Absorption, metabolism and excretion of opicapone in human healthy volunteers.

AIMS: The absorption, metabolism and excretion of opicapone (2,5-dichloro-3-(5-[3,4-dihydroxy-5-nitrophenyl]-1,2,4-oxadiazol-3-yl)-4,6-dimethylpyridine 1-oxide), a selective catechol-O-methyltransferase inhibitor, were investigated. METHODS: Plasma, urine and faeces were collected from healthy male subjects following a single oral dose of 100 mg [14 C]-opicapone. The mass balance of [14 C]-opicapone and metabolic profile were evaluated. RESULTS: The recovery of total administered radioactivity averaged >90% after 144 hours. Faeces were the major route of elimination, representing 70% of the administered dose; 5% and 20% were excreted in urine and expired air, respectively. The Cmax of total radioactivity matched that of unchanged opicapone, whereas the total radioactivity remained quantifiable for a longer period, attributed to the contribution of opicapone metabolites, involving primarily 3-O-sulfate conjugation (58.6% of total circulating radioactivity) at the nitrocatechol ring. Other circulating metabolites, accounting for <10% of the radioactivity exposure, were formed by glucuronidation, methylation, N-oxide reduction and gluthatione conjugation. Additionally, various other metabolites resulting from combinations with the opicapone N-oxide reduced form at the 2,5-dichloro-4,6-dimethylpyridine 1-oxide moiety, including nitro reduction and N-acetylation, reductive opening and cleavage of the 1,2,4-oxadiazole ring and the subsequent hydrolysis products were identified, but only in faeces, suggesting the involvement of gut bacteria. CONCLUSION: [14 C]-opicapone was fully excreted through multiple metabolic pathways. The main route of excretion was in faeces, where opicapone may be further metabolized via reductive metabolism involving the 1,2,4-oxadiazole ring-opening and subsequent hydrolysis.

Effect of opicapone multiple-dose regimens on levodopa pharmacokinetics.

AIMS: To compare the levodopa/carbidopa (LC) and levodopa/benserazide (LB) pharmacokinetic profiles following repeated doses of opicapone (OPC) administered apart from levodopa. METHODS: Two randomized, double blind, sex-balanced, placebo-controlled studies in four groups of 12 or 18 healthy subjects each. In each group, enrolled subjects received a once-daily morning (5, 15 and 30 mg) or evening (5, 15 and 50 mg) administration of OPC or placebo for up to 28 days. On the morning of Day 11, 12 h after the OPC or placebo evening dose, or the morning of Day 21, 1 h after the OPC or placebo dose, a single dose of immediate-release 100/25 mg LC was administered. Similarly, on Day 18 morning, 12 h after the OPC or placebo evening dose, or Day 28 morning, 1 h after the OPC or placebo dose, a single dose of immediate-release 100/25 mg LB was administered. RESULTS: All OPC treatments, in relation to the placebo group, presented a higher extent of exposure (AUC) to levodopa following either LC or LB doses. A relevant but not dose-dependent increase in the levodopa AUC occurred with all OPC dose groups in relation to placebo. All active treatments significantly inhibited both peak (Emax ) and extent (AUEC) of the catechol-O-methyltransferase activity in relation to placebo. The tolerability profile was favourable. CONCLUSION: Opicapone, as once-daily oral evening regimen and/or 1 h apart from levodopa therapy, increases the bioavailability of levodopa associated with its pronounced, long-lasting and sustained catechol-O-methyltransferase inhibition. The tolerability profile was favourable and similar between OPC and placebo.

Role of P-glycoprotein and permeability upon the brain distribution and pharmacodynamics of etamicastat: a comparison with nepicastat.

1. This study explores the impact of permeability and P-glycoprotein (P-gp) efflux, upon brain exposure to etamicastat, a new dopamine-ß-hydroxylase (DBH) inhibitor and consequently brain levels of catecholamines. 2. Brain exposure to etamicastat (10 mg/kg), following intravenous administration to mice, was residual and upon oral administration of the same dose no compound was detected, concurring with the absence of effects upon brain catecholamines. The intravenous co-administration of elacridar (1.0 mg/kg), a known P-gp/BCRP dual modulator, significantly increased brain etamicastat exposure, but the levels attained were very low when compared to those of nepicastat, a centrally active DBH inhibitor. 3. In vitro permeability studies from apical-to-basal direction conducted in Caco-2 cells and MDCK-II cells showed that etamicastat apparent permeability was 1.2 × 10(-5) and 1.1 × 10(-6 )cm/s, respectively, 5- and 50-fold lower as compared to nepicastat. The secretory efflux ratio in MDCK-II cells overexpressing human P-gp showed an efflux ratio greater than 2, for both compounds, which was significantly decreased by elacridar. Despite its lower bioavailability and higher clearance, as compared to nepicastat, etamicastat showed preferential distribution to peripheral tissues and high plasma free fraction (15.5%), which may explain its effects upon peripheral DBH and catecholamine levels. 4. Though P-gp-mediated efflux may contribute to the limited brain penetration of etamicastat, the low permeability along with the pharmacokinetic properties of etamicastat may be perceived as the main contributors for its peripheral selectivity, which is advantageous for a cardiovascular drug candidate.

