3071Peptidomimetic targeting of CavBeta2 improves contractility in models of senescence- or genetically (MYBPC3 KI)-induced heart failure

Background

L-type calcium channel (LTCC) trafficking controls LTCC density at T-tubule levels for optimal Excitation-Coupling (EC) and resultant adaptive heart work. In some forms of heart failure (HF), abnormalities in calcium-induced calcium-release have been proposed to arise from alteration of T-tubular dyad architecture (LTCC-RyRs) associated with impaired LTCC density. Recently, the R7W-MP peptide, working as a binder of the LTCC Cavβ2 chaperone, was shown to restore the altered density of LTCC current by both promoting forward and reducing reverse trafficking, which consequently improved cellular calcium homeostasis. Accordingly, R7W-MP improved the impaired cardiomyocyte calcium current density and the reduced Ejection Fraction (EF%) in a pharmacologically-induced diabetes model (STZ mice).

We aimed to investigate further the benefit to improve LTCC trafficking pathway with R7W-MP in a more physiological model of HF (senescent mice) and in a Dilated Cardiomyopathy (DCM) model (HO MYBPC3 targeted KI mutant).

Methods

Senescent male C57Bl/6J mice (26 months) or HO MYBPC3 KI male mice (2 months) were treated with R7W-MP (3 mg/kg/d IP for 3 days). Echocardiographies (echo) were conducted before treatment and 4-hours after the last injection. When applied, Pressure-Volume (PV)-loop investigations were conducted one day post-echo 4 hours following an additional R7W-MP injection.

Results

In senescent mice population, HF was characterized by a midrange ejection fraction (EF%= 43±2 vs 55±1 for young adult mice) associated with enlarged ventricles and decreased cardiac contractility. In contrast to a scrambled peptide (scrP), R7W-MP markedly increased EF% monitored by echo (+38%, 63±3 vs 45±1 for scrP, p≤0.001, n=6–7) without modification of heart rate. EF% improvement was confirmed by PV-loop analysis (78±3 vs 51±4 for scrP (+54%), p≤0.001, n=5), associated with a marked, although not significant, 2.5-fold increase in myocardial contractility [end systolic pressure volume relationship (ESPVR) = 12.1±3.6 vs 4.9±1.3 for scrP, p=0.10, n=4]. Stroke volume, cardiac output and end diastolic volume tended to decrease suggesting an impaired LV filling at this dose regimen. In the DCM model, HF was more severe with a dramatically low EF% (26±1, n=8), impaired myocardial contractility and a pronounced left ventricle enlargement. R7W-MP significantly increased EF% (+17%, reaching 31±1, p≤0.01, n=8) without altering heart rate. Stroke volume was significantly increased by 36% (32±3 vs 24±3 mL at baseline, p≤0.01), without any impairment of diastolic function. All parameters returned to baseline after a 2 week-washout period.

Conclusions

R7W-MP displays potent positive inotrope properties in senescent or DCM mice models. Although further asses tsments of diastolic function are needed (different dosing and duration), these data underline the potential benefit brought by LTCC trafficking modulation to treat severe dilated cardiomyopathy.

A Human Stem Cell Model of Fabry Disease Implicates LIMP-2 Accumulation in Cardiomyocyte Pathology

Here, we have used patient-derived induced pluripotent stem cell (iPSC) and gene-editing technology to study the cardiac-related molecular and functional consequences of mutations in GLA causing the lysosomal storage disorder Fabry disease (FD), for which heart dysfunction is a major cause of mortality. Our in vitro model recapitulated clinical data with FD cardiomyocytes accumulating GL-3 and displaying an increased excitability, with altered electrophysiology and calcium handling. Quantitative proteomics enabled the identification of >5,500 proteins in the cardiomyocyte proteome and secretome, and revealed accumulation of the lysosomal protein LIMP-2 and secretion of cathepsin F and HSPA2/HSP70-2 in FD. Genetic correction reversed these changes. Overexpression of LIMP-2 directly induced the secretion of cathepsin F and HSPA2/HSP70-2, implying causative relationship, and led to massive vacuole accumulation. In summary, our study has revealed potential new cardiac biomarkers for FD, and provides valuable mechanistic insight into the earliest pathological events in FD cardiomyocytes.

