A comprehensive review on secondary metabolites and health-promoting effects of edible lichen

Enhanced accumulation of biologically active compounds in lichens with potential functional food applications

Lichens have great potential as food, functional food additives or flavourings. The presence of specific substances with multiple biological activities is one of the characteristics of lichens. However, research on lichens as a food source or functional food additive is limited. The present study simulated, for the first time, the potential bioaccessibility of active compounds from 6 lichen species in simulated gastric and intestinal conditions. An in vitro digestion showed that the lichen substances had different bioaccessibility and stability during digestion. It was found that the application of some metabolic modulators significantly altered the accumulation of metabolites in most species. In addition, the study demonstrated the antimicrobial activity of the tested extracts as well as of 14 isolated lichen metabolites. These multi-directional studies demonstrate the potential of lichens in terms of their use as antimicrobial functional food additives.

Usnic acid alleviates testicular ischemia/reperfusion injury in rats by modulating endoplasmic reticulum stress

Testicular torsion (TT) is a urological condition that can result in infertility in men. The etiopathogenesis of TT includes ischemia/reperfusion injury (IRI) characterized by oxidative stress (OS), inflammation and apoptosis resulting from increased levels of free radicals. Usnic acid (UA), a dibenzofuran, is one of the most common metabolites found in lichens and is known to possess powerful antioxidant properties. The aim of this study was to investigate the potential protective activity of UA in an experimental testicular IRI model for the first time. A total of 18 rats were randomly assigned to three groups (n=6): sham control, IRI and IRI+UA. The IRI groups underwent a four-hour period of ischemia and a two-hour period of reperfusion. The OS, inflammation, endoplasmic reticulum stress (ERS) and apoptosis markers in testicular tissue were evaluated using colorimetric methods. Furthermore, tissue samples were subjected to histological examination, with staining using hematoxylin and eosin. Histopathological findings supported by increased OS, inflammation, ERS and apoptosis levels were obtained in IRI group compared with sham control group. However, UA treatment restored these pathological and biochemical changes. Although this study provides the first preliminary evidence that UA may be used as a useful molecule against testicular IRI, further extensive molecular preclinical studies should be performed before clinical use is considered.

Surfactant-mediated bio-manufacture: A unique strategy for promoting microbial biochemicals production

Biochemicals are widely used in the medicine and food industries and are more efficient and safer than synthetic chemicals. The amphipathic surfactants can interact with the microorganisms and embed the extracellular metabolites, which induce microbial metabolites secretion and biosynthesis, performing an attractive prospect of promoting the biochemical production. However, the commonness and differences of surfactant-mediated bio-manufacture in various fields are largely unexplored. Accordingly, this review comprehensively summarized the properties of surfactants, different application scenarios of surfactant-meditated bio-manufacture, and the mechanism of surfactants increasing metabolites production. Various biochemical productions such as pigments, amino acids, and alcohols could be enhanced using the cloud point and the micelles of surfactants. Besides, the amphiphilicity of surfactants also promoted the utilization of fermentation substrates, especially lignocellulose and waste sludge, by microorganisms, indirectly increasing the metabolites production. The increase in target metabolites production was attributed to the surfactants changing the permeability and composition of the cell membrane, hence improving the secretion ability of microorganisms. Moreover, surfactants could regulate the energy metabolism, the redox state and metabolic flow in microorganisms, which induced target metabolites synthesis. This review aimed to broaden the application fields of surfactants and provide novel insights into the production of microbial biochemicals.

Determination of phytochemical contents by LC/QTOF/MS and evaluation of in-vitro biological activities of 2 Peltigera lichens from Bursa

Lichens are symbiotic associations of algae and fungi. They are edible as food and have been used in traditional medicine for years. It is aimed to screen Peltigera praetextata (Flörke ex Sommerf.) Zopfand and Peltigera elisabethae Gyeln. phytochemically by LC/QTOF/MS and according to the constituents to evaluate the antioxidant, tyrosinase inhibitory, and antibacterial activities. In total 54 of metabolites detected by LC/QTOF/MS were common in both species. According to LC/QTOF/MS scanning results, alkaloids, iridoid glycosides, phenolics, cyanogenetic glycosides, and terpenic structures were detected. DPPH, ABTS, superoxide radical scavenging activities, and metal chelating capacity IC50 values were 84.55, 9.349; 51.27, 9.127; 95.01, 58.65 and 20.57, 70.08 µg/mL., respectively. The CUPRAC reducing power was determined as 4.69 and 9.57 TEACCUPRAC, respectively. Tyrosinase inhibitor activity were found to be 86.95 and 196.7 µg/mL. Both lichens did not show antimicrobial effects. As a result of the antioxidant and tyrosinase inhibitor activities it was seen that their activities were significant and further in vivo studies could be carried out on this lichens.

