Expression of neonatal Nav1.5 in human brain astrocytoma and its effect on proliferation, invasion and apoptosis of astrocytoma cells

Voltage-gated sodium channels in cancer and their specific inhibitors

Voltage-gated sodium channels (VGSCs) participate in generating and spreading action potentials in electrically excited cells such as neurons and muscle fibers. Abnormal expression of VGSCs has been observed in various types of tumors, while they are either not expressed or expressed at a low level in the matching normal tissue. Hence, this abnormal expression suggests that VGSCs confer some advantage or viability on tumor cells, making them a valuable indicator for identifying tumor cells. In addition, overexpression of VGSCs increased the ability of cancer cells to metastasize and invade, as well as correlated with the metastatic behavior of different cancers. Therefore, blocking VGSCs presents a new strategy for the treatment of cancers. A portion of this review summarizes the structure and function of VGSCs and also describes the correlation between VGSCs and cancers. Most importantly, we provide an overview of current research on various subtype-selective VGSC inhibitors and updates on ongoing clinical studies.

Voltage-gated sodium channels: from roles and mechanisms in the metastatic cell behavior to clinical potential as therapeutic targets

During the second half of the last century, the prevalent knowledge recognized the voltage-gated sodium channels (VGSCs) as the proteins responsible for the generation and propagation of action potentials in excitable cells. However, over the last 25 years, new non-canonical roles of VGSCs in cancer hallmarks have been uncovered. Their dysregulated expression and activity have been associated with aggressive features and cancer progression towards metastatic stages, suggesting the potential use of VGSCs as cancer markers and prognostic factors. Recent work has elicited essential information about the signalling pathways modulated by these channels: coupling membrane activity to transcriptional regulation pathways, intracellular and extracellular pH regulation, invadopodia maturation, and proteolytic activity. In a promising scenario, the inhibition of VGSCs with FDA-approved drugs as well as with new synthetic compounds, reduces cancer cell invasion in vitro and cancer progression in vivo. The purpose of this review is to present an update regarding recent advances and ongoing efforts to have a better understanding of molecular and cellular mechanisms on the involvement of both pore-forming α and auxiliary β subunits of VGSCs in the metastatic processes, with the aim at proposing VGSCs as new oncological markers and targets for anticancer treatments.

Voltage-Gated Sodium Channel NaV1.7 Inhibitors with Potent Anticancer Activities in Medullary Thyroid Cancer Cells

Our results from quantitative RT-PCR, Western blotting, immunohistochemistry, and the tissue microarray of medullary thyroid cancer (MTC) cell lines and patient specimens confirm that VGSC subtype NaV1.7 is uniquely expressed in aggressive MTC and not expressed in normal thyroid cells and tissues. We establish the druggability of NaV1.7 in MTC by identifying a novel inhibitor (SV188) and investigate its mode of binding and ability to inhibit INa current in NaV1.7. The whole-cell patch-clamp studies of the SV188 in the NaV1.7 channels expressed in HEK-293 cells show that SV188 inhibited the INa current in NaV1.7 with an IC50 value of 3.6 µM by a voltage- and use-dependent blockade mechanism, and the maximum inhibitory effect is observed when the channel is open. SV188 inhibited the viability of MTC cell lines, MZ-CRC-1 and TT, with IC50 values of 8.47 μM and 9.32 μM, respectively, and significantly inhibited the invasion of MZ-CRC-1 cells by 35% and 52% at 3 μM and 6 μM, respectively. In contrast, SV188 had no effect on the invasion of TT cells derived from primary tumor, which have lower basal expression of NaV1.7. In addition, SV188 at 3 μM significantly inhibited the migration of MZ-CRC-1 and TT cells by 27% and 57%, respectively.

Ion channels as molecular targets of glioblastoma electrotherapy

Therapies with weak, non-ionizing electromagnetic fields comprise FDA-approved treatments such as Tumor Treating Fields (TTFields) that are used for adjuvant therapy of glioblastoma. In vitro data and animal models suggest a variety of biological TTFields effects. In particular, effects ranging from direct tumoricidal, radio- or chemotherapy-sensitizing, metastatic spread-inhibiting, up to immunostimulation have been described. Diverse underlying molecular mechanisms, such as dielectrophoresis of cellular compounds during cytokinesis, disturbing the formation of the spindle apparatus during mitosis, and perforating the plasma membrane have been proposed. Little attention, however, has been paid to molecular structures that are predestinated to percept electromagnetic fields-the voltage sensors of voltage-gated ion channels. The present review article briefly summarizes the mode of action of voltage sensing by ion channels. Moreover, it introduces into the perception of ultra-weak electric fields by specific organs of fishes with voltage-gated ion channels as key functional units therein. Finally, this article provides an overview of the published data on modulation of ion channel function by diverse external electromagnetic field protocols. Combined, these data strongly point to a function of voltage-gated ion channels as transducers between electricity and biology and, hence, to voltage-gated ion channels as primary targets of electrotherapy.

