1999 George Lyman Duff memorial lecture: lipid transfer proteins, HDL metabolism, and atherogenesis

Cholesterol Metabolism in Chronic Kidney Disease: Physiology, Pathologic Mechanisms, and Treatment

High plasma levels of lipids and/or lipoproteins are risk factors for atherosclerosis, nonalcoholic fatty liver disease (NAFLD), obesity, and diabetes. These four conditions have also been identified as risk factors leading to the development of chronic kidney disease (CKD). Although many pathways that generate high plasma levels of these factors have been identified, most clinical and physiologic dysfunction results from aberrant assembly and secretion of lipoproteins. The results of several published studies suggest that elevated levels of low-density lipoprotein (LDL)-cholesterol are a risk factor for atherosclerosis, myocardial infarction, coronary artery calcification associated with type 2 diabetes, and NAFLD. Cholesterol metabolism has also been identified as an important pathway contributing to the development of CKD; clinical treatments designed to alter various steps of the cholesterol synthesis and metabolism pathway are currently under study. Cholesterol synthesis and catabolism contribute to a multistep process with pathways that are regulated at the cellular level in renal tissue. Cholesterol metabolism may also be regulated by the balance between the influx and efflux of cholesterol molecules that are capable of crossing the membrane of renal proximal tubular epithelial cells and podocytes. Cellular accumulation of cholesterol can result in lipotoxicity and ultimately kidney dysfunction and failure. Thus, further research focused on cholesterol metabolism pathways will be necessary to improve our understanding of the impact of cholesterol restriction, which is currently a primary intervention recommended for patients with dyslipidemia.

Low-Density Lipoprotein Inhibits Secretion of Phospholipid Transfer Protein in Human Trophoblastic BeWo Cells

Human plasma phospholipid transfer protein (PLTP) plays an important role in lipoprotein metabolism. In this study, we investigated the effects of lipoproteins on the secretion of PLTP in cultured BeWo choriocarcinoma cells. Low-density lipoproteins (LDLs) decreased PLTP secretion in a dose- and time-dependent manner, whereas very low density lipoproteins and high-density lipoproteins (HDLs) had little effect. LDL suppression of PLTP secretion was not altered by the inhibition of both LDL receptor and LDL receptor–related protein with receptor-associated protein. Mitogen-activated protein kinase (MAPK) kinase (MEK) inhibitor, U0126, could abolish the LDL-mediated inhibition of PLTP secretion. Furthermore, LDL, but not HDL, could stimulate the expression of MAPK phosphatase-1 (MKP-1) in BeWo cells that resulted in the inactivation of p44/p42 extracellular signal-regulated kinase (ERK) 1 and 2, the family members of MAPKs. These results support the conclusion that LDL-mediated suppression of PLTP secretion in BeWo cells is through a LDL receptor-independent MAPK signaling pathway.

High-Density Lipoprotein, Lecithin: Cholesterol Acyltransferase, and Atherosclerosis

Epidemiological data clearly show the existence of a strong inverse correlation between plasma high-density lipoprotein cholesterol (HDL-C) concentrations and the incidence of coronary heart disease. This relation is explained by a number of atheroprotective properties of HDL, first of all the ability to promote macrophage cholesterol transport. HDL are highly heterogeneous and are continuously remodeled in plasma thanks to the action of a number of proteins and enzymes. Among them, lecithin:cholesterol acyltransferase (LCAT) plays a crucial role, being the only enzyme able to esterify cholesterol within lipoproteins. LCAT is synthetized by the liver and it has been thought to play a major role in reverse cholesterol transport and in atheroprotection. However, data from animal studies, as well as human studies, have shown contradictory results. Increased LCAT concentrations are associated with increased HDL-C levels but not necessarily with atheroprotection. On the other side, decreased LCAT concentration and activity are associated with decreased HDL-C levels but not with increased atherosclerosis. These contradictory results confirm that HDL-C levels per se do not represent the functionality of the HDL system.

New therapies for reducing low-density lipoprotein cholesterol

Although the past 4 decades have been the most productive in transitioning from an low-density lipoprotein cholesterol (LDL-C) hypothesis to demonstration of clinical benefit, cardiovascular disease remains a major cause of mortality and morbidity. It is fortunate that most of the effective lipid-lowering drugs, the statins, have become generic and inexpensive. However, there remains a large unmet medical need for new and effective agents that are also well tolerated and safe, especially for patients unable to either tolerate statins or achieve optimal LDL-C on current therapies. It is likely that the agents discussed in this review will fill that need.

Looking into the Crystal Ball—Upcoming Drugs for Dyslipidemia

Dyslipidaemia is a critical risk factor for the development of cardiovascular complications such as ischemic heart disease and stroke. Although statins are effective anti-dyslipidemic drugs, their usage is fraught with issues such as failure of adequate lipid control in 30% of cases and intolerance in select patients. The limited potential of other alternatives such as fibrates, bile acid sequestrants and niacin has spurred the search for novel drug molecules with better efficacy and safety. CETP inhibitors such as evacetrapib and anacetrapib have shown promise in raising HDL besides LDL lowering property. Microsomal triglyceride transfer protein (MTP) inhibitors such as lomitapide and Apo CIII inhibitors such as mipomersen have recently been approved in Familial Hypercholesterolemia but experience in the non-familial setting is pretty much limited. One of the novel anti-dyslipidemic drugs which is greatly anticipated to make a mark in LDL-C control is the PCSK9 inhibitors. Some of the anti-dyslipidemic drugs which work by PCSK9 inhibition include evolocumab, alirocumab and ALN-PCS. Other approaches that are being given due consideration include farnesoid X receptor modulation and Lp-PLA2 inhibition. While it may not be an easy proposition to dismantle statins from their current position as a cholesterol reducing agent and as a drug to reduce coronary and cerebro-vascular atherosclerosis, our improved understanding of the disease and appropriate harnessing of resources using sound and robust technology could make rapid in-roads in our pursuit of the ideal anti-dyslipidemic drug.

