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

Phosphate in Cardiovascular Disease: From New Insights Into Molecular Mechanisms to Clinical Implications

Hyperphosphatemia is a common feature in patients with impaired kidney function and is associated with increased risk of cardiovascular disease. This phenomenon extends to the general population, whereby elevations of serum phosphate within the normal range increase risk; however, the mechanism by which this occurs is multifaceted, and many aspects are poorly understood. Less than 1% of total body phosphate is found in the circulation and extracellular space, and its regulation involves multiple organ cross talk and hormones to coordinate absorption from the small intestine and excretion by the kidneys. For phosphate to be regulated, it must be sensed. While mostly enigmatic, various phosphate sensors have been elucidated in recent years. Phosphate in the circulation can be buffered, either through regulated exchange between extracellular and cellular spaces or through chelation by circulating proteins (ie, fetuin-A) to form calciprotein particles, which in themselves serve a function for bulk mineral transport and signaling. Either through direct signaling or through mediators like hormones, calciprotein particles, or calcifying extracellular vesicles, phosphate can induce various cardiovascular disease pathologies: most notably, ectopic cardiovascular calcification but also left ventricular hypertrophy, as well as bone and kidney diseases, which then propagate phosphate dysregulation further. Therapies targeting phosphate have mostly focused on intestinal binding, of which appreciation and understanding of paracellular transport has greatly advanced the field. However, pharmacotherapies that target cardiovascular consequences of phosphate directly, such as vascular calcification, are still an area of great unmet medical need.

Similarities and Differences of Vascular Calcification in Diabetes and Chronic Kidney Disease

Presently, the mechanism of occurrence and development of vascular calcification (VC) is not fully understood; a range of evidence suggests a positive association between diabetes mellitus (DM) and VC. Furthermore, the increasing burden of central vascular disease in patients with chronic kidney disease (CKD) may be due, at least in part, to VC. In this review, we will review recent advances in the mechanisms of VC in the context of CKD and diabetes. The study further unveiled that VC is induced through the stimulation of pro-inflammatory factors, which in turn impairs endothelial function and triggers similar mechanisms in both disease contexts. Notably, hyperglycemia was identified as the distinctive mechanism driving calcification in DM. Conversely, in CKD, calcification is facilitated by mechanisms including mineral metabolism imbalance and the presence of uremic toxins. Additionally, we underscore the significance of investigating vascular alterations and newly identified molecular pathways as potential avenues for therapeutic intervention.

Vascular Calcification: In Vitro Models under the Magnifying Glass

Vascular calcification is a systemic disease contributing to cardiovascular morbidity and mortality. The pathophysiology of vascular calcification involves calcium salt deposition by vascular smooth muscle cells that exhibit an osteoblast-like phenotype. Multiple conditions drive the phenotypic switch and calcium deposition in the vascular wall; however, the exact molecular mechanisms and the connection between vascular smooth muscle cells and other cell types are not fully elucidated. In this hazy landscape, effective treatment options are lacking. Due to the pathophysiological complexity, several research models are available to evaluate different aspects of the calcification process. This review gives an overview of the in vitro cell models used so far to study the molecular processes underlying vascular calcification. In addition, relevant natural and synthetic compounds that exerted anticalcifying properties in in vitro systems are discussed.

High Intakes of Bioavailable Phosphate May Promote Systemic Oxidative Stress and Vascular Calcification by Boosting Mitochondrial Membrane Potential-Is Good Magnesium Status an Antidote?

Chronic kidney disease is characterized by markedly increased risk for cardiovascular mortality, vascular calcification, and ventricular hypertrophy, and is associated with increased systemic oxidative stress. Hyperphosphatemia, reflecting diminished glomerular phosphate (Pi) clearance, coupled with a compensatory increase in fibroblast growth factor 23 (FGF23) secretion are thought to be key mediators of this risk. Elevated serum and dietary Pi and elevated plasma FGF23 are associated with increased cardiovascular and total mortality in people with normal baseline renal function. FGF23 may mediate some of this risk by promoting cardiac hypertrophy via activation of fibroblast growth factor receptor 4 on cardiomyocytes. Elevated serum Pi can also cause a profound increase in systemic oxidative stress, and this may reflect the ability of Pi to act directly on mitochondria to boost membrane potential and thereby increase respiratory chain superoxide production. Moreover, elevated FGF23 likewise induces oxidative stress in vascular endothelium via activation of NADPH oxidase complexes. In vitro exposure of vascular smooth muscle cells to elevated Pi provokes an osteoblastic phenotypic transition that is mediated by increased mitochondrial oxidant production; this is offset dose-dependently by increased exposure to magnesium (Mg). In vivo, dietary Mg is protective in rodent models of vascular calcification. It is proposed that increased intracellular Mg opposes Pi’s ability to increase mitochondrial membrane potential; this model could explain its utility for prevention of vascular calcification and predicts that Mg may have a more global protective impact with regard to the direct pathogenic effects of hyperphosphatemia.

