Structural determinants for calcium mobilization by prostaglandin E2 and prostaglandin F2alpha glyceryl esters in RAW 264.7 cells and H1819 cells

Molecular networks underlying cannabinoid signaling in skeletal muscle plasticity

The cannabinoid system is ubiquitously present and is classically considered to engage in neural and immunity processes. Yet, the role of the cannabinoid system in the whole body and tissue metabolism via central and peripheral mechanisms is increasingly recognized. The present review provides insights in (i) how cannabinoid signaling is regulated via receptor-independent and -dependent mechanisms and (ii) how these signaling cascades (might) affect skeletal muscle plasticity and physiology. Receptor-independent mechanisms include endocannabinoid metabolism to eicosanoids and the regulation of ion channels. Alternatively, endocannabinoids can act as ligands for different classic (cannabinoid receptor 1 [CB₁ ], CB₂ ) and/or alternative (e.g., TRPV1, GPR55) cannabinoid receptors with a unique affinity, specificity, and intracellular signaling cascade (often tissue-specific). Antagonism of CB₁ might hold clues to improve oxidative (mitochondrial) metabolism, insulin sensitivity, satellite cell growth, and muscle anabolism, whereas CB₂ agonism might be a promising way to stimulate muscle metabolism and muscle cell growth. Besides, CB₂ ameliorates muscle regeneration via macrophage polarization toward an anti-inflammatory phenotype, induction of MyoD and myogenin expression and antifibrotic mechanisms. Also TRPV1 and GPR55 contribute to the regulation of muscle growth and metabolism. Future studies should reveal how the cannabinoid system can be targeted to improve muscle quantity and/or quality in conditions such as ageing, disease, disuse, and metabolic dysregulation, taking into account challenges that are inherent to modulation of the cannabinoid system, such as central and peripheral side effects.

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.

The endocannabinoidome in neuropsychiatry: Opportunities and potential risks

The endocannabinoid system (ECS) comprises two cognate endocannabinoid receptors referred to as CB1R and CB2R_. ECS dysregulation is apparent in neurodegenerative/neuro-psychiatric disorders including but not limited to schizophrenia, major depressive disorder and potentially bipolar disorder. The aim of this paper is to review mechanisms whereby both receptors may interact with neuro-immune and neuro-oxidative pathways, which play a pathophysiological role in these disorders. CB1R is located in the presynaptic terminals of GABAergic, glutamatergic, cholinergic, noradrenergic and serotonergic neurons where it regulates the retrograde suppression of neurotransmission. CB1R plays a key role in long-term depression, and, to a lesser extent, long-term potentiation, thereby modulating synaptic transmission and mediating learning and memory. Optimal CB1R activity plays an essential neuroprotective role by providing a defense against the development of glutamate-mediated excitotoxicity, which is achieved, at least in part, by impeding AMPA-mediated increase in intracellular calcium overload and oxidative stress. Moreover, CB1R activity enables optimal neuron-glial communication and the function of the neurovascular unit. CB2R receptors are detected in peripheral immune cells and also in central nervous system regions including the striatum, basal ganglia, frontal cortex, hippocampus, amygdala as well as the ventral tegmental area. CB2R upregulation inhibits the presynaptic release of glutamate in several brain regions. CB2R activation also decreases neuroinflammation partly by mediating the transition from a predominantly neurotoxic "M1" microglial phenotype to a more neuroprotective "M2" phenotype. CB1R and CB2R are thus novel drug targets for the treatment of neuro-immune and neuro-oxidative disorders including schizophrenia and affective disorders.

Harmaline Analogs as Substrate-Selective Cyclooxygenase-2 Inhibitors

We report the design, synthesis, and evaluation of a series of harmaline analogs as selective inhibitors of 2-arachidonylglycerol (2-AG) oxygenation over arachidonic acid (AA) oxygenation by purified cyclooxygenase-2 (COX-2). A fused tricyclic harmaline analog containing a CH₃O substituent at C-6 and a CH₃ group at the C-1 position of 4,9-dihydro-3H-pyrido[3,4-b]indole (compound 3) was the best substrate-selective COX-2 inhibitor of those evaluated, exhibiting a 2AG-selective COX-2 inhibitory IC₅₀ of 0.022 μM as compared to >1 μM for AA. The 2.66 Å resolution crystal complex of COX-2 with compound 3 revealed that this series of tricyclic indoles binds in the cyclooxygenase channel by flipping the side chain of L531 toward the dimer interface. This novel tricyclic indole series provides the foundation for the development of promising substrate-selective molecules capable of increasing endocannabinoid (EC) levels in the brain to offer new treatments for a variety of diseases, from pain and inflammation to stress and anxiety disorders.

