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

Neurotrophic Natural Products

Neurotrophins (NGF, BDNF, NT3, NT4) can decrease cell death, induce differentiation, as well as sustain the structure and function of neurons, which make them promising therapeutic agents for the treatment of neurodegenerative disorders. However, neurotrophins have not been very effective in clinical trials mostly because they cannot pass through the blood-brain barrier owing to being high-molecular-weight proteins. Thus, neurotrophin-mimic small molecules, which stimulate the synthesis of endogenous neurotrophins or enhance neurotrophic actions, may serve as promising alternatives to neurotrophins. Small-molecular-weight natural products, which have been used in dietary functional foods or in traditional medicines over the course of human history, have a great potential for the development of new therapeutic agents against neurodegenerative diseases such as Alzheimer's disease. In this contribution, a variety of natural products possessing neurotrophic properties such as neurogenesis, neurite outgrowth promotion (neuritogenesis), and neuroprotection are described, and a focus is made on the chemistry and biology of several neurotrophic natural products.

Indole Diketopiperazine Alkaloids from the Marine Sediment-Derived Fungus Aspergillus chevalieri against Pancreatic Ductal Adenocarcinoma

A new prenylated indole diketopiperazine alkaloid, rubrumline P (1), was isolated along with six more analogues and characterized from the fermentation culture of a marine sediment-derived fungus, Aspergillus chevalieri, collected at a depth of 15 m near the lighthouse in Dahab, Red Sea, Egypt. In the current study, a bioassay-guided fractionation allowed for the identification of an active fraction displaying significant cytotoxic activity against the human pancreatic adenocarcinoma cell line PANC-1 from the EtOAc extract of the investigated fungus compared to the standard paclitaxel. The structures of the isolated compounds from the active fraction were established using 1D/2D NMR spectroscopy and mass spectrometry, together with comparisons with the literature. The absolute configuration of the obtained indole diketopiperazines was established based on single-crystal X-ray diffraction analyses of rubrumline I (2) and comparisons of optical rotations and NMR data, as well as on biogenetic considerations. Genome sequencing indicated the formation of prenyltransferases, which was subsequently confirmed by the isolation of mono-, di-, tri-, and tetraprenylated compounds. Compounds rubrumline P (1) and neoechinulin D (4) confirmed preferential cytotoxic activity against PANC-1 cancer cells with IC50 values of 25.8 and 23.4 µM, respectively. Although the underlying mechanism-of-action remains elusive in this study, cell cycle analysis indicated a slight increase in the sub-G1 peak after treatment with compounds 1 and 4.

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.

Marine-Derived Components: Can They Be a Potential Therapeutic Approach to Parkinson's Disease?

The increase in the life expectancy average has led to a growing elderly population, thus leading to a prevalence of neurodegenerative disorders, such as Parkinson's disease (PD). PD is the second most common neurodegenerative disorder and is characterized by a progressive degeneration of the dopaminergic neurons in the substantia nigra pars compacta (SNpc). The marine environment has proven to be a source of unique and diverse chemical structures with great therapeutic potential to be used in the treatment of several pathologies, including neurodegenerative impairments. This review is focused on compounds isolated from marine organisms with neuroprotective activities on in vitro and in vivo models based on their chemical structures, taxonomy, neuroprotective effects, and their possible mechanism of action in PD. About 60 compounds isolated from marine bacteria, fungi, mollusk, sea cucumber, seaweed, soft coral, sponge, and starfish with neuroprotective potential on PD therapy are reported. Peptides, alkaloids, quinones, terpenes, polysaccharides, polyphenols, lipids, pigments, and mycotoxins were isolated from those marine organisms. They can act in several PD hallmarks, reducing oxidative stress, preventing mitochondrial dysfunction, α-synuclein aggregation, and blocking inflammatory pathways through the inhibition translocation of NF-kB factor, reduction of human tumor necrosis factor α (TNF-α), and interleukin-6 (IL-6). This review gathers the marine natural products that have shown pharmacological activities acting on targets belonging to different intracellular signaling pathways related to PD development, which should be considered for future pre-clinical studies.

Fiscalin Derivatives as Potential Neuroprotective Agents

Neurodegenerative diseases (ND) share common molecular/cellular mechanisms that contribute to their progression and pathogenesis. In this sense, we are here proposing new neuroprotection strategies by using marine-derived compounds as fiscalins. This work aims to evaluate the protective effects of fiscalin derivatives towards 1-methyl-4-phenylpyridinium (MPP⁺)- and iron (III)-induced cytotoxicity in differentiated SH-SY5Y cells, an in vitro disease model to study ND; and on P-glycoprotein (P-gp) transport activity, an efflux pump of drugs and neurotoxins. SH-SY5Y cells were simultaneously exposed to MPP⁺ or iron (III), and noncytotoxic concentrations of 18 fiscalin derivatives (0–25 μM), being the cytotoxic effect of both MPP⁺ and iron (III) evaluated 24 and 48 h after exposure. Fiscalins 1a and 1b showed a significant protective effect against MPP⁺-induced cytotoxicity and fiscalins 1b, 2b, 4 and 5 showed a protective effect against iron (III)-induced cytotoxicity. Fiscalins 4 and 5 caused a significant P-gp inhibition, while fiscalins 1c, 2a, 2b, 6 and 11 caused a modest increase in P-gp transport activity, thus suggesting a promising source of new P-gp inhibitors and activators, respectively. The obtained results highlight fiscalins with promising neuroprotective effects and with relevance for the synthesis of new derivatives for the treatment/prevention of ND.

