Patency of cryopreserved saphenous vein grafts as conduits for coronary artery bypass surgery

Bioengineering Human Tissues and the Future of Vascular Replacement

Cardiovascular defects, injuries, and degenerative diseases often require surgical intervention and the use of implantable replacement material and conduits. Traditional vascular grafts made of synthetic polymers, animal and cadaveric tissues, or autologous vasculature have been utilized for almost a century with well-characterized outcomes, leaving areas of unmet need for the patients in terms of durability and long-term patency, susceptibility to infection, immunogenicity associated with the risk of rejection, and inflammation and mechanical failure. Research to address these limitations is exploring avenues as diverse as gene therapy, cell therapy, cell reprogramming, and bioengineering of human tissue and replacement organs. Tissue-engineered vascular conduits, either with viable autologous cells or decellularized, are the forefront of technology in cardiovascular reconstruction and offer many benefits over traditional graft materials, particularly in the potential for the implanted material to be adopted and remodeled into host tissue and thus offer safer, more durable performance. This review discusses the key advances and future directions in the field of surgical vascular repair, replacement, and reconstruction, with a focus on the challenges and expected benefits of bioengineering human tissues and blood vessels.

Nonautologous Grafts in Coronary Artery Bypass Surgery: A Systematic Review

BACKGROUND

Suitable autologous conduits may be lacking when performing coronary artery bypass grafting. The aim of this review is to determine the status of nonautologous grafts in coronary artery bypass grafting.

METHODS

We conducted a literature search on MEDLINE All, Embase Classic, and Embase through Ovid from 1960 to April 2020.

RESULTS

Of the 1579 records identified, 21 studies were included in the review. The following grafts were assessed for patency: 109 homologous saphenous veins (patency rates ranged from 66.7% at a median follow-up of 8.5 months to 0% at 6-12 months and 7-18 months, respectively), 29 expanded polytetrafluoroethylene grafts (from 80% at a median follow-up of 5 months to 14.3% at 45 months), 12 human umbilical veins (50% at a median follow-up of 6 months), 50 Bioflow bovine internal mammary arteries (from 15.8% to 0% at a mean follow-up of 9.5 months and 19 months, respectively), 39 Perma-Flow grafts (80% and 76.9% at 1-3 months and 12 months, respectively), 20 No-React bovine internal mammary arteries (57.1% at a median follow-up of 28 months and 23.1% at a mean follow-up of 7 months), 40 autologous venous endothelial cell-seeded expanded polytetrafluoroethylene grafts (94.7% and 81% at a mean follow-up of 27 months and 60 months, respectively), and 12 autologous venous endothelial cell-seeded cryopreserved homologous veins (83.3% at a mean follow-up of 8.5 months).

CONCLUSIONS

The goal of an alternative conduit with patency and attributes that match those of autografts remains elusive. Autologous endothelial cell-seeded synthetic grafts have demonstrated promising results but require further investigation.

Comparative efficacy of autologous versus cadaveric saphenous vein grafts in cerebral revascularization surgery

OBJECTIVE

Cerebral bypasses are performed for the purpose of either flow augmentation for ischemic cerebrovascular disease or flow replacement for vessel sacrifice during complex aneurysm or tumor surgery. Saphenous vein grafts (SVGs) are commonly used interposition grafts. The authors of this study sought to compare the efficacy of autologous versus cadaveric SVGs in a large series of cerebral bypasses using interposition vein grafts with long-term angiographic follow-up.

METHODS

All intracranial bypass procedures performed between 2001 and 2018 were reviewed. Demographic, clinical, angiographic, and operative data were recorded and then analyzed according to SVG type.

