Low doses of lipopolysaccharide and minimally oxidized low-density lipoprotein cooperatively activate macrophages via nuclear factor kappa B and activator protein-1: possible mechanism for acceleration of atherosclerosis by subclinical endotoxemia

Oxidized LDL and LOX-1 in experimental sepsis

Oxidized low-density lipoproteins (oxLDL) and the lectin-like oxLDL receptor-1 (LOX-1) are upregulated in inflammation. Because of the importance of inflammation and capillary leakage in the impairment of the microcirculation, which in turn contributes to the development of sepsis and multiorgan failure, the role of oxidized LDL and LOX-1 as players of intestinal inflammation is of great interest. In fact, the blockade of LOX-1 during experimental endotoxemia was effective in reducing leukocyte activation. There are several mechanisms by which oxLDL can participate in local and systemic inflammation, including cell proliferation, apoptosis, capillary perfusion, leukocyte-endothelial cell interactions, and endothelial activation. This review highlights the evidence relating oxLDL and LOX-1 to proinflammatory disease mechanisms. We also indicate situations when oxLDL, because of exposure time, dose, or degree of oxidization, is involved in disease resolution. Modulation of LOX-1 response could be utilized for the treatment of local and systemic inflammation, but the successful use of this target requires further understanding of its broad effects.

The influence of innate and adaptive immune responses on atherosclerosis

Both the chronic development of atherosclerotic lesions and the acute changes in lesion phenotype that lead to clinical cardiovascular events are significantly influenced by the innate and adaptive immune responses to lipoprotein deposition and oxidation in the arterial wall. The rapid pace of discovery of mechanisms of immunologic recognition, effector functions, and regulation has significantly influenced the study of atherosclerosis, and our new knowledge is beginning to affect how we treat this ubiquitous disease. In this review, we discuss recent advances in our understanding of how innate and adaptive immunity contribute to atherosclerosis, as well as therapeutic opportunities that arise from this knowledge.

Cationic peptide mR18L with lipid lowering properties inhibits LPS-induced systemic and liver inflammation in rats

The cationic single domain peptide mR18L has demonstrated lipid-lowering and anti-atherogenic properties in different dyslipidemic mouse models. Lipopolysaccharide (LPS)-mediated inflammation is considered as one of the potential triggers for atherosclerosis. Here, we evaluated anti-inflammatory effects of mR18L peptide against LPS-mediated inflammation. First, we tested the efficacy and tolerance of 1, 2.5 and 5mg/kg mR18L in normolipidemic rats stimulated with 5mg/kg LPS. LPS and then mR18L were injected in different intraperitoneal regions. By 2h post LPS, mR18L inhibited LPS-mediated plasma TNF-α elevation at all doses, with the effect being stronger for 2.5mg/kg (P<0.05 vs. 1mg/kg, non-significant vs. 5mg/kg). In a similar model, 2.5mg/kg mR18L reduced LPS-mediated inflammation in the liver, as assessed by microscopic examination of liver sections and measurements of iNOS expression in the liver tissue. In plasma, 2.5mg/kg mR18L decreased levels of TNF-α and IL-6, decreased endotoxin activity and enhanced HDL binding to LPS. In another similar experiment, mR18L administered 1h post LPS, prevented elevation of plasma triglycerides by 6h post LPS and increased plasma activity of anti-oxidant enzyme paraoxonase 1, along with noted trends in reducing plasma levels of endotoxin and IL-6. Surface plasmon resonance study revealed that mR18L readily binds LPS. We conclude that mR18L exerts anti-endotoxin activity at least in part due to direct LPS-binding and LPS-neutralizing effects. We suggest that anti-endotoxin activity of mR18L is an important anti-inflammatory property, which may increase anti-atherogenic potential of this promising orally active lipid-lowering peptide.

A starring role for stellate cells in the pancreatic cancer microenvironment

Pancreatic ductal adenocarcinoma is a devastating disease, and patient outcomes have not improved in decades. Treatments that target tumor cells have largely failed. This could be because research has focused on cancer cells and the influence of the stroma on tumor progression has been largely ignored. The focus of pancreatic cancer research began to change with the identification of pancreatic stellate cells, which produce the pancreatic tumor stroma. There is compelling in vitro and in vivo evidence for the influence of pancreatic stellate cells on pancreatic cancer development; several recent preclinical studies have reported encouraging results with approaches designed to target pancreatic stellate cells and the stroma. We review the background and recent advances in these areas, along with important areas of future research that could improve therapy.

CD14 and TLR4 mediate cytokine release promoted by electronegative LDL in monocytes

AIMS

Electronegative LDL (LDL(-)), a minor modified LDL present in the circulation, induces cytokine release in monocytes. We aimed to determine the role of the receptor CD14 and toll-like receptors 2 and 4 (TLR2, TLR4) in the inflammatory action promoted by LDL(-) in human monocytes.

METHODS AND RESULTS

Monocytes were preincubated with antibodies to neutralize CD14, TLR2 and TLR4. The release of monocyte chemoattractant protein 1 (MCP1), and interleukin 6 and 10 (IL6 and IL10) promoted by LDL(-) was inhibited 70-80% by antiCD14 and antiTLR4, and 15-25% by antiTLR2. The involvement of CD14 and TLR4 was confirmed by gene silencing experiments. The human monocytic THP1 cell line overexpressing CD14 released more cytokines in response to LDL(-) than the same THP1 cell line without expressing CD14. VIPER, a specific inhibitor of the TLR4 signaling pathway, blocked 75-90% the cytokine release promoted by LDL(-). Cell binding experiments showed that monocytes preincubated with neutralizing antibodies presented lesser LDL(-) binding than non-preincubated monocytes The inhibitory capacity was antiCD14>antiTLR4>>antiTLR2. Cell-free experiments performed in CD14-coated microtiter wells confirmed that CD14 was involved in LDL(-) binding. When LDL(-) and lipopolysaccharide (LPS) were added simultaneously to monocytes, cytokine release was similar to that promoted by LDL(-) alone. Binding experiments showed that LDL(-) and LPS competed for binding to monocytes and to CD14 coated-wells.

CONCLUSIONS

CD14 and TLR4 mediate cytokine release induced by LDL(-) in human monocytes. The cross-competition between LPS and LDL(-) for the same receptors could be a counteracting action of LDL(-) in inflammatory situations.

Very low density lipoproteins derived from periodontitis patients facilitate macrophage activation via lipopolysaccharide function

OBJECTIVE

Periodontitis, a chronic oral infection caused mainly by gram-negative bacteria, induces endotoxemia and associates with the risk for atherosclerosis. We investigated the effect of periodontal treatment on proatherogenic properties of very low density lipoproteins (VLDL).

