Gas-generating systems in acute renal allograft rejection in the rat. Co-induction of heme oxygenase and nitric oxide synthase

The roles of heme oxygenase-1 in renal disease

Heme oxygenase (HO), a heat shock protein containing hemoglobin, is an important enzyme in heme catabolism. It is involved in cell homeostasis and has anti-inflammatory, antioxidant, anti-apoptosis, immunomodulation, and other functions. It is expressed at a modest level in most normal tissues. When the body suffers from ischemia hypoxia, injury, toxins, and other nociceptive stimuli, the expression increases, which can transform the oxidative microenvironment into an antioxidant environment to promote tissue recovery from damage. In recent years, research has continued to verify its value in a variety of human bodily systems. It is also regarded as a key target for the treatment of numerous disorders. With the advancement of studies, its significance in renal disease has gained increasing attention. It is thought to have a significant protective function in preventing acute kidney injury and delaying the progression of chronic renal diseases. Its protective mechanisms include anti-inflammatory, antioxidant, cell cycle regulation, apoptosis inhibition, hemodynamic regulation, and other aspects, which have been demonstrated in diverse animal models. Furthermore, as a protective factor, its potential therapeutic efficacy in renal disease has recently become a hot area of research. Although a large number of preclinical trials have confirmed its therapeutic potential in reducing kidney injury, due to the problems and side effects of HO-1 induction therapy, its efficacy and safety in clinical application need to be further explored. In this review, we summarize the current state of research on the mechanism, location, and treatment of HO and its relationship with various renal diseases.

Immunomodulatory Effects of Heme Oxygenase-1 in Kidney Disease

Kidney disease is a general term for heterogeneous damage that affects the function and the structure of the kidneys. The rising incidence of kidney diseases represents a considerable burden on the healthcare system, so the development of new drugs and the identification of novel therapeutic targets are urgently needed. The pathophysiology of kidney diseases is complex and involves multiple processes, including inflammation, autophagy, cell-cycle progression, and oxidative stress. Heme oxygenase-1 (HO-1), an enzyme involved in the process of heme degradation, has attracted widespread attention in recent years due to its cytoprotective properties. As an enzyme with known anti-oxidative functions, HO-1 plays an indispensable role in the regulation of oxidative stress and is involved in the pathogenesis of several kidney diseases. Moreover, current studies have revealed that HO-1 can affect cell proliferation, cell maturation, and other metabolic processes, thereby altering the function of immune cells. Many strategies, such as the administration of HO-1-overexpressing macrophages, use of phytochemicals, and carbon monoxide-based therapies, have been developed to target HO-1 in a variety of nephropathological animal models, indicating that HO-1 is a promising protein for the treatment of kidney diseases. Here, we briefly review the effects of HO-1 induction on specific immune cell populations with the aim of exploring the potential therapeutic roles of HO-1 and designing HO-1-based therapeutic strategies for the treatment of kidney diseases.

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.

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.

Heat shock proteins and kidney disease: perspectives of HSP therapy

Heat shock proteins (HSPs) mediate a diverse range of cellular functions, prominently including folding and regulatory processes of cellular repair. A major property of these remarkable proteins, dependent on intracellular or extracellular location, is their capacity for immunoregulation that optimizes immune activity while avoiding hyperactivated inflammation. In this review, recent investigations are described, which examine roles of HSPs in protection of kidney tissue from various traumatic influences and demonstrate their potential for clinical management of nephritic disease. The HSP70 class is particularly attractive in this respect due to its multiple protective effects. The review also summarizes current understanding of HSP bioactivity in the pathophysiology of various kidney diseases, including acute kidney injury, diabetic nephropathy, chronic glomerulonephritis, and lupus nephritis-along with other promising strategies for their remediation, such as DNA vaccination.

Heme Oxygenase-1 in Kidney Health and Disease

SIGNIFICANCE

Acute kidney injury (AKI) and chronic kidney disease (CKD) represent a considerable burden in healthcare. The heme oxygenase (HO) system plays an important role in regulating oxidative stress and is protective in a variety of human and animal models of kidney disease. Preclinical studies of the HO system have led to the development of several clinical trials targeting the enzyme or its products.

RECENT ADVANCES

Connection of HO, ferritin, and other proteins involved in iron regulation has provided important insight into mechanisms of damage in AKI. Also, HO-1 expression is important in the pathogenesis of hypertension, diabetic kidney disease, and progression to end-stage renal disease.

CRITICAL ISSUES

Despite intriguing discoveries, no drugs targeting the HO system have been translated to the clinic. Meanwhile, treatments for AKI and CKD are urgently needed. Many factors have likely contributed to challenges in clinical translation, including variation in animal models, difficulties in obtaining human tissue, and complexity of the disease processes being studied.

FUTURE DIRECTIONS

The HO system represents a promising avenue of investigation that may lead to targeted therapeutics. Tissue-specific gene modulation, widening the scope of animal studies, and continued clinical research will provide valuable insight into the role HO plays in kidney homeostasis and disease. Antioxid. Redox Signal. 25, 165-183.

Glucocorticoids downregulate systemic nitric oxide synthesis and counteract overexpression of hepatic heme oxygenase-1 during endotoxin tolerance

Heme oxygenase (HO)-1 has antioxidant and cytoprotective properties if properly expressed, whereas nitric oxide (NO) impairs tissue perfusion when greatly increased in the blood circulation. Here we hypothesized that the NO and HO-1 systems are altered during lipopolysaccharide (LPS) tolerance, and that glucocorticoids are crucial modulators of systemic NO production and hepatic HO-1 expression during this intriguing phenomenon of cellular reprogramming. Adrenalectomized (ADX) rats with or without administration of dexamethasone (DEX) were challenged with LPS for 3 consecutive days. The plasma levels of corticosterone and nitrate (NOx), and expression of HO-1 protein were assessed. During tolerance, corticosterone levels were elevated, NOx reduced, and HO-1 overexpressed. ADX rats challenged with LPS for 3 consecutive days exhibited a ∼9-fold increase in NOx and a ∼6-fold increase in HO-1, reverted by DEX. Our findings strongly support the fact that glucocorticoids downregulate systemic NO synthesis and counteract hepatic HO-1 overexpression during LPS tolerance.

Brain death induces renal expression of heme oxygenase-1 and heat shock protein 70

Background

Kidneys derived from brain dead donors have lower graft survival and higher graft-function loss compared to their living donor counterpart. Heat Shock Proteins (HSP) are a large family of stress proteins involved in maintaining cell homeostasis. We studied the role of stress-inducible genes Heme Oxygenase-1 (HO-1), HSP27, HSP40, and HSP70 in the kidney following a 4 hour period of brain death.

Methods

Brain death was induced in rats (n=6) by inflating a balloon catheter in the epidural space. Kidneys were analysed for HSPs using RT-PCR, Western blotting, and immunohistochemistry.

Results

RT-PCR data showed a significant increase in gene expression for HO-1 and HSP70 in kidneys of brain dead rats. Western blotting revealed a massive increase in HO-1 protein in brain dead rat kidneys. Immunohistochemistry confirmed these findings, showing extensive HO-1 protein expression in the renal cortical tubules of brain dead rats. HSP70 protein was predominantly increased in renal distal tubules of brain dead rats treated for hypotension.

Conclusion

Renal stress caused by brain death induces expression of the cytoprotective genes HO-1 and HSP70, but not of HSP27 and HSP40. The upregulation of these cytoprotective genes indicate that renal damage occurs during brain death, and could be part of a protective or recuperative mechanism induced by brain death-associated stress.