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.

Liquid chromatography-electrospray ionization-mass spectrometry/mass spectrometry characterization of depsides and depsidones from the Chilean lichen Parmotrema perlatum

Lichens are recognized by their unique compounds and diverse applications in food, medicines, and cosmetics. Using ultra-high pressure liquid chromatography, coupled with a high-resolution mass spectrometer, metabolomic profiling of the lichen Parmotrema perlatum, from a methanolic extract, was performed. Based on characteristic fragmentation patterns, twenty-five lichenic substances were tentatively identified including 5 depsides, 12 depsidones, 2 diphenyl ethers, 1 aromatic considered as possible artifact, 1 dibenzofuran, 1 carbohydrate, 1 organic acid, and 2 undefined compounds. To the best of our knowledge, this is a more complete report of their phytochemistry from P perlatum. Our findings of the P perlatum profile may contribute and complement the current data of the Parmotrema genus.

Syringic acid alleviates cisplatin-induced ovarian injury through modulating endoplasmic reticulum stress, inflammation and Nrf2 pathway

BACKGROUND

Reproductive toxicity is one of the most important side effects of cisplatin (CIS) and leading to discontinuation of treatment. Syringic acid (SA) is a phenolic acid whose industrial use has increased in recent years due to its antioxidant properties. Recent reports highlight the importance of the supressed Nrf2 pathway in the molecular pathogenesis of CIS toxicity. Therefore, this study aimed to evaluate the therapeutic effect of SA on CIS-induced ovotoxicity through the Nrf2 pathway for the first time.

MATERIAL AND METHODS

Thirty female rats were divided into 5 groups: control, CIS, CIS+SA (5 and 10 mg/kg) and only SA (per se, 10 mg/kg). CIS was administered intraperitoneally at a dose of 5 mg/kg on the 1st day, injections of SA followed by three consecutive days in the rats. Serum anti-mullerian hormone (AMH) levels and ovarian oxidative stress (OS), inflammation, endoplasmic reticulum stress (ERS), apoptosis and Nrf2 pathway markers were determined colorimetrically. Histopathological examinations of the ovaries with hematoxylin and eosin staining were also used to evaluate CIS-induced ovotoxicity.

RESULTS

The CIS treatment depleted serum AMH levels, caused histopathological findings and increased OS, inflammation, ERS and apoptosis levels in ovarian tissue. However, treatments with SA significantly ameliorated CIS-induced biochemical and histopathological changes by activating Nrf2 pathway.

CONCLUSION

The promising adjuvant potential of SA to alleviate CIS-related ovarian damage should be supported by more comprehensive studies.

Evernia prunastri lichen as a source of bioactive glucans with potential for topical applications

Microwave hydrothermal treatment was selected to extract valuable fractions with bioactive and gelling properties from Evernia prunastri lichen with potential for topical applications. The impact of the extraction processing conditions on the soluble extracts, mucilage fraction and residual solid phase was analyzed within a lichen global valorization approach. A particular stress was made on the thermo-rheological and structural characteristics of the extracted glucan and galactomannan polymers, the corresponding gelled matrices, and their cosmetic feasibility. Results revealed that the proposed microwave-assisted treatment showed a relevant influence on the phytochemical features of the aqueous soluble extracts, accounting the major protein content at 120 °C and the enhanced antioxidant and anti-tyrosinase properties at 140 °C. Extracts at 200 °C showed the highest anti-inflammatory (COX-1 and COX-2 inhibition) efficacies. The biopolymer analyses indicated that those recovered after lichen hydrothermal treatment at 160 °C featured a good extraction performance, the highest molecular weight, apparent viscosity, and antiproliferative potential. The thermo-rheological properties of the corresponding matrices formulated at 10 % and 60 or 80 °C exhibited the strongest and most thermo-reversible characteristics, as well as antifreezing feasibility. Another advantage of the selected fractions was the absence of skin irritation according to the in vitro skin irritation assay.

