Diannexin, a novel annexin V homodimer, protects rat liver transplants against cold ischemia-reperfusion injury

Role of Heavy Water in Modified University of Wisconsin Solution for Extended Cold Storage of Rat Liver

To resolve the critical donor shortage worldwide, enlarging the potential donor pool to include expanded criteria donors is necessary. Despite numerous attempts to establish new preservation solutions, no dramatic innovation has occurred since University of Wisconsin (UW) solution displaced Euro Collins' solution; UW solution remains the global gold standard. We previously developed a heavy water (D2O)-containing organ storage solution, Dsol, which is effective for livers subjected to extended cold storage (CS), and reported its effectiveness. Dsol is a modified UW solution; however, the substances or conditions that exhibit a synergistic or additive effect with D2O are unclear. Here we made UWD solution by removing hydroxyethyl starch (HES) from and adding 30%-D2O to UW solution, and compared the effects of these solutions. After 48 hours of CS, the livers were reperfused at 37 °C on an isolated perfused rat liver apparatus, and their perfusion kinetics, functions, and injuries were compared. In the UW group, portal vein resistance significantly increased and the oxygen consumption rate and bile production decreased; in contrast, these changes were suppressed in the UWD group. Organ expansion and liver damage progressed in both groups. These results confirmed that the removal of HES from and addition of D2O to the UW solution reduced CS-induced cellular function impairments and microcirculatory disorders. However, to reduce injury during reperfusion after CS, it is necessary to provide conditions that inhibit injury progression after reperfusion.

Cellular and molecular mechanisms of cell damage and cell death in ischemia-reperfusion injury in organ transplantation

Ischemia-reperfusion injury (IRI) is a critical pathological condition in which cell death plays a major contributory role, and negatively impacts post-transplant outcomes. At the cellular level, hypoxia due to ischemia disturbs cellular metabolism and decreases cellular bioenergetics through dysfunction of mitochondrial electron transport chain, causing a switch from cellular respiration to anaerobic metabolism, and subsequent cascades of events that lead to increased intracellular concentrations of Na+, H+ and Ca2+ and consequently cellular edema. Restoration of blood supply after ischemia provides oxygen to the ischemic tissue in excess of its requirement, resulting in over-production of reactive oxygen species (ROS), which overwhelms the cells' antioxidant defence system, and thereby causing oxidative damage in addition to activating pro-inflammatory pathways to cause cell death. Moderate ischemia and reperfusion may result in cell dysfunction, which may not lead to cell death due to activation of recovery systems to control ROS production and to ensure cell survival. However, prolonged and severe ischemia and reperfusion induce cell death by apoptosis, mitoptosis, necrosis, necroptosis, autophagy, mitophagy, mitochondrial permeability transition (MPT)-driven necrosis, ferroptosis, pyroptosis, cuproptosis and parthanoptosis. This review discusses cellular and molecular mechanisms of these various forms of cell death in the context of organ transplantation, and their inhibition, which holds clinical promise in the quest to prevent IRI and improve allograft quality and function for a long-term success of organ transplantation.

Annexin A5 ameliorates traumatic brain injury-induced neuroinflammation and neuronal ferroptosis by modulating the NF-ĸB/HMGB1 and Nrf2/HO-1 pathways

Traumatic brain injury often causes poor outcomes and has few established treatments. Neuroinflammation and ferroptosis hinder therapeutic progress in this domain. Annexin A5 (A5) has anticoagulant, anti-apoptotic and anti-inflammatory bioactivities. However, its protective effects on traumatic brain injury remain unclear. Thus, we explored whether inhibiting ferroptosis and neuroinflammation using A5 could ameliorate traumatic brain injury. We injected recombinant A5 (50 µg/kg) in the tail vein of mice 30 min after fluid percussion injury. We then assessed modified neurologic severity scores, Morris water maze performance, rotarod test performance, brain water content, and blood-brain barrier permeability to document the neuroprotective effects of A5. Two days after the traumatic brain injury, we collected injured cortex tissues for western blot, Perl's staining, apoptosis staining, Nissl staining, immunofluorescence/immunohistochemistry, and enzyme-linked immunosorbent assay. We also quantified superoxide dismutase and glutathione peroxidase activity and glutathione and malondialdehyde levels. A5 improved neurological deficits, weight loss, cerebral hypoperfusion, brain edema, blood-brain barrier disruption, neuronal apoptosis, and ferroptosis. It also increased the ratio of M2/M1 phenotype microglia, reduced interleukin 1β and 6 levels, decreased peripheral immune cell infiltration, and increased interleukin 10 levels. A5 reduced neuronal iron accumulation, p53-related cell death, and oxidative stress damage. Finally, A5 downregulated HMGB1 and NF-ĸB pathways and upregulated the nuclear erythroid 2-related factor (Nrf2) and HO-1 pathways. These results suggest that A5 exerts neuroprotection in traumatic brain injury mice and ameliorates neuroinflammation, oxidative stress, and ferroptosis by regulating the NF-kB/HMGB1 pathway and the Nrf2/HO-1 antioxidant system.

Hyperinflammation, apoptosis, and organ damage

The cytokine storm (CS) in hyperinflammation is characterized by high levels of cytokines, extreme activation of innate as well as adaptive immune cells and initiation of apoptosis. High levels of apoptotic cells overwhelm the proper recognition and removal system of these cells. Phosphatidylserine on the apoptotic cell surface, which normally provides a recognition signal for removal, becomes a target for hemostatic proteins and secretory phospholipase A2. The dysregulation of these normal pathways in hemostasis and the inflammasome result in a prothrombotic state, cellular death, and end-organ damage. In this review, we provide the argument that this imbalance in recognition and removal is a common denominator regardless of the inflammatory trigger. The complex reaction of the immune defense system in hyperinflammation leads to self-inflicted damage. This common endpoint may provide additional options to monitor the progression of the inflammatory syndrome, predict severity, and may add to possible treatment strategies.

