人血清极低密度脂蛋白体外代谢的研究

本文利用脂蛋白脂肪酶(LPL)在体外研究人血清极低密度脂蛋白(VLDL)的代谢变化,及其与其他脂蛋白的关系。发现在适宜条件下,LPL水解VLDL核中的甘油三酯(TG),释放游离脂肪酸(FFA),同时VLDL浊度变小,透光度增加。反应后产物通过密度梯度超速离心方法分离,发现分解代谢产物在密度为1.020～1.045g/ml之间有新生组分产生,其电泳迁移率增快,着色带增宽。电镜观察这些新组分的颗粒比天然VLDL为小,而比低密度脂蛋白(LDL)为大,并有空泡状不规则脂质体的单层形成,以及一些非球形、具有触角或尾巴状的构形,很可能是脂解后VLDL的过剩表面,是新生高密度脂蛋白(HDL)的前体。这些结果说明人血清VLDL经LPL分解代谢后,其结构,形态和组分均发生了明显的变化。     

脂蛋白酯酶研究进展及对动脉粥样硬化的影响北大核心CSCD

脂蛋白脂酶(lipoprotein lipase,LPL)主要在脏器实质细胞合成和分泌,可以水解乳糜微粒(chylomicron,CM)、低密度脂蛋白(low-density lipoproteins,LDL)及极低密度脂蛋白(very low-den-sity lipoproteins,VLDL)中的甘油三酯(triglyceride,TG),对清除体内过多的TG至关重要。新近研究发现LPL的基因结构、合成、分泌及降解具有复杂性,生物功能的发挥和基因的表达也受到多种转录因子、微小RNA(microRNA,miRNA)、相关蛋白及营养激素的调控,其在动脉硬化性疾病中的作用也存在较大的争议。因此,本文主要针对LPL基因的结构、合成与降解、生物功能、表达调控及与动脉硬化性心血管疾病关系的研究进展做一综述,以期进一步明确LPL在心血管疾病中的作用和意义。     

哺乳动物脂蛋白脂肪酶基因的进化研究

脂蛋白脂肪酶(LPL)是脂肪细胞、心肌细胞、骨骼肌细胞、乳腺细胞以及巨噬细胞等实质细胞合成和分泌的一种糖蛋白,其生理功能为促进乳糜微粒和极低密度脂蛋白中甘油三脂(TG)的分解,此外,lpl基因的异常可导致血TG水平的升高和高密度脂蛋白胆固醇(HDL-C)水平的降低,导致冠状动脉粥样硬化等疾病的形成和发展。采用生物信息学手段来分析在不同哺乳动物中lpl基因的长度多态性、终止密码子多态性、ORF多态性以及氨基酸序列的同源性,建立不同哺乳动物lpl基因上的进化关系图谱,为了解哺乳动物脂蛋白脂肪酶基因的演化关系,研究该基因的作用机理提供资料。     

巨噬细胞极低密度脂蛋白受体的调节作用

本文研究了小鼠腹腔巨噬细胞极低密度脂蛋白(VLDL)受体的调节。用富含甘油三酯(TG)的VLDL与小鼠巨噬细胞预温育后,细胞结合~(125)I-VLDL的最大结合容量(Bmax)比对照细胞只降低5％(1071/1127ng/mg细胞蛋白质),当细胞内TG增加到对照的2.5倍时,细胞摄取及降解~(125)I-VLDL的量分别下降40％和22％;乙酰-低密度脂蛋白(AC-LDL)预温育的细胞结合~(125)I-VLDL的Bmax比对照细胞只降低14％(633/831ng/mg细胞蛋白质),当细胞内胆固醇(Ch)增加到对照的23倍时,细胞摄取及降解~(125)I-VLDL的量只分别下降10％和21％。此后随着细胞内TG或Ch含量的增加,摄取及降解~(125)I-VLDL的量仍保持不变。 结论:细胞内TG或Ch含量对VLDL受体的调节作用微弱,与TG相比,Ch的调节作用更弱。     

鸡血清极低密度脂蛋白对鸡颗粒细胞孕酮合成的影响

用鸡的颗粒细胞(granulosa cell,G·C·)进行极低密度脂蛋白(VLDL)对于孕酮合成的研究。按序列超速离心法分离鸡血清脂蛋白。用放射免疫法测定孕酮的量。实验分组:G·C·加绵羊促黄体生成素(OLH),其浓度范围为1—50 ng/ml,此为OLH组;G·C·加VLDL(最终浓度400μg/ml)再加OLH,此为VLDL组;G·C未加VLDL和OLH则为对照组。实验结果:(1).OLH组能促进G·C·孕酮的合成而且孕酮的生成量随着OLH量的增加而增加。(2)VLDL组孕酮生成量较OLH组显著增高,两者之间有显著性差异(P<0.001)。(3)用3次实验结果合并计算VLDL组和OLH组的平均数相当于对照组平均数的百分数,发现VLDL组明显高于OLH组。实验结果说明VLDL是携带胆固醇的脂蛋白,从而在OLH作用下,使颗粒细胞合成孕酮的量增多。     

