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: Xiao-Ling Chen, Xin-Yan Li, Su-Bo Qian, Yan-Chao Wang, Pei-Zhuo Zhang, Xian-Jun Zhou, Yong-Xiang Wang
• Journal: Biochemical and biophysical research communications (Biochem Biophys Res Commun) Vol. 421 Issue 3 Pg. 501-7 (May 11 2012) ISSN: 1090-2104 [Electronic] United States
• PMID: 22521889 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2012 Elsevier Inc. All rights reserved.

Chemical References

• RNA, Small Interfering
• Formaldehyde
• D-Amino-Acid Oxidase

Topics

• Analgesia (methods)
• Animals
• Astrocytes (enzymology, physiology)
• D-Amino-Acid Oxidase (antagonists & inhibitors, genetics)
• Down-Regulation
• Epithelial Cells (enzymology)
• Formaldehyde (pharmacology)
• Injections, Spinal
• Kidney Tubules (enzymology)
• Male
• Pain (chemically induced, enzymology, physiopathology)
• RNA Interference
• RNA, Small Interfering (administration & dosage, genetics)
• Rats
• Rats, Sprague-Dawley
• Spinal Cord (enzymology, physiopathology)
• Transgenes