The Protective Effect Of Losartan On Paraquat-induced Pulmonary Fibrosis And Its Mechanism In Rats

Objective:To explore the protection effects of losartan on paraquat-induced acute lung damage and pulmonary fibrosis and its mechanism.Methods:Adult male Sprague-Dawley rats (n=32,180-220g) were randomly assigned to four groups including control group, PQ group, Losartan 7d group and Losartan 14d group. Animals in control group were treated with sterile saline for 15 consecutive days, and animals in PQ group were intoxicated with a single dose of PQ (40 mg/kg i.g.) followed by daily ig of sterile saline on the following day for 14 consecutive days, but animals in Losartan 7d and 14d groups were given dairy ig of losartan (10mg/kg i.g.) in the consecutive 7d and 14d days after a single dose of PQ (40 mg/kg i.g.). All rats were sacrificed on the 16th day after PQ intoxication, and lung tissue samples were immediately harvested. (1) The HE staining was used to examine the extent of lung injury. (2) The Masson trichrome staining was used to examine the extent of pulmonary fibrosis. (3) Alkaline hydrolysis method was used to detect hydroxyproline content in lung tissues. (4) Western blot technique was used to detect the relative expression of collagen type I and Ⅲ. (5) The activities of catalase (CAT), superoxide dismutase (SOD) and total antioxidant capacity (T-AOC) and the content of lipid peroxide (LPO) were detected by spectrophotometry. (6) Real-time quantitive PCR was used to detect the levels of NF-κB, TGF-β1, Mmp9 and TIMP-1 mRNA in lung tissues.Results:(1) The HE staining showed that acute lung injury appeared and there was a large amount of inflammatory cell infiltration in lung tissues in PQ group, but which were reversed by losartan treatment. (2) Masson’s trichrome staining showed that significant pulmonary fibrosis appeared in PQ group and there was a large amount of collagen deposition in alveolar septa, but losartan could significantly attenuate the extent of pulmonary fibrosis. (3) Compared to control group, the content of hydroxyproline increased significantly in PQ group (P<0.05). Compared to PQ group, the content of hydroxyproline in losartan 7d group decreased slightly and reduced significantly in losartan 14d group (P<0.05). (4) Compared to control group, the levels of collagen type I and Ⅲ increased significantly in PQ group (P<0.05). Compared to PQ group, the levels of collagen type I and Ⅲ decreased significantly in losartan 7d and 14d groups (P<0.05), and which nearly returned to normal levels in losartan 7d and 14d groups. (5) Compared with control group, the levels of SOD, CAT and T-AOC decreased while the content of LPO increased significantly in PQ group (P<0.05). Compared with PQ group, the levels of SOD, CAT and T-AOC increased and the content of LPO decreased in losartan 7d and 14d groups (P<0.05), and the levels of T-AOC and LPO in losartan 7d and 14 d groups and the activities of SOD and CAT in losartan 14d group nearly returned to normal levels. (6) Compared with control group, the levels of NF-κB, TGF-(β1, Mmp9 and TIMP-1 mRNA increased significantly in PQ group (P<0.05). Compared to PQ group, the levels of NF-κB, TGF-01, Mmp9 and TIMP-1 mRNA expression decreased significantly in Losartan 7d and 14d groups (P<0.05), and which nearly returned to normal levels in Losartan 7d and 14d groups.Conclusions:Acute pulmonary injury and fibrosis appeared after PQ intoxication, and which was reversed by losartan treatment. The possible intervention mechanism may be that losartan could improve the antioxidant capacity and down-regulate the mRNA levels of NF-κB and TGF-β1.