Therapeutic Potential of Annexins in Sepsis and COVID-19

Sepsis is a continuing problem in modern healthcare, with a relatively high prevalence, and a significant mortality rate worldwide. Currently, no specific anti-sepsis treatment exists despite decades of research on developing potential therapies. Annexins are molecules that show efficacy in preclinical models of sepsis but have not been investigated as a potential therapy in patients with sepsis. Human annexins play important roles in cell membrane dynamics, as well as mediation of systemic effects. Most notably, annexins are highly involved in anti-inflammatory processes, adaptive immunity, modulation of coagulation and fibrinolysis, as well as protective shielding of cells from phagocytosis. These discoveries led to the development of analogous peptides which mimic their physiological function, and investigation into the potential of using the annexins and their analogous peptides as therapeutic agents in conditions where inflammation and coagulation play a large role in the pathophysiology. In numerous studies, treatment with recombinant human annexins and annexin analogue peptides have consistently found positive outcomes in animal models of sepsis, myocardial infarction, and ischemia reperfusion injury. Annexins A1 and A5 improve organ function and reduce mortality in animal sepsis models, inhibit inflammatory processes, reduce inflammatory mediator release, and protect against ischemic injury. The mechanisms of action and demonstrated efficacy of annexins in animal models support development of annexins and their analogues for the treatment of sepsis. The effects of annexin A5 on inflammation and platelet activation may be particularly beneficial in disease caused by SARS-CoV-2 infection. Safety and efficacy of recombinant human annexin A5 are currently being studied in clinical trials in sepsis and severe COVID-19 patients.

Secretory phospholipase A2 in SARS-CoV-2 infection and multisystem inflammatory syndrome in children (MIS-C)

Secretory phospholipase 2 (sPLA2) acts as a mediator between proximal and distal events of the inflammatory cascade. Its role in SARS-CoV-2 infection is unknown, but could contribute to COVID-19 inflammasome activation and cellular damage. We present the first report of plasma sPLA2 levels in adults and children with COVID-19 compared with controls. Currently asymptomatic adults with a history of recent COVID-19 infection (≥4 weeks before) identified by SARS-CoV-2 IgG antibodies had sPLA2 levels similar to those who were seronegative (9 ± 6 vs.17 ± 28 ng/mL, P = 0.26). In contrast, children hospitalized with severe COVID-19 had significantly elevated sPLA2 compared with those with mild or asymptomatic SARS-CoV-2 infection (269 ± 137 vs. 2 ± 3 ng/mL, P = 0.01). Among children hospitalized with multisystem inflammatory syndrome in children (MIS-C), all had severe disease requiring pediatric intensive care unit (PICU) admission. sPLA2 levels were significantly higher in those with acute illness <10 days versus convalescent disease ≥10 days (540 ± 510 vs. 2 ± 1, P = 0.04). Thus, sPLA2 levels correlated with COVID-19 severity and acute MIS-C in children, implicating a role in inflammasome activation and disease pathogenesis. sPLA2 may be a useful biomarker to stratify risk and guide patient management for children with acute COVID-19 and MIS-C. Therapeutic compounds targeting sPLA2 and inflammasome activation warrant consideration.

Diannexin Can Ameliorate Acute Respiratory Distress Syndrome in Rats by Promoting Heme Oxygenase-1 Expression

Background

The recombinant protein diannexin can inhibit platelet-mediated events, which contribute to acute respiratory distress syndrome (ARDS). Here, we investigated the effect of diannexin and its effect on heme oxygenase-1 (HO-1) in ARDS.

Methods

A total of 32 rats were randomized into sham, ARDS, diannexin (D), and diannexin+HO-1 inhibitor (DH) groups. Alveolar-capillary permeability was evaluated by testing the partial pressure of oxygen to fraction of inspired oxygen (PaO₂/FiO₂) ratio, lung wet/dry weight ratio, and protein levels in the lung. Inflammation was assessed by measuring cytokine levels in the bronchial alveolar lavage fluid (BALF) and serum and nuclear factor-κB (NF-κB) in the lung tissue. Inducible nitric oxide synthase (iNOS), malondialdehyde (MDA), and myeloperoxidase (MPO) were measured to evaluate the oxidative stress response. Lung tissue pathology and apoptosis were also evaluated. We measured HO-1 expression in the lung tissue to investigate the effect of diannexin on HO-1 in ARDS.

Results

Compared with the ARDS group, diannexin improved PaO₂/FiO₂, lung wet/dry weight ratio, and protein levels in the BALF and decreased levels of cytokines and NF-κB in the lung and serum. Diannexin inhibited the oxidative stress response and significantly ameliorated pathological lung injury and apoptosis. The partial reversal of diannexin effects by a HO-1 inhibitor suggests that diannexin may promote HO-1 expression to ameliorate ARDS.

Conclusions

We showed that diannexin can improve alveolar-capillary permeability, inhibit the oxidative stress response and inflammation, and protect against ARDS-induced lung injury and apoptosis.

Plasma microparticles of sickle patients during crisis or taking hydroxyurea modify endothelium inflammatory properties

Microparticles (MPs) are submicron extracellular vesicles exposing phosphatidylserine (PS), detected at high concentration in the circulation of sickle cell anemia (SS) patients. Several groups studied the biological effects of MPs generated ex vivo. Here, we analyzed for the first time the impact of circulating MPs on endothelial cells (ECs) from 60 sickle cell disease (SCD) patients. MPs were collected from SCD patients and compared with MPs isolated from healthy individuals (AA). Other plasma MPs were purified from SS patients before and 2 years after the onset of hydroxyurea (HU) treatment or during a vaso-occlusive crisis and at steady-state. Compared with AA MPs, SS MPs increased EC ICAM-1 messenger RNA and protein levels, as well as neutrophil adhesion. We showed that ICAM-1 overexpression was primarily caused by MPs derived from erythrocytes, rather than from platelets, and that it was abolished by MP PS capping using annexin V. MPs from SS patients treated with HU were less efficient to induce a proinflammatory phenotype in ECs compared with MPs collected before therapy. In contrast, MPs released during crisis increased ICAM-1 and neutrophil adhesion levels, in a PS-dependent manner, compared with MPs collected at steady-state. Furthermore, neutrophil adhesion was abolished by a blocking anti-ICAM-1 antibody. Our study provides evidence that MPs play a key role in SCD pathophysiology by triggering a proinflammatory phenotype of ECs. We also uncover a new mode of action for HU and identify potential therapeutics: annexin V and anti-ICAM-1 antibodies.