The Relationship between Advanced Oxidation Protein Products, Vascular Calcifications and Arterial Stiffness in Predialysis Chronic Kidney Disease Patients

Background and Objectives: Cardiovascular morbidity and mortality are increased in patients with chronic kidney disease (CKD). It is likely that the accumulation of uremic toxins resulting in increased oxidative stress (OS) is a major contributing factor, but no clear link has been identified. The purpose of this research is to establish if advanced oxidation protein product (AOPP) levels in the serum of predialysis patients are a contributing factor to vascular calcification and increased arterial stiffness. Materials and Methods: After obtaining the informed consent, 46 predialysis patients (CKD stages G3-G5) were included in the study. In order to identify vascular calcifications, hand and pelvic radiographs were performed. Valvular calcifications were identified using cardiac ultrasound. AOPP were measured using a commercially available ELISA kit. The relationships between serum AOPP values and biochemical parameters relevant in the evaluation of CKD patients were analyzed. In addition to identifying the differences in AOPP levels between patients with/without vascular or valvular calcifications, the research focused on describing the relationship between OS and arterial stiffness assessed by oscillometric pulse-wave velocity (PWV) measurement. Results: No significant relationship between serum AOPP and vascular or valvular calcifications was highlighted, but significant correlations of AOPP with C-reactive protein (p = 0.025), HDL-cholesterol levels (p = 0.04), HbA1c (p = 0.05) and PWV values (p = 0.02) were identified. Conclusions: The usefulness of (OS) measurement in clinical practice remains debatable; however, the relationship between AOPP and arterial stiffness could be valuable in improving cardiovascular risk assessment of patients with CKD.

Oxidative stress in vascular calcification

Vascular calcification (VC), which is closely associated with significant mortality in cardiovascular disease, chronic kidney disease (CKD), and/or diabetes mellitus, is characterized by abnormal deposits of hydroxyapatite minerals in the arterial wall. The impact of oxidative stress (OS) on the onset and progression of VC has not been well described. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidases, xanthine oxidases, myeloperoxidase (MPO), nitric oxide synthases (NOSs), superoxide dismutase (SOD) and paraoxonases (PONs) are relevant factors that influence the production of reactive oxygen species (ROS). Furthermore, excess ROS-induced OS has emerged as a critical mediator promoting VC through several mechanisms, including phosphate balance, differentiation of vascular smooth muscle cells (VSMCs), inflammation, DNA damage, and extracellular matrix remodeling. Because OS is a significant regulator of VC, antioxidants may be considered as novel treatment options.

Circadian rhythm disorder: a potential inducer of vascular calcification?

Over the past decades, circadian rhythm has drawn a great attention in cardiovascular diseases. The expressions of rhythm genes fluctuate in accordance with the diurnal changes of vascular physiology, which highlights the pivotal effect of vascular clock. Recent researches show that the circadian clock can directly regulate the synthetic and secretory function of endothelial cells and phenotypic switch of vascular smooth muscle cells to adjust vascular relaxation and contraction. Importantly, dysfunction of vascular cells is involved in vascular calcification. Secretion of osteogenic cytokines and calcified vesicles in the vessel, osteogenic phenotype switch of vascular smooth muscle cells are all implicated in the calcification process. Moreover, circadian rhythm disorder can lead to abnormal hormone secretion, oxidative stress, inflammatory reaction, and autophagy, all of which should not be ignored in vascular calcification. Vascular senescence is another pathogenetic mechanism in vascular calcification. Accelerated vascular senescence may act as an important intermediate factor to promote vascular calcification in circadian rhythm disorders. In this review, we elaborate the potential effect of circadian rhythm disorder in vascular calcification and try to provide a new direction in the prevention of vascular calcification.

Arterial Stiffness: A Focus on Vascular Calcification and Its Link to Bone Mineralization

This review focuses on the association between vascular calcification and arterial stiffness, highlighting the important genetic factors, systemic and local microenvironmental signals, and underlying signaling pathways and molecular regulators of vascular calcification. Elevated oxidative stress appears to be a common procalcification factor that induces osteogenic differentiation and calcification of vascular cells in a variety of disease conditions such as atherosclerosis, diabetes mellitus, and chronic kidney disease. Thus, the role of oxidative stress and oxidative stress-regulated signals in vascular smooth muscle cells and their contributions to vascular calcification are highlighted. In relation to diabetes mellitus, the regulation of both hyperglycemia and increased protein glycosylation, by AGEs (advanced glycation end products) and O-linked β-N-acetylglucosamine modification, and its role in enhancing intracellular pathophysiological signaling that promotes osteogenic differentiation and calcification of vascular smooth muscle cells are discussed. In the context of chronic kidney disease, this review details the role of calcium and phosphate homeostasis, parathyroid hormone, and specific calcification inhibitors in regulating vascular calcification. In addition, the impact of the systemic and microenvironmental factors on respective intrinsic signaling pathways that promote osteogenic differentiation and calcification of vascular smooth muscle cells and osteoblasts are compared and contrasted, aiming to dissect the commonalities and distinctions that underlie the paradoxical vascular-bone mineralization disorders in aging and diseases.

Research Models for Studying Vascular Calcification

Calcification of the vessel wall contributes to high cardiovascular morbidity and mortality. Vascular calcification (VC) is a systemic disease with multifaceted contributing and inhibiting factors in an actively regulated process. The exact underlying mechanisms are not fully elucidated and reliable treatment options are lacking. Due to the complex pathophysiology, various research models exist evaluating different aspects of VC. This review aims to give an overview of the cell and animal models used so far to study the molecular processes of VC. Here, in vitro cell culture models of different origins, ex vivo settings using aortic tissue and various in vivo disease-induced animal models are summarized. They reflect different aspects and depict the (patho)physiologic mechanisms within the VC process.

