Carbonic anhydrase inhibitor sulthiame reduces intracellular pH and epileptiform activity of hippocampal CA3 neurons

Metabolic trajectories of diabetic ketoacidosis onset described by breath analysis

Purpose

This feasibility study aimed to investigate the use of exhaled breath analysis to capture and quantify relative changes of metabolites during resolution of acute diabetic ketoacidosis under insulin and rehydration therapy.

Methods

Breath analysis was conducted on 30 patients of which 5 with DKA. They inflated Nalophan bags, and their metabolic content was subsequently interrogated by secondary electrospray ionization high-resolution mass spectrometry (SESI-HRMS).

Results

SESI-HRMS analysis showed that acetone, pyruvate, and acetoacetate, which are well known to be altered in DKA, were readily detectable in breath of participants with DKA. In addition, a total of 665 mass spectral features were found to significantly correlate with base excess and prompt metabolic trajectories toward an in-control state as they progress toward homeostasis.

Conclusion

This study provides proof-of-principle for using exhaled breath analysis in a real ICU setting for DKA monitoring. This non-invasive new technology provides new insights and a more comprehensive overview of the effect of insulin and rehydration during DKA treatment.

Pharmacokinetic Variability of Sulthiame: The Impact of Age, Drug-Drug Interactions, and Biochemical Markers of Toxicity in Patients with Epilepsy

PURPOSE

Sulthiame is an antiseizure medication increasingly used for epilepsy. The aim of this study was to investigate the pharmacokinetic variability of sulthiame in children and adults with epilepsy with respect to age, comedication, dose, serum concentration, and biochemical markers of toxicity in a clinical setting.

METHOD

Retrospective quantitative data from the therapeutic drug monitoring (TDM) database at the Section for Clinical Pharmacology, the National Center for Epilepsy, Norway (2015-2021), were used.

RESULTS

TDM data from 326 patients (127 female/199 male) were included [mean age, 11.4 (range 2-44) years; mean weight, 41 (range 14-109) kg]. Interindividual pharmacokinetic variability in the concentration/(dose/body weight) (C/(D/kg)) ratio was 16-fold; intraindividual variability was up to 8-fold (coefficient of variation = 10%-78%). Young children (younger than 6 years) had a significantly lower C/(D/kg) ratio than older age groups ( P < 0.05). Various comedications did not significantly affect the C/(D/kg) ratio, possibly owing to the small sample size. However, CYP2C19-mediated inhibition by sulthiame was indicated because patients using clobazam and sulthiame (n = 28) had a 3.5-fold higher N-desmethylclobazam C/(D/kg) ratio than those using neutral comedication (n = 45; P < 0.001). Patients with pH values below the adjusted normal range (7.32-7.42; n = 15) had a 33% higher sulthiame concentration than those with normal pH values (n = 22; P < 0.05). Blood gas measurements, especially pH, may serve as markers of toxicity and can be used in combination with clinical data when toxicity is suspected.

CONCLUSIONS

This study revealed the extensive intraindividual and interindividual pharmacokinetic variability of sulthiame, with age as a contributing factor. Sulthiame has clinically relevant interactions with clobazam. The use of TDM and pH as a biochemical marker may contribute to individualized and safe sulthiame treatment.

Thiosuccinimide enabled S-N bond formation to access N-sulfenylated sulfonamide derivatives with synthetic diversity

A thiosuccinimide enabled S-N cross-coupling strategy has been established for the intermolecular N-sulfenylation of clinically approved sulfa drugs under additive-free conditions. This approach features simple operation, high chemoselectivity for sulfenylating the phenylamino group of sulfonamides, wide substrate scope, and easy scale production, affording N-sulfenylated products in moderate to excellent yields (up to 90%). In addition, we also found that this transformation can be realized in a one-pot manner by employing readily available thiols as starting materials, and the obtained sulfonamide derivatives are capable of various late-stage functionalizations, including oxidation, arylation, benzylation, and methylation.

A simple yet multifaceted 90 years old, evergreen enzyme: Carbonic anhydrase, its inhibition and activation

Advances in the carbonic anhydrase (CA, EC 4.2.1.1) research over the last three decades are presented, with an emphasis on the deciphering of the activation mechanism, the development of isoform-selective inhibitors/ activators by the tail approach and their applications in the management of obesity, hypoxic tumors, neurological conditions, and as antiinfectives.

Use of sulthiame as add-on therapy in children with non-self-limited focal epilepsies of childhood

PURPOSE

This retrospective study aimed to evaluate the efficacy and tolerability of sulthiame (STM) as an add-on treatment in 49 patients with non-self-limited focal epilepsies of childhood (non-SeLFE) resistant to other antiseizure medications (ASM) and/or non-pharmacological treatment.

METHODS

Patients with non-SeLFE who had failed to respond to at least five previous ASM, alone or in combination, were included in the study. All patients underwent neurological examination, brain magnetic resonance imaging repeated prolonged electroencephalography (EEG) or video-EEG studies, and neurometabolic studies. School achievements and/or performance on neuropsychological tests were also assessed. Sulthiame was added in doses ranging from 10 to 40 mg/kg/day. Efficacy was measured by comparing seizure frequency before and after initiating STM therapy.

RESULTS

Twenty-nine of 49 patients (59.1%) who received STM as add-on therapy had a greater than 50% decrease in seizures after a mean follow-up of 35 months. One patient (2%) became seizure-free. Fourteen patients (40%) had a 25-50% seizure reduction. The mean time of response was 5 months (range, 3.5 to 6 months). No differences were found either between patients with a response of more or less than 50% or between the response of the focal seizure types (motor or non-motor, with or without consciousness impairment).

CONCLUSION

In our study, STM was found to be effective and well-tolerated in children and adolescents with non-SeLFE. In the patients who responded, improvement in the EEG was seen.

A rise in saliva and urine pH in children with SCN1A-related epilepsy: An exploratory prospective controlled study

Objective

SCN1A, encoding the alpha 1 subunit of the sodium channel, is associated with a range of related epilepsy. This study aims to assess saliva and urine pH in children with SCN1A-related epilepsy.

Methods

A prospective controlled observational study with a 1:1 ratio was conducted on seven patients with SCN1A-related epilepsy and seven healthy children of the same family, gender, and age but without a history of seizures. The pH of saliva and urine was measured by pH test paper. Parents of patients with epilepsy recorded seizures to compare the relationship between pH and seizures.

Results

The fourteen participants were all males, aged 1 to 14 years. Seven patients had different pathogenic SCN1A variants. The pH of saliva and urine was monitored for 21–95 days. The pH of saliva and urine was higher in patients with SCN1A-related epilepsy than in the healthy group. The urine pH in Dravet syndrome patients was high compared with other epilepsy patients. The urine pH in patients with seizures was higher than that in patients without seizures, which occurred during the study.

Conclusions

The pH of saliva and urine was chronically high in patients with SCN1A-related epilepsy, and urine pH was higher in patients with seizures and with Dravet syndrome.

Acetazolamide: Old drug, new evidence?

Acetazolamide is an old drug used as an antiepileptic agent, amongst other indications. The drug is seldom used, primarily due to perceived poor efficacy and adverse events. Acetazolamide acts as a noncompetitive inhibitor of carbonic anhydrase, of which there are several subtypes in humans. Acetazolamide causes an acidification of the intracellular and extracellular environments activating acid‐sensing ion channels, and these may account for the anti‐seizure effects of acetazolamide. Other potential mechanisms are modulation of neuroinflammation and attenuation of high‐frequency oscillations. The overall effect increases the seizure threshold in critical structures such as the hippocampus. The evidence for its clinical efficacy was from 12 observational studies of 941 patients. The 50% responder rate was 49%, 20% of patients were rendered seizure‐free, and 30% were noted to have had at least one adverse event. We conclude that the evidence from several observational studies may overestimate efficacy because they lack a comparator; hence, this drug would need further randomized placebo‐controlled trials to assess effectiveness and harm.

