Channelopathies, painful neuropathy, and diabetes: which way does the causal arrow point?

Sodium channels in non-excitable cells: powerful actions and therapeutic targets beyond Hodgkin and Huxley

Voltage-gated sodium channels (VGSCs) are best known for their role in the generation and propagation of action potentials in neurons, muscle cells, and cardiac myocytes, which have traditionally been labeled as 'excitable'. However, emerging evidence challenges this traditional perspective. It is now clear that VGSCs are also expressed in a broad spectrum of cells outside the neuromuscular realm, where they regulate diverse cellular functions. In this review, we summarize current knowledge on the expression, regulation, and function of VGSCs in non-neuromuscular cells, highlighting their contributions to physiological processes and pathological conditions. Dynamic expression patterns of VGSCs in different cell types, involvement of VGSCs in cellular functions, such as phagocytosis, motility, and cytokine release, and their potential as therapeutic targets for diseases that include inflammatory disorders, osteoarthritis (OA), and cancer, are discussed. This new understanding of VGSCs and their effects on cells outside the neuromuscular realm opens new avenues for research and therapeutic interventions.

Painful diabetic neuropathy: The role of ion channels

Painful diabetic neuropathy (PDN) is a common chronic complication of diabetes that causes neuropathic pain and negatively affects the quality of life. The management of PDN is far from satisfactory. At present, interventions are primarily focused on symptomatic treatment. Ion channel disorders are a major cause of PDN, and a complete understanding of their roles and mechanisms may provide better options for the clinical treatment of PDN. Therefore, this review summarizes the important role of ion channels in PDN and the current drug development targeting these ion channels.

The analgesic effects of botulinum neurotoxin by modulating pain-related receptors; A literature review

Botulinum neurotoxins (BoNTs), produced by Clostridium botulinum, have been used for the treatment of various central and peripheral neurological conditions. Recent studies have suggested that BoNTs may also have a beneficial effect on pain conditions. It has been hypothesized that one of the mechanisms underlying BoNTs' analgesic effects is the inhibition of pain-related receptors' transmission to the neuronal cell membrane. BoNT application disrupts the integration of synaptic vesicles with the cellular membrane, which is responsible for transporting various receptors, including pain receptors such as TRP channels, calcium channels, sodium channels, purinergic receptors, neurokinin-1 receptors, and glutamate receptors. BoNT also modulates the opioidergic system and the GABAergic system, both of which are involved in the pain process. Understanding the cellular and molecular mechanisms underlying these effects can provide valuable insights for the development of novel therapeutic approaches for pain management. This review aims to summarize the experimental evidence of the analgesic functions of BoNTs and discuss the cellular and molecular mechanisms by which they can act on pain conditions by inhibiting the transmission of pain-related receptors.

Expanding the genetic causes of small-fiber neuropathy: SCN genes and beyond

Small-fiber neuropathy (SFN) is a disorder that exclusively affects the small nerve fibers, sparing the large nerve fibers. Thinly myelinated Aδ-fibers and unmyelinated C-fibers are damaged, leading to development of neuropathic pain, thermal dysfunction, sensory symptoms, and autonomic disturbances. Although many SFNs are secondary and due to immunological causes or metabolic disturbances, the etiology is unknown in up to half of the patients. Over the years, this proportion of "idiopathic SFN" has decreased, as familial and genetic causes have been discovered, thus shifting a proportion of once "idiopathic" cases to the genetic category. After the discovery of SCN9A-gene variants in 2012, SCN10A and SCN11A variants have been found to be pathogenic in SFN. With improved accessibility of SFN diagnostic tools and genetic tests, many non-SCN variants and genetically inherited systemic diseases involving the small nerve fibers have also been described, but only scattered throughout the literature. There are 80 SCN variants described as causing SFN, 8 genes causing hereditary sensory autonomic neuropathies (HSAN) described with pure SFN, and at least 7 genes involved in genetically inherited systemic diseases associated with SFN. This systematic review aims to consolidate and provide an updated overview on the genetic variants of SFN to date---SCN genes and beyond. Awareness of these genetic causes of SFN is imperative for providing treatment directions, prognostication, and management of expectations for patients and their health-care providers.

