Protective roles of endogenous carbon monoxide in neointimal development elicited by arterial injury

Adrenomedullin induces heme oxygenase-1 gene expression and cGMP formation in rat vascular smooth muscle cells

Adrenomedullin (ADM) is a potent vasodilatory peptide. It regulates blood pressure by increasing cyclic adenosine monophosphate (cAMP) and guanosine-3',5'-monophosphate (cGMP). We sought to investigate the effect of ADM on heme oxygenase-1 (HO-1) gene expression and cGMP formation in cultured rat vascular smooth muscle cells (VSMCs). ADM treatment, 10(-9) and 10(-8) mol/L, increased cGMP production, and it increased the intracellular cGMP content of platelets coincubated with VSMCs. It increased cGMP content by 158.8% and 273.5%, respectively; increased HO-1 activity by 49.5% and 87%, respectively; augmented HO-1 protein levels by 66% and 126%, respectively; upregulated the steady-state level of HO-1 mRNA by 73% and 159%, respectively, and increased HO-1 mRNA transcription synthesis by four- and seven-fold, respectively. These results suggest that ADM induces HO-1 gene expression and cGMP formation in rat VSMCs.

Effects of genetic ablation of bach1 upon smooth muscle cell proliferation and atherosclerosis after cuff injury

Bach1 is a transcriptional repressor of the cytoprotective enzyme heme oxygenase-1 (HO-1). Although HO-1 protects against atherosclerosis, the function of Bach1 in this process is poorly understood. We isolated peritoneal macrophages and aortic smooth muscle cells (SMC) from wild-type and bach1-deficient mice. bach1-Deficient macrophages expressed increased levels of HO-1 and showed elevated phagocytic activity when incubated with 0.75 microm microspheres. In SMC, bach1-ablation resulted in increased expression of HO-1 and decreased proliferation in bromodeoxyuridine incorporation assay as compared with wild-type cells. The up-regulated phagocytic activity and reduced SMC proliferation of bach1-deficient cells were not restored by Zinc (II) protoporphyrin IX, an inhibitor of HO, suggesting that HO-independent mechanisms are also involved in the regulation of phagocytosis of macrophages and proliferation of SMC by Bach1. In wild-type mice, cuff placement around femoral artery caused pronounced intimal proliferation without affecting the media, thus resulting in intimal to medial (I/M) volume ratio of 65.6%. bach1-deficient mice had less degree of intimal growth (I/M ratio of 45.6%). These results indicate that Bach1 plays a critical role in the regulation of HO-1 expression, macrophage function, SMC proliferation and neointimal formation. Bach1 may regulate gene expression in these cells during inflammation and atherogenesis.

Heme oxygenase-1 attenuates interleukin-1beta-induced nitric oxide synthase expression in vascular smooth muscle cells

Heme oxygenase-1 (HO-1) has been implicated in antioxidant and anti-inflammatory actions. To characterize the role of HO-1 in the vascular inflammatory response, we examined the effect of HO-1 on the expression of inducible nitric oxide synthase (iNOS) induced by interleukin-1beta (IL-1beta) in rat vascular smooth muscle cells (VSMCs). Western blot analysis demonstrated that IL-1beta-induced iNOS expression was significantly reduced by hemin cotreatment or adenovirus-mediated HO-1 gene transfer. Scavenging carbon monoxide (CO), one of the by-products of heme degradation by HO-1, significantly attenuated HO-1-mediated suppression of iNOS gene induction as revealed by Northern blot analysis. Exposure of cells to CO or a CO donor, the tricarbonyldichlororuthenium(II) dimer, also markedly inhibited IL-1beta-induced iNOS expression. Transient transfection experiments with a reporter gene construct carrying the rat iNOS gene promoter demonstrated that IL-1beta-induced promoter activity was substantially reduced by cotreatment with CO or a CO donor. Furthermore, the effects of CO on iNOS gene promoter activity and protein expression were diminished by cotreatment with the specific guanylate cyclase inhibitor, 1H-[1,2,4]oxadiazolo-(4,3-a)quinoxalin-1-one. These data support the finding that HO-1 attenuates IL-1beta-induced iNOS gene expression in VSMCs. CO appears to mediate the suppressive effect of HO-1, at least in part, through downregulating transcriptional activation of the iNOS gene via a cGMP-dependent pathway.

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

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

Thymidine phosphorylase gene transfer inhibits vascular smooth muscle cell proliferation by upregulating heme oxygenase-1 and p27KIP1

OBJECTIVE

Thymidine phosphorylase (TP) reportedly promotes endothelial cell migration and induces heme oxygenase (HO)-1 expression. However, its effect on vascular smooth muscle cells (VSMCs) is poorly understood. In this study, we examined the effect of TP on VSMCs in vitro and in vivo.

METHODS AND RESULTS

Phagemid vector encoding human TP gene was transfected into rat VSMCs, and a clone overexpressing TP was selected (C2). C2 showed a slower migration and proliferation than VSMCs cloned with empty vector (pC) under basal, serum-stimulated, and hypoxic conditions. This decrease in proliferation correlated with TP-induced HO-1 expression and was reversed by inhibitors of either TP or HO activity. Furthermore, in C2, the cyclin-dependent kinase inhibitor (p27KIP1) was much more abundant than in pC, and the cell cycle was arrested at the G1 phase. TP or HO activity inhibitors decreased p27(KIP1) expression in C2 to the level seen in pC. Adventitial TP gene delivery significantly reduced neointimal VSMC migration and neointima formation in balloon-injured rat carotid arteries.

