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

MicroRNAs miR-451a and Let-7i-5p Profiles in Circulating Exosomes Vary among Individuals with Different Sickle Hemoglobin Genotypes and Malaria

Sickle cell disease (SCD) occurs when two alleles of mutated hemoglobin (HbS or HbC) are inherited (HbSS and HbSC) rather than one (HbAS or HbAC), which indicates a person carries the sickle cell trait. The high prevalence of these two alleles in Africa have been associated with reduced malaria susceptibility. Recent in vitro research has been shown that microRNAs (miRNAs) miR-451a and let-7i-5p are differentially expressed in HbSS erythrocytes compared to healthy controls (HbAA) and are overexpressed in Plasmodium-infected malaria erythrocytes. However, these miRNAs have not been fully examined in the plasma of people with different sickle hemoglobin genotypes. Plasma circulating miRNAs are commonly encapsulated in extracellular vesicles, such as exosomes, and are thought to play a role in disease development. Circulating exosomal miR-451a and let-7i-5p were quantified from individuals with various hemoglobin genotypes (HbAA, HbAS, HbAC, HbSS, HbSC, and HbCC) with (+) and without (-) malaria. The results showed a higher level of exosomal let-7i-5p and miR-451a in HbSS-. Exosomal let-7i-5p and miR-451a levels were lower in HbSS+ compared to other genotypes. Based on the area under the curve (AUC) of the Receiver Operating Characteristics (ROCs), both exosomal miRNAs may be useful disease biomarkers for SCD with malaria. Finally, miR-451a and let-7i-5p modulate genes involved in inflammation, making them potential biomarkers of pathogenesis for both diseases.

Combination of Early Allograft Dysfunction and Protein Expression Patterns Predicts Outcome of Liver Transplantation From Donation After Cardiac Death

Early allograft dysfunction (EAD) after liver transplantation (LT) accompanies poor prognosis. This study aims to explore the relationship between pretransplant intrahepatic proteins and the incidence of EAD, and the value of combined EAD and protein profiles for predicting recipient and graft survival prognosis. Liver biopsy specimens of 105 pretransplant grafts used for LT were collected and used for immunohistochemistry analysis of 5 proteins. And matched clinical data of donor, recipient, transplantation, and prognosis were analyzed. The incidence of EAD was 41.9% (44/105) in this cohort. Macrovesicular steatosis (P = 0.016), donor body mass index (P = 0.013), recipients' pretransplant serum creatinine (P = 0.036), and intrahepatic expression of heme oxygenase 1 (HO1) (P = 0.015) and tumor necrosis factor α (TNF-α) (P = 0.039) were independent predictors of EAD. Inferior graft and recipient prognosis were observed in patients who experienced EAD (P = 0.028 and 0.031) or received grafts with higher expression of sirtuin 1 (P = 0.005 and 0.013). The graft and recipient survival were worst in patients with both EAD and high expression of sirtuin 1 (P = 0.001 and 0.004). In conclusion, pretransplant intrahepatic expression of HO1 and TNF-α are associated with the incidence of EAD. The combination of EAD and EAD-unrelated proteins showed superiority in distinguishing recipients with worse prognosis.

Tender Coconut Water Protects Mice From Ischemia-Reperfusion-Mediated Liver Injury and Secondary Lung Injury

ABSTRACT

Organ injury by oxidative and inflammatory mediators occurs during ischemia-reperfusion (I/R) of the liver. Remote organ injury secondary to liver I/R increases the systemic insult. Tender coconut water (TCW) has been studied in chemical and fructose-induced liver injury but its ability to decrease tissue injury in clinically relevant injury models is unknown. We evaluated the therapeutic potential of TCW in preventing liver I/R injury and associated remote organ injury. Mice were fed sugar water (SUG; control) or TCW for a week and then subjected to 60 min of liver ischemia followed by reperfusion for 6 h. Plasma alanine transaminase levels, tissue damage, and mRNA levels of Nos2, Tnf, and Il6 were significantly lower in mice fed TCW prior to I/R. Plasma cytokines followed liver cytokine patterns. TCW increased mRNA levels of the anti-oxidant genes Hmox1 and Ptgs2 in the liver of mice subjected to I/R. Remote lung injury from liver I/R was also decreased by TCW feeding as evident by less neutrophil infiltration, decreased pro-inflammatory Il6, and increased anti-inflammatory Il10 mRNA levels in the lung. To examine macrophage activation as a potential mechanism, TCW pretreatment decreased the amount of nitrite produced by RAW264.7 macrophages stimulated with LPS. The levels of Nos2, Il1b, Tnf, and Il6 were decreased while Il10 and Hmox1 mRNA levels were significantly up-regulated upon LPS stimulation of TCW pretreated RAW264.7 macrophages. Collectively, our results indicate that TCW decreased hepatic I/R-mediated damage to liver and lung and suggest that decreased macrophage activation contributes to this effect.

The Protective Role of the Heme Catabolic Pathway in Hepatic Disorders

Significance: As the central metabolic organ, the liver is exposed to a variety of potentially cytotoxic, proinflammatory, profibrotic, and carcinogenic stimuli. To protect the organism from these deleterious effects, the liver has evolved a number of defense systems, which include antioxidant substrates and enzymes, anti-inflammatory tools, enzymatic biotransformation systems, and metabolic pathways. Recent Advances: One of the pivotal systems that evolved during phylogenesis was the heme catabolic pathway. Comprising the important enzymes heme oxygenase and biliverdin reductase, this complex pathway has a number of key functions including enzymatic activities, but also cell signaling, and DNA transcription. It further generates two important bile pigments, biliverdin and bilirubin, as well as the gaseous molecule carbon monoxide. These heme degradation products have potent antioxidant, immunosuppressive, and cytoprotective effects. Recent data suggest that the pathway participates in the regulation of metabolic and hormonal processes implicated in the pathogenesis of hepatic and other diseases. Critical Issues: This review discusses the impact of the heme catabolic pathway on major liver diseases, with particular focus on the involvement of cellular targeting and signaling in the pathogenesis of these conditions. Future Directions: To utilize the biological consequences of the heme catabolic pathway, several unique therapeutic strategies have been developed. Research indicates that pharmaceutical, nutraceutical, and lifestyle modifications positively affect the pathway, delivering potentially long-term clinical benefits. However, further well-designed studies are needed to confirm the clinical benefits of these approaches. Antioxid. Redox Signal. 35, 734-752.

Heme Oxygenase-1 in Gastrointestinal Tract Health and Disease

Heme oxygenase 1 (HO-1) is the rate-limiting enzyme of heme oxidative degradation, generating carbon monoxide (CO), free iron, and biliverdin. HO-1, a stress inducible enzyme, is considered as an anti-oxidative and cytoprotective agent. As many studies suggest, HO-1 is highly expressed in the gastrointestinal tract where it is involved in the response to inflammatory processes, which may lead to several diseases such as pancreatitis, diabetes, fatty liver disease, inflammatory bowel disease, and cancer. In this review, we highlight the pivotal role of HO-1 and its downstream effectors in the development of disorders and their beneficial effects on the maintenance of the gastrointestinal tract health. We also examine clinical trials involving the therapeutic targets derived from HO-1 system for the most common diseases of the digestive system.

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.

Hepatitis C virus core or NS3/4A protein expression preconditions hepatocytes against oxidative stress and endoplasmic reticulum stress

Objectives: The occurrence of oxidative stress and endoplasmic reticulum (ER) stress in hepatitis C virus (HCV) infection has been demonstrated and play an important role in liver injury. During viral infection, hepatocytes must handle not only the replication of the virus, but also inflammatory signals generating oxidative stress and damage. Although several mechanisms exist to overcome cellular stress, little attention has been given to the adaptive response of hepatocytes during exposure to multiple noxious triggers.

