Platelet-endothelial cell interactions during hepatic ischemia-reperfusion in vivo: a systematic analysis

Intravital Imaging of Thrombosis Models in Mice

Intravital microscopy is a powerful tool to study thrombosis in real time. The kinetics of thrombus formation and progression in vivo is studied after inflicting damage to the endothelium through mechanical, chemical, or laser injury. Mouse models of atherosclerosis are also used to induce thrombus formation. Vessels of different sizes and from different vascular beds such as carotid artery or vena cava, mesenteric or cremaster arterioles, can be targeted. Using fluorescent dyes, antibodies, or reporter mouse strains allows to visualize key cells and factors mediating the thrombotic processes. Here, we review the latest literature on using intravital microscopy to study thrombosis as well as thromboinflammation following transient middle cerebral artery occlusion, infection-induced immunothrombosis, and liver ischemia reperfusion.

Liver ischaemia-reperfusion injury: a new understanding of the role of innate immunity

Liver ischaemia-reperfusion injury (LIRI), a local sterile inflammatory response driven by innate immunity, is one of the primary causes of early organ dysfunction and failure after liver transplantation. Cellular damage resulting from LIRI is an important risk factor not only for graft dysfunction but also for acute and even chronic rejection and exacerbates the shortage of donor organs for life-saving liver transplantation. Hepatocytes, liver sinusoidal endothelial cells and Kupffer cells, along with extrahepatic monocyte-derived macrophages, neutrophils and platelets, are all involved in LIRI. However, the mechanisms underlying the responses of these cells in the acute phase of LIRI and how these responses are orchestrated to control and resolve inflammation and achieve homeostatic tissue repair are not well understood. Technological advances allow the tracking of cells to better appreciate the role of hepatic macrophages and platelets (such as their origin and immunomodulatory and tissue-remodelling functions) and hepatic neutrophils (such as their selective recruitment, anti-inflammatory and tissue-repairing functions, and formation of extracellular traps and reverse migration) in LIRI. In this Review, we summarize the role of macrophages, platelets and neutrophils in LIRI, highlight unanswered questions, and discuss prospects for innovative therapeutic regimens against LIRI in transplant recipients.

The Lactate-to-Platelet Ratio: A Novel Predictor for Short-Term Early Allograft Failure After Liver Transplantation

BACKGROUND

Early allograft dysfunction (EAD) is a criterion to evaluate initial graft dysfunction associated with inferior graft survival and postoperative complications after liver transplantation (LT). This study defined the lactate-to-platelet ratio (LPR) as lactate level immediately post-LT/platelet count on postoperative day 1 and evaluated its association with EAD and short-term graft failure.

MATERIALS AND METHODS

This study reviewed 434 deceased-donor LTs from individuals with confirmed brain death between January 2008 and December 2014. The area under the curve (AUC) was used to compare the predictive capacity for 3-month graft survival between EAD and the LPR. Along with LPR, the risk factors for 3-month graft failure were analyzed by multivariate analysis.

RESULTS

EAD was reported in 127 patients (31%). The LPR in patients with EAD was significantly higher than that in patients without EAD (9.8 vs 5.9, P < .001). In the multivariate analysis, both the LPR (per 1.0 increase) and EAD were independent risk factors for 3-month graft failure (hazard ratio [HR] =1.03, P = .03; and HR = 9.14, P = .001). The comparison of the AUCs between the LPR and EAD showed no significant difference (0.79 vs 0.78, P = .84), whereas the combination of EAD and LPR had a better predictive capacity than EAD alone (0.86 vs 0.78, P < .001). The LPR showed an inverse relationship for predicting 3-month graft survival.

CONCLUSIONS

The LPR is a continuous parameter that enables prediction of initial graft function and estimation of the 3-month graft failure rate with the advantages of early availability and simple calculations.

Platelets Stimulate Liver Regeneration in a Rat Model of Partial Liver Transplantation

Living donor liver transplantation (LDLT) is sometimes associated with impaired regeneration and severe ischemia/reperfusion injury (IRI) in the graft, resulting in small-for-size syndrome (SFSS). Platelets were previously reported to stimulate liver regeneration in models of hepatectomy, but the evidence in partial liver transplantation (LT) is lacking. In this study, a rat model of partial LT was used, and the impact of thrombopoietin (TPO)-induced perioperative thrombocytosis on graft regeneration, IRI, and survival was investigated. In experiment 1, a 30% partial LT was performed. Under thrombocytosis, SFSS was attenuated, as shown by decreased levels of serum aminotransferases, bilirubin, and ascites. Serum hepatocyte regeneration-related cytokines, including insulin-like growth factor-1, hepatocyte growth factor, interleukin 6 (IL6), and tumor necrosis factor α (TNF-α), were elevated. In addition, the proliferative signaling pathways, Ki-67-labeling index, proliferating cell nuclear antigen (PCNA)-labeling index, mitotic index, and liver/body weight ratio were increased under thrombocytosis. The platelet-induced regeneration was independent of TPO because increases in the Ki-67-labeling and PCNA-labeling indexes were eliminated after reducing platelet counts by antiplatelet serum in rats administered with TPO. For IRI, thrombocytosis did not aggravate oxidative stress or downstream signaling pathways, necrosis, or apoptosis in the graft. After Kupffer cell (KC) depletion, the platelet-induced attenuation of serum aminotransferases, increased serum levels of IL6 and TNF-α, and proliferation-related signaling pathways were eliminated. Moreover, platelet accumulation in the graft decreased substantially. In experiment 2, a 20% partial LT was performed, and thrombocytosis improved postoperative survival. In conclusion, our results suggested that thrombocytosis stimulated graft regeneration and prolonged survival without aggregating IRI after partial LT, and KCs vitally contributed to platelet-derived regeneration. Platelet therapies to increase perioperative platelet counts may improve the outcomes after LDLT.

Intercellular crosstalk of hepatic stellate cells in liver fibrosis: New insights into therapy

Liver fibrosis is a dynamic wound-healing process characterized by the net accumulation of extracellular matrix. There is no efficient antifibrotic therapy other than liver transplantation to date. Activated hepatic stellate cells (HSCs) are the major cellular source of matrix-producing myofibroblasts, playing a central role in the initiation and progression of liver fibrosis. Paracrine signals from resident and inflammatory cells such as hepatocytes, liver sinusoidal endothelial cells, hepatic macrophages, natural killer/natural killer T cells, biliary epithelial cells, hepatic progenitor cells, and platelets can directly or indirectly regulate HSC differentiation and activation. Intercellular crosstalk between HSCs and those "responded" cells has been a critical event involved in HSC activation and fibrogenesis. This review summarizes recent advancement regarding intercellular communication between HSCs and other "responded cells" during liver fibrosis and experimental models of intercellular crosstalk systems, and provides novel ideas for potential antifibrotic therapeutic strategy.

Treatment of hepatotoxicity induced by γ-radiation using platelet-rich plasma and/or low molecular weight chitosan in experimental rats

Background and aim: Platelet-rich plasma (PRP) is rich in growth factors and plays an important role in tissue healing and cytoprotection. Also, it has been proved that low molecular weight chitosan (LMC) possesses many outstanding health benefits. The aim of this study was to assess the possibility of using PRP and/or fungal LMC to treat hepatotoxicity induced by γ-radiation in albino rats.Materials and methods: Forty-eight adult male albino rats were randomly divided into eight groups. Group I (control), Group II (PRP alone), Group III (LMC alone), Group IV (PRP + LMC), Group V (γ-irradiated alone), Group VI (γ-irradiated + PRP), Group VII (γ-irradiated + LMC), and Group VIII (γ-irradiated + PRP + LMC). The irradiated rats were whole body exposed to γ-radiation (8 Gy) as fractionated doses (2 Gy) twice a week for 2 consecutive weeks. The treated groups received PRP (0.5 mL/kg body weight, s.c.) and/or LMC (10 mg/kg body weight, s.c.) 2 days a week 1 h after every dose of γ-radiation and continued for another week after the last dose of radiation. Serum alanine transaminase (ALT) and aspartate transaminase (AST) activities, as well as reduced glutathione (GSH) content, malondialdehyde (MDA), total antioxidant capacity (TAC), and nuclear factor erythroid 2-related factor 2 (Nrf2) levels in the liver tissue and relative expression of microRNA-21 (miR-21) in serum were measured, in addition to histopathological examination.Results: Exposure of rats to γ-radiation resulted in a significant increase in serum ALT and AST activities, hepatic MDA levels, and serum miR-21 relative expression, along with a significant decrease in hepatic GSH content, TAC, and Nrf2 levels. Treatment with PRP and/or fungal LMC after exposure to γ-radiation ameliorated these parameters and improved the histopathological changes induced by γ-radiation.Conclusions: The results demonstrated that PRP and/or LMC inhibited γ-radiation-induced hepatotoxicity and using both of them together seems more effective. They can be a candidate to be studied toward the development of a therapeutic strategy for liver diseases.

