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Thrombus formation is dependent on the interaction of platelets, leukocytes and endothelial cells as well as proteins of the coagulation cascade. This interaction is tightly controlled by phospho-regulated pathways involving protein kinase CK2. A growing number of studies have demonstrated an important role of this kinase in the regulation of primary and secondary hemostasis. Inhibition of CK2 downregulates the expression of important adhesion molecules on platelets and endothelial cells, such as glycoprotein (GP)IIb/IIIa, P-selectin, von Willebrand factor and vascular cell adhesion molecule. Moreover, the reduced CK2-dependent phosphorylation of different coagulation factors prevents the conversion of fibrinogen to fibrin. Targeting these mechanisms may open the door for the development of novel anti-thrombotic therapies.

Background: Ischemia and reperfusion (I/R) causes tissue injury by inflammatory processes. This involves the upregulation of endothelial surface proteins by phospho-regulated signaling pathways, resulting in enhanced interactions of leukocytes with endothelial cells. Recently, we found that protein kinase CK2 is a crucial regulator of leukocyte-mediated inflammation. Therefore, in this study we investigated the involvement of CK2 in leukocyte-endothelial cell interactions during I/R injury., Methods: We first analyzed the inhibitory action of (E)-3-(2,3,4,5-tetrabromophenyl)acrylic acid (TBCA) and CX-4945 on CK2 kinase activity and the viability of human dermal microvascular endothelial cells (HDMEC). To mimic I/R conditions in vitro, HDMEC were exposed to hypoxia and reoxygenation and the expression of adhesion molecules was analyzed by flow cytometry. Moreover, we analyzed in vivo the effect of CK2 inhibition on leukocyte-endothelial cell interactions in the dorsal skinfold chamber model of I/R injury by means of repetitive intravital fluorescence microscopy and immunohistochemistry., Results: We found that TBCA and CX-4945 suppressed the activity of CK2 in HDMEC without affecting cell viability. This was associated with a significant downregulation of E-selectin and intercellular adhesion molecule (ICAM)-1 after in vitro hypoxia and reoxygenation. In vivo, CX-4945 treatment significantly decreased the numbers of adherent and transmigrated leukocytes in striated muscle tissue exposed to I/R., Conclusion: Our findings indicate that CK2 is involved in the regulation of leukocyte-endothelial cell interactions during I/R by mediating the expression of E-selectin and ICAM-1., (© 2016 S. Karger AG, Basel.)

Introduction: Thrombus formation is a complex process, which is characterized by the dynamic interaction of platelets, leukocytes and endothelial cells. The activation of these cells is strictly mediated by different phospho-regulated signaling pathways. Recently, it has been reported that inhibition of protein kinase CK2 affects platelet function by suppressing phosphatidylinositol-4,5-bisphosphate-3-kinase (PI3K) signaling. Based on this finding, we herein analyzed whether CK2 acts as a crucial regulator of thrombus formation., Materials and Methods: We examined the effect of CK2 inhibition on platelet activation and aggregation, the formation of platelet-leukocyte aggregates (PLA), the endothelial expression of von Willebrand factor (vWF), intercellular adhesion molecule (ICAM)-1 and vascular cell adhesion molecule (VCAM)-1, and the subcellular localization of nuclear factor of activated T-cells cytoplasmic 1 (NFATc1) and phospho-p65 in human dermal microvascular endothelial cells (HDMEC). Dorsal skinfold chambers were prepared in BALB/c mice to analyze in vivo the effect of CK2 inhibition on photochemically induced thrombus formation using intravital fluorescence microscopy., Results: CK2 inhibition by CX-4945 suppressed adenosin diphosphate (ADP)- and proteinase-activated receptor-1-peptide (PAR-1-AP)-stimulated platelet aggregation, which was associated with down-regulation of P-selectin, GPIIb/IIIa and a reduced formation of PLA. Expression and secretion of vWF was diminished in CX-4945-treated HDMEC. Moreover, CK2 inhibition attenuated the endothelial expression of VCAM-1, whereas the expression of ICAM-1 was not affected. Finally, CX-4945-treated mice exhibited a significantly delayed photochemically induced thrombus formation when compared to vehicle-treated controls., Conclusion: These results indicate that CK2 is a pleiotropic regulator of thrombus formation, affecting multiple interactions of platelets, leukocytes and endothelial cells., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Objective: P-selectin glycoprotein ligand-1 (PSGL-1) has been shown to play a significant role in septic lung injury. However, the detailed role of PSGL-1 in the pulmonary leukocyte recruitment remains elusive. We have developed a method based on intravital fluorescence microscopy of the lung microcirculation to examine the role of PSGL-1 in the extravasation process of leukocytes in septic lung damage., Methods: Male C57BL/6 mice were treated with a control antibody or an anti-PSGL-1 antibody prior to cecal ligation and puncture (CLP). Leukocyte-endothelium interactions and microvascular hemodynamics were studied in pulmonary arterioles, capillaries and venules 4 h after CLP., Results: Immunoneutralization of PSGL-1 decreased CLP-induced leukocyte rolling in pulmonary arterioles and venules significantly. Inhibition of PSGL-1 had no effect on leukocyte adhesion in venules, whereas the number of adherent leukocytes in lung arterioles and the number of trapped leukocytes in capillaries were markedly decreased. Moreover, immunoneutralization of PSGL-1 improved microvascular perfusion in the lung of septic animals., Conclusions: Taken together, these results document that PSGL-1 mediates leukocyte rolling in arterioles and venules. However, inhibition of PSGL-1 only decreases leukocyte adhesion in arterioles, suggesting that leukocyte rolling is not a prerequisite for pulmonary venular adhesion of leukocytes in sepsis. In addition, our data show that capillary trapping of leukocytes is dependent on PSGL-1 function.

Leukocyte accumulation is a rate-limiting step in inflammatory lung injury. The aim of this study was to define the role of CD11a/CD18 and CD11b/CD18 in sepsis-induced leukocyte rolling and adhesion in lung arterioles, capillaries and venules in male C57BL/6 mice using intravital fluorescence microscopy. Cecal ligation and puncture (CLP) markedly increased leukocyte rolling in arterioles and venules but not in capillaries in the lung. Immunoneutralization of CD11a, but not CD11b, decreased CLP-provoked leukocyte rolling in lung arterioles. Inhibition of CD11a or CD11b abolished CLP-induced arteriolar and venular leukocyte adhesion. Immunoneutralization of CD11a and CD11b reduced sepsis-induced leukocyte sequestration in pulmonary capillaries. Moreover, blocking CD11a or CD11b function improved microvascular blood flow in the lung of CLP animals. Considered together, our novel findings show that CD11a and CD11b mediate leukocyte adhesion in both arterioles and venules as well as trapping in capillaries in the lung. In addition, our data demonstrate that CD11a but not CD11b supports leukocyte rolling in pulmonary arterioles. Thus, these findings elucidate the molecular mechanisms behind leukocyte-endothelium interactions in the lung during systemic inflammation., (Copyright © 2013 Elsevier B.V. All rights reserved.)

The mechanisms of leukocyte recruitment in the pulmonary microvasculature in response to local and systemic inflammation remain elusive. Male C57BL/6 mice received lipopolysaccharide (LPS) intrapulmonary (intratracheally, it) or systemically (intravenously, iv) for 1-18 h. Leukocyte responses in lung were analyzed by use of intravital fluorescence microscopy. Plasma and lung levels of CXC chemokines as well as Mac-1 and F-actin expression in leukocytes and bronchoalveolar leukocytes were quantified. Venular leukocyte rolling was markedly increased in response to local LPS but only marginally after systemic LPS. Leukocyte adhesion in venules was enhanced in both groups although adhesion was higher in mice receiving LPS intratracheally compared with LPS intravenously. Systemic LPS caused more leukocytes trapping in capillaries compared with local LPS. The ratio of adherent leukocytes in venules compared with capillaries was higher in response to local LPS, suggesting that leukocytes were more prone to accumulate in venules in local inflammation and in capillaries in systemic inflammation. Systemic LPS triggered higher F-actin formation and Mac-1 expression in leukocytes compared with local LPS. Local and systemic LPS caused similar increases in CXC chemokines in the lung whereas intravenous endotoxin provoked higher levels of CXC chemokines in the circulation. Interestingly, intratracheal LPS increased recruitment of leukocytes in the alveolar space whereas intravenous LPS was ineffective in promoting leukocyte accumulation in the bronchoalveolar space. In conclusion, our data demonstrate that pulmonary microvascular recruitment of leukocytes differs in local and systemic inflammation, which might be related to premature activation and stiffening of circulating leukocytes in endotoxemia.