Anti-inflammatory, analgesic, and antipyretic potential of Oxystelma esculentum (L. f.) Sm. using in vitro, in vivo, and in silico studies

The objective of the current study was to evaluate the anti-inflammatory, analgesic, and antipyretic potential of Oxystelma esculentum using different animal models. The phytochemical profile was determined by assessing its total phenolic content (TPC) and total flavonoid content (TFC), followed by the high-performance liquid chromatography (HPLC) technique. The in vitro anti-inflammatory potential of O. esculentum ethanolic extract (OEE) was evaluated by lipoxygenase enzyme inhibition activity and a human red blood cell (HRBC) membrane stability assay. The in vivo anti-inflammatory potential of the plant was determined by the carrageenan-induced paw edema test, and the analgesic potential by the hot plate test, tail-flick test, formalin-induced analgesia, acetic acid-induced writhing activities, and yeast-induced elevation of body temperature. The values of total phenolic content (212.6 ± 3.18 µg GAE/g) and total flavonoid content (37.6 ± 1.76 µg QE/g) were observed. The results showed that OEE exhibited significant antioxidant capacity in DPPH (2,2-diphenyl-1-picrylhydrazyl) (266.3 ± 7.35 μmol TE/g), ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (1,066.3 ± 7.53 μmol TE/g), and FRAP (ferric reducing antioxidant power) (483.6 ± 3.84 μmol TE/g) assays. The HPLC analysis demonstrated phytocompounds with anti-inflammatory potential, such as chlorogenic acid, gallic acid, 4-hydroxybenzoic acid, caffeic acid, ferulic acid, and coumarin. The plant showed in vitro anti-inflammatory activity through the inhibition of lipoxygenase enzyme with a high percentage (56.66%) and HRBC membrane stability (67.29%). In in vivo studies, OEE exhibited significant (p < 0.05) anti-inflammatory (carrageenan-induced paw edema model), analgesic (hot plate test, tail-flick test, formalin-induced analgesia, and acetic acid-induced writhing), and antipyretic (rectal temperature reduction) responses at different doses (100, 300, and 500 mg/kg). Molecular docking studies showed significant binding affinities of phytocompounds compared to indomethacin and predicted various binding interactions for stable conformations. The results of in vitro, in vivo, and in silico studies supported the anti-inflammatory, analgesic, and antipyretic potential of O. esculentum.

Parietin, the Vibrant Natural Dye in Xanthoria parietina

The use of natural dyes in several areas is regulated by current European and non-European legislation, due to various problems with synthetic dyes. The analysis revealed that the lichen studied: Xanthoria parietina has potential natural dye sources and provides bright colors for extraction solvents. Furthermore, dyed wool and toile fabric have good fastness properties in ammonia fermentation and boiling water, both with and without mordants. The sample dyes with Xanthoria parietina were characterized by several analytical techniques: high-performance liquid chromatography with diode array detection (HPLC-DAD) and electrospray ionization with tandem mass spectrometry (HPLC-ESI-Q-ToF). As compounds from Xanthoria parietina form a complex with mordants and tissues, it is impossible to identify the molecules responsible for coloring using chromatographic techniques. However, we have evaluated the dyeing power of their major molecule, parietin. To further confirm the coloring power of the isolated parietin molecule, we performed a dye test with pure parietin. Thus, CIALAB analyses have shown parietin is the molecule responsible for the coloring obtained by Xanthoria parietina. The utilization of parietin derived from lichens facilitates the development of sustainable dyes for textile coloring, presenting an environmentally friendly alternative to synthetic dyes while simultaneously enriching lichen biodiversity.

Chemical Constituents Isolated from the Lichen Biome of Selected Species Native to North America

A lichen is a symbiotic association composed of a primary mycobionts and one or more photobionts living mutualistically together, forming a distinct morphological entity beneficial to their partnership and to other associated fungi, photobionts, and bacteria that collectively make up the lichen biome. The taxonomic identification of a lichen species often requires determination of the primary mycobiont's secondary metabolites, the key morphological characteristics of the thallus, and how it relates to other lichen species as seen in DNA phylogeny. This chapter covers lichens and their bionts, taxonomic identification, and their chemical constituents as exemplified by what is found in lichen biomes, especially those endemic to North America. Extraction and isolation, as well as updates on dereplication methods using mass spectrometric GNPS and NMR spectroscopic spin network fingerprint procedures, and marker-based techniques to identify lichens are discussed. The isolation and structure elucidation of secondary metabolites of an endolichenic Penicillium species that produces bioactive compounds will be described in detail.

The mitogenomes characterization of two Peltigera species (Peltigera elisabethae and Peltigera polydactylon) and comparative mitogenomic analyses of six Peltigera

In the present study, the mitochondrial genomes of Peltigera elisabethae and P. polydactylon were sequenced and assembled. The two mitogenomes were composed of circular DNA molecules, with sizes of 64,034 bp and 59,208 bp, respectively. Comparative analysis showed that the genome size, GC content, GC skew, and AT skew varied between the two mitochondrial genomes. In codon analysis, phenylalanine (Phe), isoleucine (Ile), and leucine (Leu) were most frequently used in six Peltigera genomes. Evolutionary analysis showed that all 14 protein-coding genes (PCGs) were subject to purifying selection in the six Peltigera species. Regarding gene rearrangement, the PCGs of Peltigera had the same gene sequence and gene content, and a few intron sequences and spacer sequences were rearranged in Peltigera. In the phylogenetic analysis, we used Bayesian and ML methods to construct a phylogenetic tree. Two phylogenetic trees with consistent topology with high support indicate that mitochondrial genes were reliable molecular markers for analyzing the phylogenetic relationships. The present study enriches the mitochondrial genome data of Peltigera and promotes further understanding of the genetics and evolution of the Peltigera genus.

