Acupuncture regulating the gut-brain axis for postoperative ileus: Neuroimmune mechanisms and clinical translation prospects

Figure 1 Schematic diagram illustrating the mechanism by which acupuncture enhances gastrointestinal motility via the gut-brain axis. This figure depicts the multi-pathway mechanism of acupuncture: ① Acupuncture stimulation suppresses the overactivity of the hypothalamic-pituitary-adrenal axis, reducing glucocorticoid levels, thereby disinhibiting gastrointestinal motility; ② Simultaneously, the acupuncture signal is transmitted to the central nervous system via afferent nerves for integration, which enhances vagus nerve activity and promotes the release of acetylcholine (ACh); ③ ACh acts directly on enteroendocrine cells to upregulate the levels of motilin and gastrin, directly promoting gastrointestinal motility; ④ Furthermore, ACh inhibits macrophage function, reducing pro-inflammatory cytokine levels; ⑤ The decrease in pro-inflammatory cytokines attenuates their suppressive effect on inhibitors of gastrointestinal motility, such as vasoactive intestinal peptide and nitric oxide, thereby indirectly promoting motility; ⑥ This anti-inflammatory environment further helps to increase the abundance of beneficial gut bacteria; ⑦ Short-chain fatty acids produced by beneficial bacterial metabolism enhance the function of regulatory T cells, which in turn feedback to inhibit macrophages, forming a positive feedback loop that consolidates the anti-inflammatory effect; and ⑧ Finally, the enhanced gastrointestinal motility also helps to improve the intestinal environment, promoting the colonization and growth of beneficial bacteria, thereby completing a virtuous cycle. Solid arrow indicates activation or promotion; T-bar arrow indicates inhibition. Created with Figdraw (Supplementary material). HPA: Hypothalamic-pituitary-adrenal; Ach: Acetylcholine; EECs: Enteroendocrine cells; Treg: Regulatory T cell; SCFAs: Short-chain fatty acids; MTL: Motilin; GAS: Gastrin; VIP: Vasoactive intestinal peptide; NO: Nitric oxide.