Renal function and genetic polymorphisms in pediatric heart transplant recipients

BACKGROUND

Common genetic variations influence rejection, infection, drug metabolism, and side effect profiles after pediatric heart transplantation. Reports in adults suggest that genetic background may influence post-transplant renal function. In this multicenter study, we investigated the association of genetic polymorphisms (GPs) in a panel of candidate genes on renal function in 453 pediatric heart transplant recipients.

METHODS

We performed genotyping for functional GPs in 19 candidate genes. Renal function was determined annually after transplantation by calculation of the estimated glomerular filtration rate (eGFR). Mixed-effects and Cox proportional hazard models were used to assess recipient characteristics and the effect of GPs on longitudinal eGFR and time to eGFR < 60 mL/min/1.73m(2).

RESULTS

Mean age at transplantation was 6.2 ± 6.1 years. Mean follow-up was 5.1 ± 2.5 years. Older age at transplant and black race were independently associated with post-transplant renal dysfunction. Univariate analyses showed FASL (C-843T) T allele (p = 0.014) and HO-1 (A326G) G allele (p = 0.0017) were associated with decreased renal function. After adjusting for age and race, these associations were attenuated (FASL, p = 0.075; HO-1, p = 0.053). We found no associations of other GPs with post-transplant renal function, including GPs in TGFβ1, CYP3A5, ABCB1, and ACE.

CONCLUSIONS

In this multicenter, large, sample of pediatric heart transplant recipients, we found no strong associations between GPs in 19 candidate genes and post-transplant renal function. Our findings contradict reported associations of CYP3A5 and TGFβ1 with renal function and suggest that genotyping for these GPs will not facilitate individualized immunosuppression for the purpose of protecting renal function after pediatric heart transplantation.

In vivo regulation of the heme oxygenase-1 gene in humanized transgenic mice

Heme oxygenase-1 (HO-1) catalyzes the rate-limiting step in heme degradation producing equimolar amounts of carbon monoxide, iron, and biliverdin. Induction of HO-1 is a beneficial response to tissue injury in diverse animal models of diseases including acute kidney injury. In vitro analysis has shown that the human HO-1 gene is transcriptionally regulated by changes in chromatin conformation but whether such control occurs in vivo is not known. To enable such analysis, we generated transgenic mice, harboring an 87-kb bacterial artificial chromosome expressing human HO-1 mRNA and protein and bred these mice with HO-1 knockout mice to generate humanized BAC transgenic mice. This successfully rescued the phenotype of the knockout mice including reduced birth rates, tissue iron overload, splenomegaly, anemia, leukocytosis, dendritic cell abnormalities and survival after acute kidney injury induced by rhabdomyolysis or cisplatin nephrotoxicity. Transcription factors such as USF1/2, JunB, Sp1, and CTCF were found to associate with regulatory regions of the human HO-1 gene in the kidney following rhabdomyolysis. Chromosome Conformation Capture and ChIP-loop assays confirmed this in the formation of chromatin looping in vivo. Thus, these bacterial artificial chromosome humanized HO-1 mice are a valuable model to study the human HO-1 gene providing insight to the in vivo architecture of the gene in acute kidney injury and other diseases.

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.

Heme degradation and vascular injury

Heme is an essential molecule in aerobic organisms. Heme consists of protoporphyrin IX and a ferrous (Fe(2+)) iron atom, which has high affinity for oxygen (O(2)). Hemoglobin, the major oxygen-carrying protein in blood, is the most abundant heme-protein in animals and humans. Hemoglobin consists of four globin subunits (alpha(2)beta(2)), with each subunit carrying a heme group. Ferrous (Fe(2+)) hemoglobin is easily oxidized in circulation to ferric (Fe(3+)) hemoglobin, which readily releases free hemin. Hemin is hydrophobic and intercalates into cell membranes. Hydrogen peroxide can split the heme ring and release "free" redox-active iron, which catalytically amplifies the production of reactive oxygen species. These oxidants can oxidize lipids, proteins, and DNA; activate cell-signaling pathways and oxidant-sensitive, proinflammatory transcription factors; alter protein expression; perturb membrane channels; and induce apoptosis and cell death. Heme-derived oxidants induce recruitment of leukocytes, platelets, and red blood cells to the vessel wall; oxidize low-density lipoproteins; and consume nitric oxide. Heme metabolism, extracellular and intracellular defenses against heme, and cellular cytoprotective adaptations are emphasized. Sickle cell disease, an archetypal example of hemolysis, heme-induced oxidative stress, and cytoprotective adaptation, is reviewed.

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.

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.

Intravenous bilirubin provides incomplete protection against renal ischemia-reperfusion injury in vivo

Exogenous bilirubin (BR) substitutes for the protective effects of heme oxygenase (HO) in several organ systems. Our objective was to investigate the effects of exogenous BR in an in vivo model of ischemia-reperfusion injury (IRI) in the rat kidney. Four groups of male Sprague-Dawley rats were anesthetized using isoflurane in oxygen and treated with 1) 5 mg/kg intravenous (iv) BR, 1 h before ischemia and 6-h reperfusion; 2) vehicle 1 h before ischemia and 6-h reperfusion; 3) 20 mg/kg iv BR, 1 h before and during ischemia; and 4) vehicle 1 h before and during ischemia. Bilateral renal clamping (30 min) was followed by 6-h reperfusion. Infusion of 5 mg/kg iv BR achieved target levels in the serum at 6 h postischemia (31 ± 9 μmol/l). Infusion of 20 mg/kg BR reached 50 ± 22 μmol/l at the end of ischemia, and a significant improvement was seen in serum creatinine at 6 h (1.07 ± 28 vs. 1.38 ± 0.18 mg/dl, P = 0.043). Glomerular filtration rate, estimated renal plasma flow, fractional excretion of electrolytes, and renal vascular resistance were not significantly improved in BR-treated groups. Histological grading demonstrated a trend toward preservation of cortical proximal tubules in rats receiving 20 mg/kg iv BR compared with control; however, neither BR dose provided protection against injury to the renal medulla. At the doses administered, iv BR did not provide complete protection against IRI in vivo. Combined supplementation of both BR and carbon monoxide may be required to preserve renal blood flow and adequately substitute for the protective effects of HO in vivo.

Stress associated proteins metallothionein, HO-1 and HSP 70 in human zero-hour biopsies of transplanted kidneys

Light microscopic alterations reflecting both previous and preservation-induced changes in the donor organ are usually not very distinctive. The ischemia/reperfusion-associated injury depends primarily on the conditions of donor organ preservation. The present study examined human kidney biopsies with special attention paid to the molecular mechanisms of preservation-induced injury preceding reperfusion. Stress-associated proteins hemeoxygenase-1 (HO-1), heat shock protein 70 (HSP 70), and metallothionein (MT) were studied in human zero-hour biopsies of transplanted kidneys prior to reperfusion in 29 patients. Protein expression was evaluated by semiquantitative immunohistochemistry and Western blotting for HO-1 and HSP 70. These findings were correlated with terminal deoxynucleotidyltransferase-mediated 2'-deoxyuridine 5'-triphosphate-digoxigenin nick end labeling (TUNEL) staining and follow up. Compared to controls, MT and HSP 70 expression was significantly higher at zero hour. In contrast, HO-1 and the number of TUNEL-positive cells were not elevated. MT and HO-1 immunoexpression were inversely associated with graft function, and hence, were of prognostic relevance. MT and HSP 70 were sensitive to the duration of cold ischemia. MT and HO-1 are suitable indicators for tissue injury during ischemia and may serve as new predictive markers that need to be validated in further independent studies.

