Mechanisms of neutrophil-induced parenchymal cell injury

The immune system and cardiac repair

Myocardial infarction is the most common cause of cardiac injury and results in acute loss of a large number of myocardial cells. Because the heart has negligible regenerative capacity, cardiomyocyte death triggers a reparative response that ultimately results in formation of a scar and is associated with dilative remodeling of the ventricle. Cardiac injury activates innate immune mechanisms initiating an inflammatory reaction. Toll-like receptor-mediated pathways, the complement cascade and reactive oxygen generation induce nuclear factor (NF)-kappaB activation and upregulate chemokine and cytokine synthesis in the infarcted heart. Chemokines stimulate the chemotactic recruitment of inflammatory leukocytes into the infarct, while cytokines promote adhesive interactions between leukocytes and endothelial cells, resulting in transmigration of inflammatory cells into the site of injury. Monocyte subsets play distinct roles in phagocytosis of dead cardiomyocytes and in granulation tissue formation through the release of growth factors. Clearance of dead cells and matrix debris may be essential for resolution of inflammation and transition into the reparative phase. Transforming growth factor (TGF)-beta plays a crucial role in cardiac repair by suppressing inflammation while promoting myofibroblast phenotypic modulation and extracellular matrix deposition. Myofibroblast proliferation and angiogenesis result in formation of highly vascularized granulation tissue. As the healing infarct matures, fibroblasts become apoptotic and a collagen-based matrix is formed, while many infarct neovessels acquire a muscular coat and uncoated vessels regress. Timely resolution of the inflammatory infiltrate and spatial containment of the inflammatory and reparative response into the infarcted area are essential for optimal infarct healing. Targeting inflammatory pathways following infarction may reduce cardiomyocyte injury and attenuate adverse remodeling. In addition, understanding the role of the immune system in cardiac repair is necessary in order to design optimal strategies for cardiac regeneration.

Roles of heat shock proteins and gamma delta T cells in inflammation

Elimination of activated inflammatory cells that infiltrate and damage host organs can reduce morbidity and mortality. A better understanding of the mechanisms by which these processes occur may lead to new approaches to prevent tissue damage. The lungs, gastrointestinal tract, and skin are particularly prone to infection and collateral damage by inflammatory cells. Specialized lymphocytes protect these organs from collateral tissue damage by eliminating neutrophils and macrophages from inflamed tissues. These lymphocytes recognize signals produced by inflammatory cells. One such signal is heat shock protein (Hsp) expressed on the cell surface of inflamed phagocytes. Mammalian Hsp molecules closely resemble their microbial equivalents, and therefore phagocytes decorated with these molecules are recognized as target cells. T lymphocytes bearing the gammadelta T cell receptor (TCR) elicit cytotoxic activity toward macrophages and neutrophils that express Hsp60 and Hsp70, respectively, protecting host organs from collateral tissue damage by phagocytes.

Apolipoprotein A-I attenuates renal ischemia/reperfusion injury in rats

Apolipoprotein A-I (ApoA-I), the major protein component of serum high-density lipoprotein (HDL), exhibits its anti-inflammatory activity in inflammatory responses. As renal inflammation plays an important role in ischemia/reperfusion (I/R) injury of the kidney, the aim of this study was to investigate the beneficial effect of ApoA-I on renal I/R injury in rats and the underlined mechanism. Using rats subjected to renal I/R by occlusion of bilateral renal pedicles, we found that administration of ApoA-I significantly reduced serum creatinine levels, serum TNF-alpha and IL-1beta levels as well as tissue myeloperoxidase (MPO) activity, compared with I/R controls. Moreover, ApoA-I treatment suppresses the expression of intercellular adhesion molecules-1 (ICAM-1) and P-selectin on endothelium, thus diminishing neutrophil adherence and the subsequent tissue injury. These results showed that ApoA-I reduced I/R-induced inflammatory responses, decreased renal microscopic damage and improved renal function. It seems likely that ApoA-I protects kidney from I/R injury by inhibiting inflammatory cytokines release and neutrophil infiltration and activation.

Interaction of CD44 and hyaluronan is the dominant mechanism for neutrophil sequestration in inflamed liver sinusoids

Adhesion molecules known to be important for neutrophil recruitment in many other organs are not involved in recruitment of neutrophils into the sinusoids of the liver. The prevailing view is that neutrophils become physically trapped in inflamed liver sinusoids. In this study, we used a biopanning approach to identify hyaluronan (HA) as disproportionately expressed in the liver versus other organs under both basal and inflammatory conditions. Spinning disk intravital microscopy revealed that constitutive HA expression was restricted to liver sinusoids. Blocking CD44-HA interactions reduced neutrophil adhesion in the sinusoids of endotoxemic mice, with no effect on rolling or adhesion in postsinusoidal venules. Neutrophil but not endothelial CD44 was required for adhesion in sinusoids, yet neutrophil CD44 avidity for HA did not increase significantly in endotoxemia. Instead, activation of CD44-HA engagement via qualitative modification of HA was demonstrated by a dramatic induction of serum-derived HA-associated protein in sinusoids in response to lipopolysaccharide (LPS). LPS-induced hepatic injury was significantly reduced by blocking CD44-HA interactions. Administration of anti-CD44 antibody 4 hours after LPS rapidly detached adherent neutrophils in sinusoids and improved sinusoidal perfusion in endotoxemic mice, revealing CD44 as a potential therapeutic target in systemic inflammatory responses involving the liver.

Immunomodulatory properties of Achyrocline satureioides (Lam.) D.C. infusion: a study on human leukocytes

AIM OF THE STUDY

Achyrocline satureioides (Lam.) D.C. is a South American native medicinal herb known by the popular name of "Marcela". Its infusion is widely utilized for the treatment of several digestive ailments, as an anti-inflammatory preparation, as a sedative and anti-atherosclerotic. Circumstantial evidence suggests that extracts of Achyrocline satureioides may have immunomodulatory properties. The present study was therefore devised to investigate the in vitro effects Achyrocline satureioides infusion on human peripheral blood mononuclear cells (PBMCs) and polymorphonuclear leukocytes (PMNs).

MATERIALS AND METHODS

Experiments were performed on cells isolated from venous blood obtained from healthy donors. PBMC proliferation and cytokine production were assessed by standard ELISA methods. Reactive oxygen species (ROS) production by PMNs was evaluated by spectrofluorimetry.

RESULTS

In PBMCs, Achyrocline satureioides infusion in the 0.06-0.24microg/ml quercetin equivalent (QE) concentration range concentration-dependently reduced PHA-induced proliferation and production of interferon (IFN)-gamma and interleukin (IL)-4. Lower concentrations of the infusion (0.006-0.03microg/ml QE), which were ineffective on cell proliferation, significantly increased the production of both IFN-gamma and IL-4 and decreased the ratio IFN-gamma/IL-4. In PMNs, Achyrocline satureioides infusion slightly increased the spontaneous generation of ROS only at concentrations > or =0.06microg/ml QE. On the contrary, in the 0.0012-0.03microg/ml QE concentration range the infusion profoundly inhibited fMLP-induced ROS generation as well as spontaneous and fMLP-induced IL-8 production.

CONCLUSIONS

The present results provide evidence that Achyrocline satureioides infusion may exert several immunomodulatory effects, in line with its traditional use as an anti-inflammatory agent in many disease conditions. Further studies are warranted to better characterize such effects and to assess their therapeutic relevance.

Secondary necrosis in multicellular animals: an outcome of apoptosis with pathogenic implications

In metazoans apoptosis is a major physiological process of cell elimination during development and in tissue homeostasis and can be involved in pathological situations. In vitro, apoptosis proceeds through an execution phase during which cell dismantling is initiated, with or without fragmentation into apoptotic bodies, but with maintenance of a near-to-intact cytoplasmic membrane, followed by a transition to a necrotic cell elimination traditionally called “secondary necrosis”. Secondary necrosis involves activation of self-hydrolytic enzymes, and swelling of the cell or of the apoptotic bodies, generalized and irreparable damage to the cytoplasmic membrane, and culminates with cell disruption. In vivo, under normal conditions, the elimination of apoptosing cells or apoptotic bodies is by removal through engulfment by scavengers prompted by the exposure of engulfment signals during the execution phase of apoptosis; if this removal fails progression to secondary necrosis ensues as in the in vitro situation. In vivo secondary necrosis occurs when massive apoptosis overwhelms the available scavenging capacity, or when the scavenger mechanism is directly impaired, and may result in leakage of the cell contents with induction of tissue injury and inflammatory and autoimmune responses. Several disorders where secondary necrosis has been implicated as a pathogenic mechanism will be reviewed.

