Comparison of saccharides as osmotic impermeants during hypothermic lung graft preservation

Trehalose protects against spinal cord ischemia in rabbits

OBJECTIVE

This study tested to see if trehalose, a cytoprotective disaccharide, protects against spinal cord ischemia in a rabbit model.

METHODS

The infrarenal aorta was mobilized in four groups of 10 rabbits. In groups I, II, and III, it was clamped proximally and distally for 20 minutes. In group I, the clamped aorta was infused at 2.5 L/min for 2 hours with lactated Ringer's (LR) solution. In group II, the clamped aorta was infused with 5% trehalose in LR. LR was administered intravenously (2.0 mL/min) in groups I and II starting 30 minutes before clamping. In group III, 5% trehalose in LR was infused intravenously only. Group IV was a sham-operated control group without aortic clamping. At 8, 24, and 48 hours after reperfusion, hind limb function was scored using the Tarlov score (paralysis = 0, perceptible joint movement = 1, good joint movement but unable to stand = 2, able to walk = 3, normal = 4). Histologic analysis and electron microscopy were performed on anterior horn cells.

RESULTS

The Tarlov scores in groups I, II, and III were, respectively, 1.1 ± 1.4, 3.5 ± 0.5, and 2.9 ± 0.9 at 8 hours; 0.8 ± 1.2, 3.9 ± 0.3, and 2.9 ± 0.9 at 24 hours; and 0.6 ± 0.7, 3.9 ± 0.3, and 2.7 ± 0.9 at 48 hours after reperfusion. Group IV scores were normal (4 ± 0) at all assessments. These scores were higher in groups II and III than in group I (P < .01) at all assessments. Scores at 24 and 48 hours were higher in group II than in group III (P < .05). In group III, delayed paraparesis developed in one rabbit at 24 hours and in two more at 48 hours. Histopathologic analysis showed the number of normal neurons was higher in groups II (P < .0001), III (P = .006), and IV (P < .0001) vs group I. Electron microscopy confirmed preserved neuronal cell ultrastructure in rabbits with normal limb function.

CONCLUSIONS

Transaortic trehalose infusion was protective against paraplegia, whereas intravenous trehalose reduced spinal cord ischemia. This study was preliminary and further studies are needed.

Evaluation of a Novel Cold Storage Solution (HBS) in a Rat Kidney Transplant Model

We developed an improved solution for hypothermic storage (0-4 degrees C) of kidneys. The cold storage solution (HBS) was composed of macromolecules, high-energy cellular substrates, and a mixture of antiproteolytic amino acids, antioxidants, and anti-inflammatory compounds. The objectives in developing this solution were to achieve superior metabolic support of the kidney during cold storage and to protect against ischemic injury. Inbred Brown Norway rats, weighing 225-250 g, were subjected to orthotopic ultrarapid technique for kidney isotransplantation to minimize warm ischemia and to test the preservation process. The kidney was transplanted after 12 h of preservation. The animals were divided into three groups based upon the preservation solution utilized: HBS solution, HTK solution (Custodiol), and UW solution (UWS)(ViaSpan). Among the recipients, each group had two subsets. The first subset of animals was used to assess survival at 7 days as well as the reperfusion damage index (RDI) based on the macroscopic physical characteristics of the kidney at the time of transplantation. The second subset in each group was utilized to measure serum creatinine and blood urea nitrogen at 4 and 7 days, and histology at death or sacrifice. Mean +/- standard deviation (M +/- SD) was used for all parameters studied. The HBS solution showed significantly better protection at 12 h when compared to HTK and UW solutions. The reperfusion damage index (RDI) showed excellent preservation in the HBS (14 +/- 1), good preservation in UWS (13 +/- 1.5), and moderate preservation in the HTK (11 +/- 2) group. Histology was in concordance with the RDI, showing better histological findings with HBS and UW solutions than with the HTK group. Serum creatinine was significantly better in the HBS group when compared to HTK and UWS. Survival was statistically different, with 80% survival at 7 days in the HBS group, 20% survival in the HTK group, and 50% survival in the UWS group (p < .05). The HBS solution offered a new alternative for kidney cold storage with significantly better results when compared to the current gold standards of HTK and UW solutions in Brown Norway rats. This solution warrants further testing in other mammals.

