A theoretical model for ozone therapy in depression treatment: enhancing metabotropic glutamate signaling through controlled oxidative stress

Major depressive disorder is a leading cause of disability globally, affecting millions and imposing significant social and economic burdens.1 Despite the availability of various treatments, a considerable proportion of patients do not respond adequately to conventional therapies, underscoring the need for innovative strategies.2 Neurobiological research has increasingly highlighted the glutamatergic system as a promising target for antidepressant interventions.1,2

Glutamate, the primary excitatory neurotransmitter in the central nervous system (CNS), is crucial for modulating synaptic plasticity, neurogenesis, and cognitive function. Metabotropic glutamate receptors (mGluRs), a subset of glutamate receptors, have gained particular attention for their ability to modulate synaptic activity through slower, more complex mechanisms. Recent preclinical studies suggest that specific mGluR subtypes, such as mGluR2/3 and mGluR5, may exert antidepressant effects by regulating glutamatergic neurotransmission and synaptic plasticity.3,4

We propose that modulated oxidative stress could enhance extracellular glutamate levels, thereby increasing the activation of mGluRs. Exploring the mechanisms through which oxidative stress may modulate glutamate output could open new avenues for neuromodulation, with potential therapeutic implications for depression and other CNS disorders.

In this context, ozone therapy emerges as a promising technique for generating modulated oxidative stress. Already employed for its oxidative and anti-inflammatory properties, ozone therapy could deliver a controlled oxidative pulse that triggers adaptive cellular responses. Preliminary studies indicate that ozone therapy may improve quality of life and reduce depressive symptoms, suggesting a potential neuromodulatory effect. This technique may thus offer a practical approach to activating mGluRs by modulating the antioxidant and glutamatergic systems.

Mechanisms of mGluRs: mGluRs are G-protein-coupled receptors that play significant roles in modulating synaptic transmission and plasticity in the CNS. Their involvement in mood regulation and their potential as targets for antidepressant therapy have been increasingly recognized.2,3 mGluRs, specifically mGlu1, mGlu2/3, and mGlu5, influence glutamatergic neurotransmission through various mechanisms.3 mGlu2/3 modulate glutamatergic transmission primarily through presynaptic inhibition of glutamate release. These receptors, located on presynaptic neurons, postsynaptic neurons, and glial cells, inhibit adenylate cyclase activity via G proteins when activated by glutamate, reducing cyclic AMP reducing glutamate release into the synaptic cleft. Additionally, activation of mGlu2/3 receptors modulates ion channels by inhibiting voltage-gated calcium channels and activating potassium channels, further contributing to the reduction of glutamate release 1.5,6 On postsynaptic neurons, activation of these receptors influences signal transduction, synaptic plasticity, and neuronal excitability. In glial cells, such as astrocytes, mGlu2/3 receptors regulate the release of gliotransmitters and the uptake of glutamate from the synaptic cleft, preventing excitotoxicity. mGlu5 and mGlu1 receptors are primarily located postsynaptically and are coupled to G proteins. When activated they start a cascade resulting in the activation of protein kinase C, which enhances synaptic plasticity and neuronal excitability.6 These receptors are heavily involved in long-term potentiation and long-term depression, which are crucial for learning and memory, particularly in the hippocampus, a brain region crucial for mood regulation and cognitive function. By facilitating long-term potentiation, activation may counteract the synaptic deficits observed in depression. mGluRs have been also implicated in promoting neurogenesis and providing neuroprotective effects and this can help replenish neural populations and restore normal brain function in depressive states.3,4,5,6 By enhancing the activity of these receptors through a controlled oxidative pulse, ozone therapy may offer a non-pharmacological approach to activating mGluRs and promoting neuroprotection and mood stability. The oxidative stimulation may indirectly activate these receptors by modulating glutamate levels, thus providing an innovative pathway for treating depression and other CNS disorders.

Oxidative stress and glutamate output: Oxidative stress occurs when there is an overproduction of reactive oxygen species, potentially damaging cellular components like DNA, proteins, and lipids.7 In response, cells activate antioxidant defenses to restore redox balance, with one key pathway involving the nuclear factor erythroid 2–related factor 2 (Nrf2).8 Under normal conditions, Nrf2 is sequestered in the cytoplasm by Kelch-like ECH-associated protein 1, but during oxidative stress, reactive oxygen species-induced modifications lead to its release. Once free, Nrf2 translocates to the nucleus and binds to antioxidant response elements to activate genes involved in redox homeostasis.9,10

A critical gene regulated by Nrf2 is SLC7A11, encoding the cystine/glutamate antiporter system Xc^–, which exchanges extracellular cystine for intracellular glutamate, supporting both glutathione synthesis and cellular redox balance.7,8,9,10 By upregulating this antiporter, Nrf2 facilitates increased glutamate efflux, which could indirectly modulate synaptic activity through mGluRs. We propose that a controlled oxidative pulse, such as that provided by ozone therapy, could leverage this pathway, activating Nrf2 and enhancing extracellular glutamate levels to influence neuromodulation.

Theoretical model of ozone therapy and glutamate regulation: Ozone therapy, by delivering controlled oxidative stress, temporarily reduces cellular antioxidant levels such as glutathione, triggering the activation of Nrf2.11 This, in turn, stimulates the expression of the cystine/glutamate antiporter, facilitating cystine uptake for glutathione synthesis and supporting redox homeostasis. As a result, extracellular glutamate levels rise, potentially enhancing the activation of presynaptic mGlu2/3 receptors, which modulate glutamatergic transmission and may provide neuroprotective and antidepressant benefits (Figure 1).

Figure 1.

