Saponins enriched in the epidermal layer of Holothuria leucospilota body wall

Saponins are secondary metabolites that provide medicinal benefits in controlling body homeostasis and metabolic functions. Sea cucumber has been consumed in many Asian countries due to their health benefits. Active chemicals found in sea cucumber include natural source of saponins which are enriched in their tissues, including the Cuvierian tubules and the body wall. Tissue origin of the saponin biosynthesis and accumulation is limitedly known. The present study is to indicate major compositions and distributions of saponins in the body wall of Holothuria leucospilota. Structurally, their body wall consisted of the pigmented layer of the epidermis, the dermal connective tissues, and inner muscular layers. Interestingly, release of the pigmented granules from the epidermis was related to detection of epidermal saponins. Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) revealed identical mass spectra in the saponin extracts and compared to the known compounds of holothurians. To investigate the release of epidermal saponins, the epidermis dissolved in either butanol or distilled water were analyzed and presented the saponin masses with two prominent masses of m/z 1,243.3 (holothurin A and scabraside B) and 1,259.3 (holothurin A3). MALDI-IMS also demonstrated strong signals of the known saponins which were only localized in the epidermis of the body wall. Taken together, this study shows that granule release from epidermal pigmented cells is somehow related to the amount of epidermal saponins released to surrounding seawater. Hence, the future research in the sea cucumber better focuses on epidermal cells that are the enriched site of saponins, although several active compounds require further investigation.