Lecithin: cholesterol acyltransferase--from biochemistry to role in cardiovascular disease

Acyl chain-dependent effect of lysophosphatidylcholine on cyclooxygenase (COX)-2 expression in endothelial cells

Objective

Previously we identified palmitoyl-, oleoyl- linoleoyl-, and arachidonoyl-lysophosph-atidylcholine (LPC 16:0, 18:1, 18:2 and 20:4) as the most prominent LPC species generated by endothelial lipase (EL). In the present study, we examined the capacity of those LPC to modulate expression of cyclooxygenase (COX)-2 in vascular endothelial cells.

Methods & results

LPC 16:0 and 20:4 promoted both COX-2 mRNA- and protein synthesis with different potencies and kinetics. While LPC 18:1 induced a weak and transient increase in COX-2 mRNA, but not protein, LPC 18:2 increased COX-2 protein, without impacting mRNA. Chelation of intracellular Ca²⁺ and inhibition of p38 MAPK markedly attenuated 16:0 LPC- and 20:4 LPC- elicited induction of COX-2 expression, whereas inhibition of phospholipase C (PLC) attenuated only the effect of 16:0 LPC. LPC 16:0 and 20:4 differed markedly in their potencies to increase cytosolic Ca²⁺ concentration and in the kinetics of p38 MAPK activation. While the effects of 16:0 and 20:4 LPC on COX-2 expression were profoundly sensitive to silencing of either c-Jun or p65 (NF-κB), respectively, silencing of cyclic AMP responsive element binding protein (CREB) attenuated markedly the effect of both LPC.

Conclusion

Our results indicate that the tested LPC species are capable of inducing COX-2 expression, whereby the efficacy and the relative contribution of underlying signaling mechanisms markedly differ, due to the length and degree of saturation of LPC acyl chains.

Lecithin:cholesterol acyltransferase deficiency protects against cholesterol-induced hepatic endoplasmic reticulum stress in mice

We recently reported that lecithin:cholesterol acyltransferase (LCAT) knock-out mice, particularly in the LDL receptor knock-out background, are hypersensitive to insulin and resistant to high fat diet-induced insulin resistance (IR) and obesity. We demonstrated that chow-fed Ldlr-/-xLcat+/+ mice have elevated hepatic endoplasmic reticulum (ER) stress, which promotes IR, compared with wild-type controls, and this effect is normalized in Ldlr-/-xLcat-/- mice. In the present study, we tested the hypothesis that hepatic ER cholesterol metabolism differentially regulates ER stress using these models. We observed that the Ldlr-/-xLcat+/+ mice accumulate excess hepatic total and ER cholesterol primarily attributed to increased reuptake of biliary cholesterol as we observed reduced biliary cholesterol in conjunction with decreased hepatic Abcg5/g8 mRNA, increased Npc1l1 mRNA, and decreased Hmgr mRNA and nuclear SREBP2 protein. Intestinal NPC1L1 protein was induced. Expression of these genes was reversed in the Ldlr-/-xLcat-/- mice, accounting for the normalization of total and ER cholesterol and ER stress. Upon feeding a 2% high cholesterol diet (HCD), Ldlr-/-xLcat-/- mice accumulated a similar amount of total hepatic cholesterol compared with the Ldlr-/-xLcat+/+ mice, but the hepatic ER cholesterol levels remained low in conjunction with being protected from HCD-induced ER stress and IR. Hepatic ER stress correlates strongly with hepatic ER free cholesterol but poorly with hepatic tissue free cholesterol. The unexpectedly low ER cholesterol seen in HCD-fed Ldlr-/-xLcat-/- mice was attributable to a coordinated marked up-regulation of ACAT2 and suppressed SREBP2 processing. Thus, factors influencing the accumulation of ER cholesterol may be important for the development of hepatic insulin resistance.

Ajuga iva aqueous extract improves reverse cholesterol transport in streptozotocin-induced diabetic rat

Objectives

The aim of this study was to determine the effects of Ajuga iva aqueous extract on lecithin : cholesterol acyltransferase (LCAT) activity and amount and composition of high-density lipoprotein (HDL)2 and (HDL)3, in streptozotocin (STZ)-induced diabetic rats.

Methods

Diabetes was induced in male Wistar rats by intraperitoneal injection of STZ (60 mg/kg body weight). Diabetic rats (n = 12) were divided into two groups. The diabetic control group (D) received a 20% casein diet and the diabetic treated group received the same diet supplemented with A. iva aqueous extract (0.5 g/100 g diet) (DAi), for 4 weeks.

