A steryl glycoside fraction from Momordica charantia seeds with an inhibitory action on lipid metabolism in vitro.

A saponin fraction was isolated from Momordica charantia seeds by delipidation, saline extraction, ammonium sulfate precipitation, and extraction of the resulting supernatant with n-butanol. Thin-layer chromatography, in the upper phase of the n-butanol--ethyl acetate--water (4:1:5, by volume) system on plastic sheets coated with silica gel 60 F254, revealed the presence of a single spot after spraying with 10% sulfuric acid. The lack of contamination of the saponin preparation with proteins was judged by the absence of protein bands in sodium dodecyl sulfate--polyacrylamide gel electrophoresis, agarose electrophoresis and agarose diffusion, and by the absence of an absorption maximum around 278 nm. The saponin acted as a noncompetitive inhibitor of corticotropin, glucagon, and epinephrine in lipolysis in isolated rat adipocytes, and it also antagonized dibutyryl cAMP induced lipolysis. The antilipolytic activity was resistant to heat, trypsin, chymotrypsin, pronase, and glutathione, in keeping with the chemical nature of saponin. Incorporation of [3-3H]glucose into lipid was inhibited. Adipocyte viability and ATP content were not affected by the saponin, suggesting that its inhibitory effects on lipolysis and lipogenesis were not due to an adverse effect on cell viability.