Assessment of glutamate in striatal subregions in obsessive-compulsive disorder with proton magnetic resonance spectroscopy

New horizons for obsessive-compulsive disorder drug discovery: is targeting glutamate receptors the answer?

INTRODUCTION

Over the past decade, glutamate has emerged as a prominent focus in the field of obsessive-compulsive disorder (OCD) pathophysiology. A convergence of evidence from genetic, preclinical, and clinical studies points to glutamatergic dysfunction as a key feature of this condition. In light of these findings, there has been a growing interest in exploring the potential of glutamatergic agents in the treatment of OCD.

AREAS COVERED

This paper reviews the literature on glutamate transmission in OCD. In addition, the authors examine the results of clinical trials investigating the efficacy of glutamatergic agents in the treatment of OCD patients.

EXPERT OPINION

Along with the recognition of neuroinflammation in the brain in OCD, the evidence of glutamate dysfunction represents one of the most promising recent discoveries for understanding the mechanisms involved in OCD. The importance of this discovery lies primarily in its pharmacological implications and has led to intense research activity in the field of glutamatergic agents. While this research has not yet had a substantial clinical impact, targeting glutamate receptors remains a promising horizon for the successful treatment of OCD patients.

Proton magnetic resonance spectroscopy-based evaluation of metabolic abnormalities in the right dorsolateral prefrontal cortex and caudate nucleus in treatment-naïve patients with obsessive-compulsive disorder

Background

Obsessive-compulsive disorder (OCD) is a common psychiatric disorder whose underlying pathophysiology is insufficiently understood. The pathophysiology of OCD may be related to abnormalities in the biochemistry of neurotransmitters.

Aim

The aim of the present study was to measure the absolute concentration of various metabolites in the right dorsolateral prefrontal cortex (DLPFC) and caudate nucleus (CN) in treatment-naive patients with OCD and compare it with healthy controls (HCs).

Methods

The present study investigated the metabolic profile of two brain regions, namely right DLPFC and CN, by using single voxel in-vivo proton magnetic resonance spectroscopy (1H MRS) in drug-naive patients with OCD (n = 17, mean age = 30.71 ± 10.104 years) and compared it with healthy controls (n = 13, mean age = 30.77 ± 5.449 years). The patients with OCD were recruited after appropriate psychometric assessments. The 1H-MRS experiments were performed using the 3 Tesla (3T) human MR scanner, and absolute concentrations of metabolites were estimated using the LC model.

Results

Significantly lower concentration of tNAA in the right DLPFC was observed in the patients with OCD compared to the controls, which may be indicative of neurodegeneration in this region. However, no significant differences were observed in the concentrations of the metabolites between the patients and controls in the CN region. The level of tNAA in DLPFC significantly correlated with the disability level (WHO-DAS) of the patients.

Conclusions

The present study demonstrates abnormalities in the metabolic profile of an important region, DLPFC of the CSTC circuit, which is suggestive of neurodegeneration in the region in OCD patients.

Clozapine-Induced Obsessive-Compulsive Symptoms and Augmentation with Clonazepam: Risks and Rationales

Obsessive-compulsive symptoms induced by clozapine negatively affect treatment compliance. In some studies, clonazepam was shown to be beneficial in obsessive-compulsive disorder. However, in literature there are case reports of life-threatening complications associated with the combined use of clozapine and benzodiazepines. In this article, the efficacy and safety of the clonazepam augmentation were discussed in two patients who had obsessive-compulsive symptoms induced by clozapine. No life-threatening complications were detected during the follow-up period of more than two years, and the patients benefited dramatically from the addition of clonazepam. In treatment-resistant patients, clonazepam can be used with close monitoring for obsessivecompulsive symptoms associated with atypical antipsychotics. Keywords: Atypical antipsychotics, clonazepam, clozapine, obsessivecompulsive symptoms.

