Cytotoxic Naphtho-γ-pyrones from the Mangrove Endophytic Fungus Aspergillus tubingensis (GX1-5E)

Mangrove-associated endomycota: diversity and functional significance as a source of novel drug leads

Endophytic fungi are known for their unprecedented ability to produce novel lead compounds of clinical and pharmaceutical importance. This review focuses on the unexplored fungal diversity associated with mangroves, emphasizing their biodiversity, distribution, and methodological approaches targeting isolation, and identification. Also highlights the bioactive compounds reported from the mangrove fungal endophytes. The compounds are categorized according to their reported biological activities including antimicrobial, antioxidant and cytotoxic property. In addition, protein kinase, α-glucosidase, acetylcholinesterase, tyrosinase inhibition, antiangiogenic, DNA-binding affinity, and calcium/potassium channel blocking activity are also reported. Exploration of these endophytes as a source of pharmacologically important compounds will be highly promising in the wake of emerging antibiotic resistance among pathogens. Thus, the aim of this review is to present a detailed report of mangrove derived endophytic fungi and to open an avenue for researchers to discover the possibilities of exploring these hidden mycota in developing novel drug leads.

A Review of the Chemistry and Biological Activities of Natural Colorants, Dyes, and Pigments: Challenges, and Opportunities for Food, Cosmetics, and Pharmaceutical Application

Natural pigments are important sources for the screening of bioactive lead compounds. This article reviewed the chemistry and therapeutic potentials of over 570 colored molecules from plants, fungi, bacteria, insects, algae, and marine sources. Moreover, related biological activities, advanced extraction, and identification approaches were reviewed. A variety of biological activities, including cytotoxicity against cancer cells, antioxidant, anti-inflammatory, wound healing, anti-microbial, antiviral, and anti-protozoal activities, have been reported for different pigments. Considering their structural backbone, they were classified as naphthoquinones, carotenoids, flavonoids, xanthones, anthocyanins, benzotropolones, alkaloids, terpenoids, isoprenoids, and non-isoprenoids. Alkaloid pigments were mostly isolated from bacteria and marine sources, while flavonoids were mostly found in plants and mushrooms. Colored quinones and xanthones were mostly extracted from plants and fungi, while colored polyketides and terpenoids are often found in marine sources and fungi. Carotenoids are mostly distributed among bacteria, followed by fungi and plants. The pigments isolated from insects have different structures, but among them, carotenoids and quinone/xanthone are the most important. Considering good manufacturing practices, the current permitted natural colorants are: Carotenoids (canthaxanthin, β-carotene, β-apo-8'-carotenal, annatto, astaxanthin) and their sources, lycopene, anthocyanins, betanin, chlorophyllins, spirulina extract, carmine and cochineal extract, henna, riboflavin, pyrogallol, logwood extract, guaiazulene, turmeric, and soy leghemoglobin.

Production of Fungal Pigments: Molecular Processes and Their Applications

Due to the negative environmental and health effects of synthetic colorants, pigments of natural origins of plants and microbes constitute an abundant source for the food, cosmetic, textile, and pharmaceutical industries. The demands for natural alternatives, which involve natural colorants and natural biological processes for their production, have been growing rapidly in recent decades. Fungi contain some of the most prolific pigment producers, and they excel in bioavailability, yield, cost-effectiveness, and ease of large-scale cell culture as well as downstream processing. In contrast, pigments from plants are often limited by seasonal and geographic factors. Here, we delineate the taxonomy of pigmented fungi and fungal pigments, with a focus on the biosynthesis of four major categories of pigments: carotenoids, melanins, polyketides, and azaphilones. The molecular mechanisms and metabolic bases governing fungal pigment biosynthesis are discussed. Furthermore, we summarize the environmental factors that are known to impact the synthesis of different fungal pigments. Most of the environmental factors that enhance fungal pigment production are related to stresses. Finally, we highlight the challenges facing fungal pigment utilization and future trends of fungal pigment development. This integrated review will facilitate further exploitations of pigmented fungi and fungal pigments for broad applications.

