In Vitro Screening for Antioxidant Activity

The protective “tone” of a tissue against oxidative stress depends on a balance between endogenous antioxidants (enzymatic and non-enzymatic) and the amount of pro-oxidant reactive oxygen lipid peroxides (1 –3 ). Lipid and cholesterol peroxides are transported in lipoproteins (primarily low-density lipoproteins [LDL]) and these pre-existing peroxides make LDL highly susceptible for propagation reactions (4 ,5 ). Lipid peroxidation is thought to be an important signalling event in triggering pathophysiological change (6 ). Increased levels of these compounds may respond to α-tocopherol, glutathione (GSH), phytonutrients like carotenoids and flavonoids, ascorbate, coenzyme Q10 (ubiquinone), N-acetylcysteine, transresveratol in red wine, and lipoic acid, which have been studied extensively as dietary supplements to improve antioxidant reserve and thereby help regulate oxidative stress (7 –17 ). Interest in synthetic compounds with radical scavenging activity and those obtained from plant/herbal sources is growing rapidly. Some examples are the nonhormonal, nonglucocorticoid 21-aminosteroids (18 ), sulfonylurea (19 ), enzyme replacement with high molecular weight (MW) polyethylene-superoxide dismutase (SOD) conjugates (20 ), enzyme mimics such as Ebselen that have glutathione peroxidase (GSHPx) and scavenging activity (2 ,21 ), as well as Manganese-based porphyrin and cyclopentane SOD mimetics (22 ,23 ) and GSH mimics (24 ,25 ). Another novel approach is to induce gene expression of antioxidant enzymes by cytokine activation of nuclear factors (26 ).