Innate and adaptive immunity: the understudied driving force of heart valve disease

Calcific aortic valve disease (CAVD), and its clinical manifestation that is calcific aortic valve stenosis, is the leading cause for valve disease within the developed world, with no current pharmacological treatment available to delay or halt its progression. Characterized by progressive fibrotic remodelling and subsequent pathogenic mineralization of the valve leaflets, valve disease affects 2.5% of the western population, thus highlighting the need for urgent intervention. Whilst the pathobiology of valve disease is complex, involving genetic factors, lipid infiltration, and oxidative damage, the immune system is now being accepted to play a crucial role in pathogenesis and disease continuation. No longer considered a passive degenerative disease, CAVD is understood to be an active inflammatory process, involving a multitude of pro-inflammatory mechanisms, with both the adaptive and the innate immune system underpinning these complex mechanisms. Within the valve, 15% of cells evolve from haemopoietic origin, and this number greatly expands following inflammation, as macrophages, T lymphocytes, B lymphocytes, and innate immune cells infiltrate the valve, promoting further inflammation. Whether chronic immune infiltration or pathogenic clonal expansion of immune cells within the valve or a combination of the two is responsible for disease progression, it is clear that greater understanding of the immune systems role in valve disease is required to inform future treatment strategies for control of CAVD development.

Interferons Are Pro-Inflammatory Cytokines in Sheared-Stressed Human Aortic Valve Endothelial Cells

Calcific aortic valve disease (CAVD) is an athero-inflammatory process. Growing evidence supports the inflammation-driven calcification model, mediated by cytokines such as interferons (IFNs) and tumor necrosis factor (TNF)-α. Our goal was investigating IFNs' effects in human aortic valve endothelial cells (VEC) and the potential differences between aortic (aVEC) and ventricular (vVEC) side cells. The endothelial phenotype was analyzed by Western blot, qPCR, ELISA, monocyte adhesion, and migration assays. In mixed VEC populations, IFNs promoted the activation of signal transducers and activators of transcription-1 and nuclear factor-κB, and the subsequent up-regulation of pro-inflammatory molecules. Side-specific VEC were activated with IFN-γ and TNF-α in an orbital shaker flow system. TNF-α, but not IFN-γ, induced hypoxia-inducible factor (HIF)-1α stabilization or endothelial nitric oxide synthase downregulation. Additionally, IFN-γ inhibited TNF-α-induced migration of aVEC. Also, IFN-γ triggered cytokine secretion and adhesion molecule expression in aVEC and vVEC. Finally, aVEC were more prone to cytokine-mediated monocyte adhesion under multiaxial flow conditions as compared with uniaxial flow. In conclusion, IFNs promote inflammation and reduce TNF-α-mediated migration in human VEC. Moreover, monocyte adhesion was higher in inflamed aVEC sheared under multiaxial flow, which may be relevant to understanding the initial stages of CAVD.

Crosslinking porcine aortic valve by radical polymerization for the preparation of BHVs with improved cytocompatibility, mild immune response, and reduced calcification

Over one million artificial heart valve transplantations are performed each year due to valvular stenosis or regurgitation. Among them, bioprosthetic heart valves (BHVs) are increasingly being used because of the absence of the need for lifelong anticoagulation. Almost all of the commercial BHVs are treated with Glutaraldehyde (GLUT). As GLUT-treated BHVs are prone to calcification and structural degradation, their durability is greatly reduced with a service life of only 12-15 years. The physiological structure and mechanical properties of the porcine aortic valve (PAV) are closer to that of a human heart valve, so in this study, PAV is used as the model to explore the comprehensive properties of the prepared BHVs by radical polymerization crosslinking method. We found that PAV treated by radical polymerization crosslinking method showed similar ECM stability and biaxial mechanical properties with GLUT-treated PAV. However, radical polymerization crosslinked PAV exhibited better cytocompatibility and endothelialization potential in vitro cell experiment as better anticalcification potential and reduced immune response than GLUT-treated PAV through subcutaneous animal experiments in rats. To conclude, a novel crosslinking method of non-glutaraldehyde fixation of xenogeneic tissues for the preparation of BHVs is expected.

Simvastatin reduces the TLR4-induced inflammatory response in human aortic valve interstitial cells

BACKGROUND

Calcific aortic stenosis is a chronic inflammatory disease. Proinflammatory stimulation via toll-like receptor 4 (TLR4) causes the aortic valve interstitial cell (AVIC) to undergo phenotypic change. The AVIC first assumes an inflammatory phenotype characterized by the production of inflammatory mediators such as intercellular adhesion molecule-1 (ICAM-1), interleukin-8 (IL-8), and monocyte chemoattractant protein-1 (MCP-1). This change has been linked with an osteogenic phenotypic response. Statins have recently been shown to have anti-inflammatory properties. We therefore hypothesized that statins may have an anti-inflammatory effect on human AVICs by downregulation of TLR4-stimulated inflammatory responses. Our purposes were (1) to determine the effect of simvastatin on TLR4-induced expression of inflammatory mediators in human AVICs and (2) to determine the mechanism(s) through which simvastatin exert this effect.

MATERIALS AND METHODS

Human AVICs were isolated from the explanted hearts of four patients undergoing cardiac transplantation. Cells were treated with simvastatin (50 μM) for 1 h before stimulation with TLR4 agonist lipopolysaccharide (LPS, 0.2 μg/mL). Immunoblotting (IB) was used to analyze cell lysates for ICAM-1 expression, and enzyme-linked immunosorbent assay was used to detect IL-8 and MCP-1 in cell culture media. Likewise, lysates were analyzed for TLR4 and nuclear factor-kappa B activation (IB). After simvastatin treatment, lysates were analyzed for TLR4 levels (IB). Statistics were by analysis of variance (P < 0.05).

RESULTS

Simvastatin reduced TLR4-induced ICAM-1, IL-8, and MCP-1 expression in AVICs. Simvastatin down-regulated TLR4 levels and suppressed TLR4-induced phosphorylation of nuclear factor-kappa B.

CONCLUSIONS

These data demonstrate the potential of a medical therapy (simvastatin) to impact the pathogenesis of aortic stenosis.

Lymphocyte and monocyte subpopulations in severe aortic stenosis at the time of surgical intervention

INTRODUCTION

Aortic stenosis (AS) is the most common acquired valvular heart disease in adults. Immune system involvement becomes evident during AS development. We sought to investigate the role of different circulating lymphocyte and monocyte subpopulations, with focus on CD4⁺CD8⁺ and natural killer T (NKT) cells, in AS.

MATERIAL AND METHODS

Blood samples and aortic valves were obtained from patients undergoing elective aortic valve surgery. Valves were dissected and underwent genetic analyses and calcium content assessment. Lymphocytes and monocytes subsets were assessed by flow cytometry.

RESULTS

Thirty-eight AS patients were studied. Maximal transvalvular pressure gradient (PG_max) as well as mean transvalvular pressure gradient (PG_mean) correlated with the CD4⁺CD8⁺ lymphocyte count (r=0.35, P=.03 and r=0.43, P=.006, respectively) and fraction (r=0.43, P=.007 and r=0.48, P=.002, respectively). PG_max and PG_mean correlated with CD16⁺CD56⁺CD3⁺ NKT cell count (r=0.39, P=.01 and r=0.43, P=.007, respectively) and fraction (r=0.49, P=.002 and r=0.47, P=.003, respectively). The classical monocyte subpopulation increased after the surgery by 68% (P<.0001). Patients after mini-sternotomy surgery had 47% lower nonclassical monocyte counts than those with full-sternotomy (P=.03). Patients treated with statins had significantly lower postoperative levels of both classical (-25%, P=.04) and nonclassical monocytes (-37%, P=.004) than nontreated individuals.

CONCLUSIONS

In patients with severe isolated AS, CD4⁺CD8⁺ T cells and CD16⁺CD56⁺CD3⁺ NKT cells are associated with AV pressure gradients. Postoperative monocyte levels are affected by procedure invasiveness and use of statins.

Immunologic Responses in Biological and Mechanical Valve Prostheses: Inflammation and Functionality Are Not Always Related

BACKGROUND AND AIM OF THE STUDY

The aim of this retrospective study was to evaluate the inflammatory response in patients with aortic and/or mitral prostheses, and to correlate the level of inflammatory markers with prosthesis functionality.

METHODS

A total of 48 patients with biological or mechanical prostheses was included in the study, in which levels of tumor necrosis factor-alpha (TNFα), interleukin (IL)-1, -4, and -6, interferon-gamma (IFNγ), osteopontin (OPN), intercellular adhesion molecule (ICAM), vascular cell adhesion molecule (VCAM), endothelin-1 and C-reactive protein were analyzed. Functionality of the prosthesis was evaluated using transthoracic echocardiography at three years after surgery.

RESULTS

The mean period from the date of surgery was seven years. High levels of IL-1 were found in patients with mechanical prostheses compared to those with bioprostheses (p = 0.04). Patients with aortic bioprostheses and stenosis had higher levels of OPN and endothelin-1, those with aortic mechanical prostheses with stenosis had increased levels of matrix metalloproteinase (MMP)-9, OPN and ICAM, and those with aortic mechanical leakage had increased levels of MMP-1 and endothelin-1. In mitral bioprostheses with leakage of endothelin-1, ICAM and MMP-9 levels were increased, while in mechanical prostheses with leakage there were increases of ICAM and endothelin-1. Tricuspid bioprostheses with double lesions had increased levels of OPN and endothelin-1.

