Group V and X secretory phospholipase A(2)s-induced modification of high-density lipoprotein linked to the reduction of its antiatherogenic functions

The quantitative or qualitative decline of high-density lipoprotein (HDL) is linked to the pathogenesis of atherosclerosis because of its antiatherogenic functions, including the mediation of reverse cholesterol transport from the peripheral cells to the liver. We have recently shown that group X secretory phospholipase A(2) (sPLA(2)-X) is involved in the pathogenesis of atherosclerosis via potent lipolysis of low-density lipoprotein (LDL) leading to macrophage foam cell formation. We demonstrate here that sPLA(2)-X as well as group V secretory PLA(2) (sPLA(2)-V), another group of sPLA(2) that can potently hydrolyze phosphatidylcholine (PC), also possess potent hydrolytic potency for PC in HDL linked to the production of a large amount of unsaturated fatty acids and lysophosphatidylcholine (lysoPC). In contrast, the classical types of group IB and IIA secretory PLA(2)s evoked little, if any, lypolytic modification of HDL. Treatment with sPLA(2)-X or -V also caused an increase in the negative charge of HDL with no oxidation and little modification of apolipoprotein AI (apoAI). Modification with sPLA(2)-X or -V resulted in significant decrease in the capacity of HDL to cause cellular cholesterol efflux from lipid-loaded macrophages. Immunohistochemical analysis revealed significant expression of sPLA(2)-X in foam cell lesions in the arterial intima of Watanabe heritable hyperlipidemic (WHHL) rabbit. These findings suggest that lipolytic modification of HDL by sPLA(2)-X or -V causes drastic change of HDL in terms of the production of a large amount of unsaturated fatty acids and lysoPC linked to the reduction of its antiatherogenic functions. These sPLA(2)-mediated modifications of plasma lipoproteins might be relevant to the pathogenesis of atherosclerosis.     

Differences between group X and group V secretory phospholipase A2 in lipolytic modification of lipoproteins

Secretory phospholipases A(2) (sPLA(2)s) are a diverse family of low molecular mass enzymes (13-18 kDa) that hydrolyze the sn-2 fatty acid ester bond of glycerophospholipids to produce free fatty acids and lysophospholipids. We have previously shown that group X sPLA(2) (sPLA(2)-X) had a strong hydrolyzing activity toward phosphatidylcholine in low-density lipoprotein (LDL) linked to the formation of lipid droplets in the cytoplasm of macrophages. Here, we show that group V sPLA(2) (sPLA(2)-V) can also cause the lipolysis of LDL, but its action differs remarkably from that of sPLA(2)-X in several respects. Although sPLA(2)-V released almost the same amount of fatty acids from LDL, it released more linoleic acid and less arachidonic acid than sPLA(2)-X. In addition, the requirement of Ca(2+) for the lipolysis of LDL was about 10-fold higher for sPLA(2)-V than sPLA(2)-X. In fact, the release of fatty acids from human serum was hardly detectable upon incubation with sPLA(2)-V in the presence of sodium citrate, which contrasted with the potent response to sPLA(2)-X. Moreover, sPLA(2)-X, but not sPLA(2)-V, was found to specifically interact with LDL among the serum proteins, as assessed by gel-filtration chromatography as well as sandwich enzyme-immunosorbent assay using anti-sPLA(2)-X and anti-apoB antibodies. Surface plasmon resonance studies have revealed that sPLA2-X can bind to LDL with high-affinity (K(d) = 3.1 nM) in the presence of Ca(2+). Selective interaction of sPLA(2)-X with LDL might be involved in the efficient hydrolysis of cell surface or intracellular phospholipids during foam cell formation.     

Distinctiveness of secretory phospholipase A2 group IIA and V suggesting unique roles in atherosclerosis

Clinical observations strongly support an association of circulating levels of secretory phospholipases A(2) (sPLA(2)) in atherosclerotic cardiovascular disease (ACVD). Two modes of action can provide causal support for these statistical correlations. One is the action of the enzymes on circulating lipoproteins and the other is direct action on the lipoproteins once in the arterial extracellular intima. In this review we discuss results suggesting a distinct profile of characteristics related to localization, action on plasma lipoproteins and interaction with arterial proteoglycans for sPLA(2)-IIA and sPLA(2)-V. The differences observed indicate that these enzymes may contribute to atherosclerosis through dissimilar pathways. Furthermore, we comment on recent animal studies from our laboratory indicating that the expression of type V enzyme is up-regulated by genetically and nutritionally-induced dyslipidemias but not the group type IIA enzyme, which is well known to be up-regulated by acute inflammation. The results suggest that if similar up-regulation occurs in humans in response to hyperlipidemia, it may create a distinctive link between the group V enzyme and the disease.     

