Role of the GRO family of chemokines in monocyte adhesion to MM-LDL-stimulated endothelium

The Potential Importance of CXCL1 in the Physiological State and in Noncancer Diseases of the Cardiovascular System, Respiratory System and Skin

In this paper, we present a literature review of the role of CXC motif chemokine ligand 1 (CXCL1) in physiology, and in selected major non-cancer diseases of the cardiovascular system, respiratory system and skin. CXCL1, a cytokine belonging to the CXC sub-family of chemokines with CXC motif chemokine receptor 2 (CXCR2) as its main receptor, causes the migration and infiltration of neutrophils to the sites of high expression. This implicates CXCL1 in many adverse conditions associated with inflammation and the accumulation of neutrophils. The aim of this study was to describe the significance of CXCL1 in selected diseases of the cardiovascular system (atherosclerosis, atrial fibrillation, chronic ischemic heart disease, hypertension, sepsis including sepsis-associated encephalopathy and sepsis-associated acute kidney injury), the respiratory system (asthma, chronic obstructive pulmonary disease (COPD), chronic rhinosinusitis, coronavirus disease 2019 (COVID-19), influenza, lung transplantation and ischemic-reperfusion injury and tuberculosis) and the skin (wound healing, psoriasis, sunburn and xeroderma pigmentosum). Additionally, the significance of CXCL1 is described in vascular physiology, such as the effects of CXCL1 on angiogenesis and arteriogenesis.

Inflammatory Chemokines in Atherosclerosis

Atherosclerosis is a long-term, chronic inflammatory disease of the vessel wall leading to the formation of occlusive or rupture-prone lesions in large arteries. Complications of atherosclerosis can become severe and lead to cardiovascular diseases (CVD) with lethal consequences. During the last three decades, chemokines and their receptors earned great attention in the research of atherosclerosis as they play a key role in development and progression of atherosclerotic lesions. They orchestrate activation, recruitment, and infiltration of immune cells and subsequent phenotypic changes, e.g., increased uptake of oxidized low-density lipoprotein (oxLDL) by macrophages, promoting the development of foam cells, a key feature developing plaques. In addition, chemokines and their receptors maintain homing of adaptive immune cells but also drive pro-atherosclerotic leukocyte responses. Recently, specific targeting, e.g., by applying cell specific knock out models have shed new light on their functions in chronic vascular inflammation. This article reviews recent findings on the role of immunomodulatory chemokines in the development of atherosclerosis and their potential for targeting.

Clonal Hematopoiesis: Somatic Mutations in Blood Cells and Atherosclerosis

The most important prognostic factor for atherosclerotic cardiovascular disease is age, independent of all other recognized risk factors. Recently, exome sequence analyses showed that somatic mutations in blood cells, a process termed clonal hematopoiesis, are common and increase in prevalence with age, with at least 1 in 10 adults older than 70 years affected. Carriers of clonal hematopoiesis have been shown to be not only at heightened risk for hematologic malignancy but also at increased risk for atherosclerotic cardiovascular disease. Here, we review the prior literature of clonal selection and expansion of hematopoietic stem cells and the evidence supporting its causal association with atherosclerotic cardiovascular disease.

Clonal Hematopoiesis and Risk of Atherosclerotic Cardiovascular Disease

BACKGROUND

Clonal hematopoiesis of indeterminate potential (CHIP), which is defined as the presence of an expanded somatic blood-cell clone in persons without other hematologic abnormalities, is common among older persons and is associated with an increased risk of hematologic cancer. We previously found preliminary evidence for an association between CHIP and atherosclerotic cardiovascular disease, but the nature of this association was unclear.

METHODS

We used whole-exome sequencing to detect the presence of CHIP in peripheral-blood cells and associated such presence with coronary heart disease using samples from four case-control studies that together enrolled 4726 participants with coronary heart disease and 3529 controls. To assess causality, we perturbed the function of Tet2, the second most commonly mutated gene linked to clonal hematopoiesis, in the hematopoietic cells of atherosclerosis-prone mice.

RESULTS

In nested case-control analyses from two prospective cohorts, carriers of CHIP had a risk of coronary heart disease that was 1.9 times as great as in noncarriers (95% confidence interval [CI], 1.4 to 2.7). In two retrospective case-control cohorts for the evaluation of early-onset myocardial infarction, participants with CHIP had a risk of myocardial infarction that was 4.0 times as great as in noncarriers (95% CI, 2.4 to 6.7). Mutations in DNMT3A, TET2, ASXL1, and JAK2 were each individually associated with coronary heart disease. CHIP carriers with these mutations also had increased coronary-artery calcification, a marker of coronary atherosclerosis burden. Hypercholesterolemia-prone mice that were engrafted with bone marrow obtained from homozygous or heterozygous Tet2 knockout mice had larger atherosclerotic lesions in the aortic root and aorta than did mice that had received control bone marrow. Analyses of macrophages from Tet2 knockout mice showed elevated expression of several chemokine and cytokine genes that contribute to atherosclerosis.

CONCLUSIONS

The presence of CHIP in peripheral-blood cells was associated with nearly a doubling in the risk of coronary heart disease in humans and with accelerated atherosclerosis in mice. (Funded by the National Institutes of Health and others.).

The Therapeutic Potential of Anti-Inflammatory Exerkines in the Treatment of Atherosclerosis

Although many cardiovascular (CVD) medications, such as antithrombotics, statins, and antihypertensives, have been identified to treat atherosclerosis, at most, many of these therapeutic agents only delay its progression. A growing body of evidence suggests physical exercise could be implemented as a non-pharmacologic treatment due to its pro-metabolic, multisystemic, and anti-inflammatory benefits. Specifically, it has been discovered that certain anti-inflammatory peptides, metabolites, and RNA species (collectively termed “exerkines”) are released in response to exercise that could facilitate these benefits and could serve as potential therapeutic targets for atherosclerosis. However, much of the relationship between exercise and these exerkines remains unanswered, and there are several challenges in the discovery and validation of these exerkines. This review primarily highlights major anti-inflammatory exerkines that could serve as potential therapeutic targets for atherosclerosis. To provide some context and comparison for the therapeutic potential of exerkines, the anti-inflammatory, multisystemic benefits of exercise, the basic mechanisms of atherosclerosis, and the limited efficacies of current anti-inflammatory therapeutics for atherosclerosis are briefly summarized. Finally, key challenges and future directions for exploiting these exerkines in the treatment of atherosclerosis are discussed.

Neuregulin-1β induces proliferation, survival and paracrine signaling in normal human cardiac ventricular fibroblasts

Neuregulin-1β (NRG-1β) is critical for cardiac development and repair, and recombinant forms are currently being assessed as possible therapeutics for systolic heart failure. We previously demonstrated that recombinant NRG-1β reduces cardiac fibrosis in an animal model of cardiac remodeling and heart failure, suggesting that there may be direct effects on cardiac fibroblasts. Here we show that NRG-1β receptors (ErbB2, ErbB3, and ErbB4) are expressed in normal human cardiac ventricular (NHCV) fibroblast cell lines. Treatment of NHCV fibroblasts with recombinant NRG-1β induced activation of the AKT pathway, which was phosphoinositide 3-kinase (PI3K)-dependent. Moreover, the NRG-1β-induced PI3K/AKT signaling in these cells required phosphorylation of both ErbB2 and ErbB3 receptors at tyrosine (Tyr)1248 and Tyr1289 respectively. RNASeq analysis of NRG-1β-treated cardiac fibroblasts obtained from three different individuals revealed a global gene expression signature consistent with cell growth and survival. We confirmed enhanced cellular proliferation and viability in NHCV fibroblasts in response to NRG-1β, which was abrogated by PI3K, ErbB2, and ErbB3 inhibitors. NRG-1β also induced production and secretion of cytokines (interleukin-1α and interferon-γ) and pro-reparative factors (angiopoietin-2, brain-derived neurotrophic factor, and crypto-1), suggesting a role in cardiac repair through the activation of paracrine signaling.

