Expression of heme oxygenase-1 in lung tissue of paraquat poisoned mice and its significance

Abstract

To investigate the expression of heme oxygenase-1 (HO-1) in lung tissue of mice with acute paraquat poisoning, and discuss its pathological mechanism. Fifty-eight healthy male mice were randomly divided into control group (n = 8) and poisoned group (n = 50). The mice in poisoned group were lavaged with 20% paraquat (50 mg/kg), and those in control group with equal amount of normal saline. The mice were sacrificed on the day of experiment in control group, and those in poisoned group at 6 hours and 1, 3, 7, 14 days after poisoning. The lung tissue was harvested to observe the changes in pathology of lung with hematoxylin and eosin (HE) staining. The positive expression of HO-1 was determined with immunohistochemistry, and the protein expression of HO-1 was determined with Western Blot. The contents of superoxide dismutase (SOD) and malonaldehyde (MDA) were determined. The mice showed shortness of breath and signs of exhaustion 1 hour after poisoning, getting worse on 3-5 days, but returned to normal 14 days after poisoning. Under the light microscope, it showed that the control group had no significant pathological changes in lung tissue. One day after the ingestion, pulmonary alveolar structure disorder, obvious hemorrhage, edema and infiltration of inflammatory cells were found. At 3 days, the pathological changes in the lung tissue were more pronounced. They were less pronounced on 7 days, and inflammatory changes disappeared on 14th day, but alveolar structure disorder remained. Immunohistochemical test showed that HO-1 was seldom expressed in the lung tissue, and a little amount was expressed in the mucosal epithelial cells of the airway in control group. It was shown that inflammatory cell and endothelial were mainly distributed in the mucosal epithelial cells of airway 1 day after poisoning followed by a gradually decrease tendence, and came to normal level of control group 7 days after poisoning. It was shown by Western Blot that HO-1 (gray value) in lung tissue increased 6 hours after poisoning (2.438 ± 0.467 vs. 0.475 ± 0.167, P < 0.01), peaked at 1 day (9.200 ± 0.940 vs. 0.475 ± 0.167, P < 0.01), continued to increase till 7 days after poisoning, and it lowered to normal level thereafter (0.825 ± 0.260 vs. 0.475 ± 0.167, P > 0.05). The SOD activity (μU/L) in lung tissue was lowered 6 hours after poisoning, and it was significantly lower than that of control group (649.681 ± 13.951 vs. 1 167.051 ± 15.744, P < 0.01), and it continued to decrease up to 14 days after poisoning ( 859.733 ± 121.079 vs. 1 167.051 ± 14.744, P < 0.01). MDA content (μmol/L) in the lung tissue homogenate was elevated 6 hours after poisoning with significant difference compared with that of the control group (4.542 ± 0.266 vs. 3.705 ± 0.176, P < 0.01). It peaked on day 1 (5.956 ± 0.281 vs. 3.705 ± 0.176, P < 0.01), then it declined and reached normal level 3 days after poisoning (4.134 ± 0.168 vs. 3.705 ± 0.176, P > 0.05). HO-1 expression was increased significantly in lung tissue of mice with acute paraquat poisoning, which may be considered as an important protection mechanism against paraquat poisoning.