Advances in Life Science and Technology www.iiste.org ISSN 2224-7181 (Paper) ISSN 2225-062X (Online) DOI: 10.7176/ALST Vol.73, 2019 53 The Supportive Role of Dietary Antioxidants in Antioxidant Defence System Abiodun Olusoji Owoade* Adewale Adetutu Olubukola Sinbad Olorunnisola Department of Biochemistry, Ladoke Akintola University of Technology, Ogbomosho, Nigeria Abstract Reactive oxygen and nitrogen species are generated both endogenously and in response to external factors, such as diet and lifestyle, and play a major role in the aetiology of several degenerative diseases. The effect of reactive oxygen species (ROS) and reactive nitrogen species (RNS) is balanced by the antioxidant action of enzymatic antioxidants such as superoxide dismutase, glutathione peroxidase, catalase, antioxidant compounds such as, thioredoxin, lipoic acid and dietary antioxidant such as Vitamin C, Vitamin E, carotenoids, flavonoids. Antioxidant defences are extremely important as they represent the direct removal of free radicals, thus providing protection for biological sites. However, as this protection may not be sufficient to entirely prevent the damage by ROS/RNS, consumption of food rich in dietary antioxidants which offers supportive role in antioxidant defence system in removing excessive ROS/RNS become even more important in protecting cell biomolecules against oxidative damage. Keywords: Reactive oxygen species, Free radicals, Antioxidants, Cell biomolecules, Oxidative damage. DOI: 10.7176/ALST/73-06 Publication date: April 30 th 2019 1. Diets and Diseases Diets appear to play an important role in human health and in the development of certain diseases such as cancer and cardiovascular disease (Rahman, 2001; Liu, 2004). These two diseases are the top causes of death in the United States and in most industrialized countries (Liu, 2004). Interestingly, several epidemiological studies have consistently shown that diets rich in fruit and vegetables promote health, and attenuate, or delay the onset of chronic diseases (Fraga, 2007). Therefore, changes in dietary behaviour, such as increasing consumption of fruits, vegetables and whole grains is a practical strategy for significantly reducing the incidence of chronic diseases (Liu, 2004). Plant based foods contain significant amounts of bioactive phytochemicals (e.g Polyphenols) which may provide desirable health benefits beyond basic nutrition to reduce the risk of chronic diseases (Liu, 2004). There is more and more convincing evidence to suggest that the health benefits of phytochemicals in fruits and vegetables may be due to their antioxidant action, because oxidative stress induced by free radicals is involved in the aetiology of wide range of chronic diseases (Sayre et al., 2001; Jenner, 2003; Dalle-Donne et al., 2006). 2. Reactive Oxygen and Nitrogen Species Reactive oxygen species (ROS) and Reactive nitrogen species (RNS) are generated in vivo from incomplete reaction of oxygen during aerobic metabolism, stimulated host phagocytes, or from exposure to environmental agents such as radiation and redox cycling agents (Park et al., 2003). ROS include free radicals (which are defined as molecules or molecular fragments containing one or more unpaired electrons) such as superoxide (O2 • ‾), hydroxyl (OH • ), peroxyl (ROO • ), hydroperoxyl (HROO • ) as well as non-radical species such as hydrogen peroxide (H2O2) and hypochlorous acid (HOCl) (Evans et al., 2002; Turko and Murad, 2002). RNS include free radicals like nitric oxide (NO • ) and nitrogen dioxide (NO • 2), as well as nonradicals such as peroxynitrite (ONOO‾), nitrous oxide (HNO2) and alkyl peroxynitrates (RONOO) (Evans et al., 2002; Turko and Murad, 2002). Reactive oxygen and nitrogen species play a dual role in biological systems, since they can be either harmful or beneficial to living systems (Valko et al., 2006). Beneficial effects of ROS which occur at low/moderate concentrations include (a) physiological roles in cellular responses to stress, as for example in defence against infectious agents and (b) the induction of a mitogenic response (Valko et al., 2006). The harmful effect of ROS includes widespread damage to macromolecules leading to lipid peroxidation, protein oxidation and DNA base modification and strand breaks (Poli et al., 2004; Stocker and Keaney, 2004). This damage effect is termed oxidative and nitrosative stress (Kovacic and Jacintho, 2001; Ridnour et al., 2005). Oxidative and nitrosative stress is defined in general as excess formation and/or insufficient removal of highly reactive molecules such as reactive oxygen species (ROS) and reactive nitrogen species (RNS) (Turko et al., 2001; Maritim et al., 2003). This occurs in biological systems when there is an overproduction of ROS/RNS on one side and a deficiency of enzymatic and non-enzymatic antioxidants on the other (Valko et al., 2007). The excess ROS are harmful because they can damage cellular lipids, proteins, and DNA which are the most important biomolecules in the human body (Orhan et al., 2006). Because of this, oxidative stress has been implicated in the development of many ageing-related diseases, like cancer, cataract and heart diseases (Dalle-Donne et al., 2006).