Structure-activity Relationships of Neoechinulin A Analogues with Cytoprotection against Peroxynitrite-induced PC12 Cell Death

Anti-cancer activity of secreted aspartyl proteinase protein from Candida tropicalis on human cervical cancer HeLa cells

Cervical cancer is the fourth leading cause of cancer-related death in women worldwide. Microbial products are valuable sources of anti-cancer drugs. The aim of this study was to isolate secreted aspartyl proteinase protein from Candida tropicalis, investigate its inhibitory effect on human cervical cancer HeLa cells, and analyze the expression profiling of selected nuclear stem cell-associated transcription factors. The presence of secreted aspartyl proteinase protein was confirmed by the expression of SAP2 and SAP4 genes in C. tropicalis during the yeast-hyphae transition phase. The enzyme was purified and characterized using the aqueous two-phase system purification method, as well as proteolytic activity and the Bradford and micro-Kjeldahl methods, respectively. The in vitro anti-cancer properties of secreted aspartyl proteinase protein were evaluated by MTT assay, microscopic image analysis, nitric oxide (NO) scavenging activity assay, intracellular reactive oxygen species (ROS) production assay, and RT-qPCR. The isolated C. tropicalis secreted aspartyl proteinase protein exhibited proteinase activity with values ranging from 93.72 to 130.70 μg/mL and 89.88-127.72 μg/mL according to the Bradford and micro-Kjeldahl methods, respectively. Secreted aspartyl proteinase showed effective cytotoxicity in HeLa cell line leading to significant morphological changes. Additionally, it exhibited increased free radical scavenging activity compared to the untreated control group, as evidenced by nitrite inhibition. ROS production increased in HeLa cells exposed to secreted aspartyl proteinase. The expression levels of the nuclear stem cell-associated transcription factors octamer-binding transcription factor 4 (OCT4), sex determining region Y-box 2 (SOX2), and Nanog homeobox (NANOG) were significantly downregulated in the HeLa cells treated with secreted aspartyl proteinase. Secreted aspartyl proteinase protein may be a promising anti-cancer agent, as it effectively affects gene expression and may ultimately reduce the development and progression of cervical cancer. Targeting the genes related to nuclear stem cell-associated transcription factors may provide a novel amenable to cancer treatment.

Isolation and Identification of Indole Alkaloids from Aspergillus amstelodami BSX001 and Optimization of Ultrasound-Assisted Extraction of Neoechinulin A

This study aimed to investigate the alkaloid secondary metabolites of Aspergillus amstelodami BSX001, a fungus isolated from Anhua dark tea, and to improve the extraction yield of the active ingredients by optimizing the extraction process. The structural characterization of the compounds was investigated using mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy. The antioxidant activity of echinulin-related alkaloids was evaluated by determining the total reducing power and DPPH radical scavenging capacity. The extraction process of the compound with optimum activity was optimized by a single-factor test and response surface methodology (RSM) combined with Box-Behnken design (BBD). The optimized result was validated. Finally, a new alkaloid 8-hydroxyechinulin (1), and four known alkaloids, variecolorin G (2), echinulin (3), neoechinulin A (4), and eurocristatine (5), were isolated. Echinulin-related compounds 1, 3, and 4 possessed certain antioxidant activities, with IC50 values of 0.587 mg/mL, 1.628 mg/mL, and 0.219 mg/mL, respectively, against DPPH radicals. Their total reducing power at a concentration of 0.5 mg/mL was 0.29 mmol/L, 0.17 mmol/L, and 4.25 mmol/L. The extraction process of neoechinulin A was optimized with the optimum extraction parameters of 72.76% methanol volume fraction, 25 mL/g solid-liquid ratio, and 50.8 °C soaking temperature. Under these conditions, the extraction yield of neoechinulin A was up to 1.500 mg/g.

Metabolomic profiling of Medicago sativa-derived fungal endophytes and evaluation of their biological activities

This study aimed to discover the potential of Medicago sativa-derived fungal endophytes as a prospective source of bioactive metabolites. In the present study, three different strains of fungal endophyte Aspergillus terreus were isolated from leaves L, roots T and stems St of Medicago sativa to explore their biological and chemical diversity. These isolated fungi were exposed to different fermentation conditions by adding various chemical elicitors to their solid fermentation media. According to LC-HRESIMS-based metabolomics and multivariate analysis, each chemical treatment had a different effect on the chemical profiles of the fungi. Orthogonal Projections to Latent Structures Discriminant Analysis (OPLS-DA) proposed several compounds with anticancer action against MCF-7 (a human breast cancer cell line) and MDA-MB-231 (a human epithelial breast cancer cell line).