RESULTS

A total of 308 consecutive intracranial bypasses were performed during the study period, 53 (17.2%) of which were bypasses with an interposition SVG (38 autologous, 15 cadaveric). At a median follow-up of 2.2 months (IQR 0.2-29.1), 39 (73.6%) bypasses were patent (26 [68.4%] autologous, 13 [86.7%] cadaveric, p = 0.30). Comparing autologous and cadaveric SVG recipients, there were no statistically significant differences in age (p = 0.50), sex (p > 0.99), history of smoking (p = 0.75), hypertension (p > 0.99), diabetes mellitus (p = 0.13), indication for bypass (p = 0.27), or SVG diameter (p = 0.65). While there were higher intraoperative (autologous, 100.0 ml/min, IQR 84.3-147.5; cadaveric, 80.0 ml/min, IQR 47.3-107.8; p = 0.11) and postoperative (autologous, 142.2 ml/min, IQR 76.8-160.8; cadaveric, 92.0 ml/min, IQR 69.2-132.2; p = 0.42) volumetric flow rates in the autologous SVGs compared to those in the cadaveric SVGs, the difference between the two groups did not reach statistical significance. In addition, the blood flow index, or ratio of postoperative to intraoperative blood flow, for each bypass was similar between the groups (autologous, 1.3, IQR 0.9-1.6; cadaveric, 1.5, IQR 1.0-2.3; p = 0.37). Kaplan-Meier estimates showed no difference in bypass patency rates over time between autologous and cadaveric SVGs (p = 0.58).

CONCLUSIONS

Cadaveric SVGs are a reasonable interposition graft option in cerebral revascularization surgery when autologous grafts are not available.

High compliance vascular grafts based on semi-interpenetrating networks

Current synthetic vascular grafts have poor patency rates in small diameter applications (<6 mm) due to intimal hyperplasia arising from a compliance mismatch between the graft and native vasculature. Enormous efforts have focused on improving biomechanical properties; however, polymeric grafts are often constrained by an inverse relationship between burst pressure and compliance. We have developed a new, semi-interpenetrating network (semi-IPN) approach to improve compliance without sacrificing burst pressure. The effects of heat treatment on graft morphology, fiber architecture, and resultant biomechanical properties are presented. In addition, biomechanical properties after equilibration at physiological temperature were investigated in relation to polyurethane microstructure to better predict in vivo performance. Compliance values as high as 9.2 ± 2.7 %/mmHg x 10-4 were observed for the semi-IPN graft while also maintaining high burst pressure, 1780 ± 230 mm Hg. The high compliance of these heat-treated poly(carbonate urethane) (PCU) and semi-IPN grafts is expected to improve long-term patency rates beyond even saphenous vein autografts by preventing intimal hyperplasia. The fundamental structure-property relationships gained from this work may also be utilized to advance biomedical device designs based on thermoplastic polyurethanes.

Transplantation of an allogeneic vein bioengineered with autologous stem cells: a proof-of-concept study

BACKGROUND

Extrahepatic portal vein obstruction can have severe health consequences. Variceal bleeding associated with this disorder causes upper gastrointestinal bleeding, leading to substantial morbidity and mortality. We report the clinical transplantation of a deceased donor iliac vein graft repopulated with recipient autologous stem cells in a patient with extrahepatic portal vein obstruction.

METHODS

A 10 year old girl with extrahepatic portal vein obstruction was admitted to the Sahlgrenska University Hospital in Gothenburg, Sweden, for a bypass procedure between the superior mesenteric vein and the intrahepatic left portal vein (meso Rex bypass). A 9 cm segment of allogeneic donor iliac vein was decellularised and subsequently recellularised with endothelial and smooth muscle cells differentiated from stem cells obtained from the bone marrow of the recipient. This graft was used because the patient's umbilical vein was not suitable and other strategies (eg, liver transplantation) require lifelong immunosuppression.