Heme oxygenase-1: a provenance for cytoprotective pathways in the kidney and other tissues

Heme oxygenase (HO) is the rate-limiting enzyme in the degradation of heme, converting heme to biliverdin, during which iron is released and carbon monoxide (CO) is emitted; biliverdin is subsequently converted to bilirubin by biliverdin reductase. At least two isozymes possess HO activity: HO-1 represents the isozyme induced by diverse stressors, including ischemia, nephrotoxins, cytokines, endotoxin, oxidants, and vasoactive substances; HO-2 is the constitutive, glucocorticoid-inducible isozyme. HO-1 is upregulated in the kidney in assorted conditions and diseases. Interest in HO is driven by the capacity of this system to protect the kidney against injury, a capacity likely reflecting, at least in part, the cytoprotective properties of its products: in relatively low concentrations, CO exerts vasorelaxant, antiapoptotic, and anti-inflammatory effects while bile pigments are antioxidant and anti-inflammatory metabolites. This article reviews the HO system and the extent to which it influences the function of the healthy kidney; it summarizes conditions and stimuli that elicit HO-1 in the kidney; and it explores the significance of renal expression of HO-1 as induced by ischemia, nephrotoxins, nephritides, transplantation, angiotensin II, and experimental diabetes. This review also points out the tissue specificity of the HO system, and the capacity of HO-1 to induce renal injury in certain settings. Studies of HO in other tissues are discussed insofar as they aid in elucidating the physiologic and pathophysiologic significance of the HO system in the kidney.

Products of heme oxygenase and their potential therapeutic applications

Heme oxygenase 1 (HO-1) is induced in response to cellular stress and is responsible for converting the prooxidant heme molecule into equimolar quantities of biliverdin (BV), carbon monoxide (CO), and iron. BV is then converted to bilirubin (BR) by the enzyme biliverdin reductase. Experimental evidence suggests that induction of the HO system is an important endogenous mechanism for cytoprotection and that the downstream products of heme degradation, CO, BR, and BV, may mediate these powerful beneficial effects. These molecules, which were once considered to be toxic metabolic waste products, have recently been shown to have dose-dependent vasodilatory, antioxidant, and anti-inflammatory properties that are particularly desirable for tissue protection during organ transplantation. In fact, recent work has demonstrated that administration of exogenous CO, BR, or BV may offer a simple, inexpensive method to substitute for the cytoprotective effects of HO-1 in a variety of clinically applicable models. This review will attempt to summarize the relevant biochemical and cytoprotective properties of CO, BR, and BV, and will discuss emerging studies involving the therapeutic applications of these molecules in the kidney and other organ systems.

Therapeutic applications of carbon monoxide-releasing molecules

Carbon monoxide (CO), which is formed in mammalian cells through the oxidation of haem by the enzyme haem oxygenase, actively participates in the regulation of key intracellular functions. Emerging evidence reveals that an increased generation of haem oxygenase-derived CO plays a critical role in the resolution of inflammatory processes and alleviation of cardiovascular disorders. The authors have identified a novel class of substances, CO-releasing molecules (CO-RMs), which are capable of exerting a variety of pharmacological activities via the liberation of controlled amounts of CO in biological systems. A wide range of CO carriers containing manganese (CORM-1), ruthenium (CORM-2 and -3), boron (CORM-A1) and iron (CORM-F3) are currently being investigated to tailor therapeutic approaches for the prevention of vascular dysfunction, inflammation, tissue ischaemia and organ rejection.

Hemodialysis reduces inhibitory effect of plasma ultrafiltrate on LDL oxidation and subsequent endothelial reactions

Oxidative modification of low-density lipoprotein (LDL) and its deleterious effect on endothelium is implicated in the pathogenesis of atherosclerosis. Endothelium responds to such an insult by upregulating the synthesis of heme oxygenase-1 (HO-1) and ferritin. Endothelial cell damage and dysfunction have been observed in patients with chronic kidney disease (CKD) on maintenance hemodialysis (HD). We studied the effect of low-molecular-weight components of uremic plasma on LDL oxidation and LDL-oxidation-provoked endothelial cell reactions, such as the induction of cytotoxicity and the upregulation of cell-protective HO-1 and ferritin. Plasma ultrafiltrate (molecular weight<5000 Da) from CKD patients on HD or when treated conservatively exhibited a pronounced inhibition on heme-mediated oxidative modification of LDL. Endothelial cell cytotoxicity provoked by LDL oxidation was also attenuated by plasma ultrafiltrate from CKD patients. During HD treatment, a dramatic drop occurred in the retardation of oxidative reactions, and a loss of endothelial cytoprotection exerted by plasma ultrafiltrate was noted. The upregulation of HO-1 and ferritin in response to oxidative stress of LDL was blunted by uremic plasma ultrafiltrate that was released by the end of HD. The decreased antioxidant capacity of ultrafiltrate after HD occurred as a consequence of the intradialytic removal of L-ascorbic acid, uric acid, bilirubin, 3-indoxyl sulfate, indoxyl-beta-D-glucuronide, p-cresol, and phenol. Intradialytic removal of L-ascorbic acid, uric acid, bilirubin, 3-indoxyl sulfate, indoxyl-beta-D-glucuronide, p-cresol, and phenol increases the risk of LDL oxidation and subsequent endothelial cell damage, which underlines the importance of activation of cytoprotective HO-1 and ferritin in endothelium.

Treatment with CO-RMs during cold storage improves renal function at reperfusion

Low concentrations of carbon monoxide (CO) can protect tissues against ischemia-reperfusion (I-R) injury. We have recently identified a novel class of compounds, CO-releasing molecules (CO-RMs), which exert important pharmacological activities by carrying and delivering CO to biological systems. Here, we examined the possible beneficial effects of CO liberated from CO-RMs on the damage inflicted by cold storage and I-R in isolated perfused kidneys. Hemodynamic and biochemical parameters as well as mitochondrial respiration were measured in isolated perfused rabbit kidneys that were previously flushed with CO-RMs and stored at 4 degrees C for 24 h. Two water-soluble CO-RMs were tested: (1) sodium boranocarbonate (CORM-A1), a boron-containing carbonate that releases CO at a slow rate, and (2) tricarbonylchloro(glycinato)ruthenium(II) (CORM-3), a transition metal carbonyl that liberates CO very rapidly in solution. Kidneys flushed with Celsior solution supplemented with CO-RMs (50 microM) and stored at 4 degrees C for 24 h displayed at reperfusion a significantly higher perfusion flow rate (PFR), glomerular filtration rate, and sodium and glucose reabsorption rates compared to control kidneys flushed with Celsior solution alone. Addition of 1H-[1,2,4]oxadiazolo[4,3-alpha]quinoxalin-1-one (ODQ), a guanylate cyclase inhibitor, prevented the increase in PFR mediated by CO-RMs. The respiratory control index from kidney mitochondria treated with CO-RMs was also markedly increased. Notably, renal protection was lost when kidneys were flushed with Celsior containing an inactive compound (iCO-RM), which had been deliberately depleted of CO. CO-RMs are effective therapeutic agents that deliver CO during kidney cold preservation and can be used to ameliorate vascular activity, energy metabolism and renal function at reperfusion.

An integral role for heme oxygenase-1 and carbon monoxide in maintaining peripheral tolerance by CD4+CD25+ regulatory T cells

Over the past decade, a great deal of interest and attention has been directed toward a population of regulatory T cells (Treg) coexpressing the markers CD4 and CD25. The hallmark phenotype of this cell population resides in its ability to dominantly maintain peripheral tolerance and avert autoimmunity. Despite robust research interest in Treg, their mechanism of action and interaction with other cell populations providing immune regulation remains unclear. In this study, we present a model for Treg activity that implicates carbon monoxide, a by-product of heme oxygenase-1 activity, as an important and underappreciated facet in the suppressive capacity of Treg. Our hypothesis is based on recent evidence supporting a role for heme oxygenase-1 in regulating immune reactivity and posit carbon monoxide to function as a suppressive molecule. Potential roles for indoleamine 2,3-dioxygenase, costimulatory molecules, and cytokines in tolerance induction are also presented. This model, if validated, could act as a catalyst for new investigations into Treg function and ultimately result in novel methods to modulate Treg biology toward therapeutic applications.

