Prodopaminergic Drugs for Treating the Negative Symptoms of Schizophrenia: Systematic Review and Meta-analysis of Randomized Controlled Trials

Psychostimulant Substitution Therapy for the Treatment of Stimulant Use Disorders in Patients with Schizophrenia or Schizoaffective Disorder: A Systematic Review

Objective: Co-occurrence of schizophrenia/schizoaffective disorder (SSD) and stimulant use disorder (StUD) is an ongoing clinical problem and can lead to poor outcomes. Although emerging evidence has suggested psychostimulant substitution therapy may result in improved outcomes in those with StUD, the efficacy and safety of psychostimulant substitution therapy for StUD in those with concurrent SSD is uncertain. This review aims to systematically find and assess all available efficacy and safety evidence on the use of prescription psychostimulants in those with co-occurring SSD and StUD. Methods: Electronic searches of MEDLINE, PsycINFO, Embase, Scopus, ClinicalTrials, EU Clinical Trials, and CADTH were conducted from inception to February 27, 2024. Any study design was accepted if they involved the following concepts 1) SSD and StUD and 2) prescription psychostimulants. Given the paucity of trials meeting criteria, outcomes of interest were described qualitatively. Risk of bias was assessed using Q-Coh and ROB2. Results: Only seven articles met criteria, and most of these were case reports and series. The single RCT included was at high risk of bias. Outcomes included abstinence, reductions in non-prescribed stimulant use, psychiatric hospitalizations, levels of craving, improvements in mental health, improvements in psychosocial functioning, adherence to antipsychotic medications, and retention in treatment. Most of the results indicated that psychostimulant substitution therapy in individuals with SSD-StUD was not associated with improved outcomes. Conclusion: Available evidence for treatment of StUD via psychostimulant substitution therapy in individuals with SSD is lacking. More exploration is required for this clinical question to allow for current practice to be backed by evidence.

Negative Symptoms in Schizophrenia: An Update on Research Assessment and the Current and Upcoming Treatment Landscape

The negative symptoms of schizophrenia include diminished emotional expression, avolition, alogia, anhedonia, and asociality, and due to their low responsiveness to available treatments, are a primary driver of functional disability in schizophrenia. This narrative review has the aim of providing a comprehensive overview of the current research developments in the treatment of negative symptoms in schizophrenia, and begins by introducing the concepts of primary, secondary, prominent, predominant, and broadly defined negative symptoms. We then compare and contrast commonly used research assessment scales for negative symptoms and review the evidence for the specific utility of widely available off-label and investigational treatments that have been studied for negative symptoms. Mechanism of action/putative treatments included are antipsychotics (D2R antagonists), N-methyl-D-aspartate receptor (NMDAR) and other glutamatergic modulators, serotonin receptor (5-HTR) modulators, anti-inflammatory agents, antidepressants, pro-dopaminergic modulators (non-D2R antagonists), acetylcholine modulators, oxytocin, and phosphodiesterase (PDE) inhibitors. With the caveat that no compounds are definitively proven as gold-standard treatments for broadly defined negative symptoms, the evidence base supports several potentially beneficial off-label and investigational medications for treating negative symptoms in schizophrenia, such as monotherapy with cariprazine, olanzapine, clozapine, and amisulpride, or adjunctive use of memantine, setrons such as ondansetron, minocycline, and antidepressants. These medications are widely available worldwide, generally tolerable and could be considered for an off-label, time-limited trial for a predesignated period of time, after which a decision to switch or stay can be made based on clinical response. Among investigational medications, NMDAR agonists, muscarinic agonists, and LB-102 remain under study. Suggestions for future research include reducing placebo effects by designing studies with a smaller number of high-quality study sites, potentially increasing the use of more precise rating scales for negative symptoms, and focused studies in people with predominant negative symptoms.

