Arterial calcification: a review of mechanisms, animal models, and the prospects for therapy

Arterial calcification in race horses

Calcification of large arteries has been sporadically reported in horses. The pathogenesis is still unknown, but recent studies in humans suggest that this is a regulated biomineralizing process. This study surveyed the prevalence, distribution, and severity of vascular calcification in Thoroughbred and Standardbred racehorses. Histopathologic, ultrastructural imaging, and energy dispersive X-ray elemental analyses were used to examine the lesions. Calcification of the tunica media, predominantly the pulmonary artery, was found in 82% of horses (83/101). Young adult horses (mean [SD] age in years, 4.44 +/- 2.17) of both breeds and sexes were similarly affected. Lesions appeared as white-to-yellowish, hard, and gritty plaques of variable size. On microscopic examination, elastic fibers within the tunica media were thinned, fragmented, and calcified, and surrounded by dense collagen matrix. Elemental analysis showed distinct peaks for calcium and phosphorus, consistent with hydroxyapatite mineral. The frequent occurrence of calcification in the tunica media of large pulmonary arteries of young racing horses indicates the need to investigate its pathogenesis and potential clinical implications.

Media calcification and intima calcification are distinct entities in chronic kidney disease

Calcification of the vascular tree is common in physiologic and pathologic conditions, i.e., aging, diabetes, dyslipidemia, genetic diseases, and diseases with disturbances of calcium metabolism. In chronic kidney disease, vascular calcification is even more common, develops early, and contributes to the markedly increased cardiovascular risk in this particular population. Pathomorphologically, atherosclerosis (i.e., plaque-forming degenerative changes of the aorta and of large elastic arteries) and arteriosclerosis (i.e., concentric media thickening of muscular arteries) can be distinguished. Increasing knowledge about calcification together with improved imaging techniques provided evidence that also vascular calcification has to be divided into two distinct entities according to the specific sites of calcification within the vascular wall: Patchy calcification of the intima in the vicinity of lipid or cholesterol deposits as present in plaque calcification and calcification of the media in the absence of such lipid or cholesterol deposits, known as Mönckeberg-type atherosclerosis. The two types of calcification may vary according to the type of vessel (large elastic versus smaller muscular type artery) and proximal versus distal sites of the arterial tree. Furthermore, clinical studies showed that it is not purely academic to distinguish between intimal and medial calcification but rather relevant for the clinical presentation, treatment, and prognosis because each type leads to different clinical consequences. In vivo studies in animal models provided evidence in favor of common pathomechanisms between vascular calcification and atherosclerosis; however, there is other, strong experimental and clinical evidence that pleads for the continued distinction between intimal and medial calcification.

Sequential activation of matrix metalloproteinase 9 and transforming growth factor beta in arterial elastocalcinosis

OBJECTIVE

Isolated systolic hypertension is associated with increased elastase activity, vascular calcification, and vascular stiffness. We sought to determine the importance of elastase activity and matrix degradation in the development of elastocalcinosis.

METHODS AND RESULTS

Elastocalcinosis was induced in vivo and ex vivo using warfarin. Hemodynamic parameters, calcium deposition, elastin degradation, transforming growth factor (TGF)-beta signaling, and elastase activity were evaluated at different time points in the in vivo model. Metalloproteinases, serine proteases, and cysteine proteases were blocked to measure their relative implication in elastin degradation. Gradual elastocalcinosis was obtained, and paralleled the elastin degradation pattern. Matrix metalloproteinase (MMP)-9 activity was increased at 5 days of warfarin treatment, whereas TGF-beta signaling was increased at 7 days. Calcification was significantly elevated after 21 days. Blocking metalloproteinases activation with doxycycline and TGF-beta signaling with SB-431542 were able to prevent calcification.

CONCLUSIONS

Early MMP-9 activation precedes the increase of TGF-beta signaling, and overt vascular elastocalcinosis and stiffness. Modulation of matrix degradation could represent a novel therapeutic avenue to prevent the gradual age-related stiffening of large arteries, leading to isolated systolic hypertension.

Cardiovascular risks of calcium supplements in women

Increased risk of myocardial infarction outweighs the reduction in fractures

Effects of the blood coagulation vitamin K as an inhibitor of arterial calcification

INTRODUCTION

The transformation of smooth muscle cells (VSMCs) in the vessel wall to osteoblast like cells is known to precede arterial calcification which may cause bleeding complications. The vitamin K-dependent protein MGP has been identified as an inhibitor of this process by binding BMP-2, a growth factor known to trigger the transformation. In this study, we determined if the vitamin K-dependent Gla region in MGP by itself can inhibit the growth factor activity of BMP-2 and if menaquinone-4 (MK4) regulates gene expression in VSMCs.

MATERIALS AND METHODS

A synthetic gamma-carboxyglutamic acid (Gla) containing peptide covering the Gla region in human MGP was used to test its ability to inhibit BMP-2 induced transformation of mouse pro-myoblast C2C12 cells into osteoblasts. MK4 was tested by microarray analysis as a gene regulatory molecule in VSMCs.

RESULTS AND CONCLUSIONS

The results show that the Gla - but not the Glu-peptide inhibited the transformation which provide evidence that the Gla region in MGP is directly involved in the BMP-2/MGP interaction and emphasizes the importance of the vitamin K-dependent modification of MGP. From the data obtained from the microarray analysis, we focused on two quantitatively altered cDNAs representing proteins known to be associated with vessel wall calcification. DT-diaphorase of the vitamin K-cycle, showed increased gene expression with a 4.8-fold higher specific activity in MK4 treated cells. Osteoprotegrin gene expression was down regulated and osteoprotegrin protein secretion from the MK4 treated cells was lowered to 1.8-fold. These findings suggest that MK4 acts as an anti-calcification component in the vessel wall.

A cardiovascular phenotype in warfarin-resistant Vkorc1 mutant rats

BACKGROUND: The inhibition of the vitamin K cycle by warfarin promotes arterial calcification in the rat. Conceivably, genetically determined vitamin K-deficiency owing to a mutant epoxide reductase subcomponent 1 (Vkorc1) gene, a key component of the vitamin K cycle, might also promote arterial calcification. In the absence of an available Vkorc1 gene knockout model we used a wild-derived Vkorc1 mutant rat strain (Rattus norvegicus) to explore the validity of this hypothesis. METHODS: We provide histopathological descriptions of a naturally occurring Vkorc1 gene knockdown: wild-derived lab-reared rats that are resistant to the anticoagulant warfarin owing to a non-synonymous mutation in the Vkorc1 gene (Vkorc1(Y->C)), which, in vitro, reduces the basal activity of the vitamin K epoxide reductase enzyme complex by ~52%. H&E stained sections of heart and kidney were compared between homozygous Vkorc1(Y->C/ Y->C), heterozygous Vkorc1(Y->C/+) and wildtype Vkorc1(+/+) rats of both sexes. RESULTS: We observed that the aorta of the heart was mineralized in the Vkorc1(Y->C/ Y->C) male rats but lesions were virtually absent from Vkorc1(Y->C/+) and Vkorc1(+/+) male and all female rats. The renal arteries were mineralized in Vkorc1(Y->C/ Y->C) and Vkorc1(Y->C/+) mutant rats, regardless of sex. CONCLUSIONS: Results support a hypothesis that posits that Vkorc1 genetic polymorphisms reducing basal enzyme activity could affect cardiovascular health, with dependencies on genotype, sex, and tissue. The undercarboxylation of the vitamin K-dependent Matrix Gla protein may be the crucial component of the pathway promoting this mineralization.

Novel inhibitors of alkaline phosphatase suppress vascular smooth muscle cell calcification

We report three novel inhibitors of the physiological pyrophosphatase activity of alkaline phosphatase and show that these compounds are capable of reducing calcification in two models of vascular calcification (i.e., they suppress in vitro calcification by cultured Enpp1(-/-) VSMCs and they inhibit the increased pyrophosphatase activity in a rat aortic model).

INTRODUCTION

Genetic ablation of tissue-nonspecific alkaline phosphatase (TNALP) leads to accumulation of the calcification inhibitor inorganic pyrophosphate (PP(i)). TNALP deficiency ameliorates the hypermineralization phenotype in Enpp1(-/-) and ank/ank mice, two models of osteoarthritis and soft tissue calcification. We surmised that the pharmacological inhibition of TNALP pyrophosphatase activity could be used to prevent/suppress vascular calcification.

