SCAview: an Intuitive Visual Approach to the Integrative Analysis of Clinical Data in Spinocerebellar Ataxias.

With SCAview, we present a prompt and comprehensive tool that enables scientists to browse large datasets of the most common spinocerebellar ataxias intuitively and without technical effort. Basic concept is a visualization of data, with a graphical handling and filtering to select and define subgroups and their comparison. Several plot types to visualize all data points resulting from the selected attributes are provided. The underlying synthetic cohort is based on clinical data from five different European and US longitudinal multicenter cohorts in spinocerebellar ataxia type 1, 2, 3, and 6 (SCA1, 2, 3, and 6) comprising > 1400 patients with overall > 5500 visits. First, we developed a common data model to integrate the clinical, demographic, and characterizing data of each source cohort. Second, the available datasets from each cohort were mapped onto the data model. Third, we created a synthetic cohort based on the cleaned dataset. With SCAview, we demonstrate the feasibility of mapping cohort data from different sources onto a common data model. The resulting browser-based visualization tool with a thoroughly graphical handling of the data offers researchers the unique possibility to visualize relationships and distributions of clinical data, to define subgroups and to further investigate them without any technical effort. Access to SCAview can be requested via the Ataxia Global Initiative and is free of charge.

Integrative data semantics through a model-enabled data stewardship.

MOTIVATION: The importance of clinical data in understanding the pathophysiology of complex disorders has prompted the launch of multiple initiatives designed to generate patient-level data from various modalities. While these studies can reveal important findings relevant to the disease, each study captures different yet complementary aspects and modalities which, when combined, generate a more comprehensive picture of disease etiology. However, achieving this requires a global integration of data across studies, which proves to be challenging given the lack of interoperability of cohort datasets. RESULTS: Here, we present the Data Steward Tool (DST), an application that allows for semi-automatic semantic integration of clinical data into ontologies and global data models and data standards. We demonstrate the applicability of the tool in the field of dementia research by establishing a Clinical Data Model (CDM) in this domain. The CDM currently consists of 277 common variables covering demographics (e.g. age and gender), diagnostics, neuropsychological tests and biomarker measurements. The DST combined with this disease-specific data model shows how interoperability between multiple, heterogeneous dementia datasets can be achieved. AVAILABILITY AND IMPLEMENTATION: The DST source code and Docker images are respectively available at https://github.com/SCAI-BIO/data-steward and https://hub.docker.com/r/phwegner/data-steward. Furthermore, the DST is hosted at https://data-steward.bio.scai.fraunhofer.de/data-steward. SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.

Scaling of recovery rates influences T-type Ca2+ channel availability following IPSPs.

The excitability of neuronal membranes is crucially modulated by T-type Ca2+ channels (I CaT) due to their low threshold of activation. I CaT inactivates steeply at potentials close to the resting membrane potential. Therefore, the availability of I CaT following changes in membrane potential depends on the time course of the onset of inactivation as well as on the time course of recovery from inactivation. It was previously shown that the time course of recovery from inactivation depends on the duration of the conditioning pulse in cloned T-type Ca2+ channel subunits (Cav3.1-Cav3.3(Uebachs et al., 2006)). This provides a potential mechanism for an intrinsic form of short term plasticity. Here, we address the question, whether this mechanism results in altered availability of I CaT following physiological changes in membrane potential. We found that the recovery of I CaT during an IPSP depends on the duration of a preceding depolarized period.

Targeting pharmacoresistant epilepsy and epileptogenesis with a dual-purpose antiepileptic drug.