Transdiagnostic role of glutamate and white matter damage in neuropsychiatric disorders: A Systematic Review

Neuropsychiatric disorders including generalized anxiety disorder (GAD), obsessive-compulsive disorder (OCD), major depressive disorder (MDD), bipolar disorder (BD), and schizophrenia (SZ) have been considered distinct categories of diseases despite their overlapping characteristics and symptomatology. We aimed to provide an in-depth review elucidating the role of glutamate/Glx and white matter (WM) abnormalities in these disorders from a transdiagnostic perspective. The PubMed online database was searched for studies published between 2010 and 2021. After careful screening, 401 studies were included. The findings point to decreased levels of glutamate in the Anterior Cingulate Cortex in both SZ and BD, whereas Glx is elevated in the Hippocampus in SZ and MDD. With regard to WM abnormalities, the Corpus Callosum and superior Longitudinal Fascicle were the most consistently identified brain regions showing decreased fractional anisotropy (FA) across all the reviewed disorders, except GAD. Additionally, the Uncinate Fasciculus displayed decreased FA in all disorders, except OCD. Decreased FA was also found in the inferior Longitudinal Fasciculus, inferior Fronto-Occipital Fasciculus, Thalamic Radiation, and Corona Radiata in SZ, BD, and MDD. Decreased FA in the Fornix and Corticospinal Tract were found in BD and SZ patients. The Cingulum and Anterior Limb of Internal Capsule exhibited decreased FA in MDD and SZ patients. The results suggest a gradual increase in severity from GAD to SZ defined by the number of brain regions with WM abnormality which may be partially caused by abnormal glutamate levels. WM damage could thus be considered a potential marker of some of the main neuropsychiatric disorders.

Bidirectional Behavioral Selection in Mice: A Novel Pre-clinical Approach to Examining Compulsivity

Obsessive-compulsive disorder (OCD) and related disorders (OCRD) is one of the most prevalent neuropsychiatric disorders with no definitive etiology. The pathophysiological attributes of OCD are driven by a multitude of factors that involve polygenic mechanisms, gender, neurochemistry, physiological status, environmental exposures and complex interactions among these factors. Such complex intertwining of contributing factors imparts clinical heterogeneity to the disorder making it challenging for therapeutic intervention. Mouse strains selected for excessive levels of nest- building behavior exhibit a spontaneous, stable and predictable compulsive-like behavioral phenotype. These compulsive-like mice exhibit heterogeneity in expression of compulsive-like and other adjunct behaviors that might serve as a valuable animal equivalent for examining the interactions of genetics, sex and environmental factors in influencing the pathophysiology of OCD. The current review summarizes the existing findings on the compulsive-like mice that bolster their face, construct and predictive validity for studying various dimensions of compulsive and associated behaviors often reported in clinical OCD and OCRD.

Magnetic Resonance Spectroscopy (MRS) and Positron Emission Tomography (PET) Imaging in Obsessive-Compulsive Disorder

Obsessive-compulsive disorder (OCD) is characterised by structural and functional deficits in the cortico-striato-thalamic-cortical (CSTC) circuitry and abnormal neurochemical changes are thought to modulate these deficits. The hypothesis that an imbalanced concentration of the brain neurotransmitters, in particular glutamate (Glu) and gamma-amino-butyric acid (GABA), could impair the normal functioning of the CSTC, thus leading to OCD symptoms, has been tested in humans using magnetic resonance spectroscopy (MRS) and positron emission tomography (PET). This chapter summarises these neurochemical findings and represents an attempt to condense such scattered literature. We also discuss potential challenges in the field that may explain the inconsistent findings and suggest ways to overcome them. There is some convergent research from MRS pointing towards abnormalities in the brain concentration of neurometabolite markers of neuronal integrity, such as N-acetylaspartate (NAA) and choline (Cho). Lower NAA levels have been found in dorsal and rostral ACC of OCD patients (as compared to healthy volunteers), which increase after CBT and SSRI treatment, and higher Cho concentration has been reported in the thalamus of the OCD brain. However, findings for other neurometabolites are very inconsistent. Studies have reported abnormalities in the concentrations of creatine (Cr), GABA, glutamate (Glu), glutamine (Gln), Ins (myo-inositol), and serotonin (5-HT), but most of the results were not replicated. The question remains whether the NAA and Cho findings are genuinely the only neurochemical abnormalities in OCD or whether the lack of consistent findings for the other neurometabolites is caused by the lower magnetic field (1-3 Tesla (T)) used by the studies conducted so far, their small sample sizes or a lack of proper control for medication effects. To answer these questions and to further inform the biological underpinning of the symptoms and the cognitive problems at the basis of OCD we need better controlled studies using clear medicated vs unmedicated groups, larger sample sizes, stronger magnetic fields (e.g. at 7 T), and more consistency in the definition of the regions of interest.