Impact of Different Clinical Perfusates During Normothermic Ex Situ Liver Perfusion on Pig Liver Transplant Outcomes in a DCD Model

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Background

Human albumin/dextran (HA-D), bovine-gelatin (BG), and packed red blood cells plus plasma have been used in European and North-American clinical trials of normothermic ex situ liver perfusion (NEsLP). We compared the effects of these perfusates in a porcine model during NEsLP and after transplantation.

Methods

Porcine livers were retrieved 30 minutes after circulatory death. After 5 hours of NEsLP, grafts were transplanted. Three groups (n = 6) were assessed (HA-D vs BG vs whole blood [WB]). One group of static cold storage (SCS) was evaluated for comparison with the perfusion groups. Hemodynamic variables, liver and endothelial injury, and function were assessed during NEsLP and posttransplantation.

Results

Hepatic artery flow was higher since the beginning of NEsLP in the HA-D group (HA-D, 238 ± 90 mL/min vs BG, 97 ± 33 mL/min vs WB, 148 ± 49 mL/min; P = 0.01). Hyaluronic acid was lower in the HA-D at the end of perfusion (HA-D, 16.28 ± 7.59 ng/μL vs BG, 76.05 ± 15.30 ng/μL vs WB, 114 ± 46 ng/μL; P < 0.001). After transplant, aspartate aminotransferase was decreased in the HA-D group when compared with the rest of the groups (HA-D, 444 ± 226 IU/L vs BG, 1033 ± 694 IU/L vs WB, 616 ± 444 IU/L vs SCS, 2235 ± 1878 IU/L). At 5 hours after transplant, lactate was lower in the HA-D group (HA-D, 3.88 ± 1.49 mmol/L vs BG, 7.79 ± 2.68 mmol/L vs WB, 8.16 ± 3.86 mmol/L vs SCS, 9.06 ± 3.54 mmol/L; P = 0.04). International Normalized Ratio was improved in HA-D group compared to the rest of the groups (HA-D, 1.23 ± 0.30 vs BG, 1.63 ± 0.20 vs WB, 1.50 ± 0.31 vs SCS, 1.97 ± 1.55; P = 0.03) after transplantation. In contrast, BG displayed lower aspartate aminotransferase levels during NEsLP (HA-D, 183 ± 53 IU/L vs BG, 142 ± 52 IU/L vs WB, 285 ± 74 IU/L; P = 0.01) and less cleaved-caspase-3 staining (HA-D, 2.05 ± 0.73% vs BG, 0.95 ± 1.14% vs WB, 1.74 ± 0.54% vs SCS, 7.95 ± 2.38%) compared with the other groups. On the other hand, the bile from the WB showed higher pH (HA-D, 7.54 ± 0.11 vs BG, 7.34 ± 0.37 vs WB, 7.59 ± 0.18) and lower glucose levels (HA-D, 0.38 ± 0.75 mmol/L vs BG, 1.42 ± 1.75 mmol/L vs WB, 0 ± 0 mmol/L) by the end of perfusion.

Conclusions

Overall HA-D displayed more physiologic conditions during NEsLP that were reflected in less graft injury and improved liver function and survival after transplantation. Optimization of the perfusates based on the beneficial effects found with these different solutions would potentially improve further the outcomes through the use of NEsLP in marginal grafts.

Mechanism of free radical generation in platelets and primary hepatocytes: A novel electron spin resonance study

Oxygen free radicals have been implicated in the pathogenesis of toxic liver injury and are thought to be involved in cardiac dysfunction in the cirrhotic heart. Therefore, direct evidence for the electron spin resonance (ESR) detection of how D‑galactosamine (GalN), an established experimental hepatotoxic substance, induced free radicals formation in platelets and primary hepatocytes is presented in the present study. ESR results demonstrated that GalN induced hydroxyl radicals (OH•) in a resting human platelet suspension; however, radicals were not produced in a cell free Fenton reaction system. The GalN‑induced OH• formation was significantly inhibited by the cyclooxygenase (COX) inhibitor indomethasin, though it was not affected by the lipoxygenase (LOX) or cytochrome P450 inhibitors, AA861 and 1‑aminobenzotriazole (ABT), in platelets. In addition, the present study demonstrated that baicalein induced semiquinone free radicals in platelets, which were significantly reduced by the COX inhibitor without affecting the formed OH•. In the mouse primary hepatocytes, the formation of arachidonic acid (AA) induced carbon‑centered radicals that were concentration dependently enhanced by GalN. These radicals were inhibited by AA861, though not affected by indomethasin or ABT. In addition, GalN did not induce platelet aggregation prior to or following collagen pretreatment in human platelets. The results of the present study indicated that GalN and baicalein may induce OH• by COX and LOX in human platelets. GalN also potentiated AA induced carbon‑centered radicals in hepatocytes via cytochrome P450. The present study presented the role of free radicals in the pathophysiological association between platelets and hepatocytes.

Review article: the role of the microcirculation in liver cirrhosis

BACKGROUND

Intrahepatic microvascular derangements and microcirculatory dysfunction are key in the development of liver cirrhosis and its associated complications. While much has been documented relating to cirrhosis and the dysfunction of the microcirculation in the liver parenchyma, far less is known about the state of the extrahepatic microcirculation and the role this may have in the pathogenesis of multiple organ failure in end stage liver cirrhosis.

AIM

To provide an update on the role of the microcirculation in the pathophysiology of cirrhosis and its associated complications and briefly discuss some of the imaging techniques which may be used to directly investigate the microcirculation.

METHODS

A Medline literature search was conducted using the following search terms: 'cirrhosis', 'microcirculation', 'circulation', 'systemic', 'inflammation', 'peripheral', 'hepatorenal' and 'hepatopulmonary'.

RESULTS

Significant heterogeneous microvascular alterations exist in patients with cirrhosis. Data suggest that the systemic inflammation, associated with advanced cirrhosis, induces microcirculatory dysregulation and contributes to haemodynamic derangement. The resultant vasoconstriction and hypoperfusion in the systemic extrahepatic microvasculature, is likely to be instrumental in the pathophysiology of organ failure in decompensated cirrhosis, however the mechanistic action of vasoactive agents used to correct the circulatory disturbance of advanced cirrhosis is poorly understood.

CONCLUSIONS

Further research into the role of the microcirculation in patients with liver cirrhosis, will improve physicians understanding of the pathophysiology of cirrhosis, and may provide a platform for real time evaluation of an individual's microcirculatory response to vasoactive mediators, thus guiding their therapy.

The impact of sterile inflammation in acute liver injury

BACKGROUND

The liver has a number of functions in innate immunity. These functions predispose the liver to innate immune-mediated liver injury when inflammation goes unchecked. Significant progress has been made in the last 25 years on sterile inflammatory liver injury in a number of models; however, a great deal of controversy and many questions about the nature of sterile inflammation still exist.

AIM

The goal of this article is to review sterile inflammatory liver injury using both a basic approach to what constitutes the inflammatory injury, and through examination of current models of liver injury and inflammation. This information will be tied to human patient conditions when appropriate.

RELEVANCE FOR PATIENTS

Inflammation is one of the most critical factors for managing in-patient liver disease in a number of scenarios. More information is needed for both scientists and clinicians to develop rational treatments.

A Novel and Sensitive Approach for the Evaluation of Liver Ischemia-Reperfusion Injury After Liver Transplantation

OBJECTIVES

The purpose of our study was to evaluate the potential of x-ray propagation-based phase-contrast imaging (PCI) computed tomography (CT) for the detection and characterization of early changes after ischemia-reperfusion (IR) in a standardized rat liver transplantation (LTx) model.

