title: The FAAH inhibitor URB597 efficiently reduces tyrosine hydroxylase expression through CB₁- and FAAH-independent mechanisms.
abstract: BACKGROUND
  Anandamide and 2-arachidonoylglycerol are neuromodulatory lipids interacting with cannabinoid receptors, whose availability is regulated by the balance between 'on demand' generation and enzymatic degradation [by fatty acid amide hydrolase (FAAH)/monoacylglycerol lipase]. Given the reported effects of anandamide on dopamine transmission, we investigated the influence of endocannabinoids and URB597, a well-known FAAH inhibitor, on the expression of tyrosine hydroxylase (TH), the rate-limiting enzyme in dopamine synthesis.
  
  
  METHODS
  We investigated TH expression in N1E115 neuroblastoma using a reporter gene assay, as well as mRNA and protein quantifications. FAAH inhibition was confirmed by measuring radiolabelled substrate hydrolysis and endogenous endocannabinoids.
  
  
  RESULTS
  Anandamide decreased TH promoter activity in N1E115 cells through CB₁ receptor activation. Unexpectedly, URB597 reduced TH expression (pEC₅₀ = 8.7 ± 0.2) through FAAH-independent mechanisms. Indeed, four structurally unrelated inhibitors of FAAH had no influence on TH expression, although all the inhibitors increased endocannabinoid levels. At variance with the endocannabinoid responses, the use of selective antagonists indicated that the URB597-mediated decrease in TH expression was not directed by the CB₁ receptor, but rather by abnormal-cannabidiol-sensitive receptors and PPARs. Further supporting the physiological relevance of these in vitro data, URB597 administration resulted in reduced TH mRNA levels in mice brain.
  
  
  CONCLUSIONS
  While confirming the implication of endocannabinoids on the modulation of TH, we provide strong evidence for additional physiologically relevant off-target effects of URB597. In light of the numerous preclinical studies involving URB597, particularly in anxiety and depression, the existence of non-CB₁ and non-FAAH mediated influences of URB597 on key enzymes of the catecholaminergic transmission system should be taken into account when interpreting the data.
authors.affiliation: Medicinal Chemistry Research Group, Louvain Drug Research Institute, Université Catholique de Louvain, Bruxelles, Belgium.
authors.forename: Barbara
authors.initials: B
authors.lastname: Bosier
authors.forename: Giulio G
authors.initials: GG
authors.lastname: Muccioli
authors.forename: Didier M
authors.initials: DM
authors.lastname: Lambert
mesh_terms: D000581:Amidohydrolases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000818:Animals; D021461:Animals, Outbred Strains; D014151:Anti-Anxiety Agents / Q000494:pharmacology; D000928:Antidepressive Agents / Q000494:pharmacology; D001549:Benzamides / Q000494:pharmacology*; D002185:Cannabidiol / Q000037:antagonists & inhibitors / Q000378:metabolism; D063387:Cannabinoid Receptor Antagonists / Q000494:pharmacology; D002219:Carbamates / Q000494:pharmacology*; D045744:Cell Line, Tumor; D003342:Corpus Striatum / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D059290:Dopaminergic Neurons / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D063388:Endocannabinoids / Q000037:antagonists & inhibitors / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D017930:Genes, Reporter / Q000187:drug effects; D006624:Hippocampus / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D051379:Mice; D009419:Nerve Tissue Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D047492:Peroxisome Proliferator-Activated Receptors / Q000037:antagonists & inhibitors / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000187:drug effects; D043884:Receptor, Cannabinoid, CB1 / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism; D014446:Tyrosine 3-Monooxygenase / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D000099252:Fatty Acid Amide Hydrolases
chemical_list: D000581:Amidohydrolases; D014151:Anti-Anxiety Agents; D000928:Antidepressive Agents; D001549:Benzamides; D002185:Cannabidiol; D063387:Cannabinoid Receptor Antagonists; D002219:Carbamates; D063388:Endocannabinoids; D004791:Enzyme Inhibitors; D009419:Nerve Tissue Proteins; D047492:Peroxisome Proliferator-Activated Receptors; D043884:Receptor, Cannabinoid, CB1; D014446:Tyrosine 3-Monooxygenase; D000099252:Fatty Acid Amide Hydrolases; C578453:CNR1 protein, mouse; C500528:cyclohexyl carbamic acid 3'-carbamoylbiphenyl-3-yl ester