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

Effect of hypoxia in mice mesenteric arteries surrounded by adipose tissue

AIM

To investigate the influence of hypoxia on the vasoactive effect of peri-vascular white adipose tissue.

METHODS

Isometric tension recordings were performed on mesenteric arteries from Swiss male mice with or without adherent adipose tissue.

RESULTS

Hypoxia (bubbling with 95% N(2), 5% CO(2)) induced a biphasic response, i.e. vasoconstriction followed by vasorelaxation, in pre-contracted (noradrenaline, 10 μm) mesenteric arteries with adipose tissue in the presence of indomethacin (10 μm) and N(ω) -nitro-l-arginine (0.1 mm). Only a small vasorelaxation was observed in arteries without adipose tissue. Pre-contraction with 60 or 120 mm K(+) , incubation with tetraethylammoniumchloride (1 and 3 mm), apamin (1 μm) combined with charybdotoxin (0.1 μm) or 1-[(2-chlorophenyl) diphenylmethyl]-1H-pyrazole (TRAM-34) (10 μm) significantly impaired the hypoxic vasorelaxation. Removal of the endothelium only reduced the hypoxic vasorelaxation. Apamin (1 μm) and charybdotoxin (0.1 μm) did not influence the vasorelaxation of sodium hydrosulfide hydrate. Zinc protoporphyrin IX (10 μm), miconazole (10 μm), 8-(p-sulfophenyl)theophylline (0.1 mm), 1 H-[1, 2, 4]oxadiazolo[4,3- A]quinoxalin-1-one (10 μm), apocynin (0.3 mm), diphenyliodonium (1 μm), catalase (2500 U mL(-1)) and tempol (0.1 mm) did not influence the hypoxic vasorelaxation. In contrast to losartan (0.1 mm), indomethacin (10 μm) and SQ-29548 (10 μm) significantly reduced the hypoxic vasoconstriction.

CONCLUSIONS

Moderate hypoxia induces a biphasic vasomotor response in mice mesenteric arteries surrounded by adipose tissue. The hypoxic vasoconstriction is endothelium independent, whereas the vasodilation is endothelium dependent, soluble guanylyl cyclase independent and in part mediated by opening K(Ca) channels. Cyclooxygenase metabolites mediate the hypoxic vasoconstriction, while endothelium-derived hyperpolarizing factor plays a small role in the hypoxic vasorelaxation.

Induction of heme oxygenase-1 attenuates sFlt-1-induced hypertension in pregnant rats

Preeclampsia (PE) is one of the leading causes of fetal and maternal morbidity, affecting 5-10% of all pregnancies, and lacks an effective treatment. The exact etiology of the disorder is unclear, but placental ischemia has been shown to be a central causative agent. In response to placental ischemia, the antiangiogenic protein fms-like tyrosine kinase-1 (sFlt-1), a VEGF antagonist, and reactive oxygen species are secreted, leading to the maternal syndrome. One promising therapeutic approach to treat PE is through manipulation of the heme oxygenase-1 (HO-1) protein. It has been previously reported that HO-1 and carbon monoxide downregulate sFlt-1 production in vitro, and we have recently shown that HO-1 induction significantly attenuates placental ischemia-induced hypertension, partially through normalization of the sFlt-1-to-VEGF ratio in the placenta. The purpose of this study was to determine whether HO-1 induction would have beneficial effects independently of sFlt-1 suppression. To that end, pregnant rats were continuously infused with recombinant sFlt-1 from gestational days 14-19, and circulating sFlt-1 increased approximately twofold, similar to rats with experimentally induced placental ischemia. In response, mean arterial pressure increased 17 mmHg, which was completely normalized by HO-1 induction. Unbound circulating VEGF was decreased ∼17% in response to sFlt-1 infusion but was increased ∼50% in response to HO-1 induction. Finally, endothelial function was improved as measured by reductions in vascular expression of preproendothelin mRNA. In conclusion, manipulation of HO-1 presents an intriguing therapeutic approach to the treatment of PE.

