Christina A. Bursill

CCR1 and CCR5 promote hepatic fibrosis in mice

Hepatic fibrosis develops as a response to chronic liver injury and almost exclusively occurs in a proinflammatory environment. However, the role of inflammatory mediators in fibrogenic responses of the liver is only poorly understood. We therefore investigated the role of CC chemokines and their receptors in hepatic fibrogenesis. The CC chemokines MIP-1alpha, MIP-1beta, and RANTES and their receptors CCR1 and CCR5 were strongly upregulated in 2 experimental mouse models of fibrogenesis. Neutralization of CC chemokines by the broad-spectrum CC chemokine inhibitor 35k efficiently reduced hepatic fibrosis, and CCR1- and CCR5-deficient mice displayed substantially reduced hepatic fibrosis and macrophage infiltration. Analysis of fibrogenesis in CCR1- and CCR5-chimeric mice revealed that CCR1 mediates its profibrogenic effects in BM-derived cells, whereas CCR5 mediates its profibrogenic effects in resident liver cells. CCR5 promoted hepatic stellate cell (HSC) migration through a redox-sensitive, PI3K-dependent pathway. Both CCR5-deficient HSCs and CCR1- and CCR5-deficient Kupffer cells displayed strong suppression of CC chemokine-induced migration. Finally, we detected marked upregulation of RANTES, CCR1, and CCR5 in patients with hepatic cirrhosis, confirming activation of the CC chemokine system in human fibrogenesis. Our data therefore support a role for the CC chemokine system in hepatic fibrogenesis and suggest distinct roles for CCR1 and CCR5 in Kupffer cells and HSCs.

Magnetic Resonance Imaging of Endothelial Adhesion Molecules in Mouse Atherosclerosis Using Dual-Targeted Microparticles of Iron Oxide

Objective—Microparticles of iron oxide (MPIO) distort magnetic field creating marked contrast effects far exceeding their physical size. We hypothesized that antibody-conjugated MPIO would enable magnetic resonance imaging (MRI) of endothelial cell adhesion molecules in mouse atherosclerosis. Methods and Results—MPIO (4.5 &mgr;m) were conjugated to monoclonal antibodies against vascular cell adhesion molecule-1 (VCAM–MPIO) or P-selectin (P-selectin–MPIO). In vitro, VCAM–MPIO bound, in dose-dependent manner, to tumor necrosis factor (TNF)-&agr; stimulated sEND-1 endothelial cells, as quantified by light microscopy (R2=0.94, P=0.03) and by MRI (R2=0.98, P=0.01). VCAM–MPIO binding was blocked by preincubation with soluble VCAM-1. To mimic leukocyte binding, MPIO targeting both VCAM-1 and P-selectin were administered in apolipoprotein E−/− mice. By light microscopy, dual-targeted MPIO binding to endothelium overlying aortic root atherosclerosis was 5- to 7-fold more than P-selectin–MPIO (P<0.05) or VCAM–MPIO (P<0.01) alone. Dual-targeted MPIO, injected intravenously in vivo bound aortic root endothelium and were quantifiable by MRI ex vivo (3.5-fold increase versus control; P<0.01). MPIO were well-tolerated in vivo, with sequestration in the spleen after 24 hours. Conclusions—Dual-ligand MPIO bound to endothelium over atherosclerosis in vivo, under flow conditions. MPIO may provide a functional MRI probe for detecting endothelial-specific markers in a range of vascular pathologies.

Smooth muscle cells in human atherosclerotic plaques express the fractalkine receptor CX3CR1 and undergo chemotaxis to the CX3C chemokine fractalkine (CX3CL1).

