Antifungal activity of lichen compounds against dermatophytes: a review

A spectrophotometric analysis of extracted water-soluble phenolic metabolites of lichens

MAIN CONCLUSION

Rainwater most probably constitutes a relatively effective solvent for lichen substances in nature which have the potential to provide for human and environmental needs in the future. The aims were (i) to test the hypothesis on the potential solubility of lichen phenolic compounds using rainwater under conditions that partly reflect the natural environment and (ii) to propose new and effective methods for the water extraction of lichen substances. The results of spectrophotometric analyses of total phenolic metabolites in rainwater-based extracts from epigeic and epiphytic lichens, employing the Folin-Ciocalteu (F.-C.) method, are presented. The water solvent was tested at three pH levels: natural, 3, and 9. Extraction methods were undertaken from two perspectives: the partial imitation of natural environmental conditions and the potential use of extraction for economic purposes. From an ecological perspective, room-temperature water extraction ('cold' method) was used for 10-, 60-, and 120-min extraction periods. A variant of water extraction at analogous time intervals was an 'insolation' with a 100W light bulb to simulate the heat energy of the sun. For economic purposes, the water extraction method used the Soxhlet apparatus and its modified version, the 'tea-extraction' method ('hot' ones). The results showed that those extractions without an external heat source were almost ineffective, but insolation over 60- and 120-min periods proved to be more effective. Both tested 'hot' methods also proved to be effective, especially the 'tea-extraction' one. Generally, an increase in the concentration of phenolic compounds in water extracts resulted from an increasing solvent pH. The results show the probable involvement of lichen substances in biogeochemical processes in nature and their promising use for a variety of human necessities.

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.

Lichen Depsidones with Biological Interest

Depsidones are some of the most abundant secondary metabolites produced by lichens. These compounds have aroused great pharmacological interest due to their activities as antioxidants, antimicrobial, and cytotoxic agents. Hence, this paper aims to provide up-to-date knowledge including an overview of the potential biological interest of lichen depsidones. So far, the most studied depsidones are fumarprotocetraric acid, lobaric acid, norstictic acid, physodic acid, salazinic acid, and stictic acid. Their pharmacological activities have been mainly investigated in in vitro studies and, to a lesser extent, in in vivo studies. No clinical trials have been performed yet. Depsidones are promising cytotoxic agents that act against different cell lines of animal and human origin. Moreover, these compounds have shown antimicrobial activity against both Gram-positive and Gram-negative bacteria and fungi, mainly Candida spp. Furthermore, depsidones have antioxidant properties as revealed in oxidative stress in vitro and in vivo models. Future research should be focused on further investigating the mechanism of action of depsidones and in evaluating new potential actions as well as other depsidones that have not been studied yet from a pharmacological perspective. Likewise, more in vivo studies are prerequisite, and clinical trials for the most promising depsidones are encouraged.

A review of the potential of lichen substances as antifungal agents: the effects of extracts and lichen secondary metabolites on Fusarium fungi

The present meta-analysis provides literature data on the effect of lichen extracts and single secondary metabolites used against Fusarium spp. moulds. Lichen extracts were obtained from 51 corticolous, 17 terricolous and 18 saxicolous lichen species and 37 secondary compounds were tested against eight fungal species, i.e., Fusarium acuminatum, F. avenaceum, F. culmorum, F. fujikuroi, F. oxysporum, F. roseum, F. solani and F. udum. The researchers used several test methods, mostly to determine MIC and IZ. Extracts were obtained using several solvents, mainly organic ones with use of the Soxhlet apparatus. The most frequently tested species was F. oxysporum, against which lichen substances from Alectoria sarmentosa, Cladonia mitis, C. rangiferina, Flavoparmelia caperata, Hypotrachyna cirrhata, Leucodermia leucomelos, Parmotrema austrosinense, P. reticulatum, Physcia aipolia, Pseudevernia furfuracea, Roccella montagnei and Umbilicaria nylanderiana and secondary metabolites such as 2-hydroxy-4-methoxy-3,6-dimethylbenzoic acid, atranorin, lecanoric and (+)-usnic acids showed the highest antifungal potential. These agencies could compete with the potential of fungicides, such as flucytosine and fluconazole. Other species have been poorly investigated. Statistical analysis of literature data showed that the fungistatic potential of lichen extracts is significantly different from individual secondary metabolites. Similarly, the potential of secondary metabolites often differs significantly from that of non-lichen substances. This meta-analysis indicates the potential of lichen substances as future anti-fusarial agents.

