Effect Of Heme Oxygenase - 1 On Lung Injury Induced By Cardiopulmonary Bypass And Its Mechanism

Objects: The aim of this study is to determine the effects of heme oxygenase-1 on lung injury after cardiopulmonary bypass,and to investigate its probable mechanisms. Methods: 144 male Wistar rats were divided into3 groups: group A(control group), group B(cobalt protoporphyrin, Co PP), group C [Co PP and zinc protoporphyrin,(Zn PP)] randomly. A modified rat model of CPB-induced lung injury was established. Normal saline was injected 24 h before modified rat model establishment in group A intraperitoneally,and Co PP(5mg/kg) in Group B,Co PP(5mg/kg)and Zn PP(5mg/kg) in group C respectively. After the modified rat model was established, the lung tissues were taken at different time for the relevant indicators test: before CPB(T0), 0 min after CPB(T1), 2 h after CPB(T2), 6h(T3),12h(T4), and 24h(T5). Lung tissue wet/dry weight(W/D) ratio was detected in the part of the left lung. Partial right lung tissue of rats in each group was fixed by paraformaldehyde as soon as excision, and then it was embedded in paraffin, then used for HE staining observation under the light microscope, and for the test the expression of Bcl-2protein and HO-1 in each group by immunohistochemistry, and for TUNEL test of cell apoptosis. The rest of the lung tissue was placed in liquid nitrogen for detection of lung tissue homogenate bilirubin content, determination of superoxide dismutase(SOD), the activity of malondialdehyde(MDA), myeloperoxidase(MPO), total antioxidant capacity(TAOC), and the determination of TNF-α expression by ELISA method. Results: The HO-1 ptotein expressions in lung tissue in group B were higher than those in group A and group C in any given time interval, and the same as HO-1 activity(P<0.05). There was no significant difference of Bcl-2 expression of rats lung tissue before CPB in each group(P>0.05). The Bcl-2 protein reduced gradually after CPB. The expressions of Bcl-2 protein in group B at all time point after bypass were higher than those in group A and group C, and the difference was statistically significant(P<0.05). The lung tissue apoptosis index(AI) was no significant difference before CPB in each group(P>0.05), and increased gradually after CPB, most obvious at T2 point, and then decreased gradually. AI in group B at any point after bypass were lower than those in group A and group C(P<0.05). There was no significant difference in SOD, MPO,MDA, and TAOC in the lung tissues of each groups(P>0.05) before CPB. The activity of SOD and TAOC decreased gradually after CPB, the activity in group B in any given time interval after CPB were higher than those of group A and group C(P<0.05). MDA content and MPO activity increased gradually after CPB, the activity in group B in any given time interval after bypass were lower than those of group A and group C(P<0.05). TNF-α content in group B at all time point after bypass were lower than those of group A and group C(P<0.05). W/D ratio and pathological section observation of lung tissue showed that the damage of lung tissue aggravated gradually after CPB, and the most serious damage was observed at 2 hours after CPB. In group A and group C, there were significant inflammatory cells exudation, hemorrhage and inflammatory effusion in the alveolar cavity, and interstitial edema and thickening. But the lung tissue injury was significantly reduced after Co PP pretreatment in group B, alveolar interstitial edema and neutrophil infiltration decreased significantly. Conclusion: Co PP can induce a large amount of HO-1 expression in lung tissue, and it is still highly expressed after CPB, so as to reduce the lung injury. The high expression of HO-1 play its protective effect on lung tissue after CPB possiblely through various ways such as anti inflammatory response,anti-oxidative stress, and anti apoptosis and so on.