Homozygosity for the SCN10A Polymorphism rs6795970 Is Associated With Hypoalgesic Inflammatory Bowel Disease Phenotype

Heterologous expression of the human wild-type and variant NaV 1.8 (A1073V) in rat sensory neurons

BACKGROUND

Silent inflammatory bowel disease (IBD) is a condition in which individuals with the active disease experience minor to no pain. Voltage-gated Na+ (NaV ) channels expressed in sensory neurons play a major role in pain perception. Previously, we reported that a NaV 1.8 genetic polymorphism (A1073V, rs6795970) was more common in a cohort of silent IBD patients. The expression of this variant (1073V) in rat sympathetic neurons activated at more depolarized potentials when compared to the more common variant (1073A). In this study, we investigated whether expression of either NaV 1.8 variant in rat sensory neurons would exhibit different biophysical characteristics than previously observed in sympathetic neurons.

METHODS

Endogenous NaV 1.8 channels were first silenced in DRG neurons and then either 1073A or 1073V human NaV 1.8 cDNA constructs were transfected. NaV 1.8 currents were recorded with the whole-cell patch-clamp technique.

KEY RESULTS

The results indicate that 1073A and 1073V NaV 1.8 channels exhibited similar activation values. However, the slope factor (k) for activation determined for this same group of neurons decreased by 5 mV, suggesting an increase in voltage sensitivity. Comparison of inactivation parameters indicated that 1073V channels were shifted to more depolarized potentials than 1073A-expressing neurons, imparting a proexcitatory characteristic.

CONCLUSIONS AND INFERENCES

These findings differ from previous observations in other expression models and underscore the challenges with heterologous expression systems. Therefore, the use of human sensory neurons derived from induced pluripotent stem cells may help address these inconsistencies and better determine the effect of the polymorphism present in IBD patients.

Pharmacologic Characterization of LTGO-33, a Selective Small Molecule Inhibitor of the Voltage-Gated Sodium Channel NaV1.8 with a Unique Mechanism of Action

Discovery and development of new molecules directed against validated pain targets is required to advance the treatment of pain disorders. Voltage-gated sodium channels (NaVs) are responsible for action potential initiation and transmission of pain signals. NaV1.8 is specifically expressed in peripheral nociceptors and has been genetically and pharmacologically validated as a human pain target. Selective inhibition of NaV1.8 can ameliorate pain while minimizing effects on other NaV isoforms essential for cardiac, respiratory, and central nervous system physiology. Here we present the pharmacology, interaction site, and mechanism of action of LTGO-33, a novel NaV1.8 small molecule inhibitor. LTGO-33 inhibited NaV1.8 in the nM potency range and exhibited over 600-fold selectivity against human NaV1.1-NaV1.7 and NaV1.9. Unlike prior reported NaV1.8 inhibitors that preferentially interacted with an inactivated state via the pore region, LTGO-33 was state-independent with similar potencies against closed and inactivated channels. LTGO-33 displayed species specificity for primate NaV1.8 over dog and rodent NaV1.8 and inhibited action potential firing in human dorsal root ganglia neurons. Using chimeras combined with mutagenesis, the extracellular cleft of the second voltage-sensing domain was identified as the key site required for channel inhibition. Biophysical mechanism of action studies demonstrated that LTGO-33 inhibition was relieved by membrane depolarization, suggesting the molecule stabilized the deactivated state to prevent channel opening. LTGO-33 equally inhibited wild-type and multiple NaV1.8 variants associated with human pain disorders. These collective results illustrate LTGO-33 inhibition via both a novel interaction site and mechanism of action previously undescribed in NaV1.8 small molecule pharmacologic space. SIGNIFICANCE STATEMENT: NaV1.8 sodium channels primarily expressed in peripheral pain-sensing neurons represent a validated target for the development of novel analgesics. Here we present the selective small molecule NaV1.8 inhibitor LTGO-33 that interdicts a distinct site in a voltage-sensor domain to inhibit channel opening. These results inform the development of new analgesics for pain disorders.

Lifestyle Factors and Silent Inflammatory Bowel Disease

Introduction

Hypoalgesic or silent inflammatory bowel disease (IBD) is a poorly understood condition that has been associated with poor clinical outcomes. There is evidence that lifestyle factors, including diet, exercise, and substance use can influence inflammatory activity and symptoms in IBD. It is unclear, though, whether these issues impact pain experience in IBD. We performed this study to evaluate the potential relationship between several key lifestyle factors and silent IBD.

