Impact of estrogens on atherosclerosis and bone in the apolipoprotein E-deficient mouse model

Teriparatide administration is osteoanabolic but does not impact atherosclerotic plaque calcification and progression in a mouse model of menopause

Menopause exacerbates osteoporosis and increases the risk of atherosclerotic plaque rupture, leading to cardiovascular mortality. Osteoporotic women are increasingly treated with teriparatide (TPTD, 1-34 parathyroid hormone), one of the few treatments that stimulate bone formation. Despite the fact that atherosclerotic plaque calcification is a hallmark of plaque development, the impact of TPTD administration on plaque calcification remain unclear. In this context, we sought to determine the effects of TPTD administration on atherosclerosis in ovariectomized (OVX) apolipoprotein E deficient mice (ApoE-/-), as a model of postmenopausal osteoporosis. OVX ApoE-/- mice, fed a high fat, high cholesterol diet to induce atherosclerosis, received either vehicle or TPTD daily injections (40 μg/kg/d) for 4 or 10 weeks, at which points plaques are respectively weakly and heavily calcified. After sacrifice, bone remodeling was evaluated by serum markers and bone histomorphometry. Bone architectural parameters were measured by μCT. Aortic plaques were analyzed histologically, and their calcification with von Kossa staining and the calcium tracer Osteosense. Plaque inflammation and calcification markers were measured by RT-qPCR. Intermittent TPTD increased bone volume in OVX mice, due to a higher stimulation of bone formation relatively to bone resorption. These effects were not accompanied by changes in serum levels of cholesterol, triglycerides, glucose or insulin. TPTD neither significantly affected aortic plaque size, inflammation, and calcification, even if it slightly increased vascular smooth muscle cell transdifferentiation into calcifying cells. In conclusion, TPTD exhibits osteoanabolic effects in OVX ApoE-/- mice, without significantly influencing atherosclerotic plaque progression or calcification in the short term.

Combining Raman Microspectroscopy and X-ray Microcomputed Tomography for the Study of Bone Quality in Apolipoprotein-Deficient Animal Models

Raman microspectroscopy and X-ray microcomputed tomography (micro-CT) were used for assessment of the quality of the femur and tibia bones in apolipoprotein-deficient mice compared to control littermates. The cortical and trabecular bone was investigated separately. Raman spectra revealed no differences in the bioapatite-to-collagenous matrix ratio of the cortical bone. The quantities of calcium and collagen, which were measured using atomic absorption spectrometry and thermogravimetric analysis, respectively, were also found to be equal in the two groups. Density and morphometric parameters, which were measured using micro-CT, verified the cortical mineral stability. Bone quality indices were measured using Raman spectra. A decreased collagen crosslink (trivalent-to-divalent) ratio revealed delayed maturation of the collagen network. Such a decrease has been reported in the literature to be connected to decreased bone strength. For the trabecular bone, micro-CT revealed severe osteoporosis in the knock-out group, which was evident from a decreased mineral density, trabecular thickness and increased bone surface/volume ratio. The trabecular bone was not accessible for Raman spectroscopy. According to these results, the cortical and trabecular femur bone is expected to exhibit proneness to fracturing, each for a different reason. A combination of the two techniques was regarded as necessary for an overall assessment of bone quality.

Hypothalamic astrocytic-BMAL1 regulates energy homeostasis in a sex-dependent manner

Here, we demonstrate that hypothalamic astrocytic BMAL1 computes cyclic metabolic information to optimize energetic resources in a sexually dimorphic manner. Knockdown of BMAL1 in female astrocytes leads to negative energy balance and alters basal metabolic cycles without affecting circadian locomotor activity. Thus, astrocytic BMAL1 contributes to the control of energy balance through the modulation of the metabolic rate, hepatic and white adipose tissue lipogenesis, and the activity of brown adipose tissue. Importantly, most of these alterations are specific to hypothalamic astrocytic BMAL1. Moreover, female mice with BMAL1 knockdown in astrocytes exhibited a "male-like" metabolic obese phenotype when fed a high-fat diet. Overall, our results suggest a sexually dimorphic effect of astrocytic BMAL1 on the regulation of energy homeostasis, which may be of interest in the physiopathology of obesity and related comorbidities.