Phosphatidylserine is an overlooked mediator of COVID-19 thromboinflammation

A ubiquitous component of cell membrane, phosphatidylserine (PS), is likely to play a major, but as yet unrecognized, role in the thromboinflammation of COVID-19 and other critical illnesses. PS is present in all plasma membranes but is "hidden" on the inner surface by the action of an ATP-requiring enzyme. Failure of PS to be sequestered on the inner surface of cell membranes, release of PS-containing microparticles from cells, or shedding of enveloped viruses allows it to interact with extracellular proteins, including those of the coagulation and complement systems. Detection and quantification of circulating PS is not standardized, and current methodologies have either focused on circulating cellular elements or subcellular plasma components, but not both. PS may also promote thromboinflammation without circulating if expressed on the surface of endothelial cells, a condition that might only be documented if novel imaging techniques are developed. Research into the role of PS in inflammation and coagulation, called here a "procoagulant phospholipidopathy" may provide novel insights and therapeutic approaches for patients with a variety of illnesses.

Protective Effect of Phosphatidylserine Blockade in Hemorrhagic Shock

BACKGROUND

Phosphatidylserine (PS) is a key cell membrane phospholipid normally maintained on the inner cell surface but externalizes to the outer surface in response to cellular stress. We hypothesized that PS exposure mediates organ dysfunction in hemorrhagic shock. Our aims were to evaluate PS blockade on (1) pulmonary, (2) renal, and (3) gut function, as well as (4) serum lysophosphatidic acid (LPA), an inflammatory mediator generated by PS externalization, as a possible mechanism mediating organ dysfunction.

MATERIALS AND METHODS

Rats were either (1) monitored for 130 min (controls, n = 3), (2) hemorrhaged then resuscitated (hemorrhage only group, n = 3), or (3) treated with Diannexin (DA), a PS blocking agent, followed by hemorrhage and resuscitation (DA + hemorrhage group, n = 4). Pulmonary dysfunction was assessed by arterial partial pressure of oxygen, renal dysfunction by serum creatinine, and gut dysfunction by mesenteric endothelial permeability (L_P). LPA levels were measured in all groups.

RESULTS

Pulmonary: there was no difference in arterial partial pressure of oxygen between groups. Renal: after resuscitation, creatinine levels were lower after PS blockade with DA versus hemorrhage only group (P = 0.01). Gut: L_P was decreased after PS blockade with DA versus hemorrhage only group (P < 0.01). Finally, LPA levels were also lower after PS blockade with DA versus the hemorrhage only group but higher than the control group (P < 0.01).

CONCLUSIONS

PS blockade with DA decreased renal and gut dysfunction associated with hemorrhagic shock and attenuated the magnitude of LPA generation. Our findings suggest potential for therapeutic targets in the future that could prevent organ dysfunction associated with hemorrhagic shock.

Protective effect of phosphatidylserine blockade in sepsis induced organ dysfunction

BACKGROUND

Phosphatidylserine is usually an intracellularly oriented cell membrane phospholipid. Externalized phosphatidylserine on activated cells is a signal for phagocytosis. In sepsis, persistent phosphatidylserine exposure is also a signal for activation of the coagulation and inflammatory cascades. As such, phosphatidylserine may be a key molecule in sepsis induced cellular and organ injury. We hypothesize that phosphatidylserine blockade provides a protective effect in sepsis induced organ dysfunction.

METHODS

Sepsis was induced in adult female rats using an endotoxin model. Diannexin, a homodimer of annexin A5, was administered for phosphatidylserine blockade. Rats were allocated to control (n = 5), sepsis (n = 6), or sepsis and phosphatidylserine blockade (n = 9) groups. Gut, pulmonary, renal, and hematologic dysfunctions were evaluated by mesenteric microvascular fluid leak, partial pressure of oxygen, serum creatinine, activated clotting time, and glomerular fibrin deposition, respectively.

RESULTS

Rats in the sepsis group demonstrated gut, renal, and hematologic dysfunction. Phosphatidylserine blockade reversed signs of gut dysfunction and mesenteric microvascular leak (P < .01). In addition, phosphatidylserine blockade corrected systemic coagulopathy, as measured by activated clotting time (P = .03) and glomerular fibrin deposition (P = .008). There was no difference in renal dysfunction (P = .1) or pulmonary dysfunction in any of the groups (P = .6).

CONCLUSION

In sepsis, phosphatidylserine blockade had a protective effect on gut dysfunction and coagulopathy. Increased phosphatidylserine exposure may be a key mediator of organ dysfunction and coagulopathy during sepsis. These data may provide insights into novel treatment options for septic patients.

Heme Oxygenase 1 Attenuates Hypoxia-Reoxygenation Injury in Mice Liver Sinusoidal Endothelial Cells

BACKGROUND

Heme oxygenase 1 (HO-1), a heat shock protein, can be involved in the resolution of inflammation by modulating cytokine expression and apoptotic cell death. Based on recent evidence that liver sinusoidal endothelial cells (LSECs) is the critical target in early period of liver ischemia-reperfusion injury (IRI), this study aims to clarify whether overexpression of HO-1 gene provides a protective effect on mice LSECs.

METHODS

LSECs were transfected with adenovirus vectors encoding mice HO-1 gene (Ad-HO-1) or green fluorescent protein. Controls were not infected with any vector. LSECs were then treated with hypoxic or normoxic culture. We used low serum culture medium and hypoxia-reoxygenation (H-R) conditions to cause IRI in vitro. The transfection efficiency of HO-1 gene in LSECs, after 48 hours of transfection, and the effect of HO-1 on the model of H-R injury in LSECs were observed.