Background—Chemokines are important mediators of inflammatory cell recruitment that play a significant role in atherosclerosis. Fractalkine (CX3CL1) is an unusual membrane-bound chemokine that mediates chemotaxis through the CX3CR1 receptor. Recently, functional polymorphisms in the human CX3CR1 gene have been described that are associated with coronary artery disease. Methods and Results—We investigated the expression of the CX3C chemokine fractalkine and its receptor CX3CR1 in human coronary artery plaques by immunocytometry. We show that a subset of mononuclear cells expresses high levels of fractalkine in human coronary atherosclerotic plaques and that smooth muscle cells within the neointima express the fractalkine receptor CX3CR1. There is a positive correlation between the number of fractalkine-expressing cells and the number of CX3CR1-positive cells in human atherosclerotic plaques (r =0.70, n=15 plaques). Furthermore, we demonstrate that cultured vascular smooth muscle cells express the CX3CR1 receptor and undergo chemotaxis to fractalkine that can be inhibited by G protein inactivation by pertussis toxin. Conclusions—These results suggest that in human atherosclerosis, fractalkine, rather than mediating inflammatory cell recruitment, can act as a mediator of smooth muscle cell migration.

The role of chemokines in atherosclerosis: recent evidence from experimental models and population genetics.

Purpose of review Atherosclerosis is an inflammatory disease process. This review discusses the recent genetic evidence from animal models and human populations that highlight the importance of chemokines in atherosclerosis. Recent findings CC-chemokine/CC-chemokine receptors (CCR), including CCR2/ MCP-1 (monocyte chemoattractant protein-1) and CCR5/RANTES (regulated on activation, normal T-cell expressed and secreted), have been shown in animal knockout and transgenic studies to have significant effects on atherosclerotic lesion size and macrophage recruitment. More recently fractalkine (CX3C1) and its receptor (CX3CR1) have emerged as another important pathway in atherosclerosis. For example, fractalkine is present in human atherosclerotic lesions and is able to stimulate platelet activation and adhesion. CX3CR1 is expressed on human aortic smooth muscle cells and CX3CR1/apolipoprotein E double knockout mice have significantly reduced atherosclerotic lesion size and macrophage recruitment. Human population genetic studies have tried to assess the importance of chemokines in human atherosclerosis. Currently, there is conflicting evidence regarding an association between polymorphisms in CCR2/MCP-1 and CCR5/RANTES and coronary artery disease. There is evidence, however, for an association between the fractalkine receptor polymorphism (CX3CR1-I249) and coronary artery disease in both human population and function studies. Summary Recent transgenic and gene knockout studies in murine models of atherosclerosis have highlighted the importance of chemokines and their receptors in atherosclerosis. Genetic evidence for a role of chemokines and their receptors in human population studies remains under investigation. Identifying chemokine polymorphisms could help to determine pathways that are important in atherosclerosis disease pathology and that may suggest novel therapeutic targets.

High-Density Lipoproteins Suppress Chemokines and Chemokine Receptors In Vitro and In Vivo

Objective—To investigate whether high-density lipoproteins (HDLs) suppress chemokine (CCL2, CCL5, and CX3CL1) and chemokine receptor (CCR2 and CX3CR1) expression, a mechanism for the atheroprotective properties of HDLs. Methods and Results—Apolipoprotein (apo) E−/− mice were fed a high-fat diet for 12 weeks. Before being euthanized, the mice received 5 consecutive daily injections of lipid-free apoA-I, 40 mg/kg, or saline (control). The injection of apoA-I reduced CCR2 and CX3CR1 expression in plaques compared with controls (P<0.05). ApoA-I–injected mice had lower plasma CCL2 and CCL5 levels. Hepatic CCL2, CCL5, and CX3CL1 levels were also reduced (P<0.05). In vitro studies found that reconstituted HDL (rHDL) reduced monocyte CCR2 and CX3CR1 expression and inhibited their migration toward CCL2 and CX3CL1 (P<0.05). Preincubation with rHDL reduced CCL2, CCL5, and CX3CL1 expression in monocytes and human coronary artery endothelial cells. The stimulation of CX3CR1 with peroxisome proliferator–activated receptor &ggr; agonist CAY10410 was suppressed by preincubation with rHDL but did not affect the peroxisome proliferator–activated receptor &ggr; antagonist (GW9664)–mediated increase in CCR2. In monocytes and human coronary artery endothelial cells, rHDL reduced the expression of the nuclear p65 subunit, I&kgr;B kinase activity, and the phosphorylation of I&kgr;B&agr; (P<0.05). Conclusion—Lipid-free apoA-I and rHDL reduce the expression of chemokines and chemokine receptors in vivo and in vitro via modulation of nuclear factor &kgr;B and peroxisome proliferator–activated receptor &ggr;.

