Antiviral activities of anthraquinones, bianthrones and hypericin derivatives from lichens

Lipid-Centric Approaches in Combating Infectious Diseases: Antibacterials, Antifungals and Antivirals with Lipid-Associated Mechanisms of Action

One of the global challenges of the 21st century is the increase in mortality from infectious diseases against the backdrop of the spread of antibiotic-resistant pathogenic microorganisms. In this regard, it is worth targeting antibacterials towards the membranes of pathogens that are quite conservative and not amenable to elimination. This review is an attempt to critically analyze the possibilities of targeting antimicrobial agents towards enzymes involved in pathogen lipid biosynthesis or towards bacterial, fungal, and viral lipid membranes, to increase the permeability via pore formation and to modulate the membranes' properties in a manner that makes them incompatible with the pathogen's life cycle. This review discusses the advantages and disadvantages of each approach in the search for highly effective but nontoxic antimicrobial agents. Examples of compounds with a proven molecular mechanism of action are presented, and the types of the most promising pharmacophores for further research and the improvement of the characteristics of antibiotics are discussed. The strategies that pathogens use for survival in terms of modulating the lipid composition and physical properties of the membrane, achieving a balance between resistance to antibiotics and the ability to facilitate all necessary transport and signaling processes, are also considered.

Screening and identification of emodin as an EBV DNase inhibitor to prevent its biological functions

BACKGROUND

The Epstein-Barr virus (EBV) is a prevalent oncovirus associated with a variety of human illnesses. BGLF5, an EBV DNase with alkaline nuclease (AN) activity, plays important roles in the viral life cycle and progression of human malignancies and has been suggested as a possible diagnostic marker and target for cancer therapy. Methods used conventionally for the detection of AN activity, radioactivity-based nuclease activity assay and DNA digestion detection by gel electrophoresis, are not suitable for screening AN inhibitors; the former approach is unsafe, and the latter is complicated. In the present study, a fluorescence-based nuclease activity assay was used to screen several natural compounds and identify an EBV DNase inhibitor.

RESULTS

Fluorescence-based nuclease activity assays, in which the DNA substrate is labelled with PicoGreen dye, are cheaper, safer, and easier to perform. Herein, the results of the fluorescence-based nuclease activity assay were consistent with the results of the two conventional methods. In addition, the PicoGreen-labelling method was applied for the biochemical characterisation of viral nucleases. Using this approach, we explored EBV DNase inhibitors. After several rounds of screening, emodin, an anthraquinone derivative, was found to possess significant anti-EBV DNase activity. We verified the efficacy of emodin using the conventional DNA-cleavage assay. Furthermore, using comet assay and micronucleus formation detection, we confirmed that emodin can inhibit DNase-induced DNA damage and genomic instability. Additionally, emodin treatment inhibited EBV production.

CONCLUSIONS

Using a PicoGreen-mediated nuclease activity assay, we successfully demonstrated that emodin has the potential to inhibit EBV DNase nuclease activity. Emodin also inhibits EBV DNase-related biological functions, suggesting that it is a potential inhibitor of EBV DNase.

On the Sensitivity of the Virion Envelope to Lipid Peroxidation

Emerging viruses are a public health threat best managed with broad spectrum antivirals. Common viral structures, like capsids or virion envelopes, have been proposed as targets for broadly active antiviral drugs. For example, a number of lipoperoxidators have been proposed to preferentially affect viral infectivity by targeting metabolically inactive enveloped virions while sparing metabolically active cells. However, this presumed preferential virion sensitivity to lipoperoxidation remains untested. To test whether virions are indeed more sensitive to lipoperoxidation than are cells, we analyzed the effects of two classic generic lipoperoxidators: lipophilic 2,2'-azobis(2,4-dimethylvaleronitrile) (AMVN) and hydrophilic 2,2'-azobis(2-methylpropionamidine) dihydrochloride (AAPH) on Vero and human foreskin fibroblasts (HFF) cell viability, HSV-1 plaquing efficiency, and virion and cell lipoperoxidation. Cells or virions were incubated with the lipoperoxidators at 37°C for 2 h or incubated in atmospheric O₂, and dose responses (half maximal cytotoxic and effective concentration [CC₅₀ and EC₅₀]) were evaluated by three or four parameter regression. The HSV-1 virions were slightly more sensitive to lipoperoxidators than were the cells (selectivity index [SI], 3.3 to 7.4). The effects of the lipophilic AMVN on both cell and virion viability directly correlated with the extent of membrane lipoperoxidation as evaluated by two different probes, C11-Bodipy and liperfluo. Moreover, the hydrophilic AAPH-induced virion inactivation at lower concentrations than did lipoperoxidation. Known lipoperoxidators inhibit infectivity via lipoperoxidation-independent mechanisms. Antioxidants protected against a loss of viral infectivity by less than 5-fold. Carrier bovine serum albumin (BSA) protected against both peroxidators to a similar extent when present together with the lipoperoxidating agents, suggesting that BSA quenches them as expected. Virions incubated in atmospheric oxidative conditions suffered losses of infectivity that were similar to those of chemically peroxidated virions, and they were protected by water soluble vitamin C and BSA with no evident lipoperoxidation, indicating predominant peroxidative damage to nonlipid virion components. Thus, lipoperoxidation is not a mechanism by which to specifically inhibit the infectivity of enveloped viruses, and the effects of known lipoperoxidators on virion infectivity are not solely mediated by lipoperoxidation. IMPORTANCE Small molecules that induce lipoperoxidation have been proposed repeatedly as potential antiviral drugs based on a presumed unique sensitivity of virions to this type of damage. Several small molecules that inactivate virions without affecting cells have been proposed to act primarily by inducing lipoperoxidation. However, the preferential sensitivity of virions to lipoperoxidators had not been experimentally evaluated. Using two of the best characterized small molecule lipoperoxidators, which are widely considered to be the prototypical water soluble and liposoluble lipoperoxidators, we show that lipoperoxidators have no preference for virions over cells. Moreover, they also inactivate virions by mechanisms other than the induction of lipoperoxidation. Therefore, the general induction of lipoperoxidation is not a path by which to develop antivirals. Moreover, molecules with specific antiviral activity which are not cytotoxic and have no preference to localize to virions over cells are unlikely to act primarily by inducing lipoperoxidation.

