Endothelial lipase and HDL metabolism

Effect of Selective Androgen Receptor Modulator on Cholesterol Efflux Capacity, Size and Subspecies of HDL Particles

Context

Selective androgen receptor modulators (SARMs), because of their preferential muscle vs prostate selectivity, are being developed for muscle-wasting conditions. Oral SARMs suppress high-density lipoprotein cholesterol (HDL-C) but their effects on functional capacity and atherogenic potential of HDL particles are unknown.

Objective

To determine the effects of an oral SARM (OPK-88004) on cholesterol efflux capacity, HDL particle number and size, apolipoprotein particle number and size and HDL subspecies

Methods

We measured cholesterol efflux capacity (CEC); HDL particle number and size; APOB; APOA1; and protein-defined HDL subspecies associated with coronary heart disease (CHD) risk in men, who had undergone prostatectomy for low-grade prostate cancer during 12-week treatment with placebo or 1, 5, or 15 mg of an oral SARM (OPK-88004).

Results

SARM significantly suppressed HDL-C (P < .001) but HDL particle size did not change significantly. SARM had minimal effect on CEC of HDL particles (change + 0.016, –0.036, +0.070, and –0.048%/µmol-HDL/L^–1 at 0, 1, 5, and 15 mg SARM, P = .045). SARM treatment suppressed APOAI (P < .001) but not APOB (P = .077), and reduced APOA1 in HDL subspecies associated with increased (subspecies containing α2-macroglobulin, complement C3, or plasminogen) as well as decreased (subspecies containing APOC1 or APOE) CHD risk; relative proportions of APOA1 in these HDL subspecies did not change. SARM increased hepatic triacylglycerol lipase (HTGL) (P < .001).

Conclusion

SARM treatment suppressed HDL-C but had minimal effect on its size or cholesterol efflux function. SARM reduced APOA1 in HDL subspecies associated with increased as well as decreased CHD risk. SARM-induced increase in HTGL could contribute to HDL-C suppression. These data do not support the simplistic notion that SARM-associated suppression of HDL-C is necessarily proatherogenic; randomized trials are needed to determine SARM’s effects on cardiovascular events.

Effect of thyroid function on pre-β1 high-density lipoprotein levels in patients with Graves' disease undergoing radioiodine treatment

CONTEXT

The metabolism of HDL is altered in thyroid dysfunctions. Preβ-1 HDL is a very small discoidal precursor HDL and promotes cholesterol efflux via ABCA₁. The effects of thyroid dysfunctions on pre-β1 HDL are unknown. Thyroid hormone regulates ANGPTL3 expression, which may participate in HDL metabolism in thyroid dysfunctions.

OBJECTIVE

To determine the variation of HDL subfractions, especially preβ-1 HDL in thyroid dysfunctions, and whether ANGPTL3 mediates the effect of thyroid function on HDL metabolism.

METHODS

We recruited 26 patients with Graves' disease undergoing radioiodine treatment. They were evaluated at three time points: at baseline, when they were hypothyroid after radioiodine treatment, and when they were on stable levothyroxine replacement and euthyroid.

RESULTS

The concentrations of smaller HDL particles Preβ-1 HDL and HDL3 were highest at the hyperthyroid state, and lowest at the hypothyroid state. While the larger HDL particles HDL2 and HDL1 changed just the opposite. Preβ1-HDL and HDL3 were positively correlated to fT₃ and fT₄, while were negatively correlated to TSH. In contrast, HDL1 was negatively associated with fT₃ and fT₄, while was positively associated with TSH. The correlations between thyroid hormones and HDL subfractions remained significant after adjusting for ANGPTL3.

CONCLUSIONS

There is a shift form smaller HDL particles pre-β1 HDL and HDL3 to larger HDL particles HDL2 and HDL1 in hypothyroidism, while the change is just the opposite in hyperthyroidism. In future, cholesterol efflux capacity should be measured to determine if the function of HDL particles also changes with the shifting of HDL subfractions.

Iran diabetes research study; knowledge discovery in diagnosis: a scoping review

Introduction

The rising prevalence of diabetes shows high health and socio-economic burdens. Therefore, the development and evaluation of new diagnostic methods may improve the detection of disease and its complications in the early stages. This study aimed to analyze the scope of the studies related to diabetes diagnosis.

Material and method

Publications from January 2015 until December 2019 (5 years) were searched with keywords of (diabetes OR diabetic) AND (Iran) in Scopus and PubMed databases. All data were reviewed by two reviewers and the included publications were categorized based on the subjects, study design, and publication year.

Results

Based on the selected criteria, 103 articles were included. The highest number of publications was observed in 2019. The trend of publication was slightly increased during the study period (2015-2019). Case-control and cross-sectional studies were the most common type of study design used in the included documents. Publications in the field of diagnostic models, biomarkers, and biosensors from 2015 to 2019 showed an increasing trend compared to others subjects.

