Lipid oxidation products have opposite effects on calcifying vascular cell and bone cell differentiation. A possible explanation for the paradox of arterial calcification in osteoporotic patients

Bone and fat relationships in postadolescent black females: a pQCT study

Despite adolescent black females experiencing the highest rates of obesity, the effect of excess fat mass on bone structure and strength in this population is unknown. Our findings in postadolescent black females suggest that excess weight in the form of fat mass may adversely influence cortical bone structure and strength.

INTRODUCTION

Although adolescent obesity has been associated with reduced bone structure and strength in white females, this relationship has not been studied in adolescent black females, a population experiencing the highest rates of obesity. Our objective was to compare bone structure and strength between postadolescent black females with normal and high levels of adiposity.

METHODS

Black females with ≤ 32% body fat were classified as normal body fat (NF; n = 33, aged 19.3 ± 1.3 years); females exceeding this cutoff were classified as high body fat (HF; n = 15, aged 19.0 ± 1.1 years). Using peripheral quantitative computed tomography, tibial and radial bones were scanned at the 4% (trabecular) and 20% (cortical) sites from the distal metaphyses. Fat-free soft-tissue mass (FFST) and %body fat were assessed by dual-energy X-ray absorptiometry.

RESULTS

After controlling for either FFST or body weight, the HF vs. NF group had lower total cross-sectional area (CSA; 9-17%), cortical CSA (6-15%), and strength-strain index (SSI; 13-24%) at the cortical site of the tibia (all p < 0.05). At the cortical site of the radius, the HF vs. NF group had lower total CSA (14%, p = 0.03), cortical CSA (9%, p = 0.04), and SSI (15%, p = 0.07) after control for body weight. There were no group differences in either the FFST-adjusted cortical bone values at the radius or in the trabecular bone parameters (body weight- or FFST-adjusted) at the tibia and radius.

CONCLUSIONS

Consistent with our adiposity and bone data in late-adolescent white females, our findings in black females entering adulthood also suggest that obesity may adversely influence cortical bone strength.

Bicuspid aortic valve disease: the role of oxidative stress in Lrp5 bone formation

The bicuspid aortic valve is a common congenital cardiac anomaly, having a prevalence of 0.9% to 1.37% in the general population and a male preponderance ratio of 2:1. The recognition of a bicuspid aortic valve is clinically relevant because of its association with aortic stenosis or regurgitation, aortic aneurysm or dissection, and infective endocarditis. Although some patients with a bicuspid aortic valve may go undetected without clinical complications for a lifetime, the vast majority will require intervention, most often surgery, at some point. In fact, the natural history of bicuspid aortic valve is that of valve calcification and progressive stenosis that typically occur at a faster rate than in tricuspid aortic valves. This pattern of presentation supports the hypothesis that shear stress in patients with congenitally abnormal aortic valves may contribute to an earlier leaflet calcification. However, there is emerging research data showing that the valve calcification process might have a similar pathophysiologic process to that of vascular atherosclerosis. This review focuses on the current knowledge of the cellular mechanisms of bicuspid aortic valve.

Bisphosphonate Use and Prevalence of Valvular and Vascular Calcification in Women MESA (The Multi-Ethnic Study of Atherosclerosis)

OBJECTIVES

the aim of this study was to determine whether nitrogen-containing bisphosphonate (NCBP) therapy is associated with the prevalence of cardiovascular calcification.

BACKGROUND

cardiovascular calcification correlates with atherosclerotic disease burden. Experimental data suggest that NCBP might limit cardiovascular calcification, which has implications for disease prevention.

METHODS

the relationship of NCBP use to the prevalence of aortic valve, aortic valve ring, mitral annulus, thoracic aorta, and coronary artery calcification (AVC, AVRC, MAC, TAC, and CAC, respectively) detected by computed tomography was assessed in 3,710 women within the MESA (Multi-Ethnic Study of Atherosclerosis) with regression modeling.

RESULTS

Analyses were age-stratified, because of a significant interaction between age and NCBP use (interaction p values: AVC p < 0.0001; AVRC p < 0.0001; MAC p = 0.002; TAC p < 0.0001; CAC p = 0.046). After adjusting for age; body mass index; demographic data; diabetes; smoking; blood pressure; cholesterol levels; and statin, hormone replacement, and renin-angiotensin inhibitor therapy, NCBP use was associated with a lower prevalence of cardiovascular calcification in women ≥ 65 years of age (prevalence ratio: AVC 0.68 [95% confidence interval (CI): 0.41 to 1.13]; AVRC 0.65 [95% CI: 0.51 to 0.84]; MAC 0.54 [95% CI: 0.33 to 0.93]; TAC 0.69 [95% CI: 0.54 to 0.88]; CAC 0.89 [95% CI: 0.78 to 1.02]), whereas calcification was more prevalent in NCBP users among the 2,181 women <65 years of age (AVC 4.00 [95% CI: 2.33 to 6.89]; AVRC 1.92 [95% CI: 1.42 to 2.61]; MAC 2.35 [95% CI: 1.12 to 4.84]; TAC 2.17 [95% CI: 1.49 to 3.15]; CAC 1.23 [95% CI: 0.97 to 1.57]).

CONCLUSIONS

among women in the diverse MESA cohort, NCBPs were associated with decreased prevalence of cardiovascular calcification in older subjects but more prevalent cardiovascular calcification in younger ones. Further study is warranted to clarify these age-dependent NCBP effects.

Tumor necrosis factor-α accelerates the calcification of human aortic valve interstitial cells obtained from patients with calcific aortic valve stenosis via the BMP2-Dlx5 pathway

Calcific aortic valve stenosis (CAS) is the most frequent heart valve disease in the elderly, accompanied by valve calcification. Tumor necrosis factor-α (TNF-α), a pleiotropic cytokine secreted mainly from macrophages, has been detected in human calcified valves. However, the role of TNF-α in valve calcification remains unclear. To clarify whether TNF-α accelerates the calcification of aortic valves, we investigated the effect of TNF-α on human aortic valve interstitial cells (HAVICs) obtained from patients with CAS (CAS group) and with aortic regurgitation or aortic dissection having a noncalcified aortic valve (control group). HAVICs (2 × 10(4)) were cultured in a 12-well dish in Dulbecco's modified Eagle's medium with 10% fetal bovine serum. The medium containing TNF-α (30 ng/ml) was replenished every 3 days after the cells reached confluence. TNF-α significantly accelerated the calcification and alkaline phosphatase (ALP) activity of HAVICs from CAS but not the control group after 12 days of culture. Furthermore, gene expression of calcigenic markers, ALP, bone morphogenetic protein 2 (BMP2), and distal-less homeobox 5 (Dlx5) were significantly increased after 6 days of TNF-α treatment in the CAS group but not the control group. Dorsomorphin, an inhibitor of mothers against decapentaplegic homologs (Smads) 1/5/8 phosphorylation, significantly inhibited the enhancement of TNF-α-induced calcification, ALP activity, Smad phosphorylation, and Dlx5 gene expression of HAVICs from the CAS group. These results suggest that HAVICs from the CAS group have greater sensitivity to TNF-α, which accelerates the calcification of aortic valves via the BMP2-Dlx5 pathway.

The involvement of oxidative stress in the mechanisms of damaging cadmium action in bone tissue: a study in a rat model of moderate and relatively high human exposure

It was investigated whether cadmium (Cd) may induce oxidative stress in the bone tissue in vivo and in this way contribute to skeleton damage. Total antioxidative status (TAS), antioxidative enzymes (glutathione peroxidase, superoxide dismutase, catalase), total oxidative status (TOS), hydrogen peroxide (H(2)O(2)), lipid peroxides (LPO), total thiol groups (TSH) and protein carbonyl groups (PC) as well as Cd in the bone tissue at the distal femoral epiphysis and femoral diaphysis of the male rats that received drinking water containing 0, 5, or 50mg Cd/l for 6 months were measured. Cd, depending on the level of exposure and bone location, decreased the bone antioxidative capacity and enhanced its oxidative status resulting in oxidative stress and oxidative protein and/or lipid modification. The treatment with 5 and 50mg Cd/l decreased TAS and activities of antioxidative enzymes as well as increased TOS and concentrations of H(2)O(2) and PC at the distal femur. Moreover, at the higher exposure, the concentration of LPO increased and that of TSH decreased. The Cd-induced changes in the oxidative/antioxidative balance of the femoral diaphysis, abundant in cortical bone, were less advanced than at the distal femur, where trabecular bone predominates. The results provide evidence that, even moderate, exposure to Cd induces oxidative stress and oxidative modifications in the bone tissue. Numerous correlations noted between the indices of oxidative/antioxidative bone status, and Cd accumulation in the bone tissue as well as indices of bone turnover and bone mineral status, recently reported by us (Toxicology 2007, 237, 89-103) in these rats, allow for the hypothesis that oxidative stress is involved in the mechanisms of damaging Cd action in the skeleton. The paper is the first report from an in vivo study indicating that Cd may affect bone tissue through disorders in its oxidative/antioxidative balance resulting in oxidative stress.