2,5-Diketopiperazines (DKPs): Promising Scaffolds for Anticancer Agents

2,5-Diketopiperazine (2,5-DKP) derivatives represent a family of secondary metabolites widely produced by bacteria, fungi, plants, animals, and marine organisms. Many natural products with DKP scaffolds exhibited various pharmacological activities such as antiviral, antifungal, antibacterial, and antitumor. 2,5-DKPs are recognized as privileged structures in medicinal chemistry, and compounds that incorporate the 2,5-DKP scaffold have been extensively investigated for their anticancer properties. This review is a thorough update on the anti-cancer activity of natural and synthesized 2,5-DKPs from 1997 to 2022. We have explored various aspects of 2,5-DKPs modifications and summarized their structure-activity relationships (SARs) to gain insight into their anticancer activities. We have also highlighted the novel approaches to enhance the specificity and pharmacokinetics of 2,5-DKP-based anticancer agents.

Secondary Metabolites from the Genus Eurotium and Their Biological Activities

Eurotium is the teleomorph genus associated with the section Aspergillus. Eurotium comprises approximately 20 species, which are widely distributed in nature and human environments. Eurotium is usually the key microorganism for the fermentation of traditional food, such as Fuzhuan brick tea, Liupao tea, Meju, and Karebushi; thus, Eurotium is an important fungus in the food industry. Eurotium has been extensively studied because it contains a series of interesting, structurally diverse, and biologically important secondary metabolites, including anthraquinones, benzaldehyde derivatives, and indol diketopiperazine alkaloids. These secondary metabolites have shown multiple biological activities, including antioxidative, antimicrobial, cytotoxic, antitumor, insecticidal, antimalarial, and anti-inflammatory activities. This study presents an up-to-date review of the phytochemistry and biological activities of all Eurotium species. This review will provide recent advances on the secondary metabolites and their bioactivities in the genus Eurotium for the first time and serve as a database for future research and drug development from the genus Eurotium.

A review on nonviral, nonbacterial infectious agents toxicity involved in neurodegenerative diseases

Neuronal death, decreased activity or dysfunction of neurotransmitters are some of the pathophysiological reasons for neurodegenerative diseases like Alzheimer's, Parkinson's and multiple sclerosis. Also, there is evidence for the role of infections and infectious agents in neurodegenerative diseases and the effect of some metabolites in microorganisms in the pathophysiology of these diseases. In this study, we intend to evaluate the existing studies on the role of infectious agents and their metabolites on the pathophysiology of neurodegenerative diseases. PubMed, Scopus, Google Scholar and Web of Science search engines were searched. Some infectious agents have been observed in neurodegenerative diseases. Also, isolations of some fungi and microalgae have an improving effect on Parkinson's and Alzheimer's.

Endophytic fungi: a potential source for drugs against central nervous system disorders

Neuroprotection is one of the important protection methods against neuronal cells and tissue damage caused by neurodegenerative diseases such as Alzheimer's, Parkinson's, Huntington's, and multiple sclerosis. Various bioactive compounds produced by medicinal plants can potentially treat central nervous system (CNS) disorders. Apart from these resources, endophytes also produce diverse secondary metabolites capable of protecting the CNS. The bioactive compounds produced by endophytes play essential roles in enhancing the growth factors, antioxidant defence functions, diminishing neuroinflammatory, and apoptotic pathways. The efficacy of compounds produced by endophytic fungi was also evaluated by enzymes, cell lines, and in vivo models. Acetylcholine esterase (AChE) inhibition is frequently used to assess in vitro neuroprotective activity along with cytotoxicity-induced neuronal cell lines. Some of drugs, such as tacrine, donepezil, rivastigmine, galantamine, and other compounds, are generally used as reference standards. Furthermore, clinical trials are required to confirm the role of these natural compounds in neuroprotection efficacy and evaluate their safety profile. This review illustrates the production of various bioactive compounds produced by endophytic fungi and their role in preventing neurodegeneration.

