Abstract
The exposure of living organisms to environmental stress triggers defensive responses resulting in the activation of protective processes. Whenever the exposure occurs at low doses, defensive effects overwhelm the adverse effects of the exposure; this adaptive situation is referred to as “hormesis”. Environmental, physical, and nutritional hormetins lead to the stimulation and strengthening of the maintenance and repair systems in cells and tissues. Exercise, heat, and irradiation are examples of physical hormetins, which activate heat shock-, DNA repair-, and anti-oxidative-stress responses. The health promoting effect of many bio-actives in fruits and vegetables can be seen as the effect of mildly toxic compounds triggering this adaptive stimulus. Numerous studies indicate that living organisms possess the ability to adapt to adverse environmental conditions, as exemplified by the fact that DNA damage and gene expression profiling in populations living in the environment with high levels of air pollution do not correspond to the concentrations of pollutants. The molecular mechanisms of the hormetic response include modulation of (a) transcription factor Nrf2 activating the synthesis of glutathione and the subsequent protection of the cell; (b) DNA methylation; and (c) microRNA. These findings provide evidence that hormesis is a toxicological event, occurring at low exposure doses to environmental stressors, having the benefit for the maintenance of a healthy status.
Highlights
Environmental stresses are present for all living beings
Since hormesis appears to be a relatively common phenomenon in many areas, the objective of this review is to explore its occurrence related to low exposure doses to environmental stressors, having the benefit for the maintenance of a healthy status
An interesting example of this mutation strategy is the induction of mutation in aryl hydrocarbon receptor 2 gene (AHR2) in tomcods exposed to polychlorinated biphenyl (PCB) in the Hudson River [36,37]
Summary
Environmental stresses are present for all living beings. The term stress can be used to refer to the organism’s response to a stressful stimulus, or to the consequences of this response [1]. Environmental factors interact with genome and gene transcription modulating the epigenetic machinery [6] This adaptive epigenetic arrangement, starts since the early stages of the development of the organism during pregnancy [7], blows up at the delivery of newborns in terms of oxidative stress targeting the lung [8], proceeds during infancy and adulthood [9], and overwhelms the defensive machinery of the organism during aging [10]. These arrangements are the cumulative result of exposure to low doses and the resulting hormetic reactions [11]. Since hormesis appears to be a relatively common phenomenon in many areas, the objective of this review is to explore its occurrence related to low exposure doses to environmental stressors, having the benefit for the maintenance of a healthy status
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