Broad-Spectrum CC-Chemokine Blockade by Gene Transfer Inhibits Macrophage Recruitment and Atherosclerotic Plaque Formation in Apolipoprotein E–Knockout Mice

Background—The CC-chemokines (CKs) recruit monocytes/macrophages to sites of inflammation; several different CC-CKs play a role in the pathogenesis of atherosclerosis. The vaccinia virus expresses a 35-kDa soluble protein (35K) that binds to and inactivates nearly all of the CC-CKs, providing a potentially useful therapeutic strategy for broad-spectrum CC-CK inhibition in atherosclerosis. A recombinant adenovirus encoding soluble 35K (Ad35K) was generated to investigate the effect of 35K gene transfer on atherosclerosis in Western diet–fed apolipoprotein E–knockout (ApoE KO) mice. Methods and Results—ApoE KO mice received tail-vein injections of phosphate-buffered saline, Ad35K, or control adenovirus AdGFP encoding green fluorescence protein. Two weeks after Ad35K gene transfer, atherosclerotic lesion area was significantly reduced in aortic roots by 55% compared with PBS or AdGFP control mice (P<0.05). Furthermore, 35K gene transfer strikingly reduced the macrophage content in aortic root lesions by 85% (P<0.01) and reduced lipid deposition in descending aortas by more than half (P<0.05). By an in vitro chemotaxis assay, plasma and aortic homogenates from 35K gene transfer mice promoted significantly less CC-CK–induced cell migration than did PBS or AdGFP controls. Conclusions—These findings show that a single intravenous injection of a recombinant adenovirus encoding the broad-spectrum CC-CK inhibitor 35K can reduce atherosclerosis by inhibiting CC-CK–induced macrophage recruitment in atherosclerotic ApoE KO mice. These experiments suggest that CC-CKs play an important role in atherogenesis and are a rational target for therapeutic intervention.

Murine Model of Wound Healing

Wound healing and repair are the most complex biological processes that occur in human life. After injury, multiple biological pathways become activated. Impaired wound healing, which occurs in diabetic patients for example, can lead to severe unfavorable outcomes such as amputation. There is, therefore, an increasing impetus to develop novel agents that promote wound repair. The testing of these has been limited to large animal models such as swine, which are often impractical. Mice represent the ideal preclinical model, as they are economical and amenable to genetic manipulation, which allows for mechanistic investigation. However, wound healing in a mouse is fundamentally different to that of humans as it primarily occurs via contraction. Our murine model overcomes this by incorporating a splint around the wound. By splinting the wound, the repair process is then dependent on epithelialization, cellular proliferation and angiogenesis, which closely mirror the biological processes of human wound healing. Whilst requiring consistency and care, this murine model does not involve complicated surgical techniques and allows for the robust testing of promising agents that may, for example, promote angiogenesis or inhibit inflammation. Furthermore, each mouse acts as its own control as two wounds are prepared, enabling the application of both the test compound and the vehicle control on the same animal. In conclusion, we demonstrate a practical, easy-to-learn, and robust model of wound healing, which is comparable to that of humans.

Colchicine Acutely Suppresses Local Cardiac Production of Inflammatory Cytokines in Patients With an Acute Coronary Syndrome