MATERIALS AND METHODS

Comprehensive chemical libraries were screened to identify novel drug-like compounds that could inhibit TNALP pyrophosphatase function at physiological pH. We used these novel compounds to block calcification by cultured vascular smooth muscle cells (VSMCs) and to inhibit the upregulated pyrophosphatase activity in a rat aortic calcification model.

RESULTS

Using VSMC cultures, we determined that Enpp1(-/-) and ank/ank VSMCs express higher TNALP levels and enhanced in vitro calcification compared with wildtype cells. By high-throughput screening, three novel compounds, 5,361,418, 5,923,412, and 5,804,079, were identified that inhibit TNALP pyrophosphatase function through an uncompetitive mechanism, with high affinity and specificity when measured at both pH 9.8 and 7.5. These compounds were shown to reduce the calcification by Enpp1(-/-) VSMCs. Furthermore, using an ex vivo rat whole aorta PP(i) hydrolysis assay, we showed that pyrophosphatase activity was inhibited by all three lead compounds, with compound 5,804,079 being the most potent at pH 7.5.

CONCLUSIONS

We conclude that TNALP is a druggable target for the treatment and/or prevention of ectopic calcification. The lead compounds identified in this study will serve as scaffolds for medicinal chemistry efforts to develop drugs for the treatment of soft tissue calcification.

Polymorphisms at the Osteoprotegerin and Interleukin-6 Genes in Relation to First-Ever Stroke

BACKGROUND

Arterial calcification and osteoporosis often coexist, especially in postmenopausal women. Osteoporosis associates with a substantially increased risk of stroke in elderly women, suggesting that impaired estrogen signaling may link stroke and osteoporosis. Osteoprotegerin (OPG, TNFRSF11B) and interleukin-6 (IL-6, IL6) are putative target genes for estrogen signaling and have been implicated in both cardiovascular diseases and osteoporosis. We hypothesized that specific polymorphisms in these genes may be associated with increased risk of ischemic stroke or intracerebral hemorrhage (ICH).

METHODS

We performed a population-based prospective nested case-control study, in which the relationships between polymorphisms (OPG-1181G/C, OPG-950T/C and IL6-174G/C) and ischemic stroke and ICH were examined. Definitive first-ever stroke events (n = 388), i.e. ischemic stroke (n = 320), ICH (n = 61) and unspecified stroke (n = 7) cases, and controls without cardiovascular disease (n = 773), matched for age, sex and geographical region were studied. Univariate and multivariate models using conditional logistic regression, which included traditional risk factors, were used to test for association.

RESULTS

Carriers of the OPG-1181C/C genotype had a significantly (p = 0.018) increased risk of ICH (OR, 2.69; 95% CI, 1.19-6.12) in the univariate analysis. After adjustments (hypertension, diabetes, BMI and triglycerides), this genotype remained significantly (p = 0.005) associated with ICH (OR, 6.04; 95% CI, 1.71-21.29). By contrast, no correlations were found between this genotype and ischemic stroke, nor between the OPG-950T/C or IL6-174G/C polymorphisms and stroke subtypes.

CONCLUSIONS

In this population, the OPG-1181C/C genotype associates with first-ever ICH, implying that alterations in OPG-mediated signaling in the vasculature may be involved in the pathophysiology of this disease.

Role of osteoprotegerin in arterial calcification: development of new animal model

OBJECTIVES

Enhanced osteoclastogenesis, increased bone resorption, and osteoporosis have been reported in osteoprotegerin-deficient (OPG (-/-)) mice. OPG (-/-) mice available in Japan usually do not show vascular calcification. We have found that arterial calcification can be quickly induced by a simple procedure in OPG (-/-) mice.

METHODS AND RESULTS

Male OPG (-/-), OPG (+/-), and OPG (+/+) mice were fed a high phosphate diet from 6 to 10 weeks after birth, and then 1alpha,25-dihydroxyvitamin D3 (calcitriol) was injected for 3 days. We found that severe calcification developed in the media of the aorta in OPG (-/-) mice. Under electron microscopy, calcium deposits were observed in the cytoplasm and extracellular matrix of vascular smooth muscle cells (VSMCs). Neither apoptosis of VSMCs nor infiltration of macrophages was observed. Alkaline phosphatase (ALP) activity of aortic tissue correlated with the calcified lesion area. Mouse aorta and bone extracts revealed an identical pattern by ALP electrophoresis.

CONCLUSIONS

Our results demonstrated that OPG had anticalcification activity in the aorta, probably through the downregulation of ALP activity. Because the time course of arterial calcification after the injection of calcitriol is accurate and reproducible, this mouse model will be useful for further investigation of vascular calcification.

Presence of an established calcification marker in trabecular meshwork tissue of glaucoma donors

PURPOSE

To determine the presence of calcification markers in the trabecular meshwork tissue from glaucoma donors and in trabecular meshwork cells insulted by dexamethasone (DEX) and transforming growth factor beta2 (TGFbeta2), factors associated with glaucoma. To investigate as well the effect of silencing the inhibitor of calcification matrix Gla (MGP) in the trabecular meshwork cells.

METHODS

Trabecular meshwork tissue was obtained from perfused postmortem anterior segments of glaucomatous and normal eyes. Primary trabecular meshwork cells were obtained from residual corneal rims after surgical corneal transplantation. Calcification marker alkaline phosphatase (ALP) enzyme activity was assayed by fluorescence produced after substrate cleavage. DNA quantification was evaluated by fluorescence produced after binding to the Hoechst dye. Transfection of siRNA to primary cells was accomplished by nucleofector electroporation with trabecular meshwork-optimized conditions. cDNA quantification was performed with the use of TaqMan real-time PCR.

RESULTS

Human trabecular meshworks from glaucoma donors exhibited significantly higher levels of ALP activity than their matched counterparts with normal eyes. The normalized ALP of the control specimens was 7.3 +/- 1.6 ng ALP/microg DNA (n = 4), whereas that of the glaucomatous tissue was 37.0 +/- 10.7 ng ALP/microg genomic DNA (n = 5; P

CONCLUSIONS

The increased activity of the calcification marker, ALP, in glaucomatous trabecular meshworks might be indicative of an undergoing mineralization process during development of the disease. Inhibition of the calcification mechanism represented by the presence of active MGP appears to be compromised in glaucomatous tissue.

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Key Words Collapse

MESH Headings

• Adult
• Aged
• Aged, 80 and over
• Alkaline Phosphatase/metabolism
• Biomarkers/metabolism
• Calcinosis/enzymology
• Calcium-Binding Proteins/genetics
• Cells, Cultured
• Dexamethasone/pharmacology
• Electroporation/methods
• Extracellular Matrix Proteins/genetics
• Female
• Gene Silencing
• Glaucoma/enzymology
• Humans
• Male
• Middle Aged
• Polymerase Chain Reaction
• RNA, Small Interfering/pharmacology
• Tissue Donors
• Trabecular Meshwork/drug effects
• Trabecular Meshwork/enzymology
• Transfection
• Transforming Growth Factor beta2/pharmacology
• Up-Regulation
• Matrix Gla Protein

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Grants

• R01 EY013126 NEI NIH HHS
• R01 EY013126-08 NEI NIH HHS
• R01 EY011906 NEI NIH HHS
• R01 EY011906-10 NEI NIH HHS
• EY13126 NEI NIH HHS
• EY11906 NEI NIH HHS

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Affiliation(s)

Wei Xue Department of Ophthalmology, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599-7041, USA
Núria Comes
Teresa Borrás

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Tanshinone II A attenuates atherosclerotic calcification in rat model by inhibition of oxidative stress

AIM

We have previously proved that oxidized low-density lipoprotein (oxLDL), a proatherogenic lipoprotein, plays a pivotal role in the development of atherosclerotic calcification (AC). The present study was performed to investigate whether tanshinone II A (TS II A), an anti-oxidant which has been shown to inhibit in vitro oxidation of LDL, has the effects to inhibit AC in rat model and by which, if any, mechanisms.

METHODS

Rat AC model was induced by excessive vitamin D(2) (VD) and high cholesterol diet (HCD), which was proven to be successful histopathologically and biochemically.