Role of neutrophils in the pathogenesis of acute inflammatory liver injury

Polymorphonuclear leukocytes (neutrophils) are essential in the defense against invading microorganisms, tissue trauma or any inciting inflammatory signals. Hepatic infiltration of neutrophils is an acute response to recent or ongoing liver injury, hepatic stress or unknown systemic inflammatory signals. Once neutrophils reach the liver, they can cause mild-to-severe tissue damage and consequent liver failure. For neutrophils to appear in the liver, neutrophils have to undergo systemic activation (priming) by inflammatory mediators such as cytokines, chemokines, complement factors, immune complexes, opsonized particles and other biologically active molecules, e.g., platelet activating factor. Neutrophils accumulated in the hepatic microvasculature (sinusoids and postsinusoidal venules) can extravasate (transmigrate) into the hepatic parenchyma if they receive a signal from distressed cells. Transmigration can be mediated by a chemokine gradient established towards the hepatic parenchyma and generally involves orchestration by adhesion molecules on neutrophils (beta(2) integrins) and on endothelial cells (intracellular adhesion molecules, ICAM-1). After transmigration, neutrophils adhere to distressed hepatocytes through their beta(2) integrins and ICAM-1 expressed on hepatocytes. Neutrophil contact with hepatocytes mediate oxidative killing of hepatocytes by initiation of respiratory burst and neutrophil degranulation leading to hepatocellular oncotic necrosis. Neutrophil-mediated liver injury has been demonstrated in a variety of diseases and chemical/drug toxicities. Relevant examples are discussed in this review.

Predictive value of white blood cell subtypes for long-term outcome following myocardial infarction

INTRODUCTION

Elevation of total white blood cells (WBC) count is associated with higher mortality in patients with acute coronary syndromes. However, it is unknown which specific subset of leukocytes best correlates with increased risk of adverse outcome.

METHODS AND RESULTS

We prospectively studied the predictive value of WBC subtypes for long-term outcome in 1037 patients with acute myocardial infarction (AMI). Total WBC, neutrophil, monocyte and lymphocyte counts, and high-sensitivity C-reactive protein (CRP) were obtained in each patient. The median duration of follow up was 23 months (range, 6-42 months). Analyzed separately, baseline total WBC (HR 2.2, 95% CI 1.5-3.3; P<0.0001), neutrophil (HR 2.7, 95% CI 1.8-4.1; P<0.0001) and monocyte (HR 1.9, 95% CI 1.3-2.8; P=0.001) counts in the upper quartile, and lymphocyte count in the lower quartile (HR 1.5, 95% CI 1.1-2.3; P=0.03), were all independent predictors of mortality. Comparing nested models, adding other WBC data failed to improve model based on neutrophil count. In contrast, adding neutrophil count to the models based on total WBC (P=0.01), on monocyte count (P<0.0001) or on lymphocyte count (P<0.0001) improved the prediction of the models. Neutrophil count in the upper quartile (>or=9800 microL(-1)) remained a strong independent predictor of mortality after adjustment for left ventricular systolic function and for CRP (HR 2.2, 95% CI 1.6-3.0; P<0.0001).

CONCLUSION

Of all WBC subtypes, elevated neutrophil count best correlates with mortality in patients with AMI. Neutrophil count provides additive prognostic information when combined with CRP.

Peroxisome proliferator-activated receptor-gamma protects against hepatic ischemia/reperfusion injury in mice

The function of peroxisome proliferator-activated receptor-gamma (PPARgamma) in hepatic inflammation and injury is unclear. In this study, we sought to determine the role of PPARgamma in hepatic ischemia/reperfusion injury in mice. Male mice were subjected to 90 minutes of partial hepatic ischemia followed by up to 8 hours of reperfusion. PPARgamma was found to be constitutively activated in hepatocytes but not in nonparenchymal cells. Upon induction of ischemia, hepatic PPARgamma activation rapidly decreased and remained suppressed throughout the 8-hour reperfusion period. This reduced activation was not a result of decreased protein availability as hepatic nuclear PPARgamma, retinoid X receptor-alpha (RXRalpha), and PPARgamma/RXRalpha heterodimer expression was maintained. Accompanying the decrease in PPARgamma activation was a decrease in the expression of the natural ligand 15-deoxy-Delta(12,14)-prostaglandin J(2). This was associated with reduced interaction of PPARgamma and the coactivator, p300. To determine whether PPARgamma activation is hepatoprotective during hepatic ischemia/reperfusion injury, mice were treated with the PPARgamma agonists, rosiglitazone and connecting peptide. These treatments increased PPARgamma activation and reduced liver injury compared to untreated mice. Furthermore, PPARgamma-deficient mice had more liver injury after ischemia/reperfusion than their wild-type counterparts.

CONCLUSION

These data suggest that PPARgamma is an important endogenous regulator of, and potential therapeutic target for, ischemic liver injury.

Chronic intermittent hypoxia causes hepatitis in a mouse model of diet-induced fatty liver

Obstructive sleep apnea (OSA) causes chronic intermittent hypoxia (CIH) during sleep. OSA is associated with nonalcoholic steatohepatitis (NASH) in obese individuals and may contribute to progression of nonalcoholic fatty liver disease from steatosis to NASH. The purpose of this study was to examine whether CIH induces inflammatory changes in the liver in mice with diet-induced hepatic steatosis. C57BL/6J mice (n = 8) on a high-fat, high-cholesterol diet were exposed to CIH for 6 mo and were compared with mice on the same diet exposed to intermittent air (control; n = 8). CIH caused liver injury with an increase in serum ALT (461 +/- 58 U/l vs. 103 +/- 16 U/l in the control group; P < 0.01) and AST (637 +/- 37 U/l vs. 175 +/- 13 U/l in the control group; P < 0.001), whereas alkaline phosphatase and total bilirubin levels were unchanged. Histology revealed hepatic steatosis in both groups, with mild accentuation of fat staining in the zone 3 hepatocytes in mice exposed to CIH. Animals exposed to CIH exhibited lobular inflammation and fibrosis in the liver, which were not evident in control mice. CIH caused significant increases in lipid peroxidation in serum and liver tissue; significant increases in hepatic levels of myeloperoxidase and proinflammatory cytokines IL-1beta, IL-6, and CXC chemokine MIP-2; a trend toward an increase in TNF-alpha; and an increase in alpha1(I)-collagen mRNA. We conclude that CIH induces lipid peroxidation and inflammation in the livers of mice on a high-fat, high-cholesterol diet.

Role of osteopontin in neutrophil function

Osteopontin (OPN) is important for the function of fibroblasts, macrophages and lymphocytes during inflammation and wound healing. In recent studies of experimental colitis we demonstrated exacerbated tissue destruction in OPN-null mice, associated with reduced tumour necrosis factor-alpha expression and increased myeloperoxidase activity. The objective of this investigation therefore was to determine the importance of OPN expression in neutrophil function. Although, in contrast to macrophages, neutrophils expressed low levels of OPN with little or no association with the CD44 receptor, intraperitoneal recruitment of neutrophils in OPN-null mice was impaired in response to sodium periodate. The importance of exogenous OPN for neutrophil recruitment was demonstrated by a robust increase in peritoneal infiltration of PMNs in response to injections of native or recombinant OPN. In vitro, OPN(-/-) neutrophils exhibited reduced chemokinesis and chemotaxis towards N-formyl methionyl leucyl phenylalanine (fMLP), reflecting a reduction in migration speed and polarization. Exogenous OPN, which was chemotactic for the neutrophils, rescued the defects in polarization and migration speed of the OPN(-/-) neutrophils. In contrast, the defensive and cytocidal activities of OPN(-/-) neutrophils, measured by assays for phagocytosis, generation of reactive oxygen species, cytokine production and matrix metalloproteinase-9, were not impaired. These studies demonstrate that, while exogenous OPN may be important for the recruitment and migration of neutrophils, expression of OPN by neutrophils is not required for their destructive capabilities.

Mechanisms of drug-induced liver disease

Drug-induced liver injury depends initially on development of hepatocyte stress and cell death, which can be induced directly by parent drugs or by toxic metabolites. Hepatocyte stress can lead to activation of built-in death programs for apoptosis or necrosis. Subsequently, the innate immune system's participation is recruited. The interplay between proinflammatory and anti-inflammatory components of innate immune system determines the outcome of drug-induced liver injury. Both environmental factors and genetic differences in cellular responses to stress and the innate immune response may account for different susceptibilities between individuals to drug-induced liver injury.

