Elevated fatty acid amide hydrolase in the prefrontal cortex of borderline personality disorder: a [11C]CURB positron emission tomography study

"Weeding out" violence? Translational perspectives on the neuropsychobiological links between cannabis and aggression

Recent shifts in societal attitudes towards cannabis have led to a dramatic increase in consumption rates in many Western countries, particularly among young people. This trend has shed light on a significant link between cannabis use disorder (CUD) and pathological reactive aggression, a condition involving disproportionate aggressive and violent reactions to minor provocations. The discourse on the connection between cannabis use and aggression is frequently enmeshed in political and legal discussions, leading to a polarized understanding of the causative relationship between cannabis use and aggression. However, integrative analyses from both human and animal research indicate a complex, bidirectional interplay between cannabis misuse and pathological aggression. On the one hand, emerging research reveals a shared genetic and environmental predisposition for both cannabis use and aggression, suggesting a common underlying biological mechanism. On the other hand, there is evidence that cannabis consumption can lead to violent behaviors while also being used as a self-medication strategy to mitigate the negative emotions associated with pathological reactive aggression. This suggests that the coexistence of pathological aggression and CUD may result from overlapping vulnerabilities, potentially creating a self-perpetuating cycle where each condition exacerbates the other, escalating into externalizing and violent behaviors. This article aims to synthesize existing research on the intricate connections between these issues and propose a theoretical model to explain the neurobiological mechanisms underpinning this complex relationship.

Plasma Endocannabinoid Levels in Patients with Borderline Personality Disorder and Healthy Controls

Borderline personality disorder (BPD) is a highly prevalent psychiatric disorder and presents a complex therapeutic challenge due to limited treatment modalities. Recent focus has converged on the endocannabinoid system (ECS) as a prospective modulator of psychopathological processes in BPD. To address this hypothesis, we analysed plasma endocannabinoid concentrations, specifically anandamide (AEA) and 2-arachidonoylglycerol (2-AG), in a cohort of 49 female BPD patients and 32 matched healthy controls (HC). Additionally, we examined the effect of the FAAH polymorphism rs324420 and correlates with psychopathology. The results indicate heightened AEA levels and, by trend, augmented 2-AG levels within the patient group, as compared to the HC group. Significant between group differences in AEA levels were evident in the CC genotype (FAAH_rs324420) but not in A-allele carriers while the commonly observed difference in AEA levels between A-allele carriers as compared to the CC genotype was not evident in patients. An effect of genotype was found with higher ratings of depression (Beck's depression inventory, BDI-II) in the CC genotype compared to A-allele carriers (FAAH_rs32442), particularly in the patients. Significant alterations in AEA (and by trend in 2-AG) in patients with BPD may relate to compensatory ECS activity. The finding that the effect is most pronounced in CC homozygotes, might point towards a countermeasure to balance physiologically lower baseline AEA levels. The findings warrant further research to develop potentially beneficial psychopharmacological therapies.

FAAH rs324420 Polymorphism: Biological Pathways, Impact on Elite Athletic Performance and Insights for Sport Medicine

Gene variation linked to physiological functions is recognised to affect elite athletic performance by modulating training and competition-enabling behaviour. The fatty acid amide hydrolase (FAAH) has been investigated as a good candidate for drug targeting, and recently, its single-nucleotide polymorphism (SNP) rs324420 was reported to be associated with athletic performance. Given the implications, the biological pathways of this genetic polymorphism linked to elite athletic performance, considering sport type, psychological traits and sports injuries, need to be dissected. Thus, a narrative review of the literature concerning the biological mechanisms of this SNP was undertaken. In addition to its role in athletic performance, FAAH rs324420 is also involved in important mechanisms underlying human psychopathologies, including substance abuse and neural dysfunctions. However, cumulative evidence concerning the C385A variant is inconsistent. Therefore, validation studies considering homogeneous sports modalities are required to better define the role of this SNP in elite athletic performance and its impact on stress coping, pain regulation and inflammation control.

