Antioxidants are crucial for neutralizing free radicals and preventing oxidative stress, which can damage DNA, proteins, and lipids. Free radicals, such as superoxide anion (O₂⁻), hydroxyl radical (·OH), and peroxynitrite (ONOO⁻), are produced during cellular metabolism and can cause significant cellular damage. Antioxidants can directly scavenge these radicals or indirectly by inhibiting the activity of free radical-generating enzymes or enhancing the activity of intracellular antioxidant enzymes like superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX). The chemical and cell-free biological systems are important tools for studying the mechanisms of antioxidants. Antioxidants can be natural or synthetic, with natural sources including fruits, vegetables, spices, and herbs. They contain various compounds such as phenolics, flavonoids, carotenoids, and thiols. These antioxidants help protect cells from oxidative stress and reduce the risk of chronic diseases. Synthetic antioxidants, such as tert-butylhydroxyl-toluene, are used in the food industry but are not preferred for pharmacologic use due to toxicological concerns. Antioxidants can be evaluated using various methods, including DPPH and ABTS radical scavenging assays, which measure their ability to neutralize free radicals. These assays are widely used in biological systems such as cell cultures, animal models, and clinical trials. The scavenging of superoxide and other ROS is a key area of research, with methods like the NBT reduction assay and lucigenin luminescence being used to detect and measure superoxide levels. The scavenging of hydroxyl radicals and other ROS is also important, with methods such as the Gutteridge method and spin-trapping agents like DMPO being used to assess antioxidant activity. Stable radical scavenging is another area of research, with DPPH, ABTS, and DMPD radicals being used as probes. These methods help determine the antioxidant capacity of various compounds. Metal ion chelating is another important function of antioxidants, particularly in preventing oxidative stress caused by transition metals like iron and copper. Antioxidants can chelate these ions, reducing their activity and thus decreasing the formation of ROS. Studies have shown that compounds like curcumin, capsaicin, and S-allylcysteine have significant metal-chelating abilities. Inhibition of free radical-generating enzymes such as NADPH oxidase and xanthine oxidase is also a key area of research. These enzymes are major sources of ROS and their inhibition can help reduce oxidative stress. Natural antioxidants like polyphenols and coumarins have shown potential in inhibiting these enzymes. Activation of internal antioxidant enzymes is another important mechanism by which antioxidants protect cells. Enzymes such as SOD, CAT, GPX, and GRd play crucial roles in neutralizing ROS andAntioxidants are crucial for neutralizing free radicals and preventing oxidative stress, which can damage DNA, proteins, and lipids. Free radicals, such as superoxide anion (O₂⁻), hydroxyl radical (·OH), and peroxynitrite (ONOO⁻), are produced during cellular metabolism and can cause significant cellular damage. Antioxidants can directly scavenge these radicals or indirectly by inhibiting the activity of free radical-generating enzymes or enhancing the activity of intracellular antioxidant enzymes like superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX). The chemical and cell-free biological systems are important tools for studying the mechanisms of antioxidants. Antioxidants can be natural or synthetic, with natural sources including fruits, vegetables, spices, and herbs. They contain various compounds such as phenolics, flavonoids, carotenoids, and thiols. These antioxidants help protect cells from oxidative stress and reduce the risk of chronic diseases. Synthetic antioxidants, such as tert-butylhydroxyl-toluene, are used in the food industry but are not preferred for pharmacologic use due to toxicological concerns. Antioxidants can be evaluated using various methods, including DPPH and ABTS radical scavenging assays, which measure their ability to neutralize free radicals. These assays are widely used in biological systems such as cell cultures, animal models, and clinical trials. The scavenging of superoxide and other ROS is a key area of research, with methods like the NBT reduction assay and lucigenin luminescence being used to detect and measure superoxide levels. The scavenging of hydroxyl radicals and other ROS is also important, with methods such as the Gutteridge method and spin-trapping agents like DMPO being used to assess antioxidant activity. Stable radical scavenging is another area of research, with DPPH, ABTS, and DMPD radicals being used as probes. These methods help determine the antioxidant capacity of various compounds. Metal ion chelating is another important function of antioxidants, particularly in preventing oxidative stress caused by transition metals like iron and copper. Antioxidants can chelate these ions, reducing their activity and thus decreasing the formation of ROS. Studies have shown that compounds like curcumin, capsaicin, and S-allylcysteine have significant metal-chelating abilities. Inhibition of free radical-generating enzymes such as NADPH oxidase and xanthine oxidase is also a key area of research. These enzymes are major sources of ROS and their inhibition can help reduce oxidative stress. Natural antioxidants like polyphenols and coumarins have shown potential in inhibiting these enzymes. Activation of internal antioxidant enzymes is another important mechanism by which antioxidants protect cells. Enzymes such as SOD, CAT, GPX, and GRd play crucial roles in neutralizing ROS and