Introduction: Microcirculatory dysfunction causes ischemia resulting in tissue necrosis. N-acetylcysteine (NAC) has been shown capable of protecting tissue from ischemic necrosis. However, the mechanism of action of NAC is yet not fully understood., Objective: Herein, we studied whether NAC is capable of attenuating microvascular perfusion failure in critically ischemic musculo-cutaneous tissue., Material and Methods: A laterally based skin flap was elevated in the dorsum of C57BL/6 mice and fixed into a dorsal skinfold chamber. Arteriolar perfusion, functional capillary density, leukocytic inflammation, apoptotic cell death, and non-perfused tissue area were repetitively analyzed over 10 days by intravital fluorescence microscopy. Treatment with either 100mg/kg NAC or saline (control) was started 30 min before surgery and was continued until day 10 after flap elevation., Results: Surgery induced leukocytic inflammation, microvascular perfusion failure, apoptosis, and tissue perfusion failure. NAC was capable of significantly attenuating the area of non-perfused tissue. This was associated by a marked arteriolar dilation and an increased capillary perfusion. NAC further reduced the ischemia-associated leukocytic response and significantly attenuated apoptotic cell death in all areas of the flap., Conclusion: NAC is effective to attenuate leukocytic inflammation and microvascular perfusion failure in critically ischemic tissue. Thus, NAC treatment may represent a promising approach to improve the outcome of ischemically endangered flap tissue., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Background and Aims: Leukocyte recruitment is a key feature in ischemia-reperfusion (I/R)-induced tissue injury. The aim of the present study was to investigate the effect of Rho-kinase inhibition on I/R-provoked leukocyte recruitment in the colon., Methods: C57BL/6 mice were subjected to 30 min of ischemia by clamping of the superior mesenteric artery followed by 120 min of reperfusion. Intraperitoneal pretreatment with the selective Rho-kinase inhibitors fasudil (4-40 mg/kg) and Y-27632 (1-10 mg/kg) was administered prior to induction of colonic I/R. Leukocyte-endothelium interactions were analyzed by intravital fluorescence microscopy. Colonic content of tumour necrosis factor-alpha (TNF-alpha) and the CXC chemokines macrophage inflammatory protein-2 (MIP-2) and cytokine-induced neutrophil chemoattractant (KC) were determined by ELISA. Additionally, colonic activity of myeloperoxidase (MPO), a marker of leukocyte infiltration, and malondialdehyde (MDA), were quantified., Results: Fasudil and Y-27632 pretreatment decreased I/R-induced leukocyte rolling and adhesion by 76% and 96%, respectively. Moreover, Rho-kinase interference reduced formation of TNF-alpha, MIP-2 and KC by more than 68% in the reperfused colon. Additionally, the reperfusion-provoked increase in the levels of MPO and MDA in the colon decreased after Rho-kinase inhibition by 69% and 42%, respectively., Conclusions: Our data demonstrate that inhibition of Rho-kinase activity decrease I/R-induced leukocyte rolling, adhesion and recruitment in the colon. Moreover, these findings show that Rho-kinase signalling regulates TNF-alpha and CXC chemokine formation as well as lipid peroxidation in the reperfused colon. Thus, targeting Rho-kinase signalling may be a useful strategy in order to protect against pathological inflammation in the colon.

Purpose: Lipopolysaccharide (LPS) represents a highly toxic substance which may aggravate morbidity and mortality in septic diseases. A recent study has reported that the induction of heme oxygenase (HO)-1 protects from LPS-induced liver injury. The mechanisms of action however, have not been clarified yet. Therefore, we analyzed in vivo the effects of HO-1 on the liver microcirculation under conditions of LPS exposure., Methods: In C57BL/6 mice, endotoxemia was induced by intraperitoneal (i.p.) administration of LPS (500 microg/kg) and D-galactosamine (Gal, 800 mg/kg). HO-1 was induced in vivo by pretreatment with hemin dissolved in DMSO (50 micromol/kg i.p.). Animals treated with DMSO only served as controls. Six hours after LPS exposure the hepatic microcirculation and leukocyte-endothelial cell interaction were analyzed by intravital fluorescence microscopy. HO-1 expression was determined by Western blot analysis. Hepatocellular damage was assessed by measuring the serum levels of aspartate aminotransferase and alanine aminotransferase. In addition, leukocyte transmigration and hepatocellular apoptosis were analyzed by histology and immunohistochemistry., Results: In controls, LPS/Gal caused severe liver injury, as indicated by increased liver enzyme levels and apoptotic cell death. This was associated with distinct sinusoidal perfusion failure and microvascular intrahepatic leukocyte accumulation. Of interest, induction of HO-1 significantly reduced numbers of adherent and extravascular leukocytes when compared to controls. Moreover, microvascular perfusion was significantly improved, resulting in a decrease of AST and ALT and a reduction of hepatocellular apoptosis., Conclusions: Our novel data indicate that induction of HO-1 protects the liver from LPS-mediated injury by reducing leukocytic inflammation and improving intrahepatic microcirculation.

Objective: Leukocytes mediate hepatocellular injury in obstructive cholestasis. The aim of the present study was to define the role of P-selectin glycoprotein ligand-1 (PSGL-1) in cholestasis-induced leukocyte recruitment and liver damage., Methods: C57BL/6 mice were pre-treated with an anti-PSGL-1 antibody or a control antibody prior to bile duct ligation (BDL) for 12 h. Hepatic recruitment of leukocytes and sinusoidal perfusion were determined by means of intravital fluorescence microscopy. Liver damage was monitored by measuring serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Hepatic levels of CXC chemokines were determined by ELISA., Results: BDL caused significant hepatocellular damage indicated by increased serum activities of ALT and AST as well as decreased sinusoidal perfusion and clear-cut hepatic infiltration of leukocytes. Administration of the anti-PSGL-1 antibody reduced BDL-induced levels of ALT by 78% and AST by 77%. Inhibition of PSGL-1 decreased BDL-provoked leukocyte rolling and adhesion in post-sinusoidal venules by more than 81%. Moreover, we found that immunoneutralisation of PSGL-1 restored sinusoidal perfusion and decreased hepatic formation of CXC chemokines in cholestatic mice., Conclusions: Our novel data show that PSGL-1 plays an important role in cholestatic liver damage by regulating leukocyte rolling in post-sinusoidal venules. Consequently, interference with PSGL-1 attenuates cholestasis-provoked leukocyte adhesion and extravasation in the liver. Thus, inhibition of PSGL-1 may help to protect against hepatocellular damage in cholestatic diseases.

Background: Endotoxemia is well known to be associated with an excessive host response to bacteria or microbial compounds, resulting in systemic inflammation and organ injury. The aim of the present study was to examine the effects of simvastatin on endotoxemic liver injury., Methods: Male C57BL/6J mice were challenged intraperitoneally with 0.5 mg/kg Escherichia coli-lipopolysaccharide (LPS) and 0.9 g/kg d-galactosamine (Gal). Mice were pretreated with 0.2 mg/kg simvastatin. Lipopolysaccharide/d-Gal-injected mice without simvastatin served as endotoxemic controls, and sham mice served as negative controls. Additional mice were challenged with LPS/d-Gal and co-treated with simvastatin and 10 mg/kg mevalonate to determine the role of 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase. After 6 hours of endotoxemia serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities as well as caspase-3 and myeloperoxidase activity were determined., Results: Endotoxemia caused a substantial hepatocellular injury as indicated by significantly elevated serum ALT and AST levels and hepatocellular apoptosis. Leukocyte infiltration in the liver was significantly elevated in endotoxemic mice. Simvastatin significantly reduced endotoxin-induced hepatocellular damage and apoptosis. Moreover, hepatic accumulation of leukocytes was attenuated by simvastatin in endotoxemic animals. Co-administration of mevalonate abolished protective effects of simvastatin on endotoxin-provoked increases in ALT, AST, and hepatocellular apoptosis as well as leukocyte recruitment., Conclusions: Simvastatin has the capacity to prevent endotoxemic liver injury by inhibiting leukocyte infiltration and hepatocellular apoptosis. These protective effects exerted by simvastatin are dependent on the 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase pathway. Thus, simvastatin may represent a potential approach to prevent endotoxemia-associated liver dysfunction.

Background: Our objective was to examine the role of p38 mitogen-activated protein kinase (MAPK) in ischemia-reperfusion (I/R)-induced recruitment or leukocytes in the colon., Methods: C57/Bl6 mice were subjected to 30 minutes of ischemia by clamping the superior mesenteric artery followed by 2 hours of reperfusion. Animals were pretreated with the selective p38 MAPK inhibitors SB 239063 and SKF 86002 before induction of I/R. Leukocyte-endothelium interactions were quantified by use of intravital fluorescence microscopy. Additionally, the role of p38 MAPK in mast cell-generated tumor necrosis factor-alpha (TNF-alpha) as well as neutrophil adhesion and P-selectin expression were examined in vitro., Results: SB 239063 and SKF 86002 decreased both I/R-provoked leukocyte rolling and adhesion by > 75%. Inhibition of p38 MAPK decreased dose-dependently the mast cell generated TNF-alpha production as well as TNF-alpha-induced expression of P-selectin and neutrophil adhesion on endothelial cells., Conclusion: We conclude that p38 MAPK regulates leukocyte rolling and adhesion in colonic I/R. Moreover, inhibition of p38 MAPK activity decreases formation of TNF-alpha and P-selectin-dependent leukocyte attachment to activated endothelial cells. Thus, our findings suggest that interference with the p38 MAPK signaling pathway could be an effective strategy to protect against I/R-induced inflammation in the colon.

