Biochemical and histological evidence of deteriorated bioprosthetic valve leaflets: the accumulation of fibrinogen and plasminogen

Transcatheter aortic valve durability, predictors of bioprosthetic valve dysfunction, longer-term outcomes - a review

INTRODUCTION

Transcatheter aortic valve implantation (TAVI) is one of the most significant inventions in cardiology, as it provides a viable minimally invasive treatment option for patients with aortic stenosis, the most common valvular disease in the developed world and one with a poor prognosis when left untreated. Using data available to date, this review aims to discuss and identify possible predictors of TAVI valve durability - an essential requirement for the device's wide-spread use, especially in younger patients.

AREAS COVERED

This article explores the main causes of bioprosthetic valve dysfunction (BVD) based on pathophysiology and available data, and reviews possible predictors of BVD including prosthesis-related, procedure-related, and patient-related factors. An emphasis is made on affectable predictors, which could potentially be targeted with prevention management and improve valve durability. A literature search of online medical databases was conducted using relevant key words and dates; significant clinical trials were identified. A brief overview of important randomized controlled trials with mid to long-term follow-up is included in this article.

EXPERT OPINION

Identifying modifiable predictors of valve dysfunction presents an opportunity to enhance and predict valve durability - a necessity as patients with longer life-expectancies are being considered for the procedure.

A high throughput microphysiological model of prosthetic valve endocarditis for investigating factors that influence bacterial adhesion under fluid shear stress

Prosthetic heart valves are associated with almost one quarter of cases of infective endocarditis, a rare but serious condition with a staggering 25 % mortality rate. Without the endothelium of native valves, the risk of infection is exacerbated for implanted devices exposed to blood. There are currently no physiologically relevant in vitro or animal models of prosthetic valve endocarditis (PVE). Of particular importance, Staphylococcus aureus, a common agent of PVE, has demonstrated enhanced binding to blood plasma proteins (e.g., fibrinogen) and exposed matrix under fluid shear stress (FSS). An in vitro platform that mimics the multiple physiological determinants for S. aureus adhesion to prosthetic valve materials would facilitate the discovery of new treatments to minimize PVE. To this end, we developed a first-of-its-kind microphysiological model of PVE to study the effects of several key variables (endothelial cell coverage, fibrinogen deposition, surface treatments, and FSS) on S. aureus adhesion to bioprosthetic material surfaces. Our model demonstrated that viable endothelial monolayers diminished the deposition of fibrinogen and that fibrinogen was required for the subsequent adhesion of S. aureus to the bioprosthetic surface model. Next, we examined factors that affected endothelial cell coverage, such as FSS and glutaraldehyde, a common chemical treatment for bioprosthetic materials. In particular, glutaraldehyde treatment obstructed endothelialization of otherwise biocompatible collagen-coated surfaces, further enabling fibrinogen and S. aureus deposition. In future work, this model could impact multiple research areas, such as screening candidate bioprosthetic valve materials and new surface treatments to prevent PVE and further understanding host-pathogen interactions.

Biomimetic-modified bioprosthetic heart valves with Cysteine-Alanine-Glycine peptide for anti-thrombotic, endothelialization and anti-calcification

In recent years, bioprosthetic heart valves (BHVs) prepared by cross-linking porcine or bovine pericardium with glutaraldehyde (Glut) have received widespread attention due to their excellent hemocompatibility and hydrodynamic properties. However, the failure of BHVs induced by thrombosis and difficulty in endothelialization still exists in clinical practice. Improving the biocompatibility and endothelialization potential of BHVs is conducive to promoting their anti-thrombosis properties and prolonging their service life. Herein, Cysteine-Alanine-Glycine (CAG) peptide was introduced into the biomimetic BHV materials modified by 2-methacryloyloxyethyl phosphorylcholine (MPC) to improve their anti-thrombosis and promoting-endothelialization performances. MPC can improve the anti-adsorption performance of BHV materials, as well as, CAG contributes to the adhesion and proliferation of endothelial cells on the surface of BHV materials. The results of experiments showed that the biomimetic modification strategy with MPC and CAG reduce the thrombosis of BHV materials and improve their endothelialization in vitro. More importantly, the calcification of BHV significantly reduced by inhibiting the expression of M1 macrophage-related factors (IL-6, iNOS) and promoting the expression of M2 macrophage-related factors (IL-10, CD206). We believe that the valve-modified strategy is expected to provide effective solutions to clinical valve problems.

