ANALYSIS OF LIPOPROTEIN DIENE FORMATION IN HUMAN SERUM EXPOSED TO COPPER

The susceptibility of low density lipoprotein (LDL) to oxidative modif ication can be determined by analyzing the lag phase for initiation of diene formation in isolated LDL exposed to Cu2+. However, the applica bility of this assay for clinical studies is limited by the requiremen t of a preparative ultracentrifugation of LDL and that the influence o f water soluble antioxidants and other lipoproteins is not accounted f or. The present paper describes a modification of this assay allowing determination of lag phase for iipoprotein diene formation in serum. T he formation of dienes in serum exposed to Cu2+ begins following the c onsumption of serum alpha-tocopherol, correlates to the formation of t hiobarbituric acid reactive substances (r = 0.987, n = 8), is inhibite d by the addition of ascorbic acid and is absent in lipoprotein-defici ent serum. It is also accompanied by an increased mobility of serum li poproteins on agarose gel electrophoresis and with an ability of serum to displace isolated copper-oxidized LDL from binding sites mediating degradation in mouse peritoneal macrophages. The coefficient of varia nce of the analysis is below 3%. It is concluded that this technique a llows analysis of lipoprotein oxidation susceptibility in serum sample s and may prove to be useful in clinical analysis of the lipoprotein o xidation susceptibility.