LDL phospholipid hydrolysis produces modified electronegative particles with an unfolded apoB-100 protein

Abstract

Electronegative low density lipoprotein (LDL−) formation that structurally resembles LDL− isolated from plasma was evaluated after LDL treatment with snake venom phospholipase A2 (PLA2). PLA2 treatment of LDL increased its electrophoretic mobility in proportion to the amount of LDL− formed without evidence of lipid peroxidation. These changes dose-dependently correlated with the degree of phospholipid hydrolysis. Strong immunoreactivity of LDL− subfraction from plasma and PLA2-treated LDL (PLA2-LDL) to amyloid oligomer-specific antibody was observed. Higher β-strand structural content and unfolding proportionate to the loss of α-helical structure of apolipoprotein B-100 (apoB-100) of LDL− isolated from both native and PLA2-LDLs was demonstrated by circular dichroism (CD) spectropolarimetry. These structural changes resembled the characteristics of some oxidatively modified LDLs and soluble oligomeric aggregates of amyloidogenic proteins. PLA2-LDL was also more susceptible to nitration by peroxynitrite, likely because of exposure of otherwise inaccessible hydrophilic and hydrophobic domains arising from apoB-100 unfolding. This was also demonstrated for plasma LDL−. In contrast, PLA2-LDL was more resistant to copper-mediated oxidation that was reversed upon the addition of small amounts of unsaturated fatty acids.The observed similarities between PLA2-LDL−-derived LDL− and plasma LDL− implicate a role for secretory PLA2 in producing modified LDL− that is facilitated by unfolding of apoB-100.

Keywords

• apolipoprotein B-100
• atherogenic low density lipoprotein
• lipid peroxidation
• oxidation
• nitrotyrosine
• unsaturated fatty acids