Platelet activating factor antagonist enhances lung preservation in a canine model of single lung allotransplantation

Cytosolic phospholipase A2 inhibition attenuates ischemia-reperfusion injury in an isolated rat lung model

BACKGROUND

Arachidonic acid metabolites and platelet-activating factor (PAF) are potentially involved in ischemia-reperfusion (IR) lung injury. A key enzyme regulating their metabolism is cytosolic phospholipase A2 (cPLA2). Arachidonyl trifluoromethyl ketone (AACOCF3) is reported to be a potent cPLA2 inhibitor. In the present study, we hypothesized that pharmacological inhibition of cPLA2 might ameliorate IR lung injury.

METHODS

To test the hypothesis, we examined the effects of AACOCF3 in an isolated rat lung model. Three groups were defined (n=6, each): in the vehicle group, lungs were perfused for 2 hours without an ischemic period. In the ischemic groups, 20 mg/kg of AACOCF3 (AACOCF3 group) or saline (control group) was i.v. administered 15 min before lung harvest. Lungs were flushed with LPD solution, cold-stored 18 hours, and reperfused for 2 hours.

RESULTS

IR increased cPLA2 activity mainly via alveolar macrophages, sPLA2 activity, thromboxane and leukotriene formation, and the expression of PAF receptor, whereas AACOCF3 treatment significantly reduced all of these. Compared to the vehicle group, the wet-to-dry ratio, proteins in BAL, and MPO activity increased significantly by twofold, fourfold, and threefold, respectively. Furthermore, the PO2 dropped from 615.7+/-31.2 to 452.1+/-30.9 mmHg at the end of reperfusion (P<0.001). AACOCF3 treatment maintained the PO2 at a level similar to the vehicle group throughout reperfusion and reduced significantly the alveolar-capillary leakage, edema formation, and neutrophil extravasation.

CONCLUSION

Pharmacological inhibition of the cPLA2 cascade decreases bioactive lipid formation and attenuates IR-induced lung injury.

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.

Platelet activating factor acetylhydrolase decreases lung reperfusion injury

BACKGROUND

Ischemia-reperfusion injury involves free radical production, polymorphonuclear neutrophil chemotaxis/degranulation, and production of proteolytic enzymes, complement components, coagulation factors, and cytokines. Activated polymorphonuclear neutrophils, endothelial cells, and macrophages produce platelet activating factor, which further promotes these inflammatory reactions. The recently cloned plasma form of platelet activating factor-acetylhydrolase (PAF-AH) demonstrates antiinflammatory effects by degrading platelet activating factor. We evaluated the effects of PAF-AH in an isolated perfused rat lung model by adding it to the flush solutions or to the reperfusion blood.

METHODS

Rat lungs were isolated, flushed with EuroCollins (EC) or University of Wisconsin (UW) solution, stored at 4 degrees C for 6 or 12 hours, and reperfused using a cross-circulating syngeneic support rat. During reperfusion, oxygenation, compliance, and capillary filtration coefficient were calculated. There were four groups in the study; group I (control) had no PAF-AH added, group II had PAF-AH added to the flush solution, group III had PAF-AH added to reperfusion blood, and group IV had PAF-AH added to both flush solution and reperfusion blood.

RESULTS

After 6 hours of storage, oxygenation, compliance, and capillary filtration coefficient significantly improved for EC in group IV. For UW, oxygenation improved in group IV whereas compliance improved in groups II, III, and IV. After 12 hours of storage, compliance improved for EC in group IV and capillary filtration coefficient improved in groups III and IV. For UW, oxygenation and compliance improved in groups II and IV, whereas capillary filtration coefficient improved in group IV.

CONCLUSIONS

Addition of PAF-AH to intracellular organ preservation solutions and to the blood reperfusate significantly improves postreperfusion oxygenation and compliance, and reduces lung capillary permeability.

Combined treatment with endothelin- and PAF-antagonists reduces posttransplant lung ischemia/reperfusion injury

BACKGROUND

Pathophysiologic changes of posttransplant lung ischemia/reperfusion injury are mediated by redundant cellular and humoral mechanisms. We investigated the protective effect of combined administration of platelet activating factor (PAF) and endothelin (ET) antagonists after prolonged ischemia in a small animal lung transplantation model.