Key findings

Total cholesterol and HDL3-C were respectively decreased by 32% and 55% in the DAi group compared with the D group, whereas HDL2-C was increased by 30%. The amounts of HDL2 and HDL3, which were the sum of apolipoproteins, unesterified cholesterol (UC), cholesteryl esters (CEs), triacylglycerols (TGs) and phospholipids (PLs), showed no significant difference. A. iva treatment increased LCAT by 33% and its cofactor-activator, apolipoprotein A-I, by 58%. HDL3-PL (enzyme substrate) and HDL3-UC (acyl group acceptor) were respectively decreased by 70% and 57%, whereas HDL2-CE (product of LCAT reaction) was enhanced by 30%.

Conclusions

In STZ-induced diabetic rats, A. iva improves reverse cholesterol transport by enhancing LCAT activity, leading to anti-atherogenic effects.

Regulation of plasma cholesterol esterification by sphingomyelin: effect of physiological variations of plasma sphingomyelin on lecithin-cholesterol acyltransferase activity

Although sphingomyelin (SM) is the most abundant phospholipid in the plasma, next to phosphatidylcholine (PC), its physiological function in plasma is unclear. Here we employed plasma from various genetic models of mice which naturally differ in their plasma SM/PC ratios, to study the role of SM as a modulator of LCAT, the enzyme responsible for HDL maturation and the synthesis of cholesteryl esters (CE) in normal plasma. Serine palmitoyltransferase deficient mice, and SM synthase deficient mice, both of which have below normal SM/PC ratios, showed significantly elevated LCAT activities when assayed with the endogenous substrates. On the other hand, LDL receptor knockout mice, and apo E knockout mice, both of which have high SM/PC ratios, had markedly reduced (-80%) LCAT activities. The LCAT levels in plasma, as assayed with an exogenous substrate, were similar in all groups, except for a 45% decrease in apo E knockout mice. Plasma samples with high SM/PC ratios had lower percentage of 20:4, 22:5, and 22:6 CE all of which are formed by LCAT, and a higher percentage of the atherogenic 18:1 CE which is mainly derived from the action of liver ACAT, showing that in vivo, the contribution of LCAT to plasma CE is reduced while that of liver ACAT is increased. These results show that SM is a physiological modulator of LCAT activity as well as plasma CE composition, and this may contribute to the previously reported pro-atherogenic effect of high plasma SM levels.

Carriers of lecithin cholesterol acyltransferase gene mutations have accelerated atherogenesis as assessed by carotid 3.0-T magnetic resonance imaging [corrected]

OBJECTIVES

The aim of this study was to investigate the role of reduced lecithin: cholesterol acyltransferase (LCAT) function on atherogenesis using 3.0-T carotid magnetic resonance imaging (MRI) and B-mode ultrasound.

BACKGROUND

The role of low high-density lipoprotein cholesterol as a causal factor in atherogenesis has recently been questioned. LCAT plays a key role in high-density lipoprotein cholesterol metabolism.

METHODS

Carotid 3.0-T MRI and B-mode ultrasound measurements were performed in 40 carriers of LCAT gene mutations and 40 controls, matched for age. Patients with cardiovascular disease were excluded.

RESULTS

Carriers had 31% lower LCAT activity levels and 38% decreased high-density lipoprotein cholesterol levels (both p < 0.001 vs. controls). Carriers presented with a 10% higher normalized wall index (0.34 ± 0.07 vs. 0.31 ± 0.04, p = 0.002), a 22% higher mean wall area (17.3 ± 8.5 mm(2) vs. 14.2 ± 4.1 mm(2), p = 0.01), and a 22% higher total wall volume (1,039 ± 508 mm(3) vs. 851 ± 247 mm(3), p = 0.01 vs. controls) as measured by MRI. The prevalence (20 vs. 5, p = 0.002) and the total volume (102 mm(3) vs. 3 mm(3)) of atherosclerotic plaque components on MRI relating to lipid-rich tissue or calcification were also higher in carriers than in controls. All differences retained significance after adjustment for age, sex, blood pressure, low-density lipoprotein cholesterol, body mass index, smoking, and family history of cardiovascular disease. Common carotid intima-media thickness measured with ultrasound was increased in carriers by 12.5% (0.72 ± 0.33 mm vs. 0.64 ± 0.15 mm, p = 0.14).

