The Heme Oxygenase(s)-Phytochrome System of Pseudomonas aeruginosa

For many pathogenic bacteria like Pseudomonas aeruginosa heme is an essential source of iron. After uptake, the heme molecule is degraded by heme oxygenases to yield iron, carbon monoxide, and biliverdin. The heme oxygenase PigA is only induced under iron-limiting conditions and produces the unusual biliverdin isomers IXbeta and IXdelta. The gene for a second putative heme oxygenase in P. aeruginosa, bphO, occurs in an operon with the gene bphP encoding a bacterial phytochrome. Here we provide biochemical evidence that bphO encodes for a second heme oxygenase in P. aeruginosa. HPLC, (1)H, and (13)C NMR studies indicate that BphO is a "classic" heme oxygenase in that it produces biliverdin IXalpha. The data also suggest that the overall fold of BphO is likely to be the same as that reported for other alpha-hydroxylating heme oxygenases. Recombinant BphO was shown to prefer ferredoxins or ascorbate as a source of reducing equivalents in vitro and the rate-limiting step for the oxidation of heme to biliverdin is the release of product. In eukaryotes, the release of biliverdin is driven by biliverdin reductase, the subsequent enzyme in heme catabolism. Because P. aeruginosa lacks a biliverdin reductase homologue, data are presented indicating an involvement of the bacterial phytochrome BphP in biliverdin release from BphO and possibly from PigA.

Heme oxygenase-1 modulates early inflammatory responses: evidence from the heme oxygenase-1-deficient mouse

Induction of heme oxygenase-1 (HO-1) is protective in tissue injury in models of allograft rejection and vascular inflammation through either prevention of oxidative damage or via immunomodulatory effects. To examine the specific role of HO-1 in modulating the immune response, we examined the differences in immune phenotype between HO-1 knockout (HO-1(-/-)) and wild-type (HO-1(+/+)) mice. Consistent with previous findings, marked splenomegaly and fibrosis were observed in HO-1(-/-) mice. The lymph nodes of HO-1-deficient mice demonstrated a relative paucity of CD3- and B220-positive cells, but no such abnormalities were observed in the thymus. Flow cytometric analysis of isolated splenocytes demonstrated no differences in the proportions of T lymphocytes, B lymphocytes or monocytes/macrophages between the HO-1(-/-) and HO-1(+/+) mice. Significantly higher baseline serum IgM levels were observed in HO-1(-/-) versus HO-1(+/+) mice. Under mitogen stimulation with either lipopolysaccharide or anti-CD3/anti-CD28, HO-1(-/-) splenocytes secreted disproportionately higher levels of pro-inflammatory Th1 cytokines as compared to those from HO-1(+/+) mice. These findings demonstrate significant differences in the immune phenotype between the HO-1(-/-) and the HO-1(+/+) mice. The absence of HO-1 correlates with a Th1-weighted shift in cytokine responses suggesting a general pro-inflammatory tendency associated with HO-1 deficiency.

Probucol Protects Against Smooth Muscle Cell Proliferation by Upregulating Heme Oxygenase-1

Background— Evidence suggests that induction of heme oxygenase-1 (HO-1) inhibits proliferation of vascular smooth muscle cells and intimal thickening after arterial injury, and therapeutic molecules induce HO-1. Probucol is the only oral drug that inhibits restenosis in humans and intimal thickening in animals, although its underlying mechanism remains unclear.

Methods and Results— Aortas were harvested from New Zealand White rabbits fed normal or 0.75% (wt/wt) probucol-fortified chow, with or without endothelial denudation of the abdominal aorta on day 21, and analyzed for heme oxygenase and apoptosis. Uninjured aortas were harvested on day 21 and balloon-injured aortas on days 22 and 25. Probucol significantly increased mRNA of HO-1 assessed by real-time PCR and HO activity in aortas at all time points. Probucol also enhanced apoptosis of medial cells in the injured aorta, as evidenced by the TUNEL assay. Furthermore, probucol (100 μmol/L) increased HO-1 mRNA and HO activity when added to rabbit aortic smooth muscle cells (RASMCs) cultured in serum-free medium for 24 hours. Induction of HO-1 mRNA was inhibited by actinomycin D and was associated with inhibition of RASMC proliferation. This probucol-induced increase in HO-1 mRNA and inhibition of RASMC proliferation was prevented by the HO inhibitor Sn(IV) protoporphyrin or transfection with small interference RNA (siRNA) to knockdown HO-1, but not by inactive Cu(II) protoporphyrin or scrambled siRNA.

Conclusions— Probucol induces HO-1, and this contributes to the inhibition of vascular SMC proliferation. This novel finding may explain how probucol inhibits restenosis and highlights HO-1 as a target for therapeutic intervention against occlusive vascular disease.

Heme oxygenase does not contribute to control of basal vascular tone in isolated blood-perfused rat lung

BACKGROUND

Vasoconstriction in pulmonary ischemia-reperfusion injury may involve dysfunction of the physiologic vasodilation of pulmonary arteries. Little is known of the relative importance of heme oxygenase (HO)/carbon monoxide (CO)-dependent vs nitric oxide synthase (NOS)/nitric oxide (NO)-dependent vasodilation of the pulmonary vasculature. We evaluated the significance of HO function on basal pulmonary vascular resistance (PVR) and compared it with the function of NOS.

METHODS

Using an isolated blood-perfusion model, lungs of Lewis rats were assigned to 3 groups (n = 6/group). After stabilization, either an inhibitor of HO (tin-protoporphyrin-9 [SnPP-9]) or an inhibitor of NOS (NG-nitro-L-arginine methylester [L-NAME]) was added to the perfusate (50 micromol/liter and 1 mmol/liter as the final concentration, respectively). Lungs receiving saline served as controls. Gas exchange, hemodynamic and respiratory functions and the levels of cyclic 3',5'-guanosine monophosphate (cGMP) in the perfusate were measured.

RESULTS

Inhibition of NOS by L-NAME resulted in a significant (p < 0.01) increase in PVR (DeltaPVR: 0.110 +/- 0.012 cm H(2)O/ml. min) within 5 minutes. In contrast, PVR was minimally affected by SnPP-9 (DeltaPVR: 0.005 +/- 0.005 cm H(2)O/ml. min), which was comparable to control lungs (DeltaPVR: 0.012 +/- 0.005 cm H(2)O/ml. min). The level of cGMP in the perfusate 5 minutes after drug application was markedly, but not significantly, lower in the L-NAME group (1.67 +/- 0.74 nmol/liter) when compared with controls (2.69 +/- 0.89 nmol/liter) and SnPP-9-treated lungs (2.65 +/- 0.66 nmol/liter).

CONCLUSIONS

NOS but not HO contributes to the control of basal vascular tone in the rat lung.

Simvastatin Induces Heme Oxygenase-1

Background— Evidence from experimental and clinical studies indicates that statins can protect the vessel wall through cholesterol-independent mechanisms. The “pleiotropic” effects include the prevention of inflammation and proliferation of vascular cells. Here, we studied whether heme oxygenase-1 (HO-1), an important cytoprotective molecule, is induced by simvastatin and the role of HO-1 in the pleiotropic effects of simvastatin.

Methods and Results— Human and rat aortic smooth muscle cells treated with simvastatin showed an elevated level of HO-1 for up to 24 hours. The induction of HO-1 by simvastatin was not found in cultured endothelial cells and macrophages. Injecting C57BL/6J mice intraperitoneally with simvastatin increased the level of HO-1 in vascular SMCs (VSMCs) in the tunica media. Treating VSMCs with zinc protoporphyrin, an HO-1 inhibitor, or HO-1 small interfering RNA (siRNA) blocked the antiinflammatory effect of simvastatin, including the inhibition of nuclear factor-κB activation and nitric oxide production. Blockade of HO-1 also abolished the simvastatin-induced p21 Waf1 and the associated antiproliferative effect. Simvastatin activated p38 and Akt in VSMCs, and the respective inhibitor of p38 and phosphoinositide 3-kinase (PI3K) greatly reduced the level of simvastatin-induced HO-1, which suggests the involvement of p38 and the PI3K-Akt pathway in HO-1 induction.

Conclusions— Simvastatin activates HO-1 in VSMCs in vitro and in vivo. The antiinflammatory and antiproliferative effects of simvastatin occur largely through the induced HO-1.

