Maximal period of cryopreservation with the Bicell biofreezing vessel for rat tracheal isografts

Surgical Skills Training with Cryopreserved Rat Stomachs

The objective of this study is to present a high-fidelity bench model of cryopreserved stomachs that can be used while learning surgical skills. Thirty stomachs were harvested from Wistar rats at the end of non-abdominal research studies. The stomachs were washed with cold saline solution and filled with hyaluronic acid solution. The organs were then placed into cryovials and cryopreserved at -30 °C for 60 days. The stomachs were thawed to room temperature on the day of the surgical skills practice and two full-thickness incisions were made. Reporting on their experiences, 22 participants (73.33%) felt that the cryopreserved stomach was identical to in vivo rat stomachs, 24 (80.00%) reported that the stomach was easy to handle, and 27 (90%) reported the tissue was non-friable. Moreover, 29 participants (96.6%) finished the suturing without tears and 100% recommended it as a biomaterial for surgical training. The cryopreserved stomach is a practical, reproducible, low-cost, and high-fidelity bench model that allows surgical fellows to learn how to handle a stomach and improve their surgical abilities before performing surgery on patients or laboratory animals.

Cryopreservation of the tracheal grafts: Review and perspective

Transplantation of the trachea may become the preferred method for the reconstruction of extensive tracheal defects, however, several unresolved problems must be addressed, such as immunosuppression, preservation and donor shortage. In this manuscript, the cryopreservation of tracheal grafts is reviewed, which potentially is associated with a lessened immunological response. Cryopreservation may be used clinically for long-term preservation and may solve the donor shortage. It is very important to confirm the immunomodulatory effect of cryopreservation on tracheal allografts in order to expand the potential clinical application of tracheal transplantation in the future. The cartilage as well as the epithelium and lamina propria serve as targets for rejection. However, the effect of cryopreservation on chondrocytes could be associated with reduced allogenicity of the trachea. The long-term cryopreservation of cartilage must be investigated in basic research models of chondrocyte viability. Growth of cryopreserved tracheal allografts is less well understood. Further studies are needed to elucidate the mechanism of synergistic effects of both cryopreservation and adequate immunosuppression for tracheal xenografts.

Bone marrow-derived mesenchymal stem cells enhance cryopreserved trachea allograft epithelium regeneration and vascular endothelial growth factor expression

BACKGROUND

Epithelium regeneration and revascularization of tracheal implants are challenging issues to be solved in tracheal transplantation research. Bone marrow-derived mesenchymal stem cells (BMSCs) can migrate to the damaged tissue and promote functional restoration. Here, we applied intravenous transplantation of BMSCs combined with a cryopreserved allograft to investigate the role of BMSCs in enhancing implant survival, tracheal epithelium regeneration and revascularization.

METHODS

After transplantation with cryopreserved allografts, PKH-26 labeled 3 to 5 passage BMSCs were injected into recipient rats through the tail vein. Rats in the control groups were injected with a comparable amount of phosphate-buffered saline. We observed the histology of the tracheal allograft and measured vascular endothelial growth factor (VEGF) protein levels in the epithelium to evaluate the effect of BMSCs on epithelium regeneration and revascularization.

RESULTS

Histologic observation of the rats from the BMSCs injection groups showed that the tracheal lumen was covered by pseudostriated ciliated columnar epithelium. The cartilage structure was intact. There were no signs of denaturation or necrosis. PKH-26 labeled BMSCs migrated to the implant site and exhibited red fluorescence, with the brightest red fluorescence at the anastomotic site. VEGF protein levels in the allograft epithelium of the BMSCs injection group were higher than the levels in the phosphate-buffered saline injection group.

CONCLUSIONS

Our results indicate that given systemic administration, BMSCs may enhance epithelium regeneration and revascularization by upregulating VEGF expression.

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

Cultured human periosteal sheets constitute a promising grafting material for periodontal tissue regenerative therapy. However, preparation of these sheets usually requires six weeks or longer, and this lengthy commitment and delay limits both clinical applicability and availability. The aim of this study is to develop an efficient, practical, cost-effective cryopreservation method for periosteal tissue segments (PTSs). Human PTSs were aseptically excised from alveolar bone and pre-cultured in Medium 199+10% fetal bovine serum (FBS) for the indicated number of days before they were slowly frozen down to -75°C in a commercial freezing vessel using medium containing 10% dimethyl sulfoxide (Me(2)SO) and various concentrations of FBS. After fast-thawing at 37°C, PTSs were again cultured, and their growth and responses to standard osteogenic induction were evaluated (vs. freshly excised PTSs). Proliferating cells were obtained at the highest levels from cryopreserved PTSs that were pre-cultured for 14 days before freezing. When a concentration of 50% or more FBS was included in the cryopreservation solution, cells migrated out more actively and grew faster. Importantly, osteoinduction up-regulated alkaline phosphatase (ALP) activity and osteoblastic marker mRNAs in cryopreserved PTS-derived sheets just as effectively as it did in native PTS-derived ones. These data suggest that pre-conditioned PTSs can be efficiently cryopreserved in a freezing solution containing high FBS by traditional manual cryopreservation methods without aid of a program freezer or more elaborate equipment.

