Production of an anti-allergic triterpene bryonolic acid, by plant cell cultures.
Cell suspension cultures of Luffa cylindrica, Citrullus lanatus, and related cucurbitaceous plants accumulate large quantities of bryonolic acid (3 beta-hydroxy-D:C-friedoolean-8-en-29-oic acid) [1], an acidic, pentacyclic triterpene found exclusively in the roots of the intact plants. This compound could readily be isolated from cultured cells with CHCl3 and purified simply by recrystallization. Pharmacological tests using mice demonstrated that bryonolic acid or its derivative is active against at least three types of allergies and that its activity could be increased significantly by preparing synthetic derivatives, in particular a potassium salt of its succinate ester. The biosynthesis of bryonolic acid from mevalonic acid via isomultiflorenol has been elucidated by tracer and enzymological experiments using cultured cells of watermelon both in vitro and in vivo. Furthermore, cell fractionation and electron microscopic studies on subcellular structures of luffa cells suggested that minute vesicles originating from elongated, rough endoplasmic reticulum probably play an important role in the transport of bryonolic acid which largely accumulates in the cell wall of cultured cells. The results obtained from the present study indicate that plant cell culture would be useful not only as a biological system for elucidating biosynthetic mechanisms but also as a potential source of new pharmacologically active compounds.