Use of sulthiame as add-on therapy in children with myoclonic atonic epilepsy: A study of 35 patients

PURPOSE

The aim of this retrospective study was to evaluate efficacy and tolerability of sulthiame (STM) as add-on treatment in 35 patients with myoclonic atonic epilepsy (MAE) resistant to other antiseizure medications (ASMs) and/or non-pharmacological treatment.

METHODS

Patients were selected according to the diagnostic definition of MAE and were resistant to at least four previous to ASM, alone or in combination. Neurologic examinations, brain magnetic resonance imaging, and repeated prolonged electroencephalography (EEG) or video-EEG studies as well as neurometabolic studies were performed in all cases. Genetic studies were performed in 15 patients. Data on school achievements and/or neuropsychological evaluations were obtained over a mean follow-up of 30 months. Sulthiame was added in doses ranging from 10 to 30 mg/kg/day. Efficacy was assessed by comparing seizure frequency before and after initiating STM therapy.

RESULTS

Twenty-one of 35 patients (60%) who received STM as add-on therapy had a greater than 50% seizure decrease after a mean follow-up of 30 months. Complete seizure freedom was achieved in two patients (5.8%). The remaining 14 patients (40%) had a 25-50% seizure reduction. Adverse effects, consisting of hyperpnea and dyspnea, decreased appetite, nausea, drowsiness, headache, and irritability, were observed in 11 (31.4%). The adverse effects were mild and transient in all cases. Discontinuation of STM was not necessary.

CONCLUSION

Add-on STM led to a more than 50% seizure reduction in 21 of 35 patients with MAE with only mild or moderate adverse effects.

Seizures and risks for recurrence in critically ill patients: an observational cohort study

Background

To assess the frequency and clinical characteristics of seizures in adult critically ill patients, to identify predictors of recurrent seizures not transforming into status epilepticus and to characterize their effects on course and outcome.

Methods

ICU patients at a Swiss academic medical center with seizures not transforming into status epilepticus from 2015 to 2020 were included. Recurrent seizures and associated clinical characteristics were primary, death, and return to premorbid neurologic function were secondary outcomes.

Results

Two hundred of 26,370 patients (0.8%) with a median age of 65 years had seizures during ICU stay. Seizure semiology was described in 82% (49% generalized; 33% focal) with impaired consciousness during seizures in 80% and motor symptoms in 62%. Recurrent seizures were reported in 71% (36% on EEG) and associated with longer mechanical ventilation (p = 0.031), higher consultation rate by neurologists (p < 0.001), and increased use of EEG (p < 0.001) when compared to single seizures. The use of EEG was not associated with secondary outcomes. Acidosis at seizure onset and prior emergency operations were associated with decreased odds for seizure recurrence (OR 0.43; 95% CI 0.20–0.94 and OR 0.48; 95% CI 0.24–0.97). Epilepsy had increased odds for seizure recurrence (OR 3.56; 95% CI 1.14–11.16).

Conclusions

Seizures in ICU patients are infrequent, but mostly recurrent, and associated with higher resource utilization. Whenever seizures are observed, clinicians should be vigilant about the increased risk of seizures recurrence and the need for antiseizure treatment must be carefully discussed. While known epilepsy seems to promote recurrent seizures, our results suggest that both acidosis and previous emergency surgery seem to have protective/antiseizure effects.

Trial registration

Clinicaltrials.gov (No. NCT03860467).

Sulthiame monotherapy for epilepsy

BACKGROUND

This is an updated version of the original Cochrane Review published in 2014. Epilepsy is a common neurological condition characterised by recurrent seizures. Pharmacological treatment remains the first choice to control epilepsy. Sulthiame (STM) is widely used as an antiepileptic drug in Europe and Israel. In this review, we have presented a summary of evidence for the use of STM as monotherapy in epilepsy.

OBJECTIVES

To assess the efficacy and side effect profile of STM as monotherapy when compared with placebo or another antiepileptic drug for people with epilepsy.

SEARCH METHODS

We searched the following databases on 13 April 2020: the Cochrane Register of Studies (CRS Web), MEDLINE (Ovid, 1946 to 10 April 2020). CRS Web includes randomised or quasi-randomised controlled trials from PubMed, Embase, ClinicalTrials.gov, the World Health Organization International Clinical Trials Registry Platform, the Cochrane Central Register of Controlled Trials (CENTRAL), and the specialised registers of Cochrane Review Groups including Cochrane Epilepsy. We imposed no language restrictions. We contacted the manufacturers of STM and researchers in the field to ask about ongoing and unpublished studies.

SELECTION CRITERIA

Randomised controlled monotherapy trials of STM in people of any age with epilepsy of any aetiology.

DATA COLLECTION AND ANALYSIS

We followed standard Cochrane methodology. Two review authors independently selected trials for inclusion and extracted the relevant data. We assessed the following outcomes: treatment withdrawal; seizure-free at six months; adverse effects; and quality of life scoring. We conducted the primary analyses by intention-to-treat where possible, and presented a narrative analysis of the data.

MAIN RESULTS

We included four studies involving a total of 355 participants: three studies (209 participants) with a diagnosis of benign epilepsy of childhood with centrotemporal spikes (BECTS), and one study (146 participants) with a diagnosis of generalised tonic-clonic seizures (GTCS). STM was given as monotherapy compared with placebo and with levetiracetam in the BECTS studies, and compared with phenytoin in the GTCS study. An English translation of the full text of one of the BECTS studies could not be found, and analysis of this study was based solely on the English translation of the abstract. For the primary outcome, the total number of dropouts caused either by seizure recurrence or adverse reaction was significantly higher in the levetiracetam treatment arm compared to the STM treatment arm (RR 0.32, 95% Cl 0.10 to 1.03; 1 study, 43 participants; low-certainty evidence). For the secondary outcomes for this comparison, results for seizure freedom were inconclusive (RR 1.12, 95% Cl 0.88 to 1.44; 1 study, 43 participants; low-certainty evidence). Reporting of adverse effects was incomplete. Participants receiving STM were significantly less likely to develop gingival hyperplasia than participants receiving phenytoin in the GTCS study (RR 0.03, 95% CI 0.00 to 0.58; 1 study, 146 participants; low-certainty evidence). No further statistically significant adverse events were noted when STM was compared with phenytoin or placebo. The most common adverse events were related to behavioural disturbances when STM was compared with levetiracetam (RR 0.95, 95% Cl 0.59 to 1.55; 1 study, 43 participants; low-certainty evidence), with the same incidence in both groups. No data were reported for quality of life. Overall, we assessed one study at high risk of bias and one study at unclear bias across the seven domains, mainly due to lack of information regarding study design. Only one trial reported effective methods for blinding. The risk of bias assessments for the other two studies ranged from low to high. We rated the overall certainty of the evidence for the outcomes as low using the GRADE approach.

AUTHORS' CONCLUSIONS

This review provides insufficient information to inform clinical practice. Small sample sizes, poor methodological quality, and lack of data on important outcome measures precluded any meaningful conclusions regarding the efficacy and tolerability of sulthiame as monotherapy in epilepsy. More trials, recruiting larger populations, over longer periods, are needed to determine whether sulthiame has a clinical use.

Emerging role of carbonic anhydrase inhibitors

Inhibition of carbonic anhydrase (CA, EC 4.2.1.1) was clinically exploited for decades, as most modern diuretics were obtained considering as lead molecule acetazolamide, the prototypical CA inhibitor (CAI). The discovery and characterization of multiple human CA (hCA) isoforms, 15 of which being known today, led to new applications of their inhibitors. They include widely clinically used antiglaucoma, antiepileptic and antiobesity agents, antitumor drugs in clinical development, as well as drugs for the management of acute mountain sickness and idiopathic intracranial hypertension (IIH). Emerging roles of several CA isoforms in areas not generally connected to these enzymes were recently documented, such as in neuropathic pain, cerebral ischemia, rheumatoid arthritis, oxidative stress and Alzheimer's disease. Proof-of-concept studies thus emerged by using isoform-selective inhibitors, which may lead to new clinical applications in such areas. Relevant preclinical models are available for these pathologies due to the availability of isoform-selective CAIs for all human isoforms, belonging to novel classes of compounds, such as coumarins, sulfocoumarins, dithiocarbamates, benzoxaboroles, apart the classical sulfonamide inhibitors. The inhibition of CAs from pathogenic bacteria, fungi, protozoans or nematodes started recently to be considered for obtaining anti-infectives with a new mechanism of action.

