Assessment of hepatic phagocytic activity by in vivo microscopy after liver transplantation in the rat

Imaging Plasmodium immunobiology in the liver, brain, and lung

Plasmodium falciparum malaria is responsible for the deaths of over half a million African children annually. Until a decade ago, dynamic analysis of the malaria parasite was limited to in vitro systems with the typical limitations associated with 2D monocultures or entirely artificial surfaces. Due to extremely low parasite densities, the liver was considered a black box in terms of Plasmodium sporozoite invasion, liver stage development, and merozoite release into the blood. Further, nothing was known about the behavior of blood stage parasites in organs such as the brain where clinical signs manifest and the ensuing immune response of the host that may ultimately result in a fatal outcome. The advent of fluorescent parasites, advances in imaging technology, and availability of an ever-increasing number of cellular and molecular probes have helped illuminate many steps along the pathogenetic cascade of this deadly tropical parasite.

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.

Taurine protects from liver injury after warm ischemia in rats: the role of kupffer cells

BACKGROUND/AIMS

Warm ischemia to liver with subsequent Kupffer cell-dependent pathology is associated with many clinical conditions. Taurine prevents Kupffer cell activation and improves graft survival after experimental cold ischemia and liver transplantation. Thus this study was designed to assess its effects after warm hepatic ischemia.

METHODS

The left liver lobe of female Sprague-Dawley rats (170-210 g) underwent 60 min of warm ischemia. Animals were given either intravenous taurine or Ringer's solution 10 min prior to warm ischemia. Transaminases, histology, in vivo microscopy, intercellular adhesion molecules-1 (ICAM-1) expression, TNF-alpha and tissue hydroperoxide were compared between groups using analysis of variance (ANOVA) or ANOVA on ranks as appropriate.

RESULTS

Taurine significantly decreased transaminases and improved histologic outcome. Phagocytosis of latex beads, serum TNF-alpha levels and tissue hydroperoxide concentrations were also significantly reduced. Stickers in sinusoids and post-sinusoidal venules significantly decreased. In parallel, both leukocyte infiltration and ICAM-1 expression decreased (p < 0.05), while flow velocity of red blood cells as well as sinusoidal perfusion rate were improved (p < 0.05).

CONCLUSION

This study demonstrates that taurine blunts Kupffer cell-dependent hepatic pathology after warm ischemia in vivo via mechanisms including leukocyte-endothelial interaction, microcirculation disturbances and protection against lipid peroxidation.

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.

Intravenous administration of glutathione protects parenchymal and non-parenchymal liver cells against reperfusion injury following rat liver transplantation

AIM: To investigated the effects of intravenous administration of the antioxidant glutathione (GSH) on reperfusion injury following liver transplantation.

METHODS: Livers of male Lewis rats were transplanted after 24 h of hypothermic preservation in University of Wisconsin solution in a syngeneic setting. During a 2-h reperfusion period either saline (controls, n = 8) or GSH (50 or 100 μmol/(h·kg), n = 5 each) was continuously administered via the jugular vein.

RESULTS: Two hours after starting reperfusion plasma ALT increased to 1 457 ± 281 U/L (mean ± SE) in controls but to only 908 ± 187 U/L (P < 0.05) in animals treated with 100 μmol GSH/(h·kg). No protection was conveyed by 50 μmol GSH/(h·kg). Cytoprotection was confirmed by morphological findings on electron microscopy: GSH treatment prevented detachment of sinusoidal endothelial cells (SEC) as well as loss of microvilli and mitochondrial swelling of hepatocytes. Accordingly, postischemic bile flow increased 2-fold. Intravital fluorescence microscopy revealed a nearly complete restoration of sinusoidal blood flow and a significant reduction of leukocyte adherence to sinusoids and postsinusoidal venules. Following infusion of 50 μmol and 100 μmol GSH/(h·kg), plasma GSH increased to 65 ± 7 mol/L and 97 ± 18 mol/L, but to only 20 ± 3 mol/L in untreated recipients. Furthermore, plasma glutathione disulfide (GSSG) increased to 7.5 ± 1.0 mol/L in animals treated with 100 μmol/(h·kg) GSH but did not raise levels of untreated controls (1.8 ± 0.5 mol/L) following infusion of 50 μmol GSH/(h·kg) (2.2 ± 0.2 mol/L).

