ImKTx88, a novel selective Kv1.3 channel blocker derived from the scorpion Isometrus maculates

Scorpion venom peptides: Molecular diversity, structural characteristics, and therapeutic use from channelopathies to viral infections and cancers

Animal venom is an important evolutionary innovation in nature. As one of the most representative animal venoms, scorpion venom contains an extremely diverse set of bioactive peptides. Scorpion venom peptides not only are 'poisons' that immobilize, paralyze, kill, or dissolve preys but also become important candidates for drug development and design. Here, the review focuses on the molecular diversity of scorpion venom peptides, their typical structural characteristics, and their multiple therapeutic or pharmaceutical applications in channelopathies, viral infections and cancers. Especially, the group of scorpion toxin TRPTx targeting transient receptor potential (TRP) channels is systematically summarized and worthy of attention because TRP channels play a crucial role in the regulation of homeostasis and the occurrence of diseases in human. We also further establish the potential relationship between the molecular characteristics and functional applications of scorpion venom peptides to provide a research basis for modern drug development and clinical utilization of scorpion venom resources.

Bioactive peptides from scorpion venoms: therapeutic scaffolds and pharmacological tools

Evolution and natural selection have endowed animal venoms, including scorpion venoms, with a wide range of pharmacological properties. Consequently, scorpions, their venoms, and/or their body parts have been used since time immemorial in traditional medicines, especially in Africa and Asia. With respect to their pharmacological potential, bioactive peptides from scorpion venoms have become an important source of scientific research. With the rapid increase in the characterization of various components from scorpion venoms, a large number of peptides are identified with an aim of combating a myriad of emerging global health problems. Moreover, some scorpion venom-derived peptides have been established as potential scaffolds helpful for drug development. In this review, we summarize the promising scorpion venoms-derived peptides as drug candidates. Accordingly, we highlight the data and knowledge needed for continuous characterization and development of additional natural peptides from scorpion venoms, as potential drugs that can treat related diseases.

Optimization of Pichia pastoris Expression System for High-Level Production of Margatoxin

Margatoxin (MgTx) is a high-affinity blocker of voltage-gated potassium (Kv) channels. It inhibits Kv1.1–Kv1.3 ion channels in picomolar concentrations. This toxin is widely used to study physiological function of Kv ion channels in various cell types, including immune cells. Isolation of native MgTx in large quantities from scorpion venom is not affordable. Chemical synthesis and recombinant production in Escherichia coli need in vitro oxidative refolding for proper disulfide bond formation, resulting in a very low yield of peptide production. The Pichia pastoris expression system offers an economical approach to overcome all these limitations and gives a higher yield of correctly refolded recombinant peptides. In this study, improved heterologous expression of recombinant MgTx (rMgTx) in P. pastoris was obtained by using preferential codons, selecting the hyper-resistant clone against Zeocin, and optimizing the culturing conditions. About 36 ± 4 mg/L of >98% pure His-tagged rMgTx (TrMgTx) was produced, which is a threefold higher yield than has been previously reported. Proteolytic digestion of TrMgTx with factor Xa generated untagged rMgTx (UrMgTx). Both TrMgTx and UrMgTx blocked the Kv1.2 and Kv1.3 currents (patch-clamp) (K_d for Kv1.2 were 64 and 14 pM, and for Kv1.3, 86 and 50 pM, respectively) with comparable potency to the native MgTx. The analysis of the binding kinetics showed that TrMgTx had a lower association rate than UrMgTx for both Kv1.2 and Kv1.3. The dissociation rate of both the analogues was the same for Kv1.3. However, in the case of Kv1.2, TrMgTx showed a much higher dissociation rate with full recovery of the block than UrMgTx. Moreover, in a biological functional assay, both peptides significantly downregulated the expression of early activation markers IL2R and CD40L in activated CD4⁺ T_EM lymphocytes whose activation was Kv1.3 dependent. In conclusion, the authors report that the Pichia expression system is a powerful method to produce disulfide-rich peptides, the overexpression of which could be enhanced noticeably through optimization strategies, making it more cost-effective. Since the presence of the His-tag on rMgTx only mildly altered the block equilibrium and binding kinetics, recombinant toxins could be used in ion channel research without removing the tag and could thus reduce the cost and time demand for toxin production.

