MARKERS OF PROTEIN OXIDATION BY HYDROXYL RADICAL AND REACTIVE NITROGEN SPECIES IN TISSUES OF AGING RATS

Many lines of evidence implicate oxidative damage in aging. Possible p athways include reactions that modify aromatic amino acid residues on proteins. o-Tyrosine is a stable marker for oxidation of protein-bound phenylalanine by hydroxyl radical, whereas 3-nitrotyrosine is a marke r for oxidation of protein-bound tyrosine by reactive nitrogen species . To test the hypothesis that proteins damaged by hydroxyl radical and reactive nitrogen accumulate with aging, we used isotope dilution gas chromatography-mass spectrometry to measure levels of o-tyrosine and 3-nitrotyrosine in heart, skeletal muscle, and liver from young adult (9 mo) and old (24 mo) female Long-Evans/Wistar hybrid rats. We also m easured these markers in young adult and old rats that received antiox idant supplements (alpha-tocopherol, beta-carotene, butylated hydroxyt oluene, and ascorbic acid) from the age of 5 mo. We found that aging d id not significantly increase levels of protein-bound o-tyrosine or 3- nitrotyrosine in any of the tissues. Antioxidant supplementation had n o effect on the levels of protein-bound o-tyrosine and 3-nitrotyrosine in either young or old animals. These observations indicate that the o-tyrosine and 3-nitrotyrosine do not increase significantly in heart, skeletal muscle, and liver in old rats, suggesting that proteins dama ged by hydroxyl radical and reactive nitrogen species do not accumulat e in these tissues with advancing age.