Methods: In the present study, Huh-7 cells and hepatocytes expressing HCV Core or NS3/4A proteins, both inducers of oxidative and ER stress, were additionally challenged with the superoxide anion generator menadione to mimic external oxidative stress. The production of reactive oxygen species (ROS) as well as the response to oxidative stress and ER stress were investigated.

Results: We demonstrate that hepatocytes diminish oxidative stress through a reduction in ROS production, ER-stress markers (HSPA5 [GRP78], sXBP1) and apoptosis (caspase-3 activity) despite external oxidative stress. Interestingly, the level of the autophagy substrate protein p62 was downregulated together with HCV Core degradation, suggesting that hepatocytes can overcome excess oxidative stress through autophagic degradation of one of the stressors, thereby increasing cell survival.

Duscussion: In conclusion, hepatocytes exposed to direct and indirect oxidative stress inducers are able to cope with cellular stress associated with viral hepatitis and thus promote cell survival.

Identification of HO-1 as a novel biomarker for graft acute cellular rejection and prognosis prediction after liver transplantation

Background

Liver transplantation (LT) is the most effective treatment for patients with end-stage liver diseases, but acute rejection is still a major concern. However, the mechanisms underlying rejection remain unclear. Biomarkers are lacking for predicting rejection and long-term survival after LT.

Methods

Isobaric tags for relative and absolute quantitation (iTRAQ)-based proteomics was performed between acute cellular rejection (ACR) and non-rejection recipients. The molecular signature differences and potential biomarkers were identified by comprehensive bioinformatics. Heme oxygenase-1 (HO-1) expression and its association with clinical outcomes were investigated by tissue microarrays consisted of liver specimens from recipients with (n=80) and without ACR (n=57).

Results

A total of 287 differentially expressed proteins (DEPs) were identified. Pathway analysis revealed that T/B cell activation, integrin/inflammation signaling pathway, etc. were significantly correlated with ACR. Through comprehensive bioinformatics, HO-1 was identified as a candidate potential biomarker for ACR. In tissue microarray (TMA) analysis, HO-1 expression was significantly higher in ACR group than in non-rejection group (P<0.01). Preoperative Child-Pugh and Meld scores were significantly higher in recipients with high HO-1 expression (P<0.01). In a mean 5-year follow-up, recipients with high HO-1 expression were associated with a shorter overall survival (P<0.05). Further multivariate analyses indicated that HO-1 could be an independent adverse prognostic factor for post-transplant survival (P=0.005).

Conclusions

A total of 287 DEPs were identified, providing a set of targets for further research. Recipients with high preoperative HO-1 expression were associated with ACR. HO-1 may be used as a potential biomarker for predicting the development of post-transplant allograft ACR and recipient's survival.

Evaluation and Exploration of Potentially Bioactive Peptides in Casein Hydrolysates against Liver Oxidative Damage in STZ/HFD-Induced Diabetic Rats

Hyperglycemia-induced oxidative stress can cause liver damage in diabetes, and protein hydrolysates with antidiabetic and antioxidant properties are emerging as a potential therapy. In this study, protective effects of casein hydrolysates against live oxidative damage in streptozotocin/high-fat-induced diabetic rats were studied and potentially bioactive peptides were explored by an integrated approach of differential peptide and in silico analysis. Results showed that different casein hydrolysates significantly alleviated liver oxidative damage (p < 0.05) via different mechanisms. Particularly, casein hydrolyzed by a papain-flavourzyme combination (P-FCH) treatment significantly improved liver antioxidant enzyme activities by enhancing nuclear factor erythroid 2-related factor 2 (Nrf2) transcription (p < 0.05). Furthermore, 18 peptides were screened as potential bioactive peptides by analyzing differential peptides among different hydrolysates combined with in silico prediction. Among them, the dipeptide WM might directly inhibit the Kelch-like ECH-associated protein 1 (Keap1)-Nrf2 interaction as potential Nrf2 activators. These results suggested that P-FCH might be an alternative way to treat liver damage in diabetes.

Recipient HO-1 inducibility is essential for posttransplant hepatic HO-1 expression and graft protection: From bench-to-bedside

By documenting potent antioxidative and anti-inflammatory functions, preclinical studies encourage heme oxygenase-1 (HO-1)-inducing regimens in clinical orthotopic liver transplantation (OLT). We aimed to determine the importance of recipient-derived HO-1 in murine and human OLTs. Hepatic biopsies from 51 OLT patients were screened for HO-1 expression (Western blots) prior to put-in (basal) and post reperfusion (stressed) and correlated with the hepatocellular function. In parallel, livers from HO-1 proficient mice (WT; C57/BL6), subjected to ex vivo cold storage (18 hour), were transplanted to syngeneic myeloid HO-1 deficient (mHO-1 KO) or FLOX (control) hosts, and sampled postreperfusion (6 hour). In human OLT, posttransplant but not pretransplant HO-1 expression correlated negatively with ALT levels (P = .0178). High posttransplant but not pretransplant HO-1 expression trended with improved OLT survival. Compared with controls, livers transplanted into mHO-1 KO recipient mice had decreased HO-1 levels, exacerbated hepatic damage/frequency of TUNEL+ cells, increased mRNA levels coding for TNFα/CXCL1/CXCL2/CXCL10, higher frequency of Ly6G+/4HN+ neutrophils; and enhanced MPO activity. Peritoneal neutrophils from mHO-1 KO mice exhibited higher CellRox+ ratio and increased TNFα/CXCL1/CXCL2/CXCL10 expression. By demonstrating the importance of posttransplant recipient HO-1 phenotype in hepatic macrophage/neutrophil regulation and function, this translational study identifies recipient HO-1 inducibility as a novel biomarker of ischemic stress resistance in OLT.

Heme oxygenase-1 regulates sirtuin-1-autophagy pathway in liver transplantation: From mouse to human

Liver ischemia-reperfusion injury (IRI) represents a major risk factor of early graft dysfunction and a key obstacle to expanding the donor pool in orthotopic liver transplantation (OLT). Although graft autophagy is essential for resistance against hepatic IRI, its significance in clinical OLT remains unknown. Despite recent data identifying heme oxygenase-1 (HO-1) as a putative autophagy inducer, its role in OLT and interactions with sirtuin-1 (SIRT1), a key autophagy regulator, have not been studied. We aimed to examine HO-1-mediated autophagy induction in human OLT and in a murine OLT model with extended (20 hours) cold storage, as well as to analyze the requirement for SIRT1 in autophagy regulation by HO-1. Fifty-one hepatic biopsy specimens from OLT patients were collected under an institutional review board protocol 2 hours after portal reperfusion, followed by Western blot analyses. High HO-1 levels correlated with well-preserved hepatocellular function and enhanced SIRT1/LC3B expression. In mice, HO-1 overexpression by genetically modified HO-1 macrophage therapy was accompanied by decreased OLT damage and increased SIRT1/LC3B expression, whereas adjunctive inhibition of SIRT1 signaling diminished HO-1-mediated hepatoprotection and autophagy induction. Our translational study confirms the clinical relevance of HO-1 cytoprotection and identifies SIRT1-mediated autophagy pathway as a new essential regulator of HO-1 function in IR-stressed OLT.

Macrophage heme oxygenase-1-SIRT1-p53 axis regulates sterile inflammation in liver ischemia-reperfusion injury

BACKGROUND & AIMS

Hepatic ischemia-reperfusion injury (IRI), characterized by exogenous antigen-independent local inflammation and hepatocellular death, represents a risk factor for acute and chronic rejection in liver transplantation. We aimed to investigate the molecular communication involved in the mechanism of liver IRI.

METHODS

We analyzed human liver transplants, primary murine macrophage cell cultures and IR-stressed livers in myeloid-specific heme oxygenase-1 (HO-1) gene mutant mice, for anti-inflammatory and cytoprotective functions of macrophage-specific HO-1/SIRT1 (sirtuin 1)/p53 (tumor suppressor protein) signaling.