Two and five-factor models of negative symptoms in schizophrenia are differentially associated with trait affect, defeatist performance beliefs, and psychosocial functioning

Recent factor analytic evidence supports both two-factor (motivation and pleasure, MAP; diminished expression, EXP) and five-factor (anhedonia, asociality, avolition, blunted affect, alogia) conceptualizations of negative symptoms. However, it is unclear whether these two conceptualizations of the latent structure of negative symptoms have differential associations with external correlates. The current study evaluated external correlates of the two- and five-factor structures by examining associations with variables known to have critical relations with negative symptoms: trait affect, defeatist performance beliefs, neurocognition, and community-based psychosocial functioning. Participants included a total of 245 outpatients diagnosed with schizophrenia who were rated on the Brief Negative Symptom Scale and completed a battery of additional measures during periods of clinical stability. These additional measures included the Positive and Negative Affect Schedule, Defeatist Performance Beliefs scale, MATRICS Consensus Cognitive Battery, and Level of Function Scale. Pearson correlations indicated differential patterns of associations between the BNSS scores and the external correlates. Support for the two-factor model was indicated by a stronger association of MAP with positive affect and psychosocial functioning, compared to EXP with neurocognition. Significance tests examining a differential magnitude of associations showed that the two-dimension negative symptom structure masked unique correlational relationships among the five negative symptom domains with neurocognition and social/vocational community functioning and captured unique patterns of correlation with trait affect. Support for the five-factor model was shown by a stronger association between Blunted Affect with Attention/Vigilance, and stronger associations between Avolition, Anhedonia, and Asociality with psychosocial functioning. Results offer support for both the two-dimension and five-domain model of negative symptoms as well as a hierarchical two-dimensions-five-domains model of negative symptoms. Findings may have implications for diagnostic criteria and descriptions of the Diagnostic and Statistical Manual of Mental Disorders (5th ed.; DSM-5), as well as possible treatment targets of negative symptoms.

Modafinil, an atypical CNS stimulant?

Modafinil is a central nervous system stimulant approved for the treatment of narcolepsy and sleep disorders. Due to its wide range of biochemical actions, modafinil has been explored for other potential therapeutic uses. Indeed, it has shown promise as a therapy for cognitive disfunction resulting from neurologic disorders like ADHD, and as a smart drug in non-medical settings. The mechanism(s) of actions underlying the therapeutic efficacy of this agent remains largely elusive. Modafinil is known to inhibit the dopamine transporter, thus decreasing dopamine reuptake following neuronal release, an effect shared by addictive psychostimulants. However, modafinil is unique in that only a few cases of dependence on this drug have been reported, as compared to other psychostimulants. Moreover, modafinil has been tested, with some success, as a potential therapeutic agent to combat psychostimulant and other substance use disorders. Modafinil has additional, but less understood, actions on other neurotransmitter systems (GABA, glutamate, serotonin, norepinephrine, etc.). These interactions, together with its ability to activate selected brain regions, are likely one of the keys to understand its unique pharmacology and therapeutic activity as a CNS stimulant. In this chapter, we outline the pharmacokinetics and pharmacodynamics of modafinil that suggest it has an "atypical" CNS stimulant profile. We also highlight the current approved and off label uses of modafinil, including its beneficial effects as a treatment for sleep disorders, cognitive functions, and substance use disorders.

Management of cognitive and negative symptoms in schizophrenia

Currently available antipsychotics provide only modest benefit in managing the cognitive and negative symptoms of schizophrenia even though these symptoms are often the most impairing in patients' daily lives. Certain antipsychotics may have slight benefits over others, and several nonpharmacologic and pharmacologic adjunctive treatments have been evaluated in recent clinical trials. Recently published meta-analyses and clinical studies of such treatments are reviewed. Potential strategies to manage cognitive and negative symptoms, including deprescribing of medications that may exacerbate these symptoms, are described using theoretical case examples.

