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

Complement-targeting therapeutics for ischemia-reperfusion injury in transplantation and the potential for ex vivo delivery

Organ shortages and an expanding waitlist have led to increased utilization of marginal organs. All donor organs are subject to varying degrees of IRI during the transplant process. Extended criteria organs, including those from older donors and organs donated after circulatory death are especially vulnerable to ischemia-reperfusion injury (IRI). Involvement of the complement cascade in mediating IRI has been studied extensively. Complement plays a vital role in the propagation of IRI and subsequent recruitment of the adaptive immune elements. Complement inhibition at various points of the pathway has been shown to mitigate IRI and minimize future immune-mediated injury in preclinical models. The recent introduction of ex vivo machine perfusion platforms provides an ideal window for therapeutic interventions. Here we review the role of complement in IRI by organ system and highlight potential therapeutic targets for intervention during ex vivo machine preservation of donor organs.

Significance of Complement System in Ischemic Stroke: A Comprehensive Review

The complement system is an essential part of innate immunity, typically conferring protection via eliminating pathogens and accumulating debris. However, the defensive function of the complement system can exacerbate immune, inflammatory, and degenerative responses in various pathological conditions. Cumulative evidence indicates that the complement system plays a critical role in the pathogenesis of ischemic brain injury, as the depletion of certain complement components or the inhibition of complement activation could reduce ischemic brain injury. Although multiple candidates modulating or inhibiting complement activation show massive potential for the treatment of ischemic stroke, the clinical availability of complement inhibitors remains limited. The complement system is also involved in neural plasticity and neurogenesis during cerebral ischemia. Thus, unexpected side effects could be induced if the systemic complement system is inhibited. In this review, we highlighted the recent concepts and discoveries of the roles of different kinds of complement components, such as C3a, C5a, and their receptors, in both normal brain physiology and the pathophysiology of brain ischemia. In addition, we comprehensively reviewed the current development of complement-targeted therapy for ischemic stroke and discussed the challenges of bringing these therapies into the clinic. The design of future experiments was also discussed to better characterize the role of complement in both tissue injury and recovery after cerebral ischemia. More studies are needed to elucidate the molecular and cellular mechanisms of how complement components exert their functions in different stages of ischemic stroke to optimize the intervention of targeting the complement system.

Complement Activation in Liver Transplantation: Role of Donor Macrosteatosis and Implications in Delayed Graft Function

The complement system anchors the innate inflammatory response by triggering both cell-mediated and antibody-mediated immune responses against pathogens. The complement system also plays a critical role in sterile tissue injury by responding to damage-associated molecular patterns. The degree and duration of complement activation may be a critical variable controlling the balance between regenerative and destructive inflammation following sterile injury. Recent studies in kidney transplantation suggest that aberrant complement activation may play a significant role in delayed graft function following transplantation, confirming results obtained from rodent models of renal ischemia/reperfusion (I/R) injury. Deactivating the complement cascade through targeting anaphylatoxins (C3a/C5a) might be an effective clinical strategy to dampen reperfusion injury and reduce delayed graft function in liver transplantation. Targeting the complement cascade may be critical in donor livers with mild to moderate steatosis, where elevated lipid burden amplifies stress responses and increases hepatocyte turnover. Steatosis-driven complement activation in the donor liver may also have implications in rejection and thrombolytic complications following transplantation. This review focuses on the roles of complement activation in liver I/R injury, strategies to target complement activation in liver I/R, and potential opportunities to translate these strategies to transplanting donor livers with mild to moderate steatosis.

Inhibition of complement C3 might rescue vascular hyporeactivity in a conscious hemorrhagic shock rat model

BACKGROUND

Vascular hyporeactivity in severe hemorrhagic shock could induce refractory hypotension and is an important cause of death. The global acute inflammatory response induced in shock triggers the over-expression of reactive oxygen species, NO, ET1 and TNF-α, which play essential roles in the pathology of vascular hyporeactivity. This leads to a hypothesis that inhibition of the complement system, the mediator of the inflammatory cascade, might be a promising therapeutic exploration for vascular hyporeactivity.

