Increased calcification in osteoprotegerin-deficient smooth muscle cells: Dependence on receptor activator of NF-κB ligand and interleukin 6

Dietary inflammation and vascular calcification: a comprehensive review of the associations, underlying mechanisms, and prevention strategies

Cardiovascular disease (CVD) is one of the leading causes of death globally, and vascular calcification (VC) has been recognized as an independent and strong predictor of global CVD and mortality. Chronic inflammation has been demonstrated to play a significant role in the progression of VC. This review aims to summarize the literature that aimed to elucidate the associations between dietary inflammation (DI) and VC as well as to explore the mechanisms underlying the association and discuss strategies (including dietary interventions) to prevent VC. Notably, diets rich in processed foods, carbohydrates with high glycemic index/load, saturated fatty acids, trans-fatty acids, cholesterol, and phosphorus were found to induce inflammatory responses and accelerate the progression of VC, indicating a close relationship between DI and VC. Moreover, we demonstrate that an imbalance in the composition of the gut microbiota caused by the intake of specific dietary choices favored the production of certain metabolites that may contribute to the progression of VC. The release of inflammatory and adhesion cytokines, activation of inflammatory pathways, oxidative stress, and metabolic disorders were noted to be the main mechanisms through which DI induced VC. To reduce and slow the progression of VC, emphasis should be placed on the intake of diets rich in omega-3 fatty acids, dietary fiber, Mg, Zn, and polyphenols, as well as the adjustment of dietary pattern to reduce the risk of VC. This review is expected to be useful for guiding future research on the interplay between DI and VC.

Circulating osteoprotegerin levels and cardiovascular outcomes in patients with pre-dialysis chronic kidney disease: results from the KNOW-CKD study

While the relationship between circulating osteoprotegerin (OPG) and cardiovascular events is well-established in the general population, its association with cardiovascular risks in chronic kidney disease (CKD) patients remains less robust. This study hypothesized that elevated circulating OPG levels might be associated with an increased risk of major adverse cardiac events (MACE) in CKD patients, a total of 2,109 patients with CKD stages 1 through pre-dialysis 5 from the KNOW-CKD cohort were categorized into quartiles based on serum OPG levels. The primary outcome of the study was 3-point MACE, defined as a composite of nonfatal myocardial infarction, nonfatal stroke, or cardiac death. The median follow-up duration was 7.9 years. The cumulative incidence of 3-point MACE significantly varied across serum OPG levels in Kaplan-Meier curve analysis (P < 0.001, log-rank test), with the highest incidence observed in the 4th quartile. Cox regression analysis indicated that, relative to the 1st quartile, the risk of 3-point MACE was significantly higher in the 3rd (adjusted hazard ratio 2.901, 95% confidence interval 1.009 to 8.341) and the 4th quartiles (adjusted hazard ratio 4.347, 95% confidence interval 1.410 to 13.395). In conclusion, elevated circulating OPG levels are associated with adverse cardiovascular outcomes in pre-dialysis CKD patients.

Organ aging signatures in the plasma proteome track health and disease

Animal studies show aging varies between individuals as well as between organs within an individual1-4, but whether this is true in humans and its effect on age-related diseases is unknown. We utilized levels of human blood plasma proteins originating from specific organs to measure organ-specific aging differences in living individuals. Using machine learning models, we analysed aging in 11 major organs and estimated organ age reproducibly in five independent cohorts encompassing 5,676 adults across the human lifespan. We discovered nearly 20% of the population show strongly accelerated age in one organ and 1.7% are multi-organ agers. Accelerated organ aging confers 20-50% higher mortality risk, and organ-specific diseases relate to faster aging of those organs. We find individuals with accelerated heart aging have a 250% increased heart failure risk and accelerated brain and vascular aging predict Alzheimer's disease (AD) progression independently from and as strongly as plasma pTau-181 (ref. 5), the current best blood-based biomarker for AD. Our models link vascular calcification, extracellular matrix alterations and synaptic protein shedding to early cognitive decline. We introduce a simple and interpretable method to study organ aging using plasma proteomics data, predicting diseases and aging effects.

Association between dietary vitamin C and abdominal aortic calcification among the US adults

BACKGROUND

Cardiovascular disease (CVD) is the leading cause of mortality, and vascular calcification has been highly correlated with CVD events. Abdominal aortic calcification (AAC) has been shown to predict subclinical CVD and incident CVD events. However, the relationship between vitamin C and abdominal aortic calcification remains unclear.

OBJECTIVE

To investigate the relationship of dietary vitamin C with AAC among the adult population in the US.

METHODS

The National Health and Nutrition Examination Survey (NHANES) 2013-2014 provided the data for the cross-sectional study. 2297 subjects (1089 males) were included in the study. Two scoring systems, AAC 24-point scale (Kauppila) and AAC 8-point scale (Schousboe), were used for the measurement of AAC score. Dietary vitamin C intake was calculated as the average of two rounds of 24-h interview recall data and classified in tertiles for analysis. We applied weighted multiple regression analyses to assess the relationship of dietary vitamin C with AAC score and the risk of having AAC. To ensure the robustness of the findings, subgroup and sensitivity analyses were performed. Additionally, smooth curve fittings, using generalized additive models (GAM) were employed to visualize potential nonlinear relationships. Furthermore, an exploratory analysis on the relationship of vitamin C supplements with AAC was also conducted.

RESULTS

The results showed that higher dietary vitamin C intake was related to a reduction in AAC score (AAC-24: β = -0.338, 95% confidence interval [CI] -0.565, -0.111, P = 0.004; AAC-8: β = -0.132, 95%CI -0.217, -0.047, P = 0.002), and lower risk of AAC (odds ratio [OR] = 0.807, 95%CI 0.659, 0.989, P = 0.038). However, the relationship of vitamin C supplements with AAC was not identified.

CONCLUSIONS

The study revealed that higher intake of dietary vitamin C rather than vitamin C supplements was related to reduced AAC score and lower risk of AAC, indicating that diets rich in vitamin C are recommended due to its potential benefits for protecting against vascular calcification and CVD among the adult population in the US.

Serum OPG and RANKL Levels as Risk Factors for the Development of Cardiovascular Calcifications in End-Stage Renal Disease Patients in Hemodialysis

Cardiovascular calcifications (CVC) are frequently observed in chronic kidney disease (CKD) patients and contribute to their cardiovascular mortality. The aim of the present study was to investigate the impact of osteoprotegerin (OPG)/Receptor Activator of NF-κΒ (RANK)/RANK ligand (RANKL) pathway in the development and evolution of CVCs in hemodialysis patients. In total, 80 hemodialysis patients were assessed for the presence of vascular (abdominal aorta and muscular arteries) calcifications and results were correlated to serum OPG and RANKL levels and the OPG/RANKL ratio. Traditional cardiovascular risk factors and mineral bone disease parameters were also estimated. The presence of VCs was also evaluated 5 years after the initiation of the study, and results were correlated to the initial serum OPG levels. Age, diabetes mellitus, coronary artery disease and OPG levels (p < 0.001) were associated with VCs, whereas RANKL levels were not. Multivariate analysis though revealed that only OPG levels were significantly associated with abdominal aorta calcifications (p = 0.026), but they were not correlated with the progression of VCs. Serum OPG levels are positively and independently associated with VCs in HD patients, but not with their progression. RANKL levels did not show any associations, whereas further studies are needed to establish the significance of OPG/RANKL ratio.

Do bisphosphonates and RANKL inhibitors alter the progression of coronary artery calcification? A systematic review and meta-analysis protocol

INTRODUCTION

Whether bisphosphonates and RANKL inhibitors play a novel role in delaying cardiovascular calcification is unknown. Their action on regulatory enzymes in the mevalonic acid pathway, which is implicated in both bone and lipid metabolism, may be a novel therapeutic target to manage coronary artery disease (CAD). Such therapies may particularly be relevant in those for whom traditional cardiovascular therapies are no longer sufficient to control disease progression.

METHODS AND ANALYSIS

We will perform a systematic review which aims to synthesise evidence regarding whether use of bisphosphonates or use of the RANKL inhibitor denosumab delays coronary artery calcium (CAC) progression. Eligible studies will include longitudinal studies investigating CAC progression in patients aged >18 years taking either a bisphosphonate or denosumab compared with those who do not. Embase, MEDLINE and Cochrane will be searched using prespecified search terms. Studies will be screened by title and abstract independently and then in full to determine suitability for inclusion in the review. Extracted data will include that relating to study and participant characteristics. The primary outcome will be the CAC score. Secondary outcomes will include aortic and carotid artery calcification. Meta-analysis will be performed if sufficient data are available.