CONCLUSION: Plasma GSH levels above a critical level may act as a “sink” for ROS produced in the hepatic vasculature during reperfusion of liver grafts. Therefore, GSH can be considered a candidate antioxidant for the prevention of reperfusion injury after liver transplantation, in particular since it has a low toxicity in humans.

Microcirculatory failure after rat liver transplantation is related to Kupffer cell-derived oxidant stress but not involved in early graft dysfunction

BACKGROUND

Microcirculatory failure, activation of Kupffer cells (KC), and the formation of reactive oxygen species (ROS) are considered pivotal mechanisms of reperfusion injury after orthotopic liver transplantation. However, the sequence of these events and their impact on early graft function remain controversial. We therefore investigated whether KC induce microcirculatory disturbances through ROS release and whether microcirculatory failure contributes to early graft function after liver transplantation.

METHODS

Donor livers of Lewis rats were pretreated either with saline or with gadolinium chloride (GdCl3), an inhibitor of KC function (n=8 each). Syngeneic OLT was performed after 24 hr of hypothermic preservation in University of Wisconsin solution.

RESULTS

Intravital microscopy revealed significantly higher sinusoidal perfusion rates in GdCl3-treated allografts (92+/-1.1% vs. 75.7+/-0.8%; P<0.001) compared with untreated controls; permanent leukocyte sticking in sinusoids (23.5+/-2.1 vs. 62.6+/-3.3 cells/lobule, P<0.001) and in postsinusoidal venules (153.1+/-10.4 vs. 446.6+/-46.4 cells/mm(2), P<0.001) were markedly attenuated in GdCl3-treated allografts. Improvement of microcirculatory parameters in GdCl3-treated livers was correlated with a significant reduction of plasma glutathione disulfide formation by KC-derived ROS (0.96+/-0.1 microM vs. 1.79+/-0.5 microM; P<0.01). Despite these beneficial effects, GdCl3-pretreatment failed to improve postischemic alanine aminotransferase release and bile flow.

CONCLUSIONS

Microcirculatory failure after liver transplantation is related to KC-derived oxidant stress but not involved in early graft dysfunction.

Role of hepatocytes and bile duct cells in preservation-reperfusion injury of liver grafts

In liver transplantation, it is currently hypothesized that nonparenchymal cell damage and/or activation is the major cause of preservation-related graft injury. Because parenchymal cells (hepatocytes) appear morphologically well preserved even after extended cold preservation, their injury after warm reperfusion is ascribed to the consequences of nonparenchymal cell damage and/or activation. However, accumulating evidence over the past decade indicated that the current hypothesis cannot fully explain preservation-related liver graft injury. We review data obtained in animal and human liver transplantation and isolated perfused animal livers, as well as isolated cell models to highlight growing evidence of the importance of hepatocyte disturbances in the pathogenesis of normal and fatty graft injury. Particular attention is given to preservation time-dependent decreases in high-energy adenine nucleotide levels in liver cells, a circumstance that (1) sensitizes hepatocytes to various stimuli and insults, (2) correlates well with graft function after liver transplantation, and (3) may also underlie the preservation time-dependent increase in endothelial cell damage. We also review damage to bile duct cells, which is increasingly being recognized as important in the long-lasting phase of reperfusion injury. The role of hydrophobic bile salts in that context is particularly assessed. Finally, a number of avenues aimed at preserving hepatocyte and bile duct cell integrity are discussed in the context of liver transplantation therapy as a complement to reducing nonparenchymal cell damage and/or activation.

