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

Hepatoprotective potentials of Usnea longissima Ach. and Xanthoparmelia somloensis (Gyelnik) Hale extracts in ethanol-induced liver injury

In our study, the antioxidant and anti-inflammatory effects of different lichen applications were investigated in rats using an experimental ethanol toxicity model. 48 rats were used in the study and they were divided into 6 groups with 8 rats in each group. These groups were: control, ethanol (2 g/kg), ethanol + Usnea longissima Ach. (200 mg/kg), ethanol + Usnea longissima Ach. (400 mg/kg), ethanol + Xanthoparmelia somloensis (Gyelnik) Hale (100 mg/kg) and ethanol + Xanthoparmelia somloensis (Gyelnik) Hale (200 mg/kg). The experimental work continued for 21 days. Lichen extracts and ethanol were administered by gavage to rats divided into groups. According to the experimental protocol, the experimental animals were sacrificed and their liver tissues were isolated. Biochemical parameters in serum, histological examinations, oxidative stress and inflammation parameters both at biochemical and molecular level in liver tissues were performed. Oxidative stress and inflammatory response were increased in the liver tissue of rats treated with ethanol for 21 days, and liver functions were impaired. It was found that U. longissima and X. somloensis extracts showed good antioxidant activity and conferred protective effects against ethanol-induced oxidative stress and inflammation. This could be attributed to the presence of secondary metabolites in the extract, which act as natural antioxidants and could be responsible for increasing the defence mechanisms against free radical production induced by ethanol administration.

Antibacterial mechanism of the methanol extract of Thamnolia subuliformis (Ehrh.) W. Culb against Staphylococcus aureus

Thamnolia subuliformis (Ehrh.) W. Culb is a species of lichen with edible and medicinal applications in China. Our previous studies demonstrated that the methanol extract of Thamnolia subuliformis (METS) exhibits broad antibacterial activity and stability against foodborne pathogens. This study aimed to investigate the antibacterial mechanism of METS against Staphylococcus aureus using nontargeted metabolomics, focusing on cell wall and membrane damage. The results revealed that the minimum inhibitory concentration (MIC) was 0.625 mg ml-1 and that METS had good biosafety at this concentration. METS caused significant damage to the cell wall and membrane integrity, based on both morphological observation by electron microscopy and the leakage of alkaline phosphatase, protein, and nucleic acid in the cell cultures. Treatment with METS at the MIC disrupted the lipid metabolism of S. aureus, causing a decrease in the metabolism of various phospholipids and sphingolipids in the cell membrane and an increase in the ratio of saturated fatty acids to unsaturated fatty acids. Moreover, it influenced intracellular amino acid and energy metabolism. These results shed light on the antibacterial mechanism of METS against S. aureus while also serving as a reference for the further development of natural antibacterial compounds derived from Thamnolia subuliformis.

Chemical composition and antioxidant, enzyme inhibition and cytoprotective activity of two Antarctic lichens of the genus Psoroma (Pannariaceae)

Lichens contain different types of chemical compounds with multiple biological activities that demonstrate their potential pharmacological use. This research aims to report the metabolomic identification of the ethanolic extracts of P. antarcticum and P. hypnorum, their antioxidant, enzyme inhibitory, and their cytoprotection activity. Sixteen metabolites were identified in P. antarcticum and twelve in P. hypnorum; the extracts reported variable antioxidant activity with IC50 >350 µg/mL in DPPH·, values >18 µmol Trolox/g in ORAC and >40 µmol Trolox/g in FRAP and a phenolic compound content >10 mg GAE/g, as well as significant results in cholinesterases, α-glucosidase, pancreatic lipase, α-amylase, and tyrosinase enzyme inhibition activities with IC50 ranging from 18 to 510 µg/mL, and which were complemented by molecular docking experiments. Both extracts showed improved cytoprotection at the concentrations of 0.5 to 1.0 μg/mL. This study contributes to the knowledge of the chemical diversity of Antarctic lichen extracts and their effectiveness in the evaluation of biological activities related to neurodegenerative diseases and metabolic syndrome.