Nutritional genomics for the characterization of the effect of bioactive molecules in lipid metabolism and related pathways

Cardiovascular disease and cancer are the main causes of morbidity and mortality worldwide. Thus, investigators have focused their efforts on gaining insight into understanding the mechanisms involved in the development and evolution of these diseases. In the past decade, and with the contribution of the -omics technologies, strong evidence has supported an essential role of gene-nutrient interactions in these processes, pointing at natural bioactive molecules as promising complementary agents that are useful in preventing or mitigating these diseases. In addition, alterations in lipid metabolism have recently gained strong interest since they have been described as a common event required for the progression of both diseases. In the present review, we give an overview of lipid metabolism, mainly focusing on lipoprotein metabolism and the mechanisms controlling lipid homeostasis. In addition, we review the modulation of lipid metabolism by bioactive molecules, highlighting their potential use as therapeutic agents in preventing, and treating chronic diseases such as cardiovascular disease and cancer. Finally, we report the usefulness of the -omics technologies in nutritional research, focusing on recent findings, within nutritional genomics, in the interaction of bioactive components from foods with several genes that are involved in the development and progression of these diseases.

Evacetrapib is a novel, potent, and selective inhibitor of cholesteryl ester transfer protein that elevates HDL cholesterol without inducing aldosterone or increasing blood pressure

Cholesteryl ester transfer protein (CETP) catalyses the exchange of cholesteryl ester and triglyceride between HDL and apoB containing lipoprotein particles. The role of CETP in modulating plasma HDL cholesterol levels in humans is well established and there have been significant efforts to develop CETP inhibitors to increase HDL cholesterol for the treatment of coronary artery disease. These efforts, however, have been hampered by the fact that most CETP inhibitors either have low potency or have undesirable side effects. In this study, we describe a novel benzazepine compound evacetrapib (LY2484595), which is a potent and selective inhibitor of CETP both in vitro and in vivo. Evacetrapib inhibited human recombinant CETP protein (5.5 nM IC(50)) and CETP activity in human plasma (36 nM IC(50)) in vitro. In double transgenic mice expressing human CETP and apoAI, evacetrapib exhibited an ex vivo CETP inhibition ED(50) of less than 5 mg/kg at 8 h post oral dose and significantly elevated HDL cholesterol. Importantly, no blood pressure elevation was observed in rats dosed with evacetrapib at high exposure multiples compared with the positive control, torcetrapib. In addition, in a human adrenal cortical carcinoma cell line (H295R cells), evacetrapib did not induce aldosterone or cortisol biosynthesis whereas torcetrapib dramatically induced aldosterone and cortisol biosynthesis. Our data indicate that evacetrapib is a potent and selective CETP inhibitor without torcetrapib-like off-target liabilities. Evacetrapib is currently in phase II clinical development.

D-4F, an apoA-1 mimetic, decreases airway hyperresponsiveness, inflammation, and oxidative stress in a murine model of asthma

Asthma is characterized by oxidative stress and inflammation of the airways. Although proinflammatory lipids are involved in asthma, therapies targeting them remain lacking. Ac-DWFKAFYDKVAEKFKEAFNH(2) (4F) is an apolipoprotein (apo)A-I mimetic that has been shown to preferentially bind oxidized lipids and improve HDL function. The objective of the present study was to determine the effects of 4F on oxidative stress, inflammation, and airway resistance in an established murine model of asthma. We show here that ovalbumin (OVA)-sensitization increased airway hyperresponsiveness, eosinophil recruitment, and collagen deposition in lungs of C57BL/6J mice by a mechanism that could be reduced by 4F. OVA sensitization induced marked increases in transforming growth factor (TGF)β-1, fibroblast specific protein (FSP)-1, anti-T15 autoantibody staining, and modest increases in 4-hydroxynonenal (4-HNE) Michael's adducts in lungs of OVA-sensitized mice. 4F decreased TGFβ-1, FSP-1, anti-T15 autoantibody, and 4-HNE adducts in the lungs of the OVA-sensitized mice. Eosinophil peroxidase (EPO) activity in bronchial alveolar lavage fluid (BALF), peripheral eosinophil counts, total IgE, and proinflammatory HDL (p-HDL) were all increased in OVA-sensitized mice. 4F decreased BALF EPO activity, eosinophil counts, total IgE, and p-HDL in these mice. These data indicate that 4F reduces pulmonary inflammation and airway resistance in an experimental murine model of asthma by decreasing oxidative stress.

Ciprofibrate increases cholesteryl ester transfer protein gene expression and the indirect reverse cholesterol transport to the liver

Background

CETP is a plasma protein that modulates atherosclerosis risk through its HDL-cholesterol reducing action. The aim of this work was to examine the effect of the PPARα agonist, ciprofibrate, on the CETP gene expression, in the presence and absence of apolipoprotein (apo) CIII induced hypertriglyceridemia, and its impact on the HDL metabolism.

Results

Mice expressing apo CIII and/or CETP and non-transgenic littermates (CIII, CIII/CETP, CETP, non-Tg) were treated with ciprofibrate during 3 weeks. Drug treatment reduced plasma triglycerides (30-43%) and non-esterified fatty acids (19-47%) levels. Cholesterol (chol) distribution in plasma lipoprotein responses to ciprofibrate treatment was dependent on the genotypes. Treated CIII expressing mice presented elevation in VLDL-chol and reduction in HDL-chol. Treated CETP expressing mice responded with reduction in LDL-chol whereas in non-Tg mice the LDL-chol increased. In addition, ciprofibrate increased plasma post heparin lipoprotein lipase activity (1.3-2.1 fold) in all groups but hepatic lipase activity decreased in treated CETP and non-Tg mice. Plasma CETP activity and liver CETP mRNA levels were significantly increased in treated CIII/CETP and CETP mice (30-100%). Kinetic studies with ³H-cholesteryl ether (CEt) labelled HDL showed a 50% reduction in the ³H-CEt found in the LDL fraction in ciprofibrate treated compared to non-treated CETP mice. This means that ³H-CEt transferred from HDL to LDL was more efficiently removed from the plasma in the fibrate treated mice. Accordingly, the amount of ³H-CEt recovered in the liver 6 hours after HDL injection was increased by 35%.

Conclusion

Together these data showed that the PPARα agonist ciprofibrate stimulates CETP gene expression and changes the cholesterol flow through the reverse cholesterol transport, increasing plasma cholesterol removal through LDL.

Atherogenesis and atherothrombosis--focus on diabetes mellitus

Diabetes mellitus represents a major cause of cardiovascular morbidity and mortality in developed countries, and atherothrombosis accounts for most deaths among patients with diabetes mellitus. Atherothrombosis is defined as atherosclerotic lesion disruption with superimposed thrombus formation. As a long-term, progressive disease process, atherosclerosis often results in an acute atherothrombotic event through plaque rupture and formation of a platelet-rich thrombus. The principal clinical manifestations of atherothrombosis are sudden cardiac death, myocardial infarction, ischaemic stroke, and peripheral arterial ischaemia comprising both intermittent claudication and critical limb ischaemia. Atherosclerosis is the leading cause of morbidity and mortality in the industrialized world, and diabetes mellitus magnifies the risk of cardiovascular events. In addition to the well-known microvascular complications of diabetes mellitus - such as nephropathy, retinopathy and neuropathy - the risk of macrovascular complications affecting the large conduit arteries markedly increases in patients with diabetes mellitus.