Alteration of heme-oxygenase-carbon monoxide pathway in calcified rat vascular smooth muscle cells

OBJECTIVE

The aim of the present study was to investigate the changes in heme-oxygenase (HO)-carbon monoxide (CO)-cyclic guanosine monophosphate (cGMP) pathway in clacified rat vascular smooth muscle cells (VSMCs).

METHODS

Calcification of cultured rat VSMCs was induced by incubation of VSMCs with beta-glycerophosphate. Cellular calcium content, ALP activities and (45)Ca uptake were measured. HO activity, HbCO formation and content of cGMP in VSMCs were determined. Immunocytochemistry for HO-1 expression was observed.

RESULTS

In comparison of control VSMCs, the cellular calcium content, ALP activity and (45)Ca uptake in calcified VSMCs were obviously increased. Immunocytochemistry showed that HO-1 expression was weak and not well distributed in calcified cells as compared to non-calcified VSMCs, but interestingly, there was stronger staining in calcified nodules than in VSMCs. Compared with VSMCs, HO-1 activity in calcified cells decreased by 42.7% [36.4 +/- 2.8 pmol (mg Pr x h)(-1) vs 63.5 x 5.3 pmol (mg Pr x h)(-1), p < 0.01], and HbCO formation decreased by 39.2% (3.38 x 0.69 micromol/mg Pr vs 5.56 +/- 0.48 micromol/mg Pr, p < 0.05). The cGMP content in calcified VSMCs was 78.1% lower than that of non-calcified VSMCs (4.3 +/- 0.51 vs 19.6 +/- 1.2 pmol/mg, p < 0.01).

CONCLUSION

The results showed that HO-CO-cGMP pathway in calcified vascular cells obviously changed, which might contribute to disturbance of vascular function.

Free radicals: key to brain aging and heme oxygenase as a cellular response to oxidative stress

Aging is one of the unique features in all organisms. The impaired functional capacity of many systems characterizes aging. When such impairments occur in the brain, the susceptibility to neurodegenerative diseases amplifies considerably. The free radical theory of aging posits that the functional impairments in brains are due to the attack on critical cellular components by free radicals, reactive oxygen species, and reactive nitrogen species produced during normal metabolism. In this review, we examine this concept based on the parameters of oxidative stress in correlation to aging. The parameters for lipid peroxidation are phospholipid composition, reactive aldehydes, and isoprostanes. The parameters for protein oxidation are protein carbonyl levels, protein 3-nitrotyrosine levels, electron paramagnetic resonance, and oxidative stress-sensitive enzyme activities. We conclude that free radicals are, at least partially, responsible for the functional impairment in aged brains. The aging brain, under oxidative stress, responds by induction of various protective genes, among which is heme oxygenase. The products of the reaction catalyzed by heme oxygenase, carbon monoxide, iron, and biliverdin (later to bilirubin) each have profound effects on neurons. Although there may be other factors contributing to brain aging, free radicals are involved in the damaging processes associated with brain aging, and cellular stress response genes are induced under free radical oxidative stress. Therefore, this review supports the proposition that free radicals are, indeed, a key to brain aging.

Endogenous heme oxygenase induction is a critical mechanism attenuating apoptosis and restoring microvascular perfusion following limb ischemia/reperfusion

BACKGROUND

A protective role for endogenous heme oxygenase (HO) in the initiation of remote liver injury after limb ischemia/reperfusion has been established. This study expands on our previous work by investigating the role of endogenous HO on hepatocellular injury, hepatocyte death (necrotic and apoptotic), and microvascular perfusion at protracted post-reperfusion times.

METHODS

Remote liver injury was studied after 1 hour of bilateral hind limb ischemia and 3, 6, or 24 hours of reperfusion in male C57BL6 mice. Inhibition of HO was achieved with the use of chromium mesoporphrin (CrMP). Established intravital videomicroscopy techniques were used to evaluate microvascular perfusion and hepatocyte death. Hepatocellular injury was quantified by serum alanine transaminase. Apoptosis was measured by using DNA laddering, Cell Death ELISA, and caspase-3 activity.

RESULTS

Although significant perfusion deficits and hepatocellular injury/death occurred after 3 hours, progression of hepatocellular death beyond 6 hours was not observed. A transient increase in apoptosis was observed at 6 hours. By 24 hours, microvascular perfusion was completely restored. This lack of progression correlated with increased HO activity, observed throughout the protocol. Administration of CrMP reduced HO activity to sham nonstressed levels, and caused increased microvascular perfusion deficits, hepatocellular injury, and hepatocyte death over 24 hours. The transient increase in apoptosis was increased in duration and magnitude in CrMP-treated animals.

CONCLUSIONS

These results suggest that endogenous HO activity prevents the progression of remote liver injury after limb ischemia/reperfusion.

Carbon monoxide produced by heme oxygenase-1 suppresses T cell proliferation via inhibition of IL-2 production

Heme oxygenase-1 (HO-1) catabolizes heme into CO, biliverdin, and free iron and serves as a protective enzyme by virtue of its anti-inflammatory, antiapoptotic, and antiproliferative actions. Previously, we have demonstrated that human CD4(+) T cells express HO-1 and that HO-1-overexpressing Jurkat T cells tend to display lower proliferative response. The aim of this study is to elucidate the mechanism(s) by which HO-1 can mediate its antiproliferative effect on CD4(+) T cells. Among the three HO-1 byproducts, only CO showed suppressive effect on T cell proliferation in response to anti-CD3 plus anti-CD28 Abs, mimicking the antiproliferative action of HO-1. CO blocked the cell cycle entry of T cells, which was independent of the guanylate cyclase/cGMP pathway. CO also suppressed the secretion of IL-2, and this suppressive effect of CO on IL-2 secretion mediated the antiproliferative action of CO. CO selectively inhibited the extracellular signal-regulated kinase pathway, which could explain the suppressive effects of CO on T cell proliferation and IL-2 secretion. Based on these findings, we suggest that HO-1/CO suppresses T cell proliferation and IL-2 secretion, possibly via its inhibition of extracellular signal-regulated kinase activation.

Heme oxygenase-1 modulates the expression of adhesion molecules associated with endothelial cell activation

Heme oxygenase-1 (HO-1) cleaves the porphyrin ring of heme into carbon monoxide, Fe2+, and biliverdin, which is then converted into bilirubin. Heme-derived Fe2+ induces the expression of the iron-sequestering protein ferritin and activates the ATPase Fe2+-secreting pump, which decrease intracellular free Fe2+ content. Based on the antioxidant effect of bilirubin and that of decreased free cellular Fe2+, we questioned whether HO-1 would modulate the expression of proinflammatory genes associated with endothelial cell (EC) activation. We tested this hypothesis specifically for the genes E-selectin (CD62), ICAM-1 (CD54), and VCAM-1 (CD106). We found that HO-1 overexpression in EC inhibited TNF-alpha-mediated E-selectin and VCAM-1, but not ICAM-1 expression, as tested at the RNA and protein level. Heme-driven HO-1 expression had similar effects to those of overexpressed HO-1. In addition, HO-1 inhibited the activation of NF-kappaB, a transcription factor required for TNF-alpha-mediated up-regulation of these genes in EC. Bilirubin and/or Fe2+ chelation mimicked the effects of HO-1, whereas biliverdin or carbon monoxide did not. In conclusion, HO-1 inhibits the expression of proinflammatory genes associated with EC activation via a mechanism that is associated with the inhibition of NF-kappaB activation. This effect of HO-1 is mediated by bilirubin and/or by a decrease of free intracellular Fe2+ but probably not by biliverdin or carbon monoxide.

Role of nuclear factor-kappaB and heme oxygenase-1 in the mechanism of action of an anti-inflammatory chalcone derivative in RAW 264.7 cells

The synthetic chalcone 3',4',5',3,4,5-hexamethoxy-chalcone (CH) is an anti-inflammatory compound able to reduce nitric oxide (NO) production by inhibition of inducible NO synthase protein synthesis. In this work, we have studied the mechanisms of action of this compound. CH (10-30 microm) prevents the overproduction of NO in RAW 264.7 macrophages stimulated with lipopolysaccharide (1 microg ml(-1)) due to the inhibition of nuclear factor kappaB (NF-kappaB) activation. We have shown that treatment of cells with CH results in diminished degradation of the NF-kappaB-IkappaB complex leading to inhibition of NF-kappaB translocation into the nucleus, DNA binding and transcriptional activity. We also demonstrate the ability of this compound to activate NfE2-related factor (Nrf2) and induce heme oxygenase-1 (HO-1). Our results indicate that CH determines a rapid but nontoxic increase of intracellular oxidative species, which could be responsible for Nrf2 activation and HO-1 induction by this chalcone derivative. This novel anti-inflammatory agent simultaneously induces a cytoprotective response (HO-1) and downregulates an inflammatory pathway (NF-kappaB) with a mechanism of action different from antioxidant chalcones.

