Photochemiluminescent detection of antiradical activity. VI. Antioxidant characteristics of human blood plasma, low density lipoprotein, serum albumin and amino acids during in vitro oxidation

During investigation of the mechanism of therapeutic efficacy of UV (254 nm )-irradiated autologous blood, the antioxidant capacity (AC) of plasma, ser um albumin, 20 amino acids, uric acid, ascorbic acid and cc-tocopherol was measured after irradiation in vitro. AC of plasma demonstrated a biphasic t ime course (decrease to in a minimum (greater zero) followed by an increase ). AC of uric acid, ascorbic acid and a-tocopherol diminished under irradia tion to zero. In contrast, albumin and seven amino acids developed AC follo wing irradiation. During the Cu+2-induced oxidation of low-density lipoprot ein (LDL), the AC measured in a system for water-soluble substances appeare d, after a lag-phase, to be comparable to that of the conjugated diene form ation; AC of LDL measured in a system for lipid-soluble substances demonstr ated a biphasic course. Our results suggest that: (a) the oxidized products of some amino acids and proteins acquire antiradical properties at the sam e time that they are being produced; (b) the biphasic character of changes of antioxidant properties of blood plasma during UV irradiation represents the overlapping of two processes: disappearing of antioxidants and acquisit ion of AC by (lipo)proteins; and (c) the measurement of AC of blood plasma (lipo)proteins can possibly serve to detect the existence and extence of ox idative stress in human organism. Copyright (C) 1999 John Wiley & Sons, Ltd .