Imbricaric acid and perlatolic acid: multi-targeting anti-inflammatory depsides from Cetrelia monachorum

Antiproliferative, antimigratory, and apoptotic effects of diffractaic and vulpinic acids as thioredoxin reductase 1 inhibitors on cervical cancer

Cervical cancer is among the most frequently observed cancer types in females. New therapeutic targets are needed because of the side impacts of existing cancer drugs and the inadequacy of treatment methods. Thioredoxin reductase 1 (TrxR1) is often overexpressed in many cancer cells, and targeting TrxR1 has become an attractive target for cancer therapy. This study investigated the anticancer impacts of diffractaic and vulpinic acids, lichen secondary metabolites, on the cervical cancer HeLa cell line. XTT findings demonstrated showed that diffractaic and vulpinic acids suppressed the proliferation of HeLa cells in a dose- and time-dependent manner and IC50 values were 22.52 μg/ml and 66.53 μg/ml at 48 h, respectively. Each of these lichen metabolites significantly suppressed migration. Diffractaic acid showed an increase in both the BAX/BCL2 ratio by qPCR analysis and the apoptotic cell population via flow cytometry analysis on HeLa cells. Concerning vulpinic acid, although it decreased the BAX/BCL2 ratio in this cells, it increased apoptotic cells according to the flow cytometry analysis results. Diffractaic and vulpinic acids significantly suppressed TrxR1 enzyme activity rather than the gene and protein expression levels in HeLa cells. This research demonstrated for the first time, that targeting TrxR1 with diffractaic and vulpinic acids was an effective therapeutic strategy for treating cervical cancer.

Lichen or Associated Micro-Organism Compounds Are Active against Human Coronaviruses

(1) Background: Since the emergence of SARS-CoV-2, responsible for the COVID-19 pandemic, efforts have been made to identify antiviral compounds against human coronaviruses. With the aim of increasing the diversity of molecule scaffolds, 42 natural compounds, of which 28 were isolated from lichens and 14 from their associated microorganisms (bacteria and fungi), were screened against human coronavirus HCoV-229E. (2) Methods: Antiviral assays were performed using HCoV-229E in Huh-7 and Huh-7/TMPRSS2 cells and SARS-CoV-2 in a Vero-81-derived clone with a GFP reporter probe. (3) Results: Four lichen compounds, including chloroatranol, emodin, perlatolic acid and vulpinic acid, displayed high activities against HCoV-229E (IC50 = 68.86, 59.25, 16.42 and 14.58 μM, respectively) and no toxicity at active concentrations. Kinetics studies were performed to determine their mode of action. The four compounds were active when added at the replication step. Due to their significant activity, they were further tested on SARS-CoV-2. Perlatolic acid was shown to be active against SARS-CoV-2. (4) Conclusions: Taken together, these results show that lichens are a source of interesting antiviral agents against human coronaviruses. Moreover, perlatolic acid might be further studied for its pan-coronavirus antiviral activity.

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.

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).

Two New Fumarprotocetraric Acid Lactones Identified and Characterized by UHPLC-PDA/ESI/ORBITRAP/MS/MS from the Antarctic Lichen Cladonia metacorallifera

Lichens are symbiotic organisms between algae and fungi, which are makers of secondary compounds named as lichen substances. Hyphenated techniques have significantly helped natural product chemistry, especially UHPLC/ESI/MS/MS in the identification, separation, and tentative characterization of secondary metabolites from natural sources. Twenty-five compounds were detected from the Antarctic lichen Cladonia metacorallifera for the first time using UHPLC-PDA/ESI/Orbitrap/MS/MS. Compounds 5 and 7 are reported as new compounds, based on their MS/MS fragmentation routes, and considered as fumarprotocetraric acid derivatives. Besides, ten known phenolic identified as orsellinic acid, ethyl 4-carboxyorsellinate, psoromic acid isomer, succinprotocetraric acid, siphulellic acid, connorstictic acid, cryptostictic acid, lecanoric acid, lobaric acid and gyrophoric acid are noticed for the first time in the Cladonia genus.

Lipoxygenase Inhibitors as Cancer Chemopreventives: Discovery, Recent Developments and Future Perspectives

BACKGROUND

Leukotrienes (LTs) constitute a bioactive group of Polyunsaturated Fatty Acid (PUFA) metabolites molded by the enzymatic activity of lipoxygenase (LO) and have a pivotal role in inflammation and allergy. Evidence is accumulating both by in vitro cell culture experiments and animal tumor model studies in support of the direct involvement of aberrant metabolism of arachidonic acid (ACD) in the development of several types of human cancers such as lung, prostate, pancreatic and colorectal malignancies. Several independent experimental data suggest a correlation between tumoral cells viability and LO gene expression, especially, 5-lipoxygenase (5-LO). Overexpressed 5-LO cells live longer, proliferate faster, invade more effectively through extracellular matrix destruction and activate the anti-apoptotic signaling mechanisms more intensively compared to the normal counterparts. Thus, some groups of lipoxygenase inhibitors may be effective as promising chemopreventive agents.