Is the mechanism of action of antiseizure drugs a key element in the choice of treatment?

About 25 antiseizure drugs are available for the treatment of patients with epilepsy. The choice of the most suited drug for a specific patient is primarily based on the results of the pivotal randomized clinical trials and on the patient's characteristics and comorbidities. Whether or not the mechanism of action of the antiseizure drugs should be also taken into account to better predict the patient's response to the treatment remains a matter of debate. Despite the apparent complexity and diversity of antiseizure drug mechanisms of action, the reality unfortunately remains that they are very close, in particular with regard to their relationship with the pathophysiology of epilepsy. With the only exception of the association between lamotrigine and sodium valproate, there are no clinical data that formally support a synergistic association between certain antiseizure drugs in terms of efficacy. However, anticipating risk of adverse events by limiting as far as possible the combination of drugs, which share the same mechanisms of action, is undoubtedly an important driver of daily therapeutic decisions.

A fully validated HPLC-UV method for determination of sulthiame in human serum/plasma samples

Sulthiame is an old antiepileptic medicine with controversial history, whose effectiveness and safety in use have been stated in some current studies. However, there is still a need for further clinical examinations for confirmation of its usefulness and tolerability in monotherapy and add-on therapy for epilepsy of various etiologies. A fully validated RP HPLC-UV method for determination of sulthiame in serum/plasma samples using desethylatrazine as the internal standard was developed. The biological fluid was prepared for analysis by a simple precipitation method with acetonitrile. The following validation parameters of the method were determined: selectivity/specificity, linearity range (0.2-50.0 μl/ml, R²  > 0.9999), limits of detection (0.19 μl/ml) and quantification (0.58 μl/ml), precision (intra-day CV 1.06% and inter-day CV 1.25%), extraction recovery (~100%), accuracy (bias, -4.61-0.80%), carryover and ruggedness. Moreover, the stability of the medicine in plasma samples under different storage conditions was also tested. The usability of the method for clinical examinations was checked by analysis of serum samples originating from 19 patients treated with sulthiame. The proposed method is appropriate for determination of sulthiame in serum/plasma samples for drug monitoring purposes, as well as for pharmacokinetic studies.

Sulthiame add-on treatment in children with epileptic encephalopathy with status epilepticus: an efficacy analysis in etiologic subgroups

PURPOSE

Sulthiame (STM) has been recommended as an effective antiepileptic drug (AED) in children with epileptic encephalopathy with status epilepticus in sleep (ESES). The aim of this study is to evaluate the efficacy of STM add-on treatment in children with pattern of ESES with respect to the etiologic subgroup.

METHODS

Twenty-nine children with ESES pattern with three different etiologic subgroups (epileptic syndromes: 14, structural/infectious: 9, unknown: 6) who were given STM as add-on treatment were included into the study. The efficacy of STM was evaluated in terms of seizure control, electroencephalography (EEG) findings, need of the new AEDs after add-on STM, and behavioral and cognitive improvement.

RESULTS

The range of the follow-up duration after add-on STM treatment was between 5 and 51 months. At the end of 1 year of STM treatment, the most successful electrophysiologic improvement was identified in the well-defined epileptic syndrome group; epileptic syndrome, 71.4% (10/14); structural/infectious, 33.3% (3/9); and unknown, 0% (0/6). Patients who had complete response or persistent ESES pattern at the 3rd month were still in the same condition at the 6th and 12th months. However, the ESES pattern reappeared in 35.2% of the patients who had partial electrophysiological improvement at the 3rd month. In the epilepsy syndrome group, eight out of ten patients who had either complete or partial EEG response after 1 year of STM treatment displayed behavioral and cognitive improvement.

CONCLUSION

Sulthiame might be a valid add-on treatment of ESES especially in children with epilepsy syndromes.

Topiramate Decelerates Bicarbonate-Driven Acid-Elimination of Human Neocortical Neurons: Strategic Significance for its Antiepileptic, Antimigraine and Neuroprotective Properties

BACKGROUND

Mammalian central neurons regulate their intracellular pH (pHi) strongly and even slight pHi-fluctuations can influence inter-/intracellular signaling, synaptic plasticity and excitability.

OBJECTIVE

For the first time, we investigated topiramate´s (TPM) influence on pHi-behavior of human central neurons representing a promising target for anticonvulsants and antimigraine drugs.

METHODS

In slice-preparations of tissue resected from the middle temporal gyrus of five adults with intractable temporal lobe epilepsy, BCECF-AM-loaded neocortical pyramidal-cells were investigated by fluorometry. The pHi-regulation was estimated by using the recovery-slope from intracellular acidification after an Ammonium-Prepulse (APP).

RESULTS

Among 17 pyramidal neurons exposed to 50 μM TPM, seven (41.24%) responded with an altered resting-pHi (7.02±0.12), i.e., acidification of 0.01-0.03 pH-units. The more alkaline the neurons, the greater the TPM-related acidifications (r=0.7, p=0.001, n=17). The recovery from APPacidification was significantly slowed under TPM (p<0.001, n=5). Further experiments using nominal bicarbonate-free (n=2) and chloride-free (n=2) conditions pointed to a modulation of the HCO3 -- driven pHi-regulation by TPM, favoring a stimulation of the passive Cl-/HCO3 --antiporter (CBT) - an acid-loader predominantly in more alkaline neurons.

CONCLUSION

TPM modulated the bicarbonate-driven pHi-regulation, just as previously described in adult guinea-pig hippocampal neurons. We discussed the significance of the resulting subtle acidifications for beneficial antiepileptic, antimigraine and neuroprotective effects as well as for unwanted cognitive deficits.

Sultiame pharmacokinetic profile in plasma and erythrocytes after single oral doses: A pilot study in healthy volunteers

A pilot study was conducted aiming at specifying sultiame's pharmacokinetic profile, completed by in vitro assays evaluating the intraerythrocytic transfer of sultiame and by a pharmacokinetic model assessing its distribution. Single oral doses of sultiame (Ospolot^® 50, 100, and 200 mg) were administered in open‐label to four healthy volunteers. Serial plasma, whole blood, and urine samples were collected. A spiking experiment was also performed to characterize sultiame's exchanges between plasma and erythrocytes in vitro. Pharmacokinetic parameters were evaluated using standard noncompartmental calculations and nonlinear mixed‐effect modeling. The plasma maximal concentrations (C_max) showed striking nonlinear disposition of sultiame, with a 10‐fold increase while doses were doubled. Conversely, whole blood C_max increased less than dose proportionally while staying much higher than in plasma. Quick uptake of sultiame into erythrocytes observed in vivo was confirmed in vitro, with minimal efflux. A two‐compartment model with first‐order absorption, incorporating a saturable ligand to receptor binding, described the data remarkably well, indicating apparent plasma clearance of 10.0 L/h (BSV: 29%) and distribution volume of 64.8 L; saturable uptake into an intracellular compartment of 3.3 L with a maximum binding capacity of 111 mg accounted for nonlinearities observed in plasma and whole blood concentrations. Pharmacokinetic characteristics of sultiame are reported, including estimates of clearance and volume of distribution that were so far unpublished. The noticeable nonlinearity in sultiame disposition should be taken into account for the design of future studies and the interpretation of therapeutic drug monitoring results.

Action of antiepileptic drugs on neurons

The recent development of various new antiepileptic drugs (AEDs) has provided a wide range of therapeutic strategies for epilepsy. Information regarding the mechanisms of the action of AEDs is valuable when selecting drugs for individual epilepsy patients. AEDs can be categorized as those acting at the excitatory synapse, at the inhibitory synapse, on the extrasynaptic neuronal membrane, or with multiple or miscellaneous mechanisms of action. We herein briefly summarize and illustrate the action of AEDs on neurons and related findings that are pertinent to the clinical aspect of epileptology.

