Induction of cellular Phase 2 enzymes (e.g.,glutathione transferases, glucuronosyltransferases, NAD(P)H:quinone oxidoreductase) and elevation of glutathione levels are now recognized as effective strategies for reducing the risk of developing neoplasms caused by electrophilic carcinogens and reactive forms of oxygen. Transcriptional activation of the genes of Phase 2 enzymes is evoked by nine classes of chemical agents, many of which are present in edible plants and already widely consumed in our diets (isothiocyanates, phenols, quinones, phenylpropenoids, Michael reaction acceptors). The ultimate goals are to identify dietary Phase 2 enzyme inducers with low toxicity and consequently suitable for rapid evaluation of efficacy and long-term use in humans. This project focuses on a detailed evaluation of novel glucosinolates (the stable biological precursors of isothiocyanates) which are widely consumed and recognized as potentially valuable protectors against carcinogenesis.
Aim 1 is designed to identify edible plants that contain substantial quantities of glucosinolates with structural features that have been previously shown to result in high inducer potency; and to isolate, crystallize, and characterize these glucosinolates in adequate quantities for biological evaluation in cells and animals.
Aim 2 proposes the isolation and detailed characterization of an unusual rhamnosyloxybenzyl glucosinolate (whose corresponding isothiocyanate is an exceedingly potent Phase 2 inducer) that is abundant in all parts of the pantropical, totally edible, and widely consumed drumstick tree (Moringa oleifera). Related multiply glycosylated glucosinolates will also be isolated from various Moringa species, examined for inducer activity, and assessed for inhibition of carcinogenesis in appropriate cell and animal models.
Aim 3 will establish in healthy volunteers the absorption, pharmacokinetics, metabolism and excretion of carefully characterized plant extracts containing glucosinolates of special interest, beginning with the rhamnosyloxybenzyl glucosinolate and its cognate isothiocyanate. These pharmacokinetic studies will set the stage for the development of safe and effective dietary chemoprotectors for human use.
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