Methods

We performed a retrospective analysis using an IBD natural history registry based in a single tertiary care referral center. We compared demographic and clinical features in 2 patient cohorts defined using data from simultaneous pain surveys and ileocolonoscopy: (a) active IBD without pain (silent IBD) and (b) active IBD with pain. We also evaluated the relative incidence of characteristics related to diet, exercise, sexual activity, and substance abuse.

Results

One hundred and eighty IBD patients had active disease and 69 (38.3%) exhibited silent IBD. Silent IBD patients exhibited incidences of disease type, location, and severity as pain-perceiving IBD patients. Silent IBD patients were more likely to be male and less likely to exhibit anxiety and/or depression or to use cannabis, analgesic medication, or corticosteroids. There were no significant differences in dietary, exercise-related, or sexual activities between silent and pain-perceiving IBD patients.

Conclusions

Silent IBD was associated with reduced incidence of substance and analgesic medication use. No relationships were found between silent IBD and diet, exercise, or sexual activity, though specific elements of each require further dedicated study.

Peripheral temperature dysregulation associated with functionally altered NaV1.8 channels

The voltage-gated sodium channel NaV1.8 is prominently expressed in the soma and axons of small-caliber sensory neurons, and pathogenic variants of the corresponding gene SCN10A are associated with peripheral pain and autonomic dysfunction. While most disease-associated SCN10A variants confer gain-of-function properties to NaV1.8, resulting in hyperexcitability of sensory neurons, a few affect afferent excitability through a loss-of-function mechanism. Using whole-exome sequencing, we here identify a rare heterozygous SCN10A missense variant resulting in alteration p.V1287I in NaV1.8 in a patient with a 15-year history of progressively worsening temperature dysregulation in the distal extremities, particularly in the feet. Further symptoms include increasingly intensifying tingling and numbness in the fingers and increased sweating. To assess the impact of p.V1287I on channel function, we performed voltage-clamp recordings demonstrating that the alteration confers loss- and gain-of-function characteristics to NaV1.8 characterized by a right-shifted voltage dependence of channel activation and inactivation. Current-clamp recordings from transfected mouse dorsal root ganglion neurons further revealed that NaV1.8-V1287I channels broaden the action potentials of sensory neurons and increase their firing rates in response to depolarizing current stimulations, indicating a gain-of-function mechanism of the variant at the cellular level in a heterozygous setting. The data support the hypothesis that the properties of NaV1.8 p.V1287I are causative for the patient's symptoms and that nonpainful peripheral paresthesias should be considered part of the clinical spectrum of NaV1.8-associated disorders.

Abdominal Pain in Inflammatory Bowel Disease: An Evidence-Based, Multidisciplinary Review

Abdominal pain is one of the most common and impactful symptoms associated with inflammatory bowel disease (IBD), including both Crohn's disease and ulcerative colitis. A great deal of research has been undertaken over the past several years to improve our understanding and to optimize management of this issue. Unfortunately, there is still significant confusion about the underlying pathophysiology of abdominal pain in these conditions and the evidence underlying treatment options in this context. There is also a relative paucity of comprehensive reviews on this topic, including those that simultaneously evaluate pharmacological and nonpharmacological therapeutic options. In this review, our multidisciplinary team examines evidence for various currently available medical, surgical, and other analgesic options to manage abdominal pain in IBD.

Association between single nucleotide polymorphisms in candidate genes and success of pulpal anesthesia following inferior alveolar nerve block

INTRODUCTION

The present study aimed to investigate the possible association between the single-nucleotide polymorphisms (SNPs) in the SCN9A, SCN10A, SCN11A, OPRM1, and COMT genes and the success rate of pulpal anesthesia after inferior alveolar nerve block (IANB).

METHODS

A total of 70 patients (45 females and 25 males) presenting mandibular molar teeth with symptomatic irreversible pulpitis were included. Saliva samples were collected from the participants before the application of IANB. A standard IANB was performed with 1.8 mL 4% articaine with 1:100,000 epinephrine. Endodontic treatment was initiated 15 minutes after injection, and the patients were asked to report their pain level during the procedure on a 170-mm Heft-Parker visual analog scale. If the patient recorded a pain level of lower than 54 on the visual analog scale (no pain or mild pain), the anesthesia was considered successful. The DNA isolation and genotyping were performed, and the association between rs4286289, rs6746030, rs6795970, rs6801957, rs11709492, rs1799971, rs1799973, rs4680, rs6269, rs4633, and rs740603 SNPs and the success rate of anesthesia was investigated.