CONCLUSIONS

Carriers of LCAT gene mutations exhibit increased carotid atherosclerosis, indicating an increased risk of cardiovascular disease. The present findings imply that increasing LCAT activity may be an attractive target in cardiovascular prevention strategies.

Danshen-Gegen decoction exerts proliferative effect on rat cardiac myoblasts H9c2 via MAPK and insulin pathways

ETHNOPHARMACOLOGICAL RELEVANCE

Danshen (root of Salvia miltiorrhiza) and Gegen (roots of Pueraria lobata) are traditional Chinese medicines that have been used in combination for cardiovascular disease treatment.

AIM OF THE STUDY

The present study was performed to investigate the effect of Danshen-Gegen decoction on rat myocardium cell line H9c2 and the possible molecular mechanisms.

MATERIALS AND METHODS

Rat heart myocardium H9c2 cells were treated with or without Danshen-Gegen decoction (DG) ranging from 10 to 1000μg/ml for 24h. Cell viability was measured by Alarma blue assay and cell proliferation assay was performed by BrdU Cell Proliferation ELISA kit. The activation of mitogen-activated protein kinase and insulin pathways was analyzed by Luminex technology and the growth factors and cytokine expression of H9c2 cells induced by DG was evaluated by protein array. Moreover, a rat functional specific cDNA microarray was constructed to study the gene expression profiles of H9c2 cells upon the DG treatment at 50μg/ml for 24h.

RESULTS

DG promoted H9c2 cell viability and cell proliferation at dose-dependent manner within the range between 0 and 250μg/ml. A Bio-Plex assay kit (Bio-Rad Bioscience) was used to detect the expression level of phosphoprotein as well as total proteins involved in the MAPK and insulin pathways. Significant phosphorylation of ERK, c-Jun, JNK, p38, AKT, IGF-IR, IRS-1and I kappa B were observed after DG treatment at 2h or 4h. A rat cytokine antibody array was used to detect and quantify 22 growth factors and cytokines in samples collected from the control and DG treated H9c2 cells. In the category of growth factors, GM-CSF, CNIF and b-NGF were stimulated by DG, while the expression of TIMP-1 was suppressed. For cytokine expression, it was found that DG stimulated three interleukin subclasses, IL-1α, 1X and 6, respectively. However, the expression of pro-inflammatory factors such as TNF-α and IFN-γ were down-regulated significantly. Moreover, the microarray analysis revealed that DG significantly up-regulated anti-apoptosis related genes such as Cdkn2c and Ppp3ca, and several cardiovascular disease suppressers and anti-inflammatory mediators; on the other hand, pro-apoptotic related genes including Caspase and Tnf-α were down-regulated by DG. Based on the results, a tentative scheme was proposed to show that the activation of the MAPK and insulin pathways are involved in the bioactive effect of Danshen-Gegen decoction on cardiomyocytes.

CONCLUSION

Our study suggested that Danshen-Gegen decoction has proliferative effect on myocardium cells via MAPK and insulin signaling pathways. The molecular mechanism of the action may include the up-regulation of IRS/AKT and JNK pathways as well as the inhibition of TNF and p38 pathways.

Apolipoproteins: metabolic role and clinical biochemistry applications

Lipoprotein metabolism is dependent on apolipoproteins, multifunctional proteins that serve as templates for the assembly of lipoprotein particles, maintain their structure and direct their metabolism through binding to membrane receptors and regulation of enzyme activity. The three principal functions of lipoproteins are contribution to interorgan fuel (triglyceride) distribution (by means of the fuel transport pathway), to the maintenance of the extracellular cholesterol pool (by means of the overflow pathway) and reverse cholesterol transport. The most important clinical application of apolipoprotein measurements in the plasma is in the assessment of cardiovascular risk. Concentrations of apolipoprotein B and apolipoprotein AI (and their ratio) seem to be better markers of cardiovascular risk than conventional markers such as total cholesterol and LDL-cholesterol. Apolipoprotein measurements are also better standardized than the conventional tests. We suggest that measurements of apolipoprotein AI and apolipoprotein B are included as a part of the specialist lipid profile. We also suggest that lipoprotein (a) should be measured as part of the initial assessment of dyslipidaemias because of its consistent association with cardiovascular risk. Genotyping of apolipoprotein E isoforms remains useful in the investigation of mixed dyslipidaemias. Lastly, the role of postprandial metabolism is increasingly recognized in the context of atherogenesis, obesity and diabetes. This requires better markers of chylomicrons, very-low-density lipoproteins and remnant particles. Measurements of apolipoprotein B48 and remnant lipoprotein cholesterol are currently the key tests in this emerging field.

