Metabolism of native and naturally occurring multiple modified low density lipoprotein in smooth muscle cells of human aortic intima

Edible bird's nest regulates glucose and lipid metabolic disorders via the gut-liver axis in obese mice

Edible bird's nest (EBN) is a traditional food known for its nourishing and functional properties and is found to be involved in anti-oxidation, anti-aging, and anti-influenza mechanisms, immune regulation, and improving cardiovascular diseases, among others. However, the potential of EBN to improve glycolipid metabolism disorders in high-fat-diet induced obesity and the underlying mechanisms remain unexplored. We examined the effects of EBN on glycolipid metabolism in obese mice fed a high-fat diet. Male C57BL/6J mice were fed a high-fat diet for 8 weeks to establish an obesity model. The obese mice were selected and divided into six groups: two model control groups (normal and high-fat diets) and four intervention groups [Neu5Ac and low-, medium-, and high-dose EBN], with 12 mice in each group. After 10 weeks of continuous gavage intervention, only mice in the high-dose EBN intervention group had lower body weight and total fat content, especially visceral fat. Meanwhile, intervention with three doses of EBN reduced serum FBG, TC, LDL, Ox-LDL, IL-1β, IL-6, and TNF-α levels and increased serum HDL levels and energy expenditure. Using the high dosage as a paradigm, EBN intervention increased the sialic acid content in LDL, decreased TMAO in the liver, and increased GLP-1 levels in sera. EBN increased the colonic abundances of Akkermansia, Lactobacillus, and Desulfovibrio and reduced those of Lysinibacillus and Bacillus. The changes in the microbial community contribute to increasing colonic bile acids, reducing lipopolysaccharide synthesis to protect the intestinal barrier, and lowering inflammation levels. Changes were also observed in colonic transcripts and metabolites and liver gene transcripts and metabolites, which were mainly enriched in pathways of glycolipid metabolism, immune function amelioration, inflammatory signal mitigation, circadian rhythm, bile acid metabolism and insulin resistance. Therefore, EBN may enhance the gut microbiota and intestinal immunity, relieve chronic inflammation levels in serum, improve antioxidant capacity and circadian rhythm in the liver, promote bile acid metabolism, and decrease lipid absorption and lipid synthesis via the gut-liver axis. Consequently, this may reduce blood lipid and fat accumulation as well as improve islet function and reduce blood glucose levels.

The many roles of cathepsins in restenosis

Drug-eluting stents (DES) and dual antiplatelet regimens have significantly improved the clinical management of ischemic heart disease; however, the drugs loaded with DES in clinical practice are mostly paclitaxel or rapamycin derivatives, which target symptoms of post implantation proliferation and inflammation, leading to delayed re-endothelialization and neo-atherosclerosis. Along with the treatments already in place, there is a need for novel strategies to lessen the negative clinical outcomes of DES delays as well as a need for greater understanding of their pathobiological mechanisms. This review concentrates on the function of cathepsins (Cats) in the inflammatory response and granulation tissue formation that follow Cat-induced damage to the vasculature scaffold, as well as the functions of Cats in intimal hyperplasia, which is characterized by the migration and proliferation of smooth muscle cells, and endothelial denudation, re-endothelialization, and/or neo-endothelialization. Additionally, Cats can alter essential neointima formation and immune response inside scaffolds, and if Cats are properly controlled in vivo, they may improve scaffold biocompatibility. This unique profile of functions could lead to an original concept for a cathepsin-based coronary intervention treatment as an adjunct to stent placement.

Local Accumulation of Lymphocytes in the Intima of Human Aorta Is Associated with Giant Multinucleated Endothelial Cells: Possible Explanation for Mosaicism of Atherosclerosis

Distribution of different types of atherosclerotic lesions in the arterial wall is not diffuse, but is characterized by mosaicism. The causes of such distribution remain to be established. At the early stages of atherogenesis, low-density lipoprotein (LDL) particles and immune cells penetrate into the intimal layer of the arterial wall through the endothelium. In adult humans, the luminal surface of the arterial wall is a heterogeneous monolayer of cells with varying morphology including typical endothelial cells (ECs) and multinucleated variant endothelial cells (MVECs). We hypothesized that distribution of MVECs in the endothelial monolayer can be related to the distribution pattern of early atherosclerotic lesions. We obtained en face preparations of intact adult (22–59 years old) aortic wall sections that allowed us to study the endothelial monolayer and the subendothelial layer. We compared the distribution of MVECs in the endothelial monolayer with the localization of early atherosclerotic lesions in the subendothelial layer, which were characterized by lipid accumulation and immune cell recruitment. In primary culture, MVECs demonstrated increased phagocytic activity compared to mononuclear ECs. Moreover, we have shown that unaffected aortic intima contained associates formed as a result of aggregation and/or fusion of LDL particles that are non-randomly distributed. This indicated that MVECs may be involved in the accumulation of LDL in the subendothelial layer through increased transcytosis. Interaction of LDL with subendothelial cells of human aorta in primary culture increased their adhesive properties toward circulating immune cells. Study of unaffected aortic intima revealed non-random distribution of leukocytes in the subendothelial layer and increased localization of CD45+ leukocytes in the subendothelial layer adjacent to MVECs. Together, our observations indicate that MVECs may be responsible for the distribution of atherosclerotic lesions in the arterial wall by participating in LDL internalization and immune cell recruitment.

Lipoprotein sialylation in atherosclerosis: Lessons from mice

Sialylation is a dynamically regulated modification, which commonly occurs at the terminal of glycan chains in glycoproteins and glycolipids in eukaryotic cells. Sialylation plays a key role in a wide array of biological processes through the regulation of protein-protein interactions, intracellular localization, vesicular trafficking, and signal transduction. A majority of the proteins involved in lipoprotein metabolism and atherogenesis, such as apolipoproteins and lipoprotein receptors, are sialylated in their glycan structures. Earlier studies in humans and in preclinical models found a positive correlation between low sialylation of lipoproteins and atherosclerosis. More recent works using loss- and gain-of-function approaches in mice have revealed molecular and cellular mechanisms by which protein sialylation modulates causally the process of atherosclerosis. The purpose of this concise review is to summarize these findings in mouse models and to provide mechanistic insights into lipoprotein sialylation and atherosclerosis.

