Nonalcoholic fatty liver disease (NAFLD) is the leading risk factor for common chronic liver disease and is often regarded as a prevalent metabolic disorder tightly associated with obesity. However, the existence of metabolically healthy obesity (MHO) indicates that some important factors may participate in protecting individuals with MHO free of NAFLD, even with excessive adiposity. To explore factors independent of obesity that may be involved in the occurrence of NAFLD, we performed an iTRAQ-based proteomic study to identify proteins differentially expressed in serum between NAFLD and MHO subjects. Compared with the MHO group, ten proteins were upregulated and five were downregulated significantly in the NAFLD group. Gene Ontology analysis indicated significant changes in the immune response and triglyceride metabolism-related pathways between MHO and NAFLD. We further validated three candidates markedly dysregulated in NAFLD by Western blotting and ELISA, including two upregulated proteins (afamin and apolipoprotein H) and one downregulated protein (apolipoprotein C-1). Detection of serum apolipoprotein H levels in a large-scale cohort with MHO and different stages of NAFLD indicated that apolipoprotein H may be a potential blood biomarker for distinguishing NAFLD from MHO and an independent risk factor for predicting NAFLD.