CONCLUSIONS

TP overexpression upregulated HO-1 expression and consequently increased p27(KIP1) in cultured VSMCs, and inhibited VSMC migration and proliferation in vitro and in vivo. TP represents a promising target for treating vascular obstructive disease.

Development of vascular biology over the past 10 years: heme oxygenase-1 in cardiovascular homeostasis

The study of vascular biology has provided strong evidence for the role that free radical attack plays in the pathogenesis of cardiovascular diseases. The endothelial cell (EC) dysfunction that results from exposure to oxidative stresses, such as oxidized LDL, influences vascular cell gene expression, promoting smooth muscle cell (SMC) mitogenesis and apoptosis. These factors also play an important role in atherogenesis, which is attenuated by antioxidants. Thus, antioxidants are important to understanding the pathophysiology of cardiovascular diseases and to constructing an effective treatment strategy for these patients. Over the last decade, there has been a tremendous interest in the biology of heme oxygenase-1 (HO-1), which exhibits antioxidant effects in various forms of tissue injury. Moreover, the reaction is also the major source of carbon dioxide (CO) in the body, which is a physiologically important gaseous vasodilator that inhibits SMC proliferation. Thus, HO-1-derived products provide various mechanisms to maintain cardiovascular homeostasis. We review recent work on the cellular and molecular biological aspects of the HO/CO system in vascular pathophysiology.

Role of oxidative modifications in atherosclerosis

This review focuses on the role of oxidative processes in atherosclerosis and its resultant cardiovascular events. There is now a consensus that atherosclerosis represents a state of heightened oxidative stress characterized by lipid and protein oxidation in the vascular wall. The oxidative modification hypothesis of atherosclerosis predicts that low-density lipoprotein (LDL) oxidation is an early event in atherosclerosis and that oxidized LDL contributes to atherogenesis. In support of this hypothesis, oxidized LDL can support foam cell formation in vitro, the lipid in human lesions is substantially oxidized, there is evidence for the presence of oxidized LDL in vivo, oxidized LDL has a number of potentially proatherogenic activities, and several structurally unrelated antioxidants inhibit atherosclerosis in animals. An emerging consensus also underscores the importance in vascular disease of oxidative events in addition to LDL oxidation. These include the production of reactive oxygen and nitrogen species by vascular cells, as well as oxidative modifications contributing to important clinical manifestations of coronary artery disease such as endothelial dysfunction and plaque disruption. Despite these abundant data however, fundamental problems remain with implicating oxidative modification as a (requisite) pathophysiologically important cause for atherosclerosis. These include the poor performance of antioxidant strategies in limiting either atherosclerosis or cardiovascular events from atherosclerosis, and observations in animals that suggest dissociation between atherosclerosis and lipoprotein oxidation. Indeed, it remains to be established that oxidative events are a cause rather than an injurious response to atherogenesis. In this context, inflammation needs to be considered as a primary process of atherosclerosis, and oxidative stress as a secondary event. To address this issue, we have proposed an "oxidative response to inflammation" model as a means of reconciling the response-to-injury and oxidative modification hypotheses of atherosclerosis.

Effect of Smoking on Restenosis during the 1st Year after Lower-Limb Endovascular Interventions

PURPOSE

To investigate whether smoking has an effect on recurrent lumen narrowing after percutaneous transluminal angioplasty (PTA) or stent placement in lower-limb arteries.

MATERIALS AND METHODS

A total of 650 patients (median age, 70 years; 389 men) with peripheral artery disease who underwent iliac artery PTA (n = 95), iliac artery stent placement (n = 83), femoropopliteal PTA (n = 406), or femoropopliteal stent placement (n = 66) were selected from a prospective database. Patients were categorized according to their preintervention smoking habits as nonsmokers (n = 352), light smokers (one to nine cigarettes daily) (n = 54), habitual smokers (10-20 cigarettes daily) (n = 82), or heavy smokers (>20 cigarettes daily) (n = 162). Multivariate Cox proportional hazards analysis was used to determine whether there was an association between smoking habits and restenosis (> or =50%) in the treated vessel segment within 1 year after treatment.

RESULTS

Cumulative restenosis rates at 6 and 12 months according to patients' smoking habits were 99 and 190 nonsmokers, 18 and 22 light smokers, 16 and 29 habitual smokers, and 26 and 47 heavy smokers, respectively (P <.001). Adjusted hazard ratios for restenosis in smokers compared with nonsmokers were 1.51 (95% CI: 0.92, 2.50) for light smokers, 0.49 (95% CI: 0.28, 0.87) for habitual smokers, and 0.46 (95% CI: 0.30, 0.71) for heavy smokers, indicating a reduced restenosis risk in patients who smoked 10 or more cigarettes daily. These patients had reduced restenosis rates after either iliac (P =.011) or femoropopliteal intervention (P =.009). However, endovascular treatment at a younger age, coronary artery disease, and history of myocardial or cerebrovascular infarction were more frequently found in smokers.

CONCLUSION

Smoking 10 or more cigarettes daily is associated with a reduced rate of intermediate-term restenosis after lower-limb endovascular interventions.

