Heme oxygenase-1 gene expression attenuates angiotensin II-mediated DNA damage in endothelial cells

Keap1-Nrf2 Heterodimer: A Therapeutic Target to Ameliorate Sickle Cell Disease

Sickle cell disease (SCD) is a monogenic inheritable disease characterized by severe anemia, increased hemolysis, and recurrent, painful vaso-occlusive crises due to the polymerization of hemoglobin S (HbS)-generated oxidative stress. Up until now, only four drugs are approved for SCD in the US. However, each of these drugs affects only a limited array of SCD pathologies. Importantly, curative therapies, such as gene therapy, or hematopoietic stem cell transplantation are not available for every patient because of their high costs, availability of donor matching, and their serious adverse effects. Therefore, there is an unmet medical need for novel therapeutic strategies that target broader SCD sequelae. SCD phenotypic severity can be alleviated by increasing fetal hemoglobin (HbF) expression. This results in the inhibition of HbS polymerization and thus sickling, and a reduction in oxidative stress. The efficacy of HbF is due to its ability to dilute HbS levels below the threshold required for polymerization and to influence HbS polymer stability in RBCs. Nuclear factor-E2-related factor 2 (Nrf2)/Kelch-like ECH-associated protein-1 (Keap1)-complex signaling is one of the most important cytoprotective signaling controlling oxidative stress. Nrf2 is present in most organs and, after dissociation from Keap1, it accumulates in the cytoplasm, then translocates to the nucleus where it binds to the antioxidant response element (ARE) sequences and increases the expression of various cytoprotective antioxidant genes. Keeping this in mind, various researchers have proposed a role of multiple agents, more importantly tert-Butylhydroquinone (tBHQ), curcumin, etc., (having electrophilic properties) in inhibiting keap1 activity, so that Nrf2 can translocate to the nucleus to activate the gamma globin gene, thus maintaining alpha-hemoglobin-stabilizing protein (AHSP) and HbF levels. This leads to reduced oxidative stress, consequently minimizing SCD-associated complications. In this review, we will discuss the role of the Keap-1–Nrf2 complex in hemoglobinopathies, especially in SCD, and how this complex might represent a better target for more effective treatment options.

Hydroxyproline alleviates 4-hydroxy-2-nonenal-induced DNA damage and apoptosis in porcine intestinal epithelial cells

Oxidative stress has been confirmed in relation to intestinal mucosa damage and multiple bowel diseases. Hydroxyproline (Hyp) is an imino acid abundant in sow's milk. Compelling evidence has been gathered showing the potential antioxidative properties of Hyp. However, the role and mechanism of Hyp in porcine intestinal epithelial cells in response to oxidative stress remains unknown. In this study, small intestinal epithelial cell lines of piglets (IPEC-1) were used to evaluate the protective effects of Hyp on 4-hydroxy-2-nonenal (4-HNE)-induced oxidative DNA damage and apoptosis. IPEC-1 pretreated with 0.5 to 5 mmol/L Hyp were exposed to 4-HNE (40 μmol/L) in the presence or absence of Hyp. Thereafter, the cells were subjected to apoptosis detection by Hoechst staining, flow cytometry, and Western blot or DNA damage analysis by comet assay, immunofluorescence, and reverse-transcription quantitative PCR (RT-qPCR). Cell apoptosis and the upregulation of cleaved-caspase-3 induced by 4-HNE (40 μmol/L) were inhibited by 5 mmol/L of Hyp. In addition, 5 mmol/L Hyp attenuated 4-HNE-induced reactive oxygen species (ROS) accumulation, glutathione (GSH) deprivation and DNA damage. The elevation in transcription of GADD45a (growth arrest and DNA-damage-inducible protein 45 alpha) and GADD45b (growth arrest and DNA-damage-inducible protein 45 beta), as well as the phosphorylation of H2AX (H2A histone family, member X), p38 MAPK (mitogen-activated protein kinase), and JNK (c-Jun N-terminal kinase) in cells treated with 4-HNE were alleviated by 5 mmol/L Hyp. Furthermore, Hyp supplementation increased the protein abundance of Krüppel like factor 4 (KLF4) in cells exposed to 4-HNE. Suppression of KLF4 expression by kenpaulone impeded the resistance of Hyp-treated cells to DNA damage and apoptosis induced by 4-HNE. Collectively, our results indicated that Hyp serves to protect against 4-HNE-induced apoptosis and DNA damage in IPEC-1 cells, which is partially pertinent with the enhanced expression of KLF4. Our data provides an updated explanation for the nutritional values of Hyp-containing animal products.

Heme Oxygenase-1 Signaling and Redox Homeostasis in Physiopathological Conditions

Heme-oxygenase is the enzyme responsible for degradation of endogenous iron protoporphyirin heme; it catalyzes the reaction’s rate-limiting step, resulting in the release of carbon monoxide (CO), ferrous ions, and biliverdin (BV), which is successively reduced in bilirubin (BR) by biliverdin reductase. Several studies have drawn attention to the controversial role of HO-1, the enzyme inducible isoform, pointing out its implications in cancer and other diseases development, but also underlining the importance of its antioxidant activity. The contribution of HO-1 in redox homeostasis leads to a relevant decrease in cells oxidative damage, which can be reconducted to its cytoprotective effects explicated alongside other endogenous mechanisms involving genes like TIGAR (TP53-induced glycolysis and apoptosis regulator), but also to the therapeutic functions of heme main transformation products, especially carbon monoxide (CO), which has been shown to be effective on GSH levels implementation sustaining body’s antioxidant response to oxidative stress. The aim of this review was to collect most of the knowledge on HO-1 from literature, analyzing different perspectives to try and put forward a hypothesis on revealing yet unknown HO-1-involved pathways that could be useful to promote development of new therapeutical strategies, and lay the foundation for further investigation to fully understand this important antioxidant system.

