Anti-proliferative effects of lichen-derived inhibitors of 5-lipoxygenase on malignant cell-lines and mitogen-stimulated lymphocytes

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.

The Anti-Proliferative Lichen-Compound Protolichesterinic Acid Inhibits Oxidative Phosphorylation and Is Processed via the Mercapturic Pathway in Cancer Cells

The lichen compound protolichesterinic acid (PA) has an anti-proliferative effect against several cancer cell lines of different origin. This effect cannot be explained by the known inhibitory activity of PA against 5- and 12-lipoxygenases. The aim was therefore to search for mechanisms for the anti-proliferative activity of PA. Two cancer cell lines of different origin, both sensitive to anti-proliferative effects of PA, were selected for this study, T-47D from breast cancer and AsPC-1 from pancreatic cancer. Morphological changes were assessed by transmission electron microscopy, HPLC coupled with TOF spectrometry was used for metabolomics, mitochondrial function was measured using the Agilent Seahorse XFp Real-time ATP assay and glucose/lactate levels by radiometry. Levels of glutathione, NADP/NADPH and reactive oxygen species [ROS] were measured by luminescence. Following exposure to PA both cell lines showed structural changes in mitochondria that were in line with a measured reduction in oxidative phosphorylation and increased glycolysis. These changes were more marked in T-47D, which had poorer mitochondrial function at baseline. PA was processed and expelled from the cells via the mercapturic pathway, which consumes glutathione. Nevertheless, glutathione levels were increased after 24 hours of exposure to PA, implying enhanced synthesis. Redox balance was not much affected and ROS levels were not increased. We conclude that PA is metabolically processed and expelled from cells, leading indirectly to increased glutathione levels with minimal effects on redox balance. The most marked effect was on mitochondrial structure and metabolic function implying that effects of PA may depend on mitochondrial fitness.

The Genus Cetraria s. str.-A Review of Its Botany, Phytochemistry, Traditional Uses and Pharmacology

The genus Cetraria s. str. (Parmeliaceae family, Cetrarioid clade) consists of 15 species of mostly erect brown or greenish yellow fruticose or subfoliose thallus. These Cetraria species have a cosmopolitan distribution, being primarily located in the Northern Hemisphere, in North America and in the Eurasia area. Phytochemical analysis has demonstrated the presence of dibenzofuran derivatives (usnic acid), depsidones (fumarprotocetraric and protocetraric acids) and fatty acids (lichesterinic and protolichesterinic acids). The species of Cetraria, and more particularly Cetraria islandica, has been widely employed in folk medicine for the treatment of digestive and respiratory diseases as decoctions, tinctures, aqueous extract, and infusions. Moreover, Cetraria islandica has had an important nutritional and cosmetic value. These traditional uses have been validated in in vitro and in vivo pharmacological studies. Additionally, new therapeutic activities are being investigated, such as antioxidant, immunomodulatory, cytotoxic, genotoxic and antigenotoxic. Among all Cetraria species, the most investigated by far has been Cetraria islandica, followed by Cetraria pinastri and Cetraria aculeata. The aim of the current review is to update all the knowledge about the genus Cetraria covering aspects that include taxonomy and phylogeny, morphology and distribution, ecological and environmental interest, phytochemistry, traditional uses and pharmacological properties.

Lichens as a repository of bioactive compounds: an open window for green therapy against diverse cancers

Lichens, algae and fungi-based symbiotic associations, are sources of many important secondary metabolites, such as antibiotics, anti-inflammatory, antioxidants, and anticancer agents. Wide range of experiments based on in vivo and in vitro studies revealed that lichens are a rich treasure of anti-cancer compounds. Lichen extracts and isolated lichen compounds can interact with all biological entities currently identified to be responsible for tumor development. The critical ways to control the cancer development include induction of cell cycle arrests, blocking communication of growth factors, activation of anti-tumor immunity, inhibition of tumor-friendly inflammation, inhibition of tumor metastasis, and suppressing chromosome dysfunction. Also, lichen-based compounds induce the killing of cells by the process of apoptosis, autophagy, and necrosis, that inturn positively modulates metabolic networks of cells against uncontrolled cell division. Many lichen-based compounds have proven to possess potential anti-cancer activity against a wide range of cancer cells, either alone or in conjunction with other anti-cancer compounds. This review primarily emphasizes on an updated account of the repository of secondary metabolites reported in lichens. Besides, we discuss the anti-cancer potential and possible mechanism of the most frequently reported secondary metabolites derived from lichens.

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.

Reduction of paw edema and liver oxidative stress in carrageenan-induced acute inflammation by Lobaria pulmonaria and Parmelia caperata, lichen species, in mice

Paw edema volume reduction is a useful marker in determining the anti-inflammatory effect of drugs and plant extracts in carrageenan-induced acute inflammation. In this study, the anti-inflammatory effect of Lobaria pulmonaria (LP) and Parmelia caperata (PC), two lichen species, was examined in carrageenan-induced mouse paw edema test. Compared to the controls in carrageenan-induced inflammation (n = 5/group), our results showed that pretreatment by single oral doses with PC extract (50-500 mg/kg) gives better results than LP extract (50-500 mg/kg) in terms of anti-edematous activity, as after 4 h of carrageenan subplantar injection, paw edema formation was inhibited at 82-99% by PC while at 35-49% by LP. The higher anti-inflammatory effect of PC, at all doses, was also observed on the time-course of carrageenan-induced paw edema, displaying profile closely similar to that obtained with diclofenac (25 mg/kg), an anti-inflammatory drug reference (all p < 0.001). Both LP and PC, at all doses, significantly ameliorated liver catalase (CAT) activity (all p < 0.05). However, superoxide dismutase (SOD) activity, glutathione peroxidase (GPx) activity and glutathione (GSH) levels were found increased in liver of PC- compared to LP-carrageenan-injected mice. Our findings demonstrated on one hand higher preventive effects of PC compared to LP in a mouse carrageenan-induced inflammatory model and suggested, on the other hand, that anti-inflammatory effects elicited by the two lichens were closely associated with the amelioration in the endogenous antioxidant status of liver.