METHODS

VLDL were isolated from 30 systemically healthy periodontitis patients before (pre-treatment) and 3 months after treatment (post-treatment). The mass compositions were analyzed, and VLDL-induced changes in cellular cholesterol content and expression of selected genes of human THP-1 macrophages were measured.

RESULTS

Periodontal treatment decreased the local inflammation in the periodontium, but did not have a significant effect on C-reactive protein (CRP) levels, VLDL composition, or VLDL potential to induce cholesterol uptake or gene expression by the macrophages. Incubation of macrophages in the presence of VLDL resulted in more than twofold increase in their cellular cholesterol content. Uptake of VLDL with ensuing macrophage cholesterol accumulation correlated positively with VLDL-associated lipopolysaccharide (LPS) activity (r=0.436, P=.016) and apolipoprotein E content (r=0.374, P=.046). Pre-treatment VLDL derived from the patients with high CRP levels displayed higher LPS activity than that of VLDL derived from patients with low CRP (above vs. below median, P=.007). In addition, pre-treatment VLDL isolated from patients with high systemic inflammation induced higher relative mRNA expression of CD14, TNF-α, MCP-1, and IL-6 in the macrophages.

CONCLUSION

Inflammation and endotoxemia induced by severe periodontitis may increase VLDL-dependent macrophage activation and cellular cholesterol accumulation, and thereby atherogenesis.

mRNA-binding protein ZFP36 is expressed in atherosclerotic lesions and reduces inflammation in aortic endothelial cells

OBJECTIVE

We studied the expression and function of an mRNA-binding protein, zinc finger protein-36 (ZFP36), in vascular endothelial cells in vivo and in vitro. We tested the hypotheses that ZFP36 regulates inflammation in vascular endothelial cells and that it functions through direct binding to target cytokine mRNAs. We also tested whether ZFP36 inhibits nuclear factor-κB-mediated transcriptional responses in vascular endothelial cells.

APPROACH AND RESULTS

ZFP36 was minimally expressed in healthy aorta but was expressed in endothelial cells overlying atherosclerotic lesions in mice and humans. The protein was also expressed in macrophage foam cells of atherosclerosis. ZFP36 was expressed in human aortic endothelial cells in response to bacterial lipopolysaccharide, glucocorticoid, and forskolin, but not oxidized low-density lipoproteins or angiotensin II. Functional studies demonstrated that ZFP36 reduces the expression of inflammatory cytokines in target cells by 2 distinct mechanisms: ZFP36 inhibits nuclear factor-κB transcriptional activation and also binds to cytokine mRNAs, leading to reduced transcript stability.

CONCLUSIONS

ZFP36 is expressed in vascular endothelial cells and macrophage foam cells where it inhibits the expression of proinflammatory mRNA transcripts. The anti-inflammatory effects of ZFP36 in endothelial cells occur via both transcriptional and posttranscriptional mechanisms. Our data suggest that enhancing vascular ZFP36 expression might reduce vascular inflammation.

Therapeutic gene targeting approaches for the treatment of dyslipidemias and atherosclerosis

PURPOSE OF REVIEW

Despite improved therapies, cardiovascular diseases are the leading cause of morbidity and mortality worldwide. Therefore, new therapeutic approaches are still needed. In the gene therapy field, RNA interference (RNAi) and regulation of microRNAs (miRNAs) have gained a lot of attention in addition to traditional overexpression based strategies. Here, recent findings in therapeutic gene silencing and modulation of small RNA expression related to atherogenesis and dyslipidemia are summarized.

RECENT FINDINGS

Novel gene therapy approaches for the treatment of hyperlipidemia have been addressed. Antisense oligonucleotide and RNAi-based therapies against apolipoprotein B100 and proprotein convertase subtilisin/kexin type 9 have shown already efficacy in preclinical and clinical trials. In addition, several miRNAs dysregulated in atherosclerotic lesions and regulating cholesterol homeostasis have been found, which may represent novel targets for future therapies.

SUMMARY

New therapies for lowering lipid levels are now being tested in clinical trials, and both antisense oligonucleotide and RNAi-based therapies have shown promising results in lowering cholesterol levels. However, the modulation of inflammatory component in atherosclerosis by gene therapy and targeting of the effects to plaques are still difficult challenges.

Oxidation-specific epitopes and immunological responses: Translational biotheranostic implications for atherosclerosis

Oxidation-specific epitopes (OSE), present on oxidized LDL (OxLDL), apoptotic cells, cell debris and modified proteins in the vessel wall, accumulate in response to hypercholesterolemia, and generate potent pro-inflammatory, disease-specific antigens. They represent an important class of 'danger associated molecular patterns' (DAMPs), against which a concerted innate immune response is directed. OSE are recognized by innate 'pattern recognition receptors', such as scavenger receptors present on dendritic cells and monocyte/macrophages, as well as by innate proteins, such as IgM natural antibodies and soluble proteins, such as C-reactive protein and complement factor H. These innate immune responses provide a first line of defense against atherosclerosis-specific DAMPs, and engage adaptive immune responses, provided by T and B-2 cells, which provide a more specific and definitive response. Such immune responses are ordinarily directed to remove foreign pathogens, such as those found on microbial pathogens, but when persistent or maladaptive, lead to host damage. In this context, atherosclerosis can be considered as a systemic chronic inflammatory disease initiated by the accumulation of OSE type DAMPs and perpetuated by maladaptive response of the innate and adaptive immune system. Understanding this paradigm leads to new approaches to defining cardiovascular risk and suggests new modes of therapy. Therefore, OSE have become potential targets of diagnostic and therapeutic agents. Human and murine OSE-targeting antibodies have been developed and are now being used as biomarkers in human studies and experimentally in translational applications of non-invasive molecular imaging of oxidation-rich plaques and immunotherapeutics.

