Plasma Atherogenic Lipoproteins Research Articles

Abstract P273: Omega-3 Fatty Acids in Erythrocyte Membranes are Associated With Predictive Equations for Estimation of Cardiovascular Risk in Brazilian Individuals

Introduction: Although several mechanisms confirm the cardioprotective role of omega-3 fatty acids (n-3 PUFA), there is still controversy regarding its impact on cardiovascular outcomes. We hypothesized that the n-3 PUFA in erythrocytes membranes reflect better intake and metabolization of these fatty acids, allowing identify their cardiovascular benefits. Objective: To evaluate the association of the n-3 PUFA with cardiometabolic biomarkers and absolute cardiovascular risk. Methods: A crossectional study based on the baseline time of CARDIONUTRI clinical trial (n = 356) with individuals of both sexes (30-74 years) who showed at least one of the following risk factors: smoking, hypertension, dyslipidemias, diabetes mellitus or obesity, but without previous cardiovascular events, monitored by clinical evaluation and ECG. By direct interviews, information about demographic data, medication, blood pressure, diet, and physical activity were investigated by physician and dietician. After 12h of fasting, the lipid profile, lipoprotein sub fractions, LDL(-), glucose, HbA1c, insulin, HOMA-IR and inflammation biomarkers were analyzed by standard and validated methods. After lipid extraction from erythrocytes, fatty acids were analyzed by gas chromatography using internal (C17) and external (FAME 37) standard. The 10-years projection of absolute cardiovascular risk was estimated by the Framingham (FRS), Reynolds (RRS) and ACC/AHA 2013 risk scores. Association between fatty acids, biomarkers and cardiovascular risk scores were performed by linear and logistic regression models and factorial analysis (SPSS v.20.0 and Stata v.14.0). Results: Individuals with n-3 PUFA > 6.24% and n-6/n-3 ≤ 1.27 had less plasma non-HDL cholesterol, Apo B, TG, LDL(-) and highest LDL size. Regarding FRS, the total n-3 PUFA had association with lower cardiovascular risk (OR=0.811; IC95%=0.675- 0.976) and the membrane 1 model rich in n-6 was and poor in n-3 PUFA was associated with higher risk (OR=1.469; IC95%=1.056-2.043). Regarding RRS, the same membrane model was associated with higher risk (OR: 1.276; IC95%=1.010-1.612) while the opposite pattern was observed for membrane 2 model (rich in n-3 and poor in n-6 PUFA), had association with lower risk (OR=0,747; IC95%=0,589-0,948). Conclusion: High content of n-3 in erythrocyte membranes containing was associated with a lipid profile characterized by less plasma atherogenic lipoproteins, reduced TG and modified LDL. This profile was associated with reduced chance to be classified as moderate or higher cardiovascular risk by the Reynolds and Framingham Risk Scores.

Colesterol-no HDL como objetivo terapéutico

Although cholesterol linked to low-density lipoproteins (c-LDL) is well established as a risk factor for cardiovascular disease, there is often a more complex dyslipidaemia pattern that contributes to the formation of atherosclerotic plaque. Non-HDL cholesterol (c-NO-HDL) is used to estimate the total amount of atherogenic lipoproteins in plasma, some of which are not usually determined in daily clinical practice. c-NO-HDL is easily calculated from the subtraction of total plasma cholesterol from the cholesterol content carried by high density lipoproteins. The c-NO-HDL has a predictive value superior to that of C-LDL to estimate the risk of major cardiovascular events in epidemiological studies. Genetic studies by analysis of the complete genome, together with those based on Mendelian randomisation, point to the aetiological character of c-NO-HDL on ischaemic heart disease (IHD). Intervention studies, and the meta-analyses derived from them, close the causal circle between c-NO-HDL and IHD, by demonstrating that any intervention that decreases the concentrations of the former reduces the incidence of arteriosclerotic heart disease. The European ESC/EAS 2016 guide for the management of dyslipidaemia considers c-NO-HDL as a therapeutic target with a Class IIa recommendation (should be performed) Level B (data from a single randomised clinical trial [RCT]) or from several non-RCTs), and sets its target at less than 100 or 130mg/dL for those patients with very high risk or high risk, respectively. These achievable c-NO-HDL values are easily calculated by adding 30mg/dL to the c-LDL targets.

