Antioxidant Enzymes and Fatty Acid Status in Erythrocytes of Down Syndrome Patients (Enzymes and Protein Markers‪)‬

Reactive oxygen (RO) (4) species are substances that are released during oxidative metabolism. RO species include the superoxide anion (OZ-), hydrogen peroxide ([H.sub.2][O.sub.2]), and the hydroxyl radical (O[H.sup.*]) (1). The reactions of RO species with macromolecules can lead to DNA mutations, changes in the structure and function of proteins, and peroxidative damage of cell-membrane lipids (2). There is a primary defense system against oxidative stress, mediated by sequential enzymatic reactions. In the first step of the process, CuZn-superoxide dismutase (SOD1) catalyzes the dismutation of [O.sub.2.sup.-] to [H.sub.2][0.sub.2]. Glutathione peroxidase (GPx) and catalase (CAT) then independently convert [H.sub.2][0.sub.2] to water (3). Any increase in SOD1 catalytic activity, therefore, produces an excess of [H.sub.2][0.sub.2] that must be efficiently neutralized by either GPx or CAT. Otherwise, [H.sub.2][0.sub.2] reacts with [O.sub.2.sup.-], producing O[H.sup.*], which is one of the most active RO species. Thus the activity of the first-step (SOD1) and second-step (GPx, CAT) antioxidant enzymes must be balanced to prevent cell damage. In addition to the antioxidant enzymatic system, some micronutrients act as nonenzymatic antioxidants by scavenging RO species. [alpha]-Tocopherol (vitamin E) is the most important nonenzymatic antioxidant system in the organism (4). Its action occurs mostly in cell membranes by protecting them from lipoperoxidation. An imbalance between the oxidative stress and the cell antioxidant system may produce cell membrane damage by oxidation of its lipid matrix, particularly polyunsaturated fatty acids (PUFAs), which are the main substrates for lipid peroxidation (5).