Novel function of lecithin-cholesterol acyltransferase. Hydrolysis of oxidized polar phospholipids generated during lipoprotein oxidation

Association of Plasma Vitamins and Carotenoids, DNA Methylation of LCAT, and Risk of Age-Related Macular Degeneration

Dysregulation of lipid metabolism has been implicated in age-related macular degeneration (AMD), the leading cause of blindness among the elderly. Lecithin cholesterol acyltransferase (LCAT) is an important enzyme responsible for lipid metabolism, which could be regulated by DNA methylation during the development of various age-related diseases. This study aimed to assess the association between LCAT DNA methylation and the risk of AMD, and to examine whether plasma vitamin and carotenoid concentrations modified this association. A total of 126 cases of AMD and 174 controls were included in the present analysis. LCAT DNA methylation was detected by quantitative real-time methylation-1specific PCR (qMSP). Circulating vitamins and carotenoids were measured using reversed-phase high-performance liquid chromatography (RP-HPLC). DNA methylation of LCAT was significantly higher in patients with AMD than those in the control subjects. After multivariable adjustment, participants in the highest tertile of LCAT DNA methylation had a 5.37-fold higher risk (95% CI: 2.56, 11.28) of AMD compared with those in the lowest tertile. Each standard deviation (SD) increment of LCAT DNA methylation was associated with a 2.23-fold (95% CI: 1.58, 3.13) increased risk of AMD. There was a J-shaped association between LCAT DNA methylation and AMD risk (P_{non-linearity} = 0.03). Higher concentrations of plasma retinol and β-cryptoxanthin were significantly associated with decreased levels of LCAT DNA methylation, with the multivariate-adjusted β coefficient being -0.05 (95% CI: -0.08, -0.01) and -0.25 (95% CI: -0.42, -0.08), respectively. In joint analyses of LCAT DNA methylation and plasma vitamin and carotenoid concentrations, the inverse association between increased LCAT DNA methylation and AMD risk was more pronounced among participants who had a lower concentration of plasma retinol and β-cryptoxanthin. These findings highlight the importance of comprehensively assessing LCAT DNA methylation and increasing vitamin and carotenoid status for the prevention of AMD.

HDL Functions-Current Status and Future Perspectives

Cardiovascular disease (CVD) is the leading cause of death in Western countries. A low HDL-C is associated with the development of CVD. However, recent epidemiology studies have shown U-shaped curves between HDL-C and CVD mortality, with paradoxically increased CVD mortality in patients with extremely high HDL-C levels. Furthermore, HDL-C raising therapy using nicotinic acids or CETP inhibitors mostly failed to reduce CVD events. Based on this background, HDL functions rather than HDL-C could be a novel biomarker; research on the clinical utility of HDL functionality is ongoing. In this review, we summarize the current status of HDL functions and their future perspectives from the findings of basic research and clinical trials.

Oxidative modification of HDL by lipid aldehydes impacts HDL function

Reduced levels of high-density lipoprotein (HDL) cholesterol correlate with increased risk for atherosclerotic cardiovascular diseases and HDL performs functions including reverse cholesterol transport, inhibition of lipid peroxidation, and suppression of inflammation, that would appear critical for cardioprotection. However, several large clinical trials utilizing pharmacologic interventions that elevated HDL cholesterol levels failed to provide cardioprotection to at-risk individuals. The reasons for these unexpected results have only recently begun to be elucidated. HDL cholesterol levels and HDL function can be significantly discordant, so that elevating HDL cholesterol levels may not necessarily lead to increased functional capacity, particularly under conditions that cause HDL to become oxidatively modified, resulting in HDL dysfunction. Here we review evidence that oxidative modifications of HDL, including by reactive lipid aldehydes generated by lipid peroxidation, reduce HDL functionality and that dicarbonyl scavengers that protect HDL against lipid aldehyde modification are beneficial in pre-clinical models of atherosclerotic cardiovascular disease.

A highly conserved host lipase deacylates oxidized phospholipids and ameliorates acute lung injury in mice

Oxidized phospholipids have diverse biological activities, many of which can be pathological, yet how they are inactivated in vivo is not fully understood. Here, we present evidence that a highly conserved host lipase, acyloxyacyl hydrolase (AOAH), can play a significant role in reducing the pro-inflammatory activities of two prominent products of phospholipid oxidation, 1-palmitoyl-2-glutaryl-sn-glycero-3-phosphocholine and 1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphocholine. AOAH removed the sn-2 and sn-1 acyl chains from both lipids and reduced their ability to induce macrophage inflammasome activation and cell death in vitro and acute lung injury in mice. In addition to transforming Gram-negative bacterial lipopolysaccharide from stimulus to inhibitor, its most studied activity, AOAH can inactivate these important danger-associated molecular pattern molecules and reduce tissue inflammation and injury.

Good Cholesterol Gone Bad? HDL and COVID-19

The transmissible respiratory disease COVID-19, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has affected millions of people worldwide since its first reported outbreak in December of 2019 in Wuhan, China. Since then, multiple studies have shown an inverse correlation between the levels of high-density lipoprotein (HDL) particles and the severity of COVID-19, with low HDL levels being associated with an increased risk of severe outcomes. Some studies revealed that HDL binds to SARS-CoV-2 particles via the virus's spike protein and, under certain conditions, such as low HDL particle concentrations, it facilitates SARS-CoV-2 binding to angiotensin-converting enzyme 2 (ACE2) and infection of host cells. Other studies, however, reported that HDL suppressed SARS-CoV-2 infection. In both cases, the ability of HDL to enhance or suppress virus infection appears to be dependent on the expression of the HDL receptor, namely, the Scavenger Receptor Class B type 1 (SR-B1), in the target cells. SR-B1 and HDL represent crucial mediators of cholesterol metabolism. Herein, we review the complex role of HDL and SR-B1 in SARS-CoV-2-induced disease. We also review recent advances in our understanding of HDL structure, properties, and function during SARS-CoV-2 infection and the resulting COVID-19 disease.

Changing Perspectives on HDL: From Simple Quantity Measurements to Functional Quality Assessment

High-density lipoprotein (HDL) comprises a heterogeneous group of particles differing in size, density, and composition. HDL cholesterol (HDL-C) levels have long been suggested to indicate cardiovascular risk, inferred from multiple epidemiological studies. The failure of HDL-C targeted interventions and genetic studies has raised doubts on the atheroprotective role of HDL-C. The current consensus is that HDL-C is neither a biomarker nor a causative agent of cardiovascular disorders. With better understanding of the complex nature of HDL which comprises a large number of proteins and lipids with unique functions, recent focus has shifted from HDL quantity to HDL quality in terms of atheroprotective functions. The current research is focused on developing laboratory assays to assess HDL functions for cardiovascular risk prediction. Also, HDL mimetics designed based on the key determinants of HDL functions are being investigated to modify cardiovascular risk. Improving HDL functions by altering its composition is the key area of future research in HDL biology to reduce cardiovascular risk.