Dietary saturated fatty acid intake elevated plasma atherogenic lipoproteins in mice

Dietary saturated fatty acid intake elevated plasma atherogenic lipoproteins in mice

Postprandial remnant lipoproteins as targets for the prevention of atherosclerosis.

Oxidized low-density lipoprotein (Ox-LDL) and chylomicron remnants were previously proposed as the most atherogenic lipoproteins for the causal lipoproteins of atherosclerosis. However, there are still controversies on these hypothesizes. Therefore, we have proposed a new hypothesis based on our recent findings of remnant lipoproteins (RLPs) in postprandial plasma. Plasma RLP-C and RLP-TG increased significantly after fat load. More than 80% of the increased triglycerides after fat load consisted of the triglycerides in RLP, which contained greater amount of apoB100 than apoB48 particles as mostly very low density lipoproteins (VLDL) remnants. The majority of lipoprotein lipase (LPL) in plasma was found in RLP as RLP-LPL complex, which is released into circulation after hydrolysis. LPL activity and concentration in plasma did not increase after food intake associated with the insufficient hydrolysis of chylomicrons and VLDL and resulted in the significant increase of RLP-TG. Plasma LPL was inversely correlated with RLP particle size and number. VLDL remnants have been shown as the major atherogenic lipoproteins in postprandial plasma associated with LPL activity as the targets for prevention of atherosclerosis. We also proposed a new definition of RLPs, 'LPL bound TG-rich lipoproteins' based on the findings of RLP-LPL complex.

Atherogenic Versus Non-atherogenic Lipoprotein Profiles in Healthy Individuals. Is There a Need to Change Our Approach to Diagnosing Dyslipidemia?

The electrophoretic separation of lipoproteins on polyacrylamide gels enables the quantification of nonatherogenic and atherogenic plasma lipoproteins including small dense low density lipoprotein (sdLDL) particles, which represent the atherogenic lipoprotein subpopulations in plasma. This methodology could help distinguish between nonatherogenic hyperlipidemia, normolipidemia with an atherogenic lipoprotein profile, non-atherogenic normolipidemia, and atherogenic hyperlipidemia. According to our pilot research of a normolipidemic population, the atherogenic lipoprotein profile might be present in about 6% of normolipidemic young healthy individuals. Therefore, if confirmed by other studies, it will be necessary to consider a different diagnostic approach and risk stratification for patients with atherogenic normolipidemia (as well as non-atherogenic hypercholesterolemia).

Size of low‑density lipoprotein particles in patients after stroke

30 Introduction Acute stroke is a severe clinical man‑ ifestation of atherothrombosis. Atherothrombo‑ sis and its complications are currently the most frequent cause of morbidity in the world. The ma‑ jor factors contributing to accelerated athero‑ thrombosis in humans are dyslipoproteinemias and hypertension, among others. The presence of atherogenic lipoproteins in plasma leads to the development of endothelial dysfunction, in‑ creases the vessel tone, and contributes to further deterioration of cerebral perfusion leading to ce‑ rebral ischemia. The aim of the present study was to evaluate atherogenic lipoproteins in patients with acute ischemic stroke admitted to the in‑ tensive care unit. Patients and methods We followed up 50 con‑ secutive patients with acute ischemic stroke (24 men and 26 women), aged from 35 to 90 years (mean age, 77.5 years ±11.8 years), and admit‑ ted to the 2nd Department of Internal Medicine of the Comenius University in Bratislava, Slo‑ vakia. The diagnosis of stroke was confirmed by a neurologist and by computed tomography. Af‑ ter admission, blood samples from the cubital vein were collected to measure routine biochem‑ ical parameters, including complete lipid profile

HDL quality in atherosclerosis: can ratios between apolipoproteins of HDL be used effectively to indicate risk of premature myocardial infarction?