Vasoactivity of the gasotransmitters hydrogen sulfide and carbon monoxide in the chicken ductus arteriosus

Besides nitric oxide (NO) and carbon monoxide (CO), hydrogen sulfide (H(2)S) is a third gaseous messenger that may play a role in controlling vascular tone and has been proposed to serve as an O(2) sensor. However, whether H(2)S is vasoactive in the ductus arteriosus (DA) has not yet been studied. We investigated, using wire myography, the mechanical responses induced by Na(2)S (1 μM-1 mM), which forms H(2)S and HS(-) in solution, and by authentic CO (0.1 μM-0.1 mM) in DA rings from 19-day chicken embryos. Na(2)S elicited a 100% relaxation (pD(2) 4.02) of 21% O(2)-contracted and a 50.3% relaxation of 62.5 mM KCl-contracted DA rings. Na(2)S-induced relaxation was not affected by presence of the NO synthase inhibitor l-NAME, the soluble guanylate cyclase (sGC) inhibitor ODQ, or the K(+) channel inhibitors tetraethylammonium (TEA; nonselective), 4-aminopyridine (4-AP, K(V)), glibenclamide (K(ATP)), iberiotoxin (BK(Ca)), TRAM-34 (IK(Ca)), and apamin (SK(Ca)). CO also relaxed O(2)-contracted (60.8% relaxation) and KCl-contracted (18.6% relaxation) DA rings. CO-induced relaxation was impaired by ODQ, TEA, and 4-AP (but not by L-NAME, glibenclamide, iberiotoxin, TRAM-34 or apamin), suggesting the involvement of sGC and K(V) channel stimulation. The presence of inhibitors of H(2)S or CO synthesis as well as the H(2)S precursor L-cysteine or the CO precursor hemin did not significantly affect the response of the DA to changes in O(2) tension. Endothelium-dependent and -independent relaxations were also unaffected. In conclusion, our results indicate that the gasotransmitters H(2)S and CO are vasoactive in the chicken DA but they do not suggest an important role for endogenous H(2)S or CO in the control of chicken ductal reactivity.

Acute reductions in blood flow restricted to the dorsomedial medulla induce a pressor response in rats

OBJECTIVES

The brainstem nucleus of the solitary tract (nucleus tractus solitarii, NTS) is a pivotal region for regulating the set-point of arterial pressure, the mechanisms of which are not fully understood. Based on evidence that the NTS exhibits O2-sensing mechanisms, we examined whether a localized disturbance of blood supply, resulting in hypoxia in the NTS, would lead to an acute increase in arterial pressure.

METHODS

Male Wistar rats were used. Cardiovascular parameters were measured before and after specific branches of superficial dorsal medullary veins were occluded; we assumed these were drainage vessels from the NTS and would produce stagnant hypoxia. Hypoxyprobe-1, a marker for detecting cellular hypoxia in the post-mortem tissue, was used to reveal whether vessel occlusion induced hypoxia within the NTS.

RESULTS

Following vessel occlusion, blood flow in the dorsal surface of the medulla oblongata including the NTS region showed an approximately 60% decrease and was associated with hypoxia in neurons located predominantly in the caudal part of the NTS as revealed using hypoxyprobe-1. Arterial pressure increased and this response was pronounced significantly in both magnitude and duration when baroreceptor reflex afferents were sectioned.

CONCLUSION

These results suggest that localized hypoxia in the NTS increases arterial pressure. We suggest this represents a protective mechanism whereby the elevated systemic pressure is a compensatory mechanism to enhance cerebral perfusion. Whether this physiological mechanism has any relevance to neurogenic hypertension is discussed.

Ion channels as effectors in carbon monoxide signaling

A wealth of recent studies has highlighted the diverse and important influences of carbon monoxide (CO) on cellular signaling pathways. Such studies have implicated CO, and the enzymes from which it is derived (heme oxygenases) as potential therapeutic targets, particularly (although not exclusively) in inflammation, immunity and cardiovascular disease.1 In a recent study,2 we demonstrated that CO inhibited cardiac L-type Ca(2+) channels. This effect arose due to the ability of CO to bind to mitochondria (presumably at complex IV of the electron transport chain) and so cause electron leak, which resulted in increased production of reactive oxygen species. These modulated the channel's activity through interactions with three cysteine residues in the cytosolic C-terminus of the channel's major, pore-forming subunit. Our study provided a potential mechanism for the cardioprotective effects of CO and also highlighted ion channels as a major potential target group for this gasotransmitter.

