Adipocyte Fatty Acid–Binding Protein Is a Plasma Biomarker Closely Associated with Obesity and Metabolic Syndrome

BACKGROUND: Adipocyte fatty acid-binding protein (A-FABP) is traditionally thought to be a cytosolic fatty acid chaperone expressed in adipocytes. Mice with targeted disruption of the A-FABP gene exhibit a striking phenotype with strong protection from insulin resistance, hyperglycemia, and atherosclerosis. The clinical relevance of these findings remains to be confirmed. METHODS: We used tandem mass spectrometry-based proteomic analysis to identify proteins secreted from adipocytes and present in human serum. We measured serum A-FABP concentrations in 229 persons (121 men and 108 women; age range, 33-72 years), including 100 lean [body mass index (BMI) 25 kg/m2) selected from a previous cross-sectional study. RESULTS: A-FABP was released from adipocytes and was abundantly present in human serum. Mean (SD) circulating concentrations of A-FABP were significantly higher in overweight/obese than in lean persons [32.3 (14.8) vs 20.0 (9.8) microg/L; P < 0.001]. Age- and sex-adjusted serum A-FABP concentrations correlated positively (P < 0.005) with waist circumference, blood pressure, dyslipidemia, fasting insulin, and the homeostasis model assessment insulin resistance index. Moreover, we observed a significant increase in A-FABP concentrations corresponding with increases in the number of components of the metabolic syndrome (P < 0.05). CONCLUSIONS: A-FABP is a circulating biomarker closely associated with obesity and components of the metabolic syndrome, and measurement of serum concentrations of A-FABP might be useful for clinical diagnosis of obesity-related metabolic and cardiovascular disorders.