The protective effect of ApolipoproteinA-I on myocardial ischemia–reperfusion injury in rats

It is well established that reperfusion of heart is the optimal method for salvaging ischemic myocardium, however, the success of this therapy could be limited by reperfusion injury, which is involved in inflammatory responses. High density lipoprotein (HDL) has an anti-inflammatory function and can protect the heart from ischemia-reperfusion (I/R) injury. In this study, we investigated the cardioprotective role of apolipoprotein A-I (ApoA-I), the major apolipoprotein of HDL, in I/R injury. Using rats subjected to myocardial I/R by ligation of left anterior descending coronary artery (LAD), we found that administration of ApoA-I (20 mg/kg, iv) before the onset of reperfusion of myocardial infarction can significantly reduce serum creatine kinase (CK) levels (62.1+/-13.8%, p<0.01) and heart TNF-alpha as well as IL-6 levels, compared with saline controls (40.4+/-14.7%, 44+/-9.8%, p<0.01 respectively). Moreover, ApoA-I treatment suppresses the expression of ICAM-1 on endothelium, thus diminishing neutrophil adherence, transendothelial migration, and the subsequent myocyte injury. We concluded that ApoA-I could effectively protect rat heart from I/R injury.

CB2-receptor stimulation attenuates TNF-alpha-induced human endothelial cell activation, transendothelial migration of monocytes, and monocyte-endothelial adhesion

Targeting cannabinoid-2 (CB(2)) receptors with selective agonists may represent a novel therapeutic avenue in various inflammatory diseases, but the mechanisms by which CB(2) activation exerts its anti-inflammatory effects and the cellular targets are elusive. Here, we investigated the effects of CB(2)-receptor activation on TNF-alpha-induced signal transduction in human coronary artery endothelial cells in vitro and on endotoxin-induced vascular inflammatory response in vivo. TNF-alpha induced NF-kappaB and RhoA activation and upregulation of adhesion molecules ICAM-1 and VCAM-1, increased expression of monocyte chemoattractant protein, enhanced transendothelial migration of monocytes, and augmented monocyte-endothelial adhesion. Remarkably, all of the above-mentioned effects of TNF-alpha were attenuated by CB(2) agonists. CB(2) agonists also decreased the TNF-alpha- and/or endotoxin-induced ICAM-1 and VCAM-1 expression in isolated aortas and the adhesion of monocytes to aortic vascular endothelium. CB(1) and CB(2) receptors were detectable in human coronary artery endothelial cells by Western blotting, RT-PCR, real-time PCR, and immunofluorescence staining. Because the above-mentioned TNF-alpha-induced phenotypic changes are critical in the initiation and progression of atherosclerosis and restenosis, our findings suggest that targeting CB(2) receptors on endothelial cells may offer a novel approach in the treatment of these pathologies.

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.

Perinecrotic hypoxia contributes to ischemia/reperfusion-accelerated outgrowth of colorectal micrometastases

Ischemia/reperfusion (I/R) is often inevitable during hepatic surgery and may stimulate the outgrowth of colorectal micrometastases. Postischemic microcirculatory disturbances contribute to I/R damage and may induce prolonged tissue hypoxia and consequent stabilization of hypoxia-inducible factor (HIF)-1alpha. The aim of this study was to evaluate the contribution of postischemic microcirculatory disturbances, hypoxia, and HIF-1alpha to I/R-accelerated tumor growth. Partial hepatic I/R attributable to temporary clamping of the left liver lobe induced microcirculatory failure for up to 5 days. This was accompanied by profound and prolonged perinecrotic tissue hypoxia, stabilization of HIF-1alpha, and massive perinecrotic outgrowth of pre-established micrometastases. Restoration of the microcirculation by treatment with Atrasentan and L-arginine minimized hypoxia and HIF-1alpha stabilization and reduced the accelerated outgrowth of micrometastases by 50%. Destabilization of HIF-1alpha by the HSP90 inhibitor 17-DMAG caused an increase in tissue necrosis but reduced I/R-stimulated tumor growth by more than 70%. In conclusion, prevention of postischemic microcirculatory disturbances and perinecrotic hypoxia reduces the accelerated outgrowth of colorectal liver metastases after I/R. This may, at least in part, be attributed to the prevention of HIF-1alpha stabilization. Prevention of tissue hypoxia or inhibition of HIF-1alpha may represent attractive approaches to limiting recurrent tumor growth after hepatic surgery.

Cathepsin g is required for sustained inflammation and tissue injury after reperfusion of ischemic kidneys

Neutrophil activation to release granules containing proteases and other enzymes is a primary cause of tissue damage during ischemia/reperfusion injury. Because the contribution of specific granule enzymes to this injury remains poorly defined, the role of cathepsin G in renal ischemia/reperfusion injury was tested. Bilateral renal ischemia led to the expiration of 64% of wild-type mice within 4 days of reperfusion, whereas all cathepsin G-deficient mice survived. Serum creatinine increased to similar levels at 24 hours after reperfusion and then decreased to background in both groups of mice. Ischemic kidneys from both groups had similar levels of neutrophil infiltration and of CXCL1, CXCL2, and myeloperoxidase protein 9 hours after reperfusion, but at 24 hours, these acute inflammatory response components were decreased more than 50% in kidneys from cathepsin G-deficient versus wild-type mice. Ischemic kidneys from surviving wild-type mice had severe tubular necrosis and tubular cell apoptosis 24 hours after reperfusion with subsequent development of fibrosis 30 days later. In contrast, ischemic kidneys from cathepsin G-deficient mice had a 70% decrease in tubular cell apoptosis with little detectable collagen deposition. These data identify cathepsin G as a critical component sustaining neutrophil-mediated acute tissue pathology and subsequent fibrosis after renal ischemia/reperfusion injury.

Reduced inflammatory response and increased microcirculatory disturbances during hepatic ischemia-reperfusion injury in steatotic livers of ob/ob mice

Steatosis is a major risk factor for complications after liver surgery. Since neutrophil cytotoxicity is critical for ischemia-reperfusion injury in normal livers, the aim of the present study was to evaluate whether an exaggerated inflammatory response could cause the increased injury in steatotic livers. In C57Bl/6 mice, 60 min of warm hepatic ischemia triggered a gradual increase in hepatic neutrophil accumulation during reperfusion with peak levels of 100-fold over baseline at 12 h of reperfusion. Neutrophil extravasation and a specific neutrophil-induced oxidant stress (immunostaining for hypochlorous acid-modified epitopes) started at 6 h of reperfusion and peaked at 12-24 h. Ob/ob mice, which had a severe macrovesicular steatosis, suffered significantly higher injury (alanine transaminase activity: 18,000 +/- 2,100 U/l; 65% necrosis) compared with lean littermates (alanine transaminase activity: 4,900 +/- 720 U/l; 24% necrosis) at 6 h of reperfusion. However, 62% fewer neutrophils accumulated in steatotic livers. This correlated with an attenuated increase in mRNA levels of several proinflammatory genes in ob/ob mice during reperfusion. In contrast, sham-operated ob/ob mice had a 50% reduction in liver blood flow and 35% fewer functional sinusoids compared with lean littermates. These deficiencies in liver blood flow and the microcirculation were further aggravated only in ob/ob mice during reperfusion. The attenuated inflammatory response and reduced neutrophil-induced oxidant stress observed in steatotic livers during reperfusion cannot be responsible for the dramatically increased injury in ob/ob mice. In contrast, the aggravated injury appears to be mediated by ischemic necrosis due to massive impairment of blood and oxygen supply in the steatotic livers.

Fasciotomy closure using simultaneous vacuum-assisted closure and hyperbaric oxygen

Fasciotomies performed for compartment syndrome and ischemic vascular disease often requires closure in 2 to 4 weeks by skin graft. This leaves the patient with an unsightly scar and a limb with reduced strength. The use of vacuum-assisted closure (VAC) and hyperbaric oxygen therapy (HBOT) quickly reduce the edema and permit earlier closure with adjacent skin. A study of three trauma patients with compartment syndrome, fasciotomies, and the use of the VAC and HBOT to close the fasciotomy wounds with adjacent skin is presented. The pathophysiology of compartment syndrome and ischemia-reperfusion syndrome is discussed. These patients had closure of the fasciotomy wounds in 3 to 18 days. The simultaneous use of HBOT and VAC accelerates the reduction of edema in a synergistic fashion, permitting early closure of fasciotomy wounds.

