Abstract
BackgroundCalotropis 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-κB pathway.MethodsThe 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, 1H and 13C 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.ResultsCompounds 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.Conclusions9,11-dehydroergosterol peroxide (1) and ergosterol peroxide (2) were isolated from the flowers of C. gigantea and exhibited in vitro inhibitory activities towards IKK-β.Electronic supplementary materialThe online version of this article (doi:10.1186/s13020-016-0081-1) contains supplementary material, which is available to authorized users.
Highlights
Calotropis gigantea (Asclepiadaceae) (Niu jiao gua) has been used as a poultice in Chinese medicine for treating inflammatory skin diseases, e.g., neurodermatitis
Isolation and structural elucidation of compounds 1 and 2 The methanolic extract of the air dried flowers of C. gigantea was subjected to a series of normal and reverse phase chromatographic purification process to obtain compounds 1 and 2 (Fig. 1)
High resolution mass spectrometry (HRMS) analysis revealed fragment ions with m/z values of 409.3087, 393.3134 and 375.3031, corresponding to [M−H2O+H]+, [M−H2O2+H]+ and [M−H2O2−H2O+H]+, respectively, which suggested the presence of hydroxyl and peroxy groups in this molecule
Summary
Calotropis gigantea (Asclepiadaceae) (Niu jiao gua) has been used as a poultice in Chinese medicine for treating inflammatory skin diseases, e.g., neurodermatitis. The two epidioxysterols 9,11-dehydroergosterol peroxide (1) and ergosterol peroxide (2), which are shown, are normally found in medicinal mushrooms These compounds have been reported to exhibit a wide variety of pharmacological properties, including antiinflammatory and anticancer activities [13,14,15]. IκBα undergoes phosphorylation by the IκB kinase (IKK) complex, followed by ubiquitination-dependent degradation. This degradation process leads to the nuclear translocation of NF-κB to a specific DNA sequence, which results in the transcription of genes related to immune, inflammatory and tumorigenic responses [16,17,18]. The discovery of new agents capable of inhibiting IKK-β, especially those from natural sources, could be useful for developing novel drugs for the treatment of inflammatory diseases and cancer
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