Arterial calcification is driven by RAGE in Enpp1-/- mice

BACKGROUND/AIMS

Ectopic osteochondral differentiation, driven by ENPP1-catalyzed generation of the chondrogenesis and calcification inhibitor inorganic pyrophosphate (PP(i)), promotes generalized arterial calcification of infancy. The multiligand receptor for advanced glycation end-products (RAGE), which promotes atherosclerosis and diabetic cardiovascular and renal complications, also mediates chondrocyte differentiation in response to RAGE ligand calgranulins such as S100A11. Here, we tested RAGE involvement in ENPP1 deficiency-associated arterial calcification.

METHODS

Because ectopic artery calcification in Enpp1-/- mice is P(i)-dependent and mediated by PP(i) deficiency, in vitro studies on effects of S100A11 and RAGE on mouse aortic explants were conducted using exogenous P(i), as well as alkaline phosphatase to hydrolyze ambient PP(i).

RESULTS

S100A11 induced cartilage-specific collagen IX/XI expression and calcification dependent on RAGE in mouse aortic explants that was inhibited by the endogenous RAGE signaling inhibitor soluble RAGE (sRAGE). Enpp1-/- aortic explants demonstrated decreased P(i)-stimulated release of sRAGE, and increased calcification and type IX/XI collagen expression that were suppressed by exogenous sRAGE and by Rage knockout. Last, Rage knockout suppressed spontaneous aortic calcification in situ in Enpp1-/- mice.

CONCLUSION

Cultured Enpp1-/- aortic explants have decreased P(i)-stimulated release of sRAGE, and RAGE promotes ectopic chondrogenic differentiation and arterial calcification in Enpp1-/- mice.

Bone density and hyperlipidemia: the T-lymphocyte connection

Osteoporosis, which contributes to morbidity and mortality, often coexists with cardiovascular disease, especially atherosclerosis. We have reported recently that in vitro exposure of human T-lymphocytes to oxidized lipids induced expression of a key osteoclastogenic cytokine, receptor activator of NF-κB ligand (RANKL). Our previous studies have shown that mice fed an atherogenic high-fat diet developed osteopenia and that bone marrow preosteoclasts from these hyperlipidemic mice have increased osteoclastic potential. To investigate the role of T-lymphocytes in the diet-induced bone loss, C57BL/6 mice were fed either chow or a high-fat diet, and bone parameters and T-lymphocyte activation were assessed at 6 and 11 months. Consistent with our previous findings, peripheral quantitative computed tomographic (pQCT) analysis showed that mice in the high-fat group had lower bone mineral content than mice in the chow group. Furthermore, histomorphometric analysis showed decreased structural parameters in the high-fat group. Coculture studies showed that bone marrow cells isolated from the high-fat group, which contained increased levels of activated memory T-lymphocytes compared with bone marrow cells from the chow mice, supported osteoclastic differentiation of RAW 264.7 cells. Additionally, RANKL expression was upregulated significantly in the T-lymphocytes isolated from the bone marrow of the high-fat group. Splenic T-lymphocytes isolated from the high-fat group also had increased expression of transcripts for the receptor for oxidized lipids (LOX-1) as well as for inflammatory and osteoclastogenic cytokines, including RANKL, interleukin 6 (IL-6), tumor necrosis factor α (TNF-α), IL-1β, and interferon γ (IFN-γ). Together these findings suggest that T-lymphocytes play a key role in the osteoclastogenesis induced by a high-fat diet and may contribute to the bone loss associated with diet-induced osteopenia.

The bone-vascular axis in chronic kidney disease

PURPOSE

This review highlights the most recent publications addressing the relationship between bone and vascular calcification in patients with chronic and end-stage kidney disease.

RECENT FINDINGS

The relatively new term 'chronic kidney disease-mineral bone disorder' reflects the growing reach of chronic kidney disease research into the realm of systems physiology, involving a triad of renal, skeletal, and vascular tissues. Recent studies address underlying mechanisms of the bone and vascular complications of chronic kidney disease and point to a variety of biochemical factors, including phosphatonins (fibroblast growth factor-23, matrix extracellular phosphoglycoprotein), bone morphogenetic protein 7, osteoprotegerin, matrix GLA protein, ectonucleotide pyrophosphatase/phosphodiesterase 1, alkaline phosphatase, and lipid oxidation products. Studies also demonstrate that agents used for treatment of one component of the triad often act on the other components of the triad - beneficially or adversely. These findings emphasize the importance of avoiding the subspecialty, single organ viewpoint when treating individual components of chronic kidney disease-mineral bone disorder.

SUMMARY

The consistent synchrony among chronic kidney disease, aortic calcification, and bone loss offers clues to underlying mechanisms for the systemic abnormalities.

Relationship between visceral adiposity and bone mineral density in Korean adults

The objective of the study was to investigate the relationship between visceral and subcutaneous adiposity measured by computed tomography and bone mineral density (BMD) and to identify the metabolic factors associated with BMD. We studied 461 subjects recruited from the health-care center at Severance Hospital, Yonsei University College of Medicine. Multivariate regression analyses were conducted to examine the cross-sectional associations between body composition-related or metabolic parameters and BMD. After adjusting for body weight and other confounders, visceral fat area had an inverse association with BMD in men (beta = -0.133, P = 0.049 for lumbar spine; beta = -0.135, P = 0.037 for femoral neck; beta = -0.179, P = 0.005 for total hip) and women (beta = -0.424, P < 0.001 for lumbar spine; beta = -0.302, P = 0.005 for femoral neck; beta = -0.274, P = 0.014 for total hip). However, the subcutaneous fat area showed no statistically significant relationship with BMD at most sites. Among the metabolic parameters, HDL cholesterol was positively associated with BMD, while LDL cholesterol was negatively associated with BMD in men. In women, total and LDL cholesterol were negatively associated with BMD at the lumbar spine. We conclude that visceral adiposity is inversely associated with BMD after adjusting for confounders and that metabolic factors may partly contribute to this inverse relation.

PKA-induced receptor activator of NF-kappaB ligand (RANKL) expression in vascular cells mediates osteoclastogenesis but not matrix calcification

Vascular calcification is a predictor of cardiovascular mortality and is prevalent in patients with atherosclerosis and chronic renal disease. It resembles skeletal osteogenesis, and many bone cells as well as bone-related factors involved in both formation and resorption have been localized in calcified arteries. Previously, we showed that aortic medial cells undergo osteoblastic differentiation and matrix calcification both spontaneously and in response to PKA agonists. The PKA signaling pathway is also involved in regulating bone resorption in skeletal tissue by stimulating osteoblast-production of osteoclast regulating cytokines, including receptor-activator of nuclear κB ligand (RANKL) and interleukins. Therefore, we investigated whether PKA activators regulate osteoclastogenesis in aortic smooth muscle cells (SMC). Treatment of murine SMC with the PKA agonist forskolin stimulated RANKL expression at both mRNA and protein levels. Forskolin also stimulated expression of interleukin-6 but not osteoprotegerin (OPG), an inhibitor of RANKL. Consistent with these results, osteoclastic differentiation was induced when monocytic preosteoclasts (RAW264.7) were cocultured with forskolin-treated aortic SMC. Oxidized phospholipids also slightly induced RANKL expression in T lymphocytes, another potential source of RANKL in the vasculature. Because previous studies have shown that RANKL treatment alone induces matrix calcification of valvular and vascular cells, we next examined whether RANKL mediates forskolin-induced matrix calcification by aortic SMC. RANKL inhibition with OPG had little or no effect on osteoblastic differentiation and matrix calcification of aortic SMC. These findings suggest that, as in skeletal tissues, PKA activation induces bone resorptive factors in the vasculature and that aortic SMC calcification specifically induced by PKA, is not mediated by RANKL.

Regulatory mechanisms in vascular calcification

In the past decade, the prevalence, significance, and regulatory mechanisms of vascular calcification have gained increasing recognition. Over a century ago, pathologists recognized atherosclerotic calcification as a form of extraskeletal ossification. Studies are now identifying the mechanism of this remarkable process as a recapitulation of embryonic endochondral and membranous ossification through phenotypic plasticity of vascular cells that function as adult mesenchymal stem cells. These embryonic developmental programs, involving bone morphogenetic proteins and potent osteochondrogenic transcription factors, are triggered and modulated by a variety of inflammatory, metabolic, and genetic disorders, particularly hyperlipidemia, chronic kidney disease, diabetes, hyperparathyroidism, and osteoporosis. They are also triggered by loss of powerful inhibitors, such as fetuin A, matrix Gla protein, and pyrophosphate, which ordinarily restrict biomineralization to skeletal bone. Teleologically, soft-tissue calcification might serve to create a wall of bone to sequester noxious foci such as chronic infections, parasites, and foreign bodies. This Review focuses on atherosclerotic and medial calcification. The capacity of the vasculature to produce mineral in culture and to produce de novo, vascularized, trabecular bone and cartilage tissue, even in patients with osteoporosis, should intrigue investigators in tissue engineering and regenerative biology.