Cryopreserved Tracheal Grafts: A Review of the Literature

Cryopreserved tracheal grafts have been used in several experimental models of long segment replacement. The clinical application of the procedure has been limited due to the fact that contradictory results have been reported. The purpose of this article is to present a review of the literature on tracheal cryopreservation. Despite the fact that most authors indicate that cryopreserved tracheal allografts retain viability and have a low immunological response, though they continue to function after transplantation with good epithelialization and patency, cryopreservation leads to significant damage to cartilage, the degree of which is based on the freezing-storage methods that affect the function and durability of a graft. The long-term storage of cartilage must therefore be investigated in more detail in basic research models of cartilage viability: the evaluation of chondrocyte apoptosis, and the use of different solutions for tracheal cryopreservation other than RPMI-1640, Dulbecco's modified Eagle's, Eurocollins, and TC-199. Furthermore, problems that involve improving the blood supply to the graft after extensive resection and immunosuppression must be resolved before tracheal cryopreservation can become a clinically established method for tracheal grafts.

The fate of homograft tracheal transplants in sheep

OBJECTIVE

An established method of tracheal substitution is not yet available, but homograft tracheal transplantation might provide a realistic tracheal replacement. With the objective of sequentially examining the healing of tracheal homografts, we have established a suitable large-animal model.

METHODS

Five sheep received orthotopic tracheal transplantation of a 4-cm cervical tracheal homograft. The trachea was supported for 6 weeks with a self-expanding polyester stent. The plan was to euthanize the animals after 2, 4, 8, 12 and 16 weeks, or whenever complications occurred.

RESULTS

The implantation itself was performed without complications. After 2 weeks the homograft was firmly encapsulated by connective tissue, without signs of necrosis or abscess. The original mucous membrane no longer existed; the cartilage rings were exposed. In all animals that were euthanized at the later dates, the homografts were completely absorbed and replaced by inflammatory scar tissue. This, in turn, was covered with a shiny cellular surface layer.

CONCLUSIONS

The results from this animal experiment reveal-contrary to data published to date-that tracheal homografts are not incorporated but absorbed. They are replaced by scar/granulation tissue that cannot secure the stability of the trachea. Therefore, further experiments with respect to the biocompatability of homografts appear to be necessary.

Efficacy of Multiglycosidorum tripterygii for rat tracheal allografts

BACKGROUND

A new immunosuppressant must be developed because graft rejection remains the leading cause of death after lung transplantation. We evaluated the efficacy of Multiglycosidorum tripterygii as a new immunosuppressant using a heterotopic rat tracheal allotransplantation model.

METHODS

We performed short- and long-term experiments using a short-course of treatment with Multiglycosidorum tripterygii. To assess the immunosuppessive power of Multiglycosidorum tripterygii, we compared its efficacy (at 90, or 150 mg/kg/day) with that of tacrolimus (at 0.5, 1.0, or 1.5 mg/kg/day) at 4 weeks after transplantation. We then evaluated the effect of 150 mg/kg/day of Multiglycosidorum tripterygii treatment at 12 weeks after transplantation.

RESULTS

The efficacy of 150 mg/kg/day Multiglycosidorum tripterygii was superior to that of 90 mg/kg/day of the same drug and was comparable to that of 1.0 mg/kg/day tacrolimus, as demonstrated by morphologic assessment of the graft. Treatment with 150 mg/kg/day Multiglycosidorum tripterygii maintained graft morphology for 4 weeks but could not maintain graft viability for 12 weeks. Animals tolerated this dosage of Multiglycosidorum tripterygii for 12 weeks after administration.

CONCLUSIONS

We conclude that the efficacy of Multiglycosidorum tripterygii is acceptable for rat tracheal allografts. Further studies are necessary to investigate Multiglycosidorum tripterygii treatment for clinical use in humans.

