Estradiol Enhances the Resistance of LDL to Oxidation by Stabilizing apoB-100 Conformation

Abstract

Among different proposed mechanisms to account for the protection exerted by estrogens against cardiovascular diseases, the antioxidant effect has attracted considerable attention. We confirmed that 17-beta-estradiol (E2), when added to human LDL at a 6:1 ratio to apoB-100, markedly delays the phase of massive LDL lipid peroxidation induced by Cu(2+). We also observed an increased oxidative resistance of E2-treated LDL by monitoring the early phase of oxidative degradation on the basis of increased LDL surface polarity by the generalized polarization of the lipophilic fluorescent probe 2-(dimethylamino)-6-lauroylnaphthalene (Laurdan). A scavenging of free radicals by E2 is ruled out since, consistent with its structure, its rate constant for the reduction of peroxy radicals is extremely low, i.e., 0.02% of that of vitamin E. Tryptophan fluorescence lifetime and circular dichroism measurements revealed that (i) apoB-100 undergoes a conformational modification and a progressive loss of secondary structure during lipid peroxidation; (ii) E2 increases apoB-100 secondary structure and modifies its conformation; and (iii) the apoB-100 conformational change induced by E2 makes this protein resistant to modifications brought about by lipid peroxidation. We propose that E2, by affecting apoB-100 secondary structure and conformation, modifies the interaction of this protein with the outer layer of the LDL particle thus increasing its overall oxidative resistance.

Hormonal and Chemical Regulation of Paraoxonases in Mice

“…In rats, 17␤-estradiol treatment increases the peroxidation of LDL (Butterworth et al, 1998;Chiang et al, 2004;Eybl et al, 2004), but in humans estradiol at physiological concentrations is unlikely to act as an antioxidant and even as a pro-oxidant in women with high estradiol levels who have increased myeloperoxidase protein in their plasma (Santanam et al, 1998). However, there is evidence that estrogens protect against oxidation of LDL in humans (Arteaga et al, 1998;Brunelli et al, 2000;Ruiz-Sanz et al, 2001;Rontu et al, 2004). Therefore, it seems that estrogens can function to either decrease or increase Pon1/PON1 expression and activity and depends on the dosage of estrogens and species studied.…”

Metabolism and Modification of Apolipoprotein B-Containing Lipoproteins Involved in Dyslipidemia and Atherosclerosis

“…307) However, the overall secondary structure of lipid-free apoB is highly conserved, suggesting the solubilization of lipid-free apoB by NaDC may lead to only partial unfolding of the secondary structure in apoB rather than global protein unfolding as shown in oxLDL or LDL(−). 299,300,303,307,308) I have investigated the cytotoxic effect of lipid-free apoB solubilized with NaDC, as a model for denatured apoB. Lipidfree apoB has cytotoxicity to J774 macrophages, HepG2 cells and Chinese hamster ovary cells, whereas LDL-apoB and lipid-free apoA-I have no effect on the cell viability.…”

Phytosterols inhibit the tumor growth and lipoprotein oxidizability induced by a high-fat diet in mice with inherited breast cancer

“…2-Dimethylamino-6-lauroylnaphthalene (Laurdan, Molecular Probes Inc., Eugene, OR, USA) was incorporated into pooled samples of mouse HDL as previously described [22]. Briefly, mouse HDL (50 μg of protein per milliliter) were labeled with Laurdan using a final probe concentration of 0.375 μM.…”

“…5D, the value of Laurdan GP was found to be significantly decreased in HDL obtained from mice consuming added phytosterols compared to those who did not (P=.0286). Decreased Laurdan GP values are associated with increased packing of the surface lipids [22], a phenomenon that promotes lipoprotein resistance to oxidative processes [25]. By contrast, these phytosterolinduced changes were not associated with changes in apolipoprotein (apo)A-I or apoA-IV concentrations nor in paraoxonase (PON1) and platelet-activated factor acetyl-hydrolase activities, which are thought to confer part of the antioxidant properties on HDL (data not shown).…”