Depside as potent inhibitor of prostaglandin biosynthesis: a new active site model for fatty acid cyclooxygenase

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.

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.

Discovery of depsides and depsidones from lichen as potent inhibitors of microsomal prostaglandin E2 synthase-1 using pharmacophore models

Nature in silico: Virtual screening using validated pharmacophore models identified lichen depsides and depsidones as potential inhibitors of mPGES-1, an emerging target for NSAIDs. Evaluation of the virtual hits in a cell-free assay revealed physodic acid and perlatolic acid as potent inhibitors of mPGES-1 (IC(50) = 0.4 and 0.43 μM, respectively), indicating that these natural products have potential as novel anti-inflammatory agents.

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.

Novel depsides as potential anti-inflammatory agents with potent inhibitory activity against Escherichia coli-induced interleukin-8 production

Sixteen novel depsides were synthesized for the first time. Their chemical structures were clearly determined by (1)H NMR, ESI mass spectra, and elemental analyses. All the compounds were assayed for antibacterial activities against three Gram-positive bacterial strains (Bacillus subtilis ATCC 6633, Staphylococcus aureus ATCC 6538, and Streptococcus faecalis ATCC 9790) and three Gram-negative bacterial strains (Escherichia coli ATCC 35218, Pseudomonas aeruginosa ATCC 13525, and Enterobacter cloacae ATCC 13047) by the MTT method. Compound 2-(2-methoxy-2-oxoethyl)phenyl 5-bromonicotinate (5) exhibited significant antibacterial activities against E. coli ATCC 35218 with an MIC of 0.78 microg/mL, which was superior to the positive control kanamycin B. In addition, compound 5 showed potent inhibitory activity against E. coli-induced interleukin-8 production.

Potent inhibition of in vivo angiogenesis and tumor growth by a novel cyclooxygenase-2 inhibitor, enoic acanthoic acid

Recent studies have shown that cyclooxygenase-2 is crucially involved in angiogenesis. In fact, several specific cyclooxygenase-2 inhibitors suppress angiogenesis in vivo, suggesting that cyclooxygenase-2 is a promising target for the treatment of angiogenesis-related diseases. In the present study we investigate the activity of a new cyclooxygenase-2 inhibitor, enoic acanthoic acid (EAA), which was synthesized from the known natural cyclooxygenase-2 inhibitor, acanthoic acid (AA). The demonstration of a high correlation between EAA- and celecoxib-induced gene expression signatures in microarray experiments validated the specificity of EAA on cyclooxygenase-2. In angiogenesis assays, EAA potently inhibited basic fibroblast growth factor-induced invasion and tube formation of bovine aortic endothelial cells in vitro. Moreover, this inhibitor prevented both neovascularization of the chorioallantoic membrane of growing chick embryo and basic fibroblast growth factor-induced mouse corneal angiogenesis in vivo. EAA also significantly suppressed the growth of bladder tumors in a mouse model, showing better antitumor activity than celecoxib. Furthermore, gelatin zymogram analysis revealed that EAA potently inhibited the activities of matrix metalloproteinase 2 and 9. These results clearly demonstrate that EAA is a promising agent for the prevention and treatment of angiogenesis-related diseases including cancer.

Bioactive depsides and anthocyanins from jaboticaba (Myrciaria cauliflora)

A new depside, jaboticabin (1), together with 17 known compounds were isolated from the fruit of jaboticaba (Myrciaria cauliflora). The structure of 1 was elucidated by spectroscopic data interpretation. Known compounds were identified by comparison of their spectroscopic data with literature values or by comparison to authentic standards. Compound 1 and the related depside 2-O-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxyphenylacetic acid (2) significantly inhibited chemokine interleukin (IL)-8 production before and after cigarette smoke treatment of cells. Compound 1 was cytotoxic in the HT29 colon cancer cell line (IC50 = 65 microM), and 2 was active against HCT116 colon cancer cells (IC50 = 30 microM). Compounds 1 and 2 also exhibited antiradical activity in the 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay (IC50 = 51.4 and 61.8 microM, respectively). Two anthocyanins, cyanidin 3-glucoside (3) and delphinidin 3-glucoside (4), also showed good activity in these assays.

