Heme oxygenase inhibitor restores arteriolar nitric oxide function in dahl rats

Therapeutic potential of carbon monoxide in hypertension-induced vascular smooth muscle cell damage revisited: from physiology and pharmacology

As a chronic and progressive disorder, hypertension remains to be a serious public health problem around the world. Among the different types of hypertension, pulmonary arterial hypertension (PAH) is a devastating disease associated with pulmonary arteriole remodeling, right ventricular failure and death. The contemporary management of systemic hypertension and PAH has substantially grown since more therapeutic targets and/or agents have been developed. Evolving treatment strategies targeting the vascular remodeling lead to improving outcomes in patients with hypertension, nevertheless, significant advancement opportunities for developing better antihypertensive drugs remain. Carbon monoxide (CO), an active endogenous gasotransmitter along with hydrogen sulfide (H₂S) and nitric oxide (NO), is primarily generated by heme oxygenase (HO). Cumulative evidence suggests that CO is considered as an important signaling molecule under both physiological and pathological conditions. Studies have shown that CO confers a number of biological and pharmacological properties, especially its involvement in the pathological process and treatment of hypertension-related vascular remodeling. This review will critically outline the roles of CO in hypertension-associated vascular remodeling and discuss the underlying mechanisms for the protective effects of CO against hypertension and vascular remodeling. In addition, we will propose the challenges and perspectives of CO in hypertensive vascular remodeling. It is expected that a comprehensive understanding of CO in the vasculature might be essential to translate CO to be a novel pharmacological agent for hypertension-induced vascular remodeling.

Involvement of the Heme Oxygenase System in the Development of Preeclampsia and as a Possible Therapeutic Target

The enzyme heme oxygenase (HO) is an important regulatory molecule present in most nucleated mammalian cells which functions to break down the pro-oxidant molecule heme into three products, carbon monoxide (CO), biliverdin and free iron. The HO system has been associated with many physiologic functions, including vascular tone, regulation of inflammation and apoptosis, angiogenesis and antioxidant capabilities. Deficiencies in HO are associated with several pregnancy disorders, including preeclampsia. With no present cure, this disorder continues to affect 5–7% of all pregnancies worldwide, leading to maternal and fetal morbidity and mortality. Researchers continue to strive for therapeutic potentials and this review will outline the possible use of the HO/CO system as a target treatment/prevention of preeclampsia in the future.

Gas what: NO is not the only answer to sexual function

The ability to get and keep an erection is important to men for several reasons and the inability is known as erectile dysfunction (ED). ED has started to be accepted as an early indicator of systemic endothelial dysfunction and subsequently of cardiovascular diseases. The role of NO in endothelial relaxation and erectile function is well accepted. The discovery of NO as a small signalling gasotransmitter led to the investigation of the role of other endogenously derived gases, carbon monoxide (CO) and hydrogen sulphide (H2 S) in physiological and pathophysiological conditions. The role of NO and CO in sexual function and dysfunction has been investigated more extensively and, recently, the involvement of H2 S in erectile function has also been confirmed. In this review, we focus on the role of these three sister gasotransmitters in the physiology, pharmacology and pathophysiology of sexual function in man, specifically erectile function. We have also reviewed the role of soluble guanylyl cyclase/cGMP pathway as a common target of these gasotransmitters. Several studies have proposed alternative therapies targeting different mechanisms in addition to PDE-5 inhibition for ED treatment, since some patients do not respond to these drugs. This review highlights complementary and possible coordinated roles for these mediators and treatments targeting these gasotransmitters in erectile function/ED.

The multifunctional role and therapeutic potential of HO-1 in the vascular endothelium

SIGNIFICANCE

Heme oxygenases (HO-1 and HO-2) catalyze the degradation of the pro-oxidant heme into carbon monoxide (CO), iron, and biliverdin, which is subsequently converted to bilirubin. In the vasculature, particular interest has focused on antioxidant and anti-inflammatory properties of the inducible HO-1 isoform in the vascular endothelium. This review will present evidence that illustrates the potential therapeutic significance of HO-1 and its products, with special emphasis placed on their beneficial effects on the endothelium in vascular diseases.

RECENT ADVANCES

The understanding of the molecular basis for the regulation and functions of HO-1 has led to the identification of a variety of drugs that increase HO-1 activity in the vascular endothelium. Moreover, therapeutic delivery of HO-1 products CO, biliverdin, and bilirubin has been shown to have favorable effects, notably on endothelial cells and in animal models of vascular disease.

CRITICAL ISSUES

To date, mechanistic data identifying the downstream target genes utilized by HO-1 and its products to exert their actions remain relatively sparse. Likewise, studies in man to investigate the efficacy of therapeutics known to induce HO-1 or the consequences of the tissue-specific delivery of CO or biliverdin/bilirubin are rarely performed.

FUTURE DIRECTIONS

Based on the promising in vivo data from animal models, clinical trials to explore the safety and efficacy of the therapeutic induction of HO-1 and the delivery of its products should now be pursued further, targeting, for example, patients with severe atherosclerotic disease, ischemic limbs, restenosis injury, or at high risk of organ rejection.

Age-dependent salt hypertension in Dahl rats: fifty years of research

Fifty years ago, Lewis K. Dahl has presented a new model of salt hypertension - salt-sensitive and salt-resistant Dahl rats. Twenty years later, John P. Rapp has published the first and so far the only comprehensive review on this rat model covering numerous aspects of pathophysiology and genetics of salt hypertension. When we summarized 25 years of our own research on Dahl/Rapp rats, we have realized the need to outline principal abnormalities of this model, to show their interactions at different levels of the organism and to highlight the ontogenetic aspects of salt hypertension development. Our attention was focused on some cellular aspects (cell membrane function, ion transport, cell calcium handling), intra- and extrarenal factors affecting renal function and/or renal injury, local and systemic effects of renin-angiotensin-aldosterone system, endothelial and smooth muscle changes responsible for abnormal vascular contraction or relaxation, altered balance between various vasoconstrictor and vasodilator systems in blood pressure maintenance as well as on the central nervous and peripheral mechanisms involved in the regulation of circulatory homeostasis. We also searched for the age-dependent impact of environmental and pharmacological interventions, which modify the development of high blood pressure and/or organ damage, if they influence the salt-sensitive organism in particular critical periods of development (developmental windows). Thus, severe self-sustaining salt hypertension in young Dahl rats is characterized by pronounced dysbalance between augmented sympathetic hyperactivity and relative nitric oxide deficiency, attenuated baroreflex as well as by a major increase of residual blood pressure indicating profound remodeling of resistance vessels. Salt hypertension development in young but not in adult Dahl rats can be attenuated by preventive increase of potassium or calcium intake. On the contrary, moderate salt hypertension in adult Dahl rats is attenuated by superoxide scavenging or endothelin-A receptor blockade which do not affect salt hypertension development in young animals.