Background Interleukin (IL)-1β, IL-18, and downstream IL-6 are key inflammatory cytokines in the pathogenesis of coronary artery disease. Colchicine is believed to block the NLRP3 inflammasome, a cytosolic complex responsible for the production of IL-1β and IL-18. In vivo effects of colchicine on cardiac cytokine release have not been previously studied. This study aimed to (1) assess the local cardiac production of inflammatory cytokines in patients with acute coronary syndromes (ACS), stable coronary artery disease and in controls; and (2) determine whether acute administration of colchicine inhibits their production. Methods and Results Forty ACS patients, 33 with stable coronary artery disease, and 10 controls, were included. ACS and stable coronary artery disease patients were randomized to oral colchicine treatment (1 mg followed by 0.5 mg 1 hour later) or no colchicine, 6 to 24 hours prior to cardiac catheterization. Blood samples from the coronary sinus, aortic root (arterial), and lower right atrium (venous) were collected and tested for IL-1β, IL-18, and IL-6 using ELISA. In ACS patients, coronary sinus levels of IL-1β, IL-18, and IL-6 were significantly higher than arterial and venous levels (P=0.017, <0.001 and <0.001, respectively). Transcoronary (coronary sinus-arterial) gradients for IL-1β, IL-18, and IL-6 were highest in ACS patients and lowest in controls (P=0.077, 0.033, and 0.014, respectively). Colchicine administration significantly reduced transcoronary gradients of all 3 cytokines in ACS patients by 40% to 88% (P=0.028, 0.032, and 0.032, for IL-1β, IL-18, and IL-6, respectively). Conclusions ACS patients exhibit increased local cardiac production of inflammatory cytokines. Short-term colchicine administration rapidly and significantly reduces levels of these cytokines.

Gene transfer of a broad spectrum CC-chemokine inhibitor reduces vein graft atherosclerosis in apolipoprotein E-knockout mice.

Background—Accelerated atherosclerosis is a major cause of vein graft failure after bypass surgery. Several CC-chemokines (CC-CKs) mediate monocyte/macrophage recruitment in native atherosclerotic plaques; we hypothesized that CC-CKs may be critical in the development of accelerated atherosclerosis in vein grafts. Methods and Results—Using in vivo gene transfer, we administered a soluble CC-CK binding protein (“35K”) to apolipoprotein E–knockout (ApoE−/−) mice that underwent interposition bypass grafting of the vena cava from isogenic donor mice to the common carotid artery. Two days before operation, a recombinant adenovirus encoding either 35K (Ad35K) or green fluorescent protein (AdGFP; control) was injected into recipient mice via the tail vein. 35K greatly reduced CC-CK activity in mouse plasma. After 14 days, vein graft atherosclerotic lesion area, smooth muscle α-actin–positive neointimal area, and total vessel wall thickness were strikingly reduced by Ad35K gene transfer compared with AdGFP controls. Furthermore, 35K gene transfer dramatically reduced macrophage content by ≈90% and cell proliferation by 95%. After 28 days, lesion area and vessel wall thickness remained significantly less in Ad35K mice. Conclusion—A single intravenous injection of the CC-CK inhibitor 35K significantly reduced atherosclerosis in carotid–caval vein grafts in ApoE−/− mice. This study highlights the importance of the CC-CK class in accelerated atherosclerosis, and its role as a potential target for improving vein graft patency.

The apolipoprotein A-I mimetic peptide ETC-642 exhibits anti-inflammatory properties that are comparable to high density lipoproteins

OBJECTIVES Mimetic peptides of apolipoprotein A-I (apoA-I) present a new strategy for promoting the biological activity of high density lipoproteins (HDL). This study aimed to compare the anti-inflammatory effects of ETC-642, a new apoA-I mimetic peptide, with discoidal reconstituted HDL (rHDL). METHODS New Zealand White rabbits (n=42) received daily infusions of saline, rHDL or discoidal complexes of an amphipathic peptide, ETC-642 (1-30 mg/kg), prior to insertion of non-occlusive carotid collars. Human coronary artery endothelial cells (HCAECs) were pre-incubated with ETC-642 or rHDL before TNF-α stimulation. Monocyte adhesion was investigated by pre-incubating HCAECs with rHDL or ETC-642, stimulating with TNF-α and incubating with THP-1 monocytes. RESULTS Infusion of ETC-642 resulted in dose-dependent reductions of collar-induced expression of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) in the artery wall (p<0.05). Pre-incubation of HCAECs with ETC-642 and rHDL reduced TNF-α-induced THP-1 monocyte adhesion (p<0.01). Furthermore, ETC-642 and rHDL treatment reduced TNF-α induced mRNA levels of inflammatory markers VCAM-1, fractalkine, MCP-1 and the p65 subunit of NF-κB (p<0.05). CONCLUSION These studies demonstrate that ETC-642 exhibits anti-inflammatory properties that are comparable to apoA-I both in vivo and in vitro and that these effects are mediated via the NF-κB signaling pathway.