A mouse model of hepatic encephalopathy: bile duct ligation induces brain ammonia overload, glial cell activation and neuroinflammation

Abstract

Hepatic encephalopathy (HE) is a common complication of chronic liver disease, characterized by an altered mental state and hyperammonemia. Insight into the brain pathophysiology of HE is limited due to a paucity of well-characterized HE models beyond the rat bile duct ligation (BDL) model. Here, we assess the presence of HE characteristics in the mouse BDL model. We show that BDL in C57Bl/6j mice induces motor dysfunction, progressive liver fibrosis, liver function failure and hyperammonemia, all hallmarks of HE. Swiss mice however fail to replicate the same phenotype, underscoring the importance of careful strain selection. Next, in-depth characterisation of metabolic disturbances in the cerebrospinal fluid of BDL mice shows glutamine accumulation and transient decreases in taurine and choline, indicative of brain ammonia overload. Moreover, mouse BDL induces glial cell dysfunction, namely microglial morphological changes with neuroinflammation and astrocyte reactivity with blood–brain barrier (BBB) disruption. Finally, we identify putative novel mechanisms involved in central HE pathophysiology, like bile acid accumulation and tryptophan–kynurenine pathway alterations. Our study provides the first comprehensive evaluation of a mouse model of HE in chronic liver disease. Additionally, this study further underscores the importance of neuroinflammation in the central effects of chronic liver disease.

Experimental hepatic encephalopathy causes early but sustained glial transcriptional changes

“…Confirming earlier data [ 24 ], no significant differences were detected in the percentage of microglia and astrocytes in BDL mice at either timepoint compared to sham controls, indicating there is no apparent glial cell death nor proliferation (Fig. 1 B, C).…”

“…1 A). These timepoints were chosen as microglial morphological changes are apparent in BDL mouse brains 14 days after induction, while astrocyte reactivity becomes morphologically apparent 28 days after induction [ 24 ]. After exclusion of debris, doublets and dead cells, microglia were defined as CD45 lo-int CD11b + cells.…”

“…There are relatively few animal models that recapitulate core HE characteristics in the setting of CLD [ 23 ]. We recently evaluated the characteristics of the mouse bile duct ligation (BDL) model, an archetypical model for secondary biliary cirrhosis, observing hyperammonemia and increased cerebrospinal fluid (CSF) glutamine from 14 days after induction [ 24 ]. Interestingly, we have shown that both astrocytes and microglia exhibit morphological changes in this model, with microglial arborization decreasing from 14 days after injury and astrocyte arborization significantly increasing 28 days after injury.…”

“…However, morphological assessment does not reveal all aspects of the underlying cell state, as it is becoming increasingly clear that in different diseases, both morphologically reactive astrocytes [ 26 ] and microglia [ 27 ] exhibit various underlying molecular states. Importantly, in our previous work, the expression of astrocyte reactivity marker genes was increased before morphological changes were apparent, raising the question whether molecular alterations precede morphological ones [ 24 ]. Determination of the underlying cell state could provide insights and possible therapeutic targets for further study in preclinical HE.…”

The Glymphatic System May Play a Vital Role in the Pathogenesis of Hepatic Encephalopathy: A Narrative Review

“…The exact pathophysiological mechanisms of HE are not fully understood. However, numerous studies have demonstrated that HE has complex pathology at the cellular molecular levels, e.g., astrocyte dysfunction plays a critical role in the pathogenesis of both forms of HE (i.e., ALF and CLD) [ 4 , 5 , 6 , 7 , 8 , 9 ]. Furthermore, substances including ammonia, glutamine, glutamate, aromatic amino acids, lactate, alanine, bile acids, and neurosteroids accumulate in the brain parenchyma during HE [ 10 , 11 , 12 ] and are directly implicated in the pathogenesis.…”