Relation of baseline plasma phospholipid transfer protein (PLTP) activity to left ventricular systolic dysfunction in patients referred for coronary angiography

Phospholipid transfer protein (PLTP) is an important modulator of phospholipid transfer and exchange among proteins. It also plays a role in inflammation and oxidative stress. Accordingly, PLTP has been implicated in the development of atherosclerosis. Left ventricular (LV) systolic dysfunction is common in patients with atherosclerosis, and both inflammation and oxidative stress have also been implicated in its development and progression. The goal of the present study was to examine the relation between plasma PLTP activity and LV systolic function. Baseline plasma PLTP activity was measured in 389 male patients referred for coronary angiography for a variety of indications. Detailed clinical, angiographic and laboratory characteristics were available for the patients. Compared to those patients with normal LV function (defined as an ejection fraction of >or=55% on ventriculography), patients with any degree of LV dysfunction had elevated PLTP activity (median PLTP 17.8 pmol/microl/h versus 15.9 pmol/microl/h, p=0.0038). Using multivariate analysis, and adjusting for a variety of confounding variables known to affect both LV function and PLTP activity, PLTP activity was an independent predictor of the presence of any left ventricular systolic dysfunction in the entire population (OR 1.47, 95% CI 1.12-1.93, p=0.0052). Furthermore, PLTP activity was an independent predictor of the presence of LV dysfunction in both patients with and without myocardial infarction on presentation (OR 2.39, 95% CI 1.18-4.86, p=0.0161 and OR 1.41, 95% CI 1.05-1.89, p=0.0206, respectively). In conclusion, PLTP activity may represent a novel marker of LV systolic dysfunction in patients with known or suspected coronary artery disease.

Transferência de lípides para a lipoproteína de alta densidade (HDl) em mulheres com diabetes melito tipo 1

INTRODUÇÃO: Os portadores de diabetes melito tipo 1 (DM1) possuem aumentado risco de doença cardiovascular e, ainda assim, podem apresentar perfil lipídico normal. Para esclarecer se os níveis normais de HDL podem ocultar defeitos na função, foram estudados a transferência de lípides para a HDL em DM1. MÉTODOS: Vinte e uma mulheres jovens portadoras de DM1 foram comparadas com 21 mulheres não-diabéticas. Nanoemulsões foram usadas como doadoras de lípides para HDL: uma marcada com ³H-triglicérides e 14C-colesterol livre e outra com ³H-éster de colesterol e 14C-fosfolípides. Após 1 hora de incubação com amostras de plasma, seguida por precipitação química, o sobrenadante, contendo HDL, teve a radioatividade contada. RESULTADOS: Nenhuma diferença foi encontrada nas transferências dos ésteres de colesterol, triglicérides, colesterol livre e fosfolípides para as HDL. CONCLUSÃO: A transferência de lípides para a HDL não está afetada em portadoras de DM1. Isso sugere que a doença não altera a composição de lipoproteínas e a ação de proteínas de transferência.

Genetically based hypertension generated through interaction of mild hypoalphalipoproteinemia and mild hyperhomocysteinemia

BACKGROUND

Hyperhomocysteinemia and hypoalphalipoproteinemia are two well-reported risk factors for cardiovascular disease. The effects of the synergistic combination of these two factors on vascular function need to be investigated.

METHODS AND RESULTS

Four groups of male mice were used: a control wild-type group; a group of mice heterozygous for cystathionine beta-synthase deficiency; a group of mice heterozygous for apolipoprotein A-I deficiency; and, finally, a group of double heterozygous mice, with both cystathionine beta-synthase and apolipoprotein A-I deficiency. To characterize the resulting phenotype, several parameters including plasma apolipoproteins, lipid profiles, homocysteine, blood pressure and aortic protein were analyzed. As expected, our results indicate that double heterozygous mice are a model of mild hypoalphalipoproteinemia and hyperhomocysteinemia. Further, the additive combination of both risk factors resulted in a significant increase in blood pressure compared with control animals (136 +/- 8.0 versus 126 +/- 7.5 mm Hg, P < 0.01) that was not present in single heterozygous mice. The increase in blood pressure was associated with decreased plasma nitric oxide levels, left ventricle hypertrophy and was independent of low-density lipoprotein (LDL) cholesterol, para-oxonase activity and kidney histological changes. Concomitant decreases in levels of apolipoprotein A-IV (APOA-IV) and caveolin-1 content were also found in the double heterozygous group.

CONCLUSIONS

Our findings suggest an additive adverse effect of hypoalphalipoproteinemia and hyperhomocysteinemia on endothelial function to generate clinical hypertension and cardiac muscle hypertrophy mediated by dysregulation in nitric oxide metabolism.

Lipids changes in liver cancer

Liver is one of the most important organs in energy metabolism. Most plasma apolipoproteins and endogenous lipids and lipoproteins are synthesized in the liver. It depends on the integrity of liver cellular function, which ensures homeostasis of lipid and lipoprotein metabolism. When liver cancer occurs, these processes are impaired and the plasma lipid and lipoprotein patterns may be changed. Liver cancer is the fifth common malignant tumor worldwide, and is closely related to the infections of hepatitis B virus (HBV) and hepatitis C virus (HCV). HBV and HCV infections are quite common in China and other Southeast Asian countries. In addition, liver cancer is often followed by a procession of chronic hepatitis or cirrhosis, so that hepatic function is damaged obviously on these bases, which may significantly influence lipid and lipoprotein metabolism in vivo. In this review we summarize the clinical significance of lipid and lipoprotein metabolism under liver cancer.

Metabolism of high density lipoproteins in liver cancer

Liver plays a vital role in the production and catabolism of plasma lipoproteins. It depends on the integrity of cellular function of liver, which ensures homeostasis of lipid and lipoprotein metabolism. When liver cancer occurs these processes are impaired and high-density lipoproteins are changed.

Phospholipid transfer protein in hemodialysis patients

INTRODUCTION

Phospholipid transfer protein (PLTP) is mainly involved in high-density lipoprotein (HDL) metabolism. The role of PLTP in atherogenesis is still controversial. We aimed to investigate PLTP activity in hemodialysis (HD) patients, a population which has an increased risk for the development of atherosclerosis.

