Effectors of thioredoxin reductase: Brevetoxins and manumycin-A

Karenia brevis Extract Induces Cellular Entry through Distinct Mechanisms in Phagocytic RAW 264.7 Macrophages versus Non-Phagocytic Vero Cells

Marine algae extracts are an important area of potential drug discovery; however, nearly all studies to date have used non-fluorescent-based methods to determine changes in target cell activity. Many of the most robust immunological and cellular analyses rely on fluorescent probes and readouts, which can be problematic when the algae extract is fluorescent itself. In this study, we identified the fluorescent spectrum of an isolated extract from the marine dinoflagellate Karenia brevis, which included two fluorescing components: chlorophyll α and pheophytin α. When excited at 405 nm and 664 nm, the extract emitted fluorescence at 676 nm and 696 nm, respectively. The extract and its fluorescing components, chlorophyll α and pheophytin α, entered phagocytic RAW 264.7 macrophages and non-phagocytic Vero kidney cells through distinct mechanisms. When incubated with the extract and its main components, both the RAW 264.7 macrophages and the Vero cells accumulated fluorescence as early as 30 min and continued through 48 h. Vero kidney cells accumulated the K. brevis fluorescent extract through a dynamin-independent and acidified endosomal-dependent mechanism. RAW 264.7 macrophages accumulated fluorescent extract through a dynamin-independent, acidified endosomal-independent mechanism, which supports accumulation through phagocytosis. Furthermore, RAW 264.7 macrophages downregulated cell-surface expression of CD206 in response to extract stimulation indicating activation of phagocytic responses and potential immunosuppression of these immune cells. This study represents the first characterization of the cellular update of K. brevis extracts in phagocytic versus non-phagocytic cells. The data suggest the importance of understanding cellular uptake of fluorescing algae extracts and their mechanism of action for future drug discovery efforts.

Toxic dinoflagellate Karenia mikimotoi induces apoptosis in Neuro-2a cells through an oxidative stress-mediated mitochondrial pathway

The dinoflagellate Karenia mikimotoi is a toxic bloom-forming species that threatens aquaculture and public health worldwide. Previous studies showed that K. mikimotoi induces neurotoxicity; however, the underlying mechanism is poorly understood. In this study, three neural cell lines were used to investigate the potential neurotoxicity of K. mikimotoi. The tested cells were exposed to a ruptured cell solution (RCS) of K. mikimotoi at different concentrations (0.5 × 105, 1.0 × 105, 2.0 × 105, 4.0 × 105, and 6 × 105 cells mL-1) for 24 h, and the RCS decreased cell viabilities and promoted Neuro-2a (N2A) cell apoptosis in a dose-dependent manner. The underlying mechanism was further investigated in N2A cells. At the biochemical level, the RCS stimulated reactive oxygen species (ROS) and malondialdehyde (MDA) formation, decreased SOD activity, and reduced mitochondrial membrane potential (MMP). At the gene level, the moderate RCS treatment (2.0 × 105 cells mL-1) upregulated antioxidant response genes (e.g., nrf-2, HO-1, NQO-1, and cat) to alleviate RCS-induced oxidative stress, while the high RCS treatment (4.0 × 105 cells mL-1) downregulated these genes, thereby aggravating oxidative stress. Meanwhile, apoptosis-related genes (e.g., p53, caspase 3, and bax2) were significantly upregulated and the anti-apoptotic gene bcl2 was suppressed after RCS treatment. Western blotting results for Caspase 3, Bax2 and Bcl2 were consistent with the mRNA trends. These results revealed that K. mikimotoi RCS can induce neural cell apoptosis via the oxidative stress-mediated mitochondrial pathway, providing novel insights into the neurotoxicity of K. mikimotoi.

Brevetoxin induces a shift in the redox state of the proteome and unfolded protein response in human lymphoblast cells that can be alleviated with the acrolein scavenger MESNA

Human lymphoblast cells were treated with the marine algal toxin, brevetoxin-2 (PbTx-2), and its effects on the proteome were assessed by redox proteomics using cysteine reactive tandem mass tags (TMT). Additionally, cells were simultaneously treated with PbTx-2 and the antioxidant and acrolein scavenger sodium 2-mercaptoethylsulfonate (MESNA) to determine if MESNA could prevent the proteomic effects of brevetoxin-2. A massive shift in the redox state of the proteome of brevetoxin-2 treated cells was observed. The main pathway affected was genetic information processing. Significantly oxidized proteins included Trx-1, peroxyredoxins (Prxs), ribosomal proteins, and the eukaryotic initiation factor 2 β subunit (eIF2β). Proteins that were overexpressed in brevetoxin-treated cells included four folding chaperones. These effects were diminished in the presence of MESNA indicating that MESNA may act through its antioxidant properties or as a brevetoxin scavenger. These studies provide novel insights into new prophylactics for brevetoxicosis in humans and wildlife.