RESULTS

Administration of AC rats with TS II A (35, 70 mg/kg) dose-dependently attenuated the AC pathological changes, meanwhile reduced the vessel contents of lipid and calcium. However, TS II A had no effects on serum levels of lipids, calcium and 25-OH VD. Further studies revealed that TS II A decreased serum concentration of oxLDL, reduced the superoxide anion production and malondialdehyde (MDA) in vessel. In addition, TS II A increased vessel Cu/Zn SOD activity, upregulated vessel mRNA and protein expression of Cu/Zn SOD.

CONCLUSION

The results suggested that TS II A significantly attenuated the AC in rat model, which might be attributed to its inhibition of oxLDL production independent of the serum levels of lipids, calcium and 25-OH VD, and that increasing of Cu/Zn SOD activity as well as mRNA and protein expression by TS II A might protect LDL against oxidation induced by superoxide anion in vessel.

Identification of Abcc6 as the major causal gene for dystrophic cardiac calcification in mice through integrative genomics

The genetic factors contributing to the complex disorder of myocardial calcification are largely unknown. Using a mouse model, we fine-mapped the major locus (Dyscalc1) contributing to the dystrophic cardiac calcification (DCC) to an 840-kb interval containing 38 genes. We then identified the causal gene by using an approach integrating genetic segregation and expression array analyses to identify, on a global scale, cis-acting DNA variations that perturb gene expression. By studying two intercrosses, in which the DCC trait segregates, a single candidate gene (encoding the ATP-binding cassette transporter ABCC6) was identified. Transgenic complementation confirmed Abcc6 as the underlying causal gene for Dyscalc1. We demonstrate that in the cross, the expression of Abcc6 is highly correlated with the local mineralization regulatory system and the BMP2-Wnt signaling pathway known to be involved in the systemic regulation of calcification, suggesting potential pathways for the action of Abcc6 in DCC. Our results demonstrate the power of the integrative genomics in discovering causal genes and pathways underlying complex traits.

Antioxidant Vitamin Intake and Subclinical Coronary Atherosclerosis

Numerous studies have evaluated the association between antioxidants and coronary atherosclerosis but have been limited by its study among individuals with advanced atherosclerosis. The authors studied 865 consecutive patients, 39-45 years of age, without known coronary artery disease and presenting for a periodic physical examination. Antioxidant intake was assessed with the Block Dietary Questionnaire, and coronary atherosclerosis was identified by measuring coronary artery calcification using electron beam computed tomography. The mean age was 42 (+/-2), 83% were male, and the prevalence of coronary artery calcification was 20%. Vitamin supplements were used by 56% of the participants, and the mean (+/-SD) daily intake (dietary plus supplemental) of vitamins A, C, and E were 1683 mg (+/-1245), 371 mg (+/-375), and 97 mg (+/-165), respectively. There was no significant correlation between coronary artery calcification score and individual vitamin or total antioxidant vitamin intake, even after adjusting for traditional cardiac risk factors. The highest quartile of vitamin E was positively associated with calcification (odds ratio=1.77; 95% confidence interval, 1.02-3.06). Antioxidant vitamin intake is not significantly related to coronary artery calcification, implying that there is no effect on the development of early coronary atherosclerosis. High doses of vitamin E may confer an increased risk of calcified atherosclerosis.

Serum osteoprotegerin levels in patients with acute atherothrombotic stroke and lacunar infarct

BACKGROUND

Arterial calcification is associated with increased risk of cardiovascular events. Osteoprotegerin (OPG) is a cytokine involved in the bone metabolism and vascular calcification. Recent data support a relationship between high serum levels of OPG and increased risk for cardiovascular disease in human. The aim of this study was to evaluate the OPG serum levels in acute ischemic stroke. Our study was further designed to detect differences in serum OPG levels between subtypes of ischemic stroke.

MATERIALS AND METHODS

The study consisted of 51 patients with acute ischemic stroke and 28 control subjects. Stroke subtypes were defined by the TOAST classifications. Serum OPG levels were measured with the ELISA method.

RESULTS

OPG serum levels were significantly higher in patients with ischemic stroke than in control subjects (p<0.001). OPG serum levels were significantly higher in large-vessel disease (LVD) subtype compared with small-vessel disease (SVD) subtype and controls (p<0.001, p<0.001). There was no significant difference in OPG serum levels between SVD group and control subjects. Serum OPG levels were correlated with age (r=0.407, p=0.005) and fasting glucose levels (r=0.542, p=0.001) in ischemic stroke group. Logistic regression analysis showed that plasma OPG levels (OR 2.1, 95% CI, 1.16 to 3.4, p=0.01) associated with presence of stroke independently of the other risk factors.

CONCLUSIONS

High serum OPG levels were associated with the LVD stroke subtype, suggesting that OPG levels may play role in pathogenesis of atherothrombotic stroke. The precise mechanism for the role of OPG in atherosclerosis needs to be investigated further.

Hypercholesterolemia accelerates vascular calcification induced by excessive vitamin D via oxidative stress

Hypercholesterolemia plays an important role in the initiation and progression of atherosclerosis and has a positive correlation with cardiovascular disease. Calcification is a common feature of atherosclerotic lesions and contributes to cardiovascular dysfunctions. The present study investigated the role of hypercholesterolemia in vascular calcification and its potential mechanism. Models of vascular calcification were established by administering vitamin D2 (VD) to rats alone or combined with a high-cholesterol diet (HCD) and by treating rat aorta smooth muscle cells (RASMCs) with beta-glycerophosphate (GP) alone or combined with oxidized low-density lipoprotein (oxLDL) in vitro. In rats, the combination of VD with HCD significantly enhanced vessel calcium deposition and the activity and mRNA expression of vessel alkaline phosphatase (ALP) compared to treatment with VD alone. This combination also enhanced serum levels of total cholesterol, oxLDL, and malondialdehyde as well as vascular production of superoxide anion, while it reduced the vascular activity of superoxide dismutase. Both simvastatin, a cholesterol-lowering agent, and antioxidant vitamin E antagonized the effects of the above combination. In RASMCs, oxLDL accumulation dependently accelerated calcium deposition in cell layers initiated by GP alone. Also, oxLDL stimulated ALP activity and mRNA expression in RASMCs in a concentration-dependent manner. Taken together, these results suggest that acceleration of vascular calcification by hypercholesterolemia might be attributed to oxidative stress and such calcification may be another target of statin or antioxidant action in antiatherosclerosis.

Expression of osteonectin and matrix Gla protein in scleroderma patients with and without calcinosis

OBJECTIVES

Our aim was to evaluate (i) whether the bone matrix proteins osteonectin and matrix gamma-carboxyglutamic acid protein (MGP) are up-regulated in skin biopsies from patients with systemic sclerosis (SSc) and (ii) whether there is differential expression between patients with and without dermal calcinosis, a distressing and debilitating complication of SSc.

METHODS

Skin punch biopsies were taken from the forearms of 38 SSc patients with the limited cutaneous subtype of SSc [17 without calcinosis (lcSSc) and 21 with calcinosis (lcSScCal)] and from 11 healthy control subjects. Immunohistochemistry was performed with antibodies to osteonectin and MGP. Staining was assessed semiquantitatively in the microvascular endothelium and in dermal fibroblasts. The Kruskal-Wallis one-way ANOVA was used to compare the data between patient groups.

RESULTS

Both lcSSc and lcSScCal groups showed a statistically significant increase in the percentage of microvessels with osteonectin-positive endothelial cells (EC) (especially the lcSScCal group), whereas lcSScCal alone showed an increase in the percentage of microvessels with MGP-positive EC when compared with controls. In both SSc groups, the percentage of osteonectin and MGP-stained fibroblasts was increased in the reticular dermis (for osteonectin this was more marked in the lcSScCal group). In the papillary dermis, the percentage of osteonectin-stained fibroblasts was increased in both SSc groups but the lcSScCal group alone had a higher percentage of MGP-stained fibroblasts.

CONCLUSIONS

When compared with controls, protein expression of osteonectin and MGP was greater in SSc patients generally, and osteonectin expression was significantly higher in EC and fibroblasts of the lcSScCal patients than the lcSSc patients without calcinosis.