METHODS

PLTP activity and other markers were analyzed in blood samples from 68 HD patients and in a matched group of 68 healthy controls.

RESULTS

Serum PLTP activity was nearly doubled in HD patients in comparison to healthy controls (median 43.0 vs. 22.4 pmol/mul/h, p < 0.001). In HD patients, PLTP activity correlated with HDL-C (r = 0.342, p = 0.004), but not with CRP (r = -0.057, p = 0.644) or leukocyte count (r = 0.116, p = 0.345). After a follow-up of 2 years, 26 HD patients had died. Kaplan-Meier analyses showed that low CRP (p = 0.047) but neither high HDL-C (p = 0.071) nor low PLTP activity (p = 0.853) were relevantly related to survival of HD patients.

CONCLUSION

An elevated PLTP activity in HD patients may be considered as a further aspect of uremic dyslipidemia in HD patients. However, PLTP activity was not related to markers of inflammation or to survival of HD patients, even though it correlated with HDL-C. Thus, we conclude that PLTP does not influence the prognostically relevant inflammatory process in HD patients although it does influence the composition of HDL particles.

Familial dyslipidaemias: an overview of genetics, pathophysiology and management

Plasma lipid disorders can occur either as a primary event or secondary to an underlying disease or use of medications. Familial dyslipidaemias are traditionally classified according to the electrophoretic profile of lipoproteins. In more recent texts, this phenotypic classification has been replaced with an aetiological classification. Familial dyslipidaemias are generally grouped into disorders leading to hypercholesterolaemia, hypertriglyceridaemia, a combination of hyper-cholesterolaemia and hypertriglyceridaemia, or abnormal high-density lipoprotein-cholesterol (HDL-C) levels. The management of these disorders requires an understanding of plasma lipid and lipoprotein metabolism. Lipid transport and metabolism involves three general pathways: (i) the exogenous pathway, whereby chylomicrons are synthesised by the small intestine, and dietary triglycerides (TGs) and cholesterol are transported to various cells of the body; (ii) the endogenous pathway, whereby very low-density lipoprotein-cholesterol (VLDL-C) and TGs are synthesised by the liver for transport to various tissues; and (iii) the reverse cholesterol transport, whereby HDL cholesteryl ester is exchanged for TGs in low-density lipoptrotein (LDL) and VLDL particles through cholesteryl ester transfer protein in a series of steps to remove cholesterol from the peripheral tissues for delivery to the liver and steroidogenic organs. The plasma lipid profile can provide a framework to guide the selection of appropriate diet and drug treatment. Many patients with hyperlipoproteinaemia can be treated effectively with diet. However, dietary regimens are often insufficient to bring lipoprotein levels to within acceptable limits. In this article, we review lipid transport and metabolism, discuss the more common lipid disorders and suggest some management guidelines. The choice of a particular agent depends on the baseline lipid profile achieved after 6-12 weeks of intense lifestyle changes and possible use of dietry supplements such as stanols and plant sterols. If the predominant lipid abnormality is hypertriglyceridaemia, omega-3 fatty acids, a fibric acid derivative (fibrate) or nicotinic acid would be considered as the first choice of therapy. In subsequent follow-up, when LDL-C is >130 mg/dL (3.36 mmol/L) then an HMG-CoA reductase inhibitor (statin) should be added as a combination therapy. If the serum TG levels are <500 mg/dL (2.26 mmol/L) and the LDL-C values are over 130 mg/dL (3.36 mmol/L) then a statin would be the first drug of choice. The statin dose can be titrated up to achieve the therapeutic goal or, alternatively, ezetimibe can be added. A bile acid binding agent is an option if the serum TG levels do not exceed 200 mg/dL (5.65 mmol/L), otherwise a fibrate or nicotinic acid should be considered. The decision to treat a particular person has to be individualised.

Genetics of high-density lipoproteins

PURPOSE OF REVIEW

High-density lipoproteins have multi-factorial anti-atherosclerosis properties: they have potent anti-oxidant effects and prevent the oxidation of low-density lipoproteins; they have anti-inflammatory effects; they modulate vascular endothelial cell function and transport cholesterol back to the liver for excretion into the bile - a process called reverse cholesterol transport. The present review focuses on genetic aspects of high-density lipoprotein metabolism, with genomic approaches used to identify genes that regulate high-density lipoproteins in humans.

RECENT FINDINGS

Disorders of the many genes that code for proteins, including transporters, enzymes, receptors, transfer proteins and lipases, involved in high-density lipoprotein metabolism have been identified in humans as causing extremes of high-density lipoprotein cholesterol, and provide potential novel therapeutic avenues. These, however, explain fewer than 5% of the causes of low high-density lipoprotein cholesterol in the general population.

SUMMARY

Genome-wide linkage studies of large cohorts, with discrete as well as quantitative trait loci analyses, followed by association studies have enabled the identification of large chromosomal regions that may harbor genes that modulate high-density lipoprotein cholesterol levels in humans. Using mouse genetics, the results of the HapMap project and novel genetic approaches will allow the discovery of novel genes in high-density lipoprotein metabolism.

Putting cholesterol in its place: apoE and reverse cholesterol transport

To avoid toxic overload of cholesterol in peripheral cells, the reverse cholesterol transport pathway directs excess cholesterol through HDL acceptors to the liver for elimination. In this issue of the JCI, a study by Matsuura et al. reveals new features of this pathway, including the importance of the ATP-binding cassette transporter G1 in macrophages and apoE in cholesteryl efflux from cells to cholesterol ester-rich (CE-rich) HDL(2) acceptors (see the related article beginning on page 1435). One proposal for boosting reverse cholesterol transport has been to elevate plasma HDL levels by inhibiting CE transfer protein (CETP), which transfers CE from HDL to lower-density lipoproteins. However, there has been concern that large, CE-rich HDL(2) generated by CETP inhibition might impair reverse cholesterol transport. ApoE uniquely facilitates reverse cholesterol transport by allowing CE-rich core expansion in HDL. In lower species, these large HDLs are not atherogenic. Thus, CETP might not be essential for reverse cholesterol transport in humans, raising hope of using a CETP inhibitor to elevate HDL levels.