Discussion and conclusion

Studies about proper diabetes diagnostic procedures such as new diagnostic techniques, using diagnostic models, and evaluation of new diagnostic biomarkers in Iran are remarkably increased. However, more original and review studies are needed to improve scientific methods in the field of early detection of diabetes.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40200-021-00843-x.

Exercise and Health-Related Risks of Physical Deconditioning After Spinal Cord Injury

A sedentary lifestyle occurring soon after spinal cord injury (SCI) may be in contrast to a preinjury history of active physical engagement and is thereafter associated with profound physical deconditioning sustained throughout the lifespan. This physical deconditioning contributes in varying degrees to lifelong medical complications, including accelerated cardiovascular disease, insulin resistance, osteopenia, and visceral obesity. Unlike persons without disability for whom exercise is readily available and easily accomplished, exercise options for persons with SCI are more limited. Depending on the level of injury, the metabolic responses to acute exercise may also be less robust than those accompanying exercise in persons without disability, the training benefits more difficult to achieve, and the risks of ill-considered exercise both greater and potentially irreversible. For exercise to ultimately promote benefit and not impose additional impairment, an understanding of exercise opportunities and risks if exercise is undertaken by those with SCI is important. The following monograph will thus address common medical challenges experienced by persons with SCI and typical modes and benefits of voluntary exercise conditioning.

Caryocar coriaceum Wittm. (Pequi) fixed oil presents hypolipemic and anti-inflammatory effects in vivo and in vitro

Caryocar coriaceum Wittm. (Pequi) is found in southern Ceará, where the fruit is used as food and in folk medicine as an anti-inflammatory, and to promote healing. However, little is known about the effects of repeated administration of its oil on the biochemical parameters of the blood. This work aimed to evaluate the effects Caryocar coriaceum fixed oil (OFCC); on the lipid profiles of healthy mice, on dyslipidemia induced by tyloxapol, and to study its anti-inflammatory effect both in vivo and in vitro. The results revealed significant reduction in total serum cholesterol and triglycerides, and an increase in HDL-C. The paw edema (induced by carrageenan) and myeloperoxidase (MPO), in polymorphonuclear culture cells, was reduced at all dose levels. Results demonstrated that Caryocar coriaceum's fix oil present anti-inflammatory activity and, for the first time describe the hypolipidemic effects, supporting its traditional use and suggest that present a potential cardioprotective effect.

Effects of Regular Recreational Exercise Training on Serum ANGPTL3-Like Protein and Lipid Profile in Young Healthy Adults

Evidence of the role of ANGPTL3, a liver-secreted glycoprotein, in serum lipid turnover, led us to hypothesize that this protein may be involved in modification of the lipid profile induced by exercise-training. Given the lack of data regarding this issue, the main goal of the present study was to investigate the effects of regular participation in a recreational physical activity program on serum ANGPTL3 and selected lipid profile measures in young, apparently healthy female and male adults. We compared serum ANGPTL3, lipid profile measures, common lipid ratios, the Atherogenic Index of Plasma (AIP) and glucose in fasting blood samples derived from 22 active physical education students including active females (AF, N=6) and males (AM, N=16) with samples from 28 relatively sedentary age-matched peers, including female (SF, N=9) and male (SM, N=19) individuals not involved in any regular physical conditioning program. Despite high inter-individual variability of serum ANGPTL3, there was a general tendency toward higher serum ANGPTL3 and HDL-C in women compared to men, but without significant differences related to their physical activity status. Based on both routine lipid profile measures and lipid ratios, all participants had normal lipid profiles, normal glycemia, as well as favorable anthropometric indices not suggesting increased cardiometabolic risk. However, lower levels of the TG/HDL-C ratio and AIP in physically active compared to relatively sedentary participants, reflecting the predominance of large, buoyant LDL particles, strongly support the view of beneficial health-promoting effects of regular participation in recreational sport activities.

The Regulation of Reverse Cholesterol Transport and Cellular Cholesterol Homeostasis by MicroRNAs

MicroRNAs (miRNAs) are small, non-coding RNAs that have the ability to post-transcriptionally regulate gene expression. Hundreds of miRNAs have been identified in humans and they are involved in the regulation of almost every process, including cholesterol transport, metabolism, and maintenance of cholesterol homeostasis. Because of their small size and their ability to very specifically regulate gene expression, miRNAs are attractive targets for the regulation of dyslipidemias and other lipid-related disorders. However, the complex interactions between miRNAs, transcription factors, and gene expression raise great potential for side effects as a result of miRNA overexpression or inhibition. Many dietary components can also target specific miRNAs, altering the expression of downstream genes. Therefore, much more research is necessary to fully understand the role(s) of each miRNA in the body and how they may be impacted by diet and health. The present review aims to summarize the known roles of miRNAs in the regulation of reverse cholesterol transport and the maintenance of cholesterol homeostasis, as well as the potential clinical consequences of their manipulation.