The SYK side of TLR4: signalling mechanisms in response to LPS and minimally oxidized LDL

Spleen tyrosine kinase (SYK) is the best known for its involvement in immune receptor signalling, mediated by binding of SYK tandem Src-homology 2 domains to tandem phosphotyrosine in immunoreceptor tyrosine-based activation motifs (ITAMs). ITAM adaptors or ITAM-containing receptor tails mediate signalling from B- and T-cell receptors, Fc receptors and many C-type lectins, including dectin-1. Recent data point to constitutive binding of SYK to the cytoplasmic domain of toll-like receptor-4 (TLR4). This SYK-TLR4 binding increases upon TLR4 dimerization and phosphorylation, and SYK plays a prominent role in TLR4 signalling in response to LPS in neutrophils and monocytes. SYK also plays an important role in TLR4-mediated macrophage responses to minimally oxidized low-density lipoprotein (mmLDL), which is a form of oxidized LDL relevant to development of human atherosclerosis. Interestingly, mmLDL-induced effects in macrophages, which occur via TLR4, are predominantly MyD88 independent. This unmasks the role of the SYK branch of TLR4 signalling, which mediates modest cytokine release via activation of AP-1 transcription and robust reactive oxygen species generation and cytoskeletal rearrangements. The latter results in extensive membrane ruffling and macropinocytosis, leading to lipoprotein uptake and foam cell formation, a hallmark of atherosclerotic lesions. Because inhibitors of SYK activity, such as fostamatinib, are in advanced clinical trials for rheumatoid arthritis and other autoimmune diseases, understanding the role of SYK in signalling via TLR4 is of immediate importance. This signalling pathway seems to be particularly important in TLR4 activation by host-derived, damage-associated molecular pattern ligands, such as mmLDL, relevant to development of atherosclerosis and other chronic inflammatory diseases.

Losartan Inhibits Nuclear Factor-κB Activation Induced by Small, Dense LDL Cholesterol Particles in Human Umbilical Vein Endothelial Cells

Objective

We aimed to investigate how losartan exerts protective effects on human umbilical vein endothelial cell injury induced by small, dense, LDL (sLDL) cholesterol particles.

Methods

sLDL cholesterol was isolated by a 2-steps method and the nuclear translocation and activation of nuclear factor-κB (NF-κB) in endothelial cells was observed by confocal microscopy and electrophoretic mobility shift assays.

Results

Losartan greatly inhibited the nuclear translocation of NF-κB induced by sLDL cholesterol in a dose-dependent manner.

Conclusions

sLDL cholesterol may be involved in endothelial dysfunction possibly through NF-κB activation; losartan protects against sLDL cholesterol-inducing endothelial cell injury by inhibiting NF-κB activation, suggesting that losartan may play a role in the prevention and treatment of cardiovascular disease.

Oxidized LDLs inhibit TLR-induced IL-10 production by monocytes: a new aspect of pathogen-accelerated atherosclerosis

It is widely accepted that oxidized low-density lipoproteins and local infections or endotoxins in circulation contribute to chronic inflammatory process at all stages of atherosclerosis. The hallmark cells of atherosclerotic lesions-monocytes and macrophages-are able to detect and integrate complex signals derived from lipoproteins and pathogens, and respond with a spectrum of immunoregulatory cytokines. In this study, we show strong inhibitory effect of oxLDLs on anti-inflammatory interleukin-10 production by monocytes responding to TLR2 and TLR4 ligands. In contrast, pro-inflammatory tumor necrosis factor secretion was even slightly increased, when stimulated with lipopolysaccharide from Porphyromonas gingivalis-an oral pathogen associated with atherosclerosis. The oxLDLs modulatory activity may be explained by altered recognition of pathogen-associated molecular patterns, which involves serum proteins, particularly vitronectin. We also suggest an interaction between vitronectin receptor, CD11b, and TLR2. The presented data support a novel pathway for pathogen-accelerated atherosclerosis, which relies on oxidized low-density lipoprotein-mediated modulation of anti-inflammatory response to TLR ligands.

Oxidized LDLs inhibit TLR-induced IL-10 production by monocytes: a new aspect of pathogen-accelerated atherosclerosis

It is widely accepted that oxidized low-density lipoproteins and local infections or endotoxins in circulation contribute to chronic inflammatory process at all stages of atherosclerosis. The hallmark cells of atherosclerotic lesions-monocytes and macrophages-are able to detect and integrate complex signals derived from lipoproteins and pathogens, and respond with a spectrum of immunoregulatory cytokines. In this study, we show strong inhibitory effect of oxLDLs on anti-inflammatory interleukin-10 production by monocytes responding to TLR2 and TLR4 ligands. In contrast, pro-inflammatory tumor necrosis factor secretion was even slightly increased, when stimulated with lipopolysaccharide from Porphyromonas gingivalis-an oral pathogen associated with atherosclerosis. The oxLDLs modulatory activity may be explained by altered recognition of pathogen-associated molecular patterns, which involves serum proteins, particularly vitronectin. We also suggest an interaction between vitronectin receptor, CD11b, and TLR2. The presented data support a novel pathway for pathogen-accelerated atherosclerosis, which relies on oxidized low-density lipoprotein-mediated modulation of anti-inflammatory response to TLR ligands.

A strategy to study pathway cross-talks of cells under repetitive exposure to stimuli

Background

Cells are subject to fluctuating and multiple stimuli in their natural environment. The signaling pathways often crosstalk to each other and give rise to complex nonlinear dynamics. Specifically repetitive exposure of a cell to a same stimulus sometime leads to augmented cellular responses. Examples are amplified proinflammatory responses of innate immune cells pretreated with a sub-threshold then a high dose of endotoxin or cytokine stimulation. This phenomenon, called priming effect in the literature, has important pathological and clinical significances.

Results

In a previous study, we enumerated possible mechanisms for priming using a three-node network model. The analysis uncovered three mechanisms. Based on the results, in this work we developed a straightforward procedure to identify molecular candidates contributing to the priming effect and the corresponding mechanisms. The procedure involves time course measurements, e.g., gene expression levels, or protein activities under low, high, and low + high dose of stimulant, then computational analysis of the dynamics patterns, and identification of functional roles in the context of the regulatory network. We applied the procedure to a set of published microarray data on interferon-γ-mediated priming effect of human macrophages. The analysis identified a number of network motifs possibly contributing to Interferon-γ priming. A further detailed mathematical model analysis further reveals how combination of different mechanisms leads to the priming effect.

Conclusions

One may perform systematic screening using the proposed procedure combining with high throughput measurements, at both transcriptome and proteome levels. It is applicable to various priming phenomena.

Molecular mechanisms responsible for the reduced expression of cholesterol transporters from macrophages by low-dose endotoxin

OBJECTIVE

Atherosclerosis is characterized as a chronic inflammatory condition that involves cholesterol deposition in arteries. Together with scavenger receptor B1 (SR-B1), the ATP-binding cassette transporters ABCA1 and ABCG1 are the major components of macrophage cholesterol efflux. Recent studies have shown that low-grade inflammation plays a distinct regulatory role in the expression of SR-B1 and ABCA1/ABCG1. However, the mechanisms linking low-grade inflammation and cholesterol accumulation are poorly understood.

