Studies on terrein as a new class of proteasome inhibitors

Unearthing the fungal endophyte Aspergillus terreus for chemodiversity and medicinal prospects: a comprehensive review

Aspergillus terreus microorganism represents a promising prospective source for drug discovery since it is rich in diverse kinds of bioactive secondary metabolites. It contributed to many biotechnological applications and its metabolites are used in the synthesis of certain pharmaceuticals and food products, in addition to its useful uses in fermentation processes. There are about 346 compounds identified from marine and terrestrial-derived A. terreus from 1987 until 2022, 172 compounds of them proved a vast array of bioactivity. This review aimed to create an up-to-date comprehensive literature data of A. terreus's secondary metabolites classes supported by its different bioactivity data to be a scientific record for the next work in drug discovery.

Fungal Secondary Metabolites as Inhibitors of the Ubiquitin-Proteasome System

The ubiquitin–proteasome system (UPS) is the major non-lysosomal pathway responsible for regulated degradation of intracellular proteins in eukaryotes. As the principal proteolytic pathway in the cytosol and the nucleus, the UPS serves two main functions: the quality control function (i.e., removal of damaged, misfolded, and functionally incompetent proteins) and a major regulatory function (i.e., targeted degradation of a variety of short-lived regulatory proteins involved in cell cycle control, signal transduction cascades, and regulation of gene expression and metabolic pathways). Aberrations in the UPS are implicated in numerous human pathologies such as cancer, neurodegenerative disorders, autoimmunity, inflammation, or infectious diseases. Therefore, the UPS has become an attractive target for drug discovery and development. For the past two decades, much research has been focused on identifying and developing compounds that target specific components of the UPS. Considerable effort has been devoted to the development of both second-generation proteasome inhibitors and inhibitors of ubiquitinating/deubiquitinating enzymes. With the feature of unique structure and bioactivity, secondary metabolites (natural products) serve as the lead compounds in the development of new therapeutic drugs. This review, for the first time, summarizes fungal secondary metabolites found to act as inhibitors of the UPS components.

Recent Advances in Isolation, Synthesis and Biological Evaluation of Terrein

Terrein is a small-molecule polyketide compound with a simple structure mainly isolated from fungi. Since its discovery in 1935, many scholars have conducted a series of research on its structure identification, isolation source, production increase, synthesis and biological activity. Studies have shown that terrein has a variety of biological activities, not only can inhibit melanin production and epidermal hyperplasia, but also has anti-cancer, anti-inflammatory, anti-angiopoietic secretion, antibacterial, insecticidal activities, and so on. It has potential application prospects in beauty, medicine, agriculture and other fields. This article reviews the process of structural identification of terrein since 1935, and summarizes the latest advances in its isolation, source, production increase, synthesis, and biological activity evaluation, with a view to providing a reference and helping for the in-depth research of terrein.

Aspergillus terreus Species Complex

Infections due to Aspergillus species are an acute threat to human health; members of the Aspergillus section Fumigati are the most frequently occurring agents, but depending on the local epidemiology, representatives of section Terrei or section Flavi are the second or third most important. Aspergillus terreus species complex is of great interest, as it is usually amphotericin B resistant and displays notable differences in immune interactions in comparison to Aspergillus fumigatus. The latest epidemiological surveys show an increased incidence of A. terreus as well as an expanding clinical spectrum (chronic infections) and new groups of at-risk patients being affected. Hallmarks of these non-Aspergillus fumigatus invasive mold infections are high potential for tissue invasion, dissemination, and possible morbidity due to mycotoxin production. We seek to review the microbiology, epidemiology, and pathogenesis of A. terreus species complex, address clinical characteristics, and highlight the underlying mechanisms of amphotericin B resistance. Selected topics will contrast key elements of A. terreus with A. fumigatus. We provide a comprehensive resource for clinicians dealing with fungal infections and researchers working on A. terreus pathogenesis, aiming to bridge the emerging translational knowledge and future therapeutic challenges on this opportunistic pathogen.