Vitamin D-regulated osteocytic sclerostin and BMP2 modulate uremic extraskeletal calcification

We induced chronic kidney disease (CKD) with adenine in WT mice, mice with osteocyte-specific deletion of Cyp27b1, encoding the 25-hydroxyvitamin D 1(OH)ase [Oct-1(OH)ase-/-], and mice with global deletion of Cyp27b1 [global-1α(OH)ase-/-]; we then compared extraskeletal calcification. After adenine treatment, mice displayed increased blood urea nitrogen, decreased serum 1,25(OH)2D, and severe hyperparathyroidism. Skeletal expression of Cyp27b1 and of sclerostin and serum sclerostin all increased in WT mice but not in Oct-1α(OH)ase-/- mice or global-1α(OH)ase-/- mice. In contrast, skeletal expression of BMP2 and serum BMP2 rose in the Oct-1α(OH)ase-/- mice and in the global-1α(OH)ase-/- mice. Extraskeletal calcification occurred in muscle and blood vessels of mice with CKD and was highest in Oct-1α(OH)ase-/-mice. In vitro, recombinant sclerostin (100 ng/mL) significantly suppressed BMP2-induced osteoblastic transdifferentiation of vascular smooth muscle A7r5 cells and diminished BMP2-induced mineralization. Our study provides evidence that local osteocytic production of 1,25(OH)2D stimulates sclerostin and inhibits BMP2 production in murine CKD, thus mitigating osteoblastic transdifferentiation and mineralization of soft tissues. Increased osteocytic 1,25(OH)2D production, triggered by renal malfunction, may represent a "primary defensive response" to protect the organism from ectopic calcification by increasing sclerostin and suppressing BMP2 production.

Role of AGEs in the progression and regression of atherosclerotic plaques

The formation of advanced glycation end-products(AGEs) is an important cause of metabolic memory in diabetic patients and a key factor in the formation of atherosclerosis(AS) plaques in patients with diabetes mellitus. Related studies showed that AGEs could disrupt hemodynamic steady-state and destroy vascular wall integrity through the endothelial barrier damage, foam cell(FC) formation, apoptosis, calcium deposition and other aspects. At the same time, AGEs could initiate oxidative stress and inflammatory response cascade via receptor-depended and non-receptor-dependent pathways, promoting plaques to develop from a steady state to a vulnerable state and eventually tend to rupture and thrombosis. Numerous studies have confirmed that these pathological processes mentioned above could lead to acute coronary heart disease(CHD) and other acute cardiovascular and cerebrovascular events. However, the specific role of AGEs in the progression and regression of AS plaques has not yet been fully elucidated. In this paper, the formation, source, metabolism, physical and chemical properties of AGEs and their role in the migration of FCs and plaque calcification are briefly described, we hope to provide new ideas for the researchers that struggling in this field.

Dipeptidyl peptidase-4 inhibitor gemigliptin protects against vascular calcification in an experimental chronic kidney disease and vascular smooth muscle cells

Although dipeptidyl peptidase-4 inhibitors, a class of antidiabetic drugs, have various pleiotropic effects, it remains undetermined whether gemigliptin has a beneficial effect on vascular calcification. Therefore, this study was performed to evaluate the effect of gemigliptin on vascular calcification in a rat model of adenine-induced chronic kidney disease and in cultured vascular smooth muscle cells. Gemigliptin attenuated calcification of abdominal aorta and expression of RUNX2 in adenine-induced chronic kidney disease rats. In cultured vascular smooth muscle cells, phosphate-induced increase in calcium content was reduced by gemigliptin. Gemigliptin reduced phosphate-induced PiT-1 mRNA expression, reactive oxygen species generation, and NADPH oxidase mRNA expression (p22phox and NOX4). The reduction of oxidative stress by gemigliptin was associated with the downregulation of phospho-PI3K/AKT expression. High phosphate increased the expression of frizzled-3 (FDZ3) and decreased the expression of dickkopf-related protein-1 (DKK-1) in the Wnt pathway. These changes were attenuated by gemigliptin treatment. Gemigliptin restored the decreased expression of vascular smooth muscle cells markers (α-SMA and SM22α) and increased expression of osteogenic makers (CBFA1, OSX, E11, and SOST) induced by phosphate. In conclusion, gemigliptin attenuated vascular calcification and osteogenic trans-differentiation in vascular smooth muscle cells via multiple steps including downregulation of PiT-1 expression and suppression of reactive oxygen species generation, phospho-PI3K/AKT, and the Wnt signaling pathway.

