Fundamental role for HO-1 in the self-protection of renal allografts

The Role of Heme Oxygenase-1 as an Immunomodulator in Kidney Disease

The protein heme oxygenase (HO)-1 has been implicated in the regulations of multiple immunological processes. It is well known that kidney injury is affected by immune mechanisms and that various kidney-disease forms may be a result of autoimmune disease. The current study describes in detail the role of HO-1 in kidney disease and provides the most recent observations of the effect of HO-1 on immune pathways and responses both in animal models of immune-mediated disease forms and in patient studies.

Identification of Cytoprotective Small-Molecule Inducers of Heme-Oxygenase-1

Acute kidney injury (AKI) is a major public health concern with significant morbidity and mortality and no current treatments beyond supportive care and dialysis. Preclinical studies have suggested that heme-oxygenase-1 (HO-1), an enzyme that catalyzes the breakdown of heme, has promise as a potential therapeutic target for AKI. Clinical trials involving HO-1 products (biliverdin, carbon monoxide, and iron), however, have not progressed beyond the Phase ½ level. We identified small-molecule inducers of HO-1 that enable us to exploit the full therapeutic potential of HO-1, the combination of its products, and yet-undefined effects of the enzyme system. Through cell-based, high-throughput screens for induction of HO-1 driven by the human HO-1 promoter/enhancer, we identified two novel small molecules and broxaldine (an FDA-approved drug) for further consideration as candidate compounds exhibiting an Emax ≥70% of 5 µM hemin and EC50 <10 µM. RNA sequencing identified shared binding motifs to NRF2, a transcription factor known to regulate antioxidant genes, including HMOX1. In vitro, the cytoprotective function of the candidates was assessed against cisplatin-induced cytotoxicity and apoptosis. In vivo, delivery of a candidate compound induced HO-1 expression in the kidneys of mice. This study serves as the basis for further development of small-molecule HO-1 inducers as preventative or therapeutic interventions for a variety of pathologies, including AKI.

Carbon monoxide mechanism of protection against renal ischemia and reperfusion injury

Carbon monoxide is quickly moving past its historic label as a molecule once feared, to a therapeutic drug that modulates inflammation. The development of carbon monoxide releasing molecules and utilization of heme oxygenase-1 inducers have shown carbon monoxide to be a promising therapy in reducing renal ischemia and reperfusion injury and other inflammatory diseases. In this review, we will discuss the developments and application of carbon monoxide releasing molecules in renal ischemia and reperfusion injury, and transplantation. We will review the anti-inflammatory mechanisms of carbon monoxide in respect to mitigating apoptosis, suppressing dendritic cell maturation and signalling, inhibiting toll-like receptor activation, promoting anti-inflammatory responses, and the effects on renal vasculature.

Roles of Heme Oxygenase-1 in Neuroinflammation and Brain Disorders

The heme oxygenase (HO) system is believed to be a crucial mechanism for the nervous system under stress conditions. HO degrades heme to carbon monoxide, iron, and biliverdin. These heme degradation products are involved in modulating cellular redox homeostasis. The first identified isoform of the HO system, HO-1, is an inducible protein that is highly expressed in peripheral organs and barely detectable in the brain under normal conditions, whereas HO-2 is a constitutive protein that is highly expressed in the brain. Several lines of evidence indicate that HO-1 dysregulation is associated with brain inflammation and neurodegeneration, including Parkinson’s and Alzheimer’s diseases. In this review, we summarize the essential roles that the HO system plays in ensuring brain health and the molecular mechanism through which HO-1 dysfunction leads to neurodegenerative diseases and disruption of nervous system homeostasis. We also provide a summary of the herbal medicines involved in the regulation of HO-1 expression and explore the current situation regarding herbal remedies and brain disorders.

The Role of Heme Oxygenase-1 Promoter Polymorphisms in Perinatal Disease

Heme oxygenase (HO) is the rate-limiting enzyme in the heme catabolic pathway, which degrades heme into equimolar amounts of carbon monoxide, free iron, and biliverdin. Its inducible isoform, HO-1, has multiple protective functions, including immune modulation and pregnancy maintenance, showing dynamic alteration during perinatal periods. As its contribution to the development of perinatal complications is speculated, two functional polymorphisms of the HMOX1 gene, (GT)_n repeat polymorphism (rs3074372) and A(-413)T single nucleotide polymorphism (SNP) (rs2071746), were studied for their association with perinatal diseases. We systematically reviewed published evidence on HMOX1 polymorphisms in perinatal diseases and clarified their possible significant contribution to neonatal jaundice development, presumably due to their direct effect of inducing HO enzymatic activity in the bilirubin-producing pathway. However, the role of these polymorphisms seems limited for other perinatal complications such as bronchopulmonary dysplasia. We speculate that this is because the antioxidant or anti-inflammatory effect is not directly mediated by HO but by its byproducts, resulting in a milder effect. For better understanding, subtyping each morbidity by the level of exposure to causative environmental factors, simultaneous analysis of both polymorphisms, and the unified definition of short and long alleles in (GT)_n repeats based on transcriptional capacity should be further investigated.

Heme Oxygenase 1: A Defensive Mediator in Kidney Diseases

The incidence of kidney disease is rising, constituting a significant burden on the healthcare system and making identification of new therapeutic targets increasingly urgent. The heme oxygenase (HO) system performs an important function in the regulation of oxidative stress and inflammation and, via these mechanisms, is thought to play a role in the prevention of non-specific injuries following acute renal failure or resulting from chronic kidney disease. The expression of HO-1 is strongly inducible by a wide range of stimuli in the kidney, consequent to the kidney's filtration role which means HO-1 is exposed to a wide range of endogenous and exogenous molecules, and it has been shown to be protective in a variety of nephropathological animal models. Interestingly, the positive effect of HO-1 occurs in both hemolysis- and rhabdomyolysis-dominated diseases, where the kidney is extensively exposed to heme (a major HO-1 inducer), as well as in non-heme-dependent diseases such as hypertension, diabetic nephropathy or progression to end-stage renal disease. This highlights the complexity of HO-1's functions, which is also illustrated by the fact that, despite the abundance of preclinical data, no drug targeting HO-1 has so far been translated into clinical use. The objective of this review is to assess current knowledge relating HO-1's role in the kidney and its potential interest as a nephroprotection agent. The potential therapeutic openings will be presented, in particular through the identification of clinical trials targeting this enzyme or its products.