Activation of renal haeme oxygenase-1 alleviates gentamicin-induced acute nephrotoxicity in rats

Objectives

This study aimed to investigate whether activation of haeme oxygenase (HO)-1 enzyme by haemin would have beneficial effects on the functional and histological outcome against gentamicin-induced renal damage in rats and sought to elucidate the underlying mechanisms of the therapeutic action.

Methods

Nephrotoxicity was induced by injection of gentamicin (80 mg/kg, i.p.) once daily for seven days. Haemin (50 μmol/kg, i.p.) was given to the control and gentamicin-treated rats in the presence or absence of a HO-1 inhibitor, zinc protoporphyrin IX (ZnPP, 50 μmol/kg per day, i.p.).

Key findings

Haemin treatment prevented gentamicin-induced elevated serum creatinine, urinary protein levels and ameliorated the impaired creatinine clearance. Haemin compensated the deficits in antioxidant enzyme activity and attenuated lipid peroxidation along with decreased reactive oxygen species (ROS) production in renal tissues due to gentamicin. Moreover, haemin pre-administration evoked increased renal HO-1 activity. Additionally, haemin significantly attenuated elevated renal tumour necrosis factor-α (TNF-α), nuclear factor-kappaB (NF-κB) levels and caspase-3 activity alongside ameliorating glomerular pathology. These therapeutic effects were abolished by ZnPP pretreatment.

Conclusions

Here is the first evidence demonstrating the protective effect of HO-1 against gentamicin-associated nephrotoxicity. Suppression of oxidative/inflammatory insults alongside the corresponding decline of apoptosis were presumably responsible for this renoprotection.

Environmental carbon monoxide related to pregnancy hypertension

Carbon monoxide pollution frequently occurs due to auto exhaust, industrial emissions, and/or cigarette smoke. Exogenous and endogenous carbon monoxide affects blood pressure; however, the relation of carbon monoxide exposure to pregnancy hypertension has not been systematically examined. For the present study the authors recruited a total of 2,707 apparently healthy, non-obese, non-smoking mothers, aged between 15 and 40 years, who had singleton births, and who lived within two miles of the selected air monitoring stations in Tehran, Iran, to study the relation of ambient carbon monoxide to pregnancy hypertension (>140 mmHg systolic and/or >90 mmHg diastolic after the 20th week of gestation). A relatively small but statistically significant elevation in mean postpartum diastolic blood pressure (mean ± SD, 69.5 ± 9.8 mmHg) was observed in the mothers' who were exposed to relatively high ambient carbon monoxide (mean = 14.1 ppm) compared to mothers exposed to lower carbon monoxide (mean = 1.8 ppm) concentrations (mean ± SD, 68.0 ± 8.3 mmHg, p < 0.01). The authors found twice the rate of pregnancy hypertension in the relatively higher carbon monoxide exposed mothers than the mothers with lower exposure (adjusted odds ratio = 2.02, 95% CI 1.35-3.03). Findings of the present study suggest that high level ambient carbon monoxide exposure is associated with pregnancy hypertension.

Reactive Oxygen Species Modulation of Na/K-ATPase Regulates Fibrosis and Renal Proximal Tubular Sodium Handling

The Na/K-ATPase is the primary force regulating renal sodium handling and plays a key role in both ion homeostasis and blood pressure regulation. Recently, cardiotonic steroids (CTS)-mediated Na/K-ATPase signaling has been shown to regulate fibrosis, renal proximal tubule (RPT) sodium reabsorption, and experimental Dahl salt-sensitive hypertension in response to a high-salt diet. Reactive oxygen species (ROS) are an important modulator of nephron ion transport. As there is limited knowledge regarding the role of ROS-mediated fibrosis and RPT sodium reabsorption through the Na/K-ATPase, the focus of this review is to examine the possible role of ROS in the regulation of Na/K-ATPase activity, its signaling, fibrosis, and RPT sodium reabsorption.

Heme induction with delta-aminolevulinic Acid stimulates an increase in water and electrolyte excretion

Purpose. Studies were performed to examine hemodynamic and renal function before and after acute induction of the endogenous CO system with delta-aminolevulinic acid (DALA), which drives HO activity. Methods. In vivo studies were conducted on Inactin-anesthetized male Sprague Dawley rats (250–300 g) either with or without chronic pretreatment with L-NAME (50 mg/Kg, q12 hours x4d). Results. DALA (80 μmol/Kg, IV bolus) administration acutely increased endogenous CO production and HO-1 protein. In untreated and L-NAME-pretreated rats, DALA did not alter BP, GFR, or RBF but increased UF, U_NaV, and U_KV (untreated: Δ108.8 ± 0.28%, 172.1 ± 18.4%, and 165.2 ± 45.9%; pretreated: Δ109.4 ± 0.29%, 187.3 ± 26.9%, and 197.2 ± 45.7%). Acute administration of biliverdin (20 mg/kg, IV) and bilirubin (30 mg/kg, IV) to similarly treated animals did not alter UF, U_NaV, and U_KV. Conclusion. These results demonstrate that heme oxygenase induction increases urine and electrolyte excretion and suggest a direct tubular action of endogenous carbon monoxide.

Changing standard chow diet promotes vascular NOS dysfunction in Dahl S rats

We hypothesized that vascular nitric oxide synthase (NOS) function and expression is differentially regulated in adult Dahl salt-sensitive rats maintained on Teklad or American Institutes of Nutrition (AIN)-76A standard chow diets from 3 to 16 wk old. At 16 wk old, acetylcholine (ACh)-mediated vasorelaxation and phenylephrine (PE)-mediated vasoconstriction in the presence and absence of NOS inhibitor, N(ω)-nitro-L-arginine methyl ester (L-NAME), was assessed in small-resistance mesenteric arteries and aortas. Rats maintained on either diet throughout the study had similar responses to ACh and PE in the presence or absence of L-NAME in both vascular preparations. We reasoned that changing from one diet to another as adults may induce vascular NOS dysfunction. In the absence of L-NAME, small arteries from Teklad-fed rats switched to AIN-76 diet and vice versa had similar responses to ACh and PE. Small-arterial NOS function was maintained in rats switched to AIN-76A from Teklad diet, whereas NOS function in response to ACh and PE was lost in the small arteries from rats changed to Teklad from AIN-76A diet. This loss of NOS function was echoed by reduced expression of NOS3, as well as phosphorylated NOS3. The change in NOS phenotype in the small arteries was observed without changes in blood pressure. Aortic responses to ACh or PE in the presence or absence of L-NAME were similar in all diet groups. These data indicate that changing standard chow diets leads to small arterial NOS dysfunction and reduced NOS signaling, predisposing Dahl salt-sensitive rats to vascular disease.

