Tissue-specific distribution of cytotoxic triterpene saponins in three Red Sea sea cucumbers

Sea cucumbers are widely exported from the Middle-East to East Asia being consumed as traditional food. Due to paucity of knowledge concerning biochemical analysis of Red Sea Holothurians, we studied the distribution of triterpene saponins in the external muscular body walls and internal visceral organs of three edible sea cucumbers of the Red Sea using LC-qTOF-MS/MS. Saponins in H. atra and Bohadschia vitiensis were generally localised in the walls whereas they showed higher relative abundance in the viscera of Holothuria impatiens. Cell Counting Kit-8 (CCK-8) and Sulforhodamine B (SRB) assays showed superiority of H. impatiens viscera in reducing the viabilities of all tested cancer cell lines. Bioassay-guided fractionation revealed strong cytotoxicity for the dichloromethane (DCM) fraction of H. impatiens visceral extract. Bioactive molecular networking showed triterpenes to contribute to the cytotoxic activity of the DCM fraction. LC-qTOF-MS/MS analysis and molecular networking of the bioactive fraction showed enrichment of the triterpenes bivittosides C and D. KEGG pathway enrichment analysis showed that bivittosides most probably affect cancer pathways such as PI3K/Akt, interleukins signaling, and receptor tyrosine kinases. Molecular docking showed good binding scores for bivittosides C and D on STAT3, Akt1, and EGFR proteins.