Plasma lipid profiling across species for the identification of optimal animal models of human dyslipidemia

In an attempt to understand the applicability of various animal models to dyslipidemia in humans and to identify improved preclinical models for target discovery and validation for dyslipidemia, we measured comprehensive plasma lipid profiles in 24 models. These included five mouse strains, six other nonprimate species, and four nonhuman primate (NHP) species, and both healthy animals and animals with metabolic disorders. Dyslipidemic humans were assessed by the same measures. Plasma lipoprotein profiles, eight major plasma lipid fractions, and FA compositions within these lipid fractions were compared both qualitatively and quantitatively across the species. Given the importance of statins in decreasing plasma low-density lipoprotein cholesterol for treatment of dyslipidemia in humans, the responses of these measures to simvastatin treatment were also assessed for each species and compared with dyslipidemic humans. NHPs, followed by dog, were the models that demonstrated closest overall match to dyslipidemic humans. For the subset of the dyslipidemic population with high plasma triglyceride levels, the data also pointed to hamster and db/db mouse as representative models for practical use in target validation. Most traditional models, including rabbit, Zucker diabetic fatty rat, and the majority of mouse models, did not demonstrate overall similarity to dyslipidemic humans in this study.

Early postnatal changes of lipoprotein subclass profile in late preterm infants

BACKGROUND

Late preterm infants (LPIs; 34-37 gestational weeks at birth) have higher risk for several morbidities than do term infants (TIs). It has been suggested that a cholesterol and fatty acid supply may improve their outcomes. We investigated the lipoprotein subclass profile in LPIs to evaluate their early postnatal lipid metabolism.

METHODS

Eighty-one infants (25 LPIs, 56 TIs) were included. Cholesterol and triglyceride (TG) concentrations in 12 lipoprotein subclasses were measured at birth and at 1 month using HPLC.

RESULTS

In LPIs, the cord blood exhibited higher cholesterol concentrations in medium and large subclasses of very low-density lipoprotein (VLDL), low-density lipoprotein (LDL) and high-density lipoprotein (HDL) compared to the values in TIs. During the first month of life, LPIs had greater increases in cholesterol concentrations of medium and large subclasses of VLDL than TIs, whereas postnatal increases in cholesterol concentrations of medium and large subclasses of LDL and HDL were smaller. TG concentrations were not different in each VLDL subclass at birth and at 1 month.

CONCLUSIONS

In LPIs, cord blood lipoprotein subclass profiles and the early postnatal change exhibited different, especially in cholesterol concentrations.

Imaging apolipoprotein AI in vivo

Coronary disease risk increases inversely with high-density lipoprotein (HDL) level. The measurement of the biodistribution and clearance of HDL in vivo, however, has posed a technical challenge. This study presents an approach to the development of a lipoprotein MRI agent by linking gadolinium methanethiosulfonate (Gd[MTS-ADO3A]) to a selective cysteine mutation in position 55 of apo AI, the major protein of HDL. The contrast agent targets both liver and kidney, the sites of HDL catabolism, whereas the standard MRI contrast agent, gadolinium-diethylenetriaminepentaacetic acid-bismethylamide (GdDTPA-BMA, gadodiamide), enhances only the kidney image. Using a modified apolipoprotein AI to create an HDL contrast agent provides a new approach to investigate HDL biodistribution, metabolism and regulation in vivo.

Lecithin cholesterol acyltransferase: an anti- or pro-atherogenic factor?

Lecithin cholesterol acyl transferase (LCAT) is a plasma enzyme that esterifies cholesterol and raises high-density lipoprotein cholesterol, but its role in atherosclerosis is not clearly established. Studies of various animal models have yielded conflicting results, but studies done in rabbits and non-human primates, which more closely simulate human lipoprotein metabolism, indicate that LCAT is likely atheroprotective. Although suggestive, there are also no biomarker studies that mechanistically link LCAT with cardiovascular disease. Imaging studies of patients with LCAT deficiency have also not yielded a clear answer to the role of LCAT in atherosclerosis. Recombinant LCAT, however, is currently being developed as a therapeutic product for enzyme replacement therapy of patients with genetic disorders of LCAT for the prevention and/or treatment of renal disease, but it may also have value for the treatment of acute coronary syndrome.