Targeting heme oxygenase-1 in vascular disease

Heme oxygenase-1 (HO-1) metabolizes heme to generate carbon monoxide (CO), biliverdin, and iron. Biliverdin is subsequently metabolized to bilirubin by biliverdin reductase. HO-1 has recently emerged as a promising therapeutic target in the treatment of vascular disease. Pharmacological induction or gene transfer of HO-1 ameliorates vascular dysfunction in animal models of atherosclerosis, post-angioplasty restenosis, vein graft stenosis, thrombosis, myocardial infarction, and hypertension, while inhibition of HO-1 activity or gene deletion exacerbates these disorders. The vasoprotection afforded by HO-1 is largely attributable to its end products: CO and the bile pigments, biliverdin and bilirubin. These end products exert potent anti-inflammatory, antioxidant, anti-apoptotic, and anti-thrombotic actions. In addition, CO and bile pigments act to preserve vascular homeostasis at sites of arterial injury by influencing the proliferation, migration, and adhesion of vascular smooth muscle cells, endothelial cells, endothelial progenitor cells, or leukocytes. Several strategies are currently being developed to target HO-1 in vascular disease. Pharmacological induction of HO-1 by heme derivatives, dietary antioxidants, or currently available drugs, is a promising near-term approach, while HO-1 gene delivery is a long-term therapeutic goal. Direct administration of CO via inhalation or through the use of CO-releasing molecules and/or CO-sensitizing agents provides an attractive alternative approach in targeting HO-1. Furthermore, delivery of bile pigments, either alone or in combination with CO, presents another avenue for protecting against vascular disease. Since HO-1 and its products are potentially toxic, a major challenge will be to devise clinically effective therapeutic modalities that target HO-1 without causing any adverse effects.

Inhibition of heme oxygenase augments tubular sodium reabsorption

Heme oxygenase (HO) catalyzes the degradation of heme to form iron, biliverdin, and carbon monoxide (CO). The vascular actions of CO include direct vasodilation of vascular smooth muscle and indirect vasoconstriction through inhibition of nitric oxide synthase (NOS). This study was performed to examine the effects in the kidney of inhibition of heme oxygenase alone or combined with NOS inhibition. Chromium mesoporphyrin (CrMP; 45 μmol/kg ip), a photostable HO inhibitor, was given to control rats and N(G)-nitro-l-arginine methyl ester (l-NAME)-treated hypertensive rats (50 mg·kg⁻¹·day⁻¹), 12 h, 4 days). In control animals, CrMP decreased CO levels, renal HO-1 levels, urine volume, and sodium excretion, but had no effect on arterial pressure, renal blood flow (RBF), plasma renin activity (PRA), or glomerular filtration rate (GFR). In l-NAME-treated hypertensive rats, CrMP decreased endogenous CO and renal HO-1 levels and had no effect on arterial pressure, RBF, or GFR but decreased sodium and water excretion in a similar manner to control animals. An increase in PRA was observed in untreated rats but not in l-NAME-infused rats, indicating that this effect is associated with an absent NO system. The results suggest that inhibition of HO promotes water and sodium excretion by a direct tubular action that is independent of renal hemodynamics or the NO system.

Heme oxygenase regulates renal arterial resistance and sodium excretion in cirrhotic rats

BACKGROUND & AIMS

Heme oxygenase (HO) catabolizes heme into biliverdin, carbon monoxide (CO), and free iron. CO generated in endothelial and smooth muscle layers of blood vessels modulates vascular tone by inducing relaxation of vascular smooth muscle cells. The aim of this study was to verify the role played by HO in regulating renal arterial resistance and Na(+) excretion in cirrhosis.

METHODS

Twenty control rats and 20 rats with CCl(4)(-) induced cirrhosis, 10 of which were chronically treated with the HO inducer cobalt-protoporphyrin (CoPP), were studied. Pressurized renal interlobar arteries were challenged with increasing doses of phenylephrine (PE) and acetylcholine (ACh). Dose-response curves were evaluated under basal conditions and after inhibition of HO with chromium-mesoporphyrin (CrMP). HO-1 (inducible form) and HO-2 (constitutive form) expression was measured in the main and interlobar renal arteries. Serum and urinary levels of Na(+) and creatinine were also evaluated.

RESULTS

In renal interlobar arteries from cirrhotic rats, the response to PE was increased, while that to ACh was blunted. After HO inhibition, the responsiveness to these vasoactive substances was comparable in the two groups. In cirrhotic rats, HO-1 expression was impaired in the main and the interlobar renal arteries. Chronic HO induction normalized the response to the vasoconstrictor, but not to the vasodilator. Cirrhotic rats treated with CoPP showed higher urinary Na(+) concentration and fractional Na(+) excretion, compared to both untreated cirrhotic and control rats.

CONCLUSIONS

In cirrhotic rats, an impaired HO-1 expression promotes vasoconstriction of renal interlobar arteries. Chronic HO induction normalizes the sensitivity to PE and promotes Na(+) excretion.

Putative role of carbon monoxide signaling pathway in penile erectile function

INTRODUCTION

Erectile response depends on nitric oxide (NO) generated by NO synthase (NOS) enzyme of the nerves and vascular endothelium in the cavernous tissue. NO activates soluble guanylate cyclase (sGC), leading to the production of cyclic guanosine monophosphate (cGMP). cGMP activates cGMP-dependent protein kinase that activates Ca(2+)/ATPase pump that activates Ca(2+)/K efflux pump extruding Ca(2+) across the plasma membrane with consequent smooth muscle cell relaxation. A role similar to that of NOS/NO signaling has been postulated for carbon monoxide (CO) produced in mammals from heme catabolism by heme oxygenase (HO) enzyme.

AIM

To assess CO signaling pathway for erectile function by reviewing published studies.

METHODS

A systematic review of published studies on this affair based on Pubmed and Medical Subject Heading databases, with search for all concerned articles.

MAIN OUTCOME MEASURES

Documentation of positive as well as negative criteria of CO/HO signaling focused on penile tissue.

