Ultrastructural and Immunohistochemical Detection of Hydroxyapatite Nucleating Role by rRNA and Nuclear Chromatin Derivatives in Aortic Valve Calcification: In Vitro and In Vivo Pro-Calcific Animal Models and Actual Calcific Disease in Humans.

Calcification starts with hydroxyapatite (HA) crystallization on cell membranous components, as with aortic valve interstitial cells (AVICs), wherein a cell-membrane-derived substance containing acidic phospholipids (PPM/PPLs) acts as major crystal nucleator. Since nucleic acid removal is recommended to prevent calcification in valve biosubstitutes derived from decellularized valve scaffolds, the involvement of ribosomal RNA (rRNA) and nuclear chromatin (NC) was here explored in three distinct contexts: (i) bovine AVIC pro-calcific cultures; (ii) porcine aortic valve leaflets that had undergone accelerated calcification after xenogeneic subdermal implantation; and (iii) human aortic valve leaflets affected by calcific stenosis. Ultrastructurally, shared AVIC degenerative patterns included (i) the melting of ribosomes with PPM/PPLs, and the same for apparently well-featured NC; (ii) selective precipitation of silver particles on all three components after adapted von Kossa reactions; and (iii) labelling by anti-rRNA immunogold particles. Shared features were also provided by parallel light microscopy. In conclusion, the present results indicate that rRNA and NC contribute to AVIC mineralization in vitro and in vivo, with their anionic charges enhancing the HA nucleation capacity exerted by PPM/PPL substrates, supporting the concept that nucleic acid removal is needed for valve pre-implantation treatments, besides better elucidating the modality of pro-calcific cell death.

Calcium-Dependent Cytosolic Phospholipase A2α as Key Factor in Calcification of Subdermally Implanted Aortic Valve Leaflets.

Calcium-dependent cytosolic phospholipase A2α (cPLA2α) had been previously found to be overexpressed by aortic valve interstitial cells (AVICs) subjected to in vitro calcific induction. Here, cPLA2α expression was immunohistochemically assayed in porcine aortic valve leaflets (iAVLs) that had undergone accelerated calcification subsequent to 2- to 28-day-long implantation in rat subcutis. A time-dependent increase in cPLA2α-positive AVICs paralleled mineralization progression depending on dramatic cell membrane degeneration with the release of hydroxyapatite-nucleating acidic lipid material, as revealed by immunogold particles decorating organelle membranes in 2d-iAVLs, as well as membrane-derived lipid byproducts in 7d- to 28d-iAVLs. Additional positivity was detected for (i) pro-inflammatory IL-6, mostly exhibited by rat peri-implant cells surrounding 14d- and 28d-iAVLs; (ii) calcium-binding osteopontin, with time-dependent increase and no ossification occurrence; (iii) anti-calcific fetuin-A, mostly restricted to blood plasma within vessels irrorating the connective envelopes of 28d-iAVLs; (iv) early apoptosis marker annexin-V, limited to sporadic AVICs in all iAVLs. No positivity was found for either apoptosis executioner cleaved caspase-3 or autophagy marker MAP1. In conclusion, cPLA2α appears to be a factor characterizing AVL calcification concurrently with a distinct still uncoded cell death form also in an animal model, as well as a putative target for the prevention and treatment of calcific valve diseases.

Critical Involvement of Calcium-Dependent Cytosolic Phospholipase A2α in Aortic Valve Interstitial Cell Calcification.

The involvement of calcium-dependent cytosolic phospholipase A2α (cPLA2α) in aortic valve calcification is not exhaustively elucidated. Here, cPLA2α expression in aortic valve interstitial cell (AVIC) pro-calcific cultures simulating either metastatic or dystrophic calcification was estimated by qPCR, Western blotting, and counting of cPLA2α-immunoreactive cells, with parallel ultrastructural examination of AVIC calcific degeneration. These evaluations also involved pro-calcific AVIC cultures treated with cPLA2α inhibitor dexamethasone. cPLA2α over-expression resulted for both types of pro-calcific AVIC cultures. Compared to controls, enzyme content was found to increase by up to 300% and 186% in metastatic and dystrophic calcification-like cultures, respectively. Increases in mRNA amounts were also observed, although they were not as striking as those in enzyme content. Moreover, cPLA2α increases were time-dependent and strictly associated with mineralization progression. Conversely, drastically lower levels of enzyme content resulted for the pro-calcific AVIC cultures supplemented with dexamethasone. In particular, cPLA2α amounts were found to decrease by almost 88% and 48% in metastatic and dystrophic calcification-like cultures, respectively, with mRNA amounts showing a similar trend. Interestingly, these drastic decreases in cPLA2α amounts were paralleled by drastic decreases in mineralization degrees, as revealed ultrastructurally. In conclusion, cPLA2α may be regarded as a crucial co-factor contributing to AVIC mineralization in vitro, thus being an attractive potential target for designing novel therapeutic strategies aimed to counteract onset or progression of calcific aortic valve diseases.

