High-density lipoproteins: multifunctional vanguards of the cardiovascular system

HDL as a prognostic biomarker for coronary atherosclerosis: the role of inflammation

INTRODUCTION

Emerging evidence suggests that the role of high density lipoprotein (HDL) in the atherosclerotic process is not as clear as previously thought, since atheroprotective HDL becomes atherogenic in states of increased inflammatory processes.

AREAS COVERED

In this review we aim to elucidate the role of HDL as a prognostic biomarker and we discuss therapeutic approaches that aim to increase HDL and their possible clinical benefit.

EXPERT OPINION

Given the structural variability and biological complexity of the HDL particle, its role in the atherosclerotic process is far from clear. According to current evidence, the atheroprotective role of HDL turns atherogenic in states of increased inflammatory processes, while even minor alterations in systemic inflammation are likely to hinder the endothelial protective effects of HDL. In accordance, significant data have revealed that HDL-related drugs may be effective in reducing cardiovascular mortality; however they are not as encouraging or unanimous as expected. Possible future goals could be to quantify either HDL subclasses or functions in an attempt to reach safer conclusions as to the prognostic importance of HDL in coronary atherosclerosis. Having achieved that, a more targeted therapy that would aim to raise either HDL functionality or to remodel HDL structure would be more easily designed.

Pharmacogenomics in the development and characterization of atheroprotective drugs

Atherosclerosis is the main cause of cardiovascular disease (CVD) and can lead to stroke, myocardial infarction, and death. The clinically available atheroprotective drugs aim mainly at reducing the levels of circulating low-density lipoprotein (LDL), increasing high-density lipoprotein (HDL), and attenuating inflammation. However, the cardiovascular risk remains high, along with morbidity, mortality, and incidence of adverse drug events. Pharmacogenomics is increasingly contributing towards the characterization of existing atheroprotective drugs, the evaluation of novel ones, and the identification of promising, unexplored therapeutic targets, at the global molecular pathway level. This chapter presents highlights of pharmacogenomics investigations and discoveries that have contributed towards the elucidation of pharmacological atheroprotection, while opening the way to new therapeutic approaches.

Important considerations for treatment with dietary supplement versus prescription niacin products

Niacin is a water-soluble B vitamin (B3) known to have favorable effects on multiple lipid parameters, including raising high-density lipoprotein cholesterol (HDL-C) levels and lowering triglycerides (TGs), lipoprotein(a), and low-density lipoprotein cholesterol (LDL-C). Although LDL-C remains the primary target of lipid-altering therapy, current guidelines emphasize HDL-C and other modifiable lipid factors as key secondary targets. Thus, niacin is considered an important therapeutic option to help reduce the risk of cardiovascular disease in patients with mixed dyslipidemia who, in addition to high LDL-C, have elevated TGs and low HDL-C. Although available prescription niacin products, including immediate-release niacin (IR; Niacor) and an extended-release niacin formulation (Niaspan), have demonstrated safety and efficacy in randomized clinical trials, confusion remains among health care providers and their patients regarding the various commercially available nonprescription dietary supplement niacin products. These dietary supplements, which include IR, sustained-release (SR), and "no-flush" or "flush-free" niacin products, are not subject to the same stringent US Food and Drug Administration regulations as prescription drugs. In fact, both the American Heart Association and the American Pharmacists Association recommend against the use of dietary supplement niacin as a substitute for prescription niacin. Although some dietary supplement IR and SR niacin products have demonstrated a lipid response in clinical trials, products labeled as "no-flush" or "flush-free" that are intended to avoid the common niacin-associated adverse effect of flushing generally contain minimal or no free, pharmacologically active niacin and therefore lack beneficial lipid-modifying effects. To clarify important differences between available prescription and dietary supplement niacin products, this article contrasts current regulatory standards for dietary supplements and prescription drugs and provides an overview of available clinical data from key trials of niacin.