Transfer and Enzyme-Mediated Metabolism of Oxidized Phosphatidylcholine and Lysophosphatidylcholine between Low- and High-Density Lipoproteins

Oxidized low-density lipoprotein (oxLDL) and oxidized high-density lipoprotein (oxHDL), known as risk factors for cardiovascular disease, have been observed in plasma and atheromatous plaques. In a previous study, the content of oxidized phosphatidylcholine (oxPC) and lysophosphatidylcholine (lysoPC) species stayed constant in isolated in vivo oxLDL but increased in copper-induced oxLDL in vitro. In this study, we prepared synthetic deuterium-labeled 1-palmitoyl lysoPC and palmitoyl-glutaroyl PC (PGPC), a short chain-oxPC to elucidate the metabolic fate of oxPC and lysoPC in oxLDL in the presence of HDL. When LDL preloaded with d₁₃-lysoPC was mixed with HDL, d₁₃-lysoPC was recovered in both the LDL and HDL fractions equally. d₁₃-LysoPC decreased by 50% after 4 h of incubation, while d₁₃-PC increased in both fractions. Diacyl-PC production was abolished by an inhibitor of lecithin-cholesterol acyltransferase (LCAT). When d₁₃-PGPC-preloaded LDL was incubated with HDL, d₁₃-PGPC was transferred to HDL in a dose-dependent manner when both LCAT and lipoprotein-associated phospholipase A₂ (Lp-PLA₂) were inhibited. Lp-PLA₂ in both HDL and LDL was responsible for the hydrolysis of d₁₃-PGPC. These results suggest that short chain-oxPC and lysoPC can transfer between lipoproteins quickly and can be enzymatically converted from oxPC to lysoPC and from lysoPC to diacyl-PC in the presence of HDL.

Lipoproteins and lipids in cardiovascular disease: from mechanistic insights to therapeutic targeting

With cardiovascular disease being the leading cause of morbidity and mortality worldwide, effective and cost-efficient therapies to reduce cardiovascular risk are highly needed. Lipids and lipoprotein particles crucially contribute to atherosclerosis as underlying pathology of cardiovascular disease and influence inflammatory processes as well as function of leukocytes, vascular and cardiac cells, thereby impacting on vessels and heart. Statins form the first-line therapy with the aim to block cholesterol synthesis, but additional lipid-lowering drugs are sometimes needed to achieve low-density lipoprotein (LDL) cholesterol target values. Furthermore, beyond LDL cholesterol, also other lipid mediators contribute to cardiovascular risk. This review comprehensively discusses low- and high-density lipoprotein cholesterol, lipoprotein (a), triglycerides as well as fatty acids and derivatives in the context of cardiovascular disease, providing mechanistic insights into their role in pathological processes impacting on cardiovascular disease. Also, an overview of applied as well as emerging therapeutic strategies to reduce lipid-induced cardiovascular burden is provided.

Lipoproteins in Atherosclerosis Process

BACKGROUND

Dyslipidaemias is a recognized risk factor for atherosclerosis, however, new evidence brought to light by trials investigating therapies to enhance HDLcholesterol have suggested an increased atherosclerotic risk when HDL-C is high.

RESULTS

Several studies highlight the central role in atherosclerotic disease of dysfunctional lipoproteins; oxidised LDL-cholesterol is an important feature, according to "oxidation hypothesis", of atherosclerotic lesion, however, there is today a growing interest for dysfunctional HDL-cholesterol. The target of our paper is to review the functions of modified and dysfunctional lipoproteins in atherogenesis.

CONCLUSION

Taking into account the central role recognized to dysfunctional lipoproteins, measurements of functional features of lipoproteins, instead of conventional routine serum evaluation of lipoproteins, could offer a valid contribution in experimental studies as in clinical practice to stratify atherosclerotic risk.

Unravelling HDL-Looking beyond the Cholesterol Surface to the Quality Within

High-density lipoprotein (HDL) particles have experienced a turbulent decade of falling from grace with widespread demotion from the most-sought-after therapeutic target to reverse cardiovascular disease (CVD), to mere biomarker status. HDL is slowly emerging from these dark times due to the HDL flux hypothesis wherein measures of HDL cholesterol efflux capacity (CEC) are better predictors of reduced CVD risk than static HDL-cholesterol (HDL-C) levels. HDL particles are emulsions of metabolites, lipids, protein, and microRNA (miR) built on the backbone of Apolipoprotein A1 (ApoA1) that are growing in their complexity due to the higher sensitivity of the respective “omic” technologies. Our understanding of particle composition has increased dramatically within this era and has exposed how our understanding of these particles to date has been oversimplified. Elucidation of the HDL proteome coupled with the identification of specific miRs on HDL have highlighted the “hormonal” characteristics of HDL in that it carries and delivers messages systemically. HDL can dock to most peripheral cells via its receptors, including SR-B1, ABCA1, and ABCG1, which may be a critical step for facilitating HDL-to-cell communication. The composition of HDL particles is, in turn, altered in numerous disease states including diabetes, auto-immune disease, and CVD. The consequence of changes in composition, however, on subsequent biological activities of HDL is currently poorly understood and this is an important avenue for the field to explore in the future. Improving HDL particle quality as opposed to HDL quantity may, in turn, prove a more beneficial investment to reduce CVD risk.

Antioxidative activity of high-density lipoprotein (HDL): Mechanistic insights into potential clinical benefit

Uptake of low-density lipoprotein (LDL) particles by macrophages represents a key step in the development of atherosclerotic plaques, leading to the foam cell formation. Chemical modification of LDL is however necessary to induce this process. Proatherogenic LDL modifications include aggregation, enzymatic digestion and oxidation. LDL oxidation by one-electron (free radicals) and two-electron oxidants dramatically increases LDL affinity to macrophage scavenger receptors, leading to rapid LDL uptake and fatty streak formation. Circulating high-density lipoprotein (HDL) particles, primarily small, dense, protein-rich HDL3, provide potent protection of LDL from oxidative damage by free radicals, resulting in the inhibition of the generation of pro-inflammatory oxidized lipids. HDL-mediated inactivation of lipid hydroperoxides involves their initial transfer from LDL to HDL and subsequent reduction to inactive hydroxides by redox-active Met residues of apolipoprotein A-I. Several HDL-associated enzymes are present at elevated concentrations in HDL3 relative to large, light HDL2 and can be involved in the inactivation of short-chain oxidized phospholipids. Therefore, HDL represents a multimolecular complex capable of acquiring and inactivating proatherogenic lipids. Antioxidative function of HDL can be impaired in several metabolic and inflammatory diseases. Structural and compositional anomalies in the HDL proteome and lipidome underlie such functional deficiency. Concomitant normalization of the metabolism, circulating levels, composition and biological activities of HDL particles, primarily those of small, dense HDL3, can constitute future therapeutic target.

Preferential hydrolysis of truncated oxidized glycerophospholipids by lysosomal phospholipase A2

Truncated oxidized glycerophospholipids (ox-PLs) are bioactive lipids resulting from oxidative stress. The catabolic pathways for truncated ox-PLs are not fully understood. Lysosomal phospholipase A2 (LPLA2) with phospholipase A and transacylase activities is a key enzyme in phospholipid homeostasis. The present study assessed whether LPLA2 could hydrolyze truncated ox-PLs. Incubation of LPLA2 with liposomes consisting of 1,2-O-octadecenyl-sn-glycero-3-phosphocholine (DODPC)/1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) or truncated oxidized phosphatidylcholine (ox-PC)/N-acetylsphingosine (NAS) under acidic conditions resulted in the preferential deacylation at the sn-1 position of the truncated ox-PCs. Additionally, the release of free fatty acid from the truncated ox-PCs preferentially occurred compared with the NAS-acylation. Incubation of LPLA2 with the liposomes consisting of DODPC/DOPC/truncated ox-PC/NAS resulted in the same preferential fatty acid release from the truncated ox-PC. The cationic amphiphilic drug, amiodarone, did not inhibit such fatty acid release, indicating that truncated ox-PCs partition from the lipid membrane into the aqueous phase and react with free LPLA2. Consistent with this mechanism, the hydrolysis of some truncated ox-PCs, but not DOPC, by LPLA2 was detected at neutral pH. Additionally, LPLA2-overexpressed Chinese hamster ovary cells efficiently catabolized truncated ox-PC and were protected from growth inhibition. These findings support the existence of a novel catabolic pathway for truncated ox-PLs via LPLA2.

