HO-1 Upregulation Suppresses Type 1 IFN Pathway in Hepatic Ischemia/Reperfusion Injury

Role of the immune system in liver transplantation and its implications for therapeutic interventions

Liver transplantation (LT) stands as the gold standard for treating end-stage liver disease and hepatocellular carcinoma, yet postoperative complications continue to impact survival rates. The liver's unique immune system, governed by a microenvironment of diverse immune cells, is disrupted during processes like ischemia-reperfusion injury posttransplantation, leading to immune imbalance, inflammation, and subsequent complications. In the posttransplantation period, immune cells within the liver collaboratively foster a tolerant environment, crucial for immune tolerance and liver regeneration. While clinical trials exploring cell therapy for LT complications exist, a comprehensive summary is lacking. This review provides an insight into the intricacies of the liver's immune microenvironment, with a specific focus on macrophages and T cells as primary immune players. Delving into the immunological dynamics at different stages of LT, we explore the disruptions after LT and subsequent immune responses. Focusing on immune cell targeting for treating liver transplant complications, we provide a comprehensive summary of ongoing clinical trials in this domain, especially cell therapies. Furthermore, we offer innovative treatment strategies that leverage the opportunities and prospects identified in the therapeutic landscape. This review seeks to advance our understanding of LT immunology and steer the development of precise therapies for postoperative complications.

The different facets of heme-oxygenase 1 in innate and adaptive immunity

Heme oxygenase (HO) enzymes are responsible for the main oxidative step in heme degradation, generating equimolar amounts of free iron, biliverdin and carbon monoxide. HO-1 is induced as a crucial stress response protein, playing protective roles in physiologic and pathological conditions, due to its antioxidant, anti-apoptotic and anti-inflammatory effects. The mechanisms behind HO-1-mediated protection are being explored by different studies, affecting cell fate through multiple ways, such as reduction in intracellular levels of heme and ROS, transcriptional regulation, and through its byproducts generation. In this review we focus on the interplay between HO-1 and immune-related signaling pathways, which culminate in the activation of transcription factors important in immune responses and inflammation. We also discuss the dual interaction of HO-1 and inflammatory mediators that govern resolution and tissue damage. We highlight the dichotomy of HO-1 in innate and adaptive immune cells development and activation in different disease contexts. Finally, we address different known anti-inflammatory pharmaceuticals that are now being described to modulate HO-1, and the possible contribution of HO-1 in their anti-inflammatory effects.

Personalized profiles of antioxidant signaling pathway in patients with tuberculosis

BACKGROUND/PURPOSE

The non-protein thiol glutathione is protective against infection by Mycobacterium tuberculosis (MTB) and, together with the transcription factor NRF2 (the nuclear factor erythroid 2-related factor 2), plays a crucial role in counteracting MTB-induced redox imbalance. Many genes implicated in the antioxidant response belong to the NRF2-signalling pathway, whose central role in the pathogenesis of tuberculosis (TB) has been recently proposed.

METHODS

In this study, we measured GSH levels in blood of patients with active TB and analysed the individual NRF2-mediated redox profile, in order to provide additional tools for discriminating the pathologic TB state and addressing therapeutic interventions.

RESULTS

Our findings show a systemic individual modulation of GSH and NRF2 signaling pathway in patients with TB, with a "personalized" induction of NRF2-target genes.

CONCLUSION

This study can provide useful tools to monitor the course of the infection and address patients' treatment.

Understanding the Reciprocal Interplay Between Antibiotics and Host Immune System: How Can We Improve the Anti-Mycobacterial Activity of Current Drugs to Better Control Tuberculosis?

