GSH and Zinc Supplementation Attenuate Cadmium-Induced Cellular Stress and Stimulation of Choline Uptake in Cultured Neonatal Rat Choroid Plexus Epithelia.

Choroid plexus (CP) sequesters cadmium and other metals, protecting the brain from these neurotoxins. These metals can induce cellular stress and modulate homeostatic functions of CP, such as solute transport. We previously showed in primary cultured neonatal rat CP epithelial cells (CPECs) that cadmium induced cellular stress and stimulated choline uptake at the apical membrane, which interfaces with cerebrospinal fluid in situ. Here, in CPECs, we characterized the roles of glutathione (GSH) and Zinc supplementation in the adaptive stress response to cadmium. Cadmium increased GSH and decreased the reduced GSH-to-oxidized GSH (GSSG) ratio. Heat shock protein-70 (Hsp70), heme oxygenase (HO-1), and metallothionein (Mt-1) were induced along with the catalytic and modifier subunits of glutamate cysteine ligase (GCL), the rate-limiting enzyme in GSH synthesis. Inhibition of GCL by l-buthionine sulfoximine (BSO) enhanced stress protein induction and stimulation of choline uptake by cadmium. Zinc alone did not induce Hsp70, HO-1, or GCL subunits, or modulate choline uptake. Zinc supplementation during cadmium exposure attenuated stress protein induction and stimulation of choline uptake; this effect persisted despite inhibition of GSH synthesis. These data indicated up-regulation of GSH synthesis promotes adaptation to cadmium-induced cellular stress in CP, but Zinc may confer cytoprotection independent of GSH.

Adrenergic supersensitivity and impaired neural control of cardiac electrophysiology following regional cardiac sympathetic nerve loss.

Myocardial infarction (MI) can result in sympathetic nerve loss in the infarct region. However, the contribution of hypo-innervation to electrophysiological remodeling, independent from MI-induced ischemia and fibrosis, has not been comprehensively investigated. We present a novel mouse model of regional cardiac sympathetic hypo-innervation utilizing a targeted-toxin (dopamine beta-hydroxylase antibody conjugated to saporin, DBH-Sap), and measure resulting electrophysiological and Ca2+ handling dynamics. Five days post-surgery, sympathetic nerve density was reduced in the anterior left ventricular epicardium of DBH-Sap hearts compared to control. In Langendorff-perfused hearts, there were no differences in mean action potential duration (APD80) between groups; however, isoproterenol (ISO) significantly shortened APD80 in DBH-Sap but not control hearts, resulting in a significant increase in APD80 dispersion in the DBH-Sap group. ISO also produced spontaneous diastolic Ca2+ elevation in DBH-Sap but not control hearts. In innervated hearts, sympathetic nerve stimulation (SNS) increased heart rate to a lesser degree in DBH-Sap hearts compared to control. Additionally, SNS produced APD80 prolongation in the apex of control but not DBH-Sap hearts. These results suggest that hypo-innervated hearts have regional super-sensitivity to circulating adrenergic stimulation (ISO), while having blunted responses to SNS, providing important insight into the mechanisms of arrhythmogenesis following sympathetic nerve loss.

Aging Disrupts Normal Time-of-Day Variation in Cardiac Electrophysiology.

BACKGROUND: Cardiac gene expression and arrhythmia occurrence have time-of-day variation; however, daily changes in cardiac electrophysiology, arrhythmia susceptibility, and Ca2+ handling have not been characterized. Furthermore, how these patterns change with age is unknown. METHODS: Hearts were isolated during the light (zeitgeber time [ZT] 4 and ZT9) and dark cycle (ZT14 and ZT21) from adult (12-18 weeks) male mice. Hearts from aged (18-20 months) male mice were isolated at ZT4 and ZT14. All hearts were Langendorff-perfused for optical mapping with voltage- and Ca2+-sensitive dyes (n=4-7/group). Cardiac gene and protein expression were assessed with real-time polymerase chain reaction (n=4-6/group) and Western blot (n=3-4/group). RESULTS: Adult hearts had the shortest action potential duration (APD) and Ca2+ transient duration (CaTD) at ZT14 (APD80: ZT4: 45.4±4.1 ms; ZT9: 45.1±8.6 ms; ZT14: 34.7±4.2 ms; ZT21: 49.2±7.6 ms, P<0.05 versus ZT4 and ZT21; and CaTD80: ZT4: 70.1±3.3 ms; ZT9: 72.7±2.7 ms; ZT14: 64.3±3.3 ms; ZT21: 74.4±1.2 ms, P<0.05 versus other time points). The pacing frequency at which CaT alternans emerged was faster, and average CaT alternans magnitude was significantly reduced at ZT14 compared with the other time points. There was a trend for decreased spontaneous premature ventricular complexes and pacing-induced ventricular arrhythmias at ZT14, and the hearts at ZT14 had diminished responses to isoproterenol compared with ZT4 (ZT4: 49.5.0±5.6% versus ZT14: 22.7±9.5% decrease in APD, P<0.01). In contrast, aged hearts exhibited no difference between ZT14 and ZT4 in nearly every parameter assessed (except APD80: ZT4: 39.7±1.9 ms versus ZT14: 33.8±3.1 ms, P<0.01). Gene expression of KCNA5 (potassium voltage-gated channel subfamily A member 5; encoding Kv1.5) was increased, whereas gene expression of ADRB1 (encoding ß1-adrenergic receptors) was decreased at ZT14 versus ZT4 in adult hearts. No time-of-day changes in expression or phosphorylation of Ca2+ handling proteins (SERCA2 [sarco/endoplasmic reticulum Ca2+-ATPase], RyR2 [ryanodine receptor 2], and PLB [phospholamban]) was found in ex vivo perfused adult isolated hearts. CONCLUSIONS: Isolated adult hearts have strong time-of-day variation in cardiac electrophysiology, Ca2+ handling, and adrenergic responsiveness, which is disrupted with age.

