ATP acts as a survival signal and prevents the mineralization of aortic valve

β,γ-Methylene-ATP and its metabolite medronic acid affect both arterial media calcification and bone mineralization in non-CKD and CKD rats

Arterial media calcification or pathological deposition of calcium-phosphate crystals in the vessel wall contributes significantly to the high mortality rate observed in patients with CKD. Extracellular nucleotides (ie, ATP or UTP) regulate the arterial calcification process by interacting with (1) purinergic receptors and (2) breakdown via ecto-nucleotidases, such as ectonucleotide pyrophosphatase/phosphodiesterase NPP1 or NPP3, affecting the local levels of calcification inhibitor, pyrophosphate, and stimulator inorganic phosphate (PPi/Pi ratio). Also, it has been shown that ATP analogs (ie, β,γ-methylene-ATP [β,γ-meATP]) inhibit vascular smooth muscle cell calcification in vitro. In the first experiment, daily dosing of β,γ-meATP (2 mg/kg) was investigated in rats fed a warfarin diet to trigger the development of non-CKD-related arterial medial calcifications. This study showed that β,γ-meATP significantly lowered the calcium scores in the aorta and peripheral vessels in warfarin-exposed rats. In a second experiment, daily dosing of 4 mg/kg β,γ-meATP and its metabolite medronic acid (MDP) was analyzed in rats fed an adenine diet to promote the development of CKD-related arterial medial calcification. Administration of β,γ-meATP and MDP did not significantly decrease aortic calcification scores in this model. Moreover, both compounds induced deleterious effects on physiological bone mineralization, causing an imminent risk for worsening the already compromised bone status in CKD. Due to this, it was not possible to raise the dosage of both compounds to tackle CKD-related arterial calcification. Again, this points out the difficult task of targeting solely ectopic calcifications without negatively affecting physiological bone mineralization. On the other hand, aortic mRNA expression of Enpp1 and Enpp3 was significantly and positively associated with aortic calcification scores, suggesting that normalizing the aortic NPP1/3 activity to control values might be a possible target to treat (CKD-induced) arterial media calcifications.

Influence of Aortic Valve Stenosis and Wall Shear Stress on Platelets Function

Aortic valve stenosis (AS) is a common heart valve disease in the elderly population, and its pathogenesis remains an interesting area of research. The degeneration of the aortic valve leaflets gradually progresses to valve sclerosis. The advanced phase is marked by the presence of extracellular fibrosis and calcification. Turbulent, accelerated blood flow generated by the stenotic valve causes excessive damage to the aortic wall. Elevated shear stress due to AS leads to the degradation of high-molecular weight multimers of von Willebrand factor, which may involve bleeding in the mucosal tissues. Conversely, elevated shear stress has been associated with the release of thrombin and the activation of platelets, even in individuals with acquired von Willebrand syndrome. Moreover, turbulent blood flow in the aorta may activate the endothelium and promote platelet adhesion and activation on the aortic valve surface. Platelets release a wide range of mediators, including lysophosphatidic acid, which have pro-osteogenic effects in AS. All of these interactions result in blood coagulation, fibrinolysis, and the hemostatic process. This review summarizes the current knowledge on high shear stress-induced hemostatic disorders, the influence of AS on platelets and antiplatelet therapy.

Molecular Mechanisms Underlying the Progression of Aortic Valve Stenosis: Bioinformatic Analysis of Signal Pathways and Hub Genes

The calcification of the aortic valve causes increased leaflet stiffness and leads to the development and progression of stenotic aortic valve disease. However, the molecular and cellular mechanisms underlying stenotic calcification remain poorly understood. Herein, we examined the gene expression associated with valve calcification and the progression of calcific aortic valve stenosis. We downloaded two publicly available gene expression profiles (GSE83453 and GSE51472) from NCBI-Gene Expression Omnibus database for the combined analysis of samples from human aortic stenosis and normal aortic valve tissue. After identifying the differentially expressed genes (DEGs) using the GEO2R online tool, we performed Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses. We also analyzed the protein-protein interactions (PPIs) of the DEGs using the NetworkAnalyst online tool. We identified 4603 upregulated and 6272 downregulated DEGs, which were enriched in the positive regulation of cell adhesion, leukocyte-mediated immunity, response to hormones, cytokine signaling in the immune system, lymphocyte activation, and growth hormone receptor signaling. PPI network analysis identified 10 hub genes: VCAM1, FHL2, RUNX1, TNFSF10, PLAU, SPOCK1, CD74, SIPA1L2, TRIB1, and CXCL12. Through bioinformatic analysis, we identified potential biomarkers and therapeutic targets for aortic stenosis, providing a theoretical basis for future studies.

Oxidative stress and valvular endothelial cells in aortic valve calcification

Calcified aortic valve disease (CAVD) is a common cardiovascular disease in elderly individuals. Although it was previously considered a degenerative disease, it is, in fact, a progressive disease involving multiple mechanisms. Aortic valve endothelial cells, which cover the outermost layer of the aortic valve and are directly exposed to various pathogenic factors, play a significant role in the onset and progression of CAVD. Hemodynamic changes can directly damage the structure and function of valvular endothelial cells (VECs). This leads to inflammatory infiltration and oxidative stress, which promote the progression of CAVD. VECs can regulate the pathological differentiation of valvular interstitial cells (VICs) through NO and thus affect the process of CAVD. Under the influence of pathological factors, VECs can also be transformed into VICs through EndMT, and then the pathological differentiation of VICs eventually leads to the formation of calcification. This review discusses the role of VECs, especially the role of oxidative stress in VECs, in the process of aortic valve calcification.

Aortic stenosis: a review on acquired pathogenesis and ominous combination with diabetes mellitus

BACKGROUND

Aortic stenosis (AS) is a progressive disease, with no pharmacological treatment. The prevalence of diabetes mellitus (DM) among AS patients is higher than in the general population. DM significantly increases the risk of AS development and progression from mild to severe. The interplay between AS and DM's mechanism is not entirely known yet.

MAIN BODY

The increased accumulation of advanced glycation end products (AGEs) was linked to increased valvular oxidative stress, inflammation, expression of coagulation factors, and signs of calcification, according to an analysis of aortic stenotic valves. It is interesting to note that in diabetic AS patients, valvular inflammation did not correlate with serum glucose levels but rather only with long-term glycemic management markers like glycated haemoglobin and fructosamine. Transcatheter aortic valve replacement, which has been shown to be safer than surgical aortic valve replacement, is advantageous for AS patients who also have concurrent diabetes. Additionally, novel anti-diabetic medications have been proposed to lower the risk of AS development in DM patients, including sodium-glucose cotransporter-2 inhibitors and glucagon-like peptide-1 receptor agonist that target reduction of AGEs-mediated oxidative stress.

CONCLUSIONS

There are little data on the effects of hyperglycemia on valvular calcification, but understanding the interactions between them is essential to develop a successful treatment strategy to stop or at least slow the progression of AS in DM patients. There is a link among AS and DM and that DM negatively impacts the quality of life and longevity of AS patients. The sole successful treatment, despite ongoing efforts to find new therapeutic modalities, involves aortic valve replacement. More research is required to find methods that can slow the advancement of these conditions, enhancing the prognosis and course of people with AS and DM.

Calcific aortic valve disease: mechanisms, prevention and treatment

Calcific aortic valve disease (CAVD) is the most common disorder affecting heart valves and is characterized by thickening, fibrosis and mineralization of the aortic valve leaflets. Analyses of surgically explanted aortic valve leaflets have shown that dystrophic mineralization and osteogenic transition of valve interstitial cells co-occur with neovascularization, microhaemorrhage and abnormal production of extracellular matrix. Age and congenital bicuspid aortic valve morphology are important and unalterable risk factors for CAVD, whereas additional risk is conferred by elevated blood pressure and plasma lipoprotein(a) levels and the presence of obesity and diabetes mellitus, which are modifiable factors. Genetic and molecular studies have identified that the NOTCH, WNT-β-catenin and myocardin signalling pathways are involved in the control and commitment of valvular cells to a fibrocalcific lineage. Complex interactions between valve endothelial and interstitial cells and immune cells promote the remodelling of aortic valve leaflets and the development of CAVD. Although no medical therapy is effective for reducing or preventing the progression of CAVD, studies have started to identify actionable targets.

