Aspects of Prostaglandin Glycerol Ester Biology

Endocannabinoid signaling in adult hippocampal neurogenesis: A mechanistic and integrated perspective

Dentate gyrus of the hippocampus continuously gives rise to new neurons, namely, adult-born granule cells, which contribute to conferring plasticity to the mature brain throughout life. Within this neurogenic region, the fate and behavior of neural stem cells (NSCs) and their progeny result from a complex balance and integration of a variety of cell-autonomous and cell-to-cell-interaction signals and underlying pathways. Among these structurally and functionally diverse signals, there are endocannabinoids (eCBs), the main brain retrograde messengers. These pleiotropic bioactive lipids can directly and/or indirectly influence adult hippocampal neurogenesis (AHN) by modulating, both positively and negatively, multiple molecular and cellular processes in the hippocampal niche, depending on the cell type or stage of differentiation. Firstly, eCBs act directly as cell-intrinsic factors, cell-autonomously produced by NSCs following their stimulation. Secondly, in many, if not all, niche-associated cells, including some local neuronal and nonneuronal elements, the eCB system indirectly modulates the neurogenesis, linking neuronal and glial activity to regulating distinct stages of AHN. Herein, we discuss the crosstalk of the eCB system with other neurogenesis-relevant signal pathways and speculate how the hippocampus-dependent neurobehavioral effects elicited by (endo)cannabinergic medications are interpretable in light of the key regulatory role that eCBs play on AHN.

Inhibiting degradation of 2-arachidonoylglycerol as a therapeutic strategy for neurodegenerative diseases

Endocannabinoids are endogenous lipid signaling mediators that participate in a variety of physiological and pathological processes. 2-Arachidonoylglycerol (2-AG) is the most abundant endocannabinoid and is a full agonist of G-protein-coupled cannabinoid receptors (CB1R and CB2R), which are targets of Δ⁹-tetrahydrocannabinol (Δ⁹-THC), the main psychoactive ingredient in cannabis. While 2-AG has been well recognized as a retrograde messenger modulating synaptic transmission and plasticity at both inhibitory GABAergic and excitatory glutamatergic synapses in the brain, growing evidence suggests that 2-AG also functions as an endogenous terminator of neuroinflammation in response to harmful insults, thus maintaining brain homeostasis. Monoacylglycerol lipase (MAGL) is the key enzyme that degrades 2-AG in the brain. The immediate metabolite of 2-AG is arachidonic acid (AA), a precursor of prostaglandins (PGs) and leukotrienes. Several lines of evidence indicate that pharmacological or genetic inactivation of MAGL, which boosts 2-AG levels and reduces its hydrolytic metabolites, resolves neuroinflammation, mitigates neuropathology, and improves synaptic and cognitive functions in animal models of neurodegenerative diseases, including Alzheimer's disease (AD), multiple sclerosis (MS), Parkinson's disease (PD), and traumatic brain injury (TBI)-induced neurodegenerative disease. Thus, it has been proposed that MAGL is a potential therapeutic target for treatment of neurodegenerative diseases. As the main enzyme hydrolyzing 2-AG, several MAGL inhibitors have been identified and developed. However, our understanding of the mechanisms by which inactivation of MAGL produces neuroprotective effects in neurodegenerative diseases remains limited. A recent finding that inhibition of 2-AG metabolism in astrocytes, but not in neurons, protects the brain from TBI-induced neuropathology might shed some light on this unsolved issue. This review provides an overview of MAGL as a potential therapeutic target for neurodegenerative diseases and discusses possible mechanisms underlying the neuroprotective effects of restraining degradation of 2-AG in the brain.

Endocannabinoid 2-Arachidonoylglycerol Synthesis and Metabolism at Neuronal Nuclear Matrix Fractions Derived from Adult Rat Brain Cortex

