Novel Aeruginosin-865 from Nostoc sp. as a potent anti-inflammatory agent

Cyanobacterial metabolites: aeruginosin 98A, microginin-FR1, anabaenopeptin-A, cylindrospermopsin and their mixtures affect behavioral and physiological responses of Daphnia magna

We determined the effects influence of cyanobacterial products metabolites: aeruginosin-A (AER-A), microginin-FR1 (MG-FR1), anabaenopeptin-A (ANA-A), cylindrospermopsin (CYL) and their binary and quadruple mixtures on swimming behavior, heart rate, thoracic limb activity, oxygen consumption and in vivo cell health of Daphnia magna. The study showed that CYL induced mortality of daphnids at the highest concentrations, however three oligopeptides had no lethal effect. All the tested Each single metabolites inhibited swimming speed. The mixtures AER+MG-FR1 and AER-A+ANA-A induced antagonistic and the quadruple mixture synergistic effects. Physiological endpoints were depressed by CYL, however they were simulated by the oligopeptides and their binary mixtures. The quadruple mixture inhibited the physiological parameters with antagonistic interactions between the components were antagonistic. Single CYL, MG-FR1 and ANA-A induced cytotoxicity with synergistic interactions and the metabolites in mixtures showed. The study suggests that swimming behavior and physiological parameters may be affected by single cyanobacterial oligopeptides, however their mixtures may induce different total effects.

Effects of cyanobacterial metabolites: Aeruginosin 98A, microginin-FR1, anabaenopeptin-A, cylindrospermopsin in binary and quadruple mixtures on the survival and oxidative stress biomarkers of Daphnia magna

The aim of our study was to determine the effects of aeruginosin 98 A (ARE-A), microginin-FR1 (MG-FR1), anabaenopeptin-A (ANA-A) cylindrospermopsin (CYL) and their binary and quadruple mixtures on the survival and the levels of oxidative stress biomarkers in Daphnia magna: total glutathione (GSH), catalase (CAT), dismutase (SOD) and malondialdehyde (MDA). The biochemical indicators were measured with ELISA kits and the interactive effects were determined by isobole and polygonal analysis with Compusyn® computer software. The study revealed that oligopeptides did not decrease daphnid survival, only CYL inhibited this parameter, with synergistic effects when it was used as a component. The single metabolites at the two highest concentrations and all the binary and quadruple mixtures at all concentrations diminished GSH level, however both in the binary and in the quadruple mixtures most of the interactions between the metabolites were antagonistic. Nearly additive effects were found only in AER-A + CYL and MG-FR1+CYL. On the other hand, CAT activity was slightly increased in daphnids exposed to the binary mixtures with antagonistic interactions, however nearly addivive effects were found in animals exposed to the mixture of AER-A + ANA-A and synergistic in the quadruple mixture. SOD was elevated in daphnids exposed to single AER-A and MG-FR1, however it was diminished in the animals exposed to ANA-A and CYL. Binary mixtures in which CYL was present as a component decreased the level of this enzyme with nearly additive interactions in ANA-A + CYL. The quadruple mixture increased SOD level, with antagonistic interactions. Both single cyanobacterial metabolites, their binary and quadruple mixtures induced lipid peroxidation measured by MDA level and most of interactions in the binary mixtures were synergistic. The study suggested that antioxidative system of Daphnia magna responded to the tested metabolites and the real exposure to mixtures of these products may lead to various interactive effects with varied total toxicity.

Diversity, Biosynthesis and Bioactivity of Aeruginosins, a Family of Cyanobacteria-Derived Nonribosomal Linear Tetrapeptides

Aeruginosins, a family of nonribosomal linear tetrapeptides discovered from cyanobacteria and sponges, exhibit in vitro inhibitory activity on various types of serine proteases. This family is characterized by the existence of the 2-carboxy-6-hydroxy-octahydroindole (Choi) moiety occupied at the central position of the tetrapeptide. Aeruginosins have attracted much attention due to their special structures and unique bioactivities. Although many studies on aeruginosins have been published, there has not yet been a comprehensive review that summarizes the diverse research ranging from biogenesis, structural characterization and biosynthesis to bioactivity. In this review, we provide an overview of the source, chemical structure as well as spectrum of bioactivities of aeruginosins. Furthermore, possible opportunities for future research and development of aeruginosins were discussed.

