Dynamic Cytoplasmic Anchoring of the Transcription Factor Bach1 by Intracellular Hyaluronic Acid Binding Protein IHABP

Bach1 functions as a transcriptional repressor of heme oxygenase-1 (HO-1) and the beta-globin genes. The enhancer regions of these genes contain multiple Maf recognition elements (MAREs) to which Bach1 can bind. Previous studies have shown that increased levels of heme and cadmium induce the nuclear export of Bach1, resulting in cytoplasmic accumulation. By means of a yeast two hybrid screening using Bach1 as bait, we identified the intracellular hyaluronic acid binding protein (IHABP) as a potential regulator of Bach1. IHABP is a microtubule-associated protein that may regulate the organization of the cytoskeletal network. A series of domain analyses revealed that a region of Bach1 previously implicated in cytoplasmic accumulation was necessary for IHABP-binding. A C-terminal region of IHABP was necessary for Bach1-binding. Overexpressed Bach1 colocalized with IHABP in the cytoplasm, forming fiber-like structures on microtubules. Fluorescence recovery after photobleaching (FRAP) analysis revealed a dynamic nature of the Bach1-IHABP interaction in living cells. The repression of HO-1 reporter activity by Bach1 was attenuated by co-transfecting IHABP in a dose-dependent manner. Moreover, the overexpression of IHABP induced the endogenous HO-1 gene in NIH3T3 cells. The overall results suggest that IHABP regulates the subcelluar localization of Bach1 in order to fine-tune transactivation of Bach1 target genes such as HO-1.

Anti-inflammatory effect of heme oxygenase 1: glycosylation and nitric oxide inhibition in macrophages

Flavonoids including the aglycones, hesperetin (HT; 5,7,3'-trihydroxy-4'-methoxy-flavanone), and naringenin (NE; 5,7,4'-trihydroxy flavanone) and glycones, hesperidin (HD; 5,7,3'-trihydroxy-4'-methoxy-flavanone 7-rhamnoglucoside) and naringin (NI; 5,7,4'-trihydroxy flavanone 7-rhamno glucoside), were used to examine the importance of rutinose at C7 on the inhibitory effects of flavonoids on lipopolysaccharide (LPS)-induced nitric oxide production in macrophages. Both HT and NE, but not their respective glycosides HD and NI, induced heme oxygenase 1 (HO-1) protein expression in the presence or absence of LPS and showed time and dose-dependent inhibition of LPS-induced nitric oxide (NO) production and inducible nitric oxide synthase (iNOS) expression in RAW264.7, J774A.1, and thioglycolate-elicited peritoneal macrophages. Additive inhibitory effect of an HO-1 inducer hemin and NE or NI on LPS-induced NO production and iNOS expression was identified, and HO enzyme inhibitor tin protoporphyrin (SnPP) attenuated the inhibitory effects of HT, NE, and hemin on LPS-induced NO production. Both NE and HT showed no effect on iNOS mRNA and protein stability in RAW264.7 cells. Removal of rutinose at C7 of HD and NI by enzymatic digestion using hesperidinase (HDase) and naringinase (NIase) produce inhibitory activity on LPS-induced NO production, according to the production of the aglycones, HT and NE, by high-performance liquid chromatography (HPLC) analysis. Furthermore, the amount of NO produced by LPS or lipoteichoic acid (LTA) was significantly reduced in HO-1-overexpressing cells (HO-1/RAW264.7) compared to that in parental cells (RAW264.7). Results of the present study provide scientific evidence to suggest that rutinose at C7 is a negative moiety in flavonoid inhibition of LPS-induced NO production, and that HO-1 is involved in the inhibitory mechanism of flavonoids on LPS-induced iNOS and NO production.

Change in renal heme oxygenase expression in cyclosporine A-induced injury

Cyclosporine A (CsA) is the first immunosuppressant used in allotransplantation. Its use is associated with side effects that include nephrotoxicity. This study explored the anatomic structures involved in CsA nephrotoxicity and the effect of heme oxygenase (HO) in preventing CsA injury. Rats were divided into four groups, which were treated with olive oil, CsA (15 mg/kg/day), CsA plus the HO inhibitor (SnMP; 30 microM/kg/day), and with the HO inducer (CoPP; 5 mg/100 g bw). Renal tissue was treated for morphological, biochemical, and immunohistochemical studies. CsA-treated rats showed degenerative changes with renal fibrosis localized mainly around proximal tubules. Collapsed vessels were sometimes seen in glomeruli. No HO-1 expression and increased expression of endothelin-1 (ET-1) were observed in CsA-treated rats compared with controls. In CsA plus SnMP-treated rats, HO-1 expression was further reduced and the morphology was not changed compared to the CsA group, whereas CsA plus CoPP-treated animals again showed normal morphology and with restoration and an increase in HO-1 levels. HO activity and immunohistochemical data showed similar alterations as HO expression. No changes were observed for HO-2 analysis. The observations indicate that HO-1 downregulation and ET-1 upregulation by CsA might be one mechanism underlying CsA-induced nephrotoxicity. Therefore, attempts to preserve HO levels attenuate CsA nephrotoxicity.

