Mechanisms of acupuncture-electroacupuncture on inflammatory pain

Acupuncture, a millennia-old traditional Chinese therapy recommended by the World Health Organization for the treatment of various conditions, has demonstrated notable efficacy in relieving inflammatory pain. This study reviews recent scientific advances in understanding the mechanisms by which acupuncture and electroacupuncture exert their analgesic and anti-inflammatory effects.

Inflammatory pain represents a significant public health problem, especially in developing countries and older populations. Conventional medications, although widely used, often show limited efficacy and substantial adverse effects, including respiratory depression, drug resistance, and chemical dependency with opioids, or unsatisfactory therapeutic benefits with nonsteroidal anti-inflammatory drugs. Acupuncture emerges as a promising alternative due to its substantial analgesic effects and the absence of serious adverse effects, characteristics that have driven its growing worldwide acceptance.

The objective of this review was to systematize and analyze recent scientific evidence on the molecular mechanisms by which acupuncture treats inflammatory pain. The methodology included the analysis of studies published in the last five years using various animal models of inflammatory pain, especially those induced by complete Freund's adjuvant. The investigators examined the effects of manual acupuncture and electroacupuncture at different frequencies and intensities, focusing primarily on point ST-36, although other points such as BL-60, SP-6, and GB-34 were also investigated. The analysis encompassed both the peripheral and central mechanisms involved in pain relief.

The findings revealed that the analgesic effects of acupuncture depend significantly on the stimulation parameters, particularly frequency. For chronic inflammatory pain induced by complete Freund's adjuvant, electroacupuncture at 100 Hz demonstrated greater efficacy, while for acute gouty arthritis and inflammatory muscle pain, the combined 2/100 Hz frequency proved superior. At the peripheral level, acupuncture modulates complex interactions between immune cells and nociceptors. The treatment promotes the activation of regulatory T cells, increasing the production of the anti-inflammatory cytokine interleukin-10, while simultaneously reducing the number of pro-inflammatory macrophages and neutrophils.

In addition, acupuncture regulates purinergic pathways by increasing local levels of adenosine, which binds to specific receptors and inhibits the release of substance P by dorsal root ganglia. The endocannabinoid system also plays a crucial role, with acupuncture activating CB2 receptors on macrophages, promoting autophagy and inhibiting the NLRP3 inflammasome. In the central nervous system, the mechanisms are equally complex, involving multiple neural pathways and neurotransmitters at the spinal and cerebral levels. Acupuncture modulates glutamate receptors, regulates microglial activation, and influences GABAergic interneurons in important brain regions such as the anterior cingulate cortex and the periaqueductal gray matter.

For patients suffering from inflammatory pain, these findings offer encouraging perspectives. The growing scientific understanding of the mechanisms of acupuncture provides a solid basis for its clinical application as an effective and safe treatment. For healthcare professionals, the results suggest that acupuncture can be integrated into conventional therapeutic protocols, potentially reducing reliance on medications with significant adverse effects. The specificity of the stimulation parameters indicates that different inflammatory conditions may benefit from personalized acupuncture protocols, optimizing therapeutic outcomes.

The multiple mechanisms identified also explain why acupuncture demonstrates efficacy not only in pain relief but also in the treatment of frequently associated comorbidities, such as anxiety and depression related to chronic pain.

Despite significant advances in understanding the mechanisms of acupuncture, several important limitations remain. Most studies focus on point ST-36, with limited research on the therapeutic differences between various acupuncture points. In addition, the complex interrelationships between the multiple mechanisms identified have not yet been fully elucidated, particularly the connections between different brain regions involved in pain processing. Future studies should explore these gaps, investigate preventive treatment protocols that have shown superior efficacy, and examine more deeply the correlations between pain relief and improvement of associated emotional symptoms.

The continuation of this line of research promises to further refine our understanding of this ancient therapy, consolidating its place in evidence-based modern medicine.