Lichen Acids May Be Used as A Potential Drug For Cancer Therapy; by Inhibiting Mitochondrial Thioredoxin Reductase Purified From Rat Lung

Background:

Thioredoxin reductase (E.C 1.6.4.5.; TrxR) is a widely distributed flavoprotein that catalyzes the NADPH-dependent reduction of thioredoxin (Trx) in many cellular events such as DNA synthesis, DNA repair, angiogenesis, antioxidative defense, and regulating apoptosis. Although TrxR is indispensible in protecting cells against oxidative stress, the overexpression of TrxR is seen in many aggressive tumors. Therefore, targeted inhibition of TrxR has been accepted as a new approach for chemotherapy.

Objective:

In this study, in vitro inhibition effect of the lichen acids (diffractaic, evernic, lobaric, lecanoric, and vulpinic acid) on mitochondrial TrxR purified from rat lung was investigated.

Method:

It was the first time the enzyme was purified from rat lungs by using 2’, 5’-ADP Sepharose 4B affinity chromatography. The purity of the enzyme was checked with SDS-PAGE. In vitro inhibition effect of the lichen acids was investigated spectrophotometrically. To emphasize the importance of the obtained data, the commercial anticancer drugs cisplatin and doxorubicin were used as positive controls.

Results:

Molecular mass of the enzyme was calculated as approximately 52.4 kDa. The enzyme was purified with a 63.6% yield, 208.3 fold, and 0.5 EU/mg proteins specific activity. The IC50 values of five lichen acids were significantly lower than IC50 values of anticancer drugs.

Conclusion:

All of the lichen acids, especially lecanoric and vulpinic acid, exhibited much stronger inhibitory effect on TrxR than the anticancer drugs cisplatin and doxorubicin. These lichen acids have pharmacological potential as effective natural antioxidants, antimicrobials, and anticancer agents.

Natural products: a hope for glioblastoma patients

Glioblastoma (GBM) is one of the most aggressive malignant tumors with an overall dismal survival averaging one year despite multimodality therapeutic interventions including surgery, radiotherapy and concomitant and adjuvant chemotherapy. Few drugs are FDA approved for GBM, and the addition of temozolomide (TMZ) to standard therapy increases the median survival by only 2.5 months. Targeted therapy appeared promising in in vitro monolayer cultures, but disappointed in preclinical and clinical trials, partly due to the poor penetration of drugs through the blood brain barrier (BBB). Cancer stem cells (CSCs) have intrinsic resistance to initial chemoradiation therapy (CRT) and acquire further resistance via deregulation of many signaling pathways. Due to the failure of classical chemotherapies and targeted drugs, research efforts focusing on the use of less toxic agents have increased. Interestingly, multiple natural compounds have shown antitumor and apoptotic effects in TMZ resistant and p53 mutant GBM cell lines and also displayed synergistic effects with TMZ. In this review, we have summarized the current literature on natural products or product analogs used to modulate the BBB permeability, induce cell death, eradicate CSCs and sensitize GBM to CRT.

Anti-Cancer Activity of Lobaric Acid and Lobarstin Extracted from the Antarctic Lichen Stereocaulon alpnum

Lobaric acid and lobarstin, secondary metabolites derived from the antarctic lichen Stereocaulon alpnum, exert various biological activities, including antitumor, anti-proliferation, anti-inflammation, and antioxidant activities. However, the underlying mechanisms of these effects have not yet been elucidated in human cervix adenocarcinoma and human colon carcinoma. In the present study, we evaluated the anticancer effects of lobaric acid and lobarstin on human cervix adenocarcinoma HeLa cells and colon carcinoma HCT116 cells. We show that the proliferation of Hela and HCT116 cells treated with lobaric acid and lobarstin significantly decreased in a dose- and time-dependent manner. Using flow cytometry analysis, we observed that the treatment with these compounds resulted in significant apoptosis in both cell lines, following cell cycle perturbation and arrest in G2/M phase. Furthermore, using immunoblot analysis, we investigated the expression of cell cycle and apoptosis-related marker genes and found a significant downregulation of the apoptosis regulator B-cell lymphoma 2 (Bcl-2) and upregulation of the cleaved form of the poly (ADP-ribose) polymerase (PARP), a DNA repair and apoptosis regulator. These results suggest that lobaric acid and lobarstin could significantly inhibit cell proliferation through cell cycle arrest and induction of apoptosis via the mitochondrial apoptotic pathway in cervix adenocarcinoma and colon carcinoma cells. Taken together, our data suggests that lobaric acid and lobarstin might be novel agents for clinical treatment of cervix adenocarcinoma and colon carcinoma.

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.

