Important role of P-selectin for leukocyte recruitment, hepatocellular injury, and apoptosis in endotoxemic mice

The Effect of Hypothermic Machine Perfusion to Ameliorate Ischemia-Reperfusion Injury in Donor Organs

Hypothermic machine perfusion (HMP) has become the new gold standard in clinical donor kidney preservation and a promising novel strategy in higher risk donor livers in several countries. As shown by meta-analysis for the kidney, HMP decreases the risk of delayed graft function (DGF) and improves graft survival. For the liver, HMP immediately prior to transplantation may reduce the chance of early allograft dysfunction (EAD) and reduce ischemic sequelae in the biliary tract. Ischemia-reperfusion injury (IRI), unavoidable during transplantation, can lead to massive cell death and is one of the main causes for DGF, EAD or longer term impact. Molecular mechanisms that are affected in IRI include levels of hypoxia inducible factor (HIF), induction of cell death, endothelial dysfunction and immune responses. In this review we have summarized and discussed mechanisms on how HMP can ameliorate IRI. Better insight into how HMP influences IRI in kidney and liver transplantation may lead to new therapies and improved transplant outcomes.

Immunohistochemical Study of Adhesion Molecules in Irritable Bowel Syndrome: A Comparison to Inflammatory Bowel Diseases

Background:

The surface of endothelial cells is covered with cell adhesion molecules including E-selectin, intercellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule 1 (VCAM-1) that mediate the adhesion and extravasation of leukocytes and play a pivotal role in inflammatory response. The aim of this study was to investigate the role of expression of adhesion molecules in inflammatory bowel disease (IBD) patients, irritable bowel syndrome (IBS) patients, and normal colonic mucosa.

Materials and Methods:

IBS and IBD patients along with normal colonic mucosa were recruited in the study. In all groups, two biopsies were taken from each of the three anatomical sites (terminal ileum, cecum, and rectum). Three monoclonal antibodies, E-selectin mAb, VCAM-1 mAb, and ICAM-1 mAb, were applied for immunohistochemical analysis.

Results:

In IBD patients, the expression of intensity of E-selectin, VCAM-1, and ICAM-1 was found decreased, at least in cecum and rectum, in comparison with IBS patients and controls (P < 0.001, P < 0.005, and P < 0.007, respectively). Comparison of the expression of intensity of the aforementioned molecules in IBS patients and controls revealed significant augmentation at the cecum and rectum of IBS patients.

Conclusions:

The expression of adhesion molecules appeared lower in IBD patients compared to IBS patients and controls. In addition, the expression of adhesion molecules appeared higher in IBS compared to the control group. Therefore, it could be hypothesized that the expression of adhesion molecules could be considered as an early event in the process of proinflammatory IBS group and may be other factors play a crucial role in the process of intestinal inflammation in IBD patients.

Use of TLR9 and TLR7/8 agonists in combination with d-galactosamine in exploring models for distinct severities of systemic inflammation relative to liver injury

Challenges with various TLR ligands (TLRLs)in combination with D-galactosamine (GalN) in rodents may mimic diverse conditions of acute inflammation and organ failure. Here, we report that CpG (ODN1826, TLR9 agonist)/GalN induced a liver-specific injury with modest systemic effects, whereas R848 (resiquimod, TLR7/8 agonist)/GalN exhibited systemic and liver toxicity. We also observed the protective effect of Gr-1+ cells (the population containing neutrophils) against liver injury in both the R848/GalN and CpG/GalN models. In cytokine measurements, the intraperitoneal administration of antibodies showed a non-specific tolerance induction effect, which was more pronounced in the CpG/GalN than in the R848/GalN model. Cytokine analyses also suggested that the TLR9 agonist/GalN induced a limited degree of systemic inflammation compared to TLR7/8 agonist/GalN models. The relevance of this finding to the TLR9-mediated induction of stress tolerance (protective effect) in non-immune cells is discussed.

The vimentin rod domain blocks P-selectin-P-selectin glycoprotein ligand 1 interactions to attenuate leukocyte adhesion to inflamed endothelium

Acute inflammation begins with leukocyte P-selectin glycoprotein ligand-1 (PSGL-1) binding to P-selectin on inflamed endothelium and platelets. In pathologic conditions, this process may contribute to secondary organ damage, like sepsis-induced liver injury. Therefore, developing novel therapies to attenuate inflammation may be beneficial. We previously reported that recombinant human vimentin (rhVim) binds P-selectin to block leukocyte adhesion to endothelium and platelets. In this study, we used SPOT-peptide arrays to identify the rod domain as the active region within rhVim that interacts with P-selectin. Indeed, recombinant human rod domain of vimentin (rhRod) binds to P-selectin with high affinity, with in silico modeling suggesting that rhRod binds P-selectin at or near the PSGL-1 binding site. Using bio-layer interferometry, rhRod decreases PSGL-1 binding to immobilized P-selectin, corroborating the in silico data. Under parallel-plate flow, rhRod blocks leukocyte adhesion to fibrin(ogen)-captured platelets, P-selectin/Fc-coated channels, and IL-1β/IL-4-co-stimulated human umbilical vein endothelial cells. Finally, using intravital microscopy in endotoxemic C57Bl/6 mice, rhRod co-localizes with P-selectin in the hepatic sinusoids and decreases neutrophil adhesion to hepatic sinusoids. These data suggest a potential role for rhRod in attenuating inflammation through directly blocking P-selectin-PSGL-1 interactions.

An inflammatory vascular endothelium-mimicking microfluidic device to enable leukocyte rolling and adhesion for rapid infection diagnosis

Recruitment of circulating leukocytes to sites of infection is of utmost importance in the development, propagation, and outcome of sepsis. These multi-step processes are mediated by interactions between adhesion receptors of leukocytes and cell adhesion molecules (CAMs) of endothelial cells, such as P-selectin, E-selectin and ICAM-1. However, the potential utility of the CAMs-facilitated leukocyte capture has not been thoroughly investigated as an index of the host response to infection for diagnostic purposes. Here, we report that the systemic infection affects the expression of CAMs ligands on leukocytes, upregulating the expression of P-selectin ligand-1 (PSGL-1) and increasing the number of PSGL-1- and E-selectin ligand-1 (ESL-1)-expressing leukocyte levels in septic blood. We leveraged this finding to determine infection by measuring the increased adhesion of leukocytes to an inflammatory vascular endothelium-mimicking microchannel coated with CAMs. We successfully validated that the proposed method can significantly differentiate infection in bacteremia and endotoxemia models in rats as early as an hour post-infection using a finger-prick volume of blood (50 μL), which were unachievable with the conventional diagnostic methods.

Triterpenoids Extracted From Antrodia cinnamomea Mycelia Attenuate Acute Alcohol-Induced Liver Injury in C57BL/6 Mice via Suppression Inflammatory Response

Excessive alcohol consumption causes liver injury–induced mortality. Here we systematically analyzed the structure of triterpenoids extracted from Antrodia cinnamomea mycelia (ACT) and investigated their protective effects against acute alcohol-induced liver injury in mice. Liquid chromatography–mass spectrometry and liquid chromatography with tandem mass spectrometry were performed to determine the structures of ACT constituents. Alcohol-induced liver injury was generated in C57BL/6 mice by oral gavage of 13 g/kg white spirit (a wine at 56% ABV). Mice were treated with either silibinin or ACT for 2 weeks. Liver injury markers and pathological signaling were then quantified with enzyme-linked immunosorbent assays, antibody array assays, and Western blots, and pathological examinations were performed using hematoxylin-eosin staining and periodic acid–Schiff staining. Triterpenoids extracted from A. cinnamomea mycelia contain 25 types of triterpenoid compounds. A 2-weeks alcohol consumption treatment caused significant weight loss, liver dyslipidemia, and elevation of alanine aminotransferase, aspartate aminotransferase, γ-glutamyl transferase, and alkaline phosphatase activities in the serum and/or liver. These effects were markedly reversed after 2-weeks ACT administration. Triterpenoids extracted from A. cinnamomea mycelia alleviated the organ structural changes and inflammatory infiltration of alcohol-damaged tissues. Triterpenoids extracted from A. cinnamomea mycelia inhibited proinflammatory cytokine levels and enhanced anti-inflammatory cytokine levels. Acute alcohol treatment promoted inflammation with significant correlations to hypoxia-inducible factor 1α (HIF-1α), which was reduced by ACT and was partially related to modulation of the protein kinase B (Akt)/70-kDa ribosomal protein S6 kinase phosphorylation (p70S6K) and Wnt/β-catenin signaling pathways. In conclusion, ACT protected against acute alcohol-induced liver damage in mice mainly through its suppression of the inflammatory response, which may be related to HIF-1α signaling.

The role of adhesion molecules in inflammatory bowel disease in children. Assessment of the possible risk of cardiovascular complications

Introduction

Inflammatory bowel diseases (IBD) are chronic diseases that proceed with exacerbation and remission phases. Adhesion molecules play a significant role in inflammatory processes. The same adhesion molecules play an important role in atherogenesis.