Interleukin 10 attenuates neointimal proliferation and inflammation in aortic allografts by a heme oxygenase-dependent pathway

Interleukin 10 (IL-10) is a pleiotropic cytokine with well known antiinflammatory, immunosuppressive, and immunostimulatory properties. Chronic allograft rejection, characterized by vascular neointimal proliferation, is a major cause of organ transplant loss, particularly in heart and kidney transplant recipients. In a Dark Agouti to Lewis rat model of aortic transplantation, we evaluated the effects of a single intramuscular injection of a recombinant adeno-associated viral vector (serotype 1) encoding IL-10 (rAAV1-IL-10) on neointimal proliferation and inflammation. rAAV1-IL-10 treatment resulted in a significant reduction of neointimal proliferation and graft infiltration with macrophages and T and B lymphocytes. The mechanism underlying the protective effects of IL-10 in aortic allografts involved heme oxygenase 1 (HO-1) because inhibition of HO activity reversed not only neointimal proliferation but also inflammatory cell infiltration. Our results indicate that IL-10 attenuates neointimal proliferation and inflammatory infiltration and strongly imply that HO-1 is an important intermediary through which IL-10 regulates the inflammatory responses associated with chronic vascular rejection.

The story so far: Molecular regulation of the heme oxygenase-1 gene in renal injury

Heme oxygenases (HOs) catalyze the rate-limiting step in heme degradation, resulting in the formation of iron, carbon monoxide, and biliverdin, the latter of which is subsequently converted to bilirubin by biliverdin reductase. Recent attention has focused on the biological effects of product(s) of this enzymatic reaction, which have important antioxidant, anti-inflammatory, and cytoprotective functions. Two major isoforms of the HO enzyme have been described: an inducible isoform, HO-1, and a constitutively expressed isoform, HO-2. A third isoform, HO-3, closely related to HO-2, has also been described. Several stimuli implicated in the pathogenesis of renal injury, such as heme, nitric oxide, growth factors, angiotensin II, cytokines, and nephrotoxins, induce HO-1. Induction of HO-1 occurs as an adaptive and beneficial response to these stimuli, as demonstrated by studies in renal and non-renal disease states. This review will focus on the molecular regulation of the HO-1 gene in renal injury and will highlight the interspecies differences, predominantly between the rodent and human HO-1 genes.

Donor heme oxygenase-1 genotype is associated with renal allograft function1

BACKGROUND

The heme oxygenase (HO) isoenzyme HO-1 has recently been suggested to protect transplants from ischemia/reperfusion and immunologic injury. Inducibility of this enzyme is modulated by a (GT)n dinucleotide length polymorphism in the HO-1 gene promoter. Short (class S) repeats are associated with greater up-regulation of HO-1 than are long repeats. In the present study we investigated the impact of the promoter polymorphism of kidney allograft donors on clinical outcomes after transplantation.

METHODS

We enrolled 101 recipients of cadaveric donor kidney allografts (who underwent transplantation between June 1998 and September 1999) in this retrospective study. The HO-1 genotype was assessed using genomic DNA isolated from cryopreserved donor splenocytes.

RESULTS

Fifty patients (49.5%) had received a kidney from a donor with at least one class S allele. Recipients of allografts from a class S allele carrier had significantly lower 1-year serum creatinine levels (median 1.46 mg/dL, interquartile range 1.17-1.68 mg/dL) compared with recipients of a non-class S allele donor kidney (median 1.61 mg/dL, interquartile range 1.38-2.22 mg/dL, P =0.01). After adjustment for cold ischemia time, retransplantation, donor age, delayed graft function, and HLA mismatch, recipients of a class S allele transplant had serum creatinine levels 0.81 times (95% confidence interval: 0.70-0.95, P =0.01) those of recipients of a non-class S allele transplant. The two patient groups did not differ significantly with respect to the incidence of delayed graft function, allograft rejection, or immunologic graft loss.

CONCLUSION

Our data suggest an influence of the HO-1 gene promoter polymorphism on kidney allograft function and thus support previous studies indicating a protective effect of HO-1 induction in organ transplantation.

Induction of heme oxygenase-1 in kidneys during ex vivo warm perfusion

BACKGROUND

Reperfusion injury plays a pivotal role in the occurrence of delayed graft function and chronic rejection. Heme oxygenase-1 (HO-1), an inducible heat shock protein, is known to have cytoprotective effects against reperfusion injury. We report on the potential for ex vivo induction of HO-1 expression during acellular warm perfusion of canine kidneys, using cobalt protoporphyrin (CoPP) as an HO-1 inducer and zinc protoporphyrin as an HO-1 inhibitor.

METHODS

Canine kidneys were used to evaluate HO-1 increase after exposure to warm ischemia (WI), hypothermic perfusion (mechanical perfusion [MP], 4 degrees C), warm perfusion (exsanguineous metabolic support [EMS], 32 degrees C), or various combinations.

RESULTS

WI alone, MP, or EMS with or without WI, had no effect on HO-1 activity. However, the presence of CoPP during EMS perfusion resulted in a significant increase in kidney HO-1 activity, whereas zinc protoporphyrin reduced HO-1 activity. The presence of CoPP during MP did not induce elevated HO-1 expression. The results of our study demonstrate that sufficient metabolism supporting new protein synthesis resulting in the expression of the protective gene, HO-1, can be accomplished during an acellular near-normothermic perfusion using CoPP. Most importantly, the time required for ex vivo HO-1 induction with this method is compatible with the current time frame for which organs are preserved clinically.

CONCLUSIONS

The ability to induce HO-1 expression ex vivo eliminates the need for donor therapy to induce HO-1 increase before retrieving organs and also prevents the potential of decreasing HO-1 enzyme activity that is known to occur with temperature-mediated inhibition of oxidative metabolism during hypothermic organ storage.

Gene transfer-induced local heme oxygenase-1 overexpression protects rat kidney transplants from ischemia/reperfusion injury

Heme oxygenase-1 (HO-1) overexpression using gene transfer protects rat livers against ischemia/reperfusion (I/R) injury. This study evaluates the effects of Ad-HO-1 gene transfer in a rat renal isograft model. Donor LEW kidneys were perfused with Ad-HO-1, Ad-beta-gal, or PBS, stored at 4 degrees C for 24 h, and transplanted orthotopically into LEW recipients, followed by contralateral native nephrectomy. Serum creatinine, urine protein/creatinine ratios, severity of histologic changes, HO-1 mRNA/protein expression, and HO enzymatic activity were analyzed. Ad-HO-1 gene transfer conferred a survival advantage when compared with PBS- and Ad-beta-gal-treated controls, with median survival of 100, 7, and 7 d, respectively (P < 0.01). Serum creatinine levels were elevated at day 7 in all groups (range, 2.2 to 5.8 mg/dl) but recovered to 1.0 mg/dl by day 14 (P < 0.01) in Ad-HO-1 group, which was sustained thereafter. Urine protein/creatinine ratio at day 7 was elevated in both PBS and Ad-beta-gal, as compared with the Ad-HO-1 group (12.0 and 9.8 versus 5.0; P < 0.005); histologically, ATN and glomerulosclerosis was more severe in Ad-beta-gal group at all time points. Reverse transcriptase-PCR-based HO-1 gene expression was significantly increased before reperfusion (P < 0.001) and remained increased in the Ad-HO-1-treated group for 3 d after transplantation. Concomitantly, HO enzymatic activity was increased at transplantation and at 3 d posttransplant in the Ad-HO-1 group, compared with Ad-beta-gal controls (P < 0.05); tubular HO-1 expression was discernible early posttransplant in the Ad-HO-1 group alone. These findings are consistent with protective effects of HO-1 overexpression using a gene transfer approach against severe renal I/R injury, with reduced mortality and attenuation of tissue injury.

