Protective role of phospholipid oxidation products in endotoxin-induced tissue damage

Effects of ozone oxidative preconditioning on different hepatic biomarkers of oxidative stress in endotoxic shock in mice

In endotoxic shock, variations are known to occur in different biochemical parameters of oxidative stress. Ozone oxidative preconditioning (OOP) is a good candidate to restore the redox balance on different tissue. This investigation examined the effect of OOP on different biomarkers of oxidative stress in hepatic tissue of mice treated with lipopolysaccharide (LPS). LPS doses of 30 mg/kg were administered intraperitoneally (i.p.) and pretreatment with ozone/oxygen mixture (OOM) was applied i.p. at 0.2, 0.4, and 1.2 mg/kg once daily during 5 days before LPS injection. The mice were euthanized under ether atmosphere at different times, 1 and 24 h after LPS injection. Hepatic tissue from all animals was taken for biochemical determinations of oxidative stress parameters such as thiobarbituric acid reactive substances (TBARS) content and activity of antioxidant enzymes superoxide dismutase (SOD), glutathione peroxidase (GPx), and glutathione S-transferase (GST). The results demonstrated that OOP reduces levels of TBARS content and increases the activity of GPx in hepatic tissue. In conclusion, OOP was able to recover the redox balance and in this way to protect the animals against the oxidative damage induced by endotoxemia.

Host derived inflammatory phospholipids regulate rahU (PA0122) gene, protein, and biofilm formation in Pseudomonas aeruginosa

This study describes the role of "inflammatory" oxidized (Ox) phospholipids in regulation of rahU (PA0122) expression and biofilm formation in Pseudomonas aeruginosa (383) wild type (rahU(+)) and rahU mutant (rahU(-)) strains. Functional analysis of RahU protein from P. aeruginosa in presence of Ox-phospholipids show: (a) LysoPC modulates RahU gene/and protein expression in rahU(+) cells; (b) rahU promoter activity is increased by lysoPC and inhibited by PAPC, Ox-PAPC and arachidonic acid; the latter inhibitory effect can be reversed by lysoPC, which was enzymatically derived from PAPC; (c) biofilm formation increased in rahU(-) cells as compared to rahU(+); and (d) inhibition of rahU promoter activity by PAPC and AA (but not lysoPC) showed significantly augmented biofilm formation in rahU(+) but not in rahU(-) cells. This study shows that host derived Ox-phospholipids affect P. aeruginosa-rahU gene and protein expression, which in turn modulates biofilm formation. The accompanying paper describes the role of RahU protein in eukaryotic-host cells.

Oxidation-specific epitopes are danger-associated molecular patterns recognized by pattern recognition receptors of innate immunity

Oxidation reactions are vital parts of metabolism and signal transduction. However, they also produce reactive oxygen species, which damage lipids, proteins and DNA, generating "oxidation-specific" epitopes. In this review, we discuss the hypothesis that such common oxidation-specific epitopes are a major target of innate immunity, recognized by a variety of "pattern recognition receptors" (PRRs). By analogy with microbial "pathogen-associated molecular patterns" (PAMPs), we postulate that host-derived, oxidation-specific epitopes can be considered to represent "danger (or damage)-associated molecular patterns" (DAMPs). We also argue that oxidation-specific epitopes present on apoptotic cells and their cellular debris provided the primary evolutionary pressure for the selection of such PRRs. Furthermore, because many PAMPs on microbes share molecular identity and/or mimicry with oxidation-specific epitopes, such PAMPs provide a strong secondary selecting pressure for the same set of oxidation-specific PRRs as well. Because lipid peroxidation is ubiquitous and a major component of the inflammatory state associated with atherosclerosis, the understanding that oxidation-specific epitopes are DAMPs, and thus the target of multiple arcs of innate immunity, provides novel insights into the pathogenesis of atherosclerosis. As examples, we show that both cellular and soluble PRRs, such as CD36, toll-like receptor-4, natural antibodies, and C-reactive protein recognize common oxidation-specific DAMPs, such as oxidized phospholipids and oxidized cholesteryl esters, and mediate a variety of immune responses, from expression of proinflammatory genes to excessive intracellular lipoprotein accumulation to atheroprotective humoral immunity. These insights may lead to improved understanding of inflammation and atherogenesis and suggest new approaches to diagnosis and therapy.

Altered or impaired immune response upon vaccination in WNIN/Ob rats

The present study was aimed to study the immune response in three months old male and female naïve obese animals and upon hepatitis B vaccination in three months old female WNIN/Ob obese mutant rats, established at our institute in comparison with its lean litter mates. Altered immune profile was seen in naïve obese mutant rats in terms of percentage of splenic CD8(+) cytotoxic cells in males and percentages of splenic CD3(+) T lymphocytes and CD4(+) T helper cells in females respectively. Furthermore these obese mutant rats also exhibited impaired immune response to hepatitis B vaccine with low specific Hepatitis B surface antigen (HBsAg) specific IgG response and splenic lymphocyte proliferative response to HBsAg compared to the lean counterpart. The loss of immunological memory following vaccination could be attributed to the metabolic and hormonal changes associated with obesity. This observation has implication in public health policies related to vaccination in developed as well as developing countries.

Hypertonicity-enhanced TNF-α release from activated human monocytic THP-1 cells requires ERK activation

BACKGROUND

Hypertonic stress enhances tumor necrosis factor (TNF)-α expression in activated monocytes. However, the underlying mechanism is unknown. The produced TNF-α is primarily cleaved and released by TNF-α-converting enzyme (TACE), and the surface expression of TACE is down-regulated by endocytosis. As hypertonicity inhibits endocytosis, we evaluated the mechanism of hypertonicity-induced TNF-α release from activated human monocytic THP-1 cells.

METHODS

THP-1 cells were stimulated with lipopolysaccharide (LPS) or phorbol 12-myristate 13-acetate (PMA) in the presence or absence of hypertonic agents (150 mM sucrose or 150-300 mM NaCl). The amount of TNF-α mRNA and protein, surface expression of TACE and activation of signaling pathways (mitogen-activated protein kinase, Akt and NF-κB) were assayed.

RESULTS

Hypertonic sucrose and NaCl significantly enhanced TNF-α release from THP-1 cells upon LPS or PMA stimulation. Hypertonic sucrose and other endocytosis inhibitors increased surface expression of TACE, but their effects on TNF-α release were inconsistent. This enhancement effect by hypertonicity was not attenuated by inhibition of TACE or IκB kinase, but it was blocked by cycloheximide and a MAP/ERK kinase inhibitor. The LPS- or PMA-induced TNF-α mRNA expression was not increased; rather, it was inhibited by hypertonicity. ERK1/2 was re-activated after sucrose treatment in LPS-stimulated THP-1 cells.

CONCLUSIONS

Hypertonicity-enhanced TNF-α protein synthesis from LPS- or PMA-activated THP-1 cells requires ERK activation and may proceed without TACE.

GENERAL SIGNIFICANCE

A vast amount of TNF-α production was regulated by a crucial post-transcriptional manner in activated human monocytic leukemia cells, and it may possibly be contributed to the cachexia condition.

[Effects of Chinese herbal medicine Dusuqing Granule on toll-like receptor 4 signaling in multiple organ injury induced by bacterial pneumonia in aged rats]

OBJECTIVE

To study the protective mechanism of Dusuqing Granule, a compound Chinese herbal medicine, on the senile multiple organ injury caused by bacterial pneumonia by observing the expression changes of molecules related to toll-like receptor 4 (TLR4) signaling.