Donor-Derived Myeloid Heme Oxygenase-1 Controls the Development of Graft-Versus-Host Disease

Graft-versus-host disease (GVHD) remains a major clinical drawback of allogeneic hematopoietic stem cell transplantation (HSCT). Here, we investigated how the stress responsive heme catabolizing enzyme heme oxygenase-1 (HO-1, encoded by HMOX1) regulates GVHD in response to allogeneic hematopoietic stem cell transplantation in mice and humans. We found that deletion of the Hmox1 allele, specifically in the myeloid compartment of mouse donor bone marrow, promotes the development of aggressive GVHD after allogeneic transplantation. The mechanism driving GVHD in mice transplanted with allogeneic bone marrow lacking HO-1 expression in the myeloid compartment involves enhanced T cell alloreactivity. The clinical relevance of these observations was validated in two independent cohorts of HSCT patients. Individuals transplanted with hematopoietic stem cells from donors carrying a long homozygous (GT)n repeat polymorphism (L/L) in the HMOX1 promoter, which is associated with lower HO-1 expression, were at higher risk of developing severe acute GVHD as compared to donors carrying a short (GT)n repeat (S/L or S/S) polymorphism associated with higher HO-1 expression. In this study, we showed the unique importance of donor-derived myeloid HO-1 in the prevention of lethal experimental GVHD and we corroborated this observation by demonstrating the association between human HMOX1 (GT)n microsatellite polymorphisms and the incidence of severe acute GVHD in two independent HSCT patient cohorts. Donor-derived myeloid HO-1 constitutes a potential therapeutic target for HSCT patients and large-scale prospective studies in HSCT patients are necessary to validate the HO-1 L/L genotype as an independent risk factor for developing severe acute GVHD.

New insights into the role of heme oxygenase-1 in acute kidney injury

Acute kidney injury (AKI) is attended by injury-related biomarkers appearing in the urine and serum, decreased urine output, and impaired glomerular filtration rate. AKI causes increased morbidity and mortality and can progress to chronic kidney disease and end-stage kidney failure. AKI is without specific therapies and is managed by supported care. Heme oxygenase-1 (HO-1) is a cytoprotective, inducible enzyme that degrades toxic free heme released from destabilized heme proteins and, during this process, releases beneficial by-products such as carbon monoxide and biliverdin/bilirubin and promotes ferritin synthesis. HO-1 induction protects against assorted renal insults as demonstrated by in vitro and preclinical models. This review summarizes the advances in understanding of the protection conferred by HO-1 in AKI, how HO-1 can be induced including via its transcription factor Nrf2, and HO-1 induction as a therapeutic strategy.

Heme-Oxygenase and Kidney Transplantation: A Potential for Target Therapy?

Kidney transplantation is a well-established therapy for patients with end-stage renal disease. While a significant improvement of short-term results has been achieved in the short-term, similar results were not reported in the long-term. Heme-oxygenase (HO) is the rate-limiting enzyme in heme catabolism, converting heme to iron, carbon monoxide, and biliverdin. Heme-oxygenase overexpression may be observed in all phases of transplant processes, including brain death, recipient management, and acute and chronic rejection. HO induction has been proved to provide a significant reduction of inflammatory response and a reduction of ischemia and reperfusion injury in organ transplantation, as well as providing a reduction of incidence of acute rejection. In this review, we will summarize data on HO and kidney transplantation, suggesting possible clinical applications in the near future to improve the long-term outcomes.

Heme Oxygenase-1 dictates innate - adaptive immune phenotype in human liver transplantation

Liver transplantation (LT) has become the standard of care for patients with end-stage liver disease and those with hepatic malignancies, while adaptive immune-dominated graft rejection remains a major challenge. Despite potent anti-inflammatory and cytoprotective functions of heme oxygenase-1 (HO-1) overexpression upon innate immune-driven hepatic ischemia reperfusion injury, its role in adaptive immune cell-driven responses remains to be elucidated. We analyzed human biopsies from LT recipients (n = 55) to determine putative association between HO-1 levels and adaptive/co-stimulatory gene expression programs in LT. HO-1 expression negatively correlated with innate (CD68, Cathepsin G, TLR4, CXCL10), adaptive (CD4, CD8, IL17) and co-stimulatory (CD28, CD80, CD86) molecules at the graft site. LT recipients with high HO-1 expression showed a trend towards improved overall survival. By demonstrating the association between graft HO-1 levels and adaptive/co-stimulatory gene programs, our study provides important insights to the role of HO-1 signaling in LT patients.

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.

Genetic predictors of long-term graft function in kidney and pancreas transplant patients

Kidney and pancreas transplantation have helped transform the lives of people with end-stage renal failure and individuals with type 1 diabetes who have poor glycaemic control/severe secondary complications, respectively. Despite an improvement in immunosuppressive regimes, operative techniques and decreased initial rejection rates, there has been little improvement in long-term graft survival rates over the past decade. Whilst limited progress has been made in establishing clinical markers of graft function, several genetic markers of long-term graft function have been identified. These genetic markers have the potential to (i) assist in selecting marginal donor organs for transplantation, (ii) provide better understanding of the mechanisms behind graft loss enabling identification of new, or repurposing, current treatments to extend graft function and (iii) provide a window of opportunity to identify and treat individuals before graft failure has occurred. This review will discuss the different genetic variants screened for a role in predicting transplant longevity, examine their findings and limitations and introduce where the future of genetic research within the transplantation field lies.