The antioxidant, wound healing properties and proteomic analysis of water extracts from the tropical cyanobacteria, Nostoc NIES-2111_MUM004

Cyanobacteria bioactive compounds are chemical treasure troves for product discovery and development. The wound healing effects and antioxidant capacities of water extracts from Nostoc NIES-2111_MUM004 were evaluated via in vitro wound scratch assay and three antioxidant assays respectively. Results showed that the water extracts were protein-rich and exhibited good antioxidant properties in ABTS radical scavenging (11.27 ± 0.205 mg TAE g^-1 extract), Ferric reducing antioxidant power (1652.71 ± 110.71 mg TAE g^-1 extract) and β-carotene bleaching assay (354.90 ± 31.80 mg TAE g^-1 extract). Also, extracts were non-cytotoxic in concentrations up to 250 µg/mL as reflected in cytotoxicity assay. Importantly, water extracts showed considerable proliferation and migration activity at 125 µg/mL with wound closure rate as high as 42.67%. Statistical correlation revealed no significant relationship (p > 0.05) between protein fraction and the wound healing properties, confirming that phycobiliproteins were not solely responsible for wound healing activities. Subsequent Q-TOF-LCMS analysis identified six protein families involved in enhancing the proliferation and migration of epithelial cells. These findings are antecedent in the uncovering of continuous supplies of bioactive compounds from new and sustainable sources. Ultimately, enriching the microalgae menu for applications in pharmaceutical, nutraceutical and cosmeceuticals.

Cyanobacterial secondary metabolites towards improved commercial significance through multiomics approaches

Cyanobacteria are ubiquitous photosynthetic prokaryotes responsible for the oxygenation of the earth's reducing atmosphere. Apart from oxygen they are producers of a myriad of bioactive metabolites with diverse complex chemical structures and robust biological activities. These secondary metabolites are known to have a variety of medicinal and therapeutic applications ranging from anti-microbial, anti-viral, anti-inflammatory, anti-cancer, and immunomodulating properties. The present review discusses various aspects of secondary metabolites viz. biosynthesis, types and applications, which highlights the repertoire of bioactive constituents they harbor. Majority of these products have been produced from only a handful of genera. Moreover, with the onset of various OMICS approaches, cyanobacteria have become an attractive chassis for improved secondary metabolites production. Also the intervention of synthetic biology tools such as gene editing technologies and a variety of metabolomics and fluxomics approaches, used for engineering cyanobacteria, have significantly enhanced the production of secondary metabolites.

Review of Cyanotoxicity Studies Based on Cell Cultures

Cyanotoxins (CTs) are a large and diverse group of toxins produced by the peculiar photosynthetic prokaryotes of the domain Cyanoprokaryota. Toxin-producing aquatic cyanoprokaryotes can develop in mass, causing “water blooms” or “cyanoblooms,” which may lead to environmental disaster—water poisoning, extinction of aquatic life, and even to human death. CT studies on single cells and cells in culture are an important stage of toxicological studies with increasing impact for their further use for scientific and clinical purposes, and for policies of environmental protection. The higher cost of animal use and continuous resistance to the use of animals for scientific and toxicological studies lead to a progressive increase of cell lines use. This review aims to present (1) the important results of the effects of CT on human and animal cell lines, (2) the methods and concentrations used to obtain these results, (3) the studied cell lines and their tissues of origin, and (4) the intracellular targets of CT. CTs reviewed are presented in alphabetical order as follows: aeruginosins, anatoxins, BMAA (β-N-methylamino-L-alanine), cylindrospermopsins, depsipeptides, lipopolysaccharides, lyngbyatoxins, microcystins, nodularins, cyanobacterial retinoids, and saxitoxins. The presence of all these data in a review allows in one look to advance the research on CT using cell cultures by facilitating the selection of the most appropriate methods, conditions, and cell lines for future toxicological, pharmacological, and physiological studies.