Inhibitory effects of surfactant protein A on surfactant phospholipid hydrolysis by secreted phospholipases A2

Hydrolysis of surfactant phospholipids by secreted phospholipases A(2) (sPLA(2)) contributes to surfactant dysfunction in acute respiratory distress syndrome. The present study demonstrates that sPLA(2)-IIA, sPLA(2)-V, and sPLA(2)-X efficiently hydrolyze surfactant phospholipids in vitro. In contrast, sPLA(2)-IIC, -IID, -IIE, and -IIF have no effect. Since purified surfactant protein A (SP-A) has been shown to inhibit sPLA(2)-IIA activity, we investigated the in vitro effect of SP-A on the other active sPLA(2) and the consequences of sPLA(2)-IIA inhibition by SP-A on surfactant phospholipid hydrolysis. SP-A inhibits sPLA(2)-X activity, but fails to interfere with that of sPLA(2)-V. Moreover, in vitro inhibition of sPLA(2)-IIA-induces surfactant phospholipid hydrolysis correlates with the concentration of SP-A in surfactant. Intratracheal administration of sPLA(2)-IIA to mice causes hydrolysis of surfactant phosphatidylglycerol. Interestingly, such hydrolysis is significantly higher for SP-A gene-targeted mice, showing the in vivo inhibitory effect of SP-A on sPLA(2)-IIA activity. Administration of sPLA(2)-IIA also induces respiratory distress, which is more pronounced in SP-A gene-targeted mice than in wild-type mice. We conclude that SP-A inhibits sPLA(2) activity, which may play a protective role by maintaining surfactant integrity during lung injury.     

Diverse cellular localizations of secretory phospholipase A2 enzymes in several human tissues

The secretory phospholipase A2 (sPLA2) family in mammals contains more than 10 enzymes. In this study, we examined by immunohistochemistry the localization of six sPLA2s (IIA, IID, IIE, IIF, V and X) in human heart, kidney, liver and stomach. In normal hearts, sPLA2-IIA was detected in coronary vascular smooth muscle cells (VSMC) and sPLA2-V in cardiomyocytes beneath the endocardium. In infarcted hearts, expression of these two enzymes was markedly increased in damaged cardiomyocytes, and expression of sPLA2-IID and-IIE, which was undetectable in normal hearts, was elevated in damaged cardiomyocytes and VSMC, respectively. In infarcted kidneys, sPLA2-IIA and-V were markedly induced in the uriniferous tubular epithelium. In livers affected by viral hepatitis, sPLA2-IIA and-V were expressed in hepatocytes with fatty degeneration. In the gastric glands exhibiting intestinal metaplasia, sPLA2-IIA was localized in the glandular base, sPLA2-IID and-V in the glandular body epithelium, sPLA2-IIE and-IIF in goblet cells in the foveolar epithelium, and sPLA2-X in both glandular body epithelial cells and foveolar epithelial goblet cells. In the gastric submucosal tissues, sPLA2-IIA and-IIE were located in VSMC and sPLA2-V was in the interstitial fibroblasts. In addition, sPLA2-IIA,-IIE,-IIF and-X were highly expressed in gastric signet ring cell carcinoma. Thus, individual sPLA2s exhibit unique cellular localizations in each tissue, suggesting their distinct roles in pathophysiology.     

