Vascular calcification: mechanisms and clinical ramifications

Composition of the stable carotid plaque: insights from a multidetector computed tomography study of plaque volume

BACKGROUND AND PURPOSE

Calcification has been associated with carotid plaque stability; however, an acceptable in vivo method to define plaques based on this component remains to be developed. The purpose of our study was to compare calcified and noncalcified volumes of carotid artery culprit symptomatic plaques with asymptomatic plaques using multidetector computed tomography.

METHODS

We identified 102 patients with > or =50% stenosis using NASCET criteria by multidetector computed tomography angiography between January 2004 and May 2006, which included 35 symptomatic (stenosis: 82.0+/-11.9%) and 67 asymptomatic patients (stenosis: 79.4+/-10.8%). Total plaque volume, noncalcified plaque volume, calcified plaque volume, and calcified/total ratio were measured for the 102 index plaques causing stenosis.

RESULTS

In a model including age, stenosis, and cardiovascular risk factors, calcified plaque volume/total plaque volume was significantly inversely associated with the occurrence of symptoms (P=0.012; odds ratio, 0.047; 95% CI, 0.004 to 0.511). There was a notable overlap in the calcified plaque volume/total plaque volume ratio between 0% and 45% for symptomatic and asymptomatic plaques. However, calcification >45% of the total plaque was very specific: 97.1% (34/35) for absence of symptoms (sensitivity: 28.4% 19/67). No significant association between total plaque volume, noncalcified plaque volume, or calcified plaque volume and symptomatology was found.

CONCLUSIONS

The proportion of carotid plaque calcification, rather than absolute volume, is associated with stability in patients with stenosis. Specifically, for a subset of patients, plaque calcification >45% of the total volume may represent a clinically useful cutoff. The carotid plaque calcium ratio, determined by multidetector computed tomography volume measurements, may help noninvasively risk stratify patients with asymptomatic stenosis.

Immunologic response enhances atherosclerosis-type 1 helper T cell (Th1)-to-type 2 helper T cell (Th2) shift and calcified atherosclerosis in Bacillus Calmette-Guerin (BCG)-treated apolipoprotein E-knockout (apo E-/-) mice

Although immunocompetent hosts develop protective type 1 helper T cell (Th1) responses in mycobacterial infections, seroepidemiologic studies show that patients with atherosclerosis commonly express high antibody titers against mycobacterial heat shock protein (HSP) 65 and may develop a nonprotective type 2 helper T cell (Th2) response and advanced disease. These studies were undertaken to define mycobacterial dose requirements and kinetics for development of antibodies to HSP65, the Th1 to Th2 shift of immune response, and calcified atherosclerotic lesion development in the apo E-/- mouse. Fourteen-week apo E-/- female mice were treated intraperitoneally (ip) with heat-killed M. bovis Bacillus Calmette-Guerin (BCG), and 14 days later, cross-sections from the ascending aortas were stained for measurement of lesion size and calcium deposition. At 14 days, 0.01-mg BCG induced Th1 responses against HSP65. In contrast, 1-mg BCG induced splenic PGE2-releasing macrophages with a Th1-to-Th2 shift of responses to HSP65, which was PGE2-dependent. Treatment with 1-mg BCG significantly lowered bone density with increases in marrow osteoclastogenesis and development of calcified lesions in the aorta. At 14 days, 0.01-mg BCG induced Th1-dependent HSP65 responses and did not advance atherosclerosis. In contrast, for 1-mg BCG, a PGE2-dependent Th1-to-Th2 shift of responses to HSP65 and evidence of bone resorption are associated with advanced calcified atherosclerotic lesions.

Vascular calcification: pathobiological mechanisms and clinical implications

Once thought to result from passive precipitation of calcium and phosphate, it now appears that vascular calcification is a consequence of tightly regulated processes that culminate in organized extracellular matrix deposition by osteoblast-like cells. These cells may be derived from stem cells (circulating or within the vessel wall) or differentiation of existing cells, such as smooth muscle cells (SMCs) or pericytes. Several factors induce this transition, including bone morphogenetic proteins, oxidant stress, high phosphate levels, parathyroid hormone fragments, and vitamin D. Once the osteogenic phenotype is induced, cells gain a distinctive molecular fingerprint, marked by the transcription factor core binding factor alpha1. Alternatively, loss of inhibitors of mineralization, such as matrix gamma-carboxyglutamic acid Gla protein, fetuin, and osteopontin, also contribute to vascular calcification. The normal balance between promotion and inhibition of calcification becomes dysregulated in chronic kidney disease, diabetes mellitus, atherosclerosis, and as a consequence of aging. Once the physiological determinants of calcification are perturbed, calcification may occur at several sites in the cardiovascular system, including the intima and media of vessels and cardiac valves. Here, calcification may occur through overlapping yet distinct molecular mechanisms, each with different clinical ramifications. A variety of imaging techniques are available to visualize vascular calcification, including fluoroscopy, echocardiography, intravascular ultrasound, and electron beam computed tomography. These imaging modalities vary in sensitivity and specificity, as well as clinical application. Through greater understanding of both the mechanism and clinical consequences of vascular calcification, future therapeutic strategies may be more effectively designed and applied.

Calcific tendonitis : a model

Calcific tendonitis is a common clinical condition associated with high rates of tendon rupture, prolonged symptoms, and poor response to therapy. Little is known about the pathogenesis of calcifications in tendons and consequently few effective therapies are available. We hypothesized that tendon calcification, like pathologic calcification in other sites, was generated by extracellular organelles known as matrix vesicles and that isolated matrix vesicles would constitute the basis for a useful model of this process. Tendon matrix vesicles were isolated from adult porcine patellar tendons using enzymatic digestion and differential centrifugation. Vesicle morphology was examined with electron microscopy. Levels of calcium, phosphate, pyrophosphate, ATP, and mineralization-associated enzymes were measured and compared with articular cartilage vesicles from porcine articular cartilage. Vesicles were embedded in agarose gels with or without type I collagen or dermatan sulfate and incubated in calcifying salt solution trace labeled with (45)calcium. (45)Calcium in the vesicle fraction was measured after 5-7 days. The type of mineral formed was determined by micro-x-ray diffraction. Matrix vesicles isolated from adult porcine tendon were similar morphologically to those obtained from articular cartilage. They contained mineralization-related enzymes and formed hydroxyapatite mineral in vitro. Mineralization was suppressed by levamisole and modulated by extracellular matrix components. Matrix vesicles isolated from tendons mineralize in vitro. This model may aid in the study of the pathogenesis of calcific tendonitis as well as serve as a means to identify effective therapies for this common disorder.

The pulsewave reflections model: Exploring for a fundamental mechanism of cardiovascular calcification

Cardiovascular calcification occurs in a variety of location and structure in the heart and the vasculature. Many hypotheses exist in describing local phenomena, however, there is no known global and unifying mechanism to explain all types of cardiovascular soft tissue calcification. The observed calcific changes in the cardiovascular system, however, does have a general pattern of occurring at structurally altered sites either due to disease processes or surgical manipulations. Areas of structural alterations, in conjunction with the pulsatile environment of the cardiovascular system, have been shown to disrupt normal pulsewave transmission throughout the arterial tree and induce local junctional or interfacial stress gradients. As such, these induced stress gradients can potentially aggregate and deposit cellular products and ionic particles at local sites to initiate calcification. A fundamental mechanism influencing all cardiovascular calcification is proposed based on pathophysiologic pulsewave propagations and reflections at these sites of structural changes. Initial supporting results of the theoretical model and experimentations are discussed leading to a call for future research in this direction.

