Kunitz-Type Peptides from the Sea Anemone Heteractis crispa Demonstrate Potassium Channel Blocking and Anti-Inflammatory Activities

A review on inflammation modulating venom proteins/peptide therapeutics and their delivery strategies: A review

Inflammation is an initial biological reaction that occurs in response to infection caused by foreign pathogens or injury. This process involves a tightly controlled series of signaling events at the molecular and cellular levels, with the ultimate goal of restoring tissue balance and protecting against invading pathogens. Malfunction in the process of inflammation can result in a diverse array of diseases, such as cardiovascular, neurological, and autoimmune disorders. Therefore, the management of inflammation is of utmost importance in modern medicine. Nonsteroidal anti-inflammatory drugs (NSAIDs) and corticosteroids have long been the mainstays of pharmacological treatment for inflammation, effectively alleviating symptoms in many patients. Recently, toxins and venom, formerly seen as mostly harmful to the human body, have been recognized as possible medicinal substances for treating inflammation. Organisms that are venomous, such as spiders, scorpions, snakes, and certain marine species, have developed a wide range of powerful toxins that can effectively disable or discourage predators. Remarkably, the majority of these poisons and venoms consist of proteins and peptides, which are acknowledged as significant bioactive compounds with medicinal potential. The goal of this review is to investigate the medicinal potential of peptides derived from venoms and their complex mechanism of action in suppressing inflammation. This review also discusses various challenges and future prospects for effective venom delivery.

Revealing the Diversity of Sequences, Structures, and Targets of Peptides from South China Sea Macrodactyla doreensis Based on Transcriptomics

The South China Sea is rich in sea anemone resources, and the protein and peptide components from sea anemone toxins comprise an important treasure trove for researchers to search for leading compounds. This study conducted a comprehensive transcriptomic analysis of the tentacles and column of Macrodactyla doreensis and explored the distribution and diversity of proteins and peptides in depth using bioinformatics, initially constructing a putative protein and peptide database. In this database, typical peptide families are identified through amino acid sequence analysis, and their 3D structures and potential biological activities are revealed through AlphaFold2 modeling and molecular docking. A total of 4239 transcripts were identified, of which the putative protein accounted for 81.53%. The highest content comprised immunoglobulin and a variety of proteases, mainly distributed in the column and related to biological functions. Importantly, the putative peptide accounted for 18.47%, containing ShK domain and Kunitz-type peptides, mainly distributed in the tentacles and related to offensive predatory behavior. Interestingly, 40 putative peptides belonging to eight typical peptide families were identified, and their structures and targets were predicted. This study reveals the diversity and complexity of Macrodactyla doreensis toxins and predicts their structure and targets based on amino acid sequences, providing a feasible approach for research regarding the discovery of peptides with potentially high activity.

Structure and functional studies of Avt1, a novel peptide from the sea anemone Aulactinia veratra

Sea anemones are a rich source of peptide toxins spanning a diverse range of biological activities, typically targeting proteins such as ion channels, receptors and transporters. These peptide toxins and their analogues are usually highly stable and selective for their molecular targets, rendering them of interest as molecular tools, insecticides and therapeutics. Recent transcriptomic and proteomic analyses of the sea anemone Aulactinia veratra identified a novel 28-residue peptide, designated Avt1. Avt1 was produced using solid-phase peptide synthesis, followed by oxidative folding and purification of the folded peptide using reversed-phase high-performance liquid chromatography. The liquid chromatography-mass spectrometry profile of synthetic Avt1 showed a pure peak with molecular mass 6 Da less than that of the reduced form of the peptide, indicating the successful formation of three disulfide bonds. The solution structure determined by NMR revealed that Avt1 adopts an inhibitor cystine knot (ICK) fold, in which a ring is formed by two disulfide bonds with a third disulfide penetrating the ring to create the pseudo-knot. This structure provides ICK peptides with high structural, thermal and proteolytic stability. Consistent with its ICK structure, Avt1 was resistant to proteolysis by trypsin, chymotrypsin and pepsin, although it was not a trypsin inhibitor. Avt1 at 100 nM showed no activity in patch-clamp electrophysiological assays against several mammalian voltage-gated ion channels, but has structural features similar to toxins targeting insect sodium ion channels. Although sequence homologues of Avt1 are found in a number of sea anemones, this is the first representative of this family to be characterised structurally and functionally.