In this report, we describe the kinetics characteristics of the diacylglycerol lipase-α (DGLα) located at the nuclear matrix of nuclei derived from adult cortical neurons. Thus, using high-resolution fluorescence microscopy, classical biochemical subcellular fractionation, and Western blot techniques, we demonstrate that the DGLα enzyme is located in the matrix of neuronal nuclei. Furthermore, by quantifying the 2-arachidonoylglycerol (2-AG) level by liquid chromatography and mass spectrometry when 1-stearoyl-2-arachidonoyl-sn-glycerol (SAG) was exogenously added as substrate, we describe the presence of a mechanism for 2-AG production through DGLα dependent biosynthesis with an apparent K_m (K_m^app) of 180 µM and a V_max of 1.3 pmol min^-1 µg^-1 protein. We also examined the presence of enzymes with hydrolytic and oxygenase activities that are able to use 2-AG as substrate, and described the localization and compartmentalization of the major 2-AG degradation enzymes, namely monoacylglycerol lipase (MGL), fatty acid amide hydrolase (FAAH), α/β-hydrolase domain 12 protein (ABHD12) and cyclooxygenase-2 (COX2). Of these, only ABHD12 exhibited the same distribution with respect to chromatin, lamin B1, SC-35 and NeuN as that described for DGLα. When 2-AG was exogenously added, we observed the production of arachidonic acid (AA), which was prevented by inhibitors (but not specific MGL or ABHD6 inhibitors) of the ABHD family. Overall, our results expand knowledge about the subcellular distribution of neuronal DGLα, and provide biochemical and morphological evidence to ensure that 2-AG is produced in the neuronal nuclear matrix. Thus, this work paves the way for proposing a working hypothesis about the role of 2-AG produced in neuronal nuclei.

Carboxylesterase 1d Inactivation Augments Lung Inflammation in Mice

Carboxylesterases are members of the serine hydrolase superfamily and metabolize drugs, pesticides, and lipids. Previous research showed that inhibition of carboxylesterase 1 (CES1) in human macrophages altered the immunomodulatory effects of lipid mediators called prostaglandin glyceryl esters, which are produced by cyclooxygenase-catalyzed oxygenation of the endocannabinoid 2-arachidonoylglycerol (2-AG). Ces1d - the mouse ortholog of human CES1 - is the most abundant Ces isoform in murine lung tissues and alveolar macrophages and a major target of organophosphate poisons. Monoacylglycerol lipase (Magl) is also expressed in murine lung and is the main enzyme responsible for 2-AG catabolism. Several metabolic benefits are observed in Ces1d-/- mice fed a high-fat diet; thus, we wondered whether pharmacological and genetic inactivation of Ces1d in vivo might also ameliorate the acute inflammatory response to lipopolysaccharide (LPS). C57BL/6 mice were treated with WWL229 (Ces1d inhibitor) or JZL184 (Magl inhibitor), followed 30 min later by either LPS or saline. Wild-type (WT) and Ces1d-/- mice were also administered LPS to determine the effect of Ces1d knockout. Mice were sacrificed at 6 and 24 h, and cytokines were assessed in serum, lung, liver, and adipose tissues. Lipid mediators were quantified in lung tissues, while activity-based protein profiling and enzyme assays determined the extent of lung serine hydrolase inactivation by the inhibitors. WWL229 was shown to augment LPS-induced lung inflammation in a female-specific manner, as measured by enhanced neutrophil infiltration and Il1b mRNA. The marked Ces inhibition in female lung by 4 h after drug treatment might explain this sex difference, although the degree of Ces inhibition in female and male lungs was similar at 6 h. In addition, induction of lung Il6 mRNA and prostaglandin E2 by LPS was more pronounced in Ces1d-/- mice than in WT mice. Thus, WWL229 inhibited lung Ces1d activity and augmented the female lung innate immune response, an effect observed in part in Ces1d-/- mice and Ces1d/CES1-deficient murine and human macrophages. In contrast, JZL184 attenuated LPS-induced Il1b and Il6 mRNA levels in female lung, suggesting that Ces1d and Magl have opposing effects. Mapping the immunomodulatory molecules/pathways that are regulated by Ces1d in the context of lung inflammation will require further research.

α/β-Hydrolase Domain-Containing 6 (ABHD6)- A Multifunctional Lipid Hydrolase

α/β-hydrolase domain-containing 6 (ABHD6) belongs to the α/β-hydrolase fold superfamily and was originally discovered in a functional proteomic approach designed to discover monoacylglycerol (MAG) hydrolases in the mouse brain degrading the endocannabinoid 2-arachidonoylglycerol. Subsequent studies confirmed that ABHD6 acts as an MAG hydrolase regulating cannabinoid receptor-dependent and -independent signaling processes. The enzyme was identified as a negative modulator of insulin secretion and regulator of energy metabolism affecting the pathogenesis of obesity and metabolic syndrome. It has been implicated in the metabolism of the lysosomal co-factor bis(monoacylglycerol)phosphate and in the surface delivery of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-type glutamate receptors. Finally, ABHD6 was shown to affect cancer cell lipid metabolism and tumor malignancy. Here, we provide new insights into the experimentally derived crystal structure of ABHD6 and its possible orientation in biological membranes, and discuss ABHD6's functions in health and disease.