Oxidized low density lipoprotein inhibits phosphate signaling and phosphate-induced mineralization in osteoblasts. Involvement of oxidative stress

BACKGROUND

It is well admitted that oxidized LDL (OxLDL) plays a major role in the generation and progression of atherosclerosis. Since atherosclerosis is often accompanied by osteoporosis, the effects of OxLDL on phosphate-induced osteoblast mineralization were investigated.

METHODS

Calcium deposition, expression of osteoblast markers and inorganic phosphate (Pi) signaling were determined under OxLDL treatment.

RESULTS

OxLDL, within the range of 10-50 μg protein/ml, inhibited Pi-induced UMR106 rat osteoblast mineralization. In parallel, the expression of Cbfa1/Runx2 transcription factor was decreased, and the intracellular level of the osteoblast marker osteopontin (OPN) was reduced. The extracellular level of another marker, receptor activator of nuclear factor kappa B ligand (RANKL), was also diminished. OxLDL inhibited Pi signaling via ERK/JNK kinases and AP1/CREB transcription factors. OxLDL triggered the generation of reactive oxygen species (ROS), either in the absence or presence of Pi. Furthermore, the effects of OxLDL on Pi-induced mineralization, generation of ROS and extracellular level OPN were reproduced by the lipid extract of the particle, whereas the antioxidant vitamin E prevented them.

CONCLUSIONS

This work demonstrates that OxLDL, by generation of an oxidative stress, inhibits of Pi signaling and impairs Pi-induced osteoblast differentiation.

GENERAL SIGNIFICANCE

This highlights the role of OxLDL in bone remodeling and in degenerative disorders other than atherosclerosis, especially in osteoporosis.

Associations of long-term and early adult atherosclerosis risk factors with aortic and mitral valve calcium

OBJECTIVES

To determine the association of long-term exposure to atherosclerosis risk factors with valvular calcification.

BACKGROUND

Traditional atherosclerosis risk factors have been associated with aortic and mitral valve calcium in cross-sectional studies, but long-term prospective data are lacking.

METHODS

This was a prospective, community-based cohort study with 27-year follow-up (median follow-up 26.9 years; range 23.1 to 29.6 years). Participants from the Framingham Offspring Study (n = 1,323, enrolled between 1971 and 1975, mean age at enrollment 34 +/- 9 years; 52% women) underwent cardiac multidetector computed tomography assessment between 2002 and 2005. Associations between the long-term average of each cardiovascular risk factor and valve calcium were estimated using logistic regression.

RESULTS

Aortic valve calcium was present in 39% of participants and mitral valve calcium in 20%. In multivariable models, the odds ratio for aortic valve calcium associated with every SD increment in long-term mean total cholesterol was 1.74 (p < 0.0001); with every SD increment in high-density lipoprotein cholesterol, it was 0.77 (p = 0.002); and with every 9 cigarettes smoked per day, it was 1.23 (p = 0.002). Associations of similar magnitude were seen for mitral valve calcium. The mean of 3 serum C-reactive protein measurements was associated with mitral valve calcium (odds ratio: 1.29 per SD increment in C-reactive protein levels; p = 0.002). A higher Framingham risk score in early adulthood (40 years age or younger) was associated with increased prevalence and severity of aortic valve calcium measured 3 decades later.

CONCLUSIONS

Exposure to multiple atherosclerotic risk factors starting in early to mid-adulthood is associated with aortic and mitral valve calcium. Studies evaluating early risk factor modification to reduce the burden of valve disease are warranted.

Generation and biological activities of oxidized phospholipids

Glycerophospholipids represent a common class of lipids critically important for integrity of cellular membranes. Oxidation of esterified unsaturated fatty acids dramatically changes biological activities of phospholipids. Apart from impairment of their structural function, oxidation makes oxidized phospholipids (OxPLs) markers of "modified-self" type that are recognized by soluble and cell-associated receptors of innate immunity, including scavenger receptors, natural (germ line-encoded) antibodies, and C-reactive protein, thus directing removal of senescent and apoptotic cells or oxidized lipoproteins. In addition, OxPLs acquire novel biological activities not characteristic of their unoxidized precursors, including the ability to regulate innate and adaptive immune responses. Effects of OxPLs described in vitro and in vivo suggest their potential relevance in different pathologies, including atherosclerosis, acute inflammation, lung injury, and many other conditions. This review summarizes current knowledge on the mechanisms of formation, structures, and biological activities of OxPLs. Furthermore, potential applications of OxPLs as disease biomarkers, as well as experimental therapies targeting OxPLs, are described, providing a broad overview of an emerging class of lipid mediators.

D-003 does not possess oestrogenic potential in-vivo: findings of the uterotrophic assay

D-003 is a mixture of long-chain fatty acids purified from sugarcane wax that inhibits both cholesterol synthesis prior to mevalonate formation, and lipid peroxidation. D-003 has been shown to prevent bone loss and bone resorption in ovariectomized rats, and significantly improves bone resorption markers in postmenopausal women with reduced bone mineral density. As hormone-replacement therapy, D-003 displays cholesterol-lowering and anti-resorptive effects. We have studied its potential oestrogenic activity in-vivo using the uterotrophic assay. Rats were randomly distributed into five groups: a sham-operated group and four groups of ovariectomized rats, one treated with vehicle, one with D-003 (50 mg kg−1), one with oestradiol benzoate (30 μg kg−1) and one with D-003 (50 mg kg−1) plus oestradiol benzoate (30 μg kg−1). Treatments were administered for 14 days. Ovariectomy decreased the values of relative uterus weight, epithelium cell height and endometrial thickness compared with sham-operated rats, and these effects were all significantly reduced with oestradiol benzoate, but not with D-003. Concurrent administration of D-003 and oestradiol benzoate had statistically similar effects on all variables as oestradiol benzoate alone. In conclusions, D-003 orally given at 50 mg kg−1, a dose that prevents bone loss and bone resorption in ovariectomized rats, did not display oestrogenic/anti-oestrogenic activity in-vivo, as assessed in the uterotrophic assay.

Age-modification of lipoprotein, lipid, and lipoprotein ratio-associated risk for coronary artery calcium (from the Multi-Ethnic Study of Atherosclerosis [MESA])

Although abnormal lipoproteins and lipoprotein ratios are powerful risk factors for clinical cardiovascular events, these associations are stronger in younger than in older subjects. Whether age modifies the relation of lipoproteins and lipoprotein ratios to the relative risk of subclinical cardiovascular disease (CVD), as assessed by coronary artery calcium (CAC) scores, has not been examined in a contemporary, multiethnic cohort. We performed multivariate relative risk regression analyses to determine the relative risks for associations of lipoproteins and lipoprotein ratios with prevalent CAC in participants in Multi-Ethnic Study of Atherosclerosis (MESA). The participants were community-dwelling adults aged 45 to 84 years without clinically apparent CVD at baseline. We excluded those taking lipid-lowering therapy (15%) and stratified the results by decades of age. A total of 5,092 participants met the inclusion criteria. In the fully adjusted models, per SD of low-density lipoprotein, the age-stratified, adjusted relative risk for CAC was 1.17 (95% confidence interval [CI] 1.07 to 1.28) for those aged 45 to 84 years but was 1.05 (95% CI 1.01 to 1.10) for those aged 75 to 84 years (p-interaction = 0.12). The relative risk per SD of total/high-density lipoprotein cholesterol ratio was 1.20 (95% CI 1.12 to 1.29) for those aged 45 to 54 years but only 1.04 (95% CI 1.00 to 1.09) for those aged 75 to 84 years (p-interaction <0.001). The lipoproteins levels and lipoprotein ratios were associated with increased relative risks for CAC across all age categories. However, these associations were markedly attenuated by age. In conclusion, abnormal lipoprotein levels in middle age are a powerful risk factor for early atherosclerosis, as manifested by prevalent CAC.

Ferritin ferroxidase activity: a potent inhibitor of osteogenesis

Hemochromatosis is a known cause of osteoporosis, and iron overload has deleterious effects on bone. Although iron overload and its association with osteoporosis has long been recognized, the pathogenesis and exact role of iron have been undefined. Bone is an active tissue with constant remodeling capacity. Osteoblast (OB) development and maturation are under the influence of core binding factor alpha-1 (CBF-alpha1), which induces expression of OB-specific genes, including alkaline phosphatase, an important enzyme in early osteogenesis, and osteocalcin, a noncollagenous protein deposited within the osteoid. This study investigates the mechanism by which iron inhibits human OB activity, which in vivo may lead to decreased mineralization, osteopenia, and osteoporosis. We demonstrate that iron-provoked inhibition of OB activity is mediated by ferritin and its ferroxidase activity. We confirm this notion by using purified ferritin H-chain and ceruloplasmin, both known to possess ferroxidase activity that inhibited calcification, whereas a site-directed mutant of ferritin H-chain lacking ferroxidase activity failed to provide any inhibition. Furthermore, we are reporting that such suppression is not restricted to inhibition of calcification, but OB-specific genes such as alkaline phosphatase, osteocalcin, and CBF-alpha1 are all downregulated by ferritin in a dose-responsive manner. This study corroborates that iron decreases mineralization and demonstrates that this suppression is provided by iron-induced upregulation of ferritin. In addition, we conclude that inhibition of OB activity, mineralization, and specific gene expression is attributed to the ferroxidase activity of ferritin.