Dysfunctional HDL: from structure-function-relationships to biomarkers

Reduced plasma levels of HDL-C are associated with an increased risk of CAD and myocardial infarction, as shown in various prospective population studies. However, recent clinical trials on lipid-modifying drugs that increase plasma levels of HDL-C have not shown significant clinical benefit. Notably, in some recent clinical studies, there is no clear association of higher HDL-C levels with a reduced risk of cardiovascular events observed in patients with existing CAD. These observations have prompted researchers to shift from a cholesterol-centric view of HDL towards assessing the function and composition of HDL particles. Of importance, experimental and translational studies have further demonstrated various potential antiatherogenic effects of HDL. HDL has been proposed to promote macrophage reverse cholesterol transport and to protect endothelial cell functions by prevention of oxidation of LDL and its adverse endothelial effects. Furthermore, HDL from healthy subjects can directly stimulate endothelial cell production of nitric oxide and exert anti-inflammatory and antiapoptotic effects. Of note, increasing evidence suggests that the vascular effects of HDL can be highly heterogeneous and HDL may lose important anti-atherosclerotic properties and turn dysfunctional in patients with chronic inflammatory disorders. A greater understanding of mechanisms of action of HDL and its altered vascular effects is therefore critical within the context of HDL-targeted therapies.

Functionality of HDL: antioxidation and detoxifying effects

High-density lipoproteins (HDL) are complexes of multiple talents, some of which have only recently been recognised but all of which are under active investigation. Clinical interest initially arose from their amply demonstrated role in atherosclerotic disease with their consequent designation as a major cardiovascular disease (CVD) risk factor. However, interest is no longer confined to vascular tissues, with the reports of impacts of the lipoprotein on pancreatic, renal and nervous tissues, amongst other possible targets. The ever-widening scope of HDL talents also encompasses environmental hazards, including infectious agents and environmental toxins. In almost all cases, HDL would appear to have a beneficial impact on health. It raises the intriguing question of whether these various talents emanate from a basic ancestral function to protect the cell.The following chapter will illustrate and review our current understanding of some of the functions attributed to HDL. The first section will look at the antioxidative functions of HDL and possible mechanisms that are involved. The second section will focus specifically on paraoxonase-1 (PON1), which appears to bridge the divide between the two HDL functions discussed herein. This will lead into the final section dealing with HDL as a detoxifying agent protecting against exposure to environmental pathogens and other toxins.

HDL and atherosclerosis: Insights from inherited HDL disorders

Plasma high density lipoproteins (HDL) comprise a highly heterogeneous family of lipoprotein particles, differing in density, size, surface charge, and lipid and protein composition. Epidemiological studies have shown that plasma HDL level inversely correlates with atherosclerotic cardiovascular disease. The most relevant atheroprotective function of HDL is to promote the removal of cholesterol from macrophages within the arterial wall and deliver it to the liver for excretion in a process called reverse cholesterol transport. In addition, HDLs can contribute to the maintenance of endothelial cell homeostasis and have potent antioxidant properties. It has been long suggested that individual HDL subclasses may differ in terms of their functional properties, but which one is the good particle remains to be defined. Inherited HDL disorders are rare monogenic diseases due to mutations in genes encoding proteins involved in HDL metabolism. These disorders are not only characterized by extremely low or high plasma HDL levels but also by an abnormal HDL subclass distribution, and thus represent a unique tool to understand the relationship between plasma HDL concentration, HDL function, and HDL-mediated atheroprotection. This article is part of a Special Issue entitled Linking transcription to physiology in lipodomics.

Time course-changes in phosphatidylcholine profile during oxidative modification of low-density lipoprotein

Background

Oxidized phosphatidylcholines (oxPC) and lysophosphatidylcholine (lysoPC) generated during the formation of oxidized low-density lipoprotein (oxLDL) are involved in atherosclerotic lesion development. We investigated the time course-changes in phosphatidylcholine (PC) molecular species during oxidation of LDL to determine how those atherogenic PCs are produced.

Methods

Human and rabbit LDLs were pretreated with or without a selective platelet-activating factor acetylhydrolase (PAF-AH) inhibitor. LDL was oxidized by incubation with copper sulfate, and PC profiles were analyzed by liquid chromatography-tandem mass spectrometry.

Results

When human LDL was oxidized, the peak areas for polyunsaturated fatty acid (PUFA)-containing PC species dramatically decreased after a short lag period, concomitantly lysoPC species increased sharply. Although a variety of oxPC species containing oxidized fatty acyl groups or cleaved acyl chains are formed during LDL oxidation, only a few oxPC products accumulated in oxLDL: 1-palmitoyl-2-(9-oxo-nonanoyl) PC and long-chain oxPC with two double bonds. Pretreatment of LDL with the PAF-AH inhibitor greatly reduced lysoPC production while it had no effect on lipid peroxidation reactions and oxPC profiles. Rabbit LDL, which has a different composition of PC molecular species and needs a longer time to reach achieve full oxidation than human LDL, also accumulated lysoPC during oxidation. The increase in lysoPC in rabbit oxLDL was suppressed by pretreatment with the PAF-AH inhibitor. The major oxPC species formed in rabbit oxLDL were almost the same as human oxLDL.

Conclusions

These results suggest that lysoPC species are the major products and PAF-AH activity is crucial for lysoPC generation during oxidation of LDL. The oxPC species accumulated are limited when LDL is oxidized with copper ion in vitro.

High density lipoproteins and endothelial functions: mechanistic insights and alterations in cardiovascular disease

Prospective population studies in the primary prevention setting have shown that reduced plasma levels of HDL cholesterol are associated with an increased risk of coronary disease and myocardial infarction. Experimental and translational studies have further revealed several potential anti-atherogenic effects of HDL, including protective effects on endothelial cell functions. HDL has been suggested to protect endothelial cell functions by prevention of oxidation of LDL and its adverse endothelial effects. Moreover, HDL from healthy subjects can directly stimulate endothelial cell production of nitric oxide and anti-inflammatory, anti-apoptotic, and anti-thrombotic effects as well as endothelial repair processes. However, several recent clinical trials using HDL cholesterol-raising agents, such as torcetrapib, dalcetrapib, and niacin, did not demonstrate a significant reduction of cardiovascular events in patients with coronary disease. Of note, growing evidence suggests that the vascular effects of HDL can be highly heterogeneous and vasoprotective properties of HDL are altered in patients with coronary disease. Characterization of underlying mechanisms and understanding of the clinical relevance of this "HDL dysfunction" is currently an active field of cardiovascular research. Notably, in some recent studies no clear association of higher HDL cholesterol levels with a reduced risk of cardiovascular events was observed in patients with already established coronary disease. A greater understanding of mechanisms of action of HDL and its altered vascular effects is therefore critical within the context of HDL-targeted therapies. In this review, we will address different effects of HDL on endothelial cell functions potentially relevant to atherosclerotic vascular disease and explore molecular mechanisms leading to "dysfunctional HDL".

Lecithin: cholesterol acyltransferase and na(+)-k(+)-ATPase activity in patients with breast cancer

Purpose

The aim of this study was to determine whether plasma lecithin:cholesterol acyltransferase (pLCAT) and erythrocyte membrane Na⁺-K⁺-ATPase ase (emNaKATPs) activity have a correlation in breast cancer. This study compared these parameters at time points before and after treatment with radiotherapy.

Methods

The levels of pLCAT and emNaKATPs were assessed in 30 patients with breast carcinoma and 20 control subjects. While emNaKATPs was measured with spectrophotometric method, pLCAT levels was measured using a specific enzyme-linked immunosorbent assay.

Results

pLCAT levels, both before and after radiotherapy, were found to be decreased in breast cancer patients than in the controls groups (p<0.001 and p<0.001, respectively). Also, pLCAT levels after radiotherapy were found to be decreased in breast cancer patients than the pLCAT levels before radiotherapy (p<0.001). The emNaKATPs activity were higher in the control group than in the breast cancer patients before/after radiotherapy (RT) (p<0.001 and p<0.001, respectively). At the same time, emNaKATPs activity before RT was higher in the breast cancer patients than emNaKATPs activity after RT (p<0.001). There was a significant correlation between pLCAT and emNaKATPs activity in breast cancer patients receiving radiotherapy (r=0.63, p<0.001), but no correlation between in breast cancer patients before RT and control group (r=0.023, p>0.05).