Kupffer cell-initiated remote hepatic injury following bilateral hindlimb ischemia is complement dependent

Intravital fluorescence microscopy was applied to the livers of male Wistar rats to test the hypothesis that complement mobilization stimulates Kupffer cells and subsequently initiates hepatic injury after hindlimb ischemia/reperfusion (I/R). Following 3 h of limb reperfusion, hepatocellular viability (serum levels of alanine transaminase and cell death via propidium iodide labeling) decreased significantly from levels in sham-operated animals. Inhibition of complement mobilization with soluble complement receptor type 1 (20 mg/kg body wt) and interruption of Kupffer cell function with GdCl(3) (1 mg/100g body wt) resulted in significant hepatocellular protection. Although the effects of hindlimb I/R on hepatic microvascular perfusion were manifest as increased heterogeneity, both complement inhibition and suppression of Kupffer cell function resulted in marked improvements. No additional hepatocellular protection and microvascular improvements were provided by combining the interventions. Furthermore, inhibition of complement mobilization significantly depressed Kupffer cell phagocytosis by 42% following limb reperfusion. These results suggest that the stimulation of Kupffer cells via complement mobilization is necessary but is not the only factor contributing to the early pathogenesis of hepatic injury following hindlimb I/R.

Anti-ICAM-1 blockade reduces postsinusoidal WBC adherence following cold ischemia and reperfusion, but does not improve early graft function in rat liver transplantation

BACKGROUND/AIM

The present in vivo study investigated the impact of a monoclonal antibody directed against the intercellular adhesion molecule-1 (ICAM-1) on initial microvascular reperfusion injury after liver transplantation.

METHODS

Orthotopic, syngeneic liver transplantation including arterial reconstruction was performed in male Lewis rats after 24 h graft storage in University of Wisconsin (UW) solution at 4 degrees C. Animals received either an anti-ICAM-1 antibody (n=7), an IgG1 control antibody (n=8) or saline only (n=7). Hepatic microvascular alterations during the initial 90 min of reperfusion were assessed using intravital fluorescence microscopy. Early graft dysfunction was determined by analysis of bile flow.

RESULTS

After treatment with anti-ICAM-1 mAb, hepatic microvascular perfusion was found improved when compared with that of IgG1- and saline-treated controls. In addition, anti-ICAM-1 mAb effectively reduced the number of permanently adherent white blood cells in postsinusoidal venules (284.4+/-59.1 mm(-2) vs IgG1: 371.9+/-26.7 mm(-2) and saline: 431.8+/-46.4 mm(-2); p<0.05). In contrast, the number of stagnant white blood cells in sinusoids was higher (p<0.05) in liver grafts with blocked ICAM-1 (320.6+/-17.2 mm(-2)) compared with that of IgG1- (215.2+/-11.1 mm(-2)) and saline-treated controls (226.4+/-14.0 mm(-2)). Measurement of hepatic uptake of fluorescent-labeled latex particles did not reveal significant differences in phagocytic activity. Finally, bile flow also did not differ between the three groups studied.

CONCLUSION

Together these results indicate that ICAM-1 is involved in the process that mediates white blood cells adherence in postsinusoidal venules, whereas in hepatic sinusoids other mechanisms apart from ICAM-1-mediated white blood cells adherence seem to be fundamental for posttransplant white blood cells accumulation. Our data further suggest that white blood cells adherence in postsinusoidal venules via ICAM-1 does not make a major contribution to the pathogenesis of early cold ischemia/reperfusion injury after liver transplantation.

Evaluation of hepatic microcirculation by in vivo microscopy

In vivo microscopy is an excellent technique for investigating the microcirculation and until recently the only one that allowed direct visualization. Rat liver has been widely studied, because microcirculatory disorders play a pivotal role in the pathogenesis of organ failure during hepatic ischemia, transplantation, hemorrhagic shock, endotoxemia, and sepsis. The state of the microcirculation is an important prognostic factor for the reestablishment of organ function after these injuries. This article introduces the most common procedures for in vivo microscopy of the rat liver, summarizes the available fluorescent dyes, and gives an overview of criteria for the expression and evaluation of microscopic findings. Particular emphasis is given to a description of the different parameters assessed by direct observation of hepatic microcirculation, such as perfusion rate, leukocyte-endothelium interactions, leukocyte velocities, and phagocytic activity. Examples of normal range values are given. This overview is intended to help those wanting to introduce this method into their research and who are embarking on intravital microscopy for the first time, and to enable them to decide which techniques are appropriate for answering special questions.

