Long-term Behaviour of Cryopreserved Arterial Grafts Versus Prosthetic Micrografts

Implantation of Adipose-Derived Mesenchymal Stromal Cells (ADSCs)-Lining Prosthetic Graft Promotes Vascular Regeneration in Monkeys and Pigs

BACKGROUND

Current replacement procedures for stenosis or occluded arteries using prosthetic grafts have serious limitations in clinical applications, particularly, endothelialization of the luminal surface is a long-standing unresolved problem.

METHOD

We produced a cell-based hybrid vascular graft using a bioink engulfing adipose-derived mesenchymal stromal cells (ADSCs) and a 3D bioprinting process lining the ADSCs on the luminal surface of GORE-Tex grafts. The hybrid graft was implanted as an interposition conduit to replace a 3-cm-long segment of the infrarenal abdominal aorta in Rhesus monkeys.

RESULTS

Complete endothelium layer and smooth muscle layer were fully developed within 21 days post-implantation, along with normalized collagen deposition and crosslinking in the regenerated vasculature in all monkeys. The regenerated blood vessels showed normal functionality for the longest observation of more than 1650 days. The same procedure was also conducted in miniature pigs for the interposition replacement of a 10-cm-long right iliac artery and showed the same long-term effective and safe outcome.

CONCLUSION

This cell-based vascular graft is ready to undergo clinical trials for human patients.

Outcomes of long storage times for cryopreserved vascular grafts in outflow reconstruction in living donor liver transplantation

The outflow reconstruction of the right anterior sector in a right liver graft (RLG) with cryopreserved vascular grafts (CVGs) is crucial for preventing graft congestion in living donor liver transplantation (LDLT). The impact of the duration of cryopreservation has not been evaluated so far. From 2006 to 2009, 250 LDLT were performed: 47 of these patients (group 1) received CVGs stored for ≦1 year, and 33 patients (group 2) received CVGs stored for >1 year. Single or multiple segment 8 hepatic veins were reconstructed. The number of anastomoses did not affect vascular graft patency (P = 0.21). The length of the cryopreservation time did not affect the histological findings for CVGs. The preoperative and postoperative liver graft volumes were 783.8 ± 129.7 and 1102 ± 194.7 cc, respectively, for group 1 and 753.7 ± 158.5 and 1097.2 ± 178.7 cc, respectively, for group 2. The regeneration indices for liver grafts in the whole patient group, group 1, and group 2 were 48.9%, 47.4%, and 51.05%, respectively. In conclusion, the storage duration has no impact on the patency of CVGs in outflow reconstruction or on the regeneration of RLGs in LDLT. CVGs stored for >1 year can be safely used for the outflow reconstruction of RLGs in LDLT.

Right renal vein extension with cryopreserved external iliac artery allografts in living-donor kidney transplantations

INTRODUCTION

A short right renal vein remains a challenge for renal transplant surgery, especially in the living donor. Our objective was to report on a new technique to solve this problem.

TECHNICAL CONSIDERATIONS

We describe our experience with the use of cryopreserved iliac artery grafts for right renal vein extension. Two renal grafts from living donors with a short right renal vein were subjected to an extension with a cryopreserved external iliac artery allograft. There were no perioperative or postoperative complications. There were also no changes in ischemia times. The renal implantation was performed easily and conveniently using our standard technique. For the first and second procedures, at 3 and 3.5 years after surgery, respectively, both vascular grafts maintain good patency, and the renal function of both recipients is optimal.

CONCLUSION

Tissue-banked cryopreserved cadaveric vessels can be a useful tool in renal transplant surgery. The use of a cryopreserved iliac artery for renal vein extension is a simple and effective new technique that can be added to the pool of surgical solutions for a short renal vein in living-donor kidney transplantation. To our knowledge, this is the first time that the use of such grafts for this purpose has been described.

Inhibiting connexin channels protects against cryopreservation-induced cell death in human blood vessels

OBJECTIVES

Cryopreserved blood vessels are being increasingly employed in vascular reconstruction procedures but freezing/thawing is associated with significant cell death that may lead to graft failure. Vascular cells express connexin proteins that form gap junction channels and hemichannels. Gap junction channels directly connect the cytoplasm of adjacent cells and may facilitate the passage of cell death messengers leading to bystander cell death. Two hemichannels form a gap junction channel but these channels are also present as free non-connected hemichannels. Hemichannels are normally closed but may open under stressful conditions and thereby promote cell death. We here investigated whether blocking gap junctions and hemichannels could prevent cell death after cryopreservation.