Purinergic Signaling in Pathologic Osteogenic Differentiation of Aortic Valve Interstitial Cells from Patients with Aortic Valve Calcification

Purinergic signaling is associated with a vast spectrum of physiological processes, including cardiovascular system function and, in particular, its pathological calcifications, such as aortic valve stenosis. Aortic valve stenosis (AS) is a degenerative disease for which there is no cure other than surgical replacement of the affected valve. Purinergic signaling is known to be involved in the pathologic osteogenic differentiation of valve interstitial cells (VIC) into osteoblast-like cells, which underlies the pathogenesis of AS. ATP, its metabolites and related nucleotides also act as signaling molecules in normal osteogenic differentiation, which is observed in pro-osteoblasts and leads to bone tissue development. We show that stenotic and non-stenotic valve interstitial cells significantly differ from each other, especially under osteogenic stimuli. In osteogenic conditions, the expression of the ecto-nucleotidases ENTPD1 and ENPP1, as well as ADORA2b, is increased in AS VICs compared to normal VICs. In addition, AS VICs after osteogenic stimulation look more similar to osteoblasts than non-stenotic VICs in terms of purinergic signaling, which suggests the stronger osteogenic differentiation potential of AS VICs. Thus, purinergic signaling is impaired in stenotic aortic valves and might be used as a potential target in the search for an anti-calcification therapy.

Cellular-scale sex differences in extracellular matrix remodeling by valvular interstitial cells

Males acquire calcific aortic valve disease (CAVD) twice as often as females, yet stenotic valves from females display significantly higher levels of fibrosis compared to males with similar extent of disease. Fibrosis occurs as an imbalance between the production and degradation of the extracellular matrix (ECM), specifically type I collagen. This work characterizes ECM production and remodeling by male and female valvular interstitial cells (VICs) to better understand the fibrocalcific divergence between sexes evident in CAVD. Male and female VICs were assessed for gene and protein expression of myofibroblastic markers, ECM components, matrix metalloproteinases (MMPs), and tissue inhibitors of MMPs (TIMPs) via qRT-PCR and western blot. Overall metabolic activity was also measured. Activity assays for collagenase and gelatinase were performed to examine degradation behavior. Male VICs produced greater levels of myofibroblastic markers while female VICs showed greater metabolic activity and collagen production. In general, females displayed a greater level of MMP expression and production than males, but no sex differences were observed in TIMP production. Male VICs also displayed a greater level of collagenase and gelatinase activity than female VICs. This work displays sex differences in ECM remodeling by VICs that could be related to the sexual dimorphism in ECM structure seen in clinical CAVD.

Oxidative Stress in Calcific Aortic Valve Stenosis: Protective Role of Natural Antioxidants

Calcific aortic valve stenosis (CAVS) is the most prevalent heart valvular disease worldwide and a slowly progressive disorder characterized by thickening of the aortic valve, calcification, and subsequent heart failure. Valvular calcification is an active cell regulation process in which valvular interstitial cells involve phenotypic conversion into osteoblasts/chondrocytes-like cells. The underlying pathophysiology is complicated, and there have been no pharmacological treatments for CAVS to date. Recent studies have suggested that an increase in oxidative stress is the major trigger of CAVS, and natural antioxidants could ameliorate the detrimental effects of reactive oxygen species in the pathogenesis of CAVS. It is imperative to review the current findings regarding the role of natural antioxidants in CAVS, as they can be a promising therapeutic approach for managing CAVS, a disorder currently without effective treatment. This review summarizes the current findings on molecular mechanisms associated with oxidative stress in the development of valvular calcification and discusses the protective roles of natural antioxidants in the prevention and treatment of CAVS.

Role of oxidative stress in calcific aortic valve disease and its therapeutic implications

Calcific aortic valve disease (CAVD) is the end result of active cellular processes that lead to the progressive fibrosis and calcification of aortic valve leaflets. In western populations, CAVD is a significant cause of cardiovascular morbidity and mortality, and in the absence of effective drugs, it will likely represent an increasing disease burden as populations age. As there are currently no pharmacological therapies available for preventing, treating, or slowing the development of CAVD, understanding the mechanisms underlying the initiation and progression of the disease is important for identifying novel therapeutic targets. Recent evidence has emerged of an important causative role for reactive oxygen species (ROS)-mediated oxidative stress in the pathophysiology of CAVD, inducing the differentiation of valve interstitial cells into myofibroblasts and then osteoblasts. In this review, we focus on the roles and sources of ROS driving CAVD and consider their potential as novel therapeutic targets for this debilitating condition.

MicroRNA-22 promoted osteogenic differentiation of valvular interstitial cells by inhibiting CAB39 expression during aortic valve calcification

Calcific aortic valve disease (CAVD) is a common valve disease characterized by the fibro-calcific remodeling of the aortic valves, which is an actively regulated process involving osteogenic differentiation of valvular interstitial cells (VICs). MicroRNA (miRNA) is an essential regulator in diverse biological processes in cells. The present study aimed to explore the role and mechanism of miR-22 in the osteogenic differentiation of VICs. The expression profile of osteogenesis-related miRNAs was first detected in aortic valve tissue from CAVD patients (n = 33) and healthy controls (n = 12). miR-22 was highly expressed in calcified valve tissues (P < 0.01), and the expression was positively correlated with the expression of OPN (rs = 0.820, P < 0.01) and Runx2 (rs = 0.563, P < 0.01) in VICs isolated from mild or moderately calcified valves. The sustained high expression of miR-22 was also validated in an in-vitro VICs osteogenic model. Adenovirus-mediated gain-of-function and loss-of-function experiments were then performed. Overexpression of miR-22 significantly accelerated the calcification process of VICs, manifested by significant increases in calcium deposition, alkaline phosphate activity, and expression of osteoblastic differentiation markers. Conversely, inhibition of miR-22 significantly negated the calcification process. Subsequently, calcium-binding protein 39 (CAB39) was identified as a target of miR-22. Overexpression of miR-22 significantly reduced the expression of CAB39 in VICs, leading to decreased catalytic activity of the CAB39-LKB1-STRAD complex, which, in turn, exacerbated changes in the AMPK-mTOR signaling pathway, and ultimately accelerated the calcification process. In addition, ROS generation and autophagic activity during VIC calcification were also regulated by miR-22/CAB39 pathway. These results indicate that miR-22 is an important accelerator of the osteogenic differentiation of VICs, and a potential therapeutic target in CAVD.

Purinergic Receptor P2Y2 Stimulation Averts Aortic Valve Interstitial Cell Calcification and Myofibroblastic Activation

Rationale—Calcific aortic valve stenosis (CAVS) is a pathological condition of the aortic valve with a prevalence of 3% in the general population. It is characterized by massive rearrangement of the extracellular matrix, mostly due to the accumulation of fibro-calcific deposits driven by valve interstitial cells (VIC), and no pharmacological treatment is currently available. The aim of this study was to evaluate the effects of P2Y2 receptor (P2RY2) activation on fibro-calcific remodeling of CAVS. Methods—We employed human primary VICs isolated from CAVS leaflets treated with 2-thiouridine-5′-triphosphate (2ThioUTP, 10 µM), an agonist of P2RY2. The calcification was induced by inorganic phosphate (2 mM) and ascorbic acid (50 µg/mL) for 7 or 14 days, while the 2ThioUTP was administered starting from the seventh day. 2ThioUTP was chronically administered for 5 days to evaluate myofibroblastic activation. Results—P2RY2 activation, under continuous or interrupted pro-calcific stimuli, led to a significant inhibition of VIC calcification potential (p < 0.01). Moreover, 2ThioUTP treatment was able to significantly reduce pro-fibrotic gene expression (p < 0.05), as well as that of protein α-smooth muscle actin (p = 0.004). Conclusions—Our data suggest that P2RY2 activation should be further investigated as a pharmacological target for the prevention of CAVS progression, acting on both calcification and myofibroblastic activation.

