Lipids of human atheroma

Dicarbonyl-Dependent Modification of LDL as a Key Factor of Endothelial Dysfunction and Atherosclerotic Vascular Wall Damage

The review presents evidence that the main damage to the vascular wall occurs not from the action of “oxidized” LDL, which contain hydroperoxy acyls in the phospholipids located in their outer layer, but from the action of LDL particles whose apoprotein B-100 is chemically modified with low molecular weight dicarbonyls, such as malondialdehyde, glyoxal, and methylglyoxal. It has been argued that dicarbonyl-modified LDL, which have the highest cholesterol content, are particularly “atherogenic”. High levels of dicarbonyl-modified LDL have been found to be characteristic of some mutations of apoprotein B-100. Based on the reviewed data, we hypothesized a common molecular mechanism underlying vascular wall damage in atherosclerosis and diabetes mellitus. The important role of oxidatively modified LDL in endothelial dysfunction is discussed in detail. In particular, the role of the interaction of the endothelial receptor LOX-1 with oxidatively modified LDL, which leads to the expression of NADPH oxidase, which in turn generates superoxide anion radical, is discussed. Such hyperproduction of ROS can cause destruction of the glycocalyx, a protective layer of endotheliocytes, and stimulation of apoptosis in these cells. On the whole, the accumulated evidence suggests that carbonyl modification of apoprotein B-100 of LDL is a key factor responsible for vascular wall damage leading to atherogenesis and endothelial dysfunction. Possible ways of pharmacological correction of free radical processes in atherogenesis and diabetogenesis are also discussed.

Endogenous cholesterol ester hydroperoxides modulate cholesterol levels and inhibit cholesterol uptake in hepatocytes and macrophages

Dysregulation of cholesterol metabolism represents one of the major risk factors for atherosclerotic cardiovascular disease (CVD). Oxidized cholesterol esters (oxCE) in low-density lipoprotein (LDL) have been implicated in CVD but the underlying mechanisms remain poorly defined. We use a targeted lipidomic approach to demonstrate that levels of oxCEs in human plasma are associated with different types of CVD and significantly elevated in patients with myocardial infarction. We synthesized a major endogenous cholesterol ester hydroperoxide (CEOOH), cholesteryl-13(cis, trans)-hydroperoxy-octadecadienoate (ch-13(c,t)-HpODE) and show that this endogenous compound significantly increases plasma cholesterol level in mice while decrease cholesterol levels in mouse liver and peritoneal macrophages, which is primarily due to the inhibition of cholesterol uptake in macrophages and liver. Further studies indicate that inhibition of cholesterol uptake by ch-13(c,t)-HpODE in macrophages is dependent on LXRα-IDOL-LDLR pathway, whereas inhibition on cholesterol levels in hepatocytes is dependent on LXRα and LDLR. Consistently, these effects on cholesterol levels by ch-13(c,t)-HpODE are diminished in LDLR or LXRα knockout mice. Together, our study provides evidence that elevated plasma cholesterol levels by CEOOHs are primarily due to the inhibition of cholesterol uptake in the liver and macrophages, which may play an important role in the pathogenesis of CVD.

The action of peroxyl radicals, powerful deleterious reagents, explains why neither cholesterol nor saturated fatty acids cause atherogenesis and age-related diseases

Cells respond to alterations in their membrane structure by activating hydrolytic enzymes. Thus, polyunsaturated fatty acids (PUFAs) are liberated. Free PUFAs react with molecular oxygen to give lipid hydroperoxide molecules (LOOHs). In case of severe cell injury, this physiological reaction switches to the generation of lipid peroxide radicals (LOO(·)). These radicals can attack nearly all biomolecules such as lipids, carbohydrates, proteins, nucleic acids and enzymes, impairing their biological functions. Identical cell responses are triggered by manipulation of food, for example, heating/grilling and particularly homogenization, representing cell injury. Cholesterol as well as diets rich in saturated fat have been postulated to accelerate the risk of atherosclerosis while food rich in unsaturated fatty acids has been claimed to lower this risk. However, the fact is that LOO(·) radicals generated from PUFAs can oxidize cholesterol to toxic cholesterol oxides, simulating a reduction in cholesterol level. In this review it is shown how active LOO(·) radicals interact with biomolecules at a speed transcending usual molecule-molecule reactions by several orders of magnitude. Here, it is explained how functional groups are fundamentally transformed by an attack of LOO(·) with an obliteration of essential biomolecules leading to pathological conditions. A serious reconsideration of the health and diet guidelines is required.

Standard operation protocol for analysis of lipid hydroperoxides in human serum using a fully automated method based on solid-phase extraction and liquid chromatography-mass spectrometry in selected reaction monitoring

Standard operating procedures (SOPs) are of paramount importance in the analytical field to ensure the reproducibility of the results obtained among laboratories. SOPs gain special interest when the aim is the analysis of potentially unstable compounds. An SOP for analysis of lipid hydroperoxides (HpETEs) is here reported after optimization of the critical steps to be considered in their analysis in human serum from sampling to final analysis. The method is based on automated hyphenation between solid-phase extraction (SPE) and liquid chromatography-mass spectrometry (LC-MS). The developed research involves: (i) optimization of the SPE and LC-MS steps with a proper synchronization; (ii) validation of the method-viz. accuracy study (estimated as 86.4% as minimum value), evaluation of sensitivity and precision, which ranged from 2.5 to 7.0 ng/mL (0.25-0.70 ng on column) as quantification limit and precision below 13.2%), and robustness study (reusability of the cartridge for 5 times without affecting the accuracy and precision of the method); (iii) stability study, involving freeze-thaw stability, short-term and long-term stability and stock solution stability tests. The results thus obtained allow minimizing both random and systematic variation of the metabolic profiles of the target compounds by correct application of the established protocol.

Atherogenic lipids induce high-density lipoprotein uptake and cholesterol efflux in human macrophages by up-regulating transmembrane chemokine CXCL16 without engaging CXCL16-dependent cell adhesion

Atherosclerosis is a complex pathologic process in which chemokine-mediated leukocyte accumulation in arterial walls is thought to be an important mechanism of pathogenesis. An interesting exception to this paradigm is the chemokine CXCL16, also known as the scavenger receptor for phosphatidylserine and oxidized low density lipoprotein, which is highly expressed in mouse and human atherosclerotic lesions, yet appears to be atheroprotective. In this study, we address potential mechanisms responsible for this activity. Consistent with its presence in atherosclerotic plaque, we found that atherogenic lipids up-regulated CXCL16 in primary human monocyte-derived macrophages. However, the same lipids down-regulated the CXCL16-targeted protease ADAM10, resulting in preferential expression of CXCL16 as the transmembrane form, not the shed form. Although transmembrane CXCL16 is known to mediate cell-cell adhesion by binding its receptor CXCR6, and atherogenic lipids are known to stimulate macrophage adhesion to coronary artery smooth muscle cells, we found that heterotypic adhesion of these cell types occurred in a CXCL16-independent manner. Instead we found that in macrophages, CXCL16 promoted internalization of both oxidized low density lipoprotein and high density lipoprotein, as well as release of cholesterol. Moreover, CXCL16 deficiency in macrophages interfered with oxidized low density lipoprotein-induced up-regulation of atheroprotective genes: adenosine triphosphate-binding cassette transporter A1 and G1 as well as apolipoprotein E. Thus, our findings support the hypothesis that CXCL16 mediates atheroprotection through its scavenger role in macrophages and not by cell-cell adhesion.

