Pathways to new drug discovery in neuropsychiatry

Metformin is Protective Against the Development of Mood Disorders

INTRODUCTION

Mood disorders are a major cause of disability, and current treatment options are inadequate for reducing the burden on a global scale. The aim of this project was to identify drugs suitable for repurposing to treat mood disorders.

METHODS

This mixed-method study utilized gene expression signature technology and pharmacoepidemiology to investigate drugs that may be suitable for repurposing to treat mood disorders.

RESULTS

The transcriptional effects of a combination of drugs commonly used to treat mood disorders included regulation of the steroid and terpenoid backbone biosynthesis pathways, suggesting a mechanism involving cholesterol biosynthesis, and effects on the thyroid hormone signaling pathway. Connectivity Map analysis highlighted metformin, an FDA-approved treatment for type 2 diabetes, as a drug having global transcriptional effects similar to the mood disorder drug combination investigated. In a retrospective cohort study, we found evidence that metformin is protective against the onset of mood disorders.

DISCUSSION

These results provide proof-of-principle of combining gene expression signature technology with pharmacoepidemiology to identify potential novel drugs for treating mood disorders. Importantly, metformin may have utility in the treatment of mood disorders, warranting future randomized controlled trials to test its efficacy.

Associations of Cardiovascular Agents and Metformin with Depression Symptoms: A Cross-Sectional Analysis from the HUNT Study, Norway

BACKGROUND

Cardiovascular agents, including angiotensin-converting enzyme inhibitors, angiotensin II receptor inhibitors, acetylsalicylic acid, statins, and metformin, have demonstrated benefits for depression. However, there is scant evaluation of these drugs' antidepressant properties in large population settings.

OBJECTIVE

This study aimed to examine cross-sectional associations between depression symptoms and the use of cardiovascular agents and metformin in populations with cardiovascular diseases or diabetes mellitus.

METHODS

Participants in the Trøndelag Health Study 2006-08 (HUNT3, n = 40,516) and 2017-19 (HUNT4, n = 42,103) were included and data on their drug use from 2006 to 2019 was retrieved from the Norwegian Prescription Database. The outcome was self-reported depression symptoms defined by the Hospital Anxiety and Depression Scale. Associations between cardiovascular agents or metformin use and self-reported depression were analyzed by multi-level logistic regression in sex-stratified samples.

RESULTS

Among men with cardiovascular diseases, use of acetylsalicylic acid was associated with reduced depression symptoms compared with acetylsalicylic acid non-users (reference) in HUNT3 and HUNT4 [risk ratio = 0.76; 95% confidence interval 0.59-0.94, risk ratio = 0.67; 95% CI 0.52-0.82, respectively]. Similarly, male statin users had a lower likelihood of reporting depression than statin non-users in HUNT3 (risk ratio = 0.70; 95% confidence interval 0.54-0.86) and HUNT4 (risk ratio = 0.67; 95% confidence interval 0.51-0.84). Associations between statins or acetylsalicylic acid use and reduced depression symptoms were detected in women with cardiovascular diseases in HUNT4. We found no statistical support for associations between other cardiovascular agents or metformin use and a reduced or increased depression symptom risk.

CONCLUSIONS

Results suggest negative associations between acetylsalicylic acid or statin use and depression symptoms. However, longitudinal cohort studies and randomized controlled trials are required to confirm the antidepressant effects of these drugs.

Targeting NMDA receptors in neuropsychiatric disorders by drug screening on human neurons derived from pluripotent stem cells

NMDA receptors (NMDARs), a prominent subtype of glutamatergic receptors, are implicated in the pathogenesis and development of neuropsychiatric disorders such as epilepsy, intellectual disability, autism spectrum disorder, and schizophrenia, and are therefore a potential therapeutic target in treating these disorders. Neurons derived from induced pluripotent stem cells (iPSCs) have provided the opportunity to investigate human NMDARs in their native environment. In this review, we describe the expression, function, and regulation of NMDARs in human iPSC-derived neurons and discuss approaches for utilizing human neurons for identifying potential drugs that target NMDARs in the treatment of neuropsychiatric disorders. A challenge in studying NMDARs in human iPSC-derived neurons is a predominance of those receptors containing the GluN2B subunit and low synaptic expression, suggesting a relatively immature phenotype of these neurons and delayed development of functional NMDARs. We outline potential approaches for improving neuronal maturation of human iPSC-derived neurons and accelerating the functional expression of NMDARs. Acceleration of functional expression of NMDARs in human iPSC-derived neurons will improve the modeling of neuropsychiatric disorders and facilitate the discovery and development of novel therapeutics targeting NMDARs for the treatment of these disorders.