Background and Aims: Recruitment of leukocytes in the tissue microvasculature is considered to be a rate-limiting step in ischemia-reperfusion (I/R)-induced inflammation. The objective of this study was to examine the role of mast cells in CXC-chemokine- and I/R-provoked leukocyte recruitment in the colon., Materials and Methods: Balb/c- and mast-cell-deficient mice were challenged with the CXC chemokines macrophage inflammatory protein-2 (MIP-2) and cytokine-induced neutrophil chemoattractant (KC) for 3 h. Leukocyte-endothelium interactions in the colonic microvascular bed were analyzed using an inverted intravital fluorescence microscopy technique. In separate experiments, mice were subjected to I/R by clamping of the superior mesenteric artery for 30 min followed by 120 min of reperfusion., Results: MIP-2 and KC induced a clear-cut increase in the number of rolling and adherent leukocytes in the colon. I/R increased the expression of MIP-2 and KC as well as leukocyte rolling and adhesion in the large bowel. Interestingly, leukocyte rolling and adhesion was reduced by more than 91% in mast-cell-deficient mice in response to CXC chemokine challenge. Moreover, I/R-induced leukocyte rolling and adhesion was decreased by more than 57% in mast-cell-deficient animals. Administration of MIP-2 increased the colonic expression of E-selectin mRNA in wild type but not in mast-cell-deficient mice., Conclusion: Our data demonstrate that CXC chemokine-induced leukocyte rolling and adhesion is regulated by mast cells. Moreover, these findings also show that mast cells play a crucial role in supporting I/R-induced leukocyte rolling and adhesion in the colonic microvascular bed via secretion of CXC chemokines.

Background and Aims: Mesh implantation for hernia repair bears the risk of bacterial mesh infection. In this study, we analyzed whether this complication is supported by an increased interaction of bacteria and leukocytes with the microvascular endothelium at the implantation site., Materials and Methods: Ultrapro meshes were implanted into the dorsal skinfold chamber of Syrian golden hamsters. After 12 days, fluorescein isothiocyanate (FITC)-labeled staphylococci were injected in the animals. Subsequently, we analyzed bacterial adherence, leukocyte-endothelial cell interaction, and microhemodynamics in venules of the mesh border zone and of distant control tissue under baseline conditions and during TNF-alpha-induced inflammation using intravital fluorescence microscopy. The results were compared to animals which did not receive any bacteria., Results: Under baseline conditions, leukocyte-endothelial cell interaction and bacterial adherence were not affected by the implanted biomaterial. TNF-alpha-induced inflammation significantly increased numbers of adherent leukocytes and bacteria in venules located in direct vicinity to the mesh however without any differences to control tissue. Comparable results were found for the leukocyte-endothelial cell interaction when animals were not exposed to bacteria., Conclusion: Implanted Ultrapro meshes do neither increase microvascular Staphylococcus aureus adherence nor sensitize for leukocytic inflammation. Thus, we suggest that a mesh-induced increase of bacterial adherence in vessels of the implantation site cannot be considered as a primary cause for the development of mesh infection.

Background: Although it is well known that extrahepatic cholestasis induces liver damage, the mechanisms are still not completely understood. The aim of the present study was to evaluate the role of platelets and P-selectin in cholestasis-induced liver injury., Experimental Approach: C57BL/6 mice underwent bile duct ligation (BDL) and pretreatment with an anti-GP1balpha antibody, which depletes platelets, an anti-P-selectin antibody or a control antibody. Hepatic platelet and leukocyte recruitment as well as microvascular perfusion were determined by intravital fluorescence microscopy., Key Results: BDL caused significant liver damage and sinusoidal perfusion failure. BDL further induced hepatic platelet accumulation with widespread intravascular platelet aggregates, increased platelet adhesion in postsinusoidal venules and massive platelet accumulation in liver sinusoids. Administration of the anti-GP1balpha antibody reduced systemic platelet count by 90%. Depletion of platelets in BDL mice not only abolished accumulation and adhesion of platelets in sinusoids and venules but also restored sinusoidal perfusion and reduced liver enzymes by more than 83%. Platelet depletion further reduced BDL-associated sinusoidal leukocyte accumulation by 48% although leukocyte-endothelium interactions in venules were not affected. Immunoneutralization of P-selectin also inhibited hepatic microvascular accumulation of platelets and leukocytes, and protected against cholestasis-provoked hepatocellular damage., Conclusions and Implications: Platelets play an important role in BDL-induced liver injury by promoting leukocyte recruitment and deteriorating microvascular perfusion. Moreover, our findings demonstrate that cholestasis-induced accumulation of platelets is mediated by P-selectin. Thus, targeting platelet accumulation may be a useful strategy against liver damage associated with obstructive jaundice.

Objective and Design: Leukocyte recruitment is a key feature in ischemia-reperfusion (I/R) -provoked tissue injury. This study evaluated the role of P-selectin-glycoprotein ligand-1 (PSGL-1) in CXC chemokine- and ischemia-reperfusion- induced leukocyte rolling and adhesion in the colon., Materials: Balb/c mice were used in an inverted intravital fluorescence microscopy study of the microvascular bed in the colon., Treatment: Mice were challenged with macrophage inflammatory protein-2 (MIP-2) intraperitonally and leukocyte-endothelium interactions were analysed 3 h later. In separate experiments, mice were exposed to I/R by clamping of the superior mesenteric artery for 30 min and leukocyte rolling and adhesion were analysed after 120 min of reperfusion., Results: MIP-2 dose-dependently increased leukocyte rolling and adhesion in the colon. Pretreatment with an anti-PSGL-1 antibody reduced MIP-2-provoked leukocyte rolling and adhesion by more than 89%. I/R increased expression of MIP-2 as well as leukocyte rolling and adhesion. Immunoneutralization of PSGL-1 decreased reperfusion-induced leukocyte rolling by 85% and adhesion by 93% in colonic venules., Conclusions: Our data demonstrates that PSGL-1 is a dominant adhesion molecule supporting MIP-2- and I/R-provoked leukocyte rolling. Inhibition of PSGL-1 abolished leukocyte rolling and abrogated I/R-induced leukocyte adhesion in colonic venules. These findings suggest that targeting PSGL-1 may be an effective strategy to prevent I/R-induced inflammation in the colon.

Objective: Secondary complications involving inflammation limit postoperative results in cardiac surgery. Because heparin-protamine can elicit inflammatory reactions, this study evaluates in vivo whether treatment with heparin-protamine aggravates local endotoxin-induced injury., Methods: Mice received intravenous injections of either heparin-protamine, protamine alone or PBS for controls, before local air pouch challenge with LPS. Leukocytes recruited within the air pouches were collected and analyzed by flow cytometry., Results: LPS provoked a local leukocytic infiltration in a dose- and time-dependent manner with significantly elevated numbers of 1.75 +/- 0.29 x 10 (6) cells after four hours compared to non-LPS-stimulated controls (0.55 +/- 0.08 x 10 (6) cells). Recruited cells comprised of 74 +/- 4 % PMNLs and 26 +/- 4 % MNLs. The largest fraction of MNLs was positive for the T cell-specific marker CD90.2 (59 +/- 6 %). B cells were only rarely observed (4 +/- 1 %). In non-LPS-challenged air pouches, heparin-protamine provoked a leukocytic infiltration, which was comparable to that observed after LPS (1.51 +/- 0.22 x 10 (6) cells). However, neither heparin-protamine nor protamine alone aggravated the LPS-mediated leukocyte recruitment (2.25 +/- 0.25 x 10 (6) and 1.77 +/- 0.23 x 10 (6) cells). Neither treatment influenced the distribution of leukocyte subpopulations compared to PBS-treated controls. Furthermore, surface expression of CD11a and CD11b on blood leukocytes did not differ between the groups, indicating that protamine does not increase the activation of circulating leukocytes during LPS-induced local inflammation., Conclusions: Our data indicate that heparin-protamine, although pro-inflammatory in nature, does not aggravate local inflammation provoked by LPS. Thus, enhanced inflammation during the perioperative course of cardiac surgery patients seems not to be attributable to the intraoperative use of heparin-protamine.

