The Immunostimulating Role of Lichen Polysaccharides: A Review

Lichen pectin-containing polysaccharide from Xanthoria elegans and its ability to effectively protect LX-2 cells from H2O2-induced oxidative damage

Xanthoria elegans, a drought-tolerant lichen, is the original plant of the traditional Chinese medicine "Shihua" and effectively treats a variety of liver diseases. However, thus far, the hepatoprotective effects of polysaccharides, the most important chemical constituents of X. elegans, have not been determined. The aim of this study was to screen the polysaccharide fraction for hepatoprotective activity by using free radical scavenging assays and a H2O2-induced Lieming Xu-2 cell (LX-2) oxidative damage model and to elucidate the chemical composition of the bioactive polysaccharide fraction. In the present study, three polysaccharide fractions (XEP-50, XEP-70 and XEP-90) were obtained from X. elegans by hot-water extraction, DEAE-cellulose anion exchange chromatography separation and ethanol gradient precipitation. Among the three polysaccharide fractions, XEP-70 exhibited the best antioxidant activity in free radical scavenging capacity and reducing power assays. Structural studies showed that XEP-70 was a pectin-containing heteropolysaccharide fraction that was composed mainly of (1 → 4)-linked and (1 → 4,6)-linked α-D-Glcp, (1 → 4)-linked α-D-GalpA, (1 → 2)-linked, (1 → 6)-linked and (1 → 2,6)-linked α-D-Manp, and (1 → 6)-linked and (1 → 2,6)-linked β-D-Galf. Furthermore, XEP-70 exhibited effectively protect LX-2 cells against H2O2-induced oxidative damage by enhancing cellular antioxidant capacity by activating the Nrf2/Keap1/ARE signaling pathway. Thus, XEP-70 has good potential to protect hepatic stellate cells against oxidative damage.

Synthesis of galactomannan fragments to help NMR assignment of polysaccharides extracted from lichens

The synthesis of six model trisaccharides representative of galactomannans produced by lichens was performed through stereoselective glycosylation. These standards include linear and branched galactomannans bearing either galactofuranosyl or galactopyranosyl entities. The complete assignment of 1H and 13C signals for both forms of synthetically reduced oligosaccharides was performed. The resulting NMR data were used to quickly demonstrate the structural characteristics of minor polysaccharides within different extracts of three representative lichens.

Evernia prunastri lichen as a source of bioactive glucans with potential for topical applications

Microwave hydrothermal treatment was selected to extract valuable fractions with bioactive and gelling properties from Evernia prunastri lichen with potential for topical applications. The impact of the extraction processing conditions on the soluble extracts, mucilage fraction and residual solid phase was analyzed within a lichen global valorization approach. A particular stress was made on the thermo-rheological and structural characteristics of the extracted glucan and galactomannan polymers, the corresponding gelled matrices, and their cosmetic feasibility. Results revealed that the proposed microwave-assisted treatment showed a relevant influence on the phytochemical features of the aqueous soluble extracts, accounting the major protein content at 120 °C and the enhanced antioxidant and anti-tyrosinase properties at 140 °C. Extracts at 200 °C showed the highest anti-inflammatory (COX-1 and COX-2 inhibition) efficacies. The biopolymer analyses indicated that those recovered after lichen hydrothermal treatment at 160 °C featured a good extraction performance, the highest molecular weight, apparent viscosity, and antiproliferative potential. The thermo-rheological properties of the corresponding matrices formulated at 10 % and 60 or 80 °C exhibited the strongest and most thermo-reversible characteristics, as well as antifreezing feasibility. Another advantage of the selected fractions was the absence of skin irritation according to the in vitro skin irritation assay.

Proposed mechanisms of action of herbal drugs and their biologically active constituents in the treatment of coughs: an overview

Various medicinal plants find their use in cough treatment, based on traditions and long-term experience. Pharmacological principles of their action, however, are much less known. Herbal drugs usually contain a mixture of potentially active compounds, which can manifest diverse effects. Expectorant or antitussive effects, which can be accompanied by others, such as anti-inflammatory or antibacterial, are probably the most important in the treatment of coughs. The aim of this review is to summarize the current state of knowledge of the effects of medicinal plants or their constituents on cough, based on reliable pharmacological studies. First, a comprehensive description of each effect is provided in order to explain the possible mechanism of action in detail. Next, the results related to individual plants and substances are summarized and critically discussed based on pharmacological in vivo and in vitro investigation.

