Heme oxygenase-1 system in organ transplantation

Heme oxygenase-1-derived carbon monoxide protects hearts from transplant associated ischemia reperfusion injury

Heme oxygenase-1 (HO-1) degrades heme into iron, biliverdin, and carbon monoxide (CO). HO-1 expression can be used therapeutically to ameliorate undesirable consequences of ischemia reperfusion injury (IRI), but the mechanism by which this occurs, remains to be established. Rat hearts, exposed to a prolonged period (24 h) of cold (4 degrees C) ischemia, failed to function upon transplantation into syngeneic recipients. Induction of HO-1 expression by administration of cobalt protoporphyrin IX (CoPPIX) to the graft donor restored graft function. Inhibition of HO-1 enzymatic activity, by administration of zinc protoporphyrin (ZnPPIX) at the time of transplantation, reversed the protective effect of HO-1. Exposure of the graft donor as well as the graft (during ischemia) to exogenous CO mimicked the protective effect of HO-1. This was associated with a significant reduction in the number of cells undergoing apoptosis in the graft with no apparent decrease of intravascular fibrin polymerization, platelet aggregation, or P-selectin expression. In conclusion, HO-1-derived CO prevents IRI associated with cardiac transplantation based on its antiapoptotic action. The observation that exposure of the donor and the graft to CO is sufficient to afford this protective effect should have important clinical implications in terms of preventing IRI associated with heart transplantation in humans.

Technique for expanding the donor liver pool: heat shock preconditioning in a rat fatty liver model

Fatty liver is a common predisposing risk factor for postoperative liver failure and accounts for most discarded livers during triage of donors. We investigated the effect of heat shock preconditioning (HPc) on recipient survival in a rat fatty liver transplantation model. Fatty liver donor rats were exposed to brief whole-body hyperthermia (10 minutes at 42.5 degrees C) and allowed to recover. HPc induced heat shock proteins (HSPs) (HSP72, HSP90, and heme oxygenase [HO]-1) in donor livers, with levels peaking 12 to 48 hours after HPc. Subsequently, donor livers were harvested 24 hours after HPc, placed in cold storage for 10 hours, and transplanted into normal rats. At 3 hours posttransplantation, HPc reduced serum liver enzymes in the recipients and almost completely suppressed the release of tumor necrosis factor (TNF)-alpha and interleukin (IL)-10. Histologic evaluation 3 and 24 hours after transplantation showed that HPc significantly reduced hepatic inflammation and hepatocellular necrosis without affecting the steatotic appearance of hepatocytes. One week after transplantation, control non-heat-shocked and heat-shocked fatty liver recipients exhibited survival rates of less than 10% and more than 80%, respectively. The evaluation of the survival of recipients receiving fatty livers at different times after HPc showed that the protective effect of HPc was significant when donor livers were transplanted 3 to 48 hours after HPc, with the maximum effect seen 6 to 48 hours after HPc. In conclusion, HPc is a promising avenue to salvage rejected donor fatty livers and enhance the survival rate of fatty liver recipients. We estimate that this technique could increase the annual donor pool by 600 livers.

Gene therapy for liver transplantation using adenoviral vectors: CD40-CD154 blockade by gene transfer of CD40Ig protects rat livers from cold ischemia and reperfusion injury

Liver injury induced by ischemia/reperfusion (I/R) is the prime factor in delayed or loss graft function following transplantation. CD4+ T lymphocytes are key cellular mediators of antigen-independent inflammatory response triggered by I/R. We attempted to modulate rat liver I/R injury by targeted gene therapy with CD40Ig, which blocks the CD40-CD154 costimulation pathway. One hundred percent of Ad-CD40Ig-pretreated orthotopic liver transplants (OLTs) subjected to 24 h of cold (4 degrees C) ischemia survived > 14 days (vs 50% in untreated/Ad-beta-gal groups). Ad-CD40Ig treatment decreased sGOT levels and depressed neutrophil infiltration, compared with controls. These functional data correlated with histological Suzuki's grading of hepatic injury, which in untreated/Ad-beta-gal groups showed severe necrosis (> 60%) and moderate to severe sinusoidal congestion; the Ad-CD40Ig-pretreated group revealed minimal sinusoidal congestion/necrosis. Unlike in controls, OLT expression of mRNA coding for IL-2/IFN-gamma remained depressed, whereas that of IL-4/IL-13 reciprocally increased in the Ad-CD40Ig group. Ad-CD40Ig reduced frequency of TUNEL+ cells and pro-apoptotic Caspase-3, but enhanced antioxidant HO-1 and anti-apoptotic Bcl-2/Bcl-xl expression. Thus, prolonged blockade of CD40-CD154 by CD40Ig exerts potent cytoprotection against hepatic I/R injury. These results provide the rationale for a novel gene therapy approach to maximize the organ donor pool through the safer use of liver transplants exposed to prolonged cold ischemia.