METHODS

A total of 55 male Sprague-Dawley aged rats were divided into control group, untreated group, Dusuqing group and lomefloxacin group. There were 25 rats in the untreated group and 10 rats in each of the other three groups. Multiple organ injury in a rat model of pneumonia was induced by injection of Klebsiella pneumoniae through tracheal intubation. By means of immunohistochemistry and reverse transcription-polymerase chain reaction (RT-PCR), examinations were made on mRNA expressions of lipopolysaccharide-binding protein (LBP), CD14, TLR4 and interleukin-1 receptor-associated kinase-1 (IRAK-1) in the tissues of the lung, heart and small intestine, and also on the protein expressions of TLR4, tumor necrosis factor receptor-associated factor 6 (TRAF6) and nuclear factor-κB (NF-κB).

RESULTS

Expressions of LBP, CD14, TLR4 and IRAK-1 mRNAs in the tissues of the lung, heart and small intestine in the untreated group were stronger than those in the control group (P<0.01 or Plt;0.05). The protein expressions of TLR4, TRAF6 and NF-κB were increased dramatically in the untreated group as compared with the control group (Plt;0.01 or Plt;0.05). Compared with the untreated group, the expressions of LBP, CD14, TLR4 and IRAK-1 mRNAs in the tissues of the lung, heart and small intestine in the Dusuqing group were weakened significantly (Plt;0.01 or Plt;0.05). Meanwhile, the protein expressions of TLR4, TRAF6 and NF-κB were decreased markedly in the Dusuqing group (Plt;0.01 or Plt;0.05).

CONCLUSION

Dusuqing Granule is effective in suppressing toll-like receptor signal transduction activation and reducing the secretion of cytokines and inflammatory mediators, which can further reduce the organ tissue injury. Dusuqing Granule can decrease the levels of TLR signal transduction activation including the targets LBP, CD-14, TLR4, IRAK-1, TRAF6 and NF-κB, which is different from the special inhibitor that acts only on some segments.

Modified phospholipids as anti-inflammatory compounds

PURPOSE OF REVIEW

Oxidized phospholipids (OxPLs) are abundantly found at sites of inflammation and are considered to play an active role in the modulation of the immune response. Whereas most studies attributed a proinflammatory role to OxPLs, recent studies demonstrate that some products of phospholipid oxidation may in fact exhibit anti-inflammatory properties. This study summarizes the proinflammatory and anti-inflammatory properties of OxPLs and sheds light on the therapeutic potential of OxPL derivatives or analogs for treatment of chronic inflammatory disorders.

RECENT FINDINGS

OxPLs may inhibit activation of several Toll-like receptors and can epigenetically reduce the capacity of dendritic cells to function as mature, fully functional immunostimulatory cells. These data demonstrate that OxPLs can induce anti-inflammatory effects. Moreover, VB-201, an orally available synthetic phospholipid analog of the Lecinoxoid family, was found to attenuate inflammation in various preclinical animal models and is currently employed in a phase II clinical trial in psoriasis.

SUMMARY

Chemical or biological modifications of phospholipids yield various products, some of which may exhibit anti-inflammatory properties. Identification of such species and generation of more stable/potent anti-inflammatory OxPL variants may represent a novel approach for the treatment of immune-mediated diseases such as psoriasis, atherosclerosis, multiple sclerosis and rheumatoid arthritis.

p190RhoGAP mediates protective effects of oxidized phospholipids in the models of ventilator-induced lung injury

Products resulting from oxidation of cell membrane phospholipid 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (OxPAPC) exhibit potent protective effects against lung endothelial cell (EC) barrier dysfunction caused by pathologically relevant mechanical forces and inflammatory agents. These effects were linked to enhancement of peripheral cytoskeleton and cell adhesion interactions mediated by small GTPase Rac and inhibition of Rho-mediated barrier-disruptive signaling. However, the mechanism of OxPAPC-induced, Rac-dependent Rho downregulation critical for vascular barrier protection remains unclear. This study tested the hypothesis that Rho negative regulator p190RhoGAP is essential for OxPAPC-induced lung barrier protection against ventilator-induced lung injury (VILI), and investigated potential mechanism of p190RhoGAP targeting to adherens junctions (AJ) via p120-catenin. OxPAPC induced peripheral translocation of p190RhoGAP, which was abolished by knockdown of Rac-specific guanine nucleotide exchange factors Tiam1 and Vav2. OxPAPC also induced Rac-dependent tyrosine phosphorylation and association of p190RhoGAP with AJ protein p120-catenin. siRNA-induced knockdown of p190RhoGAP attenuated protective effects of OxPAPC against EC barrier compromise induced by thrombin and pathologically relevant cyclic stretch (18% CS). In vivo, p190RhoGAP knockdown significantly attenuated protective effects of OxPAPC against ventilator-induced lung vascular leak, as detected by increased cell count and protein content in the bronchoalveolar lavage fluid, and tissue neutrophil accumulation in the lung. These results demonstrate for the first time a key role of p190RhoGAP for the vascular endothelial barrier protection in VILI.

Cholesterol slows down the lateral mobility of an oxidized phospholipid in a supported lipid bilayer

We investigated the mobility and phase-partitioning of the fluorescent oxidized phospholipid analogue 1-palmitoyl-2-glutaroyl-sn-glycero-3-phospho-N-Alexa647-ethanolamine (PGPE-Alexa647) in supported lipid bilayers. Compared to the conventional phospholipid dihexadecanoylphosphoethanolamine (DHPE)-Bodipy we found consistently higher diffusion constants. The effect became dramatic when immobile obstacles were inserted into the bilayer, which essentially blocked the diffusion of DHPE-Bodipy but hardly influenced the movements of PGPE-Alexa647. In a supported lipid bilayer made of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), the differences in probe mobility leveled off with increasing cholesterol content. Using coarse-grained molecular dynamics simulations, we could ascribe this effect to increased interactions between the oxidized phospholipid and the membrane matrix, concomitant with a translation in the headgroup position of the oxidized phospholipid: at zero cholesterol content, its headgroup is shifted to the outside of the DOPC headgroup region, whereas increasing cholesterol concentrations pulls the headgroup into the bilayer plane.

Oxidized phospholipids are more potent antagonists of lipopolysaccharide than inducers of inflammation

Polyunsaturated fatty acids are precursors of multiple pro- and anti-inflammatory molecules generated by enzymatic stereospecific and positionally specific insertion of oxygen, which is a prerequisite for recognition of these mediators by cellular receptors. However, nonenzymatically oxidized free and esterified polyunsaturated fatty acids also demonstrate activities relevant to inflammation. In particular, phospholipids containing oxidized fatty acid residues (oxidized phospholipids; OxPLs) were shown to induce proinflammatory changes in endothelial cells but paradoxically also to inhibit inflammation induced via TLR4. In this study, we show that half-maximal inhibition of LPS-induced elevation of E-selectin mRNA in endothelial cells developed at concentrations of oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine (OxPAPC) 10-fold lower than those required to induce proinflammatory response. Similar concentration difference was observed for other classes and molecular species of OxPLs. Upon injection into mice, OxPAPC did not elevate plasma levels of IL-6 and keratinocyte chemoattractant but strongly inhibited LPS-induced upregulation of these inflammatory cytokines. Thus, both in vitro and in vivo, anti-LPS effects of OxPLs are observed at lower concentrations than those required for their proinflammatory action. Quantification of the most abundant oxidized phosphatidylcholines by HPLC/tandem mass spectrometry showed that circulating concentrations of total oxidized phosphatidylcholine species are close to the range where they demonstrate anti-LPS activity but significantly lower than that required for induction of inflammation. We hypothesize that low levels of OxPLs in circulation serve mostly anti-LPS function and protect from excessive systemic response to TLR4 ligands, whereas proinflammatory effects of OxPLs are more likely to develop locally at sites of tissue deposition of OxPLs (e.g., in atherosclerotic vessels).