ETHICS AND DISSEMINATION

This study does not require ethics as it is a systematic review of the literature. The results of the review described within this protocol will be distributed via presentations at relevant conferences and publication within a peer-reviewed journal.

PROSPERO REGISTRATION NUMBER

The systematic review pertaining to this protocol is registered with PROSPERO (Registration ID: CRD42022312377).

The two facets of receptor tyrosine kinase in cardiovascular calcification-can tyrosine kinase inhibitors benefit cardiovascular system?

Tyrosine kinase inhibitors (TKIs) are widely used in cancer treatment due to their effectiveness in cancer cell killing. However, an off-target of this agent limits its success. Cardiotoxicity-associated TKIs have been widely reported. Tyrosine kinase is involved in many regulatory processes in a cell, and it is involved in cancer formation. Recent evidence suggests the role of tyrosine kinase in cardiovascular calcification, specifically, the calcification of heart vessels and valves. Herein, we summarized the accumulating evidence of the crucial role of receptor tyrosine kinase (RTK) in cardiovascular calcification and provided the potential clinical implication of TKIs-related ectopic calcification. We found that RTKs, depending on the ligand and tissue, can induce or suppress cardiovascular calcification. Therefore, RTKs may have varying effects on ectopic calcification. Additionally, in the context of cardiovascular calcification, TKIs do not always relate to an unfavored outcome-they might offer benefits in some cases.

von Willebrand Factor: A Central Regulator of Arteriovenous Fistula Maturation Through Smooth Muscle Cell Proliferation and Outward Remodeling

Background Arteriovenous fistula (AVF) maturation failure is a main limitation of vascular access. Maturation is determined by the intricate balance between outward remodeling and intimal hyperplasia, whereby endothelial cell dysfunction, platelet aggregation, and vascular smooth muscle cell (VSMC) proliferation play a crucial role. von Willebrand Factor (vWF) is an endothelial cell-derived protein involved in platelet aggregation and VSMC proliferation. We investigated AVF vascular remodeling in vWF-deficient mice and vWF expression in failed and matured human AVFs. Methods and Results Jugular-carotid AVFs were created in wild-type and vWF^-/- mice. AVF flow was determined longitudinally using ultrasonography, whereupon AVFs were harvested 14 days after surgery. VSMCs were isolated from vena cavae to study the effect of vWF on VSMC proliferation. Patient-matched samples of the basilic vein were obtained before brachio-basilic AVF construction and during superficialization or salvage procedure 6 weeks after AVF creation. vWF deficiency reduced VSMC proliferation and macrophage infiltration in the intimal hyperplasia. vWF^-/- mice showed reduced outward remodeling (1.5-fold, P=0.002) and intimal hyperplasia (10.2-fold, P<0.0001). AVF flow in wild-type mice was incremental over 2 weeks, whereas flow in vWF^-/- mice did not increase, resulting in a two-fold lower flow at 14 days compared with wild-type mice (P=0.016). Outward remodeling in matured patient AVFs coincided with increased local vWF expression in the media of the venous outflow tract. Absence of vWF in the intimal layer correlated with an increase in the intima-media ratio. Conclusions vWF enhances AVF maturation because its positive effect on outward remodeling outweighs its stimulating effect on intimal hyperplasia.

Lipoprotein(a), a Lethal Player in Calcific Aortic Valve Disease

Calcified aortic valve disease (CAVD) is the most common valvular cardiovascular disease with increasing incidence and mortality. The primary treatment for CAVD is surgical or transcatheter aortic valve replacement and there remains a lack of effective drug treatment. Recently, lipoprotein (a) (Lp(a)) has been considered to play a crucial role in CAVD pathophysiology. Multiple studies have shown that Lp(a) represents an independent risk factor for CAVD. Moreover, Lp(a) mediates the occurrence and development of CAVD by affecting aortic valve endothelial dysfunction, indirectly promoting foam cell formation through oxidized phospholipids (OxPL), inflammation, oxidative stress, and directly promotes valve calcification. However, there is a lack of clinical trials with Lp(a) reduction as a primary endpoint. This review aims to explore the relationship and mechanism between Lp(a) and CAVD, and focuses on the current drugs that can be used as potential therapeutic targets for CAVD.

ILF3 is responsible for hyperlipidemia-induced arteriosclerotic calcification by mediating BMP2 and STAT1 transcription

Calcification is common in atherosclerotic plaque and can induce vulnerability, which further leads to myocardial infarction, plaque rupture and stroke. The mechanisms of atherosclerotic calcification are poorly characterized. Interleukin enhancer binding factor 3 (ILF3) has been identified as a novel factor affecting dyslipidemia and stroke subtypes. However, the precise role of ILF3 in atherosclerotic calcification remains unclear. In this study, we used smooth muscle-conditional ILF3 knockout (ILF3SM-KO) and transgenic mice (ILF3SM-Tg) and macrophage-conditional ILF3 knockout (ILF3M-KO) and transgenic (ILF3M-Tg) mice respectively. Here we showed that ILF3 expression is increased in calcified human aortic vascular smooth muscle cells (HAVSMCs) and calcified atherosclerotic plaque in humans and mice. We then found that hyperlipidemia increases ILF3 expression and exacerbates calcification of VSMCs and macrophages by regulating bone morphogenetic protein 2 (BMP2) and signal transducer and activator of transcription 1 (STAT1) transcription. We further explored the molecular mechanisms of ILF3 in atherosclerotic calcification and revealed that ILF3 acts on the promoter regions of BMP2 and STAT1 and mediates BMP2 upregulation and STAT1 downregulation, which promotes atherosclerotic calcification. Our results demonstrate the effect of ILF3 in atherosclerotic calcification. Inhibition of ILF3 may be a useful therapy for preventing and even reversing atherosclerotic calcification.

Restoration of 5-methoxytryptophan protects against atherosclerotic chondrogenesis and calcification in ApoE-/- mice fed high fat diet

Background

Toll-like receptor-2 (TLR2) promotes vascular smooth muscle cell (VSMC) transdifferentiation to chondrocytes and calcification in a p38 MAPK-dependent manner. Vascular 5-methoxytryptophan (5-MTP) is a newly identified factor with anti-inflammatory actions. As 5-MTP targets p38 MAPK for its actions, we postulated that 5-MTP protects against vascular chondrogenesis and calcification.

Methods

High-fat diet-induced advanced atherosclerosis in mice were performed to investigate the effect of 5-MTP on atherosclerotic lesions and calcification. VSMCs were used to determine the role of 5-MTP in VSMC chondrogenic differentiation and calcification. Alizarin red S and Alcian blue staining were used to measure VSMC calcification and chondrogenic differentiation, respectively.

Results

5-MTP was detected in aortic tissues of ApoE^−/− mice fed control chow. It was reduced in ApoE^−/− mice fed high-fat diet (HFD), but was restored in ApoE^−/−Tlr2^−/− mice, suggesting that HFD reduces vascular 5-MTP production via TLR2. Intraperitoneal injection of 5-MTP or its analog into ApoE^−/− mice fed HFD reduced aortic atherosclerotic lesions and calcification which was accompanied by reduction of chondrogenesis and calcium deposition. Pam3CSK4 (Pam3), ligand of TLR2, induced SMC phenotypic switch to chondrocytes. Pretreatment with 5-MTP preserved SMC contractile proteins and blocked Pam3-induced chondrocyte differentiation and calcification. 5-MTP inhibited HFD-induced p38 MAPK activation in vivo and Pam3-induced p38 MAPK activation in SMCs. 5-MTP suppressed HFD-induced CREB activation in aortic tissues and Pam3-induced CREB and NF-κB activation in SMCs.

Conclusions

These findings suggest that 5-MTP is a vascular arsenal against atherosclerosis and calcification by inhibiting TLR2–mediated SMC phenotypic switch to chondrocytes and the consequent calcification. 5-MTP exerts these effects by blocking p38 MAPK activation and inhibiting CREB and NF-κB transactivation activity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12929-021-00771-1.