A radiographic study on the associations of age and prevalence of vertebral fractures with abdominal aortic calcification in Japanese postmenopausal women and men

The purpose of the present study was to determine the associations of age and history of non- and low-traumatic fractures with the severity of abdominal aortic calcification in Japanese postmenopausal women and men. Four hundred and one Japanese persons (24 men and 377 postmenopausal women, mean age: 73.8 years) for whom thoracic and lumbar spine radiographs had been obtained to evaluate their posture prior to patient participation in a fall-prevention exercise program were enrolled. The associations of sex, age, history of hip fracture, prevalence of vertebral fracture, and spondylosis grade (the Nathan degree) with the severity of abdominal aortic calcification (length of calcification, as evaluated according to the number of vertebral bodies) were analyzed. Nine subjects (2.2%) had a history of hip fracture, and 221 (55.1%) had at least one prevalent vertebral fracture. Two hundred and sixty-seven subjects (66.6%) had first-degree spondylosis. Age and the number of prevalent vertebral fractures, but not sex, history of hip fracture, or spondylosis grade, were significantly associated with the severity of abdominal aortic calcification. The present study confirmed that age and the number of vertebral fractures were associated with the severity of abdominal aortic calcification in Japanese postmenopausal women and men.

Tumor necrosis factor-alpha increases alkaline phosphatase expression in vascular smooth muscle cells via MSX2 induction

Vascular calcification is implicated in many diseases including atherosclerosis and diabetes. Tumor necrosis factor-alpha (TNF-alpha) has been shown to promote vascular calcification both in vitro and in vivo. However, the molecular mechanism of TNF-alpha-mediated vascular calcification has not yet been fully defined. Therefore, in this study, we aimed to investigate whether MSX2 acts as a crucial regulator in TNF-alpha-induced vascular calcification and to define the regulatory mechanism of MSX2 induction in human vascular smooth muscle cells (VSMCs). TNF-alpha increased the expression of osteogenic marker genes including RUNX2, osterix, alkaline phosphatase (ALP), and bone sialoprotein, and it also promoted matrix mineralization in VSMCs. In addition, TNF-alpha enhanced MSX2 expression in a dose- and time-dependent manner. MSX2 over-expression alone induced ALP expression, whereas knockdown of MSX2 with small interfering RNA completely blocked TNF-alpha-induced ALP expression. New protein synthesis was dispensable for MSX2 induction by TNF-alpha, and the inhibition of NF-kappaB by BAY-11-7082 or by dominant negative IkappaBalpha abolished the TNF-alpha-directed induction of MSX2 expression. However, inhibition of NADPH oxidase did not affect MSX2 expression. In conclusion, our study suggests that TNF-alpha directly induces MSX2 expression through the NF-kappaB pathway, which in turn induces expression of ALP, a key molecule in mineralization, in VSMCs.

Bone mineral density, arterial stiffness, and coronary atherosclerosis in healthy postmenopausal women

OBJECTIVE

The aim of this study was to assess the correlation between bone mineral density (BMD), arterial stiffness, and coronary atherosclerosis in healthy postmenopausal women.

METHODS

We performed a retrospective review of 152 postmenopausal women who visited the health promotion center for a routine checkup, after excluding participants who had factors affecting BMD and coronary artery disease. BMD was evaluated by dual-energy x-ray absorptiometry in the lumbar spine and femur. Arterial stiffness was measured by brachial-ankle pulse wave velocity (baPWV), and coronary atherosclerosis was assessed by 64-row multidetector computed tomography.

RESULTS

Women with osteoporosis had a significantly higher baPWV than those in the osteopenia and normal BMD groups. Higher baPWV was also associated with the presence of atherosclerosis. The baPWV was significantly positively correlated with age, systolic blood pressure, diastolic blood pressure, and neutrophil to lymphocyte ratio and negatively correlated with femur BMD. The optimum predictive value of baPWV in coronary atherosclerosis was estimated using the receiver operating characteristic curve. A cutoff of 1,506 cm/second would give a sensitivity of 83.3% and specificity of 82.9%. A higher overall risk for coronary atherosclerosis emerges with higher baPWV levels (>1,500 cm/s) after controlling for age and cardiovascular risk factors.

CONCLUSIONS

Arterial stiffness by measuring baPWV can be a useful independent predictor for coronary atherosclerosis. In addition, our results suggest that postmenopausal women with osteoporosis should be considered for further evaluation of coronary atherosclerosis.

Association between low bone mass and aortic valve sclerosis in Koreans

BACKGROUND

Osteoporosis or low bone mass has been associated with cardiovascular disease and calcification in several clinical studies. However, few studies have assessed the relationship between bone mass and valvular calcification. The aim of this study was to evaluate the relationship between low bone mass and aortic valve sclerosis in Korean men and women.

METHODS

A total of 211 men and 117 women were included in this study. Each subject's bone mineral density (BMD) was measured with dual-energy X-ray absorptiometry, and aortic valve sclerosis was assessed using transthoracic echocardiography. Association between low bone mass and aortic valve sclerosis was assessed with multivariate logistic regression analysis in this cross-sectional study.

RESULTS

Of 328 total subjects enrolled in this study, 50 men (23.7%) and 18 women (15.4%) were found to have aortic valve sclerosis. The mean (+/-SD) BMD T-scores were -0.5 (+/-0.8) in men and -0.9 (+/-1.0) in women. After adjusting for covariates, only women with aortic valve sclerosis had significantly lower BMD T-scores than those without it. Multivariate logistic regression analysis showed that age, smoking and hypertension were independently associated with increased risk of aortic valve sclerosis in men. In women, however, logistic regression analysis showed that BMD T-score, as well as age, was an independent variable for aortic valve sclerosis. We also found that a T-score of less than -1.5 was significantly associated with increased risk of aortic valve sclerosis in women compared to normal T-scores.

CONCLUSION

Low bone mass might be independently associated with increased risk of aortic valve sclerosis in women, but not in men. Women with low bone mass should be further evaluated for the presence of aortic valve sclerosis and related cardiovascular diseases.

Regulation of interleukin-6 expression in osteoblasts by oxidized phospholipids

Epidemiological evidence suggests that cardiovascular disease is associated with osteoporosis, independent of age. Bone resorptive surface is increased in mice on a high-fat diet, and osteoclastic differentiation of bone marrow preosteoclasts is promoted by oxidized phospholipids. Because osteoclastic differentiation requires cytokines produced by osteoblasts, we hypothesized that the stimulatory mechanism of oxidized phospholipids is via induction of osteoclast-regulating cytokines in osteoblasts. To investigate the effects of oxidized phospholipids on expression of such cytokines, murine calvarial preosteoblasts, MC3T3-E1, were treated with oxidized 1-palmitoyl-2-arachidonyl-sn-glycero-3-phosphocholine (ox-PAPC), an active component of oxidized lipoproteins. Results showed that ox-PAPC increased expression of interleukin-6 (IL-6) and tumor necrosis factor-alpha. IL-6 expression was also elevated in calvarial tissues from hyperlipidemic but not in wild-type mice. Ox-PAPC also induced IL-6 protein levels in both MC3T3-E1 and primary calvarial cells. Promoter-reporter assay analysis showed that ox-PAPC, but not PAPC, induced murine IL-6 promoter activity. Effects of ox-PAPC on IL-6 expression and the promoter activity were attenuated by H89, a PKA inhibitor. Analysis of deletion and mutant IL-6 promoter constructs suggested that CAAT/enhancer binding protein (C/EBP) partly mediates the ox-PAPC effects. Taken together, the data suggest that oxidized phospholipids induce IL-6 expression in osteoblasts in part via C/EBP.

Lower bone mineral density is associated with higher coronary calcification and coronary plaque burdens by multidetector row coronary computed tomography in pre- and postmenopausal women

OBJECTIVES

There is growing evidence for the association between bone mineral density (BMD) and vascular calcification, which is related to cardiovascular disease. Coronary multidetector row computed tomography (MDCT) is a noninvasive tool developed to evaluate coronary status precisely. We used MDCT to evaluate this association.

DESIGN AND PATIENTS

Eight hundred and fifteen subjects received routine checkups. After excluding subjects with factors affecting bone metabolism and cardiovascular disease, 467 subjects were analysed.

MEASUREMENTS

Coronary calcification was measured with MDCT and BMD was measured with dual X-ray absorptiometry (DXA).

