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

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.

Structure and Function of Porcine Arteries Are Preserved for up to 6 Days Using the HypoRP Cold-storage Solution

BACKGROUND

Maintaining functional vessels during preservation of vascularized composite allografts (VCAs) remains a major challenge. The University of Wisconsin (UW) solution has demonstrated significant short-term benefits (4-6 h). Here we determined whether the new hypothermic resuscitation and preservation solution HypoRP improves both structure, survival, and function of pig arteries during storage for up to 6 days.

METHODS

Using porcine swine mesenteric arteries, the effects of up to 6-day incubation in a saline (PBS), UW, or HypoRP solution on the structure, cell viability, metabolism, and function were determined.

RESULTS

After incubation at 4°C, for up to 6 days, the structures of the arteries were significantly disrupted, especially the tunica media, following incubation in PBS, in contrast with incubation in the HypoRP solution and to a lesser extent, in UW solution. Those disruptions were associated with increased active caspase 3 indicative of apoptosis. Additionally, while incubation in PBS led to a significant decrease in the metabolic activity, UW and HypoRP solutions allowed a stable to increased metabolic activity following 6 days of cold storage. Functional responsiveness to phenylephrine (PE) and sodium nitroprusside (SNP) decreased over time for artery rings stored in PBS and UW solution but not for those stored in HypoRP solution. Moreover, artery rings cold-stored in HypoRP solution were more sensitive to ATP.

CONCLUSIONS

The HypoRP solution improved long-term cold storage of porcine arteries by limiting structural alterations, including the collagen matrix, reducing apoptosis, and maintaining artery contraction-relaxation functions for up to 6 days.

University of Wisconsin vs normal saline solutions for preservation of blood vessels of brain dead donors: A histopathological study

OBJECTIVE

To compare the cellular changes of harvested arteries which were preserved in normal saline (NS) and the standard and routinely used University of Wisconsin (UW) solution.

METHODS

This experimental study was conducted on 20 brain dead patients. The femoral and iliac arteries were bilaterally removed and were placed in NS and UW solutions. The vascular change indices including endothelial detachment (ED), medial detachment (MD), and internal elastic membrane disruption (IEMD) were surveyed for each preserver in the first, 5th, 10th, and 21st day.

RESULTS

The mean age of the included patients was 32.28 ± 8.88 years, and there were 13 (65.0%) men and 7 (35.0%) women among the patients. The NS and UW preservation solutions were comparable regarding the indices of vascular changes at first, 5th, and 10th day of the study. Only in 21st day of the study, there was a significant difference between 2 group regarding MD changes (P = .049).

CONCLUSION

The results of this in vitro study demonstrated that NS can be used as a worthy preserver for harvested vessels for up to 21 days, especially in resource-limited transplantation centers.

Influence of the selected antioxidants on the stability of the Celsior solution used for perfusion and organ preservation purposes

The purpose of the following research was to improve the original Celsior solution in order to obtain a higher degree of stability and effectiveness. The solution was modified by the addition of selected antioxidants such as vitamin C, cysteine, and fumaric acid in the following concentrations: 0.1, 0.3, and 0.5 mmol/l. The solution's stability was estimated using an accelerated stability test based on changes in histidine concentrations in the solution using Pauly's method for determining concentrations. Elevated temperatures, the factor accelerating substances' decomposition reaction rate, were used in the tests. The research was conducted at four temperatures at intervals of 10 degrees C: 60 +/- 0.2 degrees C, 70 +/- 0.2 degrees C, 80 +/- 0.2 degrees C, and 90 +/- 0.2 degrees C. It was stated that the studied substances' decomposition occurred in accordance with the equation for first-order reactions. The function of the logarithmic concentration (log%C) over time was revealed to be rectilinear. This dependence was used to determine the kinetics of decomposition reaction rate parameters (the rate constant of decomposition k, activation energy E (a), and frequency factor A). On the basis of these parameters, the stability of the modified solution was estimated at +5 degrees C. The results obtained show that the proposed antioxidants have a significant effect on lengthening the Celsior solution's stability. The best results were reached when combining two antioxidants: vitamin C and cysteine in 0.5 mmol/l concentrations. As a result, the Celsior solution's stability was lengthened from 22 to 299 days, which is 13.5 times. Vitamin C at a concentration of 0.5 mmol/l increased the solution's stability by 5.2 times (t(90) = 115 days), cysteine at a concentration of 0.5 mmol/l caused a 4.4 times stability increase (t(90) = 96 days), and fumaric acid at a concentration of 0.5 mmol/l extended the stability by 2.1 times (t(90) = 48 days) in relation to the original solution.

Mechanics of Fresh, Refrigerated, and Frozen Arterial Tissue

Arterial grafts and experimental soft tissues are commonly preserved using refrigeration and freezing. The present study was designed to investigate effects of common storage protocols on arterial mechanics. Porcine aortas were axially distracted to failure implementing fresh, refrigerated, and frozen storage conditions. Fresh tissues were tested within 24 h of sacrifice; refrigerated tissues were stored at +4 degrees C for 24 or 48 h prior to testing, and frozen tissues were stored at -20 or -80 degrees C for 3 months prior to testing. Blunt arterial injury experimentally occurred in distraction with intimal subfailure before ultimate failure in 82% of specimens. Subfailure stress decreased in refrigerated (0.59 +/- 0.19 MPa) compared to fresh (0.83 +/- 0.39 MPa) and frozen (0.99 +/- 0.41 MPa) specimens. Ultimate stress was also significantly decreased in refrigerated (0.83 +/- 0.19 MPa) compared to fresh (1.15 +/- 0.39 MPa) and frozen (1.32 +/- 0.31 MPa) specimens. Subfailure and ultimate strain were not significantly dependent upon storage technique. Young's modulus significantly decreased in refrigerated (1.89 +/- 0.63 MPa) compared to fresh (2.98 +/- 1.45 MPa) and frozen (3.49 +/- 1.32 MPa) specimens. Physiological, subfailure, and ultimate failure mechanics between fresh and frozen specimens were not significantly different. Clinically relevant intimal failures can be reproduced and injury mechanics determined while adhering to experimental protocols of freezing specimens before testing. However, short-term tissue refrigeration may affect mechanics.