METHODS

We use cobra venom factor (CVF) and the soluble form of CR1 (sCR1) which deplete or inhibit complement C3 respectively to examine its role in vascular hyporeactivity in a conscious hemorrhagic shock rat model.

RESULTS

We first confirmed the over-activation of C3 during shock and the down-regulation effects of CVF and sCR1 on C3. Then, both CVF and sCR1 could significantly mitigate the over-expression of serum NO, ET-1, TNF-α and reactive oxygen species. Finally, the vascular reactivity of superior mesenteric arteries (SMA) was examined in vitro, which confirmed the massive reduction of vascular reactivity in shock, which was significantly rescued by both CVF and sCR1.

CONCLUSIONS

Inhibition of C3 might improve the reactivity of SMA to norepinephrine during hemorrhagic shock possibly through the downregulation of NO, ET1, TNF-α and reactive oxygen radicals.

Targeted complement inhibition and microvasculature in transplants: a therapeutic perspective

Active complement mediators play a key role in graft-versus-host diseases, but little attention has been given to the angiogenic balance and complement modulation during allograft acceptance. The complement cascade releases the powerful proinflammatory mediators C3a and C5a anaphylatoxins, C3b, C5b opsonins and terminal membrane attack complex into tissues, which are deleterious if unchecked. Blocking complement mediators has been considered to be a promising approach in the modern drug discovery plan, and a significant number of therapeutic alternatives have been developed to dampen complement activation and protect host cells. Numerous immune cells, especially macrophages, develop both anaphylatoxin and opsonin receptors on their cell surface and their binding affects the macrophage phenotype and their angiogenic properties. This review discusses the mechanism that complement contributes to angiogenic injury, and the development of future therapeutic targets by antagonizing activated complement mediators to preserve microvasculature in rejecting the transplanted organ.

A systematic review of pharmacological treatment options used to reduce ischemia reperfusion injury in rat liver transplantation

BACKGROUND

Although animal studies models are frequently used for the purpose of attenuating ischemia reperfusion injury (IRI) in liver transplantation (LT), many of pharmacological agents have not become part of clinical routine.

METHODS

A search was performed using the PubMed database to identify agents, from which 58 articles containing 2700 rat LT procedures were selected. The identified pharmacological agents were categorized as follows: I - adenosine agonists, nitric oxide agonists, endothelin antagonists, and prostaglandins, II - Kupffer cell inactivator, III - complement inhibiter, IV - antioxidant, V - neutrophil inactivator, VI -anti-apoptosis agent, VII - heat shock protein and nuclear factor kappa B inducer, VIII - metabolic agent, IX - traditional Chinese medicine, and X - others. Meta-analysis using 7-day-survival rate was also performed with Mantel-Haenszel's Random effects model.

RESULTS

The categorization revealed that the rate of donor-treated experiments in each group was highest for agents from Group II (70%) and VII (71%), whereas it was higher for agents from Group V (83%) in the recipient-treated experiments. Furthermore, 90% of the experiments with agents in Group II provided 7-day-survival benefits. The Risk Ratio (RR) of the meta-analysis was 2.43 [95% CI: 1.88-3.14] with moderate heterogeneity. However, the RR of each of the studies was too model-dependent to be used in the search for the most promising pharmacological agent.

CONCLUSION

With regard to hepatic IRI pathology, the categorization of agents of interest would be a first step in designing suitable multifactorial and pleiotropic approaches to develop pharmacological strategies.

