The comparison of cytotoxic and genotoxic activities of glucosinolates, isothiocyanates, and indoles

Chemopreventive properties of Brassica vegetables are attributed mainly to their characteristic compounds-glucosinolates (GLs) and their main hydrolysis products-isothiocyanates (ITCs) and indoles. In this study, we compared antiproliferative activity (MTT test in HT29 cells) and genotoxic effects (comet assay in HT29 cells and restriction analysis in a cell-free system) of three GLs (sinigrin (SIN), glucotropaeolin (GTL), and glucobrassicin (GLB)) with that of their major degradation products. Intact GLs did not exhibit cytotoxic activity, possibly due to their limited bioavailability. However, in the presence of myrosinase (MYR), GLs gained the ability to inhibit HT29 cells' growth. The addition of MYR caused the hydrolysis of GLs to the corresponding ITCs or indoles, i.e. compounds that show stronger biological activity than parent GLs. Pure ITC/indole solutions showed the strongest antiproliferative activity. Based on the results of restriction analysis, it was found that GLs to a greater extent than ITCs caused DNA modification in a cell-free system. In the case of GLs, metabolic activation by the S9 fraction increased this effect, and at the same time changed the preferential binding site from the area of base pairs AT to GC base pairs. Of all compounds tested, only benzyl ITC caused DNA damage detectable in the comet assay, but it required relatively high concentrations.

Automated summary

The chemopreventive properties of Brassica vegetables are mainly attributed to their characteristic compounds, glucosinolates (GLs) and their degradation products, isothiocyanates (ITCs) and indoles. This study found that intact GLs did not show cytotoxic activity on cancer cells, but their conversion to ITCs or indoles by myrosinase led to significant inhibition of cancer cell growth. The pure ITC/indole solutions showed the strongest antiproliferative activity. GLs were found to cause DNA modification to a greater extent than ITCs, and metabolic activation increased this effect.