Widespread effects of nicotinic acid on gene expression in insulin-sensitive tissues: implications for unwanted effects of nicotinic acid treatment

Nicotinic acid (NA; or niacin) has been used as a hypolipidemic agent for more than 4 decades. However, the mechanisms underlying the effects of NA treatment (wanted and unwanted) are still poorly understood. In the present study, we discovered that NA infusion in rats resulted in dephosphorylation (ie, activation) of the forkhead transcription factor FOXO1 in insulin-sensitive tissues such as skeletal and cardiac muscles, liver, and adipose tissue. These NA effects were opposite to the effects of insulin to increase FOXO1 phosphorylation. To test whether NA alters gene expression in these tissues, rats were infused for 7 hours with NA (30 μmol/h) and/or insulin (5 mU/[kg min]); and gene expression was evaluated using a microarray analysis. Nicotinic acid had widespread effects on gene expression in all of the tissues studied, and the number of genes affected by NA greatly exceeded that of genes affected by insulin. A systematic (or strategic) analysis of the microarray data revealed that there were numerous genes whose expression was regulated inversely by insulin and NA in correlation with FOXO1 phosphorylation, representing potential FOXO1 target genes. We also identified a group of genes whose expression was altered by NA exclusively in adipose tissue, presumably because of stimulation of the NA receptor in this tissue. Finally, there were genes whose expression was altered by both NA and insulin, likely via lowering plasma free fatty acid levels, including lipoprotein lipase and adenosine triphosphate-binding cassette A1, which play a major role in the regulation of circulating lipids. Thus, our data suggest that NA alters gene expression in insulin-sensitive tissues by various mechanisms. Some of the NA-induced changes in gene expression are discussed as potential mechanisms underlying wanted and unwanted effects of NA treatment.

Pleiotropic effects on subclasses of HDL, adiposity, and glucose metabolism in adult Alaskan Eskimos

The aim of this study was to analyze the heritability and the presence of pleiotropic effects on subfractions of high-density lipoproteins (HDLs) as measured by nuclear magnetic resonance (NMR), parameters for adiposity, and glucose metabolism in adult Alaskan Eskimos. The present family study included 1,214 adult Alaskan Eskimos (537 male/677 female). Body weight, height, circumferences, selected skinfolds, and blood pressure were measured in all participants. Blood samples were collected under fasting conditions for the isolation of plasma. Glucose, insulin, subclasses and size of lipoproteins, triglycerides, total, and HDL cholesterol and lipoprotein (a) were measured in plasma. HbA1c was measured in total blood. Univariate and bivariate quantitative genetic analyses were conducted between HDL subclasses and size and the anthropometric and biochemical measures using the variance decomposition approach. Variation in all the analyzed traits exhibits a significant genetic component. Heritabilities ranged between 0.18 +/- 0.11 for LDL(2) (intermediate) and 0.89 +/- 0.07 for small HDL. No common genetic effects were found on the HDL subclasses (small, intermediate, and large). Small HDL particles were genetically correlated with LDL particles and HbA1c. Negative genetic correlations were observed between intermediate and large HDL subfractions, HDL size and measures of adiposity, and LDL and parameters for glucose metabolism (HbA1, insulin). These observations confirm the presence of possible pleiotropic effects on HDL, adiposity, and cardiovascular risk factors and provide novel insight on the relationship between HDL subclasses, adiposity, and glucose regulation.

Apolipoprotein A1 Is a Stronger Prognostic Marker Than Are HDL and LDL Cholesterol for Cardiovascular Disease and Mortality in Elderly Men

The aim of this study was to compare apolipoprotein A1 (ApoA1) and B (ApoB) with high-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C) as markers for cardiovascular mortality and morbidity in elderly men. We analyzed serum ApoA1, ApoB, total cholesterol, HDL-C, and LDL-C in a group of 77-year-old men (n = 785). The results were correlated with data from the Swedish cause of death registry. Receiver-operating characteristic curves showed that, of the studied serum markers, ApoA1 was the best predictor for ischemic heart disease mortality (area under the curve = 0.724, 95% confidence interval, 0.691-0.755). There were also significant correlations between the apolipoproteins and other known risk markers for cardiovascular disease such as triglycerides, high-sensitivity C-reactive protein (hsCRP), and cystatin C. Serum ApoA1 is a better risk marker than are ApoB, ApoB/ApoA1 ratio, HDL-C, and LDL-C for cardiovascular disease and mortality in elderly men.