Specific expression of heme oxygenase-1 by myeloid cells modulates renal ischemia-reperfusion injury

Renal ischemia-reperfusion injury (IRI) is a major risk factor for delayed graft function in renal transplantation. Compelling evidence exists that the stress-responsive enzyme, heme oxygenase-1 (HO-1) mediates protection against IRI. However, the role of myeloid HO-1 during IRI remains poorly characterized. Mice with myeloid-restricted deletion of HO-1 (HO-1^M-KO), littermate (LT), and wild-type (WT) mice were subjected to renal IRI or sham procedures and sacrificed after 24 hours or 7 days. In comparison to LT, HO-1^M-KO exhibited significant renal histological damage, pro-inflammatory responses and oxidative stress 24 hours after reperfusion. HO-1^M-KO mice also displayed impaired tubular repair and increased renal fibrosis 7 days after IRI. In WT mice, HO-1 induction with hemin specifically upregulated HO-1 within the CD11b⁺ F4/80^lo subset of the renal myeloid cells. Prior administration of hemin to renal IRI was associated with significant increase of the renal HO-1⁺ CD11b⁺ F4/80^lo myeloid cells in comparison to control mice. In contrast, this hemin-mediated protection was abolished in HO-1^M-KO mice. In conclusion, myeloid HO-1 appears as a critical protective pathway against renal IRI and could be an interesting therapeutic target in renal transplantation.

Heme Oxygenase 1 as a Therapeutic Target in Acute Kidney Injury

A common clinical condition, acute kidney injury (AKI) significantly influences morbidity and mortality, particularly in critically ill patients. The pathophysiology of AKI is complex and involves multiple pathways, including inflammation, autophagy, cell-cycle progression, and oxidative stress. Recent evidence suggests that a single insult to the kidney significantly enhances the propensity to develop chronic kidney disease. Therefore, the generation of effective therapies against AKI is timely. In this context, the cytoprotective effects of heme oxygenase 1 (HO-1) in animal models of AKI are well documented. HO-1 modulates oxidative stress, autophagy, and inflammation and regulates the progression of cell cycle via direct and indirect mechanisms. These beneficial effects of HO-1 induction during AKI are mediated in part by the by-products of the HO reaction (iron, carbon monoxide, and bile pigments). This review highlights recent advances in the molecular mechanisms of HO-1-mediated cytoprotection and discusses the translational potential of HO-1 induction in AKI.

Targeting Iron Homeostasis in Acute Kidney Injury

Iron is an essential metal involved in several major cellular processes required to maintain life. Because of iron's ability to cause oxidative damage, its transport, metabolism, and storage is strictly controlled in the body, especially in the small intestine, liver, and kidney. Iron plays a major role in acute kidney injury and has been a target for therapeutic intervention. However, the therapies that have been effective in animal models of acute kidney injury have not been successful in human beings. Targeting iron trafficking via ferritin, ferroportin, or hepcidin may offer new insights. This review focuses on the biology of iron, particularly in the kidney, and its implications in acute kidney injury.

Heme Oxygenases in Cardiovascular Health and Disease

Heme oxygenases are composed of two isozymes, Hmox1 and Hmox2, that catalyze the degradation of heme to carbon monoxide (CO), ferrous iron, and biliverdin, the latter of which is subsequently converted to bilirubin. While initially considered to be waste products, CO and biliverdin/bilirubin have been shown over the last 20 years to modulate key cellular processes, such as inflammation, cell proliferation, and apoptosis, as well as antioxidant defense. This shift in paradigm has led to the importance of heme oxygenases and their products in cell physiology now being well accepted. The identification of the two human cases thus far of heme oxygenase deficiency and the generation of mice deficient in Hmox1 or Hmox2 have reiterated a role for these enzymes in both normal cell function and disease pathogenesis, especially in the context of cardiovascular disease. This review covers the current knowledge on the function of both Hmox1 and Hmox2 at both a cellular and tissue level in the cardiovascular system. Initially, the roles of heme oxygenases in vascular health and the regulation of processes central to vascular diseases are outlined, followed by an evaluation of the role(s) of Hmox1 and Hmox2 in various diseases such as atherosclerosis, intimal hyperplasia, myocardial infarction, and angiogenesis. Finally, the therapeutic potential of heme oxygenases and their products are examined in a cardiovascular disease context, with a focus on how the knowledge we have gained on these enzymes may be capitalized in future clinical studies.

Modulation of antigen processing by haem-oxygenase 1. Implications on inflammation and tolerance

Haem-oxygenase-1 (HO-1) is an enzyme responsible for the degradation of haem that can suppress inflammation, through the production of carbon monoxide (CO). It has been shown in several experimental models that genetic and pharmacological induction of HO-1, as well as non-toxic administration of CO, can reduce inflammatory diseases, such as endotoxic shock, type 1 diabetes and graft rejection. Recently, it was shown that the HO-1/CO system can alter the function of antigen-presenting cells (APCs) and reduce T-cell priming, which can be beneficial during immune-driven inflammatory diseases. The molecular mechanisms by which the HO-1 and CO reduce both APC- and T-cell-driven immunity are just beginning to be elucidated. In this article we discuss recent findings related to the immune regulatory capacity of HO-1 and CO at the level of recognition of pathogen-associated molecular patterns and T-cell priming by APCs. Finally, we propose a possible regulatory role for HO-1 and CO over the recently described mitochondria-dependent immunity. These concepts could contribute to the design of new therapeutic tools for inflammation-based diseases.

