Inverse correlation between plasma 2-arachidonoylglycerol levels and subjective severity of depression

Endocannabinoid concentrations in major depression: effects of childhood maltreatment and relation to hippocampal volume

Evidence from preclinical animal models suggests that the stress-buffering function of the endocannabinoid (eCB) system may help protect against stress-related reductions in hippocampal volume, as is documented in major depressive disorder (MDD). However, stress exposure may also lead to dysregulation of this system. Thus, pathways from marked stress histories, such as childhood maltreatment (CM), to smaller hippocampal volumes and MDD in humans may depend on dysregulated versus intact eCB functioning. We examined whether the relation between MDD and peripheral eCB concentrations would vary as a function of CM history. Further, we examined whether eCBs moderate the relation of CM/MDD and hippocampal volume. Ninety-one adults with MDD and 62 healthy comparison participants (HCs) were recruited for a study from the Canadian Biomarker Integration Network in Depression program (CAN-BIND-04). The eCBs, anandamide (AEA) and 2-arachidonylglycerol (2-AG), were assessed from blood plasma. Severe CM history was assessed retrospectively via contextual interview. MDD was associated with eCBs, though not all associations were moderated by CM or in the direction expected. Specifically, MDD was associated with higher AEA compared to HCs regardless of CM history, a difference that could be attributed to psychotropic medications. MDD was also associated with higher 2-AG, but only for participants with CM. Consistent with hypotheses, we found lower left hippocampal volume in participants with versus without CM, but only for those with lower AEA, and not moderate or high AEA. Our study presents the first evidence in humans implicating eCBs in stress-related mechanisms involving reduced hippocampal volume in MDD.

Endocannabinoids and Stress-Related Neurospsychiatric Disorders: A Systematic Review and Meta-Analysis of Basal Concentrations and Response to Acute Psychosocial Stress

Background: Dysregulation of the endocannabinoid (eCB) system is implicated in various stress-related neuropsychiatric disorders (SRDs), including anxiety, depression, and post-traumatic stress disorder (PTSD). In this systematic review and meta-analysis, our objectives were to characterize circulating anandamide (AEA) and 2-arachidonoylglycerol (2-AG) concentrations at rest and in response to acute laboratory-based psychosocial stress in individuals with SRDs and without (controls). Our primary aims were to assess the effects of acute psychosocial stress on eCB concentrations in controls (Aim 1), compare baseline (prestress) eCB concentrations between individuals with SRDs and controls (Aim 2), and explore differential eCB responses to acute psychosocial stress in individuals with SRDs compared with controls (Aim 3). Methods: On June 8, 2023, a comprehensive review of the MEDLINE (PubMed) database was conducted to identify original articles meeting inclusion criteria. A total of 1072, 1341, and 400 articles were screened for inclusion in Aims 1, 2, and 3, respectively. Results: Aim 1, comprised of seven studies in controls, revealed that most studies reported stress-related increases in AEA (86%, with 43% reporting statistical significance) and 2-AG (83%, though none were statistically significant except for one study in saliva). However, meta-analyses did not support these patterns (p's>0.05). Aim 2, with 20 studies, revealed that most studies reported higher baseline concentrations of both AEA (63%, with 16% reporting statistical significance) and 2-AG (60%, with 10% reporting statistical significance) in individuals with SRDs compared with controls. Meta-analyses confirmed these findings (p's<0.05). Aim 3, which included three studies, had only one study that reported statistically different stress-related changes in 2-AG (but not AEA) between individuals with PTSD (decrease) and controls (increase), which was supported by the meta-analysis (p<0.001). Meta-analyses showed heterogeneity across studies and aims (I2=14-97%). Conclusion: Despite substantial heterogeneity in study characteristics, samples, and methodologies, consistent patterns emerged, including elevated baseline AEA and 2-AG in individuals with SRDs compared with controls, as well as smaller stress-related increases in 2-AG in individuals with SRDs compared with controls. To consider eCBs as reliable biomarkers and potential intervention targets for SRDs, standardized research approaches are needed to clarify the complex relationships between eCBs, SRDs, and psychosocial stress.

Elucidating genetic and molecular basis of altered higher-order brain structure-function coupling in major depressive disorder