Oxidized-Desialylated Low-Density Lipoprotein Inhibits the Antitumor Functions of Lymphokine Activated Killer Cells

Elevated concentrations of circulating low density lipoprotein (LDL) that is abnormally oxidized and desialylated is both a precursor to and a hallmark of atherosclerosis. Peripheral blood mononuclear cells (PBMCs) treated in vitro with interleukin-2 (IL-2) become lymphokine activated killer (LAK) cells, the primary effectors of which are NK cells and NKT cells. LAK cells display antitumor functions such as increased cytotoxicity and IFN-γ production, and they have been evaluated as a potential cancer therapeutic. Atherosclerotic processes may influence innate immunity against cancer. Because prior studies have shown that low density lipoprotein (LDL) reduces T-cell and NK cell antitumor functions, we asked whether oxidized-desialylated LDL affects the functionality of LAK cells in vitro. We show here that LAK cells take up oxidized-desialylated LDL to a significantly greater extent than native LDL over a period of 72 hours. This resulted in a significant downregulation of LAK cell cytotoxicity against K562 cells. In particular, the expression of IFN-γ, CD56, and NKG2D were reduced upon oxidized-desialylated LDL treatment of LAK cells and, conversely, their expression was enhanced with native LDL. It was also observed that as the number of CD56 and NKG2D positive cells decreased upon treatment with oxidized-desialylated LDL, the number of CD3 positive cells increased in proportion. Additionally, only a slight inhibition of LAK cell cytotoxicity was observed with desialylation alone of LDL, and no significant inhibition was observed with oxidation alone of LDL. Thus, this study describes a new role of oxidized-desialylated LDL as an inhibitor of the antitumor functions of LAK cells. These observations have implications for how atherosclerosis processes, namely oxidation and desialylation of LDL, may influence LAK cell antitumor activity.

Impact of protein glycosylation on lipoprotein metabolism and atherosclerosis

Protein glycosylation is a post-translational modification consisting in the enzymatic attachment of carbohydrate chains to specific residues of the protein sequence. Several types of glycosylation have been described, with N-glycosylation and O-glycosylation being the most common types impacting on crucial biological processes, such as protein synthesis, trafficking, localization, and function. Genetic defects in genes involved in protein glycosylation may result in altered production and activity of several proteins, with a broad range of clinical manifestations, including dyslipidaemia and atherosclerosis. A large number of apolipoproteins, lipoprotein receptors, and other proteins involved in lipoprotein metabolism are glycosylated, and alterations in their glycosylation profile are associated with changes in their expression and/or function. Rare genetic diseases and population genetics have provided additional information linking protein glycosylation to the regulation of lipoprotein metabolism.

Sialic acid metabolism as a potential therapeutic target of atherosclerosis

Sialic acid (Sia), the acylated derivative of the nine-carbon sugar neuraminic acid, is a terminal component of the oligosaccharide chains of many glycoproteins and glycolipids. In light of its important biological and pathological functions, the relationship between Sia and coronary artery disease (CAD) has been drawing great attentions recently. Large-scale epidemiological surveys have uncovered a positive correlation between plasma total Sia and CAD risk. Further research demonstrated that N-Acetyl-Neuraminic Acid, acting as a signaling molecule, triggered myocardial injury via activation of Rho/ROCK-JNK/ERK signaling pathway both in vitro and in vivo. Moreover, there were some evidences showing that the aberrant sialylation of low-density lipoprotein, low-density lipoprotein receptor and blood cells was involved in the pathological process of atherosclerosis. Significantly, the Sia regulates immune response by binding to sialic acid-binding immunoglobulin-like lectin (Siglecs). The Sia-Siglecs axis is involved in the immune inflammation of atherosclerosis. The generation of Sia and sialylation of glycoconjugate both depend on many enzymes, such as sialidase, sialyltransferase and trans-sialidase. Abnormal activation or level of these enzymes associated with atherosclerosis, and inhibitors of them might be new CAD treatments. In this review, we focus on summarizing current understanding of Sia metabolism and of its relevance to atherosclerosis.

The Atherogenic Role of Circulating Modified Lipids in Atherosclerosis

Lipid accumulation in the arterial wall is a crucial event in the development of atherosclerotic lesions. Circulating low-density lipoprotein (LDL) is the major source of lipids that accumulate in the atherosclerotic plaques. It was discovered that not all LDL is atherogenic. In the blood plasma of atherosclerotic patients, LDL particles are the subject of multiple enzymatic and non-enzymatic modifications that determine their atherogenicity. Desialylation is the primary and the most important atherogenic LDL modification followed by a cascade of other modifications that also increase blood atherogenicity. The enzyme trans-sialidase is responsible for the desialylation of LDL, therefore, its activity plays an important role in atherosclerosis development. Moreover, circulating modified LDL is associated with immune complexes that also have a strong atherogenic potential. Moreover, it was shown that antibodies to modified LDL are also atherogenic. The properties of modified LDL were described, and the strong evidence indicating that it is capable of inducing intracellular accumulation of lipids was presented. The accumulated evidence indicated that the molecular properties of modified LDL, including LDL-containing immune complexes can serve as the prognostic/diagnostic biomarkers and molecular targets for the development of anti-atherosclerotic drugs.

Inhibiting Extracellular Cathepsin D Reduces Hepatic Steatosis in Sprague⁻Dawley Rats †

Dietary and lifestyle changes are leading to an increased occurrence of non-alcoholic fatty liver disease (NAFLD). Using a hyperlipidemic murine model for non-alcoholic steatohepatitis (NASH), we have previously demonstrated that the lysosomal protease cathepsin D (CTSD) is involved with lipid dysregulation and inflammation. However, despite identifying CTSD as a major player in NAFLD pathogenesis, the specific role of extracellular CTSD in NAFLD has not yet been investigated. Given that inhibition of intracellular CTSD is highly unfavorable due to its fundamental physiological function, we here investigated the impact of a highly specific and potent small-molecule inhibitor of extracellular CTSD (CTD-002) in the context of NAFLD. Treatment of bone marrow-derived macrophages with CTD-002, and incubation of hepatic HepG2 cells with a conditioned medium derived from CTD-002-treated macrophages, resulted in reduced levels of inflammation and improved cholesterol metabolism. Treatment with CTD-002 improved hepatic steatosis in high fat diet-fed rats. Additionally, plasma levels of insulin and hepatic transaminases were significantly reduced upon CTD-002 administration. Collectively, our findings demonstrate for the first time that modulation of extracellular CTSD can serve as a novel therapeutic modality for NAFLD.