Natural Indole Alkaloids from Marine Fungi: Chemical Diversity and Biological Activities

The indole scaffold is one of the most important heterocyclic ring systems for pharmaceutical development, and serves as an active moiety in several clinical drugs. Fungi derived from marine origin are more liable to produce novel indole-containing natural products due to their extreme living environments. The indole alkaloids from marine fungi have drawn considerable attention for their unique chemical structures and significant biological activities. This review attempts to provide a summary of the structural diversity of marine fungal indole alkaloids including prenylated indoles, diketopiperazine indoles, bisindoles or trisindoles, quinazoline-containing indoles, indole-diterpenoids, and other indoles, as well as their known biological activities, mainly focusing on cytotoxic, kinase inhibitory, antiinflammatory, antimicrobial, anti-insecticidal, and brine shrimp lethal effects. A total of 306 indole alkaloids from marine fungi have been summarized, covering the references published from 1995 to early 2021, expecting to be beneficial for drug discovery in the future.

Neoechinulins: Molecular, cellular, and functional attributes as promising therapeutics against cancer and other human diseases

Neoechinulins are fungal and plant-derived chemicals extracted from Microsporum sp., Eurotium rubrum, Aspergillus sp., etc. Two analogues of neoechinulin, i.e., A and B, exerted extensive pharmacological properties described in this review. Neoechinulin is an indole alkaloid and has a double bond between C8/C9, which tends to contribute to its cytoprotective nature. Neoechinulin A exhibits protection to PC12 cells against nitrosative stress via increasing NAD(P)H reserve capacity and decreasing cellular GSH levels. It also confers protection via rescuing PC12 cells from rotenone-induced stress by lowering LDH leakage. This compound has great positive potential against neurodegenerative diseases by inhibiting SIN-1 induced cell death in neuronal cells. Together with these, neoechinulin A tends to inhibit Aβ42-induced microglial activation and confers protection against neuroinflammation. Alongside, it also inhibits cervical cancer cells by caspase-dependent apoptosis and via upregulation of apoptosis inducing genes like Bax, it suppresses LPS-induced inflammation in RAW264.7 macrophages and acts as an antidepressant. Whereas, another analogue, Neoechinulin B tends to interfere with the cellular mechanism thereby, inhibiting the entry of influenza A virus and it targets Liver X receptor (LXR) and decreases the infection rate of Hepatitis C. The present review describes the pharmaceutical properties of neoechinulins with notes on their molecular, cellular, and functional basis and their therapeutic properties.

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.

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.

Neuroprotective Activity of Some Marine Fungal Metabolites in the 6-Hydroxydopamin- and Paraquat-Induced Parkinson's Disease Models

A new melatonin analogue 6-hydroxy-N-acetyl-β-oxotryptamine (1) was isolated from the marine-derived fungus Penicillium sp. KMM 4672. It is the second case of melatonin-related compounds isolation from microfilamentous fungi. The neuroprotective activities of this metabolite, as well as 3-methylorsellinic acid (2) and 8-methoxy-3,5-dimethylisochroman-6-ol (3) from Penicillium sp. KMM 4672, candidusin A (4) and 4″-dehydroxycandidusin A (5) from Aspergillus sp. KMM 4676, and diketopiperazine mactanamide (6) from Aspergillus flocculosus, were investigated in the 6-hydroxydopamine (6-OHDA)- and paraquat (PQ)-induced Parkinson's disease (PD) cell models. All of them protected Neuro2a cells against the damaging influence of 6-OHDA to varying degrees. This effect may be realized via a reactive oxygen species (ROS) scavenging pathway. The new melatonin analogue more effectively protected Neuro2A cells against the 6-OHDA-induced neuronal death, in comparison with melatonin, as well as against the PQ-induced neurotoxicity. Dehydroxylation at C-3″ and C-4″ significantly increased free radical scavenging and neuroprotective activity of candidusin-related p-terphenyl polyketides in both the 6-OHDA- and PQ-induced PD models.

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.

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.

The Pael-R gene does not mediate the changes in rotenone-induced Parkinson's disease model cells

In this study, we established cell models for Parkinson's disease using rotenone. An RNA interference vector targeting Parkin-associated endothelin receptor-like receptor (Pael-R) was transfected into the model cells. The results of reverse-transcription polymerase chain reaction and western blot analysis showed that Pael-R expression was decreased after RNA interference compared with the control group (no treatment) and the model group (rotenone treatment), while the rate of apoptosis and survival of dopaminergic cells did not differ significantly between groups, as detected by flow cytometry and an MTT assay. These experimental findings indicate that the Pael-R gene has no role in the changes in rotenone-induced Parkinson's disease model cells.