Dysregulation of endogenous carbon monoxide and nitric oxide production in patients with advanced ischemic or nonischemic cardiomyopathy

Carbon monoxide (CO) and nitric oxide (NO) are endogenous vasoregulatory molecules whose role in heart failure is not fully known. Exhaled CO and NO measurement provide novel noninvasive assessment of their endogenous production. We compared exhaled CO and NO in 24 patients with advanced ischemic and nonischemic cardiomyopathy and in 13 control subjects without known cardiac disease at rest and at 1 and 5 minutes after exercise testing. Exhaled CO was lower in patients with cardiomyopathy at rest (1.66 +/- 0.2 vs 1.80 +/- 0.5 ppm, p = 0.02) and 1 minute after exercise (1.35 +/- 0.2 vs 1.81 +/- 0.5 ppm, p = 0.009), with a similar trend at 5 minutes after exercise (1.45 +/- 0.3 vs 1.81 +/- 0.5 ppm, p = 0.14). Exhaled CO decreased in patients with cardiomyopathy after exercise (p <0.001 and p = 0.02 at rest vs 1 and 5 minutes after exercise, respectively) but was maintained in controls. Exhaled NO did not differ between patients with cardiomyopathy and controls at rest (9.48 +/- 1.4 vs 9.68 +/- 1.5 ppb, p = NS) and after exercise (1 minute: 10.91 +/- 1.8 vs 9.19 +/- 1.2 ppb; 5 minutes: 10.52 +/- 1.5 vs 8.90 +/- 1.2 ppb, p = NS). Exhaled NO increased after exercise in patients with cardiomyopathy (p = 0.01 and p = 0.04 rest vs exercise at 1 and 5 minutes, respectively), but was maintained in controls. Exhaled CO and NO were not correlated with peak oxygen consumption in patients with cardiomyopathy. The differential responses in exhaled CO and NO at rest or with exercise between patients with cardiomyopathy and normal controls may point to dysregulation in endogenous CO and NO production.

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

Association of a promoter variant of the haeme oxygenase-1 gene with hypertension in women

OBJECTIVE

To examine the relationship between the gene for haeme oxygenase (HO)-1 (HMOX-1) and human essential hypertension, because both the acute and systemic induction of HMOX-1 have been suggested to attenuate vascular tone and blood pressure.

METHODS

We screened for sequence variations in HMOX-1 and conducted an association study, using these polymorphisms, in a large cohort (1998 individuals) representing the general Japanese population. RESULTS We sequenced HMOX-1 and found a T(-413)A polymorphism in the promoter region. The frequency of hypertensive individuals and the use of antihypertensive drugs were significantly greater in the AA genotype than in other genotypes among women: 45.5, 34.2, and 35.0% (P = 0.0099) and 23.4, 17.5, and 15.0% (P = 0.038), respectively, for the AA, AT, and TT genotypes, respectively. However, this association was not observed in men. Multiple logistic analyses indicated that the T(-413)A (AA/TA+TT) polymorphism, age, and body mass index affected the occurrence of hypertension in women. The odds ratio of the AA genotype for hypertension in women was 1.59 (P = 0.0058; 95% confidence interval 1.14 to 2.20). A luciferase reporter assay indicated that the A allele-promoter had eight-fold greater activity than the T allele promoter (P < 0.01).

CONCLUSIONS

The AA genotype of HMOX-1 is associated with an increased incidence of hypertension in women. Oestrogen attenuates vasoconstriction by increasing the expression of inducible nitric oxide synthase. As carbon monoxide, which is one of the products of HO-1, can attenuate nitric oxide-induced vasodilatation, a high expression of HO-1 may cause hypertension, especially in women.

Heme oxygenase-1 in growth control and its clinical application to vascular disease

Heme oxygenase-1 (HO-1) catalyzes the degradation of heme to carbon monoxide (CO), iron, and biliverdin. Biliverdin is subsequently metabolized to bilirubin by the enzyme biliverdin reductase. Although interest in HO-1 originally centered on its heme-degrading function, recent findings indicate that HO-1 exerts other biologically important actions. Emerging evidence suggests that HO-1 plays a critical role in growth regulation. Deletion of the HO-1 gene or inhibition of HO-1 activity results in growth retardation and impaired fetal development, whereas HO-1 overexpression increases body size. Although the mechanisms responsible for the growth promoting properties of HO-1 are not well established, HO-1 can indirectly influence growth by regulating the synthesis of growth factors and by modulating the delivery of oxygen or nutrients to specific target tissues. In addition, HO-1 exerts important effects on critical determinants of tissue size, including cell proliferation, apoptosis, and hypertrophy. However, the actions of HO-1 are highly variable and may reflect a role for HO-1 in maintaining tissue homeostasis. Considerable evidence supports a crucial role for HO-1 in blocking the growth of vascular smooth muscle cells (SMCs). This antiproliferative effect of HO-1 is mediated primarily via the release of CO, which inhibits vascular SMC growth via multiple pathways. Pharmacologic or genetic approaches targeting HO-1 or CO to the blood vessel wall may represent a promising, novel therapeutic approach in treating vascular proliferative disorders.

Induction of heme oxygenase-1 and stimulation of cGMP production by hemin in aortic tissues from hypertensive rats

Heme oxygenase (HO) and carbon monoxide (CO) have been implicated in the modulation of various cardiovascular functions including blood pressure (BP) regulation. Up-regulating the HO/CO system lowers BP in young (8-week-old) but not in adult (20-week-old) spontaneously hypertensive rats (SHRs). The mechanisms for this selective effect are largely unknown. We investigated the effects of HO-1 inducer, hemin, on the HO/CO-soluble gyanylyl cyclase (sGC)/cGMP system in the aorta of prehypertensive (4-week-old) young and adult SHRs as well as age-matched Wistar-Kyoto rats (WKYs). Reduced expressions of HO-1, HO-2, and sGC proteins associated with depressed HO activity and cGMP levels were detected in young SHRs. These deficiencies were significantly reversed by hemin treatment. Macrophage infiltration of vascular tissues was more significant in adult SHRs than adult WKYs, but invisible in young SHRs and WKYs. Hemin treatment did not alter macrophage infiltration of vascular tissues in young SHRs. The same hemin administration resulted in a significant decrease in BP (from 148.6 +/- 3.2 to 125.8 +/- 2.6 mmHg, P <.01) in young SHRs, but not in prehypertensive or adult SHRs or WKYs of all ages. The HO inhibitor zinc protoporphyrin abrogated the hemin effect in young SHRs. Aortic tissues became desensitized to YC-1, an activator sGC, in adult SHRs. Thus, in young SHRs the expression and function of the HO/CO-sGC/cGMP system were suppressed, constituting a pathogenic mechanism for the development of hypertension. In adult SHRs, the HO/CO-sGC/cGMP system appeared normal, but desensitization of the sGC/cGMP pathway caused hypertension to prevail.