RESULTS

The BMD of the femur and the lumbar spine (L-spine) were negatively associated with the coronary calcium score (CCS) after adjusting for age in women but not in men. This inverse correlation was stronger in women with a longer time since menopause (r = -0.35 at femur, postmenopausal women vs. r = -0.10 at femur, premenopausal women, P < 0.05), and it was stronger at the femur than in the L-spine (r = -0.35 at femur vs. r = -0.16 at L-spine, P < 0.01). The relationship was also stronger in postmenopausal women with osteoporosis and osteopaenia than in women with normal BMD. The lower BMD was associated with higher coronary plaque burdens and multidiseased coronary vessels in both men and women (P < 0.01).

CONCLUSIONS

Increased CCS and subclinical atherosclerosis of plaque burdens as revealed by MDCT was associated with a low BMD in all women, independent of cardiovascular risk factors and age.

Evolution of coronary artery calcifications following kidney transplantation: relationship with osteoprotegerin levels

We prospectively assessed the evolution of coronary artery calcification (CAC) and osteoprotegerin (OPG) levels after renal transplantation (RT). Eighty-three recipients were followed-up prospectively during 1 year. Blood was collected before (baseline) and after RT for determination of mineral metabolism parameters including OPG. CAC was measured by multidetector computed tomography at transplantation (baseline) and 1 year later. Progression of CAC was defined as a difference between the follow-up square-root transformed volume (SRV) and the baseline SRV >or= 2.5. By multivariate analysis, baseline OPG level, age and low LDL levels were significantly associated with baseline CAC. RT was accompanied by mineral metabolism improvement with a decrease of OPG from 955 [395-5652] to 527 [217-1818] pg/mL and parathyroid hormone from 94 [1-550] to 62 [16-410] pg/mL. Thirty-one percent of patients did not exhibit CAC at baseline. CAC diminished in 14.5%, stabilized in 59.2% and progressed in 26.3% of patients. Baseline CAC was associated with progression (OR 2.92 [1.02-8.36]). No significant association was found between OPG and CAC progression despite a higher baseline OPG level in progressors (1046 [456-3285]) vs. non-progressors (899 [396-5952] pg/mL). CAC at baseline, but not 1 year after RT, is independently associated with baseline OPG; posttransplant CAC progression is predicted by baseline CAC score.

Low bone mineral density is related to atherosclerosis in postmenopausal Moroccan women

BACKGROUND

Some studies have implicated several possible metabolic linkages between osteoporosis and vascular calcification, including estrogen deficiency, vitamin D excess, vitamin K deficiency and lipid oxidation products. Nevertheless, it remains unclear whether osteoporosis and atherosclerosis are related to each other or are independent processes, both related to aging. The aim of this cross-sectional study was to evaluate the correlation between arterial thickening and bone status in a sample of apparently healthy Moroccan women.

METHODS

Seventy-two postmenopausal women were studied. All patients were without secondary causes that might affect bone density. Bone status was assessed by bone mineral density (BMD) in lumbar spine and all femoral sites. Arterial wall thickening was assessed by intima-media thickness (IMT) in carotid artery (CA) and femoral artery (FA). Prevalent plaques were categorized into four groups ranging from low echogenicity to high echogenicity.

RESULTS

The mean age was 59.2 +/- 8.3 years. 84.7% had at least one plaque. By Spearman Rank correlation, CA IMT was negatively correlated to Femoral total BMD (r = -0.33), Femoral neck BMD (r = -0.23), Ward triangle BMD (r = -0.30) and Trochanter BMD (r = -0.28) while there was no association with lumbar BMD. In multiple regression analysis, CA IMT emerged as an independent factor significantly associated with all femoral sites BMD after adjusting of confounding factors. FA IMT failed to be significantly associated with both Femoral and Lumbar BMD. No significant differences between echogenic, predominantly echogenic, predominantly echolucent and echolucent plaques groups were found concerning lumbar BMD and all femoral sites BMD CONCLUSION: Our results demonstrate a negative correlation between bone mineral density (BMD) qnd carotid intima-media thickness (IMT) in postmenopausal women, independently of confounding factors. We suggest that bone status should be evaluated in patients with vascular disease to assess whether preventive or therapeutic intervention is necessarry.

Ethnic-specific risks for atherosclerotic calcification of the thoracic and abdominal aorta (from the Multi-Ethnic Study of Atherosclerosis)

The aims of this study were to (1) determine the association between ethnicity and thoracic aortic calcium (TAC) and abdominal aortic calcium (AAC) and (2) investigate associations between cardiovascular disease (CVD) risk factors and TAC and AAC. Participants were 1,957 men and women enrolled in the Multi-Ethnic Study of Atherosclerosis who had computed tomographic scans of the chest and abdomen. These scans were obtained at the same clinic visit and calcium scores were computed using the Agatston method. Regression analyses were conducted using relative risk regression. Mean age was 65 years and 50% were women. Forty percent were white, 26% Hispanic, 21% African-American, and 13% Chinese. Whites had the highest prevalence of AAC (80%), which was significantly higher than Hispanics (68%, p <0.001), African-Americans (63%, p <0.001), and Chinese (74%, p = 0.029). Similarly, whites had the highest prevalence of TAC (42%), which was significantly higher than in Hispanics (30%, p <0.01) and African-Americans (27%, p <0.001) but was not significantly different from that in Chinese (38%). Compared to whites and after adjustment for age, gender, body mass index, hypertension, diabetes, dyslipidemia, smoking, and family history of CVD, Hispanics and African-Americans, but not Chinese-Americans, had a significantly lower risk for the presence of any AAC or any TAC. In these models, diabetes, smoking, and dyslipidemia had stronger associations with AAC, whereas hypertension was stronger for TAC. In conclusion, compared to whites, African-Americans and Hispanics, but not Chinese, have evidence of less atherosclerosis in the thoracic and abdominal aortas, which does not appear to be accounted for by traditional CVD risk factors.

Bone mineral density and atherosclerosis: the Multi-Ethnic Study of Atherosclerosis, Abdominal Aortic Calcium Study

CONTEXT

Molecular and cell biology studies have demonstrated an association between bone and arterial wall disease, but the significance of a population-level association is less clear and potentially confounded by inability to account for shared risk factors.

OBJECTIVE

To test population-level associations between atherosclerosis types and bone integrity.

MAIN OUTCOME MEASURES

Volumetric trabecular lumbar bone mineral density (vBMD), ankle-brachial index (ABI), intima-media thickness (IMT) of the common carotid (CCA-IMT) and internal carotid (ICA-IMT) arteries, and carotid plaque echogenicity.

DESIGN, SETTING AND PARTICIPANTS

A random subset of participants from the Multi-Ethnic Study of Atherosclerosis (MESA) assessed between 2002 and 2005.

RESULTS

904 post-menopausal female (62.4 years; 62% non-white; 12% ABI <1; 17% CCA-IMT >1mm; 33% ICA-IMT >1mm) and 929 male (61.4 years; 58% non-white; 6% ABI <1; 25% CCA-IMT >1mm; 40% ICA-IMT >1mm) were included. In serial, sex-specific regression models adjusting for age, ethnicity, body mass index, dyslipidemia, hypertension, smoking, alcohol consumption, diabetes, homocysteine, interleukin-6, sex hormones, and renal function, lower vBMD was associated with lower ABI in men (p for trend <0.01) and greater ICA-IMT in men (p for trend <0.02). CCA-IMT was not associated with vBMD in men or women. Carotid plaque echogenicity was independently associated with lower vBMD in both men (trend p=0.01) and women (trend p<0.04). In all models, adjustment did not materially affect results.

CONCLUSIONS

Lower vBMD is independently associated with structural and functional measures of atherosclerosis in men and with more advanced and calcified carotid atherosclerotic plaques in both sexes.

Advanced oxidation protein products induce vascular calcification by promoting osteoblastic trans-differentiation of smooth muscle cells via oxidative stress and ERK pathway

Vascular calcification is an actively regulated process similar to bone formation. Advanced oxidation protein products (AOPPs) have been demonstrated to be novel markers of oxidant-mediated protein damage. The present study investigated the role of AOPPs in inducing osteoblastic trans-differentiation and calcification of smooth muscle cells in vitro. We found that AOPPs directly increased the calcium deposition and expression of core binding factor-alpha1 (CBF-alpha1) and osteopontin (OPN) and significantly decreased SM-alpha-actin expression in human aortic smooth muscle cells (HASMCs). AOPPs increased intracellular oxidative stress, which was inhibited by vitamin E. Vitamin E also inhibited AOPP-induced calcium content and osteoblast differentiation of HASMCs. Furthermore, the inhibitor of ERK significantly suppressed the effects of AOPPs on calcification and osteoblast marker expression. These findings suggest that AOPPs induce vascular calcification by promoting osteoblast differentiation of smooth muscle cells via oxidative stress and ERK pathway.