Aspergillus derived mycotoxins in food and the environment: Prevalence, detection, and toxicity

Aspergillus species are the paramount ubiquitous fungi that contaminate various food substrates and produce biochemicals known as mycotoxins. Aflatoxins (AFTs), ochratoxin A (OTA), patulin (PAT), citrinin (CIT), aflatrem (AT), secalonic acids (SA), cyclopiazonic acid (CPA), terrein (TR), sterigmatocystin (ST) and gliotoxin (GT), and other toxins produced by species of Aspergillus plays a major role in food and human health. Mycotoxins exhibited wide range of toxicity to the humans and animal models even at nanomolar (nM) concentration. Consumption of detrimental mycotoxins adulterated foodstuffs affects human and animal health even trace amounts. Bioaerosols consisting of spores and hyphal fragments are active elicitors of bronchial irritation and allergy, and challenging to the public health. Aspergillus is the furthermost predominant environmental contaminant unswervingly defile lives with a 40-90 % mortality risk in patients with conceded immunity. Genomics, proteomics, transcriptomics, and metabolomics approaches useful for mycotoxins' detection which are expensive. Antibody based detection of toxins chemotypes may result in cross-reactivity and uncertainty. Aptamers (APT) are single stranded DNA (ssDNA/RNA), are specifically binds to the target molecules can be generated by systematic evolution of ligands through exponential enrichment (SELEX). APT are fast, sensitive, simple, in-expensive, and field-deployable rapid point of care (POC) detection of toxins, and a better alternative to antibodies.

Large-Scale Production of Bioactive Terrein by Aspergillus terreus Strain S020 Isolated from the Saudi Coast of the Red Sea

The diversity of symbiotic fungi derived from two marine sponges and sediment collected off Obhur, Jeddah (Saudi Arabia), was investigated in the current study. A total of 23 isolates were purified using a culture-dependent approach. Using the morphological properties combined with internal transcribed spacer-rDNA (ITS-rDNA) sequences, 23 fungal strains (in the majority Penicillium and Aspergillus) were identified from these samples. The biological screening (cytotoxic and antimicrobial activities) of small-scale cultures of these fungi yielded several target fungal strains which produced bioactive secondary metabolites. Amongst these isolates, the crude extract of Aspergillus terreus strain S020, which was cultured in fermentation static broth, 21 L, for 40 days at room temperature on potato dextrose broth, displayed strong antimicrobial activities against Pseudomonas aeruginosa and Staphylococcus aureus and significant antiproliferative effects on human carcinoma cells. Chromatographic separation of the crude extract by silica gel column chromatography indicated that the S020 isolate could produce a series of chemical compounds. Among these, pure crystalline terrein was separated with a high yield of 537.26 ± 23.42 g/kg extract, which represents the highest fermentation production of terrein to date. Its chemical structure was elucidated on the basis of high-resolution electrospray ionization mass spectrometry (HRESIMS) or high-resolution mass spectrometry (HRMS), 1D, and 2D NMR spectroscopic analyses and by comparison with reported data. The compound showed strong cytotoxic activity against colorectal carcinoma cells (HCT-116) and hepatocellular carcinoma cells (HepG2), with IC₅₀ values of 12.13 and 22.53 µM, respectively. Our study highlights the potential of A. terreus strain S020 for the industrial production of bioactive terrein on a large scale and the importance of future investigations of these strains to identify the bioactive leads in these fungal extracts.

Modification of artificial sea water for the mass production of (+)-terrein by Aspergillus terreus strain PF26 derived from marine sponge Phakellia fusca

(+)-Terrein shows multiple bioactivities, however, its mass production is a big challenge. Aspergillus terreus strain PF26 derived from South China Sea sponge Phakellia fusca has been cultured to produce (+)-terrein successfully, but artificial sea water (ASW) of high salinity used in the fermentation medium may cause the corrosion risk of metal bioreactor, which limits the fermentation on a large scale. In this study, we modified the components of ASW by removing NaCl and CaCl2 from the original formula, which reduced about 80% salinity of ASW. As a result, 7·56 g l(-1) (+)-terrein production was achieved in shake flask, which was 78·72% higher than using the original ASW, and the cultivation time was decreased from 24 to 15 days. Then, the modified ASW was used for the fermentation of A. terreus strain PF26 in a 500 l stirred bioreactor, consequently 2·5 g l(-1) of (+)-terrein production was achieved.

SIGNIFICANCE AND IMPACT OF THE STUDY

The fermentation of marine micro-organisms always needs to use sea water or artificial sea water (ASW), which limits the fermentation on a large scale, as the high-salinity medium may cause the corrosion risk of bioreactor. In this study, the ASW formula is simplified to reduce the sea water salinity and improve the yield of (+)-terrein, finally, the modified ASW was successfully used for the mass production of (+)-terrein by A. terreus strain PF26 in a 500 l bioreactor.