Effects of eslicarbazepine acetate on acute and chronic latrunculin A-induced seizures and extracellular amino acid levels in the mouse hippocampus.

BACKGROUND: Latrunculin A microperfusion of the hippocampus induces acute epileptic seizures and long-term biochemical changes leading to spontaneous seizures. This study tested the effect of eslicarbazepine acetate (ESL), a novel antiepileptic drug, on latrunculin A-induced acute and chronic seizures, and changes in brain amino acid extracellular levels. Hippocampi of Swiss mice were continuously perfused with a latrunculin A solution (4 µM, 1 µl/min, 7 h/day) with continuous EEG and videotape recording for 3 consecutive days. Microdialysate samples were analyzed by HPLC and fluorescence detection of taurine, glycine, aspartate, glutamate and GABA. Thereafter, mice were continuously video monitored for two months to identify chronic spontaneous seizures or behavioral changes. Control EEG recordings (8 h) were performed in all animals at least once a week for a minimum of one month. RESULTS: Oral administration of ESL (100 mg/kg), previous to latrunculin A microperfusion, completely prevented acute latrunculin A-induced seizures as well as chronic seizures and all EEG chronic signs of paroxysmal activity. Hippocampal extracellular levels of taurine, glycine and aspartate were significantly increased during latrunculin A microperfusion, while GABA and glutamate levels remained unchanged. ESL reversed the increases in extracellular taurine, glycine and aspartate concentrations to basal levels and significantly reduced glutamate levels. Plasma and brain bioanalysis showed that ESL was completely metabolized within 1 h after administration to mainly eslicarbazepine, its major active metabolite. CONCLUSION: ESL treatment prevented acute latrunculin A-induced seizures as well as chronic seizures and all EEG chronic signs of paroxysmal activity, supporting a possible anti-epileptogenic effect of ESL in mice.

Human disposition, metabolism and excretion of etamicastat, a reversible, peripherally selective dopamine ß-hydroxylase inhibitor.

AIMS: Etamicastat is a reversible dopamine-ß-hydroxylase inhibitor that decreases noradrenaline levels in sympathetically innervated tissues and slows down sympathetic nervous system drive. In this study, the disposition, metabolism and excretion of etamicastat were evaluated following [(14)C]-etamicastat dosing. METHODS: Healthy Caucasian males (n = 4) were enrolled in this single-dose, open-label study. Subjects were administered 600 mg of unlabelled etamicastat and 98 µCi weighing 0.623 mg [(14)C]-etamicastat. Blood samples, urine and faeces were collected to characterize the disposition, excretion and metabolites of etamicastat. RESULTS: Eleven days after administration, 94.0% of the administered radioactivity had been excreted; 33.3 and 58.5% of the administered dose was found in the faeces and urine, respectively. Renal excretion of unchanged etamicastat and its N-acetylated metabolite (BIA 5-961) accounted for 20.0 and 10.7% of the dose, respectively. Etamicastat and BIA 5-961 accounted for most of the circulating radioactivity, with a BIA 5-961/etamicastat ratio that was highly variable both for the maximal plasma concentration (19.68-226.28%) and for the area under the plasma concentration-time curve from time zero to the last sampling time at which the concentration was above the limit of quantification (15.82- 281.71%). Alongside N-acetylation, metabolism of etamicastat also occurs through oxidative deamination of the aminoethyl moiety, alkyl oxidation, desulfation and glucuronidation. CONCLUSIONS: Etamicastat is rapidly absorbed, primarily excreted via urine, and its biotransformation occurs mainly via N-acetylation (N-acetyltransferase type 2), although glucuronidation, oxidation, oxidative deamination and desulfation also take place.

HR/MS-based lipidome analysis of rat brain modulated by tolcapone.

