Osteopontin is elevated during neointima formation in rat arteries and is a novel component of human atherosclerotic plaques

Association of plasma osteopontin levels with coronary calcification evaluated by tomographic coronary calcium scoring

Evidence indicates that proteins controlling bone mineralization are also involved in the regulation of coronary calcification. The aim of the present study is to evaluate the association between plasma osteopontin (OPN) levels and coronary calcification quantified by using tomographic coronary calcium scoring. Plasma OPN levels were measured from samples of 80 intermediate-risk asymptomatic patients (56 +/- 10 years) who underwent tomographic coronary calcium scoring via multislice computed tomography for incremental risk stratification. There was no significant difference regarding OPN levels between patients with and without coronary calcification in the whole study population. Of 49 patients not receiving renin-angiotensin system inhibitors and/or statins, plasma OPN levels of patients with coronary calcification (38.7%) were significantly higher than those without coronary calcification (61.3%) (8.88 +/- 2.85 vs. 6.79 +/- 2.41, P = 0.008, respectively). On a binary logistic regression model, only age and plasma OPN level were found to be significant independent associated variables for the presence of coronary calcification in patients not receiving these medications (odds ratio for age, 1.15, P = 0.017; for plasma OPN levels, 1.63, P = 0.014). Our results indicate that plasma OPN levels may be predictive of coronary calcification, suggesting an important role of OPN in the atherosclerotic calcification pathogenesis.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Age-related medial elastocalcinosis in arteries: mechanisms, animal models, and physiological consequences

With age, the calcium content of the arterial wall increases. Calcification occurs at two main levels: intimal plaques and the medial elastic fiber network. The latter has been referred to as medial elastocalcinosis and is the subject of this review. The mechanisms involved in elastocalcinosis are complex and involve polar, apolar, and active processes. Vascular calcification may be species specific to humans. As laboratory animals, such as the rat, grow old, they suffer from only very mild arterial calcification. Different animal models of induction of massive arterial calcification by pharmacological and other means exist. Although extrapolation from such models to the clinical situation in terms of etiology is difficult, such models could be useful in the nonclinical study of the pathophysiological consequences of vascular calcification. Vascular calcification modifies arterial wall stiffness, and this could have clinically significant consequences on cardiac function and downstream circulatory control.

Aldosterone, but not angiotensin II, increases profibrotic factors in kidney of adrenalectomized stroke-prone spontaneously hypertensive rats

An increase in angiotensin II (ANG II) under conditions of high salt intake can result in renal damage. The extent to which ANG II does this directly or by way of stimulating aldosterone (Aldo) secretion is a subject of some debate. In the present study, we sought to determine the separate effects of Aldo and ANG II on the expression of plasminogen activator inhibitor-1 (PAI-1) and other factors related to renal fibrosis in the stroke-prone spontaneously hypertensive rat (SHRSP). Saline-drinking male SHRSPs underwent adrenalectomy (ADX) or sham operation (Sham). Treatment groups consisted of ADX + ANG II (25 ng/min sc) and ADX + Aldo (40 microg.kg(-1).day(-1) sc). After 2 wk of treatment, circulating Aldo levels were reduced to the limit of detection, renal PAI-1, transforming growth factor-beta1 (TGF-beta1), and osteopontin expression, and phospho-Smad2 (p-Smad2) level were decreased severalfold, and Smad7 (an inhibitory regulator of TGF-beta1 action) expression was increased in ADX compared with Sham rats. Infusion of Aldo into ADX SHRSPs restored the renal mRNA expression of PAI-1, TGF-beta1 (along with restored p-Smad2 level), and osteopontin and reduced that of Smad7, whereas ANG II had no or a lesser effect. The findings were confirmed by histological examination of renal tissue. In summary, in the saline-drinking SHRSP, Aldo increased renal profibrotic factors and produced renal injury whereas ANG II in the absence of the adrenals had no effect.

Vitamin D receptor activators can protect against vascular calcification

An apparent conflict exists between observational studies that suggest that vitamin D receptor (VDR) activators provide a survival advantage for patients with ESRD and other studies that suggest that they cause vascular calcification. In an effort to explain this discrepancy, we studied the effects of the VDR activators calcitriol and paricalcitol on aortic calcification in a mouse model of chronic kidney disease (CKD)-stimulated atherosclerotic cardiovascular mineralization. At dosages sufficient to correct secondary hyperparathyroidism, calcitriol and paricalcitol were protective against aortic calcification, but higher dosages stimulated aortic calcification. At protective dosages, the VDR activators reduced osteoblastic gene expression in the aorta, which is normally increased in CKD, perhaps explaining this inhibition of aortic calcification. Interpreting the results obtained using this model, however, is complicated by the adynamic bone disorder; both calcitriol and paricalcitol stimulated osteoblast surfaces and rates of bone formation. Therefore, the skeletal actions of the VDR activators may have contributed to their protection against aortic calcification. We conclude that low, clinically relevant dosages of calcitriol and paricalcitol may protect against CKD-stimulated vascular calcification.

Osteopontin promoter polymorphism is associated with increased carotid intima-media thickness

BACKGROUND

Osteopontin (OPN)-transgenic mice exhibit increased carotid artery intima-media thickness (CIMT), smooth muscle cell proliferation, and atheroma formation.

METHODS

An association of the human T-66G promoter variant with CIMT was examined in Caucasian adults grouped according to metabolic syndrome criteria: present (+MetS; n = 70) or absent (-MetS; n = 70).

RESULTS

The G-allele frequency was 22%. For the entire cohort, the G group (TG and GG) was associated with significantly lower age-adjusted and gender-adjusted CIMT compared with the TT group (P = .008); similar analysis by metabolic syndrome group found a significant difference only in the -MetS group (P = .018). Stepwise multivariate regression showed that after age and waist circumference, the T-66G variant was the next most predictive of CIMT (P = .007). These data suggest that in a normoglycemic environment, human vascular OPN gene expression contributes to arterial structure, an effect diminished in dysmetabolic states.

CONCLUSION

Humans with the OPN -66 TT genotype, particularly those without metabolic syndrome, exhibit thicker CIMT.

Vitamin D and osteogenic differentiation in the artery wall

Vascular calcification is widespread, particularly in patients with chronic kidney disease, who receive, among other treatments, active vitamin D supplements. Emerging evidence indicates that vascular calcification is a regulated process that resembles embryonic endochondral osteogenesis, involving osteoblastic differentiation of vascular smooth muscle cells. In experimental animal models, high dosages of vitamin D consistently promote vascular calcification. In particular, the vitamin D-fed rat is frequently used as a model to assess putative regulators of calcific vasculopathy. The artery wall calcification in these animals most likely results from multiple mechanisms involving systems physiology of the complex, bone-vascular-renal-endocrine axis. Genetically engineered mice with upregulated vitamin D signaling pathways have also shed light on the molecular intermediaries, including fibroblast growth factor-23 and transcriptional intermediary factor 1-alpha. In contrast to the studies of animals, studies of humans show that vitamin D has an inverse relationship or little effect. This difference between in vitro and in vivo findings is most likely, again, due to the complex, systemic feedback regulatory mechanisms that control calcium-phosphate metabolism. Recent epidemiologic evidence suggests that there is a narrow range of vitamin D levels in which vascular function is optimized. Levels above or below this range seem to confer a significant increase in risk for cardiovascular disease. There is some evidence to suggest that dietary vitamin D may be carried by lipoprotein particles into cells of the artery wall and atherosclerotic plaque, where it may be converted to active form by monocyte-macrophages. These findings raise interesting questions regarding the effects of vitamin D intake on atherosclerotic calcification and cardiovascular risk.