Apolipoprotein(a) inhibits lipopolysaccharide-induced IL-6 secretion in human astrocytoma cell line by interfering with lipopolysaccharide signaling

OBJECTIVE

To examine the role of lipoprotein(a) [Lp(a)] on the inflammatory response of cells in the nervous system by investigating its effect on lipopolysaccharide (LPS)-induced interleukin-6 (IL-6) secretion.

MATERIALS AND METHODS

Human astrocytoma U373 cells were treated with recombinant apolipoprotein(a) [r-apo(a)] A10K (175-11 nM), alone or in combination with LPS (100 and 10 ng/ml). IL-6 levels were evaluated by immunoblotting. Statistical analysis was performed by one-way ANOVA.

RESULTS

r-apo(a) caused dose-dependent inhibition of LPS-induced IL-6 secretion (100 ng/ml LPS, p = 0.0205; 10 ng/ml LPS, p = 0.0005). Pre-treatment of cells with 88 nM r-apo(a), rinsing, and activation with 10 ng/ml LPS did not reverse the inhibition (p = 0.0048), which could be reversed by supplementation with excess serum (5-20%) (p = 0.0454) or recombinant CD14 (2.0-0.05 μg/ml) (p = 0.0230).

CONCLUSIONS

Our data indicate that apo(a) plays a natural anti-endotoxin role which relies on its interference with cell-associated and serum components of LPS signaling.

Toll-like receptor 4 can recognize SapC-DOPS to stimulate macrophages to express several cytokines

OBJECTIVE AND DESIGN

SapC-DOPS is a newly combined compound consisting of saposin C and dioleoylphosphatidylserine (DOPS). Our recent study showed that SapC-DOPS exhibits anti-tumor activity. However, SapC-DOPS has recognition elements of Toll-like receptor (TLR) 2 and TLR4; therefore, we want to know whether SapC-DOPS can induce abnormal immunoreaction via identification TLRs.

METHODS

We investigated the capacity of SapC-DOPS to induce cytokines in vivo and in vitro and analyzed the involvement of TLR and NF-kB in these cytokines production.

RESULTS

SapC-DOPS could activate the cytokine production by peripheral macrophages, enhance the expressions of TLR4 and stimulate the NF-κB nuclear translocation. PDTC, an NF-κB inhibitor, could decrease the SapC-DOPS inducible TNF-α and IL-1β production.

CONCLUSIONS

SapC-DOPS was similar to LPS in the immune response and may induce the production of cytokines in macrophages via the TLR4 signaling pathway and, at least in part, the alteration of the NF-κB pathway.

Plasma lipoproteins are important components of the immune system

Plasma lipoproteins (VLDL, LDL, Lp[a] and HDL) function primarily in lipid transport among tissues and organs. However, cumulative evidence suggests that lipoproteins may also prevent bacterial, viral and parasitic infections and are therefore a component of innate immunity. Lipoproteins can also detoxify lipopolysaccharide and lipoteichoic acid. Infections can induce oxidation of LDL, and oxLDL in turn plays important anti-infective roles and protects against endotoxin-induced tissue damage. There is also evidence that apo(a) is protective against pathogens. Taken together, the evidence suggests that it might be valuable to introduce the concept that plasma lipoproteins belong in the realm of host immune response.

Identification of a novel macrophage phenotype that develops in response to atherogenic phospholipids via Nrf2

RATIONALE

Macrophages change their phenotype and biological functions depending on the microenvironment. In atherosclerosis, oxidative tissue damage accompanies chronic inflammation; however, macrophage phenotypic changes in response to oxidatively modified molecules are not known.

OBJECTIVE

To examine macrophage phenotypic changes in response to oxidized phospholipids that are present in atherosclerotic lesions.

METHODS AND RESULTS

We show that oxidized phospholipid-treated murine macrophages develop into a novel phenotype (Mox) that is strikingly different from the conventional M1 and M2 macrophage phenotypes. Compared to M1 and M2, Mox macrophages show a different gene expression pattern, as well as decreased phagocytotic and chemotactic capacity. Treatment with oxidized phospholipids induces both M1 and M2 macrophages to switch to the Mox phenotype. Whole-genome expression array analysis and subsequent gene ontology clustering revealed that the Mox phenotype was characterized by abundant overrepresentation of Nrf2-mediated expression of redox-regulatory genes. In macrophages isolated from Nrf2(-/-) mice, oxidized phospholipid-induced gene expression and regulation of redox status were compromised. Moreover, we found that Mox macrophages comprise 30% of all macrophages in advanced atherosclerotic lesions of low-density lipoprotein receptor knockout (LDLR(-/-)) mice.

CONCLUSIONS

Together, we identify Nrf2 as a key regulator in the formation of a novel macrophage phenotype (Mox) that develops in response to oxidative tissue damage. The unique biological properties of Mox macrophages suggest this phenotype may play an important role in atherosclerotic lesion development as well as in other settings of chronic inflammation.

Plasma lipoproteins are important components of the immune system

Plasma lipoproteins (VLDL, LDL, Lp[a] and HDL) function primarily in lipid transport among tissues and organs. However, cumulative evidence suggests that lipoproteins may also prevent bacterial, viral and parasitic infections and are therefore a component of innate immunity. Lipoproteins can also detoxify lipopolysaccharide and lipoteichoic acid. Infections can induce oxidation of LDL, and oxLDL in turn plays important anti-infective roles and protects against endotoxin-induced tissue damage. There is also evidence that apo(a) is protective against pathogens. Taken together, the evidence suggests that it might be valuable to introduce the concept that plasma lipoproteins belong in the realm of host immune response.

Toll-like receptors and atherosclerosis: oxidized LDL as an endogenous Toll-like receptor ligand

The oxidation hypothesis of atherosclerosis suggests that oxidative modification of low-density lipoprotein (LDL) is a prerequisite for LDL atherogenicity. Recent studies demonstrate that upon oxidative modification, LDL becomes enriched with pathogen-associated molecular patterns recognized by natural (inborn) antibodies and innate immune receptors. This review focuses on recent findings showing that Toll-like receptors (TLRs)--which sense microbial pathogens and initiate immediate inflammatory responses--are potentially involved in the pathogenesis of atherosclerosis. In addition to the data that bacterial agonists of TLR4 and TLR2 accelerate atherosclerosis, new evidence suggests that minimally oxidized LDL and specific oxidized phospholipids signal via TLRs to induce cytoskeletal changes and inflammatory cytokine secretion by macrophages and endothelial cells. Identifying the signaling mechanisms by which oxidized LDL induces chronic inflammation in atherosclerotic lesions may lead to novel therapeutic targets for the treatment of atherosclerotic cardiovascular disease.

