SummaryObjective Retinol-binding protein 4 (RBP4) is a recently identified adipokine that is elevated in the serum in several insulin-resistant states. We investigated the relationship between non-alcoholic fatty liver disease (NAFLD) and serum RBP4 in nondiabetic adults. Methods One hundred and fifty-nine nondiabetic, non-alcoholic subjects (95 males and 64 females) participated in this study. Division of subjects into a NAFLD group ( n = 73; 45 males and 28 females) or a normal group ( n = 86; 50 males and 36 females) was based on the presence of fatty liver disease determined by sonography. Results Serum RBP4 levels in the NAFLD group were significantly higher than those in the normal group (62·8 ± 16·0 mg/l vs. 51·7 ± 14·6 mg/l, P < 0·0001). Multiple logistic regression analysis revealed that the RBP4 level was an independent factor associated with NAFLD ( P = 0·0042). In addition, serum RBP4 levels were positively correlated with serum alanine aminotransferase (ALT), aspartate aminotransferase (AST) and γ -glutamyltranspeptidase (GGT) levels. The significant association between serum RBP4 and GGT levels remained even after adjusting for age, gender, body mass index, the homeostasis model of assessment (HOMA) value and the presence of NAFLD ( r = 0·3097, P = 0·0002). Conclusion Serum RBP4 levels are significantly associated with NAFLD and liver enzymes.

Obesity is a steadily increasing public health dilemma that is associated with an imbalance between energy intake and expenditure [1]. The state of being overweight or obese increases the risk of developing serious diseases such as hypertension, coronary heart disease, insulin resistance type 2 diabetes, dyslipidemia, arteriosclerosis, infertility, back pain, and some cancers [2]. These situations can be due to an altered lipid metabolism, including lipogenesis and lipolysis, and accumulation of excessive abdominal fat can induce metabolic impairments [3]. The multistep processes are related to the proliferation or differentiation of adipocytes, and fatty acid oxidation or synthesis [4]. In adipocyte differentiation, various transcriptional factors including CCAAT/enhancerbinding protein (C/EBP)α, β, δ, and peroxisome proliferator-activated receptor (PPAR)γ play a role as the major regulators of adipogenesis [5,6]. C/EBPβ and C/EBPδ are expressed in the early phase of adipocyte differentiation and activate the expression of PPARγ and C/EBPα [5,7]. During adipogenesis, C/EBPα is involved in stimulating and maintaining the expression of PPARγ [6,8]. Additionally, the expressed genes are involved in the adipocytes phenotype and maintenance via lipid metabolic enzymes at the end of adipocytes differentiation [9]. Fatty acid synthase (FAS) as a representative key enzyme in the lipogenesis pathway, plays a role in catalysing all the enzymatic reactions involved in the conversion of acetyl CoA and malonyl CoA finally to palmitic acids [9,10]. Activation of 5'-adenosine monophosphate-activated protein kinase (AMPK), which functions as an energy status