Length Polymorphisms in Heme Oxygenase-1 and AKI after Cardiac Surgery

Heme oxygenase-1 (HO-1) catalyzes the degradation of heme, which may be involved in the pathogenesis of AKI. Length polymorphisms in the number of GT dinucleotide repeats in the HO-1 gene (HMOX1) promoter inversely associate with HMOX1 mRNA expression. We analyzed the association between allelic frequencies of GT repeats in the HMOX1 gene promoter and postoperative AKI in 2377 white patients who underwent cardiac surgery with cardiopulmonary bypass. We categorized patients as having the short allele (S; <27 GT repeats) or long allele (L; ≥27 GT repeats), and defined AKI as an increase in serum creatinine ≥0.3 mg/dl within 48 hours or ≥50% within 5 days, or the need for RRT. Compared with patients with the SS genotype, patients with the LL genotype had 1.58-fold (95% confidence interval, 1.06 to 2.34; P=0.02) higher odds of AKI. After adjusting for baseline and operative characteristics, the odds ratio for AKI per L allele was 1.26 (95% confidence interval, 1.05 to 1.50; P=0.01). In conclusion, longer GT repeats in the HMOX1 gene promoter associate with increased risk of AKI after cardiac surgery, consistent with heme toxicity as a pathogenic feature of cardiac surgery-associated AKI, and with HO-1 as a potential therapeutic target.

Association Between Heme Oxygenase-1 Promoter Polymorphisms and the Development of Albuminuria in Type 2 Diabetes: A Case-Control Study

Heme oxygenase (HO)-1 is a key enzyme in cytoprotective mechanisms against oxidative stress in the cardiovascular-renal system. The T(-413)A single nucleotide polymorphism (SNP) and (GT)n microsatellite polymorphism in the HO-1 gene promoter modulate the HO-1 gene transcriptional activity and these polymorphisms are associated with various human diseases.We investigated the association between HO-1 promoter polymorphisms and nephropathy in type 2 diabetes. We sequenced the T(-413)A SNP and (GT)n repeat segments of the HO-1 gene promoter in 536 patients with type 2 diabetes. (GT)n alleles were divided into 2 groups: short (S, ≤25 GT repeats) and long (L, >25 GT repeats) alleles. The presence of albuminuria was used as a marker of diabetic nephropathy.Patients with the TT genotype in the T(-413)A SNP were significantly more susceptible to albuminuria development than those carrying the A allele, with an odds ratio of 1.577 (95% confidence interval, 1.088 - 2.285; P = 0.016). Subgroup analysis showed that patients carrying the TT genotype with long duration of diabetes (≥20 years), poor glycemic control, male gender and without hypertension had higher odds ratios for the development of albuminuria. In vitro, promoter activity of the T(-413)A SNP was higher with A allele than T allele. Regarding to the (GT)n repeats, the LL genotype showed a higher odds ratio for the development of albuminuria only in patients with hypertension when compared to the S allele.In conclusion, the T(-413)A SNP in the HO-1 promoter is significantly associated with albuminuria development in type 2 diabetes patients, especially with longer duration and poor glycemic control.

Serum bilirubin affects graft outcomes through UDP-glucuronosyltransferase sequence variation in kidney transplantation

Background

Oxidative stress is a major mediator of adverse outcome after kidney transplantation. Bilirubin is produced by heme oxygenase-1 (HO-1), catalyzed by UDP-glucuronosyltransferase (UGT1A1), and has potential as an antioxidant. In this study, we investigated the effects of HO-1 and UGT1A1 sequence variations on kidney allograft outcomes.

Methods

Clinical data were collected from 429 Korean recipients who underwent kidney transplantation from 1990–2008. Genotyping for UGT1A1*28 and HO-1 (A−413T) was performed. Acute rejection and graft survival were monitored as end-points.

Results

Serum levels of total bilirubin were significantly increased after transplantation (0.41±0.19 mg/dL to 0.80±0.33 mg/dL, P<0.001). Post-transplant 1-year bilirubin level was higher in 6/7 or 7/7 carriers compared with 6/6 homozygotes in terms of the UGT1A1*28 polymorphism (6/6 vs. 6/7 vs. 7/7: 0.71±0.27 vs. 1.06±0.36 vs. 1.10±0.45 mg/dL, P<0.001). According to an additive model of genotype analysis, the 7-allele genotype had a protective effect on the development of acute rejection compared with the 6-allele (odds ratio 0.43, 95% CI 0.25–0.73, P for trend = 0.006). Multivariate Cox regression analysis revealed that individuals carrying the 7-allele had a decreased risk of graft loss, by a factor of 0.36 (95% CI 0.15–0.85, P = 0.019). The HO-1 (A−413T) polymorphism had no effect on serum bilirubin levels or graft outcomes.

Conclusions

The UGT1A1*28 polymorphism is associated with changes in serum bilirubin and with graft outcome after kidney transplantation.

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.

Graft rejection - endogenous or allogeneic?

The presence and persistence of alloantigen is necessary for graft-specific T-cell-mediated immunity. However, specificity comprises only a single facet of an extremely complex process. Evidence is accruing to suggest that immunogenicity could be manipulated by endogenous ligands released during tissue injury. Stress molecules are significantly up-regulated following transplantation and stimulate conserved receptors on a range of leucocytes, including dendritic cells (DCs). The DCs are essential for co-stimulation and the induction of adaptive immunity. Stress signals can act as an adjuvant leading to DC maturation and activation. DCs stimulated by endogens exhibit enhanced alloantigen presentation, co-stimulation and production of pro-inflammatory cytokines, such as interleukin-1β (IL-1β) and IL-18. Inflammasomes have a major role in IL-1β/IL-18 production and secretion, and can be stimulated by endogens. Importantly, the polarization toward inflammatory T helper type 17 cells as opposed to regulatory T cells is dependent upon, among other factors, IL-1β. This highlights an important differentiation pathway that may be influenced by endogenous signals. Minimizing graft damage and stress expression should hypothetically be advantageous, and we feel that this area warrants further research, and may provide novel treatment modalities with potential clinical benefit.

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.

