Role of Antioxidants in Biological Systems: Mechanisms, Sources and Clinical Implications

Abstract

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are continuously generated in biological systems as inevitable by-products of aerobic metabolism. Although these reactive molecules play important physiological roles in cell signaling and immune defense, their excessive production leads to oxidative stress, a condition characterized by imbalance between pro-oxidants and antioxidant defense systems. Oxidative stress damages essential biomolecules including lipids, proteins, carbohydrates, and nucleic acids, thereby contributing to the pathogenesis of various disorders such as cardiovascular diseases, cancer, diabetes mellitus, neurodegenerative diseases, and reproductive dysfunction. The human body possesses an integrated antioxidant defense system comprising enzymatic antioxidants such as superoxide dismutase, catalase, and glutathione peroxidase, along with non-enzymatic antioxidants including vitamins C and E, carotenoids, flavonoids, glutathione, and uric acid. Dietary antioxidants further support endogenous defense mechanisms. This article reviews the formation of free radicals, classification and mechanisms of antioxidant action, levels of antioxidant defense, sources of antioxidants, clinical significance, and limitations associated with antioxidant therapy. Understanding antioxidant biology is essential for developing preventive and therapeutic strategies against oxidative stress-mediated diseases.