Phytochemical Composition of Lichen Parmotrema hypoleucinum (J. Steiner) Hale from Algeria

In this work, we carried out studies of the chemical composition of hexane, chloroform and ethanol extracts from two samples of the lichen Parmotrema hypoleucinum collected in Algeria. Each sample of the lichen P. hypoleucinum was collected on two different supports: Olea europaea and Quercus coccifera. Hexane extracts were prepared, in Soxhlet; each hexane extract was fractionated by its solubility in methanol; the products soluble in methanol were separated (cold): 1-Hexane, 2-Hexane; and the products insoluble in methanol (cold): 1-Cires, 2-Cires. A diazomethane esterified sample of 1-Hexane, 2-Hexane, 1-Cires and 2-Cires was analyzed by GC-MS, and the components were identified as methyl esters. In the 1-Hexane and 2-Hexane fractions, the methyl esters of the predominant fatty acids in the lichen were identified: palmitic acid, linoleic acid, oleic acid and stearic acid; a hydrocarbon was also identified: 13-methyl-17-norkaur-15-ene and several derivatives of orsellinic acid. In the 1-Cires and 2-Cires fractions, the previous fatty acids were no longer observed, and only the derivatives of orsellinic acid were found. The analysis of the 1-Hexane, 2-Hexane fractions by HPLC-MS/MS allows us to identify different chemical components, and the most characteristic products of the lichen were identified, such as Atranol, Chloroatranol, Atranorin and Chloroatranorin. In the fractions of 1-Cires and 2-Cires, the HPLC-MS/MS analysis reveals that they are very similar in their chemical components; the characteristic products of this lichen in this fraction are Atranorin and Chloroatranorin. In the extracts of chloroform, 1-Chloroform and 2-Chloroform, the analysis carried out by HPLC-MS/MS shows small differences in their chemical composition at the level of secondary products; among the products to be highlighted for this work, we have chloroatranorin, the stictic acid, norstictic acid and other derivatives. In the analysis of the most polar extracts carried out in ethanol: 1-Ethanol and 2-Ethanol, HPLC-MS/MS analysis shows very similar chemical compositions in these two extracts with small differences. In these extracts, the following acids were identified as characteristic compounds of this lichen: constictic acid, stictic acid, substictic acid and methylstictic acid. In the HPLC–MS/MS analysis of all these extracts, alectoronic acid was not found.

Promising Role of Emodin as Therapeutics to Against Viral Infections

Emodin is an anthraquinone derivative that is widely present in natural plants and has a wide spectrum of pharmacological effects, such as antibacterial, anti-inflammatory, anti-fibrotic and anticancer and so on. Through reviewing studies on antiviral effect of emodin in the past decades, we found that emodin exhibits ability of inhibiting the infection and replication of more than 10 viruses in vitro and in vivo, including herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2), human cytomegalovirus (HCMV), Epstein-Barr virus (EBV), coxsackievirus B (CVB), hepatitis B virus (HBV), influenza A virus (IAV), SARS-CoV, viral haemorrhagic septicaemia rhabdovirus (VHSV), enterovirus 71 (EV71), dengue virus serotype 2 (DENV-2) and Zika virus (ZIKV). Therefore, this review aims to summarize the antiviral effect of emodin, in order to provide reference and hopes to support the further investigations.