Type 2/Th2-driven inflammation impairs olfactory sensory neurogenesis in mouse chronic rhinosinusitis model

BACKGROUND

Chronic rhinosinusitis (CRS) with nasal polyps (CRSwNP) is a chronic inflammatory disease often accompanied by impairment of sense of smell. This symptom has been somewhat overlooked, and its relationship to inflammatory cytokines, tissue compression, neuronal loss, and neurogenesis is still unclear.

METHODS

In order to elucidate potential mechanisms leading to CRS in humans, we have established a type 2/T helper type 2 cell (Th2)-mediated allergic CRS mouse model, based on house dust mite (HDM) and Staphylococcus aureus enterotoxin B (SEB) sensitization. The inflammatory status of the olfactory epithelium (OE) was assessed using histology, biochemistry, and transcriptomics. The sense of smell was evaluated by studying olfactory behavior and recording electro-olfactograms (EOGs).

RESULTS

After 22 weeks, a typical type 2/Th2-mediated inflammatory profile was obtained, as demonstrated by increased interleukin (IL)-4, IL-5, and IL-13 in the OE. The number of mast cells and eosinophils was increased, and infiltration of these cells into the olfactory mucosa was also observed. In parallel, transcriptomic and histology analyses indicated a decreased number of immature olfactory neurons, possibly due to decreased renewal. However, the number of mature sensory neurons was not affected and neither the EOG nor olfactory behavior was impaired.

CONCLUSION

Our mouse model of CRS displayed an allergic response to HDM + SEB administration, including the type 2/Th2 inflammatory profile characteristic of human eosinophilic CRSwNP. Although the sense of smell did not appear to be altered in these conditions, the data reveal the influence of chronic inflammation on olfactory neurogenesis, suggesting that factors unique to humans may be involved in CRSwNP-associated anosmia.

Functional Studies of Sodium Channels: From Target to Compound Identification

Over the last six decades, voltage-gated sodium (Na_v ) channels have attracted a great deal of scientific and pharmaceutical interest, driving fundamental advances in both biology and technology. The structure and physiological function of these channels have been extensively studied; clinical and genetic data have uncovered their implication in diseases such as epilepsy, arrhythmias, and pain, bringing them into focus as current and future drug targets. While different techniques have been established to record the activity of Na_v channels, proper determination of their properties still presents serious challenges, depending upon the experimental conditions and the desired subtype of channel to be characterized. The aim of this unit is to review the characteristics of Na_v channels, their properties, the cells in which they can be studied, and the currently available techniques. Topics covered include the determination of Na_v -channel biophysical properties as well as the use of toxins to discriminate between subtypes using electrophysiological or optical methods. Perspectives on the development of high-throughput screening assays with their advantages and limitations are also discussed to allow a better understanding of the challenges encountered in voltage-gated sodium channel preclinical drug discovery. © 2016 by John Wiley & Sons, Inc.

The antipsychotic drug loxapine is an opener of the sodium-activated potassium channel slack (Slo2.2)

Sodium-activated potassium (K(Na)) channels have been suggested to set the resting potential, to modulate slow after-hyperpolarizations, and to control bursting behavior or spike frequency adaptation (Trends Neurosci 28:422-428, 2005). One of the genes that encodes K(Na) channels is called Slack (Kcnt1, Slo2.2). Studies found that Slack channels were highly expressed in nociceptive dorsal root ganglion neurons and modulated their firing frequency (J Neurosci 30:14165-14172, 2010). Therefore, Slack channel openers are of significant interest as putative analgesic drugs. We screened the library of pharmacologically active compounds with recombinant human Slack channels expressed in Chinese hamster ovary cells, by using rubidium efflux measurements with atomic absorption spectrometry. Riluzole at 500 μM was used as a reference agonist. The antipsychotic drug loxapine and the anthelmintic drug niclosamide were both found to activate Slack channels, which was confirmed by using manual patch-clamp analyses (EC(50) = 4.4 μM and EC(50) = 2.9 μM, respectively). Psychotropic drugs structurally related to loxapine were also evaluated in patch-clamp experiments, but none was found to be as active as loxapine. Loxapine properties were confirmed at the single-channel level with recombinant rat Slack channels. In dorsal root ganglion neurons, loxapine was found to behave as an opener of native K(Na) channels and to increase the rheobase of action potential. This study identifies new K(Na) channel pharmacological tools, which will be useful for further Slack channel investigations.

