Psychopharmacology is the scientific study of the effects drugs have on mood, sensation, thinking, behavior, judgment and evaluation, and memory. It is distinguished from neuropsychopharmacology, which emphasizes the correlation between drug-induced changes in the functioning of cells in the nervous system and changes in consciousness and behavior.
Serine is an α-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group, a carboxyl group, and a side chain consisting of a hydroxymethyl group, classifying it as a polar amino acid. It can be synthesized in the human body under normal physiological circumstances, making it a nonessential amino acid. It is encoded by the codons UCU, UCC, UCA, UCG, AGU and AGC.
Serotonin–norepinephrine reuptake inhibitors (SNRIs) are a class of antidepressant medications used to treat major depressive disorder (MDD), anxiety disorders, obsessive–compulsive disorder (OCD), social phobia, attention-deficit hyperactivity disorder (ADHD), chronic neuropathic pain, fibromyalgia syndrome (FMS), and menopausal symptoms. SNRIs are monoamine reuptake inhibitors; specifically, they inhibit the reuptake of serotonin and norepinephrine. These neurotransmitters are thought to play an important role in mood regulation. SNRIs can be contrasted with the selective serotonin reuptake inhibitors (SSRIs) and norepinephrine reuptake inhibitors (NRIs), which act upon single neurotransmitters.
The norepinephrine transporter (NET), also known as noradrenaline transporter (NAT), is a protein that in humans is encoded by the solute carrier family 6 member 2 (SLC6A2) gene.
Sodium- and chloride-dependent glycine transporter 1, also known as glycine transporter 1, is a protein that in humans is encoded by the SLC6A9 gene which is promising therapeutic target for treatment of diabetes and obesity.
The glutamate hypothesis of schizophrenia models the subset of pathologic mechanisms of schizophrenia linked to glutamatergic signaling. The hypothesis was initially based on a set of clinical, neuropathological, and, later, genetic findings pointing at a hypofunction of glutamatergic signaling via NMDA receptors. While thought to be more proximal to the root causes of schizophrenia, it does not negate the dopamine hypothesis, and the two may be ultimately brought together by circuit-based models. The development of the hypothesis allowed for the integration of the GABAergic and oscillatory abnormalities into the converging disease model and made it possible to discover the causes of some disruptions.
Reuptake inhibitors (RIs) are a type of reuptake modulators. It is a drug that inhibits the plasmalemmal transporter-mediated reuptake of a neurotransmitter from the synapse into the pre-synaptic neuron. This leads to an increase in extracellular concentrations of the neurotransmitter and an increase in neurotransmission. Various drugs exert their psychological and physiological effects through reuptake inhibition, including many antidepressants and psychostimulants.
NMDA receptor modulators are a new form of antipsychotic that are in Phase II FDA studies. The first compound studied was glycine which was hypothesized by Daniel Javitt after observation that people with phencyclidine(PCP)-induced psychosis were lacking in glutamate transmission. In giving glycine to people with PCP-induced psychosis a recovery rate was noted. From there, it was hypothesized that people with psychosis from schizophrenia would benefit from increased glutamate transmission and glycine was added with strong recovery rates noted especially in the area of negative and cognitive symptoms. Glycine, however, sporadic results aside remains an adjunct antipsychotic and an unworkable compound. However, the Eli Lilly and Company study drug LY-2140023 is being studied as a primary antipsychotic and is showing strong recovery rates, especially in the area of negative and cognitive symptoms of schizophrenia. Tardive dyskinesia, diabetes and other standard complications have not been noted:
Treatment with LY2140023, like treatment with olanzapine, was safe and well-tolerated; treated patients showed statistically significant improvements in both positive and negative symptoms of schizophrenia compared to placebo. Notably, patients treated with LY-2140023 did not differ from placebo-treated patients with respect to prolactin elevation, extrapyramidal symptoms or weight gain. These data suggest that mGlu2/3 receptor agonists have antipsychotic properties and may provide a new alternative for the treatment of schizophrenia.
Pomaglumetad (LY-404,039) is an amino acid analog drug that acts as a highly selective agonist for the metabotropic glutamate receptor group II subtypes mGluR2 and mGluR3. Pharmacological research has focused on its potential antipsychotic and anxiolytic effects. Pomaglumetad is intended as a treatment for schizophrenia and other psychotic and anxiety disorders by modulating glutamatergic activity and reducing presynaptic release of glutamate at synapses in limbic and forebrain areas relevant to these disorders. Human studies investigating therapeutic use of pomaglumetad have focused on the prodrug LY-2140023, a methionine amide of pomaglumetad (also called pomaglumetad methionil) since pomaglumetad exhibits low oral absorption and bioavailability in humans.
Glycine transporters (GlyTs) are plasmalemmal neurotransmitter transporters. They serve to terminate the signaling of glycine by mediating its reuptake from the synaptic cleft back into the presynaptic neurons. There are two glycine transporters: glycine transporter 1 (GlyT1) and glycine transporter 2 (GlyT2).