Recently the idea that HDL quality is very important for atheroprotection has been gaining ground and measurable changes in HDL apolipoprotein ratios may serve as effective prognostic markers for the early identification of asymptomatic individuals at high risk for a life-threatening acute myocardial infarction. Coronary heart disease (CHD) is the most common cause of death worldwide. According to WHO, an estimated 7.2 million people died from CHD in 2008, representing approximately 12% of deaths worldwide, while in the year 2030 it is estimated that 23.6 million people will die from cardiovascular disease [101]. CHD is caused by atherosclerosis, a focal disease of the arterial wall that affects largeand medium-sized arteries [1]. Although multiple risk factors have been associated with atherosclerosis, dyslipidemia has been identified as a leading cause of CHD. In particular, an imbalance between atheroprotective and atherogenic lipoproteins in plasma is one of the most important parameters associated with atherosclerosis [2,3]. Conventional imaging technologies usually allow detection of atherosclerotic lesions that occlude 50% or more of the lumen of the arteries. Such plaques are usually stable and less prone to rapture and rarely lead to embolism and myocardial infarction (MI). By contrast, unstable atherosclerotic plaques are usually smaller in size and have a weak fibrous cap that can rapture and release the lipid core of the lesion into the circulation, creating an infarct. Such small unstable lesions are life threatening and often hard to diagnose with classical imaging techniques [4]. This deficiency in the early diagnosis of atherosclerosis increases the

The relationship between high-sensitivity C-reactive protein and ApoB, ApoB/ApoA1 ratio in general population of China

Inflammatory biomarker high-sensitivity C-reactive protein (hsCRP) is considered as a major predictor of cardiovascular events. Apolipoprotein B (ApoB) directly reflects the number of plasma atherogenic lipoproteins, and may play a major role in vascular inflammation. We aimed to assess whether an association between ApoB and hsCRP exists and, furthermore, to examine whether ApoB is more predictive of the inflammatory status than other cardiovascular risk factors. This was a cross-sectional study, with 511 apparently healthy adult subjects enrolled. Waist circumference (WC), body mass index (BMI), and blood pressure (BP) were measured. Plasma glucose levels, hsCRP, lipid profile, and insulin were collected after 10-14 h fasting. From the lowest to the highest quartile of hsCRP, the values for BMI, WC, BP, HOMA-IR, insulin, glucose level, triglyceride (TG), low-density lipoprotein cholesterol (LDL-C), ApoB and the ApoB/apolipoprotein A1 (ApoA1) ratio were increased as the hsCRP level increased (P < 0.01), and high-density lipoprotein cholesterol (HDL-C) and ApoA1 levels declined as hsCRP level increased (P < 0.0001). Pearson's correlation analysis demonstrated that hsCRP correlated with all variables (P < 0.01), except for total cholesterol (TC) (P = 0.154) and LDL-C (P = 0.087). According to forward stepwise regression analysis with hsCRP as the dependent variable, WC was the only variable entered the regression model. ApoB level correlated with hsCRP level but was not the major determinant of hsCRP. WC was stronger than other cardiovascular risk factors in the associations with hsCRP. Abdominal obesity rather than atherogenic dyslipidemia was the primary cause of chronic inflammatory status.

Anti-inflammatory, anti-proliferative and anti-atherosclerotic effects of quercetin in human in vitro and in vivo models