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb) infection, remains a global health threat despite recent advances and insights into host-pathogen interactions and the identification of diverse pathways that may be novel therapeutic targets for TB treatment. In addition, the emergence and spread of multidrug-resistant Mtb strains led to a low success rate of TB treatments. Thus, novel strategies involving the host immune system that boost the effectiveness of existing antibiotics have been recently suggested to better control TB. However, the lack of comprehensive understanding of the immunomodulatory effects of anti-TB drugs, including first-line drugs and newly introduced antibiotics, on bystander and effector immune cells curtailed the development of effective therapeutic strategies to combat Mtb infection. In this review, we focus on the influence of host immune-mediated stresses, such as lysosomal activation, metabolic changes, oxidative stress, mitochondrial damage, and immune mediators, on the activities of anti-TB drugs. In addition, we discuss how anti-TB drugs facilitate the generation of Mtb populations that are resistant to host immune response or disrupt host immunity. Thus, further understanding the interplay between anti-TB drugs and host immune responses may enhance effective host antimicrobial activities and prevent Mtb tolerance to antibiotic and immune attacks. Finally, this review highlights novel adjunctive therapeutic approaches against Mtb infection for better disease outcomes, shorter treatment duration, and improved treatment efficacy based on reciprocal interactions between current TB antibiotics and host immune cells.

Acidic Microenvironment Aggravates the Severity of Hepatic Ischemia/Reperfusion Injury by Modulating M1-Polarization Through Regulating PPAR-γ Signal

Hepatic injury induced by ischemia and reperfusion (HIRI) is a major clinical problem after liver resection or transplantation. The polarization of macrophages plays an important role in regulating the severity of hepatic ischemia/reperfusion injury. Recent evidence had indicated that the ischemia induces an acidic microenvironment by causing increased anaerobic glycolysis and accumulation of lactic acid. We hypothesize that the acidic microenvironment might cause the imbalance of intrahepatic immunity which aggravated HIRI. The hepatic ischemia/reperfusion injury model was established to investigate the effect of the acidic microenvironment to liver injury. Liposomes were used to deplete macrophages in vivo. Macrophages were cultured under low pH conditions to analyze the polarization of macrophages in vitro. Activation of the PPAR-γ signal was determined by Western blot. PPAR-γ agonist GW1929 was administrated to functionally test the role of PPAR-γ in regulating macrophage-mediated effects in the acidic microenvironment during HIRI. We demonstrate that acidic microenvironment aggravated HIRI while NaHCO₃ reduced liver injury through neutralizing the acid, besides, liposome abolished the protective ability of NaHCO₃ through depleting the macrophages. In vivo and vitro experiment showed that acidic microenvironment markedly promoted M1 polarization but inhibited M2 polarization of macrophage. Furthermore, the mechanistic study proved that the PPAR-γ signal was suppressed during the polarization of macrophages under pH = 6.5 culture media. The addition of PPAR-γ agonist GW1929 inhibited M1 polarization under acidic environment and reduced HIRI. Our results indicate that acidic microenvironment is a key regulator in HIRI which promoted M1 polarization of macrophages through regulating PPAR-γ. Conversely, PPAR-γ activation reduced liver injury, which provides a novel therapeutic concept to prevent HIRI.

Heme Oxygenase-1 in liver transplant ischemia-reperfusion injury: From bench-to-bedside

Hepatic ischemia-reperfusion injury (IRI), a major risk factor for early allograft dysfunction (EAD) and acute or chronic graft rejection, contributes to donor organ shortage for life-saving orthotopic liver transplantation (OLT). The graft injury caused by local ischemia (warm and/or cold) leads to parenchymal cell death and release of danger-associated molecular patterns (DAMPs), followed by reperfusion-triggered production of reactive oxygen species (ROS), activation of inflammatory cells, hepatocellular damage and ultimate organ failure. Heme oxygenase 1 (HO-1), a heat shock protein-32 induced under IR-stress, is an essential component of the cytoprotective mechanism in stressed livers. HO-1 regulates anti-inflammatory responses and may be crucial in the pathogenesis of chronic diseases, such as arteriosclerosis, hypertension, diabetes and steatosis. An emerging area of study is macrophage-derived HO-1 and its pivotal intrahepatic homeostatic function played in IRI-OLT. Indeed, ectopic hepatic HO-1 overexpression activates intracellular SIRT1/autophagy axis to serve as a key cellular self-defense mechanism in both mouse and human OLT recipients. Recent translational studies in rodents and human liver transplant patients provide novel insights into HO-1 mediated cytoprotection against sterile hepatic inflammation. In this review, we summarize the current bench-to-bedside knowledge on HO-1 molecular signaling and discuss their future therapeutic potential to mitigate IRI in OLT.