Inhibition of caspase activity prevents CD95-mediated hepatic microvascular perfusion failure and restores Kupffer cell clearance capacity

Using a murine model, we studied the effect of agonistic anti-CD95 antibodies (aCD95) on sinusoidal lining cells and a potential protection by caspase inhibition. C3H/HeN mice were intravenously administered aCD95 (10 microgram/mouse) or unspecific IgG (control) in the presence or absence of the caspase inhibitor z-VAD-fmk. Analysis of hepatic microcirculation using intravital fluorescence microscopy revealed severe (P<0.01) sinusoidal perfusion failure and reduced (P<0.05) phagocytic activity of Kupffer cells (KC) within 2 h. Transmission electron micrographs demonstrated loss of integrity of sinusoidal endothelial cells as early as 1 h after aCD95 application, whereas histological manifestation of hepatocellular apoptosis and hemorrhagic necrosis was most pronounced at 6 h. Blocking of caspase activity attenuated (P<0.01) both hepatic microvascular perfusion failure and KC dysfunction. Accordingly, full protection of the liver from apoptotic damage and intact microarchitecture was observed in histological sections after z-VAD-fmk treatment. Mortality rate was 40% 6 h after aCD95 administration, whereas all animals survived in the z-VAD-fmk group (P<0.05). The activation of caspases through CD95 may primarily lead to damage of sinusoidal endothelial cells and hepatic microvascular perfusion failure. Moreover, reduced phagocytic capacity of KC may contribute to accumulation of toxic metabolites released by dying cells at the local site of inflammation, further aggravating liver injury.

In vivo microscopic assessment of cremasteric microcirculation during hindlimb allograft rejection in rats

Experimental and clinical studies of vascular allogenic extremity transplantation have yielded disappointing results and have not been clinically useful. With recent advances in transplantation immunology, considerable interest has focused on the understanding of leukocyte-endothelial interaction at the microcirculatory level. The objective of this study was to characterize the alterations in leukocyte-endothelial interaction in the early stages of rat hindlimb allograft rejection. To study the changes at the microcirculatory level, a new microsurgical model was developed; the cremaster muscle was incorporated into the transplanted hindlimb. The purpose of this study was to report on the microcirculatory changes during rat hindlimb allograft rejection. A total of 24 transplantations were performed among the four experimental groups. In a control group, 12 rat hindlimb-cremaster grafts were transplanted between genetically identical animals, Lewis to Lewis. Microcirculatory measurements of graft survival were taken at 24 hours (group 1A, n = 6) and at 72 hours (group 1B, n = 6). In the rejection control group, 12 transplantations were performed across a major histocompatibility barrier between Lewis-Brown Norway and Lewis rats. Microcirculatory measurements were taken at 24 (group 2A, n = 6) and 72 hours (group 2A, n = 6) as above. The following parameters were evaluated to discover the leukocyte-endothelial interaction: endothelial edema index and the number of rolling, adherent, and transmigrating leukocytes and lymphocytes in the postcapillary venule. Physical signs of limb rejection, such as edema, erythema, scaling, plaque formation on the skin, hair loss, and skin surface temperature, were monitored. Microcirculatory signs of rejection included the following. There was a significant increase in the number of adherent leukocytes in allograft transplants at both 24 hours (205 percent; 2.05 +/- 0.38) and 72 hours (431 percent; 9.11 +/- 3.41) when compared with isograft controls (1.00 +/- 0.89 at 24 hours; 2.11 +/- 0.34 at 72 hours) (p < 0.05). The activation of leukocyte transmigration increased more than 7-fold in muscle allografts at 24 hours (0.55 +/- 0.25 versus 4.16 +/- 1.89) and more than 6-fold at 72 hours (0.72 +/- 0.38 versus 4.38 +/- 1.28) after transplantation (p < 0.05). Endothelial edema index, a measure of endothelial swelling and cellular deposit accumulation, increased more than 119 percent in the allograft group 72 hours after transplantation (1.23 +/- 0.07 versus 1.46 +/- 0.09) (p < 0.05). The first clinical signs of limb rejection were scaling of the skin or hair loss; they were observed between the seventh and ninth postoperative days. The composite rat hindlimb-cremaster model presented in this study introduces a new in vivo approach to monitor acute graft rejection using the intravital microscopy system. This is a valuable model for defining the timing, sequence, and correlation between immunologic events and clinical signs during the acute phase of allograft rejection.