Excess magnesium inhibits excess calcium-induced matrix-mineralization and production of matrix gla protein (MGP) by ATDC5 cells

We found that excessive extracellular Ca2+ and/or Mg2+ affected the process of matrix mineralization and glycosaminoglycan (GAG) production by cells of the prechondrogenic cell line, ATDC5. Excess Ca2+ induced both matrix mineralization and GAG production in the cells. On the other hand, excess Mg2+ reduced this Ca2+-mediated rise in both mineralization and GAG production in them. Next we measured the mRNA levels of cartilage-associated genes such as calcium-sensing receptor (CaSR), matrix gla protein (MGP), bone gla protein (BGP), and Runt-related transcription factor 2 (Runx2) in ATDC5 cells. Excess Ca2+ increased the MGP, BGP, and CaSR mRNA levels, and excess Mg2+ reduced the Ca2+-induced increase in the MGP mRNA level in the cells. The changes in the MGP mRNA level paralleled those in the MGP protein level. These data show that Ca2+ and Mg2+ regulated the matrix mineralization positively and negatively, respectively, in ATDC5 cells and suggest that excess Mg2+ might inhibit the excess Ca2+-promoted mineralization mediated by MGP induction in chondrocytes.

Macrophages and giant cell proliferation associated with bone protein synthesis and calcification in the trachea and bronchi of rabbits intoxicated with Solanum glaucophyllum

A histopathologic, immunohistochemical, and ultrastructural study of the trachea and the bronchi of 6 rabbits experimentally intoxicated with the calcinogenic plant Solanum glaucophyllum was performed. Histologically, infiltration of the mucosa and the submucosa of the trachea and the bronchi by macrophages, multinucleated giant cells, a few lymphocytes and mast cells, and calcium deposits in the basal lamina of the epithelium and in elastic fibers were observed. Expression of osteocalcin, osteonectin, and osteopontin was detected in the mucosa, lamina propria, and epithelium. Electron microscopic study of the corresponding areas showed numerous macrophages in the process of fusion to form multinucleated giant cells, activated mesenchymal cells, and calcium precipitation in the basal lamina of epithelium and in elastic fibers. It is suggested that the high levels of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) in the plant induces macrophage proliferation, multinucleated giant-cell formation, mesenchymal cell activation, bone-protein synthesis, and calcification. In addition, the synthesis of 1,25(OH)2D3 by local macrophages may have contributed to the calcification.

Inflammatory bowel diseases as secondary causes of osteoporosis

Inflammatory bowel disease (IBD), comprising Crohn's disease and ulcerative colitis, is associated with an increased risk of osteoporosis and bone fractures. Initial studies suggested very high rates of osteoporosis in IBD, but more recent studies have suggested that bone mineral density (BMD) is often normal in patients with IBD and typically changes little over time. Nonetheless, IBD is associated with an increased risk of fractures. Doctors managing patients with IBD must consider a variety of risk factors, not just BMD measurements, in assessing fracture risk. Advances have been made in exploring the pathogenesis of osteoporosis in IBD. The evolution of knowledge regarding receptor for activated factor of nuclear factor kappaB (RANK), its ligand RANKL, and osteoprotegerin (OPG), which serves as a decoy receptor, has enhanced the understanding of both osteoporosis and T-cell immunobiology. Recent clinical studies in patients with IBD have revealed that serum OPG levels may be elevated and inflamed intestinal tissue secretes increased amounts of OPG. It is suspected that OPG levels are elevated as a counterregulatory response to low BMD, as serum OPG levels in IBD have been found to be inversely associated with BMD. Finally, in animal models of IBD, exogenous OPG has reversed both the osteopenia and the enterocolitis, suggesting that it may have a therapeutic role in human IBD.

Klotho gene polymorphism may be a genetic risk factor for atherosclerotic coronary artery disease but not for vasospastic angina in Japanese

BACKGROUND

The klotho gene, originally identified by insertional mutagenesis in mice, suppresses multiple aging phenotypes, including atherosclerosis. We tested the hypothesis that the G-395A polymorphism of the klotho gene is associated with increased risk for 2 types of ischemic heart disease in Japanese.

METHODS

The study population consisted of 197 patients with coronary heart disease (CAD) who had >75% luminal diameter narrowing, 77 patients with vasospastic angina (VSA) without significant fixed coronary artery disease, and 331 healthy control subjects.

RESULTS

The frequency of the A allele carriers of the klotho gene was significantly higher in the CAD group than in the control group (29.9% vs. 19.0%). The unadjusted odds ratio for CAD in the A allele carriers compared with the control group was 1.82 (p=0.004) and a traditional risk-adjusted logistic regression model revealed that the A allele was an independent predictor of CAD (odds ratio, 1.76; p=0.03). In contrast, the frequency of the A allele carriers was not significantly different in the VSA group (23.4%; adjusted odds ratio, 1.18.

CONCLUSIONS

The -395A polymorphism of the human klotho gene may be a genetic risk factor for IHD and not for VSA.

Arterial calcification in mice after freeze-thaw injury

Vascular calcification is highly correlated with atherosclerosis and cardiovascular disease and is a significant predictor of cardiovascular morbidity and mortality. Studies in mice indicate a genetic contribution to this dystrophic extra osseous calcification. We sought to elaborate a method to induce dystrophic arterial calcification in mice and further examine the pathogenetical mechanisms involved in the phenotype. We established a method of freeze-thaw injury of the infrarenal aorta producing a limited tissue necrosis and histologically investigated the occurrence of dystrophic calcification within the aortic wall 1, 3 and 7 days after injury in C57BL/6 (a mouse strain shown to be resistant to dystrophic cardiac calcification after injury) and C3H/He (susceptible to dystrophic cardiac calcification). C57BL/6 mice exhibited no dystrophic calcification at all within the vessel wall upon injury of the infrarenal aorta (0/5 mice 1 day after injury and 0/10 animals 7 days after injury). By contrast C3H/He mice displayed a remarkable extent of calcification mainly present within the media of the infrarenal aorta which was evident as early as 24 h (three out of five animals 1 day after injury) and reached its maximum extent 7 days after injury (10 out of 10 animals at the seventh postoperative day, p<0.001 compared to C57BL/6 mice). Upon immuno-histological analysis calcification was accompanied by the occurrence of certain bone-matrix associated proteins. Osteopontin and Bone Morphogenetic Protein 2/4 expression was detected co-localized with the calcified lesions. Our results demonstrate that freeze-thaw injury of the infrarenal aorta is a sufficient method to induce dystrophic arterial calcification in mice. We present evidence that the occurrence of arterial calcification in C3H/He mice seems to be actively regulated by certain bone-matrix associated proteins.

Optical imaging of hydroxyapatite in the calcified vasculature of transgenic animals

OBJECTIVE

To detect the hydroxyapatite component of vascular calcification in vivo so that the process of calcium deposition can be studied in transgenic model systems.

METHODS AND RESULTS

We have previously developed a near-infrared fluorescent bisphosphonate derivative that binds with high affinity and specificity to hydroxyapatite, and an intraoperative near-infrared fluorescence imaging system for small animals. Using these tools, and a transgenic mouse strain with homozygous deletion of the matrix GLA protein (Mgp(-/-)), we demonstrate that the hydroxyapatite component of vascular calcification can be detected in vivo with high sensitivity, specificity, and resolution.

CONCLUSIONS

The hydroxyapatite component of vascular calcification can be detected optically, in real-time, without sacrifice of the animal. It is now possible to study the earliest events associated with vascular mineralization, at the cell and organ level, and to monitor the process in living animals.

Paget's Disease of Bone and Genetic Disorders of RANKL/OPG/RANK/NF- B Signaling

Identification of the RANKL/OPG/RANK/NF-kB (receptor activator of nuclear factor kappa-B ligand / osteoprotegerin) signaling pathway as the major regulatory system for osteoclastogenesis began with discovery of these ligands and receptors in the tumor necrosis factor (TNF) superfamily. Subsequently, genetically altered mice revealed physiologic roles for these proteins in bone biology. However, full appreciation of their significance for the human skeleton came from clinical characterization of several extremely rare, heritable disorders followed by discovery of their genetic bases. Familial expansile osteolysis (FEO) is an autosomal dominant disorder featuring constitutive activation of RANK due to an 18-bp tandem duplication in its gene (TNFRSF11A). A similar, 27-bp duplication causes what has been called a familial form of early-onset Paget's disease of bone (PDB2). Expansile skeletal hyperphosphatasia (ESH) is allelic to FEO and PDB2 and involves a 15-bp tandem duplication in TNFRSF11A. Autosomal recessive inheritance of deactivating mutations of the gene encoding OPG (TNFRSF11B) causes most cases of juvenile Paget disease. These disorders feature high bone turnover, deafness during early childhood, "idiopathic external lysis" of adult teeth, and sometimes focal lesions in appendicular bones that mimic active PDB. Biochemical markers indicate rapid skeletal remodeling. In FEO, osteolysis progresses to fat-filled bone rather than to osteosclerosis. Antiresorptive therapy with bisphosphonates can be effective for each disorder.