Nitric oxide-dependent and nitric oxide-independent transcriptional responses to high shear stress in endothelial cells

Shear stress modulates gene expression in endothelial cells (ECs) partly through nitric oxide (NO), acting via enhanced cGMP formation by guanylyl cyclase (GC). We addressed non-cGMP-mediated transcriptional responses to shear stress in human umbilical ECs subjected to high-laminar shear stress (25 dyn/cm2; 150 minutes). RNA was isolated, reverse-transcribed, Cy3/5-labeled, and hybridized to 19 K human microarrays. High shear (n=6), high shear with 100 micromol/L L-NAME (n=3), and high shear with 10 micromol/L ODQ (GC inhibitor) in the perfusate (n=3) was compared with samples not subjected to flow. Among genes responding to high shear were HMOX1 (up) and PPARG (down). A high percentage of gene expression modulation by shear was absent during concomitant L-NAME or ODQ. Several transcriptional modulators were found (up: SOX5, SOX25, ZNF151, HOXD10; down: SOX11); a number of genes were regulated by shear and by shear with ODQ, but not regulated during L-NAME, indicating a nitric oxide synthase (NOS)-dependent, guanylyl cyclase (GC)-independent pathway. Several genes only responded to shear stress during L-NAME, others only responded to shear during ODQ. Upstream binding site analysis indicated shear stress and NO-dependent regulation of transcription via SOX5 and SOX9. Although NO importantly modulated the effect of shear stress on EC transcription, HMOX1 was consistently induced by shear stress, but not dependent on NOS or GC. Using bio-informatics software and databases, a promoter analysis identified SOX5 and SOX9 as potential, novel, shear-sensitive, and NO-dependent transcriptional regulators. The role of HMOX1 as a potential backup for NOS and the downstream role of SOXes should be explored.

Nitric oxide synthase is downregulated, while haem oxygenase is increased, in patients with septic shock

BACKGROUND

The vasodilatation characteristic of human septic shock is conventionally attributed to increased nitric oxide production, primarily by extrapolation of animal and human in vitro studies. There are no conclusive studies of human disease, and the cellular source of nitric oxide in human sepsis is not known. Haem oxygenase is upregulated by oxidative stress, but little is known about haem oxygenase expression in human sepsis. Haem oxygenase may modulate nitric oxide production, and may also have a direct effect on vascular tone.

METHODS

Mesenteric arterial smooth muscle (ASM) (obtained during laparotomy) and peripheral blood mononuclear cells (PBMCs) were obtained from patients with early septic shock and from control patients. mRNA levels were determined by real-time RT-PCR.

RESULTS

mRNA for inducible and endothelial nitric oxide synthase was reduced in both ASM and PBMCs from septic patients. In contrast, inducible haem oxygenase mRNA was increased in sepsis in both cell types.

CONCLUSIONS

These results suggest that, rather than being induced, the enzymes which produce nitric oxide are reduced at this time point in human septic shock. Thus many of the in vitro models of sepsis studied to date may not fully replicate human disease. The increase in haem oxygenase expression confirms that these cells have been subjected to oxidative stress in sepsis. The activity of induced haem oxygenase may limit nitric oxide production, while possibly causing vasodilation through production of carbon monoxide.

Heme oxygenase-1-mediated partial cytoprotective effect by NO on cadmium-induced cytotoxicity in C6 rat glioma cells

Heme oxygenase-1 (HO-1) is a 32-kDa stress induced enzyme that degrades heme to carbon monoxide (CO) and biliverdin. By employing RT-PCR and Western blotting techniques, we have examined the HO-1 induction in C6 glioma cells that were treated with cadmium chloride (CdCl(2)) or spermine NONOate (SPER/NO). By employing a cell viability assay, we have also examined the cytoprotective effect of HO-1 induction against the cytotoxicity caused by toxic dose of CdCl(2). In C6 glioma cells exposed to CdCl(2), expression of HO-1 (mRNA and protein) was increased in a dose- and time-dependent manner. Nitric oxide (NO) generated from SPER/NO very rapidly increased HO-1 mRNA expression in the C6 glioma cells. The induction of HO-1 by SPER/NO protected the cells from toxic dose of CdCl(2). The up-regulation of HO-1 mRNA expression by CdCl(2) was inhibited by a pre-incubation of the cells with actinomycin D, a potent inhibitor of mRNA transcription. Upon the inhibition of elevated HO-1 mRNA expression by the use of zinc protoporphyrin IX (ZnPP), an inhibitor of HO activity, the change of HO-1 mRNA expression by ZnPP was not observed. Thus, the glial cell may respond to CdCl(2) toxicity by enhancing the HO-1 expression in its effort to minimize the CdCl(2)-derived oxidative damage, and to survive. In the glioma cells, when the HO-1 expression was elevated by a prior incubation with SPER/NO, the cell viability against the cytotoxicity of CdCl(2) was significantly increased. When the results of our experiment are taken together, we discovered that NO provided a rapid enhancement of HO-1 expression, and it provided a protective effect against CdCl(2)-derived oxidative injury in the C6 rat glioma cells.