Unmasking of Brugada syndrome by lamotrigine in a patient with pre-existing epilepsy: A case report with review of the literature

Brugada syndrome is an inherited cardiac channelopathy arising from mutations in voltage-gated cardiac sodium channels. Idiopathic epilepsy portrays a coalescent underlying pathophysiological mechanism pertaining to the premature excitation of neuronal voltage-gated ion channels resulting in the disruption of presynaptic neurons and the unregulated release of excitatory neurotransmitters. The coexistence of epilepsy and Brugada syndrome may be explained by mutations in voltage-gated ion channels, which are coexpressed in cardiac and neural tissue. Moreover, the incidence of sudden unexpected death in epilepsy has been associated with malignant cardiac arrhythmias in the presence of mutations in voltage-gated ion channels. Lamotrigine is an antiepileptic drug that inhibits neuronal voltage-gated sodium channels, thus stabilizing neural impulse propagation and controlling seizure activity in the brain. However, lamotrigine has been shown to inhibit cardiac voltage-gated sodium channels resulting in a potential arrhythmogenic effect and the ability to unmask Brugada syndrome in genetically susceptible individuals. We are reporting a case of a 27-year-old male patient with a background of presumed idiopathic epilepsy who was initiated on lamotrigine therapy resulting in the unmasking of Brugada syndrome and the onset of syncopal episodes. This case provides further evidence for the arrhythmogenic capacity of lamotrigine and highlights the relationship between epilepsy and Brugada syndrome. In this report, we aim to review the current literature regarding the associations between epilepsy and Brugada syndrome and the impact of lamotrigine therapy on such patients.

ELTD1 as a multi-focal target for malignant gliomas: preclinical studies

BACKGROUND

Glioblastoma (GBM) is the most aggressive malignant primary brain tumor in adults. These high-grade gliomas undergo unregulated vascular angiogenesis, migration and cell proliferation allowing the tumor cells to evade cell-cycle checkpoints and apoptotic pathways. The Epidermal growth factor, latrophilin, and seven transmembrane domain-containing 1 on chromosome 1 (ELTD1) is an angiogenic biomarker that is highly expressed in malignant gliomas. Novel treatments targeting ELTD1 with monovalent monoclonal (mmAb) and single chain variable fragment (scFv) antibodies were effective in increasing animal survival, decreasing tumor volume and normalizing the vasculature. Due to the success of our antibody treatments on angiogenesis, this study sought to determine if our anti-ELTD1 treatments affected other aspects of tumorigenesis (cell proliferation, migration, and apoptosis) in a G55 glioma xenograft preclinical mouse model.

METHODS

Tumor tissue from untreated, mmAb and scFv anti-ELTD1 treated animals was used to quantify the positivity levels of human mitochondrial antibody, c-MET and Ki-67 for cellular proliferation, migratory markers CD44v6, TRPM8, and BMP2, and cleaved caspase 3 to assess apoptotic activity.

RESULTS

This approach demonstrated that our anti-ELTD1 treatments directly affected and decreased the human tumor cells within the tumor region. Additionally, there was a significant decrease in both cellular proliferation and migration due to anti-ETLD1 therapy. Lastly, anti-ELTD1 treatments successfully increased apoptotic activity within the tumor region.

CONCLUSION

Our data suggest that anti-ELTD1 therapies would be effective against malignant gliomas by having a multi-focal effect and targeting all four aspects of tumorigenesis.