Aloin isoforms (A and B) selectively inhibits proteolytic and deubiquitinating activity of papain like protease (PLpro) of SARS-CoV-2 in vitro

The most common host entry point of human adapted coronaviruses (CoV) including SARS-CoV-2 is through the initial colonization in the nostril and mouth region which is responsible for spread of the infection. Most recent studies suggest that the commercially available oral and nasal rinse products are effective in inhibiting the viral replication. However, the anti-viral mechanism of the active ingredients present in the oral rinses have not been studied. In the present study, we have assessed in vitro enzymatic inhibitory activity of active ingredients in the oral mouth rinse products: aloin A and B, chlorhexidine, eucalyptol, hexetidine, menthol, triclosan, methyl salicylate, sodium fluoride and povidone, against two important proteases of SARS-CoV-2 PLpro and 3CLpro. Our results indicate only aloin A and B effectively inhibited proteolytic activity of PLpro with an IC₅₀ of 13.16 and 16.08 μM. Interestingly, neither of the aloin isoforms inhibited 3CLpro enzymatic activity. Computational structural modelling of aloin A and B interaction with PLpro revealed that, both aloin isoforms form hydrogen bond with Tyr²⁶⁸ of PLpro, which is critical for their proteolytic activity. Furthermore, 100 ns molecular dynamics (MD) simulation studies predicted that both aloin isoforms have strong interaction with Glu¹⁶⁷, which is required for PLpro deubiquitination activity. Our results from the in vitro deubiquitinase inhibition assay show that aloin A and B isomers exhibit deubiquitination inhibitory activity with an IC₅₀ value of 15.68 and 17.51 µM, respectively. In conclusion, the isoforms of aloin inhibit both proteolytic and the deubiquitinating activity of SARS-CoV-2 PLpro, suggesting potential in inhibiting the replication of SARS-CoV-2 virus.

Naturally occurring anthraquinones as potential inhibitors of SARS-CoV-2 main protease: an integrated computational study

The novel coronavirus disease (COVID-19) has spread throughout the globe, affecting millions of people. The World Health Organization (WHO) has declared this infectious disease a pandemic. At present, several clinical trials are going on to identify possible drugs for treating this infection. SARS-CoV-2 M^pro is one of the most critical drug targets for the blockage of viral replication. The aim of this study was to identify potential natural anthraquinones that could bind to the active site of SARS-CoV-2 main protease and stop the viral replication. Blind molecular docking studies of 13 anthraquinones and one control drug (Boceprevir) with SARS-CoV-2 M^pro were carried out using the SwissDOCK server, and alterporriol-Q that showed the highest binding affinity towards M^pro were subjected to molecular dynamics simulation studies. This study indicated that several antiviral anthraquinones could prove to be effective inhibitors for SARS-CoV-2 M^pro of COVID-19 as they bind near the active site having the catalytic dyad, HIS41 and CYS145 through non-covalent forces. The anthraquinones showed less inhibitory potential as compared to the FDA-approved drug, boceprevir. Among the anthraquinones studied, alterporriol-Q was found to be the most potent inhibitor of SARS-CoV-2 M^pro. Further, MD simulation studies for M^pro- alterporriol-Q system suggested that alterporriol-Q does not alter the structure of M^pro to a significant extent. Considering the impact of COVID-19, identification of alternate compounds like alterporriol-Q that could inhibit the viral infection will help in accelerating the process of drug discovery.

Diverse host-associated fungal systems as a dynamic source of novel bioactive anthraquinones in drug discovery: Current status and future perspectives

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Diversity and distribution of host-living fungi producing AQs in the terrestrial ecosystem are assembled.

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AQs biosynthesis and their SAR are elucidated to guide the approaches in novel drugs design and development.

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Several examples of true endophytic fungi producing AQs like their different host plants have been reported as interesting alternative sources of drugs.

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The review recapitulates the novel AQs with rare chemical skeleton that could open future venues for investigation of their biological activities.

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Lichens are assembled as unique source of several bioactive classes of AQs.

Background

Despite, a large number of bioactive anthraquinones (AQs) isolated from host-living fungi, only plant-derived AQs were introduced in the global consumer markets. Host-living fungi represents renewable and extendible resources of diversified metabolites to be exploited for bioactives production. Unique classes of AQs from fungi include halogenated and steroidal AQs, and absent from planta are of potential to explore for biological activity against urging diseases such as cancer and multidrug-resistant pathogens. The structural diversity of fungal AQs, monomers, dimers, trimers, halogenated, etc… results in a vast range of pharmacological activities.

Aim of review

The current study capitalizes on uncovering the diversity and distribution of host-living fungal systems producing AQs in different terrestrial ecosystems ranging from plant endophytes, lichens, animals and insects. Furthermore, the potential bioactivities of fungal derived AQs i.e., antibacterial, antifungal, antiviral (anti-HIV), anticancer, antioxidant, diuretic and laxative activities are assembled in relation to their structure activity relationship (SAR). Analyzing for structure–activity relationship among fungal AQs may facilitate bioengineering of more potential analogues. Withal, elucidation of AQs biosynthetic pathways in fungi is discussed from different fungal hosts to open up new possibilities for potential biotechnological applications. Such comprehensive review unravels terrestrial host-living fungal systems as a treasure trove in drug discovery, in addition to future perspectives and trends for their exploitation in pharmaceutical industries.