Protection against ischemia/reperfusion injury in cardiac and renal transplantation with carbon monoxide, biliverdin and both

Both carbon monoxide (CO) and biliverdin, products of heme degradation by heme oxygenase, have been shown to attenuate ischemia/reperfusion (I/R) injury. We hypothesized in this study that dual-treatment with CO and biliverdin would induce enhanced protective effects against cold I/R injury. Heterotopic heart and orthotopic kidney transplantation were performed in syngeneic Lewis rats after 24-h cold preservation in UW solution. While monotherapy with CO (20 ppm) or biliverdin (50 mg/kg, ip) did not alter the survival of heart grafts, dual-treatment increased survival to 80% from 0% in untreated recipients, with a significant decrease of myocardial injury and improved cardiac function. Similarly, dual-treatment significantly improved glomerular filtration rates of renal grafts and prolonged recipient survival compared to untreated controls. I/R injury-induced up-regulation of pro-inflammatory mediators (e.g. TNF-alpha, iNOS) and extravasation of inflammatory infiltrates were significantly less with dual-treatment than untreated controls. In addition, dual-treatment was effective in decreasing lipid peroxidation and improving graft blood flow through the distinctive action of biliverdin and CO, respectively. The study shows that the addition of byproducts of heme degradation with different mechanisms of action provides enhanced protection against transplant-associated cold I/R injury of heart and kidney grafts.

An integrated pharmacokinetic and pharmacodynamic study of arsenite action2. Heme oxygenase induction in mice

Heme oxygenase (HO) is the rate-limiting enzyme in heme degradation and its activity has a significant impact on intracellular heme pools. Rat studies indicate that HO induction is a sensitive, dose-dependent response to arsenite (As(III)) exposure in both liver and kidney. The objective of this study was to evaluate the relationship of HO induction to administered As(III) dose, and concentrations of inorganic arsenic (iAs) in tissues and urine. Levels of iAs, mono- (MMA) and dimethylated arsenic (DMA) as well as HO activity were determined in liver, lung and kidney over time in female B6C3F1 mice given a single oral dose of 0, 1, 10, 30 or 100 micromol/kg As(III). Increased HO activity was a time and dose-dependent response in liver and kidney, but not in lung. Activity peaked in the 4-6 h time range in liver and kidney with the responsiveness in liver being approximately 2- to 3-fold greater than kidney. The lowest observed effect levels (LOELs) in this study for HO induction are 30 and 100 micromol/kg, respectively, in liver and kidney. The predominant form of arsenic (As) was iAs in liver at all doses, whereas DMA was the predominant form of As in kidney at all doses. Three- to four-fold higher levels of iAs were achieved in liver compared to kidney. MMA was the least abundant form of As in liver and kidney, never exceeding more than 20% of the total As present. The concentration of iAs in tissue or urine demonstrated the strongest correlation with HO activity in both liver and kidney. Results of this study suggest that HO induction is a biomarker of effect that is specific for tissue iAs because a high, but nontoxic, acute dose of DMA (5220 micromol/kg) did not induce HO in mice. Thus, HO induction has potential for use as a biomarker of effect for inorganic arsenic exposure and may be used as an indicator response to further the development of a biologically-based dose response model for As.

Super-induction of HO-1 in macrophages stimulated with lipopolysaccharide by prior depletion of glutathione decreases iNOS expression and NO production

In the LPS-stimulated macrophages undergoing oxidative burst, intracellular storage of glutathione (GSH) is depleted, expression of iNOS is enhanced, and NO is overproduced. In response to the depletion of GSH, expression of HO-1 is induced and HO activity is elevated. Thus, in macrophages treated with LPS, productions of NO and CO, catalyzed, respectively, by accumulated iNOS and HO-1, are increased in sequence [Biochem. Pharmacol. 68 (2004) 1709]. In support of this, HO-1 is induced in macrophages treated only with buthionine sulfoximine (BSO), an inhibitor of GSH biosynthesis depleting the GSH level. Alternatively, when the macrophages were exposed to spermine NONOate, an exogenous NO-donor, HO-1, was induced also. When the GSH-depleted or BSO-pretreated macrophages were exposed to NO, delivered either exogenously from spermine NONOate or endogenously from LPS-derived elevation of iNOS, super-induction of HO-1 was observed. Moreover, both the BSO and LPS treatments increased the accumulation of HO-1 inducing redox-sensitive transcription factor Nrf2 in the nuclear protein fraction. Thus, when the depletion of GSH is combined with NO delivery, expression of HO-1 is enhanced to a greater extent than that enhanced either by GSH depletion or by NO delivery. In these macrophages with super-induced HO-1 and elevated HO activity, LPS-derived increase in iNOS expression was down-regulated and NO production was suppressed. This indicated that induction of HO-1 caused by the NO overproduced from up-regulated iNOS, in turn, produces a causative inhibition on iNOS expression and NO production. Thus, it appears that there is a reciprocal cross-talk between inductions of HO-1 and iNOS in macrophages stimulated with LPS leading to their survival.

