Calcium channel blocker enhances lung preservation

Lung Transplantation, Pulmonary Endothelial Inflammation, and Ex-Situ Lung Perfusion: A Review

Lung transplantation (LTx) is the gold standard treatment for end-stage lung disease; however, waitlist mortality remains high due to a shortage of suitable donor lungs. Organ quality can be compromised by lung ischemic reperfusion injury (LIRI). LIRI causes pulmonary endothelial inflammation and may lead to primary graft dysfunction (PGD). PGD is a significant cause of morbidity and mortality post-LTx. Research into preservation strategies that decrease the risk of LIRI and PGD is needed, and ex-situ lung perfusion (ESLP) is the foremost technological advancement in this field. This review addresses three major topics in the field of LTx: first, we review the clinical manifestation of LIRI post-LTx; second, we discuss the pathophysiology of LIRI that leads to pulmonary endothelial inflammation and PGD; and third, we present the role of ESLP as a therapeutic vehicle to mitigate this physiologic insult, increase the rates of donor organ utilization, and improve patient outcomes.

Lung Ischaemia-Reperfusion Injury: The Role of Reactive Oxygen Species

Lung ischaemia-reperfusion injury (LIRI) occurs in many lung diseases and during surgical procedures such as lung transplantation. The re-establishment of blood flow and oxygen delivery into the previously ischaemic lung exacerbates the ischaemic injury and leads to increased microvascular permeability and pulmonary vascular resistance as well as to vigorous activation of the immune response. These events initiate the irreversible damage of the lung with subsequent oedema formation that can result in systemic hypoxaemia and multi-organ failure. Alterations in the production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) have been suggested as crucial mediators of such responses during ischaemia-reperfusion in the lung. Among numerous potential sources of ROS/RNS within cells, nicotinamide adenine dinucleotide phosphate (NADPH) oxidases, xanthine oxidases, nitric oxide synthases and mitochondria have been investigated during LIRI. Against this background, we aim to review here the extensive literature about the ROS-mediated cellular signalling during LIRI, as well as the effectiveness of antioxidants as treatment option for LIRI.

Glycine intravenous donor preconditioning is superior to glycine supplementation to low-potassium dextran flush preservation and improves graft function in a large animal lung transplantation model after 24 hours of cold ischemia

OBJECTIVES

The potential role of glycine in combination with standard lung preservation with low-potassium dextran solution in lung ischemia-reperfusion injury has not been investigated in a preclinical porcine transplant model.

METHODS

In a control group (n = 6), donor lungs were flushed with 1 liter of low-potassium dextran solution. In a second group (LPD-glyc, n = 6), low-potassium dextran solution was supplemented with 3.75 g of glycine. In a third group (IV-glyc, n = 6), donor preconditioning was performed by intravenous administration of 3.75 g glycine 1 hour before low-potassium dextran preservation. Grafts were stored in low-potassium dextran at 4 degrees C for 24 hours. Posttransplant graft function was assessed throughout a 7-hour observation period.

RESULTS

In the control group, 2 recipients died of right-sided heart failure caused by severe ischemia-reperfusion injury. All animals of the glycine groups survived the entire observation period. Pulmonary vascular resistance remained significantly (P < .01) lower in both glycine groups when compared with controls. At the end of the observation period pulmonary vascular resistance in the control group was higher (P < .01) compared with the glycine groups (1310 +/- 319 dyn x sec x cm(-5) vs 879 +/- 127 dyn x sec x cm(-5) [LPD-glyc] vs 663 +/- 191 dyn x sec x cm(-5) [IV-glyc]). Changes of lung tissue water content were lower in the IV-glyc group compared with the LPD-control (P < .01) and LPD-glyc lungs (P < .05). Oxygenation (PO2/FiO2) was higher in the IV-glyc group compared with the LPD-glyc and control lungs (445 +/- 110 mm Hg vs 388 +/- 124 mm Hg [P < .01] vs 341 +/- 224 mm Hg [P < .001], respectively).

DISCUSSION

Modification of low-potassium dextran solution with glycine or donor preconditioning ameliorates ischemia-reperfusion injury in lung transplantation. This intriguing approach merits further evaluation with respect to the mechanisms involved and may improve results in clinical lung preservation.

