Rounding up the usual suspects in atherosclerosis. Focus on “Growth factors induce monocyte binding to vascular smooth muscle”

Conditioned medium from stem cells derived from human exfoliated deciduous teeth ameliorates NASH via the Gut-Liver axis

Non-alcoholic steatohepatitis (NASH) occurrence has been increasing and is becoming a major cause of liver cirrhosis and liver cancer. However, effective treatments for NASH are still lacking. We examined the benefits of serum-free conditioned medium from stem cells derived from human exfoliated deciduous teeth (SHED-CM) on a murine non-alcoholic steatohepatitis (NASH) model induced by a combination of Western diet (WD) and repeated administration of low doses of carbon tetrachloride intraperitoneally, focusing on the gut-liver axis. We showed that repeated intravenous administration of SHED-CM significantly ameliorated histological liver fibrosis and inflammation in a murine NASH model. SHED-CM inhibited parenchymal cell apoptosis and reduced the activation of inflammatory macrophages. Gene expression of pro-inflammatory and pro-fibrotic mediators (such as Tnf-α, Tgf-β, and Ccl-2) in the liver was reduced in mice treated with SHED-CM. Furthermore, SHED-CM protected intestinal tight junctions and maintained intestinal barrier function, while suppressing gene expression of the receptor for endotoxin, Toll-like receptor 4, in the liver. SHED-CM promoted the recovery of Caco-2 monolayer dysfunction induced by IFN-γ and TNF-α in vitro. Our findings suggest that SHED-CM may inhibit NASH fibrosis via the gut-liver axis, in addition to its protective effect on hepatocytes and the induction of macrophages with unique anti-inflammatory phenotypes.

Interacting neuroendocrine and innate and acquired immune pathways regulate neutrophil mobilization from bone marrow following hemorrhagic shock

Polymorphonuclear neutrophils (PMN) are critical innate immune effector cells that either protect the host or exacerbate organ dysfunction by migrating to injured or inflamed tissues. Resuscitated hemorrhagic shock following major trauma promotes the development of organ inflammation by priming PMN migration and activation in response to a second, often trivial, stimulus (a so-called "two hit" phenomenon). PMN mobilization from bone marrow supports a sustained, hemorrhagic shock/resuscitation (HS/R)-primed migration of PMN. We addressed the role and mechanism of HS/R in regulating PMN egress from bone marrow. We demonstrate that HS/R through the alarmin HMGB1 induces IL-23 secretion from macrophages in an autocrine and TLR4 signaling-dependent manner. In turn IL-23, through an IL-17 G-CSF-mediated mechanism, induces PMN egress from bone marrow. We also show that beta-adrenergic receptor activation by catecholamine of macrophages mediates the HS/R-induced release of HMGB1. These data indicate that HS/R, a global ischemia/reperfusion stimulus, regulates PMN mobilization through a series of interacting pathways that include neuroendocrine and innate and acquired immune systems. Blocking this novel signaling axis may present a novel therapeutic target for posttrauma inflammation.

Intestinal inflammation increases the expression of the P2Y6 receptor on epithelial cells and the release of CXC chemokine ligand 8 by UDP

Epithelial cells participate in the immune response of the intestinal mucosa. Extracellular nucleotides have been recognized as inflammatory molecules. We investigated the role of extracellular nucleotides and their associated P2Y receptors in the secretion of cytokines by epithelial cells. The effect of intestinal inflammation on P2Y(6) receptor expression was determined by PCR in the mouse, rat, and human. Localization of the P2Y(6) receptor was determined by immunofluorescence microscopy in the colon of normal and dextran sulfate sodium-treated mice. The effect of P2Y(6) activation by UDP on cytokine expression and release by epithelial cells was determined using a combination of Western blots, luciferase assays, RT-PCR, cytokine Ab arrays, and ELISA. Inflammation up-regulates P2Y(2) as well as P2Y(6) receptor expression in the mucosa of the colon of colitic mice. In vitro, we demonstrated that UDP could be released by Caco-2/15 cells. We have confirmed the increased expression of P2Y(6) by challenging intestinal epithelial cell-6 and Caco-2/15 cells with TNF-alpha and IFN-gamma and showing that stimulation of epithelial cells by UDP results in an increased expression and release of CXCL8 by an ERK1/2-dependent mechanism. The increase in CXCL8 expression was associated with a transcriptional activation by the P2Y(6) receptor. This study is the first report demonstrating the implication of P2Y receptors in the inflammatory response of intestinal epithelial cells. We show for the first time that P2Y(6), as well as P2Y(2), expression is increased by the stress associated with intestinal inflammation. These results demonstrate the emergence of extracellular nucleotide signaling in the orchestration of intestinal inflammation.