Lecithin:cholesterol acyltransferase, high-density lipoproteins, and atheroprotection in humans

The lecithin:cholesterol acyltransferase (LCAT) enzyme is responsible for the synthesis of cholesteryl esters in human plasma. Lecithin:cholesterol acyltransferase is a critical enzyme in high-density lipoprotein (HDL) metabolism, and deficiency of LCAT-mediated cholesterol esterification leads to defective HDL maturation with accumulation of nascent pre-beta HDL. In addition to its function in HDL metabolism, LCAT has also long been believed to play a critical role in macrophage reverse cholesterol transport (RCT). However, recent findings have shown that human LCAT overexpression in mice does not enhance macrophage RCT in vivo, and conversely, LCAT-deficient mice display a preserved macrophage RCT despite the severe plasma HDL reduction. In agreement with this observation, defective LCAT activity does not result in enhanced atherosclerosis, despite the reduced HDL cholesterol levels. These findings challenge the notion that LCAT is required for effective atheroprotection and suggest that elevating LCAT expression and/or activity is not a promising therapeutic strategy to reduce cardiovascular risk.

Lecithin cholesterol acyltransferase null mice are protected from diet-induced obesity and insulin resistance in a gender-specific manner through multiple pathways

Complete lecithin cholesterol acyltransferase (LCAT) deficiency uniformly results in a profound HDL deficiency. We recently reported unexpected enhanced insulin sensitivity in LCAT knock-out mice in the LDL receptor knock-out background (Ldlr(-/-)×Lcat(-/-); double knock-out (DKO)), when compared with their Ldlr(-/-)×Lcat(+/+) (single knock-out (SKO)) controls. Here, we report that LCAT-deficient mice (DKO and Lcat(-/-)) are protected against high fat high sucrose (HFHS) diet-induced obesity without hypophagia in a gender-specific manner compared with their respective (SKO and WT) controls. The metabolic phenotypes are more pronounced in the females. Changes in endoplasmic reticulum stress were examined as a possible mechanism for the metabolic protection. The female DKO mice developed attenuated HFHS-induced endoplasmic reticulum stress as evidenced by a lack of increase in mRNA levels of the hepatic unfolded protein response (UPR) markers Grp78 and CHOP compared with SKO controls. The DKO female mice were also protected against diet-induced insulin resistance. In white adipose tissue of chow-fed DKO mice, we also observed a reduction in UPR, gene markers for adipogenesis, and markers for activation of Wnt signaling. In skeletal muscles of female DKO mice, we observed an unexpected increase in UCP1 in association with increase in phospho-AMPKα, PGC1α, and UCP3 expressions. This increase in UCP1 was associated with ectopic islands of brown adipocytes between skeletal muscle fibers. Our findings suggest that LCAT deficiency confers gender-specific protection against diet-induced obesity and insulin resistance at least in part through regulation in UPR, white adipose tissue adipogenesis, and brown adipocyte partitioning.

Oral docosapentaenoic acid (22:5n-3) is differentially incorporated into phospholipid pools and differentially metabolized to eicosapentaenoic acid in tissues from young rats

The present study assessed the effect of oral supplementation with docosapentaenoic acid (DPA, 22:5n-3) on the levels of serum and tissue lipid classes and their fatty acid compositions including individual phospholipid types in rat liver, heart, and kidney. Sprague-Dawley rats received daily oral gavage over 10 days as corn oil without (controls) or with purified DPA in free fatty acid form (21.2 mg/day). The DPA group exhibited significantly lower serum lipid concentrations. The concentrations in μmol/100 g serum or μmol/g tissue of DPA in the total lipid (TL) were higher by 2.3-, 2.4-, 10.9-, and 5.1-fold in the DPA group of serum, liver, heart, and kidney, respectively, with the phospholipids (PL) being the major DPA reservoir (45.2-52.1% of the DPA in the TL). No significant differences in DHA (22:6n-3) amounts in TL appeared. The highest relative mol% values as DPA were in heart tissue (means of 11.1% in PL and 16.2% in phosphatidylinositol) and lowest in kidney. The EPA (20:5n-3) concentrations were markedly higher in the DPA group and most pronounced in the kidney (5.1 times higher in the TL as compared to controls) relative to liver and heart yielding an estimated apparent % conversion of DPA to EPA of 67% and EPA:DPA ratios reaching 5.74 in kidney phosphatidylethanolamine. The serum lipid-lowering potential of dietary DPA and its impact in the kidney with the derived EPA warrants investigation.