MATERIALS AND METHODS

Syngeneic orthotopic liver transplantation was performed in male Lewis rats. Ischemia-reperfusion injury (IRI)-induced changes of liver parenchyma were investigated in a time-dependent manner (2, 16, 24, and 32 hours). X-ray phase-contrast images of formalin-fixated liver specimens were acquired in CT mode by using a voxel size of 8 × 8 × 8 μm. Necrapoptotic cell death was visualized with the TdT-mediated dUTP-biotin nick end labeling technique, and alterations of liver graft microhemodynamics, that is, acinar and sinusoidal perfusion failure, were evaluated by in vivo fluorescence microscopy.

RESULTS

Acquired and reconstructed PCI-CT images showed an increase in necrotic liver parenchyma dependent on cold storage time, measuring 5.7% ± 1.6% after 2 hours (comparable to 2.6% ± 0.4% for sham livers), 11.5% ± 2.1% (16 hours; P < 0.05 vs control), 23.0% ± 0.5% (24 hours; P < 0.001 vs control), and 31.3% ± 2.2% (32 hours; P < 0.001 vs control). There were a significant lower number of perfused acini in dependence on increasing cold storage time. The acinar perfusion index reached 0.970 ± 0.006 after 2 hours of cold ischemia (comparable to 0.960 ± 0.009 for sham livers) and declined continuously after 16, 24, and 32 hours cold ischemia (0.58 ± 0.03, 0.49 ± 0.02, 0.41 ± 0.03, each P < 0.0001 vs controls). Comparable results were found for sinusoidal perfusion, reaching 1.8% ± 0.4% of nonperfused sinusoids for 2 hours of cold ischemia and 8.2% ± 0.8% after 16 hours, 18.8% ± 1.4% after 24 hours, and 39.0% ± 2.4% after 32 hours (each P < 0.0001 vs controls). Prolonged cold ischemia was associated with an increasing number of TdT-mediated dUTP-biotin nick end labeling-positive cells (hepatocytes and sinusoidal lining cells), reaching 0.4 ± 0.1 (sham), 0.7 ± 0.4 (2 hours), 6.4 ± 1.1 (16 hours), 2.1 ± 0.3 (24 hours), and 14.7 ± 3.5 (32 hours; P = 0.002) for hepatocytes.

CONCLUSIONS

X-ray PCI of histological liver specimens can detect IR-induced tissue necrosis and can provide detailed complementary 3-dimensional information to standard histopathologic findings.

Platelet aggregation but not activation and degranulation during the acute post-ischemic reperfusion phase in livers with no underlying disease

BACKGROUND

Platelets and P-selectin (CD62P) play an unequivocal role in the pathology of hepatic ischemia/reperfusion (I/R) injury. Inhibition or knock-out of P-selectin or immunodepletion of platelets results in amelioration of post-ischemic inflammation, reduced hepatocellular damage, and improved survival. However, P-selectin expression on platelets and endothelial cells, which concurs with platelet activation, has never been clearly demonstrated in I/R-subjected livers.

AIMS

To determine whether platelets become activated and degranulate in the acute phase of liver I/R and whether the platelets interact with neutrophils.

METHODS

Hepatic I/R was induced in male C57BL/6J mice (N = 12) using 37.5-min ischemia time. Platelets, endothelial cells, and neutrophils were fluorescently labeled by systemic administration of non-blocking antibodies. Cell kinetics were monitored by intravital spinning disk confocal microscopy during 90 min of reperfusion. Image analysis and quantification was performed with dedicated software.

RESULTS

Platelets adhered to sinusoids more extensively in post-ischemic livers compared to livers not subjected to I/R and formed aggregates, which occurred directly after ischemia. Platelets and endothelial cells did not express P-selectin in post-ischemic livers. There was no interaction between platelets and neutrophils.

CONCLUSIONS

Platelets aggregate but do not become activated and do not degranulate in post-ischemic livers. There is no platelet-neutrophil interplay during the early reperfusion phase in a moderate model of hepatic I/R injury. The mechanisms underlying the biological effects of platelets and P-selectin in this setting warrant further investigation.

RELEVANCE FOR PATIENTS

I/R in surgical liver patients may compromise outcome due to post-ischemic oxidative stress and sterile inflammation. Both processes are mediated in part by platelets. Understanding platelet function during I/R is key to developing effective interventions for I/R injury and improving clinical outcomes.

The role of platelets in the recruitment of leukocytes during vascular disease

Besides their role in the formation of thrombus during haemostasis, it is becoming clear that platelets contribute to a number of other processes within the vasculature. Indeed, the integrated function of the thrombotic and inflammatory systems, which results in platelet-mediated recruitment of leukocytes, is now considered to be of great importance in the propagation, progression and pathogenesis of atherosclerotic disease of the arteries. There are three scenarios by which platelets can interact with leukocytes: (1) during haemostasis, when platelets adhere to and are activated on sub-endothelial matrix proteins exposed by vascular damage and then recruit leukocytes to a growing thrombus. (2) Platelets adhere to and are activated on stimulated endothelial cells and then bridge blood borne leukocytes to the vessel wall and. (3) Adhesion between platelets and leukocytes occurs in the blood leading to formation of heterotypic aggregates prior to contact with endothelial cells. In the following review we will not discuss leukocyte recruitment during haemostasis, as this represents a physiological response to tissue trauma that can progress, at least in its early stages, in the absence of inflammation. Rather we will deal with scenarios 2 and 3, as these pathways of platelet–leukocyte interactions are important during inflammation and in chronic inflammatory diseases such as atherosclerosis. Indeed, these interactions mean that leukocytes possess means of adhesion to the vessel wall under conditions that may not normally be permissive of leukocyte–endothelial cell adhesion, meaning that the disease process may be able to bypass the regulatory pathways which would ordinarily moderate the inflammatory response.

The mechanisms and physiological relevance of glycocalyx degradation in hepatic ischemia/reperfusion injury

SIGNIFICANCE

Hepatic ischemia/reperfusion (I/R) injury is an inevitable side effect of major liver surgery that can culminate in liver failure. The bulk of I/R-induced liver injury results from an overproduction of reactive oxygen and nitrogen species (ROS/RNS), which inflict both parenchymal and microcirculatory damage. A structure that is particularly prone to oxidative attack and modification is the glycocalyx (GCX), a meshwork of proteoglycans and glycosaminoglycans (GAGs) that covers the lumenal endothelial surface and safeguards microvascular homeostasis. ROS/RNS-mediated degradation of the GCX may exacerbate I/R injury by, for example, inducing vasoconstriction, facilitating leukocyte adherence, and directly activating innate immune cells.

RECENT ADVANCES

Preliminary experiments revealed that hepatic sinusoids contain a functional GCX that is damaged during murine hepatic I/R and major liver surgery in patients. There are three ROS that mediate GCX degradation: hydroxyl radicals, carbonate radical anions, and hypochlorous acid (HOCl). HOCl converts GAGs in the GCX to GAG chloramides that become site-specific targets for oxidizing and reducing species and are more efficiently fragmented than the parent molecules. In addition to ROS/RNS, the GAG-degrading enzyme heparanase acts at the endothelial surface to shed the GCX.

CRITICAL ISSUES

The GCX seems to be degraded during major liver surgery, but the underlying cause remains ill-defined.

FUTURE DIRECTIONS

The relative contribution of the different ROS and RNS intermediates to GCX degradation in vivo, the immunogenic potential of the shed GCX fragments, and the role of heparanase in liver I/R injury all warrant further investigation.

Targeting platelet migration in the postischemic liver by blocking protease-activated receptor 4

BACKGROUND

Platelets play a critical role during hepatic ischemia/reperfusion (I/R). Antiplatelet strategies during liver transplantation are, however, limited because of bleeding complications. Thrombin is activated during reperfusion and regulates platelet and endothelial cell function via protease-activated receptor 4 (PAR-4). Interventions at the level of PAR-4, the main platelet receptor for thrombin, are assumed to attenuate the proinflammatory effects of thrombin without affecting blood coagulation. The aim of our study was to analyze the impact of PAR-4 blockade on platelet recruitment and microvascular injury during hepatic I/R.

METHODS

C57BL/6 mice undergoing hepatic I/R (90 min/60 min and 240 min) were treated either with a selective PAR-4 antagonist TcY-NH2 or vehicle. Sham-operated animals served as controls. Recruitment of freshly isolated and fluorescence-labeled platelets and CD4 T cells was analyzed using intravital video fluorescence microscopy. Parameters of tissue injury, regeneration, and blood coagulation were assessed in tissue/blood samples.