Mapping the binding sites of UDP and prostaglandin E2 glyceryl ester in the nucleotide receptor P2Y6

Cyclooxygenase‐2 catalyzes the biosynthesis of prostaglandins from arachidonic acid and the biosynthesis of prostaglandin glycerol esters (PG‐Gs) from 2‐arachidonoylglycerol. PG‐Gs are mediators of several biological actions such as macrophage activation, hyperalgesia, synaptic plasticity, and intraocular pressure. Recently, the human UDP receptor P2Y₆ was identified as a target for the prostaglandin E2 glycerol ester (PGE₂‐G). Here, we show that UDP and PGE₂‐G are evolutionary conserved endogenous agonists at vertebrate P2Y₆ orthologs. Using sequence comparison of P2Y₆ orthologs, homology modeling, and ligand docking studies, we proposed several receptor positions participating in agonist binding. Site‐directed mutagenesis and functional analysis of these P2Y₆ mutants revealed that both UDP and PGE₂‐G share in parts one ligand‐binding site. Thus, the convergent signaling of these two chemically very different agonists has already been manifested in the evolutionary design of the ligand‐binding pocket.

Endocannabinoid-Based Therapies

The endocannabinoids are lipid-derived messengers that play a diversity of regulatory roles in mammalian physiology. Dysfunctions in their activity have been implicated in various disease conditions, attracting attention to the endocannabinoid system as a possible source of therapeutic drugs. This signaling complex has three components: the endogenous ligands, anandamide and 2-arachidonoyl-sn-glycerol (2-AG); a set of enzymes and transporters that generate, eliminate, or modify such ligands; and selective cell surface receptors that mediate their biological actions. We provide an overview of endocannabinoid formation, deactivation, and biotransformation and outline the properties and therapeutic potential of pharmacological agents that interfere with those processes. We describe small-molecule inhibitors that target endocannabinoid-producing enzymes, carrier proteins that transport the endocannabinoids into cells, and intracellular endocannabinoid-metabolizing enzymes. We briefly discuss selected agents that simultaneously interfere with components of the endocannabinoid system and with other functionally related signaling pathways. Expected final online publication date for the Annual Review of Pharmacology and Toxicology, Volume 62 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Untargeted metabolomics reveals the synergistic mechanisms of Yuanhu Zhitong oral liquid in the treatment of primary dysmenorrhea

Primary dysmenorrhea is a prevalent gynecological disorder that severely affects the quality of life in women. Yuanhu Zhitong oral liquid (YZOL) is a standardized herbal preparation frequently used in clinical practice and is a promising alternative therapy for primary dysmenorrhea. The findings of previous studies show that YZOL exhibits significant analgesic and spasmolytic effects, however, the involved mechanism remains unclear. Herein, we performed an untargeted plasma metabolomic analysis on a mouse model of oxytocin-induced primary dysmenorrhea to investigate the underlying mechanism of YZOL. We used multivariate and pathway-driven analyses to uncover the treatment targets linked with YZOL therapy and verified the possible mechanisms through biochemical assays. Therefore, we identified 47 plasma biomarkers primarily associated with sphingolipid metabolism, amino acid metabolism, arachidonic acid metabolism, and biosynthesis of steroid hormone as well as primary bile acid. We established that the analgesic effect of YZOL on primary dysmenorrhea relies on multiple constituents that act on multiple targets in multiple pathways. Our correlation analysis showed significant correlations between the biomarkers and biochemical indicators, which is of considerable significance in elucidating the YZOL mechanisms. Moreover, we identified some novel prospective biomarkers linked to primary dysmenorrhea, including bile acids. Collectively, these data provide new insights into the mechanism of YZOL and provide evidence for the analgesic effect of YZOL in the treatment of primary dysmenorrhea.

The ALOXE3 gene variants from patients with Dravet syndrome decrease gene expression and enzyme activity

Aberrant expression or dysfunction of a number of genes in the brain contributes to epilepsy, a common neurological disorder characterized by recurrent seizures. Local overexpression of arachidonate lipoxygenase 3 (ALOXE3), a key enzyme for arachidonic acid (AA) metabolic pathway, alleviates seizure severities. However, the relationship between the ALOXE3 gene mutation and epilepsy has not been reported until now. Here we firstly characterized the promoter of human ALOXE3 gene and found that the ALOXE3 promoter could drive luciferase gene expression in the human HEK-293 and SH-SY5Y cells. We then screened the ALOXE3 promoter region and all coding exons from those patients with Dravet syndrome and identified 5 variants c.-163T > C, c.-50C > G, c.-37G > A, c. + 228G > A and c. + 290G > T in the promoter region and one missense variant c.1939A > G (p.I647 V) in the exon. Of these variants in the promoter region, only -50C > G was a novel variant located on the transcriptional factor NFII-I binding element. Luciferase reporter gene analyses indicated that the c.-50C > G could decrease gene expression by preventing the TFII-I's binding. In addition, the variant p.I647 V was conserved among all analyzed species and located within the ALOXE3 functional domain for catalyzing its substrate. In cultured cell lines, overexpression of ALOXE3 significantly decreased the cellular AA levels and overexpression of ALOXE3-I647 V could restore the AA levels, suggesting that the p.I647 V mutant led to a decrease in enzyme activity. Taken together, the present study proposes that the identified ALOXE3 variants potentially contribute to the AA-pathway-mediated epileptogenesis, which should provide a novel avenue for clinical diagnosis of epilepsy.