Computed tomography calcium quantification as a measure of atherosclerotic plaque morphology and stability

OBJECTIVES

We examined the relationship between computed tomography (CT)-quantified calcium and histopathologic atherosclerotic plaque morphology and rupture.

MATERIALS AND METHODS

Seven aortae were harvested from autopsy cases. All were scanned, ex vivo, on a 16-slice CT scanner and CT calcium scores (CTCS) were calculated using a Siemens Calcium Scoring package. The aorta segments were physically cross sectioned at 3-mm intervals corresponding to CT reconstructions. Two pathologists evaluated the cross sections for histology calcium score (HCS), plaque fibrous cap disruption, overlying thrombus, internal hemorrhage, size, lipid content, and inflammation. CT and histology data were subsequently paired using predetermined quadrant and slice conventions.

RESULTS

Three hundred forty-nine aorta cross sections yielded 41 atherosclerotic plaques. Eleven plaques demonstrated plaque disruption and thrombosis and all contained calcium. CTCS was not significantly different between atherosclerotic plaques with and without evidence of disruption/thrombosis (F[1,30] = 1.525, P = 0.227). CT was 100% sensitive for nodular calcification, but only 56% (5 of 9 plaques) sensitive for non-nodular calcification. There was no significant relationship between CTCS and intraplaque hemorrhage, lipid content, inflammation, and plaque size (P = 0.179, P = 0.230, P = 0.314, and P = 0.054). There was significant correlation between CTCS and HCS (Pearson coefficient = 0.535; P < 0.01).

CONCLUSIONS

Calcium quantity does not appear to predict plaque morphology or likelihood of rupture. CT has lower sensitivity for non-nodular compared with nodular calcification.

Are calcifying matrix vesicles in atherosclerotic lesions of cellular origin?

Over recent years, the role of matrix vesicles in the initial stages of arterial calcification has been recognized. Matrix calcifying vesicles have been isolated from atherosclerotic arteries and the biochemical composition of calcified vesicles has been studied. No studies have yet been carried out to examine the fine structure of matrix vesicles in order to visualize the features of the consequent stages of their calcification in arteries. In the present work, a high resolution ultrastructural analysis has been employed and the study revealed that matrix vesicles in human atherosclerotic lesions are heterogeneous with two main types which we classified. Type I calcified vesicles were presented by vesicles surrounded by two electron-dense layers and these vesicles were found to be resistant to the calcification process in atherosclerotic lesions in situ. Type II matrix vesicles were presented by vesicles surrounded by several electron-dense layers and these vesicles were found to represent calcifying vesicles in atherosclerotic lesions. To test the hypothesis that calcification of matrix vesicles surrounded by multilayer sheets may occur simply as a physicochemical process, independently from the cell regulation, we produced multilamellar liposomes and induced their calcification in vitro in a manner similar to that occurring in matrix vesicles in atherosclerotic lesions in situ.

Coronary artery calcification and changes in atheroma burden in response to established medical therapies

OBJECTIVES

This study sought to determine the relationship between coronary calcification and plaque progression in response to established medical therapies.

BACKGROUND

Coronary calcification correlates with the extent of atherosclerosis and predicts clinical outcome.

METHODS

Atheroma volume was determined in serial intravascular ultrasound pullbacks in matched arterial segments of 776 patients with angiographic coronary artery disease. A calcium grade at baseline was assigned for each image (total 28,876) (0 = no calcium, 1 = calcium with acoustic shadowing <90 degrees and 2 = calcium with shadowing >90 degrees). Patients with a calcium index (average of calcium scores in a pullback) below versus above the median were compared with regard to plaque burden and progression.

RESULTS

Patients with a high calcium index were older (59 vs. 54 years, p < 0.001), more likely to be male (80% vs. 68%, p < 0.001), and more likely to have a history of hypertension (71% vs. 64%, p = 0.03). These patients had a greater percentage atheroma volume (PAV) (45% vs. 34%, p < 0.001), total atheroma volume (TAV) (210 vs. 151 mm3, p < 0.001), and percentage of images with maximal plaque thickness >0.5 mm (93% vs. 72%, p < 0.001). The continuous rate of change in PAV (1.1 +/- 0.4% vs. 0.8 +/- 0.4%, p = 0.34) and TAV (1.7 +/- 2.1% vs. -0.1 +/- 2.2%, p = 0.37) was similar in patients with a lower and higher calcium index, respectively. A lower calcium index was associated with a higher rate of patients showing substantial change in atheroma burden (at least 5% change in PAV, 70% vs. 53%, p < 0.001).

CONCLUSIONS

Calcific plaques are more resistant to undergoing changes in size in response to systemic interventions targeting atherosclerotic risk factors.

Calcific Aortic Valve Stenosis in Old Hypercholesterolemic Mice

Background— Hypercholesterolemia and old age are clinical risk factors for development of aortic valve stenosis, and hypercholesterolemia is a putative therapeutic target. We tested the hypothesis that calcification and aortic valve stenosis would develop in genetically hypercholesterolemic old mice.

Methods and Results— Twenty-four low-density lipoprotein receptor–deficient apolipoprotein B-100–only ( LDLr −/− ApoB 100/100 ) mice were fed normal chow from weaning until age 20.1±0.5 months (mean±SE; range 17 to 22 months). Twenty-one age-matched (20.8±0.9 months, range 17 to 25 months) C57Bl/6 mice served as controls. Echocardiographic imaging was used to assess morphology and function of the aortic valve and left ventricle. A subset of 12 mice underwent invasive hemodynamic assessment of aortic valve function. Functionally significant aortic stenosis, with >75% reduction in valve area, occurred in 8 of 24 LDLr −/− ApoB 100/100 mice and in 0 of 21 controls ( P =0.01). In the subset that underwent catheterization, mice with echocardiographic evidence of aortic stenosis had a systolic transvalvular gradient of 57±6 mm Hg. In the group of all LDLr −/− ApoB 100/100 mice with aortic stenosis, left ventricular mass was increased by 67% ( P =0.001) and ejection fraction was decreased by 30% ( P =0.004) compared with LDLr −/− ApoB 100/100 without aortic stenosis. Von Kossa staining of the aortic valve demonstrated abundant mineralization in LDLr −/− ApoB 100/100 mice but not in control mice. Superoxide (oxyethidium fluorescence) was present in valve tissue from all 3 groups of mice and was more abundant in mice with aortic stenosis.

Conclusions— Hypercholesterolemic LDLr −/− ApoB 100/100 mice are prone to develop calcification and oxidative stress in the aortic valve, with functional valvular heart disease, mimicking the clinical syndrome. This discovery holds promise for elucidation of the pathophysiology of aortic valve disease mechanisms and for the design of effective nonsurgical treatment.