Sodium channel β1 subunits are post-translationally modified by tyrosine phosphorylation, S-palmitoylation, and regulated intramembrane proteolysis

Voltage-gated sodium channel (VGSC) β1 subunits are multifunctional proteins that modulate the biophysical properties and cell-surface localization of VGSC α subunits and participate in cell-cell and cell-matrix adhesion, all with important implications for intracellular signal transduction, cell migration, and differentiation. Human loss-of-function variants in SCN1B, the gene encoding the VGSC β1 subunits, are linked to severe diseases with high risk for sudden death, including epileptic encephalopathy and cardiac arrhythmia. We showed previously that β1 subunits are post-translationally modified by tyrosine phosphorylation. We also showed that β1 subunits undergo regulated intramembrane proteolysis via the activity of β-secretase 1 and γ-secretase, resulting in the generation of a soluble intracellular domain, β1-ICD, which modulates transcription. Here, we report that β1 subunits are phosphorylated by FYN kinase. Moreover, we show that β1 subunits are S-palmitoylated. Substitution of a single residue in β1, Cys-162, to alanine prevented palmitoylation, reduced the level of β1 polypeptides at the plasma membrane, and reduced the extent of β1-regulated intramembrane proteolysis, suggesting that the plasma membrane is the site of β1 proteolytic processing. Treatment with the clathrin-mediated endocytosis inhibitor, Dyngo-4a, re-stored the plasma membrane association of β1-p.C162A to WT levels. Despite these observations, palmitoylation-null β1-p.C162A modulated sodium current and sorted to detergent-resistant membrane fractions normally. This is the first demonstration of S-palmitoylation of a VGSC β subunit, establishing precedence for this post-translational modification as a regulatory mechanism in this protein family.

Pleiotropic Anticancer Properties of Scorpion Venom Peptides: Rhopalurus princeps Venom as an Anticancer Agent

To date, the success of conventional chemotherapy, radiotherapy, and targeted biological therapies in cancer treatment is not satisfactory. The main reasons for such outcomes rely on low target selectivity, primarily in chemo- and radiotherapy, ineffectiveness to metastatic disease, drug resistance, and severe side effects. Although immune checkpoint inhibitors may offer better clinical promise, success is still limited. Since cancer is a complex systemic disease, the need for new therapeutic modalities that can target or block several steps of cancer cell characteristics, modulate or repolarize immune cells, and are less toxic to healthy tissues is essential. Of these promising therapeutic modalities are pleiotropic natural products in which scorpion venom (SV) is an excellent example. SV consists of complex bioactive peptides that are disulfide-rich of different peptides’ length, potent, stable, and exerts various multi-pharmacological actions. SV peptides also contain ion channel inhibitors. These ion channels are dysregulated and overexpressed in cancer cells, and play essential roles in cancer development and invasion, as well as depolarizing immune cells. Furthermore, SV has been found to induce cancer cell apoptosis, and inhibit cancer cells proliferation, invasion, metastasis, and angiogenesis. In the current review, we are presenting data that show the pleiotropic effect of SV against different types of human cancer as well as revealing one potential anticancer agent, Rhopalurus princeps venom. Furthermore, we are addressing what is needed to be done to translate these potential cancer therapeutics to the clinic.

Optimized monoclonal antibody treatment against ELTD1 for GBM in a G55 xenograft mouse model

Glioblastoma is an aggressive brain tumour found in adults, and the therapeutic approaches available have not significantly increased patient survival. Recently, we discovered that ELTD1, an angiogenic biomarker, is highly expressed in human gliomas. Polyclonal anti-ELTD1 treatments were effective in glioma pre-clinical models, however, pAb binding is potentially promiscuous. Therefore, the aim of this study was to determine the effects of an optimized monoclonal anti-ELTD1 treatment in G55 xenograft glioma models. MRI was used to assess the effects of the treatments on animal survival, tumour volumes, perfusion rates and binding specificity. Immunohistochemistry and histology were conducted to confirm and characterize microvessel density and Notch1 levels, and to locate the molecular probes. RNA-sequencing was used to analyse the effects of the mAb treatment. Our monoclonal anti-ELTD1 treatment significantly increased animal survival, reduced tumour volumes, normalized the vasculature and showed higher binding specificity within the tumour compared with both control- and polyclonal-treated mice. Notch1 positivity staining and RNA-seq results suggested that ELTD1 has the ability to interact with and interrupt Notch1 signalling. Although little is known about ELTD1, particularly about its ligand and pathways, our data suggest that our monoclonal anti-ELTD1 antibody is a promising anti-angiogenic therapeutic in glioblastomas.