RESULTS

The concept that HO-derived CO could play a role in mediating erectile function acting in synergism with, or as a potentiator for, NOS/NO signaling pathway is gaining momentum. CO/HO signaling pathway has been shown to partially mediate the actions of oral phosphodiesterase type 5 inhibitors. In addition, it was shown that the use of CO releasing molecules potentiated cavernous cGMP levels. However, increased CO production or release was reported to be associated, in some studies, with vasoconstriction.

CONCLUSION

This review sheds a light on the significance of cavernous tissue CO signaling pathway that may pave the way for creation of therapeutic modalities based on this pathway.

Acute depletion of heme by succinylacetone alters vascular responses but does not induce hypertension

Heme plays a critical role in blood pressure regulation because it is required by a number of enzymes that synthesize vascular modulators, including nitric oxide (NO), carbon monoxide (CO), guanosine 3',5'-cyclic monophosphate (cGMP), endothelium-derived hyperpolarizing factor (EDHF), and prostacyclin. The goal of this study was to examine the vascular effects of a short-term depletion of heme achieved through administration of the heme-synthesis inhibitor succinylacetone (SA), an irreversible inhibitor of aminolevulinic acid dehydratase (ALAD). Rats were depleted of heme by using a 4-day treatment with SA. This treatment impacted hemoenzyme function, decreasing renal nitric oxide synthase (NOS) activity (as indicated by decreased in vitro NOS activity), and increasing kidney microsomal heme oxygenase (HO) activity by 27%. SA treatment also resulted in enhanced reduction in blood pressure after infusions of exogenous NO donor MAHMA NONOate (at high dose) and acetylcholine (at low doses). Nevertheless, this SA treatment was insufficient to produce an overt elevation of basal arterial pressure. This latter lack of effect may be the result of multiple compensatory mechanisms for the regulation of blood pressure.

Carbon monoxide decreases the level of iNOS protein and active dimer in IL-1beta-stimulated hepatocytes

There is evidence that NO can regulate CO production, however less is known about CO regulation of NO synthesis. Our studies were undertaken to define how CO regulates iNOS in cultured hepatocytes. CO (250ppm) exposure resulted in a significant decrease in iNOS protein, nitrite production, level of active iNOS dimer and cytosolic iNOS activity in cells stimulated with cytokines (IL-1beta) or transfected with the human iNOS gene. However, IL-1beta-stimulated iNOS mRNA expression was unaffected by CO. These effects of CO on iNOS protein levels were inhibited when CO was scavenged using hemoglobin. HO-1 induction with an adenoviral vector carrying HO-1 showed a decrease in total iNOS protein, nitrite production, and iNOS dimer level from cells stimulated by IL-1beta. iNOS protein level was significantly higher in lung endothelial cells isolated from HO-1 knockout mice compared to wild type cultures stimulated with cytokines mixture. CO was found to increase p38 phosphorylation and p38 inhibition using SB203580 increased iNOS protein levels in response to IL-1beta. Interestingly, proteasome inhibitors (MG132 and Lactacystin) and an autophagy inhibitor (3-methyladenine) reversed CO influence iNOS levels. Our results imply that CO exposure decreases NO production by suppressing dimer formation and increasing iNOS degradation through a process involving p38 activation.

Heme oxygenase-1 induction depletes heme and attenuates pulmonary artery relaxation and guanylate cyclase activation by nitric oxide

This study examines in endothelium-denuded bovine pulmonary arteries the effects of increasing heme oxygenase-1 (HO-1) activity on relaxation and soluble guanylate cyclase (sGC) activation by nitric oxide (NO). A 24-h organ culture with 0.1 mM cobalt chloride (CoCl2) or 30 microM Co-protoporphyrin IX was developed as a method of increasing HO-1 expression. These treatments increased HO-1 expression and HO activity by approximately two- to fourfold and lowered heme levels by 40-45%. Induction of HO-1 was associated with an attenuation of pulmonary arterial relaxation to the NO-donor spermine-NONOate. The presence of a HO-1 inhibitor 30 microM chromium mesoporphyrin during the 24-h organ culture (but not acute treatment with this agent) reversed the attenuation of relaxation to NO seen in arteries co-cultured with agents that increased HO-1. Relaxation to isoproterenol, which is thought to be mediated through cAMP, was not altered in arteries with increased HO-1. Inducers of HO-1 did not appear to alter basal sGC activity in arterial homogenates or expression of the beta(1)-subunit of sGC. However, the increase in activity seen in the presence of 1 microM spermine-NONOate was attenuated in homogenates obtained from arteries with increased HO-1. Since arteries with increased HO-1 had decreased levels of superoxide detected by the chemiluminescence of 5 microM lucigenin, superoxide did not appear to be mediating the attenuation of relaxation to NO. These data suggest that increasing HO-1 activity depletes heme, and this is associated with an attenuation of pulmonary artery relaxation and sGC activation responses to NO.

Regulation of maternal and fetal hemodynamics by heme oxygenase in mice

Heme oxygenase (HMOX) regulates vascular tone and blood pressure through the production of carbon monoxide (CO), a vasodilator derived from the heme degradation pathway. During pregnancy, the maternal circulation undergoes significant adaptations to accommodate the hemodynamic demands of the developing fetus. Our objective was to investigate the role of HMOX on maternal and fetal hemodynamics during pregnancy in a mouse model. We measured and compared maternal tissue and placental HMOX activity and endogenous CO production, represented by excreted CO and carboxyhemoglobin levels, during pregnancy (Embryonic Days 12.5-15.5) to nonpregnant controls. Micro-ultrasound was used to monitor maternal abdominal aorta diameters as well as blood flow velocities and diameters of fetal umbilical arteries. Tin mesoporphyrin, a potent HMOX inhibitor, was used to inhibit HMOX activity. Changes in maternal vascular tone were monitored by tail cuff blood pressure measurements. Effects of HMOX inhibition on placental structures were assessed by histology. We showed that maternal tissue and placental HMOX activity and CO production were significantly elevated during pregnancy. When HMOX in the placenta was inhibited, maternal and fetal hemodynamics underwent significant changes, with maternal blood pressures increasing. We concluded that increases in maternal tissue and placental HMOX activity contribute to the regulation of peripheral vascular resistance and therefore are important for the maintenance of normal maternal vascular tone and fetal hemodynamic functions during pregnancy.

