Antioxidant and cytoprotective potentials of Parmeliaceae lichens and identification of active compounds

Abstract

Lichens, symbiotic organisms with special features, are able to synthesize exclusive secondary metabolites that are attracting increasing interest in their pharmacological activities. Present study aimed to perform an initial screening of the antioxidant capacities of 29 lichens from Parmeliaceae family, and the cytoprotective potential of the most promising species in a model of central nervous system-like cells. Also, another goal was to determine the main chemical constituents of the promising lichens. After molecular identification of all lichen specimens by PCR techniques regarding the molecular marker ITS rDNA, antioxidant activity was measured in terms of free radical scavenging properties through ORAC assay. Methanol extracts of the three species with highest ORAC values (Cetrelia braunsiana (Cb), Parmotrema saccatilobum (Ps) and Usnea ghattensis (Ug)) were analyzed for phytochemical characterization through TLC and HPLC methods. We identified alectoronic acid as major metabolite in Cb, protocetraric acid in Ps and usnic, stictic and constictic acids in Ug. Concerning cytoprotective properties, their extracts were tested on human neuroblastoma cell line SH-SY5Y. Protection against H2O2- induced oxidative stress in such neuron-like model was assessed by cell viability assays, thus determining their optimal concentrations. Then, their effect on oxidative stress markers, such as intracellular ROS formation, glutathione levels and caspase-3 activity, were evaluated. In general, lichens extracts were able to reverse the oxidative damage caused by H2O2, and promoted neurons survival. Results obtained in this study imply that these lichen species might be used as promising sources for natural compounds with potential neuroprotective activity, suggesting future research avenues