What are the most useful and trustworthy noninvasive anatomic markers of existing vascular disease?

Cardiovascular disease is the leading cause of mortality and morbidity in developed countries. Evidence challenges the notion that the severity of lesions on angiography is a predictor of future cardiac events. With the recognition that subclinical coronary artery stenoses are responsible for myocardial infarcts and sudden death, it may be important to identify patients with plaque characteristics that may place them at increased risk. Intravascular ultrasound, though invasive, remains the current imaging gold standard. Computed tomography, cardiac magnetic resonance, and single-photon emission CT positron emission tomography are evolving and promising modalities. Functional studies reflecting plaque temperature and molecular imaging reflecting plaque constituents are being developed. We review the pathology of the vulnerable atherosclerotic plaque and recent innovations in imaging modalities to assess plaque complication risk.

Artery calcification in uremic rats is increased by a low protein diet and prevented by treatment with ibandronate

The present experiments investigate medial artery calcification in adult rats made uremic by feeding a synthetic diet containing 0.75% adenine for 4 weeks. Calcification was assessed by Alizarin red staining of intact aortas, by von Kossa staining of carotid artery sections, and by calcium and phosphate incorporated into the thoracic aorta. The major conclusions are as follows: Lowering the protein content of the diet from 25 to 2.5% dramatically increases the frequency and extent of medial artery calcification in uremic rats without significantly affecting the elevation in serum creatinine, phosphate, or parathyroid hormone. This observation suggests that low dietary protein intake could be a risk factor for medial artery calcification in uremic patients. Medial artery calcification in uremic rats is prevented by a dose of ibandronate that inhibits bone resorption. The observation suggests that bone resorption inhibitors could prevent artery calcification in uremic patients. Medial artery calcification in uremic rats correlates with increased serum bone Gla protein (BGP; osteocalcin), but not with serum matrix Gla protein or fetuin. This finding indicates that it could be of interest to examine the relation between serum BGP and artery calcification in uremic patients. Each of these conclusions lends support for our hypothesis that medial artery calcification is linked to bone resorption. Future investigations of the as yet unknown biochemical basis for this link will be facilitated by the present discovery that a synthetic, 2.5% protein diet containing 0.75% adenine produces consistent and dramatic medial calcification in adult rats within just 4 weeks.

Carotid artery plaque thickness is associated with increased serum calcium levels: the Northern Manhattan study

BACKGROUND

Elevated serum calcium concentrations are associated with vascular calcification and cardiovascular disease. It is unknown whether there is a relationship between high-normal serum calcium levels and sub-clinical vascular effects. We investigated the association between serum calcium and carotid plaque thickness, a powerful early predictor of clinical coronary and cerebrovascular events.

METHODS

Epidemiological study of 1194 subjects from the Northern Manhattan Study cohort, a prospective community-based study designed to investigate risk factors for vascular disease in different race-ethnic groups.

RESULTS

Subjects with carotid plaque had higher corrected serum calcium levels within the normal range than those without carotid plaque (2.21+/-0.09 mmol/L versus 2.19+/-0.09 mmol/L, p<0.002). The relationship between carotid plaque and serum calcium persisted after adjustment for traditional cardiovascular risk factors. Subjects in the top quintile of maximal carotid plaque thickness (>or=1.7 mm) were more likely to be in the highest quintile of serum calcium level (OR=1.64, 95% CI=1.17-2.29, p<0.004). The interaction of age and corrected serum calcium was the most significant predictor of carotid plaque thickness when traditional vascular risk factors were considered (p<0.001).

CONCLUSIONS

Serum calcium levels in a multi-ethnic population of older men and women were positively associated with carotid plaque thickness, a powerful early predictor of clinical coronary and cerebrovascular events.

Mechanical Response of a Calcified Plaque Model to Fluid Shear Force

Vascular calcification is associated with atherosclerosis, but whether it mechanically affects plaque stability remains controversial. To assess the effect of mineralization on plaque vulnerability to mechanical shear stress, we applied fluid shear to cultures of calcifying vascular cells (CVC), a subpopulation of smooth muscle cells that spontaneously mineralize. CVC cultures containing nodules were treated for 10 days with vehicle control or beta-glycerophosphate (BGP) to accelerate mineralization. Cultures were placed in a parallel-plate flow system and were subjected to increasing fluid shear stress (4.9 dyn/cm(2)/min up to 400 dyn/cm(2)). The number of nodules remaining attached was recorded every 10 min. Results showed that control cultures and BGP-treated cultures, which contained significantly greater calcium mineral than control cultures, had similar detachment thresholds (50-100 dyn/cm(2)), with linear portions of their stress/detachment curves from 100 to 275 dyn/cm(2). Based on repeated measure analysis of variance, BGP-treated nodules were no more likely to detach at a given shear than controls, although they showed a trend toward greater stability. Thus, calcification does not appear to increase plaque vulnerability to fluid shear stress, although it may contribute to a slight stabilization. This model may represent the first in vitro model of mechanical rupture of atherosclerotic plaque.

Homocysteine enhances apoptosis in human bone marrow stromal cells

INTRODUCTION

High plasma homocysteine (Hcy) levels have been associated with increased risk of fracture. Since Hcy has been shown to induce apoptosis in many cell types, including vascular endothelial cells, we hypothesized that Hcy would have a similar apoptotic effect on osteoblasts, leading to osteoporosis by reducing bone formation.

MATERIALS AND METHODS

Using primary human bone marrow stromal cells (hBMSC) and HS-5 cell line (human bone marrow stromal cell line), we investigated the effects of Hcy on these cells by cell viability assay and analysis of cytoplasmic histone-associated DNA fragments. Caspase activity assay, Western blots, and electrophoresis mobility shift assay (EMSA) were performed to find the mechanism of apoptosis. Intracellular reactive oxygen species (ROS) were measured by spectrometry using dichlorofluorescein diacetate, and cellular total glutathione level was determined by a commercially available kit. N-acetylcysteine (NAC) and pyrrolidine dithiocarbamate (PDTC) were used as tools for investigating the role of ROS and nuclear factor-kappaB (NF-kappaB), respectively.

RESULTS

Hcy induced apoptosis in primary human bone marrow stromal cells and the HS-5 cell line, and this apoptotic effect was caspase-dependent. In addition, Hcy increased cytochrome c release into the cytosol, and activated caspase-9 and caspase-3, but not caspase-8, indicating that Hcy induces apoptosis via the mitochondria pathway. Hcy increased ROS, and NAC inhibited the apoptotic effect of Hcy. Western blot and EMSA showed that Hcy activated the NF-kappaB pathway. PDTC blocked Hcy-induced caspase-3 activation and apoptosis.

CONCLUSION

These results suggest that Hcy induces apoptosis via the ROS-mediated mitochondrial pathway and NF-kappaB activation in hBMSCs, and that Hcy may contribute to the development of osteoporosis by reducing bone formation. Antioxidants may have a role in preventing bone loss in individuals with hyperhomocysteinemia.

