Gut Microbiota and Their Metabolites in Acute Kidney Injury: Classification, Mechanisms, and Therapeutic Potential

Acute kidney injury (AKI) is a common critical syndrome with high morbidity and mortality, and a subset of patients may progress to chronic kidney disease. Recent studies have revealed that gut microbiota and their metabolites play pivotal roles in the pathogenesis of AKI. Under AKI conditions, the gut microbiota composition undergoes significant alterations, characterized by decreased beneficial bacteria and expansion of opportunistic pathogens, accompanied by impaired intestinal barrier and disordered microbial metabolism. Gut microbiota metabolites can be classified into protective metabolites (short-chain fatty acids, secondary bile acids, tryptophan metabolites, D-amino acids, and polyamines) and toxic metabolites (indoxyl sulfate, p-cresyl sulfate, trimethylamine N-oxide, and endotoxin). The former exert renoprotective effects through anti-inflammatory, antioxidant, and barrier-maintaining mechanisms, while the latter aggravate kidney injury via oxidative stress, inflammation activation, and hemodynamic disturbance. Based on the gut–kidney axis theory, interventions targeting gut microbiota (probiotics, prebiotics, fecal microbiota transplantation) and those targeting metabolites (supplementation of protective metabolites, removal of toxic metabolites) have shown promising prospects. This narrative review summarizes the characteristics of gut microbiota changes, classification and function of key metabolites, core mechanisms driving AKI, and microbiota-based intervention strategies, aiming to provide novel insights for early recognition and precision prevention of AKI.