@ Pergamon 0278-6915(94)EOO47-Q FdChem. Toxic. Vol. 32. No. 7. pp. 671-683. 1994 Copyright ~ 1994 ElsevierScienceLtd Printed in Great Britain. All rights reserved 0278-6915/94 $26.00 + 0.00 NUTRITION AND HEALTH ASPECTS OF FREE RADICALS AND ANTIOXIDANTS O. I. ARUOMA The Pharmacology Group. University of London King's College, Manresa Road. London SW3 6LX. UK (Accepted 7 February 1994) Summary--Although the role of free radicals has continued to capture the imagination of scientists, the interest in nutritional aspects of free radicals is relatively recent. Oxidative stress, which often arises as a result of the imbalance in the human antioxidant status, has been implicated in ageing and in a number of human diseases such as cancer, atherosclerosis, malaria and in rheumatoid arthritis. This review discusses the current status of free radicals in nutrition and dietary antioxidants and considers the possibility that use of a range of antioxidants, which have been carefully evaluated, combined with methods for measuring oxidant generation, would help to delineate the contribution of nutrients to the modulation of the consequences of free radicals in the human body. Introduction The discovery of superoxide dismutase (SOD) (Me- Cord and Fridovich, 1969) gave a strong impetus to research in the role of free radicals in human diseases (Table I) (Aruoma, 1993a, Blake et aL, 1987; ttalli- well and Gutteridge, 1989; McCord, 1993; Slater, 1989), and appears to have stimulated considerable interest in the role of free radical reactions in nutri- tion and food spoilage (Aruoma, 1993b; Hudson, 1990; St Angelo, 1992). For the health conscious consumer, the words 'free radicals' and "antioxidants' have become very fashionable. Free radicals may be defined as any species capable of independent existence that possess one or more unpaired electrons, an unpaired electron being one that is alone in an orbital (the radical dot (.) is inserted to indicate the presence of one or more unpaired electrons. Electrons are more stable when paired together in orbitals: the two electrons in a pair have different directions of spin. Hence, radicals are generally less stable than non-radicals, although their reactivities vary. Most biological molecules are non- radicals containing only paired electrons. Oxygen (O,) is a toxic gas. Humans and other aerobes can tolerate it only because, at the same time that organisms were evolving electron transport chains and other enzyme systems to use it, antioxi- dant defences to protect against the toxic effects ofO, were evolving in parallel. The predecessors of the anaerobic bacteria that exist today followed the "blind" evolutionary path of restricting themselves to Ahbreriations: :gAP = a:antiproteinase: EDTA = ethyl- encdiaminctetraacetic acid: ROS = reactive oxygen species: SOD = supcroxide dismutasc; TBA = thio- barbituric acid. environments that O., did not penetrate. Hence the evolution of multicellular aerobes and of antioxidant defence mechanisms are intimately related. Figure I shows some inter-relationships between antioxidants. The endogenous antioxidant enzymes are SOD, cata- lase and glutathione pcroxidase. Reactive oxygen species (ROS) is a general term often used by scien- tists to describe not only the free radicals hydroxyl (OH'), superoxide (O;), nitric oxide (NO') and per- oxyl (ROO'), but also the non-radicals such as hydro- gen peroxide (H,O.,), ozone (O0, singlet oxygen (IO:) and hypochlorous acid (HOCI). Brief com- ments on some of the ROS follow. Ozone. This pale blue gas serves as an important protective shield against solar radiation in the atmos- phere. Close to the Earth's surface, ozone is an unwanted oxidant, and is often regarded as the most toxic air pollutant. Ozone can form in laboratories using equipment which has high-energy ultraviolet (UV)-producing lamps, and in urban air as a result of photochemical reactions and pollution. The tissue most susceptible to damage by ozone is that of the respiratory tract (O'Neill et al., 1993). Nitric" oxhle. NO is a free radical. It is widely thought that the endothelium-derived relaxing factor (EDRF) produced by vascular endothelium, which is an important mediator of vascular responses induced by scveral pharmacological agents (including bradykinin and acetylcholine) is identical to NO (Palmer et al., 1988; Sncddon and Vane. 1988). Vascular endothelial cells that line the blood vessels also seem to produce small amounts of O~, some of which could react with NO (Huie and Padmaja. 1993; Stamlcr et al., 1992), producing non-radical products such as peroxynitritc ion which can form hydroxyl radical by way of a metal-dependent reaction (Beck- man et al.. 1990). Thus, variation in the production 671