Lichen pectin-containing polysaccharide from Xanthoria elegans and its ability to effectively protect LX-2 cells from H2O2-induced oxidative damage

Xanthoria elegans, a drought-tolerant lichen, is the original plant of the traditional Chinese medicine "Shihua" and effectively treats a variety of liver diseases. However, thus far, the hepatoprotective effects of polysaccharides, the most important chemical constituents of X. elegans, have not been determined. The aim of this study was to screen the polysaccharide fraction for hepatoprotective activity by using free radical scavenging assays and a H2O2-induced Lieming Xu-2 cell (LX-2) oxidative damage model and to elucidate the chemical composition of the bioactive polysaccharide fraction. In the present study, three polysaccharide fractions (XEP-50, XEP-70 and XEP-90) were obtained from X. elegans by hot-water extraction, DEAE-cellulose anion exchange chromatography separation and ethanol gradient precipitation. Among the three polysaccharide fractions, XEP-70 exhibited the best antioxidant activity in free radical scavenging capacity and reducing power assays. Structural studies showed that XEP-70 was a pectin-containing heteropolysaccharide fraction that was composed mainly of (1 → 4)-linked and (1 → 4,6)-linked α-D-Glcp, (1 → 4)-linked α-D-GalpA, (1 → 2)-linked, (1 → 6)-linked and (1 → 2,6)-linked α-D-Manp, and (1 → 6)-linked and (1 → 2,6)-linked β-D-Galf. Furthermore, XEP-70 exhibited effectively protect LX-2 cells against H2O2-induced oxidative damage by enhancing cellular antioxidant capacity by activating the Nrf2/Keap1/ARE signaling pathway. Thus, XEP-70 has good potential to protect hepatic stellate cells against oxidative damage.

Pleiotropic Potential of Evernia prunastri Extracts and Their Main Compounds Evernic Acid and Atranorin: In Vitro and In Silico Studies

Evernia prunastri is a lichen widely distributed in the Northern Hemisphere. Its biological properties still need to be discovered. Therefore, our paper focuses on studies of E. prunastri extracts, including its main metabolites evernic acid (EA) or atranorin (ATR). Phytochemical profiles using chromatographic analysis were confirmed. The antioxidant activity was evaluated using in vitro chemical tests and in vitro enzymatic cells-free tests, namely superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione reductase (GR), and catalase (CAT). The anti-inflammatory potential using cyclooxygenase-2 (COX-2) and hyaluronidase were determined. The neuroprotective potential using acetylcholinesterase, (AChE), butyrylcholinesterase (BChE), and tyrosinase (Tyr) was estimated. The hypoglycemic activity was also confirmed (α-glucosidase). Principal component analysis was performed to determine the relationship between the biological activity of extracts. The inhibitory effect of EA and ATR on COX-2 AChE, BChE, Tyr, and α-glucosidase was evaluated using molecular docking techniques and confirmed for EA and ATR (besides α-glucosidase). The penetration of EA and ATR from extracts through the blood-brain barrier was confirmed using the parallel artificial membrane permeability assay blood-brain barrier test. In conclusion, depending on chemical surroundings and the concentration, the E. prunastri extracts, EA or ATR, showed attractive pleiotropic properties, which should be further investigated.

Salazinic Acid and Norlobaridone from the Lichen Hypotrachyna cirrhata: Antioxidant Activity, α-Glucosidase Inhibitory and Molecular Docking Studies