METHODS

A structured search of bibliographic databases for peer-reviewed research literature regarding the role of LO in the pathogenesis of cancer was performed. The characteristics of screened papers were summarized and the latest advances focused on the discovery of new LO inhibitors as anticancer agents were discussed.

RESULTS

More than 180 papers were included and summarized in this review; the majority was about the newly designed and synthesized 5-LO inhibitors as anti-inflammatory and anticancer agents. The enzyme's structure, 5-LO pathway, 5-LO inhibitors structure-activity relationships as well as the correlation between these drugs and a number of most prevalent human cancers were described. In most cases, it has been emphasized that dual cyclooxygenase-2/5-lipoxygenase (COX-2/5-LO) or dual 5-lipoxygenase/microsomal prostaglandin E synthase-1 (5-LO/mPGES-1) inhibitors possess considerable inhibitory activities against their target enzymes as well as potent antiproliferative effects. Several papers disclosing 5-lipoxygenase activating protein (FLAP) antagonists as a new group of 5-LO activity regulators are also subject to this review. Also, the potential of 12-lipoxygenase (12- LO) and 15-lipoxygenase (15-LO) inhibitors as chemopreventive agents was outlined to expand the scope of new anticancer agents discovery. Some peptides and peptidomimetics with anti-LT activities were described as well. In addition, the cytotoxic effects of lipoxygenase inhibitors and their adverse effects were discussed and some novel series of natural-product-derived inhibitors of LO was also discussed in this review.

CONCLUSION

This review gives insights into the novel lipoxygenase inhibitors with anticancer activity as well as the different molecular pharmacological strategies to inhibit the enzyme effectively. The findings confirm that certain groups of LO inhibitors could act as promising chemopreventive agents.

A Review of Anti-Cancer and Related Properties of Lichen-Extracts and Metabolites

BACKGROUND

Lichens are a composite consortium of fungus and alga. The symbiotic organisms are naturally equipped with distinct characteristics as compared to constituting organisms separately. Lichens due to their peculiar anatomy and physiology, are the reservoir of more than 600 unique secondary metabolites, also known as 'lichen substances'. Since ancient times, many ethnic groups from various parts of the world had knowledge about the applications of lichens as major provenance of food/fodder, medicine, dyes, spices, perfumes, etc. Lichen substances have shown impressive antioxidant, antimicrobial, antiviral, antitumor, and anti-inflammatory activities under experimental conditions. Usnic acid, a well-known metabolite, found in several species of lichens, possesses potent antioxidant and anti-inflammatory activities. It also has significant anti-proliferative potential as revealed through testing in different cancer cell lines. Atranorin, Lecanoric acid, Norstictic acid, Lobaric acid, Stictic acid, Ramalin, Gyrophoric acid, Salazinic acid, Protolichesterinic, and Fumarprotocetraric acid are some of the other purified lichen metabolites with potent anti-cancer activities.

OBJECTIVE

This study presents an overview of lichen derived extracts/compounds augmenting the anti-cancer (related) properties.

METHOD

The review comprehends different studies (in vivo and in vitro) backing up the possibility of lichen extracts and metabolites towards their use as antioxidant, anti-proliferative, anti-inflammatory and EMT-inhibiting agents.

RESULTS

The review focuses on anti-cancer and related properties of lichen extracts and metabolites that include their anti-oxidative, anti-inflammatory, anti-proliferative and pro-apoptotic, cancer stemness reduction, activities and, the potential of inhibition of cancer-associated Epithelial-mesenchymal transition (EMT) that is responsible for multiple drug-resistance and metastasis of cancer cells in a large proportion of cases.

CONCLUSION

Lichens can be the repertoire of a plethora of lichen metabolites with putative bioactive potential, which is needed to be explored in order to find out novel anti-cancer drugs.