CONCLUSIONS

Valvular dysfunction was similar across the types of prosthesis material. IL-1 was increased in subjects with mechanical prostheses independently of dysfunction, while in biological prostheses there were increases in OPN and endothelin-1, and these were related to valvular dysfunction. Given that in the analysis of durability and functionality there were no significant differences between biological and mechanical prostheses, biological prostheses may represent the first treatment option in patients with low economic resources, the elderly, and even young patients.

Autoantibodies and immune complexes to oxidation-specific epitopes and progression of aortic stenosis: Results from the ASTRONOMER trial

BACKGROUND AND AIMS

Elevated levels of lipoprotein(a) [Lp(a)] and oxidized phospholipids on apolipoprotein B-100 (OxPL-apoB) predict the progression of pre-existing mild-to-moderate calcific aortic valve stenosis (CAVS). Whether indirect markers of oxidation-specific epitopes (OSE) are also predictive is not known. The association between IgG and IgM autoantibodies and malondialdehyde-modified low density lipoprotein (MDA-LDL) and IgG and IgM apolipoprotein B immune complexes (apoB-IC), and the hemodynamic progression rate of CAVS was determined in the ASTRONOMER (Aortic Stenosis Progression Observation: Measuring Effects of Rosuvastatin, NCT00800800) trial.

METHODS

Plasma levels of IgG and IgM MDA-LDL and apoB-IC were measured in 220 patients with mild-to-moderate CAVS from the ASTRONOMER trial. The endpoint of this study was the progression rate of CAVS, measured by the annualized increase in peak aortic jet velocity (V_peak) over a median follow-up of 3.5 [2.9-4.5] years.

RESULTS

There was no difference in the progression rate of CAVS across tertiles of IgG and IgM MDA-LDL and apoB-IC levels (all p > 0.05). After multivariable analysis, no marker reached significance level to predict faster CAVS progression or need for aortic valve replacement (all p > 0.05). There was no interaction between the OSE antibody titers and plasma levels of Lp(a) or OxPL-apoB, as well as age, with regards to the progression rate of CAVS.

CONCLUSIONS

Autoantibody titers to MDA-LDL and apoB-IC, which are an indirect measurement of OSE, unlike direct measurements of OxPL-apoB or their major lipoprotein carrier Lp(a), do not predict the progression of CAVS or need for AVR.

Interleukin-23-Dependent γ/δ T Cells Produce Interleukin-17 and Accumulate in the Enthesis, Aortic Valve, and Ciliary Body in Mice

OBJECTIVE

The spondyloarthritides (SpA) are a group of rheumatic diseases characterized by ossification and inflammation of entheseal tissue, the region where tendon attaches to bone. Interleukin-23 (IL-23) is involved in the pathogenesis of SpA by acting on IL-23 receptor (IL-23R) expressed on enthesis-resident lymphocytes. Upon IL-23 binding, CD3+CD4-CD8- tissue-resident lymphocytes secrete IL-17A and IL-22, leading to inflammation, bone loss, and ossification. Knowledge about enthesis-resident lymphocytes remains fragmentary, and the contribution of entheseal γ/δ T cells in particular is not clear. This study was undertaken to investigate the presence of γ/δ T cells in the enthesis.

METHODS

We used 2-photon microscopy and flow cytometry to analyze entheseal lymphocytes from C57BL/6, Tcrd-H2BeGFP, Rorc-GFP, and IL-23R-eGFP mice. To analyze entheseal γ/δ T cells in IL-23-induced inflammation, Tcrd-H2BeGFP mice were crossed with mice of the susceptible B10.RIII background. Hydrodynamic injection of IL-23 minicircle DNA was performed for overexpression of IL-23 and induction of inflammation. Light-sheet fluorescence microscopy was used to visualize arthritic inflammation.

RESULTS

Activated Vγ6+CD27- γ/δ T cells were abundant in uninflamed entheseal tissue and constituted the large majority of retinoic acid receptor-related orphan nuclear receptor γt (RORγt)+IL-23R+ enthesis-resident lymphocytes. Fetal thymus-dependent γ/δ T cells were the main source of IL-17A at the enthesis. Under inflammatory conditions, γ/δ T cells increased in number at the Achilles tendon enthesis, aortic root, and adjacent to the ciliary body.

CONCLUSION

Entheseal γ/δ T cells are derived from fetal thymus and are maintained as self-renewing tissue-resident cells. As main IL-17A producers within tissues exposed to mechanical stress including enthesis, γ/δ T cells are key players in the pathogenesis of IL-23-induced local inflammation.

Antineutrophil Cytoplasmic Antibodies Associated With Infective Endocarditis

To determine the prevalence of antineutrophil cytoplasmic antibodies (ANCA) in patients with infective endocarditis (IE) in internal medicine; and to compare clinical and biochemical features and outcome between patients exhibiting IE with and without ANCA.Fifty consecutive patients with IE underwent ANCA testing. The medical records of these patients were reviewed.Of the 50 patients with IE, 12 exhibited ANCA (24%). ANCA-positive patients with IE exhibited: longer duration between the onset of first symptoms and IE diagnosis (P = 0.02); and more frequently: weight loss (P = 0.017) and renal impairment (P = 0.08), lower levels of C-reactive protein (P = 0.0009) and serum albumin (P = 0.0032), involvement of both aortic and mitral valves (P = 0.009), and longer hospital stay (P = 0.016). Under multivariate analysis, significant factors for ANCA-associated IE were: longer hospital stay (P = 0.004), lower level of serum albumin (P = 0.02), and multiple valve involvement (P = 0.04). Mortality rate was 25% in ANCA patients; death was because of IE complications in all these patients.Our study identifies a high prevalence of ANCA in unselected patients with IE in internal medicine (24%). Our findings further underscore that ANCA may be associated with a subacute form of IE leading to multiple valve involvement and more frequent renal impairment. Because death was due to IE complications in all patients, our data suggest that aggressive therapy may be required to improve such patients' outcome.

C4b-Binding Protein Deposition is Induced in Diseased Aortic Heart Valves, Coinciding with C3d

BACKGROUND AND AIM OF THE STUDY

It has been found recently that activated complement is more widespread in diseased aortic valves compared to the endogenous complement inhibitors C1-inhibitor and clusterin. Previously, another endogenous inhibitor of complement, C4b-binding protein (C4BP) has been described in atherosclerotic diseased coronary arteries. The study aim was to analyze C4BP levels in diseased aortic valves.

METHODS

Aortic valve tissue was derived from surgical procedures and classified as 'degenerative', 'atherosclerotic' or 'atherosclerotic with bacterial infection'. Valves were stained with specific antibodies against C4BP, C3d and caspase-3. Areas of positivity were then quantified using computer- assisted morphometry.

RESULTS

In atherosclerotic valves, the areas of C4BP and C3d positivity (38.8 +/- 0.4% versus 32.7 +/- 1.0%, respectively) were significantly higher compared to the degenerative and control groups. In atherosclerotic valves with bacterial infection, the area of positivity for C4BP was even further increased compared to atherosclerotic valves (65.1 +/- 1.2%; 70.1 +/- 1.9% for C3d). The areas of C4BP and C3d positivity were not significantly different in all groups. Caspase-3 was only present in <10% of endothelial cells in the atherosclerotic valves without bacterial infection and in neutrophilic granulocytes in atherosclerotic valves, with and without bacterial infection.

CONCLUSION

It has been shown for the first time that C4BP is deposited in the diseased aortic valve, coinciding with C3d. The area of C4BP positivity was more extensive compared to the areas of other endogenous complement inhibitors (C1-inhibitor and clusterin).

Non-Cytotoxic Crosslinkers for Heart Valve Tissue Engineering

BACKGROUND AND AIM OF THE STUDY

Currently, no effective crosslinking reagents are available to treat xenogenic decellularized heart valve matrices. The study aim was to evaluate the crosslinking effect of quercetin, catechin, caffeic acid and tannic acid on porcine aortic valve matrices.

METHODS

Cytotoxicity of the different crosslinkers was evaluated. The mechanical properties of crosslinked porcine matrices and control matrices (non-fixed) were examined by tensile strength testing, as was the cytocompatibility of the fixed matrices. Crosslinked and control matrices were implanted subcutaneously in Wistar rats (n = 9) and, after two weeks, their calcium contents were determined using inductively coupled plasma-mass spectrometry. The antibody reaction against porcine tissue in rat serum was also determined.

RESULTS

Cytotoxicity studies showed that crosslinkers, even at high concentrations, did not inhibit cell viability. All crosslinkers except tannic acid improved the mechanical strength of acellular porcine matrices. Moreover, the tensile strength of quercetin-fixed matrices was comparable with that of glutaraldehyde (GTA)-fixed leaflets. Light microscopic evaluation showed that crosslinked matrices caused only a mild lymphocytic inflammatory reaction. Furthermore, quercetin-fixed leaflets exhibited a well-preserved matrix without infiltration of CD3+ cells. After two weeks, calcium levels were 206.33 µg/mg for controls (non-fixed), and 151.33 µg/mg, 181 µg/mg and 163.66 µg/mg for quercetin-, catechin-, and caffeic acid-fixed matrices, respectively. At two weeks after implantation the quercetin-crosslinked matrices also elicited the lowest levels of IgG antibodies.