An oxidized lipid-peroxisome proliferator-activated receptor gamma-chemokine pathway in the regulation of macrophage-vascular smooth muscle cell adhesion

Recent genetic studies have implicated pro-inflammatory chemokines and chemokine receptors in atherogenesis. Studies at the molecular and cellular levels have suggested specific atherogenic mechanisms for two chemokine-chemokine receptor pairs, CCL2-CCR2 and CX3CL1-CX3CR1, involving differential receptor regulation by the transcription factor peroxisome proliferator-activated receptor gamma. This pathway is triggered by oxidized proatherogenic lipids, such as oxidized low-density lipoprotein and linoleic acid derivatives, which promote differentiation of CCR2(hi)CX3CR1(lo) human monocytes to CCR2(lo)CX3CR1(hi) macrophages that adhere to coronary artery smooth muscle cells in a CX3CR1- and peroxisome proliferator-activated receptor gamma-dependent manner. Switching CX3CR1 on and CCR2 off in vivo may result in cessation of CCR2-dependent migration and activation of CX3CR1-dependent retention that together may promote foam cell accumulation in the vessel wall.

Atherogenic Lipids Induce Adhesion of Human Coronary Artery Smooth Muscle Cells to Macrophages by Up-regulating Chemokine CX3CL1 on Smooth Muscle Cells in a TNFα-NFκB-dependent Manner

Recent genetic evidence has implicated the adhesive chemokine CX3CL1 and its leukocyte receptor CX3CR1 in atherosclerosis. We previously proposed a mechanism involving foam cell anchorage to vascular smooth muscle cells because: 1) CX3CL1 and CX3CR1 are expressed by both cell types in mouse and human atherosclerotic lesions; 2) foam cells are reduced in lesions in cx3cr1(-/-)apoE(-/-) mice; and 3) proatherogenic lipids (oxidized low density lipoprotein [oxLDL] and oxidized linoleic acid derivatives) induce adhesion of primary human macrophages to primary human coronary artery smooth muscle cells (CASMCs) in vitro in a macrophage CX3CR1-dependent manner. Here we analyze this concept further by testing whether atherogenic lipids regulate expression and function of CX3CL1 and CX3CR1 on CASMCs. We found that both oxLDL and oxidized linoleic acid derivatives indirectly up-regulated CASMC CX3CL1 at both the protein and mRNA levels through an autocrine feedback loop involving tumor necrosis factor alpha production and NF-kappaB signaling. Oxidized lipids also up-regulated CASMC CX3CR1 but through a different mechanism. Oxidized lipid stimulation also increased adhesion of macrophages to CASMCs when CASMCs were stimulated prior to assay, and a synergistic pro-adhesive effect was observed when both cell types were prestimulated. Selective inhibition with a CX3CL1-specific blocking antibody indicated that adhesion was strongly CASMC CX3CL1-dependent. These findings support the hypothesis that CX3CR1 and CX3CL1 mediate heterotypic anchorage of foam cells to CASMCs in the context of atherosclerosis and suggest that this chemokine/chemokine receptor pair may be considered as a pro-inflammatory target for therapeutic intervention in atherosclerotic cardiovascular disease.

Oxidized Lipid-Driven Chemokine Receptor Switch, CCR2 to CX3CR1, Mediates Adhesion of Human Macrophages to Coronary Artery Smooth Muscle Cells Through a Peroxisome Proliferator-Activated Receptor γ–Dependent Pathway

Background— Recent genetic data in mouse and humans suggest that the chemokine receptors CCR2 and CX3CR1 are involved in atherogenesis; however, detailed molecular and cellular mechanisms have not been fully delineated.

Methods and Results— Here, we show that oxidized linoleic acid metabolites, which are components of oxidized LDL found in large amounts in atherosclerotic plaque, were able to specifically induce differentiation of human monocytes to macrophages with decreased expression of CCR2, confirming a previous report, and increased expression of CX3CR1. These macrophages acquired the ability to adhere to coronary artery smooth muscle cells. The adhesion was mediated directly and predominantly by CX3CR1. Reciprocal effects of these lipids on CCR2 and CX3CR1 expression were mediated by the nuclear receptor peroxisome proliferator-activated receptor (PPAR) γ, and targeting the PPARγ gene with sRNAi dramatically reduced macrophage adhesion to coronary artery smooth muscle cells.

Conclusions— These data suggest that in atherogenesis oxidized lipid-driven activation of macrophage PPARγ in the intima may result in a proadhesive chemokine receptor switch–CCR2 off, CX3CR1 on–causing cessation of CCR2-dependent migration and activation of CX3CR1-dependent retention mechanisms, which together promote macrophage accumulation in vessel wall. Our results may explain at the molecular and cell biology levels the genetic link between CX3CR1 and atherosclerosis. Moreover, they identify macrophage binding to coronary artery smooth muscle cells as the first primary cell setting in which CX3CR1 functions as the major adhesion system.

The relation of lipid peroxidation processes with atherogenesis: A new theory on atherogenesis

The extremely high sensitivity of polyunsaturated fatty acids (PUFAs) to oxygen is apparently used by nature to induce stepwise appropriate cell responses. It is hypothesized that any alteration in the cell membrane structure induces influx of Ca2+ ions. Ca2+ ions are required to activate degrading enzymes, such as phospholipases and lipoxygenases (LOX) that transform PUFAs bound to membrane phospholipids to lipidhydroperoxides (LOOHs). Enzymatic reduction products of LOOHs seem to serve as ligands of proteins, which induce gene activation to initiate a physiological response. Increasing external impact on cells is connected with deactivation of LOX, liberation of the iron ion in its active center followed by cleavage of LOOH molecules to LO * radicals. LO * radicals induce a second set of responses leading to generation of unsaturated aldehydic phospholipids and unsaturated epoxyhydroxy acids that contribute to induction of apoptosis. Finally peroxyl radicals are generated by attack of LO * radicals on phospholipids. The latter attack nearly all types of cell constituents: Amino- and hydroxyl groups are oxidized to carbonyl functions, sugars and proteins are cleaved, molecules containing double bonds such as unsaturated fatty acids or cholesterol suffer epoxidation. LOOH molecules and iron ions at the cell wall of an injured cell are in tight contact with phospholipids of neighboring cells and transfer to these reactive radicals. Thus, the damaging processes proceed and cause finally necrosis except the chain reaction is stopped by scavengers, such as glutathione. Consequently, PUFAs incorporated into phospholipids of the cell wall are apparently equally important for the fate of a single organism as the DNA in the nucleus for conservation of the species. This review intends to demonstrate the connection of cell alteration reactions with induction of lipid peroxidation (LPO) processes and their relation to inflammatory diseases, especially atherosclerosis and a possible involvement of food. Previously it was deduced that food rich in cholesterol and saturated fatty acids is atherogenic, while food rich in n-3 PUFAs was recognized to be protective against vascular diseases. These deductions are in contradiction to the fact that saturated fatty acids withstand oxidation while n-3 PUFAs are subjected to LPO like all other PUFAs. Considering the influence of minor food constituents a new theory about atherogenesis and the influence of n-3 PUFAs is represented that might resolve the contradictory results of feeding experiments and chemical experiences. Cholesterol-PUFA esters are minor constituents of mammalian derived food, but main components of low density lipoprotein (LDL). The PUFA part of these esters occasionally suffers oxidation by heating or storage of mammalian derived food. There are indications that these oxidized cholesterol esters are directly incorporated into lipoproteins and transferred via the LDL into endothelial cells where they induce damage and start the sequence of events outlined above. The deduction that consumption of n-3 PUFAs protects against vascular diseases is based on the observation that people living on a fish diet have a low incidence to be affected by vascular diseases. Fish are rich in n-3 PUFAs; thus, it was deduced that the protective properties of a fish diet are due to n-3 PUFAs. Fish, fish oils, and vegetables contain besides n-3 PUFAs as minor constituents furan fatty acids (F-acids). These are radical scavengers and are incorporated after consumption of these nutrients into human phospholipids, leading to the assumption that not n-3 PUFAs, but F-acids are responsible for the beneficial efficiency of a fish diet.