Heme oxygenase‐1 modulates the allo‐immune response by promoting activation‐induced cell death of T cells

Heme oxygenase-1 (HO-1), which degrades heme into three products (carbon monoxide, free iron, and biliverdin), plays a protective role in many models of disease via its anti-inflammatory, anti-apoptotic, and anti-proliferative actions. Overexpression of HO-1 has been shown to suppress immune responses and prolong the survival of allografts; however, the underlying mechanism is not clear. We demonstrate two "new" properties of HO-1 that mediate activation induced cell death (AICD) of allo-antigen-responsive murine CD4+ T cells, resulting in immunomodulation. First, it functions in vivo and in vitro to "boost" the proliferative response of CD4+ T cells to allo-antigens in the early phase of allo-antigen-driven immune responses. This "boosting" effect is accompanied with a significant increase of activation markers and IL-2 production. Second, it exerts a pro-apoptotic effect in those activated T cells after the initial burst of proliferation. We further show that the AICD effect is mediated through the Fas/CD95-FasL signal transduction pathway. Correlating with the above-mentioned findings is the observed prolongation of mouse heart graft survival when HO-1 is expressed in vivo in both donor and recipient. In conclusion, induction of HO-1 expression accelerates clonal deletion of peripheral alloreactive CD4+ T cells by promoting AICD, which is presumably a key mechanism for its immunomodulatory effects such as in prolonging the survival of transplanted organs.

[Heme oxygenase induction in rat heart and vessels and peroxidative resistance of erythrocytes during hemolytic anemia development]

The hemolytic anemia development caused by phenylhydrazine injection (7 mg/100 g b.w.) was shown to be caused by the decreasing of both catalase activity and glutathione content in erythrocytes, and by the increasing of spontaneouse hemolysis level of these cells in blood stream. The increasing of heme oxygenase activity and TBA-active products in rat heart and vessels were revealed 24 hrs after phenylhydrazine injection. Possible mechanisms of heme oxygenase-1 induction under hypoxia as response to the hemolytic anemia development and it's role in defense of the cells from damage are discussed.

Redox regulation of p38 MAPK activation and expression of ICAM-1 and heme oxygenase-1 in human alveolar epithelial (A549) cells

We have explored the potential role of redox events in p38 mitogen-activated protein kinase (MAPK) activation and their relevance to the inducible expression of intercellular adhesion molecule-1 (ICAM-1) and heme oxygenase-1 (HO-1) in A549 cells. Tumor necrosis factor-alpha (TNFalpha) and hydrogen peroxide (H2O2) both activated p38, but only TNFalpha activated nuclear factor-kappaB (NF-kappaB). N-Acetyl-L-cysteine (20 mM) inhibited both H2O2- and TNFalpha-induced p38 phosphorylation (14 +/- 7 and 37 +/- 4% of control, respectively). The mitochondrial complex I and III inhibitors, rotenone and antimycin A, and allopurinol partially inhibited H2O2- but not TNFalpha-induced p38 activation. However, rotenone and antimycin A augmented intracellular oxidative stress measured by dichlorofluorescein fluorescence. TNFalpha, but not H2O2, induced ICAM-1 in A549 cells, which was attenuated by a proteasome inhibitor, but not by the p38 MAPK inhibitor SB203580. In contrast, hemin and hemoglobin, but neither TNFalpha nor H2O2, caused efficient HO-1 expression. However, hemin had no effect on p38 activation and SB203580 did not influence hemin-induced HO-1 protein expression. Collectively, these data suggest that p38 is a cytokine- and oxidative stress-responsive pathway in A549 cells. Whereas NF-kappaB appears crucial in ICAM-1 induction, p38 activation itself is not sufficient to confer HO-1 expression and may not be involved in HO-1 and ICAM-1 induction in A549 cells.