Regulation of inducible nitric oxide synthase expression in advanced glycation end product-stimulated raw 264.7 cells: the role of heme oxygenase-1 and endogenous nitric oxide

Advanced glycation end products (AGEs) are closely linked to the development of diabetic atherosclerosis. The current study examines the induction of inducible nitric oxide (NO) synthase (iNOS) and heme oxygenase (HO)-1 expression by AGEs, as well as the signaling pathways involved and the interplay between these two enzymes. The stimulation of RAW 264.7 cells with 6.64 or 33.2 microg/ml AGEs leads to HO-1 protein expression, iNOS protein expression, and nitrite accumulation. AGEs lead to the phosphorylation of p42/44 and p38 mitogen-activated protein kinase (MAPK). The inhibition of p42/44 MAPK and protein kinase C prevented, whereas inhibition of p38 MAPK augmented, AGE-induced nitrite release and iNOS expression. In contrast, HO-1 expression was downregulated by inhibition of p38 MAPK. Furthermore, the expression of both proteins was prevented by coincubation with acetovanillone (NADPH oxidase inhibitor). AGE-induced iNOS expression was negatively regulated by stimulation of HO-1 expression with cadmium chloride or endogenous NO. Tin-protoporphyrin IX (HO-1 inhibitor) partially reversed the cadmium chloride-mediated downregulation of iNOS expression. The current study demonstrates that multiple signaling molecules are involved in AGE-stimulated iNOS and HO-1 expression. There also exists a downregulation of iNOS by its own product as well as the products of HO-1.

“Lumen digestion” technique for isolation of aortic endothelial cells from heme oxygenase-1 knockout mice

Endothelial cell dysfunction plays a critical role in the pathogenesis of cardiovascular diseases. Gene targeted mutant, knockout, or transgenic mice are widely used in the laboratory investigation of these disorders. We describe a simple and reproducible “lumen digestion” technique to isolate aortic endothelial cells from mice that would be useful for researchers in endothelial cell biology. We used wild-type, homozygote, or heterozygote heme oxygenase-1 null mice from which the aorta is isolated and removed under anesthesia. After cauterizing all the branches, both ends of the aorta are cannulated using an Intramedic® PE-20 tube. After flushing the aorta with phosphate-buffered saline (PBS), the lumen is repeatedly instilled (five times) with 50 µL 0.25% trypsin in PBS, incubated for 2 min, and flushed with PBS. The outflow is collected in endothelial cell media with 20% fetal bovine serum. After centrifugation, the endothelial cells in the pellet are resuspended in media and plated in a 24-well tissue culture dish. Following culture for 2 to 3 weeks, the cells demonstrate typical cobblestone appearance, stain positive for the endothelial marker CD31, and are capable of low-density lipoprotein uptake. Following challenge with oxidized lipids, heme oxygenase-1 deficient endothelial cells demonstrate increased susceptibility to cell injury.

Hypoxemia and blunted hypoxic ventilatory responses in mice lacking heme oxygenase-2

Heme oxygenase (HO) catalyzes physiological heme degradation and consists of two structurally related isozymes, HO-1 and HO-2. Here we show that HO-2-deficient (HO-2(-/-)) mice exhibit hypoxemia and hypertrophy of the pulmonary venous myocardium associated with increased expression of HO-1. The hypertrophied venous myocardium may reflect adaptation to persistent hypoxemia. HO-2(-/-) mice also show attenuated ventilatory responses to hypoxia (10% O2) with normal responses to hypercapnia (10% CO2), suggesting the impaired oxygen sensing. Importantly, HO-2(-/-) mice exhibit normal breathing patterns with normal arterial CO2 tension and retain the intact alveolar architecture, thereby excluding hypoventilation and shunting as causes of hypoxemia. Instead, ventilation-perfusion mismatch is a likely cause of hypoxemia, which may be due to partial impairment of the lung chemoreception probably at pulmonary artery smooth muscle cells. We therefore propose that HO-2 is involved in oxygen sensing and responsible for the ventilation-perfusion matching that optimizes oxygenation of pulmonary blood.

Heme oxygenase-1 inhibits angiotensin II-induced cardiac hypertrophy in vitro and in vivo

BACKGROUND

Heme oxygenase-1 (HO-1) is a stress-response enzyme implicated in cardioprotection. To explore whether HO-1 has a role in cardiac remodeling response, the effect of its overexpression on angiotensin II (Ang II)-induced cardiac hypertrophy was examined.

METHODS AND RESULTS

HO-1 was induced in cultured rat neonatal cardiomyocytes by treatment with cobalt protoporphyrin IX (CoPPIX) or a recombinant adenovirus carrying the human HO-1 gene. Ang II-induced myocyte hypertrophy assessed by increments in cell size, [3H]leucine uptake, and protein content was suppressed by HO-1 overexpression. Cotreatment of cells with tin protoporphyrin IX, a HO inhibitor, significantly reversed the suppressive effect of HO-1. Bilirubin, one of the byproducts of heme degradation by HO-1, mediated the suppressive effect through the inhibition of Ang II-induced production of reactive oxygen species, as detected by a 2',7'-dichlorofluorescein probe. The antihypertrophic effect of HO-1 was also demonstrated in rats receiving chronic Ang II infusions. Cotreatment of animals with CoPPIX significantly attenuated Ang II-induced left ventricular hypertrophy and hyperdynamic contractions, whereas concomitant treatment with tin protoporphyrin IX abolished CoPPIX-mediated cardioprotection in vivo.

CONCLUSIONS

HO-1 attenuates Ang II-induced cardiac hypertrophy both in vitro and in vivo, and bilirubin mediates, at least in part, the antihypertrophic effect of HO-1 via inhibition of reactive oxygen species production after Ang II stimulation.

Identification of heme oxygenase-1 as a novel BCR/ABL-dependent survival factor in chronic myeloid leukemia

Chronic myeloid leukemia (CML) is a stem cell disease in which BCR/ABL promotes the survival of leukemic cells. Heme oxygenase-1 (HO-1) is an inducible stress protein that catalyzes the degradation of heme and has recently been implicated in the regulation of growth and survival of various neoplastic cells. In the present study, we analyzed the expression and role of HO-1 in CML cells. As assessed by Northern and Western blot analysis as well as immunostaining, primary CML cells were found to express HO-1 mRNA and the HO-1 protein in a constitutive manner. Exposure of these cells to the BCR/ABL tyrosine kinase inhibitor STI571 resulted in decreased expression of HO-1 mRNA and protein. In addition, BCR/ABL was found to up-regulate HO-1 promoter activity, mRNA levels, and protein levels in Ba/F3 cells. To investigate the role of HO-1 for survival of primary CML cells, the HO-1 inducer hemin was used. Hemin-induced expression of HO-1 was found to protect CML cells from STI571-induced cell death. In addition, inhibition of HO-1 by zinc-(II)-deuteroporphyrin-IX-2,4-bisethyleneglycol resulted in a substantial decrease of cell viability. Furthermore, overexpression of HO-1 in the CML-derived cell line K562 was found to counteract STI571-induced apoptosis. Together, our data identify HO-1 as a novel BCR/ABL-driven survival molecule and potential target in leukemic cells in patients with CML. The pathogenetic and clinical implications of this observation remain to be elucidated.

