Estrogen and bones after menopause: a reappraisal of data and future perspectives

Effect of Tai Chi exercise on bone health and fall prevention in postmenopausal women: a meta-analysis

BACKGROUND

The bone status of postmenopausal women is worsening. In fact, postmenopausal period is the high incidence stage of osteoporosis and falls. Notably, a recent study has pointed out that exercise can improve bone health in postmenopausal women. However, the effect of Tai Chi exercise on postmenopausal women is controversial. Therefore, a meta-analysis was designed to analyze the effect of Tai Chi exercise on bone health and fall prevention in postmenopausal women.

METHODS

The researches on Tai Chi improving the bone health of postmenopausal women before August 31, 2023 were collected from Chinese and English databases, such as PubMed, Embase, and Web of Science, etc. The risk of bias of the included studies was assessed using the Cochrane risk-of-bias tool for randomized trials. Besides, R software 4.3.1 was employed to analyze the effect sizes in the meta-analysis to summarize the impact of Tai Chi on vertebral bone mineral density, serum calcium, clinical balance scores, the number of falls, total falls, and health status scores in postmenopausal women.

RESULTS

There were 12 studies eventually included in this meta-analysis. A total of 1,272 postmenopausal women were involved, including 628 in the experimental group (intervention with Tai Chi exercise) and 644 in the control group (without any intervention). Briefly, postmenopausal women practicing Tai Chi presented a significant increase in vertebral bone density [standardized mean difference (SMD) = 0.37, 95% confidence interval (CI) (0.04-0.71), P = 0.03] and health status score [SMD = 0.25, 95% CI (0.01-0.49), P = 0.04]. In contrast, there were no significant differences for postmenopausal women between the two groups in terms of serum calcium [SMD = -0.01, 95% CI (-0.39, 0.36), P = 0.77], clinical balance [SMD = 0.17, 95% CI (-0.01, 0.46), P = 0.23], number of falls [SMD = -0.61, 95% CI (-1.24, 0.02), P = 0.06] and total falls [odds ratio = 0.35, 95% CI (0.11-1.12), P = 0.07].

CONCLUSION

Tai Chi exercise can improve the bone mineral density of postmenopausal women, thereby maintaining bone health. Hence, Tai Chi exercise is necessary to prevent osteoporosis.

The association of vasomotor symptoms with fracture risk and bone mineral density in postmenopausal women: a systematic review and meta-analysis of observational studies

BACKGROUND/AIMS

Vasomotor symptoms (VMS) adversely affect postmenopausal quality of life. However, their association with bone health has not been elucidated. This study aimed to systematically review and meta-analyze the evidence regarding the association of VMS with fracture risk and bone mineral density (BMD) in peri- and postmenopausal women.

METHODS

A literature search was conducted in PubMed, Scopus and Cochrane databases until 31 August 2023. Fracture, low BMD (osteoporosis/osteopenia) and mean change in lumbar spine (LS) and femoral neck (FN) BMD were assessed. The results are presented as odds ratio (OR) and mean difference (MD), respectively, with a 95% confidence interval (95% CI). The I2 index quantified heterogeneity.

RESULTS

Twenty studies were included in the qualitative and 12 in the quantitative analysis (n=49,659). No difference in fractures between women with and without VMS was found (n=5, OR 1.04, 95% CI 0.93-1.16, I2 16%). However, VMS were associated with low BMD (n=5, OR 1.54, 95% CI 1.42-1.67, I2 0%). This difference was evident for LS (MD -0.019 g/cm2, 95% CI -0.03 to -0.008, I2 85.2%), but not for FN BMD (MD -0.010 g/cm2, 95% CI -0.021 to 0.001, I2 78.2%). These results were independent of VMS severity, age and study design. When the analysis was confined to studies that excluded menopausal hormone therapy use, the association with BMD remained significant.

CONCLUSIONS

The presence of VMS is associated with low BMD in postmenopausal women, although it does not seem to increase fracture risk.

