Functional and morphological evaluation of canine veins following preservation in different storage media

Efficacy of Intraoperative Vein Graft Storage Solutions in Preserving Endothelial Cell Integrity during Coronary Artery Bypass Surgery

(1) Introduction: Intraoperative preservation solutions for saphenous vein grafts may influence the endothelial structure and increase the risk of graft failure after coronary surgery. The aim of the study was to compare the efficacy of three solutions in maintaining the endothelial cell integrity of venous segments. (2) Methods: We tested the efficacy of physiological saline solution (PSS), heparinized autologous blood (HAB) and DuraGraft® in preserving the endothelium of vein segments by evaluating the degree of endothelial cell apoptosis. Two incubation times (2 and 4 h from harvesting) were used for each solution. The quantification of apoptotic cells was computed as the intensity nuclei/intensity area ratio. (3) Results: After 2 h of ischemia, the degree of apoptosis decreased progressively across the use of DuraGraft, HAB and PSS (p = 0.004), although only the difference between DuraGraft and PSS yielded a statistical significance (p = 0.002). After 4 h, a similar decrease in apoptosis was shown across the three media; however, statistical significance was not reached. The analysis of the elapsed time (2 or 4 h of incubation) showed that this was a relevant factor in maintaining the endothelial structural integrity independently from the storage solution (test for interaction of media and time p = 0.010). (4) Conclusion: Within 2 h of incubation, endothelial structural integrity depended on the incubating medium. DuraGraft better protected the SVG against ischemic-induced apoptosis when compared to saline solution. Prolonged ischemia was associated with extended endothelium damage and none of the studied solutions protected the vein graft.

Endothelial damage inhibitors for improvement of saphenous vein graft patency in coronary artery bypass grafting

The saphenous vein graft (SVG) remains the most commonly used conduit in coronary artery bypass grafting (CABG). In light of this further research must be aimed at the development of strategies to optimize SVG patency and thereby improve both short- and long-term outcomes of CABG surgery. SVG patency in large part depends on the protection of the structural and functional integrity of the vascular endothelium at the time of conduit harvesting, including optimal storage conditions to prevent endothelial damage. This review provides an overview of currently available storage and preservation solutions, including novel endothelial damage inhibitors, and their role in mitigating endothelial damage and vein graft failure.

The effect of storage solutions on endothelial function and saphenous vein graft patency

Vein graft failure is a complex mechanism that can be triggered immediately after surgical harvesting. Storage solutions have a major role in preventing endothelial cell damage during harvesting. While normal saline is still widely used, buffered solutions seem to better preserve endothelial integrity and function. This review aims to summarize the current literature surrounding vein graft storage solutions.

Preservation solution impacts physiologic function and cellular viability of human saphenous vein graft

INTRODUCTION

Recent clinical data suggest intraoperative preservation of human saphenous vein (HSV) in normal saline is associated with vein graft failure. We evaluated the influence of several preservation media on acute physiologic function and cellular viability of HSV conduit.

METHODS

Unprepared (UP) HSV obtained from coronary artery bypass graft patients was characterized on a muscle bath after 2-hour storage in 6 solutions: Plasma-Lyte A, 0.9% NaCl (normal saline), University of Wisconsin solution, Celsior solution, autologous whole blood, or glutathione-ascorbic acid L-arginine (GALA) solution. Vascular smooth muscle contractility was assessed after exposure to depolarizing KCl and phenylephrine. The relaxation of phenylephrine-precontracted HSV to sodium nitroprusside and carbachol (endothelial-independent and -dependent relaxation, respectively) was also assessed. Cellular viability was determined via the methyl thiazolyl tetrazolium (MTT) assay. Rat aortae were used to assess the effect of pH during graft preservation on endothelial-dependent relaxation.

RESULTS

Preservation of HSV in normal saline and autologous whole blood impaired contractile responses to KCl relative to UP tissues, whereas preservation in University of Wisconsin solution and Celsior solution enhanced contractile responses (P < .05). Relative to UP tissues, responses to phenylephrine were decreased with preservation in normal saline, whereas preservation in University of Wisconsin solution, Celsior solution, and GALA all potentiated these responses (P < .05). Only preservation in normal saline impaired endothelial-independent relaxation (P = .005). Preservation in Plasma-Lyte A (P = .02), normal saline (P = .002), and University of Wisconsin solution (P = .02) impaired endothelial-dependent relaxation. Normal saline preservation decreased MTT viability index relative to UP tissues (0.02 ± 0.002 mg(-1)0.5 mL(-1) vs 0.033 ± 0.005 mg(-1)0.5 mL(-1); P = .03). Endothelial function was impaired by acidic pH in rat aorta.