Discovery of varlaxins, new aeruginosin-type inhibitors of human trypsins

Low-molecular weight natural products display vast structural diversity and have played a key role in the development of novel therapeutics. Here we report the discovery of novel members of the aeruginosin family of natural products, which we named varlaxins. The chemical structures of varlaxins 1046A and 1022A were determined using a combination of mass spectrometry, analysis of one- and two-dimensional NMR spectra, and HPLC analysis of Marfey's derivatives. These analyses revealed that varlaxins 1046A and 1022A are composed of the following moieties: 2-O-methylglyceric acid 3-O-sulfate, isoleucine, 2-carboxy-6-hydroxyoctahydroindole (Choi), and a terminal arginine derivative. Varlaxins 1046A and 1022A differ in the cyclization of this arginine moiety. Interestingly, an unusual α-D-glucopyranose moiety derivatized with two 4-hydroxyphenylacetic acid residues was bound to Choi, a structure not previously reported for other members of the aeruginosin family. We sequenced the complete genome of Nostoc sp. UHCC 0870 and identified the putative 36 kb varlaxin biosynthetic gene cluster. Bioinformatics analysis confirmed that varlaxins belong to the aeruginosin family of natural products. Varlaxins 1046A and 1022A strongly inhibited the three human trypsin isoenzymes with IC₅₀ of 0.62-3.6 nM and 97-230 nM, respectively, including a prometastatic trypsin-3, which is a therapeutically relevant target in several types of cancer. These results substantially broaden the genetic and chemical diversity of the aeruginosin family and provide evidence that the aeruginosin family is a source of strong inhibitors of human serine proteases.

Cytotoxic effect of Aeruginosin-865, capsaicin, and resveratrol on mouse cell lines of different origin

The aim of the study was to compare the effects of three natural bioactive compounds (and their combinations) on normal vs. tumour-transformed mouse cells. The cytotoxic effect of Aeruginosin-865 (Aer), capsaicin (Cap), resveratrol (Res) and their combinations was evaluated on normal hepatocytes (AML) and tumour cells derived from livers (Hepa) and kidneys (Renca). Various concentrations from 25 to 200 μM of tested substances were used. Only the Aer + Res combination and a low concentration of Res had a significant cytotoxic effect on Hepa and Renca and no significant cytotoxic effect on AML. Cap had a significant cytotoxic effect on all tested cell lines, but tumour-derived cells showed higher resistance than AML. A significantly increased cytotoxicity was found in the combination of Cap + Res compared to each substance alone. All types of cells showed similar sensitivity to the cytotoxic effect of Cap + Res. Because of a possible hepatotoxic effect, we recommend further investigations into side-effects of Cap + Res. No cytotoxic effect was described in Cap + Aer or in Aer alone. Only substances with a significant cytotoxic effect on tumour cells and no cytotoxic effect on normal cells can be potentially used in anticancer treatment. According to the results, only Res or the combination of Aer + Res can be recommended for further evaluation in the process of new anticancer drug development. The potential hepatotoxic effect of Cap + Res can significantly limit the utilisation of these substances in anticancer treatment.

Algal Toxic Compounds and Their Aeroterrestrial, Airborne and other Extremophilic Producers with Attention to Soil and Plant Contamination: A Review

The review summarizes the available knowledge on toxins and their producers from rather disparate algal assemblages of aeroterrestrial, airborne and other versatile extreme environments (hot springs, deserts, ice, snow, caves, etc.) and on phycotoxins as contaminants of emergent concern in soil and plants. There is a growing body of evidence that algal toxins and their producers occur in all general types of extreme habitats, and cyanobacteria/cyanoprokaryotes dominate in most of them. Altogether, 55 toxigenic algal genera (47 cyanoprokaryotes) were enlisted, and our analysis showed that besides the “standard” toxins, routinely known from different waterbodies (microcystins, nodularins, anatoxins, saxitoxins, cylindrospermopsins, BMAA, etc.), they can produce some specific toxic compounds. Whether the toxic biomolecules are related with the harsh conditions on which algae have to thrive and what is their functional role may be answered by future studies. Therefore, we outline the gaps in knowledge and provide ideas for further research, considering, from one side, the health risk from phycotoxins on the background of the global warming and eutrophication and, from the other side, the current surge of interest which phycotoxins provoke due to their potential as novel compounds in medicine, pharmacy, cosmetics, bioremediation, agriculture and all aspects of biotechnological implications in human life.