Increased phagocytic NADPH oxidase activity associates with coronary artery calcification in asymptomatic men

Vascular calcification is a common feature in atherosclerosis and associates with cardiovascular events. Oxidative stress may be involved in the pathogenesis of vascular calcification. Previous studies have shown that the phagocytic NADPH oxidase is associated with atherosclerosis. The objective of the present study was to investigate the association between phagocytic NADPH oxidase-mediated superoxide production and coronary artery calcium (CAC). NADPH oxidase-mediated superoxide production was determined by chemiluminescence and CAC by computed tomography in 159 asymptomatic men free of overt clinical atherosclerosis. Multivariate linear regression analyses were used to assess the relationship between CAC and NADPH oxidase-mediated superoxide production. Compared with individuals in the lowest score of CAC (= 0 Agatston units), those in the upper score (>400 Agatston units) showed higher superoxide production (p < 0.05). In correlation analysis, superoxide production positively (p < 0.01) correlated with CAC, which in multivariate analysis remained significant after adjusting for age, HDL-cholesterol, triglycerides, body mass index, smoking, arterial hypertension and diabetes mellitus. In conclusion, in a population of men without clinically overt atherosclerotic disease, increased NADPH oxidase-mediated superoxide production associated with enhanced CAC. Albeit descriptive, these findings suggest a potential involvement of phagocytic NADPH oxidase-mediated oxidative stress in CAC.

Eotaxin Augments Calcification in Vascular Smooth Muscle Cells

Calcification of atherosclerotic plaques in elderly patients represents a potent risk marker of cardiovascular events. Plasma analyses of patients with or without calcified plaques reveal significant differences in chemokines, particularly eotaxin, which escalates with increased calcification. We therefore, hypothesize that eotaxin in circulation augments calcification of vascular smooth muscle cells (VSMCs) possibly via oxidative stress in the vasculature. We observe that eotaxin increases the rate of calcification significantly in VSMCs as evidenced by increased alkaline phosphatase activity, calcium deposition, and osteogenic marker expression. In addition, eotaxin promotes proliferation in VSMCs and triggers oxidative stress in a NADPH oxidase dependent manner. These primary novel observations support our proposition that in the vasculature eotaxin augments mineralization. Our findings suggest that eotaxin may represent a potential therapeutic target for prevention of cardiovascular complications in the elderly. J. Cell. Biochem. 118: 647-654, 2017. © 2016 Wiley Periodicals, Inc.

Redox signaling in cardiovascular pathophysiology: A focus on hydrogen peroxide and vascular smooth muscle cells

Oxidative stress represents excessive intracellular levels of reactive oxygen species (ROS), which plays a major role in the pathogenesis of cardiovascular disease. Besides having a critical impact on the development and progression of vascular pathologies including atherosclerosis and diabetic vasculopathy, oxidative stress also regulates physiological signaling processes. As a cell permeable ROS generated by cellular metabolism involved in intracellular signaling, hydrogen peroxide (H₂O₂) exerts tremendous impact on cardiovascular pathophysiology. Under pathological conditions, increased oxidase activities and/or impaired antioxidant systems results in uncontrolled production of ROS. In a pro-oxidant environment, vascular smooth muscle cells (VSMC) undergo phenotypic changes which can lead to the development of vascular dysfunction such as vascular inflammation and calcification. Investigations are ongoing to elucidate the mechanisms for cardiovascular disorders induced by oxidative stress. This review mainly focuses on the role of H₂O₂ in regulating physiological and pathological signals in VSMC.

Cardiovascular mortality in chronic kidney disease patients: potential mechanisms and possibilities of inhibition by resin-based phosphate binders

Cardiovascular mortality has been considered as the most important risk associated with chronic kidney disease. The mechanisms underlying this include inflammation, poor control of serum phosphate, high serum calcium, increased calcification of the arteries and cardiac valves, hyperlipidemia, diabetes, severe anemia, uric acid accumulation and others. Elevated phosphate levels have been strongly associated with increased mortality, thus phosphate-binding drugs have long been used to control the increase serum phosphate levels. However, phosphate-binding drugs differ considerably and recently numerous publications suggest differences between agents in the effects on overall mortality. The resin-based phosphate binders, comprising sevelamer and colestilan, not only reduce serum phosphate but also do not raise serum calcium. In addition, they reduce serum LDL-C, inflammation, uric acid and high Hba1c values. These differences suggest that not all phosphate binders may be equal in the context of cardiovascular mortality in this patient population.

Vascular calcification: from pathophysiology to biomarkers

The link between vascular calcification (VC) and increased mortality is now well established. Over time, as clinical importance of this phenomenon has begun to be fully considered, scientists have highlighted more and more physiopathological mechanisms and signaling pathways that underlie VC. Several conditions such as diabetes, dyslipidemia and renal diseases are undoubtedly identified as predisposing factors. But even if the process is better understood, many questions still remain unanswered. This review briefly develops the various theories that attempt to explain mineralization genesis. Nonetheless, the main purpose of the article is to provide a profile of the various existing biomarkers of VC. Indeed, in the past years, a lot of inhibitors and promoters, which form a dense and interconnected network, were identified. Given importance to assess and control mineralization process, a focusing on accumulated knowledge of each marker seemed to be necessary. Therefore, we tried to define their respective role in the physiopathology and how they can contribute to calcification risk assessment. Among these, Klotho/fibroblast growth factor-23, fetuin-A, Matrix Gla protein, Bone morphogenetic protein-2, osteoprotegerin, osteopontin, osteonectin, osteocalcin, pyrophosphate and sclerostin are specifically discussed.