Aspects of Prostaglandin Glycerol Ester Biology

The Cyclooxygenase enzymes (COX-1 and COX-2) incorporate 2 molecules of O₂ into arachidonic acid (AA), resulting in an array of bioactive prostaglandins. However, much work has been done showing that COX-2 will perform this reaction on several different AA-containing molecules, most importantly, the endocannabinoid 2-arachidonoylglycerol (2-AG). The products of 2-AG oxygenation, prostaglandin glycerol esters (PG-Gs), are analogous to canonical prostaglandins. This chapter reviews the literature detailing the production, metabolism, and bioactivity of these compounds, as well as their detection in intact animals.

Human leukocytes differentially express endocannabinoid-glycerol lipases and hydrolyze 2-arachidonoyl-glycerol and its metabolites from the 15-lipoxygenase and cyclooxygenase pathways

2-Arachidonoyl-glycerol (2-AG) is an endocannabinoid with anti-inflammatory properties. Blocking 2-AG hydrolysis to enhance CB₂ signaling has proven effective in mouse models of inflammation. However, the expression of 2-AG lipases has never been thoroughly investigated in human leukocytes. Herein, we investigated the expression of seven 2-AG hydrolases by human blood leukocytes and alveolar macrophages (AMs) and found the following protein expression pattern: monoacylglycerol (MAG lipase; eosinophils, AMs, monocytes), carboxylesterase (CES1; monocytes, AMs), palmitoyl-protein thioesterase (PPT1; AMs), α/β-hydrolase domain (ABHD6; mainly AMs), ABHD12 (all), ABHD16A (all), and LYPLA2 (lysophospholipase 2; monocytes, lymphocytes, AMs). We next found that all leukocytes could hydrolyze 2-AG and its metabolites derived from cyclooxygenase-2 (prostaglandin E₂ -glycerol [PGE₂ -G]) and the 15-lipoxygenase (15-hydroxy-eicosatetraenoyl-glycerol [15-HETE-G]). Neutrophils and eosinophils were consistently better at hydrolyzing 2-AG and its metabolites than monocytes and lymphocytes. Moreover, the efficacy of leukocytes to hydrolyze 2-AG and its metabolites was 2-AG  ≥ 15-HETE-G >> PGE₂ -G for each leukocyte. Using the inhibitors methylarachidonoyl-fluorophosphonate (MAFP), 4-nitrophenyl-4-(dibenzo[d][1,3]dioxol-5-yl(hydroxy)methyl)piperidine-1-carboxylate (JZL184), Palmostatin B, 4'-carbamoylbiphenyl-4-yl methyl(3-(pyridin-4-yl)benzyl)carbamate, N-methyl-N-[[3-(4-pyridinyl)phenyl]methyl]-4'-(aminocarbonyl)[1,1'-biphenyl]-4-yl ester carbamic acid (WWL70), 4'-[[[methyl[[3-(4-pyridinyl)phenyl]methyl]amino]carbonyl]oxy]-[1,1'-biphenyl]-4-carboxylic acid, ethyl ester (WWL113), tetrahydrolipstatin, and ML349, we could not pinpoint a specific hydrolase responsible for the hydrolysis of 2-AG, PGE₂ -G, and 15-HETE-G by these leukocytes. Furthermore, JZL184, a selective MAG lipase inhibitor, blocked the hydrolysis of 2-AG, PGE₂ -G, and 15-HETE-G by neutrophils and the hydrolysis of PGE₂ -G and 15-HETE-G by lymphocytes, two cell types with limited/no MAG lipase. Using an activity-based protein profiling (ABPP) probe to label hydrolases in leukocytes, we found that they express many MAFP-sensitive hydrolases and an unknown JZL184-sensitive hydrolase of ∼52 kDa. Altogether, our results indicate that human leukocytes are experts at hydrolyzing 2-AG and its metabolites via multiple lipases and probably via a yet-to-be characterized 52 kDa hydrolase. Blocking 2-AG hydrolysis in humans will likely abrogate the ability of human leukocytes to degrade 2-AG and its metabolites and increase their anti-inflammatory effects in vivo.