Osteoprotegerin regulates vascular function through syndecan-1 and NADPH oxidase-derived reactive oxygen species

Osteogenic factors, such as osteoprotegerin (OPG), are protective against vascular calcification. However, OPG is also positively associated with cardiovascular damage, particularly in pulmonary hypertension, possibly through processes beyond effects on calcification. In the present study, we focused on calcification-independent vascular effects of OPG through activation of syndecan-1 and NADPH oxidases (Noxs) 1 and 4. Isolated resistance arteries from Wistar-Kyoto (WKY) rats, exposed to exogenous OPG, studied by myography exhibited endothelial and smooth muscle dysfunction. OPG decreased nitric oxide (NO) production, eNOS activation and increased reactive oxygen species (ROS) production in endothelial cells. In VSMCs, OPG increased ROS production, H2O2/peroxynitrite levels and activation of Rho kinase and myosin light chain. OPG vascular and redox effects were also inhibited by the syndecan-1 inhibitor synstatin (SSNT). Additionally, heparinase and chondroitinase abolished OPG effects on VSMCs-ROS production, confirming syndecan-1 as OPG molecular partner and suggesting that OPG binds to heparan/chondroitin sulphate chains of syndecan-1. OPG-induced ROS production was abrogated by NoxA1ds (Nox1 inhibitor) and GKT137831 (dual Nox1/Nox4 inhibitor). Tempol (SOD mimetic) inhibited vascular dysfunction induced by OPG. In addition, we studied arteries from Nox1 and Nox4 knockout (KO) mice. Nox1 and Nox4 KO abrogated OPG-induced vascular dysfunction. Vascular dysfunction elicited by OPG is mediated by a complex signalling cascade involving syndecan-1, Nox1 and Nox4. Our data identify novel molecular mechanisms beyond calcification for OPG, which may underlie vascular injurious effects of osteogenic factors in conditions such as hypertension and/or diabetes.

Greater Dietary Inflammatory Potential Is Associated With Higher Likelihood of Abdominal Aortic Calcification

Aims: We aimed to assess the association between dietary inflammation index (DII) and abdominal aortic calcification (AAC) in US adults aged ≥40 years. Methods: Data were obtained from the 2013-2014 National Health and Nutrition Examination Survey (NHANES). Participants who were <40 years old and missing the data of DII and AAC were excluded. DII was calculated based on a 24-h dietary recall interview for each participant. AAC score was quantified by assessing lateral spine images and severe AAC was defined as AAC score >6. Weighted multivariable regression analysis and subgroup analysis were preformed to estimate the independent relationship between DII with AAC score and severe AAC. Results: A total of 2,897 participants were included with the mean DII of -0.17 ± 2.80 and the mean AAC score of 1.462 ± 3.290. The prevalence of severe AAC was 7.68% overall, and participants in higher DII quartile tended to have higher rates of severe AAC (Quartile 1: 5.03%, Quartile 2: 7.44%, Quartile 3: 8.38%, Quartile 4: 10.46%, p = 0.0016). A positive association between DII and AAC score was observed (β = 0.055, 95% CI: 0.010, 0.101, p = 0.01649), and higher DII was associated with an increased risk of severe AAC (OR = 1.067, 95% CI: 1.004, 1.134, p = 0.03746). Subgroup analysis indicated that this positive association between DII and AAC was similar in population with differences in gender, age, BMI, hypertension status, and diabetes status and could be appropriate for different population settings. Conclusion: Higher pro-inflammatory diet was associated with higher AAC score and increased risk of severe AAC. Anti-inflammatory dietary management maybe beneficial to reduce the risk of AAC.

Resveratrol Ameliorates Aortic Calcification in Ovariectomized Rats via SIRT1 Signaling

Postmenopausal women are at an increased risk of vascular calcification which is defined as the pathological deposition of minerals in the vasculature, and is strongly linked with increased cardiovascular disease risk. Since estrogen-replacement therapy is associated with increased cancer risk, there is a strong need for safer therapeutic approaches. In this study we aimed to investigate the protective and therapeutic effects of the phytoestrogen resveratrol against vascular calcification in ovariectomized rats, a preclinical model of postmenopause. Furthermore, we aimed to compare the effects of resveratrol to those of estrogen and to explore the mechanisms underpinning those effects. Treatment with resveratrol or estrogen ameliorated aortic calcification in ovariectomized rats, as shown by reduced calcium deposition in the arterial wall. Mechanistically, the effects of resveratrol and estrogen were mediated via the activation of SIRT1 signaling. SIRT1 protein expression was downregulated in the aortas of ovariectomized rats, and upregulated in rats treated with resveratrol or estrogen. Moreover, resveratrol and estrogen reduced the levels of the osteogenic markers: runt-related transcription factor 2 (RUNX2), osteocalcin and alkaline phosphatase (ALP) which have been shown to play a role during vascular calcification. Additionally, the senescence markers (p53, p16 and p21) which were also reported to play a role in the pathogenesis of vascular calcification, were reduced upon treatment with resveratrol and estrogen. In conclusion, the phytoestrogen resveratrol may be a safer alternative to estrogen, as a therapeutic approach against the progression of vascular calcification during postmenopause.

The roles of immune cells in atherosclerotic calcification

Atherosclerosis is the leading cause of acute cardiovascular events, and vascular calcification is an important pathological phenomenon in atherosclerosis. Recently, many studies have shown that immune cells are closely associated with the development of atherosclerosis and calcification, but there are many conflicting viewpoints because of immune system complications, such as the pro-atherosclerotic and atheroprotective effects of regulatory B cells (Bregs), T helper type 2 (Th2) cells and T helper type 17 (Th17) cells. In this review, we summarize the studies on the roles of immune cells, especially lymphocytes and macrophages, in atherosclerotic calcification. Furthermore, we prepared graphs showing the relationship between T cells, B cells and macrophages and atherosclerotic calcification. Finally, we highlight some potential issues that are closely associated with the function of immune cells in atherosclerotic calcification. Based on current research results, this review summarizes the relationship between immune cells and atherosclerotic calcification, and it will be beneficial to understand the relationship of immune cells and atherosclerotic calcification.

Bone Metabolism and RANKL/OPG Ratio in Rheumatoid Arthritis Women Treated with TNF-α Inhibitors

The aim of this study was to evaluate the effect of anti-tumor necrosis factor α (anti-TNF-α) therapy in combination with methotrexate on bone remodeling and osteoclastogenesis in female patients with RA. Serum levels of bone turnover markers (i.e., C- and N-terminal propeptides of type I procollagen (PICP and PINP), C- and N-terminal cross-linking telopeptides of type I collagen (CTX-I and NTX-I), and soluble receptor activator of nuclear factor κB ligand (sRANKL) and osteoprotegerin (OPG)) were determined by immunoassay at baseline and 15 months after initiation of treatment. Bone mineral density was measured by dual-energy x-ray absorptiometry. We found a significant decrease in serum PINP levels, a biomarker of bone formation, and higher levels of CTX-I and sRANKL indicative of increased bone resorption in RA patients prior to TNFαI treatment compared to the controls. Anti-TNF-α therapy was effective in improving bone metabolism in RA patients as reflected in a decrease in CTX-I (at least partially due to the RANKL/OPG reduction) and a concomitant increase in PINP levels. The bone metabolism changes were independent of the type of TNFαI used. PINP and CTX-I were found to be useful markers of bone metabolism, which may prove the effectiveness of TNF-α therapy earlier than the bone density assessment.

The role of osteoprotegerin (OPG) in fibrosis: its potential as a biomarker and/or biological target for the treatment of fibrotic diseases

Fibrosis is defined by excessive formation and accumulation of extracellular matrix proteins, produced by myofibroblasts, that supersedes normal wound healing responses to injury and results in progressive architectural remodelling. Fibrosis is often detected in advanced disease stages when an organ is already severely damaged and can no longer function properly. Therefore, there is an urgent need for reliable and easily detectable markers to identify and monitor fibrosis onset and progression as early as possible; this will greatly facilitate the development of novel therapeutic strategies. Osteoprotegerin (OPG), a well-known regulator of bone extracellular matrix and most studied for its role in regulating bone mass, is expressed in various organs and functions as a decoy for receptor activator of nuclear factor kappa-B ligand (RANKL) and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Recently, OPG has been linked to fibrosis and fibrogenesis, and has been included in a panel of markers to diagnose liver fibrosis. Multiple studies now suggest that OPG may be a general biomarker suitable for detection of fibrosis and/or monitoring the impact of fibrosis treatment. This review summarizes our current understanding of the role of OPG in fibrosis and will discuss its potential as a biomarker and/or novel therapeutic target for fibrosis.

Calciprotein Particles: Balancing Mineral Homeostasis and Vascular Pathology

[Figure: see text].

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.