Roles of Heme Oxygenase-1 in the Antiproliferative and Antiapoptotic Effects of Nitric Oxide on Jurkat T Cells

Nitric oxide (NO) has been shown to exert antiproliferative and antiapoptotic effects on human T cells. Heme oxygenase-1 (HO-1), which degrades heme into biliverdin, free iron (Fe(2+)), and carbon monoxide (CO), has also been known to have antiproliferative and antiapoptotic effects. Recent evidence suggests that HO-1 is an important cellular target of NO; whether HO-1 expression contributes to the antiproliferative and/or antiapoptotic effects mediated by NO remains to be investigated. In the present study, we examined the effects of NO on HO-1 expression and possible roles of HO-1 in T cell proliferation and apoptosis. Using human Jurkat T cells, we found that the NO donor sodium nitroprusside (SNP) induced HO-1 expression and that preincubation with SNP suppressed T cell proliferation induced by concanavalin A and apoptosis triggered by anti-Fas antibody. Suppressions of T cell proliferation and apoptosis comparable with SNP were also observed when the T cells were preincubated with the HO-1 inducer cobalt protoporphyrin. A phosphorothioate-linked HO-1 antisense oligonucleotide blocked HO-1 expression, and subsequently abrogated the antiproliferative and antiapoptotic effects of SNP. Overexpression of the HO-1 gene after transfection into Jurkat T cells resulted in significant decreases in T cell proliferation and apoptosis. The CO donor tricarbonyldichlororuthenium (II) dimer mimicked the antiproliferative effect of SNP, and the Fe(2+) donor FeSO(4) blocked anti-Fas-induced apoptosis. Taken together, our results suggest that NO induces HO-1 expression in T cells and that suppressions of T cell proliferation and apoptosis afforded by NO are associated with an increased expression of HO-1 by NO.

Formalin-induced spinal cord calcium/calmodulin-dependent protein kinase II alpha expression is modulated by heme oxygenase in mice

The injection of formalin into the hindpaws of rats and mice is widely used as a model of inflammatory pain. The allodynia observed in this model is due in part to sensitization of spinal cord dorsal horn neurons, a form of neuroplasticity similar to long-term potentiation in the hippocampus. Ca(2+)/calmodulin-dependent kinase type IIalpha (CaMKIIalpha) is a key component of long-term potentiation. Here we report alterations in CaMKIIalpha mRNA and protein expression in spinal cord tissue from wild-type and heme oxygenase type 2 (HO-2) null mutant mice after formalin injection. Behavioral experiments demonstrated a long lived allodynia in wild-type C57Bl/6J mice after hindpaw formalin injection, but less in null mutant mice. Both CaMKIIalpha mRNA and protein expression were increased in a time-dependent manner in the spinal cords of wild-type mice after formalin injection. Confocal microscopy localized the increased expression to the superficial laminae of the spinal cord dorsal horn. In the HO-2 null mutant mice no significant change in CaMKIIalpha mRNA expression and only a small increase in protein were noted. These findings suggest that time-dependent CaMKIIalpha expression may underlie central sensitization and allodynia induced by hindpaw formalin injection, and that this process is modulated by HO-2.

The protective role of heme oxygenase-1 on the liver after hypoxic preconditioning in rats

BACKGROUND

Hypoxic preconditioning (HP) confers cytoprotection against ischemia/reperfusion (I/R) injury. This effect is in part attributable to the induction of heme oxygenase (HO)-1. This experiment evaluates liver cell damage after I/R injury in HP rats.

METHODS

HP rats were prepared by exposure (15 hr/day) to an altitude chamber (5500 m) for 2 weeks. Partial hepatic ischemia was produced in the left lobes for 45 min followed by 180 min of reperfusion. Zinc (Zn) protoporphyrin (PP), a specific inhibitor of HO enzymatic activity, was subcutaneously injected 1 hr before the I/R injury into separate groups of sea-level (SL) control and HP rats. Serum alanine aminotransferase (ALT) levels, liver HO-1 mRNA and protein, and HO enzymatic activity were measured.

RESULTS

HO-1 was induced in the livers of rats exposed to HP. The levels of HO-1 mRNA and protein were obviously overexpressed after 2 weeks of HP. HP diminished the elevation of serum ALT levels after I/R injury (83.7+/- 4.9 U/L) when compared with SL controls (280.8+/-19.4 U/L) and HP+ZnPP-pretreated groups (151.3+/-4.4 U/L). The HO activity in treated rats also was correlated with these results (237.9+/-19.8 pmol/mg of protein per hour for the HP group, 164.3+/-12.7 pmol/mg of protein per hour for the HP+ZnPP group, and 182.6+/-8 pmol/mg of protein per hour for the SL controls).

CONCLUSIONS

The authors' results indicated that the induction of HO-1 in hypoxic preconditioning played a protective role against hepatic I/R injury.

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.

Enhanced inhibition of neointimal hyperplasia by genetically engineered endothelial progenitor cells

BACKGROUND

Circulating endothelial progenitor cells (EPCs) have been reported previously. In this study, we examined the hypothesis that overexpression of vasculoprotective gene endothelial nitric oxide synthase (eNOS) and heme oxygenase-1 (HO-1) in EPCs enhances their ability to inhibit neointimal hyperplasia.

METHODS AND RESULTS

EPCs were isolated from rabbit peripheral blood, expanded in culture, and transduced with pseudotyped retroviral vectors expressing human eNOS (eNOS-EPCs), HO-1 (HO-1-EPCs), or green fluorescent protein (GFP-EPCs). Transduction efficiency of EPCs ex vivo was >90%. Four groups of rabbits (n=5 to 6 per group) were subjected to balloon angioplasty of the common carotid artery. Immediately after injury, approximately 5x10(6) autologous eNOS-EPCs or HO-1-EPCs were transplanted into the injured vessel. Control animals received an equivalent number of GFP-EPCs or Ringer's saline. Two weeks after transplantation, eNOS and HO-1 transgene transcripts and proteins were detected in the transduced rabbit vessels. Endothelialization was enhanced in the EPC-transplanted vessels independently of gene transfer. Neointimal thickening was significantly reduced in the GFP-EPC-treated vessels relative to the saline control. Neointima size was further reduced in vessels treated with eNOS-EPCs. Surprisingly, no additional reduction was seen in vessels treated with HO-1-EPCs relative to GFP-EPCs. Thrombosis occurred in approximately 50% of the saline-treated vessels but was virtually absent in all EPC-transplanted vessels.

CONCLUSIONS

We conclude that transplantation of autologous EPCs overexpressing eNOS in injured vessels enhances the vasculoprotective properties of the reconstituted endothelium, leading to inhibition of neointimal hyperplasia. This cell-based gene therapy strategy may be useful in treatment of vascular disease.

[Protective effect of carbon monoxide for organ injury]

Heme oxygenase (HO) catabolizes heme into three products: carbon monoxide (CO), biliverdin and free iron. HO-1, inducible form of HO, has been shown to be protective against various stress. CO at a low concentration has been shown to be protective in several disease models mimicking the action of HO-1. We suggest that CO, the byproduct of heme degradation, could be valuable therapeutic agents. We review the functional role of HO-1 and CO and its potential application to clinical settings.

Protection From Ischemic Heart Injury by a Vigilant Heme Oxygenase-1 Plasmid System

Although human heme oxygenase-1 (hHO-1) could provide a useful approach for cellular protection in the ischemic heart, constitutive overexpression of hHO-1 may lead to unwanted side effects. To avoid this, we designed a hypoxia-regulated hHO-1 gene therapy system that can be switched on and off. This vigilant plasmid system is composed of myosin light chain-2v promoter and a gene switch that is based on an oxygen-dependent degradation domain from the hypoxia inducible factor-1-alpha. The vector can sense ischemia and switch on the hHO-1 gene system, specifically in the heart. In an in vivo experiment, the vigilant hHO-1 plasmid or saline was injected intramyocardially into myocardial infarction mice or sham operation mice. After gene transfer, expression of hHO-1 was only detected in the ischemic heart treated with vigilant hHO-1 plasmids. Masson trichrome staining showed significantly fewer fibrotic areas in vigilant hHO-1 plasmids-treated mice compared with saline control (43.0%+/-4.8% versus 62.5%+/-3.3%, P<0.01). The reduction of interstitial fibrosis is accompanied by an increase in myocardial hHO-1 expression in peri-infarct border areas, concomitant with higher Bcl-2 levels and lower Bax, Bak, and caspase 3 levels in the ischemic myocardium compared with saline control. By use of a cardiac catheter, heart from vigilant hHO-1 plasmids-treated mice showed improved recovery of contractile and diastolic performance after myocardial infarction compared with saline control. This study documents the beneficial regulation and therapeutic potential of vigilant plasmid-mediated hHO-1 gene transfer. This novel gene transfer strategy can provide cardiac-specific protection from future repeated bouts of ischemic injury.