Evidence for a Possible Inhibitory Interaction between the HO-1/CO- and Akt/NO-Pathways in Human Endothelial Cells

OBJECTIVE

The protective properties of heme oxygenase 1 (HO-1) give reason to study this mechanism as a potential therapeutic target for inflammatory and cardiovascular diseases. Recent evidence suggests a possible interaction between the HO-1/CO- and the protein kinase Akt/NO-pathway. This study was designed to examine the effects of continuous HO-1 overexpression in endothelial cells.

METHODS

Oncoretroviral vectors were constructed to achieve constitutive overexpression of HO-1, Akt, and green fluorescence protein in human umbilical vein endothelial cells. [(3)H]thymidine-incorporation and lipid-peroxidation were measured following exposure to heme and H(2)O(2). Expression of HO-1, Akt and its downstream-target endothelial NO-synthase were quantified by Western blot analysis. NO-synthase-activity was measured using the citrulline-conversion-assay.

RESULTS

HO-1-overexpression reduced proliferative rates and DNA-synthesis of HUVEC, but provided potent protection from oxidative stress induced by heme and H(2)O(2). Phosphorylated-Akt and eNOS was downregulated in HO-1-HUVEC. eNOS-activity was reduced in HO-1-HUVEC. Co-infection with the Akt-retrovirus restored proliferative rates and eNOS-expression and -activity.

CONCLUSION

Continuously elevated HO-1-activity protects EC from oxidative stress but inhibits Akt-mediated proliferation and eNOS-expression. This inhibitory feedback mechanism could be a limitation of HO-1 as a target for the treatment of vascular disease.

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

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

An analysis of the DOCA-salt model of hypertension in HO-1-/- mice and the Gunn rat

Heme oxygenase-1 (HO-1) is induced in the vasculature in the DOCA-salt model of hypertension in rats. Whereas the HO system and its products may exert vasodilator effects, recent studies have suggested that the HO system may predispose to hypertension. The present study examined the effects of selected components of the HO system, specifically, the HO-1 isozyme and the product bilirubin in the DOCA-salt model of systemic hypertension; the experimental approach employed mutant rodent models, namely, the HO-1(-/-) mouse and the hyperbilirubinemic Gunn rat. DOCA-salt induced HO-1 protein in the aorta in HO-1(+/+) mice and provoked a significant rise in systolic arterial pressure in HO-1(-/-) mice but not in HO-1(+/+) mice; this effect could not be ascribed to impaired urinary sodium excretion or impaired glomerular filtration rate in the DOCA-salt-treated HO-1(-/-) mice. The administration of DOCA salt to uninephrectomized rats significantly increased systolic arterial pressure in wild-type rats, an effect that was attenuated in the mutant Gunn rat; this reduction in systemic hypertension in the DOCA-salt-treated Gunn rat was not due to a greater induction of HO-1 in the vasculature or to a more avid urinary sodium excretion. DOCA-salt impaired endothelium-dependent and endothelium-independent vasorelaxation in wild-type rats but not in Gunn rats; prior exposure to bilirubin repaired the defect in endothelium-dependent vasorelaxation in aortic rings in DOCA-salt-treated rats. DOCA salt stimulated vascular production of superoxide anion in wild-type but not in Gunn rats. We suggest that HO-1 and the product bilirubin may exert a countervailing effect in the DOCA-salt model of systemic hypertension.

Carbon monoxide-mediated activation of large-conductance calcium-activated potassium channels contributes to mesenteric vasodilatation in cirrhotic rats

Large-conductance calcium-activated potassium channels (BK(Ca)s) are important regulators of arterial tone and represent a mediator of the endogenous vasodilator carbon monoxide (CO). Because an up-regulation of the heme oxygenase (HO)/CO system has been associated with mesenteric vasodilatation of cirrhosis, we analyzed the interactions of BK(Ca) and of HO/CO in the endothelium-dependent dilatation of mesenteric arteries in ascitic cirrhotic rats. In pressurized mesenteric arteries (diameter, 170-350 microm) of ascitic cirrhotic rats, we evaluated the effect of inhibition of BK(Ca), HO, and guanylyl-cyclase on dilatation induced by acetylcholine and by exogenous CO; and HO-1 and BK(Ca) subunit protein expression. Inhibition of HO and of BK(Ca) reduced acetylcholine-induced vasodilatation more in cirrhotic rats than in control rats, whereas inhibition of guanylyl-cyclase had a similar effect in the two groups. CO was more effective in cirrhotic rats than in control rats, and the effect was hindered by BK(Ca) inhibition. The expression of HO-1 and of BK(Ca) alpha-subunit was higher in mesenteric arteries of cirrhotic rats compared with that of control animals, whereas the expression of the BK(Ca) beta1-subunit was lower. In conclusion, an overexpression of BK(Ca) alpha-subunits, possibly due to HO up-regulation with increased CO production, participates in the endothelium-dependent alterations and mesenteric arterial vasodilatation of ascitic cirrhotic rats.

Role of carbon monoxide in cardiovascular function

Carbon monoxide (CO) is an endogenously derived gas formed from the breakdown of heme by the enzyme heme oxygenase. Although long considered an insignificant and potentially toxic waste product of heme catabolism, CO is now recognized as a key signaling molecule that regulates numerous cardiovascular functions. Interestingly, alterations in CO synthesis are associated with many cardiovascular disorders, including atherosclerosis, septic shock, hypertension, metabolic syndrome, and ischemia-reperfusion injury. Significantly, restoration of physiologic CO levels exerts a beneficial effect in many of these settings, suggesting a crucial role for CO in maintaining cardiovascular homeostasis. In this review, we outline the actions of CO in the cardiovascular system and highlight this gas as a potential therapeutic target in treating a multitude of cardiovascular disorders.

Myocardial dysfunction and potential cardiac hypoxia in rats induced by carbon monoxide inhalation

BACKGROUND

Results from both animal and human being studies provide evidence that inhalation of concentrations of carbon monoxide (CO) at around 100 ppm has antiinflammatory effects. These low levels of CO are incriminated in ischemic heart diseases experienced by cigarette smokers and, in some cases, from air pollution. Although neurologic mechanisms have been investigated, the effects of CO on cardiovascular function are still poorly understood.

METHODS AND RESULTS

The effects of CO (250 ppm; 90 min) inhalation on myocardial function were investigated in isolated heart of rats killed immediately, and 3, 24, 48, and 96 h after CO exposure. CO exposure at 250 ppm resulted in an arterial carboxyhemoglobin (HbCO) level of approximately 11%, which was not associated with changes in mean arterial pressure and heart rate. CO exposure induced coronary perfusion pressure increases, which were associated with endothelium-dependent and -independent vascular relaxation abnormalities. CO-induced coronary vascular relaxation perturbations were observed in the presence of increased heart contractility. Spontaneous peak to maximal Ca(2+)-activated left ventricular pressure ratio was markedly increased in CO-exposed rats, indicating increases in myofilament calcium sensitivity. Heart cyclic guanosine monophosphate/cAMP ratio and myocardial permeabilized fiber respiration (complex intravenous activity) were reduced in CO-exposed rats, which lasted after 48 h of reoxygenation in air.