New frontiers in the pathology and therapy of heart valve disease: 2006 Society for Cardiovascular Pathology, Distinguished Achievement Award Lecture, United States–Canadian Academy of Pathology, Atlanta, GA, February 12, 2006

This review summarizes several areas relative to the pathology of heart valve disease in which there has been rapid and ongoing evolution, namely, our understanding of: (a) the dynamic functional biology of cardiac valves; and (b) the pathology/pathobiology of valvular heart diseases; (c) new developments in valve repair and substitution using percutaneous approaches; and (d) progress toward the exciting potential of therapeutic valvular tissue engineering and regeneration, including the challenges that will need to be overcome before such therapeutic advances can become clinically useful.

Extracellular calcium sensing in rat aortic vascular smooth muscle cells

Extracellular calcium (Ca(2+)(o)) can act as a first messenger in many cell types through a G protein-coupled receptor, calcium-sensing receptor (CaR). It is still debated whether the CaR is expressed in vascular smooth muscle cells (VSMCs). Here, we report the expression of CaR mRNA and protein in rat aortic VSMCs and show that Ca(2+)(o) stimulates proliferation of the cells. The effects of Ca(2+)(o) were attenuated by pre-treatment with MAPK kinase 1 (MEK1) inhibitor, as well as an allosteric modulator, NPS 2390. Furthermore, stimulation of the VSMCs with Ca(2+)(o)-induced phosphorylation of ERK1/2, but surprisingly did not cause inositol phosphate accumulation. We were not able to conclusively state that the CaR mediates Ca(2+)(o)-induced cell proliferation. Rather, an additional calcium-sensing mechanism may exist. Our findings may be of importance with regard to atherosclerosis, an inflammatory disease characterized by abnormal proliferation of VSMCs and high local levels of calcium.

Thematic review series: Patient-Oriented Research. Imaging atherosclerosis: state of the art

The ability to image obstructive arterial disease brought about a revolution in clinical cardiovascular care; the development of newer technologies that image arterial wall thicknesses, areas, volumes, and composition allows valid imaging of atherosclerosis for the first time. Development of noninvasive imaging of atherosclerosis has further led to a quantum shift in research in the field by enabling the study of asymptomatic populations and thus allowing investigators to focus on preclinical disease without the many biases associated with the study of symptomatic patients. These noninvasive investigations have broad implications for clinical care as well. Coronary angiography, computed tomographic (CT) imaging of coronary calcium, intravascular ultrasound, multidetector CT angiography, B mode ultrasound of the carotid arteries, and MRI of the carotid arteries all have unique strengths and weaknesses for imaging atherosclerosis. Certain of these techniques are extremely useful as outcome variables for clinical trials, and others are uniquely useful as predictors of the risk of cardiovascular disease. All are informative in one way or another with regard to the role of plaque remodeling and composition in disease causation. CT and MRI technology are advancing very rapidly, and research and clinical uses of these imaging modalities promise to further advance our understanding of atherosclerosis and its prevention.

Osteoprotegerin inactivation accelerates advanced atherosclerotic lesion progression and calcification in older ApoE-/- mice

OBJECTIVE

Osteoprotegerin (OPG), a member of the tumor necrosis factor (TNF) superfamily of proteins, plays an important role in bone remodeling and is expressed in both mouse and human atherosclerotic lesions. The current study was designed to assess whether OPG plays a role in the progression and calcification of advanced atherosclerotic lesions in apoE(-/-) mice.

METHODS AND RESULTS

Atherosclerotic lesion area and composition and aortic calcium content were examined in mice deficient in both OPG and apolipoprotein E (OPG(-/-).apoE(-/-) mice) at 20, 40, and 60 weeks of age. Littermate OPG(+/+).apoE(-/-) mice were used as controls. The average cross-sectional area of lesions in the innominate arteries was increased in OPG(-/-).apoE(-/-) mice at 40 and 60 weeks of age. The increase in lesion area was coupled with a reduced cellularity and an increase in connective tissue including laminated layers of elastin. Sixty-week-old OPG(-/-).apoE(-/-) mice also had an increase in the area of calcification of the lesions. There were no differences in markers of plaque stability. In vitro, OPG induced matrix metalloproteinase-9 (MMP-9) activity in macrophages and smooth muscle cells and acted as a survival factor for serum-deprived smooth muscle cells.

CONCLUSIONS

OPG inhibits advanced plaque progression by preventing an increase in lesion size and lesion calcification. OPG may act as a survival factor and may modulate MMP9 production in vascular cells.

Radiographic measure of aorta calcification is a site-specific predictor of bone loss and fracture risk at the hip

OBJECTIVE

To investigate whether aorta calcification (AC) - a surrogate marker of atherosclerosis - is an independent indicator of low bone mass density (BMD), accelerated bone loss, and risk of future fractures in postmenopausal women.

DESIGN

A prospective epidemiological study. Follow-up period was 7.5 years.

SETTING

Community-based sample followed by a research institute.

SUBJECTS

A total of 2662 generally healthy postmenopausal women with a mean age of 65.0 +/- 7.1 years at baseline.

MAIN OUTCOME MEASURES

Annual rate of changes in BMD (DEXA) and AC (X-rays), vertebral fractures (X-rays), hip fractures (questionnaire).

RESULTS

Advanced AC at baseline was significantly associated with lower BMD and accelerated bone loss from the proximal femur. In a multivariate logistic regression model, age (OR 1.1, 95% CI 1.0-1.2, P = 0.02), body mass index (BMI; OR 0.9, 95% CI 0.8-1.0, P = 0.03) and the severity of AC (OR 2.3, 95% CI 1.1-4.8, P = 0.03) were independent predictors of hip fractures. Adjusted OR for vertebral fracture was 1.2 (95% CI 1.0-1.5, P = 0.12).

CONCLUSIONS

Aorta calcification seems to independently contribute to the development of osteoporosis in the proximal femur. Further studies are needed to clarify whether effective atherosclerosis prevention lowers hip fracture risk.

Diseases of Wnt signaling

The Wnt signaling pathways play fundamental roles in the differentiation, proliferation, death and function of many cells and as a result are involved in critical developmental, growth and homeostatic processes in animals. There are four currently known pathways of Wnt signaling; the so-called canonical or Wnt/beta-catenin pathway, the Wnt/Ca(+2) pathway involving Protein Kinase A, the planar cell polarity pathway and a pathway involving Protein Kinase C that functions in muscle myogenesis. The best studied of these is the Wnt/beta-catenin pathway. The Wnts are an evolutionarily highly conserved family of genes/proteins. Control of the Wnt pathways is modulated by a number of the proteins that either interact with the Wnt ligands directly, or with the low density lipoprotein-receptor related proteins (LRP) 5 and 6 that along with one of several Frizzled proteins function as co-receptors for the Wnt ligands. Aberrant regulation resulting as a consequence of mutations in any of several components of the Wnt pathway and/or protein modulators of the pathway have been shown to cause a wide spectrum of diseases. This review will briefly touch on various diseases of Wnt signaling including cancer, aortic valve calcification and several bone related phenotypes. Our emerging understanding of Wnt signaling offers great hope that new molecular based screening tests and pharmaceutical agents that selectively target this pathway will be developed to diagnose and treat these diseases in the future.

Matrix metalloproteinase inhibition attenuates aortic calcification

OBJECTIVE

Arterial calcification has been associated with matrix metalloproteinase (MMP)-mediated elastin degradation. In this study, we investigated whether inhibiting MMP activity could reduce calcium accumulation in rodent models of aortic calcification.