Long-Term Treatment of Azathioprine in Rats Induces Vessel Mineralization

Medial vascular calcification (mVC) is closely related to cardiovascular disease, especially in patients suffering from chronic kidney disease (CKD). Even after successful kidney transplantation, cardiovascular mortality remains increased. There is evidence that immunosuppressive drugs might influence pathophysiological mechanisms in the vessel wall. Previously, we have shown in vitro that mVC is induced in vascular smooth muscle cells (VSMCs) upon treatment with azathioprine (AZA). This effect was confirmed in the current study in an in vivo rat model treated with AZA for 24 weeks. The calcium content increased in the aortic tissue upon AZA treatment. The pathophysiologic mechanisms involve AZA catabolism to 6-thiouracil via xanthine oxidase (XO) with subsequent induction of oxidative stress. Proinflammatory cytokines, such as interleukin (IL)-1ß and IL-6, increase upon AZA treatment, both systemically and in the aortic tissue. Further, VSMCs show an increased expression of core-binding factor α-1, alkaline phosphatase and osteopontin. As the AZA effect could be decreased in NLRP3^−/− aortic rings in an ex vivo experiment, the signaling pathway might be, at least in part, dependent on the NLRP3 inflammasome. Although human studies are necessary to confirm the harmful effects of AZA on vascular stiffening, these results provide further evidence of induction of VSMC calcification under AZA treatment and its effects on vessel structure.

Adipokines in vascular calcification

Adipose tissue (AT), a critical endocrine gland, is capable of producing and secreting abundant adipokines. Adipokines act on distant or adjacent organ tissues via paracrine, autocrine, and endocrine mechanism, which play attractive roles in the regulation of glycolipid metabolism and inflammatory response. Increasing evidence shows that adipokines can connect obesity with cardiovascular diseases by serving as promoters or inhibitors in vascular calcification. The chronic hypoxia in AT, caused by the adipocyte hypertrophy, is able to trigger imbalanced adipokine generation, which leads to apoptosis, osteogenic differentiation of vascular smooth muscle cells (VSMCs), vascular inflammation, and abnormal deposition of calcium and phosphorus in the vessel wall. The objectives of this review aim at providing a brief summary of the crucial influence of major adipokines on the formation and development of vascular calcification, which may contribute to better understanding these adipokines for establishing the appropriate therapeutic strategies to counteract obesity-associated vascular calcification.

Role of Uremic Toxins in Early Vascular Ageing and Calcification

In patients with advanced chronic kidney disease (CKD), the accumulation of uremic toxins, caused by a combination of decreased excretion secondary to reduced kidney function and increased generation secondary to aberrant expression of metabolite genes, interferes with different biological functions of cells and organs, contributing to a state of chronic inflammation and other adverse biologic effects that may cause tissue damage. Several uremic toxins have been implicated in severe vascular smooth muscle cells (VSMCs) changes and other alterations leading to vascular calcification (VC) and early vascular ageing (EVA). The above mentioned are predominant clinical features of patients with CKD, contributing to their exceptionally high cardiovascular mortality. Herein, we present an update on pathophysiological processes and mediators underlying VC and EVA induced by uremic toxins. Moreover, we discuss their clinical impact, and possible therapeutic targets aiming at preventing or ameliorating the harmful effects of uremic toxins on the vasculature.

The Influence of Calcification Factors and Endothelial-Dysfunction Factors on the Development of Unstable Atherosclerotic Plaques

Background: This study aimed to evaluate changes in markers of calcification and of endothelial dysfunction during the development of calcification and instability of atherosclerotic plaques and to identify associations of calcification factors with the formation of unstable plaques. Methods: We analyzed 44 male patients with coronary atherosclerosis who underwent endarterectomy in coronary arteries during coronary bypass surgery. The endarterectomy material (intima/media) was examined using histological and biochemical methods, and the stability and calcification degree of atherosclerotic plaques were assessed. In homogenates of the tissue samples and in blood, concentrations of osteoprotegerin, osteocalcin, osteopontin, osteonectin, monocyte-chemoattractant protein type 1 (MCP-1), soluble vascular cell adhesion molecule 1 (sVCAM-1), and E-selectin were determined by enzyme immunoassays. Results: Unstable atherosclerotic plaques proved to be calcified more frequently (80.4% of plaques) than stable ones (45.0%). Osteonectin, E-selectin, and sVCAM-1 levels were lower in unstable plaques and plaques with large calcification deposits. Osteocalcin content increased with the increasing size of the calcification deposits in plaque. Blood osteocalcin concentration directly correlated with osteocalcin concentration in atherosclerotic plaques and was higher in the blood of patients with calcified plaques in coronary arteries. Conclusions: The results provide the basis for further research on the suitability of osteocalcin as a potential biomarker of an unstable calcified atherosclerotic plaque in a coronary artery.

Uremic Toxins and Vascular Calcification-Missing the Forest for All the Trees

The cardiorenal syndrome relates to the detrimental interplay between the vascular system and the kidney. The uremic milieu induced by reduced kidney function alters the phenotype of vascular smooth muscle cells (VSMC) and promotes vascular calcification, a condition which is strongly linked to cardiovascular morbidity and mortality. Biological mechanisms involved include generation of reactive oxygen species, inflammation and accelerated senescence. A better understanding of the vasotoxic effects of uremic retention molecules may reveal novel avenues to reduce vascular calcification in CKD. The present review aims to present a state of the art on the role of uremic toxins in pathogenesis of vascular calcification. Evidence, so far, is fragmentary and limited with only a few uremic toxins being investigated, often by a single group of investigators. Experimental heterogeneity furthermore hampers comparison. There is a clear need for a concerted action harmonizing and standardizing experimental protocols and combining efforts of basic and clinical researchers to solve the complex puzzle of uremic vascular calcification.

Circulating Receptor Activator of Nuclear Factor kB Ligand and triglycerides are associated with progression of lower limb arterial calcification in type 2 diabetes: a prospective, observational cohort study

Background

Lower limb arterial calcification is a frequent, underestimated but serious complication of diabetes. The DIACART study is a prospective cohort study designed to evaluate the determinants of the progression of lower limb arterial calcification in 198 patients with type 2 diabetes.

Methods

Lower limb arterial calcification scores were determined by computed tomography at baseline and after a mean follow up of 31.20 ± 3.86 months. Serum RANKL (Receptor Activator of Nuclear factor kB Ligand) and bone remodeling, inflammatory and metabolic parameters were measured at baseline. The predictive effect of these markers on calcification progression was analyzed by a multivariate linear regression model.

Results

At baseline, mean ± SD and median lower limb arterial calcification scores were, 2364 ± 5613 and 527 respectively and at the end of the study, 3739 ± 6886 and 1355 respectively. Using multivariate analysis, the progression of lower limb arterial log calcification score was found to be associated with (β coefficient [slope], 95% CI, p-value) baseline log(calcification score) (1.02, 1.00–1.04, p < 0.001), triglycerides (0.11, 0.03–0.20, p = 0.007), log(RANKL) (0.07, 0.02–0.11, p = 0.016), previous ischemic cardiomyopathy (0.36, 0.15–0.57, p = 0.001), statin use (0.39, 0.06–0.72, p = 0.023) and duration of follow up (0.04, 0.01–0.06, p = 0.004).

Conclusion

In patients with type 2 diabetes, lower limb arterial calcification is frequent and can progress rapidly. Circulating RANKL and triglycerides are independently associated with this progression. These results open new therapeutic perspectives in peripheral diabetic calcifying arteriopathy.

Trial registration NCT02431234

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.

A novel role of FKN/CX3CR1 in promoting osteogenic transformation of VSMCs and atherosclerotic calcification

Fractalkine (FKN) and its specific receptor CX3CR1 play a critical role in the pathogenesis of atherosclerosis including recruitment of vascular cells and the development of inflammation. However, its contribution to regulating the development of atherosclerotic calcification has not been well documented. Osteogenic transformation of vascular smooth muscle cells (VSMCs) is critical in the development of calcification in atherosclerotic lesions. In this study, for the first time, we evaluated the effect of FKN/CX3CR1 on the progression of VSMCs calcification and defined molecular signaling that is operative in the FKN/CX3CR1-induced osteogenic transformation of VSMCs. We found that high-fat diet induced atherosclerotic calcification in vivo was markedly inhibited in the Apolipoprotein E (ApoE) and CX3CR1 deficient (ApoE^-/-/CX3CR1^-/-) mice compared with their control littermates. FKN and CX3CR1 were both expressed in VSMCs and up-regulated by oxidized low-density lipoprotein (ox-LDL). FKN/CX3CR1 promoted the expression of osteogenic markers, including osteopontin (OPN), bone morphogenetic protein (BMP)-2 and alkaline phosphatase (ALP) and decreased VSMCs markers, including smooth muscle (SM) α-actin and SM22-α in a dose-dependent manner. The essential role of FKN/CX3CR1 in VSMCs calcification was further confirmed by lentivirus-mediated knockdown or overexpression of CX3CR1 blocked or accelerated osteogenic transformation of VSMCs. This response was associated with reciprocal up- and down-regulation of osteogenic factor, runt-related transcription factor 2 (RUNX2), transcription factors in osteoclast differentiation, receptor activator of nuclear factor-κB (RANK), RANK ligand (RNAKL) and osteoprotegerin (OPG), respectively. Inhibition of FKN/CX3CR1-activated Jak2/Stat3 signaling by the Jak/Stat inhibitor AG490 blocked osteogenic transformation of VSMCs and RUNX2 induction concurrently. Taken together, our data uncovered novel roles of FKN/CX3CR1 in promoting VSMC osteogenic transformation and atherosclerotic calcification by activating RUNX2 through Jak2/Stat3 signaling pathway and suppressing OPG. Our findings suggest that targeting FKN/CX3CR1 may provide new strategies for the prevention and treatment of atherosclerotic calcification.

