Reactive oxygen species (ROS)

Reactive oxygen species (ROS) are a group of highly reactive molecules derived from molecular oxygen that contain at least one unpaired electron[1][5]. This group includes both radical forms—such as superoxide anion (O2^-), hydroxyl radical (OH•), hydroperoxyl radical—and non-radical forms like hydrogen peroxide (H2O2) and singlet oxygen[1][5]. ROS are produced endogenously during normal aerobic metabolism in mitochondria, peroxisomes, the endoplasmic reticulum, plasma membrane oxidases such as NADPH oxidases, and during immune responses by phagocytes[3][5]. They also arise from exogenous sources including UV radiation, pollution, toxins, drugs, or ionizing radiation. At physiological concentrations ("stationary" levels), ROS play crucial roles in cell signaling, regulation of gene expression via redox-sensitive transcription factors like NRF2/KEAP1 system or FoxO family members[2], apoptosis induction/removal of damaged cells ("programmed cell death"), muscle contraction regulation, vascular tone control,[5] antimicrobial defense mechanisms,[8] stem cell maintenance/differentiation,[2] tissue regeneration,[2] aging processes,[6], among others. However—when their production exceeds the capacity of antioxidant systems—they cause "oxidative stress," leading to irreversible damage to proteins (aggregation/denaturation), lipids (peroxidation), carbohydrates/modification of nucleotides/DNA mutations.[1][3][5] This underlies their involvement in numerous pathologies including cancer progression/inflammation/cardiovascular/neurodegenerative/metabolic diseases.[3] Is this considered a therapeutic target? No; reactive oxygen species themselves are not a single molecular target but rather a chemical category describing multiple related molecules. While many therapies aim to modulate overall ROS levels or effects through antioxidants or enzyme inhibitors/activators involved in their generation/scavenging pathways—for example targeting NADPH oxidase—the term "reactive oxygen species" does not refer to a specific receptor/enzyme/transporter/protein suitable for direct drug binding.[1] Is there something wrong with this target? Yes; "Reactive oxygen species" is not an individual molecule/receptor/protein but rather a collective term describing several chemically related entities. It is therefore *not* considered an actionable therapeutic target in the conventional sense used for drug discovery databases—it lacks specificity required for structured pharmacological targeting.[1] In summary: Reactive oxygen species refers collectively to various highly reactive molecules containing oxygen that play dual roles—as essential mediators/regulators at low concentrations but damaging agents when uncontrolled—in biological systems. They do not constitute a single canonical druggable target but represent important contributors/modulators within many disease processes due to their central role in redox biology[1][3][5].

Other names

Oxygen radicalsFree radicals (when referring to oxygen-containing)ROSOxygen free radicals

Drugs targeting ROS generally act by scavenging free radicals, enhancing endogenous antioxidant defenses, or inhibiting enzymes responsible for excessive ROS production.