Manual cryopreservation of human alveolar periosteal tissue segments: Effects of pre-culture on recovery rate

Non-destructive, spectrophotometric analysis of the thickness of the cell-multilayered periosteal sheet

Background

Autologous tissue-engineered periosteal sheets, which have been clinically applied for periodontal regeneration, sinus lift, and alveolar ridge augmentation, are enriched with osteoblast precursor cells and the abundant deposition of collagen type I in the extracellular spaces. Their quality is inspected prior to clinical use; however, most criteria cannot be evaluated without sacrificing samples. To reduce such losses, we developed a non-destructive optical method that can quantitatively evaluate the thickness of the periosteal sheet.

Methods

Dispersed periosteal cells were inoculated into small pieces of collagen sponge (Terudermis®) and plated into 60-mm dishes for further explant culture using a conventional medium and a stem-cell culture medium. The thickness of periosteal sheets was evaluated using inverted microscopic, histological, labeling (CellVue®)-based imaging and spectrophotometric (Spectro-1®) methods.

Results

The three-dimensional growth of periosteal sheets did not necessarily correlate with two-dimensional growth. The periosteal sheet prepared with the stem-cell medium formed cell multilayers, a phenomenon that could be observed qualitatively by inverted microscopy. The spectrophotometric analysis enabled the quantitative evaluation of the thickness of the cell multilayer without sacrificing the samples processed for scheduled cell therapy.

Conclusions

The growth of periosteal sheets is influenced by several major factors, including the basic quality of the individual original periosteal tissue segments, the technical expertise of doctors and operators involved in tissue harvesting and processing, and culture conditions. This newly developed spectrophotometric analysis can quantify the thickness of cell-multilayered periosteal sheets for quality assurance in a non-destructive manner, thereby contributing to better bone augmentation prior to implant therapy.

Osteoclastogenic Potential of Tissue-Engineered Periosteal Sheet: Effects of Culture Media on the Ability to Recruit Osteoclast Precursors

Cell culture media influence the characteristics of human osteogenic periosteal sheets. We have previously found that a stem cell medium facilitates growth and collagen matrix formation in vitro and osteogenesis in vivo. However, it has not yet been demonstrated which culture medium is superior for osteoclastogenesis, a prerequisite for reconstruction of normal bone metabolic basis. To address this question, we compared chemotaxis and osteoclastogenesis in tissue-engineered periosteal sheets (TPSs) prepared with two types of culture media. Periosteal tissues obtained from adult volunteers were expanded with the conventional Medium 199 or with the stem cell medium, MesenPRO. Hematopoietic enhanced-green-fluorescent-protein (EGFP)-nude mice were prepared by γ-irradiation of Balb/c nu/nu mice and subsequent transplantation of bone marrow cells from CAG-EGFP C57BL/6 mice. TPSs were implanted subcutaneously into the chimeric mice and retrieved after intervals for immunohistopathological examination. EGFP+ cells were similarly recruited to the implantation site in both the TPSs prepared, whereas the distribution of CD11b+ cells was significantly lower in the TPS prepared with the stem cell medium. Instead, osteoclastogenesis was higher in the TPS prepared with the stem cell medium than in the one prepared with the conventional medium. These findings suggest that the stem cell medium is preferable for the preparation of more functional TPSs.

Platelet-Rich Fibrin Extract: A Promising Fetal Bovine Serum Alternative in Explant Cultures of Human Periosteal Sheets for Regenerative Therapy

In 2004, we developed autologous periosteal sheets for the treatment of periodontal bone defects. This regenerative therapy has successfully regenerated periodontal bone and augmented alveolar ridge for implant placement. However, the necessity for 6-week culture is a limitation. Here, we examined the applicability of a human platelet-rich fibrin extract (PRFext) as an alternative to fetal bovine serum (FBS) for the explant culture of periosteal sheets in a novel culture medium (MSC-PCM) originally developed for maintaining mesenchymal stem cells. Small periosteum tissue segments were expanded in MSC-PCM + 2% PRFext for 4 weeks, and the resulting periosteal sheets were compared with those prepared by the conventional method using Medium199 + 10% FBS for their growth rate, cell multilayer formation, alkaline phosphatase (ALP) activity, and surface antigen expression (CD73, CD90, and CD105). Periosteal sheets grew faster in the novel culture medium than in the conventional medium. However, assessment of cell shape and ALP activity revealed that the periosteal cells growing in the novel medium were relatively immature. These findings suggest that the novel culture medium featuring PRFext offers advantages by shortening the culture period and excluding possible risks associated with xeno-factors without negatively altering the activity of periosteal sheets.