Murine breast carcinoma 4T1 cells are more sensitive to atranorin than normal epithelial NMuMG cells in vitro: Anticancer and hepatoprotective effects of atranorin in vivo

The aim of this study was to evaluate the anticancer effect of atranorin (ATR) on murine 4T1 breast carcinoma cells and compare its sensitivity with normal mammary epithelial NMuMG cells in vitro. Anti-tumor and hepatoprotective activity of ATR-therapy was examined on mouse model of 4T1-induced cancer disease. ATR significantly reduced clonogenic ability of carcinoma 4T1 cells at the concentration of 75 μM, but clonogenicity of normal NMuMG cells was not affected by any of ATR concentrations tested. Moreover, flow cytometric and BrdU incorporation analysis did not confirm the inhibited entry into S-phase of the cell cyle after ATR incubation, and on the contrary, it induced apoptosis associated with the activation of caspase-3 and PARP cleavage in 4T1 cells. Although ATR did not cause any significant changes in Bcl-xL protein expression in NMuMG cells, an apparent depletion of Bcl-xL protein in 4T1 cells after 48 h ATR therapy was confirmed. Based on this result as well as the result of the total cell number decline, we can conclude that 4T1 cells are more sensitive to ATR therapy than NMuMG cells. ATR administration resulted in significantly longer survival time of BALB/c mice inoculated with 4T1 cells, what was associated with reduced tumor size and the higher numbers of apoptotic 4T1 cells. No differences were recorded in the number of BrdU-positive tumor cells between ATR-treated group and controls. Results indicate that ATR has rather proapoptotic than antiproliferative effect on 4T1 cells in vitro and in vivo and normal NMuMG cells are less sensitive to ATR. Furthermore, our studies revealed protective effect of ATR against oxidative stress in the livers of the tumor-bearing mice.

Lobaric Acid Inhibits VCAM-1 Expression in TNF-α-Stimulated Vascular Smooth Muscle Cells via Modulation of NF-κB and MAPK Signaling Pathways

Lichens have been known to possess multiple biological activities, including anti-proliferative and anti-inflammatory activities. Vascular cell adhesion molecule-1 (VCAM-1) may play a role in the development of atherosclerosis. Hence, VCAM-1 is a possible therapeutic target in the treatment of the inflammatory disease. However, the effect of lobaric acid on VCAM-1 has not yet been investigated and characterized. For this study, we examined the effect of lobaric acid on the inhibition of VCAM-1 in tumor necrosis factor-alpha (TNF-α)-stimulated mouse vascular smooth muscle cells. Western blot and ELISA showed that the increased expression of VCAM-1 by TNF-α was significantly suppressed by the pre-treatment of lobaric acid (0.1–10 μg/ml) for 2 h. Lobaric acid abrogated TNF-α-induced NF-κB activity through preventing the degradation of IκB and phosphorylation of extracellular signal-regulated kinases (ERK), c-Jun N-terminal kinases (JNK), and p38 mitogen activated protein (MAP) kinase. Lobaric acid also inhibited the expression of TNF-α receptor 1 (TNF-R1). Overall, our results suggest that lobaric acid inhibited VCAM-1 expression through the inhibition of p38, ERK, JNK and NF-κB signaling pathways, and downregulation of TNF-R1 expression. Therefore, it is implicated that lobaric acid may suppress inflammation by altering the physiology of the atherosclerotic lesion.

Anti-proliferative and pro-apoptotic effects of lichen-derived compound protolichesterinic acid are not mediated by its lipoxygenase-inhibitory activity

Lipoxygenases (LOXs) and their products are involved in several biological functions and have been associated with carcinogenesis. Protolichesterinic acid (PA), a lichen metabolite, inhibits 5- and 12-LOX and has anti-proliferative effects on various cancer cell lines. Here, PA was shown to inhibit proliferation of multiple myeloma cells, RPMI 8226 and U266, and pancreatic cancer cells AsPC-1. Apoptosis was induced only in multiple myeloma cells. Cell-cycle associated changes in expression and sub-cellular localization of 5- and 12-LOX were not affected by PA but increased cytoplasmic localisation was found to accompany morphological changes at later stages. Assessment by mass spectrometry showed that PA entered the pancreatic cancer cells. However, effects on LOX metabolites were only evident after treatment with concentrations exceeding those having anti-proliferative effects and no effects were measurable in the myeloma cells. We conclude that the anti-proliferative and pro-apoptotic effects of PA are not mediated directly through inhibition of LOX activity.

Myxochelins target human 5-lipoxygenase

Extracts of the predatory myxobacterium Pyxidicoccus fallax HKI 727 showed antiproliferative effects on leukemic K-562 cells. Bioactivity-guided fractionation led to the isolation of the bis-catechol myxochelin A and two new congeners. The biosynthetic origin of myxochelins C and D was confirmed by feeding studies with isotopically labeled precursors. Pharmacological testing revealed human 5-lipoxygenase (5-LO) as a molecular target of the myxochelins. In particular, myxochelin A efficiently inhibited 5-LO activity with an IC50 of 1.9 μM and reduced the proliferation of K-562 cells at similar concentrations.

Enzymatic resolution of α-methyleneparaconic acids and evaluation of their biological activity

Both enantiomers of three biologically relevant paraconic acids-MB-3, methylenolactocin, and C75-were obtained with enantioselectivities up to 99% by kinetic enzymatic resolutions. Good enantiomeric excesses were obtained for MB-3 and methylenolactocin, using α-chymotrypsin and aminoacylase as enantiocomplementary enzymes, while C75 was resolved with aminoacylase. They all were evaluated for their antiproliferative, antibacterial, and antifungal activities, showing weak effects and practically no difference between enantiomers in each case. At high concentrations (16-64 µg/mL), (-)- C75 acted as an antimicrobial agent against Gram-positive bacteria.

Effects of anti-proliferative lichen metabolite, protolichesterinic acid on fatty acid synthase, cell signalling and drug response in breast cancer cells

BACKGROUND

The lichen compound (+)-protolichesterinic acid (+)-PA, isolated from Iceland moss, has anti-proliferative effects on several cancer cell lines. The chemical structure of (+)-PA is similar to a known fatty acid synthase (FASN) inhibitor C75.