Increased sphingomyelin content impairs HDL biogenesis and maturation in human Niemann-Pick disease type B

We previously reported that human Niemann-Pick Disease type B (NPD-B) is associated with low HDL. In this study, we investigated the pathophysiology of this HDL deficiency by examining both HDL samples from NPD-B patients and nascent high density lipoprotein (LpA-I) generated by incubation of lipid-free apolipoprotein A-I (apoA-I) with NPD-B fibroblasts. Interestingly, both LpA-I and HDL isolated from patient plasma had a significant increase in sphingomyelin (SM) mass ( approximately 50-100%). Analysis of LCAT kinetics parameters (V(max) and K(m)) revealed that either LpA-I or plasma HDL from NPD-B, as well as reconstituted HDL enriched with SM, exhibited severely decreased LCAT-mediated cholesterol esterification. Importantly, we documented that SM enrichment of NPD-B LpA-I was not attributable to increased cellular mass transfer of SM or unesterified cholesterol to lipid-free apoA-I. Finally, we obtained evidence that the conditioned medium from HUVEC, THP-1, and normal fibroblasts, but not NPD-B fibroblasts, contained active secretory sphingomyelinase (S-SMase) that mediated the hydrolysis of [(3)H]SM-labeled LpA-I and HDL(3). Furthermore, expression of mutant SMase (DeltaR608) in CHO cells revealed that DeltaR608 was synthesized normally but had defective secretion and activity. Our data suggest that defective S-SMase in NPD leads to SM enrichment of HDL that impairs LCAT-mediated nascent HDL maturation and contributes to HDL deficiency. Thus, S-SMase and LCAT may act in concert and play a crucial role in the biogenesis and maturation of nascent HDL particles.

Phosphatidylcholine transfer protein regulates size and hepatic uptake of high-density lipoproteins

Phosphatidylcholine transfer protein (PC-TP) is a steroidogenic acute regulatory-related transfer domain protein that is enriched in liver cytosol and binds phosphatidylcholines with high specificity. In tissue culture systems, PC-TP promotes ATP-binding cassette protein A1-mediated efflux of cholesterol and phosphatidylcholine molecules as nascent pre-beta-high-density lipoprotein (HDL) particles. Here, we explored a role for PC-TP in HDL metabolism in vivo utilizing 8-wk-old male Pctp(-/-) and wild-type littermate C57BL/6J mice that were fed for 7 days with either chow or a high-fat/high-cholesterol diet. In chow-fed mice, neither plasma cholesterol concentrations nor the concentrations and compositions of plasma phospholipids were influenced by PC-TP expression. However, in Pctp(-/-) mice, there was an accumulation of small alpha-migrating HDL particles. This occurred without changes in hepatic expression of ATP-binding cassette protein A1 or in proteins that regulate the intravascular metabolism and clearance of HDL particles. In Pctp(-/-) mice fed the high-fat/high-cholesterol diet, HDL particle sizes were normalized, whereas plasma cholesterol and phospholipid concentrations were increased compared with wild-type mice. In the absence of upregulation of hepatic ATP-binding cassette protein A1, reduced HDL uptake from plasma into livers of Pctp(-/-) mice contributed to higher plasma lipid concentrations. These data indicate that PC-TP is not essential for the enrichment of HDL with phosphatidylcholines but that it does modulate particle size and rates of hepatic clearance.

Molecular aspects of atherogenesis: new insights and unsolved questions

The development of atherosclerotic disease results from the interaction between environment and genetic make up. A key factor in atherogenesis is the oxidative modification of lipids, which is involved in the recruitment of mononuclear leukocytes to the arterial intima--a process regulated by several groups of adhesion molecules and cytokines. Activated leukocytes, as well as endothelial mitochondria, can produce reactive oxygen species (ROS) that are associated with endothelial dysfunction, a cause of reduced nitric oxide (NO) bioactivity and further ROS production. Peroxisome proliferator-activated receptors (PPAR) and liver X receptors (LXR) are nuclear receptors significantly involved in the control of lipid metabolism, inflammation and insulin sensitivity. Also, an emerging role has been suggested for G protein coupled receptors and for the small Ras and Rho GTPases in the regulation of the expression of endothelial NO synthase (eNOS) and of tissue factor, which are involved in thrombus formation and modulation of vascular tone. Further, the interactions among eNOS, cholesterol, oxidated LDL and caveola membranes are probably involved in some molecular changes observed in vascular diseases. Despite the relevance of oxidative processes in atherogenesis, anti-oxidants have failed to significantly improve atherosclerosis (ATS) prevention, while statins have proved to be the most successful drugs.

Effects of simvastatin 20 mg/d on serum lipid profiles in Japanese hyperlipidemic patients: A prospective, open-label pilot study

BACKGROUND

Hyperlipidemia is a major risk factor for ischemic heart disease. Hydroxymethylglutaryl coenzyme A reductase inhibitors ("statins") (eg, simvastatin) are considered first-line cholesterol-lowering therapy because they are effective and well tolerated, even at high doses. Based on a literature search, no studies have been published concerning the effects of simvastatin 20 mg/d in Japanese patients who had not previously received lipid-lowering treatment.

OBJECTIVE

The aim of this study was to assess the clinical tolerability and effectiveness of simvastatin 20 mg/d in achieving the target lipid concentrations recommended in the 2002 Japan Atherosclerosis Society (JAS) guidelines in Japanese patients with hyperlipidemia.

METHODS

This prospective, open-label pilot study was conducted at Kashiwa Hospital, Jikei University School of Medicine, Kashiwa, Japan. Male and postmenopausal female patients aged ≥18 to 70 years with hyperlipidemia (total cholesterol [TC], ≥220 mg/dL; triglycerides [TG], 150-400 mg/dL) who had not received lipid-lowering medications for at least 6 months before the study were enrolled. Patients received simvastatin 20 mg PO QD for 4 weeks. Effectiveness was assessed using serum concentrations of TC, low-density lipoprotein cholesterol (LDL-C), TG, and lipid peroxide, measured at 0 (baseline) and 4 weeks. Target serum TC and LDL-C concentrations as outlined by the JAS were as follows: category A, TC <240 mg/dL and LDL-C <160 mg/dL; category B1 and B2, TC <220 mg/dL and LDL-C <140 mg/dL; and category C, TC <200 mg/dL and LDL-C <120 mg/dL. A subanalysis of the correlation between baseline high-density lipoprotein cholesterol (HDL-C) and target achievement rates was conducted by baseline HDL-C concentration (<50 or ≥50 mg/dL). Tolerability was assessed using spontaneous reporting of adverse events and laboratory analysis, including liver function tests.