Sensitization of nociceptors by prostaglandin E2-glycerol contributes to hyperalgesia in mice with sickle cell disease

Pain is a characteristic feature of sickle cell disease (SCD), 1 of the most common inherited diseases. Patients may experience acute painful crises as well as chronic pain. In the Berkley transgenic murine model of SCD, HbSS-BERK mice express only human hemoglobin S. These mice share many features of SCD patients, including persistent inflammation and hyperalgesia. Cyclooxygenase-2 (COX-2) is elevated in skin, dorsal root ganglia (DRG), and spinal cord in HbSS-BERK mice. In addition to arachidonic acid, COX-2 oxidizes the endocannabinoid 2-arachidonoylglycerol (2-AG) to produce prostaglandin E₂ (PGE₂)-glycerol (PGE₂-G); PGE₂-G is known to produce hyperalgesia. We tested the hypotheses that PGE₂-G is increased in DRGs of HbSS-BERK mice and sensitizes nociceptors (sensory neurons that respond to noxious stimuli), and that blocking its synthesis would decrease hyperalgesia in HbSS-BERK mice. Systemic administration of R-flurbiprofen preferentially reduced production of PGE₂-G over that of PGE₂ in DRGs, decreased mechanical and thermal hyperalgesia, and decreased sensitization of nociceptors in HbSS-BERK mice. The same dose of R-flurbiprofen had no behavioral effect in HbAA-BERK mice (the transgenic control), but local injection of PGE₂-G into the hind paw of HbAA-BERK mice produced sensitization of nociceptors and hyperalgesia. Coadministration of a P2Y6 receptor antagonist blocked the effect of PGE₂-G, indicating that this receptor is a mediator of pain in SCD. The ability of R-flurbiprofen to block the synthesis of PGE₂-G and to normalize levels of 2-AG suggests that R-flurbiprofen may be beneficial to treat pain in SCD, thereby reducing the use of opioids to relieve pain.

Prostaglandin E2 receptor EP4 is involved in the cell growth and invasion of prostate cancer via the cAMP‑PKA/PI3K‑Akt signaling pathway

Prostate cancer (PCa) is one of the most prevalent diagnosed malignancies globally. Previous studies have demonstrated that prostaglandin E2 (PGE2) is closely associated with the tumorigenesis and progression of PCa. However, the underlying molecular mechanisms remain unclear and require further investigation. Matrix metalloproteinases (MMPs), receptor activator of nuclear factor‑κB ligand (RANKL) and runt‑related transcription factor 2 (RUNX2), which are involved in cell growth and bone metastasis, are frequently activated or overexpressed in various types of cancer, including PCa. The present study was designed to investigate the associations between PGE2 and the PGE2 receptor EP4, and MMPs, RANKL and RUNX2 in PCa, and to define their roles in PCa cell proliferation and invasion in addition to understanding the molecular mechanisms. The results of western blotting and reverse transcription‑quantitative polymerase chain reaction demonstrated that the protein and the mRNA expression levels of MMP‑2, MMP‑9, RANKL and RUNX2 in PC‑3 cells were significantly upregulated by treatment with PGE2, respectively, and knockdown of these proteins blocked PGE2‑induced cell proliferation and invasion in PC‑3 cells, as determined by Cell Counting Kit‑8 and Matrigel invasion assays, respectively. The effect of PGE2 on the protein and mRNA expression levels was primarily regulated via the EP4 receptor. EP4 receptor signaling activates the cyclic (c)AMP‑protein kinase A (PKA) signaling pathway, and forskolin, an activator of adenylate cyclase (AC), exhibited similar effects to an EP4 receptor agonist on the protein expression, while SQ22536, an inhibitor of AC, inhibited the protein expression. These results confirmed that the AC/cAMP pathway may be involved in EP4 receptor‑mediated upregulation of protein expression. By using a specific inhibitor of PKA, it was also demonstrated that cAMP/PKA was also involved in the EP4 receptor‑mediated upregulation of protein expression. In addition to the signaling pathway involving PKA, the EP4 receptor also exerts activities through activation of Akt kinase. The results in the present study confirmed the hypothesis that EP4 receptor‑mediated protein expression in PCa cells that were pretreated with a specific inhibitor of phosphatidylinositol 3‑kinase (PI3K) was significantly inhibited. In conclusion, the results of the present study indicate that PGE2 significantly upregulated the mRNA and protein expression levels of the MMP‑2, MMP‑9, RANKL and RUNX2, and the EP4 receptor was involved in the cell proliferation and invasion of PCa via the cAMP‑PKA/PI3K‑Akt signaling pathway. These results may provide novel insight into potential therapeutic strategies for the prevention and treatment of PCa.

