Increased hepatic expression is a major determinant of serum alanine aminotransferase elevation in mice with nonalcoholic steatohepatitis.
BACKGROUND
Serum alanine aminotransferase (ALT) is a biomarker for hepatitis of various aetiologies including fatty liver disease. Increased serum ALT is thought to be related to its increased release from dying hepatocytes.


OBJECTIVE
We sought to understand the mechanisms by which serum ALT is elevated in a mouse model of experimental fatty liver disease where hepatocyte death is minimal.


METHODS
To induce fatty liver disease, female A/J mice were fed a methionine-choline deficient (MCD) diet for up to 12 weeks. Serum and liver ALT expression and hepatic inflammation, necrosis and apoptosis were assessed and expressed relative to their expressions in control-diet-fed mice.


RESULTS
Feeding mice the MCD diet produced hepatic steatosis with minimal hepatic inflammation or necrosis. Liver cell apoptosis was not significantly increased by MCD diet treatment. Conversely, serum ALT activity was approximately four-fold increased at 12 weeks of diet treatment, and ALT protein expressions in serum were correspondingly increased: ALT1 1.7-fold and ALT2 1.9-fold at 12 weeks. The expressions of ALT1 and ALT2 protein in liver increased over 2-12 weeks of MCD treatment. At 12 weeks, liver ALT1 protein was 2.27+/-0.31-fold increased and ALT2 protein 4.72+/-0.48-fold increased relative to their expressions in the mice fed a diet replete with methionine and choline. Liver ALT mRNA expressions were correspondingly increased: ALT1 mRNA 2.58-fold and ALT2 mRNA 4.97-fold at 12 weeks. Linear regression analysis showed a strong correlation between serum and liver tissue expressions for both ALT1 and ALT2.


CONCLUSIONS
These findings suggest that induction of hepatic expression significantly contributes to increased serum ALT in this model of experimental fatty liver disease, whereas cell death appears not to.
Liu
Rui
R
Department of Pediatrics, Children's Memorial Research Center, Northwestern University, Feinberg School of Medicine, Chicago, IL 60614, USA.
Pan
Xiaomin
X
Whitington
Peter F
PF
D000410:Alanine Transaminase / Q000097:blood*; D000704:Analysis of Variance; D000818:Animals; D015415:Biomarkers / Q000097:blood; D015153:Blotting, Western; D017931:DNA Primers / Q000235:genetics; D005234:Fatty Liver / Q000097:blood / Q000201:enzymology*; D005260:Female; D008099:Liver / Q000378:metabolism*; D051379:Mice; D020133:Reverse Transcriptase Polymerase Chain Reaction
D015415:Biomarkers; D017931:DNA Primers; D000410:Alanine Transaminase