Antioxidant efficacy of Kalanchoe daigremontiana bufadienolide-rich fraction in blood plasma in vitro.

Context: The main source of bufadienolides is toad venom; however, plants such as members of Kalanchoe Adans. (Crassulaceae) genus may also synthesize these bioactive substances. Objective: This is the first study on antioxidant effects and cytotoxicity of bufadienolide-rich fraction isolated from Kalanchoe daigremontiana Raym.-Hamet & H. Perrier. Materials and methods: The methanolic fraction was extracted from the plant roots and contained 0.48mg bufadienolides/mg of dry mass (11 alpha, 19-dihydroksytelocinobufagin, bersaldegenin-1-acetate, bersaldegenin-1,3,5-orthoacetate, 19-(acetyloxy)-3 beta, 5 beta, 11 alpha, 14-tetrahydroxyl-12-oxo-bufa-20,22-dienolide and 19-(acetyloxy)-1 beta, 3 beta, 5 beta, 14-tetrahydroxyl-bufa-20,22-dienolide, mainly). The cytotoxicity of K. daigremontiana fraction was evaluated in an in vitro experimental model of blood platelets. The viability of blood platelets was determined on the basis of a release of lactate dehydrogenase. Results: The fraction scavenged DPPH center dot radicals, with EC50 of 21.80 mu g/mL. Studies on an experimental model of blood plasma under peroxynitrite-induced oxidative stress revealed that the plant preparation had moderate antioxidant properties. Levels of 3-nitrotyrosine and thiol groups indicated that the protective effect of K. daigremontiana was significant mainly for its concentration of 50 mu g/mL. No effect was found in prevention of oxidation of low-molecular plasma thiols (glutathione, cysteine and cysteinylglycine). Simultaneously, measurements of lipid hydroperoxides and thiobarbituric acid-reactive substances (TBARS) indicated that the examined fraction might be effective antioxidant at broader concentration range, that is 1-5 and 25-50 mu g/mL for hydroperoxides and TBARS generation, respectively. No cytotoxicity was observed at the concentration range of 1-50 mu g/mL. Conclusions: Based on the obtained results, we suggest that antioxidant activity may additionally contribute to beneficial properties of K. daigremontiana-derived extracts.