Interactions of the LIPG 584C>T polymorphism and alcohol consumption on serum lipid levels

Both endothelial lipase gene (LIPG) 584C>T (rs2000813) polymorphism and alcohol consumption modulate serum lipid levels. But their interactions on serum lipid profiles are not well known. The present study was undertaken to detect the interactions of LIPG 584C>T polymorphism and alcohol consumption on serum lipid levels. Genotyping of the LIPG 584C>T was performed in 763 unrelated nondrinkers and 520 drinkers aged 15-85 years. The levels of serum total cholesterol (TC), triglyceride (TG), high-density lipoprotein cholesterol (HDL-C), apolipoprotein (Apo) AI, and the ratio of ApoAI to ApoB were higher in drinkers than in nondrinkers (P<.01 for all). There were no significant differences in the genotypic and allelic frequencies between nondrinkers and drinkers. The levels of TC, HDL-C, and ApoAI in nondrinkers were different among the three genotypes (P<.05-.01), the subjects with CT genotype had higher TC, HDL-C, and ApoAI levels than the subjects with CC genotype. The levels of HDL-C and ApoAI in drinkers were different among the three genotypes (P<.001 and P<.05; respectively), the individuals with TT genotype had higher HDL-C and ApoAI levels than the individuals with CT and CC genotypes. The interactions between LIPG 584C>T genotypes and alcohol consumption on serum HDL-C (P<.01) and ApoAI levels (P<.05) were also detected by using a factorial regression analysis after controlling for potential confounders. The levels of TC in nondrinkers were correlated with LIPG 584C>T alleles (P<.05), whereas the levels of TG and HDL-C were associated with LIPG 584C>T alleles (P<.05) and genotypes (P<.05), respectively. These results suggest that the subjects with TT genotype benefit more from alcohol consumption than the subjects with CT and CC genotypes in increasing serum HDL-C and ApoAI levels.

O-glycosylation modulates proprotein convertase activation of angiopoietin-like protein 3: possible role of polypeptide GalNAc-transferase-2 in regulation of concentrations of plasma lipids

The angiopoietin-like protein 3 (ANGPTL3) is an important inhibitor of the endothelial and lipoprotein lipases and a promising drug target. ANGPTL3 undergoes proprotein convertase processing (RAPR(224)↓TT) for activation, and the processing site contains two potential GalNAc O-glycosylation sites immediately C-terminal (TT(226)). We developed an in vivo model system in CHO ldlD cells that was used to show that O-glycosylation in the processing site blocked processing of ANGPTL3. Genome-wide SNP association studies have identified the polypeptide GalNAc-transferase gene, GALNT2, as a candidate gene for low HDL and high triglyceride blood levels. We hypothesized that the GalNAc-T2 transferase performed critical O-glycosylation of proteins involved in lipid metabolism. Screening of a panel of proteins known to affect lipid metabolism for potential sites glycosylated by GalNAc-T2 led to identification of Thr(226) adjacent to the proprotein convertase processing site in ANGPTL3. We demonstrated that GalNAc-T2 glycosylation of Thr(226) in a peptide with the RAPR(224)↓TT processing site blocks in vitro furin cleavage. The study demonstrates that ANGPTL3 activation is modulated by O-glycosylation and that this step is probably controlled by GalNAc-T2.

Association of the LIPG 584C > T polymorphism and serum lipid levels in the Guangxi Bai Ku Yao and Han populations

BACKGROUND

Endothelial lipase (EL) is a major determinant of high-density lipoprotein-cholesterol (HDL-C) metabolism, but the association of endothelial lipase gene (LIPG) polymorphism and serum HDL-C levels is scarce and conflicting in diverse populations. Bai Ku Yao is an isolated subgroup of the Yao minority in China. This study was designed to detect the association of LIPG 584C > T (rs2000813) polymorphism and several environmental factors with serum lipid levels in the Guangxi Bai Ku Yao and Han populations.

METHODS

A total of 645 subjects of Bai Ku Yao and 638 participants of Han Chinese were randomly selected from our previous stratified randomized cluster samples. Genotyping of the LIPG 584C > T was performed by polymerase chain reaction and restriction fragment length polymorphism combined with gel electrophoresis, and then confirmed by direct sequencing.