CONCLUSION

The study results identified quercetin as the most suitable crosslinker for heart valve tissue engineering, and a possible alternative to GTA. Further studies are essential to determine whether quercetin crosslinking will allow autologous cell repopulation in order to create a viable heart valve.

BMP-2 and TGF-β1 mediate biglycan-induced pro-osteogenic reprogramming in aortic valve interstitial cells

Biglycan accumulates in aortic valves affected by calcific aortic valve disease (CAVD), and soluble biglycan upregulates BMP-2 expression in human aortic valve interstitial cells (AVICs) via Toll-like receptor (TLR) 2 and induces AVIC pro-osteogenic reprogramming, characterized by elevated pro-osteogenic activities. We sought to identify the factors responsible for biglycan-induced pro-osteogenic reprogramming in human AVICs. Treatment of AVICs with recombinant biglycan induced the secretion of BMP-2 and TGF-β1, but not BMP-4 or BMP-7. Biglycan upregulated TGF-β1 expression in a TLR4-dependent fashion. Neutralization of BMP-2 or TGF-β1 attenuated the expression of alkaline phosphatase (ALP), osteopontin, and runt-related transcription factor 2 (Runx2) in cells exposed to biglycan. However, neutralization of both BMP-2 and TGF-β1 abolished the expression of these osteogenic biomarkers and calcium deposition. Phosphorylated Smad1 and Smad3 were detected in cells exposed to biglycan, and knockdown of Smad1 or Smad3 attenuated the effect of biglycan on the expression of osteogenic biomarkers. While BMP-2 and TGF-β1 each upregulated the expression of osteogenic biomarkers, an exposure to BMP-2 plus TGF-β1 induced a greater upregulation and results in calcium deposition. We conclude that concurrent upregulation of BMP-2 and TGF-β1 is responsible for biglycan-induced pro-osteogenic reprogramming in human AVICs. The Smad 1/3 pathways are involved in the mechanism of AVIC pro-osteogenic reprogramming.

KEY MESSAGE

Biglycan upregulates BMP-2 and TGF-β1 in human aortic valve cells through TLRs. Both BMP-2 and TGF-β1 are required for aortic valve cell pro-osteogenic reprogramming. Smad signaling pathways are involved in mediating the pro-osteogenic effects of biglycan.

Butyrate impairs atherogenesis by reducing plaque inflammation and vulnerability and decreasing NFκB activation

BACKGROUND & AIMS

Butyrate is a four-carbon fatty acid that presents anti-inflammatory, anti-oxidative and apoptotic properties in colon and several cell lines. Because atherosclerosis has important oxidative and inflammatory components, butyrate could reduce oxidation and inflammation, impairing atherogenesis. We evaluated the effects of butyrate supplementation of butyrate on atherosclerosis and its mechanisms of action.

METHODS AND RESULTS

ApoE knockout mice were fed on chow diet or 1% butyrate-supplemented chow diet (Butyrate) for 10 weeks to assess atherosclerosis lesions area and inflammatory status. Macrophage and endothelial cells were also pretreated with butyrate (0.5 mM) for 2 h before oxLDL stimulation to study oxLDL uptake and pro and anti-inflammatory cytokine production. Butyrate reduced atherosclerosis in the aorta by 50%. In the aortic valve, butyrate reduced CCL2, VCAM1 and MMP2 productions in the lesion site, resulting in a lower migration of macrophage and increased collagen depositions in the lesion and plaque stability. When EA.hy926 cells were pretreated with butyrate, oxLDL uptake, CD36, VCAM1, CCL2 TNF, IL1β and IL6 productions were reduced, whereas IL10 production was increased. These effects were accompanied by a lower activation of NFκB due to a lower nuclear translocation of the p65 subunit.

CONCLUSION

Oral butyrate is able to slow the progression of atherosclerosis by reducing adhesion and migration of macrophages and increasing plaque stability. These actions are linked to the reduction of CD36 in macrophages and endothelial cells, decreased pro-inflammatory cytokines and lower activation of NFκB all of these data support a possible role for butyrate as an atheroprotective agent.

Inflammatory cytokines promote mesenchymal transformation in embryonic and adult valve endothelial cells

OBJECTIVE

Inflammatory activation of valve endothelium is an early phase of aortic valve disease pathogenesis, but subsequent mechanisms are poorly understood. Adult valve endothelial cells retain the developmental ability to undergo endothelial-to-mesenchymal transformation (EndMT), but a biological role has not been established. Here, we test whether and how inflammatory cytokines (tumor necrosis factor-α and interleukin-6) regulate EndMT in embryonic and adult valve endothelium.

METHODS AND RESULTS

Using in vitro 3-dimensional collagen gel culture assays with primary cells, we determined that interleukin-6 and tumor necrosis factor-α induce EndMT and cell invasion in dose-dependent manners. Inflammatory-EndMT occurred through an Akt/nuclear factor-κB-dependent pathway in both adult and embryonic stages. In embryonic valves, inflammatory-EndMT required canonical transforming growth factor-β signaling through activin receptor-like kinases 2 and 5 to drive EndMT. In adult valve endothelium, however, inflammatory-induced EndMT still occurred when activin receptor-like kinases 2 and 5 signaling was blocked. Inflammatory receptor gene expression was significantly upregulated in vivo during embryonic valve maturation. Endothelial-derived mesenchymal cells expressing activated nuclear factor-κB were found distal to calcific lesions in diseased human aortic valves.

CONCLUSIONS

Inflammatory cytokine-induced EndMT in valve endothelium is present in both embryonic and adult stages, acting through Akt/nuclear factor-κB, but differently using transforming growth factor-β signaling. Molecular signatures of valve EndMT may be important diagnostic and therapeutic targets in early valve disease.

Elimination of alpha-gal xenoreactive epitope: alpha-galactosidase treatment of porcine heart valves

BACKGROUND AND AIM OF THE STUDY

Porcine heart valves are among the most widely used tissue valves in clinical heart valve implantation. However, immunologic responses have been implicated as potential causes of the limited durability of xenograft heart valves. The study aim was to determine the effectiveness of alpha-galactosidase treatment used to degrade the major xenoreactive antigens found in xenograft heart valves.

METHODS

Fresh porcine heart valves and pericardium treated with alpha-galactosidase were studied to evaluate the xenoreactive galactose (alpha1,3) galactose (alpha-gal) antigen. Removal of the alpha-gal epitope from the porcine heart valve was monitored via 3,3'-diaminobenzidine staining intensity, while the removal of alpha-gal from N-glycans on porcine heart valves treated with recombinant alpha-galactosidase was determined either qualitatively or quantitatively by mass fingerprinting using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The porcine pericardium was used for monitoring the change in mechanical properties after alpha-galactosidase treatment. In addition, the biomechanical modification property of collagen fiber rearrangement on tissue was assessed using transmission electron microscopy (TEM).

RESULTS

Following a 24-h incubation at pH 7.2, 4 degrees C, employing 0.1 U/ml of Bacteroides thetaiotaomicron-derived recombinant alpha-galactosidase, the enzyme effectively removed the alpha-gal epitopes expressed on porcine heart valves. The identification type of alpha-gal N-glycan on fresh aortic valve, aortic wall, pulmonary valve, and pulmonary wall was 7.1%, 10.3%, 6% and 8%, respectively. In the presence of alpha-galactosidase treatment, alpha-gal-containing N-glycans were converted into alpha-gal-negative N-glycans. Likewise, alpha-gal-containing N-glycans were not detected when MALDI-TOF MS quantitative analysis was used. Furthermore, no significant difference was observed in the mechanical properties and findings from TEM in alpha-galactosidase-treated porcine pericardial tissue when compared to fresh porcine pericardium.

CONCLUSION

Alpha-galactosidase can effectively remove the alpha-gal epitope from porcine heart valves and pericardium. This may possibly alleviate harmful xenoreactive immunologic responses by alpha-gal, without adversely affecting the biomechanical properties of the alpha-galactosidase-processed tissue.

Sirt1 inhibits resistin expression in aortic stenosis

The development of human calcified aortic stenosis (AS) includes age-dependent processes that have been involved in atherosclerosis, such as infiltration of macrophages in aortic valves, which then promote production of many pro-inflammatory cytokines, including resistin. However, the molecular mechanisms contributing to these processes are not established. Since Sirt1 has been shown to modulate macrophage biology and inflammation, we examined its levels in human AS and tested its impact on resistin expression. Sirt1 mRNA (p = 0.01) and protein (p<0.05) levels were reduced in explanted valves from AS patients (n = 51) compared to those from control (n = 11) patients. Sirt1 mRNA levels were negatively associated with resistin mRNA levels quantified in AS valves (p = 0.02). Stimulation of Sirt1 by resveratrol or virus-driven overexpression robustly diminished resistin mRNA and protein expression in macrophages, whereas down-regulation of Sirt1 triggered a large increase in resistin expression. These effects were direct, as chromatin immunoprecipitation assays showed that Sirt1 physically interacted with the resistin promoter region at an AP-1 response element. Moreover, Sirt1 blocked c-jun-induced resistin transactivation in gene reporter assays. These findings demonstrate that, in calcified AS, levels of Sirt1 are reduced whereas those of resistin are increased within aortic valve leaflets. Our results also suggest that this loss of Sirt1 expression alleviates its inhibition of resistin transcription in macrophages. Although the overall contribution of this process to the underlying mechanisms for AS disease development remains unresolved, these observations suggest that modification of Sirt1 expression and/or activity could represent a novel approach against inflammation in AS.