UHPLC-MS Metabolomic Fingerprinting, Antioxidant, and Enzyme Inhibition Activities of Himantormia lugubris from Antarctica

Himantormia lugubris is a Chilean native small lichen shrub growing in the Antarctica region. In this study, the metabolite fingerprinting and the antioxidant and enzyme inhibitory potential from this species and its four major isolated compounds were investigated for the first time. Using ultra-high performance liquid chromatography coupled to quadrupole-Orbitrap mass spectrometry analysis (UHPLC-Q-Orbitrap-MS), several metabolites were identified including specific compounds as chemotaxonomical markers, while major metabolites were quantified in this species. A good inhibition activity against cholinesterase (acetylcholinesterase (AChE) IC₅₀: 12.38 ± 0.09 µg/mL, butyrylcholinesterase (BChE) IC₅₀: 31.54 ± 0.20 µg/mL) and tyrosinase (22.32 ± 0.21 µg/mL) enzymes of the alcoholic extract and the main compounds (IC₅₀: 28.82 ± 0.10 µg/mL, 36.43 ± 0.08 µg/mL, and 7.25 ± 0.18 µg/mL, respectively, for the most active phenolic atranol) was found. The extract showed a total phenolic content of 47.4 + 0.0 mg of gallic acid equivalents/g. In addition, antioxidant activity was assessed using bleaching of DPPH and ORAC (IC₅₀: 75.3 ± 0.02 µg/mL and 32.7 ± 0.7 μmol Trolox/g lichen, respectively) and FRAP (27.8 ± 0.0 μmol Trolox equivalent/g) experiments. The findings suggest that H. lugubris is a rich source of bioactive compounds with potentiality in the prevention of neurodegenerative or noncommunicable chronic diseases.

In vitro antifungal activity of heterocyclic organoboron compounds against Trichophyton mentagrophytes and Microsporum canis obtained from clinical isolates

The aim of this study was to investigate the in vitro activity of thirty-eight heterocyclic organoboron compounds (1a-o, 2a-j, 3a-m) against clinically isolated dermatophytes Trichophyton mentagrophytes and Microsporum canis. Minimum inhibitory concentrations (MICs) of compounds (1a-o, 2a-j, 3a-m) were determined according to published protocol Clinical and Laboratory Standards Institute (CLSI) M38-A2 broth microdilution method. The minimum fungicidal concentrations (MFCs) for both T. mentagrophytes and M. canis were found by subculturing each fungal suspension on potato dextrose agar. According to the results, heterocyclic organoboron compounds (1a-o, 2a-j, 3a-m) were found to be more effective against dermatophyte M. canis (MIC = 3.12-25 µg/ml) than T. mentagrophytes (MIC = 12.5-100 µg/ml). Our findings showed that 7-membered heterocyclic organoboron compounds (3a-m) (MIC = 12.5-50 µg/ml) have stronger in vitro antifungal activity against T. mentagrophytes than 5-membered heterocyclic organoboron compounds (1a-o, 2a-j) (MIC = 25-100 µg/ml). The MFC values for all compounds ranged from 6.25 to 200 µg/ml. The limited number of systemic antifungal agents used in the treatment of dermatophyte infections and the presence of side effects have led to the search for new treatment resources in recent years. Therefore, investigation of the effect of heterocyclic organoboron compounds against dermatophytes will be promising for the discovery of new antifungal compounds that have gained great importance today.

The effect of lichen secondary metabolites on Aspergillus fungi

A systematic review of literature data on the antifungal potential of extracted lichen compounds and individual secondary metabolites against mold species of the genus Aspergillus is provided. Crude extracts from 49 epiphytic, 16 epigeic and 22 epilithic species of lichens and 44 secondary metabolites against 10 species, Aspergillus candidus, A. flavus, A. fumigatus, A. nidulans, A. niger, A. ochraceus, A. parasiticus, A. restrictus, A. stellatus and A. ustus, were analysed. Several measuring techniques were employed for such analyses. Lichen substances were extracted with alcoholic and other organic solvents mainly using the Soxhlet apparatus. Among the three most-studied mold species, the results showed that the crude extracts from the thalli of the lichens Cladonia foliacea, Hypotrachyna cirrhata, Leucodermia leucomelos, Platismatia glauca and Pseudevernia furfuracea against Aspergillus flavus, from C. foliacea, Nephroma arcticum and Parmelia sulcata against A. fumigatus and from Evernia prunastri, Hypogymnia physodes, Umbilicaria cylindrica and Variospora dolomiticola against A. niger have the greatest antifungal potential. The lichen secondary metabolites showed a higher inhibitory potential, e.g. protolichesterinic acid against A. flavus, lecanoric acid against A. fumigatus and orsellinic acid against A. niger; the other seven species of Aspergillus have been poorly studied and require further investigation. A comparison of the inhibitory potential of the tested mixtures of lichen substances and their secondary metabolites shows that they can compete with commonly used antifungal substances, such as ketoconazole and clotrimazole against A. flavus, A. nidulans, A. niger and A. parasiticus and fluconazole in the case of A. fumigatus.