Fibroblast migration is mediated by CD44-dependent TGF beta activation

CD44 contributes to inflammation and fibrosis in response to injury. As fibroblast recruitment is critical to wound healing, we compared cytoskeletal architecture and migration of wild-type (CD44WT) and CD44-deficient (CD44KO) fibroblasts. CD44KO fibroblasts exhibited fewer stress fibers and focal adhesion complexes, and their migration was characterized by increased velocity but loss of directionality, compared with CD44WT fibroblasts. Mechanistically, we demonstrate that CD44WT cells generated more active TGFbeta than CD44KO cells and that CD44 promotes the activation of TGFbeta via an MMP-dependent mechanism. Reconstitution of CD44 expression completely rescued the phenotype of CD44KO cells whereas exposure of CD44KO cells to exogenous active TGFbeta rescued the defect in stress fibers and migrational velocity, but was not sufficient to restore directionality of migration. These results resolve the TGFbeta-mediated and TGFbeta-independent effects of CD44 on fibroblast migration and suggest that CD44 may be critical for the recruitment of fibroblasts to sites of injury and the function of fibroblasts in tissue remodeling and fibrosis.

Elevated osteopontin levels in patients with peripheral arterial disease

This study was carried out to compare concentrations of osteopontin (OPN) and osteoprotegerin (OPG) in peripheral arterial disease (PAD). The study population consisted of 200 consecutive subjects in whom both OPN/OPG and ankle-brachial index were measured. It was found that OPN levels, but not OPG levels, were significantly more increased in patients with PAD than those without PAD. Serum OPN levels were significantly lower in subjects with angiotensin converting enzyme inhibitors or angiotensin II receptor blockers than those without these agents. In this study, it has been demonstrated for the first time that serum OPN levels are related to PAD. Inhibition of renin- angiotensin system could decrease OPN levels and prevent the progression of PAD.

Relationships of thoracic aortic wall calcification to cardiovascular risk factors: the Multi-Ethnic Study of Atherosclerosis (MESA)

BACKGROUND

The aim of this article is to determine the relationships between aortic wall calcification (AWC) including ascending and descending thoracic aortic calcification and sex, race/ethnicity, age, and traditional risk factors. Allison et al (Arterioscler Thromb Vasc Biol. 2004;24:331-336) previously described the relationship of noted risk factors and AWC as detected by computed tomography (CT) in smaller cohorts. We performed a cross-sectional study to determine which of these variables are independently associated with thoracic calcium.

METHODS

The MESA population included a population-based sample of 4 ethnic groups (12% Chinese, 38% white, 22% Hispanic, and 28% black) of 6814 women and men aged 45 to 84 years. Computed tomographic scans were performed for all participants. We quantified AWC, which ranged from the lower edge of the pulmonary artery bifurcation to the cardiac apex. Multivariable logistic regression was used to evaluate relationships between AWC and measured cardiovascular risk factors.

RESULTS

Overall prevalence of AWC was 28.0%. In the ethnic groups, prevalence of AWC was 32.4% Chinese, 32.4% white, 24.9% Hispanic, and 22.4% black. All age categories of females had a higher prevalence of thoracic calcification than males (total age prevalence 29.1% and 26.8%, respectively). Aortic wall calcifications were most strongly associated with hypertension and current smoking. In addition, diabetes, hypercholesterolemia, high level of low-density lipoprotein, low level of high-density lipoprotein, family history of myocardial infarction , and high C-reactive protein were all associated with increased AWC. Overall P value for difference between sexes for prevalence of AWC is 0.037. Overall P value for difference between race for prevalence of AWC is <.001. The only significant sex differences distributed by race were for Chinese (P = .035) and Hispanic (P = .042) participants.

CONCLUSIONS

Risk factors for aortic calcification were similar to cardiovascular risk factors in a large population-based cohort. Surprisingly, AWC was similar for the Chinese and white populations despite the fact that MESA demonstrated that coronary calcium was more prevalent in the white population. Further studies are needed to investigate whether aortic calcification is a risk factor for coronary disease, independent of coronary calcification.

Role of carbonic anhydrase II in ectopic calcification

INTRODUCTION

Osteopontin (OPN) is a potent inhibitor of ectopic calcification. Previous studies suggested that, in addition to blocking apatite crystal growth, OPN promoted regression of ectopic calcification by inducing the expression of acid-generating carbonic anhydrase II (CAR2) in monocyte-derived cells.

METHODS

To test this hypothesis, OPN and CAR2 expression and calcification of subcutaneously implanted glutaraldehyde-fixed bovine pericardium (GFBP) were studied in CAR2 mutant mice.

RESULTS

Consistent with previous studies in Black Swiss mice, GFBP calcified to a greater extent in OPN-deficient mice compared to wild types on the C57Bl/6 background. GFBP implanted in CAR2-deficient mice (CAR2(-/-)) were significantly more calcified than those implanted into wild-type mice (CAR2(+/+)) [37+/-5 vs. 20+/-6.5 microg Ca/mg tissue, respectively, at 30 days (P<.001), and 42+/-5 versus 20+/-4 microg Ca/mg tissue at 60 days, respectively (P<.001)]. On the other hand, OPN levels within and surrounding the implants were similar in CAR2(+/+) and CAR2(-/-) mice, suggesting that OPN expression in the absence of CAR2 was not sufficient to mitigate ectopic calcification.

CONCLUSIONS

These results indicate that CAR2 expression is an important regulator of ectopic calcification, potentially by facilitating OPN mediated mineral regression.

Osteopontin in Rat Renal Fibroblasts

Osteopontin (OPN), a proinflammatory cytokine, plays an important role in renal fibrosis. We reported that plasma OPN levels were higher in patients with primary aldosteronism than with essential hypertension. However, the regulatory mechanism of OPN by aldosterone remains unclear. Here, we report the transcriptional regulation of OPN expression by aldosterone and the functional effects of aldosterone-mediated OPN transcription in renal fibroblasts. Aldosterone induced OPN expression in a dose-dependent manner with significant responses at 10 nmol/L (1.6±0.2-fold of controls, P <0.05, n=5) and elicited maximal effects at 10 μmol/L (3.5±0.4-fold of controls, P <0.01, n=5). Aldosterone increased OPN expression in a time-dependent manner with a maximal effect after 48 hours (2.7±0.3-fold of controls, P <0.01, n=5). This effect was abolished by the mineralocorticoid receptor (MR) antagonist spironolactone. Luciferase promoter deletion assays identified a novel cis regulatory element (−2153 to −1758) in the OPN promoter that is responsive to aldosterone. This element contains an activator protein-1 (AP-1) and nuclear factor kappa B (NFκB) site. Electrophoretic mobility shift assays, supershift assays, and chromatin immunoprecipitation assays identified both AP-1 and NFκB as the DNA binding proteins induced by aldosterone with spironolactone inhibiting aldosterone-induced AP-1 or NFκB activity. OPN-siRNA inhibited completely the induction of cell proliferation, type I, III, and IV collagen synthesis by aldosterone. These results indicate that aldosterone induced MR-mediated OPN expression through AP-1 and NFκB activation and suggest that aldosterone plays an important role in renal fibrosis through the induction of OPN.