Heart valve engineering: decellularized aortic homograft seeded with human cardiac stromal cells

BACKGROUND AND AIM OF THE STUDY

The adult human heart contains a cardiac mesenchymal stromal cell (CStC) population with residual cardiovascular plasticity. The study aim was to investigate the ability of CStCs to populate decellularized aortic homograft leaflets, without mechanical stimulation.

METHODS

The ability of CStCs to acquire valve endothelial and interstitial cell phenotypes was tested using in vitro assays. First, trypsin-decellularized aortic leaflets were seeded with CStCs under static conditions; tissue section analyses were then performed before and after decellularization, and at 10, 20, and 30 days after reseeding.

RESULTS

Following in vitro treatment, the CStCs differentiated along the endothelial lineage, as shown by their capacity to uptake acetylated low-density lipoprotein and to secrete the pro-angiogenic factor, vascular endothelial growth factor. After seeding, CStCs were able to adhere to the leaflet surface, rescuing up to the 90% of the original cell density and expressing the mature endothelial marker, von Willebrandt factor. The CStC supernatants were also positive for matrix metalloprotease-2 (MMP-2), which confirmed the ability of these cells to penetrate within the leaflet structure; this also suggested that CStCs, once engrafted, would contribute to the extracellular matrix turnover. Accordingly, although at a lower efficiency, CStC repopulation was also evident in the inner portions of the leaflet.

CONCLUSION

Seeded CStCs were able to reconstitute, without mechanical stimulation, an endothelial-like layer and to partially infiltrate decellularized homograft leaflets. Hence, CStCs appear to be a potentially useful cell type for engineered heart valves.

[Effect of decellularization on tissue composition and immunogenicity of porcine and human aortic valves]

OBJECTIVE

To study the changes of tissue composition and immunogenicity of porcine and human aortic valves after decellularization.

METHODS

Three cryopreserved human aortic valves and 4 porcine valves were decellularized with trypsin, and the leaflet tissue was homogenized for SDS-PAGE protein electrophoresis and U-937 migration assay.

RESULTS

Trypsin effectively removed the cells from the valve. SDS-PAGE demonstrated an obvious difference in the tissue composition between porcine and human valves. Although decellularization significantly diminished the differences between the valves, decellularized procine aortic valve stilled contained more protein components (between 26 000 and 43 000) than human valve. U-937 migration assay showed an obvious decrease of cell migration in the valves by decellularization (from 832.7×10(3) to 152.4∓31.1×10(3) for porcine valves, P<0.01, and from 644.9×10(3) to 91.2×10(3) for the human valves, P<0.01). Decellularized porcine valves induced a significantly greater cell migration than decellularized human valves (P<0.05).

CONCLUSION

Decellularization with trypsin can effectively decrease the immunogenicity of human or porcine heart valve, but can not completely eliminate the antigen, and decellularized porcine valve still retain strong immunogenicity.

Side-specific expression of activated leukocyte adhesion molecule (ALCAM; CD166) in pathosusceptible regions of swine aortic valve endothelium

Aortic valve sclerosis (AVS), an early form of aortic valve disease, develops preferentially on the aortic side of valve leaflets, a predilection that is reflected in an heterogeneous side-specific gene expression profile. It has been ascertained that hypercholesterolemia is sufficient to initiate the endothelial expression of activated leukocyte adhesion molecule (ALCAM; CD166), restricted to the aortic side of the leaflet. Intercellular adhesion molecule-1 (ICAM-1) or vascular cell adhesion molecule-1 (VCAM-1)--both of which are more typically associated with early arterial inflammation--are not differentially expressed. ALCAM up-regulation by hypercholesterolemia suggests a side-specific spatial role in the recruitment of leukocytes to AVS sites.

Degeneration and atherosclerosis inducing increased deposition of type IIA secretory phospholipase A2, C-reactive protein and complement in aortic valves cause neutrophilic granulocyte influx

BACKGROUND AND AIM OF THE STUDY

Recent studies have indicated that atherosclerosis-like changes are involved in the pathogenesis of aortic valve stenosis. Increased blood and valve tissue levels of C-reactive protein (CRP) have been reported in patients with aortic valve disease, although the different pathological conditions involved were not analyzed. The study aim was to monitor the deposition of CRP, its activator sPLA2-IIA and its effector complement, and the subsequent influx of neutrophilic granulocytes in degenerative and atherosclerotic aortic valves.

METHODS

Human tricuspid aortic valves (n = 57) obtained at autopsy included five control valves, 36 aortic valves with atherosclerotic changes, and 16 with degenerative changes. All valves were analyzed immunohistochemically for the presence of sPLA2-IIA, CRP, C3d and MPO (to detect neutrophilic granulocytes), and subsequently quantified using computer-assisted morphometry.

RESULTS

In aortic valves with degeneration, the areas of sPLA2-IIA, CRP and complement deposition were all significantly increased compared to control valves. These mediators were even more extensively deposited in atherosclerotically changed aortic valves. The increased deposition of these mediators coincided with a significant increase of neutrophilic granulocytes in atherosclerotic and degenerated aortic valves, compared to control valves.

CONCLUSION

The study results indicate that sPLA2-IIA, CRP, and C3d are significantly more activated in atherosclerotic aortic valves compared to degeneratively changed aortic valves. A significant increase was also identified in neutrophilic granulocytes in non-infectious, diseased valves (atherosclerosis and degeneration).

Tissue-gel electrophoresis enhances antigen removal from porcine aortic valve and bovine pericardium

BACKGROUND AND AIM OF THE STUDY

A tissue-engineered heart valve could provide a living prosthesis with characteristics of an ideal valve replacement. One approach to scaffolding a tissue-engineered heart valve is through the 'decellularization' of xenogeneic tissues. Concerns regarding the completeness of antigen removal associated with current detergent-based decellularization treatments have been raised. The study aim was to evaluate antigen removal from candidate xenogeneic bioscaffolds using a novel tissue-gel electrophoresis (TGE) method.

METHODS

Porcine aortic valve (PAV) conduit and bovine pericardium (BP) were treated sequentially with hypotonic lysis, sodium dodecyl sulfate (SDS), and TGE. The completeness of antigen removal was evaluated by immunoblot analysis of extractable soluble proteins using rabbit anti-PAV or anti-BP serum. Tissues were also evaluated by hematoxylin and eosin histology.

RESULTS

TGE enhanced antigen removal from both the PAV and BP. The effects of TGE were shown to depend on the SDS concentration and voltage (60 versus 120 V), but to be independent of time after 4 h. The effects of TGE were detectable both before and after 96 h aqueous washout. Treatment with 1.0% SDS with TGE (120 V for 4 h) resulted in complete acellularity and no detectable soluble protein antigens from the PAV conduit.

CONCLUSION

TGE is a promising adjunctive decellularization method for generating non-immunoreactive bioscaffolds from xenogeneic tissues.

Removal of alpha-Gal epitopes from porcine aortic valve and pericardium using recombinant human alpha galactosidase A

It has been reported that the immune response due to alpha-Gal epitopes is an important factor in tissue valve failure. The elimination of the interaction between the natural anti-Gal antibodies and alpha-gal epitopes on the xenografts is a prerequisite to the success of xenografts in humans. Previously, we reported that the green coffee bean alpha-galactosidase could remove all alpha-Gal epitopes from cell surface of porcine aortic valve and pericardial tissue, but it has limitations on cost effectiveness. In this study we wanted to know whether the recently produced recombinant human alpha-galactosidase A has the same effective enzymatic activity as green coffee bean alpha-galactosidase in removing alpha-Gal epitopes from the same tissues. After treating fresh porcine aortic valve and pericardial tissue with recombinant alpha-galactosidase A, each sample was stained with Griffonia simplicifolia type I isolectin B4 indirect immunoperoxidase avidin-biotin technique. We then examined whether the alpha-Gal epitopes were reduced or abolished in each consecutive concentration of recombinant alpha-galactosidase A by comparing the degree of the Griffonia simplicifolia isolectin B4 staining. As a result, the recombinant alpha-galactosidase A could remove cell surface alpha-Gals on porcine aortic valve and pericardial tissue as effectively as green coffee bean alpha-galactosidase.

Immunoblot detection of soluble protein antigens from sodium dodecyl sulfate- and sodium deoxycholate-treated candidate bioscaffold tissues

BACKGROUND AND AIMS OF THE STUDY

The detergent-based 'decellularization' of xenogeneic tissues is one approach to scaffolding a tissue-engineered heart valve construct; however, concern persists regarding the immunogenicity of decellularized xenogeneic bioscaffolds. The study aims were to: (i) develop a sensitive and robust immunoblot-based assay for the detection of soluble protein antigens in xenogeneic bioscaffolds; and (ii) evaluate the completeness of protein antigen removal from sodium dodecyl sulfate (SDS)- or sodium deoxycholate (SD)-treated bovine pericardium (BP) or porcine aortic valve (PAV) conduit.

