title: Down-regulation of spinal D-amino acid oxidase expression blocks formalin-induced tonic pain.
abstract: A series of inhibitors of d-amino acid oxidase (DAAO) are specific in blocking chronic pain, including formalin-induced tonic pain, neuropathic pain and bone cancer pain. This study used RNA interference technology to further validate the notion that spinal DAAO mediates formalin-induced pain. To target DAAO, a siRNA/DAAO formulated in polyetherimide (PEI) complexation and a shRNA/DAAO (shDAAO, with the same sequence as siRNA/DAAO after intracellular processing) expressed in recombinant adenoviral vectors were designed. The siRNA/DAAO was effective in blocking DAAO expression in NRK-52E rat kidney tubule epithelial cells, compared to the nonspecific oligonucleotides. Furthermore, multiple-daily intrathecal injections of both siRNA/DAAO and Ad-shDAAO for 7 days significantly inhibited spinal DAAO expression by 50-80% as measured by real-time quantitative PCR and Western blot, and blocked spinal DAAO enzymatic activity by approximately 60%. Meanwhile, both siRNA/DAAO and Ad-shDAAO prevented formalin-induced tonic phase pain by approximately 60%. Multiple-daily intrathecal injections of siRNA/DAAO and Ad-shDAAO also blocked more than 30% spinal expression of GFAP, a biomarker for the activation of astrocytes. These results further suggest that down-regulation of spinal DAAO expression and enzymatic activity leads to analgesia with its mechanism potentially related to activation of astrocytes in the spinal cord.
authors.affiliation: King's Lab, Shanghai Jiao Tong University School of Pharmacy, 800 Dongchuan Road, Shanghai 200240, China.
authors.forename: Xiao-Ling
authors.initials: XL
authors.lastname: Chen
authors.forename: Xin-Yan
authors.initials: XY
authors.lastname: Li
authors.forename: Su-Bo
authors.initials: SB
authors.lastname: Qian
authors.forename: Yan-Chao
authors.initials: YC
authors.lastname: Wang
authors.forename: Pei-Zhuo
authors.initials: PZ
authors.lastname: Zhang
authors.forename: Xian-Jun
authors.initials: XJ
authors.lastname: Zhou
authors.forename: Yong-Xiang
authors.initials: YX
authors.lastname: Wang
mesh_terms: D000698:Analgesia / Q000379:methods*; D000818:Animals; D001253:Astrocytes / Q000201:enzymology / Q000502:physiology; D003605:D-Amino-Acid Oxidase / Q000037:antagonists & inhibitors* / Q000235:genetics; D015536:Down-Regulation; D004847:Epithelial Cells / Q000201:enzymology; D005557:Formaldehyde / Q000494:pharmacology; D007278:Injections, Spinal; D007684:Kidney Tubules / Q000201:enzymology; D008297:Male; D010146:Pain / Q000139:chemically induced / Q000201:enzymology / Q000503:physiopathology*; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000008:administration & dosage / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D013116:Spinal Cord / Q000201:enzymology* / Q000503:physiopathology; D019076:Transgenes
chemical_list: D034741:RNA, Small Interfering; D005557:Formaldehyde; D003605:D-Amino-Acid Oxidase