Anti-inflammatory effects of methanol extracts from the Antarctic lichen, Amandinea sp. in LPS-stimulated raw 264.7 macrophages and zebrafish

The aim of the present study was to determine the anti-inflammatory effect of an extracts isolated from the lichen. Amandinea sp. was collected from the Antarctic and extracted with methanol. The basic screening of the anti-inflammatory property of the extracts was done using the NO assay. The extracts showed very little cytotoxicity, and reduced NO production in LPS-stimulated RAW 264.7 cells in a dose-dependent manner. Furthermore, the extracts inhibited LPS-induced release of pro-inflammatory cytokines such as interleukin-6 (IL-6), and tumor necrosis factor-α(TNF-α), and inflammatory mediators inducible nitric oxide synthase (iNOS), and cyclooxygenase-2 (COX-2). The extracts also reduced the cytosolic p-IκB-α level and the level of the nuclear factor p65. We examined the anti-inflammatory effects of the extracts using zebrafish in vivo. The extracts reduced the amount of reactive oxygen species (ROS) in LPS-induced zebrafish larvae and inhibited the mRNA expression of inflammatory cytokines and mediators in a tail-cutting induced model. These results are similar to those obtained in vitro with RAW 264.7 cells. Collectively, the data suggest that the extracts may contain one of more compounds with anti-inflammatory effects. Further studies are required to identify the candidate compound/s and to understand the mechanism of action of the extract.

Arenicolins: C-Glycosylated Depsides from Penicillium arenicola

During investigation of the secondary metabolism of four strains of Penicillium arenicola, two new depsides, arenicolins A (1) and B (2), were isolated and characterized. Their structures were established mainly by analysis of NMR and HRMS data and by comparison with known compounds. These depsides incorporate intriguing structural features, including dual alkyl side chains and a C-glycosyl unit, with 1 also containing an acylated 2-hydroxymethyl-4,5,6-trihydroxycyclohexenone moiety. Although the arenicolins were produced by all strains tested, arenicolin A (1) was obtained using only one of five medium compositions employed, while arenicolin B (2) was produced in all media tested. Neither compound showed antibacterial or antifungal activity, but 1 exhibited cytotoxicity toward mammalian cell lines, including colorectal carcinoma (HCT-116), neuroblastoma (IMR-32), and ductal carcinoma (BT-474), with IC50 values of 7.3, 6.0, and 9.7 μM, respectively.

Anticancer Potential of Lichens' Secondary Metabolites

Lichens produce different classes of phenolic compounds, including anthraquinones, xanthones, dibenzofuranes, depsides and depsidones. Many of them have revealed effective biological activities such as antioxidant, antiviral, antibiotics, antifungal, and anticancer. Although no clinical study has been conducted yet, there are number of in vitro and in vivo studies demonstrating anticancer effects of lichen metabolites. The main goal of our work was to review most recent published papers dealing with anticancer activities of secondary metabolites of lichens and point out to their perspective clinical use in cancer management.

Lobaric acid and pseudodepsidones inhibit NF-κB signaling pathway by activation of PPAR-γ

Herein we report the anti-inflammatory activity of lobaric acid and pseudodepsidones isolated from the nordic lichen Stereocaulon paschale. Lobaric acid (1) and three compounds (2, 7 and 9) were found to inhibit the NF-κB activation and the secretion of pro-inflammatory cytokines (IL-1β and TNF-α) in LPS-stimulated macrophages. Inhibition and docking simulation experiments provided evidence that lobaric acid and pseudodepsidones bind to PPAR-γ between helix H3 and the beta sheet, similarly to partial PPAR-γ agonists. These findings suggest that lobaric acid and pseudodepsidones reduce the expression of pro-inflammatory cytokines by blocking the NF-κB pathway via the activation of PPAR-γ.

Ingredients from Litsea garrettii as Potential Preventive Agents against Oxidative Insult and Inflammatory Response

Oxidative stress and inflammation undoubtedly contribute to the pathogenesis of many human diseases. The nuclear transcription factor erythroid 2-related factor (Nrf2) and the nuclear factor κB (NF-κB) play central roles in regulation of oxidative stress and inflammation and thus are targets for developing agents against oxidative stress- and inflammation-related diseases. Our previous study indicated that the EtOH extract of Litsea garrettii protected human bronchial epithelial cells against oxidative insult via the activation of Nrf2. In the present study, a systemic phytochemical investigation of L. garrettii led to the isolation of twenty-one chemical ingredients, which were further evaluated for their inhibitions on oxidative stress and inflammation using NAD(P)H:quinone reductase (QR) assay and nitric oxide (NO) production assay. Of these ingredients, 3-methoxy-5-pentyl-phenol (MPP, 5) was identified as an Nrf2 activator and an NF-κB inhibitor. Further studies demonstrated the following: (i) MPP upregulated the protein levels of Nrf2, NAD(P)H:quinone oxidoreductase 1 (NQO1), and glutamate-cysteine ligase regulatory subunit (GCLM); enhanced the nuclear translocation and stabilization of Nrf2; and inhibited arsenic [As(III)]-induced oxidative insult in normal human lung epithelial Beas-2B cells. And (ii) MPP suppressed the nuclear translocation of NF-κB p65 subunit; inhibited the lipopolysaccharide- (LPS-) stimulated increases of NF-κB p65 subunit, COX-2, iNOS, TNF-α, and IL-1β; and blocked the LPS-induced biodegrade of IκB-α in RAW 264.7 murine macrophages. Taken together, MPP displayed potential preventive effects against inflammation- and oxidative stress-related diseases.

