Experimental study of cryopreserved allogeneic transfer of vessel: preliminary report

Cryopreserved allogenic vascular graft in free-flap reconstructive microsurgery: case report

The use of cryopreserved allogenic vascular graft in reconstructive microsurgery has rarely been reported. Here, we report a case of lower extremity reconstruction using cryopreserved hepatic artery as the vein conduit. Postoperative flap perfusion was uneventful with satisfactory wound healing, and graft patency was observed on follow-up color Doppler. Thus, cryopreserved allogenic vascular graft could be a source of vascular conduit in microsurgery.

Effects of cryopreservation and thawing on the structure of vascular segment

The objective of this study was to analyze the importance of the quality of the vascular segment to be cryopreserved and the influence of storage in a gas phase, a liquid phase, or after accidental immersion in liquid nitrogen. In addition, we investigated the effects of rapid versus slow thawing on the occurrence of fractures and changes in the structure of the vessel wall. The tissue sources were whole thoracic and abdominal aortas from 15 pigs. Each aorta was cut into equal segments and randomly assigned to each study group. One segment of fresh unfrozen aorta of the same size was used as a control. The samples were cryopreserved using a programmed apparatus. After 2 weeks the arterial segments were thawed rapidly or slowly. A great variation in the results was obtained depending on the quality of the control. Although endothelial cells were better preserved in the liquid phase, the internal elastic lamina and elastic lamelli showed better preservation and fewer microfractures in the gas phase. The internal elastic lamina showed a greater number of microfractures when an accidental immersion in liquid nitrogen had taken place. Furthermore, better preservation of the structure of the vascular segment was observed with a slow thawing method. In general, the conditions of storage and the method of thawing seem to damage the structure of vascular segments. It is necessary to use a severe protocol of donor and vascular segment selection to optimize the post-thaw quality of the cryopreserved samples.

Patency and structural changes in cryopreserved arterial grafts used as vessel substitutes in the rat

OBJECTIVE

To evaluate the patency and structural changes that occur in the short- and mid-term when cryopreserved syngenic arterial grafts are implanted in an experimental animal model.

MATERIAL AND METHODS

Segments of iliac artery from the Spraque-Dawley rat were cryopreserved in a biological freezer according a controlled, computerized freezing protocol whereby the specimens are cooled at a rate of 1 degrees C/min. After storage at -145 degrees C in liquid N2 vapor for 30 days, the cryografts were slowly thawed. These vessels were grafted to the common iliac artery in syngenic animals. The following study groups were established: group I (GI), non-implanted cryografts; group II (GII), autografts; and group III (GIII), cryoisografts. The control group (CG) was comprised of fresh iliac arteries. The animals were sacrificed 14, 30, or 90 days post-surgery. At each of these follow-up times, graft specimens were morphologically evaluated by light and scanning and transmission electron microscopy and immunolabeling of endothelial cells (vWf). Cell damage attributed to the cryopreservation or grafting process was also determined.

RESULTS

At the time of sacrifice, graft patency was 100% for the autografts, while 26.6% of the cryoisografts showed fully occlusive thrombosis. Among other complications, two pseudoaneurysms were detected. After cryopreservation, the grafts (GI) showed patches of endothelial denudation and good cellularity of the medial layer. The intimal hyperplasia observed in autografts implanted for 14 days (GII) was significantly delayed until day 30 when the graft was cryopreserved (GIII). Cryoisografts showed general thinning of the arterial wall and degeneration accompanied by medial layer cell loss. These grafts showed most cell damage at 90 days post-implant. Expression of the vWf in all specimens showing intimal hyperplasia was confined to the outermost graft layer.

CONCLUSIONS

Cryopreservation modified the reparative response of the grafts. Owing to faster degeneration of the medial layer and a delay in the appearance of intimal hyperplasia, arterial wall thickness was reduced relative to that of the non-cryopreserved autografts. This thinning, at least in the short-term (90 days), does not seem to give rise to aneurysms owing to the generation of a neointima that stabilizes the vessel wall.

Cryopreservation alters antigenicity of allografts in a porcine model of transplant vasculopathy

The need for arterial grafts in coronary surgery to complement autologous vessels has generated interest in cryopreservation of small diameter allografts. We evaluated functional and histologic changes occurring in cryopreserved allografts 3 months after porcine femoral artery transplants.