Lichens: An update on their ethnopharmacological uses and potential as sources of drug leads

ETHNOPHARMACOLOGICAL RELEVANCE

Lichens, a unique symbiotic association between an alga/cyanobacterium and a fungus, produce secondary metabolites that are a promising source of novel drug leads. The beauty and importance of lichens have not been adequately explored despite their manifold biological activities such as anticancer, antimicrobial, antioxidant, anti-inflammatory, analgesic, antipyretic and antiparasitic.

AIM OF THE STUDY

The present review collates and discusses the available knowledge on secondary metabolites and biological activities of lichens (in vitro and in vivo).

MATERIALS AND METHODS

Using relevant keywords (lichens, secondary metabolites, bioactivity, pharmacological activities), five electronic databases, namely ScienceDirect, PubMed, Google Scholar, Scopus and Recent Literature on Lichens, were searched for past and current scientific contributions up until May 2022. Literature focusing broadly on the bioactivity of lichens including their secondary metabolites were identified and summarized.

RESULTS

A total of 50 review articles and 189 research articles were searched. Information related to antioxidant, antimicrobial, anti-inflammatory, anticancer and insecticidal activities of 90 lichen species (from 13 families) and 12 isolated metabolites are reported. Over 90% of the studies comprised in vitro investigations, such as bioassays evaluating radical scavenging properties, lipid peroxidation inhibition and reducing power, cytotoxicity and antimicrobial bioassays of lichen species and constituents. In vivo studies were scarce and available only in fish and rats. Most of the studies were done by research groups in Brazil, France, Serbia, India and Turkey. There were relatively few reports from Asia and Africa despite the ubiquitous nature of lichens and the high occurrence in these continents.

CONCLUSION

Secondary metabolites from lichens are worthy of further investigation in terms of their potential therapeutic applicability, including better understanding of their mechanism(s) of action. This would be of great importance in the search for novel drugs.

Purification, characterization and immunostimulatory activity of a novel exopolysaccharide from Bacillus sp. H5

Crude exopolysaccharides from extracellular polymeric substances produced by the marine bacterium Bacillus sp. H5 were fractionated using DEAE-Sepharose FF and Sephadex G-75 chromatography. The high molecular weight fraction (89.0 kD) from the neutral fraction was designated EPS5SH; it contained mannose, glucosamine, glucose, and galactose in a molar ratio of 1.00: 0.02: 0.07: 0.02. Infra-red, gas chromatography-mass spectrometry, electrospray ionisation-tandem mass spectrometry analysis and nuclear magnetic resonance revealed EPS5SH was a mannan with α-(1 → 4)-Manp, α-(1 → 2)-Manp, α-(1 → 4, 6)-Manp and β-terminal-Manp. Preliminary in vitro experiments revealed that EPS5SH significantly upregulated nitric oxide synthesis and release of pro-inflammatory factors in murine macrophage RAW264.7 cells. Western blot experiments verified the immunostimulatory effects of EPS5SH through the modulation of the NF-κB and MAPK signalling pathways. In conclusion, EPS5SH was a novel immunostimulatory mannan.

Physicochemical Properties and Skin Protection Activities of Polysaccharides from Usnea longissima by Graded Ethanol Precipitation

Four Usnea longissima polysaccharides (ULPs; ULP15, ULP30, ULP50, and ULP70) were obtained from the lichen U. longissima via water extraction and graded ethanol precipitation. The obtained ULPs were all heteropolysaccharides with a few proteins, with which glucose was the major monosaccharide composition. With the increase in the precipitated ethanol concentrations, the content of galactose, xylose, and mannose increased, whereas that of glucose decreased. Moreover, the antioxidant activity test demonstrated that ULP15 exhibited better reducing power and stronger scavenging ability on 2,2-diphenyl-1-picrylhydrazyl (DPPH) and hydroxyl free radicals. Importantly, ULP15 also had a better proliferative effect on human HaCaT keratinocytes and dermal fibroblasts. Meanwhile, ULP15 protected HaCaT keratinocytes from UVB-induced proliferation inhibition and exhibited tyrosinase inhibition activity. Therefore, this work provides interesting insight into the preparation of cosmetic ingredients using the polysaccharide ULP15.

