On the cytotoxity of oxidized phytosterols isolated from photoautotrophic cell cultures of Chenopodium rubrum tested on meal-worms Tenebrio molitor

Abstract

Cell injury—as evoked by oxidative stress, insect attack or ageing—causes lipid peroxidation of polyunsaturated acids, e.g. linoleic acid. Hydroperoxides (LOOH) so produced transform fatty acids, terpenes and sterols to epoxides. We describe a bioassay to determine the cytotoxity of sterol oxidation products by measuring the mortality of meal-worms ( Tenebrio molitor) after injection of diluted test compounds. LOOH was tested in concentrations from 10 −5 M up to 10 −2 M and developed recognizable mortality (25%, 10 −2M, 23 hr). A direct relation between activity and concentration was observed. 5,6-Epoxides of phytosterols and derived 3,5,6-trihydroxysteranes have been isolated from Chenopodium rubrum cell cultures. Using 5,6-epoxycholesterol and 3,5,6-trihydroxycholestane as standards of known bioactivity, the toxicity of epoxides of sitosterol and stigmasterol, as well as the trihydroxy compounds thereof, was checked. The phytosterol derivatives are by a factor of five less active than the corresponding cholesterol oxidation products. 5,6-Epoxides and 5,6-chlorohydrins showed half of the activity of the corresponding 3,5,6-trihydroxyphytosterols. These developed highest cytotoxity (40% mortality in 5 × 10 −3 M solution after 23 hr). The activity of 5,6α-and 5,6β-epoxides was found to be equal. Metabolism and proposed biological function of oxidized phytosterols is discussed.