Role of Extracellular Vesicles as Potential Diagnostic and/or Therapeutic Biomarkers in Chronic Cardiovascular Diseases

Cardiovascular diseases (CVDs) are the first cause of death worldwide. In recent years, there has been great interest in the analysis of extracellular vesicles (EVs), including exosomes and microparticles, as potential mediators of biological communication between circulating cells/plasma and cells of the vasculature. Besides their activity as biological effectors, EVs have been also investigated as circulating/systemic biomarkers in different acute and chronic CVDs. In this review, the role of EVs as potential diagnostic and prognostic biomarkers in chronic cardiovascular diseases, including atherosclerosis (mainly, peripheral arterial disease, PAD), aortic stenosis (AS) and aortic aneurysms (AAs), will be described. Mechanistically, we will analyze the implication of EVs in pathological processes associated to cardiovascular remodeling, with special emphasis in their role in vascular and valvular calcification. Specifically, we will focus on the participation of EVs in calcium accumulation in the pathological vascular wall and aortic valves, involving the phenotypic change of vascular smooth muscle cells (SMCs) or valvular interstitial cells (IC) to osteoblast-like cells. The knowledge of the implication of EVs in the pathogenic mechanisms of cardiovascular remodeling is still to be completely deciphered but there are promising results supporting their potential translational application to the diagnosis and therapy of different CVDs.

Design, synthesis and biological evaluation studies of novel small molecule ENPP1 inhibitors for cancer immunotherapy

Ecto-nucleotide pyrophosphatase/phosphodiesterases 1 (ENPP1 or NPP1), is an attractive therapeutic target for various diseases, primarily cancer and mineralization disorders. The ecto-enzyme is located on the cell surface and has been implicated in the control of extracellular levels of nucleotide, nucleoside and (di) phosphate. Recently, it has emerged as a critical phosphodiesterase that hydrolyzes cyclic 2'3'- cGAMP, the endogenous ligand for STING (STimulator of INterferon Genes). STING plays an important role in innate immunity by activating type I interferon in response to cytosolic 2'3'-cGAMP. ENPP1 negatively regulates the STING pathway and hence its inhibition makes it an attractive therapeutic target for cancer immunotherapy. Herein, we describe the design, optimization and biological evaluation studies of a series of novel non-nucleotidic thioguanine based small molecule inhibitors of ENPP1. The lead compound 43 has shown good in vitro potency, stability in SGF/SIF/PBS, selectivity, ADME properties and pharmacokinetic profile and finally potent anti-tumor response in vivo. These compounds are a good starting point for the development of potentially effective cancer immunotherapy agents.

Towards Personalized Therapy of Aortic Stenosis

Calcific aortic stenosis (CAS) is the most common cause of acquired valvular heart disease in adults with no available pharmacological treatment to inhibit the disease progression to date. This review provides an up-to-date overview of current knowledge of molecular mechanisms underlying CAS pathobiology and the related treatment pathways. Particular attention is paid to current randomized trials investigating medical treatment of CAS, including strategies based on lipid-lowering and antihypertensive therapies, phosphate and calcium metabolism, and novel therapeutic targets such as valvular oxidative stress, coagulation proteins, matrix metalloproteinases, and accumulation of advanced glycation end products.

Impact of calcific aortic valve disease on valve mechanics

The aortic valve is a highly dynamic structure characterized by a transvalvular flow that is unsteady, pulsatile, and characterized by episodes of forward and reverse flow patterns. Calcific aortic valve disease (CAVD) resulting in compromised valve function and increased pressure overload on the ventricle potentially leading to heart failure if untreated, is the most predominant valve disease. CAVD is a multi-factorial disease involving molecular, tissue and mechanical interactions. In this review, we aim at recapitulating the biomechanical loads on the aortic valve, summarizing the current and most recent research in the field in vitro, in-silico, and in vivo, and offering a clinical perspective on current strategies adopted to mitigate or approach CAVD.

The new insight into extracellular NAD+ degradation-the contribution of CD38 and CD73 in calcific aortic valve disease

Nicotinamide adenine dinucleotide (NAD+ ) is crucial for cell energy metabolism and many signalling processes. Recently, we proved the role of ecto-enzymes in controlling adenine nucleotide-dependent pathways during calcific aortic valve disease (CAVD). This study aimed to investigate extracellular hydrolysis of NAD+ and mononucleotide nicotinamide (NMN) in aortic valves and aorta fragments of CAVD patients and on the inner aortic surface of ecto-5'-nucleotidase knockout mice (CD73-/-). Human non-stenotic valves (n = 10) actively converted NAD+ and NMN via both CD73 and NAD+ -glycohydrolase (CD38) according to our analysis with RP-HPLC and immunofluorescence. In stenotic valves (n = 50), due to reduced CD73 activity, NAD+ was degraded predominantly by CD38 and additionally by ALP and eNPP1. CAVD patients had significantly higher hydrolytic rates of NAD+ (0.81 ± 0.07 vs 0.56 ± 0.10) and NMN (1.12 ± 0.10 vs 0.71 ± 0.08 nmol/min/cm2 ) compared with controls. CD38 was also primarily engaged in human vascular NAD+ metabolism. Studies using specific ecto-enzyme inhibitors and CD73-/- mice confirmed that CD73 is not the only enzyme involved in NAD+ and NMN hydrolysis and that CD38 had a significant contribution to these pathways. Modifications of extracellular NAD+ and NMN metabolism in aortic valve cells may be particularly important in valve pathology and could be a potential therapeutic target.

Impact of osteogenic activity on degenerative aortic valve disease in patients with osteoporotic hip fracture

BACKGROUND

Previous studies have proposed that osteogenic and apoptotic processes of valve interstitial cells contribute to the mineralization and then calcification of the aortic valve. Osteoblast-like cells subsequently mediate calcification of the aortic valve as part of a highly regulated process analogous to skeletal bone formation. The objective of this study was to evaluate the pathogenesis of the sclerotic/calcific changes in the aortic valve from histological and biological findings, and investigate the role of osteoblasts in the calcified pathway of aortic stenosis.

METHODS

Preoperative echocardiography in 550 consecutive patients with osteoporotic hip fracture were retrospectively examined (475 females, mean 25th-75th, 89 [85-93] years). One hundred sixteen patients were under medical treatment with anti-osteoporosis drugs. We evaluated the prevalence and degree of degenerative changes in the aortic valve and examined the associations of bone turnover biomarkers N-terminal pro-peptide of type 1 collagen (P1NP) and serum tartrate-resistant acid phosphatase (TRACP-5b) with degenerative calcific changes in the aortic valve.

RESULTS

Of 550 patients, 112 patients (20.9%) showed no leaflet calcification; 296 (53.8%), 1 leaflet calcification; and 142 (25.8%), 2 ≥ leaflets calcification. Significant (peak velocity ≥ 3.0m/s) Aortic stenosis was found in 43 patients (7.8%). In patients who were not taking anti-osteoporotic drugs, P1NP was higher in the 2 ≥ leaflets calcification group than in the other groups (p < 0.01). TRACP-5b was not significantly different among the three groups (p = 0.15).

CONCLUSIONS

Degenerative changes in the aortic valve were related to bone biomarker activation in osteoporotic hip fracture patients.

New calcification model for intact murine aortic valves

Calcific aortic valve disease (CAVD) is a common progressive disease of the aortic valves, for which no medical treatment exists and surgery represents currently the only therapeutic solution. The development of novel pharmacological treatments for CAVD has been hampered by the lack of suitable test-systems, which require the preservation of the complex valve structure in a mechanically and biochemical controllable system. Therefore, we aimed at establishing a model which allows the study of calcification in intact mouse aortic valves by using the Miniature Tissue Culture System (MTCS), an ex vivo flow model for whole mouse hearts. Aortic valves of wild-type mice were cultured in the MTCS and exposed to osteogenic medium (OSM, containing ascorbic acid, β-glycerophosphate and dexamethasone) or inorganic phosphates (PI). Osteogenic calcification occurred in the aortic valve leaflets that were cultured ex vivo in the presence of PI, but not of OSM. In vitro cultured mouse and human valvular interstitial cells calcified in both OSM and PI conditions, revealing in vitro-ex vivo differences. Furthermore, endochondral differentiation occurred in the aortic root of ex vivo cultured mouse hearts near the hinge of the aortic valve in both PI and OSM conditions. Dexamethasone was found to induce endochondral differentiation in the aortic root, but to inhibit calcification and the expression of osteogenic markers in the aortic leaflet, partly explaining the absence of calcification in the aortic valve cultured with OSM. The osteogenic calcifications in the aortic leaflet and the endochondral differentiation in the aortic root resemble calcifications found in human CAVD. In conclusion, we have established an ex vivo calcification model for intact wild-type murine aortic valves in which the initiation and progression of aortic valve calcification can be studied. The in vitro-ex vivo differences found in our studies underline the importance of ex vivo models to facilitate pre-clinical translational studies.

