Effects of oxidized LDL on mononuclear phagocytes: inhibition of induction of four inflammatory cytokine gene RNAs, release of NO, and cytolysis of tumor cells

Modified Lipoproteins Induce Arterial Wall Inflammation During Atherogenesis

Circulating apolipoprotein B-containing lipoproteins, notably the low-density lipoproteins, enter the inner layer of the arterial wall, the intima, where a fraction of them is retained and modified by proteases, lipases, and oxidizing agents and enzymes. The modified lipoproteins and various modification products, such as fatty acids, ceramides, lysophospholipids, and oxidized lipids induce inflammatory reactions in the macrophages and the covering endothelial cells, initiating an increased leukocyte diapedesis. Lipolysis of the lipoproteins also induces the formation of cholesterol crystals with strong proinflammatory properties. Modified and aggregated lipoproteins, cholesterol crystals, and lipoproteins isolated from human atherosclerotic lesions, all can activate macrophages and thereby induce the secretion of proinflammatory cytokines, chemokines, and enzymes. The extent of lipoprotein retention, modification, and aggregation have been shown to depend largely on differences in the composition of the circulating lipoprotein particles. These properties can be modified by pharmacological means, and thereby provide opportunities for clinical interventions regarding the prevention and treatment of atherosclerotic vascular diseases.

Lysosomal oxidation of LDL alters lysosomal pH, induces senescence, and increases secretion of pro-inflammatory cytokines in human macrophages

We have shown that aggregated LDL is internalized by macrophages and oxidized in lysosomes by redox-active iron. We have now investigated to determine whether the lysosomal oxidation of LDL impairs lysosomal function and whether a lysosomotropic antioxidant can prevent these alterations. LDL aggregated by SMase (SMase-LDL) caused increased lysosomal lipid peroxidation in human monocyte-derived macrophages or THP-1 macrophage-like cells, as shown by a fluorescent probe, Foam-LPO. The pH of the lysosomes was increased considerably by lysosomal LDL oxidation as shown by LysoSensor Yellow/Blue and LysoTracker Red. SMase-LDL induced senescence-like properties in the cells as shown by β-galactosidase staining and levels of p53 and p21. Inflammation plays a key role in atherosclerosis. SMase-LDL treatment increased the lipopolysaccharide-induced secretion of TNF-α, IL-6, and MCP-1. The lysosomotropic antioxidant, cysteamine, inhibited all of the above changes. Targeting lysosomes with antioxidants, such as cysteamine, to prevent the intralysosomal oxidation of LDL might be a novel therapy for atherosclerosis.

The danger model: questioning an unconvincing theory

Janeway's pattern recognition theory holds that the immune system detects infection through a limited number of the so-called pattern recognition receptors (PRRs). These receptors bind specific chemical compounds expressed by entire groups of related pathogens, but not by host cells (pathogen-associated molecular patterns (PAMPs). In contrast, Matzinger's danger hypothesis postulates that products released from stressed or damaged cells have a more important role in the activation of immune system than the recognition of nonself. These products, named by analogy to PAMPs as danger-associated molecular patterns (DAMPs), are proposed to act through the same receptors (PRRs) as PAMPs and, consequently, to stimulate largely similar responses. Herein, I review direct and indirect evidence that contradict the widely accepted danger theory, and suggest that it may be false.

The effect of oxidized low density lipoprotein (oxLDL)-induced heme oxygenase-1 on LPS-induced inflammation in RAW 264.7 macrophage cells

Macrophages take up oxidized low density lipoprotein (oxLDL) after being exposed to it in the blood vessels. oxLDL transforms macrophages into foam cells, which are a hallmark of atherosclerosis. The effects that oxLDL have on the inflammatory responses of foam cells are not clear. Here, we investigated how oxLDL modulates lipopolysaccharide (LPS)-induced inflammatory mediators in RAW 264.7 murine macrophages. Our results showed that oxLDL dramatically induced HO-1 expression, but did not increase pro-inflammatory mediators such as interleukin-1β, tumor necrosis factor-α, iNOS, and monocyte chemoattractant protein (MCP)-1. In RAW 264.7 macrophages, oxLDL markedly inhibited LPS-induced inflammatory mediators such as inducible nitric oxide synthase (iNOS), IL-1β, IL-6, granulocyte macrophage colony-stimulating factor and stromal cell-derived factor-1. Interestingly, however, the down-regulation of HO-1 by siRNA did not recover the inhibition of LPS-induced expression and/or the secretion of inflammatory mediators. oxLDL blocked LPS-induced NF-κB nuclear translocation by inhibiting inhibitory κB (IκB) degradation. Taken together, our results suggest that oxLDL could modulate LPS-induced inflammatory responses by inhibiting NF-κB signaling independently of HO-1 expression.

