 is abundantly expressed in reticular cells associated with the perivascular niches of the bone marrow (BM) and is indispensable for B lymphopoiesis. Cxcl12 promotes osteoclastogenesis and has been implicated in pathologic bone resorption. We had shown earlier that estrogen receptor α deletion in osteoprogenitors and estrogen deficiency in mice increase Cxcl12 mRNA and protein levels in the BM plasma, respectively. We have now generated female and male mice with conditional deletion of a Cxcl12 allele in Prrx1 targeted cells (Cxcl12^∆Prrx1 ) and show herein that they have a 90% decrease in B lymphocytes but increased erythrocytes and adipocytes in the marrow. Ovariectomy increased the expression of Cxcl12 and B-cell number in the Cxcl12^f/f control mice, but these effects were abrogated in the Cxcl12^∆Prrx1 mice. Cortical bone mass was not affected in Cxcl12^∆Prrx1 mice. Albeit, the cortical bone loss caused by ovariectomy was greatly attenuated. Most unexpectedly, the rate of bone turnover in sex steroid-sufficient female or male Cxcl12^∆Prrx1 mice was dramatically increased, as evidenced by a more than twofold increase in several osteoblast- and osteoclast-specific mRNAs, as well as increased mineral apposition and bone formation rate and increased osteoclast number in the endosteal surface. The magnitude of the Cxcl12^∆Prrx1 -induced changes were much greater than those caused by ovariectomy or orchidectomy in the Cxcl12^f/f mice. These results strengthen the evidence that CXCL12 contributes to the loss of cortical bone mass caused by estrogen deficiency. Moreover, they reveal for the first time that in addition to its effects on hematopoiesis, CXCL12 restrains bone turnover-without changing the balance between resorption and formation-by suppressing osteoblastogenesis and the osteoclastogenesis support provided by cells of the osteoblast lineage. © 2020 American Society for Bone and Mineral Research.

Advancements in the gold standard: Measuring steroid sex hormones by mass spectrometry

Sex hormones, such as testosterone and estrogens, play an essential role in regulating physiological and reproductive development throughout the lifetime of the individual. Although variation in levels of these hormones are observed throughout the distinct stages in life, significant deviations from reference ranges can result in detrimental effects to the individual. Alterations, by either an increase or decrease, in hormone levels are associated with physiological changes, decreased reproductive capabilities, and increased risk for diseases. Hormone therapies (HTs) and assisted reproductive technologies (ARTs) are commonly used to address these factors. In addition to these treatments, gender-affirming therapies, an iteration of HTs, are also a prominent treatment for transgender individuals. Considering that the effectiveness of these treatments relies on achieving therapeutic hormone levels, monitoring of hormones has served as a way of assessing therapeutic efficay. The need for reliable methods to achieve this task has led to great advancements in methods for evaluating hormone concentrations in biological matrices. Although immunoassays are the more widely used method, mass spectrometry (MS)-based methods have proven to be more sensitive, specific, and reliable. Advances in MS technology and its applications for therapeutic hormone monitoring have been significant, hence integration of these methods in the clinical setting is desired. Here, we provide a general overview of HT and ART, and the immunoassay and MS-based methods currently utilized for monitoring sex hormones. Additionally, we highlight recent advances in MS-based methods and discuss future applications and considerations for MS-based hormone assays.

Osteoporosis: Pathophysiology and therapeutic options

Osteoporosis is a metabolic bone disease that, on a cellular level, results from osteoclastic bone resorption not compensated by osteoblastic bone formation. This causes bones to become weak and fragile, thus increasing the risk of fractures. Traditional pathophysiological concepts of osteoporosis focused on endocrine mechanisms such as estrogen or vitamin D deficiency as well as secondary hyperparathyroidism. However, research over the last decades provided exiting new insights into mechanisms contributing to the onset of osteoporosis, which go far beyond this. Selected mechanisms such as interactions between bone and the immune system, the gut microbiome, and cellular senescence are reviewed in this article. Furthermore, an overview on currently available osteoporosis medications including antiresorptive and bone forming drugs is provided and an outlook on potential future treatment options is given.

Vertebral bone marrow fat fraction changes in postmenopausal women with breast cancer receiving combined aromatase inhibitor and bisphosphonate therapy

Background

Quantification of vertebral bone marrow (VBM) water–fat composition has been proposed as advanced imaging biomarker for osteoporosis. Estrogen deficiency is the primary reason for trabecular bone loss in postmenopausal women. By reducing estrogen levels aromatase inhibitors (AI) as part of breast cancer therapy promote bone loss. Bisphosphonates (BP) are recommended to counteract this adverse drug effect. The purpose of our study was to quantify VBM proton density fat fraction (PDFF) changes at the lumbar spine using chemical shift encoding-based water-fat MRI (CSE-MRI) and bone mineral density (BMD) changes using dual energy X-ray absorptiometry (DXA) related to AI and BP treatment over a 12-month period.

Methods

Twenty seven postmenopausal breast cancer patients receiving AI therapy were recruited for this study. 22 subjects completed the 12-month study. 14 subjects received AI and BP (AI+BP), 8 subjects received AI without BP (AI-BP).

All subjects underwent 3 T MRI. An eight-echo 3D spoiled gradient-echo sequence was used for CSE-based water-fat separation at the lumbar spine to generate PDFF maps. After manual segmentation of the vertebral bodies L1-L5 PDFF values were extracted for each vertebra and averaged for each subject.

All subjects underwent DXA of the lumbar spine measuring the average BMD of L1-L4.

Results

Baseline age, PDFF and BMD showed no significant difference between the two groups (p > 0.05). There was a relative longitudinal increase in mean PDFF (∆rel_PDFF) in both groups (AI+BP: 5.93%; AI-BP: 3.11%) which was only significant (p = 0.006) in the AI+BP group. ∆rel_PDFF showed no significant difference between the two groups (p > 0.05). There was no significant longitudinal change in BMD (p > 0.05).