Objective and Design: Emerging data suggest that Rho-kinase signaling may regulate numerous aspects of inflammatory reactions. Herein, we investigated the role of Rho-kinase in inflammatory interactions between leukocytes and the endothelium in femoral arteries and veins in vivo., Material and Methods: Mice were injected with lipopolysaccharide (LPS) and Rho-kinase was inhibited by pre-treatment with fasudil, which is a highly selective inhibitor of Rho-kinase. Six hours after LPS challenge, intravital fluorescence microscopy of the femoral vessels was performed and leukocyte-endothelium interactions were visualized after in vivo staining with rhodamine 6G., Results: LPS increased leukocyte rolling and adhesion in femoral arteries and veins. Pre-treatment with fasudil had no effect on leukocyte rolling but significantly decreased venular leukocyte adhesion by 85% and completely abrogated leukocyte adhesion in femoral arteries in endotoxin-treated mice., Conclusions: We conclude that Rho-kinase signaling regulates LPS-induced leukocyte adhesion in femoral arteries and veins in vivo and that inhibition of Rho-kinase may be useful in the treatment of pathological inflammation in large blood vessels of the vascular system.

The aims of the present study were to determine the effects and mechanisms of angiotensin II (Ang II) on leukocyte-endothelium interactions and the role of Ang II in a novel model of ischemia/reperfusion (I/R) in the mouse colon. Ang II dose-dependently increased leukocyte rolling and adhesion in colonic venules. Importantly, Ang II-induced leukocyte rolling was completely inhibited by immunoneutralization of P-selectin, and leukocyte adhesion was abolished in lymphocyte function antigen-1 (LFA-1)-deficient mice. The P-selectin-dependent rolling was found to be a precondition for the subsequent LFA-1-dependent leukocyte adhesion. Moreover, Ang II-induced leukocyte responses involved generation of reactive oxygen species and up-regulation of CXC chemokines. Notably, CXC chemokines, but not Ang II, stimulated leukocyte chemotaxis in vitro. I/R increased gene expression of angiotensin converting enzyme (ACE) in the colon and plasma concentrations of Ang II. Inhibition of ACE and the type 1 angiotensin (AT1) receptor significantly decreased the I/R-induced leukocyte adhesion. Taken together, these novel findings demonstrate that Ang II exerts potent pro-inflammatory effects in the colonic microcirculation and that inhibition of Ang II expression or function protects against I/R-induced leukocyte responses in the colon. Thus, it is suggested that Ang II is a major target to control pathological inflammation in the colon.

Apoptotic hepatocytes have been demonstrated to represent an important signal for transmigration of leukocytes sequestered in sinusoids during endotoxemia in vivo. Beside leukocytes, platelets and their adhesion to endothelial cells and leukocytes have been implicated in inflammatory liver injury. Using in vivo multifluorescence microscopy, we examined the possibility that hepatocellular apoptosis causes both leukocytes and platelets to colocalize within the sinusoidal microvasculature of endotoxemic livers. We further addressed the issue whether cellular colocalization with apoptotic hepatocytes is cause or consequence of apoptosis. Intraperitoneal exposure of rats with LPS (5 mg/kg) induced liver injury after 6 and 16 h, as given by nutritive perfusion failure (20 +/- 2 and 21 +/- 2%), intrahepatic leukocyte (60 +/- 10 and 121 +/- 48 cells/mm(2)), and platelet (12 +/- 4 and 34 +/- 4 cells/mm(2)) accumulation as well as parenchymal cell apoptosis (4 +/- 1 and 11 +/- 2 cells/mm(2)) and caspase cleavage (4.7 +/- 2.4- and 7.0 +/- 3.0-fold increase; P < 0.05 vs. saline-exposed controls). Higher doses of LPS (10 mg/kg ip) further increased intrahepatic leukocyte and platelet accumulation but not the extent of parenchymal apoptosis. Detailed spatial analysis revealed colocalization of leukocytes (range 12-24%) but barely of platelets (<6%) with apoptotic hepatocytes in all endotoxemic groups studied. It is of interest, however, that platelets were found at increasing rates in colocalization with leukocytes at 6 and 16 h after LPS exposure (5 mg/kg LPS: 7 +/- 3 and 25 +/- 6%; 10 mg/kg LPS: 11 +/- 4 and 14 +/- 1%). Platelet-leukocyte events significantly correlated with the extent of caspase cleavage as an indicator of tissue apoptosis (P < 0.05; r = 0.82). Blockade of apoptosis by a pan-caspase inhibitor caused a significant reduction of leukocyte adherence and platelet-leukocyte colocalization on LPS exposure. On the other hand, leukocytopenic animals revealed reduced hepatocyte apoptosis, although values still exceeded those of controls, and in leuko- and thrombocytopenic animals, hepatocyte apoptosis was found reduced to control values. Taken together, LPS-associated hepatocyte apoptosis seems to be initiated by circulating blood cells that become adherent within the liver but might also contribute to further sustain the inflammatory cell-cell response.

Activation and accumulation of leukocytes constitute a rate-limiting step in ischemia/reperfusion (I/R)-induced tissue injury. The signalling mechanisms, however, that regulate leukocyte rolling and adhesion in the colonic microcirculation are not known. The objective of the study was to define the role of CXC chemokines (MIP-2 and KC) in I/R-induced leukocyte-endothelial cell interactions in the mouse colon. In C57/B16 mice, colonic ischemia was induced by clamping the superior mesenteric artery for 30 min and leukocyte rolling and stationary adhesion were examined in venules after 120 and 240 min of reperfusion. I/R provoked a clear-cut increase in leukocyte rolling and adhesion in colonic venules. Both MIP-2 and KC were upregulated at the gene and protein level in the reperfused colon. Immunoneutralization of MIP-2 and KC by monoclonal antibodies reduced reperfusion-induced firm adhesion of leukocytes by 73% and 75%, respectively. Interestingly, combined inhibition of MIP-2 and KC additionally decreased leukocyte rolling by 79%, but did not further reduce the number of firmly adherent leukocytes. To study the role of oxygen free radicals (OFRs) in the regulation of CXC chemokine expression, additional animals were pretreated with the xanthine-oxidase inhibitor allopurinol. In fact, allopurinol treatment reduced the colonic levels of MIP-2 and KC by 62% and 64%, respectively. This study elucidates important interactions between OFRs and chemokines in the I/R-induced leukocyte response in the mouse colon. Moreover, our data demonstrate that CXC chemokines play a fundamental role in colonic I/R and that functional interference with CXC chemokines may protect against pathological inflammation in the colon.

Background: Leucocyte recruitment is a key feature in ischaemia-reperfusion (I/R)-triggered tissue injury. However, the mechanisms underlying leucocyte-endothelium interactions in the large bowel remain elusive because of a previous lack of models to examine the colonic microcirculation. The aim of this study was to develop and validate a novel method for studying reperfusion-induced leucocyte-endothelium interactions in the colon., Methods: The superior mesenteric artery was occluded for 30 min in male C57/Bl6 mice and leucocyte responses were analysed in colonic venules after 30-240 min of reperfusion. Analysis of leucocyte rolling and adhesion in colonic venules was made possible by an inverted approach using intravital fluorescence microscopy., Results: Thirty minutes of ischaemia and 120 min of reperfusion induced the strongest and most reproducible increase in leucocyte rolling and adhesion. This was associated with a significant increase in colonic levels of malondialdehyde (MDA). Administration of allopurinol and superoxide dismutase reduced I/R-induced leucocyte responses in a dose-dependent manner. Pretreatment with allopurinol attenuated the tissue content MDA in the colon by more than 60 per cent., Conclusion: A new method for examining I/R-induced leucocyte responses in the colonic microcirculation is described. Oxygen free radicals play an important role in triggering leucocyte rolling and adhesion in colonic venules.

1. The objective of the present study was to examine the role of the endothelial selectins (i.e. P- and E-selectin) in leukocyte-endothelium interactions in colonic venules by use of intravital microscopy. 2. Balb/c mice were exposed to dextran sodium sulphate (DSS) in the drinking water for 5 days or treated intraperitoneally (i.p.) with tumour necrosis factor-alpha (TNF-alpha) for 3 h. 3. In DSS-treated mice, mRNA of both P- and E-selectin were expressed and leukocyte rolling and adhesion was increased to 27+/-3 cells min(-1) and 36+/-8 cells mm(-1), respectively. An anti-P-selectin antibody abolished DSS-induced leukocyte rolling, whereas an antibody against E-selectin had no effect. Established leukocyte adhesion was insensitive to inhibition of the selectins. 4. DSS markedly increased production of TNF-alpha in the colon. TNF-alpha increased leukocyte rolling to 22+/-3 cells min(-1) and adhesion to 45+/-4 cells mm(-1). Only inhibition of P-selectin significantly reduced (>94%) leukocyte rolling provoked by TNF-alpha. Leukocyte adhesion was not changed by late anti-P-selectin antibody treatment. In contrast, pretreatment with the anti-P-selectin antibody not only abolished leukocyte rolling but also completely inhibited firm adhesion in response to TNF-alpha. 5. This study demonstrates that P-selectin plays an important role in leukocyte rolling in colonic venules, both in experimental colitis and when stimulated with TNF-alpha. Moreover, P-selectin-dependent leukocyte rolling was found to be a precondition for TNF-alpha-induced firm adhesion. Thus, these findings suggest that P-selectin may be a key target to reduce pathological recruitment of inflammatory cells in the colon.

