Inflammasome Is Activated in the Liver of Cholestatic Patients and Aggravates Hepatic Injury in Bile Duct-Ligated Mouse

Abstract

Background & aims: Inflammation plays an important role in the pathogenesis of cholestatic liver injury, but it is unclear whether the inflammasome is involved and is the objective of this study.

Methods: Gene expression was analyzed in the livers of patients with primary biliary cholangitis (n = 15) and primary sclerosing cholangitis (n = 15). Bile duct ligation (BDL) or sham operation was performed in wild-type (WT) and Caspase-1^-/- (Casp1^-/-) mice for 7 days. Mouse hepatocytes and macrophages were treated with bile acids.

Results: Caspase-1, NLRP1, NLRP3 and IL-1β were significantly increased in the livers of cholestatic patients when compared to healthy control subjects (n = 9). Significantly higher levels of plasma IL-1β (826 vs 345 pg/ml), ALT (674 vs 482 U/L) and ALP (900 vs 622 U/L) were seen in WT BDL mice compared to Casp1^-/- BDL mice. Caspase-1 cleavage was found only in WT BDL livers. Assessment of liver histology indicated more fibrosis in Casp1^-/- BDL mice than in WT BDL mice, confirmed by analyses of liver hydroxyproline content and the expression of fibrotic genes. Profiling of immune cells revealed that there were more macrophages in Casp1^-/- BDL livers than in WT BDL livers. Further macrophage phenotype characterization indicated that Casp1^-/- BDL livers had more M2 anti-inflammatory macrophages evidenced by more CD206 positive cells and higher expression of IL-4, CD163, Fizz1 and IL-33. When mouse hepatocytes and peritoneal macrophages were exposed to cholestatic levels of major endogenous bile acids (300μM TCA), neither IL-1β induction nor procaspase-1 cleavage were detected.

Conclusions: The inflammasome exacerbates cholestatic liver injury, but bile acids do not directly activate the inflammasome.

Keywords: Bile Acids; Cholestasis; Inflammation; Liver Injury.