FTY720 attenuates hepatic ischemia-reperfusion injury in normal and cirrhotic livers

Hepatic ischemia-reperfusion injury is an inevitable consequence during liver surgery. The outcome is particularly poor in cirrhotic livers, which are more prone to hepatic ischemia-reperfusion injury. We aim to study whether FTY720 could attenuate hepatic ischemia-reperfusion injury both in normal and in cirrhotic livers. We applied a 70% liver-ischemia (60 min) model in rats with normal or cirrhotic livers. FTY720 was given 20 min before ischemia and 10 min before reperfusion (1 mg/kg, i.v.). Liver tissues and blood were sampled at 20 min, 60 min, 90 min, 6 h and 24 h after reperfusion for detection of MAPK-Egr-1, Akt pathways and caspase cascade. Hepatic ultrastructure and apoptosis were also compared. FTY720 significantly improved liver function in the rats with normal and cirrhotic livers. Akt pathway was activated at 6 and 24 h after reperfusion. FTY720 significantly down-regulated Egr-1, ET-1, iNOS and MIP-2 accompanied with up-regulation of A20, IL-10, HO-1 and Hsp70. MAPK (Raf-MEK-Erk) pathway was down-regulated. Hepatic ultrastructure was well maintained and fewer apoptotic liver cells were found in the FTY720 groups. In conclusion, FTY720 attenuates ischemia-reperfusion injury in both normal and cirrhotic livers by activation of cell survival Akt signaling and down-regulation of Egr-1 via Raf-MEK-Erk pathway.

The pro-oxidant role of methylglyoxal in mesenteric artery smooth muscle cells

Methylglyoxal (MG), a highly reactive metabolite of glucose, causes non-enzymatic glycation of proteins to form irreversible advanced glycation endproducts (AGEs). The present study investigated whether methylglyoxal induced oxidative stress and activated nuclear factor kappa B (NF-κB) in freshly isolated and cultured smooth muscle cells (SMCs) from rat mesenteric artery. The treatment of cells with MG (50 or 100 µmol/L) induced a significant increase in AGE formation and oxidation of DCF. MG-enhanced generation of AGEs and the oxidation of DCF was markedly inhibited by antioxidant n-acetylcysteine (NAC, 600 µmol/L). MG at a concentration of 100 µmol/L increased the heme-oxygenase-1 expression in these cells. Moreover, MG activated NF-κB p65, indicated by an increased im muno cytochemistry stain for NF-κB p65 located in the nucleus after the treatment of mesenteric artery SMCs with MG. MG-induced activation of NF-κB p65 was inhibited by NAC. In summary, MG significantly increases oxidative stress and activates NF-κB p65 in mesenteric artery SMCs. The pro-oxidant role of methylglyoxal may contribute to various pathological changes of SMCs from resistance arteries.Key words: methylglyoxal, oxidative stress, NF-κB p65, vascular smooth muscle cells, mesenteric artery.

Mechanism of concentration-dependent induction of heme oxygenase-1 by resveratrol in human aortic smooth muscle cells

Resveratrol-mediated heme oxygenase-1 (HO-1) induction has been shown to occur in primary neuronal cultures and is thought to have potential neuroprotective action. Further, antioxidant properties of resveratrol have been reported to protect against coronary heart disease. We attempted to examine resveratrol's HO-1 inducing potency and its induction regulation in human aortic smooth muscle cells (HASMC). We showed that resveratrol-mediated HO-1 induction occurred in concentration- and time-dependent manners, but only at low concentrations (1-10 microM), and that it was modulated at both the transcription and translation levels. Additionally, the results of our study showed that nuclear factor-kappa B (NF-kappaB) inhibitors eliminated resveratrol-mediated HO-1 induction and promoter activity, and that deletion of NF-kappaB binding sites in the HO-1 promoter region strongly reduced promoter activity, suggesting involvement of the NF-kappaB pathway in HO-1 induction by resveratrol. Suppression of NF-kappaB activity by resveratrol at high concentrations (> or =20 microM) has been reported to be attributed to its anti-inflammatory and anti-oxidative properties. Likewise, we showed that resveratrol at concentrations of > or =20 microM blocked the activity of NF-kappaB through suppression of I kappa-B alpha (IkappaBalpha) phosphorylation, which caused inhibition of HO-1 induction. Conversely, resveratrol in a range of 1-10 microM enhanced the phosphorylation and degradation of IkappaBalpha, a key step in NF-kappaB activation, resulting in HO-1 induction. Collectively, we suggest that resveratrol-mediated HO-1 expression occurs, at least in part, through the NF-kappaB pathway, which might contribute to resveratrol's vascular-protective effect at physiological concentrations after moderate red wine consumption.