The role of G-protein-coupled receptor kinase 2 in diabetic mechanical hyperalgesia in rats

BACKGROUND

Previous studies have indicated a negative correlation between GRK2 expression and pain development and transmission. Here, we investigated whether G-protein-coupled receptor kinase 2 (GRK2) was involved in regulating diabetic mechanical hyperalgesia (DMH).

METHODS

The adeno-associated viral vectors containing the GRK2 gene (AAV-GRK2) were used to up-regulate GRK2 protein expression. The expression of GRK2 and exchange protein directly activated by cyclic adenosine monophosphate 1 (Epac1) in the dorsal root ganglion (DRG) of lumbar 4-6 was detected via immunoblotting and immunohistochemistry, and the transfection of the GRK2 gene was detected by immunofluorescence.

RESULTS

Low levels of GRK2 were able to sustain STZ-induced pain in DMH rats. Intrathecal injection of AAV-GRK2 vector up-regulated GRK2 expression, providing pain rain to rats with DMH. With an increase in DMH duration, there was a decrease in paw withdrawal threshold (PWT) value, aggravating the pain, resulting in a decreasing pattern in GRK2 protein expression over time, whereas Epac1 protein expression showed an opposite trend.

CONCLUSION

GRK2 expression regulated DMH progression and is expected to play a role in the development of targeted therapy for DMH. GRK2 and Epac1 expressions play a vital role in maintaining pain in DMH rats.

Intrafamilial Phenotypic Variability Associated with the I1739V Mutation in the SCN9A Gene

The <i>SCN9A</i> gene encodes a voltage gated sodium channel Nav1.7 in which mutations can result in a wide variety of phenotypes ranging from congenital insensitivity to pain to small fiber neuropathy. We report the genotype phenotype analysis in a family carrying a specific mutation, I1739V, in the <i>SCN9A</i> gene. Neurophysiological studies have documented the gain of function impact of this mutation on this sodium channel. Interestingly, there is significant interfamilial phenotypic variability in individuals carrying this mutation. In our family, a father daughter combination had identical genotypes analyzing the<i> SCN9A</i> gene and multiple other genes known to cause neuropathy. Both of them carry the I1739V mutation but exhibit significant phenotypic variability with complaints of decreased sensitivity to discomfort in the father while the daughter has the clinical and laboratory features consistent with a small fiber neuropathy. We hypothesize that there are modifiers of the I1739V mutation that could involve intronic or exonic gene variants which contribute to this intrafamilial phenotypic variability. Our study has implications for genetic counseling, personalized medicine and the development of drugs to treat neuropathic pain.

Diabetic neuropathy and neuropathic pain: a (con)fusion of pathogenic mechanisms?

Neuropathy is a common complication of long-term diabetes that impairs quality of life by producing pain, sensory loss and limb amputation. The presence of neuropathy in both insulin-deficient (type 1) and insulin resistant (type 2) diabetes along with the slowing of progression of neuropathy by improved glycemic control in type 1 diabetes has caused the majority of preclinical and clinical investigations to focus on hyperglycemia as the initiating pathogenic lesion. Studies in animal models of diabetes have identified multiple plausible mechanisms of glucotoxicity to the nervous system including post-translational modification of proteins by glucose and increased glucose metabolism by aldose reductase, glycolysis and other catabolic pathways. However, it is becoming increasingly apparent that factors not necessarily downstream of hyperglycemia can also contribute to the incidence, progression and severity of neuropathy and neuropathic pain. For example, peripheral nerve contains insulin receptors that transduce the neurotrophic and neurosupportive properties of insulin, independent of systemic glucose regulation, while the detection of neuropathy and neuropathic pain in patients with metabolic syndrome and failure of improved glycemic control to protect against neuropathy in cohorts of type 2 diabetic patients has placed a focus on the pathogenic role of dyslipidemia. This review provides an overview of current understanding of potential initiating lesions for diabetic neuropathy and the multiple downstream mechanisms identified in cell and animal models of diabetes that may contribute to the pathogenesis of diabetic neuropathy and neuropathic pain.