Epigenetic changes in fibroblasts drive cancer metabolism and differentiation

Genomic changes that drive cancer initiation and progression contribute to the co-evolution of the adjacent stroma. The nature of the stromal reprogramming involves differential DNA methylation patterns and levels that change in response to the tumor and systemic therapeutic intervention. Epigenetic reprogramming in carcinoma-associated fibroblasts are robust biomarkers for cancer progression and have a transcriptional impact that support cancer epithelial progression in a paracrine manner. For prostate cancer, promoter hypermethylation and silencing of the RasGAP, RASAL3 that resulted in the activation of Ras signaling in carcinoma-associated fibroblasts. Stromal Ras activity initiated a process of macropinocytosis that provided prostate cancer epithelia with abundant glutamine for metabolic conversion to fuel its proliferation and a signal to transdifferentiate into a neuroendocrine phenotype. This epigenetic oncogenic metabolic/signaling axis seemed to be further potentiated by androgen receptor signaling antagonists and contributed to therapeutic resistance. Intervention of stromal signaling may complement conventional therapies targeting the cancer cell.

In Vivo Evidence for Voltage-Gated Sodium Channel Expression in Carcinomas and Potentiation of Metastasis

A wide body of evidence suggests that voltage-gated sodium channels (VGSCs) are expressed de novo in several human carcinomas where channel activity promotes a variety of cellular behaviours integral to the metastatic cascade. These include directional motility (including galvanotaxis), pH balance, extracellular proteolysis, and invasion. Contrary to the substantial in vitro data, however, evidence for VGSC involvement in the cancer process in vivo is limited. Here, we critically assess, for the first time, the available in vivo evidence, hierarchically from mRNA level to emerging clinical aspects, including protein-level studies, electrolyte content, animal tests, and clinical imaging. The evidence strongly suggests that different VGSC subtypes (mainly Nav1.5 and Nav1.7) are expressed de novo in human carcinoma tissues and generally parallel the situation in vitro. Consistent with this, tissue electrolyte (sodium) levels, quantified by clinical imaging, are significantly higher in cancer vs. matched non-cancer tissues. These are early events in the acquisition of metastatic potential by the cancer cells. Taken together, the multi-faceted evidence suggests that the VGSC expression has clinical (diagnostic and therapeutic) potential as a prognostic marker, as well as an anti-metastatic target. The distinct advantages offered by the VGSC include especially (1) its embryonic nature, demonstrated most clearly for the predominant neonatal Nav1.5 expression in breast and colon cancer, and (2) the specifically druggable persistent current that VGSCs develop under hypoxic conditions, as in growing tumours, which promotes invasiveness and metastasis.

Voltage-gated sodium channel Nav1.5 promotes proliferation, migration and invasion of oral squamous cell carcinoma

The protein voltage-gated sodium channel Nav1.5 is highly upregulated in various types of cancer and, in general, promotes cancer cell invasiveness and metastatic progression. A previous study found that Nav1.5 was highly expressed in poorly differentiated oral squamous cell carcinoma (OSCC). However, whether Nav1.5 enhances invasiveness and metastasis of OSCC are still unknown. In this study, we found that Nav1.5 was highly expressed in OSCC cell lines compared with normal oral keratinocyte HOK cell line by using western blot analysis. CCK-8 assay results revealed that downregulation of Nav1.5 expression by its specific siRNA reduced proliferation of OSCC HSC-3 cells. Moreover, transwell assay results showed Nav1.5 knockdown significantly inhibited migration and invasion of HSC-3 cells. Meanwhile, qRT-PCR and western blot analysis results showed that epidermal growth factor (EGF) induced Nav1.5 expression in a time- and dose-dependent manner. In addition, EGF promoted proliferation, migration and invasion of HSC-3 cells. Importantly, the Nav1.5 inhibitor tetrodotoxin significantly inhibited the proliferation of HSC-3 cells and impeded the migration and invasion of HSC-3 cells. Furthermore, it was found that siRNA-mediated knockdown of Nav1.5 also lessened the proliferation of HSC-3 cells and blocked the migration and invasion of HSC-3 cells. Taken together, these results indicate that Nav1.5 is involved in the progression of OSCC and Nav1.5 promotes the proliferation, migration and invasion of OSCC cells.

Contribution of voltage-gated sodium channel β-subunits to cervical cancer cells metastatic behavior

Background

Voltage-gated sodium (Na_V) channels are heteromeric proteins consisting of a single pore forming α-subunit associated with one or two auxiliary β-subunits. These channels are classically known for being responsible of action potential generation and propagation in excitable cells; but lately they have been reported as widely expressed and regulated in several human cancer types. We have previously demonstrated the overexpression of Na_V1.6 channel in cervical cancer (CeCa) biopsies and primary cultures, and its contribution to cell migration and invasiveness. Here, we investigated the expression of Na_V channels β-subunits (Na_Vβs) in the CeCa cell lines HeLa, SiHa and CaSki, and determined their contribution to cell proliferation, migration and invasiveness.