Biology of Heme in Health and Disease

Heme is an essential molecule with contradictory biological functions. In hemoproteins such as hemoglobin and cytochromes protein-bound heme is a prosthetic group serving physiological functions as a transporter for oxygen and electrons. On the other hand free heme can have deleterious effects by generating reactive oxygen species that cause oxidative stress. Consequently, heme homeostasis of the cell must be tightly controlled. The biosynthesis of heme is catalyzed by eight enzymes that are differentially regulated in liver and erythroid cells. Recent findings on proinflammatory functions of heme and its role in the pathogenesis of diseases, such as rhabdomyolysis or atherosclerosis are summarized. The regulation of gene expression by heme in yeast and mammalian cells and the underlying molecular mechanisms are presented. Finally, we discuss the functional significance of the heme-degrading enzyme heme oxygenase and heme-binding proteins for the regulation of heme homeostasis.

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.

Heme Oxygenase-1: Transducer of Pathological Brain Iron Sequestration under Oxidative Stress

Mechanisms responsible for the pathological deposition of redox-active brain iron in human neurological disorders remain incompletely understood. Heme oxygenase-1 (HO-1) is a 32-kDa stress protein that degrades heme to biliverdin, free iron, and carbon monoxide. In this chapter, we review evidence that (1) HO-1 is overexpressed in CNS tissues affected by Alzheimer's disease (AD), Parkinson's disease (PD), multiple sclerosis (MS), and other degenerative and nondegenerative CNS diseases; (2) the pro-oxidant effects of dopamine, hydrogen peroxide, beta-amyloid, and proinflammatory cytokines stimulate HO-1 expression in some of these conditions; and (3) upregulation of HO-1 in astrocytes exacerbates intracellular oxidative stress and promotes sequestration of nontransferrin-derived iron by the mitochondrial compartment. A model is presented implicating glial HO-1 induction as a "final common pathway" leading to pathological iron sequestration and mitochondrial insufficiency in a host of human CNS disorders.

Vascular heme oxygenase-1 induction suppresses microvascular thrombus formation in vivo

OBJECTIVE

By heme degradation, heme oxygenase-1 (HO-1) provides endogenous carbon monoxide and bilirubin, both of which play major roles in vascular biology. The current study aimed to examine whether induction of HO-1 and its byproducts modulate the process of microvascular thrombus formation in vivo.

METHODS AND RESULTS

In individual microvessels of mouse cremaster muscle preparations, ferric chloride-induced thrombus formation was analyzed using intravital fluorescence microscopy. When mice were pretreated with an intraperitoneal injection of hemin, a HO-1 inducer, immunohistochemistry and Western blot protein analysis of cremaster muscle tissue displayed a marked induction of HO-1. In these animals, superfusion with ferric chloride solution induced arteriolar and venular thrombus formation, which, however, was significantly delayed when compared with thrombus formation in animals without HO-1 induction. The delay in thrombus formation in hemin-treated mice was completely blunted by tin protoporphyrin-IX, a HO-1 inhibitor, but not by copper protoporphyrin-IX, which does not inhibit the enzyme. Coadministration of the vitamin E analogue Trolox in HO-1-blocked animals almost completely restored the delay in thrombus formation, implying that, besides CO, the antioxidant HO pathway metabolite bilirubin mainly contributes to the antithrombotic property of HO-1. This was further supported by the fact that bilirubin was found as effective as hemin in delay of ferric chloride-induced thrombus formation. Animals with HO-1 induction revealed reduced P-selectin protein expression in cremaster muscle tissue, which most probably presented the molecular basis for delayed thrombus growth.

CONCLUSIONS

Local induction of HO-1 activity may be of preventive and therapeutic value for clinical disorders with increased risk of thrombotic events.

A microsatellite polymorphism in the heme oxygenase-1 gene promoter is associated with increased bilirubin and HDL levels but not with coronary artery disease

Heme oxygenase 1 (HO-1) is involved in the generation of the endogenous anti-oxidant bilirubin which exerts beneficial effects against arteriosclerosis. A (GT) repeat polymorphism in the HO-1 promoter region modulates HO-1 expression in response to oxidative stress. Recently, this polymorphism has been reported to protect from coronary artery disease in Orientals. We intended to confirm this observation in Caucasians.

We studied 649 individuals with myocardial infarction (n=258), stable coronary artery disease (n=180) and controls without coronary artery disease (n=211). Carriers of short alleles (<25 repeats) had higher bilirubin levels (median 0.66 mg/dL, IQR 0.49 to 0.91) compared to non-carriers (median 0.61mg/dL, IQR 0.45 to 0.82; p=0.03) and a more favourable lipid profile (HDL median 47mg/dL, IQR 40 to 50 vs. median 45, IQR 37 to 55, p=0.01; triglycerides median 118mg/dL, IQR 87 to 174 vs. median 132, IQR 97 to 191, p=0.03). However, no significant differences of the genotype distribution were observed between the three groups in this Caucasian study population (p=0.94).

Although potentially beneficial effects of the short HO-1 allele on lipid profile and serum bilirubin were observed, in contrast to Orientals, the HO-1 genotype was not associated with coronary artery disease in Caucasians.

Role of heme oxygenase-1 in cardiovascular function

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). Due to the properties of inducible HO (HO-1) and its products, we hypothesized that HO-1 would play an important role in the regulation of cardiovascular function. In this article we will review the role of HO-1 in cardiovascular function, and highlight our previous studies using gene deletion and gene overexpression transgenic approaches in mice. These studies will include the investigation of HO-1 in the setting of hypertension (renovascular), atherosclerosis and vascular injury (vein graft stenosis), hypotension (endotoxemia), and ischemia/reperfusion injury (heart). In a chronic renovascular hypertension model, blood pressure elevation, cardiac hypertrophy, acute renal failure, and acute mortality induced by one kidney-one clip surgery are more severe in HO-1 null mice. Moreover, absence of HO-1 leads to accelerated atherosclerotic lesion formation and vein graft disease. In addition, HO-1 null mice with endotoxemia have earlier resolution of hypotension, yet the mortality and the incidence of end organ damage are higher in the absence of HO-1. In contrast, mice with cardiac-specific overexpression of HO-1 have an improvement in cardiac function, smaller myocardial infarcts, and reduced inflammatory and oxidative damage after coronary artery ligation and reperfusion. Taken together, these studies suggest that an absence of HO-1 has detrimental consequences, while overexpression of HO-1 plays a protective role in ischemia/reperfusion injury.

Anti-inflammatory actions of the heme oxygenase-1 pathway

Heme oxygenase 1 (HO-1) is induced by oxidative or nitrosative stress, cytokines and other mediators produced during inflammatory processes, likely as part of a defence system in cells exposed to stress to provide a negative feedback for cell activation and the production of mediators, which could modulate the inflammatory response. HO-1 activity results in the inhibition of oxidative damage and apoptosis, with significant reductions in inflammatory events including edema, leukocyte adhesion and migration, and production of inflammatory cytokines. HO-1 is induced by nitric oxide (NO) in different biological systems and can control the increased production of this mediator observed in many inflammatory situations. Regulatory interactions between HO-1 and cyclooxygenase (COX) pathways have also been reported. Modulation of signal transduction pathways by HO-1 or products derived from its activity, such as carbon monoxide (CO), may mediate the anti-inflammatory effects of this protein. Regulation of HO-1 activity may be a therapeutical strategy for a number of inflammatory conditions.

