Exogenous antioxidants

Research on carotenoids and cardiovascular disease (CVD) stems from the discovery that the etiology of this disease involves oxidative processes that may be slowed by exogenous antioxidants. One of the best understood processes contributing to development of CVD is the oxidation of low-density lipoprotein (LDL). When LDL becomes oxidized, it is readily taken up by foam cells in the vascular endothelium where it contributes to the development of atherosclerotic lesion. Enhancement of the oxidative stability of LDL may also prevent other oxidative steps involved in clinical expression of coronary disease (e.g., myocardial infarction) and possibly steps not related to LDL oxidation. There is optimism about the potential role of P-carotene in prevention of CVD... 

Change in the cellular redox environment can lead to several biological effects ranging from altered signal transduction pathways, gene expression, mutagenesis and cell death (apoptosis). Oxidative stress has now been implicated in many diseases such as atherosclerosis, Parkinson s disease, Alzheimer s disease, cancer, etc. For the protection of cells from oxidative stress, supplementation with exogenous antioxidants becomes necessary. 

Tab. 3.25 Substrates acting as scavengers (endogenous and exogenous antioxidants) or adjuvant substances...

G. Perez de Lema, I. Arribas, A. Prieto, T. Parra, G. de Arriba, D. Rodriguez-Puyol, et al.. Cyclosporin a-lnduced Hydrogen Peroxide Synthesis by Cultured Human Mesangial Cells Is Blocked by Exogenous Antioxidants, Life Sci 62 (1998) 1745-53. 

Exogenous antioxidants can preserve the quality of meat products. Radical scavengers appear to be the most effective inhibitors of meat flavor deterioration. However, different substrates and systems respond in different ways. Active ferrous iron may be eliminated physically by chelation with EDTA or phosphates, or chemically by oxidation to its inactive ferric form. 

Cells protect themselves against damage by ROS and other radicals through repair processes, compartmentalization of free radical production, defense enzymes, and endogenous and exogenous antioxidants (free radical scavengers). 

Other than drugs, food is the sole source of exogenous antioxidants. These antioxidants are supplied by plants and food additives. The most active dietary antioxidants contained in plants are phenolic and polyphenolic compounds. The most important among them are tocopherols and tocotrienols (tocols), as well as flavonoids. Tocopherols retard the formation of hydroperoxides, inhibit rearrangement of cis, trans peroxyl radicals to trans, trans isomers (Porter et al., 1995), inhibit peroxide decomposition (Hopia et al., 1996 Makinen and Hopia, 2000), and inhibit the 3-scission of alkoxyl radicals (Frankel, 1998). The ability of tocopherols to inhibit the formation of hydroperoxides decreases in the order a-tocopherol > y-tocopherol > 5-tocopherol at a low initial level of addition (100 ppm), a reverse order of activity being revealed when the initial... 

The antioxidant theory is supported by results which show that some typical diseases of the elderly (Alzheimer s disease, cancer, diabetes, cardiovascular disorders) are often accompanied by the appearance of some markers of oxidative damage. However, the causal relationship is still unclear, so there is no way to tell cause from effect. The next paragraphs will surmnarize the main proven and assumed benefits of exogenous antioxidant intake. 

Juranek, I., D. Nikitovic, D. Kouretas et al., 2013. Biological importance of reactive oxygen species in relation to dif culties of treating pathologies involving oxidative stress by exogenous antioxidants. 

Thus, antioxidants in food and biological systems play an important role in neutralizing radicals, hence extending the shelf-life of food and preventing diseases in humans. While in many systems endogenous antioxidants can deliver a desired effect, in others, use of exogenous antioxidants is necessary. 

Antioxidants are substances which possess the ability to protect the body from damage caused by oxidative stress (Souri et al. 2008). The body has several mechanisms to counteract oxidative stress by producing antioxidants, either naturally generated in situ (endogenous antioxidants) or externally supplied through foods (exogenous antioxidants) (Fig. 4.3). 

Fig. 4.3 Endogenous antioxidants and exogenous antioxidants for protecting the body from damage caused by oxidative stress...

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