Chemical Characterization of the Lichen-Symbiont Microalga Asterochloris erici and Study of Its Cytostatic Effect on the L929 Murine Fibrosarcoma Cell Line

New resources of food, pharmaceuticals or biotechnological products are needed. The huge biodiversity of aero-terrestrial lichen-symbiont microalgae belonging to the Chlorophyta group remains unexplored despite they present interesting features such as extreme stress tolerance and growth in water shortage. Appropriateness for human consumption demands the demonstration of the absence of toxic effects. In vitro biocompatibility of crude homogenates of axenic microalga Asterochloris erici, isolated from the lichen Cladonia cristatella, was analyzed after treatment of cultured L929 fibroblasts with different concentrations of microalgal homogenates. The microalgal protein content (37%) was similar to spirulina or soybean. Antioxidant capacity (10.6 ± 0.6 µmol TE/g WW) or phenolic content (7.5 ± 0.5 mg GAE/g DW) were high compared to Chlorella. The results show that crude homogenates of A. erici do not induce cytotoxicity but seem to have some cytostatic effect inducing slight cell cycle alterations and intracellular reactive oxygen species (ROS) increase at the highest concentration. Carotenoid analysis demonstrates high contents of lutein (1211 µg/g microalga DW), a xanthophyll with antioxidant and cytostatic properties in vivo and high commercial added value. These findings confirm that Asterochloris erici can be suitable for the development of alimentary or pharmaceutical applications and further in vivo animal testing. The cytostatic effects should be further investigated for antitumor agents.

Methods of correcting stress adaptation of young cattle

For the first time in the conditions of the Magadan region, studies were carried out to study the effect of a new non-traditional feed additive (FA) of plant origin, consisting of kelp flour (Laminaria), lichen - alpine cladonia (Cladonia alpestris) and Icelandic cetraria (Cetraria islandica), introduced into the diets of mixed young cattle of meat direction, on morphological and biochemical parameters of blood, as well as the general resistance of young animals. It was found that the inclusion of a component feed additive in the diets of calves of the dairy period affects their growth and development, improves the physiological state, resistance of gobies in the experimental group, in comparison with the control one. This is reflected by an increase in the protein content in the blood serum of calves of the experimental group by 9.8 g / l (14.37%), hemoglobin by 0.2 g / dl (1.86%), lymphocytes by 1.2%, and a decrease in the content of leukocytes by 1.02 thousand / μl (9.57%) relative to young animals in the control group.

Exopolysaccharide from Cryptococcus heimaeyensis S20 induces autophagic cell death in non-small cell lung cancer cells via ROS/p38 and ROS/ERK signalling

OBJECTIVES

Cryptococcus heimaeyensis S20 is found in Antarctica and can produce exopolysaccharides (CHEPS). Here, we explore the anti-tumour effects of CHEPS on non-small cell lung cancer (NSCLC).

MATERIALS AND METHODS

Cell viability was assessed by CCK8 and colony formation assays. Flow cytometry was used to analyse the cell cycle, cell apoptosis and reactive oxygen species (ROS). Cell autophagy was detected by EGFP-LC3 puncta assay, Lyso-Tracker Red staining and transmission electron microscopy. mRNA and protein levels were analysed by qRT-PCR and Western blot. Related mechanisms were confirmed using appropriate inhibitors or shRNA. In vitro results were further confirmed by a tumour xenograft study.

