3-Methyl-phenanthrene (3-MP) disrupts the electrical and contractile activity of the heart of the polar fish, navaga cod (Eleginus nawaga).

Alkylated polycyclic aromatic hydrocarbons are abundant in crude oil and are enriched during petroleum refinement but knowledge of their cardiotoxicity remains limited. Polycyclic aromatic hydrocarbons (PAHs) are considered the main hazardous components in crude oil and the tricyclic PAH phenanthrene has been singled out for its direct effects on cardiac tissue in mammals and fish. Here we test the impact of the monomethylated phenanthrene, 3-methylphenanthrene (3-MP), on the contractile and electrical function of the atrium and ventricle of a polar fish, the navaga cod (Eleginus nawaga). Using patch-clamp electrophysiology in atrial and ventricular cardiomyocytes we show that 3-MP is a potent inhibitor of the delayed rectifier current IKr (IC50 = 0.25 µM) and prolongs ventricular action potential duration. Unlike the parent compound phenanthrene, 3-MP did not reduce the amplitude of the L-type Ca2+ current (ICa) but it accelerated current inactivation thus reducing charge transfer across the myocyte membrane and compromising pressure development of the whole heart. 3-MP was a potent inhibitor (IC50 = 4.7 µM) of the sodium current (INa), slowing the upstroke of the action potential in isolated cells, slowing conduction velocity across the atrium measured with optical mapping, and increasing atrio-ventricular delay in a working whole heart preparation. Together, these findings reveal the strong cardiotoxic potential of this phenanthrene derivative on the fish heart. As 3-MP and other alkylated phenanthrenes comprise a large fraction of the PAHs in crude oil mixtures, these findings are worrisome for Arctic species facing increasing incidence of spills and leaks from the petroleum industry. 3-MP is also a major component of polluted air but is not routinely measured. This is also of concern if the hearts of humans and other terrestrial animals respond to this PAH in a similar manner to fish.

Cognitive Impairment in Nonagenarians: Potential Metabolic Mechanisms Revealed by the Synergy of In Silico Gene Expression Modeling and Pathway Enrichment Analysis.

Previous studies examining the molecular and genetic basis of cognitive impairment, particularly in cohorts of long-living adults, have mainly focused on associations at the genome or transcriptome level. Dozens of significant dementia-associated genes have been identified, including APOE, APOC1, and TOMM40. However, most of these studies did not consider the intergenic interactions and functional gene modules involved in cognitive function, nor did they assess the metabolic changes in individual brain regions. By combining functional analysis with a transcriptome-wide association study, we aimed to address this gap and examine metabolic pathways in different areas of the brain of older adults. The findings from our previous genome-wide association study in 1155 older adults, 179 of whom had cognitive impairment, were used as input for the PrediXcan gene prediction algorithm. Based on the predicted changes in gene expression levels, we conducted a transcriptome-wide association study and functional analysis using the KEGG and HALLMARK databases. For a subsample of long-living adults, we used logistic regression to examine the associations between blood biochemical markers and cognitive impairment. The functional analysis revealed a significant association between cognitive impairment and the expression of NADH oxidoreductase in the cerebral cortex. Significant associations were also detected between cognitive impairment and signaling pathways involved in peroxisome function, apoptosis, and the degradation of lysine and glycan in other brain regions. Our approach combined the strengths of a transcriptome-wide association study with the advantages of functional analysis. It demonstrated that apoptosis and oxidative stress play important roles in cognitive impairment.

Machine Learning-Based Decision-Making in Geriatrics: Aging Phenotype Calculator and Survival Prognosis.

Aging is a natural process with varying effects. As we grow older, our bodies become more susceptible to aging-associated diseases. These diseases, individually or collectively, lead to the formation of distinct aging phenotypes. Identifying these aging phenotypes and understanding the complex interplay between coexistent diseases would facilitate more personalized patient management, a better prognosis, and a prolonged lifespan. Many studies distinguish between successful aging and frailty. However, this simple distinction fails to reflect the diversity of underlying causes. In this study, we sought to establish the underlying causes of frailty and determine the patterns in which these causes converge to form aging phenotypes. We conducted a comprehensive geriatric examination, cognitive assessment, and survival analysis of 2,688 long-living adults (median age = 92 years). The obtained data were clustered and used as input data for the Aging Phenotype Calculator, a multiclass classification model validated on an independent dataset of 96 older adults. The accuracy of the model was assessed using the receiver operating characteristic curve and the area under the curve. Additionally, we analyzed socioeconomic factors that could contribute to specific aging patterns. We identified five aging phenotypes: non-frailty, multimorbid frailty, metabolic frailty, cognitive frailty, and functional frailty. For each phenotype, we determined the underlying diseases and conditions and assessed the survival rate. Additionally, we provided management recommendations for each of the five phenotypes based on their distinct features and associated challenges. The identified aging phenotypes may facilitate better-informed decision-making. The Aging Phenotype Calculator (ROC AUC = 92%) may greatly assist geriatricians in patient management.