Oxidized Phospholipids Induce Expression of Human Heme Oxygenase-1 Involving Activation of cAMP-responsive Element-binding Protein

Heme oxygenase-1 (HO-1) catalyzes the rate-limiting step in heme degradation, protects against oxidative stress, and shows potent anti-inflammatory effects. Oxidized phospholipids, which are generated during inflammation and apoptosis, modulate the inflammatory response by inducing the expression of several genes including HO-1. Here we investigated the signaling pathways and transcriptional events involved in the induction of HO-1 gene expression by oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (OxPAPC) in human umbilical vein endothelial cells. OxPAPC up-regulated HO-1 mRNA and protein in a time- and concentration-dependent manner, whereas pro-inflammatory agents like TNF-alpha and lipopolysaccharide did not significantly induce HO-1 expression in human umbilical vein endothelial cells. Signaling pathways involved in the OxPAPC-mediated HO-1 induction included protein kinases A and C, as well as the mitogen-activated protein kinases p38 and ERK. The cAMP-responsive element-binding protein (CREB) was phosphorylated via these pathways in response to OxPAPC treatment and expression of a dominant-negative mutant of CREB inhibited OxPAPC-induced activity of a human heme oxygenase-1 promoter-driven luciferase reporter construct. We identified a cAMP-responsive element and a Maf recognition element to be involved in the transcriptional activation of the HO-1 promoter by OxPAPC. In gel shift assays we observed binding of CREB to the cAMP-responsive element after OxPAPC treatment. Induction of HO-1 expression by lipid oxidation products via CREB may represent a feedback mechanism to limit inflammation and associated tissue damage.

Recent insights on the mechanisms of liver preconditioning

Ischemia/reperfusion is the main cause of hepatic damage consequent to temporary clamping of the hepatoduodenal ligament during liver surgery as well as graft failure after liver transplantation. In recent years, a number of animal studies have shown that pre-exposure of the liver to transient ischemia, hyperthermia, or mild oxidative stress increases the tolerance to reperfusion injury, a phenomenon known as hepatic preconditioning. The development of hepatic preconditioning can be differentiated into 2 phases. An immediate phase (early preconditioning) occurs within minutes and involves the direct modulation of energy supplies, pH regulation, Na(+) and Ca(2+) homeostasis, and caspase activation. The subsequent phase (late preconditioning) begins 12-24 hours after the stimulus and requires the synthesis of multiple stress-response proteins, including heat shock proteins HSP70, HSP27, and HSP32/heme oxygenase 1. Hepatic preconditioning is not limited to parenchymal cells but ameliorates sinusoidal perfusion, prevents postischemic neutrophil infiltration, and decreases the production of proinflammatory cytokines by Kupffer cells. This latter effect is important in improving systemic disorders associated with hepatic ischemia/reperfusion. The signals triggering hepatic preconditioning have been partially characterized, showing that adenosine, nitric oxide, and reactive oxygen species can activate multiple protein kinase cascades involving, among others, protein kinase C and p38 mitogen-activated protein kinase. These observations, along with preliminary studies in humans, give a rationale to perform clinical trials aimed at verifying the possible application of hepatic preconditioning in preventing ischemia/reperfusion injury during liver surgery.

Cytoprotective and antiapoptotic effects of IL-13 in hepatic cold ischemia/reperfusion injury are heme oxygenase-1 dependent

Liver injury caused by ischemia/reperfusion (I/R) insult represents the major problem following orthotopic liver transplantation (OLT). I/R damage has been linked to Th1-like cytokine producers. This study evaluates putative cytoprotective effects/mechanisms of Th2-type IL-13 gene transfer. IL-13 overexpression prevented hepatic insult in a rat model of 24 h cold ischemia followed by OLT, as assessed: (i) profoundly decreased hepatocellular damage (sGOT levels), and ameliorated histological signs of I/R injury (Suzuki criteria), consistent with long-term OLT survival; (ii) prevented hepatic apoptosis (TUNEL stains) and up-regulated expression of antiapoptotic (A20, Bcl-2/Bcl-xl)/antioxidant (HO-1) genes. However, inhibition of HO-1 with tin protoporphyrin reversed cytoprotective/antiapoptotic effects of IL-13. In conclusion, cytoprotection rendered by virally induced IL-13 against hepatic I/R injury in this clinically relevant rat hepatic cold I/R injury model was accomplished via decreased apoptosis and induction of antiapoptotic/antioxidant molecules. HO-1 neutralization studies suggest that HO-1 represents one of putative IL-13 downstream effectors. This study provides the rationale for novel approaches to maximize organ donor pool through the safer use of OLTs despite prolonged periods of cold ischemia.