Oxyphospholipids in Cardiovascular Calcification

Mineralization of cardiovascular structures including blood vessels and heart valves is a common feature. We postulate that ectopic mineralization is a response-to-injury in which signals delivered to cells trigger a chain of events to restore and repair tissues. Maladaptive response to external or internal signals promote the expression of danger-associated molecular patterns, which, in turn, promote, when expressed chronically, a procalcifying gene program. Growing evidence suggest that danger-associated molecular patterns such as oxyphospholipids and small lipid mediators, generated by enzyme activity, are involved in the transition of vascular smooth muscle cells and valve interstitial cells to an osteoblast-like phenotype. Understanding the regulation and the molecular processes underpinning the mineralization of atherosclerotic plaques and cardiac valves are providing valuable mechanistic insights, which could lead to the development of novel therapies. Herein, we provide a focus account on the role oxyphospholipids and their mediators in the development of mineralization in plaques and calcific aortic valve disease.

Current Evidence and Future Perspectives on Pharmacological Treatment of Calcific Aortic Valve Stenosis

Calcific aortic valve stenosis (CAVS), the most common heart valve disease, is characterized by the slow progressive fibro-calcific remodeling of the valve leaflets, leading to progressive obstruction to the blood flow. CAVS is an increasing health care burden and the development of an effective medical treatment is a major medical need. To date, no effective pharmacological therapies have proven to halt or delay its progression to the severe symptomatic stage and aortic valve replacement represents the only available option to improve clinical outcomes and to increase survival. In the present report, the current knowledge and latest advances in the medical management of patients with CAVS are summarized, placing emphasis on lipid-lowering agents, vasoactive drugs, and anti-calcific treatments. In addition, novel potential therapeutic targets recently identified and currently under investigation are reported.

Extracellular Nucleotides Regulate Arterial Calcification by Activating Both Independent and Dependent Purinergic Receptor Signaling Pathways

Arterial calcification, the deposition of calcium-phosphate crystals in the extracellular matrix, resembles physiological bone mineralization. It is well-known that extracellular nucleotides regulate bone homeostasis raising an emerging interest in the role of these molecules on arterial calcification. The purinergic independent pathway involves the enzymes ecto-nucleotide pyrophosphatase/phosphodiesterases (NPPs), ecto-nucleoside triphosphate diphosphohydrolases (NTPDases), 5′-nucleotidase and alkaline phosphatase. These regulate the production and breakdown of the calcification inhibitor—pyrophosphate and the calcification stimulator—inorganic phosphate, from extracellular nucleotides. Maintaining ecto-nucleotidase activities in a well-defined range is indispensable as enzymatic hyper- and hypo-expression has been linked to arterial calcification. The purinergic signaling dependent pathway focusses on the activation of purinergic receptors (P1, P2X and P2Y) by extracellular nucleotides. These receptors influence arterial calcification by interfering with the key molecular mechanisms underlying this pathology, including the osteogenic switch and apoptosis of vascular cells and possibly, by favoring the phenotypic switch of vascular cells towards an adipogenic phenotype, a recent, novel hypothesis explaining the systemic prevention of arterial calcification. Selective compounds influencing the activity of ecto-nucleotidases and purinergic receptors, have recently been developed to treat arterial calcification. However, adverse side-effects on bone mineralization are possible as these compounds reasonably could interfere with physiological bone mineralization.

Evaluation of sulfonate and sulfamate derivatives possessing benzofuran or benzothiophene nucleus as inhibitors of nucleotide pyrophosphatases/phosphodiesterases and anticancer agents

Ectonucleotidases are a broad family of ectoenzymes that play a crucial role in purinergic cell signaling. Ecto-nucleotide pyrophosphatases/phosphodiesterases (NPPs) belong to this group and are important drug targets. In particular, NPP1 and NPP3 are known to be druggable targets for treatment of impaired calcification disorders (including pathological aortic calcification) and cancer, respectively. In this study, we investigated a series of sulfonate and sulfamate derivatives of benzofuran and benzothiophene as potent and selective inhibitors of NPP1 and NPP3. Compounds 1c, 1g, 1n, and 1s are the most active NPP1 inhibitors (IC₅₀ values in the range 0.12-0.95 µM). Moreover, compounds 1e, 1f, 1j, and 1l are the most potent inhibitors of NPP3 (IC₅₀ ranges from 0.12 to 0.95 µM). Compound 1d, 1f and 1t are highly selective inhibitors of NPP1 over NPP3, whereas compounds 1m and 1s are found to be highly selective towards NPP3 over NPP1. Structure-activity relationship (SAR) study has been discussed in detailed. With the aid of molecular docking studies, a common binding mode of these compounds and suramin (the standard inhibitor) was revealed, where the sulfonate group acts as a cation-binding moiety that comes in close contact with the zinc ion of the active site. Moreover, cytotoxic evaluation against MCF-7 and HT-29 cancer cell lines revealed that compound 1r is the most cytotoxic towards MCF-7 cell line with IC₅₀ value of 0.19 µM. Compound 1r is more potent and selective against cancer cells than normal cells (WI-38) as compared to doxorubicin.

Expression of Calcification and Extracellular Matrix Genes in the Cardiovascular System of the Healthy Domestic Sheep (Ovis aries)

The maintenance of a healthy cardiovascular system requires expression of genes that contribute to essential biological activities and repression of those that are associated with functions likely to be detrimental to cardiovascular homeostasis. Vascular calcification is a major disruption to cardiovascular homeostasis, where tissues of the cardiovascular system undergo ectopic calcification and consequent dysfunction, but little is known about the expression of calcification genes in the healthy cardiovascular system. Large animal models are of increasing importance in cardiovascular disease research as they demonstrate more similar cardiovascular features (in terms of anatomy, physiology and size) to humans than do rodent species. We used RNA sequencing results from the sheep, which has been utilized extensively to examine calcification of prosthetic cardiac valves, to explore the transcriptome of the heart and cardiac valves in this large animal, in particular looking at expression of calcification and extracellular matrix genes. We then examined genes implicated in the process of vascular calcification in a wide array of cardiovascular tissues and across multiple developmental stages, using RT-qPCR. Our results demonstrate that there is a balance between genes that promote and those that suppress mineralization during development and across cardiovascular tissues. We show extensive expression of genes encoding proteins involved in formation and maintenance of the extracellular matrix in cardiovascular tissues, and high expression of hematopoietic genes in the cardiac valves. Our analysis will support future research into the functions of implicated genes in the development of valve calcification, and increase the utility of the sheep as a large animal model for understanding ectopic calcification in cardiovascular disease. This study provides a foundation to explore the transcriptome of the developing cardiovascular system and is a valuable resource for the fields of mammalian genomics and cardiovascular research.

Activated platelets promote an osteogenic programme and the progression of calcific aortic valve stenosis

AIMS

Calcific aortic valve stenosis (CAVS) is characterized by a fibrocalcific process. Studies have shown an association between CAVS and the activation of platelets. It is believed that shear stress associated with CAVS promotes the activation of platelets. However, whether platelets actively participate to the mineralization of the aortic valve (AV) and the progression of CAVS is presently unknown. To identify the role of platelets into the pathobiology of CAVS.

METHODS AND RESULTS

Explanted control non-mineralized and mineralized AVs were examined by scanning electron microscope (SEM) for the presence of activated platelets. In-depth functional assays were carried out with isolated human valve interstitial cells (VICs) and platelets as well as in LDLR-/- apoB100/100 IGFII (IGFII) mice. Scanning electron microscope and immunogold markings for glycoprotein IIb/IIIa (GPIIb/IIIa) revealed the presence of platelet aggregates with fibrin in endothelium-denuded areas of CAVS. In isolated VICs, collagen-activated platelets induced an osteogenic programme. Platelet-derived adenosine diphosphate induced the release of autotaxin (ATX) by VICs. The binding of ATX to GPIIb/IIIa of platelets generated lysophosphatidic acid (LysoPA) with pro-osteogenic properties. In IGFII mice with CAVS, platelet aggregates were found at the surface of AVs. Administration of activated platelets to IGFII mice accelerated the development of CAVS by 2.1-fold, whereas a treatment with Ki16425, an antagonist of LysoPA receptors, prevented platelet-induced mineralization of the AV and the progression of CAVS.