Cluster analysis of negative symptoms identifies distinct negative symptom subgroups

The heterogeneity of schizophrenia has been acknowledged for decades because of the diverse presentation of symptoms, illness course, and treatment response noted between individuals diagnosed with the disorder. Cluster analysis has been used as a statistical method to determine whether schizophrenia subgroups might be identified based on symptom heterogeneity. However, there is very limited research examining whether heterogeneity in negative symptoms might be useful in establishing schizophrenia subtypes, particularly research examining newer models of negative symptoms based on five latent constructs including anhedonia, asociality, avolition, blunted affect, and alogia. The Brief Negative Symptom Scale was used to assess the five negative symptoms domains in a sample of 220 outpatients diagnosed with schizophrenia or schizoaffective disorder. Cluster analysis supported a four-cluster solution, comprising clusters of subjects with low negative symptoms (LNS), severe negative symptoms (SNS), and two clusters with moderate negative symptoms, one with predominantly elevated blunted affect (BA) and one with elevated avolition (AV). The LNS, SNS, BA, and AV clusters significantly differed on external validators including clinical characteristics, neurocognition, and functional outcome. Findings suggest that schizophrenia heterogeneity can be parsed according to negative symptom subtypes that have distinct clinical and neuropsychological profiles. Implications for diagnosis and treatment are discussed.

Increased ventral striatal functional connectivity in patients with schizophrenia during reward anticipation

Background

Growing evidence points towards dysfunction of the ventral striatum as a neural substrate of motivational impairments in schizophrenia. Ventral striatal activity during reward anticipation is generally reduced in patients with schizophrenia and specifically correlates with apathy. However, little is known about the cortico-striatal functional connectivity in patients with schizophrenia during reward anticipation and its relation to negative symptoms.

Objectives

The aim of this study was to identify categorical group differences in ventral striatal functional connectivity during reward anticipation between patients with schizophrenia and healthy controls, and dimensional associations between cortico-striatal functional connectivity and negative symptom severity.

Method

A total of 40 patients with schizophrenia (10 females) and 33 healthy controls (8 females) were included from two previously published studies. All participants performed a variant of the Monetary Incentive Delay Task while undergoing event-related fMRI. Functional connectivity was assessed using psychophysical interactions (PPI) with the left and right ventral striatum as seeds and the contrast [High Reward Anticipation – No Reward Anticipation]. Negative symptoms were assessed using the Brief Negative Symptom Scale.

Results

Compared to controls, patients with schizophrenia showed increased functional connectivity between the left ventral striatum and the left precuneus and right parahippocampal gyrus, two hubs of the default mode network (cluster-level threshold: FWE, p < .05). In addition, we found a negative association between apathy scores on the BNSS and increased functional connectivity between the left ventral striatum and the left ventral anterior insula / putamen and the left inferior frontal gyrus / dorsal anterior insula (cluster-level threshold: FWE, p < .05).

Conclusions

Our results indicate that the patterns of increased functional connectivity between the ventral striatum and the dorsal default mode network during reward anticipation could act as a compensatory mechanism to regulate the activity of the ventral striatum. Our results also showed that functional connectivity patterns from the ventral striatum, much like its local activity, is specifically related to apathy, and not diminished expression.

Clinical correlation but no elevation of striatal dopamine synthesis capacity in two independent cohorts of medication-free individuals with schizophrenia

Dysregulation of dopamine systems has been considered a foundational driver of pathophysiological processes in schizophrenia, an illness characterized by diverse domains of symptomatology. Prior work observing elevated presynaptic dopamine synthesis capacity in some patient groups has not always identified consistent symptom correlates, and studies of affected individuals in medication-free states have been challenging to obtain. Here we report on two separate cohorts of individuals with schizophrenia spectrum illness who underwent blinded medication withdrawal and medication-free neuroimaging with [¹⁸F]-FDOPA PET to assess striatal dopamine synthesis capacity. Consistently in both cohorts, we found no significant differences between patient and matched, healthy comparison groups; however, we did identify and replicate robust inverse relationships between negative symptom severity and tracer-specific uptake widely throughout the striatum: [¹⁸F]-FDOPA specific uptake was lower in patients with a greater preponderance of negative symptoms. Complementary voxel-wise and region of interest analyses, both with and without partial volume correction, yielded consistent results. These data suggest that for some individuals, striatal hyperdopaminergia may not be a defining or enduring feature of primary psychotic illness. However, clinical differences across individuals may be significantly linked to variability in striatal dopaminergic tone. These findings call for further experimentation aimed at parsing the heterogeneity of dopaminergic systems function in schizophrenia.