N-acetylcysteine as a potential strategy to attenuate the oxidative stress induced by uremic serum in the vascular system

AIMS

Chronic kidney disease (CKD) progression is accompanied by systemic oxidative stress, which contributes to an increase in the risk of cardiovascular diseases (CVDs). N-acetylcysteine (NAC) is among the most studied antioxidants, but its therapeutic benefits in CKD-associated CVDs remain controversial. Here, we investigated whether NAC could inhibit the oxidative stress induced by uremia in vitro and in vivo.

MAIN METHODS

Endothelial and smooth muscle cells were challenged with human uremic or non-uremic sera, and the effects of a pre-treatment with 2mM NAC were evaluated. Reactive oxygen species (ROS) production, protein oxidation and total glutathione/glutathione disulfide (tGSH/GSSG) ratios were measured. Five-sixths nephrectomized or sham-operated rats were orally treated (in the drinking water) with 60 mg/kg/day NAC or not treated for 53 days. Plasma cysteine/cystine reduction potential Eh(Cyss/2Cys) was determined as a novel marker of the systemic oxidative stress.

KEY FINDINGS

NAC inhibited all the determined oxidative stress parameters, likely by increasing the tGSH/GSSG ratio, in both cell lines exposed to uremic serum. Orally administered NAC attenuated the systemic oxidative stress in uremic rats.

SIGNIFICANCE

The present results indicate that NAC, by preventing GSH depletion in vascular cells exposed to uremic serum and by attenuating the systemic oxidative stress during CKD progression, emerges as a potential strategy to prevent the oxidative stress induced by uremic toxicity in the vascular system.

Vascular calcification: Mechanisms of vascular smooth muscle cell calcification

Vascular calcification is highly prevalent and, when present, is associated with major adverse cardiovascular events. Vascular smooth muscle cells play an integral role in mediating vessel calcification by undergoing differentiation to osteoblast-like cells and generating matrix vesicles that serve as a nidus for calcium-phosphate deposition in the vessel wall. Once believed to be a passive process, it is now recognized that vascular calcification is a complex and highly regulated process that involves activation of cellular signaling pathways, circulating inhibitors of calcification, genetic factors, and hormones. This review will examine several of the key mechanisms linking vascular smooth muscle cells to vessel calcification that may be targeted to reduce vessel wall mineralization and, thereby, reduce cardiovascular risk.

Vitamin E protection of obesity-enhanced vascular calcification in uremic rats

This study aimed to determine the extent of extraskeletal calcification in uremic Zucker rats, by comparing obese and lean phenotypes, and to evaluate the influence of vitamin E (VitE) on the development of calcifications in both uremic rats and human vascular smooth muscle cells (HVSMCs) cultured in vitro. Zucker rats of lean and obese phenotypes with normal renal function [control (C); C-lean and C-obese groups] and with uremia [5/6 nephrectomy (Nx); Nx-lean and Nx-obese groups] and uremic rats treated with VitE (Nx-lean + VitE and Nx-obese + VitE groups) were studied. Uremic groups were subjected to Nx, fed a 0.9% phosphorus diet, and treated with calcitriol (80 ng/kg ip). The aortic calcium concentration was significantly higher ( P < 0.05) in Nx-obese rats (10.0 ± 2.1 mg/g tissue) than in Nx-lean rats (3.6 ± 1.3 mg/g tissue). A decrease in plasma glutathione peroxidase activity was observed in Nx-obese rats compared with Nx-lean rats (217.2 ± 18.2 vs. 382.3 ± 15.5 nmol·min−1·ml−1, P < 0.05). Treatment with VitE restored glutathione peroxidase activity and reduced the aortic calcium concentration to 4.6 ± 1.3 mg/g tissue. The differences in mineral deposition between Nx-lean, Nx-obese, Nx-lean + VitE, and Nx-obese + VitE rats were also evidenced in other soft tissues. In HVSMCs incubated with high phosphate, VitE also prevented oxidative stress and reduced calcium content, bone alkaline phosphatase, and gene expression of core-binding factor-α1. In conclusion, uremic obese rats develop more severe calcifications than uremic lean rats and VitE reduces oxidative stress and vascular calcifications in both rats and cultures of HVSMCs.

Reduction of advanced-glycation end products levels and inhibition of RAGE signaling decreases rat vascular calcification induced by diabetes

Advanced-glycation end products (AGEs) were recently implicated in vascular calcification, through a process mediated by RAGE (receptor for AGEs). Although a correlation between AGEs levels and vascular calcification was established, there is no evidence that reducing in vivo AGEs deposition or inhibiting AGEs-RAGE signaling pathways can decrease medial calcification. We evaluated the impact of inhibiting AGEs formation by pyridoxamine or elimination of AGEs by alagebrium on diabetic medial calcification. We also evaluated if the inhibition of AGEs-RAGE signaling pathways can prevent calcification. Rats were fed a high fat diet during 2 months before receiving a low dose of streptozotocin. Then, calcification was induced with warfarin. Pyridoxamine was administered at the beginning of warfarin treatment while alagebrium was administered 3 weeks after the beginning of warfarin treatment. Results demonstrate that AGEs inhibitors prevent the time-dependent accumulation of AGEs in femoral arteries of diabetic rats. This effect was accompanied by a reduced diabetes-accelerated calcification. Ex vivo experiments showed that N-methylpyridinium, an agonist of RAGE, induced calcification of diabetic femoral arteries, a process inhibited by antioxidants and different inhibitors of signaling pathways associated to RAGE activation. The physiological importance of oxidative stress was demonstrated by the reduction of femoral artery calcification in diabetic rats treated with apocynin, an inhibitor of reactive oxygen species production. We demonstrated that AGE inhibitors prevent or limit medial calcification. We also showed that diabetes-accelerated calcification is prevented by antioxidants. Thus, inhibiting the association of AGE-RAGE or the downstream signaling reduced medial calcification in diabetes.

