Kaiware Daikon (Raphanus sativus, L.) Extract: a Naturally Multipotent Chemopreventive Agent

Brassica vegetables are attracting major attention as healthy foods due to their content in glucosinolates (GLs) that release the corresponding isothiocyanates (ITCs) upon myrosinase hydrolysis. A number of studies have so far documented the chemopreventive properties of some ITCs. On the other hand studies focusing on single nutrients detached from food itself risk to be quite “reductive”, since plants contain several classes of compounds endowed with a polyhedral mechanism of action. Our recent finding that 4-methylthio-3-butenylisothiocyanate (GRH-ITC) and 4-methylsulfinyl-3-butenyl-isothiocyanate (GRE-ITC), released by the GLs purified from Japanese (Kaiware) Daikon (Raphanus sativus, L) seeds and sprouts, had selective cytotoxic/apoptotic activity on three human colon carcinoma cell lines, prompted further research on the potential chemopreventive role of a standardized Kaiware Daikon Extract (KDE), containing 10.5% w/w GRH and 3.8% w/w GRE, compared to its purified components. KDE administered in combination with myrosinase at doses corresponding to 50 M GRH-ITC plus 15 M GRE-ITC (50 M KDE-ITC) to 3 human cancer cell lines (LoVo, HCT-116 and HT-29) significantly reduced cell growth to only 4-6% of control in six days (p<0.05), outperforming pure GRH-ITC or GRE-ITC at the same dose. On the other hand the same treatment had no significant toxicity on normal human T-lymphocytes. 50 M KDE-ITC had relevant apoptosis induction in all tested cancer cell lines, as confirmed by annexin V assay (e.g. 33% induction in LoVo compared to control, p<0.05), Bax protein induction (e.g. +20% in HT-29, p<0.05) and Bcl2 downregulation (e.g.-20% in HT-29, p<0.05), and induced Caspase-1 and PARP-1 activation in all cancer cells as shown by Western blot analysis. Unlike pure GRH or GRH-ITC, KDE had also relevant chain-breaking antioxidant activity, retarding the AMVN initiated autoxidation of methyl linoleate in SDS micelles at concentrations as low as 4.4 ppm (-50% in rate of oxygen consumption), as monitored by Clark-type microelectrode oxygen-uptake kinetics, and induced very fast quenching of DPPH• radical in methanol with t1/2 (s) = (1.47± 0.25) x 10-2 / [KDE; (g/L)], measured by stopped-flow Uv-Vis kinetics at 298 K. The potential chemopreventive role of KDE is discussed