METHODS

Orthotopic left lung transplantation was performed after 20 hours cold ischemia in male Fischer (F344) rats weighing 200-250 g. Group I served as control. In Group II, donors received 1 mg/kg body weight of the endothelin antagonist TAK-044, and recipients 2 mg/kg. Group III was treated with the PAF antagonist TCV-309 (donor: 50 microg/kg; recipient: 100 microg/kg) (Takeda Chemicals Ltd.). Group IV received a combined treatment with both substances at the same dosage. Twenty-four hours after reperfusion, the native contralateral lung was occluded to assess gas exchange of the graft only, and 5 minutes later the thoracic aorta was punctured for arterial blood gas analysis (n = 5). In other animals (n = 5), lung tissue was frozen 24 hours after reperfusion and assessed for myeloperoxidase activity (MPO) and thiobarbituric acid reactive substances.

RESULTS

Combined inhibition of PAF and ET-1 at the receptor level resulted in significantly improved graft function as compared to controls (Group I), and to groups treated with either TAK-044 or TCV-309. This was determined by a higher arterial oxygen content (112 +/- 9 mmHg, p = .00061 vs control, 48 +/- 5 mmHg), reduced MPO activity (0.35 +/- 0.02 deltaOD/mg/min, p = .000002 vs control, 1.1 +/- 0.1 deltaOD/mg/min) and reduced lipid peroxidation (59.5 +/- 2.5 pmol/g, p = .011 vs control, 78.5 +/- 4.1 pmol/g). The improvement of arterial oxygen (Group II 77 +/- 10 mmHg, p = .027 vs control; Group III 84 +/- 8 mmHg, p = .0081 vs control) and reduction of MPO activity (Group II 0.85 +/- 0.061 deltaOD/mg/min, p = .017; Group III 0.92 +/- 0.079 deltaOD/mg/min, p = .058) in groups treated with either a PAF antagonist or an ET antagonist was significantly less than in Group IV.

CONCLUSIONS

Combined donor and recipient treatment with an ET antagonist and a PAF antagonist results in superior posttransplant graft function 24 hours after reperfusion, suggesting a synergistic role of ET-1 and PAF in the mediation of reperfusion injury in this model. Single treatment with either of the antagonists revealed only a slight improvement compared to untreated controls.

Amelioration of lung reperfusion injury by L- and E- selectin blockade

OBJECTIVE

Reperfusion injury is the main reason for early graft failure after lung transplantation. Inhibition of the adherence of polymorphonuclear leukocytes to activated endothelium by blocking L- and E-selectins (antibody EL-246) could potentially inhibit reperfusion injury.

METHODS

Reperfusion injury was induced in a left lung autotransplant model in sheep. After hilar stripping the left lung was flushed with Euro-Collins solution and preserved for 2 h in situ at 15 degrees C. After reperfusion right main bronchus and pulmonary artery were occluded leaving the animal dependent on the reperfused lung (control, n = 6). Pulmonary function was assessed by alveolo-arterial oxygen difference (AaDO2) and pulmonary vascular resistance (PVR), the chemiluminescence of isolated neutrophils, as well as the release of beta-N-acetyl-glucosaminidase (beta-NAG) served as indicator of neutrophilic activation. Extravascular lung water was an indicator for pulmonary edema formation. EL-246 group animals (n = 6) were treated additionally with 1 mg/kg BW of EL-246 given prior and during reperfusion.

RESULTS

After 3 h of reperfusion five control animals developed alveolar edema compared to one animal in the EL-246 group (P = 0.08). AaDO2 (mm Hg) was significantly higher in the control compared to the EL-246 group (510 +/- 148 vs. 214 +/- 86). PVR (dyn x s x cm(-5)) was significantly increased in the control compared to the EL-246 group (656 +/- 240 vs. 317 +/- 87). Neutrophilic activation was significantly lower in the EL-246 group. Extravascular lung water was significantly lower compared to control (6.88 +/- 1.0 vs. 13.4 +/- 2.8 g/g blood-free lung weight).

CONCLUSIONS

Treatment with EL-246 results in improved pulmonary function and less in vivo PMN activation in this experimental model. Further studies are necessary to evaluate the possible role of selectin blockade in amelioration of reperfusion injury in human lung transplantation.