High temperature and hyperkalemia cause exit block of action potentials at the atrioventricular junction of rainbow trout (Oncorhynchus mykiss) heart.

At critically high temperatures, atrioventricular (AV) block causes ventricular bradycardia and collapse of cardiac output in fish. Here, the possible role of the AV canal in high temperature-induced heart failure was examined. To this end, optical mapping was used to measure action potential (AP) conduction in isolated AV junction preparations of the rainbow trout (Oncorhynchus mykiss) heart during acute warming/cooling in the presence of 4 or 8 mM external K+ concentration. The preparation included the AV canal and some atrial and ventricular tissue at its edges, and it was paced either from atrial or ventricular side at a frequency of 0.67 Hz (40 beats min-1) to trigger forward (anterograde) and backward (retrograde) conduction, respectively. The propagation of AP was fast in atrial and ventricular tissues, but much slower in the AV canal, causing an AV delay. Acute warming from 15 °C to 27 °C or cooling from 15 °C to 5 °C did not impair AP conduction in the AV canal, as both anterograde and retrograde excitations propagated regularly through the AV canal. In contrast, anterograde conduction through the AV canal did not trigger ventricular excitation at the boundary zone between the AV canal and the ventricle when extracellular K+ concentration was raised from 4 mM to 8 mM at 27 °C. Also, the retrograde conduction was blocked at the border between the AV canal and the atrium in high K+ at 27 °C. These findings suggest that the AV canal is resistant against high temperatures (and high K+), but the ventricular muscle cannot be excited by APs coming from the AV canal when temperature and external K+ concentration are simultaneously elevated. Therefore, bradycardia at high temperatures in fish may occur due to inability of AP of the AV canal to trigger ventricular AP at the junctional zone between the AV canal and the proximal part of the ventricle.

Adrenergic prolongation of action potential duration in rainbow trout myocardium via inhibition of the delayed rectifier potassium current, IKr.

Catecholamines mediate the 'fight or flight' response in a wide variety of vertebrates. The endogenous catecholamine adrenaline increases heart rate and contractile strength to raise cardiac output. The increase in contractile force is driven in large part by an increase in myocyte Ca2+ influx on the L-type Ca current (ICaL) during the cardiac action potential (AP). Here, we report a K+- based mechanism that prolongs AP duration (APD) in fish hearts following adrenergic stimulation. We show that adrenergic stimulation inhibits the delayed rectifier K+ current (IKr) in rainbow trout (Oncorhynchus mykiss) cardiomyocytes. This slows repolarization and prolongs APD which may contribute to positive inotropy following adrenergic stimulation in fish hearts. The endogenous ligand, adrenaline (1 µM), which activates both α- and ß-ARs reduced maximal IKr tail current to 61.4 ± 3.9% of control in atrial and ventricular myocytes resulting in an APD prolongation of ~20% at both 50 and 90% repolarization. This effect was reproduced by the α-specific adrenergic agonist, phenylephrine (1 µM), but not the ß-specific adrenergic agonist isoproterenol (1 µM). Adrenaline (1 µM) in the presence of ß1 and ß2-blockers (1 µM atenolol and 1 µM ICI-118551, respectively) also inhibited IKr. Thus, IKr suppression following α-adrenergic stimulation leads to APD prolongation in the rainbow trout heart. This is the first time this mechanism has been identified in fish and may act in unison with the well-known enhancement of ICaL following adrenergic stimulation to prolong APD and increase cardiac inotropy.

Effects of Na+ channel isoforms and cellular environment on temperature tolerance of cardiac Na+ current in zebrafish (Danio rerio) and rainbow trout (Oncorhynchus mykiss).

