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

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.