Sulthiame add-on therapy for epilepsy

BACKGROUND

This is an updated version of the Cochrane Review previously published in the Cochrane Database of Systematic Reviews 2015, Issue 10. Epilepsy is a common neurological condition, characterised by recurrent seizures. Most people respond to conventional antiepileptic drugs, however, around 30% will continue to experience seizures, despite treatment with multiple antiepileptic drugs. Sulthiame, also known as sultiame, is a widely used antiepileptic drug in Europe and Israel. We present a summary of the evidence for the use of sulthiame as add-on therapy in epilepsy.

OBJECTIVES

To assess the efficacy and tolerability of sulthiame as add-on therapy for people with epilepsy of any aetiology compared with placebo or another antiepileptic drug.

SEARCH METHODS

For the latest update, we searched the Cochrane Register of Studies (CRS Web), which includes the Cochrane Epilepsy Group's Specialized Register and CENTRAL (17 January 2019), MEDLINE Ovid (1946 to January 16, 2019), ClinicalTrials.gov and the WHO ICTRP Search Portal (17 January 2019). We imposed no language restrictions. We contacted the manufacturers of sulthiame, and researchers in the field to seek any ongoing or unpublished studies.

SELECTION CRITERIA

Randomised controlled trials of add-on sulthiame, with any level of blinding (single, double or unblinded) in people of any age, with epilepsy of any aetiology.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected trials for inclusion, and extracted relevant data. We assessed these outcomes: (1) 50% or greater reduction in seizure frequency between baseline and end of follow-up; (2) complete cessation of seizures during follow-up; (3) mean seizure frequency; (4) time-to-treatment withdrawal; (5) adverse effects; and (6) quality of life. We used intention-to-treat for primary analyses. We presented results as risk ratios (RR) with 95% confidence intervals (CIs). However, due to the paucity of trials, we mainly conducted a narrative analysis.

MAIN RESULTS

We included one placebo-controlled trial that recruited 37 infants with newly diagnosed West syndrome. This trial was funded by DESITIN Pharma, Germany. During the study, sulthiame was given as an add-on therapy to pyridoxine. No data were reported for the outcomes: 50% or greater reduction in seizure frequency between baseline and end of follow-up; mean seizure frequency; or quality of life. For complete cessation of seizures during a nine-day follow-up period for add-on sulthiame versus placebo, the RR was 11.14 (95% CI 0.67 to 184.47; very low-certainty evidence), however, this difference was not shown to be statistically significant (P = 0.09). The number of infants experiencing one or more adverse events was not significantly different between the two treatment groups (RR 0.85, 95% CI 0.44 to 1.64; very low-certainty evidence; P = 0.63). Somnolence was more prevalent amongst infants randomised to add-on sulthiame compared to placebo, but again, the difference was not statistically significant (RR 3.40, 95% CI 0.42 to 27.59; very low-certainty evidence; P = 0.25). We were unable to conduct meaningful analysis of time-to-treatment withdrawal and adverse effects due to incomplete data.

AUTHORS' CONCLUSIONS

Sulthiame may lead to a cessation of seizures when used as an add-on therapy to pyridoxine in infants with West syndrome, however, we are very uncertain about the reliability of this finding. The included study was small and had a significant risk of bias, largely due to the lack of details regarding blinding and the incomplete reporting of outcomes. Both issues negatively impacted the certainty of the evidence. No conclusions can be drawn about the occurrence of adverse effects, change in quality of life, or mean reduction in seizure frequency. No evidence exists for the use of sulthiame as an add-on therapy in people with epilepsy outside West syndrome.Large, multi-centre randomised controlled trials are needed to inform clinical practice, if sulthiame is to be used as an add-on therapy for epilepsy.

Levetiracetam mediates subtle pH-shifts in adult human neocortical pyramidal cells via an inhibition of the bicarbonate-driven neuronal pH-regulation - Implications for excitability and plasticity modulation

The intracellular pH (pHi) of mammalian central neurons is tightly regulated and small pHi-fluctuations can fine-tune inter-/intracellular signaling, excitability, and synaptic plasticity. The research-gap about the pHi-regulation of human brain neurons is addressed here by testing possible influences of the anticonvulsant levetiracetam (LEV). BCECF-AM-loaded neocortical pyramidal cells were fluorometrically investigated in slice-preparations of tissue resected from the middle temporal gyrus of five adults with intractable temporal-lobe epilepsy. Recovery-slope from intracellular acidification following an ammonium prepulse (APP) was used to measure the pHi-regulation. Among twenty pyramidal cells exposed to 50 μM LEV, the resting pHi (7.09 ± 0.14) was lowered in eight (40%) neurons, on average by 0.02 ± 0.011 pH-units. In three (15%) and nine (45%) neurons, a minimal alkaline shift (0.017 ± 0.004 pH-units) and no pHi-shift occurred, respectively. The LEV-induced pHi-shifts were positively correlated with the resting pHi (r = 0.6, p = 0.006, n = 20). In five neurons, which all had responded on LEV with an acidification before, the recovery from APP-acidification was significantly delayed during LEV (p < 0.001). This inhibitory LEV-effect on pHi-regulation i) was similar to that of 200 μM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (n = 2) and ii) did not occur under nominal bicarbonate-free conditions (n = 2). Thus, LEV lowered the pHi of human neocortical pyramidal cells most likely by a weakening of the transmembrane HCO3(-)-mediated acid-extrusion. This might contribute to LEV's anticonvulsive potency. Neurons with more acidic resting pHi-values showed a minimal alkalization upon LEV providing a mechanism for paradoxical proconvulsive LEV-effects rarely observed in epilepsy patients. The significance of these subtle pHi-shifts for cortical excitability and plasticity is discussed.

Pharmacokinetic considerations for anti-epileptic drugs in children

INTRODUCTION

Epilepsy is a chronic and debilitating neurological disease, with a peak of incidence in the first years of life. Today, the vast armamentarium of antiepileptic drugs (AEDs) available make even more challenging to select the most appropriate AED and establish the most effective dosing regimen. In fact, AEDs pharmacokinetics is under the influence of important age-related factors which cannot be ignored. Areas covered: Physiological changes occurring during development age (different body composition, immature metabolic patterns, reduced renal activity) can significantly modify the pharmacokinetic profile of AEDs (adsorption, volume of distribution, half-life, clearance), leading to an altered treatment response. We reviewed the main pharmacokinetic characteristics of AEDs used in children, focusing on age-related factors which are of relevance when treating this patient population. Expert opinion: To deal with this pharmacokinetic variability, physicians have at their disposal two tools: 1) therapeutic drug concentration monitoring, which may help to set the optimal therapeutic regimen for each patient and to monitor eventual fluctuation, and 2) the use of extended-release drug formulations, when available. In the next future, the development of 'ad-hoc' electronic dashboard systems will represent relevant decision-support tools making the AED therapy even more individualized and precise, especially in children.

Pharmacokinetics and Drug Interaction of Antiepileptic Drugs in Children and Adolescents

Selecting the most appropriate antiepileptic drug (AED) or combination of drugs for each patient and identifying the most suitable therapeutic regimen for their needs is increasingly challenging, especially among pediatric populations. In fact, the pharmacokinetics of several drugs vary widely in children with epilepsy because of age-related factors, which can influence the absorption, distribution, metabolism, and elimination of the pharmacological agent. In addition, individual factors, such as seizure type, associated comorbidities, individual pharmacokinetics, and potential drug interactions, may contribute to large fluctuations in serum drug concentrations and, therefore, clinical response. Therapeutic drug concentration monitoring (TDM) is an essential tool to deal with this complexity, enabling the definition of individual therapeutic concentrations and adaptive control of dosing to minimize drug interactions and prevent loss of efficacy or toxicity. Moreover, pharmacokinetic/pharmacodynamic modelling integrated with dashboard systems have recently been tested in antiepileptic therapy, although more clinical trials are required to support their use in clinical practice. We review the mechanism of action, pharmacokinetics, drug-drug interactions, and safety/tolerability profiles of the main AEDs currently used in children and adolescents, paying particular regard to issues of relevance when treating this patient population. Indications for TDM are provided for each AED as useful support to the clinical management of pediatric patients with epilepsy by optimizing pharmacological therapy.