Chemokines and microRNAs in atherosclerosis

The crucial role of chemokines in the initiation and progression of atherosclerosis has been widely recognized. Through essential functions in leukocyte recruitment, chemokines govern the infiltration with mononuclear cells and macrophage accumulation in atherosclerotic lesions. Beyond recruitment, chemokines also provide homeostatic functions supporting cell survival and mediating the mobilization and homing of progenitor cells. As a new regulatory layer, several microRNAs (miRNAs) have been found to modulate the function of endothelial cells (ECs), smooth muscle cells and macrophages by controlling the expression levels of chemokines and thereby affecting different stages in the progression of atherosclerosis. For instance, the expression of CXCL1 can be down-regulated by miR-181b, which inhibits nuclear factor-κB activation in atherosclerotic endothelium, thus attenuating the adhesive properties of ECs and exerting early atheroprotective effects. Conversely, CXCL12 expression can be induced by miR-126 in ECs through an auto-amplifying feedback loop to facilitate endothelial regeneration, thus limiting atherosclerosis and mediating plaque stabilization. In contrast, miR-155 plays a pro-atherogenic role by promoting the expression of CCL2 in M1-type macrophages, thereby enhancing vascular inflammation. Herein, we will review novel aspects of chemokines and their regulation by miRNAs during atherogenesis. Understanding the complex cross-talk of miRNAs controlling chemokine expression may open novel therapeutic options to treat atherosclerosis.

P2Y6 receptor potentiates pro-inflammatory responses in macrophages and exhibits differential roles in atherosclerotic lesion development

Background

P2Y₆, a purinergic receptor for UDP, is enriched in atherosclerotic lesions and is implicated in pro-inflammatory responses of key vascular cell types and macrophages. Evidence for its involvement in atherogenesis, however, has been lacking. Here we use cell-based studies and three murine models of atherogenesis to evaluate the impact of P2Y₆ deficiency on atherosclerosis.

Methodology/Principal Findings

Cell-based studies in 1321N1 astrocytoma cells, which lack functional P2Y₆ receptors, showed that exogenous expression of P2Y₆ induces a robust, receptor- and agonist-dependent secretion of inflammatory mediators IL-8, IL-6, MCP-1 and GRO1. P2Y₆-mediated inflammatory responses were also observed, albeit to a lesser extent, in macrophages endogenously expressing P2Y₆ and in acute peritonitis models of inflammation. To evaluate the role of P2Y₆ in atherosclerotic lesion development, we used P2Y₆-deficient mice in three mouse models of atherosclerosis. A 43% reduction in aortic arch plaque was observed in high fat-fed LDLR knockout mice lacking P2Y₆ receptors in bone marrow-derived cells. In contrast, no effect on lesion development was observed in fat-fed whole body P2Y₆xLDLR double knockout mice. Interestingly, in a model of enhanced vascular inflammation using angiotensin II, P2Y₆ deficiency enhanced formation of aneurysms and exhibited a trend towards increased atherosclerosis in the aorta of LDLR knockout mice.

Conclusions

P2Y₆ receptor augments pro-inflammatory responses in macrophages and exhibits a pro-atherogenic role in hematopoietic cells. However, the overall impact of whole body P2Y₆ deficiency on atherosclerosis appears to be modest and could reflect additional roles of P2Y₆ in vascular disease pathophysiologies, such as aneurysm formation.

Lysophosphatidic acid in atherosclerotic diseases

Lysophosphatidic acid (LPA) is a potent bioactive phospholipid. As many other biological active lipids, LPA is an autacoid: it is formed locally on demand, and it acts locally near its site of synthesis. LPA has a plethora of biological activities on blood cells (platelets, monocytes) and cells of the vessel wall (endothelial cells, smooth muscle cells, macrophages) that are all key players in atherosclerotic and atherothrombotic processes. The specific cellular actions of LPA are determined by its multifaceted molecular structures, the expression of multiple G-protein coupled LPA receptors at the cell surface and their diverse coupling to intracellular signalling pathways. Numerous studies have now shown that LPA has thrombogenic and atherogenic actions. Here, we aim to provide a comprehensive, yet concise, thoughtful and critical review of this exciting research area and to pinpoint potential pharmacological targets for inhibiting thrombogenic and atherogenic activities of LPA. We hope that the review will serve to accelerate knowledge of basic and clinical science, and to foster drug development in the field of LPA and atherosclerotic/atherothrombotic diseases.

Endothelial cell regulation of leukocyte infiltration in inflammatory tissues

Endothelial cells play an important, active role in the onset and regulation of inflammatory and immune reactions. Through the production of chemokines they attract leukocytes and activate their adhesive receptors. This leads to the anchorage of leukocytes to the adhesive molecules expressed on the endothelial surface. Leukocyte adhesion to endothelial cells is frequently followed by their extravasation. The mechanisms which regulate the passage of leukocytes through endothelial clefts remain to be clarified. Many indirect data suggest that leukocytes might transfer signals to endothelial cells both through the release of active agents and adhesion to the endothelial cell surface. Adhesive molecules (such as PECAM) on the endothelial cell surface might also ‘direct’ leukocytes through the intercellular junction by haptotaxis. The information available on the molecular structure and functional properties of endothelial chemokines, adhesive molecules or junction organization is still fragmentary. Further work is needed to clarify how they interplay in regulating leukocyte infiltration into tissues.

Touch of chemokines

Chemoattractant cytokines or chemokines constitute a family of structurally related proteins found in vertebrates, bacteria, or viruses. So far, 48 chemokine genes have been identified in humans, which bind to around 20 chemokine receptors. These receptors belong to the seven transmembrane G-protein-coupled receptor family. Chemokines and their receptors were originally studied for their role in cellular trafficking of leukocytes during inflammation and immune surveillance. It is now known that they exert different functions under physiological conditions such as homeostasis, development, tissue repair, and angiogenesis but also under pathological disorders including tumorigenesis, cancer metastasis, inflammatory, and autoimmune diseases. Physicochemical properties of chemokines and chemokine receptors confer the ability to homo- and hetero-oligomerize. Many efforts are currently performed in establishing new therapeutically compounds able to target the chemokine/chemokine receptor system. In this review, we are interested in the role of chemokines in inflammatory disease and leukocyte trafficking with a focus on vascular inflammatory diseases, the operating synergism, and the emerging therapeutic approaches of chemokines.