Antiosteoporosis therapy after discontinuation of menopausal hormone therapy: a systematic review

OBJECTIVE

Menopausal hormone therapy (MHT) has consistently shown a bone protective effect by reducing the risk of vertebral, non-vertebral, and hip fractures in postmenopausal women regardless of baseline fracture risk. However, the optimal sequential treatment after MHT discontinuation has not been determined. This systematic review aimed to obtain the best evidence regarding the effect of antiresorptive or osteoanabolic treatment on bone mineral density (BMD) and/or fracture risk following MHT.

METHODS

A comprehensive search was conducted in the PubMed, Scopus, and Cochrane databases up to October 31, 2023. Randomized-controlled trials (RCTs) and observational studies conducted in postmenopausal women were included.

RESULTS

After the exclusion of duplicates, 717 studies were identified. Two were eligible for qualitative analysis, one RCT and one retrospective cohort study. The RCT showed that alendronate 10 mg/day for 12 months further increased lumbar spine (LS) BMD by 2.3% following MHT and maintained femoral neck (FN) BMD in postmenopausal women (n = 144). It also decreased bone anabolic and resorption markers by 47 and 36%, respectively. In the retrospective study (n = 34), raloxifene 60 mg/day increased both LS and FN BMD at 12 months by 3 and 2.9%, respectively. No fractures were reported.

CONCLUSIONS

Antiresorptive therapy with either a bisphosphonate (i.e., alendronate) or raloxifene could be considered a sequential antiosteoporosis therapy after MHT withdrawal since they have been shown in studies to further increase BMD. However, no safe conclusions can be drawn from the existing literature.

The evolving roles of Wnt signaling in stem cell proliferation and differentiation, the development of human diseases, and therapeutic opportunities

The evolutionarily conserved Wnt signaling pathway plays a central role in development and adult tissue homeostasis across species. Wnt proteins are secreted, lipid-modified signaling molecules that activate the canonical (β-catenin dependent) and non-canonical (β-catenin independent) Wnt signaling pathways. Cellular behaviors such as proliferation, differentiation, maturation, and proper body-axis specification are carried out by the canonical pathway, which is the best characterized of the known Wnt signaling paths. Wnt signaling has emerged as an important factor in stem cell biology and is known to affect the self-renewal of stem cells in various tissues. This includes but is not limited to embryonic, hematopoietic, mesenchymal, gut, neural, and epidermal stem cells. Wnt signaling has also been implicated in tumor cells that exhibit stem cell-like properties. Wnt signaling is crucial for bone formation and presents a potential target for the development of therapeutics for bone disorders. Not surprisingly, aberrant Wnt signaling is also associated with a wide variety of diseases, including cancer. Mutations of Wnt pathway members in cancer can lead to unchecked cell proliferation, epithelial-mesenchymal transition, and metastasis. Altogether, advances in the understanding of dysregulated Wnt signaling in disease have paved the way for the development of novel therapeutics that target components of the Wnt pathway. Beginning with a brief overview of the mechanisms of canonical and non-canonical Wnt, this review aims to summarize the current knowledge of Wnt signaling in stem cells, aberrations to the Wnt pathway associated with diseases, and novel therapeutics targeting the Wnt pathway in preclinical and clinical studies.

Age at natural or surgical menopause, all-cause mortality, and lifespan among postmenopausal women in the United States

OBJECTIVE

This study investigated the association of age at natural menopause with or without undergoing hysterectomy and/or bilateral oophorectomy after menopause and age at surgical menopause with all-cause mortality and lifespan in postmenopausal women.

METHODS

The data stemmed from the National Health and Nutrition Examination Survey (NHANES) (1999-2018) and NHANES III (1988-1994), including 14,161 postmenopausal women over 40. Cox proportional hazard models were used to estimate unadjusted and adjusted hazard ratios (HRs) (95% confidence intervals [CIs]). We also used Cox proportional hazard models with penalized splines to depict the association between continuous age at menopause and all-cause mortality and nonparametric regression with smoothing splines to illustrate the association between age at menopause and lifespan in deceased participants.