METHODS

Twenty recipient and 15 donor pigs included a control group of 16 fresh and 12 cryopreserved nonimplant arteries were used. Fresh (n=5) and cryopreserved (n=5) autografts were implanted to assess cryopreservation effects in the absence of rejection. Fresh allografts with or without treatment with cyclosporine (CsA) (n=6 of 8) and cryopreserved allografts with or without treatment with CsA (n=6 of 10) were performed to study the antigenicity of cryopreserved allografts. Arteries were stained with hematoxylin and eosin, Masson's trichrome, and orcein for morphometric analyses and immunostained to identify endothelial cells, smooth muscle cells, T lymphocytes, and macrophages.

RESULTS

Among nonimplant arteries, cryopreservation reduced alpha-actin expression and increased the luminal area. All implanted autografts were patent. Cryopreserved autografts showed reduced alpha-actin expression and developed intimal hyperplasia compared to fresh autografts. Treatment with CsA improved the patency of fresh allografts from 0% to 83% (P <.01) and of cryopreserved allografts from 40% to 100% (P <.05). Cryopreserved allografts showed substantial intimal hyperplasia, and fresh allografts had more T lymphocyte infiltration in the intimal layer with aneurysmal dilatation.

CONCLUSIONS

Cryopreservation reduces the deposition of inflammatory cells and prevents the thrombosis or aneurysmal lesions observed in fresh allografts. Therefore, cryopreservation modifies the antigenicity of vascular allografts.

Long-term Behaviour of Cryopreserved Arterial Grafts Versus Prosthetic Micrografts

INTRODUCTION

When a patient has no suitable vessels for use as grafts in bypass or reconstruction procedures, two of the options available are the use of a cryopreserved vessel or an expanded polytetrafluoroethylene (ePTFE) prosthesis. This study was designed to compare the long-term behaviour of these vascular substitutes.

MATERIAL AND METHODS

We established three study groups by grafting the following vessel substitutes to the iliac artery in Spraque-Dawley rats: arterial autografts (GI, n=12), cryopreserved syngenic arterial grafts (cryoisografts) (GII, n=12), and ePTFE micrografts (GIII, n=12). The animals were sacrificed 180 days after surgery, at which time the graft specimens were morphologically evaluated by light and electron microscopy, immunolabelling (ED1/alpha-actin) and morphometric analysis of the neointima.

RESULTS

At the time of sacrifice, graft patency was 100% for the autografts and cryoisografts, while 10% of the ePTFE micrografts showed fully-occlusive thrombosis. Intimal hyperplasia was observed in grafts in GI and GII; the neointima being thinner in the cryoisografts (54.36 +/- 2.26 microm) than the autografts (161.30 +/- 3.91 microm). The endothelium formed over the prosthetic micrografts was unstable, with areas of subendothelial thickening (9.37 +/- 3.18 microm). Cell loss and medial layer degeneration were observed in both GI and GII specimens, while the GIII grafts were colonised by cells on their luminal surface.

CONCLUSIONS

All three grafts show good long-term tolerance when used in an arterial setting. Following long-term implant, autografts and cryoisografts show similar alterations that give rise to the complete loss of the muscle component of the tunica media along with the formation of a stable neointima. This new layer takes on the role of the tunica media.

New approach to improving endothelial preservation in cryopreserved arterial substitutes

The endothelial loss provoked by the methods of vascular cryopreservation used at most human vessel banks is one of the main factors leading to the failure of grafting procedures performed using cryopreserved vessel substitutes. This study evaluates the effects of the storage temperature and thawing protocol on the endothelial cell loss suffered by cryopreserved vessels, and optimises the thawing temperature and protocol for cryopreserving arterial grafts in terms of that producing least endothelial loss. Segments of the common iliac artery of the minipig (n = 20) were frozen at a temperature reduction rate of 1 degrees C/min in a biological freezer. After storing the arterial fragments for 30 days, study groups were established according to the storage temperature (-80, -145 or -196 degrees C) and subsequent thawing procedure (slow or rapid thawing). Fresh vessel segments served as the control group. Once thawed, the specimens were examined by light, transmission, and scanning electron microscopy. The covered endothelial surface was determined by image analysis. Data for the different groups were compared by one way ANOVA. When cryopreservation at each of the storage temperatures was followed by slow thawing, the endothelial cells showed improved morphological features and viability over those of specimens subjected to rapid thawing. Rapidly thawed endothelial cells showed irreversible ultrastructural damage such as mitochondrial dilation and rupture, reticular fragmentation, and peripheral nuclear condensation. In contrast, slow thawing gave rise to changes compatible with reversible damage in a large proportion of the endothelial cells: general swelling, reticular dilation, mitochondrial swelling, and nuclear chromatin condensation. Gradually thawed cryopreserved arteries showed a lower proportion of damaged cells identified by the TUNEL method compared to the corresponding rapidly thawed specimens (p < 0.05, for all temperatures). In all the groups in which vessels underwent rapid thawing (except at -145 degrees C), significant differences (p < 0.05) in endothelial cover values were recorded with respect to control groups. Storage of cryopreserved vessels at -80 degrees C followed by rapid thawing led to greatest endothelial cell loss (61.36+/-9.06% covered endothelial surface), while a temperature of -145 degrees C followed by slow thawing was best at preserving the endothelium of the vessel wall (89.38+/-16.67% surface cover). In conclusion, storage at a temperature of -145 degrees C in nitrogen vapour followed by gradual automated thawing seems to be the best way of preserving the endothelial surface of the arterial cryograft. This method gives rise to best endothelial cell viability and cover values, with obvious benefits for subsequent grafting.

