Pulmonary expression of inducible heme-oxygenase after ischemia/reperfusion of the lower extremities in rats

Background. Expression of inducible heme-oxygenase (HO-1) has been shown to be increased in various inflammatory disorders, which may confer a protective role. The aim of our study was to assess pulmonary expression of HO-1 after ischemia/reperfusion (I/R) of the lower limbs in rats. Materials and methods. We compared three groups of rats (n = 5/group): one Sham group, and two I/R groups (aorta cross-clamped for 2 h followed by 2 h of reperfusion), one of which pre-treated with Zn-protoporphyrin (Zn-PP), a competitive inhibitor of HO (50 mu mol/kg, i.p.). At the end of experiment, lungs were harvested for determination of HO activity and HO-1 expression by Western blot and immunohistochemistry. Lung injury was assessed by bronchoalveolar lavage, histological study, and determination of the lung Evans Blue dye content, an index of microvascular permeability. Results. I/R of the lower limbs was responsible for acute lung injury (ALI), characterized by neutrophilic infiltration (87 +/- 20 X 10(3) neutrophils/mm(3), Sham group versus 191 38 X 103 neutrophils/mm(3), L/R group; P < 0.002) and an increase in lung Evans blue dye content: (74 6 mu g/g, Sham group versus 122 48 mu g/g, I/R group; P < 0.05). Pre-treatment with Zn-PP further increases the Evans Blue content (122 +/- 48 mu g/g, I/R group versus 179 23 mu g/g Zn-PP group P < 0.05) and the neutrophilic infiltration. Pulmonary heme-oxygenase activity, and HO-1 content were increased after I/R. (10.5 +/- 12 pmol bilirubin/mg protein/h, Sham group versus 101.2 +/- 66 pmol bilirubin/mg protein/h, I/R group; P < 0.02). Immuno-histochemistry revealed that the expression of HO-1 was mainly localized to inflammatory cells. Conclusions. ALI following I/R of the lower limbs in rats is associated with an increase of pulmonary expression of HO-1, inhibition of this expression increase the severity of ALI. (c) 2005 Elsevier Inc. All rights reserved.