脂蛋白酯酶在动脉粥样硬化发生发展中的作用

脂蛋白酯酶(lipoprotein lipase, LPL)是调节甘油三酯代谢的关键酶,在动脉粥样硬化(atherosclerosis,As)的发生发展中起重要作用。LPL产生部位的差异决定了其具有促As作用还是抗As作用。其次,不同因素对LPL的调控也会使LPL对As产生相反的作用效果。本文综述了LPL在As发生发展中的作用机制以及不同因素对LPL的调控机制,对于As的防治具有重要意义。     

肾病综合征高脂血症发病机制研究进展

肾病综合征脂质代谢紊乱包括胆固醇(CH)和低密度脂蛋白(LDL)代谢异常、富含甘油三脂(TG)的脂蛋白代谢异常、高密度脂蛋白(HDL)代谢异常.根据目前的研究结果,CH和LDL代谢异常主要是由于羟甲基戊二酰辅酶A还原酶(HMG-CoA还原酶)和肝脂酰CoA胆固醇脂酰转移酶(ACAT)上调以及LDL受体和HDL受体下调所致;而富含TG的脂蛋白代谢异常主要与脂蛋白脂肪酶(LPL)、肝脂肪酶和极低密度脂蛋白(VLDL)受体的下调有关;HDL的代谢异常则主要是由于尿液中大量丢失卵磷脂胆固醇脂酰转移酶(LCAT)和HDL受体下调所致.上述代谢异常使肾病综合征患者心血管并发症的发生显著增加.     

脂蛋白脂酶与糖尿病心肌病

脂蛋白脂酶(lipoprotein lipase,LPL)通过水解血浆中富含甘油三酯(triglyceride,TG)的脂蛋白,为心肌组织提供游离脂肪酸(free fatty acid,FFA)供能。糖尿病期间,由于心肌组织减弱对葡萄糖的利用能力,导致心脏供能不足。此时,机体通过一系列机制上调心肌LPL活性,促进血浆极低密度脂蛋白(very low density lipoprotein,VLDL)和乳糜微粒(chylomicrons,CM)的水解,以增强FFA为心肌组织代偿性供能。糖尿病患者通过上调心肌LPL活性,进而促使血浆FFA浓度显著升高,导致大量活性氧、脂质等在心肌细胞内蓄积,并潜在地诱发糖尿病心肌病(diabetic cardiomyopathy,DCM)。因此,本文主要针对糖尿病对心肌LPL的调控机制及LPL如何潜在地诱发DCM做一综述,以期为DCM提供新的治疗靶点和途径。     

miRNAs与脂蛋白酯酶

miRNAs是一类具有调控基因功能的非编码RNAs,它在细胞核中合成,可转运至细胞质,调控脂质代谢相关性疾病的发生发展。脂蛋白酯酶(lipoprotein lipase,LPL)作为甘油三酯水解的限速酶,由心肌、脂肪、骨骼肌、乳腺及巨噬细胞等实质细胞合成和分泌,在脂蛋白转运和脂质代谢过程中发挥重要作用。近期研究证实多种miRNAs,包括miR-29、miR-467b、miR-590、miR-27、miR-134和miR-186,可通过调控脂蛋白酯酶LPL的表达,进而影响脂质代谢。为了深入探讨miRNAs对LPL的影响,本文以miRNAs对LPL的调控作用进行综述,期望以miRNAs为靶点,为脂质代谢相关性疾病的防治提供治疗方案。     

微粒体甘油三脂转运蛋白MTP的研究进展

微粒体甘油三酯转运蛋白MTP(microsomaltriglyceridetransferprotein ,MTP)首先是从牛的肝细胞微粒体碎片中分离获得的 ,其作用是加速甘油三脂 (triglyceride ,TG)、胆固醇 (cholesterylester ,CE)和磷脂酰胆碱 (phos phatidylcholine ,PC)的转运和细胞或亚细胞膜的生物合成。它后来在肝细胞和小肠的微粒体膜中发现[1 ] ,由于它的位置及其转运TG可以推测与血浆脂蛋白中极低密度脂蛋白 (verylowdensitylipoprotein ,VLDL)和乳糜微粒 (chylomi crons ,CM)的组装过程有关。     

