Genotoxic properties of glucosinolates and isothiocyanates present in Brassica vegetables

The bioactive phytochemicals found in Brassica vegetables, in this number glucosinolates (GLS), as well as products of their degradation such as isothiocyanates (ITC) and indoles, are regarded as the most promising chemopreventive compounds. These secondary metabolites display stron antibiological activity and constitute defence system preventing the development of agrophages attacking Brassica plants. Such properties suggest that they may also pose some risk for humans when ingested in higher amounts in a form of e.g. dietary supplements. Degradation of GLS generates electrophilic species (e.g. stable ITC) able to react with nucleophiles such as nucleobases in DNA. Our studies are aimed at examining the possibility of induction of genotoxic damage by GLS degradation products either generated in situ enzymatically with the aid of myrosinase or as pre-formed ITCs. Two effects were tested: induction of mutagenicity by Ames test and formation of covalent DNA adducts by restriction analysis. The microplate Ames test MPF did not reveal any mutagenicity of pre-formed ITCs, however the myrosinase generated in situ GLS degradation products markedly increased the number of Salmonella typhimurium TA 98 revertants. Also no DNA binding by ITC alone or activated with microsomal fraction S9 was seen in restriction analysis. The currently carried out experiments examine DNA binding ability of in situ generated metabolites liberated as a result of GLS hydrolysis by myrosinase. The results of this study should shed some light on the safety of dietary supplements containing bioactive phytochemicals isolated from Brassica plants