The use of cyanobacterial metabolites as natural medical and biotechnological tools: review article

Cyanobacteria are photosynthetic, Gram-negative bacteria that are considered one of the most morphologically diverse groups of prokaryotes with a chief role in the global nutrient cycle as they fixed gaseous carbon dioxide and nitrogen to organic materials. Cyanobacteria have significant adaptability to survive in harsh conditions due to they have different metabolic pathways with unique compounds, effective defensive mechanisms, and wide distribution in different habitats. Besides, they are successfully used to face different challenges in several fields, including industry, aquaculture, agriculture, food, dairy products, pollution control, bioenergy, and pharmaceutics. Analysis of 680 publications revealed that nearly 1630 cyanobacterial molecules belong to different families have a wide range of applications in several fields, including cosmetology, agriculture, pharmacology (immunosuppressant, anticancer, antibacterial, antiprotozoal, antifungal, anti-inflammatory, antimalarial, anticoagulant, anti-tuberculosis, antitumor, and antiviral activities) and food industry. In this review, we nearly mentioned 92 examples of cyanobacterial molecules that are considered the most relevant effects related to anti-inflammatory, antioxidant, antimicrobial, antiviral, and anticancer activities as well as their roles that can be used in various biotechnological fields. These cyanobacterial products might be promising candidates for fighting various diseases and can be used in managing viral and microbial infections.Communicated by Ramaswamy H. Sarma.

Anti-inflammatory Activity of Bioactive Compounds from Microalgae and Cyanobacteria by Focusing on the Mechanisms of Action

Microalgae and cyanobacteria are the potentially valuable source of bioactive compounds applied in the various industries and human usage in different fields of pharmaceutical, nutraceutical, and cosmetic disciplines. One of the interesting aspects is their application as the anti-inflammatory agents for treatment of inflammation related mal-conditions. Natural compounds are of great importance in the treatment of inflammations to reduce the reaction of immune system against pathogens, toxic compounds and damaged cells. A wide range of different metabolites with various chemical structures, including small molecules and peptides and proteins, polysaccharides, fatty acids and their derivatives have been found in microalgae and cyanobacteria which have anti-inflammatory activity. In this review, we summarized different metabolites with anti-inflammatory activity that were extracted from these microorganisms and their mechanisms. The bioactive compounds from microalgae and cyanobacteria have exhibited anti-inflammatory activity through different mechanisms acting intra- or extra- cellularly. So, they could be considered as promising anti-inflammatory agents in treatment of related diseases.

15N Stable Isotope Labeling and Comparative Metabolomics Facilitates Genome Mining in Cultured Cyanobacteria

As genome mining becomes a more widely used approach to identify bacterial natural products, the challenge of matching biosynthetic gene clusters to their cognate secondary metabolites has become more apparent. Bioinformatic platforms such as AntiSMASH have made great progress in predicting chemical structures from genetic information, however the predicted structures are often incomplete. This complicates identifying the predicted compounds by mass spectrometry. Secondary metabolites produced by cyanobacteria represent a unique opportunity for bridging this gap. Cultured cyanobacteria incorporate inorganic nitrogen provided in chemically defined media into all nitrogen-containing secondary metabolites. Thus, stable isotope labeling with ¹⁵N labeled nitrate and subsequent comparative metabolomics can be used to match biosynthetic gene clusters to their cognate compounds in cell extracts. Analysis of the sequenced genome of Nostoc sp. UIC 10630 identified six biosynthetic gene clusters predicted to encode the production of a secondary metabolite with at least one nitrogen atom. Comparative metabolomic analysis of the ¹⁵N labeled and unlabeled cell extracts revealed four nitrogen containing compounds that contained the same number of nitrogen atoms as were predicted in the biosynthetic gene clusters. Two of the four compounds were new secondary metabolites, and their structures were elucidated by NMR, HRESIMS, and MS/MS.

