Lichens in Pharmacological Action: What Happened in the Last Decade?

Isolation, Chemical Characterization, and Antimicrobial Activity of Secondary Metabolites from Pseudocyphellaria faveolata

INTRODUCTION

Antimicrobial resistance is a global threat, highlighting the urgent need for novel antimicrobial agents. Among the mechanisms of resistance, bacteria can release drug-degrading enzymes and express efflux pumps, as well as grow in protected aggregates known as biofilms. Pseudomonas aeruginosa and Staphylococcus aureus are among the most prevalent biofilm infections in chronic wounds, respiratory and urinary tract infections, and device-associated infections. Pseudocyphellaria faveolata (Delise) Malme is a lichen with metabolites with unexplored antimicrobial potential.

AIMS

To identify and characterize the major metabolites present in Pseudocyphellaria Faveolata and to determine their antimicrobial activity against Staphylococcus aureus and Pseudomonas aeruginosa.

METHODS

The molecules were purified by column chromatography and characterized by NMR spectroscopy. The antimicrobial activity of the compounds was determined in terms of proliferation, adhesion, and viability against P. aeruginosa and S. aureus by the broth microdilution method and crystal violet staining. Viability was determined by the resazurin reduction assay on normal human fibroblasts to determine cytotoxicity over human cells.

RESULTS

The major metabolites were spectroscopically characterized and identified as physciosporin and methyl virensate. Physciosporin showed antimicrobial activity on S. aureus, with a MIC of 32 μg/mL and MBC of 128 μg/mL, and prevented biofilm formation from 16 μg/mL. Methyl virensate also had antimicrobial activity on S. aureus (MIC = 64 μg/mL). None of these metabolites significantly affected P. aeruginosa proliferation, viability, or adhesion. Cytotoxicity of physciosporin at 16 ug/mL on normal human fibroblasts was below 20%.

CONCLUSIONS

This is the first report on the study of the antimicrobial activity of these compounds. Physciosporin showed promising activity in preventing the formation of S. aureus biofilms, which are responsible for chronic infections. These findings provide a foundation for exploring the antimicrobial potential of other lichenic depsidones.

DNA protection, molecular docking, antioxidant, antibacterial, enzyme inhibition, and enzyme kinetic studies for parietin, isolated from Xanthoria parietina (L.) Th. Fr

Parietin was isolated from Xanthoria parietina (L.) Th. Fr.' (methanol:chloroform) extract, using a silica column. 13 C NMR and 1H NMR were used to confirm the structure of the isolated parietin. For the first time, parietin was investigated for its antioxidant, antibacterial and DNA protective activities. Molecular docking was carried out to determine the binding affinity and interactions between the enzymes and our molecule. Inhibition and kinetic mechanism studies for the action of the enzymes were performed too. Parietin exhibited high metal chelating activity. The MIC values of parietin were sufficient to inhibit different bacterial strains; E. coli, P. aeruginosa, K. pneumoniae and S. aureus. Molecular docking applications exhibited that acetylcholinesterase (AChE), butyrylcholinesterase (BChE), lipase, and tyrosinase have high potential for binding with the parietin. Especially, the parietin's highest binding affinity was recorded with AChE and tyrosinase. These results were confirmed by the inhibition and kinetics results, where, parietin observed a potent inhibition with an IC50 values between 0.013-0.003 µM. Moreover, parietin acts' as a non-competitive inhibitor against AChE, BChE, and lipase, and as a competitive inhibitor against tyrosinase with a high rate of inhibition stability. The promising biological properties of parietin revealed its effectiveness in terms of suitability in the food and pharmaceutical industries.Communicated by Ramaswamy H. Sarma.