Effect of the oxidation state of LDL on the modulation of arterial vasomotor response in vitro

Oxysterols in Central and Peripheral Synaptic Communication

Cholesterol is a key molecule for synaptic transmission, and both central and peripheral synapses are cholesterol rich. During intense neuronal activity, a substantial portion of synaptic cholesterol can be oxidized by either enzymatic or non-enzymatic pathways to form oxysterols, which in turn modulate the activities of neurotransmitter receptors (e.g., NMDA and adrenergic receptors), signaling molecules (nitric oxide synthases, protein kinase C, liver X receptors), and synaptic vesicle cycling involved in neurotransmitters release. 24-Hydroxycholesterol, produced by neurons in the brain, could directly affect neighboring synapses and change neurotransmission. 27-Hydroxycholesterol, which can cross the blood-brain barrier, can alter both synaptogenesis and synaptic plasticity. Increased generation of 25-hydroxycholesterol by activated microglia and macrophages could link inflammatory processes to learning and neuronal regulation. Amyloids and oxidative stress can lead to an increase in the levels of ring-oxidized sterols and some of these oxysterols (4-cholesten-3-one, 5α-cholestan-3-one, 7β-hydroxycholesterol, 7-ketocholesterol) have a high potency to disturb or modulate neurotransmission at both the presynaptic and postsynaptic levels. Overall, oxysterols could be used as "molecular prototypes" for therapeutic approaches. Analogs of 24-hydroxycholesterol (SGE-301, SGE-550, SAGE718) can be used for correction of NMDA receptor hypofunction-related states, whereas inhibitors of cholesterol 24-hydroxylase, cholestane-3β,5α,6β-triol, and cholest-4-en-3-one oxime (olesoxime) can be utilized as potential anti-epileptic drugs and (or) protectors from excitotoxicity.

The Effect of Effort Test on the Levels of Ischemia Modified Albumin, 7-ketocholesterol and Cholestan-3β , 5α , 6β -triol and their Role in the Diagnosis of Coronary Artery Disease

Background

Oxysterols have been shown to play a role in plaque formation while ischemia modified albumin (IMA) is widely accepted as an acute marker for ischemia. The effort test is one of the methods used to identify the presence of coronary artery disease. Thus, there may be a relationship between effort test result and the levels of IMA, 7-ketocholesterol (7-KC) and cholestane-3β,5α,6β-triol (C-triol).

Methods

Thirty patients who underwent effort test and 30 healthy subjects were included in the study. IMA levels were determined with the albumin-cobalt binding test, 7-KC and C-triol levels were determined with LC-MS/MS. Among the patients, two subgroups were identified according to the results of the effort test, group 1 consisted of patients with a positive effort test (n = 12), and group 2 consisted of patients who had a negative effort test (n = 18).

Results

7-KC levels of patients were significantly higher compared to healthy subjects (39.87 ± 2.13 ng/mL, 20.26 ± 1.35 ng/mL; p=0.001). In patients, post-test 7-KC levels were significantly lower than pre-test levels (post-test vs. pre-test: 37.73 ± 2.44 ng/mL vs. 41.07 ± 2.18 ng/mL; p<0.001). There was a significant difference in post-test 7-KC levels among all study groups (negative, positive and healthy: 37.73 ± 2.44 ng/mL, 39.87 ± 2.13 ng/mL, 20.26 ± 1.35 ng/mL, respectively). There was no significant difference in IMA levels.

Conclusions

Patients with positive effort test had significantly higher levels of 7-KC. Additionally, after the effort test, the 7-KC value was reduced. 7-KC is a biomarker of oxidative damage and its value or changes before and after the effort test may be used as a biomarker in the diagnosis and follow-up of coronary artery disease.