Conclusions

Over a 12-month period, VBM PDFF assessed with CSE-MRI significantly increased in subjects receiving AI and BP. The present results contradict previous results regarding the effect of only BP therapy on bone marrow fat content quantified by magnetic resonance spectroscopy and bone biopsies. Future longer-term follow-up studies are needed to further characterize the effects of combined AI and BP therapy.

Independent Roles of Estrogen Deficiency and Cellular Senescence in the Pathogenesis of Osteoporosis: Evidence in Young Adult Mice and Older Humans

Estrogen deficiency is a seminal mechanism in the pathogenesis of osteoporosis. Mounting evidence, however, establishes that cellular senescence, a fundamental mechanism that drives multiple age-related diseases, also causes osteoporosis. Recently, we systematically identified an accumulation of senescent cells, characterized by increased p16^Ink4a and p21^Cip1 levels and development of a senescence-associated secretory phenotype (SASP), in mouse bone/marrow and human bone with aging. We then demonstrated that elimination of senescent cells prevented age-related bone loss using multiple approaches, eg, treating old mice expressing a "suicide" transgene, INK-ATTAC, with AP20187 to induce apoptosis of p16^Ink4a -senescent cells or periodically treating old wild-type mice with "senolytics," ie, drugs that eliminate senescent cells. Here, we investigate a possible role for estrogen in the regulation of cellular senescence using multiple approaches. First, sex steroid deficiency 2 months after ovariectomy (OVX, n = 15) or orchidectomy (ORCH, n = 15) versus sham surgery (SHAM, n = 15/sex) in young adult (4-month-old) wild-type mice did not alter senescence biomarkers or induce a SASP in bone. Next, in elderly postmenopausal women, 3 weeks of estrogen therapy (n = 10; 74 ± 5 years) compared with no treatment (n = 10; 78 ± 5 years) did not alter senescence biomarkers or the SASP in human bone biopsies. Finally, young adult (4-month-old) female INK-ATTAC mice were randomized (n = 17/group) to SHAM+Vehicle, OVX+Vehicle, or OVX+AP20187 for 2 months. As anticipated, OVX+Vehicle caused significant trabecular/cortical bone loss compared with SHAM+Vehicle. However, treatment with AP20187, which eliminates senescent cells in INK-ATTAC mice, did not rescue the OVX-induced bone loss or alter senescence biomarkers. Collectively, our data establish independent roles of estrogen deficiency and cellular senescence in the pathogenesis of osteoporosis, which has important implications for testing novel senolytics for skeletal efficacy, as these drugs will need to be evaluated in preclinical models of aging as opposed to the current FDA model of prevention of OVX-induced bone loss. © 2019 American Society for Bone and Mineral Research.

Medical Treatment for Osteoporosis: From Molecular to Clinical Opinions

Osteoporosis is a major concern all over the world. With aging, a gradual loss of bone mass results in osteopenia and osteoporosis. Heritable factors account for 60–80% of optimal bone mineralization. Modifiable factors, such as weight-bearing exercise, nutrition, body mass, and hormonal milieu, play an important role in the development of osteopenia and osteoporosis in adulthood. Currently, anti-resorptive agents, including estrogen, bisphosphonates, and selective estrogen receptor modulators (SERMs), are the drugs of choice for osteoporosis. Other treatments include parathyroid hormone (PTH) as well as the nutritional support of calcium and vitamin D. New treatments such as tissue-selective estrogen receptor complexes (TSECs) are currently in use too. This review, which is based on a systematic appraisal of the current literature, provides current molecular and genetic opinions on osteoporosis and its medical treatment. It offers evidence-based information to help researchers and clinicians with osteoporosis assessment. However, many issues regarding osteoporosis and its treatment remain unknown or controversial and warrant future investigation.

Effects of Rhizoma Drynariae Cataplasm on Fracture Healing in a Rat Model of Osteoporosis

BACKGROUND Osteoporosis is an increasingly prevalent disease characterized by decreased bone mass and deterioration of the bone microstructure, which contribute to increased fragility and subsequent fragility fractures, especially in elderly individuals. Rhizoma Drynariae (DRE) is among the most frequently used herbal medicines for the treatment of osteoporosis. Transdermal delivery is a proven novel pathway for drug treatment and has several advantages over traditional drug delivery routes. MATERIAL AND METHODS Female Sprague-Dawley osteoporotic fracture model rats were divided into 3 groups: the control group, the DRE (90 mg/kg/day) group and the DRE cataplasm (containing 30 mg DRE, administered at right femur site daily) group. At 3 and 6 weeks after operation, we performed x-ray, histological, and biomechanical analyses, and evaluated bone marrow density of the femur. RESULTS Treatment with DRE increased callus formation and bone union compared with the control group. Moreover, DRE enhanced bone strength at the femoral diaphysis in the osteoporotic fractures in rats by increasing the ultimate load and stiffness compared with the control group. Furthermore, DRE restored the trabecular bone mineral density in the femur compared with the control group. DRE cataplasm application further enhanced the therapeutic effects against osteoporotic fracture in this rat model. CONCLUSIONS DRE cataplasm application might be useful against osteoporotic fracture.

