Marcoux C, Lussier-Cacan S, Davignon J, Cohn J S
Hyperlipidemia and Atherosclerosis Research Group, Clinical Research Institute of Montreal, Quebec, Canada.
Biochim Biophys Acta. 1997 Jun 23;1346(3):261-74. doi: 10.1016/s0005-2760(97)00049-0.
The majority of apolipoprotein (a) [apo(a)] in plasma is characteristically associated with Lipoprotein (a) [Lp(a)], having a buoyant density (1.05-1.08 g/ml) intermediate between low density lipoproteins (LDL) and high density lipoproteins (HDL). In the fed (postprandial) state or in the presence of fasting (endogenous) hypertriglyceridemia, a small proportion of plasma apo(a) is found in the density < 1.006 g/ml fraction of plasma, associated with larger and less dense triglyceride-rich lipoproteins (TRL). In order to further characterize the presence of apo(a) in ultracentrifugally-separated TRL (UTC-TRL), this lipoprotein fraction was isolated from plasma obtained in the fed state (three hours after an oral fat load) from healthy normolipidemic subjects (Lp(a): 38 +/- 8 mg/dl (mean +/- S.E.), n = 4) and also from plasma obtained after an overnight fast from hypertriglyceridemic patients (plasma TG: 8.16 +/- 2.00 mmol/l, Lp(a): 41 +/- 3 mg/dl, n = 18). Apo(a) in 3 h-postprandial UTC-TRL (5 +/- 2% of total plasma apo(a)) and in hypertriglyceridemic UTC-TRL (8 +/- 2% total apo(a)) was separable by electrophoresis and/or gel chromatography (FPLC) from the majority of UTC-TRL lipid. Apo(a) in UTC-TRL fractions had slow pre-beta electrophoretic mobility and was isolated in a lipoprotein size-range smaller than VLDL and larger than LDL, consistent with it being Lp(a). Recentrifugation of UTC-TRL resulted in the majority of apo(a) being recovered in the density > 1.006 g/ml fraction. Addition of proline to plasma samples before ultracentrifugation (final concentration: 0.1 M) substantially reduced the amount of Lp(a) in UTC-TRL. TRL separated from plasma by FPLC contained less apo(a) (2-5% of total plasma apo(a)), but this apo(a) was also readily dissociable from TRL lipid, had slow pre-beta electrophoretic mobility, and was associated with a lipoprotein with the size of Lp(a). Our data suggest that apo(a) in the TRL fraction of subjects with postprandial triglyceridemia or endogenous hypertriglyceridemia is not an integral component of plasma VLDL or chylomicrons, but represents the presence of non-covalently bound Lp(a).
血浆中的大多数载脂蛋白(a)[apo(a)]通常与脂蛋白(a)[Lp(a)]相关联，其漂浮密度(1.05 - 1.08 g/ml)介于低密度脂蛋白(LDL)和高密度脂蛋白(HDL)之间。在进食(餐后)状态或存在空腹(内源性)高甘油三酯血症时，血浆中一小部分apo(a)存在于密度<1.006 g/ml的血浆组分中，与更大且密度更低的富含甘油三酯的脂蛋白(TRL)相关。为了进一步表征超速离心分离的TRL(UTC - TRL)中apo(a)的存在情况，从健康血脂正常受试者(进食状态，口服脂肪负荷3小时后采集血浆，Lp(a)：38±8 mg/dl(平均值±标准误)，n = 4)以及高甘油三酯血症患者过夜禁食后采集的血浆(血浆甘油三酯：8.16±2.00 mmol/l，Lp(a)：41±3 mg/dl，n = 18)中分离出该脂蛋白组分。餐后3小时UTC - TRL中的apo(a)(占血浆总apo(a)的5±2%)以及高甘油三酯血症UTC - TRL中的apo(a)(占总apo(a)的8±2%)可通过电泳和/或凝胶色谱法(FPLC)与大多数UTC - TRL脂质分离。UTC - TRL组分中的apo(a)具有缓慢的前β电泳迁移率，并且分离得到的脂蛋白大小范围小于极低密度脂蛋白(VLDL)且大于低密度脂蛋白(LDL)，这与它是Lp(a)一致。对UTC - TRL进行再次超速离心后，大多数apo(a)在密度>1.006 g/ml的组分中回收。在超速离心前向血浆样品中添加脯氨酸(终浓度：0.1 M)可显著降低UTC - TRL中Lp(a)的含量。通过FPLC从血浆中分离得到的TRL含有的apo(a)较少(占血浆总apo(a)的2 - 5%)，但该apo(a)也很容易与TRL脂质解离，具有缓慢的前β电泳迁移率，并且与Lp(a)大小的脂蛋白相关。我们的数据表明，餐后甘油三酯血症或内源性高甘油三酯血症患者的TRL组分中的apo(a)不是血浆VLDL或乳糜微粒的组成部分，而是代表非共价结合的Lp(a)的存在。