RESULTS

Twenty-two patients participated in the study (16 women, 6 men; mean [SD] age, 56.0 [8.0] years; mean [SD] body mass index, 23.6 [3.4] kg/m(2)). Mean serum TC, LDL-C, TG, and lipid peroxide concentrations significantly decreased from baseline (changes, -28.6%, -40.4%, -24.0%, and -14.5%, respectively; P < 0.001, <0.001, <0.001, and <0.01, respectively). The mean HDL-C concentration significantly increased from baseline (change, 7.2%; P < 0.001); the mean increase was significantly greater in patients with baseline HDL-C <50 mg/dL compared with those with baseline HDL-C ≥50 mg/dL (changes, 11.3% vs 4.4%; P < 0.05). Target TC and LDL-C concentrations were achieved in 90.9% of patients. No serious adverse events were observed, and liver enzyme and creatine kinase concentrations did not increase to above-normal values.

CONCLUSIONS

The results of this study suggest that simvastatin 20 mg/d might be useful in the clinical treatment of hyperlipidemia in Japanese patients. The study drug was well tolerated.

Persistence of high density lipoprotein particles in obese mice lacking apolipoprotein A-I

Obese mice without leptin (ob/ob) or the leptin receptor (db/db) have increased plasma HDL levels and accumulate a unique lipoprotein referred to as LDL/HDL1. To determine the role of apolipoprotein A-I (apoA-I) in the formation and accumulation of LDL/HDL1, both ob/ob and db/db mice were crossed onto an apoA-I-deficient (apoA-I(-/-)) background. Even though the obese apoA-I(-/-) mice had an expected dramatic decrease in HDL levels, the LDL/HDL1 particle persisted. The cholesterol in this lipoprotein range was associated with both alpha- and beta-migrating particles, confirming the presence of small LDLs and large HDLs. Moreover, in the obese apoA-I(-/-) mice, LDL particles were smaller and HDLs were more negatively charged and enriched in apoE compared with controls. This LDL/HDL1 particle was rapidly remodeled to the size of normal HDL after injection into C57BL/6 mice, but it was not catabolized in obese apoA-I(-/-) mice even though plasma hepatic lipase (HL) activity was increased significantly. The finding of decreased hepatic scavenger receptor class B type I (SR-BI) protein levels may explain the persistence of LDL/HDL1 in obese apoA-I(-/-) mice. Our studies suggest that the maturation and removal of large HDLs depends on the integrity of a functional axis of apoA-I, HL, and SR-BI. Moreover, the presence of large HDLs without apoA-I provides evidence for an apoA-I-independent pathway of cholesterol efflux, possibly sustained by apoE.

Parotid secretory protein is an HDL-associated protein with anticandidal activity

High-density lipoprotein (HDL) is part of innate immunity, protecting against infection and inflammation. Using a proteomic approach, we identified an amino acid sequence in a hamster HDL protein that showed homology to rat and mouse parotid secretory protein (PSP), a salivary protein secreted from the parotid glands. We cloned the cDNA encoding a putative hamster homolog of rat and mouse PSP. Searches for conserved domains of the protein showed that the COOH terminus of hamster PSP contains a region homologous to the NH2termini of a family of HDL-associated proteins, including LPS-binding protein, cholesteryl ester transfer protein, and phospholipid transfer protein. In mice, PSP was also associated with HDL but was not detected in very-low-density lipoprotein, low-density lipoprotein, or lipoprotein-deficient sera. In addition to salivary glands, we found that PSP mRNA was expressed in lung, testis, and ovary. The level of PSP in HDL was increased after endotoxin injection in hamsters, but not in mice. Recombinant PSP inhibits growth of Candida albicans in culture. In summary, our results showed that PSP is a novel anticandidal protein associated with HDL.

Cholesteryl ester transfer protein TaqIB polymorphism and its relation to parameters of the insulin resistance syndrome in an Austrian cohort

The cholesteryl ester transfer protein (CETP) is responsible for the exchange of triglycerides and cholesteryl esters between lipoprotein particles leading to an increased hepatic clearance of HDL-cholesteryl esters. A high CETP activity reduces serum HDL levels, whereas persons without CETP activity have high HDL levels. We investigated the association of the TaqIB CETP polymorphism and various parameters of the insulin resistance syndrome in a cross sectional population based study. We included 1029 persons without known cardiovascular disease or diabetes mellitus consecutively enrolled in our SAPHIR program (Salzburg Atherosclerosis Prevention program in persons with a High Infarction Risk). Numerous clinical and laboratory data were accomplished. Insulin sensitivity was measured by a short insulin tolerance test. The TaqIB CETP polymorphism was determined by PCR, TaqI restriction and electrophoresis. 35.2% were homozygous for the prevalence (B1B1), 46.7% were heterozygous (B1B2), and 18.1% homozygous for the absence (B2B2) of the restriction site. HDL cholesterol and apolipoprotein A1 were lower and small dense low-density lipoproteins (sdLDL) higher in B1B1 compared to B2B1 and B2B2 persons. In women, we found a significant interaction effect between CETP genotype and adiposity for HDL cholesterol. B1B1 women with a BMI and a waist circumference above the median had 9.7 mg/dl lower HDL than B1B2 and 9.1 mg/dl lower HDL than B2B2 women (P < 0.001). In men, no interaction effect but a marked genotype to HDL correlation was found. There was a high CETP effect on sdLDL detected in men (P = 0.001). B1B1 men had sdLDL in 36%, B1B2 in 24.6%, and B2B2 in only 14.5%. Men with adiposity and insulin resistance had twice as many sdLDL as insulin sensitive men. We found a significant sex specific effect of the TaqIB CETP polymorphism on the insulin resistance parameters HDL-cholesterol and sdLDL in an Austrian population based study.

ATP-binding cassette transporter AI and its role in HDL formation

PURPOSE OF REVIEW

ATP-binding cassette transporter AI (ABCA1)-mediated assembly of phospholipid and free cholesterol with apoA-I plays an important role in HDL biogenesis. This review focuses on recent progress in ABCA1-mediated HDL formation and regulation of ABCA1 expression.

RECENT FINDINGS

Studies of hepatic ABCA1 overexpression suggest that the liver is a major site for HDL formation. Lipidation of apoA-I by ABCA1 increases its potential for reverse cholesterol transport based on the following findings: (1) apoA-I/lipid complexes formed by ABCA1 are better acceptors of cellular lipid via non-ABCA1-mediated efflux pathways than lipid-free apoA-I in vitro and (2) lipidation of apoA-I prevents it from rapidly associating with plasma HDL in vivo, resulting in more available nascent pre-beta HDL for cellular lipid efflux. Several novel regulatory mechanisms for ABCA1 at the post-transcriptional level have been identified recently. Interaction of apoA-I with ABCA1 prevents phosphorylation of a sequence rich in proline, glutamic acid, serine and threonine in a cytoplasmic domain of ABCA1, resulting in less degradation by calpain proteolysis and increased surface expression of ABCA1. In addition, destabilization and decreased cellular surface expression of ABCA1 protein by unsaturated fatty acids have been identified.

