Handbook of Vitamin C Research

16Kelsey H. Fisher-Wellman and Richard J. Bloomerprevention of free radical mediated damage. Elimination of circulating levels of freetransition metals is accomplished via various iron and copper transport proteins, such astransferrin, ceruloplasmin, and albumin. Binding of transition metals to their respectivetransport protein inhibits their ability to initiate lipid peroxidation, inhibit certain antioxidants(vitamin C), or lead to the formation of hydroxyl radical (by way of the Fenton reaction; [15].Moreover, transferrin iron-binding capacity in plasma is three times greater than the amountof iron needing to be transported [15], thereby further illustrating the critical importance oftransition metal sequestration in the prevention/ attenuation of oxidative damage in vivo.Nutritional AntioxidantsBecause exogenous compounds contribute to the antioxidant capacity of the system,dietary habits and/or antioxidant supplementation may have the ability to decrease anindividual‘s susceptibility to oxidative damage. As such, various antioxidant supplementssuch as vitamins, carotenoids, carnitine, alpha lipoic acid, coenzyme Q10, and polyphenols[21], as well as the dietary consumption of high amounts of antioxidant-rich foods [85] havebeen shown to decrease an individual‘s susceptibility to oxidative damage. Furthermore,other nutrients such as certain essential fatty acids and/or plant sterols have been shown topossess antioxidant and anti-inflammatory properties [86].VitaminsVitamins C and E are among the most commonly researched antioxidant supplementsand have both been shown to exhibit antioxidant properties when administered independently[87,88] and/or in combination [87]. Carotenoids, such as the vitamin A precursor betacarotene,have also been shown to attenuate oxidative stress when administered alone [89],and in conjunction with vitamins C and E [90]. Vitamins E and C play a key role as chainbreaking antioxidants during lipid peroxidation, acting in both the lipid and aqueous phase,respectively. Moreover, the vitamins are often supplemented simultaneously based on theknown role of vitamin C in regenerating vitamin E in vivo during lipid peroxidation [21]. Asvitamin C is the primary focus of this chapter, particular attention will be given to its use asan antioxidant supplement in a later section in relation to studies involving exercise-inducedoxidative stress and tissue injuryPharmacological AntioxidantsIn addition to the nutritional antioxidants listed above, certain pharmacological agentssuch as thiazolinediones, statins, angiotensin converting enzyme inhibitors (ACE-inhibitors),and agiotensin I receptor blockers have also been shown to possess antioxidant properties invivo [91].