Distinct arachidonate-releasing functions of mammalian secreted phospholipase A2s in human embryonic kidney 293 and rat mastocytoma RBL-2H3 cells through heparan sulfate shuttling and external plasma membrane mechanisms

We analyzed the ability of a diverse set of mammalian secreted phospholipase A(2) (sPLA(2)) to release arachidonate for lipid mediator generation in two transfected cell lines. In human embryonic kidney 293 cells, the heparin-binding enzymes sPLA(2)-IIA, -IID, and -V promote stimulus-dependent arachidonic acid release and prostaglandin E(2) production in a manner dependent on the heparan sulfate proteoglycan glypican. In contrast, sPLA(2)-IB, -IIC, and -IIE, which bind weakly or not at all to heparanoids, fail to elicit arachidonate release, and addition of a heparin binding site to sPLA(2)-IIC allows it to release arachidonate. Heparin nonbinding sPLA(2)-X liberates arachidonic acid most likely from the phosphatidylcholine-rich outer plasma membrane in a glypican-independent manner. In rat mastocytoma RBL-2H3 cells that lack glypican, sPLA(2)-V and -X, which are unique among sPLA(2)s in being able to hydrolyze phosphatidylcholine-rich membranes, act most likely on the extracellular face of the plasma membrane to markedly augment IgE-dependent immediate production of leukotriene C(4) and platelet-activating factor. sPLA(2)-IB, -IIA, -IIC, -IID, and -IIE exert minimal effects in RBL-2H3 cells. These results are also supported by studies with sPLA(2) mutants and immunocytostaining and reveal that sPLA(2)-dependent lipid mediator generation occur by distinct (heparanoid-dependent and -independent) mechanisms in HEK293 and RBL-2H3 cells.     

Induction of distinct sets of secretory phospholipase A(2) in rodents during inflammation

Although the expression of the prototypic secretory phospholipase A(2) (sPLA(2)), group IIA (sPLA(2)-IIA), is known to be up-regulated during inflammation, it remains uncertain if other sPLA(2) enzymes display similar or distinct profiles of induction under pathological conditions. In this study, we investigated the expression of several sPLA(2)s in rodent inflammation models. In lipopolysaccharide (LPS)-treated mice, the expression of sPLA(2)-V, and to a lesser extent that of sPLA(2)-IID, -IIE, and -IIF, were increased, whereas that of sPLA(2)-X was rather constant, in distinct tissues. 12-O-Tetradecanoylphorbol-13-acetate (TPA)-induced mouse ear edema, in which the expression of sPLA(2)-IID, -IIF and -V was increased, was significantly reduced by YM-26734, a competitive sPLA(2)-IIA inhibitor that turned out to inhibit sPLA(2)-IID, -IIE, -V and -X as well. In contrast, sPLA(2)-IIA was dominant in carageenin-induced pleurisy in rats, where the accumulation of exudate fluids and leukocytes was significantly ameliorated by YM-26734. These results indicate that distinct sPLA(2)s can participate in inflammatory diseases according to tissues, animal species, and types of inflammation.     

Redundant and segregated functions of granule-associated heparin-binding group II subfamily of secretory phospholipases A2 in the regulation of degranulation and prostaglandin D2 synthesis in mast cells

We herein demonstrate that mast cells express all known members of the group II subfamily of secretory phospholipase A2 (sPLA2) isozymes, and those having heparin affinity markedly enhance the exocytotic response. Rat mastocytoma RBL-2H3 cells transfected with heparin-binding (sPLA2-IIA, -V, and -IID), but not heparin-nonbinding (sPLA2-IIC), enzymes released more granule-associated markers (beta-hexosaminidase and histamine) than mock- or cytosolic PLA2alpha (cPLA2alpha)-transfected cells after stimulation with IgE and Ag. Site-directed mutagenesis of sPLA2-IIA and -V revealed that both the catalytic and heparin-binding domains are essential for this function. Confocal laser and electron microscopic analyses revealed that sPLA2-IIA, which was stored in secretory granules in unstimulated cells, accumulated on the membranous sites where fusion between the plasma membrane and granule membranes occurred in activated cells. These results suggest that the heparin-binding sPLA2s bind to the perigranular membranes through their heparin-binding domain, and lysophospholipids produced in situ by their enzymatic action may facilitate the ongoing membrane fusion. In contrast to the redundant role of sPLA2-IIA, -IID, and -V in the regulation of degranulation, only sPLA2-V had the ability to markedly augment IgE/Ag-stimulated immediate PGD2 production, which reached a level comparable to that elicited by cPLA2alpha. The latter observation reveals an unexplored functional segregation among the three related isozymes expressed in the same cell population.     