Developments in Biological Mechanisms and Treatments for Negative Symptoms and Cognitive Dysfunction of Schizophrenia

The causal mechanisms and treatment for the negative symptoms and cognitive dysfunction in schizophrenia are the main issues attracting the attention of psychiatrists over the last decade. The first part of this review summarizes the pathogenesis of schizophrenia, especially the negative symptoms and cognitive dysfunction from the perspectives of genetics and epigenetics. The second part describes the novel medications and several advanced physical therapies (e.g., transcranial magnetic stimulation and transcranial direct current stimulation) for the negative symptoms and cognitive dysfunction that will optimize the therapeutic strategy for patients with schizophrenia in future.

Intranasal Oxytocin for Negative Symptoms of Schizophrenia: Systematic Review, Meta-Analysis, and Dose-Response Meta-Analysis of Randomized Controlled Trials

BACKGROUND

Negative symptoms are a core aspect of psychopathology in schizophrenia. Currently available pharmacological agents have proven minimally efficacious for remediating negative symptoms. A promising treatment avenue is the intranasal administration of the neuropeptide oxytocin. However, there have been inconsistencies in effects of oxytocin on negative symptoms throughout the literature, and factors leading to inconsistent effects are unclear.

METHODS

We conducted a systematic review and meta-analysis of randomized clinical trials to compare the effectiveness of oxytocin with placebo for the treatment of negative symptoms and determine moderators of treatment effect. Random effects meta-analyses and dose-response meta-analysis were performed on mean changes in negative symptoms.

RESULTS

In an initial analysis of all 9 identified randomized clinical trials, intranasal oxytocin showed no significant effect on negative symptoms. For higher doses (>40-80 IU), a beneficial effect on negative symptoms was found with a moderate effect size, but this effect disappeared after exclusion of 1 outlier study. The dose-response meta-analysis predicted that higher doses of oxytocin may be more efficacious for negative symptoms. For positive symptoms, no beneficial effect of oxytocin was found in the main meta-analysis, but the dose-response meta-analysis suggested a potential advantage of higher doses.

CONCLUSIONS

The present results show no consistent beneficial effect of intranasal oxytocin for the treatment of negative and positive symptoms. The dose-response meta-analysis does not allow drawing any firm conclusions but suggests that high doses of intranasal oxytocin may be more efficacious. If future studies are conducted, an effort to reach adequate CNS concentrations for a sufficient duration is required.

Pramipexole to Improve Cognition in Bipolar Disorder: A Randomized Controlled Trial

BACKGROUND

Adults with bipolar disorder (BD) often experience neurocognitive impairment that negatively impacts functioning and quality of life. Previous trials have found that dopamine agonist agents improve cognition in healthy volunteers and that adults with BD who have stable mood and mild cognitive deficits may also benefit. We hypothesized that pramipexole, a dopamine agonist, would improve neurocognitive function in patients with BD.

METHODS

We recruited 60 adults (aged 18-65 years) with a diagnosis of BD I or II for an 8-week, double-blind, placebo-controlled trial (NCT02397837). All had stable mood and clinically significant neurocognitive impairment at baseline. Participants were randomized to receive pramipexole (n = 31) or a placebo (n = 29), dose was initiated at 0.125 mg 2 times a day and increased to a target of 4.5 mg/d.

RESULTS

At trial end, the primary outcome, MATRICS Consensus Cognitive Battery composite score, had not improved more in the pramipexole group (mean [SD] = 1.15 [5.4]) than in the placebo group (mean [SD] = 4.12 [5.2], Cohen's d = 0.56, P = 0.049), and mixed models, controlling for symptoms, showed no association between treatment group and MATRICS Consensus Cognitive Battery scores. No serious adverse events were reported.