METHODS AND RESULTS

Using primary bone-marrow-derived macrophages, we demonstrate that subclinical low-dose lipopolysaccharide potently reduces the expression of SR-B1 and ABCA1/ABCG1, as well as cholesterol efflux from macrophages through interleukin-1 receptor-associated kinase 1 and Toll-interacting-protein. Low-dose lipopolysaccharide downregulates the nuclear levels of retinoic acid receptor-α, leading to their reduced binding to the promoters of SR-B1 and ABCA1/ABCG1. We observe that glycogen synthase kinase 3β activation by low-dose lipopolysaccharide through interleukin-1 receptor-associated kinase 1 and Toll-interacting-protein is responsible for reduced levels of retinoic acid receptor-α, and reduced expression of SR-B1 and ABCA1/ABCG1. Interleukin-1 receptor-associated kinase M, however, counteracts the function of interleukin-1 receptor associated kinase 1.

CONCLUSIONS

Collectively, our data reveal a novel intracellular network regulated by low-dose endotoxemia that disrupts cholesterol efflux from macrophages and leads to the pathogenesis of atherosclerosis.

A new metabolomic assay to examine inflammation and redox pathways following LPS challenge

BACKGROUND

Shifts in intracellular arginine (Arg) and sulfur amino acid (SAA) redox metabolism modulate macrophage activation, polarization and phenotype. Despite their importance in inflammation and redox regulatory pathways, comprehensive analysis of these metabolic networks was not previously possible with existing analytical methods.

METHODS

The Arg/thiol redox LC-MS/MS metabolomics assay permits simultaneous assessment of amino acids and derivative products generated from Arg and SAA metabolism. Using this assay, LPS-induced changes in macrophage amino acid metabolism were monitored to identify pathway shifts during activation and their linkage to cellular redox regulation.

RESULTS

Metabolite concentrations most significantly changed after treatment of a macrophage-like cell line (RAW) with LPS for 24 hrs were citrulline (Cit) (48-fold increase), ornithine (Orn) (8.5-fold increase), arginine (Arg) (66% decrease), and aspartic acid (Asp) (73% decrease). The ratio Cit + Orn/Arg + Asp (CO/AA) was more sensitive to LPS stimulation than other amino acid ratios commonly used to measure LPS-dependent inflammation (e.g., SAM/SAH, GSH/GSSG) and total media NOx. The CO/AA ratio was also the first ratio to change significantly after LPS treatment (4 hrs). Changes in the overall metabolomic profile over time indicated that metabolic pathways shifted from Arg catabolism to thiol oxidation.

CONCLUSIONS

Simultaneous quantification of Arg and SAA metabolic pathway shifts following LPS challenge of macrophage indicate that, in this system, the Arg-Citrulline/NO cycle and arginase pathways are the amino acid metabolic pathways most sensitive to LPS-challenge. The cellular (Cit + Orn)/(Arg + Asp) ratio, which summarizes this pathway, was more responsive to lower concentrations of LPS and responded earlier than other metabolic biomarkers of macrophage activation including GSH redox. It is suggested that the CO/AA ratio is a redox- independent early biomarker of macrophage activation. The ability to measure both the CO/AA and GSH-redox ratios simultaneously permits quantification of the relative effects of LPS challenge on macrophage inflammation and oxidative stress pathways. The use of this assay in humans is discussed, as are clinical implications.

Astragaloside IV attenuates Toll-like receptor 4 expression via NF-κB pathway under high glucose condition in mesenchymal stem cells

Diabetic hyperglycemia causes a variety of pathological changes. Astragaloside IV (AS-IV) was widely used for the treatment of cardiovascular diseases in China. The aim of this study was to determine the effect of AS-IV on bone marrow mesenchymal stem cells (MSCs) and the underlying mechanism in diabetes. We used reverse transcription polymerase chain reaction and western blotting to determine the expression of Toll-like receptor 4 (TLR4), matrix metalloproteinase-2 (MMP-2) and NF-κB p65 in MSCs under high glucose (HG) with or without pretreatment with AS-IV. The surface expression of TLR4 was checked by flow cytometry and the expression of TNF-α and MCP-1 were detected by ELISA in diabetes patients treated with AS-IV. AS-IV promoted the proliferation of MSCs and attenuated the increased expression of TLR4 induced by HG. In addition, AS-IV decreased the HG-induced translocation of NF-κB p65 and increased the MMP-2 expression in MSCs. AS-IV decreased the TLR4, TNF-α and MCP-1 expression in patients. Collectively,our data revealed that AS-IV attenuated TLR4 expression through the NF-κB signaling pathway in MSCs.

microRNA-181a represses ox-LDL-stimulated inflammatory response in dendritic cell by targeting c-Fos

Oxidized LDL (ox-LDL) activates dendritic cells (DCs), thereby initiating inflammation responses in atherosclerosis, yet the modulatory mechanisms remain unclear. MicroRNAs (miRNAs) are important regulators for DC functions. This study evaluated the regulation by miRNAs of the ox-LDL-induced DC immune response. In CD11c⁺ DCs from ApoE-deficient mice with hyperlipidemia, microRNA miR-181a was significantly up-regulated. In cultured bone marrow-derived DCs (BMDCs), ox-LDL promoted DC maturation and up-regulated miR-181a expression. Abundance of miR-181a attenuated ox-LDL-induced CD83 and CD40 expression, inhibited the secretion of interleukin (IL)-6 and TNF-α, and up-regulated IL-10, an important anti-inflammatory cytokine that was inhibited by ox-LDL. Inhibition of the endogenous miR-181a reversed the effects on CD83 and CD40 as well as the effects on IL-6 and TNF-α. The putative target genes of miR-181a were evaluated by gene ontology assessment, and the c-Fos-mediated inflammation pathway was identified. miR-181a targeted the 3′ untranslated region of c-Fos mRNA by luciferase experiments. Thus, abundance of miR-181a reduced c-Fos protein, whereas inhibition of miR-181a increased c-Fos protein in BMDCs. We therefore suggest that miR-181a attenuates ox-LDL-stimulated immune inflammation responses by targeting c-Fos in DCs.