Effect of cryopreservation on patency and histological changes of arterial isogeneic and allogeneic grafts in the rat model

Vascular grafting is used frequently in the management of length discrepancies between blood vessels. Cryopreservation permits vascular graft storage and aids availability; however, long-term patency of cryopreserved arterial allografts is not well established. Fifty Fisher and 55 Wistar rats were used in the study. Thirty-eight cryopreserved Fisher femoral arterial grafts were transplanted into the femoral arteries of 15 Fisher (cryoisografts) and 23 Wistar rats (cryoallografts). Thirty-two fresh Fisher arterial grafts were implanted into 32 Wistar femoral arteries (fresh allografts). The animals were killed at 1, 4, and 8 months in each group, and graft patency was assessed. One-month graft patency was 100% in all groups. At 4 months, graft patencies were 86%, 100%, and 75% in the cryoisografts, cryoallografts, and fresh allografts respectively. All cryoisografts and fresh allografts were patent, whereas all the cryoallografts were occluded at 8 months ( < 0.01). Cryopreserved rat arterial allografts offered satisfactory graft patency up to 4 months after implantation and may therefore be applicable clinically in selected cases.

Gradual thawing improves the preservation of cryopreserved arteries

This study was designed to test a slow, controlled, automated process for the thawing of cryopreserved arteries, whereby specimen warming is synchronized with the warming of its environment. Segments of minipig iliac artery, 4-5 cm in length, were subjected to controlled, automated cryopreservation in a biological freezer at a cooling rate of 1 degrees C/min to -120 degrees C, followed by storage in liquid nitrogen at -196 degrees C for 30 days. Following storage, the arterial segments were subjected to rapid (warming rate of approximately 100 degrees C/min) or gradual (1 degrees C/min) thawing. Thawed specimens were processed for light microscopy and for scanning and transmission electron microscopy, Cell death was determined by the TUNEL method. Metalloproteinase (MMP) expression was estimated by immunohistochemical analysis. Most of the cryopreserved vessels subjected to rapid thawing showed spontaneous fractures, mainly microfractures, whereas these were absent in slowly thawed specimens. In rapidly thawed vessels, the proportion of damaged cells was double that observed in those thawed more gradually. Increased intensity and extent of MMP-2 expression was shown by rapidly thawed specimens. The slow-thawing protocol tested avoids the formation of spontaneous fractures and microfractures and the accumulation of fluid within the arterial wall tissue. This results in improved tissue preservation.

Rapid thawing increases the fragility of the cryopreserved arterial wall

OBJECTIVE

To extend present knowledge of the biomechanical and structural changes which occur in the cryopreserved, rapidly thawed arterial wall.

MATERIALS AND METHODS

Minipig iliac arterial segments were cryopreserved at -196 degrees C in either minimum essential medium or Wisconsin solution. Fresh segments served as the control group. After 1 month, the specimens were rapidly thawed (37 degrees C) and processed for biomechanical, ultrastructural, morphological and immunohistochemical (MMP-1, MMP-2, MMP-3 and MMP-9) analysis. Visualisation of apoptotic cells was performed by TUNEL method. For the mechanical distension analysis, an in vitro circuit was designed.