Matrix GLA protein function in human trabecular meshwork cells: inhibition of BMP2-induced calcification process

PURPOSE

The matrix GLA (MGP) gene has been found to be among the 10 most highly expressed genes in the human trabecular meshwork (TM), and its expression is affected by conditions associated with glaucoma. Because MGP protein has been shown to play a key role in inhibiting calcification in cartilage and arterial vessels, MGP's function in human TM was investigated.

METHODS

Perfused TM tissue and primary human TM (HTM) cells originated from donors of nonglaucomatous eyes. MGP mRNA was assayed by relative quantitative and real-time PCR. AdhMGP recombinant adenovirus was generated by bacterial transposition. Western blot analyses were cross-reacted with MGP N-terminal- and conformational-specific antibodies. MGP/BMP2 colocalization was analyzed by confocal microscopy. gamma-Carboxylation activity was measured by incorporation of 14CO2 into FLEEL synthetic peptide. Alkaline phosphatase (ALP) activity was used as a marker of osteogenic differentiation and a calcification precursor. Calcification was assessed by measuring direct calcium (o-cresolphthalein). Normalization was conducted with a telomerase probe (genomic DNA).

RESULTS

HTM cells contained high levels of gamma-carboxylase activity and were able to convert MGP to its active conformation. Overexpression of MGP in HTM cells reduced ALP activity in a model of BMP2-induced osteogenesis. MGP colocalized intracellularly with BMP2. HTM cells aged in culture exhibited increased calcium content, increased ALP, decreased normalized MGP expression and lower gamma-carboxylase activity.

CONCLUSIONS

MGP protein is active and functions as an inhibitor of BMP2-induced ALP activity in the HTM cells. The human TM may undergo a calcification process with age. Inhibition of the calcification mechanism mediated by MGP could be used to regulate resistance and elevated IOP.

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.

Vitamin K in the treatment and prevention of osteoporosis and arterial calcification

PURPOSE

The role of vitamin K in the prevention and treatment of osteoporosis and arterial calcification is examined.

SUMMARY

Vitamin K is essential for the activation of vitamin K-dependent proteins, which are involved not only in blood coagulation but in bone metabolism and the inhibition of arterial calcification. In humans, vitamin K is primarily a cofactor in the enzymatic reaction that converts glutamate residues into gamma-carboxyglutamate residues in vitamin K-dependent proteins. Numerous studies have demonstrated the importance of vitamin K in bone health. The results of recent studies have suggested that concurrent use of menaquinone and vitamin D may substantially reduce bone loss. Menaquinone was also found to have a synergistic effect when administered with hormone therapy. Several epidemiologic and intervention studies have found that vitamin K deficiency causes reductions in bone mineral density and increases the risk of fractures. Arterial calcification is an active, cell-controlled process that shares many similarities with bone metabolism. Concurrent arterial calcification and osteoporosis have been called the "calcification paradox" and occur frequently in postmenopausal women. The results of two dose-response studies have indicated that the amount of vitamin K needed for optimal gamma-carboxylation of osteocalcin is significantly higher than what is provided through diet alone and that current dosage recommendations should be increased to optimize bone mineralization. Few adverse effects have been reported from oral vitamin K.

CONCLUSION

Phytonadione and menaquinone may be effective for the prevention and treatment of osteoporosis and arterial calcification.

Osteoporosis, inflammation and ageing

Osteoporosis is a condition characterized by low bone mass and increased bone fragility, putting patients at risk of fractures, which are major causes of morbidity substantially in older people. Osteoporosis is currently attributed to various endocrine, metabolic and mechanical factors. However, emerging clinical and molecular evidence suggests that inflammation also exerts significant influence on bone turnover, inducing osteoporosis. Numerous proinflammatory cytokines have been implicated in the regulation of osteoblasts and osteoclasts, and a shift towards an activated immune profile has been hypothesized as important risk factor. Chronic inflammation and the immune system remodelling characteristic of ageing, as well as of other pathological conditions commonly associated with osteoporosis, may be determinant pathogenetic factors. The present article will review the current perspectives on the interaction between bone and immune system in the elderly, providing an interpretation of osteoporosis in the light of inflamm-ageing.

Higher circulating hsCRP levels are associated with lower bone mineral density in healthy pre- and postmenopausal women: evidence for a link between systemic inflammation and osteoporosis

Factors involved in inflammation are linked with those critical for bone remodeling. We examined the association between serum high sensitivity C-reactive protein (hsCRP) levels and bone mineral density (BMD) in healthy women. Serum concentrations of hsCRP and total alkaline phosphatase (ALP) were measured in premenopausal ( n =3,662) and postmenopausal ( n =1,031) women aged 30 years or older. BMD was measured at the femoral neck and lumbar spine using dual energy X-ray absorptiometry. According to the WHO definition, osteopenia was diagnosed at -2.5< T -score < -1.0 SD, and osteoporosis was diagnosed at T -score < or = -2.5 SD at any sites. Compared with normal subjects, log-transformed serum hsCRP levels were higher in osteopenic and osteoporotic subjects (all, P < 0.001) with linearity ( P for trend <0.001), after adjustment for age, BMI and menopausal status. Menopausal status did not have a significant interaction on the association ( P =0.457). In both premenopausal and postmenopausal women, serum total ALP levels were higher in the subjects with higher hsCRP quintiles than those with the lowest quintile (all, P for trend < 0.001). Multivariate-adjusted odds ratio (OR) for osteoporosis and osteopenia were 1.35 (95% CI, 1.08 to 1.68) in the highest hsCRP quintile of premenopausal women, and OR for osteoporosis was 1.54 (95% CI, 1.10 to 2.53) in the highest hsCRP quintile of postmenopausal women. These findings suggest that subclinical systemic inflammation may be associated with bone turnover rate and bone mass in healthy women.

Vitamin K1 intake and coronary calcification

OBJECTIVES

The activity of matrix Gla-protein (MGP), a potent inhibitor of vascular calcification, is dependent on carboxylation using vitamin K as a co-factor. In animals, low intake of total vitamin K has been shown to accelerate vascular calcification via the MGP mechanism. This has led to the hypothesis that low levels of dietary vitamin K intake may be a risk factor for accelerated vascular calcification in humans due to decreased MGP activity. Additionally, some authors have suggested that current recommended daily intake values for vitamin K might be insufficient to fully inhibit vascular calcification via the MGP mechanism. The aim of this study was to examine the relationship between dietary vitamin K1 (the most prevalent dietary form of vitamin K) intake and premature coronary artery calcification (CAC) in an asymptomatic screening population.

METHODS

We conducted a prospective study of 807 consecutive active-duty US Army personnel, 39-45 years of age, without known coronary heart disease. Vitamin K1 intake was measured with the Block Dietary Questionnaire and CAC was identified using electron-beam computed tomography (EBCT).

RESULTS

We found no significant correlation between CAC score and vitamin K1 intake (r = 0.132, P = 0.106). Multivariate analysis with adjustment for cardiac risk factors showed no association between dietary vitamin K1 intake and CAC.

CONCLUSIONS

Dietary vitamin K1 (phylloquinone) intake appears to be unrelated to premature coronary calcification in a screening population. Further investigation into the relationship of vascular calcification and other forms of vitamin K1 (menaquinones) is indicated.

Regression of medial elastocalcinosis in rat aorta: a new vascular function for carbonic anhydrase

BACKGROUND

We sought to determine whether carbonic anhydrase (CA), which plays an important role in bone resorption, contributes to vascular mineral loss induced by an endothelin receptor antagonist.

METHODS AND RESULTS

Wistar rats were compared with rats receiving warfarin and vitamin K1 (WVK) for 8 weeks alone or in association with the endothelin receptor antagonist darusentan (30 mg/kg per day), the CA inhibitor acetazolamide (100 mg/kg per day), or both for the last 4 weeks. Rats were also treated with WVK for 5 or 6 weeks, and darusentan was added for the last week or last 2 weeks of treatment, respectively. Treatment with WVK produced medial elastocalcinosis in the aorta and carotid arteries. Immunohistochemistry revealed that CA II was already abundant in the adventitia and in calcified areas of aortic sections from WVK-treated rats. Darusentan did not significantly modify its abundance or distribution. In contrast, CA IV immunostaining, which was weak in WVK-treated rats, became apparent after 1 week of darusentan treatment and declined toward basal levels thereafter. These findings were confirmed by a parallel increase in CA IV protein abundance and activity in the aorta. The mineral loss induced by darusentan was blunted by acetazolamide treatment, confirming the functional relevance of the biochemical findings. Moreover, CA IV immunostaining was enhanced much later in the carotids, where darusentan did not cause regression of elastocalcinosis.