Generation and biological activities of oxidized phospholipids

Glycerophospholipids represent a common class of lipids critically important for integrity of cellular membranes. Oxidation of esterified unsaturated fatty acids dramatically changes biological activities of phospholipids. Apart from impairment of their structural function, oxidation makes oxidized phospholipids (OxPLs) markers of "modified-self" type that are recognized by soluble and cell-associated receptors of innate immunity, including scavenger receptors, natural (germ line-encoded) antibodies, and C-reactive protein, thus directing removal of senescent and apoptotic cells or oxidized lipoproteins. In addition, OxPLs acquire novel biological activities not characteristic of their unoxidized precursors, including the ability to regulate innate and adaptive immune responses. Effects of OxPLs described in vitro and in vivo suggest their potential relevance in different pathologies, including atherosclerosis, acute inflammation, lung injury, and many other conditions. This review summarizes current knowledge on the mechanisms of formation, structures, and biological activities of OxPLs. Furthermore, potential applications of OxPLs as disease biomarkers, as well as experimental therapies targeting OxPLs, are described, providing a broad overview of an emerging class of lipid mediators.

Topical alpha-selective p38 MAP kinase inhibition reduces acute skin inflammation in guinea pig

Certain skin pathologies, including psoriasis, are thought to be immune-mediated inflammatory diseases. Available literature clearly indicates the involvement of inflammatory cells (neutrophils, T cells, and macrophages), their cytokines, and the p38 mitogen-activated protein kinase (MAPK) signaling pathway in the pathophysiology of psoriasis. Neutrophils play an important role in the formation of acute inflammatory changes in psoriasis. Acute inflammation or acute flares in psoriasis remain poorly addressed in clinical medicine. In this communication, we first establish a simple and reproducible model for studying neutrophil-mediated acute skin inflammation. Using the hairless guinea pig, due to the similarity of skin architecture to that of human, acute inflammation was induced with an intradermal injection of 50 μg/mL lipopolysaccharide (LPS) in 50 μL solution. Myeloperoxidase (MPO) activity was measured by MPO-positive neutrophils and shown to increase for 24-hours post-injection. Simultaneously, the level of phosphorylated p38 MAPK was documented for 48-hours post-LPS injection in the skin. Next, we used this model to examine the therapeutic potential of an α-selective p38 MAPK inhibitor, SCIO-469. A comparison of topical application of SCIO-469 at 5 mg/mL or 15 mg/mL to vehicle revealed that SCIO-469 dose-dependently reduces acute skin inflammation and that this effect is statistically significant at the higher dose. Further examination of tissues that received this dose also revealed statistically significant reduction of MPO activity, phosphorylated p38 MAPK, interleukin-6, and cyclooxygenase-2. These data suggest that the α-selective p38 MAPK inhibitor, SCIO-469, acts as a topical anti-inflammatory agent via the p38 MAPK pathway to reduce neutrophil induced acute inflammation in the skin. These observations suggest that α-selective p38 MAPK inhibition may be an effective therapeutic strategy to manage acute skin inflammation

Epigenetic regulation of dendritic cell differentiation and function by oxidized phospholipids

Dendritic cells (DCs) are the key cell type in the regulation of an adaptive immune response. Under inflammatory conditions monocytes can give rise to immunostimulatory DCs, depending on microenvironmental stimuli. Here we show that oxidized phospholipids (Ox-Pls), which are generated during inflammatory reactions, dysregulate the differentiation of DCs. DCs generated in the presence of Ox-Pls up-regulated the typical DC marker DC-SIGN but did not express CD1a, CD1b, and CD1c. These DCs generated in the presence of Ox-Pls had a substantially diminished T cell-stimulating capacity after stimulation with Toll-like receptor ligands. Toll-like receptor ligand-induced production of interleukin-12 also was strongly diminished, whereas induction of CD83 was not altered. In addition, we found that Ox-Pls strongly inhibit inflammatory stimuli-induced phosphorylation of histone H3, a key step of interleukin-12 production, yet leaving activation of nuclear factor-kappaB unaltered. Taken together, Ox-Pls present during differentiation yielded DCs with a reduced capacity to become immunostimulatory mature DCs. Furthermore, the presence of Ox-Pls blocked histone modifications required for full activation of DCs. Therefore, inflammation-derived Ox-Pls control DC functions in part by epigenetic mechanisms.

Natural antibodies against phosphorylcholine in cardiovascular disease

Atherosclerosis is a chronic inflammatory disease characterized by the presence of activated immune-competent cells in the lesions, producing mainly proinflammatory cytokines. Atherosclerosis is the underlying cause of cardiovascular disease (CVD), to a large extent occurring after damage and/or rupture of the atherosclerotic plaques. One major factor implicated as a cause of this immune activation is modified low-density lipoproteins (LDL), especially oxidized forms (oxLDL), which are abundant in plaques, both in foam cells and in the necrotic core. The LDL-oxidation process is very complex, and the nature of the antigens has been difficult to identify. We and others have focused on the phospholipids (PL) in oxLDL, especially oxidized forms of PL, including platelet-activating factor (PAF)-like lipids and lysophosphatidylcholine (LPC), and demonstrated that these could play a major role through proinflammatory effects. One common epitope is phosphorylcholine (PC), which is also exposed on some microorganisms (including Streptococcus pneumoneae) and on apoptotic cells. Natural IgM antibodies against PC (anti-PC) have been known for a long time, but little has been reported about their role in human disease, especially in CVD. We have demonstrated that anti-PC IgM are negatively associated with atherosclerosis development in hypertensive individuals and that low levels of anti-PC independently predict development of CVD. Anti-PC IgM could, therefore, be a novel risk marker in CVD. Animal experiments indicate that both active immunization with PC and passive immunization with anti-PC ameliorate atherosclerosis development. The possibility that anti-PC could be used therapeutically in humans deserves further study.

Low level natural antibodies against phosphorylcholine: a novel risk marker and potential mechanism in atherosclerosis and cardiovascular disease

Atherosclerosis is an inflammatory condition characterised by an abundance of activated immunocompetent cells in plaques which cause cardiovascular disease (CVD) when they rupture. Oxidized forms of low density lipoprotein (OxLDL) are a major constituent of atherosclerotic plaques and have proinflammatory effects, making oxLDL a candidate factor promoting atherosclerosis. In previous studies we and others demonstrated that platelet-activating factor (PAF)-like lipids in oxLDL may cause oxLDL-induced immune-stimulatory effects. A common denominator is phosphorylcholine (PC), a hapten-like epitope which is exposed on OxLDL and some microorganisms. We recently demonstrated that anti-PC has anti-inflammatory properties and that low levels of anti-PC predict the development of stroke and myocardial infarction. We hypothesize that low anti-PC represents a novel paradigm as a cause of chronic inflammatory diseases such as atherosclerosis where oxidized and/or inflammatory phospholipids play a role. It is possible that anti-PC can be used as a novel diagnostic tool and therapy in atherosclerotic disease.

