Effects of External Focused Ultrasound on Inflammatory Markers in Neuropathic Pain Caused by Common Peroneal Nerve Injury

Abstract

INTRODUCTION Various rodent models have long been employed to study treatments for chronic pain. However, these studies have resulted in unsuccessful phase-I and II human trials that have failed to result in viable options for patients. Though limitations of animal models are no doubt one issue, lack of objective markers corresponding with pain relief play a role. Our lab has shown significant pain relief in a common peroneal nerve injury (CPNI) rat model following administration of external pulsed low-intensity focused ultrasound (liFUS), thus, establishing external liFUS as a promising technique for treatment of neuropathic pain. Current knowledge of liFUS effects are limited to observable behavioral changes, and little is known of the mechanism of action. To successfully translate this device into the clinic, we examine molecular changes in the inflammatory cascade. METHODS Male rats underwent CPNI to induce neuropathic pain. External liFUS treatment was performed on the L5 dorsal root ganglion (DRG) in the neuropathic model, which was determined from responses to Von Frey fibers (VFF). 24 h post liFUS treatment, L5 DRGs were obtained from 4 distinct cohorts: rats that underwent CPNI with liFUS, CPNI with sham liFUS, sham CPNI with liFUS, and sham CPNI sham liFUS (n = 4 for each group). Using a membrane-based sandwich immunoassay (Proteome Profiler Rat Cytokine Array Kit from R&D System), we assessed relative abundances of 6 anti-inflammatory cytokines and 16 pro-inflammatory cytokines. RESULTS CPNI resulted in an 82.5% decrease of tumor necrosis factor alpha (TNFa) and a 61.8% increase of macrophage inflammatory protein 1-alpha (MIP-1a). liFUS led to a 60% decrease in MIP-1a and a 40% increase in TNFa. Other changes in cytokines were not affected by CPNI or liFUS. CONCLUSION liFUS resulted in similar changes in TNFa and MIP-1a, as compared to spinal cord stimulation and other medical treatments for pain syndromes. Further work will examine inflammatory responses over time and in female rats.