ROS and Phenolic Compounds

Reactive oxygen and nitrogen species (ROS and RNS) are detrimental to human health because they initiate free radical–catalyzed oxidations of fundamental biomolecules such as DNA, proteins, lipids in low-density lipoprotein (LDL) and cell membranes, polysaccharides, etc. Molecular oxygen in its triplet ground state (the oxygen we breathe), 3O2, is the oxidant species in these processes called autoxidation or peroxidation. Cells are equipped with defensive systems able to quench most of the radicals responsible for initiating or propagating autoxidation in organic matter. Enzymes (superoxide dismutases, catalases, glutathione peroxidases, and peroxiredoxins) destroy radicals such as O2·− or non-radical species such as H2O2 and ROOH. Other small molecules, mainly phenols, present in the diet are able to react with radicals and hence may cooperate with the enzymes in keeping “oxidative stress” at bay. However, the physiological concentrations of phenols are frequently low, and this has cast doubt on their effectiveness in vivo. On the other hand, there is evidence that vitamin E is an effective peroxyl radical (ROO·) scavenger both in vitro and in vivo with rate constants of ~106 M−1 s−1. Its effectiveness in vivo against other radicals and non-radical oxidative species (HO·, R·, NO2 ·, RS·, 1O2, O3, and HOCl) is however uncertain. Vitamin C and ubiquinol-10 are able to regenerate vitamin E from its radicals.