Conclusion

The results of the present study demonstrated that decreased pLCAT and emNaKATPs activity levels in breast cancer patients after/before RT than control group. In addition, decreased emNaKATPs activity in breast cancer patients receiving radiotherapy may be due to decreased pLCAT concentrations and RT beam. In our opinion, altered activities of pLCAT and emNaKATPs are linked to the treatment effect of radiotherapy. These data may clarify the development of cell membrane dysfunction and lipid metabolism in breast cancer patients receiving radiotherapy.

Myeloperoxidase-derived chlorinating species induce protein carbamylation through decomposition of thiocyanate and urea: novel pathways generating dysfunctional high-density lipoprotein

AIMS

Protein carbamylation through cyanate is considered as playing a causal role in promoting cardiovascular disease. We recently observed that the phagocyte protein myeloperoxidase (MPO) specifically induces high-density lipoprotein (HDL) carbamylation, rather than chlorination, in human atherosclerotic lesions, raising the possibility that MPO-derived chlorinating species are involved in cyanate formation.

RESULTS

Here, we show that MPO-derived chlorinating species rapidly decompose the plasma components thiocyanate (SCN) and urea, thereby promoting (lipo)protein carbamylation. Strikingly, the presence of physiologic concentrations of SCN completely prevented MPO-induced 3-chlorotyrosine formation in HDL. SCN scavenged a 2.5-fold molar excess of hypochlorous acid, promoting HDL carbamylation, but not chlorination. Cyanate significantly impaired (i) HDL's ability to activate lecithin-cholesterol acyltransferase; (ii) the activity of paraoxonase, a major HDL-associated anti-inflammatory enzyme; and (iii) the antioxidative activity of HDL.

INNOVATION

Here, we report that MPO-derived chlorinating species preferentially induce protein carbamylation-rather than chlorination-in the presence of physiologically relevant SCN concentrations. The carbamylation of HDL results in the loss of its anti-inflammatory and antioxidative activities.

CONCLUSION

MPO-mediated decomposition of SCN and/or urea might be a relevant mechanism for generating dysfunctional HDL in human disease.

Lipid oxidation in carriers of lecithin:cholesterol acyltransferase gene mutations

OBJECTIVE

Lecithin:cholesterol acyltransferase (LCAT) has been shown to play a role in the depletion of lipid oxidation products, but this has so far not been studied in humans. In this study, we investigated processes and parameters relevant to lipid oxidation in carriers of functional LCAT mutations.

METHODS AND RESULTS

In 4 carriers of 2 mutant LCAT alleles, 63 heterozygotes, and 63 family controls, we measured activities of LCAT, paraoxonase 1, and platelet-activating factor-acetylhydrolase; levels of lysophosphatidylcholine molecular species, arachidonic and linoleic acids, and their oxidized derivatives; immunodetectable oxidized phospholipids on apolipoprotein (apo) B-containing and apo(a)-containing lipoproteins; IgM and IgG autoantibodies to malondialdehyde-low-density lipoprotein and IgG and IgM apoB-immune complexes; and the antioxidant capacity of high-density lipoprotein (HDL). In individuals with LCAT mutations, plasma LCAT activity, HDL cholesterol, apoA-I, arachidonic acid, and its oxidized derivatives, oxidized phospholipids on apo(a)-containing lipoproteins, HDL-associated platelet-activating factor-acetylhydrolase activity, and the antioxidative capacity of HDL were gene-dose-dependently decreased. Oxidized phospholipids on apoB-containing lipoproteins was increased in heterozygotes (17%; P<0.001) but not in carriers of 2 defective LCAT alleles.

CONCLUSIONS

Carriers of LCAT mutations present with significant reductions in LCAT activity, HDL cholesterol, apoA-I, platelet-activating factor-acetylhydrolase activity, and antioxidative potential of HDL, but this is not associated with parameters of increased lipid peroxidation; we did not observe significant changes in the oxidation products of arachidonic acid and linoleic acid, immunoreactive oxidized phospholipids on apo(a)-containing lipoproteins, and IgM and IgG autoantibodies against malondialdehyde-low-density lipoprotein. These data indicate that plasma LCAT activity, HDL-associated platelet-activating factor-acetylhydrolase activity, and HDL cholesterol may not influence the levels of plasma lipid oxidation products.

Lecithin:cholesterol acyltransferase: old friend or foe in atherosclerosis?

Lecithin:cholesterol acyltransferase (LCAT) is a key enzyme that catalyzes the esterification of free cholesterol in plasma lipoproteins and plays a critical role in high-density lipoprotein (HDL) metabolism. Deficiency leads to accumulation of nascent preβ-HDL due to impaired maturation of HDL particles, whereas enhanced expression is associated with the formation of large, apoE-rich HDL(1) particles. In addition to its function in HDL metabolism, LCAT was believed to be an important driving force behind macrophage reverse cholesterol transport (RCT) and, therefore, has been a subject of great interest in cardiovascular research since its discovery in 1962. Although half a century has passed, the importance of LCAT for atheroprotection is still under intense debate. This review provides a comprehensive overview of the insights that have been gained in the past 50 years on the biochemistry of LCAT, the role of LCAT in lipoprotein metabolism and the pathogenesis of atherosclerosis in animal models, and its impact on cardiovascular disease in humans.

High Density Lipoprotein and it's Dysfunction

Plasma high-density lipoprotein cholesterol(HDL-C) levels do not predict functionality and composition of high-density lipoprotein(HDL). Traditionally, keeping levels of low-density lipoprotein cholesterol(LDL-C) down and HDL-C up have been the goal of patients to prevent atherosclerosis that can lead to coronary vascular disease(CVD). People think about the HDL present in their cholesterol test, but not about its functional capability. Up to 65% of cardiovascular death cannot be prevented by putative LDL-C lowering agents. It well explains the strong interest in HDL increasing strategies. However, recent studies have questioned the good in using drugs to increase level of HDL. While raising HDL is a theoretically attractive target, the optimal approach remains uncertain. The attention has turned to the quality, rather than the quantity, of HDL-C. An alternative to elevations in HDL involves strategies to enhance HDL functionality. The situation poses an opportunity for clinical chemists to take the lead in the development and validation of such biomarkers. The best known function of HDL is the capacity to promote cellular cholesterol efflux from peripheral cells and deliver cholesterol to the liver for excretion, thereby playing a key role in reverse cholesterol transport (RCT). The functions of HDL that have recently attracted attention include anti-inflammatory and anti-oxidant activities. High antioxidant and anti-inflammatory activities of HDL are associated with protection from CVD.This review addresses the current state of knowledge regarding assays of HDL functions and their relationship to CVD. HDL as a therapeutic target is the new frontier with huge potential for positive public health implications.

Neuroprotection and neurodegeneration in Alzheimer's disease: role of cardiovascular disease risk factors, implications for dementia rates, and prevention with aerobic exercise in african americans

Prevalence of Alzheimer's disease (AD) will reach epidemic proportions in the United States and worldwide in the coming decades, and with substantially higher rates in African Americans (AAs) than in Whites. Older age, family history, low levels of education, and ɛ4 allele of the apolipoprotein E (APOE) gene are recognized risk factors for the neurodegeneration in AD and related disorders. In AAs, the contributions of APOE gene to AD risk continue to engender a considerable debate. In addition to the established role of cardiovascular disease (CVD) risk in vascular dementia, it is now believed that CVD risk and its endophenotype may directly comediate AD phenotype. Given the pleiotropic effects of APOE on CVD and AD risks, the higher rates of CVD risks in AAs than in Whites, it is likely that CVD risks contribute to the disproportionately higher rates of AD in AAs. Though the advantageous effects of aerobic exercise on cognition is increasingly recognized, this evidence is hardly definitive, and data on AAs is lacking. In this paper, we will discuss the roles of CVD risk factors in the development of AD and related dementias, the susceptibility of these risk factors to physiologic adaptation, and fitness-related improvements in cognitive function. Its relevance to AD prevention in AAs is emphasized.