MATERIALS AND METHODS

Inclusion of Gap27, a connexin channel inhibitory peptide, during cryopreservation and thawing of human saphenous veins and femoral arteries was evaluated by terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) assays and histological examination.

RESULTS

We report that Gap27 significantly reduces cell death in human femoral arteries and saphenous veins when present during cryopreservation/thawing. In particular, smooth muscle cell death was reduced by 73% in arteries and 71% in veins, while endothelial cell death was reduced by 32% in arteries and 51% in veins.

CONCLUSIONS

We conclude that inhibiting connexin channels during cryopreservation strongly promotes vascular cell viability.

The relationship between gestational age and compliance in human umbilical vein and its possible application in vascular grafting

The aim of this study was to provide a theoretical basis, using biomechanical properties, for the clinical application of human umbilical vein (HUV) as material for vascular grafting. This was a nonrandomized, non-controlled in vitro study. The experiment was conducted in the Laboratory of Medical Biomechanics, Yunyang Medical College. HUVs of 50 normal fetuses were collected on spontaneous miscarriage or labor with the pregnant women's permission by the Department of Obstetrics and Gynecology, Taihe Hospital, Shiyan, Hubei Province. Gestational aged ranged 24-42 weeks, and parturients were 20-30 years old. The pressure-volume (P-V) relationship of HUV was measured on the biomechanical experiment stand for soft tissues, and then compliance was calculated. The P-V relationship of HUV corresponded to a parabolic curve. The compliance of HUV increased gradually with gestational age [24-27 weeks (2.22+/-0.34) x 10(-4) mL/(kPa * cm), 28-32 weeks (3.65+/-0.46) x 10(-4) mL/(kPa * cm), 33-36 weeks (4.22+/-0.55) x 10(-4) mL/(kPa * cm), 37 weeks (7.63+/-0.48) x 10(-4) mL/(kPa * cm), 38 weeks (8.32+/-0.76) x 10(-4) mL/(kPa * cm)]. However, after 39 weeks of gestation, compliance decreased gradually with gestational age [39 weeks 7.61+/-0.46) x 10(-4) mL/(kPa * cm), 40 weeks (7.53+/-0.72) x 10(-4) mL/(kPa * cm), 41 weeks (4.13+/-0.35) x 10(-4) mL/(kPa * cm), 42 weeks (2.25+/-0.62) x 10(-4) mL/(kPa * cm)]. The compliance of HUVs collected at 37-40 weeks of gestational age was similar. When the HUVs older than 42 weeks or under 28 weeks were compared, there was significant difference in their compliance (F=65.84-86.52, p<0.01). The results of the present study suggest that HUVs collected at 37-40 weeks of gestational age have good compliance, i.e., a good P-V relationship, and therefore may be a suitable material for vascular grafting. HUV is one of several graft materials that may be used when autogenous saphenous vein is absent or inadequate. HUV is very biocompatible and shows promise for use in orthopedic implants.

The Structural and Cellular Viability in Cryopreserved Rabbit Carotid Arteries

OBJECTIVE

We investigated the histological and mechanical changes in addition to viable cellular recovery in cryopreserved blood vessels.

MATERIALS AND METHODS

Rabbit carotids were cryopreserved in a cryoprotective medium containing 1.5 M of 1,2-propanediol (PD) and then were thawed slowly in an ice bag that had been precooled in liquid nitrogen. Fresh carotids were used as the control. The fresh and freeze-thawed arteries were cultured for the growth of vascular smooth muscle cells (VSMCs). The freeze-thawed arterial tissues were perfused in vitro for 6, 12, or 24 h, respectively, to assess the integrity of carotid walls and the mechanical properties.

RESULTS

The results showed that it took almost the same time (24 approximately 36 h) for the VSMCs of the PD-cryopreserved arteries to regenerate as those from the fresh arteries. Their growing speeds also were similar. On the contrary, Me2SO-cryopreserved (1.5 M) arteries were unable to regenerate VSMCs in culture. After freeze-thawing, the mechanical properties decreased significantly (P < 0.003 for elastic modulus and P < 0.001 for fracture strength). After in vitro perfusion of the freeze-thawed carotid arteries, all of the survived endothelial cells fell off, and some of the VSMCs denaturalized or necrosed. The internal elastic fibers and collagen showed various degrees of cracking. The mechanical properties were decreased (P < 0.05).

CONCLUSION

Our findings demonstrate that the PD-containing cryoprotective medium can preserve regenerative capacity of VSMCs, which makes it a useful technique for viable VSMC recovery. However, the freeze-thawing process and the in vitro perfusion caused serious disruption in the arterial mechanical properties, rendering the cryopreserved blood vessels less useful for vessel reconstruction.