The current state of knowledge of hepatic ischemia-reperfusion injury based on its study in experimental models

The present review focuses on the numerous experimental models used to study the complexity of hepatic ischemia/reperfusion (I/R) injury. Although experimental models of hepatic I/R injury represent a compromise between the clinical reality and experimental simplification, the clinical transfer of experimental results is problematic because of anatomical and physiological differences and the inevitable simplification of experimental work. In this review, the strengths and limitations of the various models of hepatic I/R are discussed. Several strategies to protect the liver from I/R injury have been developed in animal models and, some of these, might find their way into clinical practice. We also attempt to highlight the fact that the mechanisms responsible for hepatic I/R injury depend on the experimental model used, and therefore the therapeutic strategies also differ according to the model used. Thus, the choice of model must therefore be adapted to the clinical question being answered.

A complement-dependent balance between hepatic ischemia/reperfusion injury and liver regeneration in mice

Massive liver resection and small-for-size liver transplantation pose a therapeutic challenge, due to increased susceptibility of the remnant/graft to ischemia reperfusion injury (IRI) and impaired regeneration. We investigated the dual role of complement in IRI versus regeneration in mice. Complement component 3 (C3) deficiency and complement inhibition with complement receptor 2-complement receptor 1-related protein y (CR2-Crry, an inhibitor of C3 activation) provided protection from hepatic IRI, and while C3 deficiency also impaired liver regeneration following partial hepatectomy (PHx), the effect of CR2-Crry in this context was dose dependent. In a combined model of IRI and PHx, either C3 deficiency or high-dose CR2-Crry resulted in steatosis, severe hepatic injury, and high mortality, whereas low-dose CR2-Crry was protective and actually increased hepatic proliferative responses relative to control mice. Reconstitution experiments revealed an important role for the C3a degradation product acylation-stimulating protein (ASP) in the balance between inflammation/injury versus regeneration. Furthermore, liver regeneration was dependent on the putative ASP receptor, C5L2. Several potential mechanisms of hepatoprotection and recovery were identified in mice treated with low-dose CR2-Crry, including enhanced IL-6 expression and STAT3 activation, reduced hepatic ATP depletion, and attenuated oxidative stress. These data indicate that a threshold of complement activation, involving ASP and C5L2, promotes liver regeneration and suggest a balance between complement-dependent injury and regeneration.

Ethanol preconditioning reduces hepatic I/R injury by inhibiting the complement system activation

BACKGROUND

Ethanol preconditioning (EtOH-PC) refers to a phenomenon in which cerebral, intestinal, and myocardial tissues are protected from the deleterious effects of ischemia/reperfusion (I/R) by prior ingestion of ethanol at low to moderate levels. Whether EtOH-PC can offer protective effects against hepatic I/R injury and whether these effects are associated with inhibition of complement activation were investigated.

METHODS

Male SD rats were divided into four groups, i.e., sham operation, ethanol control, IR, and ethanol-pretreatment I/R (EIR) groups. EtOH-PC was induced by gavaging rats with 40% ethanol at a dose of 5 g/kg body weight 24 h prior to experiment. Animal survival rate was compared. Liver function, hepatic MDA level, plasma complement C3 level, and serum hemolytic activity were determined. Histologic changes and complement C3 deposition in liver section were examined. Expression of liver complement 3 mRNA was analyzed by quantitative real-time -PCR.

RESULTS

The 14-d survival rates were remarkably higher in the EIR groups than in the corresponding IR groups when hepatic ischemia time was 110, 120, and 130 min. Serum ALT, AST, IL-1β, and liver tissue MDA were significantly lower, and histopathologic changes significantly milder in the EIR group than in the IR group (P <0.05). Compared with the IR group, both the reduction in CH50 and plasma C3 were significantly suppressed, and the staining of C3 in liver tissue significantly reduced in the EIR group. There were no significant differences of hepatic C3 mRNA among four groups.

CONCLUSIONS

Ethanol preconditioning reduces hepatic I/R injury, and the effect is associated with inhibition of complement activation.