Methods

We assessed the expression of Na_Vβs in CeCa cell lines by performing RT-PCR and western blotting experiments. We also evaluated CeCa cell lines proliferation, migration, and invasion by in vitro assays, both in basal conditions and after inducing changes in Na_Vβs levels by transfecting specific cDNAs or siRNAs. The potential role of Na_Vβs in modulating the expression of Na_V α-subunits in the plasma membrane of CeCa cells was examined by the patch-clamp whole-cell technique. Furthermore, we investigated the role of Na_Vβ1 on cell cycle in SiHa cells by flow cytometry.

Results

We found that the four Na_Vβs are expressed in the three CeCa cell lines, even in the absence of functional Na_V α-subunit expression in the plasma membrane. Functional in vitro assays showed differential roles for Na_Vβ1 and Na_Vβ4, the latter as a cell invasiveness repressor and the former as a migration abolisher in CeCa cells. In silico analysis of Na_Vβ4 expression in cervical tissues corroborated the downregulation of this protein expression in CeCa vs normal cervix, supporting the evidence of Na_Vβ4’s role as a cell invasiveness repressor.

Conclusions

Our results contribute to the recent conception about Na_Vβs as multifunctional proteins involved in cell processes like ion channel regulation, cell adhesion and motility, and even in metastatic cell behaviors. These non-canonical functions of Na_Vβs are independent of the presence of functional Na_V α-subunits in the plasma membrane and might represent a new therapeutic target for the treatment of cervical cancer.

Electronic supplementary material

The online version of this article (10.1186/s12935-019-0757-6) contains supplementary material, which is available to authorized users.

The invasiveness of human cervical cancer associated to the function of NaV1.6 channels is mediated by MMP-2 activity

Voltage-gated sodium (Na_V) channels have been related with cell migration and invasiveness in human cancers. We previously reported the contribution of Na_V1.6 channels activity with the invasion capacity of cervical cancer (CeCa) positive to Human Papilloma Virus type 16 (HPV16), which accounts for 50% of all CeCa cases. Here, we show that Na_V1.6 gene (SCN8A) overexpression is a general characteristic of CeCa, regardless of the HPV type. In contrast, no differences were observed in Na_V1.6 channel expression between samples of non-cancerous and cervical intraepithelial neoplasia. Additionally, we found that CeCa cell lines, C33A, SiHa, CaSki and HeLa, express mainly the splice variant of SCN8A that lacks exon 18, shown to encode for an intracellularly localized Na_V1.6 channel, whereas the full-length adult form was present in CeCa biopsies. Correlatively, patch-clamp experiments showed no evidence of whole-cell sodium currents (I_Na) in CeCa cell lines. Heterologous expression of full-length Na_V1.6 isoform in C33A cells produced I_Na, which were sufficient to significantly increase invasion capacity and matrix metalloproteinase type 2 (MMP-2) activity. These data suggest that upregulation of Na_V1.6 channel expression occurs when cervical epithelium have been transformed into cancer cells, and that Na_V1.6-mediated invasiveness of CeCa cells involves MMP-2 activity. Thus, our findings support the notion about using Na_V channels as therapeutic targets against cancer metastasis.

Blocking the Nav1.5 channel using eicosapentaenoic acid reduces migration and proliferation of ovarian cancer cells

Activity of the voltage-gated Nav1.5 sodium channel has been reported to be involved in cell proliferation, cancer invasion and gene expression. In addition, eicosapentaenoic acid (EPA) has recently been suggested to inhibit ovarian cancer cell growth and suppress tumor metastasis. The present study aimed to explore the association between EPA, the Nav1.5 sodium channel and ovarian cancer cells. Using patch-clamp technique and RNA interference approaches, sodium currents were recorded in epithelial ovarian cancer cells, and it was confirmed that the Nav1.5 channel carried the sodium currents. Furthermore, EPA effectively inhibited sodium currents in a dose-dependent manner, shifted the steady-state inactivation curve of sodium currents to the hyperpolarizing direction and reduced sodium window currents. In addition, EPA induced a shift in the inactivation curve in a dose-dependent manner. Inhibition of the sodium channel, either by EPA or by Nav1.5 knockdown, attenuated ovarian cancer cell migration and proliferation. To the best of our knowledge, the present study is the first to conduct sodium current recording in ovarian cancer cells, and revealed that EPA may inhibit Nav1.5-mediated ovarian cancer cell migration and growth. These findings not only present a potential prognostic biomarker for ovarian cancer, but also provide a strategy towards the development of novel pharmacological treatments for patients with ovarian cancer.