巨噬细胞对正常人极低密度脂蛋白亚组分代谢的研究

本文研究了小鼠腹腔巨噬细胞对正常人极低密度脂蛋白(N-VLDL)两种亚组分VLDL_1和VLDL_3的代谢。两种亚组分都能以受体方式和非特异性方式被巨噬细胞摄取和降解。在受体途径中以VLDL_1的摄入量居多。对胞内甘油三酯(TG)的堆积作用以VLDL_1较强,对胆固醇酶(CE)的堆积则以VLDL_3较强。表明两者在促进巨噬细胞向泡沫细胞转变中的作用有所不同。     

ASP enhances in situ lipoprotein lipase activity by increasing fatty acid trapping in adipocytes

Acylation-stimulating protein (ASP) increases triglyceride (TG) storage (fatty acid trapping) in adipose tissue and plays an important role in postprandial TG clearance. We examined the capacity of ASP and insulin to stimulate the activity of lipoprotein lipase (LPL) and the trapping of LPL-derived nonesterified fatty acid (NEFA) in 3T3-L1 adipocytes. Although insulin increased total LPL activity (secreted and cell-associated; P < 0.001) in 3T3-L1 adipocytes, ASP moderately stimulated secreted LPL activity (P = 0.04; 5% of total LPL activity). Neither hormone increased LPL translocation from adipocytes to endothelial cells in a coculture system. However, ASP and insulin increased the V(max) of in situ LPL activity ([(3)H]TG synthetic lipoprotein hydrolysis and [(3)H]NEFA incorporation into adipocytes) by 60% and 41%, respectively (P 相似文献   

Lipoprotein lipase activation by red ginseng saponins in hyperlipidemia model animals.

The effect of ginseng saponins isolated from red ginseng (a steamed and dried root of Panax ginseng) has been studied in a cyclophosphamide (CPM)-induced hyperlipidemia model in fasted rabbits. In this model, chylomicrons and very low density lipoprotein (VLDL) accumulation was known to occur as a result of reduction in lipoprotein lipase (LPL) activity in the heart and heparin-releasable heart LPL. Oral administration of ginseng saponins at a dose of 0.01 g/kg for 4 weeks was found to reverse the increase in serum triglycerides (TG) and concomitant increase in cholesterol produced by CPM treatment, especially in chylomicrons and VLDL. In addition, ginseng saponins treatment led to a recovery in postheparin plasma LPL activity and heparin-releasable heart LPL activity, which were markedly reduced by CPM treatment. In rats given 15% glycerol/15% fructose solution, postheparin plasma LPL activity declined to two third of normal rats, whereas ginseng saponins reversed it to normal levels. In the present study we first demonstrated that ginseng saponins sustained LPL activity at a normal level or protected LPL activity from being decreased by several factors, resulting in the decrease of serum TG and cholesterol.     

Reduced kidney lipoprotein lipase and renal tubule triglyceride accumulation in cisplatin-mediated acute kidney injury

Peroxisome proliferator-activated receptor-α (PPARα) activation attenuates cisplatin (CP)-mediated acute kidney injury by increasing fatty acid oxidation, but mechanisms leading to reduced renal triglyceride (TG) accumulation could also contribute. Here, we investigated the effects of PPARα and CP on expression and enzyme activity of kidney lipoprotein lipase (LPL) as well as on expression of angiopoietin protein-like 4 (Angptl4), glycosylphosphatidylinositol-anchored-HDL-binding protein (GPIHBP1), and lipase maturation factor 1 (Lmf1), which are recognized as important proteins that modulate LPL activity. CP caused a 40% reduction in epididymal white adipose tissue (WAT) mass, with a reduction of LPL expression and activity. CP also reduced kidney LPL expression and activity. Angptl4 mRNA levels were increased by ninefold in liver and kidney tissue and by twofold in adipose tissue of CP-treated mice. Western blots of two-dimensional gel electrophoresis identified increased expression of a neutral pI Angptl4 protein in kidney tissue of CP-treated mice. Immunolocalization studies showed reduced staining of LPL and increased staining of Angptl4 primarily in proximal tubules of CP-treated mice. CP also increased TG accumulation in kidney tissue, which was ameliorated by PPARα ligand. In summary, a PPARα ligand ameliorates CP-mediated nephrotoxicity by increasing LPL activity via increased expression of GPHBP1 and Lmf1 and by reducing expression of Angptl4 protein in the proximal tubule.     

The relationship of serum lipoprotein lipase mass with fasting serum apolipoprotein B-48 and remnant-like particle triglycerides in type 2 diabetic patients.