AIMS

To test whether the anti-proliferative activity of (+)-PA is associated with effects on FASN and HER2 (human epidermal growth factor receptor 2) and major signalling pathways. Synergism between (+)-PA and lapatinib, a HER2 active drug, was also evaluated.

MATERIALS AND METHODS

Pure compound was isolated by preparative high-performance liquid chromatography (HPLC) and purity of (+)-PA analyzed by analytical HPLC. Cell viability was assessed using Crystal violet staining. FASN and HER2 expression was estimated by immunofluorescence. The Meso Scale Discovery (MSD)(®) assay was used to measure activation of ERK1/2 and AKT. Synergism was estimated by the CalcuSyn software.

RESULTS

Treatment with (+)-PA increased FASN expression in SK-BR-3 cells, which overexpress FASN and HER2, implying a compensatory response to inhibition of FASN activity. HER2 expression was decreased suggesting secondary downregulation. ERK1/2 and AKT signalling pathways were inhibited, probably due to reduced levels of HER2. No effects were observed in T-47D cells. Synergism between (+)-PA and lapatinib was observed in the SK-BR-3 cells.

CONCLUSION

Results suggest that the primary effect of (+)-PA is inhibition of FASN activity. Synergistic effects with lapatinib were seen only in SK-BR-3 cells, and not T-47D cells, further supporting the notion that (+)-PA acts by inhibiting FASN with secondary effects on HER2 expression and signalling. (+)-PA could therefore be a suitable agent for further testing, alone or in combination treatment against HER2-overexpressing breast cancer.

Estonian folk traditional experiences on natural anticancer remedies: from past to the future

CONTEXT

Despite diagnostic and therapeutic advancements, the burden of cancer is still increasing worldwide. Toxicity of current chemotherapeutics to normal cells and their resistance to tumor cells highlights the urgent need for new drugs with minimal adverse side effects. The use of natural anticancer agents has entered into the area of cancer research and increased efforts are being made to isolate bioactive products from medicinal plants.

OBJECTIVE

To lead the search for plants with potential cytotoxic activity, ethnopharmacological knowledge can give a great contribution. Therefore, the attention of this review is devoted to the natural remedies traditionally used for the cancer treatment by Estonian people over a period of almost 150 years.

METHODS

Two massive databases, the first one stored in the Estonian Folklore Archives and the second one in the electronic database HERBA ( http://herba.folklore.ee/ ), containing altogether more than 30 000 ethnomedicinal texts were systematically reviewed to compile data about the Estonian folk traditional experiences on natural anticancer remedies.

RESULTS AND CONCLUSION

As a result, 44 different plants with potential anticancer properties were elicited, 5 of which [Angelica sylvestris L. (Apiaceae), Anthemis tinctoria L. (Asteraceae), Pinus sylvestris L. (Pinaceae), Sorbus aucuparia L. (Rosaceae), and Prunus padus L. (Rosaceae)] have not been previously described with respect to their tumoricidal activities in the scientific literature, suggesting thus the potential herbal materials for further investigations of natural anticancer compounds.

The antioxidant and antigenotoxic potential of methanol extract of Cladonia foliacea (Huds.) Willd

In this article, the genotoxic and antigenotoxic effects of methanol extract of of Cladonia foliacea (Huds.) Willd. (CME) were studied using WP2, Ames (TA1535 and TA1537), and sister chromatid exchange (SCE) test systems. The results of our studies showed that 5 µM concentration of aflatoxin B1(AFB1) changed the frequencies of SCE and malondialdehyde (MDA) levels, superoxide dismutase (SOD), glutathione (GSH), and glutathione peroxidase (GPx) activities. When 5 and 10 µg/mL concentrations of CME was added to AFB1, the frequencies of SCE and MDA level were decreased and SOD, GSH, and GPx levels were increased. The extract CME did not show any mutagenicity on Ames (Salmonella typhimurium TA1535, TA1537) and WP2 (Escherichia coli) test systems. On the other hand, CME has antimutagenicity on the mentioned test systems. The results of this experiment have clearly shown that CME has a significant antioxidative and antigenotoxic effect, which is thought to be due to the antigenotoxic activities of antioxidant enzymes.

Expectorant and antioxidant activities of purified fumarprotocetraric acid from Cladonia verticillaris lichen in mice

The lichen Cladonia verticillaris produces bioactive secondary metabolites, such as fumarprotocetraric (FUM) and protocetraric acids. Species of the genus Cladonia demonstrate anti-tumor, anti-inflammatory and antipyretic activities and have been used in folk medicine to treat respiratory diseases (throat irritation, cough, asthma and tuberculosis). The aim of the present study was to evaluate the expectorant and mucolytic activities of fumarprotocetraric acid in albino Swiss mice. FUM was extracted and purified from an acetone extract of C. verticillaris. The phenol red quantification method was used on the bronchoalveolar lavage fluid following the administration of FUM (25, 50 or 100 mg/kg orally or intraduodenally and 12.5, 25 or 50 mg/kg, intraperitoneally) for the evaluation of expectorant activity. Control groups received either saline solution (7.5 mL/kg) or ambroxol (1 mg/kg) through the same administration routes. Antioxidant activity was evaluated using the thiobarbituric acid reactive species assay in mouse lung tissue treated with the FUM at 25, 50 or 100 mg/kg orally, followed by a lipopolysaccharide solution at 1 mg/kg intrapleurally. The same protocol was used for the control groups using either saline solution (7.5 mL/kg, orally) or N-acetylcysteine (20 mg/kg, orally).