METHODS AND RESULTS

Aortic calcification was first induced in male Sprague-Dawley rats by administration of vitamin D3. Treatment with doxycycline decreased aortic calcium and phosphorus accumulation, and it reduced aortic gelatinase levels; however, it also prevented the bone resorption associated with high doses of vitamin D3. Using an in vivo model of localized aortic calcification, systemic doxycycline treatment reduced aortic calcium accumulation without affecting serum calcium levels, suggesting a more specific effect of doxycycline in the arterial wall. In organ culture, doxycycline limited aortic calcification caused by exposure to alkaline phosphatase and inorganic phosphate. When GM6001, a synthetic and specific inhibitor of MMPs, was used instead of doxycycline, it had a similar effect. In vivo, periadventitial delivery of GM6001 to calcifying arteries significantly reduced calcification compared with controls.

CONCLUSIONS

These results suggest that MMPs are involved in aortic calcification, and inhibiting MMP activity could reduce calcium accumulation in the arterial wall.

Parathyroid hormone and leptin--new peptides, expanding clinical prospects

There are three injectable and one oral bone-building (i.e., bone anabolic) parathyroid hormone (PTH) peptides. One of the four, Lilly's injectable teriparatide (Forteo), is currently being used, and the other three are in clinical trials. They are being used or assessed only for treating postmenopausal osteoporosis. However, their potential clinical targets now extend far beyond osteoporosis. They can accelerate the mending of even severe non-union fractures; they will probably be used to strengthen the anchorage of pros-theses to bone; they have been shown to treat psoriasis that has resisted other treatments; they can increase the size of haematopoietic stem cell proliferation and accelerate the endogenous repopulation or repopulation by donor transplants of bone marrow depleted by chemotherapeutic drugs; and they may prevent vascular ossification. Leptin, a member of the cytokine superfamily has a PTH-like osteogenic activity and may even partly mediate PTH action. But leptin has two drawbacks that cloud its therapeutic future. First, apart from directly stimulating osteoblastic cells, it targets cells in the hypothalamic ventromedial nuclei and through them it reduces oestrogenic activity by promoting osteoblast-suppressing adrenergic activity. Second, it stimulates vascular and heart valve ossification, which leads to such events as heart failure and diabetic limb amputations.

Molecular mechanisms of vascular calcification: lessons learned from the aorta

Vascular calcification increasingly afflicts our aging and dysmetabolic population. Once considered a passive process, it has emerged as an actively regulated form of calcified tissue metabolism, resembling the mineralization of endochondral and membranous bone. Executive cell types familiar to bone biologists, osteoblasts, chondrocytes, and osteoclasts, are seen in calcifying macrovascular specimens. Lipidaceous matrix vesicles, with biochemical and ultrastructural "signatures" of skeletal matrix vesicles, nucleate vascular mineralization in diabetes, dyslipidemia, and uremia. Skeletal morphogens (bone morphogenetic protein-2 (BMP) and BMP4 and Wnts) divert aortic mesoangioblasts, mural pericytes (calcifying vascular cells), or valve myofibroblasts to osteogenic fates. Paracrine signals provided by these molecules mimic the epithelial-mesenchymal interactions that induce skeletal development. Vascular expression of pro-osteogenic morphogens is entrained to physiological stimuli that promote calcification. Inflammation, shear, oxidative stress, hyperphosphatemia, and elastinolysis provide stimuli that: (1) promote vascular BMP2/4 signaling and matrix remodeling; and (2) compromise vascular defenses that limit calcium deposition, inhibit osteo/chondrogenic trans-differentiation, and enhance matrix vesicle clearance. In this review, we discuss the biology of vascular calcification. We highlight how aortic fibrofatty tissue expansion (adventitia, valve interstitium), the adventitial-medial vasa, vascular matrix, and matrix vesicle metabolism contribute to the regulation of aortic calcium deposition, with greatest emphasis placed on diabetic vascular disease.

Noninvasive Assessment of Plaque Morphology and Composition in Culprit and Stable Lesions in Acute Coronary Syndrome and Stable Lesions in Stable Angina by Multidetector Computed Tomography

OBJECTIVES

The purpose of this study was to assess morphology and composition of culprit and stable coronary lesions by multidetector computed tomography (MDCT).

BACKGROUND

Noninvasive identification of culprit lesions has the potential to improve noninvasive risk stratification in patients with acute chest pain.

METHODS

Thirty-seven patients with acute coronary syndrome (ACS) or stable angina underwent coronary 16-slice MDCT and invasive selective angiography. In all significant coronary lesions two observers measured the degree of stenosis, plaque area at stenosis, and remodeling index and assessed plaque composition. Differences between culprit lesions in patients with ACS and stable lesions in patients with ACS or stable angina were determined.

RESULTS

We analyzed 40 lesions with excellent image quality in 14 patients with ACS and 9 patients with stable angina. Culprit lesions in patients with ACS (n = 14) had significantly greater plaque area and a higher remodeling index than both stable lesions in patients with ACS (n = 13) and in patients with stable angina (n = 13) (17.5 +/- 5.9 mm2 vs. 9.1 +/- 4.8 mm2 vs. 13.5 +/- 10.7 mm2, p = 0.02; and 1.4 +/- 0.3 vs. 1.0 +/- 0.4 vs. 1.2 +/- 0.3, p = 0.04, respectively). The prevalence of non-calcified plaque was 100%, 62%, and 77%, respectively, and the prevalence of calcified plaque was 71%, 92%, and 85%, respectively, in culprit lesions in patients with ACS and in stable lesions in patients with ACS or stable angina.

CONCLUSIONS

We introduce the concept of noninvasive detection and characterization of coronary atherosclerotic lesions in patients with ACS by MDCT. We identified differences in lesion morphology and plaque composition between culprit lesions in ACS and stable lesions in ACS or stable angina, consistent with previous intravascular ultrasound studies.

Vascular calcification in patients with chronic kidney disease

Chronic kidney disease (CKD) represents an extremely common condition, and cardiovascular diseases are frequently reported in this patient population. Traditional risk factors are not accurate prognostic predictors in CKD patients, and new potential markers to predict the cardiovascular involvement in uremic patients need to be identified. Vascular calcification (VC) represents a hallmark of the atherosclerotic process in CKD. This review summarizes the processes responsible for VC (particularly focusing on the mechanisms operative in the presence of renal dysfunction), discusses the utility of computer tomography modalities in the detection of VC in patients with CKD, and reports the potential role of VC as pathophysiological link between kidney disease and cardiovascular events.

