Studying the biological activities of Roccella tinctoria DC. lichen and its main phenolic compounds

Lichens are fascinating organisms resulting from the symbiotic association between a fungus (mycobiont, usually an ascomycete) and an alga or cyanobacterium (photobiont) [1]. The genus Roccella boasts over 20 species of fruticose lichens, which contain a rich pool of phytochemicals, including depsides, monoaromatic phenols, and aliphatic acids and have been found to possess promising bioactivities, including antimicrobial, antifungal and antiproliferative ones, making them potential sources of new bioactive compounds for pharmacological purposes. Based on this evidence, present study was aimed at characterizing the phytochemical composition and bioactivities of Roccella tinctoria DC., a common species in Italy, known for its use as a source of purple dye [2]. To this end, two extracts, namely DF3 and DF4, from the thallus of R. tinctoria, obtained through a Soxhlet extraction with solvents of increasing polarity, and maceration with methanol, were used. The extracts underwent spectrophotometric, chromatographic and NMR analysis in order to characterize and purify the characteristic polyphenols, in particular erythrin, methyl orsellinate and montagnetol. Moreover, a screening of bioactivities, including radical scavenging, chelating and reducing activities, as well as cytotoxicity in diverse human cancerous and noncancerous cell lines from airway (i.e. bronchial epithelial BEAS-2B and lung cancer A549 cells) and biliary tract (i.e. H9 cholangiocytes and Mz-CHA-1 cholangiocarcinoma cells), and cytoprotection against oxidative damage induced by tert-butyl hydroperoxide (tBOOH), were performed [3]. The cytoprotective effects of both extracts and pure compounds were measured in terms of cell viability and intracellular oxidative stress. DF3 was found to contain higher levels of tannins and polyphenols than DF4, with methyl orsellinate predominant in DF3 while erythrin in DF4. Both extracts were able to scavenge both DPPH and ABTS radicals and to chelate both ferrous and ferric ions, while the pure compounds were exhibited only scavenging properties towards ABTS radical, suggesting a possible contribution in the extract. Neither extracts nor the pure compounds possessed ferric reducing activity. In the cytotoxicity assay, the extracts showed a dose-dependent cytotoxicity in A549 and Mz-CHA-1 cancer cells, with DF4 being more potent than DF3, with a less toxicity profile in noncancerous cells, while the isolated compounds, especially erythrin, showed an opposite trend. At nontoxic concentrations, the tested samples, especially DF3 and DF4 extracts, were able to affect the oxidative damage induced by tBOOH in all the cell models, by restoring cell viability in a concentration-dependent manner and reducing the intracellular ROS levels. In non-cancerous cells, DF4 was slightly more potent than DF3 and its cytoprotection was similar to positive control. A mixture of pure compounds showed a stronger cytoprotection than DF4, thus suggesting the presence of antagonistic or interfering compounds in the whole extracts. These findings are consistent with the results of antioxidant activity assays and encourage future studies to clarify the interest in R. tinctoria as a possible source of nutraceuticals. References [1] Shukla et al. Phytochem. Rev. 2010, 9, 303-314. [2] Duong et al. VNUHCM J. Nat. Sci. 2018, 2. [3] Frezza et al. Pharmaceutics, 16(3), 331.