Complement and renal transplantation: from donor to recipient

Long-term kidney graft survival is affected by different variables including donor condition, ischemia-reperfusion injury, and graft rejection during the transplantation process. The complement system is an important mediator of renal ischemia-reperfusion injury and in rejecting allografts. However, donor complement C3 seems to be crucial in renal transplantation-related injury as renal injury is attenuated in C3 deficient kidney grafts. Interestingly, before ischemia-reperfusion induced C3 expression, C3 is already induced in donors suffering from brain death. Therefore, strategies targeting complement activation in the brain-dead donor may increase graft viability and transplant outcome.

The membrane attack complex (C5b-9) in liver cold ischemia and reperfusion injury

Activation of the complement cascade represents an important event during ischemia/reperfusion injury (IRI). This work was designed to investigate the role of the membrane attack complex (MAC; C5b-9) in the pathogenesis of hepatic IRI. Livers from B&W/Stahl/rC6(+) and C6(-) rats were harvested, stored for 24 hours at 4 degrees C, and then transplanted [orthotopic liver transplantation (OLT)] to syngeneic recipients. There were 4 experimental groups: (1) C6(+)-->C6(+), (2) C6(+)-->C6(-), (3) C6(-)-->C6(+), and (4) C6(-)-->C6(-). At day +1, C6(-) OLTs showed decreased vascular congestion/necrosis, contrasting with extensive necrosis in C6(+) livers, that was independent of the recipient C6 status (Suzuki score: 7.2 +/- 0.9, 7.3 +/- 1.3, 4.5 +/- 0.6, and 4.8 +/- 0.4 for groups 1-4, respectively, P < 0.05). The liver function improved in recipients of C6(-) grafts (serum glutamic oxaloacetic transaminase: 2573 +/- 488, 1808 +/- 302, 1170 +/- 111, and 1188 +/- 184 in groups 1-4, respectively, P < 0.05). Intragraft macrophage infiltration (ED-1 immunostaining) and neutrophil infiltration (myeloperoxidase activity) were reduced in C6(-) grafts versus C6(+) grafts (P = 0.001); these data were confirmed by esterase staining (naphthol). The expression of proinflammatory interferon-gamma, interleukin-1beta, and tumor necrosis factor messenger RNA/protein was also reduced in C6(-) OLTs in comparison with C6(+) OLTs. Western blot-assisted expression of proapoptotic caspase-3 was decreased in C6(-) OLTs versus C6(+) OLTs (P = 0.006), whereas antiapoptotic Bcl-2/Bag-1 was enhanced in C6(-) OLTs compared with C6(+) OLTs (P = 0.001). Terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling staining of apoptotic cells was enhanced (P < 0.05) in C6(+) OLTs compared with C6(-) OLTs. Thus, the terminal products of the complement system are essential in the mechanism of hepatic IRI. This is the first report using a clinically relevant liver cold ischemia model to show that local MAC inhibition attenuates IRI cascade in OLT recipients.

Vascular disease in scleroderma: mechanisms of vascular injury

Vascular endothelial injury in systemic sclerosis (SSc) includes a spectrum of changes that involve predominantly the microcirculation and arterioles. The pathologic changes in the blood vessels adversely impact the physiology of many organ systems, with a reduction in the size of microvascular beds leading to decreased organ blood flow and ultimately to a state of chronic ischemia. Current hypotheses in SSc vascular disease suggest a possible chemical or infectious trigger.

Strategies of therapeutic complement inhibition

The involvement of complement in the pathogenesis of a great number of partly life threatening diseases defines the importance to develop inhibitors which specifically interfere with its deleterious action. Endogenous soluble complement-inhibitors, antibodies or low molecular weight antagonists, either blocking key proteins of the cascade reaction or neutralizing the action of the complement-derived anaphylatoxins have successfully been tested in various animal models over the past years. Promising results consequently led to first clinical trials. This review is focused on different approaches for the development of inhibitors, on their site of action in the cascade, on possible indications for complement inhibition based on experimental animal data, and on potential side effects of such treatment.