Bioactive Peptides Produced by Cyanobacteria of the Genus Nostoc: A Review

Cyanobacteria of the genus Nostoc are widespread in all kinds of habitats. They occur in a free-living state or in association with other organisms. Members of this genus belong to prolific producers of bioactive metabolites, some of which have been recognized as potential therapeutic agents. Of these, peptides and peptide-like structures show the most promising properties and are of a particular interest for both research laboratories and pharmaceutical companies. Nostoc is a sole source of some lead compounds such as cytotoxic cryptophycins, antiviral cyanovirin-N, or the antitoxic nostocyclopeptides. Nostoc also produces the same bioactive peptides as other cyanobacterial genera, but they frequently have some unique modifications in the structure. This includes hepatotoxic microcystins and potent proteases inhibitors such as cyanopeptolins, anabaenopeptins, and microginins. In this review, we described the most studied peptides produced by Nostoc, focusing especially on the structure, the activity, and a potential application of the compounds.

Antimicrobial activity and bioactive profiling of heterocytous cyanobacterial strains using MS/MS-based molecular networking

The rapid emergence of resistance in pathogenic bacteria together with a steep decline in economic incentives has rendered a new wave in the drug development by the pharmaceutical industry and researchers. Since cyanobacteria are recognized as wide producers of pharmaceutically important compounds, we investigated thirty-four cyanobacterial extracts prepared by solvents of different polarities for their antimicrobial potential. Almost all tested cyanobacterial strains exhibited some degree of antimicrobial bioactivity, with more general effect on fungal strains compared with bacteria. Surprisingly ~50% of cyanobacterial extracts exhibited specific activity against one or few bacterial indicator strains with Gram-positive bacteria being more affected. Extracts of two most promising strains were subjected to activity-guided fractionation and determination of the minimum inhibitory concentration (MIC) against selected bacterial and fungal isolates. Multiple fractions were responsible for their antimicrobial effect with MIC reaching low-micromolar concentrations and in some of them high level of specificity was recorded. Twenty-six bioactive fractions analyzed on LC-HRMS/MS and Global Natural Product Social Molecular Networking (GNPS) online workflow using dereplication resulted in identification of only forty-nine peptide spectrum matches (PSMs) with eleven unique metabolites spectrum matches (MSMs). Interestingly, only three fractions from Nostoc calcicola Lukešová 3/97 and four fractions from Desmonostoc sp. Cc2 showed the presence of unique MSMs suggesting the presence of unknown antimicrobial metabolites among majority of bioactive fractions from both the strains. Our results highlight potential for isolation and discovery of potential antimicrobial bioactive lead molecules from cyanobacterial extracts.

Cyanobacterial bioactive metabolites-A review of their chemistry and biology

Cyanobacterial blooms occur when algal densities exceed baseline population concentrations. Cyanobacteria can produce a large number of secondary metabolites. Odorous metabolites affect the smell and flavor of aquatic animals, whereas bioactive metabolites cause a range of lethal and sub-lethal effects in plants, invertebrates, and vertebrates, including humans. Herein, the bioactivity, chemistry, origin, and biosynthesis of these cyanobacterial secondary metabolites were reviewed. With recent revision of cyanobacterial taxonomy by Anagnostidis and Komárek as part of the Süβwasserflora von Mitteleuropa volumes 19(1-3), names of many cyanobacteria that produce bioactive compounds have changed, thereby confusing readers. The original and new nomenclature are included in this review to clarify the origins of cyanobacterial bioactive compounds. Due to structural similarity, the 157 known bioactive classes produced by cyanobacteria have been condensed to 55 classes. This review will provide a basis for more formal procedures to adopt a logical naming system. This review is needed for efficient management of water resources to understand, identify, and manage cyanobacterial harmful algal bloom impacts.