HO-1 overexpression and underexpression: Clinical implications

In this review we examine the effects of both over- and under-production of heme oxygenase-1 (HO-1) and HO activity on a broad spectrum of biological systems and on vascular disease. In a few instances e.g., neonatal jaundice, overproduction of HO-1 and increased HO activity results in elevated levels of bilirubin requiring clinical intervention with inhibitors of HO activity. In contrast HO-1 levels and HO activity are low in obesity and the HO system responds to mitigate the deleterious effects of oxidative stress through increased levels of bilirubin (anti-inflammatory) and CO (anti-apoptotic) and decreased levels of heme (pro-oxidant). Site specific HO-1 overexpression diminishes adipocyte terminal differentiation and lipid accumulation of obesity mediated release of inflammatory molecules. A series of diverse strategies have been implemented that focus on increasing HO-1 and HO activity that are central to reversing the clinical complications associated with diseases including, obesity, metabolic syndrome and vascular disease.

Comet assay and its use for evaluating oxidative DNA damage in some pathological states

The comet assay, or single-cell gel electrophoresis (SCGE), is a sensitive, rapid, relatively simple and inexpensive method for detecting DNA strand breaks in individual cells. It is used in a broad variety of applications and as a tool to investigate DNA damage and repair. The sensitivity and specificity of the assay are greatly enhanced if the DNA incubated with an enzyme, whichrecognizes a specific kind of DNA damage. This damage induced by oxidative stress plays a pivotal role in many diseases and in aging. This article is a critical review of the possible application of the comet assay in some pathological states in clinical practice. Most of the studies relate to evaluating the response of an organism to chemotherapy or radiotherapy with statistically significant evidence of DNA damage in patients. Other useful applications have been demonstrated for patients with heart or neurodegenerative diseases. Only a few studies have been published on the use of this method in critically ill patients, although its use would be appropriate. There are also other scenarios where the comet assay could prove to be very useful in the future, such as in predicting the likelihood of certain pathological conditions.

Translational Significance of Heme Oxygenase in Obesity and Metabolic Syndrome

The global epidemic of obesity continues unabated with sequelae of diabetes and metabolic syndrome. This review reflects the dramatic increase in research on the role of increased expression of heme oxygenase (HO)-1/HO-2, biliverdin reductase, and HO activity on vascular disease. The HO system engages with other systems to mitigate the deleterious effects of oxidative stress in obesity and cardiovascular disease (CVD). Recent reports indicate that HO-1/HO-2 protein expression and HO activity have several important roles in hemostasis and reactive oxygen species (ROS)-dependent perturbations associated with metabolic syndrome. HO-1 protects tissue during inflammatory stress in obesity through the degradation of pro-oxidant heme and the production of carbon monoxide (CO) and bilirubin, both of which have anti-inflammatory and anti-apoptotic properties. By contrast, repression of HO-1 is associated with increases of cellular heme and inflammatory conditions including hypertension, stroke, and atherosclerosis. HO-1 is a major focus in the development of potential therapeutic strategies to reverse the clinical complications of obesity and metabolic syndrome.

Vascular hyperpermeability and aging

Vascular hyperpermeability, the excessive leakage of fluid and proteins from blood vessels to the interstitial space, commonly occurs in traumatic and ischemic injuries. This hyperpermeability causes tissue vasogenic edema, which often leads to multiple organ failure resulting in patient death. Vascular hyperpermeability occurs most readily in small blood vessels as their more delicate physical constitution makes them an easy target for barrier dysfunction. A single layer of endothelial cells, linked to one another by cell adhesion molecules, covers the interior surface of each blood vessel. The cell adhesion molecules play a key role in maintaining barrier functions like the regulation of permeability. Aging is a major risk factor for microvascular dysfunction and hyperpermeability. Apart from age-related remodeling of the vascular wall, endothelial barrier integrity and function declines with the advancement of age. Studies that address the physiological and molecular basis of vascular permeability regulation in aging are currently very limited. There have been many cellular and molecular mechanisms proposed to explain aging-related endothelial dysfunction but their true relationship to barrier dysfunction and hyperpermeability is not clearly known. Among the several mechanisms that promote vascular dysfunction and hyperpermeability, the following are considered major contributors: oxidative stress, inflammation, and the activation of apoptotic signaling pathways. In this review we highlighted (a) the physiological, cellular and molecular changes that occur in the vascular system as a product of aging; (b) the potential mechanisms by which aging leads to barrier dysfunction and vascular hyperpermeability in the peripheral and the blood-brain barrier; (c) the mechanisms by which the age-related increases in oxidative stress, inflammatory markers and apoptotic signaling etc. cause endothelial dysfunction and their relationship to hyperpermeability; and (d) the relationship between aging, vascular permeability and traumatic injuries.

Bilirubin attenuates the renal tubular injury by inhibition of oxidative stress and apoptosis

Background

Bilirubin (BIL) has been recognized as an endogenous antioxidant that shows a protective effect for cardiorenal diseases. We investigated whether administration of BIL had a protective effect on cyclosporine (CsA)-induced nephropathy (CIN), and examined the effects of BIL on the oxidative stress and apoptosis.