LDL and UV-oxidized LDL induce upregulation of iNOS and NO in unstimulated J774 macrophages and HUVEC

Oxidized low-density lipoprotein (LDL) diminishes NO production from activated macrophages. The interaction between LDL and inactivated macrophages is neglected and controversial. This study examines the effect of LDL, 7-oxysterols and iron compounds on NO production in unstimulated J774 macrophages. J774 cells and human umbilical vein endothelial cells (HUVEC) were either incubated for 24 h with native LDL (LDL) or ultraviolet (UV)-oxidized LDL (UVoxLDL), in the absence or presence of an inducible nitric oxide synthase (iNOS)- or an endothelial constitutive nitric oxide synthase (eNOS)-inhibitor. J774 cells were also incubated with lipopolysaccharide (LPS), in the absence or presence of an iNOS- or an eNOS-inhibitor. Nitrite was analysed as a marker of NO production. The mRNA levels of iNOS were evaluated by reverse transcriptase polymerase chain reaction. LDL and UVoxLDL significantly increased NO production from unstimulated J774 macrophages. This increase in NO was accompanied by enhanced expression of iNOS mRNA, and was inhibited by the iNOS inhibitor. Furthermore, NO production was elevated and angiotensin-converting enzyme (ACE) activity was reduced in HUVEC following the exposure to LDL and UVoxLDL. In conclusion, LDL may serve as an important inflammatory activator of macrophages and HUVEC, inducing inducible nitric oxide production but diminishing ACE. After its oxidation, this function of LDL may be further enhanced and may contribute to the regulation and progression of atheroma formation.

Lipid peroxidation and decomposition--conflicting roles in plaque vulnerability and stability

The low density lipoprotein (LDL) oxidation hypothesis has generated considerable interest in oxidative stress and how it might affect atherosclerosis. However, the failure of antioxidants, particularly vitamin E, to affect the progression of the disease in humans has convinced even staunch supporters of the hypothesis to take a step backwards and reconsider alternatives. Preponderant evidence for the hypothesis came from animal antioxidant intervention studies. In this review we point out basic differences between animal and human atherosclerosis development and suggest that human disease starts where animal studies end. While initial oxidative steps in the generation of early fatty streak lesions might be common, the differences might be in the steps involved in the decomposition of peroxidized lipids into aldehydes and their further oxidation into carboxylic acids. We suggest that these steps may not be amenable to attenuation by antioxidants and antioxidants might actually counter the stabilization of plaque by preventing the formation of carboxylic acids which are anti-inflammatory in nature. The formation of such dicarboxylic acids may also be conducive to plaque stabilization by trapping calcium. We suggest that agents that would prevent the decomposition of lipid peroxides and promote the formation and removal of lipid hydroxides, such as paraoxonase (PON 1) or apo A1/high density lipoprotein (HDL) might be more conducive to plaque regression.

Oxidized lipids: The two faces of vascular inflammation

Elevated plasma levels of low-density lipoprotein and generation of oxidized low-density lipoprotein have been directly associated with the pathogenesis of atherosclerosis, and lipid oxidation products have been directly linked with induction and propagation of monocytic subendothelial accumulation and other inflammatory reactions associated with chronic vascular inflammation. However, accumulating data suggest that oxidized lipids may also exhibit anti-inflammatory potential and serve as potent inhibitors of nuclear factor-kappaB-dependent proinflammatory cascade. In addition, we have characterized a group of bioactive components of oxidized phospholipids with barrier-protective effects towards endothelial cells in the models of agonist-induced endothelial permeability and lipopolysaccharide-induced lung dysfunction. This review discusses the role of oxidized lipids in the progression of atherosclerosis as well as the important anti-inflammatory effects of oxidized phospholipids and their potential role in the modulation of vascular barrier integrity.