Downregulation of adult and neonatal Nav1.5 in the dorsal root ganglia and axon of peripheral sensory neurons of rats with spared nerve injury

Previous studies demonstrated that Nav1.5 splice variants, including Nav1.5a and Nav1.5c, were expressed in dorsal root ganglia (DRG) neurons. However, since nine Nav1.5 isoforms have been identified, whether other Nav1.5 splice variants, especially the neonatal Nav1.5 splice variant, express in the DRG neurons is still unknown. In this study, we systematically investigated the expression of adult and neonatal Nav1.5 isoforms in the DRG neurons and axon of peripheral sensory neurons of rats with spared nerve injury (SNI) by RT-PCR, DNA sequencing, restriction enzyme digestion, immunohistochemistry and immunofluorescence methods. The results demonstrated that both adult and neonatal Nav1.5 isoforms were expressed in the DRG neurons, but their expression ratio was ~2.5:1. In SNI rat models, the expression of both adult and neonatal Nav1.5 decreased by approximately a half in both mRNA and protein levels. In contrast, the expression of protein kinase C (PKC)-γ, one of the negative modulators for sodium currents, increased by ~1-fold. Taken together, this study first confirmed the expression of both adult and neonatal Nav1.5 isoforms in the DRG neurons and axon of peripheral sensory neurons of rat, but their expression level decreased in pain models. The upregulation of PKC-γ may directly or indirectly downregulate the expression of Nav1.5 isoforms in SNI rat models, which may further involve in the pathological process of neuropathic pain.

Molecular expression of multiple Nav1.5 splice variants in the frontal lobe of the human brain

Voltage-gated sodium channels serve an essential role in the initiation and propagation of action potentials for central neurons. Previous studies have demonstrated that two novel variants of Nav1.5, designated Nav1.5e and Nav1.5f, were expressed in the human brain cortex. To date, nine distinct sodium channel isoforms of Nav1.5 have been identified. In the present study, the expression of Nav1.5 splice variants in the frontal lobe of the human brain cortex was systematically investigated. The results demonstrated that wild Nav1.5 and its splice variants, Nav1.5c and Nav1.5e, were expressed in the frontal lobe of the human brain cortex. Nav1.5a, Nav1.5b and Nav1.5d splice variants were not detected. However, the expression level of different Nav1.5 variants was revealed to vary. The expression ratio of wild Nav1.5 vs. Nav1.5c and Nav1.5e was approximately 5:1 and 1:5, respectively. Immunochemistry results revealed that Nav1.5 immunoreactivity was predominantly in neuronal cell bodies and processes, including axons and dendrites, whereas little immunoreactivity was detected in the glial components. These results revealed that a minimum of four Nav1.5 splice variants are expressed in the frontal lobe of the human brain cortex. This indicates that the previously reported tetrodotoxin-resistant sodium current was a compound product of different Nav1.5 variants. The present study revealed that Nav1.5 channels have a more abundant expression in the human brain than previously considered. It also provided further insight into the complexity and functional significance of Nav1.5 channels in human brain neurons.

Distribution and function of voltage-gated sodium channels in the nervous system

Voltage-gated sodium channels (VGSCs) are the basic ion channels for neuronal excitability, which are crucial for the resting potential and the generation and propagation of action potentials in neurons. To date, at least nine distinct sodium channel isoforms have been detected in the nervous system. Recent studies have identified that voltage-gated sodium channels not only play an essential role in the normal electrophysiological activities of neurons but also have a close relationship with neurological diseases. In this study, the latest research findings regarding the structure, type, distribution, and function of VGSCs in the nervous system and their relationship to neurological diseases, such as epilepsy, neuropathic pain, brain tumors, neural trauma, and multiple sclerosis, are reviewed in detail.