CONCLUSION

Preservation of HSV in normal saline causes graft injury leading to impaired physiologic function and decreased viability of the HSV. This harm is mitigated by the use of buffered salt solutions as preservation media.

Vein graft preservation solutions, patency, and outcomes after coronary artery bypass graft surgery: follow-up from the PREVENT IV randomized clinical trial

IMPORTANCE

In vitro and animal model data suggest that intraoperative preservation solutions may influence endothelial function and vein graft failure (VGF) after coronary artery bypass graft (CABG) surgery. Clinical studies to validate these findings are lacking.

OBJECTIVE

To evaluate the effect of vein graft preservation solutions on VGF and clinical outcomes in patients undergoing CABG surgery.

DESIGN, SETTING, AND PARTICIPANTS

Data from the Project of Ex-Vivo Vein Graft Engineering via Transfection IV (PREVENT IV) study, a phase 3, multicenter, randomized, double-blind, placebo-controlled trial that enrolled 3014 patients at 107 US sites from August 1, 2002, through October 22, 2003, were used. Eligibility criteria for the trial included CABG surgery for coronary artery disease with at least 2 planned vein grafts.

INTERVENTIONS

Preservation of vein grafts in saline, blood, or buffered saline solutions.

MAIN OUTCOMES AND MEASURES

One-year angiographic VGF and 5-year rates of death, myocardial infarction, and subsequent revascularization.

RESULTS

Most patients had grafts preserved in saline (1339 [44.4%]), followed by blood (971 [32.2%]) and buffered saline (507 [16.8%]). Baseline characteristics were similar among groups. One-year VGF rates were much lower in the buffered saline group than in the saline group (patient-level odds ratio [OR], 0.59 [95% CI, 0.45-0.78; P < .001]; graft-level OR, 0.63 [95% CI, 0.49-0.79; P < .001]) or the blood group (patient-level OR, 0.62 [95% CI, 0.46-0.83; P = .001]; graft-level OR, 0.63 [95% CI, 0.48-0.81; P < .001]). Use of buffered saline solution also tended to be associated with a lower 5-year risk for death, myocardial infarction, or subsequent revascularization compared with saline (hazard ratio, 0.81 [95% CI, 0.64-1.02; P = .08]) and blood (0.81 [0.63-1.03; P = .09]) solutions.

CONCLUSIONS AND RELEVANCE

Patients undergoing CABG whose vein grafts were preserved in a buffered saline solution had lower VGF rates and trends toward better long-term clinical outcomes compared with patients whose grafts were preserved in saline- or blood-based solutions.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00042081.

Nafamostat mesilate: can it be used as a conduit preserving agent in coronary artery bypass surgery?

Background

Graft vessel preservation solution in coronary artery bypass surgery is used to maintain the graft conduit in optimal condition during the perioperative period. Nafamostat mesilate (NM) has anticoagulation and anti-inflammatory properties. Therefore, we investigated NM as a conduit preservative agent and compared it to papaverine.

Methods

Sprague-Dawley (SD) rat thoracic aortas were examined for their contraction-relaxation ability using phenylephrine (PE) and acetylcholine (ACh) following preincubation with papaverine and NM in standard classical organ baths. Human umbilical vein endothelial cells (HUVECs) were cultured to check for the endothelial cell viability. Histopathological examination and terminal deoxynucleotidyl transferase dUTP nick end labeling assay were performed on the thoracic aortas of SD rats.

Results

The anti-contraction effects of papaverine were superior to those of NM at PE (p<0.05). The relaxation effect of NM on ACh-induced vasodilatation was not statistically different from that of papaverine. Viability assays using HUVECs showed endothelial cell survival rates of >90% in various concentrations of both NM and papaverine. A histopathological study showed a protective effect against necrosis and apoptosis (p<0.05) in the NM group.

