Seaweed (marine algae) is a major dietary source in Asian countries, particularly in Japan. Numerous beneficial effects of seaweed consumption have been reported, but only some of which have been attributed to individual chemical components. An apparent common denominator of seaweed's health-promoting effects is the antioxidant activity which may counteract cancer-causing oxidative stress induced damage. Concomitantly, the incidence of several types of cancer is extremely low in Japan and inverse correlations with seaweed consumption have been reported. Prostate cancer risk in particular is almost negligible in Japan. Prostate cancer is characterized by the silencing of one glutathione-S-transferase (GST) gene, a phase II detoxification enzyme. Phase II and other antioxidant enzymes are commonly regulated by the antioxidant response element (ARE) which is activated by transcription factor Nrf2. The activation of the Nrf2-ARE pathway is a valid cancer preventive strategy, and sulforaphane, a constituent of broccoli, is the best known example of a cancer preventive natural product that acts through this mechanism. Preliminary data indicate that certain seaweed extracts activate the ARE-luciferase reporter in IMR-32 human neuroblastoma cells. It is hypothesized here that some seaweeds are able to activate the Nrf2-ARE cancer preventive signaling pathway and that some of the beneficial, particularly antioxidant properties, may be mediated through ARE activation. First, small-scale collections of seaweed will be carried out in Florida coastal habitats. Various extracts will then be prepared and briefly fractionated. Crude extracts and fractions are arrayed in 96-well plates and then screened in cellular models for oxidative stress and cancer prevention using an ARE reporter gene assay. Natural product mixtures that activate the ARE by causing oxidative stress or toxicity will be eliminated in counter screens. Hits will be further prioritized using a variety of secondary biochemical assays. Following re- collections of most promising seaweed species, the corresponding extracts or fractions will then be tested for their ability to activate the ARE in vivo using ARE reporter mice, which serves as an additional layer of prioritization. Bioassay-guided fractionation will be executed to isolate pure ARE activators from in vivo active mixtures. The active principle(s) will then be structurally identified by analytical techniques, primarily NMR. The proposed study is complemented by ongoing research in the PI's laboratory which aims in characterizing the Nrf2-ARE pathway and which has been yielding potential molecular targets for cancer preventive and anti- degenerative agents acting through this mechanism. This application is in line with NIH's goal to identify effective disease-preventive strategies.
Oxidative stress results in cancer-causing cellular damage which can be attenuated or prevented by boosting the endogenous defense system. Seaweed is a dietary source that is hypothesized here to enhance levels of humans'antioxidant and detoxification factors through a specific signaling pathway. The identification of cancer-preventing seaweeds and of individual active components may become the basis for the development of new health-promoting strategies.
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