Recombinant human activated protein C reduces cardiac 3-nitrotyrosine and malondialdehyde levels in ovine acute respiratory distress syndrome and septic shock

Introduction

We have recently shown that recombinant human activated protein C (rhAPC) improved pulmonary function [1] and cardiac performance [2] in ovine acute respiratory distress syndrome and sepsis. Peroxynitrite (ONOO^-) is known to inactivate adrenoreceptors in sepsis. It can be detected with equal amounts of 3-nitrotyrosine (3-NT). rhAPC has been effective to reduce lung 3-NT levels in sepsis [1]. We therefore hypothesized that rhAPC might reduce cardiac 3-NT levels as well, and studied cellular enzymes involved with the ONOO^- pathway in cardiac tissue.

Methods

Fifteen sheep (33 to 38 kg) were operatively prepared for chronic study and randomly allocated to either the sham (uninjured, untreated), control (injured) or treatment (rhAPC) groups (n = 5 each). After a tracheotomy, acute lung injury was produced in the control and rhAPC groups by insufflation of cotton smoke, followed by instillation of Pseudomonas aeruginosa bacteria into the lungs according to an established protocol [1]. The sheep were studied for 24 hours in the awake state and ventilated with FiO₂ 1.0. In the treatment group, rhAPC (24 μg/kg/hour) was intravenously administered, beginning 1 hour post injury. Heart tissue 3-NT, myeloperoxidase (MPO), and malondialdehyde (MDA) contents were measured (ELISA) after 24 hours. Data presented as the mean ± SEM; *significance, P < 0.05.

Results

After 24 hours, 3-NT levels (nM/ml/mg) were 19 ± 3 in sham and were significantly increased in the control group (101 ± 11*). The rhAPC group (22 ± 18*) showed significantly lower 3-NT tissue levels then controls. MDA levels (μM/ml/mg) were 48 ± 5 in sham and were significantly increased in the control group (85 ± 3*). The rhAPC group (41 ± 3*) showed significantly lower MDA tissue levels then controls. The MPO activity (mU/mg) showed no differences between groups: sham (180 ± 11), control (200 ± 15), and rhAPC (210 ± 20), respectively.

Conclusion

rhAPC has no influence on cardiac MPO levels, but significantly reduced heart tissue 3-NT and MDA levels in ovine acute respiratory distress syndrome and septic shock, thereby improving cardiac performance. These findings may lead to further investigations of rhAPC and cardiovascular function.