Inhibition of IKK- β by epidioxysterols from the flowers of Calotropis gigantea ( Niu jiao gua )

Background Calotropis gigantea (Asclepiadaceae) ( Niu jiao gua ) has been used as a poultice in Chinese medicine for treating inflammatory skin diseases, e.g., neurodermatitis. This study aims to isolate the epidioxysterols from the flowers of C. gigantea , elucidate their structures and evaluate their possible inhibitory effects on the NF- κ B pathway. Methods The two epidioxysterols 9,11-dehydroergosterol peroxide ( 1 ) and ergosterol peroxide ( 2 ) were isolated from the powdered flowers of C. gigantea by ultrasonic-assisted extraction, followed by the purification of the crude extract by column chromatography (i.e., silica gel and MCI-gel CHP 20P open columns). The chemical structures of these compounds were identified through a comparison of their HRMS, 1 H and 13 C NMR data with those in the literature. The in vitro IKK- β inhibitory activities of compounds 1 and 2 (1–100 µM) were evaluated using an IKK α and β Assay/Inhibitor Screening Kit, which is a single-site, semi-quantitative immunoassay. Berberine was used as a positive control. The IKK- β inhibitory activities between compounds 1 and 2 were compared by a two-tailed Student’s t test to summarize the structure activity relationship. Results Compounds 1 and 2 exhibited a dose-dependent inhibitory activity towards IKK- β in a similar manner to that of berberine. The IKK- β inhibitory activities of these two epidioxysterols were significantly stronger ( P = 0.001 for compound 1 and P = 0.028 for compound 2 ) than that of berberine at the concentration of 100 µM. Furthermore, at the same concentration the suppressive effect of compound 1 towards IKK- β was greater than that of compound 2 ( P = 0.041), while their activities at 10 and 50 µM were comparable. The difference in the results at 100 µM therefore suggested that the double bond between C-9 and C-11 in compound 1 could be responsible for its higher inhibitory activity towards IKK- β at this concentration. Conclusions 9,11-dehydroergosterol peroxide ( 1 ) and ergosterol peroxide ( 2 ) were isolated from the flowers of C. gigantea and exhibited in vitro inhibitory activities towards IKK- β .