Oxidized phospatidylcholine but not native phosphatidylcholine inhibits inducible nitric oxide synthase in RAW 264.7 macrophages

This study was designed to compare the effects of oxidized 1-palmitoyl-2-arachidonyl-sn-glycero-3-phosphorylcholine (PAPC) and native PAPC on the inducible nitric oxide synthase (iNOS) in the macrophage cell line RAW 264.7. Macrophages stimulated by bacterial lipopolysaccharide (1 microg/ml) were incubated with increasing amounts of native or oxidized PAPC (oxPAPC, 10-20 microg/ml). Cells incubated with oxPAPC showed a dose-dependent inhibition of inducible nitric oxide synthesis, as well as reduced iNOS protein expression and mRNA levels. Additionally, chromatin immunoprecipitation assay revealed that oxPAPC reduced the interaction of the active NF-kappaB subunit p65 with the iNOS promoter region when compared to native PAPC.

The state of macrophage differentiation determines the TNF alpha response to nitrated lipoprotein uptake

Inflammatory cytokine synthesis by monocyte-macrophages in the developing plaque represents an important amplification point in atherosclerotic disease progression. Here we have investigated whether the state of monocyte-macrophage differentiation can influence TNF alpha synthesis in response to scavenged modified low-density lipoprotein (LDL). We show that LDL modified by nitration induces TNF alpha synthesis when added to undifferentiated human monocytes or a mouse cell line (RAW264.7) bearing an incompletely differentiated phenotype. However, significantly reduced levels of TNF alpha were released from in vitro differentiated human macrophages (P=0.006) or a mouse cell line (IC-21) bearing a well-differentiated macrophage phenotype (P<0.001). A possible scavenging insufficiency in macrophagic cell types was ruled out by lipoprotein-uptake studies and competency to synthesise TNF alpha was confirmed using lipopolysaccharide (LPS) as a stimulus. However, LPS-induced TNF alpha secretion in IC-21 cells was partially suppressed by pre-treatment with nitrated LDL (46%, P=0.0076), with no equivalent effect seen in RAW264.7 cells. Based on these data, we hypothesise that the state of differentiation of intimal monocyte-macrophages may play an important role in their inflammatory response to scavenged modified lipoproteins and that the fully differentiated macrophage end-point may be associated with a non-inflammatory and therefore, atheroprotective, phenotype.

Decreased inducibility of TNF expression in lipid-loaded macrophages

BACKGROUND

Inflammation and immune responses are considered to be very important in the pathogenesis of atherosclerosis. Lipid accumulation in macrophages of the arterial intima is a characteristic feature of atherosclerosis which can influence the inflammatory potential of macrophages. We studied the effects of lipid loading on the regulation of TNF expression in human monocyte-derived macrophages.

RESULTS

In macrophages incubated with acetylated low density lipoprotein (ac-LDL) for 2 days, mRNA expression of TNF in cells stimulated with TNF decreased by 75%. In cell cultures stimulated over night with IL-1beta, lipid loading decreased secretion of TNF into culture medium by 48%. These results suggest that lipid accumulation in macrophages makes them less responsive to inflammatory stimuli. Decreased basal activity and inducibility of transcription factor AP-1 was observed in lipid-loaded cells, suggesting a mechanism for the suppression of cytokine expression. NF-kappaB binding activity and inducibility were only marginally affected by ac-LDL. LDL and ac-LDL did not activate PPARgamma. In contrast, oxidized LDL stimulated AP-1 and PPARgamma but inhibited NF-kappaB, indicating that the effects of lipid loading with ac-LDL were not due to oxidation of lipids.

CONCLUSIONS

Accumulation of lipid, mainly cholesterol, results in down-regulation of TNF expression in macrophages. Since monocytes are known to be activated by cell adhesion, these results suggest that foam cells in atherosclerotic plaques may contribute less potently to an inflammatory reaction than newly arrived monocytes/macrophages.

Oxidized LDLs influence thrombotic response and cyclooxygenase 2

Oxidative modification of low-density lipoproteins (LDLs) plays a key role in the development of atherosclerosis and the onset of coronary artery disease. LDL oxidation alters the antithrombotic balance of human endothelial cells inducing surface tissue factor (TF) pathway activity, which results in enhanced fibrin deposition. Fibrinolysis, which is strictly regulated by plasminogen activator inhibitor-1 (PAL-1) and tissue-type plasminogen activator (tPA). Is also dysregulated by LDL oxidation with a net increase in the inhibitory rate. Oxidized LDLs (oxLDLs) also affect many aspects of macrophage function linked to the inflammatory response of these cells, In particular, oxLDLs downregulate inducible cyclooxigenase (Cox-2) in human monocyte-derived macrophages exposed to bacterial lipopolysaccharide. This observation may support the hypothesis that, within atheromata, the transformation macrophages into foam cells results in the attenuation of the inflammatory response, thus contributing to the progression of athrogenesis. Among lipid constituents of oxLDLs, Ox-PAPC, a mixture of oxidized arachidonic acid-containing phospholipids, prevents Cox-2 expression, suggesting that it could be considered responsible for the biological activity of oxLDLs.