The effects of pretreatment with donor antigen and immunosuppressive agents on fully allogenic tracheal graft

BACKGROUND

Obliterative bronchiolitis is a major clinical problem in cases involving a transplanted lung. We examined drug-induced tolerance to a fully allogenic tracheal graft in a murine heterotopic transplantation model.

MATERIALS AND METHODS

Recipient mice (C57BL/6) were primed iv with 1 x 10(8) splenocytes of donor mice (BALB/c). Day 0 was the day of the splenocyte injection. Cyclophosphamide and Busulfan were injected intraperitoneally on day 2. On day 3, 1 x 10(7) donor bone marrow cells were intravenously injected. On day 28, a donor tracheal graft was implanted into a subcutaneous pocket. Grafts were harvested at 3-week intervals, and the degree of obstruction of the inner cavity, the condition of epithelium, and the viability of chondrocytes were examined.

RESULTS

All of the isograft controls (BALB/c) and grafts implanted in the T cell-free recipients (BALB/c-nu) showed patent, lined epithelium and viable chondrocytes. All allografts tested showed total luminal occlusion by granulative tissue and inflammatory cells, and the epithelium was totally absent. Five of 11 drug-treated grafts were completely patent, although the epithelium was almost absent and the chondrocytes were substantially destroyed. However, when the chimerism was analyzed by flow cytometry analysis of the recipient T cells, approximately 90% of the donor cells were recognized.

CONCLUSIONS

Even by this pre-treatment-induced chimerism, a transplanted allogenic trachea was not completely preserved. The present results suggest that a non-allogenic response might have contributed to the rejection.

Allowable warm ischemic time to tracheal extraction for allotransplantation of cryopreserved trachea

OBJECTIVE

The allowable warm ischemic time from circulatory arrest to tracheal extraction for allotransplantation of cryopreserved tracheal grafts from cadaveric donors was examined in adult mongrel dogs.

SUBJECTS AND METHODS

The animals were divided into 4 groups (n = 28) according to the warm ischemic time of less than 1 hour, 3 hours, 6 hours, and 12 hours, after transplantation, and comparisons were made. The grafts were cryopreserved for at least 2 months and were evaluated by extraction from the recipients generally 2 months after transplantation.

RESULTS

All the grafts with a warm ischemic time of less than 1 hour were viable and did not show stenosis. This group did not differ significantly from the groups with a warm ischemic time of 3 and 6 hours in terms of viability. However, all of the grafts with a warm ischemic time of 12 hours showed stenosis, and there was a significantly lower viability rate. Histological examination of the grafts showed that warm ischemia caused necrosis of the tracheal cartilage.

CONCLUSION

Based on these results, it was concluded that 6 hours was the maximum allowable warm ischemic time for cryopreserved tracheal transplantation, and that necrosis of the tracheal cartilage due to warm ischemia reduced the viability of the grafts.

The immunomodulatory effect of cryopreservation in rat tracheal allotransplantation

BACKGROUND

Cryopreservation is one solution to the problem of donor organ deficit. To investigate the effect of cryopreservation on tracheal allografts, we performed 2 experiments in rats.

METHODS

In Experiment 1, we assessed second-set graft rejection. Two weeks after primary heterotopic transplantation (Group 1, fresh isografts; Group 2, fresh allografts from Lewis rats; and Group 3, cryopreserved allografts from Lewis rats; n = 5, respectively), each animal underwent secondary heterotopic grafting with isografts and allografts from Lewis and Wistar Furth rats (n = 5, respectively). Four weeks after the secondary transplantation, all grafts were retrieved for histologic analysis. In Experiment 2, we assessed the long-term results of allograft cryopreservation, without immunosuppression therapy. Six months after transplantation of fresh (Group 4) and cryopreserved (Group 5) allografts, the tracheal segments (each group, n = 5) were histologically evaluated.

RESULTS

In Experiment 1, only the secondary allografts from Lewis rats in Group 2 did not maintain lumen structure and often showed dislocated or destroyed cartilage. Second-set graft rejection was specifically recognized in Group 2, but not in Group 1 or 3. In Experiment 2, the cryopreserved allografts appeared almost normal and lumen rigidity was preserved 6 months after transplantation. These allografts were superior to the fresh allografts in patency and in cartilage dislocation and mononuclear cell infiltration scores, but not in the viable chondrocyte ratio.

CONCLUSIONS

We conclude that cryopreservation may produce successful long-term results because of its immunomodulatory effect on tracheal allografts.