Key Scientific Concepts of Review

Such comprehensive review unravels terrestrialhost-living fungal systems as a treasure trove in drug discovery, in addition to future perspectives and trends for their exploitation in pharmaceutical industries.

Photosensitizing Antivirals

Antiviral action of various photosensitizers is already summarized in several comprehensive reviews, and various mechanisms have been proposed for it. However, a critical consideration of the matter of the area is complicated, since the exact mechanisms are very difficult to explore and clarify, and most publications are of an empirical and "phenomenological" nature, reporting a dependence of the antiviral action on illumination, or a correlation of activity with the photophysical properties of the substances. Of particular interest is substance-assisted photogeneration of highly reactive singlet oxygen (1O2). The damaging action of 1O2 on the lipids of the viral envelope can probably lead to a loss of the ability of the lipid bilayer of enveloped viruses to fuse with the lipid membrane of the host cell. Thus, lipid bilayer-affine 1O2 photosensitizers have prospects as broad-spectrum antivirals against enveloped viruses. In this short review, we want to point out the main types of antiviral photosensitizers with potential affinity to the lipid bilayer and summarize the data on new compounds over the past three years. Further understanding of the data in the field will spur a targeted search for substances with antiviral activity against enveloped viruses among photosensitizers able to bind to the lipid membranes.

Emerging paradigms of viral diseases and paramount role of natural resources as antiviral agents

In the current scenario, the increasing prevalence of diverse microbial infections as well as emergence and re-emergence of viral epidemics with high morbidity and mortality rates are major public health threat. Despite the persistent production of antiviral drugs and vaccines in the global market, viruses still remain as one of the leading causes of deadly human diseases. Effective control of viral diseases, particularly Zika virus disease, Nipah virus disease, Severe acute respiratory syndrome, Coronavirus disease, Herpes simplex virus infection, Acquired immunodeficiency syndrome, and Ebola virus disease remain promising goal amidst the mutating viral strains. Current trends in the development of antiviral drugs focus solely on testing novel drugs or repurposing drugs against potential targets of the viruses. Compared to synthetic drugs, medicines from natural resources offer less side-effect to humans and are often cost-effective in the productivity approaches. This review intends not only to emphasize on the major viral disease outbreaks in the past few decades and but also explores the potentialities of natural substances as antiviral traits to combat viral pathogens. Here, we spotlighted a comprehensive overview of antiviral components present in varied natural sources, including plants, fungi, and microorganisms in order to identify potent antiviral agents for developing alternative therapy in future.

The anti-hepatitis B virus therapeutic potential of anthraquinones derived from Aloe vera

Although the approved hepatitis B virus (HBV)-polymerase inhibitors (e.g., lamivudine) often lead to drug-resistance, several natural products have shown promising efficacies. Though Aloe vera (AV) gel and its constituents are shown inhibitors of many viruses, their anti-HBV activity still remains elusive. We therefore, tested the anti-HBV potential of AV extract and its anthraquinones in hepatoma cells, including molecular docking, high-performance thin layer chromatography (HPTLC), and cytochrome P450 (CYP3A4) activation analyses. Our anti-HBV assays (HBsAg/HBeAg Elisa) showed maximal inhibition of viral antigens production by aloe-emodin (~83%) > chrysophanol (~62%) > aloin B (~61%) > AV extract (~37%) in HepG2.2.15 cells. Interestingly, the effect of aloe-emodin was comparable with lamivudine (~86%). Moreover, sequential treatment with lamivudine (pulse) followed by aloe-emodin (chase) enhanced the efficacy of monotherapy by ~12%. Docking (AutoDock Vina) of the anthraquinones indicated strong interactions with HBV-polymerase residues that formed stable complexes with high Gibbs's free energy. Further, identification of aloe-emodin and aloin B by validated HPTLC in AV extract strongly endorsed its anti-HBV potential. In addition, our luciferase-reporter gene assay of transfected HepG2 cells showed moderate induction of CYP3A4 by aloe-emodin. In conclusion, this is the first report on anti-HBV potential of AV-derived anthraquinones, possibly via HBV-polymerase inhibition. Of these, although aloin B exhibits novel antiviral effect, aloe-emodin appears as the most promising anti-HBV natural drug with CYP3A4 activating property towards its enhanced therapeutic efficacy.

The Importance of Anthraquinone and Its Analogues and Molecular Docking Calculation

In drug-delivery systems containing nano-drug structures, targeting the tumorous tissue by anthraquinone molecules with high biological activity, and reaching and destroying tumors by their tumor-killing effect reveals remarkable results for the treatment of tumors. The various biological activities of anthraquinones and their derivatives depend on molecular conformation; hence, their intra-cell interaction mechanisms including deoxyribonucleic acid (DNA), ribonucleic acid (RNA), enzymes, and hormones. Computer-based drug design plays an important role in the design of drugs and the determination of goals for them. Molecular docking has been widely used in structure-based drug design. The effects of anthraquinone analogues in tumor cells as a result of their interaction with DNA strand has increased the number of studies done on them, and they have been shown to have a wide range of applications in chemistry, medicine, pharmacy, materials, and especially in the field of biomolecules.