Neuroprotective effects of a novel peptide from Lignosus rhinocerotis against 6-hydroxydopamine-induced apoptosis in PC12 cells by inhibiting NF-κB activation

According to previous studies, oxidative stress is a leading cause of dopaminergic neuron death and may contribute to the pathogenesis of Parkinson's disease (PD). In the current study, we used chromatography of gel filtration to identify a novel peptide (Lignosus rhinocerotis peptide [LRP]) from the sclerotium of Lignosus rhinocerotis (Cooke) Ryvarden. Its neuroprotective effect was evaluated using an in vitro PD model constructed by 6-hydroxydopamine (6-OHDA)-stimulated to apoptosis in PC12 cells. The molecular weight of LRP is determined as 1532 Da and the secondary structure is irregular. The simple amino acid sequence of LRP is Thr-Leu-Ala-Pro-Thr-Phe-Leu-Ser-Ser-Leu-Gly-Pro-Cys-Leu-Leu. Notably, LRP has the ability to significantly boost the viability of PC12 cells after exposure to 6-OHDA, as well as enhance the cellular activity of antioxidative enzymes like superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px). LRP also lowers the level of malondialdehyde (MDA), decreases the activation performance of Caspase-3, and reduces 6-OHDA-induced apoptosis via inhibition of nuclear factor-kappa B (NF-κB) activation. These data indicate that LRP may have the potential to act as a neuroprotective agent.

Multifunctional role of natural products for the treatment of Parkinson's disease: At a glance

Natural substances originating from plants have long been used to treat neurodegenerative disorders (NDs). Parkinson's disease (PD) is a ND. The deterioration and subsequent cognitive impairments of the midbrain nigral dopaminergic neurons distinguish by this characteristic. Various pathogenic mechanisms and critical components have been reported, despite the fact that the origin is unknown, such as protein aggregation, iron buildup, mitochondrial dysfunction, neuroinflammation and oxidative stress. Anti-Parkinson drugs like dopamine (DA) agonists, levodopa, carbidopa, monoamine oxidase type B inhibitors and anticholinergics are used to replace DA in the current treatment model. Surgery is advised in cases where drug therapy is ineffective. Unfortunately, the current conventional treatments for PD have a number of harmful side effects and are expensive. As a result, new therapeutic strategies that control the mechanisms that contribute to neuronal death and dysfunction must be addressed. Natural resources have long been a useful source of possible treatments. PD can be treated with a variety of natural therapies made from medicinal herbs, fruits, and vegetables. In addition to their well-known anti-oxidative and anti-inflammatory capabilities, these natural products also play inhibitory roles in iron buildup, protein misfolding, the maintenance of proteasomal breakdown, mitochondrial homeostasis, and other neuroprotective processes. The goal of this research is to systematically characterize the currently available medications for Parkinson's and their therapeutic effects, which target diverse pathways. Overall, this analysis looks at the kinds of natural things that could be used in the future to treat PD in new ways or as supplements to existing treatments. We looked at the medicinal plants that can be used to treat PD. The use of natural remedies, especially those derived from plants, to treat PD has been on the rise. This article examines the fundamental characteristics of medicinal plants and the bioactive substances found in them that may be utilized to treat PD.

A Review on Bioactive Compounds from Marine-Derived Chaetomium Species

Filamentous marine fungi have proven to be a plentiful source of new natural products. Chaetomium, a widely distributed fungal genus in the marine environment, has gained much interest within the scientific community. In the last 20 years, many potential secondary metabolites have been detected from marine-derived Chaetomium. In this review, we attempt to provide a comprehensive summary of the natural products produced by marine-derived Chaetomium species. A total of 122 secondary metabolites that were described from 2001 to 2021 are covered. The structural diversity of the compounds, along with details of the sources and relevant biological properties are also provided, while the relationships between structures and their bioactivities are discussed. It is our expectation that this review will be of benefit to drug development and innovation.