RESULTS

Decreased HO-1 expression in human post-reperfusion liver transplant biopsies correlated with a deterioration in hepatocellular function (serum ALT; p<0.05) and inferior patient survival (p<0.05). In the low HO-1 liver transplant biopsy group, SIRT1/Arf (alternative reading frame)/p53/MDM2 (murine double minute 2) expression levels decreased (p<0.05) while cleaved caspase 3 and frequency of TUNEL+cells simultaneously increased (p<0.05). Immunofluorescence showed macrophages were the principal source of HO-1 in human and mouse IR-stressed livers. In vitro macrophage cultures revealed that HO-1 induction positively regulated SIRT1 signaling, whereas SIRT1-induced Arf inhibited ubiquitinating activity of MDM2 against p53, which in turn attenuated macrophage activation. In a murine model of hepatic warm IRI, myeloid-specific HO-1 deletion lacked SIRT1/p53, exacerbated liver inflammation and IR-hepatocellular death, whereas adjunctive SIRT1 activation restored p53 signaling and rescued livers from IR-damage.

CONCLUSION

This bench-to-bedside study identifies a new class of macrophages activated via the HO-1-SIRT1-p53 signaling axis in the mechanism of hepatic sterile inflammation. This mechanism could be a target for novel therapeutic strategies in liver transplant recipients.

LAY SUMMARY

Post-transplant low macrophage HO-1 expression in human liver transplants correlates with reduced hepatocellular function and survival. HO-1 regulates macrophage activation via the SIRT1-p53 signaling network and regulates hepatocellular death in liver ischemia-reperfusion injury. Thus targeting this pathway in liver transplant recipients could be of therapeutic benefit.

Ischemia/Reperfusion

Ischemic disorders, such as myocardial infarction, stroke, and peripheral vascular disease, are the most common causes of debilitating disease and death in westernized cultures. The extent of tissue injury relates directly to the extent of blood flow reduction and to the length of the ischemic period, which influence the levels to which cellular ATP and intracellular pH are reduced. By impairing ATPase-dependent ion transport, ischemia causes intracellular and mitochondrial calcium levels to increase (calcium overload). Cell volume regulatory mechanisms are also disrupted by the lack of ATP, which can induce lysis of organelle and plasma membranes. Reperfusion, although required to salvage oxygen-starved tissues, produces paradoxical tissue responses that fuel the production of reactive oxygen species (oxygen paradox), sequestration of proinflammatory immunocytes in ischemic tissues, endoplasmic reticulum stress, and development of postischemic capillary no-reflow, which amplify tissue injury. These pathologic events culminate in opening of mitochondrial permeability transition pores as a common end-effector of ischemia/reperfusion (I/R)-induced cell lysis and death. Emerging concepts include the influence of the intestinal microbiome, fetal programming, epigenetic changes, and microparticles in the pathogenesis of I/R. The overall goal of this review is to describe these and other mechanisms that contribute to I/R injury. Because so many different deleterious events participate in I/R, it is clear that therapeutic approaches will be effective only when multiple pathologic processes are targeted. In addition, the translational significance of I/R research will be enhanced by much wider use of animal models that incorporate the complicating effects of risk factors for cardiovascular disease. © 2017 American Physiological Society. Compr Physiol 7:113-170, 2017.

Plasmodium-infected erythrocytes (pRBC) induce endothelial cell apoptosis via a heme-mediated signaling pathway

Heme is cytotoxic to the plasmodium parasite, which converts it to an insoluble crystalline form called hemozoin (malaria pigment) in erythrocytes during replication. The increased serum levels of free heme cause tissue damage, activation of microvascular endothelial and glial cells, focal inflammation, activation of apoptotic pathways, and neuronal tissue damage. Several hypotheses have been proposed to explain how these causative factors exacerbate fatal malaria. However, none of them fully explain the detailed mechanisms leading to the high morbidity and mortality associated with malaria. We have previously reported that heme-induced brain microvascular endothelial cell (HBVEC) apoptosis is a major contributor to severe malaria pathogenesis. Here, we hypothesized that heme (at clinically relevant levels) induces inflammation and apoptosis in HBVEC, a process that is mediated by independent proinflammatory and proapoptotic signaling pathways. In this study, we determined the key signaling molecules associated with heme-mediated apoptosis in HBVEC in vitro using RT2 profiler polymerase chain reaction array technology and confirmed results using immunostaining techniques. While several expressed genes in HBVEC were altered upon heme stimulation, we determined that the apoptotic effects of heme were mediated through p73 (tumor protein p73). The results provide an opportunity to target heme-mediated apoptosis therapeutically in malaria-infected individuals.

Endogenous carbon monoxide downregulates hepatic cystathionine-γ-lyase in rats with liver cirrhosis

The aim of the present study was to investigate the effect of endogenous carbon monoxide (CO) on the hydrogen sulfide/cystathionine-γ-lyase (H₂S/CSE) pathway in cirrhotic rat livers. The rats were allocated at random into four groups: Sham, cirrhosis, cobalt protoporphyrin (CoPP) and zinc protoporphyrin IX (ZnPP). The expression of hepatic CSE mRNA was evaluated using a quantitative polymerase chain reaction, while CSE protein expression was determined using immunohistochemical analysis. Hematoxylin and eosin staining was performed for the histological evaluation of liver fibrosis. The levels of H₂S, alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bilirubin (TBIL) and carboxyhemoglobin (COHb) in the arterial blood were determined, in addition to the portal vein pressure. The mRNA and protein expression levels of hepatic CSE and the serum levels of H₂S were significantly decreased in the cirrhosis group compared with those in the sham group (P<0.05). Compared with the cirrhosis group, rats in the ZnPP group had significantly lower levels of serum ALT, AST and TBIL, arterial COHb and hepatic fibrosis, while hepatic CSE expression and the production of H₂S were significantly increased (P<0.05). The CoPP group exhibited decreased hepatic CSE expression and H₂S production, but aggravated hepatic function and fibrosis (P<0.05). In conclusion, the H₂S/CSE pathway is involved in the formation of liver cirrhosis and serves a crucial function in protecting liver cells against the progression of liver fibrosis. Endogenous CO downregulates hepatic CSE mRNA and protein expression and the production of H₂S in rats with liver cirrhosis.

Hepatocellular heme oxygenase-1: a potential mechanism of erythropoietin-mediated protection after liver ischemia-reperfusion injury

Hepatic ischemia-reperfusion (IR) results in progressive injury; initiated by oxidative stress during ischemia and compounded by cytokine-mediated inflammation during reperfusion. Recovery requires strict regulation of these events. Recombinant human erythropoietin (rhEPO) is thought to mitigate hepatocellular IR injury by altering the nonparenchymal liver microenvironment. This study sought to identify additional mechanisms whereby rhEPO is protective after liver IR injury. Mice were treated with rhEPO (4 units/g s.c.) at the onset of partial liver ischemia and assessed for transaminase and histologic injury at intervals after reperfusion. Induction of cytokines, activation of signal transducers and activators of transcription (STATs), suppressors of cytokine signaling (Socs1, Socs3, Cis), caspase-3 activation, and heme oxygenase-1 (HO-1) expression were assessed in postischemic liver. Effects of rhEPO stimulation were further characterized in whole-liver lysates from mice undergoing rhEPO injection alone and in cultured AML-12 hepatocytes. Recombinant human erythropoietin treatment at the onset of severe (90 min) hepatic IR confirmed commensurate biochemical and histological protection without affecting tissue cytokine levels. Although Socs3 and STAT5 activation were induced in normal liver after in vivo rhEPO injection, this treatment did not augment expression beyond that seen with IR alone, and neither was induced in cultured hepatocytes treated with rhEPO. Recombinant human erythropoietin inhibited caspase-3 activation in nonparenchymal cells, whereas hepatocellular HO-1 was rapidly induced both in vivo and in vitro with rhEPO treatment. These data suggest HO-1 as a potent mechanism of rhEPO-mediated protection after liver IR, which involves both direct hepatocellular and nonparenchymal mechanisms.