Prostaglandin E2 glyceryl ester is an endogenous agonist of the nucleotide receptor P2Y6

Cyclooxygenase-2 catalyses the biosynthesis of prostaglandins from arachidonic acid but also the biosynthesis of prostaglandin glycerol esters (PG-Gs) from 2-arachidonoylglycerol. Previous studies identified PG-Gs as signalling molecules involved in inflammation. Thus, the glyceryl ester of prostaglandin E₂, PGE₂-G, mobilizes Ca²⁺ and activates protein kinase C and ERK, suggesting the involvement of a G protein-coupled receptor (GPCR). To identify the endogenous receptor for PGE₂-G, we performed a subtractive screening approach where mRNA from PGE₂-G response-positive and -negative cell lines was subjected to transcriptome-wide RNA sequencing analysis. We found several GPCRs that are only expressed in the PGE₂-G responder cell lines. Using a set of functional readouts in heterologous and endogenous expression systems, we identified the UDP receptor P2Y₆ as the specific target of PGE₂-G. We show that PGE₂-G and UDP are both agonists at P2Y₆, but they activate the receptor with extremely different EC₅₀ values of ~1 pM and ~50 nM, respectively. The identification of the PGE₂-G/P2Y₆ pair uncovers the signalling mode of PG-Gs as previously under-appreciated products of cyclooxygenase-2.

The Endocannabinoid Metabolite Prostaglandin E2 (PGE2)-Glycerol Inhibits Human Neutrophil Functions: Involvement of Its Hydrolysis into PGE2 and EP Receptors

The endocannabinoids 2-arachidonoyl-glycerol and N-arachidonoyl-ethanolamine mediate an array of pro- and anti-inflammatory effects. These effects are related, in part, to their metabolism by eicosanoid biosynthetic enzymes. For example, N-arachidonoyl-ethanolamine and 2-arachidonoyl-glycerol can be metabolized by cyclooxygenase-2 into PG-ethanolamide (PG-EA) and PG-glycerol (PG-G), respectively. Although PGE₂ is a recognized suppressor of neutrophil functions, the impact of cyclooxygenase-derived endocannabinoids such as PGE₂-EA or PGE₂-G on neutrophils is unknown. This study's aim was to define the effects of these mediators on neutrophil functions and the underlying cellular mechanisms involved. We show that PGE₂-G, but not PGE₂-EA, inhibits leukotriene B₄ biosynthesis, superoxide production, migration, and antimicrobial peptide release. The effects of PGE₂-G were prevented by EP₁/EP₂ receptor antagonist AH-6809 but not the EP₄ antagonist ONO-AE2-227. The effects of PGE₂-G required its hydrolysis into PGE₂, were not observed with the non-hydrolyzable PGE₂-serinol amide, and were completely prevented by methyl-arachidonoyl-fluorophosphate and palmostatin B, and partially prevented by JZL184 and WWL113. Although we could detect six of the documented PG-G hydrolases in neutrophils by quantitative PCR, only ABHD12 and ABHD16A were detected by immunoblot. Our pharmacological data, combined with our protein expression data, did not allow us to pinpoint one PGE₂-G lipase, and rather support the involvement of an uncharacterized lipase and/or of multiple hydrolases. In conclusion, we show that PGE₂-G inhibits human neutrophil functions through its hydrolysis into PGE₂, and by activating the EP₂ receptor. This also indicates that neutrophils could regulate inflammation by altering the balance between PG-G and PG levels in vivo.

Identification of the major prostaglandin glycerol ester hydrolase in human cancer cells

Prostaglandin glycerol esters (PG-Gs) are produced as a result of the oxygenation of the endocannabinoid, 2-arachidonoylglycerol, by cyclooxygenase 2. Understanding the role that PG-Gs play in a biological setting has been difficult because of their sensitivity to enzymatic hydrolysis. By comparing PG-G hydrolysis across human cancer cell lines to serine hydrolase activities determined by activity-based protein profiling, we identified lysophospholipase A2 (LYPLA2) as a major enzyme responsible for PG-G hydrolysis. The principal role played by LYPLA2 in PGE2-G hydrolysis was confirmed by siRNA knockdown. Purified recombinant LYPLA2 hydrolyzed PG-Gs in the following order of activity: PGE2-G > PGF2α-G > PGD2-G; LYPLA2 hydrolyzed 1- but not 2-arachidonoylglycerol or arachidonoylethanolamide. Chemical inhibition of LYPLA2 in the mouse macrophage-like cell line, RAW264.7, elicited an increase in PG-G production. Our data indicate that LYPLA2 serves as a major PG-G hydrolase in human cells. Perturbation of this enzyme should enable selective modulation of PG-Gs without alterations in endocannabinoids, thereby providing a means to decipher the unique functions of PG-Gs in biology and disease.