Lipoprotein-derived lysophosphatidic acid promotes atherosclerosis by releasing CXCL1 from the endothelium

Oxidatively modified low-density lipoprotein (oxLDL) plays a key role in the initiation of atherosclerosis by increasing monocyte adhesion. The mechanism that is responsible for the oxLDL-induced atherogenic monocyte recruitment in vivo, however, still remains unknown. Oxidation of LDL generates lysophosphatidylcholine, which is the main substrate for the lysophosphatidic acid (LPA) generating enzyme autotaxin. We show that oxLDL requires endothelial LPA receptors and autotaxin to elicit CXCL1-dependent arterial monocyte adhesion. Unsaturated LPA releases endothelial CXCL1, which is subsequently immobilized on the cell surface and mediates LPA-induced monocyte adhesion. Local and systemic application of LPA accelerates the progression of atherosclerosis in mice. Blocking the LPA receptors LPA(1) and LPA(3) reduced hyperlipidemia-induced arterial leukocyte arrest and atherosclerosis in the presence of functional CXCL1. Thus, atherogenic monocyte recruitment mediated by hyperlipidemia and modified LDL crucially depends on LPA, which triggers endothelial deposition of CXCL1, revealing LPA signaling as a target for cardiovascular disease treatments.

Erythrocyte Duffy antigen receptor for chemokines (DARC): diagnostic and therapeutic implications in atherosclerotic cardiovascular disease

Atherosclerosis is an inflammatory disease. The last three decades efforts have been made to elucidate the biochemical pathways that are implicated in the process of atherogenesis and plaque development. Chemokines are crucial mediators in every step of this process. Additionally, cellular components of the peripheral blood have been proved important mediators in the formation and progression of atherosclerotic lesions. However, until recently data were mostly focusing on leukocytes and platelets. Erythrocytes were considered unreceptive bystanders and limited data supported their importance in the progression and destabilization of the atherosclerotic plaque. Recently erythrocytes, through their Duffy antigen receptor for chemokines (DARC), have been proposed as appealing regulators of chemokine-induced pathways. Dissimilar to every other chemokine receptor DARC possesses high affinity for several ligands from both CC and CXC chemokine sub-families. Moreover, DARC is not coupled to a G-protein or any other intracellular signalling system; thus it is incapable of generating second messages. The exact biochemical role of erythrocyte DARC remains to be determined. It is however challenging the fact that DARC is a regulator of almost every CC and CXC chemokine ligand and therefore DARC antagonism could effectively block the complex pre-inflammatory chemokine network. In the present review we intent to provide recent evidence supporting the role of erythrocytes in atherosclerosis focusing on the erythrocyte-chemokine interaction through the Duffy antigen system.

Therapeutic implications of chemokine-mediated pathways in atherosclerosis: realistic perspectives and utopias

Current perspectives on the pathogenesis of atherosclerosis strongly support the involvement of inflammatory mediators in the establishment and progression of atherosclerostic lesions. Chemokine-mediated mechanisms are potent regulators of such processes by orchestrating the interactions of inflammatory cellular components of the peripheral blood with cellular components of the arterial wall. The increasing evidence supporting the role of chemokine pathways in atherosclerosis renders chemokine ligands and their receptors potential therapeutic targets. In the following review, we aim to highlight the special structural and functional features of chemokines and their receptors in respect to their roles in atherosclerosis, and examine to what extent available data can be applied in disease management practices.

Overexpression of the CXCL3 gene in response to oxidized low-density lipoprotein is associated with the presence of tendon xanthomas in familial hypercholesterolemia

To examine if overexpression of certain chemokines and proinflammatory cytokines in response to oxidized low-density lipoprotein could be involved in the onset and development of tendon xanthomas (TX), we quantified IL-1beta, TNF-alpha, and IL-8 and compared gene expression of PPAR-gamma, NF-kappaBIA, IL-8, IL-1beta, CXCL3, tryptase, and TNF-alpha in macrophages of familial hypercholesterolemia subjects with and without TX stimulated with oxidized low-density lipoprotein at 1, 3, 6, and 18 h of incubation. We propose that chemokines belonging to the CXC family could play an important role in the etiology of TX, with CXCL3 being a possible biological marker of onset and development of TX.

Increased sensitivity for troglitazone-induced cytotoxicity using a human in vitro co-culture model

Drug-induced hepatotoxicity is a major reason for withdrawal of drugs from development as well as from the market. A major problem predicting hepatotoxicity is the lack of suitable predictive in vitro system. Drug-induced hepatotoxicity is usually associated with the recruitment of immune cells to the liver accelerating an inflammatory response often initiated by activation of the Kupffer cells. In order to evaluate whether the introduction of inflammatory cells could increase the sensitivity for drug-induced cytotoxicity we developed an in vitro co-culture system based on two human cell lines; a hepatoma (Huh-7) and monocytic (THP-1) cell line. As model drugs we chose two peroxisome proliferator activated receptor gamma (PPAR gamma) agonists, the hepatotoxic troglitazone and the non-hepatotoxic rosiglitazone. In the co-cultures, troglitazone caused an enhanced cytotoxicity as compared to single cultures of either cell line, whereas little cytotoxicity was seen after treatment with rosiglitazone. Troglitazone treatment increased gene expression of pro-inflammatory mediators and stress-related genes in both cell types, which in general was more pronounced in co-cultures than in single cell cultures. Based on these results we suggest that co-cultures of human hepatoma cells and monocytes might provide an important in vitro system for better prediction of cytotoxicity mediated by potential hepatotoxins.

The role of the chemokines MCP-1, GRO-alpha, IL-8 and their receptors in the adhesion of monocytic cells to human atherosclerotic plaques

Monocyte adhesion to the arterial endothelium and subsequent migration into the intima are central events in the pathogenesis of atherosclerosis. Previous experimental models have shown that chemokines can enhance monocyte–endothelial adhesion by activating monocyte integrins. Our study assesses the role of chemokines IL-8, MCP-1 and GRO-α, together with their monocyte receptors CCR2 and CXCR2 in monocyte adhesion to human atherosclerotic plaques. In an adhesion assay, a suspension of monocytic U937 cells was incubated with human atherosclerotic artery sections and the levels of endothelial adhesion were quantified. Adhesion performed in the presence of a monoclonal antibody to a chemokine, chemokine receptor or of an isotype matched control immunoglobulin, shows that antibodies to all chemokines tested, as well as their receptors, inhibit adhesion compared to the control immunoglobulins. Immunohistochemistry demonstrated the expression of MCP-1, GRO-α and their receptors in the endothelial cells and intima of all atherosclerotic lesions. These results suggest that all these chemokines and their receptors can play a role in the adhesion of monocytes to human atherosclerotic plaques. Furthermore, they suggest that these chemokine interactions provide potential targets for the therapy of atherosclerosis.