RESULTS

Transfection of LSECs with Ad-HO-1 was at an optimal dose (multiplicity of infection = 80) to markedly express HO-1 mRNA and protein. Groups of overexpressed HO-1 showed lower levels of inflammatory factor mediators IL-6 and TNF-α. Survival rate of the cells after H-R injury was higher and attributed to overexpressed HO-1. In contrast, the control adenovirus expressing the enhanced green fluorescent protein failed to induce HO-1 expression and stimulated cell apoptosis. HO-1 expression was downregulated in all H-R groups compared with normoxia groups, which may be related to the disruption of the LSEC structure.

CONCLUSIONS

Upregulation of HO-1 can attenuate H-R injury in LSECs by inhibiting proinflammatory cytokine release and diminishing apoptotic cell death.

Extracellular vesicles: how they interact with endothelium, potentially contributing to metastatic cancer cell implants

Extracellular vesicles (EV) are blebs of cellular membranes, which entrap small portions of subjacent cytosol. They are released from a variety of cells, circulate in the blood for an unknown length of time and come to rest on endothelial surfaces. They contribute to an array of physiologic pathways, the complexity of which is still being investigated. They contribute to metastatic malignant cell implants and tumor-related angiogenesis, possibly abetted by the tissue factor that they carry. It is thought that the adherence of the EV to endothelium is dependent upon a combination of their P-selectin glycoprotein ligand-1 and exposed phosphatidylserine, the latter of which is normally hidden on the inner bilayer of the intact cellular membrane. This manuscript reviews what is known about EV origins, their clearance from the circulation and how they contribute to malignant cell implants upon endothelium surfaces and subsequent tumor growth.

DIANNEXIN DOWN-MODULATES TNF-INDUCED ENDOTHELIAL MICROPARTICLE RELEASE BY BLOCKING MEMBRANE BUDDING PROCESS

BACKGROUND

Microparticles are now recognised as true biological effectors with a role in immunopathology through their ability to disseminate functional properties. Diannexin, a homodimer of annexin V, binds to PS with a higher affinity and longer blood half-life than the monomer, inhibits prothrombinase complex activity thereby diminishing coagulation and reperfusion injury mediators and prevent microvesicle-mediated material transfer. Our aim was to determine if Diannexin could modulate microparticle production by endothelial cells by interacting with the phosphatidylserine exposure occurring during the release of these vesicles.

RESULTS

In this study we showed that fluorescently labelled Diannexin binds to calcimycin-activated endothelial cells but not to resting cells. After overnight incubation, Diannexin enters cells and their released MP carry Diannexin. Some Diannexin seems to be processed via early endosomes and later is found in lysosomes. Both unlabelled Diannexin and fluorescent Diannexin inhibit MP release from TNF-activated endothelial cells. However, Diannexin treatment does not prevent endothelial activation by TNF. In addition, the inhibitory effect of Diannexin on MP release could be observed when cells were pre-, concomitantly or post-treated with cytokines. Scanning electron microscopy showed differences in the numbers and types of protuberances at the cell surface when cells were treated or not with Diannexin. Finally, there is no apparent congruency between fluorescent Diannexin labelling and surface protuberances as shown by correlative microscopy.

CONCLUSIONS

Altogether these data suggest that Diannexin can inhibit endothelial vesiculation by binding PS present either at the cell surface or at the level of the inner leaflet of the plasma membrane.

Annexin V homodimer protects against ischemia reperfusion-induced acute lung injury in lung transplantation

OBJECTIVE

We hypothesized that administration of a homodimer of recombinant annexin V, diannexin, could shield phosphatidylserine on the endothelium, and inhibit leukocyte and platelet adhesion, thereby potentially reducing ischemia reperfusion injury (IRI) in lung transplantation. This hypothesis was tested using a rat syngeneic single left-lung transplant model.

METHODS

Rats were randomly assigned to receive diannexin (DN group; n = 10) or normal saline (control group; n = 10). Diannexin (1000 μg/kg) was administered to the donor lung in the pulmonary flush solution, and to the recipient intravenously, 5 minutes after initiation of reperfusion. Grafts were reperfused for 2 hours.

RESULTS

The transplanted grafts in the DN group performed significantly better in gas exchange with higher partial pressure of oxygen (control group: 179 ± 121 vs DN group: 330 ± 54 mm Hg; P = .007) and lower partial pressure of carbon dioxide (control: 55.1 ± 26 vs DN: 34.2 ± 11 mm Hg; P = .04), as well as lower peak airway pressure (control: 20.5 ± 8.5 vs DN: 12.0 ± 7.9 cm H2O; P = .035) after 2 hours of reperfusion. Wet-to-dry lung weight ratio (P = .054), and alveolar fibrin deposition score (P = .04), were reduced in the DN group. Caspase-cleaved cytokeratin 18 in plasma (a marker of epithelial apoptosis) was significantly reduced in the DN group (P = .013). Furthermore, gene-expression levels of proinflammatory cytokines in the transplanted graft, including interleukin-6 (P = .04) and macrophage inflammatory protein 2 (P = .03) were significantly decreased in the DN group.

CONCLUSIONS

A homodimer of recombinant annexin V reduced ischemia reperfusion injury in a lung transplant animal model, by reducing cell death and tissue inflammation.

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.

T-cell immunoglobulin and mucin domain 4 (TIM-4) signaling in innate immune-mediated liver ischemia-reperfusion injury

Hepatic ischemia-reperfusion injury (IRI), an innate immunity-driven inflammation response, occurs in multiple clinical settings including liver resection, transplantation, trauma, and shock. T-cell immunoglobulin and mucin (TIM)-4, the only TIM protein not expressed on T cells, is found on macrophages and dendritic cells. The regulatory function of macrophage TIM-4 in the engulfment of apoptotic/necrotic bodies in innate immunity-mediated disease states remains unknown. This study focuses on the putative role of TIM-4 signaling in a model of liver warm ischemia (90 minutes) and reperfusion. The ischemia insult triggered TIM-4 expression by stressed hepatocellular phosphatidylserine (PS) presentation, peaking at 6 hours of reperfusion, and coinciding with the maximal hepatocellular damage. TIM-4-deficient or wild-type WT mice treated with antagonistic TIM-4 monoclonal antibody (mAb) were resistant against liver IRI, evidenced by diminished serum alanine aminotransferase (sALT) levels and well-preserved hepatic architecture. Liver hepatoprotection rendered by TIM-4 deficiency was accompanied by diminished macrophage infiltration/chemoattraction, phagocytosis, and activation of Toll-like receptor (TLR)2/4/9-dependent signaling. Correlating with in vivo kinetics, the peak of TIM-4 induction in lipopolysaccharide (LPS)-activated bone marrow derived-macrophages (BMM) was detected in 6-hour cultures. To mimic liver IRI, we employed hydrogen peroxide-necrotic hepatocytes, which readily present PS. Indeed, necrotic hepatocytes were efficiently captured/engulfed by WT (TIM-4+) but not by TIM-4-deficient BMM. Finally, in a newly established model of liver IRI, adoptive transfer of WT but not TIM-4-deficient BMM readily recreated local inflammation response/hepatocellular damage in the CD11b-DTR mouse system.

