The antimicrobial activity of extracts of the lichen Hypogymnia tubulosa and its 3-hydroxyphysodic acid constituent

Biosynthetic Potential of Hypogymnia Holobionts: Insights into Secondary Metabolite Pathways

Lichens are symbiotic associations consisting of a photobiont (algae or cyanobacteria) and a mycobiont (fungus). They are known to produce a variety of unique secondary metabolites. To access this biosynthetic potential for biotechnological applications, deeper insights into the biosynthetic pathways and corresponding gene clusters are necessary. Here we provide a comprehensive view of the biosynthetic gene clusters of all organisms comprising a lichen thallus: fungi, green algae, and bacteria. We present two high-quality PacBio metagenomes, in which we identified a total of 460 biosynthetic gene clusters. Lichen mycobionts yielded 73-114 clusters, other lichen associated ascomycetes 8-40, green algae of the genus Trebouxia 14-19, and lichen-associated bacteria 101-105 clusters. The mycobionts contained mainly T1PKSs, followed by NRPSs, and terpenes; Trebouxia reads harbored mainly clusters linked to terpenes, followed by NRPSs and T3PKSs. Other lichen-associated ascomycetes and bacteria contained a mix of diverse biosynthetic gene clusters. In this study, we identified for the first time the biosynthetic gene clusters of entire lichen holobionts. The yet untapped biosynthetic potential of two species of the genus Hypogymnia is made accessible for further research.

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.

Chemical Composition and Antimicrobial Activity of Two Sri Lankan Lichens, Parmotrema rampoddense, and Parmotrema tinctorum against Methicillin-Sensitive and Methicillin-Resistant Staphylococcus aureus

Introduction

Medicinal utility of lichens is ascribed to the presence of various secondary metabolites of low molecular weight and they have been used in traditional medicine including Ayurveda in the treatment of wounds and skin disorders. Despite the urgent need to effectively address the antibiotic resistance worldwide, the discovery of new antibacterial drugs has declined in the recent past. This emphasizes the increasing importance of investigating and developing new classes of antibiotics that can withstand antibiotic resistance. Aims of the study. The present study was conducted to investigate the chemical composition and the antibacterial activity of hexane, ethanol, and aqueous extracts of Parmotrema rampoddense and Parmotrema tinctorum, two lichens collected from Belihuloya, Sri Lanka, against Gram-negative and Gram-positive bacteria including twenty clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA). Materials and methods. Phytochemical analysis, thin layer chromatography (TLC), and Gas Chromatography Mass Spectrometry (GC-MS) were performed to determine the chemical composition of the two lichens. Hexane, ethanol, and aqueous extracts of both lichens were tested against clinical isolate of Gram-negative and Gram-positive bacteria including twenty clinical isolates of MRSA. Bacterial susceptibility was tested using a disc diffusion assay. Minimum inhibitory concentration (MIC) was determined by a broth microdilution method. Vancomycin was used as the positive control.

Results

Alectorialic acid, atranorin, atraric acid, orcinol, and O-orsellinaldehyde were among the secondary metabolites identified by the TLC and GC-MS analysis. None of the lichen extracts were active against Gram-negative bacteria but both lichens showed a concentration-dependent activity against methicillin-sensitive Staphylococcus aureus (MSSA) and MRSA. Ethanol extract of P. rampoddense showed the highest activity against MSSA with the MIC, 0.0192 mg/ml, but all MRSA isolates investigated showed MIC between 0.096 and 2.4 mg/ml for the same extract.

Conclusion

Both lichens, P. rampoddense and P. tinctorum, represent potentially important sources of future antimicrobial drugs. Further investigation on the ethanol extract of P. rampoddense will enable us to determine the most active phytoconstituents responsible for the activity, their mechanism of action against bacterial pathogens, and also their cytotoxicity against normal cells.