Lipids play key roles in the body, influencing cellular regulation, function, and signalling. Tolcapone, a potent catechol-O-methyltransferase (COMT) inhibitor described to enhance cognitive performance in healthy subjects, was previously shown to impact fatty acid ß-oxidation and oxidative phosphorylation. However, its impact on the brain lipidome remains unexplored. Hence, this study aimed to assess how tolcapone affects the lipidome of the rat pre-frontal cortex (PFC), a region of the brain highly relevant to tolcapone therapeutic effect, while evaluating its influence on operant behaviour. Tolcapone at 20 mg/kg was chronically administered to Wistar rats during a behavioural task and an untargeted liquid chromatography high-resolution mass spectrometry (LC-HR/MS) approach was employed to profile lipid species. The untargeted analysis identified 7227 features, of which only 33% underwent statistical analysis following data pre-processing. The results revealed an improved cognitive performance and a lipidome remodelling promoted by tolcapone. The lipidomic analysis showed 32 differentially expressed lipid species in tolcapone-treated animals (FC ≥ 1.2, p-value ≤ 0.1), and among these several triacylglycerols, cardiolipins and N-acylethanolamine (NAE 16:2) were found upregulated whereas fatty acids, hexosylceramides, and several phospholipids including phosphatidylcholines and phosphatidylethanolamines were downregulated. These preliminary findings shed light on tolcapone impact on lipid pathways within the brain. Although tolcapone improved cognitive performance and literature suggests the significance of lipids in cognition, this study did not conclusively establish that lipids directly drove or contributed to this outcome. Nevertheless, it underscores the importance of lipid modulation and encourages further exploration of tolcapone-associated mechanisms in the central nervous system (CNS).

N-acetylation of etamicastat, a reversible dopamine-ß-hydroxylase inhibitor.

Etamicastat [(R)-5-(2-aminoethyl)-1-(6,8-difluorochroman-3-yl)-1H-imidazole-2(3H)-thione hydrochloride] is a reversible dopamine-ß-hydroxylase inhibitor that decreases norepinephrine levels in sympathetically innervated tissues. After in vivo administration, N-acetylation of etamicastat was found to be a main metabolic pathway. The purpose of the current study was to characterize the N-acetylation of etamicastat by N-acetyltransferases (NAT1 and NAT2) and evaluate potential species differences in etamicastat N-acetylation using a sensitive and specific liquid chromatography-mass spectrometry assay. Marked differences in etamicastat N-acetylation were observed among the laboratory species and humans. After oral administration, the rat, hamster, and human subjects presented the highest rates of etamicastat N-acetylation, whereas almost no acetylation was observed in the mouse, rabbit, minipig, and monkey and no acetylation was observed in the dog. In in vitro studies, rats and humans showed similar acetylation rates, whereas no acetylation was detected in the dog. Studies performed with human recombinant NAT1 4 and NAT2 4 enzymes revealed that both were able to conjugate etamicastat, although at different rates. NAT1 had lower affinity compared with NAT2 (Km, 124.8 ± 9.031 µM and 17.14 ± 3.577 µM, respectively). A significant correlation (r(2) = 0.65, P < 0.05) was observed in a comparison of etamicastat N-acetylation by human single-donor enzymes and sulfamethazine, a selective substrate to NAT2. No correlation was observed with p-aminosalicylic acid, a NAT1 selective substrate. In conclusion, these results suggest that NAT2 and, to a lesser extent, NAT1 contribute to etamicastat N-acetylation. Furthermore, the high interspecies and intraspecies differences in N-acetylation should be taken into consideration when evaluating the in vivo bioavailability of etamicastat.

Opicapone: a short lived and very long acting novel catechol-O-methyltransferase inhibitor following multiple dose administration in healthy subjects.

AIMS: The aim of this study was to assess the tolerability, pharmacokinetics and inhibitory effect on erythrocyte soluble catechol-O-methyltransferase (S-COMT) activity following repeated doses of opicapone. METHODS: This randomized, placebo-controlled, double-blind study enrolled healthy male subjects who received either once daily placebo or opicapone 5, 10, 20 or 30 mg for 8 days. RESULTS: Opicapone was well tolerated. Its systemic exposure increased in an approximately dose-proportional manner with an apparent terminal half-life of 1.0 to 1.4 h. Sulphation was the main metabolic pathway. Opicapone metabolites recovered in urine accounted for less than 3% of the amount of opicapone administered suggesting that bile is likely the main route of excretion. Maximum S-COMT inhibition (Emax ) ranged from 69.9% to 98.0% following the last dose of opicapone. The opicapone-induced S-COMT inhibition showed a half-life in excess of 100 h, which was dose-independent and much longer than plasma drug exposure. Such a half-life translates into a putative underlying rate constant that is comparable with the estimated dissociation rate constant of the COMT-opicapone complex. CONCLUSION: Despite its short elimination half-life, opicapone markedly and sustainably inhibited erythrocyte S-COMT activity making it suitable for a once daily regimen.

DESI-MSI-based technique to unravel spatial distribution of COMT inhibitor Tolcapone.