Antioxidant activity of the thioredoxin system

The thioredoxin system is composed of thioredoxin (Trx), thioredoxin reductase (TR) and reduced nicotinamide adenine dinucleotide phosphate. Trx is an important antioxidant molecule that can resist cell death caused by various stresses and plays a prominent role in redox reactions. TR is a protein that contains selenium (selenocysteine), in three main forms, namely, TR1, TR2 and TR3. TR1, TR2 and TR3 are mainly distributed in the cytoplasm, mitochondria, and testes, respectively. TR can regulate cell growth and apoptosis. After a cell becomes cancerous, the expression of TR is increased to promote cell growth and metastasis. The Trx system is closely related to neurodegenerative diseases, parasitic infections, acquired immunodeficiency syndrome, rheumatoid arthritis, hypertension, myocarditis, and so on. In addition, the Trx system can remove the reactive oxygen species in the body and keep the inside and outside of the cell in a balanced state. In summary, the Trx system is an important target for the drug treatment of many diseases.

Application of a Cholesterol-Based Stationary Phase for the Analysis of Brevetoxins

A high-performance liquid chromatography protocol for the analysis of brevetoxins has been developed using a silica hydride-based cholesterol column. Brevetoxins are neurotoxins produced by harmful algae that have additional potential as drugs for a number of illnesses/diseases. To develop the optimum conditions, a number of different experimental approaches were tested. These include isocratic and gradient elution, different organic mobile phase components, and temperature variations. A separate protocol was developed for the compounds brevenal and brevenol, also produced by the same algae that make brevetoxins. Brevenal is a natural product under investigation as a therapy for chronic respiratory diseases, such as cystic fibrosis or asthma. The goal of this study was to provide a protocol for the analysis of these compounds that could be further developed into a validated method depending on a particular laboratory's capabilities and to highlight some of the unique features of the cholesterol stationary phase.

Reduced Fitness and Elevated Oxidative Stress in the Marine Copepod Tigriopus japonicus Exposed to the Toxic Dinoflagellate Karenia mikimotoi

Blooms of the toxic dinoflagellate Karenia mikimotoi cause devastation to marine life, including declines of fitness and population recruitment. However, little is known about the effects of them on benthic copepods. Here, we assessed the acute and chronic effects of K. mikimotoi on the marine benthic copepod Tigriopus japonicus. Results showed that adult females maintained high survival (>85%) throughout 14-d incubation, but time-dependent reduction of survival was detected in the highest K. mikimotoi concentration, and nauplii and copepodites were more vulnerable compared to adults. Ingestion of K. mikimotoi depressed the grazing of copepods but significantly induced the generation of reactive oxygen species (ROS), total antioxidant capacity, activities of antioxidant enzymes (superoxide dismutase, catalase, and glutathione peroxidase), and acetylcholinesterase. Under sublethal concentrations for two generations, K. mikimotoi reduced the fitness of copepods by prolonging development time and decreasing successful development rate, egg production, and the number of clutches. Our findings suggest that the bloom of K. mikimotoi may threaten copepod population recruitment, and its adverse effects are associated with oxidative stress.

Natural Products from Actinobacteria as a Potential Source of New Therapies Against Colorectal Cancer: A Review

Colorectal cancer (CRC) is a common, and deadly disease. Despite the improved knowledge on CRC heterogeneity and advances in the medical sciences, there is still an urgent need to cope with the challenges and side effects of common treatments for the disease. Natural products (NPs) have always been of interest for the development of new medicines. Actinobacteria are known to be prolific producers of a wide range of bioactive NPs, and scientific evidence highlights their important protective role against CRC. This review is a holistic picture on actinobacter-derived cytotoxic compounds against CRC that provides a good perspective for drug development and design in near future. This review also describes the chemical structure of 232 NPs presenting anti-CRC activity with the being majority of quinones, lactones, alkaloids, peptides, and glycosides. The study reveals that most of these NPs are derived from marine actinobacteria followed by terrestrial and endophytic actinobacteria, respectively. They are predominantly produced by Streptomyces, Micromonospors, Saliniospors and Actinomadura, respectively, in which Streptomyces, as the predominant contributor generating over 76% of compounds exclusively. Besides it provides a valuable snapshot of the chemical structure-activity relationship of compounds, highlighting the presence or absence of some specific atoms and chemical units in the structure of compounds can greatly influence their biological activities. To the best of our knowledge, this is the first comprehensive review on natural actinobacterial compounds affecting different types of CRC. Our study reveals that the high diversity of actinobacterial strains and their NPs derivatives, described here provides a new perspective and direction for the production of new anti-CRC drugs and paves the way to innovation for drugs discovery in the future. The knowledge obtain from this review can help us to understand the pivotal application of actinobacteria in future drugs development.

