Molecular biological studies on the formation of atherogenic small dense low density lipoprotein (sLDL)

我们系统地研究了循环中小而致密的低密度脂蛋白(SLDL)的形成机制，它被认为是动脉粥样硬化的危险因素之一。由于sLDL在IV型高甘油三酯血症患者中非常常见，我们首先试图通过监测32名非糖尿病IV型高甘油三酯血症患者肝素后血浆中LPL免疫反应性质量进行第一次筛查，然后使用PCR-SSCP和直接测序方法第二次筛查LPL基因异常，以阐明IV型高甘油三酯血症患者的潜在病因。通过这种方法，我们发现LPL杂合性缺乏是IV型高甘油三酯血症的一种潜在的遗传性疾病，并且LPL杂合性缺乏的人在获得甘油三酯(TG)合成刺激因子(如高酒精摄入量)时容易出现IV型高甘油三酯血症。为了了解高甘油三酯血症下sLDL的形成机制，比较了30例IV型高甘油三酯血症患者和30名正常人的脂蛋白。高密度脂蛋白(HDLTG/CE)中甘油三酯(TG)与胆固醇(CE)的比值与血清中的甘油三酯(TG)浓度相关，进一步寻找与低密度脂蛋白(LDL)大小变化相关的因素，低密度脂蛋白(LDL)大小的变化与高密度脂蛋白(HDLTG/CE)比值和肝甘油三酯酶(HTGL)免疫活性物质呈负相关。这一统计数据被体外实验所证实，即高密度脂蛋白的脂质成分通过与对应于IV型高甘油三酯血症的大量VLDL相互作用而转变为富甘油三酯和贫甘油三酯颗粒。低密度脂蛋白通过与富含TG/Ce的高密度脂蛋白相互作用转化为富含Tg的颗粒和贫Ce的颗粒，最后通过HTGL作用使低密度脂蛋白发生甘油三酯的水解反应生成sLDL。

We have systematically investigated the mechanism of formation of small dense low density lipoprotein (sLDL) in the circulation which is known to be one of risk factors for atherosclerosis. As sLDL is high frequently found on patients with type IV hypertriglyceridemia, we first attempted to clarify an underlying etiology of type IV hypertriglyceridemia by monitoring LPL immunoreactive mass in postheparin plasma of 32 non-diabetic patients with type IV hypertriglyceridemia using our sandwich-EIA technique for the first screenig, followed by a second screening for LPL gene aberrations using PCR-SSCP and direct sequencing methods. By this approach, we found that heterozygous LPL deficiency was an underlying genetic disorder of type IV hypertriglyceridemia, and that subjects with heterozygous LPL deficiency are prone to manifest type IV hypertriglyceridemia when they acquire triglyceride (TG) synthesis stimulating factors like high alcohol intake.In order to understand the mechanism of the formation of sLDL under hypertriglyceridemia, lipoproteins isolated from 30 subjects with type IV hypertriglyceridemia and 30 normal subjects were compared. The ratio of TG over cholesterol ester (CE) in HDL (HDL-TG/CE) was correlated with serum TG concentration derived from TG-rich lipoproteins such as VLDL.Factors correlating with LDL size variation were further searched, and the variation of LDL size was reversely correlated with HDL-TG/CE ratio and hepatic triglyceride lipase (HTGL) immunoreactive mass in PHP.These statistical data were confirmed by in vitro experiments in which lipid composition of HDL is changed into TG-rich and CE-poor particle via lipid transfer protein action by interacting with high amount of VLDL corresponding to type IV hypertriglyceridemia, and LDL is converted into TG-rich and CE-poor particle by interacting with TG-rich/CE-poor HDL,and in the final step TG hydrolysis of LDL by HTGL action results in the formation of sLDL.