Positive association of high-density lipoprotein cholesterol with lumbar and femoral neck bone mineral density in postmenopausal women

OBJECTIVE

Experimental studies suggest that lipids affect bone metabolism. We aimed to elucidate whether lipid levels are associated with bone mineral density (BMD) in a cohort of postmenopausal women.

DESIGN

A cross-sectional study of participants in the Chronic Ailment Reduction after MENopause (CARMEN) cohort. Women underwent assessment of clinical and analytical parameters, including fasting lipid levels. BMD was assessed at both lumbar spine and hip. Homogeneity in the cohort was optimized by filtering out a series of confounding variables with a known impact on bone.

MAIN OUTCOME MEASURES

Association of BMD at lumbar spine and femoral neck with lipid levels.

RESULTS

A total of 667 of the 1304 screened women were analyzed. A strong correlation was revealed between total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), and high-density lipoprotein cholesterol (HDL-C) in univariate analysis. Multivariate analysis detected a significant positive association of HDL-C with BMD at both spine (p = 0.007) and femoral neck (p = 0.013). Other independent predictors of spine BMD were years since menopause (ysm, negatively associated), and body mass index (BMI) and estradiol, both positively associated with BMD. The other independent variables in the femoral neck were ysm and glucose (negatively associated) and BMI, estradiol, and phosphate, all positively associated with BMD.

CONCLUSION

Levels of HDL-C, but not TC, LDL-C or triglycerides, were positively associated with BMD at both the lumbar spine and femoral neck in a homogeneous cohort of postmenopausal women.

Are Oxidative Stress and Inflammation Mediators of Bone Loss Due to Estrogen Deficiency? A Review of Current Evidence

Osteoporosis is one of the major health issues associated with menopause-related estrogen deficiency. Various reports suggest that the hormonal changes related to menopausal transition may lead to the derangement of redox homeostasis and ultimately oxidative stress. Estrogen deficiency and oxidative stress may enhance the expression of genes involved in inflammation. All these factors may contribute, in synergy, to the development of postmenopausal osteoporosis. Previous studies suggest that estrogen may act as an antioxidant to protect the bone against oxidative stress, and as an antiinflammatory agent in suppressing pro-inflammatory and pro-osteoclastic cytokines. Thus, the focus of the current review is to examine the relationship between estrogen deficiency, oxidative stress and inflammation, and the impacts of these phenomena on skeletal health in postmenopausal women.

Associations between the lipid profile and the lumbar spine bone mineral density and trabecular bone score in elderly Iranian individuals participating in the Bushehr Elderly Health Program: a population-based study

We hypothesized that the lipid profile or dyslipidemia may have an influence on the bone mineral density and bone microstructure in an elderly Iranian population. The results of this study showed some significant associations between the serum lipid levels and the lumbar spine and femoral areal bone mineral densities and the trabecular bone score (TBS).

PURPOSE

Serum lipid abnormalities are possible risk factors for cardiovascular diseases and osteoporosis. Our aim was to evaluate the associations between the lipid profile and the areal bone mineral density (aBMD) and trabecular bone score in an elderly Iranian population.

METHODS

The study subjects included 2426 elderly women and men participating in the second stage of the Bushehr Elderly Health program, a population-based prospective cohort study. The aBMDs of the lumbar spine and femoral neck and the lumbar spine texture were measured using dual-energy X-ray absorptiometry and the TBS algorithm, respectively. The associations between the lipid profiles and the aBMDs and TBSs were examined using multivariable linear regression analyses stratified by sex and adjusted for potential confounders.

RESULTS

In men, we found negative correlations between the lumbar spine aBMD and TBS and the total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C) levels (TC: p < 0.001 and p < 0.006, HDL-C: p = 0.002 and p = 0.004, and LDL-C: p < 0.001 and p < 0.009, respectively). However, only the HDL-C level was negatively associated with the aBMD in women (p = 0.016). A positive and statistically significant correlation was found between the serum triglyceride (TG) level and the aBMD in the women (p < 0.001). The TG level and the TBS were not statistically significantly correlated in either sex, and the TBS was not correlated with any of the lipid values in women.

CONCLUSION

The results of this study showed some significant but generally weak associations between the lipid profile and the aBMD. The associations that were significant for both the men and the women included positive associations between the TG level and the femoral neck aBMD, as well as the HDL-C level and the femoral neck and lumbar spine aBMDs.