Embedding and Backscattered Scanning Electron Microscopy (EM-BSEM) Is Preferential over Immunophenotyping in Relation to Bioprosthetic Heart Valves

Hitherto, calcified aortic valves (AVs) and failing bioprosthetic heart valves (BHVs) have been investigated by similar approaches, mostly limited to various immunostaining techniques. Having employed multiple immunostaining combinations, we demonstrated that AVs retain a well-defined cellular hierarchy even at severe stenosis, whilst BHVs were notable for the stochastic degradation of the extracellular matrix (ECM) and aggressive infiltration by ECM-digesting macrophages. Leukocytes (CD45+) comprised ≤10% cells in the AVs but were the predominant cell lineage in BHVs (≥80% cells). Albeit cells with uncertain immunophenotype were rarely encountered in the AVs (≤5% cells), they were commonly found in BHVs (≥80% cells). Whilst cell conversions in the AVs were limited to the endothelial-to-mesenchymal transition (represented by CD31+α-SMA+ cells) and the formation of endothelial-like (CD31+CD68+) cells at the AV surface, BHVs harboured numerous macrophages with a transitional phenotype, mostly CD45+CD31+, CD45+α-SMA+, and CD68+α-SMA+. In contrast to immunostaining, which was unable to predict cell function in the BHVs, our whole-specimen, nondestructive electron microscopy approach (EM-BSEM) was able to distinguish between quiescent and matrix-degrading macrophages, foam cells, and multinucleated giant cells to conduct the ultrastructural analysis of organelles and the ECM, and to preserve tissue integrity. Hence, we suggest EM-BSEM as a technique of choice for studying the cellular landscape of BHVs.

Graft rejection in paediatric congenital heart disease

Congenital heart disease (CHD) affects around 1.35 million neonates worldwide per annum, and surgical repair is necessary in approximately 25% of cases. Xenografts, usually of bovine or porcine origin, are often used for the surgical reconstruction. These xenografts elicit an immune response due to significant immunological incompatibilities between host and donor. Current techniques to dampen the initial hyperacute rejection response involve aldehyde fixation to crosslink xenoantigens, such as galactose-α1,3-galactose and N-glycolylneuraminic acid. While this temporarily masks the epitopes, aldehyde fixation is a suboptimal solution, degrading over time, resulting in cytotoxicity and rejection. The immune response to foreign tissue eventually leads to chronic inflammation and subsequent graft failure, necessitating reintervention to replace the defective bioprosthetic. Decellularisation to remove immunoincompatible material has been suggested as an alternative to fixation and may prove a superior solution. However, incomplete decellularisation poses a significant challenge, causing a substantial immune rejection response and subsequent graft rejection. This review discusses commercially available grafts used in surgical paediatric CHD intervention, looking specifically at bovine jugular vein conduits as a substitute to cryopreserved homografts, as well as decellularised alternatives to the aldehyde-fixed graft. Mechanisms of biological prosthesis rejection are explored, including the signalling cascades of the innate and adaptive immune response. Lastly, emerging strategies of intervention are examined, including the use of tissue from genetically modified pigs, enhanced crosslinking and decellularisation techniques, and augmentation of grafts through in vitro recellularisation or functionalisation with human surface proteins.

Soft Biomimetic Approach for the Development of Calcinosis-Resistant Glutaraldehyde-Fixed Biomaterials for Cardiovascular Surgery

Pathological aseptic calcification is the most common form of structural valvular degeneration (SVD), leading to premature failure of heart valve bioprostheses (BHVs). The processing methods used to obtain GA-fixed pericardium-based biomaterials determine the hemodynamic characteristics and durability of BHVs. This article presents a comparative study of the effects of several processing methods on the degree of damage to the ECM of GA-fixed pericardium-based biomaterials as well as on their biostability, biocompatibility, and resistance to calcification. Based on the assumption that preservation of the native ECM structure will enable the creation of calcinosis-resistant materials, this study provides a soft biomimetic approach for the manufacture of GA-fixed biomaterials using gentle decellularization and washing methods. It has been shown that the use of soft methods for preimplantation processing of materials, ensuring maximum preservation of the intactness of the pericardial ECM, radically increases the resistance of biomaterials to calcification. These obtained data are of interest for the development of new calcinosis-resistant biomaterials for the manufacture of BHVs.

