New Polyhydroxysteroid Glycosides with Antioxidant Activity from the Far Eastern Sea Star Ceramaster patagonicus

Four new glycosides of polyhydroxysteroids, ceramasterosides A, B, D, and E (1-4), and two previously known compounds, ceramasteroside C₁ (5) and attenuatoside B-I (6), were isolated from an extract of a deep-sea sea star species, the orange cookie star Ceramaster patagonicus. The structures of 1-4 were elucidated by the extensive NMR and ESIMS methods. Steroid monoglycosides 1 and 2 had a common 3β,6α,8,15β,16β-pentahydroxysteroid nucleus and a C-29 oxidized stigmastane side chain and differed from each other only in monosaccharide residues. Ceramasteroside A (1) contained 3-O-methyl-4-O-sulfated β-D-xylopyranose, while ceramasteroside B (2) had 3-O-methyl-4-O-sulfated β-D-glucopyranose, recorded from starfish-derived steroid glycosides for the first time. Their biological activity was studied using a model of lipopolysaccharide-induced (LPS) inflammation in a SIM-A9 murine microglial cell line. During the LPS-induced activation of microglial cells, 1, 3, and 5, at a non-toxic concentration of 1 µM, showed the highest efficiency in reducing the production of intracellular NO, while 4 proved to be most efficient in reducing the extracellular nitrite production. All the test compounds reduced the LPS-induced malondialdehyde (MDA) production. The in vitro experiments have demonstrated, for the first time, the antioxidant activity of the compounds under study.