Hepatic Inflammation and Liver Injury in a Model of Bacterial Infection Triggered Acute-on-Chronic Liver Injury

Acute-on-chronic liver failure (ACLF) is characterized by acute decompensation of chronic liver disease in the presence of an acute trigger, and bacterial infection (BI) is the most common trigger of ACLF. Therefore, we aimed to establish a mouse model that mimics bacterial infection-related acute-on-chronic liver failure (BI-ACLF) to study the ongoing pathophysiological processes during disease progression.

Wild-type C57BL/6J (n = 12; wild-type, WT) and Abcb4^-/- (n = 12; knockout, KO) with underlying chronic fibrosing liver disease were intraperitoneally injected either with 0.9% NaCl or 4-mg/kg lipopolysaccharide (LPS) to establish four experimental groups, namely, a control group (WT-NaCl), an acute injury group (WT-LPS), a chronic liver disease group (KO-NaCl), and an acute-on-chronic group (KO-LPS). Hepatic expressions (relative to Gapdh) of Il-6, Crp, Tnf-α, Rantes, Tlr4, Mcp1, Il-10, Il-2, Il-22, Il-17a, and Tgf-β were quantified by the 2^-ΔΔCt method. Liver injury and inflammation were evaluated by Sirius red and H&E stainings, respectively. Immunohistochemical stainings were used to assess apoptosis (Ck-18 and H2Ax), necrosis (Cas-1 and Hmgb-1), and macrophage polarization (M1 markers CD64 and CD86; M2 markers CD206 and Arg1). M1 markers (CD64 and CCR7) and M2 markers (CD163 and Arg1) were further analyzed by western blot analysis.

Hepatic cytokines and chemokines, monocyte chemoattractant protein-1 (Mcp-1), interleukins Il-2, Il-22, and regulated on activation, normal T-cell expressed and secreted (Rantes) were significantly upregulated in mice of KO-LPS groups compared to their counterparts. Induction of pyroptosis, apoptosis, and macrophage polarization towards the M1 phenotype was evident.

Differential expression of hepatic cytokines and chemokines in Abcb4^-/- mice upon LPS challenge provides insight into potential mediators of disease progression in this dual-hit model of BI-ACLI. Our findings suggest that increased expression of IL-6, IL-2, IL-22, and RANTES may be associated with inflammatory responses that contribute to disease exacerbation in this refined model.