RESULTS

CHEPS inhibited the proliferation of NSCLC cells by inducing S- and G2/M-phase arrest and autophagic cell death, but not apoptosis. CHEPS was less toxic to normal human embryonic lung fibroblasts. CHEPS activated the MAPK pathway in NSCLC cells, and p38 and ERK promoted CHEPS-induced cell death. Further studies showed that p38 and ERK promoted CHEPS-induced NSCLC cell autophagy and ERK promoted CHEPS-induced S- and G2/M-phase arrest. ROS were induced by CHEPS. A ROS scavenger attenuated CHEPS-induced p38 and ERK activation, autophagy and cell death. Finally, CHEPS reduced orthotopic lung tumour growth without organ-related toxicity. CHEPS also induced ROS, activated p38 and ERK, and triggered autophagy in vivo.

CONCLUSIONS

CHEPS induces autophagic cell death and S- and G2/M-phase arrest in NSCLC cells via ROS/p38 and ROS/ERK signalling.

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.

Polysaccharide fraction from the Indian mistletoe, Dendrophthoe falcata (L.f.) Ettingsh enhances innate immunity and disease resistance in Oreochromis niloticus (Linn.)

The polysaccharide fraction (PF) isolated from the hemiparasitic mistletoe, Dendrophthoe falcata (L.f.) Ettingsh (DF) leaves was tested for its immunostimulatory properties in Oreochromis niloticus (Linn.). Different groups of experimental fish were fed for 1, 2 or 3 weeks with three different doses [low (0.01%), mid (0.1%), or high (1%)] of D. falcata polysaccharide fraction (DFPF) - supplemented diet. After every feeding regimen, the fish were assessed for non-specific immunological parameters, immune related gene expression and disease protection. The DFPF treated groups showed significant (P < 0.05) enhancement of non-specific immune parameters. Significant (P < 0.05) upregulation of lysozyme and TNF-α gene expression was observed in DFPF treated groups. In pathogen challenge studies using Aeromonas hydrophila, the DFPF treated groups displayed significant (P < 0.05) decrease in percentage mortality and the consequent increase in relative percent survival (RPS). Supplementation of 1% DFPF in the feed for a week conferred the maximum protection against the virulent pathogen challenge, recording a RPS of 100. These results suggest that DFPF has the potential to be used as an immunostimulating feed additive in finfish aquaculture.

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.

Purification and activity characterization of polysaccharides in the medicinal lichen Umbilicaria tornata from Taibai Mountain, China

Water-soluble polysaccharides from Umbilicaria tornata (UTP) were purified and preliminarily characterized. The antioxidant and antitumor activities of crude UTP and two purified fractions (UTP-1 and UTP-2) were evaluated using in vitro experiments. The results showed that the molecular weights of UTP-1 and UTP-2 were 84.86 and 28.66 kDa, respectively. Both UTP-1 and UTP-2 were composed of glucose and xylose, with their molar ratios being 1.3:0.9 and 0.9:4.6, respectively. In addition, crude UTP, UTP-1 and UTP-2 showed dose-dependent DPPH and hydroxyl radical scavenging and reducing activities. However, crude UTP exhibited stronger antioxidant activity than UTP-1 and UTP-2, particularly in terms of DPPH radicals. Crude UTP and the two purified fractions inhibited the growth of HeLa, HepG2, A375, MCF-7, SGC7901 and Caco2 cancer cells in vitro. Compared with UTP-1 and UTP-2, crude UTP presented significantly higher antitumor activity in vitro against HeLa and HepG2 cells (p < 0.05). These findings provide a scientific basis for the deeper exploration and resource development of U. tornata.

Sargassum fusiforme polysaccharides inhibit VEGF-A-related angiogenesis and proliferation of lung cancer in vitro and in vivo