RESULTS

Orally administered FUM at doses of 25 and 50 mg/kg promoted significantly greater dose-dependent phenol red activity in the bronchoalveolar lavage and expectorant activity in comparison to the controls (p < 0.05). Lipid peroxidation (malondialdehyde equivalent) was reduced by 50% in the lung tissue.

CONCLUSION

The results confirm the expectorant and antioxidant properties of fumarprotocetraric acid produced by the lichen C. verticillaris.

Biopharmaceutical potential of lichens

CONTEXT

Lichens are composite organisms consisting of a symbiotic association of a fungus (the mycobiont) with a photosynthetic partner (the phytobiont), usually either a green alga or cyanobacterium. The morphology, physiology and biochemistry of lichens are very different from those of the isolated fungus and alga in culture. Lichens occur in some of the most extreme environments on the Earth and may be useful to scientists in many commercial applications.

OBJECTIVE

Over the past 2 decades, there has been a renewed and growing interest in lichens as a source of novel, pharmacologically active biomolecules. This review summarizes the past and current research and development trends in the characterization and use of lichens and their bioactive compounds in traditional medicine and other biopharmaceutical applications of commercial interest.

METHODS

The present review contains 10 illustrations and 188 references compiled from major databases including Science Direct, Chemical Abstracts, PubMed and Directory of Open Access Journals.

RESULTS

Lichen morphology, symbiosis, diversity and bioactivities including enzyme inhibitory, antimicrobial, antifungal, antiviral, anticancer, anti-insecticidal and antioxidant actions were reviewed and summarized. Recent progress in lichens and lichen-forming fungi was discussed with emphasis on their potential to accelerate commercialization of lichen-based products.

CONCLUSIONS

Lichens are an untapped source of biological activities of industrial importance and their potential is yet to be fully explored and utilized. Lichen-derived bioactive compounds hold great promise for biopharmaceutical applications as antimicrobial, antioxidant and cytotoxic agents and in the development of new formulations or technologies for the benefit of human life.

Cytotoxic activity and antioxidant capacity of purified lichen metabolites: an in vitro study

The purpose of this study was to investigate the effects of six lichen metabolites (diffractaic acid, lobaric acid, usnic acid, vicanicin, variolaric acid, protolichesterinic acid) on proliferation, viability and reactive oxygen species (ROS) level towards three human cancer cell lines, MCF-7 (breast adenocarcinoma), HeLa (cervix adenocarcinoma) and HCT-116 (colon carcinoma). Cells were treated with different concentrations (2.5-100 μM) of these compounds for 48 h. In this comparative study, our lichen metabolites showed various cytotoxic effects in a concentration-dependent manner, and usnic acid was the most potent cytotoxic agent, while variolaric acid did not inhibit the proliferation of any of the three cell lines used. All tested lichen compounds did not exhibit free radical scavenging activity using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay. The lichen metabolites did not significantly increase the intracellular ROS level and did not prevent oxidative injury induced by t-butylhydroperoxide in HeLa cells. To better clarify the mechanism(s) of cytotoxic effect induced by protolichesterinic acid in HeLa cells, we investigated apoptotic markers such as condensation and fragmentation of nuclear chromatin and activation of caspase-3, 8 and 9. Our results revealed that the antiproliferative activity of 40 μM protolichesterinic acid in HeLa cells is related to its ability to induce programmed cell death involving caspase-3, 8 and 9 activation.

Antioxidant, antimicrobial and antiproliferative activities of five lichen species

The antioxidative, antimicrobial and antiproliferative potentials of the methanol extracts of the lichen species Parmelia sulcata, Flavoparmelia caperata, Evernia prunastri, Hypogymnia physodes and Cladonia foliacea were evaluated. The total phenolic content of the tested extracts varied from 78.12 to 141.59 mg of gallic acid equivalent (GA)/g of extract and the total flavonoid content from 20.14 to 44.43 mg of rutin equivalent (Ru)/g of extract. The antioxidant capacities of the lichen extracts were determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals scavenging. Hypogymnia physodes with the highest phenolic content showed the strongest DPPH radical scavenging effect. Further, the antimicrobial potential of the lichen extracts was determined by a microdilution method on 29 microorganisms, including 15 strains of bacteria, 10 species of filamentous fungi and 4 yeast species. A high antimicrobial activity of all the tested extracts was observed with more potent inhibitory effects on the growth of Gram (+) bacteria. The highest antimicrobial activity among lichens was demonstrated by Hypogymnia physodes and Cladonia foliacea. Finally, the antiproliferative activity of the lichen extracts was explored on the colon cancer adenocarcinoma cell line HCT-116 by MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) viability assay and acridine orange/ethidium bromide staining. The methanol extracts of Hypogymnia physodes and Cladonia foliacea showed a better cytotoxic activity than the other extracts. All lichen species showed the ability to induce apoptosis of HCT-116 cells.

Does usnic acid affect microtubules in human cancer cells?

Usnic acid, a lichen metabolite, is known to exert antimitotic and antiproliferative activities against normal and malignant human cells. Many chemotherapy agents exert their activities by blocking cell cycle progression, inducing cell death through apoptosis. Microtubules, protein structure involved in the segregation of chromosomes during mitosis, serve as chemotherapeutical targets due to their key role in cellular division as well as apoptosis. The aim of this work was to investigate whether usnic acid affects the formation and/or stabilisation of microtubules by visualising microtubules and determining mitotic indices after treatment. The breast cancer cell line MCF7 and the lung cancer cell line H1299 were treated with usnic acid 29 µM for 24 hours and two positive controls: vincristine (which prevents the formation of microtubules) or taxol (which stabilizes microtubules). Treatment of MCF7 and H1299 cells with usnic acid did not result in any morphological changes in microtubules or increase in the mitotic index. These results suggest that the antineoplastic activity of usnic acid is not related to alterations in the formation and/or stabilisation of microtubules.