Photodynamic Inactivation of Herpes Simplex Viruses

Herpes simplex virus (HSV) infections can be treated with direct acting antivirals like acyclovir and foscarnet, but long-term use can lead to drug resistance, which motivates research into broadly-acting antivirals that can provide a greater genetic barrier to resistance. Photodynamic inactivation (PDI) employs a photosensitizer, light, and oxygen to create a local burst of reactive oxygen species that inactivate microorganisms. The botanical plant extract Orthoquin^TM is a powerful photosensitizer with antimicrobial properties. Here we report that Orthoquin also has antiviral properties. Photoactivated Orthoquin inhibited herpes simplex virus type 1 (HSV-1) and herpes simplex virus type 2 (HSV-2) infection of target cells in a dose-dependent manner across a broad range of sub-cytotoxic concentrations. HSV inactivation required direct contact between Orthoquin and the inoculum, whereas pre-treatment of target cells had no effect. Orthoquin did not cause appreciable damage to viral capsids or premature release of viral genomes, as measured by qPCR for the HSV-1 genome. By contrast, immunoblotting for HSV-1 antigens in purified virion preparations suggested that higher doses of Orthoquin had a physical impact on certain HSV-1 proteins that altered protein mobility or antigen detection. Orthoquin PDI also inhibited the non-enveloped adenovirus (AdV) in a dose-dependent manner, whereas Orthoquin-mediated inhibition of the enveloped vesicular stomatitis virus (VSV) was light-independent. Together, these findings suggest that the broad antiviral effects of Orthoquin-mediated PDI may stem from damage to viral attachment proteins.

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.

Anti-cytomegalovirus activity of the anthraquinone atanyl blue PRL

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The anthraquinone atanyl blue PRL inhibits human cytomegalovirus replication.

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The block to viral replication appears early after entry and substantially reduces viral immediate early gene expression.

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In vitro, atanyl blue PRL inhibits the nuclease activity of purified viral alkaline nuclease, UL98.

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The antiviral activity of atanyl blue PRL may be manifested through inhibition of UL98’s nuclease activity.

Human cytomegalovirus (CMV) causes significant disease in immunocompromised patients and serious birth defects if acquired in utero. Available CMV antivirals target the viral DNA polymerase, have significant toxicities, and suffer from resistance. New drugs targeting different pathways would be beneficial. The anthraquinone emodin is proposed to inhibit herpes simplex virus by blocking the viral nuclease. Emodin and related anthraquinones are also reported to inhibit CMV. In the present study, emodin reduced CMV infectious yield with an EC₅₀ of 4.9 μM but was cytotoxic at concentrations only twofold higher. Related anthraquinones acid blue 40 and alizarin violet R inhibited CMV at only high concentrations (238–265 μM) that were also cytotoxic. However, atanyl blue PRL inhibited infectious yield of CMV with an EC₅₀ of 6.3 μM, significantly below its 50% cytotoxic concentration of 216 μM. Atanyl blue PRL reduced CMV infectivity and inhibited spread. When added up to 1 h after infection, it dramatically reduced CMV immediate early protein expression and blocked viral DNA synthesis. However, it had no antiviral activity when added 24 h after infection. Interestingly, atanyl blue PRL inhibited nuclease activities of purified CMV UL98 protein with IC₅₀ of 4.5 and 9.3 μM. These results indicate that atanyl blue PRL targets very early post-entry events in CMV replication and suggest it may act through inhibition of UL98, making it a novel CMV inhibitor. This compound may provide valuable insights into molecular events that occur at the earliest times post-infection and serve as a lead structure for antiviral development.

Polyhydroxyanthraquinones as quorum sensing inhibitors from the guttates of Penicillium restrictum and their analysis by desorption electrospray ionization mass spectrometry

The endophytic fungus Penicillium restrictum was isolated from the stems of a milk thistle (Silybum marianum) plant. In culture, the fungus produced distinct red guttates, which have been virtually uninvestigated, particularly from the standpoint of chemistry. Hence, this study examined the chemical mycology of P. restrictum and, in doing so, uncovered a series of both known and new polyhydroxyanthraquinones (1-9). These compounds were quorum sensing inhibitors in a clinical isolate of methicillin-resistant Staphylococcus aureus (MRSA), with IC50 values ranging from 8 to 120 μM, suggesting antivirulence potential for the compounds. Moreover, the spatial and temporal distribution of the polyhydroxyanthraquinones was examined in situ via desorption electrospray ionization-mass spectrometry (DESI-MS) imaging, demonstrating the first application of this technique to a guttate-forming fungus and revealing both the concentration of secondary metabolites at the ventral surface of the fungus and their variance in colonies of differing ages.

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.

