Free radicals--the bad guys It is widely held (1) that free radicals are involved in the initiation and propagation of many and various illnesses, including cancer, heart disease, stroke, rheumatoid arthritis, diabetes, and multiple sclerosis (MS). The list runs on, and even the process of ageing itself is believed to be driven by free radicals, also called reactive oxygen species (ROS) or reactive oxygen intermediates (ROI). Now, the species classified as ROS or ROI are derived from molecular oxygen ([O.sub.2]) which obviously we need to breathe to stay alive. In the main, ROS are the superoxide radical anion ([O.sup.-*.sub.2]), its conjugate acid, the hydroperoxyl radical (HO[O.sup.*]), the hydroxyl radical (H[O.sup.*]), organic peroxyl radicals (RO[O.sup.*]), alkoxyl radicals (R[O.sup.*]) as bona fide free radical (unpaired electron) molecules, but also included on the list are molecular (especially, singlet) oxygen ([O.sub.2]), organic hydroperoxides, ROOH and hydrogen peroxide itself, [H.sub.2][O.sub.2]. It can be said that all oxygen free radicals are ROS/ROI but not all ROS/ROI are free radicals. As respired [O.sub.2] enters living cells it is metabolised e.g. by the mitochondria to [O.sup.-*.sub.2], which is not in itself strongly oxidising, but it provides a source of other ROS. To avoid living cells being overwhelmed by [O.sup.-*.sub.2], they contain the enzyme superoxide dismutase which catalyses the reaction [equation (I)]: 2[O.sup.-*.sub.2] + 2[H.sup.+] [right arrow] [H.sub.2][O.sub.2] + [O.sub.2] (1) Now [H.sub.2][O.sub.2] is not harmless in cells since it can provide a source of H[O.sup.*] radicals, particularly if there is free iron present, which promotes the Fenton Reaction [equation (2)]: [Fe.sup.2+] + [H.sub.2][O.sub.2] [right arrow] [Fe.sup.3+] + H[O.sup.*] + [sup.- ]OH (2) H[O.sup.*] radicals can attack sensitive molecules in cells, including membrane lipids, carbohydrates and proteins and, if they are formed in the cell nucleus, DNA bases too, potentially leading to strand-breaks and cell mutations. The attack of HO and other kinds of radicals on lipids can initiate the process known as lipid peroxidation, which is responsible for the rancidification of foodstuffs including meat. That our human meat does not become rancid while we remain alive is due to the fact that living cells contain antioxidants, in particular, catalase which is a common enzyme found in nearly all living organisms that are exposed to oxygen. Catalase is able to catalyse the decomposition of hydrogen peroxide to water and oxygen, and has one of the highest turnover numbers of all enzymes--one catalase molecule can convert 40 million molecules of hydrogen peroxide to water and oxygen per second. Glutathione peroxidise also catalyses the decomposition of [H.sub.2][O.sub.2] by combining its reduction to water with the oxidation of reduced glutathione (GSH), a thiol-containing tripeptide (glu-cys-gly) [equation (3)]: [H.sub.2][O.sub.2] + 2GSH [right arrow] GSSG + 2[H.sub.2]O (3) The product, oxidised glutathione (GSSG), contains a disulfide bridge, and can be converted back to GSH by glutathione reductase enzymes. It is now thought that peroxiredoxins may be even more important (2) in removing [H.sub.2][O.sub.2] from cells in animals, bacteria, and probably plants. There are at least three classes of these enzymes, but in the function of all of them a cys-SH group present on the peroxiredoxin is oxidised by [H.sub.2][O.sub.2] to a sulfenic acid, cys-SOH. The interception of ROS is not perfect and around 1% of respired [O.sub.2] ends-up as ROS. Over a year this amounts to 1.7 kg of ROS, since humans are fairly large animals and breathe substantial amounts of oxygen. To cope with what ROS remain, there are both intrinsic and extrinsic antioxidants present in cells, the latter being brought into the living organism and hence its cells by ingestion, i.e. in our food and in the form of deliberately taken dietary supplements. …