INTRODUCTION: Acute-on-chronic liver failure (ACLF) is the result of a dysbalance within the gut-liver axis culminating by the translocation of bacteria and bacterial compounds of the gut barrier. A chronically affected but balanced liver disease status is driven from multidrug-resistant (MDR) Gram-negative bacterial infections to an acute organ failure with high mortality rates.

METHODS: Liver cells (HepG2) and intestinal cells (Caco2) were infected with either Klebsiella pneumoniae ATCC 700603 and two clinical isolates (one MDR) or Acinetobacter baumannii ATCC 19606 and two clinical isolates (one MDR) for 6h hours, each. For identification of toxic effects on liver cells, supernatants were analyzed for secreted cytokines and released metabolites. Using proteome profiler analysis, secretion of cytokines upon infection was brodly analyzed and confirmed by specific ELISAs. Bacterial and host cell metabolites were identified using HPLC/mass spectrometry.

RESULTS: Proteome Profiler assays revealed an increased secretion of the pro-inflammatory cytokines IL-18 and MIF, the anti-inflammatory cytokine IL-13 and the primary inhibitor of tissue-type plasminogen activator SerpinE1. These results were confirmed for MIF and SerpinE1 using ELISA assays. By applying targeted and untargeted metabolomics analysis, the metabolic pathways that are affected during Gram-negative bacterial infection were identified. Fumaric acid, a metabolite of the Krebs cycle, was increased upon infection of liver and intestinal cells, and indole-3-acetic acid, a metabolite derived from aromatic amino acids cycles was increased. Interestingly, uridine and deoxycytidine, both metabolites resulting from nucleic acid metabolism, were increased during A. baumannii infections but decreased upon K. pneumoniae infections.

DISCUSSION: We speculate that the translocation of MDR bacteria or bacterial compounds or metabolites from the gut to the liver is decisive in the development of ACLF. Exact analysis of the role of inflammatory cytokines, bacterial compounds and metabolites might explain the pathogenic mechanisms underlying ACLF and might represent an attractive target for therapeutic intervention.