Seeking for a modified
lipoprotein present in plasma that could account for the atherogenic effect of high
cholesterol, several years ago electronegative
LDL(-) was identified. The peculiar feature of
LDL(-) is an
apoprotein misfolding that triggers the formation of aggregates, perfectly fitting in size the subendothelial droplets observed in early phases of
atherogenesis.
Apoprotein misfolding was therefore proposed as a possible atherogenic modification.
LDL(-) can be spontaneously produced in vitro by plasma incubation through
phospholipid hydrolysis catalyzed by the activity of endogenous
phospholipases. As a consequence,
apoprotein is misfolded. 17beta-Estradiol (E2), a specific
ligand to
apoB-100, was used to unravel the relationship between negative charge of the
lipoprotein and
apoprotein structural/conformational shift. Although E2 addition to plasma does not prevent
LDL(-) generation nor
phospholipase activity, it deeply stabilizes
apoB-100 structure, thus preventing its structural and conformational shift.
Apoprotein stabilization extends to
lipids. Indeed, while a loosening of
lipid packing is observed together with
apoprotein misfolding, conversely, when E2 stabilizes
apoprotein,
lipid structure is preserved. Finally, even in the presence of
LDL(-), the E2-stabilized
LDL is resistant to aggregation, unambiguously demonstrating that misfolding, but not negative charge, primes aggregation. In conclusion, electronegative charge and misfolding are independent and distinct features of
LDL(-), and
apoprotein misfolding rather than the increase in the negative charge emerges both as a valid
biomarker and as an appealing pharmacological and nutritional target.