Targeting HIF-1α to Prevent Renal Ischemia-Reperfusion Injury: Does It Work?

Partial nephrectomy (open or minimally invasive) usually requires temporary renal arterial occlusion to limit intraoperative bleeding and improve access to intrarenal structures. This is a time-critical step due to the critical ischemia period of renal tissue. Prolonged renal ischemia may lead to irreversible nephron damage in the remaining tissue and, ultimately, chronic kidney disease. This is potentiated by the incompletely understood ischemia-reperfusion injury (IRI). A key mechanism in IRI prevention appears to be the upregulation of an intracellular transcription protein, Hypoxia-Inducible Factor (HIF). HIF mediates metabolic adaptation, angiogenesis, erythropoiesis, cell growth, survival, and apoptosis. Upregulating HIF-1α via ischemic preconditioning (IPC) or drugs that simulate hypoxia (hypoxia-mimetics) has been investigated as a method to reduce IRI. While many promising chemical agents have been trialed for the prevention of IRI in small animal studies, all have failed in human trials. The aim of this review is to highlight the techniques and drugs that target HIF-1α and ameliorate IRI associated with renal ischemia. Developing a technique or drug that could reduce the risk of acute kidney injury associated with renal IRI would have an immediate worldwide impact on multisystem surgeries that would otherwise risk ischemic tissue injury.

Mycobacterium tuberculosis Induction of Heme Oxygenase-1 Expression Is Dependent on Oxidative Stress and Reflects Treatment Outcomes

The antioxidant enzyme heme oxygenase-1 (HO-1) is implicated in the pathogenesis of tuberculosis (TB) and has been proposed as a biomarker of active disease. Nevertheless, the mechanisms by which Mycobacterium tuberculosis (Mtb) induces HO-1 as well as how its expression is affected by HIV-1 coinfection and successful antitubercular therapy (ATT) are poorly understood. We found that HO-1 expression is markedly increased in rabbits, mice, and non-human primates during experimental Mtb infection and gradually decreased during ATT. In addition, we examined circulating concentrations of HO-1 in a cohort of 130 HIV-1 coinfected and uninfected pulmonary TB patients undergoing ATT to investigate changes in expression of this biomarker in relation to HIV-1 status, radiological disease severity, and treatment outcome. We found that plasma levels of HO-1 were elevated in untreated HIV-1 coinfected TB patients and correlated positively with HIV-1 viral load and negatively with CD4⁺ T cell count. In both HIV-1 coinfected and Mtb monoinfected patients, HO-1 levels were substantially reduced during successful TB treatment but not in those who experienced treatment failure or subsequently relapsed. To further delineate the molecular mechanisms involved in induction of HO-1 by Mtb, we performed a series of in vitro experiments using mouse and human macrophages. We found that Mtb-induced HO-1 expression requires NADPH oxidase-dependent reactive oxygen species production induced by the early-secreted antigen ESAT-6, which in turn triggers nuclear translocation of the transcription factor NRF-2. These observations provide further insight into the utility of HO-1 as a biomarker of both disease and successful therapy in TB monoinfected and HIV-TB coinfected patients and reveal a previously undocumented pathway linking expression of the enzyme with oxidative stress.