Oxysterols and calcium signal transduction

Ionised calcium (Ca(2+)) is a key second messenger, regulating almost every cellular process from cell death to muscle contraction. Cytosolic levels of this ion can be increased via gating of channel proteins located in the plasma membrane, endoplasmic reticulum and other membrane-delimited organelles. Ca(2+) can be removed from cells by extrusion across the plasma membrane, uptake into organelles and buffering by anionic components. Ca(2+) channels and extrusion mechanisms work in concert to generate diverse spatiotemporal patterns of this second messenger, the distinct profiles of which determine different cellular outcomes. Increases in cytoplasmic Ca(2+) concentration are one of the most rapid cellular responses upon exposure to certain oxysterol congeners or to oxidised low-density lipoprotein, occurring within seconds of addition and preceding increases in levels of reactive oxygen species, or changes in gene expression. Furthermore, exposure of cells to oxysterols for periods of hours to days modulates Ca(2+) signal transduction, with these longer-term alterations in cellular Ca(2+) homeostasis potentially underlying pathological events within atherosclerotic lesions, such as hyporeactivity to vasoconstrictors observed in vascular smooth muscle, or ER stress-induced cell death in macrophages. Despite their candidate roles in physiology and disease, little is known about the molecular mechanisms that couple changes in oxysterol concentrations to alterations in Ca(2+) signalling. This review examines the ways in which oxysterols could influence Ca(2+) signal transduction and the potential roles of this in health and disease.

Multiple antioxidants and L-arginine modulate inflammation and dyslipidemia in chronic renal failure rats

The kidney is an important source of L-arginine, the endogenous precursor of nitric oxide (NO). Surgical problems requiring extensive renal mass reduction (RMR) decrease renal NO production, leading to multiple hemodynamic and homeostatic disorders manifested by hypertension, oxidative stress, and increased inflammatory cytokines. Using the RMR model of chronic renal failure (CRF), we assessed the effects of twelve weeks' administration of L-arginine and/or a mixture of antioxidants (L-carnitine, catechin, vitamins E and C) on plasma cytokines, soluble intercellular adhesion molecule-1 (sICAM-1), nitrate and nitrites (NO(2)/NO(3)), lipid profile, blood pressure, and renal function. CRF rats showed increased plasma IL-1 alpha, IL1-beta, IL-6, TNF-alpha, and sICAM-1 levels and decreased anti-inflammatory cytokines IL-4 and 10 levels, hypertension, and dyslipidemia. L-arginine treatment improved kidney functions, decreased systolic blood pressure, and decreased inflammatory cytokines levels. Antioxidants administration decreased inflammatory cytokines and sICAM-1 levels and increased IL-4 levels. Combined use of both L-arginine and the antioxidant mixture were very effective in their tendency to recover normal values of kidney functions, plasma cytokines, sICAM-1, blood pressure, NO(2)/NO(3), cholesterol, and triglycerides concentrations. Indeed, the effects of L-arginine and the antioxidants on the reduction of proinflammatory cytokines may open new perspectives in the treatment of uremia.

A prospective study of early-pregnancy plasma malondialdehyde concentration and risk of preeclampsia

OBJECTIVES

Preeclampsia is associated with elevated plasma malondialdehyde concentration, but prospective data are scarce. We examined the relation between early-pregnancy plasma malondialdehyde and subsequent preeclampsia risk.

DESIGN AND METHODS

In a nested case-control analysis, we measured malondialdehyde concentrations in 22 women who developed preeclampsia and 711 who remained normotensive during pregnancy. We calculated adjusted odds ratios (OR) and 95% confidence intervals (CI). We repeated analyses after adjustment for early-pregnancy plasma lipid concentrations, which are related to preeclampsia risk and lipid peroxidation measures.

RESULTS

After adjustment for confounders, preeclampsia risk increased across tertiles of malondialdehyde concentration (trend P = 0.04). Further adjustment for triglyceride concentration slightly strengthened the association. Middle- and high-tertile malondialdehyde ORs were 3.2 (CI 0.8-12.2) and 4.2 (1.1-16.0) versus low-tertile exposure.

CONCLUSIONS

Early-pregnancy plasma malondialdehyde concentration is positively associated with subsequent preeclampsia risk independent of plasma lipid concentrations. These results support lipid peroxidation as an etiologic component of preeclampsia.

