Predominant role of obesity ⁄ insulin resistance in oxidative stress development Massimo D’Archivio * , Giovanni Annuzzi † ,Rosaria Varı` * , Carmelina Filesi * , Rosalba Giacco ‡ , Beatrice Scazzocchio * , Carmela Santangelo * , Claudio Giovannini * , Angela A. Rivellese † and Roberta Masella * * Department of Veterinary Public Health and Food Safety, Italian National Institute of Health, Rome, Italy, † Department of Clinical and Experimental Medicine, Federico II University, Naples, Italy, ‡ National Research Council, Institute of Food Science, Avellino, Italy ABSTRACT Background Hyperlipidaemia, hyperglycaemia and hyperinsulinaemia, hallmarks of the postprandial state, have been also associated with increased oxidative stress and lipoprotein oxidation contributing to vascular injury and atherosclerosis. However, the specific links among metabolic disorders, postprandial state, insulin resistance and oxidative stress are still to be clarified. This study aimed at investigating the individual role played by obesity, insulin resistance and type 2 diabetes in the occurrence of fasting and postprandial oxidative stress. Design Biomarkers of oxidative stress [F2-isoprostanes and circulating oxidized low-density lipoproteins (LDL)], LDL oxidability (conjugated diene kinetic, thiobarbituric acid reactive substances (TBARs) formation and electro- negativity increase) and antioxidant vitamins (b-carotene, a-tocopherol and retinol) were evaluated at fasting and 6 h after a standard fat-rich meal in 10 obese diabetic (ObD), 11 obese and 11 normal-weight control men. Insulin sensitivity was evaluated by euglycaemic hyperinsulinaemic clamp. Results ObD and obese subjects, characterized by a similar level of adiposity and insulin resistance, showed higher urinary F2-isoprostanes and circulating oxidized LDL, an increased susceptibility to oxidation of plasma LDL (lower lag phase, higher TBARs formation, and higher relative electrophoretic mobility), and lower plasma content of b-carotene and retinol than control subjects, both at fasting and after the test meal. Conclusions Obesity and insulin resistance, more than type 2 diabetes, play the most relevant role in oxidative stress development. The correction of obesity and insulin resistance might be a useful strategy in counteracting systemic oxidative stress. Keywords Insulin resistance, obesity, oxidative stress, oxLDL, type 2 diabetes. Eur J Clin Invest 2012; 42 (1): 70–78 Introduction Although oxidative reactions have a central role in energy production as well as in intermediary metabolism, they can produce potentially dangerous reactive oxygen species (ROS) [1]. ROS can damage biological molecules, leading to the gen- eration of oxidized products that alter cell functions. When the level of ROS exceeds the antioxidant capacity of the cell, the intracellular redox homeostasis is altered and oxidative stress ensues [2]. A chronic condition of redox imbalance may contribute to the development and progression of chronic diseases, such as diabetes, atherosclerosis and cancer [3,4]. In particular, increased oxidative stress has been associ- ated with the occurrence of insulin resistance, b-cell dysfunc- tion, impaired glucose tolerance and, finally, type 2 diabetes [5,6]. Lipids, in particular the polyunsaturated fatty acyl chains contained in phospholipids, represent a main target of ROS attack [7]. The term lipid peroxidation refers to a complex of chain reactions that generate an enormous variety of oxidized products. Radical attack produces fatty acyl peroxyl radicals and, subsequently, hydroperoxides [8]. The peroxyl radicals are unstable and give rise to products such as malondialdehyde by chain cleavage or, with further oxidation, F2-isoprostanes, a 70 European Journal of Clinical Investigation Vol 42 DOI: 10.1111/j.1365-2362.2011.02558.x ORIGINAL ARTICLE