Methods

BIL was pretreated intraperitoneally three times for a week (60 mg/kg), and CsA was injected for 4 weeks (15 mg/kg/day, subcutaneous). Proximal tubular epithelial (HK2) cells were pretreated with 0.1mg/ml of BIL for 24 hours, and then treated with 20 μM of CsA for another 24 hours.

Results

CsA induced marked increases in urine kidney injury molecule-1 (Kim-1) and neutrophil gelatinase-associated lipocalin (NGAL) concentrations (P < 0.05). BIL reduced urine Kim-1 in CIN (P < 0.05), while urine NGAL exhibited a decreasing tendency. In CsA-treated rat kidneys, the protein expression of NOX4 and p22phox was reduced by BIL (P < 0.05). BIL ameliorated CsA-induced arteriolopathy, tubulointerstitial fibrosis, tubular injury, and the apoptosis examined by TUNEL assay (P < 0.01). In HK2 cells, BIL reduced intracellular reactive oxygen species in CsA-treated cells. CsA increased the protein expression of bax, cleaved caspase-9, caspase-3 and the activity of caspase-3; however, the anti-apoptotic bcl-2 protein was reduced. These changes were recovered by BIL (P < 0.05).

Conclusions

The direct administration of BIL protected against CsA-induced tubular injury via inhibition of oxidative stress and apoptosis.

Xyloketal B exhibits its antioxidant activity through induction of HO-1 in vascular endothelial cells and zebrafish

We previously reported that a novel marine compound, xyloketal B, has strong antioxidative actions in different models of cardiovascular diseases. Induction of heme oxygenase-1 (HO-1), an important endogenous antioxidant enzyme, has been considered as a potential therapeutic strategy for cardiovascular diseases. We here investigated whether xyloketal B exhibits its antioxidant activity through induction of HO-1. In human umbilical vein endothelial cells (HUVECs), xyloketal B significantly induced HO-1 gene expression and translocation of the nuclear factor-erythroid 2-related factor 2 (Nrf-2) in a concentration- and time-dependent manner. The protection of xyloketal B against angiotensin II-induced apoptosis and reactive oxygen species (ROS) production could be abrogated by the HO-1 specific inhibitor, tin protoporphyrin-IX (SnPP). Consistently, the suppressive effects of xyloketal B on NADPH oxidase activity could be reversed by SnPP in zebrafish embryos. In addition, xyloketal B induced Akt and Erk1/2 phosphorylation in a concentration- and time-dependent manner. Furthermore, PI3K inhibitor LY294002 and Erk1/2 inhibitor U0126 suppressed the induction of HO-1 and translocation of Nrf-2 by xyloketal B, whereas P38 inhibitor SB203580 did not. In conclusion, xyloketal B can induce HO-1 expression via PI3K/Akt/Nrf-2 pathways, and the induction of HO-1 is mainly responsible for the antioxidant and antiapoptotic actions of xyloketal B.

Upregulation of haeme oxygenase-1 by zinc in HCT-116 cells

Haeme oxygenase-1 (HO-1) is often viewed as a cytoprotective gene. Toxic heavy metals induce HO-1, but it is unclear whether particular metal micronutrients also induce HO-1. Hence, the ability of exogenously-added copper, iron and zinc to influence HO-1 expression in HCT-116 cells was evaluated. Under the chosen experimental conditions, only zinc noticeably increased the expression of HO-1 mRNA and protein. Concurrently, zinc decreased non-protein thiol levels to a certain extent, but zinc did not increase the production of reactive oxygen species (ROS). Moreover, ascorbate and Trolox did not inhibit zinc-induced HO-1 upregulation. In contrast, deferoxamine blunted the induction of HO-1 mRNA, protein, and enzymatic activity caused by zinc. Additionally, N-acetylcysteine and Tiron inhibited zinc-induced HO-1 upregulation and also nuclear translocation of nuclear factor erythroid 2-related factor 2 (Nrf2). Collectively, these findings suggest that zinc at above normal levels upregulates HO-1 expression in HCT-116 cells in a ROS-independent manner.

Oxidative and non-oxidative DNA damage and cardiovascular disease

Evidence for the association of DNA damage with cardiovascular disease has been obtained from in vitro cell culture models, experimental cardiovascular disease and analysis of samples obtained from humans with disease. There is general acceptance that several factors associated with the risk of developing cardiovascular disease cause oxidative damage to DNA in cell culture models with both nuclear and mitochondrial DNA as targets. Moreover, evidence obtained over the past 10 years points to a possible mechanistic role for DNA damage in experimental atherosclerosis culminating in recent studies challenging the assumption that DNA damage is merely a biomarker of the disease process. This kind of mechanistic insight provides a renewed impetus for further studies in this area.

Superoxide anion and hydrogen peroxide-induced signaling and damage in angiotensin II and aldosterone action

The formation of reactive oxygen species (ROS) can be induced by xenobiotic substances, such as redox cycling molecules, but also by endogenous substances such as hormones and cytokines. Recent research shows the importance of ROS in cellular signaling. Here, the signaling pathways of the two blood pressure-regulating hormones angiotensin II and aldosterone are presented, focusing on both their physiological effects and the change of signaling owing to the action of increased concentrations or prolonged exposure. When present in high concentrations, both angiotensin II and aldosterone, as various other endogenous substances, activate NADPH oxidase, which produces superoxide. In this review the generation of superoxide anions and hydrogen peroxide in cells stimulated with angiotensin II or aldosterone, as well as the subsequently induced signaling processes and DNA damage is discussed.