Calpain inhibition attenuates iNOS production and midzonal hepatic necrosis in a repeat dose model of endotoxemia in rats

Systemic exposure to bacterial lipopolysaccharide (LPS, endotoxin) induces hypotension, disseminated intravascular coagulation and neutrophil infiltration in various organs including the lung, kidney and liver. A rat endotoxemic neutrophilic hepatitis model (repeat dose LPS, 10 mg/kg, i.v. 24 hours apart) was developed exhibiting hepatic neutrophil infiltration and mid-zonal hepatic necrosis. The goal of the study was to investigate the role of the intracellular enzyme calpain in the development of neutrophilic hepatitis with midzonal necrosis in this model. A second goal was to compare the observed protective effects of calpain inhibition with a relatively selective inducible nitric oxide synthase (iNOS) inhibitor aminoguanidine (AG) and an inhibitor of coagulation, heparin. When compared to rats administered LPS alone, administration of calpain 1 inhibitor prior to LPS significantly reduced hepatic iNOS expression, hepatic neutrophil infiltration and attenuated midzonal hepatic necrosis. Administration of AG or heparin prior to LPS also decreased liver iNOS expression, hepatic neutrophil infiltration and liver pathology comparable to calpain inhibition. Blood neutrophil activation, as measured by the neutrophil adhesion molecule CD11b integrin, was upregulated in all the LPS treated groups regardless of inhibitor administration. We conclude that amelioration of liver pathology via calpain inhibition is likely dependent on the down-regulation of iNOS expression in the rat model of LPS-mediated hepatitis.

Hepatocyte NF-kappaB activation is hepatoprotective during ischemia-reperfusion injury and is augmented by ischemic hypothermia

The present study examined the role of hepatocyte NF-kappaB activation during ischemia-reperfusion injury. Second, we evaluated the effects of ischemic hypothermia on NF-kappaB activation and liver injury. C57BL/6 mice underwent 90 min of partial hepatic ischemia and up to 8 h of reperfusion. Body temperature was regulated during the ischemic period between 35 and 37 degrees C, 33 and 35 degrees C, 29 and 33 degrees C or unregulated, where temperature fell to <29 degrees C. Liver injury, as measured by serum alanine aminotransferase as well as liver histopathology, was inversely proportional to regulated body temperature, with the unregulated group (<29 degrees C) being highly protected and the normothermic group (35-37 degrees C) displaying the greatest injury. Inflammation, as measured by production of TNF-alpha and liver recruitment of neutrophils, was greatest in the normothermic groups and lowest in the ischemic hypothermia groups. Interestingly, hepatocyte NF-kappaB activation was highest in the hypothermic group and least in the normothermic group. Paradoxically, degradation of IkappaB proteins, IkappaB-alpha and IkappaB-beta, was greatest in the normothermic group, suggesting an alternate NF-kappaB regulatory mechanism during ischemia-reperfusion injury. Subsequently, we found that NF-kappaB p65 protein was increasingly degraded in normothermic versus hypothermic groups, and this degradation was specific for hepatocytes and was associated with decreased expression of the peptidyl-prolyl isomerase Pin1. The data suggest that NF-kappaB activation in hepatocytes is a protective response during ischemia-reperfusion and can be augmented by ischemic hypothermia. Furthermore, it appears that Pin1 promotes NF-kappaB p65 protein stability such that decreased expression of Pin1 during ischemia-reperfusion results in p65 degradation, reduced nuclear translocation of NF-kappaB, and enhanced hepatocellular injury.

Ischemia-Reperfusion Injury is More Severe in Older Versus Young Rat Livers

BACKGROUND

Hepatic warm ischemia during surgery remains a significant problem, particularly in organs with possible baseline dysfunction. The objective of this study was to investigate whether age influences the degree of warm ischemia-reperfusion injury in rat livers.

MATERIALS AND METHODS

The left and median lobes of young (3 months) and adult (9 months) male rats were exposed to 75 min of ischemia followed by reperfusion. Each age group was divided into two sub-groups. One sub-group was observed for 8 h, whereas the other was allowed to survive. Animals in the 8-h groups (young and adult) were sacrificed, and blood and tissue were taken to determine liver enzymes, neutrophil accumulation, and blood metabolic profiles and to examine the histology.

RESULTS

Hepatocellular injury was significantly greater in adult rats after 8 h of reperfusion, as determined by hepatic enzyme levels and histology. Liver enzyme levels were massively elevated in adult rats and were significantly higher compared with those of young rats. The degree of necrosis and neutrophil accumulation was significantly higher in adult rats. After 8 h of reperfusion, the metabolic profiling of the blood revealed elevated levels of creatine, creatinine, allantoin, and amino acids (tyrosine, methionine) in the adult rats. At 24 h of reperfusion, all adult rats died, in contrast to young rats, which all survived.

CONCLUSIONS

Aging in rats is associated with greater hepatocellular injury and poor survival rate after 75 min of warm hepatic ischemia.

The mechanistic basis of infarct healing

Myocardial infarction triggers an inflammatory cascade that results in healing and replacement of the damaged tissue with scar. Cardiomyocyte necrosis triggers innate immune mechanisms eliciting Toll-like receptor- mediated responses, activating the complement cascade and generating reactive oxygen species. Subsequent activation of NF-kappaB is a critical element in the regulation of cytokine, chemokine, and adhesion molecule expression in the ischemic myocardium. Chemokine induction mediates leukocyte recruitment in the myocardium. Pleiotropic proinflammatory cytokines, such as TNF-alpha, IL-1, and IL-6, are also upregulated in the infarct and exert a wide range of effects on a variety of cell types. Timely repression of proinflammatory gene synthesis is crucial for optimal healing; IL-10 and TGF-beta-mediated pathways may be important for suppression of chemokine and cytokine expression and for resolution of the leukocytic infiltrate. In addition, TGF-beta may be critically involved in inducing myofibroblast differentiation and activation, promoting extracellular matrix protein deposition in the infarcted area. The composition of the extracellular matrix plays an important role in regulating cell behavior. Both structural and matricellular proteins modulate cell signaling through interactions with specific surface receptors. The molecular and cellular changes associated with infarct healing directly influence ventricular remodeling and affect prognosis in patients with myocardial infarction.

ESSENTIAL ROLE FOR PLATELETS IN ORGAN INJURY AND INFLAMMATION IN RESUSCITATED HEMORRHAGIC SHOCK

Platelets are known to contribute to ischemia/reperfusion in several organs, but their role in inflammation and organ injury after hemorrhagic shock (HS) has not been examined. To address this issue, we rendered mice thrombocytopenic (20% of normal platelet count) by treatment with pOp3, a rat monoclonal antibody against platelet glycoprotein Ibalpha, 24 h before subjecting them to either a standard HS or sham protocol. Liver apoptosis increased 3- to 5-fold (P<0.05), and focal liver necrosis increased 11-fold (P<0.01) in placebo-treated shock mice compared with sham; these increased indices of liver injury were completely prevented by pOp3 pretreatment. Neutrophils infiltrating the liver increased nearly 3-fold in placebo-treated shock mice versus sham (P<0.05); this shock-induced increase in neutrophil infiltration was also eliminated by pretreatment with pOp3. Alveolar cross-sectional area, used to histologically assess interstitial lung edema and cellular infiltration, was reduced by 25% in pOp3-treated shock mice versus placebo-treated shock mice (P<0.05). Similar to the results in liver, pOp3 pretreatment decreased neutrophil infiltration in the lung after HS. Thus, platelets contribute to the inflammatory injuries of the liver and lung after HS, in part, perhaps by facilitating neutrophil infiltration into tissues.

Role of neutrophils in acute inflammatory liver injury

Hepatic infiltration of polymorphonuclear leukocytes (neutrophils) is an early response to tissue injury, cellular stress or systemic inflammation. Neutrophil activation is vital for host-defense and the removal of cell debris but can also cause additional tissue damage or even liver failure. In order to prevent the detrimental effects of neutrophils without compromising host-defense reactions, it is important to understand the mechanisms of neutrophil hepatotoxicity. The first step in the pathophysiology is the priming and recruitment of neutrophils into the liver vasculature by inflammatory mediators, e.g. cytokines, chemokines, or complement factors. Most critical for parenchymal cell damage is the accumulation in sinusoids, which does not depend on cellular adhesion molecules. The next step is the extravasation into the parenchyma. This process requires a chemotactic signal from hepatocytes or already extravasated neutrophils and depends on cellular adhesion molecules on neutrophils (beta(2) or beta(1) integrins) and on endothelial cells (intercellular or vascular cell adhesion molecules). The third step is the direct contact with target cells (hepatocytes), which involves beta(2) integrins and triggers the full activation of the neutrophil with a long-lasting adherence-dependent oxidant stress and degranulation. The oxidants diffuse into hepatocytes and trigger an intracellular oxidant stress, mitochondrial dysfunction and eventually cause oncotic necrotic cell death. Neutrophil-derived proteases facilitate extravasation and are involved in the regulation of inflammatory mediator production. Based on these mechanisms, it appears that strengthening of the intracellular defense mechanisms in hepatocytes may be the most promising therapeutic approach to selectively prevent neutrophil-mediated tissue damage without compromising their host-defense function.