Lichens as a source of chemical compounds with anti-inflammatory activity

Symptoms of inflammation accompany a number of diseases. In order to mitigate them, folk medicine has used a variety of medicinal substances, including herbs and mushrooms. Lichens are less known organisms, containing specific secondary metabolites with interesting biological properties. One of their biological actions is the anti-inflammatory activity that has been confirmed by in vitro and animal studies. It has been proven that compounds and extracts from lichens inhibit the enzymes involved in the inflammatory process. The following paper is a review of research on the little-known anti-inflammatory properties of lichens.

Natural products as inhibitors of prostaglandin E2 and pro-inflammatory 5-lipoxygenase-derived lipid mediator biosynthesis

Non-steroidal anti-inflammatory drugs (NSAIDs) inhibit prostanoid formation and represent prevalent therapeutics for treatment of inflammatory disorders. However, NSAIDs are afflicted with severe side effects, which might be circumvented by more selective suppression of pro-inflammatory eicosanoid biosynthesis. This concept led to dual inhibitors of microsomal prostaglandin E₂ synthase (mPGES)-1 and 5-lipoxygenase that are crucial enzymes in the biosynthesis of pro-inflammatory prostaglandin E₂ and leukotrienes. The potential of their dual inhibition in light of superior efficacy and safety is discussed. Focus is placed on natural products, for which direct inhibition of mPGES-1 and leukotriene biosynthesis has been confirmed.

Anti-mutagenic and Anti-oxidant Potencies of Cetraria Aculeata (Schreb.) Fr., Cladonia Chlorophaea (Flörke ex Sommerf.) Spreng. and Cetrelia olivetorum (Nyl.) W.L. Culb. & C.F. Culb.)

In this study, the mutagenic and anti-mutagenic effects of methanol extract of three lichen species (Cetraria aculeata, Cladonia chlorophaea and Cetrelia olivetorum) were investigated by using E. coli-WP2, Ames-Salmonella (TA1535 and TA1537) and sister chromatid exchange (SCE) test systems. The results obtained from bacterial test systems demonstrated that methanol extracts of three lichen species have strong anti-mutagenic potencies on TA1535, TA1537 strains and to a lesser extent on E. coli-WP2 strain. The anti-oxidant level of human lymphocytes cells was determined in order to clarify the mechanism underlying the anti-mutagenic effects of these lichen species. Co-treatments of 5, 10 and 20 µg/mL concentrations of these three lichen species with AFB decreased the frequencies of SCE and the level of MDA and increased the amount of SOD, GSH and GPx which decreased by aflatoxin. The findings of this work have clearly demonstrated that Cetraria aculeata, Cladonia chlorophaea and Cetrelia olivetorum have significant anti-mutagenic effects which are thought to be partly due to the anti-oxidant activities and the interaction capability of lichen extracts with mutagen agents (Sodium azide, acridin, N-methyl-N'-nitro-N-nitrosoguanidine and aflatoxin B₁).

Potential Antiosteoporotic Natural Product Lead Compounds That Inhibit 17β-Hydroxysteroid Dehydrogenase Type 2

17β-Hydroxysteroid dehydrogenase type 2 (17β-HSD2) converts the active steroid hormones estradiol, testosterone, and 5α-dihydrotestosterone into their weakly active forms estrone, Δ⁴-androstene-3,17-dione, and 5α-androstane-3,17-dione, respectively, thereby regulating cell- and tissue-specific steroid action. As reduced levels of active steroids are associated with compromised bone health and onset of osteoporosis, 17β-HSD2 is considered a target for antiosteoporotic treatment. In this study, a pharmacophore model based on 17β-HSD2 inhibitors was applied to a virtual screening of various databases containing natural products in order to discover new lead structures from nature. In total, 36 hit molecules were selected for biological evaluation. Of these compounds, 12 inhibited 17β-HSD2 with nanomolar to low micromolar IC₅₀ values. The most potent compounds, nordihydroguaiaretic acid (1), IC₅₀ 0.38 ± 0.04 μM, (-)-dihydroguaiaretic acid (4), IC₅₀ 0.94 ± 0.02 μM, isoliquiritigenin (6), IC₅₀ 0.36 ± 0.08 μM, and ethyl vanillate (12), IC₅₀ 1.28 ± 0.26 μM, showed 8-fold or higher selectivity over 17β-HSD1. As some of the identified compounds belong to the same structural class, structure-activity relationships were derived for these molecules. Thus, this study describes new 17β-HSD2 inhibitors from nature and provides insights into the binding pocket of 17β-HSD2, offering a promising starting point for further research in this area.

