Commentary: Ultraviolet radiation triggers "preparation for oxidative stress" antioxidant response in animals: Similarities and interplay with other stressors.

Preparation for oxidative stress (POS), i.e., the upregulation of endogenous antioxidants, is a widespread response of animals exposed to extreme conditions. This response has been described for more than 80 animal species belonging to eight phyla during hypometabolism or situations that limit oxygen availability. The pattern of the typical POS-response, in which a mild redox imbalance triggers antioxidant adjustments that results in increased tolerance to subsequent oxidative insults, roughly follows the curve of hormetic phenomena. A similar pattern has been reported for various animal species exposed to ultraviolet radiation (UVR) - these studies, on animals from six phyla, are discussed herein. In the light of the similarities in the redox-response of animals exposed to either oxygen restriction or UVR, we argue in this essay that UVR elicits a type of response that fits the POS theory. Exposure to UVR induces both reactive species formation and antioxidant adaptation, which is the essence of typical POS-responses. Thus, antioxidant response to UVR in animals can be categorized as a POS-type mechanism. Moreover, considering that animals are exposed to multiple stressors simultaneously in nature, this would represent an ecologically relevant process, by which one stressor (e.g., UV or ionizing radiation) may enhance the tolerance to other. We also discuss a possible role of low doses of ionizing radiation as inductor of POS-like responses in animals.