CONCLUSION

These findings document the importance of macrophage-specific TIM-4 activation in the mechanism of hepatic IRI. Macrophage TIM-4 may represent a therapeutic target to minimize innate inflammatory responses in IR-stressed organs.

CD39 modulates hematopoietic stem cell recruitment and promotes liver regeneration in mice and humans after partial hepatectomy

OBJECTIVE

To study molecular mechanisms involved in hematopoietic stem cell (HSC) mobilization after liver resection and determine impacts on liver regeneration.

BACKGROUND

Extracellular nucleotide-mediated cell signaling has been shown to boost liver regeneration. Ectonucleotidases of the CD39 family are expressed by bone marrow-derived cells, and purinergic mechanisms might also impact mobilization and functions of HSC after liver injury.

METHODS

Partial hepatectomy was performed in C57BL/6 wild-type, Cd39 ectonucleotidase-null mice and in chimeric mice after transplantation of wild-type or Cd39-null bone marrow. Bone marrow-derived HSCs were purified by fluorescence-activated cell sorting and administered after hepatectomy. Chemotactic studies were performed to examine effects of purinergic receptor agonists and antagonists in vitro. Mobilization of human HSCs and expression of CD39 were examined and linked to the extent of resection and liver tests.

RESULTS

Subsets of HSCs expressing Cd39 are preferentially mobilized after partial hepatectomy. Chemotactic responses of HSCs are increased by CD39-dependent adenosine triphosphate hydrolysis and adenosine signaling via A2A receptors in vitro. Mobilized Cd39 HSCs boost liver regeneration, potentially limiting interleukin 1β signaling. In clinical studies, mobilized human HSCs also express CD39 at high levels. Mobilization of HSCs correlates directly with the restoration of liver volume and function after partial hepatectomy.

CONCLUSIONS

We demonstrate CD39 to be a novel HSC marker that defines a functionally distinct stem cell subset in mice and humans. HSCs are mobilized after liver resection, limit inflammation, and boost regeneration in a CD39-dependent manner. These observations have implications for monitoring and indicate future therapeutic avenues.

Canine tracheal cartilage cryopreservation: freezing injury is not related to caspase-3 expression

Currently, there are no surgical strategies to treat tracheal lesions longer than 7 cm. Such patients are not candidates for tracheal resection or end-to-end anastomosis and are thus left with only repeated palliative procedures to relieve their respiratory insufficiency. Experimental studies using cryopreserved trachea have produced contradictory results, limiting the clinical application of this technique. We evaluated caspase-3 expression and the histological integrity of canine tracheal cartilage cryopreserved using two different solutions, two temperatures, and varying lengths of storage time. Thirty canine tracheal segments of 5 rings were studied. Group 1: Control without cryopreservation. Groups 2 and 4: Cryopreserved in F12K media with 20% fetal bovine serum (FBS) at -70°C for 48 hours. Groups 3 and 5: Cryopreserved in 90% FBS at -70°C for 48 hours. Groups 4 and 5 were then stored for 15 days in liquid nitrogen. All of the segments were thawed, fixed in wax, and cut into rings. Three rings were selected for caspase-3 expression and histological evaluation. Staining of cartilage matrices was significantly modified in the tracheal segments of Group 5. The central region of the cartilage ring was more vulnerable to the effects of freezing than the edges. Under the same cryopreservation temperature and storage time, tracheal cartilage integrity is better preserved when F12K media is used. Caspase-3 expression is not related to cartilage injury from the cryopreservation process.

Diannexin, an annexin A5 homodimer, binds phosphatidylserine with high affinity and is a potent inhibitor of platelet-mediated events during thrombus formation

BACKGROUND

Shielding of procoagulant phosphatidylserine (PS) with annexin A5 attenuates thrombosis, but annexin A5 (35.7 kDa) is rapidly cleared from the circulation. In contrast, Diannexin, a 73.1 kDa homodimer of annexin A5, has an extended half-life.

OBJECTIVES

To quantify the affinity of Diannexin for PS, examine its interaction with activated platelets and determine its effects on platelet-mediated events during thrombus formation.

METHODS

The affinities of Diannexin and annexin A5 for PS-containing lipid bilayers were compared using surface plasmon resonance, and binding to activated platelets was assessed by flow cytometry. Calibrated automated thrombography and thromboelastography were employed to study the effects of Diannexin on thrombin generation and platelet-fibrin clot formation, respectively, whereas intravital videomicroscopy was used to examine its effect on platelet accumulation and activation after laser-induced injury to murine cremaster arterioles, and a tail tip bleeding model was used to explore its effects on hemostasis.

RESULTS

Diannexin and annexin A5 bind PS with K(D) values of 0.6 and 5 nm, respectively, and both bind to the same subpopulation of PS-exposing platelets. Diannexin inhibited thrombin generation and platelet-fibrin clot formation in vitro at 10 nm (P<0.05-0.001 compared with control), and reduced platelet accumulation at 1 μg g(-1) (P<0.05) and activation at 0.25 μg g(-1) (P<0.001) in experimentally induced arterial thrombi in mice while increasing blood loss at 1 μg g(-1) (P<0.01).

CONCLUSIONS

Diannexin binds to PS with high affinity and is a potent inhibitor of platelet-mediated events during thrombus formation.