BACKGROUND: There have been no previous reports showing specifically the relation between lipoprotein lipase (LPL) and apolipoprotein (apo) B-48 or remnant metabolism. In this study, we have clarified the relationships of LPL mass in pre-heparin with serum apo B-48 measured by enzyme-linked immunosorbent assay, triglycerides (TG), and remnant-like particle triglycerides (RLP-TG). MATERIAL AND METHODS: Seventy-nine type 2 diabetic subjects [age, 55+/-13; body mass index (BMI), 25+/-5.0 kg/m2; fasting plasma glucose (FPG), 7.39+/-2.22 mmol/l, HbA1c, 6.5+/-1.3%, total cholesterol (TC), 5.36+/-1.09 mmol/l, TG, 2.32+/-2.53 mmol/l; HDL-C, 1.22+/-0.44 mmol/l; serum LPL mass, 45+/-22 ng/ml; apo B-48, 6.6+/-6.3 microg/ml] were recruited in this study. Fasting serum apo B-48 were measured by ELISA using anti-human apo B-48 monoclonal antibodies (MoAb) and LPL mass by ELISA using anti-bovine milk LPL MoAb. RLP-TG levels were measured using monoclonal antibodies to apo B-100 and apo A-1. RESULTS: There was no relationship of LPL mass to age, BMI, FPG, and HbA1c. Serum LPL mass was correlated inversely with TG (r=-0.529 p<0.0001) and positively with HDL-C (r=0.576, p<0.0001). Also, LPL mass showed inverse correlations with apo B-48 (r=-0.383 p<0.0001) and RLP-TG (r=-0.422 p<0.0001, n=51). Multiple regression analysis with TG, apo B-48, or RLP-TG as dependent variables, and age, gender, BMI, plasma glucose, and LPL mass as independent variables showed that LPL mass was associated independently with TG, apo B-48, or RLP-TG. CONCLUSION: The decrease in LPL protein mass could cause an increase in serum apo B-48 and RLP-TG levels, which is related to the retardation of remnant metabolism.     

Lipoprotein ApoC-II activation of lipoprotein lipase. Modulation by apolipoprotein A-IV

Lipoprotein lipase (LPL)-mediated hydrolysis of triglycerides (TG) contained in chylomicrons requires the presence of a cofactor, apolipoprotein (apo) C-II. The physiological mechanism by which chylomicrons gain apoC-II necessary for LPL activation in whole plasma is not known. Using a gum arabic stabilized TG emulsion, activation of LPL by lipoprotein apoC-II was studied. Hydrolysis of TG by LPL was greater in the presence of serum than with addition of either high density lipoproteins (HDL) or very low density lipoproteins (VLDL). LPL activation by either VLDL or HDL increased with addition of the lipoprotein-free fraction of plasma. A similar increase in LPL activity by addition of the lipoprotein-free fraction together with HDL or VLDL was observed when another TG emulsion (Intralipid) or TG-rich lipoproteins from an apoC-II deficient subject were used as a substrate. Human apoA-IV, apoA-I, apoE, and cholesteryl ester transfer protein were assessed for their ability to increase LPL activity in the presence of VLDL. At and below physiological concentrations, only apoA-IV increased LPL activity. One hundred percent of LPL activity measured in the presence of serum was achieved using VLDL plus apoA-IV. In the absence of an apoC-II source, apoA-IV had no effect on LPL activity. Removal of greater than 80% of the apoA-IV from the nonlipoprotein-containing fraction of plasma by incubation with Intralipid markedly reduced its ability to activate LPL in the presence of VLDL or HDL. Gel filtration chromatography demonstrated that incubation of the nonlipoprotein-containing fraction of plasma with HDL and the TG emulsion caused increased transfer of apoC-II to the emulsion and association of apoA-IV with HDL. Our studies demonstrate that apoA-IV increases LPL activation in the presence of lipoproteins. We hypothesize that apoA-IV is required for efficient release of apoC-II from either HDL or VLDL, which then allows for LPL-mediated hydrolysis of TG in nascent chylomicrons.     

Structure-activity and in vivo evaluation of a novel lipoprotein lipase (LPL) activator

Elevated triglycerides (TG) contribute towards increased risk for cardiovascular disease. Lipoprotein lipase (LPL) is an enzyme that is responsible for the metabolism of core triglycerides of very-low density lipoproteins (VLDL) and chylomicrons in the vasculature. In this study, we explored the structure-activity relationships of our lead compound (C10d) that we have previously identified as an LPL agonist. We found that the cyclopropyl moiety of C10d is not absolutely necessary for LPL activity. Several substitutions were found to result in loss of LPL activity. The compound C10d was also tested in vivo for its lipid lowering activity. Mice were fed a high-fat diet (HFD) for four months, and treated for one week at 10 mg/kg. At this dose, C10d exhibited in vivo biological activity as indicated by lower TG and cholesterol levels as well as reduced body fat content as determined by ECHO-MRI. Furthermore, C10d also reduced the HFD induced fat accumulation in the liver. Our study has provided insights into the structural and functional characteristics of this novel LPL activator.     