RESULTS

The adjusted HRs (95% CIs) for age at natural menopause of <40, 40 to 44, and 55+ years in women without undergoing hysterectomy or bilateral oophorectomy after menopause were 1.48 (1.15-1.91), 1.16 (1.00-1.35), and 0.91 (0.77-1.07) compared with age at natural menopause of 45 to 54, respectively. The respective HRs (95% CIs) for age at surgical menopause were 1.39 (1.11-1.75), 1.09 (0.86-1.38), and 0.83 (0.53-1.32). However, no significant association was found between age at natural menopause and all-cause mortality among women undergoing hysterectomy and/or bilateral oophorectomy after menopause. When treated as continuous variables, age at natural menopause without undergoing hysterectomy or bilateral oophorectomy after menopause presented inverse and nonlinear associations with all-cause mortality, whereas age at surgical menopause was linearly inversely associated with all-cause mortality. The association between age at menopause and lifespan was linearly positive regardless of menopausal type.

CONCLUSION

Young age at menopause was associated with increased risks of all-cause mortality. The later menopause age was related to a longer lifespan.

Icariin, a phytoestrogen, exerts rapid estrogenic actions through crosstalk of estrogen receptors in osteoblasts

Icariin, a flavonoid glycoside derived from Epimedium brevicornum Maxim, exerts bone protective effects via estrogen receptors (ERs). This study aimed to investigate the role of ER-α66, ER-α36, and GPER in bone metabolism in osteoblasts following treatment with icariin. Human osteoblastic MG-63 cells and osteoblast-specific ER-α66 knockout mice were employed. The ERs crosstalk in the estrogenic action of icariin was evaluated in ER-α66-negative human embryonic kidney HEK293 cells. Icariin, like E2, regulated ER-α36 and GPER protein expression in osteoblasts by downregulating them and upregulating ER-α66. ER-α36 and GPER suppressed the actions of icariin and E2 in bone metabolism. However, the in vivo administration of E2 (2 mg/kg/day) or icariin (300 mg/kg/day) restored bone conditions in KO osteoblasts. ER-α36 and GPER expression increased significantly and rapidly activated and translocated in KO osteoblasts after treatment with E2 or icariin. ER-α36 overexpression in KO osteoblasts further promoted the OPG/RANKL ratio induced by E2 or icariin treatment. This study showed icariin and E2 elicit rapid estrogenic responses in bone through recruiting ER-α66, ER-α36, and GPER. Notably, in osteoblasts lacking ER-α66, ER-α36, and GPER mediate the estrogenic effects of icariin and E2, while in intact osteoblasts, ER-α36 and GPER act as negative regulators of ER-α66.

Review of mendelian randomization studies on age at natural menopause

Menopause marks the end of the reproductive phase of life. Based on epidemiological studies, abnormal age at natural menopause (ANM) is thought to contribute to a number of adverse outcomes, such as osteoporosis, cardiovascular disease, and cancer. However, the causality of these associations remains unclear. A powerful epidemiological method known as Mendelian randomization (MR) can be used to clarify the causality between ANM and other diseases or traits. The present review describes MR studies that included ANM as an exposure, outcome and mediator. The findings of MR analyses on ANM have revealed that higher body mass index, poor educational level, early age at menarche, early age at first live birth, early age at first sexual intercourse, and autoimmune thyroid disease appear to be involved in early ANM etiology. The etiology of late ANM appears to be influenced by higher free thyroxine 4 and methylene tetrahydrofolate reductase gene mutations. Furthermore, early ANM has been found to be causally associated with an increased risk of osteoporosis, fracture, type 2 diabetes mellitus, glycosylated hemoglobin, and the homeostasis model of insulin resistance level. In addition, late ANM has been found to be causally associated with an increased systolic blood pressure, higher risk of breast cancer, endometrial cancer, endometrioid ovarian carcinoma, lung cancer, longevity, airflow obstruction, and lower risk of Parkinson's disease. ANM is also a mediator for breast cancer caused by birth weight and childhood body size. However, due to the different instrumental variables used, some results of studies are inconsistent. Future studies with more valid genetic variants are needed for traits with discrepancies between MRs or between MR and other types of epidemiological studies.