Decellularized aortic conduits: could their cryopreservation affect post-implantation outcomes? A morpho-functional study on porcine homografts.

Decellularized porcine aortic valve conduits (AVCs) implanted in a Vietnamese Pig (VP) experimental animal model were matched against decellularized and then cryopreserved AVCs to assess the effect of cryopreservation on graft hemodynamic performance and propensity to in vivo repopulation by host's cells. VPs (n = 12) underwent right ventricular outflow tract substitution using AVC allografts and were studied for 15-month follow-up. VPs were randomized into two groups, receiving AVCs treated with decellularization alone (D; n = 6) or decellularization/cryopreservation (DC; n = 6), respectively. Serial echocardiography was carried out to follow up hemodynamic function. All explanted AVCs were processed for light and electron microscopy. No signs of dilatation, progressive stenosis, regurgitation, and macroscopic calcification were echocardiographically observed in both D and DC groups. Explanted D grafts exhibited near-normal features, whereas the presence of calcification, inflammatory infiltrates, and disarray of elastic lamellae occurred in some DC grafts. In the unaltered regions of AVCs from both groups, almost complete re-endothelialization was observed for both valve cusps and aorta walls. In addition, side-by-side repopulation by recipient's fibroblasts, myofibroblasts, and smooth muscle cells was paralleled by ongoing tissue remodeling, as revealed by the ultrastructural identification of typical canals of collagen fibrillogenesis and elastogenesis-related features. Incipient neo-vascularization and re-innervation of medial and adventitial tunicae of grafted aortic walls were also detected for both D and DC groups. Cryopreservation did not affect post-implantation AVC hemodynamic behavior and was topically propensive to cell repopulation and tissue renewal, although graft deterioration including calcification was present in several areas. Thus, these preliminary data provide essential information on feasibility of decellularization and cryopreservation coupling in the perspective of treatment optimization and subsequent clinical trials using similarly treated human allografts as innovative heart valve substitutes.

Preservation by cold storage vs ex vivo normothermic perfusion of marginal donor hearts: clinical, histopathologic, and ultrastructural features.

BACKGROUND: The aim of this study was to match clinical outcomes of heart transplantation (HTx) against histopathologic and ultrastructural characteristics of marginal grafts preserved by cold storage (CS) or ex vivo normothermic perfusion. METHODS: Since 2011, 100 patients had undergone HTx at our institution by using marginal donors (aged ≥55 years, expected ischemic time of >4 hours, left ventricular ejection fraction of ≤50%, interventricular septum thickness of ≥14 mm, drug abuse history, episodes of cardiac arrest, and presence of mild coronary artery disease). CS was utilized in 79 cases (Group 1, 79%), and ex vivo perfusion was utilized in 21 (Group 2, 21%). Pre-operative data, survival, and complications in the first 5 years after HTx were analyzed. Myocardial biopsies were collected at graft harvesting, just before implantation, and immediately after aortic declamping. RESULTS: Pre-operative demographics were similar in the 2 groups. Graft utilization rate with ex vivo perfusion was 81%. Ischemic, cardiopulmonary bypass, and surgical times were shorter in Group 2 patients, who showed a lower incidence of overall complications (33% vs 13%, p = 0.04) and better 5-year survival (log-rank, p = 0.04). Moreover, restoration of hypertrophy-related sarcomere changes and mitigation of reperfusion-dependent myocardium injuries were more frequently observed in Group 2 hearts. CONCLUSIONS: Ex vivo perfusion allows for continuous evaluation of marginal donor hearts, favoring exclusion of unsuitable grafts, reduction of complications, and optimal survival of up to 5 years. Such results, supported by consistent histopathologic and ultrastructural findings, suggest better myocardial preservation.

Ectopic mineralization in heart valves: new insights from in vivo and in vitro procalcific models and promising perspectives on noncalcifiable bioengineered valves.