Substrate-selective COX-2 inhibition as a novel strategy for therapeutic endocannabinoid augmentation

Pharmacologic augmentation of endogenous cannabinoid (eCB) signaling is an emerging therapeutic approach for the treatment of a broad range of pathophysiological conditions. Thus far, pharmacological approaches have focused on inhibition of the canonical eCB inactivation pathways - fatty acid amide hydrolase (FAAH) for anandamide and monoacylglycerol lipase (MAGL) for 2-arachidonoylglycerol. We review here the experimental evidence that cyclooxygenase-2 (COX-2)-mediated eCB oxygenation represents a third mechanism for terminating eCB action at cannabinoid receptors. We describe the development, molecular mechanisms, and in vivo validation of 'substrate-selective' COX-2 inhibitors (SSCIs) that prevent eCB inactivation by COX-2 without affecting prostaglandin (PG) generation from arachidonic acid (AA). Lastly, we review recent data on the potential therapeutic applications of SSCIs with a focus on neuropsychiatric disorders.

COX-2-derived endocannabinoid metabolites as novel inflammatory mediators

Cyclooxygenase-2 (COX-2) is an enzyme that plays a key role in inflammatory processes. Classically, this enzyme is upregulated in inflammatory situations and is responsible for the generation of prostaglandins (PGs) from arachidonic acid (AA). One lesser-known property of COX-2 is its ability to metabolize the endocannabinoids, N-arachidonoylethanolamine (AEA) and 2-arachidonoylglycerol (2-AG). Endocannabinoid metabolism by COX-2 is not merely a means to terminate their actions. On the contrary, it generates PG analogs, namely PG-glycerol esters (PG-G) for 2-AG and PG-ethanolamides (PG-EA or prostamides) for AEA. Although the formation of these COX-2-derived metabolites of the endocannabinoids has been known for a while, their biological effects remain to be fully elucidated. Recently, several studies have focused on the role of these PG-G or PG-EA in vivo. In this review we take a closer look at the literature concerning these novel bioactive lipids and their role in inflammation.

Parsing the players: 2-arachidonoylglycerol synthesis and degradation in the CNS

The endogenous cannabinoid signalling system, composed of endogenous cannabinoids, cannabinoid receptors and the enzymes that synthesize and degrade the endogenous cannabinoids, is much more complex than initially conceptualized. 2-Arachidonoylglycerol (2-AG) is the most abundant endocannabinoid and plays a major role in CNS development and synaptic plasticity. Over the past decade, many key players in 2-AG synthesis and degradation have been identified and characterized. Most 2-AG is synthesized from membrane phospholipids via sequential activation of a phospholipase Cβ and a diacylglycerol lipase, although other pathways may contribute in specialized settings. 2-AG breakdown is more complicated with at least eight different enzymes participating. These enzymes can either degrade 2-AG into its components, arachidonic acid and glycerol, or transform 2-AG into highly bioactive signal molecules. The implications of the precise temporal and spatial control of the expression and function of these pleiotropic metabolizing enzymes have only recently come to be appreciated. In this review, we will focus on the primary organization of the synthetic and degradative pathways of 2-AG and then discuss more recent findings and their implications, with an eye towards the biological and therapeutic implications of manipulating 2-AG synthesis and metabolism.

LINKED ARTICLES

This article is part of a themed section on Cannabinoids 2013. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-6.

Inactivation of lipid glyceryl ester metabolism in human THP1 monocytes/macrophages by activated organophosphorus insecticides: role of carboxylesterases 1 and 2