Reduced anterior cingulate glutamate of comorbid skin-picking disorder in adults with obsessive-compulsive disorder

BACKGROUND

Obsessive Compulsive Disorder (OCD) is characterized by hyperactivity in a network of forebrain structures, including the anterior cingulate cortex (ACC). Convergent evidence suggests that glutamatergic dysfunction may contribute to the disorder. Skin picking disorder (SPD) was listed as one of the obsessive-compulsive and related disorders, which is often comorbid with OCD and share overlapping phenomenology and pathophysiology. However, potential confounding effects between the two diagnostic effects on neurotransmitter levels remain largely unexamined.

METHODS

We examined the pregenual anterior cingulate cortex (pACC) glutamate and other neurochemicals in 62 subjects using a single-voxel acquisition 1H MRS at 3Tesla; of these, 47 subjects yielded usable measurements of both glutamate and glutamine and were included in the analysis (17 medicated with OCD alone, 13 medicated with comorbid OCD + SPD, 17 healthy control).

RESULTS

OCD with comorbid SPD showed significantly lower pACC glutamate than in patients without SPD (p = 0.001) or control subjects (p = 0.035). OCD without SPD subjects showed pACC glutamate levels indistinguishable from controls (p = 0.501). In the OCD with SPD subjects, glutamate was correlated with Y-BOCS total score in female patients (n = 9, r = 0.69, p = 0.041).

LIMITATIONS

The main limitation of the study was the cross-sectional data. Our patients were on SSRI medication which may have modified the effect of SPD and OCD interaction on glutamate activity.

CONCLUSION

Our results suggest that alterations of the glutamatergic system may play an important role in the pathophysiology of a subgroup of OCD and reduced pACC glutamate may be a biomarker of a distinct subset of OCD patients.

Toward identifying reproducible brain signatures of obsessive-compulsive profiles: rationale and methods for a new global initiative

BACKGROUND

Obsessive-compulsive disorder (OCD) has a lifetime prevalence of 2-3% and is a leading cause of global disability. Brain circuit abnormalities in individuals with OCD have been identified, but important knowledge gaps remain. The goal of the new global initiative described in this paper is to identify robust and reproducible brain signatures of measurable behaviors and clinical symptoms that are common in individuals with OCD. A global approach was chosen to accelerate discovery, to increase rigor and transparency, and to ensure generalizability of results.

METHODS

We will study 250 medication-free adults with OCD, 100 unaffected adult siblings of individuals with OCD, and 250 healthy control subjects at five expert research sites across five countries (Brazil, India, Netherlands, South Africa, and the U.S.). All participants will receive clinical evaluation, neurocognitive assessment, and magnetic resonance imaging (MRI). The imaging will examine multiple brain circuits hypothesized to underlie OCD behaviors, focusing on morphometry (T1-weighted MRI), structural connectivity (Diffusion Tensor Imaging), and functional connectivity (resting-state fMRI). In addition to analyzing each imaging modality separately, we will also use multi-modal fusion with machine learning statistical methods in an attempt to derive imaging signatures that distinguish individuals with OCD from unaffected siblings and healthy controls (Aim #1). Then we will examine how these imaging signatures link to behavioral performance on neurocognitive tasks that probe these same circuits as well as to clinical profiles (Aim #2). Finally, we will explore how specific environmental features (childhood trauma, socioeconomic status, and religiosity) moderate these brain-behavior associations.

DISCUSSION

Using harmonized methods for data collection and analysis, we will conduct the largest neurocognitive and multimodal-imaging study in medication-free subjects with OCD to date. By recruiting a large, ethno-culturally diverse sample, we will test whether there are robust biosignatures of core OCD features that transcend countries and cultures. If so, future studies can use these brain signatures to reveal trans-diagnostic disease dimensions, chart when these signatures arise during development, and identify treatments that target these circuit abnormalities directly. The long-term goal of this research is to change not only how we conceptualize OCD but also how we diagnose and treat it.