PTP1B inhibitory effects of tridepside and related metabolites isolated from the Antarctic lichen Umbilicaria antarctica

The selective inhibition of PTP1B has been widely recognized as a potential drug target for the treatment of type 2 diabetes and obesity. In the course of screening for PTP1B inhibitory natural products, the MeOH extract of the dried sample of the Antarctic lichen Umbilicaria antarctica was found to exhibit significant inhibitory effect, and the bioassay-guided fractionation and purification afforded three related lichen metabolites 1-3. Compounds 1-3 were identified as gyrophoric acid (1), lecanoric acid (2), and methyl orsellinate (3) mainly by analysis of NMR and MS data. These compounds inhibited PTP1B activity with 50% inhibitory concentration values of 3.6 +/- 0.04 microM, 31 +/- 2.7 microM, and 277 +/- 8.6 microM, respectively. Furthermore, the kinetic analysis of PTP1B inhibition by compound 1 suggested that the compound inhibited PTP1B activity in a non-competitive manner.

Determination of genotoxic, antigenotoxic and cytotoxic potential of the extract from lichen Cetraria aculeata (Schreb.) Fr. in vitro

Naturally occurring compounds can have protective effects towards mutagens and carcinogens as shown by numerous studies. In the present study, the genotoxic/antigenotoxic activities of the extract from lichen Cetraria aculeata (Schreb.) Fr., which has been identified as an antibacterial agent in former studies, were investigated against known mutagens such as 4-nitro-o-phenylenediamine (4-NPD) and 2-aminofluorene (2-AF) in TA98 and TA100 strains of Salmonella typhimurium in the presence or absence of metabolic activity. Further genotoxicity/antigenotoxicity of the extract against mitomycin C for micronucleus formation was also evaluated in human lymphocytes. The cytotoxic effects of the extract on mammalian cells were investigated in three different cell line types by MTT assay. The results obtained show that the extract of C. aculeata has a significant antigenotoxic activity in bacterial systems, but not in mammalian cells and cytotoxic activity in some mammalian cancer cells. However, it was not mutagenic in all systems. The findings suggest that the lichen extract may have a possible therapeutic potential and therefore this must be further investigated by other multiple in vitro bioassays for the development of therapeutic agents.

Lipoxygenase Pathway of Arachidonic Acid Metabolism in Growth Control of Tumor Cells of Different Type

The influence of inhibitors of different lipoxygenases (LOX) on the growth of human tumor cells with different profiles of synthesized eicosanoids was studied. The studied LOX inhibitors had virtually no influence on the growth of A549 cells actively synthesizing cyclooxygenase and lipoxygenase metabolites of arachidonic acid (AA). The inhibitor of 12-LOX, baicalein, significantly inhibited proliferation in cultures of A431 epidermoid carcinoma cells with a characteristic domination of the major lipoxygenase metabolite of AA, 12-hydroxyeicosatetraenoic acid (12-HETE), in the profile of synthesized eicosanoids and reduced to 70% the incorporation of [3H]thymidine into DNA. Treatment of these cultures with 12-HETE virtually restored the growth potential of the tumor cells. The findings suggest that the lipoxygenase metabolite of AA, 12-HETE, is a growth-limiting factor for tumor cells of definite type.

Usnic acid: a non-genotoxic compound with anti-cancer properties

The majority of human tumors bear inactive p53 or cellular factors that down-regulate the expression and activity of the p53 network. Therefore, finding therapies that are effective in such tumors is of great interest. Usnic acid, a normal component of lichens, showed activity against the wild-type p53 breast cancer cell line MCF7 as well as the non-functional p53 breast cancer cell line MDA-MB-231 and the lung cancer cell line H1299 (null for p53). In MCF7 cells treated with usnic acid, although there was an accumulation of p53 and p21 proteins, the transcriptional activity of p53 remained unaffected. We also found that there was no phosphorylation of p53 at Ser15 after treatment of MCF7 cells with usnic acid, suggesting that the oxidative stress and disruption of the normal metabolic processes of cells triggered by usnic acid does not involve DNA damage. The property of usnic acid as a non-genotoxic anti-cancer agent that works in a p53-independent manner makes it a potential candidate for novel cancer therapy.

Effect of usnic acid from the lichen Cladonia substellata on Trypanosoma cruzi in vitro: an ultrastructural study

Chemotherapy for Chagas' disease is still unsatisfactory due to toxicity and limited effectiveness of the available drugs. In this work we have investigated the effect of usnic acid, isolated from lichen Cladonia substellata, against Trypanosoma cruzi, in vitro. Incubation of culture epimastigotes with 5-30microg/ml of this compound resulted in growth inhibition in a dosis-dependent manner. Ultrastructural analysis of treated epimastigotes showed damage to mitochondria, with a marked increase in kinetoplast volume and vacuolation of the mitochondrial matrix. Intense lysis of bloodstream trypomastigotes was observed with all drug concentrations tested. Besides mitochondrial and kinetoplast damage, trypomastigotes also presented enlargement of the flagellar pocket, as well as intense cytoplasm vacuolation. Treatment of infected macrophages with 40 or 80microg/ml usnic acid induced marked cytoplasm vacuolation in intracellular amastigote forms, with disorganization of parasite kinetoplast and mitochondria, but with no significant ultrastructural damage to the host cells.