SSR180711, a novel selective alpha7 nicotinic receptor partial agonist: (1) binding and functional profile

In this paper, we report on the pharmacological and functional profile of SSR180711 (1,4-Diazabicyclo[3.2.2]nonane-4-carboxylic acid, 4-bromophenyl ester), a new selective alpha7 acetylcholine nicotinic receptor (n-AChRs) partial agonist. SSR180711 displays high affinity for rat and human alpha7 n-AChRs (K(i) of 22+/-4 and 14+/-1 nM, respectively). Ex vivo (3)[H]alpha-bungarotoxin binding experiments demonstrate that SSR180711 rapidly penetrates into the brain (ID(50)=8 mg/kg p.o.). In functional studies performed with human alpha7 n-AChRs expressed in Xenopus oocytes or GH4C1 cells, the compound shows partial agonist effects (intrinsic activity=51 and 36%, EC(50)=4.4 and 0.9 microM, respectively). In rat cultured hippocampal neurons, SSR180711 induced large GABA-mediated inhibitory postsynaptic currents and small alpha-bungarotoxin sensitive currents through the activation of presynaptic and somato-dendritic alpha7 n-AChRs, respectively. In mouse hippocampal slices, the compound increased the amplitude of both glutamatergic (EPSCs) and GABAergic (IPSCs) postsynaptic currents evoked in CA1 pyramidal cells. In rat and mouse hippocampal slices, a concentration of 0.3 muM of SSR180711 increased long-term potentiation (LTP) in the CA1 field. Null mutation of the alpha7 n-AChR gene totally abolished SSR180711-induced modulation of EPSCs, IPSCs and LTP in mice. Intravenous administration of SSR180711 strongly increased the firing rate of single ventral pallidum neurons, extracellularly recorded in anesthetized rats. In microdialysis experiments, administration of the compound (3-10 mg/kg i.p.) dose-dependently increased extracellular acetylcholine (ACh) levels in the hippocampus and prefrontal cortex of freely moving rats. Together, these results demonstrate that SSR180711 is a selective and partial agonist at human, rat and mouse alpha7 n-AChRs, increasing glutamatergic neurotransmission, ACh release and LTP in the hippocampus.

Neurochemical, electrophysiological and pharmacological profiles of the selective inhibitor of the glycine transporter-1 SSR504734, a potential new type of antipsychotic

