Structural Characterization and Profiles of Saponins from Two Algerian Sea Cucumbers

Sea cucumbers are benthic marine invertebrate members of the phylum Echinodermata. Due to the absence of a rigid skeleton, these species have developed chemical defenses based on the production of saponins (triterpene glycosides). These secondary metabolites are bioactive molecules with a broad biological, ecological, and pharmaceutical spectrum. However, the saponin profiles of several species of sea cucumbers are not known yet. The present study aims to highlight the mixture of saponins in two sea cucumber species from the Algerian coast, namely Holothuria (Holothuria) algeriensis, which has been recently described in central and western Algerian waters, and Holothuria (Roweothuria) arguinensis, originating from the Atlantic Ocean and reported in Algeria for the first time in 2014. Saponin extracts from three individuals of H. (H.) algeriensis and two individuals of H. (R.) arguinensis were analyzed using mass spectrometry, i.e., Matrix-assisted Laser Desorption/Ionization mass spectrometry (MALDI-MS), MALDI-High Resolution MS (MALDI-HRMS), Liquid Chromatography MS (LC-MS) and tandem MS (LC-MS/MS). These analyses allow us to detect 11 and 18 elemental compositions for H. (H.) algeriensis and H. (R.) arguinensis, respectively, each presenting several isomers. In total, 13 new saponin structures are proposed, of which four are common between the two species, six are specific to H. (H.) algeriensis and three to H. (R.) arguinensis. The saponin profiles of the two species were compared to those of other species of the same genus existing on the Algerian coast and the results showed that they share non-sulfated saponins with Holothuria (Panningothuria) forskali and Holothuria (Platyperona) sanctori and sulfated saponins with Holothuria (Holothuria) tubulosa and Holothuria (Roweothuria) poli.