Mycobiome analysis of asymptomatic and symptomatic Norway spruce trees naturally infected by the conifer pathogens Heterobasidion spp

Plant microbiome plays an important role in maintaining the host fitness. Despite a significant progress in our understanding of the plant microbiome achieved in the recent years, very little is known about the effect of plant pathogens on composition of microbial communities associated with trees. In this study, we analysed the mycobiome of different anatomic parts of asymptomatic and symptomatic Norway spruce trees naturally infected by Heterobasidion spp. We also investigated the primary impact of the disease on the fungal communities, which are associated with Norway spruce trees. Our results demonstrate that the structure of fungal communities residing in the wood differed significantly among symptomatic and asymptomatic Heterobasidion-infected trees. However, no significant differences were found in the other anatomic regions of the trees. The results also show that not only each of individual tree tissues (wood, bark, needles and roots) harbours a unique fungal community, but also that symptomatic trees were more susceptible to co-infection by other wood-degrading fungi compared to the asymptomatic ones.

Hypogymnia tubulosa extracts: chemical profile and biological activities

This study reports for the first time in the chemical composition of acetone, ether, ethyl acetate and dichloromethane extracts of Hypogymnia tubulosa determined by HPLC-UV, GC-FID and GC-MS as well as effect of H. tubulosa acetone extract on micronucleus distribution on human lymphocytes and on cholinesterase activity. Additionally, antioxidant (estimated via DPPH, ABTS, TRP, CUPRAC and TPC assays) and antibacterial activity against two Gram-positive and three Gram-negative bacteria were also determined. The HPLC-UV analysis revealed the presence of depsidones, 3-hydroxyphysodic, 4-O-methyl physodic acid, physodic and physodalic acid together with two depsides, atranorin and chloroatranorin. GC-FID and GC-MS analyses enabled the identification of atranol, chloroatranol, atraric acid, olivetol, olivetonide and 3-hydroxyolivetonide as the main components. The results of present study show that H. tubulosa acetone extract is a promising candidate for in vivo experiments considering antioxidant activity.

Cytotoxic activity of physodic acid and acetone extract from Hypogymnia physodes against breast cancer cell lines

CONTEXT

Lichens produce specific secondary metabolites with different biological activity.

OBJECTIVE

This study investigated the cytotoxic effects of physodic acid, in addition to the total phenolic content and cytotoxic and antioxidant activity of acetone extract from Hypogymnia physodes (L.) Nyl. (Parmeliaceae).

MATERIALS AND METHODS

Cytotoxicity of physodic acid (0.1-100 μM) was assessed in MDA-MB-231, MCF-7 and T-47D breast cancer cell lines and a nontumorigenic MCF-10A cell line using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, neutral red uptake and crystal violet assays during 72 h of incubation. An MTT assay was also used to assess the cytotoxic effects of the acetone extract (0.1-100 μg/mL) in the MDA-MB-231, MCF-7, T-47D breast cancer cell lines after 72 h. The total phenolic content of the acetone extract, expressed as the gallic acid equivalent, was investigated using Folin-Ciocalteu reagent. The antioxidant activity of the extract was assessed by 2,2-diphenyl-1-picrylhydrazyl and ferric-reducing antioxidant power assays.

RESULTS

The cytotoxic activity of physodic acid appeared to be strong in the tumorigenic cell lines (IC₅₀ 46.0-93.9 μM). The compound was inactive against the nontumorigenic MCF-10A cell line (IC₅₀>100 μM). The acetone extract showed cytotoxicity in the breast cancer cell lines (IC₅₀ 46.2-110.4 μg/mL). The acetone extract was characterized by a high content of polyphenols, and it had significant antioxidant activity.

DISCUSSION AND CONCLUSION

Physodic acid and acetone extract from H. physodes displayed cytotoxic effects in the breast cancer cell lines. Furthermore, acetone extract from H. physodes possessed significant antioxidant properties.

