Reduction of endothelial injury after hypothermic lung preservation by initial leukocyte-depleted reperfusion

Blockade of receptor for advanced glycation end product attenuates pulmonary reperfusion injury in mice

OBJECTIVE

The receptor for advanced glycation end products (RAGE) is expressed at high levels in the lung, particularly in type 1 alveolar cells, and has been shown to amplify injury triggered by acute stress. Previous studies suggest serum concentrations of soluble RAGE increase during pulmonary reperfusion injury after transplantation. RAGE blockade has been shown to suppress hepatic and cardiac ischemia and reperfusion injury in mice. Thus we tested the hypothesis that RAGE mediates tissue-injury mechanisms in ischemia and reperfusion injury in the lung.

METHODS

C57BL/6 mice were subjected to 30 minutes of pulmonary ischemia by clamping the left hilum, followed by 60 minutes of reperfusion. Lung function was assessed by means of blood gas analysis, and capillary leak was assessed by injecting fluorescein isothiocyanate-labeled albumin and comparing fluorescence in bronchial lavage fluid with that in serum. Histologic analysis of the lung was performed by a pathologist naive to the experimental conditions.

RESULTS

In animals subjected to RAGE blockade, significant increases in Po(2) (108 vs 73 mm Hg, P = .0094) and more than 3-fold decrease in capillary leak Relative Fluorescent Units (RFU, 6.12 vs 1.75; P = .001) were observed. Histologic examination revealed significant injury reduction in soluble RAGE-treated animals versus control animals. RAGE knockout mice exhibited a protected phenotype when exposed to pulmonary ischemia and reperfusion. Additionally, interleukin 8 production and nuclear factor kappaB activation were increased in control mice.

CONCLUSION

Abrogation of RAGE signaling attenuates pulmonary ischemia and reperfusion injury. This study suggests that RAGE might play a central role in pulmonary reperfusion injury and in transplantation and that blockade of RAGE might offer a potential target to abrogate pulmonary reperfusion injury in clinical transplantation.

Leukocyte filtration to decrease the number of adherent leukocytes in the cerebral microcirculation after a period of deep hypothermic circulatory arrest

OBJECTIVE

Cardiopulmonary bypass and hypothermic circulatory arrest induce a systemic inflammatory response, including a cascade of leukocyte and endothelial cell activity, during the postischemic reperfusion phase. Accumulation of leukocytes in the brain can lead to neurologic problems after cardiac surgery. The beneficial effects of a leukocyte-depleting filter have been documented, but because of contradictory results the underlying function of the filter remains unclear.

METHODS

Twenty-two juvenile piglets (6 to 8 weeks) were randomly assigned to undergo cardiopulmonary bypass with or without a leukocyte-depleting filter 60 minutes before and 60 minutes after a 75-minute hypothermic circulatory arrest at 18 degrees C. The cerebral vessels were visualized with intravital microscopy through a cranial window placed over the parietal cortex. Rhodamine staining was used to observe adherent and rolling leukocytes in the cerebral postcapillary venules. The animals were electively killed 1 hour after weaning from cardiopulmonary bypass.

RESULTS

There were no significant differences between the study groups regarding hemodynamic data. Numbers of adherent activated leukocytes were lower in the leukocyte filtration group, reaching borderline statistical significance when assessed throughout the experiment (between-groups P = .069) and actual statistical significance when assessed during the rewarming period (between-groups P = .029).

CONCLUSION

The leukocyte-depleting filter succeeded in reducing the number of adherent leukocytes during the reperfusion period in an experimental operation with deep hypothermic circulatory arrest. Such a filter thus could mitigate cerebral reperfusion injury after cardiac surgery.

Pentoxifylline is as effective as leukocyte depletion for modulating pulmonary reperfusion injury

OBJECTIVE

Previous studies have suggested the amelioration of lung reperfusion injury when initial reperfusion is undertaken with leukocyte-depleted blood. Pharmacologic agents, such as pentoxifylline, are also effective, but no previous studies have demonstrated which is superior. We investigated these agents in a porcine model of left single-lung transplantation.

METHODS

Donor lungs were preserved with modified Euro-Collins solution for a mean ischemic time of 18.6 hours. Gas exchange, pulmonary vascular resistance, neutrophil elastase level, and free radical release (measured on the basis of malonaldehyde levels) were assessed over a 12-hour period. Group A (n = 5) was a control group with no interventions added. Group B was reperfused through an extracorporeal circuit incorporating a leukocyte-depleting filter for 30 minutes before conventional blood flow was restored. Group C was reperfused with the addition of intravenous pentoxifylline (2 mg x kg(-1) x h(-1)).