IN SILICO MODELS OF ACUTE INFLAMMATION IN ANIMALS

Trauma and hemorrhagic shock elicit an acute inflammatory response, predisposing patients to sepsis, organ dysfunction, and death. Few approved therapies exist for these acute inflammatory states, mainly due to the complex interplay of interacting inflammatory and physiological elements working at multiple levels. Various animal models have been used to simulate these phenomena, but these models often do not replicate the clinical setting of multiple overlapping insults. Mathematical modeling of complex systems is an approach for understanding the interplay among biological interactions. We constructed a mathematical model using ordinary differential equations that encompass the dynamics of cells and cytokines of the acute inflammatory response, as well as global tissue dysfunction. The model was calibrated in C57Bl/6 mice subjected to (1) various doses of lipopolysaccharide (LPS) alone, (2) surgical trauma, and (3) surgery + hemorrhagic shock. We tested the model's predictive ability in scenarios on which it had not been trained, namely, (1) surgery +/- hemorrhagic shock + LPS given at times after the beginning of surgical instrumentation, and (2) surgery + hemorrhagic shock + bilateral femoral fracture. Software was created that facilitated fitting of the mathematical model to experimental data, as well as for simulation of experiments with various inflammatory challenges and associated variations (gene knockouts, inhibition of specific cytokines, etc.). Using this software, the C57Bl/6-specific model was recalibrated for inflammatory analyte data in CD14-/- mice and was used to elucidate altered features of inflammation in these animals. In other experiments, rats were subjected to surgical trauma +/- LPS or to bacterial infection via fibrin clots impregnated with various inocula of Escherichia coli. Mathematical modeling may provide insights into the complex dynamics of acute inflammation in a manner that can be tested in vivo using many fewer animals than has been possible previously.

Role of inflammation in the mechanism of acetaminophen-induced hepatotoxicity

Acetaminophen (AAP) overdose and the resulting hepatotoxicity is an important clinical problem. In addition, AAP is widely used as a prototype hepatotoxin to study mechanisms of chemical-induced cell injury and to test the hepatoprotective potential of new drugs and herbal medicines. Because of its importance, the mechanisms of AAP-induced liver cell injury have been extensively investigated and controversially discussed for > 30 years. This review highlights recent new insight into intracellular events critical for liver cell death. In addition, the relevance of the inflammatory response is addressed, including cytotoxic and inflammatory mediators generated by activated inflammatory cells, that is, resident macrophages and lymphocytes as well as newly recruited blood-derived leukocytes. Inflammation is a critical component of the overall pathophysiology, not only as a potential factor that may aggravate cell damage, but more importantly as a vital response to limit cell injury, remove cell debris and promote regeneration.

Human galectin-1, -2, and -4 induce surface exposure of phosphatidylserine in activated human neutrophils but not in activated T cells

Cellular turnover is associated with exposure of surface phosphatidylserine (PS) in apoptotic cells, leading to their phagocytic recognition and removal. But recent studies indicate that surface PS exposure is not always associated with apoptosis. Here we show that several members of the human galectin family of glycan binding proteins (galectins-1, -2, and -4) induce PS exposure in a carbohydrate-dependent fashion in activated, but not resting, human neutrophils and in several leukocyte cell lines. PS exposure is not associated with apoptosis in activated neutrophils. The exposure of PS in cell lines treated with these galectins is sustained and does not affect cell viability. Unexpectedly, these galectins bind well to activated T lymphocytes, but do not induce either PS exposure or apoptosis, indicating that galectin's effects are cell specific. These results suggest novel immunoregulatory contribution of galectins in regulating leukocyte turnover independently of apoptosis.

Mild hypothermia reduces the inflammatory response and hepatic ischemia/reperfusion injury in rats

BACKGROUND/AIMS

Hypothermia is known to protect against ischemia/reperfusion (I/R) injury. The mechanisms of protection are incompletely understood and a temperature threshold for protection has not been established.

METHODS

In anesthetized Wistar rats, partial (70%) hepatic ischemia was applied for 45 min. Three study groups were used. Group T31 (n = 6) spontaneously cooled to 31.3 +/- 0.8 degrees C, while group T34 (n = 6) spontaneously cooled to 34 degrees C and was then maintained at 34.0 +/- 0.1 degrees C using a heat lamp. The normothermic group (T37, n = 6) was maintained at 37.1 +/- 0.3 degrees C. Hepatic injury, inflammation, lipid peroxidation and metabolic function (using quantitative 1H-NMR) were assessed 24 h after reperfusion.

RESULTS

At 24 h following reperfusion, alanine aminotransferase and aspartate aminotransferase increased to 5101 +/- 2378 and 6409 +/- 4202 U/l in the normothermic T37 group (P < 0.05 vs. T34 and T31), whereas transaminases in hypothermic groups (T31 and T34) were significantly lower. Severe liver necrosis was only noted with T37. Myeloperoxidase activity was increased in the T37 group when compared with hypothermic groups (223 +/- 161 (T37) vs. 16 +/- 10 (T31) and 8 +/- 5 (T34) mU/min/mg of tissue, P<0.05 vs. T31 and T34). 1H-NMR analysis of the blood of normothermic animals revealed metabolic changes consistent with increased ischemic injury, which was almost completely ameliorated in T34 and T31 groups.

CONCLUSIONS

Mild hypothermia of 34 degrees C is sufficient to reduce I/R injury by inhibiting the inflammatory response. Further spontaneous cooling to 31 degrees C did not demonstrate any additional protective effect.

Mechanisms and pathophysiological implications of sinusoidal endothelial cell gap formation following treatment with galactosamine/endotoxin in mice

Neutrophil extravasation from sinusoids is a critical step for acute inflammatory tissue injury. However, the role of sinusoidal endothelial cells (SECs) in this process remains unclear. Matrix metalloproteinases (MMPs) have been shown to involve gap formation in SECs in several liver diseases. Therefore, the present study examined SEC modifications elicited by galactosamine (Gal)/endotoxin (ET). Treatment of male C3Heb/FeJ mice with Gal/ET or Gal/TNF caused the formation of numerous gaps in SECs at 4 h when no neutrophil extravasation occurred. Six hours after Gal/ET or Gal/TNF treatment, blood elements started to penetrate to the extrasinusoidal space through large gaps. Treatment with ET alone caused sinusoidal neutrophil accumulation but no gap formation, neutrophil extravasation, or hemorrhage. Gal/ET treatment increased hepatic MMP-2 and MMP-9 mRNA expression (6.7- and 11-fold, respectively). Pretreatment with 2-[(4-biphenylsulfonyl) amino]-3-phenyl-propionic acid, an MMP-2/MMP-9 inhibitor (5 mg/kg), minimized gap formation after Gal/ET and Gal/TNF treatment. The MMP inhibitor reduced injury only in the Gal/ET model mainly due to reduced TNF formation. The MMP inhibitor attenuated sinusoidal neutrophil accumulation at 6 h but failed to attenuate Gal/TNF-induced liver injury at 7 h due to excessive apoptosis. These results suggest that Gal/ET or Gal/TNF activates MMPs, which are responsible for SEC gap formation. Although the initial appearance of gap formation is independent of neutrophils, the gaps allow initial contact of neutrophils with damaged hepatocytes. In addition, MMP activation promotes neutrophil accumulation in sinusoids.

Role of innate immunity in acetaminophen-induced hepatotoxicity

Acetaminophen (APAP) hepatotoxicity is currently the single most important cause of acute liver failure in the US, and is associated with a significant number of deaths. The toxic response to APAP is triggered by a highly reactive metabolite N-acetyl-p-benzoquinone-imine. Following the hepatocellular initiation events, such as glutathione depletion and covalent binding, intracellular stress simultaneously activates signal transduction and transcription factor pathways that are protective or toxic (directly or through sensitisation). Subsequently, pro- and anti-inflammatory cascades of the innate immune system are simultaneously activated, the balance of which plays a major role in determining the progression and severity of APAP-induced hepatotoxicity. The threshold and susceptibility to APAP hepatotoxicity is determined by the interplay of injury promoting and inhibiting events downstream of the initial production of toxic metabolite. The environmental and genetic control of these intracellular and intercellular responses to toxic metabolites may be of critical importance in determining susceptibility to APAP hepatotoxicity and presumably idiosyncratic drug hepatotoxicity.