Pimarane cyclooxygenase 2 (COX-2) inhibitor and its structure-activity relationship

The structure-activity relationship and molecular modelings of a novel pimarane COX-2 inhibitor are reported. Particularly, a series of linker extended analogues designed on the basis of these studies exhibited significantly enhanced COX-2 inhibitory activities and selectivities.

Antiplatelet and anticancer isothiocyanates in Japanese domestic horseradish, Wasabi

6-Methylsulfinylhexyl isothiocyanate (MS-ITC) was isolated from wasabi (Wasabia japonica, Japanese domestic horseradish) as a potential inhibitor of human platelet aggregation in vitro through our extensive screening of vegetables and fruits. In the course of an another screening for the induction of glutathione S-transferase (GST) activity in RL34 cells, MS-ITC was inadvertently isolated from wasabi as a potential inducer of GST. MS-ITC administered to rats or mice also showed both activities in vivo. As a result from elucidation of the platelet aggregation inhibition and the GST induction mechanisms of MS-ITC, the isothiocyanate moiety of MS-ITC plays an important role for antiplatelet and anticancer activities because of its high reactivity with sulfhydryl (RSH) groups in biomolecules (GSH, cysteine residue in a certain protein, etc.).

Evaluation of selected lichens from iceland for cancer chemopreventive and cytotoxic activity

Cancer chemopreventive effects of organic extracts from 29 species of lichens collected in Iceland were evaluated using a panel of in vitro bioassays whereby extracts were tested for potential to induce quinone reductase (QR) and differentiation of human promyelocytic leukemia (HL-60) cells, inhibit cyclooxygenase-1 (COX-1), phorbol ester-induced ornithine decarboxylase (ODC), aromatase and sulfatase, as well as for antioxidant, estrogenic/anti-estrogenic and antiproliferative activity. In addition, the extracts were tested for cytotoxicity against 12 cancer cell lines. The most significant results were exhibited by extracts from Xanthoria elegans and Alectoria nigricans , which respectively, induced QR activity (concentration to double activity = 4.8 µg/ml) and inhibited phorbol ester-induced ODC activity with mouse 308 cells in culture (IC 50 = 2.6 µg/ml). Moderate inhibition of [ 3 H]thymidine incorporation with HL-60 cells was exhibited by the Peltigera leucophlebia extract. Several extracts prevented estrogen formation from estrogen precursors by inhibiting the enzymatic activities of aromatase ( Sphaerophorus globosus , Cetrariella delisei , Melanelia hepatizon ) and sulfatase ( Cladonia gracilis , Sphaerophorus fragilis , S. globosus ). None of the extracts demonstrated significant cytotoxic effects with selected cell lines.

Lichen metabolites. 1. Inhibitory action against leukotriene B4 biosynthesis by a non-redox mechanism

Of several lichen metabolites isolated from Parmelia nepalensis and Parmelia tinctorum, the didepsides atranorin (4) and diffractaic acid (5), as well as (+)-protolichesterinic acid (7), inhibited LTB4 biosynthesis in polymorphonuclear leukocytes. Ethyl hematommate (3) and (+)-usnic acid (1) were only weak inhibitors, while methyl beta-orcinolcarboxylate (2) and gyrophoric acid (6) were inactive at concentrations up to 60 microM. Redox properties of the compounds were evaluated in terms of inhibition of nonenzymatic lipid peroxidation in model membranes, reactivity against the stable free radical 2,2-diphenyl-1-picrylhydrazyl, and deoxyribose degradation as a measure of hydroxyl-radical generation. The results revealed that lichen metabolites neither acted as antioxidants against the peroxidation process in model membranes nor did they scavenge or produce free radicals, suggesting that the inhibitory effects on LTB4 biosynthesis was due to specific enzyme interaction rather than a nonspecific redox mechanism.

The inhibitory effect of glabridin from licorice extracts on melanogenesis and inflammation

