Early increase in serum fatty acid binding protein 4 levels in patients with acute myocardial infarction

Background: Acute myocardial infarction (AMI) induces marked activation of the sympathetic nervous system. Fatty acid binding protein 4 (FABP4) is not only an intracellular protein, but also a secreted adipokine that contributes to obesity-related metabolic complications. Here, we examined the role of serum FABP4 as a pathophysiological marker in patients with AMI. Methods and results: We studied 106 patients presenting to the emergency unit with a final diagnosis of AMI, including 12 patients resuscitated from out-of-hospital cardiac arrest (OHCA) caused by ventricular fibrillation. FABP4 levels peaked on admission or just after percutaneous coronary intervention and declined thereafter. Regression analysis revealed no significant correlation between peak FABP4 and peak cardiac troponin T determined by Roche high-sensitive assays (hs-TnT). Notably, FABP4 levels were particularly elevated in AMI patients who were resuscitated from OHCA (median 130.2 ng/mL, interquartile range (IQR) 51.8-243.9 ng/mL) compared with those without OHCA (median 26.1 ng/ml, IQR 17.1-43.4 ng/mL), while hs-TnT levels on admission were not associated with OHCA. Immunohistochemistry of the human heart revealed that FABP4 is abundantly present in adipocytes within myocardial tissue and epicardial adipose tissue. An in vitro study using cultured adipocytes showed that FABP4 is released through a 3-adrenergic receptor (AR)-mediated mechanism. Conclusions: FABP4 levels were significantly elevated during the early hours after the onset of AMI and were robustly increased in OHCA survivors. Together with the finding that FABP4 is released from adipocytes via 3-AR-mediated lipolysis, our data provide a novel hypothesis that serum FABP4 may represent the adrenergic overdrive that accompanies acute cardiovascular disease, including AMI.