Rehmannia glutinose Ameliorates Renal Function in the Ischemia/Reperfusion-Induced Acute Renal Failure Rats

The present study was designed to examine whether aqueous extract of steamed root of Rehmannia glutinose (ARR) has an ameliorative effect on renal functional parameters in association with the expressions of aquaporin 2 (AQP 2), Na,K-ATPase, and heme oxygenase-1 (HO-1) in the ischemia-reperfusion induced acute renal failure (ARF) rats. Polyuria caused by down-regulation of renal AQP 2 in the ischemia-induced ARF rats was markedly restored by administration of ARR (200 mg/kg, p.o.) with restoring expression of AQP 2 in the kidney. The expressions of Na,K-ATPase alpha1 and beta1 subunits in the renal medullar and cortex of the ARF rats were also restored in the ARF rats by administration of ARR. On the other hand, administration of ARR lowered the renal expression of HO-1 up-regulated in rats with ischemia-induced ARF. The renal functional parameters including creatinine clearance, urinary sodium excretion, urinary osmolality, and solute-free reabsorption were also markedly restored in ischemia-ARF rats by administration of ARR. Taken together, these data indicate that RSR ameliorates renal defects in rats with ischemia-induced ARF.

[Effect of the antioxidants on NO-dependent induction of heme oxigenase 1 gene in U937 monocytes]

Previously it was shown that thiol antioxidants are potent inhibitors of the NO-dependent induction of heme oxygenase 1 (HOX-1) gene. However, the mechanism of HOX-1 gene down-regulation by thiol antioxidants and underlying signaling pathway remain unclear. In this study we have examined, whether the scavenging of reactive oxygen and reactive nitrogen species (ROS and RNS) is the major cause for thiol-mediated suppression of the HOX-1 induction by NO. Further, to identify the ROS family members implicated in the HOX-1 induction, we also exposed cells to various non-thiol antioxidants: dimethyl sulfoxide, dimetylthiourea, sodium salicylate, sodium formate, uric acid, catalase, and superoxide dismutase. A partial inhibition of HOX-1 induction occurred in the presence of non-polar hydroxyl radical scavengers, dimethyl sulfoxide and dimetylthiourea. The other non-thiol antioxidants were ineffective towards HOX-1 expression. Then, in order to determine, whether RNS scavenging is implicated in the HOX-1 down-regulation by thiol antioxidants, we took advantage of the capacity of suboptimal concentrations of the NO scavenger PTIO (2-phenyl-4,4,5,5-tetramethylimidazole-1-oxyl-3-oxide) to oxidize NO to nitrosating species. We showed that simultaneous cell treatment with NO donor and PTIO significantly enhanced the rate of the HOX-1 gene NO-dependent induction indicating that RNS are mediators of HOX-1 gene transcriptional activation. Thiol antioxidants completely suppressed PTIO stimulatory action. These findings imply that inhibitory action of thiol antioxidants is mediated by RNS scavenging. The study provides an approach for pharmacologycal modulation of cell response to NO and its derivatives through the use of antioxidants.

Inhalation of carbon monoxide prevents liver injury and inflammation following hind limb ischemia/reperfusion

The induction of heme oxygenase (HO), the rate limiting enzyme in the conversion of heme into carbon monoxide (CO) and biliverdin, limits liver injury following remote trauma such as hind limb ischemia/reperfusion (I/R). Using intravital video microscopy, we tested the hypothesis that inhaled CO (250 ppm) would mimic HO-derived liver protection. Hind limb I/R significantly decreased sinusoidal diameter and volumetric flow, increased leukocyte accumulation within sinusoids, increased leukocyte rolling and adhesion within postsinusoidal venules, and significantly increased hepatocyte injury compared with naive animals. Inhalation of CO alone did not alter any microcirculatory or inflammatory parameters. Inhalation of CO following I/R restored volumetric flow, decreased stationary leukocytes within sinusoids, decreased leukocyte rolling and adhesion within postsinusoidal venules, and significantly reduced hepatocellular injury following hind limb I/R. HO inhibition did not alter microcirculatory parameters in naive mice, but did increase inflammation, as well as increase hepatocyte injury following hind limb I/R. Inhalation of CO during HO inhibition significantly reduced such microcirculatory deficits, hepatic inflammation, and injury in response to hind limb I/R. In conclusion, these results suggest that HO-derived hepatic protection is mediated by CO, and inhalation of low concentrations of CO may represent a novel therapeutic approach to prevent remote organ injury during systemic inflammatory response syndrome, or SIRS.

Identification of key elements that are responsible for heme-mediated induction of the avian heme oxygenase-1 gene

Heme oxygenase (HO) catalyzes the conversion of heme to biliverdin with the release of iron and carbon monoxide. HO-1 is highly inducible by a large number of physical and chemical factors. In recent work, we had identified a metalloporphyrin-responsive element (MPRE) that localized at -3.7 kb upstream of the transcription start site of the chick HO-1 gene. Here, we identify four additional heme-responsive elements (HeREs), which are "expanded" AP-1 sites, in the 5'-flanking region of the chick HO-1 gene. These sites, located at -4675, -4599, -3660, and -3625 bp from the transcription start site of the gene, were necessary and sufficient for up-regulation of luciferase reporter gene expression in the presence of heme and cobalt protoporphyrin (CoPP), but not several other metalloporphyrins. Site-directed mutagenesis was carried out using pcHO7.1Luc or pcHO7.1-4.6Luc as templates. Single and multiple mutations of HeREs and MPRE significantly abrogated the heme- and CoPP-dependent up-regulation of reporter gene expression in transient or stable transfection experiments.

