Deregulation of iron homeostasis and cold-preservation injury to rat liver stored in University of Wisconsin solution

Effects of prolonged cold ischemia on the DCD kidney function and Inflammasome expression in rat kidney transplants

BACKGROUND

Acute kidney injury (AKI) is the main reason for the bad outcome of the donation of circulatory death (DCD) kidney after transplantation. Prolonged cold storage (CS) is a risk factor for the occurrence of the delayed graft function in DCD kidney. The protein NLR-domain containing receptor 3 (NLRP3) plays a crucial role in renal ischemia reperfusion injury by triggering inflammasome formation. Herein, we investigated whether the NLRP3 signal participate in the CS-induced damage of DCD kidney in rat kidney transplantation models.

MATERIALS AND METHODS

DCD kidney and living donor (LD) kidney of SD rats were preserved in UW solution at 4 °C for 2 h or 18 h, and then transplanted into syngeneic recipient. Thus, the animals were randomly divided into 4 groups: 2-h LD group, 2-h DCD group, 18-h LD group and 18-h DCD group. The renal function and pathological changes were determined. The expressions of NLRP3 and inflammatory factor IL-1β were assessed. The concentration of ferrous iron (Fe²⁺) was analyzed both in kidneys and in the preservation solution. The renal morphological changes were examined by hematoxylin eosin staining.

RESULTS

Our results showed that the levels of Cr and BUN were higher in 18-h LD group as compared to the 2-h LD group, which were remarkably increased in 18-h DCD group. The expression levels of NLRP3 and IL-1β were increased by 18-h CS compared to 2-h CS in both LD kidney and DCD kidney. In addition, the Fe²⁺ concentration has significantly increased in 18-h LD group than that in 2-h LD group, and the elevation of Fe²⁺ was more remarkable in DCD kidneys.

CONCLUSION

In conclusion, our study demonstrated that prolonged hypothermic storage of DCD kidney deteriorated the graft function via the increased Fe²⁺ concentration, which was associated with the upregulation of NLRP3 expression.

Heavy Water (D2O) Containing Preservation Solution Reduces Hepatic Cold Preservation and Reperfusion Injury in an Isolated Perfused Rat Liver (IPRL) Model

Background: Heavy water (D₂O) has many biological effects due to the isotope effect of deuterium. We previously reported the efficacy of D₂O containing solution (Dsol) in the cold preservation of rat hearts. Here, we evaluated whether Dsol reduced hepatic cold preservation and reperfusion injury. Methods: Rat livers were subjected to 48-hour cold storage in University of Wisconsin (UW) solution or Dsol, and subsequently reperfused on an isolated perfused rat liver. Graft function, injury, perfusion kinetics, oxidative stress, and cytoskeletal integrity were assessed. Results: In the UW group, severe ischemia and reperfusion injury (IRI) was shown by histopathology, higher liver enzymes leakage, portal resistance, and apoptotic index, oxygen consumption, less bile production, energy charge, and reduced glutathione (GSH)/oxidized glutathione (GSSG) ratio (versus control). The Dsol group showed that these injuries were significantly ameliorated (versus the UW group). Furthermore, cytoskeletal derangement was progressed in the UW group, as shown by less degradation of α-Fodrin and by the inactivation of the actin depolymerization pathway, whereas these changes were significantly suppressed in the Dsol group. Conclusion: Dsol reduced hepatic IRI after extended cold preservation and subsequent reperfusion. The protection was primarily due to the maintenance of mitochondrial function, cytoskeletal integrity, leading to limiting oxidative stress, apoptosis, and necrosis pathways.