Ascertaining compound exposure and its spatial distribution are essential steps in the drug development process. Desorption electrospray ionization mass spectrometry (DESI-MSI) is a label-free imaging technique capable of simultaneously identify and visualize the distribution of a diverse range of biomolecules. In this study, DESI-MSI was employed to investigate spatial distribution of tolcapone in rat liver and brain coronal - frontal and striatal -sections after a single oral administration of 100 mg/Kg of tolcapone, brain-penetrant compound. Tolcapone was evenly distributed in liver tissue sections whereas in the brain it showed differential distribution across brain regions analyzed, being mainly located in the olfactory bulb, basal forebrain region, striatum, and pre-frontal cortex (PFC; cingulate, prelimbic and infralimbic area). Tolcapone concentration in tissues was compared using DESI-MSI and liquid-chromatography mass spectrometry (LC-MS/MS). DESI-MSI technique showed a higher specificity on detecting tolcapone in liver sections while in the brain samples DESI-MSI did not allow a feasible quantification. Indeed, DESI-MSI is a qualitative technique that allows to observe heterogeneity on distribution but more challenging regarding accurate measurements. Overall, tolcapone was successfully localized in liver and brain tissue sections using DESI-MSI, highlighting the added value that this technique could provide in assisting tissue-specific drug distribution studies.

Metabolism and disposition of opicapone in the rat and metabolic enzymes phenotyping.

Opicapone (2,5-dichloro-3-(5-(3,4-dihydroxy-5-nitrophenyl)-1,2,4-oxadiazol-3-yl)-4,6-dimethylpyridine 1-oxide) is a selective catechol-O-methyltransferase inhibitor that has been granted marketing authorization in Europe, Japan, and United States. The present work describes the metabolism and disposition of opicapone in the rat obtained in support to its development and regulatory filling. Plasma levels and elimination of total radioactivity were determined after oral and intravenous administration of [14 C]-opicapone. The maximum plasma concentrations of opicapone-related radioactivity were reached at early time points followed by a gradual return to baseline with a biphasic elimination. Fecal excretion was the primary route of elimination of total radioactivity. Quantitative distribution of drug-related radioactivity demonstrated that opicapone and related metabolites did not distribute to the central nervous system. Opicapone was extensively metabolized in rats resulting in more than 20 phase I and phase II metabolites. Although O-glucuronidation, -sulfation, and -methylation of the nitrocatechol moiety were the principal metabolic pathways, small amount of the N-acetyl derivative was detected, as a result of reduction of the nitro group and subsequent conjugation. Other metabolic transformations included N-oxide reduction to the pyridine derivative and reductive cleavage of 1,2,4-oxadiazole ring followed by further conjugative reactions. Reaction phenotyping studies suggested that SULT 1A1*1 and *2 and UGT1A7, UGT1A8, UGT1A9, and UGT1A10 may be involved in opicapone sulfation and glucuronidation, respectively. However, the reductive metabolic pathways mediated by gut microflora cannot be excluded. Opicapone, in the rat, was found to be rapidly absorbed, widely distributed to peripheric tissues, metabolized mainly via conjugative pathways at the nitro catechol ring, and primarily excreted via feces.

Hepatic UDP-glucuronosyltransferase is responsible for eslicarbazepine glucuronidation.

Eslicarbazepine acetate (ESL) is a once-daily novel antiepileptic drug approved in Europe for use as adjunctive therapy for refractory partial-onset seizures with or without secondary generalization. Metabolism of ESL consists primarily of hydrolysis to eslicarbazepine, which is then subject to glucuronidation followed by renal excretion. In this study, we have identified that human liver microsomes (HLM) enriched with uridine 5'-diphosphoglucuronic acid give origin to a single Escherichia coli ß-glucuronidase-sensitive eslicarbazepine glucuronide (most likely the O-glucuronide). The kinetics of eslicarbazepine glucuronidation in HLM was investigated in the presence and absence of bovine serum albumin (BSA). The apparent K(m) were 412.2 ± 63.8 and 349.7 ± 74.3 µM in the presence and absence of BSA, respectively. Incubations with recombinant human UDP glucuronosyltransferases (UGTs) indicated that UGT1A4, UGT1A9, UGT2B4, UGT2B7, and UGT2B17 appear to be involved in eslicarbazepine conjugation. The UGT with the highest affinity for conjugation was UGT2B4 (K(m) = 157.0 ± 31.2 and 28.7 ± 10.1 µM, in the absence and presence of BSA, respectively). There was a significant correlation between eslicarbazepine glucuronidation and trifluoperazine glucuronidation, a typical UGT1A4 substrate; however, no correlation was found with typical substrates for UGT1A1 and UGT1A9. Diclofenac inhibited eslicarbazepine glucuronidation in HLM with an IC(50) value of 17 µM. In conclusion, glucuronidation of eslicarbazepine results from the contribution of UGT1A4, UGT1A9, UGT2B4, UGT2B7, and UGT2B17, but the high-affinity component of the UGT2B4 isozyme may play a major role at therapeutic plasma concentrations of unbound eslicarbazepine.