Failure of airway healing in an ovine autotransplantation model that includes basic fibroblast growth factor

OBJECTIVE

Basic fibroblast growth factor is among the most potent promoters of angiogenesis. Its ability to enhance the blood supply to ischemic airways or nonvascularized tracheal autograft has been demonstrated. Its cumulative effect with muscular wrapping and its efficacy in a noncanine large animal model remain unknown. Treatment with basic fibroblast growth factor and muscular wrapping were compared with no special treatment and with muscular wrapping alone in an ovine tracheal autotransplantation model.

METHODS

All sheep underwent orthotopic tracheal transplantation with 5 to 8 ring autografts in the cervical trachea. Fifteen sheep were classified randomly into the following three groups: no treatment (group A, n = 5), muscular wrapping with the right sternomastoid muscle (group B, n = 5), and topical administration of fibrin glue enriched with 2 microg/cm(2) basic fibroblast growth factor (group C, n = 5).

RESULTS

Devascularized tracheal autografts were unable to maintain their structural integrity without other treatment (group A). However, the grafts were surrounded by well-vascularized connective tissue. In the muscular wrapping group (group B), infections occurred around the grafts, and the muscular wrapping was subject to necrosis. No neovascularization of the grafts occurred. Therapy with basic fibroblast growth factor (group C) led to improved muscular wrapping circulation and to adherence to the tracheal stumps. However, no success was achieved in validating the circulation in the grafts.

CONCLUSIONS

In contrast to the results achieved by other authors with canine models, the neovascularization of tracheal autografts was not achieved in sheep with the topical administration of basic fibroblast growth factor. Cranially pediculated muscular wrapping led to poorer circulation in the tissue around the graft than did no therapy at all.

Effect of cryopreservation period on rat tracheal allografts

BACKGROUND

The effect of cryopreservation on tracheal allogenicity is still unclear. Therefore, in this study, we assessed the effect of cryopreservation period on tracheal allografts in 62 rats.

METHODS

Each transplant consisted of a 3-ring segment of the trachea harvested from 8 Lewis rats, immersed in preservation solution, and cryopreserved and stored in a Bicell biofreezing vessel in a deep freezer at -80 degrees C. Six tracheal grafts without cryopreservation that underwent a heterotopically syngeneic transplantation into the omentum served as controls. Forty-eight tracheal segments were randomly assigned to 8 groups according to period of cryopreservation, which ranged from 0 to 12 months (0, 0.5 [2 weeks], 1, 2, 3, 6, 9 and 12 months). The cryopreserved grafts were then thawed and heterotopically implanted into the omentum of recipient Brown-Norway rats. After 28 days, the tracheal segments were then evaluated histologically.

RESULTS

All isografts in Group 1 were intact, whereas the allografts undergoing a particularly shorter period of cryopreservation showed a more stenotic lumen. Prolonged periods of cryopreservation tended to show decreasing tendencies of viability of chondrocytes, mononuclear cell infiltration and sub-epithelial thickness, whereas all allografts showed a uniformly denuded epithelium, irrespective of the length of cryopreservation.

CONCLUSIONS

A longer period of cryopreservation may help to maintain a better patency of tracheal allografts by preventing an allogeneic response. Reduced tracheal allogenicity may be associated with a decreased viability of chondrocytes by cryopreservation.

Tracheal allotransplantation maintaining cartilage viability with long-term cryopreserved allografts

BACKGROUND

Cartilage viability of a cryopreserved tracheal allograft seems to affect graft function and durability. We previously reported the influence of warm ischemia and cryopreservation on cartilage viability of tracheal allografts. For the clinical application of tracheal allotransplantation, it is essential to preserve grafts for a long time. In this study, we assessed cartilage viability of tracheal allografts after long-term cryopreservation in transplantation models.

METHODS

The tracheas were harvested from Lewis rats. The grafts were frozen to -80 degrees C in a programmable freezer immediately after being harvested and were then stored in liquid nitrogen (-196 degrees C) for different lengths of preservation (1, 2, 6, 9, 12, 18, and 24 months; n for each group = 8). Cartilage viability was evaluated by estimating proteoglycan synthesis. After harvest or thawing of the tracheas, the cartilage was labeled with 4 muCi/mL of Na2 35SO4. Specimens were then hydrolyzed in 0.5 mol/L NaOH, and a solution of the extracts was then counted by a liquid scintillation counter. 35Sulfur incorporation before and after cryopreservation was examined in each group. Tracheal allotransplantation was performed using Lewis rats as donors and Brown Norway rats as recipients.

RESULTS

The average 35S incorporation in the cartilage before cryopreservation was 224 +/- 17 disintegrations per minute per milligram of tissue protein. The average 35S incorporation in the cartilage after cryopreservation decreased to 67% to 76% compared with that before cryopreservation. There were no significant differences among the groups in 35S incorporations after cryopreservation. Histologic examination after transplantation revealed normal tracheal cartilage in all groups.