Rapamycin induces heme oxygenase-1 in human pulmonary vascular cells: implications in the antiproliferative response to rapamycin

BACKGROUND

Rapamycin is an immunosuppressive agent with antiproliferative properties against not only lymphocytes but also vascular endothelial and smooth muscle cells, and it reduces the fibroproliferative response to vascular injury. Heme oxygenase-1 (HO-1) has also been shown to have graft protective effects and to inhibit vascular remodeling. In this study, we evaluated whether there is an interaction between rapamycin and HO-1.

METHODS AND RESULTS

In human pulmonary artery endothelial or smooth muscle cells, HO-1 expression was evaluated in response to rapamycin or wortmannin, an inhibitor of the upstream modulator of mammalian target of rapamycin (mTOR) PI-3K. We also evaluated whether the inhibitory actions of rapamycin on platelet-derived growth factor-dependent proliferation was mediated by HO using the chemical inhibitor tin protoporphyrin. Rapamycin induced HO-1 expression in both pulmonary endothelial and smooth muscle cells, whereas no to little increase was seen in response to another immunosuppressive agent, cyclosporin A. HO-1 expression was also increased in response to wortmannin, suggesting that the PI-3K-mTOR pathway is required for this induction. Inhibition of HO activity resulted in a loss of the antiproliferative activity of rapamycin in growth factor-stimulated smooth muscle cells.

CONCLUSIONS

The induction of HO-1 expression by rapamycin and, more importantly, the effects of tin protoporphyrin, an inhibitor of HO activity, on the antiproliferative actions of rapamycin suggest that the effects of rapamycin may be, at least in part, modulated by its actions on HO-1.

Heme oxygenase-1 system in organ transplantation

The heme oxygenase-1 (HO-1) system, the rate-limiting step in the conversion of heme, is among the most critical of cytoprotective mechanisms activated during cellular stress. The cytoprotection may result from the elimination of heme and the function of HO-1 downstream mediators, that is, biliverdin, carbon monoxide, and free iron. HO-1 overexpression exerts beneficial effects in a number of transplantation models, including antigen-independent ischemia/reperfusion injury, acute and chronic allograft rejection, and xenotransplantation. The HO-1 system is thought to exert four major functions: (1) antioxidant function; (2) maintenance of microcirculation; (3) modulatory function upon the cell cycle; and (4) anti-inflammatory function. The antioxidant function depends on heme degradation, oxygen consumption, biliverdin, and production of ferritin via iron accumulation. The production of carbon monoxide, which has vasodilation and antiplatelet aggregation properties, maintains tissue microcirculation and may be instrumental in antiapoptotic and cell arrest mechanisms. Heme catabolism and HO-1 overexpression exert profound direct and indirect inhibitory effects on the cascade of host inflammatory responses mediated by neutrophils, macrophages, and lymphocytes. These anti-inflammatory properties result in cytoprotection in a broad spectrum of graft injury experimental models, including ischemia/reperfusion, acute and chronic allograft, and xenotransplant rejection. Further, the multifaceted targets of HO-1-mediated cytoprotection may simultaneously benefit both local graft function and host systemic immune responses. Thus, the HO-1 system serves as a novel therapeutic concept in organ transplantation.

Heme oxygenase-1: redox regulation and role in the hepatic response to oxidative stress

Heme oxygenase (HO) catalyzes the oxidative cleavage of the alpha-mesocarbon of Fe-protoporphyrin-IX yielding equimolar amounts of biliverdin-IXalpha, free divalent iron, and carbon monoxide (CO). Among the three isoenzymes cloned to date, only HO-1 can be induced by a variety of seemingly disparate stimuli, most of which are linked by their ability to provoke oxidative stress. Although constitutive expression of HO-1 in the liver is restricted to Kupffer cells, the gene is inducible in nonparenchymal as well as in parenchymal liver cells. HO-1 induction potentially confers protection against oxidative stress in a variety of experimental models, such as liver ischemia/reperfusion secondary to transplantation or hemorrhage/resuscitation. Induction of HO-1 may protect the cell against oxidative injury by (a) controlling intracellular levels of "free" heme (a prooxidant), (b) producing biliverdin (an antioxidant), (c) improving nutritive perfusion via CO release, and (d) fostering the synthesis of the Fe-binding protein ferritin. Although protective effects of up-regulation of the HO pathway--presumably through production of bile pigments and CO--have been reported for a variety of cells and tissues, including the liver, evidence suggests that the protective action might be restricted to a rather narrow threshold of overexpression. High levels of HO-1 may even sensitize the cell to oxidative stress, e.g., through release of reactive iron. Transcriptional activation of the HO-1 gene is an integral part of the cellular response to oxidative stress, but its induction seems to be neither exclusively cytoprotective nor exclusively cytotoxic.