Role of extracellular superoxide in neutrophil activation: interactions between xanthine oxidase and TLR4 induce proinflammatory cytokine production

Reactive oxygen species (ROS) contribute to neutrophil activation and the development of acute inflammatory processes in which neutrophils play a central role. However, there is only limited information concerning the mechanisms through which extracellular ROS, and particularly cell membrane-impermeable species, such as superoxide, enhance the proinflammatory properties of neutrophils. To address this issue, neutrophils were exposed to superoxide generating combinations of xanthine oxidase and hypoxanthine or lumazine. Extracellular superoxide generation induced nuclear translocation of nuclear factor-κB (NF-κB) and increased neutrophil production of the NF-κB-dependent cytokines tumor necrosis factor-α (TNF-α) and macrophage inhibitory protein-2 (MIP-2). In contrast, there were no changes in TNF-α or MIP-2 expression when neutrophils lacking Toll-like receptor-4 (TLR4) were exposed to extracellular superoxide. Immunoprecipitation, confocal microscopy, and fluorescence resonance energy transfer (FRET) studies demonstrated association between TLR4 and xanthine oxidase. Exposure of neutrophils to heparin attenuated binding of xanthine oxidase to the cell surface as well as interactions with TLR4. Heparin also decreased xanthine oxidase-induced nuclear translocation of NF-κB as well as production of proinflammatory cytokines. These results demonstrate that extracellular superoxide has proinflammatory effects on neutrophils, predominantly acting through an TLR4-dependent mechanism that enhances nuclear translocation of NF-κB and increases expression of NF-κB-dependent cytokines.

Systemic inflammation and remote organ injury following trauma require HMGB1

High-mobility group box 1 (HMGB1) is a 30-kDa DNA-binding protein that displays proinflammatory cytokine-like properties. HMGB1-dependent inflammatory processes have been demonstrated in models of sterile injury, including ischemia-reperfusion injury and hemorrhagic shock. Here, we tested the hypothesis that the systemic inflammatory response and associated remote organ injury that occur after peripheral tissue injury are highly dependent on HMGB1. Toll-like receptor 4 (TLR4) wild-type (WT) mice subjected to bilateral femur fracture after treatment with neutralizing antibodies to HMGB1 had lower serum IL-6 and IL-10 levels compared with mice treated with nonimmune control IgG. Similarly, compared with injured mice treated with control IgG, anti-HMGB1 antibody-treated mice had lower serum alanine aminotransferase levels and decreased hepatic and gut mucosal NF-κB DNA binding. TLR4 mutant (C3H/HeJ) mice subjected to bilateral femur fracture had less systemic inflammation and liver injury than WT controls. Residual trauma-induced systemic inflammation and hepatocellular injury were not ameliorated by treatment with a polyclonal anti-HMGB1 antibody, even though HMGB1 levels were transiently elevated just 1 h after injury in both WT and C3H/HeJ mice. Collectively, these data demonstrate a critical role for a TLR4-HMGB1 pathway in the initiation of systemic inflammation and end-organ injury following isolated peripheral tissue injury.

Characterization of heme as activator of Toll-like receptor 4

Heme is an ancient and ubiquitous molecule present in organisms of all kingdoms, composed of an atom of iron linked to four ligand groups of porphyrin. A high amount of free heme, a potential amplifier of the inflammatory response, is a characteristic feature of diseases with increased hemolysis or extensive cell damage. Here we demonstrate that heme, but not its analogs/precursors, induced tumor necrosis factor-alpha (TNF-alpha) secretion by macrophages dependently on MyD88, TLR4, and CD14. The activation of TLR4 by heme is exquisitely strict, requiring its coordinated iron and the vinyl groups of the porphyrin ring. Signaling of heme through TLR4 depended on an interaction distinct from the one established between TLR4 and lipopolysaccharide (LPS) since anti-TLR4/MD2 antibody or a lipid A antagonist inhibited LPS-induced TNF-alpha secretion but not heme activity. Conversely, protoporphyrin IX antagonized heme without affecting LPS-induced activation. Moreover, heme induced TNF-alpha and keratinocyte chemokine but was ineffective to induce interleukin-6, interleukin-12, and interferon-inducible protein-10 secretion or co-stimulatory molecule expression. These findings support the concept that the broad ligand specificity of TLR4 and the different activation profiles might in part reside in its ability to recognize different ligands in different binding sites. Finally, heme induced oxidative burst, neutrophil recruitment, and heme oxygenase-1 expression independently of TLR4. Thus, our results presented here reveal a previous unrecognized role of heme as an extracellular signaling molecule that affects the innate immune response through a receptor-mediated mechanism.