Genes overexpressed in cerebral arteries following salt-induced hypertensive disease are regulated by angiotensin II, JunB, and CREB

Although changes in gene expression are necessary for arterial remodeling during hypertension, the genes altered and their mechanisms of regulation remain uncertain. The goal of this study was to identify cerebral artery genes altered by hypertension and define signaling pathways important in their regulation. Intact cerebral arteries from Dahl salt-sensitive normotensive and hypertensive high-salt (HS) rats were examined by immunostaining, revealing an increased phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) and expression of the proliferative marker Ki-67 in arteries from hypertensive animals. Arterial RNA analyzed by microarray and validated with RT-quantitative PCR revealed that jun family member junB and matricellular genes plasminogen activator inhibitor-1 (PAI-1) and osteopontin (OPN) were significantly overexpressed in HS arteries. Fisher exact test and annotation-based gene subsets showed that genes upregulated by Jun and Ca2+/cAMP-response element-binding protein (CREB) were overrepresented. A model of cultured rat cerebrovascular smooth muscle cells was used to test the hypothesis that angiotensin II (ANG II), JunB, and CREB are important in the regulation of genes identified in the rat hypertension model. ANG II induced a transient induction of junB and a delayed induction of PAI-1 and OPN mRNA levels, which were reduced by ERK inhibition with U-0126. Silencing junB using small-interfering RNA reduced mRNA levels of OPN but not PAI-1. The silencing of CREB reduced PAI-1 induction by ANG II but enhanced the transcription of OPN. Together, these results suggest that salt-induced hypertensive disease promotes changes in matricellular genes that are stimulated by ANG II, regulated by ERK, and selectively regulated by JunB and CREB.

Aortic calcification in urolithiasis patients

OBJECTIVE

To examine the relationship between urolithiasis and calcification of the aortic artery.

MATERIAL AND METHODS

We examined the relationship between urolithiasis and calcification of the aortic artery in 181 patients with urinary calcium stones (stone group) and in 181 without a history of urolithiasis (control group). All patients underwent abdominal CT to score the degree of calcification at the aortic arterial wall, as follows: 0, none; 1, <120 degrees calcification; 2, > or =120 degrees to <240 degrees calcification; and 3, > or =240 degrees calcification. Both the stone and control groups were further classified into three groups each according to gender and age.

RESULTS

Aortic calcification scores differed significantly between the stone and control groups in males aged > or =20-<40 years (0.43+/-0.50 vs 0.13+/-0.35, respectively) and in females aged > or =60 years (1.81+/-0.74 vs 1.44+/-0.64, respectively).

CONCLUSION

These findings suggest that common causative factors are associated with urolithiasis and arteriosclerosis and that adult males with arteriosclerosis develop urolithiasis more easily than those without.

The link between osteoporosis and cardiovascular disease

Cardiovascular disease (CVD) and osteoporosis are common age-related conditions associated with significant morbidity, mortality, and disability.Traditionally, these two conditions were considered unrelated and their coexistence was attributed to independent age-related processes. However, an increasing body of biological and epidemiological evidence has provided support for a link between the two conditions that cannot be explained by age alone. Several hypotheses have been proposed to explain the link between osteoporosis and CVD including: 1) shared risk factors, 2) common pathophysiological mechanisms, 3) common genetic factors, or 4) a causal association.This review highlights the epidemiologic literature on the association of bone density with cardiovascular mortality, cardiovascular morbidity, and subclinical measures of atherosclerosis. It also summarizes the different potential mechanisms involved in the link between osteoporosis and CVD.

Vascular calcification inhibitors in relation to cardiovascular disease with special emphasis on fetuin-A in chronic kidney disease

The mortality rate is extremely high in chronic kidney disease (CKD), primarily due to the high prevalence of cardiovascular disease (CVD) in this patient group. Apart from traditional Framingham risk factors, evidences suggest that nontraditional risk factors, such as inflammation, oxidative stress, endothelial dysfunction, and vascular calcification also contribute to this extremely high risk of CVD. Disturbance in the mineral metabolism, especially in the ions of Ca and PO4, are linked to enhanced calcification of blood vessels. Although the mechanism(s) of this enhanced calcification process are not fully understood, current knowledge suggests that a large number (and an imbalance between them) of circulating promoters and inhibitors of the calcification process, that is, fetuin-A (or alpha 2-Heremans-Schmid glycoprotein, AHSG), matrix-Gla protein (MGP), osteoprotegerin (OPG), osteopontin (OPN), bone morphogenetic proteins (BMPs), and inorganic pyrophosphate (PPi), are involved in the deterioration of vascular tissue. Thus, an imbalance in these factors may contribute to the high prevalence of vascular complications in CKD patients. Among these mediators, studies on fetuin-A deserve further attention as clinical studies consistently show that fetuin-A deficiency is associated with vascular calcification, all-cause and cardiovascular mortality in CKD patients. Both chronic inflammation and the uremic milieu per se may contribute to fetuin-A depletion, as well as specific mutations in the AHSG gene. Recent experimental and clinical studies also suggest an intriguing link between fetuin-A, insulin resistance, and the metabolic syndrome.

Expression of the human beta3 integrin subunit in mouse smooth muscle cells enhances IGF-I-stimulated signaling and proliferation

Optimal stimulation of signal transduction and biological functions by IGF-I in porcine smooth muscle cells (pSMC) requires ligand occupancy of the alphaVbeta3 integrin. Binding of heparin-binding domain (HBD) of vitronectin (VN) to the cysteine loop (C-loop) region of beta3 is required for pSMC to respond optimally to IGF-I stimulation. Mouse smooth muscle cells (mSMC), which express a form of beta3 whose sequence within the C-loop region is different than porcine or human beta3, do not respond optimally to IGF-I, and IGF-I stimulated beta3 and SHPS-1 phosphorylation which are necessary for optimal IGF-I signaling were undetectable. VN also had no effect on IGF-I stimulated the cell proliferation. In contrast, when human beta3 (hbeta3) was introduced into mSMC, there was an enhanced VN binding in spite of an equivalent amount of total beta3 expression, and IGF-I-dependent beta3, and SHPS-1 phosphorylation were detected. In addition, there was enhanced IGF-I-stimulated Shc association with SHPS-1, Shc tyrosine phosphorylation, Shc and Grb2 association, and MAP kinase activation leading to increased cell proliferation. These enhancements could be further augmented by adding a peptide containing the HBD of VN. To determine if these changes were mediated by the C-loop region of beta3, an antibody that reacts with that region of beta3 was utilized. The addition of the hbeta3 C-loop antibody abolished VN-induced enhancement of IGF-I signaling and IGF-I-stimulated cell proliferation. These results strongly support the conclusion that optimal SMC responsiveness to IGF-I requires ligand interaction with the C-loop domain of hbeta3.