Aim

To assess the risk of atherosclerosis in IBD in children.

Material and methods

The study included 40 patients with IBD (25 with Crohn's disease - CD and 15 with ulcerative colitis - UC) aged 4-17 years. In the study group, concentrations of selected adhesion molecules (intracellular adhesion molecule - ICAM, vascular cell adhesion molecule - VCAM, E-selectin) and selected parameters of lipid metabolism in serum were assessed.

Results

No statistically significant differences between CD and UC patients and in the control group, in mean values of selected adhesins were obtained. Average variable VCAM was significantly lower in patients with CD than in patients with UC in the active stage of the diseases. Significantly higher average levels of triglycerides (TG) and high density lipoproteins (HDL) were found in the control group than in patients with CD. Significantly higher levels of total cholesterol (CHL) and HDL were noticed in the control group patients than in the patients with UC. The HDL/CHL was significantly higher in controls than in patients with UC.

Conclusions

No increased risk of developing atherosclerosis was found in children with IBD. Decreased risk in patients during exacerbation of inflammatory bowel disease was revealed, which may result from malnutrition typical for acute disease phase.

Streptococcal M1 protein triggers chemokine formation, neutrophil infiltration, and lung injury in an NFAT-dependent manner

Streptococcus pyogenes of the M1 serotype can cause STSS, which is associated with significant morbidity and mortality. The purpose of the present study was to examine the role of NFAT signaling in M1 protein-induced lung injury. NFAT-luc mice were treated with the NFAT inhibitor A-285222 before administration of the M1 protein. Neutrophil infiltration, edema, and CXC chemokines were quantified in the lung, 4 h after challenge with the M1 protein. Flow cytometry was used to determine Mac-1 expression. Challenge with the M1 protein increased NFAT-dependent transcriptional activity in the lung, spleen, and liver in NFAT-luc mice. Administration of the NFAT inhibitor A-285222 abolished M1 protein-evoked NFAT activation in the lung, spleen, and liver. M1 protein challenge induced neutrophil recruitment, edema, and CXC chemokine production in the lung, as well as up-regulation of Mac-1 on circulating neutrophils. Inhibition of NFAT activity attenuated M1 protein-induced neutrophil infiltration by 77% and edema formation by 50% in the lung. Moreover, administration of A-285222 reduced M1 protein-evoked pulmonary formation of CXC chemokine >80%. In addition, NFAT inhibition decreased M1 protein-triggered Mac-1 up-regulation on neutrophils. These findings indicate that NFAT signaling controls pulmonary infiltration of neutrophils in response to streptococcal M1 protein via formation of CXC chemokines and neutrophil expression of Mac-1. Thus, the targeting of NFAT activity might be a useful way to ameliorate lung injury in streptococcal infections.

Platelets, selectins, and the control of tumor metastasis

The significant role of platelets and P-selectin in assisting tumor cell metastasis to the lungs has been frequently reported and reviewed. However, evidence recently has come to light on other pro-metastatic mechanisms of platelets beyond that of tumor cell protection from immune cell attack and aiding extravasation, such as promoting epithelial to mesenchymal transition in tumor cells and conveying signals from the primary tumor to distant tissues that optimize conditions for metastasis. Moreover, the role of platelets and selectins in hematogenous metastasis to frequently targeted organs other than the lungs has been less well examined. This review aims to summarize the literature on the roles of platelets in all stages of the metastatic process and to examine the participation of platelets and selectins in hematogenous metastasis to the lungs, liver, bone, and brain. In the light of the available evidence, potential therapeutic avenues for the control of metastasis are also discussed.

Chronic plus binge ethanol feeding synergistically induces neutrophil infiltration and liver injury in mice: a critical role for E-selectin

Chronic plus binge ethanol feeding acts synergistically to induce liver injury in mice, but the mechanisms underlying this phenomenon remain unclear. Here, we show that chronic plus binge ethanol feeding synergistically up-regulated the hepatic expression of interleukin-1β and tumor necrosis factor alpha and induced neutrophil accumulation in the liver, compared with chronic or binge feeding alone. In vivo depletion of neutrophils through administration of an anti-Ly6G antibody markedly reduced chronic-binge ethanol feeding-induced liver injury. Real-time polymerase chain reaction analyses revealed that hepatic E-selectin expression was up-regulated 10-fold, whereas expression of other neutrophil infiltration-related adhesion molecules (e.g., P-selectin, intercellular adhesion molecule 1, and vascular cell adhesion molecule 1) was slightly up- or down-regulated in this chronic-binge model. The genetic deletion of E-selectin prevented chronic-binge ethanol-induced hepatic neutrophil infiltration as well as elevation of serum transaminases without affecting ethanol-induced steatosis. In addition, E-selectin-deficient mice showed reduced hepatic expression of several proinflammatory cytokines, chemokines, and adhesion molecules, compared to wild-type mice, after chronic-binge ethanol feeding. Finally, the expression of E-selectin was highly up-regulated in human alcoholic fatty livers, but not in alcoholic cirrhosis.

CONCLUSIONS

Chronic-binge ethanol feeding up-regulates expression of proinflammatory cytokines, followed by the induction of E-selectin. Elevated E-selectin plays an important role in hepatic neutrophil infiltration and injury induced by chronic-binge feeding in mice and may also contribute to the pathogenesis of early stages of human alcoholic liver disease.

Increased platelet and microparticle activation in HIV infection: upregulation of P-selectin and tissue factor expression

OBJECTIVE

HIV-1-infected patients have an increased risk for atherothrombosis and cardiovascular disease, but the mechanism behind these risks is poorly understood. We have previously reported that expression of tissue factor (TF) on circulating monocytes is increased in persons with HIV infection and that TF expression is related to immune activation, to levels of HIV in plasma, and to indices of microbial translocation. In this study, we explore the activation state of platelets in HIV disease.

METHODS

Here, using flow cytometry-based assays, we measured platelet and platelet microparticle (PMP) activation in samples from HIV-1-infected donors and controls.

RESULTS

Platelets and PMPs from HIV-1-infected patients are activated (as reflected by expression of CD62 P-selectin) and also more frequently expressed the procoagulant TF than did platelets and PMPs obtained from controls. Expression of these proteins was directly related to expression of TF on monocytes, to markers of T-cell activation (CD38 and HLA-DR), and to plasma levels of soluble CD14, the coreceptor for bacterial lipopolysaccharride. Platelet and microparticle expression of TF was not related to plasma levels of HIV but expression of P-selectin was related to plasma levels of HIV; neither TF nor P-selectin expression was related to CD4 T-cell count.

CONCLUSIONS

Platelets and microparticles are activated in HIV infection, and this activated phenotype may contribute to the increased risk for cardiovascular and thrombotic events in this population although a role for other confounding cardiovascular risks cannot be completely excluded.

Rho-kinase regulates adhesive and mechanical mechanisms of pulmonary recruitment of neutrophils in abdominal sepsis

We hypothesized that Rho-kinase signaling plays a role in mechanical and adhesive mechanisms of neutrophil accumulation in lung. Male C57BL/6 mice were treated with the Rho-kinase inhibitor Y-27632 prior to cecal ligation and puncture (CLP). Lung levels of myeloperoxidase (MPO) and histological tissue damage were determined 6h and 24h after CLP. Expression of Mac-1 and F-actin formation in neutrophils were quantified by using flow cytometry 6h after CLP. Mac-1 expression and F-actin formation were also determined in isolated neutrophils up to 3h after stimulation with CXCL2. Labeled and activated neutrophils co-incubated with Y-27632, an anti-Mac-1 antibody and cytochalasin B were adoptively transferred to CLP mice. Y-27632 reduced the CLP-induced pulmonary injury and MPO activity as well as Mac-1 on neutrophils. Neutrophil F-actin formation peaked at 6h and returned to baseline levels 24h after CLP induction. Rho-kinase inhibition decreased CLP-provoked F-actin formation in neutrophils. CXCL2 rapidly increased Mac-1 expression and F-actin formation in neutrophils. Co-incubation with Y-27632 abolished CXCL2-induced Mac-1 up-regulation and formation of F-actin in neutrophils. Notably, co-incubation with cytochalasin B inhibited formation of F-actin but did not reduce Mac-1 expression on activated neutrophils. Adoptive transfer experiments revealed that co-incubation of neutrophils with the anti-Mac-1 antibody or cytochalasin B significantly decreased pulmonary accumulation of neutrophils in septic mice. Our data show that targeting Rho-kinase effectively reduces neutrophil recruitment and tissue damage in abdominal sepsis. Moreover, these findings demonstrate that Rho-kinase-dependent neutrophil accumulation in septic lung injury is regulated by both adhesive and mechanical mechanisms.