The use of a supercooling refrigerator improves the preservation of organ grafts

Current medical transplantation confronts major problems such as the shortage of donors and geographical restrictions that inhibit efficient utilization of finite donor organs within their storage lives. To overcome these issues, expanding organ preservation time has become a major concern. We investigated whether a strategy which best preserves organ grafts can be achieved by the use of a newly developed refrigerating chamber, which is capable of establishing a supercooled and unfrozen state stably by generating an electrostatic field in its inside. When adult rat organs such as heart, liver, and kidneys were stored in the supercooled conditions, the levels of major biochemical markers leaked from the preserved organs were significantly lower than in the ordinary hypothermic storage. No apparent tissue damages were observed histologically after the supercooled preservation. Our results suggest that the use of this supercooling refrigerator improves organ preservation and may provide an innovative technique for human organ transplantation.

Trends in organ preservation

Organ preservation aims to provide a viable graft with primary function post-transplant. The current basis of preservation for transplantation is static cold storage using specific preservation solutions which minimise cellular swelling and membrane pump activity, thus maintaining cellular ATP levels. The current organ shortage and consequent expansion of donor criteria places even greater reliance on minimising graft injury during preservation. This review focuses on current and future advances in preservation technology. The key areas of advance are additives to preservation solutions, alternatives/adjuncts to preservation solutions including perfluorocarbons. A major area of advance is in the modulation of organs during the storage period. This may be achieved by biochemical additives or genetic manipulation. Machine perfusion technology is improving, and this is discussed together with the recent concept of warm (normothermic) perfusion as an alternative means of preservation. The authors provide an overview over the current methods of organ preservation. Cold storage, effective in the short-term is insufficient for marginal organs, does not allow assessment of viability markers, and provokes ischaemic injury. Potential strategies for minimising ischaemic injury include additives to preservation solutions; the two-layer method with perfluorcarbons and UW solution-at present limited to pancreas preservation; organ modulation; organ preconditioning and genetic modification of organs. In particular, the authors illuminate the potential in a reappraisal of the concept of normothermic perfusion.

Low potassium dextran lung preservation solution reduces reactive oxygen species production

BACKGROUND

Low potassium dextran lung preservation solution has reduced primary graft failure in animal and human studies. Though the mechanism of reducing primary graft failure is unknown, low potassium dextran differs most significantly from solutions such as Euro-Collins (EC) and University of Wisconsin in its potassium concentration. The aim of this study was to investigate the impact that potassium concentration in lung preservation solutions had on pulmonary arterial smooth muscle cell depolarization and production of reactive oxygen species.

METHODS

Using isolated pulmonary artery smooth muscle cells from Sprague-Dawley rats, the patch-clamp technique was used to measure resting cellular membrane potential and whole cell potassium current. Measurements were recorded at base line and after exposure to low potassium dextran, EC, and University of Wisconsin solutions. Pulmonary arteries from rats were isolated from the main pulmonary artery to the fourth segmental branch. Arteries were placed into vials containing low potassium dextran, EC, low potassium EC, Celsior, and University of Wisconsin solutions with reactive oxygen species measured by lucigenin-enhanced chemiluminescence.

RESULTS

Pulmonary artery smooth muscle cell membrane potentials had a significant depolarization when placed in the University of Wisconsin or EC solutions, with changes probably related to inhibition of voltage-gated potassium channels. Low potassium dextran solution did not alter the membrane potential. Production of reactive oxygen species as measured by chemiluminescence was significantly higher when pulmonary arteries were exposed to University of Wisconsin or EC solutions (51,289 +/- 5,615 and 35,702 +/- 4353 counts/0.1 minute, respectively) compared with low potassium dextran, Celsior, and low potassium EC (12,537 +/- 3623, 13,717 +/- 3,844 and 15,187 +/- 3,792 counts/0.1 minute, respectively).

CONCLUSIONS

Preservation solutions with high potassium concentration are clearly able to depolarize the pulmonary artery smooth muscle cells and increase pulmonary artery reactive oxygen species production. Low potassium preservations solutions may limit reactive oxygen species production and thus reduce the incidence of primary graft failure in lung transplantation.

Nitroglycerin alters alveolar type II cell ultrastructure after ischemia and reperfusion

BACKGROUND

Although administration of nitric oxide (NO) has been suggested to reduce pulmonary reimplantation response, concerns remain about cytotoxic side effects.

METHODS

Using light and electron microscopy, we examined the effects of the NO donor nitroglycerin (NTG) (0.1 mg/ml) as a supplement to the preservation solution Celsior on the structural integrity of rat lungs after extracorporeal ischemia (4 hours at 10 degrees C) and reperfusion (50 minutes) (IR). We performed evaluation in comparison with Celsior alone after IR using either standard antegrade perfusion through the pulmonary artery or retrograde perfusion through the left atrium as an alternative way to improve the preservation quality. Untreated, non-ischemic lungs served as controls (n = 5 per group). We recorded respiratory and hemodynamic parameters during reperfusion. Tissue collection using systematic uniform random sampling was representative for the whole organ and allowed stereologic quantification of structures.