Cytoprotection behind heme oxygenase-1 in renal diseases

Renal insults are considered a public health problem and are linked to increased rates of morbidity and mortality worldwide. The heme oxygenase (HO) system consists of evolutionary specialized machinery that degrades free heme and produces carbon monoxide, biliverdin and free iron. In this sense, the inducible isoform HO-1 seems to develop an important role and is widely studied. The reaction involved with the HO-1 molecule provides protection to injured tissue, directly by reducing the toxic heme molecule and indirectly by the release of its byproducts. The up regulation of HO-1 enzyme has largely been described as providing antioxidant, antiapoptotic, anti-inflammatory and immunomodulatory properties. Several works have explored the importance of HO-1 in renal diseases and they have provided consistent evidence that its overexpression has beneficial effects in such injuries. So, in this review we will focus on the role of HO-1 in kidney insults, exploring the protective effects of its up regulation and the enhanced deleterious effects of its inhibition or gene deletion.

Haem oxygenase-1: non-canonical roles in physiology and pathology

HO-1 (haem oxygenase-1) is a ubiquitously expressed inducible enzyme degrading haem to CO, biliverdin and Fe2+. Its activation reduces oxidative stress in cells and inhibits inflammation, both due to removal of haem and because of the biological activity of HO-1 products. CO may act similarly to NO, activating soluble guanylate cyclase and elevating cGMP production. It inhibits platelet aggregation, reduces leucocyte adhesion, decreases apoptosis and lowers the production of some pro-inflammatory cytokines. Biliverdin is converted into bilirubin by biliverdin reductase, and both compounds are potent antioxidants, free radical scavengers and inhibitors of the complement cascade. Iron ions can be potentially toxic, increasing the generation of hydroxyl radicals, but simultaneous induction of ferritin and activation of the Fe-ATPase iron transporter protects cells from oxidative stress. Importantly, basal and induced expression of HO-1 is very variable in the human population because of the highly polymorphic (GT)n fragment in the promoter, which may have clinical relevance. The recognized roles of HO-1 are far beyond cytoprotection. The enzyme is important in the regulation of cell proliferation, differentiation and apoptosis. Its activity improves neovascularization, attenuates inflammation and modulates the immune response, thereby influencing carcinogenesis, wound healing, transplant survival and the progression of cardiovascular diseases. Recent results indicate that HO-1 may also act through the regulation of microRNAs, which suggests a much broader involvement of HO-1 in the modulation of cell functions and offers a potential explanation for some well-known activities whose mechanism has hitherto been unclear.

UW is superior compared with HTK after prolonged preservation of renal grafts

BACKGROUND

In recent clinical studies, the efficacy of histidine-tryptophan-ketoglutarate (HTK) in kidney transplantation was questioned. This study compares the efficacy of University of Wisconsin (UW) and HTK solutions on transplantation outcome.

MATERIALS AND METHODS

Rat kidneys were preserved for different periods of cold ischemia (CIT). Heat capacity of the solutions, temperature of the grafts, renal function (RF), and histology were assessed before and after transplantation, respectively.

RESULTS

After prolonged CIT, recipient survival was superior in the UW - (100%) compared with the HTK group (10%). In the latter, severe tubular necrosis, DNA damage, and renal inflammation were observed, reflected by an increased KIM-1, IL6, and P-selectin expression. CIT correlated negatively with RF in both groups. RF recovered significantly faster in the UW group. LDH-release and ATP depletion after cold storage of tubular cells were lower in UW than in HTK. Heat capacity was significantly higher for UW than for HTK. Accordingly, renal temperature was lower.

CONCLUSIONS

Prolonged preservation in UW solution results in a better renal function and less tissue damage compared with HTK, possibly due to improved cooling and better cell viability of the graft. The use of HTK for renal allografts should therefore be reconsidered, particularly when CIT is expected to be long.

Association between the heme oxygenase-1 promoter polymorphism and renal transplantation outcome in Greece

BACKGROUND

Heme oxygenase-1 (HO-1) is the enzyme that catabolizes heme into carbon monoxide, biliverdin, and free iron. The induction of this enzyme is an important cytoprotective mechanism, which occurs as an adaptive and beneficial response to a wide variety of oxidant stimuli. HO-1 has recently been suggested to protect transplants from ischemia/reperfusion and immunologic injury. HO-1 inducibility is mainly modulated by a (GT)(n) repeat polymorphism in the promoter region, and has been shown that short repeats (S) are associated with greater upregulation of HO-1, compared with long repeats (L). In the present study we investigated the influence of this HO-1 gene polymorphism on clinical outcome after transplantation and on renal transplant function.

METHODS

DNA from 175 donor/recipient pairs who underwent transplantation between October 2002 and June 2007 was genotyped. We divided the HO-1 alleles into 2 subclasses, the S ≤ 27 repeats and L > 27 repeats.

RESULTS

There has been significant relevance between the genotype of the donor and the outcome of the graft, as far as recipients with normal graft function and recipients with deteriorated graft function are concerned (P = .021). In patients with normal graft function, grafts from L-homozygotes were found in 24%, whereas in patients with deteriorated function, grafts from L-homozygotes exhibited in higher rate (50%). Neither the donor's nor the recipient's polymorphism influenced the graft survival (log-rank test P = .228 for the donors and log-rank test P = 0.844 for the recipients). There was no evidence of a gene-dose effect on graft survival (P = .469). Recipients of allografts from S-carriers donors had significantly lower serum creatinine levels at 24 months compared with recipients of allografts from L-homozygotes donors (P = .016).