Cannabis Improves Obsessive-Compulsive Disorder-Case Report and Review of the Literature

Although several lines of evidence support the hypothesis of a dysregulation of serotoninergic neurotransmission in the pathophysiology of obsessive-compulsive disorder (OCD), there is also evidence for an involvement of other pathways such as the GABAergic, glutamatergic, and dopaminergic systems. Only recently, data obtained from a small number of animal studies alternatively suggested an involvement of the endocannabinoid system in the pathophysiology of OCD reporting beneficial effects in OCD-like behavior after use of substances that stimulate the endocannabinoid system. In humans, until today, only two case reports are available reporting successful treatment with dronabinol (tetrahydrocannabinol, THC), an agonist at central cannabinoid CB1 receptors, in patients with otherwise treatment refractory OCD. In addition, data obtained from a small open uncontrolled trial using the THC analogue nabilone suggest that the combination of nabilone plus exposure-based psychotherapy is more effective than each treatment alone. These reports are in line with data from a limited number of case studies and small controlled trials in patients with Tourette syndrome (TS), a chronic motor and vocal tic disorder often associated with comorbid obsessive compulsive behavior (OCB), reporting not only an improvement of tics, but also of comorbid OCB after use of different kinds of cannabis-based medicines including THC, cannabis extracts, and flowers. Here we present the case of a 22-year-old male patient, who suffered from severe OCD since childhood and significantly improved after treatment with medicinal cannabis with markedly reduced OCD and depression resulting in a considerable improvement of quality of life. In addition, we give a review of current literature on the effects of cannabinoids in animal models and patients with OCD and suggest a cannabinoid hypothesis of OCD.

Neuroimaging findings in obsessive-compulsive disorder: A narrative review to elucidate neurobiological underpinnings

Obsessive compulsive disorder (OCD) is a common psychiatric illness and significant research has been ongoing to understand its neurobiological basis. Neuroimaging studies right from the 1980s have revealed significant differences between OCD patients and healthy controls. Initial imaging findings showing hyperactivity in the prefrontal cortex (mainly orbitofrontal cortex), anterior cingulate cortex and caudate nucleus led to the postulation of the cortico-striato-thalamo-cortical (CSTC) model for the neurobiology of OCD. However, in the last two decades emerging evidence suggests the involvement of widespread associative networks, including regions of the parietal cortex, limbic areas (including amygdala) and cerebellum. This narrative review discusses findings from structural [Magnetic Resonance Imaging (MRI), Diffusion Tensor Imaging(DTI)], functional [(functional MRI (fMRI), Single photon emission computed tomography (SPECT), Positron emission tomography (PET), functional near-infrared spectroscopy (fNIRS)], combined structural and functional imaging studies and meta-analyses. Subsequently, we collate these findings to describe the neurobiology of OCD including CSTC circuit, limbic system, parietal cortex, cerebellum, default mode network and salience network. In future, neuroimaging may emerge as a valuable tool for personalised medicine in OCD treatment.

Metabolic abnormality in the right dorsolateral prefrontal cortex in patients with obsessive-compulsive disorder: proton magnetic resonance spectroscopy

OBJECTIVE

Proton magnetic resonance spectroscopy (1H-MRS) was used to evaluate metabolic changes in the dorsolateral prefrontal cortex (DLPFC) in patients with obsessive-compulsive disorder (OCD).

METHODS

In total, 14 OCD patients (mean age 28.9±7.2 years) and 14 healthy controls (mean age 32.6±7.1 years) with no history of neurological and psychiatric illness participated in this study. Brain metabolite concentrations were measured from a localised voxel on the right DLPFC using a 3-Tesla 1H-MRS.

RESULTS

The metabolic concentration of myo-inositol in patients with OCD increased significantly by 52% compared with the healthy controls, whereas glutamine/glutamate was decreased by 11%. However, there were no significant differences in N-acetylaspartate, choline, lactate and lipid between the two groups.