An internal enhancer regulates heme- and cadmium-mediated induction of human heme oxygenase-1

Heme oxygenase-1 (HO-1) catalyzes the rate-limiting step in heme degradation, releasing iron, carbon monoxide, and biliverdin. Induction of HO-1 is an adaptive and beneficial response in renal and nonrenal settings of tissue injury. The purpose of this study was to characterize the regulation of the human HO-1 gene in renal proximal tubule and aortic endothelial cells in response to heme and cadmium. Evaluation of multiple human HO-1 promoter-reporter constructs up to -9.1 kb demonstrated only a partial response to heme and cadmium. In an effort to mimic endogenous stimulus-dependent levels of HO-1 induction, we evaluated the entire 12.5 kb of the human HO-1 gene, including introns and exons, in conjunction with a -4.5-kb human HO-1 promoter and observed significant heme- and cadmium-mediated induction of the reporter gene, suggesting the presence of an internal enhancer. Enhancer function was orientation independent and required a region between -3.5 and -4.5 kb of the human HO-1 promoter. Our studies identified a novel enhancer internal to the human HO-1 gene that, in conjunction with the HO-1 promoter, recapitulates heme- and cadmium-mediated induction of the endogenous HO-1 gene. Elucidation of the molecular regulation of the human HO-1 gene will allow for the development of therapeutic strategies to manipulate HO-1 gene expression in pathological states.

Inflammatory mediators expressed in human islets of Langerhans: implications for islet transplantation

Expression of immune modulating mediators in human Islets of Langerhans could have important implications for development of autoimmunity in type 1 diabetes and influence the outcome of clinical islet transplantation. Islets obtained from five donors were analyzed at various times after isolation using cDNA array technology. The Atlas Human Cytokine/Receptor and Hematology/Immunology nylon membranes representing 268 genes and 406, respectively, were used and the relative expression of each gene analyzed. Of the 51 gene products identified, high mRNA expression of MCP-1, MIF, VEGF, and thymosin beta-10 was detected in all islet samples. IL-8, IL-1-beta, IL-5R, and INF-gamma antagonist were expressed in islets cultured for 2 days. IL-2R was expressed in islets cultured for more than 6 days. In conclusion, several inflammatory mediators were expressed in isolated islets, particularly at an early stage after isolation, indicating that a few days of culture could be beneficial for the outcome of islet transplantation.

Biliverdin protects rat livers from ischemia/reperfusion injury

OBJECTIVE

To explore putative cytoprotective functions of biliverdin during hepatic ischemia/reperfusion (I/R) injury in rat models.

MATERIAL AND METHODS

Male Sprague Dawley (SD) rat livers were harvested and stored for 24 hours at 4 degrees C in University of Wisconsin (UW) solution (n=18), and then perfused with blood for 2 hours on an isolated rat liver perfusion apparatus equipped for temperature (37 degrees C), pressure (13 cm H2O), and pH (7.3) maintenance. Biliverdin was added to the blood at concentrations of 10 and 50 micromol in two groups of six animals. Portal vein blood flow, bile production, and GOT/GPT levels were assessed serially. At the conclusion of the experiment, liver samples were collected for histologic evaluation using Suzuki criteria.

RESULTS

BV exerted protective effects against liver I/R injury. Adjunctive biliverdin improved portal venous blood flow (mL/min/g) from the beginning of reperfusion (1.33+/-0.17 versus 0.98+/-0.15; P<.001) and increased bile production (mL/g) as compared with the control group (3.40 versus 1.88; P<.003). I/R-induced hepatocellular damage as measured by GOT/GPT release (IU/L) was diminished in the biliverdin group (91 versus 171 and 46 versus 144, respectively; P<.0001). Improved liver function by biliverdin was accompanied by preservation of the histologic structure as assessed by Suzuki criteria (3.7+/-1.4 versus 6.8+/-0.8 in untreated controls; P<.005).

CONCLUSIONS

Biliverdin attenuates the ischemia/early reperfusion injury of rat liver grafts as assessed by hemodynamics, function, enzyme analysis, and histology. This study provides the rationale for novel therapeutic approaches using biliverdin to maximize the organ donor pool through the safer use of liver transplants despite prolonged periods of cold ischemia.

