Elucidation of molecular diversity and body distribution of saponins in the sea cucumber Holothuria forskali (Echinodermata) by mass spectrometry

Sea cucumbers contain triterpene glycosides called saponins. We investigated the complex saponin mixture extracted from the common Mediterranean species Holothuria forskali. Two different body components were analyzed separately: the body wall (which protects the animal and is moreover the most important organ in terms of surface and weight) and the Cuvierian tubules (a defensive organ that can be expelled on predators in response to an attack). MALDI/MS and MALDI/MS/MS were used to detect saponins and describe their molecular structures. As isomers have been found in the Cuvierian tubules, LC/MS and LC/MS/MS were performed to identify each saponin separately. Twelve saponins have been detected in the body wall and 26 in the Cuvierian tubules. All the saponins from the body wall are also present in the Cuvierian tubules but the latter also contain 14 specific saponins. The presence of isomeric saponins complicated structure elucidation for the whole set but 16 saponins have been described tentatively. Among these, 3 had already been reported in the literature as holothurinosides A and C, and desholothurin A. Molecular structures have been proposed for the 13 others which, in the present work, have been provisionally named holothurinosides E, F, G, H, I, A(1), C(1), E(1), F(1), G(1), H(1) and I(1) and desholothurin A(1). The diversity and organ specificity of the saponins described here are much higher than what had been reported to date in any sea cucumber species.