Blockade of Kv1.3 potassium channel inhibits CD8+ T cell-mediated neuroinflammation via PD-1/Blimp-1 signaling

Kv1.3 potassium channel is considered as a target for the treatment of autoimmune diseases such as multiple sclerosis (MS), since Kv1.3 blockade suppresses memory T cell activation including cytotoxic CD8⁺ T cells. However, the underlying signaling pathway related to autoimmune CD8⁺ T cell inhibition by Kv1.3 channel in neuroinflammatory diseases remains unclear. We found that ImK, a selective Kv1.3 blocker, reduced auto-reactive CD8⁺ T cell infiltration in the spinal cords of experimental autoimmune encephalomyelitis (EAE) rats, an animal model of MS. ImK suppressed transcriptional factor Blimp-1 expression and reduced the cytotoxicity of CD8⁺ T cells on neuronal cells. Furthermore, ImK upregulated co-inhibitory molecule PD-1 to inhibit B lymphocyte-induced maturation protein (Blimp-1) in an IL-2 independent way. In addition, PD-1 inhibitor impaired the suppression of ImK on CD8⁺ T cells and accelerated EAE progression. Our study demonstrated a novel regulatory mechanism of Kv1.3 blockade on modulating CD8⁺ T cell differentiation through PD-1/Blimp-1 signaling. This work expands the understanding of Kv1.3 channel for modulating neuroinflammation.

Effect of Ultrafine Powderization and Solid Dispersion Formation via Hot-Melt Extrusion on Antioxidant, Anti-Inflammatory, and the Human Kv1.3 Channel Inhibitory Activities of Angelica gigas Nakai

Angelica gigas Nakai (AGN) was first processed by ultrafine grinding technology and hot-melt extrusion (HME). The potential antioxidant and anti-inflammatory activities of AGN with a different process were compared, and the effect on the human Kv1.3 potassium channel was detected. The process of ultrafine powderization on AGN significantly increased the total phenolic and flavonoid contents, antioxidant activity, and DNA damage protective effect. On the contrary, AGN solid dispersion (AGN-SD) based on Soluplus^® showed the highest inhibitory effect on NO production and the human Kv1.3 channel. In addition, AGN-SD inhibited the production of prostaglandin E2 and intracellular reactive oxygen species and the mRNA expression of inducible nitric oxide synthase, cyclooxygenase-2, interleukin 1β, and interleukin 6. Taken together, these results suggest that ultrafine powderization and solid dispersion formation via HME can significantly improve the biological activities of AGN. The results also suggested that ultrafine powderization and HME may be developed and applied in the pharmaceutical industry.

ImKTx96, a peptide blocker of the Kv1.2 ion channel from the venom of the scorpion Isometrus maculates

Scorpion venom contains diverse bioactive peptides that can recognize and interact with membrane proteins such as ion channels. These natural toxins are believed to be useful tools for exploring the structure and function of ion channels. In this study, we characterized a K⁺-channel toxin gene, ImKTx96, from the venom gland cDNA library of the scorpion Isometrus maculates. The peptide deduced from the ImKTx96 precursor nucleotide sequence contains a signal peptide of 27 amino acid residues and a mature peptide of 29 residues with three disulfide bridges. Multiple sequence alignment indicated that ImKTx96 is similar with the scorpion toxins that typically target K⁺-channels. The recombined ImKTx96 peptide (rImKTx96) was expressed in the Escherichia coli system, and purified by GST-affinity chromatography and RP-HPLC. Results from whole-cell patch-clamp experiments revealed that rImKTx96 can inhibit the current of the Kv1.2 ion channel expressed in HEK293 cells. The 3D structure of ImKTx96 was constructed by molecular modeling, and the complex formed by ImKTx96 interacting with the Kv1.2 ion channel was obtained by molecular docking. Based on its structural features and pharmacological functions, ImKTx96 was identified as one member of K⁺-channel scorpion toxin α-KTx10 group and may be useful as a molecular probe for investigating the structure and function of the Kv1.2 ion channel.

Scorpion toxins targeting Kv1.3 channels: insights into immunosuppression

Scorpion venoms are natural sources of molecules that have, in addition to their toxic function, potential therapeutic applications. In this source the neurotoxins can be found especially those that act on potassium channels. Potassium channels are responsible for maintaining the membrane potential in the excitable cells, especially the voltage-dependent potassium channels (Kv), including Kv1.3 channels. These channels (Kv1.3) are expressed by various types of tissues and cells, being part of several physiological processes. However, the major studies of Kv1.3 are performed on T cells due its importance on autoimmune diseases. Scorpion toxins capable of acting on potassium channels (KTx), mainly on Kv1.3 channels, have gained a prominent role for their possible ability to control inflammatory autoimmune diseases. Some of these toxins have already left bench trials and are being evaluated in clinical trials, presenting great therapeutic potential. Thus, scorpion toxins are important natural molecules that should not be overlooked in the treatment of autoimmune and other diseases.