CONCLUSIONS

These findings suggest a novel role for platelets in the progression of CAVS.

Synthesis of biphenyl oxazole derivatives via Suzuki coupling and biological evaluations as nucleotide pyrophosphatase/phosphodiesterase-1 and -3 inhibitors

Oxazole derivatives are important medicinal compounds which are inhibitors of various enzymes such as NPP1, NPP2, NPP3, tyrosine kinase, dipeptidyl-peptidase IV, cyclooxygenase-2, and protein tyrosine phosphatase. In this study, an extensive range of new biologically active biphenyl oxazole derivatives was synthesized in high to excellent yields (57-93%) through Suzuki-Miyaura cross-coupling of bromophenyloxazole with different boronic acids. The reaction was carried out in wet toluene under mild conditions. Overexpression of nucleotide pyrophosphatase/phosphodiesterase-1 (NPP1) and NPP3 has been associated with various health disorders including chondrocalcinosis, cancer, osteoarthritis, and type 2 diabetes. We evaluated the inhibitory potential and selectivity of the synthesized compounds (3a-3q) towards NPP1 and NPP3 at 100 μM concentrations. We found two compounds that were selective and potent inhibitors of these two enzymes on the artificial substrate thymidine 5'-monophosphate para-nitrophenyl ester: compound 3n inhibited NPP1 with an IC₅₀ of 0.15 μM, and compound 3f inhibited NPP3 with an IC₅₀ value of 0.17 μM. The compounds with promising inhibitory potential were docked inside the proteins of NPP1 and NPP3 isozymes to get insight into the plausible binding interactions with active site residues.

Zinc ameliorates human aortic valve calcification through GPR39 mediated ERK1/2 signalling pathway

AIMS

Calcific aortic valve disease (CAVD) is the most common heart valve disease in the Western world. It has been reported that zinc is accumulated in calcified human aortic valves. However, whether zinc directly regulates CAVD is yet to be elucidated. The present study sought to determine the potential role of zinc in the pathogenesis of CAVD.

METHODS AND RESULTS

Using a combination of a human valve interstitial cell (hVIC) calcification model, human aortic valve tissues, and blood samples, we report that 20 μM zinc supplementation attenuates hVIC in vitro calcification, and that this is mediated through inhibition of apoptosis and osteogenic differentiation via the zinc-sensing receptor GPR39-dependent ERK1/2 signalling pathway. Furthermore, we report that GPR39 protein expression is dramatically reduced in calcified human aortic valves, and there is a significant reduction in zinc serum levels in patients with CAVD. Moreover, we reveal that 20 μM zinc treatment prevents the reduction of GPR39 observed in calcified hVICs. We also show that the zinc transporter ZIP13 and ZIP14 are significantly increased in hVICs in response to zinc treatment. Knockdown of ZIP13 or ZIP14 significantly inhibited hVIC in vitro calcification and osteogenic differentiation.

CONCLUSIONS

Together, these findings suggest that zinc is a novel inhibitor of CAVD, and report that zinc transporter ZIP13 and ZIP14 are important regulators of hVIC in vitro calcification and osteogenic differentiation. Zinc supplementation may offer a potential therapeutic strategy for CAVD.

Aortic Valve Stenosis: From Basic Mechanisms to Novel Therapeutic Targets

Aortic valve stenosis is the most prevalent heart valve disease worldwide. Although interventional treatment options have rapidly improved in recent years, symptomatic aortic valve stenosis is still associated with high morbidity and mortality. Calcific aortic valve stenosis is characterized by a progressive fibro-calcific remodeling and thickening of the aortic valve cusps, which subsequently leads to valve obstruction. The underlying pathophysiology is complex and involves endothelial dysfunction, immune cell infiltration, myofibroblastic and osteoblastic differentiation, and, subsequently, calcification. To date, no pharmacotherapy has been established to prevent aortic valve calcification. However, novel promising therapeutic targets have been recently identified. This review summarizes the current knowledge of pathomechanisms involved in aortic valve calcification and points out novel treatment strategies.

Nucleotide ecto-enzyme metabolic pattern and spatial distribution in calcific aortic valve disease; its relation to pathological changes and clinical presentation

BACKGROUND

Extracellular nucleotide metabolism contributes to chronic inflammation, cell differentiation, and tissue mineralization by controlling nucleotide and adenosine concentrations and hence its purinergic effects. This study investigated location-specific changes of extracellular nucleotide metabolism in aortic valves of patients with calcific aortic valve disease (CAVD). Individual ecto-enzymes and adenosine receptors involved were analyzed together with correlation with CAVD severity and risk factors.

RESULTS

Nucleotide and adenosine degradation rates were adversely modified on the aortic surface of stenotic valve as compared to ventricular side, including decreased ATP removal (1.25 ± 0.35 vs. 2.24 ± 0.61 nmol/min/cm2) and adenosine production (1.32 ± 0.12 vs. 2.49 ± 0.28 nmol/min/cm2) as well as increased adenosine deamination (1.28 ± 0.31 vs. 0.67 ± 0.11 nmol/min/cm2). The rates of nucleotide to adenosine conversions were lower, while adenosine deamination was higher on the aortic sides of stenotic vs. non-stenotic valve. There were no differences in extracellular nucleotide metabolism between aortic and ventricular sides of non-stenotic valves. Furthermore, nucleotide degradation rates, measured on aortic side in CAVD (n = 62), negatively correlated with echocardiographic and biochemical parameters of disease severity (aortic jet velocity vs. ATP hydrolysis: r = - 0.30, p < 0.05; vs. AMP hydrolysis: r = - 0.44, p < 0.001; valvular phosphate concentration vs. ATP hydrolysis: r = - 0.26, p < 0.05; vs. AMP hydrolysis: r = - 0.25, p = 0.05) while adenosine deamination showed positive correlation trend with valvular phosphate deposits (r = 0.23, p = 0.07). Nucleotide and adenosine conversion rates also correlated with CAVD risk factors, including hyperlipidemia (AMP hydrolysis vs. serum LDL cholesterol: r = - 0.28, p = 0.05; adenosine deamination vs. total cholesterol: r = 0.25, p = 0.05; LDL cholesterol: r = 0.28, p < 0.05; triglycerides: r = 0.32, p < 0.05), hypertension (adenosine deamination vs. systolic blood pressure: r = 0.28, p < 0.05) and thrombosis (ATP hydrolysis vs. prothrombin time: r = - 0.35, p < 0.01). Functional assays as well as histological and immunofluorescence, flow cytometry and RT-PCR studies identified all major ecto-enzymes engaged in nucleotide metabolism in aortic valves that included ecto-nucleotidases, alkaline phosphatase, and ecto-adenosine deaminase. We have shown that changes in nucleotide-converting ecto-enzymes were derived from their altered activities on valve cells and immune cell infiltrate. We have also demonstrated a presence of A1, A2a and A2b adenosine receptors with diminished expression of A2a and A2b in stenotic vs. non-stenotic valves. Finally, we revealed that augmenting adenosine effects by blocking adenosine deamination with deoxycoformycin decreased aortic valve thickness and reduced markers of calcification via adenosine-dependent pathways in a mouse model of CAVD.

CONCLUSIONS

This work highlights profound changes in extracellular nucleotide and adenosine metabolism in CAVD. Altered extracellular nucleotide hydrolysis and degradation of adenosine in stenotic valves may affect purinergic responses to support a pro-stenotic milieu and valve calcification. This emphasizes a potential mechanism and target for prevention and therapy. .

