Pulmonary Expression of Inducible Heme-Oxygenase after Ischemia/Reperfusion of the Lower Extremities in Rats

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. 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 μmol/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. I/R of the lower limbs was responsible for acute lung injury (ALI), characterized by neutrophilic infiltration (87 ± 20 × 10 3 neutrophils/mm 3, Sham group versus 191 ± 38 × 10 3 neutrophils/mm 3, I/R group; P < 0.002) and an increase in lung Evans blue dye content: (74 ± 6 μg/g, Sham group versus 122 ± 48 μg/g, I/R group; P < 0.05). Pre-treatment with Zn-PP further increases the Evans Blue content (122 ± 48 μg/g, I/R group versus 179 ± 23 μg/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). Immunohistochemistry revealed that the expression of HO-1 was mainly localized to inflammatory cells. 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.