Antioxidant Activity of Medicinal Plants: Phytochemical Profiling, Molecular Redox Mechanisms, Experimental Models, and Clinical Evidence Review

Oxidative stress is a fundamental pathological mechanism implicated in the progression of chronic diseases including cancer, cardiovascular disorders, diabetes mellitus, neurodegeneration, hepatic injury and inflammatory syndromes. Excessive production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) leads to lipid peroxidation, DNA damage, protein oxidation, mitochondrial dysfunction and activation of pro-inflammatory cascades. Medicinal plants represent a rich reservoir of natural antioxidants including flavonoids, phenolic acids, tannins, alkaloids, terpenoids and saponins. Numerous plant extracts and isolated phytoconstituents have demonstrated potent antioxidant activity in in vitro assays such as DPPH, ABTS, FRAP, ORAC, nitric oxide scavenging and superoxide inhibition, as well as in vivo models involving CCl₄, paracetamol, streptozotocin and ischemia-reperfusion injury. This review systematically compiles mechanistic insights, phytochemical classes, experimental antioxidant models and clinical evidence of major medicinal plants with validated antioxidant potential. Particular emphasis is placed on molecular signaling pathways including Nrf2/Keap1/ARE, NF-κB, MAPK, PI3K/Akt and mitochondrial redox regulation. Despite robust preclinical evidence, challenges remain in extract standardization, pharmacokinetic profiling and large-scale clinical validation. Future research should focus on translational approaches integrating phytochemistry, nanotechnology-based delivery systems, and controlled clinical trials to establish plant-derived antioxidants in modern therapeutics.