Noncompetitive N-methyl-D-aspartate (NMDA) blockers induce schizophrenic-like symptoms in humans, presumably by impairing glutamatergic transmission. Therefore, a compound potentiating this neurotransmission, by increasing extracellular levels of glycine (a requisite co-agonist of glutamate), could possess antipsychotic activity. Blocking the glycine transporter-1 (GlyT1) should, by increasing extracellular glycine levels, potentiate glutamatergic neurotransmission. SSR504734, a selective and reversible inhibitor of human, rat, and mouse GlyT1 (IC50=18, 15, and 38 nM, respectively), blocked reversibly the ex vivo uptake of glycine (mouse cortical homogenates: ID50: 5 mg/kg i.p.), rapidly and for a long duration. In vivo, it increased (minimal efficacious dose (MED): 3 mg/kg i.p.) extracellular levels of glycine in the rat prefrontal cortex (PFC). This resulted in an enhanced glutamatergic neurotransmission, as SSR504734 potentiated NMDA-mediated excitatory postsynaptic currents (EPSCs) in rat hippocampal slices (minimal efficacious concentration (MEC): 0.5 microM) and intrastriatal glycine-induced rotations in mice (MED: 1 mg/kg i.p.). It normalized activity in rat models of hippocampal and PFC hypofunctioning (through activation of presynaptic CB1 receptors): it reversed the decrease in electrically evoked [3H]acetylcholine release in hippocampal slices (MEC: 10 nM) and the reduction of PFC neurons firing (MED: 0.3 mg/kg i.v.). SSR504734 prevented ketamine-induced metabolic activation in mice limbic areas and reversed MK-801-induced hyperactivity and increase in EEG spectral energy in mice and rats, respectively (MED: 10-30 mg/kg i.p.). In schizophrenia models, it normalized a spontaneous prepulse inhibition deficit in DBA/2 mice (MED: 15 mg/kg i.p.), and reversed hypersensitivity to locomotor effects of d-amphetamine and selective attention deficits (MED: 1-3 mg/kg i.p.) in adult rats treated neonatally with phencyclidine. Finally, it increased extracellular dopamine in rat PFC (MED: 10 mg/kg i.p.). The compound showed additional activity in depression/anxiety models, such as the chronic mild stress in mice (10 mg/kg i.p.), ultrasonic distress calls in rat pups separated from their mother (MED: 1 mg/kg s.c.), and the increased latency of paradoxical sleep in rats (MED: 30 mg/kg i.p.). In conclusion, SSR504734 is a potent and selective GlyT1 inhibitor, exhibiting activity in schizophrenia, anxiety and depression models. By targeting one of the primary causes of schizophrenia (hypoglutamatergy), it is expected to be efficacious not only against positive but also negative symptoms, cognitive deficits, and comorbid depression/anxiety states.

SSR591813, a novel selective and partial alpha4beta2 nicotinic receptor agonist with potential as an aid to smoking cessation

(5aS,8S,10aR)-5a,6,9,10-Tetrahydro,7H,11H-8,10a-methanopyrido[2',3':5,6]pyrano[2,3-d]azepine (SSR591813) is a novel compound that binds with high affinity to the rat and human alpha4beta2 nicotinic acetylcholine receptor (nAChR) subtypes (Ki = 107 and 36 nM, respectively) and displays selectivity for the alpha4beta2 nAChR (Ki, human alpha3beta4 > 1000, alpha3beta2 = 116; alpha1beta1deltagamma > 6000 nM and rat alpha7 > 6000 nM). Electrophysiological experiments indicate that SSR591813 is a partial agonist at the human alpha4beta2 nAChR subtype (EC50 = 1.3 micro M, IA =19% compared with the full agonist 1,1-dimethyl-4-phenyl-piperazinium). In vivo findings from microdialysis and drug discrimination studies confirm the partial intrinsic activity of SSR591813. The drug increases dopamine release in the nucleus accumbens shell (30 mg/kg i.p.) and generalizes to nicotine or amphetamine (10-20 mg/kg i.p.) in rats, with an efficacy approximately 2-fold lower than that of nicotine. Pretreatment with SSR591813 (10 mg/kg i.p.) reduces the dopamine-releasing and discriminative effects of nicotine. SSR591813 shows activity in animal models of nicotine dependence at doses devoid of unwanted side effects typically observed with nicotine (hypothermia and cardiovascular effects). The compound (10 mg/kg i.p.) also prevents withdrawal signs precipitated by mecamylamine in nicotine-dependent rats and partially blocks the discriminative cue of an acute precipitated withdrawal. SSR591813 (20 mg/kg i.p.) reduces i.v. nicotine self-administration and antagonizes nicotine-induced behavioral sensitization in rats. The present results confirm important role for alpha4beta2 nAChRs in mediating nicotine dependence and suggest that SSR591813, a partial agonist at this particular nAChR subtype, may have therapeutic potential in the clinical management of smoking cessation.