Role of the heme oxygenases in abnormalities of the mesenteric circulation in cirrhotic rats

Carbon monoxide (CO), a product of heme metabolism by heme-oxygenase (HO), has biological actions similar to those of nitric oxide (NO). The role of CO in decreasing vascular responses to constrictor agents produced by experimental cirrhosis induced by carbon tetrachloride was evaluated before and after inhibition of HO with tin-mesoporphyrin (SnMP) in the perfused superior mesenteric vasculature (SMV) of cirrhotic and normal rats and in normal rats transfected with the human HO-1 (HHO-1) gene. Perfusion pressure and vasoconstrictor responses of the SMV to KCl, phenylephrine (PE), and endothelin-1 (ET-1) were decreased in cirrhotic rats. SnMP increased SMV perfusion pressure and restored the constrictor responses of the SMV to KCl, PE, and ET-1 in cirrhotic rats. The relative roles of NO and CO in producing hyporeactivity of the SMV to PE in cirrhotic rats were examined. Vasoconstrictor responses to PE were successively augmented by stepwise inhibition of CO and NO production, suggesting a complementary role for these gases in the regulation of reactivity of the SMV. Expression of constitutive but not of inducible HO (HO-1) was increased in the SMV of cirrhotic rats as was HO activity. Administration of adenovirus containing HHO-1 gene produced detection of HHO-1 RNA and increased HO activity in the SMV within 7 days. Rats transfected with HO-1 demonstrated reduction in both perfusion pressure and vasoconstrictor responses to PE in the SMV. We propose that HO is an essential component in mechanisms that modulate reactivity of the mesenteric circulation in experimental hepatic cirrhosis in rats.

Heme oxygenase-1-related carbon monoxide production and ventricular fibrillation in isolated ischemic/reperfused mouse myocardium

Heme oxygenase-1 (HO-1)-dependent carbon monoxide (CO) production related to reperfusion-induced ventricular fibrillation (VF) was studied in HO-1 wild-type (+/+), heterozygous (+/-), and homozygous (-/-) isolated ischemic/reperfused mouse heart. In HO-1 homozygous myocardium, under aerobic conditions, HO-1 enzyme activity, HO-1 mRNA, and protein expression were not detected in comparison with aerobically perfused wild-type and heterozygous myocardium. In wild-type, HO-1 hetero- and homozygous hearts subjected to 20 min ischemia followed by 2 h of reperfusion, the expression of HO-1 mRNA, protein, and HO-1 enzyme activity was detected in various degrees. A reduction in the expression of HO-1 mRNA, protein, and enzyme activity in fibrillated wild-type and heterozygous myocardium was observed. In reperfused/nonfibrillated wild-type and heterozygous hearts, a reduction in HO-1 mRNA, protein expression, and HO-1 enzyme activity was not observed, indicating that changes in HO-1 mRNA, protein, and enzyme activity could be related to the development of VF. These changes were reflected in the HO-1-related endogenous CO production measured by gas chromatography. In HO-1 knockout ischemic/reperfused myocardium, all hearts showed VF, and no detection in HO-1 mRNA, protein, and enzyme activity was observed. Thus, interventions that are able to increase endogenous CO may prevent the development of VF.

Beneficial effects of heme oxygenase-1 up-regulation in the development of experimental inflammation induced by zymosan

Heme oxygenase-1 (HO-1) is part of the integrated response to oxidative stress. This enzyme may exert anti-inflammatory effects in some animal models, although the precise mechanisms are not fully understood. We have examined the role of HO-1 in the inflammatory response induced by zymosan in the mouse air pouch. Zymosan administration induced HO-1 protein expression in leukocytes migrating to exudates, with maximal levels in the late phase of this response (24-48 h). This was accompanied by ferritin induction and bilirubin accumulation, indicating that this enzyme is active in our model. HO-1 expression by zymosan treatment was partly reduced by aminoguanidine, suggesting the participation of endogenous nitric oxide in the mechanisms leading to HO-1 synthesis in the zymosan-injected mouse air pouch. Up-regulation of HO-1 by hemin administration resulted in inhibition of nitric-oxide synthase-2 activity, cellular infiltration into the air pouch exudate, and plasmatic exudation. Leukotriene B4 levels in exudates were significantly decreased in the early phase of this response (4 h), whereas interleukin-1beta and tumor necrosis factor-alpha were inhibited at all time points. Inhibition of HO-1 activity by zinc protoporphyrin IX prevented most of the effects caused by hemin administration. Our results indicate that HO-1 exerts anti-inflammatory effects on the response to zymosan in the mouse air pouch and support a role for this enzyme in the modulation of inflammatory processes.

Heme oxygenase-1 and its reaction product, carbon monoxide, prevent inflammation-related apoptotic liver damage in mice

Heme oxygenase-1 (HO-1), a stress-responsive enzyme that catabolizes heme into carbon monoxide (CO), biliverdin, and iron, has previously been shown to protect grafts from ischemia/reperfusion injury and rejection. Here we investigated the protective potential of HO-1 in 5 models of immune-mediated liver injury. We found that up-regulation of endogenous HO-1 by cobalt-protoporphyrin-IX (CoPP) protected mice from apoptotic liver damage induced by anti-CD95 antibody (Ab) or d-galactosamine in combination with either anti-CD3 Ab, lipopolysaccharide (LPS), or tumor necrosis factor alpha (TNF-alpha). HO-1 induction prevented apoptotic liver injury, measured by inhibition of caspase 3 activation, although it did not protect mice from caspase-3-independent necrotic liver damage caused by concanavalin A (Con A) administration. In addition, overexpression of HO-1 by adenoviral gene transfer resulted in protection from apoptotic liver injury, whereas inhibition of HO-1 enzymatic activity by tin-protoporphyrin-IX (SnPP) abrogated the protective effect. HO-1-mediated protection seems to target parenchymal liver cells directly because CoPP treatment protected isolated primary hepatocytes from anti-CD95-induced apoptosis in vitro. Furthermore, depletion of Kupffer cells (KCs) did not interfere with the protective effect in vivo. Exogenous CO administration or treatment with the CO-releasing agent methylene chloride mimicked the protective effect of HO-1, whereas treatment with exogenous biliverdin or overexpression of ferritin by recombinant adenoviral gene transfer did not. In conclusion, HO-1 is a potent protective factor for cytokine- and CD95-mediated apoptotic liver damage. Induction of HO-1 might be of a therapeutic modality for inflammatory liver diseases.

Effects of exogenous heme on renal function: role of heme oxygenase and cyclooxygenase

We examined the effects of heme administration (15 mg/kg IV) on indexes of renal carbon monoxide production and contrasted the renal functional response to heme in anesthetized rats pretreated and not pretreated with stannous mesoporphyrin (40 micromol/kg IV) to inhibit heme oxygenase or sodium meclofenamate (5 mg/kg IV plus infusion at 10 microg/kg per minute) to inhibit cyclooxygenase. In rats without drug pretreatment, heme administration decreased renal vascular resistance and increased renal blood flow, urine volume, and sodium excretion associated with augmented urinary excretion of 6-keto-PGF1alpha and enhanced concentration of carbon monoxide in the renal cortical microdialysate. Pretreatment with stannous mesoporphyrin did not prevent heme from producing renal vasodilation and increasing renal blood flow but abolished the diuretic and natriuretic responses. Conversely, pretreatment with sodium meclofenamate blunted the renal vasodilatory effect of heme but affected neither the diuretic nor the natriuretic effect. We conclude that heme-induced renal vasodilation is a cyclooxygenase-dependent response involving increased synthesis of PGI2, whereas heme-induced diuresis and natriuresis are heme oxygenase-dependent responses involving inhibition of tubular reabsorption of sodium and water through undefined mechanisms.

Suppression of inflammatory cytokine production by carbon monoxide involves the JNK pathway and AP-1

The stress-inducible protein heme oxygenase-1 provides protection against oxidative stress and modulates pro-inflammatory cytokines. As the sepsis syndrome results from the release of pro-inflammatory mediators, we postulated that heme oxygenase-1 and its enzymatic product CO would protect against lethality in a murine model of sepsis. Mice treated with a lethal dose of lipopolysaccharide (LPS) and subsequently exposed to inhaled CO had significantly better survival and lower serum interleukin (IL)-6 and IL-1beta levels than their untreated counterparts. In vitro, mouse macrophages exposed to LPS and CO had significantly attenuated IL-6 production; this effect was concentration-dependent and occurred at a transcriptional level. The same effect was seen with increased endogenous CO production through overexpression of heme oxygenase-1. Mutation within the AP-1-binding site in the IL-6 promoter diminished the effect of CO on promoter activity, and treatment of macrophages with CO decreased AP-1 binding in an electrophoretic mobility shift assay. Electrophoretic mobility supershift assay indicated that the JunB, JunD, and c-Fos components of AP-1 were particularly affected. Upstream of AP-1, CO decreased JNK phosphorylation in murine macrophages and lung endothelial cells. Mice deficient in the JNK pathway had decreased serum levels of IL-6 and IL-1beta in response to LPS compared with control mice, and no effect of CO on these cytokine levels was seen in Jnk1 or Jnk2 genedeleted mice. In summary, these results suggest that CO provides protection in a murine model of sepsis through modulation of inflammatory cytokine production. For the first time, the effect of CO is shown to be mediated via the JNK signaling pathway and the transcription factor AP-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.