RESULTS

The levels of serum total cholesterol (TC), HDL-C, low-density lipoprotein cholesterol (LDL-C) and apolipoprotein (Apo) AI and ApoB were lower in Bai Ku Yao than in Han (P < 0.05 - 0.001). The frequency of C and T alleles was 73.5% and 26.5% in Bai Ku Yao, and 67.9% and 32.1% in Han (P < 0.01); respectively. The frequency of CC, CT and TT genotypes was 50.4%, 46.2% and 3.4% in Bai Ku Yao, and 41.4%, 53.1% and 5.5% in Han (P < 0.01); respectively. Serum HDL-C levels in both ethnic groups were different among the three genotypes (P < 0.05 for each). Serum TC levels in both ethnic groups were also different between the CC and CT/TT genotypes (P < 0.05 for each). The T allele carriers had higher serum HDL-C and TC levels than the T allele noncarriers. Multivariate logistic regression analysis showed that the levels of HDL-C and ApoB were correlated with genotypes in Bai Ku Yao (P < 0.05 for each), whereas the levels of TC and HDL-C were associated with genotypes in Han Chinese (P < 0.05 and P < 0.01). Serum lipid parameters were also correlated with several environmental factors in the both ethnic groups.

CONCLUSIONS

The frequency of LIPG 584T allele is lower in Bai Ku Yao than in Han Chinese. The LIPG 584T allele is associated with increased serum HDL-C, TC and ApoB levels. The differences in serum HDL-C, TC and ApoB levels between the two ethnic groups might partly result from different genotypic and allelic frequencies of LIPG 584C > T or different LIPG-enviromental interactions.

High density lipoprotein structure-function and role in reverse cholesterol transport

High density lipoprotein (HDL) possesses important anti-atherogenic properties and this review addresses the molecular mechanisms underlying these functions. The structures and cholesterol transport abilities of HDL particles are determined by the properties of their exchangeable apolipoprotein (apo) components. ApoA-I and apoE, which are the best characterized in structural terms, contain a series of amphipathic alpha-helical repeats. The helices located in the amino-terminal two-thirds of the molecule adopt a helix bundle structure while the carboxy-terminal segment forms a separately folded, relatively disorganized, domain. The latter domain initiates lipid binding and this interaction induces changes in conformation; the alpha-helix content increases and the amino-terminal helix bundle can open subsequently. These conformational changes alter the abilities of apoA-I and apoE to function as ligands for their receptors. The apoA-I and apoE molecules possess detergent-like properties and they can solubilize vesicular phospholipid to create discoidal HDL particles with hydrodynamic diameters of ~10 nm. In the case of apoA-I, such a particle is stabilized by two protein molecules arranged in an anti-parallel, double-belt, conformation around the edge of the disc. The abilities of apoA-I and apoE to solubilize phospholipid and stabilize HDL particles enable these proteins to be partners with ABCA1 in mediating efflux of cellular phospholipid and cholesterol, and the biogenesis of HDL particles. ApoA-I-containing nascent HDL particles play a critical role in cholesterol transport in the circulation whereas apoE-containing HDL particles mediate cholesterol transport in the brain. The mechanisms by which HDL particles are remodeled by lipases and lipid transfer proteins, and interact with SR-BI to deliver cholesterol to cells, are reviewed.

Dietary diacylglycerol oil has no effect on hypertriacylglycerolaemia in lipoprotein lipase-deficient cats

A commercially available vegetable oil containing a high concentration (87 %, w/w) of diacylglycerol (DAG) has been investigated in humans and animals for potential beneficial effects in reducing serum TAG concentrations in fasting and postprandial states. Effects of DAG oil as a sole dietary fat source (25 % metabolisable energy) were evaluated in a feline model of hypertriacylglycerolaemia. Eleven adult (1.5 (sem 0.1) years) male cats deficient of lipoprotein lipase (LPL) catalytic activity from a heritable point mutation of the LPL gene were acclimatised to a semi-purified diet containing TAG oil for 21 d. After assignment into two groups, pair-matched by serum TAG concentrations (range 6.1-31.6 mmol/l), the cats were fed the diet with either TAG or DAG oil for 8 d. The dietary fat source was crossed-over and presented for 8 d more. Non-fasting serum concentrations of TAG, cholesterol and NEFA were measured on days 6-8 and days 14-16. Dietary fat source (DAG v. TAG) did not significantly affect food intake (491 (sem 16) v. 486 (sem 14) kJ/kg0.67), body weight or serum concentrations (mmol/l) of TAG (37.1 (sem 4.5) v. 33.9 (sem 3.4)), cholesterol (4.8 (sem 0.3) v. 4.8 (sem 0.2)) and NEFA (1.4 (sem 0.2) v. 1.4 (sem 0.2)). The results show that for a feeding trial of 8 d, DAG oil was well accepted and tolerated by cats but did not reduce hypertriacylglycerolaemia resulting from a deficiency of LPL catalytic activity.