A short-term preservation of human cultured periosteal sheets, osteogenic grafting materials, using a commercial preservation solution containing epigallocatechin-3-gallate (Theliokeep(®)) under hypothermic conditions

In the past decade, it has increasingly been reported that epigallocatechin-3-gallate (EGCG), a major catechin derivative extracted from Green tea, has various bioactivities, including a cell-protective action on mammalian cells and tissues. In this study, we have tested a commercial preservation solution containing EGCG (Theliokeep(®)) in both two- and three-dimensional cultures of human periosteal sheets, which have been used as an osteogenic grafting material for periodontal regenerative therapy. When periosteal sheets were 3D-cultured on collagen mesh, cell viability was maintained for 2 days using the hypothermic EGCG preservation solution. Replenishment of EGCG solution with 2-day intervals prevented the time-dependent decline in cell viability at 3 days and later. As observed in nonpreserved control cultures, most cells were positive for proliferating cell-nuclear antigen (PCNA) in the cultures preserved at 4°C in the EGCG solution, whereas PCNA-negative cells were increased in the cultures preserved at 4°C in the MesenPRO medium. In periosteal sheets 2D-cultured in plastic dishes, the EGCG solution occasionally was associated with vacuole formation in the cytoplasm, but cells could again expand in the culture medium at 37°C. As observed in the nonpreserved periosteal sheets control, the osteogenic induction upregulated alkaline phosphatase in those cells and tissues preserved in the EGCG solution. The EGCG solution protected cells from the cold shock-induced membrane phospholipid peroxidation. Our data suggest that the EGCG solution acts as an antioxidant to protect periosteal cells from cold shock and preserves cells under chilled conditions. The limited period of preservation time could be expanded by repeating replenishment of the EGCG solution or by optimizing the formula to be more favorable for human periosteal sheets without sacrificing cell viability. This methodology of preserving human cultured periosteal sheets with EGCG would be expected to support and spread the clinical use of regenerative therapy with autologous periosteal sheets.

Real-time quantitative polymerase chain reaction and flow cytometric analyses of cell adhesion molecules expressed in human cell-multilayered periosteal sheets in vitro

BACKGROUND AIMS

Cultured human periosteal sheets more effectively function as an osteogenic grafting material at implantation sites than do dispersed periosteal cells. Because adherent cell growth and differentiation are regulated by cell-cell and cell-extracellular matrix contacts, we hypothesized that this advantage is a result of the unique cell adhesion pattern formed by their multiple cell layers and abundant extracellular matrix. To test this hypothesis, we prepared three distinct forms of periosteal cell cultures: three-dimensional cell-multilayered periosteal sheets, two-dimensional dispersed cell cultures, and three-dimensional hybrid mock-ups of cells dispersed onto collagen sponges.

METHODS

Periosteal cells were obtained from human alveolar bone. Cell adhesion and extracellular matrix molecules were quantitatively determined at the messenger RNA and protein levels by means of real-time quantitative polymerase chain reaction and flow cytometry, respectively.

RESULTS

Real-time quantitative polymerase chain reaction analysis demonstrated that regardless of culture media α1 integrin, vascular cell adhesion molecule-1, fibronectin and collagen type 1 were substantially upregulated, whereas CD44 was strongly downregulated in periosteal sheets compared with dispersed cell monolayers. With increased thickness, stem cell medium upregulated several integrins (β1, α1 and α4), CD146, vascular cell adhesion molecule-1, fibronectin and collagen type 1 in the periosteal sheets. Flow cytometric analysis revealed that the active configuration of β1 integrin was substantially downregulated in the stem cell medium-expanded cell cultures. The cell adhesion pattern found in the mock-up cultures was almost identical to that of genuine periosteal sheets.

CONCLUSIONS

Integrin α1β1 and CD44 function as the main cell adhesion molecule in highly cell-multilayered periosteal sheets and dispersed cells, respectively. This difference may account for the more potent osteogenic activity shown by the thicker periosteal sheets.