Cellular components that functionally interact with signaling phospholipase A(2)s

Accumulating evidence has suggested that cytosolic phospholipase A(2) (cPLA(2)) and several secretory PLA(2) (sPLA(2)) isozymes are signaling PLA(2)s that are functionally coupled with downstream cyclooxygenase (COX) isozymes for prostaglandin (PG) biosynthesis. Arachidonic acid (AA) released by cPLA(2) and sPLA(2)s is supplied to both COX-1 and COX-2 in the immediate, and predominantly to COX-2 in the delayed, PG-biosynthetic responses. Vimentin, an intermediate filament component, acts as a functional perinuclear adapter for cPLA(2), in which the C2 domain of cPLA(2) associates with the head domain of vimentin in a Ca(2+)-sensitive manner. The heparin-binding signaling sPLA(2)-IIA, IID and V bind the glycosylphosphatidylinositol-anchored heparan sulfate proteoglycan glypican, which plays a role in sorting of these isozymes into caveolae and perinuclear compartments. Phospholipid scramblase, which facilitates transbilayer movement of anionic phospholipids, renders the cellular membranes more susceptible to signaling sPLA(2)s. There is functional cooperation between cPLA(2) and signaling sPLA(2)s in that prior activation of cPLA(2) is required for the signaling sPLA(2)s to act properly. cPLA(2)-derived AA is oxidized by 12/15-lipoxygenase, the products of which not only augment the induction of sPLA(2) expression, but also cause membrane perturbation, leading to increased cellular susceptibility to the signaling sPLA(2)s. sPLA(2)-X, a heparin-non-binding sPLA(2) isozyme, is capable of releasing AA from intact cells in the absence of cofactors. This property is attributed to its ability to avidly hydrolyze zwitterionic phosphatidylcholine, a major phospholipid in the outer plasma membrane. sPLA(2)-V can also utilize this route in several cell types. Taken together, the AA-releasing function of sPLA(2)s depends on the presence of regulatory cofactors and interfacial binding to membrane phospholipids, which differ according to cell type, stimuli, secretory processes, and subcellular distributions.     

Potent modification of low density lipoprotein by group X secretory phospholipase A2 is linked to macrophage foam cell formation

The deposition of cholesterol ester within foam cells of the artery wall is fundamental to the pathogenesis of atherosclerosis. Modifications of low density lipoprotein (LDL), such as oxidation, are prerequisite events for the formation of foam cells. We demonstrate here that group X secretory phospholipase A2 (sPLA2-X) may be involved in this process. sPLA2-X was found to induce potent hydrolysis of phosphatidylcholine in LDL leading to the production of large amounts of unsaturated fatty acids and lysophosphatidylcholine (lyso-PC), which contrasted with little, if any, lipolytic modification of LDL by the classic types of group IB and IIA secretory PLA2s. Treatment with sPLA2-X caused an increase in the negative charge of LDL with little modification of apolipoprotein B (apoB) in contrast to the excessive aggregation and fragmentation of apoB in oxidized LDL. The sPLA2-X-modified LDL was efficiently incorporated into macrophages to induce the accumulation of cellular cholesterol ester and the formation of non-membrane-bound lipid droplets in the cytoplasm, whereas the extensive accumulation of multilayered structures was found in the cytoplasm in oxidized LDL-treated macrophages. Immunohistochemical analysis revealed marked expression of sPLA2-X in foam cell lesions in the arterial intima of high fat-fed apolipoprotein E-deficient mice. These findings suggest that modification of LDL by sPLA2-X in the arterial vessels is one of the mechanisms responsible for the generation of atherogenic lipoprotein particles as well as the production of various lipid mediators, including unsaturated fatty acids and lyso-PC.     

Regulation of type V phospholipase A2 expression and function by proinflammatory stimuli.

Types IIA and V secretory phospholipase A2 (sPLA2) are structurally related to each other and their genes are tightly linked to the same chromosome locus. An emerging body of evidence suggests that sPLA2-IIA plays an augmentative role in long-term prostaglandin (PG) generation in cells activated by proinflammatory stimuli; however, the mechanism underlying the functional regulation of sPLA2-V remains largely unknown. Here we show that sPLA2-V is more widely expressed than sPLA2-IIA in the mouse, in which its expression is elevated by proinflammatory stimuli such as lipopolysaccharide. In contrast, proinflammatory stimuli induced sPLA2-IIA in marked preference to sPLA2-V in the rat. Cotransfection of sPLA2-V with cyclooxygenase (COX)-2, but not with COX-1, into human embryonic kidney 293 cells dramatically increased the interleukin-1-dependent PGE2 generation occurring over a 24 h of culture period. Rat mastocytoma RBL-2H3 cells overexpressing sPLA2-V exhibited increased IgE-dependent PGD2 generation and accelerated beta-hexosaminidase exocytosis. These results suggest that sPLA2-V acts as a regulator of inflammation-associated cellular responses. This possible compensation of sPLA2-V for sPLA2-IIA in many, if not all, tissues may also explain why some mouse strains with natural disruption of the sPLA2-IIA gene exhibit few abnormalities during their life-spans.     