Effects of atorvastatin on serum lipids, lipoproteins, and hemostasis

Serum levels of lipids and lipoproteins were examined in individuals with hyperlipidemia treated with atorvastatin or colestimide and in healthy volunteers. Modified low-density lipoprotein (LDL) was measured by its faster electrophoretic mobility and expressed as charge modification frequency (CMF). Serum levels of total cholesterol (t-chol), triglyceride (TG), very low-density lipoprotein (VLDL)-chol, low-density lipoprotein (LDL)-chol, and CMF were significantly higher in hyperlipidemia, but there was no significant difference in serum high-density lipoprotein (HDL)-chol levels between hyperlipidemic and healthy subjects. Treatment with atorvastatin resulted in significant decreases of serum t-chol, TG, and LDL-chol levels but not serum HDL-chol and VLDL-chol. Treatment with colestimide significantly reduced serum t-chol, HDL-chol, and LDL-chol levels but not those of TG and VLDL-chol. CMF was significantly reduced by treatment with atorvastatin but not by colestimide. Atorvastatin significantly reduced plasma levels of thrombomodulin, thrombin antithrombin complex (TAT) and tissue type plasminogen activator-plasminogen activator inhibitor-I complex. Colestimide moderately prolonged activated partial thromboplastin time and reduction of TAT. Based on its actions of lowering modified LDL and improving hemostatic abnormalities, we postulate that atorvastatin might inhibit the onset of ischemic diseases.

Role of oxidative modifications in atherosclerosis

This review focuses on the role of oxidative processes in atherosclerosis and its resultant cardiovascular events. There is now a consensus that atherosclerosis represents a state of heightened oxidative stress characterized by lipid and protein oxidation in the vascular wall. The oxidative modification hypothesis of atherosclerosis predicts that low-density lipoprotein (LDL) oxidation is an early event in atherosclerosis and that oxidized LDL contributes to atherogenesis. In support of this hypothesis, oxidized LDL can support foam cell formation in vitro, the lipid in human lesions is substantially oxidized, there is evidence for the presence of oxidized LDL in vivo, oxidized LDL has a number of potentially proatherogenic activities, and several structurally unrelated antioxidants inhibit atherosclerosis in animals. An emerging consensus also underscores the importance in vascular disease of oxidative events in addition to LDL oxidation. These include the production of reactive oxygen and nitrogen species by vascular cells, as well as oxidative modifications contributing to important clinical manifestations of coronary artery disease such as endothelial dysfunction and plaque disruption. Despite these abundant data however, fundamental problems remain with implicating oxidative modification as a (requisite) pathophysiologically important cause for atherosclerosis. These include the poor performance of antioxidant strategies in limiting either atherosclerosis or cardiovascular events from atherosclerosis, and observations in animals that suggest dissociation between atherosclerosis and lipoprotein oxidation. Indeed, it remains to be established that oxidative events are a cause rather than an injurious response to atherogenesis. In this context, inflammation needs to be considered as a primary process of atherosclerosis, and oxidative stress as a secondary event. To address this issue, we have proposed an "oxidative response to inflammation" model as a means of reconciling the response-to-injury and oxidative modification hypotheses of atherosclerosis.

The role of vitamin E in atherosclerosis

Epidemiological and biochemical studies infer that oxidative processes, including the oxidation of low-density lipoprotein (LDL), are involved in atherosclerosis. Vitamin E has been the focus of several large supplemental studies of cardiovascular disease, yet its potential to attenuate or even prevent atherosclerosis has not been realised. The scientific rationale for vitamin E supplements protecting against atherosclerosis is based primarily on the oxidation theory of atherosclerosis, the assumption that vitamin E becomes depleted as disease progresses, and the expectation that vitamin E prevents the oxidation of LDL in vivo and atherogenic events linked to such oxidation. However, it is increasingly clear that the balance between vitamin E and other antioxidants may be crucial for in vivo antioxidant protection, that vitamin E is only minimally oxidised and not deficient in atherosclerotic lesions, and that vitamin E is not effective against two-electron oxidants that are increasingly implicated in both early and later stages of the disease. It also remains unclear as to whether oxidation plays a bystander or a casual role in atherosclerosis. This lack of knowledge may explain the ambivalence of vitamin E and other antioxidant supplementation in atherosclerosis.

Disease stage-dependent accumulation of lipid and protein oxidation products in human atherosclerosis

Oxidative modification of low-density lipoprotein is thought to promote arterial lipid accumulation and atherogenesis. Previous studies reported on the presence of certain lipid or protein oxidation products in lesions, although a systematic investigation measuring several oxidation parameters and the accumulation of nonoxidized lipids and antioxidants at various stages of atherosclerosis has not been performed in the same tissue. Using the intimal lipoprotein-containing fraction of human aortic lesions, we demonstrate here that cholesterol accumulated with lesion development and that this increase was already significant at the fatty streak stage. By comparison, cholesterylesters increased significantly only in fibro-fatty and more complex lesions that also contained significantly increased amounts of cholesterylester hydro(pero)xides and 27-hydroxycholesterol. Cholesterylester hydroxides were the major lipid oxidation product detected. Despite accumulation of oxidized lipid, alpha-tocopherol was also present and maintained at a comparable level over the disease process. Of the oxidized protein moieties measured only o,o-dityrosine increased with disease, although chlorotyrosines were present at relatively high levels in all lesions compared to healthy vessels. Our data show that accumulation of nonoxidized lipid precedes that of oxidized lipid in human aortic lesions.

Lipid peroxidation in aging and age-dependent diseases

Aging is related with an increase in oxidation products derived from nucleic acids, sugars, sterols and lipids. Evidence will be presented that these different oxidation products are generated by processes induced by changes in the cell membrane structure (CMS), and not by superoxide, as commonly assumed. CMS activate apparently membrane bound phospholipases A2 in mammals and plants. Such changes occur by proliferation, aging and especially by wounding. After activation of phospholipases, influx of Ca2+ ions and activation of lipoxygenases (LOX) is induced. The LOX transform polyunsaturated fatty acids (PUFAs) into lipid hydroperoxides (LOOHs), which seem to be decomposed by action of enzymes to signalling compounds. Following severe cell injury, LOX commit suicide. Their suicide liberates iron ions that induce nonenzymic lipid peroxidation (LPO) processes by generation of radicals. Radicals attack all compounds with the structural element -CH=CH-CH(2)-CH=CH-. Thus, they act on all PUFAs independently either in free or conjugated form. The most abundant LPO products are derived from linoleic acid. Radicals induce generation of peroxyl radicals, which oxidise a great variety of biological compounds including proteins and nucleic acids. Nonenzymic LPO processes are induced artificially by the treatment of pure PUFAs with bivalent metal ions. The products are separable after appropriate derivatisation by gas chromatography (GC). They are identified by electron impact mass spectrometry (EI/MS). The complete spectrum of LPO products obtained by artificial LPO of linoleic acid is detectable after wounding of tissue, in aged individuals and in patients suffering from age-dependent diseases. Genesis of different LPO products derived from linoleic acid will be discussed in detail. Some of the LPO products are of high chemical reactivity and therefore escape detection in biological surrounding. For instance, epoxides and highly unsaturated aldehydic compounds that apparently induce apoptosis.