Characterization of Complete Mitochondrial Genomes of the Five Peltigera and Comparative Analysis with Relative Species

In the present study, the complete mitochondrial genomes of five Peltigera species (Peltigera elisabethae, Peltigera neocanina, Peltigera canina, Peltigera ponojensis, Peltigera neckeri) were sequenced, assembled and compared with relative species. The five mitogenomes were all composed of circular DNA molecules, and their ranged from 58,132 bp to 69,325 bp. The mitochondrial genomes of the five Peltigera species contain 15 protein-coding genes (PCGs), 2 rRNAs, 26-27 tRNAs and an unidentified open reading frame (ORF). The PCG length, AT skew and GC skew varied among the 15 PCGs in the five mitogenomes. Among the 15 PCGs, cox2 had the least K2P genetic distance, indicating that the gene was highly conserved. The synteny analysis revealed that the coding regions were highly conserved in the Peltigera mitochondrial genomes, but gene rearrangement occurred in the intergenic regions. The phylogenetic analysis based on the 14 PCGs showed that the 11 Peltigera species formed well-supported topologies, indicating that the protein-coding genes in the mitochondrial genome may be used as a reliable molecular tool in the study of the phylogenetic relationship of Peltigera.

Cytotoxic, anti-proliferative, and apoptotic evaluation of Ramalina sinensis (Ascomycota, Lecanoromycetes), lichenized fungus on oral squamous cell carcinoma cell line; in-vitro study

BACKGROUND

Scientists and medical professionals are actively striving to improve the efficacy of treatment methods for oral squamous cell carcinoma (OSCC), the most frequently occurring cancer within the oral cavity, by exploring the potential of natural products. The active pharmacological compounds found in lichenized fungi have shown potential for aiding in cancer treatment. Recent research aims to evaluate the impact of the lichenized fungus Ramalina sinensis (R. sinensis) on the cell viability and apoptosis of OSCC cell lines, considering the anti-inflammatory and anti-cancer capabilities of lichens.

METHODS

Ramalina sinensis (Ascomycota, Lecanoromycetes) was selected for investigation of its effects on a human oral squamous cell carcinoma cell line. Acetone and methanol extracts of R. sinensis on an OSCC cell line (KB cell line, NCBI Code: C152) were investigated. Viability was assessed by MTT assay analysis, and apoptotic cells were measured using flow cytometry analysis. Scratch assay was used to assess cell migration. The chemical composition and metabolic profiling of R. sinensis were investigated.

RESULTS

The growth and multiplication of KB cells were observed to undergo a gradual but remarkable inhibition when exposed to various concentrations. Specifically, concentrations of 6.25, 12.5, 25, 50, 100, and 200 μg/mL exhibited a significant suppressive effect on the proliferation of KB cells. The inhibition of cell proliferation exhibited a statistically significant difference between the extracts obtained from acetone and methanol. Flow cytometry results show an increase in apoptosis of OSCC cells by acetone extract. R. sinensis exerted a concentration-dependent inhibitory effect on the migration of OSCC cells. The chemical composition of R. sinensis was investigated using liquid chromatography positive ion electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS), and 33 compounds in the acetone and methanol extracts of R. sinensis were detected.

CONCLUSION

The findings provide evidence supporting the beneficial effects of R. sinensis extract on inducing apoptosis in OSCC cells and exerting anti-cancer properties.

Discovery and excavation of lichen bioactive natural products

Lichen natural products are a tremendous source of new bioactive chemical entities for drug discovery. The ability to survive in harsh conditions can be directly correlated with the production of some unique lichen metabolites. Despite the potential applications, these unique metabolites have been underutilized by pharmaceutical and agrochemical industries due to their slow growth, low biomass availability, and technical challenges involved in their artificial cultivation. At the same time, DNA sequence data have revealed that the number of encoded biosynthetic gene clusters in a lichen is much higher than in natural products, and the majority of them are silent or poorly expressed. To meet these challenges, the one strain many compounds (OSMAC) strategy, as a comprehensive and powerful tool, has been developed to stimulate the activation of silent or cryptic biosynthetic gene clusters and exploit interesting lichen compounds for industrial applications. Furthermore, the development of molecular network techniques, modern bioinformatics, and genetic tools is opening up a new opportunity for the mining, modification, and production of lichen metabolites, rather than merely using traditional separation and purification techniques to obtain small amounts of chemical compounds. Heterologous expressed lichen-derived biosynthetic gene clusters in a cultivatable host offer a promising means for a sustainable supply of specialized metabolites. In this review, we summarized the known lichen bioactive metabolites and highlighted the application of OSMAC, molecular network, and genome mining-based strategies in lichen-forming fungi for the discovery of new cryptic lichen compounds.