Heat tolerance of heart rate in fish is suggested to be limited by impaired electrical excitation of the ventricle due to the antagonistic effects of high temperature on Na+ (INa) and K+ (IK1) ion currents (INa is depressed at high temperatures while IK1 is resistant to them). To examine the role of Na+ channel proteins in heat tolerance of INa, we compared temperature dependencies of zebrafish (Danio rerio, warm-dwelling subtropical species) and rainbow trout (Oncorhynchus mykiss, cold-active temperate species) ventricular INa, and INa generated by the cloned zebrafish and rainbow trout NaV1.4 and NaV1.5 Na+ channels in human embryonic kidney (HEK) cells. Whole-cell patch-clamp recordings showed that zebrafish ventricular INa has better heat tolerance and slower inactivation kinetics than rainbow trout ventricular INa. In contrast, heat tolerance and inactivation kinetics of zebrafish and rainbow trout NaV1.4 channels are similar when expressed in the identical cellular environment of HEK cells. The same applies to NaV1.5 channels. These findings indicate that thermal adaptation of ventricular INa is largely achieved by differential expression of Na+ channel alpha subunits: zebrafish that tolerate higher temperatures mainly express the slower NaV1.5 isoform, while rainbow trout that prefer cold waters mainly express the faster NaV1.4 isoform. Differences in elasticity (stiffness) of the lipid bilayer and/or accessory protein subunits of the channel assembly may also be involved in thermal adaptation of INa. The results are consistent with the hypothesis that slow Na+ channel kinetics are associated with increased heat tolerance of cardiac excitation.

Ionic basis of atrioventricular conduction: ion channel expression and sarcolemmal ion currents of the atrioventricular canal of the rainbow trout (Oncorhynchus mykiss) heart.

Atrioventricular (AV) nodal tissue synchronizes activities of atria and ventricles of the vertebrate heart and is also a potential site of cardiac arrhythmia, e.g., under acute heat stress. Since ion channel composition and ion currents of the fish AV canal have not been previously studied, we measured major cation currents and transcript expression of ion channels in rainbow trout (Oncorhynchus mykiss) AV tissue. Both ion current densities and expression of ion channel transcripts indicate that the fish AV canal has a characteristic electrophysiological phenotype that differs from those of sinoatrial tissue, atrium and ventricle. Two types of cardiomyocytes were distinguished electrophysiologically in trout AV nodal tissue: the one (transitional cell) is functionally intermediate between working atrial/ventricular myocytes and the other (AV nodal cell) has a less negative resting membrane potential than atrial and ventricular myocytes and is a more similar to the sinoatrial nodal cells in ion channel composition. The AV nodal cells are characterized by a small or non-existent inward rectifier potassium current (IK1), low density of fast sodium current (INa) and relatively high expression of T-type calcium channels (CACNA3.1). Pacemaker channel (HCN4 and HCN2) transcripts were expressed in the AV nodal tissue but If current was not found in enzymatically isolated nodal myocytes. The electrophysiological properties of the rainbow trout nodal cells are appropriate for a slow rate of action potential conduction (small INa) and a moderate propensity for pacemaking activity (absence of IK1).

Small G-protein RhoA is a potential inhibitor of cardiac fast sodium current.

Small G-proteins of Rho family modulate the activity of several classes of ion channels, including K+ channels Kv1.2, Kir2.1, and ERG; Ca2+ channels; and epithelial Na+ channels. The present study was aimed to check the RhoA potential regulatory effects on Na+ current (INa) transferred by Na+ channel cardiac isoform NaV1.5 in heterologous expression system and in native rat cardiomyocytes. Whole-cell patch-clamp experiments showed that coexpression of NaV1.5 with the wild-type RhoA in CHO-K1 cell line caused 2.7-fold decrease of INa density with minimal influence on steady-state activation and inactivation. This effect was reproduced by the coexpression with a constitutively active RhoA, but not with a dominant negative RhoA. In isolated ventricular rat cardiomyocytes, a 5-h incubation with the RhoA activator narciclasine (5 × 10-6 M) reduced the maximal INa density by 38.8%. The RhoA-selective inhibitor rhosin (10-5 M) increased the maximal INa density by 25.3%. Experiments with sharp microelectrode recordings in isolated right ventricular wall preparations showed that 5 × 10-6 M narciclasine induced a significant reduction of action potential upstroke velocity after 2 h of incubation. Thus, RhoA might be considered as a potential negative regulator of sodium channels cardiac isoform NaV1.5.