Isoprostane levels in lipids extracted from atherosclerotic arteries of nonhuman primates

Nonhuman primates used in these studies had been fed for 5 years diets enriched with cholesterol and one of three classes of fatty acids: saturated, monounsaturated, or polyunsaturated fatty acids. Atherosclerotic iliac artery lipid extracts were quantitatively analyzed for cholesterol, cholesteryl esters, fatty acid composition, and a marker of lipid oxidation, the F(2)-isoprostanes. There was no significant difference in the mean accumulation of F(2)-isoprostanes among the different diet groups. To account for the small, individual variation in the arachidonate concentration the F(2)-isoprostane mass from each sample was normalized by dividing by arachidonate mass: F(2)-isoprostane mass/(mass arachidonate). At lower levels of cholesterol accumulation, the F(2)-isoprostane mass/(mass arachidonate) ratio was greater in lipids from POLY arteries compared to SAT arteries, but the reverse was true at high levels of cholesterol. F(2)-isoprostane/(mass arachidonate) increased with mole fraction linoleate for the SAT group, but decreased for the POLY group. In summary, these studies demonstrated that there is no simple explanation of how F(2)-isoprostane accumulation did not depend on the concentration of oxidizable lipids that promote free-radical lipid oxidation.

Circulating autoantibodies to oxidized LDL correlate with arterial accumulation and depletion of oxidized LDL in LDL receptor-deficient mice

Autoantibodies to oxidized low density lipoprotein (OxLDL) are elevated in some human populations with increased risk of atherosclerosis. To determine whether autoantibody levels to epitopes of OxLDL reflect the extent of aortic atherosclerosis and the content of OxLDL, we measured IgG and IgM autoantibody titers to malondialdehyde (MDA)-LDL and copper-oxidized LDL (Cu-OxLDL) in 43 LDL receptor-deficient mice consuming atherogenic and regression diets. Antibody titers were correlated to percent atherosclerotic surface area, aortic weight, and aortic OxLDL content, measured as the in vivo uptake of (125)I-MDA2, a monoclonal antibody to MDA-LDL. All mice were fed an atherogenic diet for 6 months, and 1 group was euthanized. The other 3 groups were fed an atherogenic diet (fat/CHOL group), normal mouse chow (chow group), or mouse chow supplemented with vitamins E and C (chow+VIT group) for an additional 6 months. After dietary intervention, compared with their own baseline, autoantibody titers to MDA-LDL and Cu-OxLDL increased significantly in the fat/CHOL group, whereas they did not change or decreased significantly in the chow and chow+VIT groups. Aortic weight and surface area showed significant progression in the fat/CHOL group, mild progression in the chow group, and no progression in the chow+VIT group (P<0.001), whereas OxLDL content actually decreased in the latter 2 groups (P<0.001). Significant correlations were seen with MDA-LDL autoantibody titers and OxLDL content (IgM, R=0.64 and P=0.0009; IgG, R=0.52 and P=0.009), as well as with percent surface area and aortic weight. These data support the hypothesis that autoantibody titers to OxLDL reflect changes in OxLDL content in atherosclerotic lesions of LDL receptor-deficient mice. Whether autoantibody titers to OxLDL will provide similar valuable insights into the extent of human atherosclerosis, particularly anatomic measurements of plaque burden and OxLDL content, remains to be determined.

Effects of trilinolein on superoxide dismutase activity and mrna levels in aortic smooth muscle cells

1. Atherosclerotic cardiovascular disease is still the leading cause of death in Western countries. Oxygen free radicals are considered to be intimately involved in the development of atherosclerosis. Anti-oxidants may help to protect mammalian cells from the damage induced by these reactive oxygen species. Many reports have indicated that anti-oxidants used in the treatment or prevention of disease could modify the levels of superoxide dismutase (SOD). However, the effects of long-term anti-oxidant treatment on the levels of SOD in smooth muscle cells (SMC) is still unclear. In the present study, the effects of the lipophilic anti-oxidant trilinolein on the activity and gene expression of SOD in SMC were evaluated. 2. After 2 days incubation with 0.1 micromol/L trilinolein, the activity and mRNA levels of SOD were increased in rat aortic SMC (A7r5), but there was no significant change in these parameters with a higher concentration of 1 micromol/L trilinolein. 3. In contrast, after 7 days incubation with trilinolein, both the activity and mRNA levels of SOD were lowered in a dose-dependent manner. 4. These data emphasize the importance of choosing an optimal dosage for supplementation with anti-oxidants in humans for the scavenging of oxygen free radicals.

Physiological aspects of low-density lipoprotein oxidation

The oxidation of LDL is thought to be a major contributor to the development of atherosclerosis. Considerable descriptive evidence has been accumulated showing that oxidized LDL promotes pro-atherogenic events. However, direct evidence that oxidized LDL causes atherosclerosis is lacking. This article summarizes the results of recent studies that demonstrate how oxidized LDL affects cellular function, and highlights key issues that should be addressed to link LDL oxidation with atherosclerosis.

Cholesteryl ester hydroperoxide lability is a key feature of the oxidative susceptibility of small, dense LDL

Abundant evidence has been provided to substantiate the elevated cardiovascular risk associated with small, dense, low density lipoprotein (LDL) particles. The diminished resistance of dense LDL to oxidative stress in both normolipidemic and dyslipidemic subjects is established; nonetheless, the molecular basis of this phenomenon remains indeterminate. We have defined the primary molecular targets of lipid hydroperoxide formation in light, intermediate, and dense subclasses of LDL after copper-mediated oxidation and have compared the relative stabilities of the hydroperoxide derivatives of phospholipids and cholesteryl esters (CEs) as a function of the time course of oxidation. LDL subclasses (LDL1 through LDL5) were isolated from normolipidemic plasma by isopycnic density gradient ultracentrifugation, and their content of polyunsaturated molecular species of phosphatidylcholine (PC) and CE and of lipophilic antioxidants was quantified by reverse-phase high-performance liquid chromatography. The molar ratio of the particle content of polyunsaturated CE and PC species containing linoleate or arachidonate relative to alpha-tocopherol or beta-carotene did not differ significantly between LDL subspecies. Nonetheless, dense LDL contained significantly less polyunsaturated CE species (400 mol per particle) compared with LDL1 through LDL4 (range, approximately 680 to 490 mol per particle). Although the formation of PC-derived hydroperoxides did not vary significantly between LDL subspecies as a function of the time course of copper-mediated oxidation, the abundance of the C18:2 and C20:4 CE hydroperoxides was uniquely deficient in dense LDL (23 and 0.6 mol per particle, respectively, in LDL5; 47 to 58 and 1.9 to 2.3 mol per particle, respectively, in other LDL subclasses) at propagation half-time. When expressed as a lability ratio (mol hydroperoxides formed relative to each 100 mol of substrate consumed) at half-time, the oxidative lability of CE hydroperoxides in dense LDL was significantly elevated (lability ratio <25:100) relative to that in lighter, larger LDL particle subclasses (lability ratio >40:100) throughout the oxidative time course. We conclude that the elevated lability of CE hydroperoxides in dense LDL underlies the diminished oxidative resistance of these particles. Moreover, this phenomenon appears to result not only from the significantly elevated PC to free cholesterol ratio (1.54:1) in dense LDL particles (1.15:1 to 1.25:1 for other LDL subclasses) but also from their unique structural features, including a distinct apoB100 conformation, which may facilitate covalent bond formation between oxidized CE and apoB100.