FINDINGS

The graft immediately provided the recipient with a functional blood supply (25-30 cm/s in the portal vein and 40 mL/s in the artery was measured intraoperatively and confirmed with ultrasound). The patient had normal laboratory values for 9 months. However, at 1 year the blood flow was low and, on exploration, the shunt was patent but too narrow due to mechanical obstruction of tissue in the mesocolon. Once the tissue causing the compression was removed the graft dilated. We therefore used a second stem-cell populated vein graft to lengthen the previous graft. After this second operation, the portal pressure was reduced from 20 mm Hg to 13 mm Hg and blood flow was 25-40 cm/s in the portal vein. With restored portal circulation the patient has substantially improved physical and mental function and growth. The patient has no anti-endothelial cell antibodies and is receiving no immunosuppressive drugs.

INTERPRETATION

An acellularised deceased donor vein graft recellularised with autologous stem cells can be considered for patients in need of vascular vein shunts without the need for immunosuppression.

FUNDING

Swedish Government.

Multilayer vascular grafts based on collagen-mimetic proteins

A major roadblock in the development of an off-the-shelf, small-caliber vascular graft is achieving rapid endothelialization of the conduit while minimizing the risk of thrombosis, intimal hyperplasia, and mechanical failure. To address this need, a collagen-mimetic protein derived from group A Streptococcus, Scl2.28 (Scl2), was conjugated into a poly(ethylene glycol) (PEG) hydrogel to generate bioactive hydrogels that bind to endothelial cells (ECs) and resist platelet adhesion. The PEG-Scl2 hydrogel was then reinforced with an electrospun polyurethane mesh to achieve suitable biomechanical properties. In the current study, initial evaluation of this multilayer design as a potential off-the-shelf graft was conducted. First, electrospinning parameters were varied to achieve composite burst pressure, compliance, and suture retention strength that matched reported values of saphenous vein autografts. Composite stability following drying, sterilization, and physiological conditioning under pulsatile flow was then demonstrated. Scl2 bioactivity was also maintained after drying and sterilization as indicated by EC adhesion and spreading. Evaluation of platelet adhesion, aggregation, and activation indicated that PEG-Scl2 hydrogels had minimal platelet interactions and thus appear to provide a thromboresistant blood contacting layer. Finally, evaluation of EC migration speed demonstrated that PEG-Scl2 hydrogels promoted higher migration speeds than PEG-collagen analogs and that migration speed was readily tuned by altering protein concentration. Collectively, these results indicate that this multilayer design warrants further investigation and may have the potential to improve on current synthetic options.

The decellularized vascular allograft as an experimental platform for developing a biocompatible small-diameter graft conduit in a rat surgical model

PURPOSE

The present study was aimed to assess the feasibility of using decellularized aortic allograft in a rat small animal surgical model for conducting small diameter vascular tissue engineering research.

MATERIALS AND METHODS

Decellularized aortic allografts were infra-renally implanted in 12 Sprague-Dawley (SD) adult rats. The conduits were harvested at 2 (n = 6) and 8 weeks (n = 6), and assessed by hematoxylin and eosin (H&E), van Gieson, Masson Trichrome staining, and immunohistochemistry for von Willebrand factor, CD 31(+), and actin.

RESULTS

Consistent, predictable, and reproducible results were produced by means of a standardized surgical procedure. All animals survived without major complications. Inflammatory immune reaction was minimal, and there was no evidence of aneurysmal degeneration or rupture of the decellularized vascular implants. However, the aortic wall appeared thinner and the elastic fibers in the medial layer showed decreased undulation compared to the normal aorta. There was also minimal cellular repopulation of the vascular media. The remodeling appeared progressive from 2 to 8 weeks with increased intimal thickening and accumulation of both collagen and cells staining for actin. Although the endothelial like cells appeared largely confluent at 8 weeks, they were not as concentrated in appearance as in the normal aorta.

CONCLUSION

The results showed the present rat animal model using decellularized vascular allograft implants to be a potentially durable and effective experimental platform for conducting further research on small diameter vascular tissue engineering.