Recent advances in research for potential utilization of unexplored lichen metabolites

Several research studies have shown that lichens are productive organisms for the synthesis of a broad range of secondary metabolites. Lichens are a self-sustainable stable microbial ecosystem comprising an exhabitant fungal partner (mycobiont) and at least one or more photosynthetic partners (photobiont). The successful symbiosis is responsible for their persistence throughout time and allows all the partners (holobionts) to thrive in many extreme habitats, where without the synergistic relationship they would be rare or non-existent. The ability to survive in harsh conditions can be directly correlated with the production of some unique metabolites. Despite the potential applications, these unique metabolites have been underutilised by pharmaceutical and agrochemical industries due to their slow growth, low biomass availability and technical challenges involved in their artificial cultivation. However, recent development of biotechnological tools such as molecular phylogenetics, modern tissue culture techniques, metabolomics and molecular engineering are opening up a new opportunity to exploit these compounds within the lichen holobiome for industrial applications. This review also highlights the recent advances in culturing the symbionts and the computational and molecular genetics approaches of lichen gene regulation recognized for the enhanced production of target metabolites. The recent development of multi-omics novel biodiscovery strategies aided by synthetic biology in order to study the heterologous expressed lichen-derived biosynthetic gene clusters in a cultivatable host offers a promising means for a sustainable supply of specialized metabolites.

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.

Chronicle of Research into Lichen-Associated Bacteria

Lichens are mutually symbiotic systems consisting of fungal and algal symbionts. While diverse lichen-forming fungal species are known, limited species of algae form lichens. Plasticity in the combination of fungal and algal species with different eco-physiological properties may contribute to the worldwide distribution of lichens, even in extreme habitats. Lichens have been studied systematically for more than 200 years; however, plasticity in fungal-algal/cyanobacterial symbiotic combinations is still unclear. In addition, the association between non-cyanobacterial bacteria and lichens has attracted attention in recent years. The types, diversity, and functions of lichen-associated bacteria have been studied using both culture-based and culture-independent methods. This review summarizes the history of systematic research on lichens and lichen-associated bacteria and provides insights into the current status of research in this field.

Comprehensive Lichenometabolomic Exploration of Ramalina conduplicans Vain Using UPLC-Q-ToF-MS/MS: An Identification of Free Radical Scavenging and Anti-Hyperglycemic Constituents

In this study, we propose ultra-performance liquid chromatography coupled with quadrupole/time-of-flight mass spectrometry (UPLC-QToF-MS/MS)-guided metabolite isolation as a choice analytical approach to the ongoing structure−activity investigations of chemical isolates from the edible lichen, Ramalina conduplicans Vain. This strategy led to the isolation and identification of a new depside (5) along with 13 known compounds (1−4, 6−14), most of which being newly described in this lichen species. The structures of the isolates were established by detailed analysis of their spectral data (IR, NMR, and Mass). The acetone extract was further analyzed by UPLC-Q-ToF-MS/MS in a negative ionization mode, which facilitated the identification and confirmation of 18 compounds based on their fragmentation patterns. The antioxidant capacities of the lichen acetone extract (AE) and isolates were measured by tracking DPPH and ABTS free radical scavenging activities. Most isolates displayed marked radical scavenging activities against ABTS while moderate activities were observed against DPPH radical scavenging. Except for atranol (14), oxidative DNA damage was limited by all the tested compounds, with a marked protection for the novel isolated compound (5), as previously noted for the acetone extract (p < 0.001). Furthermore, compound (4) and acetone extract (AE) have inhibited intestinal α-glucosidase enzyme significantly (p < 0.01). Although some phytochemical studies were already performed on this lichen, this study provided new insights into the isolation and identification of bioactive compounds, illustrating interest in future novel analytical techniques.

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.