Conclusion

NM exhibited good vascular relaxation and a reasonable anti-vasocontraction effect with a better cell protecting effect than papaverine; therefore, we concluded that NM is a good potential conduit preserving agent.

Storage of saphenous vein grafts prior to coronary artery bypass grafting: is autologous whole blood more effective than saline in preserving graft function?

A best evidence topic in thoracic surgery was written according to a structured protocol. The question addressed was: 'Is storage of saphenous vein grafts in autologous whole blood prior to coronary artery bypass grafting (CABG) more effective than storage in saline in preserving graft function?' Altogether more than 580 papers were found using the reported search, of which, 10 represented the best evidence to answer the clinical question. The authors, journal, date, country of publication, patient group studied, study type, relevant outcomes and results of these papers are tabulated. Preservation of the vein graft endothelium during graft preparation is of well-recognized importance in forestalling graft occlusion and saphenous vein graft disease following CABG, however, the different preservation capabilities of saline vs autologous whole blood are not well validated. Although there is a complete lack of randomized clinical trials addressing this issue, some studies using basic in vitro techniques and animal models can be extrapolated to answer the clinical question in hand. All are consistent in demonstrating the detrimental effects of saline on vascular endothelium and therefore graft patency, but there is some disagreement in the literature as to whether autologous whole blood is superior as a storage medium. Though three well-designed studies suggest preserved endothelial function when saphenous vein grafts are stored in saline compared with storage in autologous whole blood, data from other studies are unimpressive, with two studies showing no difference. Furthermore, two elegant experiments that seek to mimic in vivo conditions by comparing outcomes postarterialization show no benefit of prior storage in autologous whole blood, despite the initial better-preserved endothelium. Instead, some notice should be taken of alternative storage solutions such as the University of Wisconsin solution, as some early studies suggest that it may be advantageous over both blood and crystalloid solution.

Maintained geometry, elasticity and contractility of human saphenous vein segments stored in a complex tissue culture medium

OBJECTIVE

Improved maintenance of endothelial function and higher viability of saphenous vein grafts stored in a complex tissue culture medium (TCM) have been demonstrated. This article studies the biomechanical properties of saphenous vein segments.

DESIGN

Biomechanical properties of 72 saphenous vein segments remaining from coronary bypass grafting of 32 patients have been studied after different storage procedures.

MATERIALS

The materials studied included fresh segments, segments stored in a cooled conventional physiological salt solution (normal Krebs-Ringer (nKR)) for 1-2 weeks, segments stored in a cooled chemically defined TCM (X-Vivo) for 1,2,3 and 4 weeks and segments cryopreserved for a few weeks.

METHODS

Specimens were cannulated at both ends and pressure-diameter curves were recorded in the 0-85-mmHg range in nKR with 10 microM norepinephrine added to induce maximum smooth muscle contraction, as well as in Ca(2+)-free medium to induce full relaxation. Tensile strength was checked at 300 mmHg. Distensibility, elastic modulus and active strain were computed.

RESULTS

Segments stored in nKR dilated morphologically, their distensibility decreased and they lost their ability to contract (1.5+/-0.7% from 10.1+/-1.5% of control) in 1 week. The TCM-stored segments preserved their contractility until 1 week, and this parameter only slowly decreased afterwards (first week, 11.5+/-7.3%; fourth week, 3.9+/-0.6%). There was a slight decrease in wall thickness but the lumen diameter was not affected. The elastic parameters of these segments were practically identical to those of fresh segments. Cryopreserved segments narrowed morphologically, their wall thickened and contractility diminished.

CONCLUSIONS

Storage in TCM helps preserve the passive and active biomechanical properties of human saphenous vein segments. Such properties can be expected to improve graft tissue viability.

Multi-photon microscopic evaluation of saphenous vein endothelium and its preservation with a new solution, GALA

BACKGROUND

Injury to endothelium can compromise the patency of bypass grafts harvested during coronary artery bypass graft (CABG) surgery. Maintaining structural and functional viability of endothelium in grafts may lead to improved long-term patency. The information gained from the application of multi-photon microscopy in transmission and epifluorescence mode was used to assess the structural and functional integrity of human saphenous vein segments stored in multiple preservation solutions, and to design a superior storage solution.