LCAT, HDL cholesterol and ischemic cardiovascular disease: a Mendelian randomization study of HDL cholesterol in 54,500 individuals

BACKGROUND

Epidemiologically, high-density lipoprotein (HDL) cholesterol levels associate inversely with risk of ischemic cardiovascular disease. Whether this is a causal relation is unclear.

METHODS

We studied 10,281 participants in the Copenhagen City Heart Study (CCHS) and 50,523 participants in the Copenhagen General Population Study (CGPS), of which 991 and 1,693 participants, respectively, had developed myocardial infarction (MI) by August 2010. Participants in the CCHS were genotyped for all six variants identified by resequencing lecithin-cholesterol acyltransferase in 380 individuals. One variant, S208T (rs4986970, allele frequency 4%), associated with HDL cholesterol levels in both the CCHS and the CGPS was used to study causality of HDL cholesterol using instrumental variable analysis.

RESULTS

Epidemiologically, in the CCHS, a 13% (0.21 mmol/liter) decrease in plasma HDL cholesterol levels was associated with an 18% increase in risk of MI. S208T associated with a 13% (0.21 mmol/liter) decrease in HDL cholesterol levels but not with increased risk of MI or other ischemic end points. The causal odds ratio for MI for a 50% reduction in plasma HDL cholesterol due to S208T genotype in both studies combined was 0.49 (0.11-2.16), whereas the hazard ratio for MI for a 50% reduction in plasma HDL cholesterol in the CCHS was 2.11 (1.70-2.62) (P(comparison) = 0.03).

CONCLUSION

Low plasma HDL cholesterol levels robustly associated with increased risk of MI but genetically decreased HDL cholesterol did not. This may suggest that low HDL cholesterol levels per se do not cause MI.

Hydroxyalkenals and oxidized phospholipids modulation of endothelial cytoskeleton, focal adhesion and adherens junction proteins in regulating endothelial barrier function

Lipid peroxidation of polyunsaturated fatty acids generates bioactive aldehydes, which exhibit pro- and anti-inflammatory effects in cells and tissues. Accumulating evidence indicates that 4-hydroxynonenal (4-HNE), a major aldehyde derived from lipid peroxidation of n-6 polyunsaturated fatty acids trigger signals that modulates focal adhesion and adherens junction proteins thereby inducing endothelial barrier dysfunction. Similarly, oxidized phospholipids (Ox-PLs) generated by lipid peroxidation of phospholipids with polyunsaturated fatty acids have been implicated in atherogenesis, inflammation and gene expression. Interestingly, physiological concentration of Ox-PLs is anti-inflammatory and protect against endotoxin- and ventilator-associated acute lung injury. Thus, excess generation of bioactive hydroxyalkenals and Ox-PLs during oxidative stress contributes to pathophysiology of various diseases by modulating signaling pathways that regulate pro- and anti-inflammatory responses and barrier regulation. This review summarizes the role of 4-HNE and Ox-PLs affecting cell signaling pathways and endothelial barrier dysfunction through modulation of the activities of proteins/enzymes by Michael adducts formation, enhancing the level of protein tyrosine phosphorylation of the target proteins, and by reorganization of cytoskeletal, focal adhesion, and adherens junction proteins. A better understanding of molecular mechanisms of hydroxyalkenals- and Ox-PLs-mediated pro-and anti-inflammatory responses and barrier function may lead to development of novel therapies to ameliorate oxidative stress related cardio-pulmonary disorders.

Antiatherogenic function of HDL particle subpopulations: focus on antioxidative activities

Oxidative stress, an emerging risk factor for premature atherosclerosis and cardiovascular disease, mediates the formation of proinflammatory, pro-atherogenic oxidized low-density lipoprotein (oxLDL) in the arterial intima. Circulating HDL particles, and particularly small, dense, protein-rich HDL3, may provide potent protection of LDL in vivo from oxidative damage by free radicals in the arterial intima, resulting in the inhibition of the generation of proinflammatory oxidized lipids, primarily lipid hydroperoxides (LOOH) but also short-chain oxidized phospholipids (oxPL). HDL-mediated inactivation of LOOH involves initial transfer of phospholipid hydroperoxides (PLOOH) from LDL to HDL3, which is governed by the rigidity of the surface monolayer of HDL, and subsequent reduction of PLOOH by redox-active Met residues of apolipoprotein A-I (apoA-I) with the formation of phospholipid hydroxides (PLOH) and methionine sulphoxides. HDL-associated enzymes may in turn contribute to the hydrolytic inactivation of short-chain oxPL. Mounting evidence suggests that the integrated antioxidative activity of HDL appear to be defective in atherogenic dyslipidaemias involving low HDL-cholesterol levels; anomalies in the proteome and lipidome of HDL particles in dyslipidaemic patients may underlie such functional deficiency. Pharmacological normalization of HDL metabolism concomitantly with correction of circulating levels, composition and biological activities of HDL particles, with enrichment in apoA-I and reduction in HDL surface rigidity, may constitute an efficacious therapeutic approach to attenuate atherosclerosis in dyslipidaemic patients at high cardiovascular risk.

Generation and biological activities of oxidized phospholipids

Glycerophospholipids represent a common class of lipids critically important for integrity of cellular membranes. Oxidation of esterified unsaturated fatty acids dramatically changes biological activities of phospholipids. Apart from impairment of their structural function, oxidation makes oxidized phospholipids (OxPLs) markers of "modified-self" type that are recognized by soluble and cell-associated receptors of innate immunity, including scavenger receptors, natural (germ line-encoded) antibodies, and C-reactive protein, thus directing removal of senescent and apoptotic cells or oxidized lipoproteins. In addition, OxPLs acquire novel biological activities not characteristic of their unoxidized precursors, including the ability to regulate innate and adaptive immune responses. Effects of OxPLs described in vitro and in vivo suggest their potential relevance in different pathologies, including atherosclerosis, acute inflammation, lung injury, and many other conditions. This review summarizes current knowledge on the mechanisms of formation, structures, and biological activities of OxPLs. Furthermore, potential applications of OxPLs as disease biomarkers, as well as experimental therapies targeting OxPLs, are described, providing a broad overview of an emerging class of lipid mediators.

Anti-oxidant properties of high-density lipoprotein and atherosclerosis

1. High-density lipoprotein (HDL) is one of the major carriers of cholesterol in the blood. It attracts particular attention because, in contrast with other lipoproteins, many physiological functions of HDL influence the cardiovascular system in favourable ways unless HDL is modified pathologically. 2. The best known function of HDL is the capacity to promote cellular cholesterol efflux from peripheral cells and deliver cholesterol to the liver for excretion, thereby playing a key role in reverse cholesterol transport. The functions of HDL that have recently attracted attention include anti-inflammatory and anti-oxidant activities. High anti-oxidant and anti-inflammatory activities of HDL are associated with protection from cardiovascular disease. 3. Atheroprotective activities, as well as a functional deficiency of HDL, ultimately depend on the protein and lipid composition of HDL. Conversely, these activities are compromised in many pathological states associated with inflammation. 4. The focus of the present review is on the anti-oxidant and anti-inflammatory functions of HDL and its individual components in relation to protection from atherosclerosis.

