title: In vitro morphine metabolism by rat microglia.
abstract: Morphine is mainly transformed to morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G) in the liver. Glucuronidation is also performed by rat brain homogenates and UDP-glucuronosyltransferases (UGTs) are present in the brain. Here we investigated the possibility that microglia transforms morphine into its metabolites M3G and M6G. Primary cultures of neonatal rat microglia were incubated for different intervals of time in basal conditions or with different concentrations of morphine. The following measures were performed on these cultures and/or in the medium: (i) morphine as well as M3G and M6G concentrations; (ii) levels of mRNA coding for UGT1A1, UGT1A6, UGT1A7, and UGT2B1 as well as their protein levels; (iii) released prostaglandin (PG)E2 and nitrite concentrations. Results show that in basal conditions morphine and M3G are produced by microglia; accordingly, these cells expressed UGT1A1, UGT1A6 and UGT1A7, but not UGT2B1. When cultures were exposed to different concentrations of exogenous morphine, M6G was also synthesized. This shift in the glucuronidation was associated with variations in the expression of UGT isozymes. In particular, UGT1A7 expression was rapidly upregulated and this event was translated into enhanced protein levels of UGT1A7; lesser effects were exerted on UGT1A1 and UGT1A6. Upon prolonged exposure to morphine, microglial cell UGT expression returned to baseline conditions or even to reduced levels of expression. Morphine exposure did not affect the synthesis of both PGE2 and nitrites, ruling out a generalized priming of microglia by morphine. In conclusion, this study suggests that morphine glucuronides found in the cerebrospinal liquor upon peripheral morphine administration may at least in part be brain-born, reconciling the conceptual gap between the high hydrophilic features of morphine glucuronides and their presence beyond the blood-brain barrier.
authors.affiliation: Department of Physiology and Pharmacology "Vittorio Erspamer", Sapienza University of Rome, P.le A. Moro 5, 00185 Rome, Italy.
authors.forename: Anna Rita
authors.initials: AR
authors.lastname: Togna
authors.affiliation: Department of Physiology and Pharmacology "Vittorio Erspamer", Sapienza University of Rome, P.le A. Moro 5, 00185 Rome, Italy.
authors.forename: Letizia
authors.initials: L
authors.lastname: Antonilli
authors.affiliation: Department of Neuroscience and Imaging, "G. d'Annunzio" University, Via dei Vestini 31, 66100 Chieti, Italy; Center of Excellence on Aging (CeSI), "Gabriele d'Annunzio" University Foundation, Via dei Vestini 31, 66100 Chieti, Italy.
authors.forename: Melania
authors.initials: M
authors.lastname: Dovizio
authors.affiliation: Department of Physiology and Pharmacology "Vittorio Erspamer", Sapienza University of Rome, P.le A. Moro 5, 00185 Rome, Italy.
authors.forename: Adele
authors.initials: A
authors.lastname: Salemme
authors.affiliation: Department of Physiology and Pharmacology "Vittorio Erspamer", Sapienza University of Rome, P.le A. Moro 5, 00185 Rome, Italy.
authors.forename: Lorenza
authors.initials: L
authors.lastname: De Carolis
authors.affiliation: Department of Physiology and Pharmacology "Vittorio Erspamer", Sapienza University of Rome, P.le A. Moro 5, 00185 Rome, Italy.
authors.forename: Giuseppina I
authors.initials: GI
authors.lastname: Togna
authors.affiliation: Department of Neuroscience and Imaging, "G. d'Annunzio" University, Via dei Vestini 31, 66100 Chieti, Italy; Center of Excellence on Aging (CeSI), "Gabriele d'Annunzio" University Foundation, Via dei Vestini 31, 66100 Chieti, Italy.
authors.forename: Paola
authors.initials: P
authors.lastname: Patrignani
authors.affiliation: Department of Physiology and Pharmacology "Vittorio Erspamer", Sapienza University of Rome, P.le A. Moro 5, 00185 Rome, Italy. Electronic address: paolo.nencini@uniroma1.it.
authors.forename: Paolo
authors.initials: P
authors.lastname: Nencini
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology; D002853:Chromatography, Liquid; D015232:Dinoprostone / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D014453:Glucuronosyltransferase / Q000235:genetics / Q000378:metabolism; D008840:Microfilament Proteins / Q000378:metabolism; D017628:Microglia / Q000187:drug effects / Q000378:metabolism*; D009020:Morphine / Q000378:metabolism* / Q000494:pharmacology*; D009022:Morphine Derivatives / Q000378:metabolism; D009294:Narcotics / Q000378:metabolism* / Q000494:pharmacology*; D009573:Nitrites / Q000378:metabolism; D051381:Rats; D053719:Tandem Mass Spectrometry; D013997:Time Factors
chemical_list: C100745:Aif1 protein, rat; D002135:Calcium-Binding Proteins; D008840:Microfilament Proteins; D009022:Morphine Derivatives; D009294:Narcotics; D009573:Nitrites; C035349:morphine-6-glucuronide; D009020:Morphine; D014453:Glucuronosyltransferase; D015232:Dinoprostone; C018108:morphine-3-glucuronide
keywords: Microglia; Morphine-3-glucuronide; Morphine-6-glucuronide; Rat; UGT