There are two

previously published proteomics studies using serum25 or liver tissue26 from patients across the spectrum of NAFLD. In the first and BGB324 only other proteomics study using serum samples, Younossi et al.25 identified 12 protein peaks with significant differential expression when patient groups and controls were compared. In a recent proteomics study utilizing liver tissue from patients with NAFLD and controls, Charlton et al.26 identified nine proteins with differential expression between study groups, and all proteins exhibited functions previously implicated in the pathogenesis of NAFLD and NASH, including biological response to increased hepatic lipid content, inflammation, mediation of fibrosis, and fatty acid transport. Our study utilized an ion-intensity based, label-free quantitative proteomics approach (LFQP) that has gained popularity in recent years as the performance of mass spectrometers has improved.27–30 Using this LFQP approach, we detected 1,738 proteins in serum samples obtained from control subjects and NAFLD patients. Of these proteins, expression of 605 proteins differed significantly (q < 0.05) between any two patient groups. Further analysis revealed that expression of 229 proteins differed significantly when control subjects were compared with any

of the three NAFLD patient groups. There were no significant differences observed between the simple steatosis and NASH groups, Galeterone Selleck MK0683 suggesting that systemic markers of fatty liver and NASH may not be present in serum from patients with mild disease. However, there were 55 proteins that were different between the simple steatosis and NASH F3/F4 group and 15 proteins that differed between the NASH and NASH F3/F4 patients. These proteins may be particularly helpful in identifying biomarkers to diagnose and stage NAFLD and NASH. We further analyzed the biological significance of all priority 1 proteins with a significant change (q < 0.05) of at least 14% (1.14-fold change) based on the maximum observed change of the internal standard, chicken lysozyme. As described

below, several of these biological processes have been previously implicated in the pathogenesis of NAFLD and NASH and many of these identified proteins are only synthesized by the liver. Fifteen of the proteins that changed significantly are involved in immune system regulation and inflammation. One example is retinol binding protein 4 (RBP4), a protein we identified as having significantly decreased expression with increasing NAFLD severity. RBP4 is a cytokine synthesized by both the liver and adipose tissue that carries vitamin A in the blood and is involved in the development of insulin resistance.31, 32 Although some studies have shown an increase in serum RBP4 levels in patients with NAFLD,33, 34 a recent study by Nobili et al.