Application of stem-cell media to explant culture of human periosteum: An optimal approach for preparing osteogenic cell material

As part of our clinical tests on bone regeneration using cultured periosteal sheets, here, we prepared cultured periosteal sheets in two types of stem-cell culture media, STK1 and STK3. Human periosteum was expanded either in 1% human serum–supplemented STK1 for 28 days, in 1% human serum–supplemented STK1 for 14 days followed by 1% human serum–supplemented STK3 for 14 days (1% human serum–supplemented STK1+3), or in 10% fetal bovine serum–supplemented Medium 199 for 28 days (control). Cultured periosteal sheet diameter and DNA content were significantly higher, and the multilayer structure was prominent in 1% human serum–supplemented STK1 and 1% human serum–supplemented STK1+3. The messenger RNA of osteoblastic markers was significantly upregulated in 1% human serum–supplemented STK1+3. Osteopontin-immunopositive staining and mineralization were evident across a wide area of the cultured periosteal sheet in 1% human serum–supplemented STK1+3. Subcutaneous implantation in nude mice following expansion in 1% human serum–supplemented STK1+3 produced the highest cultured periosteal sheet osteogenic activity. Expansion in 1% human serum–supplemented STK1+3 successfully induced cultured periosteal sheet growth while retaining osteogenic potential, and subsequent osteoblastic induction promoted the production of homogeneous cell material.

An improved freeze-dried PRP-coated biodegradable material suitable for connective tissue regenerative therapy

We previously published an investigation indicating freeze-dried platelet-rich plasma (PRP)-coated polyglactin mesh was a promising wound-dressing material. However, one of its disadvantages was the inflammatory nature due to degradation of the polyglactin. Therefore, in this study, we investigated the use of a collagen sponge as the carrier for PRP. When implanted subcutaneously in nude mice, the PRP-coated sponge alone rapidly induced angiogenesis and infiltration of surrounding connective tissue without inducing appreciable inflammation. Moreover, addition of periosteal fibroblastic cells substantially augmented the angiogenic response. With in vitro studies, the PRP-coated sponge provided various major growth factors at high levels to stimulate the proliferation of cells cultured on plastic dishes, but did not stimulate the proliferation of cells inoculated into the PRP-coated sponge. Cells were embedded in the fibrin mesh and maintained their spherical shape without stretching. The atomic force microscopic analysis demonstrated that the fibrin gel formed on the PRP-coated sponge was much softer (approx. 22 kPa) than the cross-linked collagen that formed the sponge base (appox. 1.9 MPa). Because insoluble matrices have recently and increasingly been considered important regulatory factors of cellular behavior, as are soluble growth factors, it is suggested that this soft fibrin mesh possibly suppresses cell survival. Overall, our investigation has successfully demonstrated improved wound-healing and regenerative potential of the PRP-coated mesh by combining it with the collagen sponge. In the clinical setting, this PRP-coated collagen sponge is a promising material for connective tissue regenerative therapy, such as periodontal therapy, burn victim treatment and in cosmetic or plastic surgery.

Tissue culture of human alveolar periosteal sheets using a stem-cell culture medium (MesenPRO-RS™): In vitro expansion of CD146-positive cells and concomitant upregulation of osteogenic potential in vivo

We have previously demonstrated that multilayered periosteal sheets prepared from the explant culture of alveolar periosteum serve as a promising osteogenic grafting material in periodontal tissue regeneration. For the preparation of more potent periosteal sheets, we examined the applicability of stem-cell culture media. Compared to the control medium (Medium 199+10% FBS), periosteal sheets expanded with MesenPRO-RS™ medium exhibited these features: Cells grew three-dimensionally and deposited collagen in the extracellular spaces to form thicker multilayers of cells. Chondrocytic markers were not significantly upregulated. Contractile force was generated in proportion with the increased thickness of the periosteal sheets and the formation of cytoplasmic α-smooth muscle actin fibers. However, myofibroblastic markers were not significantly upregulated. The surface marker CD146 was substantially upregulated, while both CD73 and CD105 were downregulated. Alkaline phosphatase, a representative osteoblastic marker, was not upregulated by osteogenic induction. However, these expanded periosteal sheets exhibited substantially stronger osteogenic differentiation when implanted in nude mice. Therefore, despite our reservations, MesenPRO medium effectively expanded the cells contained in periosteal sheets to promote the formation of thicker multilayers of cells in vitro, and these enhanced periosteal sheets expressed increased osteogenic potential at implantation sites in vivo. In conjunction with data indicating that CD146-positive cells were notably expanded and the recently proposed concept that CD146 is a marker for osteogenic progenitor cells found in the bone marrow stroma, our findings suggest that MesenPRO medium improves the preparation of highly osteogenic periosteal sheets suitable for clinical application largely through the induction of CD146-positive cells.