Antimicrobial secondary metabolites from an endophytic fungus Aspergillus polyporicola

Two new nucleoside derivatives, kipukasins O (1) and P (2), one new cyclohexenone derivative, arthropsadiol D (5), and one new natural product, (+)-2,5-dimethyl-3(2H)-benzofuranone (6), together with eleven known compounds (3, 4, 7-15), were obtained from the culture broth of the endophytic fungus Aspergillus polyporicola R2 isolated from the roots of Synsepalum dulcificum. Among them, the absolute configuration of compound 5 was determined by quantum chemical calculations of NMR chemical shifts and ECD spectrum. The antimicrobial activities of these compounds were evaluated. Compound 11 exhibited obvious inhibitory activity against MRSA, Staphylococcus aureus, Salmonella typhimurium, Botrytis cinerea, and Fusarium graminearum with MIC values of 4, 4, 4, 32, and 16 μg/mL, respectively. Compound 12 exhibited antibacterial activity against S. typhimurium and MRSA with MIC values of 4 and 16 μg/mL. Compound 6 exhibited antifungal activity against F. graminearum with MIC value of 32 μg/mL.

Secondary metabolites from mangrove-associated fungi: source, chemistry and bioactivities

Covering 1989 to 2020The mangrove forests are a complex ecosystem occurring at tropical and subtropical intertidal estuarine zones and nourish a diverse group of microorganisms including fungi, actinomycetes, bacteria, cyanobacteria, algae, and protozoa. Among the mangrove microbial community, mangrove associated fungi, as the second-largest ecological group of the marine fungi, not only play an essential role in creating and maintaining this biosphere but also represent a rich source of structurally unique and diverse bioactive secondary metabolites, attracting significant attention of organic chemists and pharmacologists. This review summarizes the discovery relating to the source and characteristics of metabolic products isolated from mangrove-associated fungi over the past thirty years (1989-2020). Its emphasis included 1387 new metabolites from 451 papers, focusing on bioactivity and the unique chemical diversity of these natural products.

Evaluation of Dimer of Epicatechin from an Endophytic Fungus Curvularia australiensis FC2AP on Acute Toxicity Levels, Anti-Inflammatory and Anti-Cervical Cancer Activity in Animal Models

Cervical cancer, as the most frequent cancer in women globally and accounts almost 14% in India. It can be prevented or treated with vaccines, radiation, chemotherapy, and brachytherapy. The chemotherapeutic agents cause adverse post effects by the destruction of the neighboring normal cells or altering the properties of the cells. In order to reduce the severity of the side effects caused by the chemically synthesized therapeutic agents, the current research developed an anti-cancer agent dimer of epicatechin (DoE), a natural bioactive secondary metabolite (BSM) mediated from an endophytic fungus Curvularia australiensis FC2AP. The investigation has initiated with the evaluation of inhibiting the angiogenesis which is a main activity in metastasis, and it was assessed through Hen’s Egg Test on Chorio Allantoic Membrane (HET-CAM) test; the BSM inhibited the growth of blood vessels in the developing chick embryo. Further the DoE was evaluated for its acute toxicity levels in albino mice, whereas the survival dose was found to be 1250 mg/kg and the lethal dose was 1500 mg/kg body weight of albino mice; hematological, biochemical, and histopathological analyses were assessed. The anti-inflammatory responses of the DoE were evaluated in carrageenan induced Wistar rats and the reduction of inflammation occurred in a dose-dependent manner. By fixing the effective dose for anti-inflammation analysis, the DoE was taken for the anti-cervical cancer analysis in benzo (a) pyrene induced female Sprague-Dawley rats for 60 days trial. After the stipulated days, the rats were taken for hematological antioxidants, lipid peroxidation (LPO), member bound enzymes, cervical histopathological and carcinogenic markers analyses. The results specified that the DoE has the capability of reducing the tumor in an efficient way. This is the first report of flavonoid-DoE production from an endophytic fungus C. australiensis has the anticancer potentiality and it can be stated as anti-cancer drug.