Vascular calcification; Stony bridge between kidney and heart

Vascular calcification is a high prevalent complication that arises as a consequence of impaired calcium and phosphate balance amongst cardiovascular patients. Multiple inducer/ inhibitory molecules and pathways as well as genetic background and lifestyle play role in this phenomenon. According to which vessel layer (intima, media or both) is involved different types of vascular calcification take place. Actual mechanism and consensus pathways have not been elucidated yet and needs further investigations.

SLC37A2, a phosphorus-related molecule, increases in smooth muscle cells in the calcified aorta

Vascular calcification is major source of cardiovascular disease in patients with chronic kidney disease. Hyperphosphatemia leads to increased intracellular phosphorus influx, which leads to an increase in osteoblast-like cells in vascular smooth muscle cell. PiT-1 transports phosphate in vascular smooth muscle cell. However, the mechanism of vascular calcification is not completely understood. This study investigated candidate phosphorus-related molecules other than PiT-1. We hypothesized that phosphorus-related molecules belonging to the solute-carrier (SLC) superfamily would be involved in vascular calcification. As a result of DNA microarray analysis, we focused on SLC37A2 and showed that mRNA expression of these cells increased on calcified aotic smooth muscle cells (AoSMC). SLC37A2 has been reported to transport both glucose-6-phosphate/phosphate and phosphate/phosphate exchanges. In vitro analysis showed that SLC37A2 expression was not affected by inflammation on AoSMC. The expression of SLC37A2 mRNA and protein increased in calcified AoSMC. In vivo analysis showed that SLC37A2 mRNA expression in the aorta of chronic kidney disease rats was correlated with osteogenic marker genes. Furthermore, SLC37A2 was expressed at the vascular calcification area in chronic kidney disease rats. As a result, we showed that SLC37A2 is one of the molecules that increase with vascular calcification in vitro and in vivo.

The bone-vessel axis in chronic kidney disease: An update on biochemical players and its future role in laboratory medicine

Vascular wall calcification (VC) is highly prevalent in patients with chronic kidney disease (CKD). In CKD, VC is more frequent and severe than in the general population and it is associated with increased cardiovascular mortality and morbidity. In the last years, laboratory and clinical evidence have drawn the attention to the relationship between bone disease and VC in CKD patients, leading to the concept of a bone-vessel or bone-vascular axis. It means that disorders of bone volume and bone turnover may influence the risk of VC and ultimately the high risk of cardiovascular mortality. In fact, a higher burden of VC has been associated to low bone volume and low bone turnover in hemodialysis (HD) patients with renal osteodystrophy characterized by histomorphometric evaluation of bone biopsies. The molecular mechanisms underlying the regulation of bone cells and vascular cells in CKD are poorly understood. In this review, we discuss relevant evidence linking bone disorders and VC in CKD and also rising molecular players involved in this bone-vascular axis. Indeed, accumulating data is available for two proposed systems: receptor activator for nuclear factor kB (RANK)/ RANK ligand (RANKL)/osteoprotegerin (OPG) system and inhibitors of Wnt signaling - mainly sclerostin. Although they are promising biochemical markers linking bone formation and bone reabsorption with VC, there is a long way to go as long evidence from laboratory studies is often divergent to the clinical data as will be discussed. Future prospective studies are needed in order to evaluate the role of these biochemical players as useful clinical markers for VC, bone volume and perhaps bone turnover.

Targeting androgen receptor in macrophages inhibits phosphate-induced vascular smooth muscle cell calcification by decreasing IL-6 expression

Vascular calcification (VC) is a common complication of chronic kidney disease (CKD). However, its mechanisms remain unclear. VC, similar to atherosclerosis, is an inflammatory disease. Vascular smooth muscle cells (VSMCs) play a key role in VC progression. The androgen receptor (AR) in monocytes/macrophages plays an important role in inflammatory diseases. Here, we define the role of macrophage (MФ) AR in inorganic phosphate-induced VSMC calcification. Our results show that the conditioning medium (CM) of silencing AR in macrophages inhibits inorganic phosphate-induced human aortic smooth muscle cell (HASMC) calcification, and alleviates the transdifferentiation of HASMCs into osteoblasts for the protein expression of osteoblasts marker Runt-related transcription factor-2 (Runx2) in HASMCs decreased while that of smooth muscle cell marker SM22α increased. The effect of AR on HASMC calcification might mainly be mediated by the inflammatory cytokine IL-6. Silencing AR in monocytes/macrophages can dramatically decrease IL-6 expression. We also investigated how macrophage AR regulates IL-6. ChIP and luciferase assays indicate that AR directly binds to the ARE sequence in the promoter of the IL-6 gene to accelerate transcription and expression. To our knowledge, this is the first investigation that has established the correlation between AR and VC and identified the contribution of AR in the calcification of VSMCs. In addition, this study describes a novel target for therapeutic intervention in VC.

Engineering anisotropic 3D tubular tissues with flexible thermoresponsive nanofabricated substrates

Tissue engineering aims to capture the structural and functional aspects of diverse tissue types in vitro. However, most approaches are limited in their ability to produce complex 3D geometries that are essential for tissue function. Tissues, such as the vasculature or chambers of the heart, often possess curved surfaces and hollow lumens that are difficult to recapitulate given their anisotropic architecture. Cell-sheet engineering techniques using thermoresponsive substrates provide a means to stack individual layers of cells with spatial control to create dense, scaffold-free tissues. In this study, we developed a novel method to fabricate complex 3D structures by layering multiple sheets of aligned cells onto flexible scaffolds and casting them into hollow tubular geometries using custom molds and gelatin hydrogels. To enable the fabrication of 3D tissues, we adapted our previously developed thermoresponsive nanopatterned cell-sheet technology by applying it to flexible substrates that could be folded as a form of tissue origami. We demonstrated the versatile nature of this platform by casting aligned sheets of smooth and cardiac muscle cells circumferentially around the surfaces of gelatin hydrogel tubes with hollow lumens. Additionally, we patterned skeletal muscle in the same fashion to recapitulate the 3D curvature that is observed in the muscles of the trunk. The circumferential cell patterning in each case was maintained after one week in culture and even encouraged organized skeletal myotube formation. Additionally, with the application of electrical field stimulation, skeletal myotubes began to assemble functional sarcomeres that could contract. Cardiac tubes could spontaneously contract and be paced for up to one month. Our flexible cell-sheet engineering approach provides an adaptable method to recapitulate more complex 3D geometries with tissue specific customization through the addition of different cell types, mold shapes, and hydrogels. By enabling the fabrication of scaled biomimetic models of human tissues, this approach could potentially be used to investigate tissue structure-function relationships, development, and maturation in the dish.

Pathogenesis of atherosclerosis in the tunica intima, media, and adventitia of coronary arteries: An updated review

Atherosclerosis is a chronic inflammatory disease of arteries and it affects the structure and function of all three layers of the coronary artery wall. Current theories suggest that the dysfunction of endothelial cells is one of the initial steps in the development of atherosclerosis. The view that the tunica intima normally consists of a single layer of endothelial cells attached to the subendothelial layer and internal elastic membrane has been questioned in recent years. The structure of intima changes with age and it becomes multilayered due to migration of smooth muscle cells from the media to intima. At this stage, the migration and proliferation of smooth muscle cells do not cause pathological changes in the intima. The multilayering of intima is classically considered to be an important stage in the development of atherosclerosis, but in fact atherosclerotic plaques develop only focally due to the interplay of various processes that involve the resident and invading inflammatory cells. The tunica media consists of multiple layers of smooth muscle cells that produce the extracellular matrix, and this layer normally does not contain microvessels. During the development of atherosclerosis, the microvessels from the tunica adventitia or from the lumen may penetrate thickened media to provide nutrition and oxygenation. According to some theories, the endothelial dysfunction of these nutritive vessels may significantly contribute to the atherosclerosis of coronary arteries. The adventitia contains fibroblasts, progenitor cells, immune cells, microvessels, and adrenergic nerves. The degree of inflammatory cell infiltration into the adventitia, which can lead to the formation of tertiary lymphoid organs, correlates with the severity of atherosclerotic plaques. Coronary arteries are surrounded by perivascular adipose tissue that also participates in the atherosclerotic process.

