Potent and selective pharmacodynamic synergy between the metabotropic glutamate receptor subtype 2-positive allosteric modulator JNJ-46356479 and levetiracetam in the mouse 6-Hz (44-mA) model.

OBJECTIVE: We previously demonstrated that positive allosteric modulators (PAMs) of metabotropic glutamate subtype 2 (mGlu2 ) receptors have potential synergistic interactions with the antiseizure drug levetiracetam (LEV). The present study utilizes isobolographic analysis to evaluate the combined administration of JNJ-46356479, a selective and potent mGlu2 PAM, with LEV as well as sodium valproate (VPA) and lamotrigine (LTG). METHODS: The anticonvulsant efficacy of JNJ-46356479 was evaluated in the 6-Hz model of psychomotor seizures in mice. JNJ-46356479 was administered in combination with LEV using 3 fixed dose-ratio treatment groups in the mouse 6-Hz (44-mA) seizure test. The combination of JNJ-46356479 with LEV was also evaluated in the mouse corneal kindling model. The potential interactions of JNJ-46356479 with the antiseizure drugs VPA and LTG were also evaluated using fixed dose-ratio combinations. Plasma levels were obtained for analysis of potential pharmacokinetic interactions for each combination studied in the mouse 6-Hz model. RESULTS: JNJ-46356479 was active in the 6-Hz model at both 32-mA and 44-mA stimulus intensities (median effective dose = 2.8 and 10.2 mg/kg, respectively). Using 1:1, 1:3, and 3:1 fixed dose-ratio combinations (LEV:JNJ-46356479), coadministration was significantly more potent than predicted for additive effects, and plasma levels suggest this synergism was not due to pharmacokinetic interactions. Studies in kindled mice further demonstrate the positive pharmacodynamic interaction of LEV with JNJ-46356479. Using 1:1 dose-ratio combinations of JNJ-46356479 with either VPA or LTG, there were no significant differences observed for coadministration. SIGNIFICANCE: These studies demonstrate a synergistic interaction of JNJ-46356479 with LEV, whereas no such effect occurred for JNJ-46356479 with either VPA or LTG. The synergy seems therefore to be specific to LEV, and the combination LEV/mGlu2 PAM has the potential to result in a rational polypharmacy approach to treat patients with refractory epilepsy, once it has been confirmed in clinical studies.

Selective and interactive effects of D2 receptor antagonism and positive allosteric mGluR4 modulation on waiting impulsivity.

BACKGROUND: Metabotropic glutamate receptor 4 (mGluR4) and dopamine D2 receptors are specifically expressed within the indirect pathway neurons of the striato-pallidal-subthalamic pathway. This unique expression profile suggests that mGluR4 and D2 receptors may play a cooperative role in the regulation and inhibitory control of behaviour. We investigated this possibility by testing the effects of a functionally-characterised positive allosteric mGluR4 modulator, 4-((E)-styryl)-pyrimidin-2-ylamine (Cpd11), both alone and in combination with the D2 receptor antagonist eticlopride, on two distinct forms of impulsivity. METHODS: Rats were trained on the five-choice serial reaction time task (5-CSRTT) of sustained visual attention and segregated according to low, mid, and high levels of motor impulsivity (LI, MI and HI, respectively), with unscreened rats used as an additional control group. A separate group of rats was trained on a delay discounting task (DDT) to assess choice impulsivity. RESULTS: Systemic administration of Cpd11 dose-dependently increased motor impulsivity and impaired attentional accuracy on the 5-CSRTT in all groups tested. Eticlopride selectively attenuated the increase in impulsivity induced by Cpd11, but not the accompanying attentional impairment, at doses that had no significant effect on behavioural performance when administered alone. Cpd11 also decreased choice impulsivity on the DDT (i.e. increased preference for the large, delayed reward) and decreased locomotor activity. CONCLUSIONS: These findings demonstrate that mGluR4s, in conjunction with D2 receptors, affect motor- and choice-based measures of impulsivity, and therefore may be novel targets to modulate impulsive behaviour associated with a number of neuropsychiatric syndromes.

Effect of pomaglumetad methionil on the QT interval in subjects with schizophrenia.