RESULTS

The cryopreserved segments showed a 42% incidence of spontaneous fracture and the appearance of microfractures which affected the endoluminal third of the vessel. An accumulation of liquid in the subelastica was observed. An increased expression of wall-degradative enzymes (mainly MMP-2) was also observed following cryopreservation. No significant differences were detected in the proportional elasticity module or tensile strength of the specimen groups. No differences in mechanical distension were observed between groups after the vessel segments were subjected to the pulsatile circuit flow for 72 h. Cell damage was most intense in the specimens cryopreserved in Wisconsin solution.

CONCLUSIONS

Cryopreservation in both the solutions employed, followed by rapid thawing, induce changes in the permeability which increase the fragility of the cryopreserved arterial wall. Both increased expression of wall-degradative enzymes and accumulation of liquid may contribute to graft failure after implantation.

Cartilaginous injury limits cryopreservation of tracheal isograft

OBJECTIVE

Histological recovery of tracheal grafts after cryopreservation was investigated using a rat heterotopic tracheal transplant model in order to evaluate the clinical applicability of tracheal cryopreservation.

METHODOLOGY

Heterotopic syngeneic tracheal transplantation was performed between F344 rats. Recipient animals received either a non-cryopreserved or a cryopreserved tracheal graft for direct comparison with regard to the effect of cryo-injury. In the non-cryopreserved group (CP(-)), tracheal segments were transplanted syngeneically between F344 rats immediately after harvest. Grafts were implanted into the abdominal space and wrapped with the greater omentum. In the cryopreserved group (CP(+)), grafts were implanted after cryopreservation for 7 days at -85 degrees C. Recipient rats were killed on days 7, 14, 21, 28, and at 2 months after surgery. Epithelial regeneration and cartilage changes were evaluated using a semiquantitative four grade scoring system.

RESULTS

Squamous epithelium without ciliated structure was observed on day 7 in both groups. Bronchial epithelium was then regenerated gradually and normally ciliated epithelium was observed on day 28 in both groups. The condition of the epithelium was still well maintained in the CP(-) group at 2 months post-transplantation; however, a severe epithelial defect was observed in the CP(+) group. Bronchial cartilage showed a normal shape and mostly viable chondrocytes with proliferative cell nuclear antigen (PCNA) positive staining at all time points in the CP(-) group until 2 months after surgery. However, in the CP(+) group, a massive loss of viable chondrocytes was observed at 2 months post-transplantation. Macroscopically, CP(+) grafts showed a diminished structure without satisfactory airway lumen at 2 months.

CONCLUSION

The epithelium of a tracheal graft can be temporarily recovered after implantation followed by 7 days cryopreservation. However, bronchial cartilage may be severely damaged by freezing, which results in late destruction with loss of viable chondrocytes. It is suggested here that establishing a method of safe cryopreservation for tracheal cartilage will be imperative to making tracheal cryopreservation possible.

Arterial damage induced by cryopreservation is irreversible following organ culture

OBJECTIVES

The aim of the present study was to investigate the changes which occur to the arterial wall following cryopreservation and thawing and to determine whether these changes are reversible after a week of culture in an organ bath.

MATERIALS AND METHODS

Rat iliac arterial segments were cryopreserved. Once thawed, the arterial segments were cultured for a period of 0, 1, 2, 4 or 7 days. Freshly isolated rat iliac vessels cultured for 7 days served as the control group. Evaluation was made of ultrastructural changes, the expression of metalloproteinase activity (MMP-1, MMP-3 and MMP-9) and the apoptotic state of cells.

RESULTS

The freezing-thawing process induced damage to the arterial segments compared to fresh control vessels. After 1 week of culture, arteries showed a high degree of tissue degeneration. Only a few individual endothelial cells remained on the luminal surface. There was a gradual increase in the proportion of apoptotic cells. The sequential expression of MMP-1 during the first 2 days and subsequent expression of MMP-3 and MMP-9 were of most significance.

CONCLUSIONS

Cryopreservation induced damage to the vessels which could not be reversed by organ culture. The changes observed in the expression of metalloproteinases may be indicative of the degenerative process which occurs in the extracellular matrix.