The Contribution of Environmental Enrichment to Phenotypic Variation in Mice and Rats

The reproducibility and translation of neuroscience research is assumed to be undermined by introducing environmental complexity and heterogeneity. Rearing laboratory animals with minimal (if any) environmental stimulation is thought to control for biological variability but may not adequately test the robustness of our animal models. Standard laboratory housing is associated with reduced demonstrations of species typical behaviors and changes in neurophysiology that may impact the translation of research results. Modest increases in environmental enrichment (EE) mitigate against insults used to induce animal models of disease, directly calling into question the translatability of our work. This may in part underlie the disconnect between preclinical and clinical research findings. Enhancing environmental stimulation for our model organisms promotes ethological natural behaviors but may simultaneously increase phenotypic trait variability. To test this assumption, we conducted a systematic review and evaluated coefficients of variation (CVs) between EE and standard housed mice and rats. Given findings of suboptimal reporting of animal laboratory housing conditions, we also developed a methodological reporting table for enrichment use in neuroscience research. Our data show that animals housed in EE were not more variable than those in standard housing. Therefore, environmental heterogeneity introduced into the laboratory, in the form of enrichment, does not compromise data integrity. Overall, human life is complicated, and by embracing such nuanced complexity into our laboratories, we may paradoxically improve on the rigor and reproducibility of our research.

Towards High-Throughput Chemobehavioural Phenomics in Neuropsychiatric Drug Discovery

Identifying novel marine-derived neuroactive chemicals with therapeutic potential is difficult due to inherent complexities of the central nervous system (CNS), our limited understanding of the molecular foundations of neuro-psychiatric conditions, as well as the limited applications of effective high-throughput screening models that recapitulate functionalities of the intact CNS. Furthermore, nearly all neuro-modulating chemicals exhibit poorly characterized pleiotropic activities often referred to as polypharmacology. The latter renders conventional target-based in vitro screening approaches very difficult to accomplish. In this context, chemobehavioural phenotyping using innovative small organism models such as planarians and zebrafish represent powerful and highly integrative approaches to study the impact of new chemicals on central and peripheral nervous systems. In contrast to in vitro bioassays aimed predominantly at identification of chemicals acting on single targets, phenotypic chemobehavioural analysis allows for complex multi-target interactions to occur in combination with studies of polypharmacological effects of chemicals in a context of functional and intact milieu of the whole organism. In this review, we will outline recent advances in high-throughput chemobehavioural phenotyping and provide a future outlook on how those innovative methods can be utilized for rapidly screening and characterizing marine-derived compounds with prospective applications in neuropharmacology and psychosomatic medicine.

Resilience priming: Translational models for understanding resiliency and adaptation to early life adversity

Despite the increasing attention to early life adversity and its long-term consequences on health, behavior, and the etiology of neurodevelopmental disorders, our understanding of the adaptations and interventions that promote resiliency and rescue against such insults are underexplored. Specifically, investigations of the perinatal period often focus on negative events/outcomes. In contrast, positive experiences (i.e. enrichment/parental care//healthy nutrition) favorably influence development of the nervous and endocrine systems. Moreover, some stressors result in adaptations and demonstrations of later-life resiliency. This review explores the underlying mechanisms of neuroplasticity that follow some of these early life experiences and translates them into ideas for interventions in pediatric settings. The emerging role of the gut microbiome in mediating stress susceptibility is also discussed. Since many negative outcomes of early experiences are known, it is time to identify mechanisms and mediators that promote resiliency against them. These range from enrichment, quality parental care, dietary interventions and those that target the gut microbiota.

Alcohol use in bipolar disorder: A neurobiological model to help predict susceptibility, select treatments and attenuate cortical insult

In a series of neurophysiological and neuroimaging studies we investigated the neurobiology related to alcohol use in young people with bipolar disorder. Impairments were identified across frontal and temporal representations of event-related potential and proton magnetic resonance spectroscopy markers; mismatch negativity and in vivo glutathione, respectively. We propose these findings reflect impairments in the N-methyl-D-aspartate receptor and antioxidant capacity. This review seeks to place these findings within the broader literature in the context of two propositions: 1. Pathophysiological impairments in N-methyl-D-aspartate receptor functioning in bipolar disorder contribute to susceptibility toward developing alcohol problems. 2. Alcohol aggravates bipolar disorder neuroprogression via oxidative stress. A neurobiological model that incorporates these propositions is presented, with a focus on the potential for N-methyl-D-aspartate receptor antagonism and glutathione augmentation as potential adjunctive pharmacotherapies to treat the comorbidity. While this review highlights the importance of alcohol monitoring and reduction strategies in the treatment of bipolar disorder, the clinical impact of the proposed model remains limited by the lack of controlled trials of novel pharmacological interventions.