The interplay between diabetes mellitus and menopause: clinical implications

The menopausal transition is an impactful period in women's lives, when the risk of cardiovascular disease is accelerated. Similarly, diabetes mellitus profoundly impacts cardiovascular risk. However, the interplay between menopause and diabetes mellitus has not been adequately studied. The menopausal transition is accompanied by metabolic changes that predispose to diabetes mellitus, particularly type 2 diabetes mellitus (T2DM), as menopause results in increased risk of upper body adipose tissue accumulation and increased incidence of insulin resistance. Equally, diabetes mellitus can affect ovarian ageing, potentially causing women with type 1 diabetes mellitus and early-onset T2DM to experience menopause earlier than women without diabetes mellitus. Earlier age at menopause has been associated with a higher risk of T2DM later in life. Menopausal hormone therapy can reduce the risk of T2DM and improve glycaemic control in women with pre-existing diabetes mellitus; however, there is not enough evidence to support the administration of menopausal hormone therapy for diabetes mellitus prevention or control. This Review critically appraises studies published within the past few years on the interaction between diabetes mellitus and menopause and addresses all clinically relevant issues, such as the effect of menopause on the development of T2DM, and the management of both menopause and diabetes mellitus.

Identifying potential causal effects of age at menopause: a Mendelian randomization phenome-wide association study

Age at natural menopause (ANM) is associated with a range of health-related traits, including bone health, female reproductive cancers, and cardiometabolic health. Our objective was to conduct a Mendelian randomization phenome-wide association study (MR-pheWAS) of ANM. We conducted a hypothesis-free analysis of the genetic risk score (GRS) for ANM with 18,961 health-related traits among 181,279 women in UK Biobank. We also stratified the GRS according to the involvement of SNPs in DNA damage response. We sought to replicate our findings in independent cohorts. We conducted a negative control MR-pheWAS among men. Among women, we identified potential effects of ANM on 221 traits (1.17% of all traits) at a false discovery rate (P value ≤ 5.83 × 10^-4), and 91 (0.48%) potential effects when using Bonferroni threshold (P value ≤ 2.64 × 10^-6). Our findings included 55 traits directly related to ANM (e.g. hormone replacement therapy, gynaecological conditions and menstrual conditions), and liver function, kidney function, lung function, blood-cell composition, breast cancer and bone and cardiometabolic health. Replication analyses confirmed that younger ANM was associated with HbA1c (adjusted mean difference 0.003 mmol/mol; 95% CI 0.001, 0.006 per year decrease in ANM), breast cancer (adjusted OR 0.96; 95% CI 0.95, 0.98), and bone-mineral density (adjusted mean difference - 0.05; 95% CI - 0.07, - 0.03 for lumbar spine). In men, 30 traits were associated with the GRS at a false discovery rate (P value ≤ 5.49 × 10^-6), and 11 potential effects when using Bonferroni threshold (P value ≤ 2.75 × 10^-6). In conclusion, our results suggest that younger ANM has potential causal effects on a range of health-related traits.

Bone Health in Patients with Dyslipidemias: An Underestimated Aspect

Beyond being aging-related diseases, atherosclerosis and osteoporosis share common pathogenetic pathways implicated in bone and vascular mineralization. However, the contributory role of dyslipidemia in this interplay is less documented. The purpose of this narrative review is to provide epidemiological evidence regarding the prevalence of bone disease (osteoporosis, fracture risk) in patients with dyslipidemias and to discuss potential common pathophysiological mechanisms linking osteoporosis and atherosclerosis. The effect of hypolipidemic therapy on bone metabolism is also discussed. Despite the high data heterogeneity and the variable quality of studies, dyslipidemia, mainly elevated total and low-density lipoprotein cholesterol concentrations, is associated with low bone mass and increased fracture risk. This effect may be mediated directly by the increased oxidative stress and systemic inflammation associated with dyslipidemia, leading to increased osteoclastic activity and reduced bone formation. Moreover, factors such as estrogen, vitamin D and K deficiency, and increased concentrations of parathyroid hormone, homocysteine and lipid oxidation products, can also contribute. Regarding the effect of hypolipidemic medications on bone metabolism, statins may slightly increase BMD and reduce fracture risk, although the evidence is not robust, as it is for omega-3 fatty acids. No evidence exists for the effects of ezetimibe, fibrates, and niacin. In any case, more prospective studies are needed further to elucidate the association between lipids and bone strength.

