Activities of lipoprotein lipase and hepatic triglyceride lipase in postheparin plasma of patients with low concentrations of HDL cholesterol

Obesity-Related Changes in High-Density Lipoprotein Metabolism and Function

In obese individuals, atherogenic dyslipidemia is a very common and important factor in the increased risk of cardiovascular disease. Adiposity-associated dyslipidemia is characterized by low high-density lipoprotein cholesterol (HDL-C) levels and an increase in triglyceride-rich lipoproteins. Several factors and mechanisms are involved in lowering HDL-C levels in the obese state and HDL quantity and quality is closely related to adiponectin levels and the bioactive lipid sphingosine-1-phosphate. Recent studies have shown that obesity profoundly alters HDL metabolism, resulting in altered HDL subclass distribution, composition, and function. Importantly, weight loss through gastric bypass surgery and Mediterranean diet, especially when enriched with virgin olive oil, is associated with increased HDL-C levels and significantly improved metrics of HDL function. A thorough understanding of the underlying mechanisms is crucial for a better understanding of the impact of obesity on lipoprotein metabolism and for the development of appropriate therapeutic approaches. The objective of this review article was to summarize the newly identified changes in the metabolism, composition, and function of HDL in obesity and to discuss possible pathophysiological consequences.

The cross-sectional study of hepatic lipase SNPs and plasma lipid levels

By the combination of meta‐analysis, the data of the 1,000 Genomes Project Phase 3, and the promoter sequence of hepatic lipase (LIPC), we performed the cross‐sectional study to explore the associations of four variants (rs1077835; rs1077834; rs1800588 [C‐514T], and rs2070895 [G‐250A]) in LIPC promoter with plasma lipid levels. Our results indicate that the first and the next three of the four SNPs are, respectively, reported to be associated with the decreased and increased HDL‐c level. Meta‐analysis of 87 studies with 101,988 participants indicates that HDL‐c level in rs1800588 (C‐514T) (pooled mean difference = 0.03, 95%CI (0.03, 0.04), p < .001) and rs2070895 (G‐250A) (pooled mean difference = 0.07, 95%CI (0.05, 0.09), p < .001) is higher in allele T or A carriers. Similarly, LDL‐c, TC, TG, and BMI levels are generally increased in T or A alleles carriers. We failed to conduct the meta‐analysis of rs1077835 and rs1077834 due to the limited previous reports. Data from the 1,000 Genomes indicate that the allele frequencies of the four SNPs in total or subpopulations are almost equal to each other. The paired value r² and D' of the four SNPs are larger than 0.8, which indicate the linkage disequilibrium of the four variants. The analysis of LIPC promoter indicate that C‐514T and G‐250A are, respectively, located in transcriptional factor binding sites of USF1and Pbx1b, which may partly explain the effect of the two SNPs on the decreased LIPC activity in the alleles carriers and the corresponding increased plasma lipids hydrolyzed by LIPC. These results may help us to better understand the different effects of the four SNPs on the plasma lipid levels among subpopulations and offer clues for future clinical treatment of dyslipidemia‐related diseases.

Multipronged Therapeutic Effects of Chinese Herbal Medicine Qishenyiqi in the Treatment of Acute Myocardial Infarction

Background: Based on global gene expression profile, therapeutic effects of Qishenyiqi (QSYQ) on acute myocardial infarction (AMI) were investigated by integrated analysis at multiple levels including gene expression, pathways involved and functional group.

Methods: Sprague-Dawley (SD) rats were randomly divided into 3 groups: Sham-operated, AMI model (left anterior descending coronary artery ligation) and QSYQ-treated group. Cardiac tissues were obtained for analysing digital gene expression. Sequencing and transcriptome analyses were performed collaboratively, including analyses of differential gene expression, gene co-expression network, targeted attack on network and functional grouping. In this study, a new strategy known as keystone gene-based group significance analysis was also developed.

Results: Analysis of top keystone QSYQ-regulated genes indicated that QSYQ ameliorated ventricular remodeling (VR), which is an irreversible process in the pathophysiology of AMI. At pathway level, both well-known cardiovascular diseases and cardiac signaling pathways were enriched. The most remarkable finding was the novel therapeutic effects identified from functional group analysis. This included anti-inflammatory effects mediated via suppression of arachidonic acid lipoxygenase (LOX) pathway and elevation of nitric oxide (NO); and amelioration of dyslipidaemia mediated via fatty acid oxidation. The regulatory patterns of QSYQ on key genes were confirmed by western blot, immunohistochemistry analysis and measurement of plasma lipids, which further validated the therapeutic effects of QSYQ proposed in this study.

Conclusions: QSYQ exerts multipronged therapeutic effects on AMI, by concurrently alleviating VR progression, attenuating inflammation induced by arachidonic acid LOX pathway and NO production; and ameliorating dyslipidaemia.

The rs2070895 (-250G/A) Single Nucleotide Polymorphism in Hepatic Lipase (HL) Gene and the Risk of Coronary Artery Disease in North Indian Population: A Case-Control Study

INTRODUCTION

Several Single Nucleotide Polymorphisms (SNPs) in lipid transport genes have been shown to be associated with Coronary Artery Disease (CAD). The Hepatic Lipase (HL)glycoprotein is a key component that catalyzes the hydrolysis of triglycerides and phospholipids in all major classes of lipoproteins.

AIM

We studied whether the HL gene-250G/A polymorphism affect blood lipid level and the CAD in a North Indian population.

MATERIALS AND METHODS

A total number of 477 subjects were enrolled in the study after approval of the Institutional Ethics Committee. Out of 477 subjects, 233 were with coronary artery disease as study group and 244 subjects without coronary artery disease as control group. All subjects recruited with matched ethnicity in age group of 40-70 years. Blood samples were collected in EDTA vials and genomic DNA was extracted from blood using the phenol-chloroform method. Lipid profile was estimated by using a commercially available kit. Polymorphisms in the HL (-250 G/A) gene were analysed by using restriction fragment length polymorphism-polymerase chain reaction (PCR-RFLP) method. The effect of this polymorphism on plasma lipids, lipoproteins and coronary artery disease was determined.

RESULTS

In Human Hepatic Lipase (LIPC)-250G/A genotype, the frequencies of GG, GA and AA genotype in CAD group was 80.69%, 15.45% and 3.86%, respectively; in the control group, the corresponding frequencies were 90.16%, 9.02% and 0.82%, respectively. A significant difference was found in the genotype (LIPC-250G/A) distribution between the two groups. Further logistic regression analysis indicated that the GA and AA genotypes in SNP-250G/A were significantly associated with CAD in all genetic models (In codominant model- GA vs. GG, OR=1.91, 95% CI=1. 09-3.37, p=0. 03 and AA vs. GG, OR= 5.26, 95% CI= 1.10-24.60, p=0.04; in dominant model- GA+AA vs. GG, OR=2.19, p=0.004 and in recessive model- AA vs. GG+GA, OR=5.26, p=0.04 whereas, A allele at nucleotide -250G/A in the LIPC gene had an association with increased risk of CAD (OR=2.33, p=<0.008).

CONCLUSION

Our findings indicated that the higher frequency of a dominant model (GA+AA) as well as mutant allele A of LIPC-250 G/A polymorphism is significantly associated with risk of CAD and the lipid profile can be used as a predictor of CAD.

Inflammatory, lipid, and body composition responses to interval training or moderate aerobic training

PURPOSE

The goal of this study was to compare the effect of work- and duration-matched interval training (HIIT) versus moderate aerobic endurance training (ET) on acute and chronic inflammation, along with changes in the lipid profile, to determine which may be more beneficial for improving cardiovascular health.