Alpha-lipoic acid attenuates atherosclerotic lesions and inhibits proliferation of vascular smooth muscle cells through targeting of the Ras/MEK/ERK signaling pathway

An infectious burden has been suggested to be associated with atherosclerosis in humans, based on the shared and underlying inflammatory responses during infection and atherosclerosis. However, the efficacy of anti-atherogenic drugs is yet to be tested against atherosclerosis in a scenario involving an infectious burden. We have examined alpha-lipoic acid (ALA) for anti-atherogenic effects in a hypercholesterolemic diet-induced atherosclerotic mouse model with inflammatory stimulation. C57BL/6 mice were fed with a hypercholesterolemic diet for 12 weeks to induce atherosclerosis. Lipopolysaccharide was intraperitoneally injected for the 1st week of study to simulate underlying infectious burden during development of atherosclerosis. ALA treatment alleviated atherosclerotic pathologies and reduced serum cholesterol and inflammatory cytokines. Consistently, atherosclerotic markers were improved by ALA treatment. In addition, ALA attenuated the proliferation and migration of vascular smooth muscle cells upon platelet-derived growth factor stimulation through the targeting of the Ras-MEK1/2-ERK1/2 pathway. This study demonstrates the efficacy of ALA on atherosclerosis with immunological complication, by showing that ALA modulates multiple pathogenic aspects of atherosclerosis induced by a hypercholesterolemic diet with inflammatory stimulation consisting of hypercholesterolemia, inflammation and VSMC activation.

Characterization of lipopolysaccharide-stimulated cytokine expression in macrophages and monocytes

OBJECTIVE

In vitro cell culture models are widely used in inflammation research; however, information regarding the time- and dose-dependency of inflammatory responses toward LPS in these cell lines is scattered in the literature.

MATERIAL

J774A.1 mouse macrophage and THP-1 human monocyte cell lines.

TREATMENT

J774A.1 and THP-1 cells were treated with 0-500 ng/mL lipopolysaccharide for 0-24 h.

METHODS

SRB and BCA tests were used to measure total protein. Real-time PCR was used to determine gene expression levels, and ELISA was used to assess the protein levels. One-way ANOVA and Tukey's Honestly Significant Difference test were used to test the significance levels.

RESULTS

In J774A.1 and THP-1 cells, cytokines responded in distinct patterns upon LPS stimulation in a time- and dose-dependent manner, and the differential regulation of the response to LPS between J774A.1 and THP-1 cells appeared to correlate with the differential regulation of TLR4 at the mRNA level.

CONCLUSION

In summary, this study indicated that temporal and dose-dependent responses to LPS need to be controlled for and that extrapolation of data on mechanisms may differ between cell lines of different origin.

Molecular mechanisms responsible for the selective and low-grade induction of proinflammatory mediators in murine macrophages by lipopolysaccharide

Low-dose endotoxemia is prevalent in humans with adverse health conditions, and it correlates with the pathogenesis of chronic inflammatory diseases such as atherosclerosis, diabetes, and neurologic inflammation. However, the underlying molecular mechanisms are poorly understood. In this study, we demonstrate that subclinical low-dose LPS skews macrophages into a mild proinflammatory state, through cell surface TLR4, IL-1R-associated kinase-1, and the Toll-interacting protein. Unlike high-dose LPS, low-dose LPS does not induce robust activation of NF-κB, MAPKs, PI3K, or anti-inflammatory mediators. Instead, low-dose LPS induces activating transcription factor 2 through Toll-interacting protein-mediated generation of mitochondrial reactive oxygen species, allowing mild induction of proinflammatory mediators. Low-dose LPS also suppresses PI3K and related negative regulators of inflammatory genes. Our data reveal novel mechanisms responsible for skewed and persistent low-grade inflammation, a cardinal feature of chronic inflammatory diseases.

Network topologies and dynamics leading to endotoxin tolerance and priming in innate immune cells

The innate immune system, acting as the first line of host defense, senses and adapts to foreign challenges through complex intracellular and intercellular signaling networks. Endotoxin tolerance and priming elicited by macrophages are classic examples of the complex adaptation of innate immune cells. Upon repetitive exposures to different doses of bacterial endotoxin (lipopolysaccharide) or other stimulants, macrophages show either suppressed or augmented inflammatory responses compared to a single exposure to the stimulant. Endotoxin tolerance and priming are critically involved in both immune homeostasis and the pathogenesis of diverse inflammatory diseases. However, the underlying molecular mechanisms are not well understood. By means of a computational search through the parameter space of a coarse-grained three-node network with a two-stage Metropolis sampling approach, we enumerated all the network topologies that can generate priming or tolerance. We discovered three major mechanisms for priming (pathway synergy, suppressor deactivation, activator induction) and one for tolerance (inhibitor persistence). These results not only explain existing experimental observations, but also reveal intriguing test scenarios for future experimental studies to clarify mechanisms of endotoxin priming and tolerance.

Oxidized low-density lipoprotein as a biomarker of in vivo oxidative stress: from atherosclerosis to periodontitis

Oxidized low-density lipoprotein is known as an important factor in the development of atherosclerosis. The introduction of a sensitive procedure for the determination of oxidized low-density lipoprotein in human circulating plasma using a monoclonal antibody recognizing oxidized phosphatidylcholines has opened new fields of research based on in vivo oxidized low-density lipoprotein. The plasma oxidized low-density lipoprotein levels are significantly elevated in patients with acute myocardial infarction, cerebral infarction or chronic renal failure accompanied by hemodialysis. It was found that the plasma oxidized low-density lipoprotein level increased prior to aortic atherosclerotic lesion enlargement in apolipoprotein E-knockout mice. Recent studies have pointed out that oxidized low-density lipoprotein is transferrable between vessel wall tissue and the circulation, so it is a reasonable hypothesis that plasma oxidized low-density lipoprotein levels reflect the oxidative status at local sites of atherogenesis. Oxidized low-density lipoprotein measurement has been applied to human gingival crevicular fluids, which can be collected easily and safely, and relatively high levels of oxidized low-density lipoprotein were shown to be present. These findings, together with recent clinical follow-up studies, suggest that oxidized low-density lipoprotein is a predictive biomarker of a variety of diseases related to oxidative stress. This review summarizes the current understanding of in vivo oxidized low-density lipoprotein and its potential significance as a biomarker of disease.

Epidemiology, risk factors, and the promotion of pancreatic cancer: role of the stellate cell

There are approximately 277,000 new cases of pancreatic cancer and 266,000 deaths from pancreatic cancer annually, indicating a mortality rate of 96% of the cases diagnosed. Because of the ineffectiveness of therapies, a major emphasis needs to be placed on prevention. This paper reviews the epidemiology and risk factors for pancreatic cancer, and uses this information to propose plausible research directions for determining the biological mechanisms mediating the effects of risk factors on the promotion of pancreatic cancer, with a focus on the pancreatic stellate cell.