Targeted complement inhibition by C3d recognition ameliorates tissue injury without apparent increase in susceptibility to infection

Previous studies indicate a pivotal role for complement in mediating both local and remote injury following ischemia and reperfusion of the intestine. Here, we report on the use of a mouse model of intestinal ischemia/reperfusion injury to investigate the strategy of targeting complement inhibition to sites of complement activation by linking an iC3b/C3dg-binding fragment of mouse complement receptor 2 (CR2) to a mouse complement-inhibitory protein, Crry. We show that the novel CR2-Crry fusion protein targets sites of local and remote (lung) complement activation following intestinal ischemia and reperfusion injury and that CR2-Crry requires a 10-fold lower dose than its systemic counterpart, Crry-Ig, to provide equivalent protection from both local and remote injury. CR2-Crry has a significantly shorter serum half-life than Crry-Ig and, unlike Crry-Ig, had no significant effect on serum complement activity at minimum effective therapeutic doses. Furthermore, the minimum effective dose of Crry-Ig significantly enhanced susceptibility to infection in a mouse model of acute septic peritonitis, whereas the effect of CR2-Crry on susceptibility to infection was indistinguishable from that of PBS control. Thus, compared with systemic inhibition, CR2-mediated targeting of a complement inhibitor of activation improved bioavailability, significantly enhanced efficacy, and maintained host resistance to infection.

A randomized, placebo-controlled trial of complement inhibition in ischemia-reperfusion injury after lung transplantation in human beings

OBJECTIVE

Complement activation has been shown to play a significant role in ischemia-reperfusion injury after lung transplantation. TP-10 (soluble complement receptor 1 inhibitor) inhibits the activation of complement by inactivating C3a and C5a convertases. This was a clinical trial of TP-10 to reduce ischemia-reperfusion injury in lung transplantation.

METHODS

In a randomized, double-blinded, multicenter, placebo-controlled trial, 59 patients from four lung transplant programs received TP-10 (10 mg/kg, n = 28) or placebo (n = 31) before reperfusion. This dose achieved 90% complement inhibition for 24 hours, and activity had returned toward normal by 72 hours.

RESULTS

At 24 hours, 14 of 28 patients in the TP-10 group (50%) were extubated, whereas only 6 of 31 patients in the placebo group (19%) were (P = .01). The total times on the ventilator and in the intensive care unit both tended to be shorter in the TP-10 group, but these differences did not achieve statistical significance. Among patients requiring cardiopulmonary bypass (n = 5 in placebo group and n = 7 in TP-10 group), the mean duration of mechanical ventilation was reduced by 11 days in the TP-10 group (10.6 +/- 5.0 days vs 21.5 +/- 5.9 days in placebo group, P = .2). Operative deaths, incidences of infection and rejection, and length of hospital stay were not significantly different between the two groups.

CONCLUSIONS

Short-term complement inhibition with TP-10 led to early extubation in a significantly higher proportion of lung transplant recipients. The effect of TP-10 was greater among patients undergoing cardiopulmonary bypass, with a large reduction in ventilator days. Complement inhibition thus significantly decreases the duration of mechanical ventilation and could be useful in improving the outcome of lung transplant recipients.

ROLE OF C5A IN INFLAMMATORY RESPONSES

The complement system not only represents an effective innate immune mechanism of host defense to eradicate microbial pathogens, but it is also widely involved in many forms of acute and chronic inflammatory diseases including sepsis, acute lung injury, ischemia-reperfusion injury, and asthma, to give just a few examples. The complement-activated product, C5a, displays powerful biological activities that lead to inflammatory sequelae. C5a is a strong chemoattractant and is involved in the recruitment of inflammatory cells such as neutrophils, eosinophils, monocytes, and T lymphocytes, in activation of phagocytic cells and release of granule-based enzymes and generation of oxidants, all of which may contribute to innate immune functions or tissue damage. Accumulating data suggest that C5a provides a vital bridge between innate and adaptive immune functions, extending the roles of C5a in inflammation. Herein, we review human and animal data describing the cellular and molecular mechanisms of C5a in the development of inflammatory disorders, sepsis, acute lung injury, ischemia-reperfusion injury, and asthma.

