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

我们系统地研究了小密度低密度脂蛋白（sLDL）在血液循环中的形成机制，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，我们首先使用三明治- eia技术进行第一次筛查，通过监测32例非糖尿病型高甘油三酯血症患者的肝素后血浆中的LPL免疫反应性块，然后使用PCR-SSCP和直接测序方法进行第二次筛查LPL基因异常，试图阐明IV型高甘油三酯血症的潜在病因。通过这种方法，我们发现杂合性LPL缺乏症是IV型高甘油三酯血症的潜在遗传疾病，并且杂合性LPL缺乏症的受试者在获得甘油三酯（TG）合成刺激因素（如高酒精摄入）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形成的机制，我们比较了30例IV型高甘油三酯血症患者和30例正常人的脂蛋白。HDL中TG/胆固醇酯（CE）的比值（HDL-TG/CE）与血清中由富含TG的脂蛋白（如VLDL）产生的TG浓度相关。进一步寻找LDL大小变化的相关因素，发现LDL大小变化与PHP中HDL-TG/CE比值和肝甘油三酯脂肪酶（HTGL）免疫反应质量呈负相关。这些统计数据通过体外实验得到证实，HDL的脂质组成通过脂质转移蛋白作用与IV型高甘油三酯血症对应的大量VLDL相互作用，转化为富TG和贫ce的颗粒，LDL通过与富TG /贫ce的HDL相互作用转化为富TG和贫ce的颗粒，最后通过HTGL作用TG水解LDL形成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.