Evolution of optogenetic microdevices

Implementation of optogenetic techniques is a recent addition to the neuroscientists' preclinical research arsenal, helping to expose the intricate connectivity of the brain and allowing for on-demand direct modulation of specific neural pathways. Developing an optogenetic system requires thorough investigation of the optogenetic technique and of previously fabricated devices, which this review accommodates. Many experiments utilize bench-top systems that are bulky, expensive, and necessitate tethering to the animal. However, these bench-top systems can make use of power-demanding technologies, such as concurrent electrical recording. Newer portable microdevices and implantable systems carried by freely moving animals are being fabricated that take advantage of wireless energy harvesting to power a system and allow for natural movements that are vital for behavioral testing and analysis. An investigation of the evolution of tethered, portable, and implantable optogenetic microdevices is presented, and an analysis of benefits and detriments of each system, including optical power output, device dimensions, electrode width, and weight is given. Opsins, light sources, and optical fiber coupling are also discussed to optimize device parameters and maximize efficiency from the light source to the fiber, respectively. These attributes are important considerations when designing and developing improved optogenetic microdevices.

The diminished pipeline for medications to treat mental health and substance use disorders

OBJECTIVE

Psychotropic drug development is perceived to be lagging behind other pharmaceutical development, even though there is a need for more effective psychotropic medications. This study examined the state of the current psychotropic drug pipeline and potential barriers to psychotropic drug development.

METHODS

The authors scanned the recent academic and "grey" literature to evaluate psychotropic drug development and to identify experts in the fields of psychiatry and substance use disorder treatment and psychotropic drug development. On the basis of that preliminary research, the authors interviewed six experts and analyzed drugs being studied for treatment of major psychiatric disorders in phase III clinical trials.

RESULTS

Interviews and review of clinical trials of drugs in phase III of development confirmed that the psychotropic pipeline is slim and that a majority of the drugs in phase III trials are not very innovative. Among the barriers to development are incentives that encourage firms to focus on incremental innovation rather than take risks on radically new approaches. Other barriers include human brain complexity, failure of animal trials to translate well to human trials, and a drug approval threshold that is perceived as so high that it discourages development.

CONCLUSIONS

Drivers of innovation in psychotropic drug development largely parallel those for other drugs, yet crucial distinctions have led to slowing psychotropic development after a period of innovation and growth. Various factors have acted to dry up the pipeline for psychotropic drugs, with expert opinion suggesting that in the near term, this trend is likely to continue.

Evaluating differential developmental trajectories to adolescent-onset mood and psychotic disorders

BACKGROUND

It is an open question as to whether differential developmental trajectories, potentially representing underlying pathophysiological processes, can form the basis of a more useful typology in young persons who present for mental health care.

METHODS

A cohort of 605 young people was recruited from youth mental health services that target the early phases of anxiety, mood or psychotic disorders. Participants were assigned to one of three clinical sub-types (anxious-depression; mania-fatigue; developmental-psychotic) according to putative developmental trajectories.

RESULTS

The distribution of subtypes was: 51% anxiety-depression, 25% mania-fatigue and 24% developmental-psychotic, with key differences in demographic, clinical, family history and neuropsychological characteristics. When analyses were limited to 286 cases with 'attenuated' or sub-threshold syndromes, the pattern of differences was similar. Multinomial logistic regression demonstrated that compared to the developmental-psychotic subtype, both the mania-fatigue and anxiety-depression subtypes were younger and more depressed at presentation, but less functionally impaired. Other discriminating variables between the developmental-psychotic and mania-fatigue sub-types were that the latter were significantly more likely to have a family history of bipolar disorder but have less likelihood of impaired verbal learning; whilst the anxious-depression group were more anxious, more likely to have a family history of depression, and had a higher premorbid IQ level.

CONCLUSIONS

This cross-sectional evaluation provides preliminary support for differing developmental trajectories in young persons presenting for mental health care. Prospective follow-up is needed to examine the predictive validity of this approach and its relationships to underlying pathophysiological mechanisms.