Cytogenetic and oxidative effects of three lichen extracts on human peripheral lymphocytes

In the present study, we investigated cytogenetic and oxidative [total antioxidant capacity (TAC), total oxidant status (TOS)] effects of methanol and water extracts of Cladonia chlorophaea (Flörke ex Sommerf.) Sprengel, Dermatocarpon miniatum (L.) W.Mann and Parmelia saxatilis (L.) Ach. on cultured human lymphocytes. In addition, different phenolic compounds in the extracts were quantified by high performance liquid chromatography (HPLC) analysis. As a result of HPLC analysis, methanol extracts of all lichen species tested had higher phenolic compounds. Likewise, methanol extracts of each lichen increased TAC levels in lymphocytes more than water extracts. The TOS levels of the cells treated with different concentrations (1-100 mg/L) of the extracts decreased due to the increasing concentration of the extracts. Genotoxicity experiments revealed that the tested lichen extracts did not significantly increase (p > 0.05) the level of genotoxicity on human peripheral lymphocyte culture compared to the negative control group. The results showed that C. chlorophaea, D. miniatum and P. saxatilis lichens, which were found to be a rich source of phenolic compounds, might be of interest in the pharmaceutical and food industries.

Antimicrobial and Antiproliferative Activities of Depside Compound Isolated from the Mycobiont Culture of Parmotrema austrosinense (Zahlbr.) Hale

Substances which are normally secondary metabolites in a lichen are known to possess various medicinal properties but little is known about the biological activities of compounds present in these mycobiont culture extract. The objectives of the present study were isolation and optimization of growth conditions of the mycelia from Parmotrema austrosinense and assess the antiproliferative and antimicrobial activities of acetone extracts. The extraction of bioactive compound from mycobiont culture was achieved by using acetone and standard Soxhlet extraction procedures. The culture extract was subjected to silica gel column chromatography and detection of compound in thin layer chromatography. HPLC, UV vis, IR spectra, microcrystallization and NMR were done for the purified compound. The antimicrobial activity in the extracts were assayed using the standard disc diffusion and broth microdilution protocol against microbial strains. The lecanoric acid in the extracts was purified and MTT method was applied to assess antiproliferative activity against DLA cancer cells. The culture extract containing lecanoric acid exhibited antimicrobial activity against the test strains with the Minimum Inhibitory Concentrations varied between 0.83±0.28 and 2.3±1.5 mg mL−1. The lecanoric acid inhibited the growth of DLA cancer cells with inhibitory concentration (IC50) of about 42±1.5 µg mL−1. Conclusion: The result of the present study suggests that this compound might possess potent antitumor property and should be further analysed using appropriate animal model and clinical trials.

Review: Usnic acid-induced hepatotoxicity and cell death

Increasing prevalence of herbal and dietary supplement-induced hepatotoxicity has been reported worldwide. Usnic acid (UA) is a well-known hepatotoxin derived from lichens. Since 2000, more than 20 incident reports have been received by the US Food and Drug Administration after intake of UA containing dietary supplement resulting in severe complications. Scientists and clinicians have been studying the cause, prevention and treatment of UA-induced hepatotoxicity. It is now known that UA decouples oxidative phosphorylation, induces adenosine triphosphate (ATP) depletion, decreases glutathione (GSH), and induces oxidative stress markedly leading to lipid peroxidation and organelle stress. In addition, experimental rat liver tissues have shown massive vacuolization associated with cellular swellings. Additionally, various signaling pathways, such as c-JNK N-terminal kinase (JNK), store-operated calcium entry, nuclear erythroid 2-related factor 2 (Nrf2), and protein kinase B/mammalian target of rapamycin (Akt/mTOR) pathways are stimulated by UA causing beneficial or harmful effects. Nevertheless, there are controversial issues, such as UA-induced inflammatory or anti-inflammatory responses, cytochrome P450 detoxifying UA into non-toxic or transforming UA into reactive metabolites, and unknown mechanism of the formation of vacuolization and membrane pore. This article focused on the previous and latest comprehensive putative mechanistic findings of UA-induced hepatotoxicity and cell death. New insights on controversial issues and future perspectives are also discussed and summarized.