CONCLUSIONS

These results suggest that pramipexole is not an efficacious cognitive enhancement agent in BD, even in a sample enriched for characteristics that were associated with a beneficial response in prior work. There are distinct cognitive subgroups among adults with BD and may be related differences in neurobiology that affect response to pramipexole. Additional research to better understand the onset and nature of the cognitive deficits in people with BD will be an important step toward a more personalized approach to treatment.

Review and meta-analysis of add-on tranylcypromine with antipsychotic drugs for the treatment of schizophrenia with predominant negative symptoms: a restoration of evidence

BACKGROUND

Treatment using add-on antidepressants with antipsychotic drugs in negative symptoms of schizophrenia has been reviewed recently in comprehensive meta-analyses. Tranylcypromine (TCP), an irreversible monoamine oxidase (MAO)-A/B inhibitor applied in treatment resistant depression, was not included because of strict requirements for quality of study design. To get a clear picture of available evidence for this resource in the treatment of schizophrenia, we conducted a review and meta-analysis of add-on TCP in the treatment of predominant negative symptoms of schizophrenia (negative schizophrenia).

METHODS

Seven controlled studies of add-on TCP in schizophrenia with predominant negative symptoms were found in a search of multiple databases. A subset of four studies of the prospective and parallel comparison of add-on TCP with antipsychotic drugs vs. antipsychotic drug monotherapy and meeting minimum quality criteria formed the primary meta-analysis. The effect size was calculated as the natural logarithm of the odds ratio (logOR) of responders and non-responders.

RESULTS

In the primary meta-analysis, a pooled logOR = 1.092 with 95%CI 0.410-1.774 (I² = 43.4%, moderate heterogeneity) was calculated according to a fixed-effect model. Heterogeneity was reduced for three double-blind studies of add-on TCP with trifluoperazine (TFP) vs. TFP-monotherapy and resulted a pooled logOR = 0.916 with 95%CI 0.216-1.616 (I² negative, no heterogeneity). A significant logOR = 1.558 with 95%CI 0.340-2.776 was found for TCP/TFP compared to placebo in one study. In a meta-analysis of extrapyramidal adverse effects, studies were very heterogeneous and revealed no significant differences between treatments. The risk of exacerbation of positive symptoms with add-on TCP was found to be very low for a duration of treatment of 12-16 weeks. No cases of hypertensive crisis were reported. The main methodical limitations were insufficient description of randomization or matching of patients without randomization. The main clinical limitation is a gap of data for add-on TCP with second-generation antipsychotics.

CONCLUSION

New studies are needed for add-on TCP with antipsychotic drugs in schizophrenia with predominant negative symptoms. Trials of this treatment may be possible in rare and selected cases. The therapeutic effect of add-on TCP may be explained by a strong dopaminergic activity.

Add on yoga treatment for negative symptoms of schizophrenia: A multi-centric, randomized controlled trial

The efficacy of antipsychotic medications in the treatment of negative symptoms of schizophrenia is modest at best. Preliminary studies suggest the beneficial effects of add on Yoga, a traditional Indian practice, in the treatment of schizophrenia. Hence, in this study, we examined the efficacy of yoga as an add-on treatment for negative symptoms of schizophrenia in a randomized, wait-list controlled design from two clinical institutes in south India. 89 patients (age - 34.20 ± 8.06 years; education - 14.22 ± 2.69 years; 28 females) were randomized into the add-on yoga or treatment as usual (TAU - wait-list control) group. Patients had a mean illness duration of 10.97 ± 7.24 years with an age at onset of 23.34 ± 5.81 years. Central block randomization was followed to ensure concealed allocation. Participants randomized to the yoga treatment group attended 12 supervised yoga training sessions over two weeks and practiced yoga sessions at home for the subsequent 10 weeks. 64 patients completed the trial. An intent to treat analysis was conducted with 89 participants using a linear mixed model. Improvement in negative symptoms was our primary outcome measure. The two groups were matched on demographic variables and baseline psychopathology severity. Participants in the add-on yoga group had significantly greater improvement in negative symptoms (SANS baseline: 49.13 ± 2.30; 12-weeks follow up: 31.55 ± 2.53) compared to the TAU group (SANS baseline: 51.22 ± 2.40; 12-weeks follow up: 45.30 ± 2.93; t = 3.36; p = 0.006; Cohen's d-0.65). The current study findings suggest the efficacy of yoga as an add-on treatment for negative symptoms of schizophrenia. The effectiveness of yoga practice as a regular clinical intervention for patients needs to be explored in future studies by integrating yoga services along with other clinical services.