Besides its central role in coagulatory pathways, thrombin is known to be a key mediator of macrophage and granulocyte activation in vitro. During recent years the concept of thrombin inhibition by the specific thrombin inhibitor, hirudin, has been established to treat septic disorders. Since basic mechanisms of sepsis include leukocyte/endothelial cell interaction and deterioration of capillary perfusion, we hypothesized that hirudin modulates leukocyte activation and microvascular injury. Severe endotoxemia was induced in Syrian hamsters by intravenous administration of endotoxin (lipopolysaccharide [LPS], E. coli, 2mg/kg) at 0 h. Hirudin (0.25 mg/kg/h) was substituted intravenously during the 4 h after the induction of endotoxemia (n = 7, hirudin). In control animals (n = 6, control) LPS was given without hirudin substitution. In skinfold chamber preparations leukocyte/endothelial cell interaction and functional capillary density (FCD, measure of capillary perfusion) were analyzed during a 24-h period after LPS injection using intravital fluorescence microscopy. Hirudin effectively normalized thromboplastin time and antithrombin activity when compared to controls (P < 0.05, ANOVA). However, hirudin did not attenuate LPS-induced arteriolar and venular leukocyte adherence, and even tended to increase leukocyte adherence after 24 h (P > 0.05, MANOVA). In parallel, addition of hirudin led to a significant deterioration of FCD over time when compared to controls (hirudin: baseline = 171 +/- 19 cm(-1) versus 16 +/- 9 at 24 h; control: baseline = 150 +/- 20 cm(-1) versus 62 +/- 18 at 24 h; P < 0.05). The fall in FCD in hirudin animals was associated with a significant increase of wet-to-dry weight ratios in lung, kidney, muscle, and small intestine (P < 0.05 versus control, ANOVA). Thus our study does not indicate a protective effect of hirudin on microcirculation during endotoxemia, despite an improvement of coagulatory parameters. This result may at least in part explain the lack of efficacy of hirudin on lethality during endotoxemia and sepsis.

A co-ordinated expression of specific adhesion molecules regulates leucocyte-endothelium interactions in the microcirculation. In the present study, we used intravital microscopy of the cremaster muscle in CD11a gene-targeted mice to examine the role of lymphocyte function antigen 1 (LFA-1, CD11a/CD18) in tumour necrosis factor alpha (TNF-alpha)-induced leucocyte rolling and firm adhesion in venules. We found that 30 min after TNF-alpha administration leucocyte rolling was unchanged compared with phosphate-buffered saline (PBS)-treated mice and similar in LFA-1-deficient and wild-type animals. In contrast, firm leucocyte adhesion in venules increased by almost 10-fold following 30 min of TNF-alpha challenge in LFA-1-expressing animals, whereas no increase was observed in LFA-1-deficient mice. Four hours after intrascrotal administration of TNF-alpha, venular leucocyte adhesion was found to be markedly increased, but similar in extent to LFA-1-deficient and wild-type mice. Histological examination of haematoxylin-eosin-stained tissue sections revealed that approximately 90% of the leucocytes in the TNF-alpha-stimulated venules in both wild-type and LFA-1-deficient mice were polymorphonuclear. Taken together, our functional in vivo data demonstrate that LFA-1 is an important adhesion molecule in early TNF-alpha-induced venular leucocyte adhesion.

Antithrombin (AT) is known as the most important natural inhibitor of thrombin activity and has been shown to improve distinct clinical parameters during the course of septic (endotoxin)-induced multiple organ dysfunction. We hypothesized that AT acts by inhibiting leukocyte activation and microvascular injury via the promotion of endothelial release of PGI(2), and therefore, we studied the effects of AT on leukocyte/endothelial cell interaction and microvascular perfusion during endotoxemia. In a skinfold preparation of Syrian hamsters, severe endotoxemia was induced by repeated administration of endotoxin intravenously [lipopolysaccharide (LPS), Escherichia coli, 2 mg/kg] at 0 and 48 h. AT (250 IU/kg) was administered intravenously at 0, 24, and 48 h (n = 6, AT group). In control animals (n = 5, control), LPS was given without AT supplementation. By intravital fluorescence microscopy, leukocyte-endothelial cell interaction and functional capillary density (FCD; measure of capillary perfusion) were analyzed during a 72-h period after the first LPS injection. AT significantly attenuated LPS-induced arteriolar and venular leukocyte adherence after both the first and the second LPS injection [P < 0.01, measures analysis of variance (MANOVA)]. In parallel, AT was effective in preventing LPS-induced depression of FCD after the first and the second LPS administration (P < 0.05, MANOVA). By pretreatment with the cyclooxygenase inhibitor indomethacin (n = 6), effects of AT on leukocyte adherence and FCD were found completely abolished. Thus our study indicates that AT exerts its beneficial effects in endotoxemia by reducing leukocyte-endothelial cell interaction and microvascular perfusion failure probably via liberation of prostacyclin from endothelial cells.

Background: Surface cooling is frequently used in a number of conditions, especially traumatic, ischemic, burn, and neurologic injury to reduce the tissue damage. However, the protective mechanisms of cold therapy on traumatized tissues remain unclear. Tumor necrosis factor-alpha (TNF-alpha) is a fundamental mediator in inflammatory reactions and trauma-induced tissue injury. In the present study, we examined the microvascular response to TNF-alpha challenge and the effects of local cooling on the TNF-alpha-induced changes in the striated muscle of hamsters., Methods: By the use of the dorsal skinfold chamber preparation and in vivo fluorescence microscopy in combination with computer-based image analysis, we determined TNF-alpha-induced leukocyte rolling and adhesion to microvascular endothelium, capillary perfusion, venular leakage, and cellular apoptosis with and without surface cooling., Results: We found that topical administration of 2000 units TNF-alpha caused a progressive impairment of microvascular perfusion and increased leukocyte recruitment and vascular macromolecular leakage. Local cooling to 10 degrees C for 60 minutes markedly (P < .05) inhibited the TNF-alpha-induced capillary perfusion failure and leukocyte response and slightly attenuated the increase of microvascular permeability after 180 minutes of stimulation. Furthermore, it was observed that 24 hours of TNF-alpha stimulation increased the number of apoptotic cells (i.e., nuclear condensation and fragmentation) by 10-fold. This TNF-alpha-mediated effect was almost abolished by treatment with local hypothermia., Conclusion: These data suggest that the protective effect of surface cooling of traumatized tissue is due to its attenuation of the microvascular inflammatory response associated with the inhibition of the process of apoptosis.

Sepsis-induced microvascular leukocyte/endothelial cell interaction may result in a deterioration of capillary perfusion that finally leads to septic organ dysfunction. The aim of the present study was to characterize a novel, sublethal, two-hit model of chronic systemic sepsis that allows the repeated analysis of microcirculation by intravital microscopy. In Syrian golden hamsters the effect of a single i.v. endotoxin (LPS, 2 mg/kg, E. coli) injection (SH-LPS group, n = 5 animals) vs. a double LPS injection (DH-LPS group, n = 6 animals) was analyzed. After monitoring baseline parameters (t1), measurements were performed at 30 min (t2), 3 h (t3), 8 h (t4), 24 h (t5), 48 h (t6), 56 h (t7) and 72 h (t8) (both groups) after initial LPS exposure. In DH-LPS animals, a second LPS injection (2 mg/kg) was given at t6 (48 h). Intravital fluorescence microscopy was performed in a dorsal skin fold chamber preparation and allowed determination of leukocyte-endothelial cell interaction (leukocyte rolling and sticking), and measurement of functional capillary density (FCD), which served as a measure of capillary perfusion. The first LPS injection comparably altered leukocyte/endothelial cell interaction and capillary perfusion in both groups (t1-t6, P > 0.05, MANOVA). Between t6 and t8 leukocyte adherence decreased in SH-LPS animals, whereas in DH-LPS animals adherence remained constantly elevated (SH-LPS: -53.0 +/- 6.2% between t6 and t8 vs. DH-LPS: -3 +/- 5; P < 0.05). The ongoing inflammatory response in DH-LPS animals was associated with a progressive deterioration of FCD, whereas FCD remained constant in SH-LPS animals (DH-LPS: -71.5 +/- 17% between t6 and t8 vs. SH-LPS: 3.0 +/- 13%; P < 0.05). In parallel, coagulatory parameters were found significantly altered only in DH-LPS animals but not in SH-LPS animals. We conclude that "double hit" LPS exposure is an appropriate model (i) to analyze repeatedly over time microcirculatory disorders under conditions of persistent endotoxemia-induced inflammatory response, and (ii) to prove the effectiveness of novel anti-inflammatory strategies.