Subunit composition of rat ventral spinal cord GABA(A) receptors, assessed by single cell RT-multiplex PCR

We analyzed the expression of native GABA(A) receptors in choline acetyltransferase and glutamic acid decarboxilase positive cells, from lamina IX of the lumbar region of rat spinal cord. More than one isoform of each subunit was detected within a single cell. The alpha3, alpha5, alpha1, beta3 and gamma2 subunit was the most frequent combination in both cell populations. However, the total number of subunit expressed by each cell type was different, being the ChAT positive cells the simplest. Interestingly, the ChAT and GAD positive cells also displayed a different pattern of distribution of both spliced isoforms of the gamma2 subunit. These results indicate that several GABA(A) receptors, with different molecular composition, are expressed in a single cell and that different cell types can express different GABA(A) receptors.

Transmembrane domain III plays an important role in ion binding and permeation in the glycine transporter GLYT2

The neuronal glycine transporter GLYT2 takes up glycine from the extracellular space by an electrogenic process where this neurotransmitter is co-transported with sodium and chloride ions. We report in this paper that tyrosine at position 289 of GLYT2a is crucial for ion coupling, glycine affinity and sodium selectivity, stressing the essential role played by this residue of transmembrane domain III in the mechanism of transport. Substitution to tryptophan (Y289W), phenylalanine (Y289F), or serine (Y289S), renders transporters unable to catalyze glycine uptake. Measurements of glycine evoked steady-state currents in transfected HEK-293 cells reveal EC(50) values for glycine 17-fold (Y289F) and 45-fold (Y289S) higher than that of the wild type transporter. Sodium dependence is severely altered in tyrosine 289 mutants, both at the level of apparent affinity and cooperativity, with the more dramatic change corresponding to the less conservative substitution (Y289S). Accordingly, sodium selectivity is gradually lost in Y289F and Y289S mutants, and chloride dependence of glycine evoked currents is markedly decreased in Y289F and Y289S mutants. In the absence of three-dimensional information from these transporters, these results provide experimental evidence supporting the hypothesis of transmembrane domain III being part of a common permeation pathway for substrate and co-transported ions.

R- and L-type Ca2+ channels are insensitive to eliprodil in rat cultured cerebellar granule neurons

We have investigated, by using the whole-cell patch-clamp technique, the Ca2+ channel antagonist properties of eliprodil in cultured cerebellar granule cells which are known to express L-, N-, P- as well as Q- and R-type Ca2+ channels. Eliprodil maximally antagonized 50% of the voltage-dependent Ba2+ current with an IC50 of 4 microM. omega-Conotoxin-GVIA (3.2 microM) and omega-agatoxin-IVA (0.5 microM) blocked 28 and 43% of the current, respectively. When eliprodil (30 microM) was added to omega-conotoxin-GVIA or omega-agatoxin-IVA the magnitude of the maximal inhibition was identical to that obtained with eliprodil alone confirming a full blockade by eliprodil of N-, P- and Q-type Ca2+ channels. The L-type channel antagonist nimodipine (10 microM) blocked 24% of the current; this blockade was fully additive to that of eliprodil, indicating that the nimodipine-sensitive component of the current is eliprodil-insensitive. In the presence of eliprodil and nimodipine a residual Cd2+ sensitive current (25%), identified as the R-type current, remained unblocked. We conclude that in cerebellar granule neurons R- and L-type Ca2+ channels are insensitive to eliprodil. The nimodipine-sensitive channels present in cerebellar granule neurons may represent a neuronal subtype of L channels distinct from that (eliprodil-sensitive/nimodipine-sensitive) present in cortical or hippocampal neurons.