Antimicrobial Activities against Opportunistic Pathogenic Bacteria Using Green Synthesized Silver Nanoparticles in Plant and Lichen Enzyme-Assisted Extracts

Enzyme-assisted extraction is a valuable tool for mild and environmentally-friendly extraction conditions to release bioactive compounds and sugars, essential for silver nanoparticle (AgNP) green synthesis as capping and reducing agents. In this research, plant and fungal kingdoms were selected to obtain the enzyme-assisted extracts, using green synthesized AgNPs. For the synthesis, pseudo-cereal Fagopyrum esculentum (F. esculentum) and lichen Certaria islandica (C. islandica) extracts were used as environmentally-friendly agents under heating in an aqueous solution. Raw and enzyme-assisted extracts of AgNPs were characterized by physicochemical, phytochemical, and morphological characteristics through scanning and transmission electron microscopy (SEM and TEM), as well as Fourier transform infrared spectroscopy (FTIR). The synthesized nanoparticles were spherical in shape and well dispersed, with average sizes ranging from 10 to 50 nm. This study determined the total phenolic content (TPC) and in vitro antioxidant activity in both materials by applying standard methods. The results showed that TPC, ABTS^•+, FRAP, and DPPH^• radical scavenging activities varied greatly in samples. The AgNPs derived from enzymatic hydrolyzed aqueous extracts C. islandica and F. esculentum exhibited higher antibacterial activity against the tested bacterial pathogens than their respective crude extracts. Results indicate that the extracts’ biomolecules covering the AgNPs may enhance the biological activity of silver nanoparticles and enzyme assistance as a sustainable additive to technological processes to achieve higher yields and necessary media components.

Phytochemical Analysis, Antioxidant, Antimicrobial, and Cytotoxic Activity of Different Extracts of Xanthoparmelia stenophylla Lichen from Stara Planina, Serbia

The aim of this study was to identify some of the secondary metabolites present in acetonic, methanolic, and hexanic extracts of lichen Xanthoparmelia stenophylla and to examine their antioxidant, antimicrobial, and cytotoxic activity. Compounds of the depsid structure of lecanoric acid, obtusic acid, and atranorin as well as usnic acid with a dibenzofuran structure were identified in the extracts by HPLC. The acetone extract was shown to have the highest total phenolic (167.03 ± 1.12 mg GAE/g) and total flavonoid content (178.84 ± 0.93 mg QE/g) as well as the best antioxidant activity (DPPH IC50 = 81.22 ± 0.54). However, the antimicrobial and antibiofilm tests showed the best activity of hexanic extract, especially against strains of B. cereus, B. subtilis, and S. aureus (MIC < 0.08, and 0.3125 mg/mL, respectively). Additionally, by using the MTT method, the acetonic extract was reported to exhibit a strong cytotoxic effect on the HeLa and HCT-116 cell lines, especially after 72 h (IC50 = 21.17 ± 1.85 and IC50 = 21.48 ± 3.55, respectively). The promising antioxidant, antimicrobial, and cytotoxic effects of Xanthoparmelia stenophylla extracts shown in the current study should be further investigated in vivo and under clinical conditions.

Advances in the Characterization of Usnea barbata (L.) Weber ex F.H. Wigg from Călimani Mountains, Romania

Usnea barbata (L.) Weber ex F.H. Wigg (U. barbata) is a medicinal representative of the lichens from the Usnea genus (Parmeliaceae, lichenized Ascomycetes), containing bioactive secondary metabolites. The aim of this study is a comparative analysis between two separated parts of the thallus layers: medulla–cortex (mcUB) and central cord (ccUB) and the whole dried U. barbata thallus (dUB). These three samples were examined regarding color differences. The U. barbata thallus morphology was examined through fluorescent microscopy (FM) and scanning electron microscopy (SEM). The mineral content was measured using inductively coupled plasma mass spectrometry (ICP-MS), and Fourier transform infrared spectroscopy (FT-IR) preliminarily established the differences in the metabolite content. Finally, extracts in different solvents (ethanol and acetone) were obtained from all studied samples, and their total phenolic content (TPC) and free radical scavenging activity (antiradical activity, AA) were evaluated by spectrophotometry. The ICP-MS results showed that from 23 elements analyzed, 18 minerals were quantified in mcUB, 13 in dUB, and only 12 in ccUB. The ccUB fraction recorded the lowest mineral content, color intensity (chroma), luminosity (L*), and TPC value, followed in increasing order by dUB and mcUB. FT-IR spectra displayed different peaks in ccUB and dUB samples compared to mcUB. The mcUB fraction also showed the highest TPC, significantly correlated with AA. However, dUB had the highest antiradical activity, followed by mcUB and ccUB, with noticeable differences in the acetone extract. The final correlation between all variable data obtained indicates that 99.31% of the total variance was associated with all minerals, total phenolics, and color parameters and was also related to the antiradical activity. These obtained results complete our previous studies on autochthonous U. barbata. Moreover, being a source of bioactive metabolites, extracting them from the mcUB fraction could increase this process’s yield and selectivity.

