Partial Agonists and Dual Disorders: Focus on Dual Schizophrenia

Dual disorder is a term applied to patients with an addictive disorder and other mental disorder. Epidemiological studies have established that dual disorders are an expectation rather than an exception. They are difficult to diagnose and treat and constitute a huge burden for both patients and their relatives and society. Current treatments are a combination of those needed to treat the addictive disorder with those focused on the co-occurring psychiatric disorder. Focusing specifically on schizophrenia, growing scientific evidence supports the existence of a shared vulnerability for substance use in these patients and those at risk. Various antipsychotics have been found to be useful in the treatment of psychotic symptoms and disorders; however, few effective treatments have been identified until now for substance use disorders in patients with dual schizophrenia. Partial agonism stands as a new pharmacological option available in recent years. Molecules with this kind of action may act as functional agonists or as antagonists, depending on the surrounding levels of the neurotransmitter. Studies have found their efficacy in schizophrenia, addiction, anxiety and depression. Certain partial agonist antipsychotics seem to have a role in the treatment of dual schizophrenia. That could be the case with cariprazine. Because of its higher affinity for dopaminergic D3 receptors compared to D2, a potential to prevent relapse to addiction, added to its antipsychotic efficacy, has been suggested. Here we briefly review current advances and future directions and introduce some personal insights into the role of partial agonists in co-occurring schizophrenia and substance use.

A RARE CASE REPORT OF AMISULPRIDE INDUCED URINARY RETENTION

Amisulpride is an atypical antipsychotic with the preferential action on D2/D3 receptors. Its common adverse effects are extrapyramidal symptoms, insomnia, hyperkinesia, anxiety, weight gain, agitation, hyperprolactinemia. We have witnessed a adverse effect of urinary retention induced by amisulpride at minimal dosage and would like to present the same.

Influence of vitamin D provision on the course of acute respiratory infections in children

The review article provides data from modern studies confirming the multifaceted effect of vitamin D in the human body. Vitamin D3 receptors (VDRs) have been shown to be present in most organs and tissues of the body. This confirms the importance of vitamin D not only in the formation of the skeletal system, but also in many of its extraosseous effects. Calcitriol affects the modulation of cell growth, neuromuscular conduction, inflammation processes, and is also an important stimulator of innate immunity due to the synthesis of antimicrobial peptides that provide protection against bacteria and viruses. In recent years, the relationship between the concentration of vitamin D in the blood and the incidence of respiratory infections in children has been actively studied. Many studies have shown that low vitamin D status is characteristic of most children with respiratory infections, and an adequate level of 25(OH)D in serum has a positive effect on the frequency of these infections and the severity of their course. Most authors demonstrate the benefits of vitamin D supplementation in the prevention of respiratory diseases in children, but there is no consensus regarding the frequency and dosage of vitamin D. The authors declare that they have no conflicts of interest. Key words: vitamin D, children, deficiency, respiratory diseases, prevention.

Protracted Hiccups Induced by Aripiprazole and Regressed after Administration of Gabapentin

Hiccups are sudden, repeated, and involuntary contractions of the diaphragm muscle (myoclonic contraction). It involves a reflex arc that, once activated, causes a strong contraction of the diaphragm immediately followed by the closure of the glottis translating into the classic “hic” sound. Hiccups can be short, persistent, and intractable depending on the duration. The most disabling hiccups often represent the epiphenomenon of a medical condition such as gastrointestinal and cardiovascular disorders; central nervous system (CNS) abnormalities; ear, nose, and throat (ENT) conditions or pneumological problems; metabolic/endocrine disorders; infections; and psychogenic disorders. Some drugs, such as aripiprazole, a second-generation antipsychotic, can induce the onset of variable hiccups. We describe herein the cases of three hospitalized patients who developed insistent hiccups after taking aripiprazole and who positively responded to low doses of gabapentin. It is probable that aripiprazole, prescribed at a low dosage (<7.5 mg/day), would act as a dopamine agonist by stimulating D2 and D3 receptors at the “hiccup center” level—located in the brain stem—thus triggering the hiccup. On the other hand, gabapentin led to a complete regression of the hiccup probably by reducing the nerve impulse transmission and modulating the diaphragmatic activity. The present case series suggests the use of low doses of gabapentin as an effective treatment for aripiprazole-induced hiccups. However, our knowledge of the neurotransmitter functioning of the hiccup reflex arc is still limited, and further research is needed to characterize the neurotransmitters involved in hiccups for potential novel therapeutic targets.