Native macrophages genetically modified to express heme oxygenase 1 protect rat liver transplants from ischemia/reperfusion injury

We investigated whether native macrophages overexpressing heme oxygenase 1 (HO-1) could protect rat orthotopic liver transplant (OLT) against cold ischemia/reperfusion injury (IRI). Livers from Sprague-Dawley rats were stored at 4°C in University of Wisconsin solution for 24 hours, and then they were transplanted into syngeneic recipients. Bone marrow-derived macrophages (BMMs) that were transfected ex vivo with heme oxygenase 1 adenovirus (Ad-HO-1), β-galactosidase adenovirus (Ad-β-gal), or HO-1 small interfering RNA (siRNA) were infused directly into the OLT before reperfusion. Controls were OLT conditioned with unmodified or scrambled siRNA-transfected cells. The transfer of Ad-HO-1/BMMs increased the survival of OLT to 100% (versus 40%-50% for controls) and decreased serum alanine aminotransferase levels and histological features of hepatocellular damage. In contrast, an infusion of macrophages transfected with HO-1 siRNA/Ad-β-gal failed to affect IRI. Gene therapy-induced HO-1 suppressed toll-like receptor 4 expression, decreased expression of proinflammatory tumor necrosis factor α, interleukin-1β, monocyte chemoattractant protein 1, and chemokine (C-X-C motif) ligand 10, and attenuated endothelial intercellular cell adhesion molecule 1 expression with resultant diminished OLT leukocyte sequestration. Although Ad-HO-1/BMMs decreased the frequency of apoptotic cells positive for terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling and ameliorated caspase-3 activity, the expression of interleukin-10 and antiapoptotic B cell lymphoma 2/B cell lymphoma extra large increased in well-functioning OLT. Thus, the transfer of native macrophages transfected ex vivo with HO-1 can rescue rat iso-OLT from IRI. Our study validates a novel and clinically attractive concept: native macrophages transfected ex vivo with the antioxidant HO-1 can be applied at the time of transplantation to mitigate otherwise damaging antigen-independent liver inflammation and injury resulting from the peritransplant harvesting insult. If this new, refined strategy is proven to be effective in allo-OLT recipients, it should be considered in clinical settings to increase the supply of usable donor organs and ultimately improve the overall success of liver transplantation.

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.

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.

HO-1 polymorphism as a genetic determinant behind the malaria resistance afforded by haemolytic disorders

Malaria affects thousands of people around the world representing a critical issue regarding health policies in tropical countries. Similarly, also haemolytic diseases such as sickle cell disease and thalassemias are a concern in different parts of the globe. It is well established that haemolytic diseases, such as sickle cell disease (SCD) and thalassemias, represent a resistance factor to malaria, which explains the high frequencies of such genetic variants in malaria endemic areas. In this context, it has been shown that the rate limiting enzyme heme oxygenase I (HO-1), responsible for the catabolism of the free heme in the body, is an important resistance factor in malaria and is also important in the physiopathology of haemolytic diseases. Here, we suggest that allelic variants of HO-1, which display significant differences in terms of protein expression, have been selected in endemic malaria areas since the HO-1 enzyme can enhance the protection against malaria conferred by haemolytic diseases This protection apply mainly in what concerns protection against severe malaria forms. Therefore, HO-1 genotyping would be fundamental to determine resistance of a given individual to lethal forms of malaria as well as to common clinical complications typical to haemolytic diseases and would be helpful in the establishment of public health politics.

Adoptive transfer of ex vivo HO-1 modified bone marrow-derived macrophages prevents liver ischemia and reperfusion injury

Macrophages play a critical role in the pathophysiology of liver ischemia and reperfusion (IR) injury (IRI). However, macrophages that overexpress antioxidant heme oxygenase-1 (HO-1) may exert profound anti-inflammatory functions. This study explores the cytoprotective effects and mechanisms of ex vivo modified HO-1-expressing bone marrow-derived macrophages (BMDMs) in well-defined mouse model of liver warm ischemia followed by reperfusion. Adoptive transfer of Ad-HO-1-transduced macrophages prevented IR-induced hepatocellular damage, as evidenced by depressed serum glutamic-oxaloacetic transaminase (sGOT) levels and preserved liver histology (Suzuki scores), compared to Ad-beta-gal controls. This beneficial effect was reversed following concomitant treatment with HO-1 siRNA. Ad-HO-1-transfected macrophages significantly decreased local neutrophil accumulation, TNF-alpha/IL-1beta, IFN-gamma/E-selectin, and IP-10/MCP-1 expression, caspase-3 activity, and the frequency of apoptotic cells, as compared with controls. Unlike in controls, Ad-HO-1-transfected macrophages markedly increased hepatic expression of antiapoptotic Bcl-2/Bcl-xl and depressed caspase-3 activity. These results establish the precedent for a novel investigative tool and provide the rationale for a clinically attractive new strategy in which native macrophages can be transfected ex vivo with cytoprotective HO-1 and then infused, if needed, to prospective recipients exposed to hepatic IR-mediated local inflammation, such as during liver transplantation, resection, or trauma.

High weight differences between donor and recipient affect early kidney graft function--a role for enhanced IL-6 signaling

The frequency of delayed function of kidney transplants varies greatly and is associated with quality of graft, donor age and the duration of cold ischemia time. Furthermore, body weight differences between donor and recipient can affect primary graft function, but the underlying mechanism is poorly understood. We transplanted kidney grafts from commensurate body weight (L-WD) or reduced body weight (H-WD) donor rats into syngeneic or allogeneic recipients. Twenty-four hours posttransplantation, serum creatinine levels in H-WD recipients were significantly higher compared to L-WD recipients indicating impaired primary graft function. This was accompanied by upregulation of IL-6 transcription and increased tubular destruction in grafts from H-WD recipients. Using DNA microarray analysis, we detected decreased expression of genes associated with kidney function and an upregulation of other genes such as Cyp3a13, FosL and Trib3. A single application of IL-6 into L-WD recipients is sufficient to impair primary graft function and cause tubular damage, whereas immediate neutralization of IL-6 receptor signaling in H-WD recipients rescued primary graft function with well-preserved kidney graft architecture and a normalized gene expression profile. These findings have strong clinical implication as anti-IL6R treatment of patients receiving grafts from lower-weight donors could be used to improve primary graft function.