METHODS

Homogenized BP or PAV were injected into rabbits to generate immune serum towards these tissues. Soluble proteins were extracted from untreated BP and PAV. Immunoblot analyses of the extracts were performed using pre-immune and 14-, 28-, 42-, 56- and 70-day post-immune serum. BP and PAV were treated sequentially with 4 h hypotonic lysis; with 0, 0.01, 0.025, 0.05, 0.1, 0.25 or 0.5% SDS or SD for 24 h; and with 96 h of aqueous wash-out. Immunoblot analyses of protein extracts from treated tissues were performed using 70-day post-immune rabbit serum.

RESULTS

Immunoblot analysis of untreated BP or PAV with pre-immune serum showed no immune banding. The immune banding density increased progressively when immunoblots were performed with 14-day through 70-day post-immune serum. The immunoblot analysis of treated BP and PAV showed that soluble protein antigen removal from SDS- or SD-treated tissues was incomplete.

CONCLUSION

Immunoblot analysis is a sensitive and robust assay for detecting soluble protein xenogeneic antigens after the decellularization of xenogeneic bioscaffolds. Under the study conditions, hypotonic lysis, SDS or SD detergent treatment, and aqueous wash-out-based decellularization of bovine pericardium and porcine aortic valve conduit did not completely remove detectable protein antigens.

Pathogen burden in degenerative aortic valves is associated with inflammatory and immune reactions

BACKGROUND AND AIM OF THE STUDY

The presence of five pathogens was assessed, together with a possible correlation of the total pathogen burden on inflammation and (auto)immunity in aortic stenosis (AS) and degenerative aortic valve bioprosthesis (BP).

METHODS

Diseased valve specimens from a total of 68 patients (52 with AS, 16 with BP) were studied. The presence and localization was assessed of Chlamydia pneumoniae (cHSP60), Helicobacter pylori (HP), cytomegalovirus (CMV), Epstein-Barr virus (EBV) and herpes simplex virus (HSV), as well as of macrophages (CD68), C-reactive protein (CRP) and human heat shock protein 60 (hHSP60), by using immunohistochemical and morphometric analyses.

RESULTS

In the majority of degenerative aortic valves, specific pathogens, inflammation and immunity were localized predominantly in the fibrosa of AS patients, and in superficial regions of the BP. The categorization of valves as having four or more pathogens (n = 37) or fewer pathogens (n = 31) demonstrated an increased signaling of CD68 (p = 0.03) and CRP (p = 0.02). Specifically, cHSP60, HP and hHSP60 levels were increased in valves where one or two bacteria were identified (n = 59) compared to those without bacterial presence (n = 9) (p = 0.04).

CONCLUSION

The pathogen burden may contribute to valvular degeneration by promoting further deleterious inflammatory and (auto)immune processes at the level of the valvular fibrosa.

Endocarditis associated with antineutrophil cytoplasmic antibodies: a case report and review of the literature

We report a case of subacute bacterial endocarditis associated with small vessel vasculitis and a strongly positive cytoplasmic antineutrophil cytoplasmic antibody (c-ANCA) test. It is important to recognize this cause of positive c-ANCA because infectious endocarditis may closely mimic the clinical manifestations of ANCA-associated vasculitides such as Wegener granulomatosis or microscopic polyangiitis. Furthermore, ANCA-associated vasculitis may result in noninfectious endocarditis, which may be confused with bacterial endocarditis. In this paper, we review reported cases of ANCA-positive bacterial endocarditis and compare them to the reported cases of ANCA-associated idiopathic vasculitis with endocardial compromise.

Aortic root replacement with a novel decellularized cryopreserved aortic homograft: Postoperative immunoreactivity and early results

OBJECTIVE

Novel antigen-reduction SynerGraft technology (CryoLife Inc, Kennesaw, Ga) reduces the cellular components of a cadaver homograft with an enzymatic and washing process, leaving the extracellular matrix intact. We report the immunoreactivity (positive panel reactive antibody assay) and early operative results of the CryoLife SynerGraft aortic valve conduit homograft.

METHODS

Twenty-two patients (age 53 +/- 14 years, range 31-80 years) from April 2002 to July 2003 underwent aortic root replacement with a CryoLife SynerGraft aortic valve conduit homograft (CryoLife Inc, Kennesaw, Ga) for congenital or acquired aortic valve disease, aortic aneurysm with aortic valve disease, or native or prosthetic aortic valve endocarditis. Baseline percentage positive panel reactive antibody results were negative (<10%) for all and were assessed at 1 month, 3 months, and 1-year. Homograft function was evaluated by echocardiography.

RESULTS

Early mortality was 0%. Two late deaths at 1 postoperative year were unrelated to homograft function. At 1 postoperative month, panel reactive antibody results were negative in 20 patients (91%). At 3 months, 19 of 22 patients (86%) had negative results, including 1 with previous positive results. At 1 year, 19 of 20 patients (95%) had negative results, including 2 of the 3 with previous positive results. The mean aortic valve gradients were 12 +/- 8 mm Hg (n = 21) at discharge and 11 +/- 7 mm Hg (n = 18) at 1 year. At a mean follow-up of 30.3 +/- 5.2 months, the mean gradient was 8.8 +/- 6.3 mm Hg.

CONCLUSION

The SynerGraft decellularization technology successfully removed antigens from an aortic valve homograft conduit. Aortic root reconstruction with the CryoLife SynerGraft aortic valve homograft resulted in low transvalvular gradients, similar to those seen with standard cryopreserved homografts. These early results suggest an advancement in homograft technology. The low panel reactive antibody response may enhance durability by eliminating immune complex-mediated reaction against the homograft. The lack of allosensitization in patients who may require organ transplantation in the future is an added benefit.

Factors influencing late allograft valve failure

Allograft valves are a valuable valve replacement substitute in the surgical management of heart valve disease. It remains the valve substitute of choice in the reconstruction of the right ventricular outflow tract in children with congenital heart disease and in the Ross procedure. However, its durability remains suboptimal, particularly in children. This article reviews the mechanisms and factors implicated in late allograft dysfunction, with a focus on the evidence for an immunological cause for allograft valve failure. Unravelling the mechanisms of allograft valve failure may allow modification of the allograft to improve its long-term durability.

Rare complication of dissection of valsalva sinus with aorto-left atrial fistula in active aortic valve endocarditis

We present a rare case of dissection of the sinus of Valsalva associated with an aortic annular abscess that perforated into the left atrium. A 61-year-old patient with infective endocarditis underwent emergent operation due to progressive heart failure, in whom echocardiography showed the dissection of sinus of Valsalva with aorto-left atrial communication. Procedure included autologous pericardial patch repair of the dissecting sinus of Valsalva and bioprosthetic valve replacement with a successful outcome. Microscopic examination showed excessive neutrophil infiltration in the aortic valve and annulus without involvement of the sinus of Valsalva.

Congenital semilunar valvulogenesis defect in mice deficient in phospholipase C epsilon

Phospholipase Cepsilon is a novel class of phosphoinositide-specific phospholipase C, identified as a downstream effector of Ras and Rap small GTPases. We report here the first genetic analysis of its physiological function with mice whose phospholipase Cepsilon is catalytically inactivated by gene targeting. The hearts of mice homozygous for the targeted allele develop congenital malformations of both the aortic and pulmonary valves, which cause a moderate to severe degree of regurgitation with mild stenosis and result in ventricular dilation. The malformation involves marked thickening of the valve leaflets, which seems to be caused by a defect in valve remodeling at the late stages of semilunar valvulogenesis. This phenotype has a remarkable resemblance to that of mice carrying an attenuated epidermal growth factor receptor or deficient in heparin-binding epidermal growth factor-like growth factor. Smad1/5/8, which is implicated in proliferation of the valve cells downstream of bone morphogenetic protein, shows aberrant activation at the margin of the developing semilunar valve tissues in embryos deficient in phospholipase Cepsilon. These results suggest a crucial role of phospholipase Cepsilon downstream of the epidermal growth factor receptor in controlling semilunar valvulogenesis through inhibition of bone morphogenetic protein signaling.

In vivo study of the effects of cryopreservation on heart valve xenotransplantation

BACKGROUND

Recent reports have suggested that cryopreservation reduces the immunogenicity of donor tissue. The immunomodulation by cryopreservation might influence on the tissue durability after xenotransplantation. We investigated the in vivo morphologic changes in cryopreserved xenograft (CXG) heart valves.

MATERIAL AND METHOD

We transplanted a fresh (fresh xenograft; FXG) and a cryopreserved (CXG) porcine aortic root and a cryopreserved canine (cryopreserved allograft; CAG) aortic root into the abdominal aorta of a dog without any immunosuppressive agents. Explanted grafts on the 21st to 49th days after implantation were analyzed morphologically with light microscopy using some special stains, immunohistochemical analysis, and scanning electron microscopy (SEM).

RESULT

Light microscopy showed the absence of smooth muscle cells in the media of the aorta in any group after transplantation. FXG valves did not maintain any cellularity after transplantation. CXG valves contained cellular infiltration in themselves. CAG valves contained numerous fibroblasts, which showed the maintenance of tissue integrity without allowing cellular infiltration. The structure of elastic fibers was well maintained, even in the part of CXG valve with cellular infiltration. Immunohistochemical studies documented the infiltration of T lymphocytes in CXG valves that were labeled by anti-CD3 antibodies. SEM demonstrated that no endothelia were seen on the surface of the valves in any group after transplantation.