RESULTS

The anesthesia success rate was significantly lower for the GG genotypes (45%) than the GA and AA genotypes (90%) for rs6795970 in the SCN10A gene. Additionally, the A allele for rs6795970 and the T allele for rs6801957 in the SCN10A gene were significantly associated with higher anesthesia success rates.

CONCLUSIONS

SNPs in the SCN10A gene affect the success rate of pulpal anesthesia after IANB.

Prevalence of primary painless chronic pancreatitis: A systematic review and meta-analysis

BACKGROUND/OBJECTIVES

While pain is the predominant symptom of chronic pancreatitis (CP), a subset of patients may experience a painless course. This systematic review aimed to determine the prevalence of primary painless CP.

METHODS

MEDLINE (PubMed), EMBASE and Web of Science Core Collection databases were searched for published studies through September 15, 2020 that included at least 10 consecutive patients with CP and which reported the number with painless CP. The presence of a history of recurrent acute pancreatitis (RAP), exocrine pancreatic insufficiency (EPI), diabetes mellitus (DM) and pancreatic adenocarcinoma (PA) in the painless CP patients was also recorded. A random effects model was used to determine pooled prevalence estimates with 95% confidence intervals (95% CI).

RESULTS

Among the 5057 studies identified and screened, 42 full-text articles were included in the final analysis. There were a total of 14,277 patients with CP among whom 1569 had painless CP. The pooled prevalence of painless CP was 12% (95% CI 10-15%). Among a subset of studies that reported on calcifications (n = 11), DM (n = 12), EPI (n = 8) and history of RAP (n = 14), the pooled prevalence estimates were 96% (95% CI 73-100%), 51% (95% CI 32-70%), and 47% (95% CI 15-81%), respectively. Alcohol, idiopathic/genetic and other etiologies were attributed to be the cause of painless CP in 32.4%, 56.9% and 8.9% patients, respectively.

CONCLUSION

Approximately one in ten patients with CP have primary painless disease with the majority being attributable to an idiopathic/genetic etiology. Further research is needed to determine the optimal management of these patients.

Psychiatric Disease Susceptibility and Pain in Chronic Pancreatitis: Association or Causation?

Pain perception in chronic pancreatitis (CP) is governed by the transmission of nociceptive inputs into the pain processing centers of the brain. These regions of the brain overlap with those that regulate and process emotions and cognition. Disorders in these regions also result in psychiatric conditions such as depression, anxiety, and posttraumatic stress disorder. The present study by Dunbar et al. evaluated 24 single nucleotide polymorphisms associated with anxiety and/or posttraumatic stress disorder and found correlations with constant and severe pain phenotypes in CP patients from a large cross-sectional cohort study. Although causation cannot be proven, the findings suggest that there may be a role for neuromodulator drugs for the treatment of pain in CP based on individual genetic susceptibility.

Post-inflammatory Abdominal Pain in Patients with Inflammatory Bowel Disease During Remission: A Comprehensive Review

Patients with inflammatory bowel disease often experience ongoing pain even after achieving mucosal healing (i.e., post-inflammatory pain). Factors related to the brain-gut axis, such as peripheral and central sensitization, altered sympatho-vagal balance, hypothalamic-pituitary-adrenal axis activation, and psychosocial factors, play a significant role in the development of post-inflammatory pain. A comprehensive study investigating the interaction between multiple predisposing factors, including clinical psycho-physiological phenotypes, molecular mechanisms, and multi-omics data, is still needed to fully understand the complex mechanism of post-inflammatory pain. Furthermore, current treatment options are limited and new treatments consistent with the underlying pathophysiology are needed to improve clinical outcomes.

Genetics of pain: From rare Mendelian disorders to genetic predisposition to pain

Background and aim of the work:

Pain is defined by the International Association for the Study of Pain as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage”. In this mini-review, we focused on the Mendelian disorders with chronic pain as the main characteristic or where pain perception is disrupted, and on the polymorphisms that can impart susceptibility to chronic pain.

Methods:

We searched PubMed and Online Mendelian Inheritance in Man (OMIM) databases and selected only syndromes in which pain or insensitivity to pain were among the main characteristics. Polymorphisms were selected from the database GWAS catalog (https://www.ebi.ac.uk/gwas/home).

