High pressure pasteurization: Simultaneous native tissue decellularization and sterilization

Introduction

Terminal sterilization is important for the clinical applicability of decellularized xenografts. High hydrostatic pressurization (HHP) process is a potential strategy for decellularization and decontamination of xenografts; however, its disinfection efficiency remains poorly elucidated. This study investigated the disinfection efficacy of the HHP process at physiologically relevant 36 °C against difficult-to-kill spore-forming bacteria.

Methods

Bacillus atrophaeus and Geobacillus stearothermophilus were suspended in a pressurization medium with or without antibiotic agents and pressurized under two different HHP procedures: repeated and sustained pressurization.

Results

The sustained pressurizing conditions, exploited for the conventional tissue decellularization, did not effectively eliminate the bacteria; however, repeated pressurization greatly increased the disinfection effect. Moreover, the antibiotic-containing pressurization medium further increased the disinfection efficiency to the level required for sterilization.

Conclusions

The optimized high hydrostatic pressurization can be used to sterilize biological tissues during the decellularization process and is a promising strategy for manufacturing tissue-derived healthcare products.

Development of a novel regenerative therapy for malignant bone tumors using an autograft containing tumor inactivated by high hydrostatic pressurization (HHP)

Surgical resection of malignant bone tumors leads to significant defects in the normal surrounding tissues that should be reconstructed to avoid amputation. Our research aimed to inactivate osteosarcoma (OS)-affected bone to obtain autologous bone grafts for bone defect reconstruction using a novel therapy called high hydrostatic pressurization (HHP) therapy. The key points are complete tumor death and preservation of the non-denatured native extracellular matrix (ECM) and bone tissue by HHP. Previously, we found that HHP at 200 MPa for 10 min can completely inactivate cells in normal skin and skin tumors, including malignant melanoma and squamous cell carcinoma while maintaining their original biochemical properties and biological components. Based on our previous research, this study used HHP at 200 MPa for 10 min to eradicate OS. We prepared an OS cell line (LM8), pressurized it at 200 MPa for 10 min, and confirmed its inactivation through morphological observation, WST-8 assay, and live/dead assay. We then injected OS cells with or without HHP into the bone marrow of the murine tibia, after which we implanted tumor tissues with or without HHP into the anterior surface of the tibia. After HHP, OS cells did not proliferate and were assessed using a live/dead assay. The pressurized cells and tumors did not grow after implantation. The pressurized bone was well prepared as tumor-free autologous bone tissues, resulting in the complete eradication of OS. This straightforward and short-pressing treatment was proven to process the tumor-affected bone to make a transplantable and tumor-free autologous bone substitute.

Perfusion decellularization for vascularized composite allotransplantation

Vascularized composite allotransplantation is becoming the emerging standard for reconstructive surgery treatment for patients with limb trauma and facial injuries involving soft tissue loss. Due to the complex immunogenicity of composite grafts, patients who undergo vascularized composite allotransplantation are reliant on lifelong immunosuppressive therapy. Decellularization of donor grafts to create an extracellular matrix bio-scaffold provides an immunomodulatory graft that preserves the structural and bioactive function of the extracellular matrix. Retention of extracellular matrix proteins, growth factors, and signaling cascades allow for cell adhesion, migration, proliferation, and tissue regeneration. Perfusion decellularization of detergents through the graft vasculature allows for increased regent access to all tissue layers, and removal of cellular debris through the venous system. Grafts can subsequently be repopulated with appropriate cells through the vasculature to facilitate tissue regeneration. The present work reviews methods of decellularization, process parameters, evaluation of adequate cellular and nuclear removal, successful applications of perfusion decellularization for use in vascularized composite allotransplantation, and current limitations.

Decellularized extracellular matrix scaffolds: Recent trends and emerging strategies in tissue engineering

The application of scaffolding materials is believed to hold enormous potential for tissue regeneration. Despite the widespread application and rapid advance of several tissue-engineered scaffolds such as natural and synthetic polymer-based scaffolds, they have limited repair capacity due to the difficulties in overcoming the immunogenicity, simulating in-vivo microenvironment, and performing mechanical or biochemical properties similar to native organs/tissues. Fortunately, the emergence of decellularized extracellular matrix (dECM) scaffolds provides an attractive way to overcome these hurdles, which mimic an optimal non-immune environment with native three-dimensional structures and various bioactive components. The consequent cell-seeded construct based on dECM scaffolds, especially stem cell-recellularized construct, is considered an ideal choice for regenerating functional organs/tissues. Herein, we review recent developments in dECM scaffolds and put forward perspectives accordingly, with particular focus on the concept and fabrication of decellularized scaffolds, as well as the application of decellularized scaffolds and their combinations with stem cells (recellularized scaffolds) in tissue engineering, including skin, bone, nerve, heart, along with lung, liver and kidney.

