Plasma ferritin concentration is positively associated with in vivo fatty acid mobilization and insulin resistance in obese women

High rates of fatty acid (FA) mobilization from adipose tissue are associated with insulin resistance (IR) in obesity. In vitro evidence suggests that iron stimulates lipolysis in adipocytes, but whether iron is related to in vivo FA mobilization is unknown. We hypothesized that plasma ferritin concentration ([ferritin]), a marker of body iron stores, would be positively associated with FA mobilization. We measured [ferritin], the rate of appearance of FA in the systemic circulation (FA Ra; stable isotope dilution), key adipose tissue lipolytic proteins and IR (hyperinsulinaemic-euglycaemic clamp) in 20 obese, premenopausal women. [Ferritin] was correlated with FA Ra (r = 0.65; P = 0.002) and IR (r = 0.57; P = 0.008); these relationships remained significant after controlling for body mass index and plasma [C-reactive protein] (a marker of systemic inflammation) in multiple regression analyses. We then stratified subjects into tertiles based on [ferritin] to compare subjects with 'High-ferritin' versus 'Low-ferritin'. Plasma [hepcidin] was more than fivefold greater (P < 0.05) in the High-ferritin versus Low-ferritin group, but there was no difference in plasma [C-reactive protein] between groups, indicating that the large difference in plasma [ferritin] reflects a difference in iron stores, not systemic inflammation. We found that FA Ra, adipose protein abundance of hormone-sensitive lipase and adipose triglyceride lipase, and IR were significantly greater in subjects with High-ferritin versus Low-ferritin (all P < 0.05). These data provide the first evidence linking iron and in vivo FA mobilization and suggest that elevated iron stores might contribute to IR in obesity by increasing systemic FA availability.