The appearance of L-selectin(low) polymorphonuclear leukocytes in the circulating pool of peripheral blood during myocardial infarction correlates with neutrophilia and with the size of the infarct

Whole body and hematopoietic ADAM8 deficiency does not influence advanced atherosclerotic lesion development, despite its association with human plaque progression

Although A Disintegrin And Metalloproteinase 8 (ADAM8) is not crucial for tissue development and homeostasis, it has been implicated in various inflammatory diseases by regulating processes like immune cell recruitment and activation. ADAM8 expression has been associated with human atherosclerosis development and myocardial infarction, however a causal role of ADAM8 in atherosclerosis has not been investigated thus far. In this study, we examined the expression of ADAM8 in early and progressed human atherosclerotic lesions, in which ADAM8 was significantly upregulated in vulnerable lesions. In addition, ADAM8 expression was most prominent in the shoulder region of human atherosclerotic lesions, characterized by the abundance of foam cells. In mice, Adam8 was highly expressed in circulating neutrophils and in macrophages. Moreover, ADAM8 deficient mouse macrophages displayed reduced secretion of inflammatory mediators. Remarkably, however, neither hematopoietic nor whole-body ADAM8 deficiency in mice affected atherosclerotic lesion size. Additionally, except for an increase in granulocyte content in plaques of ADAM8 deficient mice, lesion morphology was unaffected. Taken together, whole body and hematopoietic ADAM8 does not contribute to advanced atherosclerotic plaque development, at least in female mice, although its expression might still be valuable as a diagnostic/prognostic biomarker to distinguish between stable and unstable lesions.

Stem cells, including a population of very small embryonic-like stem cells, are mobilized into peripheral blood in patients after skin burn injury

BACKGROUND

Developmentally early cells, including hematopoietic stem progenitor cells (HSPCs), as well as very small embryonic-like stem cells (VSELs), are mobilized into peripheral blood (PB) in response to tissue and organ injury (e.g., heart infarct or stroke).

OBJECTIVE

We seek to determine whether these cells are also mobilized into PB in patients with skin burn injuries.

METHODS

Forty-four (44) patients (33-57 years of age) with total body surface burn area of 30-60%, as well as 23 healthy control subjects, were recruited and PB samples were harvested during the first 24 hours, day +2, and day +5 after burn injury and compared to normal controls. The circulating human CD34(+)CD133(+) cells enriched for HSPCs, as well as small CXCR4(+)CD34(+)CD133(+) subsets of Lin(-)CD45(-) cells that correspond to the population of VSELs, were counted by FACS and evaluated by direct immunofluorescence staining for pluripotency markers (Oct-4, Nanog, and SSEA-4). In parallel, we also measured by ELISA the serum concentration of factors that regulate stem cell trafficking, such as SDF-1, VEGF, and HGF.

RESULTS

Our data indicate that skin burn injury mobilizes cells expressing stem cell-associated markers, such as CD133, CD34, and CXCR4, into PB. More importantly, we found an increase in the number of circulating primitive, small Oct-4(+)Nanog(+)SSEA-4(+)CXCR4(+)lin(-)CD45(-) VSELs. All these changes were accompanied by increased serum concentrations of SDF-1 and VEGF.

LIMITATIONS

Further studies are needed to fully assess the role of mobilized stem cells in the healing process to see if they can contribute to skin regeneration.

CONCLUSION

Skin burn injury triggers the mobilization of HSPCs and CXCR4(+) VSELs, while the significance and precise role of mobilized VSELs in skin repair requires further study.

Regulation of neutrophil trafficking from the bone marrow

Neutrophils are an essential component of the innate immune response and a major contributor to inflammation. Consequently, neutrophil homeostasis in the blood is highly regulated. Neutrophil number in the blood is determined by the balance between neutrophil production in the bone marrow and release from the bone marrow to blood with neutrophil clearance from the circulation. This review will focus on mechanisms regulating neutrophil release from the bone marrow. In particular, recent data demonstrating a central role for the chemokines CXCL12 and CXCL2 in regulating neutrophil egress from the bone marrow will be discussed.