Apolipoprotein mimetic peptides: Mechanisms of action as anti-atherogenic agents

Apolipoprotein mimetic peptides are short synthetic peptides that share structural, as well as biological features of native apolipoproteins. The early positive clinical trials of intravenous preparations of apoA-I, the main protein component of high density lipoproteins (HDL), have stimulated great interest in the use of apolipoprotein mimetic peptides as possible therapeutic agents. Currently, there are a wide variety of apolipoprotein mimetic peptides at various stages of drug development. These peptides typically have been designed to either promote cholesterol efflux or act as anti-oxidants, but they usually exert other biological effects, such as anti-inflammatory and anti-thrombotic effects. Uncertainty about which of these biological properties is the most important for explaining their anti-atherogenic effect is a major unresolved question in the field. Structure-function studies relating the in vitro properties of these peptides to their ability to reduce atherosclerosis in animal models may uncover the best rationale for the design of these peptides and may lead to a better understanding of the mechanisms behind the atheroprotective effect of HDL.

Acyl chain-dependent effect of lysophosphatidylcholine on endothelial prostacyclin production

Previously we identified palmitoyl-lysophosphatidylcholine (16:0 LPC), linoleoyl-LPC (18:2 LPC), arachidonoyl-LPC (20:4 LPC), and oleoyl-LPC (18:1 LPC) as the most prominent LPC species generated by the action of endothelial lipase (EL) on high-density lipoprotein. In the present study, the impact of those LPC on prostacyclin (PGI(2)) production was examined in vitro in primary human aortic endothelial cells (HAEC) and in vivo in mice. Although 18:2 LPC was inactive, 16:0, 18:1, and 20:4 LPC induced PGI(2) production in HAEC by 1.4-, 3-, and 8.3-fold, respectively. LPC-elicited 6-keto PGF1α formation depended on both cyclooxygenase (COX)-1 and COX-2 and on the activity of cytosolic phospholipase type IVA (cPLA2). The LPC-induced, cPLA2-dependent (14)C-arachidonic acid (AA) release was increased 4.5-fold with 16:0, 2-fold with 18:1, and 2.7-fold with 20:4 LPC, respectively, and related to the ability of LPC to increase cytosolic Ca(2+) concentration. In vivo, LPC increased 6-keto PGF(1α) concentration in mouse plasma with a similar order of potency as found in HAEC. Our results indicate that the tested LPC species are capable of eliciting production of PGI(2), whereby the efficacy and the relative contribution of underlying mechanisms are strongly related to acyl-chain length and degree of saturation.

Effect of recombinant human lecithin cholesterol acyltransferase infusion on lipoprotein metabolism in mice

Lecithin cholesterol acyl transferase (LCAT) deficiency is associated with low high-density lipoprotein (HDL) and the presence of an abnormal lipoprotein called lipoprotein X (Lp-X) that contributes to end-stage renal disease. We examined the possibility of using LCAT an as enzyme replacement therapy agent by testing the infusion of human recombinant (r)LCAT into several mouse models of LCAT deficiency. Infusion of plasma from human LCAT transgenic mice into LCAT-knockout (KO) mice rapidly increased HDL-cholesterol (C) and lowered cholesterol in fractions containing very-low-density lipoprotein (VLDL) and Lp-X. rLCAT was produced in a stably transfected human embryonic kidney 293f cell line and purified to homogeneity, with a specific activity of 1850 nmol/mg/h. Infusion of rLCAT intravenously, subcutaneously, or intramuscularly into human apoA-I transgenic mice showed a nearly identical effect in increasing HDL-C approximately 2-fold. When rLCAT was intravenously injected into LCAT-KO mice, it showed a similar effect as plasma from human LCAT transgenic mice in correcting the abnormal lipoprotein profile, but it had a considerably shorter half-life of approximately 1.23 ± 0.63 versus 8.29 ± 1.82 h for the plasma infusion. rLCAT intravenously injected in LCAT-KO mice crossed with human apolipoprotein (apo)A-I transgenic mice had a half-life of 7.39 ± 2.1 h and increased HDL-C more than 8-fold. rLCAT treatment of LCAT-KO mice was found to increase cholesterol efflux to HDL isolated from mice when added to cells transfected with either ATP-binding cassette (ABC) transporter A1 or ABCG1. In summary, rLCAT treatment rapidly restored the normal lipoprotein phenotype in LCAT-KO mice and increased cholesterol efflux, suggesting the possibility of using rLCAT as an enzyme replacement therapy agent for LCAT deficiency.

