dynorphins and Schizophrenia

The kappa opioid receptor (KOR) and its endogenous ligands dynorphins (DYN) have been implicated in the development or symptomatology of a variety of neuropsychiatric disorders. This review covers a brief history of the development of KOR agonists and antagonists, their effects in healthy volunteers, and the potential role of DYN/KOR dysfunction in schizophrenia and major depressive disorder from a translational perspective. The potential role of DYN/KOR dysfunction in schizophrenia is based on several lines of evidence. Selective KOR agonists induce affective states in healthy volunteers with similarities to the symptoms of schizophrenia. Studies have shown increased DYN in patients with schizophrenia, although the data have been mixed. Finally, meta-analytic data have shown that opioid antagonists are associated with reductions in the symptoms of schizophrenia. The potential role of DYN/KOR dysfunction in major depressive disorder is also based on a combination of preclinical and clinical data. Selective KOR agonists have shown pro-depressive effects in human volunteers, while selective KOR antagonists have shown robust efficacy in several preclinical models of antidepressant activity. Small studies have shown that nonselective KOR antagonists may have efficacy in treatment-resistant depression. Additionally, recent clinical data have shown that the KOR may be an effective target for treating anhedonia, a finding relevant to both schizophrenia and depression. Finally, recommendations are provided for translating preclinical models for schizophrenia and major depressive disorder into the clinic.

Topics: Depressive Disorder, Major; Dynorphins; Humans; Narcotic Antagonists; Receptors, Opioid, kappa; Schizophrenia

Schizophrenia is a debilitating mental illness that affects approximately 1% of the world's population. Despite much research in its neurobiology to aid in developing new treatments, little progress has been made. One system that has not received adequate attention is the kappa opioid system and its potential role in the emergence of symptoms, as well as its therapeutic potential. Here we present an overview of the kappa system and review various lines of evidence derived from clinical studies for dynorphin and kappa opioid receptor involvement in the pathology of both the positive and negative symptoms of schizophrenia. This overview includes evidence for the psychotomimetic effects of kappa opioid receptor agonists in healthy volunteers and their reversal by the pan-opioid antagonists naloxone and naltrexone and evidence for a therapeutic benefit in schizophrenia for 4 pan-opioid antagonists. We describe the interactions between kappa opioid receptors and the dopaminergic pathways that are disrupted in schizophrenia and the histologic evidence suggesting abnormal kappa opioid receptor signaling in schizophrenia. We conclude by discussing future directions.

Topics: Animals; Antipsychotic Agents; Dynorphins; Humans; Narcotic Antagonists; Receptors, Opioid, kappa; Schizophrenia

Nardilysin is a metalloprotease that cleaves peptides, such as dynorphin-A, α-neoendorphin, and glucagon, at the N-terminus of arginine and lysine residues in dibasic moieties. It has various functionally important molecular interaction partners (heparin-binding epidermal growth factor-like growth factor, tumour necrosis factor-α-converting enzyme, neuregulin 1, beta-secretase 1, malate dehydrogenase, P42(IP4)/centaurin-α1, the histone H3 dimethyl Lys4, and others) and is involved in a plethora of normal brain functions. Less is known about possible implications of nardilysin for brain diseases. This review, which includes some of our own recent findings, attempts to summarize the current knowledge on possible roles of nardilysin in Alzheimer disease, Down syndrome, schizophrenia, mood disorders, alcohol abuse, heroin addiction, and cancer. We herein show that nardilysin is a Janus-faced enzyme with regard to brain pathology, being probably neuropathogenic in some diseases, but neuroprotective in others.

Topics: Alzheimer Disease; Brain Diseases; Brain Neoplasms; Down Syndrome; Dynorphins; Endorphins; Glucagon; Humans; Metalloendopeptidases; Mood Disorders; Nerve Tissue Proteins; Protein Precursors; Schizophrenia; Substance-Related Disorders

Topics: Dynorphins; Humans; Neurobiology; Receptors, Opioid, kappa; Schizophrenia

This study investigated human-induced pluripotent stem cell (hiPSC) -derived neurons for their ability to secrete neurotransmitters in an activity-dependent manner, the fundamental property required for chemical neurotransmission. Cultured hiPSC neurons showed KCl stimulation of activity-dependent secretion of catecholamines--dopamine (DA), norepinephrine (NE), and epinephrine (Epi)--and the peptide neurotransmitters dynorphin and enkephlain. hiPSC neurons express the biosynthetic enzymes for catecholamines and neuropeptides. Because altered neurotransmission contributes to schizophrenia (SZ), we compared SZ to control cultures of hiPSC neurons and found that SZ cases showed elevated levels of secreted DA, NE, and Epi. Consistent with increased catecholamines, the SZ neuronal cultures showed a higher percentage of tyrosine hydroxylase (TH)-positive neurons, the first enzymatic step for catecholamine biosynthesis. These findings show that hiPSC neurons possess the fundamental property of activity-dependent neurotransmitter secretion and can be advantageously utilized to examine regulation of neurotransmitter release related to brain disorders.