Palmitic acid increases medial calcification by inducing oxidative stress

BACKGROUND

Aortic medial calcification is a cellular-regulated process leading to arterial stiffness. Although epidemiological studies have suggested an association between the saturation of fatty acids (FA) and arterial stiffness, there is no evidence that saturated FA can induce arterial calcification. This study investigated the capacity of palmitic acid (PA) to induce medial calcification and the signaling pathway(s) implicated in this process.

METHODS

Rat aortic segments and vascular smooth muscle cells (VSMC) were exposed to calcification medium supplemented with PA. In vivo, rats were treated with warfarin to induce calcification and fed a PA-enriched diet.

RESULTS

In vitro and ex vivo, palmitate increases calcification and ROS production. Palmitate increases extracellular-signal-regulated kinase (ERK1/2) phosphorylation and osteogenic gene expression. Inhibition of NADPH oxidase with apocynin or an siRNA prevents these effects. ERK1/2 inhibition attenuates the amplification of osteogenic gene expression and calcification induced by palmitate. In vivo, a PA-enriched diet amplified medial calcification and pulse wave velocity (PWV). These effects are mediated by ROS production as indicated by the inhibition of calcification and PWV normalization in rats concomitantly treated with apocynin.

CONCLUSION

ROS induction by palmitate leads to ERK1/2 phosphorylation and subsequently induces the osteogenic differentiation of VSMC. © 2013 S. Karger AG, Basel.

Balanced mineralization in the arterial system: possible role of osteoclastogenesis/osteoblastogenesis in abdominal aortic aneurysm and stenotic disease

Arterial calcification is the result of the same highly organized processes as seen in bone, which rely on a delicate balance between osteoblasts and osteoclasts. Although previously understood as passive precipitation, evidence has accumulated to suggest that arterial calcification is the result of organized, regulated processes bearing many similarities to osteogenesis in bone, including the presence of subpopulations of arterial wall cells that retain osteoblastic lineage potential. These cells have the potential to form mineralized nodules and express osteoblast markers, including bone morphogenetic protein-2, osteocalcin, osteopontin, and alkaline phosphatase. By contrast, osteoclast-like cells mediate the catabolic process of mineral resorption. Recent data shows that cells positive for tartrate-resistant acid phosphatase, a major marker for osteoclasts, have been histologically identified in atherosclerotic lesions and are referred to as osteoclast-like cells. Evidence has accumulated to suggest that initial arterial calcification through passive precipitation of calcium phosphate initiates balanced mineralization regulated by osteoclast-like and osteoblast-like cells. Subsequently, various pathogenic conditions may trigger an imbalance between osteoblastogenesis and osteoclastogenesis, leading to either calcification in stenotic/occlusive disease or destruction of the extracellular matrix in aneurysmal disease. Further elucidation of these newly emerging concepts could lead to a novel therapeutic approach to arterial stenotic/occlusive disease and/or abdominal aortic aneurysm.

Vascular calcification: pathophysiology and risk factors

Vascular calcification can occur in nearly all arterial beds and in both the medial and intimal layers. The initiating factors and clinical consequences depend on the underlying disease state and location of the calcification. The best studied manifestation is coronary artery calcification, in part because of the obvious clinical consequences, but also because of CT-based imaging modalities. In the general population, the presence of coronary artery calcification increases cardiovascular risk above that predicted by traditional Framingham risk factors, suggesting the presence of nontraditional risk factors. In patients with chronic kidney disease (CKD), coronary artery calcification is more prevalent and markedly more severe than in the general population. In these CKD patients, nontraditional risk factors such as oxidative stress, advanced glycation end products, and disordered mineral metabolism are also more prevalent and more severe and offer mechanistic insight into the pathogenesis of vascular calcification.

Hydrogen peroxide-induced poly(ADP-ribosyl)ation regulates osteogenic differentiation-associated cell death

We set out to investigate the role of poly(ADP-ribosylation), the attachment of NAD(+)-derived (ADP-ribose)(n) polymers to proteins, in the regulation of osteogenic differentiation of SAOS-2 cells and mesenchymal stem cells. In osteogenic differentiation medium, SAOS-2 cells showed mineralization and expressed alkaline phosphatase and osteoblastic marker genes such as Runx2, osterix, BMP2, and osteopontin. The cells also released hydrogen peroxide, displayed poly(ADP-ribose) polymerase (PARP) activation, and showed commitment to cell death (apoptosis and necrosis). Scavenging reactive oxygen species by glutathione or decomposing hydrogen peroxide by the addition of catalase reduced differentiation, PARP activation, and cell death. We silenced the expression of the main PAR-synthesizing enzyme PARP-1 and the PAR-degrading enzyme poly(ADP-ribose) glycohydrolase (PARG) in SAOS-2 osteosarcoma cells (shPARP-1 and shPARG, respectively). Both shPARP-1- and shPARG-silenced cells exhibited altered differentiation, with the most notable change being increased osteopontin expression but decreased alkaline phosphatase activity. PARP-1 silencing suppressed both apoptotic and necrotic cell death, but the PARP inhibitor PJ34 sensitized cells to cell death, indicating that the effects of PARP-1 silencing are not related to the activity of the enzyme. PARG silencing resulted in more apoptosis and, in the last days of differentiation, a shift from apoptosis toward necrosis. In conclusion our data prove that hydrogen peroxide-induced poly(ADP-ribose) signaling regulates cell death and osteodifferentiation.