The theoretical model for ozone therapy in depression treatment.

Created with Paintbrush (Apple version) Version 2.6. Keap1: Kelch-like ECH-associated protein 1; mGlu2/3R: metabotropic glutamate receptor; Nrf2: nuclear factor erythroid 2–related factor 2; Xc^–: cystine/glutamate antiporter; γGCS: γ-glutamylcysteine synthetase.

This model suggests that a carefully calibrated oxidative pulse, sub-maximal and administered with a frequency that allows full antioxidant recovery, could serve as an effective neuromodulatory strategy. Unlike traditional “ligand-receptor” mechanisms, this approach envisions cellular responses that are tunable based on the amplitude, frequency, and intensity of the oxidative signal. Further research should focus on validating this approach and refining the parameters for oxidative impulse delivery to optimize cellular and neuroprotective outcomes.

Discussion: The hypothesis that controlled oxidative stress can elevate extracellular glutamate levels, enhancing the activation of mGluRs, represents a novel approach to neuromodulation. This discussion evaluates its potential implications, challenges, and future directions.

Neuromodulation and neuroprotection: The proposed mechanism suggests that oxidative stress, mediated through the activation of Nrf2 and upregulation of the cystine/glutamate antiporter, may increase extracellular glutamate levels and enhance mGlu2/3 receptor activation. This could provide a non-pharmacological means of boosting synaptic plasticity and neuroprotection, with promising applications in depression and neurodegenerative diseases. Ozone therapy, as a source of controlled oxidative stress, could thus be explored as a tool to activate these pathways.

Antidepressant potential: mGlu2/3 and mGlu5 receptors have shown antidepressant effects by regulating synaptic activity and promoting neurogenesis. The ability of ozone therapy to generate controlled oxidative stress and activate these receptors could offer a potential new avenue for treatment-resistant depression, either as a standalone or complementary intervention alongside conventional therapies.

Therapeutic strategy: This hypothesis hinges on the careful application of oxidative stress—sub-maximal reduction of cellular antioxidant levels followed by full recovery. This cyclic oxidative pulse could maximize therapeutic effects while minimizing cellular damage. Further studies are needed to establish protocols for optimizing these cycles in clinical applications.

Experimental validation: Experimental validation remains a key challenge. Initial in vitro studies are essential to observe the effects of oxidative pulses on glutamate output and mGluR activation. Following in vitro findings, in vivo studies in animal models of depression and neurodegeneration will be crucial to assess therapeutic potential and safety.

Safety and calibration: While low oxidative stress can trigger beneficial adaptive responses, excessive levels pose risks of cellular damage and apoptosis. Precise calibration and monitoring are therefore essential to safely harness oxidative stress in therapeutic contexts. More studies are needed to precisely define the individual susceptibility to oxidative stress (linked to antioxidant levels or genetic predisposition) with the aim to personalize the therapy. However, therapeutics protocol studied for ozone therapy keeps oxidative stress far from toxicity level, allowing a safe and secure tapering.

Quantification and monitoring: For practical application, quantifying oxidative pulses and establishing recovery periods are essential. Developing real-time biomarkers and imaging techniques to monitor oxidative stress and glutamate levels could enhance both the precision and feasibility of this approach. Currently, there are no standards available to quantify the levels of response to oxidative stimuli; further studies are necessary to define new standards, which will be critical for ensuring consistency and reliability in both research and clinical applications.

Combination with pharmacological treatments: As a non-pharmacological strategy, oxidative stress modulation through ozone therapy could either stand alone or complement existing treatments. Exploring the synergies between this approach and pharmacological agents may facilitate comprehensive treatment protocols for neuropsychiatric and neurodegenerative conditions.

In summary, this perspective suggests that ozone therapy may offer a unique, non-invasive means of activating mGluRs through oxidative modulation. Further research should aim to optimize this approach and verify its efficacy and safety in clinical settings.

This study is based on a theoretical model that lacks experimental validation. While preclinical data support the role of oxidative stress in modulating glutamatergic signaling, direct evidence linking ozone therapy to mGluR activation remains limited. Experimental studies are needed to confirm if controlled oxidative pulses from ozone can effectively modulate extracellular glutamate and activate mGlu2/3 and mGlu5 receptors.

Additionally, individual variability in response to oxidative stress, including differences in antioxidant capacity and genetic factors, may influence outcomes. Establishing the precise dose and frequency for ozone therapy that maximizes benefits while minimizing cellular damage is a key challenge. Safety concerns regarding potential oxidative damage underscore the need for careful calibration and monitoring.

Finally, the interactions between ozone therapy and existing treatments for depression and neurodegenerative diseases remain unexplored. Future studies should investigate these combinations to optimize therapeutic protocols.

Conclusion: This perspective proposed a theoretical model to explore the possibility of interacting with cells through signals generated by targeted and modulated oxidative stimuli. The model suggests that such interactions could enhance glutamate efflux and activate metabotropic receptors, potentially leading to neuromodulatory effects. However, the inherent limitations of the theoretical model, such as the lack of experimental validation and the potential influence of unaccounted variables, necessitate a cautious interpretation of these findings.

As such, the results presented here should not be taken as support for immediate clinical applications or definitive conclusions. Instead, they should be regarded as preliminary hypotheses that require rigorous experimental validation through future in vitro and in vivo studies. While the clinical implications proposed may appear promising, they remain speculative at this stage and are far from practical applicability.

We aim for this work to serve as a foundation for future research, sparking discussion and experimental exploration to validate the mechanisms proposed. This approach has the potential to open new avenues in neurology and pharmacology, but further evidence will be necessary to substantiate its relevance and practical applications.