title: Supraspinal peroxynitrite modulates pain signaling by suppressing the endogenous opioid pathway.
abstract: Peroxynitrite (PN, ONOO(-)) is a potent oxidant and nitrating agent that contributes to pain through peripheral and spinal mechanisms, but its supraspinal role is unknown. We present evidence here that PN in the rostral ventromedial medulla (RVM) is essential for descending nociceptive modulation in rats during inflammatory and neuropathic pain through PN-mediated suppression of opioid signaling. Carrageenan-induced thermal hyperalgesia was associated with increased 3-nitrotyrosine (NT), a PN biomarker, in the RVM. Furthermore, intra-RVM microinjections of the PN decomposition catalyst Fe(III)-5,10,15,20-tetrakis(N-methyl-pyridinium-4-yl)porphyrin (FeTMPyP(5+)) dose-dependently reversed this thermal hyperalgesia. These effects of FeTMPyP(5+) were abrogated by intra-RVM naloxone, implicating potential interplay between PN and opioids. In support, we identified NT colocalization with the endogenous opioid enkephalin (ENK) in the RVM during thermal hyperalgesia, suggesting potential in situ interactions. To address the functional significance of such interactions, we exposed methionine-enkephalin (MENK) to PN and identified the major metabolite, 3-nitrotyrosine-methionine-sulfoxide (NSO)-MENK, using liquid chromatography-mass spectrometry. Next, we isolated, purified, and tested NSO-MENK for opioid receptor binding affinity and analgesic effects. Compared to MENK, this NSO-MENK metabolite lacked appreciable binding affinity for δ, μ, and κ opioid receptors. Intrathecal injection of NSO-MENK in rats did not evoke antinociception, suggesting that PN-mediated chemical modifications of ENK suppress opioid signaling. When extended to chronic pain, intra-RVM FeTMPyP(5+) produced naloxone-sensitive reversal of mechanical allodynia in rats following chronic constriction injury of the sciatic nerve. Collectively, our data reveal the central role of PN in RVM descending facilitation during inflammatory and neuropathic pain potentially through anti-opioid activity.
authors.affiliation: Saint Louis University School of Medicine, Saint Louis, Missouri 63104, USA.
authors.forename: Joshua W
authors.initials: JW
authors.lastname: Little
authors.forename: Zhoumou
authors.initials: Z
authors.lastname: Chen
authors.forename: Timothy
authors.initials: T
authors.lastname: Doyle
authors.forename: Frank
authors.initials: F
authors.lastname: Porreca
authors.forename: Mahsa
authors.initials: M
authors.lastname: Ghaffari
authors.forename: Leesa
authors.initials: L
authors.lastname: Bryant
authors.forename: William L
authors.initials: WL
authors.lastname: Neumann
authors.forename: Daniela
authors.initials: D
authors.lastname: Salvemini
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D039481:CD11b Antigen / Q000378:metabolism; D002351:Carrageenan / Q000009:adverse effects; D002461:Cell Line, Transformed; D002853:Chromatography, Liquid; D002908:Chronic Disease; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D055664:Electrochemical Techniques; D004744:Enkephalin, Methionine / Q000627:therapeutic use; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D006801:Humans; D006930:Hyperalgesia / Q000139:chemically induced / Q000188:drug therapy* / Q000473:pathology; D007278:Injections, Spinal; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects / Q000378:metabolism*; D008665:Metalloporphyrins / Q000627:therapeutic use; D008845:Microinjections; D009457:Neuroglia / Q000378:metabolism; D009474:Neurons / Q000378:metabolism; D018847:Opioid Peptides / Q000378:metabolism*; D010146:Pain / Q000188:drug therapy*; D010147:Pain Measurement; D030421:Peroxynitrous Acid / Q000008:administration & dosage*; D010751:Phosphopyruvate Hydratase / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects; D011869:Radioligand Assay; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects*; D014443:Tyrosine / Q000031:analogs & derivatives / Q000378:metabolism
chemical_list: C492721:5,10,15,20-tetrakis(N-methyl-4'-pyridyl)porphyrinato-iron(III); D039481:CD11b Antigen; D005904:Glial Fibrillary Acidic Protein; D008665:Metalloporphyrins; D018847:Opioid Peptides; D030421:Peroxynitrous Acid; C002744:3-nitrotyrosine; D014443:Tyrosine; D004744:Enkephalin, Methionine; D002351:Carrageenan; D010751:Phosphopyruvate Hydratase