Innate immune signals in atherosclerosis

Atherosclerosis is a chronic disease characterised by lipid retention and inflammation in the arterial intima. Innate immune mechanisms are central to atherogenesis, involving activation of pattern-recognition receptors (PRRs) and induction of inflammatory processes. In a complex tissue, such as the atherosclerotic lesion, innate signals can originate from several sources and promote atherogenesis through ligation of PRRs. The receptors recognise conserved molecular patterns on pathogens and endogenous products of tissue injury and inflammation. Activation of PRRs might affect several aspects of atherosclerosis by acting on lesion resident cells. Scavenger receptors mediate antigen uptake and clearance of lipoproteins, thereby promoting foam cell formation. Signalling receptors, such as Toll-like receptors (TLRs), lead to induction of pro-inflammatory cytokines and antigen-specific immune responses. In this review we describe the innate mechanisms present in the plaque. We focus on TLRs, their cross-talk with other PRRs, and how their signalling cascades influence inflammation within the atherosclerotic lesion.

Soy phosphatidylcholine inhibited TLR4-mediated MCP-1 expression in vascular cells

Inflammatory signaling via Toll-like receptor 4 (TLR4) has been shown to facilitate atherogenesis. Recent lines of evidence show that saturated fatty acids (SFAs) induce the inflammatory response via the TLR4 pathway in macrophages and adipocytes. The aims of this study are to confirm the role of SFAs in TLR4-mediated inflammatory signaling in vascular cells and to propose soy phosphatidylcholine (SPC) as an effective inhibitor against TLR4-mediated agonists. SFAs such as palmitate and stearate increased the expression and secretion of MCP-1 in human umbilical vein endothelial cells (HUVECs) and rat vascular smooth muscle cells (VSMCs). SFAs up-regulated the activity of MCP-1 promoter through the activation of NF-kappaB. Knockdown of TLR4 using siRNA diminished the SFA-induced MCP-1 expression in HUVECs and rat VSMCs, while PKC or ceramide signal inhibitor did not inhibit the expression. Furthermore, we found that SPC effectively inhibited the MCP-1 expression induced by palmitate or LPS in a dose-dependent manner. However, SPC did not inhibit the mRNA expression of MCP-1 induced by cytokines such as TNF-alpha and IL-1beta, or by agonists binding to TLRs other than TLR4. In addition, SPC did not affect the activity of LPS assessed by clotting activity of the Limulus amoebocyte lysate. These results clearly show that SPC specifically inhibits the inflammatory responses induced by the TLR4-dependent signal. In conclusion, we have demonstrated a role of SFAs for inflammatory response via TLR4-NF-kappaB signaling in vascular cells. Moreover, we propose that SPC can be useful as a selective inhibitor to suppress the TLR4-mediated inflammatory signaling.

Anionic pulmonary surfactant phospholipids inhibit inflammatory responses from alveolar macrophages and U937 cells by binding the lipopolysaccharide-interacting proteins CD14 and MD-2

Lipopolysaccharide (LPS), derived from Gram-negative bacteria, is a major cause of acute lung injury and respiratory distress syndrome. Pulmonary surfactant is secreted as a complex mixture of lipids and proteins onto the alveolar surface of the lung. Surfactant phospholipids are essential in reducing surface tension at the air-liquid interface and preventing alveolar collapse at the end of the respiratory cycle. In the present study, we determined that palmitoyl-oleoyl-phosphatidylglycerol and phosphatidylinositol, which are minor components of pulmonary surfactant, and synthetic dimyristoylphosphatidylglycerol regulated the inflammatory response of alveolar macrophages. The anionic lipids significantly inhibited LPS-induced nitric oxide and tumor necrosis factor-alpha production from rat and human alveolar macrophages and a U937 cell line by reducing the LPS-elicited phosphorylation of multiple intracellular protein kinases. The anionic lipids were also effective at attenuating inflammation when administered intratracheally to mice challenged with LPS. Binding studies revealed high affinity interactions between the palmitoyl-oleoyl-phosphatidylglycerol and the Toll-like receptor 4-interacting proteins CD14 and MD-2. Our data clearly identify important anti-inflammatory properties of the minor surfactant phospholipids at the environmental interface of the lung.

Induction of CCR2-dependent macrophage accumulation by oxidized phospholipids in the air-pouch model of inflammation

OBJECTIVE

Macrophages are key players in the pathogenesis of rheumatoid synovitis as well as in atherosclerosis. To determine whether atherogenic oxidized phospholipids potentially contribute to synovial inflammation and subsequent monocyte/macrophage recruitment, we examined the effects of oxidized 1- palmitoyl-2-arachidonoyl-sn-3-glycero-phosphorylcholine (OxPAPC) on chemokine expression and leukocyte recruitment in a facsimile synovium in vivo using the murine air-pouch model.

METHODS

Air pouches were raised by 2 injections of sterile air, and inflammation was induced by injecting either lipopolysaccharide (LPS) or OxPAPC into the pouch lumen. Inflammation was assessed by analysis of inflammatory gene expression using reverse transcription-polymerase chain reaction or immunohistochemical analysis, and leukocytes were quantified in the lavage fluid and in the pouch wall after staining with Giemsa or after enzymatic digestion followed by fluorescence-activated cell sorter analysis.

RESULTS

Application of OxPAPC resulted in selective recruitment of monocyte/macrophages into the air-pouch wall, but not in the lumen. In contrast, LPS induced both monocyte and neutrophil accumulation in the pouch lumen as well as in the wall. LPS, but not OxPAPC, induced the expression of adhesion molecules E-selectin, P-selectin, intercellular adhesion molecule 1, and vascular cell adhesion molecule 1. OxPAPC increased the expression of the CCR2 ligands monocyte chemotactic protein 1 (MCP-1), MCP-3, and MCP-5, as well as RANTES and growth-related oncogene alpha (GROalpha), while it down-regulated the expression of CCR2 on macrophages. Moreover, oxidized phospholipid-induced macrophage accumulation was abrogated in CCR2-/- mice.

CONCLUSION

These data demonstrate that oxidized phospholipids trigger a type of inflammatory response that leads to selective macrophage accumulation in vivo, a process relevant for the pathogenesis of chronic inflammatory rheumatic diseases.

Naturally occurring antioxidant nutrients reduce inflammatory response in mice

The effects of mixed dietary coenzyme Q(9), alpha-tocopherol, and beta-carotene on immune cell activity and blood cytokine profile were studied in peritoneal macrophages, spleen lymphocytes, and blood plasma from mice with acute inflammation induced by lipopolysaccharide (LPS). The activity of each fat-soluble antioxidant was also investigated separately in several model systems, both in vivo and in vitro. NMRI male mice were fed a diet supplemented with fat-soluble antioxidants for 15 days prior to LPS injection. LPS-induced inflammation resulted in induction of cellular production of pro-inflammatory cytokines such as TNF-alpha, IL-1alpha, IL-1beta, IL-2, IL-6, IFN-gamma, and also IL-10, an anti-inflammatory cytokine, and subsequent accumulation of these cytokines in blood plasma. In animals fed the antioxidant-rich diet, the inflammatory response to LPS injection was significantly reduced. The production of anti-inflammatory cytokine IL-10 in response to toxic stress and its accumulation in plasma were not modified by the diet. In addition, the expression of the inducible form of heat-shock protein 70 in mice treated with endotoxin was reduced in the animals pretreated with the antioxidant-rich diet. We showed that the diet suppressed phosphorylation of NF-kappaB, I kappaB kinase and SAPK/JNK proteins, thereby preventing the activation of the NF-kappaB kinase and SAPK/JNK signaling pathways in LPS-treated mice. In this report we demonstrate the potential effectiveness of naturally occurring antioxidant nutrients in the reduction of the inflammatory response. Therefore, it may be possible to develop novel therapeutic combinations, containing coenzyme Q(9), alpha-tocopherol, and beta-carotene, which promote immune stimulation.