Preclinical Neuropathic Pain Assessment; the Importance of Translatability and Bidirectional Research

For patients suffering with chronic neuropathic pain the need for suitable novel therapies is imperative. Over recent years a contributing factor for the lack of development of new analgesics for neuropathic pain has been the mismatch of primary neuropathic pain assessment endpoints in preclinical vs. clinical trials. Despite continuous forward translation failures across diverse mechanisms, reflexive quantitative sensory testing remains the primary assessment endpoint for neuropathic pain and analgesia in animals. Restricting preclinical evaluation of pain and analgesia to exclusively reflexive outcomes is over simplified and can be argued not clinically relevant due to the continued lack of forward translation and failures in the clinic. The key to developing new analgesic treatments for neuropathic pain therefore lies in the development of clinically relevant endpoints that can translate preclinical animal results to human clinical trials. In this review we discuss this mismatch of primary neuropathic pain assessment endpoints, together with clinical and preclinical evidence that supports how bidirectional research is helping to validate new clinically relevant neuropathic pain assessment endpoints. Ethological behavioral endpoints such as burrowing and facial grimacing and objective measures such as electroencephalography provide improved translatability potential together with currently used quantitative sensory testing endpoints. By tailoring objective and subjective measures of neuropathic pain the translatability of new medicines for patients suffering with neuropathic pain will hopefully be improved.

Design, Synthesis, and Pharmacological Evaluation of Analogues Derived from the PLEV Tetrapeptide as Protein-Protein Interaction Modulators of Voltage-Gated Sodium Channel 1.6

The voltage-gated Na⁺ (Na_v) channel is the molecular determinant of excitability. Disruption of protein-protein interactions (PPIs) between Na_v1.6 and fibroblast growth factor 14 (FGF14) leads to impaired excitability of neurons in clinically relevant brain areas associated with channelopathies. Here, we designed, synthesized, and pharmacologically characterized new peptidomimetics based on a PLEV tetrapeptide scaffold derived from the FGF14:Na_v1.6 PPI interface. Addition of an N-terminal 1-adamantanecarbonyl pharmacophore significantly improved peptidomimetic inhibitory potency. Surface plasmon resonance studies revealed that while this moiety was sufficient to confer binding to FGF14, altering the C-terminal moiety from methoxy (21a) to π bond-containing (23a and 23b) or cycloalkane substituents (23e) abrogated the binding to Na_v1.6. Whole-cell patch-clamp electrophysiology subsequently revealed that 21a had functionally relevant interactions with both the C-terminal tail of Na_v1.6 and FGF14. Collectively, these findings support that 21a (PW0564) may serve as a promising lead to develop target-selective neurotherapeutics by modulating protein-channel interactions.

Ion Channels of the Islets in Type 2 Diabetes

Ca²⁺ is an essential signal for pancreatic β-cell function. Ca²⁺ plays critical roles in numerous β-cell pathways such as insulin secretion, transcription, metabolism, endoplasmic reticulum function, and the stress response. Therefore, β-cell Ca²⁺ handling is tightly controlled. At the plasma membrane, Ca²⁺ entry primarily occurs through voltage-dependent Ca²⁺ channels. Voltage-dependent Ca²⁺ channel activity is dependent on orchestrated fluctuations in the plasma membrane potential or voltage, which are mediated via the activity of many ion channels. During the pathogenesis of type 2 diabetes the β-cell is exposed to stressful conditions, which result in alterations of Ca²⁺ handling. Some of the changes in β-cell Ca²⁺ handling that occur under stress result from perturbations in ion channel activity, expression or localization. Defective Ca²⁺ signaling in the diabetic β-cell alters function, limits insulin secretion and exacerbates hyperglycemia. In this review, we focus on the β-cell ion channels that control Ca²⁺ handling and how they impact β-cell dysfunction in type 2 diabetes.