In human epilepsy, pharmacoresistance to antiepileptic drug therapy is a major problem affecting a substantial fraction of patients. Many of the currently available antiepileptic drugs target voltage-gated sodium channels, leading to a rate-dependent suppression of neuronal discharge. A loss of use-dependent block has emerged as a potential cellular mechanism of pharmacoresistance for anticonvulsants acting on voltage-gated sodium channels. There is a need both for compounds that overcome this resistance mechanism and for novel drugs that inhibit the process of epileptogenesis. We show that eslicarbazepine acetate, a once-daily antiepileptic drug, may constitute a candidate compound that addresses both issues. Eslicarbazepine acetate is converted extensively to eslicarbazepine after oral administration. We have first tested using patch-clamp recording in human and rat hippocampal slices if eslicarbazepine, the major active metabolite of eslicarbazepine acetate, shows maintained activity in chronically epileptic tissue. We show that eslicarbazepine exhibits maintained use-dependent blocking effects both in human and experimental epilepsy with significant add-on effects to carbamazepine in human epilepsy. Second, we show that eslicarbazepine acetate also inhibits Cav3.2 T-type Ca(2+) channels, which have been shown to be key mediators of epileptogenesis. We then examined if transitory administration of eslicarbazepine acetate (once daily for 6 weeks, 150 mg/kg or 300 mg/kg) after induction of epilepsy in mice has an effect on the development of chronic seizures and neuropathological correlates of chronic epilepsy. We found that eslicarbazepine acetate exhibits strong antiepileptogenic effects in experimental epilepsy. EEG monitoring showed that transitory eslicarbazepine acetate treatment resulted in a significant decrease in seizure activity at the chronic state, 8 weeks after the end of treatment. Moreover, eslicarbazepine acetate treatment resulted in a significant decrease in mossy fibre sprouting into the inner molecular layer of pilocarpine-injected mice, as detected by Timm staining. In addition, epileptic animals treated with 150 mg/kg, but not those that received 300 mg/kg eslicarbazepine acetate showed an attenuated neuronal loss. These results indicate that eslicarbazepine potentially overcomes a cellular resistance mechanism to conventional antiepileptic drugs and at the same time constitutes a potent antiepileptogenic agent.

Function of inhibitory micronetworks is spared by Na+ channel-acting anticonvulsant drugs.

The mechanisms of action of many CNS drugs have been studied extensively on the level of their target proteins, but the effects of these compounds on the level of complex CNS networks that are composed of different types of excitatory and inhibitory neurons are not well understood. Many currently used anticonvulsant drugs are known to exert potent use-dependent blocking effects on voltage-gated Na(+) channels, which are thought to underlie the inhibition of pathological high-frequency firing. However, some GABAergic inhibitory neurons are capable of firing at very high rates, suggesting that these anticonvulsants should cause impaired GABAergic inhibition. We have, therefore, studied the effects of anticonvulsant drugs acting via use-dependent block of voltage-gated Na(+) channels on GABAergic inhibitory micronetworks in the rodent hippocampus. We find that firing of pyramidal neurons is reliably inhibited in a use-dependent manner by the prototypical Na(+) channel blocker carbamazepine. In contrast, a combination of intrinsic and synaptic properties renders synaptically driven firing of interneurons essentially insensitive to this anticonvulsant. In addition, a combination of voltage imaging and electrophysiological experiments reveal that GABAergic feedforward and feedback inhibition is unaffected by carbamazepine and additional commonly used Na(+) channel-acting anticonvulsants, both in control and epileptic animals. Moreover, inhibition in control and epileptic rats recruited by in vivo activity patterns was similarly unaffected. These results suggest that sparing of inhibition is an important principle underlying the powerful reduction of CNS excitability exerted by anticonvulsant drugs.

The effects of eslicarbazepine on persistent Na⁺ current and the role of the Na⁺ channel ß subunits.

Eslicarbazepine is the major active metabolite of eslicarbazepine acetate, a once-daily antiepileptic drug approved in Europe as adjunctive therapy for refractory partial-onset seizures in adults. This study was aimed to determine the effects of eslicarbazepine on persistent Na(+) currents (INaP) and the role of ß subunits in modulating these effects. To study the role of ß subunits of the Na(+) channel we used a mouse line genetically lacking either the ß1 or ß2 subunit, encoded by the SCN1B or SCN2B gene, respectively. Whole cell patch-clamp recordings were performed on CA1 neurons in hippocampal slices under control conditions and application of 300 µM eslicarbazepine. We examined INaP in acutely isolated CA1 neurons and repetitive firing in hippocampal slices of mice lacking ß subunits and corresponding wild-type littermates. We found that eslicarbazepine caused a significant reduction of maximal INaP conductance and an efficient reduction of the firing rate in wild-type mice. We have shown previously a paradoxical increase of conductance of INaP caused by carbamazepine in mice lacking ß1 subunits in the subthreshold range, leading to a failure in affecting neuronal firing (Uebachs et al., 2010). In contrast, eslicarbazepine did not cause this paradoxical effect on INaP in SCN1B null mice. Consequently, the effects of eslicarbazepine on repetitive firing were maintained in these animals. These results indicate that eslicarbazepine exerts effects on INaP similar to those known for carbamazepine. However, in animals lacking the ß1 Na(+) channel subunit these effects are maintained. Therefore, eslicarbazepine potentially overcomes a previously described putative mechanism of resistance to established Na(+) channel acting antiepileptic drugs.

Impaired D-serine-mediated cotransmission mediates cognitive dysfunction in epilepsy.