Lichen Secondary Metabolites Inhibit the Wnt/β-Catenin Pathway in Glioblastoma Cells and Improve the Anticancer Effects of Temozolomide

Lichens are a source of secondary metabolites with significant pharmacological potential. Data regarding their possible application in glioblastoma (GBM) treatment are, however, scarce. The study aimed at analyzing the mechanism of action of six lichen secondary metabolites: atranorin, caperatic acid, physodic acid, squamatic acid, salazinic acid, and lecanoric acid using two- and three-dimensional GBM cell line models. The parallel artificial membrane permeation assay was used to predict the blood-brain barrier penetration ability of the tested compounds. Their cytotoxicity was analyzed using the MTT test on A-172, T98G, and U-138 MG cells. Flow cytometry was applied to the analysis of oxidative stress, cell cycle distribution, and apoptosis, whereas qPCR and microarrays detected the induced transcriptomic changes. Our data confirm the ability of lichen secondary metabolites to cross the blood-brain barrier and exert cytotoxicity against GBM cells. Moreover, the compounds generated oxidative stress, interfered with the cell cycle, and induced apoptosis in T98G cells. They also inhibited the Wnt/β-catenin pathway, and this effect was even stronger in case of a co-treatment with temozolomide. Transcriptomic changes in cancer related genes induced by caperatic acid and temozolomide were the most pronounced. Lichen secondary metabolites, caperatic acid in particular, should be further analyzed as potential anti-GBM agents.

Phylogenetic Studies and Metabolite Analysis of Sticta Species from Colombia and Chile by Ultra-High Performance Liquid Chromatography-High Resolution-Q-Orbitrap-Mass Spectrometry

Eleven species of lichens of the genus Sticta, ten of which were collected in Colombia (S. pseudosylvatica S. luteocyphellata S. cf. andina S. cf. hypoglabra, S. cordillerana, S. cf. gyalocarpa S. leucoblepharis, S. parahumboldtii S. impressula, S. ocaniensis) and one collected in Chile (S. lineariloba), were analyzed for the first time using hyphenated liquid chromatography with high-resolution mass spectrometry. In the metabolomic analysis, a total of 189 peaks were tentatively detected; the analyses were divided in five (5) groups of compounds comprising lipids, small phenolic compounds, saturated acids, terpenes, and typical phenolic lichen compounds such as depsides, depsidones and anthraquinones. The metabolome profiles of these eleven species are important since some compounds were identified as chemical markers for the fast identification of Sticta lichens for the first time. Finally, the usefulness of chemical compounds in comparison to traditional morphological traits to the study of ancestor–descendant relationships in the genus was assessed. Chemical and morphological consensus trees were not consistent with each other and recovered different relationships between taxa.

Elemental Analysis and In Vitro Evaluation of Antibacterial and Antifungal Activities of Usnea barbata (L.) Weber ex F.H. Wigg from Călimani Mountains, Romania

This study aims to complete our research on Usnea barbata (L.) Weber ex F.H. Wigg (U. barbata) from the Călimani Mountains, Romania, with an elemental analysis and to explore its antibacterial and antifungal potential. Thus, we analyzed twenty-three metals (Ca, Fe, Mg, Mn, Zn, Al, Ag, Ba, Co, Cr, Cu, Li, Ni, Tl, V, Mo, Pd, Pt, Sb, As, Pb, Cd, and Hg) in dried U. barbata lichen (dUB) by inductively coupled plasma mass spectrometry (ICP-MS). For the second study, we performed dried lichen extraction with five different solvents (ethyl acetate, acetone, ethanol, methanol, and water), obtaining five U. barbata dry extracts (UBDE). Then, using an adapted disc diffusion method (DDM), we examined their antimicrobial activity against seven bacterial species-four Gram-positive (Staphylococcus aureus, Enterococcus casseliflavus, Streptococcus pyogenes, and Streptococcus pneumoniae) and three Gram-negative (Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa)-and two fungi species (Candida albicans and Candida parapsilosis). Usnic acid (UA) was used as a positive control. The ICP-MS data showed a considerable Ca content (979.766 µg/g), followed by, in decreasing order, Mg, Mn, Al, Fe, and Zn. Other elements had low levels: Ba, Cu, Pb, and Cr (3.782-1.002 µg/g); insignificant amounts (<1 µg/g) of Hg and V were also found in dUB. The trace elements Ag, As, Cd, Co, Li, Tl, Mo, Pd, Pt, and Sb were below detection limits (<0.1 µg/g). The DDM results-expressed as the size (mm) of the inhibition zone diameter (IZs)-proved that the water extract did not have any inhibitory activity on any pathogens (IZs = 0 mm). Gram-positive bacteria displayed the most significant susceptibility to all other UBDE, with Enterococcus casseliflavus showing the highest level (IZs = 20-22 mm). The most susceptible Gram-negative bacterium was Pseudomonas aeruginosa (IZs = 16-20 mm); the others were insensitive to all U. barbata dry extracts (IZs = 0 mm). The inhibitory activity of UBDE and UA on Candida albicans was slightly higher than on Candida parapsilosis.

