The Effect And Molecular Mechanism Of Propofol On Acute Lung Injury Induced By Normothermic Partial Cardiopulmonary Bypass In Rats

Object: Acute lung injury (ALI) is a common clinical complication after cardiopulmonary bypass (CPB) and remains a significant cause of postoperative morbidity and mortality of patients after cardiac surgery. However, whether CPB itself is directly responsible for postcardiopulmonary bypass lung dysfunction is still controversial. On the other hand, despite the important role of system inflammatory response syndrome (SIRS) in CPB-associated ALI has already been confirmed, the understanding of further exact molecular mechanism behind the complex pathophysiology remains incomplete. A major cause is the lack of a economic, simple and reproducible animal model. The purpose of this experiment was to study whether CPB itself can directly cause ALI by establishing a model of normothermic partial cardiopulmonary bypass in rats. We also sought to observe the effects of propofol and pyrrolidine dithiocarbamate (PDTC) on ALI induced by cadiopulmonary bypass. At last, we evaluated the activity of nuclear factor-kappa B (NF-κB) and the expression of intercellular adhesion molecule-1 (ICAM-1), inducible nitric oxide synthase (iNOS) mRNA in lungs at 60min after CPB in order to further explore the potential molecular mechanism involved in the pathophysiology of CPB-associated ALI and the regulatory effects of propofol and PDTC on the transcriptional level.Methods: Twenty-eight Sprague - Dawley rats were randomly divided into four groups (n=7 each). Rats in groups â… -â…¢ were undergone CPB as experimental groups and group IV undergone shame procedure as control group. Anesthesia were induced and maintained with midazolam and fentanyl in animals in groups â…  , â…¡ and â…£, whereas in group â…¢ with propofol instead of midazolam. In addition, rats in groupâ…¡ were injected intraperitoneally pyrrolidine dithiocarbamate (PDTC)100 mg·kg^-1 30 minbefore the initiation of CPB. After anesthesia induction, the trachea was intubated and positive pressure ventilation with 100% oxygen was initiated. The CPB circuit consisted of a venous blood reservoir, peristaltic pump, a special designed membrane oxygenator and corresponding lines. The apparatus was primed with approximately 20 ml solution. CPB was performed by the right internal jugular vein and femoral artery cannulation respectively. The central venous blood was drained by gravity into a venous reservoir and the oxygenated arterial blood returned to rats through right femoral artery. The perfusion flow rate was 100ml ·kg^-1· min^-1 and continued for 60min. Then the rat was observed for another 60 min after CPB termination. The temperature was maintained at about 37 ℃ during experiment. The rats in group IV underwent the same experimental procedure as the other three groups except not on CPB. Arterial blood gas were analyzed before the initiation of CPB(T1),at the end of CPB(T2) and 60min afterwards (T3). Respiratory index (RI) at T1 and T3 were calculated based on the results of blood gas analysis. The expression of CD11b on neutrophils (PMN) were simultaneously analyzed with flow cytometry. At the end of experiment bronchoalveolar lavage was performed and bronchoalveolar lavage fluid (BALF) was collected for PMN counting and measurement of IL-8 and protein. After that all rats were sacrificed and lungs were harvested. The right upper lung lobe was used for histopathological observation, the right lower lobe was homogenized for measuring the concentration of maleic dialdehyde (MDA). At last, the activity of NF-κB and expression of ICAM-1, iNOS mRNA in left lung tissue were evaluated by using electrophoretic mobility shift assay (EMSA) and RT-PCR methods respectively.Result: The total dose of anesthetics administered was similar in all groups. The results of blood gas analyse demonstrated PaO₂ at 60 min after CPB was slightly decreased as compared to those before CPB, although the difference was not statistically significant. However RI at T3 in group â…  increased significantly as compared to T1 (P<0.01) . As comparison with group â… , the count of PMN, the level of IL-8 in BALF in all other three groups and the content of protein in group â…¡, â…£ decreased markedly, withP<0.05 or 0.01 respectively. Furthermore, the analysis of spearman correlation revealed the increase in the PMN in BALF correlated significantly well with the increase in the level of IL-8, the contents of protein in BALIF and RI or the decrease in PaO₂, all with P< 0.01. The concentration of MDA in lungs in group I was significantly increased more than in the other three groups (P<0.01) . The flow cytometry analysis demonstrated there was an increase tendency in expression of CD11b on PMN in three CPB groups at the termination of CPB compared with those before CPB, and mildly decreased at 60 min after CPB. But the difference was not statistically significant. The histopathological examination of lungs showed PMN significantly accumulated in the lung tissue including interstitial and alveolar space accompanied with markedly exudation in group â… . In contrast, group IV revealed only slightly PMN accumulated in alveolar capillaries without exudation. The histopathological changes in lungs in group â…¡ and â…¢ was between group I and IV. The activity of NF-κB and expression of iNOS mRNA in lungs were almost ignored except for a lower level ICAM-1 mRNA in group â…£. However, the activity of NF-κB and expression of ICAM-1, iNOS mRNA were significantly increased in group â…  than in group â…£ (P< 0.05 or 0.01), and the degree of NF-κB activation and iNOS mRNA expression in group â…¡ were also decreased as compared to those in group â… ( P<0.05). There was no significant difference between group I and group â…¢.Conclusion: Normothermic partial cardiopulmonary bypass in rats could directly induce some degree of ALL Such injury could be the result of PMN accumulation and activation in lungs and increase of oxidative stress. CPB could also induce the increase of NF-κB activation and thus promote the expression of ICAM-1, iNOS mRNA in lungs. These changes may be an important molecular mechanism in the pathogenesis of CPB-associated ALL Propofol and PDTC can attenuate ALI after CPB. The protect effects of propofol and PDTC can be attributed to their inhibition on activation of PMN and anti-oxidative characteristics, but the results of EMSA and RT-PCR suggest the two drugs may exert their anti-inflammatory effects through different molecular mechanism.