The modulation of synaptic plasticity by NMDA receptor (NMDAR)-mediated processes is essential for many forms of learning and memory. Activation of NMDARs by glutamate requires the binding of a coagonist to a regulatory site of the receptor. In many forebrain regions, this coagonist is d-serine. Here, we show that experimental epilepsy in rats is associated with a reduction in the CNS levels of d-serine, which leads to a desaturation of the coagonist binding site of synaptic and extrasynaptic NMDARs. In addition, the subunit composition of synaptic NMDARs changes in chronic epilepsy. The desaturation of NMDARs causes a deficit in hippocampal long-term potentiation, which can be rescued with exogenously supplied d-serine. Importantly, exogenous d-serine improves spatial learning in epileptic animals. These results strongly suggest that d-serine deficiency is important in the amnestic symptoms of temporal lobe epilepsy. Our results point to a possible clinical utility of d-serine to alleviate these disease manifestations.

Chronic homocysteine exposure causes changes in the intrinsic electrophysiological properties of cultured hippocampal neurons.

Homocystinuria is an inborn error of metabolism characterized by plasma homocysteine levels up to 500 µM, premature vascular events and mental retardation. Mild elevations of homocysteine plasma levels up to 25 µM, which are common in the general population, are associated with vascular disease, cognitive impairment and neurodegeneration. Several mechanisms of homocysteine neurotoxicity have been investigated. However, information on putative effects of hyperhomocysteinemia on the electrophysiology of neurons is limited. To screen for such effects, we examined primary cultures of mouse hippocampal neurons with the whole-cell patch-clamp technique. Homocysteine was applied intracellularly (100 µM), or cell cultures were incubated with 100 µM homocysteine for 24 h. Membrane voltage was measured in current-clamp mode, and action potential firing was induced with short and prolonged current injections. Single action potentials induced by short current injections (5 ms) were not altered by acute application or incubation of homocysteine. When we elicited trains of action potentials with prolonged current injections (200 ms), a broadening of action potentials during repetitive firing was observed in control neurons. This spike broadening was unaltered by acute application of homocysteine. However, it was significantly diminished when incubation with homocysteine was extended to 24 h prior to recording. Furthermore, the number of action potentials elicited by low current injections was reduced after long-term incubation with homocysteine, but not by the acute application. After 24 h of homocysteine incubation, the input resistance was reduced which might have contributed to the observed alterations in membrane excitability. We conclude that homocysteine exposure causes changes in the intrinsic electrophysiological properties of cultured hippocampal neurons as a mechanism of neurological symptoms of hyperhomocysteinemia.

Loss of ß1 accessory Na+ channel subunits causes failure of carbamazepine, but not of lacosamide, in blocking high-frequency firing via differential effects on persistent Na+ currents.

PURPOSE: In chronic epilepsy, a substantial proportion of up to 30% of patients remain refractory to antiepileptic drugs (AEDs). An understanding of the mechanisms of pharmacoresistance requires precise knowledge of how AEDs interact with their targets. Many commonly used AEDs act on the transient and/or the persistent components of the voltage-gated Na(+) current (I(NaT) and I(NaP) , respectively). Lacosamide (LCM) is a novel AED with a unique mode of action in that it selectively enhances slow inactivation of fast transient Na(+) channels. Given that functional loss of accessory Na(+) channel subunits is a feature of a number of neurologic disorders, including epilepsy, we examined the effects of LCM versus carbamazepine (CBZ) on the persistent Na(+) current (I(NaP) ), in the presence and absence of accessory subunits within the channel complex. METHODS: Using patch-clamp recordings in intact hippocampal CA1 neurons of Scn1b null mice, I(NaP) was recorded using slow voltage ramps. Application of 100 µm CBZ or 300 µm LCM reduced the maximal I(NaP) conductance in both wild-type and control mice. KEY FINDINGS: As shown previously by our group in Scn1b null mice, CBZ induced a paradoxical increase of I(NaP) conductance in the subthreshold voltage range, resulting in an ineffective block of repetitive firing in Scn1b null neurons. In contrast, LCM did not exhibit such a paradoxical increase, and accordingly maintained efficacy in blocking repetitive firing in Scn1b null mice. SIGNIFICANCE: These results suggest that the novel anticonvulsant LCM maintains activity in the presence of impaired Na(+) channel ß(1) subunit expression and thus may offer an improved efficacy profile compared with CBZ in diseases associated with an impaired expression of ß sub-units as observed in epilepsy.

Efficacy loss of the anticonvulsant carbamazepine in mice lacking sodium channel beta subunits via paradoxical effects on persistent sodium currents.