Increased calcium intake reduces plasma cholesterol and improves vasorelaxation in experimental renal failure

Chronic renal failure (CRF) is associated with abnormal lipid metabolism and high prevalence of vascular complications. Calcium salts are commonly used in CRF as phosphate binders. Increased calcium intake may also lower plasma cholesterol and beneficially influence vascular tone. Therefore, we investigated the influence of increasing dietary calcium from 0.3% to 3.0% for 8 wk after 5/6 nephrectomy (NTX) on plasma cholesterol and mesenteric resistance vessel tone in male Sprague-Dawley rats. The groups were Sham, Sham-Calcium, NTX, and NTX-Calcium ( n = 10–11). Blood pressure was modestly elevated after NTX, whereas the plasma creatinine, urea nitrogen, phosphate, and parathyroid hormone levels were clearly increased. The high-calcium diet suppressed plasma phosphate and parathyroid hormone but was without effect on blood pressure. The NTX resulted in 1.6-fold elevation in plasma total cholesterol and 40% reduction in high density-to-low density lipoprotein ratio (HDL/LDL). However, the lipid profile in NTX rats on the high-calcium diet did not differ from sham-operated controls. The endothelium-mediated relaxations induced by acetylcholine were impaired in NTX rats, whereas the response was normalized by a high-calcium diet. No differences in vasorelaxations by the endothelium-independent vasodilator nitroprusside were detected. In conclusion, improved vasorelaxation after a high-calcium diet could be due to reduced plasma total cholesterol and ameliorated HDL/LDL ratio, although decreased plasma phosphate and parathyroid hormone may also play a significant role in the vascular effects of increased calcium intake.

Inflammatory and thrombotic mechanisms in coronary atherosclerosis

Many molecular and cellular mechanisms link inflammation and haemostatic mechanisms. Inflammation, and perhaps chronic infection, may play important roles in the initiation and progression of atherosclerosis. Atherosclerotic lesions are heavily infiltrated by cellular components associated with inflammation (macrophages and T lymphocytes), and acute plaque rupture is also associated with inflammatory components. Several markers of systemic inflammation may predict future cardiovascular events in apparently healthy subjects as well as in patients with chronic and acute syndromes. There may thus be therapeutic potential in modifying the atherosclerotic, vasomotor, and thrombotic components of ischaemic heart disease.

Prevention of LDL alpha-tocopherol consumption, cholesterol oxidation, and vascular endothelium dysfunction by polyphenolic compounds from red wine

Red wine polyphenolic compounds (RWPCs) have been demonstrated to possess antioxidant properties, and several studies have suggested that they might constitute a relevant dietary factor in the protection from coronary heart disease. The aim of the present study was to determine further the mechanism by which RWPCs can prevent the formation of vasoactive compounds in oxidized LDL. RWPCs were obtained from the Cabernet-Sauvignon grape variety. Human LDL was oxidized in the presence of CuSO(4) (ox-LDL). Vascular reactivity studies were conducted on rabbit aortic rings. RWPCs significantly reduced the formation of 7 beta-hydroxycholesterol and 7-ketocholesterol and in a lower extent the emergence of lysophosphatidylcholine in ox-LDL. The ability of RWPCs to prevent cholesterol oxide formation was directly dependent on the LDL alpha-tocopherol content. Once the LDL alpha-tocopherol has been consumed, RWPCs were no longer effective, indicating that RWPCs act by sparing endogenous alpha-tocopherol. As a consequence of the preservation of the endogenous alpha-tocopherol content of LDL, RWPCs could prevent the inhibition of the acetylcholine-mediated endothelium-dependent relaxation of rabbit aorta which was linked to a direct effect on NO release. Independently of a treatment with ox-LDL, RWPC exerted a concentration-dependent and persistent inhibitory effect on the norepinephrine-induced contraction of rabbit aorta. In conclusion, RWPCs can preserve a normal vascular reactivity by acting at different stages of the cascade that leads to lipid oxidation, endothelium dysfunction and vasospasm.