Diversity analysis of sea anemone peptide toxins in different tissues of Heteractis crispa based on transcriptomics

Peptide toxins found in sea anemones venom have diverse properties that make them important research subjects in the fields of pharmacology, neuroscience and biotechnology. This study used high-throughput sequencing technology to systematically analyze the venom components of the tentacles, column, and mesenterial filaments of sea anemone Heteractis crispa, revealing the diversity and complexity of sea anemone toxins in different tissues. A total of 1049 transcripts were identified and categorized into 60 families, of which 91.0% were proteins and 9.0% were peptides. Of those 1049 transcripts, 416, 291, and 307 putative proteins and peptide precursors were identified from tentacles, column, and mesenterial filaments respectively, while 428 were identified when the datasets were combined. Of these putative toxin sequences, 42 were detected in all three tissues, including 33 proteins and 9 peptides, with the majority of peptides being ShKT domain, β-defensin, and Kunitz-type. In addition, this study applied bioinformatics approaches to predict the family classification, 3D structures, and functional annotation of these representative peptides, as well as the evolutionary relationships between peptides, laying the foundation for the next step of peptide pharmacological activity research.

Spatial Distribution and Biochemical Characterization of Serine Peptidase Inhibitors in the Venom of the Brazilian Sea Anemone Anthopleura cascaia Using Mass Spectrometry Imaging

Sea anemones are known to produce a diverse array of toxins with different cysteine-rich peptide scaffolds in their venoms. The serine peptidase inhibitors, specifically Kunitz inhibitors, are an important toxin family that is believed to function as defensive peptides, as well as prevent proteolysis of other secreted anemone toxins. In this study, we isolated three serine peptidase inhibitors named Anthopleura cascaia peptide inhibitors I, II, and III (ACPI-I, ACPI-II, and ACPI-III) from the venom of the endemic Brazilian sea anemone A. cascaia. The venom was fractionated using RP-HPLC, and the inhibitory activity of these fractions against trypsin was determined and found to range from 59% to 93%. The spatial distribution of the anemone peptides throughout A. cascaia was observed using mass spectrometry imaging. The inhibitory peptides were found to be present in the tentacles, pedal disc, and mesenterial filaments. We suggest that the three inhibitors observed during this study belong to the venom Kunitz toxin family on the basis of their similarity to PI-actitoxin-aeq3a-like and the identification of amino acid residues that correspond to a serine peptidase binding site. Our findings expand our understanding of the diversity of toxins present in sea anemone venom and shed light on their potential role in protecting other venom components from proteolysis.

Recombinant Analogs of Sea Anemone Kunitz-Type Peptides Influence P2X7 Receptor Activity in Neuro-2a Cells

Purinergic P2X7 receptors (P2X7) have now been proven to play an important role and represent an important therapeutic target in many pathological conditions including neurodegeneration. Here, we investigated the impact of peptides on purinergic signaling in Neuro-2a cells through the P2X7 subtype in in vitro models. We have found that a number of recombinant peptides, analogs of sea anemone Kunitz-type peptides, are able to influence the action of high concentrations of ATP and thereby reduce the toxic effects of ATP. The influx of calcium, as well as the fluorescent dye YO-PRO-1, was significantly suppressed by the studied peptides. Immunofluorescence experiments confirmed that the peptides reduce the P2X7 expression level in neuronal Neuro-2a cells. Two selected active peptides, HCRG1 and HCGS1.10, were found to specifically interact with the extracellular domain of P2X7 and formed stable complexes with the receptor in surface plasmon resonance experiments. The molecular docking approach allowed us to establish the putative binding sites of the most active HCRG1 peptide on the extracellular domain of the P2X7 homotrimer and propose a mechanism for regulating its function. Thus, our work demonstrates the ability of the Kunitz-type peptides to prevent neuronal death by affecting signaling through the P2X7 receptor.

The Sea Anemone Neurotoxins Modulating Sodium Channels: An Insight at Structure and Functional Activity after Four Decades of Investigation

Many human cardiovascular and neurological disorders (such as ischemia, epileptic seizures, traumatic brain injury, neuropathic pain, etc.) are associated with the abnormal functional activity of voltage-gated sodium channels (VGSCs/NaVs). Many natural toxins, including the sea anemone toxins (called neurotoxins), are an indispensable and promising tool in pharmacological researches. They have widely been carried out over the past three decades, in particular, in establishing different NaV subtypes functional properties and a specific role in various pathologies. Therefore, a large number of publications are currently dedicated to the search and study of the structure-functional relationships of new sea anemone natural neurotoxins-potential pharmacologically active compounds that specifically interact with various subtypes of voltage gated sodium channels as drug discovery targets. This review presents and summarizes some updated data on the structure-functional relationships of known sea anemone neurotoxins belonging to four structural types. The review also emphasizes the study of type 2 neurotoxins, produced by the tropical sea anemone Heteractis crispa, five structurally homologous and one unique double-stranded peptide that, due to the absence of a functionally significant Arg14 residue, loses toxicity but retains the ability to modulate several VGSCs subtypes.

