Typical and atypical neuroleptics

Tourette syndrome and other tic disorders of childhood

Tics are repetitive, patterned, and nonrhythmic movements or vocalizations/audible sounds that are misplaced in context. Phenomenology and characteristics of tics (e.g., premonitory urge, suppressibility) differentiate them from compulsions, stereotypies, functional tic-like behaviors, and other types of hyperkinetic movement disorders. With a prevalence of approximately 1% in school-aged boys, Tourette syndrome (TS) is considered a common childhood-onset neurodevelopmental disorder, defined by the combination of at least two motor tics and at least one phonic tic lasting more than 1 year. TS is a highly heritable disorder, with a wide spectrum of severity. In some individuals, tics can cause pain, distress, functional impairment, or stigmatization. About 90% of individuals with TS have at least one mental health comorbidity (attention-deficit/hyperactivity disorder, obsessive-compulsive disorder, anxiety/depressive disorders). These comorbidities significantly impact patients' quality of life and must therefore be screened and managed accordingly in this population. Treatment of tics is based on behavioral therapies targeting tics (habit reversal training included in the comprehensive behavioral intervention for tics, and exposure and response prevention for tics), in association with medication if needed (e.g., alpha-2-agonists, second-generation antipsychotics). Deep brain stimulation is considered an experimental option in the most severe, treatment-resistant patients. In adulthood, less than 25% of individuals still have moderate or severe tics.

Potential Therapeutic Application for Nicotinic Receptor Drugs in Movement Disorders

Emerging studies indicate that striatal cholinergic interneurons play an important role in synaptic plasticity and motor control under normal physiological conditions, while their disruption may lead to movement disorders. Here we discuss the involvement of the cholinergic system in motor dysfunction, with a focus on the role of the nicotinic cholinergic system in Parkinson's disease and drug-induced dyskinesias. Evidence for a role for the striatal nicotinic cholinergic system stems from studies showing that administration of nicotine or nicotinic receptor drugs protects against nigrostriatal degeneration and decreases L-dopa-induced dyskinesias. In addition, nicotinic receptor drugs may ameliorate tardive dyskinesia, Tourette's syndrome and ataxia, although further study is required to understand their full potential in the treatment of these disorders. A role for the striatal muscarinic cholinergic system in movement disorders stems from studies showing that muscarinic receptor drugs acutely improve Parkinson's disease motor symptoms, and may reduce dyskinesias and dystonia. Selective stimulation or lesioning of striatal cholinergic interneurons suggests they are primary players in this regulation, although multiple central nervous systems appear to be involved.

IMPLICATIONS

Accumulating data from preclinical studies and clinical trials suggest that drugs targeting CNS cholinergic systems may be useful for symptomatic treatment of movement disorders. Nicotinic cholinergic drugs, including nicotine and selective nAChR receptor agonists, reduce L-dopa-induced dyskinesias, as well as antipsychotic-induced tardive dyskinesia, and may be useful in Tourette's syndrome and ataxia. Subtype selective muscarinic cholinergic drugs may also provide effective therapies for Parkinson's disease, dyskinesias and dystonia. Continued studies/trials will help address this important issue.

Experimental treatment of antipsychotic-induced movement disorders

Antipsychotic drugs are extensively prescribed for the treatment of schizophrenia and other related psychiatric disorders. These drugs produced their action by blocking dopamine (DA) receptors, and these receptors are widely present throughout the brain. Therefore, extended antipsychotic use also leads to severe extrapyramidal side effects. The short-term effects include parkinsonism and the later appearing tardive dyskinesia. Currently available treatments for these disorders are mostly symptomatic and insufficient, and are often linked with a number of detrimental side effects. Antipsychotic-drug-induced tardive dyskinesia prompted researchers to explore novel drugs with fewer undesirable extrapyramidal side effects. Preclinical studies suggest a role of 5-hydroxytryptamine (serotonin)-1A and 2A/2C receptors in the modulation of dopaminergic neurotransmission and motivating a search for better therapeutic strategies for schizophrenia and related disorders. In addition, adjunctive treatment with antioxidants such as vitamin E, red rice bran oil, and curcumin in the early phases of illness may prevent additional oxidative injury, and thus improve and prevent further possible worsening of related neurological and behavioral deficits in schizophrenia. This review explains the role of serotonergic receptors and oxidative stress, with the aim of providing principles for prospect development of compounds to improve therapeutic effects of antischizophrenic drugs.

