, a bio/informatics shared resource is still "open for business" - Visit the CDS website
The publication data currently available has been vetted by Vanderbilt faculty, staff, administrators and trainees. The data itself is retrieved directly from NCBI's PubMed and is automatically updated on a weekly basis to ensure accuracy and completeness.
If you have any questions or comments, please contact us.
2-hydroxybenzylamine (2-HOBA), a compound found in buckwheat, is a potent scavenger of reactive γ-ketoaldehydes, which are increased in diseases associated with inflammation and oxidative stress. While the potential of 2-HOBA is promising, studies were needed to characterize the safety of the compound before clinical trials. In a series of experiments, the risks of 2-HOBA-mediated mutagenicity and cardio-toxicity were assessed in vitro. The effects of 2-HOBA on the mRNA expression of select cytochrome P450 (CYP) enzymes were also assessed in cryopreserved human hepatocytes. Further, the distribution and metabolism of 2-HOBA in blood were determined. Our results indicate that 2-HOBA is not cytotoxic or mutagenic in vitro and does not induce the expression of CYP1A2, CYP2B6, or CYP3A4 in human hepatocytes. The results of the hERG testing showed a low risk of cardiac QT wave prolongation. Plasma protein binding and red blood cell distribution characteristics indicate low protein binding and no preferential distribution into erythrocytes. The major metabolites identified were salicylic acid and the glycoside conjugate of 2-HOBA. Together, these findings support development of 2-HOBA as a nutritional supplement and provide important information for the design of further preclinical safety studies in animals as well as for human clinical trials with 2-HOBA.
Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.
BACKGROUND - A 27-year-old woman was seen for long QT syndrome. She was found to be a carrier of 2 variants, KCNQ1 Val162Met and KCNH2 Ser55Leu, and both were classified as "pathogenic" by a diagnostic laboratory, in part because of sequence proximity to other known pathogenic variants.
OBJECTIVE - The purpose of this study was to assess the relationship between both the KCNQ1 and KCNH2 variants and clinical significance using protein structure, in vitro functional assays, and familial segregation.
METHODS - We used co-segregation analysis of family, patch clamp in vitro electrophysiology, and structural analysis using recently released cryo-electron microscopy structures of both channels.
RESULTS - The structural analysis indicates that KCNQ1 Val162Met is oriented away from functionally important regions while Ser55Leu is positioned at domains critical for KCNH2 fast inactivation. Clinical phenotyping and electrophysiology study further support the conclusion that KCNH2 Ser55Leu is correctly classified as pathogenic but KCNQ1 Val162Met is benign.
CONCLUSION - Proximity in sequence space does not always translate accurately to proximity in 3-dimensional space. Emerging structural methods will add value to pathogenicity prediction.
Copyright © 2018 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.
IMPORTANCE - Large-scale DNA sequencing identifies incidental rare variants in established Mendelian disease genes, but the frequency of related clinical phenotypes in unselected patient populations is not well established. Phenotype data from electronic medical records (EMRs) may provide a resource to assess the clinical relevance of rare variants.
OBJECTIVE - To determine the clinical phenotypes from EMRs for individuals with variants designated as pathogenic by expert review in arrhythmia susceptibility genes.
DESIGN, SETTING, AND PARTICIPANTS - This prospective cohort study included 2022 individuals recruited for nonantiarrhythmic drug exposure phenotypes from October 5, 2012, to September 30, 2013, for the Electronic Medical Records and Genomics Network Pharmacogenomics project from 7 US academic medical centers. Variants in SCN5A and KCNH2, disease genes for long QT and Brugada syndromes, were assessed for potential pathogenicity by 3 laboratories with ion channel expertise and by comparison with the ClinVar database. Relevant phenotypes were determined from EMRs, with data available from 2002 (or earlier for some sites) through September 10, 2014.
EXPOSURES - One or more variants designated as pathogenic in SCN5A or KCNH2.