Iron-induced oxidative rat liver injury after non-heart-beating warm ischemia is mediated by tumor necrosis factor α and prevented by deferoxamine

This study investigated iron-induced injury after warm ischemia in a non-heart-beating (NHB) rat liver model and the effects of deferoxamine (DFO). Livers from heart-beating (HB) rats or rats that were NHB for 60 minutes were stored in University of Wisconsin solution for 5 hours at 4°C [cold storage (CS)] and then were subjected to 2 hours of machine reperfusion (MRP) at 37°C. Three NHB groups were compared: (1) no DFO, (2) DFO 30 minutes before cardiac arrest and during CS and MRP, and (3) DFO during CS and MRP. Aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) levels in the NHB perfusate were significantly elevated (P < 0.01) in comparison with levels in HB controls after CS and MRP. After CS, the levels of iron and tumor necrosis factor α (TNF-α) were 0.077 ± 0.007 μmol/g and 151 ± 26 pg/g, respectively, in the NHB group and 0.022 ± 0.004 μmol/g and 17 ± 7 pg/g, respectively, in the HB group (P < 0.01). After MRP, LDH significantly correlated with iron (R(2)  = 0.81, P < 0.01). The DFO pretreatment of NHB donors decreased AST (7.3 ± 0.8 versus 4.0 ± 0.5 U/g of liver, P < 0.05) and LDH (42.5 ± 4.1 versus 20.4 ± 2.5 U/g of liver, P < 0.05) with 2 hours of MRP and increased bile flow during MRP (142 ± 34 versus 240 ± 18 μL/g, P < 0.05). It also reduced the levels of iron (0.077 ± 0.007 versus 0.050 ± 0.008 μmol/g, P < 0.05) and TNF-α (151 ± 26 versus 51 ± 13 pg/g, P < 0.05) after CS and the levels of lipid peroxidation products F2-isoprostane (149 ± 11 versus 99 ± 10 ng/g, P < 0.05) and malondialdehyde (1.58 ± 0.1 versus 1.14 ± 0.08 μmol/g, P < 0.05) after MRP. In conclusion, iron-initiated oxidative stress is likely involved in NHB donor liver injury, and importantly, DFO pretreatment reduces liver damage.

Desferrioxamine in warm reperfusion media decreases liver injury aggravated by cold storage

AIM: To evaluate whether desferrioxamine decreases ischemia and perfusion injury aggravated by cold storage (CS) in a rat liver perfusion model.

METHODS: Isolated rat livers were kept in CS in University of Wisconsin Solution for 20 h at 4 °C, then exposed to 25 min of warm ischemia (WI) at 37 °C followed by 2 h of warm perfusion (WP) at 37 °C with oxygenated (95% oxygen and 5% carbon dioxide) Krebs-Henseleit buffer. Desferrioxamine (DFO), an iron chelator, was added at different stages of storage, ischemia and perfusion: in CS only, in WI only, in WP only, in WI and perfusion, or in all stages. Effluent samples were collected after CS and after WI. Perfusate samples and bile were collected every 30 min (0, 0.5, 1, 1.5 and 2 h) during liver perfusion. Cellular injury was assessed by the determination of lactate dehydrogenase (LDH) and aspartate aminotransferase (AST) in the effluent and perfusate samples. Total iron was analysed in the perfusate samples. After WP, the liver was collected for the determination of liver swelling (wet to dry ratio) and liver morphological examination (hematoxylin and eosin staining).

RESULTS: Increased CS time caused increased liver dysfunction during WP. After 2 h of WP, liver injury was indicated by increased release of AST (0.5 h CS: 9.4 ± 2.2 U/g liver vs 20 h CS: 45.9 ± 10.8 U/g liver, P < 0.05) and LDH (0.5 h CS: 59 ± 14 U/g liver vs 20 h CS: 297 ± 71 U/g liver, P < 0.05). There was an associated increase in iron release into the perfusate (0.5 h CS: 0.11 ± 0.03 μmoL/g liver vs 20 h CS: 0.58 ± 0.10 μmoL/g liver, P < 0.05) and reduction in bile flow (0.5 h CS: 194 ± 12 μL/g vs 20 h CS: 71 ± 8 μL/g liver, P < 0.05). When DFO was added during WI and WP following 20 h of CS, release of iron into the perfusate was decreased (DFO absent 0.58 ± 0.10 μmoL/g liver vs DFO present 0.31 ± 0.06 μmoL/g liver, P < 0.05), and liver function substantially improved with decreased release of AST (DFO absent 45.9 ± 10.8 U/g liver vs DFO present 8.1 ± 0.9 U/g liver, P < 0.05) and LDH (DFO absent 297 ± 71 U/g liver vs DFO present 56 ± 7 U/g liver, P < 0.05), and increased bile flow (DFO absent 71 ± 8 μL/g liver vs DFO present 237 ± 36 μL/g liver, P < 0.05). DFO was also shown to improve liver morphology after WP. Cellular injury (the release of LDH and AST) was significantly reduced with the addition of DFO in CS medium but to a lesser extent compared to the addition of DFO in WP or WI and perfusion. There was no effect on liver swelling or bile flow when DFO was only added to the CS medium.