RIP1 kinase inhibitor halts the progression of an immune-induced demyelination disease at the stage of monocyte elevation

Demyelination in the central nervous system (CNS) underlies many human diseases, including multiple sclerosis (MS). We report here the findings of our study of the CNS demyelination process using immune-induced [experimental autoimmune encephalomyelitis (EAE)] and chemical-induced [cuprizone (CPZ)] mouse models of demyelination. We found that necroptosis, a receptor-interacting protein 3 (RIP3) kinase and its substrate mixed lineage kinase domain-like protein (MLKL)-dependent cell death program, played no role in the demyelination process, whereas the MLKL-dependent, RIP3-independent function of MLKL in the demyelination process initially discovered in the peripheral nervous system in response to nerve injury, also functions in demyelination in the CNS in these models. Moreover, a receptor-interacting protein 1 (RIP1) kinase inhibitor, RIPA-56, blocked disease progression in the EAE-induced model but showed no effect in the CPZ-induced model. It does so most likely at a step of monocyte elevation downstream of T cell activation and myelin-specific antibody generation, although upstream of breakdown of the blood-brain barrier. RIP1-kinase dead knock-in mice shared a similar result as mice treated with the RIP1 inhibitor. These results indicate that RIP1 kinase inhibitor is a potential therapeutic agent for immune-mediated demyelination diseases that works by prevention of monocyte elevation, a function previously unknown for RIP1 kinase.

A Kv1.3 channel-specific blocker alleviates neurological impairment through inhibiting T-cell activation in experimental autoimmune encephalomyelitis

AIM

Multiple sclerosis (MS) is a neurological autoimmune disorder characterized by mistaken attacks of inflammatory cells against the central nervous system (CNS), resulting in demyelination and axonal damage. Kv1.3 channel blockers can inhibit T-cell activation and have been designed for MS therapy. However, little is known about the effects of Kv1.3 blockers on protecting myelin sheaths/axons in MS. This study aimed at investigating the neuroprotection efficacy of a selective Kv1.3 channel blocker ImKTx88 (ImK) in MS animal model.

METHODS

Experimental autoimmune encephalomyelitis (EAE) rat model was established. The neuroprotective effect of ImK was assessed by immunohistochemistry and transmission electron microscopy (TEM). In addition, the antiinflammatory effect of ImK by suppressing T-cell activation was assessed by flow cytometry and ELISA in vitro.

RESULTS

Our results demonstrated that ImK administration ameliorated EAE clinical severity. Moreover, ImK increased oligodendrocytes survival, preserved axons, and myelin integrity and reduced the infiltration of activated T cells into the CNS. This protective effect of the peptide may be related to its suppression of autoantigen-specific T-cell activation via calcium influx inhibition.

CONCLUSION

ImK prevents neurological damage by suppressing T-cell activation, suggesting the applicability of this peptide in MS therapy.

Kv1.3 channel blocker (ImKTx88) maintains blood-brain barrier in experimental autoimmune encephalomyelitis

BACKGROUND

Disruption of blood-brain barrier (BBB) and subsequent infiltration of auto-reactive T lymphocytes are major characteristics of multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE). Kv1.3 channel blockers are demonstrated potential therapeutic effects on MS patients and EAE models, maybe via reducing activation of T cells. However, it remains to be explored whether Kv1.3 channel blockers maintain integrity of BBB in MS model.

RESULTS

In this study, ImKTx88, a highly selective Kv1.3 channel blocker, was used to determine the role of Kv1.3 channel in the pathogenesis of EAE, particularly in the maintenance of BBB. ImKTx88 ameliorated pathological severity in the EAE rats, and reduced extravasation into CNS. ImKTx88 also ameliorated the severity of loss or redistribution of tight junction proteins, and inhibited over-expression of ICAM-1 and VCAM-1 in the brain from EAE rats. Furthermore ImKTx88 protection was associated with activation of Ang-1/Tie-2 axis, and might be due to decreased IL-17 production.

CONCLUSIONS

ImKTx88 may be a novel therapeutic agent for MS treatment by stabilizing the BBB.