Hydrostatic pressure can induce apoptosis of the skin

We previously showed that high hydrostatic pressure (HHP) treatment at 200 MPa for 10 min induced complete cell death in skin and skin tumors via necrosis. We used this technique to treat a giant congenital melanocytic nevus and reused the inactivated nevus tissue as a dermis autograft. However, skin inactivated by HHP promoted inflammation in a preclinical study using a porcine model. Therefore, in the present study, we explored the pressurization conditions that induce apoptosis of the skin, as apoptotic cells are not believed to promote inflammation, so the engraftment of inactivated skin should be improved. Using a human dermal fibroblast cell line in suspension culture, we found that HHP at 50 MPa for ≥ 36 h completely induced fibroblast cell death via apoptosis based on the morphological changes in transmission electron microscopy, reactive oxygen species elevation, caspase activation and phosphatidylserine membrane translocation. Furthermore, immunohistochemistry with terminal deoxynucleotidyl transferase dUTP nick-end labeling and cleaved caspase-3 showed most cells in the skin inactivated by pressurization to be apoptotic. Consequently, in vivo grafting of apoptosis-induced inactivated skin resulted in successful engraftment and greater dermal cellular density and macrophage infiltration than our existing method. Our finding supports an alternative approach to hydrostatic pressure application.

Exploration of the Pressurization Condition for Killing Human Skin Cells and Skin Tumor Cells by High Hydrostatic Pressure

High hydrostatic pressure (HHP) is a physical method for inactivating cells or tissues without using chemicals such as detergents. We previously reported that HHP at 200 MPa for 10 min was able to inactivate all cells in skin and giant congenital melanocytic nevus (GCMN) without damaging the extracellular matrix. We also reported that HHP at 150 MPa for 10 min was not sufficient to inactivate them completely, while HHP at 200 MPa for 10 min was able to inactivate them completely. We intend to apply HHP to treat malignant skin tumor as the next step; however, the conditions necessary to kill each kind of cell have not been explored. In this work, we have performed a detailed experimental study on the critical pressure and pressurization time using five kinds of human skin cells and skin tumor cells, including keratinocytes (HEKas), dermal fibroblasts (HDFas), adipose tissue-derived stem cells (ASCs), epidermal melanocytes (HEMa-LPs), and malignant melanoma cells (MMs), using pressures between 150 and 200 MPa. We pressurized cells at 150, 160, 170, 180, or 190 MPa for 1 s, 2 min, and 10 min and evaluated the cellular activity using live/dead staining and proliferation assays. The proliferation assay revealed that HEKas were inactivated at a pressure higher than 150 MPa and a time period longer than 2 min, HDFas and MMs were inactivated at a pressure higher than 160 MPa and for 10 min, and ASCs and HEMa-LPs were inactivated at a pressure higher than 150 MPa and for 10 min. However, some HEMa-LPs were observed alive after HHP at 170 MPa for 10 min, so we concluded that HHP at a pressure higher than 180 MPa for 10 min was able to inactivate five kinds of cells completely.

Simple and efficient method for consecutive inactivation-cryopreservation of porcine skin grafts

We previously reported that inactivation treatment by high hydrostatic pressurization (HHP) has potential utility as a novel skin regeneration therapy for various skin tumors. In this study, we evaluated whether glycerol-cryopreservation could be applied in order to preserve inactivated skin by HHP using a porcine model. Twenty full-thickness skin grafts (1.5 × 1.5 cm) were prepared from a minipig. The skin samples were inactivated by the HHP in normal saline or glycerol/fructose solution, followed by cryopreservation for 5 weeks at - 80 °C in each same solution. Another 10 grafts immediately after inactivation were prepared as non-cryopreserved controls. Nine grafts in each group were randomly implanted on the fascia of a host pig and removed at 1, 4 and 11 weeks after grafting. All grafts showed engraftment macroscopically. Hematoxylin eosin staining showed the cellular components in all areas of the dermis at 4 and 11 weeks after grafting, and immunohistochemical staining for CD31 showed the presence of capillaries in the grafts in all groups. The surface and cross-sectional areas of grafts in the normal saline solution cryopreserved group decreased between 1 and 11 weeks, whereas these areas in the glycerol cryopreserved group did not decrease significantly. Glycerol cryopreservation may therefore be a simple and efficient method for preserving porcine skin inactivated by HHP.