Therapeutic Potential of Neoechinulins and Their Derivatives: An Overview of the Molecular Mechanisms Behind Pharmacological Activities

Neoechinulins are diketopiperazine type indole alkaloids that demonstrate radical scavenging, anti-inflammatory, antiviral, anti-neurodegenerative, neurotrophic factor-like, anticancer, pro-apoptotic, and anti-apoptotic properties. An array of neoechinulins such as neoechinulins A-E, isoechinulins A-C, cryptoechunilin have been isolated from various fungal sources like Aspergillus sp., Xylaria euglossa, Eurotium cristatum, Microsporum sp., etc. Besides, neoechinulin derivatives or stereoisomers were also obtained from diverse non-fungal sources viz. Tinospora sagittata, Opuntia dillenii, Cyrtomium fortunei, Cannabis sativa, and so on. The main purpose of this review is to provide update information on neoechinulins and their analogues about the molecular mechanisms of the pharmacological action and possible future research. The recent data from this review can be used to create a basis for the discovery of new neoechinulin-based drugs and their analogues in the near future. The online databases PubMed, Science and Google scholar were researched for the selection and collection of data from the available literature on neoechinulins, their natural sources and their pharmacological properties. The published books on this topic were also analysed. In vitro and in vivo assays have established the potential of neoechinulin A as a promising anticancer and anti-neuroinflammatory lead molecule. Neoechinulin B was also identified as a potential antiviral drug against hepatitis C virus. Toxicological and clinical trials are needed in the future to improve the phyto-pharmacological profile of neoquinolines. From the analysis of the literature, we found that neoechinulins and their derivatives have special biological potential. Although some modern pharmacological analyzes have highlighted the molecular mechanisms of action and some signalling pathways, the correlation between these phytoconstituents and pharmacological activities must be validated in the future by preclinical toxicological and clinical studies.

Marine endophytic fungi associated with Halopteris scoparia (Linnaeus) Sauvageau as producers of bioactive secondary metabolites with potential dermocosmetic application

Marine fungi and, particularly, endophytic species have been recognised as one of the most prolific sources of structurally new and diverse bioactive secondary metabolites with multiple biotechnological applications. Despite the increasing number of bioprospecting studies, very few have already evaluated the cosmeceutical potential of marine fungal compounds. Thus, this study focused on a frequent seaweed in the Portuguese coast, Halopteris scoparia, to identify the endophytic marine fungi associated with this host, and assess their ability to biosynthesise secondary metabolites with antioxidative, enzymatic inhibitory (hyaluronidase, collagenase, elastase and tyrosinase), anti-inflammatory, photoprotective, and antimicrobial (Cutibacterium acnes, Staphylococcus epidermidis and Malassezia furfur) activities. The results revealed eight fungal taxa included in the Ascomycota, and in the most representative taxonomic classes in marine ecosystems (Eurotiomycetes, Sordariomycetes and Dothideomycetes). These fungi were reported for the first time in Portugal and in association with H. scoparia, as far as it is known. The screening analyses showed that most of these endophytic fungi were producers of compounds with relevant biological activities, though those biosynthesised by Penicillium sect. Exilicaulis and Aspergillus chevalieri proved to be the most promising ones for being further exploited by dermocosmetic industry. The chemical analysis of the crude extract from an isolate of A. chevalieri revealed the presence of two bioactive compounds, echinulin and neoechinulin A, which might explain the high antioxidant and UV photoprotective capacities exhibited by the extract. These noteworthy results emphasised the importance of screening the secondary metabolites produced by these marine endophytic fungal strains for other potential bioactivities, and the relevance of investing more efforts in understanding the ecology of halo/osmotolerant fungi.

Prenylation and Dehydrogenation of a C2-Reversely Prenylated Diketopiperazine as a Branching Point in the Biosynthesis of Echinulin Family Alkaloids in Aspergillus ruber

The echinulin family alkaloids can be grouped into three series depending on the number of the exo double bonds adjacent to the diketopiperazine core structure. Heterologous expression of the putative echinulin biosynthetic gene cluster from Aspergillus ruber in Aspergillus nidulans led to accumulation of echinulin without a double bond and neoechinulin A with one double bond (Δ¹⁰) as major products. Their analogues with a different number of prenyl moieties were detected as minor products. Neoechinulin B and analogues with two double bonds (Δ^10,14) were not observed. Feeding experiments confirmed that the cytochrome P450 enzyme EchP450 only catalyzes the formation of the double bond between C10 and C11. Coincubation and substrate concentration dependent assays with the prenyltransferase EchPT2 revealed that the reversely C2-prenylated preechinulin without a double bond is a much better substrate than neoechinulin A. These results prove that preechinulin serves as a common substrate for the formation of echinulin by two regiospecific prenylation steps with EchPT2 or for EchP450 to introduce one double bond and subsequent prenylations with low regioselectivity.