Growth-related oncogene-alpha induces endothelial dysfunction through oxidative stress and downregulation of eNOS in porcine coronary arteries

Growth-related oncogene-alpha (GRO-alpha) is a member of the CXC chemokine family, which is involved in the inflammatory process including atherosclerosis. We hypothesized that GRO-alpha may affect endothelial functions in both porcine coronary arteries and human coronary artery endothelial cells (HCAECs). Vasomotor function was analyzed in response to thromboxane A2 analog U-46619 for contraction, bradykinin for endothelium-dependent vasorelaxation, and sodium nitroprusside (SNP) for endothelium-independent vasorelaxation. In response to 10(-6) M bradykinin, GRO-alpha (50 and 100 ng/ml) significantly reduced endothelium-dependent vasorelaxation by 34.73 and 48.8%, respectively, compared with controls (P < 0.05). There were no changes in response to U-46619 or SNP between treated and control groups. With the lucigenin-enhanced chemiluminescence assay, superoxide anion production in GRO-alpha-treated vessels (50 and 100 ng/ml) was significantly increased by 50 and 86%, respectively, compared with controls (P < 0.05). With real-time PCR analysis, endothelial nitric oxide synthase (eNOS) mRNA levels in porcine coronary arteries and HCAECs after GRO-alpha treatment were significantly decreased compared with controls (P < 0.05). The eNOS protein levels by both immunohistochemistry and Western blot analyses were also decreased in GRO-alpha-treated vessels. Antioxidant seleno-l-methionine and anti-GRO-alpha antibody effectively blocked these effects of GRO-alpha on both porcine coronary arteries and HCAECs. In addition, GRO-alpha immunoreactivity was substantially increased in the atherosclerotic regions compared with nonatherosclerotic regions in human coronary arteries. Thus GRO-alpha impairs endothelium-dependent vasorelaxation in porcine coronary arteries through a mechanism of overproduction of superoxide anion and downregulation of eNOS. GRO-alpha may contribute to human coronary artery disease.

Coincident activation of Th2 T cells with onset of the disease and differential expression of GRO-gamma in peripheral blood leukocytes in minimal change disease

BACKGROUND

Involvement of Th2 T cells/NFkappaB in minimal change disease (MCD) has been postulated. A promising but unconfirmed glomerular permeability factor (GPF) from MCD T cells has been described. We explored whether GPF was the consequence of Th2 cell activation.

METHODS

Peripheral blood leukocytes (PBL) from 16 MCD patients and 7 normal controls were analyzed and the results were statistically compared.

RESULTS

Flow cytometry demonstrated a significant expansion of CD4+ T cell population and dramatically increased CD69+ cells among CD4+ T cells in MCD, suggesting coincident activation of T cells with onset of the disease. RT-PCR on RNA from either freshly isolated PBL or post in vitroactivation showed high-level expression of the Th2 cytokine interleukin-4 in all MCD patients. Importantly, both antibody microarray assay on sera and RT-PCR on mRNA of PBL revealed expression of a CXC chemokine GRO-gamma (growth-related oncogene) in all MCD patients as compared with one of 7 controls.

CONCLUSIONS

Our results reveal an association between onset of MCD and activation of Th2 cells. The GRO family has been implicated in the function of endothelial cells, and its expression is under NFkappaB regulation. Thus, GRO-gamma is a promising candidate for Th2-associated GPF in MCD.

Altered phenotype and gene transcription in endothelial cells, induced by Plasmodium falciparum-infected red blood cells: pathogenic or protective?

Severe malaria is associated with sequestration of Plasmodium falciparum-infected red blood cells (PRBC) in the microvasculature and elevation of intercellular adhesion molecule-1 (ICAM-1) and TNF. In vitro co-culture of human umbilical vein endothelial cells (HUVEC), with either PRBC or uninfected RBC, required the presence of low level TNF (5 pg/ml) for significant up-regulation of ICAM-1, which may contribute to increased cytoadhesion in vivo. These effects were independent of P. falciparum erythrocyte membrane protein-1 (PfEMP-1)-mediated adhesion but critically dependent on cell–cell contact. Further changes included increases in IL8 release and soluble TNF receptor shedding. Microarray analysis of HUVEC transcriptome following co-culture, using a human Affymetrix microarray chip, showed significant differential regulation of genes which defined gene ontologies such as cell communication, cell adhesion, signal transduction and immune response. Our data demonstrate that endothelial cells have the ability to mobilise immune and pro-adhesive responses when exposed to both PRBC and TNF. In addition, there is also a previously un-described positive regulation by RBC and TNF and a concurrent negative regulation of a range of genes involved in inflammation and cell-death, by PRBC and TNF. We propose that the balance between positive and negative regulation demonstrated in our study will determine endothelial pathology during a malaria infection.

Chemokines: inflammatory mediators of atherosclerosis

Atherosclerosis as the underlying mechanisms of myocardial infarction, stroke and peripheral artery disease remains the major cause of morbidity and mortality in developed countries. Recent developments in vascular biology have indicated that atherosclerosis can be best characterized as a chronic inflammatory disease of the vessel wall that promotes lesion development and progression. Chemokines regulate and control these processes by orchestrating adhesive interactions of circulating blood cells with the arterial wall and their subsequent extravasation. Exhibiting a high degree of specialization and cooperation, different chemokines mediate distinct steps during the atherogenic recruitment of monocytes and T cells. This diversity of chemokine expression and function might lead to the identification of selective therapeutic targets for the prevention and treatment of atherosclerosis.

Multiple Innate Inflammatory Responses Induced after Systemic Adenovirus Vector Delivery Depend on a Functional Complement System

Excessive complement activation can result in extreme tissue damage and systemic inflammatory responses, similar to innate immune responses rapidly elicited after systemic adenovirus (Ad) injections. To determine if Ad interactions with the complement system impact upon Ad-induced innate immune responses, we injected Ad into complement-deficient, C3-knockout mice (C3-KO) or wild-type mice (WT) and quantitatively compared multiple anti-Ad innate immune responses in both strains of mice. In Ad-treated WT mice, we noted rapid increases in plasma KC levels (1 h post injection), followed by increases in IL-6, IFN-gamma, RANTES, IL-12(p40), IL-5, G-CSF, and GM-CSF and subsequently thrombocytopenia. Conversely, in Ad-treated C3-KO mice, many of these inflammatory responses were significantly blunted, including the avoidance of Ad-induced thrombocytopenia. Global liver transcriptome responses in Ad-treated WT mice were assessed by RT-PCR-validated gene array analysis and were found to be also significantly affected by the lack of complement activity in Ad-treated C3-KO mice. Finally, our results confirmed the ability of high dose Ads to transduce hepatocytes despite a lack of complement activity. In summary, Ad interactions with the mammalian complement system are significant and likely initiate and/or exacerbate many of the inflammatory responses noted after systemic Ad injections.

Heparin Displaces Interferon-γ–Inducible Chemokines (IP-10, I-TAC, and Mig) Sequestered in the Vasculature and Inhibits the Transendothelial Migration and Arterial Recruitment of T Cells

Background— Heparin, used clinically as an anticoagulant, also has antiinflammatory properties and has been described to inhibit interferon (IFN)-γ responses in endothelial cells. We investigated the effects of heparin on the IFN-γ–inducible chemokines IP-10/CXCL10, I-TAC/CXCL11, and Mig/CXCL9, which play important roles in the vascular recruitment of IFN-γ–producing Th1 cells through interactions with their cognate receptor, CXCR3.

Methods and Results— Patients undergoing coronary artery bypass grafting were studied because coronary atherosclerosis is recognized as a Th1-type inflammatory disease and the subjects required systemic heparinization. Plasma levels of IP-10, I-TAC, and Mig increased immediately after heparin administration and diminished promptly after heparin antagonism with protamine. These effects were independent of detectable circulating IFN-γ or the IFN-γ inducer interleukin-12. We confirmed previous reports that heparin inhibits the IFN-γ–dependent production of CXCR3 chemokine ligands using atherosclerotic coronary arteries in organ culture. In addition to prolonged treatment decreasing chemokine secretion, heparin rapidly displaced membrane-associated IP-10 from cultured endothelial cells that did not express CXCR3 and reduced the IP-10–dependent transendothelial migration of T helper cells under conditions of venular shear stress. Finally, heparin administration to immunodeficient mouse hosts decreased both the recruitment and accumulation of memory T cells within allogeneic human coronary arteries.