Pathways of smooth muscle foam cell formation in atherosclerosis

PURPOSE OF REVIEW

Smooth muscle cells (SMCs) are the major cell type in human atherosclerosis-prone arteries and take up excess lipids, thereby contributing to luminal occlusion. Here we provide a focused review on pathways by which smooth muscle cells (SMCs) can become foam cells in atherosclerosis.

RECENT FINDINGS

A synthesis of recent and older investigations provides key mechanistic insights into SMC foam cell formation. LDL and other apoB-containing lipoproteins are modified by a diverse array of oxidative, enzymatic, and nonenzymatic processes present in the arterial intima. These modifications of LDL all promote the aggregation of LDL (agLDL), a key finding from analysis of arterial lesion particles. Scavenger receptor and phagocytic capacity of SMCs can vary greatly, perhaps related to differences in SMC phenotype or in-vitro cell culture environments, and can be increased with exposure to cytokines, growth factors, and cholesterol. Macrophages promote the formation of SMC foam cells in direct or indirect co-culture models.

SUMMARY

SMCs contribute significantly to the foam cell population in atherosclerosis. Further investigation and identification of key mechanisms of SMC foam cell formation will help drive new therapeutics to reduce cardiovascular disease.

Novel Approaches to Anti-atherosclerotic Therapy: Cell-based Models and Herbal Preparations (Review of Our Own Data)

Atherosclerosis is a chronic arterial disease characterized by vascular inflammation, accumulation of lipids in the arterial wall, and formation and growth of atherosclerotic plaques followed by ischemia. In subclinical atherosclerosis, cholesterol retention in subendothelial cells leads to induction of local inflammation, generation of foam cells and lesion formation, followed by a chain of other pathogenic events. Atherosclerotic progression can frequently be fatal, since plaque rupture may lead to thrombosis and acute events, such as myocardial infarction, stroke and sudden death. Traditional anti-atherosclerotic therapy is mainly focused on improving the blood lipid profile and does not target various stages of plaque progression. Obviously, treating the disease at initial stages is better than beginning treatment at advanced stages and, in that regard, current atherosclerosis management can be improved. Cholesterol retention is an important component of atherogenesis that precedes plaque formation. Therapeutic targeting of cholesterol retention may be beneficial for preventing further atherogenic progression. For this purpose, we suggest using herbal preparations due to good tolerability and suitability for long-lasting treatment. We developed test systems based on cultured human intimal aortic cells for rapid screening of potential anti-atherogenic drugs. With the help of these test systems, we selected several natural substances with significant anti-atherogenic activity and further use these compounds to prepare herbal preparations for anti-atherosclerotic therapy. These preparations were clinically tested and showed good safety and a potent anti-atherogenic potential.

Low-density lipoprotein net charge is a risk factor for atherosclerosis in lupus patients independent of lipid concentrations

AIMS

Patients with systemic lupus erythematosus (SLE) suffer from accelerated atherosclerosis. Their most common cause of death is a cardiovascular disease (CVD), in spite of the presence of moderate lipid alterations and normal cardiovascular risk scores. However, cholesterol still accumulates in the arteries of SLE patients, so we aim to identify additional factors that may help explain the residual risk that exists in these patients. We focus on investigating whether the net charge contributes significantly to both the development and the progression of atherosclerosis in patients with SLE.

METHODS

The lipoproteins from 78 patients with SLE and 32 controls were isolated via sequential ultracentrifugation. Lipoprotein subclasses distributions were analyzed via nuclear magnetic resonance spectroscopy and the net charges of very low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), low-density lipoprotein (LDL) and high-density lipoprotein (HDL) were measured using a Zetasizer Nano-ZS. The degree of atherosclerosis (carotid intima-media thickness [cIMT]) was determined in all the participants.

RESULTS

Each lipoprotein class exhibited a negative net charge. IDL and LDL net charge correlated negatively with cIMT (r = -0.274, P = 0.034; r = -0.288; P = 0.033, respectively) in patients with SLE. This effect was independent of age, body mass index (BMI), gender, tobacco consumption, high-sensitivity C-reactive protein (hsCRP), lipid concentration and lipoprotein particle number. LDL net charge explained 4% of the cIMT variability among these patients; this contribution was also independent of age, BMI, gender, tobacco consumption, lipids levels, apolipoproteins and hsCRP.

CONCLUSIONS

Low-density lipoprotein net charge may be considered a new independent contributor to subclinical atherosclerosis in SLE patients. The observed relationship was independent of lipid concentrations and extends the prominent role that IDL and LDL play in cardiovascular risk.

One-Year Conservative Care Using Sodium Bicarbonate Supplementation Is Associated with a Decrease in Electronegative LDL in Chronic Kidney Disease Patients: A Pilot Study

Background

Chronic kidney disease (CKD) patients develop metabolic acidosis when approaching stages 3 and 4, a period in which accelerated atherogenesis may ensue. Studies in vitro show that low pH may increase low-density lipoprotein (LDL) oxidation, suggesting a role for chronic metabolic acidosis in atherosclerosis. The present study attempted to evaluate the effects of conservative care using oral sodium bicarbonate (NaHCO₃) supplementation on the electronegative LDL [LDL(-)], a minimally oxidized LDL, plasma levels in CKD patients.

Methods

Thirty-one CKD patients were followed by a multidisciplinary team during 15 months of care in which 1.0 mmol/kg/day oral NaHCO₃ supplementation was first given in the third month. Blood samples were collected 3 months before the initiation of oral NaHCO₃ supplementation (T1), at the time of the beginning of supplementation (T2), and thereafter, each 4 months (T3, T4 and T5) until month 15 of care. Blood parameters and LDL(-) were measured from these collections.

Results

After 12 months of conservative care, creatinine clearance (MDRD) was kept stable, and serum bicarbonate (HCO₃^-) increased from 20.5 ± 2.9 to 22.6 ± 1.1 mM (p < 0.003). LDL(-) plasma levels declined from 4.5 ± 3.3 to 2.1 ± 0.9 U/L (p < 0.007) after reaching mean serum HCO₃^- levels of 22.6 ± 1.1 mM.

Conclusions

Conservative care using oral NaHCO₃ supplementation was able to stabilize renal function and decrease serum levels of LDL(-), a modified proatherogenic lipoprotein, only when mean serum HCO₃^- levels approached 22 mM. This study constitutes evidence that alkali therapy, in addition to its beneficial effect on renal disease progression, might serve as a preventive strategy to attenuate atherogenesis in CKD patients.