CONCLUSION: DFO added during WI and perfusion decreased liver perfusion injury aggravated by extended CS.

Iron and oxidative stress in cold-initiated necrotic death of rat hepatocyte

Iron chelators and antioxidants have been shown to prevent hypothermia-induced apoptosis in hepatocytes. This study examined whether iron chelation and antioxidants could also prevent hypothermia-induced necrosis. Isolated rat hepatocytes were incubated at 4 degrees C for 6 hours and then rewarmed at 37 degrees C for 18 hours with or without the iron chelator deferoxamine and a selection of antioxidants. There was no evidence of increased cell death or adenosine triphosphate depletion during hypothermic incubation. After hypothermia and rewarming, the majority of rat hepatocytes died of necrosis as indicated by the absence of DNA fragmentation, caspase 3 activity, and apoptotic bodies. Cell death was significantly reduced if deferoxamine or a selection of antioxidants were present during hypothermia and rewarming. Deferoxamine was more effective in preventing cell death when added prior to hypothermia, indicating cell death processes were likely initiated during hypothermia.

N-octanoyl dopamine, a non-hemodyanic dopamine derivative, for cell protection during hypothermic organ preservation

Background

Although donor dopamine treatment reduces the requirement for post transplantation dialysis in renal transplant recipients, implementation of dopamine in donor management is hampered by its hemodynamic side-effects. Therefore novel dopamine derivatives lacking any hemodynamic actions and yet are more efficacious in protecting tissue from cold preservation injury are warranted. We hypothesized that variation of the molecular structure would yield more efficacious compounds avoid of any hemodynamic effects.

Methodology/Principal Findings

To this end, we assessed protection against cold preservation injury in HUVEC by the attenuation of lactate dehydrogenase (LDH) release. Modification of dopamine by an alkanoyl group increased cellular uptake and significantly improved efficacy of protection. Further variation revealed that only compounds bearing two hydroxy groups in ortho or para position at the benzene nucleus, i.e. strong reductants, were protective. However, other reducing agents like N-acetyl cysteine and ascorbate, or NADPH oxidase inhibition did not prevent cellular injury following cold storage. Unlike dopamine, a prototypic novel compound caused no hemodynamic side-effects.

Conclusions/Significance

In conclusion, we demonstrate that protection against cold preservation injury by catecholamines is exclusively governed by strong reducing capacity and sufficient lipophilicity. The novel dopamine derivatives might be of clinical relevance in donor pre-conditioning as they are completely devoid of hemodynamic action, their increased cellular uptake would reduce time of treatment and therefore also may have a potential use for non-heart beating donors.

Failure of P-selectin blockade alone to protect the liver from ischemia-reperfusion injury in the isolated blood-perfused rat liver

AIM: To determine if blockade of P-selectin in the isolated blood-perfused cold ex vivo rat liver model protects the liver from ischemia-reperfusion injury.

METHODS: The effect of P-selectin blockade was assessed by employing an isolated blood-perfused cold ex vivo rat liver with or without P-selectin antibody treatment before and after 6 h of cold storage in University of Wisconsin solution.

