The Endothelin Axis and Gelatinase Activity in Alveolar Macrophages After Brain-stem Death Injury: A Pilot Study

Background

Endothelin-1 (ET-1) is a potent vasoconstricting mitogen that has been implicated in the development of primary graft dysfunction. Increased activity of matrix metalloproteinases (MMPs), specifically MMP-2 and -9, has been associated with tissue damage in acute lung injury and after lung transplantation. Using a validated model of brain-stem death (BSD), we aimed to determine whether alveolar macrophage up-regulation in the pulmonary system is an early feature of BSD injury and if expression levels of ET-1, endothelin A receptors (ET_AR) and endothelin B receptors (ET_BR), as well as MMP-2 and -9, are increased in comparison to sham controls.

Methods

Six control and 8 experimental Wistar–Kyoto rats had a balloon catheter inserted into their subdural space. In the experimental group the balloon was inflated for 4 hours. Lung specimens were immunohistochemically labeled with CD68, ET-1, ET_AR, ET_BR, MMP-2 and MMP-9, and 10 fields per slide were assessed.

Results

The ratio of alveolar macrophages to polymorphonuclear neutrophils was significantly greater in the BSD group than in controls (9 ± 4.1 vs 3 ± 0.5, p = 0.004) and adventitial macrophages increased in BSD lung parenchyma (p < 0.0001). ET-1, ET_AR and ET_BR levels were elevated in the experimental group (27.6 ± 5.7 vs 7 ± 2.3, 36.1 ± 4.6 vs 17.7 ± 2.6 and 60 ± 7.1 vs 19.8 ± 3.7, p < 0.0001 inclusive). BSD expression of MMP-2 and MMP-9 was double that of controls (14.9 ± 3.4 vs 30.7 ± 3.4 and 14.2 ± 2.2 vs 37 ± 3.6, respectively, p < 0.0001 inclusive).

Conclusions

Alveolar macrophages are rapidly recruited after BSD and may affect peri-operative lung function via increased expression of ET-1, ET_AR, ET_BR, MMP-2 and MMP-9.