Transgenic expression of group V, but not group X, secreted phospholipase A2 in mice leads to neonatal lethality because of lung dysfunction

In an effort to elucidate the functions of secreted phospholipase A2 (sPLA2) enzymes in vivo, we generated transgenic (Tg) mice for group V sPLA2 (sPLA2-V) and group X sPLA2 (sPLA2-X), which act potently on phosphatidylcholine in vitro.We found that sPLA2-V Tg mice died in the neonatal period because of respiratory failure. The lungs of sPLA2-V Tg mice exhibited atelectasis with thickened alveolar walls and narrow air spaces, accompanied by infiltration of macrophages and only modest changes in eicosanoid levels. This severe pulmonary defect in sPLA2-V Tg mice was attributable to marked reduction of the lung surfactant phospholipids, phosphatidylcholine and phosphatidylglycerol. Given that the expression of sPLA2-V is greatly elevated in human lungs with severe inflammation, our present results raise the intriguing possibility that this isozyme may contribute to ongoing surfactant hydrolysis often observed in the lungs of patients with respiratory distress syndrome. In contrast, sPLA2-X Tg neonates displayed minimal abnormality of the respiratory tract with normal alveolar architecture and surfactant composition. This unexpected result was likely because sPLA2-X protein existed as an inactive zymogen in most tissues. The active form of sPLA2-X was detected in tissues with inflammatory granulation in sPLA2-X Tg mice. These results suggest that sPLA2-X mostly remains inactive under physiological conditions and that its proteolytic activation occurs during inflammation or other as yet unidentified circumstances in vivo.     

Group X secretory phospholipase A(2) induces potent productions of various lipid mediators in mouse peritoneal macrophages

We have previously shown the expression of group X secretory phospholipase A(2) (sPLA(2)-X) in mouse splenic macrophages and its powerful potency for releasing fatty acids from various intact cell membranes. Here, we examined the potency of sPLA(2)-X in the production of lipid mediators in murine peritoneal macrophages. Mouse sPLA(2)-X was found to induce a marked release of fatty acids including arachidonic acid and linoleic acid, which contrasted with little, if any, release by the action of group IB and IIA sPLA(2)s. In resting macrophages, sPLA(2)-X elicited a modest production of prostaglandin E(2) and thromboxane A(2). After the induction of cyclooxygenase-2 (COX-2) by pretreatment with lipopolysaccharide, a dramatic increase in the production of these eicosanoids was observed in sPLA(2)-X-treated macrophages, which was completely blocked by the addition of either the specific sPLA(2) inhibitor indoxam or the COX inhibitor indomethacin. In accordance with its higher hydrolyzing activity toward phosphatidylcholine, mouse sPLA(2)-X induced a potent production of lysophosphatidylcholine. These findings strongly suggest that sPLA(2)-X plays a critical role in the production of various lipid mediators from macrophages. These events might be relevant to the progression of various pathological states, including chronic inflammation and atherosclerosis.     

Purified group X secretory phospholipase A(2) induced prominent release of arachidonic acid from human myeloid leukemia cells