Bisphenol A Regulates Sodium Ramp Currents in Mouse Dorsal Root Ganglion Neurons and Increases Nociception

17β-Estradiol mediates the sensitivity to pain and is involved in sex differences in nociception. The widespread environmental disrupting chemical bisphenol A (BPA) has estrogenic activity, but its implications in pain are mostly unknown. Here we show that treatment of male mice with BPA (50 µg/kg/day) during 8 days, decreases the latency to pain behavior in response to heat, suggesting increased pain sensitivity. We demonstrate that incubation of dissociated dorsal root ganglia (DRG) nociceptors with 1 nM BPA increases the frequency of action potential firing. SCN9A encodes the voltage-gated sodium channel Na_v1.7, which is present in DRG nociceptors and is essential in pain signaling. Na_v1.7 and other voltage-gated sodium channels in mouse DRG are considered threshold channels because they produce ramp currents, amplifying small depolarizations and enhancing electrical activity. BPA increased Na_v-mediated ramp currents elicited with slow depolarizations. Experiments using pharmacological tools as well as DRG from ERβ^−/− mice indicate that this BPA effect involves ERα and phosphoinositide 3-kinase. The mRNA expression and biophysical properties other than ramp currents of Na_v channels, were unchanged by BPA. Our data suggest that BPA at environmentally relevant doses affects the ability to detect noxious stimuli and therefore should be considered when studying the etiology of pain conditions.

Rare NaV1.7 variants associated with painful diabetic peripheral neuropathy

Diabetic peripheral neuropathy (DPN) is a common disabling complication of diabetes. Almost half of the patients with DPN develop neuropathic pain (NeuP) for which current analgesic treatments are inadequate. Understanding the role of genetic variability in the development of painful DPN is needed for improved understanding of pain pathogenesis for better patient stratification in clinical trials and to target therapy more appropriately. Here, we examined the relationship between variants in the voltage-gated sodium channel NaV1.7 and NeuP in a deeply phenotyped cohort of patients with DPN. Although no rare variants were found in 78 participants with painless DPN, we identified 12 rare NaV1.7 variants in 10 (out of 111) study participants with painful DPN. Five of these variants had previously been described in the context of other NeuP disorders and 7 have not previously been linked to NeuP. Those patients with rare variants reported more severe pain and greater sensitivity to pressure stimuli on quantitative sensory testing. Electrophysiological characterization of 2 of the novel variants (M1852T and T1596I) demonstrated that gain of function changes as a consequence of markedly impaired channel fast inactivation. Using a structural model of NaV1.7, we were also able to provide further insight into the structural mechanisms underlying fast inactivation and the role of the C-terminal domain in this process. Our observations suggest that rare NaV1.7 variants contribute to the development NeuP in patients with DPN. Their identification should aid understanding of sensory phenotype, patient stratification, and help target treatments effectively.

Quercetin relieved diabetic neuropathic pain by inhibiting upregulated P2X4 receptor in dorsal root ganglia

The upregulation of nociceptive ion channels expressed in dorsal root ganglia (DRG) contributes to the development and retaining of diabetic pain symptoms. The flavonoid quercetin (3,3′,4′,5,7‐pentahydroxyflavone) is a component extracted from various fruits and vegetables and exerts anti‐inflammatory, analgesic, anticarcinogenic, antiulcer, and antihypertensive effects. However, the exact mechanism underlying quercetin's analgesic action remains poorly understood. The aim of this study was to investigate the effects of quercetin on diabetic neuropathic pain related to the P2X4 receptor in the DRG of type 2 diabetic rat model. Our data showed that both mechanical withdrawal threshold and thermal withdrawal latency in diabetic rats treated with quercetin were higher compared with those in untreated diabetic rats. The expression levels of P2X4 messenger RNA and protein in the DRG of diabetic rats were increased compared with the control rats, while quercetin treatment significantly inhibited such enhanced P2X4 expression in diabetic rats. The satellite glial cells (SGCs) enwrap the neuronal soma in the DRG. Quercetin treatment also lowered the elevated coexpression of P2X4 and glial fibrillary acidic protein (a marker of SGCs) and decreased the upregulation of phosphorylated p38 mitogen‐activated protein kinase (p38MAPK) in the DRG of diabetic rats. Quercetin significantly reduced the P2X4 agonist adenosine triphosphate‐activated currents in HEK293 cells transfected with P2X4 receptors. Thus, our data demonstrate that quercetin may decrease the upregulation of the P2X4 receptor in DRG SGCs, and consequently inhibit P2X4 receptor‐mediated p38MAPK activation to relieve the mechanical and thermal hyperalgesia in diabetic rats.