RESULTS

Results show that treatment with TcY-NH2 attenuated I/R-induced platelet and CD4 T-cell recruitment, improved sinusoidal perfusion failure, and reduced apoptotic and necrotic injury. The protective effect of PAR-4 blockade did not suppress hemostasis or liver regeneration.

CONCLUSION

Our in vivo data suggest PAR-4 as a potential target for future therapeutic strategies against platelet-mediated liver injury on transplantation.

Signal transduction of platelet-induced liver regeneration and decrease of liver fibrosis

Platelets contain three types of granules: alpha granules, dense granules, and lysosomal granules. Each granule contains various growth factors, cytokines, and other physiological substances. Platelets trigger many kinds of biological responses, such as hemostasis, wound healing, and tissue regeneration. This review presents experimental evidence of platelets in accelerating liver regeneration and improving liver fibrosis. The regenerative effect of liver by platelets consists of three mechanisms; i.e., the direct effect on hepatocytes, the cooperative effect with liver sinusoidal endothelial cells, and the collaborative effect with Kupffer cells. Many signal transduction pathways are involved in hepatocyte proliferation. One is activation of Akt and extracellular signal-regulated kinase (ERK)1/2, which are derived from direct stimulation from growth factors in platelets. The other is signal transducer and activator of transcription-3 (STAT3) activation by interleukin (IL)-6 derived from liver sinusoidal endothelial cells and Kupffer cells, which are stimulated by contact with platelets during liver regeneration. Platelets also improve liver fibrosis in rodent models by inactivating hepatic stellate cells to decrease collagen production. The level of intracellular cyclic adenosine monophosphate (cyclic AMP) is increased by adenosine through its receptors on hepatic stellate cells, resulting in inactivation of these cells. Adenosine is produced by the degradation of adenine nucleotides such as adenosine diphosphate (ADP) and adenosine tri-phosphate (ATP), which are stored in abundance within the dense granules of platelets.

Effect of Platelet-Rich Plasma on CCl4-Induced Chronic Liver Injury in Male Rats

Platelet-rich plasma (PRP) has been of great concern to the scientists and doctors who are involved in wound healing and regenerative medicine which focuses on repairing and replacing damaged cells and tissues. Growth factors of platelet-rich plasma are cost-effective, available, and is more stable than recombinant human growth factors. Given these valuable properties, we decided to assess the effect of PRP on CCl4-induced hepatotoxicity on rats. The rats received CCl4 (1 mL/kg, i.p. 1 : 1 in olive oil) twice per week for 8 weeks. Five weeks after CCl4 injection, the rats also received PRP (0.5 mL/kg, s.c.) two days a week for three weeks. Twenty-four hours after last CCl4 injection, the animals bled and their livers dissected for biochemical and histopathological studies. Blood analysis was performed to evaluate enzyme activity. The results showed that PRP itself was not toxic for liver and could protect the liver from CCl4-induced histological damages and attenuated oxidative stress by increase in glutathione content and decrease in lipid peroxidative marker of liver tissue. The results of the present study lend support to our beliefs in hepatoprotective effects of PRP.

Protective effect of heme oxygenase-1 on hepatic ischemia-reperfusion injury through inhibition of platelet adhesion to the sinusoids

BACKGROUND AND AIM

Heme oxygenase-1 (HO-1) acts as a protector against hepatic inflammatory injury. HO-1 catalyzes the conversion of heme protein to biliverdin, free iron, and carbon monoxide. Pro-inflammatory responses play critical roles in hepatic ischemia-reperfusion (I/R) injury, and carbon monoxide effectively downregulates I/R injury. The aim of this study was to evaluate the mechanism by which HO-1 reduces warm I/R injury.

METHODS

Sprague-Dawley rats were divided into two groups: the 20-min ischemia group (control group; n = 6) and the 20-min ischemia with cobalt protoporphyrin (CoPP group; n = 6). CoPP is an inducer of HO-1 in the sinusoids. Kupffer cells were labeled using the liposome entrapment method, and platelets were labeled with rhodamine-6G. The adherent platelets were observed for up to 120 min after reperfusion by intravital microscopy.

RESULTS

In the control group, the number of adherent platelets significantly increased than in the CoPP group. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling-positive cells were observed after 120 min of reperfusion in the control group. They were not observed in the CoPP group. In the CoPP group, serum alanine transaminase and interleukin-6 levels reduced after reperfusion. Moreover, the flow velocity of platelets in the hepatic sinusoid markedly increased.

CONCLUSIONS

This study suggests that HO-1 inhibits platelet adhesion to sinusoids. Such inhibition leads to the prevention of hepatic I/R injury.

Novel therapy for liver regeneration by increasing the number of platelets

Platelets are the smallest blood constitutes which contain three types of granules; alpha granules, dense granules, and lysosomal granules. Each granule contains various biophysiological substances such as growth factors, cytokines, etc. Platelets have been conventionally viewed as a trigger of inflammatory responses and injury in the liver. Some studies revealed that platelets have strong effects on promoting liver regeneration. This review presents experimental evidence of platelets in accelerating liver regeneration and describes three different mechanisms involved; (1) the direct effect on hepatocytes, where platelets translocate to the space of Disse and release growth factors through direct contact with hepatocytes, (2) the cooperative effect with liver sinusoidal endothelial cells, where the dense concentration of sphingosine-1-phosphate in platelets induces excretion of interleukin-6 from liver sinusoidal endothelial cells, and (3) the collaborative effect with Kupffer cells, where the functions of Kupffer cells are enhanced by platelets.

The sterile immune response during hepatic ischemia/reperfusion

Hepatic ischemia and reperfusion elicits an immune response that lacks a microbial constituent yet poses a potentially lethal threat to the host. In this sterile setting, the immune system is alarmed by endogenous danger signals that are release by stressed and dying liver cells. The detection of these immunogenic messengers by sentinel leukocyte populations constitutes the proximal trigger for a self-perpetuating cycle of inflammation, in which consecutive waves of cytokines and chemokines orchestrate the influx of various leukocyte subsets that ultimately confer tissue destruction. This review focuses on the temporal organization of sterile hepatic inflammation, using surgery-induced trauma as a template disease state.

Mechanistic overview of reactive species-induced degradation of the endothelial glycocalyx during hepatic ischemia/reperfusion injury

Endothelial cells are covered by a delicate meshwork of glycoproteins known as the glycocalyx. Under normophysiological conditions the glycocalyx plays an active role in maintaining vascular homeostasis by deterring primary and secondary hemostasis and leukocyte adhesion and by regulating vascular permeability and tone. During (micro)vascular oxidative and nitrosative stress, which prevails in numerous metabolic (diabetes), vascular (atherosclerosis, hypertension), and surgical (ischemia/reperfusion injury, trauma) disease states, the glycocalyx is oxidatively and nitrosatively modified and degraded, which culminates in an exacerbation of the underlying pathology. Consequently, glycocalyx degradation due to oxidative/nitrosative stress has far-reaching clinical implications. In this review the molecular mechanisms of reactive oxygen and nitrogen species-induced destruction of the endothelial glycocalyx are addressed in the context of hepatic ischemia/reperfusion injury as a model disease state. Specifically, the review focuses on (i) the mechanisms of glycocalyx degradation during hepatic ischemia/reperfusion, (ii) the molecular and cellular players involved in the degradation process, and (iii) its implications for hepatic pathophysiology. These topics are projected against a background of liver anatomy, glycocalyx function and structure, and the biology/biochemistry and the sources/targets of reactive oxygen and nitrogen species. The majority of the glycocalyx-related mechanisms elucidated for hepatic ischemia/reperfusion are extrapolatable to the other aforementioned disease states.

Interaction between Kupffer cells and platelets in the early period of hepatic ischemia-reperfusion injury--an in vivo study

BACKGROUND

Hepatic ischemia-reperfusion (I/R) leads to activation of Kupffer cells (KCs). The activated KCs cause platelet and leukocyte adhesion to the sinusoidal endothelium. Previously, we reported that platelet-endothelium interactions occur earlier than leukocyte responses. The aim of this study was to evaluate the interaction between platelets and KCs in the hepatic microcirculation after I/R.