The role of Nrf2 and MAPK pathways in PFOS-induced oxidative stress in zebrafish embryos

Perfluorooctane sulfonate (PFOS) is a persistent organic pollutant and causes oxidative stress, apoptosis, and developmental toxicity in zebrafish embryos. In the present study, we examined nuclear factor erythroid 2-related factor 2 (Nrf2)- and mitogen-activated protein kinases (MAPKs)-mediated oxidative stress pathways in zebrafish embryos upon exposure to PFOS. Four-hour postfertilization (hpf) zebrafish embryos were exposed to 0.2, 0.4, and 1.0 mg/l PFOS until 96 hpf. PFOS enhanced production of reactive oxygen species (ROS) in a concentration-dependent manner. Activity of antioxidative enzymes, including superoxide dismutase, catalase, and glutathione peroxidase, was significantly induced in zebrafish larvae in all PFOS-treated groups relative to the control. Exposure to 1.0 mg/l PFOS significantly increased malondialdehyde production in zebrafish larvae. The Nrf2 and heme oxygenase-1 (HO-1) gene expressions were both significantly upregulated compared with the control group. For MAPKs, we investigated gene expression profiles of extracellular signal-regulated protein kinase (ERK), c-Jun NH (2)-terminal kinase (JNK), and p38. The ERK gene expression levels were unchanged, whereas JNK and p38 gene expressions were significantly upregulated, which could be linked to PFOS-induced cell apoptosis in zebrafish larvae. In addition, we found that coexposure with sulforaphane, an Nrf2 activator, could significantly protect against PFOS-induced ROS generation, whereas inhibition of MAPKs did not exhibit significant effects on PFOS-induced HO-1 gene expression and ROS production. Furthermore, we showed that morpholino-mediated knockdown of Nrf2 reduced PFOS-induced HO-1 gene expression. These findings demonstrate that Nrf2 is protective against PFOS-induced oxidative stress in zebrafish larvae.

Heme oxygenase: the key to renal function regulation

Heme oxygenase (HO) plays a critical role in attenuating the production of reactive oxygen species through its ability to degrade heme in an enzymatic process that leads to the production of equimolar amounts of carbon monoxide and biliverdin/bilirubin and the release of free iron. The present review examines the beneficial role of HO-1 (inducible form of HO) that is achieved by increased expression of this enzyme in renal tissue. The influence of the HO system on renal physiology, obesity, vascular dysfunction, and blood pressure regulation is reviewed, and the clinical potential of increased levels of HO-1 protein, HO activity, and HO-derived end products of heme degradation is discussed relative to renal disease. The use of pharmacological and genetic approaches to investigate the role of the HO system in the kidney is key to the development of therapeutic approaches to prevent the adverse effects that accrue due to an impairment in renal function.

Targeting heme oxygenase: therapeutic implications for diseases of the cardiovascular system

Heme oxygenase (HO) is important in attenuating the overall production of reactive oxygen species through its ability to degrade heme and to produce carbon monoxide, biliverdin/bilirubin, and release of free iron. Excess free heme catalyzes the formation of reactive oxygen species, which leads to endothelial cell (EC) dysfunction as seen in numerous pathologic vascular conditions including systemic hypertension and diabetes, as well as in ischemia/reperfusion injury.The up-regulation of HO-1 can be achieved through the use of pharmaceutical agents such as metalloporphyrins and statins. In addition, atrial natriuretic peptide and nitric oxide donors are important modulators of the heme-HO system, either through induction of HO-1 or the increased biologic activity of its products. Gene therapy and gene transfer, including site- and organ-specific targeted gene transfer have become powerful tools for studying the potential role of the 2 isoforms of HO, HO-1/HO-2, in the treatment of cardiovascular disease, as well as diabetes. HO-1 induction by pharmacological agents or the in vitro gene transfer of human HO-1 into ECs increases cell cycle progression and attenuates angiotensin II, tumor necrosis factor-alpha, and heme-mediated DNA damage; administration in vivo corrects blood pressure elevation after angiotensin II exposure. Delivery of human HO-1 to hyperglycemic rats significantly lowers superoxide levels and prevents EC damage and sloughing of vascular EC into the circulation. In addition, administration of human HO-1 to rats in advance of ischemia/reperfusion injury considerably reduces tissue damage.The ability to up-regulate HO-1 either through pharmacological means or through the use of gene therapy may offer therapeutic strategies for the prevention of cardiovascular disease in the future. This review discusses the implications of HO-1 delivery during the early stages of cardiovascular system injury or in early vascular pathology, and suggests that pharmacological agents that regulate HO activity or HO-1 gene delivery itself may become powerful tools for preventing the onset or progression of various cardiovascular diseases.

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.

The role of cyp1a and heme oxygenase 1 gene expression for the toxicity of 3,4-dichloroaniline in zebrafish (Danio rerio) embryos

Expression profiling of exposed cells or organisms can reveal genes sensitive to environmental contaminants or toxic compounds. However, the mechanistic relevance of altered gene expression often remains to be elucidated. Toxicant-dependent differential gene expression may indicate protection to or mediation of toxicity. Previous studies revealed a number of differentially transcribed genes in zebrafish embryos exposed to the model compound 3,4-dichloroaniline (3,4-DCA). To evaluate the significance of two of the most sensitive genes, cytochrome P 450 1a (cyp1a) and heme oxygenase 1 (hmox1), for 3,4-DCA toxicity, RNA interference-mediated knockdown and overexpression studies have been conducted. Knockdown of gene transcription by siRNA for cyp1a and hmox1 enhanced the frequency of developmental disorders in embryos exposed to 3,4-DCA. Vice versa, injection of cyp1a and hmox1 mRNA reduced the number of disorders. The opposite effects of siRNA and mRNA injection clearly indicate a protective role of the corresponding proteins. Functional studies such as the one presented could be applied to a wide variety of genes. They would be ideally suited to study the role of genes identified from toxicogenomic studies in the zebrafish embryo model.