MAIN OUTCOMES AND MEASURES - Arrhythmia or electrocardiographic (ECG) phenotypes defined by International Classification of Diseases, Ninth Revision (ICD-9) codes, ECG data, and manual EMR review.
RESULTS - Among 2022 study participants (median age, 61 years [interquartile range, 56-65 years]; 1118 [55%] female; 1491 [74%] white), a total of 122 rare (minor allele frequency <0.5%) nonsynonymous and splice-site variants in 2 arrhythmia susceptibility genes were identified in 223 individuals (11% of the study cohort). Forty-two variants in 63 participants were designated potentially pathogenic by at least 1 laboratory or ClinVar, with low concordance across laboratories (Cohen κ = 0.26). An ICD-9 code for arrhythmia was found in 11 of 63 (17%) variant carriers vs 264 of 1959 (13%) of those without variants (difference, +4%; 95% CI, -5% to +13%; P = .35). In the 1270 (63%) with ECGs, corrected QT intervals were not different in variant carriers vs those without (median, 429 vs 439 milliseconds; difference, -10 milliseconds; 95% CI, -16 to +3 milliseconds; P = .17). After manual review, 22 of 63 participants (35%) with designated variants had any ECG or arrhythmia phenotype, and only 2 had corrected QT interval longer than 500 milliseconds.
CONCLUSIONS AND RELEVANCE - Among laboratories experienced in genetic testing for cardiac arrhythmia disorders, there was low concordance in designating SCN5A and KCNH2 variants as pathogenic. In an unselected population, the putatively pathogenic genetic variants were not associated with an abnormal phenotype. These findings raise questions about the implications of notifying patients of incidental genetic findings.
BACKGROUND - Long-QT syndrome (LQTS) is characterized by such striking clinical heterogeneity that, even among family members carrying the same mutation, clinical outcome can range between sudden death and no symptoms. We investigated the role of genetic variants as modifiers of risk for cardiac events in patients with LQTS.
METHODS AND RESULTS - In a matched case-control study including 112 patient duos with LQTS from France, Italy, and Japan, 25 polymorphisms were genotyped based on either their association with QTc duration in healthy populations or on their role in adrenergic responses. The duos were composed of 2 relatives harboring the same heterozygous KCNQ1 or KCNH2 mutation: 1 with cardiac events and 1 asymptomatic and untreated. The findings were then validated in 2 independent founder populations totaling 174 symptomatic and 162 asymptomatic patients with LQTS, and a meta-analysis was performed. The KCNQ1 rs2074238 T-allele was significantly associated with a decreased risk of symptoms 0.34 (0.19-0.61; P<0.0002) and with shorter QTc (P<0.0001) in the combined discovery and replication cohorts.
CONCLUSIONS - We provide evidence that the KCNQ1 rs2074238 polymorphism is an independent risk modifier with the minor T-allele conferring protection against cardiac events in patients with LQTS. This finding is a step toward a novel approach for risk stratification in patients with LQTS.
The human Ether-à-go-go-related gene (hERG)-encoded K(+) current, I(Kr) is essential for cardiac repolarization but is also a source of cardiotoxicity because unintended hERG inhibition by diverse pharmaceuticals can cause arrhythmias and sudden cardiac death. We hypothesized that a small molecule that diminishes I(Kr) block by a known hERG antagonist would constitute a first step toward preventing hERG-related arrhythmias and facilitating drug discovery. Using a high-throughput assay, we screened a library of compounds for agents that increase the IC(70) of dofetilide, a well characterized hERG blocker. One compound, VU0405601, with the desired activity was further characterized. In isolated, Langendorff-perfused rabbit hearts, optical mapping revealed that dofetilide-induced arrhythmias were reduced after pretreatment with VU0405601. Patch clamp analysis in stable hERG-HEK cells showed effects on current amplitude, inactivation, and deactivation. VU0405601 increased the IC(50) of dofetilide from 38.7 to 76.3 nM. VU0405601 mitigates the effects of hERG blockers from the extracellular aspect primarily by reducing inactivation, whereas most clinically relevant hERG inhibitors act at an inner pore site. Structure-activity relationships surrounding VU0405601 identified a 3-pyridiyl and a naphthyridine ring system as key structural components important for preventing hERG inhibition by multiple inhibitors. These findings indicate that small molecules can be designed to reduce the sensitivity of hERG to inhibitors.