RESULTS

Groups B and C were similar in terms of oxygenation, pulmonary vascular resistance, and free radical release. Group B displayed increased levels of neutrophil elastase. Both groups were superior with regard to these outcome measures compared with control group A.

CONCLUSIONS

Pentoxifylline, when administered to recipient animals, attenuates reperfusion injury to a degree similar to that seen with leukocyte-depleted reperfusion. This technique is simple, safe, and as effective as using a more complex extracorporeal circuit incorporating a leukocyte-depleting filter to ameliorate acute lung injury.

Effect of antibodies to intercellular adhesion molecule type 1 on the protection of distant organs during reperfusion syndrome in rats

We investigated kidney and lung alterations caused by intercellular adhesion molecule type 1 (ICAM-1) blockade after ischemia and reperfusion of hind limb skeletal muscles. Rats were submitted to ligature of the infrarenal aorta for 6 h. The animals were randomized into three groups of 6 rats each: group I, sacrificed after ischemia; group II, reperfusion for 24 h, and group III, reperfusion for 24 h after receiving monoclonal anti-ICAM-1 antibodies. At the end of the experiment, blood samples were collected for creatinine, lactate dehydrogenase, creatine phosphokinase, potassium, pH and leukocyte counts. Samples were taken from the muscles of the hind limbs and from the kidneys and lungs for histological analysis and measurement of the neutrophil infiltrate by myeloperoxidase staining. The groups did not differ significantly with regard to the laboratory tests. There were no major histological alterations in the kidneys. An intense neutrophil infiltrate in the lungs, similar in all groups, was detected. Myeloperoxidase determination showed that after reperfusion there was significantly less retention of polymorphonuclear neutrophils in the muscles (352 +/- 70 vs 1451 +/- 235 x 10(2) neutrophils/mg; P<0.01) and in the kidneys (526 +/- 89 vs 852 +/- 73 10(2) neutrophils/mg; P<0.01) of the animals that received anti-ICAM-1 before perfusion compared to the group that did not. The use of anti-ICAM-1 antibodies in this experimental model minimized neutrophil influx, thus reducing the inflammatory process, in the muscles and kidneys after ischemia and reperfusion of the hind limbs.

The role of leukocyte depletion in ex vivo evaluation of pulmonary grafts from (non-)heart-beating donors

If lungs could be retrieved for transplantation after circulatory arrest, the shortage of donors might be significantly alleviated. An important issue in using lungs from these so-called non-heart-beating donors is the development of a technique to assess their quality prior to transplantation without jeopardizing the life of the recipient. In our laboratory we tested the reliability of an ex vivo model for such an evaluation. We used pig lungs from optimal control animals, in casu heart-beating donors. This model enabled us to preserve and evaluate lungs with perfect function up to 24 hours after death. The intermediate assessment is performed in an isolated circuit where the lungs are being ventilated and reperfused via the pulmonary artery (PA) with autologous and haemodiluted blood. Haemodynamic, aerodynamic and oxygenation parameters are measured at 37.5 degrees C and a maximum PA pressure of 20 mmHg. These data were correlated with premortem values. During this ex vivo evaluation, leukocyte depletion plays an important role since neutrophils have been recognized as critical components in the inflammatory cascade, which is responsible for graft dysfunction soon and long after transplantation.

Leukocyte filtration in lung transplantation

Controlled reperfusion of the transplanted lung has been used in nine consecutive patients to decrease manifestations of lung reperfusion injury. An extracorporeal circuit containing a roller pump, heat exchanger and leukodepleting filter is primed with substrate-enhanced reperfusion solution mixed with approximately 2000 ml of the patient's blood. This solution is slowly recirculated to remove leukocytes prior to reperfusion. When the pulmonary anastomoses are completed, the pulmonary artery is cannulated through the untied anastomosis using a catheter containing a pressure lumen for measurement of infusion pressure. An atrial clamp is left in place on the patient's native atrial cuff to decrease the risk of systemic air embolism during the brief period of reperfusion from the extracorporeal reservoir. During reperfusion, the water bath to the heat exchanger is kept at 35 degrees C and the flow rate for reperfusion solution is between 150 and 200 m/min, keeping the pulmonary artery pressure <14 mmHg. Eight of nine patients were ventilated on 40% inspired oxygen within a few hours of operation and 7/9 were extubated on or before postoperative day 1. Six of nine patients are long-term survivors.