Inactivation of CES1 Blocks Prostaglandin D2 Glyceryl Ester Catabolism in Monocytes/Macrophages and Enhances Its Anti-inflammatory Effects, Whereas the Pro-inflammatory Effects of Prostaglandin E2 Glyceryl Ester Are Attenuated

Human monocytic cells in blood have important roles in host defense and express the enzyme carboxylesterase 1 (CES1). This metabolic serine hydrolase plays a critical role in the metabolism of many molecules, including lipid mediators called prostaglandin glyceryl esters (PG-Gs), which are formed during cyclooxygenase-mediated oxygenation of the endocannabinoid 2-arachidonoylglycerol. Some PG-Gs have been shown to exhibit anti-inflammatory effects; however, they are unstable compounds, and their hydrolytic breakdown generates pro-inflammatory prostaglandins. We hypothesized that by blocking the ability of CES1 to hydrolyze PG-Gs in monocytes/macrophages, the beneficial effects of anti-inflammatory prostaglandin D₂-glyceryl ester (PGD₂-G) could be augmented. The goals of this study were to determine whether PGD₂-G is catabolized by CES1, evaluate the degree to which this metabolism is blocked by small-molecule inhibitors, and assess the immunomodulatory effects of PGD₂-G in macrophages. A human monocytic cell line (THP-1 cells) was pretreated with increasing concentrations of known small-molecule inhibitors that block CES1 activity [chlorpyrifos oxon (CPO), WWL229, or WWL113], followed by incubation with PGD₂-G (10 μM). Organic solvent extracts of the treated cells were analyzed by liquid chromatography with tandem mass spectrometry to assess levels of the hydrolysis product PGD₂. Further, THP-1 monocytes with normal CES1 expression (control cells) and "knocked-down" CES1 expression (CES1KD cells) were employed to confirm CES1's role in PGD₂-G catabolism. We found that CES1 has a prominent role in PGD₂-G hydrolysis in this cell line, accounting for about 50% of its hydrolytic metabolism, and that PGD₂-G could be stabilized by the inclusion of CES1 inhibitors. The inhibitor potency followed the rank order: CPO > WWL113 > WWL229. THP-1 macrophages co-treated with WWL113 and PGD₂-G prior to stimulation with lipopolysaccharide exhibited a more pronounced attenuation of pro-inflammatory cytokine levels (interleukin-6 and TNFα) than by PGD₂-G treatment alone. In contrast, prostaglandin E₂-glyceryl ester (PGE₂-G) had opposite effects compared to those of PGD₂-G, which appeared to be dependent on the hydrolysis of PGE₂-G to PGE₂. These results suggest that the anti-inflammatory effects induced by PGD₂-G can be further augmented by inactivating CES1 activity with specific small-molecule inhibitors, while pro-inflammatory effects of PGE₂-G are attenuated. Furthermore, PGD₂-G (and/or its downstream metabolites) was shown to activate the lipid-sensing receptor PPARγ, resulting in altered "alternative macrophage activation" response to the Th2 cytokine interleukin-4. These findings suggest that inhibition of CES1 and other enzymes that regulate the levels of pro-resolving mediators such as PGD₂-G in specific cellular niches might be a novel anti-inflammatory approach.

Review of the Endocannabinoid System

The endocannabinoid system (ECS) is a widespread neuromodulatory network involved in the developing central nervous system as well as playing a major role in tuning many cognitive and physiological processes. The ECS is composed of endogenous cannabinoids, cannabinoid receptors, and the enzymes responsible for the synthesis and degradation of endocannabinoids. In addition to its endogenous roles, cannabinoid receptors are the primary target of Δ⁹-tetrahydrocannabinol, the intoxicating component of cannabis. In this review, we summarize our current understanding of the ECS. We start with a description of ECS components and their role in synaptic plasticity and neurodevelopment, and then discuss how phytocannabinoids and other exogenous compounds may perturb the ECS, emphasizing examples relevant to psychosis.