Block of P-type Ca2+ channels by the NMDA receptor antagonist eliprodil in acutely dissociated rat Purkinje cells

The effect of eliprodil on P-type Ca2+ channels was investigated in acutely dissociated rat Purkinje neurons, by using the whole-cell patch-clamp technique. Eliprodil inhibited in a reversible manner the omega-agatoxin-IVA-sensitive Ba2+ current elicited by step depolarizations from a -80 mV holding voltage (IC50 = 1.9 microM). The Ba2+ current showed steady-state inactivation (V1/2 = -61 mV) which was shifted toward more positive values when the intracellular Ca2+ buffering was increased. In these conditions, the potency of eliprodil was decreased (IC50 = 8.2 microM), suggesting a modulation by intracellular Ca2+ of the eliprodil blockade. The potency of eliprodil was not modified at more depolarized holding potentials and was not dependent on the frequency at which the step-depolarizations were applied (0-0.2 Hz) indicating a lack of voltage and use dependence of the eliprodil blockade. When eliprodil was applied in the patch-pipette at a concentration which causes full block when applied externally, the Ba2+ current amplitude was not affected and external application of eliprodil was still efficacious, indicating an extracellular location of the binding site. Analysis of the time course of recovery from Ca2+ channel blockade obtained by concomitant application of eliprodil with Cd2+, omega-agatoxin-IVA or fluspirilene, indicated that these later compounds did not interact with eliprodil, suggesting that eliprodil acts at a different site. These results demonstrate that eliprodil blocks P-type Ca2+ channels in cerebellar Purkinje neurons and suggest that this property may contribute to its neuroprotective activity.

Modulation of the gamma-aminobutyric acid type A receptor by the antiepileptic drugs carbamazepine and phenytoin

We report here that carbamazepine and phenytoin, two widely used antiepileptic drugs, potentiate gamma-aminobutyric acid (GABA)-induced Cl- currents in human embryonic kidney cells transiently expressing the alpha 1 beta 2 gamma 2 subtype of the GABAA receptor and in cultured rat cortical neurons. In cortical neuron recordings, the current induced by 1 microM GABA was enhanced by carbamazepine and phenytoin with EC50 values of 24.5 nM and 19.6 nM and maximal potentiations of 45.6% and 90%, respectively. The potentiation by these compounds was dependent upon the concentration of GABA, suggesting an allosteric modulation of the receptor, but was not antagonized by the benzodiazepine (omega) modulatory site antagonist flumazenil. Carbamazepine and phenytoin did not modify GABA-induced currents in human embryonic kidney cells transiently expressing binary alpha 1 beta 2 recombinant GABAA receptors. The alpha 1 beta 2 recombinant is known to possess functional barbiturate, steroid, and picrotoxin sites, indicating that these sites are not involved in the modulatory effects of carbamazepine and phenytoin. When tested in cells containing recombinant alpha 1 beta 2 gamma 2, alpha 3 beta 2 gamma 2, or alpha 5 beta 2 gamma 2 GABAA receptors, carbamazepine and phenytoin potentiated the GABA-induced current only in those cells expressing the alpha 1 beta 2 gamma 2 receptor subtype. This indicates that the nature of the alpha subunit isoform plays a critical role in determining the carbamazepine/phenytoin pharmacophore. Our results therefore illustrate the existence of one or more new allosteric regulatory sites for carbamazepine and phenytoin on the GABAA receptor. These sites could be implicated in the known anticonvulsant properties of these drugs and thus may offer new targets in the search for novel antiepileptic drugs.

The NMDA receptor antagonist eliprodil (SL 82.0715) blocks voltage-operated Ca2+ channels in rat cultured cortical neurons

The effect of the non-competitive NMDA receptor antagonist eliprodil on NMDA receptor- and voltage-operated Ca2+ currents was investigated in rat cultured cortical neurons by using the whole-cell patch clamp technique. With neurons voltage-clamped at -40 mV, eliprodil reduced in a concentration-dependent manner the inward current induced by N-methyl-D-aspartate (NMDA) (10 microM) in the presence of D-serine with an IC50 of 0.67 microM (Imax = 83%). Eliprodil also blocked the total inward Ba2+ current carried in part by L- and N-type Ca2+ channels with an IC50 of 1.48 microM (Imax = 87%). These results suggest that the neuroprotective properties of eliprodil could be due to its combined ability to antagonize the NMDA receptor- and voltage-operated Ca2+ channels.