''Iatrogenic Gilbert syndrome''--a strategy for reducing vascular and cancer risk by increasing plasma unconjugated bilirubin

The catabolism of heme, generating biliverdin, carbon monoxide, and free iron, is mediated by heme oxygenase (HO). One form of this of this enzyme, heme oxygenase-1, is inducible by numerous agents which promote oxidative stress, and is now known to provide important antioxidant protection, as demonstrated in many rodent models of free radical-mediated pathogenesis, and suggested by epidemiology observing favorable health outcomes in individuals carrying high-expression alleles of the HO-1 gene. The antioxidant impact of HO-1 appears to be mediated by bilirubin, generated rapidly from biliverdin by ubiquitously expressed biliverdin reductase. Bilirubin efficiently scavenges a wide range of physiological oxidants by electron donation. In the process, it is often reconverted to biliverdin, but biliverdin reductase quickly regenerates bilirubin, thereby greatly boosting its antioxidant potential. There is also suggestive evidence that bilirubin inhibits the activity or activation of NADPH oxidase. Increased serum bilirubin is associated with reduced risk for atherogenic disease in epidemiological studies, and more limited data show an inverse correlation between serum bilirubin and cancer risk. Gilbert syndrome, a genetic variant characterized by moderate hyperbilirubinemia attributable to reduced hepatic expression of the UDP-glucuronosyltransferase which conjugates bilirubin, has been associated with a greatly reduced risk for ischemic heart disease and hypertension in a recent study. Feasible strategies for boosting serum bilirubin levels may include administration of HO-1 inducers, supplementation with bilirubin or biliverdin, and administration of drugs which decrease the efficiency of hepatic bilirubin conjugation. The well-tolerated uricosuric drug probenecid achieves non-competitive inhibition of hepatic glucuronidation reactions by inhibiting the transport of UDP-glucuronic acid into endoplasmic reticulum; probenecid therapy is included in the differential diagnosis of hyperbilirubinemia, and presumably could be used to induce an ''iatrogenic Gilbert syndrome''. Other drugs, such as rifampin, can raise serum bilirubin through competitive inhibition of hepatocyte bilirubin uptake--although unfortunately rifampin is not as safe as probenecid. Measures which can safely achieve moderate serum elevations of bilirubin may prove to have value in the prevention and/or treatment of a wide range of disorders in which oxidants play a prominent pathogenic role, including many vascular diseases, cancer, and inflammatory syndromes. Phycobilins, algal biliverdin metabolites that are good substrates for biliverdin reductase, may prove to have clinical antioxidant potential comparable to that of bilirubin.

Angiotensin II-induced genomic damage in renal cells can be prevented by angiotensin II type 1 receptor blockage or radical scavenging

Hypertensive patients exhibit elevated cancer incidence, especially of cancers of the kidney. Elevated levels of ANG II, the active peptide of the renin-angiotensin system, regulating blood pressure and cardiovascular homeostasis, are known to cause hypertension and kidney diseases. There is evidence that ANG II is an activator of NAD(P)H oxidase, leading to the formation of free radicals, which are known to participate in the induction of DNA damage. This study was undertaken to characterize ANG II-induced DNA damage. DNA damage was measured by comet assay and micronucleus frequency test. Incubation of pig kidney cells (LLC-PK(1)) in vitro with ANG II concentrations between 85 and 340 nM led to a 6- to 15-fold increase of DNA damage compared with the control as revealed by comet assay analysis. Micronuclei were induced about fourfold compared with the control in pig and rat kidney cells (LLC-PK(1), NRK) and in human promyelocytic cells (HL-60). ANG II-induced DNA damage could be prevented by coincubation with the ANG II type 1 receptor blocker candesartan and the antioxidants N-acetylcysteine and alpha-tocopherol. The ANG II type 2 receptor antagonist PD123319 could not reduce ANG II-induced DNA damage. Measurement of reactive oxygen species (ROS) by flow cytometry showed an enhanced formation after exposure to ANG II and a reduction of ROS after candesartan, N-acetylcysteine, and alpha-tocopherol. The present findings support our hypothesis that ANG II causes DNA damage via ANG II type 1 receptor binding and subsequent formation of oxidative stress.

HO-1 induction lowers blood pressure and superoxide production in the renal medulla of angiotensin II hypertensive mice

Heme oxygenase-1 (HO-1) induction can attenuate the development of angiotensin II (ANG II)-dependent hypertension. However, the mechanism by which HO-1 lowers blood pressure in this model is not clear. The goal of this study was to test the hypothesis that induction of HO-1 in the kidney can attenuate the increase in reactive oxygen species (ROS) generation in the kidney that occurs during ANG II-dependent hypertension. Mice were divided into four groups, control (Con), cobalt protoporphyrin (CoPP), ANG II, and ANG II + CoPP. CoPP treatment (50 mg/kg) was administered in a single subcutaneous injection 2 days prior to implantation of an osmotic minipump that infused ANG II at a rate of 1 microg x kg(-1) x min(-1). At the end of this period, mean arterial blood pressure (MAP) averaged 93 +/- 5, 90 +/- 5, 146 +/- 8, and 105 +/- 6 mmHg in Con, CoPP-, ANG II-, and ANG II + CoPP-treated mice. To determine whether HO-1 induction resulted in a decrease in ANG II-stimulated ROS generation in the renal medulla, superoxide production was measured. Medullary superoxide production was increased by ANG II infusion and normalized in mice pretreated with CoPP. The reduction in ANG II-mediated superoxide production in the medulla with CoPP was associated with a decrease in extracellular superoxide dismutase protein but an increase in catalase protein and activity. These results suggest that reduction in superoxide and possibly hydrogen peroxide production in the renal medulla may be a potential mechanism by which induction of HO-1 with CoPP lowers blood pressure in ANG-II dependent hypertension.