The sustained release of basic fibroblast growth factor accelerates angiogenesis and the engraftment of the inactivated dermis by high hydrostatic pressure

We developed a novel skin regeneration therapy combining nevus tissue inactivated by high hydrostatic pressure (HHP) in the reconstruction of the dermis with a cultured epidermal autograft (CEA). The issue with this treatment is the unstable survival of CEA on the inactivated dermis. In this study, we applied collagen/gelatin sponge (CGS), which can sustain the release of basic fibroblast growth factor (bFGF), to the inactivated skin in order to accelerate angiogenesis. Murine skin grafts from C57BL6J/Jcl mice (8 mm in diameter) were prepared, inactivated by HHP and cryopreserved. One month later, the grafts were transplanted subcutaneously onto the back of other mice and covered by CGS impregnated with saline or bFGF. Grafts were harvested after one, two and eight weeks, at which point the engraftment was evaluated through the histology and angiogenesis-related gene expressions were determined by real-time polymerase chain reaction. Histological sections showed that the dermal cellular density and newly formed capillaries in the bFGF group were significantly higher than in the control group. The relative expression of FGF-2, PDGF-A and VEGF-A genes in the bFGF group was significantly higher than in the control group at Week 1. This study suggested that the angiogenesis into grafts was accelerated, which might improve the engraftment of inactivated dermis in combination with the sustained release of bFGF by CGSs.

Repair of cartilage defects with devitalized osteochondral tissue: A pilot animal study

Devitalization using high hydrostatic pressure (HHP) treatment inactivates cells while matrix structure and biomechanical properties are maintained. Because of strong chondroinductive potential of HHP-devitalized cartilage matrix, it may be used as scaffold for reconstruction of (osteo-)chondral lesions. In this pilot study, we evaluated the feasibility of HHP-devitalized osteochondral tissue to repair osteochondral defects in a rabbit model. Removal and reimplantation of osteochondral plugs were performed in 12 female New Zealand White rabbits. From the knee joint of each animal, osteochondral plugs (diameter = 4 mm; depth = 2.5 mm) were harvested and devitalized by HHP (452 MPa for 10 min). Afterward, the plugs were reimplanted into the respective cavity, from where they were taken. Animals were sacrificed 12 weeks postoperatively and the integration of osteochondral plugs was examined using μ-CT, MRI, and histological staining. Furthermore, revitalization of HHP-treated osteochondral plugs was characterized by gene expression analyses. Macroscopic evaluation of tissue repair at implantation sites of HHP-treated osteochondral plugs showed an adequate defect filling 12 weeks after implantation. Plug margins were hardly detectable indicating successful tissue integration. Additionally, gene expression analyses demonstrated initial revitalization of the HHP-treated tissue 12 weeks postoperatively. Our preliminary data revealed that HHP-treated osteochondral plugs could be used to refill osteochondral defects in the knee joint and promote cell migration into defect site. Data indicated that HHP-treated tissue has the potential to act as functional scaffolds for reconstruction of cartilage defects. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 2354-2364, 2019.

Melanin pigments in the melanocytic nevus regress spontaneously after inactivation by high hydrostatic pressure

We report a novel treatment for giant congenital melanocytic nevi (GCMN) that involves the reuse of resected nevus tissue after high hydrostatic pressurization (HHP). However, the remaining melanin pigments in the inactivated nevus tissue pose a problem; therefore, we performed a long-term observation of the color change of inactivated nevus tissue after HHP. Pressurized nevus specimens (200 MPa group, n = 9) and non-pressurized nevus tissues (control group, n = 9) were subcutaneously implanted into nude mice (BALB/c-nu) and then harvested 3, 6, and 12 months later. Color changes of the nevus specimens were evaluated. In the 200 MPa group, the specimen color gradually regressed and turned white, and brightness values were significantly higher in the 200 MPa group than in the control group after 6 months. This indicated that melanin pigments in the pressurized nevus tissue had spontaneously degraded and regressed. Therefore, it is not necessary to remove melanin pigments in HHP-treated nevus tissue.