Protective role of heme oxygenase-1 induction in carbon tetrachloride-induced hepatotoxicity

Reductive metabolism of carbon tetrachloride (CCl(4)) is thought to cause lipid peroxidation which results in hepatic injury. Heme oxygenase-1 (HO-1) (EC 1.14.99.3), the rate-limiting enzyme in heme catabolism, is known to be induced by oxidative stress and to confer protection against oxidative tissue injuries. In this study, we examined the role of HO-1 induction in a rat model of CCl(4)-induced acute liver injury. CCl(4) treatment (1 mL/kg, intraperitoneally) produced severe hepatic injury in rats as revealed by significant increases in serum alanine transaminase (ALT) (EC 2.6.1.2) activity and hepatic malondialdehyde (MDA) content, severe liver cell injury, and increases in hepatic tumor necrosis factor-alpha (TNF-alpha) mRNA expression and DNA binding activity of nuclear factor-kappa B (NF-kappa B). Following CCl(4) treatment, hepatic HO-1 expression was markedly increased both at transcriptional and protein levels in hepatocytes, especially around the central vein. HO-1 induction was mediated in part through a rapid increase in microsomal free heme concentration presumably derived from hepatic cytochrome P450. Inhibition of HO activity by tin-mesoporphyrin (Sn-MP), which resulted in a sustained increase in microsomal free heme concentration, exacerbated liver injury, as judged by the sustained increase in serum ALT activity, extensive hepatocytes injuries, a more pronounced expression of hepatic TNF-alpha mRNA and an enhanced NF-kappa B activation. These findings indicate that induction of HO-1 is an adaptive response to CCl(4) treatment, and it may be critical in the recovery of hepatocytes from injury. Our findings also suggest that HO-1 induction may play an important role in conferring protection on hepatocytes from oxidative damage caused by free heme.

Absence of heme oxygenase-1 exacerbates atherosclerotic lesion formation and vascular remodeling

To examine the role of heme oxygenase (HO)-1 in the pathophysiology of vascular diseases, we generated mice deficient in both HO-1 and apolipoprotein E (HO-1-/-apoE-/-). Despite similar total plasma cholesterol levels in response to hypercholesterolemia, HO-1-/-apoE-/- mice, in comparison with HO-1+/+apoE-/- mice, had an accelerated and more advanced atherosclerotic lesion formation. In addition to greater lipid accumulation, these advanced lesions from HO-1-/-apoE-/- mice contained macrophages and smooth muscle alpha-actin-positive cells. We further tested the role of HO-1 on neointimal formation in a mouse model of vein graft stenosis. Autologous vein grafts in HO-1-/- mice showed robust neointima consisting of alpha-actin-positive vascular smooth muscle cells (VSMC) 10 days after surgery in comparison to the smaller neointima formed in autologous vein grafts in HO-1+/+ mice. However, at 14 days after surgery, the neointima from composite vessels of HO-1-/- mice was composed mainly of acellular material, indicative of substantial VSMC death. VSMC isolated from HO-1-/- mice were susceptible to oxidant stress, leading to cell death. Our data demonstrate that HO-1 plays an essential protective role in the pathophysiology of atherosclerosis and vein graft stenosis.

Different faces of the heme-heme oxygenase system in inflammation

The heme-heme oxygenase system has recently been recognized to possess important regulatory properties. It is tightly involved in both physiological as well as pathophysiological processes, such as cytoprotection, apoptosis, and inflammation. Heme functions as a double-edged sword. In moderate quantities and bound to protein, it forms an essential element for various biological processes, but when unleashed in large amounts, it can become toxic by mediating oxidative stress and inflammation. The effect of this free heme on the vascular system is determined by extracellular factors, such as hemoglobin/heme-binding proteins, haptoglobin, albumin, and hemopexin, and intracellular factors, including heme oxygenases and ferritin. Heme oxygenase (HO) enzyme activity results in the degradation of heme and the production of iron, carbon monoxide, and biliverdin. All these heme-degradation products are potentially toxic, but may also provide strong cytoprotection, depending on the generated amounts and the microenvironment. Pre-induction of HO activity has been demonstrated to ameliorate inflammation and mediate potent resistance to oxidative injury. A better understanding of the complex heme-heme

[Expression and tissue localization of hemeoxygenase in human placenta]

OBJECTIVE

The purpose of this study was to investigate the expression and localization of the two known isoforms of hemeoxygenase (HO) in normal human first trimester placenta and third trimester placenta.

METHODS

Reverse transcription polymerase chain reaction (RT-PCR) and immunohistochemistry were resorted to demonstrate the expression and localization of HO-1 and HO-2 in normal placenta tissue, obtained from 6 approximately 10 week gestation women (20 cases) and the third trimester woman (20 cases).

RESULTS

Compared with glyceraldehydes-3-phosphate dehydrogenase (GAPDH), the expression of HO-1 was lower, there was no significant difference between the first trimester (0.31 +/- 0.19) and third trimester (0.28 +/- 0.14) (P > 0.05); the expression of HO-2 was higher, it is significantly higher at third trimester (1.12 +/- 0.58) compared with first trimester placenta (0.70 +/- 0.48) (P < 0.05). The result of immunohistochemistry demonstrated that HO-1 was predominantly localized in villous stroma cell and trophoblast; HO-2 predominantly localized in trophoblast as well as capillaries, with weak staining of villous stroma. The staining score were not normally distributed. The median staining scorse of HO-1 in trophoblast, villous stroma and capillaries at first trimester were 9.0, 2.6 and 2.8, respectively, at third trimester were 8.7, 2.0 and 1.4, there was no difference between the two groups (P > 0.05). The median staining score of HO-2 in capillaries at first trimester was 5.8, significantly lower than that of the third trimester (9.3) (P < 0.05). There was no significant difference between the staining score of HO-2 in trophoblast (10.5, 8.0) and villous stroma (3.6, 2.4) between the first trimester and the third trimester (P > 0.05).

CONCLUSIONS

HO-1 and HO-2 as endogenous system may regulate feto-placental circulation, indicated their different roles in placental vascular development and regulation. They may offer protection against cyto-toxic damage in the placenta, and influence immunological function.

Graft protective effects of heme oxygenase 1 in mouse tracheal transplant-related obliterative bronchiolitis

BACKGROUND

Heme oxygenase (HO)-1, long believed to be a cytoprotective protein, has recently been identified as a graft survival gene. This study evaluates the role of HO-1 in a murine heterotopic tracheal allograft model for obliterative bronchiolitis.

METHODS

Mice with deficient or experimentally enhanced HO-1 expression underwent subcutaneous implantation of murine tracheal isografts and allografts. Grafts were excised after 9, 16, or 21 days and evaluated by histologic examination, immunohistochemistry for HO-1 and interleukin (IL)-10 proteins, and terminal deoxynucleotide transferase-mediated dUTP nick-end labeling. To evaluate the relationships between IL-10 and HO-1, the effects of modulation of HO-1 expression on IL-10 expression were evaluated and HO-1 expression was examined in tracheal transplants from IL-10 null mice.

RESULTS

Isografts demonstrated normal histology with minimal HO-1 staining, whereas allografts showed features of human airway rejection (loss of respiratory epithelium, luminal granulation tissue, lymphocytic tracheitis) with increased HO-1 staining in macrophages and mesenchymal cells. HO-1-deficient mice demonstrated a more rapid progression of the tracheal allograft injury as compared with control allografts, and this was associated with a decrease in the anti-inflammatory cytokine, IL-10. Tracheal transplants using IL-10-deficient mice also resulted in a more severe injury, and this was accompanied by a decrease in HO-1 staining.

CONCLUSIONS

HO-1 protein expression is increased in murine heterotopic airway rejection, and deficiency of HO-1 accelerates the development of the obliterative bronchiolitis-like lesion. IL-10 protein expression parallels expression of HO-1, suggesting that IL-10 may participate in the genesis of HO-1's effects on the inflammatory processes triggered by allotransplantation.