Adaptive evolution of insect selective excitatory β-type sodium channel neurotoxins from scorpion venom

Insect selective excitatory β-type sodium channel neurotoxins from scorpion venom (β-NaScTxs) are composed of about 70-76 amino acid residues and share a common scaffold stabilized by four unique disulfide bonds. The phylogenetic analysis of these toxins was hindered by limited sequence data. In our recent study, two new insect selective excitatory β-NaScTxs, LmIT and ImIT, were isolated from Lychas mucronatus and Isometrus maculatus, respectively. With the sequences previously reported, we examined the adaptive molecular evolution of insect selective excitatory β-NaScTxs by estimating the nonsynonymous-to-synonymous rate ratio (ω=d_N/d_S). The results revealed 12 positively selected sites in the genes of insect selective excitatory β-NaScTxs. Moreover, these positively selected sites match well with the sites important for interacting with sodium channels, as demonstrated in previous mutagenesis study. These results reveal that adaptive evolution after gene duplication is one of the most important genetic mechanisms of scorpion neurotoxin diversification.

Scorpion toxin peptide action at the ion channel subunit level

This review categorizes functionally validated actions of defined scorpion toxin (SCTX) neuropeptides across ion channel subclasses, highlighting key trends in this rapidly evolving field. Scorpion envenomation is a common event in many tropical and subtropical countries, with neuropharmacological actions, particularly autonomic nervous system modulation, causing significant mortality. The primary active agents within scorpion venoms are a diverse group of small neuropeptides that elicit specific potent actions across a wide range of ion channel classes. The identification and functional characterisation of these SCTX peptides has tremendous potential for development of novel pharmaceuticals that advance knowledge of ion channels and establish lead compounds for treatment of excitable tissue disorders. This review delineates the unique specificities of 320 individual SCTX peptides that collectively act on 41 ion channel subclasses. Thus the SCTX research field has significant translational implications for pathophysiology spanning neurotransmission, neurohumoral signalling, sensori-motor systems and excitation-contraction coupling. This article is part of the Special Issue entitled 'Venom-derived Peptides as Pharmacological Tools.'

Toxins Targeting the Kv1.3 Channel: Potential Immunomodulators for Autoimmune Diseases

Autoimmune diseases are usually accompanied by tissue injury caused by autoantigen-specific T-cells. K_V1.3 channels participate in modulating calcium signaling to induce T-cell proliferation, immune activation and cytokine production. Effector memory T (T_EM)-cells, which play major roles in many autoimmune diseases, are controlled by blocking K_V1.3 channels on the membrane. Toxins derived from animal venoms have been found to selectively target a variety of ion channels, including K_V1.3. By blocking the K_V1.3 channel, these toxins are able to suppress the activation and proliferation of T_EM cells and may improve T_EM cell-mediated autoimmune diseases, such as multiple sclerosis and type I diabetes mellitus.

Scorpion venom components that affect ion-channels function

The number and types of venom components that affect ion-channel function are reviewed. These are the most important venom components responsible for human intoxication, deserving medical attention, often requiring the use of specific anti-venoms. Special emphasis is given to peptides that recognize Na(+)-, K(+)- and Ca(++)-channels of excitable cells. Knowledge generated by direct isolation of peptides from venom and components deduced from cloned genes, whose amino acid sequences are deposited into databanks are nowadays in the order of 1.5 thousands, out of an estimate biodiversity closed to 300,000. Here the diversity of components is briefly reviewed with mention to specific references. Structural characteristic are discussed with examples taken from published work. The principal mechanisms of action of the three different types of peptides are also reviewed. Na(+)-channel specific venom components usually are modifier of the open and closing kinetic mechanisms of the ion-channels, whereas peptides affecting K(+)-channels are normally pore blocking agents. The Ryanodine Ca(++)-channel specific peptides are known for causing sub-conducting stages of the channels conductance and some were shown to be able to internalize penetrating inside the muscle cells.

Expression and characterization of a novel scorpine-like peptide Ev37, from the scorpion Euscorpiops validus

Scorpion venom contains a group of two-domain peptides that function to block potassium channels or have cytolytic activities. These peptides, whose functions are poorly studied, are named β-KTx or scorpine-like peptides. Ev37, the first identified gene in the Euscorpiidae family, which encoded a novel scorpine-like peptide, was cloned from the venom cDNA library of scorpion Euscorpiops validus. Sequence analysis showed that the mature Ev37 peptide contained 78 amino acid residues, which formed two structural domains: a putative α-helical N-terminus and a C-terminus with the cysteine-stabilized α/β motif. The peptide rEv37 and two truncated peptides representing the individual structural domains (Ev37-N and Ev37-C) were expressed in Escherichia coli and purified for functional study. Unlike classic scorpine-like peptides, rEv37 and truncated peptides showed no cytolytic activity against bacteria or eukaryotic cells. Interestingly, rEv37 selectively inhibited Kv1.3 channel without effectively blocking Kv1.1 and Kv1.2 channels. Neither Ev37-N nor Ev37-C blocked Kv1.3 channel, suggesting that both the N-terminal and C-terminal domain of Ev37 are likely involved in the interaction with Kv1.3 channel. These results not only enrich our knowledge of scorpion toxins from scorpine-like subfamily but also provide a novel template with unique structure for designing new types of selective Kv1.3 blockers.

