Prooxidant

A prooxidant is a substance or condition that promotes oxidation in biological systems, typically by increasing the production of reactive oxygen species (ROS) or by facilitating redox cycling. In living organisms, prooxidants tilt the cellular redox balance toward oxidation and can contribute to oxidative stress when antioxidant defenses are overwhelmed. They may act directly as oxidants or indirectly by catalyzing reactions that generate ROS, such as iron- or copper-catalyzed Fenton chemistry, or by impairing antioxidant systems.

Endogenous prooxidants include metabolic byproducts and enzymes that generate ROS, such as mitochondria during respiration or NADPH oxidases. Exogenous prooxidants include environmental pollutants, ultraviolet radiation, cigarette smoke, certain drugs, and metal ions. Prooxidants can have signaling roles at low levels, participating in redox regulation and cellular adaptation, but at high levels they damage lipids, proteins, and DNA, contributing to aging and disease.

Some agents can act as prooxidants under specific conditions or concentrations. For example, certain antioxidants may exert prooxidant effects in the presence of transition metals or at high doses. Therapeutically, prooxidants are explored to selectively kill cancer cells by overwhelming their antioxidant capacity, but they also pose risks for normal tissues.

Assessment of prooxidant activity involves measuring ROS production or oxidative damage markers and evaluating the balance with antioxidant defenses, including enzymes such as superoxide dismutase, catalase, and glutathione peroxidase, as well as nonenzymatic antioxidants.