DIETARY IRON OVERLOAD INDUCES VISCERAL ADIPOSE TISSUE INSULIN RESISTANCE ASSOCIATED WITH HYPER-RESISTINEMIA, AND SYNERGIZES WITH OBESITY AND FATTY LIVER IN INDUCING SYSTEMIC INSULIN RESISTANCE
Dr. Luca Valenti [Biography]
Italy
Background & Aims: Insulin resistance is the key pathogenic feature underlying nonalcoholic fatty liver disease and the metabolic syndrome. Excess body iron is frequently observed in patients with metabolic syndrome, and associated with more severe insulin resistance and organ damage. However, whether iron overload has a causal role in the pathophysiology of these syndromes is not well understood, and likewise the molecular mechanisms involved are still unknown. Aim of this study was to assess the effects of dietary modulation of iron status on glucose metabolism and to investigate the underlying mechanisms in mouse models. Methods: Wild-type or genetically obese (ob/ob) 4 week-old male C57Bl/6 mice were fed for 16 weeks with a standard iron concentration diet (8 mg/kg, control diet, CD, n=15) or with an iron enriched diet (30g/kg, IED, n=15) and high-fructose diet (HFD). Results: IED was associated with increased serum iron and hepatic iron concentration (which was comparable to that observed in patients with metabolic syndrome associated with altered iron status) compared to CD. Despite IED was associated with reduced weight gain, which was explained by reduced visceral adipose tissue mass (VAT; perigonadal fat pad: -60%, p=0.02), it induced a progressive increase in glucose levels due to insulin resistance, which was confirmed by i.p. insulin tolerance test. In ob/ob mice IED led to overt diabetes development, and in mice fed high fructose diet increased insulin resistance by about 100%, associated with decreased VAT mass despite no changes in total body mass, thus suggesting VAT insulin resistance. IED was associated with increased VAT (but not hepatic) insulin resistance, as shown by decreased fasting pAKT/AKT ratio (-80%, p=0.03), and VAT iron accumulation with oxidative stress and unfolded protein response activation. In addition, IED induced increased VAT resistin mRNA levels (p=0.005), which resulted in hyper-resistinemia (p=0.01) and increased VAT expression of SOCS3 (p<0.05), a known resistin target implicated in the pathogenesis of insulin resistance. Conclusions: IED induces insulin resistance in C57/Bl6 mice and synergizes with obesity and dietary factors in the pathogenesis of metabolic complications. We are currently evaluating the relationship between iron metabolism and insulin resistance in VAT.