Protective role of hemeoxygenase-1 in gastrointestinal diseases

Disorders and diseases of the gastrointestinal system encompass a wide array of pathogenic mechanisms as a result of genetic, infectious, neoplastic, and inflammatory conditions. Inflammatory diseases in general are rising in incidence and are emerging clinical problems in gastroenterology and hepatology. Hemeoxygenase-1 (HO-1) is a stress-inducible enzyme that has been shown to confer protection in various organ-system models. Its downstream effectors, carbon monoxide and biliverdin have also been shown to offer these beneficial effects. Many studies suggest that induction of HO-1 expression in gastrointestinal tissues and cells plays a critical role in cytoprotection and resolving inflammation as well as tissue injury. In this review, we examine the protective role of HO-1 and its downstream effectors in modulating inflammatory diseases of the upper (esophagus and stomach) and lower (small and large intestine) gastrointestinal tract, the liver, and the pancreas. Cytoprotective, anti-inflammatory, anti-proliferative, antioxidant, and anti-apoptotic activities of HO-1 make it a promising if not ideal therapeutic target for inflammatory diseases of the gastrointestinal system.

Phosphodiesterase-4 inhibition with rolipram attenuates hepatocellular injury in hyperinflammation in vivo and in vitro without influencing inflammation and HO-1 expression

Objective:

To investigate the impact of the phophodiesterase-4 inhibition (PD-4-I) with rolipram on hepatic integrity in lipopolysaccharide (LPS) induced hyperinflammation.

Materials and Methods:

Liver microcirculation in rats was obtained using intravital microscopy. Macrohemodynamic parameters, blood assays, and organs were harvested to determine organ function and injury. Hyperinflammation was induced by LPS and PD-4-I rolipram was administered intravenously one hour after LPS application. Cell viability of HepG2 cells was measured by EZ4U-kit based on the dye XTT. Experiments were carried out assessing the influence of different concentrations of tumor necrosis factor alpha (TNF-α) and LPS with or without PD-4-I.

Results:

Untreated LPS-induced rats showed significantly decreased liver microcirculation and increased hepatic cell death, whereas LPS + PD-4-I treatment could improve hepatic volumetric flow and cell death to control level whithout influencing the inflammatory impact. In HepG2 cells TNF-α and LPS significantly reduced cell viability. Coincubation with PD-4-I increased HepG2 viability to control levels. The heme oxygenase 1 (HO-1) pathway did not induce the protective effect of PD-4-I.

Conclusion:

Intravenous PD-4-I treatment was effective in improving hepatic microcirculation and hepatic integrity, while it had a direct protective effect on HepG2 viability during inflammation.

Expression of hemopexin in acute rejection of rat liver allograft identified by serum proteomic analysis

Acute rejection (AR) and acceptance of allograft after liver transplantation (LTx) remain critical issues that need addressing to improve prognosis. We therefore performed rat orthotopic LTx and proteomic analyses to screen for immune response-related biomarkers in sera. Markers identified were validated at the mRNA and/or protein levels, and the molecules of interest were functionally explored. Compared with syngeneic controls, signs of AR as well as spontaneous acceptance were observed in hematoxylin and eosin-stained sections of liver allografts. In accordance with the severity of AR, 30 protein spots displaying significant changes in abundance were identified using two-dimensional differential gel electrophoresis. Ultimately, 14 serum proteins were sequenced and five spots of interest were identified as hemopexin (HPX). Expression of HPX was significantly and inversely associated with the severity of AR at both the mRNA and protein levels. In vitro, Mt-1, Ho-1, Fth, Ifn-γ, and Il-17 transcripts were significantly upregulated in lysates of lymphocytes stimulated with HPX, whereas Il-10 markedly was remarkably downregulated. Interferon-γ, IL-10, and IL-17 proteins in the supernatant of HPX-stimulated lymphocytes were significantly altered in keeping with the mRNA level. Our data facilitated the generation of a proteomic profile to enhance the understanding of rat liver AR. In view of finding that the HPX serum level is negatively associated with the severity of AR of rat liver allograft, we propose that in vitro treatment with HPX regulates cytokine expression in rat lymphocytes.

The immunophenotype of antigen presenting cells of the mononuclear phagocyte system in normal human liver--a systematic review

The mononuclear phagocytic system (MPS), comprised of monocytes, macrophages, and dendritic cells, is essential in tissue homeostasis and in determining the balance of the immune response through its role in antigen presentation. It has been identified as a therapeutic target in infectious disease, cancer, autoimmune disease and transplant rejection. Here, we review the current understanding of the immunophenotype and function of the MPS in normal human liver. Using well-defined selection criteria, a search of MEDLINE and EMBASE databases identified 76 appropriate studies. The majority (n=67) described Kupffer cells (KCs), although the definition of KC differs between sources, and little data were available regarding their function. Only 10 papers looked at liver dendritic cells (DCs), and largely confirmed the presence of the major dendritic cell subsets identified in human blood. Monocytes were thoroughly characterized in four studies that utilized flow cytometry and fluorescent microscopy and highlighted their prominent role in liver homeostasis and displayed subtle differences from circulating monocytes. There was some limited evidence that liver DCs are tolerogenic but neither liver dendritic cell subsets nor macrophages have been thoroughly characterized, using either multi-colour flow cytometry or multi-parameter fluorescence microscopy. The lobular distribution of different subsets of liver MPS cells was also poorly described, and the ability to distinguish between passenger leukocytes and tissue resident cells remains limited. It was apparent that further research, using modern immunological techniques, is now required to accurately characterize the cells of the MPS in human liver.

Octreotide attenuates liver fibrosis by inhibiting hepatic heme oxygenase-1 expression

The aim of the present study was to investigate the effects of octreotide treatment on hepatic heme oxygenase-1 (HO-1) expression, together with the influence of altered hepatic HO-1 expression levels on hepatic function and fibrosis in bile duct-ligated rats. The rats were divided randomly into sham, cirrhotic, cobalt protoporphyrin and octreotide treatment groups. The expression levels of hepatic HO-1 mRNA were measured by reverse-transcription polymerase chain reaction, while the protein expression was determined by western blotting and immunohistochemical analysis. Hematoxylin and eosin, and Van Gieson's staining, along with determination of the hydroxyproline content in the liver, were performed to determine the degree of liver fibrosis. The serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bilirubin (TBIL) and carboxyhemoglobin (COHb) in arterial blood, and the mean arterial pressure and portal vein pressure were also measured. As compared with the sham group, hepatic HO-1 mRNA and protein expression levels, serum levels of ALT, AST and TBIL, COHb in arterial blood, hydroxyproline and collagen type I content were all significantly increased in the cirrhotic group. As compared with the cirrhotic group, the octreotide-treated group exhibited significantly reduced hepatic HO-1 expression levels, serum levels of ALT, AST and TBIL, COHb in arterial blood and the extent of hepatic fibrosis, whereas the cobalt protoporphyrin group exhibited significantly increased hepatic HO-1 expression levels, as well as aggravated hepatic function and fibrosis (P<0.05). In conclusion, octreotide inhibited hepatic HO-1 overexpression in cirrhotic rats, reduced hepatic HO-1 expression levels to relieve liver injury and attenuated liver fibrosis.