Anti-Inflammatory and Organ-Protective Effects of Resveratrol in Trauma-Hemorrhagic Injury

Resveratrol, a natural polyphenolic compound of grape and red wine, owns potential anti-inflammatory effects, which results in the reduction of cytokines overproduction, the inhibition of neutrophil activity, and the alteration of adhesion molecules expression. Resveratrol also possesses antioxidant, anti-coagulation and anti-aging properties, and it may control of cell cycle and apoptosis. Resveratrol has been shown to reduce organ damage following traumatic and shock-like states. Such protective phenomenon is reported to be implicated in a variety of intracellular signaling pathways including the activation of estrogen receptor, the regulation of the sirtuin 1/nuclear factor-kappa B and mitogen-activated protein kinases/hemeoxygenase-1 pathway, and the mediation of proinflammatory cytokines and reactive oxygen species formation and reaction. In the recent studies, resveratrol attenuates hepatocyte injury and improves cardiac contractility due to reduction of proinflammatory mediator expression and ameliorates hypoxia-induced liver and kidney mitochondrial dysfunction following trauma and hemorrhagic injuries. Moreover, through anti-inflammatory effects and antioxidant properties, the resveratrol is believed to protect organ function in trauma-hemorrhagic injury. In this review, the organ-protective and anti-inflammatory effects of resveratrol in trauma-hemorrhagic injury will be discussed.

The microRNA miR-155 controls CD8(+) T cell responses by regulating interferon signaling

We found upregulation of expression of the microRNA miR-155 in primary effector and effector memory CD8(+) T cells, but low miR-155 expression in naive and central memory cells. Antiviral CD8(+) T cell responses and viral clearance were impaired in miR-155-deficient mice, and this defect was intrinsic to CD8(+) T cells, as miR-155-deficient CD8(+) T cells mounted greatly diminished primary and memory responses. Conversely, miR-155 overexpression augmented antiviral CD8(+) T cell responses in vivo. Gene-expression profiling showed that miR-155-deficient CD8(+) T cells had enhanced type I interferon signaling and were more susceptible to interferon's antiproliferative effect. Inhibition of the type I interferon-associated transcription factors STAT1 or IRF7 resulted in enhanced responses of miR-155-deficient CD8(+) T cells in vivo. We have thus identified a previously unknown role for miR-155 in regulating responsiveness to interferon and CD8(+) T cell responses to pathogens in vivo.

Heme mediated STAT3 activation in severe malaria

Background

The mortality of severe malaria [cerebral malaria (CM), severe malaria anemia (SMA), acute lung injury (ALI) and acute respiratory distress syndrome (ARDS)] remains high despite the availability associated with adequate treatments. Recent studies in our laboratory and others have revealed a hitherto unknown correlation between chemokine CXCL10/CXCR3, Heme/HO-1 and STAT3 and cerebral malaria severity and mortality. Although Heme/HO-1 and CXCL10/CXCR3 interactions are directly involved in the pathogenesis of CM and fatal disease, the mechanism dictating how Heme/HO-1 and CXCL10/CXCR3 are expressed and regulated under these conditions is still unknown. We therefore tested the hypothesis that these factors share common signaling pathways and may be mutually regulated.

Methods

We first clarified the roles of Heme/HO-1, CXCL10/CXCR3 and STAT3 in CM pathogenesis utilizing a well established experimental cerebral malaria mouse (ECM, P. berghei ANKA) model. Then, we further determined the mechanisms how STAT3 regulates HO-1 and CXCL10 as well as mutual regulation among them in CRL-2581, a murine endothelial cell line.

Results

The results demonstrate that (1) STAT3 is activated by P. berghei ANKA (PBA) infection in vivo and Heme in vitro. (2) Heme up-regulates HO-1 and CXCL10 production through STAT3 pathway, and regulates CXCL10 at the transcriptional level in vitro. (3) HO-1 transcription is positively regulated by CXCL10. (4) HO-1 regulates STAT3 signaling.