Cardiac sympathetic nerve transdifferentiation reduces action potential heterogeneity after myocardial infarction.

Cardiac sympathetic nerves undergo cholinergic transdifferentiation following reperfused myocardial infarction (MI), whereby the sympathetic nerves release both norepinephrine (NE) and acetylcholine (ACh). The functional electrophysiological consequences of post-MI transdifferentiation have never been explored. We performed MI or sham surgery in wild-type (WT) mice and mice in which choline acetyltransferase was deleted from adult noradrenergic neurons [knockout (KO)]. Electrophysiological activity was assessed with optical mapping of action potentials (AP) and intracellular Ca2+ transients (CaT) in innervated Langendorff-perfused hearts. KO MI hearts had similar NE content but reduced ACh content compared with WT MI hearts (0.360 ± 0.074 vs. 0.493 ± 0.087 pmol/mg; KO, n = 6; WT, n = 4; P < 0.05). KO MI hearts also had higher basal ex vivo heart rates versus WT MI hearts (328.5 ± 35.3 vs. 247.4 ± 62.4 beats/min; KO, n = 8; WT, n = 6; P < 0.05). AP duration at 80% repolarization was significantly shorter in the remote and border zones of KO MI versus WT MI hearts, whereas AP durations (APDs) were similar in infarct regions. This APD heterogeneity resulted in increased APD dispersion in the KO MI versus WT MI hearts (11.9 ± 2.7 vs. 8.2 ± 2.3 ms; KO, n = 8; WT, n = 6; P < 0.05), which was eliminated with atropine. CaT duration at 80% and CaT alternans magnitude were similar between groups both with and without sympathetic nerve stimulation. These results indicate that cholinergic transdifferentiation following MI prolongs APD in the remote and border zone and reduces APD heterogeneity.NEW & NOTEWORTHY Cardiac sympathetic neurons undergo cholinergic transdifferentiation following myocardial infarction; however, the electrophysiological effects of corelease of norepinephrine and acetylcholine (ACh) have never been assessed. Using a mouse model in which choline acetyltransferase was deleted from adult noradrenergic neurons and optical mapping of innervated hearts, we found that corelease of ACh reduces dispersion of action potential duration, which may be antiarrhythmic.

Different paths, same destination: divergent action potential responses produce conserved cardiac fight-or-flight response in mouse and rabbit hearts.