Improvement of normothermic rat liver ischemia/reperfusion by muramyl dipeptide

Normothermic ischemia and reperfusion (I/R) of the liver remains a major problem after liver surgery and transplantation. Activation of Kupffer cells (KCs) after normothermic I/R is responsible for a massive release of various monokines such as tumor necrosis factor alpha (TNF-alpha) and a decrease in phagocytic activity. Muramyl dipeptide (MDP) is an immunostimulant that increases phagocytic activity of KCs. The aim of this study was to demonstrate that MDP pretreatment might protect the liver against I/R injury by a modification of KC functions. Rats were divided into three groups: group 1, control, Ringer's lactate administration; group 2, MDP (N-acetyl-muramyl-d-alanyl-d-isoglutamine) treatment; group 3, sham-operated control animals. MDP (500 microg/250 g) was injected intravenously 5 min before the induction of 90 min ischemia. Survival rates were compared and serum activities of TNF-alpha, aspartate aminotransferase, and alanine aminotransferase were assessed in the blood collected from the suprahepatic vena cava. Histology of the liver and KC activity were assessed 6 and 9 h after the end of ischemia, respectively. MDP treatment significantly increased 7-day survival (86.6%) compared with nontreated rats (40%, P < 0.001). Serum activities of TNF-alpha and aminotransferases were significantly decreased after MDP treatment, whereas phagocytic capacity of KCs was partially restored. The extent of liver necrosis was decreased after MDP administration. A significant difference was observed for other histological parameters studied, except for steatosis. Our findings have demonstrated that MDP is able to protect the liver from ischemic insult by modulation of KC activity (TNF-alpha release and phagocytic capacity). Control of macrophage activity may offer a new strategy to reduce ischemic injury of the liver.

Background and prognostic implications of perireperfusion tissue injuries in human liver transplants: a panel histochemical study

BACKGROUND

Hepatic graft reperfusion is associated with inflammatory processes of unknown relevance to the fate of graft. This study aimed to clarify this relevance by histochemical analyses of human hepatic grafts.

METHODS

Paired tissue samples were taken at the end of cold preservation and 2 hr after reperfusion (n=39). From six additional grafts, biopsies were performed at the end of cold preservation only. Injury or inflammatory markers of sinusoidal endothelium (von Willebrand factor-related antigen [vWF]), Kupffer cells (25F9), platelets (CD62), neutrophil leukocytes (CD11b), interleukin (IL)-1beta, intercellular adhesion molecule (ICAM)-1, and HLA-DR were evaluated semiquantitatively by indirect immunoperoxidase staining. Steatosis was also evaluated by hematoxylin and eosin staining.

RESULTS

vWF, CD62+ platelet aggregation, CD11b+ leukocytes, and IL-1beta levels increased after reperfusion, and these levels correlated with prereperfusion levels. Not only vWF, CD62+ platelets, CD11b+ leukocytes, IL-1beta, ICAM-1, and steatosis after reperfusion, but also IL-1beta, ICAM-1, and steatosis before reperfusion correlated with postoperative peak transaminase. Furthermore, vWF, CD11b+ leukocytes, 25F9+ macrophages, and ICAM-1 after reperfusion were associated with primary graft nonfunction and strong expressions of ICAM-1 or HLA-DR with early acute rejection. Although some markers (IL-1beta, CD62+ platelets, and CD11b+ leukocytes) correlated with preharvesting parameters (donor age or length of intensive care unit stay), none showed any significant correlation with cold preservation.

CONCLUSION

Synergistic inflammatory events in the hepatic graft at reperfusion, which have a significant impact on the later clinical course, are largely defined and precipitated by injury or activation of nonparenchymal cells preceding reperfusion or even graft harvesting.

Complement inhibition by soluble complement receptor type 1 improves microcirculation after rat liver transplantation

BACKGROUND

Recent observations provide evidence that complement is involved in the pathophysiology of ischemia/reperfusion injury. In this study, we assessed the impact of complement inhibition on hepatic microcirculation and graft function using a rat model of liver transplantation.

METHODS

Arterialized orthotopic liver transplantation was performed in Lewis rats after cold preservation (University of Wisconsin solution, 4 degrees C, 24 h). Eight animals received the physiological complement regulator soluble complement receptor type 1 (sCR1) intravenously 1 min before reperfusion. Controls received Ringer's solution (n=8). Microvascular perfusion, leukocyte adhesion, and Kupffer cell phagocytic activity were studied 30-100 min after reperfusion by in vivo microscopy.