Osteopontin

Osteopontin (OPN) is a multifunctional molecule highly expressed in chronic inflammatory and autoimmune diseases, and it is specifically localized in and around inflammatory cells. OPN is a secreted adhesive molecule, and it is thought to aid in the recruitment of monocytes-macrophages and to regulate cytokine production in macrophages, dendritic cells, and T-cells. OPN has been classified as T-helper 1 cytokine and thus believed to exacerbate inflammation in several chronic inflammatory diseases, including atherosclerosis. Besides proinflammatory functions, physiologically OPN is a potent inhibitor of mineralization, it prevents ectopic calcium deposits and is a potent inducible inhibitor of vascular calcification. Clinically, OPN plasma levels have been found associated with various inflammatory diseases, including cardiovascular burden. It is thus imperative to dissect the OPN proinflammatory and anticalcific functions. OPN recruitment functions of inflammatory cells are thought to be mediated through its adhesive domains, especially the arginine-glycine-aspartate (RGD) sequence that interacts with several integrin heterodimers. However, the integrin receptors and intracellular pathways mediating OPN effects on immune cells are not well established. Furthermore, several studies show that OPN is cleaved by at least 2 classes of proteases: thrombin and matrix-metalloproteases (MMPs). Most importantly, at least in vitro , fragments generated by cleavage not only maintain OPN adhesive functions but also expose new active domains that may impart new activities. The role for OPN proteolytic fragments in vivo is almost completely unexplored. We believe that further knowledge of the effects of OPN fragments on cell responses might help in designing therapeutics targeting inflammatory and cardiovascular diseases.

The expression of osteopontin is increased in vessels with blood-brain barrier impairment

AIMS

We previously reported that the blood-brain barrier (BBB) function was deteriorated in vessels located along hippocampal fissures in stroke-prone spontaneously hypertensive rats (SHRSP). In this study, we examined changes of gene expression in the BBB-damaged vessels of SHRSP.

METHODS

Vascular samples were microdissected from the hippocampi of SHRSP and Wistar-Kyoto (WKY) as a control and the difference in gene expression between the BBB-damaged vessels in SHRSP and vessels without BBB damage in WKY was examined by a microarray. The differences in gene and protein expression between brain tissues in the two strains of rats were examined using real-time quantitative reverse transcriptase-polymerase chain reaction (RT-PCR), Western blotting and immunohistochemistry.

RESULTS

The microarray assay revealed that the ratio of osteopontin gene expression in the vascular tissue of the hippocampi of SHRSP to that of WKY was the highest among 8435 genes. Real-time RT-PCR analysis revealed that the gene expression of osteopontin was significantly increased in the hippocampal samples of SHRSP compared with that in the hippocampal samples of WKY rats or with that in the cortical samples of SHRSP. Immunohistochemical and Western blot analyses showed that the osteopontin protein expression was seen in perivascular ED1-positive macrophages/microglial cells located around hippocampal fissures and significantly increased in the hippocampi of SHRSP compared with that of WKY.

CONCLUSIONS

These findings indicate that the expression of osteopontin is increased in BBB-damaged vessels in hypertensive SHRSP compared with that in vessels without BBB impairment in WKY rats, suggesting a role for osteopontin in BBB function.

Plasma and crevicular fluid osteopontin levels in periodontal health and disease

BACKGROUND AND OBJECTIVE

The level of osteopontin in gingival crevicular fluid has been found to correlate with clinical measures of periodontal disease. The present study was designed to assess the relationship between clinical parameters and osteopontin levels of the gingival crevicular fluid from inflamed gingivae, periodontitis sites and after treatment of periodontitis sites, and to correlate them to the osteopontin levels of the plasma.

MATERIAL AND METHODS

Thirty, gender-matched subjects were divided into three groups--healthy, gingivitis and chronic periodontitis--based on modified gingival index scores and clinical attachment loss. The fourth group consisted of 10 subjects in the periodontitis group, 6-8 wk after initial therapy. Plasma and gingival crevicular fluid samples were collected and quantified for osteopontin using an enzyme immunoassay.

RESULTS

The highest mean gingival crevicular fluid and plasma osteopontin concentrations were observed in the periodontitis group (1575.01 and 1273.21 ng/mL, respectively) and the lowest in the healthy group (1194.80 and 476.35 ng/mL, respectively). After treatment of the periodontitis group, the level of osteopontin decreased to 1416.15 in gingival crevicular fluid and to 1051.68 ng/mL in plasma. In all groups the gingival crevicular fluid osteopontin levels showed a statistically significant positive correlation with that of plasma and clinical attachment loss.

CONCLUSION

Osteopontin levels were highest in the gingival crevicular fluid from sites with periodontal destruction; however, periodontal treatment resulted in the reduction of osteopontin levels. Gingival crevicular fluid and plasma osteopontin levels showed a positive correlation in all of the groups.

Phytate inhibits bovine pericardium calcification in vitro

OBJECTIVE

The present study examined the inhibitory effects of pyrophosphate, etidronate, and phytate on bovine pericardium calcification in vitro.

METHODS

Bovine pericardium was glutaraldehyde fixed and then placed in a flow chamber in the presence of a synthetic physiological fluid alone (control) or the fluid plus various concentrations of pyrophosphate, etidronate, or phytate. Following a 96-h incubation, fragments were removed and assayed for calcification by measuring calcium and phosphorus levels.

RESULTS

The data indicated that both pyrophosphate and etidronate at 1 mg/l (5.75 and 4.95 microM, respectively) inhibited bovine pericardium calcification, whereas neither agent had an effect at 0.5 mg/l (2.87 and 2.47 microM, respectively). Phytate was the most potent inhibitor of calcification, and the effects of this agent were apparent at levels as low as 0.25 mg/l (0.39 microM).

CONCLUSIONS

While pyrophosphate, etidronate, and phytate were all able to inhibit bovine pericardium calcification in vitro, phytate was found to be the most effective.

A modular tissue engineering construct containing smooth muscle cells and endothelial cells

Human umbilical vein endothelial cells (HUVEC) were seeded on sub-mm sized collagen cylinders containing embedded umbilical vein smooth muscle cells (UVSMC). These cylindrical "modules" are intended to be used as a vascularized construct, in which HUVEC lined channels are created by the random packing of the modules in situ or within a larger container. Embedding UVSMC cultured in medium containing 10% FBS had an adverse effect on subsequently seeded HUVEC junction morphology; HUVEC/UVSMC co-culturing was done in HUVEC medium (2% FBS with the addition of 0.03 mg/mL endothelial cell growth supplement) as compared to HUVEC seeded on collagen-only modules. In contrast, embedding UVSMC cultured in serum-free medium prior to embedding improved EC junction morphology. Such serum-free culturing, also prevented the UVSMC induced contraction of the collagen modules. On the other hand, embedding serum-free cultured UVSMC promoted HUVEC proliferation and NO secretion compared to those modules embedded with 10% serum cultured UVSMC. These results suggest, not surprisingly, that embedded UVSMC phenotype plays an important role in the seeded HUVEC phenotype, and that the response can be modulated by the UVSMC culture medium serum concentration. These studies were undertaken with a view to using the UVSMC to modulate the thrombogenicity of the HUVEC. Exploration of this outcome awaits further studies directed to understanding the mechanism of the cellular interactions.

Relationship between angiotensin-converting enzyme gene polymorphism and severity of aortic valve calcification

OBJECTIVE

To investigate the role of angiotensin-converting enzyme (ACE) gene polymorphism in patients with degenerative aortic valve calcification (AVC).

PATIENTS AND METHODS

Our study consisted of 305 Turkish patients of European descent (139 male, 166 female; mean plus or minus age, 68 plus or minus 9 years) referred to our echocardiography laboratory for aortic valve evaluation between June 2, 2003, and April 29, 2005. The severity of AVC was graded from 1 to 6 by echocardiography. We used polymerase chain reaction to determine ACE gene polymorphism.