CONCLUSIONS

These findings suggest that CO deteriorates heart oxygen supply to utilization and potentially may induce myocardial hypoxia through mechanisms that include increased oxygen demand due to increased contractility, reduced coronary blood flow reserve, and cardiomyocyte respiration inhibition.

Heme oxygenase-1/carbon monoxide: from basic science to therapeutic applications

The heme oxygenases, which consist of constitutive and inducible isozymes (HO-1, HO-2), catalyze the rate-limiting step in the metabolic conversion of heme to the bile pigments (i.e., biliverdin and bilirubin) and thus constitute a major intracellular source of iron and carbon monoxide (CO). In recent years, endogenously produced CO has been shown to possess intriguing signaling properties affecting numerous critical cellular functions including but not limited to inflammation, cellular proliferation, and apoptotic cell death. The era of gaseous molecules in biomedical research and human diseases initiated with the discovery that the endothelial cell-derived relaxing factor was identical to the gaseous molecule nitric oxide (NO). The discovery that endogenously produced gaseous molecules such as NO and now CO can impart potent physiological and biological effector functions truly represented a paradigm shift and unraveled new avenues of intense investigations. This review covers the molecular and biochemical characterization of HOs, with a discussion on the mechanisms of signal transduction and gene regulation that mediate the induction of HO-1 by environmental stress. Furthermore, the current understanding of the functional significance of HO shall be discussed from the perspective of each of the metabolic by-products, with a special emphasis on CO. Finally, this presentation aspires to lay a foundation for potential future clinical applications of these systems.

Endothelial dysfunction: a multifaceted disorder (The Wiggers Award Lecture)

Endothelial cells synthesize and release various factors that regulate angiogenesis, inflammatory responses, hemostasis, as well as vascular tone and permeability. Endothelial dysfunction has been associated with a number of pathophysiological processes. Oxidative stress appears to be a common denominator underlying endothelial dysfunction in cardiovascular diseases. However, depending on the pathology, the vascular bed studied, the stimulant, and additional factors such as age, sex, salt intake, cholesterolemia, glycemia, and hyperhomocysteinemia, the mechanisms underlying the endothelial dysfunction can be markedly different. A reduced bioavailability of nitric oxide (NO), an alteration in the production of prostanoids, including prostacyclin, thromboxane A2, and/or isoprostanes, an impairment of endothelium-dependent hyperpolarization, as well as an increased release of endothelin-1, can individually or in association contribute to endothelial dysfunction. Therapeutic interventions do not necessarily restore a proper endothelial function and, when they do, may improve only part of these variables.

Regulation and expression of heme oxygenase enzymes in aged-rat brain: age related depression in HO-1 and HO-2 expression and altered stress-response

The heme oxygenase isozymes, HO-1 and HO-2, oxidatively cleave the heme molecule to produce biliverdin and the gaseous messenger, CO. The cleavage results in the release of iron, a regulator of transferrin, ferritin, and nitric oxide (NO) synthase gene expression. Biliverdin reductase (BVR) then catalyzes the reduction of biliverdin, generating the potent intracellular antioxidant, bilirubin. We report an age-related decrease in HO-1 and HO-2 expression present in select brain regions including the hippocampus and the substantia nigra, that are involved in the high order cognitive processes of learning and memory. The age-related loss of monoxide-producing potential in select regions of the brain was not specific to the HO system but was also observed in neuronal NO-generating system. Furthermore, compared to 2-month old rats, the ability of aged brain tissue to respond to hypoxic/hyperthermia was compromised at both the protein and the transcription levels as judged by attenuated induction of HO-1 immunoreactive protein and its 1.8 Kb transcript. Neotrofin (AIT), a cognitive-enhancing and neuroprotective drug, caused a robust increase in HO-1 immunoreactive protein in select neuronal regions and increased the expression of HO-2 transcripts. The potential interplay between regulation of HO-2 gene expression and the serum levels of the adrenal steroids is discussed. We suggest the search for therapeutic agents that reverse the decline and aberrant stress response of HO enzymes may lead to effective treatment regimens for age-associated neuronal deficits.

Effect of pressure overload and its recovery on the rat carotid artery: change of vascular reactivity and remodeling process

Compared to chronic hypertension, little is known about the pathophysiology of acute hypertension and its recovery. To characterize this, we investigated the functional and structural properties of the common carotid arteries (CCA) from 35 rats. We established a unilateral and reversible carotid arterial hypertension model using the partial transverse aortic constriction (TAC) technique. By TAC, the right CCAs were made to endure a pressure-overload environment, while the left CCAs remained under normotension. The TACs were removed 2 weeks later, which unloaded the hypertensive effects. We compared the contractile, histological, and molecular responses of the CCA before TAC, during TAC (the hypertension period), and after removal of TAC (the recovery period). Vessel contractility was nearly abolished during 2 weeks of TAC. The recovery process from hypertension showed an initial hypercontractile period within a week. The relaxation response due to acetylcholine, as measured during the recovery period, showed a longer time course than the contractility for recovering its magnitude. During the hypertension period, the media thickness increased and this persisted throughout the recovery period. Apoptosis of the endothelial layer was significantly increased during the hypertension period and this disappeared 2 weeks after recovery. Expression of endothelial NO synthase was not detectable at the end of the hypertension period, but this gradually returned to the basal level after 2 weeks of recovery. Although increased contractility is usually expected in chronic hypertensive vessels, an abrupt pressure overload decreases contractility and the endothelium-dependent relaxation. It also increases endothelial apoptosis and the media thickness. These findings have clinical relevance, and they could be applied to human acute and severe hypertension and its recovery.