P-selectin mediates neutrophil rolling and recruitment in acute pancreatitis

BACKGROUND

The adhesive mechanisms regulating leucocyte-endothelium interactions in the pancreas remain elusive, but selectins may play a role. This study examined the molecular mechanisms mediating leucocyte rolling along the endothelium in the pancreas and the therapeutic potential of targeting the rolling adhesive interaction in acute pancreatitis (AP).

METHODS

Pancreatitis was induced by retrograde infusion of 5 per cent sodium taurocholate into the pancreatic duct, repeated intraperitoneal administration of caerulein (50 µg/kg) or intraperitoneal administration of L-arginine (4 g/kg) in C57BL/6 mice. A control and a monoclonal antibody against P-selectin were administered before and after induction of AP. Serum and tissue were sampled to assess the severity of pancreatitis, and intravital microscopy was used to study leucocyte rolling.

RESULTS

Taurocholate infusion into the pancreatic duct increased the serum level of trypsinogen, trypsinogen activation, pancreatic neutrophil infiltration, macrophage inflammatory protein (MIP) 2 formation and tissue damage. Immunoneutralization of P-selectin decreased the taurocholate-induced increase in serum trypsinogen (median (range) 17·35 (12·20-30·00) versus 1·55 (0·60-15·70) µg/l; P = 0·017), neutrophil accumulation (4·00 (0·75-4·00) versus 0·63 (0-3·25); P = 0·002) and tissue damage, but had no effect on MIP-2 production (14·08 (1·68-33·38) versus 3·70 (0·55-51·80) pg/mg; P = 0·195) or serum trypsinogen activating peptide level (1·10 (0·60-1·60) versus 0·45 (0-1·80) µg/l; P = 0·069). Intravital fluorescence microscopy revealed that anti-P-selectin antibody inhibited leucocyte rolling completely in postcapillary venules of the inflamed pancreas.

CONCLUSION

Inhibition of P-selectin protected against pancreatic tissue injury in experimental pancreatitis. Targeting P-selectin may be an effective strategy to ameliorate inflammation in AP.

Blockade of gC1qR/p33, a receptor for C1q, inhibits adherence of Staphylococcus aureus to the microvascular endothelium

Endovascular infections with Staphylococcus aureus (S. aureus) are associated with high mortality. gC1qR/p33 (gC1qR), a receptor for the complement component C1q expressed on endothelial cells, interacts with protein A of S. aureus and gC1qR blockade reduces S. aureus colonization during infective endocarditis. The aim of this study was to analyze in vivo whether this observation is due to a decreased interaction of S. aureus with the microvascular endothelium. A dorsal skinfold chamber was prepared in Syrian golden hamsters, which were treated with the monoclonal antibody (MAb) 74.5.2 directed against gC1qR or vehicle. The interaction of fluorescein isothiocyanate (FITC)-labeled staphylococci and leukocytes with the endothelium was analyzed under physiological conditions as well as after TNF-α-induced inflammation using intravital fluorescence microscopy. Administration of MAb 74.5.2 significantly reduced adherence of S. aureus to the endothelium in untreated and TNF-α-exposed tissue. In addition, we could demonstrate in vitro that S. aureus adherence to human endothelial cells was inhibited by MAb 74.5.2. Blockade of gC1qR did not affect leukocyte-endothelial cell interaction. In conclusion, our findings indicate that immunological inhibition of gC1qR may be therapeutically used to decrease the interaction of S. aureus with the microvascular endothelium.

Mutation of mitochondrial ATP8 gene improves hepatic energy status in a murine model of acute endotoxemic liver failure

AIMS

Mitochondria not only generate and modulate bioenergy but also serve as biosensors for oxidative stress, and eventually become effector organelles for cell viability. Therefore, the implications of mitochondrial (dys)function in the development of multiple organ failure are profound. We investigated whether a mutation in the ATPase subunit-8 gene affects the course of endotoxemic acute liver failure.

MAIN METHODS

C57BL/6J (ATP8 wild type) and C57BL/6J-mt(FVB/N) (ATP8 mutant) mice were challenged with d-galactosamine (GalN) and Escherichia coli lipopolysaccharide (LPS) for induction of acute liver failure, and studied 6 h thereafter. Control mice received physiological saline only. Analysis included in vivo fluorescence microscopy of hepatic microcirculation and levels of hepatocellular apoptosis, hepatic adenosine nucleotides and oxidative stress. Additionally, survival rates were assessed.

KEY FINDINGS

Induction of endotoxemic liver failure provoked marked liver damage, which was coexistent with a drop of total adenosine nucleotide levels and increased oxidative stress. Of interest, oxidative stress was higher in the GalN/LPS challenged ATP8 mutants compared to wild types. Concomitantly, adenosine triphosphate (ATP) levels in livers of mice carrying the ATP8 mutation remained higher than those in wild type mice. As net result, ATP8 mutants showed lower transaminase release and a tendency to better survival rate upon GalN/LPS exposure compared to wild types.

SIGNIFICANCE

Our findings demonstrate that mutation in the ATPase subunit-8 partially protects mice against endotoxemic stress, most probably due to better hepatic energy status despite elevated oxidative stress. Thus, modulating mitochondrial function to preserve bioenergetic status may be an effective strategy to protect against sepsis-induced multiorgan dysfunction.

Kupffer cell depletion reduces hepatic inflammation and apoptosis but decreases survival in abdominal sepsis

OBJECTIVE

During abdominal sepsis, the activation of hepatic Kupffer cells (KC) and its consequences are of central interest. This study evaluates the impact of selective KC depletion on hepatic microcirculation, cytokine release, and systemic alterations in the colon ascendens stent peritonitis (CASP), a model of polymicrobial abdominal sepsis.

METHODS

For KC depletion clodronate liposomes were injected 24 h before CASP surgery in female C57BL/6N mice. Three and 12 h after CASP, in-vivo fluorescence microscopy of the liver was performed. Analysis of hepatocellular apoptosis was conducted by immunohistochemistry. In addition, levels of tumor necrosis factor (TNF), IL-6, and IL-10 in the liver, lungs, spleen, and plasma were determined, and bacteriology and survival analysis were performed.

RESULTS

CASP led to significant sinusoidal perfusion failure, increased leukocyte recruitment, hepatocellular apoptosis and increased levels of TNF, IL-6, and IL-10 in the liver and plasma. KC depletion before CASP significantly reduced leukocyte recruitment to the liver and hepatocellular apoptosis. IL-10 secretion decreased dramatically in the liver and plasma of KC-depleted septic mice. In contrast, TNF levels were clearly elevated after clodronate treatment. In the lung and spleen, a compensatory upregulation of IL-10 could be detected after KC depletion. Clodronate treatment resulted in a significant reduction in survival.

CONCLUSION

The results indicate that KC depletion is locally protective in polymicrobial abdominal sepsis, as it reduces hepatic inflammation and apoptosis. These effects could be observed in the presence of clearly elevated TNF levels. However, the lack of IL-10 in KC-depleted mice resulted in a detrimental systemic proinflammation.

Distamycin A inhibits HMGA1-binding to the P-selectin promoter and attenuates lung and liver inflammation during murine endotoxemia

BACKGROUND

The architectural transcription factor High Mobility Group-A1 (HMGA1) binds to the minor groove of AT-rich DNA and forms transcription factor complexes ("enhanceosomes") that upregulate expression of select genes within the inflammatory cascade during critical illness syndromes such as acute lung injury (ALI). AT-rich regions of DNA surround transcription factor binding sites in genes critical for the inflammatory response. Minor groove binding drugs (MGBs), such as Distamycin A (Dist A), interfere with AT-rich region DNA binding in a sequence and conformation-specific manner, and HMGA1 is one of the few transcription factors whose binding is inhibited by MGBs.

OBJECTIVES

To determine whether MGBs exert beneficial effects during endotoxemia through attenuating tissue inflammation via interfering with HMGA1-DNA binding and modulating expression of adhesion molecules.

METHODOLOGY/PRINCIPAL FINDINGS

Administration of Dist A significantly decreased lung and liver inflammation during murine endotoxemia. In intravital microscopy studies, Dist A attenuated neutrophil-endothelial interactions in vivo following an inflammatory stimulus. Endotoxin induction of P-selectin expression in lung and liver tissue and promoter activity in endothelial cells was significantly reduced by Dist A, while E-selectin induction was not significantly affected. Moreover, Dist A disrupted formation of an inducible complex containing NF-kappaB that binds an AT-rich region of the P-selectin promoter. Transfection studies demonstrated a critical role for HMGA1 in facilitating cytokine and NF-kappaB induction of P-selectin promoter activity, and Dist A inhibited binding of HMGA1 to this AT-rich region of the P-selectin promoter in vivo.

CONCLUSIONS/SIGNIFICANCE

We describe a novel targeted approach in modulating lung and liver inflammation in vivo during murine endotoxemia through decreasing binding of HMGA1 to a distinct AT-rich region of the P-selectin promoter. These studies highlight the ability of MGBs to function as molecular tools for dissecting transcriptional mechanisms in vivo and suggest alternative treatment approaches for critical illness.