Heme oxygenase and renal disease

The cellular content of heme, derived from the breakdown of heme proteins, is regulated via the heme oxygenase (HO) enzyme system. HO catalyzes the rate-limiting step in heme degradation resulting in the formation of iron, carbon monoxide, and biliverdin. Recent studies have focused on the biologic effects of product(s) of this reaction, which have important antioxidant, antiapoptotic, anti-inflammatory, and cytoprotective properties. Two isoforms of the HO enzyme have been described: an inducible isoform (HO-1) and a constitutively expressed isoform (HO-2). Induction of HO-1 occurs as a beneficial response to several injurious stimuli and has been implicated in many clinically relevant disease states including sepsis, hypertension, atherosclerosis, and acute lung and kidney injury. This review focuses on the role of HO-1 in kidney diseases.

The heme oxygenase-1 genotype is a risk factor to renal impairment of IgA nephropathy at diagnosis, which is a strong predictor of mortality

The induction of heme oxygenase-1 (HO-1) ameliorates oxidative stress and inflammatory process, which play important roles in IgA nephropathy. We hypothesized length polymorphism in the promoter region of the HO-1 gene, which is related to the level of gene transcription, is associated with disease severity of IgA nephropathy. The subjects comprised 916 patients with IgA nephropathy and gene data. Renal impairment was defined as an estimated glomerular filtration rate less than 60 mL/min/1.73 m(2) at diagnosis. The short (S: <23), medium (M: 23-28), and long (L: >28) (GT) repeats in the HO-1 gene was determined. The frequencies of S/S, S/M, M/M, S/L, L/M, and L/L genotypes were 7.2%, 6.9%, 3.1%, 30.8%, 22.7%, and 29.4%, respectively. The baseline characteristics were not different. In the S/S genotypic group, the renal impairment rate was 18.2%, which was lower than 32.2% in the group with M/M, L/M, or L/L genotype. The odds ratio of renal impairment in S/S genotype, compared to that in M/M, L/M, or L/L genotype, was 0.216 (95% confidence interval, 0.060-0.774, p=0.019). The HO-1 gene promoter length polymorphism was related to the renal impairment of IgA nephropathy at diagnosis, which is an important risk factor for mortality in IgA nephropathy patients.

Heme oxygenase-1 and the vascular bed: from molecular mechanisms to therapeutic opportunities

Heme oxygenase-1, an enzyme degrading heme to carbon monoxide, iron, and biliverdin, has been recognized as playing a crucial role in cellular defense against stressful conditions, not only related to heme release. HO-1 protects endothelial cells from apoptosis, is involved in blood-vessel relaxation regulating vascular tone, attenuates inflammatory response in the vessel wall, and participates in blood-vessel formation by means of angiogenesis and vasculogenesis. The latter functions link HO-1 not only to cardiovascular ischemia but also to many other conditions that, like development, wound healing, or cancer, are dependent on neovascularization. The aim of this comprehensive review is to address the mechanisms of HO-1 regulation and function in cardiovascular physiology and pathology and to demonstrate some possible applications of the vast knowledge generated so far. Recent data provide powerful evidence for the involvement of HO-1 in the therapeutic effect of drugs used in cardiovascular diseases. Novel studies open the possibilities of application of HO-1 for gene and cell therapy. Therefore, research in forthcoming years should help to elucidate both the real role of HO-1 in the effect of drugs and the clinical feasibility of HO-1-based cell and gene therapy, creating the effective therapeutic avenues for this refined antioxidant system.

Association of donor inflammation- and apoptosis-related genotypes and delayed allograft function after kidney transplantation

BACKGROUND

Delayed renal allograft survival (delayed graft function [DGF]) after deceased donor kidney transplantation is associated with an increased risk of allograft loss. Inflammatory response and apoptosis are associated with increased risk of DGF.

STUDY DESIGN

Cross-sectional study.

SETTING & PARTICIPANTS

We first recruited 616 recipients of kidneys from 512 deceased kidney donors, and donor DNA was genotyped. These recipients, who were included in a prospective cohort study of 9 transplant centers in the Delaware Valley region, had their DGF outcome obtained through medical record abstraction. We then identified the recipient (n = 349) of the contralateral deceased kidney donor, if not part of the cohort, through the US Renal Data System registry. The final cohort consisted of 965 recipients of deceased donor kidneys from 512 donors.

PREDICTORS

Donor single-nucleotide polymorphisms in genes for tumor necrosis factor alpha (TNF), transforming growth factor beta1 (TGFB1), interleukin 10 (IL10), p53 (TP53), and heme oxygenase 1 (HMOX1).

OUTCOMES

DGF, defined as the need for dialysis therapy in the first week posttransplantation. Secondary outcomes included acute rejection and estimated glomerular filtration rate.

MEASUREMENTS

Information for DGF, acute rejection, and estimated glomerular filtration rate for recipients in the Delaware Valley Cohort was obtained through medical record abstraction. For other recipients, information for DGF was obtained from United Network for Organ Sharing forms and Centers for Medicare & Medicaid Services claims in the US Renal Data System registry.

RESULTS

No association was detected between the TGFB1, IL10, TP53, and HMOX1 genes and DGF. The G allele of the TNF polymorphism rs3093662 was associated with DGF in an adjusted analysis (odds ratio, 1.85 compared with A allele; 95% confidence interval, 1.16 to 2.96; P = 0.01). However, this association did not achieve statistical significance after adjusting for multiple comparisons.

LIMITATIONS

Inadequate sample size for infrequent genotypes and multiple comparisons.

CONCLUSION

Because of the low frequency of donor single-nucleotide polymorphisms of interest, a larger sample size and replication are necessary to confirm these findings on the association of donor genotypes with DGF.