New therapeutic opportunities for 5-HT2C receptor ligands in neuropsychiatric disorders

The 5-HT2C receptor (R) displays a widespread distribution in the CNS and is involved in the action of 5-HT in all brain areas. Knowledge of its functional role in the CNS pathophysiology has been impaired for many years due to the lack of drugs capable of discriminating among 5-HT2R subtypes, and to a lesser extent to the 5-HT1B, 5-HT5, 5-HT6 and 5-HT7Rs. The situation has changed since the mid-90s due to the increased availability of new and selective synthesized compounds, the creation of 5-HT2C knock out mice, and the progress made in molecular biology. Many pharmacological classes of drugs including antipsychotics, antidepressants and anxiolytics display affinities toward 5-HT2CRs and new 5-HT2C ligands have been developed for various neuropsychiatric disorders. The 5-HT2CR is presumed to mediate tonic/constitutive and phasic controls on the activity of different central neurobiological networks. Preclinical data illustrate this complexity to a point that pharmaceutical companies developed either agonists or antagonists for the same disease. In order to better comprehend this complexity, this review will briefly describe the molecular pharmacology of 5-HT2CRs, as well as their cellular impacts in general, before addressing its central distribution in the mammalian brain. Thereafter, we review the preclinical efficacy of 5-HT2C ligands in numerous behavioral tests modeling human diseases, highlighting the multiple and competing actions of the 5-HT2CRs in neurobiological networks and monoaminergic systems. Notably, we will focus this evidence in the context of the physiopathology of psychiatric and neurological disorders including Parkinson's disease, levodopa-induced dyskinesia, and epilepsy.

Long-term clinical course and outcome of schizophrenia in rural Ethiopia: 10-year follow-up of a population-based cohort

BACKGROUND

Although the few available studies from LMICs report favorable outcome, the course of schizophrenia is more complex than has been indicated so far.

METHODS

A sample of 361 people with a standardized clinical diagnosis of schizophrenia were recruited from a predominantly rural community in Ethiopia and followed up regularly for an average of 10years. Psychiatrists used the Longitudinal Interval Follow-up Evaluation chart to carry out assessment of illness course. Duration of time in clinical remission was the primary outcome.

RESULT

About 61.0% of the patients remained under active follow-up, while 18.1% (n=65) were deceased. The mean percentage of follow-up time in complete remission was 28.4% (SD=33.0). Female patients were significantly more likely to have episodic illness course with no inter-episode residual or negative symptoms (χ(2)=6.28, P=0.012). Nearly 14.0% had continuous psychotic symptoms for over 75% of their follow-up time. Only 18.1% achieved complete remission for over 75% of their follow-up time. Later onset of illness was the only significant predictor of achieving full remission for over 50% of follow-up time in a fully adjusted model. Conventional antipsychotic medications were fairly well tolerated in 80% of the patients and 4.2% (n=15) experienced tardive dyskinesia.

CONCLUSION

This population-based study is one of the very few long-term outcome studies of schizophrenia in LMICs. The study demonstrated clearly a differential and more favorable course and outcome for female patients but overall course and outcome of schizophrenia appeared less favorable in this setting than has been reported from other LMICs.

Incidence of tardive dyskinesia: a comparison of long-acting injectable and oral paliperidone clinical trial databases

BACKGROUND

To assess the tardive dyskinesia (TD) rate in studies of once-monthly long-acting injectable (LAI) paliperidone palmitate (PP) and once-daily oral paliperidone extended release (Pali ER).

METHODS

Completed schizophrenia and bipolar studies for PP and Pali ER (≥ 6 month duration with retrievable patient-level data) were included in this post hoc analysis. Schooler-Kane research criteria were applied using Abnormal Involuntary Movement Scale (AIMS) scores to categorise probable (qualifying AIMS scores persisting for ≥ 3 months) and persistent TD (score persisting ≥ 6 months). Spontaneously reported TD adverse events (AEs) were also summarised. Impact of exposure duration on dyskinesia (defined as AIMS total score ≥ 3) was assessed by summarising the monthly dyskinesia rate.

RESULTS

In the schizophrenia studies, TD rates for PP (four studies, N = 1689) vs. Pali ER (five studies, N = 2054), were: spontaneously reported AE, 0.18% (PP) vs. 0.10% (Pali ER); probable TD, 0.12% (PP) vs. 0.19% (Pali ER) and persistent TD, 0.12% (PP) vs. 0.05% (Pali ER). In the only bipolar study identified [Pali ER (N = 614)], TD rate was zero (spontaneously reported AE reporting, probable and persistent TD assessments). Dyskinesia rate was higher within the first month of treatment with both PP (13.1%) and Pali ER (11.7%) and steadily decreased over time (months 6-7: PP: 5.4%; Pali ER: 6.4%). Mean exposure: PP, 279.6 days; Pali ER, 187.2 days.

CONCLUSIONS

Risk of TD with paliperidone was low (< 0.2%), regardless of the formulation (oral or LAI), in this clinical trial dataset. Longer cumulative exposure does not appear to increase the risk of dyskinesias.