Autoregulation of Osteocyte Sema3A Orchestrates Estrogen Action and Counteracts Bone Aging

Osteocyte survival is key to bone homeostasis and is perturbed in menopause and aging. However, it remains unknown how osteocyte-mediated maintenance of the skeleton is regulated by the osteoprotective factor semaphorin 3A (Sema3A), a secreted protein that is known to reduce bone resorption and enhance bone formation. Here, we show that estrogen induces osteocyte expression of Sema3A, which acts on its receptor on osteocytes to promote their survival and maintain bone homeostasis. Postnatal global and conditional deletion of Sema3a in osteoblastic cells resulted in a severe osteoporotic phenotype marked by fewer osteocytes. This phenotype was recapitulated by osteocyte-specific deficiency of either Sema3A or its receptor component neuropilin-1 (Nrp1). A stimulator of soluble guanylate cyclase-cGMP signaling mimicked Sema3A action and ameliorated bone loss after ovariectomy. We further show that serum levels of SEMA3A decreased with age or after menopause in humans. Thus, we provide a mechanistic insight into the estrogen action and a promising therapeutic approach to protect against bone-related aging.

Combined Extracts of Herba Epimedii and Fructus Ligustri Lucidi Rebalance Bone Remodeling in Ovariectomized Rats

This study aimed to investigate the osteoprotective effect and the possible molecular mechanisms of the combined extracts of Herba Epimedii and Fructus Ligustri Lucidi on postmenopausal osteoporosis (PMOP). Forty-eight female SD rats were sham-operated (Sham, n = 8) or ovariectomized (OVX, n = 40). Then after a week, OVX rats were divided randomly into five groups (n = 8 in each group): OVX, extracts of Herba Epimedii (HE, 0.35 g/kg), extracts of Fructus Ligustri Lucidi (FLL, 0.35 g/kg), combined extracts of HE and FLL (HE & FLL, 0.20 g/kg HE plus 0.15 g/kg FLL), and Raloxifene hydrochloride (RH, 6.25 mg/kg) groups. All groups were administered once daily for 12 weeks. Indicators related to bone remodeling were detected, including estradiol (E₂), bone mineral density (BMD), maximal load, ultimate deflection, micro-CT properties, tartrate-resistant acid phosphatase (TRACP) and alkaline phosphatase (ALP) levels in serum and bone, and the protein and mRNA expression of bone turnover markers (RANKL, M-CSF, Wnt5a, Atp6v0d2, OPG, IGF-1, TGF-β1, and Bmp-2). Results showed that the combined extracts could increase serum E₂ levels and BMD, enhance bone strength, reserve bone microstructure degeneration, promote bone formation, and inhibit bone resorption through upregulating the mRNA and protein expression of OPG, IGF-1, TGF-β1, and Bmp-2, while downregulating RANKL, M-CSF, Wnt5a, and Atp6v0d2. These findings demonstrated that the combined extracts of Herba Epimedii and Fructus Ligustri Lucidi with bone protective effects on OVX rats might be an alternative medicine for the treatment of PMOP.

Green tea (Camellia sinensis) aqueous extract alleviates postmenopausal osteoporosis in ovariectomized rats and prevents RANKL-induced osteoclastogenesis in vitro

Background

Green tea (Camelliasinensis [L.] Kuntze) belongs to the plant family Theaceae and is mainly distributed in East Asia, the Indian subcontinent and Southeast Asia. This plant has been proven to be beneficial to human health, and green tea is the second most consumed beverage in the world after water. However, until now, the effect of green tea aqueous extract (GTE) upon postmenopausal osteoporosis has remained unclear. In this study, we investigated the therapeutic effects of GTE on estrogen deficiency-induced osteoporosis and explored the possible mechanisms in vivo and in vitro.

Materials and methods

Ovariectomized (OVX) female rats were orally administered with GTE at doses of 60, 120, and 370 mg kg⁻¹ for 13 consecutive weeks. The biochemical parameters, bone gla protein, alkaline phosphatase, acid phosphatase, estrogen, interleukin-1β, and interleukin-6 in blood samples were detected, and histological change in bones was analyzed by hematoxylin and eosin staining. Meanwhile, the mechanisms of GTE on osteoclast formation were explored in RAW 264.7 cells induced by receptor activation of the nuclear factor kappa B ligand (RANKL).

Results

The results showed that GTE could increase bone mass and inhibit trabecular bone loss in OVX rats. Furthermore, real-time quantitative reverse transcription polymerase chain reaction analysis from in vitro experiments also showed that GTE reduced the mRNA expression of osteoclast-associated genes such as cathepsin K (cath-K), c-Fos, matrix metalloproteinase 9, nuclear factor of activated T cells cytoplasmic 1 (NFATc1) and tartrate-resistant acid phosphatase. In addition, GTE caused a reduction in the protein levels of NFATc1, c-Fos, c-src and cath-K.

Conclusion

Evidence from both animal models and in vitro experiments suggested that GTE might effectively ameliorate the symptoms of osteoporosis in OVX rats and inhibit RANKL-induced osteoclast-specific gene and protein expression.

ERα expression in T lymphocytes is dispensable for estrogenic effects in bone

Estrogen treatment has positive effects on the skeleton, and we have shown that estrogen receptor alpha (ERα) expression in cells of hematopoietic origin contributes to a normal estrogen treatment response in bone tissue. T lymphocytes are implicated in the estrogenic regulation of bone mass, but it is not known whether T lymphocytes are direct estrogen target cells. Therefore, the aim of this study was to determine the importance of ERα expression in T lymphocytes for the estrogenic regulation of the skeleton using female mice lacking ERα expression specifically in T lymphocytes (Lck-ERα^-/-) and ERα^flox/flox littermate (control) mice. Deletion of ERα expression in T lymphocytes did not affect bone mineral density (BMD) in sham-operated Lck-ERα^-/- compared to control mice, and ovariectomy (ovx) resulted in a similar decrease in BMD in control and Lck-ERα^-/- mice compared to sham-operated mice. Furthermore, estrogen treatment of ovx Lck-ERα^-/- led to an increased BMD that was indistinguishable from the increase seen after estrogen treatment of ovx control mice. Detailed analysis of both the appendicular (femur) and axial (vertebrae) skeleton showed that both trabecular and cortical bone parameters responded to a similar extent regardless of the presence of ERα in T lymphocytes. In conclusion, ERα expression in T lymphocytes is dispensable for normal estrogenic regulation of bone mass in female mice.

