Induction of NAD(P)H Quinone Oxidoreductase by Vegetables Widely Consumed in Catalonia, Spain

Abstract

Monofunctional inducers (MIs) enhance phase 2 enzymes such as nicotinamide-adenine-dinucleotide-phosphate [NAD(P)H] quinone oxidoreductase (NQO1) without modifying oxidation enzymes. The induction of these protective enzymes appears to be mediated by genetic regulatory elements in their promoter regions known as the antioxidant response element (ARE). The aim of this study was to identify, through an in vitro study, which of the 30 fruits and vegetables commonly consumed in Catalonia, Spain, contain MIs of NQO1. We assayed the capacity of extracts of these fruits and vegetables to induce NQO1 [by more than 1.5-fold: ratio of induction (cells treated/control) >1.5, 8-mg/ml dose] in two murine hepatoma cell lines: Hepa 1c1c7 and BPrC1, a modified cell line that possesses a nonfunctional aryl hydrocarbon receptor nuclear translocator system and is thus nonresponsive to bifunctional inducers. We also used a third cell line, papiloma (PE) murine keratinocytes, a stably transfected cell line with an ARE-luc+ plasmid (AREPE cell line) for verifying induction through the ARE with a simple luminescence screening assay. Broccoli (Hepa 1c1c7, ratio = 5.5; BPrC1, ratio = 2.3), calcot (Allium cepa L.) (Hepa 1c1c7, ratio = 4.7; BPrC1, ratio =1.5), green onion (Hepa 1c1c7, ratio = 4.6; BPrC1, ratio = 2), green cabbage (Hepa 1c1c7, ratio = 3.6; BPrC1, ratio = 2.7), purple cabbage (Hepa 1c1c7, ratio = 3.4; BPrC1, ratio = 2), and black cabbage (Hepa 1c1c7, ratio = 3; BPrC1, ratio = 3) were active NQO1 inducers in both murine hepatoma cell lines. Extracts from broccoli (ratio = 3.5), calcot (ratio = 4.8), cauliflower (ratio = 4.2), cabbage (ratio = 2.2), green onion (ratio = 3.2), green cabbage (ratio = 3.6), black cabbage (ratio = 4.5), and purple cabbage (ratio = 3.7) were confirmed to contain MIs in the AREPE cell line. These results are very similar to those described for vegetables consumed in the United States, with the exception of calcot, which is common in Catalonia but is not grown or consumed widely in the United States.