Systemic rather than local heme oxygenase-1 overexpression improves cardiac allograft outcomes in a new transgenic mouse

Heme oxygenase-1 (HO-1), a rate-limiting enzyme in heme catabolism, exhibits potent antioxidant and anti-inflammatory properties. We developed HO-1 transgenic (Tg) mice using a rat HO-1 genomic transgene under the control of the endogenous promoter. Transgene expression was demonstrated by RT-PCR in all studied tissues, and a modest HO-1 overexpression was documented by Western, ELISA, and enzyme activity assays. To assess the effect of local vs systemic HO-1 in the acute rejection response, we used Tg mice as organ donors or recipients of MHC-incompatible heart grafts. In the local HO-1 overexpression model, Tg allografts survived 10.5 +/- 0.7 days (n = 10), compared with 6.5 +/- 0.4 days (n = 6) for wild-type donor controls (p = 0.0001). In the systemic HO-1 overexpression model, Tg recipients maintained allografts for 26.8 +/- 3.4 days (n = 10), compared with 6.3 +/- 0.1 days (n = 12) in wild-type controls (p = 0.00009). Inhibition of HO activity by treatment with tin protoporphyrin blunted survival advantage in Tg mice and resulted in acute graft rejection (n = 3). Increased carboxyhemoglobin levels were consistently noted in Tg mice. Comparisons of grafts at day 4 indicated that HO-1 overexpression was inversely associated with vasculitis/inflammatory cell infiltrate in both models. Hearts transplanted into Tg recipients showed decreased CD4(+) lymphocyte infiltration and diminished immune activation, as judged by CD25 expression. Thus, although local and systemic HO-1 overexpression improved allograft outcomes, systemic HO-1 led to a more robust protection and resulted in a significant blunting of host immune activation. This Tg mouse provides a valuable tool to study mechanisms by which HO-1 exerts beneficial effects in organ transplantation.

The utility of marginal donors in liver transplantation

The shortage of organs has led centers to expand their criteria for the acceptance of marginal donors. The combination of multiple marginal factors seems to be additive on graft injury. In this review, the utility of various marginal donors in patients requiring liver transplantation will be described, including older donors, steatotic livers, non-heart-beating donors, donors with viral hepatitis, and donors with malignancies. The pathophysiology of the marginal donor will be discussed, along with strategies for minimizing the ischemia reperfusion injury experienced by these organs. Finally, new strategies for improving the function of the marginal/expanded donor liver will be reviewed.

Carbon monoxide induces cytoprotection in rat orthotopic lung transplantation via anti-inflammatory and anti-apoptotic effects

Successful lung transplantation has been limited by the high incidence of acute graft rejection. There is mounting evidence that the stress response gene heme oxygenase-1 (HO-1) and/or its catalytic by-product carbon monoxide (CO) confers cytoprotection against tissue and cellular injury. This led us to hypothesize that CO may protect against lung transplant rejection via its anti-inflammatory and antiapoptotic effects. Orthotopic left lung transplantation was performed in Lewis rat recipients from Brown-Norway rat donors. HO-1 mRNA and protein expression were markedly induced in transplanted rat lungs compared to sham-operated control lungs. Transplanted lungs developed severe intraalveolar hemorrhage, marked infiltration of inflammatory cells, and intravascular coagulation. However, in the presence of CO exposure (500 ppm), the gross anatomy and histology of transplanted lungs showed marked preservation. Furthermore, transplanted lungs displayed increased apoptotic cell death compared with the transplanted lungs of CO-exposed recipients, as assessed by TUNEL and caspase-3 immunostaining. CO exposure inhibited the induction of IL-6 mRNA and protein expression in lung and serum, respectively. Gene array analysis revealed that CO also down-regulated other proinflammatory genes, including MIP-1alpha and MIF, and growth factors such as platelet-derived growth factor, which were up-regulated by transplantation. These data suggest that the anti-inflammatory and antiapoptotic properties of CO confer potent cytoprotection in a rat model of lung transplantation.

Expression of transforming growth factor-beta1 and hypoxia-inducible factor-1alpha in an experimental model of kidney transplantation

BACKGROUND

Ischemia-reperfusion syndrome has been recognized as an important pathogenic factor in renal transplantation, not only in the development of delayed graft function but also in the development of acute and chronic rejection. Hypoxia-inducible factor (HIF)-1 activates transcription of several genes implicated in cell survival, such as vascular endothelial growth factor (VEGF), and in tissue repair transforming growth factor (TGF)-beta. The purpose of this study was to characterize TGF-beta1, VEGF, and HIF-1alpha expression profiles during renal transplantation with heart-beating donors (HBD) and non-heart-beating donors (NHBD).