N-3 fatty acids inhibit vascular calcification via the p38-mitogen-activated protein kinase and peroxisome proliferator-activated receptor-gamma pathways

Fish oil supplementation is associated with lower risk of coronary artery disease in humans, and it has been shown to reduce ectopic calcification in an animal model. However, whether N-3 fatty acids, active ingredients of fish oil, have direct effects on calcification of vascular cells is not clear. In this report, we investigated the effects of eicosapentaenoic acid and docosahexaenoic acid (DHA) on osteoblastic differentiation and mineralization of calcifying vascular cells (CVCs), a subpopulation of bovine aortic medial cells that undergo osteoblastic differentiation and form calcified matrix in vitro. Results showed that N-3 fatty acids inhibited alkaline phosphatase (ALP) activity and mineralization of vascular cells, suggesting that they directly affect osteoblastic differentiation in vascular cells. By Western blot analysis, DHA activated p38-mitogen-activated protein kinase (MAPK) but not extracellular-regulated kinase (ERK) or Akt. An inhibitor of p38-MAPK partially reversed the inhibitory effects of DHA on osteoblastic differentiation and mineralization. Transient transfection experiments showed that DHA also activated peroxisome proliferator-activated receptor-gamma (PPAR-gamma). Both p38-MAPK activator and PPAR-gamma agonists reproduced the inhibitory effects of DHA on CVC mineralization. Pretreatment with DHA also inhibited interleukin-6-induced ALP activity and mineralization. Together, these results suggest that N-3 fatty acids directly inhibit vascular calcification, and that the inhibitory effects are mediated by the p38-MAPK and PPAR-gamma pathways.

Hydrogen sulfide ameliorates vascular calcification induced by vitamin D3 plus nicotine in rats

AIM

To investigate the role of the endogenous cystathionine gamma-synthase (CSE)/hydrogen sulfide (H2S) pathway in vascular calcification in vivo.

METHODS

A rat vascular calcification model was established by administration of vitamin D3 plus nicotine (VDN). The amount of CSE and osteopontin (OPN) mRNA was determined by using semi-quantitative reverse-transcription polymerase chain reaction. The calcium content, 45Ca2+ accumulation and alkaline phosphatase (ALP) activity were measured. H2S production and CSE activity were measured.

RESULTS

von Kossa staining produced strong positive black/brown staining in areas among the elastic fibers of the medial layer in the calcified aorta. The calcium content, 45Ca2+ accumulation and ALP activity in calcified arteries increased by 6.77-, 1.42-, and 1.87-fold, respectively, compared with controls. The expression of the OPN gene was upregulated (P<0.01). Expression of the CSE gene was downregulated. However, calcium content, 45Ca2+ uptake and ALP activity in the VDN plus NaHS group was lower than that in the VDN group. The content of calcium and 45Ca2+ accumulation and activity of ALP in the aorta were 34.8%, 40.75% and 63.5% lower in the low-dosage NaHS group than in the VDN group, respectively (P<0.01), and the calcium content and deposition of 45Ca2+ and activity of ALP was 83.9%, 37.8 % and 46.2% lower in the aorta in the high-dosage NaHS group than in the VDN group, respectively (P<0.01). The expression of the OPN gene was downregulated.

CONCLUSION

The production of H2S, and CSE activity were decreased and CSE gene expression was downregulated in rats with vascular calcification. H2S can ameliorate vascular calcification, suggesting that the H2S/CSE pathway plays a regulatory role in the pathogenesis of vascular calcification.

The unified hypothesis of interactions among the bone, adipose and vascular systems: 'osteo-lipo-vascular interactions'

Epidemiological evidence has established a link among hyperlipidemia, visceral obesity, osteoporosis, and cardiovascular diseases (CVD). We here propose the hypothesis that the associations of those disorders are based on interaction of the three organs, i.e. the bone, adipose, and vascular tissues, possibly through multiple interactions among several humoral factors and/or transcription factors. The unified hypothesis of three organs, which we call 'osteo-lipo-vascular interactions', may be explained by the common origin of the cells in each organ. The mesenchymal stem cells are capable of differentiating into osteoblasts, vascular smooth muscle cells, and adipocytes. Alternatively, macrophages may evolve into osteoclasts or infiltrate both the vascular and adipose tissues, thereby leading to chronic inflammation. This unified concept of three organs may provide insights into the development of a new drug for the treatment of osteoporosis, obesity, hyperlipidemia or CVD.

Vascular calcification in patients with renal failure: culprit or innocent bystander?

The mortality from cardiovascular events in CKD and dialysis patients is substantially higher than in the general population. VC is ubiquitous and progresses rapidly in this patient population. Although there has been progress in the understanding of the pathogenesis and correlates of VC, much work needs to be done in this area. The role of calcium and, probably, phosphate (obligatory participants) is unquestionable, but the understanding of the paracrine and molecular determinants of VC in renal failure is continuously evolving. VC is probably a dynamic process resulting from the imbalance between molecules that promote and those that inhibit VC. The understanding of latter area has recently evolved with identification of new signaling pathways with molecules such as osteoprotegerin, fetuin-A, and MPG. From a clinical perspective, new modalities such as EBCT and MDCT allow noninvasive detection and quantification of VC. VC may represent a potential useful index for prognostic stratification and treatment planning in patients who have renal failure. At present, however, the data on the prognostic value of VC are available only in populations of patients who have normal renal function. Large-scale, prospective, observational studies should be designed to identify the determinants of VC and to define the prognostic role of calcium scoring in cohorts of patients who have predialysis CKD and with ESRD.

Chlamydia pneumoniae in foci of "early" calcification of the tunica media in arteriosclerotic arteries: an incidental presence?

Only a few previous works investigated the involvement of Chlamydia pneumoniae (Chlamydophila pneumoniae) in arterial calcification. The present study investigated a possible association between C. pneumoniae and medial calcification. Carotid artery segments obtained by endarterectomy from 60 patients were examined by PCR and immunohistochemistry to identify the presence of C. pneumoniae. Arterial specimens showing double-positive (n = 17), double-negative (n = 22), and single-positive results (n = 21) were further analyzed by a combination of histology, immunohistochemistry, and electron microscopy. Medial calcification occurred in 10 of 17 (58.8%) C. pneumoniae double-positive arterial specimens, but no medial calcification was observed in any of 22 C. pneumoniae double-negative arterial specimens. Electron microscopy indicated C. pneumoniae in smooth muscle cells (SMCs) in foci of medial calcification. Medial SMCs showing damage to the cytoplasm and basement membrane contained the structures with the appearance of elementary, reticulate, and aberrant bodies of C. pneumoniae. The presence of C. pneumoniae in SMCs was confirmed by electron-microscopic immunocytochemistry. In the extracellular matrix, calcification was observed in C. pneumoniae aberrant bodies that exited the SMCs. The findings offer a new hypothesis of arterial calcification: they suggest that C. pneumoniae infection of medial SMCs may be associated with the pathophysiological events of arteriosclerotic calcification of the tunica media.

Relationship between osteoporosis and cardiovascular disease in postmenopausal women

In the placebo group of the MORE study, including 2576 postmenopausal women (mean age, 66.5 years), the authors describe a strong linear association between the severity grade of osteoporosis (from low BMD to presence of severe vertebral fractures) and the future risk of cardiovascular events. Accordingly, treatment of postmenopausal osteoporosis should include consideration of measures to prevent adverse cardiovascular outcomes.

INTRODUCTION

Observations indicate an inverse association between BMD and the severity of peripheral atherosclerosis in postmenopausal women. The predictive value of osteoporosis and its different severity stages for the risk of acute cardiovascular events remains unknown.