Carbon Monoxide: Endogenous Production, Physiological Functions, and Pharmacological Applications

Over the last decade, studies have unraveled many aspects of endogenous production and physiological functions of carbon monoxide (CO). The majority of endogenous CO is produced in a reaction catalyzed by the enzyme heme oxygenase (HO). Inducible HO (HO-1) and constitutive HO (HO-2) are mostly recognized for their roles in the oxidation of heme and production of CO and biliverdin, whereas the biological function of the third HO isoform, HO-3, is still unclear. The tissue type-specific distribution of these HO isoforms is largely linked to the specific biological actions of CO on different systems. CO functions as a signaling molecule in the neuronal system, involving the regulation of neurotransmitters and neuropeptide release, learning and memory, and odor response adaptation and many other neuronal activities. The vasorelaxant property and cardiac protection effect of CO have been documented. A plethora of studies have also shown the importance of the roles of CO in the immune, respiratory, reproductive, gastrointestinal, kidney, and liver systems. Our understanding of the cellular and molecular mechanisms that regulate the production and mediate the physiological actions of CO has greatly advanced. Many diseases, including neurodegenerations, hypertension, heart failure, and inflammation, have been linked to the abnormality in CO metabolism and function. Enhancement of endogenous CO production and direct delivery of exogenous CO have found their applications in many health research fields and clinical settings. Future studies will further clarify the gasotransmitter role of CO, provide insight into the pathogenic mechanisms of many CO abnormality-related diseases, and pave the way for innovative preventive and therapeutic strategies based on the physiologic effects of CO.

Metabolic syndrome increases endogenous carbon monoxide production to promote hypertension and endothelial dysfunction in obese Zucker rats

Vascular heme oxygenase (HO) metabolizes heme to form carbon monoxide (CO). Increased heme-derived CO inhibits nitric oxide synthase and can contribute to hypertension via endothelial dysfunction in Dahl salt-sensitive rats. Obese Zucker rats (ZR) are models of metabolic syndrome. This study tests the hypothesis that endogenous CO formation is increased and contributes to hypertension and endothelial dysfunction in obese ZR. Awake obese ZR showed increased respiratory CO excretion, which was lowered by HO inhibitor administration [zinc deuteroporphyrin 2,4-bis glycol (ZnDPBG) 25 micromol.kg(-1).24 h(-1) ip]. In awake obese ZR, chronically instrumented with femoral arterial catheters, blood pressure was elevated but was decreased by the HO inhibitor ZnDPBG. Body weight, blood glucose, glycated hemoglobin, plasma insulin, total and LDL cholesterol, oxidized LDL, and triglyceride levels were elevated in obese ZR, and, except for LDL cholesterol, were unchanged by HO inhibition. Total HO-1 protein levels were not different between lean and obese ZR aortas. In vitro experiments used isolated skeletal muscle arterioles with constant pressure and no flow, or constant midpoint, but altered endpoint pressures to establish graded levels of luminal flow. In obese ZR arterioles, responses to ACh and flow were attenuated. Acute in vitro pretreatment with an HO inhibitor, chromium mesoporphyrin, enhanced ACh and flow-induced dilation and abolished the differences between groups. Furthermore, exogenous CO prevented the restoration of flow-induced dilation by the HO inhibitor in obese ZR arterioles. These results suggest that HO-derived CO production is increased and promotes hypertension and arteriolar endothelial dysfunction in obese ZR with metabolic syndrome independent of affecting metabolic parameters.

Heme Oxygenase and Atherosclerosis

Overproduction of reactive oxygen species under pathophysiological conditions, including dyslipidemia, hypertension, diabetes, and smoking, is integral in the development of cardiovascular diseases (CVD). The reactive oxygen species released from all types of vascular cells regulate various signaling pathways that mediate not only vascular inflammation in atherogenesis but also antioxidative and antiinflammatory responses. One such protective and stress-induced protein is heme oxygenase (HO). HO is the first rate-limiting enzyme in heme breakdown to generate equimolar quantities of carbon monoxide, biliverdin, and free ferrous iron. Accumulating evidence has shown that inducible HO (HO-1) and its products function as adaptive molecules against oxidative insults. The proposed mechanisms by which HO-1 exerts its cytoprotective effects include its abilities to degrade the pro-oxidative heme, to release biliverdin and subsequently convert it bilirubin, both of which have antioxidant properties, and to generate carbon monoxide, which has antiproliferative and antiinflammatory as well as vasodilatory properties. Herein, I highlight the relationship of HO and cardiovascular disease, especially atherosclerosis, gene-targeting approaches in animal models, and the potential for and concern about HO-1 as a novel therapeutic target for cardiovascular diseases.

Heme oxygenase-derived carbon monoxide promotes arteriolar endothelial dysfunction and contributes to salt-induced hypertension in Dahl salt-sensitive rats

Vascular tissues express heme oxygenase (HO), which metabolizes heme to form carbon monoxide (CO). Heme-derived CO inhibits nitric oxide synthase and promotes endothelium-dependent vasoconstriction. After 4 wk of high-salt diet, Dahl salt-sensitive (Dahl-S) rats display hypertension, increased vascular HO-1 expression, and attenuated vasodilator responses to ACh that can be completely restored by acute treatment with an inhibitor of HO. In this study, we examined the temporal development of HO-mediated endothelial dysfunction in isolated pressurized first-order gracilis muscle arterioles, identified the HO product responsible, and studied the blood pressure effects of HO inhibition in Dahl-S rats on a high-salt diet. Male Dahl-S rats (5–6 wk) were placed on high-salt (8% NaCl) or low-salt (0.3% NaCl) diets for 0–4 wk. Blood pressure increased gradually, and responses to an endothelium-dependent vasodilator, ACh, decreased gradually with the length of high-salt diet. Flow-induced dilation was abolished in hypertensive Dahl-S rats. Acute in vitro pretreatment with an inhibitor of HO, chromium mesoporphyrin (CrMP), restored endothelium-dependent vasodilation and abolished the differences between groups. The HO product CO prevented the restoration of endothelium-dependent dilation by CrMP. Furthermore, administration of an HO inhibitor lowered blood pressure in Dahl-S rats with salt-induced hypertension but did not do so in low-salt control rats. These results suggest that hypertension and HO-mediated endothelial dysfunction develop gradually and simultaneously in Dahl-S rats on high-salt diets. They also suggest that HO-derived CO underlies the impaired endothelial dysfunction and contributes to hypertension in Dahl-S rats on high-salt diets.