IgM binding to injured tissue precedes complement activation during skeletal muscle ischemia-reperfusion

BACKGROUND

Skeletal muscle reperfusion injury is mediated by IgM natural antibodies and by complement activation, as shown by the attenuation of reperfusion injury seen in mice with no natural IgM [] and in mice deficient in complement C3 and C4 []. We postulate that tissue, when ischemic, expresses neoantigens to which preformed natural IgM antibodies bind, in turn producing harmful complement activation and reperfusion injury.

MATERIALS AND METHODS

C57Bl/6 mice were subjected to 2 h of tourniquet-induced hind limb ischemia followed by variable periods of reperfusion. Two hours of ischemia and 3 h of reperfusion produced severe muscle necrosis and edema. Deposition of IgM and C3 in tissue was assessed using immunohistochemistry on both frozen and Formalin-fixed tissue samples.

RESULTS

IgM binding to the endothelium and muscle bundles of the hind limb began during the ischemic period and continued throughout reperfusion up to 6 h. C3 deposition was not present during ischemia and, in contrast, began to appear at 1 h of reperfusion and increased progressively thereafter.

CONCLUSIONS

These data demonstrate that IgM binding to ischemic tissues precedes the damaging complement activation by a significant period of time. This has important therapeutic implications when considering anti-inflammatory therapy for reperfusion injury.

The role of the complement system in ischemia-reperfusion injury

Ischemia-reperfusion (I/R) injury is a common clinical event with the potential to seriously affect, and sometimes kill, the patient. Interruption of blood supply causes ischemia, which rapidly damages metabolically active tissues. Paradoxically, restoration of blood flow to the ischemic tissues initiates a cascade of pathology that leads to additional cell or tissue injury. I/R is a potent inducer of complement activation that results in the production of a number of inflammatory mediators. The use of specific inhibitors to block complement activation has been shown to prevent local tissue injury after I/R. Clinical and experimental studies in gut, kidney, limb, and liver have shown that I/R results in local activation of the complement system and leads to the production of the complement factors C3a, C5a, and the membrane attack complex. The novel inhibitors of complement products may find wide clinical application because there are no effective drug therapies currently available to treat I/R injuries.

Liver transplantation from non-heart-beating donors: current status and future prospects

Liver transplantation is the treatment of choice for many patients with acute and chronic liver failure, but its application is limited by a shortage of donor organs. Donor organ shortage is the principal cause of increasing waiting lists, and a number of patients die while awaiting transplantation. Non-heart-beating donor (NHBD) livers are a potential means of expanding the donor pool. This is not a new concept. Prior to the recognition of brainstem death, organs were retrieved from deceased donors only after cardiac arrest. Given the preservation techniques available at that time, this restricted the use of extrarenal organs for transplantation. In conclusion, after establishment of brain death criteria, deceased donor organs were almost exclusively from heart-beating donors (HBDs). To increase organ availability, there is now a resurgence of interest in NHBD liver transplantation. This review explores the basis for this and considers some of the published results.

