Context: FABP4 (adipocyte-specific fatty acid-binding protein 4, also known as aP2) is a cytoplasmic lipid chaperon involved in lipid metabolism, glucose homeostasis, and the regulation of inflammatory response. Its expression is limited to adipocytes, macrophages, skeletal muscle, and bronchial epithelia. Recently, a polymorphic allele of the aP2 promoter (−87T→C) has been shown to be associated with decreased FABP4 expression in fat tissue, lowered triglyceride levels, and reduced risk for cardiovascular disease as well as type 2 diabetes (Proc Natl Acad Sci USA, 103:6970, 2006). However, circulating FABP4 levels in various disease states remains to be investigated.
Objective: The aim of this study was to determine circulating FAP4 levels in hypothyroidism.
Design: After having obtained local Ethical Committee approval, circulating FABP4 levels were measured in 38 adult patients with hypothyroidism before and two months after restoration of euthyroid state, and were compared to those levels in 34 age- and sex-matched control subjects.
Main outcome measures: Plasma FABP4 is measured using an ELISA kit (Human FABP4 ELISA, BioVendor-GmbH, Heidelberg). We also measured thyroid hormones, plasma lipids, insulin, and glucose levels. As FABP4 levels were not normally distributed data are given as median (interquartile range).
Results: We found that plasma FABP4 levels are elevated in hypothyroidism (0.67 ng/ml vs. 1.23 ng/ml; P<0.001), and restoration of euthyroid state is associated with normalization of FABP4 levels. Hypothyroid state was also associated with elevated LDL-cholesterol, triglycerides, and HOMA-IR all of which decreased significantly following thyroid hormone replacement (P<0.001, P<0.01, and P=0.004; respectively). We did not detect any correlation between plasma FABP4 levels and lipid parameters or HOMA-IR.
Conclusions: This is the first study to report plasma FABP4 levels in hypothyroidism. Our findings suggest that elevated FABP4 levels may be involved in the atherosclerotic process associated with hypothyroidism.