Acute neuroinflammation provokes intracellular acidification in mouse hippocampus

Background

Maintaining pH levels within the physiological norm is an important component of brain homeostasis. However, in some pathological or physiological conditions, the capacity of the pH regulatory system could be overpowered by various factors resulting in a transient or permanent alteration in pH levels. Such changes are often observed in pathological conditions associated with neuroinflammation. We hypothesized that neuroinflammation itself is a factor affecting pH levels in neural tissue. To assess this hypothesis, we examined the effects of acute LPS-induced neuroinflammation on intra- and extracellular pH (pHi and pHo) levels in the CA1 region of mouse hippocampus.

Methods

Acute neuroinflammation was induced using two approaches: (1) in vivo by i.p. injections of LPS (5 mg/kg) and (2) in vitro by incubating hippocampal slices of naïve animals in the LPS-containing media (1 μg/mL, 1 h at 35 °C). Standard techniques were used to prepare hippocampal slices. pHi was measured using ratiometric pH-sensitive fluorescent dye BCECF-AM. pHo was assessed using calibrated pH-sensitive micropipettes. The presence of neuroinflammation was verified with immunohistochemistry (IL-1β and Iba1) and ELISA (IL-1β and TNF-α).

Results

A significant reduction of pHi was observed in the slices of the LPS-injected 3-month-old (LPS 7.13 ± 0.03; Sal 7.22 ± 0.03; p = 0.043, r = 0.43) and 19-month-old (LPS 6.78 ± 0.08; Sal 7.13 ± 0.03; p = 0.0001, r = 0.32) mice. In contrast, the levels of pHo within the slice, measured in 19-month-old animals, were not affected (LPS 7.27 ± 0.02; Sal 7.26 ± 0.02; p = 0.6, r = 0.13). A reduction of pHi was also observed in the LPS-treated slices during the interval 3.5–7 h after the LPS exposure (LPS 6.92 ± 0.07; Veh 7.28 ± 0.05; p = 0.0001, r = 0.46).

Conclusions

Acute LPS-induced neuroinflammation results in a significant intracellular acidification of the CA1 neurons in mouse hippocampus, while the pHo remains largely unchanged. Such changes may represent a specific protective reaction of neural tissue in unfavorable external conditions or be a part of the pathological process.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0747-8) contains supplementary material, which is available to authorized users.

Stability-Indicating High-Performance Liquid Chromatography Assay for the Determination of Sulthiame in Pharmaceutical Dosage Forms

A stability-indicating assay by reversed-phase high performance liquid chromatography method was developed and validated for the determination of sulthiame (STM). The chromatographic separation was achieved on a reversed-phase NovaPack C18 column and an isocratic mobile phase consisting of deionized water:methanol (70:30, v/v). The flow rate was 1.0 mL/min (ultraviolet detection at 210 nm). The STM was separated within 2.83 min. The linearity of the method was demonstrated in the range of 20.0–200.0 μg/mL and a coefficient of determination of r² = 0.9999. The limits of detection and quantification were 4.2 and 9.5 μg/mL, respectively. The intraday and interday precisions were less than 1%. Accuracy of the method ranged from 98.3% to 101.7%, with a relative standard deviation of <1%. STM was degraded by accelerated breakdown in alkaline, acidic, or oxidative stress conditions. This method allows accurate and reliable determination of STM for drug stability assay in pharmaceutical studies.

Emerging roles of Na⁺/H⁺ exchangers in epilepsy and developmental brain disorders

Epilepsy is a common central nervous system (CNS) disease characterized by recurrent transient neurological events occurring due to abnormally excessive or synchronous neuronal activity in the brain. The CNS is affected by systemic acid-base disorders, and epileptic seizures are sensitive indicators of underlying imbalances in cellular pH regulation. Na(+)/H(+) exchangers (NHEs) are a family of membrane transporter proteins actively involved in regulating intracellular and organellar pH by extruding H(+) in exchange for Na(+) influx. Altering NHE function significantly influences neuronal excitability and plays a role in epilepsy. This review gives an overview of pH regulatory mechanisms in the brain with a special focus on the NHE family and the relationship between epilepsy and dysfunction of NHE isoforms. We first discuss how cells translocate acids and bases across the membrane and establish pH homeostasis as a result of the concerted effort of enzymes and ion transporters. We focus on the specific roles of the NHE family by detailing how the loss of NHE1 in two NHE mutant mice results in enhanced neuronal excitability in these animals. Furthermore, we highlight new findings on the link between mutations of NHE6 and NHE9 and developmental brain disorders including epilepsy, autism, and attention deficit hyperactivity disorder (ADHD). These studies demonstrate the importance of NHE proteins in maintaining H(+) homeostasis and their intricate roles in the regulation of neuronal function. A better understanding of the mechanisms underlying NHE1, 6, and 9 dysfunctions in epilepsy formation may advance the development of new epilepsy treatment strategies.

Acetazolamide during acute hypoxia improves tissue oxygenation in the human brain

Low doses of the carbonic anhydrase inhibitor acetazolamide provides accelerated acclimatization to high-altitude hypoxia and prevention of cerebral and other symptoms of acute mountain sickness. We previously observed increases in cerebral O2 metabolism (CMRO2 ) during hypoxia. In this study, we investigate whether low-dose oral acetazolamide (250 mg) reduces this elevated CMRO2 and in turn might improve cerebral tissue oxygenation (PtiO2 ) during acute hypoxia. Six normal human subjects were exposed to 6 h of normobaric hypoxia with and without acetazolamide prophylaxis. We determined CMRO2 and cerebral PtiO2 from MRI measurements of cerebral blood flow (CBF) and cerebral venous O2 saturation. During normoxia, low-dose acetazolamide resulted in no significant change in CBF, CMRO2 , or PtiO2 . During hypoxia, we observed increases in CBF [48.5 (SD 12.4) (normoxia) to 65.5 (20.4) ml·100 ml(-1)·min(-1) (hypoxia), P < 0.05] and CMRO2 [1.54 (0.19) to 1.79 (0.25) μmol·ml(-1)·min(-1), P < 0.05] and a dramatic decline in PtiO2 [25.0 to 11.4 (2.7) mmHg, P < 0.05]. Acetazolamide prophylaxis mitigated these rises in CBF [53.7 (20.7) ml·100 ml(-1)·min(-1) (hypoxia + acetazolamide)] and CMRO2 [1.41 (0.09) μmol·ml(-1)·min(-1) (hypoxia + acetazolamide)] associated with acute hypoxia but also reduced O2 delivery [6.92 (1.45) (hypoxia) to 5.60 (1.14) mmol/min (hypoxia + acetazolamide), P < 0.05]. The net effect was improved cerebral tissue PtiO2 during acute hypoxia [11.4 (2.7) (hypoxia) to 16.5 (3.0) mmHg (hypoxia + acetazolamide), P < 0.05]. In addition to its renal effect, low-dose acetazolamide is effective at the capillary endothelium, and we hypothesize that local interruption in cerebral CO2 excretion accounts for the improvements in CMRO2 and ultimately in cerebral tissue oxygenation during hypoxia. This study suggests a potentially pivotal role of cerebral CO2 and pH in modulating CMRO2 and PtiO2 during acute hypoxia.

Sulthiame add-on therapy for epilepsy

BACKGROUND

Epilepsy is a common neurological condition characterised by recurrent seizures. Most patients respond to conventional antiepileptic drugs, however, around 30% will continue to experience seizures despite multiple antiepileptic drugs. Sulthiame, also known as sultiame, is a widely used antiepileptic drug in Europe and Israel. We present a summary of the evidence for the use of sulthiame as add-on therapy in epilepsy.