METHODS

Twelve sedentary males (maximal oxygen consumption = 41.6 ± 5.4 mL kg(-1) min(-1)) completed 8 weeks of aerobic interval training or moderate aerobic training, with variables including C-reactive protein (CRP) for chronic inflammation, interleukin-6 (IL-6) response for the acute inflammatory response, plasma concentrations of high-density lipoprotein (HDL), total cholesterol (TC), triglycerides (TRG), and low-density lipoprotein, and body composition measured before and after the training period.

RESULTS

HIIT decreased plasma TRG from 92 ± 32 to 61 ± 12 mg dL(-1), which was significantly different from ET, while ET improved the TC:HDL ratio from 4.67 ± 0.85 to 4.07 ± 0.96 and reduced the percentage of android fat from 36.78 ± 9.60 to 34.18 ± 11.39 %. Neither training protocol resulted in an acute IL-6 response on the first nor the last day of exercise, a change in chronic levels of CRP, or a significant increase in HDL, despite previous research finding these changes.

CONCLUSIONS

It seems that in order to maximize the health outcomes from physical activity, both HIIT and ET should be included. The acute inflammatory response and reductions in chronic inflammation resulting from exercise training may not be as common as the literature suggests.

Interaction between cholesteryl ester transfer protein and hepatic lipase encoding genes and the risk of type 2 diabetes: results from the Telde study

Background and Aim

Diabetic dyslipidaemia is common in type 2 diabetes (T2D) and insulin resistance and often precedes the onset of T2D. The Taq1B polymorphism in CETP (B1 and B2 alleles) (rs708272) and the G-250A polymorphism in LIPC (rs2070895) are associated with changes in enzyme activity and lipid concentrations. Our aim was to assess the effects of both polymorphisms on the risk of T2D.

Methods and Results

In a case-control study from the population-based Telde cohort, both polymorphisms were analysed by PCR-based methods. Subjects were classified, according to an oral glucose tolerance test, into diabetic (N = 115) and pre-diabetic (N = 116); 226 subjects with normal glucose tolerance, matched for age and gender, were included as controls. Chi-square (comparison between groups) and logistic regression (identification of independent effects) were used for analysis. The B1B1 Taq1B CETP genotype frequency increased with worsening glucose metabolism (42.5%, 46.1% and 54.3% in control, IGR and diabetic group; p = 0.042). This polymorphism was independently associated with an increased risk of diabetes (OR: 1.828; IC 95%: 1.12–2.99; p = 0.016), even after adjusting by confounding variables, whereas the LIPC polymorphism was not. Regarding the interaction between both polymorphisms, in the B1B1 genotype carriers, the absence of the minor (A) allele of the LIPC polymorphism increased the risk of having diabetes.

Conclusion

The presence of the B1B1 Taq1B CETP genotype contributes to the presence of diabetes, independently of age, sex, BMI and waist. However, among carriers of B1B1, the presence of GG genotype of the -250 LIPC polymorphism increases this risk further.

Ethnicity, obesity and the metabolic syndrome: implications on assessing risk and targeting intervention

Pediatric obesity threatens the future health of a growing number of children worldwide. An added challenge in identifying the patients at greatest need for intervention due to their elevated risk for future disease is that pediatric obesity and the associated metabolic syndrome manifest differently among different ethnic groups. African-Americans and Hispanics are more likely to exhibit obesity and insulin resistance and are at a higher risk for developing Type 2 diabetes. Nevertheless, using current criteria, African-American adolescents are much less likely to be diagnosed with metabolic syndrome, largely owing to lower rates of dyslipidemia. Further development is needed in ethnicity-inclusive means of risk identification among adolescents to accurately target treatment toward children at highest risk for future disease and to motivate adolescent patients and their families towards lifestyle improvement. Effective targeting and intensive treatment efforts may help in avoiding future sequelae of obesity among all ethnicities.

Role of endothelial lipase in plasma HDL levels in a murine model of hypertriglyceridemia

AIM

Hypertriglyceridemia is the most common cause of low plasma high-density lipoprotein cholesterol (HDL-C) levels; however, the correlation between high triglyceride (TG) and low HDL-C remains unclear. Endothelial lipase (EL) is a determinant of plasma HDL levels. We investigated the role of EL in HDL metabolism in a murine model of acute hypertriglyceridemia.

METHODS AND RESULTS

To establish TG-dominant hyperlipidemia, EL-/- and wild-type (WT) mice were injected with Poloxamer-407 (P-407, 0.5 g/kg, i.p.). A single injection of P-407 resulted in a marked increase in plasma TG and cholesterol levels together with a decrease in HDL-C levels. Although plasma TG levels were similar in EL-/- and WT mice after P-407 injection, HDL-C levels were 80% higher and the HDL particle size was significantly larger in EL-/- mice than in WT mice. P-407 treatment inhibited plasma lipoprotein lipase activity and EL phospholipase activity, without decreasing their expressions. Adenovirus-mediated overexpression of EL in the liver reduced plasma HDL-C levels in both normo- and hyperlipidemic mice, while overexpression of catalytically inactive EL reduced HDL-C levels in hyperlipidemic mice. Cell culture experiments revealed that both catalytically active and inactive EL promoted cellular HDL uptake to the same extent.

CONCLUSION

EL regulates plasma HDL levels in mice in the normolipidemic as well as the acute hypertriglyceridemic state. EL can modulate plasma HDL-CHOL levels through both its lipolytic and ligand-binding functions in hypertriglyceridemic mice, while lipolytic activity appears to be the main determinant for its effects on HDL metabolism in normolipidemic mice.

The -250G>A promoter variant in hepatic lipase associates with elevated fasting serum high-density lipoprotein cholesterol modulated by interaction with physical activity in a study of 16,156 Danish subjects

CONTEXT

Hepatic lipase plays a pivotal role in the metabolism of high-density lipoprotein (HDL) and low-density lipoprotein by involvement in reverse cholesterol transport and the formation of atherogenic small dense low-density lipoprotein.

OBJECTIVES

The objective was to investigate the impact of variants in LIPC on metabolic traits and type 2 diabetes in a large sample of Danes. Because behavioral factors influence hepatic lipase activity, we furthermore examined possible gene-environment interactions in the population-based Inter99 study.

DESIGN

The LIPC -250G>A (rs2070895) variant was genotyped in the Inter99 study (n = 6070), the Anglo-Danish-Dutch Study of Intensive Treatment in People with Screen Detected Diabetes in Primary Care Denmark screening cohort of individuals with risk factors for undiagnosed type 2 diabetes (n = 8662), and in additional type 2 diabetic patients (n = 1,064) and glucose-tolerant control subjects (n = 360).

RESULTS

In the Inter99 study, the A allele of rs2070895 associated with a 0.057 mmol/liter [95% confidence interval (CI) 0.039-0.075] increase in fasting serum HDL-cholesterol (HDL-c) (P = 8 x 10(-10)) supported by association in the Anglo-Danish-Dutch Study of Intensive Treatment in People with Screen Detected Diabetes in Primary Care study [0.038 mmol/liter per allele (95% CI 0.024-0.053); P = 2 x 10(-7)). The allelic effect on HDL-c was modulated by interaction with self-reported physical activity (P(interaction) = 0.002) because vigorous physically active homozygous A-allele carriers had a 0.30 mmol/liter (95% CI 0.22-0.37) increase in HDL-c compared with homozygous G-allele carriers.

