Exploring the antioxidant and protective effects of usnic acid: Opportunities and challenges

Lichens are symbiotic organisms that produce a variety of secondary metabolites, including the well-known usnic acid (C18H16O7), which has garnered attention for its diverse biological activities and potential applications. Usnic acid, primarily found in lichen species such as Usnea and Cladonia, is a yellowish-green compound with notable antimicrobial, antiviral, and anti-inflammatory properties. Its antioxidant activity is particularly significant, with the ability to neutralize free radicals, inhibit lipid peroxidation, and stabilize cell membranes. Usnic acid, a secondary metabolite found in various lichen species, is recognized for its potent antioxidant properties. Its structure, characterized by a dibenzofuran backbone and phenolic hydroxyl groups, allows it to neutralize free radicals and inhibit lipid peroxidation, protecting cells from oxidative stress. Usnic acid can also chelate metal ions like iron and copper, preventing them from catalyzing reactions that produce harmful reactive oxygen species. This antioxidant capacity is of interest in both pharmaceutical and cosmetic fields. Usnic acid’s ability to reduce oxidative damage makes it a promising ingredient in sunscreens and anti-aging products, where it protects the skin from ultraviolet (UV) radiation and environmental pollutants. Additionally, its potential to modulate antioxidant enzymes like superoxide dismutase (SOD) and catalase may further enhance its protective effects against oxidative stress-related damage, including inflammation and cell aging. Usnic acid effectively neutralizes free radicals, and its ability to prevent lipid peroxidation is comparable to that of vitamin E. However, this may vary depending on specific conditions. Vitamin C is particularly potent against ROS types in aqueous environments, but its ability to directly prevent lipid peroxidation is more limited compared to vitamin E or usnic acid. However, the practical use of usnic acid is limited by its potential hepatotoxicity at high concentrations, particularly in systemic applications. Despite these challenges, usnic acid remains a valuable compound for ongoing research, especially for topical products aimed at combating oxidative stress and protecting against skin damage.