Heme oxygenase (HO)-1 protects from lipopolysaccharide (LPS)-mediated liver injury by inhibition of hepatic leukocyte accumulation and improvement of microvascular perfusion

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.

Capture of platelets to the endothelium of the femoral vein is mediated by CD62P and CD162

Platelets contribute to blood coagulation at sites of vascular injury and to the recruitment of leukocytes at sites of inflammation. Under pathological conditions, platelets are involved in numerous diseases and clinical complications, such as deep venous thrombosis, embolism and atherosclerosis. But so far, little is known about the mechanisms of inflammation in large veins and the role of platelets in inflamed large veins. For this purpose, we investigated primary and secondary interactions between platelets, leukocytes and endothelial cells in the femoral vein in vivo with special regard to the role of CD62P (P-selectin) and CD162 (PSGL-1). Mice were challenged with lipopolysaccharide (LPS)/D-galactosamine (D-gal) and either CD162 or CD62P was blocked by intravenous administration of a corresponding antibody at the time point of LPS/D-gal injection. Four hours after LPS/gal injection, intravital fluorescence microscopy of the femoral vein was performed and primary and secondary platelet-leukocyte-endothelial cell-interactions were visualized after in vivo platelet and leukocyte staining with rhodamine 6G. Analysis of intravital fluorescence microscopy revealed that LPS/D-gal caused a strong inflammatory reaction of the venous endothelium with significant induction of platelet and leukocyte tethering, rolling and adhesion. Secondary interactions of platelets to adherent or rolling platelets or leukocytes were also increased after LPS/D-gal-injection. Immunoneutralization of either CD162 or CD62P significantly decreased platelet primary and secondary capture as well as leukocyte rolling and adhesion. CD162 and CD62P play a central role in mediating inflammatory primary and secondary interactions of platelets and leukocytes to the endothelium in inflamed large veins in vivo. Thus, blocking CD162 or CD62P might be an attractive tool for preventing platelet and leukocyte-driven venous diseases.

The hepatic microcirculation: mechanistic contributions and therapeutic targets in liver injury and repair

The complex functions of the liver in biosynthesis, metabolism, clearance, and host defense are tightly dependent on an adequate microcirculation. To guarantee hepatic homeostasis, this requires not only a sufficient nutritive perfusion and oxygen supply, but also a balanced vasomotor control and an appropriate cell-cell communication. Deteriorations of the hepatic homeostasis, as observed in ischemia/reperfusion, cold preservation and transplantation, septic organ failure, and hepatic resection-induced hyperperfusion, are associated with a high morbidity and mortality. During the last two decades, experimental studies have demonstrated that microcirculatory disorders are determinants for organ failure in these disease states. Disorders include 1) a dysregulation of the vasomotor control with a deterioration of the endothelin-nitric oxide balance, an arterial and sinusoidal constriction, and a shutdown of the microcirculation as well as 2) an overwhelming inflammatory response with microvascular leukocyte accumulation, platelet adherence, and Kupffer cell activation. Within the sequelae of events, proinflammatory mediators, such as reactive oxygen species and tumor necrosis factor-alpha, are the key players, causing the microvascular dysfunction and perfusion failure. This review covers the morphological and functional characterization of the hepatic microcirculation, the mechanistic contributions in surgical disease states, and the therapeutic targets to attenuate tissue injury and organ dysfunction. It also indicates future directions to translate the knowledge achieved from experimental studies into clinical practice. By this, the use of the recently introduced techniques to monitor the hepatic microcirculation in humans, such as near-infrared spectroscopy or orthogonal polarized spectral imaging, may allow an early initiation of treatment, which should benefit the final outcome of these critically ill patients.

P-selectin glycoprotein ligand-1-mediated leukocyte recruitment regulates hepatocellular damage in acute obstructive cholestasis in mice

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.

Thrombopoietin limits IL-6 release but fails to attenuate liver injury in two hepatic stress models

OBJECTIVE

Various pleiotropic substances have been suggested as candidates that directly reduce the severity of liver injury after hepatic ischemia/reperfusion (I/R) and upon acute liver failure (ALF). Herein, we studied whether thrombopoietin (TPO), the main regulator of megakaryopoiesis and thrombopoiesis, showed hepatoprotective effects and might mediate an antiapoptotic function in liver tissue under stress.

METHODS/RESULTS

In livers with ALF or undergoing warm hepatic I/R, injury was quantified by intravital fluorescence microscopy, chemical, and immunohistochemical analysis as well as western immunoblot. Induction of both ALF and I/R injury led to hepatocellular expression of c-mpl, the receptor of TPO. Exogenous application of recombinant TPO in a low (12.5 microg/kg) as well as a high (75 microg/kg) dose, however, did not ameliorate postischemic perfusion and leukocyte endothelial cell interaction, but slightly aggravated transaminase release upon I/R. Similarly, TPO was unable to dampen hepatic microcirculatory deteriorations after the induction of ALF, but caused an increase of leukocyte accumulation and transaminase activity when applied in high dose. Low dose of TPO did not influence the amount of hepatocellular apoptosis, whereas high-dose TPO slightly diminished the activation of caspase 3. Interestingly, exogenous TPO application completely reversed the stress-induced increase of plasma IL-6 levels, suggesting a negative feedback of TPO on IL-6 release.

CONCLUSION

Although the existence of the TPO-receptor on target liver cells TPO plays only a minor role in mediating hepatocyte apoptosis and does not provide protection against hepatic injury, contrasting the efficacy of the related hematopoietic growth factor erythropoietin.

Thoracic epidural anesthesia reverses sepsis-induced hepatic hyperperfusion and reduces leukocyte adhesion in septic rats

INTRODUCTION

Liver dysfunction is a common feature of severe sepsis and is associated with a poor outcome. Both liver perfusion and hepatic inflammatory response in sepsis might be affected by sympathetic nerve activity. However, the effects of thoracic epidural anesthesia (TEA), which is associated with regional sympathetic block, on septic liver injury are unknown. Therefore, we investigated hepatic microcirculation and inflammatory response during TEA in septic rats.

METHODS

Forty-five male Sprague-Dawley-rats were instrumented with thoracic epidural catheters and randomized to receive a sham procedure (Sham), cecal ligation and puncture (CLP) without epidural anesthesia (Sepsis) and CLP with epidural infusion of 15 ul/h bupivacaine 0.5% (Sepsis + TEA). All animals received 2 ml/100 g/h NaCl 0.9%. In 24 (n = 8 in each group) rats, sinusoidal diameter, loss of sinusoidal perfusion and sinusoidal blood flow as well as temporary and permanent leukocyte adhesion to sinusoidal and venolar endothelium were recorded by intravital microscopy after 24 hours. In 21 (n = 7 in each group) separate rats, cardiac output was measured by thermodilution. Blood pressure, heart rate, serum transaminase activity, serum TNF-alpha concentration and histologic signs of tissue injury were recorded.

RESULTS

Whereas cardiac output remained constant in all groups, sinusoidal blood flow increased in the Sepsis group and was normalized in rats subjected to sepsis and TEA. Sepsis-induced sinusoidal vasoconstriction was not ameliorated by TEA. In the Sepsis + TEA group, the increase in temporary venolar leukocyte adherence was blunted. In contrast to this, sinusoidal leukocyte adherence was not ameliorated in the Sepsis + TEA group. Sepsis-related release of TNF-alpha and liver tissue injury were not affected by Sepsis + TEA.

CONCLUSIONS

This study demonstrates that TEA reverses sepsis-induced alterations in hepatic perfusion and ameliorates hepatic leukocyte recruitment in sepsis.

In vivo biocompatibility and vascularization of biodegradable porous polyurethane scaffolds for tissue engineering

Scaffolds for tissue engineering should be biocompatible and stimulate rapid blood vessel ingrowth. Herein, we analyzed in vivo the biocompatibility and vascularization of three novel types of biodegradable porous polyurethane scaffolds. The polyurethane scaffolds, i.e., PU-S, PU-M and PU-F, were implanted into dorsal skinfold chambers of BALB/c mice. Using intravital fluorescence microscopy we analyzed vascularization of the implants and venular leukocyte-endothelial cell interaction in the surrounding host tissue over a 14 day period. Incorporation of the scaffolds was analyzed by histology, and a WST-1 assay was performed to evaluate their cell biocompatibility in vitro. Our results indicate that none of the polyurethane scaffolds was cytotoxic. Accordingly, rolling and adherent leukocytes in venules of the dorsal skinfold chamber were found in a physiological range after scaffold implantation and did not significantly differ between the groups, indicating a good in vivo biocompatibility. However, the three scaffolds induced a weak angiogenic response with a microvessel density of only approximately 47-60 and approximately 3-10cm/cm(2) in the border and centre zones of the scaffolds at day 14 after implantation. Histology demonstrated that the scaffolds were incorporated in a granulation tissue, which exhibited only a few blood vessels and inflammatory cells. In conclusion, PU-S, PU-M and PU-F scaffolds may be used to generate tissue constructs which do not induce a strong inflammatory reaction after implantation into patients. However, the scaffolds should be further modified or conditioned in order to accelerate and improve the process of vascularization.