Improved renal function after kidney transplantation is associated with heme oxygenase-1 polymorphism

Heme oxygenase-1 (HO-1) has a microsatellite polymorphism based on the number of guanosine-thymidine nucleotide repeats (GT) repeats that regulates expression levels and could have an impact on organ survival post-injury. We correlated HO-1 polymorphism with renal graft function. The HO-1 gene was sequenced (N = 181), and the allelic repeats were divided into subclasses: short repeats (S) (<27 repeats) and long repeats (L) (>/=27 repeats). A total of 47.5% of the donors carried the S allele. The allograft function was statistically improved six months, two and three yr after transplantation in patients receiving kidneys from donors with an S allele. For the recipients carrying the S allele (50.3%), the allograft function was also better throughout the follow-up, but reached statistical significance only three yr after transplantation (p = 0.04). Considering only those patients who had chronic allograft nephropathy (CAN; 74 of 181), allograft function was also better in donors and in recipients carrying the S allele, two and three yr after transplantation (p = 0.03). Recipients of kidney transplantation from donors carrying the S allele presented better function even in the presence of CAN.

Heme oxygenase 1: does it have a role in renal cytoprotection?

Heme oxygenase (HO) was first identified as the rate-limiting enzyme in the degradative pathway of heme, but is now recognized to be involved in diverse biological processes. Different isoforms of HO exist; HO-1 (HMOX1) is ubiquitously present in mammalian tissue with low constitutive expression under physiological conditions, but is upregulated in response to a variety of potentially noxious stimuli. HO-1, an integral component of an important cytoprotective mechanism, mediates its action through removal of heme, the generation of heme breakdown reaction products (biliverdin, free iron, and carbon monoxide), and modulation of key cellular molecules. Data from experimental models in which HO-1 was induced or inhibited, together with observations in genetically modified animals, showed a beneficial effect of HO-1 in several pathways leading to kidney injury. The discovery of a functional guanosine thymine tandem repeat polymorphism in the promoter region of the human HO-1 gene has stimulated clinical investigations in a variety of diseases. However, despite theoretical and experimental support for an important pathophysiological role for HO-1, the relevance of this polymorphism in native kidney or renal transplant function is equivocal. This article reviews the molecular genetics of HO-1, its myriad cytoprotective effects allied to how these are mediated, and relates these findings to experimental and clinical evidence of HO-1 involvement in renal disease.

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.

Heme oxygenase-1 in tumors: is it a false friend?

Heme oxygenase-1 (HO-1) catalyzes the oxidation of heme to biologically active products: carbon monoxide (CO), biliverdin, and ferrous iron. It participates in maintaining cellular homeostasis and plays an important protective role in the tissues by reducing oxidative injury, attenuating the inflammatory response, inhibiting cell apoptosis, and regulating cell proliferation. HO-1 is also an important proangiogenic mediator. Most studies have focused on the role of HO-1 in cardiovascular diseases, in which its significant, beneficial activity is well recognized. A growing body of evidence indicates, however, that HO-1 activation may play a role in carcinogenesis and can potently influence the growth and metastasis of tumors. HO-1 is very often upregulated in tumor tissues, and its expression is further increased in response to therapies. Although the exact effect can be tissue specific, HO-1 can be regarded as an enzyme facilitating tumor progression. Accordingly, inhibition of HO-1 can be suggested as a potential therapeutic approach sensitizing tumors to radiation, chemotherapy, or photodynamic therapy.

Heme oxygenase 1 gene polymorphisms and outcome of renal transplantation

Heme oxygenase isoenzyme HO-1 has been linked to several cytoprotective functions with a potentially beneficial role in transplantation. In the present study, the effect of genetic variation in HO-1 on renal allograft outcome was investigated. Six hundred and eighty patients subject to renal transplantation in a single transplant unit and their cadaveric kidney donors were included in this study. Four single-nucleotide polymorphisms and one microsatellite marker in the HO-1 gene region were analysed. Some statistically nominally significant associations were observed in preliminary analyses between polymorphisms studied and clinical outcomes, but after correction for multiple comparisons none remained significant. Our data suggest that the HO-1 gene polymorphisms studied have no significant role on outcome of kidney transplantation in the Finnish population.

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 gene promoter polymorphism is associated with risk of gastric adenocarcinoma and lymphovascular tumor invasion

PURPOSE

Heme oxygenase-1 (HO-1) gene, which encodes an oxidative response protein, plays a role in cytoprotection. A (GT)n dinucleotide repeat in HO-1 promoter is polymorphic and modulates the transcriptional activity of the gene. A HO-1 gene promoter polymorphism was reported to be associated with the risks of lung adenocarcinoma and oral squamous cancer. In this study, the correlation between the HO-1 gene promoter polymorphism and the clinicopathological characteristics, along with the risk of gastric cancer, was analyzed.

EXPERIMENTAL DESIGN

We examined the genotypic frequencies of (GT)n repeats in 183 gastric cancer patients and 250 control subjects by PCR-based genotyping and DNA sequencing. The length polymorphisms of (GT)n repeats were classified into short (S) component (n <or= 25), medium (M) component (26 <or= n <or= 30) and long (L) component (n >or= 31). The distribution of S, M and L components in patient and control groups were evaluated to determine the correlation with susceptibility and clinicopathological characteristics of gastric adenocarcinoma.

RESULTS

Higher frequencies of L-allele, L-allele carrier (S/L, M/L, L/L) and S/L genotype were found in gastric cancer patients. The frequencies of M-allele, M-allele carrier (M/M, M/L, M/S) and M/M genotype were significantly lower in patients with gastric cancer than controls. Furthermore, the frequency of lymphovascular tumor invasion was significantly lower in M-allele carriers compared to non-M-allele carriers (S/S, S/L, L/L) (p = 0.009).

CONCLUSIONS

These findings suggest that the long (GT)n repeat of HO-1 gene promoter was associated with a higher frequency of gastric adenocarcinoma, and the medium (GT)n repeat might possess protective effect against gastric adenocarcinoma with a lower frequency of lymphovascular invasion in tumors.