Induction of heme oxygenase-1 protects mouse liver from apoptotic ischemia/reperfusion injury

Ischemia/reperfusion (I/R) injury is the main cause of primary graft dysfunction of liver allografts. Cobalt-protoporphyrin (CoPP)-dependent induction of heme oxygenase (HO)-1 has been shown to protect the liver from I/R injury. This study analyzes the apoptotic mechanisms of HO-1-mediated cytoprotection in mouse liver exposed to I/R injury. HO-1 induction was achieved by the administration of CoPP (1.5 mg/kg body weight i.p.). Mice were studied in in vivo model of hepatic segmental (70 %) ischemia for 60 min and reperfusion injury. Mice were randomly allocated to four main experimental groups (n = 10 each): (1) A control group undergoing sham operation. (2) Similar to group 1 but with the administration of CoPP 72 h before the operation. (3) Mice undergoing in vivo hepatic I/R. (4) Similar to group 3 but with the administration of CoPP 72 h before ischemia induction. When compared with the I/R mice group, in the I/R+CoPP mice group, the increased hepatic expression of HO-1 was associated with a significant reduction in liver enzyme levels, fewer apoptotic hepatocytes cells were identified by morphological criteria and by immunohistochemistry for caspase-3, there was a decreased mean number of proliferating cells (positively stained for Ki67), and a reduced hepatic expression of: C/EBP homologous protein (an index of endoplasmic reticulum stress), the NF-κB's regulated genes (CIAP2, MCP-1 and IL-6), and increased hepatic expression of IκBa (the inhibitory protein of NF-κB). HO-1 over-expression plays a pivotal role in reducing the hepatic apoptotic IR injury. HO-1 may serve as a potential target for therapeutic intervention in hepatic I/R injury during liver transplantation.

STAT3 regulates MMP3 in heme-induced endothelial cell apoptosis

BACKGROUND

We have previously reported that free Heme generated during experimental cerebral malaria (ECM) in mice, is central to the pathogenesis of fatal ECM. Heme-induced up-regulation of STAT3 and CXCL10 promotes whereas up-regulation of HO-1 prevents brain tissue damage in ECM. We have previously demonstrated that Heme is involved in the induction of apoptosis in vascular endothelial cells. In the present study, we further tested the hypothesis that Heme reduces blood-brain barrier integrity during ECM by induction of apoptosis of brain vascular endothelial cells through STAT3 and its target gene matrix metalloproteinase three (MMP3) signaling.

METHODS

Genes associated with the JAK/STAT3 signaling pathway induced upon stimulation by Heme treatment, were assessed using real time RT(2) Profile PCR arrays. A human MMP3 promoter was cloned into a luciferase reporter plasmid, pMMP3, and its activity was examined following exposure to Heme treatment by a luciferase reporter gene assay. In order to determine whether activated nuclear protein STAT3 binds to the MMP3 promoter and regulates MMP3 gene, we conducted a ChIP analysis using Heme-treated and untreated human brain microvascular endothelial cells (HBVEC), and determined mRNA and protein expression levels of MMP3 using qRT-PCR and Western blot. Apoptosis in HBVEC treated with Heme was evaluated by MTT and TUNEL assay.

RESULTS

The results show that (1) Heme activates a variety of JAK/STAT3 downstream pathways in HBVEC. STAT3 targeted genes such as MMP3 and C/EBPb (Apoptosis-related genes), are up regulated in HBVEC treated with Heme. (2) Heme-induced HBVEC apoptosis via activation of STAT3 as well as its downstream signaling molecule MMP3 and upregulation of CXCL10 and HO-1 expressions. (3) Phosphorylated STAT3 binds to the MMP3 promoter in HBVEC cells, STAT3 transcribed MMP3 and induced MMP3 protein expression in HBVEC cells.

CONCLUSIONS

Activated STAT3 binds to the MMP3 promoter region and regulates MMP3 in Heme-induced endothelial cell apoptosis.

Inhibiting heme oxygenase-1 attenuates rat liver fibrosis by removing iron accumulation

AIM: To investigate the effects of the heme oxygenase (HO)-1/carbon monoxide system on iron deposition and portal pressure in rats with hepatic fibrosis induced by bile duct ligation (BDL).

METHODS: Male Sprague-Dawley rats were divided randomly into a Sham group, BDL group, Fe group, deferoxamine (DFX) group, zinc protoporphyrin (ZnPP) group and cobalt protoporphyrin (CoPP) group. The levels of HO-1 were detected using different methods. The serum carboxyhemoglobin (COHb), iron, and portal vein pressure (PVP) were also quantified. The plasma and mRNA levels of hepcidin were measured. Hepatic fibrosis and its main pathway were assessed using Van Gieson’s stain, hydroxyproline, transforming growth factor-β1 (TGF-β1), nuclear factor-E2-related factor 2 (Nrf2), matrix metalloproteinase-2 (MMP-2) and tissue inhibitor of metalloproteinase-1 (TIMP-1).

RESULTS: Serum COHb and protein and mRNA expression levels of HO-1 and Nrf2 were increased in the BDL group compared with the Sham group and were much higher in the CoPP group. The ZnPP group showed lower expression of HO-1 and Nrf2 and lower COHb. The levels of iron and PVP were enhanced in the BDL group but were lower in the ZnPP and DFX groups and were higher in the CoPP and Fe groups. Hepcidin levels were higher, whereas superoxide dismutase levels were increased and malonaldehyde levels were decreased in the ZnPP and DFX groups. The ZnPP group also showed inhibited TGF-β1 expression and regulated TIMP-1/MMP-2 expression, as well as obviously attenuated liver fibrosis.

CONCLUSION: Reducing hepatic iron deposition and CO levels by inhibiting HO-1 activity though the Nrf2/Keap pathway could be helpful in improving hepatic fibrosis and regulating PVP.

Gene polymorphisms in the heme degradation pathway and outcome of severe human sepsis

Heme and its breakdown products CO, Fe, and bilirubin are being recognized as signaling molecules or even therapeutic agents, but also exert adverse effects when released at high concentrations. Manipulating the pathway confers protection in rodent sepsis models via both control of free heme and formation of its first and higher-order products. Thus, regulatory elements present in human heme oxygenase 1 (HMOX1) and biliverdin reductases (BLVRA/B) genes might impact outcome. We tested whether a highly polymorphic (GT)n microsatellite and single-nucleotide polymorphisms in HMOX1 and BLVRA/B genes are associated with outcome of sepsis. Two cohorts (n = 430 and 398 patients) with severe sepsis were screened for single-nucleotide polymorphisms and/or the microsatellite by fragment length analysis and genotyping techniques. Heme oxygenase 1 plasma levels were determined in additional patients with severe sepsis (n = 92) by enzyme-linked immunosorbent assay. Based on mean Sepsis-related Organ Failure Assessment scores, patients homozygous for rs2071746 A allele or medium length (GT)n microsatellites of HMOX1 showed higher 28-day mortality (P = 0.047 and P = 0.033) in one cohort compared with other genotypes, whereas 90-day mortality rates showed no association. The T allele was less frequently observed in both cohorts than would be expected according to Hardy-Weinberg equilibrium. Heme oxygenase 1 plasma levels were elevated in septic patients, independent of the genotype. Single-nucleotide polymorphisms within BLVRA/B showed no association with outcome. Short (GT)n repeats that are in linkage disequilibrium with the T allele of rs2071746 in HMOX1 are associated with favorable outcome, whereas no association with gene variants of BLVRA/B, involved in the generation of higher-order metabolites, was noticed.

Disruption of Type-I IFN pathway ameliorates preservation damage in mouse orthotopic liver transplantation via HO-1 dependent mechanism

Ischemia/reperfusion injury (IRI) remains unresolved problem in clinical organ transplantation. We analyzed the role of Type-I interferon (IFN) pathway in a clinically relevant murine model of extended hepatic cold preservation followed by orthotopic liver transplantation (OLT). Livers from Type-I IFN receptor (IFNAR) knockout (KO) or wild-type (WT) mice (C57/BL6) were harvested, preserved at 4°C in UW solution for 20 h and transplanted to groups of syngeneic IFNAR KO or WT recipients. Liver graft but not recipient IFNAR deficiency was required to consistently ameliorate IRI in OLTs. Indeed, disruption of Type-I IFN signaling decreased serum alanine aminotransferase (sALT) levels (p < 0.001), diminished Suzuki's score of histological OLT damage (p < 0.01) and improved 14-day survival (from 42%[5/12] in WT to 92%[11/12] in IFNAR KO; p < 0.05). Unlike in WT group, IFNAR deficiency attenuated OLT expression of TNF-α, IL-1β, IL-6, MCP-1, CXCL-10, ICAM-1; diminished infiltration by macrophages/PMNs; and enhanced expression of antioxidant HO-1/Nrf2. The frequency of TUNEL+ apoptotic cells and caspase-3 activity/expression selectively decreased in IFNAR KO group. Small interfering (si)RNA-directed targeting of HO-1 restored cardinal features of liver IRI in otherwise resistant IFNAR-deficient OLTs. Thus, intact Type-I IFN signaling is required for hepatic IRI, whereas HO-1 is needed for cytoprotection against innate immunity-dominated organ preservation damage in IFNAR-deficient liver transplants.