Simvastatin attenuates hepatic sensitization to lipopolysaccharide after partial hepatectomy

BACKGROUND

Hepatic resection may be curative in patients with hepatobiliary malignancies but excessive loss of liver volume may cause hepatic dysfunction and increase susceptibility to subsequent postoperative infections and sepsis. Herein, we hypothesized that pretreatment with simvastatin may protect against lipopolysaccharide (LPS)-induced liver damage after partial hepatectomy.

MATERIALS AND METHODS

Male C57Bl/6 mice underwent 68% hepatectomy and exposed to LPS after 24h. Animals were pretreated with simvastatin (0.02 and 0.2mg/kg). Serum alanine aminotransferase (ALT) and tumor necrosis factor-alpha (TNF-alpha) as well as leukocyte infiltration and hepatocyte apoptosis were examined 6h after LPS challenge. An in vitro endothelial cell adhesion assay was used to study the mechanisms of simvastatin on leukocyte adhesion and the role of P-selectin and lymphocyte function antigen-1 (LFA-1).

RESULTS

Partial hepatectomy increased the sensitivity of the remnant liver tissue to LPS-provoked tissue injury. Simvastatin pretreatment reduced the LPS-induced increase in serum levels of ALT by 65% in hepatectomized animals. Moreover, simvastatin decreased leukocyte infiltration and hepatocyte apoptosis in the liver remnant of endotoxemic mice. LPS-provoked serum levels of TNF-alpha were decreased by 83% in hepatectomized animals treated with simvastatin. TNF-alpha-induced leukocyte adhesion as well as P-selectin expression in endothelial cells and LFA-1 function were inhibited by simvastatin in vitro.

CONCLUSIONS

These novels findings demonstrate that simvastatin protects the remnant liver against endotoxemic injury following major hepatectomy. Thus, simvastatin reduced LPS-induced leukocyte recruitment and hepatocyte apoptosis in the liver remnant. One key mechanism appears to be related to the inhibition of TNF-alpha formation and function (P-selectin expression) as well as to direct actions on LFA-1 function. Thus, simvastatin may represent a novel therapeutic approach to prevent septic liver damage after partial liver resection.

Sepsis-induced intestinal microvascular and inflammatory responses in obese mice

Although clinical obesity is associated with increases in the morbidity and mortality of sepsis, little is known about the mechanisms that underlie the influence of obesity on sepsis. The objective of this study was to determine (a) whether obesity is associated with exaggerated inflammatory and thrombogenic responses in the intestinal microvasculature of septic mice and (b) whether these microvascular alterations are related to changes in the serum levels of cytokines that are produced by adipose tissue. Intravital microscopy was used to quantify leukocyte and platelet adhesion in intestinal postcapillary venules of lean wild-type (WT) mice, and two murine models of obesity, that is, ob/ob and db/db mice. Sepsis was induced by cecal ligation and perforation (CLP). Serum cytokine levels were measured using a cytometric bead assay, whereas adipokines were quantified using enzyme-linked immunosorbent assay. Cecal ligation and perforation elicited significant increases in the adhesion of leukocytes and platelets in venules of lean WT mice. These CLP-induced adhesive interactions were much more pronounced in the microvasculature of both ob/ob and db/db mice. Cecal ligation and perforation was associated with significant increases in serum cytokines in both WT and ob/ob mice, but such changes were not detected in db/db mice. However, db/db (but not WT or ob/ob) mice did exhibit significant increases in serum leptin and adiponectin levels after CLP. Sepsis promotes more intense inflammatory and thrombogenic responses in the gut microcirculation of obese mice than in their lean counterparts. The obesity-enhanced microvascular dysfunction in septic mice shows no consistent correlation with serum cytokines or adipokines.

Uncoupling protein-2 deficiency provides protection in a murine model of endotoxemic acute liver failure

OBJECTIVE

Liver injury and cell death are prominent features in the pathogenesis of acute liver failure. Mitochondrial uncoupling protein 2 plays a controversial role in liver cell death through its involvement in the production of reactive oxygen species and adenosine triphosphate.

DESIGN

This randomized controlled animal study was designed to investigate the exact role of uncoupling protein 2 in the pathogenesis of endotoxemic acute liver failure.

SETTING

Research laboratory of an academic institution. SUBJECTS, INTERVENTIONS, AND MEASUREMENTS: Uncoupling protein 2+/+ and uncoupling protein 2-/- mice were challenged with D-galactosamine (Gal, 720 mg/kg intraperitoneally) and Escherichia coli lipopolysaccharide (10 microg/kg intraperitoneally) and studied 6 hrs thereafter (n = 5 per group). Control mice received physiologic saline (n = 5 per group). Analysis included in vivo fluorescence microscopy of hepatic microcirculation and hepatocellular apoptosis as well as plasma malondialdehyde concentrations as reactive oxygen species-dependent lipid peroxidation product and hepatic adenosine triphosphate levels.

MAIN RESULTS

Administration of Gal-lipopolysaccharide in uncoupling protein 2+/+ mice caused systemic cytokine release and malondialdehyde production. Further, it provoked marked hepatic damage, characterized by intrahepatic leukocyte recruitment (10.5 +/- 1.3 n/mm2 vs. 3.3 +/- 0.5 n/mm2), microvascular perfusion failure (33.1% +/- 1.6% vs. 2.3% +/- 0.4%), and adenosine triphosphate depletion (3.4 +/- 0.9 micromol/g vs. 6.4 +/- 0.9 micromol/g). Furthermore, uncoupling protein +/+ mice revealed a huge rise in cell apoptosis, given by high numbers of hepatocytes exhibiting nuclear chromatin fragmentation (44.9 +/- 11.5 n/mm2 vs. 0.0 +/- 0.0 n/mm2) and cleaved caspase-3 expression (1.24 +/- 0.24 vs. 0.06 +/- 0.04). Liver injury was coexistent with enzyme release (alanine aminotransferase 442 +/- 126 U/L vs. 57 +/- 12 U/L) and necrotic cell death. Of interest, Gal-lipopolysaccharide-exposed uncoupling protein 2-/- mice exhibited higher rates of hepatocellular apoptosis (135.6 +/- 46.0 n/mm2) as well as cleaved caspase-3 expression (1.75 +/- 0.25), however, preserved hepatic adenosine triphosphate (6.4 +/- 1.7), milder perfusion failure (24.5 +/- 2.4) and decreased leukocyte recruitment (2.7 +/- 0.2), less necrotic injury, lower transaminase levels (340 +/- 91), and finally better survival rates.

CONCLUSION

The higher adenosine triphosphate availability in uncoupling protein 2-deficient mice might allow hepatocytes to undergo apoptosis as an energy-consuming mode of cell death, while at the same time cellular adenosine triphosphate levels seem to increase hepatic resistance against harmful effects upon Gal-lipopolysaccharide exposure. As net result, uncoupling protein 2 deficiency provided protection under endotoxemic stress conditions, underlining the significant role of the bioenergetic status in critical illness.

Cholestatic liver damage is mediated by lymphocyte function antigen-1-dependent recruitment of leukocytes

BACKGROUND

The role of specific adhesion molecules in cholestasis-induced leukocyte recruitment in the liver is not known. Therefore, the aim of our experimental study was to evaluate the role of lymphocyte function antigen-1 (LFA-1) in cholestatic liver injury.

METHODS

C57BL/6 mice underwent bile duct ligation for 12 hours. Mice were pretreated with an anti-LFA-1 antibody or control antibody. Subsequently, hepatic accumulation of leukocytes and sinusoidal perfusion were determined by means of intravital fluorescence microscopy. Hepatocellular damage was monitored by measuring serum levels of alanine aminotransferase and aspartate aminotransferase. CXC chemokines in the liver were determined by enzyme-linked immunosorbent assay.

RESULTS

Bile duct ligation provoked clear-cut recruitment of leukocytes and liver damage, as indicated by increased serum activities of liver enzymes and sinusoidal perfusion failure. Neutrophils expressed greater levels of LFA-1 and inhibition of LFA-1 significantly decreased serum activity of alanine aminotransferase and aspartate aminotransferase levels in cholestatic mice. Immunoneutralization of LFA-1 reduced leukocyte adhesion in postsinusoidal venules that had been induced by bile duct ligation, whereas leukocyte rolling and sinusoidal accumulation were not changed. Moreover, blocking LFA-1 function restored sinusoidal perfusion in cholestatic animals.

