Age and Interleukin-15 Levels Are Independently Associated With Intima-Media Thickness in Obesity-Related NAFLD Patients

Abstract

Common carotid intima-media thickness (IMT) represents a functional and structural marker of early, precocious, and subclinical atherosclerosis, independently from the carotid plaque. Macrophage cells, which have been detected in adipose tissue and atherosclerotic plaques, are regulated by interleukin-15 (IL-15). At the light of the conflicting results concerning the role of IL-15 in atherosclerosis, the aim of the study was to retrospectively evaluate in a population of 80 obese patients, with median age of 46 years (IQR 34–53 years), with a low rate of comorbidities but with non-alcoholic fatty liver disease (NAFLD) or hepatic steatosis (HS), the relationship between IMT and serum concentrations of IL-15. Anthropometric measures, metabolic profile, and serum inflammatory markers, as well as the levels of IL-15, MCP-1, b FGF, and GM-CSF, were analyzed by a bead-based assay. IMT, HS, subcutaneous, and visceral adipose tissues were detected by ultrasonography. The IL-15 levels of the obese patients were increased with respect to those of 44 young healthy subjects, i.e., 2.77 (1.21–4.8) vs. 1.55 (1–2.4) pg/mL (P = 0.002). In the univariate analysis, IL-15 levels were associated to IMT and to those of MCP-1, b FGF, and GM-CSF, without any relation to other inflammatory markers such as CRP and ferritin, except fibrinogen. In the multivariate analysis, after adjusting the HS severity for the extent of visceral adiposity, a dramatic change in prediction of IMT by HS was shown (β from 0.29 to 0.10, P from 0.008 to 0.37). When the visceral adipose tissue was combined with IL-15, on the one hand, and the well-known coronary artery disease (CAD) risk factors—i.e., age, gender, smoking status, HDL-cholesterol concentrations, triglycerides levels, and HOMA—on the other, only age and IL-15 remained the predictors of IMT (β = 0.60, P = 0.0001 and β = 0.25, P = 0.024, respectively). There was no association of IL-15 with various anthropometric parameters nor with body fat distribution and severity of HS, also after adjusting for age. Age is resulted to be the main factor in the prediction of IMT and thus of early atherosclerosis. The prediction of IMT by IL-15 coupled with the lack of prediction by the well-known CAD risks is in agreement with recent data, which emphasizes the main role of the immune system in the onset/worsening of atherosclerosis, even though the role of visceral adiposity should be further deepened. Age and IL-15 levels were both predictors of early atherosclerosis in this population of obese patients with NAFLD, suggesting a possible role of this cytokine in the atherosclerosis process.