Beyond monoamines: II. Novel applications for PET imaging in psychiatric disorders

Early applications of positron emission tomography (PET) in psychiatry sought to identify derangements of cerebral blood flow and metabolism. The need for more specific neurochemical imaging probes was soon evident, and these probes initially targeted the sites of action of neuroleptic (dopamine D₂ receptors) and psychoactive (serotonin receptors) drugs. For nearly 30 years, the centrality of monoamine dysfunction in psychiatric disorders drove the development of an armamentarium of monoaminergic PET radiopharmaceuticals and imaging methodologies. However, continued investments in monoamine-enhancing drug development realized only modest gains in efficacy and tolerability. As patent protection for many widely prescribed and profitable psychiatric drugs lapsed, drug development pipelines shifted away from monoamines in search of novel targets with the promises of improved efficacy, or abandoned altogether. Over this period, PET radiopharmaceutical development activities closely parallelled drug development priorities, resulting in the development of new PET imaging agents for non-monoamine targets. In part two of this review, we survey clinical research studies using the novel targets and radiotracers described in part one across major psychiatric application areas such as substance use disorders, anxiety disorders, eating disorders, personality disorders, mood disorders, and schizophrenia. Important limitations of the studies described are discussed, as well as key methodologic issues, challenges to the field, and the status of clinical trials seeking to exploit these targets for novel therapeutics.

Fatty Acid Amide Hydrolase: An Integrative Clinical Perspective

Introduction: Fatty acid amide hydrolase (FAAH) is one of the main terminating enzymes of the endocannabinoid system (ECS). Since being discovered in 1996, the modulation of FAAH has been viewed as a compelling alternative strategy to obtain the beneficial effect of the ECS. With a considerable amount of FAAH-related publication over time, the next step would be to comprehend the proximity of this evidence for clinical application. Objective: This review intends to highlight the rationale of FAAH modulation and provide the latest evidence from clinical studies. Methods: Publication searches were conducted to gather information focused on FAAH-related clinical evidence with an extension to the experimental research to understand the biological plausibility. The subtopics were selected to be multidisciplinary to offer more perspective on the current state of the arts. Discussion: Experimental and clinical studies have demonstrated that FAAH was highly expressed not only in the central nervous system but also in the peripheral tissues. As the key regulator of endocannabinoid signaling, it would appear that FAAH plays a role in the modulation of mood and emotional response, reward system, pain perception, energy metabolism and appetite regulation, inflammation, and other biological processes. Genetic variants may be associated with some conditions such as substance/alcohol use disorders, obesity, and eating disorder. The advancement of functional neuroimaging has enabled the evaluation of the neurochemistry of FAAH in brain tissues and this can be incorporated into clinical trials. Intriguingly, the application of FAAH inhibitors in clinical trials seems to provide less striking results in comparison with the animal models, although some potential still can be seen. Conclusion: Modulation of FAAH has an immense potential to be a new therapeutic candidate for several disorders. Further exploration, however, is still needed to ensure who is the best candidate for the treatment strategy.

Fatty acid amide hydrolase C385A polymorphism affects susceptibility to various diseases

The endocannabinoid (eCB) system is an important neuromodulatory system with its extensive network of receptors throughout the human body that has complex actions in the nervous system, immune system, and all of the body's other organs. Fatty acid amide hydrolase (FAAH) is an important membrane-bound homodimeric degrading enzyme that controls the biological activity of N-arachidonoylethanolamide (AEA) in the eCB system and other relevant bioactive lipids. It has been shown that several single nucleotide polymorphisms (SNPs) of FAAH are associated with various phenotypes and diseases including cardiovascular, endocrine, drug abuse, and neuropsychiatric disorders. A common functional and most studied polymorphism of this gene is C385A (rs324420), which results in the replacement of a conserved proline to threonine in the FAAH enzyme structure, leads to a reduction of the activity and expression of FAAH, compromises the inactivation of AEA and causes higher synaptic concentrations of AEA that can be associated with several various phenotypes. The focus of this review is on evidence-based studies on the associations of the FAAH C385A polymorphism and the various diseases or traits. Although there was variability in the results of these reports, the overall consensus is that the FAAH C385A genotype can affect susceptibility to some multifactorial disorders and can be considered a potential therapeutic target.

Cannabis-Based Medicinal Products in the Management of Emotionally Unstable Personality Disorder (EUPD): A Narrative Review and Case Series

Emotionally unstable personality disorder (EUPD) is a common mental health disorder, manifesting with a range of chronic and debilitating symptoms, including impaired social functioning, unstable mood, and risky impulsive or self-injurious behaviour. Whilst the exact aetiology has not been fully elucidated, implicated factors seem to include genetic factors, environmental causes such as trauma, and neurotransmitter deficits. The literature suggests that impaired functioning of the endocannabinoid system in key brain regions responsible for emotional processing and stress response may underlie the manifestation of EUPD symptoms. The National Institute for Health and Care Excellence (NICE) 2009 guidelines state that “no drugs have established efficacy in treating or managing EUPD”, and yet, patients are commonly prescribed medication which includes antipsychotics, antidepressants, and mood stabilisers. Here we present a case series of seven participants diagnosed with EUPD and treated with cannabis-based medicinal products (CBMPs). Participants were given an initial assessment and followed up one month after CBMPs prescription. Improvement in symptoms was assessed by the completion of ratified rating scales by the participant and psychiatrist. Our results indicate that CBMPs were effective and well tolerated, as six participants reported a noticeable improvement in their symptoms and functioning. Although promising, further research is needed to ascertain the long-term tolerability, efficacy, and dosing strategy for CBMPs in EUPD.