Recent advances in immunosuppressive therapy for prevention of renal allograft rejection

PURPOSE OF REVIEW

Current immunosuppressive therapies are highly successful at regulating acute allograft rejection and inducing long-term transplanted kidney survival; however, currently available medications are associated with generalized immune suppression and drug toxicities, including nephrotoxicity. In recent years, advances in immunosuppression that target specific pathways involved in immune activation have been developed.

RECENT FINDINGS

In particular, promising medications are currently under evaluation that target ischemia-reperfusion injury as well as the cellular and humoral branches of the adaptive immune response. Targets of T-cell-mediated activation include antibodies and fusion proteins interfering with LFA-1/ICAM-1, CD2/LFA-3, CD40/CD154, and CD28/B7.1 and B7.2 interactions. Intracellular targets involved in T- and B-cell activation pathways are being evaluated, including protein kinase C inhibitors, Janus-associated kinase (JAK) inhibitors, and proteasome inhibitors. Several new medications demonstrate promise in inhibiting donor-directed humoral immunity by targeting B-cell-activating factor (BAFF) and complement activation pathways.

SUMMARY

The present review evaluates the recent clinical advances in immunosuppressive therapies for kidney transplantation. Publications regarding advances in immunosuppressive therapies over the past year were evaluated in the context of the specific immune pathways involved in allograft rejection.

Sotrastaurin, a protein kinase C inhibitor, ameliorates ischemia and reperfusion injury in rat orthotopic liver transplantation

Sotraustaurin (STN), a small molecule, targeted protein kinase C (PKC) inhibitor that prevents T-lymphocyte activation via a calcineurin-independent pathway, is currently being tested in Phase II renal and liver transplantation clinical trials. We have documented the key role of activated T cells in the inflammation cascade leading to liver ischemia/reperfusion injury (IRI). This study explores putative cytoprotective functions of STN in a clinically relevant rat model of hepatic cold ischemia followed by orthotopic liver transplantation (OLT). Livers from Sprague-Dawley rats were stored for 30 h at 4°C in UW solution, and then transplanted to syngeneic recipients. STN treatment of liver donors/recipients or recipients only prolonged OLT survival to >90% (vs. 40% in controls), decreased hepatocellular damage and improved histological features of IRI. STN treatment decreased activation of T cells, and diminished macrophage/neutrophil accumulation in OLTs. These beneficial effects were accompanied by diminished apoptosis, NF-κB/ERK signaling, depressed proapoptotic cleaved caspase-3, yet upregulated antiapoptotic Bcl-2/Bcl-xl and hepatic cell proliferation. In vitro, STN decreased PKCθ/IκBα activation and IL-2/IFN-γ production in ConA-stimulated spleen T cells, and diminished TNF-α/IL-1β in macrophage-T cell cocultures. This study documents positive effects of STN on liver IRI in OLT rat model that may translate as an additional benefit of STN in clinical liver transplantation.

Diannexin protects against renal ischemia reperfusion injury and targets phosphatidylserines in ischemic tissue

Renal ischemia/reperfusion injury (IRI) frequently complicates shock, renal transplantation and cardiac and aortic surgery, and has prognostic significance. The translocation of phosphatidylserines to cell surfaces is an important pro-inflammatory signal for cell-stress after IRI. We hypothesized that shielding of exposed phosphatidylserines by the annexin A5 (ANXA5) homodimer Diannexin protects against renal IRI. Protective effects of Diannexin on the kidney were studied in a mouse model of mild renal IRI. Diannexin treatment before renal IRI decreased proximal tubule damage and leukocyte influx, decreased transcription and expression of renal injury markers Neutrophil Gelatinase Associated Lipocalin and Kidney Injury Molecule-1 and improved renal function. A mouse model of ischemic hind limb exercise was used to assess Diannexin biodistribution and targeting. When comparing its biodistribution and elimination to ANXA5, Diannexin was found to have a distinct distribution pattern and longer blood half-life. Diannexin targeted specifically to the ischemic muscle and its affinity exceeded that of ANXA5. Targeting of both proteins was inhibited by pre-treatment with unlabeled ANXA5, suggesting that Diannexin targets specifically to ischemic tissues via phosphatidylserine-binding. This study emphasizes the importance of phosphatidylserine translocation in the pathophysiology of IRI. We show for the first time that Diannexin protects against renal IRI, making it a promising therapeutic tool to prevent IRI in a clinical setting. Our results indicate that Diannexin is a potential new imaging agent for the study of phosphatidylserine-exposing organs in vivo.

Diannexin decreases inflammatory cell infiltration into the islet graft, reduces β-cell apoptosis, and improves early graft function

BACKGROUND

A major unmet challenge is to reduce the islet mass needed for insulin independence in type 1 diabetic recipients after islet transplantation. The recombinant homodimer of human annexin V, diannexin, has completed a Phase II Clinical Trial in Kidney Transplantation (NCT00615966).

METHODS

We developed a marginal islet mass transplantation model (10-12 islets per gram of recipient body weight) and investigated whether diannexin prevents β-cell apoptosis and improves islet graft function. Diannexin was administered to islet cell donors shortly before pancreas harvest, added to isolation reagents, and infused into recipients at the time of transplantation and repeated daily until day 4.

RESULTS

In the syngeneic marginal islet mass transplantation model, the median time needed to achieve normoglycemia was reduced from 17.0 days among untreated controls to 3.5 days among diannexin-treated recipients (P=0.004). Histologic analysis of islet grafts harvested on day 3 posttransplantation revealed decreased macrophage (44.7%±9.8% vs. 19.2%±3.2%, P=0.007) and T-cell infiltration (25.9%±5.5% vs. 9.1%±1.1%, P=0.004), and a lower rate of islet cell apoptosis (20.5%±2.8% vs. 7.6%±2.3%, P=0.01) with diannexin treatment. Expression profiling of the islet grafts showed significantly lower levels of mRNA for the proapoptotic molecule Bid, but higher levels of interleukin-6, interferon-γ, and immunosuppressive cytokine interleukin-10.

