The Protective Effects Of Usnic Acid On Lipopolysaccharide-induced Acute Lung Injury And Bleomycin-induced Pulmonary Fibrosis In Mice

ObjectiveAcute lung injury (ALI) and pulmonary fibros’is (PF) are two closely related lung diseases. Many causes could result in acute lung injury and pulmonary fibrosis. The pathogenesis of ALI/PF are unclear. Usnic is a traditional Chinese medicine, which always be applied to treat many Respiratory diseases, such as Chronic bronchitis and Tuberculosis. Usnic acid (UA) is a dibenzofuran derivative found in several lichen species, which has been shown to possess several activities, including antiviral, antibiotic, antitumoral, antioxidative and anti-inflammatory activities. The aim of our study was to explore the effect and possible mechanism of usnic acid on LPS-induced lung injury and bleomycin-induced pulmonary fibrosis.Methods1. The effect of UA on ALITo evaluate mortality rate, the LPS+UA (25,50 or 100mg/kg body weight, p.o.) and LPS+Dexamethasone (5mg/kg, p.o.) group was given once a day for 5 consecutive days, while the Control and LPS group were given an equal volume of 0.5% Tween-80. One hour after the last administration, all animals were anesthetized by 3% chloral hydrate. And mice from LPS group and LPS+UA groups received intratracheal administration of LPS at 20mg/kg, while mice from the Control group were given an equal volume of phosphate buffered saline (PBS). The survival rate of mice was checked twice every day for 6 days after LPS stimulation.In the other experiments, the UA+LPS and DEX+LPS groups, mice were administrated with UA (25,50 or 100mg/kg, p.o.) or DEX (5mg/kg, p.o.) once a day for 5 consecutive days. Meanwhile mice from the Control and LPS groups were given an equal volume of 0.5% Tween-80 instead of UA and DEX. One hour after the last administration, mice from LPS, LPS+UA and LPS+DEX groups were anesthetized by 3% chloral hydrate before being received intratracheal administration of LPS (20mg/kg,50μl) to cause ALL And mice from the Control group received an equal volume of PBS. The mice were humanely sacrificed 24 hours after LPS stimulation. Lung tissues were collected for the analysis of the W/D ratio, histological study, MPO, SOD, H2O2, GSH and MDA. And the lungs from other mice were lavaged with 1.5mL ice-cold PBS three times, the recovery ratio of the fluid was about 90%. The bronchoalveolar lavage fluid (BALF) was collected for protein concentration analyses and inflammatory cell counts, the analysis of TNF-a, IL-6, IL-8.IL-10 and M1P-2.2. The effect of UA on PFIn the BLM, UA+BLM and PA+BLM groups, mice were administrated with BLM (15 mg/kg, i.p.), while the mice from Control group with normal saline injection instead. From the 2nd day after injection, In the UA+BLM and PA+BLM groups, mice were administrated with UA (25,50 or 100mg/kg, p.o.) or PA (5mg/kg, p.o.) once a day for 21 consecutive days. Meanwhile mice from the Control and BLM groups were given an equal volume of 0.5% Tween-80 instead of UA and PA.1 hour after the last administration, the mice were humanely sacrificed. Lung tissues were collected for the analysis of lung coefficient, histological study, MDA, SOD, HYP, TNF-α, IL-1β、IL-6 and TGF-β1.Results1. The effect of UA on ALIIn our study, the results showed that pretreatment with UA significantly increased survival rate and lung pathological change, attenuated lung vascular permeability and edema, also decreased MPO, MDA and H2O2 activities and increased SOD and GSH levels in the lung tissue. A decreased expression of pro-inflammatory cytokines and chemokines TNF-a, IL-6, IL-8 and MIP-2, and an increased level of anti-inflammatory cytokine IL-10 in the BALF also were found in our study.2. The effect of U A on PFUA significantly improved lung coefficient and lung pathological change, also decreased MDA, HYP, TNF-α, IL-1β, IL-6 and TGF-β1 activities and increased SOD levels in the lung tissue. The protective effects of UA on BLM-induced PF in mice was possibly related to the suppressive effect of excessive inflammatory responses and oxidative stress in lung tissue.ConclusionThese results demonstrated that UA significantly improved inflammatory responses and oxidative damage in lung tissue of mice with LPS-induced ALI. The protective effect of UA on LPS-induced ALI in mice was possibly associated with the suppression of excessive inflammatory responses and oxidative stress in lung tissue. These findings suggested that UA might be a potential therapy for ALI.The results showed that treatment with UA significantly improved lung coefficient and lung pathological change, also decreased HYP and MDA activities and increased SOD levels in the lung tissue. A decreased expression of pro-inflammatory cytokines TNF-a, IL-1β, IL-6 and TGF-β1 in the lung tissue also were found in our study.