Dysregulation of prefrontal parvalbumin interneurons leads to adult aggression induced by social isolation stress during adolescence

Social isolation during the juvenile stage results in structural and functional impairment of the brain and deviant adult aggression. However, the specific subregions and cell types that underpin this deviant behavior are still largely unknown. Here, we found that adolescent social isolation led to a shortened latency to attack onset and extended the average attack time, accompanied by anxiety-like behavior and deficits in social preference in adult mice. However, when exposed to social isolation during adulthood, the mice did not show these phenotypes. We also found that the structural plasticity of prefrontal pyramidal neurons, including the dendritic complexity and spine ratio, was impaired in mice exposed to adolescent social isolation. The parvalbumin (PV) interneurons in the prefrontal infralimbic cortex (IL) are highly vulnerable to juvenile social isolation and exhibit decreased cell numbers and reduced activation in adulthood. Moreover, chemogenetic inactivation of IL-PV interneurons can mimic juvenile social isolation-induced deviant aggression and social preference. Conversely, artificial activation of IL-PV interneurons significantly attenuated deviant aggression and rescued social preference during adulthood in mice exposed to adolescent social isolation. These findings implicate juvenile social isolation-induced damage to IL-PV interneurons in long-term aggressive behavior in adulthood.

Borderline Personality Disorder: Updates in a Postpandemic World

Progress in understanding borderline personality disorder has unfolded in the last decade, landing in a new COVID-19-influenced world. Borderline personality disorder is now firmly established as a valid diagnosis, distinct from its co-occurring mood, anxiety, trauma-related, and behavioral disorders. Further, it is also understood as a reflection of general personality dysfunction, capturing essential features shared among all personality disorders. Neuroimaging research, representing the vast neurobiological advances made in the last decade, illustrates that the disorder shares frontolimbic dysfunction with many psychiatric diagnoses but has a distinct signature of interpersonal and emotional hypersensitivity. This signature is the conceptual basis of the psychotherapies and clinical management approaches proven effective for the disorder. Medications remain adjunctive and are contraindicated by some guidelines internationally. Less invasive brain-based therapeutics show promise. The most significant change in the treatment landscape is a focus on briefer, less intensive formats of generalist management. Shorter variants of therapies, such as dialectical behavior therapy and mentalization-based treatment, are in the process of being shown to be adequately effective. Earlier intervention and greater emphasis on functional improvement are needed to more effectively curb the disabilities and risks of borderline personality disorder for patients and their families. Remote interventions show promise in broadening access to care.

Combinatorial approaches for treating neuropsychiatric social impairment

Social behaviour is an essential component of human life and deficits in social function are seen across multiple psychiatric conditions with high morbidity. However, there are currently no FDA-approved treatments for social dysfunction. Since social cognition and behaviour rely on multiple signalling processes acting in concert across various neural networks, treatments aimed at social function may inherently require a combinatorial approach. Here, we describe the social neurobiology of the oxytocin and endocannabinoid signalling systems as well as translational evidence for their use in treating symptoms in the social domain. We leverage this systems neurobiology to propose a network-based framework that involves pharmacology, psychotherapy, non-invasive brain stimulation and social skills training to combinatorially target trans-diagnostic social impairment. Lastly, we discuss the combined use of oxytocin and endocannabinoids within our proposed framework as an illustrative strategy to treat specific aspects of social function. Using this framework provides a roadmap for actionable treatment strategies for neuropsychiatric social impairment. This article is part of the theme issue 'Interplays between oxytocin and other neuromodulators in shaping complex social behaviours'.

Aggression in borderline personality disorder: A systematic review of neuroimaging studies

Aggressive behaviors are prevalent among patients with Borderline Personality Disorder (BPD). Neuroimaging studies have linked aggression in BPD patients to neurochemical, structural, functional, and metabolic alterations in various brain regions, especially in frontal-limbic areas. This systematic review summarizes current neuroimaging results on aggression among BPD patients and provides an overview of relevant brain mechanisms. A systematic search of PubMed and Web of Science databases, in addition to manual check of references, identified thirty-two eligible articles, including two magnetic resonance spectrum (MRS), thirteen structural magnetic resonance imaging (sMRI), six functional magnetic resonance imaging (fMRI), and eleven positron emission tomography (PET) studies. The reviewed studies have highlighted the abnormalities in prefrontal cortices and limbic structures including amygdala and hippocampus. Less studies have zoomed in the roles of parietal and temporal regions or taken a network perspective. Connectivity studies have shed light on the importance of the frontal-limbic interactions in regulating aggression. Conflicted findings might be attributed to disparity in controlling gender, anatomical subdivisions, and comorbidities, which shall be considered in future studies.