A new role for anandamide: defective link between the systemic and skin endocannabinoid systems in hypertrophic human wound healing.

The use of cannabinoids to treat fibrotic skin diseases is an emergent issue. Therefore, we aimed to evaluate systemic and skin endocannabinoid responses in the wound-healing process in humans. A prospective study was performed in 50 patients who underwent body-contouring surgery. Anandamide (N-arachidonoylethanolamine, AEA), 2-arachidonoylglycerol (2-AG), palmitoylethanolamide (PEA) and oleoylethanolamide (OEA) were quantified using LC-MS/MS. Ten (20%) patients developed hypertrophic (HT) scars. No significant changes were observed between the normal (N) scar and HT scar groups in terms of plasma and skin endocannabinoids. Nevertheless, a positive correlation between plasma and skin AEA concentrations was found in the N group (r = 0.38, p = 0.015), which was absent in the HT group. Moreover, the AEA concentration was significantly lower in HT scar tissue than in normal scar tissue (0.77 ± 0.12 ng/g vs 1.15 ± 0.15 ng/g, p < 0.001). Interestingly, in all patients, the surgical intervention produced a time-dependent effect with a U shape for AEA, PEA and OEA plasma concentrations. In contrast, 2-AG plasma concentrations increased 5 days after surgery and were reduced and stabilized 3 months later. These results suggest crosstalk between systemic and local skin endocannabinoid systems during human wound healing. AEA appears to be the most likely candidate for this link, which is deficient in patients with HT scars.

Preclinical pharmacological evaluation of the fatty acid amide hydrolase inhibitor BIA 10-2474.

BACKGROUND AND PURPOSE: In 2016, one person died and four others had mild-to-severe neurological symptoms during a phase I trial of the fatty acid amide hydrolase (FAAH) inhibitor BIA 10-2474. EXPERIMENTAL APPROACH: Pharmacodynamic and pharmacokinetic studies were performed with BIA 10-2474, PF-04457845 and JNJ-42165279 using mice, rats and human FAAH expressed in COS cells. Selectivity was evaluated by activity-based protein profiling (APBB) in rats. BIA 10-2474 effect in stroke-prone spontaneously hypertensive rats (SHRSP) was investigated. KEY RESULTS: BIA 10-2474 was 10-fold less potent than PF-04457845 in inhibiting human FAAH in situ but inhibited mouse brain and liver FAAH with ED50 values of 13.5 and 6.2 µg·kg-1 , respectively. Plasma and brain BIA 10-2474 levels were consistent with in situ potency and neither BIA 10-2474 nor its metabolites accumulated following repeat administration. FAAH and α/ß-hydrolase domain containing 6 were the primary targets of BIA 10-2474 and, at higher exposure levels, ABHD11, PNPLA6, PLA2G15, PLA2G6 and androgen-induced protein 1. At 100 mg·kg-1 for 28 days, the level of several lipid species containing arachidonic acid increased. Daily treatment of SHRSP with BIA 10-2474 did not affect mortality rate or increased the incidence of haemorrhage or oedema in surviving animals. CONCLUSIONS AND IMPLICATIONS: BIA 10-2474 potently inhibits FAAH in vivo, similarly to PF-04457845 and interacts with a number of lipid processing enzymes, some previously identified in human cells as off-targets particularly at high levels of exposure. These interactions occurred at doses used in toxicology studies, but the implication of these off-targets in the clinical trial accident remains unclear.

Pharmacokinetic-pharmacodynamic interaction between nebicapone, a novel catechol-o-methyltransferase inhibitor, and controlled-release levodopa/carbidopa 200 mg/50 mg : randomized, double-blind, placebo-controlled, crossover study in healthy subjects.

