Murdoch S J, Breckenridge W C
Department of Biochemistry, Dalhousie University, Halifax, Nova Scotia, Canada.
Atherosclerosis. 1995 Dec;118(2):193-212. doi: 10.1016/0021-9150(95)05606-8.
In order to study the relative effects of lipolytic enzymes on the removal of lipids and apolipoproteins, in particular apolipoprotein (apo) E and cholesteryl ester, from human very low density lipoprotein (VLDL) during its conversion to product lipoproteins, the action of lipoprotein lipase (LPL) and the combined action of lipoprotein lipase and hepatic lipase (HL) were studied in the presence of physiological proportions of high density lipoprotein (HDL) (10 mg protein), VLDL (2 mg protein) and albumin in an amount sufficient for the binding of all released fatty acids. The HDL used in the incubation was free of apo E in order to facilitate assessment of apo E transfer from VLDL to HDL. The redistribution of lipid and apolipoprotein mass and the movement of labeled cholesteryl ester from VLDL to other lipoprotein fractions was assessed by density gradient ultracentrifugation. Following 90%-95% lipolysis of VLDL triglycerides by rat heart LPL in 2 h, there was an almost complete transfer of apo C-II and apo C-III to HDL but only 20% of VLDL apo E was transferred to HDL. There was significant augmentation of HDL unesterified cholesterol and phospholipid mass during LPL action despite a substantial overall phospholipid hydrolysis (30%). The transfer of cholesteryl ester mass to HDL was variable (0%-13%) with a mean transfer of 7% of VLDL cholesteryl ester. Transfer of labeled VLDL cholesteryl ester to HDL was 3%-6%. A considerable amount of the VLDL lipid mass appeared in the light fraction of the low density lipoprotein (LDL) region, but a substantial amount remained in the VLDL/intermediate density lipoprotein (IDL) region. The post-lipolysis particles that were isolated in the VLDL-LDL density range were larger than LDL and contained a high ratio of surface lipids relative to core lipids as compared to plasma LDL. The inclusion of human HL with LPL did not alter the redistribution of apolipoproteins proteins or lipids from VLDL to LDL or to HDL. The major effect of HL, relative to that observed with LPL alone, was a marked hydrolysis of HDL triglycerides (68%). Despite the combined action of LPL and HL on VLDL in the presence of HDL and over 90% lipolysis of triglycerides, a major portion of residual VLDL mass remained in fractions lighter than normal LDL density and retained apo E. It is concluded that lipoprotein lipase of LPL in combination with HL are ineffective in bringing about the complete conversion of plasma VLDL to LDL. Lipoprotein lipase was effective in substantially augmenting the HDL mass including cholesteryl while the major effect of HL was the selective hydrolysis of HDL triglycerides.
为了研究脂解酶对人极低密度脂蛋白（VLDL）在转化为产物脂蛋白过程中脂质和载脂蛋白，特别是载脂蛋白（apo）E和胆固醇酯的去除效果，我们在生理比例的高密度脂蛋白（HDL）（10mg蛋白质）、VLDL（2mg蛋白质）和足以结合所有释放脂肪酸的白蛋白存在的情况下，研究了脂蛋白脂肪酶（LPL）的作用以及脂蛋白脂肪酶和肝脂肪酶（HL）的联合作用。孵育中使用的HDL不含apo E，以便于评估apo E从VLDL转移到HDL的情况。通过密度梯度超速离心评估脂质和载脂蛋白质量的重新分布以及标记胆固醇酯从VLDL到其他脂蛋白组分的移动。大鼠心脏LPL在2小时内使VLDL甘油三酯发生90%-95%的脂解后，apo C-II和apo C-III几乎完全转移到HDL，但只有20%的VLDL apo E转移到HDL。尽管总体磷脂水解程度较高（30%），但在LPL作用期间HDL未酯化胆固醇和磷脂质量仍显著增加。胆固醇酯质量向HDL的转移情况各不相同（0%-13%），平均转移量为VLDL胆固醇酯的7%。标记的VLDL胆固醇酯向HDL的转移率为3%-6%。相当一部分VLDL脂质质量出现在低密度脂蛋白（LDL）区域的轻组分中，但仍有相当一部分留在VLDL/中间密度脂蛋白（IDL）区域。在VLDL-LDL密度范围内分离出的脂解后颗粒比LDL大，并且与血浆LDL相比，其表面脂质与核心脂质的比例较高。将人HL与LPL一起使用并没有改变载脂蛋白或脂质从VLDL到LDL或HDL的重新分布。相对于单独使用LPL时观察到的情况，HL的主要作用是显著水解HDL甘油三酯（68%）。尽管在HDL存在的情况下LPL和HL对VLDL联合作用且甘油三酯脂解超过90%，但大部分残留的VLDL质量仍留在比正常LDL密度轻的组分中并保留了apo E。结论是，LPL与HL联合的脂蛋白脂肪酶在使血浆VLDL完全转化为LDL方面无效。脂蛋白脂肪酶在显著增加包括胆固醇酯在内的HDL质量方面有效，而HL的主要作用是选择性水解HDL甘油三酯。