ST2 regulates bone loss in a site-dependent and estrogen-dependent manner

Interleukin-33 (IL-33) and its receptor, ST2, are implicated in bone remodeling. The lack of estrogen after menopause results in an accelerated bone loss. Here we investigated the role of ST2 in the bone loss induced by estrogen deficiency. ST2-deficient mice (ST2^-/- ) and their littermates (wildtype [WT]) were ovariectomized (OVX), while ovary-intact mice were used as controls. Bone sites were analyzed by microcomputed tomography, histomorphometry, and quantitative real-time polymerase chain reaction (qPCR). Deletion of IL-33 or ST2 resulted in a similar bone loss in the femur and maxilla. Ovariectomy in WT mice caused bone loss in the same areas. The lack of ST2 in OVX mice did not alter bone remodeling in the femur but prevented bone loss in the maxilla. Consistently, ovariectomy increased the IL-33 messenger RNA (mRNA) levels in the maxilla but not in the femur. Under mechanical stimulation, ovariectomy and ST2 deletion independently increased bone remodeling induced by orthodontic tooth movement, which was also associated with a greater number of osteoclasts and a reduced number of osteoblasts in the maxillary bone. ST2^-/- OVX mice, however, displayed twice as many osteoblasts as that of WT OVX mice. Ovariectomy and ST2 deletion differently altered the cytokine mRNA levels in the maxilla. Remarkably, interleukin-10 expression was decreased in both WT OVX and ST2^-/- mice, and this reduction was completely restored in ST2^-/- OVX mice. The results demonstrate that estrogen and IL33/ST2 independently protect against bone loss. However, the ovariectomy-induced bone loss is IL-33/ST2-dependent in the maxilla but not in the femur, indicating a bimodal and site-specific role of ST2 in bone remodeling.

[Osteocalcin, a key molecule for bone endocrine functions]

The maintenance of our physiological functions and their adaptive response to environmental changes depend on precise crosstalk between organs. Recent advances in mouse genetics have helped demonstrate that this holistic view of physiology extends to the skeletal system, where many unexpected signaling axes are found to play essential roles affecting numerous organs. After being long regarded as a static tissue, functioning merely as a structural support system, the skeleton has seen its image evolve into a much more complex picture. The skeleton reveals itself as a key endocrine organ for the homeostasis of our body, both by its central position in our body, but also by the large number of physiological functions it influences. In this review, we discuss the multiple endocrine roles of osteocalcin, an osteoclast-derived molecule (Ocn), where its functional importance has steadily increased over the last 15 years.

Xenoestrogen regulation of ERα/ERβ balance in hormone-associated cancers

The hormone 17β-estradiol (E2) contributes to body homeostasis maintenance by regulating many different physiological functions in both male and female organs. E2 actions in reproductive and non-reproductive tissues rely on a complex net of nuclear and extra-nuclear signal transduction pathways triggered by at least two estrogen receptor subtypes (ERα and ERβ). Consequently, the de-regulation of E2:ER signaling contributes to the pathogenesis of many diseases including cancer. Among other factors, the ERα/ERβ ratio is considered one of the pivotal mechanisms at the root of E2 action in cancer progression. Remarkably, several natural or synthetic exogenous chemicals, collectively called xenoestrogens, bind to ERs and interfere with their signals and intracellular functions. In this review, the molecular mechanism(s) through which xenoestrogens influence ERα and ERβ intracellular concentrations and the consequences of this influence on E2-related cancer will be discussed.

Bone mineral density and breast cancer risk: Results from the Vorarlberg Health Monitoring & Prevention Program and meta-analysis

We investigated the association between bone mineral density (BMD) and breast cancer risk in a large prospective cohort and quantified the evidence in a meta-analysis of prospective studies.

Baseline BMD has been measured by dual energy X-ray absorptiometry (DXA, N = 1418). Data on medication and lifestyle has been collected by questionnaire. Cox proportional Hazards models were applied to calculate Hazard Ratios for breast cancer. In addition, a meta-analysis on categorical and dose-response values including the current results has been performed applying random-effects models.

During mean follow-up of 16.3 (SD 3.3) years of 1380 women (mean age 55.5 ± 6.3 years), 52 cases of invasive breast cancer were identified. We found no statistically significant association of BMD with breast cancer risk (per one z-score increase, HR 0.91, 95% CI 0.67–1.23).

In the meta-analysis, however, breast cancer risk increased by 15% and 16% per 0.1 g/m² increase in BMD at the lumbar spine (95% CI 0.99–1.33) and at the femoral neck (95% CI 1.02–1.32), respectively. Compared to the lowest, the HRs for breast cancer were statistically significant for the highest BMD category, i.e. 1.49 (95% CI 1.04–2.13) at the lumbar spine and 1.66 (95% CI 1.26–2.18) at the femur.

We found no association between BMD (DXA) and breast cancer risk in our cohort. However, overall the present meta-analysis extends and confirms the statistically significant association between increasing BMD and increased breast cancer risk.

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In the VHM&PP BMD (DXA) was not associated with breast cancer risk.

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A meta-analysis showed a positive association between BMD and breast cancer risk in postmenopausal women.

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Per 0.1 g/m² increase in BMD breast cancer risk increased by 15% at the lumbar spine and 16% at the femoral neck.