SUMMARY

Initial lipidation of apoA-I by hepatic ABCA1 is critical for plasma HDL formation because it enables pre-beta HDL to function more efficiently as a cholesterol acceptor for other pathways of cholesterol efflux in the reverse cholesterol transport pathway and prevents apoA-I from rapidly associating with preexisting plasma HDL particles, resulting in greater availability of pre-beta HDL particles for cholesterol efflux.

Simvastatin and Preparation of Polyunsaturated Phospholipids Produce Similar Changes in the Phospholipid Composition of High-Density Lipoproteins during Hypercholesterolemia

We studied the phospholipid composition of high-density lipoproteins in patients with coronary heart disease and hypercholesterolemia treated with simvastatin (Zocor, inhibitor of the key enzyme of cholesterol synthesis) and preparation of polyunsaturated phospholipids (lipostabil forte). Simvastatin produced a hypolipidemic effect and modulates the phospholipid composition of high-density lipoproteins (similarly to lipostabil forte). These changes contribute to functional activity of high-density lipoproteins in the reverse cholesterol transport.

Modulation of high-density lipoprotein cholesterol metabolism and reverse cholesterol transport

Low high-density lipoprotein (HDL)-cholesterol (C) is an important risk factor for coronary heart disease. In vitro, HDL exerts several potentially anti-atherogenic effects including reverse cholesterol transport (RCT) from peripheral cells to the liver. Hence, raising HDL-C has become an interesting target for anti-atherosclerotic drug therapy. Levels of HDL-C and the composition of HDL subclasses in plasma are regulated by apolipoproteins, lipolytic enzymes, lipid transfer proteins, receptors, and cellular transporters. The interplay of these factors leads to RCT and determines the composition and thereby the anti-atherogenic properties of HDL. Recent findings suggest that the mechanism of HDL modification rather than a sole increase in HDL-C determines the efficacy of anti-atherosclerotic drug therapy. In several controlled and prospective intervention studies, patients with low HDL-C and additional risk factors benefited from treatment with fibrates or statins. However, in only some of the fibrate trials was prevention of coronary events in patients with low HDL-C and hypertriglyceridaemia related to an increase in HDL-C. This may be because currently available drugs increase HDL-C levels only moderately and because HDL levels per se do not necessarily correlate with the functionality of HDL. However, several novel targets to modify RCT have emerged from the recent understanding of HDL synthesis, maturation and catabolism. The four major targets for an anti-atherogenic strategy in HDL metabolism include stimulation of apoA-I synthesis and secretion, the stimulation of ABCA1 expression, the inhibition of cholesterol ester transfer protein, and the up-regulation of scavenger receptor BI. These and other modulations of HDL metabolism are thought to result in improved RCT making them attractive targets for the development of new regimens of anti-atherogenic drug therapy.

Population-based study of SR-BI genetic variation and lipid profile

The variability of the Class B Type I Scavenger Receptor (SR-BI) gene in human populations and the relation of its variants to blood lipids was investigated in a random sample of 1756 untreated adult residents of Geneva, Switzerland, during 1999-2000. A three-step study approach yielded the following results: (1) resequencing the gene's exons and flanking regions in 95 subjects identified four common single nucleotide polymorphisms (SNPs with rare allele frequency >3%); (2) association study of the four common SNPs in subjects with extreme HDL-cholesterol (HDL-C) and LDL-C phenotypes (186 "atherogenic cases" and 185 "non-atherogenic controls") showed that the synonymous exon 8 C-T (allelic frequency 48%) polymorphism, A350A, was associated with atheroprotection in men (odds ratios (OR) = 0.36, 95% confidence intervals (CI) = 0.15-0.90, P < 0.03), but not in women (2.09, 0.79-5.49, P = 0.14); and (3) population clinical effects of A350A genotypes assessed in all 1756 subjects, showed that the case-control study findings reflected a protective HDL-C effect in men (CC: 1.17 mmol/L, CT: 1.22 mmol/L, and TT: 1.24 mmol/L, trend P = 0.0062) and a deleterious LDL-C effect in women (CC: 3.58 mmol/L, CT: 3.72 mmol/L, and TT: 3.79 mmol/L, trend P = 0.014). The allelic frequencies of the common SR-BI variants appear to be very similar in European and North American populations. The HDL-C effect increased with age. SR-BI A350A appears to have gender-specific and age-related effects on cholesterol transport lipoproteins.

Conjugated linoleic acid supplementation, insulin sensitivity, and lipoprotein metabolism in patients with type 2 diabetes mellitus

BACKGROUND

Some animal studies have suggested that conjugated linoleic acid (CLA) supplementation may have therapeutic potential with respect to insulin sensitivity and lipid metabolism, which are important cardiovascular disease (CVD) risk factors associated with type 2 diabetes mellitus.

OBJECTIVE

We investigated the effect of CLA supplementation on markers of glucose and insulin metabolism, lipoprotein metabolism, and inflammatory markers of CVD in subjects with type 2 diabetes.

DESIGN

The study was a randomized, double-blind, placebo-controlled trial. Thirty-two subjects with stable, diet-controlled type 2 diabetes received CLA (3.0 g/d; 50:50 blend of cis-9,trans-11 CLA and trans-10,cis-12 CLA) or control for 8 wk. A 3-h 75-g oral-glucose-tolerance test was performed, and fasting plasma lipid concentrations and inflammatory markers were measured before and after the intervention.

RESULTS

CLA supplementation significantly increased fasting glucose concentrations (6.3%; P < 0.05) and reduced insulin sensitivity as measured by homeostasis model assessment, oral glucose insulin sensitivity, and the insulin sensitivity index (composite) (P = 0.05). Total HDL-cholesterol concentrations increased by 8% (P < 0.05), which was due to a significant increase in HDL(2)-cholesterol concentrations (P < 0.05). The ratio of LDL to HDL cholesterol was significantly reduced (P < 0.01). CLA supplementation reduced fibrinogen concentrations (P < 0.01) but had no effect on the inflammatory markers of CVD (C-reactive protein and interleukin 6).