The cardiotoxic potential of cytotoxic cancer chemotherapy is well known. Prime examples are the anthracyclines, which are highly efficacious agents for hemopoietic malignancies and solid tumors, but their clinical use is limited primarily by cardiotoxicity. Besides the conventional chemotherapeutics, new cancer drugs were developed in the last decade with the goal to specifically inhibit selected molecular targets such as growth factor receptors or intracellular tyrosine kinases in cancer cells. However, the outcome of combining conventional and newer cancer therapies could have unexpected side effects not anticipated so far and the long-term outcome is not known. Sometimes, however, unexpected side effects also shed light on previously unknown physiological functions. For example, the anti-HER2 cancer therapeutic trastuzumab (Herceptin), which can induce cardiac dysfunction, has demonstrated the importance of the ErbB/neuregulin signaling system in the adult heart. Subsequently, the role of endothelial-myocardial communication in maintaining phenotype and survival of adult cardiomyocytes has increasingly been recognized.
AIMS - The 'rhythmonome' is the term we have adopted to describe the set of genes that determine the normal coordinated electrical activity in the heart. Elements of this set include pore-forming ion channels, function-modifying proteins and intracellular calcium control elements. Rare mutations in many of these genes are known to cause unusual congenital monogenic arrhythmia syndromes, and single common variants have been reported to modify arrhythmia phenotypes. Here, we report an evaluation of the variation and haplotype structure in six key components of the rhythmonome.
MATERIALS & METHODS - SNPs were typed using DNA extracted from Coriell cell lines to survey allele frequencies and haplotype structure in six genes (ANK2, SCN5A, KCNE1 and 2 gene cluster, KCNQ1, KCNH2 and RYR2) across four human populations (African-American, European American, Han Chinese and Mexican American).
RESULTS - A total of 307 SNPs were analyzed across the six genes, revealing significant allele-frequency differences between populations and clear differences in haplotype structure.
CONCLUSIONS - The pattern of variation we report is an important step towards incorporating common variation across the rhythmonome in studies of arrhythmia susceptibility.
Human ether-a-go-go-related gene (HERG) encodes the rapid, outwardly rectifying K(+) current I(Kr) that is critical for repolarization of the cardiac action potential. Congenital HERG mutations or unintended pharmaceutical block of I(Kr) can lead to life-threatening arrhythmias. Here, we assess the functional role of the alanine at position 653 (HERG-A653) that is highly conserved among evolutionarily divergent K(+) channels. HERG-A653 is close to the 'glycine hinge' implicated in K(+) channel opening, and is flanked by tyrosine 652 and phenylalanine 656, which contribute to the drug binding site. We substituted an array of seven (I, C, S, G, Y, V and T) amino acids at position 653 and expressed individual variants in heterologous systems to assess changes in gating and drug binding. Substitution of A653 resulted in negative shifts of the V(1/2) of activation ranging from -23.6 (A653S) to -62.5 (A653V) compared to -11.2 mV for wild-type (WT). Deactivation was also drastically altered: channels with A653I/C substitutions exhibited delayed deactivation in response to test potentials above the activation threshold, while A653S/G/Y/V/T failed to deactivate under those conditions and required hyperpolarization and prolonged holding potentials at -130 mV. While A653S/G/T/Y variants showed decreased sensitivity to the I(Kr) inhibitor dofetilide, these changes could not be correlated with defects in channel closure. Homology modelling suggests that in the closed state, A653 forms tight contacts with several residues from the neighbouring subunit in the tetramer, playing a key role in S6 helix packing at the narrowest part of the vestibule. Our study suggests that A653 plays an important functional role in the outwardly rectifying gating behaviour of HERG, supporting channel closure at membrane potentials negative to the channel activation threshold.