Bielicki J K, Forte T M, McCall M R
Lawrence Berkeley National Laboratory, Life Sciences Division, University of California at Berkeley 94720, USA.
J Lipid Res. 1996 May;37(5):1012-21.
The oxidation of low density lipoproteins (LDL) has been implicated in the development of atherosclerosis. As a variety of highly reactive lipid peroxidation products can transfer from oxidized LDL to HDL, we evaluated the potential deleterious effects of LDL oxidation on HDL-cholesterol metabolism. To address this issue, we exposed the HDL-containing d > 1.063 g/ml fraction of human plasma to copperoxidized LDL and assessed lecithin:cholesterol acyltransferase (LCAT) activity and apolipoproteinA-I (apoA-I) structure. To determine whether LCAT was directly affected by oxidized LDL, independent of crosslinking of apoA-I, we used an exogenous, [14C]cholesterol-labeled proteoliposome substrate to measure plasma LCAT activity. We observed an inhibition of LCAT activity where copper-oxidized LDL possessing only 2.3 +/- 0.1 and 7.3 +/- 1.4 TBARS produced 24 +/- 3% and 47 +/- 10% reductions in [14C]cholesterol esterification by 1 h, respectively. Copper-oxidized LDL that had been passed through a GF-5 desalting column, while retaining only one-third of its original TBARS, possessed nearly all of its LCAT inhibitory capacity suggesting that the LCAT inhibitory factor(s) was a lipophilic oxidation product. Analysis of polarlipids isolated from copper-oxidized LDL indicated that phospholipid and sterol fractions effectively inhibited LCAT. Copper-oxidized LDL, with as little as 6.3 TBARS, also produced intermolecular crosslinking of apoA-I molecules. Taken together, these data suggest that products of LDL oxidation may adversely affect HDL-cholesterol metabolism by two separate mechanisms: 1) a direct inhibitory effect on LCAT activity and 2) through crosslinking of apoA-I. If occurring in vivo, minimally oxidized LDL may impair cholesteryl ester formation on HDL thereby limiting the ability of HDL to function efficiently in the putative antiatherogenic reverse cholesterol transport pathway.
低密度脂蛋白（LDL）的氧化与动脉粥样硬化的发展有关。由于多种高反应性脂质过氧化产物可从氧化的LDL转移至HDL，我们评估了LDL氧化对HDL胆固醇代谢的潜在有害影响。为解决此问题，我们将人血浆中密度大于1.063 g/ml的含HDL部分暴露于铜氧化的LDL中，并评估卵磷脂胆固醇酰基转移酶（LCAT）活性和载脂蛋白A-I（apoA-I）结构。为确定LCAT是否直接受氧化LDL影响而与apoA-I交联无关，我们使用外源的、[14C]胆固醇标记的蛋白脂质体底物来测量血浆LCAT活性。我们观察到LCAT活性受到抑制，其中仅含有2.3±0.1和7.3±1.4硫代巴比妥酸反应物（TBARS）的铜氧化LDL，在1小时内分别使[14C]胆固醇酯化减少了24±3%和47±10%。通过GF-5脱盐柱的铜氧化LDL，虽然仅保留了其原始TBARS的三分之一，但其几乎保留了所有的LCAT抑制能力，这表明LCAT抑制因子是一种亲脂性氧化产物。对从铜氧化LDL中分离出的极性脂质的分析表明，磷脂和甾醇部分可有效抑制LCAT。铜氧化LDL，即使只有6.3 TBARS，也会使apoA-I分子发生分子间交联。综上所述，这些数据表明LDL氧化产物可能通过两种不同机制对HDL胆固醇代谢产生不利影响：1）对LCAT活性的直接抑制作用；2）通过apoA-I交联。如果在体内发生，轻度氧化的LDL可能会损害HDL上胆固醇酯的形成，从而限制HDL在假定的抗动脉粥样硬化逆向胆固醇转运途径中有效发挥功能的能力。
