Robustaflavone-4′-dimethyl ether from Selaginella uncinata attenuated lipopolysaccharide-induced acute lung injury via inhibiting FLT3-mediated neutrophil activation

Neutrophils act as both messenger and effector which contributed to the pathogenesis of acute lung injury (ALI). Targeting neutrophils could be a novel strategy for prevention and treatment of ALI. Selaginella uncinata is widely used as an antitussive, antipyretic and anti-inflammatory herb to treat various pulmonary diseases, including lung cancer, asthma, pulmonary fibrosis and pneumonia. However, its effective constituents remain unknown. In the present study, the protective effects of flavonoids from S. uncinata (SUF) and its major compound robustaflavone-4'-dimethyl ether (RDE) against lipopolysaccharide (LPS)-induced ALI were investigated in mice and in neutrophils. The results showed that both SUF and RDE had the same inhibition on LPS-induced lung edema and neutrophil infiltration as well as the increased levels of IL-6, TNF-alpha, P-selectin and ICAM-1 in serum of LPS-challenged mice. Furthermore, RDE significantly inhibited inducible neutrophil activation in a concentration-dependent manner, and also reduced the levels of intracellular calcium as well as the expressions of CCR2. Rescue experiment showed that RDE suppressed FLT3 and its downstream p-p38 and p-AKT, which could be abolished by FLT3 agonist FLT3L but partly by MAPK agonist PDBu or AKT agonist SC79. Therefore, these results indicated that RDE as the main bioactive compound in SUF alleviated LPS-induced acute lung injury and inhibited neutrophil activation via inhibition of FLT3-mediatied AKT and MAPK pathways.