Inhibition of murine macrophage IL-12 production by natural and synthetic DNA

DNA is a complex macromolecule whose immunological properties vary with sequence and structure. To determine whether DNA can inhibit immune responses, the effects of mammalian DNA and synthetic phosphodiester (Po) and phosphorothioate (Ps) oligonucleotides (ODNs) on IL-12 production were tested using murine macrophages. With bacterial DNA as a stimulant, calf thymus DNA and human placenta DNA blocked IL-12 production by splenic and bone marrow macrophages. A (dG)(30) Po ODN and all single-base Ps 30 mer ODNs were also effective inhibitors. The Ps ODNs also blocked IL-12 production induced by lipopolysaccharide (LPS) and a stimulatory Ps ODN. With the J774 cell line, single-base Ps ODNs inhibited IL-12 production induced by bacterial DNA, LPS, and a stimulatory Ps ODN. Together, these results indicate that DNA has inhibitory properties, suggesting that mammalian DNA could limit immune activation during inflammation and counteract the effects of bacterial DNA.

Oxidized low density lipoprotein suppresses expression of inducible cyclooxygenase in human macrophages

Atherogenesis involves several aspects of chronic inflammation and wound healing. Indeed, the atheroma is considered a special case of tissue response to injury. Injurious stimuli may include lipoproteins trapped within lesions where protein and lipid moieties have undergone chemical modifications. We have studied the effect of oxidized low density lipoproteins (ox-LDL) on inducible cyclooxygenase (Cox-2) in human monocyte-derived macrophages exposed to bacterial lipopolysaccharide (LPS). Levels of both Cox-2 and constitutive cyclooxygenase (Cox-1) were assessed using Western blot analysis. Prior incubation of macrophages with ox-LDL resulted in a strong inhibition of Cox-2 induced by LPS, without effect on Cox-1. The inhibitory effect was dependent on ox-LDL concentration and its onset was early in time (already detectable 1 hour after macrophage exposure to ox-LDL). Native LDL, and other forms of modified LDL, were without effect. The inhibition was dependent on endocytosis of ox-LDL and could be reproduced using the lipid extract from ox-LDL. Lysophosphatidylcholine, 7beta-hydroxycholesterol, and 7-oxocholesterol failed to mimic the inhibition, but oxidized arachidonic acid-containing phospholipids, produced by autoxidation of 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine, markedly inhibited Cox-2. The observation that ox-LDL downregulates Cox-2 in human macrophages may explain the fact that, within atheromata, the transformation of macrophages into foam cells results in attenuation of the inflammatory response, thus contributing to progression of atherogenesis.

4-Hydroxynonenal prevents NF-kappaB activation and tumor necrosis factor expression by inhibiting IkappaB phosphorylation and subsequent proteolysis

Extensively oxidized low density lipoprotein (ox-LDL), a modulator of atherogenesis, down-regulates the lipopolysaccharide (LPS)-induced activation of transcription factor NF-kappaB. We investigated whether 4-hydroxynonenal (HNE), a prominent aldehyde component of ox-LDL, represents one of the inhibitory substances. NF-kappaB activation by stimuli such as LPS, interleukin (IL)-1beta, and phorbol ester, but not tumor necrosis factor (TNF), was reversibly inhibited by HNE in a dose-dependent manner in human monocytic cells, whereas AP-1 binding was unaffected. Using similar HNE concentrations, LPS-induced kappaB- and TNF or IL-8 promoter-dependent transcription was prevented. Furthermore, pretreatment with HNE suppressed TNF production but not lactate dehydrogenase levels. Under these conditions the binding of LPS to monocytic cells was not significantly affected. However, induced proteolysis of the inhibitory proteins IkappaB-alpha, IkappaB-beta, and, at a later time point, IkappaB-epsilon was prevented. This is not due to inhibition of the proteasome, the major proteolytic activities of which remain unaffected, but rather to a specific prevention of the activation-dependent phosphorylation of IkappaB-alpha. This is the first report which demonstrates that HNE specifically inhibits the NF-kappaB/Rel system. Down-modulation of NF-kappaB-regulated gene expression may contribute at certain stages of atherosclerosis to low levels of chronic inflammation and may also be involved in other inflammatory/degenerative diseases.