Heme oxygenase-1 is an antifibrogenic protein in human hepatic myofibroblasts

BACKGROUND & AIMS

Hepatic myofibroblasts play a key role in the development of liver fibrosis associated with chronic liver diseases. We have shown that oxidative stress is a messenger of 15-deoxy-delta-12,14-prostaglandin J2 (15-d-PGJ2) in human hepatic myofibroblasts. The aim of the present study was to investigate the role of a stress-inducible protein, heme oxygenase-1 (HO-1), in the action of 15-d-PGJ2.

METHODS

Expression of HO-1 was characterized in biopsy specimens of normal human liver and active cirrhosis by immunohistochemistry, and in cultured human hepatic myofibroblasts by Northern and Western blot analysis. Functional studies also were performed in cultured human hepatic myofibroblasts.

RESULTS

Immunohistochemistry showed that in biopsy specimens from normal livers, HO-1 protein expression was restricted to Kupffer cells. Biopsy specimens from cirrhotic patients displayed HO-1 protein both in macrophages and in myofibroblasts within fibrotic septa. HO-1 messenger RNA (mRNA) and protein also were detected in cultured human hepatic myofibroblasts and increased in response to 15-d-PGJ2 in a time- and dose-dependent manner. Induction of HO-1 in human hepatic myofibroblasts mediated 2 major antifibrogenic properties of 15-d-PGJ2, namely, inhibition of proliferation and of procollagen I mRNA expression. These effects were ascribed to bilirubin, one of the products of HO-1-mediated heme degradation.

CONCLUSIONS

This study shows that HO-1 is expressed in human hepatic myofibroblasts and induced during chronic liver injury. Moreover, these data unravel HO-1 as a major antifibrogenic pathway.

Systemic rather than local heme oxygenase-1 overexpression improves cardiac allograft outcomes in a new transgenic mouse

Heme oxygenase-1 (HO-1), a rate-limiting enzyme in heme catabolism, exhibits potent antioxidant and anti-inflammatory properties. We developed HO-1 transgenic (Tg) mice using a rat HO-1 genomic transgene under the control of the endogenous promoter. Transgene expression was demonstrated by RT-PCR in all studied tissues, and a modest HO-1 overexpression was documented by Western, ELISA, and enzyme activity assays. To assess the effect of local vs systemic HO-1 in the acute rejection response, we used Tg mice as organ donors or recipients of MHC-incompatible heart grafts. In the local HO-1 overexpression model, Tg allografts survived 10.5 +/- 0.7 days (n = 10), compared with 6.5 +/- 0.4 days (n = 6) for wild-type donor controls (p = 0.0001). In the systemic HO-1 overexpression model, Tg recipients maintained allografts for 26.8 +/- 3.4 days (n = 10), compared with 6.3 +/- 0.1 days (n = 12) in wild-type controls (p = 0.00009). Inhibition of HO activity by treatment with tin protoporphyrin blunted survival advantage in Tg mice and resulted in acute graft rejection (n = 3). Increased carboxyhemoglobin levels were consistently noted in Tg mice. Comparisons of grafts at day 4 indicated that HO-1 overexpression was inversely associated with vasculitis/inflammatory cell infiltrate in both models. Hearts transplanted into Tg recipients showed decreased CD4(+) lymphocyte infiltration and diminished immune activation, as judged by CD25 expression. Thus, although local and systemic HO-1 overexpression improved allograft outcomes, systemic HO-1 led to a more robust protection and resulted in a significant blunting of host immune activation. This Tg mouse provides a valuable tool to study mechanisms by which HO-1 exerts beneficial effects in organ transplantation.

The heme-heme oxygenase system: a molecular switch in wound healing

When cells are injured they release their contents, resulting in a local accumulation of free heme proteins and heme. Here, we investigated the involvement of heme and its degrading enzyme heme oxygenase (HO) in the inflammatory process during wound healing. We observed that heme directly accumulates at the edges of the wound after inflicting a wound in the palate of Wistar rats. This coincided with an increased adhesion molecule expression and the recruitment of leukocytes. To prove that heme is responsible for the recruitment of leukocytes, heme was administered intradermally 24 hours prior to injury. A clear heme-induced influx of both macrophages and granulocytes was observed. When examining the HO isoforms, HO-1 and HO-2, we found that HO-2 was present in the entire submucosa. Surprisingly, we observed also that HO-1 is significantly expressed in the epithelium of both the mucosa and the skin of animals without wounds. On inflammation, HO-1 expression increased, particularly in infiltrating cells during the resolution phase of inflammation. Interestingly, we observed that heme-induced influx of leukocytes was highly elevated after pharmacologic inhibition of HO activity. These observations suggest that the heme-HO system is closely involved in the control of wound healing. Our results demonstrate that the local release of heme may be a physiologic trigger to start inflammatory processes, whereas HO-1 antagonizes inflammation by attenuating adhesive interactions and cellular infiltration. Moreover, the basal level of HO expression in the skin may serve as a first protective environment against acute oxidative and inflammatory insults.

Heme-oxygenase-1 mRNA expression affects hemorrhagic shock-induced leukocyte adherence

BACKGROUND

Hemorrhagic shock-related leukocyte adherence to endothelial cells is a key step in microvascular injury-related organ damage. Heme-oxygenase-1 (HO-1) metabolizes heme, a potent cytotoxic agent, to carbon monoxide and biliverdin. We hypothesized that changing HO-1 expression would change leukocyte adherence after hemorrhagic shock.

METHODS

Rats were administered hemin, zinc protoporphyrin, or vehicle 6 hours before surgery. HO-1 expression was determined by reverse-transcriptase polymerase chain reaction in various tissues. Shock was induced in urethane-anesthetized animals by decreasing mean arterial blood pressure to 40 mm Hg for 60 minutes, followed by standard resuscitation measures. Leukocyte adherence was measured by intravital microscopy in rat mesenteric venules.

RESULTS

Hemin, hemorrhagic shock, and the combination resulted in significantly increased HO-1 expression, whereas zinc-protoporphyrin (ZNPP) resulted in significantly decreased leukocyte adherence. After hemorrhagic shock and hemin administration, leukocyte adherence was significantly decreased 60 minutes into resuscitation (7.92 +/- 2.29 vs. 4.84 +/- 0.71 cells/100 microm, p < 0.05) and significantly increased after ZNPP plus shock (14.08 +/- 3.95, p <or= 0.01).

CONCLUSION

The results demonstrate that hemin increases and ZNPP decreases HO-1 mRNA expression and attenuates hemorrhagic shock-induced leukocyte adherence, whereas ZNPP decreases it. These results suggest that by changing HO-1 expression, leukocyte adherence resulting from oxidant injury may be altered.

Heme oxygenase-mediated vasodilation involves vascular smooth muscle cell hyperpolarization

Chronic hypoxia is associated with both blunted agonist-induced and myogenic vascular reactivity and is possibly due to an enhanced production of heme oxygenase (HO)-derived carbon monoxide (CO). However, the mechanism of endogenous CO-meditated vasodilation remains unclear. Isolated pressurized mesenteric arterioles from chronically hypoxic rats were administered the HO substrate heme-l-lysinate (HLL) in the presence or absence of iberiotoxin, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), ryanodine, or free radical spin traps (N-tert-butyl-alpha-phenylnitrone and 4,5-dihydroxy-1,3-benzenedisulfonic acid disodium salt). The effects of HLL administration on vascular smooth muscle (VSM) membrane potential were assessed in superior mesenteric artery strips in the presence and absence of zinc protoporphyrin IX or iberiotoxin. The vasodilatory responses to exogenous CO were assessed in the presence and absence of ODQ or iberiotoxin. HLL administration produced a dose-dependent vasodilatory response that was nearly eliminated in the presence of iberiotoxin. Neither ODQ, spin traps, nor ryanodine altered the vasodilatory response to HLL, although ODQ abolished the vasodilatory response to S-nitroso-N-acetyl-penicillamine. HLL administration produced a zinc protoporphyrin IX- and iberiotoxin-sensitive VSM cell hyperpolarization. Iberiotoxin and ODQ inhibited the vasodilatory response to exogenous CO. Thus the vasodilatory response to endogenous CO involves cGMP-independent activation of VSM large-conductance Ca2+-activated K+ channels and does not likely involve the formation of Ca2+ sparks emanating from ryanodine-sensitive stores.