METHODS

An experimental model of renal transplantation using 40 pairs of large, white, Landrace pigs and including HBD and NHBD was used. Cold-ischemia time was the same in all groups (6 hr), and three groups of NHBD (30, 45, and 90 min) were studied. Immunosuppressive therapy consisted of cyclosporine, except in one HBD group, which was treated with azathioprine. TGF-beta1, VEGF, and HIF-1alpha expression profiles were performed in renal biopsies obtained at different times: after anesthetic induction (basal); 30, 45, and 90 min after warm ischemia; after cold ischemia; 1 hr after reperfusion; and 5 days after transplantation.

RESULTS

TGF-beta1 expression increased after cold ischemia in HBD and remained unaltered during the surgical process in all NHBD groups. HIF-1alpha and VEGF expression were not greatly modified during surgery in the HBD or NHBD groups. All groups showed a significant increase in TGF-beta1 and HIF-1alpha expression as well as down-regulation of VEGF 5 days after transplantation, and these effects were independent of immunosuppressive treatment. There were no statistically significant differences among the groups at 5 days after transplantation, although the increase in TGF-beta1 was more pronounced in the HBD groups, especially in azathioprine-treated animals.

CONCLUSIONS

The initial up-regulation of TGF-beta1 observed in HBD immediately after cold ischemia could have a positive effect on epithelial-tubular regeneration. Warm ischemia has a detrimental effect on TGF-beta1 expression during the early phases of renal transplantation and has no effect on VEGF and HIF-1alpha expression. The up-regulation of TGF-beta1 and HIF-1alpha observed after transplantation could have a positive effect on tubular repair. TGF-beta1 expression was lower in animals treated with cyclosporine, probably because of cellular toxicity.

Hepatic ischemia/reperfusion injury--a fresh look

Ischemia/reperfusion (I/R) injury is a multifactorial process that affects graft function after liver transplantation. An understanding of the mechanisms involved in I/R injury is essential for the design of therapeutic strategies to improve the outcome of liver transplantation. The generation of reactive oxygen species subsequent to reoxygenation inflicts tissue damage and initiates a cascade of deleterious cellular responses leading to inflammation, cell death, and ultimate organ failure. Increased experimental evidence has suggested that Kupffer cells and T cells mediate the activation of neutrophil inflammatory responses. Activated neutrophils infiltrate the injured liver in parallel with increased expression of adhesion molecules on endothelial cells. The heme oxygenase system is among the most critical of the cytoprotective mechanisms activated during cellular stress, exerting antioxidant and anti-inflammatory functions, modulating the cell cycle, and maintaining the microcirculation. Finally, the activation of toll-like receptors on Kupffer cells may play a fundamental role in exploring new therapeutic strategies based on the concept that hepatic I/R injury represents a case for a host "innate" immunity.

Stat4 and Stat6 signaling in hepatic ischemia/reperfusion injury in mice: HO-1 dependence of Stat4 disruption-mediated cytoprotection

Ischemia/reperfusion (I/R) injury remains an important problem in clinical organ transplantation. There is growing evidence that T lymphocytes, and activated CD4+ T cells in particular, play a key role in hepatic I/R injury. This study analyzes the role of signal transducer and activator of transcription 4 (Stat4) and Stat6 signaling in liver I/R injury. Using a partial lobar warm ischemia model, groups of wild-type (WT), T cell-deficient, Stat4-/Stat6-deficient knockout (KO) mice were assessed for the extent/severity of I/R injury. Ninety minutes of warm ischemia followed by 6 hours of reperfusion induced a fulminant liver failure in WT and Stat6 KO mice, as assessed by hepatocellular damage (serum alanine aminotransferase [sALT] levels), neutrophil accumulation (myeloperoxidase [MPO] activity) and histology (Suzuki scores). In contrast, T cell deficiency (nu/nu mice) or disruption of Stat4 signaling (Stat4 KO mice) reduced I/R insult. Unlike adoptive transfer of WT or Stat6-deficient T cells, infusion of Stat4-deficient T cells failed to restore hepatic I/R injury and prevented tumor necrosis factor alpha (TNF-alpha) production in nu/nu mice. Diminished TNF-alpha/Th1-type cytokine messenger RNA (mRNA)/protein elaborations patterns, along with overexpression of heme oxygenase-1 (HO-1)-accompanied hepatic cytoprotection in Stat4 KO recipients. In contrast, HO-1 depression restored hepatic injury in otherwise I/R resistant Stat4 KOs. In conclusion, Stat4 signaling is required for, whereas Stat4 disruption protects against, warm hepatic I/R injury in mice. The cytoprotection rendered by Stat4 disruption remains HO-1-dependent.