First Anti-Inflammatory Peptide AnmTX Sco 9a-1 from the Swimming Sea Anemone Stomphia coccinea

A novel peptide AnmTX Sco 9a-1 with the β-hairpin fold was isolated from the swimming sea anemone Stomphia coccinea (Actinostolidae family). The peptide consists of 28 amino acid residues, including modified hydroxyproline residue, and its measured molecular mass is 2960 Da. The peptide was not toxic on mice; however, it stimulated their exploratory motivation and active search behavior, and demonstrated an anti-anxiety effect. AnmTX Sco 9a-1 at doses of 0.1 and 1 mg/kg reduced the volume of edema during 24 h better than the nonsteroidal anti-inflammatory drug, Diclofenac, at dose of 1 mg/kg in a model of acute local λ-carrageenan-induced inflammation. ELISA analysis of the animal’s blood showed that peptide at a dose of 1 mg/kg reduced the content of tumor necrosis factor-α (TNF-α), a pro-inflammatory mediator responsible in the edema development, up to the level of TNF-α in the intact group. Besides, AnmTX Sco 9a-1 demonstrated a significant analgesic effect on acute pain sensitivity in the carrageenan-induced thermal hyperalgesia model at doses of 0.1 and 1 mg/kg. Activity of AnmTX Sco 9a-1 was shown not to be associated with modulation of nociceptive ASIC channels.

Pharmacological Screening of Venoms from Five Brazilian Micrurus Species on Different Ion Channels

Coral snake venoms from the Micrurus genus are a natural library of components with multiple targets, yet are poorly explored. In Brazil, 34 Micrurus species are currently described, and just a few have been investigated for their venom activities. Micrurus venoms are composed mainly of phospholipases A₂ and three-finger toxins, which are responsible for neuromuscular blockade—the main envenomation outcome in humans. Beyond these two major toxin families, minor components are also important for the global venom activity, including Kunitz-peptides, serine proteases, 5′ nucleotidases, among others. In the present study, we used the two-microelectrode voltage clamp technique to explore the crude venom activities of five different Micrurus species from the south and southeast of Brazil: M. altirostris, M. corallinus, M. frontalis, M. carvalhoi and M. decoratus. All five venoms induced full inhibition of the muscle-type α1β1δε nAChR with different levels of reversibility. We found M. altirostris and M. frontalis venoms acting as partial inhibitors of the neuronal-type α7 nAChR with an interesting subsequent potentiation after one washout. We discovered that M. altirostris and M. corallinus venoms modulate the α1β2 GABA_AR. Interestingly, the screening on K_V1.3 showed that all five Micrurus venoms act as inhibitors, being totally reversible after the washout. Since this activity seems to be conserved among different species, we hypothesized that the Micrurus venoms may rely on potassium channel inhibitory activity as an important feature of their envenomation strategy. Finally, tests on Na_V1.2 and Na_V1.4 showed that these channels do not seem to be targeted by Micrurus venoms. In summary, the venoms tested are multifunctional, each of them acting on at least two different types of targets.

Anti-epileptic Kunitz-like peptides discovered in the branching coral Acropora digitifera through transcriptomic analysis

Approximately 50 million people are suffering from epilepsy worldwide. Corals have been used for treating epilepsy in traditional Chinese medicine, but the mechanism of this treatment is unknown. In this study, we analyzed the transcriptome of the branching coral Acropora digitifera and obtained its Kyoto Encyclopedia of Genes and Genomes (KEGG), EuKaryotic Orthologous Groups (KOG) and Gene Ontology (GO) annotation. Combined with multiple sequence alignment and phylogenetic analysis, we discovered three polypeptides, we named them AdKuz1, AdKuz2 and AdKuz3, from A. digitifera that showed a close relationship to Kunitz-type peptides. Molecular docking and molecular dynamics simulation indicated that AdKuz1 to 3 could interact with GABA_A receptor but AdKuz2-GABA_A remained more stable than others. The biological experiments showed that AdKuz1 and AdKuz2 exhibited an anti-inflammatory effect by decreasing the aberrant level of nitric oxide (NO), IL-6, TNF-α and IL-1β induced by LPS in BV-2 cells. In addition, the pentylenetetrazol (PTZ)-induced epileptic effect on zebrafish was remarkably suppressed by AdKuz1 and AdKuz2. AdKuz2 particularly showed superior anti-epileptic effects compared to the other two peptides. Furthermore, AdKuz2 significantly decreased the expression of c-fos and npas4a, which were up-regulated by PTZ treatment. In addition, AdKuz2 reduced the synthesis of glutamate and enhanced the biosynthesis of gamma-aminobutyric acid (GABA). In conclusion, the results indicated that AdKuz2 may affect the synthesis of glutamate and GABA and enhance the activity of the GABA_A receptor to inhibit the symptoms of epilepsy. We believe, AdKuz2 could be a promising anti-epileptic agent and its mechanism of action should be further investigated.