Glabridin is the main ingredient in hydrophobic fraction of licorice extract affecting on skins. In this study, we investigated inhibitory effects of glabridin on melanogenesis and inflammation using cultured B16 murine melanoma cells and guinea pig skins. The results indicated that glabridin inhibits tyrosinase activity of these cells at concentrations of 0.1 to 1.0 microg/ml and had no detectable effect on their DNA synthesis. Combined analysis of SDS-polyacrylamide gel electrophoresis and DOPA staining on the large granule fraction of these cells disclosed that glabridin decreased specifically the activities of T1 and T3 tyrosinase isozymes. It was also shown that UVB-induced pigmentation and erythema in the skins of guinea pigs were inhibited by topical applications of 0.5% glabridin. Anti-inflammatory effects of glabridin in vitro were also shown by its inhibition of superoxide anion productions and cyclooxygenase activities. These data indicated that glabridin is a unique compound possessing more than one function; not only the inhibition of melanogenesis but also the inhibition of inflammation in the skins. By replacing each of hydroxyl groups of glabridin with others, it was revealed that the inhibitory effect of 2'-O-ethyl glabridin was significantly stronger than that of 4'-O-ethyl-glabridin on melanin synthesis in cultured B16 cells at the concentration of 1.0 mg/ml. With replacement of both of two hydroxyl groups, the inhibitory effect was totally lost. Based on these data, we concluded that two hydroxyl groups of glabridin are important for the inhibition of melanin synthesis and that the hydroxyl group at the 4' position of this compound is more closely related to melanin synthesis.

Inhibitory effect of aryl thienyl-ketones and -thioketones on arachidonic acid-induced malondialdehyde formation in human platelets: biological data and molecular modelling

A series of anti-thrombotic aryl thienyl-ketones and -thioketones was assayed in vitro for their inhibitory effect on malondialdehyde (MDA) production induced by arachidonic acid in human platelets. For several compounds MDA formation was strongly inhibited indicating that the anti-platelet target was situated on the cyclooxygenase pathway. A comparison between the inhibition constant Ki and the IC50 values revealed competitive inhibition kinetics. The molecular structure of one active compound was analysed by X-ray diffraction and theoretical calculations to provide information on its electronic and lipophilic properties.

Higher oxidation states of prostaglandin H synthase. EPR study of a transient tyrosyl radical in the enzyme during the peroxidase reaction

Purified prostaglandin H synthase (EC 1.14.99.1), reconstituted with hemin, was reacted with substrates of the cyclooxygenase and peroxidase reaction. The resulting EPR spectra were measured below 90 K. Arachidonic acid, added under anaerobic conditions, did not change the EPR spectrum of the native enzyme due to high-spin ferric heme. Arachidonic acid with O2, as well as prostaglandin G2 or H2O2, decreased the spectrum of the native enzyme and concomitantly a doublet signal at g = 2.005 was formed with maximal intensity of 0.35 spins/enzyme and a half-life of less than 20 s at -12 degrees C. From the conditions for the formation and the effect of inhibitors, this doublet signal was assigned to an enzyme intermediate of the peroxidase reaction, namely a higher oxidation state. The doublet signal with characteristic hyperfine structure was nearly identical to the signal of the tyrosyl radical in ribonucleotide reductase (EC 1.17.4.1). Hence the signal of prostaglandin H synthase was assigned to a tyrosyl radical. Electronic spectra as well as decreased power saturation of the tyrosyl radical signal indicated heme in its ferryl state which coupled to the tyrosyl radical weakly. [FeIVO(protoporphyrin IX)]...Tyr+. was suggested as the structure of this two-electron oxidized state of the enzyme. A hypothetical role for the tyrosyl radical could be the abstraction of a hydrogen at C-13 of arachidonic acid which is assumed to be the initial step of the cyclooxygenase reaction.

Structure of the active site of prostaglandin synthase from studies of depsides: an alternate view

Evaluation of the structure of the lichen depside, 4-0-methylcryptochlorophaeic acid, the most potent inhibitor of prostaglandin synthesis known, and its potential interaction with heme supports a model of the active site of prostaglandin synthase initially suggested by studies of arachidonic acid-heme interaction.

The effect of various acrylonitriles and related compounds on prostaglandin biosynthesis

We have studied the effect of nearly 90 arylacrylonitrile derivatives, and several related compounds, on the biosynthesis of prostaglandins from bovine seminal vesicle microsomes. This effect was compared to that of triarylacrylonitrile derivatives known for their inhibiting properties. Several arylacrylonitrile derivatives have also proved good inhibitors, especially certain N-trisubstituted compounds: trans (dimethylamino-4 phenyl)-3 (methoxy-4' phenyl)-2 acrylonitrile was the best inhibitor of the group, with an IC50 of 0.07 microM. The absence of carboxy groups in these derivatives precludes the application of any of the site-models proposed to date. We suggest that the electronic charges carried especially by the three aromatic rings play an important role in the inhibiting mechanism.