The present study was intended for the identification of secondary metabolites in acetone extract of the lichen Hypotrachyna cirrhata using UPLC-ESI-QToF-MS/MS and the detection of bioactive compounds. This study led to the identification of 22 metabolites based on their MS/MS spectra, accurate molecular masses, molecular formula from a comparison of the literature database (DNP), and fragmentation patterns. In addition, potent antioxidant and α-glucosidase inhibitory potentials of acetone extract of H. cirrhata motivated us to isolate 10 metabolites, which were characterized as salazinic acid (11), norlobaridone (12), atranorin (13), lecanoric acid (14), lichesterinic acid (15), protolichesterinic acid (16), methyl hematommate (17), iso-rhizonic acid (18), atranol (19), and methylatratate (20) based on their spectral data. All these isolates were assessed for their free radicals scavenging, radical-induced DNA damage, and intestinal α-glucosidase inhibitory activities. The results indicated that norlobaridone (12), lecanoric acid (14), methyl hematommate (17), and atranol (19) showed potent antioxidant activity, while depsidones (salazinic acid (11), norlobaridone (12)) and a monophenolic compound (iso-rhizonic acid, (18)) displayed significant intestinal α-glucosidase inhibitory activities (p < 0.001), which is comparable to standard acarbose. These results were further correlated with molecular docking studies, which indicated that the alkyl chain of norlobaridione (12) is hooked into the finger-like cavity of the allosteric pocket; moreover, it also established Van der Waals interactions with hydrophobic residues of the allosteric pocket. Thus, the potency of norlobaridone to inhibit α-glucosidase enzyme might be associated with its allosteric binding. Also, MM-GBSA (Molecular Mechanics-Generalized Born Surface Area) binding free energies of salazinic acid (11) and norlobaridone (12) were superior to acarbose and may have contributed to their high activity compared to acarbose.

Antioxidant and antidiabetic activity and phytoconstituents of lichen extracts with temperate and polar distribution

The objective of this research was to characterize the chemical composition of ethanolic extracts of the lichen species Placopsis contortuplicata, Ochrolechia frigida, and Umbilicaria antarctica, their antioxidant activity, and enzymatic inhibition through in vitro and molecular docking analysis. In total phenol content, FRAP, ORAC, and DPPH assays, the extracts showed significant antioxidant activity, and in in vitro assays for the inhibition of pancreatic lipase, α-glucosidase, and α-amylase enzymes, together with in silico studies for the prediction of pharmacokinetic properties, toxicity risks, and intermolecular interactions of compounds, the extracts evidenced inhibitory potential. A total of 13 compounds were identified by UHPLC-ESI-QTOF-MS in P. contortuplicata, 18 compounds in O. frigida, and 12 compounds in U. antarctica. This study contributes to the knowledge of the pool of bioactive compounds present in lichens of temperate and polar distribution and biological characteristics that increase interest in the discovery of natural products that offer alternatives for treatment studies of diseases related to oxidative stress and metabolic syndrome.

Lichen-Derived Diffractaic Acid Inhibited Dengue Virus Replication in a Cell-Based System

Dengue is a mosquito-borne flavivirus that causes 21,000 deaths annually. Depsides and depsidones of lichens have previously been reported to be antimicrobials. In this study, our objective was to identify lichen-derived depsides and depsidones as dengue virus inhibitors. The 18 depsides and depsidones of Usnea baileyi, Usnea aciculifera, Parmotrema dilatatum, and Parmotrema tsavoense were tested against dengue virus serotype 2. Two depsides and one depsidone inhibited dengue virus serotype 2 without any apparent cytotoxicity. Diffractaic acid, barbatic acid, and Parmosidone C were three active compounds further characterized for their efficacies (EC₅₀), cytotoxicities (CC₅₀), and selectivity index (SI; CC₅₀/EC₅₀). Their EC₅₀ (SI) values were 2.43 ± 0.19 (20.59), 0.91 ± 0.15 (13.33), and 17.42 ± 3.21 (8.95) μM, respectively. Diffractaic acid showed the highest selectivity index, and similar efficacies were also found in dengue serotypes 1-4, Zika, and chikungunya viruses. Cell-based studies revealed that the target was mainly in the late stage with replication and the formation of infectious particles. This report highlights that a lichen-derived diffractaic acid could become a mosquito-borne antiviral lead as its selectivity indices ranged from 8.07 to 20.59 with a proposed target at viral replication.

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).