Linoleic acid peroxidation--the dominant lipid peroxidation process in low density lipoprotein--and its relationship to chronic diseases

Modern separation and identification methods enable detailed insight in lipid peroxidation (LPO) processes. The following deductions can be made: (1) Cell injury activates enzymes: lipoxygenases generate lipid hydroperoxides (LOOHs), proteases liberate Fe ions--these two processes are prerequisites to produce radicals. (2) Radicals attack any activated CH2-group of polyunsaturated fatty acids (PUFAs) with about a similar probability. Since linoleic acid (LA) is the most abundant PUFA in mammals, its LPO products dominate. (3) LOOHs are easily reduced in biological surroundings to corresponding hydroxy acids (LOHs). LOHs derived from LA, hydroxyoctadecadienoic acids (HODEs), surmount other markers of LPO. HODEs are of high physiological relevance. (4) In some diseases characterized by inflammation or cell injury HODEs are present in low density lipoproteins (LDL) at 10-100 higher concentration, compared to LDL from healthy individuals.

The rabbit 15-lipoxygenase preferentially oxygenates LDL cholesterol esters, and this reaction does not require vitamin E

The oxidation of low density lipoprotein (LDL) by mammalian 15-lipoxygenases (15-LOX) was implicated in early atherogenesis. We investigated the molecular mechanism of 15-LOX/LDL interaction and found that during short term incubations, LDL cholesterol esters are oxygenated preferentially by the enzyme. Even when the LDL particle was loaded with free linoleic acid, cholesteryl linoleate constituted the major LOX substrate. In contrast, only small amounts of free oxygenated fatty acid isomers were detected, and re-esterification of oxidized fatty acids into the LDL ester lipid fraction was ruled out. When LDL was depleted from alpha-tocopherol, specific oxygenation of the cholesterol esters was not prevented, and the product pattern was not altered. Similar results were obtained at low (LDL/LOX ratio of 1:1) and high LOX loading (LDL/LOX ratio of 1:10) of the LDL particle. During long term incubations (up to 24 h), a less specific product pattern was observed. However, when the hydroperoxy lipids formed by the 15-LOX were immediately reduced by the phospholipid hydroperoxide glutathione peroxidase, when the reaction was carried out with vitamin E-depleted LDL, or when the assay sample was diluted, the specific pattern of oxygenation products was retained over a long period of time. These data suggest that mammalian 15-LOX preferentially oxidize LDL cholesterol esters, forming a specific pattern of oxygenation products. During long term incubations, free radical-mediated secondary reactions, which lead to a more unspecific product pattern, may become increasingly important. These secondary reactions appear to be suppressed when the hydroperoxy lipids formed are immediately reduced, when alpha-tocopherol-depleted LDL was used, or when the incubation sample was diluted. It may be concluded that 15-LOX-initiated LDL oxidation constitutes a dual-type oxygenase reaction with an initial enzymatic and a subsequent nonenzymatic phase. The biological relevance of this dual-type reaction for atherogenesis will be discussed.

Cholesteryl hydroperoxyoctadecadienoate from oxidized low density lipoprotein inactivates platelet-derived growth factor

Both oxidized low density lipoprotein (ox-LDL) and platelet-derived growth factor (PDGF) have been implicated in the genesis of various inflammatory responses, including atherosclerosis. We demonstrate here a novel interaction between specific oxidized lipids derived from ox-LDL and PDGF. The lipid moieties of ox-LDL caused concentration-dependent inactivation of PDGF as measured by loss of its mitogenic activity and its binding to high affinity receptors. Reverse-phase and normal-phase HPLC were used to purify the inactivating component in the lipid mixture. By fast atom bombardment mass spectrometry and infrared spectroscopy, we identified the inactivating lipids as the 9- and 13-hydroperoxy derivatives of cholesteryl linoleate, cholesteryl hydroperoxyoctadecadienoate. When a series of cholesteryl esters were subjected to oxidizing conditions, only those containing two or more double bonds caused inactivation of PDGF; the extent of inactivation increased with increased levels of oxidation. Exposing PDGF to cumene hydroperoxide, t-butyl hydroperoxide, or hydrogen peroxide did not affect the activity of the mitogen. The oxidized lipid had no effect on the mitogenic activity of epidermal growth factor but did abolish the mitogenic activity of basic fibroblast growth factor and the antiproliferative activity of transforming growth factor beta1. The inactivation of PDGF and other cytokines by lipid hydroperoxides may occur in such processes as vascular disease, inflammation, and wound healing.

Separation and characterization of cholesteryl oxo- and hydroxy-linoleate isolated from human atherosclerotic plaque

In previous work we demonstrated that up to 30% of cholesteryl linoleate in homogenates of advanced human plaque samples is present in oxidized forms. Here we show that the material from plaque hexane extracts which co-elutes with cholesteryl hydroxy-linoleate on reversed phase HPLC (Anal Biochem 1993;213:79), is composed of several isomers of cholesteryl hydroxy- and cholesteryl oxo-octadecadienoate. Enzymatic hydrolysis and measurement of liberated cholesterol and disappearance of the esters revealed that almost all of the material consisted of unoxidized cholesterol esterified to oxidized derivatives of octadecadienoate. Semi-preparative reversed-phase HPLC was used to obtain sufficient quantities of this co-eluting material to undertake normal phase HPLC separation of these components. The nature of such separated and isolated compounds was identified, by co-chromatography with authentic standards, UV spectroscopy and chemical ionization and electron impact mass spectrometry, as cholesteryl hydroxy- and cholesteryl oxo-octadecadienoate. These oxidized fatty acids have been observed previously in plaque, in agreement with our new unambiguous demonstration of their presence as cholesteryl esters. The application of the methods described for the separation of the various forms of oxidized cholesteryl octadecadienoate may aid mechanistic studies of in vitro and in vivo lipoprotein lipid oxidation.

