Metabolomic interplay between gut microbiome and plasma metabolome in cardiac surgery‐associated acute kidney injury

Cardiac surgery-associated acute kidney injury (CSA-AKI) is a prevalent complication of cardiac surgery, which may be associated with a great risk of developing chronic kidney disease and mortality. This study aimed to investigate the possible links between gut microbiota metabolism and CSA-AKI.A prospective cohort of patients who underwent cardiac surgery was continuously recruited, who were further divided into CSA-AKI group and Non-AKI group based on clinical outcomes. Their faecal and plasma samples were collected before surgery and were separately analysed by nontargeted and targeted metabolomics. The differential metabolites related to CSA-AKI were screened out using statistical methods, and altered metabolic pathways were determined by examining the Kyoto Encyclopedia of Genes and Genomes database.Nearly 1000 faecal metabolites were detected through high-resolution mass spectrometry (MS) and bioinformatics at high and mid confidence levels, and 49 differential metabolites at high confidence level may perform essential biological functions and provide potential diagnostic indicators. Compared with the Non-AKI group, the patients in the CSA-AKI group displayed dramatic changes in gut microbiota metabolism, including amino acid metabolism, nicotinate and nicotinamide metabolism, purine metabolism and ATP-binding cassette (ABC) transporters. Meanwhile, 188 plasma metabolites were identified and quantified by tandem MS, and 34 differential plasma metabolites were screened out between the two groups using univariate statistical analysis. These differential plasma metabolites were primarily enriched in the following metabolic pathways: sulphur metabolism, amino acid biosynthesis, tryptophan metabolism and ABC transporters. Furthermore, the content of indole metabolites in the faecal and plasma samples of the CSA-AKI group was higher than that of the Non-AKI group.Patients with CSA-AKI may have dysbiosis of their intestinal microbiota and metabolic abnormalities in their gut system before cardiac surgery. Thus, some metabolites and related metabolic pathways may be potential biomarkers and new therapeutic targets for the disease.