Isosteroid alkaloids with different chemical structures from Fritillariae cirrhosae bulbus alleviate LPS-induced inflammatory response in RAW 264.7 cells by MAPK signaling pathway

•The anti-flammatory activity and underlying mechanism of imperialine (A), verticinone (B), verticine (C), delavine (D) and peimisine (E) were investigated for the first time.•The five isosteroid alkaloids from Fritillariae Cirrhosae Bulbus all inhibited the production of inflammatory meditators and suppressed the TNF-α and IL-6 mRNA levels on LPS-stimulated RAW 264.7 macrophages.•The phosphorylation of MAPKs signaling pathway was downregulated by the five isosteroid alkaloids.•The important differences of the structure-activity relationships for five isosteroid alkaloids were preliminarily elucidated.