CONCLUSION

These findings demonstrate an important role of LFA-1 in supporting cholestasis-induced leukocyte recruitment in the liver. Thus, targeting LFA-1 may help to protect against pathologic inflammation and liver damage in cholestatic liver diseases.

Mast-cell-dependent secretion of CXC chemokines regulates ischemia-reperfusion-induced leukocyte recruitment 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.

Role of preprotachykinin-A gene products on multiple organ injury in LPS-induced endotoxemia

Endotoxemia is a life-threatening, inflammatory condition that involves multiple organ injury and dysfunction. Preprotachykinin-A (PPT-A) gene products, substance P (SP), and neurokinin-A have been shown to play an important role in neurogenic inflammation. To investigate the role of PPT-A gene products on multiple organ injury in LPS-induced endotoxemia, endotoxemia was induced by LPS administration (10 mg/kg, i.p.) in PPT-A gene-deficient mice (PPTA(-/-)) and the wild-type (WT) control mice (PPT-A+/+). I.p. administration of LPS to WT mice caused a significant increase in circulating levels of SP as well as in liver, lung, and kidney. PPT-A gene deletion significantly protected against liver, pulmonary, and renal injury following LPS-induced endotoxemia, as evidenced by tissue myeloperoxidase activities, plasma alanine aminotransferase, aspartate aminotransferase levels, and histological examination. Furthermore, PPT-A(-/-) mice had significantly attenuated chemokines, proinflammatory cytokines, and adhesion molecule levels in the liver, lung, and kidney. These results show that PPT-A gene products are critical proinflammatory mediators in endotoxemia and the associated multiple organ injury. In addition, the data suggest that deletion of the PPT-A gene protected mice against organ damage in endotoxemia by disruption in neutrophil recruitment.

Simvastatin protects against cholestasis-induced liver injury

BACKGROUND

Bile duct obstruction is associated with hepatic accumulation of leukocytes and liver injury. The aim of this study was to evaluate the effect of simvastatin on cholestasis-induced liver inflammation and tissue damage.

EXPERIMENTAL APPROACH

C57BL/6 mice were treated with simvastatin (0.02 and 0.2 mg.kg(-1)) and vehicle before and after undergoing bile duct ligation (BDL) for 12 h. Leukocyte recruitment and microvascular perfusion in the liver were analysed using intravital fluorescence microscopy. CXC chemokines in the liver were determined by enzyme-linked immunosorbent assay. Liver damage was monitored by measuring serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Hepatic levels of myeloperoxidase (MPO) were also determined.

KEY RESULTS

Administration of 0.2 mg.kg(-1) simvastatin decreased ALT and AST by 87% and 83%, respectively, in BDL mice. This dose of simvastatin reduced hepatic formation of CXC chemokines by 37-82% and restored sinusoidal perfusion in cholestatic animals. Moreover, BDL-induced leukocyte adhesion in sinusoids and postsinusoidal venules, as well as MPO levels in the liver, was significantly reduced by simvastatin. Notably, administration of 0.2 mg.kg(-1) simvastatin 2 h after BDL induction also decreased cholestatic liver injury and inflammation.

CONCLUSIONS AND IMPLICATIONS

These findings show that simvastatin protects against BDL-induced liver injury. The hepatoprotective effect of simvastatin is mediated, at least in part, by reduced formation of CXC chemokines and leukocyte recruitment. Thus, our novel data suggest that the use of statins may be an effective strategy to protect against the hepatic injury associated with obstructive jaundice.

Hepatic microcirculation in murine sepsis: role of lymphocytes

Sepsis is a leading cause of death in pediatric intensive care units. There is growing evidence that lymphocytes play a pivotal role in mediating the microvascular dysfunction during sepsis. The objective of this study was to define the role of different subsets of lymphocytes in mediating the hepatic microvascular alterations elicited by cecal ligation and puncture (CLP), an experimental model of sepsis. Intravital video microscopy was used to quantify leukocyte and platelet adhesion in the hepatic microcirculation of wild type (WT) mice, immunodeficient SCID mice, SCID mice reconstituted with CD3+ cells, and mice deficient either in B-cells, CD4+- or CD8+-T-cells subjected to CLP. Blood cell counts, and serum concentrations of ALT and different cytokines (TNF-alpha, IL-10, MCP-1, IL-6, IFN-gamma and IL-12) were also monitored in these groups. CLP (at 6 h) caused a significantly increased adhesion of leukocytes and platelets in WT mice, compared to WT sham mice (P < 0.05). In SCID mice, the adhesion of blood cells in terminal hepatic venules was significantly decreased compared to WT-CLP mice, whereas the values in CD3+ cell-reconstituted SCID-mice, B-cell-deficient and CD4+- and CD8+-T-cell deficient mice did not differ from WT-CLP mice. ALT levels were significantly elevated only in the SCID group, when compared to WT-sham and WT-CLP mice. These findings indicate that lymphocytes mediate the microvascular dysfunction, but protect against the hepatocellular injury associated with murine sepsis.

Critical role of P-selectin and lymphocyte function antigen-1 in radiation-induced leukocyte-endothelial cell interactions in the colon

PURPOSE

Radiation therapy is frequently used in treating different types of tumors, although associated with serious side effects, such as fibrosis and complicated diarrhea. This study was designed to define the adhesive mechanisms behind radiotherapy-induced leukocyte recruitment in the colon.

METHODS

All mice, except control animals, were radiated with a single dose of 20 Gy. Mice were pretreated with an isotype-matched control antibody or a monoclonal antibody directed against P-selectin. In separate experiments, lymphocyte function antigen-1-deficient animals were used. Leukocyte rolling and firm adhesion were determined by use of inverted intravital fluorescence microscopy 16 hours after radiation.

RESULTS

It was found that immunoneutralization of P-selectin reduced leukocyte rolling by 83 percent and adhesion by 87 percent in radiated mice. Moreover, radiation-induced leukocyte adhesion in LFA-1-deficient mice was decreased by 94 percent compared with wild-type animals.

CONCLUSIONS

This study demonstrates that leukocyte rolling is mediated by P-selectin and that firm leukocyte adhesion is supported by lymphocyte function antigen-1 in radiation-induced enteritis. Moreover, P-selectin-dependent leukocyte rolling is a precondition for subsequent leukocyte adhesion in radiation-induced intestinal injury. Thus, targeting P-selectin and/or lymphocyte function antigen-1 may protect against pathologic inflammation in the colon induced by radiotherapy.

Platelet-dependent accumulation of leukocytes in sinusoids mediates hepatocellular damage in bile duct ligation-induced cholestasis

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.

Platelets promote liver regeneration in early period after hepatectomy in mice

BACKGROUND

Platelets contain several growth factors, including platelet-derived growth factor and hepatocyte growth factor.

MATERIALS AND METHODS

We examined the effects of platelet increment on liver regeneration after 70% hepatectomy. Hepatectomies were carried out in male BALB/c mice, and subsequently divided into three groups: (i) untreated mice, (ii) thrombocytotic mice induced with thrombopoietin, and (iii) thrombocytopenic mice induced with anti-platelet antibody. Growth kinetics in the liver were analyzed as a function of the liver/body weight ratio, the mitotic index, the proliferating cell nuclear antigen labeling index and Ki-67 labeling index. Activation of signal transduction pathways relating to cell proliferation were examined, including the STAT3, Akt, and ERK1/2 pathways. Platelet accumulation in the residual liver was quantified by immunohistochemistry and transmission electron microscopy.

RESULTS

In thrombocytotic and thrombocytopenic mice, liver/body weight ratios and Ki-67 labeling indices were significantly increased and significantly decreased, respectively, compared with untreated mice 48 hours post-hepatectomy. The Akt pathway was strongly activated, and platelet accumulation was significantly increased in thrombocytotic group 5 minutes post-hepatectomy compared with normal and thrombocytopenic groups. After hepatectomy platelets accumulated in the sinusoids of liver and promoted hepatocyte proliferation in early period after hepatectomy.

CONCLUSION

By increasing or decreasing the platelet, marked changes in liver regeneration can occur, due to differences in cellular signaling and mitosis.

Attenuation of inflammation and apoptosis by pre- and posttreatment of darbepoetin-alpha in acute liver failure of mice

In many liver disorders inflammation and apoptosis are important pathogenic components, finally leading to acute liver failure. Erythropoietin and its analogues are known to affect the interaction between apoptosis and inflammation in brain, kidney, and myocardium. The present study aimed to determine whether these pleiotropic actions also exert hepatoprotection in a model of acute liver injury. C57BL/6J mice were challenged with d-galactosamine (Gal) and Escherichia coli lipopolysaccharide (LPS) and studied 6 hours thereafter. Animals were either pretreated (24 hours before Gal-LPS exposure) or posttreated (30 minutes after Gal-LPS exposure) with darbepoetin-alpha (DPO, 10 mug/kg i.v.). Control mice received physiological saline. Administration of Gal-LPS caused systemic cytokine release and provoked marked hepatic damage, characterized by leukocyte recruitment and microvascular perfusion failure, caspase-3 activation, and hepatocellular apoptosis as well as enzyme release and necrotic cell death. DPO-pretreated and -posttreated mice showed diminished systemic cytokine concentrations, intrahepatic leukocyte accumulation, and hepatic perfusion failure. Hepatocellular apoptosis was significantly reduced by 50 to 75% after DPO pretreatment as well as posttreatment. In addition, treatment with DPO also significantly abrogated necrotic cell death and liver enzyme release. In conclusion, these observations may stimulate the evaluation of DPO as hepatoprotective therapy in patients with acute liver injury.

