(Poly)phenols and the regulation of NADPH oxidases

Nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOXs) are enzymes that generate superoxide anion (O₂•^-) and hydrogen peroxide (H₂O₂), and that are widely distributed in mammalian tissues. Many bioactives, especially plant (poly)phenols are being studied for their capacity to regulate NOXs. The modulation of these enzymes are of central relevance to maintain redox homeostasis and regulate cell signaling. In in vitro and ex vivo assays, and in experimental animal models, different (poly)phenols are able to modulate NOX-dependent generation of O₂•^- and H₂O₂. Mechanistically, most of the known effects of (poly)phenols and of their metabolites on NOX1, NOX2, and NOX4, include the modulation of: i) the expression of the different constituent subunits, and/or ii) posttranslational modifications involved in the assembly and translocation of the protein complexes. Very limited evidence is available on a direct action of (poly)phenols on NOX active site (electron-transferring protein). Moreover, it is suggested that the regulation by (poly)phenols of systemic events, e.g. inflammation, is frequently associated with their capacity to regulate NOX activation. Although of physiological significance, more studies are needed to understand the specific targets/mechanisms of NOX regulation by (poly)phenols, and the (poly)phenol chemical structures and moieties directly involved in the observed effects. It should be kept in mind the difficulties of NOX's studies associated with the complexity of NOXs biochemistry and the methodological limitations of O₂•^- and H₂O₂ the determinations. Studies relating human ingestion of specific (poly)phenols, with NOX activity and disease conditions, are guaranteed to better understand the health importance of (poly)phenol consumption and the involvement of NOXs as biological targets.