The impairment of endothelium-dependent arterial relaxation by 7-ketocholesterol is associated with an early activation of protein kinase C

Among components of oxidized low density lipoproteins, cholesterol derivatives oxidized in position 7 inhibit endothelium-dependent arterial relaxation by decreasing the release of the main endothelium-derived relaxing factor, nitric oxide (NO). The aim of the present study was to bring new insights into the molecular mechanism by which 7-ketocholesterol can block the endothelium-dependent arterial relaxation. Superoxide dismutase did not prevent the inhibitory effect of 7-ketocholesterol on endothelium-dependent relaxation, and consistent observations were made whether superoxide dismutase was conjugated or not to polyethylene glycol. In addition, neither glutathione supplementation, nor oxypurinol, i.e. a xanthine oxidase inhibitor could reverse the effect of 7-ketocholesterol, indicating that NO was not inactivated by superoxide anion. A direct alteration of the activity of the calcium-dependent NO synthase could also be ruled out, since identical relaxing effects of the calcium ionophore A23187 were observed whether arterial rings were treated or not with 7-ketocholesterol. 4 Whereas the above observations come in support of an early, inhibitory action of 7-ketocholesterol, the specific blockade of one given subtype of membrane receptors could be discarded, and similar inhibitions were observed when either muscarinic or purinergic receptors were stimulated. Finally, the blockade of protein kinase C activity by chelerythrine arose as the sole relevant tool in preventing the effect of 7-ketocholesterol on the endothelium-dependent relaxation of rabbit aortic rings. In addition, complementary studies on cultured bovine aortic endothelial cells came in direct support of the ability of 7-ketocholesterol to activate PKC. In conclusion, 7-ketocholesterol that is present in human hypercholesterolaemic plasma, in atherosclerotic arteries, and in many processed foods can block the release of NO by vascular endothelial cells through its ability to activate PKC.

Nitric oxide, cholesterol oxides and endothelium-dependent vasodilation in plasma of patients with essential hypertension

The objective of the present study was to identify disturbances of nitric oxide radical (.NO) metabolism and the formation of cholesterol oxidation products in human essential hypertension. The concentrations of.NO derivatives (nitrite, nitrate, S-nitrosothiols and nitrotyrosine), water and lipid-soluble antioxidants and cholesterol oxides were measured in plasma of 11 patients with mild essential hypertension (H: 57.8 +/- 9.7 years; blood pressure, 148.3 +/- 24.8/90.8 +/- 10.2 mmHg) and in 11 healthy subjects (N: 48.4 +/- 7.0 years; blood pressure, 119.4 +/- 9.4/75.0 +/- 8.0 mmHg). Nitrite, nitrate and S-nitrosothiols were measured by chemiluminescence and nitrotyrosine was determined by ELISA. Antioxidants were determined by reverse-phase HPLC and cholesterol oxides by gas chromatography. Hypertensive patients had reduced endothelium-dependent vasodilation in response to reactive hyperemia (H: 9.3 and N: 15.1% increase of diameter 90 s after hyperemia), and lower levels of ascorbate (H: 29.2 +/- 26.0, N: 54.2 +/- 24.9 micro M), urate (H: 108.5 +/- 18.9, N: 156.4 +/- 26.3 micro M), beta-carotene (H: 1.1 +/- 0.8, N: 2.5 +/- 1.2 nmol/mg cholesterol), and lycopene (H: 0.4 +/- 0.2, N: 0.7 +/- 0.2 nmol/mg cholesterol), in plasma, compared to normotensive subjects. The content of 7-ketocholesterol, 5alpha-cholestane-3beta,5,6beta-triol and 5,6alpha-epoxy-5alpha-cholestan-3alpha-ol in LDL, and the concentration of endothelin-1 (H: 0.9 +/- 0.2, N: 0.7 +/- 0.1 ng/ml) in plasma were increased in hypertensive patients. No differences were found for.NO derivatives between groups. These data suggest that an increase in cholesterol oxidation is associated with endothelium dysfunction in essential hypertension and oxidative stress, although.NO metabolite levels in plasma are not modified in the presence of elevated cholesterol oxides.