Lipid hydroperoxides inhibit nitric oxide production in RAW264.7 macrophages

The effects of oxidatively modified low density lipoprotein (oxLDL) on atherogenesis may be partly mediated by alterations in the production of nitric oxide (NO) by vascular cells. Lipid hydroperoxides (LOOH) and lysophosphatidylcholine (lysoPC) are the major primary products of LDL oxidation. The purpose of this study was to characterize the effects of oxLDL, LOOH and lysoPC on NO production and the expression of inducible nitric oxide synthase (iNOS) gene in lipopolysaccharide (LPS) stimulated macrophages. LDL was oxidized using an azo-initiator 2,2'-azobis (2-amidinopropane) HCl (ABAP) and octadecadienoic acid was oxidized by lipoxygenase to generate 13-hydroperoxyl octadecadienoic acid (13-HPODE). Our study showed that oxLDL markedly decreased the production of NO, the levels of iNOS protein and iNOS mRNA in LPS stimulated macrophages. The inhibition potential of oxLDL on NO production and iNOS gene expression depended on the levels of LOOH formed in oxLDL and was not due to oxLDL cytotoxicity. Furthermore, 13-HPODE markedly reduced NO production and iNOS protein levels, whereas lysoPC showed only slight reduction. The effects of 13-HPODE and lysoPC did not require an acetylated LDL carrier. Our results suggest that 13-HPODE is a much more potent inhibitor of NO production and iNOS gene expression than lysoPC in LPS stimulated RAW264.7 macrophages.

The influence of DNA sequence on the immunostimulatory properties of plasmid DNA vectors

To determine the influence of DNA sequence on immunostimulatory properties of vaccine vectors, we tested the induction of in vitro and in vivo immune responses by plasmids modified to contain extended runs of dG sequences. Studies with oligonucleotides indicate that dG sequences can directly stimulate B cells as well as enhance the activity of immunostimulatory CpG motifs because of interaction with the macrophage scavenger receptor (MSR); this receptor can bind a variety of polyanions including dG sequences. To modify vectors, we introduced stretches of 20-60 dG residues into the pCMV-beta and pSG5rab.gp vectors and measured the ability of these plasmids to induce IL-12 and IFN-gamma production by murine splenocytes. The induction of in vivo antibody responses to rabies glycoprotein was also assessed with the pSG5rab.gp vectors. In in vitro cultures, cytokine production induced by plasmids with and without dG sequences was similar. Furthermore, the addition of dG sequences to pSG5rab.gp vectors failed to enhance the anti-rabies glycoprotein response to immunization. To assess further mechanisms by which plasmids stimulate macrophages, we measured the effects of MSR ligands on in vitro cytokine induction. In in vitro cultures, poly(G), dG30, and fucoidan inhibited IL-12 induction by plasmids. IL-12 induction was also inhibited by mammalian DNA but was unaffected by polyanions that are not MSR ligands. Together, these results suggest that the addition of 20 to 60-base dG sequences to plasmids does not significantly affect their properties as immunostimulators or vaccines. Furthermore, these results suggest that MSR ligands can block cytokine induction by plasmid DNA whether or not the plasmid contains extended runs of dG.

Plasma lipid concentrations correlate inversely with CPB-induced interleukin-6 release

PURPOSE

Cardiopulmonary bypass (CPB) is characterized by translocation of intestinal endotoxin and subsequent endogenous production of the pro-inflammatory cytokine interleukin-6 (IL-6). Plasma lipid fractions, especially high density lipoproteins, bind and neutralize endotoxin and, therefore, inhibit endotoxin-induced macrophage cytokine production, including IL-6. Increased IL-6 plasma levels have been implicated in adverse consequences associated with CPB. Previous studies demonstrated large interpatient variability in IL-6 plasma levels after CPB. The purpose of this study was to evaluate the relationship between plasma lipid concentrations and the concentrations of IL-6 following CPB in humans.

METHODS

In a prospective study, a group of 15 patients selected to exclude variables known to influence post-CPB plasma levels of IL-6 (preoperative left ventricular ejection fraction > 45%, similar durations of aortic cross clamping and total CPB time, similar temperature control during CPB, and avoidance of platelet transfusion and shed mediastinal blood re-infusion), IL-6 was measured at baseline, one and 24 hr post-CPB.