RESULTS

Microvascular perfusion in hepatic sinusoids was improved in the sCR1 group (87+/-0.7% vs. 50+/-1%; P < 0.001). The number of adherent leukocytes was reduced in sinusoids (68.3+/-4.7 vs. 334.1+/-15.8 [adherent leukocytes per mm < or = liver surface]; P < 0.001) and in postsinusoidal venules after sCR1 treatment (306.6+/-21.8 vs. 931.6+/-55.9 [adherent leukocytes per mm < or = endothelial surface]; P < 0.001). Kupffer cell phagocytic activity was decreased in the sCR1 group compared to controls. Postischemic bile production reflecting hepatocellular function was increased by almost 200% (P = 0.004) after complement inhibition. Plasmatic liver enzyme activity was decreased significantly upon sCR1 treatment, indicating reduced parenchymal cell injury.

CONCLUSIONS

Our results provide further evidence that the complement system plays a decisive role in hepatic ischemia/reperfusion injury. We conclude that complement inhibition by sCR1 represents an effective treatment to prevent reperfusion injury in liver transplantation.

Amelioration of sinusoidal endothelial cell damage by Kupffer cell blockade during cold preservation of rat liver

Recent studies have shown that Kupffer cell function is enhanced in the cold-preserved liver, and blockade of Kupffer cells attenuates the injury induced by cold preservation with subsequent reperfusion. This study was designed to investigate the contribution of Kupffer cell blockade with gadolinium chloride (GdCl3) to the rescue of sinusoidal endothelial cell (SEC) damage by comparing the time-related morphological and ultrastructural changes. GdCl3 injection reduced the number of Kupffer cells reactive with monoclonal antibodies ED2 and Ki-M2R directed against macrophage. Scanning electron microscopy revealed the prominent string-like appearance of the SEC processes at 24 hr of preservation in the control; the SECs were better preserved in the GdCl3-pretreated group. Transmission electron microscopy showed detachment of the sinusoidal epithelia at 12 hr of preservation in the control; it was not seen in the GdCl3-pretreated group. At 24 hr of preservation, the SECs were better preserved in the GdCl3-pretreated group. Microvascular casts from the control group showed a disturbance in the radial arrangement of the sinusoids, significant dilation of the sinusoidal caliber at 24 hr, and discontinuity of the sinusoids with extravasation of the casting material at 36 hr of preservation. These changes were also minimized in the GdCl3-pretreated group. In conclusion, the present study demonstrates that Kupffer cells are strongly involved in the morphological integrity of SECs and that blockade of the activation of Kupffer cells would be effective for the prevention of damage to SECs and maintenance of the sinusoidal architecture during cold preservation of the liver tissure.

In vivo assessment of hepatic alterations following gadolinium chloride-induced Kupffer cell blockade

BACKGROUND/AIMS

In recent years, Gadolinium chloride (GdCl3), a rare earth metal, has frequently been used to study the role and function of Kupffer cells under physiological and pathological conditions. This study was performed to elucidate the consequences of GdCl3-induced Kupffer cell blockade for hepatic microcirculation, hepatocellular function and integrity.

METHODS/RESULTS

Using intravital fluorescence microscopy, we studied the hepatic microcirculation of rats pretreated with either GdCl3 (n = 12; 10 mg/kg; 1 ml i.v. for 2 d) or saline (n = 9; 1 ml). The GdCl3-treated animals revealed a significantly lower phagocytic activity of Kupffer cells when compared to controls. Concomitantly, GdCl3-treatment resulted in a pronounced rise of serum cytokine activity (tumor necrosis factor-alpha; interleukin-6). The hepatic microvascular perfusion was characterized by a moderate increase in the number of non-perfused sinusoids accompanied by a reduction of bile flow. In addition, GdCl3-treatment caused a slight increase in liver enzyme activity (< 200 U/l) (aspartate aminotransferase and alanine aminotransferase) with no substantial parenchymal tissue injury (light microscopy). The groups did not differ in concentrations of circulating endotoxin (GdCl3-treatment: 0.044 +/- 0.042 ng/ml; controls: 0.052 +/- 0.014 ng/ml).