BACKGROUND AND OBJECTIVES: Levodopa is the most effective symptomatic treatment for Parkinson's disease (PD), but its use is often associated with development of motor complications. These adverse responses to fluctuations in dopaminergic stimulation can be reduced by concomitant administration of a catechol-O-methyltransferase (COMT) inhibitor. Nebicapone is a new COMT inhibitor currently being developed for use as an adjunct to levodopa/dopa decarboxylase inhibitor in the treatment of PD. This article aimed to investigate the effect of single oral doses (50 mg, 100 mg and 200 mg) of nebicapone on levodopa pharmacokinetics and erythrocyte-soluble COMT (S-COMT) activity when coadministered with a single dose of controlled-release (CR) levodopa/carbidopa 200 mg/50 mg (Sinemet((R)) CR 200/50) in healthy subjects (n = 16). METHODS: This was a randomized, double-blind, placebo-controlled, four-way crossover study in healthy subjects, with at least 5 days of washout between treatment periods. RESULTS: There was a dose-dependent and significant increase in levodopa extent of exposure (area under the plasma concentration-time curve from time zero to infinity [AUC(infinity)]) without a significant change in peak exposure (maximum plasma concentration; [C(max)]). Using placebo as a reference, levodopa geometric mean ratios (GMRs) and 90% CIs following nebicapone 50 mg, 100 mg and 200 mg were, respectively, 1.13 (0.98, 1.30), 1.04 (0.90, 1.19) and 1.10 (0.96, 1.27) for C(max) and 1.26 (1.16, 1.34), 1.37 (1.27, 1.75) and 1.47 (1.42, 1.65) for AUC(infinity). For 3-O-methyldopa (3-OMD), the GMRs and 90% CIs were, respectively, 0.61 (0.55, 0.67), 0.45 (0.41, 0.50) and 0.33 (0.30, 0.36) for C(max) and 0.69 (0.61, 0.78), 0.53 (0.41, 0.61) and 0.41 (0.37, 0.47) for AUC(infinity). Nebicapone dose dependently and significantly decreased COMT activity. Maximum COMT inhibition occurred at 1.5-2.4 hours post-dose and ranged from 56% to 73% with nebicapone 50 mg and 200 mg, respectively. There was a good correlation between plasma concentrations of nebicapone and inhibition of S-COMT activity. Treatments were well tolerated. CONCLUSION: Following concomitant administration with levodopa/carbidopa CR 200 mg/50 mg, single doses of nebicapone 50 mg, 100 mg and 200 mg significantly and dose-dependently inhibited S-COMT activity, increased systemic exposure to levodopa, and reduced 3-OMD formation.

Discovery of a Potent, Long-Acting, and CNS-Active Inhibitor (BIA 10-2474) of Fatty Acid Amide Hydrolase.

Fatty acid amide hydrolase (FAAH) can be targeted for the treatment of pain associated with various medical conditions. Herein we report the design and synthesis of a novel series of heterocyclic-N-carboxamide FAAH inhibitors that have a good alignment of potency, metabolic stability and selectivity for FAAH over monoacylglycerol lipase (MAGL) and carboxylesterases (CEs). Lead optimization efforts carried out with benzotriazolyl- and imidazolyl-N-carboxamide series led to the discovery of clinical candidate 8 l (3-(1-(cyclohexyl(methyl)carbamoyl)-1H-imidazol-4-yl)pyridine 1-oxide; BIA 10-2474) as a potent and long-acting inhibitor of FAAH. However, during a Phase I clinical trial with compound 8 l, unexpected and unpredictable serious neurological adverse events occurred, affecting five healthy volunteers, including the death of one subject.

Bioavailability and bioequivalence of two enteric-coated formulations of omeprazole in fasting and fed conditions.

OBJECTIVE: To investigate the relative bioavailability and bioequivalence, in fasting and fed conditions, of repeated doses of two omeprazole enteric-coated formulations in healthy volunteers. MATERIAL AND METHODS: Open label, single-centre study consisting of two consecutive randomised, two-way crossover trials (a fasting trial and a fed trial). Each trial consisted of two 7-day treatment periods in which subjects received one daily dose of the test (Ompranyt((R))) or reference (Mopral((R))) formulations. At day 7 and day 14 (fasting trial), products were administered in fasting conditions and blood samples were taken for omeprazole plasma assay over 12 hours. At day 21 and day 28 (fed trial), products were administered after a standard high-calorie and high-fat meal and 12-hour blood samples taken. Omeprazole plasma concentrations were quantified by a validated method using a reverse-phase high performance liquid chromatography with UV detection (HPLC-UV). RESULTS: Twenty-four subjects were enrolled and 23 completed the study. Under fasting conditions, the mean +/- SD maximum omeprazole plasma concentration (C(max)) was 797 +/- 471 mug/L for Ompranyt((R)) and 747 +/- 313 mug/L for Mopral((R)) with a point estimate (PE) of 1.01 and a 90% confidence interval (CI) of 0.88, 1.16. The mean +/- SD area under the plasma concentration curve from administration to last observed concentration (AUC(0-12)) was 1932 +/- 1611 mug . h/L and 1765 +/- 1327 mug . h/L for Ompranyt((R)) and Mopral((R)), respectively (PE = 1.09; 90% CI 0.95, 1.25). In the presence of food, the C(max) was 331 +/- 227 mug/L and 275 +/- 162 mug/L (PE = 1.21; 90% CI 0.92, 1.59) and AUC(0-12) was 1250 +/- 966 mug . h/L and 1087 +/- 861 mug . h/L (PE = 1.16; 90% CI 0.92, 1.47) for Ompranyt((R)) and Mopral((R)), respectively. Bioequivalence of the formulations in the fasting condition was demonstrated both for AUC(0-12) and for C(max) because the 90% CI lay within the acceptance range of 0.80-1.25. In contrast with the fasting condition, there were significant reductions in rate (C(max)) and extent (AUC(0-12)) of systemic exposure when test and reference formulations were administered with food. The food effect was more marked with Mopral((R)) than with Ompranyt((R)), and the bioequivalence criterion was not fulfilled because the 90% CI fell out of the acceptance range of 0.80, 1.25, for both C(max) and AUC(0-12). The two formulations were similarly well tolerated. CONCLUSION: Bioequivalence of Ompranyt((R)) (test formulation) and Mopral((R)) (reference) formulations was demonstrated after repeated dosing in the fasting condition. Following a high-calorie and high-fat meal, there was a significant reduction in rate and extent of systemic exposure for both products, with Ompranyt((R)) being less affected than Mopral((R)) by the presence of food.