CONCLUSION

We concluded that the cryopreservation method might provide an immunomodulation of xenogeneic heart valves for transplantation.

[Cardiac lesion in psoriasis]

The heart of 12 patients with psoriasis at the stage of exacerbation compared to that of 16 practically healthy persons who had died of trauma was studied at the necropsy medical-forensic examination. Microcirculatory vessels with the wall thickening, plasmatic impregnation, mononuclear cell proliferation, focal stromal sclerosis were observed in the myocardium. Disorganization of connective tissue with mucoid edema and diffuse mononuclear cell infiltration of mitral and aortal valves was observed. These alterations correspond to slowly progressing chronic myocarditis and diffuse valvulitis.

Six-year monitoring of the donor-specific immune response to cryopreserved aortic allograft valves: Implications with valve dysfunction

BACKGROUND

The immune rejection has been anticipated as one of the major causes of allograft aortic valve (AAV) degeneration. The purpose of this study was to prospectively serially measure the magnitude and evolution of the recipient anti-HLA class I antibody response up to 6 years from AAV implant and to correlate serologic data with valve performance by means of a concurrent echocardiographic survey.

METHODS

Cryopreserved AAVs were obtained from multiorgan HLA-typed donors. Nineteen patients younger than 50 years (mean age, 43.3 +/- 8 years) were prospectively studied. After successful surgery, all AAV recipient underwent at 3 and 6 months and each year postoperatively (mean follow-up, 71.9 months) concomitant serum sample collection and two-dimensional transthoracic echocardiography. The presence of anti-HLA antibodies was tested against a panel of lymphocytes obtained from 30 blood donors.

RESULTS

Progressive structural valve deterioration was seen in 6 patients (31.5%) of whom 4 (21%) were reoperated. All pretransplant recipients sera were panel-reactive antibody negative. Seventeen patients (89.4%) demonstrated significant panel-reactive antibody levels, which peaked at 6 months postoperatively, declined from 6 to 24 months, and slowly decreased afterward. In 14 of 19 cases (73.6%) donor-specific HLA antibodies were identified. A strong immunization (6-year persistence of panel-reactive antibody > 70% and peak panel-reactive antibody > 80%) was detected in 31.5% and 36.8% of recipients, respectively. Strong immunization was found to be significantly associated with progressive structural deterioration.

CONCLUSIONS

The immune reaction after cryopreserved AAV implantation is a peculiar long-lasting response occurring in the majority of recipients younger than 50 years of age. An association between a sustained and pronounced immunization and an aggressive AAV degeneration was observed.

Role of inflammation in allogeneic and xenogeneic heart valve degeneration: immunohistochemical evaluation of inflammatory endothelial cell activation

BACKGROUND AND AIM OF THE STUDY

Biological heart valve prostheses undergo degenerative changes which lead ultimately to dysfunction or even complete destruction. The study aim was to evaluate immunological factors and their potential role in biological heart valve destruction.

METHODS

Allogeneic (n = 10) and xenogeneic (n = 3) aortic valve prostheses, as well as aortic valves retrieved from transplanted human hearts which had to be replaced due to chronic graft rejection (n = 4), were analyzed. Aortic valves from human donor hearts (n = 4) served as controls. Evaluated adhesion molecule expression included: selectin family ELAM-1, CD62; integrin family VLA-1, -2, -3, -4, -5 and -6; immuoglobulin supergene family PECAM-1, ICAM-1 and -2, and class I heavy chain proteins; complementary adhesion molecules CD34, CD44 and von Willebrand factor.

RESULTS

ELAM-1, ICAM-1 and -2, CD34, CD44 and class I heavy chain proteins, which play significant roles during inflammatory processes, showed stronger expression patterns in allogeneic and xenogeneic aortic heart valve prostheses compared to native or chronically rejected valves. Furthermore, allogeneic and xenogeneic valves showed a strong thrombogenicity which stained positive for von Willebrand factor outside endothelial cells on these valves. Integrin molecules as well as CD62 showed only mild differences.

CONCLUSION

Immunological reactions play a pivotal role in the degeneration of biological heart valve prostheses. As immunosuppressive therapy after heart valve replacement is not a viable option, novel approaches in 'tissue engineering' may help to avoid tissue degeneration while preserving the advantage of biological tissue origin.

Aortic valve allograft structural deterioration is associated with a subset of antibodies to human leukocyte antigens

BACKGROUND AND AIM OF THE STUDY

The association between aortic valve allograft dysfunction in patients with long-term follow up and human leukocyte class 2 antigen donor/recipient mismatch suggests that elements of the anti-donor immune response penetrate and damage the aortic valve allograft. An aortic valve allograft recipient cohort was studied to determine whether presence of recipient antibodies to donor human leukocyte class 1 or 2 antigen was associated with shorter time to aortic valve allograft dysfunction.

METHODS

Both donor and recipient human leukocyte antigen (HLA) type, HLA antibody information and echocardiography data were available for 148 recipients of cryopreserved aortic valve allografts between 1986 and 1998. Structural deterioration of the aortic valve allograft was defined as at least moderate aortic stenosis or regurgitation by echocardiography. Recipient sera were assayed for anti-HLA (class 1 and 2) antibodies using three assays: complement-dependent cytotoxicity (CDC) on T- and B-lymphocyte panels (CDC PRA); flow cytometry using HLA-coated beads (Flow PRA); and an ELISA using HLA-coated microwells. The donor specificity of anti-class 1 and 2 HLA antibodies was determined on T- and B-cell panels using CDC. Associations between the results of the three assays and donor-specific class 1 and 2 antibodies and time to structural deterioration were analyzed using Kaplan-Meier curves of freedom from structural deterioration. Cox proportional-hazards were used to determine independent predictors of time to structural deterioration.

RESULTS

Patients highly positive for HLA class 2 antibodies using an ELISA had a significant association (p = 0.007) with shorter time to aortic valve allograft structural deterioration using both a log rank test and Cox proportional-hazards analysis. Patients (n = 15) with donor-specific antibodies to class 2 antigen (DR antigens) had significantly more structural deterioration (p = 0.035) than those without specific antibodies.

CONCLUSION

The association between aortic valve allograft structural deterioration and high titer human leukocyte class 2 antigen antibodies, a subset detected by ELISA adds further information about the link between HLA class 2 mismatch and structural deterioration. Further studies are needed to confirm the importance of class 2 antibodies on outcome, and to determine by which method these antibodies should be detected. Potential recipients with pre-existing antibodies of these specific types might be expected to sustain accelerated allograft damage.

The pathology of fresh and cryopreserved homograft heart valves: an analysis of forty explanted homograft valves

OBJECTIVE

Tissue degeneration reduces the durability of aortic and pulmonary homograft heart valves. Homograft valves can evoke cellular and humoral immune responses that might be detrimental to the valve tissue. Analyzing explanted homograft valves helps in understanding the different factors that eventually lead to tissue degeneration.

METHODS

A total of 40 homografts was acquired from patients whose grafts had been explanted because of stenosis (n = 22), insufficiency (n = 8), paravalvular leakage (n = 4), other technical problems (n = 4), noncardiac death (n = 1), and stenosis with endocarditis (n = 1). The period of implantation varied from 14 days to 16 years (median, 4 years). Cryopreserved valves (n = 31) were, in the majority, derived from beating-heart donors, whereas the fresh valves were sterilized with antibiotics and stored at 4 degrees C for an average of 32 days. Four unimplanted cryopreserved valves, 1 native aortic valve, and 1 native pulmonary valve were used as references. Analysis included macroscopy, light microscopy with routine hematoxylin and eosin staining (cellularity and tissue structure), and immunohistochemical studies to allow identification of macrophages (CD68) and T lymphocytes (CD3), endothelial cells, leukocyte adhesion molecules (CD54, CD106, and CD62E), and immunoglobulin (IgG) and complement factor (C3) depositions. In situ hybridization for the Y chromosome was performed in 10 cases, with host-donor sex mismatch, to distinguish between host and donor cells. The outcomes of histology and immunohistochemistry were related to clinical factors, such as implantation time and reason for explantation.

RESULTS

In the first year after implantation, a strong reduction in cellularity of the valve tissue was observed, with almost acellular tissues after 1 year. Trilaminar tissue architecture disappeared with the same speed, whereas endothelial cells were almost absent in all explants. Macrophages and T lymphocytes were encountered in 85% and 78% of the leaflets, respectively. Expression of leukocyte adhesion molecules was low in almost all grafts, and IgG and C3 depositions were not increased. Valve tissue cellularity consisted mainly of ingrown host cells when the implantation time exceeded 1 year.

CONCLUSIONS

During the first year of implantation, homograft valves rapidly lose their cellular components and normal tissue architecture. A low-grade inflammatory response was observed, but no convincing evidence of immune-mediated injury was found.