Oxidized lipids enhance RANKL production by T lymphocytes: implications for lipid-induced bone loss

Osteoporosis is a systemic disease that is associated with increased morbidity, mortality and health care costs. Whereas osteoclasts and osteoblasts are the main regulators of bone homeostasis, recent studies underscore a key role for the immune system, particularly via activation-induced T lymphocyte production of receptor activator of NFkappaB ligand (RANKL). Well-documented as a mediator of T lymphocyte/dendritic cell interactions, RANKL also stimulates the maturation and activation of bone-resorbing osteoclasts. Given that lipid oxidation products mediate inflammatory and metabolic disorders such as osteoporosis and atherosclerosis, and since oxidized lipids affect several T lymphocyte functions, we hypothesized that RANKL production might also be subject to modulation by oxidized lipids. Here, we show that short term exposure of both unstimulated and activated human T lymphocytes to minimally oxidized low density lipoprotein (LDL), but not native LDL, significantly enhances RANKL production and promotes expression of the lectin-like oxidized LDL receptor-1 (LOX-1). The effect, which is also observed with 8-iso-Prostaglandin E2, an inflammatory isoprostane produced by lipid peroxidation, is mediated via the NFkappaB pathway, and involves increased RANKL mRNA expression. The link between oxidized lipids and T lymphocytes is further reinforced by analysis of hyperlipidemic mice, in which bone loss is associated with increased RANKL mRNA in T lymphocytes and elevated RANKL serum levels. Our results suggest a novel pathway by which T lymphocytes contribute to bone changes, namely, via oxidized lipid enhancement of RANKL production. These findings may help elucidate clinical associations between cardiovascular disease and decreased bone mass, and may also lead to new immune-based approaches to osteoporosis.

The 'valvulo-metabolic' risk in calcific aortic valve disease

Calcific aortic stenosis (AS) has been considered a degenerative and unmodifiable process resulting from aging and 'wear and tear' of the aortic valve. Over the past decade, studies in the field of epidemiology, molecular biology and lipid metabolism have highlighted similarities between vascular atherosclerosis and calcific AS. In particular, work from the Quebec Heart Institute and from that of others has documented evidence of valvular infiltration by oxidized low-density lipoproteins and the presence of inflammatory cells, along with important tissue remodelling in valves explanted from patients with AS. Recent studies have also emphasized the role of visceral obesity in the development and progression of AS. In addition, visceral obesity, with its attendant metabolic complications, commonly referred to as the metabolic syndrome, has been associated with degenerative changes in bioprosthetic heart valves. The purpose of the present review is to introduce the concept of 'valvulo-metabolic risk' and to provide an update on the recent and important discoveries regarding the pathogenesis of heart valve diseases in relation to obesity, and to discuss how these novel mechanisms might translate into clinical practice.

Vascular calcification: the killer of patients with chronic kidney disease

Cardiovascular complications are the leading cause of death in patients with chronic kidney disease (CKD). Vascular calcification is a common complication in CKD, and investigators have demonstrated that the extent and histoanatomic type of vascular calcification are predictors of subsequent vascular mortality. Although research efforts in the past decade have greatly improved our knowledge of the multiple factors and mechanisms involved in vascular calcification in patients with kidney disease, many questions remain unanswered. No longer can we accept the concept that vascular calcification in CKD is a passive process resulting from an elevated calcium-phosphate product. Rather, as a result of the metabolic insults of diabetes, dyslipidemia, oxidative stress, uremia, and hyperphosphatemia, "osteoblast-like" cells form in the vessel wall. These mineralizing cells as well as the recruitment of undifferentiated progenitors to the osteochondrocyte lineage play a critical role in the calcification process. Important transcription factors such as Msx 2, osterix, and RUNX2 are crucial in the programming of osteogenesis. Thus, the simultaneous increase in arterial osteochondrocytic programs and reduction in active cellular defense mechanisms creates the "perfect storm" of vascular calcification seen in ESRD. Innovative clinical studies addressing the combined use of inhibitors that work on vascular calcification through distinct molecular mechanisms, such as fetuin-A, osteopontin, and bone morphogenic protein 7, among others, will be necessary to reduce significantly the accrual of vascular calcifications and cardiovascular mortality in kidney disease. In addition, the roles of oxidative stress and inflammation on the fate of smooth muscle vascular cells and their function deserve further translational investigation.

Osteoporosis and cardiovascular risk among premenopausal women in Sri Lanka

We examined the association between bone mineral density (BMD) and cardiovascular risk in a group of premenopausal women selected from the Southern province of Sri Lanka. One hundred six previously healthy premenopausal volunteers (aged 30-54 yr) were recruited by open invitations. Subjects with previous history of diabetes, hypertension, epilepsy, chronic renal or liver disease, hyperlipidemia, ischemic heart disease, endocrine diseases, or prolonged inflammatory conditions were excluded. Subjects who were taking medications that can affect bone density, blood sugar, serum lipids, or blood pressure (BP) were also excluded. Women with the history of previous fractures were not excluded. BMDs in the spine, hip, and total body (TB) were measured using a Hologic Discovery scanner (Hologic Inc, Bedford, MA). BP, fasting glucose, and fasting lipids were also measured. Independent of body mass index (BMI) and age, TB bone mineral content (BMC) and spine BMD showed inverse and significant correlations with total cholesterol (TC), low density cholesterol, and the ratio between TC and high density lipoprotein cholesterol (r ranged from -0.24 to -0.27, p<0.05 for all). The highest mean lipid levels were seen among the women in the lowest third of spine BMD, whereas women in the upper third of spine BMD had the lowest lipid levels. The number of women with metabolic syndrome in the 3 tirtiles of spine BMD was not significantly different. Fasting glucose or BP had no association with either BMD or BMC. In conclusion, our data demonstrates an association, independent of age and BMI, between BMD and BMC or lipid levels among previously healthy, premenopausal women. This may explain the high cardiovascular risk seen in women with osteoporosis in old age.

HDL3 reduces the association and modulates the metabolism of oxidized LDL by osteoblastic cells: a protection against cell death

Oxidized low density lipoproteins (OxLDL) are known to promote atherosclerosis, but it is only recently that OxLDL have been associated with alterations of the functions of bone-forming osteoblasts and osteoporosis. Although high density lipoproteins (HDL) are recognized for their anti-atherogenic action, there is less information about their ability to protect against osteoporosis. Therefore, we investigated the capacity of HDL3 to prevent the cell death induced by OxLDL in human osteoblastic cells. Simultaneous exposure of the cells to HDL3 and OxLDL abolished the reduction of cell viability monitored by MTT activity measurement and the induction of apoptosis determined by annexin V staining indicating that HDL3 prevent the apoptosis of osteoblasts induced by OxLDL. This protection correlated with the displacement by HDL3 of OxLDL association to osteoblasts, signifying that OxLDL binding and/or internalization are/is necessary for their cytotoxic effects. We also found that exposition of osteoblastic cells to HDL3 prior to incubation with OxLDL reduced cell death and preserved the lysosomal integrity. This protection was correlated with an increase of SR-BI expression, a modification of OxLDL metabolism with less global uptake of OxLDL and greater selective uptake of cholesterol from OxLDL. These results strongly suggest that, as for atherosclerosis, HDL may exert beneficial actions on bone metabolism.

Association between serum cholesterol and bone mineral density

BACKGROUND

Hypercholesterolaemia has been associated with low bone mineral density (BMD) in some but not all studies.

OBJECTIVES

To examine the influence of age, menopausal status and hormone replacement therapy (HRT) on the relationship between serum cholesterol and BMD in women.

PATIENTS AND MEASUREMENTS

497 female participants (age range 20-81) comprising 224 premenopausal and 273 postmenopausal women (156 on HRT and 117 no HRT) underwent measurements of bone mineral density (BMD) and serum lipid profile.

RESULTS

Total serum cholesterol (TC) and low density lipoprotein (LDL) levels were higher and lumbar spine BMD was lower in postmenopausal women not taking HRT compared to those taking HRT. TC and LDL were negatively associated with BMD at all measured sites among postmenopausal women not taking HRT in univariate regression analysis (all p<0.05). High density lipoprotein (HDL) had inverse relationships with BMD at all sites in pre-menopausal women and those who were exposed to HRT (p<0.05). In fully adjusted regression models the relationships between TC and BMD remained significant at the lumbar spine and whole body (p<0.05) and between LDL and lumbar spine BMD only (p<0.05). For subjects in the other groups, no significant associations between TC or LDL and BMD were found. Significant interactions between total cholesterol and LDL levels with HRT were detected among post-menopausal women in the regression analyses (all p<0.05). No such interactions were found between HDL levels and HRT.

CONCLUSION

There is a modest inverse relationship between lumbar spine and whole body BMD and serum TC and LDL levels and in post-menopausal women and HDL in pre-menopausal women. HRT use appears to modify these relationships. The mechanisms of this relationship require further study.

