Pulmonary fibrosis(PF)is a progressive,interstitial fibrotic lung disease characterized by persistent scar formation in the lung parenchyma,and a reduced quality of life and poor prognosis for patients.The pathogenesis of PF is unknown and there is a lack of effective therapeutic agents;however,animal models are currently the main tool used to explore the pathogenesis of the disease and to find effective therapeutic agents.PF can be induced by various factors and to different degrees according to known etiologies.Among these,bleomycin-induced models are widely used because of their reproducibility and the similarity between the fibrosis pathology and clinical conditions.The main induction method include intratracheal drip,intratracheal nebulization,tail vein injection,intraperitoneal injection,and transnasal inhalation,and these can be classified into single and multiple doses,according to the frequency of induction.Based on the relevant literature,the current review summarizes the characteristics of the bleomycin-induced PF model using different induction frequencies and method,to provide a basis for the application of this model.

Objective A rat model of pulmonary fibrosis was constructed using a single or two intratracheal drops of bleomycin(BLM)and the modeling rate and stability of the two modeling modalities were compared.Methods A total of 150 specific pathogen-free SD rats were divided randomly into blank control(control),single intratracheal drop of bleomycin(BLM-S),and two intratracheal drops of bleomycin(BLM-M)groups.Rats in the BLM-S group received a single dose of 3 mg/kg BLM by noninvasive intratracheal instillation,and rats in BLM-M group received 3 mg/kg BLM on day 1 and BLM 2 mg/kg on day 14.Rats in the control group were given intratracheal instillation of 0.9％sodium chloride(1 mL/kg).The rats were euthanized on days 28,42,56,and 84 after modelling,respectively.Deep inspiratory capacity(IC),vital capacity(VC),static lung compliance(Cchord),and dynamic lung complication(Cdyn)were measured in all rats.Pathological changes in lung tissue were observed,and the extent of alveolitis and fibrosis was graded.Collagen-Ⅲ(COL-Ⅲ)expression in rat lung tissue was detected by immunohistochemistry.Results(1)The survival rates in the control,BLM-S,and BLM-M groups were 100％,80％,and 66％,respectively.Rats in the BLM-S and BLM-M groups had significantly lower body weights on days 14～42 compared with the control group(P＜0.05,P＜0.01),and rats in the BLM-M group had significantly lower body weight on days 28～42 than rats in the control and BLM-S groups(P＜0.05,P＜0.01).(2)Regarding lung function,IC,VC,Cchord,and Cdyn were all markedly decreased in the BLM-S group compared with the control group(P＜0.05,P＜0.01)and IC,VC,and Cchord were significantly decreased in the BLM-M group(P＜0.05,P＜0.01)on day 28.IC,VC,and Cchord were significantly decreased in rats in the BLM-S group on day 42(P＜0.05,P＜0.01),and were also significantly decreased in rats in the BLM-M group on days 42～84(P＜0.05,P＜0.01).(3)In terms of lung pathology,inflammatory infiltration and fibrous cords appeared in the BLM-S group from days 28～84 and then gradually decreased(P＜0.05,P＜0.01),while fibrosis and alveolitis were relatively stable in the BLM-M group(P＜0.05,P＜0.01).(4)COL-Ⅲ expression levels in lung tissue were significantly higher in rats in the BLM-S and BLM-M groups compared with the control group(P＜0.05,P＜0.01),and the COL-Ⅲ content in the BLM-S group was significantly lower at 42～84 days than at 28 days(P＜0.05).Conclusions Both method are capable of effectively creating pulmonary fibrosis models.The single-dose approach is straightforward,has a lower death rate,and the degree of fibrosis is clearly visible by day 28,but progressively recovers after 42 days.In contrast,the two-dose instillation model has a greater success rate and better stability,with over half the rats still exhibiting visible fibrosis on day 84.

Objective To compare the success rate and stability of rat pulmonary fibrosis(PF)models induced by intratracheal instillation of different doses of bleomycin(BLM).Methods One hundred and fifty Sprague Dawley rats were divided randomly into control,low-dose BLM 3 mg/kg(BL-L),and high-dose BLM 5 mg/kg(BL-H)groups.General status,mortality,and weight changes were observed,and the lung inspiratory capacity(IC),vital capacity(VC),chord compliance(Cchord),and dynamic compliance(Cdyn)were detected on days 28,42,56,and 84.Lung coefficients were recorded and pathological changes in lung tissue were observed by hematoxylin and eosin and Masson staining.The lung hydroxyproline(HYP)content was detected and collagen type Ⅲ(COL Ⅲ)was detected by immunohistochemistry.Results The mortality rates in the BL-L and BL-H groups were 20％and 28％,respectively.Body weight was significantly lower in the BL-L group compared with the control group on days 0～56,and weight recovery after day 56.Body weight was significantly lower in the BL-H group compared with the control and BL-L groups from days 0～56(P＜0.01).Regarding lung function,IC,VC,Cchord,and Cdyn were significantly lower in the BL-L group compared with the control group on day 28(P＜0.01,P＜0.05),and IC and Cdyn were significantly lower in the BL-H group(P＜0.01).IC,VC,and Cchord were significantly decreased in the BL-L group on day 42(P＜0.01,P＜0.05),while IC,VC,Cchord,and Cdyn were significantly decreased in the BL-H group(P＜0.01,P＜0.05),and IC,VC,and Cchord were significantly lower compared with in the BL-L group(P＜0.01).Cchord was significantly lower in the BL-H group compared with the control and BL-L groups on day 56(P＜0.01).The lung coefficients on day 28 were significantly higher in the BL-L and BL-H groups compared with the control group(P＜0.01),and were significantly higher in the BL-H group from days 42～56 compared with the BL-L and control groups(P＜0.01).Regarding lung histopathology and immunohistochemistry,inflammatory infiltration,fibrotic streaks,and COL Ⅲ expression were observed in the BL-L group from days 28～56,and almost complete disappearance of the fibrotic lesions on day 84.In contrast,fibrotic lesions could be observed from days 28～84 in the BL-H group,with significantly elevated COL Ⅲ expression compared with the control group(P＜0.01).The HYP content was significantly higher in the BL-L group compared with the control group from days 28～42(P＜0.05,P＜0.01),and then gradually decreased,and the HYP content was significantly higher in the BL-H group than in the control group from days 28～84(P＜0.01).Conclusions Both 3 and 5 mg/kg BLM can successfully induce PF rat models.Rats treated with 3 mg/kg BLM developed fibrosis on day 28,which lasted until day 42 and then gradually recovered.Rats treated with 5 mg/kg BLM developed fibrosis on day 28,and the degree of fibrosis was more severe with the higher compared with the lower dose,with stable fibrotic lesions up to day 56 and moderate-to-severe fibrosis still present in half of the rats until day 84.