Background: Hemeoxygenase-1 induction in response to adverse circulatory conditions is protective. Our recent study has shown that administration of sirtinol attenuates hepatic injury in male Sprague-Dawley rats after trauma-hemorrhage; however, the mechanism by which sirtinol produces the salutary effects remains unknown. We hypothesized that sirtinol administration in male Sprague-Dawley rats after trauma-hemorrhage decreases cytokine production and protects against lung injury through a hemeoxygenase-1 related pathway.
Methods: Male Sprague-Dawley rats (n = 8 per group) underwent trauma-hemorrhage (mean arterial blood pressure 40 mm Hg for 90 min, then resuscitation). A single dose of sirtinol (1 mg/kg of body weight) with or without a hemeoxygenase enzyme inhibitor (chromium-mesoporphyrin) or vehicle was administered IV during resuscitation. Twenty-four hours thereafter, myeloperoxidase activity (a marker of neutrophil sequestration) and tumor necrosis factor alpha, interleukin-6, and interleukin-10 levels in the lung, protein concentrations in bronchoalveolar lavage fluid and tissue histology were measured. Lung hemeoxygenase-1 protein level was also determined.
Results: In the sirtinol-treated rats subjected to trauma-hemorrhage, there were significant improvements in lung myeloperoxidase activity (4.68 +/- 0.31 vs 9.36 +/- 1.03 U/mg protein, P < 0.05), tumor necrosis factor alpha levels (710.7 +/- 28 vs 1288 +/- 40.69 pg/mg protein, P < 0.05), interleukin-6 levels (343.6 +/- 18.41 vs 592.7 +/- 22.3 pg/mg protein, P < 0.05), and protein concentrations (303.8 +/- 24.54 vs 569.6 +/- 34.82 microg/mL, P < 0.05) and lesser damage in histology. There was no statistically significant difference in interleukin-10 levels in the lung between sirtinol-treated trauma-hemorrhaged rats and vehicle-treated trauma-hemorrhaged rats (842.5 +/- 54.18 vs 756.2 +/- 41.34 pg/mg protein, respectively). Lung hemeoxygenase-1 protein levels were increased in rats receiving sirtinol treatment as compared with vehicle-treated trauma-hemorrhaged rats (5.18 +/- 0.25 vs 2.70 +/- 0.16, P < 0.05). Administration of the hemeoxygenase inhibitor chromium-mesoporphyrin prevented the sirtinol-induced attenuation of shock-induced lung damage.
Conclusion: The salutary effects of sirtinol administration on attenuation of lung inflammation after trauma-hemorrhage are mediated via upregulation of hemeoxygenase-1 expression.