Factors Associated with Bone Health in Malaysian Middle-Aged and Elderly Women Assessed via Quantitative Ultrasound

Risk factors for osteoporosis may vary according to different populations. We aimed to investigate the relationship between risk factors of osteoporosis and bone health indices determined via calcaneal quantitative ultrasound (QUS) in a group of Malaysian women aged 50 years or above. A cross-sectional study was performed on 344 Malaysian women recruited from a tertiary medical centre in Kuala Lumpur, Malaysia. They answered a self-administered questionnaire on their social-demographic details, medical history, lifestyle, and physical activity status. Their height was measured using a stadiometer, and their body composition estimated using a bioelectrical impedance device. Their bone health status was determined using a water-based calcaneal QUS device that generated three indices, namely speed of sound (SOS), broadband ultrasound attenuation (BUA), and stiffness index (SI). A T-score was computed from SI values using a reference database from a mainland Chinese population. Women with three or more lifetime pregnancies, who were underweight and not drinking coffee had a significantly lower BUA. Stepwise multiple linear regression showed that SOS was predicted by age alone, BUA and SI by years since menopause, body mass index (BMI), and number of lifetime pregnancies, and T-score by years since menopause and percentage of body fat. As a conclusion, suboptimal bone health in middle-aged and elderly Malaysian women as indicated by QUS is associated with old age, being underweight, having a high body fat percentage, and a high number of lifetime pregnancies. Women having several risk factors should be monitored more closely to protect their bones against accelerated bone loss.

Effects of Combination Therapy of Alendronate and Hormonal Therapy on Bone Mineral Density in Postmenopausal Korean Women: Multicenter, Randomized Controlled Clinical Trial

This study evaluated the effects of combination treatment with alendronate (ALEN) and hormone therapy (HT) on bone mineral density (BMD) in postmenopausal Korean women. This multicenter, randomized, controlled clinical trial enrolled 344 postmenopausal women with low BMD. The women received HT (0.625 mg/day of conjugated equine estrogen and 2.5 mg/day of medroxyprogesterone acetate) alone or in combination with ALEN (10 mg/day) for 1 year. Changes in BMD and biochemical markers of bone turnover were evaluated. Data from 203 women (HT alone, 99; combination treatment, 104) who completed this study were analyzed. BMD at the lumbar spine and total hip increased significantly in both treatment groups after 1 year. There were no significant differences between HT alone vs. the combination of ALEN and HT in mean BMD increase at the lumbar spine (6.9% vs. 7.9%) and total hip (3.7% vs. 3.8%). Combined therapy suppressed serum osteocalcin and urinary deoxypyridinoline to a greater extent than HT alone. In conclusion, compared to HT alone, combination treatment with ALEN and HT for 1 year did not offer a benefit in BMD in postmenopausal Korean women with low BMD.

Antioxidant Effect of Fructus Ligustri Lucidi Aqueous Extract in Ovariectomized Rats Is Mediated through Nox4-ROS-NF-κB Pathway

Purpose: This study is designed to explore whether Fructus ligustri lucidi (FLL) exhibits antioxidant effect in ovariectomized (OVX) rats, and to identify the signaling pathway involved in this process.

Methods: OVX rats were treated with FLL aqueous extract (3.5 g/kg) for 12 weeks. Serum, uteri, and tibias were harvested from the rats and the levels of total antioxidant capacity (TAC), nitric oxide (NO), malondialdehyde (MDA), 8-hydroxy-desoxyguanosine (8-OHdG), and superoxide dismutase (SOD) were determined. Changes in the levels of NF-κB-p65, phosphorylation of NF-κB-p65 (NF-κB-pp65), NF-κB inhibitor alpha (IκBα), phosphorylation of IκBα (p-IκBα), and NADPH oxidase 4 (Nox4) in uteri and tibias were determined by western blot, immunofluorescent and immunohistochemical analysis, respectively. In addition, the expression of cytochrome C (Cyto-C) and B-cell lymphoma-2 (Bcl-2) were determined in the tibias of rats. Histopathological changes in the bones were evaluated by hematoxylin-eosin staining. Bone mineral density (BMD) was determined in rat femurs by dual X-ray absorptiometry.

Results: Treatment of OVX rats with FLL aqueous extract improved redox homeostasis by increasing the levels of TAC and NO as well as decreasing the levels of MDA and 8-OHdG in serum, tibias, and uteri. Further, FLL extract also downregulated the expression of Nox4, NF-κB-p65, NF-κB-pp65, and p-IκBα in the uteri and tibias. Furthermore, administration of FLL–OVX rats increased Bcl-2 expression and prevented cytoplasmic release of mitochondrial Cyto-C in the tibias. In addition, FLL treatment also improved bone microstructure and increased cortical bone thickness as well as increased BMD values in the femurs of OVX rats.

Conclusions: FLL treatment may suppress oxidative stress response in OVX rats via regulating the Nox4/ROS/NF-κB signaling pathway. These results suggest the potential of using FLL as a natural antioxidant agent in preventing the development of osteoporosis.

Estrogens and Androgens in Skeletal Physiology and Pathophysiology

Estrogens and androgens influence the growth and maintenance of the mammalian skeleton and are responsible for its sexual dimorphism. Estrogen deficiency at menopause or loss of both estrogens and androgens in elderly men contribute to the development of osteoporosis, one of the most common and impactful metabolic diseases of old age. In the last 20 years, basic and clinical research advances, genetic insights from humans and rodents, and newer imaging technologies have changed considerably the landscape of our understanding of bone biology as well as the relationship between sex steroids and the physiology and pathophysiology of bone metabolism. Together with the appreciation of the side effects of estrogen-related therapies on breast cancer and cardiovascular diseases, these advances have also drastically altered the treatment of osteoporosis. In this article, we provide a comprehensive review of the molecular and cellular mechanisms of action of estrogens and androgens on bone, their influences on skeletal homeostasis during growth and adulthood, the pathogenetic mechanisms of the adverse effects of their deficiency on the female and male skeleton, as well as the role of natural and synthetic estrogenic or androgenic compounds in the pharmacotherapy of osteoporosis. We highlight latest advances on the crosstalk between hormonal and mechanical signals, the relevance of the antioxidant properties of estrogens and androgens, the difference of their cellular targets in different bone envelopes, the role of estrogen deficiency in male osteoporosis, and the contribution of estrogen or androgen deficiency to the monomorphic effects of aging on skeletal involution.