Lichen-derived compounds show potential for central nervous system therapeutics

BACKGROUND

Natural products from lichens are widely investigated for their biological properties, yet their potential as central nervous system (CNS) therapeutic agents is less explored.

PURPOSE

The present study investigated the neuroactive properties of selected lichen compounds (atranorin, perlatolic acid, physodic acid and usnic acid), for their neurotrophic, neurogenic and acetylcholine esterase (AChE) activities.

METHODS

Neurotrophic activity (neurite outgrowth) was determined using murine neuroblastoma Neuro2A cells. A MTT assay was performed to assess the cytotoxicity of compounds at optimum neurotrophic activity. Neuro2A cells treated with neurotrophic lichen compounds were used for RT-PCR to evaluate the induction of genes that code for the neurotrophic markers BDNF and NGF. Immunoblotting was used to assess acetyl H3 and H4 levels, the epigenetic markers associated with neurotrophic and/or neurogenic activity. The neurogenic property of the compounds was determined using murine hippocampal primary cultures. AChE inhibition activity was performed using a modified Ellman's esterase method.

RESULTS

Lichen compounds atranorin, perlatolic acid, physodic acid and (+)-usnic acid showed neurotrophic activity in a preliminary cell-based screening based on Neuro2A neurite outgrowth. Except for usnic acid, no cytotoxic effects were observed for the two depsides (atranorin and perlatolic acid) and the alkyl depsidone (physodic acid). Perlatolic acid appears to be promising, as it also exhibited AChE inhibition activity and potent proneurogenic activity. The neurotrophic lichen compounds (atranorin, perlatolic acid, physodic acid) modulated the gene expression of BDNF and NGF. In addition, perlatolic acid showed increased protein levels of acetyl H3 and H4 in Neuro2A cells.

CONCLUSION

These lichen depsides and depsidones showed neuroactive properties in vitro (Neuro2A cells) and ex vivo (primary neural stem or progenitor cells), suggesting their potential to treat CNS disorders.

Natural Products to Counteract the Epidemic of Cardiovascular and Metabolic Disorders

Natural products have always been exploited to promote health and served as a valuable source for the discovery of new drugs. In this review, the great potential of natural compounds and medicinal plants for the treatment or prevention of cardiovascular and metabolic disorders, global health problems with rising prevalence, is addressed. Special emphasis is laid on natural products for which efficacy and safety have already been proven and which are in clinical trials, as well as on plants used in traditional medicine. Potential benefits from certain dietary habits and dietary constituents, as well as common molecular targets of natural products, are also briefly discussed. A glimpse at the history of statins and biguanides, two prominent representatives of natural products (or their derivatives) in the fight against metabolic disease, is also included. The present review aims to serve as an "opening" of this special issue of Molecules, presenting key historical developments, recent advances, and future perspectives outlining the potential of natural products for prevention or therapy of cardiovascular and metabolic disease.

Drugs from nature targeting inflammation (DNTI): a successful Austrian interdisciplinary network project

ABSTRACT

Inflammation is part of numerous pathological conditions, which are lacking satisfying treatment and effective concepts of prevention. A national research network project, DNTI, involving scientists from six Austrian universities as well as several external partners aimed to identify and characterize natural products capable of combating inflammatory processes specifically in the cardiovascular system. The combined use of computational techniques with traditional knowledge, high-tech chemical analysis and synthesis, and a broad range of in vitro, cell-based, and in vivo pharmacological models led to the identification of a series of promising anti-inflammatory drug lead candidates. Mechanistic studies contributed to a better understanding of their mechanism of action and delivered new knowledge on the molecular level of inflammatory processes. Herein, the used approaches and selected highlights of the results of this interdisciplinary project are presented.

GRAPHICAL ABSTRACT

Chemotaxonomic discrimination of lichen species using an infrared chalcogenide fibre optic sensor: a useful tool for on-field biosourcing

Spectral analysis of lichen extracts obtained by MIR-FEWS permits to discriminate species and the identification of their major compounds. MIR-FEWS is a rapid, efficient and convenient tool for metabolic profiling.