Isoforskolin alleviates pulmonary fibrosis in mice by inhibiting inflammatory and fibrotic cytokines

We investigated the therapeutic effect and mechanism of isoforskolin on bleomycin-induced pulmonary fibrosis in mice. The animal welfare and experimental process were in accordance with the Regulations of Animal Ethics Committee of Kunming Medical University. Male Kunming mice were randomly divided into five groups: sham operation group (intratracheal instillation of normal saline), bleomycin group (intratracheal instillation of bleomycin 5 mg·kg^-1) , positive drug control group (intratracheal instillation of bleomycin 5 mg·kg^-1 + intraperitoneal injection of dexamethasone sodium phosphate 2.5 mg·kg^-1), isoforskolin (2.5 and 10 mg·kg^-1) groups (intratracheal instillation of bleomycin 5 mg·kg^-1 + intragastric administration of isoforskolin 2.5 and 10 mg·kg^-1). The method of drug administration was once a day for 28 days. On the 7^th and 28^th day of the experiment, the mice were killed, and the lung tissue and bronchoalveolar lavage fluid samples were collected. Hematoxylin eosin (H&E) staining and Masson staining were used to detect the pathological changes of lung tissue. The content of hydroxyproline in lung tissue was detected by alkaline hydrolysis method. The levels of tumor necrosis factor α (TNF-α) and interleukin 1β (IL-1β) in bronchoalveolar lavage fluid (BALF) were detected by enzyme linked immunosorbent assay (ELISA). The expressions of transforming growth factor β1 (TGF-β1) and connective tissue growth factor (CTGF) in lung tissue were detected by Western blot. The experimental results showed that compared with the bleomycin group, the degree of inflammation and fibrosis in the lung tissue of mice in 10 mg·kg^-1 isoforskolin group was significantly reduced, the content of hydroxyproline in the lung tissue was decreased, the levels of TNF-α and IL-1β in BALF were decreased, and the protein expressions of TGF-β1 and CTGF in the lung tissue were downregulated, the differences were statistically significant (P < 0.05). The results suggest that isoforskolin can inhibit the release of inflammatory cytokines TNF-α and IL-1β, downregulate the protein expression of profibrotic factors TGF-β1 and CTGF, and exert anti pulmonary fibrosis effect through both anti-inflammatory and anti fibrotic effect.