Previous studies have shown that major depressive disorder (MDD) patients exhibit structural and functional impairments, but few studies have investigated changes in higher-order coupling between structure and function. Here, we systematically investigated the effect of MDD on higher-order coupling between structural connectivity (SC) and functional connectivity (FC). Each brain region was mapped into embedding vector by the node2vec algorithm. We used support vector machine (SVM) with the brain region embedding vector to distinguish MDD patients from health controls (HCs) and identify the most discriminative brain regions. Our study revealed that MDD patients had decreased higher-order coupling in connections between the most discriminative brain regions and local connections in rich-club organization and increased higher-order coupling in connections between the ventral attentional network and limbic network compared with HCs. Interestingly, transcriptome-neuroimaging association analysis demonstrated the correlations between regional rSC-FC coupling variations between MDD patients and HCs and α/β-hydrolase domain-containing 6 (ABHD6), β 1,3-N-acetylglucosaminyltransferase-9(β3GNT9), transmembrane protein 45B (TMEM45B), the correlation between regional dSC-FC coupling variations and retinoic acid early transcript 1E antisense RNA 1(RAET1E-AS1), and the correlations between regional iSC-FC coupling variations and ABHD6, β3GNT9, katanin-like 2 protein (KATNAL2). In addition, correlation analysis with neurotransmitter receptor/transporter maps found that the rSC-FC and iSC-FC coupling variations were both correlated with neuroendocrine transporter (NET) expression, and the dSC-FC coupling variations were correlated with metabotropic glutamate receptor 5 (mGluR5). Further mediation analysis explored the relationship between genes, neurotransmitter receptor/transporter and MDD related higher-order coupling variations. These findings indicate that specific genetic and molecular factors underpin the observed disparities in higher-order SC-FC coupling between MDD patients and HCs. Our study confirmed that higher-order coupling between SC and FC plays an important role in diagnosing MDD. The identification of new biological evidence for MDD etiology holds promise for the development of innovative antidepressant therapies.

Peripheral endocannabinoids in major depressive disorder and alcohol use disorder: a systematic review

BACKGROUND

Major Depressive Disorder (MDD) and Alcohol Use Disorder (AUD) are two high-prevalent conditions where the Endocannabinoid system (ECS) is believed to play an important role. The ECS regulates how different neurotransmitters interact in both disorders, which is crucial for controlling emotions and responses to stress and reward stimuli. Measuring peripheral endocannabinoids (eCBs) in human serum and plasma can help overcome the limitations of detecting endocannabinoid levels in the brain. This systematic review aims to identify levels of peripheral eCBs in patients with MDD and/or AUD and find eCBs to use as diagnostic, prognostic biomarkers, and potential therapeutic targets.

METHODS

We conducted a systematic literature search according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines from the earliest manuscript until October 22, 2023, in three electronic databases. We included studies of human adults who had a current diagnosis of AUD and/or MDD and evaluated plasma or serum endocannabinoids. We carefully considered known variables that may affect endocannabinoid levels.

RESULTS

We included 17 articles in this systematic review, which measured peripheral eCBs in 170 AUD and 359 MDD patients. Stressors increase peripheral 2-arachidonyl-glycerol (2-AG) concentrations, and 2-AG may be a particular feature of depression severity and chronicity. Anxiety symptoms are negatively correlated with anandamide (AEA) concentrations, and AEA significantly increases during early abstinence in AUD. Studies suggest a negative correlation between Oleoylethanolamide (OEA) and length of abstinence in AUD patients. They also show a significant negative correlation between peripheral levels of AEA and OEA and fatty acid amide hydrolase (FAAH) activity. Eicosapentaenoylethanolamide (EPEA) is correlated to clinical remission rates in depression. Included studies show known variables such as gender, chronicity, symptom severity, comorbid psychiatric symptoms, length of abstinence in the case of AUD, and stress-inducibility that can affect peripheral eCBs.

CONCLUSIONS

This systematic review highlights the important role that the ECS plays in MDD and AUD. Peripheral eCBs appear to be useful biomarkers for these disorders, and further research may identify potential therapeutic targets. Using accessible biological samples such as blood in well-designed clinical studies is crucial to develop novel therapies for these disorders.

How depression and antidepressant drugs affect endocannabinoid system?-review of clinical and preclinical studies

As major depressive disorder is becoming a more and more common issue in modern society, it is crucial to discover new possible grip points for its diagnosis and antidepressive therapy. One of them is endocannabinoid system, which has been proposed as a manager of emotional homeostasis, and thus, endocannabinoid alterations have been found in animals undergoing various preclinical models of depression procedures as well as in humans suffering from depressive-like disorders. In this review article, studies regarding those alterations have been summed up and analyzed. Another important issue raised by the researchers is the impact of currently used antidepressive drugs on endocannabinoid system so that it would be possible to predict reversibility of endocannabinoid alterations following stress exposure and, in the future, to be able to design individually personalized therapies. Preclinical studies investigating this topic have been analyzed and described in this article. Unfortunately, too few clinical studies in this field exist, what indicates an urgent need for collecting such data, so that it would be possible to compare them with preclinical outcomes and draw reliable conclusions.

Endocannabinoid hydrolases differentially distribute in platelets and red blood cells and are differentially released by thrombin

BACKGROUND

Plasma levels of the major endocannabinoids 2-arachidonoylgycerol (2AG) and anandamide (N-arachidonoylethanolamine, AEA) have been identified to vary independently with particular pathological conditions. The levels of these endocannabinoids are tightly regulated by two hydrolytic enzymes, monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase (FAAH), respectively.