CONCLUSIONS

We conclude that hepatic alterations following Kupffer cell blockade with GdCl3 may possibly be the consequence of cytokine release as a response to the phagocytic challenge of GdCl3-aggregates. If used for Kupffer cell blockade, the hepatic alterations following GdCl3-treatment described in the present study should be taken into consideration.

Intravital studies on beneficial effects of warm Ringer's lactate rinse in liver transplantation

This quantitative in vivo fluorescence microscopy study investigated the impact of warm versus cold Ringer's lactate (RL) graft rinse on various microvascular manifestations of ischemia-reperfusion injury after liver transplantation in the rat. Syngeneic orthotopic liver transplantation, including arterial revascularization, was performed in male Lewis rats following 24 h of cold storage in University of Wisconsin (UW) solution. In one group (n = 8) liver grafts were rinsed with 4 degrees C (cold) RL, whereas in the other group (n = 8) grafts were rinsed with 37 degrees C (warm) RL immediately prior to revascularization. Hepatic microvascular perfusion, leukocyteendothelium interaction, and Kupffer cell activation were quantified 30-90 min after graft reperfusion by direct visualization with intravital fluorescence microscopy. Moreover, biliary excretory graft function was analyzed by determination of bile flow and bile salt excretion during the first 90 min after reperfusion. Compared to grafts rinsed with cold RL, acinar and sinusoidal perfusion were found to be significantly increased after rinsing the grafts with warm RL. The amount of nonperfused acini declined from 18.1% +/- 4.0% to 7.4% +/- 1.6% (P < 0.05), and the total percentage of perfused sinusoids increased from 80.1 +/- 1.4 to 88.4 +/- 1.2 (P < 0.001) after cold and warm rinse, respectively. After rinsing the graft with warm RL, WBC adherence in sinusoids and especially in postsinusoidal venules decreased significantly by 28% (P < 0.001) and 33% (P < 0.001), respectively. Kupffer cell activation was markedly reduced after rinsing with RL at 37 degrees C, as indicated by a decelerated adherence of latex particles injected 80 min after reperfusion. Excretory graft function was dramatically increased following warm RL rinse during the 90-min observation period. Bile flow was enhanced from 1.04 +/- 0.5 to 3.9 +/- 0.8 ml/100 g liver per 90 min (P < 0.01), with a parallel rise in bile salt excretion from 24.3 +/- 5.8 to 128.0 +/- 19.8 mmol/ 100 g liver per 90 min (P < 0.05) when compared to cold RL. These data strongly suggest that rinsing liver grafts with warm RL prior to reperfusion represents a simple and inexpensive way to reduce the incidence of primary graft failure secondary to ischemia and reperfusion injury in liver transplantation.

Impact of N-acetylcysteine on the hepatic microcirculation after orthotopic liver transplantation

Recent observations showed an improvement of hepatic macro- and microhemodynamics as well as survival rates after warm ischemia of the liver following treatment with N-acetylcysteine (NAC). In this study we assessed the influence of NAC on the hepatic microcirculation after orthotopic liver transplantation (OLT) using intravital fluorescence microscopy. OLT with simultaneous arterialization was performed in 16 male Lewis rats following cold storage in University of Wisconsin solution for 24 hr. Within the experimental group (n = 8) donors received NAC (400 mg/kg) 25 min before hepatectomy. In addition, high-dose treatment of recipients with NAC (400 mg/kg) was started with reperfusion. Control animals (n = 8) received an equivalent amount of Ringer's solution. Intravital fluorescence microscopy was performed 30-90 min after reperfusion assessing acinar and sinusoidal perfusion, leukocyte-endothelium interaction, and phagocytic activity. Treatment with NAC reduced the number of nonperfused sinusoid from 52.4 +/- 0.8% to 15.7 +/- 0.5% (p = 0.0001) (mean +/- SEM). Furthermore, we achieved a significant reduction of leukocytes adhering to sinusoidal endothelium (per mm2 liver surface) from 351.9 +/- 13.0 in controls to 83.6 +/- 4.2 in the experimental group (P = 0.0001). In postsinusoidal venules, treatment with NAC decreased the number of sticking leukocytes (per mm2 endothelium) from 1098.5 +/- 59.6 to 425.9 +/- 37.7 (P = 0.0001). Moreover, bile flow was significantly increased after therapy with NAC (4.3 +/- 1.2 vs. 2.2 +/- 0.7 ml/90 min x 100g liver) (P < 0.05). Phagocytic activity was not influenced by application of NAC. We conclude that high-dose therapy with NAC in OLT attenuates manifestations of microvascular perfusion failure early after reperfusion and should be considered as a means to reduce reperfusion injury.

