Targeting KCa1.1 Channels with a Scorpion Venom Peptide for the Therapy of Rat Models of Rheumatoid Arthritis

Exploring the therapeutic opportunities of potassium channels for the treatment of rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease that affects the synovial joint, which leads to inflammation, loss of function, joint destruction, and disability. The disease biology of RA involves complex interactions between genetic and environmental factors and is strongly associated with various immune cells, and each of the cell types contributes differently to disease pathogenesis. Several immunomodulatory molecules, such as cytokines, are secreted from the immune cells and intervene in the pathogenesis of RA. In immune cells, membrane proteins such as ion channels and transporters mediate the transport of charged ions to regulate intracellular signaling pathways. Ion channels control the membrane potential and effector functions such as cytotoxic activity. Moreover, clinical studies investigating patients with mutations and alterations in ion channels and transporters revealed their importance in effective immune responses. Recent studies have shown that voltage-gated potassium channels and calcium-activated potassium channels and their subtypes are involved in the regulation of immune cells and RA. Due to the role of these channels in the pathogenesis of RA and from multiple pieces of clinical evidence, they can be considered therapeutic targets for the treatment of RA. Here, we describe the role of voltage-gated and calcium-activated potassium channels and their subtypes in RA and their pharmacological application as drug targets.

The Bi-Functional Paxilline Enriched in Skin Secretion of Tree Frogs (Hyla japonica) Targets the KCNK18 and BKCa Channels

The skin secretion of tree frogs contains a vast array of bioactive chemicals for repelling predators, but their structural and functional diversity is not fully understood. Paxilline (PAX), a compound synthesized by Penicillium paxilli, has been known as a specific antagonist of large conductance Ca2+-activated K+ Channels (BKCa). Here, we report the presence of PAX in the secretions of tree frogs (Hyla japonica) and that this compound has a novel function of inhibiting the potassium channel subfamily K member 18 (KCNK18) channels of their predators. The PAX-induced KCNK18 inhibition is sufficient to evoke Ca2+ influx in charybdotoxin-insensitive DRG neurons of rats. By forming π-π stacking interactions, four phenylalanines located in the central pore of KCNK18 stabilize PAX to block the ion permeation. For PAX-mediated toxicity, our results from animal assays suggest that the inhibition of KCNK18 likely acts synergistically with that of BKCa to elicit tingling and buzzing sensations in predators or competitors. These results not only show the molecular mechanism of PAX-KCNK18 interaction, but also provide insights into the defensive effects of the enriched PAX.

A bioengineered probiotic for the oral delivery of a peptide Kv1.3 channel blocker to treat rheumatoid arthritis

Engineered microbes for the delivery of biologics are a promising avenue for the treatment of various conditions such as chronic inflammatory disorders and metabolic disease. In this study, we developed a genetically engineered probiotic delivery system that delivers a peptide to the intestinal tract with high efficacy. We constructed an inducible system in the probiotic Lactobacillus reuteri to secrete the Kv1.3 potassium blocker ShK-235 (LrS235). We show that LrS235 culture supernatants block Kv1.3 currents and preferentially inhibit human T effector memory (T_EM) lymphocyte proliferation in vitro. A single oral gavage of healthy rats with LrS235 resulted in sufficient functional ShK-235 in the circulation to reduce inflammation in a delayed-type hypersensitivity model of atopic dermatitis mediated by T_EM cells. Furthermore, the daily oral gavage of LrS235 dramatically reduced clinical signs of disease and joint inflammation in rats with a model of rheumatoid arthritis without eliciting immunogenicity against ShK-235. This work demonstrates the efficacy of using the probiotic L. reuteri as a novel oral delivery platform for the peptide ShK-235 and provides an efficacious strategy to deliver other biologics with great translational potential.