Superoxide production: a procalcifying cell signalling event in osteoblastic differentiation of vascular smooth muscle cells exposed to calcification media

Recent studies showed that hydrogen peroxide (H(2)O(2)) enhanced bone markers expression in vascular smooth muscle cells (VSMCs) implicated in osteoblastic differentiation. This study aimed at investigating the role of NAD(P)H oxidase in vascular calcification processes. A7r5 rat VSMCs were incubated with beta-glycerophosphate (10 mm) or uremic serum to induce a diffuse mineralization. H(2)O(2) production by VSMCs was determinated by chemiluminescence. NAD(P)H oxidase sub-unit (p22(phox)), Cbfa-1, ERK phosphorylation and bone alkaline phosphatase (ALP) expressions were measured by Western blotting. VSMCs exhibited higher production of H(2)O(2) and early expression of p22(phox) with beta-glycerophosphate or uremic serum within 24 h of treatment. beta-glycerophosphate-induced oxidative stress was associated with Cbfa-1 expression followed by ALP expression and activity, meanwhile the VSMCs expressing ALP diffusely calcified their extracellular matrix. Interestingly, diphenyleneiodonium partly prevented the osteoblastic differentiation. Results from this model strongly suggest a major implication of vascular NAD(P)H oxidase in vascular calcification supported by VSMCs osteoblastic differentiation.

Association of coronary artery and aortic calcium with lumbar bone density: the MESA Abdominal Aortic Calcium Study

Atherosclerosis and osteoporosis share many risk factors, but their independent association is unclear. The authors investigated the independent associations between volumetric trabecular bone mineral density (vBMD) of the lumbar spine and coronary artery calcium (CAC) and abdominal aortic calcium (AAC). During 2002-2005, they used quantitative computed tomography to assess vBMD and the presence and extent of CAC and AAC among 946 women (mean age = 65.5 years) and 963 men (mean age = 64.1 years) in a substudy of the Multi-Ethnic Study of Atherosclerosis. Prevalences of CAC were 47% and 68% in women and men, respectively, and AAC prevalences were 70% and 73%. Sequential, sex-specific regression models included adjustment for age, ethnicity, body mass index, hypertension, dyslipidemia, diabetes mellitus, smoking, alcohol consumption, physical activity, interleukin-6, C-reactive protein, homocysteine, and sex hormones. After full adjustment, lower vBMD was associated with greater CAC score among women (P < 0.002) and greater AAC score among women (P = 0.004) and men (P < 0.001). After adjustment, vBMD quartile was inversely associated with CAC prevalence (P-trend = 0.05) in women and AAC prevalence (P-trend < 0.01) in men. Partially and fully adjusted models showed similar results. Though modest, these significant, independent associations suggest that atherosclerosis and bone loss may be related.

Oxysterol-induced osteogenic differentiation of marrow stromal cells is regulated by Dkk-1 inhibitable and PI3-kinase mediated signaling

Osteoporosis and its complications cause morbidity and mortality in the aging population, and result from increased bone resorption by osteoclasts in parallel with decreased bone formation by osteoblasts. A widely accepted strategy for improving bone health is targeting osteoprogenitor cells in order to stimulate their osteogenic differentiation and bone forming properties through the use of osteoinductive/anabolic factors. We previously reported that specific naturally occurring oxysterols have potent osteoinductive properties, mediated in part through activation of hedgehog signaling in osteoprogenitor cells. In the present report, we further demonstrate the molecular mechanism(s) by which oxysterols induce osteogenesis. In addition to activating the hedgehog signaling pathway, oxysterol-induced osteogenic differentiation is mediated through a Wnt signaling-related, Dkk-1-inhibitable mechanism. Bone marrow stromal cells (MSC) treated with oxysterols demonstrated increased expression of osteogenic differentiation markers, along with selective induced expression of Wnt target genes. These oxysterol effects, which occurred in the absence of beta-catenin accumulation or TCF/Lef activation, were inhibited by the hedgehog pathway inhibitor, cyclopamine, and/or by the Wnt pathway inhibitor, Dkk-1. Furthermore, the inhibitors of PI3-Kinase signaling, LY 294002 and wortmanin, inhibited oxysterol-induced osteogenic differentiation and induction of Wnt signaling target genes. Finally, activators of canonical Wnt signaling, Wnt3a and Wnt1, inhibited spontaneous, oxysterol-, and Shh-induced osteogenic differentiation of bone marrow stromal cells, suggesting the involvement of a non-canonical Wnt pathway in pro-osteogenic differentiation events. Osteogenic oxysterols are, therefore, important small molecule modulators of critical signaling pathways in pluripotent mesenchymal cells that regulate numerous developmental and post-developmental processes.

Rosuvastatin increased serum osteocalcin levels independent of its serum cholesterol-lowering effect in patients with type 2 diabetes and hypercholesterolemia

OBJECTIVE

Accumulating evidence suggests that statins might positively affect bone metabolism. In the present study, we compared the effect of rosuvastatin with that of ezetimibe on bone turnover markers in patients with type 2 diabetes mellitus as well as hypercholesterolemia.

DESIGN AND METHODS

A total of 36 Japanese patients were enrolled in this open-label study and randomized to either rosuvastatin (2.5 mg/day) or ezetimibe (10 mg/day) groups at Shimane University Hospital. Bone turnover markers, such as bone-specific alkaline phosphatase, serum osteocalcin, urinary N-terminal telopeptide of type 1 collagen, and urinary deoxypyridinoline, were collected and compared between at baseline and at 3 months of treatment in each group.

RESULTS

Background data was not significantly different between the two groups. Total cholesterol and LDL cholesterol levels were significantly decreased at 3 months in both groups. Serum osteocalcin levels in the rosuvastatin group were significantly increased with mean changes of 0.48 (95% confidence interval; 0.05 to 0.91, p=0.03), while no other bone marker in the ezetimibe group was changed. Changes in total cholesterol or LDL cholesterol levels were not significantly correlated with the changes in bone turnover markers.

CONCLUSION

Rosuvastatin may have a beneficial effect on bone metabolism in patients with type 2 diabetes and hypercholesterolemia by stimulating osteoblast function and bone formation, which seems to be independent of its cholesterol-lowering effect.

Vitamin C intake inhibits serum lipid peroxidation and osteoclast differentiation on alveolar bone in rats fed on a high-cholesterol diet

OBJECTIVE

A high-cholesterol diet stimulates osteoclast differentiation, which may be induced by increased serum lipid peroxidation. The inhibition of serum lipid peroxidation by vitamin C may offer beneficial effects on osteoclast differentiation including increased expression of receptor activator of nuclear factor (NF)-kappaB ligand (RANKL) and NF-kappaB. This study investigated the effects of vitamin C intake on RANKL and NF-kappaB expression in periodontal tissue of rats fed a high-cholesterol diet.

DESIGN

Twenty-four rats (8 weeks old) were divided into four groups: a control group (fed a regular diet) and three experimental groups (fed a high-cholesterol diet supplemented with 0, 1 and 2 g/l vitamin C/day) in this 12-week study. Vitamin C was provided by its addition to drinking water. As an index of serum lipid peroxidation, hexanoyl-lysine (HEL) level was determined by a competitive enzyme-linked immunosorbent assay method. Immunohistological analysis was performed to evaluate RANKL and NF-kappaB expression on the alveolar bone surface. The number of tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts was also counted.

RESULTS

Feeding a high-cholesterol diet increased not only the serum HEL level but also the number of TRAP-positive osteoclasts on the alveolar bone surface, with an increase in RANKL and NF-kappaB expression on alveolar bone surface. Intake of vitamin C reduced the serum HEL level and osteoclast differentiation, with decreasing RANKL and NF-kappaB expression.

CONCLUSIONS

Vitamin C intake could suppress osteoclast differentiation, including RANKL and NF-kappaB expression on the alveolar bone surface, by decreasing serum lipid peroxidation in rats fed a high-cholesterol diet.

Oxidized low-density lipoprotein acts synergistically with beta-glycerophosphate to induce osteoblast differentiation in primary cultures of vascular smooth muscle cells

Previous studies have localized osteoblast specific markers to sites of calcified atherosclerotic lesions. We therefore decided to use an established in vitro model of vascular calcification in order to confirm earlier reports of oxidized low-density lipoprotein (oxLDL) promoting the osteogenic differentiation of vascular smooth muscle cells. Treatment of primary bovine aortic smooth muscle cells (BASMCs) with beta-glycerophosphate was found to induce a time-dependent increase in osteoblast differentiation. In contrast, no effect was seen when BASMCs were cultured in the presence of oxLDL alone. However, when the BASMCs were cultured in the presence of both beta-glycerophosphate and oxLDL, beta-glycerophosphate's ability to induce osteoblast differentiation was significantly enhanced. In an attempt to resolve the mechanism by which this effect was occurring, we examined the effect of beta-glycerophosphate and oxLDL on several pathways known to be critical to the differentiation of osteoblasts. Surprisingly, beta-glycerophosphate alone was found to enhance Osterix (Osx) expression by inducing both Smad 1/5/8 activation and Runx2 expression. In contrast, oxLDL did not affect either Smad 1/5/8 activation or Runx2 activation but rather, it enhanced both beta-glycerophosphate-induced Osx expression and osteoblast differentiation in an extracellular signal-regulated kinase 1 and 2 (Erk 1 and 2) -dependent manner. When taken together, these findings suggest a plausible mechanism by which oxLDL may promote osteogenic differentiation and vascular calcification in vivo. J. Cell. Biochem. 105: 185-193, 2008. (c) 2008 Wiley-Liss, Inc.