Eslicarbazepine and the enhancement of slow inactivation of voltage-gated sodium channels: a comparison with carbamazepine, oxcarbazepine and lacosamide.

This study aimed at evaluating the effects of eslicarbazepine, carbamazepine (CBZ), oxcarbazepine (OXC) and lacosamide (LCM) on the fast and slow inactivated states of voltage-gated sodium channels (VGSC). The anti-epileptiform activity was evaluated in mouse isolated hippocampal slices. The anticonvulsant effects were evaluated in MES and the 6-Hz psychomotor tests. The whole-cell patch-clamp technique was used to investigate the effects of eslicarbazepine, CBZ, OXC and LCM on sodium channels endogenously expressed in N1E-115 mouse neuroblastoma cells. CBZ and eslicarbazepine exhibit similar concentration dependent suppression of epileptiform activity in hippocampal slices. In N1E-115 mouse neuroblastoma cells, at a concentration of 250 µM, the voltage dependence of the fast inactivation was not influenced by eslicarbazepine, whereas LCM, CBZ and OXC shifted the V0.5 value (mV) by -4.8, -12.0 and -16.6, respectively. Eslicarbazepine- and LCM-treated fast-inactivated channels recovered similarly to control conditions, whereas CBZ- and OXC-treated channels required longer pulses to recover. CBZ, eslicarbazepine and LCM shifted the voltage dependence of the slow inactivation (V0.5, mV) by -4.6, -31.2 and -53.3, respectively. For eslicarbazepine, LCM, CBZ and OXC, the affinity to the slow inactivated state was 5.9, 10.4, 1.7 and 1.8 times higher than to the channels in the resting state, respectively. In conclusion, eslicarbazepine did not share with CBZ and OXC the ability to alter fast inactivation of VGSC. Both eslicarbazepine and LCM reduce VGSC availability through enhancement of slow inactivation, but LCM demonstrated higher interaction with VGSC in the resting state and with fast inactivation gating.

Eslicarbazepine acetate for the treatment of focal epilepsy: an update on its proposed mechanisms of action.

Eslicarbazepine acetate (ESL) is a once daily antiepileptic drug (AED) approved by the European Medicines Agency (EMA), the Food and Drug Administration (FDA) and Health Canada as an adjunctive therapy in adults with partial-onset seizures (POS). In humans and in relevant animal laboratory species, ESL undergoes extensive first pass hydrolysis to its major active metabolite eslicarbazepine that represents ∼95% of circulating active moieties. ESL and eslicarbazepine showed anticonvulsant activity in animal models. ESL may not only suppress seizure activity but may also inhibit the generation of a hyperexcitable network. Data reviewed here suggest that ESL and eslicarbazepine demonstrated the following in animal models: (1) the selectivity of interaction with the inactive state of the voltage-gated sodium channel (VGSC), (2) reduction in VGSC availability through enhancement of slow inactivation, instead of alteration of fast inactivation of VGSC, (3) the failure to cause a paradoxical upregulation of persistent Na(+) current (I NaP), and (4) the reduction in firing frequencies of excitatory neurons in dissociated hippocampal cells from patients with epilepsy who were pharmacoresistant to carbamazepine (CBZ). In addition, eslicarbazepine effectively inhibited high- and low-affinity hCaV3.2 inward currents with greater affinity than CBZ. These preclinical findings may suggest the potential for antiepileptogenic effects; furthermore, the lack of effect upon KV7.2 outward currents may translate into a reduced potential for eslicarbazepine to facilitate repetitive firing.