A reappraisal of saphenous vein grafting

Autologous saphenous vein grafting has been broadly used as a bypass conduit, interposition graft, and patch graft in a variety of operations in cardiac, thoracic, neurovascular, general vascular, vascular access, and urology surgeries, since they are superior to prosthetic veins. Modified saphenous vein grafts (SVG), including spiral and cylindrical grafts, and vein cuffs or patches, are employed in vascular revascularization to satisfy the large size of the receipt vessels or to obtain a better patency. A loop SVG helps flap survival in a muscle flap transfer in plastic and reconstructive surgery. For dialysis or transfusion purposes, a straight or loop arteriovenous fistula created in the forearm or the thigh with an SVG has acceptable patency. The saphenous vein has even been used as a stent cover to minimize the potential complications of standard angioplasty technique. However, the use of saphenous vein grafting is now largely diminished in treating cerebrovascular disorders, superior vena cava syndrome, and visceral revascularization due to the introduction of angioplasty and stenting techniques. The SVG remains the preferable biomaterial in coronary artery bypass, coronary osteoplasty, free flap transfer, and surgical treatment of Peyronie disease. Implications associated with saphenous vein grafting in vascular access surgery for the purpose of dialysis and chemotherapy are considerable. Vascular cuffs and patches have been developed as an important and effective means of enhancing the patency rates of the grafts by linking the synthetic material to the receipt vessel. In addition, saphenous veins can be a cell source for tissue engineering. We review the versatile roles that saphenous vein grafting has played as well as its current status in therapy.

Impact of freezing/thawing procedures on the post-thaw viability of cryopreserved human saphenous vein conduits

BACKGROUND

Cryopreserved human blood vessels are important tools in reconstructive surgery. However, patency of frozen/thawed conduits depends largely on the freezing/thawing procedures employed.

METHODS

Changes in tone were recorded on rings from human saphenous vein (SV) and used to quantify the degree of cryoinjury after different periods of exposure at room temperature to the cryomedium (Krebs-Henseleit solution containing 1.8M dimethyl sulfoxide and 0.1M sucrose) and after different cooling speeds and thawing rates following storage at -196 degrees C.

RESULTS

Without freezing, exposure of SV to the cryomedium for up to 240 min did not modify contractile responses to noradrenaline (NA). Pre-freezing exposure to the cryomedium for 10-120 min attenuated significantly post-thaw maximal contractile responses to NA, endothelin-1 (ET-1) and potassium chloride (KCl) by 30-44%. Exposure for 240 min attenuated post-thaw contractile responses to all tested agents markedly by 62-67%. Optimal post-thaw contractile activity was obtained with SV frozen at about -1.2 degrees C/min and thawed slowly at about 15 degrees C/min. In these SV maximal contractile responses to NA, ET-1 and KCl amounted to 66%, 70% and 60% of that produced by unfrozen controls. Following cryostorage of veins for up to 10 years the responsiveness of vascular smooth muscle to NA was well maintained.

CONCLUSION

Cryopreservation allows long-term banking of viable human SV with only minor loss in contractility.

A Comparison of Cryopreserved Vein Allografts and Prosthetic Grafts for Hemodialysis Access