RESULTS: In our isolated blood-perfused rat liver model, pre-treatment with P-selectin antibody failed to protect the liver from ischemia-reperfusion injury, as judged by the elevated aspartate aminotransferase activity. In addition, P-selectin antibody treatment did not significantly reduced hepatic polymorphonuclear leukocyte accumulation after 120 min of perfusion. Histological evaluation of liver sections obtained at 120 min of perfusion showed significant oncotic necrosis in liver sections of both ischemic control and P-selectin antibody-treated groups. However, total bile production after 120 min of perfusion was significantly greater in P-selectin antibody-treated livers, compared to control livers. No significant difference in P-selectin and ICAM-1 mRNAs and proteins, GSH, GSSG, and nuclear NF-κB was found between control and P-selectin antibody-treated livers.

CONCLUSION: In conclusion, we have shown that blockade of P-selectin alone failed to reduced polymorphonuclear leukocyte accumulation in the liver and protect hepatocytes from ischemia-reperfusion injury in the isolated blood-perfused cold-ex vivo rat liver model.

Liver ischemia and ischemia-reperfusion induces and trafficks the multi-specific metal transporter Atp7b to bile duct canaliculi: possible preferential transport of iron into bile

Both Atp7b (Wilson disease gene) and Atp7a (Menkes disease gene) have been reported to be trafficked by copper. Atp7b is trafficked to the bile duct canaliculi and Atp7a to the plasma membrane. Whether or not liver ischemia or ischemia-reperfusion modulates Atp7b expression and trafficking has not been reported. In this study, we report for the first time that the multi-specific metal transporter Atp7b is significantly induced and trafficked by both liver ischemia alone and liver ischemia-reperfusion, as judged by immunohistochemistry and Western blot analyses. Although hepatocytes also stained for Atp7b, localized intense staining of Atp7b was found on bile duct canaliculi. Inductive coupled plasma-mass spectrometry analysis of bile copper, iron, zinc, and manganese found a corresponding significant increase in biliary iron. In our attempt to determine if the increased biliary iron transport observed may be a result of altered bile flow, lysosomal trafficking, or glutathione biliary transport, we measured bile flow, bile acid phosphatase activity, and glutathione content. No significant difference was found in bile flow, bile acid phosphatase activity, and glutathione, between control livers and livers subjected to ischemia-reperfusion. Thus, we conclude that liver ischemia and ischemia-reperfusion induction and trafficking Atp7b to the bile duct canaliculi may contribute to preferential iron transport into bile.

Oxidative stress causes a decline in lysosomal integrity during hypothermic incubation of rat hepatocytes

Oxidative stress during cold preservation has been identified as a significant cause of cell injury but the process by which injury occurs is poorly understood. We examined loss of lysosomal integrity as a possible cause of cell injury during extended cold storage of isolated rat hepatocytes. After 21 h of hypothermia, there was a marked decline in lysosomal integrity, which was correlated with an increase in lipid peroxidation. When lipid peroxidation was prevented with the antioxidant Trolox (a vitamin E analog) or the iron chelator desferrioxamine, lysosomal integrity was preserved. In contrast, increasing lysosomal iron with ferric chloride caused an increase in lipid peroxidation and decreased lysosomal integrity. Loss of lysosomal integrity during cold preservation in this experimental model was consistent with iron-initiated oxidative stress. The progressive loss of lysosomal integrity during hypothermic incubation has the potential to affect liver function after transplantation.

Expression of heme oxygenase-1 in human livers before transplantation correlates with graft injury and function after transplantation

Upregulation of heme oxygenase-1 (HO-1) has been proposed as an adaptive mechanism protecting against ischemia/reperfusion (I/R) injury. We investigated HO-1 expression in 38 human liver transplants and correlated this with I/R injury and graft function. Before transplantation, median HO-1 mRNA levels were 3.4-fold higher (range: 0.7-9.3) in donors than in normal controls. Based on the median value, livers were divided into two groups: low and high HO-1 expression. These groups had similar donor characteristics, donor serum transaminases, cold ischemia time, HSP-70 expression and the distribution of HO-1 promoter polymorphism. After reperfusion, HO-1 expression increased significantly further in the initial low HO-1 expression group, but not in the high HO-1 group. Postoperatively, serum transaminases were significantly lower and the bile salt secretion was higher in the initial low HO-1 group, compared to the high expression group. Immunofluorescence staining identified Kupffer cells as the main localization of HO-1. In conclusion, human livers with initial low HO-1 expression (<3.4 times controls) are able to induce HO-1 further during reperfusion and are associated with less injury and better function than initial high HO-1 expression (>3.4 times controls). These data suggest that an increase in HO-1 during transplantation is more protective than high HO-1 expression before transplantation.