Differential effect of heme oxygenase-1 in endothelial and smooth muscle cell cycle progression

Arterial remodeling in response to pathological insult is a complex process that depends in part on the balance between vascular cell apoptosis and proliferation. Studies in experimental models suggest that HO-1 mediates neointimal formation while limiting lumen stenosing, indicating a differential effect on vascular endothelial (EC) and smooth muscle cells (SMC). We investigated the effect of HO-1 expression on cell cycle progression in EC and SMC. The addition of SnMP (10 microM), an inhibitor of HO activity, to EC or SMC for 24h, resulted in significant abnormalities in DNA distribution and cell cycle progression compared to cells treated with the HO-1 inducers, heme (10 microM) or SnCl(2) (10 microM). SnMP increased G(1) phase and decreased S and G(2)/M phases in EC while heme or SnCl(2) decreased G(1) phase, but increased S and G(2)/M phases (p<0.05). Opposite effects were obtained in SMC. SnMP decreased G(1) phase and increased S and G(2)/M phases while heme or SnCl(2) increased G(1) phase but decreased S and G(2)/M phases (p<0.05). Our data demonstrate that HO-1 regulates the cell cycle in a cell-specific manner; it increases EC but decreases SMC cycle progression. The mechanisms underlying the HO-1 cell-specific effect on cell cycle progression within the vascular wall are yet to be explored. Nevertheless, these findings suggest that cell-specific targeting of HO-1 expression may provide a novel therapeutic strategy for the treatment of cardiovascular diseases.

Selective regulation of blood pressure by heme oxygenase-1 in hypertension

Heme oxygenase (HO) and carbon monoxide (CO) participate in the homeostatic control of cardiovascular functions, including the regulation of blood pressure (BP). Upregulation of the HO/CO system has been shown to lower BP in young (8 weeks) but not in adult (20 weeks) spontaneously hypertensive rats (SHR). The underlying mechanism for this selective effect, however, has been unknown and was investigated in the present study. The administration of hemin resulted in a marked decrease in BP (from 148.6+/-3.2 to 125.8+/-2.6 mm Hg, P<0.01) in young but not in prehypertensive (4 weeks) or adult SHR or Wistar-Kyoto rats at all ages. The inhibition of HO with chromium mesoporphyrin abrogated the BP-lowering effect of hemin. Significantly lower expression levels of HO-1 and soluble gyanylyl cyclase (sGC) as well as reduced cGMP content were detected in 8-week SHR but not in adult SHR or Wistar-Kyoto rats of all ages. These deficiencies were all corrected by hemin treatment. The expression of HO-2 protein was not different among all animal groups tested and not affected by hemin treatment. Desensitization of the sGC/cGMP pathway in adult SHR was demonstrated by the reduced vasorelaxant potency of the sGC activator 3-(5' -hydroxymethyl-2-'furyl)-1-benzylindazole. Thus, in young and prehypertensive SHR, a defective HO/CO-sGC/cGMP system might constitute a pathogenic mechanism for the development of hypertension. The HO/CO-sGC/cGMP system appears normal in adult SHR, but desensitization of the downstream targets of the system to sGC/cGMP may endow SHR at this stage a persistent hypertension status.

Gene transfer of heme oxygenase-1 and carbon monoxide delivery inhibit chronic rejection

The hallmark of chronic rejection is the occlusion of the artery lumen by intima hyperplasia as a consequence of leukocyte infiltration and vascular smooth muscle cell (VSMC) migration and proliferation. Heme oxygenase-1 (HO-1) is a tissue protective molecule which degrades heme into carbon monoxide (CO), free iron and biliverdin. We analyzed the effects of HO-1 gene transfer into the vessel wall using an adenoviral vector (AdHO-1) and of CO delivery in a model of chronic allogeneic aorta rejection in rats. Carbon monoxide treatment was achieved by a new pharmacological approach in transplantation using methylene chloride (MC), which releases CO after degradation. AdHO-1-mediated gene transfer into aorta endothelial cells (ECs) or CO delivery resulted in a significant reduction in intimal thickness compared to untreated or noncoding adenovirus-treated controls. Aortas transduced with AdHO-1 or treated with CO showed a reduction in the number of leukocytes as well as in the expression of adhesion molecules, costimulatory molecules and cytokines, with the gene transfer treatment displaying a more pronounced effect than the CO treatment. Conversely, CO inhibited VSMC accumulation in the intima more efficiently than AdHO-1 treatment. Gene transfer of HO-1 and pharmacological manipulation of CO are novel approaches to the analysis and treatment of chronic rejection.

Carbon monoxide and bile pigments: surprising mediators of vascular function

Heme oxygenase (HO) catalyzes the degradation of heme to CO, iron, and biliverdin. Biliverdin is subsequently metabolized to bilirubin by the enzyme biliverdin reductase. Although long considered irrelevant byproducts of heme catabolism, recent studies indicate that CO and the bile pigments biliverdin and bilirubin may play an important physiological role in the circulation. The release of CO by vascular cells may modulate blood flow and blood fluidity by inhibiting vasomotor tone, smooth muscle cell proliferation, and platelet aggregation. CO may also maintain the integrity of the vessel wall by directly blocking vascular cell apoptosis and by inhibiting the release of pro-apoptotic inflammatory cytokines from the vessel wall. These effects of CO are mediated via multiple pathways, including activation of soluble guanylate cyclase, potassium channels, p38 mitogen-activated protein kinase, or inhibition of cytochrome P450. In addition, the release of bile pigments may serve to sustain vascular homeostasis by protecting vascular cells from oxidative stress and by inhibiting the adhesion and infiltration of leukocytes into the vessel wall. Induction of HO-1 gene expression and the subsequent release of CO and bile pigments are observed in numerous vascular disorders and may provide an important adaptive mechanism to preserve homeostasis at sites of vascular injury. Thus, the HO-catalyzed formation of CO and bile pigments by vascular cells may function as a critical endogenous vasoprotective system. Moreover, pharmacological or genetic approaches targeting HO-1 to the vessel wall may represent a novel therapeutic approach in treating vascular disease.