Genetic-epidemiological evidence on genes associated with HDL cholesterol levels: a systematic in-depth review

High-density lipoprotein (HDL) particles exhibit multiple antiatherogenic effects. They are key players in the reverse cholesterol transport which shuttles cholesterol from peripheral cells (e.g. macrophages) to the liver or other tissues. This complex process is thought to represent the basis for the antiatherogenic properties of HDL particles. The amount of cholesterol transported in HDL particles is measured as HDL cholesterol (HDLC) and is inversely correlated with the risk for coronary artery disease: an increase of 1mg/dL of HDLC levels is associated with a 2% and 3% decrease of the risk for coronary artery disease in men and women, respectively. Genetically determined conditions with high HDLC levels (e.g. familial hyperalphalipoproteinemia) often coexist with longevity, and higher HDLC levels were found among healthy elderly individuals. HDLC levels are under considerable genetic control with heritability estimates of up to 80%. The identification and characterization of genetic variants associated with HDLC concentrations can provide new insights into the background of longevity. This review provides an extended overview on the current genetic-epidemiological evidence from association studies on genes involved in HDLC metabolism. It provides a path through the jungle of association studies which are sometimes confusing due to the varying and sometimes erroneous names of genetic variants, positions and directions of associations. Furthermore, it reviews the recent findings from genome-wide association studies which have identified new genes influencing HDLC levels. The yet identified genes together explain only a small amount of less than 10% of the HDLC variance, which leaves an enormous room for further yet to be identified genetic variants. This might be accomplished by large population-based genome-wide meta-analyses and by deep-sequencing approaches on the identified genes. The resulting findings will probably result in a re-drawing and extension of the involved metabolic pathways of HDLC metabolism.

A high-throughput screen for endothelial lipase using HDL as substrate

Endothelial lipase (EL) is a 482-amino-acid protein from the triglyceride lipase gene family that uses a Ser-His-Asp triad for catalysis. Its expression in endothelial cells and preference for phospholipids rather than triglycerides are unique. Animal models in which it is overexpressed or knocked out indicate EL levels are inversely correlated with high-density lipoprotein cholesterol (HDL-C). HDL-C is commonly referred to as the good form of cholesterol because it is involved in the reverse cholesterol transport pathway, in which excess cholesterol is effluxed from peripheral tissues for excretion or reabsorption. Thus, EL inhibition in humans is expected to lead to increases in HDL levels and possibly a decrease in cardiovascular disease. To discover inhibitors of EL, a coupled assay for EL has been developed, using its native substrate, HDL. Hydrolysis of HDL by EL yields free fatty acids, which are coupled through acyl-CoA synthetase, acyl-CoA oxidase, and horseradish peroxidase to produce the fluorescent species resorufin. This assay was developed into a 5-microL, 1536-well assay format, and a high-throughput screen was executed against the GSK collection. In addition to describing the screening results, novel post-HTS mechanism-of-action studies were developed for EL and applied to 1 of the screening hits as an example.

Endothelial lipase gene polymorphism is associated with acute myocardial infarction, independently of high-density lipoprotein-cholesterol levels

BACKGROUND

Endothelial lipase (EL) is a major determinant of high-density lipoprotein-cholesterol (HDL-C) metabolism and promotes monocytes recruitment. The local expression of EL could influence atherogenesis directly, in addition to its systemic role in HDL metabolism. The EL gene has a common 584C/T polymorphism, but it is unclear whether this polymorphism is associated with HDL-C levels or acute myocardial infarction (AMI).

METHODS AND RESULTS

A case-control study of 107 AMI patients and 107 control subjects was conducted. T allele frequency was lower in the AMI group than in controls (0.18 vs 0.26, p<0.05). No significant association was found between the 584C/T polymorphism and HDL-C levels. Multivariate regression analyses showed that the association of the T allele with AMI was statistically significant and independent of other risk factors when age, sex, hypertension, hypercholesterolemia, and diabetes mellitus were included in the analyses (odds ratio (OR), 0.52; 95% confidence interval (95% CI) 0.28-0.98; p=0.04). However, when smoking status was included, the association of the T allele with AMI did not remain statistically significant (OR, 0.61; 95% CI 0.32-1.18; p=0.14).

CONCLUSIONS

The 584C/T polymorphism of the EL gene was associated with AMI independently of HDL-C levels and thus may be involved in the pathogenesis of AMI.

Coordinate up-regulation of TMEM97 and cholesterol biosynthesis genes in normal ovarian surface epithelial cells treated with progesterone: implications for pathogenesis of ovarian cancer

Background

Ovarian cancer (OvCa) most often derives from ovarian surface epithelial (OSE) cells. Several lines of evidence strongly suggest that increased exposure to progesterone (P4) protects women against developing OvCa. However, the underlying mechanisms of this protection are incompletely understood.

Methods

To determine downstream gene targets of P4, we established short term in vitro cultures of non-neoplastic OSE cells from six subjects, exposed the cells to P4 (10^-6 M) for five days and performed transcriptional profiling with oligonucleotide microarrays containing over 22,000 transcripts.