Fibrin deposition on bovine pericardium tissue used for bioprosthetic heart valve drives its calcification

Background

Bioprosthetic heart valves (BHVs) are less thrombogenic than mechanical prostheses; however, BHV thrombosis has been proposed as a risk factor for premature BHV degeneration.

Objectives

We aimed to explore whether fibrin deposition on bovine pericardium tissue could lead to calcification.

Method

Fibrin clot was obtained by blending three reagents, namely, CRYOcheck™ Pooled Normal Plasma (4/6), tissue factor + phospholipids (Thrombinoscope BV), and 100 mM calcium (1/6), and deposited on pericardium discs. Non-treated and fibrin-treated bovine pericardium discs were inserted into the subcutaneous tissue of 12-day-old Wistar rats and sequentially explanted on days 5, 10, and 15. Calcium content was measured with acetylene flame atomic absorption spectrophotometry. Histological analysis was performed using hematoxylin-eosin staining, Von Kossa staining, and immunohistochemistry.

Results

Calcification levels were significantly higher in fibrin-treated bovine pericardium discs compared to those in non-treated bovine pericardium discs (27.45 ± 23.05 µg/mg vs. 6.34 ± 6.03 µg/mg on day 5, 64.34 ± 27.12 µg/mg vs. 34.21 ± 19.11 µg/mg on day 10, and 64.34 ± 27.12 µg/mg vs. 35.65 ± 17.84 µg/mg on day 15; p < 0.001). Von Kossa staining confirmed this finding. In hematoxylin-eosin staining, the bovine pericardium discs were more extensively and deeply colonized by inflammatory-like cells, particularly T lymphocytes (CD3+ cells), when pretreated with fibrin.

Conclusion

Fibrin deposition on bovine pericardium tissue treated with glutaraldehyde, used for BHV, led to increased calcification in a rat model. BHV thrombosis could be one of the triggers for calcification and BHV deterioration.

Bioprosthetic Valve Deterioration: Accumulation of Circulating Proteins and Macrophages in the Valve Interstitium

Histologic evaluations revealed excessive accumulations of macrophages and absence of fibroblastic interstitial cells in explanted bioprosthetic valves. Comprehensive gene and protein expression analysis and histology unveiled an accumulation of fibrinogen and plasminogen, an activator of infiltrated macrophages, from degenerated valve surfaces in the interstitial spaces. These pathologies were completely reproduced in a goat model replaced with an autologous pericardium-derived aortic valve. Further preclinical animal experiments using goats demonstrated that preventing infiltration of macrophages and circulating proteins by increasing collagen density and leaflet strength is an effective treatment option.

Patient-specific fluid simulation of transcatheter mitral valve replacement in mitral annulus calcification

Introduction

Transcatheter mitral valve replacement is a promising alternative to open-heart surgery in elderly patients. Patients with severe mitral annulus calcification (MAC) are a particularly high-risk population, where postprocedural complications can have catastrophic effects. Amongst these, obstruction of the left ventricular outflow tract can lead to ventricular hypertrophic remodeling and subsequent heart failure, while subclinical valve thrombosis can result in early bioprosthetic valve failure.

Methods

To elucidate the mechanisms of left ventricular outflow tract obstruction and valve thrombosis following valve-in-MAC procedures, we used image processing and Computational Fluid Dynamics (CFD) software to generate patient- and device-specific models based on preprocedural CT data. Personalized computer simulations were performed to predict the left ventricular haemodynamics after implantation in three patients with severe MAC.

Results

The simulations have successfully captured the increased pressure gradient in the left ventricular outflow tract as a result of the partial obstruction due to the implanted valve. Regions of wall shear stress above the threshold value for platelet activation were also observed on the bioprosthetic frame as a result of the reduced outflow tract area, which led to increases in flow resistance and blood residence time inside the ventricle. Consistent with these findings, areas of slow recirculating flow and blood stasis formed near the valve frame, creating potential pro-thrombotic conditions.