Conclusions— Besides inhibiting IFN-γ responses, heparin has further immunomodulatory effects by competing for binding with IP-10, I-TAC, and Mig on endothelial cells. Disruption of CXCR3 + Th1 cell trafficking to arteriosclerotic arteries may contribute to the therapeutic efficacy of heparin in inflammatory arterial diseases, and nonanticoagulant heparin derivatives may represent a novel antiinflammatory strategy.

The unfolded protein response is an important regulator of inflammatory genes in endothelial cells

OBJECTIVE

Oxidized 1-palmitoyl-2-arachidonyl-sn-3-glycero-phosphorylcholine (oxPAPC) accumulates in atherosclerotic lesions and in vitro studies suggest that it mediates chronic inflammatory response in endothelial cells (ECs). The goal of our studies was to identify pathways mediating the induction of inflammatory genes by oxPAPC.

METHODS AND RESULTS

Using expression arrays, quantitative polymerase chain reaction (PCR), and immunoblotting we demonstrate that oxPAPC leads to endoplasmic reticulum stress and activation of the unfolded protein response (UPR) in human aortic ECs. Immunohistochemistry analysis of human atherosclerotic lesions indicated that UPR is induced in areas containing oxidized phospholipids. Using the UPR inducing agent tunicamycin and selective siRNA targeting of the ATF4 and XBP1 branches of the UPR, we demonstrate that these transcription factors are essential mediators of IL8, IL6, and MCP1 expression in human aortic ECs required for maximal inflammatory gene expression in the basal state and after oxPAPC treatment. We also identify a novel oxPAPC-induced chemokine, the CXC motif ligand 3 (CXCL3), and show that its expression requires XBP1.

CONCLUSIONS

These data suggest that the UPR pathway is a general mediator of vascular inflammation and EC dysfunction in atherosclerosis, and, likely, other inflammatory disorders.

Circulating adhesion molecules levels in type 2 diabetes mellitus and hypertension

BACKGROUND

Risk factors for atherosclerosis such as hypertension, type 2 diabetes, obesity and dyslipidemia affect endothelial function and stimulate adhesion molecules expression. The aim of the study was to examine endothelial activation in type 2 diabetes and hypertension as indicated by adhesion molecule levels and further to investigate whether the coexistence of the above conditions has a different effect.

METHODS

Serum levels of soluble E-selectin, ICAM-1 and VCAM-1 were measured in 17 hypertensive type 2 diabetic patients (DM-HY), 32 normotensive type 2 diabetic patients (DM), 11 hypertensive nondiabetic patients (HY) and 15 healthy subjects.

RESULTS

In diabetic patients (either DM-HY or DM), soluble E-selectin levels were significantly increased compared to healthy subjects (p<0.001). In HY patients, both sE-selectin (66.44+/-71.59 vs. 29.42+/-15.56 ng/ml, p=0.033) and sVCAM-1 (1529+/-433.33 vs. 1027+/-243.56 ng/ml, p=0.03) levels were found significantly higher compared to healthy subjects (p<0.05). The coexistence of diabetes and hypertension (DM-HY) did not have an additive effect on circulating adhesion molecules levels compared with the levels observed in either diabetes or hypertension. Systolic and diastolic blood pressure (BP) were independent factors correlated respectively with sE-selectin and sVCAM-1 levels (R=0.454, p=0.034 and R=0.578, p=0.005) in nondiabetic subjects (hypertensive and normotensive).

CONCLUSIONS

Type 2 diabetes mellitus and hypertension induce endothelial activation as indicated by elevated levels of soluble adhesion molecules. This effect is not different when comorbidity is present.

Up-regulated expression of the CXCR2 ligand KC/GRO-alpha in atherosclerotic lesions plays a central role in macrophage accumulation and lesion progression

Macrophage-mediated inflammation is central to atherogenesis. We have determined previously that the CXC chemokine receptor CXCR2 is involved in advanced atherosclerosis. We sought to determine whether one of the ligands of CXCR2, KC/GRO-alpha, can also modulate atherogenesis. KC/GRO-alpha(-/-) mice were generated and mated with the atherosclerosis-prone LDLR(-/-) mice. There was a significant reduction in atherosclerosis in mice lacking KC/GRO-alpha; however, this reduction was only approximately half that seen previously in mice lacking CXCR2 in the leukocyte. To determine whether CXCR2 is involved in the early formation of atherosclerosis, leukocyte-specific CXCR2(-/-) chimeric mice on LDLR(-/-) background were generated. Early fatty streak lesion formation in these mice was not affected by leukocyte CXCR2 deficiency whereas lesions were less developed in mice lacking leukocyte CXCR2 when atherosclerosis was allowed to progress to the intermediate stage. Macrophages were relatively sparse in the lesions of leukocyte CXCR2(-/-) mice despite robust MCP-1 expression. These studies indicate that KC/GRO-alpha/CXCR2 does not play a critical role in recruitment of macrophages into early atherosclerotic lesions but both arterial KC/GRO-alpha and leukocyte-specific CXCR2 expression are central to macrophage accumulation in established fatty streak lesions.

GRO family chemokines are specialized for monocyte arrest from flow

Chemokines participate in various processes of monocyte recruitment including monocyte arrest and migration. Our group and others have demonstrated that growth-related oncogene (GRO)-alpha (CXCL1) can support monocyte arrest in models of inflammation. Here we employed a parallel plate-flow chamber and Transwell reconstitution assay to test whether GRO family chemokines were sufficient for Mono Mac 6 (a human monocytic cell line) and isolated human monocyte recruitment. Our study shows that 1) GRO-alpha, -beta (CXCL2), and -gamma (CXCL3) all act as arrest chemokines for monocyte adhesion on vascular cell adhesion molecule (VCAM)-1 under flow in the presence of P-selectin; 2) CXCR2 is the functional receptor for GRO-family chemokines in monocyte arrest; however, CXCR2 is not an arrest chemokine receptor in general, since epithelial neutrophil-activating peptide ENA-78 failed to arrest monocytes; 3) GRO-alpha, -beta, and -gamma all fail to increase intracellular free Ca2+ or mediate monocyte chemotaxis; and 4) signaling through G alpha(i) protein, phosphoinositide 3-kinase, and actin polymerization but not Ca2+ mobilization or the mitogen-activated kinases p38 and MAPK/extracellular signal-related kinase are necessary for GRO-alpha-mediated Mono Mac 6 cell arrest under flow. We conclude that the GRO-family chemokines are specialized monocyte-arrest chemokines. Their role in monocyte recruitment in inflammation can be inhibited by blocking CXCR2 function or downstream signaling events.