RESULTS

Interleukin-6 plasma concentrations (mean +/- SD) increased at one (142 +/- 89 pg.ml-1, P < 0.05) and 24 (129 +/- 82 pg.ml-1, P < 0.05) hr post-CPB compared with baseline (1.5 +/- 1 pg.ml-1) concentrations. An inverse correlation was found between IL-6 plasma concentrations at one hour post-CPB and plasma cholesterol concentrations (r = -0.592, P = 0.02), high density lipoprotein (r = -0.595, P = 0.02), and low density lipoprotein (r = -0.656, P = 0.01).

CONCLUSIONS

These results suggest that plasma lipids attenuate the production of IL-6 during CPB and may partly explain the variability of interpatient levels of IL-6 reported post-CPB by others.

Hypochlorite-modified LDL: chemotactic potential and chemokine induction in human monocytes

Within blood vessels the accumulation of monocytes/macrophages at sites of modified lipoproteins is an important feature in atherosclerosis. Recently the presence of LDL and other proteins modified by hypochlorous acid (HOCl-LDL) was demonstrated in human atherosclerotic vessels and human inflammatory kidney disease by immunohistology and protein chemistry. Chemokines contribute to a specific and directed migration of inflammatory cells. IL-8 (alpha-chemokine) attracts mainly neutrophils and distinct T-cell subsets while MCP-1 (beta-chemokine) preferentially acts on monocytes/macrophages. In the present study it was postulated that HOCl-LDL may induce and amplify inflammatory reactions by the induction of chemokine synthesis in local monocytes. After exposure of human monocytes to HOCl-LDL, it was found that mRNA and protein of the chemokine IL-8 was strongly induced, while the chemokine MCP-1 was not. HOCl-LDL itself led to a chemotactic migration of neutrophils. A chemotactic response of human monocytes toward HOCl-LDL was not detectable. We propose that HOCl-LDL may represent a form of LDL modification in the atherosclerotic process which initiates leukocyte infiltration; these mononuclear cells have been observed in the early stages of atherosclerosis.

Oxidized cholesterol in oxidized low density lipoprotein may be responsible for the inhibition of LPS-induced nitric oxide production in macrophages

Previous work has shown that oxidized low density lipoprotein (Ox-LDL) inhibited lipopolysacchride (LPS)-induced nitric oxide (NO) production in macrophages. In this paper, the role of different components of Ox-LDL in the inhibitory effect was studied by measuring nitrite in media. Ox-LDL inhibited LPS-induced NO production in macrophage cell line J774.A1. When compared with Ox-LDL, native and acetylated LDL had a lesser effect on NO production. Pre-clearance of lipid hydroperoxides (LOOH) in Ox-LDL and removal of soluble thiobarbituric acid reactive substances (TBARS) in Ox-LDL solution by dialysis had no influence on the inhibitory effect of Ox-LDL. The protein moiety of Ox-LDL had no effect on NO production, but the lipid moiety inhibited NO production to about the same extent as intact Ox-LDL. Linoleic acid and phosphatidylcholine, the main components of LDL lipid, whether oxidized separately or together, had no effect on NO production. However, if linoleic acid and cholesterol oxidized together, there was very strong inhibition of NO production. Cholesterol oxidized alone also had some inhibitory effect. These results suggest that oxidized cholesterol in Ox-LDL might be responsible for the inhibition of NO production in macrophages.

Tumor necrosis factor-alpha induces c-fms RNA expression in murine tissue macrophages

The macrophage-colony stimulating factor receptor, c-fms, is induced by IL-2 in monocytes and is suppressed by LPS, LPS plus IFN-gamma, phorbol esters, and colony stimulating factor in monocytes/macrophages. Here we show that c-fms RNA is induced by treatment of murine tissue macrophages with TNF-alpha. This induction is suppressed by co-treatment with LPS, IFN-gamma, LPS plus IFN-gamma, aspirin, and ox LDL. c-fms expression is required for the proliferation, differentiation, and survival of monocytes/macrophages. Our findings indicate a way by which TNF-alpha, as well as LPS, IFN-gamma, aspirin, and ox LDL impinge upon macrophage biology.

