Developmental toxicology of solamargine and solasonine glycoalkaloids in frog embryos

As part of an effort to improve the safety of plant foods, a need exists to define the relative toxicities of structurally different glycoalkaloids and metabolites which may be present in Solanum plant species such as potatoes, tomatoes and eggplants. The objectives of this study were to determine the relative toxicities and the modes of action of the eggplant (Solanum melongena) glycoalkaloids solamargine and solasonine in Xenopus laevis frog embryos, using membrane potential and embryo growth and teratogenicity assays. In the cell membrane assays, adverse effects on embryos were evaluated by measuring membrane potentials using an electrochromic dye, di-4-ANEPPS, as a fluorescence probe for the integrity of the membranes. In the embryo growth and teratogenesis assays, the survival of the embryos and organ malformations was used as an index of embryo toxicity. The relative potencies of glycoalkaloids are similar for frog embryo effects (survival and teratogenicities) and for membrane effects (membrane potential). Experiments with solasonine at pH 6 and 8 suggest that the unprotonated form of the glycoalkaloids appears to be involved in the membrane effects. The nature of the carbohydrate side-chains of the steroidal glycosides governs relative potencies. The possible significance of the findings to food safety and plant physiology and possible application of the membrane assays to bacterial toxins are discussed.