Lipoprotein(a) as Orchestrator of Calcific Aortic Valve Stenosis

Aortic valve stenosis (AVS) is the most prevalent valvular heart disease in the Western World with exponentially increased incidence with age. If left untreated, the yearly mortality rates increase up to 25%. Currently, no effective pharmacological interventions have been established to treat or prevent AVS. The only treatment modality so far is surgical or transcatheter aortic valve replacement (AVR). Lipoprotein(a) [Lp(a)] has been implicated as a pivotal player in the pathophysiology of calcification of the valves. Patients with elevated levels of Lp(a) have a higher risk of hospitalization or mortality due to the presence of AVS. Multiple studies indicated Lp(a) as a likely causal and independent risk factor for AVS. This review discusses the most important findings and mechanisms related to Lp(a) and AVS in detail. During the progression of AVS, Lp(a) enters the aortic valve tissue at damaged sites of the valves. Subsequently, autotaxin converts lysophosphatidylcholine in lysophosphatidic acid (LysoPA) which in turn acts as a ligand for the LysoPA receptor. This triggers a nuclear factor-κB cascade leading to increased transcripts of interleukin 6, bone morphogenetic protein 2, and runt-related transcription factor 2. This progresses to the actual calcification of the valves through production of alkaline phosphatase and calcium depositions. Furthermore, this review briefly mentions potentially interesting therapies that may play a role in the treatment or prevention of AVS in the near future.

Calcium Phosphate Bions Cause Intimal Hyperplasia in Intact Aortas of Normolipidemic Rats through Endothelial Injury

Calcium phosphate bions (CPBs) are formed under blood supersaturation with calcium and phosphate owing to the mineral chaperone fetuin-A and representing mineralo-organic particles consisting of bioapatite and multiple serum proteins. While protecting the arteries from a rapid medial calcification, CPBs cause endothelial injury and aggravate intimal hyperplasia in balloon-injured rat aortas. Here, we asked whether CPBs induce intimal hyperplasia in intact rat arteries in the absence of cardiovascular risk factors. Normolipidemic Wistar rats were subjected to regular (once/thrice per week over 5 weeks) tail vein injections of either spherical (CPB-S) or needle-shaped CPBs (CPB-N), magnesium phosphate bions (MPBs), or physiological saline (n = 5 per group). Neointima was revealed in 3/10 and 4/10 rats which received CPB-S or CPB-N, respectively, regardless of the injection regimen or blood flow pattern in the aortic segments. In contrast, none of the rats treated with MPBs or physiological saline had intimal hyperplasia. The animals also did not display signs of liver or spleen injury as well as extraskeletal calcium deposits. Serum alanine/aspartate transaminases, interleukin-1β, MCP-1/CCL2, C-reactive protein, and ceruloplasmin levels did not differ among the groups. Hence, CPBs may provoke intimal hyperplasia via direct endothelial injury regardless of their shape or type of blood flow.

Inflammatory cell infiltrates, hypoxia, vascularization, pentraxin 3 and osteoprotegerin in abdominal aortic aneurysms - A quantitative histological study

Information about the tissue characteristics of abdominal aortic aneurysms (AAAs), some of which may be reflected in the serum, can help to elucidate AAA pathogenesis and identify new AAA biomarkers. This information would be beneficial not only for diagnostics and follow-up but also for potential therapeutic intervention. Therefore, the aim of our study was to compare the expression of structural proteins, immune factors (T and B lymphocytes, macrophages, neutrophils and pentraxin 3 (PTX3)), osteoprotegerin (OPG), microvessels and hypoxic cells in AAA and nonaneurysmal aortic walls. We examined specimens collected during surgery for AAA repair (n = 39) and from the abdominal aortas of kidney donors without AAA (n = 8). Using histochemical and immunohistochemical methods, we quantified the areas positive for smooth muscle actin, desmin, elastin, collagen, OPG, CD3, CD20, MAC387, myeloperoxidase, PTX3, and hypoxia-inducible factor 1-alpha and the density of CD31-positive microvessels. AAA samples contained significantly less actin, desmin, elastin and OPG, more collagen, macrophages, neutrophils, T lymphocytes, B lymphocytes, hypoxic cells and PTX3, and a greater density of vasa vasorum (VV) than those in non-AAA samples. Hypoxia positively correlated with actin and negatively correlated with collagen. Microvascular density was related to inflammatory cell infiltrates, hypoxia, PTX3 expression and AAA diameter. The lower OPG expression in AAAs supports the notion of its protective role in AAA remodeling. AAA contained altered amounts of structural proteins, implying reduced vascular elasticity. PTX3 was upregulated in AAA and colocalized with inflammatory infiltrates. This evidence supports further evaluation of PTX3 as a candidate marker of AAA. The presence of aortic hypoxia, despite hypervascularization, suggests that hypoxia-induced neoangiogenesis may play a role in AAA pathogenesis. VV angiogenesis of the AAA wall increases its vulnerability.

Tumour necrosis factor-alpha in uraemic serum promotes osteoblastic transition and calcification of vascular smooth muscle cells via extracellular signal-regulated kinases and activator protein 1/c-FOS-mediated induction of interleukin 6 expression

Background

Vascular calcification is enhanced in uraemic chronic haemodialysis patients, likely due to the accumulation of midsize uraemic toxins, such as interleukin 6 (IL-6) and tumor necrosis factor-alpha (TNF-α). Here we have assessed the impact of uraemia on vascular smooth muscle cell (VSMC) calcification and examined the role of IL-6 and TNF-α as possible mediators and, most importantly, its underlying signalling pathway in VSMCs.

Methods

VSMCs were incubated with samples of uraemic serum obtained from patients treated with haemodialysis for renal failure in the Permeability Enhancement to Reduce Chronic Inflammation-I clinical trial. The VSMCs were assessed for IL-6 gene regulation and promoter activation in response to uraemic serum and TNF-α with reporter assays and electrophoretic mobility shift assay and for osteoblastic transition, cellular calcification and cell viability upon osteogenic differentiation.

Results

Uraemic serum contained higher levels of TNF-α and IL-6 compared with serum from healthy individuals. Exposure of VSMCs to uraemic serum or recombinant TNF-α lead to a strong upregulation of IL-6 mRNA expression and protein secretion, which was mediated by activator protein 1 (AP-1)/c-FOS-pathway signalling. Uraemic serum induced osteoblastic transition and calcification of VSMCs could be strongly attenuated by blocking TNF-α, IL-6 or AP-1/c-FOS signalling, which was accompanied by improved cell viability.

Conclusion

These results demonstrate that uraemic serum contains higher levels of uraemic toxins TNF-α and IL-6 and that uraemia promotes vascular calcification through a signalling pathway involving TNF-α, IL-6 and the AP-1/c-FOS cytokine-signalling axis. Thus treatment modalities aiming to reduce systemic TNF-α and IL-6 levels in chronic haemodialysis patients should be evaluated in future clinical trials.

Role of smooth muscle cells in vascular calcification: implications in atherosclerosis and arterial stiffness

Vascular calcification is associated with a significant increase in all-cause mortality and atherosclerotic plaque rupture. Calcification has been determined to be an active process driven in part by vascular smooth muscle cell (VSMC) transdifferentiation within the vascular wall. Historically, VSMC phenotype switching has been viewed as binary, with the cells able to adopt a physiological contractile phenotype or an alternate ‘synthetic’ phenotype in response to injury. More recent work, including lineage tracing has however revealed that VSMCs are able to adopt a number of phenotypes, including calcific (osteogenic, chondrocytic, and osteoclastic), adipogenic, and macrophagic phenotypes. Whilst the mechanisms that drive VSMC differentiation are still being elucidated it is becoming clear that medial calcification may differ in several ways from the intimal calcification seen in atherosclerotic lesions, including risk factors and specific drivers for VSMC phenotype changes and calcification. This article aims to compare and contrast the role of VSMCs in driving calcification in both atherosclerosis and in the vessel media focusing on the major drivers of calcification, including aging, uraemia, mechanical stress, oxidative stress, and inflammation. The review also discusses novel findings that have also brought attention to specific pro- and anti-calcifying proteins, extracellular vesicles, mitochondrial dysfunction, and a uraemic milieu as major determinants of vascular calcification.