RESULTS

The ACE insertion/deletion genotype distributions for the study population were in Hardy-Weinberg equilibrium (chi square equals 3.5, P equals .18). The study population was divided into 3 groups based on the severity of AVC: those with grade 1 calcification were in group 1, those with grades 2 to 4 in group 2, and those with grades 5 to 6 in group 3. Group 1 patients were significantly younger, less likely to have hypertension and diabetes, and had higher high-density lipoprotein cholesterol levels. The genotype frequencies were significantly different among groups, with the insertion/insertion genotype being less prevalent in group 3 patients. In multivariate analysis, independent predictors of severe AVC were hypertension (odds ratio [OR], 5.6; 95% confidence interval [CI], 2.8 to 11.0; P less than .001), low high-density lipoprotein cholesterol (OR, 2.7; 95 percent CI, 1.5 to 4.9; P equals .001), and the deletion/deletion and insertion/deletion vs insertion/insertion genotype (OR, 3.2; 95 percent CI, 1.5 to 7.2; P equals .004).

CONCLUSION

These results suggest that ACE gene polymorphism may be associated with severe AVC.

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.

Osteopontin Overexpression Inhibits in Vitro Re-endothelialization via Integrin Engagement

The extracellular matrix protein osteopontin (OPN) plays a nonredundant role in atherosclerosis and restenosis. Here we investigated the impact of OPN up-regulation in an in vitro model of re-endothelialization after mechanical injury of the endothelial cell monolayer. Murine aortic endothelial (MAE) cells interact via alpha(v) integrins with the integrin-binding Arg-Gly-Asp OPN sequence and adhere to immobilized OPN. On this basis, MAE cells were stably transfected with a wild-type OPN cDNA (OPN-MAE cells), with an OPN mutant lacking the Arg-Gly-Asp sequence (DeltaRGD-OPN-MAE cells), or with vector alone (mock-MAE cells). When compared with mock-MAE and DeltaRGD-OPN-MAE cells, OPN-MAE cells showed a reduced sprouting activity in fibrin gel, a reduced motility in a Boyden chamber assay, and a reduced capacity to repair the wounded monolayer. Accordingly, OPN-MAE cells at the edge of the wound were unable to form membrane ruffles, to reorganize their cytoskeleton, and to activate the focal adhesion kinase and the small GTPase Rac1, key regulators of the cell entry into the first phase of the cell migration cycle. Accordingly, wounded OPN-MAE cells failed to activate the intracellular signals RhoA and ERK1/2, involved in the later phases of the cell migration cycle. Also, parental MAE cells showed reduced re-endothelialization after wounding when seeded on immobilized OPN and exhibited increased adhesiveness to OPN-enriched extracellular matrix. In conclusion, OPN up-regulation impairs re-endothelialization by inhibiting the first phase of the cell migration cycle via alpha(v) integrin engagement by the extracellular matrix-immobilized protein. This may contribute to the adverse effects exerted by OPN in restenosis and atherosclerosis.

The association of bone mineral density measures with incident cardiovascular disease in older adults

The associations of volumetric and areal bone mineral density (BMD) measures with incident cardiovascular disease (CVD) were studied in a biracial cohort of 2,310 older adults. BMD measures were inversely related to CVD in women and white men, independent of age and shared risk factors for osteoporosis and CVD.

INTRODUCTION

We investigated the associations of volumetric (vBMD) and areal (aBMD) bone mineral density measures with incident cardiovascular disease (CVD) in older adults enrolled in the Health, Aging, and Body Composition study.

METHODS

The incidence of CVD was ascertained in 2,310 well-functioning white and black participants (42% black; 55% women), aged 68-80 years. aBMD measures of the hip were assessed using DXA. Spine trabecular, integral, and cortical vBMD measures were obtained using QCT.

RESULTS

During an average follow-up of 5.4 years, 23% of men and 14% of women had incident CVD. Spine vBMD measures were inversely associated with incident CVD in white men [HR(integral)=1.39, 95% CI 1.03-1.87; HR(cortical)=1.38, 95% CI 1.03-1.84], but not in black men. In women, aBMD measures of the total hip (HR = 1.36, 95% CI 1.03-1.78), femoral neck (HR = 1.44, 95% CI 1.10-1.90), and trochanter (HR = 1.34, 95% CI 1.04-1.72) exhibited significant associations with CVD in blacks, but not in whites. All associations were independent of age and shared risk factors between osteoporosis and CVD, and were not explained by inflammatory cytokines or oxidized LDL.

CONCLUSION

Our results provide support for an inverse association between BMD and incident CVD. Further research should elucidate possible pathophysiological mechanisms linking osteoporosis and CVD.

Differential effects of vitamin D receptor activators on vascular calcification in uremic rats

Vascular calcification is associated with cardiovascular disease, the most common cause of death in chronic kidney disease (CKD). Patients with CKD are treated with vitamin D receptor activators (VDRAs); therefore, we determined if this treatment affects vascular calcification. Uremic rats were given vehicle, calcitriol, paricalcitol, or doxercalciferol three times a week for 1 month. Calcitriol significantly increased the serum calcium-phosphate product and aortic calcium content. Paricalcitol had no effect but the same dose of doxercalciferol significantly increased the calcium-phosphate product and the aortic calcium content, the latter being confirmed by von Kossa staining. To see if the increased aortic calcium was due to an increased serum calcium-phosphate product or to a differential effect of the two VDRAs, we lowered the dose of doxercalciferol and increased the dose of paricalcitol. A lower doxercalciferol did not increase the calcium-phosphate product but increased the aortic calcium content. A higher dose of paricalcitol still had no effect. Doxercalciferol treatment increased the mRNA and protein expression of the bone-related markers Runx2 and osteocalcin in the aorta, whereas paricalcitol did not. Hence, different VDRAs have different effects on vascular calcification in uremic rats. The effects are independent of the serum calcium-phosphate product suggesting independent mechanisms.

Blockade of integrin beta3-FAK signaling pathway activated by osteopontin inhibits neointimal formation after balloon injury

BACKGROUND

Osteopontin (OPN) promotes the migration and adhesion of vascular smooth muscle cells (VSMCs) through cell surface receptor, integrin beta3. In order to elucidate the signaling pathway by which OPN is involved in neointimal formation, we focused on integrin beta3-focal adhesion kinase (FAK) upon VSMC migration.

METHODS

The integrin beta3 and FAK expression in VSMC and in neointima was detected by Western blot and immunohistochemistry staining. FAK phosphorylation induced by OPN was verified using a linear OPN 13 peptide containing RGD motif and anti-OPN antibody. The role of integrin beta3-FAK pathway in VSMC adhesion and migration induced with OPN was tested by the overexpression of FAK-related nonkinase and integrin beta3 cytoplasmic domain.

RESULTS

The results showed that OPN increased integrin beta3 expression and induced rapid and transient FAK phosphorylation. Inhibition of the phosphorylation of FAK significantly suppressed VSMC migration induced by OPN. Similarly, blockade of the interaction of integrin beta3 with OPN inhibited VSMC adhesion induced by OPN. The experiment, in vivo, demonstrated that OPN expression level was consistent with neointimal thickening. Administration of anti-OPN antibody for blocking OPN function suppressed integrin beta3 and FAK expression induced by balloon injury, and neointimal thickening was inhibited.

CONCLUSIONS

These data indicate that integrin beta3-FAK signaling modulates OPN-induced VSMC migration during neointimal formation.