New Indole Diketopiperazine Alkaloids from Soft Coral-Associated Epiphytic Fungus Aspergillus sp. EGF 15-0-3

Three new indole diketopiperazine alkaloids, 11-methylneoechinulin E and variecolorin M, and (+)-variecolorin G, along with 12 known analogs, were isolated from a soft coral-associated epiphytic fungus Aspergillus sp. EGF 15-0-3. The structures of the new compounds were unambiguously established by extensive spectroscopic analyses including HR-ESI-MS, 1D and 2D NMR spectroscopy and optical rotation measurements. The absolute configurations of (+)- and (-)-variecolorin G were determined by experimental and quantum-chemical ECD investigations and single-crystal X-ray diffraction analysis. Variecolorin G is a pair of enantiomeric mixtures with a ratio of 1 : 2. Moreover, (+)-neoechinulin A is firstly reported as a natural product. The cytotoxic activities of all the isolated compounds against NCI-H1975 gefitinib resistance (NCI-H1975/GR) cell lines were preliminarily evaluated by MTT method.

Biologically Active Echinulin-Related Indolediketopiperazines from the Marine Sediment-Derived Fungus Aspergillus niveoglaucus

Seven known echinulin-related indolediketopiperazine alkaloids (1–7) were isolated from the Vietnamese sediment-derived fungus Aspergillus niveoglaucus. Using chiral HPLC, the enantiomers of cryptoechinuline B (1) were isolated as individual compounds for the first time. (+)-Cryptoechinuline B (1a) exhibited neuroprotective activity in 6-OHDA-, paraquat-, and rotenone-induced in vitro models of Parkinson’s disease. (−)-Cryptoechinuline B (1b) and neoechinulin C (5) protected the neuronal cells against paraquat-induced damage in a Parkinson’s disease model. Neoechinulin B (4) exhibited cytoprotective activity in a rotenone-induced model, and neoechinulin (7) showed activity in the 6-OHDA-induced model.

Marine-Derived Natural Compounds for the Treatment of Parkinson's Disease

Parkinson’s disease (PD) is a neurodegenerative disorder caused by the loss of dopaminergic neurons, leading to the motor dysfunctions of patients. Although the etiology of PD is still unclear, the death of dopaminergic neurons during PD progress was revealed to be associated with the abnormal aggregation of α-synuclein, the elevation of oxidative stress, the dysfunction of mitochondrial functions, and the increase of neuroinflammation. However, current anti-PD therapies could only produce symptom-relieving effects, because they could not provide neuroprotective effects, stop or delay the degeneration of dopaminergic neurons. Marine-derived natural compounds, with their novel chemical structures and unique biological activities, may provide anti-PD neuroprotective effects. In this study, we have summarized anti-PD marine-derived natural products which have shown pharmacological activities by acting on various PD targets, such as α-synuclein, monoamine oxidase B, and reactive oxygen species. Moreover, marine-derived natural compounds currently evaluated in the clinical trials for the treatment of PD are also discussed.

Identification of proteins that bind to the neuroprotective agent neoechinulin A

Neoechinulin A is an indole alkaloid with several biological activities. We previously reported that this compound protects neuronal PC12 cells from cytotoxicity induced by the peroxynitrite generator 3-morpholinosydnonimine (SIN-1), but the target proteins and precise mechanism of action of neoechinulin A were unclear. Here, we employed a phage display screen to identify proteins that bind directly with neoechinulin A. Our findings identified two proteins, chromogranin B and glutaredoxin 3, as candidate target binding partners for the alkaloid. QCM analyses revealed that neoechinulin A displays high affinity for both chromogranin B and glutaredoxin 3. RNA interference-mediated depletion of chromogranin B decreased the sensitivity of PC12 cells against SIN-1. Our results suggested chromogranin B is a plausible target of neoechinulin A.