Osteoporosis and vascular calcification: A shared scenario

Osteoporosis is a systemic skeletal disease, characterised by low bone mass and deterioration in the micro-architecture of bone tissue, which causes increased bone fragility and consequently greater susceptibility to fractures. It is the most frequent metabolic bone disease in our population, and fractures resulting from osteoporosis are becoming more common. Furthermore, vascular calcification is a recognised risk factor of cardiovascular morbidity and mortality that historically has been considered a passive and degenerative process. However, it is currently recognised as an active process, which has histopathological characteristics, mineral composition and initiation and development mechanisms characteristic of bone formation. Paradoxically, patients with osteoporosis frequently show vascular calcifications. Traditionally, they have been considered as independent processes related to age, although more recent epidemiological studies have shown that there is a close relationship between the loss of bone mass and vascular calcification, regardless of age. In fact, both conditions share risk factors and pathophysiological mechanisms. These include the relationship between proteins of bone origin, such as osteopontin and osteoprotegerin (OPG), with vascular pathology, and the intercellular protein system RANK/RANKL/OPG and the Wnt signalling pathway. The mechanisms linked in both pathologies should be considered in clinical decisions, given that treatments for osteoporosis could have unforeseen effects on vascular calcification, and vice versa. In short, a better understanding of the relationship between both entities can help in proposing strategies to reduce the increasing prevalence of vascular calcification and osteoporosis in the aging population.

Signaling pathways involved in vascular smooth muscle cell calcification during hyperphosphatemia

Medial vascular calcification has emerged as a putative key factor contributing to the excessive cardiovascular mortality of patients with chronic kidney disease (CKD). Hyperphosphatemia is considered a decisive determinant of vascular calcification in CKD. A critical role in initiation and progression of vascular calcification during elevated phosphate conditions is attributed to vascular smooth muscle cells (VSMCs), which are able to change their phenotype into osteo-/chondroblasts-like cells. These transdifferentiated VSMCs actively promote calcification in the medial layer of the arteries by producing a local pro-calcifying environment as well as nidus sites for precipitation of calcium and phosphate and growth of calcium phosphate crystals. Elevated extracellular phosphate induces osteo-/chondrogenic transdifferentiation of VSMCs through complex intracellular signaling pathways, which are still incompletely understood. The present review addresses critical intracellular pathways controlling osteo-/chondrogenic transdifferentiation of VSMCs and, thus, vascular calcification during hyperphosphatemia. Elucidating these pathways holds a significant promise to open novel therapeutic opportunities counteracting the progression of vascular calcification in CKD.

Impaired bone matrix glycoprotein pattern is associated with increased cardio-metabolic risk profile in patients with type 2 diabetes mellitus

PURPOSE

Osteopontin (OPN), osteoprotegerin (OPG) and osteocalcin (OC) are matrix glycoproteins which mediate bone mineralization; moreover, their effects on glucose/insulin homeostasis have recently been demonstrated. Higher circulating OPN and OPG levels have been associated with the presence of insulin resistance, atherosclerosis and coronary heart disease. No data are available on contextual changes of these markers in type 2 diabetes mellitus (T2DM). Therefore, aims of this study were to evaluate serum OPN, OPG and OC levels in T2DM patients and their clinical correlates.

METHODS

We recruited 83 consecutive T2DM patients referring to our diabetes outpatient clinics at Sapienza, University of Rome, and 71 non-diabetic sex and age-comparable subjects as a control group. Study population underwent metabolic characterization and carotid ultrasound for intima-media thickness measurement. Plasma OPN, OPG and OC were measured by MILLIPLEX Multiplex Assays Luminex.

RESULTS

T2DM patients had significantly higher circulating OPN and OPG levels than controls (14.3 ± 13.6 vs 10.6 ± 13.7 ng/ml p < 0.001, 0.70 ± 0.60 vs 0.54 ± 4.1 ng/ml, p = 0.02) while OC levels were similar in the two cohorts (6.35 ± 5.8 vs 7.80 ± 7.0 ng/ml, p = n.s). OPN and OPG positively correlated with greater systolic blood pressure (SBP) values, HOMA-IR and HOMA-β, and with the presence of dyslipidemia and carotid atherosclerosis. The association between greater OPN and OPG levels and SBP was independent from possible confounders (both p = 0.01).

CONCLUSIONS

Circulating OPN and OPG levels are increased in T2DM patients and identify a particularly unfavourable metabolic profile, mostly expressed by higher SBP. Bone peptides may represent novel markers of vascular stress and accelerated atherosclerosis in diabetes, constituting a possible tool for cardiovascular risk stratification in diabetes.

TLR2 Promotes Vascular Smooth Muscle Cell Chondrogenic Differentiation and Consequent Calcification via the Concerted Actions of Osteoprotegerin Suppression and IL-6–Mediated RANKL Induction

Objective—

Vascular smooth muscle cell (VSMC) transformation to an osteochondrogenic phenotype is an initial step toward arterial calcification, which is highly correlated with cardiovascular disease–related morbidity and mortality. TLR2 (Toll-like receptor 2) plays a pathogenic role in the development of vascular diseases, but its regulation in calcification of arteries and VSMCs remains unclear. We postulate that TLR2-mediated inflammation participates in mediating atherosclerotic arterial calcification and VSMC calcification.

Approach and Results—

We found that ApoE −/− Tlr2 −/− genotype in mice suppressed high-fat diet–induced atherosclerotic plaques formation during initiation but progressively lost its preventative capacity, compared with ApoE −/− mice. However, TLR2 deficiency prohibited high-fat diet–induced advanced atherosclerotic calcification, chondrogenic metaplasia, and OPG (osteoprotegerin) downregulation in the calcified lesions. Incubation of VSMCs in a calcifying medium revealed that TLR2 agonists significantly increased VSMC calcification and chondrogenic differentiation. Furthermore, TLR2 deficiency suppressed TLR2 agonist–mediated VSMC chondrogenic differentiation and consequent calcification, which were triggered via the concerted actions of IL (interleukin)-6–mediated RANKL (receptor activator of nuclear factor κB ligand) induction and OPG suppression. Inhibition experiments with pharmacological inhibitors demonstrated that IL-6–mediated RANKL induction is signaled by p38 and ERK1/2 (extracellular signal-regulated kinase 1/2) pathways, whereas the OPG is suppressed via NF-κB (nuclear factor κB) dependent signaling mediated by ERK1/2.

Conclusions—

We concluded that on ligand binding, TLR2 activates p38 and ERK1/2 signaling to selectively modulate the upregulation of IL-6–mediated RANKL and downregulation of OPG. These signaling pathways act in concert to induce chondrogenic transdifferentiation of VSMCs, which in turn leads to vascular calcification during the pathogenesis of atherosclerosis.

Rosmarinic acid exerts an antagonistic effect on vascular calcification by regulating the Nrf2 signalling pathway

Vascular calcification (VC) is a process in which calcium phosphate crystals deposit within the intima and middle membrane of the vascular wall. Rosmarinic acid (RA) is a common phenolic compound. It possesses antioxidation, anti-inflammatory, antimicrobial effects. Our experiment aims to investigate the role and molecular mechanism of RA in VC. Rats were fed high-fat feed and injected with vitamin D3 to establish a VC model. β-Glyerophosphate (β GP) was selected to stimulate rat aortic smooth muscle cells (VSMCs) in order to establish the cell calcification model. Kits were used to detect the antioxidant index and calcification index. RA significantly reduced the levels of ALP, MDA, Ca, and P but increased SOD levels. Quantitative real-time polymerase chain reaction (RT-qPCR) and western blot analysis were used to detect various antioxidant-related genes and calcified genes on an mRNA and protein level. The results showed that nuclear factor red cell-2 related factors (Nrf2), haem oxygenase-1 (HO-1), NAD(P)H quinone dehydrogenase (NQO1), and osteoprotegerin (OPG) were up regulated by RA at both the mRNA and protein levels, but kelch-like ECH-associated protein 1 (Keap1), nuclear factor kappa B(NF-κB), cadherin associated protein (β-catenin) and osteogenic transcription factor (Runx2) expression at both the mRNA and protein levels was significantly inhibited. Microscopic examination showed that RA significantly decreased the content of calcified nodules and the production of reactive oxygen species (ROS). When Nrf2 is disturbed, the role of RA is significantly blocked. Our results showed that RA can improve VC by regulating the Nrf2 pathway.