Discussion

This study provides insight into the relationship between size and shape of the outflow tract post-implantation, pressure gradients and pro-thrombotic flow metrics such as wall shear stress and blood residence time. Results show the potential of CFD modeling to bring key functional metrics into preprocedural assessment for a comprehensive evaluation of post-procedural risks beyond anatomical factors. Following further validation and extension to the atrial chamber, this approach can provide an in-depth analysis of the likelihood of valvular thrombosis.

A functionalized biological heart valve by double bond crosslinking with enhanced biocompatibility and antithrombogenicity

With the advancement of minimally invasive interventional therapy, biological heart valves (BHVs) have been extensively used in clinics. However, BHVs are generally prone to degeneration within 10-15 years after implantation due to defects including cytotoxicity, immune response, calcification and thrombosis, which are closely related to glutaraldehyde-crosslinking. In this work, we prepared a functionalized BHV through the in situ polymerization of methacrylated porcine pericardium and 2-hydroxyethyl methacrylate to avoid and overcome the defects of glutaraldehyde-crosslinked BHVs. The functionalized BHV was proven to be stable against enzymatic degradation and compatible towards HUVECs. After implantation in rats subcutaneously, a significantly mitigated immune response and reduced calcification were observed in the functionalized BHV. With the grafting of hydrophilic 2-hydroxyethyl methacrylate polymers, the antithrombogenicity of BHV was markedly enhanced by resisting the unfavorable adhesion of blood components. Moreover, the hydrodynamics of the functionalized BHV totally conformed to ISO 5840-3 under a wide range of simulated physiological conditions. These results indicate that the functionalized BHV with enhanced biocompatibility, anticalcification property and antithrombogenicity exhibited a low risk of degeneration and should be explored for further application.

Hybrid heart valves with VEGF-loaded zwitterionic hydrogel coating for improved anti-calcification and re-endothelialization

With the aging of the population in worldwide, valvular heart disease has become one of the most prominent life-threatening diseases in human health, and heart valve replacement surgery is one of the therapeutic methods for valvular heart disease. Currently, commercial bioprosthetic heart valves (BHVs) for clinical application are prepared with xenograft heart valves or pericardium crosslinked by glutaraldehyde. Due to the residual cell toxicity from glutaraldehyde, heterologous antigens, and immune response, there are still some drawbacks related to the limited lifespan of bioprosthetic heart valves, such as thrombosis, calcification, degeneration, and defectiveness of re-endothelialization. Therefore, the problems of calcification, defectiveness of re-endothelialization, and poor biocompatibility from the use of bioprosthetic heart valve need to be solved. In this study, hydrogel hybrid heart valves with improved anti-calcification and re-endothelialization were prepared by taking decellularized porcine heart valves as scaffolds following grafting with double bonds. Then, the anti-biofouling zwitterionic monomers 2-methacryloyloxyethyl phosphorylcholine (MPC) and vascular endothelial growth factor (VEGF) were utilized to obtain a hydrogel-coated hybrid heart valve (PEGDA-MPC-DHVs@VEGF). The results showed that fewer platelets and thrombi were observed on the surface of the PEGDA-MPC-DHVs@VEGF. Additionally, the PEGDA-MPC-DHVs@VEGF exhibited excellent collagen stability, biocompatibility and re-endothelialization potential. Moreover, less calcification deposition and a lower immune response were observed in the PEGDA-MPC-DHVs@VEGF compared to the glutaraldehyde-crosslinked DHVs (Glu-DHVs) after subcutaneous implantation in rats for 30 days. These studies demonstrated that the strategy of zwitterionic hydrogels loaded with VEGF may be an effective approach to improving the biocompatibility, anti-calcification and re-endothelialization of bioprosthetic heart valves.

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A new and promising strategy of overcoming defects of bioprosthetic heart valves.

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The zwitterionic hydrogel with VEGF is utilized to improve anti-calcification and re-endothelialization properties of heart valves.

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The hybrid heart valves with a VEGF-loaded zwitterionic hydrogel coating exhibits excellent biocompatibility.

