Cardiorespiratory fitness and electroanatomical remodelling in patients with atrial fibrillation

Funding Acknowledgements

Type of funding sources: None.

Introduction

Atrial fibrillation (AF) is the most common clinically-relevant arrhythmia. Its initiation and maintenance is linked to the presence cardiovascular risk factors such as hypertension and obesity. Higher cardiorespiratory fitness (CRF) has been associated with a better prognosis. However, specific electroanatomical features associated with baseline CRF have not been described. 

Purpose

Compare electroanatomical substrate across exercise capacity levels in patients with AF

Methods

Patients referred for de novo AF radiofrequency ablation at the Centre for Heart Rhythm Disorders from August 2017 until June 2020 were screened for inclusion and CRF was evaluated in metabolic equivalents (METs) by a symptom-limited maximal treadmill exercise test using the standard Bruce protocol prior to ablation. Predicted CRF was calculated based on established equations and patients were categorized according to the percentage of predicted CRF achieved; low (<85%), adequate (85-100%) and high (>100%). Total mean and regional peak-to-peak bipolar voltages, percent of low voltage areas (% LVA), conduction velocity (CV) and percent of complex fractionated electrograms (% CFE) in sinus rhythm were compared across groups. 

Results

There were no between-group differences in baseline characteristics, medication use or echocardiographic features. Total mean voltage was significantly lower in the low CRF group compared to both adequate and high CRF. Compared to the high CRF group, roof (3.25 ± 1.2 mV vs 1.9 ± 1.3 mV, p < 0.05), posterior (3.8 ± 1.8 mV vs 1.7 ± 0.9 mV, p < 0.001) and inferior mean voltages (3.4 ± 2 mV vs 1.6 ± 0.7 mV, p < 0.05) were significantly lower in the low CRF group (figure 1A). Furthermore, compared with the adequate CRF group, mean voltages were significantly lower in the posterior (3.7 ± 1.5 mV vs 1.7 ± 0.9 mV, p < 0.001), inferior (3.4 ± 1 mV vs 1.6 ± 0.7 mV, p < 0.001) and lateral (4.2 ± 2.2 mV vs 2.1 ± 1.4 mV, p < 0.05) walls of the low CRF group. Anterior and septal mean voltages were not significantly different across CRF groups (P for trend = 0.07, 0.3 and 0.15, respectively). Conduction velocities were not significantly different across groups. The inferior %LVA was significantly higher in the low CRF (5.6 ± 6%) compared to adequate CRF group (23 ± 18%) (p < 0.05) (figure 1B). Total and regional % CFE was higher in the low CRF compared to adequate and high CRF.

Conclusion

Participants in the lower baseline CRF category showed significant reductions in regional voltages along with higher fractionation with preserved conduction velocities. Research on the effect of physical activity and CRF on left atrial arrhythmogenic substrate is required.

Abstract Figure. Global and regional mV and % LVA by CRF

Toxicités sévères des immunothérapies du cancer

L’immunothérapie représente une avancée récente et importante en cancérologie. Les inhibiteurs de checkpoints immunitaires, ciblant les protéines PD-1, PD-L1 et CTLA-4, sont les thérapies les plus prometteuses et sont utilisés dans la prise en charge de plusieurs cancers. Les toxicités associées à ces traitements sont généralement moins fréquentes et moins graves que celles associées aux chimiothérapies et à la plupart des thérapies ciblées. Cependant, il existe un certain nombre de toxicités spécifiques de ce type de traitement, qui peuvent parfois être sévères et dont les plus fréquentes sont les toxicités pulmonaire, digestive, endocrinienne et cutanée. Dans cette mise au point, nous reviendrons sur la fréquence, le mécanisme et les principes de traitement des différentes toxicités sévères associées à l’immunothérapie.

Transcriptional activity of multiple copies of a subtelomerically located olfactory receptor gene that is polymorphic in number and location

We report here on the transcriptional activity of multiple copies of a subtelomerically located olfactory receptor (OR) gene, OR-A. Due to recent duplication events, both the copy number and chromosomal location of OR-A vary among humans. Sequence analyses of 180 copies of this gene, derived from 12 chromosome ends in 22 individuals, show that the main coding exon of all but one copy is an intact open reading frame with 0-5 predicted amino acid differences. We detected transcription of OR-A in both olfactory epithelium and testis tissue using RT-PCR amplification with primers designed on the basis of a computationally predicted gene structure. Two alternatively spliced forms of transcripts, one encoding an isoform with an extended N-terminus, were found in both tissues. A third transcript, derived from a second promoter, was also observed in testes. The start methionine is predicted in all transcripts to lie in an upstream exon rather than the main coding exon, as is typical for most other OR genes. By examining sequence variants among transcripts, we show that transcription of this gene occurs at multiple chromosomal locations. Our results lend credence to the idea that OR diversity could be generated in rearrangement-prone subtelomeric regions and show that polymorphism in subtelomeric regions could lead to individual-to-individual variation in the expressed repertoire of OR genes.