ObjectivePolyphenols such as quercetin may exert several beneficial effects, including those resulting from anti-inflammatory activities, but their impact on cardiovascular health is debated. We investigated the effect of quercetin on cardiovascular risk markers including human C-reactive protein (CRP) and on atherosclerosis using transgenic humanized models of cardiovascular disease. MethodsAfter evaluating its anti-oxidative and anti-inflammatory effects in cultured human cells, quercetin (0.1%, w/w in diet) was given to human CRP transgenic mice, a humanized inflammation model, and ApoE*3Leiden transgenic mice, a humanized atherosclerosis model. Sodium salicylate was used as an anti-inflammatory reference. ResultsIn cultured human endothelial cells, quercetin protected against H2O2-induced lipid peroxidation and reduced the cytokine-induced cell-surface expression of VCAM-1 and E-selectin. Quercetin also reduced the transcriptional activity of NFκB in human hepatocytes. In human CRP transgenic mice (quercetin plasma concentration: 12.9±1.3μM), quercetin quenched IL1β-induced CRP expression, as did sodium salicylate. In ApoE*3Leiden mice, quercetin (plasma concentration: 19.3±8.3μM) significantly attenuated atherosclerosis by 40% (sodium salicylate by 86%). Quercetin did not affect atherogenic plasma lipids or lipoproteins but it significantly lowered the circulating inflammatory risk factors SAA and fibrinogen. Combined histological and microarray analysis of aortas revealed that quercetin affected vascular cell proliferation thereby reducing atherosclerotic lesion growth. Quercetin also reduced the gene expression of specific factors implicated in local vascular inflammation including IL-1R, Ccl8, IKK, and STAT3. ConclusionQuercetin reduces the expression of human CRP and cardiovascular risk factors (SAA, fibrinogen) in mice in vivo. These systemic effects together with local anti-proliferative and anti-inflammatory effects in the aorta may contribute to the attenuation of atherosclerosis.

The Structure of Apolipoprotein A-I in High Density Lipoproteins

Not long ago, high density lipoproteins (HDL)2 were second class citizens with regard to therapeutic strategies for lowering the risk of atherosclerosis and coronary artery disease (CAD). To date, most successful approaches have focused on the better understood pathways of cholesterol synthesis and low density lipoprotein (LDL) production, the “forward” cholesterol transport pathway. For example, the statin class of cholesterol synthesis inhibitors significantly reduces LDL levels resulting in a less atherogenic plasma lipoprotein profile. However, the relatively modest improvements in mortality conferred by these drugs suggest that other factors also play significant roles in defining CAD risk. The recent discoveries of HDL-interacting cell surface proteins such as scavenger receptor BI (SR-BI) and ATP-binding cassette transporters A1 (ABCA1) and G1 (for recent reviews see Refs. 1 and 2) have helped define the steps of reverse cholesterol transport (RCT), i.e. the movement of cholesterol from the periphery to the liver for catabolism (3, 4). Additionally, there is growing evidence that HDL anti-inflammatory properties may contribute significant protective effects (5), apparently via specific cell signaling pathways (6). These discoveries have fueled a new interest in HDL as a target for CAD treatment (7). Unfortunately, a complete understanding ofHDL function has been hampered by a lack of information on its structure and the molecular basis of its interactions with other proteins. This review summarizes the latest efforts in understanding the structure of the defining protein component of HDL, apoA-I, in the various stages of the RCT pathway.

Adiponectin and the metabolic syndrome: mechanisms mediating risk for metabolic and cardiovascular disease

Adiponectin is secreted exclusively by adipocytes, aggregates in multimeric forms, and circulates at high concentrations in blood. This review summarizes recent studies highlighting cellular effects of adiponectin and its role in human lipid metabolism and atherosclerosis. Adiponectin is an important autocrine/paracrine factor in adipose tissue that modulates differentiation of preadipocytes and favors formation of mature adipocytes. It also functions as an endocrine factor, influencing whole-body metabolism via effects on target organs. Adiponectin multimers exert differential biologic effects, with the high-molecular-weight multimer associated with favorable metabolic effects (i.e. greater insulin sensitivity, reduced visceral adipose mass, reduced plasma triglycerides, and increased HDL-cholesterol). Adiponectin influences plasma lipoprotein levels by altering the levels and activity of key enzymes (lipoprotein lipase and hepatic lipase) responsible for the catabolism of triglyceride-rich lipoproteins and HDL. It thus influences atherosclerosis by affecting the balance of atherogenic and antiatherogenic lipoproteins in plasma, and by modulating cellular processes involved in foam cell formation. Recent studies emphasize the role played by adiponectin in the homeostasis of adipose tissue and in the pathogenesis of the metabolic syndrome, type 2 diabetes, and atherosclerosis. These pleiotropic effects make it an attractive therapeutic target for obesity-related conditions.