Platelet-activating factor modulates activity of cyclic nucleotides in fetal ovine pulmonary vascular smooth muscle

At birth, release of endogenous vasodilators such as nitric oxide and prostacyclin facilitate pulmonary vasodilation via the cyclic nucleotides, cGMP and cAMP. Interaction of cyclic nucleotides and platelet-activating factor (PAF)-mediated responses in pulmonary vascular smooth muscle is not known. We studied the effects of cGMP and cAMP on PAF-mediated responses in ovine fetal intrapulmonary venous smooth muscle cells. Studies were done in hypoxia or normoxia with buffer with 8-Br-cGMP (BGMP) and 8-Br-cAMP (BAMP), as well as cGMP-dependent protein kinase (PKG) and cAMP-dependent protein kinase (PKA) inhibitors. All groups were treated with 1 nM PAF and incubated for 30 min for the binding assay or 20 min for measurement of inositol 1,4,5-phosphate (IP(3)) production. BGMP and BAMP decreased PAF binding in normoxia by 63 and 14%, respectively. Incubations with the PKG inhibitor Rp-8-(4-chlorophenylthio)-guanosine-3',5'-cyclic monophosphorothioate sodium and the PKA inhibitor Rp-adenosine-3',5'-cyclic monophosphorothioate abrogated the inhibitory effects of BGMP and BAMP. PAF-stimulated IP(3) production was 8565 +/- 314 dpm/10(6) cells in hypoxia and 5418 +/- 118 dpm/10(6) cells in normoxia, a 40% decrease. BGMP attenuated PAF-stimulated IP(3) production by 67 and 37% in hypoxia and normoxia, respectively; the value for BAMP was 44% under both conditions. Pretreatment with PKG or PKA inhibitor abrogated BGMP and BAMP inhibition of IP(3) release. PAF receptor (PAFr) protein expression decreased in normoxia, but pretreatment with 10 nM PAF up-regulated PAFr expression. Pretreatment with PAF decreased expression and activities of PKG or PKA proteins in normoxia and hypoxia. Our data demonstrate the existence of cGMP/cAMP-PAF cross-talk in pulmonary vascular smooth muscle cells, which may be one mechanism by which PAFr-mediated vasoconstriction is down-regulated at birth.

Systemic inflammation and remote organ damage following bilateral femur fracture requires Toll-like receptor 4

Extensive soft tissue injury and bone fracture are significant contributors to the initial systemic inflammatory response in multiply injured patients. Systemic inflammation can lead to organ dysfunction remote from the site of traumatic injury. The mechanisms underlying the recognition of peripheral injury and the subsequent activation of the immune response are unknown. Toll-like receptors (TLRs) recognize microbial products but also may recognize danger signals released from damaged tissues. Here we report that peripheral tissue trauma initiates systemic inflammation and remote organ dysfunction. Moreover, this systemic response to a sterile local injury requires toll-like receptor 4 (TLR4). Compared with wild-type (C3H/HeOuJ) mice, TLR4 mutant (C3H/HeJ) mice demonstrated reduced systemic and hepatic inflammatory responses to bilateral femur fracture. Trauma-induced nuclear factor (NF)-κB activation in the liver required functional TLR4 signaling. CD14−/− mice failed to demonstrate protection from fracture-induced systemic inflammation and hepatocellular injury. Therefore, our results also argue against a contribution of intestine-derived LPS to this process. These findings identify a critical role for TLR4 in the rapid recognition and response pathway to severe traumatic injury. Application of these findings in an evolutionary context suggests that multicellular organisms have evolved to use the same pattern recognition receptor for surviving traumatic and infectious challenges.

Estradiol improves cardiac and hepatic function after trauma-hemorrhage: role of enhanced heat shock protein expression

Although studies indicate that 17β-estradiol administration after trauma-hemorrhage (T-H) improves cardiac and hepatic functions, the underlying mechanisms remain unclear. Because the induction of heat shock proteins (HSPs) can protect cardiac and hepatic functions, we hypothesized that these proteins contribute to the salutary effects of estradiol after T-H. To test this hypothesis, male Sprague-Dawley rats (∼300 g) underwent laparotomy and hemorrhagic shock (35–40 mmHg for ∼90 min) followed by resuscitation with four times the shed blood volume in the form of Ringer lactate. 17β-estradiol (1 mg/kg body wt) was administered at the end of the resuscitation. Five hours after T-H and resuscitation there was a significant decrease in cardiac output, positive and negative maximal rate of left ventricular pressure. Liver function as determined by bile production and indocyanine green clearance was also compromised after T-H and resuscitation. This was accompanied by an increase in plasma alanine aminotransferase (ALT) levels and liver perfusate lactic dehydrogenase levels. Furthermore, circulating levels of TNF-α, IL-6, and IL-10 were also increased. In addition to decreased cardiac and hepatic function, there was an increase in cardiac HSP32 expression and a reduction in HSP60 expression after T-H. In the liver, HSP32 and HSP70 were increased after T-H. There was no change in heart HSP70 and liver HSP60 after T-H and resuscitation. Estradiol administration at the end of T-H and resuscitation increased heart/liver HSPs expression, ameliorated the impairment of heart/liver functions, and significantly prevented the increase in plasma levels of ALT, TNF-α, and IL-6. The ability of estradiol to induce HSPs expression in the heart and the liver suggests that HSPs, in part, mediate the salutary effects of 17β-estradiol on organ functions after T-H.