Fresh and cryopreserved arterial homografts in the treatment of prosthetic graft infections: experience of the Italian Collaborative Vascular Homograft Group

Following the experience of cardiac surgeons with homografts in the treatment of infective aortic valve endocarditis, cardiovascular surgeons have investigated in situ revascularization by means of homografts in the management of vascular prosthetic graft infections. Preliminary results are encouraging, but their late fate in long-term follow-up and the influence of preservation techniques are still under investigation. This article reports the experience of the Italian Collaborative Vascular Homograft Group, with the use of fresh and cryopreserved arterial homografts for the treatment of prosthetic graft infections. Between March 1994 and December 1996, 44 patients with prosthetic graft infection were treated with homografts (13 preserved at 4 degrees C, 31 cryopreserved). The mean age of the patients was 65 years. Emergency surgical procedures were performed in eight patients (18%). Sepsis was diagnosed in 11 patients, aortoenteric fistula in 13, and false aneurysms in 10. Staphylococcus was the main cause of infection. The types of vascular reconstruction with homograft were: 32 aortobifemoral, 3 aortoaortic, 2 iliofemoral, 4 peripheral, and 3 axillobifemoral. Human lymphocyte antigen (HLA) and antibody (ABO) blood group system compatibility between donors and recipients was not respected. The mean duration of follow-up was 15 months (range 1-33). Clinical and duplex scanning evaluations were routinely performed. Computed tomography (CT) or magnetic resonance (MR) scanning or arteriography were performed on the basis of duplex scanning results. There were six deaths during the early postoperative period (30 days) with a mortality rate of 13.6%. During the follow-up there were five late deaths with a mortality rate of 11.4%. Eight patients had graft occlusion. Three cases were successfully treated with thrombectomy. Two cases were successfully treated with femoropopliteal bypass with autologous vein. In three cases leg amputation was necessary. The results of fresh and cryopreserved homograft were compared. No significative differences of early postoperative mortality, late mortality, homograft related mortality, and graft occlusion were observed. We have evaluated the actuarial survival of the patients and the actuarial patency of the homografts on the aortoiliac reconstructions. Twelve months after the surgery the actuarial survival of the patients was 73% and the actuarial patency of the homografts was 56%. In our preliminary experience, we have not observed any significant difference in terms of clinical outcome by using fresh rather than cryopreserved homografts. In the near future it will be our policy to employ only cryopreserved homografts. Moreover, we will extend vessel harvesting to nonheart-beating donors, thus maximizing retrieval. The aforementioned solutions will supply the best graft availability to obtain dimensional and ABO compatibility between donors and recipients.

Long-term cryopreservation can prevent rejection of canine tracheal allografts with preservation of graft viability

We previously reported that cryopreservation of tracheas for 1 month was possible in a canine tracheal autotransplantation model with use of a preservative solution containing trehalose. Realizing that the allogenicity of many organs is decreased by freezing, we examined the possibility of immunosuppressant-free canine tracheal allotransplantation after long-term cryopreservation. Six to 10 rings of the trachea were removed from donor dogs (n = 12), immersed in the preservative solution, and cryopreserved in a deep freezer at -85 degrees C for 285 +/- 28 days (cryopreservation group). Five rings of the mediastinal trachea of recipient dogs were removed. The cryopreserved tracheas were thawed and transplanted to replace the excised mediastinal tracheas. In a control group (n = 6), the graft was preserved in Euro-Collins solution at 10 degrees C for 16 to 17 hours. Allotransplantation of tracheas was done as in the cryopreservation group. The anastomotic site and graft were covered with an omental pedicle in both groups. In the cryopreservation group, every animal, except one that was killed for pathologic examination, survived more than 2 months. All the grafts of this group were viable, and no stenosis or tracheomalacia was observed. In the control group, most of the animals died within 1 month of tracheal stenosis caused by rejection. These findings reveal that immunosuppressant-free canine tracheal allotransplantation was consistently possible after long-term cryopreservation of the graft in a preservative solution containing trehalose. This simple method could solve both donor shortage and immunosuppression problems.

Cold stored femoral vessels as microvascular allografts: a preliminary study

Cold stored femoral arteries or veins have been reinserted successfully as autografts into rabbits. The present study examines whether grafting with cold stored vascular allografts is equally successful. Rabbit femoral arteries and veins were stored at 4 degrees C for 4 weeks before insertion as allografts into unrelated animals. Three weeks after insertion into the femoral artery all venous allografts and 80% of arterial allografts were patent, but patency of both graft types declined over the next few weeks. A small number of cold stored venous allografts when inserted into the femoral vein occluded within 3 weeks. No histological evidence of rejection was apparent. The findings suggest that cold stored vascular allografts could be used successfully as an arterial "prosthesis" to support free flaps where relatively short term patency is required until the flap can establish sufficient peripheral inset to survive in its own right. This technique could be applied when autologous veins are not available or not justified.