GENE GUN PARTICLE ENCODING PREPROENKEPHALIN cDNA PRODUCES ANALGESIA AGAINST CAPSAICIN- INDUCED BLADDER PAIN IN RATS YAO-CHI CHUANG, L.-C. YANG, PO-HUI CHIANG, HONG-YO KANG, WEN-LUNG MA, P.-C. WU, FERNANDO DEMIGUEL, MICHAEL B. CHANCELLOR, AND NAOKI YOSHIMURA ABSTRACT Objectives. To evaluate the efficacy of gene therapy using a gene gun or direct injection for the transfer of human preproenkephalin (PPE) plasmid cDNA using a capsaicin-induced bladder pain model in rats. Opioid peptides play an essential role in the modulation of micturition reflex and control of inflammatory pain. PPE is one such precursor molecule. Methods. Human PPE cDNA was cloned into a modified pCMV plasmid and delivered into the bladder wall of adult female rats by direct injection or gene gun. At 4 and 7 days after gene therapy, continuous cystometrograms were performed under urethane anesthesia by filling the bladder (0.08 mL/min) with saline, followed by 15 M capsaicin. Immunohistochemical staining was used to detect enkephalins in the bladder after PPE cDNA transfer. Results. The intercontraction interval was decreased after intravesical instillation of capsaicin (65.0% and 63.1% decrease) in the control group or direct PPE gene injection group, respectively. However, the gene gun-treated group showed a significantly reduced response to capsaicin instillation at day 4 and day 7 (intercontraction interval 16.2% and 42.8% decrease, respectively). This analgesic effect was reversed by intravenous naloxone, an opioid antagonist (5 mg/kg). Increased enkephalin immunoreactivity in the bladder was observed in the gene gun-treated group at day 4, which was reduced at day 7. Conclusions. The PPE gene can be effectively transferred and suppress the nociceptive response in the bladder using the gene gun method. These results support potential clinical application of PPE gene gun delivery system for the treatment of bladder pain and other types of visceral pain. UROLOGY 65: 804–810, 2005. © 2005 Elsevier Inc. I nterstitial cystitis (IC) is a chronic inflammatory disease of the bladder characterized by bladder pain, frequency, and urgency without obvious pathologic factors. Although its etiology is poorly understood, it is hypothesized that the final com- mon pathway of IC is activation of subepithelial afferent nerves with provoked bladder pain and a hypersensitive bladder. 1,2 Various modes of thera- pies for IC are available; however, current methods have had limited clinical effects on this frustrating disease. 3 Thus, it is imperative to develop new therapies for those with refractory IC and bladder pain. Previous studies have shown that endogenous and exogenous opioid peptides can interact with receptors on sensory nerves to inhibit nociceptive responses during inflammation, as well as suppres- sion of micturition. 4,5 Peripherally acting opioid agonists, unable to cross the blood-brain barrier and devoid of central side effects such as respira- tory depression, 6 could be developed for the atten- uation of nociception and treatment of painful bladder conditions. This peripheral endogenous opioid-mediated analgesia could possibly be in- duced by implantation of a therapeutic painkiller gene to control the inflammatory pain, such as This study was supported by NIH grant R21 DK066095 and Tai- wan-NSC grant 93-2314-B-182A-195 and CMRPG 8021. From the Departments of Urology and Anesthesiology, and Center for Menopause and Reproductive Medicine Research, Chang Gung Memorial Hospital, Kaohsiung, Taiwan; and De- partment of Urology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania Reprint requests: Michael B. Chancellor, M.D., Department of Urology, University of Pittsburgh School of Medicine, 3471 Fifth Avenue, Kaufmann Building, Suite 700, Pittsburgh, PA 15213. E-mail: chancellormb@msx.upmc.edu Submitted: July 12, 2004, accepted (with revisions): October 28, 2004 BASIC SCIENCE © 2005 ELSEVIER INC. 0090-4295/05/$30.00 804 ALL RIGHTS RESERVED doi:10.1016/j.urology.2004.10.070