Spleen tyrosine kinase regulates AP-1 dependent transcriptional response to minimally oxidized LDL

Oxidative modification of low-density lipoprotein (LDL) turns it into an endogenous ligand recognized by pattern-recognition receptors. We have demonstrated that minimally oxidized LDL (mmLDL) binds to CD14 and mediates TLR4/MD-2-dependent responses in macrophages, many of which are MyD88-independent. We have also demonstrated that the mmLDL activation leads to recruitment of spleen tyrosine kinase (Syk) to TLR4 and TLR4 and Syk phosphorylation. In this study, we produced a macrophage-specific Syk knockout mouse and used primary Syk(-/-) macrophages in our studies. We demonstrated that Syk mediated phosphorylation of ERK1/2 and JNK, which in turn phosphorylated c-Fos and c-Jun, respectively, as assessed by an in vitro kinase assay. c-Jun phosphorylation was also mediated by IKKε. c-Jun and c-Fos bound to consensus DNA sites and thereby completed an AP-1 transcriptional complex and induced expression of CXCL2 and IL-6. These results suggest that Syk plays a key role in TLR4-mediated macrophage responses to host-generated ligands, like mmLDL, with subsequent activation of an AP-1 transcription program.

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.

HIV infection and aging of the innate immune system

The increased life expectancy of HIV-infected individuals due to improved treatment has revealed an unexpected increase in non-AIDS comorbidities that are typically associated with older age including cardiovascular disease, dementia and frailty. The majority of these diseases arise as the result of dysregulated systemic inflammation, and both the aged and HIV-infected individuals exhibit elevated basal levels of inflammation. In the elderly, increased inflammation and age-related diseases are associated with a state of impaired immunity called immunosenescence, which is thought to result from a lifetime of immune stimulation. It is now apparent that HIV induces premature immunosenescence within T-cells; however, the impact of HIV on aging of cells of the innate arm of the immune system is unknown. Innate immune cells play a central role in inflammation and are thus critical for the pathogenesis of inflammatory diseases. Limited evidence suggests HIV infection mimics age-related changes to innate immune cells; however, the extent of this effect and the mechanism underlying these changes remain to be defined. This review focuses on the impact of HIV infection on the function and aging of innate immune cells and discusses potential drivers of premature immunosenescence including chronic endotoxaemia, residual viraemia, telomere attrition and altered cellular signalling.

Modified low density lipoprotein stimulates complement C3 expression and secretion via liver X receptor and Toll-like receptor 4 activation in human macrophages

Complement C3 is a pivotal component of three cascades of complement activation. C3 is expressed in human atherosclerotic lesions and is involved in atherogenesis. However, the mechanism of C3 accumulation in atherosclerotic lesions is not well elucidated. We show that acetylated low density lipoprotein and oxidized low density lipoprotein (oxLDL) increase C3 gene expression and protein secretion by human macrophages. Modified LDL (mLDL)-mediated activation of C3 expression mainly depends on liver X receptor (LXR) and partly on Toll-like receptor 4 (TLR4), whereas C3 secretion is increased due to TLR4 activation by mLDL. LXR agonist TO901317 stimulates C3 gene expression in human monocyte-macrophage cells but not in human hepatoma (HepG2) cells. We find LXR-responsive element inside of the promoter region of the human C3 gene, which binds to LXRβ in macrophages but not in HepG2 cells. We show that C3 expression and secretion is decreased in IL-4-treated (M2) and increased in IFNγ/LPS-stimulated (M1) human macrophages as compared with resting macrophages. LXR agonist TO901317 potentiates LPS-induced C3 gene expression and protein secretion in macrophages, whereas oxLDL differently modulates LPS-mediated regulation of C3 in M1 or M2 macrophages. Treatment of human macrophages with anaphylatoxin C3a results in stimulation of C3 transcription and secretion as well as increased oxLDL accumulation and augmented oxLDL-mediated up-regulation of the C3 gene. These data provide a novel mechanism of C3 gene regulation in macrophages and suggest new aspects of cross-talk between mLDL, C3, C3a, and TLR4 during development of atherosclerotic lesions.

DBZ blocks LPS-induced monocyte activation and foam cell formation via inhibiting nuclear factor-ĸB

BACKGROUND/AIMS

It has been widely accepted that chronic inflammation plays important roles in the atherogenesis. Danshensu Bingpian Zhi (DBZ) is a novel synthetic compound derived from the traditional Chinese medicine (TCM) formula Fu Fang Dan Shen (FFDS), which is effective on atherosclerosis clinically. We hypothesized that DBZ possessed the anti-atherosclerosis potentials. Here, we examined the inhibitory effects of DBZ on LPS-induced monocyte activation and foam cell formation.

METHODS

The effects of DBZ were assessed on LPS-induced inflammatory factors expression in monocyte/macrophage. Activation of NF-κB and AP-1 was analyzed by luciferase reporter assay and signaling pathway of NF-κB was investigated to elucidate mechanisms underlying DBZ mediated anti-inflammatory activity. Effects of DBZ on macrophage lipid accumulation were evaluated in native LDL and LPS co-incubated macrophages.

RESULTS

DBZ inhibited LPS-induced inflammatory factors expression dose dependently in monocytes. DBZ inhibited NF-κB activation strongly and AP-1 slightly. DBZ suppressed the LPS-induced degradation of IκBα, thereby decreasing the translocation of p65 to nucleus. Furthermore, DBZ suppressed LPS-activated macrophages lipid accumulation, partly due to inhibiting the expression of LPS-induced aP2 and ADRP in macrophges.

CONCLUSION

These results demonstrate that DBZ has potentials on anti-atherosclerosis by suppressing monocyte activation and foam cell formation.

Modest effect on plaque progression and vasodilatory function in atherosclerosis-prone mice exposed to nanosized TiO(2)

Background

There is growing evidence that exposure to small size particulate matter increases the risk of developing cardiovascular disease.

Methods

We investigated plaque progression and vasodilatory function in apolipoprotein E knockout (ApoE^-/-) mice exposed to TiO₂. ApoE^-/- mice were intratracheally instilled (0.5 mg/kg bodyweight) with rutile fine TiO₂ (fTiO₂, 288 nm), photocatalytic 92/8 anatase/rutile TiO₂ (pTiO₂, 12 nm), or rutile nano TiO₂ (nTiO₂, 21.6 nm) at 26 and 2 hours before measurement of vasodilatory function in aorta segments mounted in myographs. The progression of atherosclerotic plaques in aorta was assessed in mice exposed to nanosized TiO₂ (0.5 mg/kg bodyweight) once a week for 4 weeks. We measured mRNA levels of Mcp-1, Mip-2, Vcam-1, Icam-1 and Vegf in lung tissue to assess pulmonary inflammation and vascular function. TiO₂-induced alterations in nitric oxide (NO) production were assessed in human umbilical vein endothelial cells (HUVECs).