USP25 Expression in Peripheral Blood Mononuclear Cells Is Associated With Bone Mineral Density in Women

Osteoporosis is the most common metabolic bone disease in postmenopausal women. As precursors of osteoclasts, peripheral blood mononuclear cells are accessible and considered suitable models for studying osteoporosis pathology. Ubiquitination is a crucial protein degradation system in bone metabolism. The aim of this study was to identify potential ubiquitination-related genes in PBMCs that are related to osteoporosis pathogenesis. Therefore, we performed an integrated analysis of osteoporosis-related microarray datasets. With the obtained ubiquitination-related gene set, weighted gene coexpression network analysis was performed. The results showed that genes in the turquoise module were correlated with menopause, and 48 genes were identified as hub genes. A differential expression analysis revealed 43 differentially expressed genes between pre- and postmenopausal samples. After integrating the information on differentially expressed menopause-related genes, we found that several members of the ubiquitin-specific protease (USP) family (USP1, USP7, USP9X, USP16, and USP25) were highly expressed in samples from postmenopausal female and that, USP25 expression was significantly higher in low-BMD samples than in high-BMD samples among samples from premenopausal subjects (p = 0.0013) and among all samples (p = 0.013). Finally, we verified the protein expression of USP25 in PBMCs by performing Western blot analysis, which yielded results consistent with the aforementioned results. Moreover, by assessing GTEx datasets, we found that USP25 expression was highly correlated with TRAF6 expression in whole blood (p < 0.001). We also tested the protein expression levels of TRAF6 in PBMCs and found that it was positively correlated with USP25 expression (p = 0.036). Our results reveal that the ubiquitin-specific protease family may play important roles in menopause and that USP25 is related to osteoporosis pathogenesis.

Biased and allosteric modulation of bone cell-expressing G protein-coupled receptors as a novel approach to osteoporosis therapy

On the cellular level, osteoporosis (OP) is a result of imbalanced bone remodeling, in which osteoclastic bone resorption outcompetes osteoblastic bone formation. Currently available OP medications include both antiresorptive and bone-forming drugs. However, their long-term use in OP patients, mainly in postmenopausal women, is accompanied by severe side effects. Notably, the fundamental coupling between bone resorption and formation processes underlies the existence of an undesirable secondary outcome that bone anabolic or anti-resorptive drugs also reduce bone formation. This drawback requires the development of anti-OP drugs capable of selectively stimulating osteoblastogenesis and concomitantly reducing osteoclastogenesis. We propose that the application of small synthetic biased and allosteric modulators of bone cell receptors, which belong to the G-protein coupled receptors (GPCR) family, could be the key to resolving the undesired anti-OP drug selectivity. This approach is based on the capacity of these GPCR modulators, unlike the natural ligands, to trigger signaling pathways that promote beneficial effects on bone remodeling while blocking potentially deleterious effects. Under the settings of OP, an optimal anti-OP drug should provide fine-tuned regulation of downstream effects, for example, intermittent cyclic AMP (cAMP) elevation, preservation of Ca²⁺ balance, stimulation of osteoprotegerin (OPG) and estrogen production, suppression of sclerostin secretion, and/or preserved/enhanced canonical β-catenin/Wnt signaling pathway. As such, selective modulation of GPCRs involved in bone remodeling presents a promising approach in OP treatment. This review focuses on the evidence for the validity of our hypothesis.

Predictable increase in female reproductive window: A simple model connecting age of reproduction, menopause, and longevity

With the ever-increasing lifespan along with societal changes, women can marry and procreate later than in previous centuries. However, pathogenic genetic variants segregating in the population can lead to female subfertility or infertility well before the average age of normal menopause, leading to counter-selection of such deleterious alleles. In reviewing this field, we speculate that a logical consequence would be the later occurrence of menopause and the extension of women's reproductive lifespan. We illustrate this point with a simple model that applies to other variants that contribute to female infertility, including epigenetic variation. We also consider the effect of medical interventions and lifestyle.