Neuronal excitability is critically determined by the properties of voltage-gated Na(+) currents. Fast transient Na(+) currents (I(NaT)) mediate the fast upstroke of action potentials, whereas low-voltage-activated persistent Na(+) currents (I(NaP)) contribute to subthreshold excitation. Na(+) channels are composed of a pore-forming alpha subunit and beta subunits, which modify the biophysical properties of alpha subunits. We have examined the idea that the presence of beta subunits also modifies the pharmacological properties of the Na(+) channel complex using mice lacking either the beta(1) (Scn1b) or beta(2) (Scn2b) subunit. Classical effects of the anticonvulsant carbamazepine (CBZ), such as the use-dependent reduction of I(NaT) and effects on I(NaT) voltage dependence of inactivation, were unaltered in mice lacking beta subunits. Surprisingly, CBZ induced a small but significant shift of the voltage dependence of activation of I(NaT) and I(NaP) to more hyperpolarized potentials. This novel CBZ effect on I(NaP) was strongly enhanced in Scn1b null mice, leading to a pronounced increase of I(NaP) within the subthreshold potential range, in particular at low CBZ concentrations of 10-30 microm. A combination of current-clamp and computational modeling studies revealed that this effect causes a complete loss of CBZ efficacy in reducing repetitive firing. Thus, beta subunits modify not only the biophysical but also the pharmacological properties of Na(+) channels, in particular with respect to I(NaP). Consequently, altered expression of beta subunits in other neurological disorders may cause altered neuronal sensitivity to drugs targeting Na(+) channels.

Diminished response of CA1 neurons to antiepileptic drugs in chronic epilepsy.

PURPOSE: A substantial proportion of epilepsy patients ( approximately 30%) continue to have seizures despite carefully optimized treatment with antiepileptic drugs (AEDs). One key concept to explain the development of pharmacoresistance is that epilepsy-related changes in the properties of CNS drug targets result in AED-insensitivity of these targets. These changes then contribute to drug-resistance on a clinical level. We have tested this hypothesis in hippocampal CA1 neurons in experimental epilepsy. METHODS: Using patch-clamp techniques, we thoroughly examined the effects of carbamazepine (CBZ) and phenytoin (PHT) on voltage-gated Na(+) currents (I(Na)) in hippocampal CA1 neurons of sham-control and chronically epileptic rats. RESULTS: We find that there were significant changes in the effects of PHT, but not CBZ on the voltage-dependence of inactivation, resulting in a significant reduction in voltage-dependent blocking effects in chronically epileptic animals. Conversely, CBZ effects on the time course of recovery from inactivation of I(Na) were significantly less pronounced in epileptic compared to sham-control animals, whereas PHT effects remained unaltered. CONCLUSIONS: Our findings indicate that AED-sensitivity of Na(+) currents is reduced in chronic epilepsy. The reduction in sensitivity is due to different biophysical mechanisms for CBZ and PHT. Furthermore, comparison to published work suggests that the loss of AED-sensitivity is less pronounced in CA1 neurons than in dentate granule neurons. Thus, these results suggest that target mechanisms of drug resistance are cell type and AED specific. Unraveling these complex mechanisms is likely to be important for a better understanding of the cellular basis of drug-resistant epilepsy.

Nanodomains of single Ca2+ channels contribute to action potential repolarization in cortical neurons.

The precise shape of action potentials in cortical neurons is a key determinant of action potential-dependent Ca2+ influx, as well as of neuronal signaling, on a millisecond scale. In cortical neurons, Ca2+-sensitive K+ channels, or BK channels (BKChs), are crucial for action potential termination, but the precise functional interplay between Ca2+ channels and BKChs has remained unclear. In this study, we investigate the mechanisms allowing for rapid and reliable activation of BKChs by single action potentials in hippocampal granule cells and the impact of endogenous Ca2+ buffers. We find that BKChs are operated by nanodomains of single Ca2+ channels. Using a novel approach based on a linear approximation of buffered Ca2+ diffusion in microdomains, we quantitatively analyze the prolongation of action potentials by the Ca2+ chelator BAPTA. This analysis allowed us to estimate that the mean diffusional distance for Ca2+ ions from a Ca2+ channel to a BKCh is approximately 13 nm. This surprisingly short diffusional distance cannot be explained by a random distribution of Ca2+ channels and renders the activation of BKChs insensitive to the relatively high concentrations of endogenous Ca2+ buffers in hippocampal neurons. These data suggest that tight colocalization of the two types of channels permits hippocampal neurons to regulate global Ca2+ signals by a high cytoplasmic Ca2+ buffer capacity without affecting the fast and brief activation of BKChs required for proper repolarization of action potentials.