Abstract
Pulmonary emphysema is one of the most important pathological manifestations of chronic obstructive pulmonary disease and is commonly associated with cigarette smoking. Previous studies have indicated that necroptosis, a novel non-apoptotic cell death mechanism associated with inflammation and oxidative stress, may contribute to the development of pulmonary emphysema. Theaflavin-3,3'-digallate (TF-3), one of the theaflavins present in black tea, is known to possess several bioactive properties. In the present study, it was demonstrated that TF-3 significantly reduced the generation of reactive oxygen species and the mRNA expression levels of TNF-α, IL-1β and IL-6 in CSE-treated human normal lung epithelial BEAS-2B cells. To further explore the role of TF-3 in necroptosis, the necroptotic rates of BEAS-2B cells were examined via flow cytometry and immunofluorescence assays. The results demonstrated that TF-3 may suppress necroptosis in CSE-treated BEAS-2B cells. Furthermore, it was determined that TF-3 significantly inhibited the CSE-induced phosphorylation of p38 MAPK, receptor-interacting serine/threonine-protein kinase three (RIPK3) and mixed lineage kinase domain-like (MLKL) in BEAS-2B cells. Another experiment demonstrated that a pharmacological inhibitor of the p38 MAPK pathway, SB203580, significantly reduced the protein expression levels of phosphorylated (p)-RIPK3 and phosphorylated (p-)MLKL, which indicated that TF-3 suppressed necroptosis via the p38 MAPK/RIPK3/MLKL signaling pathways. In vivo, it was observed that TF-3 treatment significantly attenuated morphological lung injury in mice with CSE-induced emphysema. Moreover, TF-3 significantly reduced the levels of proinflammatory cytokines, TNF-α and IL-1β and significantly enhanced the antioxidant capacity of the lung tissues in mice with emphysema. TF-3 also significantly inhibited the levels of p-RIPK3 and p-MLKL in the lungs of mice with emphysema. Therefore, the present study indicated that TF-3 may attenuate CSE-induced emphysema in mice by inhibiting necroptosis.