A hapten generated from an oxidation fragment of docosahexaenoic acid is sufficient to initiate age-related macular degeneration

The protein adduct carboxyethylpyrrole (CEP) is present in age-related macular degeneration (AMD) eye tissue and in the blood of AMD patients at higher levels than found in age-matched non-AMD tissues. Autoantibodies to CEP are also higher in AMD blood samples than in controls. To test the hypothesis that this hapten is causally involved in initiating an inflammatory response in AMD, we immunized C57BL/6J mice with mouse serum albumin (MSA) adducted with CEP. Immunized mice develop antibodies to CEP, fix complement component-3 in Bruch's membrane, accumulate drusen below the retinal pigment epithelium during aging, show decreased a- and b-wave amplitudes in response to light, and develop lesions in the retinal pigment epithelium mimicking geographic atrophy, the blinding end-stage condition characteristic of the dry form of AMD. Inflammatory cells are present in the region of lesions and may be actively involved in the pathology observed. We conclude that early immunization of mice with CEP-adducted MSA sensitizes these animals to the ongoing production of CEP adducts in the outer retina where DHA is abundant and the conditions for oxidative damage are permissive. In response to this early sensitization, the immune system mounts a complement-mediated attack on the cells of the outer retina where CEP adducts are formed. This animal model for AMD is the first that was developed from an inflammatory signal discovered in eye tissue and blood from AMD patients. It provides a novel opportunity for dissecting the early pathology of AMD and the immune response contributing to this disorder. The availability of a mouse with a mechanistically based AMD-like disease that progresses rapidly is highly desirable. Such a model will allow for the efficient preclinical testing of the much-needed therapeutics quickly and inexpensively.

HDL3-Mediated Inactivation of LDL-Associated Phospholipid Hydroperoxides Is Determined by the Redox Status of Apolipoprotein A-I and HDL Particle Surface Lipid Rigidity

Objectives— Small dense HDL3 particles of defined lipidome and proteome potently protect atherogenic LDL against free radical-induced oxidation; the molecular determinants of such antioxidative activity in these atheroprotective, antiinflammatory particles remain indeterminate.

Methods and Results— Formation of redox-active phosphatidylcholine hydroperoxides (PCOOH) and redox-inactive phosphatidylcholine hydroxides (PCOH) was initiated in LDL by free radical-induced oxidation. Human HDL3 inactivated LDL-derived PCOOH (−62%, P <0.01) and enhanced accumulation of PCOH (2.1-fold, P <0.05); in parallel, HDL3 accumulated minor amounts of PCOOH. Enzyme-deficient reconstituted dense HDL potently inactivated PCOOH (−43%, P <0.01). HDL3-mediated reduction of PCOOH to PCOH occurred concomitantly with oxidation of methionine residues in HDL3-apolipoprotein AI (apoAI). Preoxidation of methionine residues by chloramine T markedly attenuated PCOOH inactivation (−35%); by contrast, inhibition of HDL3-associated enzymes was without effect. PCOOH transfer rates from oxidized LDL to phospholipid liposomes progressively decreased with increment in the rigidity of the phospholipid monolayer.

Conclusions— The redox status of apoAI and surface lipid rigidity represent major determinants of the potent HDL3-mediated protection of LDL against free radical-induced oxidation. Initial transfer of PCOOH to HDL3 is modulated by the surface rigidity of HDL3 particles with subsequent reduction of PCOOH to PCOH by methionine residues of apoAI.

Anti-(apolipoprotein A-1) IgGs are associated with high levels of oxidized low-density lipoprotein in acute coronary syndrome

ApoA-1 (apolipoprotein A-1) is the main component of HDL (high-density lipoprotein) and stabilizes PON-1 (paraoxonase-1), which prevents lipid peroxidation and oxLDL (oxidized low-density lipoprotein) formation. Autoantibodies against apoA-1 [anti-(apoA-1) IgG] have been found in antiphospholipid syndrome and systemic lupus erythematosous, two diseases with an increased risk of thrombotic events, as well as in ACS (acute coronary syndrome). OxLDL levels are also elevated in these diseases. Whether anti-(apoA-1) IgGs exist in other prothrombotic conditions, such as APE (acute pulmonary embolism) and stroke, has not been studied and their potential association with oxLDL and PON-1 activity is not known. In the present study, we determined prospectively the prevalence of anti-(apoA-1) IgG in patients with ACS (n=127), APE (n=58) and stroke (n=34), and, when present, we tested their association with oxLDL levels. The prevalance of anti-(apoA-1) IgG was 11% in the ACS group, 2% in the control group and 0% in the APE and stroke groups. The ACS group had significantly higher median anti-(apoA-1) IgG titres than the other groups of patients. Patients with ACS positive for anti-(apoA-1) IgG had significantly higher median oxLDL values than those who tested negative (226.5 compared with 47.7 units/l; P<0.00001) and controls. The Spearman ranked test revealed a significant correlation between anti-(apoA-1) IgG titres and serum oxLDL levels (r=0.28, P<0.05). No association was found between PON-1 activity and oxLDL or anti-(apoA-1) IgG levels. In conclusion, anti-(apoA-1) IgG levels are positive in ACS, but not in stroke or APE. In ACS, their presence is associated with higher levels of oxLDL and is directly proportional to the serum concentration of oxLDL. These results emphasize the role of humoral autoimmunity as a mediator of inflammation and coronary atherogenesis.

Inconsistencies in the genetic prediction of HDL cholesterol versus atherosclerosis

PURPOSE OF REVIEW

High-density lipoprotein (HDL) is generally perceived as having a protective role with respect to cardiovascular disease. The metabolism of HDL is mediated through a complex network of apoproteins, enzymes and transfer proteins. Genetic variants within this network can increase plasma HDL, but not with uniformly beneficial clinical outcomes. The purpose of this review is to explore and propose mechanisms for these discrepant observations.

RECENT FINDINGS

Recent developments in this area include new observations of genetic variants that paradoxically increase both HDL and cardiovascular risk. Also discussed are newly observed, function-altering modifications of the HDL particle. Proposed explanations include the segregation of the genetic variants associated with the respective endpoints of plasma HDL and cardiovascular risk. Functionally impaired but quantitatively robust plasma HDL and the emerging understanding of proinflammatory HDL also may contribute to our understanding of discordant observations.

SUMMARY

Enhanced understanding of these relationships may allow a more accurate assessment of clinical risk based on plasma HDL and help explain why HDL may, in some circumstances, be an inappropriate therapeutic target.

A dual role for lecithin:cholesterol acyltransferase (EC 2.3.1.43) in lipoprotein oxidation

Lecithin:cholesterol acyltransferase (LCAT) is a key enzyme involved in lipoprotein metabolism. It mediates the transesterification of free cholesterol to cholesteryl ester in an apoprotein A-I-dependent process. We have isolated purified LCAT from human plasma using anion-exchange chromatography and characterized the extracted LCAT in terms of its molecular weight, molar absorption coefficient, and enzymatic activity. The participation of LCAT in the oxidation of very low density lipoproteins (VLDL) and low-density lipoproteins (LDL) was examined by supplementing lipoproteins with exogenous LCAT over a range of protein concentrations. LCAT-depleted lipoproteins were also prepared and their oxidation kinetics examined. Our results provide evidence for a dual role for LCAT in lipoprotein oxidation, whereby it acts in a dose-responsive manner as a potent pro-oxidant during VLDL oxidation, but as an antioxidant during LDL oxidation. We believe this novel pro-oxidant effect may be attributable to the LCAT-mediated formation of oxidized cholesteryl ester in VLDL, whereas the antioxidant effect is similar to that of chain-breaking antioxidants. Thus, we have demonstrated that the high-density lipoprotein-associated enzyme LCAT may have a significant role to play in lipoprotein modification and hence atherogenesis.