CONCLUSIONS

We validate the association of LIPC promoter variation with fasting serum HDL-c and present data supporting an interaction with physical activity implying an increased effect on HDL-c in vigorous physically active subjects carrying the -250 A allele. This interaction may have potential implications for public health and disease prevention.

No change in apolipoprotein AI metabolism when subcutaneous insulin infusion is replaced by intraperitoneal insulin infusion in type 1 diabetic patients

In type 1 diabetic patients, the replacement of subcutaneous insulin infusion by intraperitoneal insulin infusion restores the normal physiological gradient between the portal vein and the peripheral circulation, which is likely to modify HDL metabolism. This stable isotope kinetic study was designed to compare HDL apolipoprotein (apo) AI metabolism in seven type 1 diabetic patients first treated by continuous subcutaneous insulin infusion by an external pump and then 3 months after the beginning of intraperitoneal insulin infusion by an implantable pump. Glycaemic control was comparable under subcutaneous and intraperitoneal insulin infusion (HbA1c=7.34+/-0.94% versus 7.24+/-1.00%, NS). HDL composition was similar under both insulin regimens (esterified cholesterol=20.1+/-2.5% versus 24.0+/-3.0% (NS), free cholesterol=3.4+/-1.1% versus 3.3+/-0.9% (NS), triglycerides=2.4+/-0.9% versus 2.1+/-0.9% (NS), phospholipids=22.7+/-5.3% versus 25.2+/-6.5% (NS) and proteins=51.2+/-6.3% versus 45.5+/-4.7% (NS)). The replacement of subcutaneous insulin infusion by intraperitoneal insulin infusion induced significant changes neither in apoAI fractional catabolic rate, nor in apoAI production rate, nor in apoAI pool size (respectively, 0.199+/-0.051 pool d(-1) versus 0.211+/-0.017 pool d(-1), 12.0+/-3.2 mg kg(-1)d(-1) versus 12.1+/-1.8 mg kg(-1)d(-1), 60.4+/-5.0 mg kg(-1) versus 57.5+/-7.5 mg kg(-1)). In conclusion, HDL metabolism is not modified by the replacement of subcutaneous insulin infusion by intraperitoneal insulin infusion when glycaemia is well controlled under both insulin regimens. As far as HDL metabolism is concerned there is no advantage in favour of one way of insulin administration or another.

Obesity and atherogenic dyslipidemia

Obesity is associated with an increased risk of coronary heart disease, in part due to its strong association with atherogenic dyslipidemia, characterized by high triglycerides and low high-density lipoprotein (HDL) cholesterol. There has been substantial research effort focused on the mechanisms of the link between obesity and atherogenic dyslipidemia, both in the absence and presence of insulin resistance. After a brief overview of the epidemiology of atherogenic dyslipidemia, this article details the known molecular mechanisms of adipocyte function and its relationship to apoB-containing lipoprotein assembly and metabolism, both in the healthy as well as in the obese states. We also discuss the pathophysiology of low HDL cholesterol in obesity and the implications for cardiovascular disease risk.

Functionally defective high-density lipoprotein: a new therapeutic target at the crossroads of dyslipidemia, inflammation, and atherosclerosis

High-density lipoproteins (HDL) possess key atheroprotective biological properties, including cellular cholesterol efflux capacity, and anti-oxidative and anti-inflammatory activities. Plasma HDL particles are highly heterogeneous in physicochemical properties, metabolism, and biological activity. Within the circulating HDL particle population, small, dense HDL particles display elevated cellular cholesterol efflux capacity, afford potent protection of atherogenic low-density lipoprotein against oxidative stress and attenuate inflammation. The antiatherogenic properties of HDL can, however be compromised in metabolic diseases associated with accelerated atherosclerosis. Indeed, metabolic syndrome and type 2 diabetes are characterized not only by elevated cardiovascular risk and by low HDL-cholesterol (HDL-C) levels but also by defective HDL function. Functional HDL deficiency is intimately associated with alterations in intravascular HDL metabolism and structure. Indeed, formation of HDL particles with attenuated antiatherogenic activity is mechanistically related to core lipid enrichment in triglycerides and cholesteryl ester depletion, altered apolipoprotein A-I (apoA-I) conformation, replacement of apoA-I by serum amyloid A, and covalent modification of HDL protein components by oxidation and glycation. Deficient HDL function and subnormal HDL-C levels may act synergistically to accelerate atherosclerosis in metabolic disease. Therapeutic normalization of attenuated antiatherogenic HDL function in terms of both particle number and quality of HDL particles is the target of innovative pharmacological approaches to HDL raising, including inhibition of cholesteryl ester transfer protein, enhanced lipidation of apoA-I with nicotinic acid and infusion of reconstituted HDL or apoA-I mimetics. A preferential increase in circulating concentrations of HDL particles possessing normalized antiatherogenic activity is therefore a promising therapeutic strategy for the treatment of common metabolic diseases featuring dyslipidemia, inflammation, and premature atherosclerosis.

Determinants of plasma HDL concentrations and reverse cholesterol transport

PURPOSE OF REVIEW

One of the major mechanisms whereby HDL particles are felt to protect against atherosclerosis is that of reverse cholesterol transport from atherosclerotic lesion macrophages to the liver, with subsequent excretion of cholesterol in the bile. This review focuses on recent progress in our understanding of reverse cholesterol transport and the factors that determine plasma HDL cholesterol concentrations.

RECENT FINDINGS

The liver and intestine are the major sites of apolipoprotein A-I synthesis and nascent HDL particle secretion. The liver has recently been shown to be a major contributor to the plasma HDL-cholesterol concentration, but the precise site or mechanism whereby hepatically-synthesized HDL acquire the bulk of their lipid content remains to be determined. Contrastingly, macrophages contribute little to the plasma HDL cholesterol pool, whereas the quantitatively small macrophage-specific reverse cholesterol transport contributes disproportionately to protection against atherosclerosis. Studies have highlighted the coordinate action of cell surface lipid transporters, cholesterol esterification enzymes and lipid transfer factors in the early steps of reverse cholesterol transport and the recycling of pre-beta HDL particles to create a ready supply of cholesterol acceptor HDL particles. Most of the variation in plasma HDL-cholesterol levels in human populations is accounted for by variations in HDL clearance rather than production.

SUMMARY

Our understanding of the in-vivo metabolism of HDL particles and their role in reverse cholesterol transport is rapidly evolving, with long-standing concepts being constantly challenged by emerging evidence. An in-depth understanding of HDL metabolism will guide the rational design of novel pharmacological therapies that effectively protect against atherosclerosis.

Human genetics of variation in high-density lipoprotein cholesterol

Longitudinal population studies have confirmed plasma levels of high-density lipoprotein (HDL) cholesterol to be an important inverse coronary risk factor. Although environmental influences are known to regulate HDL cholesterol levels, genetic factors are also known to be important, and over 25 candidate genes have been proposed to be associated with variation in HDL cholesterol levels. A variety of monogenic conditions of extremely low or high HDL cholesterol has helped to delineate the physiology of HDL cholesterol metabolism in humans, which has led to the development of new therapeutic approaches to HDL cholesterol. However, most causes of genetic variation in HDL cholesterol in the general population are likely oligogenic or polygenic. We review the monogenic disorders associated with both high and low HDL cholesterol and the relevance of mutations and polymorphisms in these genes to variation in HDL cholesterol levels in the general population.