Marine natural products

Covering: 2020This review covers the literature published in 2020 for marine natural products (MNPs), with 757 citations (747 for the period January to December 2020) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1407 in 420 papers for 2020), together with the relevant biological activities, source organisms and country of origin. Pertinent reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. A meta analysis of bioactivity data relating to new MNPs reported over the last five years is also presented.

A Tale of Toxin Promiscuity: The Versatile Pharmacological Effects of Hcr 1b-2 Sea Anemone Peptide on Voltage-Gated Ion Channels

Sea anemones are a rich source of biologically active compounds. Among approximately 1100 species described so far, Heteractis crispa species, also known as sebae anemone, is native to the Indo-Pacific area. As part of its venom components, the Hcr 1b-2 peptide was first described as an ASIC1a and ASIC3 inhibitor. Using Xenopus laevis oocytes and the two-electrode voltage-clamp technique, in the present work we describe the remarkable lack of selectivity of this toxin. Besides the acid-sensing ion channels previously described, we identified 26 new targets of this peptide, comprising 14 voltage-gated potassium channels, 9 voltage-gated sodium channels, and 3 voltage-gated calcium channels. Among them, Hcr 1b-2 is the first sea anemone peptide described to interact with isoforms from the Kv7 family and T-type Cav channels. Taken together, the diversity of Hcr 1b-2 targets turns this toxin into an interesting tool to study different types of ion channels, as well as a prototype to develop new and more specific ion channel ligands.

AsKC11, a Kunitz Peptide from Anemonia sulcata, Is a Novel Activator of G Protein-Coupled Inward-Rectifier Potassium Channels

(1) Background: G protein-coupled inward-rectifier potassium (GIRK) channels, especially neuronal GIRK1/2 channels, have been the focus of intense research interest for developing drugs against brain diseases. In this context, venom peptides that selectively activate GIRK channels can be seen as a new source for drug development. Here, we report on the identification and electrophysiological characterization of a novel activator of GIRK1/2 channels, AsKC11, found in the venom of the sea anemone Anemonia sulcata. (2) Methods: AsKC11 was purified from the sea anemone venom by reverse-phase chromatography and the sequence was identified by mass spectrometry. Using the two-electrode voltage-clamp technique, the activity of AsKC11 on GIRK1/2 channels was studied and its selectivity for other potassium channels was investigated. (3) Results: AsKC11, a Kunitz peptide found in the venom of A. sulcata, is the first peptide shown to directly activate neuronal GIRK1/2 channels independent from Gi/o protein activity, without affecting the inward-rectifier potassium channel (IRK1) and with only a minor effect on K_V1.6 channels. Thus, AsKC11 is a novel activator of GIRK channels resulting in larger K⁺ currents because of an increased chord conductance. (4) Conclusions: These discoveries provide new insights into a novel class of GIRK activators.

Deep-Sea Anemones Are Prospective Source of New Antimicrobial and Cytotoxic Compounds

The peculiarities of the survival and adaptation of deep-sea organisms raise interest in the study of their metabolites as promising drugs. In this work, the hemolytic, cytotoxic, antimicrobial, and enzyme-inhibitory activities of tentacle extracts from five species of sea anemones (Cnidaria, orders Actiniaria and Corallimorpharia) collected near the Kuril and Commander Islands of the Far East of Russia were evaluated for the first time. The extracts of Liponema brevicorne and Actinostola callosa demonstrated maximal hemolytic activity, while high cytotoxic activity against murine splenocytes and Ehrlich carcinoma cells was found in the extract of Actinostola faeculenta. The extracts of Corallimorphus cf. pilatus demonstrated the greatest activity against Ehrlich carcinoma cells but were not toxic to mouse spleen cells. Sea anemones C. cf. pilatus and Stomphia coccinea are promising sources of antimicrobial and antifungal compounds, being active against Gram-positive bacteria Bacillus subtilis, Staphylococcus aureus, and yeast Candida albicans. Moreover, all sea anemones contain α-galactosidase inhibitors. Peptide mass fingerprinting of L. brevicorne and C. cf. pilatus extracts provided a wide range of peptides, predominantly with molecular masses of 4000–5900 Da, which may belong to a known or new structural class of toxins. The obtained data allow concluding that deep-sea anemones are a promising source of compounds for drug discovery.