(+)‑Terrein inhibits human hepatoma Bel‑7402 proliferation through cell cycle arrest

Hepatoma is a common malignant tumor. Thus, the development of a high‑efficacy therapeutic drug for hepatoma is required. In this study, (+)‑terrein isolated from the marine sponge‑derived Aspergillus terreus PF‑26 against cell growth, apoptosis and cell cycle were assessed by MTT and flow cytometry. mRNA array containing 73 cell cycle‑related genes and three cell morphology‑related genes was generated and its performance evaluated. The cell cycle pathway map was created using the pathview package. The results showed that (+)‑terrein inhibited the growth of Bel‑7402 cells with alterations in cell morphology and a reduced transcript expression of cell morphology genes (fibronectin, N‑cadherin, and vimentin). In addition, flow cytometric analysis revealed that (+)‑terrein arrested the Bel‑7402 cell cycle without inducing apoptosis. Based on multiple mRNA analysis, the downregulated expression of the CCND2, CCNE2, CDKN1C, CDKN2B, ANAPC, PKMYT1, CHEK2 and PCNA genes was observed in 10 µM (+)‑terrein‑treated Bel‑7402 cells (>2‑fold and P≤0.05), compared with the controls. Thus, the antiprolife-rative mechanism of (+)‑terrein against Bel‑7402 cells may be due to the cell cycle arrest by blocking cell cycle gene expression and changing cell morphology.

Synthetic (+)-terrein suppresses interleukin-6/soluble interleukin-6 receptor induced-secretion of vascular endothelial growth factor in human gingival fibroblasts

Interleukin (IL)-6 is a proinflammatory cytokine that performs a wide variety of biological functions, including important roles in the progression of chronic inflammatory diseases such as periodontal disease. (+)-Terrein, a secondary bioactive fungal metabolite isolated from Aspergillus terreus, has various biological activities; however, its anti-inflammatory effects are still unknown. The purpose of this study was to examine the effect of synthetic (+)-terrein on IL-6 signaling and related protein production in human gingival fibroblasts. To our knowledge, this study is the first to report that synthetic (+)-terrein is not cytotoxic at concentrations less than 20 μM and suppresses IL-6/soluble IL-6 receptor (sIL-6R)-induced phosphorylation of signal transducer and activator of transcription-3, extracellular signal-regulated kinase 1/2, and c-jun N-terminal kinase 1/2-signaling proteins that are downstream of IL-6 signaling. In addition, synthetic (+)-terrein suppresses IL-6/sIL-6R-induced vascular endothelial growth factor (VEGF) secretion in a concentration-dependent manner (p<0.01). These data suggest that synthetic (+)-terrein has potential anti-IL-6 signaling activity and suppresses VEGF-associated inflammatory disease progression.

Terrein biosynthesis in Aspergillus terreus and its impact on phytotoxicity

Terrein is a fungal metabolite with ecological, antimicrobial, antiproliferative, and antioxidative activities. Although it is produced by Aspergillus terreus as one of its major secondary metabolites, not much is known about its biosynthetic pathway. Here, we describe an unexpected discovery of the terrein biosynthesis gene locus made while we were looking for a PKS gene involved in production of conidia coloration pigments common for Aspergilli. The gene, ATEG_00145, here named terA, is essential for terrein biosynthesis and heterologous production of TerA in Aspergillus niger revealed an unusual plasticity in the products formed, yielding a mixture of 4-hydroxy-6-methylpyranone, orsellinic acid, and 6,7-dihydroxymellein. Biochemical and molecular genetic analyses indicate a low extension cycle specificity of TerA. Furthermore, 6-hydroxymellein was identified as a key intermediate in terrein biosynthesis. We find that terrein production is highly induced on plant-derived media, that terrein has phytotoxic activity on plant growth, and induces lesions on fruit surfaces.

