Flavonoid antioxidants

In order to ascertain the role of dietary flavonoids as antioxidants in viv o it is necessary to understand the chemical nature of the absorbed forms i n the circulation in vivo and how the multiplicity of research findings in vitro reflect the bioactivity of flavonoids in vivo. Only when we gain adeq uate information on the circulating forms can we begin to understand the ta rgeting to the tissues, whether flavonoids cross the blood-brain barrier, f or example, and in what forms. Flavonoids are powerful antioxidants in vitr o, but their overall function in vivo has yet to be clarified, whether anti oxidant, anti-inflammatory, enzyme inhibitor, enzyme inducer, inhibitor of cell division, or some other role. It should also be emphasised that the re ducing properties of flavonoids might contribute to redox regulation in cel ls, independently of their antioxidant properties, and thus might protect a gainst cell ageing, for example, by working together with the intracellular reductant network. To gain understanding of these issues the factors influ encing the absorption of flavonoids in the gastrointestinal tract needs to be established, namely the questions of: de-glycosylation before absorption , conjugation in the small intestine through glucuronidation, sulphation or methylation etc, metabolism and degradation in the colon to smaller phenol ic molecules. The forms in which they circulate in vivo will influence thei r polarity and, thus, their localization and bioactivities in vivo. Finally if antioxidant activities are important, the elucidation of how such prope rties in vitro relate to the potential for conjugates and metabolites in vi vo to act as antioxidants is required. The absorbed flavonoid components mi ght function in the aqueous phase (like vitamin C) or in the lipophilic mil ieu (as vitamin E) in vivo. This will depend on their polarity properties o n uptake, how they are metabolised on absorption, and their resulting struc tural forms in the circulation.