Inhibition of vascular smooth muscle cell calcification by ATP analogues

Arterial medial calcification (AMC) has been associated with phenotypic changes in vascular smooth muscle cells (VSMCs) that reportedly makes them more osteoblast-like. Previous work has shown that ATP/UTP can inhibit AMC directly via P2 receptors and indirectly by NPP1-mediated hydrolysis to produce the mineralisation inhibitor, pyrophosphate (PP_i). This study investigated the role of P2X receptors in the inhibitory effects of extracellular nucleotides on VSMC calcification. We found that Bz-ATP, α,β-meATP and β,γ-meATP inhibited calcification by up to 100%. Culture in a high-phosphate medium (2 mM) was associated with increased VSMC death and apoptosis; treatment with Bz-ATP, α,β-meATP and β,γ-meATP reduced apoptosis to levels seen in non-calcifying cells. Calcification was also associated with alterations in the protein levels of VSMC (e.g. SM22α and SMA) and osteoblast-associated (e.g. Runx2 and osteopontin) markers; Bz-ATP, α,β-meATP and β,γ-meATP attenuated these changes in protein expression. Long-term culture with Bz-ATP, α,β-meATP and β,γ-meATP resulted in lower extracellular ATP levels and an increased rate of ATP breakdown. P2X receptor antagonists failed to prevent the inhibitory effects of these analogues suggesting that they act via P2X receptor-independent mechanisms. In agreement, the breakdown products of α,β-meATP and β,γ-meATP (α,β-meADP and methylene diphosphonate, respectively) also dose-dependently inhibited VSMC calcification. Furthermore, the actions of Bz-ATP, α,β-meATP and β,γ-meATP were unchanged in VSMCs isolated from NPP1-knockout mice, suggesting that the functional effects of these compounds do not involve NPP1-mediated generation of PP_i. Together, these results indicate that the inhibitory effects of ATP analogues on VSMC calcification and apoptosis in vitro may be mediated, at least in part, by mechanisms that are independent of purinergic signalling and PP_i.

Synthesis, biological evaluation, and molecular docking study of sulfonate derivatives as nucleotide pyrophosphatase/phosphodiesterase (NPP) inhibitors

A new series of sulfonate derivatives 1a-zk were synthesized and evaluated as inhibitors of nucleotide pyrophosphatases. Most of the compounds exhibited good to moderate inhibition towards NPP1, NPP2, and NPP3 isozymes. Compound 1m was a potent and selective inhibitor of NPP1 with an IC₅₀ value of 0.387 ± 0.007 µM. However, the most potent inhibitor of NPP3 was found as 1x with an IC₅₀ value of 0.214 ± 0.012 µM. In addition, compound 1e was the most active inhibitor of NPP2 with an IC₅₀ value of 0.659 ± 0.007 µM. Docking studies of the most potent compounds were carried out, and the computational results supported the in vitro results.

Autotaxin and Lipoprotein Metabolism in Calcific Aortic Valve Disease

Calcific aortic valve disease (CAVD) is a complex trait disorder characterized by calcific remodeling of leaflets. Genome-wide association (GWA) study and Mendelian randomization (MR) have highlighted that LPA, which encodes for apolipoprotein(a) [apo(a)], is causally associated with CAVD. Apo(a) is the protein component of Lp(a), a LDL-like particle, which transports oxidized phospholipids (OxPLs). Autotaxin (ATX), which is encoded by ENPP2, is a member of the ecto-nucleotidase family of enzymes, which is, however, a lysophospholipase. As such, ATX converts phospholipids into lysophosphatidic acid (LysoPA), a metabolite with potent and diverse biological properties. Studies have recently underlined that ATX is enriched in the Lp(a) lipid fraction. Functional experiments and data obtained in mouse models suggest that ATX mediates inflammation and mineralization of the aortic valve. Recent findings also indicate that epigenetically-driven processes lower the expression of phospholipid phosphatase 3 (PLPP3) and increased LysoPA signaling and inflammation in the aortic valve during CAVD. These recent data thus provide novel insights about how lipoproteins mediate the development of CAVD. Herein, we review the implication of lipoproteins in CAVD and examine the role of ATX in promoting the osteogenic transition of valve interstitial cells (VICs).

Recent Advances on Relationship Between Inorganic Phosphate and Pathologic Calcification: Is Calcification After Breast Augmentation with Fat Grafting Correlated with Locally Increased Concentration of Inorganic Phosphate?

BACKGROUND

Pathologic calcification has frequently occurred after breast augmentation with fat grafting as well as other conditions such as breast cancer, trauma, myocardial infarction, arteriosclerosis and even after reduction mammoplasty. Inorganic phosphate, correlated with fat metabolism, is an important factor that induces pathologic calcification such as vascular calcification.

METHODS

A literature search was conducted using PubMed with the keywords: calcification, inorganic phosphate, fat. Studies related to the process of pathologic calcification, correlation between inorganic phosphate and pathologic calcification, between inorganic phosphate and fat metabolism in pathologic calcification were collected.

RESULTS

Various mechanisms were referred to in pathologic calcification among which inorganic phosphate played an important role. Inorganic phosphate could be liberated, under the effect of various enzymes, in the process of fat metabolism. The authors hypothesized that a large-scale necrotizing zone, which could occur in fat grafting with large amounts per cannula, might provide a high-phosphate environment which might contribute to differentiation of surrounding cells such as stem cells or regenerated vessel cells into osteoblast-like cells that induce pathologic calcification.

CONCLUSION

Inorganic phosphate, which was correlated with fat metabolism, played a significant role in pathologic calcification. We firstly hypothesize that calcification after fat grafting may be related to locally increasing concentrations of phosphate in a necrotizing zone. Further research should be conducted to verify this hypothesis.

LEVEL OF EVIDENCE V

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Involvement of inflammatory responses in the early development of calcific aortic valve disease: lessons from statin therapy

Calcific aortic valve disease (CAVD) is the most common degenerative heart valve disease. Among the many risk factors for this disease are age, hypercholesterolemia, hypertension, smoking, type-2 diabetes, rheumatic fever, and chronic kidney disease. Since many of these overlap with risk factors for atherosclerosis, the molecular and cellular mechanisms of CAVD development have been presumed to be similar to those for atherogenesis. Thus, attempts have been made to evaluate the therapeutic efficacy of statins, representative anti-atherosclerosis drugs with lipid-lowering and anti-inflammatory effects, against CAVD. Unfortunately, statins have shown little or no effect on CAVD development. But some reports suggest that statins may prevent or reduce the development of early stage CAVD in which having calcification is absent or minimal. These results suggest that therapeutic approaches should differ according to the stage of disease, and that a precise understanding of the mechanism of aortic valve calcification is required to identify novel therapeutic targets for advanced CAVD. Given the involvement of inflammatory processes in the development and progression of CAVD, current therapeutic approaches for chronic inflammatory cardiovascular disease like atherosclerosis may help to prevent or minimize the early development of CAVD. In this review, we focus on several inflammatory cellular and molecular components involved in CAVD that might be considered drug targets for preventing CAVD.

Highly Selective and Potent Ectonucleotide Pyrophosphatase-1 (NPP1) Inhibitors Based on Uridine 5'-Pα,α-Dithiophosphate Analogues

Ectonucleotide pyrophosphatase/phosphodiesterase-1 (NPP1) hydrolyzes phosphodiester bonds of nucleotides such as ATP, resulting mainly in the formation of AMP and pyrophosphate. NPP1 activity plays a deleterious function in calcified aortic valve disease and calcium pyrophosphate deposition disease. Thus, inhibitors of NPP1 represent a medical need. We developed novel NPP1 inhibitors based on uridine 5'-P_α,α-dithiophosphate analogues, 9-12. All these analogues potently inhibited hNPP1 (80-100% inhibition) at 100 μM, with no, or minimal, inhibition of NPP3 and other ectonucleotidases (NTPDase1,2,3,8). These compounds showed nearly no activity at uracil-nucleotide sensitive P2Y_2,4,6-receptors and thus represent highly selective NPP1 inhibitors. The most promising inhibitor was diuridine 5'-P_α,α,5″-P_α,α-tetrathiotetraphosphate, 12, exhibiting K_i of 27 nM. Analogues 9-12 proved to be highly stable to air oxidation and to acidic and basic pH. Docking simulations suggested that the enhanced NPP1 inhibitory activity and selectivity of analogue 12 could be attributed to the simultaneous occupancy of two sites (the AMP site and an alternative site) of NPP1 by this compound.