OBJECTIVES

To compare the efficacy and side-effect profile of sulthiame as add-on therapy compared with placebo or another antiepileptic drug.

SEARCH METHODS

We searched the Cochrane Epilepsy Group's Specialised Register, the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, ClinicalTrials.gov and the WHO ICTRP Search Portal on 11 August 2015. No language restrictions were imposed. We contacted the manufacturers of sulthiame and researchers in the field to seek any ongoing or unpublished studies.

SELECTION CRITERIA

Randomised controlled add-on trials of sulthiame in people of any age with epilepsy of any aetiology.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected trials for inclusion and extracted relevant data. The following outcomes were assessed: 1) reduction in seizure frequency of 50% or greater between baseline and end of follow-up; 2) complete cessation of seizures during follow-up; 3) mean seizure frequency; 4) time to treatment withdrawal; 5) adverse drug effects; and 6) quality of life scoring. Primary analyses were intention-to-treat. We present a narrative analysis.

MAIN RESULTS

We included one trial with 37 participants with a new diagnosis of West syndrome. Sulthiame was given as an add-on therapy to pyridoxine. No data were reported for outcomes 1), 3) or 6). Overall risk ratio with 95% confidence intervals (CI) for complete cessation of seizures during a nine-day follow-up period versus placebo was 0.71 (95% CI 0.53 to 0.96). Meaningful analysis of time to treatment withdrawal and adverse drug effects was not possible due to incomplete data.

AUTHORS' CONCLUSIONS

Sulthiame may lead to a cessation of seizures when used as an add-on therapy to pyridoxine in patients with West syndrome. The included study was small and had a significant risk of bias which limits the impact of the evidence. No conclusions can be drawn about the occurrence of adverse drug effects, change in quality of life or mean reduction in seizure frequency. No evidence exists for the use of sulthiame as an add-on therapy in patients with epilepsy outside West syndrome. Large, multi-centre randomized controlled trials are necessary to inform clinical practice if sulthiame is to be used as an add-on therapy for epilepsy.

Sulfonamides and their isosters as carbonic anhydrase inhibitors

Molecules containing the sulfonamide group (R-SO2NH2) as well as its structurally related isosters, sulfamido (R-NH-SO2NH2) and sulfamato (R-O-SO2NH2), constitute the most important class of inhibitors acting on the metalloenzyme carbonic anhydrase (EC 4.2.1.1). Despite their presence in the literature, in general the reports lack of a clear and organic overview linking the main structural features of the clinically used inhibitors with the therapeutic aspects. The current review is intended to highlight the structural basis of the interactions of sulfonamide-like groups within the active site of the carbonic anhydrases and will summarize the clinical use of the most interesting molecules for the treatment of relevant pathologies, such as glaucoma, obesity, cancer and CNS-affecting diseases.

Binding of carbonic anhydrase IX to 45S rDNA genes is prevented by exportin-1 in hypoxic cells

Carbonic anhydrase IX (CA IX) is a surrogate marker of hypoxia, involved in survival and pH regulation in hypoxic cells. We have recently characterized its interactome, describing a set of proteins interacting with CA IX, mainly in hypoxic cells, including several members of the nucleocytoplasmic shuttling apparatuses. Accordingly, we described complex subcellular localization for this enzyme in human cells, as well as the redistribution of a carbonic anhydrase IX pool to nucleoli during hypoxia. Starting from this evidence, we analyzed the possible contribution of carbonic anhydrase IX to transcription of the 45 S rDNA genes, a process occurring in nucleoli. We highlighted the binding of carbonic anhydrase IX to nucleolar chromatin, which is regulated by oxygen levels. In fact, CA IX was found on 45 S rDNA gene promoters in normoxic cells and less represented on these sites, in hypoxic cells and in cells subjected to acetazolamide-induced acidosis. Both conditions were associated with increased representation of carbonic anhydrase IX/exportin-1 complexes in nucleoli. 45 S rRNA transcript levels were accordingly downrepresented. Inhibition of nuclear export by leptomycin B suggests a model in which exportin-1 acts as a decoy, in hypoxic cells, preventing carbonic anhydrase IX association with 45 S rDNA gene promoters.

Sulthiame monotherapy for epilepsy

BACKGROUND

Epilepsy is a common neurological condition characterised by recurrent seizures. Sulthiame (STM) is widely used as an antiepileptic drug in Europe and Israel. In this review, we present a summary of evidence for the use of STM as monotherapy in epilepsy.

OBJECTIVES

To examine the efficacy and side effect profile of STM as monotherapy when compared with placebo or another antiepileptic drug.

SEARCH METHODS

We searched the Cochrane Epilepsy Group Specialised Register (24 October 2013), the Cochrane Central Register of Controlled Trials (CENTRAL) (2013, Issue 9), MEDLINE Ovid (1946 to 24 October 2013), SCOPUS (1823 to 24 October 2013), the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) search portal (28 October 2013) and ClinicalTrials.gov (28 October 2013). We imposed no language restrictions. We contacted the manufacturers of STM and researchers in the field to ask about ongoing and unpublished studies.

SELECTION CRITERIA

Randomised controlled monotherapy trials of STM in people of any age with epilepsy of any aetiology.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected trials for inclusion and extracted the relevant data.The following outcomes were assessed: (1) time to treatment failure; (2) time to 12-month remission; (3) proportion seizure free at 12 months; (4) adverse effects; and (5) quality of life scoring. Primary analyses were intention-to-treat when possible. A narrative analysis of the data was presented.

MAIN RESULTS

Two studies representing 100 participants with a diagnosis of benign epilepsy of childhood with centrotemporal spikes (BECTS) and one study representing 146 participants with a diagnosis of generalised tonic-clonic seizures (GTCS) were included. STM was given as monotherapy compared with placebo in the BECTS studies and compared with phenytoin in the GTCS study. An English translation of the full text of one of the BECTS studies could not be found, and analysis of this study was based solely on the English translation of the abstract. No data were reported for outcome (1), (2), (3) or (5). Reporting of adverse effects was incomplete. Participants receiving STM were significantly less likely to develop gingival hyperplasia than were participants receiving phenytoin in the GTCS study (risk ratio (RR) 0.03, 95% confidence interval (CI) 0.00 to 0.58). No further statistically significant adverse events were noted when STM was compared with phenytoin or placebo. Two ongoing studies comparing STM monotherapy versus placebo or levetiracetam in BECTS were identified.

AUTHORS' CONCLUSIONS

Small sample size, poor methodological quality and lack of data on important outcome measures prevent any meaningful conclusions regarding the efficacy and safety of sulthiame as monotherapy in epilepsy.

Sulthiame add-on therapy for epilepsy

BACKGROUND

Epilepsy is a common neurological condition characterised by recurrent seizures. Most patients respond to conventional antiepileptic drugs, however, around 30% will continue to experience seizures despite multiple antiepileptic drugs. Sulthiame is a widely used antiepileptic drug in Europe and Israel. We present a summary of the evidence for the use of sulthiame as add-on therapy in epilepsy.

OBJECTIVES

To compare the efficacy and side-effect profile of sulthiame as add-on therapy compared with placebo or another antiepileptic drug.

SEARCH METHODS

We searched the Cochrane Epilepsy Group's Specialised Register, the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE and the WHO IRCTRP Search Portal on 28th August 2012. No language restrictions were imposed. We contacted the manufacturers of sulthiame and researchers in the field to seek any ongoing or unpublished studies.

SELECTION CRITERIA

Randomised placebo-controlled add-on trials of sulthiame in people of any age with epilepsy of any aetiology.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected trials for inclusion and extracted relevant data. The following outcomes were assessed: (1) reduction in seizure frequency of 50% or greater between baseline and end of follow-up (2) complete cessation of seizures during follow-up (3) mean seizure frequency (4) time to treatment withdrawal (5) adverse drug effects (6) quality of life scoring. Primary analyses were intention-to-treat. Narrative analysis is presented.