Endothelial lipase and the metabolic syndrome

Several in-vitro and in-vivo animal studies indicate that endothelial lipase plays a key role in the intravascular remodeling of lipoproteins, particularly HDL. This review integrates this body of knowledge with more recent data in humans linking endothelial lipase to HDL metabolism and other features of the metabolic syndrome. Human studies generally support the involvement of endothelial lipase in modulating plasma HDL. The association between endothelial lipase and metabolism of apolipoprotein B-containing lipoproteins in humans, however, has not been entirely consistent with previous findings in vitro and in animals. Finally, elevated plasma endothelial lipase has been associated with abdominal obesity and hypertension, and there is now compelling evidence that inflammation and in-vivo regulation of endothelial lipase may be intrinsically related. Accumulating evidence indicates that endothelial lipase plays a role in the etiology of the atherogenic plasma lipoprotein profile characteristic of the metabolic syndrome. Increased endothelial lipase activity is linked to the underlying proinflammatory state in this condition. Further studies are required, however, to define the extent to which endothelial lipase contributes to the dyslipidemia of the metabolic syndrome relative to other important regulating factors, such as lipoprotein lipase, hepatic lipase, and cholesterol ester transfer protein.

Transgenic expression of CYP7A1 in LDL receptor-deficient mice blocks diet-induced hypercholesterolemia

Constitutive expression of a cholesterol-7alpha-hydroxylase (CYP7A1) transgene in LDL receptor-deficient mice blocked the ability of a cholesterol-enriched diet to increase plasma levels of apolipoprotein B-containing lipoproteins. LDL receptor-deficient mice expressing the CYP7A1 transgene exhibited complete resistance to diet-induced hypercholesterolemia and to the accumulation of cholesterol in the liver. Hepatic mRNA expression of liver X receptor-inducible ABCG5 and ABCG8 was decreased in CYP7A1 transgenic, LDL receptor-deficient mice fed a cholesterol-enriched diet. Thus, increased biliary cholesterol excretion could not account for the maintenance of cholesterol homeostasis. CYP7A1 transgenic, LDL receptor-deficient mice fed the cholesterol-enriched diet exhibited decreased jejunal Niemann-Pick C1-Like 1 protein (NPC1L1) mRNA expression, an important mediator of intestinal cholesterol absorption. A taurocholate-enriched diet also decreased NPC1L1 mRNA expression in a farnesoid X receptor-independent manner. Reduced expression of NPC1L1 mRNA was associated with decreased cholesterol absorption ( approximately 20%; P < 0.05) exhibited by CYP7A1 transgenic LDL receptor-deficient mice fed the cholesterol-enriched diet. The combined data show that enhanced expression of CYP7A1 is an effective means to prevent the accumulation of cholesterol in the liver and of atherogenic apolipoprotein B-containing lipoproteins in plasma.

Galactose-specific asialoglycoprotein receptor is involved in lipoprotein (a) catabolism.

Lp(a) [lipoprotein (a)] is a highly atherogenic plasma lipoprotein assembled from low-density lipoprotein and the glycoprotein apolipoprotein (a). The rate of Lp(a) biosynthesis correlates significantly with plasma Lp(a) concentrations, whereas the fractional catabolic rate does not have much influence. So far, little is known about Lp(a) catabolism. To study the site and mode of Lp(a) catabolism, native or sialidase-treated Lp(a) was injected into hedgehogs or ASGPR (asialoglycoprotein receptor)-knockout (ASGPR-) mice or wild-type (ASGPR+) mice, and the decay of the plasma Lp(a) concentration was followed. COS-7 cells were transfected with high- (HL-1) and low-molecular-mass ASGPR subunits (HL-2), and binding and degradation of intact or desialylated Lp(a) were measured. In hedgehogs, one of the few species that synthesize Lp(a), most of the Lp(a) was taken up by the liver, followed by kidney and spleen. Lp(a) and asialo-Lp(a) were catabolized with apparent half-lives of 13.8 and 0.55 h respectively. Asialo-orosomucoide increased both half-lives significantly. In mice, the apparent half-life of Lp(a) was 4-6 h. Catabolism of native Lp(a) by wild-type mice was significantly faster compared with ASGPR- mice and there was a significantly greater accumulation of Lp(a) in the liver of ASGPR+ mice compared with ASGPR- mice. The catabolism of asialo-Lp(a) in ASGPR- mice was 8-fold faster when compared with native Lp(a) in wild-type mice. Transfected COS-7 cells expressing functional ASGPR showed approx. 5-fold greater binding and 2-fold faster degradation of native Lp(a) compared with control cells. Our results for the first time demonstrate a physiological function of ASGPR in the catabolism of Lp(a).