Heme oxygenase, inflammation, and fibrosis: the good, the bad, and the ugly?

Upon injury, prolonged inflammation and oxidative stress may cause pathological wound healing and fibrosis, leading to formation of excessive scar tissue. Fibrogenesis can occur in most organs and tissues and may ultimately lead to organ dysfunction and failure. The underlying mechanisms of pathological wound healing still remain unclear, and are considered to be multifactorial, but so far, no efficient anti-fibrotic therapies exist. Extra- and intracellular levels of free heme may be increased in a variety of pathological conditions due to release from hemoproteins. Free heme possesses pro-inflammatory and oxidative properties, and may act as a danger signal. Effects of free heme may be counteracted by heme-binding proteins or by heme degradation. Heme is degraded by heme oxygenase (HO) that exists as two isoforms: inducible HO-1 and constitutively expressed HO-2. HO generates the effector molecules biliverdin/bilirubin, carbon monoxide, and free iron/ferritin. HO deficiency in mouse and man leads to exaggerated inflammation following mild insults, and accumulating epidemiological and preclinical studies support the widely recognized notion of the cytoprotective, anti-oxidative, and anti-inflammatory effects of the activity of the HO system and its effector molecules. In this review, we address the potential effects of targeted HO-1 induction or administration of HO-effector molecules as therapeutic targets in fibrotic conditions to counteract inflammatory and oxidative insults. This is exemplified by various clinically relevant conditions, such as hypertrophic scarring, chronic inflammatory liver disease, chronic pancreatitis, and chronic graft rejection in transplantation.

Diazoxide attenuates ischemia/reperfusion injury via upregulation of heme oxygenase-1 after liver transplantation in rats

AIM: To evaluate the effects of diazoxide on ischemia/reperfusion (I/R)-injured hepatocytes and further elucidate its underlying mechanisms.

METHODS: Male Sprague-Dawley rats were randomized (8 for donor and recipient per group) into five groups: I/R group (4 h of liver cold ischemia followed by 6 h of reperfusion); heme oxygenase-1 (HO-1) small interfering RNA (siRNA) group (injection of siRNA via donor portal vein 48 h prior to harvest); diazoxide (DZ) group (injection of DZ via donor portal vein 10 min prior to harvest); HO-1 siRNA + DZ group; and siRNA control group. Blood and liver samples were collected at 6 h after reperfusion. The mRNA expressions and protein levels of HO-1 were determined by reverse transcription polymerase chain reaction and Western blotting, and tissue morphology was examined by light and transmission electron microscopy. Serum transaminases level and cytokines concentration were also measured.

RESULTS: We observed that a significant reduction of HO-1 mRNA and protein levels in HO-1 siRNA and HO-1 siRNA + DZ group when compared with I/R group, while the increases were prominent in the DZ group. Light and transmission electron microscopy indicated severe disruption of tissue with lobular distortion and mitochondrial cristae damage in the HO-1 siRNA and HO-1 siRNA + DZ groups compared with DZ group. Serum alanine aminotransferase, aspartate transaminase, tumor necrosis factor-α and interleukin-6 levels increased in the HO-1 siRNA and HO-1 siRNA + DZ groups, and decreased in the DZ group.

CONCLUSION: The protective effect of DZ may be induced by upregulation of HO-1. By inhibiting expression of HO-1, this protection pretreated with DZ was abolished.

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.

Cell biology of ischemia/reperfusion injury

Disorders characterized by ischemia/reperfusion (I/R), such as myocardial infarction, stroke, and peripheral vascular disease, continue to be among the most frequent causes of debilitating disease and death. Tissue injury and/or death occur as a result of the initial ischemic insult, which is determined primarily by the magnitude and duration of the interruption in the blood supply, and then subsequent damage induced by reperfusion. During prolonged ischemia, ATP levels and intracellular pH decrease as a result of anaerobic metabolism and lactate accumulation. As a consequence, ATPase-dependent ion transport mechanisms become dysfunctional, contributing to increased intracellular and mitochondrial calcium levels (calcium overload), cell swelling and rupture, and cell death by necrotic, necroptotic, apoptotic, and autophagic mechanisms. Although oxygen levels are restored upon reperfusion, a surge in the generation of reactive oxygen species occurs and proinflammatory neutrophils infiltrate ischemic tissues to exacerbate ischemic injury. The pathologic events induced by I/R orchestrate the opening of the mitochondrial permeability transition pore, which appears to represent a common end-effector of the pathologic events initiated by I/R. The aim of this treatise is to provide a comprehensive review of the mechanisms underlying the development of I/R injury, from which it should be apparent that a combination of molecular and cellular approaches targeting multiple pathologic processes to limit the extent of I/R injury must be adopted to enhance resistance to cell death and increase regenerative capacity in order to effect long-lasting repair of ischemic tissues.

Preoperative fasting protects mice against hepatic ischemia/reperfusion injury: mechanisms and effects on liver regeneration

We show that brief periods of fasting induce functional changes similar to those induced by long-term dietary restriction in mice, and these changes include protection from ischemia/reperfusion (I/R) injury. In this study, we investigated the mechanisms of protection induced by fasting, and we determined the effect on liver regeneration after partial hepatectomy. Partial hepatic ischemia (75 minutes) was induced in ad libitum fed mice and in 1- to 3-day-fasted mice, and one-third or two-thirds hepatectomy was performed in ad libitum fed mice and 3-day-fasted mice. Preoperative fasting for 2 or 3 days significantly decreased hepatocellular I/R injury. Hepatic gene expression of heme oxygenase 1 (HO-1), superoxide dismutase 2 (SOD2), glutathione peroxidase 1 (Gpx1), and glutathione reductase (GSR) was significantly up-regulated in 3-day-fasted mice at the baseline and 6 hours after reperfusion. After reperfusion, p-selectin and interleukin-6 (IL-6) levels were significantly lower, and superoxide radical generation, lipid peroxidation, and neutrophil influx were significantly attenuated in 3-day-fasted mice. Preoperative fasting did not affect liver regeneration after one-third hepatectomy. Hepatic gene expression of IL-6 and transforming growth factor β1 was significantly higher in 3-day-fasted mice before and after one-third hepatectomy. Tumor necrosis factor α expression significantly increased after one-third hepatectomy in 3-day-fasted mice. After a 3-day fast and two-thirds hepatectomy, liver regeneration and subsequent postoperative recovery were compromised. In conclusion, up-regulation of the stress response gene HO-1 and the antioxidant enzymes SOD2, Gpx1, and GSR at the baseline and a better response after reperfusion likely underlie the protection induced by fasting against hepatic I/R injury. Preoperative fasting may be a promising new strategy for protecting the liver against I/R injury during liver transplantation and minor liver resections, although its effect on extended hepatectomy warrants further exploration.

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.

New insights into fatty liver preservation using Institute Georges Lopez preservation solution

Institute Georges Lopez preservation solution (IGL-1) has been demonstrated to be useful for fatty liver preservation. The mechanisms responsible for this effective graft protection against ischemia-reperfusion injury are pivotal actions on generation of nitric oxide a diffusible molecule with vasodilator properties, that facilitates the up-regulation of other well-known cytoprotective genes, such as hypoxia-inducible factor-1 alpha (HIF-1alpha) and heme-oxygenase 1 (HO-1). During normoxic reperfusion, the presence of nitric oxide permits HIF-1alpha accumulation to inhibit prolyl-hydoxylases, thus promoting an additional overexpression of the HO-1 in steatotic and nonsteatotic graft livers preserved in IGL-1.