Objectives: Cellular metabolism is dependent on the local temperature in tissues. Induced hypothermia has been shown to be protective in a number of conditions, especially traumatic, ischemic, burn, and neurological injury. However, the protective mechanisms of cold therapy remain controversial and the hemodynamic changes in the microcirculation of striated muscles in response to hypothermia have not been studied in detail previously., Methods: In this study, we investigated the microvascular response of local cooling and rewarming in the striated muscle of hamsters by use of the dorsal skinfold preparation and in vivo fluorescence microscopy., Results: We found that reduction of the surface temperature to 8 degrees C for 30 minutes caused arteriolar vasoconstriction with a decrease in diameters by 43+/-7% while the venular and capillary diameters remained unchanged. The cooling procedure also markedly reduced the functional capillary density and the blood flow velocity and diameters in all vessel types, i.e., arterioles, venules, and capillaries. Moreover, the percentage of capillaries with no flow increased from 0.4+/-0.5% to 44+/-14% after 10 minutes of cold therapy. However, these hemodynamic changes induced by local hypothermia were completely reversed to the precooling values after termination of cooling and 30 min of rewarming. Strikingly, we found no increase in the number of adherent leukocytes and vascular permeability after the cooling and rewarming period, while, in contrast, additional experiments with warm ischemia (30 minutes) and reperfusion (30 minutes), i.e., reduced microvascular perfusion and reperfusion at normothermia, caused a sustained decrease in local perfusion and a nine-fold increase in venular leukocyte adhesion., Conclusions: Taken together, our functional data demonstrate that hypothermia markedly reduces microvascular perfusion, which is completely restored upon rewarming. The reduced microvascular perfusion during hypothermia did not provoke an inflammatory response, whereas leukocyte recruitment was prominent after reduced perfusion at normothermia, indicating that transient hypothermia has no adverse effects on microvascular parameters in the striated muscle in vivo.

In contrast to the anticipation that in sepsis granulocyte colony-stimulating factor (G-CSF) would overactivate the nonspecific immune system by recruiting and priming leukocytes with consequent aggravation of inflammatory tissue lesions, recombinant (r) G-CSF pretreatment was protective in various experimental non-neutropenic models of inflammation. The mechanisms of protection, however, are not fully understood. Using intravital fluorescence microscopy, we show that rG-CSF enhances leukocyte endothelial cell interaction within the microvasculature of normal rat livers, whereas rG-CSF pretreatment of animals exposed to lipopolysaccharide (LPS) attenuates the LPS-induced leukocytic response, including stasis in sinusoids as well as rolling and adherence in postsinusoidal venules with subsequent tissue infiltration. Moreover, rG-CSF, which did not affect Kupffer cell activity in normal rat livers, reduced the immediate activation of Kupffer cells on LPS exposure, as indicated in vivo by the delayed adherence/phagocytosis of intra-arterially administered latex particles associated with attenuation of proinflammatory cytokine release (tumor necrosis factor alpha and interleukin-6). Finally, rG-CSF reduced LPS-induced nutritive perfusion failure and hepatocellular excretory dysfunction. This study provides evidence for a distinct, possibly tumor necrosis factor alpha-dependent modulation of LPS-induced cellular response within the liver by rG-CSF, thereby achieving protection against microcirculatory perfusion failure and hepatic dysfunction.

Postischemic reperfusion injury is caused by microcirculatory disturbances, including both nutritive perfusion failure (no reflow) and leukocyte activation (reflow paradox). Recent studies brought evidence that pentoxifylline (PTX) reduces tissue injury, decreases enzyme release, and improves survival after normothermic liver ischemia/reperfusion. The mechanisms of action, however, by which PTX protects postischemic tissue from injury have not been elucidated yet. With the use of fluorescence microscopy in a rat hepatic ischemia/reperfusion model, we studied in vivo the action of PTX on the manifestation of postischemic sinusoidal perfusion failure and microvascular leukocyte adherence. Microvascular reperfusion after 20 min portal triad cross-clamping was characterized by the cessation of blood flow within individual sinusoids (no reflow) and accumulation of leukocytes within the hepatic microvasculature, with stasis in sinusoids and rolling and firm adherence in postsinusoidal venules. PTX (20 mg/kg x hr i.v.) significantly (P < 0.05) attenuated microvascular leukocyte accumulation (44,600 +/- 1833 mm(-3) vs 67,684 +/- 2620 mm(-3) in saline-treated controls) and firm adherence of leukocytes in postsinusoidal venules (316.9 +/- 40.9 mm(-2) vs 522.9 +/- 95.0 mm(-2)); however, PTX did not influence manifestation of individual sinusoidal perfusion failure. Since reperfusion-induced parenchymal cell damage was found reduced in treated animals, we conclude that PTX attenuates postischemic injury in rat liver by reduction of leukocytic/inflammatory response but not by prevention of nutritive perfusion failure.

Leukocytic response plays a major role in the manifestation of hepatic ischemia/reperfusion (I/R) injury. To clarify whether post-ischemic hepatic leukocyte accumulation is based on increased leukocyte flux to the hepatic tissue due to systemic inflammation or chemoattractant activities or whether it represents solely a local tissue response without changing overall leukocyte flux and trafficking characteristics through the microvasculature, we studied acinar and sinusoidal leukocyte flux and distribution in rat livers in vivo both under normal (sham, n = 8) and post-ischemic (60' ischemia/75' reperfusion) conditions (I/R, n = 8), using fluorescence epi-illumination microscopy (rhodamine-6G). Hepatic ischemia/reperfusion significantly (p < 0.05) increased acinar leukocyte flux (58.4 +/- 20.9 cells/min vs 36.4 +/- 12.8 cells/min in sham controls); however, it did not exhibit increased heterogeneity of acinar leukocyte distribution, as indicated by the unchanged coefficient of variance (CV) of 0.36 +/- 0.16 (sham controls: 0.31 +/- 0.14). In parallel, analysis of individual sinusoidal leukocyte flux demonstrated significantly (p < 0.05) higher values (8.9 +/- 3.7 cells/min) after ischemia/reperfusion when compared with sham controls (5.7 +/- 1.9 cells/min), which, however, was not associated with increased heterogeneity of sinusoidal leukocyte trafficking (CV: 0.85 +/- 0.15 vs 0.85 +/- 0.16 in sham controls) and manifestation of preferential pathways. Analysis of blood cell count did not demonstrate an overall increase of total blood leukocyte count; however, an increased (p < 0.01) fraction of polymorphonuclear leukocytes (65.2 +/- 11.2%) and stab cells (9.5 +/- 7.9%) during post-ischemic reperfusion when compared with sham controls (8.8 +/- 3.5% and 0.2 +/- 0.4%) was demonstrated. Thus, the increase of hepatic leukocyte flux after ischemia/reperfusion may be the result of both the manifestation of a systemic inflammatory response and the increase of local chemoattractant activities, such as the production and release of the cytokine-induced neutrophil chemoattractant of the IL-8 family.

ACE inhibitors have been proven to be effective in the reduction of ischemia/reperfusion damage after myocardial ischemia. In an attempt to investigate this effect in a model of syngeneic liver transplantation in the rat, we compared a control group with an ACE inhibitor treatment group, in which enalapril was given i.v. before and during reperfusion. By means of in vivo microscopy, sinusoidal perfusion rate, permanent leukocyte sticking in sinusoids and postsinusoidal venules, and leukocyte rolling in postsinusoidal venules were assessed. Liver function was evaluated by measuring bile output. The sinusoidal perfusion rate was significantly improved by enalapril treatment. Leukocyte sticking in both sinusoids and postsinusoidal venules was found to be remarkably reduced in enalapril-treated animals; the fraction of rolling leukocytes remained unchanged. Bile output was increased in enalapril-treated animals. These results demonstrated, in a model of rat liver transplantation, that ACE inhibition by enalapril is effective in reducing hepatic ischemia/reperfusion damage as assessed by the leukocyte-endothelium interaction using in vivo microscopy and postreperfusion bile production.

Background/aims: We have previously demonstrated that endotoxemia induces an immediate leukocytic response within the hepatic microvasculature, with leukostasis in sinusoids and leukocyte adherence in post-sinusoidal venules. We have now studied the role of intercellular adhesion molecule-1 in endotoxin-induced hepatic leukocyte-endothelial cell interaction in vivo using fluorescence microscopy., Methods: Sprague-Dawley rats were pretreated with either 1 mg/kg (n = 5) or 2 mg/kg (n = 4) of a monoclonal anti-rat anti-intercellular adhesion molecule-1 antibody intravenously, followed by exposure to endotoxin (E. coli LPS 10 mg/kg iv). Animals pretreated with an isotype-matched IgG1 control antibody (n = 5) served as controls. Intravital fluorescence microscopy for analysis of the hepatic microcirculation was performed prior to and 1 h after lipopolysaccharide exposure., Results: At 1 h after lipopolysaccharide-exposure, control animals showed a marked reduction of systemic leukocyte count, which was associated with a significant (p < 0.01) hepatic microvascular accumulation of leukocytes with stasis in sinusoids, as well as rolling and adherence in postsinusoidal venules. Pretreatment with anti-intercellular adhesion molecule-1 was not effective in preventing either systemic leukopenia or intravascular sequestration of leukocytes in endotoxemic livers., Conclusions: Intercellular adhesion molecule-1 does not mediate endotoxin-induced early leukocytic response within the hepatic microcirculation.

