Plasma oxysterols and tocopherol in patients with diabetes mellitus and hyperlipidemia

The plasma levels of free oxysterols (7-ketocholesterol; 7 alpha-hydroxy-,7 beta-hydroxy-, 25-hydroxy-, and 27-hydroxycholesterol; and 5 alpha,6 alpha -epoxycholestanol) in patients with diabetes mellitus and hypercholesterole mia were determined using gas chromatography-mass spectrometry with selecti ve ion monitoring. We studied 39 patients with diabetes mellitus, 20 nondia betic patients with hypercholesterolemia, and 37 normal controls. Plasma ch olesterol levels in diabetic and hypercholesterolemic patients showed no st atistical difference. Plasma 7-ketocholesterol was significantly higher in patients with diabetes (31.6 +/- 2.8 ng/mL) or hypercholesterolemia (52.3 /- 5.9) than in the control group (22.4 +/- 1.2). The increased plasma chol esterol can be regarded as an oxidation substrate for the oxidant stress an d the higher absolute levels of oxysterols in hypercholesterolemic plasma c ompared with the control plasma. This difference disappeared when 7-ketocho lesterol was expressed in proportion to total cholesterol. The oxidizabilit y of plasma cholesterol was evaluated by comparing the increased ratio of 7 -ketocholesterol after CuSO4 oxidation to the ratio before. We demonstrated that the patients with diabetes showed increased oxidizability (77.5%) com pared with the control (36.6%) or hyperlipemic group (45.3%), which is like ly due to the lower amounts of alpha-tocopherol in the diabetics. Measureme nt of oxysterols may serve as a marker for in vivo oxidized lipoproteins in diabetes and hyperlipemia.