Iron metabolism is associated with adipocyte insulin resistance and plasma adiponectin: The Cohort on Diabetes and Atherosclerosis Maastricht (CODAM) study
OBJECTIVE-Adipocyte insulin resistance (IR) is a key feature early in the pathogenesis of type 2 diabetes mellitus (T2DM), and although scarce, data in the literature suggest a direct role for iron and iron metabolism-related factors in adipose tissue function and metabolism. Serum ferritin and transferrin were shown to be associated with muscle insulin resistance (IR) and T2DM, but little is known about the role of iron metabolism on adipose tissue. We therefore investigated whether markers of iron metabolism were associated with adipocyte IR and plasma adiponectin. RESEARCH DESIGN AND METHODS-Serum ferritin, transferrin, total iron, non- transferrin-bound iron (NTBI), transferrin saturation, and plasma adiponectin were determined in 492 individuals. Adipocyte IR was defined by the product of fasting insulin and nonesterified fatty acids (NEFAs). Using linear regression analyses, we investigated the difference in adipocyte IR or adiponectin (in %) according to differences in iron metabolism markers. RESULTS-Serum ferritin (b = 1.00% increase in adipocyte IR per 10 mg/L [95% CI 0.66- 1.34]), transferrin (4.18% per 0.1 g/L [2.88-5.50] ), total iron (1.36% per mmol/L [0.61-2.12]), and NTBI (5.14% per mmol/L [1.88-8.52] ) were associated with adipocyte IR after adjustment for several covariates, including inflammatory markers. All markers of iron metabolism were also associated with NEFAs (all P < 0.01). In addition, ferritin and transferrin were inversely associated with adiponectin (both P < 0.01). CONCLUSIONS-The observed associations of several markers of iron metabolism with adipocyte IR and adiponectin suggest that factors related to iron and iron metabolism may contribute to adipocyte IR early in the pathogenesis of T2DM.