In hemodialysis patients with insufficient vasculature for creation of a native arteriovenous fistula (AVF), a polytetrafluoroethylene (PTFE) graft is commonly utilized. Because of PTFE complications, our group and others have used cryopreserved cadaver femoral vein allografts (Synergraft [SYN], CryoLife, Marietta, GA) in selected patients. Based on our experience with these allografts, we hypothesized that they were more resistant to thrombosis than PTFE grafts. The purpose of this study was to compare the thrombosis rates of SYN and PTFE grafts in a prospective, randomized fashion. Our study was interrupted when the FDA ordered CryoLife, Inc. to retain certain vascular tissue products, and patient accrual stopped in 2003. Most patients referred for hemodialysis access are evaluated with bilateral, upper extremity Doppler ultrasound. Starting in 2001, those with insufficient vasculature for native AVF were offered randomization into the PTFE or SYN groups. All accesses were placed in the upper extremity, above the elbow. Access patency and complications were recorded, and failure was defined as access removal, abandonment, or replacement of > 50% with a new conduit. Prior to FDA interruption of the study, 27 patients were randomized into each group. Patient characteristics were similar, but there were significantly more males and African-Americans in the SYN group. No significant differences were seen in primary or secondary patency, number of thrombectomies, revisions, or total interventions. Significantly more fistulagrams were performed in the SYN group (p < 0.05). No infections were seen in either group, but 2 aneurysms occurred in the SYN group. Nine (33%) patients in each group died with functioning access. Access failures: In the SYN group, 8 of 27 (30%) failed, with 5 failing from multiple access stenoses unresponsive to balloon angioplasty; in the PTFE group 4 of 27 (18%) failed, with 2 failing from multiple stenoses. In conclusion, for initial hemodialysis access in patients without sufficient vasculature for native AVF, our results do not support the routine use of SYN allografts in the general dialysis population.

One-Year Coronary Bypass Graft Patency

Background— Off-pump coronary bypass surgery has become a widely used technique during recent years. However, limited data are available with regard to 1-year patency of bypass grafts implanted on the beating heart in unselected consecutive bypass surgery candidates. The aim of this study was to compare 1-year angiographic patency of bypass grafts done on the beating heart (off pump) with those done classically (on pump).

Methods and Results— The PRAGUE-4 trial randomized 400 consecutive nonselected cardiac surgery candidates into group A (on pump; n=192) and group B (off pump; n=208). One-year follow-up coronary angiography was done in 255 patients. The arterial graft patency after 1 year was 91% in both groups. Saphenous graft patency was 59% (on pump) versus 49% (off pump; P =NS). Saphenous graft patency per patient was lower in the off-pump group: 0.7 patent anastomosis per patient versus 1.1 patent anastomosis in the on-pump group ( P <0.01). There were 46% on-pump patients with all grafts patent versus 52% off-pump patients ( P =NS). Grafts anastomosed distally to collateralized chronic total occlusions of native coronary arteries remained patent in 100% on the left anterior descending artery compared with 23% on other arteries ( P <0.0001).

Conclusions— The patency of arterial coronary bypass grafts done on the beating heart is excellent and equal to grafts done on pump. The off-pump procedure in the unselected patient population results in fewer patent saphenous grafts per patient.

Experience with cryopreserved cadaveric femoral vein allografts used for hemodialysis access

The purpose of this study was to review the patency and complications of cryopreserved vein allografts used for hemodialysis access, and to compare them to a group with polytetrafluoroethylene (PTFE) grafts. Patients without adequate vasculature for native fistula were implanted with vein allografts or PTFE grafts at the surgeon's discretion. Only cryopreserved (CRY) veins were used until January 2001, when decellularized, cryopreserved Synergraft (SYN) veins became available. The CRY group had 48 patients; the SYN group, 42 patients; the PTFE group, 100 patients, who were selected from billing records listing PTFE graft insertion. Patient demographics were similar. Primary and secondary patencies were not significantly different at 1 or 2 years between groups. Complications in PTFE versus CRY and SYN groups were as follows: infection, 10 % vs. 0% (p < 0.01); aneurysm, 2% vs. 18% (p < 0.001); and steal syndrome, 12% vs. 12% (p = NS). Significantly more vein allograft patients lost their accesses to aneurysm (p < 0.01) and multiple stenoses (p < 0.05), whereas PTFE patients lost significantly more accesses to infection (p < 0.01) and recurrent thrombosis (p < 0.05). We conclude that cadaver vein allografts have similar patency to PTFE grafts. These allografts are more resistant to infection but significantly more susceptible to aneurysms. When used, vein allografts should be monitored aggressively for the development of aneurysms.