The role of ion channels in immune-related diseases

Ion channel is an integral membrane protein that allows the permeation of charge ions across hydrophobic phospholipid membranes, including plasma membranes and organelle membranes (such as mitochondria, endoplasmic reticulum and vacuoles), which are widely distributed in various cells and tissues, such as cardiomyocytes, smooth muscle cells, and nerve cells. Ion channels establish membrane potential by regulating ion concentration and membrane potential. Membrane potential plays an important role in cells. Studies have shown that ion channels play a role in a number of immune-related diseases caused by functional defects in ion channels on immune or non-immune cells in major human organs, usually affecting specific organs or multiple organs. The present review discusses the relationship between ion channels and immune diseases in major organs of the human body.

Mapping the functional expression of auxiliary subunits of KCa1.1 in glioblastoma

Glioblastoma (GBM) is the most aggressive glial tumor, where ion channels, including K_Ca1.1, are candidates for new therapeutic options. Since the auxiliary subunits linked to K_Ca1.1 in GBM are largely unknown we used electrophysiology combined with pharmacology and gene silencing to address the functional expression of K_Ca1.1/β subunits complexes in both primary tumor cells and in the glioblastoma cell line U-87 MG. The pattern of the sensitivity (activation/inhibition) of the whole-cell currents to paxilline, lithocholic acid, arachidonic acid, and iberiotoxin; the presence of inactivation of the whole-cell current along with the loss of the outward rectification upon exposure to the reducing agent DTT collectively argue that K_Ca1.1/β3 complex is expressed in U-87 MG. Similar results were found using human primary glioblastoma cells isolated from patient samples. Silencing the β3 subunit expression inhibited carbachol-induced Ca²⁺ transients in U-87 MG thereby indicating the role of the K_Ca1.1/β3 in the Ca²⁺ signaling of glioblastoma cells. Functional expression of the K_Ca1.1/β3 complex, on the other hand, lacks cell cycle dependence. We suggest that the K_Ca1.1/β3 complex may have diagnostic and therapeutic potential in glioblastoma in the future.

A non-lethal method for studying scorpion venom gland transcriptomes, with a review of potentially suitable taxa to which it can be applied

Scorpion venoms are mixtures of proteins, peptides and small molecular compounds with high specificity for ion channels and are therefore considered to be promising candidates in the venoms-to-drugs pipeline. Transcriptomes are important tools for studying the composition and expression of scorpion venom. Unfortunately, studying the venom gland transcriptome traditionally requires sacrificing the animal and therefore is always a single snapshot in time. This paper describes a new way of generating a scorpion venom gland transcriptome without sacrificing the animal, thereby allowing the study of the transcriptome at various time points within a single individual. By comparing these venom-derived transcriptomes to the traditional whole-telson transcriptomes we show that the relative expression levels of the major toxin classes are similar. We further performed a multi-day extraction using our proposed method to show the possibility of doing a multiple time point transcriptome analysis. This allows for the study of patterns of toxin gene activation over time a single individual, and allows assessment of the effects of diet, season and other factors that are known or likely to influence intraindividual venom composition. We discuss the gland characteristics that may allow this method to be successful in scorpions and provide a review of other venomous taxa to which this method may potentially be successfully applied.

New potential therapeutic approaches targeting synovial fibroblasts in rheumatoid arthritis

Synovial cells play a key role in joint destruction during chronic inflammation. In particular, activated synovial fibroblasts (SFs) undergo intrinsic alterations leading to an aggressive phenotype mediating cartilage destruction and bone erosion in rheumatoid arthritis (RA). Recent research has revealed a number of targets to control arthritogenic changes in SFs. Therefore, identification of SF phenotypes, control of epigenetic changes, modulation of cellular functions, or regulation of the activity of cation channels and different signaling pathways has been investigated. Although many of these approaches have shown efficacy in vitro and in animal models of RA, further research is needed to select the most relevant targets for drug development. This review is focused on the role of SFs as a potential strategy to discover novel therapeutic targets in RA aimed at preserving joint architecture and function.