Group X secretory phospholipase A(2) (sPLA(2)-X) possesses several structural features characteristic of both group IB and IIA sPLA(2)s (sPLA(2)-IB and -IIA) and is postulated to be involved in inflammatory responses owing to its restricted expression in the spleen and thymus. Here, we report the purification of human recombinant COOH-terminal His-tagged sPLA(2)-X, the preparation of its antibody, and the purification of native sPLA(2)-X. The affinity-purified sPLA(2)-X protein migrated as various molecular species of 13-18 kDa on SDS-polyacrylamide gels, and N-glycosidase F treatment caused shifts to the 13- and 14-kDa bands. NH(2)-terminal amino acid sequencing analysis revealed that the 13-kDa form is a putative mature sPLA(2)-X and the 14-kDa protein possesses a propeptide of 11 amino acid residues attached at the NH(2) termini of the mature protein. Separation with reverse-phase high performance liquid chromatography revealed that N-linked carbohydrates are not required for the enzymatic activity and pro-sPLA(2)-X has a relatively weak potency compared with the mature protein. The mature sPLA(2)-X induced the release of arachidonic acid from phosphatidylcholine more efficiently than other human sPLA(2) groups (IB, IIA, IID, and V) and elicited a prompt and marked release of arachidonic acid from human monocytic THP-1 cells compared with sPLA(2)-IB and -IIA with concomitant production of prostaglandin E(2). A prominent release of arachidonic acid was also observed in sPLA(2)-X-treated human U937 and HL60 cells. Immunohistochemical analysis of human lung preparations revealed its expression in alveolar epithelial cells. These results indicate that human sPLA(2)-X is a unique N-glycosylated sPLA(2) that releases arachidonic acid from human myeloid leukemia cells more efficiently than sPLA(2)-IB and -IIA.     

Group IID heparin-binding secretory phospholipase A(2) is expressed in human colon carcinoma cells and human mast cells and up-regulated in mouse inflammatory tissues.

Group IID secretory phospholipase A(2) (sPLA(2)-IID), a heparin-binding sPLA(2) that is closely related to sPLA(2)-IIA, augments stimulus-induced cellular arachidonate release in a manner similar to sPLA(2)-IIA. Here we identified the residues of sPLA(2)-IID that are responsible for heparanoid binding, are and therefore essential for cellular function. Mutating four cationic residues in the C-terminal portion of sPLA(2)-IID resulted in abolition of its ability to associate with cell surface heparan sulfate and to enhance stimulus-induced delayed arachidonate release, cyclooxygenase-2 induction, and prostaglandin generation in 293 cell transfectants. As compared with several other group II subfamily sPLA(2)s, which were equally active on A23187- and IL-1-primed cellular membranes, sPLA(2)-IID showed apparent preference for A23187-primed membranes. Several human colon carcinoma cell lines expressed sPLA(2)-IID and sPLA(2)-X constitutively, the former of which was negatively regulated by IL-1. sPLA(2)-IID, but not other sPLA(2) isozymes, was expressed in human cord blood-derived mast cells. The expression of sPLA(2)-IID was significantly altered in several tissues of mice with experimental inflammation. These results indicate that sPLA(2)-IID may be involved in inflammation in cell- and tissue-specific manners under particular conditions.     

Acidity and lipolysis by group V secreted phospholipase A(2) strongly increase the binding of apoB-100-containing lipoproteins to human aortic proteoglycans

Local acidic areas characterize diffuse intimal thickening (DIT) and advanced atherosclerotic lesions. The role of acidity in the modification and extra- and intracellular accumulation of triglyceride-rich VLDL and IDL particles has not been studied before. Here, we examined the effects of acidic pH on the activity of recombinant human group V secreted phospholipase A(2) (sPLA(2)-V) toward small VLDL (sVLDL), IDL, and LDL, on the binding of these apoB-100-containing lipoproteins to human aortic proteoglycans, and on their uptake by human monocyte-derived macrophages. At acidic pH, the ability of sPLA(2)-V to lipolyze the apoB-100-containing lipoproteins was moderately, but significantly, increased while binding of the lipoproteins to proteoglycans increased >60-fold and sPLA(2)-V-modification further doubled the binding. Moreover, acidic pH more than doubled macrophage uptake of soluble complexes of sPLA(2)-V-LDL with aortic proteoglycans. Proteoglycan-affinity chromatography at pH 7.5 and 5.5 revealed that sVLDL, IDL, and LDL consisted of populations with different proteoglycan-binding affinities, and, surprisingly, the sVLDL fractions with the highest proteoglycan-affinity contained only low amounts of apolipoproteins E and C-III. Our results suggest that in atherosclerotic lesions with acidic extracellular pH, sPLA(2)-V is able to lipolyze sVLDL, IDL, and LDL, and increase their binding to proteoglycans. This is likely to provoke extracellular accumulation of lipids derived from these atherogenic lipoprotein particles and to increase the progression of the atherosclerotic lesions.