Heme-oxygenase upregulation ameliorates angiotensin II-induced tubulointerstitial injury and salt-sensitive hypertension

BACKGROUND

Heme oxygenase-1 (HO-1) has been implicated in the modulation of several diseases including hypertension (HTN) and renal injury. The tubulointerstitial (TI) injuries are supposed to be the main determinants for the development of salt-sensitive HTN. Therefore, this study examined the role of HO-1 in angiotensin II (AngII)-induced TI injury and salt-sensitive HTN.

METHODS

Sprague-Dawley rats on a high salt diet were treated by AngII infusion plus either hemin, an inducer of HO-1, or hemin + zinc protoporphyrin, a HO-1 inhibitor, for 2 weeks, and then followed for 6 weeks.

RESULTS

The AngII infusion resulted in acute HTN and proteinuria. Light microscopy revealed focal areas of tubular atrophy with mononuclear cell infiltration and interstitial expansion. The overexpression of osteopontin and TGF-beta(1) accompanied by diminished expression of rat endothelial cell antigen-1, the hallmarks of TI injury, were observed. At 2 weeks, all interventions were withdrawn and systolic blood pressure returned towards normal. After a brief normal salt diet, rats were again placed on high salt diet, resulting in progressive increase in systolic blood pressure in the HO-1-inhibited group.

CONCLUSION

The induction of HO-1 attenuated the development of HTN, suggesting that HO-1 plays a crucial role in significant attenuation of AngII-mediated TI injury and resultant salt-sensitive HTN.

Genomic damage in chronic renal failure--potential therapeutic interventions

In end-stage renal failure, genomic damage is enhanced. This has been shown both in the predialysis and dialysis phase by various biomarkers, such as micronuclei frequency and single cell gel electrophoresis in lymphocytes as well as with 8-hydroxy-2'-deoxyguanosine in leukocytes. There are also data about mitochondrial DNA deletions and chromosomal abnormalities. Genomic damage may be induced by a multitude of toxic factors and mutagens, in particular via enhanced generation of reactive oxygen species. In in vitro studies, incubation of tubular cells with various AGEs (carboxymethyllysine-BSA, AGE-BSA, and methylglyoxal-BSA) and angiotensin II resulted in a marked DNA damage. Coincubation with various antioxidants as well as the angiotensin II receptor blocker, candesartan, suppressed the toxic action. Moreover, an improved uremic state by daily hemodialysis ameliorated the genomic damage in lymphocytes, as compared to patients on conventional hemodialysis.

Oxidative stress in hypertension and chronic kidney disease: role of angiotensin II

Angiotensin II, via the type 1 (AT1) receptor, stimulates oxidative stress. The vasculature, interstitium, juxtaglomerular apparatus, and the distal nephron in the kidney express nicotinamide adenine dinucleotide phosphate (NADPH) oxidase that generates superoxide anion, which is an important component of angiotensin II-induced oxidative stress. The angiotensinogen gene is stimulated by NF-kappaB activation, which is sensitive to the redox ratio, providing a positive feedback loop that can upregulate angiotensin II production. Oxidative stress can accompany hypertension in many models, including the spontaneously hypertensive rat (SHR), angiotensin II-infused rats, renovascular hypertension, and the deoxycorticosterone acetate (DOCA) salt model of hypertension. AT1 receptor antagonists can abrogate the effects of angiotensin II on oxidative stress, thus providing an important mechanistic insight onto the renal protective effects of these agents in conditions associated with angiotensin II excess.

Expression of human heme oxygenase-1 in the thick ascending limb attenuates angiotensin II-mediated increase in oxidative injury

BACKGROUND

Heme oxygenase-1 (HO-1) catalyzes the conversion of heme to bilirubin, carbon monoxide (CO), and free iron, thus controlling the level of cellular heme. The medullary thick ascending limb of the loop of Henle (TALH) is situated in a site of markedly diminished oxygen tension and, as such, is highly vulnerable to ischemic insult. We hypothesize that selective upregulation of HO-1 in TALH by gene transfer attenuates oxidative stress caused by angiotensin II (Ang II).

METHODS

An adenoviral vector expressing the human HO-1 under the control of the TALH-specific promoter [Na(+)-K(+)-Cl(-) cotransporter (NKCC2 promoter)] was constructed and the cell specific expression of the recombinant adenovirus was examined using several types of cells, including endothelial, vascular smooth muscle, and TALH cells. The effects of HO-1 transduction on HO-1 expression, HO activity and the response to Ang II with respect to cyclooxygenase-2 (COX-2) up-regulation and oxidative injury [growth-stimulating hormone (GSH) levels and cell death] were determined.

RESULTS

Western blot and reverse transcription-polymerase chain reaction (RT-PCR) revealed that human HO-1 was selectively expressed in primary cultured TALH cells following infection with Ad-NKCC2-HO-1. In TALH cells infected with Ad-NKCC2-HO-1, Ang II-stimulated prostaglandin E(2) (PGE(2)) levels were reduced by 40%. Ang II caused a marked decrease in GSH levels and this decrease was greatly attenuated in TALH cells transduced with Ad-NKCC2-HO-1. Moreover, Ang II-mediated DNA degradation was completely blocked by the site-specific expression of human HO-1 gene.