Relationship between coronary artery and descending thoracic aortic calcification as detected by computed tomography: the Multi-Ethnic Study of Atherosclerosis

BACKGROUND

Cardiac computed tomography (CT) is a well-established tool for the detection of cardiovascular calcium. Coronary artery calcification (CAC) is highly sensitive for the detection of coronary artery disease (CAD) as well as predictive of future cardiovascular (CV) events. Descending thoracic aortic calcification (DTAC) is common in the elderly and its presence is also associated with increased risk of CV events. Previous studies demonstrate that DTAC is associated with obstructive CAD and coronary risk factors. However, no prior studies have examined the association of CAC and DTAC as detected by cardiac CT in a large population-based cohort.

METHODS

In the Multi-Ethnic Study of Atherosclerosis, the study population included a population-based sample of four ethnic groups (Chinese, White, Hispanic and African-American) of 6814 women and men ages 45-84 years old. Participants underwent non-enhanced cardiac CT and both CAC and DTAC were quantified. DTAC was measured from the lower edge of the pulmonary artery bifurcation to the cardiac apex. Multivariable relative risk regression was used to evaluate relationships between CAC, DTAC and measured cardiovascular risk factors.

RESULTS

Overall 3030 (44%) did not demonstrate any detectable CAC or DTAC. A total of 1930 (28%) had only CAC, 386 (6%) had isolated DTAC, and 1464 (22%) participants were found to have both CAC and DTAC. CAC had a higher prevalence than DTAC in men (58% vs. 45%). Participants with DTAC were older than those with CAC (mean age was 71 and 66 years old, respectively). Participants with DTAC had increased risk for the presence of CAC independent of cardiovascular risk factors (prevalence ratio [PR]: 1.17, 95% CI: 1.07-1.28). Severity of DTAC was a stronger predictor of the presence of CAC in women as compared to men (PR: 1.04, 95% CI: 1.02-1.06, and PR: 0.99, 95% CI: 0.98-1.01, respectively).

CONCLUSIONS

DTAC was found to be a strong predictor of CAC independent of CV risk factors. Ongoing follow-up of this cohort will evaluate whether DTAC is an independent marker of risk for CV events.

Osteoprotegerin, vascular calcification and atherosclerosis

The association of bone pathologies with atherosclerosis has stimulated the search for common mediators linking the skeletal and the vascular system. Since its initial discovery as a key regulator in bone metabolism, osteoprotegerin (OPG) has become the subject of intense interest for its role in vascular disease and calcification. Studies in vitro and in animal models suggest that OPG inhibits vascular calcification. Paradoxically however, clinical studies suggest that serum OPG levels increase in association with vascular calcification, coronary artery disease, stroke and future cardiovascular events. This has led to an extensive debate on the potential of OPG as a biomarker of vascular disease. However the exact significance and mechanisms by which this bone-regulatory protein influences cardiovascular pathophysiology is still unclear. The need for a more complete picture is being addressed in increasing valuable research indicating OPG as not only a marker but also a mediator of vascular pathology modulating osteogenic, inflammatory and apoptotic responses. By integrating the results of recent experimental research, animal models and clinical studies, this review summarises the present understanding of the role of OPG in vascular disease and calcification.

Hyperlipidemia impairs osteoanabolic effects of PTH

Epidemiological and in vitro studies have suggested that hyperlipidemia/oxidized phospholipids adversely affect bone. We recently found that oxidized phospholipids attenuate PTH-induced cAMP and immediate-early gene (IEG) expression in MC3T3-E1 cells, raising concerns that clinical hyperlipidemia may attenuate osteoanabolic effects of PTH in vivo. Thus, we studied whether intermittent PTH treatment has differential osteoanabolic effects in wildtype (C57BL/6) and hyperlipidemic (LDLR(-/-)) mice. Consistent with our previous in vitro studies, induction of IEGs in calvarial tissue, 45 min after a single dose of recombinant hPTH(1-34), was attenuated in LDLR(-/-) mice compared with C57BL/6 mice. Daily hPTH(1-34) injections for 5 wk significantly increased total and cortical BMD and BMC, assessed by pQCT, in C57BL/6 mice. However, this induction was completely abrogated in LDLR(-/-) mice. Similarly, PTH(1-34) failed to increase BMD in another hyperlipidemic mouse model, ApoE(-/-) mice. Histomorphometric analysis showed that trabecular bone of both mice responded similarly to PTH(1-34). Structural parameters improved significantly in response to PTH(1-34) in both mouse strains, although to a lesser degree in LDLR(-/-) mice. With PTH(1-34) treatment, osteoblast surface trended toward an increase in C57BL/6 mice and increased significantly in LDLR(-/-) mice. PTH(1-34) did not alter resorption parameters significantly, except for the eroded surface (ES/BS), which was reduced in the C57BL/6 but not in the LDLR(-/-) mice. These results show that PTH(1-34) has adverse effects on cortical bones of the hyperlipidemic mice, suggesting that the therapeutic effects of PTH may be compromised in the presence of hyperlipidemia.

Abdominal aortic calcification, BMD, and bone microstructure: a population-based study

To better define the relationship between vascular calcification and bone mass/structure, we assessed abdominal aortic calcification (AAC), BMD, and bone microstructure in an age-stratified, random sample of 693 Rochester, MN, residents. Participants underwent QCT of the spine and hip and high-resolution pQCT (HRpQCT) of the radius to define volumetric BMD (vBMD) and microstructural parameters. AAC was quantified with the Agatston scoring method. In men, AAC correlated with lower vertebral trabecular and femoral neck vBMD (p < 0.001), but not after age or multivariable (age, body mass index, smoking status) adjustment. Separation into <50 and >or=50 yr showed this pattern only in the older men. BV/TV and Tb.Th inversely correlated with AAC in all men (p < 0.001), and Tb.Th remained significantly correlated after age adjustment (p < 0.05). Tb.N positively correlated with AAC in younger men (p < 0.001) but negatively correlated in older men (p < 0.001). The opposite was true with Tb.Sp (p = 0.01 and p < 0.001, respectively). Lower Tb.N and higher Tb.Sp correlated with AAC in older men even after multivariable adjustment. Among all women and postmenopausal women, AAC correlated with lower vertebral and femoral neck vBMD (p < 0.001) but not after adjustment. Lower BV/TV and Tb.Th correlated with AAC (p = 0.03 and p = 0.04, respectively) in women, but not after adjustment. Our findings support an age-dependent association between AAC and vBMD. We also found that AAC correlates with specific bone microstructural parameters in older men, suggesting a possible common pathogenesis for vascular calcification and deterioration in bone structure. However, sex-specific differences exist.

Relationship between carotid atherosclerosis and lumbar spine bone mineral density in postmenopausal women

Osteoporosis and increased carotid intima-media thickness (IMT) have been associated with atherosclerosis. We investigated the correlation between carotid IMT and lumbar spine bone mineral density (BMD) in postmenopausal women. We studied the carotid IMT in 175 postmenopausal women, including 43 women (control) with normal spinal BMD, 73 women with osteopenia, and 59 women with osteoporosis. Carotid IMT was assessed by ultrasonography. BMD at the lumbar spine (lumbar 2 to 4 vertebrae) was measured by dual-energy X-ray absorptiometry. Age, years since menopause, and carotid IMT were significantly greater in the osteoporosis group than in the control (all p<0.01) and osteopenia groups (all p<0.01). Estradiol was significantly lower in the osteoporosis group than in the control group (p<0.05). BMD was significantly lower in the osteoporosis group than in the osteopenia or control group (both p<0.01) and in the osteopenia group than in the control group (p<0.01). After adjusting for age, years since menopause, and estradiol, women with osteoporosis had significantly greater carotid IMT than controls (p<0.05). The univariate linear regression analysis revealed that carotid IMT was significantly positively correlated with age, years since menopause, and low-density lipoprotein (LDL) cholesterol (all p<0.05) and was significantly negatively correlated with estradiol and BMD (all p<0.05), but showed no significant association with other clinical variables. In multivariate regression analysis, the carotid IMT was significantly positively correlated with LDL cholesterol (p<0.01) and negatively correlated with BMD (p<0.01), but not with other variables. Carotid atherosclerosis might be associated with lumbar spine bone mass in postmenopausal women, suggesting that postmenopausal women with osteoporosis may have more advanced carotid atherosclerosis than those with a normal bone mass.