Sargassum fusiforme (Harv.) is a brown alga belonging to the Sargasaceae family. The Sargassum fusiforme polysaccharides (SFPS) have demonstrated good anti-tumor and immunomodulatory activity. However, the underlying mechanisms of its anti-tumorigenesis, especially the anti-angiogenic activity is yet to be established. In the present study, we attempted to determine the effects of SFPS on the human lung adenocarcinoma SPC-A-1 cells and its xenograft model. The results showed that SFPS provides a concentration-dependent inhibition of SPC-A-1 cell proliferation in in vitro and the tumor growth in in vivo studies. Immunohistochemistry studies revealed that the administration of SFPS significantly decreased CD31, VEGF-A expression and the tumor microvessel density (MVD). SFPS also provided a dose-dependent impairment of cell vitality, induction of cell cycle arrest and apoptosis of human umbilical vein endothelial cells (HUVECs). SFPS inhibited the expression of VEGF-A in tumor cells and its receptor VEGFR2 in HUVECs. The HUVEC tube formation assay showed that SFPS could abrogate the tube formation with relatively decreased tubes length of tube-like capillary similar to anti-VEGF antibody, Avastin®. These findings suggested that SFPS could be used as an alternative anticancer drug as they inhibited the angiogenesis and the microvessel formation through disruption of VEGF signals apart from direct tumor cytotoxicity.

Antifungal potential of marine natural products

Fungal diseases represent an increasing threat to human health worldwide which in some cases might be associated with substantial morbidity and mortality. However, only few antifungal drugs are currently available for the treatment of life-threatening fungal infections. Furthermore, plant diseases caused by fungal pathogens represent a worldwide economic problem for the agriculture industry. The marine environment continues to provide structurally diverse and biologically active secondary metabolites, several of which have inspired the development of new classes of therapeutic agents. Among these secondary metabolites, several compounds with noteworthy antifungal activities have been isolated from marine microorganisms, invertebrates, and algae. During the last fifteen years, around 65% of marine natural products possessing antifungal activities have been isolated from sponges and bacteria. This review gives an overview of natural products from diverse marine organisms that have shown in vitro and/or in vivo potential as antifungal agents, with their mechanism of action whenever applicable. The natural products literature is covered from January 2000 until June 2015, and we are reporting the chemical structures together with their biological activities, as well as the isolation source.

Anti-tumor effects of (1→3)-β-d-glucan from Saccharomyces cerevisiae in S180 tumor-bearing mice

(1→3)-β-d-Glucan from Saccharomyces cerevisiae is a typical polysaccharide with various biological effects and is considered a candidate for the prevention and treatment of cancer in vitro. Research into the function of (1→3)-β-d-glucan in tumor-bearing animals in vivo, however, is limited. Here, we investigated the effects of (1→3)-β-d-glucan from S. cerevisiae on S180 tumor-bearing mice and on the immunity of the tumor-bearing host. The molecular mechanisms underlying the observed effects were investigated. (1→3)-β-d-Glucan was shown to exert anti-tumor effects without toxicity in normal mouse cells. The volume and weight of S180 tumors decreased dramatically following treatment with (1→3)-β-d-glucan, and treatment with the polysaccharide was furthermore shown to increase the tumor inhibition rate in a dose-dependent manner. Spleen index, T lymphocyte subsets (CD₄ and CD₈), as well as interleukins (IL)-2, (IL-2, IL-6), and tumor necrosis factor-α were assayed to detect the immunoregulatory and anti-tumor effects after (1→3)-β-d-glucan intragastrical administration. (1→3)-β-d-Glucan was shown to significantly potentiate the mouse immune responses by, among other effects, decreasing the ratio of CD₄ to CD₈. The expression levels of IL-2, IL-6, and TNF-α were also significantly increased by (1→3)-β-d-glucan. These results suggest that (1→3)-β-d-glucan enhances the host's immune function during the tumor inhibition process. S180 tumor cells treated with (1→3)-β-d-glucan also exhibited significant apoptotic characteristics. (1→3)-β-d-glucan increased the ratio of Bax to Bcl-2 at the translation level by up-regulating Bax expression and down-regulating Bcl-2 expression, resulting in the initiation of cell apoptosis in S180 tumor-bearing mice. Taken together, these results indicate that the anti-tumor effects exerted by (1→3)-β-d-glucan may be attributed to the polysaccharide's immunostimulating properties and apoptosis-inducing features. Further investigation into these properties and their associated mechanisms will contribute to the development of potent polysaccharide-based anti-tumor agents.

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.