DNA oxidative damage in birds: measuring, analyzing and comparing
Aging is a universal process of intrinsic and progressive physical deterioration that occurs over the lifetime of almost all animals. The free radical theory of aging predicts that cellular damage caused by reactive oxygen species (ROS) should accumulate as animals age, and the rate of accumulation in part determines the rate of aging. It is a challenging analytical problem to estimate the actual in vivo levels of oxidative damage in DNA due to the high level of artifactual DNA oxidative damage introduced during DNA extraction. We devised FPG / Gel electrophoresis method by conducting a sodium iodine method of DNA extract, adding deferoximine mesylate to all reaction buffers and running all reactions in an argon environment, to estimate DNA oxidative damage adduct, 8-oxo-7,8-dehydro-2'-deoxyguanosine (oxo8dG), accurately and efficiently. Age-related increase in level of 8oxodG has been observed in some mammals and related to their Maximal Lifespan Potential (MLSP). Since birds have high rates of metabolism (implying higher rates of production of reactive oxygen species, or ROS), yet surprisingly long lifespans, they promise to have greater defenses against oxidative damage and/or increased capabilities for damage repair than do mammals. DNA 8oxodG levels have been measured in very few bird species and have not been related to birds' ages. We measured nuclear DNA 8oxodG level in four bird species, zebra finches (Taeniopygia guttata), tree swallows (Tachycineta bicolor), common terns (Sterna hirundo) and Leach's storm-petrels (Oceanodroma leucorhoa), with different maximal lifespans from 5 to 36 years. We found that DNA 8oxodG level increases significantly with age in muscle (p=0.002) and brain tissues (p=0.01) in zebra finches. The same trend was not found in muscle tissues from the other three species, instead we found that old birds tended to have a lower DNA 8oxodG level than middle-aged birds of the same species, which may be due to elimination of low-fitness individuals from the population due to the high extrinsic mortality rate from their environment.