Ischemia-reperfusion of rat liver modulates hepcidin in vivo expression

The recently identified acute-phase response antimicrobial peptide hepcidin has been postulated to maintain iron homeostasis by modulating iron absorption at both the intestinal and macrophage levels. Hepcidin has also been reported to be responsible for anemia associated with chronic inflammatory diseases, and in anemia in patients with hepatic adenomas. Since Kupffer cells are known to be the primary contributor to early-phase ischemia-reperfusion injury in the liver and iron is known to modulate Kupffer cell production of proinflammatory cytokine and reactive oxygen species, we investigated hepcidin in vivo expression in the well-established rat partial-liver ischemia-reperfusion model. We found that both liver ischemia alone and liver ischemia-reperfusion significantly induced serum and liver hepcidin levels. Furthermore, currently proposed mediators of in vivo hepcidin expression, such as interleukin-6, signal transducers and activators of transcription-family transducers, and CCAAT/enhancing binding protein-alpha do not appear to modulate hepcidin expression in the liver ischemia-reperfusion acute inflammatory model. In this study we report the first in vivo evidence of liver ischemia and liver ischemia-reperfusion modulation of hepcidin expression. In conclusion, in the well-characterized liver ischemia-reperfusion model of acute inflammation, mechanism(s) other than interleukin-6 signal transduction via signal transducers and activators of transcription-3 may be responsible for hepcidin induction.

ANP-induced decrease of iron regulatory protein activity is independent of HO-1 induction

Atrial natriuretic peptide (ANP)-preconditioned livers are protected from ischemia-reperfusion injury. ANP-treated organs show increased expression of heme oxygenase (HO)-1. Because HO-1 liberates bound iron, the aim of our study was to determine whether ANP affects iron regulatory protein (IRP) activity and, thus, the levels of ferritin. Rat livers were perfused with Krebs-Henseleit buffer [+/-ANP, 8-bromo-cGMP (8-Br-cGMP), and tin protoporphyrin, 20 min], stored in University of Wisconsin solution (4 degrees C, 24 h), and reperfused (120 min). IRP activity was assessed by gel-shift assays, and ferritin, IRP phosphorylation, and PKC localization were assessed by Western blot. Control livers displayed decreased IRP activity at the end of ischemia but no change in ferritin content during ischemia and reperfusion. ANP-pretreated livers showed reduced IRP activity, an effect mimicked by 8-Br-cGMP. Ferritin levels were increased in ANP-pretreated organs. Simultaneous perfusion of livers with ANP and tin protoporphyrin did not reduce ANP-induced action, arguing against a role for HO-1 in changes in IRP activity. ANP and 8-Br-cGMP decreased membrane localization of PKC-alpha and PKC-epsilon, but this modulation of PKC seems unrelated to inhibition of IRP binding. This work shows the cGMP-mediated attenuation of IRP binding activity by ANP, which results in increased hepatic ferritin levels. This change in IRPs is independent of ANP-induced HO-1 and reduced PKC activation.

New Insights into the Cellular and Molecular Mechanisms of Cold Storage Injury

Solid organ grafts, but also other biologic materials requiring storage for a few hours to a few days, are usually stored under hypothermic conditions. To decrease graft injury during cold storage, organ preservation solutions were developed many years ago. However, since then, modern biochemical and cell biologic methods have allowed further insights into the molecular and cellular mechanisms of cold storage injury, including further insights into alterations of the cellular ion homeostasis, the occurrence of a mitochondrial permeability transition, and the occurrence of free–radical-mediated hypothermic injury and cold-induced apoptosis. These new aspects of cold storage injury, which are not covered by preservation solutions in current clinical use and offer the potential for improvement of organ and tissue preservation, are presented here.