Non-alcoholic fatty liver disease (NAFLD) is associated with hepatic steatosis, a benign condition caused by accumulation of lipids in hepatocytes, which may progress to steatohepatitis and cirrhosis. Recent studies suggest that sphingolipids are involved in the development and severity of NAFLD. The goal of this study is to identify the circulating sphingolipid species that are altered by chronic high fat diet (HFD) feeding and correlate these abnormalities with hepatic sphingolipids. We utilized a previously established experimental model of NAFLD generated by HFD feeding of 8-week-old male mice for 16 weeks. Lipids were extracted from serum samples by Folch method and analyzed with matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) in the positive and negative ion modes. MALDI-TOF detected a total of 47 serum sphingolipids including sphingomyelins, sulfatides, ceramides, phosphosphingolipids, and glycosphingolipids within the mass range of 600-2000 Da. Principle component analysis demonstrated clear separation of hepatic sphingolipids from low fat diet (LFD) and HFD groups and partial overlap of serum sphingolipids with a variance of 53.5% and 15.1%, and 11.7% in PC1, PC2, and PC3, respectively. Chronic HFD feeding significantly increased expression of SM (40:0), SM(42:2), ST(42:2), Hex(6)-Cer (40:1), and Hex(4)-HexNAc (2)-Cer (34:1) in both serum and liver. In addition, HFD mediated percent changes in hepatic sphingolipids correlate linearly with the percent changes in serum sphingolipids as determined by Pearson correlation (P = 0.0002). Elevated levels of serum and hepatic sphingomyelins and glycoceramides are key factors mediating NAFLD development and may serve as peripheral markers of hepatic steatosis.
Keywords: Hepatic steatosis; high fat diet; mass spectrometry; mouse model; non-alcoholic fatty liver disease; sphingolipidomics.