Ectopic calcification of native and bioprosthetic heart valves represents a major public health problem causing severe morbidity and mortality worldwide. Valve procalcific degeneration is known to be caused mainly by calcium salt precipitation onto membranes of suffering non-scavenged cells and dead-cell-derived products acting as major hydroxyapatite nucleators. Although etiopathogenesis of calcification in native valves is still far from being exhaustively elucidated, it is well known that bioprosthesis mineralization may be primed by glutaraldehyde-mediated toxicity for xenografts, cryopreservation-related damage for allografts and graft immune rejection for both. Instead, mechanical valves, which are free from calcification, are extremely thrombogenic, requiring chronic anticoagulation therapies for transplanted patients. Since surgical substitution of failed valves is still the leading therapeutic option, progressive improvements in tissue engineering techniques are crucial to attain readily available valve implants with good biocompatibility, proper functionality and long-term durability in order to meet the considerable clinical demand for valve substitutes. Bioengineered valves obtained from acellular non-valvular scaffolds or decellularized native valves are proving to be a compelling alternative to mechanical and bioprosthetic valve implants, as they appear to permit repopulation by the host's own cells with associated tissue remodelling, growth and repair, besides showing less propensity to calcification and adequate hemodynamic performances. In this review, insights into valve calcification onset as revealed by in vivo and in vitro procalcific models are updated as well as advances in the field of valve bioengineering.

Survival-Related Autophagic Activity Versus Procalcific Death in Cultured Aortic Valve Interstitial Cells Treated With Critical Normophosphatemic-Like Phosphate Concentrations.

Valve dystrophic calcification is a common disorder affecting normophosphatemic subjects. Here, cultured aortic valve interstitial cells (AVICs) were treated 3 to 28 days with phosphate (Pi) concentrations spanning the normal range in humans (0.8, 1.3, and 2.0 mM) alone or supplemented with proinflammatory stimuli to assess possible priming of dystrophic-like calcification. Compared with controls, spectrophotometric analyses revealed marked increases in calcium amounts and alkaline phosphatase activity for 2.0-mM-Pi-containing cultures, with enhancing by proinflammatory mediators. Ultrastructurally, AVICs treated with low/middle Pi concentrations showed an enormous endoplasmic reticulum (ER) enclosing organelle debris, so apparently executing a survival-related atypical macroautophagocytosis, consistently with ultracytochemical demonstration of ER-associated acid phosphatase activity and decreases in autophagosomes and immunodetectable MAP1LC3. In contrast, AVICs cultured at 2.0-mM Pi underwent mineralization due to intracellular release and peripheral layering of phospholipid-rich material acting as hydroxyapatite nucleator, as revealed by Cuprolinic Blue and von Kossa ultracytochemical reactions. Lack of immunoblotted caspase-3 cleaved form indicated apoptosis absence for all cultures. In conclusion, fates of cultured AVICs were crucially driven by Pi concentration, suggesting that serum Pi levels just below the upper limit of normophosphatemia in humans may represent a critical watershed between macroautophagy-associated cell restoring and procalcific cell death.

The Vietnamese pig as a translational animal model to evaluate tissue engineered heart valves: promising early experience.

Several animal models are currently used for the surgical implantation of either biologic or biopolymeric scaffolds in order to provide in vivo assessment of tissue-engineered heart valves. The Vietnamese pig (VP) is herein proposed as a suitable recipient to test the function of novel bioengineered valve substitutes, in the reconstruction of the right ventricular outflow tract (RVOT). This review aims to provide a complete and exhaustive panel of physiological parameters and methodological information for preclinical studies of tissue-engineered heart valves in the VP animal model.

Decellularized allogeneic heart valves demonstrate self-regeneration potential after a long-term preclinical evaluation.

