Stichopus

Sea cucumbers (Holothuroidea, Echinodermata) appear to be unique in their mode of squalene oxide (37) cyclization. Tritium-labeled lanosterol (33), cycloartenol (32) and parkeol (38) were individually administered to the sea cucumber Holothuria arenicola. While the former two triterpenes were not metabolized [22], parkeol was efficiently transformed into 14x-methyl-5a-cho-lest-9(l l)-en-3/ -ol (39) (Scheme 3). Other A1 sterols present in H. arenicola were not found to be radioactive and were thus assumed to be of dietary origin. The intermediacy of parkeol was confirmed by the feeding of labeled mevalonate (23) and squalene (26) to the sea cucumber Stichopus californicus [15]. Both precursors were transformed into parkeol, but not lanosterol nor cycloartenol, aqd to 4,14a-dimethyl-5a-cholest-9(ll)-en-3/J-ol (40) and 14a-methyl-5a-cholest-9(ll)-en-3/ -ol. Thus, while all other eukaryotes produce either cycloartenol or lanosterol, parkeol is the intermediate between triterpenes and the 14-methyl sterols in sea cucumbers. 

Korotchenko and coworkers detected PGs by TLC and bioassay in three sea cucumbers (Holothuroidea) Stichopus japonicus, Cucumaria fraudatrix, and C. japonica [189]. 

In echinoderms, zinc concentrations are usually higher in detrital feeders than in carnivores, higher in surface feeders than in sediment feeders, and higher in specimens collected inshore than those collected offshore in deeper waters (Eisler 1980). Sea cucumbers, Stichopus tremulus, accumulate radiozinc-65 from seawater by a factor of 1400 however, radiozinc accumulation data should be viewed with caution because addition of stable zinc can reduce zinc-65 accumulations in echinoderm viscera up to tenfold (Eisler 1981). Zinc inhibits the formation of the fertilization membrane in sea urchin eggs, possibly by interfering with cortical granule-derived proteases and proteins (Nakamura et al. 1989). 

Kariya, Y., Watabe, S., Ochial, Y., Murata, K., and Hashimoto, K. (1990). Glycosaminoglycan involved in the cation-induced change of body wall structure of sea cucumber Stichopus japonicus. Connect. Tissue Res. 25,149-159. 

Kariya, Y., Watabe, S., Kyogashima, M., Ishihara, M., and Ishii, T. (1997). Structure of fucose branches in the glycosaminoglycan from the body wall of the sea cucumber Stichopus japonicas. Carbohydr. Res. 297, 273-279. 

Li, J. Z. and Lian, E. C. (1988). Aggregation of human platelets by acidic mucopolysaccharide extracted from Stichopus japonicus Selenka. Thromb. Haemost. 59, 435-439. 

Suzuki, N., Kitazato, K., Takamatsu, J., and Saito, H. (1991). Antithrombotic and anticoagulant activity of depolymerized fragment of the glycosaminoglycan extracted from Stichopus japonicus Selenka. Thromb. Haemost. 65, 369-373. 

Frondoside B (9a), Cucumariosides A2-4 (9b) and A7-3 (9c), Fig. (9) as well as several triterpene glycosides isolated from the sea cucumbers Stichopus chloronotus (lOa-lOh) and Thelenota ananas (lOi, lOj), Fig. (10) contain the simple 3 (5-hydroxyholost-7-ene as the aglycone. An additional acetoxyl group in the side chain is present in compounds 10a-... 

Glycosides lOa-lOj were isolated from Stichopus chloronotus and Thelenota ananas, two sea cucumbers belonging to the order Aspidochirota [37]. 

Fig. (10). Structures of glycosides isolated from the sea cucumbers Stichopus chloronotus and Thelenota ananas...

Ito, S. and Kitamura, H., Induction of larval metamorphosis in the sea cucumber Stichopus japonicus by periphitic diatoms, Hydrobiologia, 358, 281, 1997. 

Some triterpene glycosides from holothurians belonging to the family Stichopodidae show also antitumor activities [67, 60]. Holotoxin Al (33) from Apostichopus (=Stichopus) japonicus inhibited the growth of the solid form of Ehrlich tumor and Sarcoma-37 in mice on 37-65 and 13-53 %, respectively, at doses of 1.25 and 2.50 mg/kg. Triterpene glycosides from Holothuria forskali have cytotoxic activities against tumor cells [68]. 

Most of sea cucumber triterpene glycosides are tetra- or pentaglycosides. The majority of tetrasaccharides show a linear chain with the most common 3-0-Me-Glc-(l—>3)-Glc-(1 4)-Qui-(l—>2)-Xyl structure. The few disaccharides that have been isolated show a Qui-(1 2)-4-0S03Na-Xyl chain attached to C-3 of the triterpenoid aglycone. Some hexasaccharides have been isolated from sea cucumbers of the order Aspidochirota Stichopus japonica, Stichopus chloronotus, Parastichopus californius and Bohadschia bivittata [55]. They are non-sulfated glycosides with a linear 3-0-Me-Glc-(1 3)-Glc-(l- 4)-Xyl chain and a branching of a linear trisaccharide at C-2 of the xylose unit. 

Several holothurins are specific for different taxonomic groups of sea cucumbers and structural characteristics of triterpene glycosides have been used to resolve taxonomic problems in the class Holothuroidea [57, 58]. For example, the triterpenoid glycosides distribution has been successfully applied in the reclassification of Stichopus mollis into the genus Australostichopus [59] and in the taxonomy of sea cucumbers belonging to the genus Cucumaria [60]. 

Several triterpene glycosides isolated from the sea cucumbers Cucumaria frondosa, Cucumaria japonica, Stichopus chloronotus and Thelenota ananas contain the simple 3P-hydroxyholost-7-ene as the aglycone (49) [55]. Recently, three new monosulfated pentaglycosides, frondosides Ai-2 (49a) A2-3 (49b) and A2-4 (49c), Fig. (18) were isolated from the sea cucumber Cucumaria frondosa [61, 62]. 

---