title: Haeme oxygenase-1 overexpression via nAChRs and the transcription factor Nrf2 has antinociceptive effects in the formalin test.
abstract: Epibatidine has shown antinociceptive effects in various pain models, being 200-fold more potent than morphine. Previous results from our laboratory demonstrated that HO-1 overexpression has an antinociceptive effect in the formalin test. Furthermore, epibatidine was able to induce haeme oxygenase-1 (HO-1). So, the aim of this study was to investigate the effect of HO-1 overexpression induced by epibatidine in nociception elicited by formalin injection in the mice hindpaw. Administration of epibatidine (4 microg/kg) 24h before the test reduced the nociceptive response during the first phase and second phase of the formalin test. This effect was prevented by treatment with tin protoporphyrin (SnPP, an inhibitor of HO-1 activity) administered via intraplantar 5min before the test, suggesting a main role of HO-1. Western blot analysis revealed that epibatidine treatment increased by 2-fold HO-1 expression in the paw; this effect was lost in knockout mice for nuclear factor-erythroid 2-related factor 2 (Nrf2) and was accompanied by the loss of its antinociceptive effect. Furthermore, the antinociceptive effect of epibatidine was related to the activation of alpha7 and/or alpha9 nAChRs since methyllycaconitine (MLA) and mecamylamine but not dihydro-beta-erythroidine (DHbetaE) reverted this effect. Finally, we showed by flow cytometry and by immunofluorescence that white blood cells of the animals injected with epibatidine expressed more HO-1 than control animals, and this expression was also reverted by MLA pre-treatment. These findings demonstrate that HO-1 induction by epibatidine has antinociceptive and anti-inflammatory effects by the activation of MLA-sensitive nAChRs.
authors: Instituto Teófilo Hernando, Departamento de Farmacología y Terapéutica, Facultad de Medicina, Universidad Autónoma de Madrid, C/Arzobispo Morcillo, 4. 28029 Madrid, Spain. javier.egea@terra.es, javier.egea@uam.es
authors: Javier
authors: J
authors: Egea
authors: Angelo O
authors: AO
authors: Rosa
authors: Silvia
authors: S
authors: Lorrio
authors: Laura
authors: L
authors: del Barrio
authors: Antonio
authors: A
authors: Cuadrado
authors: Manuela G
authors: MG
authors: López
mesh_terms: D019342:Acetic Acid; D000700:Analgesics; D000818:Animals; D015153:Blotting, Western; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D004790:Enzyme Induction / Q000187:drug effects; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D005557:Formaldehyde; D051547:Heme Oxygenase-1 / Q000096:biosynthesis*; D007150:Immunohistochemistry; D008297:Male; D051379:Mice; D051267:NF-E2-Related Factor 2 / Q000378:metabolism*; D018722:Nicotinic Agonists / Q000494:pharmacology; D010147:Pain Measurement; D011524:Protoporphyrins / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D011978:Receptors, Nicotinic / Q000378:metabolism*
chemical_list: D000700:Analgesics; D019086:Bridged Bicyclo Compounds, Heterocyclic; D051267:NF-E2-Related Factor 2; C495636:Nfe2l2 protein, mouse; D018722:Nicotinic Agonists; D011524:Protoporphyrins; D011725:Pyridines; D011978:Receptors, Nicotinic; D005557:Formaldehyde; C007095:cobaltiprotoporphyrin; D051547:Heme Oxygenase-1; C082748:epibatidine; D019342:Acetic Acid