Tissue-engineered heart valves are proposed as novel viable replacements granting longer durability and growth potential. However, they require extensive in vitro cell-conditioning in bioreactor before implantation. Here, the propensity of non-preconditioned decellularized heart valves to spontaneous in body self-regeneration was investigated in a large animal model. Decellularized porcine aortic valves were evaluated for right ventricular outflow tract (RVOT) reconstruction in Vietnamese Pigs (n = 11) with 6 (n = 5) and 15 (n = 6) follow-up months. Repositioned native valves (n = 2 for each time) were considered as control. Tissue and cell components from explanted valves were investigated by histology, immunohistochemistry, electron microscopy, and gene expression. Most substitutes constantly demonstrated in vivo adequate hemodynamic performances and ex vivo progressive repopulation during the 15 implantation months without signs of calcifications, fibrosis and/or thrombosis, as revealed by histological, immunohistochemical, ultrastructural, metabolic and transcriptomic profiles. Colonizing cells displayed native-like phenotypes and actively synthesized novel extracellular matrix elements, as collagen and elastin fibers. New mature blood vessels, i.e. capillaries and vasa vasorum, were identified in repopulated valves especially in the medial and adventitial tunicae of regenerated arterial walls. Such findings correlated to the up-regulated vascular gene transcription. Neoinnervation hallmarks were appreciated at histological and ultrastructural levels. Macrophage populations with reparative M2 phenotype were highly represented in repopulated valves. Indeed, no aspects of adverse/immune reaction were revealed in immunohistochemical and transcriptomic patterns. Among differentiated elements, several cells were identified expressing typical stem cell markers of embryonic, hematopoietic, neural and mesenchymal lineages in significantly higher number and specific topographic distribution in respect to control valves. Following the longest follow-up ever realized in preclinical models, non-preconditioned decellularized allogeneic valves offer suitable microenvironment for in vivo cell homing and tissue remodeling. Manufactured with simple, timesaving and cost-effective procedures, these promising valve replacements hold promise to become an effective alternative, especially for pediatric patients.

Ultrastructural and spectrophotometric study on the effects of putative triggers on aortic valve interstitial cells in in vitro models simulating metastatic calcification.

Metastatic calcification of cardiac valves is a common complication in patients affected by chronic renal failure. In this study, primary bovine aortic valve interstitial cells (AVICs) were subjected to pro-calcific treatments consisting in cell stimulation with (i) elevated inorganic phosphate (Pi = 3 mM), to simulate hyperphosphatemic conditions; (ii) bacterial endotoxin lipopolysaccharide (LPS), simulating direct effects by microbial agents; and (iii) conditioned media (CM) derived from cultures of either LPS-stimulated heterogenic macrophages (commercial murine RAW264.7 cells) or LPS-stimulated fresh allogenic monocytes/macrophages (bCM), simulating consequent inflammatory responses, alone or combined. Compared to control cultures, spectrophotometric assays revealed shared treatment-dependent higher values of both calcium amounts and alkaline phosphatase activity for cultures involving the presence of elevated Pi. Ultrastructurally, shared peculiar pro-calcific degeneration patterns were exhibited by AVICs from these latter cultures irrespectively of the additional treatments. Disappearance of all cytomembranes and concurrent formation of material showing positivity to Cuprolinic Blue and co-localizing with silver precipitation were followed by the outcropping of such a material, which transformed in layers outlining the dead cells. Subsequent budding of these layers resulted in the formation of bubbling bodies and concentrically laminated calcospherulae mirroring those in actual soft tissue calcification. In conclusion, the in vitro models employed appear to be reliable tools for simulating metastatic calcification and indicate that hyperphosphatemic-like conditions could trigger valve calcification per se, with LPS and allogenic macrophage-derived secretory products acting as possible calcific enhancers via inflammatory responses.

Ultrastructural evaluation of human metaphase II oocytes after vitrification: closed versus open devices.

OBJECTIVE: To compare the ultrastructural appearance of oocytes after vitrification and warming with two different devices. DESIGN: Oocytes were examined by ultrastructural analysis after vitrification and warming with use of closed (CryoTip; Irvine Scientific, Santa Ana, CA) or open (Cryotop; Kitazato BioPharma Co., Ltd., Shizuoka, Japan) devices. SETTING: Pordenone Hospital IVF Unit and Medical Morphological Research Department, University of Udine. PATIENT(S): Surplus oocytes from 10 patients (aged 31-39 years) undergoing assisted reproductive technologies at the Pathophysiology Unit of Human Reproduction and Sperm Bank between 2006 and 2008. INTERVENTION(S): Oocytes with normal invertoscopic appearance underwent vitrification and warming with closed (CryoTip) or open (Cryotop) devices and were processed for transmission electron microscopy. MAIN OUTCOME MEASURE(S): Cryodamage extent and cell alterations in oocytes after open or closed vitrification and warming procedures and their rehydration rate. RESULT(S): A higher rate of complete oocyte rehydration and less-severe ultrastructural alterations were observed after vitrification and warming with the open Cryotop device. CONCLUSION(S): These preliminary data suggest that oocyte ultrastructure is better preserved with an open rather than closed vitrification and warming protocol.

Pro-calcific responses by aortic valve interstitial cells in a novel in vitro model simulating dystrophic calcification.