Impact of sex-specific body composition on cardiovascular risk factors: the Hong Kong Cardiovascular Risk Factor Study

The aim of the study was to analyze the effects of sex-specific distribution of adiposity, particularly emphasizing the independent contribution of waist and hip circumferences relative to body mass index (BMI), on cardiovascular risk factors in a Chinese population. Blood pressure and anthropometric and biochemical parameters were measured in 2510 population-based Chinese subjects. The relative contributions of waist and hip circumferences to the presence of cardiovascular risk factors were determined. The Chinese men were significantly larger than women, with greater BMI and central adiposity. Waist and hip circumferences were both positively associated with the presence of hypertension, dyslipidemia, and diabetes. However, after adjustment for BMI and age, hip circumference exhibited a significant dose-dependent inverse relationship with dyslipidemia and diabetes in women, but not men. Sex-specific differences exist. After adjustment for age and BMI, hip circumferences independently and inversely contribute to cardiovascular risk in women, but not in men. Increasing adjusted waist circumference was associated with increased risk of hypertension and diabetes in Chinese and dyslipidemia in women only.

Postprandial lipemic response and lipoprotein composition in subjects with low or high cholesterol absorption efficiency

BACKGROUND

The purpose of this study was to investigate the effect of differences in cholesterol absorption efficiency on the postprandial lipemia and lipoprotein composition.

METHODS

Fifteen healthy subjects were divided into low and high cholesterol absorbers on the basis of serum cholestanol to cholesterol ratio. A high-performance liquid chromatographic method with evaporative light scattering detection was developed for quantitation of free and esterified cholesterol, triglycerides and major phospholipids from the same lipid extract in two runs utilizing the same internal standard.

RESULTS

The free cholesterol to phosphatidylcholine ratio of chylomicrons was higher in the high cholesterol absorption group. The total increase of cholesterol in combined chylomicron and very low density lipoprotein (VLDL) fraction was also higher in this group. Chylomicron free cholesterol and cholesterol ester responses correlated with fasting low density lipoprotein (LDL) cholesterol. VLDL and VLDL1 triglyceride responses correlated inversely with fasting insulin and homeostasis model assessment of insulin resistance.

CONCLUSIONS

High cholesterol absorption efficiency was seen in chylomicrons as higher cholesterol to phosphatidylcholine ratio during the postprandial peak. Chylomicron cholesterol response was linked to fasting LDL cholesterol and low VLDL triglyceride response to fasting insulin.

Normal triglyceride levels despite insulin resistance in African Americans: role of lipoprotein lipase

Abstract Lipoprotein lipase (LPL), the enzyme responsible for hydrolyzing triglyceride (TG) in plasma lipoproteins, is a key regulator of plasma TG levels. In Caucasians, postheparin-LPL (PH-LPL) activity is impaired in the presence of insulin resistance and leads to elevated TG levels. However, African Americans are often both insulin-resistant and normotriglyceridemic. But in African Americans, the effect of insulin resistance on PH-LPL activity has not been studied. In African Americans, if insulin resistance is not associated with a decrease in PH-LPL activity, this could account for the simultaneous presence of insulin resistance and normotriglyceridemia. Therefore, our goal was to determine in African Americans the relationship between insulin resistance and PH-LPL activity. In a cross-sectional study of 107 nondiabetic African Americans (57 men and 50 women; age mean +/- SD, 35 +/- 8 years, range 22-50 years; body mass index 31.6 +/- 7.9 kg/m 2 , range 18.5-54.7 kg/m 2 ), fasting TG levels and PH-LPL activity were determined. Visceral adipose tissue was measured by abdominal computed tomographic scan. Insulin resistance was determined by the insulin sensitivity index ( S I ). Subjects were divided into tertiles by S I . The range of S I in each tertile was 12.75 to 3.99, 3.87 to 2.20, 2.06 to 0.17 mU . L -1 . min -1 . Insulin resistance was defined as being in the third tertile. TG levels in the men and women were 82.2 +/- 35.5 versus 56.4 +/- 30.1 mg/dL, P < .001. There were no sex difference in PH-LPL activity (8.9 +/- 2.5 vs 9.6 +/- 3.2 mmol/h per liter, P = .30) or S I (3.65 +/- 2.59 vs 3.23 +/- 1.89 L . mU -1 . min -1 , P = .49). Although 47% of the subjects were obese, only 4% of subjects had hypertriglyceridemia (TG > or =150 mg/dL). By 2 separate analyses, PH-LPL was a major determinant of TG levels. First, there was a significant inverse correlation between PH-LPL activity and TG levels (men: r = -0.46, P < .001; women: r = -0.28, P = .046). Second, in the multiple regression analysis with TG as the dependent variable and PH-LPL, age, sex, S I , and visceral adipose tissue as independent variables, adjusted R 2 was 54% and the effect of PH-LPL on TG levels was highly significant( P < .001). However, insulin resistance did not appear to influence PH-LPL activity. This is demonstrated in 3 ways: first, PH-LPL activity was not different in the S I tertiles (9.10 +/- 2.75, 9.52 +/- 2.91, 9.13 +/- 2.89 mmol/h per liter, P = .78); the correlation between PH-LPL and S I was not significant (men: r = 0.09, P = .51; women: r = -0.03, P = .78), and a multiple regression with PH-LPL as the dependent variable and age, S I , body mass index, and sex as independent variables, adjusted R 2 was <2% and the contribution of S I was not significant ( P = .53). Hence, in African Americans, increased PH-LPL activity is associated with a decrease in TG levels. The lack of an effect of insulin resistance on PH-LPL could allow LPL to clear TG even in the presence of insulin resistance and explain the coexistence of insulin resistance and normotriglyceridemia in African Americans.

A normotriglyceridemic, low HDL-cholesterol phenotype is characterised by elevated oxidative stress and HDL particles with attenuated antioxidative activity

OBJECTIVE

Low levels of high density lipoprotein-cholesterol (HDL-C) are highly prevalent in subjects presenting premature atherosclerosis. It is indeterminate as to whether high cardiovascular risk in low HDL-C subjects occurs concomitantly with elevated oxidative stress and/or with biologically dysfunctional HDL particles.

METHODS AND RESULTS

Systemic oxidative stress (as plasma 8-isoprostanes) was 2.3-fold elevated (p<0.05) in normocholesterolemic, normotriglyceridemic, normoglycemic low HDL-C subjects (plasma HDL-C, <40 mg/dL; n=8) as compared to normolipidemic controls (n=15). HDL subfractions (HDL2b, 2a, 3a, 3b and 3c) isolated by density gradient ultracentrifugation from low HDL-C subjects displayed significantly lower (-21 to -43%, p<0.05) specific antioxidative activity (sAA; capacity to protect LDL from oxidation on a unit particle mass or on a particle number basis) as compared to controls. Altered chemical composition (core triglyceride enrichment, cholesteryl ester depletion) paralleled antioxidative dysfunction of HDL subfractions. Plasma 8-isoprostane levels negatively correlated with sAA of HDL subfractions and positively correlated with the total cholesterol/HDL-C ratio, which was significantly elevated in the low HDL-C phenotype.

CONCLUSIONS

Low HDL-C subjects display elevated oxidative stress and possess HDL particle subspecies with attenuated intrinsic antioxidative activity which is intimately related to their altered chemical composition.

Endothelial lipase: a modulator of lipoprotein metabolism upregulated by inflammation

Both acute and chronic inflammatory states are associated with decreased levels of high-density lipoprotein (HDL) cholesterol, yet the underlying mechanism is poorly understood. Endothelial lipase (EL), a recently described member of the triglyceride lipase family, has been shown to be a key enzyme in HDL metabolism. Expression of EL by endothelial cells is upregulated by proinflammatory cytokines and is associated with increased EL-specific triglyceride and phospholipase activity in vitro. Thus, EL may play an important role in lipid metabolism and energy homeostasis in states of acute and chronic inflammation.