Conclusion

Our data indicate that Heme/HO-1, CXCL10/CXCR3 and STAT3 molecules as well as related signaling pathways play very important roles in the pathogenesis of severe malaria. We conclude that these factors are mutually regulated and provide new opportunities to develop potential novel therapeutic targets that could be used to supplement traditional prophylactics and treatments for malaria and improve clinical outcomes while reducing malaria mortality. Our ultimate goal is to develop novel therapies targeting Heme or CXCL10-related biological signaling molecules associated with development of fatal malaria.

Hepatic ischemia-reperfusion injury and therapeutic strategies to alleviate cellular damage

Warm hepatic ischemia-reperfusion injury is a significant medical problem in many clinical conditions such as liver transplantation, hepatic surgery for tumor excision, trauma and hepatic failure after hemorrhagic shock. Partial or, mostly, total interruption of hepatic blood flow is often necessary when liver surgery is performed. This interruption of blood flow is termed "warm ischemia" and upon revascularization, when molecular oxygen is reintroduced, the organ undergoes a process called "reperfusion injury" that causes deterioration of organ function. Ischemia reperfusion results in cellular damage and tissue injury associated with a complex series of events. Pathophysiological mechanisms leading to tissue injury following ischemia-reperfusion will be discussed and therapies targeted to reduce liver damage will be summarized within this review.

Immunoregulatory properties of heme oxygenase-1

Heme oxygenase-1 (HO-1) is one of the three isoforms of the heme oxygenase enzyme that catabolyzes the degradation of heme into biliverdin with the production of free iron and CO. HO-1 is induced by its substrate and by other stimuli, including agents involved in oxidative stress and proinflammatory cytokines as well as several anti-inflammatory stimuli. A growing body of evidence points toward the capacity of this molecule to inhibit immune reactions and the pivotal role of HO-1 in inflammatory diseases. We will first review the physiological role of HO-1 as determined by the analysis of HO-1-deficient individuals. This will be followed by an examination of the effect of HO-1 within immunopathological contexts such as immune disorders (autoimmunity and allergy) or infections. A section will be devoted to the use of an HO-1 inducer as an immunosuppressive molecule in transplantation. Finally, we will review the molecular basis of HO-1 actions on different immune cells.

A new role for myeloid HO-1 in the innate to adaptive crosstalk and immune homeostasis

Increasing evidence supports the presence of a dynamic crosstalk between innate and adaptive immunity with a pivotal role played by pathways governing innate immune responses. TLRs (Toll-like receptors) and RLHs (retinoic acid-inducible gene I [RIG-I]-like helicases) are known to play a key role in these processes. A molecule of high significance in the protection against innate and adaptive immune aberrations is heme oxygenase 1 (HO-1). HO-1 is a microsomal enzyme that catalyses the degradation of heme to iron, carbon monoxide and bilirubin. These by-products appear to be the key mediators of its anti--inflammatory and cytoprotective action, mainly through the downregulation of pro-inflammatory and upregulation of anti-inflammatory molecules. Recent data from our lab support the presence of an additional direct effect of myeloid HO-1 on innate immune conditioning, and more specifically on the TLR3/TLR4/RIG-I pathway. In myeloid cells, HO-1 forms a complex with the transcription factor IRF3 (Interferon regulating factor 3) and is required for IRF3 phosphorylation and consequent type-I interferon and chemokine gene induction. Myeloid HO-1-deficient mice show reduced expression of IRF3 target genes and altered responses to infectious and organ-specific auto-immune diseases. This new frame of understanding HO-1 function should also be important for the future design of novel interventions differentially targeting the enzymatic versus the IRF3 modulating properties of HO-1.