Etiopathogenetic mechanisms in calcific aortic valve stenosis are still poorly understood despite this being the third major cause of heart disease in western world. In prior in vitro cultures simulating metastatic calcification, pro-calcific effects on aortic valve interstitial cells (AVICs) resulted by adding bacterial endotoxin lipopolysaccharide (LPS) at high inorganic phosphate (Pi) levels. Here we accomplished improved in vitro models simulating either metastatic (Pi = 2.6 mM) or dystrophic calcification (Pi = 1.3 mM), in which LPS-stimulated bovine AVICs underwent extra-stimulation with macrophage-cytokine-containing media derived from parallel cultures of allogeneic monocyte/macrophages in turn stimulated with LPS. In dystrophic calcification-like cultures, lower calcium amount was spectrometrically assessed with parallel reduced alkaline phosphatase activity with respect to metastatic calcification-like cultures, with an about three-fold slower progression of mineralization. Hydroxyapatite crystal precipitation was ultrastructurally found to correlate with AVIC degeneration processes culminating with the formation of phthalocyanin-positive lipidic layers (PPLs) at the surface of cells and cell-derived matrix-vesicle-like bodies, acting as calcium nucleators according to a pattern mirroring those we had previously found in in vivo conditions. In conclusion, an in vitro model has been developed enabling reliable simulations of the effects exerted on AVICs by putatively pro- or anti-calcific agents.

Identification of secondary targets of N-containing bisphosphonates in mammalian cells via parallel competition analysis of the barcoded yeast deletion collection.

BACKGROUND: Nitrogen-containing bisphosphonates are the elected drugs for the treatment of diseases in which excessive bone resorption occurs, for example, osteoporosis and cancer-induced bone diseases. The only known target of nitrogen-containing bisphosphonates is farnesyl pyrophosphate synthase, which ensures prenylation of prosurvival proteins, such as Ras. However, it is likely that the action of nitrogen-containing bisphosphonates involves additional unknown mechanisms. To identify novel targets of nitrogen-containing bisphosphonates, we used a genome-wide high-throughput screening in which 5,936 Saccharomyces cerevisiae heterozygote barcoded mutants were grown competitively in the presence of sub-lethal doses of three nitrogen-containing bisphosphonates (risedronate, alendronate and ibandronate). Strains carrying deletions in genes encoding potential drug targets show a variation of the intensity of their corresponding barcodes on the hybridization array over the time. RESULTS: With this approach, we identified novel targets of nitrogen-containing bisphosphonates, such as tubulin cofactor B and ASK/DBF4 (Activator of S-phase kinase). The up-regulation of tubulin cofactor B may explain some previously unknown effects of nitrogen-containing bisphosphonates on microtubule dynamics and organization. As nitrogen-containing bisphosphonates induce extensive DNA damage, we also document the role of DBF4 as a key player in nitrogen-containing bisphosphonate-induced cytotoxicity, thus explaining the effects on the cell-cycle. CONCLUSIONS: The dataset obtained from the yeast screen was validated in a mammalian system, allowing the discovery of new biological processes involved in the cellular response to nitrogen-containing bisphosphonates and opening up opportunities for development of new anticancer drugs.

The influence of heart valve leaflet matrix characteristics on the interaction between human mesenchymal stem cells and decellularized scaffolds.

The potential for in vitro colonization of decellularized valves by human bone marrow mesenchymal stem cells (hBM-MSCs) towards the anisotropic layers ventricularis and fibrosa and in homo- vs. heterotypic cell-ECM interactions has never been investigated. hBM-MSCs were expanded and characterized by immunofluorescence and FACS analysis. Porcine and human pulmonary valve leaflets (p- and hPVLs, respectively) underwent decellularization with Triton X100-sodium cholate treatment (TRICOL), followed by nuclear fragment removal. hBM-MSCs (2x10(6) cells/cm(2)) were seeded onto fibrosa (FS) or ventricularis (VS) of decellularized PVLs, precoated with FBS and fibronectin, and statically cultured for 30 days. Bioengineered PVLs revealed no histopathological features but a reconstructed endothelium lining and the presence of fibroblasts, myofibroblasts and SMCs, as in the corresponding native leaflet. The two valve layers behaved differently as regards hBM-MSC repopulation potential, however, with a higher degree of 3D spreading and differentiation in VS than in FS samples, and with enhanced cell survival and colonization effects in the homotypic ventricularis matrix, suggesting that hBM-MSC phenotypic conversion is strongly influenced in vitro by the anisotropic valve microstructure and species-specific matching between extracellular matrix and donor cells. These findings are of particular relevance to in vivo future applications of valve tissue engineering.