Inhibition of advanced glycation end product formation and serum protein infiltration in bioprosthetic heart valve leaflets: Investigations of anti-glycation agents and anticalcification interactions with ethanol pretreatment

Bioprosthetic heart valves (BHV) fabricated from heterograft tissue, such as glutaraldehyde pretreated bovine pericardium (BP), are the most frequently used heart valve replacements. BHV durability is limited by structural valve degeneration (SVD), mechanistically associated with calcification, advanced glycation end products (AGE), and serum protein infiltration. We investigated the hypothesis that anti-AGE agents, Aminoguanidine, Pyridoxamine [PYR], and N-Acetylcysteine could mitigate AGE-serum protein SVD mechanisms in vitro and in vivo, and that these agents could mitigate calcification or demonstrate anti-calcification interactions with BP pretreatment with ethanol. In vitro, each of these agents significantly inhibited AGE-serum protein infiltration in BP. However, in 28-day rat subdermal BP implants only orally administered PYR demonstrated significant inhibition of AGE and serum protein uptake. Furthermore, BP PYR preincubation of BP mitigated AGE-serum protein SVD mechanisms in vitro, and demonstrated mitigation of both AGE-serum protein uptake and reduced calcification in vivo in 28-day rat subdermal BP explants. Inhibition of BP calcification as well as inhibition of AGE-serum protein infiltration was observed in 28-day rat subdermal BP explants pretreated with ethanol followed by PYR preincubation. In conclusion, AGE-serum protein and calcification SVD pathophysiology are significantly mitigated by both PYR oral therapy and PYR and ethanol pretreatment of BP.

Mechanisms and Drug Therapies of Bioprosthetic Heart Valve Calcification

Valve replacement is the main therapy for valvular heart disease, in which a diseased valve is replaced by mechanical heart valve (MHV) or bioprosthetic heart valve (BHV). Since the 2000s, BHV surpassed MHV as the leading option of prosthetic valve substitute because of its excellent hemocompatible and hemodynamic properties. However, BHV is apt to structural valve degeneration (SVD), resulting in limited durability. Calcification is the most frequent presentation and the core pathophysiological process of SVD. Understanding the basic mechanisms of BHV calcification is an essential prerequisite to address the limited-durability issues. In this narrative review, we provide a comprehensive summary about the mechanisms of BHV calcification on 1) composition and site of calcifications; 2) material-associated mechanisms; 3) host-associated mechanisms, including immune response and foreign body reaction, oxidative stress, metabolic disorder, and thrombosis. Strategies that target these mechanisms may be explored for novel drug therapy to prevent or delay BHV calcification.

[Screening analysis of proteolytic enzymes and their inhibitors in the leaflets of epoxy-treated bioprosthetic heart valves explanted due to dysfunction]

Bioprosthetic heart valves (BHVs) are known for their lower thrombogenicity rates and excellent hemodynamic parameters similar to native valves. However, the lifespan of these medical devices is limited to 15 years due to the structural valve degeneration. One of the mechanisms underlying functional impairment and calcification of BHVs includes proteolytic degradation of biomaterials. However, proteases found in xenogeneic BHVs tissue remain poorly studied. In this study using the dot blot assay, we have performed a screening analysis of proteolytic enzymes and their inhibitors in the leaflets of five BHVs explanted due to their dysfunction. Five aortic valves (AVs) explanted due to calcific aortic valve disease were studied as a comparison group. The results of the study have demonstrated that at least 17 proteases and 19 of their inhibitors can be found in BHVs. In the AVs 20 proteases and 21 their inhibitors were identified. Small quantitative differences were noted between proteomic profiles of the BHVs and AVs. Matrix metalloproteinases (MMPs) were expressed in BHVs and AVs at comparable levels, but the level of tissue inhibitors of metalloproteinases-1/-2 and RECK protein in implant tissues was lower than in natural valves. Probably, excessive activity of MMPs cannot be counterbalanced by their inhibitors in BHVs and therefore MMPs can degrade prosthetic biomaterial. Moreover, the detection of a wide range of proteolytic enzymes and their inhibitors in the degenerated BHVs suggests the existence of several pathophysiological pathways that can lead to structural valve degeneration.