Modern clinical pharmacology approaches to negative symptom treatment in schizophrenia

Negative symptoms contribute to poor functional outcomes and quality of life for individuals with schizophrenia. Efficacy of negative symptom treatment in patients with schizophrenia are discussed by the example of a new atypical antipsychotic cariprazine (Reagila®). Discussion. Improved Receptor Profile: high affinity for D3 receptors and partial agonism for both dopamine receptor subtypes, may act as a basic mechanism for improving negative symptoms and cognitive impairment. Сonclusions. Сariprazine is the drug of choice in the treatment of adult patients both at the onset of the disease with a predominance of negative disorders, and in the chronic course of schizophrenia with positive and negative symptoms, especially in patients with a high risk of metabolic and cardiovascular disorders. Keywords: schizophrenia, negative disorders, antipsychotics, cariprazine.

ANTIPSYCHOTICS: FROM THE FIRST TO THE THIRD GENERATION

The review is devoted to comparative analysis of antipsychotics of three generations. When writing the review, a systematic search in the databases PubMed, Medline, Elsevier was carried out, a simple filter for keywords was used. Pharmacological and clinical issues of antipsychotic therapy were considered, the mechanisms of action of antipsychotics of different generations were revealed. Current trends in the development of approaches to the therapy of schizophrenia and the concept of atypicality of antipsychotics were discussed. A comparative analysis of indications for use, tolerance (safety of use) and efficacy of various antipsychotic drugs with an emphasis on the effect on negative (primary, persistent) symptoms has been conducted. The hypothesis underlying new approaches to the therapy of schizophrenia, based on the effect on dopamine autoreceptors, consisting of a high density of D2 and low density of D3 receptors, has been presented. It has been shown that antipsychotics of the third generation open up new possibilities in the therapy of psychosis within the framework of a personalized approach in psychiatry with the achievement of functional recovery of patients. The characteristics of the drugs representatives of the third generation of antipsychotics aripiprazole and cariprazine were given. The uniqueness of cariprazine as the only drug that inhibits D3 receptors in vitro, as well as in vivo in patients with schizophrenia was emphasized. The data of evidence-based studies of the effectiveness of cariprazine in the treatment of negative, including predominant negative symptoms were presented.

Fluorescent ligands for dopamine D2/D3 receptors

Fluorescent ligands are versatile tools for the study of G protein-coupled receptors. Depending on the fluorophore, they can be used for a range of different applications, including fluorescence microscopy and bioluminescence or fluorescence resonance energy transfer (BRET or FRET) assays. Starting from phenylpiperazines and indanylamines, privileged scaffolds for dopamine D2-like receptors, we developed dansyl-labeled fluorescent ligands that are well accommodated in the binding pockets of D2 and D3 receptors. These receptors are the target proteins for the therapy for several neurologic and psychiatric disorders, including Parkinson’s disease and schizophrenia. The dansyl-labeled ligands exhibit binding affinities up to 0.44 nM and 0.29 nM at D2R and D3R, respectively. When the dansyl label was exchanged for sterically more demanding xanthene or cyanine dyes, fluorescent ligands 10a-c retained excellent binding properties and, as expected from their indanylamine pharmacophore, acted as agonists at D2R. While the Cy3B-labeled ligand 10b was used to visualize D2R and D3R on the surface of living cells by total internal reflection microscopy, ligand 10a comprising a rhodamine label showed excellent properties in a NanoBRET binding assay at D3R.

Enhanced Dopamine Transmission and Hyperactivity in the Dopamine Transporter Heterozygous Mice Lacking the D3 Dopamine Receptor

Dopamine transporter knockout (DATk) mice are known to demonstrate profound hyperactivity concurrent with elevated (5-fold) extracellular dopamine in the basal ganglia. At the same time, heterozygous DAT mice (DATh) demonstrate a 2-fold increase in dopamine levels yet only a marginal elevation in locomotor activity level. Another model of dopaminergic hyperactivity is the D3 dopamine receptor knockout (D3k) mice, which present only a modest hyperactivity phenotype, predominately manifested as stereotypical behaviors. In the D3k mice, the hyperactivity is also correlated with elevated extracellular dopamine levels (2-fold) in the basal ganglia. Cross-breeding was used to evaluate the functional consequences of the deletion of both genes. In the heterozygous DAT mice, inactivation of the D3R gene (DATh/D3k) resulted in significant hyperactivity and further elevation of striatal extracellular dopamine above levels observed in respective single mutant mice. The decreased weight of DATk mice was evident regardless of the D3 dopamine receptor genotype. In contrast, measures of thermoregulation revealed that the marked hypothermia of DATk mice (−2 °C) was reversed in double knockout mice. Thus, the extracellular dopamine levels elevated by prolonging uptake could be elevated even further by eliminating the D3 receptor. These data also suggest that the hypothermia observed in DATk mice may be mediated through D3 receptors.