OBJECTIVE: This thorough QT/QTc (TQT) study assessed the effects of a supratherapeutic dose of pomaglumetad methionil, a potential treatment for schizophrenia, compared to placebo on the QT interval in subjects with schizophrenia. METHODS: This double-blind, 3-period crossover study enrolled 86 subjects aged 22 - 63 years, who met Diagnostic and Statistical Manual, Fourth Edition, Test Revision (DSM-IV-TR) criteria for schizophrenia; 78 subjects completed the study. Subjects were randomly assigned to sequences of 3 treatment periods of single oral doses of pomaglumetad methionil 400 mg, moxifloxacin 400 mg, and placebo. Quadruplicate electrocardiograms (ECGs) were extracted from 2 hours predose to 12 hours postdose and were overread by a blinded central reader. Time-matched pharmacokinetic (PK) parameters were assessed. RESULTS: At all-time points, the upper bound of the 90% 2-sided confidence interval (CI) for the least squares (LS) mean difference in changes from baseline in Fridericia's corrected QT interval (ΔQTcF) between pomaglumetad methionil and placebo was < 10 milliseconds (msec). Sufficient assay sensitivity was not achieved, likely due to food effect; although the maximum observed drug concentration (Cmax) with moxifloxacin (1,410 ng/mL) was lower than expected, the slope of the regression line of moxifloxacin plasma concentrations versus placebo-subtracted ΔQTcF was similar to that reported in the literature. CONCLUSIONS: A single supratherapeutic dose of 400 mg pomaglumetad methionil did not prolong QTcF to a clinically significant degree and, importantly, did not result in any absolute QTcF > 450 msec or increase in QTcF from predose > 30 msec.

D-amino acid aberrations in cerebrospinal fluid and plasma of smokers.

The glutamatergic neurotransmission system and the N-methyl-D-aspartate receptor (NMDAR) have been implicated in smoking and alcohol consumption behavior. Preclinical studies have demonstrated that nicotine and ethanol influence NMDAR functionality, which may have a role in tendencies to consume these substances. Nonetheless, little is known about concentrations of NMDAR coagonists in the cerebrospinal fluid (CSF) and plasma of individuals who smoke or consume alcohol. Glycine and L- and D-stereoisomers of alanine, serine, and proline were therefore measured using ultra-high-performance liquid chromatography-tandem mass spectrometry in 403 healthy subjects. Nicotine and alcohol consumption were quantified using questionnaires. Possible differences in NMDAR coagonist concentrations in plasma and CSF were investigated using ANCOVA with age, body mass index, and storage duration as covariates. The significance threshold was Bonferroni corrected (α=0.00625). Compared with non-smokers, smokers displayed lower levels of D-proline in plasma (p=0.0027, Cohen's d=-0.41) and D-proline in CSF (p=0.0026, Cohen's d=-0.43). D-Serine in CSF was higher in smokers than in non-smokers (p=0.0052, Cohen's d=0.41). After subdividing participants based on smoking quantity, dose-dependent decreases were demonstrated in smokers for D-proline in plasma (F=5.65, p=0.0039) and D-proline in CSF (F=5.20, p=0.0060). No differences in NMDAR coagonist levels between alcohol consumption groups were detected. To our knowledge, this is the first report to implicate D-amino acids in smoking behavior of humans. Whether such concentration differences lie at the root of or result from smoking habits may be addressed in prospective studies.

Pilot controlled trial of D-serine for the treatment of post-traumatic stress disorder.

Enhancement of neurotransmission mediated at N-methyl-D-aspartate subtype of glutamate receptors (NMDAR) may be beneficial in post-traumatic stress disorder (PTSD). d-serine (DSR) is an endogenous full agonist at the NMDAR-associated glycine modulatory site. Twenty-two chronic PTSD outpatients were randomly assigned to participate in a 6-wk double-blind, placebo-controlled, crossover trial with 30 mg/kg x d DSR used as monotherapy or add-on pharmacotherapy. Outcome was assessed using the Clinician-Administered PTSD scale (CAPS), Hamilton Anxiety (HAMA) and Depression (HAMD) scales and the civilian version of the Mississippi Scale for Combat-Related PTSD (MISS). DSR treatment was well tolerated and resulted in significantly (p=0.03) increased DSR serum levels. Compared with placebo administration, DSR treatment resulted in significantly reduced HAMA (p=0.007) and MISS (p=0.001) scores and a trend (p=0.07) towards improved CAPS total scores. These preliminary findings indicate that NMDAR glycine site-based pharmacotherapy may be effective in PTSD and warrant larger-sized clinical trials with optimized DSR dosages.

Quinolinic acid promotes albumin deposition in Purkinje cell, astrocytic activation and lipid peroxidation in fetal brain.