Heme oxygenase-1 genotype is a vascular anti-inflammatory factor following balloon angioplasty

PURPOSE

To investigate the association of the heme oxygenase-1 (HO-1) genotype, which has potent anti-inflammatory capability, and the inflammatory response induced by balloon angioplasty.

METHODS

Three hundred seventeen patients (188 men; median age 70 years, range 57-77) undergoing femoropopliteal balloon angioplasty (n=150) or stenting (n=61) were evaluated for upregulation of the HO-1 genotype; 106 patients undergoing lower limb angiography served as controls. The acute phase reactants C-reactive protein (CRP), serum amyloid A (SAA), and fibrinogen were measured 24 and 48 hours postintervention and compared to baseline values. An association of the relative increase (Delta, %) of these inflammatory markers with short (<25) (GT)(n) dinucleotide repeats in the HO-1 gene promoter was assessed.

RESULTS

The HO-1 genotype was significantly associated with Delta CRP(24) (p<0.0001), Delta CRP(48) (p<0.0001), Delta SAA(24) (p=0.02), and Delta SAA(48) (p=0.006) after balloon angioplasty; Delta fibrinogen showed no association. Patients with a higher Delta CRP(48) after balloon angioplasty exhibited significantly reduced odds for the presence of short (<25) (GT)(n) repeats. The adjusted odds reduction in the multivariate model was 80% (p=0.002) in the third quartile of Delta CRP(48) values and 90% (p=0.001) in the fourth quartile. No association of HO-1 genotype and inflammatory response was found 24 and 48 hours after stenting (p=0.3, p=0.5) or angiography (p=0.2, p=0.6).

CONCLUSIONS

The HO-1 promoter genotype is independently associated with the inflammatory response seen after balloon angioplasty. Short alleles (<25 GT repeats) seem to be an intrinsic vascular anti-inflammatory factor.

Heme oxygenase-1: the "emerging molecule" has arrived

Organisms on our planet have evolved in an oxidizing environment that is intrinsically inimical to life, and cells have been forced to devise means of protecting themselves. One of the defenses used most widely in nature is the enzyme heme oxygenase-1 (HO-1). This enzyme performs the seemingly lackluster function of catabolizing heme to generate bilirubin, carbon monoxide, and free iron. Remarkably, however, the activity of this enzyme results in profound changes in cells' abilities to protect themselves against oxidative injury. HO-1 has been shown to have anti-inflammatory, antiapoptotic, and antiproliferative effects, and it is now known to have salutary effects in diseases as diverse as atherosclerosis and sepsis. The mechanism by which HO-1 confers its protective effect is as yet poorly understood, but this area of invetsigation is active and rapidly evolving. This review highlights current information on the function of HO-1 and its relevance to specific pulmonary and cardiovascular diseases.

Inhibition of graft arteriosclerosis development in rat aortas following heme oxygenase-1 gene transfer

Heme oxygenase 1 (HO-1) is an enzyme which degrades heme into tree end products: biliverdin, free iron and carbon monoxide. This enzyme has recently been shown to have anti-inflammatory and tissue protective effects. HO-1 expression is involved in organ protection in pathological situations, and immunosuppressive treatments resulting in indefinite graft survival without chronic rejection have been associated with HO-1 expression by cells of the vessel wall. The aim of this study was to analyze the effect of specific HO-1 overexpression. We used a recombinant adenovirus coding for human HO-1 cDNA in a rat aorta chronic rejection model, 30 days after transplantation. Control groups included rats non treated or treated with a non-coding adenovirus Addl324. We first demonstrated that AdHO-1 was efficiently expressed in endothelial cells in vitro, and in rat aortas ex vivo after adenovirus gene transfer. We found that intimal thickening in AdHO-1 treated aortas (10.8 +/- 3.8%, n=5) was significantly decreased compared to untreated (21.2 +/- 5.6%, n = 5) or Addl324-treated (21.1 +/- 1.2%, n = 4) aortas. Immunohistology showed that treatment with AdHO-1 resulted in a significant reduction in leukocyte infiltration and a decreasing number of VSMC in the intima, compared to Addl324-treated aortas. However, this effect of HO-1 on chronic rejection did not imply modifications on numbers of apoptotic cells in the graft or of alloantibody levels. We have demonstrated, for the first time, that specific HO-1 overexpression following gene transfer of HO-1 inhibited chronic rejection by reducing leukocyte and VSMC infiltration of the aorta intima.

A novel strategy against ischemia and reperfusion injury: cytoprotection with heme oxygenase system

Much interest has recently been focused on the physiological/pathological role of the heme oxygenase (HO) system, the rate-limiting step in the conversion of heme, in inflammatory events. The HO system may be instrumental in mediating a number of cytoprotective effects, because of its end products, biliverdin, carbon monoxide (CO) and ferrous free iron (Fe2+). As each of the byproducts acts dependently and/or co-operatively with each other, their in vivo effects are complex. In general, the HO system is thought to exert three major functions in ischemia/reperfusion injury: (1) anti-oxidant effects; (2) maintenance of microcirculation; and (3) modulatory effects upon the cell cycle. The anti-oxidant functions depend on heme degradation, oxygen consumption and the production of biliverdin/ferritin via iron accumulation. On the other hand, the production of CO, which has vasodilatory and anti-platelet aggregative properties, can maintain tissue microcirculation. Strikingly, CO may also be instrumental in anti-apoptotic and cell arrest mechanisms. The HO system prevents early injury in the re-perfused organ, and inhibits the function of immune reactive cells, such as neutrophils, macrophages and lymphocytes. The role of the HO system as a novel strategy to mitigate an antigen-independent ischemia/reperfusion injury has been documented in a number of transplantation models.