Heme oxygenase 1 gene transfer prevents CD95/Fas ligand-mediated apoptosis and improves liver allograft survival via carbon monoxide signaling pathway

Apoptosis via the CD95/FasL (CD95L) pathway plays an important role in allograft rejection. Heme oxygenase 1 (HO-1), a stress-responsive cytoprotective molecule, may be essential in preventing graft rejection. We used Ad-HO-1 gene transfer to analyze HO-1-mediated effects in a rat allogeneic orthotopic liver transplantation (OLT) model. The cytotoxicity to Fas-bearing YAC-1 target cells and frequency of terminal deoxynucleotidyltransferase-mediated dUTP nick-end labeling-positive (TUNEL(+)) cells in vitro were diminished in Ad-CD95L + Ad-HO-1-transfected cells, as compared with Ad-CD95L + Ad-beta-gal controls (p < 0.001). AdHO-1 gene transfer prevented <10-day rejection of dark agouti (DA) livers in Lewis (LEW) rats (survival >32 days), and diminished apoptosis. Unlike Ad-beta-gal OLTs, which showed signs of severe acute rejection, OLTs in the Ad-HO-1 group exhibited mild to moderate rejection and improved function. These beneficial effects were abrogated after adjunctive treatment with tin protoporphyrin (SnPP), an HO-1 antagonist. Intragraft expression of HO-1 and antiapoptotic gene products (Bcl-xl/Bag-1) was enhanced in Ad-HO-1-transduced OLTs, in association with selectively depressed expression of helper T cell type 1 cytokines (interleukin 2 and interferon gamma), as compared with Ad-beta-gal controls. To deliver CO, one of the downstream HO-1 mediators, allogeneic OLT recipients were exposed to methylene chloride. Such treatment prolonged survival to >47 days, diminished apoptosis, and preserved hepatic architecture/function. Thus, Ad-HO-1 gene transfer prevents CD95/FasL-mediated apoptosis, and significantly prolongs allogeneic OLT survival via a downstream HO-1-CO signaling pathway.

Expression of protective genes in human renal allografts: a regulatory response to injury associated with graft rejection

BACKGROUND

Long-term survival of a graft requires inhibition of host immune effectors, but protective responses emanating from the graft might be equally important. Expression of the "protective" genes A20, heme-oxygenase-1 (HO-1), and Bcl-xL in rodent allo and xenografts correlates with long-term survival. Little is known of the pattern of expression of such protective genes and the implication thereof in clinical transplantation.

METHODS

We analyzed, by quantitative reverse-transcriptase polymerase chain reaction (RT-PCR) and immunohistochemistry, expression of A20, HO-1, and Bcl-xL in 31 renal allograft biopsies from patients with suspected rejection.

RESULTS

A20 is not expressed in nonrejecting (NR) grafts. Its expression is increased in grafts undergoing acute and chronic rejection (AR and CR) but is weaker in CR. HO-1 is not expressed in NR grafts; it is up-regulated in AR but not CR. Bcl-xL is detected in all biopsies with decreased levels in CR. Expression of A20, HO-1, and Bcl-xL localizes mainly to endothelial, smooth muscle, and infiltrating mononuclear cells.

CONCLUSIONS

This data demonstrate that A20 and HO-1 are up-regulated in response to immune injury inferred by AR. Given the antiapoptotic and antiinflammatory functions of these genes, we hypothesize that their expression survives to limit graft injury by maintaining cell viability and controlling inflammation. Their reduced expression in CR as compared with AR represents either inadequate response to injury or a sequelae of prior injury that jeopardizes further tissue response to immune attack.

Heme oxygenase and the kidney

Heme plays a significant pathogenic role in several diseases involving the kidney. The cellular content of heme, derived either from the delivery of filtered heme proteins such as hemoglobin and myoglobin, or from the breakdown of ubiquitous intracellular heme proteins, is regulated via the heme oxygenase enzyme system. Heme oxygenases catalyze the rate-limiting step in heme degradation, resulting in the formation of iron, carbon monoxide, and biliverdin, which is subsequently converted to bilirubin by biliverdin reductase. Recent attention has focused on the biological effects of product(s) of this enzymatic reaction, which have important antioxidant, anti-inflammatory, and cytoprotective functions. Three isoforms of heme oxygenase (HO) enzyme have been described: an inducible isoform, HO-1, and two constitutively expressed isoforms, HO-2 and HO-3. Induction of HO-1 occurs as an adaptive and beneficial response to several injurious stimuli, and has been implicated in many clinically relevant disease states including atherosclerosis, transplant rejection, endotoxic shock, hypertension, acute lung injury, acute renal injury, as well as others. This review will focus predominantly on the role of HO-1 in the kidney.

Alloantigen-induced, T-cell-dependent production of nitric oxide by macrophages infiltrating skin allografts in mice

The immunological rejection reaction occurring after organ or tissue transplantation is characterized by a strong infiltration of the graft by T cells and macrophages. Since the rejection reaction is highly specific, we tested the role of T cells in the activation of macrophages and in the induction of nitric oxide (NO) production during graft rejection. The rejection of both MHC and non-MHC antigen-disparate skin allografts was associated with a significantly increased production of NO in the graft. The kinetics of NO production after transplantation correlated with the rejection reaction and with the fate of the allograft. A significant reduction in NO production was found in immunologically hyporeactive mice treated with cyclosporine, and no specific production of NO was found in tolerated skin allografts from neonatally tolerant mice. The production of NO was completely suppressed in graft explants from mice with depleted CD4(+) cells, but remained at a normal level in skin allografts from mice treated with anti-CD8 monoclonal antibody. The treatment of recipients of fully allogeneic skin grafts with 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine (AMT), a specific inhibitor of the inducible NO synthase, resulted in a significant prolongation of graft survival. The results thus show CD4(+) T-cell-dependent, alloantigen-induced production of NO by graft-infiltrating macrophages and the role of NO in the rejection reaction. We suggest that this pathway may represent one of the local effector mechanisms of graft rejection.

Cytoprotective role of heme oxygenase (HO)-1 in human kidney with various renal diseases

BACKGROUND

We previously reported that glomerular changes in the renal specimen of a human case with heme oxygenase-1 (HO-1) deficiency were mild, but tubulointerstitial injury advanced progressively. This study examined the patterns of HO-1 production in the kidney in various renal diseases. Furthermore, the critical cytoprotective roles of HO-1 were evaluated in the kidney by comparing HO-1 production and expressions of carboxymethyllysine (CML) and pentosidine, both of which are markers of oxidative stress.

METHODS

Renal biopsy or autopsy materials were obtained from a total of 74 patients. Degrees of hematuria and proteinuria and the levels of urinary N-acetyl-beta-D-glucosaminidase (NAG), beta2-microglobulin (beta2m), and creatinine were evaluated. Immunohistochemical studies for HO-1, CML, and pentosidine expressions were performed with their specific antiserum.