Inhibition of arterial medial calcification and bone mineralization by extracellular nucleotides: The same functional effect mediated by different cellular mechanisms

Arterial medial calcification (AMC) is thought to share some outward similarities to skeletal mineralization and has been associated with the transdifferentiation of vascular smooth muscle cells (VSMCs) to an osteoblast-like phenotype. ATP and UTP have previously been shown to inhibit bone mineralization. This investigation compared the effects of extracellular nucleotides on calcification in VSMCs with those seen in osteoblasts. ATP, UTP and the ubiquitous mineralization inhibitor, pyrophosphate (PP_i ), dose dependently inhibited VSMC calcification by ≤85%. Culture of VSMCs in calcifying conditions was associated with an increase in apoptosis; treatment with ATP, UTP, and PP_i reduced apoptosis to levels seen in non-calcifying cells. Extracellular nucleotides had no effect on osteoblast viability. Basal alkaline phosphatase (TNAP) activity was over 100-fold higher in osteoblasts than VSMCs. ATP and UTP reduced osteoblast TNAP activity (≤50%) but stimulated VSMC TNAP activity (≤88%). The effects of extracellular nucleotides on VSMC calcification, cell viability and TNAP activity were unchanged by deletion or inhibition of the P2Y₂ receptor. Conversely, the actions of ATP/UTP on bone mineralization and TNAP activity were attenuated in osteoblasts lacking the P2Y₂ receptor. Ecto-nucleotide pyrophosphatase/phosphodiesterase 1 (NPP1) hydrolyses ATP and UTP to produce PP_i . In both VSMCs and osteoblasts, deletion of NPP1 blunted the inhibitory effects of extracellular nucleotides suggesting involvement of P2 receptor independent pathways. Our results show that although the overall functional effect of extracellular nucleotides on AMC and bone mineralization is similar there are clear differences in the cellular mechanisms mediating these actions.

Cell Phenotype Transitions in Cardiovascular Calcification

Cardiovascular calcification was originally considered a passive, degenerative process, however with the advance of cellular and molecular biology techniques it is now appreciated that ectopic calcification is an active biological process. Vascular calcification is the most common form of ectopic calcification, and aging as well as specific disease states such as atherosclerosis, diabetes, and genetic mutations, exhibit this pathology. In the vessels and valves, endothelial cells, smooth muscle cells, and fibroblast-like cells contribute to the formation of extracellular calcified nodules. Research suggests that these vascular cells undergo a phenotypic switch whereby they acquire osteoblast-like characteristics, however the mechanisms driving the early aspects of these cell transitions are not fully understood. Osteoblasts are true bone-forming cells and differentiate from their pluripotent precursor, the mesenchymal stem cell (MSC); vascular cells that acquire the ability to calcify share aspects of the transcriptional programs exhibited by MSCs differentiating into osteoblasts. What is unknown is whether a fully-differentiated vascular cell directly acquires the ability to calcify by the upregulation of osteogenic genes or, whether these vascular cells first de-differentiate into an MSC-like state before obtaining a “second hit” that induces them to re-differentiate down an osteogenic lineage. Addressing these questions will enable progress in preventative and regenerative medicine strategies to combat vascular calcification pathologies. In this review, we will summarize what is known about the phenotypic switching of vascular endothelial, smooth muscle, and valvular cells.

Synthesis and biological evaluation of novel quinazoline-4-piperidinesulfamide derivatives as inhibitors of NPP1

The ecto-nucleotide pyrophosphatase/phosphodiesterase-1 (NPP1) was recently shown to promote mineralization of the aortic valve, hence, its inhibition represents a significant target. A quinazoline-4-piperidine sulfamide compound (QPS1) has been described as a specific and non-competitive inhibitor of NPP1. We report herein the synthesis and in vitro inhibition studies of novel quinazoline-4-piperidine sulfamide analogues using QPS1 as the lead compound. Of the 26 derivatives prepared, four compounds were found to have K_i < 105 nM against human NPP1.

Exploiting novel valve interstitial cell lines to study calcific aortic valve disease

Calcific aortic valve disease (CAVD) involves progressive valve leaflet thickening and severe calcification, impairing leaflet motion. The in vitro calcification of primary rat, human, porcine and bovine aortic valve interstitial cells (VICs) is commonly employed to investigate CAVD mechanisms. However, to date, no published studies have utilised cell lines to investigate this process. The present study has therefore generated and evaluated the calcification potential of immortalized cell lines derived from sheep and rat VICs. Immortalised sheep (SAVIC) and rat (RAVIC) cell lines were produced by transduction with a recombinant lentivirus encoding the Simian virus (SV40) large and small T antigens (sheep), or large T antigen only (rat), which expressed markers of VICs (vimentin and α‑smooth muscle actin). Calcification was induced in the presence of calcium (Ca; 2.7 mM) in SAVICs (1.9 fold; P<0.001) and RAVICs (4.6 fold; P<0.01). Furthermore, a synergistic effect of calcium and phosphate was observed (2.7 mM Ca/2.0 mM Pi) on VIC calcification in the two cell lines (P<0.001). Analysis of SAVICs revealed significant increases in the mRNA expression of two key genes associated with vascular calcification in cells cultured under calcifying conditions, runt related transcription factor‑2 (RUNX2;1.3 fold; P<0.05 in 4.5 mM Ca) and sodium‑dependent phosphate transporter‑1 (PiT1; 1.2 fold; P<0.05 in 5.4 mM Ca). A concomitant decrease in the expression of the calcification inhibitor matrix Gla protein (MGP) was noted at 3.6 mM Ca (1.3 fold; P<0.01). Assessment of RAVICs revealed alterations in Runx2, Pit1 and Mgp mRNA expression levels (P<0.01). Furthermore, a significant reduction in calcification was observed in SAVICs following treatment with established calcification inhibitors, pyrophosphate (1.8 fold; P<0.01) and etidronate (3.2 fold; P<0.01). Overall, the present study demonstrated that the use of immortalised sheep and rat VIC cell lines is a convenient and cost effective system to investigate CAVD in vitro, and will make a useful contribution to increasing current understanding of the pathophysiological process.

Simultaneous accurate quantification of HO-1, CD39, and CD73 in human calcified aortic valves using multiple enzyme digestion - filter aided sample pretreatment (MED-FASP) method and targeted proteomics

Several proteins such as membrane-associated ectonucleotidases: ecto-5'-nucleotidase (E5NT/CD73) and ectonucleoside triphosphate diphosphohydrolase 1 (ENTPD1/CD39), and intracellular heme oxygenase-1 (HO-1) may contribute to protection from inflammation-related diseases such as calcific aortic valve stenosis (CAS). Accurate quantification of these proteins could contribute to better understanding of the disease mechanisms and identification of biomarkers. This report presents development and validation of quantification method for E5NT/CD73, ENTPD1/CD39 and HO-1. The multiplexed targeted proteomic assay involved antibody-free, multiple-enzyme digestion, filter-assisted sample preparation (MED-FASP) strategy and a nanoflow liquid chromatography/mass spectrometry under multiple reaction monitoring mode (LC-MRM/MS). The method developed presented high sensitivity (LLOQ of 5 pg/mL for each of the analytes) and accuracy that ranged from 92.0% to 107.0%, and was successfully applied for the absolute quantification of HO-1, CD39 and CD73 proteins in homogenates of human calcified and non-calcified valves. The absolute CD39 and CD73 concentrations were lower in calcified aortic valves (as compared to non-stenotic ones) and were found to be: 1.16 ± 0.39 vs. 3.15 ± 0.37 pmol/mg protein and 1.94 ± 0.21 vs. 2.39 ± 0.39 pmol/mg protein, respectively, while the quantity of HO-1 was elevated in calcified valves (10.72 ± 1.18 vs. 4.28 ± 0.42 amol/mg protein). These results were consistent but more reproducible as compared to immunoassays. In conclusion, multiplexed quantification of HO-1, CD39 and CD73 proteins by LC-MRM/MS works well in challenging human tissues such as aortic valves. This analysis confirmed the relevance of these proteins in pathogenesis of CAS and could be extended to other biomedical investigations.

Oxidative stress in ageing and disease development studied by FT-IR spectroscopy

FT-IR spectroscopy was used to investigate the effect of oxidative stress and to approach the mechanism on cancer bone demineralization, aortic valve mineralization and heterotopic ossification on disease development. The FT-IR spectra obtained from paediatric, adult bone and ex vivo irradiated adult healthy bone with a dose of 20Gy were compared with those of healthy bone. The increase of band intensity changes of vasCH_2,vsCH₂ in the region 3000-2850cm^-1 depended on aging, the disease progression and the dose of irradiation. The bands at 3080cm^-1 and 1744cm^-1, which originate from olefinic terminal bond (v=CH) and ester carbonyl group (vROCO), respectively, indicate the influence of oxidative stress on lipid degradation and peroxidation, respectively. The new bands at about 1690cm^-1 and 1516cm^-1 denote the presence of β-sheet conformation of the proteins due to the diseases, confirming the increasing amount of lipophilic environment and fibril formation. Comparison of the FT-IR spectra of calcified aortic valve and hip heterotopic ossification with that of normal bones showed that in the bone-like formation the peroxide anion free radicals play an important role in the disease.