Longitudinal Hemodynamics of Aortic Bioprosthetic Valve in Hemodialysis Patients

We examined the hemodynamic profile of bioprosthetic aortic valves in patients on hemodialysis (HD), longitudinally, and assess the incidence of adverse changes detected by echocardiography. Of 1,146 consecutive patients with severe aortic stenosis who underwent bioprosthetic aortic valve replacement (AVR), 148 patients had end-stage renal disease requiring HD. Each patient on HD was matched one-to-one with a non-HD patient on the basis of propensity scores. The mean follow-up period was 3.3 years for the HD group and 5.9 years for the non-HD group. Follow-up information was available for 95.2%. Postoperative trends of valve hemodynamics derived from linear mixed-effect models showed significant group vs time interactions between the two groups. Stable hemodynamics was consistently observed in the non-HD group, whereas the HD group showed a decrease of -0.06 cm²/y (95% confidence interval (CI), -0.10 to -0.02) in effective orifice area, an increase of 0.8 mm Hg/year (95% CI, 0.4-1.1) in mean pressure gradient, and an increase of 0.08 m/s/year (95%CI, 0.02-0.13) in peak velocity. Cumulative incidence function of SVD more than stage 2 was significantly higher in the HD group (13.1% vs 3.1% at 5 years, Gray test p = 0.01). In a multivariable Fine-Gray analysis, diabetes was independently associated with SVD more than stage 2 in the HD group (subhazard ratio, 1.91; 95% CI, 1.25-2.89; p = 0.02). Survival free-from stenotic-type SVD was significantly lower in HD patients undergoing bioprosthetic AVR. Diabetes was independently associated with postoperative stenotic-type SVD in HD patients.

Detecting native and bioprosthetic aortic valve disease using 18F-sodium fluoride: Clinical implications

Calcific aortic valve disease is the most common valvular disease and confers significant morbidity and mortality. There are currently no medical therapies that successfully halt or reverse the disease progression, making surgical replacement the only treatment currently available. The majority of patients will receive a bioprosthetic valve, which themselves are prone to degeneration and may also need replaced, adding to the already substantial healthcare burden of aortic stenosis. Echocardiography and computed tomography can identify late-stage manifestations of the disease process affecting native and bioprosthetic aortic valves but cannot detect or quantify early molecular changes. 18F-fluoride positron emission tomography, on the other hand, can non-invasively and sensitively assess disease activity in the valves. The current review outlines the pivotal role this novel molecular imaging technique has played in improving our understanding of native and bioprosthetic aortic valve disease, as well as providing insights into its feasibility as an important future research and clinical tool.

Noncalcific Mechanisms of Bioprosthetic Structural Valve Degeneration

Bioprosthetic heart valves (BHVs) largely circumvent the need for long‐term anticoagulation compared with mechanical valves but are increasingly susceptible to deterioration and reduced durability with reoperation rates of ≈10% and 30% at 10 and 15 years, respectively. Structural valve degeneration is a common, unpreventable, and untreatable consequence of BHV implantation and is frequently characterized by leaflet calcification. However, 25% of BHV reoperations attributed to structural valve degeneration occur with minimal leaflet mineralization. This review discusses the noncalcific mechanisms of BHV structural valve degeneration, highlighting the putative roles and pathophysiological relationships between protein infiltration, glycation, oxidative and mechanical stress, and inflammation and the structural consequences for surgical and transcatheter BHVs.

Degeneration of Bioprosthetic Heart Valves: Update 2020

The implantation of bioprosthetic heart valves (BHVs) is increasingly becoming the treatment of choice in patients requiring heart valve replacement surgery. Unlike mechanical heart valves, BHVs are less thrombogenic and exhibit superior hemodynamic properties. However, BHVs are prone to structural valve degeneration (SVD), an unavoidable condition limiting graft durability. Mechanisms underlying SVD are incompletely understood, and early concepts suggesting the purely degenerative nature of this process are now considered oversimplified. Recent studies implicate the host immune response as a major modality of SVD pathogenesis, manifested by a combination of processes phenocopying the long‐term transplant rejection, atherosclerosis, and calcification of native aortic valves. In this review, we summarize and critically analyze relevant studies on (1) SVD triggers and pathogenesis, (2) current approaches to protect BHVs from calcification, (3) obtaining low immunogenic BHV tissue from genetically modified animals, and (4) potential strategies for SVD prevention in the clinical setting.

Glycation and Serum Albumin Infiltration Contribute to the Structural Degeneration of Bioprosthetic Heart Valves

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Two novel and interacting mechanisms contributing to BHV SVD are reported: glycation and serum albumin infiltration.