Development of Antiatherosclerotic Drugs on the basis of Natural Products Using Cell Model Approach

Atherosclerosis including its subclinical form is one of the key medical and social problems. At present, there is no therapy available for widespread use against subclinical atherosclerosis. The use of synthetic drugs for the prevention of arteriosclerosis in its early stages is not sufficient because of the limited indications for severe side effects and high cost of treatment. Obviously, effective antiatherosclerotic drugs based on natural products would be a preferred alternative. Simple cell-based models for testing different natural products have been developed and the ability of natural products to prevent intracellular lipid accumulation in primary cell culture was evaluated. This approach utilizing cell models allowed to test effects of such direct antiatherosclerotic therapy, analyzing the effects mimicking those which can occur "at the level" of arterial wall via the inhibition of intracellular lipid deposition. The data from the carried out clinical trials support a point of view that the identification of antiatherosclerotic activity of natural products might offer a great opportunity for the prevention and treatment of atherosclerotic disease, reducing cardiovascular morbidity and mortality.

Macrophages in immunopathology of atherosclerosis: a target for diagnostics and therapy

Immunopathology plays important roles in the development of different life-threatening diseases, such as atherosclerosis and its consequences (acute myocardial infarction and stroke), cancer, chronic inflammatory diseases. Effective modulation of the immune system may significantly increase the efficacy of prevention and therapy efforts. Currently there are no marketed drugs capable of normalizing immune system function in an intrinsic and comprehensive way. Here, we describe a test system designed for complex analysis of monocyte activity in individuals to diagnose immunopathology and monitor treatment efficacy. This cell-based test system may also be useful for screening compounds with an immune-correcting effects. Both diagnostic and screening systems are based on primary culture of human monocytes and/or monocyte-derived macrophages. This is the first step in creating a method for assessment of macrophage activity, which is required for further development of immune-correcting drugs. The existing preliminary data provide the basis for realization of this idea.

Modified low density lipoprotein and lipoprotein-containing circulating immune complexes as diagnostic and prognostic biomarkers of atherosclerosis and type 1 diabetes macrovascular disease

In atherosclerosis; blood low-density lipoproteins (LDL) are subjected to multiple enzymatic and non-enzymatic modifications that increase their atherogenicity and induce immunogenicity. Modified LDL are capable of inducing vascular inflammation through activation of innate immunity; thus, contributing to the progression of atherogenesis. The immunogenicity of modified LDL results in induction of self-antibodies specific to a certain type of modified LDL. The antibodies react with modified LDL forming circulating immune complexes. Circulating immune complexes exhibit prominent immunomodulatory properties that influence atherosclerotic inflammation. Compared to freely circulating modified LDL; modified LDL associated with the immune complexes have a more robust atherogenic and proinflammatory potential. Various lipid components of the immune complexes may serve not only as diagnostic but also as essential predictive markers of cardiovascular events in atherosclerosis. Accumulating evidence indicates that LDL-containing immune complexes can also serve as biomarker for macrovascular disease in type 1 diabetes.

Approach to reduction of blood atherogenicity

We have earlier found that blood sera of patients with coronary heart disease (CHD) increase lipid levels in cells cultured from subendothelial intima of human aorta. We have also revealed that the ability of blood sera to raise intracellular cholesterol; that is, their atherogenicity is caused by at least modified low density lipoprotein (LDL) circulating in the blood of patients and autoantibodies to modified LDL. In the present work we have demonstrated significant impact of nonlipid factor(s) to blood atherogenicity. We have developed an approach to removal of nonlipid atherogenicity factor(s) from blood serum based on the use of immobilized LDL. This approach was used for extracorporeal perfusion of patient's blood through the column with immobilized LDL. Pilot clinical study confirmed the efficacy of this approach for prevention of coronary atherosclerosis progression.

The genetic polymorphisms of cathepsin S were associated with metabolic disorders in a Chinese Han population

Cathepsin S (CTSS) played an important role in the etiology of cardiovascular disease and metabolic syndrome. Few studies had been reported on the association between the polymorphisms of CTSS and metabolic disorders in Asian population. Therefore we explored the association between the polymorphisms of CTSS and metabolic disorders in a Chinese Han population. The subjects were a Chinese Han cohort with 1160 participants, and the genotyping was performed with PCR-RFLP. Polymorphism rs16827671 was associated with BMI and serum total cholesterol (P=0.001; P=0.02, respectively). Subjects with CT genotype of rs16827671 had a higher risk of hypercholesterolemia (OR=1.64, 95% CI: 1.15-2.33, P=0.006) compared with TT genotype. Subjects with AG genotype of rs11576175 had lower risks of hypertriglyceridemia and borderline hypercholesterolemia (OR=0.52, 95% CI: 0.36-0.73, P=0.0001; OR=0.52, 95% CI: 0.35-0.77, P=0.001, respectively) compared with GG genotype. Compared with the haplotype TG, haplotype TA had a lower risk of hypertriglyceridemia and a higher risk of borderline hypercholesterolemia (OR=0.62, 95% CI: 0.44-0.88, P=0.002; OR=1.59, 95% CI: 1.10-2.31, P=0.008, respectively), and haplotype CA had a lower risk of hypercholesterolemia (OR=0.35, 95% CI: 0.18-0.68, P=0.002). In conclusion, we found that the genetic polymorphisms of CTSS were associated with metabolic disorders in a Chinese Han population, which would enrich the knowledge on genetic mechanisms of the pathogenesis of metabolic disorders.

Kinetic modeling of low density lipoprotein oxidation in arterial wall and its application in atherosclerotic lesions prediction

Oxidation of low-density lipoprotein (LDL) is one of the major factors in atherogenic process. Trapped oxidized LDL (Ox-LDL) in the subendothelial matrix is taken up by macrophage and leads to foam cell generation creating the first step in atherosclerosis development. Many researchers have studied LDL oxidation using in vitro cell-induced LDL oxidation model. The present study provides a kinetic model for LDL oxidation in intima layer that can be used in modeling of atherosclerotic lesions development. This is accomplished by considering lipid peroxidation kinetic in LDL through a system of elementary reactions. In comparison, characteristics of our proposed kinetic model are consistent with the results of previous experimental models from other researches. Furthermore, our proposed LDL oxidation model is added to the mass transfer equation in order to predict the LDL concentration distribution in intima layer which is usually difficult to measure experimentally. According to the results, LDL oxidation kinetic constant is an important parameter that affects LDL concentration in intima layer so that existence of antioxidants that is responsible for the reduction of initiating rates and prevention of radical formations, have increased the concentration of LDL in intima by reducing the LDL oxidation rate.