Multiple Nav1.5 isoforms are functionally expressed in the brain and present distinct expression patterns compared with cardiac Nav1.5

It has previously been demonstrated that there are various voltage gated sodium channel (Nav) 1.5 splice variants expressed in brain tissue. A total of nine Nav1.5 isoforms have been identified, however, the potential presence of further Nav1.5 variants expressed in brain neurons remains to be elucidated. The present study systematically investigated the expression of various Nav1.5 splice variants and their associated electrophysiological properties in the rat brain tissue, via biochemical analyses and whole-cell patch clamp recording. The results demonstrated that adult Nav1.5 was expressed in the rat, in addition to the neonatal Nav1.5, Nav1.5a and Nav1.5f isoforms. Further studies indicated that the expression level ratio of neonatal Nav1.5 compared with adult Nav1.5 decreased from 1:1 to 1:3 with age development from postnatal (P) day 0 to 90. This differed from the ratios observed in the developing rat hearts, in which the expression level ratio decreased from 1:4 to 1:19 from P0 to 90. The immunohistochemistry results revealed that Nav1.5 immunoreactivity was predominantly observed in neuronal cell bodies and processes, whereas decreased immunoreactivity was detected in the glial components. Electrophysiological analysis of Nav1.5 in the rat brain slices revealed that an Na current was detected in the presence of 300 nM tetrodotoxin (TTX), however this was inhibited by ~1 µM TTX. The TTX-resistant Na current was activated at −40 mV and reached the maximum amplitude at 0 mV. The results of the present study demonstrated that neonatal and adult Nav1.5 were expressed in the rat brain and electrophysiological analysis further confirmed the functional expression of Nav1.5 in brain neurons.

Voltage-gated sodium channel Nav 1.7 promotes gastric cancer progression through MACC1-mediated upregulation of NHE1

Voltage-gated sodium channels (VGSCs), which are aberrantly expressed in several human cancers, affect cancer cell behavior; however, their role in gastric cancer (GC) and the link between these channels and tumorigenic signaling remain unclear. The aims of this study were to determine the clinicopathological significance and role of the VGSC Nav 1.7 in GC progression and to investigate the associated mechanisms. Here, we report that the SCN9A gene encoding Nav 1.7 was the most abundantly expressed VGSC subtype in GC tissue samples and two GC cell lines (BGC-823 and MKN-28 cells). SCN9A expression levels were also frequently found to be elevated in GC samples compared to nonmalignant tissues by real-time PCR. In the 319 GC specimens evaluated by immunohistochemistry, Nav 1.7 expression was correlated with prognosis, and transporter Na(+) /H(+) exchanger-1 (NHE1) and oncoprotein metastasis-associated in colon cancer-1 (MACC1) expression. Nav 1.7 suppression resulted in reduced voltage-gated sodium currents, decreased NHE1 expression, increased extracellular pH and decreased intracellular pH, and ultimately, reduced invasion and proliferation rates of GC cells and growth of GC xenografts in nude mice. Nav 1.7 inhibition led to reduced MACC1 expression, while MACC1 inhibition resulted in reduced NHE1 expression in vitro and in vivo. Mechanistically, the suppression of Nav 1.7 decreased NF-κB p65 nuclear translocation via p38 activation, thus reducing MACC1 expression. Downregulation of MACC1 decreased c-Jun phosphorylation and subsequently reduced NHE1 expression, whereas the addition of hepatocyte growth factor (HGF), a c-Met physiological ligand, reversed the effect. These results indicate that Nav 1.7 promotes GC progression through MACC1-mediated upregulation of NHE1. Therefore, Nav 1.7 is a potential prognostic marker and/or therapeutic target for GC.

Effects of Ranolazine on Astrocytes and Neurons in Primary Culture

Ranolazine (Rn) is an antianginal agent used for the treatment of chronic angina pectoris when angina is not adequately controlled by other drugs. Rn also acts in the central nervous system and it has been proposed for the treatment of pain and epileptic disorders. Under the hypothesis that ranolazine could act as a neuroprotective drug, we studied its effects on astrocytes and neurons in primary culture. We incubated rat astrocytes and neurons in primary cultures for 24 hours with Rn (10-7, 10-6 and 10-5 M). Cell viability and proliferation were measured using trypan blue exclusion assay, MTT conversion assay and LDH release assay. Apoptosis was determined by Caspase 3 activity assay. The effects of Rn on pro-inflammatory mediators IL-β and TNF-α was determined by ELISA technique, and protein expression levels of Smac/Diablo, PPAR-γ, Mn-SOD and Cu/Zn-SOD by western blot technique. In cultured astrocytes, Rn significantly increased cell viability and proliferation at any concentration tested, and decreased LDH leakage, Smac/Diablo expression and Caspase 3 activity indicating less cell death. Rn also increased anti-inflammatory PPAR-γ protein expression and reduced pro-inflammatory proteins IL-1 β and TNFα levels. Furthermore, antioxidant proteins Cu/Zn-SOD and Mn-SOD significantly increased after Rn addition in cultured astrocytes. Conversely, Rn did not exert any effect on cultured neurons. In conclusion, Rn could act as a neuroprotective drug in the central nervous system by promoting astrocyte viability, preventing necrosis and apoptosis, inhibiting inflammatory phenomena and inducing anti-inflammatory and antioxidant agents.

