Dual Role of Dietary Polyphenols: Antioxidants and Regulators of Cellular Response
Fabio Virgili and Cristina Scaccini.
Free Radical Research Group, National Institute of Nutrition, Rome - Italy
Plants produce a large variety of secondary products containing one or more phenol groups, i.e. hydroxyl groups on an aromatic ring. These compounds are a chemically heterogeneous group that includes simple phenols, flavonoids, lignin and condensed tannins. Each phenolic class contains a number of compounds that are widely distributed in plants and then present in significant amount in the human diet. Plant polyphenols are attracting growing interest in nutrition since epidemiological studies have demonstrated a negative association between consumption of polyphenol-rich foods and cardiovascular diseases. They have been therefore proposed to affect a wide spectrum of human degenerative diseases such as chronic inflammation, atherosclerosis, cardiovascular disease and cancer. Experimental investigation demonstrated that polyphenols possess a strong antioxidant effect, which may result in the protection of plasma lipoprotein from oxidation. Also their participation to different metabolic pathways, other than the antioxidant defense system, has been more recently investigated. On these basis, the beneficial activity of plant polyphenols on the human health can result, (i) from their contribution to the extracellular and intracellular antioxidant network and (ii) from their effects on gene expression, through the modulation of the activity of key enzymes in signal transduction and the activation of redox-sensitive transcription factors. The protection from lipoprotein oxidation and the effect of cell response to different stimuli (e.g. gene expression regulated by NF-kB activation, the induction of either apoptotic or proliferative responses) by the phenolic component of commonly used foods, beverages and plant extracts (tea, wine and soybean, liquorice, sage and French maritime Pine), demonstrates the potentiality of non conventional dietary components to significantly contribute to the maintenance of health and affect the pathophysiology of different diseases.