OBJECTIVES

In this study, we have quantified these enzyme activities in the major blood fractions.

PATIENTS/METHODS

In blood fractions from human volunteers, radiometric assays were used to quantify monoacylglycerol lipase and fatty acid amide hydrolase. Tagging with fluorophosphonate-rhodamine allowed quantification of platelet serine hydrolase activities.

RESULTS

Fatty acid amide hydrolase activity was highest in platelets, while MAGL activity was most abundant in erythrocytes. Sampling the blood of donors on two further occasions 15 days apart showed no significant change in platelet FAAH or erythrocyte MAGL activities. Activities were not different when comparing female donors with males. Storage of these blood fractions at - 80 °C was associated with a rapid loss in enzyme activities, which could largely by avoided by storage in liquid nitrogen. Incubation of platelets and erythrocytes in the presence of thrombin lead to release of measurable FAAH, but not MAGL, activity. Tagging of serine hydrolase activities with fluorophosphonate-rhodamine allowed confirmation of MAGL activity in platelet preparations, as well as multiple other enzymes.

CONCLUSIONS

These investigations suggest a potential role for FAAH in regulation of coagulation, while the role of MAGL in blood requires further investigation.

Endocannabinoid 2-Arachidonoylglycerol Levels in the Anterior Cingulate Cortex, Caudate Putamen, Nucleus Accumbens, and Piriform Cortex Were Upregulated by Chronic Restraint Stress

Endocannabinoid 2-arachidonoylglycerol (2-AG) has been implicated in habituation to stress, and its augmentation reduces stress-induced anxiety-like behavior. Chronic restraint stress (CRS) changes the 2-AG levels in some gross brain areas, such as the forebrain. However, the detailed spatial distribution of 2-AG and its changes by CRS in stress processing-related anatomical structures such as the anterior cingulate cortex (ACC), caudate putamen (CP), nucleus accumbens (NAc), and piriform cortex (PIR) are still unclear. In this study, mice were restrained for 30 min in a 50 mL-centrifuge tube for eight consecutive days, followed by imaging of the coronal brain sections of control and stressed mice using desorption electrospray ionization mass spectrometry imaging (DESI-MSI). The results showed that from the forebrain to the cerebellum, 2-AG levels were highest in the hypothalamus and lowest in the hippocampal region. 2-AG levels were significantly (p < 0.05) upregulated and 2-AG precursors levels were significantly (p < 0.05) downregulated in the ACC, CP, NAc, and PIR of stressed mice compared with control mice. This study provided direct evidence of 2-AG expression and changes, suggesting that 2-AG levels are increased in the ACC CP, NAc, and PIR when individuals are under chronic stress.

2-Arachidonoylglycerol Synthesis: Facile and Handy Enzymatic Method That Allows to Avoid Isomerization

A simple and practical synthesis of 2-arachidonoyl glycerol (2-AG), an endogenous agonist for cannabinoid receptors, based on a two-step enzymatic process and a chemical coupling, was achieved with a good yield and negligible amount of the isomerization product 1-AG. Commercial preparation of immobilized lipase from Mucor miehei (MML) was selected as the most suitable enzyme to catalyze the efficient protection of glycerol using vinyl benzoate as an acyl transfer reagent in tetrahydrofuran. The same enzyme was used to remove the protective groups in positions 1 and 3. Owing to the mild neutral conditions and easy suitability of the method, 2-AG was obtained without any isomerization to the more stable 1-AG and air oxidation of acid chain. The synthetic method proposed here allows us to easily obtain 2-AG from the protected precursor in a one-step reaction without purification requirement.

Commonalities for comorbidity: Overlapping features of the endocannabinoid system in depression and epilepsy

A wealth of clinical and pre-clinical data supports a bidirectional comorbidity between depression and epilepsy. This suggests commonalities in underlying mechanisms that may serve as targets for more effective treatment strategies. Unfortunately, many patients with this comorbidity are highly refractory to current treatment strategies, while others experience a worsening of one arm of the comorbidity when treating the other arm. This highlights the need for novel pharmaceutical targets that may provide safe and effective relief for both depression and epilepsy symptoms. The endocannabinoid system (ECS) of the brain has become an area of intense interest for possible roles in depression and epilepsy. Several existing literature reviews have provided in-depth analysis of the involvement of various aspects of the ECS in depression or epilepsy separately, while others have addressed the effectiveness of different treatment strategies targeting the ECS in either condition individually. However, there is not currently a review that considers the ECS when both conditions are comorbid. This mini-review will address areas of common overlap between the ECS in depression and in epilepsy, such as commonalities in endocannabinoids themselves, their receptors, and degradative enzymes. These areas of overlap will be discussed alongside their implications for treatment of this challenging comorbidity.