Solubilization of poorly soluble lichen metabolites for biological testing on cell lines

The depside atranorin and depsidone fumarprotocetraric acid, isolated from the lichens Stereocaulon alpinum and Cetraria islandica, respectively, were chosen as prototypes for poorly soluble natural compounds in an effort to facilitate testing in pharmacological models. Solubilizing agents previously identified as being non-toxic towards a malignant leukemic (K-562) cell line and suitable for testing of anti-proliferative activity of the dibenzofuran lichen metabolite (+)-usnic acid were used in solubilization studies of the depside and depsidone. Cyclodextrin derivatives were found to be most suitable for solubilizing the lichen compounds, the greatest rise in solubility being witnessed for fumarprotocetraric acid, increasing almost 300-fold from 0.03 mg/ml in water to 8.98 mg/ml in 10% 2-hydroxypropyl-beta-cyclodextrin (HPbetaCD). Subsequently, the lichen compounds, including (+)-usnic acid, were solubilized in 10% HPbetaCD and tested for effects on three malignant human cell lines; T-47D (breast), Panc-1 (pancreas) and PC-3 (prostate) in a standard proliferation assay. Atranorin and fumarprotocetraric acid did not exhibit anti-proliferative effects but usnic acid was active against all test cell lines with EC50 values of 4.3-8.2 microg/ml. The non-toxic solubilizing agents used in this study could prove useful for pharmacological testing of other poorly soluble natural products.

Anti-proliferative lichen compounds with inhibitory activity on 12(S)-HETE production in human platelets

Several lichen compounds, i.e. lobaric acid (1), a beta-orcinol depsidone from Stereocaulon alpinum L., (+)-protolichesterinic acid (2), an aliphatic alpha-methylene-gamma-lactone from Cetraria islandica Laur. (Parmeliaceae), (+)-usnic acid (3), a dibenzofuran from Cladonia arbuscula (Wallr.) Rabenh. (Cladoniaceae), parietin (4), an anthraquinone from Xanthoria elegans (Link) Th. Fr. (Calaplacaceae) and baeomycesic acid (5), a beta-orcinol depside isolated from Thamnolia vermicularis (Sw.) Schaer. var. subuliformis (Ehrh.) Schaer. were tested for inhibitory activity on platelet-type 12(S)-lipoxygenase using a cell-based in vitro system in human platelets. Lobaric acid (1) and (+)-protolichesterinic acid (2) proved to be pronounced inhibitors of platelet-type 12(S)-lipoxygenase, whereas baeomycesic acid (5) showed only weak activity (inhibitory activity at a concentration of 100 microg/ml: (1) 93.4+/-6.62%, (2) 98,5+/-1.19%, 5 14.7+/-2.76%). Usnic acid (3) and parietin (4) were not active at this concentration. 1 and 2 showed a clear dose-response relationship in the range of 3.33-100 microg/ml. According to the calculated IC50 values the highest inhibitory activity was observed for the depsidone 1 (IC50 = 28.5 microM) followed by 2 (IC50 = 77.0 microM). The activity of 1 was comparable to that of the flavone baicalein, which is known as a selective 12(S)-lipoxygenase inhibitor (IC50 = 24.6 microM).

Levels of expression of lipoxygenases and cyclooxygenase-2 in human breast cancer

Lipoxygenases and cyclooxygenase are key mediators of arachidonic acid metabolism. The eicosanoids metabolites from these oxygynases have been shown to regulate the growth and death of cancer cells. This study determined the level of expression of 5-, 12-, 15-lipoxygenase and cyclooxygenase-2 expression in a cohort of breast cancer patients and their correlation with clinical outcomes. Compared with normal breast tissues, tumour tissues exhibited a significantly higher levels of 12-lipoxygenase and cyclooxygenase-2 (P<0.05), and significantly lower level of 15-lipoxygenase (P=0.05). Lobular carcinomas had a higher level of cyclooxygenase-2 and lower level of 15-lipoxygenase than ductal carcinomas. The lowest level of 15-lipoxygenase was seen in TNM3 and TNM4 tumours and from patients who died of breast cancer. Levels of 12- and 5-lipoxygenases were also particularly high in tumours from patients who died of breast cancer. This study shows that human breast tumours aberrantly express lipoxygenases and cyclooxygenase-2 and that decreased level of 15-lipoxygenase and raised level of cyclooxygenase-2 and 12-lipoxygenase has prognostic value in patients with breast cancer.

Anti-inflammatory and antiulcerogenic effects of the aqueous extract of Lobaria pulmonaria (L.) Hoffm

An aqeuous extract of Lobaria pulmonaria (L.) Hoffm., from which a tea is prepared and consumed as treatment for various diseases in northeastern Turkey, was tested for its anti-inflammatory and antiulcerogenic effects in rats. The carrageenan-induced paw edema, cotton pellet granuloma and indomethacin-induced gastric damage models were used to determine these effects. The extract exhibited moderate anti-inflammatory and strong antiulcerogenic activities.

Cytotoxic activity of some lichen extracts on murine and human cancer cell lines

Eight lichens were extracted successively with n-hexane, diethyl ether and methanol using a Soxhlet process. The cytotoxic activity of the 24 lichen extracts was evaluated in vitro using two murine (the L1210: lymphocytic leukaemia, and the 3LL: Lewis lung carcinoma) and four human (the K-562: chronic myelogenous leukaemia, the U251: glioblastoma, the DU145: prostate carcinoma, and the MCF7: breast adenocarcinoma) cancer cell lines and non-cancerous cells, the Vero cell line (African green monkey kidney cell line). The MTT assay revealed significant cytotoxicity (IC50 < or = 20 microg/ml) on one of the tested cancer cell lines for at least one extract of each lichen species. Some extracts of Cladonia convoluta, Cladonia rangiformis, Parmelia caperata, Platismatia glauca and Ramalina cuspidata demonstrated interesting activities particularly on human cancer cell lines as good selectivity indices were recorded (SI > 3).