Decellularized cadaver vein allografts used for hemodialysis access do not cause allosensitization or preclude kidney transplantation

BACKGROUND

Dimethyl sulfoxide-cryopreserved (CRY) cadaver vein allografts used for hemodialysis access in patients with renal failure recently have been shown to cause broad recipient allosensitization, measured by panel reactive antibody (PRA) assay. Synergraft (SYN) processing is a novel method of treating tissue that decellularizes the graft (including mismatched major histocompatibility antigens) and potentially should prevent allosensitization.

METHODS

Twenty hemodialysis patients underwent placement of an SYN-processed cadaver vein allograft. PRA assay was used prospectively to assess allosensitization in these patients at baseline and 1-month intervals after engraftment. These results were compared with our historic series of CRY allograft recipients.

RESULTS

There was no significant difference in baseline PRA values for SYN and CRY patients (2.8% versus 2.6%, respectively). None of the SYN patients became allosensitized at 3 months postengraftment (mean PRA, 3.2%), whereas all CRY recipients became highly sensitized at a mean of 3.1 months (mean PRA, 84.1%). This result was highly significant (P < 0.0001).

CONCLUSION

SYN processing of cadaver vein allografts successfully removes antigenic material. The use of SYN allografts in patients with renal failure for hemodialysis access does not cause allosensitization and therefore should not preclude kidney transplantation.

Use of cryopreserved cadaveric vein allograft for hemodialysis access precludes kidney transplantation because of allosensitization

BACKGROUND

Dimethyl sulfoxide-cryopreserved cadaveric vein allografts have recently been proposed as an alternative to prosthetic grafts in the problem hemodialysis population. The transfer of mismatched major histocompatibility complex I and II molecules in association with these allografts can potentially lead to allosensitization in nonimmunosuppressed individuals.

METHODS

In a university-affiliated medical center, 20 consecutive patients receiving technically successful upper arm cadaveric vein allograft fistulas (CAVFs) for hemodialysis between April 1999 and April 2000 were studied. A control cohort of 20 patients on a kidney transplantation waiting list was selected by nurses blinded to the study. These patients were matched for age, sex, history of transfusion, pregnancy, cause of kidney failure, and prior transplantation. The panel reactive antibody (PRA) values were recorded in this group over the same time period as the CAVF group.

RESULTS

Patients receiving CAVFs had a mean PRA assay value of 84.1% (median, 96.5%) at an average of 3.1 months after engraftment (median, 1.5 months). The preengraftment PRA values were available for seven patients who were on the transplant waiting list. Six of these patients had nonreactive PRA assays before CAVF creation. All of these patients converted to positive PRA assays after CAVF creation with a mean value of 92.3% (median, 98%) at 2.85 months follow-up (median, 1.3 months). The mean PRA value for the control cohort was 5.5% (median, 2.5%), with no patients converting from a nonreactive to a reactive PRA assay during this same time interval.

CONCLUSION

The use of dimethyl sulfoxide-cryopreserved cadaveric vein allografts for hemodialysis access leads to broad allosensitization as measured by PRA assay. Cryopreserved cadaveric vein allografts should not be used for hemodialysis access in potential kidney transplant recipients.

Changes in the cooling rate and medium improve the vascular function in cryopreserved porcine femoral arteries

PURPOSE

The purpose of this study was to design an adequate technique with which to cryopreserve pig femoral arteries and to assess the influence of storage times in vascular function.

METHODS

Fifty-two femoral arteries were distributed in seven groups. In group A (control), 10 arteries were studied after harvest; in groups B1 and B2, 19 arteries were suspended in RPMI 1640 plus fetal calf serum plus dimethylsulfoxide and were cryopreserved at 1 degrees C per minute or 0.3 degrees C per minute, respectively. In groups C1 to C4, 23 arteries were suspended in modified Krebs-Henseleit plus dimethylsulfoxide plus sucrose, cryopreserved at 0.7 degrees C per minute, and kept frozen for 1, 15, 60, or 180 days, respectively. After being thawed, arteries were examined for contraction and endothelial-dependent vasodilation (organ bath studies), antithrombotic properties of the endothelial layer(perfusion studies), and vessel structure (electron microscopy).

