Figure 1.

Proposed gut–inner ear axis resulting in sensorineural hearing loss (SNHL). (1) Gut dysbiosis induced by a high-fat diet can damage the intestinal barrier and cause a leaky gut. (2) This allows gut microbiota and bacterial toxins such as lipopolysaccharide to infiltrate the bloodstream and cause a systemic inflammatory response. (3) Pathogens and inflammatory cytokines reaching the inner ear can damage the blood–labyrinth barrier (BLB). (4) Infiltration of pathogens to the inner ear leads to the activation of resident macrophages, the release of pro-inflammatory cytokines, and the overproduction of reactive oxygen species (ROS), causing apoptosis of damaged cells and immune cell infiltration in the lateral wall of the cochlea (spiral ligament and stria vascularis). Inflammatory processes in the cochlea might further increase the BLB’s permeability, perpetuating inflammation. Unresolved inflammation leads to damage of sensorineural structures, eventually causing SNHL. Abbreviations: EC, endothelial cell; TJ, tight junction; BM, basement membrane; PVM/M, perivascular-resident macrophage-like melanocytes.