Oxidative Status and Oxidative Stress: Definitions and Mechanisms

The origin of aerobic life is one of the most fascinating and elusive topics in biology. Multiple lines of evidence build a compelling case for a central role of oxygen in driving the evolution of complex multicellular life. With the transition from a reducing to an oxidising chemistry in the atmosphere and in the oceans, organisms expanded their biochemical and metabolic capacities to use oxygen to generate energy more efficiently. At the same time, organisms have evolved the so-called antioxidant mechanisms to protect themselves against the toxic effects of oxygen derivatives, such as free radicals and non-radical reactive oxygen species. There is now consensus that reactive oxygen species and antioxidants are of profound biological relevance across a wide range of organisms. In this chapter, I have summarised the definitions and fundamentals of oxidative status physiology to provide the basic background information for practitioners of the field. Specifically, I have provided (1) a general historical background and definitions of reactive oxygen species, antioxidants, and oxidative stress and (2) an overview of the main antioxidants that have so far been discovered. Finally, I have examined the circumstances under which oxidative stress can surprisingly increase phenotypic stress resistance or tolerance.