Oxidized phospholipids in control of inflammation and endothelial barrier

The levels of circulating oxidized phospholipids (OxPLs) become increased in chronic and acute pathologic conditions such as hyperlipidemia, atherosclerosis, increased intimamedia thickness in the patients with systemic Lupus erythematosus, vascular balloon injury, acute lung injury (ALI), and acute respiratory distress syndrome (ARDS). These pathologies are associated with inflammation and activation of endothelial cells. Depending on the biological context and the specific group of phospholipid oxidation products, OxPL may exhibit both proinflammatory and anti-inflammatory effects. This review will summarize the data showing a dual role of OxPL in modulation of chronic and acute inflammation as well as OxPL effects on pulmonary endothelial permeability. Recent reports show protective effects of OxPL in the models of endotoxin and ventilator-induced ALI and suggest a potential for using OxPL-derived cyclopenthenone-containing compounds with barrier-protective properties for drug design. These compounds may represent a new group of therapeutic agents for the treatment of lung syndromes associated with acute inflammation and lung vascular leak.

Akt-mediated transactivation of the S1P1 receptor in caveolin-enriched microdomains regulates endothelial barrier enhancement by oxidized phospholipids

Endothelial cell (EC) barrier dysfunction results in increased vascular permeability, leading to increased mass transport across the vessel wall and leukocyte extravasation, the key mechanisms in pathogenesis of tissue inflammation and edema. We have previously demonstrated that OxPAPC (oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine) significantly enhances vascular endothelial barrier properties in vitro and in vivo and attenuates endothelial hyperpermeability induced by inflammatory and edemagenic agents via Rac and Cdc42 GTPase dependent mechanisms. These findings suggested potential important therapeutic value of barrier-protective oxidized phospholipids. In this study, we examined involvement of signaling complexes associated with caveolin-enriched microdomains (CEMs) in barrier-protective responses of human pulmonary ECs to OxPAPC. Immunoblotting from OxPAPC-treated ECs revealed OxPAPC-mediated rapid recruitment (5 minutes) to CEMs of the sphingosine 1-phosphate receptor (S1P(1)), the serine/threonine kinase Akt, and the Rac1 guanine nucleotide exchange factor Tiam1 and phosphorylation of caveolin-1, indicative of signaling activation in CEMs. Abolishing CEM formation (methyl-beta-cyclodextrin) blocked OxPAPC-mediated Rac1 activation, cytoskeletal reorganization, and EC barrier enhancement. Silencing (small interfering RNA) Akt expression blocked OxPAPC-mediated S1P(1) activation (threonine phosphorylation), whereas silencing S1P(1) receptor expression blocked OxPAPC-mediated Tiam1 recruitment to CEMs, Rac1 activation, and EC barrier enhancement. To confirm our in vitro results in an in vivo murine model of acute lung injury with pulmonary vascular hyperpermeability, we observed that selective lung silencing of caveolin-1 or S1P(1) receptor expression blocked OxPAPC-mediated protection from ventilator-induced lung injury. Taken together, these results suggest Akt-dependent transactivation of S1P(1) within CEMs is important for OxPAPC-mediated cortical actin rearrangement and EC barrier protection.

Inhibitory effect of a phosphatidyl ethanolamine derivative on LPS-induced sepsis

Sepsis is the leading cause of death in critically ill patients. Today, around 60% of all cases of sepsis are caused by Gram-negative bacteria. The cell wall component lipopoly-saccharide (LPS) is the main initiator of the cascade of cellular reactions in Gram-negative infections. The core receptors for LPS are toll-like receptor 4 (TLR4), MD-2 and CD14. Attempts have been made to antagonize the toxic effect of endotoxin using monoclonal antibodies against CD14 and synthetic lipopolysaccharides but there is as yet no effective treatment for septic syndrome. Here, we describe an inhibitory effect of a phosphatidylethanolamine derivative, PE-DTPA (phosphatidylethanolamine diethyl-enetriaminepentaacetate) on LPS recognition. PE-DTPA bound strongly to CD14 (K ( d ), 9.52 x 10(-8) M). It dose dependency inhibited LPS-mediated activation of human myeloid cells, mouse macrophage cells and human whole blood as measured by the production of tumor necrosis factor-a (TNF-alpha) and nitric oxide, whereas other phospho-lipids including phosphatidylserine and phosphatidylethanolamine had little effect. PE-DTPA also inhibited transcription dependent on NF-kappaB activation when it was added together with LPS, and it rescued LPS-primed mice from septic death. These results suggest that PE-DTPA is a potent antagonist of LPS, and that it acts by competing for binding to CD14.

Multi-hit inhibition of circulating and cell-associated components of the toll-like receptor 4 pathway by oxidized phospholipids

OBJECTIVE

Oxidized phospholipids (OxPLs) that are abundant in atherosclerotic lesions are increasingly recognized as context-dependent lipid mediators demonstrating both pro- and antiinflammatory activities. Molecular mechanisms of their effects are largely unknown. Here we present novel information on the mechanisms whereby OxPLs modulate activation of TLR4 by lipopolysaccharide (LPS).

METHODS AND RESULTS

We show, using several cell types and various inflammatory genes as readouts, that different classes and molecular species of OxPLs do not stimulate TLR4 but exert prominent inhibitory effects on LPS-induced reactions. Our data demonstrate that binding of OxPLs to the LPS-binding protein (LBP) and CD14 prevents recognition of LPS by these proteins, thus impairing activation of TLR4. In addition, OxPLs inhibited LBP- and CD14-independent activation of TLR4 by the synthetic TLR4 agonist E6020 indicating that in parallel with LBP and CD14, OxPLs target cell-associated steps in TLR4 cascade.

CONCLUSIONS

Our data suggest that OxPLs inhibit action of LPS via a multi-hit mechanism. These results support the notion that OxPLs are endogenous inhibitors of TLR4 produced in response to oxidative stress.

The role of oxidized phospholipids in atherosclerosis

There is increasing evidence that oxidized phospholipids (OxPLs) play an important role in atherosclerosis. These phospholipids accumulate in human and mouse lesions. Specific OxPLs have been identified as major regulators of many cell types present in the vessel wall. In endothelial cells, >1,000 genes are regulated. Some of these genes are pro-atherogenic and others anti-atherogenic. The anti-atherogenic effects are likely important in slowing the atherogenic process. Several receptors and signaling pathways associated with OxPL action have been identified and shown to be upregulated in human lesions. A structural model of the mechanism by which specific OxPLs serve as CD36 ligands has been identified. Specific oxidized phospholipids are also present in plasma and associated with Lp(a) particles. In humans, OxPL/apolipoprotein B has been shown to be a prognostic indicator and a separate risk factor for coronary events. Levels of OxPL in plasma have been shown to be correlated with platelet activation. The results of these studies suggest an important role for OxPL in all stages of atherosclerosis.

