Alcohol aggravates IL-6 mediated inflammatory response and hepatic steatosis in a new mouse model of acute-on-chronic liver injury

Background:

Acute-on-chronic liver failure is a severe clinical syndrome of liver characterized by acute decompensation of pre-existing chronic liver injury, often leading to failure of one or more organs with a high short and medium term mortality. Liver injury in ACLF is usually associated with an underlying precipitating event, with bacterial infections and acute alcohol excess being the most frequent triggers.

Aims:

To combine a mouse model with pre-existing chronic liver injury (Abcb4 ^-/-/Mdr2 ^-/-) with the recently standardized ethanol feeding model (NIAAA model Nat Protoc 2013) and to dissect alcohol-induced immune responses in this combined ACLF model.

Methods:

Ten (n = 32) and 15 (n = 32) week-old C57BL/6J and Abcb4 ^-/- mice were either fed control diet (WT/Cont and ABCB4/Cont groups) or liquid ethanol diet (5% v/v), followed by an acute ethanol binge (5 mg/kg) (WT/EtOH and ABCB4/EtOH groups). Liver specific mRNA levels (relative to GAPDH) of IL6, Hgf, Crp and Col3a1 were evaluated using the 2-ΔΔCt method. IL6 and HGF plasma levels were quantified by ELISA. Hepatic collagen contents (hydroxyproline, HYP) and hepatic lipid droplet accumulation and size distributions were determined.

Results:

Hepatic collagen levels, Col3a1 and Crp expression were significantly (p < 0.05) higher in Abcb4 ^-/- mice compared to controls and further increased by ethanol challenge in all mice. In contrast to no further increase of HYP levels between 10 to 15 weeks of age, the older mice in the ABCB4/EtOH group displayed 2- to 4-fold higher IL-6 expression levels vs. 15 week-old ABCB4/Cont (p < 0.01), 15 week-old WT/EtOH (p < 0.001) and the WT/Cont groups (p < 0.001), respectively. This elevation was even more prominent in plasma, reaching a 10-fold increase (p < 0.05) of IL-6 concentrations as compared with the 15 week-old WT/Cont group, whereas HGF did not differ. Hepatic Pnpla3 expression was lowest in Abcb4 ^-/- deficient mice and correlated negatively with mean lipid droplet size.

Conclusions:

We propose a novel promising approach to model alcohol-related acute-on-chronic liver injury. Dysregulation in both immune and metabolic responses was evident by significant alterations in expression of CRP, cytokines (e.g. IL-6), and the critical triacylglycerol hydrolase PNPLA3. Acute inflammatory IL6-driven response might promote the transition from a stable chronic state to progressive liver damage in Abcb4 ^-/- mice. Repression of PNPLA3 resulted in a notable expansion in size of lipid droplets, indicating lipid remodeling in this model.