Atherogenic role of elevated CE transfer from HDL to VLDL(1) and dense LDL in type 2 diabetes : impact of the degree of triglyceridemia.

Plasma cholesteryl ester transfer protein (CETP) facilitates intravascular lipoprotein remodeling by promoting the heteroexchange of neutral lipids. To determine whether the degree of triglyceridemia may influence the CETP-mediated redistribution of HDL CE between atherogenic plasma lipoprotein particles in type 2 diabetes, we evaluated CE mass transfer from HDL to apoB-containing lipoprotein acceptors in the plasma of type 2 diabetes subjects (n=38). In parallel, we investigated the potential relationship between CE transfer and the appearance of an atherogenic dense LDL profile. The diabetic population was divided into 3 subgroups according to fasting plasma triglyceride (TG) levels: group 1 (G1), TG<100 mg/dL; group 2 (G2), 100<TG<200 mg/dL; and group 3 (G3), TG>200 mg/dL. Type 2 diabetes patients displayed an asymmetrical LDL profile in which the dense LDL subfractions predominated. Plasma levels of dense LDL subfractions were strongly positively correlated with those of plasma triglyceride (TG) (r=0.471; P:=0.0003). The rate of CE mass transfer from HDL to apoB-containing lipoproteins was significantly enhanced in G3 compared with G2 or G1 (46.2+/-8.1, 33.6+/-5.3, and 28.2+/-2.7 microg CE transferred. h(-1). mL(-1) in G3, G2, and G1, respectively; P:<0.0001 G3 versus G1, P:=0.0001 G2 versus G1, and P:=0.02 G2 versus G3). The relative capacities of VLDL and LDL to act as acceptors of CE from HDL were distinct between type 2 diabetes subgroups. LDL particles represented the preferential CE acceptor in G1 and accounted for 74% of total CE transferred from HDL. By contrast, in G2 and G3, TG-rich lipoprotein subfractions accounted for 47% and 72% of total CE transferred from HDL, respectively. Moreover, the relative proportion of CE transferred from HDL to VLDL(1) in type 2 diabetes patients increased progressively with increase in plasma TG levels. The VLDL(1) subfraction accounted for 34%, 43%, and 52% of total CE transferred from HDL to TG-rich lipoproteins in patients from G1, G2, and G3, respectively. Finally, dense LDL acquired an average of 45% of total CE transferred from HDL to LDL in type 2 diabetes patients. In conclusion, CETP contributes significantly to the formation of small dense LDL particles in type 2 diabetes by a preferential CE transfer from HDL to small dense LDL, as well as through an indirect mechanism involving an enhanced CE transfer from HDL to VLDL(1), the specific precursors of small dense LDL particles in plasma.