RESULTS

HO-1 staining was observed within tubular epithelial cells in all of the renal diseases, but was not detected within intrinsic glomerular cells. HO-1 staining tended to be more intense within distal tubuli than in proximal tubuli. Within distal tubuli, there was no significant correlation between intensity of HO-1 staining and degree of hematuria or presence of proteinuria. Within proximal tubuli, HO-1 staining tended to be more intense with greater degrees of hematuria, presence of proteinuria, and moderate tubulointerstitial damage. Intense staining of CML and pentosidine was observed within renal tubular epithelial cells only in HO-1-deficient patients.

CONCLUSIONS

HO-1 plays important roles in protecting renal tubuli from oxidative injuries, as these cells are constantly exposed to various oxidative stresses. It is suggested that renal tubular epithelia are more susceptible to oxidative stress due to the lack of this critical enzyme in HO-1 deficiency.

Exacerbation of chronic renovascular hypertension and acute renal failure in heme oxygenase-1-deficient mice

Heme oxygenase (HO) is a cytoprotective enzyme that degrades heme (a potent oxidant) to generate carbon monoxide (a vasodilatory gas that has anti-inflammatory properties), bilirubin (an antioxidant derived from biliverdin), and iron (sequestered by ferritin). Because of properties of HO and its products, we hypothesized that HO would be important for the regulation of blood pressure and ischemic injury. We studied chronic renovascular hypertension in mice deficient in the inducible isoform of HO (HO-1) using a one kidney-one clip (1K1C) model of disease. Systolic blood pressure was not different between wild-type (HO-1(+/+)), heterozygous (HO-1(+/-)), and homozygous null (HO-1(-/-)) mice at baseline. After 1K1C surgery, HO-1(+/+) mice developed hypertension (140+/-2 mm Hg) and cardiac hypertrophy (cardiac weight index of 5.0+/-0.2 mg/g) compared with sham-operated HO-1(+/+) mice (108+/-5 mm Hg and 4.1+/-0.1 mg/g, respectively). However, 1K1C produced more severe hypertension (164+/-2 mm Hg) and cardiac hypertrophy (6.9+/-0.6 mg/g) in HO-1(-/-) mice. HO-1(-/-) mice also experienced a high rate of death (56%) within 72 hours after 1K1C surgery compared with HO-1(+/+) (25%) and HO-1(+/-) (28%) mice. Assessment of renal function showed a significantly higher plasma creatinine in HO-1(-/-) mice compared with HO-1(+/-) mice. Histological analysis of kidneys from 1K1C HO-1(-/-) mice revealed extensive ischemic injury at the corticomedullary junction, whereas kidneys from sham HO-1(-/-) and 1K1C HO-1(+/-) mice appeared normal. Taken together, these data suggest that chronic deficiency of HO-1 does not alter basal blood pressure; however, in the 1K1C model an absence of HO-1 leads to more severe renovascular hypertension and cardiac hypertrophy. Moreover, renal artery clipping leads to an acute increase in ischemic damage and death in the absence of HO-1.

Heme protein-induced chronic renal inflammation: suppressive effect of induced heme oxygenase-1

BACKGROUND

Heme oxygenase (HO) is the rate-limiting enzyme in the degradation of heme; its inducible isozyme, HO-1, protects against acute heme protein-induced nephrotoxicity and other forms of acute tissue injury. This study examines the induction of HO-1 in the kidney chronically inflamed by heme proteins and the functional significance of such an induction of HO-1.

METHODS

Studies were undertaken in a patient with chronic tubulointerstitial disease in the setting of paroxysmal nocturnal hemoglobinuria (PNH), in a rat model of chronic tubulointerstitial nephropathy caused by repetitive exposure to heme proteins, and in genetically engineered mice deficient in HO-1 (HO-1 -/-) in which hemoglobin was repetitively administered.

RESULTS

The kidney in PNH evinces robust induction of HO-1 in renal tubules in the setting of chronic inflammation. The heme protein-enriched urine from this patient, but not urine from a healthy control subject, induced expression of HO-1 in renal tubular epithelial cells (LLC-PK1 cells). A similar induction of HO-1 and related findings are recapitulated in a rat model of chronic inflammation induced by repetitive exposure to heme proteins. Additionally, in the rat, the administration of heme proteins induces monocyte chemoattractant protein (MCP-1). The functional significance of HO-1 so induced was uncovered in the HO-1 knockout mouse: Repeated administration of hemoglobin to HO-1 +/+ and HO-1 -/- mice led to intense interstitial cellular inflammation in HO-1 -/- mice accompanied by striking up-regulation of MCP-1 and activation of one of its stimulators, nuclear factor-kappaB (NF-kappaB). These findings were not observed in similarly treated HO-1 +/+ mice or in vehicle-treated HO-1 -/- and HO-1 +/+ mice.

CONCLUSION

We conclude that up-regulation of HO-1 occurs in the kidney in humans and rats repetitively exposed to heme proteins. Such up-regulation represents an anti-inflammatory response since the genetic deficiency of HO-1 markedly increases activation of NF-kappaB, MCP-1 expression, and tubulointerstitial cellular inflammation.

Heme oxygenase: colors of defense against cellular stress

The discovery of the gaseous molecule nitric oxide in 1987 unraveled investigations on its functional role in the pathogenesis of a wide spectrum of biological and pathological processes. At that time, the novel concept that an endogenous production of a gaseous substance such as nitric oxide can impart such diverse and potent cellular effects proved to be very fruitful in enhancing our understanding of many disease processes including lung disorders. Interestingly, we have known for a longer period of time that there exists another gaseous molecule that is also generated endogenously; the heme oxygenase (HO) enzyme system generates the majority if not all of the endogenously produced carbon monoxide. This enzyme system also liberates two other by-products, bilirubin and ferritin, each possessing important biological functions and helping to define the uniqueness of the HO enzyme system. In recent years, interest in HO has emerged in numerous disciplines including the central nervous system, cardiovascular physiology, renal and hepatic systems, and transplantation. We review the functional role of HO in lung biology and its real potential application to lung diseases.

Mechanisms underlying induction of heme oxygenase-1 by nitric oxide in renal tubular epithelial cells

We examined whether nitric oxide-generating agents influence expression of heme oxygenase-1 (HO-1) in renal proximal tubular epithelial cells, LLC-PK(1) cells, and the mechanisms underlying any such effects. In sublytic amounts, the nitric oxide donor sodium nitroprusside induced HO-1 mRNA and protein and HO activity in a dose-dependent and time-dependent fashion; this induction was specific for nitric oxide since the nitric oxide scavenger carboxy-2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide significantly reduced such induction. The induction of HO activity by sodium nitroprusside, or by another nitric oxide donor, spermine NONOate, was markedly reduced by the iron chelator deferoxamine. Two different thiol-containing agents, N-acetylcysteine and dithiothreitol, blunted such induction of HO by nitric oxide. Downstream products of nitric oxide, such as peroxynitrite or cGMP, were not involved in inducing HO. In higher concentrations (millimolar amounts), sodium nitroprusside induced appreciable cytotoxicity as assessed by lactate dehydrogenase (LDH) release and lipid peroxidation, and both of these effects were markedly reduced by deferoxamine. Inhibition of HO did not affect the cytotoxic effects (measured by LDH release) of sodium nitroprusside. We thus provide the novel description of the induction of HO-1 in renal proximal tubular epithelial cells exposed to nitric oxide donors and provide the first demonstration in kidney-derived cells for the involvement of a redox-based mechanism in such expression. We also demonstrate that, in LLC-PK(1) cells exposed to nitric oxide donors, chelatable iron is involved in eliciting the HO-1 response observed at lower concentrations of these donors, and in mediating the cytotoxic effects of these donors when present in higher concentrations.