Liver ischemia/reperfusion injury: processes in inflammatory networks--a review

Liver ischemia/reperfusion (IR) injury is typified by an inflammatory response. Understanding the cellular and molecular events underpinning this inflammation is fundamental to developing therapeutic strategies. Great strides have been made in this respect recently. Liver IR involves a complex web of interactions between the various cellular and humoral contributors to the inflammatory response. Kupffer cells, CD4+ lymphocytes, neutrophils, and hepatocytes are central cellular players. Various cytokines, chemokines, and complement proteins form the communication system between the cellular components. The contribution of the danger-associated molecular patterns and pattern recognition receptors to the pathophysiology of liver IR injury are slowly being elucidated. Our knowledge on the role of mitochondria in generating reactive oxygen and nitrogen species, in contributing to ionic disturbances, and in initiating the mitochondrial permeability transition with subsequent cellular death in liver IR injury is continuously being expanded. Here, we discuss recent findings pertaining to the aforementioned factors of liver IR, and we highlight areas with gaps in our knowledge, necessitating further research.

Heme oxygenase-1 protects against steatohepatitis in both cultured hepatocytes and mice

BACKGROUND & AIMS

Heme oxygenase-1 (HO-1), an antioxidant defense enzyme, has been shown to protect against oxidant-induced tissue injury. We investigated the role of HO-1 in nutritional steatohepatitis in vitro and in vivo.

METHODS

AML-12 hepatocytes were cultured in methionine- and choline-deficient (MCD) medium. Cells were transfected with an adenovirus vector that expressed HO-1 (Ad-HO-1) or incubated with the HO-1 inducer hemin or the HO-1 inhibitor stannic mesoporphyrin for 24 hours. C57BL6 mice and db/db mice were fed MCD or control diets, with or without hemin, for up to 4 weeks.

RESULTS

AML-12 cells exposed to MCD medium developed significant steatosis, increased release of alanine aminotransferase, and showed signs of oxidative injury. Incubation with hemin induced HO-1 protein, suppressed steatosis, and reduced levels of alanine aminotransferase and lipid peroxidation. A comparable effect was observed in cells transfected with Ad-HO-1, whereas incubation of these cells with stannic mesoporphyrin completely abolished the Ad-HO-1- or hemin-mediated protection of hepatocytes. Mice injected with hemin significantly attenuated MCD-induced steatohepatitis and increased HO-1 protein and activity. This effect was associated with up-regulation of antioxidant chaperones and enzymes, down-regulation of proinflammatory cytokines, and up-regulation of the anti-inflammatory interleukin-22. Moreover, the reduction in steatosis caused by hemin was affected by up-regulation of peroxisome proliferator-activated receptor-alpha and by down-regulation of sterol regulatory element binding protein-1c.

CONCLUSIONS

HO-1 can interrupt progression of nutritional steatohepatitis by inducing an antioxidant pathway, suppressing production of cytokines, and modifying fatty acid turnover. Induction of HO-1 might provide a new approach for treatment of steatohepatitis.

Pretreatment with calcitonin gene-related peptide attenuates hepatic ischemia/reperfusion injury in rats

OBJECTIVE

Oxygen free radicals and apoptosis play important roles in liver ischemia/reperfusion (I/R) injury. We sought to investigate the protective effect of calcitonin gene-related peptide (CGRP) to attenuate liver I/R injury due to oxygen free radicals and apoptosis.

MATERIALS AND METHODS

Harvested rat livers were perfused via the portal vein with 60 mL of 4 degrees C histidine-tryptophan-ketoglutarate (HTK) solution alone in the control group, or with the same solution containing CGRP (3 microg/10 g body weight) in the experimental group. After 24 hours of cold storage, hepatic enzyme leakage, portal venous pressure, oxygen consumption, total adenine nucleotides (TAN), bile production, lipoperoxide (LPO) release, apoptosis, and histochemical changes were evaluated upon 45 minutes of isolated reperfusion.