Granulocyte-derived cationic Peptide enhances homing and engraftment of bone marrow stem cells after transplantation

Current strategies to accelerate hematopoietic reconstitution after transplantation include transplantation of greater numbers of hematopoietic stem/progenitor cells (HSPCs) or ex vivo expansion of harvested HSPCs before transplant. However, the number of cells available for transplantation is usually low, and strategies to expand HSPCs and maintain equivalent engraftment capability ex vivo are limited. We noted that activated granulocyte-derived cationic peptides positively primed responsiveness of HSPCs to a CXCL12 gradient. Accordingly, we noted that accelerated homing/engraftment of β-defensin-2, a well-known antimicrobial cationic peptide, primed bone marrow nucleated cells (BMNCs) compared to normal BMNCs after transplantation into lethally irradiated recipients. We envision that small cationic peptides, which primarily possess antimicrobial functions and are harmless to mammalian cells, could be applied to prime HSPCs before transplantation. This novel approach would be particularly important in cord blood transplantation, where the number of HSPCs available for transplantation is usually limited.

Novel insight into stem cell mobilization-plasma sphingosine-1-phosphate is a major chemoattractant that directs the egress of hematopoietic stem progenitor cells from the bone marrow and its level in peripheral blood increases during mobilization due to activation of complement cascade/membrane attack complex

Complement cascade (CC) becomes activated and its cleavage fragments play a crucial role in the mobilization of hematopoietic stem/progenitor cells (HSPCs). Here, we sought to determine which major chemottractant present in peripheral blood (PB) is responsible for the egress of HSPCs from the BM. We noticed that normal and mobilized plasma strongly chemoattracts HSPCs in a stromal derived factor-1 (SDF-1)-independent manner because i) plasma SDF-1 level does not correlate with mobilization efficiency, ii) the chemotactic plasma gradient is not affected in the presence of AMD3100, and iii) it is resistant to denaturation by heat. Surprisingly, the observed loss of plasma chemotactic activity after charcoal stripping suggested involvement of bioactive lipids and we focused on sphingosine-1 phosphate (S1P), a known chemoattracant of HSPCs. We found that S1P i) creates in plasma a continuously present gradient for BM-residing HSPCs, ii) is at physiologically relevant concentrations a chemoattractant several magnitudes stronger than SDF-1, and iii) its plasma level increases during mobilization due to CC activation and the interaction of membrane attack complex (MAC) with erythrocytes that are a major reservoir of S1P. We conclude and propose a new paradigm that S1P is a crucial chemoattractant for BM-residing HSPCs and that CC via MAC induces release of S1P from erythrocytes for optimal egress/mobilization of HSPCs.

Novel insight into stem cell mobilization-plasma sphingosine-1-phosphate is a major chemoattractant that directs the egress of hematopoietic stem progenitor cells from the bone marrow and its level in peripheral blood increases during mobilization due to activation of complement cascade/membrane attack complex

We reported that complement cascade (CC) becomes activated in bone marrow (BM) during mobilization of hematopoietic stem/progenitor cells (HSPCs) induced by granulocyte-colony stimulating factor (G-CSF) and C5 cleavage plays an important role in optimal egress of HSPCs. In the current work, we explored whether CC is involved in mobilization of HSPCs induced by the CXCR4 antagonist, AMD3100. To address this question, we performed mobilization studies in mice that display a defect in the activation of the proximal steps of CC (Rag^−/−, SCID, C2.Cfb^−/−) as well as in mice that do not activate the distal steps of CC (C5^−/−). We noticed that proximal CC activation-deficient mice (above C5 level), in contrast to distal step CC activation-deficient C5^−/− ones mobilize normally in response to AMD3100 administration. We hypothesized that this discrepancy in mobilization could be explained by AMD3100 activating C5 in Rag^−/−, SCID, C2.Cfb^−/− animals in a non-canonical mechanism involving activated granulocytes. To support this granulocytes i) as first egress from BM and ii) secrete several proteases that cleave/activate C5 in response to AMD3100. We conclude that AMD3100-directed mobilization of HSPCs, similarly to G-CSF-induced mobilization, depends on activation of CC; however, in contrast to G-CSF, AMD3100 activates the distal steps of CC directly at the C5 level. Overall, these data support that C5 cleavage fragments and distal steps of CC activation are required for optimal mobilization of HSPCs.