MATERIALS AND METHODS

Sprague-Dawley rats were divided into three groups: the no-ischemia group (control group; n = 6); the 20-min ischemia group (I/R group; n = 6); and the 20-min ischemia + anti-rat platelet serum group (APS group; n = 6). KCs were labeled using the liposome entrapment method. The number of adherent platelets was observed for up to 120 min after reperfusion by intravital microscopy. To investigate the effects of platelets on I/R injury, rats were injected intravenously with rabbit APS for platelet depletion.

RESULTS

In the I/R group, the number of adherent platelets increased significantly after I/R. More than 50% of the adherent platelets adhered to KCs. Electron microscopy indicated that the platelets attached to the KCs after hepatic ischemia. The histologic findings indicated liver damage and apoptosis of hepatocytes in zone 1. In the I/R group, but not in the control and APS groups, serum ALT increased immediately after reperfusion.

CONCLUSIONS

We succeeded in visualizing the dynamics of both KCs and platelets in the hepatic sinusoids. Liver ischemia induced the adhesion of platelets to KCs in the early period, which could play a key role in reperfusion injury of the liver.

Activation of CD40 with platelet derived CD154 promotes reactive oxygen species dependent death of human hepatocytes during hypoxia and reoxygenation

BACKGROUND

Hypoxia and hypoxia-reoxygenation (H-R) are pathogenic factors in many liver diseases that lead to hepatocyte death as a result of reactive oxygen species (ROS) accumulation. The tumor necrosis factor super-family member CD154 can also induce hepatocyte apoptosis via activation of its receptor CD40 and induction of autocrine/paracrine Fas Ligand/CD178 but the relationship between CD40 activation, ROS generation and apoptosis is poorly understood. We hypothesised that CD40 activation and ROS accumulation act synergistically to drive human hepatocyte apoptosis.

METHODS

Human hepatocytes were isolated from liver tissue and exposed to an in vitro model of hypoxia and H-R in the presence or absence of CD154 and/or various inhibitors. Hepatocyte ROS production, apoptosis and necrosis were determined by labelling cells with 2',7'-dichlorofluorescin, Annexin-V and 7-AAD respectively in a three-colour reporter flow cytometry assay.

RESULTS

Exposure of human hepatocytes to recombinant CD154 or platelet-derived soluble CD154 augments ROS accumulation during H-R resulting in NADPH oxidase-dependent apoptosis and necrosis. The inhibition of c-Jun N-terminal Kinase and p38 attenuated CD154-mediated apoptosis but not necrosis.

CONCLUSIONS

CD154-mediated apoptosis of hepatocytes involves ROS generation that is amplified during hypoxia-reoxygenation. This finding provides a molecular mechanism to explain the role of platelets in hepatocyte death during ischemia-reperfusion injury.

Glycine and taurine equally prevent fatty livers from Kupffer cell-dependent injury: an in vivo microscopy study

BACKGROUND

IRI still is a major problem in liver surgery due to warm ischemia and organ manipulation. Steatosis is not only induced by diabetes, hyperalimentation, alcohol and toxins, but also chemotherapy given before resection. Since steatotic livers are prone to Kupffer cell-dependent IRI, protection of steatotic livers is of special interest. This study was designed to compare the effect of taurine and glycine on IRI in steatotic livers.

MATERIALS AND METHODS

Steatosis was induced with ethanol (7 g/kg b.w.; p.o.) in female SD rats. Ten minutes after inactivation of Kupffer cells with taurine or glycine (300 mM; i.v.), left liver lobes underwent 60 minutes of warm ischemia. Controls received the same volume of valine (300 mM; i.v.) or normal saline. After reperfusion, white blood cell-endothelial interactions and latex-bead phagocytosis by Kupffer cells were investigated. Liver enzymes were measured to estimate injury. For statistical analysis, ANOVA and Student's t-test were used.

RESULTS

Glycine and taurine significantly decreased leukocyte- and platelet-endothelium interactions and latex-bead phagocytosis (p < 0.05). Liver enzymes were significantly lower after glycine and taurine (p < 0.05).

CONCLUSIONS

This study shows that preconditioning with taurine or glycine is equally effective in preventing injury to fatty livers most likely via Kupffer cell-dependent mechanisms.

Platelet adhesion in the sinusoid caused hepatic injury by neutrophils after hepatic ischemia reperfusion

Liver ischemia-reperfusion (I/R) injury is one of the most serious complications of hepatic surgery. In I/R, activated Kupffer cells cause platelet adhesion to sinusoidal endothelium as well as neutrophils and cause liver dysfunction. The aim of this study was to evaluate platelet dynamics in the hepatic microcirculation after I/R by intravital microscopy (IVM) and to clarify the relationship between platelet adhesion and neutrophil activation. Male Sprague-Dawley (SD) rats were divided into two groups: the control (administration of saline) group and the sivelestat group in which neutrophil activation was suppressed by sivelestat before I/R. The number of adherent platelets in sinusoid was observed up to 120 minutes after I/R by IVM. Samples of liver tissue and blood were taken for examination of histological findings, liver enzymes and inflammatory cytokines. The number of adherent platelets was significantly increased after I/R in both groups. Compared with the control group, the number of adherent platelets significantly decreased after hepatic I/R in the sivelestat group. Moreover, sivelestat improved changes of histological findings and elevation of liver enzymes. However, there was no significant difference in inflammatory cytokines of TNF-alpha, IL-1beta or IL-6. Platelet adhesion in the sinusoid is associated with liver dysfunction after I/R as well as neutrophils. Activated neutrophils induce platelet adhesion in the sinusoid of the liver.

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.

2-Arachidonoylglycerol Increases in Ischemia–Reperfusion Injury of the Rat Liver

Several studies have implicated endocannabinoids in various forms of shock. However, the role of endocannabinoids in hepatic ischemia-reperfusion injury remains unclear. The purpose of this study was to evaluate the changes of two endocannabinoidsin hepatic ischemia-reperfusion injury: anandamide (ANA) and 2-arachidonoylglycerol (2-AG). Male Sprague-Dawley rats were divided into 2 groups: the short (15 min) ischemic group and the long (60 min)ischemic group in the segmental (70%) hepatic tissue. Blood levels of aspartate transaminase (AST), alanine transaminase (ALT), lactate dehydrogenase (LDH), ANA, and 2-AG were examined. Serum lev-els of AST, ALT, and LDH were significantly higher in the long-ischemia group than in the short-ischemia group. Plasma levels of 2-AG showed similar augmentation prior to and after reperfusion in both the short- and long-ischemia groups, although plasma 2-AG lev-els tended to be higher in the long-ischemia group than in the short-ischemia group. Plasma levels of ANA were augmented in the early phase of reperfusion in the short-ischemia group and did not differ significantly from the normal level with time after reperfusion in the long-ischemia group. These results suggest that the endocannabinoid 2-AG increases in hepatic ischemia-reperfusion injury of rats, rather than ANA.

P-selectin inhibition reduces severity of acute experimental pancreatitis

BACKGROUND

Acute pancreatitis (AP) is characterized by disturbed pancreatic microcirculation with tissue necrosis. Platelet and leukocyte activation contributes to microcirculatory disorders and inflammatory tissue infiltration. P-selectin mediates the adhesion of both activated platelets and leukocytes to the vessel wall. The aim of this study was to investigate the effect of P-selectin inhibition by monoclonal antibodies (AB) on experimental AP.

METHODS

AP was induced in rats by glycodeoxycholic acid (GDOC) intraductally and by cerulein infusion. Animals were divided into 4 groups: (1) severe AP (GDOC); (2) severe AP + platelet inhibition (GDOC + selectin AB); (3) control (Ringer); (4) control + platelet inhibition (Ringer + selectin AB). 24 h after AP induction, histology and serum (amylase, thromboxane A2) were evaluated (6 animals per group). In additional 12 animals of each group, platelet and leukocyte activation as well as erythrocyte flow patterns were evaluated by intravital microscopy 12 h after AP induction.

RESULTS

AP induction caused significant tissue inflammation and necrosis with increased amylase and thromboxane levels. Prophylactic inhibition of P-selectin reduced tissue inflammation and necrosis significantly. Severe AP led to significantly more adherent platelets and leukocytes in capillaries and venules. In contrast, antibody-treated animals showed significantly reduced platelet-endothelium interaction compared with untreated AP animals. Antibody application in control animals without AP did not induce any changes compared with healthy control animals.

CONCLUSION

Inhibition of P-selectin reduces tissue damage in experimental AP. This is associated with a reduction in platelet- and leukocyte-endothelium interaction and an improvement in pancreatic microcirculation.