Heme oxygenase-1 protects donor livers from ischemia/reperfusion injury: the role of Kupffer cells

AIM

To examine whether heme oxygenase (HO)-1 overexpression would exert direct or indirect effects on Kupffer cells activation, which lead to aggravation of reperfusion injury.

METHODS

Donors were pretreated with cobalt protoporphyrin (CoPP) or zinc protoporphyrin (ZnPP), HO-1 inducer and antagonist, respectively. Livers were stored at 4 degrees C for 24 h before transplantation. Kupffer cells were isolated and cultured for 6 h after liver reperfusion.

RESULTS

Postoperatively, serum transaminases were significantly lower and associated with less liver injury when donors were pretreated with CoPP, as compared with the ZnPP group. Production of the cytokines tumor necrosis factor-alpha and interleukin-6 generated by Kupffer cells decreased in the CoPP group. The CD14 expression levels (RT-PCR/Western blots) of Kupffer cells from CoPP-pretreated liver grafts reduced.

CONCLUSION

The study suggests that the potential utility of HO-1 overexpression in preventing ischemia/reperfusion injury results from inhibition of Kupffer cells activation.

Preconditioning, organ preservation, and postconditioning to prevent ischemia-reperfusion injury to the liver

Ischemia and reperfusion lead to injury of the liver. Ischemia-reperfusion injury is inevitable in liver transplantation and trauma and, to a great extent, in liver resection. This article gives an overview of the mechanisms involved in this type of injury and summarizes protective and treatment strategies in clinical use today. Intervention is possible at different time points: during harvesting, during the period of preservation, and during implantation. Liver preconditioning and postconditioning can be applied in the transplant setting and for liver resection. Graft optimization is merely possible in the period between the harvest and the implantation. Given that there are 3 stages in which a surgeon can intervene against ischemia-reperfusion injury, we have structured the review as follows. The first section reviews the approaches using surgical interventions, such as ischemic preconditioning, as well as pharmacological applications. In the second section, static organ preservation and machine perfusion are addressed. Finally, the possibility of treating the recipient or postconditioning is discussed.

Heme oxygenase-1 induction in macrophages by a hemoglobin-based oxygen carrier reduces endotoxin-stimulated cytokine secretion

The inflammatory response after an insult may provoke further tissue damage, and the macrophage is central in this pathophysiology. Induction of heme oxygenase-1 (HO-1) attenuates postshock organ dysfunction, although the mechanism remains unclear. We hypothesized that HO-1 induction modifies the cytokine profile of LPS-stimulated macrophages. Heme oxygenase-1 was induced in murine and human macrophages with varying concentrations of a hemoglobin-based oxygen carrier (HBOC). Heme oxygenase-1 expression was analyzed by Western blotting of whole cell lysates. Macrophages were pretreated with HBOC for 4 h, then media with LPS were added for up to 24 h. The specific HO-1 inhibitor zinc protoporphyrin (ZnPP) was used to inhibit the effects of HO-1. Supernatants were analyzed for IL-6, IL-10, TNF-alpha, and monocyte chemotactic protein 1 (MCP-1) by enzyme-linked immunosorbent assay. Incubation of cells with HBOC produced a dose-dependent expression of HO-1. Heme oxygenase-1 expression decreased LPS-stimulated secretion of MCP-1, IL-6, IL-10, and TNF-alpha at both 4 and 24 h in murine and human macrophages. The addition of ZnPP to inhibit HO-1 partially restored MCP-1 and IL-6 secretion in murine macrophages. Furthermore, immunofluorescent microscopy revealed HBOC-induced HO-1 inhibited LPS-stimulated nuclear translocation of the p65 subunit of nuclear factor-kappaB. In summary, HBOC incubation of macrophages induced HO-1 expression, which reduced LPS-mediated cytokine release, and that MCP-1 and IL-6 secretion could be partially restored with ZnPP. These data encourage continued investigation into the role of HO-1 in protecting against posttraumatic organ dysfunction and the clinical potential of HBOC for HO-1 induction.

Natural heme oxygenase-1 inducers in hepatobiliary function

Many physiological effects of natural antioxidants, their extracts or their major active components, have been reported in recent decades. Most of these compounds are characterized by a phenolic structure, similar to that of α-tocopherol, and present antioxidant properties that have been demonstrated both in vitro and in vivo. Polyphenols may increase the capacity of endogenous antioxidant defences and modulate the cellular redox state. Changes in the cellular redox state may have wide-ranging consequences for cellular growth and differentiation. The majority of in vitro and in vivo studies conducted so far have attributed the protective effect of bioactive polyphenols to their chemical reactivity toward free radicals and their capacity to prevent the oxidation of important intracellular components. However, in recent years a possible novel aspect in the mode of action of these compounds has been suggested; that is, the ultimate stimulation of the heme oxygenase-1 (HO-1) pathway is likely to account for the established and powerful antioxidant/anti-inflammatory properties of these polyphenols. The products of the HO-catalyzed reaction, particularly carbon monoxide (CO) and biliverdin/bilirubin have been shown to exert protective effects in several organs against oxidative and other noxious stimuli. In this context, it is interesting to note that induction of HO-1 expression by means of natural compounds contributes to protection against liver damage in various experimental models. The focus of this review is on the significance of targeted induction of HO-1 as a potential therapeutic strategy to protect the liver against various stressors in several pathological conditions.

Activation of the oxygen-sensing signal cascade prevents mitochondrial injury after mouse liver ischemia-reperfusion

The mitochondrial permeability transition (MPT) plays an important role in hepatocyte death caused by ischemia-reperfusion (IR). This study investigated whether activation of the cellular oxygen-sensing signal cascade by prolyl hydroxylase inhibitors (PHI) protects against the MPT after hepatic IR. Ethyl 3,4-dihyroxybenzoate (EDHB, 100 mg/kg ip), a PHI, increased mouse hepatic hypoxia-inducible factor-1alpha and heme oxygenase-1 (HO-1). EDHB-treated and untreated mice were subjected to 1 h of warm ischemia to approximately 70% of the liver followed by reperfusion. Mitochondrial polarization, cell death, and the MPT were assessed by intravital confocal/multiphoton microscopy of rhodamine 123, propidium iodide, and calcein. EDHB largely blunted alanine aminotransferase (ALT) release and necrosis after reperfusion. In vehicle-treated mice at 2 h after reperfusion, viable cells with depolarized mitochondria were 72%, and dead cells were 2%, indicating that depolarization preceded necrosis. Mitochondrial voids excluding calcein disappeared, indicating MPT onset in vivo. NIM811, a specific inhibitor of the MPT, blocked mitochondrial depolarization after IR, further confirming that mitochondrial depolarization was due to MPT onset. EDHB decreased mitochondrial depolarization to 16% and prevented the MPT. Tin protoporphyrin (10 micromol/kg sc), an HO-1 inhibitor, partially abrogated protection by EDHB against ALT release, necrosis, and mitochondrial depolarization. In conclusion, IR causes the MPT and mitochondrial dysfunction, leading to hepatocellular death. PHI prevents MPT onset and liver damage through an effect mediated partially by HO-1.