Inflammatory mediators in atherosclerotic vascular disease

An impressive body of work has established the current paradigm of atherosclerosis as an inflammatory process that promotes lesion development and progression. Early atheroma formation is characterized by leukocyte recruitment and expression of inflammatory mediators which is confounded in the context of hyperlipidemia. Evidence for an involvement of both innate and adaptive immunity in lesion formation has emerged, supporting a causal relation between the balance of pro- and anti-inflammatory cytokines and atherogenesis. The function of chemokines in distinct steps during mononuclear cell recruitment to vascular lesions has been studied in genetically deficient mice and other suitable models, and displays a high degree of specialization and cooperation. The contribution of platelet chemokines deposited on endothelium to monocyte arrest, differences in the presentation and involvement of chemokines between native and neointimal lesion formation, and related functions of macrophage migration inhibitory factor, a cytokine with striking structural homology to chemokines are of note. A novel role of chemokines in the recruitment of vascular progenitors during neointimal hyperplasia and in the recovery of endothelial denudation underscores their relevance for atherosclerotic vascular disease. The functional diversity of chemokines in vascular inflammation may potentially allow the selective therapeutic targeting of different atherosclerotic conditions.

Chemokines

Understanding the increasingly complex role of chemokines in various manifestations of atherosclerotic vascular disease and the apparent redundancy in their expression requires improved concepts defining the specialization and cooperation of chemokines in regulating the recruitment of mononuclear cells to vascular lesions. In an attempt to elaborate such models, this review highlights recent insights into the functional role of chemokines in mediating distinct steps during the atherogenic recruitment of monocytes and T cells obtained in genetically deficient mice and in suitable models. A particular focus is placed on the contribution of platelet chemokines deposited on endothelium for monocyte arrest, on differences in the involvement of chemokines between recruitment to native lesions and to neointimal lesions after arterial injury, and on closely related functions of macrophage migration inhibitory factor, a cytokine with considerable structural homology to chemokines. As an evolving aspect of atherosclerotic vascular disease, a role of chemokines, foremost stromal cell-derived factor-1alpha, in the recruitment of mononuclear progenitors of vascular cells during neointimal hyperplasia, endothelial recovery, and angiogenesis is discussed. The functional diversity and pleiotropy of chemokines in and beyond mononuclear cell recruitment awaits further elucidation to enable therapeutic targeting of atherogenesis by context-specific blockade of nonoverlapping chemokine receptor pairs.

The oxidation hypothesis of atherogenesis: the role of oxidized phospholipids and HDL

For more than two decades, there has been continuing evidence of lipid oxidation playing a central role in atherogenesis. The oxidation hypothesis of atherogenesis has evolved to focus on specific proinflammatory oxidized phospholipids that result from the oxidation of LDL phospholipids containing arachidonic acid and that are recognized by the innate immune system in animals and humans. These oxidized phospholipids are largely generated by potent oxidants produced by the lipoxygenase and myeloperoxidase pathways. The failure of antioxidant vitamins to influence clinical outcomes may have many explanations, including the inability of vitamin E to prevent the formation of these oxidized phospholipids and other lipid oxidation products of the myeloperoxidase pathway. Preliminary data suggest that the oxidation hypothesis of atherogenesis and the reverse cholesterol transport hypothesis of atherogenesis may have a common biological basis. The levels of specific oxidized lipids in plasma and lipoproteins, the levels of antibodies to these lipids, and the inflammatory/anti-inflammatory properties of HDL may be useful markers of susceptibility to atherogenesis. Apolipoprotein A-I (apoA-I) and apoA-I mimetic peptides may both promote a reduction in oxidized lipids and enhance reverse cholesterol transport and therefore may have therapeutic potential.

Apoptotic cells as sources for biologically active oxidized phospholipids

Acute inflammation is characterized by an accumulation of polymorphonuclear cells (PMNs), generation of reactive oxygen species, subsequent apoptosis of PMNs, and finally phagocytosis of apoptotic cells by macrophages. Recently, it has been demonstrated that during apoptosis oxidation of membrane phospholipids, especially phosphatidylserine, occurs. Moreover, we have shown that membrane vesicles released from apoptotic cells contain biologically active oxidized phospholipids. The involvement of oxidized phospholipids in the development of atherosclerosis, which is described as a chronic inflammatory disease, is increasingly recognized. These oxidized phospholipids were shown to induce several proinflammatory genes, such as monocyte chemoattractant protein 1 or interleukin-8, and it is hypothesized that lipid oxidation products also play a role in other chronic inflammatory disorders. On the other hand, oxidized phospholipids were shown to exert antiendotoxin effects by inhibiting lipopolysaccharide-induced signaling, representing a possible feedback loop during gram-negative infection. Additionally, it has been described that oxidized phospholipids are capable of inducing genes such as heme oxygenase-1 that are important for the resolution of acute inflammation. Moreover, oxidized phospholipids serve as recognition signals on apoptotic cells facilitating phagocytosis. In this review, we discuss the hypothesis that oxidized phospholipids generated in apoptotic cells (a) propagate chronic inflammation and (b) contribute to the resolution of acute inflammation.

Endotoxin stimulates monocyte-endothelial cell interactions in mouse intestinal Peyer's patches and villus mucosa

Although monocyte-endothelial cell interactions represent an initial step in controlling the recruitment of monocytes in inflamed tissues, their dynamic processes in microvessels of lymphoid (Peyer's patches) and non-lymphoid (villus) regions in gut-associated lymphoid tissue remain poorly understood. We monitored the migration of fluorescence-labelled monocytes derived from the spleen in intestinal microvessels with or without lipopolysaccharide (LPS) treatment and investigated the role of adhesion molecules, P-selectin, vascular cell adhesion molecule (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1). In control mice, there were few interactions between infused monocytes and the endothelium of intestinal microvessels. The monocyte-endothelial interactions (both rolling and adhesion) were significantly increased in intestinal microvessels of LPS-treated mice compared with those in controls. Anti-P-selectin monoclonal antibody (MoAb) significantly suppressed the LPS-induced increase in monocyte rolling in postcapillary venules of Peyer's patches and submucosal venules. Anti-VCAM-1 MoAbs significantly suppressed the LPS-induced increase in monocyte adhesion to postcapillary venules (PCVs) of Peyer's patches, submucosal venules, and villus capillaries. In contrast, anti-ICAM-1 MoAb significantly suppressed the number of adherent monocytes in PCV of Peyer's patches but not in submucosal venules or villus capillaries. These observations demonstrated that LPS treatment resulted in a significant increase in recruitment of monocytes both in microvessels of lymphoid and non-lymphoid regions and that P-selectin, VCAM-1 and ICAM-1 appeared to play important roles in LPS-induced interactions.

