The effect of EDTA on the oxidation of low density lipoprotein

Low density lipoprotein (LDL) is routinely isolated and stored in buffers containing ethylene-diaminetetra-acetic acid (EDTA) to inhibit its autoxidation. We have investigated the effect of EDTA on LDL oxidation by both copper ions and macrophages. LDL oxidation by macrophages in Ham's F-10 medium containing 6 microM iron showed a large and concentration-dependent increase when EDTA was added up to about 10 microM. EDTA concentrations above about 10 microM progressively inhibited LDL oxidation as measured by macrophage degradation, thiobarbituric acid-reactive substances and electrophoretic mobility. The oxidation of LDL by 1 microM copper in Ham's F-10 medium, measured by macrophage degradation, also showed a large increase with low concentrations of EDTA (1-3 microM), with higher concentrations (10 microM or above) strongly inhibiting the oxidation. In a simple phosphate buffer, however, EDTA simply inhibited the oxidation of LDL by copper with equimolar amounts of EDTA to copper giving a complete inhibition. The results of this study indicate that when LDL oxidation by cells or by copper in Ham's F-10 medium is investigated, more oxidation may be obtained if the EDTA is not previously removed from the LDL preparation.