Purinergic Signalling: Therapeutic Developments

Purinergic signalling, i.e., the role of nucleotides as extracellular signalling molecules, was proposed in 1972. However, this concept was not well accepted until the early 1990's when receptor subtypes for purines and pyrimidines were cloned and characterised, which includes four subtypes of the P1 (adenosine) receptor, seven subtypes of P2X ion channel receptors and 8 subtypes of the P2Y G protein-coupled receptor. Early studies were largely concerned with the physiology, pharmacology and biochemistry of purinergic signalling. More recently, the focus has been on the pathophysiology and therapeutic potential. There was early recognition of the use of P1 receptor agonists for the treatment of supraventricular tachycardia and A2A receptor antagonists are promising for the treatment of Parkinson's disease. Clopidogrel, a P2Y12 antagonist, is widely used for the treatment of thrombosis and stroke, blocking P2Y12 receptor-mediated platelet aggregation. Diquafosol, a long acting P2Y2 receptor agonist, is being used for the treatment of dry eye. P2X3 receptor antagonists have been developed that are orally bioavailable and stable in vivo and are currently in clinical trials for the treatment of chronic cough, bladder incontinence, visceral pain and hypertension. Antagonists to P2X7 receptors are being investigated for the treatment of inflammatory disorders, including neurodegenerative diseases. Other investigations are in progress for the use of purinergic agents for the treatment of osteoporosis, myocardial infarction, irritable bowel syndrome, epilepsy, atherosclerosis, depression, autism, diabetes, and cancer.

Purinergic Signaling in the Cardiovascular System

There is nervous control of the heart by ATP as a cotransmitter in sympathetic, parasympathetic, and sensory-motor nerves, as well as in intracardiac neurons. Centers in the brain control heart activities and vagal cardiovascular reflexes involve purines. Adenine nucleotides and nucleosides act on purinoceptors on cardiomyocytes, AV and SA nodes, cardiac fibroblasts, and coronary blood vessels. Vascular tone is controlled by a dual mechanism. ATP, released from perivascular sympathetic nerves, causes vasoconstriction largely via P2X1 receptors. Endothelial cells release ATP in response to changes in blood flow (via shear stress) or hypoxia, to act on P2 receptors on endothelial cells to produce nitric oxide, endothelium-derived hyperpolarizing factor, or prostaglandins to cause vasodilation. ATP is also released from sensory-motor nerves during antidromic reflex activity, to produce relaxation of some blood vessels. Purinergic signaling is involved in the physiology of erythrocytes, platelets, and leukocytes. ATP is released from erythrocytes and platelets, and purinoceptors and ectonucleotidases are expressed by these cells. P1, P2Y₁, P2Y₁₂, and P2X1 receptors are expressed on platelets, which mediate platelet aggregation and shape change. Long-term (trophic) actions of purine and pyrimidine nucleosides and nucleotides promote migration and proliferation of vascular smooth muscle and endothelial cells via P1 and P2Y receptors during angiogenesis, vessel remodeling during restenosis after angioplasty and atherosclerosis. The involvement of purinergic signaling in cardiovascular pathophysiology and its therapeutic potential are discussed, including heart failure, infarction, arrhythmias, syncope, cardiomyopathy, angina, heart transplantation and coronary bypass grafts, coronary artery disease, diabetic cardiomyopathy, hypertension, ischemia, thrombosis, diabetes mellitus, and migraine.

Thiazolo[3,2-a]benzimidazol-3(2H)-one derivatives: Structure-activity relationships of selective nucleotide pyrophosphatase/phosphodiesterase1 (NPP1) inhibitors

Ecto-nucleotide pyrophosphatase/phosphodiesterase1 (NPP1) is the most important member of the NPP family, which consists of seven closely related proteins (NPP1-NPP7). This glycoprotein is a membrane-associated or secreted enzyme, which catalyzes the hydrolysis of a wide range of phosphodiester bonds, e.g., in nucleoside triphosphates, dinucleotides and nucleotide sugars. NPP1 plays a crucial role in various physiological functions including bone mineralization, soft-tissue calcification, and insulin receptor signaling. Recently, an upregulated expression of NPP1 has been observed in astrocytic brain cancers. Therefore, NPP1 has been proposed as a novel drug target for the treatment of glioblastoma. Despite their therapeutic potential, only few NPP1 inhibitors have been reported to date, which are in most cases non- or only moderately selective. The best investigated NPP1 inhibitors so far are nucleotide derivatives and analogs, however they are not orally bioavailable due to their high polarity. We identified thiazolo[3,2-a]benzimidazol-3(2H)-one derivatives as a new class of NPP1 inhibitors with drug-like properties. Among the 25 derivatives investigated in the present study, 2-[(5-iodo-2-furanyl)methylene]thiazolo[3,2-a]benzimidazol-3(2H)-one (17) was found to be the most potent NPP1 inhibitor with a Ki value of 467nM versus ATP as a substrate and an un-competitive mechanism of inhibition. Compound 17 did not inhibit other human ecto-nucleotidases, including NTPDase1 (CD39), NTPDases2-3, NPP2, NPP3, tissue-nonspecific alkaline phosphatase (TNAP), and ecto-5'-nucleotidase (eN, CD73), and is thus highly selective for NPP1.

Calcific aortic stenosis

Calcific aortic stenosis (AS) is the most prevalent heart valve disorder in developed countries. It is characterized by progressive fibro-calcific remodelling and thickening of the aortic valve leaflets that, over years, evolve to cause severe obstruction to cardiac outflow. In developed countries, AS is the third-most frequent cardiovascular disease after coronary artery disease and systemic arterial hypertension, with a prevalence of 0.4% in the general population and 1.7% in the population >65 years old. Congenital abnormality (bicuspid valve) and older age are powerful risk factors for calcific AS. Metabolic syndrome and an elevated plasma level of lipoprotein(a) have also been associated with increased risk of calcific AS. The pathobiology of calcific AS is complex and involves genetic factors, lipoprotein deposition and oxidation, chronic inflammation, osteoblastic transition of cardiac valve interstitial cells and active leaflet calcification. Although no pharmacotherapy has proved to be effective in reducing the progression of AS, promising therapeutic targets include lipoprotein(a), the renin-angiotensin system, receptor activator of NF-κB ligand (RANKL; also known as TNFSF11) and ectonucleotidases. Currently, aortic valve replacement (AVR) remains the only effective treatment for severe AS. The diagnosis and staging of AS are based on the assessment of stenosis severity and left ventricular systolic function by Doppler echocardiography, and the presence of symptoms. The introduction of transcatheter AVR in the past decade has been a transformative therapeutic innovation for patients at high or prohibitive risk for surgical valve replacement, and this new technology might extend to lower-risk patients in the near future.

Nucleotide Catabolism on the Surface of Aortic Valve Xenografts; Effects of Different Decellularization Strategies

Extracellular nucleotide metabolism controls thrombosis and inflammation and may affect degeneration and calcification of aortic valve prostheses. We evaluated the effect of different decellularization strategies on enzyme activities involved in extracellular nucleotide metabolism. Porcine valves were tested intact or decellularized either by detergent treatment or hypotonic lysis and nuclease digestion. The rates of ATP hydrolysis, AMP hydrolysis, and adenosine deamination were estimated by incubation of aorta or valve leaflet sections with substrates followed by HPLC analysis. We demonstrated relatively high activities of ecto-enzymes on porcine valve as compared to the aortic wall. Hypotonic lysis/nuclease digestion preserved >80 % of ATP and AMP hydrolytic activity but reduced adenosine deamination to <10 %. Detergent decellularization completely removed (<5 %) all these activities. These results demonstrate high intensity of extracellular nucleotide metabolism on valve surface and indicate that various valve decellularization techniques differently affect ecto-enzyme activities that could be important in the development of improved valve prostheses.