Soluble complement receptor type 1 inhibited the systemic organ injury caused by acid instillation into a lung

Acid aspiration into one lung causes contralateral lung injury and systemic organ injury; this injury is thought to be mediated by the sequestration of activated neutrophils. Recombinant human soluble complement receptor 1 (sCR1) inhibits both the classical and alternative complement pathways; this study investigated the role of the complement system in unilateral acid lung injury by measuring the effects of administering sCR1 before or immediately after acid instillation.

Anesthetized rats (n = 18 in each group) underwent tracheostomy and insertion of a cannula into the anterior segment of the left lung. Then either 0.1 ml 0.1 N hydrochloric acid (HCl group) or 0.1 ml pH 7.4 phosphate buffered-saline (PBS group) was instilled. Fifteen minutes before (pre-sCR1 group) or 15 min after (post-sCR1 group) the acid was instilled, 10 mg/kg sCR1 was administered intravenously. Four hours after the acid instillation, rats were killed. In an additional 4 rats in each group, blood and bronchoalveolar lavage fluids obtained 1 h after the instillation of either acid or PBS were analyzed for tumor necrosis factor-alpha activity.

The instillation of acid led to an increased wet-to-dry ratio of 5.2 +/- 0.1 in the acid-instilled lungs compared with their contralateral lungs (4.7 +/- 0.06). These values were greater than the values of 4.6 +/- 0.2 and 4.5 +/- 0.03 in the PBS-instilled lungs and their contralateral lungs, respectively (P < 0.05). The administration of sCR1 before or immediately after the instillation of acid did not attenuate the increase in the wet-to-dry ratio of the acid-instilled lungs. However, the small but consistent increase in the wet-to-dry ratio of the contralateral lungs was attenuated by the sCR1 infusions (P < 0.05). The instillation of acid increased the protein concentration in the bronchoalveolar lavage fluids from the injured lungs (1,000 +/- 206 micrograms/ml) compared with the protein concentration measured in the bronchoalveolar lavage fluids from their contralateral lungs (254 +/- 55 micrograms/ml). The administration of sCR1 before or immediately after the instillation of acid did not decrease the protein concentration in the bronchoalveolar lavage fluids from the acid-instilled lungs. The myeloperoxidase activity was increased in the acid-instilled lung, in their contralateral lung, and in the small intestines of the animals. The infusions of sCR1 before or immediately after the administration of acid led to significant decreases in the myeloperoxidase activities measured in the lungs and the intestines of the treated animals. Plasma tumor necrosis factor-alpha activity was only increased (2.7 +/- 1.1 U/ml) in the animals that had received acid instillations. The infusions of sCR1, administered either before or immediately after the acid instillations, significantly decreased the measured tumor necrosis factor-alpha activity in the plasma (0.5 +/- 0.6 and 1.0 +/- 0.7 U/ml, respectively).

The results suggest that the complement system plays an important role in the pathogenesis of the injury of the contralateral lung and of the small intestine after unilateral instillation of acid to the lung. Further investigation is warranted to determine the clinical utility of antiinflammatory agents in acid-induced lung injury.