Marykate Killilea
National university of Ireland, Galway, Ireland
Final year PhD student in the National University of Ireland, Galway under the supervision of Professor Antony Wheatley
A strong association has been established between psychological stress and death due to liver disease. In addition, the endocannabinoid (EC) system has been identified as a key player in several acute and chronic liver pathologies(Mallet et al, 2011).Administration of lipopolysaccharide/D-galactosamine (LPS/GalN) is widely used to mimic acute liver injury in animals.Here we tested the hypothesis that stress may predispose the liver LPS/GalN-induced injury and that alterations in the EC may play a role in the mechanism.
Methods: Male Wistar Kyoto (WKY;stress-sensitive) and Sprague-Dawley (SD) rats (Harlan, UK) were subjected to stress/anxiety-related tests including open field and elevated plus maze(n=15-16).A second cohort of rats were administered 20μg/kg LPS+200mg/kg GalN (IP) and sacrificed at 0, 6 and 24hrs (n=8).Plasma samples were analysed for liver enzyme levels while livers were processed for histology,hepatic inflammatory cytokine levels (ELISA), hepatic caspase-3 activity and protein expression using western blotting, EC levels (LC-MS/MS) and EC degrading enzymes expression (qRT-PCR).
Results: Behavioural testing confirmed an altered stress-related/anxiety-like phenotype in WKY vs SD rats.WKY rats had higher levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST) 6hr and significantly higher 24hrs post LPS/GalN vs SD counterparts.WKY rats exhibited a significantly increased caspase-3 activity and cleaved caspase-3 protein expression in the liver 24hrs post LPS/GalN compared to SD.LPS/GalN induced a significant histopathological changes in WKY compared to SD rats and caused a significant increase in IL-1beta levels 6hrs post LPS/GalN in WKY. WKY livers had reduced monoacylglycerol lipase (MAGL), fatty acid amide hydrolase (FAAH) expression and anandamide (AEA) levels but increased 2-arachidonoylglycerol (2-AG) vs SD at baseline.LPS/GalN significantly increased EC levels (AEA and 2-AG) in the liver at 6 and 24hrs and significantly reduced EC degrading enzymes FAAH
and MAGL at 24hrs vs SD counterparts.
Conclusions: Overall, we confirmed: i.The stress-related/anxiety-like phenotype of WKY rats ii. LPS/GalN-induced ALI is exacerbated in stress-sensitive WKY rats and iii.ALI in the stress sensitive WKY rat is associated with elevations in EC levels in the liver and reduction of EC degrading enzymes. In conclusion alterations in the hepatic EC system may underlie, at least in part, stress-induced exacerbation of ALI.
