Transfection of rat cells with proopiomeranocortin gene, precursor of endogenous endorphin, using radial shock waves suppresses inflammatory pain

Abstract

Study design: The effect of proopiomelanocortin (POMC) gene transfer with radial shock waves (RSW) was investigated in vitro and in vivo rat pain models.

Objective: To examine the efficacy of POMC gene transfer with RSW, efficiency of beta-endorphin production in transfected cells, and its effects and side effects in pain models.

Summary of background data: Opioids have been used to treat chronic pain originating from knee osteoarthritis and the lower back; however, several side effects have been reported. Endogenous opioids are safe, but they are not used for clinical treatment because their metabolism is very fast.

Methods: POMC plasmid was produced from pretransformed rat brain cDNA. POMC gene was added to the muscle of rat in vitro and in vivo with RSWs. We assessed beta-endorphin activity using immunohistochemistry. For assessment of pain behavior, we evaluated change in pain score and the level of the inflammatory neuropeptide, calcitonin gene-related peptide (CGRP), after transfection of the POMC gene in an adjuvant induced pain model for 28 days after treatment.

Results: POMC transfected using RSW expressed beta-endorphin at a significantly increased level in muscle cells compared with non-RSW transfection and controls in vitro and in vivo (P < 0.05).Animals showed significant pain sensitivity and increased CGRP expression in dorsal root ganglia neurons in this model; however, these findings decreased for 14 days after transfection of POMC into muscle. There was no significant difference in side effects, such as a change in the level of food pellet intake or constipation, between POMC-treated animals and untreated animals.

Conclusion: POMC transfection with RSW increased beta-endorphin expression in muscle for 14 days, and suppressed pain behavior and CGRP expression in dorsal root ganglia neurons without side effects. This suggested that transfer of POMC by RSW is an effective treatment for inflammatory pain.