In high concentrations or after prolonged exposure, the N-methyl-D-aspartate receptor agonist quinolinic acid (QUIN) induces lipid peroxidation, oxidative stress, and cell death in the adult brain, and after i.c.v. injection induces seizures and increases blood-brain barrier permeability. As QUIN is substantially increased in plasma and brain of fetal sheep after endotoxin treatment or maternal tryptophan loading, we examined the effects of increasing plasma QUIN concentrations on the brain of late gestation fetal sheep. Continuous fetal infusion of QUIN (0.1 mmol/h i.v.; n=4) for 12 h increased plasma QUIN concentrations from 22.3+/-6.0-210.8+/-31.4 microM; the infusion of vehicle [normal saline] had no effect on QUIN concentrations (n=4). At 24 h after QUIN infusion glial fibrillary acidic protein immunoreactivity was significantly increased in cerebral gray matter and the granule cell layer of cerebellum, and the lipid peroxide product 4-hydroxynonenal-immunoreactivity and albumin-immunoreactivity were present throughout the cytoplasm of cerebellar Purkinje cells. Extravasation of albumin into the brain was not observed, indicating the cerebral microvasculature with respect to permeability to plasma proteins was normal at the time of analysis. We suggest that increased glial fibrillary acidic protein and 4-hydroxynonenal result from oxidative stress induced by QUIN, and that the increased intracellular albumin in cerebellar Purkinje cells may be an adaptive response.

Metabolism and disposition of a potent group II metabotropic glutamate receptor agonist, in rats, dogs, and monkeys.

Metabolism and disposition of MGS0028 [(1R,2S,5S,6S)-2-amino-6-fluoro-4-oxobicyclo[3.1.0]hexane-2,6-dicarboxylic acid monohydrate], a potent group II metabotropic glutamate receptor agonist, were examined in three preclinical species (Sprague-Dawley rats, beagle dogs, and rhesus monkeys). In rats, MGS0028 was widely distributed and primarily excreted in urine as parent and as a single reductive metabolite, identified as the 4R-isomer MGS0034 [(1R,2S,4R,5S,6S)-2-amino-6-fluoro-4-hydroxybicyclo[3.1.0]-hexane-2,6-dicarboxylic acid]. MGS0028 had a low brain to plasma ratio at efficacious doses in rats and was eliminated more slowly in rat brain than in plasma. Exposure increased proportionally (1--10 mg/kg p.o.) in rats, with bioavailability>60% at all doses. However, bioavailability was only approximately 20% in monkeys, and MGS0034 was found in relatively high abundance in plasma. In dogs, oral bioavailability was >60%, and the metabolite was not detected. In vitro metabolism was examined in liver subcellular fractions (microsomes and cytosol) from rat, dog, monkey, and human. Reductive metabolism was observed in rat, monkey, and human liver cytosol incubations, but not in dog liver cytosol incubations. No metabolism of MGS0028 was detected in incubations with liver microsomes from any species. Similar to in vivo results, MGS0028 was reduced in cytosol stereospecifically to MGS0034. The rank order of in vitro metabolite formation (monkey >> rat approximately human >> dog) was in agreement with in vivo observations in rats, dogs, and monkeys. Based on the observation of species difference in reductive metabolism, rat and monkey were recommended to be the preclinical species for further characterization prior to testing in humans. Finally, allometric scaling predicts that human pharmacokinetic parameters would be acceptable for further development.

AV3V lesions attenuate the cardiovascular responses produced by blood-borne excitatory amino acid analogs.

Systemic injections of the excitatory amino acid (EAA) analogs, kainic acid (KA) and N-methyl-D-aspartate (NMDA), produce a pressor response in conscious rats that is caused by a centrally mediated activation of sympathetic drive and the release of arginine vasopressin (AVP). This study tested the hypothesis that the tissue surrounding the anteroventral part of the third ventricle (AV3V) plays a role in the expression of the pressor responses produced by systemically injected EAA analogs. Specifically, we examined whether prior electrolytic ablation of the AV3V region would affect the pressor responses to KA and NMDA (1 mg/kg iv) in conscious rats. The KA-induced pressor response was smaller in AV3V-lesioned than in sham-lesioned rats (11 +/- 2 vs. 29 +/- 2 mmHg; P < 0.05). After ganglion blockade, KA produced a pressor response in sham-lesioned but not AV3V-lesioned rats (+27 +/- 3 vs. +1 +/- 2 mmHg; P < 0.05). The KA-induced pressor response in ganglion-blocked sham-lesioned rats was abolished by a vasopressin V1-receptor antagonist. Similar results were obtained with NMDA. The pressor response to AVP (10 ng/kg iv) was slightly smaller in AV3V-lesioned than in sham-lesioned ganglion-blocked rats (45 +/- 3 vs. 57 +/- 4 mmHg; P < 0.05). This study demonstrates that the pressor responses to systemically injected EAA analogs are smaller in AV3V-lesioned rats. The EAA analogs may produce pressor responses by stimulation of EAA receptors in the AV3V region, or the AV3V region may play an important role in the expression of these responses.