The in vitro oxidizability of lipoprotein particles in obese and non-obese subjects.

There exists much evidence suggesting a major role for the oxidized low density lipoprotein (LDL) and VLDL particles in the pathogenesis of atherosclerosis. Although obesity is characterized by dyslipidemia, less is known about the oxidation capacity of lipoproteins in obese subjects. We measured the oxidizability in vitro in 21 premenopausal women with a BMI of 36.7+/-5.4 and compared them to 18 age-matched controls (BMI 21.9+/-1.8). The oxidizability of the non-HDL fraction is evaluated by measuring the fluorescence and thiobarbituric acid reactive substances (TBARS; MDA nM/mg non-HDL) at different time intervals of incubation. TBARS formation increased linearly with the increase of lipids both in non-obese and obese subjects. TBARS, measured every 30 min, increased in non-obese controls up to a maximum of 59.6 at 180' in contrast to a maximum of 77.1 at 180' (P < 0.001) in obese, but healthy, normocholesterolemic subjects. At each measurement the TBARS were significantly higher (P < 0.01-0.001) in obese subjects. Also the lag-time (period from zero to the start of the particle oxidation process) was significantly lower (92.5 vs. 123.4; P < 0.001) in obese subjects, when compared to lean controls. BMI correlates significantly with TBARS formation and its log transformed values (maximum P < 0.001). The lag-time was negatively related (n=39 total group, r=- 0.57, P < 0.001) to body weight and BMI. A significant relationship exists between TBARS formation (up to r=0.59) and triglyceride levels and a negative relationship exists with HDL-cholesterol levels. In vitro oxidizability of non-HDL lipoproteins is significantly increased in obese, non-diabetic subjects and related to increased body weight and triglyceride levels. Further studies are necessary to explore the underlying mechanisms for this phenomenon.