Correlation between lipid deposition, immune-inflammatory cell content and MHC class II expression in diffuse intimal thickening of the human aorta

Inflammatory reactions driven by an accumulation in the intima of immune-inflammatory cells and focal lipid depositions are the hallmarks of atherogenesis. It is commonly accepted that immune-inflammatory cell accumulation and lipid deposition are associated with the very earlier stage of atherosclerosis but no study has yet focused on the determination of quantitative values of this association. The present study examined correlations between lipid deposition, immune-inflammatory cell content and major histocompatibility complex (MHC) class II molecule HLA-DR expression in diffuse intimal thickening (DIT), which is thought to represent the earliest macroscopic manifestation of atherosclerosis. In parallel consecutive tissue sections of DIT, lipids were examined by chromatographic analysis (including triglycerides, cholesteryl esters, free cholesterol and phospholipids), histochemically, using Oil Red O staining, and by electron microscopy. Immune-inflammatory cells and HLA-DR expression were examined immunohistochemically in consecutive sections of the same tissue specimens. The study revealed that lipids exhibited a non-uniform distribution throughout the intima. In the juxtaluminal sublayer, lipids were localized both intracellularly and extracellularly, whereas in the juxtamedial musculoelastic sublayer, lipids were present predominantly along elastic fibers. Lipid deposits were found to positively correlate with HLA-DR expression (r=0.79; p<0.001). The study also identified a positive correlation between lipid deposition and immune-inflammatory cell content but the correlation values varied between different sublayers of the tunica intima. The correlation between lipid deposition and immune-inflammatory cell content in the juxtaluminal sublayer of the intima was notably stronger (r=0.69; p<0.001) than in the juxtamedial musculoelastic layer (r=0.28; p<0.001). The findings of the present study support a view that lipid accumulation in the intima plays a role in the initiation of inflammatory reaction and that at the pre-lesional stage in the development of atherosclerosis, lipid-associated immune cell activation might occur primarily in the juxtaluminal portion of the intima.

Cysteinyl cathepsins and mast cell proteases in the pathogenesis and therapeutics of cardiovascular diseases

The initiation and progression of cardiovascular diseases involve extensive arterial wall matrix protein degradation. Proteases are essential to these pathological events. Recent discoveries suggest that proteases do more than catabolize matrix proteins. During the pathogenesis of atherosclerosis, abdominal aortic aneuryms, and associated complications, cysteinyl cathepsins and mast cell tryptases and chymases participate importantly in vascular cell apoptosis, foam cell formation, matrix protein gene expression, and pro-enzyme, latent cytokine, chemokine, and growth factor activation. Experimental animal disease models have been invaluable in examining each of these protease functions. Deficiency and pharmacological inhibition of cathepsins or mast cell proteases have allowed their in vivo evaluation in the setting of pathological conditions. Recent discoveries of highly selective and potent inhibitors of cathepsins, chymase, and tryptase, and their applications in vascular diseases in animal models and non-vascular diseases in human trials, have led to the hypothesis that selective inhibition of cathepsins, chymases, and tryptase will benefit patients suffering from cardiovascular diseases. This review highlights recent discoveries from in vitro cell-based studies to experimental animal cardiovascular disease models, from protease knockout mice to treatments with recently developed selective and potent protease inhibitors, and from patients with cathepsin-associated non-vascular diseases to those affected by cardiovascular complications.

Widespread distribution of HLA-DR-expressing cells in macroscopically undiseased intima of the human aorta: a possible role in surveillance and maintenance of vascular homeostasis

The architectonics and cell composition of the human large arteries are not sufficiently understood. The present study is the first to undertake an analysis of the distribution and quantities of HLA-DR-expressing cells in grossly undiseased human intima using immunohistochemical and immunofluorescent analysis, complemented by the advantages of confocal microscopy. The study revealed a widespread distribution of HLA-DR-expressing cells throughout the intimal space where the cells were integrated into continuous networks via long cell processes. Numbers of HLA-DR+ cells were found to be significantly larger in the middle third of the intima than in the superficial and deep intimal portions. We speculate that a widespread distribution of HLA-DR-expressing cells in the intima of normal human aorta might play a role in the surveillance and maintenance of vascular homeostasis.

Alpha-tocopherol supplementation decreases electronegative low-density lipoprotein concentration [LDL(-)] in haemodialysis patients

BACKGROUND

Oxidative stress is a significant contributor to cardiovascular diseases (CVD) in haemodialysis (HD) patients, predisposing to the generation of oxidized low-density lipoprotein (oxLDL) or electronegatively charged LDL subfraction. Antioxidant therapy such as alpha-tocopherol acts as a scavenger of lipid peroxyl radicals attenuating the oxidative stress, which decreases the formation of oxLDL. The present study was designed to investigate the influence of the alpha-tocopherol supplementation on the concentration of electronegative low-density lipoprotein [LDL(-)], a minimally oxidized LDL, which we have previously described to be high in HD patients.

METHODS

Blood samples were collected before and after 120 days of supplementation by alpha-tocopherol (400 UI/day) in 19 stable HD patients (50 +/- 7.8 years; 9 males). The concentrations of LDL(-) in blood plasma [using an anti-LDL- human monoclonal antibody (mAb)] and the anti-LDL(-) IgG auto-antibodies were determined by ELISA. Calculation of body mass index (BMI) and measurements of waist circumference (WC), triceps skin folds (TSF) and arm muscle area (AMA) were performed.

RESULTS

The plasma alpha-tocopherol levels increased from 7.9 microM (0.32-18.4) to 14.2 microM (1.22-23.8) after the supplementation (P = 0.02). The mean concentration of LDL(-) was reduced from 570.9 microg/mL (225.6-1241.0) to 169.1 microg/mL (63.6-621.1) (P < 0.001). The anti-LDL(-) IgG auto-antibodies did not change significantly after the supplementation. The alpha-tocopherol supplementation also reduced the total cholesterol and LDL-C levels in these patients, from 176 +/- 42.3 mg/dL to 120 +/- 35.7 mg/dL (P < 0.05) and 115.5 +/- 21.4 mg/dL to 98.5 +/- 23.01 mg/dL (P < 0.001), respectively.

