Prophylactic Surfactant Inhalation Attenuates Warm Ischemic Injury in Rat Lungs from Donation after Cardiac Death Donors

Abstract

Background: To deal with the shortage of donor organs in lung transplantation, donation after cardiac death (DCD) has been introduced worldwide as one of the potential strategies to increase the donor pool. Considering ischemia-reperfusion injury in solid organ transplantation from DCD donors, it is very important to alleviate graft injury during warm ischemia. It was reported that surfactant function deteriorated with increasing warm ischemic time, resulting in graft injury. Therefore, we investigated the effect of surfactant inhalation against warm ischemic injury in rat lungs from DCD donors. In this experiment, only ventilation was initiated after warm ischemia, therefore, warm ischemic injury was assessed from the view of hypoxia-reoxygenation injury. Methods/Materials: Male Lewis rats were used. One hundred and ten minutes after cardiac arrest induced by ventricular fibrillation, the lungs were initiated to ventilate and flushed by Low Potassium Dextran solution. Thereafter, heart and lung block was isolated, and ex vivo lung ventilation (EVLV) was conducted. Rats were randomly allocated to 2 groups, the CTRL and SURF groups (n = 5 each). In the SURF group, surfactant was inhaled for 3 min, while nothing was inhaled in the CTRL group. Just after this inhalation period (total warm ischemic time: 135 min), dynamic compliance and airway resistance were evaluated on time throughout 60 min of ventilation. After 60 min of EVLV, lung tissue levels of ATP, ADP, and AMP were measured by high-performance liquid chromatography: messenger RNA (mRNA) expression of NO synthase (neuronal, inducible, endothelial), caspase-3, Bax, and Bcl-2 were measured by real-time RT-PCR: Hematoxylin-Eosin (H-E) staining, immunohistochemical staining for 8-hydroxy-2′-deoxyguanosine (8-OHdG), and in situ apoptosis detection (TUNEL assay) were examined. Results: During 60 min of ventilation, surfactant inhalation significantly increased dynamic compliance (p < 0.01), and decreased airway resistance (p < 0.001). Surfactant inhalation effectively increased lung tissue levels of ATP (p < 0.05). After 60 min of ventilation, mRNA levels of NO synthase (neuronal, inducible, endothelial) and caspase-3 were significantly lower, and mRNA levels of Bcl-2 were significantly higher in the SURF group than those in the CTRL group. In the histologic examination with H-E staining, both the CTRL and SURF groups showed no differences with relatively normal structure. However, in 8-OHdG stain and in TUNEL assay, there were fewer positive cells in the SURF group than those in the CTRL group. Conclusion: We confirmed that surfactant inhalation in the last phase of warm ischemia mitigated warm ischemic injury in an isolated rat lung ventilation model. Reduction of oxidative stress and inhibition of apoptosis might contribute to the protection of the warm ischemic lungs in our study.