Unusually high reactivity of apolipoprotein B-100 among proteins to radical reactions induced in human plasma

Relative reactivities of proteins to radical reactions caused in human plasma were studied for the first time utilizing an immunoblotting assay. When radical reactions were caused by Cu2+, apolipoprotein B-100 (apoB) underwent extensive fragmentation concurrently with the decrease in α-tocopherol, while human serum albumin (HSA) and transferrin (TF) were not decreased at all. When radical reactions were initiated by Cu2+ with hydrogen peroxide or 2,2′-azobis(2-amidinopropane)dihydrochloride (AAPH), α-tocopherol and apoB were also decreased steadily but HSA and TF were not decreased. These observations indicate that apoB is extremely reactive, even comparable to α-tocopherol, towards radical reactions. These results also suggest that the radical reaction of apoB is a possible process in vivo and it is involved in atherogenesis along with low density lipoprotein lipid peroxidation, which has been studied extensively.