Relationship between serum neutrophil count and infarct size in patients with acute myocardial infarction

PURPOSE

We investigated the relationship between scintigraphic infarct size and neutrophil counts after acute myocardial infarction (AMI), which has not been adequately studied with imaging tools.

METHODS

Twenty-eight consecutive patients with anterior AMI were included in the study. Total white blood cell (WBC), neutrophil counts, creatine kinase-myocardial band (CKMB), and cardiac troponin (cTnT) were obtained at admission and daily during the first 72 h after a patient's arrival. Single photon emission computed tomography studies were performed at a median interval of 4 days (range, 3-5 days) after the AMI. The severity scores of perfusion defects were calculated. WBC and neutrophil counts correlated with enzymatic and single photon emission computed tomography infarct size.

RESULTS

Leukocyte and neutrophil counts on admission and first day were positively correlated with peak CKMB, peak cTnT, and scintigraphic infarct size. There were no statistical correlations on the second and third days (P>0.05). The most significant relationship was between basal neutrophil counts and scintigraphic infarct size (r = 0.602, P<0.001). Overall, the correlation coefficients with scintigraphy were better than those with peak CKMB and cTnT levels for both WBC and neutrophil counts.

CONCLUSION

Measuring basal neutrophil counts may be considered as an alternative solution in the prediction of infarct size.

Impaired mobilization of hematopoietic stem/progenitor cells in C5-deficient mice supports the pivotal involvement of innate immunity in this process and reveals novel promobilization effects of granulocytes

We reported that complement cascade (CC) becomes activated in bone marrow (BM) during granulocyte colony-stimulating factor (G-CSF) mobilization of hematopoietic stem/progenitor cells (HSPCs) and showed that, although third CC component (C3)-deficient mice are easy mobilizers, fifth CC component (C5)-deficient mice mobilize very poorly. To explain this, we postulated that activation/cleavage of CC releases C3a and C5a anaphylatoxins that differently regulate mobilization. Accordingly, C3a, by enhancing responsiveness of HSPCs to decreasing concentrations of stromal-derived growth factor-1 (SDF-1) in BM, prevents mobilization and promotes their BM retention. Therefore, in this study, we focused on the mobilization-enhancing role of C5a. We found that C5a receptor (C5aR) is not expressed on the surface of HSPCs, and that C5a-mediated promobilization effects are mediated by stimulation of granulocytes. Overall, our data support the following model. First C5aR(+) granulocytes are chemoattracted by plasma C5 cleavage fragments, being the first wave of cells leaving BM. This facilitates a subsequent egress of HSPCs. In the next step, after leaving BM, granulocytes undergo degranulation in response to plasma C5a and secrete some cationic peptides (cathelicidin, beta-defensin) that, as shown here for the first time, highly enhance the responsiveness of HSPCs to plasma SDF-1 gradient. In conclusion, our data reveal the underappreciated central role of innate immunity in mobilization, in which C5 cleavage fragments through granulocytes orchestrate this process.

Innate immunity: a key player in the mobilization of hematopoietic stem/progenitor cells

The mobilization of hematopoietic stem/progenitor cells (HSPCs) from bone marrow into peripheral blood (PB) is still not fully understood. Different chemokines, cytokines, growth factors, and neurotransmitters have been described that facilitate this process. However, mounting evidence suggests that mobilization of HSPCs is a part of the immune response and is mediated by innate immunity. We discuss evidence showing that complement system cleavage fragments play a crucial role in both the retention and mobilization of HSPCs by modulating their responsiveness to stromal-derived growth factor-1 (SDF-1) gradient (by C3-derived anaphylatoxins) and by modulating the release of granulocytes into PB that subsequently facilitate the egress of HSPCs (by C5-derived anaphylatoxins).