CONCLUSIONS

The viability of tracheal cartilage after cryopreservation decreased to 67% to 76%. There were no significant differences in viability of cartilage among the tracheas after different lengths of cryopreservation. Tracheal allotransplantation after long-term cryopreservation can be safely performed in the rat model.

Feasibility of cryopreserved tracheal xenotransplants with the use of short-course immunosuppression

OBJECTIVE

We evaluated the feasibility of discordant xenotransplantation of the cryopreserved trachea with intermittent immunosuppression to help solve the shortage of donor tracheas.

METHODS

Two experiments were performed with heterotopic transplantation models in 14 guinea pigs and 85 rats. So that the minimal dose of FK506 for viable fresh xenografts could be determined, FK506 was given in escalating doses (0, 1.5, 2.5, and 3.5 mg/kg) for recipient animals after xenogeneic transplantation. With the goal of obtaining a long-term survival of the xenografts, the effect of cryopreservation on xenografts was assessed and thereafter different cycles of immunosuppression every third week were evaluated in fresh or cryopreserved xenografts in the second experiment.

RESULTS

An FK506 dosage of more than 2.5 mg/kg per day was much more effective than smaller dosages, as demonstrated by morphologic assessment. A higher dosage of FK506 potentially delayed the rejection of xenografts and can thus maintain tracheal xenograft viability for less than 4 weeks in rat recipients. In experiment 2, the cryopreserved xenografts showed less histologic viability than fresh xenografts but greater patency of the lumen. The patency of cryopreserved xenografts was favorably maintained for a longer period than that of fresh xenografts with either the same number or more cycles of immunosuppression.

CONCLUSIONS

We conclude that the synergistic effect of cryopreservation and adequate intermittent immunosuppression may enable tracheal xenografts to remain viable over longer periods.

Effects of warm ischemia and cryopreservation on cartilage viability of tracheal allografts

BACKGROUND

For clinical use of a cryopreserved tracheal allograft, it is important to evaluate cartilage viability. We assessed cell viability of the cartilage in a cryopreserved tracheal allograft by measurement of Na2 35SO4 incorporation. We also investigated the effects of warm ischemic time on tracheal cartilage viability.

METHODS

The tracheas from Lewis rats were harvested and preserved at different warm ischemic times from cardiac death to preservation (0, 1, 2, 4, 6, 9, and 12 hours, each group n = 8). The cartilage was labeled with 4 muCi/mL of Na2 35SO4. The specimen was hydrolyzed in 0.5 mol/L NaOH, and a solution of the extracts was then counted by liquid scintillation counter. Tracheas were transplanted into Brown Norway rats.

RESULTS

35Sulfur incorporation in the cartilage decreased as warm ischemic time increased. In addition, 35Sulfur incorporation decreased from 76% to 67% after cryopreservation. Histologic examinations of the normal tracheal cartilage before preservation and after thawing were done in all the groups. After transplantation, the cartilage had severe fibrous changes, and its layer was almost nonobservable in the 9- and 12-hour groups.

CONCLUSIONS

The viability of the tracheal cartilage decreased with warm ischemic time and from 76% to 67% after cryopreservation. In the rat tracheal transplantation model, a cryopreserved tracheal allotransplant could be done safely with a graft that was cryopreserved within 6 hours of warm ischemic time.

Limit of warm ischemia time before cryopreservation in rat tracheal isografts

BACKGROUND

The viability of cadaveric tracheal grafts undergoing cryopreservation is still unclear. We evaluated the limit of warm ischemia time before cryopreservation in rat tracheal isografts.

METHODS

Each isograft was harvested from donor rats 0 to 48 hours (0, 6, 12, 18, 24, and 48 hours) after circulatory arrest, immersed in the preservative solution, and stored in a deep freezer until reaching -80 degrees C and then was kept in liquid nitrogen for 3 months. Heterotopic transplantation into the omentum was performed after the isografts were thawed. Graft morphology 3 months after transplantation was assessed.

RESULTS

The stepwise increase of warm ischemia time significantly reduced graft survival. A prolonged period of warm ischemia had a degenerative effect on both the epithelium and cartilage. The morphology of the epithelium and cartilage in isografts undergoing warm ischemia for less than 18 hours was better preserved, whereas it deteriorated in isografts undergoing warm ischemia for more than 24 hours.

CONCLUSIONS

We thus conclude that the permissible period of warm ischemia before 3-month cryopreservation to maintain tracheal isograft viability is 18 hours in rats.