Prooxidant/antioxidant balance

Superoxide radical anion, hydroxyl radical, and hydrogen peroxide are known as prooxidants, whereas substances that neutralize their effects are called antioxidants. Oxidative stress occurs when the prooxidant-antioxidant balance becomes too favorable to the prooxidants. The effects of prooxidants can be neutralized by their direct reaction with small-molecule antioxidants, including glutathione, ascorbate, and tocopherols. In addition, oxidizing radicals are scavenged from a living system by several enzymes, including peroxidase, superoxide dismutase, and catalase. Oxidative lesions on DNA may be repaired by DNA repair enzymes. 

If the controlling processes are overwhelmed, free radicals can become highly destructive to cells and tissues. Oxidative stress is the situation in which the prooxidant-antioxidant balance is tipped in favour of the former [12], This may be due to exogenous sources of free radicals or endogenous stresses. 

A prooxidant is an agent that can induce oxidative stress, which is defined as a shift in the prooxidant-antioxidant balance toward oxidant activity. Oxidative stress induced by a prooxidant in a biological system manifests itself as increased production of bioactive free radical species, a decrease or modulation of antioxidant defenses, and/or an increase in oxidative damage. The fine balance between the oxygen center radicals and antioxidants may be dependent on the concentration of prooxidant, oxygen tension, and interactions with other antioxidants. 

Decker, E.A. 1998. Strategies for manipulating the prooxidative/antioxidative balance of foods to maximize oxidative stability. Trends in Food Science and Technology 9 241-248. 

Oxidative Stress A disturbance in the prooxidant-antioxidant balance in favor of the former, leading to potential damage. Indicators of oxidative stress include damaged DNA bases, protein oxidation products, and hpid peroxidation products (Sies, Oxidative Stress, 1991, pxv-xvi). [NIH]... 

Biological Antioxidant Models. Tea extracts, tea polyphenol fractions, and purified catechins have all been shown to be effective antioxidants in biologically-based model systems. A balance between oxidants and antioxidants is critical for maintenance of homeostasis. Imbalances between free radicals and antioxidants may be caused by an increased production of free radicals or decreased effectiveness of the antioxidants within the reaction system. These imbalances can be caused by the radicals overwhelming the antioxidants within the system, or by an excess of antioxidants leading to a prooxidant functionaHty (105—118). When antioxidant defense systems are consistently overwhelmed by oxidative reactions, significant damage can... 

Flavonoids and their metal complexes exhibit a unique redox chemistry, acting both as antioxidants to protect against potential oxidative damage, e.g. in the presence of ROS, and as prooxidant that may result in oxidative damage, depending on the reaction conditions. A fine balance of these two pathways thus determines the characteristic role of this biologically and medicinally important family of natural products. 

All these data allow us to demonstrate red/ox regulation of ionotropic receptors [33], which suggests that antioxidant/prooxidant balance in the cell manages the neurocomputing and learning process. Actually, NMDA receptors are mainly responsible for toxic effect of glutamate when brain blood supply is damaged and overproduction of SAR and NO takes place [34,35],... 

It appears from Figs. 9.5 and 9.6 that there is a huge variation in colour stability between meat from different sources. A range of intrinsic factors influence the oxidative balance in raw meat and thereby the colour stability of the meat (Bertelsen et al., 2000). Thus the oxidative stability of muscles is dependent on the composition, concentrations, and reactivity of (i) oxidation substrates (lipids, protein and pigments), (ii) oxidation catalysts (prooxidants such as transition metals and various enzymes) and (iii) antioxidants, e.g., vitamin E and various enzymes. For review see Bertelsen et al. (2000). 

FIGURE 2. The antioxidant-prooxidant balance. An excess of active oxygen species and transition metals in relation to antioxidants leads to oxidative stress. The converse situation is observed in the presence of relatively high levels of antioxidants. URI = uric acid, VITE = vitamin E. 

All the above contributions are presented as self-contained independent chapters. This has inevitably led to some element of repetition and overlap of content. In my opinion, this contributes positively to the book by providing alternative data, literature, opinions, and interpretations. Many partly answered and unanswered questions remain. Perhaps the most pertinent lie within the context of the antioxidant/prooxidant balance of ascorbic acid within different tissues and disease situations and the detailed understanding of the hydrophilic/hydrophobic interface between water-soluble ascorbic acid and the lipid-soluble antioxidants, vitamins E and A. Thus, the door remains wide open for many future investigations. 

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