Results

We identified concordant but modest gene expression changes in cholesterol/lipid homeostasis genes in three of six samples (responders), whereas the other three samples (non-responders) showed no expressional response to P4. The most up-regulated gene was TMEM97 which encodes a transmembrane protein of unknown function (MAC30). Analyses of outlier transcripts, whose expression levels changed most significantly upon P4 exposure, uncovered coordinate up-regulation of 14 cholesterol biosynthesis enzymes, insulin-induced gene 1, low density lipoprotein receptor, ABCG1, endothelial lipase, stearoyl- CoA and fatty acid desaturases, long-chain fatty-acyl elongase, and down-regulation of steroidogenic acute regulatory protein and ABCC6. Highly correlated tissue-specific expression patterns of TMEM97 and the cholesterol biosynthesis genes were confirmed by analysis of the GNF Atlas 2 universal gene expression database. Real-time quantitative RT-PCR analyses revealed 2.4-fold suppression of the TMEM97 gene expression in short-term cultures of OvCa relative to the normal OSE cells.

Conclusion

These findings suggest that a co-regulated transcript network of cholesterol/lipid homeostasis genes and TMEM97 are downstream targets of P4 in normal OSE cells and that TMEM97 plays a role in cholesterol and lipid metabolism. The P4-induced alterations in cholesterol and lipid metabolism in OSE cells might play a role in conferring protection against OvCa.

Protective effect of an endothelial lipase gene variant on coronary artery disease in a Chinese population

The aim of the present study was to assess the influence of the endothelial lipase (EL) gene 584C/T variant, which results in a change at codon 111 of the EL gene from threonine to isoleucine, on the risk of coronary artery disease (CAD) in a Chinese population. The study population consisted of 265 CAD patients and 265 age- and sex-matched control subjects. The T allele frequency was significantly lower among CAD patients than among control subjects (18.3% vs. 29.8%; P < 0.001). In both the CAD and control groups, the T allele carriers had higher high density lipoprotein cholesterol (HDL-C) levels than homozygote C allele carriers. In a multiple logistic regression model adjusted for age, sex, body mass index, smoking, hypertension, diabetes, hyperlipidemia, and low density lipoprotein cholesterol, a significantly decreased risk of developing CAD was found in subjects carrying a variant CT or TT genotype (odds ratio = 0.496, 95% confidence interval = 0.341-0.723; P < 0.001), and the significance persisted after further adjustment for HDL-C. In conclusion, our observation that the EL 584T allele was associated with protection from CAD in this Chinese population replicates the findings in a Japanese study, which found a similar association of this allele with acute myocardial infarction, independent of HDL-C levels.

Endothelial lipase and the metabolic syndrome

PURPOSE OF REVIEW

Several in-vitro and in-vivo animal studies indicate that endothelial lipase plays a key role in the intravascular remodeling of lipoproteins, particularly HDL. This review integrates this body of knowledge with more recent data in humans linking endothelial lipase to HDL metabolism and other features of the metabolic syndrome.

RECENT FINDINGS

Human studies generally support the involvement of endothelial lipase in modulating plasma HDL. The association between endothelial lipase and metabolism of apolipoprotein B-containing lipoproteins in humans, however, has not been entirely consistent with previous findings in vitro and in animals. Finally, elevated plasma endothelial lipase has been associated with abdominal obesity and hypertension, and there is now compelling evidence that inflammation and in-vivo regulation of endothelial lipase may be intrinsically related.

SUMMARY

Accumulating evidence indicates that endothelial lipase plays a role in the etiology of the atherogenic plasma lipoprotein profile characteristic of the metabolic syndrome. Increased endothelial lipase activity is linked to the underlying proinflammatory state in this condition. Further studies are required, however, to define the extent to which endothelial lipase contributes to the dyslipidemia of the metabolic syndrome relative to other important regulating factors, such as lipoprotein lipase, hepatic lipase, and cholesterol ester transfer protein.

Fluorogenic substrates for high-throughput measurements of endothelial lipase activity

Endothelial lipase (EL) has been shown to be a critical determinant for high density lipoprotein cholesterol levels in vivo; therefore, assays that measure EL activity have become important for the discovery of small molecule inhibitors that specifically target EL. Here, we describe fluorescent Bodipy-labeled substrates that can be used in homogeneous, ultra-high-throughput kinetic assays that measure EL phospholipase or triglyceride lipase activities. Triton X-100 detergent micelles and synthetic HDL particles containing Bodipy-labeled phospholipid or Bodipy-labeled triglyceride substrates were shown to be catalytic substrates for EL, LPL, and HL. More importantly, only synthetic HDL particles containing Bodipy-labeled triglyceride were ideal substrates for EL, LPL, and HL in the presence of high concentrations of human or mouse serum. These data suggest that substrate presentation is a critical factor when determining EL activity in the presence of serum.