The effect of emodin, an anthraquinone derivative extracted from the roots of Rheum tanguticum, against herpes simplex virus in vitro and in vivo

AIM OF THE STUDY

Herpes simplex viruses (HSV-1 and -2) are important pathogens for humans and the discovery of novel anti-HSV drugs with low toxicity deserves great efforts. Rhubarb is one of the oldest and best-known traditional Chinese medicines. We initiated this study to test if emodin is the active ingredients from Rheum tanguticum (R. tanguticum, one of the Chinese Rhubarb) against HSV infection and to investigate its antiviral activity on HSV infection in tissue culture cells and in a mouse model.

MATERIALS AND METHODS

Emodin (3-methyl-1,6,8-trihydroxyanthraquinone) was extracted and purified from R. tanguticum (cultivated at high mountainous area in Qinghai) and the purity was determined by high performance liquid chromatography. The antiviral experiments of emodin against HSV infection were performed in vitro and in vivo. In vivo, the HSV-infected mice were orally administered with emodin beginning at 24 h post-HSV exposures with dosages of 3.3 g/kg/day, 6.7 g/kg/day, and 11.3 g/kg/day, respectively, for 7 days.

RESULTS

Emodin was found to inhibit the replication of HSV-1 and HSV-2 in cell culture at the concentration of 50 μg/ml with antiviral index of 2.07 and 3.53, respectively. The emodin treatment increased the survival rate of HSV-infected mice, prolonged survival time and showed higher efficacy of HSV elimination from brain, heart, liver and ganglion, compared to the viral controls. In addition, the antiviral activity of emodin was found to be equivalent to that of acyclovir in vivo.

CONCLUSIONS

Our results indicate that emodin has the anti-HSV activity in vitro and in vivo and is thus a promising agent in the clinical therapy of HSV infection.

Larvicidal activity of para-benzoquinones

Plant products may be alternative sources of mosquito larval control agents, since they constitute a rich source of bioactive compounds that are biodegradable into nontoxic products. It has been reported that quinones and derivatives present toxic activity against mosquito larvae Aedes aegypti. Therefore, these facts led us to investigate the larvicidal potential of six structurally related para-benzoquinones against A. aegypti L. (Culicidae) larvae, the vector of dengue fever. All the para-benzoquinones were found to have larvicidal effect. The unsubstituted para-benzoquinone was the compound that exhibited the lowest potency, while 2-isopropyl-para-benzoquinone was the most bioactive. In general, the presence of alkyl groups results in more potent compounds. In addition, the number, position, and size of these groups modulate the potency of the compounds. The experimental results showed that by appropriate structural modification of para-benzoquinones, it may be possible to develop novel insecticidal compounds with potential use to control A. aegypti population.

Anti-proliferative effects of Lethariella zahlbruckneri extracts in human HT-29 human colon cancer cells

This study was performed to elucidate the anti-proliferative effects and the apoptotic mechanisms of extracts from Lethariella zahlbruckneri in HT-29 human colon cancer cells. Both the acetone extract (AEL) and methanolic extract (MEL) of L. zahlbruckneri decreased viable cell numbers in a dose- and time-dependent manner in HT-29 cells. The AEL showed stronger cytotoxicity than MEL. Cell death induced by AEL increased cell populations in the sub-G1 phase, as well as the formation of apoptotic bodies and nuclear condensation, whereas MEL did not. Therefore, the potential of AEL to induce apoptosis was examined. Apoptosis induced by AEL was associated with the activation of initiator caspases-8 and -9, as well as the effector caspase-3. AEL stimulated Bid cleavage. This indicated that the apoptotic action of caspase-8-mediated Bid cleavage leads to the activation of caspase-9. AEL increased the expression of the pro-apoptotic protein, Bax, and decreased the expression of the anti-apoptotic protein, Bcl-2. AEL also increased the expression of the caspase-independent mitochondrial apoptosis factor, AIF, in HT-29 cells. These results indicate that AEL inhibited HT-29 cell proliferation by inducing apoptosis, which might be mediated via both caspase-dependent and -independent pathways.

Emodin is a novel alkaline nuclease inhibitor that suppresses herpes simplex virus type 1 yields in cell cultures

BACKGROUND AND PURPOSE

Most antiviral therapies directed against herpes simplex virus (HSV) infections are limited to a small group of nucleoside analogues that target the viral polymerase. Extensive clinical use of these drugs has led to the emergence of resistant viral strains, mainly in immunocompromised patients. This highlights the need for the development of new anti-herpesviral drugs with novel targets. Herein the effects of a plant anthraquinone, emodin, on the HSV-1 alkaline nuclease activity and virus yields were investigated.

EXPERIMENTAL APPROACH

HSV-1 alkaline nuclease activity was examined by nuclease activity assay. Inhibition of virus yields was measured by plaque reduction assay and immunohistochemical staining. Interaction between emodin and alkaline nuclease was analysed by docking technology.

KEY RESULTS

Emodin specifically inhibited the nuclease activity of HSV-1 UL12 alkaline nuclease in a biochemical assay. Plaque reduction assay revealed that emodin reduced the plaque formation with an EC(50) of 21.5+/-4.4 muM. Immunohistochemical staining using the anti-nucleocapsid protein antibody demonstrated that emodin induced the accumulation of viral nucleocapsids in the nucleus in a dose-dependent manner. Docking analysis further suggested that the inhibitory effect of emodin on the UL12 activity may result from the interaction between emodin and critical catalytic amino acid residues of UL12.