Tremendous intron length differences of the BmKBT and a novel BmKBT-like peptide genes provide a mechanical basis for the rapid or constitutive expression of the peptides

The cDNA sequence encoding a novel BmKBT-like peptide (referred to as BmKBy) was cloned and sequenced from the scorpion Mesobuthus martensii Karsch. Functional analysis indicated that both BmKBT and BmKBy possess strong toxicity in mice, but very weak toxicity in cotton bollworm. Phylogenetic analysis showed that BmKBy and BmKBT represent evolutionary intermediates between the α- and β-toxins from scorpions. The genomic sequences of BmKBT and BmKBy were also obtained. It is interesting to see that two genes, which contain an intron of 225 and 1529bp, respectively, exactly code for the BmKBT peptide. One gene, which contains an intron of 1312bp, codes for BmKBy. Given that genes with long introns favor constitutive expression, whereas those with short introns are rapidly regulated in response to stimulations, the BmKBT_a and BmKBT_b genes provide a mechanical basis for either constitutive expression or rapid generation of the toxic peptides in response to different signals.

Selective inhibition of CCR7(-) effector memory T cell activation by a novel peptide targeting Kv1.3 channel in a rat experimental autoimmune encephalomyelitis model

The voltage-gated Kv1.3 K(+) channel in effector memory T cells serves as a new therapeutic target for multiple sclerosis. In our previous studies, the novel peptide ADWX-1 was designed and synthesized as a specific Kv1.3 blocker. However, it is unclear if and how ADWX-1 alleviates experimental autoimmune encephalomyelitis, a model for multiple sclerosis. In this study, the administration of ADWX-1 significantly ameliorated the rat experimental autoimmune encephalomyelitis model by selectively inhibiting CD4(+)CCR7(-) phenotype effector memory T cell activation. In contrast, the Kv1.3-specific peptide had little effect on CD4(+)CCR7(+) cells, thereby limiting side effects. Furthermore, we determined that ADWX-1 is involved in the regulation of NF-κB signaling through upstream protein kinase C-θ (PKCθ) in the IL-2 pathway of CD4(+)CCR7(-) cells. The elevated expression of Kv1.3 mRNA and protein in activated CD4(+)CCR7(-) cells was reduced by ADWX-1 engagement; however, an apparent alteration in CD4(+)CCR7(+) cells was not observed. Moreover, the selective regulation of the Kv1.3 channel gene expression pattern by ADWX-1 provided a further and sustained inhibition of the CD4(+)CCR7(-) phenotype, which depends on the activity of Kv1.3 to modulate its activation signal. In addition, ADWX-1 mediated the activation of differentiated Th17 cells through the CCR7(-) phenotype. The efficacy of ADWX-1 is supported by multiple functions, which are based on a Kv1.3(high) CD4(+)CCR7(-) T cell selectivity through two different pathways, including the classic channel activity-associated IL-2 pathway and the new Kv1.3 channel gene expression pathway.

Identification of a new specific Kv1.3 channel blocker, Ctri9577, from the scorpion Chaerilus tricostatus

Scorpion toxins are valuable resources for discovering new ion channel modulators and drug candidates. Potassium channel Kv1.3 is an important pharmacological target of T cell-mediated autoimmune diseases, which are encouraging the screening and design of the specific peptide blockers for Kv1.3 channel. Ctri9577, the first neurotoxin gene of Chaerilidae family was cloned from the venom of the scorpion Chaerilus tricostatus through the constructing its cDNA library. The sequence analysis showed that the mature peptide of Ctri9577 contained 39 amino acid residues including six conserved cysteines, whose low sequence similarity indicated that it was a new member of α-KTx15 subfamily. By using expression and purification technology, the recombinant peptide was obtained. Subsequently, the electrophysiological experiments indicated that the Ctri9577 peptide selectively inhibited Kv1.3 channel current with an IC(50) of 0.49±0.45 nM without effectively blocking potassium channels Kv1.1, Kv1.2, hERG and SK3. All these findings not only enrich the knowledge of toxins from the Chaerilidae family, but also present a novel potential drug candidate targeting Kv1.3 channels for the therapy of autoimmune diseases.