Endothelial and lipoprotein lipases in human and mouse placenta

Placenta expresses various lipase activities. However, a detailed characterization of the involved genes and proteins is lacking. In this study, we compared the expression of endothelial lipase (EL) and LPL in human term placenta. When placental protein extracts were separated by heparin-Sepharose affinity chromatography, the EL protein eluted as a single peak without detectable phospholipid or triglyceride (TG) lipase activity. The major portion of LPL protein eluted slightly after EL. This peak also had no lipase activity and most likely contained monomeric LPL. Fractions eluting at a higher NaCl concentration contained small amounts of LPL protein (most likely dimeric LPL) and had substantial TG lipase activity. In situ hybridization studies showed EL mRNA expression in syncytiotrophoblasts and endothelial cells and LPL mRNA in syncytiotrophoblasts. In contrast, immunohistochemistry showed EL and LPL protein associated with both cell types. In mouse placentas, lack of LPL expression resulted in increased EL mRNA expression. These results suggest that the cellular expression of EL and LPL in human placenta is different. Nevertheless, the two lipases might have overlapping functions in the mouse placenta. Our data also suggest that the major portions of both proteins are stored in an inactive form in human term placenta.

Proprotein Covertases Are Responsible for Proteolysis and Inactivation of Endothelial Lipase

Plasma lipoprotein metabolism is tightly regulated by several members of the triglyceride lipase family, including endothelial lipase (EL) and lipoprotein lipase (LPL). Our previous work suggested that EL is proteolytically processed. In this report, we have used a combination of epitope tagging, mutagenesis, and N-terminal sequencing to determine the precise location of the cleavage site within EL. The cleavage occurs immediately after the sequence RNKR, a known recognition sequence for the proprotein convertase (PC) family. We demonstrate that some PCs, but not all, can proteolytically cleave EL at this site and thereby directly regulate EL enzymatic activity through modulating EL cleavage. Furthermore, specific knockdown of individual PCs proves that PCs are the proteases that cleave EL in human endothelial cells. Interestingly, a homologous site in LPL is also cleaved by PCs. This action is unusual for PCs, which are traditionally known as activators of pro-proteins, and highlights a potential role of PCs in lipid metabolism through their proteolytic processing of lipases.

Effects of fluvastatin slow-release (XL 80 mg) versus simvastatin (20 mg) on the lipid triad in patients with type 2 diabetes

The lipid triad is the association of small, dense (sd) low-density lipoprotein (LDL), low high-density lipoprotein (HDL), and hypertriglyceridemia, all of which play a role in coronary artery disease in patients with type 2 diabetes. Although statins have demonstrated clear positive effects on cardiovascular morbidity/mortality in patients with diabetes and on single components of the lipid triad, it remains controversial whether they affect all components of the triad in these patients. Therefore, we performed a single-center, parallel-group, prospective, randomized, open-label, blinded-endpoint (PROBE)-type comparison of fluvastatin extended-release (XL) 80 mg (n=48) and simvastatin 20 mg (n=46), each given once daily for 2 months to patients with type 2 diabetes with the lipid triad, who were enrolled after a 1-month lifestyle modification and dietary intervention program. After fluvastatin therapy, LDL (-51%; P<.01), apolipoprotein B (ApoB; -33%; P<.01), intermediate-density LDL (idLDL) (-14.3%; P<.05), sdLDL (-45%; P<.01), and triglycerides (-38%; P<.01) were significantly decreased, and HDL (+14.3%; P<.05) and apolipoprotein A-I (ApoA-I; +7%; P<.05) were increased; large buoyant (lb) LDL did not change (P=NS). Simvastatin therapy decreased LDL (-55.1%; P<.01), ApoB (-46%; P<.01), lbLDL (-33.3%; P<.05), idLDL (-22.7%; P<.05), sdLDL (-33.3%; P<.05), and triglycerides (-47.9%; P<.01); HDL was not changed (P=NS) after simvastatin, but ApoA-I was increased (+11.3%; P<.01). HDL increases (P<.01) and sdLDL decreases (P<.01) were significantly greater after fluvastatin compared with simvastatin therapy; LDL, triglycerides, ApoB, and idLDL changes were similar after both therapies (P=NS), and lbLDL decreases were greater with simvastatin therapy (P<.05). With both treatments, classic mean LDL and ApoB target levels were achieved in most patients. We conclude that the lipid triad can be controlled with fluvastatin XL 80 mg in patients with type 2 diabetes.