Lichen-Derived Compounds and Extracts as Biologically Active Substances with Anticancer and Neuroprotective Properties

Lichens are a source of chemical compounds with valuable biological properties, structurally predisposed to penetration into the central nervous system (CNS). Hence, our research aimed to examine the biological potential of lipophilic extracts of Parmelia sulcata, Evernia prunastri, Cladonia uncialis, and their major secondary metabolites, in the context of searching for new therapies for CNS diseases, mainly glioblastoma multiforme (GBM). The extracts selected for the study were standardized for their content of salazinic acid, evernic acid, and (−)-usnic acid, respectively. The extracts and lichen metabolites were evaluated in terms of their anti-tumor activity, i.e., cytotoxicity against A-172 and T98G cell lines and anti-IDO1, IDO2, TDO activity, their anti-inflammatory properties exerted by anti-COX-2 and anti-hyaluronidase activity, antioxidant activity, and anti-acetylcholinesterase and anti-butyrylcholinesterase activity. The results of this study indicate that lichen-derived compounds and extracts exert significant cytotoxicity against GBM cells, inhibit the kynurenine pathway enzymes, and have anti-inflammatory properties and weak antioxidant and anti-cholinesterase properties. Moreover, evernic acid and (−)-usnic acid were shown to be able to cross the blood-brain barrier. These results demonstrate that lichen-derived extracts and compounds, especially (−)-usnic acid, can be regarded as prototypes of pharmacologically active compounds within the CNS, especially suitable for the treatment of GBM.

Fungi and Algae as Sources of Medicinal and Other Biologically Active Compounds: A Review

Many species of fungi including lichenized fungi (lichens) and algae have the ability to biosynthesize biologically active compounds. They produce, among others, polysaccharides with anticancer and immunostimulatory properties: (1) Background: This paper presents the characteristics of the most important bioactive compounds produced by fungi and algae; (2) Methods: Based on the example of the selected species of mushrooms, lichens and algae, the therapeutic properties of the secondary metabolites that they produce and the possibilities of their use are presented; (3) Results: The importance of fungi, especially large-fruited mushrooms, lichens and algae, in nature and human life is discussed, in particular, with regard to their use in the pharmaceutical industry and their nutritional value; (4) Conclusions: The natural organisms, such as fungi, lichenized fungi and algae, could be used as supplementary medicine, in the form of pharmaceutical preparations and food sources. Further advanced studies are required on the pharmacological properties and bioactive compounds of these organisms.

Alkylated Salicylaldehydes and Prenylated Indole Alkaloids from the Endolichenic Fungus Aspergillus chevalieri and Their Bioactivities

Sixteen metabolites, including seven C₇-alkylated salicylaldehyde derivatives (1-7) and nine prenylated indole alkaloids (8-16), three of which are new, namely, asperglaucins A and B (1 and 2) and neoechinulin F (8), were separated from the endolichenic fungus Aspergillus chevalieri SQ-8. Asperglaucin A (1) represents an unusual phthalide-like derivative with a benzo[c]thiophen-1(3H)-one scaffold. All compounds were assessed in vitro for antibacterial, antineuroinflammatory, and antioxidant activities. Notably, asperglaucins A and B exhibited potent antibacterial activities against two plant pathogens Pseudomonas syringae pv actinidae (Psa) and Bacillus cereus, with an MIC value of 6.25 μM; further SEM analyses illustrated that the possible bacteriostatic mechanisms for compounds 1 and 2 were to alter the external structure of B. cereus and Psa, and to cause the rupture or deformation of the cell membranes, respectively, and the results suggest that compounds 1 and 2 may serve as potential promising candidates for lead compounds of agrochemical bactericides. Furthermore, compounds 6 and 10 significantly inhibited nitric oxide production with an IC₅₀ value of ca. 12 μM, and the possible anti-inflammatory mechanisms involved were also studied by molecular docking. Finally, the tested phenolics 3-5 showed significant antioxidative effects. Thus, strain SQ-8 represents a novel resource of these bioactive metabolites to be utilized.