MATERIALS AND METHODS

Participants were 2576 women (mean age, 66.5 years) assigned to placebo and followed for 4 years in an osteoporosis treatment trial. Those with at least one vertebral fracture or total hip BMD T score < or = -2.5 at baseline were defined as having osteoporosis, whereas those without vertebral fracture and total hip BMD T score between -2.5 and -1 were defined as having low bone mass. The primary outcome for these posthoc analyses was the incidence of adjudicated fatal or nonfatal cardiovascular events.

RESULTS

After adjustment for potential confounders, women with osteoporosis had a 3.9-fold (95% CI, 2.0-7.7; p < 0.001) increased risk for cardiovascular events compared with women with low bone mass. Under the same boundaries, a total hip BMD T score < or = -2.5 versus a T score between -2.5 and -1 was associated with a 2.1-fold (95% CI, 1.2-3.6; p < 0.01) increase in risk, whereas presence of at least one vertebral fracture versus no vertebral fracture at baseline was associated with a 3.0-fold (95% CI, 1.8-5.1; p < 0.001) increase in risk. The risk of cardiovascular events increased incrementally with the number and increasing severity of baseline vertebral fractures (both p < 0.001).

CONCLUSIONS

Postmenopausal women with osteoporosis are at an increased risk for cardiovascular events that is proportional to the severity of osteoporosis at the time of the diagnosis. Treatment of postmenopausal osteoporosis should include consideration of measures to prevent cardiovascular outcomes.

Angiogenesis and pericytes in the initiation of ectopic calcification

Ectopic calcification of blood vessels, heart valves, and skeletal muscle is a major clinical problem. There is now good evidence that angiogenesis is associated with ectopic calcification in these tissues and that it is necessary, but not sufficient, for calcification to occur. Angiogenesis may regulate ectopic calcification in several ways. First, many angiogenic factors are now known to exert both direct and indirect effects on bone and cartilage formation. Second, cytokines released by endothelial cells can induce the differentiation of osteoprogenitor cells. Third, the new blood vessels provide oxygen and nutrients to support the growing bone. Finally, the new blood vessels can serve as a conduit for osteoprogenitor cells. These osteoprogenitor cells may be derived from the circulation or from pericytes that are present in the neovessels themselves. Indeed, there is now compelling evidence that pericytes can differentiate into osteoblasts and chondrocytes both in vitro and in vivo. Other vascular cells, including adventitial myofibroblasts, calcifying vascular cells, smooth muscle cells, and valvular interstitial cells, have also been shown to exhibit multilineage potential in vitro. Although these cells share many properties with pericytes, the precise relationship between them is not known. Furthermore, it still remains to be determined whether all or some of these cells contribute to the ectopic calcification observed in vivo. A better understanding of the underlying mechanisms that link angiogenesis, pericytes, and ectopic calcification should provide a basis for development of therapeutic strategies to treat or arrest this clinically significant condition.

Aortic calcification in haemodialysis patients with diabetes mellitus

BACKGROUND

Certain metabolic disorders, such as hyperphosphatemia induce vascular calcification in haemodialysis patients; it is unclear, however, whether these disorders contribute to aortic calcification in diabetic haemodialysis patients. This study examined the risk factors of aortic calcification in a large number of haemodialysis patients, and compared risk factors between diabetic and non-diabetic patients.

METHODS

The subjects were 667 patients on maintenance haemodialysis: 184 with type 2 diabetes and 483 without. Aortic calcification was measured semi-quantitatively using a plain computed tomography image of the abdominal aorta, and an aortic calcification index (ACI) was calculated.

RESULTS

The ACI of the diabetic subjects was significantly higher than that of those without diabetes (57.3+/-22.1 vs 44.8+/-28.3%, P < 0.0001), although the dialysis vintage of the former was significantly shorter (P < 0.001). Multiple regression analyses showed that diabetes was a significant independent risk factor for increased ACI. Multiple regression analyses, performed separately in diabetics and non-diabetics, revealed that advanced age, higher systolic blood pressure, smoking and longer haemodialysis vintage were common independent risk factors significantly associated with increased ACI in both patient groups (R2 = 0.296, P < 0.0001 for non-diabetics; R2 = 0.193, P < 0.0001 for diabetics). Higher serum phosphate concentration was not significantly associated with increased ACI in diabetic patients (P = 0.429), although it was a significant independent factor in non-diabetic patients (beta = 0.150, P < 0.0005).

CONCLUSION

Aortic calcification in diabetic haemodialysis patients is more advanced, compared with non-diabetic patients, even with short haemodialysis vintage. Since disorders of mineral metabolism are not significantly associated with aortic calcification in diabetic haemodialysis patients, aortic calcification in these patients could be affected by metabolic abnormalities associated with the diabetic state per se, independent of other confounding factors; and aortic calcification may be advanced even before haemodialysis induction.

Novel conformation-specific antibodies against matrix gamma-carboxyglutamic acid (Gla) protein: undercarboxylated matrix Gla protein as marker for vascular calcification

OBJECTIVE

Matrix gamma-carboxyglutamic acid (Gla) protein (MGP), a vitamin K-dependent protein, is a potent in vivo inhibitor of arterial calcification. We hypothesized that low endogenous production of MGP and impaired carboxylation of MGP may contribute to the development or the progression of vascular disease.

METHODS AND RESULTS

Novel conformation-specific antibodies against MGP were used for immunohistochemistry of healthy and sclerotic arteries. In healthy arteries, MGP was mainly displayed around the elastin fibers in the tunica media. The staining colocalized with that for carboxylated MGP, whereas undercarboxylated MGP (ucMGP) was not detected. In atherosclerotic arteries, ucMGP was found in the intima, where it was associated with vesicular structures. In Mönckeberg's sclerosis of the media, ucMGP was localized around all areas of calcification. The results indicate that ucMGP is strongly associated with vascular calcification of different etiologies. In a separate study, serum MGP concentrations in a cohort of 172 subjects who had undergone percutaneous coronary intervention were significantly reduced compared with an apparently healthy population.

CONCLUSIONS

These data show that impaired carboxylation of MGP is associated with intimal and medial vascular calcification and suggest the essentiality of the vitamin K modification to the function of MGP as an inhibitor of ectopic calcification.

Osteoporosis and atherosclerosis: biological linkages and the emergence of dual-purpose therapies

Osteoporosis and atherosclerosis are both widely prevalent in an ageing population, and induce serious morbidities and death. There is growing evidence that in addition to their relationship to ageing, osteoporosis and atherosclerosis are also linked by biological associations. This article reviews their clinical interrelations, discusses the basic biology of bone and the arterial wall, and presents five examples that illustrate their biological linkages. Current therapeutic approaches emerging from these linkages, including statins, bisphosphonates, and the thiazolidinediones, have dual effects on bone and the vasculature. Additional therapies derived from experimental studies that enhance bone density and reduce atherogenesis hold further promise to diminish the morbidity and mortality of osteoporosis and atherosclerosis, with attendant benefits to society.

Vascular calcification

PURPOSE OF REVIEW

Accumulating evidence suggests that the high cardiovascular mortality observed in patients with end-stage renal disease is due in part to the deleterious effects of vascular calcification that develops over time on dialysis. This review focuses on recent cell biological and animal studies that have shed light on the mechanisms and regulators of vascular smooth muscle cell calcification in end-stage renal disease.