Levomilnacipran is an antidepressant which was approved in the United States in 2013 for the treatment of major depressive disorder (MDD) in adults. It is the levorotatory enantiomer of milnacipran, and has similar effects and pharmacology, acting as a serotonin–norepinephrine reuptake inhibitor (SNRI).
Gavestinel (GV-150,526) was an investigational drug developed by GlaxoSmithKline for acute intracerebral hemorrhage, which in 2001 failed to show an effect in what was at the time, the largest clinical trial in stroke that had been conducted.
Rapastinel is a novel antidepressant that was under development by Allergan as an adjunctive therapy for the treatment of treatment-resistant depression. It is a centrally active, intravenously administered amidated tetrapeptide that acts as a novel and selective modulator of the NMDA receptor. The drug is a rapid-acting and long-lasting antidepressant as well as robust cognitive enhancer by virtue of its ability to enhance NMDA receptor-mediated signal transduction and synaptic plasticity.
7-Chlorokynurenic acid (7-CKA) is a tool compound that acts as a potent and selective competitive antagonist of the glycine site of the NMDA receptor. It produces ketamine-like rapid antidepressant effects in animal models of depression. However, 7-CKA is unable to cross the blood-brain-barrier, and for this reason, is unsuitable for clinical use. As a result, a centrally-penetrant prodrug of 7-CKA, 4-chlorokynurenine (AV-101), has been developed for use in humans, and is being studied in clinical trials as a potential treatment for major depressive disorder, and anti-nociception. In addition to antagonizing the NMDA receptor, 7-CKA also acts as a potent inhibitor of the reuptake of glutamate into synaptic vesicles, an action that it mediates via competitive blockade of vesicular glutamate transporters.
Lumateperone, sold under the brand name Caplyta, is an atypical antipsychotic medication of the butyrophenone class. It is approved for the treatment of schizophrenia as well as bipolar depression, as either monotherapy or adjunctive therapy. It is developed by Intra-Cellular Therapies, licensed from Bristol-Myers Squibb. Lumateperone was approved for medical use in the United States in December 2019 with an initial indication for schizophrenia, and became available in February 2020. It has since demonstrated efficacy in bipolar depression and received FDA approval in December 2021 for depressive episodes associated with both bipolar I and II disorders.
Brilaroxazine, also known as oxaripiprazole, is an investigational atypical antipsychotic which is under development by Reviva Pharmaceuticals for the treatment of neuropsychiatric and inflammatory disorders. It has currently completed the first of two phase III clinical trials for schizophrenia. Reviva Pharmaceuticals also intends to investigate brilaroxazine for the treatment of bipolar disorder, major depressive disorder, attention deficit hyperactivity disorder (ADD/ADHD), psychosis/agitation associated with Alzheimer's disease, Parkinson's disease psychosis, as well as the inflammatory disorders pulmonary arterial hypertension (PAH), idiopathic pulmonary fibrosis (IPF), and psoriasis. The FDA granted brilaroxazine orphan drug designation for the treatment of PAH and IPF.
L-4-Chlorokynurenine is an orally active small molecule prodrug of 7-chlorokynurenic acid, a NMDA receptor antagonist. It was investigated as a potential rapid-acting antidepressant.
Dextromethorphan/bupropion (DXM/BUP), sold under the brand name Auvelity, is a combination medication for the treatment of major depressive disorder (MDD). Its active components are dextromethorphan (DXM) and bupropion. Patients who stayed on the medication had an average of 11% greater reduction in depressive symptoms than placebo in an FDA approval trial. It is taken as a tablet by mouth.
Pesampator is a positive allosteric modulator (PAM) of the AMPA receptor (AMPAR), an ionotropic glutamate receptor, which is under development by Pfizer for the treatment of cognitive symptoms in schizophrenia. It was also under development for the treatment of age-related sensorineural hearing loss, but development for this indication was terminated due to insufficient effectiveness. As of July 2018, pesampator is in phase II clinical trials for cognitive symptoms in schizophrenia.
Iclepertin is an investigational nootropic to enhance the cognition and functional capacity in schizophrenia developed by Boehringer Ingelheim. As of May 2020, it is in phase III of clinical trial under the code name CONNEX-3. BI 425809 is an inhibitor of glycine transporter 1 (Gly-T1) that in phase II improved cognition after 12 weeks in patients with schizophrenia. Doses of 10 mg and 25 mg showed the largest separation from placebo. If these encouraging results are confirmed in phase 3 trials, BI 425809 could provide an effective treatment for cognitive impairment associated with schizophrenia. Schizophrenia is characterized by abnormalities in glutamatergic pathways related to NMDA receptor hypofunction. Inhibition of GlyT1 on the presynaptic membrane or astrocytes is hypothesized to increase glycine levels within the synapse. The NMDA receptor function may be enhanced by increasing levels of its co-agonist, glycine, within the synaptic cleft, which may lead to improvements in cognitive function.