Tunicamycin induces ubiquitination and degradation of apolipoprotein B in HepG2 cells

Apolipoprotein (apo) B-100 is an essential component of atherogenic plasma lipoproteins. Previous studies have demonstrated that the production of apoB-100 is regulated largely by intracellular degradation at both the co-translational and post-translational levels and that proteasome-mediated and non-proteasome-mediated pathways are involved in this process. ApoB-100 is a glycoprotein. The present study was undertaken to address the question of whether the inhibition of N-linked glycosylation with tunicamycin would interfere with apoB-100 production. We demonstrated that the treatment of HepG2 cells with tunicamycin decreased the net production of apoB-100 by enhancing co-translational degradation of the protein. This effect of tunicamycin was partly prevented by lactacystin, a specific proteasome inhibitor. Because lactacystin only partly reversed the effects of tunicamycin on apoB biogenesis, tunicamycin seemed also to induce apoB co-translational degradation in HepG2 cells by one or more non-proteasomal pathways. Furthermore, tunicamycin increased apoB ubiquitination approx. 4-fold. The proportion of the newly synthesized apoB-100 that was secreted and incorporated into the nascent lipoprotein particles was unaffected by tunicamycin. Thus the tunicamycin-mediated inhibition of N-linked glycosylation interferes with the production of apoB-100 that is mediated by both proteasomal and non-proteasomal pathways.

Tunicamycin induces ubiquitination and degradation of apolipoprotein B in HepG2 cells

Apolipoprotein (apo) B-100 is an essential component of atherogenic plasma lipoproteins. Previous studies have demonstrated that the production of apoB-100 is regulated largely by intracellular degradation at both the co-translational and post-translational levels and that proteasome-mediated and non-proteasome-mediated pathways are involved in this process. ApoB-100 is a glycoprotein. The present study was undertaken to address the question of whether the inhibition of N-linked glycosylation with tunicamycin would interfere with apoB-100 production. We demonstrated that the treatment of HepG2 cells with tunicamycin decreased the net production of apoB-100 by enhancing co-translational degradation of the protein. This effect of tunicamycin was partly prevented by lactacystin, a specific proteasome inhibitor. Because lactacystin only partly reversed the effects of tunicamycin on apoB biogenesis, tunicamycin seemed also to induce apoB co-translational degradation in HepG2 cells by one or more non-proteasomal pathways. Furthermore, tunicamycin increased apoB ubiquitination approx. 4-fold. The proportion of the newly synthesized apoB-100 that was secreted and incorporated into the nascent lipoprotein particles was unaffected by tunicamycin. Thus the tunicamycin-mediated inhibition of N-linked glycosylation interferes with the production of apoB-100 that is mediated by both proteasomal and non-proteasomal pathways.

LCAT modulates atherogenic plasma lipoproteins and the extent of atherosclerosis only in the presence of normal LDL receptors in transgenic rabbits.

Elevated low density lipoprotein cholesterol (LDL-C) and reduced high density lipoprotein cholesterol (HDL-C) concentrations are independent risk factors for coronary heart disease. We have previously demonstrated that overexpression of an enzyme with a well established role in HDL metabolism, lecithin:cholesterol acyltransferase (LCAT), in New Zealand White rabbits not only raises HDL-C concentrations but reduces those of LDL-C as well, ultimately preventing diet-induced atherosclerosis. In the present study, the human LCAT gene (hLCAT) was introduced into LDL receptor (LDLr)-deficient (Watanabe heritable hyperlipidemic) rabbits to (1) investigate the role of the LDLr pathway in the hLCAT-mediated reductions of LDL-C and (2) determine the influence of hLCAT overexpression on atherosclerosis susceptibility in an animal model of familial hypercholesterolemia. Heterozygosity or homozygosity for the LDLr defect was determined by polymerase chain reaction, and 3 groups of hLCAT-transgenic (hLCAT+) rabbits that differed in LDLr status were established: (1) LDLr wild-type (LDLr+/+), (2) LDLr heterozygotes (LDLr+/-), and (3) LDLr homozygotes (LDLr-/-). Data for hLCAT+ rabbits were compared with those of nontransgenic (hLCAT-) rabbits of the same LDLr status. Plasma HDL-C concentrations were significantly elevated in the hLCAT+ animals of each LDLr status. However, LDL-C levels were significantly reduced only in hLCAT+/LDLr+/+ and hLCAT+/LDLr+/- rabbits but not in hLCAT+/LDLr-/- rabbits (405+/-14 versus 392+/-31 mg/dL). Metabolic studies revealed that the fractional catabolic rate (FCR, d(-1)) of LDL apolipoprotein (apo) B-100 was increased in hLCAT+/LDLr+/+ (26+/-4 versus 5+/-0) and hLCAT+/LDLr+/- (4+/-1 versus 1+/-0) rabbits, whereas the FCR of LDL apoB-100 in both groups of LDLr-/- rabbits was nearly identical (0.16+/-0.02 versus 0.15+/-0.02). Consistently, neither aortic lipid concentrations nor the extent of aortic atherosclerosis was significantly different between hLCAT+/LDLr-/- and hLCAT-/LDLr-/- rabbits. Significant correlations were observed between the percent of aortic atherosclerosis and both LDL-C (r=0.985) and LDL apoB-100 FCR (-0.745), as well as between LDL-C and LDL apoB-100 FCR (-0.866). These data are the first to establish that LCAT modulates LDL metabolism via the LDLr pathway, ultimately influencing atherosclerosis susceptibility. Moreover, LCAT's antiatherogenic effect requires only a single functional LDLr allele, identifying LCAT as an attractive gene therapy candidate for the majority of dyslipoproteinemic patients.

