Oxidizability of core and surface of lipoproteins as early marker of metabolic syndrome

INTRODUCTION Central obesity is a principal causative factor in the development of metabolic syndrome (MS), a common and complex disorder combining hypertension, insulin resistance, and alterations in the composition and function of lipoproteins. Oxidative stress is an important pathogenic mechanism of obesity-associated MS. Peroxidation of lipoproteins not only makes LDLs atherogenic but can also reduce the anti-atherogenic properties of HDL. OBJECTIVE The aim of this study was to investigate the oxidizability of the hydrophobic core and the surrounding envelope of LDL and HDL in obese males. METHODS Fifty normal-weight (CT) and 60 obese (25< BMI<35 Kg/m2 OB; 40 without MS, wMS; 20 with MS according to ATP III criteria, MS) adult males were studied. Core and surface of LDL and HDL were labeled by incubating plasma with selective pyrenic probes before isolation of lipoproteins by ultracentrifugation. Susceptibility to 2,2'-azobis-2-methyl-propanimidamide-dihydrochloride-induced peroxidation was measured following kinetically the decrease of fluorescence of the probes. The length of the lag phase and maximum velocity of the reaction were used as indices of lipoprotein oxidizability. Lipoprotein contents of proteins, cholesterol, phospholipids and triglycerides were determined by colorimetric assays. RESULTS The oxidizability of both core and surface were higher in both LDL and HDL of OB than in CT. The oxidizability of the two lipoprotein regions was higher in MS than in wMS, especially that of HDL core. This last parameter was inversely correlated with visceral adiposity (measured as waist to hip ratio). Moreover, triglycerides levels of LDL and HDL were higher in MS than in wMS. CONCLUSIONS The elevated oxidizability of lipoproteins found in MS could be due to increased oxidative stress and alterations of the composition. These preliminary results could be the rationale of future clinical trials addressed to investigate the effects of different hypocaloric diets and/or nutritional supplementations on these parameters.