Lipoprotein lipase and its role in regulation of plasma lipoproteins and cardiac risk

For over 50 years, biologists and clinicians have studied lipoprotein lipase (LPL) and learned about its structure, function, cellular production, physiology, and human genetics. LPL is the principal enzyme that removes triglyceride from the bloodstream. It also determines plasma levels of high-density lipoprotein. Surprisingly, within the past several years, a number of new and unexpected proteins have been discovered that regulate the actions of LPL. These include the very low-density lipoprotein receptor, angiopoetin-like protein 3, and apolipoprotein A-V. In addition, mouse genetic studies have confirmed tissue culture findings of nonenzymatic roles of LPL both in lipid metabolism and atherogenesis. These basic observations are now being related to new information on human genetic polymorphism in this gene that is likely to affect clinical evaluation of lipoprotein disorders and cardiac risk.

Management of atherogenic dyslipidemia of the metabolic syndrome: evolving rationale for combined drug therapy

Atherogenic dyslipidemia is prevalent in various conditions associated with central obesity, hypertension, hyperurecemia, and impaired beta-cell function (ie, the metabolic syndrome). Because of clinical trial evidence, most high-risk patients with atherogenic dyslipidemia require statin therapy. Coadministration of drugs targeted to reduction of low-density lipoprotein precursors, however,is likely to improve the metabolic profile of all non-high-density lipoproteins and produce a significant rise in high-density lipoprotein cholesterol. Large-scale clinical trials with combined drug therapy that show coronary heart disease (CHD) risk reduction or improvement in CHD are needed. It is also possible that new drugs are needed to target fatty acid metabolism and inflammation. As understanding of the metabolic origins of atherogenic dyslipidemia increases, it is possible that new targets of therapy will be identified and that new drug combinations will prove to be even more efficacious than those currently available for treatment of this condition.

Severe hypoalphalipoproteinemia in mice expressing human hepatic lipase deficient in binding to heparan sulfate proteoglycan

Unlike human hepatic lipase (hHL) that is mainly cell surface-anchored via binding to heparan sulfate proteoglycans (HSPG), mouse HL (mHL) has a low affinity to HSPG and thus is largely blood-borne. The reduced HSPG binding of mHL is attributable to the C-terminal amino acids. To determine the functions of HSPG binding of hHL in vivo, we created adenovirus vectors encoding hHL or a chimeric protein (designated hHLmt) in which the C-terminal HSPG-binding sequences were replaced with the corresponding mouse sequences. Injecting hHLmt-expressing virus into C57BL/6J mice (1.8 x 10(10) virus particles/mouse) resulted in a 3-fold increase in pre-heparin HL activity, whereas infection with an identical dose of hHL virus did not change pre-heparin HL activity. In hHLmt-expressing mice, the concentration of total cholesterol and phospholipids was inversely related to the hHL activity in pre-heparin plasma in a dose- and time-dependent manner, and the decrease was mainly attributable to high density lipoproteins (HDL) cholesterol and HDL phospholipids. The expression of hHL exhibited no change in plasma total cholesterol or phospholipid levels as compared with control mice infected with luciferase or injected with saline. The reduced HDL lipids in the hHLmt-expressing mice were accompanied by markedly decreased plasma and hepatic apolipoprotein (apo) A-I. In primary hepatocytes isolated from hHLmt-expressing mice, the concentration of cell-associated and secreted apoA-I was decreased by 2-3-fold as compared with hepatocytes isolated from control mice, whereas the levels of apoB and apoE were unaltered. Infection of primary hepatocytes with hHLmt virus ex vivo also resulted in reduced apoA-I secretion but had no effect on cell-associated apoA-I. These results suggest that expression of HSPG binding-deficient hHL has a profound HDL-lowering effect.

Effects of nonlipolytic ligand function of endothelial lipase on high density lipoprotein metabolism in vivo

Endothelial lipase (EL) influences high density lipoprotein (HDL) metabolism in vivo and mediates bridging and uptake of HDL particles independent of its lipolytic activity in vitro. To determine whether EL has a nonlipolytic ligand function in HDL metabolism in vivo, 1 x 1011 particles of a recombinant adenovirus encoding human EL (AdEL), catalytically inactive human EL (AdELS149A), or control (Adnull) were injected into wild-type, apoA-I transgenic, and hepatic lipase knockout mice. ELS149A protein was expressed at higher levels than wild-type EL. EL and ELS149A protein were both substantially increased in the postheparin plasma compared with preheparin, indicating that both the wild-type and mutant EL were bound to cell-surface heparan sulfate proteoglycans. Overexpression of wild-type EL was associated with a significantly increased postheparin-plasma phospholipase activity and dramatically decreased levels of total cholesterol, HDL cholesterol, phospholipids, and apoA-I. Injection of AdELS149A did not result in increased phospholipase activity confirming that ELS149A was catalytically inactive. Expression of ELS149A did not decrease lipid or apoA-I levels in wild-type and apoA-I transgenic mice yet led to an intermediate reduction of total cholesterol, HDL cholesterol, and phospholipids in hepatic lipase-deficient mice compared with control and EL-expressing mice. Our study demonstrates for the first time that EL has both a lipolytic and nonlipolytic function in HDL metabolism in vivo. Lipolytic activity of EL, however, seems to be most important for its effects on systemic HDL metabolism.

Dose-dependent acceleration of high-density lipoprotein catabolism by endothelial lipase

BACKGROUND

Factors that regulate the metabolism of HDL and apolipoprotein A-I (apoA-I) are incompletely understood. Overexpression of endothelial lipase (EL) markedly reduces plasma levels of HDL cholesterol and apoA-I in mice, but the mechanisms of this effect remain unknown.

METHODS AND RESULTS

We used different doses of a recombinant adenoviral vector to overexpress human EL in mice and studied the effects on plasma phospholipase activity, plasma lipids, HDL particle size, HDL turnover, and tissue sites of HDL degradation in mice. Overexpression of EL was associated with a significant dose-dependent increase in postheparin plasma phospholipase activity. Plasma phospholipid, HDL cholesterol, and apoA-I levels were markedly decreased, even at the lowest dose of vector. Kinetic studies demonstrated a significant dose-dependent increase in the fractional catabolic rate of HDL-apolipoprotein in EL-overexpressing mice. The postheparin plasma phospholipase activity was significantly positively correlated with HDL-apolipoprotein fractional catabolic rate. The uptake of apoA-I by the kidney and the liver was significantly increased by 2.5-fold and 3-fold, respectively, in mice overexpressing EL.

CONCLUSIONS

Expression of EL in mice results in a dose-dependent increase in postheparin plasma phospholipase activity, catabolic rate of HDL-apolipoprotein, and uptake of apoA-I in both kidney and liver.

Regulation of reverse cholesterol transport and clinical implications

Plasma levels of high-density lipoprotein (HDL) cholesterol and its major protein, apolipoprotein A-I, are inversely correlated with the incidence of atherosclerotic cardiovascular disease. Low HDL cholesterol and apolipoprotein A-I levels often are found in association with other cardiovascular risk factors, including the metabolic syndrome, insulin resistance, and type 2 diabetes mellitus. However, overexpression of apolipoprotein A-I in animals has been shown to reduce progression and even induce regression of atherosclerosis, indicating that apolipoprotein A-I is directly protective against atherosclerosis. A major mechanism by which apolipoprotein A-I inhibits atherosclerosis may be by promoting cholesterol efflux from macrophages and returning it to the liver for excretion, a process termed reverse cholesterol transport. This article focuses on new developments in the regulation of reverse cholesterol transport and the clinical implications of those developments.