High-density lipoproteins: a therapeutic target for atherosclerotic cardiovascular disease

Despite great progress being made during the last two decades in cardiovascular disease prevention, especially by lowering low-density lipoprotein-cholesterol with statins, cardiovascular events continue to occur. Plasma high-density lipoprotein (HDL) exerts multiple protective effects on the arterial wall, through promotion of reverse cholesterol transport, prevention of endothelial dysfunction and inhibition of lipid oxidation. Therapeutic interventions raising plasma HDL levels or directly mimicking its beneficial effects represent the next frontier in the prevention and treatment of cardiovascular disease.

Alterations in lipoprotein defense against oxidative stress in metabolic syndrome

Metabolic syndrome (MetS) is a high-risk condition for premature atherosclerotic vascular disease. Patients with MetS display a lipoprotein profile in which dense low-density lipoproteins (LDL), which are more susceptible to oxidation, predominate. Oxidation of lipoproteins can be attenuated in vivo by enzymatic and nonenzymatic antioxidant defenses, but high-density lipoproteins (HDL) play a key role in the protection of LDL from oxidation. Such activity depends on the presence of apolipoproteins (apoA-I, apoA-II, apoA-IV, apoE) and enzymes (paraoxonase 1, platelet activating factor-acetylhydrolase, lecithin:cholesterol acyltransferase, glutathione peroxidase). The impairment of HDL antioxidative activity in MetS is partly related to an enrichment of small HDL in triglycerides and their depletion in cholesteryl esters, to the replacement of apoA-I by serum amyloid A, and to glycation and oxidation of apoA-I. Therapeutic normalization of the quantity and the quality of HDL particles may constitute a novel approach to attenuate atherosclerosis and cardiovascular risk in MetS.

Platelet-activating factor-acetylhydrolase can monodeacylate and inactivate lipoteichoic acid

Bacterial lipoteichoic acid (LTA) shares a structural motif with platelet-activating factor (PAF). Both molecules are strong inflammatory agents and have a glycerol backbone with two lipid chains at the sn-1 and sn-2 positions. PAF is normally inactivated by PAF-acetylhydrolase (PAF-AH), a phospholipase A2 (PLA2), which removes a short acyl group at the sn-2 position. To investigate whether PAF-AH can similarly degrade LTA, we studied the effects of porcine PLA2, bee venom PLA2, and recombinant human PAF-AH on pneumococcal LTA (PnLTA) and staphylococcal LTA (StLTA). After incubation with a porcine or bee venom PLA2, a large fraction of PnLTA lost 264 Da, which corresponds to the mass of the oleic acid group at the sn-2 position. After incubation with recombinant human PAF-AH, PnLTA lost 264 Da; the reduction did not occur when PAF-AH was exposed to Pefabloc SC, an irreversible inhibitor of the PAF-AH active site. Following PAF-AH treatment, PnLTA and StLTA were not able to stimulate mouse RAW 264.7 cells to produce tumor necrosis factor alpha but could stimulate CHO cells expressing human TLR2. This stimulation pattern has been observed with monoacyl PnLTA prepared by mild alkali hydrolysis (22). Taking these data together, we conclude that PAF-AH can remove one acyl chain at the sn-2 position of LTA and produce a monoacyl-LTA that is inactive against mouse cells.

Plasma PAF-acetylhydrolase: an unfulfilled promise?

Plasma Platelet-activating-Factor (PAF)-acetylhydrolase (PAF-AH also named lipoprotein-PLA(2) or PLA(2)G7 gene) is secreted by macrophages, it degrades PAF and oxidation products of phosphatidylcholine produced upon LDL oxidation and/or oxidative stress, and thus is considered as a potentially anti-inflammatory enzyme. Cloning of PAF-AH has sustained tremendous promises towards the use of PAF-AH recombinant protein in clinical situations. The reason for that stems from the numerous animal models of inflammation, atherosclerosis or sepsis, where raising the levels of circulating PAF-AH either through recombinant protein infusion or through the adenoviral gene transfer showed to be beneficial. Unfortunately, neither in human asthma nor in sepsis the recombinant PAF-AH showed sufficient efficacy. One of the most challenging questions nowadays is as to whether PAF-AH is pro- or anti-atherogenic in humans, as PAF-AH may possess a dual pro- and anti-inflammatory role, depending on the concentration and the availability of potential substrates. It is equally possible that the plasma level of PAF-AH is a diagnostic marker of ongoing atherosclerosis.

Estradiol fatty acid esterification is increased in high density lipoprotein subclass 3 isolated from hypertriglyceridemic subjects

Estrogen fatty acid esters are potent lipophilic estrogens transported exclusively in lipoproteins. They are formed in HDL in a reaction catalyzed by LCAT which is considered a prerequisite for their antioxidative action. Our previous studies in normotriglyceridemic (NTG) individuals demonstrated that estradiol (E2) esterification occurred mainly in HDL3 causing accumulation of esterified, but not of unesterified E2 in the lipoprotein particles. Using HDL obtained from hypertriglyceridemic (HTG) patients, we now investigated the effect of altered HDL composition on E2 esterification. Ultracentrifugally isolated HDL2 and HDL3 from NTG- and HTG-males were incubated in an in vitro model system with radioactive and with supraphysiological concentrations of non-radioactive E2 with and without exogenous LCAT. After purification, copper-induced oxidation of HDL was measured by monitoring conjugated diene formation. The results demonstrated that (i) E2 esterification occurring mainly in HDL3 was significantly more efficient in HTG-HDL3 compared to NTG-HDL3, (ii) triglyceride content in HDL3 correlated positively with E2 esterification rate, and (iii) addition of both exogenous LCAT and E2 into the incubation prolonged lag time of HDL3 oxidation. Thus, HDL composition regulates LCAT-facilitated E2 esterification but the in vivo role of this finding can be verified only in experiments using physiological hormone concentrations.

Cholesteryl ester transfer protein (CETP) inhibition beyond raising high-density lipoprotein cholesterol levels: pathways by which modulation of CETP activity may alter atherogenesis

Raising high-density lipoprotein cholesterol (HDL-C) is a promising strategy in the struggle to prevent cardiovascular disease, and cholesteryl ester transfer protein (CETP) inhibitors have been developed to accomplish this. The first results are encouraging, and, in fact, in rabbits, inhibition of CETP reduces atherosclerosis. Because human data regarding the reduction of atheroma burden require more time, the biochemical mechanisms underlying the putative atheroprotection of CETP inhibitors are currently dissected, and several pathways have emerged. First, CETP inhibition increases HDL-C and reduces low-density lipoprotein cholesterol (LDL-C) levels consistent with CETP lipid transfer activity and its role in reverse cholesterol transport (RCT). This coincides with putative beneficial increases in both HDL and LDL size. However, many aspects regarding the impact of CETP inhibition on the RCT pathway remain elusive, in particular whether the first step concerning cholesterol efflux from peripheral tissues to HDL is influenced. Moreover, the relevance of scavenger receptor BI and consequently the central role of HDL in human RCT is still unclear. Second, CETP inhibition was shown recently to increase antioxidant enzymes associated with HDL, in turn associated with decreased oxidation of LDL. Atheroprotection in man is currently anticipated based on the improvement of these biochemical parameters known to influence atherosclerosis, but final confirmation regarding the impact of CETP inhibition on cardiovascular outcome will have to come from trials evaluating clinical end points.