Lipids and endothelium-dependent vasodilation--a review

Studies using both in vitro and in vivo techniques have repeatedly shown that endothelium-dependent vasodilation (EDV) is impaired in different forms of experimental as well as human hypercholesterolemia. Clearly this impaired EDV can be reversed by lowering cholesterol levels by diet or medical therapy. Competitive blocking of L-arginine, changes in nitric oxide synthase activity, increased release of endothelin-1, and inactivation of nitric oxide due to superoxide ions all contribute to the impairment in EDV during dyslipidemia. The oxidation of low density lipoprotein, with its compound lysophosphatidylcholine, plays a critical role in these events. However, data on the role of triglycerides and fat-rich meals regarding EDV are not so consistent as data for cholesterol, although a view that the compositions of individual fatty acids and antioxidants are of major importance is emerging. Thus, this review shows that while impaired EDV is a general feature of hypercholesterolemia, the mechanisms involved and the therapeutic opportunities available still have to be investigated. Furthermore, discrepancies regarding the role of triglycerides and fat content in food may be explained by divergent effects of different fatty acids on the endothelium.

Anti-oxidants-- a protective role in cardiovascular disease?

Established risk factors for cardiovascular disease (CVD), such as hypertension, smoking and diabetes mellitus, explain only some of the observed variation in clinical events. This has maintained interest in other nutritional and biochemical factors that might contribute to the underlying pathophysiology of CVD. All of these risk factors are associated with increased oxidative stress in the vessel wall, which may contribute to CVD by several mechanisms. Studies in animal models of CVD have suggested that natural and synthetic anti-oxidants can prevent the development of clinical end points. These observations have generated the hypothesis that anti-oxidant therapy might also prevent CVD in human populations. This has been supported by epidemiological studies showing a negative correlation between circulating concentrations or dietary intake of natural anti-oxidant vitamins and CVD event rate. Many studies have also demonstrated a beneficial effect of anti-oxidants on surrogate markers of CVD such as endothelial function and lipoprotein oxidation. However, the results of large prospective randomised controlled intervention trials, mostly involving vitamin E in patients at increased risk of CVD, have been disappointing and have failed to demonstrate the anticipated benefits. This paper will critically examine the evidence and try to offer some explanation for the apparent failure of animal and epidemiological data to translate into meaningful clinical benefits.

25-hydroxycholesterol induces lipopolysaccharide-tolerance and decreases a lipopolysaccharide-induced TNF-alpha secretion in macrophages

Several different oxysterols are formed when LDL is oxidized. The role of oxysterols in the inflammatory process in the atherosclerotic plaque is not totally elucidated. In this study we have investigated the effect of four different oxysterols on an LPS-induced TNF-alpha secretion in human macrophages. Cultured human macrophages were incubated with 7-keto-, 7beta-hydroxy-, 27-hydroxy- and 25-hydroxycholesterol for 24 h before exposure to endotoxin (LPS) for 3 h. All oxysterols, except 7-ketocholesterol, significantly decreased an LPS-induced TNF-alpha secretion. The most pronounced effect was obtained with 25-hydroxycholesterol, where the TNF-alpha secretion was reduced to 8%. This decreased effect was also found on the TNF-alpha mRNA level. The decreased LPS-induced TNF-alpha secretion coincided with an increased binding of the transcription factors Sp1 and Sp3 to the TNF-alpha promoter. In vitro studies of the TNF-alpha promoter suggests possible interactions between Sp1 and Sp3 and the NF-kappaB transcription factor complex that might affect the transcriptional initiation.