The antioxidant tempol ameliorates arterial medial calcification in uremic rats: important role of oxidative stress in the pathogenesis of vascular calcification in chronic kidney disease

Vascular calcification is closely related to cardiovascular morbidity and mortality. Accumulating data indicate that oxidative stress is associated with dysfunction of various organs, including cardiovascular diseases in chronic kidney disease (CKD). However, it remains undetermined if oxidative stress induced by uremia promotes arterial medial calcification. The present study investigated the role of oxidative stress in the pathogenesis of arterial medial calcification in uremic rats. Rats with uremia induced by adenine-rich diet progressively developed arterial medial calcification, which was accompanied by time-dependent increases in both aortic and systemic oxidative stress. Immunohistochemical and biochemical analyses showed that the arterial medial calcification progressed in a time-dependent manner that is parallel to the osteogenic transdifferentiation of vascular smooth muscle cells. Accumulation of oxidative stress was also identified in the calcified regions. Time-course studies indicated that both oxidative stress and hyperphosphatemia correlated with arterial medial calcification. Tempol, an antioxidant, ameliorated osteogenic transdifferentiation of vascular smooth muscle cells and arterial medial calcification in uremic rats, together with reduction in aortic and systemic oxidative stress levels, without affecting serum biochemical parameters. Our data suggest that oxidative stress induced by uremia can play a role in the pathogenesis of vascular calcification in CKD, and that antioxidants such as tempol are potentially useful in preventing the progression of vascular calcification in CKD.

Nuclear factor of activated T cells mediates oxidised LDL-induced calcification of vascular smooth muscle cells

AIMS/HYPOTHESIS

Vascular calcification is a prominent feature of both atherosclerosis and diabetes, and is clinically associated with osteoporosis. The expression of bone-regulatory factors and the impact of oxidative stress in aortic calcification are well-documented. Recently, nuclear factor of activated T cells (NFAT) cytoplasmic, calcineurin-dependent 1 (NFATc1) was identified in calcified aortic valves and has been implicated in vascular calcification. Therefore, we assessed the mechanisms of osteogenic transdifferentiation of vascular smooth muscle cells induced by oxidised LDL (oxLDL) and evaluated the role of NFAT in this process.

METHODS

Human coronary artery smooth muscle cells (HCASMCs) were cultured for 21 days in medium supplemented with oxLDL. NFAT was inhibited using the NFAT inhibitor VIVIT, or by knockdown with small interfering RNA (siRNA). Osteogenic transdifferentiation was assessed by gene expression, matrix mineralisation and alkaline phosphatase activity.

RESULTS

Exposure to oxLDL caused the transformation of HCASMCs towards an osteoblast-like phenotype based on increased mineral matrix formation and RUNX2 expression. NFATc1 blockade completely prevented oxLDL-induced osteogenic transformation of HCASMCs as well as oxLDL-induced stimulation of osteoblast differentiation. In contrast, matrix mineralisation induced by osteogenic medium was independent of the NFAT pathway. Of note, oxLDL-conditioned medium from HCASMCs transferred to bone cells promoted osteoblast mineralisation. Consistent with these in vitro findings, diabetic rats with a twofold increase in oxidised lipid levels displayed higher aortic calcium concentrations and increased expression of osteogenic markers and production of NFATc1.

CONCLUSIONS/INTERPRETATION

Our results identify the NFAT signalling pathway as a novel regulator of oxLDL-induced transdifferentiation of vascular smooth muscle cells towards an osteoblast-like phenotype.

Bone morphogenetic protein-2 activates NADPH oxidase to increase endoplasmic reticulum stress and human coronary artery smooth muscle cell calcification

Bone morphogenetic protein-2 (BMP-2) increases oxidant stress and endoplasmic reticulum (ER) stress to stimulate differentiation of osteoblasts; however, the role of these signaling pathways in the transition of smooth muscle cells to a calcifying osteoblast-like phenotype remains incompletely characterized. We, therefore, treated human coronary artery smooth muscle cells (HCSMC) with BMP-2 (100ng/mL) and found an increase in NADPH oxidase activity and oxidant stress that occurred via activation of the bone morphogenetic protein receptor 2 and Smad 1 signaling. BMP-2-mediated oxidant stress also increased endoplasmic reticulum (ER) stress demonstrated by increased expression of GRP78, phospho-IRE1α, and the transcription factor XBP1. Analysis of a 1kb segment of the Runx2 promoter revealed an XBP1 binding site; electrophoretic mobility shift and chromatin immunoprecipitation assays demonstrated that XBP1 bound to the Runx2 promoter at this site in BMP-2-treated HCSMC. Inhibition of oxidant stress or ER stress decreased Runx2 expression, intracellular calcium deposition, and mineralization of BMP-2-treated HCSMC. Thus, in HCSMC, BMP-2 increases oxidant stress and ER stress to increase Runx2 expression and promote vascular smooth muscle cell calcification.