METHODS

Multi-photon microscopy was used to image deep within saphenous vein tissue harvested from patients undergoing CABG for analysis of endothelial structure and function. Endothelial cell structural viability, calcium mobilization, and nitric oxide generation were determined using specific fluorescence markers.

RESULTS

Within 60 minutes of harvest and storage in standard preservation solutions, calcium mobilization and nitric oxide generation were markedly diminished with more than 90% of endothelial cells no longer viable in the vein. In contrast, veins could be stored for 24 hours without substantial loss in cell viability in a newly formulated heparinized physiologic buffered salt solution containing glutathione, ascorbic acid, and L-arginine (GALA).

CONCLUSIONS

Standard solutions in clinical use today led to a profound decline in saphenous vein endothelial cell viability, whereas the newly designed physiologic salt solution (GALA) maintained endothelial function and structural viability for up to 24 hours. The improvements seen from using GALA as a vessel storage medium may lead to greater long-term vein graft patency following CABG surgery.

In vitro function of porcine carotid arteries preserved in UW, HTK and Celsior solutions

We compared the efficacy of histidine-tryptophan-ketoglutarate (HTK) and University of Wisconsin (UW) solution with Celsior solution using hypothermically-preserved porcine carotid arteries and studied the importance of different components of these solutions by preserving carotid arteries in modified HTK solutions. Excised carotid arteries were stored at 4 degrees C in 0.9% (w/v) NaCl, UW, HTK, Celsior, or a modified HTK solution for up to 14 days. Preservation-induced changes in smooth muscle cell and endothelial cell function were determined using an organ bath for isometric tension recording. Short-term preservation (1-3 days) in UW, HTK and Celsior did not significantly alter contractile and relaxation responses of arterial segments when compared to freshly-excised segments, but significantly impaired these responses in arterial segments stored in 0.9% (w/v) NaCl solution. Long-term hypothermic preservation of arterial segments (7 and 14 days) in 0.9% (w/v) NaCl and HTK solution almost completely abolished all responses, but only slightly reduced the responses of arterial segments stored in UW solution. Intermediate results were obtained for Celsior. Modifying HTK by replacement of chloride for sulfate and phosphate resulted in improved contractile and relaxation responses after long-term preservation. With respect to smooth muscle and endothelial function, UW is superior to HTK and Celsior and the absence of chloride or presence of sulfate and phosphate plays a relevant role in this in vitro model of hypothermic preservation of porcine carotid arteries.

University of Wisconsin solution increases hyperpolarizing mechanisms in response to bradykinin

BACKGROUND

The aim of this study was to determine the effect of University of Wisconsin solution (UWS) incubation on bradykinin-induced vasodilation.

METHODS

Porcine coronary arteries were incubated in Krebs-Henseleit solution (KHS) or UWS at 4 degrees C for 20 hours. Endothelium-dependent relaxation to bradykinin and endothelium-independent relaxation to nitric oxide were tested after U46619 or KCl pre-contraction. Nitric oxide synthase activity and protein expression was determined by [3H]-L-citrulline formation and western blot analysis, respectively.

RESULTS

The relaxation to bradykinin (0.1 to 300 nmol/liter) after U46619 (30 to 300 nmol/liter) pre-contraction was similar with both KHS and UWS pre-incubation; however, it was reduced after KCl pre-contraction (15 to 20 mmol/liter), this reduction being greater after UWS incubation. The inhibitory effect of N(G)-nitro-L-arginine methylester (0.1 mmol/liter) on bradykinin-induced relaxation was lower in UWS- than KHS-incubated segments after U46619 pre-contraction, but similar after KCl pre-contraction; however, the inhibitory effect of 0.5 mmol/liter ouabain was unaffected. Tetraethylammonium (5 mmol/liter) reduced the response to bradykinin more strongly after UWS pre-incubation. UWS did not modify relaxation to nitric oxide (0.1 to 30 micromol/liter) in pre-incubated UWS or KHS segments. UWS failed to modify both total nitric oxide synthase activity and endothelial nitric oxide synthase expression.

CONCLUSIONS

UWS incubation decreased nitric oxide participation and increased the hyperpolarizing mechanisms produced by bradykinin.