Critical Assessment of the Anti-Inflammatory Potential of Usnic Acid and Its Derivatives-A Review

Inflammation is a response of the organism to an external factor that disrupts its natural homeostasis, and it helps to eliminate the cause of tissue injury. However, sometimes the body's response is highly inadequate and the inflammation may become chronic. Thus, the search for novel anti-inflammatory agents is still needed. One of the groups of natural compounds that attract interest in this context is lichen metabolites, with usnic acid (UA) as the most promising candidate. The compound reveals a broad spectrum of pharmacological properties, among which anti-inflammatory properties have been studied both in vitro and in vivo. The aim of this review was to gather and critically evaluate the results of the so-far published data on the anti-inflammatory properties of UA. Despite some limitations and shortcomings of the studies included in this review, it can be concluded that UA has interesting anti-inflammatory potential. Further research should be directed at the (i) elucidation of the molecular mechanism of UA; (ii) verification of its safety; (iii) comparison of the efficacy and toxicity of UA enantiomers; (iv) design of UA derivatives with improved physicochemical properties and pharmacological activity; and (v) use of certain forms or delivery carriers of UA, especially in its topical application.