Carbon monoxide and hypertension

The enzymatic action of heme oxygenase yields carbon monoxide, biliverdin and iron. Carbon monoxide is implicated in many physiological processes, including the regulation of vascular tissue contractility and apoptosis. By stimulating the soluble guanylyl cyclase (sGC)/cGMP pathway and activating K channels in vascular smooth muscle cells (SMCs), carbon monoxide relaxes vascular tissues under physiological conditions. Altered metabolism and functions of carbon monoxide have been linked to the pathogenesis and maintenance of hypertension. The expression and activity of heme oxygenase-1, sGC and cGMP in vascular SMCs are associated with different stages of development of hypertension in spontaneously hypertensive rats (SHRs). The importance of altered heme oxygenase-2 expression in vascular tissues in hypertension remains unclear. Increased vascular contractility, unbalanced cellular apoptosis and proliferation in the vascular wall, increased oxidative stress, and the altered interaction of carbon monoxide and nitric oxide are among the consequences of heme oxygenase/carbon monoxide system dysfunction in hypertension. Acute application of pharmacological inducers to upregulate the expression of heme oxygenase-1 or the use of gene delivery method to overexpress heme oxygenase-1 decreases blood pressure in young SHRs and other animal models of hypertension. These blood pressure-decreasing effects are annulled by metalloporphyrins. In adult SHRs, the heme oxygenase/carbon monoxide system appears to be normalized as a compensatory reaction. To date, acute manipulation of the expression of heme oxygenase-1 has not been successful in decreasing blood pressure in adult SHRs. In conclusion, abnormality of the heme oxygenase/carbon monoxide system has a critical role in the pathogenesis of hypertension, and novel therapeutic approaches should be pursued to achieve selective improvement in the function of this system in hypertension.

Arginase inhibition restores arteriolar endothelial function in Dahl rats with salt-induced hypertension

Vascular tissues express arginase that metabolizes L-arginine to L-ornithine and urea and thus reduces substrate availability for nitric oxide formation. Dahl salt-sensitive (Dahl-S) rats with salt-induced hypertension show endothelial dysfunction, including decreased vascular nitric oxide formation. This study tests the hypothesis that increased vascular arginase activity contributes to endothelial dysfunction in hypertensive Dahl-S rats. Male Dahl-S rats (5-6 wk) were placed on high (8%) or low (0.3%) NaCl diets for 4 wk. With respect to the low-salt group, mean arterial blood pressure was increased in the high-salt animals. Immunohistochemical stainings for arginase I and II were enhanced in arterioles isolated from high-salt Dahl-S rats. Experiments used isolated Krebs buffer-superfused first-order gracilis muscle arterioles with constant pressure (80 mmHg) and no luminal flow or constant midpoint but altered endpoint pressures to establish graded levels of luminal flow (0-50 microl/min). In high-salt arterioles, responses to an endothelium-dependent vasodilator acetylcholine (1 nmol/l to 3 micromol/l) and flow-induced dilation were decreased. Acute in vitro treatment with an inhibitor of arginase, 100 micromol/l (S)-(2-boronoethyl)-L-cystine, or the nitric oxide precursor, 1 mmol/l L-arginine, similarly enhanced acetylcholine and flow-induced maximal dilations and abolished the differences between high- and low-salt arterioles. These data show that arteriolar arginase expression is increased and that endothelium-dependent vasodilation is decreased in high-salt Dahl-S rats. Acute pretreatment with an arginase inhibitor or with L-arginine restores endothelium-dependent vasodilation and abolishes the differences between high- and low-salt groups. These results suggest that enhanced vascular arginase activity contributes to endothelial dysfunction in Dahl-S rats with salt-induced hypertension and identifies arginase as a potential therapeutic target to prevent endothelial dysfunction.

Heme oxygenase-mediated endothelial dysfunction in DOCA-salt, but not in spontaneously hypertensive, rat arterioles

Vascular heme oxygenase (HO) metabolizes heme to form carbon monoxide. Carbon monoxide inhibits nitric oxide synthase and promotes endothelium-dependent vasoconstriction. We reported HO-1-mediated endothelial dysfunction in Dahl salt-sensitive hypertension. Previous studies suggested that salt-sensitive hypertensive rats, but not spontaneously hypertensive rats (SHR), display endothelial dysfunction. This study examines the hypothesis that HO-1-mediated arteriolar endothelial dysfunction develops in deoxycorticosterone acetate (DOCA)-salt hypertensive (DOCA) rats, but not in SHR. Uninephrectomized (isoflurane anesthesia) male Sprague-Dawley rats received DOCA injections and saline drinking solution for 4 wk. Rats subjected to sham surgery received vehicle injections and tap water. Blood pressure was elevated in DOCA rats and SHR compared with sham and Wistar-Kyoto (WKY) groups. Aortic HO-1 expression and blood carboxyhemoglobin levels were elevated in the DOCA group, but not in SHR. In isolated gracilis muscle arterioles, ACh caused concentration-related vasodilation in all groups, with attenuated maximum responses in DOCA, but not in SHR, arterioles. Acute pretreatment with an inhibitor of HO, chromium mesoporphyrin, restored ACh-induced responses in DOCA arterioles to sham levels. ACh responses remained the same in SHR and WKY arterioles after chromium mesoporphyrin treatment. These data show that HO-1 levels and activity are increased and arteriolar responses to ACh are decreased in DOCA rats, but not in SHR. Furthermore, in DOCA arterioles, an inhibitor of HO restores ACh-induced vasodilation to sham levels. These results suggest that elevated HO-1 levels and activity, not resulting from hypertension per se, contribute to endothelial dysfunction in DOCA rats.

Carbon monoxide promotes endothelium-dependent constriction of isolated gracilis muscle arterioles

Vascular tissues express heme oxygenase, which metabolizes heme to form carbon monoxide (CO). CO promotes relaxation of vascular smooth muscle but also inhibits nitric oxide (NO) formation. This study examines the hypothesis that CO promotes endothelium- and NO synthase-dependent vasoconstriction of isolated arterioles. Studies were conducted on pressurized first-order gracilis muscle arterioles isolated from anesthetized male Sprague-Dawley rats. Exogenous CO, as well as a heme precursor, delta-aminolevulinic acid (delta-ALA), constricted arterioles with intact endothelium pretreated with phenylephrine; these effects were abolished by removal of the endothelium. CO- and delta-ALA-induced vasoconstrictions were converted to dilations by pretreatment with an inhibitor of NO synthase, Nomega-nitro-l-arginine methyl ester, or with Nomega-nitro-l-arginine methyl ester and an NO donor, sodium nitroprusside. Furthermore, CO-induced vasoconstriction was prevented by pretreatment with the NO synthase substrate l-arginine. This study shows that exogenous, as well as endogenously formed, CO can promote endothelium-dependent vasoconstriction in isolated gracilis muscle arterioles. Because CO-induced vasoconstriction is abolished by NO synthase blockade and by l-arginine, CO most likely promotes endothelium-dependent vasoconstriction by inhibiting endothelial NO formation.

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.