Neoechinulin A induced memory improvements and antidepressant-like effects in mice

Neoechinulin A is an isoprenyl indole alkaloid that exhibits scavenging, neurotrophic factor-like, and anti-apoptotic activities. However, the effectiveness of neoechinulin A in animal models of disease has not yet been explored. In the present study, we investigated the effects of neoechinulin A on memory impairment in lipopolysaccharide (LPS)-treated mice and its antidepressant-like effects in mice. In the Y-maze test, the intracerebroventicular (i.c.v.) administration of LPS (10μg/mouse) significantly decreased spontaneous alternation behavior, which was prevented by the prior administration of neoechinulin A (300ng/mouse, i.c.v.). None of the treatments altered the locomotor activity of mice. Moreover, the administration of neoechinulin A decreased the immobility time in the forced-swim test or tail suspension test, which was prevented by the prior administration of WAY100635 (an antagonist of 5-HT1A receptors) and parachlorophenylalanine (an inhibitor of tryptophan hydroxylase). These results suggest that neoechinulin A improves memory functions in LPS-treated mice, and also exerts antidepressant-like effects through changes in the 5-HT system.

Two benzaldehyde derivatives and their artefacts from a gorgonian-derived Eurotium sp. fungus

Two new benzaldehyde derivatives, named 3'-OH-tetrahydroauroglaucin (1) and(3'S*,4'R*)-6-(3',5-epoxy-4'-hydroxy-1'-heptenyl)-2-hydroxy-3-(3''-methyl-2''-butenyl)benzaldehyde (2), were isolated from a gorgonian-derived Eurotium sp. fungus. Their structures were determined by extensive spectroscopic analysis including NMR and MS spectra. Dissolved 1 in CDCl₃ for several days could be detected its 2H-chromene skeleton derivatives (1a/1b), a pair of enantiomers with opposite configurations at C-3'. Compound 2 was also found to chemically convert to a pair of epimers non-enzymatically. The plausible mechanism to form the 2H-chromene artefacts with racemisation at C-3' undergoing nucleophilic substitution (S_N1) was proposed.

Neoechinulin B and its analogues as potential entry inhibitors of influenza viruses, targeting viral hemagglutinin

A class of prenylated indole diketopiperazine alkaloids including 15 new compounds namely rubrumlines A-O obtained from marine-derived fungus Eurotium rubrum, were tested against influenza A/WSN/33 virus. Neoechinulin B (18) exerted potent inhibition against H1N1 virus infected in MDCK cells, and is able to inhibit a panel of influenza virus strains including amantadine- and oseltamivir-resistant clinical isolates. Mechanism of action studies indicated that neoechinulin B binds to influenza envelope hemagglutinin, disrupting its interaction with the sialic acid receptor and the attachment of viruses to host cells. In addition, neoechinulin B was still efficient in inhibiting influenza A/WSN/33 virus propagation even after a fifth passage. The high potency and broad-spectrum activities against influenza viruses with less drug resistance make neoechinulin B as a new lead for the development of potential inhibitor of influenza viruses.

Natural products from marine organisms with neuroprotective activity in the experimental models of Alzheimer's disease, Parkinson's disease and ischemic brain stroke: their molecular targets and action mechanisms

Continuous increases in the incidence of neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), and brain stroke demand the urgent development of therapeutics. Marine organisms are well-known producers of natural products with diverse structures and pharmacological activities. Therefore, researchers have endeavored to identify marine natural products with neuroprotective effects. In this regard, this review summarizes therapeutic targets for AD, PD, and ischemic brain stroke and marine natural products with pharmacological activities on the targets according to taxonomies of marine organisms. Furthermore, several marine natural products on the clinical trials for the treatment of neurological disorders are discussed.

Anti-inflammatory effect of neoechinulin a from the marine fungus Eurotium sp. SF-5989 through the suppression of NF-кB and p38 MAPK Pathways in lipopolysaccharide-stimulated RAW264.7 macrophages

In the course of a bioassay-guided study of metabolites from the marine fungus Eurotium sp. SF-5989, two diketopiperazine type indole alkaloids, neoechinulins A and B, were isolated. In this study, we investigated the anti-inflammatory effects of neoechinulins A (1) and B (2) on lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages. Neoechinulin A (1) markedly suppressed the production of nitric oxide (NO) and prostaglandin E₂ (PGE₂) and the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in a dose dependent manner ranging from 12.5 µM to 100 µM without affecting the cell viability. On the other hand, neoechinulin B (2) affected the cell viability at 25 µM although the compound displayed similar inhibitory effect of NO production to neoechinulin A (1) at lower doses. Furthermore, neoechinulin A (1) decreased the secretion of pro-inflammatory cytokines, such as tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β). We also confirmed that neoechinulin A (1) blocked the activation of nuclear factor-kappaB (NF-κB) in LPS-stimulated RAW264.7 macrophages by inhibiting the phosphorylation and degradation of inhibitor kappa B (IκB)-α. Moreover, neoechinulin A (1) decreased p38 mitogen-activated protein kinase (MAPK) phosphorylation. Therefore, these data showed that the anti-inflammatory effects of neoechinulin A (1) in LPS-stimulated RAW264.7 macrophages were due to the inhibition of the NF-κB and p38 MAPK pathways, suggesting that neoechinulin A (1) might be a potential therapeutic agent for the treatment of various inflammatory diseases.

