title: Effects of palmitoylethanolamide on aqueous humor outflow.
abstract: OBJECTIVE
  To study the effects of palmitoylethanolamide (PEA), a fatty acid ethanolamide, on aqueous humor outflow facility.
  
  
  METHODS
  The effects of PEA on outflow facility were measured using a porcine anterior segment-perfused organ culture model. The involvements of different receptors in PEA-induced changes were investigated using receptor antagonists and adenovirus delivered small hairpin RNAs (shRNAs). PEA-induced activation of p42/44 mitogen-activated protein kinase (MAPK) was determined by Western blot analysis using an antiphospho p42/44 MAPK antibody.
  
  
  RESULTS
  PEA caused a concentration-dependent enhancement of outflow facility, with the maximum effect (151.08 ± 11.12% of basal outflow facility) achieved at 30 nM of PEA. Pretreatment of anterior segments with 1 μM cannabinoid receptor 2 antagonist SR144528 and 1 μM PPARα antagonist GW6471, but not 1 μM cannabinoid receptor 1 antagonist SR141716A, produced a partial antagonism on the PEA-induced increase of outflow facility. Treatment of TM cells with PEA for 10 minutes activated phosphorylation of p42/44 MAPK, which was blocked by pretreatment with SR1444528 and GW6471, but not SR141716A. Knocking down the expression of either GPR55 or PPARα receptors with specific shRNAs for these receptors partially blocked PEA-induced increase in outflow facility and abolished PEA-induced phosphorylation of p42/44 MAPK. PD98059, an inhibitor of the p42/44 MAPK pathway, blocked both PEA-induced enhancement of aqueous humor outflow facility and PEA-induced phosphorylation of p42/44 MAPK.
  
  
  CONCLUSIONS
  Our results demonstrate that PEA increases aqueous humor outflow through the TM pathway and these effects are mediated by GPR55 and PPARα receptors through activation of p42/44 MAPK.
authors.affiliation: Department of Pharmacology and Toxicology, University of Louisville School of Medicine, Louisville, Kentucky 40292, USA.
authors.forename: Akhilesh
authors.initials: A
authors.lastname: Kumar
authors.forename: Zhuanhong
authors.initials: Z
authors.lastname: Qiao
authors.forename: Pritesh
authors.initials: P
authors.lastname: Kumar
authors.forename: Zhao-Hui
authors.initials: ZH
authors.lastname: Song
mesh_terms: D000577:Amides; D000818:Animals; D001082:Aqueous Humor / Q000378:metabolism*; D015153:Blotting, Western; D001892:Camphanes / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D063388:Endocannabinoids; D004789:Enzyme Activation; D004983:Ethanolamines; D006801:Humans; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D009924:Organ Culture Techniques; D010080:Oxazoles / Q000494:pharmacology; D047493:PPAR alpha / Q000037:antagonists & inhibitors / Q000378:metabolism; D010169:Palmitic Acids / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D010766:Phosphorylation; D010880:Piperidines / Q000494:pharmacology; D011720:Pyrazoles / Q000494:pharmacology; D043884:Receptor, Cannabinoid, CB1 / Q000037:antagonists & inhibitors; D043885:Receptor, Cannabinoid, CB2 / Q000037:antagonists & inhibitors; D043882:Receptors, Cannabinoid; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism; D000077285:Rimonabant; D013552:Swine; D014129:Trabecular Meshwork / Q000187:drug effects* / Q000378:metabolism; D014443:Tyrosine / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D000577:Amides; D001892:Camphanes; D063388:Endocannabinoids; D004983:Ethanolamines; C524885:GPR55 protein, human; C449302:GW 6471; D010080:Oxazoles; D047493:PPAR alpha; D010169:Palmitic Acids; D010880:Piperidines; D011720:Pyrazoles; D043884:Receptor, Cannabinoid, CB1; D043885:Receptor, Cannabinoid, CB2; D043882:Receptors, Cannabinoid; D043562:Receptors, G-Protein-Coupled; C110630:SR 144528; D014443:Tyrosine; C005958:palmidrol; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D000077285:Rimonabant