Timing of arterialization in liver transplantation

OBJECTIVE

This study analyzed the pathophysiologic sequela of different modes of graft reperfusion in liver transplantation.

SUMMARY BACKGROUND DATA

The grafted liver may be reperfused either immediately after completion of portal anastomosis followed by delayed arterial reconstruction or simultaneously by portal and arterial blood if all vascular anastomoses are completed during the anhepatic period.

METHODS

Delayed arterialization, that is, arterial reperfusion 8 minutes after portal revascularization (n = 12), was compared with simultaneous arterialization (n = 8) using the model of syngeneic orthotopic liver transplantation in male Lewis rats. After cold storage for 24 hours in University of Wisconsin (UW) solution, intravital fluorescence microscopy was employed 30 to 90 minutes after reperfusion to assess hepatic microvascular perfusion, leukocyte accumulation, and phagocytic activity of Kupffer cells.

RESULTS

Compared with delayed arterialization, the number of both nonperfused acini and nonperfused sinusoids was reduced after simultaneous reperfusion by 71% (p = 0.008) and 78% (p < 0.001), respectively. Leukocyte accumulation in sinusoids and postsinusoidal venules after simultaneous arterialization decreased by 17% (p = 0.01) and 64% (P < 0.001), respectively. In addition, simultaneous revascularization was able to attenuate Kupffer cell activation, indicated by significantly slower adherence of latex beads injected 80 minutes after reperfusion. Improved hepatocellular excretory function after simultaneous arterialization was demonstrated by increased bile flow during the observation period of 90 minutes after reperfusion (2.24 +/- 0.7 vs. 0.95 +/- 0.4 mL/100 g liver [mean +/- SEM], p < 0.05).

CONCLUSIONS

Timing of arterial reperfusion in liver transplantation may be of critical importance in the prevention of various manifestations of reperfusion injury.

Depressed phagocytic activity of Kupffer cells after warm ischemia-reperfusion of the liver

Phagocytic activity of Kupffer cells following hepatic ischemia/reperfusion was studied in 39 livers of male Sprague-Dawley rats by in vivo fluorescence microscopy. Animals were subjected to either 20 min (group B, n = 9) and 60 min left hepatic lobar ischemia (group C, n = 9) or to 20 min of global hepatic ischemia (group D, n = 11). Sham-operated animals without ischemia served as controls (group A, n = 10). After 60 min postischemic reperfusion, fluorescent latex beads (3 x 10(8).kg body wt-1; diameter: 1.1 microns) were injected intra-arterially. The zonal distribution and kinetics of adherence of latex beads were quantified by off-line video analysis. After 20 min of left hepatic lobar ischemia, 50%, 38% and 12% of injected latex beads adhered in zones 1, 2 and 3, respectively, and did not significantly differ from control livers (group A: 57%, 32% and 11%). In contrast, after 60 min of left hepatic lobar ischemia (group C) as well as after 20 min of global hepatic ischemia (group D), a more homogeneous distribution of latex beads adherent in zones 1, 2 and 3 was observed (group C: 48%, 36% and 16%; group D: 48%, 36% and 16%). Kinetic analysis of phagocytosis (% adherence of visible latex beads 1 min and 3 min after injection) showed no significant difference between 20 min left hepatic lobar ischemia (group B: 84% and 95%) and control (group A: 81% and 95%).(ABSTRACT TRUNCATED AT 250 WORDS)

Scope and perspectives of intravital microscopy--bridge over from in vitro to in vivo

As observations in vitro become more sophisticated, it is increasingly important to be able to assess their relevance to the intact animal. Intravital microscopy provides an advanced set of tools for the dissection of the in vivo situation.