MAIN RESULTS

One trial was included representing 37 patients with a new diagnosis of West syndrome. Sulthiame was given as an add-on therapy to pyridoxine. No data were reported for outcomes (1), (3) or (6). Overall risk ratio (RR) with 95% confidence intervals (CI) for complete cessation of seizures during a nine-day follow-up period versus placebo was 0.71 (95% CI 0.53 to 0.96). Meaningful analysis of time to treatment withdrawal and adverse drug effects was impossible due to incomplete data.

AUTHORS' CONCLUSIONS

Sulthiame may lead to a cessation of seizures when used as an add-on therapy to pyridoxine in patients with West syndrome. The included study was small and had a significant risk of bias which limits the impact of the evidence. No conclusions can be drawn on the occurrence of adverse drug effects, change in quality of life or mean reduction in seizure frequency. No evidence exists for the use of sulthiame as an add-on therapy in patients with epilepsy outside West syndrome. Large, multi-centre randomised controlled trials are necessary to inform clinical practice if sulthiame is to be used as an add-on therapy for epilepsy.

Weight-reducing side effects of the antiepileptic agents topiramate and zonisamide

Drug-induced weight alteration can be a serious side effect that applies to several therapeutic agents and must be referred to in the respective approved labeling texts. The side effect may become health threatening in case of significant weight change in either direction. Several antiepileptic drugs (AEDs) are associated with weight gain such as gabapentin, pregabalin, valproic acid, and vigabatrin and to some extent carbamazepine. Others are weight neutral such as lamotrigine, levetiracetam, and phenytoin or associated with slight weight loss as, e.g., felbamate. The focus of this chapter is on the two AEDs causing strong weight loss: topiramate and zonisamide. For both drugs, several molecular mechanisms of actions are published. We provide a review of these potential mechanisms, some of which are based on in vivo studies in animal models for obesity, and of clinical studies exploring these two drugs as single entities or in combinations with other agents.

Enhancing effects of acetazolamide on neuronal activity correlate with enhanced visual processing ability in humans

Acetazolamide is a potent inhibitor of the reversible hydration of CO(2) catalyzed by the enzyme carbonic anhydrase and is commonly used to increase cerebral blood flow e.g. in order to estimate cerebrovascular reserve. However it is not known whether acetazolamide may positively affect the excitability of neurons in the brain in vivo or cortical processing abilities. To test these possibilities we intravenously administered a low dose (7 mg/kg) acetazolamide to volunteers who performed a demanding visual signal detection task while undergoing whole brain electroencephalographic examinations. Two groups were tested twice on the same task, while receiving acetazolamide or a saline treatment in between the two sessions. Our data indicate that, while the control group showed a decrease in global gamma (30-49 Hz) power across sessions, with no correlation to performance, the acetazolamide group showed increased global gamma power that strongly related to their performance in the signal detection task. This was accompanied by a decrease in the early part of the event related potential in the control group, a decrease not seen in the acetazolamide group. There were no significant differences in blood pressure, ventilation rate, or heart rate between the two groups. It is possible that the differences between the groups, observed in this study, are related to the enhancing effect of acetazolamide on the nitric oxide generation catalyzed by carbonic anhydrase, or to other actions of acetazolamide, e.g. opening of Ca(2+) activated K(+) channels and inhibition of Ca(2+) channels.

Respiratory alkalosis and metabolic acidosis in a child treated with sulthiame

OBJECTIVES

To report on severe acid-base disturbance in a child with symptomatic epilepsy treated with sulthiame.

RESULTS

A 9.5-year-old boy with chronic generalized tonic-clonic seizures was treated with carbamazepine and valproic acid. Because of poor seizure control, sulthiame was added to the treatment. Two months later, he presented at the emergency department with severe weakness, headache, dizziness, dyspnea, anorexia, and confusional state. Arterial blood gas analysis showed mixed respiratory alkalosis with high anion gap metabolic acidosis. Sulthiame-induced acid-base disturbance was suspected. The drug was withheld for the first 24 hours and then restarted at a reduced dosage. The arterial blood gases gradually normalized, the confusion disappeared, and the patient was discharged home.Three months later, 4 weeks after an increase in sulthiame dosage, the patient was once again admitted with the same clinical picture. Improvement was noted after the drug dosage was reduced.

CONCLUSIONS

This is the first report of mixed respiratory alkalosis and metabolic acidosis in a child treated with sulthiame. Monitoring of the acid-base status should be considered in patients treated with sulthiame.

Age- and region-specific effects of anticonvulsants and bumetanide on 4-aminopyridine-induced seizure-like events in immature rat hippocampal-entorhinal cortex slices

PURPOSE

Seizure-like events (SLEs) induced by 4-aminopyridine in rat organotypic slices cultures, which are prepared early after birth, are resistant to standard antiepileptic drugs. In this study we tested the hypothesis that pharmacoresistance may be an intrinsic property of the immature brain.

METHODS

Frequently recurring SLEs presumably representing status epilepticus were induced by 4-aminopyridine in acute rat hippocampal-entorhinal cortex slices obtained from postnatal day 3-19 (P3-P19), and the effects of carbamazepine, phenytoin, valproic acid, and phenobarbital were examined. In addition, bumetanide was tested, which blocks the Na(+) -K(+) -2Cl(-) (NKCC1) cotransporter, and also acetazolamide, which blocks the carbonic anhydrase and thereby the accumulation of bicarbonate inside neurons.

RESULTS

The efficacy of all antiepileptic drugs in blocking SLEs was dependent on postnatal age, with low efficacy in P3-P5 slices. Antiepileptic drugs suppressed SLEs more readily in the medial entorhinal cortex (ECm) than in the CA3. In P3-P5 slices, valproic acid and phenobarbital increased both tonic and clonic seizure-like activities in the CA3, whereas phenytoin and carbamazepine blocked tonic-like but prolonged clonic-like activity. In P3-P5 slices, bumetanide often blocked SLEs in the CA3, but was not as effective in the ECm. Like with other antiepileptic drugs, the seizure-suppressing effects of acetazolamide increased with postnatal age.

CONCLUSION

We conclude that pharmacoresistance may be inherent to very immature tissue and suggest that expression of the NKCC1 cotransporter might contribute to pharmacoresistance.

Modulatory effects of neuropsychopharmaca on intracellular pH of hippocampal neurones in vitro

BACKGROUND AND PURPOSE

The intracellular pH (pHi) of neurones is tightly regulated by, for example, membrane-bound acid-exchangers and loaders. Nevertheless, excessive bioelectric activity lowers steady-state pHi. In turn, even a moderate acidification can inhibit neuronal activity, a process believed to be part of a negative feedback loop controlling neuronal excitation. As moclobemide, an antidepressant, and also some antiepileptic drugs can reduce neuronal pHi in hippocampus slices in vitro, we screened a panel of currently used neuropsychopharmaca for comparable effects.

EXPERIMENTAL APPROACH

BCECF-AM loaded hippocampal slices were superfused with 16 different neuroleptics, antidepressants and antiepileptics under bicarbonate-buffered conditions. Changes in steady-state pHi of CA3 neurones were measured fluorometrically.

KEY RESULTS

The antipsychotics haloperidol, clozapine, ziprasidone, and the antidepressants amitriptyline, doxepin, trimipramine, citalopram, mirtazapine, as well as the anticonvulsive drug tiagabine reversibly reduced the steady-state pHi by up to 0.35 pH-units in concentrations of 5-50 microM. In contrast, venlafaxine, the anticonvulsants carbamazepine, clonazepam, gabapentin, lamotrigine, zonisamide, and the mood stabilizer lithium had no effect on neuronal pHi.

CONCLUSION AND IMPLICATIONS

These data substantiate the view that clinically relevant concentrations of neuroleptics and antidepressants can mediate changes in neuronal pHi, which may contribute to their pharmacological mode of action. Effects on pHi should be taken into account when therapeutic or even harmful effects of these drugs are evaluated.

