Antigen Clearing from Porcine Heart Valves with Preservation of Structural Integrity

Residual Bioprosthetic Valve Immunogenicity: Forgotten, Not Lost

Despite early realization of the need to control inherent immunogenicity of bioprosthetic replacement heart valves and thereby mitigate the ensuing host response and its associated pathology, including dystrophic calcification, the problem remains unresolved to this day. Concerns over mechanical stiffness associated with prerequisite high cross-link density to effect abrogation of this response, together with the insinuated role of leaching glutaraldehyde monomer in subsequent dystrophic mineralization, have understandably introduced compromises. These have become so entrenched as a benchmark standard that residual immunogenicity of the extracellular matrix has seemingly been relegated to a very subordinate role. Instead, focus has shifted toward the removal of cellular compartment antigens renowned for their implication in the failure of vascularized organ xenotransplants. While decellularization certainly offers advantages, this review aims to refocus attention on the unresolved matter of the host response to the extracellular matrix. Furthermore, by implicating remnant immune and inflammatory processes to bioprosthetic valve pathology, including pannus overgrowth and mineralization, the validity of a preeminent focus on decellularization, in the context of inefficient antigen and possible residual microbial remnant removal, is questioned.

Effects of Shenmai injection on the values of CO, SV, and EF in patients undergoing off-pump coronary artery bypass graft: A randomized, clinical trial

BACKGROUND

To explore the effects of Shenmai (SM) injection on the values of cardiac output (CO), stroke volume (SV), and the ejection fraction (EF) in patients treated with off-pump coronary artery bypass graft (OPCABG).

METHODS

Forty patients undergoing OPCABG were randomly divided into SM group (n = 20) and the 5% glucose (G) group (n = 20). The control liquids were injected from the beginning of the operation to the start of coronary artery bypass graft (CABG). The values of CO, SV, and EF before induction (t1), at the beginning of operation (t2), 30 minutes after the start of operation (t3), at the beginning of coronary artery bypass graft (t4), at the end of coronary artery bypass graft (CABG) (t5), and at the end of operation (t6) were recorded.

RESULTS

The values of CO, SV, and EF in the patients of SM group at t3 to t6 were found to be significantly higher than those at t1 (P < .05). The values of CO, SV, and EF in the patients of G group were found to be increased at t5 and t6 (P < .05). At t3 and t4, the values of CO, SV, and EF in SM group were significantly higher than those in the G group (P < .05).

CONCLUSION

In patients with OPCABG, the infusion of SM injection can effectively increase the values of CO, SV, and EF and increase the safety of anesthesia management.

Evaluation of Decellularized Extracellular Matrix of Skeletal Muscle for Tissue Engineering

Objective

We evaluated the effectiveness of enzyme-detergent methods on cell removal of mouse skeletal muscle tissue and assessed the biocompatibility of the decellularized tissues by an animal model.

Methods

The mouse latissimus dorsi (LD) muscles underwent decellularization with different enzyme-detergent mixtures (trypsin-Triton X-100, trypsin-sodium dodecyl sulfate (SDS), trypsin-Triton X-100-SDS). The effectiveness of decellularization was assessed by histology and DNA assay. The content in collagen and glycosaminoglycan was measured. The biomechanical property was evaluated in uniaxial tensile tests. For biocompatibility, the decellularized muscle specimens were implanted in situ and the tissue samples were retrieved at day 10, 20, and 30, to evaluate the host-graft inflammatory reaction.

Results

Extensive washing of the mouse LD muscles with an enzyme-detergent mixture (trypsin and Triton X-100) can yield an intact matrix devoid of cells, depleted of more than 93% nuclear component and exhibiting comparable biomechanical properties with native tissue. In addition, we observed increased infiltration of inflammatory cells into the scaffold initially, and the presence of M1 (CD68)-phenotype mononuclear cells 10 days after implantation, which decreased gradually until day 30.

Conclusions

The enzyme-detergent method can serve as an effective method for cell removal of mouse skeletal muscle. In short-term follow-up, the implanted scaffolds revealed mild inflammation with fibrotic tissue formation. The decellularized extracelluar matrix developed herein is shown to be feasible for further long-term study for detailed information about muscle regeneration, innervation, and angiogenesis in vivo.

Changes of the Structural and Biomechanical Properties of the Bovine Pericardium after the Removal of α-Gal Epitopes by Decellularization and α-Galactosidase Treatment

Background

Bovine pericardium is one of the most widely used materials in bioprosthetic heart valves. Immunologic responses have been implicated as potential causes of limited durability of xenogenic valves. This study aimed to determine the effectiveness of decellularization and α-galactosidase (α-gal) to remove major xenoreactive antigens from xenogenic tissues.

Materials and Methods

Recombinant Bacteroides thetaiotaomicron (B. thetaiotaomicron) α-gal or decellularization, or both were used to remove α-gal from bovine pericardium. It was confirmed by α-gal-bovine serum albumin-based enzyme-linked immunosorbent assay (ELISA), high-performance anion exchange chromatography, flow cytometry, 3,3'-diaminobenzidine-staining, and lectin-based ELISA. The mechanical properties of bovine pericardium after decellularization or α-gal treatment were investigated by tests of tensile-strength, permeability, and compliance. Collagen fiber rearrangement was also evaluated by a 20,000× transmission electron microscope (TEM).

Results

Recombinant B. thetaiotaomicron α-gal could effectively remove α-gal from bovine pericardium B. thetaiotaomicron (0.1 U/mL, pH 7.2) while recombinant human α-gal removed it recombinant human α-gal (10 U/mL, pH 5.0). There was no difference in the mechanical properties of fresh and recombinant α-gal-treated bovine pericardium. Furthermore, the TEM findings demonstrated that recombinant α-gal made no difference in the arrangement of collagen fiber bundles with decellularization.