CONCLUSION

These results indicate that TALH cell survival after exposure to oxidative stress injury may be facilitated by selective upregulation of HO-1, thusly blocking inflammation and apoptosis.

Steady plasma concentration of unfractionated heparin reduces infarct volume and prevents inflammatory damage after transient focal cerebral ischemia in the rat

Unfractionated heparin (UH) decreases the extent of infarction after transient focal brain ischemia in the rat and abridges neuroinflammatory damage in patients with acute stroke. This study was aimed at assessing whether controlled and steady heparinemia in plasma can reduce infarct volume and exert neuroprotective effects after ischemia. Infarct volume was measured at 24 and 7 days following a 1-hr intraluminal middle cerebral artery (MCA) occlusion in rats treated with UH or with vehicle. After testing several UH administration protocols, we choose to give a bolus of 200 U/kg, which was started 3 hr after the occlusion, followed by a 24-hr intraperitoneal perfusion of 70 U/kg/hr, which maintained a 24-hr steady plasma heparinemia (0.3-0.6 U/ml) and caused no CNS or systemic bleeding. In addition, plasma IL-10 concentration was measured by ELISA, endothelial VCAM-1 expression was evaluated by i.v. injection of a (125)I-labeled monoclonal antibody against VCAM-1, and brain hemeoxygenase-1 (HO-1) expression was determined by Western blot. UH-treated rats showed smaller infarctions than rats treated with vehicle, as well as higher IL-10 plasma levels and HO-1 brain expression and lower endothelial VCAM-1 induction. The study shows that a stable plasma concentration of UH given at nonhemorrhagic doses reduces infarct volume after ischemia-reperfusion in the rat. It also shows that UH prevented the induction of cell adhesion molecules in the cerebral vasculature and increased the expression of molecules with antiinflammatory and prosurvival properties. These findings support further testing of the clinical value of parenteral, adjusted, high-dose UH in patients with acute stroke.

Overexpression of human heme oxygenase-1 attenuates endothelial cell sloughing in experimental diabetes

Heme oxygenase (HO)-1 represents a key defense mechanism against oxidative injury. Hyperglycemia produces oxidative stress and various perturbations of cell physiology. The effect of streptozotocin (STZ)-induced diabetes on aortic HO activity, heme content, the number of circulating endothelial cells, and urinary 8-epi-isoprostane PGF2alpha (8-Epi) levels in control rats and rats overexpressing or underexpressing HO-1 was measured. HO activity was decreased in hyperglycemic rats. Hyperglycemia increased urinary 8-Epi, and this increase was augmented in rats underexpressing HO-1 and diminished in rats overexpressing HO-1. The number of detached endothelial cells and O2- formation increased in diabetic rats and in hyperglycemic animals underexpressing HO-1 and decreased in diabetic animals overexpressing HO-1 compared with controls. These data demonstrate that HO-1 gene transfer in hyperglycemic rats brings about a reduction in O2- production and a decrease in endothelial cell sloughing. Upregulation of HO-1 decreases oxidant production and endothelial cell damage and shedding and may attenuate vascular complications in diabetes.

Heme oxygenase-1 prevents superoxide anion-associated endothelial cell sloughing in diabetic rats

Heme oxygenase-1 (HO-1) represents a key defense mechanism against oxidative injury. Hyperglycemia has been linked to increased oxidative stress, leading to endothelial dysfunction, delayed cell replication, and enhanced apoptosis. The effect of streptozotocin (STZ)-induced diabetes on HO activity, HO-1 promoter activity, superoxide anion (O*-2, and the number of circulating endothelial cells was measured. The expression of HO-1/HO-2 protein was unchanged, but HO activity was decreased in aortas of diabetic rats compared with control (p < 0.05). High glucose decreased HO-1 promoter activity (p < 0.05). Hyperglycemia increased O*-2 and this increase was augmented with HO-1 inhibition and diminished with HO-1 upregulation (p < 0.05). Circulating endothelial cells were significantly higher in diabetic rats and were decreased or increased with administration of the HO-1 inducer (CoPP) or inhibitor (SnMP), respectively (p<0.05). In conclusion, HO-1 upregulation in diabetic rats brings about an increase in serum bilirubin, a reduction in O*-2 production, and a decrease in endothelial cell sloughing.

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.

Regulation of heme oxygenase-1 expression through the phosphatidylinositol 3-kinase/Akt pathway and the Nrf2 transcription factor in response to the antioxidant phytochemical carnosol

The phosphatidylinositol 3-kinase (PI3K)/Akt pathway elicits a survival signal against multiple apoptotic insults. In addition, phase II enzymes such as heme oxygenase-1 (HO-1) protect cells against diverse toxins and oxidative stress. In this work, we describe a link between these defense systems at the level of transcriptional regulation of the antioxidant enzyme HO-1. The herb-derived phenol carnosol induced HO-1 expression at both mRNA and protein levels. Luciferase reporter assays indicated that carnosol targeted the mouse ho1 promoter at two enhancer regions comprising the antioxidant response elements (AREs). Moreover, carnosol increased the nuclear levels of Nrf2, a transcription factor governing AREs. Electrophoretic mobility shift assays and luciferase reporter assays with a dominant-negative Nrf2 mutant indicated that carnosol increased the binding of Nrf2 to ARE and induced Nrf2-dependent activation of the ho1 promoter. While investigating the signaling pathways responsible for HO-1 induction, we observed that carnosol activated the ERK, p38, and JNK pathways as well as the survival pathway driven by PI3K. Inhibition of PI3K reduced the increase in Nrf2 protein levels and activation of the ho1 promoter. Expression of active PI3K-CAAX (where A is aliphatic amino acid) was sufficient to activate AREs. The use of dominant-negative mutants of protein kinase Czeta and Akt1, two kinases downstream from PI3K, demonstrated a requirement for active Akt1, but not protein kinase Czeta. Moreover, the long-term antioxidant effect of carnosol was partially blocked by PI3K or HO-1 inhibitors, further demonstrating that carnosol attenuates oxidative stress through a pathway that involves PI3K and HO-1.