PPARalpha agonists suppress osteopontin expression in macrophages and decrease plasma levels in patients with type 2 diabetes

Osteopontin (OPN) is a proinflammatory cytokine implicated in the chemoattraction of monocytes and the development of atherosclerosis. Peroxisome proliferator-activated receptor (PPAR)alpha, a ligand-activated transcription factor with pleiotropic anti-inflammatory effects in macrophages, is the molecular target for fibrates, which are frequently used to treat dyslipidemia in patients with type 2 diabetes at high risk for cardiovascular disease. In the present study, we examined the regulation of OPN by PPARalpha agonists in macrophages and determined the effect of fibrate treatment on OPN plasma levels in patients with type 2 diabetes. Treatment of human macrophages with the PPARalpha ligands bezafibrate or WY14643 inhibited OPN expression. PPARalpha ligands suppressed OPN promoter activity, and an activator protein (AP)-1 consensus site conferred this repression. Overexpression of c-Fos and c-Jun reversed the inhibitory effect of PPARalpha ligands on OPN transcription, and, in chromatin immunoprecipitation assays, PPARalpha ligands inhibited c-Fos and phospho-c-Jun binding to the OPN promoter. Moreover, c-Fos and phospho-c-Jun protein expression was inhibited by PPARalpha agonists, indicating that PPARalpha ligands suppress OPN expression through negative cross talk with AP-1-dependent transactivation of the OPN promoter. This inhibitory effect of PPARalpha ligands on OPN expression was absent in PPARalpha-deficient macrophages, suggesting a receptor-mediated mechanism of OPN suppression. Finally, treatment of type 2 diabetic patients with bezafibrate significantly decreased OPN plasma levels. These results demonstrate a novel mechanism whereby PPARalpha ligands may impact macrophage inflammatory responses and decrease early proinflammatory markers for cardiovascular disease.

The role of ERK signaling in protein hydrogel remodeling by vascular smooth muscle cells

Collagen type I and fibrin hydrogels have been used for cell-based therapies and tissue engineering. These matrices can be broken down and remodeled by cells, but the effects that these proteins have on cell function are not completely understood. We examined activation of the extracellular signal-regulated kinase (ERK) signaling pathway by vascular smooth muscle cells (VSMC) in response to 2D and 3D matrices of type I collagen, fibrin, or a 1:1 composite mixture of these proteins. After 3 days of culture, ERK phosphorylation, osteopontin secretion, and MMP-2 activation were all markedly increased in 3D matrices, compared with 2D substrates. A strong positive correlation existed between these protein markers of the synthetic phenotype and phosphorylated ERK levels, and this relationship persisted across matrix geometries and compositions. Cell proliferation in 3D matrices was inversely correlated to ERK activation, while on 2D substrates a modest positive correlation was observed. Pharmacologic inhibition of ERK signaling confirmed that this pathway was involved in the observed phenotype shifts. This study suggests that contextual activation of the ERK pathway results in different effects on cell phenotype, depending on the geometry and composition of the ECM. These findings add to our understanding of cell function and remodeling in protein-based hydrogel biomaterials.

Gene expression profiles during hepatic stellate cell activation in culture and in vivo

BACKGROUND & AIMS

Following hepatic injury, hepatic stellate cells (HSCs) transdifferentiate to become extracellular matrix-producing myofibroblasts and to promote hepatic fibrogenesis. In this study, we determine gene expression changes in 3 different models of HSC activation and investigate whether HSC culture activation reproduces gene expression changes of HSC in vivo activation.

METHODS

HSCs were isolated by density centrifugation and magnetic antibody cell sorting from normal mice, CCl(4)-treated mice, and mice that underwent bile duct ligation (BDL). Gene expression was analyzed by microarray and confirmed by polymerase chain reaction and Western blot analysis.

RESULTS

Two thousand seventy-three probe sets were differentially expressed in at least 1 of 3 models of HSC activation, including novel genes that encode proinflammatory and antiapoptotic mediators; transcription factors; cell surface receptors; and cytoskeleton components such as CXCL14, survivin, septin 4, osteopontin, PRX1, LMCD1, GPR91, leiomodin, and anillin. BDL- and CCl(4)-activated HSCs showed highly correlated gene expression patterns, whereas culture activation only partially reproduced the gene expression changes observed during BDL- and CCl(4)-induced activation. Coculture with Kupffer cells or lipopolysaccharide treatment during culture activation shifted the expression of most examined genes toward the pattern observed during in vivo activation, suggesting a role for these factors in the microenvironment that drives HSC activation.

CONCLUSIONS

The almost identical HSC gene expression patterns after BDL or CCl(4) treatment indicate that HSCs exert similar functions in different types of liver injury. Because culture activation does not properly regulate gene expression in HSCs, in vivo activation should be considered the gold standard for the study of HSC biology.

CREB mediates UTP-directed arterial smooth muscle cell migration and expression of the chemotactic protein osteopontin via its interaction with activator protein-1 sites

The transcription factor cAMP responsive element-binding protein (CREB) has been found to be involved in arterial smooth muscle cell (SMC) migration. We previously demonstrated that osteopontin (OPN) expression is a key step for UTP-mediated migration of arterial SMCs and that activator protein (AP)-1, nuclear factor kappaB, and upstream stimulatory transcription factors are involved in this OPN expression. The present study aims to determine the role of CREB in UTP-induced migration and OPN expression in cultured SMCs. We found that CREB is activated by UTP via extracellular signal-regulated kinase 1/2 and p38 mitogen-activated protein kinase pathways but not by protein kinase A. Both overexpression of a dominant negative CREB and CREB small interfering RNA treatment suppressed UTP-induced OPN expression and SMC migration. Gel-shift and chromatin immunoprecipitation assays revealed that CREB binds 2 AP-1 sites (-1870 and -76) and a cAMP responsive element-like site (-1403) on the OPN promoter. Mutations of these sites showed that only the 2 AP-1 sites were required for UTP-induced OPN expression. Moreover, gel-supershift and sequential chromatin immunoprecipitation assays suggested that CREB was associated with c-Fos on the AP-1 sites of the OPN promoter. These results demonstrate that CREB participates in the induction of UTP-activated OPN expression via its binding to 2 AP-1 sites and is thus involved in UTP-mediated SMC migration.

A constitutive endogenous osteopontin production is important for macrophage function and differentiation

Macrophages are involved in the pathological process underlying atherosclerosis and constitutively express the multifunctional protein osteopontin which has important exogenous effects on these cells. However, the effect of the endogenous osteopontin expression on macrophage function has been sparsely studied. To shed light on the importance of the endogenous osteopontin expression, RAW 264.7 macrophage-like cells were silenced in osteopontin expression using RNAi. The cells were analysed for basic functions including attachment, migration, apoptosis and for the expression of macrophage differentiation markers and cytokines. The macrophages with silenced osteopontin expression showed impaired migration and an increased rate of serum starvation-induced apoptosis as compared to osteopontin-producing control cells. Furthermore, the cells with silence osteopontin expression had an altered phenotype with monocyte-like characteristics, including decreased expression of macrophage scavenger receptor A type 1. The altered phenotype of these cells could not be reversed by presence of extracellular osteopontin. In addition the cells with silenced osteopontin expression had a lower expression of IL-12 mRNA and the anti-apoptotic Flip mRNA. We conclude that a constitutive endogenous osteopontin production is important for proper basic functions of macrophages and our study indicates that the constitutive osteopontin production is involved in maintaining macrophages in a differentiated phenotype.