Scavenger receptors may regulate nitric oxide production from macrophages stimulated by LPS

The effects of scavenger receptor (SR) ligands on nitric oxide (NO) production were investigated using mouse peritoneal macrophages stimulated by LPS. Pretreatment of macrophages with oxidized LDL, heparin, maleylated BSA, or liposomes composed of phosphatidylserine (PS-liposomes) inhibited NO production, but native LDL, acetyl LDL dextran sulfate, did not. Immunoblotting analysis suggests that the inhibitory effects could be a result of the inhibition of inducible NO synthase (iNOS) induction, but not enzyme activity. Further, tyrosine phosphorylation of a 41 kDa protein was also inhibited by OxLDL, heparin, maleylated BSA, and PS-liposomes. Chloroquine did not affect the extent of inhibition of NO production induced by these ligands, suggesting that the binding of these ligands to SR generates a signal(s) which is involved in the inhibition of NO production from macrophages stimulated by LPS. SR, which has an affinity to these ligands, may strictly regulate NO production from macrophages, and this inhibitory effect may be due to the inhibition of LPS-induced tyrosine phosphorylation of 41 kDa protein.

Isolated Apolipophorin III from Galleria mellonella Stimulates the Immune Reactions of This Insect

Apolipophorin III (apoLp-III) was isolated from the haemolymph of last instar larvae of Galleria mellonella. The ultraviolet (u.v.) spectrum and the N-terminal amino acid sequence reveal high similarities with the apoLp-III from Manduca sexta. The protein is heat-stable. The molecular mass of apoLp-III was determined to be 18 077 Da using mass spectrometry. The heat treatment (90 degrees C, 30 min) resulted in a pI shift from 6.6 for the non-heated to 6.1 for the heat-treated apoLp-III without change in the molecular mass, indicating that a conformational change might have been caused by the heat treatment, rather than covalent alterations. Intrahaemocoelic injection of pure apoLp-III into last instar G. mellonella larvae is followed by a dose-dependent increase of antibacterial activity in cell-free haemolymph of treated larvae 24 h after injection. Furthermore, pure apoLp-III enhances the phagocytic activity of isolated haemocytes in vitro. The newly discovered role of apoLp-III in inducing immune-related functions in insects is discussed in regard to the known features of this molecule in lipid metabolism. Arylphorin, another heat-stable protein in G. mellonella haemolymph, was likewise isolated in this study. The protein was identified by N-terminal protein sequencing, the sequence obtained exactly matches the known sequence data for this protein. Copyright 1997 Elsevier Science Ltd. All rights reserved

Differential responsivity of monocyte cytokine and adhesion proteins in high- and low-hostile humans

This study tested the general hypothesis that high- and low-hostile respondents would show different patterns of change in monocyte cytokine and adhesion protein (MCAP) expression in response to pharmacologically induced alterations in sympathetic nervous system (SNS) and parasympathetic nervous system (PNS) balance. On 3 separate days, 4 high- and 4 low-hostile respondents received isoproterenol infusions after saline, atropine (PNS blockade), or neostigmine (PNS stimulation) pre-treatment. Dual color flow cytometry with fluorescently labeled monoclonal antibodies to CD 14 (monocyte market), interleukin-1, leukocyte function activator (LFA-1), Class II major histocompatibility complex (MHC-II), and tumor necrosis factor was used to quantify cytokine and adhesion protein expression on monocytes in blood samples drawn before and after the combination drug infusions on the 3 test days in each respondents. Following PNS stimulation and istoproterenol infusion there was a decrease (compared to saline pretreatment) in MHC II expression in high hostiles that was significantly (p<.02) different from an increase in low hostiles. A similar trend (p = .08) was seen for LFA-1 expression, with high hostiles showing an increase and low hostiles a decrease. These findings support the broad hypothesis that high-and low-hostile respondents will show different MCAP responses to pharmacologically induced alterations in SNS-PNS balance. Such differences could contribute to accelerated atherogenesis among high-hostile individuals.

Oxidized lipoproteins including HDL and their lipid peroxidation products inhibit TNF-alpha secretion by THP-1 human macrophages

It has been established that oxidized LDL (ox-LDL) modifies cytokine secretion by macrophages, for example, by reducing tumor necrosis factor alpha (TNF-(alpha) m-RNA. However, little is known about the effects of oxidized high density lipoprotein (ox-HDL). This study reports the effects of ox-HDL subfractions 2 and 3 (ox-HDL2, ox-HDL3) compared with that of ox-LDL and some products of oxidation (hydroperoxides and aldehydes) on the secretion of TNF-alpha from THP-1 human monocytes derived macrophages in vitro. HDL2, HDL3 and LDL were oxidized with 10 microM Cu++ for 12 h and/or 24 h. Native and oxidized HDL and LDL were incubated for 24 h with macrophages with or without LPS (10 ng/ml) after which TNF-alpha secretion was measured in the culture medium. Lipid hydroperoxides and apolar aldehydes were also incubated with the cells for 2 h following which the medium was replaced and TNF-alpha secretion measured after a further 22 h of incubation. An inhibition of TNF-alpha by ox-HDL2 (p < .05), ox-HDL3 (p < .05) and ox-LDL (p < .05) from THP-1 macrophages was observed in the presence and absence of LPS. This inhibition remained the same after incubation with ox-HDL 12 h and 24 h. Hydroperoxides of linoleic acid did not modify TNF-alpha secretion by cells while five out of eight aldehydes analyzed (2,4-heptadienal, hexanal, 2-nonenal, 2-octenal, 2,4-decadienal) inhibited TNF-alpha secretion (p < .05). These findings demonstrate that ox-HDL, and some of its lipid peroxidation products, plays a role in the modulation of the inflammatory response by macrophages as previously observed for ox-LDL.