Heme oxygenase-1 attenuates glucose-mediated cell growth arrest and apoptosis in human microvessel endothelial cells

Heme oxygenase-1 (HO-1) is a stress protein that has been suggested to participate in defense mechanisms against agents that may induce oxidative injury, such as heme and inflammatory molecules. Incubation of endothelial cells in a high-glucose (33 mmol/L) medium for 7 days resulted in a decrease of HO activity by 34% and a decrease in HO-1 and HO-2 proteins compared with cells exposed to low glucose (5 mmol/L) (P<0.05) or cells exposed to mannitol (33 mmol/L). Overexpression of HO-1 was coupled with an increase in HO activity and carbon monoxide synthesis, decreased cellular heme, and acceleration in all phases of the cell cycle (P<0.001). The rate of cell cycle or cell birth rate was increased by 29% (P<0.05) in cells overexpressing HO-1 but decreased by 23% (P<0.05) in cells underexpressing HO-1 compared with control cells. Exposure to high glucose significantly decreased cell-cycle progression in control cells and in cells underexpressing HO-1 but did not decrease cell-cycle progression in cells overexpressing HO-1. High glucose induced p21 and p27 in control cells but not in cells overexpressing HO-1. The addition of tin-mesoporphyrin (SnMP), an inhibitor of HO activity, reversed the HO-1-mediated decrease of p21 and p27 in cells overexpressing HO-1. These findings identify a novel effect of HO-1 on endothelial cell growth and indicate that heme metabolism and HO-1 expression regulate signaling systems in cells exposed to high glucose, which controls cell-cycle progression.

Heme oxygenase-1 expression levels are cell cycle dependent

Heme oxygenase-1 (HO-1) is a stress protein, which has been suggested to participate in defense mechanisms against agents that may induce oxidative injury, such as angiotensin II (Ang II). The purpose of the present study was to examine the role of human HO-1 in cell-cycle progression. We investigated the effect of Ang II on HO-1 gene expression in serum-deprived media to drive human endothelial cells into G(0)/G(1) (1% FBS) compared to exponentially grown cells (10% FBS). The addition of Ang II (100 ng/ml) to endothelial cells increased HO-1 protein and activity in G(0)/G(1) in a time-dependent manner, reaching a maximum HO-1 level at 16 h. Real-time RT-PCR demonstrated that Ang II increased the levels of HO-1 mRNA in G(0)/G(1) as early as 1 h. The rate of HO-1 induction in response to Ang II was several-fold higher in serum-starved cells compared to cells cultured in continuous 10% FBS. The addition of Ang II increased the generation of 8-epi-isoprostane PGF(2 alpha). Inhibition of HO-1, by Stannis mesoporphyrin (SnMP), potentiated Ang II-mediated DNA damage and generation of 8-epi-isoprostane PGF(2 alpha). These results imply that expression of HO-1 in G(0)/G(1), in the presence of Ang II, may be a key player in attenuating DNA damage during cell-cycle progression. Thus, exposure of endothelial cells to Ang II causes a complex response involving generation of superoxide anion, which may be involved in DNA damage. Upregulation of HO-1 ensures the generation of bilirubin and carbon monoxide (CO) in G(0)/G(1) phase to counteract Ang II-mediated oxidative DNA damage. Inducibility of HO-1 in G(0)/G(1) phase is essential and probably regulated by a complex system involving oxygen species to assure controlled cell growth.

Heme oxygenase attenuated angiotensin II-mediated increase in cyclooxygenase activity and decreased isoprostane F2α in endothelial cells

Heme oxygenase (HO) regulates cellular heme levels and catalyzes the formation of bilirubin and carbon monoxide (CO). We hypothesized that the status of the endothelial HO system influences the angiotensin (Ang) II-induced increase in the endothelial cell (EC) production of PGE2, eicosanoids which modulate the vascular actions of Ang II. In this study, we investigated the effect of interventions that suppress HO activity or induce HO-1 gene expression on Ang II-mediated increase in PGE2 in cultures of human microvessel endothelial cells (EC). Incubation of EC with Ang II (100 ng/ml) for 24 h increased the levels of PGE2 in the culture media. This effect of Ang II on prostaglandin production by EC was attenuated in cells treated with heme, but was magnified in cells treated with the HO inhibitor, Stannis mesoporphyrin (SnMP). Upregulation of HO-1 gene expression by retrovirus-mediated delivery of the human HO-1 gene attenuated heme and Ang II-induced prostaglandin synthesis. We also investigated the physiological significance of human HO-1 overexpression on attenuation of Ang II-mediated oxidative stress. Decreases in COMET levels were found in EC transduced with the HO-1 gene. These results indicate that overexpression of the HO system in EC exerts an inhibitory influence on Ang II-induced synthesis of prostaglandins and attenuates DNA damage caused by exposure to Ang II.