Solubilization of the lichen metabolite (+)-usnic acid for testing in tissue culture

The pharmacological testing of natural products can often be hampered by the poor solubility of such compounds in non-toxic solvents. There is thus a need for a suitable agent for solubilization of natural substances to allow testing on a variety of cell lines in-vitro. Such an agent should ideally have no direct effects on any of the commonly used cell lines from a variety of tissues and mammalian species to allow proper comparison. In this study, the lichen metabolite (+)-usnic acid, a dibenzofuran derivative, was used as a prototype for an insoluble natural product with the aim of finding a solvent that was both capable of solubilizing usnic acid and was free of direct activity against a test cell line. Solubilization was measured at different pH values in various concentrations of co-solvents (glycofurol 75, propylene glycol, polyethylene glycol 400), surfactants (polysorbate 20 and Cremophor RH40), and the complexing agent 2-hydroxypropyl-beta-cyclodextrin. The solubility achieved in a 20% aqueous solution was 0.11 mg mL(-1) for propylene glycol, 0.19 for PEG 400, 0.27 for glycofurol 75, 0.57 for Cremophor RH40, 0.68 for 2-hydroxypropyl-beta-cyclodextrin and 0.84 for polysorbate 20. The direct effects of the various solvent systems were tested on the human leukaemia cell line K-562 in a standard proliferation assay. Most of the solvents proved toxic with the exception of propylene glycol, PEG 400 and 2-hydroxypropyl-beta-cyclodextrin. Anti-proliferative activity of usnic acid could be demonstrated with an ED50 (amount of substance required to reduce thymidine uptake to 50% of uptake by untreated control culture) of 4.7 microg mL(-1) using PEG 400 and 2-hydroxypropyl-beta-cyclodextrin but only the latter gave satisfactory solubility. 2-Hydroxypropyl-beta-cyclodextrin was thus identified as a solubilizing agent that fulfilled both set criteria of solubility and lack of toxicity against the test cells.

Effects of tenuiorin and methyl orsellinate from the lichen Peltigera leucophlebia on 5-/15-lipoxygenases and proliferation of malignant cell lines in vitro

The orcinol derivatives tenuiorin (1) and methyl orsellinate (2) were identified as active components of an extract from the lichen Peltigera leucophlebia (Nyl.) Gyeln. showing in vitro inhibitory activity against 15-lipoxygenase from soybeans. The compounds were subsequently tested for in vitro activity against 5-lipoxygenase from porcine leucocytes and proved to be moderately active, with IC50 values of 41.6 microM and 59.6 microM respectively. Tenuiorin is a known constituent of several Peltigera species but has not previously been isolated from P. leucophlebia. As correlation between 5-lipoxygenase inhibition and antiproliferative effects has earlier been witnessed for related lichen metabolites, tenuiorin and methyl orsellinate were further tested for antiproliferative activity on cultured human breast (T-47D)-, pancreatic (PANC-1)- and colon (WIDR) cancer cell lines. The monomeric methyl orsellinate exhibited no detectable antiproliferative activity whereas the trimeric tenuiorin caused moderate/weak reduction in [3H]-thymidine uptake of the pancreatic- and colon cancer cells, with ED50 values of 87.9 and 98.3 microM respectively.

Determination of antioxidant activity of lichen Cetraria islandica (L) Ach

The study was aimed at evaluating the antioxidant activity of aqueous extract of C. islandica. The antioxidant activity, reducing power, superoxide anion radical scavenging and free radical scavenging activities were studied. The antioxidant activity increased with the increasing amount of extracts (from 50 to 500 microg) added to linoleic acid emulsion. About 50, 100, 250, and 500 microg of aqueous extract of C. islandica showed higher antioxidant activity than 500 microg of alpha-tocopherol. The samples showed 96, 99, 100, and 100% inhibition on peroxidation of linoleic acid, respectively. On the other hand, the 500 microg of alpha-tocopherol showed 77% inhibition on peroxidation on linoleic acid emulsion. Like antioxidant activity, the reducing power, superoxide anion radical scavenging and free radical scavenging activities of C. islandica depends on concentration and increasing with increased amount of sample. The results obtained in the present study indicate that C. islandica is a potential source of natural antioxidant.

A comparison of the use of complementary therapies in Australia and Iceland

The use of complementary therapies in Iceland and Australia is compared in this paper, along with information regarding research into native plants in both countries. Attitudes towards complementary therapists from the medical profession are discussed, and the use of complementary medicine by pregnant women and midwives is given special emphasis.

Current prospects for controlling cancer growth with non-cytotoxic agents--nutrients, phytochemicals, herbal extracts, and available drugs

In animal or cell culture studies, the growth and spread of cancer can be slowed by many nutrients, food factors, herbal extracts, and well-tolerated, available drugs that are still rarely used in the clinical management of cancer, in part because they seem unlikely to constitute definitive therapies in themselves. However, it is reasonable to expect that mechanistically complementary combinations of these measures could have a worthwhile impact on survival times and, when used as adjuvants, could improve the cure rates achievable with standard therapies. The therapeutic options available in this regard include measures that: down-regulate serum free IGF-I; suppress the synthesis of mevalonic acid and/or certain derivatives thereof; modulate arachidonate metabolism by inhibiting 5-lipoxygenase, 12-lipoxygenase, or COX-2; antagonize the activation of AP-1 transcription factors; promote the activation of PPAR-gamma transcription factors; and that suppress angiogenesis by additional mechanisms. Many of these measures appear suitable for use in cancer prevention.