The seventh myth of lipoprotein(a): where and how is it assembled?

Our understanding of the genetics, metabolism and pathophysiology of the atherogenic plasma lipoprotein Lp(a) has considerably increased over past years. Nevertheless, the precise mechanisms regulating the biosynthesis and assembly of Lp(a) are poorly understood and controversially discussed. Lp(a) plasma concentrations are determined by synthesis and not by degradation. Transcriptional and post-translational mechanisms have been identified as regulating Lp(a) production in primary hepatocytes and transfected cell lines. Assembly of Lp(a) occurs extracellularly from newly synthesized apolipoprotein(a) and circulating LDL. This view has recently been challenged by in-vivo kinetic studies in humans which are compatible with an intracellular assembly event. Lp(a) assembly is a complex two-step process of multiple non-covalent interactions between apolipoprotein(a) and apolipoprotein B-100 of LDL followed by covalent disulfide linkage of two free cysteine residues on both proteins.

Atherosclerosis and inflammation: Mononuclear cell recruitment and adhesion molecules with reference to the implication of ICAM-1/LFA-1 pathway in atherogenesis

Recent investigations have reanimated the view that there exists a possible link between atherosclerosis and inflammation. Adhesion of monocytes as well as T lymphocytes to the arterial endothelial surface, followed by their migration into the subendothelial space is a hallmark for experimental animals fed an atherogenic diet. Human studies show identical features in the arterial wall to the animal models of atherosclerosis. The recruitment of leukocytes into areas of inflammation is mediated by interacting sets of cell adhesion molecules In atherosclerosis, focal expression of key adhesion molecules particularly triggered by plasma atherogenic lipoproteins has been detected, and these molecules may mediate the recruitment of mononuclear cells to the plaque. Among these adhesion molecules, ICAM-1, a protein of the Ig superfamily, and one of the ligands for LFA-1 have been suggested to play an important role in atherogenesis. In diet-induced hypercholesterolemic rats, we found that ICAM-1 expression is up-regulated mainly in lesion-prone areas of the aorta during the early stages of atherogenesis. Increased ICAM-1 expression was associated with a marked monocyte and T lymphocyte intimal recruitment. Further immunohistochemical studies have demonstrated that LFA-1 is expressed by more than 85% of macrophages in the lesions, and their presence therefore may point toward the involvement of the LFA-1/ICAM-1 receptor ligand pathway in the recruitment of mononuclear cells in the lesions. In order to verify this hypothesis, systemic administration of blocking antibodies was attempted; injection of anti-ICAM-1/LFA-1 monoclonal antibodies significantly reduced macrophage adherence and their emigration into the intima. Our current study suggests that ICAM-1 may act as an “athero-ELAM” for mononuclear cell intimal recruitment during atherogenesis.