Plant extracts and
phytochemicals may prevent
chronic diseases via activation of adaptive cellular stress response pathways including induction of
antioxidant and phase II detoxifying
enzymes. The regulatory regions of these inducible genes encode the electrophile-response element (EpRE). This study tested the EpRE induction ability of Maerua subcordata (fruit, leaf, root, seed)
methanol extracts and selected candidate constituents thereof, identified by liquid chromatography coupled with multistage mass spectroscopy, employing an EpRE
luciferase reporter gene assay using hepa-1c1c7 mouse
hepatoma cells. A parallel Cytotox CALUX assay using human
osteosarcoma U2OS cells was used to monitor any non-specific changes in
luciferase activity or cytotoxicity. Results showed that fruit, root, and seed extracts were non-cytotoxic up to a concentration of 30 gram dry weight per litre but the leaf extract exhibited some cytotoxicity and that the leaf (despite some cytotoxicity), fruit, and seed extracts showed strong induction of EpRE mediated gene expression while induction by the root extract was minimal. Selected candidates included
glucosinolates,
isothiocyanates, and some
biogenic amines. Subsequent studies showed that methyl-, ethyl-, isopropyl-, isobutyl-
isothiocyanates, and sec-butyl
thiocyanate as well as
glucobrassicin induced concentration (1-100 μM) dependent EpRE-mediated gene expression while the
biogenic amines stachydrine and
trigonelline acted as inhibitors of EpRE-mediated gene expression at 100 μM. The identification of glucolepidiin,
glucobrassicin,
glucocapparin,
stachydrine, and
trigonelline in all extracts was confirmed using standards and based on multiple reaction monitoring; yet,
glucobrassicin level in the root extract was negligible. In conclusion, this study provided a first report on EpRE mediated gene expression effects of M. subcordata; and despite detection of different
glucosinolates in all extracts, those containing
glucobrassicin particularly displayed high EpRE induction. Because EpRE inducers are cytoprotective and potential chemopreventive agents while inhibitors are suggested adjuvants of
chemotherapy, results of this study imply that process manipulation of this plant may result in
herbal preparations that may be used as chemopreventive agents or adjuvants of
chemotherapies.