title: In-vivo transfection of the proopiomelanocortin gene, precursor of endogenous endorphin, by use of radial shock waves alleviates neuropathic pain.
abstract: BACKGROUND
  Neuropathic pain is difficult to control and patient response to current treatment is often inadequate. Opioids have been widely used to treat a variety of pain states, but have several side effects. Endogenous opioids are clinically safe, but are not used for treatment because of rapid metabolism. However, in-vivo transfection of endogenous opioid genes could have a powerful and safe analgesic effect. The purpose of this study was to investigate the efficacy of proopiomelanocortin (POMC, a precursor of the endogenous opioid peptide β-endorphin) gene transfer by use of radial shock waves (RSWs) in a rat neuropathic pain model.
  
  
  METHODS
  As a neuropathic pain model, we used the Bennett chronic constriction injury (CCI) method. Immediately after CCI induction, POMC plasmid was injected into the rats' gastrocnemius muscle followed by exposure to RSW. Mechanical allodynia was measured for 4 weeks and dorsal root ganglion (DRG) neurons were sectioned and immunostained.
  
  
  RESULTS
  β-Endorphin blood levels and the number of β-endorphin-immunoreactive (IR) muscle fibers increased over 28 days. β-Endorphin overexpression caused a decrease in the number of calcitonin gene-related peptide (CGRP)-IR DRG neurons and suppressed neuropathic pain induced by CCI without causing adverse side effects. The size-distribution pattern of CGRP-IR DRG neurons shifted from small to large cells in the CCI group; however, the number of both small and large CGRP-IR cells decreased in the POMC group.
  
  
  CONCLUSIONS
  POMC gene transfection alleviated allodynia and reduced CGRP expression in DRG neurons without adverse effects. CGRP is not produced in large neurons under physiologic conditions; however, in this study CGRP expression was shifted to large neurons after nerve injury. This change in cell-size distribution suggests that CGRP expression in large neurons is related to neuropathic pain. These findings suggest that POMC gene transfection using RSWs is a safe and effective treatment for neuropathic pain.
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, 1-8-1 Inohana, Chuo-ku, Chiba 260-8670, Japan. ishikawa_tetsuhiro@yahoo.co.jp
authors.forename: Tetsuhiro
authors.initials: T
authors.lastname: Ishikawa
authors.forename: Masayuki
authors.initials: M
authors.lastname: Miyagi
authors.forename: Masaomi
authors.initials: M
authors.lastname: Yamashita
authors.forename: Hiroto
authors.initials: H
authors.lastname: Kamoda
authors.forename: Yawara
authors.initials: Y
authors.lastname: Eguchi
authors.forename: Gen
authors.initials: G
authors.lastname: Arai
authors.forename: Miyako
authors.initials: M
authors.lastname: Suzuki
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Sakuma
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Oikawa
authors.forename: Sumihisa
authors.initials: S
authors.lastname: Orita
authors.forename: Gen
authors.initials: G
authors.lastname: Inoue
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Ozawa
authors.forename: Yasuchika
authors.initials: Y
authors.lastname: Aoki
authors.forename: Tomoaki
authors.initials: T
authors.lastname: Toyone
authors.forename: Kazuhisa
authors.initials: K
authors.lastname: Takahashi
authors.forename: Atsushi
authors.initials: A
authors.lastname: Yamaguchi
authors.forename: Seiji
authors.initials: S
authors.lastname: Ohtori
mesh_terms: D000818:Animals; D009437:Neuralgia / Q000628:therapy*; D059408:Pain Management / Q000379:methods*; D055585:Physical Phenomena; D011333:Pro-Opiomelanocortin / Q000235:genetics*; D011846:Radio Waves; D051381:Rats; D014162:Transfection / Q000379:methods*; D001615:beta-Endorphin / Q000235:genetics
chemical_list: D001615:beta-Endorphin; D011333:Pro-Opiomelanocortin