Increased Serum Adipocyte Fatty Acid-Binding Protein Levels Are Associated with Decreased Sensitivity to Thyroid Hormones in the Euthyroid Population

Abstract

Background: Serum adipocyte fatty acid-binding protein (A-FABP) and thyroid hormones are closely associated with metabolic disorders; however, their relationship remains unknown. We aimed to investigate the associations of serum A-FABP levels with single and composite indices of the thyroid system. Methods: The study included 1057 community-based euthyroid participants (age range: 27-81 years) in Shanghai, among whom 601 were women. Serum free triiodothyronine (FT3), free thyroxine (FT4) and thyroid stimulating hormone (TSH) were measured by electrochemical luminescence immunoassay. The thyroid feedback quantile-based index (TFQI), thyroid stimulating hormone index (TSHI) and thyrotroph thyroxine resistance index (TT4RI) were calculated to evaluate central sensitivity to thyroid hormones. Peripheral sensitivity to thyroid hormones was evaluated by the FT3 to FT4 ratio (FT3/FT4). Enzyme linked immunosorbent assay was used to measure serum A-FABP levels. Results: Serum A-FABP levels were 6.41 (95% confidence interval: 6.10-6.74) ng/ml among all subjects. Multiple cardiovascular metabolic risk factors were adjusted in the multivariate linear regression analysis and the multinomial logistic regression analysis (non-ordinal). In both sexes, serum A-FABP levels were positively associated with FT4 (men: standardized β = 0.150, P = 0.001; women: standardized β = 0.218, P < 0.001), TFQI (men: standardized β = 0.119, P = 0.009; women: standardized β = 0.165, P < 0.001) and TSHI (men: standardized β = 0.108, P = 0.017; women: standardized β = 0.114, P = 0.005), while they were negatively associated with FT3/FT4 (men: standardized β = -0.122, P = 0.008; women: standardized β = -0.129, P = 0.001). Serum A-FABP levels were not associated with FT3, TSH or TT4RI. Compared with the first quartile group of TFQI, for every 10 ng/ml increase in A-FABP, the odds ratio for the third quartile group of TFQI was 2.213 in women (P = 0.035); the odds ratios for the fourth quartile group of TFQI were 2.614 in men (P = 0.022) and 3.425 in women (P = 0.002). Conclusions: In an euthyroid population, increased serum A-FABP levels were associated with decreased sensitivity to thyroid hormones, suggesting that A-FABP may mediate the “cross-talk” between adipose tissue and the thyroid system.