New Horizons in Diabetic Neuropathy: Mechanisms, Bioenergetics, and Pain

Pre-diabetes and diabetes are a global epidemic, and the associated neuropathic complications create a substantial burden on both the afflicted patients and society as a whole. Given the enormity of the problem and the lack of effective therapies, there is a pressing need to understand the mechanisms underlying diabetic neuropathy (DN). In this review, we present the structural components of the peripheral nervous system that underlie its susceptibility to metabolic insults and then discuss the pathways that contribute to peripheral nerve injury in DN. We also discuss systems biology insights gleaned from the recent advances in biotechnology and bioinformatics, emerging ideas centered on the axon-Schwann cell relationship and associated bioenergetic crosstalk, and the rapid expansion of our knowledge of the mechanisms contributing to neuropathic pain in diabetes. These recent advances in our understanding of DN pathogenesis are paving the way for critical mechanism-based therapy development.

Uncovering sensory axonal dysfunction in asymptomatic type 2 diabetic neuropathy

This study investigated sensory and motor nerve excitability properties to elucidate the development of diabetic neuropathy. A total of 109 type 2 diabetes patients were recruited, and 106 were analyzed. According to neuropathy severity, patients were categorized into G0, G1, and G2+3 groups using the total neuropathy score-reduced (TNSr). Patients in the G0 group were asymptomatic and had a TNSr score of 0. Sensory and motor nerve excitability data from diabetic patients were compared with data from 33 healthy controls. Clinical assessment, nerve conduction studies, and sensory and motor nerve excitability testing data were analyzed to determine axonal dysfunction in diabetic neuropathy. In the G0 group, sensory excitability testing revealed increased stimulus for the 50% sensory nerve action potential (P<0.05), shortened strength-duration time constant (P<0.01), increased superexcitability (P<0.01), decreased subexcitability (P<0.05), decreased accommodation to depolarizing current (P<0.01), and a trend of decreased accommodation to hyperpolarizing current in threshold electrotonus. All the changes progressed into G1 (TNSr 1–8) and G2+3 (TNSr 9–24) groups. In contrast, motor excitability only had significantly increased stimulus for the 50% compound motor nerve action potential (P<0.01) in the G0 group. This study revealed that the development of axonal dysfunction in sensory axons occurred prior to and in a different fashion from motor axons. Additionally, sensory nerve excitability tests can detect axonal dysfunction even in asymptomatic patients. These insights further our understanding of diabetic neuropathy and enable the early detection of sensory axonal abnormalities, which may provide a basis for neuroprotective therapeutic approaches.

Schwann cell interactions with axons and microvessels in diabetic neuropathy

The prevalence of diabetes worldwide is at pandemic levels, with the number of patients increasing by 5% annually. The most common complication of diabetes is peripheral neuropathy, which has a prevalence as high as 50% and is characterized by damage to neurons, Schwann cells and blood vessels within the nerve. The pathogenic mechanisms of diabetic neuropathy remain poorly understood, impeding the development of targeted therapies to treat nerve degeneration and its most disruptive consequences of sensory loss and neuropathic pain. Involvement of Schwann cells has long been proposed, and new research techniques are beginning to unravel a complex interplay between these cells, axons and microvessels that is compromised during the development of diabetic neuropathy. In this Review, we discuss the evolving concept of Schwannopathy as an integral factor in the pathogenesis of diabetic neuropathy, and how disruption of the interactions between Schwann cells, axons and microvessels contribute to the disease.

Roles of Voltage-Gated Tetrodotoxin-Sensitive Sodium Channels NaV1.3 and NaV1.7 in Diabetes and Painful Diabetic Neuropathy

Diabetes mellitus (DM) is a common chronic medical problem worldwide; one of its complications is painful peripheral neuropathy, which can substantially erode quality of life and increase the cost of management. Despite its clinical importance, the pathogenesis of painful diabetic neuropathy (PDN) is complex and incompletely understood. Voltage-gated sodium channels (VGSCs) link many physiological processes to electrical activity by controlling action potentials in all types of excitable cells. Two isoforms of VGSCs, Na_V1.3 and Na_V1.7, which are encoded by the sodium voltage-gated channel alpha subunit 3 and 9 (Scn3A and Scn9A) genes, respectively, have been identified in both peripheral nociceptive neurons of dorsal root ganglion (DRG) and pancreatic islet cells. Recent advances in our understanding of tetrodotoxin-sensitive (TTX-S) sodium channels Na_V1.3 and Na_V1.7 lead to the rational doubt about the cause–effect relation between diabetes and painful neuropathy. In this review, we summarize the roles of Na_V1.3 and Na_V1.7 in islet cells and DRG neurons, discuss the link between DM and painful neuropathy, and present a model, which may provide a starting point for further studies aimed at identifying the mechanisms underlying diabetes and painful neuropathy.

