Acupuncture-moxibustion in treating irritable bowel syndrome: How does it work?

Irritable bowel syndrome (IBS) is a functional gastrointestinal condition affecting between 5% and 20% of the world's population, characterized by abdominal pain, altered bowel habits, and significant impairment in patients' quality of life. This comprehensive review examines the mechanisms by which acupuncture-moxibustion exerts its proven therapeutic effects in the treatment of IBS. The research reveals that this ancient therapy acts simultaneously through multiple regulatory channels, offering a holistic and scientifically grounded approach. The first identified mechanism is regulation of gastrointestinal motility.

Clinical studies have demonstrated that acupuncture produces a beneficial bidirectional regulation, normalizing both intestinal hyperactivity and hypoactivity. In patients with diarrhea-predominant IBS, where peristalsis is excessive, stimulation of points such as ST-36 (Zusanli 足三里) significantly reduced the frequency of borborygmi and colonic peristalsis. Conversely, in cases of constipation where motility is decreased, the same point promoted increased intestinal contraction, demonstrating the adaptive regulatory capacity of the treatment. The second crucial mechanism is modulation of visceral hypersensitivity, one of the main pathophysiologic factors of IBS.

IBS patients have a decreased pain threshold for intestinal stimuli. Transcutaneous electrical stimulation at points such as PC-6 (Neiguan 内关) and ST-36 significantly increased rectal perception thresholds, improving pain sensation and attenuating visceral hypersensitivity. Animal-model experiments confirmed these findings, showing consistent reduction of visceral hyperalgesia after electroacupuncture treatment. The third mechanism involves the complex regulation of the brain-gut axis.

IBS is intimately related to alterations in this bidirectional communication system between the central nervous system and the gastrointestinal tract. Functional neuroimaging studies have revealed that acupuncture modifies brain activation in specific regions involved in visceral pain processing, including the anterior cingulate cortex, prefrontal cortex, and insula. Electroacupuncture at ST-25 (Tianshu 天枢) demonstrated significant reduction in glucose metabolism in brain areas related to visceral pain perception. Regulation of brain-gut peptides represents another fundamental aspect.

Serotonin (5-HT), 95% of which is produced by intestinal enterochromaffin cells, is frequently altered in IBS. Herb-partitioned moxibustion normalized elevated 5-HT levels in patients, while electroacupuncture modulated specific serotonergic receptors and serotonin transporters. Other neuropeptides such as substance P, vasoactive intestinal peptide, and corticotropin-releasing factor were also positively modulated. At the spinal cord level, acupuncture demonstrated the ability to inhibit hyperexcitability of visceral sensory neurons.

Expression of c-fos protein, a marker of nociceptive neuronal activation, was significantly reduced in IBS rats after electroacupuncture. Additionally, phosphorylation of NMDA receptors, involved in maintaining chronic visceral hyperalgesia, was favorably modulated. The enteric nervous system, often called the 'second brain,' is also a therapeutic target. IBS is associated with reduced neurons in the submucosal and myenteric plexuses.

Electroacupuncture demonstrated the ability to increase the number of neurons in these plexuses in constipation-predominant IBS models, contributing to restoration of normal intestinal function. Immune regulation represents another important mechanism. IBS involves immune system activation with alterations in T lymphocytes, immunoglobulins, and inflammatory cytokines. Herb-partitioned moxibustion corrected elevated serum IgM levels in IBS patients and restored abnormal lymphocyte transformation.

Levels of pro-inflammatory cytokines IL-18, IL-23, and TNF-α were significantly reduced after treatment, indicating anti-inflammatory modulation. Intestinal endocrine cells, particularly serotonin-producing enterochromaffin cells, showed normalization after acupuncture. The mean optical density of these cells, frequently elevated in IBS, was significantly reduced with electroacupuncture. Other emerging factors include the regulation of aquaporins, proteins responsible for intestinal water transport, and the free radical system, where acupuncture demonstrated significant increases in superoxide dismutase activity and reduction of lipid peroxidation products.

Current research limitations include the heterogeneity of animal models used, variability in acupuncture protocols, and the need for standardization of interventions. Future studies should focus on developing more representative models of human IBS and on standardizing methods of acupoint stimulation.