Synthetic and structure-activity relationship studies on bioactive natural products

This review summarizes our research into the synthesis and structure-activity relationships of epolactaene, neoechinulin A, plakevulin A, pseudodeflectusin and ustusorane C. These natural products are attractive in view of their apoptosis-inducing activity, cytoprotective activity against peroxynitrite, inhibitory activity against DNA polymerases, and cytotoxicity in cancer cells.

Neoechinulin a imparts resistance to acute nitrosative stress in PC12 cells: a potential link of an elevated cellular reserve capacity for pyridine nucleotide redox turnover with cytoprotection

Treatment of PC12 cells with fungus-derived alkaloid neoechinulin A for more than 12 h renders the cells resistant to subsequent superoxide (O₂⁻)/nitric oxide (NO) insults derived from 3-morpholinosydnonimine (SIN-1). However, the underlying mechanism(s) remains largely unclear. To elucidate the mechanism(s), we assessed the specificity of the cytoprotection afforded by neoechinulin A treatment using other cytocidal stressors and also clarified the resulting cellular alterations, focusing on the antioxidant and metabolic enzymes systems. Neoechinulin A treatment for more than 12 h endowed PC12 cells with significant resistance to transient NO toxicity, but not persistent NO toxicity, bolus H₂O₂ toxicity, or oxidative insult from the redox cycling quinone menadione. Cellular antioxidant system profiling revealed no substantial potentiation of the activity of any antioxidant enzyme in lysate from the neoechinulin A-treated cells excluding glutathione (GSH) content, which was significantly decreased (>50%), resulting in a proportional compromise in the thiol-reducing activity of the intact cells. In addition, no differences were observed in the activity for any nicotinamide adenine dinucleotide (phosphate) reduced form (NAD(P)H)-generating enzyme, steady-state NAD(P)H/nicotinamide adenine dinucleotide (phosphate) oxidized form (NAD(P)⁺) ratios, or the levels of total NAD(P)H. Nevertheless, the neoechinulin A-treated intact cells exhibited increased NAD(P)H redox turnover when driven by extracellular tetrazolium. The structurally inactive analog preechinulin failed to protect cells against NO toxicity or induce these alterations, suggesting their link with the cytoprotective mechanism. These results suggest that neoechinulin A, despite disabling the GSH defense system, confers cytoprotection against nitrosative stresses by elevating the cellular reserve capacity for NAD(P)H generation, which could offset crippling of energy-supplying systems due to nitrosative stress.

Neoechinulin a impedes the progression of rotenone-induced cytotoxicity in PC12 cells

Neoechinulin A, an indole alkaloid from marine fungi, can protect PC12 cells from the cytotoxicity of 1-methyl-4-phenylpyridinium (MPP(+)), a Parkinson disease-inducing neurotoxin, by ameliorating downstream events resulting from mitochondrial complex I inactivation. However, the cytoprotective mechanisms remained unclear. In this study, by using rotenone, another parkinsonian-inducing neurotoxin targeting mitochondrial complex I, we investigated the cytoprotective mechanism of neoechinulin A. Rotenone-induced cell death was associated with accelerated glucose consumption, and excess glucose supplementation in the culture medium almost completely suppressed cell death, suggesting that glucose deficiency in the medium is critical for triggering cell death in this model. Co-treatment with neoechinulin A, but not neoechinulin A pre-treatment before rotenone exposure, significantly impeded cell death by rotenone. Although the presence of neoechinulin A did not affect the accelerated glycolytic turnover in rotenone-treated cells, it paradoxically decreased ATP levels in the cells, suggesting increased ATP consumption. Although the link between the decreased ATP levels and cytoprotection is not clear at present, it suggests that neoechinulin A may ameliorate rotenone toxicity by activating a cytoprotective machinery that requires ATP.

