Aging, free radicals, and reactive oxygen species: An evolving concept

Abstract

Aging is a natural process, guided by the physiology of the organism and resulting in its demise at a certain point of time. Since eternity, human beings are searching for the elixirs for long healthy life. Although each organism has its own median life span, genetic, nutritional, and environmental factors may affect it substantially. In early 1950s, a young gerontologist Denham Harman first suggested the deleterious role of free radicals in aging and age-related diseases. Over the years, his “Free radical theory of aging” had undergone extensive scrutiny, argument, and controversies due to newer and newer findings either supporting it or contradicting it. For the past almost 70 years, researchers have used tools of genetics, molecular biology, cell biology, biochemistry etc. to either prove it or disprove it. In the process, our understanding of the role of free radicals and reactive oxygen species in biology has also undergone a paradigm shift, especially in the past 25 years. From noxious molecules, it has now emerged as the mediator of physiological signals, particularly when produced intracellularly at a lower level. This review summarizes the major findings in this field since its inception with an emphasis on the modern concept of redox signaling in the aging process and associated diseases.