Endogenous Calcification Inhibitors in the Prevention of Vascular Calcification: A Consensus Statement From the COST Action EuroSoftCalcNet

The physicochemical deposition of calcium-phosphate in the arterial wall is prevented by calcification inhibitors. Studies in cohorts of patients with rare genetic diseases have shed light on the consequences of loss-of-function mutations for different calcification inhibitors, and genetic targeting of these pathways in mice have generated a clearer picture on the mechanisms involved. For example, generalized arterial calcification of infancy (GACI) is caused by mutations in the enzyme ecto-nucleotide pyrophosphatase/phosphodiesterase-1 (eNPP1), preventing the hydrolysis of ATP into pyrophosphate (PP_i). The importance of PP_i for inhibiting arterial calcification has been reinforced by the protective effects of PP_i in various mouse models displaying ectopic calcifications. Besides PP_i, Matrix Gla Protein (MGP) has been shown to be another potent calcification inhibitor as Keutel patients carrying a mutation in the encoding gene or Mgp-deficient mice develop spontaneous calcification of the arterial media. Whereas PP_i and MGP represent locally produced calcification inhibitors, also systemic factors contribute to protection against arterial calcification. One such example is Fetuin-A, which is mainly produced in the liver and which forms calciprotein particles (CPPs), inhibiting growth of calcium-phosphate crystals in the blood and thereby preventing their soft tissue deposition. Other calcification inhibitors with potential importance for arterial calcification include osteoprotegerin, osteopontin, and klotho. The aim of the present review is to outline the latest insights into how different calcification inhibitors prevent arterial calcification both under physiological conditions and in the case of disturbed calcium-phosphate balance, and to provide a consensus statement on their potential therapeutic role for arterial calcification.

The Correlation of Serum Osteoprotegerin with Non-Traditional Cardiovascular Risk Factors and Arterial Stiffness in Patients with Pre-Dialysis Chronic Kidney Disease: Results from the KNOW-CKD Study

BACKGROUND

Osteoprotegerin (OPG) plays protective roles against the development of vascular calcification (VC) which greatly contributes to the increased cardiovascular events in patients with chronic kidney disease (CKD). The present study aimed to find the non-traditional, kidney-related cardiovascular risk factors correlated to serum OPG and the effect of serum OPG on the arterial stiffness measured by brachial ankle pulse wave velocity (baPWV) in patients with the pre-dialysis CKD.

METHODS

We cross-sectionally analyzed the data from the patients in whom baPWV and the serum OPG were measured at the time of enrollment in a prospective pre-dialysis CKD cohort study in Korea.

RESULTS

Along with traditional cardiovascular risk factors such as age, diabetes mellitus, pulse pressure, and baPWV, non-traditional, kidney-related factors such as albuminuria, plasma level of hemoglobin, total CO₂ content, alkaline phosphatase, and corrected calcium were independent variables for serum OPG in multivariate linear regression. Reciprocally, the serum OPG was positively associated with baPWV in multivariate linear regression. The baPWV in the 3rd and 4th quartile groups of serum OPG were higher than that in the 1st quartile group after adjustments by age, sex and other significant factors for baPWV in linear mixed model.

CONCLUSION

Non-traditional, kidney-related cardiovascular risk factors in addition to traditional cardiovascular risk factors were related to serum level of OPG in CKD. Serum OPG level was significantly related to baPWV. Our study suggests that kidney-related factors involved in CKD-specific pathways for VC play a role in the increased secretion of OPG into circulation in patients with CKD.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT01630486.

The G-protein coupled receptor ChemR23 determines smooth muscle cell phenotypic switching to enhance high phosphate-induced vascular calcification

Aims

Vascular calcification, a marker of increased cardiovascular risk, is an active process orchestrated by smooth muscle cells. Observational studies indicate that omega-3 fatty acids protect against vascular calcification, but the mechanisms are unknown. The G-protein coupled receptor ChemR23 transduces the resolution of inflammation induced by the omega-3-derived lipid mediator resolvin E1. ChemR23 also contributes to osteoblastic differentiation of stem cells and bone formation, but its role in vascular calcification is unknown. The aim of this study was to establish the role of ChemR23 in smooth muscle cell fate and calcification

Methods and results

Gene expression analysis in epigastric arteries derived from patients with chronic kidney disease and vascular calcification revealed that ChemR23 mRNA levels predicted a synthetic smooth muscle cell phenotype. Genetic deletion of ChemR23 in mice prevented smooth muscle cell de-differentiation. ChemR23-deficient smooth muscle cells maintained a non-synthetic phenotype and exhibited resistance to phosphate-induced calcification. Moreover, ChemR23-deficient mice were protected against vitamin D3-induced vascular calcification. Resolvin E1 inhibited smooth muscle cell calcification through ChemR23. Introduction of the Caenorhabditis elegans Fat1 transgene, leading to an endogenous omega-3 fatty acid synthesis and hence increased substrate for resolvin E1 formation, significantly diminished the differences in phosphate-induced calcification between ChemR23+/+ and ChemR23−/− mice.

Conclusion

This study identifies ChemR23 as a previously unrecognized determinant of synthetic and osteoblastic smooth muscle cell phenotype, favouring phosphate-induced vascular calcification. This effect may be of particular importance in the absence of ChemR23 ligands, such as resolvin E1, which acts as a calcification inhibitor under hyperphosphatic conditions.

Elevated Circulating Osteoprotegerin Levels in the Plasma of Hemodialyzed Patients With Severe Artery Calcification

We studied the correlations between circulating osteoprotegerin (OPG) level and radial artery calcification (RAC) assessed histologically and carotid artery intima-media thickness (CCA-IMT). Moreover, we studied the relationship between OPG levels and all-cause and cardiovascular (CV) mortality during a 5-year observation period. The study comprised 59 CKD patients (36 hemodialyzed (HD), 23 predialysis). The biochemical parameters included: creatinine, calcium, phosphate, intact parathormone, C-reactive protein, interleukin-6, tumor necrosis factor receptor II (TNFRII), transforming growth factor-β, hepatocyte growth factor, fibroblast growth factor 23, osteonectin (ON), osteopontin, osteoprotegerin, and osteocalcin. CCA-IMT and the presence of atherosclerotic plaques was assessed by ultrasound. Fragments of radial artery obtained during creation of HD access were prepared for microscopy and stained for calcifications with alizarin red. RAC was detected in 34 patients (58%). In multiple regression adjusted for dialysis status, TNFRII, ON and Framingham risk score (FRS) were identified as the independent predictors of OPG. Serum OPG above the median value of 7.55 pmol/L significantly predicted the presence of RAC in simple logistic regression (OR 5.33; 95%CI 1.39-20.4; P = 0.012) and in multiple logistic regression adjusted for FRS, dialysis status and CCA-IMT values (OR 6.56; 95%CI 1.06-40.6; P = 0.036). OPG levels above the median were associated with higher CCA-IMT values (1.02 ± 0.10 vs. 0.86 ± 0.13; P < 0.001) and predicted the presence of atherosclerotic plaques in carotid artery (OR 14.4; 95%CI 2.84-72.9; P < 0.001), independently of FRS, dialysis status and RAC. In this study, elevated serum OPG levels correlated with higher CCA-IMT, the presence of atherosclerotic plaques and the severity of the RAC independently of each other. During follow-up, 25 patients (42%) died, including 21 due to CV causes. In multiple Cox regression, OPG above the median predicted overall survival independently of dialysis status, Framingham risk score, CCA-IMT above the median value, and the presence of atherosclerotic plaques in CCA, but not independently of RAC. We postulate that circulating OPG may play a dual role as a marker for both medial arterial calcification and atherosclerosis, hence it seems to be a valuable tool for assessing CV risk in patients with CKD. OPG might be an early indicator of all-cause mortality in CKD patients with advanced medial arterial calcification.

The Impact of Uremic Toxins on Vascular Smooth Muscle Cell Function

Chronic kidney disease (CKD) is associated with profound vascular remodeling, which accelerates the progression of cardiovascular disease. This remodeling is characterized by intimal hyperplasia, accelerated atherosclerosis, excessive vascular calcification, and vascular stiffness. Vascular smooth muscle cell (VSMC) dysfunction has a key role in the remodeling process. Under uremic conditions, VSMCs can switch from a contractile phenotype to a synthetic phenotype, and undergo abnormal proliferation, migration, senescence, apoptosis, and calcification. A growing body of data from experiments in vitro and animal models suggests that uremic toxins (such as inorganic phosphate, indoxyl sulfate and advanced-glycation end products) may directly impact the VSMCs’ physiological functions. Chronic, low-grade inflammation and oxidative stress—hallmarks of CKD—are also strong inducers of VSMC dysfunction. Here, we review current knowledge about the impact of uremic toxins on VSMC function in CKD, and the consequences for pathological vascular remodeling.