To discover new pharmacologically active natural products, here, we performed the phytochemical analysis of a Korean medicinal plant. Euonymus alatus (Thunb.) Sieb. is a traditional medicinal plant that has been used as a remedy for various diseases in Asian countries. In particular, the cork cambium on the twigs of E. alatus has been used to treat dysmenorrhea, tumors, diabetes, and wound. Phytochemical analysis of the methanolic extract of E. alatus twigs led to the isolation of a sterol, which was identified as (3β,16α)-3,16-dihydroxypregn-5-en-20-one (1) by 1D and 2D nuclear magnetic resonance (NMR) spectroscopy and high-resolution electrospray ionization mass spectrometry. The stereochemistry of 1 was established with nuclear Overhauser effect spectroscopy (NOESY) analysis and comparison of electronic circular dichroism (ECD) data. To the best of our knowledge, the isolation of compound 1 from nature is first reported here, as well as the complete and revised NMR data assignment of 1. In lipopolysaccharide (LPS)-stimulated RAW-264.7 macrophages, compound 1 significantly inhibited nitric oxide (NO) production at an IC50 value of 12.54 ± 0.05 μM as well as the protein expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). Moreover, the pre-treatment with compound 1 attenuated the LPS-induced phosphorylation of nuclear factor kappa B (NF-κB) p65 through the inhibition of the phosphorylation of IκB kinase alpha (IKKα), IKKβ, and inhibitor of kappa B alpha (IκBα). Compound 1 also inhibited the LPS-induced phosphorylation of p38, c-Jun NH2-terminal kinase (JNK), and extracellular signal-regulated kinase (ERK). Taken together, compound 1 may serve as an anti-inflammatory constituent of E. alatus twigs and its anti-inflammatory property is thought to be associated with the inhibition of NO production via suppression of iNOS and COX-2 expression through inhibition of IKKα/β, I-κBα and NF-κB p65 activation and downregulation of p38, JNK, and ERK mitogen-activated protein kinase signal pathways in RAW 264.7 macrophages. These findings also provide experimental evidence that compound 1 identified from E. alatus twigs could be a candidate for an anti-inflammatory agent.
Keywords: Euonymus alatus; NF-κB; inducible nitric oxide synthase; nitric oxide; sterol.