Apolipoprotein A-1 regulates osteoblast and lipoblast precursor cells in mice

Imbalances in lipid metabolism affect bone homeostasis, altering bone mass and quality. A link between bone mass and high-density lipoprotein (HDL) has been proposed. Indeed, it has been recently shown that absence of the HDL receptor scavenger receptor class B type I (SR-B1) causes dense bone mediated by increased adrenocorticotropic hormone (ACTH). In the present study we aimed at further expanding the current knowledge as regards the fascinating bone-HDL connection studying bone turnover in apoA-1-deficient mice. Interestingly, we found that bone mass was greatly reduced in the apoA-1-deficient mice compared with their wild-type counterparts. More specifically, static and dynamic histomorphometry showed that the reduced bone mass in apoA-1(-/-) mice reflect decreased bone formation. Biochemical composition and biomechanical properties of ApoA-1(-/-) femora were significantly impaired. Mesenchymal stem cell (MSC) differentiation from the apoA-1(-/-) mice showed reduced osteoblasts, and increased adipocytes, relative to wild type, in identical differentiation conditions. This suggests a shift in MSC subtypes toward adipocyte precursors, a result that is in line with our finding of increased bone marrow adiposity in apoA-1(-/-) mouse femora. Notably, osteoclast differentiation in vitro and osteoclast surface in vivo were unaffected in the knock-out mice. In whole bone marrow, PPARγ was greatly increased, consistent with increased adipocytes and committed precursors. Further, in the apoA-1(-/-) mice marrow, CXCL12 and ANXA2 levels were significantly decreased, whereas CXCR4 were increased, consistent with reduced signaling in a pathway that supports MSC homing and osteoblast generation. In keeping, in the apoA-1(-/-) animals the osteoblast-related factors Runx2, osterix, and Col1a1 were also decreased. The apoA-1(-/-) phenotype also included augmented CEPBa levels, suggesting complex changes in growth and differentiation that deserve further investigation. We conclude that the apoA-1 deficiency generates changes in the bone cell precursor population that increase adipoblast, and decrease osteoblast production resulting in reduced bone mass and impaired bone quality in mice.

Advances in high-density lipoprotein physiology: surprises, overturns, and promises

Emerging evidence strongly supports that changes in the HDL metabolic pathway, which result in changes in HDL proteome and function, appear to have a causative impact on a number of metabolic disorders. Here, we provide a critical review of the most recent and novel findings correlating HDL properties and functionality with various pathophysiological processes and disease states, such as obesity, type 2 diabetes mellitus, nonalcoholic fatty liver disease, inflammation and sepsis, bone and obstructive pulmonary diseases, and brain disorders.

Bone remodeling markers and bone metastases: From cancer research to clinical implications

Bone metastasis is a frequent finding in the natural history of several types of cancers. However, its anticipated risk, diagnosis and response to therapy are still challenging to assess in clinical practice. Markers of bone metabolism are biochemical by-products that provide insight into the tumor-bone interaction, with potential to enhance the clinical management of patients with bone metastases. In fact, these markers had a cornerstone role in the development of bone-targeted agents; however, its translation to routine practice is still unclear, as reflected by current international guidelines. In this review, we aimed to capture several of the research and clinical translational challenges regarding the use of bone metabolism markers that we consider relevant for future research in bone metastasis.

Osteoporosis and cardiovascular disease: an update

Osteoporosis (OP) and cardiovascular diseases (CVD) are the most important causes of mortality and morbility in the elderly. Lots of studies showed a correlation between bone loss and cardiovascular risk mediated by the vascular calcification. The relationship between OP and CVD could be firstly explained by their common risk factors such as age, smoking, alcohol consumption, physical activity and menopause. However, other different hypotheses were proposed to clarify this link. Multiple factors, for example bone morphogenetic proteins, osteoprotegerin, receptor activator of nuclear factor κB ligand, parathyroid hormone, phosphate, oxidized lipids and vitamins D and K seemed to be involved in both conditions, indicating a possible common pathophysiologic mechanism. We review and discuss the available data describing this association. Further studies are necessary to better investigate similarities between OP and CVD.