Tsoukatos D C, Arborati M, Liapikos T, Clay K L, Murphy R C, Chapman M J, Ninio E
Department of Chemistry, University of Ioannina, Greece.
Arterioscler Thromb Vasc Biol. 1997 Dec;17(12):3505-12. doi: 10.1161/01.atv.17.12.3505.
Free radical-mediated oxidation of cholesterol-rich LDL plays a key role in atherogenesis and involves the formation of oxidized phospholipids with proinflammatory biological activity. We evaluated the production of platelet-activating factor (PAF), a potent inflammatory mediator, in human LDL subspecies on copper-initiated oxidation (4 mumol/L CuCl2, 80 micrograms/mL for hours at 37 degrees C). PAF formation was determined by biological assay of HPLC-purified lipid extracts of copper-oxidized lipoproteins; chemical identity was confirmed by gas chromatographic and mass spectrometric analyses. PAF, characterized as the C16:0 molecular species, was preferentially produced in intermediate LDL (d = 1.029 to 1.039 g/mL) (8.6 +/- 5.7 pmol PAF/3 h per mg LDL protein) and light LDL (d = 1.019 to 1.029 g/mL), but was absent from dense LDL particles (d = 1.050 to 1.063 g/mL). As PAF:acetylhydrolase inactivates PAF and oxidized forms of phosphatidylcholine, we evaluated the relationship of lipoprotein-associated PAF:acetylhydrolase to PAF formation. We confirmed that PAF:acetylhydrolase activity was elevated in native, dense LDL (41.5 +/- 9.5 nmol/min per mg protein) but low in LDL subspecies of light and intermediate density (d 1.020 to 1.039 g/mL) (3.5 +/- 1.6 nmol/min per mg protein) [Tselepis et al, Arterioscler Thromb Vasc Biol. 1995;15:1764-1773]. On copper-mediated oxidation for 3 hours at 37 degrees C, dense LDL particles conserved 20 +/- 14% of their initial enzymatic activity; in contrast, PAF:acetylhydrolase activity was abolished in light and intermediate LDL subspecies. Clearly, the elevated PAF:acetylhydrolase activity of dense LDL efficiently diminishes the potential inflammatory role of endogenously formed PAF; nonetheless, formation of proatherogenic lysophospholipids results. In contrast, LDL particles of the light and intermediate subclasses can accumulate PAF on oxidative modification.
富含胆固醇的低密度脂蛋白（LDL）的自由基介导氧化在动脉粥样硬化形成中起关键作用，且涉及具有促炎生物活性的氧化磷脂的形成。我们评估了在铜引发的氧化过程（4μmol/L氯化铜，37℃下80μg/mL，持续数小时）中，人LDL亚类中血小板活化因子（PAF，一种强效炎症介质）的产生情况。通过对铜氧化脂蛋白的HPLC纯化脂质提取物进行生物学测定来确定PAF的形成；通过气相色谱和质谱分析确认化学特性。被鉴定为C16:0分子种类的PAF优先在中间密度LDL（d = 1.029至1.039 g/mL）（每毫克LDL蛋白每3小时8.6±5.7 pmol PAF）和低密度LDL（d = 1.019至1.029 g/mL）中产生，但在高密度LDL颗粒（d = 1.050至1.063 g/mL）中不存在。由于PAF：乙酰水解酶可使PAF和磷脂酰胆碱的氧化形式失活，我们评估了脂蛋白相关的PAF：乙酰水解酶与PAF形成之间的关系。我们证实，PAF：乙酰水解酶活性在天然高密度LDL中升高（每毫克蛋白41.5±9.5 nmol/分钟），但在低密度和中间密度的LDL亚类（d 1.020至1.039 g/mL）中较低（每毫克蛋白3.5±1.6 nmol/分钟）[Tselepis等人，《动脉硬化血栓与血管生物学》。1995年；15:1764 - 1773]。在37℃下铜介导氧化3小时后，高密度LDL颗粒保留了其初始酶活性的20±14%；相比之下，低密度和中间密度LDL亚类中的PAF：乙酰水解酶活性被消除。显然，高密度LDL中升高的PAF：乙酰水解酶活性有效地降低了内源性形成的PAF的潜在炎症作用；尽管如此，仍会形成促动脉粥样硬化的溶血磷脂。相比之下，低密度和中间亚类的LDL颗粒在氧化修饰时可积累PAF。