Results:

We retrieved a total of 28 genes associated with Mendelian inheritance in which pain or insensitivity to pain were the main characteristics and 70 polymorphisms associated with modulation of pain perception.

Conclusions:

This mini-review highlights the importance of genetics in phenotypes characterized by chronic pain or pain insensitivity. We think that an effective genetic test should analyze all genes associated with Mendelian pain disorders and all SNPs that can increase the risk of pain. (www.actabiomedica.it)

Comparable clinical characteristics in Brugada syndrome patients harboring SCN5A or novel SCN10A variants

AIMS

The Brugada syndrome (BrS) is an inherited disease associated with an increased risk of sudden cardiac death. Often, the genetic cause remains undetected. Perhaps due at least in part because the NaV1.8 protein is expressed more in both the central and peripheral nervous systems than in the heart, the SCN10A gene is not included in diagnostic arrhythmia/sudden death panels in the vast majority of cardiogenetics centres.

METHODS AND RESULTS

Clinical characteristics were assessed in patients harboring either SCN5A or novel SCN10A variants. Genetic testing was performed using Next Generation Sequencing on genomic DNA. Clinical characteristics, including the arrhythmogenic substrate, in BrS patients harboring novel SCN10A variants and SCN5A variants are comparable. Clinical characteristics, including gender, age, personal history of cardiac arrest/syncope, spontaneous BrS electrocardiogram pattern, family history of sudden death, and arrhythmic substrate are not significantly different between probands harboring SCN10A or SCN5A variants.

CONCLUSION

Future studies are warranted to further characterize the role of these specific SCN10A variants.

A Novel Microduplication Spanning Exons 8-16 of ATP2C1 That Was Undetectable by Standard Sanger Sequencing in a Japanese Patient With Hailey-Hailey Disease

Hailey-Hailey disease (HHD) is genetic skin disorder characterized by repeated and exacerbated skin lesions in friction regions. ATP2C1, encoding SPCA1, was demonstrated to be the responsible gene for HHD pathogenesis. However, for some cases, no ATP2C1 mutation could be determined by standard Sanger sequencing, thereby obscuring the cause and diagnosis of HHD. In this study, we investigated the possibility that HHD is caused by complex ATP2C1 defects using multiplex ligation-dependent probe amplification (MLPA) analysis for 10 of 50 cases in our institute without ATP2C1 mutations. In one female Japanese patient and her father, who also show HHD, MLPA followed by polymerase chain reaction (PCR) analyses revealed a novel duplication of exons 8-16 of ATP2C1. The duplication was predicted to add 20,615 base pairs, 882 nt, and 294-amino-acid residues to the genome, mRNA and SPCA1 protein, respectively. By reverse transcriptase-PCR using patient skin RNA, we could confirm that a larger transcript was produced and we found that the abundance of the normal transcript was clearly reduced in the patient. Putative structures of wild-type and duplicated proteins revealed differences in arrangement of SPCA1 domains that may have functional consequences. Strikingly, the phosphorylation and the nucleotide-binding domains were interrupted by insertion of a partial actuator, transmembrane, and phosphorylation domains. The additional 294 amino acids appear to disrupt SPCA1 structure and function, causing HHD. Our study expands the spectrum of genetic defects in HHD and showed that disruption of SPCA1 structure and function by the microduplication caused HHD in the patient and her father.

Genomic analysis of 21 patients with corneal neuralgia after refractive surgery

Background

Refractive surgery, specifically laser-assisted in situ keratomileusis and photorefractive keratectomy, are widely applied procedures to treat myopia, hyperopia, and astigmatism. After surgery, a subgroup of cases suffers from persistent and intractable pain of obscure etiology, thought to be neuropathic. We aimed to investigate the contribution of genomic factors in the pathogenesis of these patients with corneal neuralgia.

Methods

We enrolled 21 cases (6 males and 15 females) from 20 unrelated families, who reported persistent pain (>3 months), after refractive surgery (20 laser-assisted in situ keratomileusis and 1 photorefractive keratectomy patients). Whole-exome sequencing and gene-based association test were performed.