In vitro antitumor activities of the lichen compounds olivetoric, physodic and psoromic acid in rat neuron and glioblastoma cells

Context Since methods utilised in the treatment of glioblastoma multiforme (GBM) are inadequate and have too many side effects, usage of herbal products in the treatment process comes into prominence. Lichens are symbiotic organisms used for medicinal purposes for many years. There are various anticancer treatments about components of two lichen species used in the present study. Objective Antitumor potential of three lichen secondary metabolites including olivetoric acid (OLA) and physodic acid (PHA) isolated from Pseudevernia furfuracea (L.) Zopf (Parmeliaceae) and psoromic acid (PSA) isolated from Rhizoplaca melanophthalma (DC.) Leuckert (Lecanoraceae) were investigated on human U87MG-GBM cell lines and primary rat cerebral cortex (PRCC) cells for the first time. Materials and methods PRCC cells used as healthy brain cells were obtained from Sprague-Dawley rats. The treatments were carried out on the cells cultured for 48 h. Cytotoxic effects of different concentrations (2.5, 5, 10, 20 and 40 mg/L) of metabolites on the cells were determined via 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and lactate dehydrogenase (LDH) analyses. Total antioxidant capacity (TAC) and total oxidant status (TOS) parameters were used for assessing oxidative alterations. Oxidative DNA damage potentials of metabolites were investigated via evaluating 8-hydroxy-2'-deoxyguanosine (8-OH-dG) levels. Results Median inhibitory concentration (IC50) values of OLA, PHA and PSA were 125.71, 698.19 and 79.40 mg/L for PRCC cells and 17.55, 410.72 and 56.22 mg/L for U87MG cells, respectively. It was revealed that cytotoxic effects of these metabolites showed positive correlation with concentration, LDH activity and oxidative DNA damage. Discussion and conclusion The present findings obtained in this study revealed that primarily OLA and then PSA had high potential for use in the treatment of GBM.

Secondary metabolites from cetrarioid lichens: Chemotaxonomy, biological activities and pharmaceutical potential

BACKGROUND

Lichens, as a symbiotic association of photobionts and mycobionts, display an unmatched environmental adaptability and a great chemical diversity. As an important morphological group, cetrarioid lichens are one of the most studied lichen taxa for their phylogeny, secondary chemistry, bioactivities and uses in folk medicines, especially the lichen Cetraria islandica. However, insufficient structure elucidation and discrepancy in bioactivity results could be found in a few studies.

PURPOSE

This review aimed to present a more detailed and updated overview of the knowledge of secondary metabolites from cetrarioid lichens in a critical manner, highlighting their potentials for pharmaceuticals as well as other applications. Here we also highlight the uses of molecular phylogenetics, metabolomics and ChemGPS-NP model for future bioprospecting, taxonomy and drug screening to accelerate applications of those lichen substances.

CHAPTERS

The paper starts with a short introduction in to the studies of lichen secondary metabolites, the biological classification of cetrarioid lichens and the aim. In light of ethnic uses of cetrarioid lichens for therapeutic purposes, molecular phylogeny is proposed as a tool for future bioprospecting of cetrarioid lichens, followed by a brief discussion of the taxonomic value of lichen substances. Then a delicate description of the bioactivities, patents, updated chemical structures and lichen sources is presented, where lichen substances are grouped by their chemical structures and discussed about their bioactivity in comparison with reference compounds. To accelerate the discovery of bioactivities and potential drug targets of lichen substances, the application of the ChemGPS NP model is highlighted. Finally the safety concerns of lichen substances (i.e. toxicity and immunogenicity) and future-prospects in the field are exhibited.

CONCLUSION

While the ethnic uses of cetrarioid lichens and the pharmaceutical potential of their secondary metabolites have been recognized, the knowledge of a large number of lichen substances with interesting structures is still limited to various in vitro assays with insufficient biological annotations, and this area still deserves more research in bioactivity, drug targets and screening. Attention should be paid on the accurate interpretation of their bioactivity for further applications avoiding over-interpretations from various in vitro bioassays.

In vitro evaluation of the antibacterial activity of extracts from 34 species of North American lichens

CONTEXT

The emergence of antibiotic resistant pathogens is a serious global health threat. Hence, the search for new antibiotic drugs from various natural sources should be given high priority. Lichens produce a variety of low molecular weight metabolic compounds and many cultures have utilized these compounds in traditional medicine for centuries.