CONCLUSION

The oral administration of alpha-tocopherol in HD patients resulted in a significant decrease in the LDL(-), total cholesterol and LDL-C levels. This effect may favour a reduction in cardiovascular risk in these patients, but a larger study is required to confirm an effect in this clinical setting.

Altered gene expression in early atherosclerosis is blocked by low level apolipoprotein E

BACKGROUND

Mice deficient in apolipoprotein E (apoE(-/-)) develop atherosclerosis. The possible linkage between expression of adhesion molecules/cofactors and atherosclerosis was probed at the level of mRNA and protein expression. The hypothesis of a linkage between changes of adhesion molecules/cofactors and atherosclerosis was tested further by suppression of aortic lesion formation in apoE(-/-) mice by expression of very low levels of transgenic apolipoprotein E.

METHODOLOGY/PRINCIPAL FINDINGS

We show that at 8.5 months of age, the apoE(-/-) mice display elevated expression of mRNA for LFA-1, MAC-1, VCAM-1, ICAM-1, and for CD44, as well as MCP-1, cathepsin B, and COX-2 (but not that for eNOS) in atherosclerotic aortic arches. At earlier age, (10-13 week old) apoE(-/-) mice already display elevated expression of mRNA of CD44, LFA-1, MAC-1, VCAM-1, ICAM-1, cathepsin, and of COX-2 in lesioned aortic arches. Expressing very low levels of transgenic apolipoprotein E suppresses both aortic lesions and the expression of mRNA of LFA-1, VCAM-1, MCP-1, cathepsin B, and of ICAM-1 in ApoE(-/-) mice. We tested at the level of protein, the observations obtained for mRNA expression. CD11a (a component of LFA-1), VCAM-1 and cathepsin B expression was found to be elevated in apoE(-/-) aortas at 8-9 months; low level expression of transgenic apolipoprotein E rectifies these changes.

CONCLUSIONS/SIGNIFICANCE

Atherosclerotic lesions in apoE(-/-) mice are detected as early as 4 weeks of age. Expression of low levels of apoE is shown to be both atheroprotective and to suppress these changes in key adhesion and inflammatory molecules observed in early atherosclerotic lesions.

Cathepsin cysteine proteases in cardiovascular disease

Extracellular matrix (ECM) remodeling is one of the underlying mechanisms in cardiovascular diseases. Cathepsin cysteine proteases have a central role in ECM remodeling and have been implicated in the development and progression of cardiovascular diseases. Cathepsins also show differential expression in various stages of atherosclerosis, and in vivo knockout studies revealed that deficiency of cathepsin K or S reduces atherosclerosis. Furthermore, cathepsins are involved in lipid metabolism. Cathepsins have the capability to degrade low-density lipoprotein and reduce cholesterol efflux from macrophages, aggravating foam cell formation. Although expression studies also demonstrated differential expression of cathepsins in cardiovascular diseases like aneurysm formation, neointima formation, and neovascularization, in vivo studies to define the exact role of cathepsins in these processes are lacking. Evaluation of the feasibility of cathepsins as a diagnostic tool revealed that serum levels of cathepsins L and S seem to be promising as biomarkers in the diagnosis of atherosclerosis, whereas cathepsin B shows potential as an imaging tool. Furthermore, cathepsin K and S inhibitors showed effectiveness in (pre) clinical evaluation for the treatment of osteoporosis and osteoarthritis, suggesting that cathepsin inhibitors may also have therapeutic effects for the treatment of atherosclerosis.

Antiatherogenic effect of grape flavonoids in an ex vivo model

The effects of grape phytoestrogens on cholesterol accumulation were studied in primary culture of human blood monocytes incubated with blood serum from postmenopausal women obtained before and 2, 4, and 6 h after single intake of plant components of grapes. Phytoestrogens from grape seeds, pressed out grapes, and fermented grape ridges prevent cholesterol accumulation in cells and can be regarded as prospective components for the development of natural preparations for the prevention of atherosclerosis in postmenopausal women.

Convergence of genes implicated in Alzheimer's disease on the cerebral cholesterol shuttle: APP, cholesterol, lipoproteins, and atherosclerosis

Polymorphic genes associated with Alzheimer's disease (see ) delineate a clearly defined pathway related to cerebral and peripheral cholesterol and lipoprotein homoeostasis. They include all of the key components of a glia/neurone cholesterol shuttle including cholesterol binding lipoproteins APOA1, APOA4, APOC1, APOC2, APOC3, APOD, APOE and LPA, cholesterol transporters ABCA1, ABCA2, lipoprotein receptors LDLR, LRP1, LRP8 and VLDLR, and the cholesterol metabolising enzymes CYP46A1 and CH25H, whose oxysterol products activate the liver X receptor NR1H2 and are metabolised to esters by SOAT1. LIPA metabolises cholesterol esters, which are transported by the cholesteryl ester transport protein CETP. The transcription factor SREBF1 controls the expression of most enzymes of cholesterol synthesis. APP is involved in this shuttle as it metabolises cholesterol to 7-betahydroxycholesterol, a substrate of SOAT1 and HSD11B1, binds to APOE and is tethered to LRP1 via APPB1, APBB2 and APBB3 at the cytoplasmic domain and via LRPAP1 at the extracellular domain. APP cleavage products are also able to prevent cholesterol binding to APOE. BACE cleaves both APP and LRP1. Gamma-secretase (PSEN1, PSEN2, NCSTN) cleaves LRP1 and LRP8 as well as APP and their degradation products control transcription factor TFCP2, which regulates thymidylate synthase (TS) and GSK3B expression. GSK3B is known to phosphorylate the microtubule protein tau (MAPT). Dysfunction of this cascade, carved out by genes implicated in Alzheimer's disease, may play a major role in its pathology. Many other genes associated with Alzheimer's disease affect cholesterol or lipoprotein function and/or have also been implicated in atherosclerosis, a feature of Alzheimer's disease, and this duality may well explain the close links between vascular and cerebral pathology in Alzheimer's disease. The definition of many of these genes as risk factors is highly contested. However, when polymorphic susceptibility genes belong to the same signaling pathway, the risk associated with multigenic disease is better related to the integrated effects of multiple polymorphisms of genes within the same pathway than to variants in any single gene [Wu, X., Gu, J., Grossman, H.B., Amos, C.I., Etzel, C., Huang, M., Zhang, Q., Millikan, R.E., Lerner, S., Dinney, C.P., Spitz, M.R., 2006. Bladder cancer predisposition: a multigenic approach to DNA-repair and cell-cycle-control genes. Am. J. Hum. Genet. 78, 464-479.]. Thus, the fact that Alzheimer's disease susceptibility genes converge on a clearly defined signaling network has important implications for genetic association studies.