Decreased Mrp2-dependent bile flow in the post-warm ischemic rat liver

BACKGROUND

The link between microcirculatory disturbance and hepatocellular dysfunction remains unknown. The present study was designed to examine the key event of warm ischemia reperfusion (WIR) injury with subsequent cholestasis.

METHODS

A left lobar 70% ischemia and reperfusion rat model was used in this study. The portal vein and hepatic artery to the left lateral lobe of the liver were subjected to 20 min of warm ischemia followed by 60 min of reperfusion to collect bile and to measure its constituents.

RESULTS

The hepatocellular injury was increased significantly in livers exposed to WIR, as judged by serum alanine aminotransferase. This event coincided with decreased bile production and biliary concentration of glutathione (GSH), suggesting impaired bile salts-independent bile flow, while biliary phospholipids and bile salts were not decreased. Additionally, hepatic adenosine triphosphate and GSH were not decreased after WIR. Since the biliary GSH, which is a major driving force for bile salts-independent bile flow, is excreted from hepatocytes into the bile via multidrug resistance protein 2 (Mrp2), we examined whether intracellular localization of Mrp2 occurred. Immunohistochemical analyses revealed hepatocellular Mrp2 was retrieved from bile canalicular membrane into the pericanalicular cytoplasm in the post-warm ischemic livers. Microcirculatory disturbance in livers exposed to 20 min of warm ischemia improved to levels comparable to controls.

CONCLUSION

Mrp2 internalization, observed in this study, may play an important determinant of cholestasis in the post-warm ischemic livers.

Platelet dynamics in the early phase of postischemic liver in vivo

BACKGROUND

In liver surgery, ischemia/reperfusion injury occasionally leads to liver failure by activating Kupffer cells (KCs) and leukocytes. However, few reports have demonstrated a relationship between KCs and platelets in vivo. This study investigated the relationship between these cells using intravital microscopy.

MATERIALS AND METHODS

Male Wistar rats were divided into two groups: (1) KC+ group, receiving 1 mL saline; and (2) KC- group, intravenously injected with liposome-encapsulated dichloromethylene disphosphonate for elimination of KCs. At 48 h after administration, 20 min of total normothermic hepatic ischemia was induced. Rhodamine-6G-labeled platelets and sinusoidal alterations were monitored using intravital microscopy up to 120 min after reperfusion. P-selectin, accumulated leukocytes and morphological damage, and alanine aminotransferase were evaluated.

RESULTS

In the KC+ group, numbers of adherent platelets increased significantly within 30 min after reperfusion. Endothelial cells of sinusoids in which KCs were mainly located were destroyed and the sinusoids were significantly constricted after reperfusion. Conversely, in the KC- group, adherent platelets in sinusoids were suppressed, and sinusoidal perfusion, endothelial cell damage and serum alanine aminotransferase levels were significantly improved. P-selectin on sinusoidal endothelial cells was not observed up to 120 min after reperfusion in either group.

CONCLUSIONS

Adherent platelets appear to reflect activation of KCs and lead to leukocyte accumulation, resulting in sinusoidal perfusion disturbance and liver failure. Evaluation of adherent platelets in the microcirculation offers an important marker of hepatic injury.

In situ micropatterning technique by cell crushing for co-cultures inside microfluidic biochips

To perform dynamic cell co-culture on micropatterned areas, we have developed a new type of "on chip and in situ" micropatterning technique. The microchip is composed of a 200 microm thick PDMS (polydimethylsiloxane) chamber at the top of which are located 100 mum thick microstamps. The PDMS chamber is bonded to a glass slide. After sterilization and cell adhesion processes, a controlled force is applied on the top of the PDMS chamber. Mechanically, the microstamps come into contact of the cells. Due to the applied force, the cells located under the microstamps are crushed. Then, a microfluidic perfusion is applied to rinse the microchip and remove the detached cells. To demonstrate the potential of this technique, it was applied successfully to mouse fibroblasts (Swiss 3T3) and liver hepatocarcinoma (HepG2/C3a) cell lines. Micropatterned areas were arrays of octagons of 150, 300 and 500 microm mean diameter. The force was applied during 30 to 60s depending on the cell types. After cell crushing, when perfusion was applied, the cells could successfully grow over the patterned areas. Cultures were successfully performed during 72 h of perfusion. In addition, monolayers of HepG2/C3a were micropatterned and then co cultured with mouse fibroblasts. Numerical simulations have demonstrated that the presence of the microstamps at the top of the PDMS chamber create non uniform flow and shear stress applied on the cells. Once fabricated, the main advantage of this technique is the possibility to use the same microchip several times for cell micropatterning and microfluidic co-cultures. This protocol avoids complex and numerous microfabrication steps that are usually required for micropatterning and microfluidic cell culture in the same time.

Platelet function in acute experimental pancreatitis

Acute pancreatitis (AP) is characterized by disturbances of pancreatic microcirculation. It remains unclear whether platelets contribute to these perfusion disturbances. The aim of our study was to investigate platelet activation and function in experimental AP. Acute pancreatitis was induced in rats: (1) control (n=18; Ringer's solution), (2) mild AP (n=18; cerulein), and (3) severe AP (n=18; glycodeoxycholic acid (GDOC)+cerulein). After 12 h, intravital microscopy was performed. Rhodamine-stained platelets were used to investigate velocity and endothelial adhesion in capillaries and venules. In addition, erythrocyte velocity and leukocyte adhesion were evaluated. Serum amylase, thromboxane A2, and histology were evaluated after 24 h in additional animals of each group. Results showed that 24 h after cerulein application, histology exhibited a mild AP, whereas GDOC induced severe necrotizing AP. Intravital microscopy showed significantly more platelet-endothelium interaction, reduced erythrocyte velocity, and increased leukocyte adherence in animals with AP compared to control animals. Thromboxane levels were significantly elevated in all AP animals and correlated with the extent of platelet activation and severity of AP. In conclusion, platelet activation plays an important role in acute, especially necrotizing, pancreatitis. Mainly temporary platelet-endothelium interaction is observed during mild AP, whereas severe AP is characterized by firm adhesion with consecutive coagulatory activation and perfusion failure.

RETRACTED: Stimulation of sensory neurons by capsaicin increases tissue levels of IGF-I, thereby reducing reperfusion-induced apoptosis in mice

Calcitonin gene-related peptide (CGRP) increases insulin-like growth factor-I (IGF-I) production in fetal rat osteoblasts in vitro, suggesting that stimulation of sensory neurons might increase IGF-I production, thereby preventing apoptosis. We examined whether stimulation of sensory neurons by capsaicin might reduce reperfusion-induced hepatic apoptosis by increasing IGF-I production. Administration of capsaicin increased tissue levels of IGF-I and IGF-I mRNA in various organs in wild-type (WT) mice, but not in CGRP-knock-out (CGRP-/-) mice. Administration of CGRP increased tissue levels of IGF-I and IGF-I mRNA in both WT and CGRP-/- mice. Increases in hepatic tissue levels of TNF, serum levels of transaminases, hepatic apoptosis and hepatic tissue levels of caspase-3 after hepatic ischemia/reperfusion (I/R) were more marked in CGRP-/- mice than in WT mice. Hepatic IGF-I levels were increased in WT mice after reperfusion, while they were not changed in CGRP-/- mice. Although administration of capsaicin enhanced increases in IGF-I levels and reduced reperfusion-induced events in WT mice, it had no effect in CGRP-/- mice. Administration of CGRP and IGF-I reduced reperfusion-induced effects in both strains of mice. These observations suggested that capsaicin-induced sensory neuron activation, which leads to release of CGRP, might increase IGF-I production, thereby reducing reperfusion-induced liver injury by reducing apoptosis.

Lung ischemia-reperfusion injury: implications of oxidative stress and platelet-arteriolar wall interactions

Pulmonary ischemia-reperfusion (IR) injury may result from trauma, atherosclerosis, pulmonary embolism, pulmonary thrombosis and surgical procedures such as cardiopulmonary bypass and lung transplantation. IR injury induces oxidative stress characterized by formation of reactive oxygen (ROS) and reactive nitrogen species (RNS). Nitric oxide (NO) overproduction via inducible nitric oxide synthase (iNOS) is an important component in the pathogenesis of IR. Reaction of NO with ROS forms RNS as secondary reactive products, which cause platelet activation and upregulation of adhesion molecules. This mechanism of injury is particularly important during pulmonary IR with increased iNOS activity in the presence of oxidative stress. Platelet-endothelial interactions may play an important role in causing pulmonary arteriolar vasoconstriction and post-ischemic alveolar hypoperfusion. This review discusses the relationship between ROS, RNS, P-selectin, and platelet-arteriolar wall interactions and proposes a hypothesis for their role in microvascular responses during pulmonary IR.