Background: Leukocytes are suggested to modulate ischemia/reperfusion injury via membrane receptor-controlled interaction with the microvascular endothelium., Methods: With the use of intravital fluorescence microscopy we investigated the role of the intercellular adhesion molecule-1 (ICAM-1) in a rat model of hepatic reperfusion injury with a neutralizing monoclonal antibody (anti-ICAM-1)., Results: Sixty minutes of left lobar ischemia and reperfusion (isotype-matched immunoglobulin G1 control antibody) caused leukostasis in sinusoids (240 +/- 15 cells per liver lobule), leukocyte adherence in postsinusoidal venules (679 +/- 76 cells per mm2 endothelial surface of postsinusoidal venules), nutritive perfusion failure (15% +/- 2% nonperfused sinusoids), excretory dysfunction (bile flow, 1.2 +/- 0.3 microliters.min-1.gm-1), and loss of hepatocellular integrity (serum aspartate aminotransferase, 1353 +/- 317 units.L-1; serum alanine aminotransferase, 1055 +/- 265 units.L-1). Anti-ICAM-1 did not affect sinusoidal leukostasis; however, it effectively inhibited postischemic leukocyte adherence to the venular endothelial lining (217 +/- 38 cells/mm2, p < 0.01). Concomitantly, hepatic reperfusion injury, including sinusoidal perfusion (6% +/- 1% nonperfused sinusoids, p < 0.01), excretory function (bile flow, 1.8 +/- 0.1 microliters.min-1.gm-1, p < 0.05), and hepatocellular integrity (aspartate aminotransferase, 480 +/- 108 units.L-1; alanine aminotransferase, 447 +/- 80 units.L-1, p < 0.05), was significantly ameliorated by anti-ICAM-1., Conclusions: These findings prove in vivo the pivotal role of ICAM-1 in leukocyte-dependent manifestation of postischemic liver damage.

To clarify the in vivo relevance of leukocyte-endothelial cell interactions in the manifestation of hepatic ischemia-reperfusion (I/R) injury, we studied leukocyte flow behavior in sinusoids and postsinusoidal venules of postischemic hepatic tissue in rats using intravital microscopy. Reperfusion following either 20 min (n = 9) or 60 min (n = 9) of left hepatic lobar ischemia resulted in a significant increase of the number of stagnant leukocytes in sinusoids and adherent cells in postsinusoidal venules compared with sham-operated controls (n = 10). Transmission electron microscopy revealed the extravasation of leukocytes from both sinusoids (into the space of Disse) and postsinusoidal venules. In parallel, hepatic I/R was associated with increased serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities and reduced bile flow. Linear regression estimates revealed significant (P < 0.01) correlations between serum ALT (r = 0.76) and AST (r = 0.65) activities, bile flow (r = -0.62), and the number of adherent leukocytes in postsinusoidal venules. In contrast, parameters of hepatocellular integrity and function did not directly correlate with the number of stagnant leukocytes in liver sinusoids. We conclude that hepatic I/R induces accumulation, adherence, and extravasation of leukocytes in both hepatic sinusoids and postsinusoidal venules. However, the adherence of leukocytes to the endothelial lining of venules, rather than of sinusoids, may determine the manifestation of hepatocellular damage and liver dysfunction.

The leukocyte beta 2-integrin Mac-1 (CD11b/CD18) and its endothelial ligand intercellular adhesion molecule 1 (ICAM-1) are involved in leukocyte adhesion to and macromolecular leakage from postcapillary venules during inflammatory reactions. Both events are also encountered after ischemia-reperfusion of striated muscle, suggesting a central role of both adhesion proteins in reperfusion injury. Using intravital fluorescence microscopy and a microcirculation model in awake BALB/C mice, we investigated the effects of monoclonal antibodies (MAb) and Fab fragments to Mac-1 and MAb to ICAM-1 on leukocyte-endothelium interaction and macromolecular leakage of fluorescein isothiocyanate-dextran (1.5 x 10(5) mol wt) in striated skin muscle after 3 h of ischemia followed by reperfusion. We demonstrated that administration of MAb and Fab to Mac-1 before reperfusion was as effective as administration of MAb to ICAM-1, which was found to be significantly upregulated in the postischemic tissue by immunohistochemical analysis, in preventing postischemic leukocyte adhesion to and macromolecular leakage from postcapillary venules, whereas postischemic leukocyte rolling was not affected after MAb administration. Postischemic capillary perfusion was efficiently preserved in animals treated with anti-Mac-1 and anti-ICAM-1 MAb compared with animals receiving the isotype-matched control antibodies.(ABSTRACT TRUNCATED AT 250 WORDS)

Superoxide radicals formed during reperfusion of ischemic tissues have been identified as a key mediator in the microvascular manifestations of postischemic tissue damage. This understanding is based on studies in laboratory animals in which high doses of superoxide dismutase (SOD; 2.0-25.0 mg/kg body wt iv) were found to inhibit postischemic leukocyte adhesion and the leakage of fluid and macromolecules. Using a dorsal skinfold chamber model in hamsters, we demonstrate now that protection from reperfusion-induced leukocyte adhesion to venular endothelium after 4 h of ischemia to striated muscle can be attained by pretreatment of the animals with a significantly lower dose of exogenous CuZn-SOD (0.25 mg/kg body wt) or with heparin (2,000 IU/kg body wt), which induces a comparable increase in SOD plasma activity through the release of endogenous extracellular SOD from endothelial cell binding sites. This protective effect was maintained until 24 h after reperfusion. In contrast, CuZn-SOD or heparin failed to attenuate the postischemic shutdown of nutritional capillary perfusion, a phenomenon that is due to ischemia-induced endothelial cell swelling, rather than due to reperfusion-associated events, and hence is not susceptible to strategies directed against oxygen radicals generated during the reperfusion phase. The results of this study 1) imply that postischemic leukocyte/endothelium interaction can be attenuated by a low and clinically more relevant dose of SOD, and 2) caveat the administration of heparin in laboratory animals (i.e., to keep catheters patent) in studies of experimental ischemia/reperfusion injury or other oxygen radical-dependent pathomechanisms.

Microvascular injury associated with ischemia/reperfusion (I/R) is characterized by both "no reflow" and "reflow paradox." Prophylactic isovolemic hemodilution with dextran 60 to a hematocrit of 30% has been shown to prevent I/R-induced capillary no reflow in striated muscle. The objective of the present study was to analyze whether hemodilution prior to ischemia has the potential to reduce postischemic leukocyte-endothelium interaction, which is known to be one of the major components of I/R-induced reflow paradox. Syrian golden hamsters (n = 21) were fitted with a dorsal skinfold chamber, which contains striated muscle and subcutaneous tissue and allows for repetitive analyses of the microcirculation by means of intravital fluorescence microscopy. Four hr of pressure-induced ischemia and 30 min of subsequent reperfusion (controls, n = 7) resulted in a significant (P < 0.05) increase of microvascular leukocyte accumulation (40,630 +/- 12,731 mm-3) and adherence to the endothelial lining of postcapillary venules (74.2% +/- 11.5%) when compared to preischemic baseline (7,502 +/- 1,700 mm-3 and 3.4% +/- 1.0%, respectively). Recovery was not complete after an observation period of 24 hr reperfusion [13,735 +/- 2,666 mm-3 (P < 0.05) and 18.5% +/- 6.0% (P < 0.05)]. Prophylactic isovolemic hemodilution with 6% dextran 60 (Dx60) to a hematocrit of 30% (Dx60, n = 7) significantly attenuated postischemic leukocyte accumulation (23,402 +/- 13,837 mm-3; P < 0.05 vs. controls) and adherence (22.6% +/- 6.4%; P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

This quantitative in vivo fluorescence microscopy study investigated the relative impact of an optimized rinse solution (warm Carolina rinse) and that of an established storage solution (University of Wisconsin solution) on various pathomechanisms of hepatic reperfusion injury after cold storage. Syngeneic orthotopic, arterialized liver transplantation was performed in male Lewis rats after 24 hr of cold ischemia (n = 24). The four experimental groups differed according to the type of preservation/rinse solution used: University of Wisconsin solution/albumin rinse (group 1), autologous blood (just external cooling)/albumin rinse (group 2), blood/Carolina rinse (group 3) and University of Wisconsin solution/Carolina rinse (group 4). Hepatic microvascular perfusion, leukocyte accumulation and phagocytic activity of Kupffer cells were assessed by means of intravital fluorescence microscopy 30 to 90 min after reperfusion. Disturbances of microvascular perfusion were most pronounced in group 2, markedly reduced by University of Wisconsin solution (group 1) and Carolina rinse (group 3) and minimized by combined use of University of Wisconsin solution and Carolina rinse in group 4. Intrahepatic leukocyte-endothelium interaction in sinusoids and postsinusoidal venules was found to depend on the application of Carolina rinse before reperfusion rather than the use of University of Wisconsin solution during cold storage. Activation of phagocytosis by Kupffer cells was most pronounced in group 1, intermediate in groups 2 and 3 and not noticeable in group 4. Hepatocellular excretory function as assessed on the basis of total bile flow and excretion of bile acids during the first 90 min after reperfusion was found to be improved by application of Carolina rinse, both after storage in blood or in University of Wisconsin solution.(ABSTRACT TRUNCATED AT 250 WORDS)