Compound Danshen injection improves endotoxin-induced microcirculatory disturbance in rat mesentery

AIM: To investigate the effect of compound Danshen injection on lipopolysaccharide (LPS)-induced rat mesenteric microcirculatory dysfunctions and the underlying possible mechanism by an inverted intravital microscope and high-speed video camera system.

METHODS: LPS was continuously infused through the jugular artery of male Wistar rats at the dose of 2 mg/kg per hour. Changes in mesenteric microcirculation, such as diameters of arterioles and venules, velocity of RBCs in venules, leukocyte rolling, adhesion and emigration, free radicals released from post-capillary venules, FITC-albumin leakage and mast cell degranulation, were observed through an inverted intravital microscope assisted with CCD camera and SIT camera. Meanwhile, the expression of adhesion molecules CD11b/CD18 and the production of free radical in neutrophils, and the expression of intercellular adhesion molecule 1 (ICAM-1) in human umbilical vein endothelial cells (HUVECs) were quantified by flow cytometry (FACS) in vitro.

RESULTS: The continuous infusion with LPS resulted in a number of responses in microcirculation, including a significant increase in the positive region of venule stained with Monastral blue B, rolling and adhesion of leukocytes, production of oxygen radical in venular wall, albumin efflux and enhanced mast cell degranulation in vivo, all of which, except for the leukocyte rolling, were attenuated by the treatment with compound Danshen injection. Experiments performed in vitro further revealed that the expression of CD11b/CD18 and the production of oxygen free radical in neutrophils, and the expression of ICAM-1 in HUVECs were increased by exposure to LPS, and they were attenuated by compound Danshen injection.

CONCLUSION: These results suggest that compound Danshen injection is an efficient drug with multi-targeting potential for improving the microcirculatory disturbance.

Antileukoproteinase protects against hepatic inflammation, but not apoptosis in the response of D-galactosamine-sensitized mice to lipopolysaccharide

BACKGROUND AND PURPOSE

There is major evidence for the strong bi-directional interrelation of parenchymal cell apoptosis and leukocyte accumulation and inflammation in acute liver injury. Therefore, the aim of this in vivo study was to investigate the anti-apoptotic and anti-inflammatory potential of antileukoproteinase (ALP) in a murine model of acute liver failure.

EXPERIMENTAL APPROACH

C57BL/6J mice were given galactosamine (D-GalN) and E. coli lipopolysaccharide (LPS) followed by administration of saline or ALP. Besides survival rate, hepatic tissue damage and inflammatory response were analyzed by intravital fluorescence microscopy 6 hours after treatment. In addition, immunohistochemical analysis of NFkappaB-p65 and hepatocellular apoptosis, plasma levels of AST/ALT, TNF-alpha and IL-10 were determined.

KEY RESULTS

Administration of D-GalN/LPS provoked hepatic damage, including marked leukocyte recruitment and microvascular perfusion failure, as well as hepatocellular apoptosis and enzyme release. NFkappaB-p65 became increasingly detectable in hepatocellular nuclei, accompanied by a rise of TNF-alpha and IL-10 plasma levels. ALP markedly reduced intrahepatic leukocyte accumulation, nuclear translocation of NFkappaB and plasma levels of TNF-alpha and IL-10. Moreover, liver enzyme levels indicated the absence of necrotic parenchymal cell death. In contrast, ALP failed to block both apoptosis and caspase-3 levels and the mortality rate of ALP-treated animals was comparable to that of saline-treated mice.

CONCLUSIONS AND IMPLICATIONS

ALP could effectively prevent D-GalN/LPS-associated intrahepatic inflammatory responses by inhibition of NFkappaB activity, but not apoptosis-driven mortality. Thus, a protease-inactivating approach such as application of ALP seems to be inadequate in damaged liver where apoptosis represents the predominant mode of cell death.

Sepsis-associated cholestasis is critically dependent on P-selectin-dependent leukocyte recruitment in mice

Cholestasis is a major complication in sepsis although the underlying mechanisms remain elusive. The aim of this study was to evaluate the role of P-selectin and leukocyte recruitment in endotoxemia-associated cholestasis. C57BL/6 mice were challenged intraperitoneally with endotoxin (0.4 mg/kg), and 6 h later the common bile duct was cannulated for determination of bile flow and biliary excretion of bromosulfophthalein. Mice were pretreated with an anti-P-selectin antibody or an isotype-matched control antibody. Leukocyte infiltration was determined by measuring hepatic levels of myeloperoxidase. Tumor necrosis factor-alpha and CXC chemokines in the liver was determined by ELISA. Liver damage was monitored by measuring serum levels of alanine aminotransferase and aspartate aminotransferase. Apoptosis was quantified morphologically by nuclear condensation and fragmentation using Hoechst 33342 staining. Endotoxin induced a significant inflammatory response with increased TNF-alpha and CXC chemokine concentrations, leukocyte infiltration, liver enzyme release, and apoptotic cell death. This response was associated with pronounced cholestasis indicated by a >70% decrease of bile flow and biliary excretion of bromosulfophthalein. Immunoneutralization of P-selectin significantly attenuated endotoxin-induced leukocyte infiltration reflected by a >60% reduction of hepatic myeloperoxidase levels. Interference with P-selectin decreased endotoxin-mediated hepatocellular apoptosis and necrosis, but did not affect hepatic levels of tumor necrosis factor-alpha and CXC chemokines. Of interest, inhibition of P-selectin restored bile flow and biliary excretion of bromosulfophthalein to normal levels in endotoxin-challenged animals. Our study demonstrates for the first time that P-selectin-mediated recruitment of leukocytes, but not the local production of proinflammatory mediators, is the primary cause of cholestasis in septic liver injury.

Role of Antithrombin and Factor XIII In Leukocyte-Independent Plasma Extravasation During Endotoxemia: An Intravital-Microscopic Study in the Rat

BACKGROUND

Platelet-endothelial interactions have been shown to be main mediators of leukocyte-independent endothelial damage. Besides altering platelet-endothelial interactions, both antithrombin and factor XIII reduce microvascular permeability in leukocyte-dependent experimental models. Thus, it was our aim to investigate the effects of antithrombin and factor XIII on microvascular permeability during leukocyte-independent endotoxemia.

MATERIAL AND METHODS

In male Wistar rats, venular wall shear rate, macromolecular efflux, and leukocyte-endothelial interaction were determined in mesenteric postcapillary venules using intravital microscopy at baseline, 60, and 120 min after the start of the experiment. Fucoidin and a continuous infusion of lipopolysaccharides were used to generate leukocyte-independent endotoxemia. The experiment was divided into two parts 1) an antithrombin study and 2) a factor XIII study.

RESULTS

No differences between groups in leukocyte rolling and venular wall shear rate could be observed in both parts of the experiment. Pretreatment with antithrombin reduced microvascular permeability significantly compared with control subjects (120 min: Fuco [untreated]: 0.14 +/- 0.03; Fuco/ETX [control]: 0.37 +/- 0.06; Fuco + ATIII/ETX: 0.15 +/- 0.02; P < 0.05). Factor XIII reduced microvascular permeability significantly after 60 min (Fuco [untreated]: 0.10 +/- 0.03; Fuco/ETX [control]: 0.36 +/- 0.07; Fuco + FXIII/ETX: 0.13 +/- 0.04; P < 0.05). This effect diminished after 120 min (Fuco [untreated]: 0.12 +/- 0.03; Fuco/ETX [control]: 0.5 +/- 0.08; Fuco + FXIII/ETX: 0.29 +/- 0.05; P < 0.05).

CONCLUSIONS

Antithrombin and factor XIII reduce leukocyte-independent microvascular permeability. Yet, factor XIII also shows a nonprotective effect on a long-term basis. These data emphasize the central role of platelets in leukocyte-independent endotoxemia.

