Unraveling the Complexity of Lipoprotein(a) Metabolism: Human Kinetic Studies

脂蛋白（a）[Lp（a）]是由Kare贝格于1963年发现的，但关于这种独特的脂蛋白仍有很多东西有待了解，它是心血管疾病（CVD）的独立危险因素。霍夫等人在30年前证实了动脉粥样硬化病变中的Lp（a），在JUPITER试验（一项高剂量他汀类药物试验）中，Lp（a）是接受瑞舒伐他汀的受试者中残余CVD风险的重要决定因素。Lp（a）水平很难改变，但新批准和开发的药物可显著降低Lp（a）血浆浓度。Lp（a）由与载脂蛋白B [apo B]共价结合的载脂蛋白（a）[apo（a）]组成，并且两种组分Lp（a）-apo（a）和Lp（a）-apo B均与CVD的发展有关。虽然Lp（a）在生物化学上与LDL密切相关，但已在通过超离心分离的apoB的不同密度级分中发现Lp（a）。许多研究强调了Lp（a）在疾病中的重要性，然而，关于Lp（a）在肝脏和/或血浆中的组装（apo（a）和apoB 100颗粒在哪里以及如何结合）以及如何从循环中去除的关键问题仍然存在。我们的实验室使用稳定同位素来检查人体内脂蛋白的清除和产生。质谱分析的最新进展使我们能够使用通过针对apo（a）的免疫沉淀从血浆中分离的Lp（a）来检查整个Lp（a）颗粒、其apo（a）和apoB组分以及apo（a）的同种型的清除和产生。Lp（a）水平在很大程度上取决于KVI-2型重复序列（同种型）的变异。本申请解决了Lp（a）代谢中存在的缺口，并检查了Lp（a）代谢和同种型大小之间的关系。我们有两个目标：目标1：我们将通过免疫沉淀（IP）从血浆中分离Lp（a），并使用稳定同位素的预充恒定输注和新建立的质谱（MS）方法测定Lp（a）-apo（a）和Lp（a）-apoB的部分清除率和分泌率。我们还将确定所有受试者中KIV-2重复的数量。我们将招募Lp（a）浓度低和高的个体（N=20，Lp（a）15 - 30 nmol/L和N=20，Lp（a）75- 350 nmol/L）。我们已经开发了全面的模型，允许Lp（a）代谢途径的表征。目的2：我们将检查来自目的1的15名具有两种可检测的apo（a）亚型的受试者。IP Lp（a）后，我们将分离两种apo（a）亚型（每一个都将与apoB 100连接），并通过MS测定分离的复合物中Lp（a）-apo（a）和Lp（a）-apoB的FCR。随着Lp（a）治疗方法的改进，我们必须详细和准确地了解调节Lp（a）水平的因素，如果KIV-2型重复对这种心血管危险因子的代谢有影响。

Lipoprotein (a) [Lp(a)] was identified by Kare Berg in 1963, but much remains to be learned about this unique lipoprotein, which is a an independent risk factor for cardiovascular disease (CVD). Hoff et al demonstrated Lp(a) within atherosclerotic lesions 30 years ago, and in the JUPITER trial (a high dose statin trial), Lp(a) was a significant determinant of residual CVD risk in subjects receiving rosuvastatin. Lp(a) levels have been difficult to alter, but newly approved and developing drugs lower Lp(a) plasma concentrations significantly. Lp(a) is comprised of apolipoprotein (a) [apo(a)] covalently bound to apolipoprotein B [apoB], and both components Lp(a)-apo(a) and Lp(a)-apoB, are implicated in the development of CVD. Although it is closely related to LDL biochemically, Lp(a) has been found in varying density fractions of apoB isolated via ultracentrifugation. Many studies have highlighted the importance of Lp(a) in disease, however, key questions remain about the assembly of Lp(a) (where and how the apo(a) and apoB100 particle bind) within the liver and/or plasma and how it is removed from the circulation. Our laboratory uses stable isotopes to examine the clearance and production of lipoproteins in humans. Recent advances in mass spectrometry has allowed us to use Lp(a) isolated from plasma by immunoprecipitation directed against apo(a) to examine clearance and production of the whole Lp(a) particle, its apo(a) and apoB components, and isoforms of apo(a). Lp(a) levels are largely determined by variation in KVI-type 2 repeats (Isoforms). The current application addresses existing gaps in Lp(a) metabolism and examines relationships between Lp(a) metabolism and isoform size. We have two aims: Aim 1: We will isolate Lp(a) from plasma by immunoprecipitation (IP) and determine the fractional clearance rates and secretion rates of Lp(a)-apo(a) and Lp(a)-apoB using primed constant infusion of stable isotopes and newly established mass spectrometry (MS) methods. We will also determine the number of KIV-2 repeats in all subjects. We will enroll individuals with low and high Lp(a) concentrations (N=20, Lp(a) 15 -30nmol/L and N=20, Lp(a) 75-350nmol/L). We have developed comprehensive models to allow characterization of pathways of Lp(a) metabolism. Aim 2: We will examine 15 subjects from Aim 1 with two detectable apo(a) isoforms. After IP of Lp(a), we will isolate two apo(a) isoforms (each will be linked to apoB100) via non-denaturing electrophoresis and determine the FCRs of Lp(a)-apo(a) and Lp(a)-apoB within the isolated complexes via MS. As improved therapeutic approaches to Lp(a) move forward, it is imperative that we have a detailed and precise understanding of the factors that regulate Lp(a) levels and if the KIV- type 2 repeats have an effect on metabolism of this cardiovascular risk factor.