It is long known that reactive oxygen species (ROS) are an unavoidable by-product of oxygen metabolism and their cellular concentrations are determined by the balance between their rates of production and their rates of clearance by various antioxidant compounds and enzymes. For a decade or two after the discovery of their presence in biological materials, ROS were thought to cause exclusively toxic effects and were associated with various pathologies. Indeed, when ROS overwhelm the cellular antioxidant defense system, oxidative stress occurs, which results in oxidative damage of nucleic acids, proteins, and lipids. This potentially harmful effect of ROS has been implicated in carcinogenesis, neurodegeneration, atherosclerosis, diabetes, and aging. However, in time the view has been formulated that the presence of ROS in cells indicates that ROS production was evolutionarily selected in order to perform some useful roles.

This view was supported by increasing evidence that while prolonged exposure to high ROS concentrations may lead, through oxidative damage of cellular constituents, to various disorders, low ROS concentrations exert their effects rather through regulation of cell signaling cascades. Indeed, ROS have important functions in cellular signaling as participants and modifiers of signaling pathways, essential for the proper development and proliferation of cells, may have mitogenic effects, and can mimic and amplify the action of growth factors. Moreover, it is apparent that biological specificity of ROS action is achieved through the amount, duration, and localization of ROS production. To date, although major ROS-sensitive signal transduction pathways involved in adaptive responses have been shown, a lot remains to be understood about their mutual interaction and the modifications during ageing and some disease states.

Because of the relevance of such topics, it appears appropriate to summarize some of the main recent advances on ROS production and their harmful and beneficial role in the living organisms, mainly focusing attention on their impact on health, diseases, and ageing.

We invite authors to submit original researches and review articles that seek to refine the aforementioned topics.

Potential topics include but are not limited to the following:

• Positive feedback loop in ROS production
• Interaction among cellular sources of ROS production
• Hormetic effects of ROS
• Oxidative and antioxidative stress
• New insight into the relationship between oxidative stress and ageing
• Role of oxidative stress in neurodegenerative and cardiovascular diseases
• Signaling pathways of ROS action