Leukocyte adhesion and subendothelial emigration, constant hallmarks of early atherogenesis, have been ascribed to the action of oxidized low-density lipoprotein (oxLDL). Using intravital fluorescence microscopy in the skinfold-chamber model in hamsters, we have previously shown that systemic administration of oxLDL stimulates leukocyte adhesion in vivo through a mechanism that depends on the generation and/or action of both leukotrienes and superoxide radicals. On the basis of the fact that oxygen radical-catalyzed peroxidation of phospholipids results in the generation of fragments with short sn2 residues, which besides authentic platelet-activating factor (PAF), activate the receptor for PAF on leukocytes and thereby induce leukocyte adhesion, we asked whether pretreatment of hamsters with a specific PAF receptor antagonist (WEB2170; 1 mg/kg of body weight IV, 10 minutes before oxLDL) attenuates leukocyte adhesion after injection of oxLDL (4 mg/kg of body weight IV, oxidized by 7.5 mumol/L Cu2+ for 18 hours at 37 degrees C). We demonstrate herein that in contrast to untreated control animals in which oxLDL elicited rolling and adhesion of circulating leukocytes to the endothelium of venules and arterioles, oxLDL-induced leukocyte adhesion was significantly attenuated in WEB2170-pretreated animals. These changes cannot be ascribed to alterations of microhemodynamic parameters and, hence, wall shear conditions. This finding indicates that oxLDL-induced leukocyte/endothelium interaction involves the PAF receptor, which may function both as a receptor for authentic PAF or for PAF-like lipids that are generated in a free radical-catalyzed peroxidation of phospholipids.

Although cigarette smoking has been identified as a major risk factor for cardiovascular diseases, the underlying pathomechanism is largely unknown. Using a dorsal skinfold chamber model in Syrian golden hamsters for intravital microscopy on striated muscle microcirculation, we investigated whether cigarette smoke (CS) affects the adhesion of circulating leukocytes to the endothelium, a constant feature of early atherogenesis and a hallmark of ischemia-reperfusion injury. Awake hamsters were exposed for 5 min to the mainstream smoke of one cigarette (2R1 research cigarette), inducing nicotine, cotinine, and carboxyhemoglobin plasma levels comparable to levels found in human smokers. In control animals (n = 7), CS exposure elicited the rolling and subsequent adhesion of fluorescently stained leukocytes to the endothelium of arterioles and postcapillary venules. Leukocyte/endothelium interaction was preceded by an early rise in xanthine oxidase activity and intravascular hemolysis. Leukocyte adhesion and xanthine oxidase (XO) activation were significantly attenuated in hamsters pretreated with superoxide dismutase (5 mg/kg, 10 min prior to CS, n = 7), suggesting a key role of superoxide in this event. These in vivo results suggest a novel pathomechanism of CS-induced cardiovascular pathology.

Leukocyte activation, adhesion, and emigration serve a protective role during a well-contained inflammatory response. However, under certain pathologic conditions such as endotoxemia, inflammatory bowel disease, and ischemia-reperfusion injury, leukocytes may turn against the host and aggravate--rather than prevent--tissue damage. Numerous experimental studies have been performed during the last decade to investigate the pathophysiologic role of leukocyte accumulation and adhesion during ischemia/reperfusion injury of various organs, in particular of the myocardium. Most of the latter studies investigated whether the consequences of experimental myocardial infarction could be attenuated by interventions aimed at the inhibition of chemotactic leukocyte infiltration or adhesion (or both) to microvascular endothelial cells. Although many promising results were reported, the consequent step towards an introduction of these strategies into experimental or even routine clinical management of patients with myocardial infarction has so far not been undertaken. In this manuscript, the authors try to give an overview on the state of the art of "antileukocyte" strategies in myocardial ischemia-reperfusion injury and to offer explanations for incongruent data obtained with diverse experimental approaches (animal species, treatment modalities, surgical and anesthesiologic artifacts, techniques for morphologic and functional evaluation of tissue damage). The authors conclude that long-term preclinical studies on suitable animal models, thoroughly investigating the positive and negative effects of antileukocyte interventions on the functional consequences of myocardial ischemia-reperfusion injury, are mandatory before the first clinical trial can be advocated.

Background: The adhesion of leukocytes to the vascular endothelium has been identified as a constant, early feature of atherogenesis. Using a skinfold chamber model in hamsters for intravital microscopy, we have recently demonstrated the chemotactic and adhesion-promoting action of oxidatively modified low density lipoprotein (oxLDL) in vivo., Experimental Design: In order to rule out a species specificity of the experimental approach, and to investigate the involvement of leukocyte adhesion receptors in oxLDL-induced leukocyte/endothelium interaction, we have adapted the skinfold chamber model to hairless mice. Using intravital fluorescence microscopy, leukocyte/endothelium interaction in a fine striated skin muscle was assessed during the time course after intravenous injection of native human LDL (4 mg/kg body weight) and oxLDL (oxidized in vitro by 7.5 microM Cu2+, 6 hours, 37 degrees C) into control mice and into mice pretreated with either the selective inhibitor of leukotriene biosynthesis MK-886 (20 mumol/kg body weight, intravenously, 10 minutes before oxLDL) or with a monoclonal antibody directed towards the CD11b subunit of the CD11b/CD18 adhesion receptor complex on leukocytes (monoclonal antibody anti-Mac1, 0.5 mg/kg, iv, 10 minutes before oxLDL)., Results: We demonstrate in this study that injection of oxLDL (4 mg LDL-cholesterol/kg, intravenously, oxidized by 7.5 microM Cu2+, 6 hours, 37 degrees C), but not of native LDL or LDL-free Cu(2+)-solution, elicits the adhesion of fluorescently stained leukocytes to the endothelium of postcapillary venules (173 +/- 75 cells/mm2 at 20 minutes after oxLDL, mean +/- SD) and arterioles (119 +/- 74 cells/mm2 at 20 minutes after oxLDL, mean +/- SD) in the mice. OxLDL-induced leukocyte adhesion was entirely prevented by pretreatment of the animals with the inhibitor of leukotriene biosynthesis or with monoclonal antibody anti-Mac-1., Conclusions: These results demonstrate the involvement of leukotrienes and of the CD11b/CD18 adhesion receptor complex in oxLDL-induced leukocyte adhesion in vivo and rule out a species specificity of this pathophysiologic event.

Although cigarette smoke (CS) has been identified as an independent risk factor for atherogenesis and sudden cardiac death, the underlying pathomechanism has not been clarified. A common factor of both atherogenesis and ischemia/reperfusion damage associated with myocardial infarction is the adhesion of circulating leukocytes to the vascular endothelium. Searching for the mechanism by which CS exerts its deleterious effects on the cardiovascular system, we used a dorsal skinfold chamber model in hamsters for intravital microscopy to examine the effect of CS on the interaction of fluorescently stained leukocytes with the microvascular endothelium in striated muscle. Exposure of awake animals (n = 7) for 5 minutes to the mainstream smoke of one cigarette (2R1 research cigarette) elicited rolling and subsequent adhesion of circulating leukocytes to the endothelium of both arterioles and postcapillary venules with a maximum 30 minutes after CS-exposure. In order to test a putative mediator role of the chemotactic and adhesion-promoting leukotrienes in this event, we pretreated another group of 7 animals with MK-886, a potent and specific inhibitor of leukotriene biosynthesis (20 mumol/kg body weight, iv, 30 minutes prior to CS exposure). While no inhibitory effect was seen on CS-induced leukocyte rolling along the microvascular endothelium. MK-886 pretreatment significantly attenuated leukocyte adhesion to arterioles (5.2 +/- 13.7 cells/mm2 vs. 54.1 +/- 54.8 in control animals. P < 0.01) and venules (37.0 +/- 33.6 cells/mm2 vs. 161.6 +/- 91.1 in control animals, P < 0.01), 30 minutes after CS exposure, suggesting a key mediator role of leukotrienes in this event. We propose that the stimulation of leukocyte/endothelium interaction by CS may provide the pathophysiologic basis for--or at least contribute to--its deleterious effects on cardiovascular mortality and morbidity. The identification of the mediator role of leukotrienes in this event may open the way to novel pharmacologic and dietary approaches for the prophylaxis of CS-induced cardiovascular pathology.