Docosahexaenoic acid decreases IRF-1 mRNA and thus inhibits activation of both the IRF-E and NFkappa d response elements of the iNOS promoter

BACKGROUND

Nitric oxide produced by inducible nitric oxide synthase (iNOS) may be cytotoxic during cardiac, hepatic, and renal acute allograft rejection. Because the incidence of rejection is decreased by fish oils that contain docosahexaenoic acid (DHA), we investigated the effects of DHA on iNOS. Using nuclear run-on assays and iNOS-promoter constructs, we previously showed that docosahexaenoic acid (DHA) inhibits activation of the iNOS gene by murine macrophages that had been stimulated in vitro by IFNgamma plus lipopolysaccharide.

METHODS

In our current investigation, our purpose has been to determine how DHA inhibits iNOS gene activation in murine macrophages, by using gel retardation and Northern blotting techniques. We studied the effects of DHA on the formation nuclear protein complexes that interact with the critical iNOS promoter's response elements for IRF-1 (IRF-E -923 to -913 bp) and NF-kappaB (NFkappa d -85 to -75 bp).

RESULTS

We now show that DHA inhibited increases of IRF-1 mRNA abundance in response to IFNgamma plus lipopolysaccharide. As expected, we found that this prevented formation of the nuclear protein complex that binds to the IRF-E DNA response element. We also found that inhibition of IRF-1 inhibited formation of the nuclear protein complex that binds to the NFkappa d DNA response element.

CONCLUSIONS

DHA decreases the abundance of IRF-1 mRNA in stimulated cells. That, in turn, results in the decreased nuclear protein binding to the major iNOS promoter response elements (IRF-E and NF-kappaB). We found that this occurred because IRF-1 is a component of both the nuclear protein complex that binds to IRF-E and the nuclear protein complex that binds to NFkappa d.

Renal response to tissue injury: lessons from heme oxygenase-1 GeneAblation and expression

Heme oxygenase-1 (HO-1) is a microsomal enzyme involved in the degradation of heme, resulting in the generation of biliverdin, iron, and carbon monoxide. Recent attention has focused on the biologic effects of product(s) of this enzymatic reaction that have important antioxidant, anti-inflammatory, and cytoprotective functions. Induction of HO-1 occurs as an adaptive and beneficial response to a wide variety of oxidant stimuli, including heme, hydrogen peroxide, cytokines, growth factors, heavy metals, nitric oxide, and oxidized LDL. HO-1 has been implicated in several clinically relevant disease states, including transplant rejection, hypertension, acute renal injury, atherosclerosis, and others. Previous studies indicate a protective role for HO-1 in heme and non-heme-mediated models of acute renal injury using chemical inducers and inhibitors of HO-1. Studies in HO-1 knockout mice further corroborate these observations, highlighting the important role of HO-1 in the pathophysiology of acute renal injury. Expression of HO-1 has been linked to prolonged xenograft survival and is important in transplant rejection as well. More recently, the first known case of human HO-1 deficiency was reported with several phenotypical similarities to the mouse HO-1 knockout. The role of HO-1 has extended far beyond its initial description as an enzyme involved in heme degradation to being an important mediator in modulating adaptive and protective responses not only in renal injury, but in other organ systems as well.

Heme oxygenase-1 gene ablation or expression modulates cisplatin-induced renal tubular apoptosis

Heme oxygenase-1 (HO-1) is a 32-kDa microsomal enzyme that catalyzes the conversion of heme to biliverdin, releasing iron and carbon monoxide. Induction of HO-1 occurs as a protective response in cells/tissues exposed to a wide variety of oxidant stimuli. The chemotherapeutic effects of cis-diamminedichloroplatinum(II) (cisplatin), a commonly used anticancer drug, are limited by significant nephrotoxicity, which is characterized by varying degrees of renal tubular apoptosis and necrosis. The purpose of this study was to evaluate the functional significance of HO-1 expression in cisplatin-induced renal injury. Our studies demonstrate that transgenic mice deficient in HO-1 (-/-), develop more severe renal failure and have significantly greater renal injury compared with wild-type (+/+) mice treated with cisplatin. In vitro studies in human renal proximal tubule cells demonstrate that hemin, an inducer of HO-1, significantly attenuated cisplatin-induced apoptosis and necrosis, whereas inhibition of HO-1 enzyme activity reversed the cytoprotective effect. Overexpression of HO-1 resulted in a significant reduction in cisplatin-induced cytotoxicity. These studies provide a basis for future studies using targeted gene expression of HO-1 as a therapeutic and preventive modality in high-risk settings of acute renal failure.

Vasoactive substances in renal transplantation

During and after transplantation the kidney experiences a variety of insults that result in functional impairment and structural damage. These changes are mediated or influenced by hormones, cytokines, enzymes and growth factors, which are excreted by endothelial, graft parenchymal as well as by graft infiltrating cells. This review evaluates the pathophysiological role of vasoactive substances (for example, the vasoconstrictors angiotensin II and endothelin, as well as vasodilators such as nitric oxide, adrenomedullin and atrial natriuretic peptide) in kidney transplantation and summarizes recent reports that indicate that targeting vasoactive substances may represent effective therapeutic strategies for the achievement of long-term allograft survival.

Gene transfer of immunomodulatory peptides correlates with heme oxygenase-1 induction and enhanced allograft survival

BACKGROUND

Decapeptides derived from human HLA class I sequences have been shown to prolong allograft survival. The mechanism of action of these peptides has been uncertain, because they act in an MHC unrestricted manner. Recently, it was found that these peptides bind heme oxygenase 1 (HO-1). In the present study, we sought to determine whether local delivery of these peptides through gene transfer could extend allograft survival, and to explore the underlying mechanisms.

METHODS

C57BL/6 neonatal hearts were transplanted to CBA/J recipients and the peptide, or plasmid DNA encoding the peptide, was injected directly into the allograft at the time of the transplant.

RESULTS

Direct injection of 1 microg of the B2702 peptide into the allograft did not prolong survival (13.3+/-0.8 vs. 13.4+/-0.8 days for untreated controls), but injection of 400 microg of peptide did extend survival (22.0+/-0.6). Injection of plasmid DNA encoding the B2702 peptide was superior to peptide delivery, extending graft survival to 30.8+/-1.5 days. Similar results were obtained using another plasmid encoding the rationally designed peptide BC1 (28.5+/-1.7), whereas no significant prolongation was observed using a plasmid encoding the control peptide B2705 (16.5+/-1.0). To explore the hypothesis that these peptides exert their immunosuppressive effect by altering HO-1 activity, animals were treated with iron protoporphyrin, an inducer of HO-1 activity, or tin protoporphyrin, an inhibitor of HO-1. Treatment with iron protoporphyrin alone extended graft survival (24.5+/-1.6) and did not alter the benefit in survival seen with BC1 gene transfer (28.0+/-0.8). In contrast, treatment with tin protoporphyrin abolished the benefit of BC1 gene transfer (17.0+/-0.6).

CONCLUSIONS

These results demonstrate that plasmid mediated gene transfer is an effective means for delivering immunosuppressive peptides to extend allograft survival. The experiments suggest that these peptides may act by increasing HO-1 activity and support a role for HO-1 in immune regulation and allograft survival.

