Phytochemicals as Multi-Target Therapeutic Agents for Oxidative Stress-Driven Pathologies: Mechanisms, Synergies, and Clinical Prospects

Plants have long served as a cornerstone for drug discovery, offering a vast repertoire of bioactive compounds with proven efficacy in combating oxidative stress, a pivotal driver of chronic diseases such as cancer, diabetes, cardiovascular disorders, and neurodegenerative conditions. This review synthesizes current knowledge on plant-derived antioxidants, emphasizing their mechanisms, therapeutic potential, and quantitative efficacy validated through standardized assays. Key phytochemicals, including polyphenols, carotenoids, flavonoids, and terpenoids, neutralize reactive oxygen species (ROS) through radical scavenging, enzyme modulation, and gene regulation. For instance, lutein, a carotenoid found in leafy greens, demonstrates potent antioxidant activity with IC50 values of 1.75 μg/mL against hydroxyl radicals and 2.2 μg/mL in lipid peroxidation inhibition, underscoring its role in mitigating cardiovascular and ocular diseases. Similarly, quercetin, a ubiquitous flavonoid in onions and berries, exhibits remarkable ROS-scavenging capacity, with IC50 values of 0.55 μg/mL, 2,2-Diphenyl-1-picrylhydrazyl (DPPH) and 1.17 μg/mL, 2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), supporting its use in reducing inflammation and neurodegeneration. The therapeutic promise of these compounds extends to disease-specific applications. Limonoids from citrus fruits, such as limonin (IC50: 15–31 μg/mL), enhance Phase II detoxification enzymes, offering protection against chemical carcinogens. Sulforaphane, a glucosinolate derived from cruciferous vegetables, shows potent anticancer activity with an IC50 of 85.66 mg in DPPH radical scavenging, while β-sitosterol (IC50: 1.43–2.42 mM) inhibits tumor proliferation and cholesterol synthesis. Synergistic interactions further amplify their efficacy: phytoestrogens like genistein (IC50: 13.00 ppm) and terpenoids such as α-pinene (IC50: 12.57 mg/mL) collectively enhance anti-inflammatory and antimicrobial responses, illustrating the multi-targeted nature of plant-based therapies. Beyond disease prevention, these compounds address age-related decline. Ascorbic acid (vitamin C), with an IC50 of 11.81 μg/mL for antioxidant activity, mitigates skin aging and accelerates wound healing, while selenium nanoparticles (IC50: 0.437 μg/mL) bolster immune function and reduce chemotherapy-induced toxicity. Dietary fibers, exemplified by sugar beet fibers (IC50: 52.32 μg/mL for DPPH scavenging), further contribute to cardiovascular health by lowering Low-Density Lipoprotein (LDL) cholesterol. This review not only catalogs the antioxidant prowess of phytochemicals but also highlights their translational potential. Advances in nanotechnology, such as nano-formulated curcumin, have overcome bioavailability challenges, enhancing clinical applicability. By integrating quantitative metrics (e.g., IC50, radical scavenging rates) with mechanistic insights, this work bridges the gap between traditional knowledge and modern pharmacology.