Hyperbaric oxygen: a new drug in myocardial revascularization and protection?

Ischemia-reperfusion injury (IRI) occurs following coronary artery revascularization. Reactive oxygen species (ROS) were initially thought to play a role in the pathogenesis of this injury. However, the evidence for this is inconclusive. Recent studies involving ischemic preconditioning have identified ROS as potential mediators for the cardioprotective effects observed following this technique. Furthermore, cardiac studies involving IRI and the use of hyperbaric oxygen (HBO) have demonstrated the ability of HBO to induce cardioprotection and to attenuate IRI. This review suggests the possible role for HBO as a new drug in the arena of myocardial revascularization and cellular protection. While there is mounting clinical evidence for this, a methodological understanding of HBO's cellular mechanisms of actions appears to be lacking. As such, this article attempts to draw the similarity between HBO and other protective oxidative stress mechanisms and then to speculate in an evidence-based manner its possible cellular mechanistic role as a drug via the generation of ROS.

Hepatic ischemia/reperfusion injury is prevented by a novel matrix metalloproteinase inhibitor, ONO-4817

BACKGROUND

Matrix metalloproteinases (MMPs) play an important role in inflammation and neoplastic invasion and metastasis. Little is known about the effects of MMP inhibitors on hepatic ischemia/reperfusion injury. The aim of this study is to examine the inhibitory effects of ONO-4817 (oral inhibitor of MMPs) in rats.

METHODS

Hepatic ischemia/reperfusion was induced in male Wister rats by clamping the portal vein and hepatic artery. The animals were randomized into an ONO-4817 group (300 mg/kg body weight per/day) and a vehicle group by oral gavage of a test substance. Serum alanine aminotransferase, histologic changes, gelatinolytic activity, MMP-2 and MMP-9 activities, tissue inhibitor of metalloproteinase 2 (TIMP-2) messenger RNA (mRNA) levels, and mRNA and serum levels of tumor necrosis factor alpha (TNFalpha) and interleukin 1beta (IL-1beta) were measured in both groups.

RESULTS

ONO-4817 prevented ischemia/reperfusion injury to the hepatocytes as shown by significant reductions of serum alanine aminotransferase and less severe histologic changes. Gelatinolytic activity was inhibited markedly in the liver of the ONO-4817 group as demonstrated by film in situ zymography. MMP-9 and MMP-2 activities also were inhibited in the ONO-4817 group as shown by gelatin zymography. TIMP-2 mRNA levels showed no significant differences between the 2 groups. TNFalpha mRNA showed no downregulation, but IL-1beta mRNA was downregulated in the liver of the ONO-4817 group 1 to 3 hours after reperfusion. Serum levels of TNFalpha and IL-1beta showed a significant decrease in the ONO-4817 group, compared with the vehicle group after reperfusion.

CONCLUSIONS

Hepatic ischemia/reperfusion injury was improved by a novel MMP inhibitor, ONO-4817, not only by inhibition of gelatinolytic activity but also by a decrease in release of inflammatory cytokines.

Past and future approaches to ischemia-reperfusion lesion associated with liver transplantation

Ischemia-reperfusion (I/R) injury associated with liver transplantation remains a serious complication in clinical practice, in spite of several attempts to solve the problem. The present review focuses on the complexity of I/R injury, summarizing conflicting results obtained from the literature about the mechanisms responsible for it. We also review the therapeutic strategies designed in past years to reduce I/R injury, attempting to explain why most of them have not been applied clinically. These strategies include improvements in pharmacological treatments, modifications of University of Wisconsin (UW) preservation solution based on a variety of additives, and gene therapy. Finally, we will consider new potential protective strategies using trimetazidine, 5-amino-4-imidazole carboxamide riboside (AICAR), melatonin, modulators of the renin-angiotensin system (RAS) and the phosphatidylinositol-3-OH kinase (PI3K)-Akt and the p42/p44 extracellular signal-regulated kinases (Erk 1/2) pathway. These strategies have shown promising results for I/R injury but have not been tested in experimental liver transplantation to date. Moreover, we will review ischemic preconditioning, taking into account the recent clinical studies that suggest that this surgical strategy could be appropriate for liver transplantation.

Neutrophil depletion protects against murine acetaminophen hepatotoxicity

We previously reported that liver natural killer (NK) and NKT cells play a critical role in mouse model of acetaminophen (APAP)-induced liver injury by producing interferon gamma (IFN-gamma) and modulating chemokine production and subsequent recruitment of neutrophils into the liver. In this report, we examined the role of neutrophils in the progression of APAP hepatotoxicity. C57BL/6 mice were given an intraperitoneal toxic dose of APAP (500 mg/kg), which caused severe acute liver injury characterized by significant elevation of serum ALT, centrilobular hepatic necrosis, and increased hepatic inflammatory cell accumulation. Flow cytometric analysis of isolated hepatic leukocytes demonstrated that the major fraction of increased hepatic leukocytes at 6 and 24 hours after APAP was neutrophils (Mac-1+ Gr-1+). Depletion of neutrophils by in vivo treatment with anti-Gr-1 antibody (RB6-8C5) significantly protected mice against APAP-induced liver injury, as evidenced by markedly reduced serum ALT levels, centrilobular hepatic necrosis, and improved mouse survival. The protection was associated with decreased FasL-expressing cells, cytotoxicity against hepatocytes, and respiratory burst in hepatic leukocytes. In intracellular adhesion molecule (ICAM)-1-deficient mice, APAP caused markedly reduced liver injury when compared with wild-type mice. The marked protection in ICAM-1-deficient mice was associated with decreased accumulation of neutrophils in the liver. Hepatic GSH depletion and APAP-adducts showed no differences among the antibody-treated, ICAM-1-deficient, and normal mice. In conclusion, accumulated neutrophils in the liver contribute to the progression and severity of APAP-induced liver injury.

Mechanisms of Liver Injury. II. Mechanisms of neutrophil-induced liver cell injury during hepatic ischemia-reperfusion and other acute inflammatory conditions

Polymorphonuclear leukocytes (neutrophils) are a vital part of the innate immune response to microbial infections and tissue trauma, e.g., ischemia-reperfusion injury, in many organs including the liver. However, an excessive inflammatory response can lead to a dramatic aggravation of the existing injury. To design interventions, which selectively target the detrimental effects of neutrophils, a detailed understanding of the pathophysiology is critical. Systemic or local exposure to proinflammatory mediators causes activation and priming of neutrophils for reactive oxygen formation and recruits them into the vascular beds of the liver without causing tissue injury. However, generation of a chemotactic signal from the parenchyma will trigger extravasation and an attack on target cells (e.g., hepatocytes). Adhesion to the target induces degranulation with release of proteases and formation of reactive oxygen species including hydrogen peroxide and hypochlorous acid, which can diffuse into hepatocytes and induce an intracellular oxidant stress and mitochondrial dysfunction. Various neutrophil-derived proteases are involved in transmigration and cell toxicity but can also promote the inflammatory response by processing of proinflammatory mediators. In addition, necrotic cells release mediators, e.g., high-mobility group box-1, which further promotes neutrophilic hepatitis and tissue damage. On the basis of these evolving insights into the mechanisms of neutrophil-mediated liver damage, the most selective strategies appear not to interfere with the cytotoxic potential of neutrophils, but rather strengthen the target cells' defense mechanisms including enhancement of the intracellular antioxidant defense systems, activation of cell survival pathways, or initiation of cell cycle activation and regeneration.

Endoplasmic and vascular surface activation during organ preservation: refining upon the benefits of machine perfusion

The endoplasmic reticulum (ER) represents a subcellular target reactive to various cytosolic impairments. The involvement of ER-stress in organ preservation was investigated, comparing machine preservation, cold storage (CS) and a novel concept of only temporary perfusion after procurement. Rat livers were retrieved 30 min after cardiac arrest and preserved for 18 h by CS, oxygenated machine perfusion for 18 h (18 h MP) or for 2 h with subsequent CS for 16 h (2 h MP + 16 h CS). Upon reperfusion, 18 h MP significantly improved enzyme leakage (ALT, LDH) and promoted a 2-fold increase of metabolic recovery compared to CS. However, vascular stress, evaluated by endothelin-release, was significantly elevated after 18 h MP. Interestingly, better viability was obtained using the short-term perfusion protocol (2 h MP + 16 h CS), which further reduced enzyme leakage, maintained energetic recovery and mitigated endothelin-release compared to 18 h MP. Caspase 12-mRNA was upregulated in the 18 h MP-group but unchanged after CS or 2 h MP + 16 h CS. Activation/cleavage of caspase 12 protein was significantly enhanced after 18 h MP and very low in the 2 h MP + 16 h CS-group. Correspondingly, electron microscopy showed ultrastructural alterations of ER after CS and especially after 18 h MP but not after 2 h MP + 16 h CS. At this time mitochondrial appearance was unaffected in all groups, suggesting the ER to be an early subcellular target of preservation injury. In our model, ER and vascular endothelium were best protected by only temporary machine perfusion, which also maintained overall graft viability.