Natural Products from Cyanobacteria: Focus on Beneficial Activities

Cyanobacteria are photosynthetic microorganisms that colonize diverse environments worldwide, ranging from ocean to freshwaters, soils, and extreme environments. Their adaptation capacities and the diversity of natural products that they synthesize, support cyanobacterial success in colonization of their respective ecological niches. Although cyanobacteria are well-known for their toxin production and their relative deleterious consequences, they also produce a large variety of molecules that exhibit beneficial properties with high potential in various fields (e.g., a synthetic analog of dolastatin 10 is used against Hodgkin's lymphoma). The present review focuses on the beneficial activities of cyanobacterial molecules described so far. Based on an analysis of 670 papers, it appears that more than 90 genera of cyanobacteria have been observed to produce compounds with potentially beneficial activities in which most of them belong to the orders Oscillatoriales, Nostocales, Chroococcales, and Synechococcales. The rest of the cyanobacterial orders (i.e., Pleurocapsales, Chroococcidiopsales, and Gloeobacterales) remain poorly explored in terms of their molecular diversity and relative bioactivity. The diverse cyanobacterial metabolites possessing beneficial bioactivities belong to 10 different chemical classes (alkaloids, depsipeptides, lipopeptides, macrolides/lactones, peptides, terpenes, polysaccharides, lipids, polyketides, and others) that exhibit 14 major kinds of bioactivity. However, no direct relationship between the chemical class and the respective bioactivity of these molecules has been demonstrated. We further selected and specifically described 47 molecule families according to their respective bioactivities and their potential uses in pharmacology, cosmetology, agriculture, or other specific fields of interest. With this up-to-date review, we attempt to present new perspectives for the rational discovery of novel cyanobacterial metabolites with beneficial bioactivity.

Cyanobacterial bioactive metabolites-A review of their chemistry and biology

Cyanobacterial blooms occur when algal densities exceed baseline population concentrations. Cyanobacteria can produce a large number of secondary metabolites. Odorous metabolites affect the smell and flavor of aquatic animals, whereas bioactive metabolites cause a range of lethal and sub-lethal effects in plants, invertebrates, and vertebrates, including humans. Herein, the bioactivity, chemistry, origin, and biosynthesis of these cyanobacterial secondary metabolites were reviewed. With recent revision of cyanobacterial taxonomy by Anagnostidis and Komárek as part of the Süβwasserflora von Mitteleuropa volumes 19(1-3), names of many cyanobacteria that produce bioactive compounds have changed, thereby confusing readers. The original and new nomenclature are included in this review to clarify the origins of cyanobacterial bioactive compounds. Due to structural similarity, the 157 known bioactive classes produced by cyanobacteria have been condensed to 55 classes. This review will provide a basis for more formal procedures to adopt a logical naming system. This review is needed for efficient management of water resources to understand, identify, and manage cyanobacterial harmful algal bloom impacts.

Immunomodulatory effects of selected cyanobacterial peptides in vitro

Cyanobacteria produce many biologically active metabolites synthesized via nonribosomal synthetic pathways such as cyclic microcystins (MCs) and linear aeruginosins (Aers). The present study aimed to investigate the effects of different MC variants and the newly isolated aerugenosin Aer-865 on macrophages, which represent one of the key effector cells within the innate immune responses. Specifically, our study included RAW 264.7 macrophage activation associated with production of cytotoxic and cytostatic nitric oxide (NO) as well as pro-inflammatory mediators like tumor necrosis factor α (TNFα) and interleukin 6 (IL-6). From the compounds investigated, commonly occurring MC variants (-RR, -YR) and Aer-865 had no significant effects within the non-cytotoxic concentrations tested, i.e. 0.001-1 μM for MCs and 0.1-50 μM for Aer-865. In contrast to known immunoactive MC-LR, the negligible immunomodulatory potential of tested MC congeners could be related to their differences in structure. The knowledge of MC structure-specific activities contributes to the understanding of complex toxicity of different MC variants and most importantly their mixtures. This study is one of the first study that evaluate the effect of larger set of cyanobacterial peptides on macrophages and compare their immunomodulatory potential.

