Autologous or bovine pericardium for aortic cusp replacement? Histomorphological and biomechanical properties as decision making tools

Background/Introduction

Aortic valve cusp replacement using autologous pericardium is a promising technique. Expected advantages are reduced immune response, proper biomechanics and lower treatment expenses. During surgery decision for preferred pericardium segment is based on visual criteria. Autologous pericardium can be affected by patient's condition and age. Bovine pericardium, also the basic material for aortic valve prostheses, is easy available and carefully pre-examined. In this study, the homogeneity of tissue thickness, elastic modulus, vessel density and ECM components of GA-treated residual pericardia after surgery is compared with bovine pericardia equivalently treated.

Purpose

Aim of the study is the comparison of homogeneity of remaining autologous pericardium after surgical aortic valve replacement with bovine pericardia to evaluate and classify the individual applicability.

Methods

Up to 12 samples of human (n=7) or bovine (n=3) pericardia were analysed. Tissues were treated with 0.6% glutaraldehyde according to surgical protocol. Picrosiriusred- and HE-staining were performed (three edges per separated leaflet). Vessel or collagen content was determined with Zen Blue resp. Fiji software (colour deconvolution plugin, user threshold values). Sample thickness was measured via thickness gauge FD50 before uniaxial tensile testing. Hydroxyproline content was determined and related to dry weight. T-Test or ANOVA were used to test inter-species or intra-individual differences, respectively.

Results

Human pericardia contain with 64.66±3.85% less collagenous fibres compared to bovine pericardia (86.01±1.713%); their vessel density is with 29.46±3.73 mm–2 significantly higher than in bovine samples (12.34±1.636 mm–2). In addition, human pericardia are with 367.7±59.2 μm significantly thinner than bovine (524.4±96.8 μm). Tensile testing (human: 36.00±15.17 MPa; bovine: 41.30±7.767 MPa) also revealed significant differences. With 77.80±11.76 mg/g merely a trend was observed for a lower hydroxyproline content in human samples (bovine 93.16±5.130 mg/g). ANOVA analyses of human pericardia illustrate significant differences for all properties, thus thickness, elastic modulus and hydroxyproline and collagen content between the individual human pericardium samples. In contrast, bovine pericardia showed an intra-individual difference only for the parameter of tissue thickness.

Conclusion

Human and bovine pericardia differ in histological and biomechanical parameters. In contrast to bovine pericardia, individual human pericardia were significantly different in most parameters investigated, leading to the conclusion that autologous materials are critically more heterogeneous than xenogeneic tissues. Vessel density in human pericardium was twofold higher than in bovine pericardia and can result in a higher risk for calcification.

Funding Acknowledgement

Type of funding sources: Public Institution(s). Main funding source(s): TU Dresden

Haemocompatibility testing allows selective adaption of GA-free SULEEI-preparation strategy for bovine pericardium

Background/Introduction

Bovine pericardium is the main natural source for patches or valve substitutes in cardiac surgery, but still, long-term durability is limited. An alternative, glutaraldehyde (GA)-free preparation combining decellularization, riboflavin/UVA crosslinking, and low-energy electron irradiation (SULEEI) procedure was established to avoid this. Protocol optimization is ongoing to further improve the final material. Haemocompatibility in vitro testing with fresh, human whole blood has advantages for material analysis, as it provides essential information on the activation of the complement system and immune cells therefore substantiating and possibly reducing the amount of animal testing.

Purpose

The haemocompatibility testing system was applied to reveal advantageous protocol adaptation of GA-free SULEEI preparation of pericardia.

Methods

Decellularized bovine pericardia were UVA-crosslinked in riboflavin/dextran solution. Protocol SULEEI B adaption includes the addition of trypsin in decellularization buffer and a 10x reduced riboflavin/dextran concentration during prolonged UVA irradiation with reduced intensity. Electron irradiation with 36 kGy was retained. Pericardia were incubated in blood chambers with heparinized human blood (2h, 37°C, GA-fixed/native controls). Inflammation (granulocyte loss and activation [CD11b]), complement activation (C5a) and haemostasis parameters (F1+2, PF4, granulocyte/platelet conjugates, platelet loss) were analyzed via flow cytometry or ELISA. Surface cell adhesion was investigated immunohistologically and via REM-analyses. Nuclear fragments were quantified in HE-stained sections.