EPA guidance on treatment of negative symptoms in schizophrenia

Negative symptoms of schizophrenia remain a major therapeutic challenge. The progress in the conceptualization and assessment is not yet fully reflected by treatment research. Nevertheless, there is a growing evidence base regarding the effects of biological and psychosocial interventions on negative symptoms. The importance of the distinction between primary and secondary negative symptoms for treatment selection might seem evident, but the currently available evidence remains limited. Good clinical practice is recommended for the treatment of secondary negative symptoms. Antipsychotic treatment should be optimized to avoid secondary negative symptoms due to side effects and due to positive symptoms. For most available interventions, further evidence is needed to formulate sound recommendations for primary, persistent, or predominant negative symptoms.

However, based on currently available evidence recommendations for the treatment of undifferentiated negative symptoms (including both primary and secondary negative symptoms) are provided. Although it has proven difficult to formulate an evidence-based recommendation for the choice of an antipsychotic, a switch to a second-generation antipsychotic should be considered for patients who are treated with a first-generation antipsychotic. Antidepressant add-on to antipsychotic treatment is an option. Social skills training is recommended as well as cognitive remediation for patients who also show cognitive impairment. Exercise interventions also have shown promise. Finally, access to treatment and to psychosocial rehabilitation should be ensured for patients with negative symptoms. Overall, there is definitive progress in the field, but further research is clearly needed to develop specific treatments for negative symptoms.

Prevalence of Major Cardiovascular Disease Events Among People Diagnosed With Schizophrenia Who Have Sleep Disturbance, Sedentary Behavior, or Muscular Weakness

Objective

To estimate prevalence of major cardiovascular events among people with schizophrenia who had experience of sleep disturbance, sedentary behavior or muscular weakness, and assess evidence for raised prevalence in these individuals compared to people with schizophrenia without these characteristics.

Methods

UK Biobank data on individuals diagnosed with schizophrenia (n = 1544) were used to examine the prevalence of major cardiovascular events, specifically myocardial infarction, stroke, heart failure and cardiovascular death, among participants with candidate risk factors. Generalized linear models were fitted to estimate prevalence ratios (PRs) for major cardiovascular events among participants with self-reported sleep disturbance, self-reported sedentary behavior, and muscular weakness measured using a handgrip dynamometer. These ratios were adjusted for QRISK3 score—a validated cardiovascular risk prediction algorithm for the UK population.

Results

Prevalence of major cardiovascular events was significantly higher among participants with daytime sleepiness, independent of QRISK3 score, and snoring, a proxy for sleep-disordered breathing (adjusted PR 1.26; 95% CI 1.03, 1.55, P = .03). Prevalence was also independently higher among participants with low muscular strength (adjusted PR1.36; 95% CI 1.05, 1.75, P = .02). The adjusted prevalence ratios among participants with short or prolonged sleep duration, insomnia, or sedentary behavior did not indicate independently raised prevalence among these groups.

Conclusion

Prevalence of major cardiovascular events among people with schizophrenia was higher in participants with muscular weakness and sleep disturbance evidenced by daytime sleepiness. Further research is required to determine how these factors can be routinely identified and addressed in the clinical management of cardiovascular risk among patients with schizophrenia.