Mechanism of total flavonoid extract from Dracocephalum moldavica on bleomycin-induced pulmonary fibrosis in mice based on pyroptosis pathway

Abstract

This study investigated the mechanism of total flavonoid extract from Dracocephalum moldavica(TFDM) in mice with bleomycin(BLM)-induced pulmonary fibrosis(PF) and explored its mechanism against the pyroptosis pathway. A mouse model of PF was established by intratracheal infusion of bleomycin(4 mg·kg~(-1)), and the normal group was treated with the same dose of saline under the same conditions. After the second day of modeling, the distilled water was given to the normal and model groups by gavage, and the corresponding drug were given to the TFDM and the dexamethasone groups for 28 consecutive days. After 28 days, lung tissues of mice with PF were taken to determine the content of hydroxyproline(HYP). The degree of lung inflammation and fibrosis was observed by hematoxylin-eosin(HE) and Masson stainings, and the content of interleukin-18(IL-18) and interleukin-1β(IL-1β) in the serum of mice with PF were measured by enzyme-linked immunosorbent assay(ELISA). Western blot was used to determine the expression levels of proteins in the lung tissues of mice with PF. HE staining showed that the BLM group had abnormal lung tissue structures and showed more inflammatory cell infiltration. Masson staining showed plenty of collagenous fibrotic tissues that were stained blue in the lung tissues. As compared with the normal group, the content of HYP and levels of IL-18 and IL-1β in the serum of rats in the BLM group were up-regulated(P<0.01). The protein expressions of type Ⅰ collagen(Col-1), fibronectin 1(FN1), α-smooth muscle actin(α-SMA), cysteinyl aspartate specific proteinase-1(caspase-1), gasdermin D(GSDMD), NOD-like receptor thermal protein domain associated protein 3(NLRP3), p62, and apoptosis-associated speck-like protein containing a CARD(ASC) in the lung tissues of mice with PF in the BLM group were increased(P<0.01), whereas the protein expressions of autophagy-related 5(ATG5) and Beclin1 were decreased(P<0.01). Compared with the BLM group, the TFDM groups and dexamethasone group showed normal lung tissue structures and reduced inflammatory cell infiltration. Less collagenous fibrous tissues in blue color were seen and the fibrosis in the lung tissue was alleviated in the TFDM groups and dexamethasone group, with the down-regulation of the content of HYP and the levels of IL-18 and IL-1β(P<0.05, P<0.01). In the TFDM groups and dexamethasone group, the protein expression levels of Col-1, FN1, α-SMA, caspase-1, GSDMD, NLRP3, p62, and ASC were decreased(P<0.01), and the protein expressions of ATG5 and Beclin1 were increased(P<0.01) in the lung tissues of mice with PF. From the above results, it is known that TFDM down-regulates the levels of inflammatory factors and related proteins, and effectively mitigates the process of BLM-induced PF by regulating the pyroptosis pathways and potentially affecting the autophagy.