Neutrophil mobilization and clearance in the bone marrow

The bone marrow is the site of neutrophil production, a process that is regulated by the cytokine granulocyte colony-stimulating factor (G-CSF). Mature neutrophils are continually released into the circulation, with an estimated 10(11) neutrophils exiting the bone marrow daily under basal conditions. These leucocytes have a short half-life in the blood of approximately 6.5 hr, and are subsequently destroyed in the spleen, liver and indeed the bone marrow itself. Additionally, mature neutrophils are retained in the bone marrow by the stromal cell-derived factor (SDF-1alpha)/chemokine (C-X-C motif) receptor 4 (CXCR4) chemokine axis and form the bone marrow reserve. Following infection or inflammatory insult, neutrophil release from the bone marrow reserve is substantially elevated and this process is mediated by the co-ordinated actions of cytokines and chemokines. In this review we discuss the factors and molecular mechanisms regulating the neutrophil mobilization and consider the mechanisms and functional significance of neutrophil clearance via the bone marrow.

Inhibition of N-ethylmaleimide-sensitive factor protects against myocardial ischemia/reperfusion injury

Exocytosis of endothelial granules promotes thrombosis and inflammation and may contribute to the pathophysiology of early reperfusion injury following myocardial ischemia. TAT-NSF700 is a novel peptide that reduces endothelial exocytosis by inhibiting the ATPase activity and disassembly activity of N-ethylmaleimide-sensitive factor (NSF), a critical component of the exocytic machinery. We hypothesized that TAT-NSF700 would limit myocardial injury in an in vivo murine model of myocardial ischemia/reperfusion injury. Mice were subjected to 30 minutes of ischemia followed by 24 hours of reperfusion. TAT-NSF700 or the scrambled control peptide TAT-NSF700scr was administered intravenously 20 minutes before the onset of ischemia. Myocardial ischemia/reperfusion caused endothelial exocytosis, myocardial infarction, and left ventricular dysfunction. However, TAT-NSF700 decreased von Willebrand factor levels after myocardial ischemia/reperfusion, attenuated myocardial infarct size by 47%, and preserved left ventricular structure and function. These data suggest that drugs targeting endothelial exocytosis may be useful in the treatment of myocardial injury following ischemia/reperfusion.

Cytoprotective effects of N,N,N-trimethylsphingosine during ischemia- reperfusion injury are lost in the setting of obesity and diabetes

N,N,N-trimethylsphingosine chloride (TMS), a stable N-methylated synthetic sphingolipid analog, has been shown to modulate protein kinase C (PKC) activity and exert a number of important biological effects, including inhibition of tumor cell growth and metastasis, inhibition of leukocyte migration and respiratory burst, and inhibition of platelet aggregation. We hypothesized that TMS would be cytoprotective in clinically relevant in vivo murine models of myocardial and hepatic ischemia-reperfusion (I/R) injury. Wild-type, obese (ob/ob), and diabetic (db/db) mice were subjected to 30 min of left coronary artery occlusion followed by 24 h of reperfusion in the myocardial I/R model. In additional studies, mice were subjected to 45 min of hepatic artery occlusion followed by 5 h of reperfusion. TMS was administered intravenously at the onset of ischemia. Myocardial infarct size, cardiac function, and serum liver enzymes were measured to assess the extent of tissue injury. TMS attenuated myocardial infarct size by 66% in the wild type and by 36% in the ob/ob mice. Furthermore, TMS reduced serum alanine transaminase levels by 43% in wild-type mice. These benefits did not extend to the ob/ob mice following hepatic I/R or to the db/db mice following both myocardial and hepatic I/R. A likely mechanism is the failure of TMS to inhibit PKC-delta translocation in the diseased heart. These data suggest that although TMS is cytoprotective following I/R in normal animals, the cytoprotective actions of TMS are largely attenuated in obese and diabetic animals.