CONCLUSIONS

Vascular mineral loss induced by the blockade of endothelin receptors seems dependent on the activation of membrane-bound CA IV, suggesting that mineral loss may proceed via local changes in pH similar to that seen in bone resorption.

Increased arterial calcification in Paget's disease of bone

When examining radiographs of patients with Paget's disease of bone (PD), we often observed calcification of the aorta and iliac or femoral arteries. The processes of extraosseous calcification or mineralization are very close to the mechanisms regulating mineralization of bone tissue. The aim of our study was to quantify the number, extent (length and thickness), and type (arteriosclerotic or medial arterial calcification) of vascular calcification in patients with Paget's disease and to compare them with those of controls, in order to discover whether PD is accompanied by increased calcification. Vascular calcification was quantified on the aorta, the iliac arteries, and their branches, the femoral, gluteal, and pelvic arteries of 42 patients with Paget's disease and 36 control subjects. Of the PD subjects, 52.4% had arteriosclerotic calcification versus 30.6% of controls (P = 0.05), and 38.6% of PD patients had medial arterial calcification versus 11.1% of controls (P = 0.05). The mean length of calcification was greater in PD patients: 1.93 +/- 2.85 cm versus 0.84 +/- 1.69 cm in controls (P = 0.04). The thickness of calcification was also greater in PD patients: 1.24 +/- 1.30 mm versus 0.56 +/- 0.94 mm (P = 0.01). Patients with Paget's disease more frequently had medial arterial or arteriosclerotic calcification than controls. These calcifications were longer and thicker. Our clinical study therefore confirms that abnormal vessel wall calcification and bone remodeling in Paget's disease are probably linked, although the mechanism of this relation is as yet unexplained.

Transcatheter placement of a low-profile biodegradable pulmonary valve made of small intestinal submucosa: A long-term study in a swine model

OBJECTIVE

We sought to investigate a placement of a percutaneous low-profile prosthetic valve constructed of small intestinal submucosa in the pulmonary position in a swine model.

METHODS

Twelve female farm pigs were stented at the native pulmonary valve to induce pulmonary insufficiency. Once right ventricular dilation occurred, the small intestinal submucosa valve was implanted. The pigs were followed up with transthoracic echocardiographic Doppler scanning. One animal died of heart failure before valve replacement. Animals were euthanized at 1 day, 1 month, 3 months, 6 months, and 12 months after valve implantation.

RESULTS

The small intestinal submucosa pulmonary valve showed effective reversal of pulmonary regurgitation. There were no misplacements during deployment. There were no embolizations. One-year echocardiographic follow-up showed minimal regurgitation and no stenosis for a valve/vessel ratio of 0.78 or greater. Histologic examination demonstrated intensive remodeling of the small intestinal submucosal valve. Within 1 month, the surface was covered by endothelium, and fibroblasts invaded the interior. Over the following months, the small intestinal submucosal valve remodeled without apparent graft rejection.

CONCLUSION

The small intestinal submucosa valve has the potential for graft longevity without the need for anticoagulation or immunosuppression. Histologic remodeling of the valve tissue provides a replacement capable of resembling a native valve that can be placed percutaneously with low-profile delivery systems.

VITAMIN D IN HEALTH AND DISEASE: The Role of Vitamin D in Vascular Calcification in Chronic Kidney Disease

Vascular calcification is a significant cause of morbidity and mortality in patients with chronic kidney disease (CKD). Disorders of mineral metabolism are likely involved in the pathogenesis of vascular calcification. Calcitriol and its analogs are effective in suppressing parathyroid hormone levels in patients with secondary hyperparathyroidism and CKD, but experimental studies demonstrate that these drugs can act directly on vascular smooth muscle cells. In some in vitro studies and in animal models of CKD, calcitriol has induced vascular calcification. Newer analogs of vitamin D appear to be less likely to induce vascular calcification, although published data are scarce. However, there is really no clear evidence in dialysis patients that calcitriol or analog administration is directly responsible for the induction of vascular calcification. However, indirectly, by oversuppression of parathyroid hormone (PTH) and induction of a low-turnover bone disease state, or by increased calcium-phosphorus product, the administration of calcitriol or its analogs may contribute to vascular calcification in patients with CKD. However, prospective randomized trials in CKD patients are necessary to fully understand the impact of calcitriol and analog therapy on vascular 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.

Ghrelin blunted vascular calcification in vivo and in vitro in rats

Ghrelin is a new peptide with regulatory actions in growth hormone secretion in the anterior pituitary gland and in energy metabolism. Currently, ghrelin has potently protective effects in cardiovascular diseases. We used an in vivo model of rat vascular calcification induced by vitamin D3 and nicotine and one of cultured rat vascular smooth muscular cells (VSMCs) calcification induced by beta-glycerophosphate to study the possible mechanism in the regulatory action of ghrelin in vascular calcification. Calcification increased total Ca2+ content and 45Ca2+ deposition in aortas and VSMCs and alkaline phosphatase (ALP) activation in plasma, aortas and VSMCs. However, calcified aortas and VSMCs showed a significant decrease in osteopontin (OPN) mRNA expression and a marked reduction of ghrelin levels in plasma and its mRNA expression in aortas. The aortic calcification was significantly attenuated by subcutaneous administration of ghrelin 30 and 300 nmol kg(-1) day(-1) for 4 weeks, and the latter dosage was more potent than the former. Ghrelin treatment at the two dosages reduced the total aorta Ca2+ content by 24.4% and 28.1%, aortic 45Ca2+ deposition by 18.4% and 24.9%, plasma ALP activity by 36.6% and 76.7%, and aortic ALP activity by 10.3% and 47.6% (all P < 0.01 or 0.05), respectively. Ghrelin at 10(-8)-10(-6) mol/L attenuated the calcification in cultured VSMCs, with decreased total Ca2+ content, 45Ca2+ deposition and ALP activity and increased OPN mRNA expression, in a concentration-dependent manner. In addition, endothelin levels in plasma and aortas and its mRNA expression in aortas significantly increased with calcification, but ghrelin treatment significantly decreased endothelin levels and mRNA expression, with the high dosage being more potent than the lower dosage. These results indicate that local ghrelin in vascular was down-regulated during vascular calcification, whereas administration of ghrelin effectively attenuated vascular and VSMCs calcification.

Serum fetuin-A in nondialyzed patients with diabetic nephropathy: relationship with coronary artery calcification

BACKGROUND

Fetuin-A is the most potent circulating inhibitor of calcium phosphorus precipitation and, possibly, an important mediator of insulin resistance.

METHODS

In order to determine the role of fetuin-A in the high coronary artery calcification (CAC) burden seen in nondialyzed individuals with diabetic nephropathy (DN), post-hoc analyses of data collected from a cross-sectional study of 88 patients with type 2 diabetes mellitus was done [age, 40-65 years; normoalbuminuria, N= 30 (Latinos); DN, N= 58 (Latinos and African Americans)].

RESULTS

The serum levels of fetuin-A were significantly higher among Latinos with DN when compared to either African Americans with DN or Latino diabetics with normoalbuminuria. Upon adjusting the data for race/ethnicity, there was a strong, direct relationship between serum fetuin-A levels and the CAC score (r= 0.22, P= 0.038) in the study cohort; however, a strong interaction between the nephropathy status and relationship of serum fetuin-A levels with CAC score was present (DN: r= 0.36, P= 0.006; diabetic controls, r= 0.0, P= 0.98). Among individuals with DN, the significance of the association persisted even after controlling the data for other predictors of CAC (partial r= 0.33, P= 0.018). Furthermore, there was a significant direct relationship between serum fetuin-A and serum triglycerides (partial r= 0.27, P= 0.01) and albumin (partial r= 0.30, P= 0.005), and an inverse relationship with glomerular filtration rate (r=-0.24, P= 0.03).

CONCLUSION

This first study in early stages of diabetic chronic kidney disease shows that the role of serum fetuin-A may be far more complex than previously described. During predialysis stage of DN, there is a direct relationship between serum fetuin-A levels and CAC score. The reasons for this association in the presence of nephropathy are unclear, but may be secondary to proatherogenic insulin resistance.