Higher trait neuroticism is associated with greater fatty acid amide hydrolase binding in borderline and antisocial personality disorders

Borderline personality disorder (BPD) and antisocial personality disorder (ASPD) are the two most frequently diagnosed and researched DSM-5 personality disorders, and both are characterized by high levels of trait neuroticism. Fatty acid amide hydrolase (FAAH), an enzyme of the endocannabinoid system (ECS), has been linked to regulation of mood through modulation of anandamide, an endocannabinoid. We hypothesized that prefrontal cortex (PFC) FAAH binding would relate to trait neuroticism in personality disorders. Thirty-one individuals with personality disorders (20 with BPD and 11 with ASPD) completed the investigation. All participants completed the revised NEO Personality Inventory, which yields standardized scores (e.g., T scores) for the traits of neuroticism, openness, conscientiousness, agreeableness, and extraversion. All participants were medication free and were not utilizing illicit substances as determined by drug urinalysis. Additionally, none of the participants had a comorbid major depressive episode, bipolar disorder, psychotic disorder, or substance use disorder. Each participant underwent one [¹¹C]CURB PET scan. Consistent with our hypothesis, neuroticism was positively correlated with PFC FAAH binding (r = 0.42, p = 0.021), controlling for genotype. Neuroticism was also positively correlated with dorsal putamen FAAH binding (r = 0.53, p = 0.0024), controlling for genotype. Elevated brain FAAH is an endophenotype for high neuroticism in BPD and ASPD. Novel pharmacological therapeutics that inhibit FAAH could emerge as potential new treatments for BPD and ASPD with high neuroticism.

Endocannabinoid markers in autism spectrum disorder: A scoping review of human studies

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by social communication deficits and patterns of restrictive and repetitive behavior. Although the neurological underpinnings of ASD remain elusive, the endocannabinoid system (ECS) may play a role in modulating social behavior in ASD. Preclinical studies have suggested that alterations in the ECS result in ASD-like phenotypes, but currently no reviews have examined ECS abnormalities in human studies. This scoping review investigated any evidence of ECS alterations in humans with ASD. A comprehensive literature search was conducted and five studies were eligible for review. Three studies reported a significant reduction of anandamide in ASD compared to controls. Other alterations included decreased 2-arachidonoylglycerol, oleoylethanolamide, and palmitoylethanolamide and elevated diacylglycerol lipase and monoacylglycerol lipase. Some discrepant findings were also noted, which included elevated or reduced CB2 receptor in three studies and elevated or reduced N-acyl phosphatidylethanolamine phospholipase D and fatty acid amide hydrolase in two studies. We conclude from this preliminary investigation that the ECS may be altered in humans with ASD. Potential limitations of the reviewed studies include medication use and psychiatric comorbidities. Further research, such as positron emission tomography studies, are necessary to fully understand the relationship between ECS markers and ASD.

Translation of animal endocannabinoid models of PTSD mechanisms to humans: Where to next?

The endocannabinoid system is known to be involved in mechanisms relevant to PTSD aetiology and maintenance, though this understanding is mostly based on animal models of the disorder. Here we review how human paradigms can successfully translate animal findings to human subjects, with the view that substantially increased insight into the effect of endocannabinoid signalling on stress responding, emotional and intrusive memories, and fear extinction can be gained using modern paradigms and methods for assessing the state of the endocannabinoid system in PTSD.

Borderline personality disorder and its symptom clusters: A review of positron emission tomography and single photon emission computed tomography studies

Positron emission tomography (PET) and single photon emission computed tomography (SPECT) are two neuroimaging techniques that have led to important insights into the pathophysiology of borderline personality disorder (BPD) and its symptom clusters. This paper provides the most up-to-date review of PET and SPECT studies targeting BPD. A systematic search of PET and SPECT studies using the databases PsycINFO, PubMed, and Embase was implemented, which yielded 30 articles in the end. Earlier PET studies largely reported decreased glucose metabolism in prefrontal brain regions. More recent PET research has pointed to alterations in monoaminergic systems, greater activation of the opioid system during sadness induction, as well as abnormalities of the brain endocannabinoid system in BPD. SPECT studies of BPD mainly identified changes in regional cerebral blood flow and alterations of the serotonergic system. Such PET and SPECT study abnormalities have been suggested to relate to the symptomatology of BPD, including impulsivity, aggression, and mood changes. The implications of these neuroimaging studies in terms of shedding new light on the pathophysiology of BPD and providing new avenues for drug development are discussed.