CONCLUSIONS

Our findings demonstrate that diannexin improves the early function of marginal mass islet grafts, and its effects are associated with reductions in inflammatory cell infiltration and β-cell death by apoptosis after islet transplantation.

Annexin 1 mimetic peptide protects against renal ischemia/reperfusion injury in rats

Inflammation is currently recognized as a key mechanism in the pathogenesis of renal ischemia-reperfusion (I/R) injury. The importance of infiltrating neutrophil, lymphocytes, and macrophage in this kind of injury has been assessed with conflicting results. Annexin 1 is a protein with potent neutrophil anti-migratory activity. In order to evaluate the effects of annexin A1 on renal I/R injury, uninephrectomized rats received annexin A1 mimetic peptide Ac2-26 (100 μg) or vehicle before 30 min of renal artery clamping and were compared to sham surgery animals. Annexin A1 mimetic peptide granted a remarkable protection against I/R injury, preventing glomerular filtration rate and urinary osmolality decreases and acute tubular necrosis development. Annexin A1 infusion aborted neutrophil extravasation and attenuated macrophage infiltration but did not prevent tissue lymphocyte traffic. I/R increased annexin A1 expression (assessed by transmission electron microscopy) in renal epithelial cells, which was attenuated by exogenous annexin A1 infusion. Additionally, annexin A1 reduced I/R injury in isolated proximal tubules suspension. Annexin A1 protein afforded striking functional and structural protection against renal I/R. These results point to an important role of annexin A1 in the epithelial cells defense against I/R injury and indicate that neutrophils are key mediators for the development of tissue injury after renal I/R. If these results were confirmed in clinical studies, annexin A1 might emerge as an important tool to protect against I/R injury in renal transplantation and in vascular surgery.

Diannexin reduces no-reflow after reperfusion in rabbits with large ischemic myocardial risk zones

INTRODUCTION AND AIMS

In patients with ST-segment elevation myocardial infarction who receive percutaneous coronary intervention and stenting, a large zone with no-reflow is associated with adverse outcomes. During myocardial ischemia/reperfusion, phosphatidylserine (PS) translocates to the surface of endothelial cells triggering attachment of platelets and leukocytes, thus impairing microvascular blood flow. Diannexin, a recombinant dimer of the endogenous human annexin V protein, binds PS and thus inhibits the adverse effects of PS. It has been shown to attenuate postischemic reperfusion injury in several experimental models. We speculated that Diannexin would reduce no-reflow in the heart after coronary artery occlusion (CAO) and reperfusion. Rabbits received: (1) Diannexin 5 min pre-CAO (diannexin pre ischemia [DPI], 400 μg/kg, n = 17), or (2) Diannexin 5 min pre-coronary reperfusion (diannexin pre reperfusion [DPR], 400 μg/kg, n = 20), or (3) saline (Cont, n = 18), with 30 min CAO and 3 h reperfusion. In a secondary analysis, rabbits were divided into two groups based on the overall average risk zone size of 29% of the left ventricle (LV): small (<29% of LV) and large (>29% of LV).

RESULTS

Overall, risk zones and infarct size, and the no-reflow zone were similar in all groups. In hearts with large risk zones the no-reflow area was significantly smaller in both drug-treated groups (DPI, 22 ± 5% and DPR, 22 ± 3% vs. control 40 ± 3%, P < 0.006), the hemorrhagic areas were significantly smaller, and infarct size was reduced at the P < 0.06 level compared with control. In animals with small risk zones there were no significant differences. Diannexin treatment did not affect hemodynamics or LV function.

CONCLUSION

Diannexin was cardioprotective in rabbits with a severe ischemic insult. This is important, because large infarcts accompanied by no-reflow in humans are associated with increased complications. In animals with small risk zones, no significant drug effect was observed.

Role of heme oxygenase-1 in transplantation

Heme oxygenase-1 (HO-1) is the rate-limiting enzyme in heme catabolism that converts heme to Fe++, carbon monoxide and biliverdin. HO-1 acts anti-inflammatory and modulates apoptosis in many pathological conditions. In transplantation, HO-1 is overexpressed in organs during brain death, when undergoing ischemic damage and rejection. However, intentionally induced, it ameliorates pathological processes like ischemia reperfusion injury, allograft, xenograft or islet rejection, facilitates donor specific tolerance and alleviates chronic allograft changes. We herein consistently summarize the huge amount of data on HO-1 and transplantation that have been generated in multiple laboratories during the last 15years and suggest possible clinical implications and applications for the near future.

Diannexin treatment decreases ischemia-reperfusion injury at the endothelial cell level of the microvascular bed in muscle flaps

Ischemia-reperfusion injury (IRI) is a common and serious complication of reperfusion following vascular occlusion. We present a novel interpretation of the pathogenesis of IRI. According to this hypothesis, anoxia resulting from ischemia allows translocation of phosphatidylserine to the surface of endothelial cells (ECs), providing an attachment site for leukocytes and platelets. This attachment impedes blood flow through the microvasculature. During IRI mediators of increased vascular permeability are produced, resulting in edema. We have developed a recombinant homodimer of human Annexin V, Diannexin, to attenuate IRI. Annexin V (36 kDa) rapidly passes from the circulation into the urine. In Diannexin 2 annexin V molecules are joined by a short peptide linker to produce a 73 kDa protein, which exceeds the renal filtration threshold. Diannexin has a half-life of about 2.5 hours in the human circulation. Diannexin also has a higher affinity for phosphatidylserine on cell surfaces than the monomer has. Such binding inhibits leukocyte attachment to ECs, and inflammatory mediator formation, during IRI. The aim of the study now reported was to ascertain the effects of Diannexin on IRI in the rat cremaster muscle flap, as revealed by intravital microscopy. During IRI there was increased attachment of leukocytes to ECs, reduced blood flow and augmented vascular permeability. Administration of Diannexin before or just after ischemia prevented these effects. Diannexin inhibited transmigration of leukocytes during IRI. Edema complicates peripheral vascular surgery, stroke, and other clinical conditions. Diannexin has proven to be safe when administered to patients after major surgical operations, and it may be useful to prevent IRI associated with peripheral vascular surgery.

