Neuroprotective Activity and Cytotoxic Potential of Two Parmeliaceae Lichens: Identification of Active Compounds

Background: Lichens are symbiotic organisms capable of producing unique secondary metabolites, whose pharmacological activities are attracting much interest.

Purpose: The present study aimed to investigate the in vitro neuroprotective effects and anticancer potential of methanol extracts of two Parmeliaceae lichens: Cetraria islandica and Vulpicida canadensis. The chemical composition of the two lichens was also determined.

Methods: Neuroprotective activity was studied with respect to the antioxidant properties of the extracts; radical scavenging tests (ORAC and DPPH assays) were performed and oxidative stress markers (intracellular ROS production, caspase-3 activity, MDA and glutathione levels) were assessed in a hydrogen peroxide-induced oxidative stress model in astrocytes. Cytotoxic activity was tested against human HepG2 (hepatocellular carcinoma) and MCF-7 (breast adenocarcinoma) cell lines.

Results: Cell viability studies identified a single concentration for each extract that was subsequently used to measure oxidative stress markers. Lichen extracts were able to reverse the oxidative damage caused by hydrogen peroxide, thus promoting astrocyte survival. Both lichen extracts also had anticancer activity in the cell lines, with IC50 values of 19.51-181.05 µg/ml. The extracts had a high total phenolic content, and the main constituents identified by HPLC were fumarprotocetraric acid in Cetraria islandica, and usnic, pinastric and vulpinic acids in Vulpicida canadensis. The biological activities of the lichen extracts can be attributed to these secondary metabolites.

Conclusion: The lichen species studied are promising sources of natural compounds with neuroprotective activity and cytotoxic potential, and warrant further research.