A comparison of the kinetics of low-density lipoprotein oxidation initiated by copper or by azobis (2-amidinopropane)

This article describes the kinetics of low density lipoprotein (LDL) oxidation catalyzed by azobis (2-amidinopropane) dihydrochloride, ABAP, or by copper. The LDLs were isolated from nonhuman primates fed diets enriched in one of three types of fatty acids: saturated fatty acids, monounsaturated fatty acids, predominantly, oleic acid, or polyunsaturated fatty acids, predominantly linoleic acid. Oxidation was followed by monitoring the formation of conjugated diene hydroperoxides from polyunsaturated fatty acids (PUFA). For both copper and ABAP-initiated oxidation, the rate of LDL oxidation depended on the concentrations of initiator, PUFA, and LDL. Except for the dependence on PUFA concentration the rate of LDL oxidation was not directly influenced by the fatty acid composition of the LDL particle. The two initiators had very different dependence on initiator concentration. Because LDL particles are essentially small, lipid-rich droplets, the kinetic descriptions of LDL oxidation assumed: (1), that there was only one chain per particle, and (2) that the radical chain was terminated when a second radical either entered or was formed in the particle. When two LDL samples having very different lag times were mixed, the oxidation profile was bimodal. This finding demonstrated that the oxidation of native LDL particles was independent of the oxidation state of the other native LDL particles in solution, i.e., LDL particles do not rapidly exchange radicals, for example, hydroperoxyl radicals. Oxidation initiated by ABAP was proportional to [ABAP]0.5, suggesting that hydroperoxyl radical recombination between the lipid hydroperoxyl radical and the ABAP-hydroperoxyl radical was the chain-terminating step. The reciprocal of the rate of copper oxidation was linearly related to the reciprocal copper concentration, demonstrating that the binding of copper to LDL was necessary to initiate oxidation. This binding constant showed considerable variability among LDL samples. The kinetic descriptions of LDL oxidation reflect the differences in the mechanisms of initiation and termination.

Human atherosclerotic plaque contains both oxidized lipids and relatively large amounts of alpha-tocopherol and ascorbate

We assessed the antioxidant status and contents of unoxidized and oxidized lipids in freshly obtained, homogenized samples of both normal human iliac arteries and carotid and femoral atherosclerotic plaque. Optimal sample preparation involved homogenization of human atherosclerotic plaque for 5 minutes, which resulted in recovery of most of the unoxidized and oxidized lipids without substantial destruction of endogenous vitamins C and E and 87% and 43% recoveries of added standards of alpha-tocotrienol and isoascorbate, respectively. The total protein, lipid, and antioxidant levels obtained from human plaque varied among donors, although the reproducibility of replicates from a single sample was within 3%, except for ubiquinone-10 and ascorbate, which varied by 20% and 25%, respectively. Plaque samples contained significantly more ascorbate and urate than control arteries, with no discernible difference in the vitamin C redox status between plaque and control materials. The concentrations of alpha-tocopherol and ubiquinone-10 were comparable in plaque samples and control arteries. However, approximately 9 mol percent of plaque alpha-tocopherol was present as alpha-tocopherylquinone, whereas this oxidation product of vitamin E was not detectable in control arteries. Coenzyme Q10 in plaque and control arteries was only detected in the oxidized form ubiquinone-10, although coenzyme Q10 oxidation may have occurred during processing. The most abundant of all studied lipids in plaque samples was free cholesterol, followed by cholesteryl oleate and cholesteryl linoleate (Ch18:2). Approximately 30% of plaque Ch18:2 was oxidized, with 17%, 12%, and 1% present as fatty acyl hydroxides, ketones, and hydroperoxides, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of lipid peroxidation and antioxidants in oxidative modification of LDL

The purpose of this study is to provide a comprehensive survey on the compositional properties of LDL (e.g., lipid classes, fatty acids, antioxidants) relevant for its susceptibility to oxidation, on the mechanism and kinetics of LDL oxidation, and on the chemical and physico-chemical properties of LDL oxidized by exposure to copper ions. Studies on the occurrence of oxidized LDL in plasma, arteries, and plaques of humans and experimental animals are discussed with particular focus on the use of poly- and monoclonal antibodies for immunochemical demonstration of apolipoprotein B modifications characteristic for lipid peroxidation. Apart from uptake of oxidized LDL by macrophages, studies describing biological effects of heavily or minimally oxidized LDL are only briefly addressed, since several reviews dealing with this subject were recently published. This article is concluded with a section on the role of natural and synthetic antioxidants in protecting LDL against oxidation, as well as some previously unpublished material from our laboratories.

Antioxidant status in relation to free radical production during stable and unstable anginal syndromes

Lipid peroxidation and the antioxidant status were studied in male patients having stable angina (SA) and unstable angina (UA) pectoris and the results were compared with that of controls. Lipid peroxides (LPx) and conjugated dienes (CD) were found to be elevated in patients with both SA (LPx: 3.96 +/- 1.07, P less than 0.001; CD: 357.09 +/- 66.23, P less than 0.01) and UA (LPx: 4.66 +/- 1.33, CD: 373.33 +/- 49.82, P less than 0.001) than in controls (LPx: 3.22 +/- 0.86, CD: 335.15 +/- 60.27). In SA, the erythrocytes expressed a diminished activity of superoxide dismutase (SOD) (SA: 435.59 +/- 76.02, control: 651.69 +/- 145.90, P less than 0.001) and normal activities of catalase and glutathione peroxidase, whereas in UA it showed enhanced activities of both SOD (UA: 735.72 +/- 145.67, P less than 0.01) and catalase (UA: 21.94 +/- 6.26, control: 18.69 +/- 6.37, P less than 0.01). A significant increase was also noticed in the levels of ceruloplasmin and vitamin E during both types of angina, but not alteration was observed in the levels of transferrin. Further, the patients with diabetes showed maximum levels of lipid peroxides compared to smokers and hypertensives. The level of lipid peroxides was also observed to increase with the severity of disease. This study indicates that free radicals are involved in the pathogenesis and progression of atherosclerotic heart disease.

Immunolocalization of native antioxidant scavenger enzymes in early hypertensive and atherosclerotic arteries. Role of oxygen free radicals

To elucidate the role of oxygen free radicals and lipid peroxidation in the pathogenesis of early hypertension and atherosclerosis, we studied the native distribution of three primary arterial antioxidant enzymes (AEs). Specific immunohistochemical localization of superoxide dismutase (Cu-Zn SOD), glutathione peroxidase (GSH-Px), and catalase (CAT) was examined in the arterial wall of New Zealand White rabbits: six sham-operated normotensive/normolipidemics (NT/NL), seven coarctation-induced hypertensive/normolipidemics (HT/NL), eight normotensive diet-induced hyperlipidemics (NT/HL), and six hypertensive/hyperlipidemics (HT/HL). All three AEs were confined primarily to the endothelium in NT/NL rabbit aortas. However, in HT and HL rabbits a greater proportion of the arterial wall, including the endothelium, inner media, and middle media, displayed immunolocalization of three AEs. Multiple linear-regression analysis revealed that more than 70% of the total variability in the depth of immunolocalization of arterial AEs could be explained by changes in blood pressure and/or total cholesterol. Also, levels of plasma and arterial cholesterol oxides were significantly different (p less than 0.05) in HT and HL rabbits compared with controls, with twofold increases in NT/HLs, threefold increases in HT/NLs, and fourfold increases in HT/HLs. We conclude that intense free-radical activity in the arterial wall of HT and HL animals is one possibility and that this occurs despite the presence of abundant AEs.

Cellular damage in mouse peritoneal macrophages exposed to cholesteryl linoleate

Mouse peritoneal macrophages readily oxidize cholesteryl linoleate/bovine serum albumin emulsions to produce soluble lipid oxidation products, some of the latter being thought to cause cell damage. Mouse peritoneal macrophages were therefore incubated in the presence of cholesteryl linoleate/bovine serum albumin emulsion with and without the addition of dl-alpha tocopherol. The macrophages were observed morphologically and cell damage was estimated by three methods: trypan blue exclusion, lactate dehydrogenase release and tritiated adenine release. All the methods showed significant cell damage which was reduced in the presence of physiological levels of dl-alpha tocopherol. Cholesteryl oleate/bovine serum albumin, which is taken up by macrophages but is not oxidized, was not toxic. dl-Alpha tocopherol was itself toxic in higher concentrations. This self-inflicted macrophage damage might explain the onset of necrosis in atherosclerotic plaques.