Synthesis and Neuroprotective Action of Optically Pure Neoechinulin A and Its Analogs

We developed an efficient, stereoselective synthetic method for the diketopiperazine moiety of neoechinulin A and its derivatives. The intramolecular cyclization at 80 ºC proceeded with minimal racemization of the stereogenic center at C-12 on neoechinulin A, even though the cyclization at 110 ºC caused partial racemization. In contrast with these results, the cyclization on diketopiperazine of 8,9-dihydroneoechinulin A derivatives did not cause epimerization of the stereogenic centers, even at 110 °C. We examined the structure-activity relationships for the cytoprotective activity against cytotoxicity induced by 3-morpholinosydnonimine (SIN-1) in nerve growth factor (NGF)-differentiated PC12 cells. The C-8/C-9 double bond, but not the stereogenic center derived from alanine, was found to play a key role in the cytoprotective activity.

Inflammation-associated gene transcription and expression in mouse lungs induced by low molecular weight compounds from fungi from the built environment

Few metabolites from fungi found indoors have been tested for inflammatory mediators endpoints in primary cultures of alveolar macrophages or in vivo. In this study, mice were intratracheally instilled with a single dose comprising 4x10(-5)moletoxin/kg lung wt dose of either atranone C, brevianamide, cladosporin, mycophenolic acid, neoechinulin A & B, sterigmatocystin or TMC-120A. These toxins are from fungi common on damp building materials. The dose used was comparable to the estimated doses of possible human exposure. Hematoxylin and eosin (H&E) histology and Alcian Blue/Periodic Acid Schiff (AB/PAS) histochemistry were used to evaluate lungs for time course (4h and 12h post-exposure (PE)) inflammatory and toxic changes. Reverse-transcription (RT)-PCR based arrays were also employed to evaluate time course inflammation-associated gene transcription in lung tissues of the different toxins. Immunohistochemistry (IHC) was used to probe MIP-2 and Tnf-alpha protein expression in treatment lungs to determine whether responses correspond with gene transcription data. Both histology and histochemistry revealed that toxin exposed lungs at 12h PE showed evidence of inflammation. H&E revealed that bronchioli were lined with irregularly thickened and sometimes sloughing epithelium and bronchiolar spaces supported infiltration of leukocytes, cellular and mucus-like debris while alveolar spaces supported swollen macrophages and modest amorphous debris accumulations. All toxin-instilled lungs exhibited copious mucus production and alveolar macrophages with red stained cytoplasm on bronchiolar surfaces, especially at 12h PE. Array analysis of 83 inflammation-associated genes extracted from lung tissue demonstrated a number of patterns, compared to controls. 82 genes assayed at 4h PE and 75 genes at 12h PE were significantly altered (p< or =0.05; >or =1.5-fold or < or =-1.5-fold change) in the different treatment animal groups. Expression of transcriptionally regulated genes was confirmed using immunohistochemistry that demonstrated MIP-2 and Tnf-alpha staining in respiratory bronchiolar epithelia, alveolar macrophages and alveolar type II cells. The transcriptional regulation in these genes in the treatment groups suggests that they may serve central roles in the immunomodulation of toxin-induced pro-inflammatory lung responses. Hierarchical cluster analysis revealed significant patterns of gene transcription linking the response of the toxins at equimolar doses in three groups: (1) brevianamide, mycophenolic acid and neoechinulin B, (2) neoechinulin A and sterigmatocystin, and (3) cladosporin, atranone C and TMC-120. The results further confirm the inflammatory nature of metabolites/toxins from such fungi can contribute to the development of non-allergenic respiratory health effects.

Neoechinulin A protects PC12 cells against MPP+-induced cytotoxicity

Neoechinulin A, an alkaloid from Eurotium rubrum, can protect neuronal PC12 cells against cytotoxicity of a potent oxidant, peroxynitrite. Because involvement of peroxynitrite has been suggested in the pathogenesis of Parkinson's disease, we assessed whether this alkaloid could also protect PC12 cells from the cytocidal action of 1-methyl-4-phenylpyridine (MPP+), a neurotoxin capable of provoking acute Parkinson's-like neurodegeneration in humans. Neoechinulin A could protect PC12 cells from MPP+ cytotoxicity without protecting against mitochondrial complex I dysfunction, suggesting the alkaloid can ameliorate downstream events of mitochondrial failure. Thus, neoechinulin A has the potential to intervene in this progressive neurodegeneration.