CONCLUSIONS AND IMPLICATIONS

Our findings suggest that emodin is a potent anti-HSV agent that inhibits the yields of HSV-1 via the suppression of a novel target, UL12.

Emodin Induces Growth Arrest and Death of Human Vascular Smooth Muscle Cells Through Reactive Oxygen Species and p53

Percutaneous coronary intervention is the main therapy for revascularization of occluded coronary arteries. However, a progressive artery restenosis caused by abnormal proliferation and migration of vascular smooth muscle cells (VSMC) hinders the effective treatment. In this study, we examined the effect of emodin, a natural anthraquinoid compound, on cultured VSMC. Lower doses of emodin suppressed cell proliferation and induced unscheduled DNA synthesis. Higher doses of emodin increased lumpy chromatin condensation and lysosomes in VSMC, suggesting the occurrence of apoptosis and autophagy. Emodin increased production of reactive oxygen species (ROS), which was abolished by an NADPH oxidase inhibitor diphenylene iodonium (DPI). DPI could also decrease the number of apoptosis induced by emodin, suggesting the involvement of ROS in emodin-induced apoptosis. Emodin upregulated the protein levels of p53 in a dose-dependent manner. Laser confocal microscope showed most of emodin scattering in the cytoplasms and a little within the nuclei. These findings collectively indicated that emodin induces both growth arrest and death of human VSMCs in 2 independent manners, implying it as a promising therapy for preventing restenosis.

The colleflaccinosides, two chiral bianthraquinone glycosides with antitumor activity from the lichen Collema flaccidum collected in Israel and Russia

Colleflaccinosides A and B, two chiral bianthraquinone glycosides from the two geographical varieties of lichen Collema flaccidum collected in Russia and Israel have been isolated as new natural products. Their structures were elucidated using UV, CD, IR, MS, 1D and 2D NMR spectral data, and chemical degradation. The colleflaccinosides B had significant antitumor activity in the crown gall tumor inhibition test.

In vitro pharmacodynamic evaluation of antiviral medicinal plants using a vector-based assay technique

AIMS

Medicinal plants are increasingly being projected as suitable alternative sources of antiviral agents. The development of a suitable in vitro pharmacodynamic screening technique could contribute to rapid identification of potential bioactive plants and also to the standardization and/or pharmacokinetic-pharmacodynamic profiling of the bioactive components.

METHODS AND RESULTS

Recombinant viral vectors (lentiviral, retroviral and adenoviral) transferring the firefly luciferase gene were constructed and the inhibition of viral vector infectivity by various concentrations of plant extracts was evaluated in HeLa or Hep2 cells by measuring the changes in luciferase activity. Cytotoxicity of the extracts was evaluated in parallel on HeLa or Hep2 cells stably expressing luciferase. Amongst the 15 extracts screened, only the methanol (ME) and the ethyl acetate (ET) fractions of the lichen, Ramalina farinacea specifically reduced lentiviral and adenoviral infectivity in a dose-dependent manner. Further, chromatographic fractionation of ET into four fractions (ET1-ET4) revealed only ET4 to be selectively antiviral with an IC50 in the 20 microg ml(-1) range. Preliminary mechanistic studies based on the addition of the extracts at different time points in the viral infection cycle (kinetic studies) revealed that the inhibitory activity was highest if extract and vectors were preincubated prior to infection, suggesting that early steps in the lentiviral or adenoviral replication cycle could be the major target of ET4. Inhibition of wild-type HIV-1 was also observed at a 10-fold lower concentration of the extract.

CONCLUSIONS

The vector-based assay is a suitable in vitro pharmacodynamic evaluation technique for antiviral medicinal plants. The technique has successfully demonstrated the presence of antiviral principles in R. farinacea.

SIGNIFICANCE AND IMPACT OF STUDY

Potential anti-HIV medicinal plants could rapidly be evaluated with the reported vector-based technique. The lichen, R. farinacea could represent a lead source of antiviral substances and is thus worthy of further studies.

Synthesis and biological evaluation of new derivatives of emodin

Drugs containing an anthraquinone moiety such as daunorubicin (Daunoblastin) and mitoxantrone (Onkotrone) constitute some of the most powerful cytostatics. They suppress tumor growth mainly by intercalation into DNA and inhibition of topoisomerase II, and are suspected to generate free radicals leading to DNA strand scission. We established a novel strategy for obtaining new highly functionalized derivatives of emodin (1,3,8-trihydroxy-6-methyl-anthraquinone). Using emodin, DIB, and an appropriate amine as starting materials, we obtained a wide range of emodin-related structures by one-pot synthesis. Several of these derivatives showed stronger cytotoxic and cytostatic activity than emodin. In particular, compound 6 was highly effective on the HepG2 tumor cell line, but did not show any cytotoxicity on normal hepatocytes. In addition to this favorable feature, compound 6 revealed interesting binding properties to a recombinant fragment of the multi-drug-resistance transporter, pgp, and reversed the multi-drug-resistance phenotype of H4-II-E cells, thus making this compound a promising potential anti-tumor drug.