Lung preservation solution substrate composition affects rat lung oxidative metabolism during hypothermic storage

Lungs harvested for transplantation utilize oxygen after procurement. We investigated the effects of storage solution substrate composition on pulmonary oxidative metabolism and energetics during the preservation interval. Rat lungs were harvested and stored at 10 degrees C in low-potassium dextran (LPD) solution. Groups of lungs were preserved with preservation solution containing 5mM carbon-13 ((13)C) labeled glucose or increasing concentrations of (13)C labeled pyruvate. Additional groups of rat lungs were studied with dichloroacetate (DCA) added to the pyruvate-modified preservation solutions. Oxidative metabolism (measured by (13)C-enrichment of glutamate) and adenine nucleotide levels were quantified. Increasing preservation solution pyruvate concentration augmented glutamate (13)C-enrichment up to a concentration of 32mM pyruvate. DCA further stimulated oxidative metabolism only at lower concentrations of pyruvate (4 and 8mM). ATP and ADP were not different among groups, but AMP levels were higher in the glucose group. These data suggest that altering the substrate composition of the preservation solution influences lung metabolism during allograft preservation for transplantation.

Effect of Modification of Ovary Preservation Solution by Adding Glucose on the Maturation and Development of Pig Oocytes after Prolonged Storage

Oocytes lose their developmental competence during prolonged storage of the ovary. In the present study, we supplemented the preservation solution for pig ovaries (phosphate buffered saline, PBS) with glucose and preserved the ovaries for 6 h at 25 C. Subsequently, we examined the glucose concentration of the follicular fluid (FF), pH of the FF, survival rate of the granulosa cells, and maturation and developmental competence of oocytes after storage. During storage, the glucose concentration of the FF (2.1 mM), pH of the FF (7.4), and survival rate of the granulosa cells (69.5%) rapidly decreased (glucose concentration: under 1.1 mM; pH: 6.8; and survival rate: 43%). On the other hand, when the preservation solution was supplemented with glucose (15 mM), the glucose concentration of the FF increased and the survival rate of the granulosa cells improved, although the pH of the FF decreased further (from 6.8 to 6.6). In addition, supplementation with glucose significantly improved the rates of oocytes at metaphase II (0 h: 65.0%; 6 h without glucose: 23.8%; and 6 h with glucose: 43.8%) and attenuated the decline in the rates of fertilization and development that resulted from prolonged storage, although there were no significant differences. In conclusion, modification of the preservation solution by the addition of glucose increased the glucose concentration of the FF and improved the rate of maturation of pig oocytes.

Lung transplantation. Lung preservation

Over the past decade, improvements in the technique of lung preservation have led to significant reduction in the incidence of ischemia-reperfusion-induced lung injury after lung transplantation. The challenge remains to improve the number of donor lungs available for transplantation. While the number of patients on the waiting list is constantly increasing, only 10% to 30% of donor lungs are currently being used for transplantation. Hence, the development of new strategies to assess, repair, and improve the quality of the lungs could have a tremendous impact on the number of transplants performed. In addition, an improved understanding of the mechanisms involved in lung preservation might help elucidate the potential link between acute lung injury and chronic graft dysfunction. In the future, genetic analysis using novel technologies such as microarray analysis will help researchers determine which genes control the injury seen in the transplantation process. Hopefully, this information will provide new insights into the mechanisms of injury and reveal potential new strategies and targets for therapies to improve lung preservation.

Ischemia-reperfusion-induced lung injury

Ischemia-reperfusion-induced lung injury is characterized by nonspecific alveolar damage, lung edema, and hypoxemia occurring within 72 hours after lung transplantation. The most severe form may lead to primary graft failure and remains a significant cause of morbidity and mortality after lung transplantation. Over the past decade, better understanding of the mechanisms of ischemia-reperfusion injury, improvements in the technique of lung preservation, and the development of a new preservation solution specifically for the lung have been associated with a reduction in the incidence of primary graft failure from approximately 30 to 15% or less. Several strategies have also been introduced into clinical practice for the prevention and treatment of ischemia-reperfusion-induced lung injury with various degrees of success. However, only three randomized, double-blinded, placebo-controlled trials on ischemia-reperfusion-induced lung injury have been reported in the literature. In the future, the development of new agents and their application in prospective clinical trials are to be expected to prevent the occurrence of this potentially devastating complication and to further improve the success of lung transplantation.