Protective effect of fasudil, a Rho-kinase inhibitor, on chemokine expression, leukocyte recruitment, and hepatocellular apoptosis in septic liver injury

Rho-kinase signaling regulates important features of inflammatory reactions. Herein, we investigated the effect and mechanisms of action of the Rho-kinase inhibitor fasudil in endotoxemic liver injury. C57/BL/6 mice were challenged with lipopolysaccharide (LPS) and D-galactosamine, with or without pretreatment with the Rho-kinase inhibitor fasudil. Six hours after endotoxin challenge, leukocyte-endothelium interactions in the hepatic microvasculature were studied by use of intravital fluorescence microscopy and tumor necrosis factor alpha (TNF-alpha); CXC chemokines as well as liver enzymes and apoptosis were determined. Administration of fasudil reduced LPS-induced leukocyte adhesion in postsinusoidal venules and sequestration in sinusoids. Moreover, we found that fasudil abolished extravascular infiltration of leukocytes as well as production of TNF-alpha and CXC chemokines in the liver of endotoxemic mice. Liver enzymes and hepatocellular apoptosis were markedly reduced, and sinusoidal perfusion was improved significantly in endotoxemic mice pretreated with fasudil. Our novel data document that fasudil is a potent inhibitor of endotoxin-induced expression of TNF-alpha and CXC chemokines as well as leukocyte infiltration and hepatocellular apoptosis in the liver. Based on the present findings, it is suggested that inhibition of the Rho-kinase signaling pathway may be a useful target in the treatment of septic liver injury.

Modulation of apoptosis as a target for liver disease

Apoptosis mediated via extrinsic or intrinsic pathways is essential for maintaining cellular homeostasis in the liver. The extrinsic pathway is triggered from the cell surface by engagement of death receptors as CD95, TRAIL (TNF-related apoptosis inducing ligand) and TNF (tumour necrosis factor) or TGF-beta (transforming growth factor beta) receptors. The intrinsic pathway is initiated from the mitochondria and can be influenced by Bcl-2 family members. Both pathways are intertwined and play a physiological role in the liver. Dysregulation of apoptosis pathways contributes to diseases as hepatocellular carcinoma, viral hepatitis, autoimmune hepatitis, ischaemia-reperfusion injury, iron or copper deposition disorders, toxic liver damage and acute liver failure. The apoptosis defects are often central pathogenetic events; hence molecular mechanisms of apoptosis give not only insight into disease mechanisms but also provide potential corresponding therapeutic candidates in liver disease. The focus of this review is the identification of apoptotic signalling components in the liver as therapeutic targets.

Short-term homing assay reveals a critical role for lymphocyte function-associated antigen-1 in the hepatic recruitment of lymphocytes in graft-versus-host disease

BACKGROUND/AIMS

The liver is a major target organ of graft versus host disease (GvHD) with massive infiltration of alloreactive lymphocytes resulting in hepatitis and hepatocyte injury. Although adhesive mechanisms have been implicated in the biology of GvHD hepatitis, the identity of homing receptors involved in the initial recruitment of cells from the blood is not known.

METHODS

We have developed a short-term homing assay in a model of murine GvHD. Splenocytes from donors at an active stage of GvHD were injected intravenously into adoptive recipients also undergoing GvHD. The recruitment of cells to the liver was assessed 6h after cell transfer.

RESULTS

Activated donor CD8 and CD4 lymphocytes expressed lymphocyte function antigen-1 (LFA-1), alpha4-integrins, and P-selectin binding ligands, and localized more efficiently than naïve T cells. Immunoneutralization of LFA-1 reduced the recruitment of CD8 and CD4 lymphocytes to the liver by more than 60%. Anti-LFA-1 antibody also markedly reduced infiltration of lymphocytes in periportal areas and protected against hepatocellular damage.

CONCLUSIONS

We demonstrate a critical role of LFA-1 in the recruitment of activated lymphocytes to the liver and in immune-cell mediated hepatitis. LFA-1 may be an effective therapeutic target for protecting the liver following bone marrow transplantation.

Molecular characterization of rat leukocyte P-selectin glycoprotein ligand-1 and effect of its blockade: protection from ischemia-reperfusion injury in liver transplantation

P-selectin glycoprotein ligand-1 (PSGL-1) mediates the initial tethering of leukocytes to activated platelets and endothelium. We report molecular cloning and characterization of the rat PSGL-1 gene. A neutralizing Ab was generated, and its binding epitope was mapped to the N-terminal binding region of rat PSGL-1. We examined the effects of early PSGL-1 blockade in rat liver models of cold ischemia, followed by ex vivo reperfusion or transplantation (orthotopic liver transplantation (OLT)) using an anti-PSGL-1 Ab with diminished Fc-mediated effector function. In the ex vivo hepatic cold ischemia and reperfusion model, pretreatment with anti-PSGL-1 Ab improved portal venous flow, increased bile production, and decreased hepatocellular damage. Rat pretreatment with anti-PSGL-1 Ab prevented hepatic insult in a model of cold ischemia, followed by OLT, as assessed by 1) decreased hepatocellular damage (serum glutamic oxaloacetic transaminase/glutamic-pyruvic transaminase levels), and ameliorated histological features of ischemia/reperfusion injury, consistent with extended OLT survival; 2) reduced intrahepatic leukocyte infiltration, as evidenced by decreased expression of P-selectin, ED-1, CD3, and OX-62 cells; 3) inhibited expression of proinflammatory cytokine genes (TNF-alpha, IL-1beta, IL-6, IFN-gamma, and IL-2); and 4) prevented hepatic apoptosis accompanied by up-regulation of antiapoptotic Bcl-2/Bcl-xL protective genes. Thus, targeting PSGL-1 with a blocking Ab that has diminished Fc-mediated effector function is a simple and effective strategy that provides the rationale for novel therapeutic approaches to maximize the organ donor pool through the safer use of liver transplants despite prolonged periods of cold ischemia.

Platelet Recruitment in the Murine Hepatic Microvasculature During Experimental Sepsis: Role of Neutrophils

OBJECTIVES

Sepsis is a major clinical problem that often results in the dysfunction or failure of multiple organs, including the liver. While inflammatory cell activation has been implicated as an early critical event in sepsis-induced liver dysfunction, there is growing evidence for the involvement of activated platelets in this pathologic process.

METHODS

Intravital microscopy was used in this study to assess the magnitude and time course of platelet adhesion in the liver microcirculation during experimental sepsis and to determine whether the platelet accumulation is linked to leukocyte infiltration. The adhesion of platelets and leukocytes in terminal hepatic venules (THV) and sinusoids was quantified at 2, 4, and 6 h after abdominal sepsis induced by cecal ligation and puncture (CLP).

RESULTS

While the rolling and firm adhesion of platelets and leukocytes in THV were not altered in the first 2 h after CLP, platelet recruitment was observed at 4 h and further elevated at 6 h after CLP. Leukocyte adhesion in THV exhibited a similar time course. A similar accumulation of blood cells in sinusoids was noted after CLP. This was accompanied by an increased number of nonperfused sinusoids. CLP-induced leukocyte and platelet recruitment in THV and sinusoids was attenuated in mice rendered neutropenic with anti-neutrophil serum.

CONCLUSION

These findings indicate that sepsis is associated with a neutrophil-dependent recruitment of platelets in the liver microcirculation that impairs sinusoidal perfusion and may contribute to the liver dysfunction associated with sepsis.

p38 mitogen-activated protein kinase-dependent chemokine production, leukocyte recruitment, and hepatocellular apoptosis in endotoxemic liver injury

OBJECTIVE

To determine the role of p38 mitogen-activated protein kinase (MAPK) signaling in endotoxin-induced liver injury.

BACKGROUND

MAPKs have been reported to play a potential role in regulating inflammatory responses, but the role of p38 MAPK signaling in chemokine production, leukocyte recruitment, and hepatocellular apoptosis in the liver of endotoxemic mice is not known.

METHODS

Endotoxin-induced leukocyte-endothelium interactions were studied by use of intravital fluorescence microscopy in the mouse liver. Tumor necrosis factor-alpha (TNF-alpha) and CXC chemokines, liver enzymes, and apoptosis were determined 6 hours after endotoxin challenge. The specific p38 MAPK inhibitor SB 239063 was given immediately prior to endotoxin exposure. Phosphorylation and activity of p38 MAPK were determined by immunoprecipitation and Western blot.

RESULTS

Endotoxin increased phosphorylation and activity of p38 MAPK in the liver, which was markedly inhibited by SB 239063. Inhibition of p38 MAPK signaling dose-dependently decreased endotoxin-induced leukocyte rolling, adhesion, and sinusoidal sequestration of leukocytes. SB 239063 markedly reduced endotoxin-induced formation of TNF-alpha and CXC chemokines in the liver. Indeed, the endotoxin-provoked increase of liver enzymes and hepatocellular apoptosis were abolished and sinusoidal perfusion was restored in endotoxemic mice treated with SB 239063.

CONCLUSIONS

This study demonstrates that p38 MAPK signaling plays an important role in regulating TNF-alpha and CXC chemokine production in endotoxemic liver injury and that inhibition of p38 MAPK activity abolishes endotoxin-induced leukocyte infiltration as well as hepatocellular apoptosis. These novel findings suggest that interference with the p38 MAPK pathway may constitute a therapeutic strategy against septic liver damage.