Conclusion

Recombinant B. thetaiotaomicron α-gal effectively removed α-gal from bovine pericardium with a small amount under physiological conditions compared to human recombinant α-gal, which may alleviate the harmful xenoreactive immunologic responses of α-gal. Recombinant α-gal treatment had no adverse effects on the mechanical properties of bovine pericardium.

Flexor tendon tissue engineering: acellularization of human flexor tendons with preservation of biomechanical properties and biocompatibility

OBJECTIVE

Acellular human tendons are a candidate scaffold for tissue engineering flexor tendons of the hand. This study compared acellularization methods and their compatibility with allogeneic human cells.

METHOD

Human flexor tendons were pretreated with 0.1% ethylenediaminetetracetic acid (EDTA) for 4  h followed by 24  h treatments of 1% Triton X-100, 1% tri(n-butyl)phosphate, or 0.1% or 1% sodium dodecyl sulfate (SDS) in 0.1% EDTA. Outcomes were assessed histologically by hematoxylin and eosin and SYTO green fluorescent nucleic acid stains and biochemically by a QIAGEN DNeasy kit, Sircol collagen assay, and 1,9 dimethylmethylene blue glycosaminoglycan assay. Mechanical data were collected using a Materials Testing System to pull to failure tendons acellularized with 0.1% SDS. Acellularized tendons were re-seeded in a suspension of human dermal fibroblasts. Attachment of viable cells to acellularized tendon was assessed biochemically by a cell viability assay and histologically by a live/dead stain. Data are reported as mean±standard deviation.

RESULT

Compared with the DNA content of fresh tendons (551±212  ng DNA/mg tendon), only SDS treatments significantly decreased DNA content (1% SDS [202.8±37.4  ng DNA/mg dry weight tendon]; 0.1% SDS [189±104  ng DNA/mg tendon]). These findings were confirmed by histology. There was no decrease in glycosaminoglycans or collagen following acellularization with SDS. There was no difference in the ultimate tensile stress (55.3±19.2 [fresh] vs. 51.5±6.9 [0.1% SDS] MPa). Re-seeded tendons demonstrated attachment of viable cells to the tendon surface using a viability assay and histology.

CONCLUSION

Human flexor tendons were acellularized with 0.1% SDS in 0.1% EDTA for 24  h with preservation of mechanical properties. Preservation of collagen and glycoaminoglycans and re-seeding with human cells suggest that this scaffold is biocompatible. This will provide a promising scaffold for future human flexor tendon tissue engineering studies to further assess biocompatibility through cell proliferation and in vivo studies.

Protein extraction and 2-DE of water- and lipid-soluble proteins from bovine pericardium, a low-cellularity tissue

Bovine pericardium (BP) is an important biomaterial used in the production of glutaraldehyde-fixed heart valves and tissue-engineering applications. The ability to perform proteomic analysis on BP is useful for a range of studies, including investigation of immune rejection after implantation. However, proteomic analysis of fibrous tissues such as BP is challenging due to their relative low-cellularity and abundance of extracellular matrix. A variety of methods for tissue treatment, protein extraction, and fractionation were investigated with the aim of producing high-quality 2-DE gels for both water- and lipid-soluble BP proteins. Extraction of water-soluble proteins with 3-(benzyldimethylammonio)-propanesulfonate followed by n-dodecyl beta-D-maltoside extraction and ethanol precipitation for lipid-soluble proteins provided the best combination of yield, spot number, and resolution on 2-DE gels (Protocol E2). ESI-quadrupole/ion trap or MALDI-TOF/TOF MS protein identifications were performed to confirm bovine origin and appropriate subcellular prefractionation of resolved proteins. Twenty-five unique, predominantly cytoplasmic bovine proteins were identified from the water-soluble fraction. Thirty-two unique, predominantly membrane bovine proteins were identified from the lipid-soluble fraction. These results demonstrated that the final protocol produced high-quality proteomic data from this important tissue for both cytoplasmic and membrane proteins.

Immunoproteomic identification of bovine pericardium xenoantigens

Bovine pericardium is an important biomaterial with current application in glutaraldehyde-fixed bioprosthetic heart valves and possible future application as an unfixed biological scaffold for tissue engineering. The importance of both humoral and cell-mediated rejection responses toward fixed and unfixed xenogeneic tissues has become increasingly apparent. However, the full scope and specific identities of bovine pericardium proteins that can elicit an immune response remain largely unknown. In this study, an immunoproteomic approach was used to survey bovine pericardium proteins for their ability to elicit a humoral immune response in rabbits. A two-stage protein extraction protocol was used to separate bovine pericardium proteins into water- and lipid-soluble fractions. Two-dimensional (2-D) gel electrophoresis was performed to separate the proteins from each fraction. Western blots were generated from 2-D gels of both bovine pericardium protein fractions. These blots were probed with serum from rabbits immunized with bovine pericardium and a secondary antibody was used to assess for IgG positivity. Western blots were compared to duplicate 2-D gels and proteins in matched spots were identified by tandem mass spectrometry. Thirty-one putative protein antigens were identified, eight of which are known to be antigenic from previous studies. All of the putative antigens demonstrated progressive staining intensity with increasing days of post-exposure serum. Identified antigenic proteins represented a variety of functional and structural protein types, and included both cellular and matrix proteins. The results of this study have implications for the use of bovine pericardium as a biomaterial in bioprostheses and tissue engineering applications, as well as xenotransplantation in general.