Selective Cerebral Perfusion Via Innominate Artery in Aortic Arch Replacement Without Deep Hypothermic Circulatory Arrest

To attain satisfactory results in aortic arch surgery a reliable method of cerebral protection, avoidance of emboli, and control of hemorrhage is mandatory. Deep hypothermic circulatory arrest is the most common technique at present but gives only a limited period of protection, whereas a complicated aortic arch operation may require more time than anticipated. Therefore the selective cannulation and perfusion of the innominate artery has not been widely used until now because it is uncertain whether the left hemisphere of the brain is adequately perfused. Between 1990 and 1995, 21 of 69 patients within the last 36 months, consisting of 15 men and 6 women averaging 45 +/- 13.4 years, underwent operative treatment for aneurysm (n = 9) or type A dissection (n = 12) involving the aortic valve and aortic arch; selective innominate perfusion (SCP [i]) in moderate hypothermia (28 degreesC) for brain protection was used. Extended perioperative monitoring included bilateral somatosensory-evoked potentials (SEP), transcranial Doppler sonography (TCD), a computer-aided topographical electro-encephalometry (CATEEM), and analysis of the arterial and venous oxygen saturation and desaturation. Mean time periods were 229.7 +/- 56.5 minutes for extracorporeal circulation, 151.7 +/- 34.1 minutes for aortic cross-clamping, and 67.05 +/- 34.03 for selective cerebral perfusion via the innominate artery. Not once did the intraoperative monitoring reveal hints of cerebral damage due to inadequate perfusion. All patients survived surgery but two could not be weaned from the respirator; one died 2 days and the other 6 days after the operation due to multiple organ failure (MOF). Another two patients died after 13 days due to untreatable septic syndrome with pulmonary insufficiency. All four patients died within 30 days, during which time they had aortic dissection involving the complete aortic arch and severe aortic valvular incompetence (grade IV). There was no late death and follow-up time of 19.76 +/- 8.04 months revealed an overall mortality rate of 19%. Only temporary neurological affections (left-sided hemiparesis) were found in two patients (9.5%). Additionally, we observed neuropsychological disturbances in one of these. Our first experience with selective cerebral perfusion via innominate artery and the attendant CATEEM monitoring for assessment of adequate bilateral cerebral perfusion suggests that this method is a useful addition to the armamentarium in complicated aortic arch surgery.

Neutrophil modulation results in improved pulmonary function after 12 and 24 hours of preservation

Neutrophils are important mediators of reperfusion injury, and suppression of neutrophil function or numbers can reduce reperfusion injury and improve long-term organ preservation in transplantation. NPC 15669, a leumedin, is a novel compound that prevents recruitment of neutrophils at inflammatory foci by inhibiting CD11b/CD18 adhesion molecule expression. NPC 15669 was used to inhibit neutrophil adhesion during reperfusion of isolated rabbit lungs after 12 and 24 hours of cold storage. Lungs (New Zealand White male rabbits, 2 to 3 kg) were flushed with 4 degrees C Euro-Collins (EC) solution, harvested en bloc, stored under various study conditions, and reperfused for 3 hours with fresh whole blood at 37 degrees C in an isolated perfusion system at constant flow and an inspired oxygen fraction of 1. Four groups (n = 6 each) were studied. Group I underwent immediate whole blood reperfusion. Group II were stored for 12 hours in 4 degrees C EC solution before reperfusion. Group III were stored for 12 hours in 4 degrees C EC solution and reperfused with whole blood containing NPC 15669 (10 mg/kg whole body weight). Group IV were stored for 24 hours in 4 degrees C EC solution and reperfused with whole blood containing NPC 15669 (10 mg/kg). Pulmonary artery and peak airway pressures were significantly lower and compliance higher in groups III and IV lungs after 3 hours of reperfusion (p < 0.05) compared with group I. Group I and III lungs had significantly less edema than group II (p < 0.05). The arterial partial pressure of oxygen was similar in all stored groups (II to IV).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of platelet-activating factor on cold-preserved liver grafts

Platelet-activating factor (PAF) may play an important role in graft injury in liver transplantation. Livers excised from male Wistar rats were preserved in University of Wisconsin solution for 6 h and then perfused with Krebs-Henseleit solution containing vehicle (bovine serum albumin) or PAF. Impairment of parenchymal cells was assessed by reference to tissue adenosine triphosphate levels, oxygen consumption and alanine aminotransferase activity in the effluent. The effect on non-parenchymal cells was evaluated by measurement of purine nucleoside phosphorylase and alanine aminotransferase levels in the effluent. Administration of as little as 1.0 ng kg-1 PAF caused a significant decrease in adenosine 5'-triphosphate concentration and oxygen consumption (P < 0.05), although non-parenchymal cell injury was not affected. PAF can therefore cause liver graft dysfunction with hepatocytes as the main target, even in the absence of microcirculatory disturbance secondary to interaction between blood cells and endothelial cells.

