Identification of optimal conditions for lung graft storage with Euro-Collins solution by use of a rat orthotopic lung transplant model

The Advent of Semi-Elective Lung Transplantation-Prolonged Static Cold Storage at 10°C

Since the early days of clinical lung transplantation the preservation of donor organs has become a fairly standardized procedure and most centers do follow similar processes. This includes the use of low-potassium high dextran flush solutions and static cold storage (SCS) in a cooler filled with ice. Depending on the length of SCS, organs usually arrive at the recipient hospital at a temperature of 0°C-4°C. The question of the optimal storage temperature for donor lung preservation has been revisited as data from large animal experiments demonstrated that organs stored at 10°C experience less mitochondrial damage. Thus, prolonged cold ischemic times can be better tolerated at 10°C-even in pre-damaged organs. The clinical applicability of these findings was demonstrated in an international multi-center observational study including three high-volume lung transplant centers. Total clinical preservation times of up to 24 hrs have been successfully achieved in organs stored at 10°C without hampering primary organ function and short-term outcomes. Currently, a randomized-controlled trial (RCT) is recruiting patients with the aim to compare standard SCS on ice with prolonged SCS protocol at 10°C. If, as anticipated, this RCT confirms data from previous studies, lung transplantation could indeed become a semi-elective procedure.

Primary graft dysfunction following lung transplantation: From pathogenesis to future frontiers

Lung transplantation is the treatment of choice for patients with end-stage lung disease. Currently, just under 5000 lung transplants are performed worldwide annually. However, a major scourge leading to 90-d and 1-year mortality remains primary graft dysfunction. It is a spectrum of lung injury ranging from mild to severe depending on the level of hypoxaemia and lung injury post-transplant. This review aims to provide an in-depth analysis of the epidemiology, pathophysiology, risk factors, outcomes, and future frontiers involved in mitigating primary graft dysfunction. The current diagnostic criteria are examined alongside changes from the previous definition. We also highlight the issues surrounding chronic lung allograft dysfunction and identify the novel therapies available for ex-vivo lung perfusion. Although primary graft dysfunction remains a significant contributor to 90-d and 1-year mortality, ongoing research and development abreast with current technological advancements have shed some light on the issue in pursuit of future diagnostic and therapeutic tools.

Protection of donor lung inflation in the setting of cold ischemia against ischemia-reperfusion injury with carbon monoxide, hydrogen, or both in rats

AIMS

Lung ischemia-reperfusion injury (IRI) may be attenuated through carbon monoxide (CO)'s anti-inflammatory effect or hydrogen (H2)'s anti-oxidant effect. In this study, the effects of lung inflation with CO, H2, or both during the cold ischemia phase on graft function were observed.

MATERIALS AND METHODS

Rat donor lungs, inflated with 40% oxygen (control group), 500ppm CO (CO group), 3% H2 (H2 group) or 500ppm CO+3% H2 (COH group), were kept at 4°C for 180min. After transplantation, the recipients' artery blood gas and pressure-volume (P-V) curves were analyzed. The inflammatory response, oxidative stress and apoptosis in the recipients were assessed at 180min after reperfusion.

KEY FINDINGS

Oxygenation in the CO and H2 groups were improved compared with the control group. The CO and H2 groups also exhibited significantly improved P-V curves, reduced lung injury, and decreased inflammatory response, malonaldehyde content, and cell apoptosis in the grafts. Furthermore, the COH group experienced enhanced improvements in oxygenation, P-V curves, inflammatory response, lipid peroxidation, and graft apoptosis compared to the CO and H2 groups.

SIGNIFICANCE

Lung inflation with CO or H2 protected against IRI via anti-inflammatory, anti-oxidant and anti-apoptotic mechanisms in a model of lung transplantation in rats, which was enhanced by combined treatment with CO and H2.

Inflation with carbon monoxide in rat donor lung during cold ischemia phase ameliorates graft injury

Carbon monoxide (CO) attenuates lung ischemia reperfusion injury (IRI) via inhalation, and as an additive dissolved in flush/preservation solution. This study observed the effects of lung inflation with CO on lung graft function in the setting of cold ischemia. Donor lungs were inflated with 40% oxygen + 60% nitrogen (control group) or with 500 ppm CO + 40% oxygen + nitrogen (CO group) during the cold ischemia phase and were kept at 4℃ for 180 min. Recipients were sacrificed by exsanguinations at 180 min after reperfusion. Rats in the sham group had no transplantation and were performed as the recipients. Compared with the sham group, the oxygenation determined by blood gas analysis and the pressure-volume curves of the lung grafts decreased significantly, while the wet weight/dry weight (W/D) ratio, inflammatory reaction, oxidative stress, and cell apoptosis increased markedly (P < 0.05). However, compared to the control group, CO treatment improved the oxygenation (381 ± 58 vs. 308 ± 78 mm Hg) and the pressure-volume curves (15.8 ± 2.4 vs. 11.6 ± 1.7 mL/kg) (P < 0.05). The W/D ratio (4.6 ± 0.6) and the serum levels of interleukin-8 (279 ± 46 pg/mL) and tumor necrosis factor-α (377 ± 59 pg/mL) in the CO group decreased significantly compared to the control group (5.8 ± 0.8, 456 ± 63 pg/mL, and 520 ± 91 pg/mL) (P < 0.05). In addition, CO inflation also significantly decreased malondialdehyde activity and apoptotic cells in grafts, and increased the superoxide dismutase content. Briefly, CO inflation in donor lungs in the setting of cold ischemia attenuated lung IRI and improved the graft function compared with oxygen.

Successful sub-zero non-freezing preservation of rat lungs at -2 degrees C utilizing a new supercooling technology

BACKGROUND

A lower temperature, namely below 0 degrees C, has been thought to be desirable for organ preservation because of the lower rate of metabolism; however, its benefits are still poorly understood. Supercooling is a non-freezing state of liquid below the freezing point, and the new development of a refrigerator for supercooling has now made it possible to preserve organs at sub-zero temperatures in a non-frozen state without cryoprotectants.

METHODS

Rat lungs were ventilated and perfused for 60 minutes in the 3 groups (n = 7 each): (1) the fresh group, in which the lungs were reperfused immediately after harvesting; (2) the 4 degrees C group, in which the lungs were stored after harvesting in ET-Kyoto solution at 4 degrees C for 17 hours before reperfusion; and (3) the supercooling group, in which lungs were preserved in ET-Kyoto solution at -2 degrees C for 17 hours.

RESULTS

Ischemia-reperfusion injury was significantly attenuated in the supercooling group, with a decrease in the pulmonary artery pressure (p < 0.02) and weight gain (p < 0.001), and an increase in the tidal volume (p = 0.001) and arterial oxygen tension (p < 0.001) compared with the 4 degrees C group. In the supercooling group, most of these indicators were equivalent to the fresh lung, with less damage to the endothelial cells of the pulmonary arteries and higher levels of adenosine triphosphate than in the 4 degrees C group.

CONCLUSIONS

Lungs stored using this new supercooling method of lung preservation showed better organ function than conventional storage at 4 degrees C.

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.