Arterial wall oxygenation, oxyradicals, and atherosclerosis

The oxygen supply of inner media and thickened intima of atherosclerosis prone arteries depends largely on diffusion from the endothelium. Conditions which increase wall thickness and oxygen diffusion or reduce oxygen transmissibility produce hypoxia and steep PO2 gradients within the wall. Cerebral injury and myocardial reperfusion studies indicate that intermittent hypoxia and steep PO2 gradients lead to oxyradical formation and tissue damage. Products of lipid and sterol peroxidation are found in atherosclerotic plaques and can be generated by arterial wall cells in culture. It is likely that peroxidation occurs directly within the arterial wall. Sufficient oxyradical generation occurs during normal oxygen metabolism that local scavenger mechanisms are required to avoid tissue damage. Experimental hypertension, hyperlipemia and balloon injury produce medial hypoxia with steep PO2 gradients and redistribution of the pattern of arterial wall antioxidant enzymes. This suggests that minor deviations from normal arterial wall anatomy and function can lead to oxyradicals which can be directly injurious and can amplify the atherogenic potential of lipoprotein infiltration.

Increased levels of monohydroxy metabolites of arachidonic acid and linoleic acid in LDL and aorta from atherosclerotic rabbits

Lipid peroxidation results in the formation of peroxy and hydroperoxy metabolites of polyunsaturated fatty acids which can directly or indirectly affect many cellular processes. Lipid hydroperoxides are rapidly metabolized to the corresponding monohydroxy products by various cellular peroxidases. We have measured the amounts of monohydroxy metabolites of linoleic acid (18:2) and arachidonic acid (20:4) in lipids derived from aorta and LDL from rabbits fed a diet enriched in cholesterol and peanut oil for either 8 or 15 weeks. Increased amounts of the 9-hydroxy, and, to a lesser extent, the 13-hydroxy metabolite of 18:2 were observed in aorta and LDL from cholesterol-fed rabbits at both 8 and 15 weeks. The amounts of esterified 11-, 12- and 15-hydroxy metabolites of 20:4 in aortae from cholesterol-fed rabbits were similar to controls after 8 weeks, but about 3-fold higher after 15 weeks. These monohydroxy metabolites of 20:4 were also detected in LDL lipids in cholesterol-fed rabbits. The greater amounts of hydroxy-18:2 in the cholesterol-fed group could be explained by an approx. 2-4-fold increase in 18:2 in aorta and LDL. In contrast, the amounts of 20:4 in aortic lipids were lower in cholesterol-fed rabbits than in controls. Thus, the percentage of esterified 20:4 which had been oxidized to its 11, 12, and 15-hydroxylated metabolites was about 5-times higher in the cholesterol-fed group. Our results would be consistent with the hypothesis that increased amounts of peroxidized 18:2 and 20:4 in lipids could be involved in the development of atherosclerotic lesions in cholesterol-fed rabbits.

Another cholesterol hypothesis: cholesterol as antioxidant

Current emphasis on cholesterol as agency if not cause of human atherosclerosis and subsequent cardiovascular disease ignores the essentiality of cholesterol in life processes. Additionally ignored is the ubiquitous presence of low levels of oxidized cholesterol derivatives (oxysterols) in human blood and select tissues, oxysterols also implicated in atherosclerosis. Whereas such oxysterols may be regarded putatively as agents injurious to the aorta, an alternative view of some of them is here proposed: that B-ring oxidized oxysterols of human blood represent past interception of blood and tissue oxidants in vivo by cholesterol as an ordinary aspect of oxygen metabolism. Such interception and subsequent efficient hepatic metabolism of oxysterols so formed, with biliary secretion and fecal excretion, constitute as in vivo antioxidant system. Whether cholesterol, oxysterols, oxidized lipoproteins, or oxidants in blood, singly or in concert, cause or exacerbate human atherosclerosis remains to be understood.

Peroxidized lipoproteins recognized by a new monoclonal antibody (DLR1a/104G) in atherosclerotic lesions

Monoclonal DLR1a/104G antibody, which recognizes peroxidized lipoproteins, was raised. Mice were immunized with the float-up fraction of the atherosclerotic arterial homogenate from WHHL rabbits. Sensitized spleen cells were fused with myeloma cells (3P/U1). Hybridoma clones were selected using peroxidized LDL prepared by CuSO4-catalyzed peroxidation and native LDL as positive and negative standards, respectively. The monoclonal DLR1a/104G antibody was highly reactive with peroxidized LDL, slightly with LDL modified with malondialdehyde, but not significantly with acetyl- or native LDL. The antigenicity in the case of peroxidized LDL did not decrease on extraction with hexane/isopropanol (3:2). The antigenicity coincided with the fluorescence (E350, F430) of the protein fraction of LDL peroxidized with CuSO4. These results suggest that an antigenic determinant exists in atherosclerotic lesions, which is the same as that for lipoproteins peroxidized with CuSO4.

Iron chelators inhibit human platelet aggregation, thromboxane A2 synthesis and lipoxygenase activity

The iron chelators desferrioxamine and 1,2-dimethyl-3-hydroxypyrid-4-one (L1) inhibited human platelet aggregation in vitro as well as thromboxane A2 synthesis and conversion of arachidonate to lipoxygenase-derived products. Non-chelating compounds related to L1 were without effect on cyclooxygenase or lipoxygenase activity. Since both cyclooxygenase and lipoxygenase are iron-containing enzymes, it is suggested that the inhibition of platelet function by these iron chelators may be related to the removal or binding of iron associated with these enzymes. These iron chelators may therefore be of potential therapeutic value as platelet antiaggregatory agents and of possible use in the treatment of atherosclerotic and inflammatory joint diseases.

Preferential hydrolysis of oxidized phospholipids by peritoneal fluid of rats treated with casein

1-Palmitoyl-2-azelaoyl-PC, which is one of the possible cytotoxic products generated by the oxyhemoglobin-induced lipid peroxidation of 1-palmitoyl-2-linoleoyl-PC, was found to be efficiently hydrolyzed by the peritoneal fluid of rats treated with casein. The rate of hydrolysis of 1-palmitoyl-2-azelaoyl-PC was approx. 15-fold higher than that observed with 1-palmitoyl-2-linoleoyl-PC. When 1-palmitoyl-2-linoleoyl-PC pretreated with oxyhemoglobin was incubated with the peritoneal fluid, oxidized products of PC were hydrolyzed more efficiently than the intact 1-palmitoyl-2-linoleoyl-PC. When 1-[(1-)14C]palmitoyl-2-azelaoyl-PC was incubated with the peritoneal fluid, radiolabeled lysoPC was formed, whereas radiolabeled neutral lipids were not formed, indicating that the hydrolytic activity was of the 'phospholipase A2' type. We previously found and purified an extracellular phospholipase A2 (Chang, H.W. et al. (1987) J. Biochem. 102, 147-154) in the peritoneal fluid of rats injected intraperitoneally with casein. Hydrolysis of 1-palmitoyl-2-azelaoyl-PC by this purified phospholipase A2 was as low as that of 1-palmitoyl-2-linoleoyl-PC. These two phospholipase A2 activities showed different pH optima and Ca2+ requirements. The present phospholipase A2 activity, which preferentially hydrolyzes oxidized products of PC, may play an important role in detoxification or repair of damaged membrane in inflamed sites.