Fungal Pigments and Their Roles Associated with Human Health

Fungi can produce myriad secondary metabolites, including pigments. Some of these pigments play a positive role in human welfare while others are detrimental. This paper reviews the types and biosynthesis of fungal pigments, their relevance to human health, including their interactions with host immunity, and recent progresses in their structure-activity relationships. Fungal pigments are grouped into carotenoids, melanin, polyketides, and azaphilones, etc. These pigments are phylogenetically broadly distributed. While the biosynthetic pathways for some fungal pigments are known, the majority remain to be elucidated. Understanding the genes and metabolic pathways involved in fungal pigment synthesis is essential to genetically manipulate the production of both the types and quantities of specific pigments. A variety of fungal pigments have shown wide-spectrum biological activities, including promising pharmacophores/lead molecules to be developed into health-promoting drugs to treat cancers, cardiovascular disorders, infectious diseases, Alzheimer's diseases, and so on. In addition, the mechanistic elucidation of the interaction of fungal pigments with the host immune system provides valuable clues for fighting fungal infections. The great potential of fungal pigments have opened the avenues for academia and industries ranging from fundamental biology to pharmaceutical development, shedding light on our endeavors for disease prevention and treatment.

Naphtho-Gamma-Pyrones Produced by Aspergillus tubingensis G131: New Source of Natural Nontoxic Antioxidants

Seven naphtho-gamma-pyrones (NγPs), including asperpyrone E, aurasperone A, dianhydroaurasperone C, fonsecin, fonsecinone A, fonsecin B, and ustilaginoidin A, were isolated from Aspergillus tubingensis G131, a non-toxigenic strain. The radical scavenging activity of these NγPs was evaluated using ABTS assay. The Trolox equivalent antioxidant capacity on the seven isolated NγPs ranged from 2.4 to 14.6 μmol L^-1. The toxicity and ability of the NγPs to prevent H₂O₂-mediated cell death were evaluated using normal/not cancerous cells (CHO cells). This cell-based assay showed that NγPs: (1) Are not toxic or weakly toxic towards cells and (2) are able to protect cells from oxidant injuries with an IC₅₀ on H₂O₂-mediated cell death ranging from 2.25 to 1800 μmol mL^-1. Our data show that A. tubingensis G131 strain is able to produce various NγPs possessing strong antioxidant activities and low toxicities, making this strain a good candidate for antioxidant applications in food and cosmetic industries.

Discovery of Natural Dimeric Naphthopyrones as Potential Cytotoxic Agents Through ROS-Mediated Apoptotic Pathway

A study on the secondary metabolites of Aspergillus sp. XNM-4, which was derived from marine algae Leathesia nana (Chordariaceae), led to the identification of one previously undescribed (1) and seventeen known compounds (2-18). Their planar structures were established by extensive spectroscopic analyses, while the stereochemical assignments were defined by electronic circular dichroism (ECD) calculations. The biological activities of the compounds were assessed on five human cancer cell lines (PANC-1, A549, MDA-MB-231, Caco-2, and SK-OV-3), and one human normal cell line (HL-7702) using an MTT [3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl tetrazolium bromide] assay. Among them, the dimeric naphthopyrones 7, 10 and 12 exhibited potent cytotoxicity. Further mechanism studies showed that 12 induced apoptosis, arrested the cell cycle at the G0/G1 phase in the PANC-1 cells, caused morphological changes and generated ROS; and it induces PANC-1 cells apoptosis via ROS-mediated PI3K/Akt signaling pathway.

Induced production of 6,9-dibromoflavasperone, a new radical scavenging naphthopyranone in the marine-mudflat-derived fungus Aspergillus niger

The addition of metal bromides (NaBr and CaBr2) during fermentation of the marine-mudflat-derived fungus Aspergillus niger induced production of a new radical scavenging brominated naphthopyranone, 6,9-dibromoflavasperone (1); and three known naphtho-γ-pyranone monomers, flavasperone (2), TMC-256A1 (3), and fonsecin (4); and one naphtho-γ-pyranone dimer, aurasperone B (5). The structure of 6,9-dibromoflavasperone (1) was assigned through the combination of spectroscopic data analyses and comparison with the spectral data of flavasperone (2). Compounds 1-5 displayed potent radical scavenging activity against 2,2-diphenyl-1-picrylhydrazyl, with IC50 values of 21, 25, 0.3, 0.02, and 0.01 μM, respectively, and 3-5 were more potent than the positive control, ascorbic acid (IC50, 20.0 μM).