Raffinose improves 24-hour lung preservation in low potassium dextran glucose solution: a histologic and ultrastructural analysis

BACKGROUND

We have previously shown that the addition of raffinose to low potassium dextran (LPD) preservation solution improves transplanted rat lung function after 24 hours of storage. The mechanisms by which raffinose acts are unclear. The aim of this study was to examine the histologic and ultrastructural correlates of this enhanced pulmonary function after preservation with raffinose.

METHODS

In a randomized, blinded study, rat lungs were flushed with LPD, or LPD containing 30 mmol/L of raffinose, and stored for 24 hours at 4 degrees C. Control lungs were flushed with LPD but not stored (n = 5 each group). Changes in postpreservation edema were determined. In addition, lungs were flushed with a trypan blue solution to quantify cell death, and examined using both light and electron microscopy.

RESULTS

The LPD lungs gained significantly more weight (25.5%+/-5.5%) compared with raffinose-LPD lungs (5.2%+/-5.3%; p < 0.0001). There were higher percentages of dead cells in the LPD lungs (29%+/-0.3% of total cells) compared with raffinose-LPD lungs (14%+/-1.4%; p < 0.001) and control lungs (0.2%+/-5%; p < 0.001). Control lungs maintained normal ultrastructure, whereas LPD lungs showed a decreased number of intact type II pneumocytes and significant cellular necrosis. Interstitial and alveolar edema with interstitial macrophage infiltration was also observed. Alveolar capillaries were collapsed. In contrast, raffinose-LPD lungs showed only mild alterations such as minimal interstitial edematous expansion, fewer damaged cells, and minimal capillary injury.

CONCLUSIONS

Raffinose exerts a cytoprotective effect on pulmonary grafts during preservation, which explains the previously documented improved function. This simple modification of LPD with raffinose may provide clinical benefit in extended pulmonary preservation.

24-hour lung preservation: simplified versus conventional University of Wisconsin solution in a porcine model

BACKGROUND

Experimentally, the University of Wisconsin solution (UW) has been shown to be superior to the EuroCollins solution (EC) for lung graft preservation. We showed previously that the inclusion of the trisaccharide raffinose as an impermeant in the UW is largely responsible for this superiority. In this study, we used a new porcine model of isolated lung reperfusion to evaluate the use of a simple solution of phosphate-buffered raffinose (PBr) for lung preservation.

METHODS

Lungs were stored for 24 hr at 4 degrees C after a single pulmonary artery flush with either UW (n = 5) or PBr (n = 5) solution. Left lungs were ventilated with room air and reperfused for 4 hr by venovenous extracorporeal circulation from a support animal. Controls (n = 5) were flushed with UW and reperfused without storage.

RESULTS

Control lungs performed better than those stored in either solution in terms of oxygenation (P = 0.034) and airway pressure (P = 0.032). There were no significant differences between the two stored groups for any parameters. Data for stored lungs after 4 hr of reperfusion (means with 95% confidence intervals) include oxygenation (mm Hg): control 101.6 (14.5), UW 85.2 (14.5), PBr 75.0 (14.5); blood flow (ml/ min): control 572 (90), UW 466 (90), PBr 468 (90); peak airway pressure (mm Hg): control 15.9 (3.0), UW 21.0 (3.0), PBr 22.6 (3.0); pulmonary artery pressure (mm Hg): control 17.5 (3.2), UW 22.3 (2.9), PBr 24.5 (2.9). Graft edema (percentage tissue water): control 86.4 (0.8), UW 89.9 (1.8), PBr 89.3 (1.0).

CONCLUSION

PBr is a far simpler and less expensive alternative to UW, and appears to provide a similar level of lung graft protection.

Raffinose improves the function of rat pulmonary grafts stored for twenty-four hours in low-potassium dextran solution

OBJECTIVES

The perfect strategy for pulmonary graft preservation remains elusive. Experimental work supports the use of perfusates, such as Euro-Collins, University of Wisconsin, and low-potassium dextran solutions. We use low-potassium dextran solution in our clinical program, but we aim for continued improvement. The trisaccharide raffinose has been shown to be responsible for the efficacy of University of Wisconsin perfusate in lung preservation. Raffinose is superior to a variety of other saccharides for this purpose. We tested the hypothesis that the addition of raffinose to low-potassium dextran solution might further improve graft function.