Effect of antioxidant protection by p-coumaric acid on low-density lipoprotein cholesterol oxidation

Mechanisms in which p-coumaric acid (CA) acts as an antioxidant are not well understood. This study investigated whether CA can act as a direct scavenger of reactive oxygen species (ROS) and whether it minimizes the oxidation of low-density lipoprotein (LDL). Rats were administered CA in drinking water at low or high doses for 10, 21, and 30 days (uptakes were 29 and 317 mg/day, respectively). Blood levels of 8-epiprostaglandin F(2alpha) were monitored as a marker of LDL oxidation. Oral administration of CA (317 mg/day) for 30 days significantly inhibited LDL oxidation. CA also reduced LDL cholesterol levels in serum but had no effect on levels of high-density lipoprotein cholesterol. In vitro studies that used electron spin resonance in combination with spin trapping techniques were used to determine the ability of CA to scavenge ROS and alter LDL oxidation. CA effectively scavenged.OH in a dose-dependent manner. IC(50) and maximum velocity for CA scavenging of.OH were 4. 72 microM and 1.2 microM/s, respectively, with a rate constant of 1. 8 x 10(11) M(-1). s(-1). Our studies suggest that the antioxidant properties of CA may involve the direct scavenging of ROS such as.OH.

Functional evidence for anti-oxidant action of fluvastatin on low-density lipoprotein using isolated macrophages and aorta

1. Fluvastatin has been reported to have not only a hypocholesterolaemic effect, but also a protective effect on low-density lipoprotein (LDL) from oxidation. We functionally evaluated the anti-oxidant effect of fluvastatin on oxidation of LDL by copper ions in vitro using mouse macrophages and rabbit aorta preparations. 2. After native LDL (N-LDL) from rabbit plasma had been pre-incubated in the presence or absence of fluvastatin (10 micromol/L) for 4 h, the N-LDL was mildly oxidized by incubation with 5 micromol/L CuCl2 for 5 h and two oxidized LDL, fluvastatin-pretreated (Flu-OxLDL) and -non-treated (OxLDL), were prepared. The level of thiobarbituric acid-reactive substances (TBARS) in Flu-OxLDL and OxLDL markedly increased compared with N-LDL. The degree of increment was significantly less in Flu-OxLDL than OxLDL. 3. When macrophages were incubated with Flu-OxLDL or OxLDL, the amount of cholesteryl ester that accumulated in the macrophages markedly increased compared with N-LDL. The degree of increment was significantly less in Flu-OxLDL than OxLDL. 4. Acetylcholine-induced endothelium-dependent relaxations in rabbit aortic rings were impaired in the presence of either Flu-OxLDL or OxLDL. The degree of impairment was significantly less in Flu-OxLDL. 5. The increased TBARS level, facilitated cholesteryl ester accumulation in macrophages and impaired endothelium-dependent relaxation elicited by OxLDL were not affected by simultaneous treatment with fluvastatin (10 micromol/L). 6. These findings indicate that fluvastatin can protect plasma LDL from oxidative modification and, thereby, prevent cholesterol accumulation in macrophages and endothelial dysfunction in blood vessels. This additional anti-oxidative effect of fluvastatin may be beneficial for preventing the progression of atherosclerosis.

Vasomotor responses of coronary stenoses to acetylcholine and their relation to serum lipid levels in stable angina pectoris

The effects of acetylcholine administration on coronary stenoses in relation to serum lipids level were evaluated in 18 patients (15 men, 3 women) with coronary artery disease and stable angina. Intracoronary acetylcholine was infused in concentrations 10(-7), 10(-6), 10(-5) M, followed by intracoronary bolus administration of isosorbide dinitrate. Computerized angiography was used to assess the changes in the diameter of stenoses and of proximal and distal segments. During acetylcholine infusion, at concentrations between 10(-7) to 10(-5) M, there was a significant (p <0.01) dose-dependent constriction of proximal and distal segments and of stenoses reversed by isosorbide dinitrate. There was no correlation between the serum total cholesterol level and the responses of proximal and distal segments to acetylcholine or nitrate. A correlation (p <0.05) was found between the serum total cholesterol level and the response of stenoses to acetylcholine, but there was no correlation with the response to isosorbide dinitrate. In conclusion, in patients with stable angina current serum total cholesterol level correlates with the vasomotor response of coronary stenoses to intracoronary acetylcholine. These findings are consistent with a direct effect of cholesterol, increasing basal coronary vasomotor tone and increasing the stimulated vasoconstrictor response of stenoses.