A New Immunomodulatory Therapy for Severe Sepsis: Ulinastatin Plus Thymosin α 1

Objectives: To study the effect of immunomodulatory therapy with ulinastatin plus thymosin α 1 on septic patients. Method: A total of 56 sepsis patients were randomized into a treatment group, receiving immunomodulatory therapy, and a placebo group, a placebo. Acute Physiology and Chronic Health Evaluation II scores, clinical data, lymphocyte subsets, immunological indexes, and coagulation parameters were determined before admission and on the 3rd, 8th, and 28th day after admission to the Intensive Care Unit. Results: The treatment group experienced a 78% cumulative survival, the placebo group experienced a 60% cumulative survival; the survival difference was mirrored by Acute Physiology and Chronic Health Evaluation II scores and more quickly improved leukocyte counts, lymphocyte counts, coagulation parameters, and cytokine levels in the treatment. Conclusions: Combined immunomodulatory therapy with ulinastatin plus thymosin α1 appears to yield improved survival for patients with sepsis; this finding should be verified in larger clinical trials.

Oxidized phospholipids: biomarker for cardiovascular diseases

Biologically active oxidized phospholipids can initiate and modulate many of the cellular events attributed to inflammation leading to atherosclerosis. Produced by enzymatic or non-enzymatic processes, these molecules interact with various cells via specific receptors and in general give rise to inflammatory signals. There is considerable evidence that oxidized phospholipids accumulate in vivo and play significant roles in atherosclerosis and thrombosis, suggesting that oxidized phospholipids could be biomarkers that reflect the global extent of these diseases in vivo. Thus, understanding the biosynthetic pathways, receptor specificity and signaling processes of oxidized phospholipids is important in understanding atherosclerosis, thrombosis and related inflammatory diseases.

Recombinant protein glutathione S-transferases P1 attenuates inflammation in mice

We have reported that intracellular glutathione S-transferases P1 (GSTP1) suppresses LPS (lipopolysaccharide)-induced excessive production of pro-inflammatory factors by inhibiting LPS-stimulated MAPKs (mitogen-activated protein kinases) as well as NF-kappaB activation. But under pathogenic circumstances, physiologic levels of GSTP1 are insufficient to stem pro-inflammatory signaling. Here we show that LPS-induced up-regulation of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in RAW246.7 cells is significantly reduced by incubating cells with recombinant GSTP1 protein. In vivo study demonstrates that treatment of mice (i.p.) with recombinant GSTP1 protein effectively suppresses the devastating effects of acute inflammation, which includes reduction of mortality rate of endotoxic shock, alleviation of LPS-induced acute lung injury and abrogation of thioglycolate (TG)-induced peritoneal deposition of leukocytes and polymorphonuclear cells (PMNs). Meanwhile, GSTP1 prevented LPS-induced TNF-alpha, IL-1beta, MCP-1 and NO production. Further investigation by using confocal microscopy and flow cytometry shows that recombinant GSTP1 protein can be delivered into RAW246.7 cells, mouse peritoneal macrophages and HEK 293 cells suggesting that extracellular GSTP1 protein could be transported across plasma membrane and act as a cytosolic protein. In conclusion our research demonstrates a new finding that increasing cellular GSTP1 level by supplement of recombinant GSTP1 effectively suppresses the devastating effects of acute inflammation.

The role of phospholipid oxidation products in inflammatory and autoimmune diseases: evidence from animal models and in humans

Since the discovery of oxidized phospholipids (OxPL) and their implication as modulators of inflammation in cardiovascular disease, roles for these lipid oxidation products have been suggested in many other disease settings. Lipid oxidation products accumulate in inflamed and oxidatively damaged tissue, where they are derived from oxidative modification of lipoproteins, but also from membranes of cells undergoing apoptosis. Thus, increased oxidative stress as well as decreased clearance of apoptotic cells has been implied to contribute to accumulation of OxPL in chronically inflamed tissues.A central role for OxPL in disease states associated with dyslipedemia, including atherosclerosis, diabetes and its complications, metabolic syndrome, and renal insufficiency, as well as general prothrombotic states, has been proposed. In addition, in organs which are constantly exposed to oxidative stress, including lung, skin, and eyes, increased levels of OxPL are suggested to contribute to inflammatory conditions. Moreover, accumulation of OxPL causes general immunmodulation and may lead to autoimmune diseases. Evidence is accumulating that OxPL play a role in lupus erythematosus, antiphospholipid syndrome, and rheumatoid arthritis. Last but not least, a role for OxPL in neurological disorders including multiple sclerosis (MS), Alzheimer's and Parkinson's disease has been suggested.This chapter will summarize recent findings obtained in animal models and from studies in humans that indicate that formation of OxPL represents a general mechanism that may play a major role in chronic inflammatory and autoimmune diseases.

Cross talk between paxillin and Rac is critical for mediation of barrier-protective effects by oxidized phospholipids

We previously reported that the barrier-protective effects of oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine (OxPAPC) on pulmonary endothelial cells (ECs) delineate the role of Rac- and Cdc42-dependent mechanisms and described the involvement of the focal adhesion (FA) protein paxillin in enhancement of the EC barrier upon OxPAPC challenge. This study examined a potential role of paxillin in the feedback mechanism of Rac regulation by FAs in OxPAPC-stimulated ECs. Our results demonstrate that OxPAPC induced Rac-dependent, Rho-independent peripheral accumulation of paxillin-containing FAs and time-dependent paxillin phosphorylation. Molecular inhibition of Rac decreased association of paxillin with the Rac-specific guanine nucleotide exchange factor beta-PIX. Molecular inhibition of paxillin also attenuated OxPAPC-induced enhancement of adherens junctions critical for the EC barrier-protective response, accumulation of vascular endothelial cadherin in the membrane fractions, and decreased activation of Rac and its effector p21-activated kinase (PAK1). Expression of paxillin with a mutated PAK1-dependent phosphorylation site (S273A) attenuated OxPAPC-induced PAK1 activation and the EC barrier-protective response. These results suggest that PAK1-specific paxillin phosphorylation at Ser(273) is critically involved in the positive-feedback regulation of the Rac-PAK1 pathway and may contribute to sustained enhancement of the EC barrier caused by oxidized phospholipids.

Endothelial cell regulation by phospholipid oxidation products

Oxidized phospholipids accumulate in atherosclerotic lesions, on lipoproteins, in other states of chronic inflammation, on apoptotic cells, necrotic cells and cells exposed to oxidative stress. These lipids regulate the transcription of over 1000 gene, regulating many endothelial functions, by activating several different cell surface receptors and multiple signaling pathways. These lipids also have important effects not involving transcription that regulate cell junctions and leukocyte binding. Thus these lipids are potent regulators of endothelial cell function with broad effects comparable in extent but differing from those of cytokines.

