Richard Porter

Glutamate and Parkinson's disease

Altered glutamatergic neurotransmission and neuronal metabolic dysfunction appear to be central to the pathophysiology of Parkinson’s disease (PD). The substantia nigra pars compacta—the area where the primary pathological lesion is located—is particularly exposed to oxidative stress and toxic and metabolic insults. A reduced capacity to cope with metabolic demands, possibly related to impaired mitochondrial function, may render nigral neurons highly vulnerable to the effects of glutamate, which acts as a neurotoxin in the presence of impaired cellular energy metabolism. In this way, glutamate may participate in the pathogenesis of PD. Degeneration of dopamine nigral neurons is followed by striatal dopaminergic denervation, which causes a cascade of functional modifications in the activity of basal ganglia nuclei. As an excitatory neurotransmitter, glutamate plays a pivotal role in normal basal ganglia circuitry. With nigrostriatal dopaminergic depletion, the glutamatergic projections from subthalamic nucleus to the basal ganglia output nuclei become overactive and there are regulatory changes in glutamate receptors in these regions. There is also evidence of increased glutamatergic activity in the striatum. In animal models, blockade of glutamate receptors ameliorates the motor manifestations of PD. Therefore, it appears that abnormal patterns of glutamatergic neurotransmission are important in the symptoms of PD. The involvement of the glutamatergic system in the pathogenesis and symptomatology of PD provides potential new targets for therapeutic intervention in this neuro-degenerative disorder.

The Embryo and Its Future

Abstract The preimplantation mammalian embryo from different species appears sensitive to the environment in which it develops, either in vitro or in vivo, for example, in response to culture conditions or maternal diet. This sensitivity may lead to long-term alterations in the characteristics of fetal and/or postnatal growth and phenotype, which have implications for clinical health and biotechnological applications. We review the breadth of environmental influences that may affect early embryos and their responses to such conditions along epigenetic, metabolic, cellular, and physiological directions. In addition, we evaluate how embryo environmental responses may influence developmental potential and phenotype during later gestation. We conclude that a complex of different mechanisms may operate to associate early embryo environment with future health.

Competitive antagonism at metabotropic glutamate receptors by (S) -4-carboxyphenylglycine and (RS) -α-methyl-4-carboxyphenylglycine

Two phenylglycine derivates, (S)-4-carboxyphenylglycine and (RS)-alpha-methyl-4-carboxyphenylglycine, competitively antagonised (1S,3R)-1-aminocyclopentane-1,3-dicarboxylate (ACPD)-stimulated phosphoinositide hydrolysis in rat cerebral cortical slices. The same phenylglycine derivatives selectively antagonized ACPD-induced depolarization in neonatal rat spinal motoneurones and rate thalamic neurones relative to depolarization or excitation induced by N-methyl-D-aspartate (NMDA) or alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA). Both phenylglycine derivatives also selectively depressed synaptic excitation in thalamic neurones evoked by noxious thermal stimuli, without affecting the synaptic stimulation of the same cells by non-noxious stimuli.

Day 3 morphology is a poor predictor of blastocyst quality in extended culture

OBJECTIVE To determine how the quality of blastocysts formed on day 5/6 of extended culture compares with their morphology on day 3. DESIGN Retrospective observational study of IVF laboratory records. SETTING Private assisted reproduction clinic. PATIENT(S) 101 IVF cycles in which 5 to 25 embryos were produced. The average maternal age was 33.1 years. INTERVENTION(S) Embryos were individually cultured in vitro in sequential media for an extended time to enable use of blastocysts for fresh transfer or cryopreservation. MAIN OUTCOME MEASURE(S) Comparison of embryo quality for putative ET or cryopreservation on day 3 with quality of embryos used for actual ET and cryopreservation on day 5/6. RESULT(S) Of 1,263 cleaving embryos, 559 were judged to have been suitable for use on day 3; 355 would have been used for ET (average per ET, 3.5) and 204 would have been frozen (equivalent to 44% utilization). In actuality, 471 blastocysts were used on day 5/6, of which 234 were transferred (average per ET, 2.3), and 237 were frozen (equivalent to 37% utilization). Only 48% embryos that would have been chosen for ET and/or cryopreservation on day 3 were eventually used in such a manner at the blastocyst stage. Historically, the rate of viable pregnancy from day 3 transfers was 30.5% per transfer; this rate increased to 45% with routine day 5/6 transfers. CONCLUSION(S) Extended culture of human embryos seems to increase discrimination of potential embryonic viability. Criteria for embryo selection on day 3 seem to be inadequate. Extended in vitro culture may therefore be an effective means of optimizing IVF clinical success.