KEY POINTS: Cardiac electrophysiology and Ca2+ handling change rapidly during the fight-or-flight response to meet physiological demands. Despite dramatic differences in cardiac electrophysiology, the cardiac fight-or-flight response is highly conserved across species. In this study, we performed physiological sympathetic nerve stimulation (SNS) while optically mapping cardiac action potentials and intracellular Ca2+ transients in innervated mouse and rabbit hearts. Despite similar heart rate and Ca2+ handling responses between mouse and rabbit hearts, we found notable species differences in spatio-temporal repolarization dynamics during SNS. Species-specific computational models revealed that these electrophysiological differences allowed for enhanced Ca2+ handling (i.e. enhanced inotropy) in each species, suggesting that electrophysiological responses are fine-tuned across species to produce optimal cardiac fight-or-flight responses. ABSTRACT: Sympathetic activation of the heart results in positive chronotropy and inotropy, which together rapidly increase cardiac output. The precise mechanisms that produce the electrophysiological and Ca2+ handling changes underlying chronotropic and inotropic responses have been studied in detail in isolated cardiac myocytes. However, few studies have examined the dynamic effects of physiological sympathetic nerve activation on cardiac action potentials (APs) and intracellular Ca2+ transients (CaTs) in the intact heart. Here, we performed bilateral sympathetic nerve stimulation (SNS) in fully innervated, Langendorff-perfused rabbit and mouse hearts. Dual optical mapping with voltage- and Ca2+ -sensitive dyes allowed for analysis of spatio-temporal AP and CaT dynamics. The rabbit heart responded to SNS with a monotonic increase in heart rate (HR), monotonic decreases in AP and CaT duration (APD, CaTD), and a monotonic increase in CaT amplitude. The mouse heart had similar HR and CaT responses; however, a pronounced biphasic APD response occurred, with initial prolongation (50.9 ± 5.1 ms at t = 0 s vs. 60.6 ± 4.1 ms at t = 15 s, P < 0.05) followed by shortening (46.5 ± 9.1 ms at t = 60 s, P = NS vs. t = 0). We determined the biphasic APD response in mouse was partly due to dynamic changes in HR during SNS and was exacerbated by ß-adrenergic activation. Simulations with species-specific cardiac models revealed that transient APD prolongation in mouse allowed for greater and more rapid CaT responses, suggesting more rapid increases in contractility; conversely, the rabbit heart requires APD shortening to produce optimal inotropic responses. Thus, while the cardiac fight-or-flight response is highly conserved between species, the underlying mechanisms orchestrating these effects differ significantly.

Structure-based design, synthesis and biological evaluation of a novel series of isoquinolone and pyrazolo[4,3-c]pyridine inhibitors of fascin 1 as potential anti-metastatic agents.

Fascin is an actin binding and bundling protein that is not expressed in normal epithelial tissues but overexpressed in a variety of invasive epithelial tumors. It has a critical role in cancer cell metastasis by promoting cell migration and invasion. Here we report the crystal structures of fascin in complex with a series of novel and potent inhibitors. Structure-based elaboration of these compounds enabled the development of a series with nanomolar affinities for fascin, good physicochemical properties and the ability to inhibit fascin-mediated bundling of filamentous actin. These compounds provide promising starting points for fascin-targeted anti-metastatic therapies.

Age-related changes in cardiac electrophysiology and calcium handling in response to sympathetic nerve stimulation.

KEY POINTS: Ageing results in changes to cardiac electrophysiology, Ca2+ handling, and ß-adrenergic responsiveness. Sympathetic neurodegeneration also occurs with age, yet detailed action potential and Ca2+ handling responses to physiological sympathetic nerve stimulation (SNS) in the aged heart have not been assessed. Optical mapping in mouse hearts with intact sympathetic innervation revealed reduced responsiveness to SNS in the aged atria (assessed by heart rate) and aged ventricles (assessed by action potentials and Ca2+ transients). Sympathetic nerve density and noradrenaline content were reduced in aged ventricles, but noradrenaline content was preserved in aged atria. These results demonstrate that reduced responsiveness to SNS in the atria may be primarily due to decreased ß-adrenergic receptor responsiveness, whereas reduced responsiveness to SNS in the ventricles may be primarily due to neurodegeneration. ABSTRACT: The objective of this study was to determine how age-related changes in sympathetic structure and function impact cardiac electrophysiology and intracellular Ca2+ handling. Innervated hearts from young (3-4 months, YWT, n = 10) and aged (20-24 months, AGED, n = 11) female mice (C57Bl6) were optically mapped using the voltage (Vm ,)- and calcium (Ca2+ )-sensitive indicators Rh237 and Rhod2-AM. Sympathetic nerve stimulation (SNS) was performed at the spinal cord (T1-T3). ß-Adrenergic responsiveness was assessed with isoproterenol (1 µM, ISO). Sympathetic nerve density and noradrenaline content were also quantified. Stimulation thresholds necessary to produce a defined increase in heart rate (HR) with SNS were higher in AGED vs. YWT hearts (5.4 ± 0.4 vs. 3.8 ± 0.4 Hz, P < 0.05). Maximal HR with SNS was lower in AGED vs. YWT (20.5 ± 3.41% vs. 73.0 ± 7.63% increase, P < 0.05). ß-Adrenergic responsiveness of the atria (measured as percentage increase in HR with ISO) was decreased in AGED vs. YWT hearts (75.3 ± 22.5% vs. 148.5 ± 19.8%, P < 0.05). SNS significantly increased action potential duration (APD) in YWT but not AGED. Ca2+ transient durations and rise times were unchanged by SNS, yet AGED hearts had an increased susceptibility to Ca2+ alternans and ventricular arrhythmias. ß-Adrenergic responsiveness of all ventricular parameters were similar between AGED and YWT. Sympathetic nerve density and noradrenaline content were decreased in the AGED ventricle, but not atria, compared to YWT. These data suggest that decreased responsiveness to SNS in the aged atria may be primarily due to decreased ß-adrenergic responsiveness, whereas decreased responsiveness to SNS in the aged ventricles may be primarily due to nerve degeneration.