CONCLUSIONS

CLA supplementation had an adverse effect on insulin and glucose metabolism. Whereas CLA had positive effects on HDL metabolism and fibrinogen, a therapeutic nutrient should not be associated with potentially adverse effects on other clinical markers of type 2 diabetes.

Therapeutic interventions targeted at the augmentation of reverse cholesterol transport

PURPOSE OF REVIEW

Serum high-density lipoproteins (HDLs) and reverse cholesterol transport (RCT) are important therapeutic targets in the management of atherosclerotic disease. This review summarizes the pathway of RCT and the currently available means by which investigators are attempting to modulate HDL levels and increase rates of RCT.

RECENT FINDINGS

Low levels of HDL are commonly encountered in patients with atherosclerotic disease. HDLs mediate a substantial number of antiatherogenic effects along blood vessel walls. One of the most important of these antiatherogenic mechanisms is RCT, a series of reactions by which HDL is able to facilitate the net translocation of cholesterol from peripheral cells to the liver for excretion. There is scientific evidence supporting the concept of RCT in both animals and humans. To facilitate RCT, it is important that therapeutic effort be made to raise serum levels of HDL. Statins, fibrates, niacin, thiazolidinediones, and various combinations of these drugs all raise HDL levels. However, in many high-risk patients with established atherosclerotic disease, the elevations in HDL achieved with these medications are frequently inadequate. Newer agents designed to raise HDL and promote RCT are currently being developed, including infusible bioengineered HDL, edible HDL composed of D-amino acids, and agents capable of inhibiting cholesterol ester transfer protein, among others.

SUMMARY

Established therapies for raising HDL can be effective either as monotherapy or when used in combination. Newer strategies are being developed to exploit more specifically the capacity of HDL to drive RCT and either prevent or reverse the course of atherosclerotic disease.

SR-BI- and ABCA1-mediated cholesterol efflux to serum from patients with Alagille syndrome

Alagille syndrome is associated with bile duct paucity resulting in liver disease. Patients can be divided into mildly and severely icteric groups, with both groups having altered lipoproteins. The incidence of ischemic heart disease is rare in severely cholestatic children despite increased total cholesterol and decreased high density lipoprotein cholesterol (HDL-C). The present studies examine the impact of altered lipid and lipoproteins on scavenger receptor class B type I (SR-BI)- and ABCA1-mediated efflux to serum from both groups. Efflux was compared with serum from 29 patients (15 with normal plasma cholesteryl ester, 14 with low cholesteryl ester). Efflux via SR-BI and ABCA1 was studied using cell systems having either low or high expression levels of these receptors. SR-BI efflux was lower (P = 0.04) with serum from severely icteric patients (3.9 +/- 1.4%) compared with serum from mildly icteric patients (5.1 +/- 1.4%) and was positively correlated with HDL-C and its apolipoproteins. SR-BI-mediated efflux was not correlated with any particular mature HDL but was negatively correlated with small lipid-poor prebeta-1 HDL. Consistent with severely icteric patients having high prebeta-1 HDL levels, the ABCA1 efflux was significantly higher with their serum (4.8 +/- 2.2%) compared with serum from mildly icteric patients (2.0 +/- 0.6%) and was positively correlated with prebeta-1 HDL. These studies demonstrated that prebeta-1 HDL is the preferred acceptor for ABCA1 efflux, whereas many particles mediate SR-BI efflux.

Effects of infection and inflammation on lipid and lipoprotein metabolism: mechanisms and consequences to the host

Infection and inflammation induce the acute-phase response (APR), leading to multiple alterations in lipid and lipoprotein metabolism. Plasma triglyceride levels increase from increased VLDL secretion as a result of adipose tissue lipolysis, increased de novo hepatic fatty acid synthesis, and suppression of fatty acid oxidation. With more severe infection, VLDL clearance decreases secondary to decreased lipoprotein lipase and apolipoprotein E in VLDL. In rodents, hypercholesterolemia occurs attributable to increased hepatic cholesterol synthesis and decreased LDL clearance, conversion of cholesterol to bile acids, and secretion of cholesterol into the bile. Marked alterations in proteins important in HDL metabolism lead to decreased reverse cholesterol transport and increased cholesterol delivery to immune cells. Oxidation of LDL and VLDL increases, whereas HDL becomes a proinflammatory molecule. Lipoproteins become enriched in ceramide, glucosylceramide, and sphingomyelin, enhancing uptake by macrophages. Thus, many of the changes in lipoproteins are proatherogenic. The molecular mechanisms underlying the decrease in many of the proteins during the APR involve coordinated decreases in several nuclear hormone receptors, including peroxisome proliferator-activated receptor, liver X receptor, farnesoid X receptor, and retinoid X receptor. APR-induced alterations initially protect the host from the harmful effects of bacteria, viruses, and parasites. However, if prolonged, these changes in the structure and function of lipoproteins will contribute to atherogenesis.

Hypertriglyceridemia in pregnancy does not contribute to the enhanced formation of remnant lipoprotein particles

BACKGROUND

During pregnancy, serum cholesterol (TC) and triglyceride (TG) concentrations are known to increase significantly, but whether remnant lipoprotein particles (RLP) increase has not been shown.

METHODS

We compared lipid profiles in 22 healthy pregnant women to 31 healthy nonpregnant women and 24 patients with diabetes mellitus (DM), by measuring cholesterol and TG concentrations in major lipoprotein classes after HPLC separation and immunoseparation of RLP.

RESULTS

Serum TG and TC concentrations were significantly higher in the pregnant group than in the healthy control or DM groups. Cholesterol and TG concentrations of all major lipoprotein classes were also significantly higher in the pregnant group than the control and DM groups, except for VLDL-TG in the DM group. RLP-C and RLP-TG concentrations were significantly higher in the pregnant group (8.7 mg/dl and 25.4 mg/dl on average) than the control group (2.4 mg/dl and 5.7 mg/dl), but not different from the DM group (8.8 mg/dl and 24.1 mg/dl). RLP-TG to RLP-C ratios were similar among the three groups and correlated with the VLDL-TG to VLDL-C ratio. The percentages of RLP-C in VLDL-C and RLP-TG in VLDL-TG in the pregnant group (15.9% and 15.7%) were significantly lower than those of the control (48.5% and 35.6%) and the DM (32.7% and 20.8%) groups.

CONCLUSIONS

RLP increased moderately during gestation with the increase in VLDL and TG, but the percentage of RLP in VLDL was significantly lower in the pregnant women compared with the control and DM patients, suggesting that hypertriglyceridemia in pregnancy is not primarily due to an increase in the atherogenic RLP.