Estrogens and Androgens in Skeletal Physiology and Pathophysiology

Estrogens and androgens influence the growth and maintenance of the mammalian skeleton and are responsible for its sexual dimorphism. Estrogen deficiency at menopause or loss of both estrogens and androgens in elderly men contribute to the development of osteoporosis, one of the most common and impactful metabolic diseases of old age. In the last 20 years, basic and clinical research advances, genetic insights from humans and rodents, and newer imaging technologies have changed considerably the landscape of our understanding of bone biology as well as the relationship between sex steroids and the physiology and pathophysiology of bone metabolism. Together with the appreciation of the side effects of estrogen-related therapies on breast cancer and cardiovascular diseases, these advances have also drastically altered the treatment of osteoporosis. In this article, we provide a comprehensive review of the molecular and cellular mechanisms of action of estrogens and androgens on bone, their influences on skeletal homeostasis during growth and adulthood, the pathogenetic mechanisms of the adverse effects of their deficiency on the female and male skeleton, as well as the role of natural and synthetic estrogenic or androgenic compounds in the pharmacotherapy of osteoporosis. We highlight latest advances on the crosstalk between hormonal and mechanical signals, the relevance of the antioxidant properties of estrogens and androgens, the difference of their cellular targets in different bone envelopes, the role of estrogen deficiency in male osteoporosis, and the contribution of estrogen or androgen deficiency to the monomorphic effects of aging on skeletal involution.

Postmenopausal osteoporosis

Osteoporosis is a metabolic bone disorder that is characterized by low bone mass and micro-architectural deterioration of bone tissue. Fractures of the proximal femur, the vertebrae and the distal radius are the most frequent osteoporotic fractures, although most fractures in the elderly are probably at least partly related to bone fragility. The incidence of fractures varies greatly by country, but on average up to 50% of women >50 years of age are at risk of fractures. Fractures severely affect the quality of life of an individual and are becoming a major public health problem owing to the ageing population. Postmenopausal osteoporosis, resulting from oestrogen deficiency, is the most common type of osteoporosis. Oestrogen deficiency results in an increase in bone turnover owing to effects on all types of bone cells. The imbalance in bone formation and resorption has effects on trabecular bone (loss of connectivity) and cortical bone (cortical thinning and porosity). Osteoporosis is diagnosed using bone density measurements of the lumbar spine and proximal femur. Preventive strategies to improve bone health include diet, exercise and abstaining from smoking. Fractures may be prevented by reducing falls in high-risk populations. Several drugs are licensed to reduce fracture risk by slowing down bone resorption (such as bisphosphonates and denosumab) or by stimulating bone formation (such as teriparatide). Improved understanding of the cellular basis for osteoporosis has resulted in new drugs targeted to key pathways, which are under development.

Effects of total flavonoids from Drynariae Rhizoma prevent bone loss in vivo and in vitro

Estrogen deficiency is one of the major causes of osteoporosis in postmenopausal women. Drynariae Rhizoma is a widely used traditional Chinese medicine for the treatment of bone diseases. In this study, we investigated the therapeutic effects of the total Drynariae Rhizoma flavonoids (DRTF) on estrogen deficiency-induced bone loss using an ovariectomized rat model and osteoblast-like MC3T3-E1 cells. Our results indicated that DRTF produced osteo-protective effects on the ovariectomized rats in terms of bone loss reduction, including decreased levels of bone turnover markers, enhanced biomechanical femur strength and trabecular bone microarchitecture deterioration prevention. In vitro experiments revealed that the actions of DRTF on regulating osteoblastic activities were mediated by the estrogen receptor (ER) dependent pathway. Our data also demonstrated that DRTF inhibited osteoclastogenesis via up-regulating osteoprotegrin (OPG), as well as down-regulating receptor activator of NF-κB ligand (RANKL) expression. In conclusion, this study indicated that DRTF treatment effectively suppressed bone mass loss in an ovariectomized rat model, and in vitro evidence suggested that the effects were exerted through actions on both osteoblasts and osteoclasts.

Klotho/fibroblast growth factor 23- and PTH-independent estrogen receptor-α-mediated direct downregulation of NaPi-IIa by estrogen in the mouse kidney

Estrogen treatment causes renal phosphate (Pi) wasting and hypophosphatemia in rats and humans; however, the signaling mechanisms mediating this effect are still poorly understood. To determine the specific roles of estrogen receptor isoforms (ERα and ERβ) and the Klotho pathway in mediating these effects, we studied the effects of estrogen on renal Pi handling in female mice with null mutations of ERα or ERβ or Klotho and their wild type (WT) using balance studies in metabolic cages. Estrogen treatment of WT and ERβ knockout (KO) mice caused a significant reduction in food intake along with increased renal phosphate wasting. The latter resulted from a significant downregulation of NaPi-IIa and NaPi-IIc protein abundance. The mRNA expression levels of both transporters were unchanged in estrogen-treated mice. These effects on both food intake and renal Pi handling were absent in ERα KO mice. Estrogen treatment of Klotho KO mice or parathyroid hormone (PTH)-depleted thyroparathyroidectomized mice exhibited a significant downregulation of NaPi-IIa with no change in the abundance of NaPi-IIc. Estrogen treatment of a cell line (U20S) stably coexpressing both ERα and ERβ caused a significant downregulation of NaPi-IIa protein when transiently transfected with a plasmid containing full-length or open-reading frame (ORF) 3'-untranslated region (UTR) but not 5'-UTR ORF of mouse NaPi-IIa transcript. In conclusion, estrogen causes phosphaturia and hypophosphatemia in mice. These effects result from downregulation of NaPi-IIa and NaPi-IIc proteins in the proximal tubule through the activation of ERα. The downregulation of NaPi-IIa by estrogen involves 3'-UTR of its mRNA and is independent of Klotho/fibroblast growth factor 23 and PTH signaling pathways.