Cytotoxic Effect of Aeruginosin-865, Resveratrol and Capsaicin on Mouse Fibroblasts and Cells Derived from Fallow Deer

Natural substances offer interesting bioactivity patterns including antiproliferative, antioxidant or cytotoxic effects. However, the safety profile of many of them has not been extensively determined. In this study, the cytotoxic effect of Aeruginosin-865, resveratrol and capsaicin at different concentrations was tested on normal mouse cells (NIH/3T3) and tumour fibroblasts (WEHI-13VAR) as well as on liver- and kidney-derived cells from fallow deer. A lactate dehydrogenase cytotoxicity assay kit was used to measure cell death in response to treatment with the test substances. It was found that NIH/3T3 cells tolerated Aeruginosin-865 (10-200 μM) and resveratrol (5-100 μM) treatment without any cytotoxic effect, while capsaicin exerted a cytotoxic effect only at the highest tested concentration (200 μ M). Mouse fibrosarcoma cells were more sensitive to the cytotoxic effect of all three compounds where Aeruginosin-865 (100-200 μM) and resveratrol (50–100 μM) showed high-dose cytotoxicity and capsaicin showed low- and high-dose cytotoxicity (25 μM and 200 μ M). The three tested compounds at the highest concentrations were found to be cytotoxic to both liver- and kidney-derived cells from fallow deer. Overall, the results indicate that the cytotoxic effects of the three tested natural substances on cells derived from fallow deer and mouse tumour fibroblasts differ significantly from those exerted on normal fibroblasts. The results demonstrate the potential of these natural compounds as therapeutic agents and pave the way for future in vivo toxicological investigations.

Production of High Amounts of Hepatotoxin Nodularin and New Protease Inhibitors Pseudospumigins by the Brazilian Benthic Nostoc sp. CENA543

Nostoc is a cyanobacterial genus, common in soils and a prolific producer of natural products. This research project aimed to explore and characterize Brazilian cyanobacteria for new bioactive compounds. Here we report the production of hepatotoxins and new protease inhibitors from benthic Nostoc sp. CENA543 isolated from a small, shallow, saline-alkaline lake in the Nhecolândia, Pantanal wetland area in Brazil. Nostoc sp. CENA543 produces exceptionally high amounts of nodularin-R. This is the first free-living Nostoc that produces nodularin at comparable levels as the toxic, bloom-forming, Nodularia spumigena. We also characterized pseudospumigins A-F, which are a novel family of linear tetrapeptides. Pseudospumigins are structurally related to linear tetrapeptide spumigins and aeruginosins both present in N. spumigena but differ in respect to their diagnostic amino acid, which is Ile/Leu/Val in pseudospumigins, Pro/mPro in spumigins, and Choi in aeruginosins. The pseudospumigin gene cluster is more similar to the spumigin biosynthetic gene cluster than the aeruginosin gene cluster. Pseudospumigin A inhibited trypsin (IC₅₀ 4.5 μM after 1 h) in a similar manner as spumigin E from N. spumigena but was almost two orders of magnitude less potent. This study identifies another location and environment where the hepatotoxic nodularin has the potential to cause the death of eukaryotic organisms.

A Genetic and Chemical Perspective on Symbiotic Recruitment of Cyanobacteria of the Genus Nostoc into the Host Plant Blasia pusilla L

Liverwort Blasia pusilla L. recruits soil nitrogen-fixing cyanobacteria of genus Nostoc as symbiotic partners. In this work we compared Nostoc community composition inside the plants and in the soil around them from two distant locations in Northern Norway. STRR fingerprinting and 16S rDNA phylogeny reconstruction showed a remarkable local diversity among isolates assigned to several Nostoc clades. An extensive web of negative allelopathic interactions was recorded at an agricultural site, but not at the undisturbed natural site. The cell extracts of the cyanobacteria did not show antimicrobial activities, but four isolates were shown to be cytotoxic to human cells. The secondary metabolite profiles of the isolates were mapped by MALDI-TOF MS, and the most prominent ions were further analyzed by Q-TOF for MS/MS aided identification. Symbiotic isolates produced a great variety of small peptide-like substances, most of which lack any record in the databases. Among identified compounds we found microcystin and nodularin variants toxic to eukaryotic cells. Microcystin producing chemotypes were dominating as symbiotic recruits but not in the free-living community. In addition, we were able to identify several novel aeruginosins and banyaside-like compounds, as well as nostocyclopeptides and nosperin.

