Contractile function of human veins after long-term storage in different media

Comparison of arterial storage conditions for delayed arterial ring testing

Objective

Arterial ring testing is the gold standard for measuring arterial function. Increased arterial tone through arterial contraction and impaired endothelial relaxation (endothelial dysfunction) are key metrics of impaired arterial health in peripheral arterial disease (PAD). To allow for comparative testing of arteries during standard laboratory hours, storage buffers and conditions have been used to extend the functional life of arteries. Various storage conditions have been compared, but there has not been a robust comparison or validation in human arteries. The objective of this work is to optimize storage of arterial segments for endothelial cell (EC) testing in a murine model and to test EC function in human PAD arteries. We hypothesized that certain storage conditions would be superior to others.

Methods

Healthy murine aortas were harvested from 10- to 14-week-old C57/Bl6J male and female mice and compared under different storage protocols (24 hours) to immediate arterial testing. The storage conditions tested were: Opti-MEM (37°C or 4°C), Krebs-HEPES with 1.8 mmol/L or 2.5 mmol/L calcium (4°C), or Wisconsin (WI) solution at 4°C. Vascular function was evaluated by isometric force testing. Endothelium-dependent and -independent relaxation were measured after precontraction with addition of methacholine or sodium nitroprusside, respectively. Arterial contraction was stimulated with potassium chloride or phenylephrine. Analysis of variance was used to determine significance compared with immediate testing with P < .05. Under institutional review board approval, 28 PAD arteries were collected at amputation and underwent vascular function testing as described. Disturbed flow conditions were determined by indirect (upstream occlusion) flow to the harvested tibial arteries. Stable flow arteries had in-line flow. Arterial calcification was quantified manually as present or not present.

Results

We found that 4°C WI and 37°C Opti-MEM best preserved endothelium-dependent relaxation and performed similarly to immediately testing aortas (termed fresh for freshly tested) (P > .95). Other storage conditions were inferior to freshly tested aortas (P < .05). Vascular smooth muscle function was tested by endothelial-independent relaxation and contractility. All storage conditions preserved endothelial-independent relaxation and contractility similar to freshly tested arteries. However, 4°C WI and 37°C Opti-MEM storage conditions most closely approximated the maximum force of contraction of freshly tested arteries in response to potassium chloride (P > .39). For human arterial testing, 28 tibial arteries were tested for relaxation and contraction with 16 arteries with peripheral artery occlusive disease (PAD with disturbed flow) and 12 without peripheral artery occlusive disease (PAD with stable flow), of which 14 were calcified and 14 were noncalcified. Endothelial-dependent relaxation data was measurable in 9 arteries and arterial contraction data was measurable in 14 arteries. When comparing flow conditions, arteries exposed to disturbed flow (n = 4) had significantly less relaxation (2% vs 59%; P = .03) compared with stable flow conditions (n = 5). In contrast, presence the (n = 6) or absence of calcification (n = 3) did not impact arterial relaxation. Arterial contraction was not different between groups in either comparison by flow (n = 9 disturbed; n = 5 stable) or calcification (n = 6 present; n = 8 absent).

Conclusions

In healthy murine aortas, arterial storage for 24 hours in 4°C WI or 37°C Opti-MEM both preserved endothelium-dependent relaxation and maximum force of contraction. In human PAD arteries stored in 4° WI, flow conditions before arterial harvest, but not arterial calcification, led to differences in arterial relaxation in human PAD arteries. Arterial contractility was more robust (11/28 arteries) compared with arterial relaxation (7/28 arteries), but was not significantly different under flow or calcification parameters. This work defines ideal storage conditions for arterial ring testing and identifies that EC dysfunction from disturbed flow may persist in delayed ex vivo arterial testing.

Cardioplegic storage solution: Is it the guardian of saphenous vein graft endothelium?

INTRODUCTION

Despite their suboptimal long-term patency, saphenous vein grafts are the most widely used conduits to achieve complete revascularization during coronary artery bypass grafting (CABG). Although vein storage critically impairs endothelial integrity, contradictory data concerning optimal storage solutions exist. The aim of this study is to explore any in vitro impact of cardioplegic solutions and temperature on vein grafts endothelial integrity during their storage.

MATERIALS AND METHODS

A single-center, prospective trial including 40 consecutive patients was conducted. Eligibility criteria included patients submitted to CABG receiving at least one vein graft. An excess segment of the graft was harvested and divided into four different parts. Each one of them was stored under different conditions; either in a conventional heparin-enriched blood solution or in a cardioplegic solution, at room temperature (20°C-22°C) and in the refrigerator (5°C). Endothelial integrity was evaluated via immunohistochemistry using an antibody against CD31.