CONCLUSIONS

The chick HO-1 promoter region contains "expanded" AP-1 sites that are important for up-regulation of the gene by heme and CoPP, but not other metalloporphyrins. These key regulatory elements consist of consensus AP-1 binding sites that have been extended by three base pairs.

Effects of cell-free hemoglobin on hypoxia-inducible factor (HIF-1alpha) and heme oxygenase (HO-1) expressions in endothelial cells subjected to hypoxia

We have investigated the impact of diaspirin cross-linked hemoglobin (DBBF-Hb), a blood substitute, on cell signaling pathways that are modulated in part by biological peroxides (i.e., hydrogen peroxide, lipid peroxide, and peroxynitrite). Bovine aortic endothelial cells (BAECs) subjected to hypoxia expressed hypoxia-inducible factor (HIF-1alpha) in a time course that paralleled the expressions of heme oxygenase (HO-1). Co-incubation of the oxy form (HbFe(2+)) with hypoxic BAECs resulted in an increase in the expression of HIF-1alpha in a manner that corresponded linearly with the decay of HbFe(2+) and accumulation of the ferric form (HbFe(3+)). Inclusion of HbFe(3+) with hypoxic BAECs produced twice as much expression in the HIF-1alpha and HO-1 proteins as opposed to HbFe(2+) alone, or HbFe(2+) plus hypoxia. In addition, higher and more persistent levels of the ferryl form (HbFe(4+)), due to the consumption of endogenous peroxides, were found in the hypoxic media containing hemoglobin. Nitric oxide (NO) released from an NO donor reduced the levels of HIF-1alpha in the hypoxic cells treated with either HbFe(2+) or HbFe(3+), but had little or no effect on the levels of HO-1. DBBF-Hb modulates key cell-signaling pathways by competing with peroxides required for the deactivation of HIF-1alpha, which may modulate important physiological mediators.

Biphasic induction of heme oxygenase-1 expression in macrophages stimulated with lipopolysaccharide

Time course relationship between inductions of iNOS and HO-1 was evaluated in RAW264.7 macrophages stimulated with LPS. Expression of HO-1 mRNA increased in a biphasic pattern, but that of xCT (cystine transporter) and iNOS mRNA increased in a monophasic manner. HO-1 protein level increased also in a biphasic manner, at 1-2 h and again between 8 and 24 h. However, iNOS protein began to increase at 4 h, quickly reaching a high level in a monophasic induction pattern. Production of NO* began to occur at 6 h and nitrite continued to accumulate in the culture medium. Total GSH level decreased markedly (50% of control) by 2 h, began to recover at 4 h, returned to control level by 6 h and increased above the control level during 10-24 h. Collectively, these results indicated that overproduced O2*- depletes GSH and triggers induction of xCT, HO-1, iNOS and HO-1 expression in sequence. Most notably, the second-phase induction of HO-1 was caused by overproduced NO*, resulting from LPS-derived iNOS induction. When this iNOS-derived delivery of NO* was combined with prior depletion of GSH using buthioninesulfoximine, an inhibitor of GSH biosynthesis, induction of HO-1 was potentiated. Furthermore, upon such super-induction of HO-1, NO* production was inhibited along with suppression of iNOS expression. Collectively, these results suggested that HO-1 is induced in a biphasic manner, sequentially by the overproduced O*2- and NO*, and the elevated HO-1 suppresses the production of these radicals in an auto-regulatory manner. This may allow the macrophages to survive from injuries that can be caused by concomitant oxidative and nitrosative stresses initiated by the LPS-driven oxidative burst.

Hypoxia inducible factor-1 alpha correlates the expression of heme oxygenase 1 gene in pulmonary arteries of rat with hypoxia-induced pulmonary hypertension