Increased atherosclerosis in mice lacking apolipoprotein A-I attributable to both impaired reverse cholesterol transport and increased inflammation

To test the hypothesis that apolipoprotein A-I (apoA-I) functions specifically to inhibit atherosclerosis independent of the level of high-density lipoprotein cholesterol (HDL-C) by promoting both reverse cholesterol transport and HDL antiinflammatory function in vivo, we established a murine atherosclerosis model of apoA-I deficiency in which the level of HDL-C is well maintained. ApoA-I-/- mice were crossed with atherosclerosis susceptible low-density lipoprotein receptor-/-/apobec-/- (LA) mice to generate LA mice with apoA-I+/+, apoA-I+/-, and apoA-I-/- genotypes. There were no major differences in the amounts of non-HDL-C and HDL-C in the plasma between different apoA-I genotypes. A significant inverse relationship was observed, however, between apoA-I gene dose and atherosclerosis in both female and male mice. Compared with LA-apoA-I+/+ mice, serum from LA-apoA-I-/- mice had a significantly reduced capacity to function as an acceptor of ABCA1- and SR-BI-mediated cellular cholesterol efflux, and also had markedly reduced lecithin cholesterol acyltransferase activity. In addition, LA-apoA-I-/- mice had significantly reduced macrophage-derived cholesterol esterification and reverse cholesterol transport in vivo. There was significantly reduced plasma paraoxonase (PON-1) activity, impaired HDL vascular antiinflammatory function, and increased basal levels of monocyte chemotactic protein-1 in the plasma of LA-apoA-I-/- mice compared with LA-apoA-I+/+ mice. In LA-apoA-I-/- mice, there was also greater induction of some, but not all, inflammatory cytokines and chemokines in response to intraperitoneal injection of lipopolysaccharide than in LA-apoA-I+/+ mice. We conclude that apoA-I inhibits atherosclerosis by promoting both macrophage reverse cholesterol transport and HDL antiinflammatory function, and that these anti-atherogenic functions of apoA-I are largely independent of the plasma level of HDL-C in this mouse model.

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.

Phospholipid mediators in the vessel wall: involvement in atherosclerosis

PURPOSE OF REVIEW

This review provides a brief update on the involvement of major phospholipid mediators, with the emphasis on platelet-activating factor and its analogues generated upon the oxidation of lipoproteins in vascular pathology, including atherogenesis.

RECENT FINDINGS

Phospholipid mediators are produced during inflammation by various enzymes, mostly from pre-existing membrane phospholipids, and trigger cellular signaling via G-coupled receptors. A short description of lysophosphatidic acid, lysophosphocholine and sphingosine-1 phosphate receptors and their actions is given, but attention is focused mainly on platelet-activating factor and its analogues. The majority of these mediators participate in leukocyte adhesiveness to the endothelium, leukocyte transmigration into the vessel wall and the subsequent formation of various chemokines leading to foam cell formation and smooth muscle cell proliferation and dedifferentiation. Platelet-activating factor and platelet-activating factor-like phospholipids are degraded in plasma by the lipoprotein-bound enzyme of myeloid origin, PAF-acetylhydrolase, also known as LDL-PLA2. Although the overexpression of PAF-acetylhydrolase shows marked anti-atherogenic properties in animal models, epidemiological data in the Caucasian population have demonstrated that its level might be a risk factor for cardiovascular disease. Recent genetic studies have shown, however, that the A379V polymorphism of this gene, responsible for slightly higher enzymatic activity, exerts a protective effect, probably by modifying the enzyme function towards a less atherogenic form.

SUMMARY

Phospholipid-borne mediators are certainly key players in inflammation and thus in atherosclerosis. The generation of such biologically active molecules is possibly dependent on nutritional habits and the availability of antioxidants, including enzymes protective against oxidative damage, including PAF-acetylhydrolase.

Delay of Iris flower senescence by protease inhibitors

Visible senescence of the flag tepals in Iris x hollandica (cv. Blue Magic) was preceded by a large increase in endoprotease activity. Just before visible senescence about half of total endoprotease activity was apparently due to cysteine proteases, somewhat less than half to serine proteases, with a minor role of metalloproteases. Treatment of isolated tepals with the purported serine protease inhibitors AEBSF [4-(2-aminoethyl)-benzenesulfonyl fluoride] or DFP (diisopropyl-fluorophosphate) prevented the increase in endoprotease activity and considerably delayed or prevented the normal senescence symptoms. The specific cysteine protease-specific E-64d reduced maximum endoprotease activity by 30%, but had no effect on the time to visible senescence. Zinc chloride and aprotinin reduced maximum endoprotease activity by c. 50 and 40%, respectively, and slightly delayed visible senescence. A proteasome inhibitor (Z-leu-leu-Nva-H) slightly delayed tepal senescence, which indicates that protein degradation in the proteasome may play a role in induction of the visible senescence symptoms. It is concluded that visible senescence is preceded by large-scale protein degradation, which is apparently mainly due to cysteine- and serine protease activity, and that two (unspecific) inhibitors of serine proteases considerably delay the senescence symptoms.

Metabolic syndrome is associated with elevated oxidative stress and dysfunctional dense high-density lipoprotein particles displaying impaired antioxidative activity

A metabolic syndrome (MetS) phenotype is characterized by insulin-resistance, atherogenic dyslipidemia, oxidative stress, and elevated cardiovascular risk and frequently involves subnormal levels of high-density lipoprotein (HDL) cholesterol. We evaluated the capacity of physicochemically distinct HDL subfractions from MetS subjects to protect low-density lipoprotein against oxidative stress.MetS subjects presented an insulin-resistant phenotype, with central obesity and elevation in systolic blood pressure and plasma triglyceride, LDL-cholesterol, apolipoprotein B, glucose, and insulin levels. Systemic oxidative stress, assessed as plasma 8-isoprostanes, was significantly higher (3.7-fold) in MetS subjects (n = 10) compared with nonobese normolipidemic controls (n = 11). In MetS, small, dense HDL3a, 3b, and 3c subfractions possessed significantly lower specific antioxidative activity (up to -23%, on a unit particle mass basis) than their counterparts in controls. In addition, HDL2a and 3a subfractions from MetS patients possessed lower total antioxidative activity (up to -41%, at equivalent plasma concentrations). The attenuated antioxidative activity of small, dense HDL subfractions correlated with systemic oxidative stress and insulin resistance and was associated with HDL particles exhibiting altered physicochemical properties (core triglyceride enrichment and cholesteryl ester depletion). We conclude that antioxidative activity of small, dense HDL subfractions of altered chemical composition is impaired in MetS and associated with elevated oxidative stress and insulin resistance. Induction of selective increase in the circulating concentrations of dense HDL subfractions may represent an innovative therapeutic approach for the attenuation of high cardiovascular risk in MetS.

Aldose reductase-catalyzed reduction of aldehyde phospholipids

Oxidation of unsaturated phospholipids results in the generation of aldehyde side chains that remain esterified to the phospholipid backbone. Such "core" aldehydes elicit immune responses and promote inflammation. However, the biochemical mechanisms by which phospholipid aldehydes are metabolized or detoxified are not well understood. In the studies reported here, we examined whether aldose reductase (AR), which reduces hydrophobic aldehydes, metabolizes phospholipid aldehydes. Incubation with AR led to the reduction of 5-oxovaleroyl, 7-oxo-5-heptenoyl, 5-hydroxy-6-oxo-caproyl, and 5-hydroxy-8-oxo-6-octenoyl phospholipids generated upon oxidation of 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine (PAPC). The enzyme also catalyzed the reduction of phospholipid aldehydes generated from the oxidation of 1-alkyl, and 1-alkenyl analogs of PAPC, and 1-palmitoyl-2-arachidonoyl phosphatidic acid or phosphoglycerol. Aldose reductase catalyzed the reduction of chemically synthesized 1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphatidylcholine (POVPC) with a K(m) of 10 mum. Addition of POVPC to the culture medium led to incorporation and reduction of the aldehyde in COS-7 and THP-1 cells. Reduction of POVPC in these cells was prevented by the AR inhibitors sorbinil and tolrestat and was increased in COS-7 cells overexpressing AR. Together, these observations suggest that AR may be a significant participant in the metabolism of several structurally diverse phospholipid aldehydes. This metabolism may be a critical regulator of the pro-inflammatory and immunogenic effects of oxidized phospholipids.