(GT)N dinucleotide repeat polymorphism of haem oxygenase-1 promotor region is not associated with inflammatory bowel disease risk or disease course

Haem oxygenase-1 (HO-1) up-regulation was suggested to reduce mucosal tissue damage in inflammatory bowel disease (IBD) and an up-regulation of HO-1 expression in patients with Crohn's disease (CD) and ulcerative colitis (UC) was demonstrated. A HO-1 gene promoter microsatellite (GT)(n) dinucleotide repeat polymorphism was associated with regulation of HO-1 in response to inflammatory stimuli. We therefore hypothesized that IBD patients might segregate into phenotypes with high or low HO-1 inducibility. Ethylenediamine tetraacetic acid blood samples were obtained from 179 CD patients, 110 UC patients and 56 control patients without inflammation. Genomic DNA was purified and the 5'-flanking region of the HO-1 gene containing the (GT)(n) dinucleotide repeat was amplified. Polymerase chain reaction (PCR) products were purified and the length of the PCR fragments was analysed. The number of (GT)(n) repeats in the population studied ranged from 13 to 42. The distribution of the allele frequencies was comparable in patients and controls for both the short and the long alleles. The frequencies of short-, middle- and long-sized alleles were not changed among the groups studied. No correlation was found between IBD and microsatellite instability detected in five individals. Our data indicate that (GT)(n) dinucleotide repeats of the HO-1 promotor region have no significance for the pathophysiology and disease course of IBD.

Protein levels of heme oxygenase-1 during reperfusion in human kidney transplants with delayed graft function

INTRODUCTION

Delayed graft function (DGF) as a consequence of ischemia reperfusion injury (IRI) is associated with a decrease in long-term allograft survival. Heme oxygenase-1 (HO-1) is a stress responsive gene that is highly expressed in multiple pathological processes. The aim of our study was to analyze whether HO-1 protein levels in human kidney transplants during IRI correlate with the incidence of DGF.

METHODS

Kidney biopsies were obtained from 27 kidney allografts at two time points: at the end of cold storage and shortly after reperfusion. Samples were analyzed for HO-1 protein levels by Western blot.

RESULTS

Heme oxygenase-1 protein levels were significantly higher in post-reperfusion biopsies (39.4 vs. 13.7 arbitrary units, p = 0.001). In pre-reperfusion biopsies no association was observed between HO-1 protein levels and DGF. In post-reperfusion biopsies, higher levels of HO-1 protein were measured in kidneys with DGF (53.7 vs. 36.2 arbitrary units, p = 0.064). DGF kidneys showed a significantly higher increase from pre- to post-reperfusion in HO-1 protein (42.0 vs. 18.7 arbitrary units, p = 0.025).

CONCLUSION

Heme oxygenase-1 protein levels shortly after allograft reperfusion are closely related with initial graft function. Assessment thereof may be considered a valuable tool to predict DGF.

Heme oxygenase-1 genotype of the donor is associated with graft survival after liver transplantation

Heme oxygenase-1 (HO-1) has been suggested as a cytoprotective gene during liver transplantation. Inducibility of HO-1 is modulated by a (GT)(n) polymorphism and a single nucleotide polymorphism (SNP) A(-413)T in the promoter. Both a short (GT)(n) allele and the A-allele have been associated with increased HO-1 promoter activity. In 308 liver transplantations, we assessed donor HO-1 genotype and correlated this with outcome variables. For (GT)(n) genotype, livers were divided into two classes: short alleles (<25 repeats; class S) and long alleles (> or =25 repeats; class L). In a subset, hepatic messenger ribonucleic acid (mRNA) expression was correlated with genotypes. Graft survival at 1 year was significantly better for A-allele genotype compared to TT-genotype (84% vs. 63%, p = 0.004). Graft loss due to primary dysfunction (PDF) occurred more frequently in TT-genotype compared to A-receivers (p = 0.03). Recipients of a liver with TT-genotype had significantly higher serum transaminases after transplantation and hepatic HO-1 mRNA levels were significantly lower compared to the A-allele livers (p = 0.03). No differences were found for any outcome variable between class S and LL-variant of the (GT)(n) polymorphism. Haplotype analysis confirmed dominance of the A(-413)T SNP over the (GT)(n) polymorphism. In conclusion, HO-1 genotype is associated with outcome after liver transplantation. These findings suggest that HO-1 mediates graft survival after liver transplantation.

Dietary flaxseed enhances antioxidant defenses and is protective in a mouse model of lung ischemia-reperfusion injury

Dietary flaxseed (FS) is a nutritional whole grain with high contents of omega-3 fatty acids and lignans with anti-inflammatory and antioxidant properties. We evaluated FS in a murine model of pulmonary ischemia-reperfusion injury (IRI) by dietary supplementation of 0% (control) or 10% (treatment) FS before IRI. Mice fed 0% FS undergoing IRI had a significant decrease in arterial oxygenation (Pa(O(2))) and a significant increase in bronchoalveolar lavage (BAL) protein compared with sham-operated mice. However, mice fed 10% FS undergoing IRI had a significant improvement in both Pa(O(2)) and BAL protein compared with mice fed 0% FS undergoing IRI. In addition, oxidative lung damage was decreased in 10% FS-supplemented mice undergoing IRI, as assessed by malondialdehyde levels. Immunohistochemical staining of lungs for iPF(2alpha)-III F(2) isoprostane, a measure of lipid oxidation, was diminished. FS-supplemented mice had less reactive oxygen species (ROS) release from the vascular endothelium in lungs in an ex vivo model of IRI, and alveolar macrophages isolated from FS-fed mice had significantly reduced ROS generation in response to oxidative burst. Pulmonary microvascular endothelial cells produced less ROS in a flow cessation model of ischemia when preincubated with purified FS lignan metabolites. Pharmacological inhibition of heme oxygenase-1 (HO-1) resulted in only a partial reduction of FS protection in the same model. We conclude that dietary FS is protective against IRI in an experimental murine model and that FS affects ROS generation and ROS detoxification via pathways not limited to upregulation of antioxidant enzymes such as HO-1.

Kidney grafts from brain dead donors: Inferior quality or opportunity for improvement?

Major improvements in immunosuppressive treatment, surgical techniques, and treatment of post-transplant complications have contributed considerably to improved outcome in renal transplantation over the past decades. Yet, these accomplishments have not led to similar improvements in transplant outcome when the results of living and deceased donors are compared. The enormous demand for donor kidneys has allowed for the increase in acceptance of suboptimal donors. The use of brain dead patients as organ donors has had a tremendous positive influence on the number of renal transplants. Unfortunately, the physiologically abnormal state of brain death has a negative effect on transplant outcome. The fact that transplanted kidneys derived from brain dead donors have a decreased viability indicates that potential grafts are already damaged before retrieval and preservation. In this review, we present an overview of the current knowledge of (patho)-physiological effects of brain death and its relevance for renal transplant outcome. In addition, several options for therapeutic intervention during brain death in the donor with the goal to improve organ viability and transplant outcome are discussed.

Heme oxygenase-1 overexpression increases liver injury after bile duct ligation in rats

AIM: To investigate the effects of heme oxygenase-1 (HO-1) against oxidant-induced injury caused by bile duct ligation (BDL).

METHODS: Either cobalt protoporphyrin (CoPP), a HO-1 inducer, or saline were injected intraperitoneally in male SD-rats. Three days later, BDL or sham-operations were performed. Rats were sacrificed 3 wk after BDL and livers were harvested for histology. Fibrosis was evaluated by sirius red staining and image analysis. Alpha-smooth muscular actin, which indicates activation of stellate cells, was detected by immunohistochemical staining, and cytokine and collagen-Iα (Col-Iα) mRNA expression was detected using RNase protection assays.

RESULTS: Serum alanine transaminase increased 8-fold above normal levels one day after BDL. Surprisingly, enzyme release was not reduced in rats receiving CoPP. Liver fibrosis was evaluated 3 wk after BDL and the sirius red-positive area was found to be increased to about 7.8%. However, in CoPP pretreated rats sirius red-positive areas were increased to about 11.7% after BDL. Collagen-Iα and TGF-β mRNA increased significantly by BDL. Again, this effect was increased by HO-1 overexpression.

CONCLUSION: Hepatic fibrosis due to BDL is not reduced by the HO-1 inducer CoPP. In contrast, HO-1 overexpression increases liver injury in rats under conditions of experimental chronic cholestasis.