Assay of antioxidant capacity of human plasma and CSF in aging and disease.

Oxidative damage to DNA and other macromolecules accumulates with age and has been postulated to be one of the major forms of endogenous damage leading to aging and has been implicated also in initiation of cancer and over a hundred other diseases. The human body has developed an antioxidant (AOX) defense system which contains enzymatic, metal chelating, and free radical scavenging properties. Thus, it is essential to consider the concentration of all AOXs in plasma and CSF when investigating the relationship between diet, oxidative stress, and disease. In the present study a luminometric TRAP-method (total peroxyl radical-trapping potential) was used to determine the activity of all chain breaking AOXs in several clinical states. We have measured TRAP of plasma, cerebrospinal fluid (CSF) and of low density lipoprotein (LDL, TRAPLDL), and the concentrations of main AOX-components (uric acid, protein SH-groups, alpha-tocopherol, ascorbic acid, ubiquinone and the fraction of unknown antioxidants) to study the effect of: 1) aging, 2) acute infection, 3) diabetes, 4) immobilization and 5) cancer. TRAP of CSF is five times lower than of plasma, mainly due to the low urate concentration in CSF. We have observed that plasma antioxidant defenses respond to the basic metabolic rate and the challenges caused by physiological or pathological stress: i) in a healthy normal population TRAP and TRAPLDL change with age and a substantial proportion of TRAP cannot be attributed to any known AOXs thus indicating the existence of unmeasured an unidentified antioxidant(s); ii) during acute infection and immobilization the exogenous AOXs (vitamin C and E) remained unchanged, whereas the activity of unidentified AOXs of plasma declined sharply; iii) in those NIDDM patients with coronary heart disease plasma TRAP is reduced. In conclusion, TRAP has revealed important information for evaluating the AOX status of human plasma, CSF and LDL. According to our studies, important, possibly endogenous AOXs still remain to be identified.