Lesion Progression in apoE-Deficient Mice: Implication of Chemokines and Effect of the AT1 Angiotensin II Receptor Antagonist Irbesartan

We recently described that a treatment with the angiotensin AT1 receptor antagonist irbesartan inhibits atherosclerotic lesion development, macrophage accumulation, and monocyte chemoattractant protein-1 (MCP-1) as well as the chemokine KC expression in apolipoprotein E-deficient (apoE-deficient) mice. The present study addresses whether these and other chemokines are expressed not only during the initiation but also during the development of atherosclerotic lesions and whether irbesartan can inhibit the expression of these chemokines during lesion progression. The time course of lesion development was assessed in apoE-deficient mice aged 1 to 9 months and the relative expression of chemokines was quantified by RT-PCR. Significant lesion formation already appeared in 3-month-old apoE-deficient mice, and progressed further to the age of 9 months. The expression of MCP-1 and KC (the mouse homologue of Groalpha), was induced at 1 month in apoE-deficient as compared with wild type (C57/Bl6) mice, and was observed before any detectable histologic changes. MCP-1 and KC expression remained high during lesion progression. The expression of macrophage inflammatory protein-2 (MIP-2, the mouse Grobeta/gamma homologue) and macrophage inflammatory protein-1alpha (MIP-1alpha) was increased in lesions from 4-month-old mice onward, whereas Regulated upon Activation of Normal T-cells Expressed and Secreted (RANTES) was significantly induced in 6- to 9-month-old mice only. Irbesartan (50 mg/kg/d) administered from the age of 3 months onward significantly reduced the progression of the lesions as well as the expression of the chemokines. A short-term treatment with irbesartan significantly inhibited the expression of MCP-1 and KC, suggesting that activation of the renin-angiotensin system is involved in up-regulation of these chemokines and that this effect represents a potential mechanism by which irbesartan inhibits plaque development and progression.

A potent and selective nonpeptide antagonist of CXCR2 inhibits acute and chronic models of arthritis in the rabbit

Much evidence implicates IL-8 as a major mediator of inflammation and joint destruction in rheumatoid arthritis. The effects of IL-8 and its related ligands are mediated via two receptors, CXCR1 and CXCR2. In the present study, we demonstrate that a potent and selective nonpeptide antagonist of human CXCR2 potently inhibits (125)I-labeled human IL-8 binding to, and human IL-8-induced calcium mobilization mediated by, rabbit CXCR2 (IC(50) = 40.5 and 7.7 nM, respectively), but not rabbit CXCR1 (IC(50) = >1000 and 2200 nM, respectively). These data suggest that the rabbit is an appropriate species in which to examine the anti-inflammatory effects of a human CXCR2-selective antagonist. In two acute models of arthritis in the rabbit induced by knee joint injection of human IL-8 or LPS, and a chronic Ag (OVA)-induced arthritis model, administration of the antagonist at 25 mg/kg by mouth twice a day significantly reduced synovial fluid neutrophils, monocytes, and lymphocytes. In addition, in the more robust LPS- and OVA-induced arthritis models, which were characterized by increased levels of proinflammatory mediators in the synovial fluid, TNF-alpha, IL-8, PGE(2), leukotriene B(4), and leukotriene C(4) levels were significantly reduced, as was erythrocyte sedimentation rate, possibly as a result of the observed decreases in serum TNF-alpha and IL-8 levels. In vitro, the antagonist potently inhibited human IL-8-induced chemotaxis of rabbit neutrophils (IC(50) = 0.75 nM), suggesting that inhibition of leukocyte migration into the knee joint is a likely mechanism by which the CXCR2 antagonist modulates disease.

Oxidized lipids as mediators of coronary heart disease

PURPOSE OF REVIEW

To summarize the recent evidence on the physiological relevance of the view that LDL lipid oxidation may play a major role in the inflammatory reaction that leads to or amplifies atherogenesis. Oxidation of LDL phospholipids containing arachidonic acid at the sn-2 position occurs when a critical concentration of 'seeding molecules' derived from the lipoxygenase pathway is reached in LDL. This generates a series of biologically active, oxidized phospholipids that mediate the cellular events seen in the developing fatty streak.

RECENT FINDINGS

We have observed that LDL from mice that are genetically predisposed to diet-induced atherosclerosis is highly proinflammatory when the mice are maintained on an atherogenic diet, when they are injected with LDL-derived oxidized phospholipids, or once they are infected with influenza A virus. Patients with coronary atherosclerosis also had highly proinflammatory LDL, despite having normal blood lipid levels or normal plasma HDL levels.

SUMMARY

We and others have hypothesized that HDL and LDL-derived oxidized phospholipids may be part of a system of nonspecific innate immunity. We therefore propose that determination of HDL capacity against LDL oxidation and the detection of proinflammatory HDL may be a useful marker of susceptibility to atherosclerosis.

Hypercholesterolaemia and circulating levels of CXC chemokines in apoE*3 Leiden mice

Hyperlipidaemia may accelerate the development of atherosclerosis by enhancing the expression of chemokines by cells within the arterial wall. Chemokines of the CC subfamily are clearly implicated in atherogenesis; however, recent reports suggest that CXC chemokines may play a hitherto unrecognised role in monocyte recruitment into atheromatous lesions expressing these molecules. Here, we examine whether circulating levels of CXC chemokines may reflect the pathogenic changes occurring during early atherogenesis. ApoE*3 Leiden mice developed marked hypercholesterolaemia, and early Type I 'fatty streak' lesions, following consumption of an atherogenic diet high in saturated fat and cholesterol, and containing sodium cholate, for up to 4 weeks. By contrast, their non-transgenic littermates (C57BL/6J) exhibited a much less pronounced hypercholesterolaemia and did not develop fatty streak lesions, when fed the same diet. Under these conditions, serum concentrations of CXC chemokines, KC and Macrophage Inflammatory Protein-2 (MIP-2) were significantly (P<or=0.0005) elevated in apoE*3 Leiden mice consuming HFC/C diet, compared with apoE*3 Leiden mice consuming a chow diet. Further, serum concentrations of KC were significantly (P<0.02) higher at 4 weeks in apoE*3 Leiden mice fed HFC/C diet compared with their non-transgenic littermates consuming the same diet. Expression of KC mRNA was detected in both aortic and hepatic tissues of apoE*3 Leiden mice, and the non-transgenic controls. Thus, hypercholesterolaemia is associated with elevated serum concentrations of CXC chemokines, KC and MIP-2 that probably reflect chronic inflammation during atherogenesis.

The chemokine KC, but not monocyte chemoattractant protein-1, triggers monocyte arrest on early atherosclerotic endothelium

In a reconstituted flow chamber system, preincubation with chemokines can trigger the arrest of rolling monocytes, suggesting that this interaction could help recruit these cells to early atherosclerotic lesions. To date, however, the contribution of endothelium-derived chemokines found in these lesion to monocyte arrests has not been investigated. The endothelium of lesion-prone carotid arteries from apolipoprotein E-deficient (ApoE(-/-)) mice, but not control mice, presents the chemokines KC (mouse GRO-alpha) and JE (mouse monocyte chemoattractant protein-1 [MCP-1]). Arrest of a monocytic cell line or mouse blood monocytes perfused through carotid arteries of ApoE(-/-) mice was reduced by treating with either pertussis toxin, an antagonist of CXCR2, or an antibody to KC, but this process was insensitive to agents that blocked CCR-2 or JE. Conversely, monocyte accumulation more than doubled upon pre-perfusion of the carotid artery with KC but not with mouse MCP-1. Blockade of alpha(4)beta(1) integrin (VLA-4) or vascular cell adhesion molecule-1, but not CD18 or intercellular adhesion molecule-1, almost completely inhibited the arrest of monocytes. We conclude that when presented by early atherosclerotic lesions, KC but not murine MCP-1 triggers VLA-4-dependent monocyte recruitment.