Monoclonal DLR1a/104G antibody recognizing peroxidized lipoproteins in atherosclerotic lesions

Monoclonal DLR1a/104G antibody which recognizes peroxidized lipoproteins was raised. Mice were immunized with the float-up fraction of the atherosclerotic arterial homogenate from WHHL rabbits. Sensitized spleen cells were fused with myeloma cells (P3/U1). Hybridoma clones were selected using peroxidized LDL prepared by CuSO4-catalyzed peroxidation and native LDL as positive and negative standards, respectively. The monoclonal DLR1a/104G antibody was highly reactive with peroxidized LDL, slightly with LDL modified with malondialdehyde, but not significantly with acetyl- or native LDL. The antigenicity in the case of peroxidized LDL did not decrease on extraction with hexane/isopropanol (3:2). The antigenicity coincided with the fluorescence (E350, F430) of the protein fraction of LDL peroxidized with CuSO4. These results suggest that an antigenic determinant exists in atherosclerotic lesions which is the same as that for lipoproteins peroxidized with CuSO4.

Characterization of the hydroperoxide-reducing activity of human plasma

A peroxidase was identified in human plasma using a novel peroxidase assay. In this assay both the substrate 5-phenyl-4-pentenyl hydroperoxide (PPHP) and its reduction product, 5-phenyl-4-pentenyl alcohol (PPA) are quantitated by HPLC. Substrate specificity studies indicated that the peroxidase requires glutathione as reducing substrate. No reduction was detected using the classical heme peroxidase reducing substrates, phenol and hydroquinone. Peroxidase activity was not due to glutathione transferases. Failure to saturate the peroxidase activity with reduced glutathione and inhibition by Cd+2 indicated that it is probably selenium dependent. The enzyme appears to be different from erythrocyte glutathione peroxidase based on kinetic and immunological experiments. The apparent Km values for PPHP are 25 microM for erythrocyte peroxidase and 54 microM for plasma peroxidase at 0.5 mM reduced glutathione. Anti-peroxidase prepared against bovine erythrocyte glutathione peroxidase partially inhibited human erythrocyte peroxidase but did not inhibit human plasma peroxidase.

Action of cholestane-3 beta,5 alpha,6 beta-triol on rats with particular reference to the aorta

Cholestane-3 beta,5 alpha,6 beta-triol, administered orally to rats in different doses and for varying lengths of times, effected toxic cell damage on aortic smooth muscle cells and endothelium. Cholesterol, applied in the same doses, did not lead to appreciable alterations of the aorta. After parenteral application of lipids with simultaneous administration of cholestane-triol there were no demonstrable fat deposits in the damaged aortic wall with angiotensin II (AII) induced hypertension. Thus, there was no recognizable influence of hypertension on increased fat passage in the arterial wall, or any action of lipids to enhance the permeability of vessels. However, the hypertension had an exacerbating effect in so far as in animals with AII-induced blood pressure rise alterations of the media were more pronounced after cholestane-triol, although we were unable to rule out a primary effect of AII. A potentiation of the cholestane-triol action by simultaneous application of cholesterol demonstrated for the rabbit did not occur in rats. Blood content was lowered mostly by cholestane-triol, also by cholesterol. HDL-cholesterol was little affected; almost no influence was observed in triglycerides. The strong cytotoxic action of cholestane-triol underlines its health-damaging role. Due to its action on the aorta of the rat, despite the animal's resistance to arteriosclerosis, involvement of this cholesterol derivative in the pathogenesis of arteriosclerotic alterations can not be excluded.

Cholesterol oxygenated derivatives induce erythrocyte accumulation and endothelium alterations in the aorta of rats. Turnover of endothelial cells in the apparently intact areas remains unchanged

In this work we have studied the effect of cholesterol autooxidation derivatives on the aortic endothelium of rat. Endothelial alterations were evident after 24 h treatment. Areas showing many spindle shaped nuclei and focal accumulation of erythrocytes were observed. Moreover, in some preparations areas with destroyed and missing endothelium were observed. Autoradiography using 3H-thymidine does not show differences in the mitotic activity between control and treated animals in those areas showing apparently intact endothelium. Therefore, we conclude that cholesterol derivatives present ability to produce important lesions in aortic endothelium and that this effect is similar to that described when cholesterol is used.

The relationship between plasma triglycerides, cholesterol, total lipids and lipid peroxidation products during human atherosclerosis

Concentrations of plasma triglycerides, cholesterol, total lipids and lipid peroxides in patients with atherosclerotic lesions of peripheral arteries, who were divided into groups according to the extent and intensity of the lesions, were estimated, as well as lipid peroxide levels in the arterial wall. Statistically highly significant increases of the estimated compounds were found in all groups in comparison with the controls. The existence of a positive correlation between the lipid peroxide concentration and other investigated components in plasma and between the lipid peroxide level in plasma and in the arterial wall was found. Possible mechanisms for lipid peroxide involvement in the process of originating atherosclerotic lesions are discussed.

Altered arachidonic acid synthesis and lipid peroxidation in diabetes mellitus: possible roles in leukocyte dysfunction and other cellular defects

Hyperglycemic diabetics are prone to unusual or especially severe infections; at the cellular level, diabetic polymorphonuclear leukocytes (PMNs) show defects in several antimicrobial functions. However, the basis for these defects is unknown, and they may not be fully ascribable to hyperglycemia, hypoinsulinemia or acidosis alone. Recently, it has been shown that several important PMN functions may be mediated (at least in part) by metabolites of arachidonic acid synthesized via the lipoxygenase pathway, especially arachidonate hydroperoxides and leukotriene (LT) B4. We speculate that synthesis of these mediators may be deficient in severely hyperglycemic diabetics (fasting plasma glucose greater than 250-300 mg/dl) due to deficiencies of substrate (arachidonic acid) synthesis and release. Such defects might be expected since, in animal studies, severe insulin lack and glucagon excess inhibit the desaturation of precursor fatty acids to arachidonic acid. On the other hand, whereas low levels of lipid peroxides or their derivatives may be required in certain cells for normal function, excessive levels of such compounds also are detrimental to cellular function and could play a role as well in the complications of milder or partially treated diabetics who manifest high basal insulin levels. For example, cells which may be particularly sensitive to an excess of peroxides include islet beta cells, PMNs and possibly vascular endothelial cells (all of which appear to be deficient in glutathione peroxidase). These observations suggest a role for accumulation of lipid peroxides in the impaired insulin secretion, defective PMN function and possibly endothelial death and increased vascular (retinal, endothelial, and renal) permeability of some milder diabetics. The available data are compatible with the speculation that in partially treated or lesser degrees of hyperglycemia, increased arachidonate synthesis and excessive lipid peroxidation may be present. Although it remains to be established that all of the results from experimentally-induced diabetics can be extrapolated to humans, these findings suggest that the cell damage attendant upon peroxide generation might be susceptible to prophylactic treatment with anti-oxidants such as alpha-tocopherol or ascorbic acid. In the more severe or later stages of hyperglycemia, a deficiency of lipoxygenase-derived products may supervene; dietary modifications designed to increase essential fatty acid availability might present a unique ancillary therapeutic approach at this stage of diabetes.