NAD(P)H oxidase contributes to the progression of remote hepatic parenchymal injury and endothelial dysfunction, but not microvascular perfusion deficits

Oxidative stress occurs in remote liver injury, but the origin of the oxidant generation has yet to be thoroughly delineated. Some reports suggest that the source of the distant oxidative stress originates from the site of initial insult [i.e., xanthine oxidase (XO)]; however, it could also be derived from sources such as phagocytic and/or vascular NAD(P)H oxidase (Nox) enzymes. With a murine model of bilateral hindlimb ischemia-reperfusion, we describe here a mechanism for Nox-dependent oxidant production that contributes, at least in part, to remote hepatic parenchymal injury and sinusoidal endothelial cell (SEC) dysfunction. To determine whether Nox enzymes were the source of oxidants, mice were treated immediately after the onset of hindlimb ischemia with specific inhibitors to XO (50 mg/kg ip allopurinol) or Nox (10 mg/kg ip gp91ds-tat and 3 mg/kg ip apocynin). After 1 h of ischemia, hindlimbs were reperfused for either 3 or 6 h. Inhibition of XO failed to provide any improvement in parenchymal injury, SEC dysfunction, neutrophil accumulation, or microvascular dysfunction. In contrast, the inhibition of Nox enzymes prevented the progression (6 h) of parenchymal injury, significantly protected against SEC dysfunction, and completely prevented signs of neutrophil-derived oxidant stress. At the same time, however, inhibition of Nox failed to protect against the early parenchymal injury and microvascular dysfunction at 3 h of reperfusion. These data confirm that microvascular perfusion deficits are not essential for the pathogenesis of remote hepatic parenchymal injury. The data also suggest that Nox enzymes, not XO, are involved in the progression of compromised hepatic parenchymal and endothelial integrity during a systemic inflammatory response.

Age-dependent responses to hepatic ischemia/reperfusion injury

The current study explored the concept that adult and pediatric populations differ in their response to major injury. Male C57BL/6 mice of a "young adult" (8-12 weeks) or "mature adult" (12-13 months) age were subjected to partial hepatic ischemia and reperfusion. Mature adult mice displayed significantly more liver injury than young adult mice as assessed histologically and by serum levels of alanine aminotransferase. Interestingly, there was far less neutrophil accumulation in the livers of mature adult mice. However, liver-recruited neutrophils from mature adult mice had a higher activation state than those from young adult mice. Activation of the inflammatory transcription factor, NF-kappaB, was suppressed in whole livers from mature adult mice. In isolated liver cells, Kupffer cells showed no difference in NF-kappaB activation, but hepatocytes from mature adult mice had delayed NF-kappaB activation in response to TNF. Furthermore, isolated hepatocytes from young adult mice produced abundant amounts of the chemokine, macrophage inflammatory protein-2, whereas hepatocytes from mature adult mice produced little, if any macrophage inflammatory protein-2. Mature adult mice had much lower hepatic expression of the cytoprotective protein, heat shock protein 70, than did young adult mice. In contrast, serum heat shock protein 70 levels, which has been linked to subsequent tissue injury, were higher in mature adult mice than in young adult mice. These data suggest that there are multiple alterations at the cellular and molecular levels that contribute to enhanced postischemic liver injury in mature adult mice.

Expression of IL-8 during Reperfusion of Renal Allografts Is Dependent on Ischemic Time

BACKGROUND

Ischemia/reperfusion injury is an inherent consequence of solid organ transplantation that increases tissue inflammation and negatively impacts organ transplant function and survival. This study investigated the expression levels of chemokine and chemokine receptor genes in living versus cadaver donor renal allografts before and after reperfusion.

METHODS

This study involved 39 renal transplant patients (19 cadaveric and 20 living donor). The ischemia biopsy was taken just before graft declamping and the reperfusion biopsy 30 min after declamping. Whole-cell RNA was isolated and chemokine (IL-8, CCL2/MCP-1, CXCL10/IP-10 and CCL5/RANTES) and chemokine receptor (CCR2 and CCR5) expression was tested by quantitative PCR.

RESULTS

Just prior to declamping, ischemic cadaveric donor grafts had higher expression of CXCL10/IP-10 but not IL-8 or CCL2/MCP-1 than living donor grafts. IL-8 expression increased 50% from ischemia to reperfusion in living donor grafts but increased more than 13-fold during reperfusion of cadaver donor grafts. Increased total ischemia time induced greater IL-8 expression during reperfusion. MCP-1 expression also increased during reperfusion of living and cadaver donor grafts but differences were not observed between the two groups of grafts. RANTES, CCR2, and CCR5 expression did not change in ischemic vs. reperfusion biopsies.

CONCLUSIONS

The expression of chemokines directing neutrophil and macrophage recruitment increases during reperfusion of living and cadaveric donor renal allografts. Expression levels of IL-8 correlate with the ischemic time imposed on the renal graft. Early tissue injury may be attenuated by strategies antagonizing chemokines directing the recruitment of neutrophils and macrophages into kidney grafts.

Blockade of neutrophil elastase attenuates severe liver injury in hepatitis B transgenic mice

Serine proteinases produced by polymorphonuclear neutrophils play important roles in neutrophil-mediated tissue injury at inflammatory sites. Although neutrophil recruitment to the liver has been shown to be involved in the exacerbation of liver inflammation, the function of neutrophil elastase (NE) in liver injury remains unclear. Here, we found that administration of an NE inhibitor (NEI) reduced serum alanine aminotransferase (sALT) activity and inflammatory cell infiltration into the liver from 8 to 24 h after injection of antigen-specific cytotoxic T lymphocytes (CTLs) into hepatitis B virus transgenic mice. Furthermore, the NEI treatment reduced the expressions of inflammatory cytokines and chemokines in the liver and tumor necrosis factor alpha production by macrophages. In addition, the NEI treatment suppressed the mRNA expressions of CC chemokine ligand 3 (CCL-3), CCL-4, and macrophage inflammatory protein 2 (MIP-2) in neutrophils in the liver at 8 h after the CTL injection. In support of these results, we confirmed that administration of anti-CCL-3, anti-CCL-4, and anti-MIP-2 monoclonal antibodies suppressed sALT activity and leukocyte migration into the liver. In conclusion, the present results suggest that NE contributes to the early step of the inflammatory cascade in acute viral hepatitis and that NEIs may have potential as therapeutic drugs against acute severe viral hepatitis.

Inhibition of inducible nitric oxide synthase prevents hepatic, but not pulmonary, injury following ischemia-reperfusion of rat liver

The aim of this study was to investigate the contribution of inducible nitric oxide synthase (iNOS)-derived nitric oxide on the liver and lung injury following hepatic ischemia-reperfusion (I/R) using a novel and potent iNOS inhibitor, ONO-1714. Rats were subjected to 90 min of partial hepatic ischemia followed by 3, 6, 12, and 24 hr of reperfusion. Expression of iNOS mRNA peaked at 3 hr of reperfusion in the liver and lung. Plasma nitric oxide levels were increased fourfold at 24 hr of reperfusion and plasma ALT was increased, reaching a peak at 12 hr of reperfusion; both were significantly inhibited by ONO-1714. Histological examination revealed extensive liver damage, whereas this was not seen in the ONO-1714 group. Lung injury was not significantly changed in groups with versus without ONO-1714. Nitrotyrosine expression was seen in regions similar to those of the histological injuries of the liver, while this staining was absent in the ONO-1714 group. These data show that generation of peroxynitrite could be involved in the pathogenesis of liver injury but not lung injury after hepatic I/R. Inhibition of iNOS could be applied for attenuation of liver injury following hepatic I/R.

Protection of early phase hepatic ischemia-reperfusion injury by cholinergic agonists

BACKGROUND

Cytokine production is critical in ischemia/reperfusion (IR) injury. Acetylcholine binds to macrophages and inhibits cytokine synthesis, through the cholinergic anti-inflammatory pathway. This study examined the role of the cholinergic pathway in cytokine production and hepatic IR- injury.

