The Effects Of Pirfenidone On Silica-induced Inflammation And Pulmonary Fibrosis

Objectives:Silicosis is caused by inhalation of a large amount of silica particles,leading to lung inflammation,pulmonary fibrosis and pulmonary dysfunction.At present,there are no specific therapeutic drugs for silicosis.Pirfenidone is a new drug with anti-fibrosis properties and is used in idiopathic pulmonary fibrosis,but its therapeutic effect in silicosis lacks a comprehensive and effective evaluation.Therefore,this project intended to observe and evaluate the anti-inflammatory and anti-fibrotic effects of pirfenidone on early and fibrotic silicosis mice.However,silicosis currently lacks a recognized animal modeling method and the pathophysiological processes are unclear.Therefore,this study explored the optimal modeling conditions for animals and explored the pathophysiological development of silicosis.Method:Wistar rats and C57BL/6J mice were induced to develop silicosis by tracheal instillation of silica.The rats were given a single dose of silica(50 mg/mouse)and examined at different time points(5 days,10 days,15 days and 30 days),while the mice were given different doses of silica(4 mg/mouse,8 mg/mouse,12 mg/mouse and 16 mg/mouse)and assessed at different time points(3 weeks,6 weeks and 9 weeks).The lung function,right heart function,inflammation and fibrosis were evaluated and then analyzed by unbiased clustering.Based on the results,we chose tracheal instillation of 12 mg/mouse silica to male C57BL/6J mice to establish a drug evaluation model,and administered pirfenidone by daily oral gavage starting on the second day(early model)and 14th day(fibrosis stage model)after silica exposure,administered for 4 weeks continuously.Pulmonary function,right heart function,the degree of inflammation and fibrosis of mice were measured to evaluate the efficacy of pirfenidone.Results:We found that the silica-induced damage to rats was time-dependent,while the exposure dose had a greater impact on silicosis mice than the exposure time.An unbiased cluster analysis of all parameters measured found that rats and mice could be classified into 4 categories,a normal phase,an inflammatory phase,an advanced phase and a fibrotic phase.In the inflammatory phase,lung inflammation was apparent,and mild fibrosis and pulmonary dysfunction has occurred;lung dysfunction was apparent in the advanced stage,while lung inflammation and fibrosis continued to deteriorate;the degree of pulmonary fibrosis and pulmonary dysfunction has deteriorated markedly in the fibrotic stage,but the inflammation did not continue to worsen.It was observed in both the early-stage and the fibrosis stage model that pirfenidone increased lung capacity,improved right heart function,reduced inflammation and fibrosis,delayed the destruction of alveolar structure and collagen deposition and reduced the number of inflammatory cells in the alveolar lavage fluid.In addition,pirfenidone had an inhibitory effect on the expression and secretion of pro-inflammatory cytokines TNF-?,IL-1? and IL-6.After intervening with pirfenidone,the content of hydroxyproline in lung tissue decreased,and the content of collagen-I and its related protein fibronectin decreased significantly.The effects of pirfenidone showed no differences between the low and high dose groups in the fibrotic stage model.Conclusions:Pirfenidone alleviated lung dysfunction and right heart dysfunction in silicosis mice,and delayed the progression of inflammation and fibrosis.High-dose(400 mg/kg)pirfenidone was more effective in fibrotic silicosis.Our research provides a comprehensive characterization of the rodent models of silicosis and supporting evidence for pirfenidone to be developed and tested as a therapeutic drug for silicosis.