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Glycation product formation and serum albumin deposition were observed in 45 clinical BHV explanted due to SVD as well as BHV tissue subcutaneously implanted in rats.

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In vitro exposure to glycation and serum albumin elicited collagen network misalignment similar to that seen in clinical and rat explant BHV tissue.

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Glycation was sufficient to impair BHV hydrodynamic function in ISO-5840-compliant pulse duplication testing and concomitant serum albumin infiltration exacerbated these effects.

Valvular heart diseases are associated with significant cardiovascular morbidity and mortality, and often require surgical and/or percutaneous repair or replacement. Valve replacement is limited to mechanical and biological prostheses, the latter of which circumvent the need for lifelong anticoagulation but are subject to structural valve degeneration (SVD) and failure. Although calcification is heavily studied, noncalcific SVD, which represent roughly 30% of BHV failures, is relatively underinvestigated. This original work establishes 2 novel and interacting mechanisms—glycation and serum albumin incorporation—that occur in clinical valves and are sufficient to induce hallmarks of structural degeneration as well as functional deterioration.

Valve Interstitial Cell-Specific Cyclooxygenase-1 Associated With Calcification of Aortic Valves

BACKGROUND

The molecular mechanisms underlying aortic valve calcification are poorly understood. Here, we aimed to identify the master regulators of calcification by comparison of genes in valve interstitial cells (VICs) with calcified and noncalcified aortic valves.

METHODS

Calcified aortic valves were surgically excised from patients with aortic valve stenosis who required aortic valve replacements. Noncalcified and calcified sections were obtained from aortic valve leaflets. Collagenase-digested tissues were seeded into dishes, and VICs adhering to the dishes were cultured for 3 weeks, followed by comprehensive gene expression analysis. Functional analyses of identified proteins were performed by in vitro calcification assays. Tissue localization was determined by immunohistochemical staining for normal (n = 11) and stenotic valves (n = 30).

RESULTS

We found 87 genes showing greater than a twofold change in calcified tissues. Among these genes, 68 were downregulated and 19 were upregulated. Cyclooxygenase-1 (COX1) messenger RNA and protein levels were upregulated in VICs from calcified tissues. The COX1 messenger RNA and protein levels in VICs were also strongly increased by stimulation with osteoblast differentiation medium. These were VIC-specific phenotypes and were not observed in other cell types. Immunohistochemical staining revealed that COX1-positive VICs were specifically localized in the calcified area of aortic valve tissues.

CONCLUSIONS

The VIC-specific COX1 overexpression played a crucial role in calcification by promoting osteoblast differentiation in aortic valve tissues.

A simple mouse model of pericardial adhesions

Background

Postoperative pericardial adhesions are considered a risk factor for redo cardiac surgery. Several large- and medium-size animal models of pericardial adhesions have been reported, but small animal models for investigating the development of anti-adhesion materials and molecular mechanisms of this condition are lacking. In this study, we aimed to establish a simple mouse model of pericardial adhesions to address this gap.

Methods

We administered blood, minocycline, picibanil, and talc into the murine pericardial cavity via one-shot injection. Micro-computed tomography analyses of contrast agent-injected mice were carried out for methodological evaluation. We investigated various dosages and treatment durations for molecules identified to be inducers of pericardial adhesion. The adhesive grade was quantified by scoring the strength and volume of adhesion tissues at sacrificed time points. Histological staining with hematoxylin and eosin and Masson’s trichrome, and immunostaining for F4/80 or αSMA was performed to investigate the structural features of pericardial adhesions, and pathological features of the pericardial adhesion tissue were compared with human clinical specimens.

Results

Administration of talc resulted in the most extensive pericardial adhesions. Micro-computed tomography imaging data confirmed that accurate injection into the pericardial cavity was achieved. We found the optimal condition for the formation of strong pericardial adhesions to be injection of 2.5 mg/g talc for 2 weeks. Furthermore, histological analysis showed that talc administration led to an invasion of myofibroblasts and macrophages in the pericardial cavity and epicardium, consistent with pathological findings in patients with left ventricular assistive devices.

Conclusions

We successfully established a simple mouse model of talc-induced pericardial adhesions, which mimics human pathology and could contribute to solving the clinical issues related to pericardial adhesions.