Transient denervation of viable myocardium after myocardial infarction does not alter arrhythmia susceptibility.

Cardiac sympathetic nerves stimulate heart rate and force of contraction. Myocardial infarction (MI) leads to the loss of sympathetic nerves within the heart, and clinical studies have indicated that sympathetic denervation is a risk factor for arrhythmias and cardiac arrest. Two distinct types of denervation have been identified in the mouse heart after MI caused by ischemia-reperfusion: transient denervation of peri-infarct myocardium and sustained denervation of the infarct. Sustained denervation is linked to increased arrhythmia risk, but it is not known whether acute nerve loss in peri-infarct myocardium also contributes to arrhythmia risk. Peri-infarct sympathetic denervation requires the p75 neurotrophin receptor (p75NTR), but removal of p75NTR alters the pattern of sympathetic innervation in the heart and increases spontaneous arrhythmias. Therefore, we targeted the p75NTR coreceptor sortilin and the p75NTR-induced protease tumor necrosis factor-α-converting enzyme/A disintegrin and metalloproteinase domain 17 (TACE/ADAM17) to selectively block peri-infarct denervation. Sympathetic nerve density was quantified using immunohistochemistry for tyrosine hydroxylase. Genetic deletion of sortilin had no effect on the timing or extent of axon degeneration, but inhibition of TACE/ADAM17 with the protease inhibitor marimastat prevented the loss of axons from viable myocardium. We then asked whether retention of nerves in peri-infarct myocardium had an impact on cardiac electrophysiology 3 days after MI using ex vivo optical mapping of transmembrane potential and intracellular Ca2+. Preventing acute denervation of viable myocardium after MI did not significantly alter cardiac electrophysiology or Ca2+ handling, suggesting that transient denervation at this early time point has minimal impact on arrhythmia risk. NEW & NOTEWORTHY Sympathetic denervation after myocardial infarction is a risk factor for arrhythmias. We asked whether transient loss of nerves in viable myocardium contributed to arrhythmia risk. We found that targeting protease activity could prevent acute peri-infarct denervation but that it did not significantly alter cardiac electrophysiology or Ca2+ handling 3 days after myocardial infarction.

Antiarrhythmic effects of interleukin 1 inhibition after myocardial infarction.

BACKGROUND: Interleukin 1ß (IL-1ß) is a key regulator of the inflammatory response after myocardial infarction (MI) by modulating immune cell recruitment, cytokine production, and extracellular matrix turnover. Elevated levels of IL-1ß are associated with adverse remodeling, and inhibition of IL-1 signaling after MI results in improved contractile function. OBJECTIVE: The goal of this study was to determine whether IL-1 signaling also contributes to post-MI arrhythmogenesis. METHODS: MI was created in 2 murine models of elevated inflammation: atherosclerotic on the Western diet or wild-type with a subseptic dose of lipopolysaccharide. The role of IL-1ß was assessed with the IL-1 receptor antagonist anakinra (10 mg/(kg·d), starting 24 hours post-MI). RESULTS: In vivo and ex vivo molecular imaging showed reduced myocardial inflammation after a 4-day course of anakinra treatment, despite no change in infarct size. At day 5 post-MI, high-speed optical mapping of transmembrane potential and intracellular Ca2+ in isolated hearts revealed that IL-1ß inhibition improved conduction velocity, reduced action potential duration dispersion, improved intracellular Ca2+ handling, decreased transmembrane potential and Ca2+ alternans magnitude, and reduced spontaneous and inducible ventricular arrhythmias. These functional improvements were linked to increased expression of connexin 43 and sarcoplasmic reticulum Ca2+-ATPase. CONCLUSION: This study revealed a novel mechanism for IL-1ß in contributing to defective excitation-contraction coupling and arrhythmogenesis in the post-MI heart. Our results suggest that inhibition of IL-1 signaling post-MI may represent a novel antiarrhythmic therapy.

Foxo3 circular RNA promotes cardiac senescence by modulating multiple factors associated with stress and senescence responses.