Valvular heart disease in patients with hypocomplementemic urticarial vasculitis syndrome associated with Jaccoud's arthropathy

BACKGROUND

Since 1973, more than 75 patients with hypocomplementemic urticarial vasculitis syndrome (HUVS) were reported, but valvular heart disease does not seem to have been noted in these patients. Since 1993, however, five patients with HUVS accompanied by Jaccoud's arthropathy (JA) were found to have serious valvular heart disease.

METHODS

To characterize the cardiac valvulopathy of the third patient with HUVS/JA to have undergone valve replacement, this study included the use of routine and special tissue stains, as well as immunohistochemical staining. We compared gross and histologic findings of this patient's valve to those of two other patients with this complex syndrome who underwent valve replacement. Pathologic findings of these latter two patients were described in separate earlier reports.

RESULTS

Histologic examination of the resected valves in all three patients showed an acute necrotizing endocarditis and fibrin deposition on the surface of valve leaflets. Beneath the surfaces of the leaflets, there was evidence of chronic inflammation, consisting of lymphocytes and histiocytes. A fibrocalcific degenerative change was also present in all three valves. Positive staining for IgG, IgA, IgM, and light-chain determinant-bearing proteins was detected primarily at the valve surface in special studies of the aortic valve of the patient described in the current report.

CONCLUSION

Patients with HUVS and associated JA should be evaluated for the presence of valvular heart disease. The latter is probably a nonrheumatic, inflammatory, and degenerative process, mediated by immune complex, as well as cellular immune mechanisms.

Anti-fibrin antibody binding in valvular vegetations and kidney lesions during experimental endocarditis

In Streptococcus sanguinis (sanguis) induced experimental endocarditis, we sought evidence that the development of aortic valvular vegetation depends on the availability of fibrin. Endocarditis was induced in New Zealand white rabbits by catheter placement into the left ventricle and inoculation of the bacteria. Fibrin was localized in the developing vegetation with 99mTechnetium (Tc)-labeled anti-fibrin antibody one or three days later. When rabbit anti-fibrin antibody was given intravenously on day 1, the mass of aortic valvular vegetation was significantly reduced at day 3; infusion of non-specific rabbit IgG showed no effect. The 99mTc-labeled anti-fibrin antibody also labeled kidneys that showed macroscopic subcapsular hemorrhage. To learn if the deposition of fibrin in the kidneys was a consequence of endocarditis required a comparison of farm-bred and specific pathogen-free rabbits before and after the induction of endocarditis. Before induction, the kidneys of farm-bred rabbits were labeled, but specific pathogen-free rabbits were free of labeling and signs of macroscopic hemorrhage. After 3 days of endocarditis, kidneys of 10 of 14 specific pathogen-free rabbits labeled with 99mTc-labeled anti-fibrin antibody and showed hemorrhage. Kidney lesions were suggested to be a frequent sequellae of S. sanguinis infective endocarditis. For the first time, fibrin was shown to be required for the continued development of aortic valvular vegetations.

The presence of immune stimulatory cells in fresh and cryopreserved donor aortic and pulmonary valve allografts

BACKGROUND AND AIM OF THE STUDY

Heart valve allografts (HVA) used for valve replacement or ventricular outflow tract reconstruction may suffer from structural deterioration due to donor-specific immune responses. The presence of immune stimulatory cells, including dendritic cells and activated endothelial cells, has not been studied thoroughly in aortic or pulmonary HVA. The presence and distribution of these cells in both aortic and pulmonary HVA, before and after cryopreservation, was analyzed immunohistochemically.

METHODS

Aortic (n = 16) and pulmonary (n = 13) HVA, discarded for implantation due to morphological or technical reasons, were obtained from 12 heart-beating and nine non-heart-beating tissue donors. Aortic and pulmonary HVA were dissected longitudinally into two symmetric sections by splicing of the non-coronary aortic and non-facing pulmonary cusps. Each symmetric half contained one-and-a-half valve cusps attached to the vascular wall. Fresh halves were directly fixed in formaldehyde, and analyzed immunohistochemically. The corresponding halves of the valves were decontaminated, cryopreserved, stored for at least three weeks and thereafter thawed according to the Heart Valve Bank protocol before analysis.

RESULTS

Activated endothelial cells, expressing PECAM-1 (CD31), VCAM-1 and HLA class II molecules covered at least 50% of fresh valvular surfaces. A comprehensive vascular network was found in the myocardial rim and adventitial layer, which was covered entirely by activated endothelial cells. HLA class II-positive macrophages (CD68) and T lymphocytes (CD3) were found scattered in the stroma and subendothelial layer of the valve leaflets. Mononuclear cell clusters were found predominantly in relation to native degenerative foci, and more often in aortic valves. No difference in cellular distribution was observed between the two donor types. Dendritic cells positive for both S100 and CD45 were not found in immuno-double-stained sections. Cryopreservation resulted in minor structural alterations in the vascular wall, and an increase of cells with pycnotic nuclei and reduction of adhesion molecule expression on endothelial cells. All fresh and cryopreserved aortic and pulmonary HVA contained abundant HLA class II-positive endothelial cells and sparse distribution of mononuclear cells in the luminal and adventitial layers.

CONCLUSION

Cryopreservation minimally affected the extracellular matrix of HVA and diminished the cellularity of the valve graft, while the HLA class II expression of cells was not abrogated. Aortic valve allografts harbor more mononuclear cells than their pulmonary counterparts. The absence of dendritic cells (professional antigen-presenting cells) is compensated by the preservation of other cells expressing HLA class II molecules predominantly in the endothelium; this may be responsible for the initiation of a specific immune response against HVA.

Frequencies of donor-reactive helper T lymphocytes correlate with rejection of aortic valve allografts in rats

BACKGROUND AND AIMS OF THE STUDY

Human valve allografts are commonly used in cardiac surgery for congenital and acquired valve diseases. Particularly in the pediatric population, these allografts are prone to fail in the long term, and require replacement. In part, this failure may be due to immunological phenomena. The frequency of helper T lymphocytes (HTLf) measured in peripheral blood and spleen serves as a parameter for acute rejection in organ transplantation. The value of this parameter in valve transplantation was studied using the 'Rotterdam' implantation model in rats.

METHODS

HTLf were determined in peripheral blood and spleen at seven and 21 days after allogeneic (WAG-->DA) and syngeneic (DA-->DA) implantation of an aortic valved conduit. Valve competence was tested pre-implantation, at days 7 and 21 after implantation, and after explantation using a retrograde saline injection. Explanted valves were examined histologically.

RESULTS

At seven days after allogeneic valve transplantation, HTLf in spleen (median 71/10(6)), but not in peripheral blood (median 26/106) were significantly elevated. At 21 days after allogeneic transplantation, a significant increase in HTLf was seen in both peripheral blood (median 10(9)/10(6)) and spleen (median 92/10(6)). All five (100%) syngeneic grafts and five of seven (71%) allografts were competent at day 7. At day 21, all five syngeneic grafts (100%) and zero allografts (0%) remained competent (p = 0.01). Histologically, mononuclear cell infiltration into the allogeneic valve leaflets and in the vascular wall was observed at day 7. At day 21, valve leaflets appeared to be acellular and deformed. All syngeneic valve grafts retained normal morphology.

CONCLUSION

After aortic valve allografting in the rat, HTLf correlate with valve dysfunction and histopathological signs of rejection. Therefore, HTLf-analysis may be a useful tool in monitoring the cellular immune response as an indicator for early graft dysfunction due to rejection in clinical valve transplantation.

Humoral immune response to allograft valve tissue pretreated with an antigen reduction process

The humoral immune response to allograft heart valves as measured by PRA was absent in 52 of 57 (91%) patients at 1 month and was absent in 43 of 49 (88%) at 3 months in allograft valves treated with the SynerGraft process for antigen reduction. Short-term valve function is satisfactory. This may be associated with improved durability and long-term function.

Prevention of allograft heart valve failure in a rat model

OBJECTIVE

Allograft heart valves are commonly used in cardiac surgery. Despite mounting evidence that these valves are immunogenic, leading to premature failure, current clinical practice does not attempt to minimize or control such a response. The objective of this study was to evaluate immune modulatory approaches to ameliorate allograft valve failure in a rat model.

METHOD

Aortic valve grafts were implanted infrarenally into Lewis rat recipients (n = 32). There were 4 transplant groups: syngeneic grafts (Lewis to Lewis), untreated allografts (Brown Norway to Lewis), allograft recipients treated with cyclosporine (INN: ciclosporin) (10 mg/kg per day for 7 or 28 days), and allograft recipients treated with anti-alpha4 integrin and anti-beta2 integrin monoclonal antibodies for 7 days. At 7 and 28 days the valves were examined for structural integrity and cellular infiltration.

RESULTS

Both cyclosporine and anti-alpha4/beta2 integrin treatment resulted in significant reduction in leaflet infiltration by macrophages (ED1(+)), T cells (CD3(+)), and CD8(+) T cells at 7 days with preservation of structural integrity when compared with control allografts. Twenty-eight days after implantation, daily treatment with cyclosporine preserved leaflet structural integrity and inhibited cellular infiltration. However, a short course of cyclosporine (7 days) failed to prevent destruction of the valves at 28 days.

CONCLUSIONS

Immune modulatory approaches aimed at T-cell activation or trafficking decrease leaflet cellular infiltration and prevent allograft valve structural failure. However, short-course therapy does not appear to be sufficient and must be maintained to allow long-term preservation of leaflet structural integrity (28 days).