University of Wisconsin solution extends lung preservation after prostaglandin E1 infusion

University of Wisconsin (UW) solution has been demonstrated to enhance and extend the preservation of the hepatic, pancreatic, renal, and cardiac allografts. Prostaglandin E1 (PGE1), which has been used to produce pulmonary vasodilatation, has improved preservation in lung transplantation. Experiments were designed to evaluate their potential role in 24-h preservation of the allografts in lung transplantation. Thirty-six dogs underwent left lung transplantation. The donor lungs (n = 6 in each group) were flushed with UW solution (group 1 and 2) or modified Euro-Collins (EC) solution (group 3) after PGE1 infusion (500 micrograms). In group 1, donor lungs were transplanted immediately. Lung allografts of group 2 and 3 were cold stored (4 degrees C) in the same preservation solution for 24 h in the inflated state and then transplanted. The right pulmonary artery and right main bronchus were ligated 1 h after completion of the transplantation, forcing the recipient dogs to survive with the transplanted left lung. The recipients were ventilated with an inspired oxygen fraction of 0.4 and end-expiratory pressure 10 cm H2O. Two dogs died prematurely in group 3, whereas all dogs in group 1 and 2 survived the experimental period. The arterial oxygen tension and saturation and dynamic lung compliance were significantly higher in dogs of group 1 and 2. Transplanted lungs of group 1 and 2 had significantly lower pulmonary vascular resistance, alveolar-arterial oxygen difference, and wet/dry lung weight ratio. Histologically, pulmonary edema, congestion, sloughing of bronchial mucosa, and peribronchial and peripulmonary arterial hemorrhage were shown in lungs of group 3, but not in those of group 1 and 2. Airway mucosa and pulmonary vascular structure were well preserved in lungs of group 1 and 2. There was no significant difference between group 1 and 2 in lung functions, hemodynamics, or morphologic features. We concluded that PGE1 and UW solution could effectively extend lung preservation up to 24 h in this in vivo canine lung allotransplantation model.

Reduction of conjugated dienes in lung transplantation: effect of BN 52021

Oxygen-derived free radicals have been identified as the mediators of tissue injury during reperfusion in organ transplantation. Lipid peroxidation of cell membrane polyunsaturated fatty acids, generating conjugated dienes (CD), is a toxicity of oxygen-derived free radicals. The CD structure in fatty acyl moieties was measured by high-pressure liquid chromatography in samples of inferior pulmonary venous blood and pulmonary tissue to assess reperfusion injury and oxygen-derived free radical-mediated damage in a canine model of left lung allotransplantation. The cold ischemic preservation interval was 6 hours and the posttransplantation monitoring period was 6 hours. Twenty-eight size- and weight-matched adult male dogs underwent left lung allotransplantation and were randomized to receive pulmonary artery flush of modified Euro-Collins (EC) (40 mL/kg) or University of Wisconsin (UW) (40 mL/kg) solutions alone or with the addition of the platelet-activating factor antagonist BN 52021 (10 mg/kg). When employed, BN 52021 was administered to donors 30 minutes before harvest and recipients 30 minutes before reperfusion. Left and right inferior pulmonary venous blood samples were obtained at baseline before transplantation and at 1, 2, 4, and 6 hours after transplantation; tissue samples were obtained after euthanasia. Serum and tissue CD levels are expressed as mean fraction of the total hydroperoxide sample +/- standard error of the mean. At 6 hours after transplantation, the EC group's (n = 7) CD fraction was 0.28 +/- 0.03, whereas that of the EC + BN 52021 group (n = 7) was 0.12 +/- 0.03 (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Lung preservation: a review of current practice and future directions

During the past 10 years, pulmonary transplantation has emerged as a successful mode of surgical therapy for suitable patients with end-stage lung disease. Current preservation techniques of donor lungs for subsequent transplantation include core-cooling and single flush perfusion. The relative merits of these are described. These methods are essentially restricted to 6 hours of ischemia. Research in lung preservation is aimed not only at extending the safe period of ischemia but also at improving the quality of preservation. Areas of interest include the ideal composition of the perfusate, relevant pharmacologic additives, and the best conditions for preservation and harvesting. Advantages and disadvantages of the various animal models are listed in addition to the methods used in assessing the quality of preservation. There have been major advances in experimental lung preservation during the past 10 years, and we are possibly on the threshold of incorporating some of these into clinical practice. Among the most important are the adoption of colloid-based perfusates, the more widespread use of free radical scavengers, and the use of leukocyte depletion.