A physiological role for endocannabinoid-derived products of cyclooxygenase-2-mediated oxidative metabolism.
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ABSTRACT:
SUBMITTER: Guindon J
PROVIDER: S-EPMC2437897 | biostudies-other | 2008 Apr
REPOSITORIES: biostudies-other
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Project description:The cyclooxygenases (COX-1 and COX-2) oxygenate arachidonic acid (AA) in the committed step of prostaglandin biogenesis. Substitutions of I434V, H513R, and I523V constitute the only differences in residues lining the cyclooxygenase channel between COX-1 and COX-2. These changes create a hydrophobic pocket in COX-2, with Arg-513 located at the base of the pocket, which has been exploited in the design of COX-2-selective inhibitors. Previous studies have shown that COX-2, but not COX-1, can oxygenate endocannabinoid substrates, including 2-arachidonoyl glycerol (2-AG). To investigate the isoform-specific structural basis of endocannabinoid binding to COX-2, we determined the crystal structure of the 2-AG isomer 1-arachidonoyl glycerol (1-AG) in complex with wild type and R513H murine (mu) COX-2 to 2.2 and 2.35 Å, respectively, and R513H muCOX-2 in complex with AA to 2.45 Å resolution. The 2,3-dihydroxypropyl moiety of 1-AG binds near the opening of the cyclooxygenase channel in the space vacated by the movement of the Leu-531 side chain, validating our previous hypothesis implicating the flexibility of the Leu-531 side chain as a determinant for the ability of COX-2 to oxygenate endocannabinoid substrates. Functional analyses carried out to compliment our structural findings indicated that Y355F and R513H muCOX-2 constructs had no effect on the oxygenation of 1-AG and 2-AG, whereas substitutions that resulted in a shortened side chain for Leu-531 had only modest effects. Both AA and 1-AG bind to R513H muCOX-2 in conformations similar to those observed in the co-crystal structures of these substrates with wild type enzyme.
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Project description:Treatment of ob/ob (obese) mice with a cannabinoid receptor 1 (Cnr1) antagonist reduces food intake, suggesting a role for endocannabinoid signaling in leptin action. We further evaluated the role of endocannabinoid signaling by analyzing the phenotype of Cnr1 knockout ob/ob mice. Double mutant animals show a more severe growth retardation than ob/ob mice with similar levels of adiposity and reduced IGF-I levels without alterations of growth hormone (GH) levels. The double mutant mice are also significantly more glucose intolerant than ob/ob mice. This is in contrast to treatment of ob/ob mice with a Cnr1 antagonist that had no effect on glucose metabolism, suggesting a possible requirement for endocannabinoid signaling during development for normal glucose homeostasis. Double mutant animals also showed similar leptin sensitivity as ob/ob mice, suggesting that there are developmental changes that compensate for the loss of Cnr1 signaling. These data establish a role for Cnr1 during development and suggest that compensatory changes during development may mitigate the requirement for Cnr1 in mediating the effects of leptin. The data also suggest a developmental role for Cnr1 to promote growth, regulate the GH/IGF-I axis, and improve β-cell function and glucose homeostasis in the setting of leptin deficiency.
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Project description:Phytocannabinoids have well-known cardiovascular implications. For instance, Δ9-tetrahydrocannabinol (Δ9-THC), the principal component of cannabis, induces tachycardia in humans. In order to understand the impact of phytocannabinoids on human cardiovascular health, there is a need to study the metabolism of phytocannabinoids by cardiac cytochromes p450 (CYPs). CYP2J2, the primary CYP of cardiomyocytes, is responsible for the metabolism of the endocannabinoid, anandamide (AEA), into cardioprotective epoxides (EET-EAs). Herein, we have investigated the kinetics of the direct metabolism of six phytocannabinoids (Δ9-THC, Δ8-tetrahydrocannabinol, cannabinol, cannabidiol, cannabigerol, and cannabichromene) by CYP2J2. CYP2J2 mainly produces 1'/1″-OH metabolites of these phytocannabinoids. These phytocannabinoids are metabolized with greater catalytic efficiency compared to the metabolism of AEA by CYP2J2. We have also determined that the phytocannabinoids are potent inhibitors of CYP2J2-mediated AEA metabolism, with Δ9-THC being the strongest inhibitor. Most of the inhibition of CYP2J2 by the phytocannabinoids follow a noncompetitive inhibition model, and therefore dramatically reduce the formation of EET-EAs by CYP2J2. Taken together, these data demonstrate that phytocannabinoids are directly metabolized by CYP2J2 and inhibit human cardiac CYP2J2, leading to a reduction in the formation of cardioprotective EET-EAs.
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Project description:Cyclooxygenase-2 (COX-2) catalyzes the formation of prostaglandins, which are involved in immune regulation, vascular function, and synaptic signaling. COX-2 also inactivates the endogenous cannabinoid (eCB) 2-arachidonoylglycerol (2-AG) via oxygenation of its arachidonic acid backbone to form a variety of prostaglandin glyceryl esters (PG-Gs). Although this oxygenation reaction is readily observed in vitro and in intact cells, detection of COX-2-derived 2-AG oxygenation products has not been previously reported in neuronal tissue. Here we show that 2-AG is metabolized in the brain of transgenic COX-2-overexpressing mice and mice treated with lipopolysaccharide to form multiple species of PG-Gs that are detectable only when monoacylglycerol lipase is concomitantly blocked. Formation of these PG-Gs is prevented by acute pharmacological inhibition of COX-2. These data provide evidence that neuronal COX-2 is capable of oxygenating 2-AG to form a variety PG-Gs in vivo and support further investigation of the physiological functions of PG-Gs.
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Project description:Cyclooxygenase-2 (COX-2) oxygenates arachidonic acid (AA) and the endocannabinoids 2-arachidonoylglycerol (2-AG) and arachidonylethanolamide to prostaglandins, prostaglandin glyceryl esters, and prostaglandin ethanolamides, respectively. A structural homodimer, COX-2 acts as a conformational heterodimer with a catalytic and an allosteric monomer. Prior studies have demonstrated substrate-selective negative allosteric regulation of 2-AG oxygenation. Here we describe AM-8138 (13(S)-methylarachidonic acid), a substrate-selective allosteric potentiator that augments 2-AG oxygenation by up to 3.5-fold with no effect on AA oxygenation. In the crystal structure of an AM-8138·COX-2 complex, AM-8138 adopts a conformation similar to the unproductive conformation of AA in the substrate binding site. Kinetic analysis suggests that binding of AM-8138 to the allosteric monomer of COX-2 increases 2-AG oxygenation by increasing kcat and preventing inhibitory binding of 2-AG. AM-8138 restored the activity of COX-2 mutants that exhibited very poor 2-AG oxygenating activity and increased the activity of COX-1 toward 2-AG. Competition of AM-8138 for the allosteric site prevented the inhibition of COX-2-dependent 2-AG oxygenation by substrate-selective inhibitors and blocked the inhibition of AA or 2-AG oxygenation by nonselective time-dependent inhibitors. AM-8138 selectively enhanced 2-AG oxygenation in intact RAW264.7 macrophage-like cells. Thus, AM-8138 is an important new tool compound for the exploration of allosteric modulation of COX enzymes and their role in endocannabinoid metabolism.
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