Direct modification of low density lipoprotein by the spin trap 3,5-dibromo-4-nitrosobenzenesulfonic acid

We have previously reported that the spin trap alpha-phenyl-tert-butyl nitrone (PBN) inhibited the oxidative modification of low density lipoprotein (LDL) (Kalyanaraman, B., Antholine, W.E. and Parthasarathy, S. (1990) Biochim. Biophys. Acta 1035, 286-292). In the present study, we report that 3,5-dibromo-4-nitrosobenzenesulfonic acid (DBNBS), a water-soluble spin trap, also inhibited the oxidation of LDL as measured by the formation of thiobarbituric acid reactive substances (TBARS). However, when compared with LDL incubated without DBNBS, the DBNBS-incubated LDL showed increased negative charge on agarose gel electrophoresis and was avidly degraded by mouse peritoneal macrophages. Despite the suggestion of biological modification, there was no decrease in lysine-amino groups in DBNBS-incubated LDL. Furthermore, reductively methylated LDL in which more than 85% of the amino group of lysines was blocked, was also modified by DBNBS. A sulfonic acid analog of PBN failed to modify LDL in a similar manner, suggesting that the presence of sulfonic acid alone does not ensure modification. When LDL was incubated with DBNBS, radical adducts associated with both lipid and protein were detected by electron paramagnetic resonance (EPR) technique. It is suggested that DBNBS may bind to the apoprotein B100 and lipids of LDL by a lysine-independent mechanism resulting in increased recognition and degradation by macrophages. The present work offers a novel approach for rapid modification of LDL.