Nutritional Proanthocyanidins, Flavonoids, and Related Phenols

Abstract

939 INTEREST IN DIETARY PHYTOCHEMICALS and components of medicinal plants for the maintenance of health and possible therapeutic intervention has increased markedly over recent years. Among these natural products, many polyphenolic compounds such as (epi)catechin and its derivatives, the oligomeric procyanidins, as well as phenolic stilbenes such as resveratrol, have captured considerable attention due to their biological, medicinal, and therapeutic potential. The objective of this Forum issue on Nutritional Proanthocyanidins, Flavonoids and Related Phenols is to summarize current research on bioavailability, mechanisms of cytoprotection, and detection of polyphenols, as well as indications and benefits. However, there are still several unanswered questions. Major issues with respect to the protective effects of the polyphenols concern factors influencing their mechanisms of absorption across the small intestine, their biotransformation, and the bioactivity and mechanisms of action of their in vivo conjugates and metabolites. In particular, is it likely that such components function as antioxidants in vivo, or by biochemical mechanisms independent of their antioxidant properties? This issue is a compilation of reviews and original research articles by leading researchers in the field. Spencer et al. provide an overview of the absorption of flavonoids and proanthocyanidins across the small intestine and the nature of the resulting conjugates and metabolites (7). The review by Bhat et al. summarizes the biological properties of resveratrol, focusing specifically on its anticancer and estrogenic activities, leading to a fuller appreciation of potential health benefits (1). The effects of phenolic components of tea, catechins, theaflavins, and other flavonoids, on growth factors, nuclear factor-kB, and stress-mediated signal transduction, with special emphasis on their bioavailability, are highlighted in the review by Wiseman et al. (8). The original research article by Bors et al. addresses the efficacy of natural polyphenols as antioxidants using pulse radiolysis, EPR, and NMR spectroscopy (2). Transportation and absorption of proanthocyanidin dimers, trimers, and polymers across monolayers of human epithelial intestinal cells are assessed in the research contribution of Deprez et al. (3). Maatta et al. discuss the antioxidant properties and biological efficacy of anthocyanins in berries and proanthocyanidins in black, red, green, and white currants (5). The role of resveratrol in the inhibition of the proliferation of breast cancer cells is discussed by Serrero and Lu (6). Kilmartin’s contribution describes the novel elec-