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.