A potent peptide-steroid conjugate accumulates in cartilage and reverses arthritis without evidence of systemic corticosteroid exposure

On-target, off-tissue toxicity limits the systemic use of drugs that would otherwise reduce symptoms or reverse the damage of arthritic diseases, leaving millions of patients in pain and with limited physical mobility. We identified cystine-dense peptides (CDPs) that rapidly accumulate in cartilage of the knees, ankles, hips, shoulders, and intervertebral discs after systemic administration. These CDPs could be used to concentrate arthritis drugs in joints. A cartilage-accumulating peptide, CDP-11R, reached peak concentration in cartilage within 30 min after administration and remained detectable for more than 4 days. Structural analysis of the peptides by crystallography revealed that the distribution of positive charge may be a distinguishing feature of joint-accumulating CDPs. In addition, quantitative whole-body autoradiography showed that the disulfide-bonded tertiary structure is critical for cartilage accumulation and retention. CDP-11R distributed to joints while carrying a fluorophore imaging agent or one of two different steroid payloads, dexamethasone (dex) and triamcinolone acetonide (TAA). Of the two payloads, the dex conjugate did not advance because the free drug released into circulation was sufficient to cause on-target toxicity. In contrast, the CDP-11R-TAA conjugate alleviated joint inflammation in the rat collagen-induced model of rheumatoid arthritis while avoiding toxicities that occurred with nontargeted steroid treatment at the same molar dose. This conjugate shows promise for clinical development and establishes proof of concept for multijoint targeting of disease-modifying therapeutic payloads.

ZhiJingSan Inhibits Osteoclastogenesis via Regulating RANKL/NF-κB Signaling Pathway and Ameliorates Bone Erosion in Collagen-Induced Mouse Arthritis

Bone erosion is the most evident pathological condition of rheumatoid arthritis (RA), which is the main cause of joint deformities and disability in RA patients. At present, the conventional RA drugs have not achieved satisfactory effect in improving bone erosion. ZhiJingSan (ZJS), which is a traditional Chinese prescription composed of scolopendra (dried body of Scolopendra subspinipes mutilans L. Koch, scolopendridae) and scorpion (dried body of Buthus martensii Karsch, Buthus), exhibits anti-rheumatism, analgesic and joint deformities improvement effects. This study aimed to assess the therapeutic effect of ZJS on RA bone erosion and to elucidate the underlying mechanism. The effect of ZJS on RA bone erosion was investigated in a murine model of bovine collagen-induced arthritis (CIA), and the underlying mechanism was investigated in vitro in an osteoclast differentiation cell model. Administration of ZJS delayed the onset of arthritis, alleviated joint inflammation, and attenuated bone erosion in the CIA mice. Meanwhile, ZJS decreased the serum levels of TNF-α, IL-6, and anti-bovine collagen II-specific antibodies. Furthermore, ZJS treatment reduced the number of osteoclasts and the expression of cathepsin K in the ankle joints of CIA mice. ZJS also inhibited receptor activator of NF-κB ligand (RANKL)-induced osteoclast differentiation and the expression of MMP9 and cathepsin K in vitro. Mechanistically, ZJS blocked RANKL-induced p65 phosphorylation, nucleation, and inhibited the expression of downstream NFATc1 and c-Fos in bone marrow-derived macrophages (BMMs). Taken together, ZJS exerts a therapeutic effect on bone erosion in CIA mice by inhibiting RANKL/NF-κB-mediated osteoclast differentiation, which suggested that ZJS is a promising prescription for treating RA bone erosion.

Activation of voltage-gated sodium channels by BmK NT1 augments NMDA receptor function through Src family kinase signaling pathway in primary cerebellar granule cell cultures