RESULTS

After IR, histochemistry revealed no breaks in the alveolo-capillary barrier and we detected no alveolar flooding. Edema formed in the peribronchovascular cuffs, of which the volume fraction was increased (p =.008). Vasoconstriction of the smaller arteries accompanied antegrade flush, which occurred neither after administration of NTG nor after retrograde flush, as shown by immunostaining for alpha-smooth muscle actin. Treatment with NTG was associated with focal disintegration of Type II cells, which displayed edematous swelling of distinct cell compartments and lysis of mitochondria and cells. Nitroglycerin prevented alveolar collapse, which was increased in the other IR groups (p = 0.013). We observed alterations in intra-alveolar surfactant components.

CONCLUSION

These findings indicate pathologic effects of NTG treatment on alveolar epithelial integrity. Therefore, we suggest further critical evaluation of NTG/NO for therapeutic use in lung transplantation.

Current strategies in lung preservation

Current methods of lung preservation allow for effective, expeditious transplantation as a treatment for end-stage pulmonary disease. However, the utilization of hypothermia, hyperkalemia, and pulmonary artery distension as a single rapid flush for perfusion is less than ideal. All these interventions result in increased pulmonary vascular resistance and suboptimal preservation of lung function. The ability to preserve lungs for longer time intervals and with less risk of tissue injury would provide significant advantages. There would be a greater likelihood that rare size or blood types could find matches by enlarging the area of organ distribution. Optimal preservation would also improve the perioperative outcomes in regard to primary graft failure and subsequently reduce the later complication of chronic rejection and graft lung dysfunction. Finally, through a better understanding of the mechanisms of lung injury during preservation and by developing means to limit the injury, it would be possible to utilize organs from donors that at this time would not be considered optimal. This would increase the donor pool without compromising the recipient's outcome.

Inhibition of angiotensin-converting enzyme by captopril: a novel approach to reduce ischemia-reperfusion injury after lung transplantation

OBJECTIVES

Ischemia-reperfusion injury after lung transplantation involves the generation of free radicals. Captopril has been shown to be protective in models of ischemia-reperfusion injury in other organs by acting as a free radical scavenger. The purpose of this study was to assess the protective effects of captopril against ischemia-reperfusion injury and to evaluate the ability of captopril to scavenge free radicals and inhibit neutrophil activation in an experimental model of lung transplantation.

METHODS

A rat single-lung transplant model was used. Donor lungs were flushed and preserved in low-potassium dextran-glucose solution with (n = 5) and without captopril (500 micromol/L; n = 5) for 18 hours at 4 degrees C and then transplanted and reperfused for 2 hours. At the conclusion of the 2-hour reperfusion period, arterial blood gases, blood pressure, and peak airway pressure were measured. Lung tissue biopsy specimens were obtained for assessment of wet/dry weight ratios, histology, and neutrophil sequestration (myeloperoxidase activity). Lipid peroxidation (F(2)-isoprostane assay) was analyzed from plasma samples and tissue lysates.

RESULTS

The addition of captopril to the lung preservation solution significantly improved postreperfusion PO (2) (312 +/- 63.3 mm Hg vs 202 +/- 21.1 mm Hg; P =.006), peak airway pressure (11.4 +/- 1.1 cm H(2)O vs 15.6 +/- 1.5 cm H(2)O; P =.001), and wet/dry weight ratio (4.9 +/- 0.4 vs 15.8 +/- 10.9; P =.008). Blood pressures did not differ significantly between groups. No significant differences were seen in myeloperoxidase activity or F(2)-isoprostane levels.

CONCLUSIONS

The use of captopril in the preservation solution ameliorates ischemia-reperfusion injury in transplanted lungs after an extended cold preservation period. The mechanisms by which captopril is protective remain elusive but do not appear to include inhibition of neutrophil sequestration or lipid peroxidation. This novel approach to ischemia-reperfusion injury may lead to improved lung function after transplantation and provide further insight into the pathogenesis of acute lung injury.

Heart and lung preservation for transplantation

Since the beginning of transplantation the search for optimal means of organ preservation has been ongoing. One of the major causes of death early following heart or lung transplantation is graft failure. Factors that play a role in this problem include recipient and donor issues, but clearly procurement techniques and preservation solutions are important. This article summarizes the history, current clinical practice, and research devoted to heart and lung preservation for transplantation.