Immune Modulating Brevetoxins: Monocyte Cytotoxicity, Apoptosis, and Activation of M1/M2 Response Elements Is Dependent on Reactive Groups

Brevetoxins are a suite of marine neurotoxins that activate voltage-gated sodium channels (VGSCs) in cell membranes, with toxicity occurring from persistent activation of the channel at high doses. Lower doses, in contrast, have been shown to elicit neuroregeneration. Brevetoxins have thus been proposed as a novel treatment for patients after stroke, when neuron regrowth and repair is critical to recovery. However, findings from environmental exposures indicate that brevetoxins may cause inflammation, thus, there is concern for brevetoxins as a stroke therapy given the potential for neuroinflammation. In this study, we examined the inflammatory properties of several brevetoxin analogs, including those that do and do not bind strongly to VGSCs, as binding has classically indicated toxicity. We found that several analogs are toxic to monocytes, while others are not, and the degree of toxicity is not directly related to VGSC binding. Rather, results indicate that brevetoxins containing aldehyde groups were more likely to cause immunotoxicity, regardless of binding affinity to the VGSC. Our results demonstrate that different brevetoxin family members can elicit a spectrum of apoptosis and necrosis by multiple possible mechanisms of action in monocytes. As such, care should be taken in treating “brevetoxins” as a uniform group, particularly in stroke therapy research.

The Marine Neurotoxin Brevetoxin (PbTx-2) Inhibits Karenia brevis and Mammalian Thioredoxin Reductases by Targeting Different Residues

The brevetoxins, neurotoxins produced by Karenia brevis, the Florida red tide dinoflagellate, effect fish and wildlife mortalities and adverse public health and economic impacts during recurrent blooms. Knowledge of the biochemical consequences of toxin production for K. brevis could provide insights into an endogenous role of the toxins, yet this aspect has not been thoroughly explored. In addition to neurotoxicity, the most abundant of the brevetoxins, PbTx-2, inhibits mammalian thioredoxin reductase (TrxR). The thioredoxin system, composed of the enzymes TrxR and thioredoxin (Trx), is present in all living organisms and is responsible in part for maintaining cellular redox homeostasis. Herein, we describe the cloning, expression, and semisynthesis of the selenoprotein TrxR from K. brevis (KbTrxR) and reductase activity toward a variety of substrates. Unlike mammalian TrxR, KbTrxR reduces oxidized glutathione (GSSG). We further demonstrate that PbTx-2 is an inhibitor of KbTrxR. Covalent adducts between KbTrxR and rat TrxR were detected by mass spectrometry. While both enzymes are adducted at or near the catalytic centers, the specific residues are distinct. Biochemical differences reported for high and low toxin producing strains of K. brevis are consistent with the inhibition of KbTrxR and suggest that PbTx-2 is an endogenous regulator of this critical enzyme.

Essential components of the xanthophyll cycle differ in high and low toxin Karenia brevis

The dinoflagellate Karenia brevis, blooms annually in the Gulf of Mexico, producing a suite of neurotoxins known as the brevetoxins. The cellular toxin content of K. brevis, however, is highly variable between or even within strains. Herein, we investigate physiological differences between high (KbHT) and low (KbLT) toxin producing cultures both derived from the Wilson strain, related to energy-dependent quenching (qE) by photosystem II, and reduced thiol content of the proteome. We demonstrate that gene and protein expression of the xanthophyll cycle enzyme diadinoxanthin de-epoxidase (Dde) and monogalactosyldiacylglycerol (MGDG) synthase are not significantly different in the two cultures. Using redox proteomics, we report a significantly higher reduced cysteine content in the low toxin proteome, including plastid localized thioredoxin reductase (Trx) which can result in inactivation of Dde and activation of MGDG synthase. We also report significant differences in the lipidomes of KbHT and KbLT with respect to MGDG, which facilitates the xanthophyll cycle.

Inhibition of Pro-Inflammatory Cytokines by Metabolites of Streptomycetes-A Potential Alternative to Current Anti-Inflammatory Drugs?

Current treatment of chronic diseases includes, among others, application of cytokines, monoclonal antibodies, cellular therapies, and immunostimulants. As all the underlying mechanisms of a particular diseases are not always fully clarified, treatment can be inefficient and associated with various, sometimes serious, side effects. Small secondary metabolites produced by various microbes represent an attractive alternative as future anti-inflammatory drug leads. Compared to current drugs, they are cheaper, can often be administered orally, but still can keep a high target-specificity. Some compounds produced by actinomycetes or fungi have already been used as immunomodulators—tacrolimus, sirolimus, and cyclosporine. This work documents strong anti-inflammatory features of another secondary metabolite of streptomycetes—manumycin-type polyketides. We compared the effect of four related compounds: manumycin A, manumycin B, asukamycin, and colabomycin E on activation and survival of human monocyte/macrophage cell line THP-1. The anti-cancer effect of manucycine A has been demonstrated; the immunomodulatory capacities of manumycin A are obvious when using micromolar concentrations. The application of all four compounds in 0.25–5 μM concentrations leads to efficient, concentration-dependent inhibition of IL-1β and TNF expression in THP-1 upon LPS stimulation, while the three latter compounds show a significantly lower pro-apoptotic effect than manumycin A. We have demonstrated the anti-inflammatory capacity of selected manumycin-type polyketides.