CONCLUSION

These findings would be helpful to understand the pathophysiology of OCD associated with the brain metabolic abnormalities in the right DLPFC.

Induced Obsessive Compulsive Symptoms (OCS) in schizophrenia patients under Atypical 2 Antipsychotics (AAPs): review and hypotheses

The prevalence of OCS and OCD is higher in schizophrenic patients than in the general population. These disorders are sometimes induced by AAPs. There is higher frequency of OCS and greater severity in patients treated with antipsychotics with predominant anti-serotoninergic profiles opposed to those with predominant dopaminergic blockade. Induced OCS may be due to complex neuromodulation involving many serotonin, dopamine and glutamate receptors and several subtypes. Concerning connectivity, AAPs differentially influence the BOLD signal, depending on the intensity of D2 receptor blockade. The OFC could play a significant role, on account of its involvement in inhibitory control. There is a paradox: AAPs are efficient as augmentation to SSRI in treatment resistant OCD, some of them such as risperidone or aripiprazole have favourable effects in schizoptypic OCD, but AAPs cause induced OCS in schizophrenic patients. When prescribing AAPs, we should inform patients about this potential side effect and assess systematically OCS with Y-BOCS assessment after 1 month of treatment. Afterwards there are different strategies: Aripiprazole in combination can reduce OCS induced by clozapine, SSRI are slightly effective and CBT shows a few encouraging results. OCS are sometimes dose-dependent, so we also recommend prescribing the minimum effective dose and gradual introduction.

Can Neuroimaging Provide Reliable Biomarkers for Obsessive-Compulsive Disorder? A Narrative Review

In this integrative review, we discuss findings supporting the use neuroimaging biomarkers in the diagnosis and treatment of obsessive-compulsive disorder (OCD). To do so, we have selected the most recent studies that attempted to identify the underlying pathogenic process associated with OCD and whether they provide useful information to predict clinical features, natural history or treatment responses. Studies using functional magnetic resonance (fMRI), voxel-based morphometry (VBM), diffusion tensor imaging (DTI) and proton magnetic resonance spectroscopy (1H MRS) in OCD patients are generally supportive of an expanded version of the earlier cortico-striatal-thalamus-cortical (CSTC) model of OCD. Although it is still unclear whether this information will be incorporated into the daily clinical practice (due to current conceptual approaches to mental illness), statistical techniques, such as pattern recognition methods, appear promising in identifying OCD patients and predicting their outcomes.

Striatal magnetic resonance spectroscopy abnormalities in young adult SAPAP3 knockout mice

BACKGROUND

Obsessive compulsive disorder (OCD) is a debilitating condition with lifetime prevalence of 1-3%. OCD typically arises in youth but delays in diagnosis impede optimal treatment and developmental studies of the disorder. Research using genetically modified rodents may provide models of etiology that enable earlier detection and intervention. The SAPAP3 knockout (KO) transgenic mouse was developed as an animal model of OCD and related disorders (OCRD). KO mice exhibit compulsive self-grooming behavior analogous to behaviors found in people with OCRD. Striatal hyperactivity has been reported in these mice and in humans with OCD.

METHODS

Striatal and medial frontal cortex 9.4 Tesla proton spectra were acquired from young adult SAPAP3 KO and wild-type control mice to determine whether KO mice have metabolic and neurochemical abnormalities.

RESULTS

Young adult KO mice had lower striatal lactate (P=0.006) and glutathione (P=0.039) levels. Among all mice, striatal lactate and glutathione levels were associated (R=0.73, P=0.007). We found no group differences in medial frontal cortex metabolites. At the age range studied, only 1 of 8 KO mice had skin lesions indicative of severe compulsive grooming.

CONCLUSION

Young adult SAPAP3 KO mice have striatal but not medial frontal cortex MRS abnormalities that may reflect striatal hypermetabolism accompanied by oxidative stress. These abnormalities typically preceded the onset of severe compulsive grooming. Our findings are consistent with striatal hypermetabolism in OCD. Together, these results suggest that striatal MRS measures of lactate or glutathione might be useful biomarkers for early detection of risk for developing compulsive behavior disorders.