Intervertebral Foramen Injection of Ozone Relieves Mechanical Allodynia and Enhances Analgesic Effect of Gabapentin in Animal Model of Neuropathic Pain

Abstract
Background
A five-year follow-up study in a hospital in southern China demonstrated that intervertebral foramen (IVF) injection of ozone at affected segmental levels significantly alleviated paroxysmal spontaneous pain and mechanical allodynia in patients with chronic, intractable postherpetic neuralgia (PHN), improving their quality of life. However, no proof-of-concept animal studies have been conducted to date.

Objective
This study aimed to investigate whether IVF ozone injection has analgesic effects in animal models of neuropathic and inflammatory pain.

Study Design
An experimental trial in rats.

Setting
Institute for Biomedical Sciences of Pain.

Methods
Male Sprague-Dawley rats in naïve, inflammatory, or neuropathic pain states were administered IVF injections of either a 50 µL ozone-oxygen mixture (30 µg/mL) or 50 µL air. Inflammatory pain was induced via bee venom or complete Freund’s adjuvant, while neuropathic pain was modeled using spared nerve injury. Pain-related behaviors were assessed for up to one month. Additionally, the combined effects of IVF ozone and systemic gabapentin (100 mg/kg) were evaluated in neuropathic pain rats five days post-ozone treatment. Finally, the long-term analgesic effects of four molecular-targeted drugs—AMD3100 (CXCR4 antagonist), A-803467 (Nav1.8 blocker), rapamycin (mTOR inhibitor), and MGCD0103 (histone deacetylase inhibitor)—were assessed following IVF injection.

Results
IVF ozone injection at L4-5 effectively reduced mechanical allodynia in neuropathic pain rats but had no effect on inflammatory pain.
The analgesic effects of IVF ozone lasted over 14 days, significantly longer than those of molecular-targeted drugs, which lasted less than 48 hours.
Combined administration of systemic gabapentin and IVF ozone produced a synergistic analgesic effect in neuropathic pain rats.
Limitations
This study did not evaluate the analgesic effects of intraplantar ozone injection.

Conclusions
For the first time, this study provides evidence that IVF ozone injection selectively relieves neuropathic pain, with prolonged effects and enhanced efficacy when combined with gabapentin. However, it does not alleviate inflammatory pain.