METHODS

In a randomized blinded study with a rat left lung transplant model, donor lungs were flushed with either standard low-potassium dextran solution or low-potassium dextran solution modified by the addition of 30 mmol/L raffinose (n = 5 for each group). Alprostadil (prostaglandin E(1), 500 microg/L) was added to the perfusates in accordance with our clinical practice. Grafts were stored inflated at 4 degrees C for 24 hours. After transplantation, recipients were ventilated with a fraction of inspired oxygen of 1 and a positive end-expiratory pressure of 2 cm H(2)O. Graft function was evaluated by measuring oxygenation at 2 hours after graft reperfusion, peak airway pressure throughout the reperfusion period, and the wet/dry lung weight ratio.

RESULTS

The group receiving low-potassium dextran solution with raffinose demonstrated significantly higher oxygenation (oxygen tension, 370 +/- 45 mm Hg vs 150 +/- 64 mm Hg; P =.0025), lower peak airway pressures at 2 hours after lung reperfusion (11 +/- 2.7 mm Hg vs 16 +/- 2.4 mm Hg; P <.001), and a lower wet/dry weight ratio (4.7 +/- 1.26 vs 11 +/- 5. 0; P =.017).

CONCLUSION

Modification of low-potassium dextran solution with the trisaccharide raffinose resulted in a significant improvement in graft function in this model and merits further evaluation with respect to the mechanisms involved.

Risk of low calcium and high magnesium in continuous warm hyperkalemic cardioplegia

BACKGROUND

The recent introduction of operations on a warm heart has prompted clinical reports on the usefulness of continuous blood cardioplegia, but no in-depth basic evaluation of continuous cardioplegia has been done. The cardioprotective effects of magnesium (Mg) and calcium (Ca) in continuous warm hyperkalemic crystalloid cardioplegic solutions were investigated in an isolated rat heart model.

METHODS

Isolated rat hearts were arrested for 180 minutes at 37 degrees C with a continuous warm hyperkalemic (20 mmol/L) modified Krebs-Henseleit bicarbonate buffer solution containing 1.2, 8.0, or 16.0 mmol/L of Mg and 0.1 to 2.5 mmol/L of Ca in different concentrations. Recovery of cardiac function and tissue damage were estimated.

RESULTS

For each Mg concentration, the percentage recovery of aortic flow generated dose-response curves depending on Ca concentration. However, as Mg concentration increased, the recovery of aortic flow decreased in the groups with 0.5 mmol/L of Ca or less.

CONCLUSIONS

In continuous warm cardioplegia the combination of low Ca and high Mg concentration caused severe cardiac injury, and normal Ca concentration avoids cardiac injury regardless of Mg concentrations.

Role of saccharides on lung preservation

BACKGROUND

Saccharides are considered to play a role as osmotic impermeants and serve as an energy source for the organ during ischemia. However, previous studies on the effectiveness of saccharides on organ preservation have yielded conflicting results. We compared the preservative effects of a monosaccharide (glucose), disaccharides (trehalose, maltose, sucrose), and a trisaccharide (raffinose) to investigate whether the effects of saccharides on lung preservation depend on their molecular weight, energy-level maintenance, and cytoprotective effects.

METHODS

We used an ex vivo rat lung model using homologous blood as the perfusate. In the fresh group, the lungs were reperfused immediately after flush. In the other groups, the lungs were flushed with one of the solutions containing glucose, trehalose, maltose, sucrose, or raffinose and preserved for 14 hours.

RESULTS

The results of the trehalose group were comparable to those of the fresh group. The glucose, maltose, and raffinose groups showed significantly higher levels of shunt fraction, pulmonary artery pressure, and peak inspiratory pressure compared with the fresh and trehalose groups. There were no differences among the groups in the levels of total adenine nucleotides, adenosine triphosphate of the lung after flush, and preservation. However, after reperfusion, levels of total adenine nucleotides became significantly lower in the glucose, sucrose, maltose, and raffinose groups. Ultrastructural examination revealed endothelial cell injury in the glucose, sucrose, maltose, and raffinose groups.

CONCLUSIONS

These results show that the effects of saccharides may depend on their cytoprotective effect rather than on impermeant activity or energy-level maintenance of the preserved lung. Trehalose proved to be superior to the other saccharides.