RESULTS

Compared with control livers, CGRP-treated organs showed significantly decreased alanine aminotransferase (ALT) and glutamate-lactate dehydrogenase (GLDH) leakage and portal venous pressure (2.0 +/- 0.3 vs 4.0 +/- 0.4 mmHg; P < .01), with significantly increased bile production (8.56 +/- 0.76 vs 3.34 +/- 0.68 microL/g/45 min; P < .01), oxygen consumption (5.14 +/- 0.4 vs 2.57 +/- 0.2 microL/g/min; P < .01), and total adenine nucleotides (TAN) (11.1 +/- 0.71 vs 7.02 +/- 0.53 micromol/g; P < .01) upon reperfusion as signs of recovered viability. We observed infrequent positive terminal deoxynucleotidyl transferase-mediated dUTP biotin nick end labeling (TUNEL) staining, especially in sinusoidal lining cells (SLC). The percentage of TUNEL-positive cells in the CGRP group was significantly decreased compared with the control group: (4.1 +/- 0.67 vs 8.0 +/- 1.27; P < .05). Perfusate levels of low molecular weight (LMW) histone-associated DNA fragments (0.36 +/- 0.04 vs 0.53 +/- 0.06 AU; P < .05) were also decreased, coupled with strong 5'-nucleotidase (5'-NT) and LDH activity staining concentrated on the endothelial cells. LPO release in the perfusate was largely decreased: (0.12 +/- 0.02 vs 0.36 +/- 0.04 nmoL/g, P < .01).

CONCLUSION

CGRP ameliorated liver I/R injury due to reactive oxygen species and apoptosis.

Modulation of inflammatory response by selective inhibition of cyclooxygenase-1 and cyclooxygenase-2 in acute kidney injury

OBJECTIVE AND DESIGN

This work explored the role of inhibition of cyclooxygenases (COXs) in modulating the inflammatory response triggered by acute kidney injury.

MATERIAL

C57Bl/6 mice were used.

TREATMENT

Animals were treated or not with indomethacin (IMT) prior to injury (days -1 and 0).

METHODS

Animals were subjected to 45 min of renal pedicle occlusion and sacrificed at 24 h after reperfusion. Serum creatinine and blood urea nitrogen, reactive oxygen species (ROS), kidney myeloperoxidase (MPO) activity, and prostaglandin E2 (PGE(2)) levels were analyzed. Tumor necrosis factor (TNF)-alpha, t-bet, interleukin (IL)-10, IL-1beta, heme oxygenase (HO)-1, and prostaglandin E synthase (PGES) messenger RNA (mRNA) were studied. Cytokines were quantified in serum.

RESULTS

IMT-treated animals presented better renal function with less acute tubular necrosis and reduced ROS and MPO production. Moreover, the treatment was associated with lower expression of TNF-alpha, PGE(2), PGES, and t-bet and upregulation of HO-1 and IL-10. This profile was mirrored in serum, where inhibition of COXs significantly decreased interferon (IFN)-gamma, TNF-alpha, and IL-12 p70 and upregulated IL-10.

CONCLUSIONS

COXs seem to play an important role in renal ischemia and reperfusion injury, involving the secretion of pro-inflammatory cytokines, activation of neutrophils, and ROS production. Inhibition of COX pathway is intrinsically involved with cytoprotection.

Influence of polymorphism within the heme oxygenase-I promoter on overall survival and transplantation-related mortality after allogeneic stem cell transplantation

Aside from major and minor histocompatibility antigens, genetic polymorphisms of various donor and host genes have been found to be risk factors for graft-versus-host disease and transplantation-related mortality (TRM). The heme oxygenase I (HO-I) protein has been implicated in regulating inflammatory response and has been described as a "protective gene" in solid organ transplantation. In humans, the promoter region displays length polymorphism due to a variable number of GT repeats. Individuals exhibiting 29 or fewer GT repeats express higher levels of HO-I on cellular stress compared with individuals with 30 or more GT repeats. We retrospectively analyzed length polymorphisms of 92 donor-host pairs undergoing allogeneic stem cell transplantation. Our findings demonstrate that mainly donor polymorphism leading to high expression of HO-1 (<30 GT repeats) on stress signals is associated with reduced overall survival, and that TRM is significantly increased in this group. This reduction in survival was most prominent when unrelated donors were used. Polymorphisms of the recipient HO-1 genes did not influence posttransplantation outcomes. We conclude that HO-1 polymorphism represents a new genetic risk factor for TRM and overall survival.