Carbonic anhydrase inhibitors. Interaction of the antiepileptic drug sulthiame with twelve mammalian isoforms: Kinetic and X-ray crystallographic studies

Sulthiame, a clinically used antiepileptic, was investigated for its interaction with 12 catalytically active mammalian carbonic anhydrase (CA, EC 4.2.1.1) isoforms. The drug is a potent inhibitor of CA II, VII, IX, and XII (K(I)s of 6-56 nM), and a medium potency inhibitor against CA IV, VA, VB, and VI (K(I)s of 81-134 nM). The high resolution crystal structure of the hCA II-sulthiame adduct revealed a large number of favorable interactions between the drug and the enzyme which explain its strong low nanomolar affinity for this isoform and may also be exploited for the design of effective inhibitors incorporating sultam moieties.

Ion channel pharmacology

Because ion channels are involved in many cellular processes, drugs acting on ion channels have long been used for the treatment of many diseases, especially those affecting electrically excitable tissues. The present review discusses the pharmacology of voltage-gated and neurotransmitter-gated ion channels involved in neurologic diseases, with emphasis on neurologic channelopathies. With the discovery of ion channelopathies, the therapeutic value of many basic drugs targeting ion channels has been confirmed. The understanding of the genotype-phenotype relationship has highlighted possible action mechanisms of other empirically used drugs. Moreover, other ion channels have been pinpointed as potential new drug targets. With regards to therapy of channelopathies, experimental investigations of the intimate drug-channel interactions have demonstrated that channel mutations can either increase or decrease affinity for the drug, modifying its potential therapeutic effect. Together with the discovery of channel gene polymorphisms that may affect drug pharmacodynamics, these findings highlight the need for pharmacogenetic research to allow identification of drugs with more specific effects on channel isoforms or mutants, to increase efficacy and reduce side effects. With a greater understanding of channel genetics, structure, and function, together with the identification of novel primary and secondary channelopathies, the number of ion channel drugs for neurologic channelopathies will increase substantially.

Inhibition of hypoxia-induced calcium responses in pulmonary arterial smooth muscle by acetazolamide is independent of carbonic anhydrase inhibition

Hypoxic pulmonary vasoconstriction (HPV) occurs with ascent to high altitude and can contribute to development of high altitude pulmonary edema (HAPE). Vascular smooth muscle contains carbonic anhydrase (CA), and acetazolamide (AZ), a CA inhibitor, blunts HPV and might be useful in the prevention of HAPE. The mechanism by which AZ impairs HPV is uncertain. Originally developed as a diuretic, AZ also has direct effects on systemic vascular smooth muscle, including modulation of pH and membrane potential; however, the effect of AZ on pulmonary arterial smooth muscle cells (PASMCs) is unknown. Since HPV requires Ca2+ influx into PASMCs and can be modulated by pH, we hypothesized that AZ alters hypoxia-induced changes in PASMC intracellular pH (pH(i)) or Ca2+ concentration ([Ca2+](i)). Using fluorescent microscopy, we tested the effect of AZ as well as two other potent CA inhibitors, benzolamide and ethoxzolamide, which exhibit low and high membrane permeability, respectively, on hypoxia-induced responses in PASMCs. Hypoxia caused a significant increase in [Ca2+](i) but no change in pH(i). All three CA inhibitors slightly decreased basal pH(i), but only AZ caused a concentration-dependent decrease in the [Ca2+](i) response to hypoxia. AZ had no effect on the KCl-induced increase in [Ca2+](i) or membrane potential. N-methyl-AZ, a synthesized compound lacking the unsubstituted sulfonamide group required for CA inhibition, had no effect on pH(i) but inhibited hypoxia-induced Ca2+ responses. These results suggest that AZ attenuates HPV by selectively inhibiting hypoxia-induced Ca2+ responses via a mechanism independent of CA inhibition, changes in pH(i), or membrane potential.

A single dose of sulthiame induces a selective increase in resting motor threshold in human motor cortex: A transcranial magnetic stimulation study

Sulthiame is a carbonic anhydrase inhibitor that is widely used to treat partial and myoclonic seizures. In 11 healthy adults, we applied transcranial magnetic stimulation (TMS) to the primary motor cortex. Using a cross-over study design, we found that a single oral dose of sulthiame (5 mg/kg) produced a significant increase of resting motor threshold relative to placebo. No other TMS measure of corticomotor excitability was altered after a single dose of sulthiame. The selective increase in motor threshold suggests that sulthiame produces its antiepileptic effect by reducing the axonal excitability of cortical neurons.

The carbonic anhydrase inhibitors methazolamide and acetazolamide have different effects on the hypoxic ventilatory response in the anaesthetized cat

We compared the effects of the carbonic anhydrase inhibitors methazolamide and acetazolamide (3 mg kg(-1), i.v.) on the steady-state hypoxic ventilatory response in 10 anaesthetized cats. In five additional animals, we studied the effect of 3 and 33 mg kg(-1) methazolamide. The steady-state hypoxic ventilatory response was described by the exponential function: *Vi= G exp(-D P(O2)) + A where *Vi is the inspired ventilation, G is hypoxic sensitivity, D is the shape factor and A is hyperoxic ventilation. In the first group of 10 animals, methazolamide did not change parameters G and D, while A increased from 0.86 +/- 0.33 to 1.30 +/- 0.40 l min(-1) (mean +/- s.d., P = 0.003). However, the subsequent administration of acetazolamide reduced G by 44% (control, 1.93 +/- 1.32; acetazolamide, 1.09 +/- 0.92 l min(-1), P = 0.003), while A did not show a further change. Acetazolamide tended to reduce D (control, 0.20 +/- 0.07; acetazolamide, 0.14 +/- 0.06 kPa(-1), P = 0.023). In the second group of five animals, neither low- nor high-dose methazolamide changed parameters G, D and A. The observation that even high-dose methazolamide, causing full inhibition of carbonic anhydrase in all body tissues, did not reduce the hypoxic ventilatory response is reminiscent of previous findings by others showing no change in magnitude of the hypoxic response of the in vitro carotid body by this agent. This suggests that normal carbonic anhydrase activity is not necessary for a normal hypoxic ventilatory response to occur. The mechanism by which acetazolamide reduces the hypoxic ventilatory response needs further study.

Acetazolamide acts directly on the human skeletal muscle chloride channel

Acetazolamide, a carbonic anhydrase inhibitor, is used empirically in neuromuscular diseases with episodic ataxia, weakness, and myotonia, although not all of the mechanisms responsible for its therapeutic effects are understood. To elucidate whether acetazolamide acts directly on the human skeletal muscle voltage-gated chloride channel (ClC-1), which is associated with myotonia, we evaluated the effects of acetazolamide on ClC-1 expressed in cultured mammalian cells, using whole-cell recording. Acetazolamide significantly shifted the voltage dependency of the open probability (P(o)) toward negative potentials in a dose-dependent manner, resulting in an increase of chloride conductance at voltages near the resting membrane potential. This effect was attenuated when using a pipette solution containing 30 mmol/L Hepes. These results suggest that acetazolamide can influence the voltage-dependent opening gate of ClC-1 through a mechanism related to intracellular acidification by inhibiting carbonic anhydrase, and that the therapeutic effects of acetazolamide in neuromuscular diseases may be mediated by activation of ClC-1.

Sulthiame but not levetiracetam exerts neurotoxic effect in the developing rat brain

Antiepileptic drugs (AEDs) used to treat seizures in pregnant women, infants, and young children can cause cognitive impairment. One mechanism implicated in the development of neurocognitive deficits is a pathologic enhancement of physiologically occurring apoptotic neuronal death in the developing brain. We investigated whether the newer antiepileptic drug levetiracetam (LEV) and the older antiepileptic drug sulthiame (SUL) have neurotoxic properties in the developing rat brain. SUL significantly enhanced neuronal death in the brains of rat pups ages 0 to 7 days at doses of 100 mg/kg and above, whereas LEV did not show this neurotoxic effect. Dosages of both drugs used in the context of this study comply with an effective anticonvulsant dose range applied in rodent seizure models. Thus, LEV is an AED which lacks neurotoxicity in the developing rat brain and should be considered in the treatment of epilepsy in pregnant women, infants, and toddlers once general safety issues have been properly addressed.