Etamicastat, a new dopamine-ß-hydroxylase inhibitor, pharmacodynamics and metabolism in rat.

Despite the importance of sympathetic nervous system in pathophysiological mechanisms of cardiac heart failure and essential hypertension, therapy specifically targeting the sympathetic nervous system is currently underutilized. Etamicastat is a novel dopamine-ß-hydroxylase (DBH) inhibitor that is oxidized into BIA 5-965 and deaminated followed by oxidation to BIA 5-998, which represents 13% of total etamicastat and quantified metabolites. However, the primary metabolic pathway of etamicastat in rats was found to be the N-acetylation (BIA 5-961), which represents 44% of total etamicastat and quantified metabolites. Trace amounts of BIA 5-961 de-sulfated and S-glucuronide were also detected. All the main metabolites of etamicastat inhibited DBH with IC50 values of 306 (228, 409), 629 (534, 741), 427 (350, 522) nM for BIA 5-965, BIA 5-998 and BIA 5-961, respectively. However, only etamicastat (IC50 of 107 (94; 121) nM) was able to reduce catecholamine levels in sympathetic nervous system innervated peripheral tissues, without effect upon brain catecholamines. Quantitative whole body autoradiography revealed a limited transfer of etamicastat related radioactivity to brain tissues and the mean recovery of radioactivity was ~90% of the administered radioactive dose, eliminated primarily via renal excretion over 5 days. The absolute oral bioavailability of etamicastat was 64% of the administered dose. In conclusion, etamicastat is a peripheral selective DBH inhibitor mainly N-acetylated in the aminoethyl moiety and excreted in urine. Etamicastat main metabolites inhibit DBH, but only etamicastat demonstrated unequivocal pharmacological effects as a DBH inhibitor with impact upon the activity of the sympathetic nervous system under in vivo conditions.

Pharmacokinetics, pharmacodynamics and tolerability of opicapone, a novel catechol-O-methyltransferase inhibitor, in healthy subjects: prediction of slow enzyme-inhibitor complex dissociation of a short-living and very long-acting inhibitor.

BACKGROUND AND OBJECTIVES: Opicapone is a novel catechol-O-methyltransferase (COMT) inhibitor. The purpose of this study was to evaluate the tolerability, pharmacokinetics (including the effect of food) and pharmacodynamics (effect on COMT activity) following single oral doses of opicapone in young healthy male volunteers. METHODS: Single rising oral doses of opicapone (10, 25, 50, 100, 200, 400, 800 and 1,200 mg) were administered to eight groups of eight subjects per group (two subjects randomized to placebo and six subjects to opicapone), under a double-blind, randomized, placebo-controlled design. In an additional group of 12 subjects, a 50 mg single dose of opicapone was administered on two occasions, once having fasted overnight and once with a high-fat high-calorie meal. RESULTS: Opicapone was well tolerated at all doses tested. The extent of systemic exposure (area under the plasma concentration-time curve and maximum plasma concentration) to opicapone and metabolites increased in an approximately dose-proportional manner and showed a decrease following concomitant ingestion of a high-fat high-calorie meal. The apparent terminal elimination half-life of opicapone was 0.8-3.2 h. Sulphation appeared to be the main metabolic pathway for opicapone, and both opicapone and the main sulphated metabolite are likely excreted by the biliary route. Maximum COMT inhibition by opicapone was dose dependent, ranged from 36.1% (10 mg) to 100% (200 mg and above), and reached statistical significance at all doses tested. The long duration of COMT inhibition by opicapone, however, tended to be independent from the dose taken. The observed half-life of opicapone-induced COMT inhibition in human erythrocytes was 61.6 h (standard deviation [SD] = 37.6 h), which reflects an underlying dissociative process with a kinetic rate constant of 3.1 × 10(-6) s(-1) (SD = 1.9 × 10(-6) s(-1)). Such a process compares well to the estimated dissociation rate constant (k(off)) of the COMT-opicapone molecular complex (k(off) = 1.9 × 10(-6) s(-1)). CONCLUSIONS: Opicapone was well-tolerated and presented dose-proportional kinetics. Opicapone demonstrated marked and sustained inhibition of erythrocyte soluble COMT activity. Based on the observation that the half-life of COMT inhibition is independent of the dose and that it reflects an underlying kinetic process that is consistent with the k(off) value of the COMT-opicapone complex, we propose that the sustained COMT inhibition, far beyond the observable point of clearance of circulating drug, is due to the long residence time of the reversible complex formed between COMT and opicapone. Globally, these promising results provide a basis for further clinical development of opicapone.