Abstract

Reactive species (RS) are produced in aerobic and anaerobic cells at different concentrations and exposure times, which may trigger diverse responses depending on the cellular antioxidant potential and defensive devices. Study searches were carried out using the PubMed database of the National Library of Medicine-National Institutes of Health. Cellular RS include reactive oxygen (ROS), nitrogen (RNS), lipid (RLS) and electrophilic species that determine either cell homeostasis or dysfunctional bio-molecules. The complexity of redox signalling is associated with the variety of RS pro-duced, the reactivity of the target biomolecules with RS, the multiplicity of the counter-acting processes available, and the exposure time. The continuous distortion in the pro-oxidant/antioxidant balance favoring the former is defined as oxidative stress, whose in-tensity determines (i) the basal not harmful unbalance (oxidative eustress) at RS levels in the pM to nM range that supports physiological processes (e.g., immune function, thyroid function, insulin action) and beneficial responses to external interventions via redox signalling; or (ii) the excessive, toxic distortion (oxidative distress) at RS levels exceed-ing those in the oxidative eustress zone, leading to the unspecific oxidation of bio-molecules and loss of their functions causing cell death with associated pathological states. The cellular redox imbalance is a complex phenomenon whose underlying mechanisms are beginning to be understood, although how RS initiates cell signalling is a mat-ter of debate. Knowledge of this aspect will provide a better understanding of how RS triggers the pathogenesis and progression of the disease and uncover future therapeutic measures. © 2023 Bentham Science Publishers.