Oxidized low-density lipoprotein (Ox-LDL) but not LDL aggravates the manifestations of experimental antiphospholipid syndrome (APS)

Abstract

SUMMARYOx-LDL is thought to play a major role in atherogenesis. The mechanisms mediating the deleterious influences of Ox-LDL include foam cell formation and cell cytotoxicity. The production of anti-Ox-LDL antibodies results in the formation of immune complexes which are taken up at enhanced rate by macrophages, leading to foam cell formation. APS is characterized by repeated venous and arterial thromboembolic phenomena, recurrent fetal loss and thrombocytopenia, associated with the presence of antibodies to negatively charged phospholipids (aPL) (i.e. cardiolipin, phosphatidylserine). Phospholipids bear structural resemblance to LDL, and several studies have indeed proved that aPL display cross-reactivity with anti-Ox-LDL antibodies. In this study we assessed the capacity of oxidized and native forms of LDL to aggravate the clinical picture of experimentally induced APS in naive mice. Mice were actively immunized intradermally with anticardiolipin antibodies and developed a clinical picture resembling APS in humans. Subsequently, the mice were infused with either Ox-LDL, native LDL or PBS, and similar regimens were applied to controls. APS mice infused with Ox-LDL were found to exhibit a significantly more severe form of the disease in comparison with native LDL-and PBS-infused mice, expressed by lower platelet counts (261 000/mm 3 , 535 000/mm 3 and 455 000/mm 3 , respectively), longer activated partial thromboplastin time (aPTT) (99 Ϯ 12 s, 63 Ϯ 8 s and 74 Ϯ 8 s, respectively) and higher fetal resorption rates (72 . 7%, 34 . 4% and 32 . 6%, respectively). The results of this study show that Ox-LDL, compared with native LDL, aggravates the clinical manifestations of experimental APS and suggest that cross-reactivity of Ox-LDL with phospholipids may provide a pathogenic explanation for this effect.

Are Anti–Oxidized Low-Density Lipoprotein Antibodies Pathogenic or Protective?

“…32,33 In a study using a mouse model of experimental antiphospholipid syndrome (APS), mice immunized with oxLDL exhibited a significantly more severe form of the disease compared with native LDL-immunized mice, as expressed by lower platelet counts, longer activated partial thromboplastin time, and higher fetal resorption rates. 34 The interaction of IgG anti-␤2GP-I antibody from the spontaneous mouse model of APS, ie, NZW x BXSB F1 mouse, with the ␤2GP-I-oxLDL complexes significantly enhanced oxLDL uptake by macrophages. 35,36 The results 34 indicate that oxLDL aggravates the clinical manifestations of APS and suggest that autoantibodies cross-reactive with oxLDL may provide a pathogenic mechanism for accelerated atherosclerosis in APS.…”

“…34 The interaction of IgG anti-␤2GP-I antibody from the spontaneous mouse model of APS, ie, NZW x BXSB F1 mouse, with the ␤2GP-I-oxLDL complexes significantly enhanced oxLDL uptake by macrophages. 35,36 The results 34 indicate that oxLDL aggravates the clinical manifestations of APS and suggest that autoantibodies cross-reactive with oxLDL may provide a pathogenic mechanism for accelerated atherosclerosis in APS.…”

Enhanced Fatty Streak Formation in C57BL/6J Mice by Immunization With Heat Shock Protein-65

“…LDL (densityϭ1.019 to 1.063 g/mL) was isolated from plasma as previously described, 20 after density adjustment with added KBr, by preparative ultracentrifugation at 50 000 rpm/min for 22 hours with a type 50 rotor. LDL preparations were washed by ultracentrifugation, dialyzed against 0.15 mol/L EDTA (pH 7.4), passed through an Acrodisc filter (0.22-m pore size) to remove aggregates, and stored under N 2 in the dark.…”

Induction of Early Atherosclerosis in LDL-Receptor–Deficient Mice Immunized With β 2 -Glycoprotein I

“…LDL (density, 1.019 to 1.063 g/L) was isolated from the plasma after density adjustment with KBr by preparative ultracentrifugation at 50 000 rpm for 22 hours with a type 50 rotor as previously described. 30 LDL preparations were washed by ultracentrifugation, dialyzed against 0.15 mol/L EDTA (pH 7.4), passed through an Acrodisc filter (0.22-m pore size) to remove aggregates, and stored under nitrogen in the dark. Copper oxidation of LDL was performed by incubation of postdialyzed LDL (1 mg of protein/mL in EDTA-free PBS) with copper sulfate (10 mol/L) for 24 hours at 37°C.…”

“…Lipoprotein oxidation was confirmed by analysis of thiobarbituric acid-reactive substances (TBARS). 30 Recombinant heat shock protein (HSP)-65 was kindly provided by Dr M. Singh, Braunschweig, Germany.…”