Role of aquaporin-4 in the development of brain oedema in liver failure.
OBJECTIVE
Liver failure is associated with progressive cytotoxic brain oedema (astrocyte swelling), which underlies hepatic encephalopathy (HE). Ammonia and superimposed inflammation are key synergistic factors in HE, but the mechanism(s) involved remain unknown. We aimed to determine whether aquaporin-4 (AQP4), an astrocyte endfeet bi-directional water channel, is associated with the brain oedema of HE.


METHODS
Rats (n=60) received sham-operation (sham), 5 days hyperammonaemia-inducing diet (HD), galactosamine (GALN) induced acute liver failure (ALF), 4 weeks bile duct-ligation (BDL) induced cirrhosis, or caecal ligation and puncture (CLP), a 24h model of bacterial peritonitis. Rats from every group (except CLP) were randomised to receive intraperitoneal injections of lipopolysaccharide (LPS; 1mg/kg) or saline, prior to termination 3h later. Brain water, AQP4 protein expression (western blot) and AQP4 localisation by immunogold electron microscopy were investigated.


RESULTS
Significant hyperammonaemia was observed in saline-injected BDL (p<0.05), GALN (p<0.01), and HD (p<0.01), compared to sham rats. LPS injection did not affect arterial ammonia or plasma biochemistry in any of the treatment groups. Increased brain water was observed in saline-injected GALN (p<0.05), HD (p<0.01), and CLP (p<0.001) compared to sham rats. Brain water was numerically increased in BDL rats, but this failed to reach significance (p=0.09). LPS treatment further increased oedema significantly in all treatment groups (p<0.05, respectively). AQP4 expression was significantly increased in saline-injected BDL (p<0.05), but not other treatment groups, compared to sham rats. Membrane polarisation was maintained in BDL rats.


CONCLUSIONS
The results suggest that AQP4 is not directly associated with the development of brain oedema in liver failure, hyperammonaemia, or sepsis. In cirrhosis, there is increased AQP4 protein expression, but membrane polarisation, is maintained, possibly in a compensatory attempt to limit severe brain oedema.
Wright
Gavin
G
Institute of Hepatology, University College London, London, UK.
Soper
Robin
R
Brooks
Heather F
HF
Stadlbauer
Vanessa
V
Vairappan
Balasubramaniyan
B
Davies
Nathan A
NA
Andreola
Fausto
F
Hodges
Stephen
S
Moss
Raymond F
RF
Davies
D Ceri
DC
Jalan
Rajiv
R
D000818:Animals; D051401:Aquaporin 4 / Q000378:metabolism*; D015153:Blotting, Western; D001929:Brain Edema / Q000209:etiology* / Q000378:metabolism* / Q000473:pathology; D004195:Disease Models, Animal; D005625:Frontal Lobe / Q000098:blood supply / Q000378:metabolism / Q000473:pathology; D006801:Humans; D022124:Hyperammonemia / Q000150:complications / Q000378:metabolism; D017093:Liver Failure / Q000150:complications* / Q000378:metabolism*; D008297:Male; D016253:Microscopy, Immunoelectron; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar; D018805:Sepsis / Q000150:complications / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
C496032:Aqp4 protein, rat; D051401:Aquaporin 4; D048051:p38 Mitogen-Activated Protein Kinases