Tissue factor pathway inhibitor is expressed by human monocyte-derived macrophages : relationship to tissue factor induction by cholesterol and oxidized LDL

Lipid-laden macrophages express tissue factor (TF), which may activate the extrinsic coagulation pathway on rupture of the atherosclerotic plaque. Tissue factor pathway inhibitor (TFPI) is a major regulator of TF-induced coagulation. We evaluated the possibility that monocyte-derived macrophages express this protein, thereby contributing to regulation of TF activity (TFact). Equally, we investigated the effect of cholesterol and of oxidized LDL (Ox-LDL) on the expression of TFPI and TF by human monocyte-derived macrophages (HMDMs). Northern blot analysis of TFPI mRNA from cultured HMDMs revealed a single band at 4.2 kb with weak intensity; this finding was confirmed by reverse transcription-polymerase chain reaction. Gel filtration of HMDM supernatants showed the presence of an active 100-kDa form of TFPI, which was confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under nonreducing conditions; under reducing conditions, however, the immunoblot revealed a 40-kDa form of TFPI. The TFPI in HMDM supernatants possessed heparin-binding affinity, suggesting potential interaction of TFPI with heparan sulfate proteoglycans. Stimulation of foam cell formation by incubation of macrophages for 48 hours with exogenous free cholesterol indicated that neither the biological activity nor the de novo synthesis of TFPI protein was affected. In contrast, cholesterol loading with exogenous free cholesterol induced significant upregulation of total TFact (2.6-fold: 25.0 versus 9.4 mU/mg cell protein, cholesterol-treated versus control cells; P<0. 05); such induction was not correlated with an elevation in TF antigen (8.5 versus 7.8 ng/mg cell protein, cholesterol-treated versus control cells). Similarly, cholesterol-rich Ox-LDL induced an increase in TFact (1.9-fold: 18.9 versus 10.0 mU/mg cell protein, Ox-LDL-treated versus control cells; P<0.05); by contrast, the amount of TF antigen remained unchanged (7.1 versus 7.9 ng/mg cell protein, Ox-LDL-treated versus control cells). Our data indicate that enhancement of the procoagulant activity of TF in macrophage-derived foam cells is not counterbalanced by upregulation of TFPI activity, suggesting that lesion foam cells are in a procoagulant state; they may therefore contribute to thrombus generation on plaque rupture.

Interleukin-8 mediates downregulation of tissue inhibitor of metalloproteinase-1 expression in cholesterol-loaded human macrophages: relevance to stability of atherosclerotic plaque

BACKGROUND

The accumulation of macrophage-derived foam cells in atherosclerotic lesions correlates with increased local release of matrix-degrading metalloproteinases (MMPs) and a thin fibrous cap. The activity of these enzymes is controlled by specific tissue inhibitors of metalloproteinases (TIMPs).

METHODS AND RESULTS

Because oxidized low-density lipoprotein (OxLDL) modulates gene expression, we investigated the effect of these particles on the levels of MMP-1, MMP-3, MMP-9, TIMP-1, and TIMP-2 in the culture media of human monocyte-derived macrophages. OxLDL but not native LDL or high-density lipoprotein reduced the level of TIMP-1 in a dose-dependent manner with maximal effect (60% of control) at approximately 100 microg protein/mL. In addition, Northern blotting revealed marked reduction in the abundance of TIMP-1 mRNA in OxLDL-treated cells. Evaluation of the effect of oxysterol components of OxLDL on TIMP-1 production revealed that 25-hydroxycholesterol (1 microg/mL) was the most potent inhibitor ( approximately 30% of control). Such inhibition was partially mediated by interleukin (IL)-8. Indeed, IL-8 (2.5 ng/mL) induced maximal inhibition of TIMP-1 accumulation (30% of control) in 4 of 6 cell preparations. In addition, the inhibitory effect of OxLDL-treated cells in the presence of an anti-IL-8 neutralizing antibody was partially reversed.