Mitochondrial reactive oxygen species promote p65 nuclear translocation mediating high-phosphate-induced vascular calcification in vitro and in vivo

Hyperphosphatemia is the major risk factor associated with vascular calcification (VC) in end-stage renal disease. As oxidative stress is increased in uremia, we studied the role of mitochondrial reactive oxygen species (ROS) and nuclear factor-κB signaling in phosphate-induced VC. In an in vitro calcification model (β-glycerophosphate (BGP) induction) using bovine aortic smooth muscle cells, the production of intracellular and mitochondrial ROS, or superoxide anion, was stimulated by increased mitochondrial membrane potential. This effect was blocked by the superoxide dismutase (SOD) mimic MnTMPyP, a respiratory chain inhibitor rotenone, or a protonophore. Calcium deposition and the switch of smooth muscle cells from a contractile to an osteogenic phenotype were decreased when mitochondrial ROS generation was inhibited by the respiratory chain inhibitor, MnTMPyP, or the overexpression of SOD1 and SOD2 and uncoupling protein 2. The phosphorylation of IkKβ, IκBα degradation, and p65 nuclear translocation were increased by BGP but reversed when mitochondrial ROS production was blocked by protonophore or MnTMPyP. Knockdown of endogenous p65 or overexpression of IκBα reduced calcium deposition in the cultured cells. Furthermore, in a rat model of dietary adenine-induced chronic renal failure, MnTMPyP reduced aortic ROS levels, p65 activation, and calcium deposition. Thus, mitochondrial ROS-mediated p65 nuclear translocation is involved in phosphate-induced VC.

Proteomic analysis of human mesenchymal stromal cells derived from adipose tissue undergoing osteoblast differentiation

BACKGROUND AIMS

Stem cells derived from human adipose tissue (ASC) have the capacity for renewal, are easily obtained and have plasticity properties that allow them to differentiate into several cell types, including osteoblast cells. With the aim of understanding the issue of the osteogenic process and finding reliable biomarkers in cells undergoing the osteogeneic differentiation process, this work took advantage of a proteomic approach to identify proteins involved in osteogenesis.

METHODS

For this purpose, ASC were analyzed under three conditions: S0, in the absence of stimulation; S1, with 2 weeks of osteogenic medium stimulation; and S2, with 4 weeks of osteogenic medium stimulation. The identification of ASC was carried out by flow cytometry using antibodies specific to known undifferentiated stem cell-surface markers. Cell viability, enzymatic activity, mineral deposition, collagen structure and production and gene analyzes were evaluated for each condition.

RESULTS

Phenotypic modifications were observed during the in vitro osteogenic differentiation process by two-dimensional (2-D) differential image gel electrophoresis (DIGE). The proteins were identified by mass espectrometry in tandem (MS/MS) analyzes using Matrix-assisted laser desorption/ionization with TOF/TOF is a tandem mass spectrometry method where two time-of-flight mass spectrometers are used consecutively (MALDI-TOF/TOF). A total of 51 differentially expressed proteins was identified when comparing the three observed conditions. Sixteen different spots were identified in the S0 stage compared with S2, while 28 different spots were found in S2 compared with S0. S1 expressed seven different spots compared with S0 and S2.

CONCLUSIONS

These findings suggest the involvement of several proteins directly related to the osteogenic pathway, which can be used to improve understanding of the osteogenic process.

Vascular smooth muscle cells ablation with endovascular nonthermal irreversible electroporation

PURPOSE

To evaluate the effect of endovascular nonthermal irreversible electroporation (NTIRE) on blood vessels.

MATERIALS AND METHODS

Specially made endovascular devices with four electrodes on top of inflatable balloons were used to apply electroporation pulses. Finite element simulations were used to characterize NTIRE protocols that would not induce thermal damage to treated tissues. Right iliac arteries of eight rabbits were treated with 90 NTIRE pulses. Angiograms were performed before and after the procedures. Arterial specimens were harvested at 7 and 35 days. Evaluation included hematoxylin and eosin, elastic von Giessen, and Masson trichrome stains. Immunohistochemistry of selected slides included smooth muscle actin (SMA), proliferating cell nuclear antigen, von Willebrand factor (VWF), and S-100 antigen.

RESULTS

At 7 days, all NTIRE-treated arterial segments displayed complete, transmural ablation of vascular smooth muscle cells (VSMC). At 35 days, similar damage to VSMC was noted. In most cases, the elastic lamina remained intact, and endothelial layer regenerated. Occasional mural inflammation and cartilaginous metaplasia were noted. After 5 weeks, there was no evidence of significant VSMC proliferation, with the dominant process being wall fibrosis with regenerated endothelium.

CONCLUSIONS

NTIRE can be applied in an endovascular approach. It efficiently ablates vessel wall within seconds and with no damage to extracellular structures. NTIRE has possible applications in many fields of clinical cardiology, including arterial restenosis and cardiac arrhythmias.