Voltage-gated sodium channels (VGSCs) are responsible for the generation and propagation of action potentials in excitable cells and are the molecular targets of an array of neurotoxins. BmK NT1, an α-scorpion toxin obtained from the scorpion Buthus martensii Karsch (BmK), produces neurotoxicity that is associated with extracellular Ca²⁺ influx through Na⁺-Ca²⁺ exchangers, N-methyl-d-aspartic acid (NMDA) receptors, and L-type Ca²⁺ channels in cultured cerebellar granule cells (CGCs). In the present study, we demonstrated that BmK NT1 triggered concentration-dependent release of excitatory neurotransmitters, glutamate and aspartate; both effects were eliminated by VGSC blocker, tetrodotoxin. More importantly, we demonstrated that a threshold concentration of BmK NT1 that produced marginal Ca²⁺ influx and neuronal death augmented glutamate-induced Ca²⁺ elevation and neuronal death in CGCs. BmK NT1-augmented glutamate-induced Ca²⁺ influx and neuronal death were suppressed by tetrodotoxin and MK-801 suggesting that the augmentation was through activation of VGSCs and NMDA receptors. Consistently, BmK NT1 also enhanced NMDA-induced Ca²⁺ influx. Further mechanistic investigations demonstrated that BmK NT1 increased the expression level of NMDA receptors on the plasma membrane and increased the phosphorylation level of NR2B at Tyr1472. Src family kinase inhibitor, 1-tert-butyl-3-(4-chlorophenyl)pyrazolo[3,4-d]pyrimidin-4-yl]amine (PP2), but not the inactive analogue, 4-amino-1-phenylpyrazolo[3,4-d]pyrimidine (PP3), eliminated BmK NT1-triggered NR2B phosphorylation, NMDA receptor trafficking, as well as BmK NT1-augmented NMDA Ca²⁺ response and neuronal death. Considered together, these data demonstrated that both presynaptic (excitatory amino acid release) and postsynaptic mechanisms (augmentation of NMDA receptor function) are critical for VGSC activation-induced neurotoxicity in primary CGC cultures.

Venom peptides in cancer therapy: An updated review on cellular and molecular aspects

Based on the high incidence and mortality rates of cancer, its therapy remains one of the most vital challenges in the field of medicine. Consequently, enhancing the efficacy of currently applied treatments and finding novel strategies are of great importance for cancer treatment. Venoms are important sources of a variety of bioactive compounds including salts, small molecules, macromolecules, proteins, and peptides that are defined as toxins. They can exhibit different pharmacological effects, and in recent years, their anti-tumor activities have gained significant attention. Several different compounds are responsible for the anti-tumor activity of venoms, and peptides are one of them. In the present review, we discuss the possible anti-tumor activities of venom peptides by highlighting molecular pathways and mechanisms through which these molecules can act effectively. Venom peptides can induce cell death in cancer cells and can substantially enhance the efficacy of chemotherapy and radiotherapy. Also, the venom peptides can mitigate the migration of cancer cells via suppression of angiogenesis and epithelial-to-mesenchymal transition. Notably, nanoparticles have been applied in enhancing the bioavailability of venom peptides and providing targeted delivery, thereby leading to their elevated anti-tumor activity and potential application for cancer therapy.

Antioxidant Carbon Nanoparticles Inhibit Fibroblast-Like Synoviocyte Invasiveness and Reduce Disease Severity in a Rat Model of Rheumatoid Arthritis

Reactive oxygen species have been involved in the pathogenesis of rheumatoid arthritis (RA). Our goal was to determine the effects of selectively scavenging superoxide (O2•-) and hydroxyl radicals with antioxidant nanoparticles, called poly(ethylene glycol)-functionalized hydrophilic carbon clusters (PEG-HCCs), on the pathogenic functions of fibroblast-like synoviocytes (FLS) from patients with rheumatoid arthritis (RA) and on the progression of an animal model of RA. We used human FLS from patients with RA to determine PEG-HCC internalization and effects on FLS cytotoxicity, invasiveness, proliferation, and production of proteases. We used the pristane-induced arthritis (PIA) rat model of RA to assess the benefits of PEG-HCCs on reducing disease severity. PEG-HCCs were internalized by RA-FLS, reduced their intracellular O2•-, and reduced multiple measures of their pathogenicity in vitro, including proliferation and invasion. In PIA, PEG-HCCs caused a 65% reduction in disease severity, as measured by a standardized scoring system of paw inflammation and caused a significant reduction in bone and tissue damage, and circulating rheumatoid factor. PEG-HCCs did not induce lymphopenia during PIA. Our study demonstrated a role for O2•- and hydroxyl radicals in the pathogenesis of a rat model of RA and showed efficacy of PEG-HCCs in treating a rat model of RA.