Role for the nicotinic cholinergic system in movement disorders; therapeutic implications

A large body of evidence using experimental animal models shows that the nicotinic cholinergic system is involved in the control of movement under physiological conditions. This work raised the question whether dysregulation of this system may contribute to motor dysfunction and whether drugs targeting nicotinic acetylcholine receptors (nAChRs) may be of therapeutic benefit in movement disorders. Accumulating preclinical studies now show that drugs acting at nAChRs improve drug-induced dyskinesias. The general nAChR agonist nicotine, as well as several nAChR agonists (varenicline, ABT-089 and ABT-894), reduces l-dopa-induced abnormal involuntary movements or dyskinesias up to 60% in parkinsonian nonhuman primates and rodents. These dyskinesias are potentially debilitating abnormal involuntary movements that arise as a complication of l-dopa therapy for Parkinson's disease. In addition, nicotine and varenicline decrease antipsychotic-induced abnormal involuntary movements in rodent models of tardive dyskinesia. Antipsychotic-induced dyskinesias frequently arise as a side effect of chronic drug treatment for schizophrenia, psychosis and other psychiatric disorders. Preclinical and clinical studies also show that the nAChR agonist varenicline improves balance and coordination in various ataxias. Lastly, nicotine has been reported to attenuate the dyskinetic symptoms of Tourette's disorder. Several nAChR subtypes appear to be involved in these beneficial effects of nicotine and nAChR drugs including α4β2*, α6β2* and α7 nAChRs (the asterisk indicates the possible presence of other subunits in the receptor). Overall, the above findings, coupled with nicotine's neuroprotective effects, suggest that nAChR drugs have potential for future drug development for movement disorders.

Molecular Docking studies of D2 Dopamine receptor with Risperidone derivatives

In this work, 3D model of D2 dopamine receptor was determined by comparative homology modeling program MODELLER. The computed model's energy was minimized and validated using PROCHECK and Errat tool to obtain a stable model structure and was submitted in Protein Model Database (PMDB-ID: PM0079251). Stable model was used for molecular docking against Risperidone and their 15 derivatives using AutoDock 4.2, which resulted in energy-based descriptors such as Binding Energy, Ligand Efficiency, Inhib Constant, Intermol energy, vdW + Hbond + desolv Energy, Electrostatic Energy, Total Internal Energy and Torsional Energy. After that, we have built quantitative structure activity relationship (QSAR) model, which was trained and tested on Risperidone and their 15 derivatives having activity value pKi in µM. For QSAR modeling, Multiple Linear Regression model was engendered using energy-based descriptors yielding correlation coefficient r2 of 0.513. To assess the predictive performance of QSAR models, different cross-validation procedures were adopted. Our results suggests that ligand-receptor binding interactions for D2 employing QSAR modeling seems to be a promising approach for prediction of pKi value of novel antagonists against D2 receptor.

Nicotine reduces antipsychotic-induced orofacial dyskinesia in rats

Antipsychotics are an important class of drugs for the management of schizophrenia and other psychotic disorders. They act by blocking dopamine receptors; however, because these receptors are present throughout the brain, prolonged antipsychotic use also leads to serious side effects. These include tardive dyskinesia, repetitive abnormal involuntary movements of the face and limbs for which there is little treatment. In this study, we investigated whether nicotine administration could reduce tardive dyskinesia because nicotine attenuates other drug-induced abnormal movements. We used a well established model of tardive dyskinesia in which rats injected with the commonly used antipsychotic haloperidol develop vacuous chewing movements (VCMs) that resemble human orofacial dyskinesias. Rats were first administered nicotine (minipump; 2 mg/kg per day). Two weeks later, they were given haloperidol (1 mg/kg s.c.) once daily. Nicotine treatment reduced haloperidol-induced VCMs by ∼20% after 5 weeks, with a significant ∼60% decline after 13 weeks. There was no worsening of haloperidol-induced catalepsy. To understand the molecular basis for this improvement, we measured the striatal dopamine transporter and nicotinic acetylcholine receptors (nAChRs). Both haloperidol and nicotine treatment decreased the transporter and α6β2* nAChRs (the asterisk indicates the possible presence of other nicotinic subunits in the receptor complex) when given alone, with no further decline with combined drug treatment. By contrast, nicotine alone increased, while haloperidol reduced α4β2* nAChRs in both vehicle and haloperidol-treated rats. These data suggest that molecular mechanisms other than those directly linked to the transporter and nAChRs underlie the nicotine-mediated improvement in haloperidol-induced VCMs in rats. The present results are the first to suggest that nicotine may be useful for improving the tardive dyskinesia associated with antipsychotic use.