Pathophysiological role of platelets in acute experimental pancreatitis: influence of endothelin A receptor blockade

The potential pathophysiological role of platelet-endothelium interactions was investigated during ischemia/reperfusion (I/R), and the effect of a selective endothelin(A) receptor antagonist (ET(A)-RA) was evaluated in an acute pancreatitis model. Acute pancreatitis was induced by warm ischemia (60 min) in Wistar rats, and its effects with and without antagonist treatment were investigated. Equivalent sham-operated animals were also studied. Microcirculatory changes were assessed by in vivo microscopy, and serum levels for lipase/amylase and histological specimens were investigated. Capillary constriction to 83.7 +/- 6.7% of sham-operated diameters was observed after 60 min of ischemia. A capillary density of 56.8 +/- 9.3% of the sham-operated group (396.3 +/- 15.8 mm(-1)) was measured after reperfusion. Stagnant leukocytes (329.5 +/- 30.4%) and platelets (337.5 +/- 32.3%) increased in postcapillary venules (P < 0.05). Administration of the ET(A)-RA significantly reduced I/R injury. Capillary diameters were maintained (101.4 +/- 4.5%), and capillary density was improved to 73.3 +/- 7.6% of sham-operated animals (P < 0.05). Stagnant leukocytes (152.3 +/- 10.6%) and platelets (207.1 +/- 19.8%) in sinusoids and postcapillary venules were reduced (P < 0.05). The extent of acute pancreatitis was reduced in the therapy group as indicated by serum lipase/amylase values and histological tissue damage (P < 0.05). Thus, ET(A)-RA therapy was effective in reducing I/R-induced pancreatitis in this experimental model.

Ciclosporin aggravates tissue damage in ischemia reperfusion-induced acute pancreatitis

OBJECTIVES

Ischemia reperfusion (I/R)-associated early graft pancreatitis is a major complication after pancreas transplantation. The influence of immunosuppressants on graft pancreatitis remains unclear. The aim of this study was to evaluate ciclosporin and tacrolimus in experimental pancreatic I/R.

METHODS

Moderate pancreatitis was induced in rats by I/R injury. Animals were assigned to 4 groups: (1) control without I/R, (2) I/R without therapy, (3) I/R + ciclosporin, or (4) I/R + tacrolimus. After 24 hours, pancreatic damage was evaluated by amylase, endothelin 1, thromboxane A2, and histology. Additionally, microcirculation was evaluated 12 hours after reperfusion by intravital microscopy.

RESULTS

I/R significantly increased amylase compared with controls, with maximum levels after ciclosporin treatment. Histology showed comparable tissue injury in control and tacrolimus-treated animals. Ciclosporin-treated animals developed significantly (P < 0.05) more inflammation and necrosis compared with the other groups. Erythrocyte velocity evaluated by intravital microscopy was reduced in all animals after I/R. This was significantly pronounced after ciclosporin application. There was a significant increase of adherent leukocytes and platelets in ciclosporin-treated animals compared with both other groups.

CONCLUSIONS

Tacrolimus does not negatively influence I/R-induced pancreatitis, whereas ciclosporin aggravates pancreatic tissue damage after I/R. These effects should be evaluated in the clinical setting of pancreas transplantation.

CD4+ T cells contribute to postischemic liver injury in mice by interacting with sinusoidal endothelium and platelets

The mechanisms by which T cells contribute to the hepatic inflammation during antigen-independent ischemia/reperfusion (I/R) are not fully understood. We analyzed the recruitment of T cells in the postischemic hepatic microcirculation in vivo and tested the hypothesis that T cells interact with platelets and activate sinusoidal endothelial cells, resulting in microvascular dysfunction followed by tissue injury. Using intravital videofluorescence microscopy, we show in mice that warm hepatic I/R (90/30-140 min) induces accumulation and transendothelial migration of CD4+, but not CD8+ T cells in sinusoids during early reperfusion. Simultaneous visualization of fluorescence-labeled CD4+ T cells and platelets showed that approximately 30% of all accumulated CD4+ T cells were colocalized with platelets, suggesting an interaction between both cell types. Although interactions of CD4+/CD40L-/- T cells with CD40L-/- platelets in wild-type mice were slightly reduced, they were almost absent if CD4+ T cells and platelets were from CD62P-/- mice. CD4 deficiency as well as CD40-CD40L and CD28-B7 disruption attenuated postischemic platelet adherence in the same manner as platelet inactivation with a glycoprotein IIb/IIIa antagonist and reduced neutrophil transmigration, sinusoidal perfusion failure, and transaminase activities. Treatment with an MHC class II antibody, however, did not affect I/R injury. In conclusion, we describe the type, kinetic, and microvascular localization of T cell recruitment in the postischemic liver. CD4+ T cells interact with platelets in postischemic sinusoids, and this interaction is mediated by platelet CD62P. CD4+ T cells activate endothelium, increase I/R-induced platelet adherence and neutrophil migration via CD40-CD40L and CD28-B7-dependent pathways, and aggravate microvascular/hepatocellular injury.

Platelet function in acute experimental pancreatitis induced by ischaemia-reperfusion

BACKGROUND

Ischaemia-reperfusion (IR)-associated microcirculatory changes play a major role in acute post-transplantation pancreatitis. The pathophysiological role of platelets in these events is unknown. The aim of this study was to examine platelet adhesion and function during early reperfusion after pancreatic ischaemia.

METHODS

Rats were subjected to warm pancreatic ischaemia by cross-clamping of the pancreatic vessels for 1 h. After 1 h of reperfusion, platelet-endothelium interaction was evaluated after platelet separation and staining by fluorescence microscopy. Amylase levels and pancreatic histology were evaluated 24 h after reperfusion. Animals treated according to an identical protocol, but without ischaemia, served as controls.

RESULTS

Mild pancreatitis had developed by 24 h after IR; serum amylase levels were significantly higher than those in control animals. The numbers of adherent platelets in capillaries and venules were significantly increased, and platelet velocity in capillaries was significantly decreased, in the IR group compared with controls. There was significantly more oedema and inflammation in pancreatic tissue after IR.

CONCLUSION

Warm ischaemia for 1 h followed by reperfusion for 24 h caused mild pancreatitis in this experimental model. The pancreatic microcirculation was characterized by pronounced platelet-endothelium interaction in capillaries and venules. These results suggest that platelet activation may play an important role in acute post-transplantation pancreatitis.

Role of adhesion molecules and dendritic cells in rat hepatic/renal ischemia-reperfusion injury and anti-adhesive intervention with anti-P-selectin lectin-EGF domain monoclonal antibody

AIM: To investigate the role of P-selectin, intercellular adhesion molecule-1 (ICAM-1) and dendritic cells (DCs) in liver/kidney of rats with hepatic/renal ischemia-reperfusion injury and the preventive effect of anti-P-selectin lectin-EGF domain monoclonal antibody (anti-PsL-EGFmAb) on the injury.

METHODS: Rat models of hepatic and renal ischemia-reperfusion were established. The rats were then divided into two groups, one group treated with anti-PsL-EGFmAb (n = 20) and control treated with saline (n = 20). Both groups were subdivided into four groups according to reperfusion time (1, 3, 6 and 24 h). The sham-operated group (n = 5) served as a control group. DCs were observed by the microscopic image method, while P-selectin and ICAM-1 were analyzed by immunohistochemistry.

RESULTS: P-selectin increased significantly in hepatic sinusoidal endothelial cells and renal tubular epithelial cells 1 h after ischemia-reperfusion, and the expression of ICAM-1 was up-regulated in hepatic sinusoid and renal vessels after 6 h. CD1a⁺CD80⁺DCs gradually increased in hepatic sinusoidal endothelium and renal tubules and interstitium 1 h after ischemia-reperfusion, and there was the most number of DCs in 24-h group. The localization of DCs was associated with rat hepatic/renal function. These changes became less significant in rats treated with anti-PsL-EGFmAb.