Regulation of vascular calcification by osteoclast regulatory factors RANKL and osteoprotegerin

Vascular calcification often occurs with advancing age, atherosclerosis, various metabolic disorders such as diabetes mellitus and end-stage renal disease, or in rare genetic diseases, leading to serious clinical consequences. Such mineralization can occur at various sites (cardiac valves, arterial intima or media, capillaries), involve localized or diffuse widespread calcification, and result from numerous causes that provoke active inflammatory and osteogenic processes or disordered mineral homeostasis. Although valuable research has defined many key factors and cell types involved, surprising new insights continue to arise that deepen our understanding and suggest novel research directions or strategies for clinical intervention in calcific vasculopathies. One emerging area in vascular biology involves the RANKL/RANK/OPG system, molecules of the tumor necrosis factor-related family recently discovered to be critical regulators of immune and skeletal biology. Evidence is accumulating that such signals may be expressed, regulated, and function in vascular physiology and pathology in unique ways to promote endothelial cell survival, angiogenesis, monocyte or endothelial cell recruitment, and smooth muscle cell osteogenesis and calcification. Concerted research efforts are greatly needed to understand these potential roles, clarify whether RANKL (receptor activator of nuclear factor kappaB ligand) promotes and osteoprotegerin (OPG) protects against vascular calcification, define how OPG genetic polymorphisms relate to cardiovascular disease, and learn whether elevated serum OPG levels reflect endothelial dysfunction in patients. Overall, the RANKL/RANK/OPG system may mediate important and complex links between the vascular, skeletal, and immune systems. Thus, these molecules may play a central role in regulating the development of vascular calcification coincident with declines in skeletal mineralization with age, osteoporosis, or disease.

Hypoxia inducible factor pathways as targets for functional foods

The etiology of most chronic angiogenic diseases such as rheumatoid arthritis, atherosclerosis, diabetes complications, and cancer includes the presence of pockets of hypoxic cells growing behind aerobic cells and away from blood vessels. Hypoxic cells are the result of uncontrolled growth and insufficient vascularization and have undergone a shift from aerobic to anaerobic metabolism. Cells respond to hypoxia by stimulating the expression of hypoxia inducible factor (HIF), which is critical for survival under hypoxic conditions and in embryogenesis. HIF is a heterodimer consisting of the O2-regulated subunit, HIF-1alpha, and the constitutively expressed aryl hydrocarbon receptor nuclear translocator, HIF-1beta. Under hypoxic conditions, HIF-1alpha is stable, accumulates, and migrates to the nucleus where it binds to HIF-1beta to form the complex (HIF-1alpha + HIF-1beta). Transcription is initiated by the binding of the complex (HIF-1alpha + HIF-1beta) to hypoxia responsive elements (HREs). The complex [(HIF-1alpha + HIF-1beta) + HREs] stimulates the expression of genes involved in angiogenesis, anaerobic metabolism, vascular permeability, and inflammation. Experimental and clinical evidence show that these hypoxic cells are the most aggressive and difficult angiogenic disease cells to treat and are a major reason for antiangiogenic and conventional treatment failure. Hypoxia occurs in early stages of disease development (before metastasis), activates angiogenesis, and stimulates vascular remodeling. HIF-1alpha has also been identified under aerobic conditions in certain types of cancer. This review summarizes the role of hypoxia in some chronic degenerative angiogenic diseases and discusses potential functional foods to target the HIF-1alpha pathways under hypoxic and normoxic conditions. It is reported that dietary quinones, semiquinones, phenolics, vitamins, amino acids, isoprenoids, and vasoactive compounds can down-regulate the HIF-1 pathways and therefore the expression of several proangiogenic factors. Considering the lack of efficiency or the side effects of synthetic antiangiogenic drugs at clinical trials, down-regulation of hypoxia-induced angiogenesis by use of naturally occurring functional foods may provide an effective means of prevention.

1,25-Dihydroxyvitamin D3 but not cinacalcet HCl (Sensipar/Mimpara) treatment mediates aortic calcification in a rat model of secondary hyperparathyroidism

BACKGROUND

Calcitriol treatment of secondary hyperparathyroidism (HPT) in chronic kidney disease (CKD) patients can lead to increased serum calcium and phosphorus, which have been associated as risk factors for vascular calcification. Cinacalcet HCl (Sensipar/Mimpara) {(alphaR)-(-)-alpha-methyl-N-[3-[3-(trifluoromethylphenyl)propyl]-1-napthalenemethanamine hydrochloride} lowers serum parathyroid hormone (PTH), calcium, phosphorus and calcium-phosphorous (CaxP) product in stage 5 CKD dialysis patients; however, its effects on vascular calcification are unknown.

METHODS

Cinacalcet HCl (10 or 1 mg/kg, p.o. gavage), 1,25-dihydroxyvitamin D(3) (0.1 microg, s.c, calcitriol) or the combination was administered daily for 26 days in a rat model of secondary HPT [5/6 nephrectomy]. After dosing, aortic calcification was determined using the von Kossa staining method. Serum PTH and blood chemistries were determined on days 0, 26 and 0, 14, 26, respectively, prior to and after dosing.

RESULTS

Calcitriol-treated rats had moderate to marked aortic calcification, whereas no significant calcification was observed in vehicle- or cinacalcet HCl-only treated groups. Co-administration of cinacalcet HCl with calcitriol did not attenuate the calcitriol-mediated increase in CaxP product or calcitriol-mediated aortic calcification. Both calcitriol and cinacalcet HCl therapy significantly reduced serum PTH levels. Calcitriol significantly elevated serum calcium, serum phosphorous and CaxP product above pretreatment levels, or those seen with vehicle or cinacalcet HCl. Cinacalcet HCl (10 or 1 mg/kg) decreased serum ionized calcium and decreased calcitriol-induced hypercalcaemia.

CONCLUSION

Cinacalcet HCl and calcitriol both effectively reduce PTH, albeit via different mechanisms, but unlike calcitriol, cinacalcet HCl did not produce hypercalcaemia, an increased CaxP product or vascular calcification.

Pathophysiology of vascular calcification in chronic kidney disease

Patients with chronic kidney disease (CKD) on dialysis have 2- to 5-fold more coronary artery calcification than age-matched individuals with angiographically proven coronary artery disease. In addition to increased traditional risk factors, CKD patients also have a number of nontraditional cardiovascular risk factors that may play a prominent role in the pathogenesis of arterial calcification, including duration of dialysis and disorders of mineral metabolism. In histological specimens from the inferior epigastric artery of dialysis patients, we have found expression of the osteoblast differentiation factor core binding factor alpha-1 (Cbfa1) and several bone-associated proteins (osteopontin, bone sialoprotein, alkaline phosphatase, type I collagen) in both the intima and medial layers when calcification was present. In cultured vascular smooth muscle cells, the addition of pooled serum from dialysis patients (versus normal healthy controls) accelerated mineralization and increased expression of Cbfa1, osteopontin, and alkaline phosphatase to a similar magnitude as does beta-glycerophosphate alone. However, a lack of inhibitors of calcification may also be important. Dialysis patients with low levels of serum fetuin-A, a circulating inhibitor of mineralization, have increased coronary artery calcification and fetuin-A can inhibit mineralization of vascular smooth muscle cells in vitro. These data support that elevated levels of phosphorus and/or other potential uremic toxins may play an important role by transforming vascular smooth muscle cells into osteoblast-like cells, which can produce a matrix of bone collagen and noncollagenous proteins. This nidus can then mineralize if the balance of pro-mineralizing factors outweighs inhibitory factors.

Serum osteoprotegerin is increased in Crohn's disease: a population-based case control study

BACKGROUND

There is a potential interface between osteoporosis and the chronic inflammation of inflammatory bowel disease (IBD), and the osteoprotegerin (OPG)/receptor for activated nuclear factor-kappaB (RANK)/RANK ligand (RANKL) signaling pathway may be an important mediator, although data are limited.

METHODS

We conducted a population-based case-control seroassay study to look for alterations in serum OPG and soluble RANKL (sRANKL). The study population included IBD patients who were 18 to 50 years old with Crohn's disease (CD; n = 287) or ulcerative colitis (UC; n = 166), age-matched healthy controls (n = 368), and nonaffected siblings of IBD patients (n = 146). Serum OPG and sRANKL were measured by enzyme-linked immunoassay. Sex-specific reference ranges were derived from the healthy controls.