Results

Whole-exome sequencing demonstrated low-frequency variants (allele frequency < 0.05) in electrogenisome-related ion channels and cornea-expressed collagens, most frequently in SCN10A (5 cases), SCN9A (4 cases), TRPV1 (4 cases), CACNA1H and CACNA2D2 (5 cases each), COL5A1 (6 cases), COL6A3 (5 cases), and COL4A2 (4 cases). Two variants, p.K655R of SCN9A and p.Q85R of TRPV1, were previously characterized as gain-of-function. Gene-based association test assessing "damaging" missense variants against gnomAD exome database (non-Finnish European or global), identified a gene, SLC9A3R1, with statistically significant effect (odds ratio = 17.09 or 17.04; Bonferroni-corrected P-value < 0.05).

Conclusion

These findings in a small patient cohort did not identify a common gene/variant among most of these cases, as found in other disorders, for example small-fiber neuropathy. Further studies of these candidate genes/variants might enhance understanding of the role of genetic factors in the pathogenesis of corneal neuralgia.

Impact of the NaV1.8 variant, A1073V, on post-sigmoidectomy pain and electrophysiological function in rat sympathetic neurons

Na_V1.8 channels play a crucial role in regulating the action potential in nociceptive neurons. A single nucleotide polymorphism in the human Na_V1.8 gene SCN10A, A1073V (rs6795970, G>A), has been linked to the diminution of mechanical pain sensation as well as cardiac conduction abnormalities. Furthermore, studies have suggested that this polymorphism may result in a "loss-of-function" phenotype. In the present study, we performed genomic analysis of A1073V polymorphism presence in a cohort of patients undergoing sigmoid colectomy who provided information regarding perioperative pain and analgesic use. Homozygous carriers reported significantly reduced severity in postoperative abdominal pain compared with heterozygous and wild-type carriers. Homozygotes also trended toward using less analgesic/opiates during the postoperative period. We also heterologously expressed the wild-type and A1073V variant in rat superior cervical ganglion neurons. Electrophysiological testing demonstrated that the mutant Na_V1.8 channels activated at more depolarized potentials compared with wild-type channels. Our study revealed that postoperative abdominal pain is diminished in homozygous carriers of A1073V and that this is likely due to reduced transmission of action potentials in nociceptive neurons. Our findings reinforce the importance of Na_V1.8 and the A1073V polymorphism to pain perception. This information could be used to develop new predictive tools to optimize patient pain experience and analgesic use in the perioperative setting.NEW & NOTEWORTHY We present evidence that in a cohort of patients undergoing sigmoid colectomy, those homozygous for the Na_V1.8 polymorphism (rs6795970) reported significantly lower abdominal pain scores than individuals with the homozygous wild-type or heterozygous genotype. In vitro electrophysiological recordings also suggest that the mutant Na_V1.8 channel activates at more depolarizing potentials than the wild-type Na⁺ channel, characteristic of hypoactivity. This is the first report linking the rs6795970 mutation with postoperative abdominal pain in humans.

Gastrointestinal hypoalgesia in inflammatory bowel disease

Background:

Pain perception is critical for detection of noxious bodily insults. Gastrointestinal hypoalgesia in inflammatory bowel disease (IBD) is a poorly understood phenomenon previously linked to poor patient outcomes. We aimed to evaluate the risk factors associated with this condition and to discern characteristics that might differentiate these patients from pain-free quiescent counterparts.

Methods:

We performed a retrospective analysis using an IBD natural history registry based in a single tertiary care referral center. We compared demographic and clinical features in 3 patient cohorts defined using data from simultaneous pain surveys and ileocolonoscopy: a) active IBD without pain (hypoalgesic IBD); b) active IBD with pain; and c) inactive IBD without pain.

Results:

One hundred fifty-three IBD patients had active disease and 43 (28.1%) exhibited hypoalgesia. Hypoalgesic IBD patients were more likely to develop non-perianal fistulae (P=0.03). On logistic regression analysis, hypoalgesic IBD was independently associated with male sex, advancing age and mesalamine use, and inversely associated with anxious/depressed state and opiate use. Hypoalgesic IBD patients were demographically and clinically similar to the pain-free quiescent IBD cohort (n=59). Platelet count and C-reactive protein were more likely to be pathologically elevated in hypoalgesic IBD (P=0.03), though >25% did not exhibit elevated inflammatory markers.

Conclusions:

Hypoalgesia is common in IBD, particularly in male and older individuals, and is associated with an increased incidence of fistulae and corticosteroid use. Novel noninvasive diagnostic tools are needed to screen for this population, as inflammatory markers are not always elevated.