Gene therapy for dyslipidemia: a review of gene replacement and gene inhibition strategies

Despite numerous technological and pharmacological advances and more detailed knowledge of molecular etiologies, cardiovascular diseases remain the leading cause of morbidity and mortality worldwide claiming over 17 million lives a year. Abnormalities in the synthesis, processing and catabolism of lipoprotein particles can result in severe hypercholesterolemia, hypertriglyceridemia or low HDL-C. Although a plethora of antidyslipidemic pharmacological agents are available, these drugs are relatively ineffective in many patients with Mendelian lipid disorders, indicating the need for new and more effective interventions. In vivo somatic gene therapy is one such intervention. This article summarizes current strategies being pursued for the development of clinical gene therapy for dyslipidemias that cannot effectively be treated with existing drugs.

High pre-beta1 HDL concentrations and low lecithin: cholesterol acyltransferase activities are strong positive risk markers for ischemic heart disease and independent of HDL-cholesterol

BACKGROUND

We hypothesized that patients with high HDL-cholesterol (HDL-C) and ischemic heart disease (IHD) may have dysfunctional HDL or unrecognized nonconventional risk factors.

METHODS

Individuals with IHD (Copenhagen University Hospital) and either high HDL-C (n = 53; women >or=735 mg/L; men >or=619 mg/L) or low HDL-C (n = 42; women <or=387 mg/L; men <or=341 mg/L) were compared with individuals without IHD (Copenhagen City Heart Study) matched by age, sex, and HDL-C concentrations (n = 110). All participants had concentrations within reference intervals for LDL-C (<1600 mg/L) and triglyceride (<1500 mg/L), and none were treated with lipid-lowering medications. Pre-beta(1) HDL and phospholipid transfer protein concentrations were measured by using commercial kits and lecithin:cholesterol acyltransferase (LCAT) activity by using a proteoliposome cholesterol esterification assay.

RESULTS

Pre-beta(1) HDL concentrations were 2-fold higher in individuals with IHD vs no IHD in both the high [63 (5.7) vs 35 (2.3) mg/L; P < 0.0001] and low HDL-C [49 (5.0) vs 27 (1.5) mg/L; P = 0.001] groups. Low LCAT activity was also associated with IHD in the high [95.2 (6.7) vs 123.0 (5.3) micromol x L(-1) x h(-1); P = 0.002] and low [93.4 (8.3) vs 113.5 (4.9) micromol x L(-1) . h(-1); P = 0.03] HDL-C groups. ROC curves for pre-beta(1) HDL in the high-HDL-C groups yielded an area under the curve of 0.71 (95% CI: 0.61-0.81) for predicting IHD, which increased to 0.92 (0.87-0.97) when LCAT was included. Similar results were obtained for low HDL-C groups. An inverse correlation between LCAT activity and pre-beta(1) HDL was observed (r(2) = 0.30; P < 0.0001) in IHD participants, which was stronger in the low HDL-C group (r(2) = 0.56; P < 0.0001).

CONCLUSIONS

IHD was associated with high pre-beta(1) HDL concentrations and low LCAT levels, yielding correct classification in more than 90% of the IHD cases for which both were measured, thus making pre-beta(1) HDL concentration and LCAT activity level potentially useful diagnostic markers for cardiovascular disease.

Novel roles for ATP-binding cassette G transporters in lipid redistribution in Toxoplasma

Toxoplasma is a protozoan parasite proficiently adapted to thrive in a parasitophorous vacuole (PV) formed in the cytoplasm of a large variety of mammalian cells. As an actively dividing organism, the parasite must adjust the lipid composition of its membranes to preserve organelle vitality and expand the size of the PV membrane to accommodate growing progeny. We showed that Toxoplasma takes up host lipids and can expel major lipids in an ATP-dependent process. In order to provide detailed mechanistic insights into lipid trafficking phenomena relevant to Toxoplasma biology, we characterized six parasite ATP-binding cassette (ABC) G family transporters and investigated their potential contribution to lipid homeostatic processes. All these transporters are expressed in the parasite and five of them are upregulated upon exposure to sterols. Four ABCG are localized to secretory organelles and the plasma membrane, and promote cholesterol and phospholipid efflux, reflecting the importance in exportation of large amounts of lipids into the PV. Interestingly, one ABCG that is associated with vesicles in the PV and the plasma membrane acts as a cholesterol importer. This last finding expands our current view on the role of some ABCG transporters in eukaryotic sterol influx.