METHODS

Adult male mice underwent 90-min of partial liver ischemia followed by reperfusion. The AChR agonists (1,1-dimethyl-4-phenyl-L-pioperazinium-iodide [DMPP], and nicotine) or saline-vehicle were administered i.p. before ischemia. Plasma cytokine tumor necrosis factor (TNF)-alpha, macrophage inflammatory protein-2, and Interleukin-6 were measured. Liver injury was assessed by plasma alanine transaminase (ALT) and liver histopathology.

RESULTS

A reperfusion time-dependent hepatocellular injury occurred as was indicated by increased plasma-ALT and histopathology. The injury was associated with marked elevation of plasma cytokines/chemokines. Pre-ischemic treatment of mice with DMPP or nicotine significantly decreased plasma-ALT and cytokines after 3 h of reperfusion. After 6 h of reperfusion, the protective effect of DMPP decreased and reached a negligible level by 24 h of reperfusion, despite significantly low levels of plasma cytokines. Histopathology showed markedly diminished hepatocellular injury in DMPP- and nicotine-pretreated mice during the early-phase of hepatic-IR, which reached a level comparable to saline-treated mice at late-phase of IR.

CONCLUSION

Pharmacological modulation of the cholinergic pathway provides a means to modulate cytokine production and to delay IR-induced heaptocellular injury.

Propofol improves endothelial dysfunction and attenuates vascular superoxide production in septic rats

OBJECTIVE

To determine the effects of propofol on vascular functions, plasma and endothelium-derived nitric oxide (EDNO), vascular NO, and cyclic guanosine monophosphate (cGMP), as well as vascular production of superoxide anion (O2*-), in septic animals.

DESIGN

Prospective, multiexperimental, randomized, controlled studies.

SETTING

University research laboratory.

SUBJECTS

Male adult Sprague-Dawley rats weighing 350-400 g.

INTERVENTIONS

Cecal ligation and puncture (CLP), with and without propofol (25 mg/kg/hr) infusion, after sham or CLP (24 hrs postsurgery).

MEASUREMENTS AND MAIN RESULTS

Plasma NOx, basal aortic NOx, and cGMP concentrations all increased, whereas acetylcholine-induced endothelium-dependent relaxation (EDR), contractile response, and EDNO all decreased in CLP vs. sham rats (p < .001). Acetylcholine stimulated aortic NOx and cGMP significantly in sham and CLP-propofol (p < .01) but not CLP rats. Thus, propofol ameliorated the CLP-induced increases in plasma NOx, basal aortic NOx, and cGMP. It restored the CLP-induced impairment of EDR, EDNO, and acetylcholine-stimulated aortic NOx and cGMP levels. More O2*- production (measured by lucigenin-enhanced chemiluminescence) was noted in carotid arteries from CLP vs. sham rats (p < .001). Nicotinamide adenine dinucleotide (NADH; 1 mM) stimulated O2*- production in all rings, with significantly more increase in CLP vs. sham (p < .001). Propofol attenuated the excessive increase in O2*- production of CLP rings.

CONCLUSIONS

Propofol treatment attenuated the overproduction of NO and O2*-, thus restoring the acetylcholine-responsive NO-cGMP pathway in CLP-induced sepsis. It also significantly improved the CLP-impaired EDR and EDNO in a parallel manner. These beneficial effects of propofol could be accounted for by improvement of the disturbed NO/O2*- balance in sepsis.

Divergent functions of CD4+ T lymphocytes in acute liver inflammation and injury after ischemia-reperfusion

Hepatic ischemia-reperfusion results in an acute inflammatory response culminating in the recruitment of activated neutrophils that directly injure hepatocytes. Recent evidence suggests that CD4+ lymphocytes may regulate this neutrophil-dependent injury, but the mechanisms by which this occurs remain to be elucidated. In the present study, we sought to determine the type of CD4+ lymphocytes recruited to the liver after ischemia-reperfusion and the manner in which these cells regulated neutrophil recruitment and tissue injury. Wild-type and CD4 knockout (CD4-/-) mice were subjected to hepatic ischemia-reperfusion. CD4+ lymphocytes were recruited in the liver within 1 h of reperfusion and remained for at least 4 h. These cells were comprised of conventional (alphabetaTCR-expressing), unconventional (gammadeltaTCR-expressing), and natural killer T cells. CD4-/- mice were then used to determine the functional role of CD4+ lymphocytes in hepatic ischemia-reperfusion injury. Compared with wild-type mice, CD4-/- mice had significantly greater liver injury, yet far less neutrophil accumulation. Adoptive transfer of CD4+ lymphocytes to CD4-/- mice recapitulated the wild-type response. In wild-type mice, neutralization of interleukin (IL)-17, a cytokine released by activated CD4+ lymphocytes, significantly reduced neutrophil recruitment in association with suppression of MIP-2 expression. Finally, oxidative burst activity of liver-recruited neutrophils was higher in CD4-/- mice compared with those from wild-type mice. These data suggest that CD4+ lymphocytes are rapidly recruited to the liver after ischemia-reperfusion and facilitate subsequent neutrophil recruitment via an IL-17-dependent mechanism. However, these cells also appear to attenuate neutrophil activation. Thus the data suggest that CD4+ lymphocytes have dual, opposing roles in the hepatic inflammatory response to ischemia-reperfusion.

Generation of hypochlorite-modified proteins by neutrophils during ischemia-reperfusion injury in rat liver: attenuation by ischemic preconditioning

Although it is well documented that neutrophils are critical for the delayed phase of hepatic ischemia-reperfusion injury, there is no direct evidence for a specific neutrophil-derived oxidant stress in vivo. Therefore, we used a model of 60 min of partial hepatic ischemia and 0-24 h of reperfusion to investigate neutrophil accumulation and to analyze biomarkers for a general oxidant stress [glutathione disulfide (GSSG) and malondialdehyde (MDA)] and for a neutrophil-specific oxidant stress [hypochlorite (HOCl)-modified epitopes] in rats. Plasma alanine transaminase activities and histology showed progressively increasing liver injury during reperfusion, when hepatic GSSG and soluble MDA levels were elevated. At that time, few neutrophils were present in sinusoids. However, the number of hepatocytes positively stained for HOCl-modified epitopes increased from 6 to 24 h of reperfusion, which correlated with the bulk of hepatic neutrophil accumulation and extravasation into the parenchyma. Consistent with a higher oxidant stress at later times, hepatic GSSG and protein-bound MDA levels further increased. Treatment with the NADPH oxidase inhibitor diphenyleneiodonium chloride attenuated postischemic oxidant stress (GSSG, protein-bound MDA, and hepatocytes positively stained for HOCl-modified epitopes) and liver injury at 24 h of reperfusion. Ischemic preconditioning suppressed all oxidant stress biomarkers, liver injury, and extravasation of neutrophils. In conclusion, extravasated neutrophils generate HOCl, which diffuses into hepatocytes and causes oxidative modifications of intracellular proteins during the neutrophil-mediated reperfusion injury phase. Ischemic preconditioning is an effective intervention for reduction of the overall inflammatory response and, in particular, for limitation of the cytotoxic activity of neutrophils during the later reperfusion period.

Antifungal activity of the local complement system in cerebral aspergillosis

Dissemination of aspergillosis into the central nervous system is associated with nearly 100% mortality. To study the reasons for the antifungal immune failure we analyzed the efficacy of cerebral complement to combat the fungus Aspergillus. Incubation of Aspergillus in non-inflammatory cerebrospinal fluid (CSF) revealed that complement levels were sufficient to obtain a deposition on the surface, but opsonization was much weaker than in serum. Consequently complement deposition from normal CSF on fungal surface stimulated a very low phagocytic activity of microglia, granulocytes, monocytes and macrophages compared to stimulation by conidia opsonized in serum. Similarly, opsonization of Aspergillus by CSF was not sufficient to induce an oxidative burst in infiltrating granulocytes, whereas conidia opsonized in serum induced a clear respiratory signal. Thus, granulocytes were capable of considerably reducing the viability of serum-opsonized Aspergillus conidia, but not of conidia opsonized in CSF. The limited efficacy of antifungal attack by cerebral complement can be partly compensated by enhanced synthesis, leading to elevated complement concentrations in CSF derived from a patient with cerebral aspergillosis. This inflammatory CSF was able to induce (i) a higher complement deposition on the Aspergillus surface than non-inflammatory CSF, (ii) an accumulation of complement activation products and (iii) an increase in phagocytic and killing activity of infiltrating granulocytes. However, levels and efficacy of the serum-derived complement were not reached. These data indicate that low local complement synthesis and activation may represent a central reason for the insufficient antifungal defense in the brain and the high mortality rate of cerebral aspergillosis.