To test the hypothesis that hypoxia inducible factor-1 alpha (HIF-1alpha) up-regulated the expression of heme oxygenase-1 (HO-1) gene in pulmonary arteries of rats with hypoxia-induced pulmonary hypertension, 8 male Wistar rats in each of 5 groups were exposed to hypoxia for 0, 3, 7, 14 or 21 d, respectively. Mean pulmonary arterial pressure (mPAP), vessel morphometry and right ventricle hypertrophy index were measured. Lungs were inflation fixed for immunohistochemistry, in situ hybridization; frozen for later measurement of HO-1 enzyme activity. mPAP increased significantly after 7 d of hypoxia [(18.4 +/- 0.4) mmHg, P<0.05], reaching its peak after 14 d of hypoxia, then remained stable. Pulmonary artery remodeling became to develop significantly after 14 d of hypoxia. HIF-1alpha protein in control was poorly positive (0.05 +/- 0.01), but was up-regulated in pulmonary arterial tunica intima of all hypoxic rats. In pulmonary arterial tunica media, the levels of HIF-1alpha protein were markedly up-regulated after 3 d and 7 d of hypoxia (0.20 +/- 0.02; 0.22 +/- 0.02, P<0.05), then declined after 14 d and 21 d of hypoxia. HIF-1alpha mRNA staining was poorly positive in control, hypoxia for 3 and 7 d, but enhanced significantly after 14 d of hypoxia (0.20 +/- 0.02, P<0.05), then remained stable. HO-1 protein increased after 7 d of hypoxia (0.10 +/- 0.01, P<0.05), reaching its peak after 14 d of hypoxia (0.21 +/- 0.02, P<0.05), then remained stable. HO-1 mRNA increased after 3 d of hypoxia, reaching its peak after 7 d of hypoxia (0.17 +/- 0.01, P<0.05), then declined. Linear correlation analysis showed that HIF-1alpha mRNA, HO-1 protein and mPAP were associated with pulmonary remodeling. HIF-1alpha protein (tunica intima) was conversely correlated with HIF-1alpha mRNA (r=0.921,P<0.01), HO-1 protein was conversely correlated with HIF-1alpha protein (tunica intima) (r=0.821, P<0.01). HIF-1alpha and HO-1 were both involved in the pathogenesis of hypoxia-induced pulmonary hypertension in rat. Hypoxia inducible factor-1 alpha correlated the expression of heme oxygenase 1 gene in pulmonary arteries of rat with hypoxia-induced pulmonary hypertension.

Angiotensin II induces carbon monoxide production in the perfused kidney: relationship to protein kinase C activation

Heme oxygenase (HO)-derived carbon monoxide (CO) attenuates vascular reactivity to constrictor stimuli. ANG II produces vasoconstriction and induces HO-1 isoform expression. However, direct evidence that ANG II promotes HO product generation is lacking. Therefore, we examined the effects of ANG II on CO release and HO isoform expression in isolated rat kidneys. Kidneys were perfused with oxygenated Krebs buffer. ANG II (1 μmol/l) increased ( P < 0.05) perfusion pressure from 97 ± 9 to 150 ± 14 mmHg; it also increased ( P < 0.05) the concentration of CO in the venous effluent (from 27.1 ± 11.9 to 45.6 ± 11.7, 62.5 ± 16.7, 94.8 ± 20.7, and 101.9 ± 13.1 nmol/l after 30, 60, 90, and 120 min, respectively). The pressor effect of ANG II was blunted ( P < 0.05) in kidneys perfused with buffer containing losartan (10 μmol/l) or PKC inhibitors staurosporine (0.1 μmol/l) or calphostin C (1 μmol/l). Kidneys perfused with buffer containing ANG II for 120 min also displayed increased ( P < 0.05) HO-1 expression. Stannous mesoporphyrin (30 μmol/l) decreased CO release ( P < 0.05) in preparations perfused with and without ANG II; the HO inhibitor also increased ( P < 0.05) perfusion pressure, more so in kidneys perfused with that without ANG II. We conclude that ANG II stimulates CO production and release in isolated, perfused rat kidneys. This action of ANG II is linked to the activation of AT1receptors and involves PKC activation and upregulation of renal HO-1 but not of HO-2 protein expression. The study suggests upregulation of renal HO-1 and CO release are protagonic events in a counterregulatory mechanism that attenuates ANG II-induced renal vasoconstriction.

Cooperative effect of biliverdin and carbon monoxide on survival of mice in immune-mediated liver injury

Induction of the heme-degrading enzyme heme oxygenase-1 (HO-1) has been shown to be beneficial in terms of improvement of liver allograft survival and prevention of CD95-mediated apoptosis in the liver. In the present study, we investigated the effects of HO-1, and its products carbon monoxide (CO), biliverdin (BV), and iron/ferritin, in a mouse model of inflammatory liver damage inducible by lipopolysaccharide (LPS) in mice sensitized with the hepatocyte-specific transcription inhibitor D-galactosamine (GalN). Our results show that HO-1 induction by cobalt-protoporphyrin-IX (CoPP) reduced cytokine expression, protected mice from liver injury, and prolonged survival. While in contrast to ferritin overexpression, single administration of the CO donor methylene chloride (MC) or of BV also protected mice from liver damage, only coadministration of both HO products prolonged survival and reduced the expression of cytokines, e.g., tumor necrosis factor (TNF) and interferon gamma (IFN-gamma). In conclusion, HO-1-induced prolongation of survival, but not the protection from liver damage, seems to be dependent on down-regulation of cytokine synthesis.