Sulfiredoxin-1 protects PC12 cells against oxidative stress induced by hydrogen peroxide

Oxidative stress results in protein oxidation and is implicated in cerebral disease, such as Parkinson's disease, Alzheimer's disease, and ischemic stroke. Sulfiredoxin-1 (Srxn1) is an endogenous antioxidant protein that has neuroprotective effects. The mechanisms of Srxn1 in oxidative stress have not been well studied, however. This study used 180 μM H2 O2 exposure for 24 hr to model oxidative stress. This experimental design allowed us to explore the protective effects and underlying mechanisms of Srxn1 in PC12 cells. To investigate Srxn1's role in oxidative stress protection, transient knockdowns of Srxn1 in PC12 cells were performed prior to treatment with 180 μM H2 O2 for 24 hr. Knockdown of Srxn1 resulted in decreased cell viability and increased cellular damage as determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide and lactate dehyrogenase analysis, respectively. Intracellular superoxide dismutase and glutathione are important indexes of oxidative stress; these were reduced in Srxn1 knockdown PC12. We further found that the decreased Srxn1 correlated with a reduction in 2-Cys Prdxs activity. Moreover, 2-Cys Prdxs protein levels were increased in the H2 O2 -dosed cells, as measured by RT-PCR and immunoblot analysis. These results suggested that Srxn1 can protect PC12 cells from H2 O2 -induced oxidative stress and are involve in Prdxs activity. Srxn1 play a protective role against oxidative injury and demonstrates potential as a target for neuroprotective intervention in oxidative stress.

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.

Whole genome expression profile in neuroblastoma cells exposed to 1-methyl-4-phenylpyridine

Mitochondrial dysfunction and subsequent energy failure is a contributing factor to degeneration of the substantia nigra pars compacta associated with Parkinson's disease (PD). In this study, we investigate molecular events triggered by cell exposure to the mitochondrial toxin 1-methyl-4-phenylpyridine (MPP+) using whole genome-expression microarray, Western Blot and metabolic studies. The data show that MPP+ (500 μM) obstructs mitochondrial respiration/oxidative phosphorylation (OXPHOS) in mouse neuroblastoma Neuro-2a cells, juxtaposing accelerated glucose consumption and production of lactic acid. While additional glucose concentrations restored viability in the presence of MPP+ (500 μM), the loss of OXPHOS was sustained, suggesting that compensatory anaerobic metabolic systems were fulfilling required energy needs. Under these conditions, MPP+ initiated significant changes to the transcription of 439 genes of which 287 DAVID IDs were identified and subsequent functional annotation clusters identified. Prominent changes were as follows; MPP+ initiated loss of mRNA for mitochondrial encoded 3-hydroxybutyratedehydrogenase, type 2(Bdh2), tv1, NADH dehydrogenase 4,5 genes, cytochrome b and NADH dehydrogenase (ubiquinone) flavoprotein 3, concomitant to rise in a mitochondrial fission gene; ganglioside-induced differentiation-associated-protein 1 (GDAP1). The negative changes to OXPHOS components were accompanied by protective forces within the mitochondria espousing elevated ratio of anti/pro-apoptotic processes. These included a loss of apoptotic Bcl-2/adenovirus E1B 19-kDa-interacting protein (BNIP3) and family with sequence similarity 162, member A (FAM162a) and rise of heat shock protein 1 and Lon peptidase 1. There were no changes indicative of free radical damage (e.g. SOD, GSH-Px), rather MPP+ initiated significant elevation in G protein signaling components (which trigger catabolic processes) and anaerobic metabolic systems involving carboxylic acid/transamination reactions (e.g. glutamate oxaloacetate transaminase 1 (GOT1), glutamic pyruvate-alanine transaminase 2 (GPT2), cystathionase and redox proteins such as cytochrome b5 reductase 1 and ferredoxin reductase. Counter-intuitively, the data show reduction of mRNA in glycolytic processes [DAVID enrichment score 9.96 p value 1.90E-19], some corroborated by Western Blot, bringing in to question the sources of lactate observed in the presence of MPP+. Examining this aspect, the data show that diverse carboxylic acids (succinate, oxaloacetate and a-ketoglutarate) are capable of contributing to the lactate pool in addition to phosph(enolpyruvate) or pyruvate in the absence of glucose by this cell line. In conclusion, these findings show that MPP+ negatively affects the transcriptome involved with complex I, but initiated an elevation of G protein signaling and anaerobic metabolic systems involved with nitrogen/carboxylic acid metabolism. Future research will be required to elucidate the survival pathways that drive anaerobic substrate level phosphorylation, and define functional ramification to the loss of mitochondrial FAM162a and BNIP3 proteins.