Evaluation of a sicilian black broccoli extract on in vitro cell models

Abstract

Vegetable crops of Brassica oleracea contain significant amounts of antioxidant compounds, such as glucosinolates (GLS) which, upon disruption of the tissue, are broken down by the endogenous enzyme myrosinase (MYR), resulting in production of isothiocyanates, thiocyanates, nitriles, goitrin and epithionitriles. In particular, isothiocyanates are known to exert beneficial effects for human health. Several studies describe isothiocyanates (ITCs) as inhibitors of mitosis and stimulators of apoptosis in human tumor cells. The Sicilian black broccoli is a neglected crop of Mt. Etna towns showing a particular GLS profile mainly represented by GRA and NGBS and their derivatives. We investigated the effects of different concentrations (0-25 μM) of various GLS: gluconasturtiin (GNT), glucoraphanin (GRA), progoitrin (PRO), sinigrin (SIN), glucoiberin (GIB), gluconapin (GNA), sinalbin (GSI), glucobrassicin (GBS), glucobrassicanapin (GBN) and glucoerucin (GER) on the growth of HT29 (colon cancer) and A2058 (melanoma cancer) cells, after 24 h of treatment, in presence or not of MYR (0.018 U, in situ method). The same cell lines were also exposed to the Sicilian black broccoli juice extract (from leaves and stems) at different amount (0.05, 0.1, 0.5, 1, and 5%), with and without MYR. Cellular viability was evaluated by MTT assay. GLS, alone and in presence of MYR, elicited different grades of toxicity in both cell lines models. GRA and GNT showed less toxicity than their breakdown products and opposite results were obtained with GBS and GBN. Black broccoli juice showed to be less toxic in presence of MYR; this effect is particular evident at higher juice percentages (1 and 5%), corresponding to 5 and 25 µM, respectively of GRA and NGBS. Certainly, juice extract activity on in vitro cell lines cannot only be explained by the peculiar GLS profile; probably, the interaction of others compounds, such as polyphenols, have to be taken into account. In conclusion, not all breakdown GLS products show more toxicity than their precursors, at least in the in vitro cell cancer models we utilized.