Ultrasonic assessment of endometrial changes in stimulated cycles in an in vitro fertilization and embryo transfer program

Four distinct patterns in the ultrasonic appearance of preovulatory endometrium can be identified and described in patients undergoing stimulated cycles in an in vitro fertilization program. Ultrasonically, this endometrial response can be seen as a quantitative change in thickness and a qualitative change in gray-scale appearance or reflectivity. The application of this additional parameter of endometrial assessment together with the conventional measurement of follicular diameter as a means of optimally timing oocyte collection has been associated with a reduction in the preoperative ovulation rate from 10.9 to 3.2%, an increase in the fertilization rate from 59.2 to 82.5%, and in a pregnancy rate per embryo transfer of 20.5% in our program without the use of hormonal assays.

CTEP: A Novel, Potent, Long-Acting, and Orally Bioavailable Metabotropic Glutamate Receptor 5 Inhibitor

The metabotropic glutamate receptor 5 (mGlu5) is a glutamate-activated class C G protein-coupled receptor widely expressed in the central nervous system and clinically investigated as a drug target for a range of indications, including depression, Parkinsons disease, and fragile X syndrome. Here, we present the novel potent, selective, and orally bioavailable mGlu5 negative allosteric modulator with inverse agonist properties 2-chloro-4-((2,5-dimethyl-1-(4-(trifluoromethoxy)phenyl)-1H-imidazol-4-yl)ethynyl)pyridine (CTEP). CTEP binds mGlu5 with low nanomolar affinity and shows >1000-fold selectivity when tested against 103 targets, including all known mGlu receptors. CTEP penetrates the brain with a brain/plasma ratio of 2.6 and displaces the tracer [3H]3-(6-methyl-pyridin-2-ylethynyl)-cyclohex-2-enone-O-methyl-oxime (ABP688) in vivo in mice from brain regions expressing mGlu5 with an average ED50 equivalent to a drug concentration of 77.5 ng/g in brain tissue. This novel mGlu5 inhibitor is active in the stress-induced hyperthermia procedure in mice and the Vogel conflict drinking test in rats with minimal effective doses of 0.1 and 0.3 mg/kg, respectively, reflecting a 30- to 100-fold higher in vivo potency compared with 2-methyl-6-(phenylethynyl)pyridine (MPEP) and fenobam. CTEP is the first reported mGlu5 inhibitor with both long half-life of approximately 18 h and high oral bioavailability allowing chronic treatment with continuous receptor blockade with one dose every 48 h in adult and newborn animals. By enabling long-term treatment through a wide age range, CTEP allows the exploration of the full therapeutic potential of mGlu5 inhibitors for indications requiring chronic receptor inhibition.

Metabolic induction and early responses of mouse blastocyst developmental programming following maternal low protein diet affecting life-long health