Effect of traditional Chinese medicine Qin-Dan-Jiang-Ya-Tang on remodeled vascular phenotype and osteopontin in spontaneous hypertensive rats

Qin-Dan-Jiang-Ya-Tang (QDJYT) is a traditional Chinese herbal medicine for the treatment of hypertension. The effect of QDJYT on blood pressure and on vascular remodeling in hypertension was investigated in the model of spontaneous hypertensive rats (SHR). Sixteen SHRs were divided into two groups, the SHR group and the SHR+QDJYT group. Eight WKY rats were a normal control group. QDJYT (750 mg/kg) was orally administered daily for 12 weeks in SHR+QDJYT group. After 12 weeks, thoracic aortas were segregated. Media thickness (MT), lumen diameter (LD), the ratio of MT to LD, the volume fraction of collagen (VFC) in media, the ultrastructure of vascular smooth muscle cells (VSMCs) and the expression of osteopontin (OPN) mRNA were examined by histological staining, transmission electron microscope (TEM), and real-time PCR, respectively. It was observed in our study that MT, MT/LD, VFC and the expression of OPN mRNA were higher in the SHRs than in the WKY rats, volume and numeral density of mitochondria in vascular smooth muscle cells (VSMCs) in media increased obviously. However, in the SHRs treated with QDJYT, we found MT, MT/LD, VFC and the expression of OPN gene were lower than in the SHRs, and the phenotype of VSMCs were close to normal. These results suggest that QDJYT could reverse the vascular remodeling in SHR, and the mechanisms may be related to the suppressive effect of QDJYT on the expression of OPN mRNA in arterial wall.

Inhibitors of calcification in blood and urine

In bone and teeth formation, coordinated calcification is a highly desirable biological process. However, heterotopic calcification at unwanted tissue sites leads to dysfunction, disease and, potentially, to death and therefore requires prevention and treatment. With the recent discovery of calcification inhibitors we now know that biological calcification is not passive but a complex, active and highly regulated process. Calcification at vascular sites is the most threatening localization and manifests as part of atherosclerosis or arteriosclerosis. Atherosclerosis is often accompanied by intimal plaque calcification, whereas arteriosclerosis is characterized by calcification of the media. The severity of calcification of cerebral or coronary atherosclerotic plaques is associated with an increased incidence of events such as stroke or myocardial infarction. Medial calcification is the major cause of arterial stiffness, which contributes to left ventricular dysfunction and heart failure. Patients with chronic kidney disease are at especially increased risk for both intimal and medial calcification. In this context, it is currently thought that calcium-regulatory factors including fetuin-A, matrix Gla protein, osteoprotegerin, and pyrophosphates act in a local or systemic manner to prevent calcifications of the vasculature, and that dys-regulations of such calcification inhibitors may contribute to progressive calcifications. Nephrolithiasis represents another process of unwanted calcification responsible for significant morbidity. More than 80% of renal stones contain calcium. Urinary factors inhibiting calcification are citrate, glycosaminoglycans, Tamm-Horsfall protein, and osteopontin. This review summarizes current experimental and clinical data underlining the biological importance of these calcification inhibitors.

Role of osteoprotegerin and its ligands and competing receptors in atherosclerotic calcification

Vascular calcification significantly impairs cardiovascular physiology, and its mechanism is under investigation. Many of the same factors that modulate bone osteogenesis, including cytokines, hormones, and lipids, also modulate vascular calcification, acting through many of the same transcription factors. In some cases, such as for lipids and cytokines, the net effect on calcification is positive in the artery wall and negative in bone. The mechanism for this reciprocal relation is not established. A recent series of reports points to the possibility that two bone regulatory factors, receptor activator of NF-kappaB ligand (RANKL) and its soluble decoy receptor, osteoprotegerin (OPG), govern vascular calcification and may explain the phenomenon. Both RANKL and OPG are widely accepted as the final common pathway for most factors and processes affecting bone resorption. Binding of RANKL to its cognate receptor RANK induces NF-kappaB signaling, which stimulates osteoclastic differentiation in preosteoclasts and induces bone morphogenetic protein (BMP-2) expression in chondrocytes. A role for RANKL and its receptors in vascular calcification is spported by several findings: a vascular calcification phenotype in mice genetically deficient in OPG; an increase in expression of RANKL, and a decrease in expression of OPG, in calcified arteries; clinical associations between coronary disease and serum OPG and RANKL levels; and RANKL induction of calcification and osteoblastic differentiation in valvular myofibroblasts.

Reactive oxygen species-selective regulation of aortic inflammatory gene expression in Type 2 diabetes

Vascular diseases are a major complication of diabetes mellitus (DM), although their etiology is poorly understood. NADPH oxidase-derived reactive oxygen species (ROS) production and inflammation are potential mediators of DM-associated vascular diseases. Using db/db mice as a Type 2 diabetes model, we examined the relationship between NADPH oxidase-derived ROS and vascular inflammation. When compared with control m+/+ mice, aortas from 4- and 12-wk-old db/db mice had higher NADPH oxidase activity and increased superoxide levels, leading to NADPH oxidase-dependent impaired vasodilation at 12 wk. Diabetes progression from 4 to 12 wk led to increased Nox1, Nox4, and p22(phox) subunit mRNAs and induced the expression of a group of matrix remodeling-related cytokines: connective tissue growth factor (CTGF), bone morphogenetic protein 4 (BMP-4), and osteopontin (OPN). After 8 wk of treatment with the superoxide scavenger Tempol, 12-wk-old db/db mice had lower superoxide production, reduced plasma glucose and lipids, and lower BMP-4 and OPN protein expression when compared with nontreated mice. No changes were observed with Tempol in CTGF or m+/+ mice. The ability of Tempol to reverse ROS production as well as OPN and BMP-4, but not CTGF, induction suggests that DM-induced vascular inflammation involves both ROS-sensitive and -insensitive pathways.

Relationship Between Brachial Arterial Endothelial Function and Lumbar Spine Bone Mineral Density in Postmenopausal Women

BACKGROUND

Osteoporosis and endothelial dysfunction have been associated with atherosclerosis. The correlation between brachial arterial endothelial function and lumbar spine bone mineral density (BMD) in postmenopausal women will be investigated.

METHODS AND RESULTS

The endothelial function in 85 postmenopausal women, including 28 women with normal spinal BMD, 27 women with osteopenia, and 30 women with osteoporosis were studied. Brachial arterial flow-mediated vasodilatation (FMD) after reactive hyperemia was assessed by ultrasonography. The BMD at the lumbar spine (lumbar 2 to 4 vertebrae) was measured by dual-energy X-ray absorptiometry. Age, years since menopause, and FMD were significantly greater in the osteoporosis group than in the normal BMD group (p<0.01, p<0.05, and p<0.05, respectively). The BMD was significantly lower in the osteoporosis group than in the osteoporosis or normal BMD group (both p<0.01). After adjusting for age and years since menopause, women with osteoporosis had significantly lesser FMD than those with normal BMD (p<0.05). The univariate linear regression analysis revealed that brachial arterial FMD was significantly positively correlated with BMD (r=0.31, p<0.01), but showed no significant association with other clinical variables. In multivariate regression analysis, the FMD was significantly positively correlated with BMD (p<0.01), but not with other variables.

CONCLUSIONS

Postmenopausal women with osteoporosis might have impaired brachial arterial endothelial function, suggesting that brachial artery endothelial function might be associated with lumbar spine bone mass in postmenopausal women.