The CXC chemokine MIP-2 stimulates neutrophil mobilization from the rat bone marrow in a CD49d-dependent manner

The acute release of neutrophils from the bone marrow is a critical step in their trafficking to sites of inflammation. This process is stimulated by systemically acting inflammatory mediators, such as the CXC chemokines. In this study we have used a novel in situ perfusion system of the rat femoral bone marrow to directly investigate the role of specific adhesion molecules in chemokine-stimulated neutrophil mobilization. We show here that neutrophils mobilized in response to rat macrophage inflammatory protein-2 (MIP-2) shed l-selectin and expressed significantly higher levels of CD11b and CD49d. However, inhibition of l-selectin sheddase activity with KD-IX-73-4 had no effect on the number of neutrophils mobilized in response to rat MIP-2. Blockade of CD18, using a neutralizing monoclonal antibody (mAb), did not inhibit neutrophil mobilization but unexpectedly increased the rate and number of neutrophils released from the bone marrow in response to chemokine, suggesting that CD18 could play a role in neutrophil retention within the bone marrow. Blockade of CD49d using either a selective mAb or a specific antagonist resulted in a dramatic inhibition (&gt; 75%) of the chemokine-stimulated neutrophil mobilization from the bone marrow. These data reveal contrasting roles for CD18 and CD49d in the retention and release of neutrophils from the bone marrow.

The effect of blockade of the CD11/CD18 integrin receptor on infarct size in patients with acute myocardial infarction treated with direct angioplasty: the results of the HALT-MI study

OBJECTIVE

The purpose of this study was to determine whether Hu23F2G (LeukoArrest), an antibody to the CD11/CD18 integrin receptors, would reduce infarct size in patients undergoing primary angioplasty for an acute myocardial infarction.

BACKGROUND

Reperfusion injury in acute myocardial infarction has been shown experimentally to be related to neutrophil accumulation. Inhibitors of the CD11/CD18 or CD18 integrin receptors have been shown to reduce infarct size in experimental models.

METHODS

Patients within 6 h of onset of chest pain with ST-segment elevation were randomized to receive either 0.3 mg/kg or 1.0 mg/kg of Hu23F2G or placebo just before angioplasty of occluded arteries (Thrombolysis in Myocardial Infarction TIMI flow grade 0 or 1). The primary end point was infarct size as measured by sestamibi single-photon emission computed tomography (SPECT) scan five to nine days later.

RESULTS

Four-hundred and twenty patients were enrolled and received a placebo or the study drug. The groups did not differ in baseline or angiographic characteristics or angioplasty results. Infarct size was 16%, 17.2% and 16.6%, for placebo, 0.3 mg/kg and 1.0 mg/kg, respectively, of the left ventricle (p = NS). No differences were evident in those patients with anterior myocardial infarction or those presenting within 2 h of onset of chest pain. Corrected TIMI frame count was also not different between groups. Clinical events at 30 days were very low, with a mortality of 0.8%, 1.4% and 3.3%, respectively. The drug was well tolerated, with a slight increase in minor infections in the high dose group.

CONCLUSIONS

The results of this multicenter, double-blind, placebo-controlled, randomized clinical trial demonstrated that an antibody to CD11/CD18 leukocyte integrin receptor did not reduce infarct size in patients who underwent primary angioplasty.

Assessment of myocardial inflammation produced by experimental coronary occlusion and reperfusion with 99mTc-RP517, a new leukotriene B4 receptor antagonist that preferentially labels neutrophils in vivo

BACKGROUND

99mTc-RP517 is a new leukotriene B4 (LTB4) receptor antagonist developed for imaging acute inflammation or infection. A unique property of 99mTc-RP517 is its ability to label white blood cells in vivo after intravenous injection. The goals of this study were to determine relative 99mTc-RP517 binding to human leukocyte subtypes and the 99mTc-RP517 uptake pattern in canine myocardium where inflammation was induced by either coronary occlusion and reperfusion or tumor necrosis factor alpha (TNFalpha) injection.

METHODS AND RESULTS

Fluorescence-activated cell sorter analysis was performed on whole human blood (n=2) and isolated neutrophils (n= 4) with a fluorescent analog of 99mTc-RP517, [F]-RP517. In whole blood, [F]-RP517 (500 nmol/L) preferentially labeled neutrophils. On isolated neutrophils, [F]-RP517 (10 nmol/L) binding was inhibited by 44% when LTB4 (400 nmol/L) was added. 99mTc-RP517 was injected intravenously in anesthetized, open-chest dogs before coronary occlusion (90 minutes) and reperfusion (120 minutes) (n=9) or before intramyocardial TNFalpha injection (n=3). Ex vivo images of heart slices were acquired. The left ventricle was divided into 72 segments for flow and 99mTc-RP517 uptake analysis. There was an inverse exponential relationship between 99mTc-RP517 uptake and occlusion flow (r=0.73). In the same 15 segments, 99mTc-RP517 uptake was highly correlated with the neutrophil enzyme myeloperoxidase (r=0.91). Ex vivo images revealed tracer uptake in the reperfused area (ischemic to normal count ratio=2.7+/-0.2).