Hepatic lipase and dyslipidemia: interactions among genetic variants, obesity, gender, and diet

Hepatic lipase (HL) plays a central role in LDL and HDL remodeling. High HL activity is associated with small, dense LDL particles and with reduced HDL2 cholesterol levels. HL activity is determined by an HL gene promoter polymorphism, by gender (lower in premenopausal women), and by visceral obesity with insulin resistance. The activity is affected by dietary fat intake and selected medications. There is evidence for an interaction of the HL promoter polymorphism with visceral obesity, dietary fat intake, and with lipid-lowering medications in determining the level of HL activity. The dyslipidemia with high HL activity is a potentially proatherogenic lipoprotein profile in the metabolic syndrome, in Type 2 diabetes, and in familial combined hyperlipidemia.

Is the gender difference in LDL size explained by the metabolic complications of visceral obesity?

BACKGROUND

Several studies have reported a significant gender difference in low-density lipoprotein (LDL) size, with men being characterized by smaller, denser LDL particles than women, and it has been suggested that the contribution of the greater accumulation of visceral adipose tissue in men compared with women may be a factor potentially contributing to the gender difference in LDL heterogeneity.

MATERIALS AND METHODS

We measured LDL particle size by 2-16% nondenaturing polyacrylamide gradient gel electrophoresis in 299 men and 231 women in whom visceral adipose tissue accumulation was measured by computed tomography. A fasting plasma lipoprotein-lipid profile was also obtained in all subjects.

RESULTS

Overall, the men were characterized by a more deteriorated metabolic risk factor profile, which included higher plasma insulin and triglyceride levels, a greater visceral adipose tissue accumulation (P < 0.001) and smaller LDL particles (251.7 +/- 5.2 vs. 254.4 +/- 4.2 A, P < 0.0001). This gender difference in LDL peak particle diameter remained significant (252.4 +/- 4.3 vs. 253.5 +/- 4.3 A, P < 0.01) after adjustment for sex-specific differences in plasma triglyceride levels by covariance analysis. Significant negative correlations were noted between the LDL particle diameter and the triglyceride concentrations in both genders (r = -0.52 and r = -0.36, P < 0.0001 for the men and women, respectively), with no gender difference in this relationship being found. However, viscerally obese women (visceral adipose tissue levels > 100 cm2) with increased plasma triglyceride concentrations (> 2.0 mmol L-1) still had larger LDL particles than viscerally obese men with a similar elevation in their triglyceride levels (251.6 +/- 4.9 vs. 248.7 +/- 4.5 A, P < 0.01).

CONCLUSIONS

Results of the present study suggest that the reduced LDL particle size observed in men compared with women cannot be entirely explained by their higher visceral adipose tissue accumulation and increased plasma triglyceride levels. Moreover, the gender difference in LDL size could be influenced, at least in part, by the severity of the hypertriglyceridaemic state.

Endothelial lipase: a new lipase on the block

Endothelial lipase (EL) is a newly described member of the triglyceride lipase gene family. It has a considerable molecular homology with lipoprotein lipase (LPL) (44%) and hepatic lipase (HL) (41%). Unlike LPL and HL, this enzyme is synthesized by endothelial cells and functions at the site where it is synthesized. Furthermore, its tissue distribution is different from that of LPL and HL. As a lipase, EL has primarily phospholipase A1 activity. Animals that overexpress EL showed reduced HDL cholesterol levels. Conversely, animals that are deficient in EL showed a marked elevation in HDL cholesterol levels, suggesting that it plays a physiologic role in HDL metabolism. Unlike LPL and HL, EL is located in the vascular endothelial cells and its expression is highly regulated by cytokines and physical forces, suggesting that it may play a role in the development of atherosclerosis. However, there is only a limited amount of information available about this enzyme. Some of our unpublished data in addition to previously published data support the possibility that the enzyme plays a role in the formation of atherosclerotic lesion.

High-density lipoproteins and atherosclerosis

High-density lipoproteins (HDLs) are strongly related to risk of atherosclerotic cardiovascular disease. Low levels of HDL cholesterol are a major cardiovascular risk factor, and overexpression of the major HDL protein, apolipoprotein (apo) A-I, markedly inhibits progression and even induces regression of atherosclerosis in animal models. Clinical data regarding the effect of increasing HDL cholesterol on vascular events are limited. HDL remains an important potential target for therapeutic intervention. A variety of gene products are involved in the regulation of HDL metabolism. Yet, the mechanisms by which HDL inhibits atherosclerosis are not yet fully understood. There remains much to be learned about HDL metabolism and its relation to atherosclerosis and other cardiovascular risk factors.

A novel allele in the promoter of the hepatic lipase is associated with increased concentration of HDL-C and decreased promoter activity

Hepatic lipase (HL) is a lipolytic enzyme involved in the metabolism of plasma lipoproteins, especially HDLs. Association of the polymorphisms in the promoter region of the LIPC gene to post-heparin plasma HL activity and the plasma HDL-C concentration has been investigated thoroughly, but to date little is known about this in the Chinese. In the present study, we analyzed the polymorphisms in the promoter region of LIPC gene in Chinese patients with coronary artery disease (CAD) using denaturing high performance liquid chromatography (DHPLC) and DNA sequencing. As the result, a novel single nucleotide polymorphism -586T-to-C was identified and no linkage of this variant with other polymorphisms in the promoter was found. Compared with the nonsymptomatic control subjects, excess of carriers of the -586T/C substitution were detected in the CAD patients (43% vs. 31%, chi(2) = 4.597, degree of freedom = 2, P = 0.032). The -586C allele carriers in the CAD patients had a significantly higher HDL-C level than the noncarriers (1.13 +/- 0.24 mmol/l vs. 0.91 +/- 0.14 mmol/l, P < 0.05). To test the functionality of this substitution, luciferase-reporter assays was performed in HepG2 cells. Promoter activity of the -586C construct was decreased 2-fold than the -586T construct. Our studies suggest that a T-to-C substitution at -586 of the LIPC promoter is associated with a lowered HL activity and that this variation may contribute to the increased plasma HDL-C concentration in the Chinese.

Identification of genetic variants in endothelial lipase in persons with elevated high-density lipoprotein cholesterol

BACKGROUND

Elevated high-density lipoprotein cholesterol (HDL-C) is associated with reduced risk of cardiovascular disease, and variation in HDL-C levels has been shown to be approximately 50% heritable. Overexpression of endothelial lipase (EL), a member of the lipoprotein lipase gene family, markedly reduces HDL-C levels in mouse models. We hypothesized that genetic variation in EL might be associated with elevated HDL-C.

METHODS AND RESULTS

All exons and 1.2 kilobase of promoter of the EL gene were sequenced in 20 unrelated human subjects with high HDL-C levels. A total of 17 variants were identified. Six of these were potentially functional and were confirmed by restriction enzyme analysis. Four variants result in amino acid changes (Gly26Ser, Thr111Ile, Thr298Ser, and Asn396Ser,) and 2 variants were in the promoter (-303A/C and -410C/G). The genotype frequencies of each variant were determined in 176 black controls, 165 white controls, and 123 whites with high HDL-C. The Thr111Ile variant was the most common, with an allele frequency of 10.3% in blacks, 31.2% in white controls, and 32.6% in the high HDL-C group. The remaining variants all had allele frequencies <5.0% but differed in frequency among the 3 groups. Interestingly, Gly26Ser, Thr298Ser, and -303A/C were found in the black and high HDL-C white cohorts but were absent in the control white group.