Adrenomedullin in sinusoidal endothelial cells play protective roles against cold injury of liver

Donor organ damage caused by cold preservation is a major problem affecting liver transplantation. Cold preservation most easily damages liver sinusoidal endothelial cells (LSECs), and information about the molecules modulating LSECs function can provide the basis for new therapeutic strategies. Adrenomedullin (AM) is a peptide known to possess anti-apoptotic and anti-inflammatory properties. AM is abundant in vascular endothelial cells, but levels are comparatively low in liver, and little is known about its function there. In this study, we demonstrated both AM and its receptors are expressed in LSECs. AM treatment reduced LSECs loss and apoptosis under cold treatment. AM also downregulated cold-induced expression of TNFalpha, IL1beta, IL6, ICAM1 and VCAM1. AM reduced apoptosis and expression of ICAM1 and VCAM1 in an in vivo liver model subjected to cold storage. Conversely, apoptosis was exacerbated in livers from AM and RAMP2 (AM receptor activity-modifying protein) knockout mice. These results suggest that AM expressed in LSECs exerts a protective effect against cold-organ damage through modulation of apoptosis and inflammation.

The emerging role of T cell immunoglobulin mucin-1 in the mechanism of liver ischemia and reperfusion injury in the mouse

The T cell immunoglobulin and mucin domain-containing molecules (TIM) protein family, which is expressed by T cells, plays a crucial role in regulating host adaptive immunity and tolerance. However, its role in local inflammation, such as innate immunity-dominated organ ischemia-reperfusion injury (IRI), remains unknown. Liver IRI occurs frequently after major hepatic resection or liver transplantation. Using an antagonistic anti-TIM-1 antibody (Ab), we studied the role of TIM-1 signaling in the model of partial warm liver ischemia followed by reperfusion. Anti-TIM-1 Ab monotherapy ameliorated the hepatocellular damage and improved liver function due to IR, as compared with controls. Histological examination has revealed that anti-TIM-1 Ab treatment decreased local neutrophil infiltration, inhibited sequestration of T lymphocytes, macrophages, TIM-1 ligand-expressing TIM-4(+) cells, and reduced liver cell apoptosis. Intrahepatic neutrophil activity and induction of proinflammatory cytokines/chemokines were also reduced in the treatment group. In parallel in vitro studies, anti-TIM-1 Ab suppressed interferon-gamma (IFN-gamma) production in concanavalin A (conA)-stimulated spleen T cells, and diminished tumor necrosis factor alpha (TNF-alpha)/interleukin (IL)-6 expression in a macrophage/spleen T cell coculture system. This is the first study to provide evidence for the novel role of TIM-1 signaling in the mechanism of liver IRI. TIM-1 regulates not only T for the role of cell activation but may also affect macrophage function in the local inflammation response. These results provide compelling data for further investigation of TIM-1 pathway in the mechanism of IRI, to improve liver function, expand the organ donor pool, and improve the overall success of liver transplantation.

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.

Rosuvastatin increases extracellular adenosine formation in humans in vivo: a new perspective on cardiovascular protection

OBJECTIVE

Statins may increase extracellular adenosine formation from adenosine monophosphate by enhancing ecto-5'-nucleotidase activity. This theory was tested in humans using dipyridamole-induced vasodilation as a read-out for local adenosine formation. Dipyridamole inhibits the transport of extracellular adenosine into the cytosol resulting in increased extracellular adenosine and subsequent vasodilation. In addition, we studied the effect of statin therapy in a forearm model of ischemia-reperfusion injury.

METHODS AND RESULTS

Volunteers randomly received rosuvastatin or placebo in a double-blind parallel design (n=21). The forearm vasodilator response to intraarterial dipyridamole was determined in the absence and presence of the adenosine antagonist caffeine. During a separate visit the vasodilator response to nitroprusside and adenosine was established. In addition, healthy men were randomly divided in 3 groups to receive either placebo (n=10), rosuvastatin (n=22), or rosuvastatin combined with intravenous caffeine (n=12). Subsequently, volunteers performed forearm ischemic exercise. At reperfusion, Tc-99m-labeled annexin A5 was infused intravenously and scintigraphic images were acquired, providing an early marker of cell injury. Rosuvastatin treatment significantly increased the vasodilator response to dipyridamole, which was prevented by caffeine. Rosuvastatin did not influence the response to either sodium nitroprusside or adenosine indicating a specific interaction between rosuvastatin and dipyridamole, which does not result from an effect of rosuvastatin on adenosine clearance nor adenosine-receptor affinity or efficacy. Rosuvastatin increased tolerance to ischemia-reperfusion injury, which was attenuated by caffeine.

CONCLUSIONS

Rosuvastatin increases extracellular adenosine formation, which provides protection against ischemia-reperfusion injury in humans in vivo. Therefore, statins and dipyridamole may interact synergistically.

Molecular mediators of liver ischemia and reperfusion injury: a brief review

Ischemia and reperfusion injury is a dynamic process that involves multiple organ systems in various clinical states including transplantation, trauma, and surgery. Research into this field has identified key molecular and signaling players that mediate, modulate, or augment cellular, tissue, and organ injury during this disease process. Further elucidation of the molecular mechanisms should provide the rationale to identify much-needed novel therapeutic options to prevent or ameliorate organ damage due to ischemia and reperfusion in clinics.

Pathophysiological role of platelets and platelet system in acute pancreatitis

The most successful approach for restoring normal long-term glucose homeostasis in type I diabetes mellitus is whole-organ pancreas transplantation. Graft pancreatitis is observed in up to 20% of patients and may lead to loss of the transplanted organ. Several pathophysiological events have been implicated in this form of pancreatitis. The most important cause of early graft pancreatitis is ischemia/reperfusion (I/R)-related disturbance of microvascular perfusion with subsequent hypoxic tissue damage. Recently, considerable evidence accumulated that, among a variety of other pathophysiological events, the activation of platelets can contribute to I/R injury in the course of acute pancreatitis experimentally and clinically. This review summarizes the events affecting platelet function and, therefore, pancreatic microcirculation leading to acute pancreatitis. Therapeutic approaches and own results are presented.