Cannabidiol Exposure During the Mouse Adolescent Period Is Without Harmful Behavioral Effects on Locomotor Activity, Anxiety, and Spatial Memory

Cannabidiol (CBD) is a non-intoxicating phytocannabinoid whose purported therapeutic benefits and impression of a high safety profile has promoted its increasing popularity. CBD’s popularity is also increasing among children and adolescents who are being administered CBD, off label, for the treatment of numerous symptoms associated with autism spectrum disorder, attention deficit hyperactivity disorder, anxiety, and depression. The relative recency of its use in the adolescent population has precluded investigation of its impact on the developing brain and the potential consequences that may present in adulthood. Therefore, there’s an urgency to identify whether prolonged adolescent CBD exposure has substantive impacts on the developing brain that impact behavioral and cognitive processes in adulthood. Here, we tested the effect of twice-daily intraperitoneal administrations of CBD (20 mg/kg) in male and female C57BL/6J mice during the adolescent period of 25–45 days on weight gain, and assays for locomotor behavior, anxiety, and spatial memory. Prolonged adolescent CBD exposure had no detrimental effects on locomotor activity in the open field, anxiety behavior on the elevated plus maze, or spatial memory in the Barnes Maze compared to vehicle-treated mice. Interestingly, CBD-treated mice had a faster rate of learning in the Barnes Maze. However, CBD-treated females had reduced weight gain during the exposure period. We conclude that prolonged adolescent CBD exposure in mice does not have substantive negative impacts on a range of behaviors in adulthood, may improve the rate of learning under certain conditions, and impacts weight gain in a sex-specific manner.

Lower amygdala fatty acid amide hydrolase in violent offenders with antisocial personality disorder: an [11C]CURB positron emission tomography study

Antisocial personality disorder (ASPD) imposes a high societal burden given the repetitive reactive aggression that affected individuals perpetrate. Since the brain endocannabinoid system (ECS) has been implicated in ASPD and aggressive behavior, we utilized [¹¹C]CURB positron emission tomography to investigate fatty acid amide hydrolase (FAAH), an enzyme of the ECS that degrades anandamide, in 16 individuals with ASPD and 16 control participants. We hypothesized that FAAH density would be lower in the amygdala for several reasons. First, decreased FAAH expression is associated with increased cannabinoid receptor 1 stimulation, which may be responsible for amygdala hyper-reactivity in reactive aggression. Second, the amygdala is the seat of the neural circuit mediating reactive aggression. Third, other PET studies of externalizing populations show reduced brain FAAH density. Conversely, we hypothesized that FAAH expression would be greater in the orbitofrontal cortex. Consistent with our hypothesis, we found that amygdala FAAH density was lower in the amygdala of ASPD (p = 0.013). Cerebellar and striatal FAAH expression were inversely related with impulsivity (cerebellum: r = -0.60, p = 0.017; dorsal caudate: r = -0.58, p = 0.023; dorsal putamen: r = -0.55, p = 0.034), while cerebellar FAAH density was also negatively associated with assaultive aggression (r = -0.54, p = 0.035). ASPD presents high levels of disruptive behavior with few, if any, efficacious treatment options. Novel therapeutics that increase FAAH brain levels in a region-specific manner could hold promise for attenuating certain symptom clusters of ASPD, although our results require replication.

Positron Emission Tomography Imaging of the Endocannabinoid System: Opportunities and Challenges in Radiotracer Development

The endocannabinoid system (ECS) is involved in a wide range of biological functions and comprises cannabinoid receptors and enzymes responsible for endocannabinoid synthesis and degradation. Over the past 2 decades, significant advances toward developing drugs and positron emission tomography (PET) tracers targeting different components of the ECS have been made. Herein, we summarized the recent development of PET tracers for imaging cannabinoid receptors 1 (CB1R) and 2 (CB2R) as well as the key enzymes monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase (FAAH), particularly focusing on PET neuroimaging applications. State-of-the-art PET tracers for the ECS will be reviewed including their chemical design, pharmacological properties, radiolabeling, as well as preclinical and human PET imaging. In addition, this review addresses the current challenges for ECS PET biomarker development and highlights the important role of PET ligands to study disease pathophysiology as well as to facilitate drug discovery.