Cloning and characterization of two Toll/Interleukin-1 receptor-like genes TIL3 and TIL4: evidence for a multi-gene receptor family in humans

Remarkable structural and functional similarities exist between the Drosophila Toll/Cactus/Dorsal signaling pathway and the mammalian cytokine-mediated interleukin-1 receptor (IL-1R)/I-kappaB/NF-kappaB activation cascade. In addition to a role regulating dorsal-ventral polarity in the developing Drosophila embryo, signaling through Drosophila Toll (dToll) activates the nonclonal, or innate, immune response in the adult fly. Recent evidence indicates that a human homologue of the dToll protein participates in the regulation of both innate and adaptive human immunity through the activation of NF-kappaB and the expression of the NF-kappaB-controlled genes IL-1, IL-6, and IL-8, thus affirming the evolutionary conservation of this host defense pathway. We report here the cloning of two novel human genes, TIL3 and TIL4 (Toll/IL-1R-like-3, -4) that exhibit homology to both the leucine-rich repeat extracellular domains and the IL-1R-like intracellular domains of human and Drosophila Toll. Northern analysis showed distinctly different tissue distribution patterns with TIL3 expressed predominantly in ovary, peripheral blood leukocytes, and prostate, and TIL4 expressed primarily in peripheral blood leukocytes and spleen. Chromosomal mapping by fluorescence in situ hybridization localized the TIL3 gene to chromosome 1q41-42 and TIL4 to chromosome 4q31.3-32. Functional studies showed that both TIL3 and TIL4 are able to activate NF-kappaB, though in a cell type-dependent fashion. Together with human Toll, TIL3 and TIL4 encode a family of genes with conserved structural and functional features involved in immune modulation.

Identification of a prion protein epitope modulating transmission of bovine spongiform encephalopathy prions to transgenic mice

There is considerable concern that bovine prions from cattle with bovine spongiform encephalopathy (BSE) may have been passed to humans (Hu), resulting in a new form of Creutzfeldt-Jakob disease (CJD). We report here the transmission of bovine (Bo) prions to transgenic (Tg) mice expressing BoPrP; one Tg line exhibited incubation times of approximately 200 days. Like most cattle with BSE, vacuolation and astrocytic gliosis were confined in the brainstems of these Tg mice. Unexpectedly, mice expressing a chimeric Bo/Mo PrP transgene were resistant to BSE prions whereas mice expressing Hu or Hu/Mo PrP transgenes were susceptible to Hu prions. A comparison of differences in Mo, Bo, and Hu residues within the C terminus of PrP defines an epitope that modulates conversion of PrPC into PrPSc and, as such, controls prion transmission across species. Development of susceptible Tg(BoPrP) mice provides a means of measuring bovine prions that may prove critical in minimizing future human exposure.

A new apolipoprotein Al variant, Trp50Arg, causes hereditary amyloidosis

A man with hereditary non-neuropathic systemic amyloidosis had amyloid fibril protein subunits consisting of N-terminal fragments (residues 1-86, 1-92 and 1-93) of a previously unknown variant of apolipoprotein Al, Trp50Arg, encoded by a thymine-cytosine transition. This is the third reported amyloidogenic apoAl variant. All involve substitutions of single neutral amino acids by the cationic residue arginine, suggesting a common mechanism of amyloidogenesis. However, the phenotypic expression of these mutations varies both within and between the seven known families with hereditary apoAl amyloidosis. These findings should facilitate analysis of the molecular basis of fibrillogenesis and of factors that modulate amyloid deposition and its consequences in vivo.

Human lysozyme gene mutations cause hereditary systemic amyloidosis

Hereditary non-neuropathic systemic amyloidosis (Ostertag-type) is a rare autosomal dominant disease in which amyloid deposition in the viscera is usually fatal by the fifth decade. In some families it is caused by mutations in the apolipoprotein AI gene but in two unrelated English families under our care the amyloid deposits did not contain apoAI, despite a report that this may have been the case in one of them. Lysozyme is a ubiquitous bacteriolytic enzyme present in external secretions and in polymorphs and macrophages, but its physiological role is not always clear. Here we report that in these two families, lysozyme is the amyloid fibril protein. Affected individuals are heterozygous for point mutations in the lysozyme gene that cause substitution of highly conserved residues, namely threonine for isoleucine at position 56 in one family, and histidine for aspartic acid at residue 67 in the other. Amyloid fibrils from one individual were composed of the full-length Thr-56 variant lysozyme molecule. To our knowledge, this is the first report of naturally occurring variants of human lysozyme and of lysozyme-associated disease. As the structures of human and hen egg-white lysozyme are known to atomic resolution and their folding and structure-function relationships have been exhaustively analysed, our observations should provide a powerful model for understanding amyloidogenesis.