Routes of FA delivery to cardiac muscle: modulation of lipoprotein lipolysis alters uptake of TG-derived FA

Long-chain fatty acids (FA) supply 70-80% of the energy needs for normal cardiac muscle. To determine the sources of FA that supply the heart, [(14)C]palmitate complexed to bovine serum albumin and [(3)H]triolein [triglyceride (TG)] incorporated into Intralipid were simultaneously injected into fasted male C57BL/6 mice. The ratio of TG to FA uptake was much greater for hearts than livers. Using double-labeled Intralipid with [(3)H]cholesteryl oleoyl ether (CE) and [(14)C]TG, we observed that hearts also internalize intact core lipid. Inhibition of lipoprotein lipase (LPL) with tetrahydrolipstatin or dissociation of LPL from the heart with heparin reduced cardiac uptake of TG by 82 and 64%, respectively (P < 0.01). Palmitate uptake by the heart was not changed by either treatment. Uptake of TG was 88% less in hearts from LPL knockout mice that were rescued via LPL expression in the liver. Our data suggest that the heart is especially effective in removal of circulating TG and core lipids and that this is due to LPL hydrolysis and not its bridging function.     

The role of LXRα in goose primary hepatocyte lipogenesis

In this study, we investigate the role of liver X receptor alpha (LXR alpha) in lipogenesis in geese in order to understand the differences in hepatic steatosis mechanisms between mammals and waterfowl. Primary goose hepatocytes were isolated and treated with the LXR alpha agonist T0901317. Triglyceride (TG) accumulation, acetyl-CoA carboxylase alpha (ACC alpha) and fatty acid synthase (FAS) activities, and gene expression levels of LXR alpha, sterol regulatory element-binding proteins-1 (SREBP-1), FAS, ACC alpha and lipoprotein lipase (LPL) were measured in primary hepatocytes. We found a dose-dependent up-regulation of TG accumulation, ACC, and FAS activities and the mRNA levels of LXR alpha, SREBP-1, FAS, ACC alpha, and LPL genes in the presence of To-901317. We also found that binding of nuclear SREBP-1 to ACC alpha SRE sequence was induced by To-901317 (P < 0.05). In conclusion, LXR alpha is involved in the induction of the lipogenic pathway through activation of SREBP-1 and its target genes in goose primary hepatocytes.     

Characterization of triacylglycerol hydrolase activities in isolated myocardial cells from rat heart.

Triacylglycerol (TG) hydrolase activities were characterized in myocytes isolated from rat hearts. Acid hydrolase activity with a pH optimum of 5 could be measured in myocyte homogenates, and the subcellular distribution suggested that this activity originated in lysosomes. Lipoprotein lipase (LPL) was also present in myocyte homogenates, as evidenced by TG hydrolase activity that was stimulated by serum and apolipoprotein CII, and inhibited by apolipoprotein CIII2, high ionic strength (NaCl and MgCl2, I = 1 M) and antibodies to LPL. Serum-independent neutral (pH 7.5) TG hydrolase activity was less sensitive to inhibition by 1 M-NaCl, by antibodies to LPL and by preincubation at 40 degrees C than was serum-stimulated hydrolase activity. Furthermore, there were modest but significant differences in the subcellular distribution of the serum-independent and serum-stimulated hydrolase activities. Hydrolase activities in myocyte homogenates could be solubilized by 7.2 mM-deoxycholate. Acid hydrolase activity was recovered in the unbound fraction after heparin-Sepharose chromatography, whereas LPL was bound to the affinity column and was eluted by 0.9-1.2 M-NaCl. Approximately one-third of the serum-independent TG hydrolase activity was not bound to the heparin-Sepharose affinity column. This unbound TG hydrolase activity had a pH optimum of 7 and was stimulated by 50 mM-MgCl2, but not by serum and was resistant to inhibition by high ionic strength (1 M-NaCl), to preincubation at 40 degrees C for 2 h, and by antibodies to LPL. It is concluded that, in addition to an acid lysosomal TG hydrolase and LPL, myocytes from rat heart contain a serum-independent TG hydrolase with unique characteristics.