Modulation of Ionic Channels and Insulin Secretion by Drugs and Hormones in Pancreatic Beta Cells

Pancreatic beta cells, unique cells that secrete insulin in response to an increase in glucose levels, play a significant role in glucose homeostasis. Glucose-stimulated insulin secretion (GSIS) in pancreatic beta cells has been extensively explored. In this mechanism, glucose enters the cells and subsequently the metabolic cycle. During this process, the ATP/ADP ratio increases, leading to ATP-sensitive potassium (KATP) channel closure, which initiates depolarization that is also dependent on the activity of TRP nonselective ion channels. Depolarization leads to the opening of voltage-gated Na(+) channels (Nav) and subsequently voltage-dependent Ca(2+) channels (Cav). The increase in intracellular Ca(2+) triggers the exocytosis of insulin-containing vesicles. Thus, electrical activity of pancreatic beta cells plays a central role in GSIS. Moreover, many growth factors, incretins, neurotransmitters, and hormones can modulate GSIS, and the channels that participate in GSIS are highly regulated. In this review, we focus on the principal ionic channels (KATP, Nav, and Cav channels) involved in GSIS and how classic and new proteins, hormones, and drugs regulate it. Moreover, we also discuss advances on how metabolic disorders such as metabolic syndrome and diabetes mellitus change channel activity leading to changes in insulin secretion.

Painful Diabetic Neuropathy: Prevention or Suppression?

Pain-sensing sensory neurons (nociceptors) of the dorsal root ganglia (DRG) and dorsal horn (DH) can become sensitized (hyperexcitable) in response to pathological conditions such as diabetes, which in turn may lead to the development of painful peripheral diabetic neuropathy (PDN). Because of incomplete knowledge about the mechanisms underlying painful PDN, current treatment for painful PDN has been limited to somewhat nonspecific systemic drugs that have significant side effects or potential for abuse. Recent studies have established that several ion channels in DRG and DH neurons are dysregulated and make a previously unrecognized contribution to sensitization of pain responses by enhancing excitability of nociceptors in animal models of type 1 and type 2 PDN. Furthermore, it has been reported that targeting posttranslational modification of nociceptive ion channels such as glycosylation and methylglyoxal metabolism can completely reverse mechanical and thermal hyperalgesia in diabetic animals with PDN in vivo. Understanding details of posttranslational regulation of nociceptive channel activity may facilitate development of novel therapies for treatment of painful PDN. We argue that pharmacological targeting of the specific pathogenic mechanism rather than of the channel per se may cause fewer side effects and reduce the potential for drug abuse in patients with diabetes.

High prevalence of concealed Brugada syndrome in patients with atrioventricular nodal reentrant tachycardia

BACKGROUND

Atrioventricular nodal reentrant tachycardia (AVNRT) may coexist with Brugada syndrome (BrS).

OBJECTIVES

The present study was designed to determine the prevalence of drug-induced type 1 Brugada ECG pattern (concealed BrS) in patients presenting with clinical spontaneous AVNRT and to investigate their electrocardiographic, electrophysiological, and genetic characteristics.

METHODS

Ninety-six consecutive patients without any sign of BrS on baseline electrocardiogram undergoing electrophysiological study and ablation for symptomatic, drug-resistant AVNRT and 66 control subjects underwent an ajmaline challenge to unmask BrS. Genetic screening was performed in 17 patients displaying both AVNRT and BrS.