CONCLUSIONS

Six new potentially functional variants in EL were discovered through sequencing of the EL gene in subjects with high HDL-C levels. Differences in allele frequencies exist between blacks and whites and between control subjects and those with high HDL-C levels.

Changes in LPLa and reverse cholesterol transport variables during 24-h postexercise period

We investigated the time course of exercise-induced lipoprotein lipase activity (LPLa) and reverse cholesterol transport (RCT) during the 24-h postexercise period. Subjects were 10 sedentary normolipidemic males [NTG; fasting triglyceride (TG) = 89.1 +/- 8.6 mg/dl] and 6 hyperlipidemic males (HTG; fasting TG = 296.8 +/- 64.0 mg/dl). Each subject performed a control trial (no exercise) and 4 exercise trials. In the exercise trials, a subject jogged on a treadmill at 60% of his maximal O(2) consumption for 1 h. Pre- and postheparin blood samples were taken before exercise (baseline) and at 4, 8, 12, and 24 h after exercise. There was no group difference in LPLa (P > 0.05) over the time points. When the LPLa data from the two groups were combined, LPLa at 24 h after exercise was higher than baseline or at 4, 8, 12 h after exercise (P < 0.05). Plasma TG and lecithin-cholesterol acyltransferase activity (LCATa) were higher in HTG than in NTG, and the total high-density lipoprotein-cholesterol (HDL(tot)-Chol) was lower in HTG than in NTG (P < 0.05). HDL(2)-Chol, LCATa, and cholesterol ester transfer protein activity did not differ during the 24-h postexercise period (P > 0.05). These results suggest that LPLa is still increasing 24 h after an acute aerobic exercise and that the magnitude of the increase in exercise-induced LPLa in HTG was similar to that in NTG. Furthermore, in the sedentary population with or without HTG, the variables related to RCT do not change during the 24-h period after exercise.

Sources of variability in genetic association studies: insights from the analysis of hepatic lipase (LIPC)

Genetic association studies have been widely used to identify loci that influence plasma lipoprotein concentrations, but few of the associations reported have proved consistently reproducible across different study populations. This lack of consistency is a widely recognized limitation of association studies, and is often ascribed to inadequate statistical power, population substructure, and population-specific linkage disequilibrium. However, few studies have assessed the causes of variability underlying a given genotype-phenotype association. We have examined two possible sources of variability in the association between the -514 polymorphism in hepatic lipase (LIPC) and plasma HDL-C concentrations. First, we compared the association between this polymorphism and hepatic lipase activity in four populations. A single copy of the -514C allele was associated with a 10 mmol.hr(-1).l(-1) increase in hepatic lipase activity in white American and Turkish men but only approximately 5 mmol.hr(-1).l(-1) in Chinese and African-American men. Second, we tested the effects of a stanozolol-induced increase in hepatic lipase activity on plasma HDL-C concentrations in men with normal (< 150mg/dl) or elevated (150-300mg/dl) levels of plasma triglyceride. The increase in hepatic lipase activity was similar in the two groups, but the resulting decline in HDL-C levels was significantly greater in normolipidemic men. These data suggest that the effect of a polymorphism on gene expression can vary among individuals, and that the resulting phenotype may be further modified by interactions with other factors. Three novel LIPC polymorphisms were identified in the study (-1596insC, -2740A>G, and -2880G>C).

Relation of the -514C/T polymorphism in the hepatic lipase gene to serum HDL and LDL cholesterol levels in postmenopausal women under hormone replacement therapy

Hepatic lipase (HL) is a lipolytic enzyme that catalyzes hydrolysis of triglycerides and phospholipids in all major classes of lipoproteins. Recently, a -514C/T polymorphism in the promoter region of the HL gene was found to be associated with variations in hepatic lipase activity and serum high density lipoprotein cholesterol (HDL-C) levels. Postmenopausal hormone replacement therapy (HRT) has known favorable effects on serum lipid and lipoprotein levels. In this study, we examined the relation between the -514C/T polymorphism and serum lipid and lipoprotein levels in postmenopausal women prior to and after 3 months of HRT. Significant associations between the -514 C/T polymorphism and HDL-C, low density lipoprotein cholesterol (LDL-C) and apolipoprotein A-I (apo A-I) levels were observed before and/or after 3 months of HRT. With HRT, serum total cholesterol (TC), LDL-C and apolipoprotein B (apo B) levels were reduced significantly (P=0.0001), and HDL-C and apo A-I levels were increased significantly (P=0.0001). However, the degrees of change in lipid and lipoprotein levels due to HRT did not differ significantly between the HL genotypes.

Lipases and HDL metabolism

Plasma levels of high-density lipoprotein (HDL) cholesterol are strongly inversely associated with atherosclerotic cardiovascular disease, and overexpression of HDL proteins, such as apolipoprotein A-I in animals, reduces progression and even induces regression of atherosclerosis. Therefore, HDL metabolism is recognized as a potential target for therapeutic intervention of atherosclerotic vascular diseases. The antiatherogenic properties of HDL include promotion of cellular cholesterol efflux and reverse cholesterol transport, as well as antioxidant, anti-inflammatory and anticoagulant properties. The molecular regulation of HDL metabolism is not fully understood, but it is influenced by several extracellular lipases. Here, we focus on new developments and insights into the role of secreted lipases on HDL metabolism and their relationship to atherosclerosis.

[Diabetes mellitus, inflammation and coronary atherosclerosis: current and future perspectives]

Type 2 diabetes mellitus is a condition associated with an increased risk of coronary artery disease. This condition is currently reaching epidemic proportions in the Western world. Epidemiological studies have shown that insulin resistance and the constellation of metabolic alterations associated with type 2 diabetes mellitus such as dyslipidaemia, systemic hypertension, obesity and hypercoagulability, have an effect on the premature onset and severity of atherosclerosis. Albeit direct, the link between insulin resistance and atherogenesis is rather complex. It is likely that its complexity relates to the interaction between genes that predispose to insulin resistance and genes that independently regulate lipid metabolism, coagulation processes and biological responses of the arterial wall. The rapid development of molecular biology in recent years has resulted in a better understanding of the immune and inflammatory mechanisms that underlie insulin resistance and atherosclerosis. For example, it is known that nuclear transcription factors such as nuclear factor kappa beta and peroxisome proliferator-activated receptor are involved in atherosclerosis. The former modulates gene expression which encodes pro-inflammatory proteins vital for the development of the atheromatous plaque. In the presence of insulin resistance there are multiple activating factors that could explain the early onset and severity of atherosclerosis. Glitazones, the new oral antidiabetic drugs and agonists of peroxisome proliferator-activated receptor, have been shown to improve peripheral insulin sensitivity and to also delay atherosclerosis progression in experimental models. Their beneficial effects have been linked to their anti-inflammatory effect.