Endocytosis and intracellular trafficking of fatty acid esters of phenylaminopropanediol, the putative etiologic agents of the toxic oil syndrome (TOS)

The toxic oil syndrome (TOS) caused by ingestion of rapeseed oil adulterated with aniline is characterized by symptoms of an allergic and/or autoimmune illness associated with vessel wall lesions similar to those of atherosclerosis. Fatty acid esters of 3-(N-phenylamino)-1,2-propanediol (PAP) have been incriminated as the etiologic agents of TOS. However, the pathogenesis of TOS is yet unknown. Here, we addressed whether PAP fatty acid esters are incorporated into lipoproteins, which after transport to vascular endothelial cells are taken up to initiate TOS vasculopathy. After loading (14)C-dioleyl-ester of PAP into LDL labeled with 1,1'-dioctadecyl-3,3,3',3'-tetramethylindolcarbocyanine (DiI) we assessed receptor mediated endocytosis and intracellular localization of these lipopoproteins in vascular endothelial cells. Our data suggest that these lipoprotein-derivatives are internalized into endothelial cells by LDL receptor mediated endocytosis. Confocal microscopy revealed that DiI-LDL loaded with dioleyl-ester of PAP and incubated for 60 min with endothelial cells colocalizes with the lysosomotropic compound LysoTracker Green, indicating that internalized PAP-loaded LDL are targetted to the endolysosomal compartment for further processing. Subcellular fractionation of endothelial-like ECV-304 cells after incubation with LDL loaded with the (14)C-dioleyl-ester of PAP for 6h showed that the radioactive label accumulated in fractions containing endosomes, the Golgi apparatus and the endoplasmic reticulum.

Sialic acid: a novel marker of cardiovascular disease?

The global burden posed by cardiovascular disease (CVD), due to a rising incidence of known risk factors, underlines an urgent need to identify other potential risk factors. Sialic acid (SA), an abundant terminal monosaccharide of glycoconjugates, is a possible risk factor for CVD. Although large-scale epidemiological surveys have shown that serum total sialic acid (TSA) is positively associated with mortality from coronary artery disease (CAD) and stroke, studies investigating the correlation between serum TSA and the severity of atherosclerosis are conflicting. Clinical and epidemiological studies indicate that serum TSA is a marker of a sustained inflammatory response in CVD, rather than causal in nature. Data also indicates ethnic variation in baseline TSA. This article reviews current methods for determining serum TSA and evidence supporting serum TSA as a risk factor for CVD. Potential mechanisms for this role are examined. The use of serum TSA as a marker of atherosclerotic disease is evaluated.

Detection of electronegative low density lipoprotein (LDL-) in plasma and atherosclerotic lesions by monoclonal antibody-based immunoassays

OBJECTIVES

To produce a monoclonal antibody (MAb) against electronegative LDL (LDL-) for detecting this modified lipoprotein in blood plasma and tissues.

DESIGN AND METHODS

LDL- was isolated from human blood plasma and used as an antigen for immunization of Balb/c mice. Lymphocytes of immunized mice were fused with myeloma cells (SP2/0) to obtain the hybridomas. LDL- was detected in blood plasma and atherosclerotic lesions of humans and rabbits by MAb-based ELISA and immunohistochemistry, respectively.

RESULTS

LDL- concentrations were higher (P < 0.05) in the blood plasma of hypercholesterolemic subjects (HC, 248 +/- 77 mg/dL of total cholesterol) than in normolipidemic subjects (NL, 173 +/- 82 mg/dL of total cholesterol) and rabbits (HC, 250 +/- 15 mg/dL of cholesterol versus NL, 81 +/- 12 mg/dL of cholesterol). Moreover, LDL- was detected in the atherosclerotic lesions of humans and rabbits.

CONCLUSION

These MAb-based immunoassays are adequate to detect LDL- in biological samples and represent an important tool for investigating the role of LDL- in atherosclerosis.

Low ionic strength promotes association of circulating modified LDL human blood

The resistance to association of circulating multiply-modified low-density lipoproteins (LDL) isolated from human blood and characterized by a decreased content of sialic acids in comparison with native LDL was studied by analysing light transmission fluctuations. LDL association was stimulated by decreasing environmental ionic strength. It is established that circulating modified LDL are less resistant to association than native LDL. Association of LDL in a medium with low ionic strength was irreversible. Probably, increased capacity to irreversible association determines the atherogenic properties of circulating modified LDL subfraction.

Contribution of HDL-apolipoproteins to the inhibition of low density lipoprotein oxidation and lipid accumulation in macrophages

High-density lipoprotein (HDL) is known as a protective factor against atherosclerosis. However, whether HDL-apolipoproteins (apo-HDL) contribute to the protection in arterial cells remains unclear. The localization patterns of human apolipoproteins in atherosclerotic arteries were determined using immunohistochemical examination. The results indicate that several apolipoproteins are retained in component cells of the coronary artery walls. To elucidate the possible roles of apo-HDL in the protection of atherosclerotic lesion formation, we investigated the effects of apo-HDL on the formation of conjugated diene (CD) in a cell-free system and thiobarbituric acid-reactive substances (TBARS) in the medium of a macrophage-mediated LDL oxidation system. The results showed that apo-HDL significantly exerted an inhibitory effect on LDL lipid oxidation in vitro. In addition, apo-HDL decreased cholesterol influx but enhanced cholesterol efflux from J774 macrophages in a dose-dependent manner. These results are consistent with the notion that there is reduced intracellular lipid accumulation in apo-HDL treated macrophages. These data provide a direct evidence for apo-HDL in protecting LDL from oxidative modification and in reducing the accumulation of cholesterol and lipid droplets by J774 macrophages.