Immunological aspects of fresh and cryopreserved aortic valve transplantation in rats

BACKGROUND

The influence of immune activation on valve allograft degeneration remains unclear. We studied the combined effect of major histocompatibility complex (MHC)-incompatibility and cryopreservation on valve performance, histomorphology, and tissue antigenicity in rats.

METHODS

Fresh or cryopreserved allogeneic aortic valves from WAG (RT1u) rats were transplanted to DA (RT1a) recipients and syngenic transplants served as controls. After 7 or 21 days, valves were examined for competence and morphology. Immune reactivity of the recipient was measured by concanavalin A (conA) stimulation and analysis of donor-reactive Helper T-lymphocyte frequencies (HTLf) in peripheral blood and spleen.

RESULTS

Syngenic grafts demonstrated normal competence and structure. Allografts lost their competence over time caused by destruction of the leaflets combined with cellular infiltration in the vascular wall. Cryopreservation induces early loss of competence and retrovalvular thrombosis. Cryopreserved allografts were also heavily infiltrated. ConA stimulation indices and HTLf were higher in allogeneic recipients compared to syngenic recipients (p < 0.03). Cryopreserved allografts elicited a lower immune response compared with fresh allografts (p < 0.03).

CONCLUSIONS

Aortic valve allografts are able to induce a donor-reactive immune response that is related to early graft destruction and incompetence. Cryopreservation appears to diminish but not eliminate the antigenicity of the allograft.

Cryopreservation of rat aortic valves results in increased structural failure

BACKGROUND

The cause of valve allograft failure is most likely multifactorial and may include mechanical, immunological, and other factors. Cryopreservation of these valves is often used to extend storage times. However, there has been considerable confusion as to the effects of cryopreservation on valve durability. Our objective was to determine the effects of cryopreservation on histopathological changes in rat aortic valve grafts.

METHODS AND RESULTS

Syngeneic rat aortic valve grafts (Lewis to Lewis; n=24) and allogeneic rat aortic valve grafts (Brown Norway to Lewis; n=24) were implanted infrarenally, either fresh or after cryopreservation. At 7, 14, and 28 days, the valves were explanted, and histological and immunohistochemical examinations were performed in a blinded fashion. Fresh syngeneic graft leaflets retained their normal structure for the 28-day period of observation. Cryopreserved syngeneic grafts showed retrovalvar thrombus formation, with leaflet destruction at 7, 14, and 28 days. Fresh allogeneic graft leaflets showed significant leaflet thickening and progressive destruction at 14 and 28 days. Cryopreserved allogeneic grafts had evidence of retrovalvar thrombus formation with leaflet destruction at 7, 14, and 28 days. Cryopreserved syngeneic grafts resulted in significant infiltration of mononuclear (ED1(+)) cells not seen with fresh syngeneic grafts but similar to fresh allogeneic grafts. All allogeneic grafts resulted in significant infiltration of T-lymphocytes (CD3(+), CD8(+), CD43(+)).

CONCLUSIONS

Cryopreservation appears to predispose syngeneic and allogeneic rat aortic valve leaflets to accelerated injury and destruction. This mode of failure resembles that of fresh allogeneic valve grafts.

T lymphocytes mediate leaflet destruction and allograft aortic valve failure in rats

BACKGROUND

Allograft heart valves are commonly used in cardiac surgery but ultimately fail. This situation is most acute in children. This study addresses the role of T cell-mediated immune damage in allograft valve failure.

METHODS

Syngeneic (Lewis to Lewis) or allogeneic (Brown Norway to Lewis) aortic valve grafts were implanted infrarenally into Lewis rat recipients (n = 24). Allogeneic valve grafts were also implanted into T cell-deficient rats (nude; n = 12). At 7, 14, and 28 days the valves were explanted and examined for structural integrity and cellular infiltration.

RESULTS

Syngeneic grafts maintained normal leaflet structure with little leaflet immune infiltration. Allografts showed leaflet infiltration (7 days), significant leaflet thickening, progressively decreased cellularity (14 days), and leaflet destruction (28 days). Infiltrates contained CD43+, CD3+, and CD8+ cells. Allografts in T cell-deficient rats showed none of the above changes and maintained normal structural integrity.

CONCLUSIONS

Allograft heart valves in the rat model undergo T cell-mediated immune rejection, resulting in structural failure.

Class I and class II anti-HLA antibodies after implantation of cryopreserved allograft material in pediatric patients

OBJECTIVES

Very little is known regarding the immune response to cryopreserved allograft valves and patch material used in the surgical repair of congenital heart defects.

METHODS

We prospectively measured the frequency of panel reactive antibodies directed against HLA class I (HLA-A, B, and C) and class II (HLA-DR/DQ) alloantigens in 24 children receiving cryopreserved allografts. We compared them with results in 11 previously reported control patients. Sixteen of the study patients underwent placement of a valved conduit (11 pulmonic, 5 aortic) between the right ventricle and pulmonary arteries, 6 underwent patch angioplasty of stenotic vessels with cryopreserved pulmonary artery, and 2 underwent placement of a pulmonary monocusp patch. Study patients had panel reactive antibodies measured before, 1 month, 3 months, and 1 year after the operation.

RESULTS

With allograft implantation, panel reactive antibodies increased from 1.9% +/- 5% before the operation to 62% +/- 33% at 31 +/- 8 days after the operation, 92% +/- 15% at 3.3 +/- 0.6 months after the operation, and 85% +/- 18% at 1.1 +/- 0.2 years after the operation. The control group showed no change in panel reactive antibodies, with a level of 1.6% +/- 1% before the operation, 3.2% +/- 1% 28 +/- 5 days after the operation, and 1.7% +/- 1% 2.7 +/- 0.3 months after the operation. Class II antibodies (anti-HLA-DR/DQ) rose to 49% +/- 35% at 30 +/- 8 days and 70% +/- 26% at 3.3 +/- 0.6 months after the operation.

CONCLUSIONS

Cryopreserved allograft material induces a marked response that involves both class I and class II anti-HLA antibodies within 3 months after operation in children. This alloantibody response may represent a form of "rejection," may have implications for those who require subsequent cardiac transplantation, and may play a role in early allograft failure.

Immunogenic human leukocyte antigen class II antigens on human cardiac valves induce specific alloantibodies

BACKGROUND

The kinetics of panel reactive antibodies (PRA) and incidence of antibodies directed against human leukocyte antigen (HLA) class II were studied in patients who received a cryopreserved cardiac valve allograft.

METHODS

A complement-dependent microlymphocytotoxicity test was used to determine the percentage of panel reactive antibodies. Anti-HLA class II antibodies were measured by two-color fluorescence assays.

RESULTS

The panel reactive antibodies became positive in 25 (78%) of 32 recipients between 1 and 16 months after implantation. Antibodies against HLA class II antigens were detected in 11 (37%) of 30 patients. In 9 (82%) of 11 cases these antibodies were donor specific. The induction of antibodies against donor HLA class II antigens suggests that intact HLA class II antigens are expressed by viable cells within the graft. Dithiothreitol analysis showed that the antibodies were of the immunoglobulin G type. Apparently, the HLA class II antigens are expressed in an immunogenic way, as activation of specific T-helper cells is essential for the switch from immunoglobulin M to immunoglobulin G antibodies.

CONCLUSIONS

Allogeneic valve transplantation is associated with the production of donor-specific anti-HLA class I and II antibodies that could contribute to graft failure. This possibly detrimental effect might be prevented by cross matching in sensitized patients.

Effect of antibiotic pretreatment on immunogenicity of human heart valves and component cells

BACKGROUND

For many years valves have been sterilized with high-dose antibiotics before implantation, but now there is an increasing trend to using "homovital" valves, which have been exposed to very low dose antibiotics.

METHODS

To investigate the immunogenicity of valve tissue, before and after exposure to high- and low-dose antibiotics, peripheral blood mononuclear cells and human allogenic T cells were cocultured with antibiotic-treated valve discs, cultured valve endothelial cells, and fibroblasts. Proliferation was measured by uptake of thymidine labeled with hydrogen 3.

RESULTS

Untreated tissue pieces stimulate peripheral blood mononuclear cells (4,080+/-980 cpm) at day 0 with similar results after 1 day in Hank's balanced salt solution (4,272.4+/-1,307 cpm) reducing to 2,442+/-926 cpm after 3 days and 1,111+/-255 cpm after 5 days; antibiotic-treated pieces are less immunogenic after 1 (2,560+/-403 cpm), 3 (1,550+/-60 cpm), 5 (717+/-295 cpm), and 7 days (633+/-174 cpm) in homovital solution, whereas sterilized pieces are not immunogenic (184+/-96 cpm) after only 1 day in strong antibiotics. Histologic analysis showed that this corresponds to a reduction of class I and class II expression by human valve endothelial cells. Human valve endothelial cells but not fibroblasts are capable of causing direct stimulation of CD4+ T cells. However, human valve endothelial cells poorly stimulate CD4+ T cells after incubation in homovital solution for 24 hours.

CONCLUSIONS

This study shows that valve tissue is immunogenic and this immunogenicity is mediated mainly by endothelial cells. However, the immunostimulatory potential of the valve can be reduced by incubating the solution in an antibiotic cocktail.