RESULTS

Analysis of variance (ANOVA) confirmed significant group differences in women for mean serum OPG (P = 0.018). CD women had higher values of OPG than UC women (P = 0.028) or healthy controls (P = 0.045), whereas the other groups were similar. OPG levels were above the reference range in 13/173 (8%) of CD women, exceeding the expected proportion (P = 0.032). In contrast, no differences in OPG were seen in men between controls, CD, or UC. Estrogen use in women (P = 0.000002) and corticosteroid use in men (P = 0.026) were associated with higher OPG levels. In multivariate analysis, CD diagnosis (P = 0.031) and estrogen use (P = 0.000002) were independently associated with higher OPG levels. No group differences were seen in mean serum sRANKL measurements.

CONCLUSIONS

An OPG:sRANKL imbalance with OPG exceeding sRANKL should inhibit osteoclastogenesis and promote bone formation. CD is associated with increased fracture risk, and possibly, the paradoxically higher OPG is a counterregulatory response to factors such as inflammatory cytokines, promoting high bone turnover. Alternatively, elevated OPG in CD may reflect T-cell activation.

Insulin Signaling in Arteries Prevents Smooth Muscle Apoptosis

OBJECTIVE

Insulin is an antiapoptotic factor of cultured vascular cells, but it is not clear whether it also exerts antiapoptotic effects on vascular cells in vivo. We studied insulin receptor signaling in the arteries of normal and diabetic rats to establish whether insulin exhibits antiapoptotic activity toward vascular smooth muscle cells in vivo as well as in vitro.

METHODS AND RESULTS

Western blot analysis and real-time polymerase chain reaction revealed alpha- and beta-subunits of the insulin receptor in association with insulin receptor substrate-1 and phosphatidylinositol 3-kinase in the media of the aorta and carotid artery. The insulin receptor signaling pathway was partially activated under physiological conditions, further activated by intravenous insulin injection, and was attenuated in streptozotocin-induced diabetic rats. Lipopolysaccharide injection induced more apoptosis of vascular smooth muscle cells in diabetic rats than in control rats, whereas insulin prevented apoptosis in the aortic wall. An in vitro study suggested that the antiapoptotic effect of insulin was mediated by phosphatidylinositol 3-kinase.

CONCLUSIONS

Insulin is an antiapoptotic factor of vascular smooth muscle cells in vitro and in vivo. Decreased insulin activity on the artery may increase smooth muscle cell death and cause unstable plaque formation associated with diabetes.

Osteoprotegerin (OPG) is localized to the Weibel-Palade bodies of human vascular endothelial cells and is physically associated with von Willebrand factor

Recent studies demonstrate roles for osteoprotegerin (OPG) in both skeletal and extra-skeletal tissues. Although its role in preventing osteoclast (OC) formation and activity is well documented, emerging evidence suggests a role of OPG in endothelial cell survival and the prevention of arterial calcification. In this communication, we show that vascular endothelial cells in situ, and human umbilical vein endothelial cells (HUVEC) in vitro, express abundant OPG. In HUVEC, OPG co-localizes with P-selectin and von Willebrand factor (vWF), within the Weibel-Palade bodies (WPB). Treatment of HUVEC with the pro-inflammatory cytokines, tumor necrosis factor (TNF)-alpha and IL-1beta, resulted in mobilization from the WPBs and subsequent secretion of OPG protein into the culture supernatant. Furthermore, TNF-alpha treatment of HUVEC resulted in a sustained increase in OPG mRNA levels and protein secretion over the 24-h treatment period. Reciprocal immunoprecipitation experiments revealed that while not associated with P-Selectin, OPG is physically complexed with vWF both within the WPB and following secretion from endothelial cells. Interestingly, this association was also identified in human peripheral blood plasma. In addition to its interaction with vWF, we show that OPG also binds with high avidity to the vWF reductase, thrombospondin (TSP-1), raising the intriguing possibility that OPG may provide a link between TSP-1 and vWF. In summary, the intracellular localization of OPG in HUVEC, in association with vWF, together with its rapid and sustained secretory response to inflammatory stimuli, strongly support a modulatory role in vascular injury, inflammation and hemostasis.

Osteogenic PTHs and vascular ossification—Is there a danger for osteoporotics?

Inflammation in vascular (mostly arterial) walls and heart valves triggered by the trans-endothelial influx of LDL particles and the action of subsequently modified (e.g., by oxidation) LDL particles can trigger true bone formation by valvar fibroblasts, by a subpopulation of re-differentiation-competent VSMCs (vascular smooth muscle cells) or by vascular pericytes. Vascular ossification can lead to heart failure and death. Elderly osteoporotic women who need osteogenic drugs to restore their lost skeletal bone are paradoxically prone to vascular ossification-the "calcification paradox." The recent introduction into the clinic of a potently osteogenic parathyroid hormone peptide, Lilly's rhPTH-(1-34)OH (Forteotrade mark), to reverse skeletal bone loss raises the question of whether this and other potently osteogenic PTHs still in clinical trial might also stimulate vascular ossification in such osteoporotic women. Indeed the VSMCs in human and rat atherosclerotic lesions hyperexpress PTHrP and the PTHR1 (or PTH1R) receptor as do maturing osteoblasts. And the evidence indicates that endogenous PTHrP with its NLS (nuclear/nucleolar localization sequence) does stimulate VSMC proliferation (a prime prerequisite for atheroma formation and ossification) via intranuclear targets that inactivate pRb, the inhibitory G1/S checkpoint regulator, by stimulating its hyperphosphorylation. But neither externally added full-length PTHrP nor the NLS-lacking PTHrP-(1-34)OH gets into the VSMC nucleus and instead they inhibit proliferation and calcification by only activating the cell's PTHR1 receptors. No PTH has an NLS and, as expected from the observations on the externally added PTHrPs, hPTH-(1-34)OH inhibits calcification by VSMCs and cannot stimulate vascular ossification in a diabetic mouse model. Encouraging though this may be for osteoporotics with their "calcification paradox," more work is needed to be sure that the skeletally osteogenic PTHs do not promote vascular ossification with its cardiovascular consequences.

Adverse effects of hyperphosphatemia on myocardial hypertrophy, renal function, and bone in rats with renal failure

BACKGROUND

Hyperphosphatemia and disturbances in calcium or parathyroid hormone (PTH) metabolism contribute to the high incidence of cardiovascular disease and renal osteodystrophy in chronic renal failure (CRF). We evaluated the effect of hyperphosphatemia on the cardiovascular system, on renal function, and on bone in experimental uremia.

METHODS

Wistar rats were submitted to parathyroidectomy (PTx) and 5/6 nephrectomy (Nx) with minipump implantation, delivering 1-34 rat PTH (physiologic rate), or were sham-operated and received vehicle. Only phosphorus content (low-phosphorus (LP) 0.2%; high-phosphorus (HP) 1.2%) differentiated diets. We divided the groups as follows: PTx +Nx +LP; sham + LP; PTx + Nx + HP; and sham + HP. Tail-cuff pressure and weight were measured weekly. After 2 months, biochemical, arterial, and myocardial histology and bone histomorphometry were analyzed.

RESULTS

Heart weight normalized to body weight (heart weight/100 g body weight) was higher in PTx + Nx + HP rats (PTx + Nx + HP = 0.36 +/- 0.01 vs. sham + HP = 0.29 +/- 0.01, PTx + Nx + LP = 0.32 +/- 0.01, sham + LP = 0.28 +/- 0.01) (P < 0.05). Serum creatinine levels were higher in PTx + Nx + HP rats than in PTx + Nx + LP rats (1.09 +/- 0.13 vs. 0.59 +/- 0.03 mg/dL) (P < 0.05). Levels of PTH did not differ significantly between the groups. Myocardial and arterial histology detected no vascular calcification or fibrosis. Bone histomorphometry revealed an association, unrelated to uremia, between HP diets and decreased trabecular connectivity.

CONCLUSION

Myocardial hypertrophy, impaired renal function, and adverse effects on bone remodeling were associated with hyperphosphatemia and were not corrected by PTH replacement. Although no vascular calcification was observed in this model, we cannot rule out an adverse effect of hyperphosphatemia on the vascular bed. Our finding underscores the importance of phosphorus control in reducing morbidity and mortality in CRF patients.