Differential expression of cysteine and aspartic proteases during progression of atherosclerosis in apolipoprotein E-deficient mice

Several groups of proteolytic enzymes are able to degrade components of the extracellular matrix. During atherosclerosis, matrix remodeling is believed to influence the migration and proliferation of cells within the plaque. In the present study, gene expression of several proteases and their inhibitors was analyzed during the development of atherosclerosis in apolipoprotein E-deficient (ApoE-/-) mice. Quantitative real-time polymerase chain reaction was used to study gene expression of proteases after 10 and 20 weeks in ApoE-/- and C57BL/6 mice and in atherosclerotic lesions and nonaffected regions of the same ApoE-/- mouse. Some of the differentially expressed proteolytic enzymes were studied by immunohistochemistry. The matrix metalloproteinase (MMP)-9 and its inhibitor TIMP-1 were differentially expressed and the expression increased with time. Urokinase-type plasminogen activator showed no major expression. In contrast, cathepsins B, D, L, and S all showed strong and increased expression in ApoE-/- mice compared to C57BL/6 mice whereas the expression of their inhibitor, cystatin C, did not differ between the two mouse strains. The expression of cathepsins was mainly localized to the lesions and not to nonaffected regions of the aorta of ApoE-/- mice. Furthermore, cathepsin expression was similar to the expression of the macrophage marker macrosialin (CD68) although expression of cathepsins B, D, and L could be demonstrated in healthy C57BL/6 mice and in nonaffected vessel segments of atherosclerotic ApoE-/- mice. Cathepsin S mRNA expression was restricted to lesions of ApoE-/- mice. Furthermore, cathepsin S was the only cathepsin that was expressed in the media and absent in lipid-rich regions. All cathepsins studied showed intimal expression, the degree and localization of which differed between individual cathepsins. In conclusion, increased expression of several cathepsins in atherosclerotic lesions suggests that these proteases may participate in the remodeling of extracellular matrix associated with the atherosclerotic process.

Human plasma trans-sialidase causes atherogenic modification of low density lipoprotein

In earlier studies we have found that incubation of low density lipoprotein (LDL) with autologous blood plasma-derived serum leads to a loss of sialic acid from lipoprotein particles. In this study we demonstrated that sialic acid removed from LDL was transferred to glycoconjugates of lipoproteins, glycoproteins and sphingolipids of human serum. This showed that human serum contained the trans-sialidase activity. Gel-filtration chromatography of human blood serum demonstrated the presence of trans-sialidase activity in lipoprotein subfractions as well as in lipoprotein-deficient serum. Trans-sialidase (about 65 kDa) was isolated from lipoprotein-deficient serum using affinity chromatography carried out with Neu5Acalpha2-8Neu5Ac-sepharose FF-6. Optimal pH values for the trans-sialidase were 3.0, 5.0 and 7.0. Calcium and magnesium ions stimulated the enzyme activity at millimolar concentrations. Isolated enzyme can remove sialic acid from LDL, IDL, VLDL, and HDL particles (in decreasing rate order). Serum trans-sialidase transferred sialic acid from glycoconjugates of plasma proteins (fetuin, transferrin) and gangliosides (GM3, GD3, GM1, GD1a, GD1b). Sialylated glycoconjugates of human blood erythrocytes also served as substrate for serum trans-sialidase. We have found that sialic acid can also be removed from N- and O-linked glycans, sialylated Le(x) and Le(a), oligosialic acids, and sphingolipid carbohydrate chains. The rate of sialic acid release decreased in the following order: alpha2,6>alpha2,3>>alpha2,8. Transferred molecule of sialic acid can form alpha2,6, alpha2,3 and to a lesser degree alpha2,8 linkage with galactose, N-acetyl-galactosamine or sialic acid of acceptors. The glycoconjugates of erythrocytes, lipoprotein particles, plasma proteins, neutral sphingolipids and gangliosides may serve as acceptors of transferred sialic acid. Trans-sialidase-treated native LDL becomes desialylated and then can induce cholesteryl ester accumulation in human aortic intimal smooth muscle cells. Thus, trans-sialidase may be involved in the early stages of atherogenesis characterized by foam cell formation.

Low-density lipoprotein modification occurring in human plasma possible mechanism of in vivo lipoprotein desialylation as a primary step of atherogenic modification

We previously found in human blood a fraction of low-density lipoprotein (LDL) that is characterized by a reduced content of sialic acid. Desialylated LDL also has a low neutral carbohydrate level, decreased content of major lipids, small size, high density, increased electronegative charge and altered tertiary apolipoprotein B structure. Unlike native LDL, this fraction of desialylated (multiple-modified) LDL induces the accumulation of lipids in smooth muscle cells cultured from unaffected human aortic intima, i.e. it exhibits atherogenic properties. In this study, we attempted to elucidate the mechanism of desialylation and other changes in the multiple-modified LDL by investigating the possibility of LDL modification by different cells and the blood plasma. A 24-h incubation at 37 degrees C of lipoprotein with intact endotheliocytes, hepatocytes, macrophages and smooth muscle cells or cell homogenates did not cause alterations either in the physical properties or in the chemical composition of native LDL. On the other hand, a significant fall in the lipoprotein sialic acid level was observed already after a 1-h incubation of native LDL with an autologous plasma-derived serum. While LDL sialic acid level continuously decreased, LDL became capable of inducing the accumulation of total cholesterol in the smooth muscle cells cultured from unaffected human aortic intima after 3 h of incubation. Starting from the sixth hour of LDL incubation with serum, a steady decrease in the lipoprotein lipid content was observed as well as the related reduction of LDL size. Following 36 h of incubation, an increase in the negative charge of lipoprotein particles was also seen. Prolonged incubation of LDL with plasma-derived serum (48 and 72 h) leads to the loss of alpha-tocopherol by the LDL as well as to an increase in LDL susceptibility to copper oxidation and to accumulation of cholesterol covalently bound to apolipoprotein B, a marker of lipoperoxidation. Degradation of apolipoprotein B starts within the same period of time. Hence, desialylation of LDL particles represents one of the first or the primary act of modification which is, apparently, a sufficient prerequisite for the development of atherogenic properties. Subsequent modifications just enhance the atherogenic potential of LDL. The loss of sialic acid by LDL occurred at neutral pH and was not inhibited by the sialidase inhibitor 2,3-dehydro-2-deoxy-N-acetylneuraminic acid. The [3H]sialic acid removed from LDL was not found in free form, but in the plasma fraction precipitated by trichloroacetic acid. These data along with the fact that cytidine-5'-triphosphate inhibited LDL desialylation suggest that enzymes close to sialyltransferases play a role in this process. Thus, this study demonstrated that the LDL modification processes imparting atherogenic properties to this lipoprotein can take place in human blood plasma. Multiple modification of LDL is a cascade of successive changes in the lipoprotein particle: desialylation, loss of lipids, reduction in particle size, increase of its electronegative charge and peroxidation of lipids.