Modulation of TRPV4 and BKCa for treatment of brain diseases

As a member of transient receptor potential family, the transient receptor potential vanilloid 4 (TRPV4) is a kind of nonselective calcium-permeable cation channel, which belongs to non-voltage gated Ca²⁺ channel. Large-conductance Ca²⁺-activated K⁺ channel (BKCa) represents a unique superfamily of Ca²⁺-activated K⁺ channel (KCa) that is both voltage and intracellular Ca²⁺ dependent. Not surprisingly, aberrant function of either TRPV4 or BKCa in neurons has been associated with brain disorders, such as Alzheimer's disease, cerebral ischemia, brain tumor, epilepsy, as well as headache. In these diseases, vascular dysfunction is a common characteristic. Notably, endothelial and smooth muscle TRPV4 can mediate BKCa to regulate cerebral blood flow and pressure. Therefore, in this review, we not only discuss the diverse functions of TRPV4 and BKCa in neurons to integrate relative signaling pathways in the context of cerebral physiological and pathological situations respectively, but also reveal the relationship between TRPV4 and BKCa in regulation of cerebral vascular tone as an etiologic factor. Based on these analyses, this review demonstrates the effective mechanisms of compounds targeting these two channels, which may be potential therapeutic strategies for diseases in the brain.

BmK NSP, a new sodium channel activator from Buthus martensii Karsch, promotes neurite outgrowth in primary cultured spinal cord neurons

Scorpion venom is a rich source of bioactive compounds that affect neuronal excitability by modulating the activities of various channels/receptors. In the current study, guided by a Ca²⁺ mobilization assay, we purified a new neuroactive peptide designated as BmK NSP (Buthus martensii Karsch neurite-stimulating peptide, MW: 7064.30 Da). The primary structure of BmK NSP was determined by Edman degradation. BmK NSP concentration-dependently elevated intracellular Ca²⁺ concentration ([Ca²⁺]_i) with an EC₅₀ value of 4.18 μM in primary cultured spinal cord neurons (SCNs). Depletion of extracellular Ca²⁺ abolished BmK NSP-triggered Ca²⁺ response. Moreover, we demonstrated that BmK NSP-induced Ca²⁺ response was partially suppressed by the inhibitors of L-type Ca²⁺ channels, Na⁺-Ca²⁺ exchangers and NMDA receptors and was abolished by voltage-gated sodium channel (VGSC) blocker, tetrodotoxin. Whole-cell patch clamp recording demonstrated that BmK NSP delayed VGSC inactivation (EC₅₀ = 1.10 μM) in SCNs. BmK NSP enhanced neurite outgrowth in a non-monotonic manner that peaked at ~30 nM in SCNs. BmK NSP-promoted neurite outgrowth was suppressed by the inhibitors of L-type Ca²⁺ channels, NMDA receptors, and VGSCs. Considered together, these data demonstrate that BmK NSP is a new α-scorpion toxin that enhances neurite outgrowth through main routes of Ca²⁺ influx. Modulation of VGSC activity by α-scorpion toxin might represent a novel strategy to regulate the neurogenesis in SCNs.

KCa1.1 and Kv1.3 channels regulate the interactions between fibroblast-like synoviocytes and T lymphocytes during rheumatoid arthritis

BACKGROUND

Fibroblast-like synoviocytes (FLS) and CCR7- effector memory T (TEM) cells are two of the major cell types implicated in the progression of rheumatoid arthritis (RA). In particular, FLS become highly invasive, whereas TEM cells proliferate and secrete proinflammatory cytokines, during RA. FLS and T cells may also interact and influence each other's phenotypes. Inhibition of the pathogenic phenotypes of both FLS and TEM cells can be accomplished by selectively blocking the predominant potassium channels that they upregulate during RA: KCa1.1 (BK, Slo1, MaxiK, KCNMA1) upregulated by FLS and Kv1.3 (KCNA3) upregulated by activated TEM cells. In this study, we investigated the roles of KCa1.1 and Kv1.3 in regulating the interactions between FLS and TEM cells and determined if combination therapies of KCa1.1- and Kv1.3-selective blockers are more efficacious than monotherapies in ameliorating disease in rat models of RA.