Adenovirus-mediated heme oxygenase-1 gene expression stimulates apoptosis in vascular smooth muscle cells

BACKGROUND

Heme oxygenase-1 (HO-1) catalyzes the degradation of heme into biliverdin, iron, and carbon monoxide (CO). Although HO-1 is induced in vascular smooth muscle cells (SMCs), the biological role of HO-1 in these cells has not been completely characterized.

METHODS AND RESULTS

In the present study, we overexpressed HO-1 in rat aortic SMCs by generating a recombinant defective adenovirus containing the rat HO-1 gene (AdHO-1) and examined the effect on SMC proliferation. Infection of SMCs with AdHO-1 resulted in a dose-dependent increase in the expression of HO-1 mRNA, protein, and activity. Infection of SMCs with AdHO-1 inhibited serum-stimulated SMC proliferation in a dose-dependent manner. In contrast, the control adenovirus expressing the green fluorescent protein failed to induce HO-1 expression and had minimal effects on SMC growth. Infection with AdHO-1 stimulated SMC apoptosis in a dose-dependent fashion, as demonstrated by DNA fragmentation, positive annexin V labeling, and caspase-3 activation. HO-1-mediated apoptosis was associated with a marked increase in the expression of the proapoptotic protein p53. Finally, the exogenous administration of biliverdin and bilirubin stimulated SMC apoptosis. In contrast, the administration of CO or iron failed to induce cell death.

CONCLUSIONS

These results demonstrate that overexpression of HO-1 or the exogenous administration of biliverdin or bilirubin stimulates SMC apoptosis. Adenovirus-mediated transfer of the HO-1 gene may provide a novel therapeutic approach in treating occlusive vascular disease.

Adenovirus-mediated heme oxygenase-1 gene delivery inhibits injury-induced vascular neointima formation

BACKGROUND

Recent studies have demonstrated that systemic pharmacological induction of heme oxygenase-1 (HO-1), the inducible isoform of the initial and rate-limiting enzyme for heme catabolism, attenuates neointima formation after experimental vascular injury. We have now investigated the ability of localized adenovirus-mediated HO-1 (Ad-HO-1) gene delivery to modify arterial remodeling after balloon angioplasty.

METHODS AND RESULTS

Two weeks after balloon angioplasty in the rat carotid artery, elevated HO-1 protein was observed in the Ad-HO-1 arteries compared with those exposed to empty adenovirus (Ad-E) or to PBS. The arteries exposed to Ad-HO-1 exhibited significantly reduced neointimal area, medial wall area, neointimal area/medial wall area ratio, and neointimal thickness compared with arteries exposed to Ad-E. The Ad-E vessels showed subtle reductions in each morphometric parameter compared with PBS vessels. In a separate group of animals, concomitant treatment of Ad-HO-1 with the HO-1 inhibitor tin protoporphyrin completely restored each morphometric parameter to control levels. Arteries exposed to Ad-HO-1 demonstrated significantly increased TUNEL labeling of apoptotic nuclei and significantly decreased PCNA labeling of DNA synthesis in the medial wall 48 hours after injury.

CONCLUSIONS

These results indicate that HO-1 represents an important in vivo vasoprotective mediator that is capable of attenuating the pathophysiological remodeling response to endovascular injury and suggest that HO-1 may be a novel target for the treatment of vascular disease.

Heme oxygenase-1 gene promoter microsatellite polymorphism is associated with restenosis after percutaneous transluminal angioplasty

PURPOSE

To determine if an association exists between postdilation restenosis and heme oxygenase-1 (HO-1), which is induced by balloon injury and inhibits neointimal formation through the action of endogenous carbon monoxide. A dinucleotide repeat in the promoter region of the HO-1 gene shows a length polymorphism that modulates the level of gene transcription.

METHODS

This cohort study included 96 consecutive patients (64 men; median age 69 years, interquartile range 60-75) who underwent successful balloon dilation in the femoropopliteal segment. Six-month patency was evaluated using oscillography, ankle-brachial index, and duplex sonography. The association of patency and the length of (GT) repeats in the HO-1 gene promoter was assessed in univariate and multivariate analyses.

RESULTS

Restenosis was found in 23 (24%) patients within the first 6 months. Patients with short (<25 GT) dinucleotide repeats in the HO-1 gene promoter on either allele had restenosis significantly less often than patients with longer (> or = 25 GT) dinucleotide repeats (p = 0.01). Multivariate analysis revealed a significantly reduced risk for restenosis in these patients compared to patients without the short allele (odds ratio 0.2, 95% Cl 0.06 to 0.70, p = 0.007).

CONCLUSIONS

Genetic risk factors for restenosis after percutaneous transluminal angioplasty have not been investigated. In this patient population, short repeat alleles of the heme oxygenase-1 gene promoter polymorphism were associated with reduced postdilation restenosis at 6 months. Upregulation of HO-1 may be an important protective factor after balloon angioplasty by inhibition of vascular smooth muscle cell proliferation.