The role of membrane ERα signaling in bone and other major estrogen responsive tissues

Estrogen receptor α (ERα) signaling leads to cellular responses in several tissues and in addition to nuclear ERα-mediated effects, membrane ERα (mERα) signaling may be of importance. To elucidate the significance, in vivo, of mERα signaling in multiple estrogen-responsive tissues, we have used female mice lacking the ability to localize ERα to the membrane due to a point mutation in the palmitoylation site (C451A), so called Nuclear-Only-ER (NOER) mice. Interestingly, the role of mERα signaling for the estrogen response was highly tissue-dependent, with trabecular bone in the axial skeleton being strongly dependent (>80% reduction in estrogen response in NOER mice), cortical and trabecular bone in long bones, as well as uterus and thymus being partly dependent (40–70% reduction in estrogen response in NOER mice) and effects on liver weight and total body fat mass being essentially independent of mERα (<35% reduction in estrogen response in NOER mice). In conclusion, mERα signaling is important for the estrogenic response in female mice in a tissue-dependent manner. Increased knowledge regarding membrane initiated ERα actions may provide means to develop new selective estrogen receptor modulators with improved profiles.

Estrogen receptors alpha and beta in bone

Estrogens are important for bone metabolism via a variety of mechanisms in osteoblasts, osteocytes, osteoclasts, immune cells and other cells to maintain bone mineral density. Estrogens bind to estrogen receptor alpha (ERα) and ERβ, and the roles of each of these receptors are beginning to be elucidated through whole body and tissue-specific knockouts of the receptors. In vitro and in vivo experiments have shown that ERα and ERβ antagonize each other in bone and in other tissues. This review will highlight the role of these receptors in bone, with particular emphasis on their antagonism.

Tissue responsiveness to estradiol and genistein in the sea bass liver and scale

As in mammals, estrogens in fish are essential for reproduction but also important regulators of mineral homeostasis. Fish scales are a non-conventional target tissue responsive to estradiol and constitute a good model to study mineralized tissues effects and mechanisms of action of estrogenic compounds, including phytoestrogens. The responsiveness to estradiol and the phytoestrogen genistein, was compared between the scales and the liver, a classical estrogenic target, in sea bass (Dicentrarchus labrax). Injection with estradiol and genistein significantly increased circulating vitellogenin (for both compounds) and mineral levels (estradiol only) and genistein also significantly increased scale enzymatic activities suggesting it increased mineral turnover. The repertoire, abundance and estrogenic regulation of nuclear estrogen receptors (ESR1, 2a and 2b) and membrane G-protein receptors (GPER and GPER-like) were different between liver and scales, which presumably explains the tissue-specific changes detected in estrogen-responsive gene expression. In scales changes in gene expression mainly consisted of small rapid increases, while in liver strong, sustained increases/decreases in gene expression occurred. Similar but not overlapping gene expression changes were observed in response to both estradiol and genistein. This study demonstrates for the first time the expression of membrane estrogen receptors in scales and that estrogens and phytoestrogens, to which fish may be exposed in the wild or in aquaculture, both affect liver and mineralized tissues in a tissue-specific manner.

Oestrogen receptor positive breast cancer metastasis to bone: inhibition by targeting the bone microenvironment in vivo

Clinical trials have shown that adjuvant Zoledronic acid (ZOL) reduces the development of bone metastases irrespective of ER status. However, post-menopausal patients show anti-tumour benefit with ZOL whereas pre-menopausal patients do not. Here we have developed in vivo models of spontaneous ER+ve breast cancer metastasis to bone and investigated the effects of ZOL and oestrogen on tumour cell dissemination and growth. ER+ve (MCF7, T47D) or ER-ve (MDA-MB-231) cells were administered by inter-mammary or inter-cardiac injection into female nude mice ± estradiol. Mice were administered saline or 100 μg/kg ZOL weekly. Tumour growth, dissemination of tumour cells in blood, bone and bone turnover were monitored by luciferase imaging, histology, flow cytometry, two-photon microscopy, micro-CT and TRAP/P1NP ELISA. Estradiol induced metastasis of ER+ve cells to bone in 80-100 % of animals whereas bone metastases from ER-ve cells were unaffected. Administration of ZOL had no effect on tumour growth in the fat pad but significantly inhibited dissemination of ER+ve tumour cells to bone and frequency of bone metastasis. Estradiol and ZOL increased bone volume via different mechanisms: Estradiol increased activity of bone forming osteoblasts whereas administration of ZOL to estradiol supplemented mice decreased osteoclast activity and returned osteoblast activity to levels comparable to that of saline treated mice. ER-ve cells require increased osteoclast activity to grow in bone whereas ER+ve cells do not. Zol does not affect ER+ve tumour growth in soft tissue, however, inhibition of bone turnover by ZOL reduced dissemination and growth of ER+ve breast cancer cells in bone.

Influence of sex steroids on inflammation and bone metabolism

Sex steroids are central to sexual development and reproduction, exerting pleiotropic effects on multiple tissues and organs throughout the lifespan of humans. Sex steroids are fundamental to skeletal development, bone homeostasis and immune function. The composite effect of sex-specific genetic architecture and circulating levels of sex-steroid hormones closely parallels differences in the immune response and may account for corresponding sex-related differences in risk for chronic periodontitis, with men exhibiting greater susceptibility than women. Age-associated reductions in sex steroids also provide insight into apparent temporal increases in susceptibility to periodontitis and alveolar bone loss, particularly among women. Chronic infection and inflammatory conditions, such as periodontal disease, provide a unique platform for exploring the interface of sex steroids, immunity and bone metabolism.

