Dialysis and gel filtration of isolated low density lipoproteins do not cause a significant loss of low density lipoprotein tocopherol and carotenoidconcentration

The resistance of isolated low density lipoprotein (LDL) to copper-initiate d oxidation is often used as a measure of effectiveness of an antioxidant i ntervention. Prior to oxidation, excess salt and EDTA are removed via dialy sis or gel filtration of the LDL sample. However, there is concern over whe ther the antioxidant content of dialyzed or gel-filtered LDL is truly repre sentative of native LDL extracted from a blood sample. Previously, the expe riments done after the storage of native and dialyzed LDL at -80 degreesC s howed that the dialysis step can cause a loss of up to 60% in the tocophero l and carotenoid content of LDL. In the present study, a comparison of the micronutrient concentration in freshly prepared dialyzed and native LDL fro m 35 subjects showed that after the correction for cholesterol, only lycope ne (13%, P < 0.001) and to a lesser extent a-carotene (8%, P< 0.02) were si gnificantly decreased, and the absolute fall in concentration was far small er than previously reported. Other experiments done with smaller numbers of samples suggested that there were minimal micronutrient losses following g el filtration and that it was important to include 10 mu mol/L EDTA in the dialysis and elution buffer; otherwise micronutrient losses did occur. In s ummary, immediate dialysis of freshly isolated LDL in the presence of 10 mu mol/L EDTA does not cause any major loss in the concentration of tocophero l and most carotenoids.