Bleomycin does not directly cause fibrosis in precision-cut lung slices, PCLS

Background: Precision-cut lung slices (PCLS) is a slice of the lung cultured ex vivo that facilitates the evaluation of various chemical agents on the lung. The anti-tumor drug bleomycin causes drug-induced interstitial pneumonia, but the mechanism is not clear. Aims: To determine whether bleomycin induces fibrosis in PCLS. Methods: We generated induced-usual interstitial pneumonia (iUIP) mouse model. PCLS from iUIP mice were cultured ex vivo with or without bleomycin. 1) Bleomycin-treated PCLS were examined to assess cell viability and cytotoxicity. For histopathological analysis, immunohistochemical staining for Ki-67 and γH2AX, and Tunel assay were performed. 2) IL-6 expression in PCLS and IL-6 production in the supernatants were measured as inflammatory markers. 3) Col1a1 was also measured as a fibrosis marker. Results: 1) Bleomycin treatment decreased cell viability only in iUIP-lung-derived PCLS, but not in controls. An increase in TUNEL-assay positive cells was also observed. In addition, the number of γH2AX positive cells decreased. 2) Bleomycin can induce IL-6 expression, but not increase IL-6 in the supernatant. 3) Bleomycin fails to increase Col1a1 even in PCLS derived from iUIP-lung. Conclusions: We conclude that bleomycin cannot directly cause pulmonary fibrosis, but is dominant in cytotoxicity in the lung due to its high sensitivity to DNA damage. Taken together with data from various in vivo studies to date, it is possible that secondary effects, such as bleomycin-mediated cell death, are causing fibrosis.