Division of Cardiology, Department of Internal Medicine, Kaohsiung Medical University Hospital, Kaohsiung Medical University, Kaohsiung, Taiwan.
PLoS One. 2013 Aug 8;8(8):e70533. doi: 10.1371/journal.pone.0070533. eCollection 2013.
Increased plasma C-reactive protein (CRP) levels are associated with the occurrence and severity of acute coronary syndrome. We investigated whether CRP can be generated in vascular endothelial cells (ECs) after exposure to the most electronegative subfraction of low-density lipoprotein (LDL), L5, which is atherogenic to ECs. Because L5 and CRP are both ligands for the lectin-like oxidized LDL receptor-1 (LOX-1), we also examined the role of LOX-1.
Plasma LDL samples isolated from asymptomatic hypercholesterolemic (LDL cholesterol [LDL-C] levels, 154.6±20 mg/dL; n = 7) patients and normocholesterolemic (LDL-C levels, 86.1±21 mg/dL; P<0.001; n = 7) control individuals were chromatographically resolved into 5 subfractions, L1-L5. The L5 percentage (L5%) and the plasma L5 concentration ([L5] = L5% × LDL-C) in the patient and control groups were 8.1±2% vs. 2.3±1% (P<0.001) and 12.6±4 mg/dL vs. 1.9±1 mg/dL (P<0.001), respectively. In hypercholesterolemic patients treated with atorvastatin for 6 months (10 mg/day), [L5] decreased from 12.6±4 mg/dL to 4.5±1.1 mg/dL (P = 0.011; n = 5), whereas both [L5] and L5% returned to baseline levels in 2 noncompliant patients 3 months after discontinuation. In cultured human aortic ECs (HAECs), L5 upregulated CRP expression in a dose- and time-dependent manner up to 2.5-fold (P<0.01), whereas the least electronegative subfraction, L1, had no effect. DiI-labeled L1, internalized through the LDL receptor, became visible inside HAECs within 30 seconds. In contrast, DiI-labeled L5, internalized through LOX-1, became apparent after 5 minutes. L5-induced CRP expression manifested at 30 minutes and was attenuated by neutralizing LOX-1. After 30 minutes, L5 but not L1 induced reactive oxygen species (ROS) production. Both L5-induced ROS and CRP production were attenuated by ROS inhibitor N-acetyl cysteine.
Our results suggest that CRP, L5, and LOX-1 form a cyclic mechanism in atherogenesis and that reducing plasma L5 levels with atorvastatin disrupts the vascular toxicity of L5.
血浆 C 反应蛋白（CRP）水平升高与急性冠状动脉综合征的发生和严重程度有关。我们研究了暴露于致动脉粥样硬化的血管内皮细胞（ECs）的 LDL 的最电负性亚组分 L5 后，CRP 是否可以在血管内皮细胞中产生。因为 L5 和 CRP 都是凝集素样氧化型 LDL 受体-1（LOX-1）的配体，所以我们还研究了 LOX-1 的作用。
从无症状性高胆固醇血症（LDL 胆固醇[LDL-C]水平，154.6±20 mg/dL；n=7）患者和正常胆固醇血症（LDL-C 水平，86.1±21 mg/dL；P<0.001；n=7）对照组的血浆 LDL 样本中，通过色谱分离出 5 个亚组分，L1-L5。患者和对照组中 L5%（L5%）和血浆 L5 浓度[L5]=L5%×LDL-C）分别为 8.1±2%比 2.3±1%（P<0.001）和 12.6±4 mg/dL 比 1.9±1 mg/dL（P<0.001）。在接受阿托伐他汀治疗 6 个月（每天 10 mg）的高胆固醇血症患者中，[L5]从 12.6±4 mg/dL 降至 4.5±1.1 mg/dL（P=0.011；n=5），而在停药 3 个月后，2 名不遵医嘱的患者的[L5]和 L5%均恢复到基线水平。在培养的人主动脉内皮细胞（HAECs）中，L5 以剂量和时间依赖的方式上调 CRP 表达高达 2.5 倍（P<0.01），而最电负性的亚组分 L1 则没有作用。通过 LDL 受体内化的 DiI 标记的 L1 在 30 秒内可见于 HAEC 内。相比之下，通过 LOX-1 内化的 DiI 标记的 L5 在 5 分钟后才变得明显。L5 诱导的 CRP 表达在 30 分钟时表现出来，并被 LOX-1 中和物减弱。30 分钟后，L5 而非 L1 诱导活性氧（ROS）的产生。ROS 抑制剂 N-乙酰半胱氨酸减弱了 L5 诱导的 ROS 和 CRP 产生。
我们的结果表明，CRP、L5 和 LOX-1 在动脉粥样硬化形成中形成了一个循环机制，阿托伐他汀降低血浆 L5 水平可破坏 L5 的血管毒性。