Terrein induces apoptosis in HeLa human cervical carcinoma cells through p53 and ERK regulation

Terrein, a fungal metabolite derived from Aspergillus terreus, has been shown to have a variety of biological activities in human cells including inhibition of melanogenesis, as well as anti-inflammatory, antioxidant and anticancer properties. In the present study, terrein was shown to have marked anticancer activity on HeLa human cervical carcinoma cells. Terrein exhibited inhibition of proliferation within the same ranges for other cancer cell types with an IC50 at 0.29 mM. The growth inhibition that induced cell death was via apoptosis mechanisms. Chromatin condensation was observed using the Hoechst 33342 stain, a DNA-specific dye. The increase of DNA fragmentation or the sub-G0 peak was also detected by flow cytometry. The signaling used by terrein to induce apoptosis was via the death-receptor and mitochondrial pathways; the cleavage of specific fluorogenic substrates by caspase-3, -8 and -9 activities are clearly demonstrated. The mitochondria were damaged as demonstrated by the decrease of the red/green ratio of the JC-1 staining and the increase of the Bax/Bcl-2 expression ratio. Further analysis of the upstream signaling by the quantitative real-time polymerase chain reaction showed that p53, p21 and ERK were upregulated which indicates the importance of their roles on terrein signaling. This study is the first to show that terrein has an effect on the anticancer properties in cervical cancer cells by inducing apoptosis through p53 and ERK regulation. Our data may help expand the function of the terrein compound and may also aid in the discovery of new anticancer agents.

Asperjinone, a nor-neolignan, and terrein, a suppressor of ABCG2-expressing breast cancer cells, from thermophilic Aspergillus terreus

Breast cancer cells express ABCG2 transporters, which mediate multidrug resistance. Discovering a novel compound that can suppress ABCG2 expression and restore drug sensitivity could be the key to improving breast cancer therapeutics. In the current work, one new nor-neolignan, asperjinone (1), as well as 12 other known compounds, was isolated from Aspergillus terreus. The structure of the new isolate was determined by spectroscopic methods. Among these isolates, terrein (2) displayed strong cytotoxicity against breast cancer MCF-7 cells. Treatment with terrein (2) significantly suppressed growth of ABCG2-expressing breast cancer cells. This suppressive effect was achieved by inducing apoptosis via activating the caspase-7 pathway and inhibiting the Akt signaling pathway, which led to a decrease in ABCG2-expressing cells and a reduction in the side-population phenotype.

New species in Aspergillus section Terrei

Section Terrei of Aspergillus was studied using a polyphasic approach including sequence analysis of parts of the β-tubulin and calmodulin genes and the ITS region, macro- and micromorphological analyses and examination of extrolite profiles to describe three new species in this section. Based on phylogenetic analysis of calmodulin and β-tubulin sequences seven lineages were observed among isolates that have previously been treated as A. terreus and its subspecies by Raper & Fennell (1965) and others. Aspergillus alabamensis, A. terreus var. floccosus, A. terreus var. africanus, A. terreus var. aureus, A. hortai and A. terreus NRRL 4017 all represent distinct lineages from the A. terreus clade. Among them, A. terreus var. floccosus, A. terreus NRRL 4017 and A. terreus var. aureus could also be distinguished from A. terreus by using ITS sequence data. New names are proposed for A. terreus var. floccosus, A. terreus var. africanus, A. terreus var. aureus, while Aspergillus hortai is recognised at species level. Aspergillus terreus NRRL 4017 is described as the new species A. pseudoterreus. Also included in section Terrei are some species formerly placed in sections Flavipedes and Versicolores. A. clade including the type isolate of A. niveus (CBS 115.27) constitutes a lineage closely related to A. carneus. Fennellia nivea, the hypothesized teleomorph is not related to this clade. Aspergillus allahabadii, A. niveus var. indicus, and two species originally placed in section Versicolores, A. ambiguus and A. microcysticus, also form well-defined lineages on all trees. Species in Aspergillus section Terrei are producers of a diverse array of secondary metabolites. However, many of the species in the section produce different combinations of the following metabolites: acetylaranotin, asperphenamate, aspochalamins, aspulvinones, asteltoxin, asterric acid, asterriquinones, aszonalenins, atrovenetins, butyrolactones, citreoisocoumarins, citreoviridins, citrinins, decaturins, fulvic acid, geodins, gregatins, mevinolins, serantrypinone, terreic acid (only the precursor 3,6-dihydroxytoluquinone found), terreins, terrequinones, terretonins and territrems. The cholesterol-lowering agent mevinolin was found in A. terreus and A. neoafricanus only. The hepatotoxic extrolite citrinin was found in eight species: A. alabamensis, A. allahabadii, A. carneus, A. floccosus, A. hortai, A. neoindicus, A. niveus and A. pseudoterreus. The neurotoxic extrolite citreoviridin was found in five species: A. neoafricanus, A. aureoterreus, A. pseudoterreus, A. terreus and A. neoniveus. Territrems, tremorgenic extrolites, were found in some strains of A. alabamensis and A. terreus.