Published online Oct 27, 2013. doi: 10.4254/wjh.v5.i10.558
Revised: September 23, 2013
Accepted: October 11, 2013
Published online: October 27, 2013
AIM: To establish a simple method to quantify lipid classes in liver diseases and to decipher the lipid profile in p62/IMP2-2/IGF2BP2-2 transgenic mice.
METHODS: Liver-specific overexpression of the insulin-like growth factor 2 mRNA binding protein p62/IMP2-2/IGF2BP2-2 was used as a model for steatosis. Steatohepatitis was induced by feeding a methionine-choline deficient diet. Steatosis was assessed histologically. For thin layer chromatographic analysis, lipids were extracted from freeze-dried tissues by hexane/2-propanol, dried, redissolved, and chromatographically separated by a two-solvent system. Dilution series of lipid standards were chromatographed, detected, and quantified. The detection was performed by either 2’,7’-dichlorofluoresceine or a sulfuric acid/ethanol mixture.
RESULTS: Histological analyses confirmed steatosis and steatohepatitis development. The extraction, chromatographic, and detection method showed high inter-assay reproducibility and allowed quantification of the different lipid classes. The analyses confirmed an increase of triglycerides and phosphatidylethanolamine and a decrease in phosphatidylcholine in the methionine-choline deficient diet. The method was used for the first time to asses the lipid classes induced in the p62-overexpressing mouse model and showed a significant increase in all detected lipid species with a prominent increase of triglycerides by 2-fold. Interestingly, the ratio of phosphatidylcholine to phosphatidylethanolamine was decreased, as previously suggested as a marker in the progression from steatosis to steatohepatitis.
CONCLUSION: The thin layer chromatography analysis allows a reliable quantification of lipid classes and provides detailed insight into the lipogenic effect of p62.
Core tip: We describe a new method to quantify lipid classes in steatosis/steatohepatitis having advantages over both histology and classical analytical methods. Since lipid classes exert differential pathophysiological actions our method should be of interest for all researchers dealing with mechanisms of steatosis and steatohepatitis. We employ our method to investigate the lipid profile in the steatotic p62 transgenic mouse model. p62 was originally identified as an autoantigen overexpressed in hepatocellular carcinoma patients, its expression correlates with poor prognosis, and it induces steatosis. The interesting lipid profile in p62 transgenic animals suggests that it might advance the step from steatosis towards steatohepatitis.