Free fatty acids are associated with metabolic syndrome and insulin resistance but not inflammation in systemic lupus erythematosus

Abstract

Free fatty acids (FFAs) are implicated in the pathogenesis of insulin resistance and atherosclerosis. Inflammatory cytokines promote lipolysis and increase FFAs, a cause of endothelial dysfunction and increased atherosclerosis risk. We hypothesized that increased inflammation is associated with increased FFAs, resulting in insulin resistance and atherosclerosis in patients with systemic lupus erythematosus (SLE). We measured clinical variables, serum FFAs, homeostasis model assessment for insulin resistance (HOMA), inflammatory cytokines, markers of endothelial activation, cholesterol concentrations and coronary artery calcium in 156 patients with SLE and 90 controls. We compared FFAs in patients with SLE and controls using Wilcoxon rank sum tests and further tested for the independent association between FFAs and disease status with adjustment for age, race and sex using multivariable regression models. We assessed the relationship between FFAs and continuous variables of interest using Spearman correlation and multivariable regression analysis. Levels of FFAs were higher in patients with SLE than controls (0.55 mmol/l (0.37-0.71) vs 0.44 mmol/l (0.32-0.60), P = 0.02). Levels of FFAs remained significantly higher among patients with SLE after adjustment for age, race and sex (P = 0.03) but not after further adjustment for body mass index (P = 0.13). FFA levels did not differ according to the usage of current immunosuppressive medications in univariate and adjusted analysis (all P > 0.05). Among patients with SLE, concentrations of FFAs were higher among those with metabolic syndrome compared to those without (0.66 mmol/l (0.46-0.81) vs 0.52 mmol/l (0.35-0.66), P < 0.001). FFAs were positively correlated with insulin resistance (HOMA) (rho = 0.23, P = 0.004, P adjusted = 0.006) and triglyceride levels (rho = 0.22, P = 0.01, P adjusted = 0.004). FFAs were not associated with inflammatory cytokines (IL-6, TNF-α) (all P > 0.05) but were positively associated with levels of E-selectin (rho = 0.33, P = < 0.001, P adjusted = 0.001) and ICAM-1 (rho = 0.35, P < 0.001, P adjusted = 0.001). FFAs were correlated with coronary artery calcium score (rho = 0.20, P = 0.01) but this was attenuated after adjustment for age, race and sex (P = 0.33). From our study we concluded that FFAs are elevated in patients with SLE, particularly those with metabolic syndrome. FFAs in patients with SLE are not associated with markers of generalized inflammation but are associated with insulin resistance and markers of endothelial activation.