Regulated expression of endothelial lipase by porcine brain capillary endothelial cells constituting the blood-brain barrier

Normal neurological function depends on a constant supply of polyunsaturated fatty acids to the brain. A considerable proportion of essential fatty acids originates from lipoprotein-associated lipids that undergo uptake and/or catabolism at the blood-brain barrier (BBB). This study aimed at identifying expression and regulation of endothelial lipase (EL) in brain capillary endothelial cells (BCEC), major constituents of the BBB. Our results revealed that BCEC are capable of EL synthesis and secretion. Overexpression of EL resulted in enhanced hydrolysis of extracellular high-density lipoprotein (HDL)-associated sn-2-labeled [(14)C]20 : 4 phosphatidylcholine. [(14)C]20 : 4 was recovered in cellular lipids, indicating re-uptake and intracellular re-esterification. To investigate local regulation of EL in the cerebrovasculature, BCEC were cultured in the presence of peroxisome-proliferator activated receptor (PPAR)- and liver X receptor (LXR)-agonists, known to regulate HDL levels. These experiments revealed that 24(S)OH-cholesterol (a LXR agonist), bezafibrate (a PPARalpha agonist), or pioglitazone (a PPARgamma agonist) resulted in down-regulation of EL mRNA and protein levels. Our findings implicate that EL could generate fatty acids at the BBB for transport to deeper regions of the brain as building blocks for membrane phospholipids. In addition PPAR and LXR agonists appear to contribute to HDL homeostasis at the BBB by regulating EL expression.

The role of endothelial lipase in high-density lipoprotein metabolism

PURPOSE OF REVIEW

Elevating high-density lipoprotein levels is increasingly being identified as an essential strategy for the prevention of atherosclerosis. Plasma levels of high-density lipoprotein cholesterol and its major protein, apoAI, are largely influenced by the rate of turnover. Lipases play an important role in modulating the metabolism of high-density lipoprotein. In particular, endothelial lipase has been shown to be an important determinant of high-density lipoprotein metabolism and levels in murine models. This article reviews new developments in our understanding of the biology of endothelial lipase and its relation to high-density lipoprotein metabolism.

RECENT FINDINGS

Inhibition of the endothelial lipase gene, either by antibody injection or by targeted gene deletion, results in an approximately 50% increase in high-density lipoprotein cholesterol levels in mice. As many as 31 single-nucleotide polymorphisms have been identified in the endothelial lipase gene. The 584 C/T mutation, which results in a threonine-to-isoleucine amino acid change, has been associated with higher high-density lipoprotein cholesterol levels in three separate studies.

SUMMARY

Increasing evidence suggests that endothelial lipase plays a significant role in high-density lipoprotein metabolism. Endothelial lipase could be an important new target for novel therapies to raise high-density lipoprotein levels.

Genetics of Variation in HDL Cholesterol in Humans and Mice

Plasma high-density lipoprotein cholesterol (HDL-C) concentrations are genetically determined to a great extent, and quantitative trait locus (QTL) analysis has been used to identify chromosomal regions containing genes regulating HDL-C levels. We discuss new genes found to participate in HDL metabolism. We also summarize 37 mouse and 30 human QTLs for plasma HDL-C levels, finding that all but three of the mouse QTLs have been confirmed by a second cross or a homologous human QTL, that the mouse QTL map is almost saturated because 92% of recently reported QTLs are repeats of those already found, and that 28 of the 30 human QTLs are located in regions homologous to mouse QTLs. This high degree of concordance between mouse and human QTLs suggests that the underlying genes may be the same. Strategies to more rapidly identify genes underlying mouse and human QTLs for HDL-C include focusing on the mouse and using mouse–human homologies, combining crosses, and haplotyping to narrow the region. Sequence analysis and expression studies can distinguish candidate genes consistent across multiple mouse crosses, and testing the candidate genes in human association studies can provide additional evidence for the candidacy of a gene. Together these strategies can accelerate the pace of finding genes that regulate HDL.

Expression of the endothelial lipase gene in murine embryos and reproductive organs

Endothelial lipase (EL) is a recently discovered member of the triglyceride-lipase family that is involved in plasma HDL metabolism. In this study, we investigated the putative role of EL in mouse reproduction by studying EL gene expression in mouse embryos and adult reproductive organs. PCR analysis revealed that EL mRNA is expressed in mouse embryos on embryonic day 8.5 (E8.5) to E11.5, but not later in development. In situ hybridization studies on E10.5 whole embryos and embryonic sections showed expression of EL mRNA in multiple tissues, although of varying intensity. High expression was found in the neuroepithelium of the brain and the neural tube, the mesenchymal cells between organs, the optic lens and cup, and the otocyst. In adult mice, EL mRNA expression was high in ovaries from pregnant mice but low in ovaries from nonpregnant mice. EL mRNA was also highly expressed in placenta and testes. In situ hybridization studies demonstrated intense EL mRNA staining of lutein cells in corpora lutei in ovaries, of spermatocytes in the late pachytene and diplotene stages in testes, and of principal cells in epididymis. These results suggest that EL, in addition to its effects on plasma lipoprotein metabolism, plays a role in murine reproduction.