The cardiac sodium channel gene SCN5A and its gene product NaV1.5: Role in physiology and pathophysiology

The gene SCN5A encodes the main cardiac sodium channel NaV1.5. This channel predominates the cardiac sodium current, INa, which underlies the fast upstroke of the cardiac action potential. As such, it plays a crucial role in cardiac electrophysiology. Over the last 60years a tremendous amount of knowledge regarding its function at the electrophysiological and molecular level has been acquired. Furthermore, genetic studies have shown that mutations in SCN5A are associated with multiple cardiac diseases (e.g. Brugada syndrome, Long QT syndrome, conduction disease and cardiomyopathy), while genetic variation in the general population has been associated with differences in cardiac conduction and risk of arrhythmia through genome wide association studies. In this review we aim to give an overview of the current knowledge (and the gaps therein) on SCN5A and NaV1.5.

The role of ion channels in malignant brain tumors

Malignant gliomas are the most common primary brain tumors and have poor clinical prognosis, despite multimodal therapeutic strategies. In recent years, ion channels have emerged as major players in tumor pathophysiology regarding all hallmarks of cancer. Since ion channels are easily accessible structures, they may prove to be effective targets for canner therapy, although their broad expression pattern and role in physiological processes should be taken into consideration. This review summarizes the current knowledge on the role of ion channels in the pathophysiology of malignant gliomas, especially glioblastoma, and evaluates their potential role in targeted antiglioma therapy.

Effects of ropivacaine, bupivacaine and sufentanil in colon and pancreatic cancer cells in vitro

The perioperative period is supposed to be a vulnerable period for cancer progression. Results of clinical studies indicate that the use of regional anesthesia can influence and improve oncological outcome of cancer patients. Uncontrolled cell proliferation and resistance to apoptotic cell death are important characteristics of solid tumors. The aim of this study was to investigate the effects of the clinically used local anesthetics ropivacaine or bupivacaine and the opioid analgesic sufentanil on cell proliferation, cell cycle distribution and apoptosis of colon (HT 29 and SW 480) and pancreatic (PaTu 8988t and PANC 1) cancer cell lines in vitro. Cell proliferation was measured by Cell Proliferation ELISA BrdU Assay. Apoptosis was analyzed by annexin V staining and cell cycle distribution was detected by flow cytometry. Ropivacaine, bupivacaine and sufentanil did not change apoptosis rate and cell cycle distribution in clinically concentration. Only high concentrations of ropivacaine or bupivacaine revealed antiproliferative potency. Protective effects of epidural anesthesia observed in clinical studies seem not to be based on direct effects of these drugs on cancer cells.

Cancer as a channelopathy: ion channels and pumps in tumor development and progression

Increasing evidence suggests that ion channels and pumps not only regulate membrane potential, ion homeostasis, and electric signaling in excitable cells but also play important roles in cell proliferation, migration, apoptosis and differentiation. Consistent with a role in cell signaling, channel proteins and ion pumps can form macromolecular complexes with growth factors, and cell adhesion and other signaling molecules. And while cancer is still not being cataloged as a channelopathy, as the non-traditional roles of ion pumps and channels are being recognized, it is increasingly being suggested that ion channels and ion pumps contribute to cancer progression. Cancer cell migration requires the regulation of adhesion complexes between migrating cells and surrounding extracellular matrix (ECM) proteins. Cell movement along solid surfaces requires a sequence of cell protrusions and retractions that mainly depend on regulation of the actin cytoskeleton along with contribution of microtubules and molecular motor proteins such as mysoin. This process is triggered and modulated by a combination of environmental signals, which are sensed and integrated by membrane receptors, including integrins and cadherins. Membrane receptors transduce these signals into downstream signaling pathways, often involving the Rho GTPase protein family. These pathways regulate the cytoskeletal rearrangements necessary for proper timing of adhesion, contraction and detachment of cells in order to find their way through extracellular spaces. Migration and adhesion involve continuous modulation of cell motility, shape and volume, in which ion channels and pumps play major roles. Research on cancer cells suggests that certain ion channels may be involved in aberrant tumor growth and channel inhibitors often lead to growth arrest. This review will describe recent research into the role of ion pumps and ion channels in cell migration and adhesion, and how they may contribute to tumor development.