Results

Haemostasis parameters F1+2 and PF4 were significantly higher in SULEEI A-pericardium (133±25 nmol/l and 1507±677 U/ml) vs. GA-fixation (2.9±2.9 nmol/l and 320±160 U/ml). Also, granulocyte/platelet conjugates (76.3±18.8%) and platelet loss (40.4±29.7%) were significantly higher after SULEEI A preparation in comparison to GA-fixation (39.3±9.9% and 20.5±6.4%). SULEEI B treated pericardia did not differ significantly. C5a complement activation was significantly lower in SULEEI A samples but comparable in SULEEI B to GA-fixed material. This is in contrast to a higher rate of nuclear fragments in SULEEI A tissue HE stained sections. Granulocyte activation of SULEEI pericardium (A: 89.8±29.7%; B: 106.2±18.8%) was significantly higher compared to native (46.1±22.6%) and for SULEEI B higher than in GA-fixed samples (67.2±9%). Granulocyte loss was comparable to GA-fixed pericardium after SULEEI B protocol. REM-analyses and histological evaluation visualized a dense blood cell and fibrin covering particular of SULEEI A-pericardium.

Conclusions

Haemocompatibility testing reveals advantageous properties of SULEEI B-pericardium. The impact of treatment substances such as dextran on high inflammatory response and dense surface covering in SULEEI A protocol is focus in ongoing experiments.

Funding Acknowledgement

Type of funding sources: Public grant(s) – EU funding. Main funding source(s): EU/EFRE

Establishment of a resazurin-based aortic valve tissue viability assay for dynamic culture in a microphysiological system

BACKGROUND/AIM

Tissue pathogenesis of aortic valve (AV) stenosis is research focus in cardiac surgery. Model limitations of conventional 2D culture of human or porcine valvular interstitial/endothelial cells (VIC/VECs) isolated from aortic valve tissues but also limited ability of (small) animal models to reflect human (patho)physiological situation in AV position raise the need to establish an in vitro setup using AV tissues. Resulting aim is to approximate (patho)physiological conditions in a dynamic pulsatile Microphysiological System (MPS) to culture human and porcine AV tissue with preservation of tissue viability but also defined ECM composition.

MATERIALS/METHODS

A tissue incubation chamber (TIC) was designed to implement human or porcine tissues (3×5 mm2) in a dynamic pulsatile culture in conventional cell culture ambience in a MPS. Cell viability assays based on lactate dehydrogenase (LDH)-release or resazurin-conversion were tested for applicability in the system and applied for a culture period of 14 days with interval evaluation of tissue viability on every other day. Resazurin-assay setup was compared in static vs. dynamic culture using varying substance saturation settings (50-300μM), incubation times and tissue masses and was consequently adapted.

RESULTS

Sterile dynamic culture of human and porcine AV tissue segments was established at a pulsatile flow rate range of 0.9-13.4μl/s. Implementation of tissues was realized by stitching the material in a thermoplastic polyurethane (TPU)-ring and insertion in the TIC-MPS-system. Culture volume of 2 ml caused LDH dilution not detectable in standard membrane integrity assay setup. Therefore, detection of resazurin-conversion of viable tissue was investigated. Optimal incubation time for viability conversion was determined at two hours at a saturated concentration of 300μM resazurin. Measurement in static conditions was shown to offer comparable results as dynamic condition but allowing optimal handling and TIC sterilization protocols for long term culture. Preliminary results revealed favourable porcine AV tissue viability over a 14 day period confirmed via resazurin-assay comparing statically cultured tissue counterparts.

CONCLUSIONS

Human and porcine AV tissue can be dynamically cultured in a TIC-MPS with monitoring of tissue viability using an adapted resazurin-assay setup. Preliminary results reveal advantageous viability of porcine AV tissues after dynamic TIC-MPS culture compared to static control.

Characterization of thoracal fat depots - expression of adipokines and remodeling factors and impact of adipocyte conditioned media in fibroblast scratch assays

Adipose tissue is not only a connective tissue but also an endocrine organ secreting adipokines like Leptin and Adiponectin, lipokines such as palmitoileic acid and extracellular vesicles. These factors and the expression of matrix remodeling enzymes impact surrounding tissues via paracrine effects. The expression of selected secretion factors and the effect of adipocyte conditioned media from four thoracal adipose tissue origins - subcutaneous, perivascular, pericardial and epicardial adipose tissues - in a fibroblast proliferation/wound healing scratch assay model were investigated. Results were compared directly and according to the type 2 diabetic mellitus (T2DM) status of the patients the tissues are originated from. Adipocyte conditioned media from non-diabetic patients resulted in a significant higher scratch closure rate compared to the media with T2DM background. Linoleic acid incubation in scratch assay resulted in a reduced scratch closure rate. Leptin, Adiponectin and Visfatin/Nampt expression and MMP2, MMP9 and FSTL1 mRNA levels did not vary according to T2DM subgroups directly, leading to the assumption that these factors are not causal for scratch assay effects observed. In contrast significant mRNA expression differences were monitored between the thoracal tissue origins implying variations in the local effects of the different adipose tissue depots.