Carboxylesterases (CES) have important roles in pesticide and drug metabolism and contribute to the clearance of ester-containing xenobiotics in mammals. Tissues with the highest levels of CES expression are the liver and small intestine. In addition to xenobiotics, CES also harness their broad substrate specificity to hydrolyze endobiotics, such as cholesteryl esters and triacylglycerols. Here, we determined if two human CES isoforms, CES1 and CES2, hydrolyze the endocannabinoids 2-arachidonoylglycerol (2AG) and anandamide (AEA), and two prostaglandin glyceryl esters (PG-Gs), which are formed by COX-mediated oxygenation of 2AG. We show that recombinant CES1 and CES2 efficiently hydrolyze 2AG to arachidonic acid (AA) but not amide-containing AEA. Steady-state kinetic parameters for CES1- and CES2-mediated 2AG hydrolysis were, respectively, kcat, 59 and 43 min(-1); Km, 49 and 46 μM; and kcat/Km, 1.2 and 0.93 μM(-1) min(-1). kcat/Km values are comparable to published values for rat monoacylglycerol lipase (MAGL)-catalyzed 2AG hydrolysis. Furthermore, we show that CES1 and CES2 also efficiently hydrolyze PGE2-G and PGF2α-G. In addition, when cultured human THP1 macrophages were treated with exogenous 2AG or PG-G (10 μM, 1 h), significant quantities of AA or PGs were detected in the culture medium; however, the ability of macrophages to metabolize these compounds was inhibited (60-80%) following treatment with paraoxon, the toxic metabolite of the insecticide parathion. Incubation of THP1 cell lysates with small-molecule inhibitors targeting CES1 (thieno[3,2-e][1]benzothiophene-4,5-dione or JZL184) significantly reduced lipid glyceryl ester hydrolase activities (40-50% for 2AG and 80-95% for PG-Gs). Immunodepletion of CES1 also markedly reduced 2AG and PG-G hydrolase activities. These results suggested that CES1 is in part responsible for the hydrolysis of 2AG and PG-Gs in THP1 cells, although it did not rule out a role for other hydrolases, especially with regard to 2AG metabolism since a substantial portion of its hydrolysis was not inactivated by the inhibitors. An enzyme (Mr 31-32 kDa) of unknown function was detected by serine hydrolase activity profiling of THP1 cells and may be a candidate. Finally, the amounts of in situ generated 2AG and PG-Gs in macrophages were enhanced by treating the cells with bioactive metabolites of OP insecticides. Collectively, the results suggest that in addition to MAGL and fatty-acid amide hydrolase (FAAH), which have both been documented to terminate endocannabinoid signaling, CES may also have a role. Furthermore, since PG-Gs have been shown to possess biological activities in their own right, CES may represent an important enzyme class that regulates their in vivo levels.

(R)-Profens are substrate-selective inhibitors of endocannabinoid oxygenation by COX-2

Cyclooxygenase-2 (COX-2) catalyzes the oxygenation of arachidonic acid and the endocannabinoids 2-arachidonoylglycerol and arachidonoylethanolamide. Evaluation of a series of COX-2 inhibitors revealed that many weak competitive inhibitors of arachidonic acid oxygenation are potent inhibitors of endocannabinoid oxygenation. (R) enantiomers of ibuprofen, naproxen and flurbiprofen, which are considered to be inactive as COX-2 inhibitors, are potent 'substrate-selective inhibitors' of endocannabinoid oxygenation. Crystal structures of the COX-2–(R)-naproxen and COX-2–(R)-flurbiprofen complexes verified this unexpected binding and defined the orientation of the (R) enantiomers relative to (S) enantiomers. (R)-Profens selectively inhibited endocannabinoid oxygenation by lipopolysaccharide-stimulated dorsal root ganglion (DRG) cells. Substrate-selective inhibition provides new tools for investigating the role of COX-2 in endocannabinoid oxygenation and a possible explanation for the ability of (R)-profens to maintain endocannabinoid tone in models of neuropathic pain.

Reciprocal cross-talk between Prostaglandin E2 and bone in prostate cancer: a current review

In this review we analyzed the role of PGE2 as a possible regulator of bone metabolism and bone metastases in prostate cancer. Published studies were identified by searching computerized bibliographic systems from January 1^st, 2000 to July 1^st, 2011.

PGE2 represents a key factor in the modulation of bone metabolism and bone metastatic disease in prostate cancer interacting with bone regulatory signals including the RANK/RANKL/OPG system and Wnt pathways. A high concentration of PGE2 exerts a prevalent stimulatory effect on osteoclastogenesis via OPG/RANK/RANKL axis activation and a inhibitory effect on osteoblastogenesis trough inhibition of Wnt pathway. An inversely low level of PGE2 exerts a stimulatory effect on osteoblastogenesis via activation of the Wnt pathway.

Our finding suggests that PGE2 acts as a regulator in maintaining normal bone mass and indicate a mechanism whereby chemical manipulation of PGE2 levels or signaling may be therapeutically beneficial for prostate cancer treatment.