TRPV1 Blocker HCRG21 Suppresses TNF-α Production and Prevents the Development of Edema and Hypersensitivity in Carrageenan-Induced Acute Local Inflammation

Currently the TRPV1 (transient receptor potential vanilloid type 1) channel is considered to be one of the main targets for pro-inflammatory mediators including TNF-α. Similarly, the inhibition of TRPV1 activity in the peripheral nervous system affects pro-inflammatory mediator production and enhances analgesia in total. In this study, the analgesic and anti-inflammatory effects of HCRG21, the first peptide blocker of TRPV1, were demonstrated in a mice model of carrageenan-induced paw edema. HCRG21 in doses of 0.1 and 1 mg/kg inhibited edema formation compared to the control, demonstrated complete edema disappearance in 24 h in a dose of 1 mg/kg, and effectively reduced the productionof TNF-α in both doses examined. ELISA analysis of blood taken 24 h after carrageenan administration showed a dramatic cytokine value decrease to 25 pg/mL by HCRG21 versus 100 pg/mL in the negative control group, which was less than the TNF-α level in the intact group (40 pg/mL). The HCRG21 demonstrated potent analgesic effects on the models of mechanical and thermal hyperalgesia in carrageenan-induced paw edema. The HCRG21 relief effect was comparable to that of indomethacin taken orally in a dose of 5 mg/kg, but was superior to this nonsteroidal anti-inflammatory drug (NSAID) in duration (which lasted 24 h) in the mechanical sensitivity experiment. The results confirm the existence of a close relationship between TRPV1 activity and TNF-α production once again, and prove the superior pharmacological potential of TRPV1 blockers and the HCRG21 peptide in particular.

Animal Venoms-Curse or Cure?

An estimated 15% of animals are venomous, with representatives spread across the majority of animal lineages. Animals use venoms for various purposes, such as prey capture and predator deterrence. Humans have always been fascinated by venomous animals in a Janus-faced way. On the one hand, humans have a deeply rooted fear of venomous animals. This is boosted by their largely negative image in public media and the fact that snakes alone cause an annual global death toll in the hundreds of thousands, with even more people being left disabled or disfigured. Consequently, snake envenomation has recently been reclassified by the World Health Organization as a neglected tropical disease. On the other hand, there has been a growth in recent decades in the global scene of enthusiasts keeping venomous snakes, spiders, scorpions, and centipedes in captivity as pets. Recent scientific research has focussed on utilising animal venoms and toxins for the benefit of humanity in the form of molecular research tools, novel diagnostics and therapeutics, biopesticides, or anti-parasitic treatments. Continued research into developing efficient and safe antivenoms and promising discoveries of beneficial effects of animal toxins is further tipping the scales in favour of the “cure” rather than the “curse” prospect of venoms.

Sea Anemone Kunitz-Type Peptides Demonstrate Neuroprotective Activity in the 6-Hydroxydopamine Induced Neurotoxicity Model

Kunitz-type peptides from venomous animals have been known to inhibit different proteinases and also to modulate ion channels and receptors, demonstrating analgesic, anti-inflammatory, anti-histamine and many other biological activities. At present, there is evidence of their neuroprotective effects. We have studied eight Kunitz-type peptides of the sea anemone Heteractis crispa to find molecules with cytoprotective activity in the 6-OHDA-induced neurotoxicity model on neuroblastoma Neuro-2a cells. It has been shown that only five peptides significantly increase the viability of neuronal cells treated with 6-OHDA. The TRPV1 channel blocker, HCRG21, has revealed the neuroprotective effect that could be indirect evidence of TRPV1 involvement in the disorders associated with neurodegeneration. The pre-incubation of Neuro-2a cells with HCRG21 followed by 6-OHDA treatment has resulted in a prominent reduction in ROS production compared the untreated cells. It is possible that the observed effect is due to the ability of the peptide act as an efficient free-radical scavenger. One more leader peptide, InhVJ, has shown a neuroprotective activity and has been studied at concentrations of 0.01–10.0 µM. The target of InhVJ is still unknown, but it was the best of all eight homologous peptides in an absolute cell viability increment on 38% of the control in the 6-OHDA-induced neurotoxicity model. The targets of the other three active peptides remain unknown.