HDL and the inflammatory response induced by LDL-derived oxidized phospholipids

Oxidation of low density lipoprotein (LDL) phospholipids containing arachidonic acid at the sn-2 position occurs when a critical concentration of "seeding molecules" derived from the lipoxygenase pathway is reached in LDL. When this critical concentration is reached, the nonenzymatic oxidation of LDL phospholipids produces a series of biologically active, oxidized phospholipids that mediate the cellular events seen in the developing fatty streak. Normal high density lipoprotein (HDL) contains at least 4 enzymes as well as apolipoproteins that can prevent the formation of the LDL-derived oxidized phospholipids or inactivate them after they are formed. In the sense that normal HDL can prevent the formation of or inactivate these inflammatory LDL-derived oxidized phospholipids, normal HDL is anti-inflammatory. HDL from mice that are genetically predisposed to diet-induced atherosclerosis became proinflammatory when the mice are fed an atherogenic diet, injected with LDL-derived oxidized phospholipids, or infected with influenza A virus. Mice that were genetically engineered to be hyperlipidemic on a chow diet and patients with coronary atherosclerosis, despite normal lipid levels, also had proinflammatory HDL. It is proposed that LDL-derived oxidized phospholipids and HDL may be part of a system of nonspecific innate immunity and that the detection of proinflammatory HDL may be a useful marker of susceptibility to atherosclerosis.

Biochemical and biological characterization of neutrophil chemotactic protein, a novel rabbit CXC chemokine from alveolar macrophages

The role of interleukin-8 (IL-8) and related CXC chemokines has been demonstrated in many human diseases. However, more profound studies, e.g., by blocking the effect of these inflammatory mediators, request animal models and hence the identification of all human counterparts for commonly used laboratory animals. In this study, we describe the identification of a novel neutrophil chemotactic protein (NCP) of the rabbit. Intact and NH(2)-terminally truncated NCP forms and IL-8 were isolated from LPS-stimulated rabbit alveolar macrophages and purified to homogeneity by a four-step purification procedure. Determination of the complete primary structure of NCP by mass spectrometry and NH(2)-terminal sequencing of natural protein revealed high structural homology with human epithelial cell-derived neutrophil attractant-78 (ENA-78) and granulocyte chemotactic protein-2 (GCP-2), two related ELR(+)CXC chemokines. Intact NCP(1-76) was found to be 10-fold less potent than truncated NCP(7, 8-76) at inducing neutrophil chemotaxis. NCP(7,8-76) was equally potent as intact rabbit IL-8 at chemoattracting human neutrophils and at inducing calcium fluxes in rabbit neutrophils, 1 ng/mL being the minimal effective concentration. However, like IL-8, NCP failed to induce monocyte or eosinophil migration at 300-fold higher concentrations. IL-8 desensitized the calcium increase induced by NCP and vice versa. Finally, intradermal injection of NCP induced a dose-dependent and significant infiltration of neutrophils in mice skin. It can be concluded that NCP is a novel rabbit CXC chemokine that is, like IL-8, implicated in animal models used to study various human disorders in which neutrophils play an important role.

Interleukin-8 and its receptor CXCR2 in atherosclerosis

The participation of inflammatory cells in atherosclerosis is a well-known process that involves numerous molecules including chemotactic cytokines (chemokines) for their entry into the vessel wall. Although the C-C chemokine monocyte chemoattractant protein-1 and its receptor, CCR2, have been implicated in atherosclerosis, the role of the classic C-X-C chemokine, interleukin-8 (KC/growth-related oncogene alpha in mice) and its receptor CXCR2 has not been studied in the pathogenesis of atherosclerosis. Our research has shown that CXCR2 is strongly expressed on macrophages (Mphi) in atherosclerotic lesion. This CXCR2 expression is proatherogenic in that CXCR2 deficiency significantly reduces the progression of advanced atherosclerosis in mice. Although the mechanism still needs to be worked out, it appears that CXCR2 expression on lesion Mphi is essential for these cells to be retained in the lesion.

CXC chemokine GRO is essential for neutrophil infiltration in LPS-induced uveitis in rabbits

The purpose of this study was to investigate the role and regulation of the CXC chemokine GRO and the interaction between GRO and IL-8 in LPS-induced uveitis in rabbits. Uveitis was induced by intravitreal injection of 100 ng of LPS in rabbits. After the LPS injection, GRO was produced in aqueous humor and peaked at 24 hr. Immunohistochemistry showed that ciliary epithelial cells were responsible for production of GRO. Blocking the activity of GRO by anti-GRO serum reduced LPS-induced aqueous neutrophil counts by 80%, but did not reduce the mononuclear cell counts or protein levels or IL-8 levels. Regulation of GRO production by TNFalpha, IL-1 and IL-8 was studied. Anti-TNFalphamAb alone did not inhibit the 24 hr LPS induced GRO levels, whereas rrIL-1Ra inhibited the GRO production by 58%. The combination of anti-TNFalpha mAb and rrIL-1Ra inhibited 93% of GRO production. Although treatment with anti-IL-8 IgG inhibited the neutrophil infiltration by 66%, treatment with this antibody did not inhibit GRO production. Taken together, our results suggest that GRO is an essential mediator for neutrophil infiltration in LPS-induced uveitis in rabbits. Most of GRO production is mediated by TNFalpha and IL-1. GRO and IL-8 act in concert to mediate neutrophil infiltration.

Stimulation of phospholipase D activity by oxidized LDL in mouse peritoneal macrophages

Oxidation of LDL is an important factor in the development of atherosclerosis. However, the mechanisms by which oxidized LDL exerts its atherogenic actions are poorly understood. In the present work, we show that oxidized LDL stimulates phospholipase D (PLD) activity in mouse peritoneal macrophages and that this effect increases with the degree of LDL oxidation. Oxidative modification of LDL results in the production of lipid peroxides and the conversion of phosphatidylcholine to lysophosphatidylcholine. Although we found that lysophosphatidylcholine alone activates PLD, the stimulation of this enzyme activity by oxidized LDL is independent of lysophosphatidylcholine formation. Also, 7-ketocholesterol, the major oxysterol in oxidized LDL, failed to stimulate PLD activity. To determine the mechanism(s) whereby oxidized LDL activates PLD, the possible involvements of protein kinase C and tyrosine phosphorylation were investigated. Pretreatment of macrophages with the protein kinase C inhibitor Ro-32-0432 or downregulation of protein kinase C activity by prolonged incubation with 100 nmol/L 4beta-phorbol 12-myristate 13-acetate did not alter the stimulatory effect of oxidized LDL on PLD activation. However, oxidized LDL stimulated tyrosine phosphorylation of several macrophage proteins, and preincubation of the macrophages with genistein, a tyrosine kinase inhibitor, blocked the activation of PLD by oxidized LDL. In addition, pretreatment with orthovanadate, which inhibits tyrosine phosphatases, enhanced basal and oxidized LDL-stimulated PLD activity. Pretreatment of macrophages with pertussis toxin decreased the stimulatory effect of oxidized LDL, indicating that GTP-binding proteins may also be involved in the activation of PLD by oxidized LDL. We also found that the platelet-activating factor receptor antagonists WEB 2086 and L-659,989 inhibit the oxidized LDL stimulation of PLD, suggesting a role for platelet-activating factor receptor in this process. The stimulation of the PLD pathway by oxidized LDL may be of importance in atherogenesis, because PLD activation leads to generation of important second messengers such as phosphatidate, lysophosphatidate, and diacylglycerol, which are known to regulate many cellular functions.