Ácidos graxos como marcadores biológicos da ingestão de gorduras

Os ácidos graxos da dieta têm sido associados ao desenvolvimento de doenças crônicas. Os inquéritos alimentares, utilizados em estudos clínicos e epidemiológicos para estimativa da ingestão de nutrientes, apresentam limitações na coleta de informações. Nesse sentido, a utilização da composição de ácidos graxos do plasma e do tecido adiposo como marcadores do tipo de gordura alimentar pode fornecer uma medida mais acurada da ingestão de gorduras. Esta pesquisa tem como objetivo evidenciar aspectos metabólicos de alguns ácidos graxos e o papel como marcadores da ingestão de gorduras, e apresentar as técnicas analíticas empregadas na sua determinação. A biópsia do tecido adiposo, com determinação da composição de ácidos graxos, fornece uma informação a longo prazo da ingestão de gorduras, enquanto que a avaliação da composição das frações lipídicas séricas representa a ingestão a curto e médio prazos. Os ácidos graxos essenciais, os ácidos graxos saturados com número ímpar de carbonos (15:0 e 17:0) e os ácidos graxos trans, por não apresentarem síntese endógena, são utilizados como marcadores biológicos da ingestão de gorduras ou de sua própria ingestão. As principais técnicas utilizadas para a determinação de ácidos graxos são a cromatografia gasosa e a cromatografia líquida de alta precisão. No presente momento, o uso de marcadores biológicos para a ingestão de gorduras, associados aos inquéritos alimentares, representa a forma mais completa de avaliação da ingestão de gorduras.

Genetics of high-density lipoproteins

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

A novel nonsense apolipoprotein A-I mutation (apoA-IE136X) causes low HDL cholesterol in French Canadians

The molecular causes of severe high-density lipoprotein cholesterol (HDL-C) deficiency was examined in a group of 54 unrelated French Canadian subjects. The lecithin:cholesterol acyl transferase (LCAT) and apolipoprotein (apo) A-I gene were analyzed in all probands by direct DNA sequencing. While no LCAT mutation was detected, a novel nonsense apoA-I mutation (E136X) was found in 3/54 probands. Genetic analysis of two kindreds showed a strong co-segregation of the apoA-I locus with the low HDL-C trait. The E136X mutation was detected in families by MaeI restriction digestion. E136X carriers (n=17) had marked HDL-C deficiency; among the nine carriers > or = 35 years old, five men had developed premature coronary artery disease (CAD). A peptide of apparent molecular weight of 14 kDa was identified in fresh plasma, the HDL fractions and lipoprotein deficient plasma from the three probands but not in normal controls (n=3), suggesting that the mutant apoA-I peptide is secreted and binds lipids. The mutation was not observed in an additional 210 chromosomes from unrelated subjects of French Canadian descent, < 60 years of age, with CAD and low HDL-C levels. We conclude that apoA-I (E136X) is a cause of HDL-C deficiency in the French Canadian population and is associated with premature CAD.

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.

Toxic effect of pregnancy intrahepatic cholestasis on liver and placenta in pregnant rats

AIM: To investigate the toxic effect of intrahepatic cholestasis of pregnancy (ICP) on the liver and placenta in pregnant rats.

METHODS: The animal model of ICP was induced by 17-a-ethinylestradiol and progesterone. Pathohistological changes of the liver and placenta of the pregnant rats were observed under light and electronic microscope.

RESULTS: The levels of serum alanine transaminase (ALT), aspartate transaminase (AST), and total bile acid (TBA) were significantly higher in ICP rats than the control (AST: 3 784±155 vs 747±158; ALT: 7 076±220 vs 847±198; TBA: 78.5±4.5 vs 25.2±3.7; P<0.01 for all of the three). Granule- and vacuole-like cells were observed in liver of ICP rats under light microscope and Bile canaliculi were dilated and deposition of substances with high electronic density was found in bile canaliculi and hepatocytes of ICP rats by electronic microscopy. Granule- and vacuole-like changes were also found in some placenta syncytiotrophoblast of ICP rats by light microscopy.

CONCLUSION: ICP with hyperbileacidemia has marked toxicity to hepatocytes and placenta trophoblasts of pregnant rats.