Previously, we have shown that a maternal low protein diet, fed exclusively during the preimplantation period of mouse development (Emb-LPD), is sufficient to induce by the blastocyst stage a compensatory growth phenotype in late gestation and postnatally, correlating with increased risk of adult onset cardiovascular disease and behavioural dysfunction. Here, we examine mechanisms of induction of maternal Emb-LPD programming and early compensatory responses by the embryo. Emb-LPD induced changes in maternal serum metabolites at the time of blastocyst formation (E3.5), notably reduced insulin and increased glucose, together with reduced levels of free amino acids (AAs) including branched chain AAs leucine, isoleucine and valine. Emb-LPD also caused reduction in the branched chain AAs within uterine fluid at the blastocyst stage. These maternal changes coincided with an altered content of blastocyst AAs and reduced mTORC1 signalling within blastocysts evident in reduced phosphorylation of effector S6 ribosomal protein and its ratio to total S6 protein but no change in effector 4E-BP1 phosphorylated and total pools. These changes were accompanied by increased proliferation of blastocyst trophectoderm and total cells and subsequent increased spreading of trophoblast cells in blastocyst outgrowths. We propose that induction of metabolic programming following Emb-LPD is achieved through mTORC1signalling which acts as a sensor for preimplantation embryos to detect maternal nutrient levels via branched chain AAs and/or insulin availability. Moreover, this induction step associates with changes in extra-embryonic trophectoderm behaviour occurring as early compensatory responses leading to later nutrient recovery.

(S)-homoquisqualate : a potent agonist at the glutamate metabotropic receptor

The synthetic quisqualate analogue, (S)‐homoquisqualate was examined for activity at the glutamate metabotropic receptor, in relation to its ability to stimulate phosphoinositide hydrolysis in rat pup cerebro‐cortical slices. The compound produced a robust increase in hydrolysis (EC50 = 50.2 ± 1.6 μm), which, in common with responses to quisqualate and (1S,3R)‐1‐aminocyclopentane‐1,3‐dicarboxylate ((1S,3R)‐ACPD), was antagonized uncompetitively by l‐2‐amino‐3‐phosphonopropionate (l‐AP3). In contrast to quisqualate which exhibits low efficacy, (S)‐homoquisqualate behaves as a full agonist at the metabotropic receptor.

Glutamate metabotropic receptor activation in neonatal rat cerebral cortex by sulphur-containing excitatory amino acids

The sulphur-containing acidic amino acids (SAAs) display neuroexcitatory actions similar to those of L-glutamate and are widely regarded as bona fide transmitter candidates. In this study, L-cysteine sulphinic acid, L-cysteic acid, DL-homocysteic acid and L-homocysteine sulphinic acid were investigated for their ability to stimulate phosphatidylinositol hydrolysis in rat pup cerebrocortical slices and compared with L-glutamate and the selective agonist (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid ((1S,3R)-ACPD). Each of the SAAs possessed agonist activity at metabotropic glutamate receptors (mGluRs) and, although they exhibited lower efficacy than L-glutamate, they were more potent (EC50s of 401-487 microM compared with 791 microM for L-glutamate). These data are consistent with the possibility that SAAs may have a physiological role as endogenous activators of metabotropic (and presumably ionotropic) excitatory amino acid receptors.

Metabotropic Glutamate Receptor 5 Negative Allosteric Modulators: Discovery of 2-Chloro-4-[1-(4-fluorophenyl)-2,5-dimethyl-1H-imidazol-4-ylethynyl]pyridine (Basimglurant, RO4917523), a Promising Novel Medicine for Psychiatric Diseases

Negative allosteric modulators (NAMs) of metabotropic glutamate receptor 5 (mGlu5) have potential for the treatment of psychiatric diseases including depression, fragile X syndrome (FXS), anxiety, obsessive-compulsive disorders, and levodopa induced dyskinesia in Parkinsons disease. Herein we report the optimization of a weakly active screening hit 1 to the potent and selective compounds chloro-4-[1-(4-fluorophenyl)-2,5-dimethyl-1H-imidazol-4-ylethynyl]pyridine (basimglurant, 2) and 2-chloro-4-((2,5-dimethyl-1-(4-(trifluoromethoxy)phenyl)-1H-imidazol-4-yl)ethynyl)pyridine (CTEP, 3). Compound 2 is active in a broad range of anxiety tests reaching the same efficacy but at a 10- to 100-fold lower dose compared to diazepam and is characterized by favorable DMPK properties in rat and monkey as well as an excellent preclinical safety profile and is currently in phase II clinical studies for the treatment of depression and fragile X syndrome. Analogue 3 is the first reported mGlu5 NAM with a long half-life in rodents and is therefore an ideal tool compound for chronic studies in mice and rats.