Expression and actions of heme oxygenase in the renal medulla of rats

Recent studies have shown that the heme oxygenase (HO) product, carbon monoxide (CO), induces vasodilation and that inhibition of HO produces a sustained hypertension in rats. Given the importance of renal medullary blood flow (MBF) in the long-term control of arterial blood pressure, we hypothesized that the HO/CO system may play an important role in maintaining the constancy of blood flow to the renal medulla, which in turn contributes to the antihypertensive effects of the renal medulla. To test this hypothesis, we first determined the expression of 2 isoforms of HO (HO-1 and HO-2) in the different kidney regions. By Northern blot analyses, the abundance of both isozyme mRNAs was found highest in the renal inner medulla and lowest in the renal cortex. The transcripts for HO-1 in the renal outer medulla and inner medulla were 2.5 and 3.7 times that expressed in the renal cortex and those for HO-2 in the outer medulla and inner medulla were 1.3 and 1.6 times that expressed in the renal cortex, respectively. Western blot analyses of both enzymes showed the same expression pattern in these kidney regions as the mRNAs. To determine the role that HO plays in the control of renal MBF, we examined the effect of the HO inhibitor zinc deuteroporphyrin 2,4-bis glycol (ZnDPBG) on cortical blood flow and MBF in anesthetized rats. ZnDPBG was given by renal medullary interstitial infusion, and cortical blood flow and MBF were measured by laser Doppler flowmetry. Renal medullary interstitial infusion of ZnDPBG at a dose of 60 nmol/kg per minute produced a 31% decrease in MBF over a period of 60 minutes as measured by laser Doppler flow signal (0.62+/-0.02 vs 0.43+/-0.04 V in control vs ZnDPBG). With the use of an in vivo microdialysis technique, ZnDPBG was found to significantly reduce renal medullary cGMP concentrations when infused into the renal medullary interstitial space. These results suggest that both HO-1 and HO-2 are highly expressed in the renal medulla, that HO and its products play an important role in maintaining the constancy of blood flow to the renal medulla, and that cGMP may mediate the vasodilator effect of HO products in the renal medullary circulation.

In vitro and in vivo immunomodulatory effects of RDP1258, a novel synthetic peptide

Peptides derived from certain regions of human class I MHC molecules are known to have immunomodulatory effects. In particular, amino acid residues 75-84 of the HLA-B7 and HLA-B2702 molecules have demonstrated allele nonspecific immunosuppression in several animal transplant models. There is evidence that these effects are mediated by binding to intracellular heat shock proteins, including heme oxygenase-1. A new derivative of these peptides, RDP1258, was developed using a novel computer-assisted rational design technique. In vitro, RDP1258 peptide inhibited rat heme oxygenase activity in a dose-dependent manner. Similar to observations made with other in vitro heme oxygenase inhibitors, in vivo administration of RDP1258 peptide to naive rats resulted in upregulation of splenic heme oxygenase activity. The effects of the peptide on alloimmune responses were then tested. Addition of RDP1258 to rat and human mixed leukocyte reactions inhibited proliferation in a dose-dependent manner. In a rat renal transplantation model, peptide therapy combined with a sub-therapeutic dose of cyclosporin A significantly prolonged allograft survival. These data provide further evidence that modulation of the heat shock protein heme oxygenase by rationally designed peptides affects immune effector functions and may allow the development of novel immunomodulatory strategies in organ transplantation.

Stress protein-induced immunosuppression: inhibition of cellular immune effector functions following overexpression of haem oxygenase (HSP 32)

This is the first report on suppression of immune effector functions following upregulation of heat shock protein 32 (HSP 32), known as haem oxygenase (HO-1). Here we evaluated the effect of cobalt-protoporphyrin (CoPP)-induced HO-1 expression on cell-mediated immune responses. Administration of CoPP to CBA mice resulted in overexpression of HO-1 in the spleen, liver and kidneys. In vitro measurements of T cell-mediated and NK-cell-mediated cytotoxicity in spleens from CoPP-treated animals demonstrated a severe suppression of their effector functions while administration of Zn-PP or vitamin B12 had no effect. Furthermore, CoPP therapy decreased the lymphoproliferative alloresponse and differentiation of cytotoxic T cells. Inhibition of proliferation appeared to be due to cell growth arrest with an increased number of cells staying in G0/G1 phase. Despite the suppressed proliferative response, IL-2 production in the MLR was not inhibited. In contrast, CoPP decreased the production of IL-10, IFN-gamma and TNF-alpha. In vivo, CoPP prolonged the survival of heterotopic heart allografts in mice. The immunosuppressive effects following CoPP-mediated upregulation of HO-1 were similar to those observed after peptide-mediated upregulation of HO-1. The results indicate that overexpression of HO results in the inhibition of several immune effector functions and thus provides an explanation for stress-induced immunosuppression.

T cells reactive to a single immunodominant self-restricted allopeptide induce skin graft rejection in mice

Alloreactive T lymphocytes can respond to foreign MHC complexed with foreign peptides through the direct pathway of allorecognition and can additionally recognize allopeptides expressed in the context of recipient (self) MHC through the indirect pathway. To better elucidate how indirect pathway-responsive CD4(+) T cells mediate allograft rejection, we isolated and characterized a TH1 T cell line from BALB/c recipients of B10.A skin that responds to a defined immunodominant, self-restricted allopeptide, I-Abetak58-71. When transferred into BALB/c severe combined immunodeficiency recipients of B10.A skin allografts, this cell line specifically induced a form of skin graft rejection characterized by the presence of TH1 cytokines, macrophage infiltration, and extensive fibrosis. Recall immune responses and immunofluorescence of the rejecting skin revealed only the presence of the peptide-specific T cells within the recipient animals, with no evidence of a direct pathway alloresponse. These studies demonstrate that T cells reactive to a single self-restricted allopeptide can mediate a form of allogeneic skin graft rejection that exhibits characteristics of a chronic, fibrosing process.

Heme oxygenase is induced in nephrotoxic nephritis and hemin, a stimulator of heme oxygenase synthesis, ameliorates disease

Heme oxygenase (HO) catalyses degradation of heme to biliverdin, iron and carbon monoxide (CO). Two isoforms exist, a constitutive form and an inducible form (HO-1). Induction of HO-1 may have protective effects in inflammation. We studied heterologous (HNTN) and accelerated (ANTN) nephrotoxic nephritis in Lewis rats. Hemin, an inducer of HO-1, (30 mumol/kg) was administered 18 hours before induction of nephritis and 72 hours later in ANTN. HO-1 was not detected immunohistochemically in normal glomeruli but was present in HNTN and ANTN in cells with the morphology of macrophages. HO-1 induction was confirmed by RT-PCR. In normal rats hemin induced glomerular HO-1 mRNA at 18 hours. In HNTN hemin markedly reduced proteinuria at 24 hours (10 +/- 4 mg/24 hr; control 54 +/- 16; P < 0.05), neutrophil infiltration at two hours (29.8 +/- 1.8 vs. 22.3 +/- 1.5 neutrophils/glomerulus, P < 0.05), and glomerular macrophage number at two hours (2.1 +/- 0.1 vs. 3.1 +/- 0.4 cells/glomerulus, P < 0.05). In ANTN proteinuria was reduced at day 1 and day 4 (36 +/- 11 vs. 60 +/- 15 and 36 +/- 7 vs. 86 +/- 9 mg protein/24 hr, respectively, P < 0.001), glomerular thrombi were reduced by hemin at day 1 and 4 (1.5 +/- 2.7 vs. 2.7 +/- 0.2 and 1.3 +/- 0.01 vs. 2.9 +/- 0.02, respectively, P < 0.001) and glomerular macrophage infiltration was reduced on day 4 (11.2 +/- 0.8 cells/glom; control 15.9 +/- 0.8, P < 0.01). Possible mechanisms by which HO-1 ameliorates disease include anti-complement or anti-oxidant effects of bilirubin and vasodilator and anti-platelet effects of carbon monoxide.