Effects of activated protein C on coagulation and fibrinolysis in rabbits with endotoxin induced acute lung injury

Background Sepsis induced acute lung injury （ALI） as a common syndrome in clinical practice has a high mortality. Recombinant human activated protein C （APC） can significantly reduce the mortality of patients with severe sepsis. Several studies have implicated that APC may be protective in ALI. Methods Twenty-one rabbits were operatively prepared and randomly divided into sham, control, or APC groups （n=7 in each group）. After a tracheotomy had been performed, ALI was produced in the control and APC groups by infusion of Escherichia coil endotoxin 100 μg/kg per hour intravenously for 1 hour. The sham group received only the vehicle, infusion of 20 ml of 0.9% saline. The rabbits were studied under anesthesia for 6 hours and were ventilated with 40% oxygen. Bovine APC （25 μg·kg^-1·h^-1） was intravenously administered. The infusion was initiated half an hour post-injury and lasted for 4 hours. The animals were resuscitated with Ringer＇s lactate solution. Results In comparison with nontreatment in the control group, the infusion of APC significantly reduced the increase of thrombomodulin level （TM; control group was （0.68±0.06） ng/ml, vs APC group of （0.62±0.07） ng/ml at 6 hours, P 〈0.05）, and significantly attenuated the fall in protein S （PS; control group was （2.32±0.03） μg/ml at 2 hours, （2.24±0.06） μg/ml at 4 hours and （2.21±0.09）μg/ml at 6 hours, vs APC group （2.46±0.04） μg/ml at 2 hours, （2.40±0.05） μg/ml at 4 hours and （2.39±0.07） μg/ml at 6 hours, P 〈0.01）. In addition, APC limited the increase in plasminogen activator inhibitor-1 （PAI-1） both in plasma （control group was （0.68±0.12） ng/ml at 1 hour, （0.84±0.06） ng/ml at 2 hours, （0.87±0.08） ng/ml at 4 hours and （0.91±0.05） ng/ml at 6 hours, vs APC group （0.42±0.16） ng/ml at 1 hour, （0.43±0.04） ng/ml at 2 hours, （0.45±0.09） ng/ml at 4 hours and （0.45±0.14） ng/ml at 6 hours, P 〈0.01） and in bronchoalveolar lavage fluid （at 6 hours： sham, （1.05±0.05） ng/ml; control, （1.13±0.06） ng/ml; APC, （1.06±0.06） ng/ml; P 〈0.05）. However, APC failed to prevent the decrease in PaO2/FiO2 ratio. APC-treated rabbits showed no significant difference in platelet count and antithrombin but exhibited less D-dimer production than did the controls. Moreover, APC limited the histopathological score of lung injury （2.6±0.8 in control, vs 1.4±0.6 in APC group, P〈0.01）. Conclusion Anti-coagulation and pro-fibrinolysis activity may be two of the possible mechanisms by which activated protein C attenuated endotoxin-induced ALI.