Protective effect of hemoglobin—induced heme oxygenase—1 on injured lungs caused by limb ischemia—reperfusion in rats

To determine the role of hemoglobin (HB) induced heme oxygenase-1 (HO-1) in injured lungs caused by limb ischemia-reperfusion (I/R) in rats. A rat model of ischemia in the hind limbs was made by clamping the infrarenal aorta with a microvascular clip, and lung injury occurred after reperfusion. To induce the expression of HO-1 in the lungs, Hb was administrated intraperitoneally at 16 hours before reperfusion. Northern blotting and Western blotting were used to detect the expression of HO-1 in the lungs, and the carboxyhemoglobin (COHb) level in arterial blood was assayed. The effect of hemoglobin (Hb) on the injured lungs after limb I/R was determined by measuring the changes of lung histology, polymorphonuclear (PMN) count, malondialdehyde (MDA) content and wet-to-dry weight ratio (W/D). Zinc protoporphyrin (ZnPP), an inhibitor of HO, was used to determine whether HO-1 was induced by Hb after lung injury. Hb led to a significant increase in HO-1 mRNA and protein expression in the lungs, accompanied by the increase of COHb level in arterial blood. Compared with the sham controls, the lung PMN count, MDA content and W/D significantly increased at 4 hours after limb I/R, which reversed by the pretreatment with Hb at 16 hours before reperfusion. ZnPP blocked this protective role of Hb in the injured lungs. Hb can induce the lung HO-1 expression, which plays an important role in the defense against I/R induced lung injury in rats.