Topics: Adult; Case-Control Studies; Catecholamines; Cells, Cultured; Dynorphins; Enkephalins; Exocytosis; Female; Humans; Induced Pluripotent Stem Cells; Infant, Newborn; Male; Neural Stem Cells; Neurons; Schizophrenia

The distribution and function of neurons coexpressing the dopamine D1 and D2 receptors in the basal ganglia and mesolimbic system are unknown. We found a subset of medium spiny neurons coexpressing D1 and D2 receptors in varying densities throughout the basal ganglia, with the highest incidence in nucleus accumbens and globus pallidus and the lowest incidence in caudate putamen. These receptors formed D1-D2 receptor heteromers that were localized to cell bodies and presynaptic terminals. In rats, selective activation of D1-D2 heteromers increased grooming behavior and attenuated AMPA receptor GluR1 phosphorylation by calcium/calmodulin kinase IIα in nucleus accumbens, implying a role in reward pathways. D1-D2 heteromer sensitivity and functional activity was up-regulated in rat striatum by chronic amphetamine treatment and in globus pallidus from schizophrenia patients, indicating that the dopamine D1-D2 heteromer may contribute to psychopathologies of drug abuse, schizophrenia, or other disorders involving elevated dopamine transmission.

Topics: Amphetamine; Animals; Basal Ganglia; Behavior, Animal; Brain; Corpus Striatum; Dopamine; Dopamine Agents; Dynorphins; Enkephalins; Globus Pallidus; Humans; Immunoenzyme Techniques; Male; Neurons; Nucleus Accumbens; Rats; Rats, Sprague-Dawley; Receptors, Dopamine D1; Receptors, Dopamine D2; Schizophrenia

Three peptide neuromodulators that are found in high concentration in the substantia nigra: dynorphin A 1-8, met5-enkephalin-arg6-gly7-leu8 and substance P, were measured by specific radioimmunoassays in nigral tissue from normals and schizophrenics postmortem. Substance P and dynorphin were unchanged between the two groups. However, the proenkephalin-derived peptide was significantly elevated in the schizophrenic group. The immunoreactivity was identified as authentic met5-enkephalin-arg6-gly7-leu8 by high pressure liquid chromatography. The data suggest that a different set of regulatory controls exists for nigral enkephalin peptides as compared to dynorphin and substance P, and that the former system may be disordered in schizophrenia.

Topics: Adult; Chromatography, High Pressure Liquid; Dynorphins; Enkephalin, Methionine; Female; Humans; Male; Middle Aged; Peptide Fragments; Radioimmunoassay; Schizophrenia; Substance P; Substantia Nigra

Radioimmunoassay procedures were used to assay levels of dynorphin A (DYN A) and substance P-like activity (SP) in cerebrospinal fluid (CSF) obtained from 10 schizophrenic patients before and after neuroleptic treatment, from 10 matched patients with other psychiatric disorders before and after treatment, and from 10 nonpsychiatric surgical controls. The highest mean concentration of CSF DYN A was found in the schizophrenic group on admission (significant vs. nonpsychiatric controls). The concentration remained almost unaltered after 4 weeks of zuclopenthixol treatment despite a highly significant decrease of overt psychopathology assessed by the Brief Psychiatric Rating Scale (BPRS). There was no significant difference between the mean CSF DYN A levels of the nonschizophrenic psychiatric patients and the surgical controls. When all psychiatric patients were pooled together, there was a significant correlation between the level of CSF DYN A and the BPRS total score. With regard to CSF SP levels, no statistically significant differences were observed within or between the groups studied. Neither was there a significant correlation between the concentration of CSF SP and overt psychopathology. Nevertheless, the mean CSF SP concentration of three patients with major depression was clearly higher than the corresponding mean concentration of the other patients in the nonschizophrenic group.

Topics: Adult; Clopenthixol; Dose-Response Relationship, Drug; Drug Administration Schedule; Dynorphins; Female; Humans; Male; Psychiatric Status Rating Scales; Schizophrenia; Schizophrenic Psychology; Substance P

Topics: Adult; Cyclic AMP; Dynorphins; Female; Humans; Male; Medicine, Chinese Traditional; Methoxyhydroxyphenylglycol; Peptide Fragments; Schizophrenia

Using a highly specific and sensitive radioimmunoassay for dynorphin(1-8) (D 1-8), and a singly blind test design, we measured D(1-8) immunoreactivity (ir D 1-8) in CSF of 35 first break cases of acute schizophrenic patients. All patients were free of psychotropic medication for at least one week before the study. Another 31 neurological patients suffered from cervical arthrosis, tumor, myelopathy etc. were studied as controls. The ir D(1-8) in CSF of schizophrenic patients were significantly lower than that of controls (91.8 +/- 5.6, means +/- S.E.M., and 131.9 +/- 6.8 fmol/ml CSF respectively, p less than 0.001).

Topics: Adolescent; Adult; Age Factors; Dynorphins; Female; Humans; Male; Peptide Fragments; Schizophrenia; Sex Factors