Results

The exposure to nTiO₂ was associated with a modest increase in plaque progression in aorta, whereas there were unaltered vasodilatory function and expression levels of Mcp-1, Mip-2, Vcam-1, Icam-1 and Vegf in lung tissue. The ApoE^-/- mice exposed to fine and photocatalytic TiO₂ had unaltered vasodilatory function and lung tissue inflammatory gene expression. The unaltered NO-dependent vasodilatory function was supported by observations in HUVECs where the NO production was only increased by exposure to nTiO₂.

Conclusion

Repeated exposure to nanosized TiO₂ particles was associated with modest plaque progression in ApoE^-/- mice. There were no associations between the pulmonary TiO₂ exposure and inflammation or vasodilatory dysfunction.

Activating transcription factor 1 directs Mhem atheroprotective macrophages through coordinated iron handling and foam cell protection

RATIONALE

Intraplaque hemorrhage (IPH) drives atherosclerosis through the dual metabolic stresses of cholesterol-enriched erythrocyte membranes and pro-oxidant heme/iron. When clearing tissue hemorrhage, macrophages are typically seen storing either iron or lipid. We have recently defined hemorrhage-associated macrophages (HA-mac) as a plaque macrophage population that responds adaptively to IPH.

OBJECTIVE

This study aimed to define the key transcription factor(s) involved in HO-1 induction by heme.

METHODS AND RESULTS

To address this question, we used microarray analysis and transfection with siRNA and plasmids. To maintain physiological relevance, we focused on human blood-derived monocytes. We found that heme stimulates monocytes through induction of activating transcription factor 1 (ATF-1). ATF-1 coinduces heme oxygenase-1 (HO-1) and Liver X receptor beta (LXR-β). Heme-induced HO-1 and LXR-β were suppressed by knockdown of ATF-1, and HO-1 and LXR-β were induced by ATF-1 transfection. ATF-1 required phosphorylation for full functional activity. Expression of LXR-β in turn led to induction of other genes central to cholesterol efflux, such as LXR-α and ABCA1. This heme-directed state was distinct from known macrophage states (M1, M2, Mox) and, following the same format, we have designated them Mhem.

CONCLUSIONS

These results show that ATF-1 mediates HO-1 induction by heme and drives macrophage adaptation to intraplaque hemorrhage. Our definition of an ATF-1-mediated pathway for linked protection from foam cell formation and oxidant stress may have therapeutic potential.

Phenotypic modulation of macrophages in response to plaque lipids

PURPOSE OF REVIEW

The accumulation of macrophages in the vascular wall is a hallmark of atherosclerosis. The biological properties of atherosclerotic plaque macrophages determine lesion size, composition, and stability. In atherosclerotic plaques, macrophages encounter a microenvironment that comprises a variety of lipid oxidation products, each of which has diverse biological effects. In this review, we summarize recent advances in our understanding of the effects of plaque lipids on macrophage phenotypic polarization.

RECENT FINDINGS

Atherosclerotic lesions in mice and in humans contain various macrophage phenotypes, which play different roles in mediating inflammation, the clearance of dead cells, and possibly resolution. Macrophages alter their phenotype and biological function in response to plaque lipids through the upregulation of specific sets of genes. Interaction of oxidized lipids with pattern recognition receptors and activation of the inflammasome by cholesterol crystals drive macrophages toward an inflammatory M1 phenotype. A new phenotype, Mox, develops when oxidized phospholipids activate stress response genes via Nrf2. Other lipid mediators such as nitrosylated-fatty acids and omega-3 fatty acid-derived products polarize plaque macrophages toward anti-inflammatory and proresolving phenotypes.

SUMMARY

A deeper understanding of how lipids that accumulate in atherosclerotic plaques affect macrophage phenotype and function and thus atherosclerotic lesion development and stability will help to devise novel strategies for intervention.

Oxidized low-density lipoprotein-induced periodontal inflammation is associated with the up-regulation of cyclooxygenase-2 and microsomal prostaglandin synthase 1 in human gingival epithelial cells

Periodontitis is characterized by chronic gingival tissue inflammation, and inflammatory mediators such as IL-8 and prostaglandin E(2) (PGE(2)) are associated with disease progression. Previously we showed that oxidatively modified low-density lipoprotein (oxLDL) was present in gingival crevicular fluid. In this study, the role of oxLDL in the gingival epithelial cell inflammatory response was further investigated using Ca9-22 cells and primary human oral keratinocytes (HOK). Treatment of Ca9-22 cells and HOK with oxLDL induced an up-regulation of IL-8 and the PGE(2)-producing enzymes, cyclooxygenase-2 and microsomal PGE(2) synthase-1. These responses induced by oxLDL were significantly suppressed by a nuclear factor-kappa B (NF-κB) inhibitor. However, unlike the result in macrophages, oxLDL did not lead to an increase in CD36 expression in these two cells. These results suggest that oxLDL elicits gingival epithelial cell inflammatory responses through an activation of the NF-κB pathway. These data suggest a mechanistic link between periodontal disease and lipid metabolism-related disorders, including atherosclerosis.

Myeloid IκBα deficiency promotes atherogenesis by enhancing leukocyte recruitment to the plaques

Activation of the transcription factor NF-κB appears to be involved in different stages of atherogenesis. In this paper we investigate the role of NF-κB inhibitor IκBα in atherosclerosis. Myeloid-specific deletion of IκBα results in larger and more advanced lesions in LDL-R-deficient mice without affecting the compositional phenotype of the plaques or systemic inflammatory markers in the plasma. We show that IκBα-deleted macrophages display enhanced adhesion to an in vitro endothelial cell layer, coinciding with an increased expression of the chemokine CCL5. Also, in vivo we found that IκBα^del mice had more leukocytes adhering to the luminal side of the endothelial cell layers that cover the atherosclerotic plaques. Moreover, we introduce ER-MP58 in this paper as a new immunohistochemical tool for quantifying newly recruited myeloid cells in the atherosclerotic lesion. This staining confirms that in IκBα^del mice more leukocytes are attracted to the plaques. In conclusion, we show that IκBα deletion in myeloid cells promotes atherogenesis, probably through an induced leukocyte recruitment to plaques.

Primary hyperparathyroidism influences the expression of inflammatory and metabolic genes in adipose tissue

Background

Primary hyperparathyroidism (PHPT) is characterised by increased production of parathyroid hormone (PTH) resulting in elevated serum calcium levels. The influence on bone metabolism with altered bone resorption is the most studied clinical condition in PHPT. In addition to this, patients with PHPT are at increased risk of non-skeletal diseases, such as impaired insulin sensitivity, arterial hypertension and increased risk of death by cardiovascular diseases (CVD), possibly mediated by a chronic low-grade inflammation. The aim of this study was to investigate whether adipose tissue reflects the low-grade inflammation observed in PHPT patients.

