Age-related phospholipid hydroperoxide levels in gerbil brain measured by HPLC-chemiluminescence and their relation to hydroxyl radical stress

Phosphatidylcholine hydroperoxide (PCOOH) was directly quantified in the hippocampus, cortex and striatum from young (3 months), middle-aged (15 months) and old (20 to 24 months) gerbils by an HPLC-chemiluminescence assay. PCOOH levels in hippocampus and cortex were found between 8.05 to 8.58 pmol/mg tissue and no statistically significant difference was found across the age groups. In striatum, however, PCOOH levels were significantly higher in middle-aged and old gerbils compared to those in young animals. The regional comparison showed that PCOOH levels were significantly higher in striatum than in cortex or hippocampus for all the age groups. Moreover, this regional difference increased with aging, from approximately 20% in young animals to 30% and 40% in middle-aged and old gerbil striatum. PCOOH to phospholipid ratio is approximately the same for all age groups at the level of 1.5/10,000, although it is slightly lower in the cortex. The hydroxyl radical levels in the brain were also measured by the formation of its salicylate trapped product 2,3-DHBA and used as a measure of oxidative stress. The PCOOH levels was used as a measure of oxygen radical-induced lipid peroxidative damage. PCOOH as a function of hydroxyl radical stress was calculated and expressed as PHOOH/2,3-DHBA, representing the oxidative damage as a function of the level of oxidative stress. It also implies the tissue susceptibility to oxidative stress and the efficiency of the antioxidant systems. In hippocampus and cortex, the ratios are high in young gerbils, decrease at middle-age and significantly increase in the old. The relatively high ratio in the young animals is proportional to the observation that antioxidants such as vitamin E and ascorbate and antioxidant enzymes such as glutathione peroxidase and phospholipid glutathione peroxidase are lowest (i.e. immature) in young animal brains. As antioxidant levels increase when the animal moves toward middle age, the ratio decreases. The second phase of increase suggests a deterioration of the efficiency of the antioxidant systems in old gerbils. Furthermore, the ratios of oxidative damage to oxidative stress are consistently higher in striatum and hippocampus than in cortex in all age groups, implying a greater susceptibility of these two regions to oxidative stress.