METHODS

We used in vitro functional assays to assess the effects of selective KCa1.1 and Kv1.3 channel inhibitors on the interactions of FLS isolated from rats with collagen-induced arthritis (CIA) with syngeneic TEM cells. We also used flow cytometric analyses to determine the effects of KCa1.1 blockers on the expression of proteins used for antigen presentation on CIA-FLS. Finally, we used the CIA and pristane-induced arthritis models to determine the efficacy of combinatorial therapies of KCa1.1 and Kv1.3 blockers in reducing disease severity compared with monotherapies.

RESULTS

We show that the interactions of FLS from rats with CIA and of rat TEM cells are regulated by KCa1.1 and Kv1.3. Inhibiting KCa1.1 on FLS reduces the ability of FLS to stimulate TEM cell proliferation and migration, and inhibiting Kv1.3 on TEM cells reduces TEM cells' ability to enhance FLS expression of KCa1.1 and major histocompatibility complex class II protein, as well as stimulates their invasion. Furthermore, we show that combination therapies of selective KCa1.1 and Kv1.3 blockers are more efficacious than monotherapies at reducing signs of disease in two rat models of RA.

CONCLUSIONS

Our results demonstrate the importance of KCa1.1 and Kv1.3 in regulating FLS and TEM cells during RA, as well as the value of combined therapies targeting both of these cell types to treat RA.

Venom content and toxicity regeneration after venom gland depletion by electrostimulation in the scorpion Centruroides limpidus

The scorpion venom is a cocktail of many components. Its composition can exhibit a level of plasticity in response to different behavioral and environmental factors, leading to intraspecific variation. The toxicity and specificity of scorpion venoms appear to be taxon-dependent, due to a co-evolutionary interaction with prey and predators, which shaped the composition at the molecular level. The venom regeneration by the venom glands is an asynchronous process, in which particular components are expressed at different stages and at different rates. According to this, it can be reasonably assumed that the regeneration of toxicity in the venom is also asynchronous. In this work, we studied the toxicity regeneration dynamics by the scorpion Centruroides limpidus after full venom depletion by electrical stimulation. For this, we evaluated the toxicity of venom samples extracted at different days post depletion, against insects (crickets) and mammals (humans, by assessing the venom activity on the human voltage-dependent Na⁺ channel Nav1.6). The regeneration of toxicity against humans lagged behind that against crickets (13 vs 10 days, respectively). Thirteen days after depletion the venom seems to be replenished. Our results show asynchrony in the regeneration of species-specific toxic activity in the venom of Centruroides limpidus. The understanding of the venom regeneration kinetics for the different scorpion species will help to design venom extraction protocols that could maximize the yield and quality of the collected venoms.

Physiological Roles and Therapeutic Potential of Ca2+ Activated Potassium Channels in the Nervous System

Within the potassium ion channel family, calcium activated potassium (K_Ca) channels are unique in their ability to couple intracellular Ca²⁺ signals to membrane potential variations. K_Ca channels are diversely distributed throughout the central nervous system and play fundamental roles ranging from regulating neuronal excitability to controlling neurotransmitter release. The physiological versatility of K_Ca channels is enhanced by alternative splicing and co-assembly with auxiliary subunits, leading to fundamental differences in distribution, subunit composition and pharmacological profiles. Thus, understanding specific K_Ca channels’ mechanisms in neuronal function is challenging. Based on their single channel conductance, K_Ca channels are divided into three subtypes: small (SK, 4–14 pS), intermediate (IK, 32–39 pS) and big potassium (BK, 200–300 pS) channels. This review describes the biophysical characteristics of these K_Ca channels, as well as their physiological roles and pathological implications. In addition, we also discuss the current pharmacological strategies and challenges to target K_Ca channels for the treatment of various neurological and psychiatric disorders.