Luteolin alleviated neutrophilic asthma by inhibiting IL-36γ secretion-mediated MAPK pathways.

ABSTRACT

CONTEXT Luteolin can affect multiple biological functions, such as anti-inflammatory, antioxidant and immune enhancement processes. Luteolin can inhibit inflammation of T2-high asthma, but its role in neutrophilic asthma has been insufficently studied. OBJECTIVE: This study determines the effect of luteolin on IL-36γ secretion-mediated MAPK pathway signalling in neutrophilic asthma. MATERIALS AND METHODS: The asthma model was established by using ovalbumin/lipopolysaccharide (OVA/LPS). Female 6-8-week-old C57BL/6 mice were divided into control, asthma, luteolin (20 mg/kg) and asthma + luteolin (20 mg/kg) groups. To explore the mechanism of anti-inflammatory effects of luteolin in neutrophilic asthma, Beas-2B cells were treated with luteolin (20 µmol/L), LPS (100 ng/mL), recombinant human IL-36γ protein (rhIL-36γ; 100 ng/mL) or IL-36γ siRNA. RESULTS: IL-36γ secretion and MAPK/IL-1ß signalling were significantly increased in the asthma mouse model compared with the control (p < 0.05). However, the levels of IL-36γ secretion and MAPK/IL-1ß signalling were reduced by luteolin (p < 0.05). In addition, luteolin inhibited IL-36γ and MAPK/IL-1ß levels after LPS (100 ng/mL) stimulation of Beas-2B cells (p < 0.05). We found that in Beas-2B cells, luteolin inhibited activation of the MAPK pathway and IL-1ß secretion following stimulation with rhIL-36γ (100 ng/mL; p < 0.05). Finally, IL-1ß and phosphorylated MAPK levels were found to be lower in the IL-36γ siRNA + LPS (100 ng/mL) group than in the nonspecific control (NC) siRNA + LPS group (p < 0.05). DISCUSSION AND CONCLUSIONS: Luteolin alleviated neutrophilic asthma by inhibiting IL-36γ secretion-mediated MAPK pathways. These findings provided a theoretical basis for the application of luteolin in the treatment of neutrophilic asthma.