Bioactive natural products derived from mangrove-associated microbes

This review summarizes new findings concerning the sources and characteristics of various natural products that can be extracted from mangrove-associated microbes over the past three years (January 2011–December 2013).

Endophytic fungi with antitumor activities: Their occurrence and anticancer compounds

Plant endophytic fungi have been recognized as an important and novel resource of natural bioactive products, especially in anticancer application. This review mainly deals with the research progress on the production of anticancer compounds by endophytic fungi between 1990 and 2013. Anticancer activity is generally associated with the cytotoxicity of the compounds present in the endophytic fungi. All strains of endophytes producing antitumor chemicals were classified taxonomically and the genera of Pestalotiopsis and Aspergillus as well as the taxol producing endophytes were focused on. Classification of endophytic fungi producing antitumor compounds has received more attention from mycologists, and it can also lead to the discovery of novel compounds with antitumor activity due to phylogenetic relationships. In this review, the structures of the anticancer compounds isolated from the newly reported endophytes between 2010 and 2013 are discussed including strategies for the efficient production of the desired compounds. The purpose of this review is to provide new directions in endophytic fungi research including integrated information relating to its anticancer compounds.

Bis-naphtho-γ-pyrones from fungi and their bioactivities

Bis-naphtho-γ-pyrones are an important group of aromatic polyketides derived from fungi. They have a variety of biological activities including cytotoxic, antitumor, antimicrobial, tyrosine kinase and HIV-1 integrase inhibition properties, demonstrating their potential applications in medicine and agriculture. At least 59 bis-naphtho-γ-pyrones from fungi have been reported in the past few decades. This mini-review aims to briefly summarize their occurrence, biosynthesis, and structure, as well as their biological activities. Some considerations regarding to synthesis, production, and medicinal and agricultural applications of bis-naphtho-γ-pyrones are also discussed.

Marine natural products

This review covers the literature published in 2011 for marine natural products, with 870 citations (558 for the period January to December 2011) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1152 for 2011), together with the relevant biological activities, source organisms and country of origin. Biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.

A new sesquiterpene from the mangrove endophytic fungus Aspergillus terreus (No. GX7-3B)

A new compound 1 (named botryosphaerin F), along with other three known compounds 2 (13,14,15,16-tetranorlabd-7-ene-19,6b:12,17-diolide), 3 (botryosphaerin B) and 4 (LL-Z1271β), has been isolated from the mangrove fungus Aspergillus terreus (No. GX7-3B). The structure of the new compound was established by analysis of spectroscopic data. The hypothetical biogenic relationship of four sesquiterpene analogues was also described in this paper. Furthermore, in the cytotoxicity assays, compound 1 showed potent inhibiting activity towards MCF-7 and HL-60 cancer cell lines with 50% inhibition of cell growth (IC50) values of 4.49 and 3.43 μM, respectively, and compound 4 exhibited promising activity against HL-60 cell line with an IC50 value of 0.6 μM.

Aromatic polyketides from a sponge-derived fungus Metarhizium anisopliae mxh-99 and their antitubercular activities

In our screening for antitubercular agents, five naphtho-γ-pyrones including two new naphtho-γ-pyrones glycosides, indigotides G and H (1 and 2), and two diphenyl ethers were isolated from the extract of a sponge-derived fungus Metarhizium anisopliae mxh-99. Their structures were established on the basis of chemical and spectroscopic evidence. The antitubercular activities of all the compounds were evaluated against Mycobacterium phlei. The known isochaetochromin B2 (6) and ustilaginoidin D (7) exhibited the highest activity with MICs 50.0 μg/mL.