Membrane-related effects underlying the biological activity of the anthraquinones emodin and barbaloin

Commercial plant extracts containing anthraquinones are being increasingly used for cosmetics, food and pharmaceuticals due to their wide therapeutic and pharmacological properties. In this work, the interaction with model membranes of two representative 1,8-dihydroxyanthraquinones, barbaloin (Aloe) and emodin (Rheum, Polygonum), has been studied in order to explain their effects in biological membranes. Emodin showed a higher affinity for phospholipid membranes than barbaloin did, and was more effective in weakening hydrophobic interactions between hydrocarbon chains in phospholipid bilayers. Whereas emodin induced the formation of hexagonal-H(II) phase, barbaloin stabilized lamellar structures. Barbaloin promoted the formation of gel-fluid intermediate structures in phosphatidylglycerol membranes at physiological pH and ionic strength values. It is proposed that emodin's chromophore group is located at the upper half of the membrane, whereas barbaloin's one is in a deeper position but having its glucopyranosyl moiety near the phospholipid/water interface. Moreover, membrane disruption by emodin or barbaloin showed specificity for the two major phospholipids present in bacterial membranes, phosphatidylethanolamine and phosphatidylglycerol. In order to relate their strong effects on membranes to their biological activity, the capacity of these compounds to inhibit the infectivity of the viral haemorrhagic septicaemia rhabdovirus (VHSV), a negative RNA enveloped virus, or the growth of Escherichia coli was tested. Anthraquinone-loaded liposomes showed a strong antimicrobial activity whereas these compounds in their free form did not. Both anthraquinones showed antiviral activity but only emodin was a virucidal agent. In conclusion, a molecular mechanism based on the effect of these compounds on the structure of biological membranes is proposed to account for their multiple biological activities. Anthraquinone-loaded liposomes may suppose an alternative for antimicrobial, pharmaceutical or cosmetic applications.

Tumor cell toxicity of hypericin and related analogs

A series of hypericin analogs were found to differ in their cytotoxic activity induced by ambient light levels. These analogs vary in their ability to partition into cells, to generate singlet oxygen as well as in other photophysical properties. The data suggest that the biological activity of hypericin is due to a combination of factors whose roles may vary under different circumstances.

In vitro antiviral activity of the anthraquinone chrysophanic acid against poliovirus

Chrysophanic acid (1,8-dihydroxy-3-methylanthraquinone), isolated from the Australian Aboriginal medicinal plant Dianella longifolia, has been found to inhibit the replication of poliovirus types 2 and 3 (Picornaviridae) in vitro. The compound inhibited poliovirus-induced cytopathic effects in BGM (Buffalo green monkey) kidney cells at a 50% effective concentration of 0.21 and 0.02 microgram/ml for poliovirus types 2 and 3, respectively. The compound inhibited an early stage in the viral replication cycle, but did not have an irreversible virucidal effect on poliovirus particles. Chrysophanic acid did not have significant antiviral activity against five other viruses tested: Coxsackievirus types A21 and B4, human rhinovirus type 2 (Picornaviridae), and the enveloped viruses Ross River virus (Togaviridae) and herpes simplex virus type 1 (Herpesviridae). Four structurally-related anthraquinones--rhein, 1,8-dihydroxyanthraquinone, emodin and aloe-emodin were also tested for activity against poliovirus type 3. None of the four compounds was as active as chrysophanic acid against the virus. The results suggested that two hydrophobic positions on the chrysophanic acid molecule (C-6 and the methyl group attached to C-3) were important for the compound's activity against poliovirus.

Phenanthrenequinone antiretroviral agents

Compounds 3 and 5 are the first phenanthrenequinones to exhibit significant virucidal activity against the retrovirus equine infectious anemia virus. They differ from hypericin in that their virucidal activity is not light dependent.

Plant products as topical microbicide candidates: assessment of in vitro and in vivo activity against herpes simplex virus type 2

There is considerable interest in developing topical microbicides; products to be used intravaginally by women for protection against sexually transmitted diseases. Many compounds derived from plants have been shown to have antimicrobial properties. We examined 19 such compounds in vitro by plaque reduction assay to determine their activity against a common sexually transmitted pathogen, herpes simplex virus type 2. Compounds with an ED50 < or = 7.0 mg/ml were tested for efficacy in vivo. Four compounds, carrageenan lambda type IV, cineole, curcumin, and eugenol, provided significant protection (P < 0.05) in a mouse model of intravaginal HSV-2 challenge. Eugenol, which provided the greatest protection in mice was also evaluated using the guinea pig model of genital HSV-2 infection where it also demonstrated significant protection. Based on these results, several plant-derived compounds appear to warrant further evaluation as potential microbicides.