Consumption of Glucosinolate-Rich Nasturtium officinale and Brassica oleracea L. var. sabellica May Reduce the Risk of Cancer Occurrence in Humans

Abstract

Vegetables containing glucosinolates, commonly referred to as crucifers, are gaining popularity due to their anticancer benefits in human.  Glucosinolates are secondary metabolites that are usually found in cruciferous vegetables belonging to the family Brassicaceae. Several studies pointed out that glucosinolates could undergo hydrolysis and produce bioactive isothiocyanates, via the action of enzyme myrosinase. In this study, the total glucosinolates in watercress (Nasturtium officinale) and kale (Brassica oleracea L. var. sabellica) were quantified using high-performance liquid chromatography (HPLC). HPLC analysis revealed that watercress contains 228.93 ± 26.39 μmol/g, while kale contains 87.60 ± 80.12 μmol/g of total glucosinolates. Analysis of cyclocondensation products via HPLC directly correlates the amount of isothiocyanates present in the extracts, which were found to be 0.398 ± 0.018 and 0.378 ± 0.014 for unhydrolyzed watercress and kale, respectively. An increase in isothiocyanate content was observed for both watercress and kale after subjecting them to hydrolysis in the presence of myrosinase enzyme. Moreover, the biological activity of the extracts derived from the plants was determined using standard assay methods. Free radical DPPH assay showed that methanolic extracts of both watercress and kale exhibit antioxidant properties with the IC₅₀ values of 13.04 ± 1.11 µg/mL and 33.14 ± 1.44 µg/mL, respectively. On the other hand, the hydrolysates showed higher scavenging activity values reported at the IC₅₀ values of 7.69 ± 0.93 µg/mL and 20.40 ± 1.26 µg/mL, for watercress and kale, respectively. PrestoBlue™ assay also revealed the ability of the aqueous extracts to selectively target cancer cells. Watercress showed anticancer potential towards breast adenocarcinoma (MCF-7, IC₅₀ = 17.67 ± 1.64 µg/mL). On the other hand, kale showed anticancer potential towards small lung cancer cell (H69PR, with IC₅₀ = 19.35 ± 1.54 µg/mL) and colon cancer cell (HT-29, IC₅₀ = 18.32 ± 2.41 µg/mL). Moreover, the extracts were found to be non-cytotoxic to normal cells (HDFn, human dermal fibroblast neonatal, IC₅₀ >100 µg/mL), which indicates that the extracts are selective towards targeting cancer cells.