Aging: Is oxidative stress a marker or is it causal?

Rapid developments in free radical biology and molecular technology have pe rmitted exploration of the free radical theory of aging. Oxidative stress h as also been implicated in the pathogenesis of a number of diseases. Studie s have found evidence of oxidative damage to macromolecules (DNA, lipids, p rotein), and data in transgenic Drosophila melanogaster support the hypothe sis that oxidative injury might directly cause the aging process. Additiona l links between oxidative stress and aging focus on mitochondria, leading t o development of the mitochondrial theory of aging. However, despite the nu mber of studies describing the association of markers of oxidative damage w ith advancing age, few, if any definitively link oxidative injury to altere d energy production or cellular function. Although a causal role for oxidat ive stress in the aging process has not been clearly established, this does not preclude attempts to reduce oxidative injury as a means to reduce morb idity and perhaps increase the healthy, useful life span of an individual. This review highlights studies demonstrating enhanced oxidative stress with advancing age and stresses the importance of the balance between oxidants as mediators of disease and important components of signal transduction pat hways.