RESULTS

A concealed BrS electrocardiogram was uncovered in 26 of 96 patients with AVNRT (27.1%) and in 3 of 66 control subjects (4.5%) (P ≤ .001). Patients with concealed BrS were predominantly female patients (n=23 [88.5%] vs n=44 [62.9%], P = .015), had higher prevalence of chest pain (n=10 [38.5%] vs n=13 [18.6%], p=0.042), migraine headaches (n=10 [38.5%] vs n=10 [14.2%], p=0.008), and drug-induced initiation and/or worsening of duration and/or frequency of AVNRT (n=4 [15.4%] vs n=1 [1.4%], p=0.006) as compared to patients with AVNRT without BrS. Genetic screening identified 19 mutations or rare variants in 13 genes in 13 of 17 patients with both AVNRT and BrS (yield = 76.5%). Ten of these 13 genotype-positive patients (76.9%) harbored genetic variants known or suspected to cause a loss of function of cardiac sodium channel current (SCN5A, SCN10A, SCN1B, GPD1L, PKP2, and HEY2).

CONCLUSION

Our results suggest that spontaneous AVNRT and concealed BrS co-occur, particularly in female patients, and that genetic variants that reduce sodium channel current may provide a mechanistic link between AVNRT and BrS and predispose to expression of both phenotypes.

Voltage-Gated Sodium Channels: Structure, Function, Pharmacology, and Clinical Indications

The tremendous therapeutic potential of voltage-gated sodium channels (Na(v)s) has been the subject of many studies in the past and is of intense interest today. Na(v)1.7 channels in particular have received much attention recently because of strong genetic validation of their involvement in nociception. Here we summarize the current status of research in the Na(v) field and present the most relevant recent developments with respect to the molecular structure, general physiology, and pharmacology of distinct Na(v) channel subtypes. We discuss Na(v) channel ligands such as small molecules, toxins isolated from animal venoms, and the recently identified Na(v)1.7-selective antibody. Furthermore, we review eight characterized ligand binding sites on the Na(v) channel α subunit. Finally, we examine possible therapeutic applications of Na(v) ligands and provide an update on current clinical studies.

Resveratrol protects PC12 cells from high glucose-induced neurotoxicity via PI3K/Akt/FoxO3a pathway

Diabetes is known to be associated with neurodegenerative diseases. Resveratrol, a plant-derived polyphenolic compound found in red wine, possesses antioxidant properties. In this study, we aimed to investigate the effects of resveratrol on the phosphatidylinositol-3-kinase/protein kinase B (PI3K/Akt)/FoxO3a pathway in mediating high glucose (HG)-induced injuries in neuronal PC12 cells. PC12 cells were exposed to HG to establish a model of HG neurotoxicity. Results showed that pre-treating PC12 cells with resveratrol before exposure to HG led to increased cell viability, decreased apoptotic cells, and reactive oxygen species generation. Western blot analysis showed that HG decreased the phosphorylation of Akt and FoxO3a and led to the nuclear localization of FoxO3a. These effects were significantly alleviated by resveratrol co-treatment. Furthermore, the protective effects of resveratrol were abolished by PI3K/Akt inhibitor LY294002. All these results demonstrate that resveratrol protected the PC12 cells from HG-induced oxidative stress and apoptosis via the activation of PI3K/Akt/FoxO3a signaling pathway.

Diabetic neuropathic pain: Physiopathology and treatment

Diabetic neuropathy is a common complication of both type 1 and type 2 diabetes, which affects over 90% of the diabetic patients. Although pain is one of the main symptoms of diabetic neuropathy, its pathophysiological mechanisms are not yet fully known. It is widely accepted that the toxic effects of hyperglycemia play an important role in the development of this complication, but several other hypotheses have been postulated. The management of diabetic neuropathic pain consists basically in excluding other causes of painful peripheral neuropathy, improving glycemic control as a prophylactic therapy and using medications to alleviate pain. First line drugs for pain relief include anticonvulsants, such as pregabalin and gabapentin and antidepressants, especially those that act to inhibit the reuptake of serotonin and noradrenaline. In addition, there is experimental and clinical evidence that opioids can be helpful in pain control, mainly if associated with first line drugs. Other agents, including for topical application, such as capsaicin cream and lidocaine patches, have also been proposed to be useful as adjuvants in the control of diabetic neuropathic pain, but the clinical evidence is insufficient to support their use. In conclusion, a better understanding of the mechanisms underlying diabetic neuropathic pain will contribute to the search of new therapies, but also to the improvement of the guidelines to optimize pain control with the drugs currently available.