Pharmacological and clinical aspects of heme oxygenase

This review is intended to stimulate interest in the effect of increased expression of heme oxygenase-1 (HO-1) protein and increased levels of HO activity on normal and pathological states. The HO system includes the heme catabolic pathway, comprising HO and biliverdin reductase, and the products of heme degradation, carbon monoxide (CO), iron, and biliverdin/bilirubin. The role of the HO system in diabetes, inflammation, heart disease, hypertension, neurological disorders, transplantation, endotoxemia and other pathologies is a burgeoning area of research. This review focuses on the clinical potential of increased levels of HO-1 protein and HO activity to ameliorate tissue injury. The use of pharmacological and genetic probes to manipulate HO, leading to new insights into the complex relationship of the HO system with biological and pathological phenomena under investigation, is reviewed. This information is critical in both drug development and the implementation of clinical approaches to moderate and to alleviate the numerous chronic disorders in humans affected by perturbations in the HO system.

Heme oxygenase-1 ameliorates ischemia/reperfusion injury by targeting dendritic cell maturation and migration

Ischemia/reperfusion injury (IRI) has a major impact on short- and long-term renal allograft survival by increasing graft immunogenicity. Donor preconditioning by inducing heme oxygenase 1 (HO-1) has been proven to exert cytoprotective and antiinflammatory effects on the graft, thus resulting in reduced graft immunogenicity. The study analyzed the effects and mechanisms of HO-1-mediated cytoprotection in rat kidney transplants exposed to cold preservation. We studied the differential gene-expression patterns of allografts after either short or long cold ischemia using a customized cDNA microarray. Prolonged cold ischemia led, 12 h after engraftment, to enhanced levels of adhesion molecules, heat-shock proteins, chemokines (CXCL10), and a remarkable upregulation of immunoproteasomes. Next we addressed the question whether induction of HO-1 or its byproduct carbon monoxide (CO) in organ donors targets these candidate markers related to enhanced immunogenicity. Induction of HO-1 or CO in organ donors 24 h before organ harvesting resulted in reduced mRNA levels of immunoproteasomes, MHC class II expression, and co-stimulatory molecules in the recipient's spleen, suggesting diminished migration and activation of donor dendritic cells. This observation suggests that HO-1/CO induction protects marginal allografts by inhibiting the immunogenicity of donor-derived dendritic cells.

Genetic overexpression of eNOS attenuates hepatic ischemia-reperfusion injury

Previous studies have shown that endothelial nitric oxide (NO) synthase (eNOS)-derived NO is an important signaling molecule in ischemia-reperfusion (I-R) injury. Deficiency of eNOS-derived NO has been shown to exacerbate injury in hepatic and myocardial models of I-R. We hypothesized that transgenic overexpression of eNOS (eNOS-TG) would reduce hepatic I-R injury. We subjected two strains of eNOS-TG mice to 45 min of hepatic ischemia and 5 h of reperfusion. Both strains were protected from hepatic I-R injury compared with wild-type littermates. Because the mechanism for this protection is still unclear, additional studies were performed by using inhibitors and activators of both soluble guanylyl cyclase (sGC) and heme oxygenase-1 (HO-1) enzymes. Blocking sGC with 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) and HO-1 with zinc (III) deuteroporphyrin IX-2,4-bisethyleneglycol (ZnDPBG) in wild-type mice increased hepatic I-R injury, whereas pharmacologically activating these enzymes significantly attenuated I-R injury in wild-type mice. Interestingly, ODQ abolished the protective effects of eNOS overexpression, whereas ZnDPBG had no effect. These results suggest that hepatic protection in eNOS-TG mice may be mediated in part by NO signaling via the sGC-cGMP pathway and is independent of HO-1 signal transduction pathways.