Simvastatin attenuates vascular leak and inflammation in murine inflammatory lung injury

Therapies to limit the life-threatening vascular leak observed in patients with acute lung injury (ALI) are currently lacking. We explored the effect of simvastatin, a 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase inhibitor that mediates endothelial cell barrier protection in vitro, in a murine inflammatory model of ALI. C57BL/6J mice were treated with simvastatin (5 or 20 mg/kg body wt via intraperitoneal injection) 24 h before and again concomitantly with intratracheally administered LPS (2 μg/g body wt). Inflammatory indexes [bronchoalveolar lavage (BAL) myeloperoxidase activity and total neutrophil counts assessed at 24 h with histological confirmation] were markedly increased after LPS alone but significantly reduced in mice that also received simvastatin (20 mg/kg; ∼35–60% reduction). Simvastatin also decreased BAL albumin (∼50% reduction) and Evans blue albumin dye extravasation into lung tissue (100%) consistent with barrier protection. Finally, the sustained nature of simvastatin-mediated lung protection was assessed by analysis of simvastatin-induced gene expression (Affymetrix platform). LPS-mediated lung gene expression was significantly modulated by simvastatin within a number of gene ontologies (e.g., inflammation and immune response, NF-κB regulation) and with respect to individual genes implicated in the development or severity of ALI (e.g., IL-6, Toll-like receptor 4). Together, these findings confirm significant protection by simvastatin on LPS-induced lung vascular leak and inflammation and implicate a potential role for statins in the management of ALI.

Monocyte retention in the pathology of atherosclerosis

Atherosclerosis is a type of chronic inflammatory disease characterized by the presence of monocyte-derived cells in all stages. Monocytes, macrophages, dendritic and foam cells play important roles in the uptake of oxidized lipids, lesion development, and ultimate plaque disruption. Much is known about the mechanisms of monocyte recruitment in the lumen; however, the fate of monocytes after they enter the artery wall is not well understood. In this review, some of the interesting recent results related to monocyte retention after their migration across the endothelium in the pathology of atherosclerosis will be highlighted. The authors have focused on monocyte inside-out equilibrium, apoptosis and proliferation regulation, and the role of vascular smooth muscle cells in monocyte retention in atherosclerosis. They have also proposed potential treatments for atherosclerosis that target inflammation and monocyte/macrophage retention.

HMGB1 contributes to the development of acute lung injury after hemorrhage

High mobility group box 1 (HMGB1) is a novel late mediator of inflammatory responses that contributes to endotoxin-induced acute lung injury and sepsis-associated lethality. Although acute lung injury is a frequent complication of severe blood loss, the contribution of HMGB1 to organ system dysfunction in this setting has not been investigated. In this study, HMGB1 was detected in pulmonary endothelial cells and macrophages under baseline conditions. After hemorrhage, in addition to positively staining endothelial cells and macrophages, neutrophils expressing HMGB1 were present in the lungs. HMGB1 expression in the lung was found to be increased within 4 h of hemorrhage and then remained elevated for more than 72 h after blood loss. Neutrophils appeared to contribute to the increase in posthemorrhage pulmonary HMGB1 expression since no change in lung HMGB1 levels was found after hemorrhage in mice made neutropenic with cyclophosphamide. Plasma concentrations of HMGB1 also increased after hemorrhage. Blockade of HMGB1 by administration of anti-HMGB1 antibodies prevented hemorrhage-induced increases in nuclear translocation of NF-kappa B in the lungs and pulmonary levels of proinflammatory cytokines, including keratinocyte-derived chemokine, IL-6, and IL-1 beta. Similarly, both the accumulation of neutrophils in the lung as well as enhanced lung permeability were reduced when anti-HMGB1 antibodies were injected after hemorrhage. These results demonstrate that hemorrhage results in increased HMGB1 expression in the lungs, primarily through neutrophil sources, and that HMGB1 participates in hemorrhage-induced acute lung injury.