CONCLUSION: DCs play an important role in immune pathogenesis of hepatic/renal ischemia-reperfusion injury. Anti-PsL-EGFmAb may regulate and inhibit local DC immigration and accumulation in liver/kidney.

Improvement of postischemic hepatic microcirculation after endothelinA receptor blockade--endothelin antagonism influences platelet-endothelium interactions

Endothelin (ET) contributes to disturbances of hepatic microcirculation after ischemia/reperfusion (I/R) by causing vasoconstriction and enhancing leukocyte- and platelet-endothelium interactions. The aim of this study was to investigate a possible protective role of a selective endothelin(A) receptor antagonist (ET(A)-RA) in this setting. In a rat model, warm ischemia of the left lateral liver lobe was induced for 90 minutes under intraperitoneal anesthesia with xylazine and ketamine. Groups of rats consisted of sham-operated (SO, n=14), untreated ischemia (n=14), and treatment with BSF208075 (5 mg/kg body weight IV, n=14). The effect of the ET(A)-RA on I/R was assessed by in vivo microscopy 20 to 90 minutes after reperfusion; by measurement of local tissue Po(2), serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), and glutathione S-transferase alpha levels, and by histologic investigation. In the untreated group, sinusoidal constriction to 69.4+/-6.7% of diameters of SO rats was observed, leading to a significant decrease in perfusion rate (74.3+/-2.1% of SO) and liver tissue Po(2) (43.5+/-3.2% of SO) (P < 0.05). In addition, we found an increased percentage of stagnant leukocytes (142.9+/-11.9%) and platelets (450.1+/-62.3%) in sinusoids and in postsinusoidal venules (P < 0.05). Hepatocellular damage (AST and ALT increase to 1330+/-157 U/L and 750+/-125 U/L respectively; previously, 27.1+/-3.5 U/L and 28.5+/-3.6 U/L) was detected 6 hours after reperfusion (P < 0.05). Administration of the ET(A)-RA before reperfusion significantly reduced I/R injury. Sinusoidal diameters were maintained (108.5+/-6.6%), and perfusion rate (93.1+/-1.8%) and tissue Po(2) (95.3+/-5.7%) were significantly increased (P < 0.05). According to reduced leukocyte-endothelium interactions after therapy, both platelet rolling and adhesion were significantly reduced (P < 0.05). The number of stagnant platelets in sinusoids was 199.5+/-12.3% of 50 (P < 0.05). After treatment, hepatocellular damage was decreased (AST and ALT levels after 6 hours of reperfusion: 513+/-106 U/L and 309+/-84 U/L, respectively; P < 0.05), and histologic changes were reduced in the long term. Our results provide evidence that the new therapeutic approach with an ET(A)-RA is effective in reducing hepatic I/R injury. In addition to reduced leukocyte-endothelium interactions, the number of stagnant and rolling platelets in sinusoids and venules was significantly reduced. The reduction in microcirculatory damages is responsible for better organ outcome.

In Vivo Visualization of Platelet/Endothelium Cell Interaction in Muscle Flaps

Increasing evidence underlines the substantial pathophysiological impact of platelets on the development of ischemia/reperfusion injury (I/R) in flaps. Methods for studying dynamic platelet mechanisms in flaps in vivo are not available. The aim of this study was to develop a model enabling quantitative analysis of platelet kinetics and platelet-endothelium cell interaction within the microcirculation of muscle flaps in vivo. Balb/c mice (n = 16) were anesthetized, and an epigastric muscle flap was prepared. Autologous platelets were separated from blood donor animals (n = 16) and labeled ex vivo by means of rhodamine-6-G. After I/R (90 minutes' clamping, 10 minutes' reperfusion), the platelets were administered intra-arterially (i.a.). Microhemodynamics and kinetics of platelets were investigated by intravital fluorescence microscopy. I/R of muscle flaps induced disturbances in microcirculation. The number of rolling platelets, as well as platelets adhering to the inner vessel wall of venules, was increased in the ischemia group. Using intravital fluorescence microscopy, platelet kinetics were analyzed directly in flap microcirculation in vivo for the first time. Since platelet/endothelial cell interaction is a key event in the pathophysiology after microsurgical procedures, this model will help to understand basic molecular mechanisms of platelet behavior during I/R.

Ultrafine Particles Exert Prothrombotic but Not Inflammatory Effects on the Hepatic Microcirculation in Healthy Mice In Vivo

Background— Air pollution episodes are strongly associated with increased cardiovascular morbidity and mortality. The effect of ultrafine particles (UFPs), when translocated after inhalation, on the microcirculation of extrapulmonary organs remains unclear.

Methods and Results— In C57BL/6 mice, either carbon black UFPs (1×10 7 and 5×10 7 ) or vehicle was infused intra-arterially. Two hours after infusion, platelet- and leukocyte-endothelial cell interactions, sinusoidal perfusion, endothelial fibrin(ogen) deposition, and phagocytic activity of Kupffer cells were analyzed by intravital video fluorescence microscopy in the liver microvasculature. Expression of fibrin(ogen), von Willebrand factor (vWF), and P-selectin on hepatic endothelium was determined by immunostaining. Apoptotic cells were quantified in TUNEL-stained tissue sections. Application of UFPs caused significantly enhanced platelet accumulation on endothelium of postsinusoidal venules and sinusoids in healthy mice. UFP-induced platelet adhesion was not preceded by platelet rolling but was strongly associated with fibrin deposition and an increase in vWF expression on the endothelial surface. In contrast, inflammatory parameters such as the number of rolling/adherent leukocytes, P-selectin expression/translocation, and the number of apoptotic cells were not elevated 2 hours after UFP exposure. In addition, UFPs did not affect sinusoidal perfusion and Kupffer cell function.

Conclusions— UFPs induce platelet accumulation in the hepatic microvasculature of healthy mice that is associated with prothrombotic changes on the endothelial surface of hepatic microvessels. Accumulation of particles in the liver exerts a strong procoagulatory impact but does not trigger an inflammatory reaction and does not induce microvascular/hepatocellular tissue injury.

5-Aminoisoquinolinone, a novel inhibitor of poly(adenosine disphosphate-ribose) polymerase, reduces microvascular liver injury but not mortality rate after hepatic ischemia-reperfusion*

OBJECTIVE

The aim of this study was to investigate the impact of the novel, potent, water-soluble inhibitor of poly(adenosine diphosphate-ribose) polymerase (PARP) 5-aminoisoquinolinone (5-AIQ) on hepatic microcirculation, hepatocellular injury, and survival in a murine model of hepatic ischemia-reperfusion.

DESIGN

Randomized animal study.

SETTING

Research laboratory.

SUBJECTS

C57BL6 mice were subjected to warm either partial (90 mins) or total (75 mins) ischemia of the liver.

INTERVENTIONS

Either PARP inhibitor 5-AIQ (3 mg/kg) or vehicle was administered to mice intravenously immediately before the start of reperfusion. Sham-operated animals served as controls.

MEASUREMENTS AND MAIN RESULTS

As shown by intravital fluorescence microscopy after 30-60 mins of reperfusion, ischemia-reperfusion significantly enhanced platelet- and leukocyte-endothelial cell interactions in hepatic microvessels and impaired sinusoidal perfusion. Hepatocellular injury was characterized by an increase in the number of necrotic and apoptotic cells, dramatic elevation of aspartate aminotransferase/alanine aminotransferase serum activity, and lipid peroxidation in liver tissue. 5-AIQ treatment attenuated ischemia-reperfusion-induced increases in the numbers of adherent platelets and leukocytes as well as of necrotic and apoptotic cells and ameliorated perfusion failure. Furthermore, PARP inhibition prevented the increase in aspartate aminotransferase activity after ischemia-reperfusion but did not affect postischemic alanine aminotransferase release. However, no protective impact of 5-AIQ on postischemic oxidative stress was observed. Although PARP inhibition did not alter the survival percentage after ischemia-reperfusion (22% in both groups), this approach prolonged survival from 1 to 24 hrs (ischemia-reperfusion + vehicle) up to 48-72 hrs in the treated group.

CONCLUSIONS

PARP inhibition with 5-AIQ during hepatic ischemia-reperfusion attenuates microvascular injury and reduces the extent of necrotic/apoptotic cell damage but does not protect from oxidative injury and does not improve postoperative survival rate.