Oxidized phospholipid inhibition of toll-like receptor (TLR) signaling is restricted to TLR2 and TLR4: roles for CD14, LPS-binding protein, and MD2 as targets for specificity of inhibition

The generation of reactive oxygen species is a central feature of inflammation that results in the oxidation of host phospholipids. Oxidized phospholipids, such as 1-palmitoyl-2-arachidonyl-sn-glycero-3-phosphorylcholine (OxPAPC), have been shown to inhibit signaling induced by bacterial lipopeptide or lipopolysaccharide (LPS), yet the mechanisms responsible for the inhibition of Toll-like receptor (TLR) signaling by OxPAPC remain incompletely understood. Here, we examined the mechanisms by which OxPAPC inhibits TLR signaling induced by diverse ligands in macrophages, smooth muscle cells, and epithelial cells. OxPAPC inhibited tumor necrosis factor-alpha production, IkappaBalpha degradation, p38 MAPK phosphorylation, and NF-kappaB-dependent reporter activation induced by stimulants of TLR2 and TLR4 (Pam3CSK4 and LPS) but not by stimulants of other TLRs (poly(I.C), flagellin, loxoribine, single-stranded RNA, or CpG DNA) in macrophages and HEK-293 cells transfected with respective TLRs and significantly reduced inflammatory responses in mice injected subcutaneously or intraperitoneally with Pam3CSK4. Serum proteins, including CD14 and LPS-binding protein, were identified as key targets for the specificity of TLR inhibition as supplementation with excess serum or recombinant CD14 or LBP reversed TLR2 inhibition by OxPAPC, whereas serum accessory proteins or expression of membrane CD14 potentiated signaling via TLR2 and TLR4 but not other TLRs. Binding experiments and functional assays identified MD2 as a novel additional target of OxPAPC inhibition of LPS signaling. Synthetic phospholipid oxidation products 1-palmitoyl-2-(5-oxovaleryl)-sn-glycero-3-phosphocholine and 1-palmitoyl-2-glutaryl-sn-glycero-3-phosphocholine inhibited TLR2 signaling from approximately 30 microm. Taken together, these results suggest that oxidized phospholipid-mediated inhibition of TLR signaling occurs mainly by competitive interaction with accessory proteins that interact directly with bacterial lipids to promote signaling via TLR2 or TLR4.

Oxidized phospholipids: emerging lipid mediators in pathophysiology

PURPOSE OF REVIEW

Oxidized phospholipids are biologically active agents that are generated by lipid peroxidation. They are associated with inflammation, oxidative stress and several diseased states as described by an increasing number of reports. In addition, information about the interaction partners, the binding sites, the intracellular signalling and the metabolizing enzymes of these compounds is rapidly increasing. This review will briefly summarize recent findings and focus on mechanisms with potential pathophysiological relevance.

RECENT FINDINGS

Reports reviewed here provide interesting insights into the involvement of oxidized phospholipids in interleukin transcription, phenotype switching of smooth muscle cells and apoptotic mechanisms of the modified phospholipids as well as the identification of metabolizing enzymes.

SUMMARY

Recent studies shed some light on oxidized phospholipid-induced signalling with regard to apoptosis, gene expression and receptor-mediated events. They support the notion that the bioactivities of these natural agents detrimentally contribute to the pathological alteration of basic mechanisms to states recognized in numerous medical conditions. Advances in the knowledge of signalling pathways and interaction partners of oxidized phospholipids will increase our understanding of inflammatory processes and molecular mechanisms of various diseases including atherosclerosis and may play an important role in the development of future therapeutic options or diagnostics.

Oxidized phospholipids induce anergy in human peripheral blood T cells

Lipids are key regulators of immune responses. In this study we investigated the direct impact of oxidized phospholipids (ox-PL) on T cell activation and function. We could demonstrate that ox-PL strongly inhibit proliferation of purified human T cells induced with anti-CD3/CD28 or anti-CD3/CD63 mAb, whereas proliferation of naive T cells from human cord blood was not affected by ox-PL. Unoxidized phospholipids showed no such effect. Inhibition of T cell proliferation by ox-PL was not due to cell death. Moreover, T cell proliferation triggered by PMA/ionomycin activation was not diminished by ox-PL. T cells activated in the presence of ox-PL produced and released low amounts of IFN-gamma and IL-2, whereas IL-4 was only slightly diminished. Ox-PL prevented the expression of de novo synthesized activation markers (CD25, MHC class II) but not expression of CD63 or CD69. We further observed that T cells stimulated in the presence of ox-PL are poorly cytotoxic T cells. Most importantly, T cells activated in the presence of ox-PL failed to proliferate in response to restimulation. This hypo-proliferative state was accompanied with an up-regulation of early growth response gene 3 and Casitas B-lineage lymphoma protein B. Taken together, our results demonstrate that ox-PL are potent and specific regulators of T cell activation and function.

ATF4-dependent transcription is a key mechanism in VEGF up-regulation by oxidized phospholipids: critical role of oxidized sn-2 residues in activation of unfolded protein response

We have shown previously that oxidized phospholipids (OxPLs), known to accumulate in atherosclerotic vessels, stimulate angiogenesis via induction of autocrine mediators, such as vascular endothelial growth factor (VEGF). We now address the pathways mediating up-regulation of VEGF in human endothelial cells treated with OxPLs. Analysis of structure-function relationship using individual species of OxPLs demonstrated a close relation between induction of VEGF and activation of the unfolded protein response (UPR). Inducers of UPR up-regulated VEGF, whereas inhibition of UPR by chemical chaperones or knock-down of cochaperone HTJ-1 inhibited elevation of VEGF mRNA induced by OxPLs. OxPLs induced protein expression of activating transcription factor-4 (ATF4), an important effector of UPR. Expression levels of VEGF in OxPL-treated cells strongly correlated with induction of the ATF4 target genes ATF3 and TRB3. Knocking down ATF4 was paralleled by loss of VEGF induction by OxPLs. Chromatin immunoprecipitation demonstrated that OxPLs stimulated binding of ATF4 to a regulatory site in the VEGFA gene. Taken together, these data characterize UPR and more specifically its ATF4 branch as an important mechanism mediating up-regulation of VEGF by OxPLs, and allow hypothesizing that the UPR cascade might play a role in pathologic angiogenesis in atherosclerotic plaques.

Identification of oxidative stress and Toll-like receptor 4 signaling as a key pathway of acute lung injury

Multiple lung pathogens such as chemical agents, H5N1 avian flu, or SARS cause high lethality due to acute respiratory distress syndrome. Here we report that Toll-like receptor 4 (TLR4) mutant mice display natural resistance to acid-induced acute lung injury (ALI). We show that TLR4-TRIF-TRAF6 signaling is a key disease pathway that controls the severity of ALI. The oxidized phospholipid (OxPL) OxPAPC was identified to induce lung injury and cytokine production by lung macrophages via TLR4-TRIF. We observed OxPL production in the lungs of humans and animals infected with SARS, Anthrax, or H5N1. Pulmonary challenge with an inactivated H5N1 avian influenza virus rapidly induces ALI and OxPL formation in mice. Loss of TLR4 or TRIF expression protects mice from H5N1-induced ALI. Moreover, deletion of ncf1, which controls ROS production, improves the severity of H5N1-mediated ALI. Our data identify oxidative stress and innate immunity as key lung injury pathways that control the severity of ALI.

Lysophospholipid metabolism facilitates Toll-like receptor 4 membrane translocation to regulate the inflammatory response

Sepsis, an overwhelming inflammatory response to infection, is a major cause of morbidity and mortality worldwide and has no specific therapy. Phospholipid metabolites, such as lysophospholipids, have been shown to regulate inflammatory responses in sepsis, although their mechanism of action is not well understood. The phospholipid-metabolizing enzymes, lysophospholipid acyltransferases, control membrane phospholipid composition, function, and the inflammatory responses of innate immune cells. Here, we show that lysophosphatidylcholine acyltransferase (LPCAT) regulates inflammatory responses to LPS and other microbial stimuli. Specific inhibition of LPCAT down-regulated inflammatory cytokine production in monocytes and epithelial cells by preventing translocation of TLR4 into membrane lipid raft domains. Our observations demonstrate a new regulatory mechanism that facilitates the innate immune responses to microbial molecular patterns and provide a basis for the anti-inflammatory activity observed in many phospholipid metabolites. This provides the possibility of the development of new classes of anti-inflammatory and antisepsis agents.