The fruticose genera in the Ramalinaceae (Ascomycota, Lecanoromycetes): their diversity and evolutionary history

We present phylogenetic analyses of the fruticose Ramalinaceae based on extensive collections from many parts of the world, with a special focus on the Vizcaíno deserts in north-western Mexico and the coastal desert in Namibia. We generate a four-locus DNA sequence dataset for accessions of Ramalina and two additional loci for Niebla and Vermilacinia. Four genera are strongly supported: the subcosmopolitan Ramalina, the new genus Namibialina endemic to SW Africa, and a duo formed by Niebla and Vermilacinia, endemic to the New World except the sorediate V. zebrina that disjunctly occurs in Namibia. The latter three genera are restricted to coastal desert and chaparral where vegetation depends on moisture from ocean fog. Ramalina is subcosmopolitan and much more diverse in its ecology. We show that Ramalina and its sister genus Namibialina diverged from each other at c. 48 Myrs, whereas Vermilacinia and Niebla split at c. 30 Myrs. The phylogeny of the fruticose genera remains unresolved to their ancestral crustose genera. Species delimitation within Namibialina and Ramalina is rather straightforward. The phylogeny and taxonomy of Vermilacinia are fully resolved, except for the two youngest clades of corticolous taxa, and support current taxonomy, including four new taxa described here. Secondary metabolite variation in Niebla generally coincides with major clades which are comprised of species complexes with still unresolved phylogenetic relationships. A micro-endemism pattern of allopatric species is strongly suspected for both genera, except for the corticolous taxa within Vermilacinia. Both Niebla and saxicolous Vermilacinia have chemotypes unique to species clades that are largely endemic to the Vizcaíno deserts. The following new taxa are described: Namibialina gen. nov. with N. melanothrix (comb. nov.) as type species, a single new species of Ramalina (R. krogiae) and four new species of Vermilacinia (V. breviloba, V. lacunosa, V. pustulata and V. reticulata). The new combination V. granulans is introduced. Two epithets are re-introduced for European Ramalina species: R. crispans (= R. peruviana auct. eur.) and R. rosacea (= R. bourgeana auct. p.p). A lectotype is designated for Vermilacinia procera. A key to saxicolous species of Vermilacinia is presented.

Is Usnic Acid a Promising Radical Scavenger?

Usnic acid (UA) is a natural product found in the lichen genera. Because of the phenolic groups in its structure, UA is suspected to be an antioxidant. Therefore, in this study, the radical scavenging of UA was investigated in physiological environments in silico by using kinetic calculations. It was found that the overall rate constant for the hydroxyl radical scavenging activity was approximately 10⁹ M^-1 s^-1 in all environments, whereas the HOO^• and CH₃OO^• radical scavenging activities were only significant in the polar environments with k in the range of 10³-10⁴ M^-1 s^-1. The results also revealed that the HO^• scavenging activity followed the single electron transfer (SET) and radical adduct formation mechanisms; however, the SET pathway (for the dianion HU^2-) played a dominant role in the scavenging of other studied radicals, including CH₃O^•, CCl₃O^•, CCl₃OO^•, NO₂, SO₄ ^•-, and N₃ ^•. The activity of UA against these radicals was as high as that of typical phenolic acids such as ferulic acid, p-coumaric acid, caffeic acid, dihydrocaffeic acid, and sinapinic acid (k _f ∼ 10⁸ M^-1 s^-1) in polar solvents. Thus, UA is a promising natural antioxidant in aqueous environments.

Biodeterioration Patterns and Their Interpretation for Potential Applications to Stone Conservation: A Hypothesis from Allelopathic Inhibitory Effects of Lichens on the Caestia Pyramid (Rome)

The colonisation of stone by different organisms often leaves biodeterioration patterns (BPs) on the surfaces even if their presence is no longer detectable. Peculiar weathering patterns on monuments and rocks, such as pitting phenomena, were recognised as a source of information on past colonisers and environmental conditions. The evident inhibition areas for new bio-patinas observed on the marble blocks of the Caestia Pyramid in Rome, recognisable as tracks of previous colonisations, seem a source for developing new natural products suitable for restoration activities. To hypothesise past occurring communities and species, which gave rise to such BPs, we carried out both in situ observations and analyses of the rich historical available iconography (mainly photographs). Moreover, we analysed literature on the lichen species colonising carbonate stones used in Roman sites. Considering morphology, biochemical properties and historical data on 90 lichen species already reported in Latium archaeological sites, we suppose lichen species belonging to the genus Circinaria (Aspicilia s.l.) to be the main aetiological agent of such peculiar BPs. These results seem relevant to highlight the long-lasting allelopathic properties of some lichen substances potentially applicable as a natural product to control colonisation, improving the environmental and economical sustainability of stone restoration.