Bone involvement in males with Kallmann disease

BACKGROUND

Kallmann syndrome (KS) is a rare genetic condition characterized by congenital early-onset hypogonadotropic hypogonadism and anosmia or hyposmia. Male subjects are more frequently affected and present absent/delayed puberty, low testosterone levels with higher risk for osteoporosis. Therefore, to maintain normal levels of sex steroids and prevent bone loss, male KS needs life-long hormonal replacement therapy (HRT).

AIMS

The objective of our study is to assess bone involvement in subjects with KS currently treated with HRT.

METHODS

In our retrospective study, we analyzed data from medical records of patients with KS treated with HRT (either gonadotropins or testosterone preparations), including clinical history, biochemical parameters, and the following outcome measures: the bone mineral density (BMD) at the lumbar spine (LS), femoral neck (FN), and total body less head (TBLH); and the Vertebral Fracture Assessment (VFA) by Dual Energy X-ray Absorptiometry (DXA).

RESULTS

Clinical and instrumental data of 32 patients with KS were evaluated; their mean age was 30.32 (± 10.09) years, their mean body mass index (BMI) was 25.71 (± 3.23) kg/m(2). Four patients (12.5%) had a LS BMD Z score below the expected range for age. Five patients had vertebral deformities observed at VFA. Duration of HRT was related to bone health parameters: BMD at all measured sites were higher in patients receiving adequate HRT for more than 2 years compared with the patients treated for less than 6 months. A deficient vitamin D status was found in 43% of cases and it was prevalent in patients with shorter HRT.

DISCUSSION AND CONCLUSION

Early starting and adequate duration of HRT are related to bone health parameters in patients with congenital hypogonadotropic hypogonadism due to KS. Restoring vitamin D sufficiency might also be advisable in this condition.

What have we learned about GPER function in physiology and disease from knockout mice?

Estrogens, predominantly 17β-estradiol, exert diverse effects throughout the body in both normal and pathophysiology, during development and in reproductive, metabolic, endocrine, cardiovascular, nervous, musculoskeletal and immune systems. Estrogen and its receptors also play important roles in carcinogenesis and therapy, particularly for breast cancer. In addition to the classical nuclear estrogen receptors (ERα and ERβ) that traditionally mediate predominantly genomic signaling, the G protein-coupled estrogen receptor GPER has become recognized as a critical mediator of rapid signaling in response to estrogen. Mouse models, and in particular knockout (KO) mice, represent an important approach to understand the functions of receptors in normal physiology and disease. Whereas ERα KO mice display multiple significant defects in reproduction and mammary gland development, ERβ KO phenotypes are more limited, and GPER KO exhibit no reproductive deficits. However, the study of GPER KO mice over the last six years has revealed that GPER deficiency results in multiple physiological alterations including obesity, cardiovascular dysfunction, insulin resistance and glucose intolerance. In addition, the lack of estrogen-mediated effects in numerous tissues of GPER KO mice, studied in vivo or ex vivo, including those of the cardiovascular, endocrine, nervous and immune systems, reveals GPER as a genuine mediator of estrogen action. Importantly, GPER KO mice have also demonstrated roles for GPER in breast carcinogenesis and metastasis. In combination with the supporting effects of GPER-selective ligands and GPER knockdown approaches, GPER KO mice demonstrate the therapeutic potential of targeting GPER activity in diseases as diverse as obesity, diabetes, multiple sclerosis, hypertension, atherosclerosis, myocardial infarction, stroke and cancer.

The Effects of Androgens on Murine Cortical Bone Do Not Require AR or ERα Signaling in Osteoblasts and Osteoclasts

In men, androgens are critical for the acquisition and maintenance of bone mass in both the cortical and cancellous bone compartment. Male mice with targeted deletion of the androgen receptor (AR) in mature osteoblasts or osteocytes have lower cancellous bone mass, but no cortical bone phenotype. We have investigated the possibility that the effects of androgens on the cortical compartment result from AR signaling in osteoprogenitors or cells of the osteoclast lineage; or via estrogen receptor alpha (ERα) signaling in either or both of these two cell types upon conversion of testosterone to estradiol. To this end, we generated mice with targeted deletion of an AR or an ERα allele in the mesenchymal (AR(f/y);Prx1-Cre or ERα(f/f);Osx1-Cre) or myeloid cell lineage (AR(f/y);LysM-Cre or ERα(f/f);LysM-Cre) and their descendants. Male AR(f/y);Prx1-Cre mice exhibited decreased bone volume and trabecular number, and increased osteoclast number in the cancellous compartment. Moreover, they did not undergo the loss of cancellous bone volume and trabecular number caused by orchidectomy (ORX) in their littermate controls. In contrast, AR(f/y);LysM-Cre, ERα(f/f);Osx1-Cre, or ERα(f/f);LysM-Cre mice had no cancellous bone phenotype at baseline and lost the same amount of cancellous bone as their controls following ORX. Most unexpectedly, adult males of all four models had no discernible cortical bone phenotype at baseline, and lost the same amount of cortical bone as their littermate controls after ORX. Recapitulation of the effects of ORX by AR deletion only in the AR(f/y);Prx1-Cre mice indicates that the effects of androgens on cancellous bone result from AR signaling in osteoblasts-not on osteoclasts or via aromatization. The effects of androgens on cortical bone mass, on the other hand, do not require AR or ERα signaling in any cell type across the osteoblast or osteoclast differentiation lineage. Therefore, androgens must exert their effects indirectly by actions on some other cell type(s) or tissue(s).