Antibacterial potencial of 12 Lichen species

In Vitro and in Silico Studies of Lichen Compounds Atranorin and Salazinic Acid as Potential Antioxidant, Antibacterial and Anticancer Agents

Lichens are symbiotic organisms made up of alga/cyanobacterium and fungus. We investigated antioxidant, antibacterial and anticancer properties of two lichen compounds, atranorin and salazinic acid, and five lichen species: Heterodermia boryi, Heterodermia diademata, Heterodermia hypocaesia, Parmotrema reticulatum, and Stereocaulon foliolosum. Free radical scavenging, Ferric reducing potential, Nitric oxide scavenging, and Trolox equivalent capacity were used to measure antioxidant activity. Strong radical scavenging action was demonstrated by atranorin and salazinic acid, with IC50 values of 39.31 μM and 12.14 μM, respectively. The Minimum Inhibitory Concentration (MIC) assay based on resazurin, was used to measure antibacterial activity. Parmotrema reticulatum demonstrated significant antibacterial activity against Raoultella planticola with MIC of 7.8 μg/mL. Cytotoxicity assay on breast cancer cell line was used to assess anticancer activity. To further understand the binding locations on the target proteins Er (Estrogen Receptor alpha), EGFR (Epidermal Growth Factor Receptor), mTOR (Mammalian Target of Rapamycin), and PgR (Progesterone Receptor), molecular docking experiments were conducted. Docking study showed that the binding energies of atranorin and salazinic acid with mTOR were -5.31 kcal/mol and -3.43 kcal/mol, respectively. The results suggest that atranorin has the potential to be a multitargeted molecule with natural antioxidant, antibacterial, and anticancer properties.

Lichen Depsides and Tridepsides: Progress in Pharmacological Approaches

Depsides and tridepsides are secondary metabolites found in lichens. In the last 10 years, there has been a growing interest in the pharmacological activity of these compounds. This review aims to discuss the research findings related to the biological effects and mechanisms of action of lichen depsides and tridepsides. The most studied compound is atranorin, followed by gyrophoric acid, diffractaic acid, and lecanoric acid. Antioxidant, cytotoxic, and antimicrobial activities are among the most investigated activities, mainly in in vitro studies, with occasional in silico and in vivo studies. Clinical trials have not been conducted using depsides and tridepsides. Therefore, future research should focus on conducting more in vivo work and clinical trials, as well as on evaluating the other activities. Moreover, despite the significant increase in research work on the pharmacology of depsides and tridepsides, there are many of these compounds which have yet to be investigated (e.g., hiascic acid, lassalic acid, ovoic acid, crustinic acid, and hypothamnolic acid).

Lichens: An update on their ethnopharmacological uses and potential as sources of drug leads

ETHNOPHARMACOLOGICAL RELEVANCE

Lichens, a unique symbiotic association between an alga/cyanobacterium and a fungus, produce secondary metabolites that are a promising source of novel drug leads. The beauty and importance of lichens have not been adequately explored despite their manifold biological activities such as anticancer, antimicrobial, antioxidant, anti-inflammatory, analgesic, antipyretic and antiparasitic.

AIM OF THE STUDY

The present review collates and discusses the available knowledge on secondary metabolites and biological activities of lichens (in vitro and in vivo).

MATERIALS AND METHODS

Using relevant keywords (lichens, secondary metabolites, bioactivity, pharmacological activities), five electronic databases, namely ScienceDirect, PubMed, Google Scholar, Scopus and Recent Literature on Lichens, were searched for past and current scientific contributions up until May 2022. Literature focusing broadly on the bioactivity of lichens including their secondary metabolites were identified and summarized.

RESULTS

A total of 50 review articles and 189 research articles were searched. Information related to antioxidant, antimicrobial, anti-inflammatory, anticancer and insecticidal activities of 90 lichen species (from 13 families) and 12 isolated metabolites are reported. Over 90% of the studies comprised in vitro investigations, such as bioassays evaluating radical scavenging properties, lipid peroxidation inhibition and reducing power, cytotoxicity and antimicrobial bioassays of lichen species and constituents. In vivo studies were scarce and available only in fish and rats. Most of the studies were done by research groups in Brazil, France, Serbia, India and Turkey. There were relatively few reports from Asia and Africa despite the ubiquitous nature of lichens and the high occurrence in these continents.

CONCLUSION

Secondary metabolites from lichens are worthy of further investigation in terms of their potential therapeutic applicability, including better understanding of their mechanism(s) of action. This would be of great importance in the search for novel drugs.