Theaflavin-3,3'-digallate attenuates cigarette smoke extract-induced pulmonary emphysema in mice by suppressing necroptosis

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-alpha, IL-1 beta 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-alpha and IL-1 beta 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.