Functional and possible physical association of scavenger receptor with cytoplasmic tyrosine kinase Lyn in monocytic THP-1-derived macrophages

Acetyl LDL (modified low-density lipoprotein), which is thought to be taken up through scavenger receptor A (SR-A), rapidly induced the appearance of phosphotyrosine proteins in monocytic THP-1-derived macrophages in vitro. The two alternative forms of Lyn (p53 and p56) were found to be tyrosine-phosphorylated within 30 s after the stimulation with acetyl LDL. The catalytic activity of Lyn measured by an in vitro kinase assay had also increased in acetyl LDL-stimulated THP-1-derived macrophages. Furthermore, Lyn could be co-immunoprecipitated with SR-A from the cell lysate. These observations suggest a functional and possible physical association of SR-A with Lyn in THP-1-derived macrophages, and also imply a possible involvement of Lyn in SR-A signal transduction.

Modified lipoproteins, cytokines and macrovascular disease in non-insulin-dependent diabetes mellitus

The processes of glycation and oxidation play a significant role in the acceleration of atherosclerosis in diabetes mellitus. Glycation is thought not only to increase the susceptibility of low-density lipoprotein (LDL) to oxidation but also to enhance the propensity of vessel wall structural proteins to bind extravasated plasma proteins, including LDL, and thus to contribute to a more marked oxidative modification of LDL. Glycated and oxidized lipoproteins induce cholesteryl ester accumulation in human macrophages and may promote platelet and endothelial cell dysfunction. Furthermore, these modified lipoproteins have the ability to trigger an autoimmune response that leads to the formation of autoantibodies and subsequently to the formation of immune complexes containing LDL. Both the modified lipoproteins and the immune complexes formed with autoantibodies reactive with modified lipoproteins may be responsible for several alternative and not mutually exclusive pathways leading to foam cell formation, macrophage activation and endothelial cell damage and may thus be of potential significance in initiating and/or contributing to the acceleration of the development of atherosclerosis. In this review we discuss how modified LDL affects lipoprotein metabolism, how immune complexes containing LDL induce the transformation of macrophages into foam cells and promote macrophage activation leading to the release of cytokines and thus initiating a sequence of events leading to endothelial cell damage and to the recruitment and activation of leucocytes. We also summarize our work showing that macrophage activation by LDL containing immune complexes leads to a paradoxical increase in LDL-receptor expression thus further impairing cholesterol homeostasis and enhancing the development of atheromatous lesions.

Oxidized low density lipoprotein suppresses activation of NF kappa B in macrophages via a pertussis toxin-sensitive signaling mechanism

The interaction of oxidized low density lipoprotein (ox-LDL) and macrophages is generally believed to be a significant inductive step in atherogenesis. Endocytosis of ox-LDL by scavenger receptors (SR) on macrophages is one result of this interaction, as is suppressed expression of several lipopolysaccharide (LPS)-stimulated, inflammatory genes such as tumor necrosis factor-alpha (TNF-alpha). Events subsequent to SR ligation, including intracellular signaling events if any, have not been established. We report here that ox-LDL initiates rapid hydrolysis of phosphatidylinositol 4,5-bisphosphate 2 (PIP2) and intracellular fluxes of Ca2+ in macrophages, both of which are sensitive to pertussis toxin. ox-LDL also suppresses the LPS-induced binding of macrophage extracts to an NF kappa B sequence oligonucleotide and the LPS-initiated accumulation of RNA specific for TNF-alpha. These latter two effects are pertussis toxin-sensitive. Ligation of SR by ox-LDL thus initiates a pertussis toxin-sensitive signaling pathway in macrophages, which involves hydrolysis of PIP2 and which can suppress expression of the TNF-alpha gene by modulating activation of NF kappa B.