Plasma levels of lecithin:cholesterol acyltransferase and risk of future coronary artery disease in apparently healthy men and women: a prospective case-control analysis nested in the EPIC-Norfolk population study

LCAT plays a key role in the maturation of HDL, as evidenced by low HDL-cholesterol levels in carriers of deleterious mutations in LCAT. However, the role of LCAT in atherosclerosis is unclear. We set out to study this in a prospective study. Plasma LCAT levels, which strongly correlate with LCAT activity, were measured in baseline nonfasting samples of 933 apparently healthy men and women who developed coronary artery disease (CAD) and 1,852 matched controls who remained free of CAD during 6 year follow-up. LCAT levels did not differ between cases and controls but were higher in women than men. Stratification into LCAT quartiles revealed a positive association with plasma LDL-cholesterol and triglyceride levels in the unexpected absence of an association with HDL-cholesterol. In mixed-gender analyses, the odds ratio (OR) for future CAD in the highest LCAT quartile versus the lowest was 1.00 [confidence interval (CI): 0.76-1.29, P for linearity = 0.902], although opposite trends were observed in men and women. In fact, high LCAT levels were associated with an increased CAD risk in women (unadjusted OR 1.45, CI: 0.94-2.22, P for linearity = 0.036). In contrast to our studies in carriers of LCAT mutations, the current data show that low LCAT plasma levels are not associated with increased atherosclerosis in the general population.

Haptoglobin inhibits phospholipid transfer protein activity in hyperlipidemic human plasma

Background

Haptoglobin is a plasma protein that scavenges haemoglobin during haemolysis. Phospholipid Transfer Protein (PLTP) transfers lipids from Low Density Lipoproteins (LDL) to High Density Lipoproteins (HDL). PLTP is involved in the pathogenesis of atherosclerosis which causes coronary artery disease, the leading cause of death in North America. It has been shown that Apolipoprotein-A1 (Apo-A1) binds and regulates PLTP activity. Haptoglobin can also bind to Apo-A1, affecting the ability of Apo-A1 to induce enzymatic activities. Thus we hypothesize that haptoglobin inhibits PLTP activity. This work tested the effect of Haptoglobin and Apo-A1 addition on PLTP activity in human plasma samples. The results will contribute to our understanding of the role of haptoglobin on modulating reverse cholesterol transport.

Results

We analyzed the PLTP activity and Apo-A1 and Haptoglobin content in six hyperlipidemic and six normolipidemic plasmas. We found that Apo-A1 levels are proportional to PLTP activity in hyperlipidemic (R² = 0.66, p < 0.05) but not in normolipidemic human plasma. Haptoglobin levels and PLTP activity are inversely proportional in hyperlipidemic plasmas (R² = 0.57, p > 0.05). When the PLTP activity was graphed versus the Hp/Apo-A1 ratio in hyperlipidemic plasma there was a significant correlation (R² = 0.69, p < 0.05) suggesting that PLTP activity is affected by the combined effect of Apo-A1 and haptoglobin. When haptoglobin was added to individual hyperlipidemic plasma samples there was a dose dependent decrease in PLTP activity. In these samples we also found a negative correlation (-0.59, p < 0.05) between PLTP activity and Hp/Apo-A1. When we added an amount of haptoglobin equivalent to 100% of the basal levels, we found a 64 ± 23% decrease (p < 0.05) in PLTP activity compared to basal PLTP activity. We tested the hypothesis that additional Apo-A1 would induce PLTP activity. Interestingly we found a dose dependent decrease in PLTP activity upon Apo-A1 addition. When both Apo-A1 and Hpt were added to the plasma samples there was no further reduction in PLTP activity suggesting that they act through a common pathway.

Conclusion

These findings suggest an inhibitory effect of Haptoglobin over PLTP activity in hyperlipidemic plasma that may contribute to the regulation of reverse cholesterol transport.