Chicken or Egg Causality Paradox Between Insulin Resistance and Epicardial Fat.

Abstract

Altin et al 1 reported that carotid intima–media thickness (cIMT) and epicardial fat thickness (EFT) are significantly increased among patients with prediabetes, particularly in those with impaired glucose tolerance (IGT), compared to the control group. Age, waist circumference, and 2-hour glucose level independently predicted cIMT, but only 2-hour glucose was an independent predictor of EFT. Insulin resistance (IR) and central obesity are key elements of the metabolic syndrome (MetS). Central obesity also causes IR, hypertension, and dyslipidemia via secretion of various cytokines from adipocytes. 2,3 Nonalcoholic fatty liver disease (NAFLD), known as the hepatic manifestation of MetS, is also significantly associated with increased cardiovascular risk. 4 In turn, MetS is associated with an increased risk of subclinical and clinical atherosclerotic diseases. 5 Epicardial adipose tissue secretes several proinflammatory molecules and plays a role similar to an endocrine or paracrine organ. 6 Epicardial fat thickness has been significantly associated with various cardiovascular risk factors and disease conditions. 7-10 Yorgun et al 7 showed that EFT measured by computerized tomography might be an indicator for the presence of MetS. They also reported a graded relationship between increasing number of MetS components and EFT. In another study, in patients with NAFLD, waist circumference, and cIMT independently predicted EFT. 11 In addition, epicardial fat was significantly associated with gamma-glutamyltransferase (GGT) activity 12 as an indicator of both MetS and NAFLD. 13 In the study by Altin et al, 1 serum GGT levels were significantly higher in patients with prediabetes, which might be due to a higher rate of NAFLD in those patients. Such a link between increased EFT and MetS might be due to IR. However, the exact pathogenesis whether increased EFT promotes IR and MetS or vice versa was unclear. 14-16 Thus, Altin et al 1 should comment on this issue. They may consider the impact of MetS components as a whole rather than including each component alone like IGT, waist circumference, and so on. We speculate that increased cIMT and EFT in the patient group of this study might be due to higher IR as measured by homeostasis model assessment index of IR and MetS components as a whole rather than impaired glucose metabolism alone.