RECENT FINDINGS

Clinical studies demonstrate that high circulating levels of phosphate or calcium predict vascular calcification. Recent cell biological studies have provided novel insights into how vascular smooth muscle cells regulate calcification in response to such insults. Vascular smooth muscle cell damage and subsequent vesicle release from viable and dying cells create an environment permissive for the nucleation of basic calcium phosphate mineral. This, combined with osteogenic conversion of vascular smooth muscle cells and consequent loss of their normal inhibitory processes/pathways, results in calcification. Circulating factors such as fetuin-A, with the potential to impact on vessel wall calcification, have also been identified. Animal studies suggest that the 'uremic milieu' potentiates calcification and have clearly established a link between vascular calcification and bone metabolism. However, our understanding of the factors that contribute to vascular smooth muscle cell calcification in end-stage renal disease remains incomplete.

SUMMARY

Systematic studies are required that integrate epidemiological studies to identify risk factors with in-vitro experiments to investigate mechanisms leading to vascular smooth muscle cell calcification in response to these factors. Animal and clinical studies can subsequently be used to assess how modifying risk factors under the complex physiological conditions of end-stage renal disease impacts on vessel wall health.

Proinflammatory Activation of Macrophages by Basic Calcium Phosphate Crystals via Protein Kinase C and MAP Kinase Pathways

Basic calcium phosphate (BCP) crystal deposition underlies the development of arterial calcification. Inflammatory macrophages colocalize with BCP deposits in developing atherosclerotic lesions and in vitro can promote calcification through the release of TNF alpha. Here we have investigated whether BCP crystals can elicit a proinflammatory response from monocyte-macrophages. BCP microcrystals were internalized into vacuoles of human monocyte-derived macrophages in vitro. This was associated with secretion of proinflammatory cytokines (TNFα, IL-1β and IL-8) capable of activating cultured endothelial cells and promoting capture of flowing leukocytes under shear flow. Critical roles for PKC, ERK1/2, JNK, but not p38 intracellular signaling pathways were identified in the secretion of TNF alpha, with activation of ERK1/2 but not JNK being dependent on upstream activation of PKC. Using confocal microscopy and adenoviral transfection approaches, we determined a specific role for the PKC-alpha isozyme. The response of macrophages to BCP crystals suggests that pathological calcification is not merely a passive consequence of chronic inflammatory disease but may lead to a positive feed-back loop of calcification and inflammation driving disease progression.

Aortic calcification

OBJECTIVES

Vascular calcification is a complicating factor observed in advanced atherosclerosis. This review summarises the present knowledge regarding abdominal aortic calcification.

DESIGN

Literature review.

METHODS

A literature review was carried using MEDLINE and PUBMED with the search terms 'abdominal', 'aortic' and 'calcification'. Articles were assessed for data regarding mechanisms, measurement, risk factors and outcomes of aortic calcification.

RESULTS

Thirty relevant studies were identified. These demonstrated a positive correlation between abdominal aortic calcification and the following factors: older age, hypertension, and smoking. Further studies are required to critically assess other risk factors such as gender, diabetes mellitus and renal failure. Calcification of the abdominal aorta is associated with an increased risk of mortality, coronary heart disease and stroke.

CONCLUSION

Aortic calcification predicts an increased incidence of cardiovascular events, however, the reasons for this association requires further investigation. Accurate measurement of aortic calcification is likely to be increasingly used to determine the risk of cardiovascular events.

Calcification of elastic fibers in human atherosclerotic plaque

The present study was undertaken to systematically investigate whether calcification of elastic fibers occurs in human atherosclerotic plaques. Fourteen carotid artery segments obtained by endarterectomy were examined by a combination of electron microscopy and cytochemistry. The analysis demonstrated that calcification of elastic fibers occurred in all 14 specimens. Two distinct types of calcification of elastic fibers were identified. In type I calcification, elastin itself was observed to undergo calcification and no visible structural alterations preceded the calcification. In type II of calcification, structural alteration of elastin preceded calcification of elastic fibers and included vacuolization of elastin accompanied by the accumulation of neutral lipids and unesterified cholesterol within altered elastic fibers. In type II calcification, calcified deposits were found to form in an association with unesterified cholesterol. Type II calcification was widespread throughout the plaque matrix while type I calcification occurred only in the deep portions of plaques.

Transdifferentiation of smooth muscle cells into chondrocytes in atherosclerotic arteries in situ: implications for diffuse intimal calcification

Several hypotheses have been offered to explain the occurrence of arteriosclerotic calcification but the mechanisms involved are still not well understood. Using a combination of electron microscopy and immunohistochemistry, atherosclerotic plaques from human arteries as well as atherosclerotic-like lesions from aortas of apo-E-deficient mice were examined to identify cell type(s) associated with calcification. Electron microscopic analysis showed that, in human atherosclerotic plaques, chondrocyte-like cells were present in areas surrounding the necrotic cores. In these areas, some smooth muscle cells displayed features of their transdifferentiation into chondrocyte-like cells. Immunohistochemical analysis confirmed that smooth muscle cells with a reduced content of alpha-smooth muscle actin expressed Sox-9. Destruction of chondrocytes resulted in the accumulation of numerous membrane-bound vesicles in the extracellular space. Membrane-bound vesicles originating from chondrocytes were found to undergo calcification. Similar processes were found to occur in atherosclerotic-like lesions in apo-E-deficient mice. These observations suggest that transdifferentiation of smooth muscle cells into chondrocytes contributes to atherosclerotic calcification.

Calcification of advanced atherosclerotic lesions in the innominate arteries of ApoE-deficient mice: potential role of chondrocyte-like cells

OBJECTIVE

Advanced atherosclerotic lesions in the innominate arteries of chow-fed apolipoprotein E-deficient mice become highly calcified with 100% frequency by 75 weeks of age. The time course, cell types, and mechanism(s) associated with calcification were investigated.

METHODS AND RESULTS

The deposition of hydroxyapatite is preceded by the formation of fibro-fatty nodules that are populated by cells that morphologically resemble chondrocytes. These cells are spatially associated with small deposits of hydroxyapatite in animals between 45 and 60 weeks of age. Immunocytochemical analyses with antibodies recognizing known chondrocyte proteins show that these cells express the same proteins as chondrocytes within developing bone. Histological and electron microscopic analyses of lesions from animals between 45 and 60 weeks of age show that the chondrocyte-like cells are surrounded by dense connective tissue that stains positive for type II collagen. Nanocrystals of hydroxyapatite can be seen within matrix vesicles derived from the chondrocyte-like cells. In mice between 75 and 104 weeks of age, the lesions have significantly reduced cellularity and contain large calcium deposits. The few remaining chondrocyte-like cells are located adjacent to or within the large areas of calcification.

CONCLUSIONS

Calcification of advanced lesions in chow-fed apolipoprotein E-deficient mice occurs reproducibly in mice between 45 and 75 weeks of age. The deposition of hydroxyapatite is mediated by chondrocytes, which suggests that the mechanism of calcification may in part recapitulate the process of endochondral bone formation.