Vascular smooth muscle cell-directed overexpression of heme oxygenase-1 elevates blood pressure through attenuation of nitric oxide-induced vasodilation in mice

To elucidate pathophysiological roles of heme oxygenase (HO)-1 in regulation of vascular tone in vivo, we have developed and characterized transgenic (Tg) mice that overexpress HO-1 site specifically in vascular smooth muscle cells (VSMCs). The Tg mice were generated by use of human HO-1 cDNA under the control of SM22-alpha promoter. The HO-1 gene overexpression was demonstrated by Northern blot analysis and coincided with increases in the protein expression in VSMCs and total HO activities. Tg mice exhibited a significant increase in arterial pressure at various ages and displayed impaired nitrovasodilatory responses in isolated aortic segments versus nontransgenic littermates while enhancing their nitric oxide (NO) production. The pressure of Tg mice was unchanged by systemic administration of either N(omega)-nitro-L-arginine or SNP. Furthermore, the isolated aorta in these mice exhibited lesser extents of NO-elicited cGMP elevation via soluble guanylate cyclase (sGC), while exhibiting no notable downregulation of sGC expression. Such impairment of the NO-elicited cGMP increase was restored significantly by tin protoporphyrin IX, an HO inhibitor. On the other hand, 3-(5'-hydroxymethyl-2' furyl)-1-benzyl-indazol (YC-1), an NO-independent activator of sGC, increased cGMP and relaxed aortas from Tg mice to levels comparable with those from nontransgenic mice, which indicates that contents of functionally intact sGC are unlikely to differ between the two systems. These findings suggest that site-specific overexpression of HO-1 in VSMCs suppresses vasodilatory response to NO and thereby leads to an elevation of arterial pressure.

Enhancement of glomerular heme oxygenase-1 expression in diabetic rats

An increase in oxidative stress in diabetic subjects is implicated to play a pivotal role in diabetic vascular complications. In response to oxidative stress, antioxidant enzymes are considered to be induced and protect cellular functions to keep in vivo homeostasis. However, it remains to be clarified whether antioxidant enzymes are induced against oxidative stress especially in renal glomeruli at an early stage of diabetes. To answer this question, we examined the gene expression of a variety of antioxidant enzymes in glomeruli isolated from streptozotocin-induced diabetic rats. The mRNA expression of antioxidant enzymes such as catalase, glutathione peroxidase, and CuZn-superoxide dismutase, was unaltered in glomeruli of diabetic rats and was comparable to control rats. In contrast, the mRNA expression of heme oxygenase-1 (HO-1) was enhanced in glomeruli of diabetic rats as compared with control rats. A treatment with insulin as well as with vitamin E (40 mg/kg body weight every other day, intra-peritoneal injection) normalized the mRNA expression of HO-1 in the glomeruli of diabetic rats. Immunohistochemical analysis revealed that the up-regulated expression of HO-1 protein was localized in glomerular cells of diabetic rats. In conclusion, these results provide the first evidence that among antioxidant enzymes HO-1 expression is preferentially increased in diabetic glomeruli.

Heme oxygenase-1 inhibits atherosclerotic lesion formation in ldl-receptor knockout mice

Heme oxygenase-1 (HO-1) is induced by a variety of conditions associated with oxidative stress. We demonstrated that mildly oxidized LDL markedly induces HO-1 in human aortic endothelial and smooth muscle cell cocultures and that its induction results in the attenuation of monocyte chemotaxis resulting from treatment with mildly oxidized LDL in vitro. To elucidate the role of HO-1 in the development of atherosclerotic lesions in vivo, we modulated HO-1 expression in LDL-receptor knockout mice fed high-fat diets. During 6-week high-fat diet trials, intraperitoneal injections of hemin (H group) or hemin and desferrioxamine (HD group) to induce HO-1, Sn-protoporphyrin IX to inhibit HO-1 (Sn group), and saline as control (C group) were performed. Both the H and HD groups showed significantly less mean atherosclerotic lesions in the proximal aorta compared with the C group, whereas the Sn group showed larger lesion compared with the C group. Modulation of HO expression and HO activities were confirmed by Northern blot analysis and HO activity assay. Immunohistochemical studies revealed significant HO-1 expression in atherosclerotic lesions, where oxidized phospholipids also localized. Major cell types expressing HO-1 were macrophages and foam cells in the lesions. HO modulations affected plasma lipid hydroperoxide (LPO) levels and nitrite/nitrate levels. These results suggest that HO-1, induced under hyperlipidemia, functioned as an intrinsic protective factor against atherosclerotic lesion formation, possibly by inhibiting lipid peroxidation and influencing the nitric oxide pathway.

Cigarette smoking, endothelial injury and cardiovascular disease

Despite the fact that the epidemiological evidence linking cigarette smoking with cardiovascular disease is overwhelming, the precise components of cigarette smoke responsible for this relationship and the mechanisms by which they exert their effect have not yet been elucidated. There are however, some promising pointers as a result of recent developments and this review concentrates on new evidence since earlier reviews of this topic. It is now known that the endothelium has a vastly more important role than was ever thought to be the case a decade ago. Its role in health and disease is increasingly understood, as is the relationship between endothelial injury and the development of atherosclerosis. There is considerable evidence that cigarette smoking can result in both morphological and biochemical disturbances to the endothelium both in vivo and in cell culture systems. Cigarette smoke is a complex mixture and only a few components have been extensively studied. Nicotine and carbon monoxide are much less damaging than is whole smoke. However the free radical components of cigarette smoke have been shown to cause damage in model systems. Further work will be necessary to consolidate the evidence base but the data reported in this review suggest that the free radical components of cigarette smoke may be responsible for the morphological and functional damage to endothelium that has been observed in model systems.