OBJECTIVE

Report the antibiotic properties of extracts from 34 North American lichens screened against four pathogenic bacteria.

MATERIALS AND METHODS

The micro-well dilution method was used to determine the minimum inhibitory concentration (MIC) of acetone and methanol extracts of 34 lichen species against four bacterial strains. Major chemical compounds in each species were identified using thin layer chromatography (TLC).

RESULTS

Most of the lichen extracts demonstrated inhibitory effects against Staphylococcus aureus, Pseudomonas aeruginosa, and methicillin-resistant S. aureus (MRSA) with MIC values ranging from 3.9 to 500 µg/ml. In addition, extracts from three species, Letharia columbiana (Nutt.) J. W. Thomson (Parmeliaceae), Letharia vulpina (L.) Hue (Parmeliaceae), and Vulpicida canadensis (Räsänen) J.-E. Mattsson & M. J. Lai (Parmeliaceae) (MIC = 125-500 µg/ml) were also effective against Escherichia coli. Generally, acetone extractions were found to be more effective than methanol extractions.

DISCUSSION AND CONCLUSION

Results of this study show that lichen extracts provide significant antimicrobial activity against both Gram-positive and Gram-negative bacteria. These results suggest that lichens may be an important potential source of antibacterial drugs.

Agrobacterium tumefaciens-mediated transformation of the lichen fungus, Umbilicaria muehlenbergii

Transformation-mediated mutagenesis in both targeted and random manners has been widely applied to decipher gene function in diverse fungi. However, a transformation system has not yet been established for lichen fungi, severely limiting our ability to study their biology and mechanism underpinning symbiosis via gene manipulation. Here, we report the first successful transformation of the lichen fungus, Umbilicaria muehlenbergii, via the use of Agrobacterium tumefaciens. We generated a total of 918 transformants employing a binary vector that carries the hygromycin B phosphotransferase gene as a selection marker and the enhanced green fluorescent protein gene for labeling transformants. Randomly selected transformants appeared mitotically stable, based on their maintenance of hygromycin B resistance after five generations of growth without selection. Genomic Southern blot showed that 88% of 784 transformants contained a single T-DNA insert in their genome. A number of putative mutants affected in colony color, size, and/or morphology were found among these transformants, supporting the utility of Agrobacterium tumefaciens-mediated transformation (ATMT) for random insertional mutagenesis of U. muehlenbergii. This ATMT approach potentially offers a systematic gene functional study with genome sequences of U. muehlenbergii that is currently underway.

Effect of Hypogymnia physodes Extracts and their Depsidones on Micronucleus Distribution in Human Lymphocytes

Three lichen depsidones, physodalic acid (1), physodic acid (2), and 3-hydroxy physodic acid (3), were isolated from Hypogymnia physodes diethyl ether extract using column chromatography, and their structures determined by comparing their UV,1H and 13C NMR spectroscopic and MS data with those given in the literature, as well as with data computed by CHEM draw ultra 11 software. The contents of 1, 2 and 3 were determined in the methanol (ME), acetone (AE), and diethyl ether (EE) extracts using reversed-phase high performance liquid chromatography with photodiode array detection. The extracts, isolated depsidones 1-3 and EE fraction F23 (consisting of 90% 2 and 3, in the ratio 5.5: 1) were evaluated for their in vitro effects on chromosome aberrations in peripheral human lymphocytes using the cytochalasin-B blocked micronucleus (CBMN) assay in doses of 1 μg/mL and 2 μg/mL of final culture solution. The frequency of MN was scored in binucleated cells, and nuclear proliferation index was calculated. It was found that 1, 2, 3, F23, and EE at 1.0 μg/mL exerted a beneficial effect on lymphocyte cells giving a significant decrease of the frequency of MN in comparison with the positive control Amifostin WR-2721. Among the tested depsidones at a concentration of 1 μg/mL, 3 exhibited the most prominent effect decreasing the frequency of MN by 30.3%, followed by 2 (28.2%) and 1 (22.0%). The extracts were less effective than the isolated depsidones.