Anti-Inflammatory Activity of Cyanobacterial Serine Protease Inhibitors Aeruginosin 828A and Cyanopeptolin 1020 in Human Hepatoma Cell Line Huh7 and Effects in Zebrafish (Danio rerio)

Intensive growth of cyanobacteria in freshwater promoted by eutrophication can lead to release of toxic secondary metabolites that may harm aquatic organisms and humans. The serine protease inhibitor aeruginosin 828A was isolated from a microcystin-deficient Planktothrix strain. We assessed potential molecular effects of aeruginosin 828A in comparison to another cyanobacterial serine protease inhibitor, cyanopeptolin 1020, in human hepatoma cell line Huh7, in zebrafish embryos and liver organ cultures. Aeruginosin 828A and cyanopeptolin 1020 promoted anti-inflammatory activity, as indicated by transcriptional down-regulation of interleukin 8 and tumor necrosis factor α in stimulated cells at concentrations of 50 and 100 µmol·L⁻¹ aeruginosin 828A, and 100 µmol·L⁻¹ cyanopeptolin 1020. Aeruginosin 828A induced the expression of CYP1A in Huh7 cells but did not affect enzyme activity. Furthermore, hatched zebrafish embryos and zebrafish liver organ cultures were exposed to aeruginosin 828A. The transcriptional responses were compared to those of cyanopeptolin 1020 and microcystin-LR. Aeruginosin 828A had only minimal effects on endoplasmic reticulum stress. In comparison to cyanopeptolin 1020 our data indicate that transcriptional effects of aeruginosin 828A in zebrafish are very minor. The data further demonstrate that pathways that are influenced by microcystin-LR are not affected by aeruginosin 828A.

Separation of Aeruginosin-865 from Cultivated Soil Cyanobacterium (Nostoc sp.) by Centrifugal Partition Chromatography combined with Gel Permeation Chromatography

Aeruginosin-865 was isolated from cultivated soil cyanobacteria using a combination of centrifugal partition chromatography (CPC) and gel permeation chromatography. The solubility of Aer-865 in different solvents was evaluated using the conductor-like screening model for real solvents (COSMO-RS). The CPC separation was performed in descending mode with a biphasic solvent system composed of water-n-BuOH-acetic acid (5:4:1, v/v/v). The upper phase was used as a stationary phase, whereas the lower phase was employed as a mobile phase at a flow rate of 10 mL/min. The revolution speed and temperature of the separation column were 1700 rpm and 25°C, respectively. Preparative CPC separation followed by gel permeation chromatography was performed on 50 mg of crude extract yielding Aer-865 (3.5 mg), with a purity over 95% as determined by HPLC. The chemical identity of the isolated compound was confirmed by comparing its spectroscopic data (UV, HRESI-MS, HRESI-MS/MS) with those of an authentic standard and data available in the literature.

Structural Characterization of New Peptide Variants Produced by Cyanobacteria from the Brazilian Atlantic Coastal Forest Using Liquid Chromatography Coupled to Quadrupole Time-of-Flight Tandem Mass Spectrometry

Cyanobacteria from underexplored and extreme habitats are attracting increasing attention in the search for new bioactive substances. However, cyanobacterial communities from tropical and subtropical regions are still largely unknown, especially with respect to metabolite production. Among the structurally diverse secondary metabolites produced by these organisms, peptides are by far the most frequently described structures. In this work, liquid chromatography/electrospray ionization coupled to high resolution quadrupole time-of-flight tandem mass spectrometry with positive ion detection was applied to study the peptide profile of a group of cyanobacteria isolated from the Southeastern Brazilian coastal forest. A total of 38 peptides belonging to three different families (anabaenopeptins, aeruginosins, and cyanopeptolins) were detected in the extracts. Of the 38 peptides, 37 were detected here for the first time. New structural features were proposed based on mass accuracy data and isotopic patterns derived from full scan and MS/MS spectra. Interestingly, of the 40 surveyed strains only nine were confirmed to be peptide producers; all of these strains belonged to the order Nostocales (three Nostoc sp., two Desmonostoc sp. and four Brasilonema sp.).