Ozone Therapy Facilitates Macrophage Efferocytosis and Reduces Neuropathic Pain via AMPK/Gas6-MerTK/SOCS3 Pathway

Study Background and Research Question

Neuropathic pain (NPP) is a chronic, multifaceted condition resulting from nerve injury or disease, affecting 7–10% of the population and posing significant therapeutic challenges. Conventional pharmacological treatments—including antidepressants, anticonvulsants, and opioids—offer limited efficacy and often introduce adverse effects, driving the search for novel interventions. One central pathogenic mechanism in NPP is the accumulation of apoptotic cells and the persistent neuroinflammation they trigger. The referenced study by Ruan et al. (Frontiers in Immunology, 2024) addresses whether promoting macrophage efferocytosis—the clearance of apoptotic cells—can attenuate pain and neuroinflammation, and examines ozone therapy as a mechanism-based strategy to achieve this effect.

Key Innovation from the Reference Study

The principal innovation lies in identifying ozone as an agent capable of upregulating macrophage efferocytosis through a defined signaling cascade—AMPK activation leading to Gas6 upregulation, MerTK receptor activation, and subsequent induction of SOCS3. This pathway collectively enhances the ability of bone marrow-derived macrophages (BMDMs) to clear apoptotic neutrophils, thereby reducing neuroinflammation and neuropathic pain. The study provides mechanistic clarity by demonstrating that inhibition of either AMPK or MerTK abrogates the beneficial effects of ozone, establishing the pathway's necessity (reference).

Methods and Experimental Design Insights

The researchers employed a chronic constriction injury (CCI) mouse model to mimic neuropathic pain. Mice were administered ozone at graded concentrations (15 mg, 30 mg, 45 mg) to determine dose-responsiveness regarding pain relief and apoptotic cell clearance. Mechanical hypersensitivity—a proxy for neuropathic pain—was quantified using established behavioral assays.

In vitro, the phagocytic capacity of BMDMs towards apoptotic neutrophils was evaluated after ozone treatment. Critical pathway components were interrogated using pharmacological inhibitors: Compound C (an AMPK inhibitor) and UNC2541 (a MerTK inhibitor) were applied to dissect the signaling mechanism. The expression of Gas6, Protein S, MerTK, SOCS3, and inflammatory cytokines (IL-1β, IL-6, TNF-α) was measured using quantitative PCR and immunoblotting to provide molecular resolution of the pathway dynamics.

Protocol Parameters

• Ozone treatment: 30 mg concentration showed maximal effect on pain alleviation and efferocytosis in CCI mice; lower (15 mg) and higher (45 mg) concentrations were comparatively less effective.
• Pharmacological inhibition: Use of Compound C and UNC2541 at doses sufficient to inhibit AMPK and MerTK, respectively, to validate pathway specificity.
• Behavioral assays: Mechanical hypersensitivity measured at defined timepoints post-injury and post-treatment; ensure consistent animal handling and blinding for reliable results.
• In vitro efferocytosis assay: BMDMs co-cultured with labeled apoptotic neutrophils, followed by quantification of phagocytic index using fluorescence microscopy.
• Molecular analysis: Quantitative PCR and immunoblotting for pathway components and cytokines; standardize sample collection timepoints post-treatment.

Core Findings and Why They Matter

The study found that ozone at 30 mg notably reduced mechanical hypersensitivity in CCI mice—indicative of analgesic action. This effect correlated with enhanced clearance of apoptotic neutrophils by BMDMs. Mechanistically, ozone activated AMPK, which selectively upregulated Gas6 (without affecting Protein S), leading to MerTK activation and downstream SOCS3 induction. SOCS3, in turn, suppressed the expression of pro-inflammatory cytokines (IL-1β, IL-6, TNF-α), consistent with reduced neuroinflammatory signaling.

Importantly, the use of pathway inhibitors demonstrated that both AMPK and MerTK are essential for ozone’s benefits, as inhibition abolished the effects on efferocytosis and pain relief. These findings position macrophage efferocytosis and its regulatory axis as actionable targets for pain modulation, moving beyond symptomatic management to address a root pathogenic process (reference).

Comparison with Existing Internal Articles

Internal literature, such as "Ozone Stimulates Macrophage Efferocytosis to Relieve Neuropathic Pain" and "Ozone Enhances Macrophage Efferocytosis to Alleviate Neuropathic Pain", corroborate the mechanistic links between apoptotic cell clearance and neuroinflammatory resolution. However, the present reference study distinguishes itself by providing detailed pathway validation using pharmacological inhibitors, thus offering higher mechanistic resolution. While the internal articles describe the general link between ozone and efferocytosis, the current research clarifies the necessity of the AMPK/Gas6-MerTK/SOCS3 axis.

Further, while not directly focused on pH regulation, the methods employed in this study align with workflows described in resources such as "BCECF: Ratiometric pH Sensing for Ion Transport and Metabolism" and "BCECF in Microenvironmental pH Regulation: Principles to Precision Practice", which outline the use of advanced fluorescent pH probes for monitoring microenvironmental changes during immune cell function and signaling. The intersection between apoptotic cell clearance and microenvironmental pH regulation represents an emerging area for future research, especially given the known impact of pH on immune cell behavior.

Limitations and Transferability

While the study robustly demonstrates the role of ozone in modulating efferocytosis and alleviating neuropathic pain in the CCI mouse model, some limitations remain. The transferability to human neuropathic pain must be approached with caution, as ozone dosing, immune cell responses, and pain pathways may differ between species. Additionally, the study focuses on a specific form of neuropathic pain induced by nerve injury; whether similar benefits extend to other etiologies of chronic pain remains to be tested. The safety and practicality of ozone therapy in clinical contexts also require further validation.

Moreover, while the pathway analysis is comprehensive, other signaling routes may contribute to the observed effects, and off-target impacts of ozone cannot be fully excluded based on the present data. Long-term outcomes and potential immune modulation beyond the acute phase were not addressed.

Research Support Resources

For researchers aiming to investigate related mechanisms—such as immune cell function, apoptotic cell clearance, or microenvironmental pH regulation in models of neuroinflammation—quantitative extracellular pH measurement is often essential. BCECF (2',7'-bis(carboxyethyl)-5(6)-Carboxyfluorescein) (SKU C5694) is a well-established, ratiometric fluorescent pH probe for ion transport studies and microenvironmental pH regulation assays. Its membrane-impermeant nature and dual-excitation design enable precise monitoring of extracellular acid-base changes in immune and neural tissues, supporting workflows analogous to those used in the referenced study. For detailed protocols and best practices in pH-sensitive probe application, consult internal resources such as "BCECF (2',7'-bis(carboxyethyl)-5(6)-Carboxyfluorescein): Reliable pH Sensing for Biomedical Research". BCECF is available from APExBIO for integration into advanced neuroinflammation and immune cell research workflows.