AIMS: Circular RNAs are a subclass of non-coding RNAs detected within mammalian cells. This study was designed to test the roles of a circular RNA circ-Foxo3 in senescence using in vitro and in vivo approaches. METHODS AND RESULTS: Using the approaches of molecular and cellular biology, we show that a circular RNA generated from a member of the forkhead family of transcription factors, Foxo3, namely circ-Foxo3, was highly expressed in heart samples of aged patients and mice, which was correlated with markers of cellular senescence. Doxorubicin-induced cardiomyopathy was aggravated by ectopic expression of circ-Foxo3 but was relieved by silencing endogenous circ-Foxo3. We also found that silencing circ-Foxo3 inhibited senescence of mouse embryonic fibroblasts and that ectopic expression of circ-Foxo3 induced senescence. We found that circ-Foxo3 was mainly distributed in the cytoplasm, where it interacted with the anti-senescent protein ID-1 and the transcription factor E2F1, as well as the anti-stress proteins FAK and HIF1α. CONCLUSION: We conclude that ID-1, E2F1, FAK, and HIF1α interact with circ-Foxo3 and are retained in the cytoplasm and could no longer exert their anti-senescent and anti-stress roles, resulting in increased cellular senescence.

The crossroads of inflammation, fibrosis, and arrhythmia following myocardial infarction.

Optimal healing of damaged tissue following myocardial infarction (MI) requires a coordinated cellular response that can be divided into three phases: inflammatory, proliferative/reparative, and maturation. The inflammatory phase, characterized by rapid influx of cytokines, chemokines, and immune cells, is critical to the removal of damaged tissue. The onset of the proliferative/reparative phase is marked by increased proliferation of myofibroblasts and secretion of collagen to replace dead tissue. Lastly, crosslinking of collagen fibers and apoptosis of immune cells marks the maturation phase. Excessive inflammation or fibrosis has been linked to increased incidence of arrhythmia and other MI-related pathologies. This review describes the roles of inflammation and fibrosis in arrhythmogenesis and prospective therapies for anti-arrhythmic treatment.

Low brain penetrant CB1 receptor agonists for the treatment of neuropathic pain.

Novel, low brain penetrant, orally bioavailable CB1 receptor agonists were designed starting from a mature lead series of potent brain penetrant CB1 receptor agonists. Increasing the calculated polar surface area was found to be a good strategy for reducing brain penetration whilst retaining drug-like properties. This in silico approach led to the discovery of LBP1, an orally bioavailable, low brain penetrant CB1 receptor agonist with robust activity in rodent models of neuropathic pain and a good preclinical therapeutic profile, which was selected for clinical development.

Design, synthesis and structure-activity relationships of (indo-3-yl) heterocyclic derivatives as agonists of the CB1 receptor. Discovery of a clinical candidate.

We report an expansion of the structure-activity relationship (SAR) of a novel series of indole-3-heterocyclic CB1 receptor agonists. Starting from the potent but poorly soluble lead, 1, a rational approach was taken in order to balance solubility, hERG activity and potency while retaining the desired long duration of action within the mouse tail flick test. This led to the discovery of compound 38 which successfully progressed into clinical development.

Discovery of potent and orally bioavailable heterocycle-based cannabinoid CB1 receptor agonists.

Novel 3-(1H-indol-3-yl)-1,2,4-oxadiazoles and -thiadiazoles were synthesized and found to be potent CB1 cannabinoid receptor agonists. The oral bioavailability of these compounds could be dramatically improved by optimization studies of the side chains attached to the indole and oxadiazole cores, leading to identification of a CB1 receptor agonist with good oral activity in a range of preclinical models of antinociception and antihyperalgesia.

Design, synthesis, and structure-activity relationships of indole-3-heterocycles as agonists of the CB1 receptor.

Novel indole-3-heterocycles were designed and synthesized and found to be potent CB1 receptor agonists. Starting from a microsomally unstable lead 1, a bioisostere approach replacing a piperazine amide was undertaken. This was found to be a good strategy for improving stability both in vitro and in vivo. This led to the discovery of 24, which had an increased duration of action in the mouse tail flick test in comparison to the lead 1.

Design, synthesis, and structure-activity relationship study of conformationally constrained analogs of indole-3-carboxamides as novel CB1 cannabinoid receptor agonists.

Novel tricyclic indole-3-carboxamides were synthesized as structurally restricted analogs of bicyclic indoles, and found to be potent CB1 cannabinoid receptor agonists. The CB1 agonist activity depended on the absolute configuration of the chiral center of the tricyclic ring. The preferred enantiomer was more potent than the structurally unconstrained lead compound. Structure-activity relationships in the amide side chain of the indole C-3 position were also investigated.