Lichens of the genus Parmelia: a promising source of antioxidant compounds with pharmacological applications

Parmelia is a genus of foliose lichens belonging to the Parmeliaceae family, distributed worldwide, and includes approximately 300 species. Along with other lichen groups, it reports a highly varied chemical composition with multiple biological activities. A compilation and analysis of recent research on the bioactive compounds present in species of the genus Parmelia and the results of their antioxidant properties were carried out. The characterization of the chemical constituents of 24 species revealed the presence of atranorin, chloratranorin, leucotylin, alectorialic, atraric, baeomycesic, caperatic, diffractaic, divaricatic, evernic, glomelliferic, gyrophoric, isonephrosterinic, isousnic, lecanoric, leucotylic, lichesterinic, nephrosterinic, norstictic, orsellinic, oxyphysodic, protocetraric, protolichesterinic, salazinic, stenosporic, stictic, usnic, 2-hydroxy-4-methoxy-3,6-dimethylbenzoic acids, arabinitol, zeorin, ethyl haematommate, ethyl orsellinate, ethyl-2,4-dihydroxy-6-methylbenzoate, methyl-β-orsellinate, orcinol, β-sitosterol, and α-tocopherol, among others. Extracts prepared with solvents and aqueous extracts from species such as P. sulcata, P. caperata, P. saxatilis, P. omphalodes, P. perlata, P. conspersa, P. arseneana, P. pertusa, P. cirrhatum, P. crinita, and P. erumpens have shown outstanding antioxidant activity in a variety of tests, including DPPH, ABTS, and total phenolic and flavonoid content measurements. The results of these tests indicated moderate-to-high antioxidant activities, depending on the concentration of the extracts used. Likewise, the major isolated compounds from these species showed significant antioxidant activity, which compares favorably with the reference standards used in the research, and in some cases, the results were even superior. In assays with cell lines of human colon carcinoma, the human lung, breast cancer, malignant melanoma, and chronic myelogenous leukemia, some extracts show high cytotoxic effects that are proportional to the concentration of the phenolic content. The genus Parmelia exhibits remarkable chemical diversity, with the presence of secondary metabolites that have demonstrated significant antioxidant properties, supporting its potential use in the prevention and treatment of diseases related to oxidative stress and the development of pharmaceutical products.