Soluble complement receptor 1 preserves endothelial barrier function and microcirculation in postischemic pancreatitis in the rat

Components of the activated complement cascade are considered to play a pivotal role in ischemia-reperfusion-induced organ injury. With the use of intravital epifluorescence microscopy, we investigated the effect of complement inhibition by the recombinant soluble complement receptor 1 (sCR1; TP10) on the effect of macromolecular microvascular permeability, functional capillary perfusion, and leukocyte endothelium interaction in postischemic pancreatitis. Anaesthetized Sprague-Dawley rats were subjected to 60 min of normothermic pancreatic ischemia induced by microclipping of the blood-supplying arteries of the organ. Rats who received sCR1 (15 mg/kg body wt iv; n = 7) during reperfusion showed a significant reduction of permeability (1.77 +/- 1.34 x 10(-8) cm/s; n = 7) of tetramethylrhodamine isothiocyanate-labeled albumin injected 90 min after the onset of reperfusion compared with vehicle-treated animals (6.95 +/- 1.56 x 10(-8) cm/s; n = 7). At 120 min after the onset of reperfusion, the length of red blood cell-perfused capillaries (functional capillary density) was significantly improved (from 279 +/- 15.7 to 330 +/- 3.7 cm(-1); n = 7) and the number of leukocytes adherent to postcapillary venules was significantly reduced (from 314 +/- 87 to 163 +/- 71 mm(-2); n = 7) by sCR1 compared with vehicle treatment. Complement inhibition by sCR1 effectively ameliorates pancreatic ischemia-reperfusion-induced microcirculatory disturbances and might be considered for treatment of postischemic pancreatitis.

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.

Impact of inhibition of complement by sCR1 on hepatic microcirculation after warm ischemia

Recent observations provide evidence that complement is implicated as an important factor in the pathophysiology of ischemia/reperfusion injury (IRI). Here, we assessed the effects of complement inhibition on hepatic microcirculation by in vivo microscopy (IVM) using a rat model of warm hepatic ischemia clamping the left pedicle for 70 min. Ten animals received the physiological complement regulator soluble complement receptor type 1 (sCR1) intravenously 1 min prior to reperfusion. Controls were given an equal amount of Ringer's solution (n = 10). Microvascular perfusion and leukocyte adhesion were studied 30 to 100 min after reperfusion by IVM. Microvascular perfusion in hepatic sinusoids was significantly improved in the sCR1 group (80.6 +/- 0.6% of all observed sinusoids were perfused [sCR1] vs 67.3 +/- 1.2% [controls]). The number of adherent leukocytes was reduced in sinusoids (49.9 +/- 3.4 [sCR1] vs 312.3 +/- 14.2 in controls [adherent leukocytes per square millimeter of liver surface]; P < 0.001) as well as in postsinusoidal venules after sCR1 treatment (230.9 +/- 21.7 [sCR1] vs 1906.5 +/- 93.5 [controls] [adherent leukocytes per square millimeter of endothelial surface]; P < 0.001). Reflecting reduced hepatocyte injury, liver transaminases were decreased significantly upon sCR1 treatment compared to controls. Our results provide further evidence that complement plays a decisive role in warm hepatic IRI. Therefore, we conclude that complement inhibition by sCR1 is effective as a therapeutical approach to reduce microcirculatory disorders after reperfusion following warm organ ischemia.

Influence of humoral immunoreaction on hepatic nonparenchymal cells in ex situ xenoperfused rat livers

BACKGROUND

The influence of xenogeneic humoral immunoreaction on hepatic nonparenchymal cells (NPCs) was evaluated ex situ in xenoperfused rat livers.

METHODS

Isolated rat livers were perfused via the portal vein (PV) for 240 min. The perfusates consisted of fresh rat blood (group 1), fresh human blood (group 2), and fresh human blood containing 5 microg/mL soluble complement receptor type 1 (Group 3).

RESULTS

Deposition of human IgM and C(5b-9) complement was observed in group 2, although only human IgM deposition was detected in group 3. Portal vein pressure in group 2 rose drastically during the first 10 min. Creatine kinase BB component gradually increased in all groups, followed by an elevation in alanine aminotransferase and both parameters were significantly higher in group 2 than in groups 1 and 3. In group 2, platelet thrombi in the peripheral PVs and periportal hemorrhage were observed after 10 min, and massive necrosis around the central veins after 240 min; these changes were not observed in group 1 or 3. Production of tumor necrosis factor alpha and alpha interferon and expression of intercellular adhesion molecule 1 (ICAM-1) were lower in group 2 than in groups 1 and 3. In group 2, there were negative areas for ICAM-1 and tumor necrosis factor alpha staining around the central veins after 240 min, which were consistent with necrotic areas.