RESULTS

Endothelial integrity (measured in a scale from 1-worst to 5-best) was significantly better after cardioplegic solution storage (2.83 ± 0.15 and 3.10 ± 0.13 in cold and room temperature, respectively) compared with storage in conventional solutions (2.23 ± 0.16 and 2.0 ± 0.15 in cold and room temperature, respectively). A significant effect of cardioplegic storage solution, as well as of cold temperature and cardioplegic solution interaction on endothelial preservation was reported, whereas storage temperature did not prove a significant factor by its own.

CONCLUSIONS

Cardioplegic storage solutions result in significantly better endothelial preservation compared with conventional heparin-enriched blood solutions. The association with superior clinical outcomes remains to be proved.

Surgical Skin Markers Impair Human Saphenous Vein Graft Smooth Muscle and Endothelial Function

Marking human saphenous vein graft (HSV) with a surgical skin marker to prevent twisting on implantation is a common practice in peripheral and coronary artery bypass procedures. This study is designed to examine the effects of surgical skin markers on the HSV smooth muscle and endothelial functional responses. De-identified HSV remnants were collected during peripheral and coronary artery bypass procedures. Physiologic responses of the HSV were measured using a muscle bath. Veins that were marked with surgical skin markers intraoperatively generated significantly less contractile force to depolarizing KC1 (110 mM) and receptor-mediated contractile agonists than unmarked HSV, suggesting that surgical skin markers impaired HSV smooth muscle contractility. To directly access the effects of chemical components in the surgical skin markers, unmarked HSV was exposed to isopropyl alcohol (a solvent commonly used in surgical skin markers) or methylene blue (a dye). Smooth muscle contractility was significantly reduced by isopropyl alcohol and methylene blue. Endothelial-dependent relaxation to carbachol was significantly reduced after exposure to surgical skin markers. Our data demonstrated that marking HSV with surgical skin markers reduces smooth muscle and endothelial functional viability.

Mechanical properties of human saphenous veins from normotensive and hypertensive patients

BACKGROUND

Different reactivities of saphenous vein grafts in hypertensive and normotensive patients could lead to differences in the postoperative patency of the grafts.

METHODS

In saphenous vein rings isolated from remnants of aorta-coronary grafts obtained from hypertensive and normotensive patients we studied the length-tension relationship; response to high levels of potassium, norepinephrine, and epinephrine; and relaxation in response to calcium deprivation.

RESULTS

The rings from hypertensive patients were stiffer and developed more force (grams force/grams weight) than the rings from normotensive subjects to 80 mmol/L potassium (59+/-16 versus 25+/-5, p < 0.05) and to 1 micromol/L norepinephrine (61+/-8 versus 36+/-7, p < 0.05), but not to 10 micromol/L epinephrine (57+/-11 and 54+/-11; not significant). The rings from hypertensive patients relaxed more slowly than those of the normotensive subjects in a calcium-free medium (time to half-relaxation of 976+/-180 versus 548+/-81 seconds; p < 0.05).

CONCLUSIONS

The saphenous vein from hypertensive patients is less distensible, slower to relax, and more reactive to at least two agonists. These differences could influence the graft's patency and the clinical outcome.

Functional assessment of human femoral arteries after cryopreservation

PURPOSE

An established method of cryostorage that might preserve the vascular and endothelial responses of human femoral arteries (HFAs) to be transplanted as allografts was studied.

METHODS

HFAs were harvested from multiorgan donors and stored at 4 degrees C in Belzer solution before cryostorage. One hundred eleven HFA rings were isolated and randomly assigned to 1 control group of unfrozen HFAs and 2 groups of HFAs cryopreserved for 7 and 30 days, respectively. Cryopreservation was performed in Elohes solution containing dimethyl sulfoxide (1.8 mmol/L), and the rate of cooling was 1.6 degrees C/min, until -141 degrees C was reached. The contractile and relaxant responses of unfrozen and frozen/thawed arteries were assessed in organ bath by measurement of isometric force generated by the HFAs.

RESULTS

After thawing, the maximal contractile responses to all the contracting agonists tested (KCl, U46619 [a thromboxane A2-mimetic], norepinephrine, serotonin, and endothelin-1) were in the range of 7% to 34% of the responses in unfrozen HFAs. The endothelium-independent relaxant responses to forskolin and verapamil were weakly altered, whereas the endothelium-independent relaxant responses to sodium nitroprusside were markedly reduced. Cryostorage of HFAs also resulted in a loss of the endothelium-dependent relaxant response to acetylcholine. The vascular and endothelial responses were similarly altered in the HFAs cryopreserved for 7 and 30 days.

CONCLUSION

The cryopreservation method used provided a limited preservation of HFAs contractility, a good preservation of the endothelium-independent relaxant responses, but no apparent preservation of the endothelium-dependent relaxation. It is possible that further refinements of the cryopreservation protocol, such as a slower rate of cooling and a more controlled stepwise addition of dimethyl sulfoxide, might allow better post-thaw functional recovery of HFAs.