Purification and characterization of a phosphatidylinositol 3-kinase complex from bovine brain by using phosphopeptide affinity columns

Specific phosphorylated tyrosine residues in the kinase insert region of the human platelet-derived-growth-factor beta-receptor mediate the formation of multienzyme complexes with this receptor. When phosphorylated, tyrosine residue 751 within the kinase insert region mediates binding of PtdIns 3-kinase to this receptor. A 17-amino-acid peptide containing this tyrosine residue was synthesized, phosphorylated by using epidermal-growth-factor receptor and then coupled to an Actigel matrix. The tyrosine-751 phosphopeptide column is used here as a final affinity step in the purification of the PtdIns 3-kinase from bovine brain to apparent homogeneity. The active resin-bound PtdIns 3-kinase is composed of two polypeptides, p110 and p85, which are elutable with SDS-containing buffers and detectable by silver staining of polyacrylamide gels. The 85 kDa protein is shown to be identical with the recently cloned p85 alpha. Phosphotyrosine is demonstrated to be an essential part of the structure required for binding of both of these proteins and PtdIns 3-kinase activity to this peptide. The active PtdIns 3-kinase complex from bovine brain, but not recombinant p85 subunits, shows specificity for binding to phosphopeptides containing a YXXM consensus sequence. Neither PtdIns 3-kinase activity, nor the complex of p85 and 110 kDa proteins, binds to several other phosphopeptide affinity columns lacking this sequence motif. The selectivity of binding of baculovirus-expressed free p85 alpha subunit of bovine brain PtdIns 3-kinase, the closely related protein p85 beta and purified bovine brain PtdIns 3-kinase to these and other phosphopeptide columns is examined.

Apolipoprotein AI mutation Arg-60 causes autosomal dominant amyloidosis

A mutation in the gene for apolipoprotein AI (apoAI) was identified in an English family with autosomal dominant non-neuropathic systemic amyloidosis. The plasma of all affected individuals contained a variant apoAI with one additional charge, as well as normal apoAI. The propositus was heterozygous; the coding region of his apoAI gene contained both the normal sequence and a single-base substitution changing the codon for residue 60 of the mature protein from CTG (leucine) to CGG (arginine). Allele-specific oligonucleotide hybridization showed that the other affected individuals were also heterozygotes and that there was concordance of the mutant allele with the presence of variant plasma apoAI. Amyloid fibrils isolated from the spleen of the propositus consisted of proteins that ran as a doublet with an apparent mass of approximately 10 kDa in SDS/PAGE and a trace band at 28 kDa. Electrospray mass spectrometry of the purified 10-kDa material revealed components with mass corresponding to the N-terminal 88, 92, 93, and 94 residues of apoAI each with substitution of arginine for leucine. These observations were confirmed by direct protein sequencing and laser desorption time-of-flight mass analysis. No material with the normal apoAI sequence was detected. The trace band at 28 kDa yielded the N-terminal sequence of mature apoAI, indicating that intact or minimally degraded apoAI was also present in the fibril preparation. Discovery of this mutation and the detailed characterization of the apoAI fragments that form the amyloid fibrils open additional avenues for investigation of amyloidogenesis.

Studies on the primary sequence requirements for PKC-alpha, -beta 1 and -gamma peptide substrates

The substrate specificity of purified PKC-alpha, -beta and -gamma has been investigated. A series of synthetic peptides based upon the sequence surrounding serine-7 in glycogen synthase were generated and used to determine the basic residue requirements of these PKC isotypes. While PKC-alpha and -beta are indistinguishable in their phosphorylation of these peptides, PKC-gamma shows a distinct specificity profile for these synthetic substrates.

Neonatal death and lung injury in rats caused by intrauterine exposure to O,O,S-trimethylphosphorothioate

O,O,S-Trimethyl phosphorothioate (OOS-TMP) is an impurity present in a number of widely used organophosphorus insecticides and has been recognized as a potent lung toxicant. OOS-TMP was given p.o. to pregnant rats on gestation day (G) 20 at 0.5, 2.5, 10 and 40 mg/kg. Control dams or pair-fed dams (pair-fed to 40 mg/kg) received 2 ml/kg corn oil. Neonates from treated dams died within 72 h after delivery in a dose-related manner: 100% at 40 mg/kg, 86% at 10 mg/kg, 15% at 2.5 mg/kg, 1% at 0.5 mg/kg, with 3% in controls and 2% in neonates from pair-fed dams. Neonates from treated (40 or 10 mg/kg) and control dams were cross-fostered. The cross-fostering did not affect mortality of neonates from either dosed dams or from control dams. Disposition of OOS-TMP was studied by using [3H]-OOS-TMP at 0.5, 2.5 and 10 mg/kg. Concentrations of OOS-TMP equivalent in fetal lung were about one half of those in mothers at all doses. In another set of experiments, dams (five dams for each dose) were dosed on G 20 with OOS-TMP p.o. at 0, 0.5, 2.5, 10, and 40 mg/kg or pair-fed (pair-fed to 40 mg/kg) and the fetuses were delivered by cesarean section (C-section) on G 23. In neonates from dams dosed with 10 and 40 mg/kg, cyanosis occurred within 4 h after C-section. Histopathological examination revealed dose-related proliferation of type II pneumocytes in dams and proliferation of interstitial cells and delayed septal/capillary development in neonates.(ABSTRACT TRUNCATED AT 250 WORDS)