Methodology/Principal Findings

Subcutaneous fat tissue from the neck was sampled from 16 non-obese patients with PHPT and from 16 patients operated for benign thyroid diseases, serving as weight-matched controls. RNA was extracted and global gene expression was analysed with Illumina BeadArray Technology. We found 608 differentially expressed genes (q-value<0.05), of which 347 were up-regulated and 261 were down-regulated. Gene ontology analysis showed that PHPT patients expressed increased levels of genes involved in immunity and defense (e.g. matrix metallopeptidase 9, S100 calcium binding protein A8 and A9, CD14, folate receptor 2), and reduced levels of genes involved in metabolic processes. Analysis of transcription factor binding sites present in the differentially expressed genes corroborated the up-regulation of inflammatory processes.

Conclusions/Significance

Our findings demonstrate that PHPT strongly influences gene regulation in fat tissue, which may result in altered adipose tissue function and release of pathogenic factors that increase the risk of CVD.

Mitochondrial dysfunction promoted by Porphyromonas gingivalis lipopolysaccharide as a possible link between cardiovascular disease and periodontitis

Oxidative stress is one of the factors that could explain the pathophysiological mechanism of inflammatory conditions that occur in cardiovascular disease (CVD) and periodontitis. Such inflammatory response is often evoked by specific bacteria, as the lipopolysaccharide (LPS) of Porphyromonas gingivalis is a key factor in this process. The aim of this research was to study the role of mitochondrial dysfunction in peripheral blood mononuclear cells (PBMCs) from periodontitis patients and to evaluate the influence of LPS on fibroblasts to better understand the pathophysiology of periodontitis and its relationship with CVD. PBMCs from patients showed lower CoQ10 levels and citrate synthase activity, together with high levels of ROS production. LPS-treated fibroblasts provoked increased oxidative stress and mitochondrial dysfunction by a decrease in mitochondrial protein expression, mitochondrial mass, and mitochondrial membrane potential. Our study supports the hypothesis that LPS-mediated mitochondrial dysfunction could be at the origin of oxidative stress in periodontal patients. Abnormal PBMC performance may promote oxidative stress and alter cytokine homeostasis. In conclusion, mitochondrial dysfunction could represent a possible link to understanding the interrelationships between two prominent inflammatory diseases: periodontitis and CVD.

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.

The augmented neutrophil respiratory burst in response to Escherichia coli is reduced in liver cirrhosis during infection

Several functional abnormalities in phagocytes from patients with liver cirrhosis contribute to an increased risk of infection. An increased resting respiratory burst has been observed in neutrophils from cirrhotic patients. We investigated whether an infection in cirrhosis affects the respiratory burst capacity of neutrophils and monocytes in response to Escherichia coli. This study included 45 hospitalized patients with liver cirrhosis and clinical signs of infection, 39 patients with liver cirrhosis in the absence of infection and 29 healthy subjects. Respiratory burst, lipopolysaccharide-binding protein (LBP), and immunoglobulin (Ig)G-autoantibodies against oxidized low-density lipoproteins (ab-oxLDL) were measured. The fraction of neutrophils spontaneously producing reactive oxygen species (ROS) was elevated in liver cirrhosis (P < 0·01). The neutrophil resting burst increased with Child-Pugh stage (P = 0·02) and correlated with augmented ROS release in response to opsonized E. coli (P < 0·05). Although LBP was increased in patients with cirrhosis (P < 0·01), higher LBP levels correlated with a lower resting burst in neutrophils (r(s)  = -0·395; P < 0·01). In the presence of infection, the resting burst was unaltered. However, neutrophil ROS release in response to E. coli was reduced markedly (P = 0·01), and it decreased as serum C-reactive protein (CRP) concentration rose (r(s)  = -0·437; P < 0·01), indicating the development of a sepsis-like immune paralysis. A positive correlation between ab-oxLDL and ROS release was observed (P < 0·01). In conclusion, the respiratory burst increases with severity of liver cirrhosis but is restrained by increasing LBP levels. Augmented ROS release in response to E. coli is accompanied by elevated markers of oxidative damage and becomes exhausted in the presence of infection.

Oxidized cholesteryl esters and phospholipids in zebrafish larvae fed a high cholesterol diet: macrophage binding and activation

A novel hypercholesterolemic zebrafish model has been developed to study early events of atherogenesis. This model utilizes optically transparent zebrafish larvae, fed a high cholesterol diet (HCD), to monitor processes of vascular inflammation in live animals. Because lipoprotein oxidation is an important factor in the development of atherosclerosis, in this study, we characterized the oxidized lipid milieu in HCD-fed zebrafish larvae. Using liquid chromatography-mass spectrometry, we show that feeding an HCD for only 2 weeks resulted in up to 70-fold increases in specific oxidized cholesteryl esters, identical to those present in human minimally oxidized LDL and in murine atherosclerotic lesions. The levels of oxidized phospholipids, such as 1-palmitoyl-2-oxovaleroyl-sn-glycero-3-phosphocholine, and of various lysophosphatidylcholines were also significantly elevated. Moreover, lipoproteins isolated from homogenates of HCD-fed larvae induced cell spreading as well as ERK1/2, Akt, and JNK phosphorylation in murine macrophages. Removal of apoB-containing lipoproteins from the zebrafish homogenates with an anti-human LDL antibody, as well as reducing lipid hydroperoxides with ebselen, resulted in inhibition of macrophage activation. The TLR4 deficiency in murine macrophages prevented their activation with zebrafish lipoproteins. Using biotinylated homogenates of HCD-fed larvae, we demonstrated that their components bound to murine macrophages, and this binding was effectively competed by minimally oxidized LDL but not by native LDL. These data provide evidence that molecular lipid determinants of proatherogenic macrophage phenotypes are present in large quantities in hypercholesterolemic zebrafish larvae and support the use of the HCD-fed zebrafish as a valuable model to study early events of atherogenesis.

Nuclear receptors and inflammation control: molecular mechanisms and pathophysiological relevance

Tissue inflammation is a tightly regulated process that normally serves to recruit the immune system to sites of infection and injury and to facilitate tissue repair processes. When an inflammatory state is excessive or prolonged, local and systemic damage to host tissues can result in loss of normal physiological functions. Here, we briefly review recent studies that advance our understanding of signaling pathways involved in initiation of inflammatory responses at the level of transcription and counterregulation of these pathways by selected members of the nuclear receptor superfamily. Studies of the intersection of nuclear receptors and inflammation have revealed mechanisms of positive and negative transcriptional control that may provide new targets for pharmacological intervention in chronic diseases, such as atherosclerosis.