Involvement of ligand occupancy in Insulin-like growth factor-I (IGF-I) induced cell growth in osteoblast like MC3T3-E1 cells

Growth factors and matrix proteins regulate the proliferation and differentiation of osteoblasts. The insulin-like growth factor (IGF) system comprises IGF-I, IGF-II, and six high-affinity IGF-binding proteins (IGFBPs). IGFs stimulate cell growth in many types of tissue; IGF-binding proteins regulate cellular actions and can affect cell growth. IGF-I is involved in differentiation, proliferation, and matrix formation in osteoblasts; IGFBP-5 is associated with the extracellular matrix (ECM) and can potentiate the actions of IGF-I. We investigated the effect of ECM proteins on the responses of MC3T3-E1 osteoblast cells to IGF-I and IGFBP-5. In addition, because extracellular signal-regulated kinases 1 and 2 (Erk 1/2) affect cell growth, we evaluated the effects of IGFBP-5 on Erk 1/2 phosphorylation in MC3T3-E1 cells. IGF-I caused an increase in IGFBP-5 expression in cultured MC3T3-E1 cells, and IGF-I plus IGFBP-5 significantly increased cell growth. Likewise, the addition of IGF-I and IGFBP-5 to cultured MC3T3-E1 cells increased the synthesis of the ECM proteins osteopontin (OPN) and thrombospondin-1 (TSP-1), which can bind to alphaVbeta3 integrin receptors on the cell surface. By contrast, the addition of an antibody against ECM proteins inhibited the effects of OPN and TSP-1 on IGFBP-5 expression. The stimulatory effect of IGFBP-5 was mediated via Erk 1/2 activation. These data suggest that IGFBP-5 regulates Erk 1/2 phosphorylation in cultured MC3T3-E1 cells via ECM proteins that may ultimately stimulate the growth of osteoblasts. We determined whether occupation of the alphaVbeta3 integrin receptor affects IGF-I receptor (IGF-IR)-mediated signaling and function in MC3T3-E1 osteoblast cells. Occupation of the alphaVbeta3 integrin receptor with ECM proteins induced IGF-I-stimulated IGF-IR phosphorylation. Conversely, in the presence of the alphaVbeta3-specific disintegrin echistatin, IGF-I-stimulated IGF-IR activation was inhibited. IGF-I-stimulated IGF-IR phosphorylation was accompanied by IRS-1 phosphorylation and MAPK activation. However, these effects were attenuated by echistatin. Thus, occupancy of the alphaVbeta3 disintegrin receptor modulates IGF-I-induced IGF-IR activation and IGF-IR-mediated function in MC 3T3-E1 osteoblasts.

Effect of Crystallization Inhibitors on Vascular Calcifications Induced by Vitamin D A Pilot Study in Sprague-Dawley Rats

BACKGROUND

Pathological calcification in soft tissues (ie, ectopic calcification) can have severe consequences. Hydroxyapatite is the common mineral phase present in all tissue calcifications. In general, the development of tissue calcifications requires a pre-existing injury as an inducer (heterogeneous nucleant), whereas further progression requires the presence of other promoter factors (such as hypercalcemia and/or hyperphosphatemia) and/or a deficiency in calcification repressor factors (crystallization inhibitors and cellular defense mechanisms). The present study investigated the capacity of etidronate (a bisphosphonate used in osteoporosis treatment) and phytate (a natural product) to inhibit vascular calcification in rats.

METHODS AND RESULTS

Six male Sprague-Dawley rats in each of the 3 treatment groups were subcutaneously injected with either a placebo (physiological serum solution), etidronate (0.825 micromol x kg(-1) x day (-1)) or phytate (0.825 micromol x kg (-1) x day(-1)) for 8 days. Four days into this regimen, calcinosis was induced by subcutaneous injections of 500,000 IU/kg vitamin D at 0 h, 24 h and 48 h. Ninety-six hours after the final vitamin D injection, the rats were killed and aortas and their hearts were removed for histological and calcium analyses. The data showed that phytate-treated rats had lower levels of aortic calcium than placebo-treated rats. All groups had similar heart calcium levels.

CONCLUSIONS

The present study found that phytate acted as a vascular calcification inhibitor. Thus, the action of polyphosphates could be important in protecting against vascular calcification.

Estradiol action in atherosclerosis and reendothelialization

Whereas hormonal replacement/menopause therapy (HRT) in postmenopausal women increases coronary artery disease risk, epidemiological studies (protection in premenopaused women) suggest and experimental studies (prevention of the development of fatty streaks in animals) demonstrate a major atheroprotective action of estradiol (E2). The understanding of the deleterious and beneficial effects of estrogens is thus required. The atheroprotective effect of E2 is absent in mice deficient in mature T and B lymphocytes, demonstrating the crucial role of the endothelium/immune system pair. The immunoinflammatory system appears to play a key role in the development of fatty streak deposit as well as in the rupture of the atherosclerotic plaque. Whereas E2 favors an anti-inflammatory effect in vitro (cultured cells), it elicits in vivo a proinflammation at the level of several subpopulations of the immunoinflammatory system, which could contribute to plaque destabilization. Endothelium appears to be an important target for E2, since it potentiates endothelial NO and prostacyclin production, thus promoting beneficial effects such as vasorelaxation and inhibition of platelet aggregation. Prostacyclin, but not NO, appear to be involved in the atheroprotective effect of E2, which also accelerates endothelial regrowth, thus favoring vascular healing. Finally, most of these E2 effects are mediated by estrogen receptor alpha and are independent of estrogen receptor beta. In summary, a better understanding of the mechanisms of estrogens on the normal and atheromatous arteries is required and should help to optimize the prevention of cardiovascular disease after menopause. These mouse models should help to screen existing and future selective estrogen receptor modulators (SERMs).

Gingival crevicular fluid osteopontin levels in periodontal health and disease

BACKGROUND

Osteopontin (OPN), a glycosylated phosphoprotein, is a bone matrix component produced by osteoblasts, osteoclasts, and macrophages as a multifunctional cytokine. OPN anchors osteoclasts to the bone surface, and its absence leads to impaired bone resorption. The aim of the present study was to assess the relation between clinical parameters and concentrations of OPN within gingival crevicular fluid (GCF) from inflamed gingiva and periodontitis sites and, subsequently, after the treatment of periodontitis sites.

METHODS

A total of 45 subjects were divided into the following three groups based on modified gingival index (MGI) and Ramfjord periodontal disease index (PDI) scores: healthy (group I), gingivitis (group II), and chronic periodontitis (group III). A fourth group consisted of 15 subjects from group III, 6 to 8 weeks after treatment (i.e., scaling and root planing [SRP]). GCF samples collected from each patient were quantified for OPN using the enzymatic immunometric assay. Further, the correlation between OPN levels in situ with clinical parameters was analyzed in all groups and before and after treatment in periodontitis patients.

RESULTS

The highest mean OPN concentration in GCF (14.347 microg/ml) was observed in group III, and the lowest mean OPN concentration in GCF (2.522 microg/ml) was observed in group I. Its levels in group III decreased to 8.419 microg/ml after treatment (group IV). Further, GCF OPN levels in all the groups showed a statistically significant positive correlation with clinical attachment loss (P <0.05).

CONCLUSIONS

OPN levels increase in GCF from healthy to periodontitis states, and periodontal treatment results in the reduction of OPN levels. The data indicate that OPN may play a key role in, and could be considered a biomarker of, periodontal disease progression.