Implication of the Blood–Brain Barrier in the Physiopathology of Hepatic Encephalopathy in Cirrhosis

Background: Hepatic encephalopathy (HE) is a severe complication of cirrhosis which independently influences prognosis. Pathophysiology of HE is still debated; hyperammonemia in conjunction with inflammation could play a central role. Improvements in cerebral imaging suggest also a vasogenic cerebral edema, suggesting alterations in blood-brain barrier (BBB) permeability. The aim of this work was to study the BBB permeability in rat HE models. Material and methods: The first model of cirrhosis used was bile duct ligation (BDL). Three groups of operated rats were considered: BDL, BDL + hyperammonic diet (“BDL-NH3”) and Sham. We added to each of these groups sodium benzoate (BNa; to activate the non-urea cycle pathway for ammonia removal) or rifaximin (RFX; antibiotic to suppress intestinal flora). HE was assessed using neurocomportemental testing (Open-field test). BBB permeability was assessed by IV injection of a fluorochrome (10 kDa) before trans-cardial washing and decapitation. Fluorescence was estimated by fluorimetry after hemisphere squeezing. To challenge the role of inflammation, we compared BDL to carbon tetrachloride (CCL4)-induced cirrhosis (compared to control rats given mineral oil). The CCL4 rats were given intra-gastric CCL4 twice a week during 8 weeks. Results; Ammonemia was significantly higher in the BDL-NH3 than in BDL rats, and higher in the BDL than in SHAM rats (P < 0.0001). Mean total distance traveled in 6 min was shorter in BDL-NH3 and BDL rats than in SHAM assessing that these animals displayed HE. Intra-cerebral fluorescence was significantly higher in the group BDL-NH3 than in BDL, and higher in BDL than in SHAM (P = 0.029) suggesting a passage of fluorochrome through the BBB. Supplementation in BNa decreased hyperammonemia in the BDL and BDL-NH3 rats (P = 0.032). Interestingly, BNa and RFX decreased intra-cerebral fluorescence in BDL and BDL-NH3 (P = 0.035 and P = 0.103 respectively). It suggests that hyperammonia have a central role in the pathophysiology of HE and that treatment by BNa or RFX could prevent alteration of BBB permeability in HE. When we challenged the BBB in CCL4 rats, we did not observe HE nor differences between intra-cerebral quantity of fluorescence (P = 0.15). These preliminary results suggest that HE could not appear without several factors, among them inflammation. Conclusion: Our results in HE animal models suggest an increased BBB permeability for low weighted molecules by a mechanism dependant on hyperammonemia. Furthermore, pathophysiology of HE depends on several factors, and among them, inflammation could act synergistically. The authors have none to declare.