Differing Effects of Probucol and Vitamin E on the Oxidation of Lipoproteins, Ceroid Accumulation and Protein Uptake by Macrophages

Abstract

Studies using ¹²⁵I-low density lipoprotein (^l25I-LDL) show that probucol (10 μM) and α-tocopherol (100 μM) inhibit protein degradation in LDL exposed to Cu (II) in vitro. The inhibitory effect of α-tocopherol on protein fragmentation exceeded that of probucol. On the other hand, probucol was more able to inhibit lipid peroxidation. The subsequent uptake of Cu (II)-oxidised ¹²⁵I-LDL by murine peritoneal macrophages (MPM) was virtually unaffected by the presence of probucol during LDL oxidation. The same was not true for α-tocopherol which led to lower levels of ¹²⁵I-LDL uptake by MPM. Thus, it appears that although the antioxidant activity of probucol exceeds that of α-tocopherol for lipid oxidation, the reverse is true for protein degradation and, perhaps more significantly, for subsequent macrophage uptake.

Further studies used artificial lipoproteins composed of cholesteryl linoleate or cholesteryl arachidonate complexed with bovine serum albumin. Culture of these artificial lipoproteins with MPM resulted in protein uptake, protein degradation, cholesterol oxidation to cholest-5-en-3β, 7β-diol and the intracellular accumulation of ceroid in MPM. The presence of α-tocopherol (0-100 μM) inhibited all of these processes. Probucol (0-10 μM) inhibited ceroid accumulation and cholesterol oxidation to the same degree as α-tocopherol (0-100 μM) but had no effect upon protein degradation and protein uptake. Control studies of lipoproteins incubated without cells showed that protein degradation by cell-independent processes was also inhibited by α-tocopherol, but not by probucol.

These observations are discussed in the context of the role of lipoprotein oxidation in atherogenesis.

Key Words:

• Oxidation
• vitamin E
• probucol
• macrophages
• ceroid
• lipoprotein uptake