Estrogen increases hepatic lipase levels in inbred strains of mice: a possible mechanism for estrogen-dependent lowering of high density lipoprotein

We have shown mouse to be an useful animal model for studies on the estrogen-mediated synthesis and secretion of lipoproteins since, unlike in rats, low density lipoprotein receptors are not upregulated in mice. This results into the elevation of plasma levels of apolipoprotein (apo) B and apoE, and lowering of apoA-1-containing particles. The mechanisms of apoB and apoE elevation by estrogen have been elucidated, but the mechanism of lowering of plasma levels of HDL is still not known. Among other factors, apoA-I, cholesterol ester transfer protein (CETP), scavenger receptor B1 (SR-B1), and hepatic lipase are potential candidates that modulate plasma levels of HDL. Since estrogen treatment increased hepatic apoA-I mRNA and apoA-I synthesis, and mouse express undetectable levels of CETP, we tested the hypothesis that estradiol-mediated lowering of HDL in mice may occur through modulation of hepatic lipase (HL). Four mouse strains (C57L, C57BL, BALB, C3H) were administered supraphysiological doses of estradiol, and plasma levels of HDL as well as HL mRNA were quantitated. In all 4 strains estradiol decreased plasma levels of HDL by 30%, and increased HL mRNA 2-3 fold. In a separate experiment groups of male C57BL mouse were castrated or sham-operated, and low and high doses of estradiol administered. We found 1.4-2.5 fold elevation of HL mRNA with concomitant lowering of HDL levels. Ten other mouse strains examined also showed estradiol-induced elevation of HL mRNA, but the extent of elevation was found to be strain-specific. Based on these studies, we conclude that hepatic lipase is an important determinant of plasma levels of HDL and that HL mRNA is modulated by estrogen which in turn may participate in the lowering of plasma levels of HDL.

Hypertriglyceridemia: associated risks and effect of drug treatment

Accumulating evidence indicates that hypertriglyceridemia (HTG) is a risk factor for cardiovascular disease. This increased risk is probably substantially mediated through the metabolic interrelationships between serum triglyceride (TG) levels and other risk factors, such as the atherogenic lipid profile (low high density lipoprotein-cholesterol levels and elevated small dense low density lipoprotein levels), insulin resistance, a prothrombotic propensity and low grade systemic inflammation. TG-lowering strategy in patients with HTG encompasses dietary modification and pharmacological agents, such as fibric acid derivatives, fish-oil and hydroxymethylglutaryl coenzyme A reductase inhibitors, which have, besides their known effects on the atherogenic lipid profile, beneficial effects on other determinants of cardiovascular disease. However, in spite of data from trials investigating fibric acid derivative-induced reduction in coronary events in patients with distinct types of hyperlipidemia, no specific trials have been performed that investigated this risk reduction in patients with HTG, in whom other cardiovascular risk factors are clustered as well. Small-scale studies on determinants of cardiovascular disease in patients with HTG and post-hoc analyses of the Helsinki Heart, Veterans Affairs High-Density Lipoprotein Cholesterol Intervention Trial and Bezafibrate Infarction Prevention trials in patients with high serum TG levels suggest a drug-induced reduction in cardiovascular events. However, a specific trial should be conducted to investigate the effects of lipid-lowering therapy on clinical end-points in patients with HTG of defined types.

Alterations of lipolytic enzymes and high-density lipoprotein subfractions induced by physical activity in type 2 diabetes mellitus

OBJECTIVE

This study investigates the effects of regular moderate physical activity on lipolytic enzymes and plasma lipid concentration, particularly high-density lipoprotein cholesterol (HDL-C) subfractions, in patients with type 2 diabetes mellitus.

DESIGN

Ten patients participated in a 3-month exercise programme without any changes in current medical therapy. The control group consisted of six patients who were matched with regard to sex, age, diabetes duration and diabetes therapy.

RESULTS

Mean (+/- SE) physical activity in the intervention group increased from 70 +/- 21 to 220 +/- 28 min per week, which resulted in an increase in total HDL-C from 1.04 +/- 0.07 to 1.28 +/- 0.12 (P < 0.001). The HDL3-C subfraction increased from 0.71 +/- 0.08 to 0.86 +/- 0.08 mM (P = 0.01) with no significant changes in the HDL2-C subfraction (0.33 +/- 0.04 vs. 0.42 +/- 0.05). These changes were paralleled by an 85% increase in hepatic lipase (HL) activity, from 25.7 +/- 5.1 to 47.4 +/- 4.9 micromol x mL(-1) x h(-1) (P < 0.001) and a 45% increase in lipoprotein lipase (LPL) activity, from 16.8 +/- 3.0-24.3 +/- 2.7 micromol x mL(-1) x h(-1) (P = 0.01). Lecithin-cholesterol acyl-transferase (LCAT) activity increased by 32%, from 156 +/- 26 to 206 +/- 32 nmol x mL(-1) x h(-1) (P < 0.001). In the control group there were no significant changes in any of the variables assessed.

CONCLUSIONS

Regular moderate physical activity in patients with type 2 diabetes led to an overall increase in HL, LPL, and LCAT. HL showed a more pronounced increase than LPL and LCAT. The changes in lipolytic and transferase enzyme pattern resulted in a significant increase of plasma HDL-C, mainly of the HDL3-C subfraction.

High-density lipoprotein metabolism: molecular targets for new therapies for atherosclerosis

New therapeutic approaches to the prevention and treatment of atherosclerotic cardiovascular disease (ASCVD) are needed. Plasma levels of high-density lipoprotein (HDL) cholesterol are inversely associated with risk of ASCVD. Genes involved in the metabolism of HDL represent potential targets for the development of such therapies. Because HDL metabolism is a dynamic process, the effect of a specific HDL-oriented intervention on atherosclerosis cannot necessarily be predicted by its effect on the plasma HDL cholesterol level. Based on available data in animal models, some gene products are candidates for pharmacologic upregulation, infusion, or overexpression, including apolipoprotein (apo)A-I, apoE, apoA-IV, lipoprotein lipase (LPL), ATP-binding cassette protein 1 (ABC1), lecithin cholesterol acyltransferase (LCAT), and scavenger receptor B-I (SR-BI). In contrast, some gene products are potential candidates for inhibition, including apoA-II, cholesteryl ester transfer protein (CETP), and hepatic lipase. The next decade will witness the transition from preclinical studies to clinical trials of a variety of new therapies targeted toward HDL metabolism and atherosclerosis.

High density lipoprotein, apolipoprotein A-I, and coronary artery disease

High density lipoproteins (HDL), one of the main lipoprotein particles circulating in plasma, is involved in the reverse cholesterol transport. Several lines of evidence suggest that elevated levels of HDL is protective against coronary heart disease. The role of HDL in the removal of body cholesterol and in the regression of atherosclerosis add to the importance of understanding the molecular-cellular processes that determine plasma levels of HDL. Factors modulating plasma levels of HDL may have influence on the predisposition of an individual to premature coronary artery disease. Apolipoprotein (apo) A-I is the main apolipoprotein component of HDL and, to a large extent, sets the plasma levels of HDL. Thus, understanding the regulation of apoA-I gene expression may provide clues to raise plasma levels of HDL. This review discusses the various pathways that alter plasma levels of HDL. Since apoA-I is the main protein component of HDL and determines the plasma levels of HDL, this review also covers the regulation of apoA-I gene expression.

Hepatic lipase and HDL metabolism

Hepatic lipase is a lipolytic enzyme that has been suggested to have a role in HDL metabolism. Evidence suggests that HDL-cholesterol level is at least partly regulated by hepatic lipase level. Recent studies have shown that hepatic lipase not only hydrolyzes triglyceride and phospholipid in HDL, but also stimulates HDL cholesterol ester uptake by hepatocytes. Therefore, hepatic lipase, together with lipid transfer proteins, determines both HDL-cholesterol level and its function in reverse cholesterol transport. These conclusions are based on observations from in-vitro model substrate studies, cell culture studies, transgenic animal studies, and clinical studies. At present time, it is not known whether hepatic lipase action increases or decreases risk of developing atherosclerosis.