CONCLUSIONS

Immunohistochemical analyses of human atherosclerotic plaques revealed the expression of TIMP-1 in some but not all macrophage-rich and IL-8-rich areas. Therefore, IL-8 may play a potential atherogenic role by inhibiting local TIMP-1 expression, thereby leading to an imbalance between MMPs and TIMPs at focal sites in the atherosclerotic plaque.

Oxysterols and atherosclerosis

Oxysterols are present in human atherosclerotic plaque and are suggested to play an active role in plaque development. Moreover, the oxysterol:cholesterol ratio in plaque is much higher than in normal tissues or plasma. Oxysterols in plaque are derived both non-enzymically, either from the diet and/or from in vivo oxidation, or (e.g. 27-hydroxycholesterol) are formed enzymically during cholesterol catabolism. While undergoing many of the same reactions as cholesterol, such as being esterified by cells and in plasma, certain oxysterols in some animal and in vitro models exhibit far more potent effects than cholesterol per se. In vitro, oxysterols perturb several aspects of cellular cholesterol homeostasis (including cholesterol biosynthesis, esterification, and efflux), impair vascular reactivity and are cytotoxic and/or induce apoptosis. Injection of relatively large doses of oxysterols into animals causes acute angiotoxicity whereas oxysterol-feeding experiments have yielded contrary results as far as their atherogenicity is concerned. There is no direct evidence yet in humans that oxysterols contribute to atherogenesis. However, oxysterol levels are elevated in human low-density lipoprotein (LDL) subfractions that are considered potentially atherogenic and two recent studies have indicated that raised plasma levels of a specific oxysterol (7beta-hydroxycholesterol) may be associated with an increased risk of atherosclerosis. At the present time there are a number of significant and quite widespread problems with current literature which preclude more than a tentative suggestion that oxysterols have a causal role in atherogenesis. Further studies are necessary to definitively determine the role of oxysterols in atherosclerosis, and considering the wide-ranging tissue levels reported in the literature, special emphasis is needed on their accurate analysis, especially in view of the susceptibility of the parent cholesterol to artifactual oxidation.

Inhibition of LPL expression in human monocyte-derived macrophages is dependent on LDL oxidation state: a key role for lysophosphatidylcholine

The regulation of macrophage lipoprotein lipase (LPL) secretion and mRNA expression by atherogenic lipoproteins is of critical relevance to foam cell formation. LPL is present in arterial lesions and constitutes a bridging ligand between lipoproteins, proteoglycans, and cell receptors, thus favoring macrophage lipoprotein uptake and lipid accumulation. We investigated the effects of native and of oxidized lipoproteins on the expression of LPL in an in vitro human monocyte-macrophage system. Exposure of mature macrophages (day 12) to highly copper-oxidized human low density lipoprotein (LDL) (100 microg protein per milliliter) led to marked reduction in the expression of LPL activity (-62%, P<0.01) and mRNA level (-47%, P<0.05); native LDL, acetylated LDL, and LDL oxidized for <6 hours were without effect. The reduction in LPL activity became significant at a threshold of 6 hours of LDL oxidation (-31%, P<0.05). Among the biologically active sterols formed during LDL oxidation, only 7beta-hydroxycholesterol (5 microg/mL) induced a minor reduction in macrophage LPL activity, whereas 25-hydroxycholesterol was without effect. By contrast, lysophosphatidylcholine, whose LDL content increased in parallel with the degree of oxidation, induced significant reductions in LPL activity and mRNA levels at concentrations of 2 to 20 micromol/L (-34% to -53%, P<0.01). Our results demonstrate that highly oxidized LDL (>6-hour oxidation) exerts negative feedback on LPL secretion in human monocytes-macrophages via a reduction in mRNA levels. By contrast, native LDL and mildly oxidized LDL (<6-hour oxidation) did not exert a feedback effect on LPL expression. We speculate that the content of lysophosphatidylcholine and, to a lesser degree, of 7beta-hydroxycholesterol in oxidized LDLs is responsible for the downregulation of LPL activity and mRNA abundance in human monocyte-derived macrophages and may therefore modulate LPL-mediated pathways of lipoprotein uptake during conversion of macrophages to foam cells.