CONCLUSIONS

In xenoperfused rat livers, humoral mediators initially caused the disturbance of microcirculation, which would induce long ischemia in the pericentral areas, resulting in massive necrosis. NPC necrosis may be responsible for less production of cytokines and adhesion molecules in the xenoperfused livers.

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.

Theory and in vivo application of electroporative gene delivery

Efficient and safe methods for delivering exogenous genetic material into tissues must be developed before the clinical potential of gene therapy will be realized. Recently, in vivo electroporation has emerged as a leading technology for developing nonviral gene therapies and nucleic acid vaccines (NAV). Electroporation (EP) involves the application of pulsed electric fields to cells to enhance cell permeability, resulting in exogenous polynucleotide transit across the cytoplasmic membrane. Similar pulsed electrical field treatments are employed in a wide range of biotechnological processes including in vitro EP, hybridoma production, development of transgenic animals, and clinical electrochemotherapy. Electroporative gene delivery studies benefit from well-developed literature that may be used to guide experimental design and interpretation. Both theory and experimental analysis predict that the critical parameters governing EP efficacy include cell size and field strength, duration, frequency, and total number of applied pulses. These parameters must be optimized for each tissue in order to maximize gene delivery while minimizing irreversible cell damage. By providing an overview of the theory and practice of electroporative gene transfer, this review intends to aid researchers that wish to employ the method for preclinical and translational gene therapy, NAV, and functional genomic research.

Autoimmunity and vascular involvement in systemic sclerosis (SSc)

Endothelial injury, obliterative microvascular lesions, and increased vascular wall thickness are present in all involved organs in scleroderma. The vascular pathology is associated with altered vascular function with increased vasospasm, reduced vasodilatory capacity and increased adhesiveness of the blood vessels to platelets and lymphocytes. The extent of injury and dysfunction is reflected by changes in the circulating levels of vascular markers. The initial triggers for the vascular pathology are not known. Possible viral triggers are visited here, including cytomegalovirus in view of increased levels of anti-CMV antibodies in scleroderma, and the remarkable similarities between CMV vasculopathies and scleroderma vascular disease. Endothelial apoptosis in scleroderma may be related to viral infection, immune reactions to viral or environmental factors, reperfusion injury or to anti-endothelial antibodies. The impact of the vascular pathology on the evolution of tissue fibrosis is not known; still, cytokines (TGFbeta, IL4), vascular factors (endothelin), and growth factors (PDGF) are possibly crucial signals that link the vascular disease to tissue fibrosis. Knowledge of the regulation of these and other factors will provide the opportunity to develop more rational therapeutic approaches to the disease.

Targeting the complement system

Interest has blossomed in the development of complement inhibitors, in parallel with a growth in our understanding of the biology of the complement cascade. The first generation of designed inhibitors was based on naturally occurring complement receptors and regulatory molecules. These agents provided useful tools for exploring the role of complement in experimental models of disease, but may have limited therapeutic application in humans because of their short half-lives, limited bioavailability and possible antigenicity. More recently, humanized antibodies and synthetic molecules that block the activation of complement have been developed, which look as though they may overcome some of these difficulties. The possibility for precision inhibition of a limited part of the complement cascade, or for inhibition confined to a single organ, may offer effective therapeutic results, while avoiding the disadvantages of nonselective complement blockade. This review examines the recent evidence that complement inhibition will reduce tissue damage resulting from organ transplantation, ischaemia-reperfusion injury, cancer, glomerulonephritis and the use of extracorporeal circuits.