RESULTS

Endothelial cells were present in both cryopreserved and control arteries. The control vessels showed a mean contraction to norepinephrine (10(-7) mol/L) of 13010 +/- 3181 mg. Arteries in groups B1 and B2 did not respond to norepinephrine. Contraction in groups C1 to C4 was as follows: C1, 5354 +/- 1222 mg; C2, 5187 +/- 2672 mg; C3, 6867 +/- 2292 mg; C4, 7000 +/- 2858 mg, which represent 50% of the control values (P <.001). Vasodilation was similar in control (99% +/- 3%) and cryopreserved arteries (C1, 90% +/- 13%; C2, 93% +/- 12%; C3, 89% +/- 15%; C4, 88% +/- 22%). Storage time did not influence vascular function. Platelet interaction was almost absent and similar in all groups.

CONCLUSION

A modified cryopreservation technique preserves endothelial function independently of the storage time up to 6 months.

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.

Functional activity and transmembrane signaling mechanisms after cryopreservation of human internal mammary arteries

PURPOSE

Cryopreserved human blood vessels are important tools in bypass surgery. However, several in vitro studies have demonstrated diminished postthaw functional activity. Therefore the aim of this study was to investigate the consequences of various freezing/thawing protocols and the role of protein kinase C in the postthaw functional activity of cryopreserved human arteries.

METHODS

In vitro responses of frozen/thawed human internal mammary arteries (IMA) were used to investigate the functional activity after thawing at 15 degrees, 30 degrees, and 100 degrees C/min and after different prefreezing equilibration times (10, 60, 120, 240 minutes) with the cryomedium (Krebs-Henseleit solution containing 1.8 mol/L dimethyl sulfoxide and 0.1 mol/L sucrose) at room temperature followed by cryostorage at -196 degrees C.

RESULTS

Prefreezing equilibration for 10 to 120 minutes diminished maximal alpha-adrenoceptor-mediated responses to noradrenaline to approximately 60%, and equilibration for 240 minutes attenuated noradrenaline effects to less than 25% of that produced by unfrozen controls. Contractile responses were slightly better when thawing was performed at 15 degrees C/min compared with 100 degrees C/min. The postthaw sensitivity to direct activation of protein kinase C by phorbol 12,13-dibutyrate was enhanced. Compared with unfrozen tissues (pD2 = 7.36 +/- 0.07, n = 32) maximal sensitization to phorbol 12,13-dibutyrate was observed in IMA that had been frozen after 60 minutes of equilibration with the cryomedium (pD2 = 8.31 +/- 0.09, n = 30). Responses to phorbol 12,13-dibutyrate of cryopreserved IMA were highly susceptible to blockade of calcium influx by nifedipine, whereas those of unfrozen IMA were resistant to nifedipine. Against noradrenaline nifedipine was equipotent in cryopreserved (pD'2 = 7.75 +/- 0.15, n = 8) and unfrozen IMA (pD'2 = 7.70 +/- 0.10, n = 6). Endothelium-dependent relaxant responses to acetylcholine were significantly attenuated after cryopreservation (Emax = 26% +/- 5%, n = 4) compared with unfrozen IMA (Emax = 71% +/- 4%, n = 4, p < 0.001); endothelium-independent relaxant responses to sodium nitroprusside were unchanged.

CONCLUSIONS

Cryopreservation of human IMA under the conditions applied in this study (1) attenuated endothelial cell function and (2) induced an activation of protein kinase C, thereby increasing calcium influx through dihydropyridine-sensitive calcium channels. These experimental data suggest that postoperative administration of calcium channel blockers alone or combined with long-acting nitrates should effectively prevent the development of spasms in arterial grafts.