CONCLUSIONS

RP517 binds to the neutrophil LTB4 receptor after intravenous injection. After reperfusion, 99mTc-RP517 uptake correlated with myeloperoxidase and was observed on ex vivo images, indicating that this tracer may have potential as an inflammation-imaging agent.

In vivo myocardial protection from ischemia/reperfusion injury by the peroxisome proliferator-activated receptor-gamma agonist rosiglitazone

BACKGROUND

Diabetes is associated with increased risk of mortality as a consequence of acute myocardial infarction. This study determined whether rosiglitazone (ROSI) could reduce myocardial infarction after ischemia/reperfusion injury.

METHODS AND RESULTS

Male Lewis rats were anesthetized, and the left anterior descending coronary artery was ligated for 30 minutes. After reperfusion for 24 hours, the ischemic and infarct sizes were determined. ROSI at 1 and 3 mg/kg IV reduced infarct size by 30% and 37%, respectively (P<0.01 versus vehicle). Pretreatment with ROSI (3 mg. kg(-1). d(-1) PO) for 7 days also reduced infarct size by 24% (P<0.01). ROSI also improved ischemia/reperfusion-induced myocardial contractile dysfunction. Left ventricular systolic pressure and positive and negative maximal values of the first derivative of left ventricular pressure (dP/dt) were significantly improved in ROSI-treated rats. ROSI reduced the accumulation of neutrophils and macrophages in the ischemic heart by 40% and 43%, respectively (P<0.01). Ischemia/reperfusion induced upregulation of CD11b/CD18 and downregulation of L-selectin on neutrophils and monocytes; these effects were significantly attenuated in ROSI-treated animals. Likewise, intercellular adhesion molecule-1 expression in ischemic hearts was markedly diminished by ROSI, as was the ischemia/reperfusion-stimulated upregulation of monocyte chemoattractant protein-1.

CONCLUSIONS

ROSI reduced myocardial infarction and improved contractile dysfunction caused by ischemia/reperfusion injury. The cardioprotective effect of ROSI was most likely due to inhibition of the inflammatory response.

Systemic response of peripheral blood leukocytes and their phagocytic activity during acute myocardial infarction

OBJECTIVES

To determine changes in leukocyte counts and phagocytic activity of peripheral blood mononuclear (MN) and polymorphonuclear (PMN) cells as potential cellular markers of systemic immunological events in acute myocardial infarction (AMI).

PATIENTS AND METHODS

Thirty patients with a first AMI and 30 healthy volunteers were examined. Immunological analyses were performed at admission and repeated at one and seven days after the acute event. MN and PMN cells were obtained from heparinized whole blood after centrifugation and separation on a density gradient, and incubated with a fixed number of heat-inactivated and labelled yeast particles. Total leukocyte counts, leukocyte populations and some parameters of phagocytic activity were determined: percentage phagocytosis, phagocytic index, absolute phagocytic index, count of phagocytes in a fixed volume of peripheral blood (CP) and phagocytic capacity.

RESULTS

Patients with AMI had increased total leukocyte counts accompanied by increased PMN counts, while there were no significant differences in total MN count and MN populations. Except for the phagocytic index, all phagocytic parameters of MN and PMN cells were increased in patients with AMI at admission and on the first day of disease. On the seventh day after AMI only the CP of MN cells had increased significantly in patients with AMI, while percentage phagocytosis, CP and capacity of phagocytosis of PMN cells increased during the acute phase of AMI.

CONCLUSIONS

These data suggest that AMI was followed with a strongly systemic inflammatory response to myocardial damage. Furthermore, activated MN and PMN cells may be a significant source of free radicals that may be involved in lipid peroxidation and produce tissue damage in the early postinfarction period.