Effect of ramp bicycle exercise on exhaled carbon monoxide in humans

The effect of exercise on the increase of exhaled CO in smokers compared to non-smokers has not been clarified yet. In this study we compared the dynamics of exhaled CO before, during and after exercise between smokers and non-smokers. A group of 8 smokers and a group of 8 non-smokers underwent a bicycle exercise in a ramp fashion to near maximum intensity. Ventilation and gas exchange, and CO exhalation were continuously measured every 30-s before, during and after the exercise. The fraction of CO (F (CO)) in the exhaled air decreased gradually, but the total amount of exhaled CO (V(CO)) increased in a linear manner during the ramp exercise, and F (CO) and returned to the pre-exercise level within several minutes after exercise in all subjects. A linear relationship was observed between V (O(2)) and V (CO) and between V (E) and V (CO) in both the whole period of measurement and during the ramp exercise period in all subjects. However, the at V (CO) 0 W, the peak V (CO) and the slope coefficients in the regression equation between V (CO) and V (O(2)) and between V (CO) and V (E) in the ramp exercise as well as the entire periods of measurement were significantly higher in smokers compared with those in non-smokers, and these were correlated with the number of cigarettes smoked per day. It was concluded that CO exhalation increases linearly with the increase of V (O(2)) and V (E) during exercise, and habitual smoking shifts these relationships upward depending on the number of cigarettes smoked daily.

Asperlin from the marine-derived fungus Aspergillus sp. SF-5044 exerts anti-inflammatory effects through heme oxygenase-1 expression in murine macrophages

Asperlin is a fungal metabolite isolated from Aspergillus sp. SF-5044. In the present study, we isolated asperlin from the marine-derived fungus Aspergillus sp. SF-5044 and demonstrated that it inhibited inducible nitric oxide synthase (iNOS) expression, reduced iNOS-derived NO, suppressed cyclooxygenase (COX)-2 expression, and reduced COX-derived prostaglandin (PG) E₂ production in lipopolysaccharide (LPS)-stimulated RAW264.7 and murine peritoneal macrophages. Similarly, asperlin reduced the production of tumor necrosis factor (TNF)-α and interleukin (IL)-1β. In addition, asperlin inhibited the phosphorylation and degradation of IκB-α, as well as the nuclear translocation of p65 caused by the stimulation of LPS in RAW264.7 macrophages. Furthermore, asperlin induced heme oxygenase (HO)-1 expression through nuclear translocation of nuclear factor E2-related factor 2 and increased HO activity in RAW264.7 macrophages. The effects of asperlin on the LPS-induced expression of iNOS and COX-2 and production of NO, PGE₂, TNF-α, and IL-1β were partially reversed by a HO-1 inhibitor, tin protoporphyrin. These findings suggest that asperlin-induced HO-1 expression plays a role in the anti-inflammatory effects of asperlin in macrophages.

Carbon monoxide affects electrical and contractile activity of rat myocardium

BACKGROUND

Carbon monoxide (CO) is a toxic gas, which also acts in the organism as a neurotransmitter. It is generated as a by-product of heme breakdown catalyzed by heme oxygenase. We have investigated changes in electrical and contractile activity of isolated rat atrial and ventricular myocardium preparations under the influence of CO.

METHODS

Standard microelectrode technique was used for intracellular registration of electrical activity in isolated preparations of atrial and ventricular myocardium. Contractions of atrial myocardial stripes were registered via force transducer.

RESULTS

CO (10(-4)-10(-3) M) caused prominent decrease of action potential duration (APD) in working atrial myocardium as well as significant acceleration of sinus rhythm. In addition CO reduced force of contractions and other parameters of contractile activity. Inhibitor of heme oxygenase zinc protoporphyrin IX exerts opposite effects: prolongation of action potential, reduction of sinus rhythm rate and enhancement of contractile function. Therefore, endogenous CO, which may be generated in the heart due to the presence of active heme oxygenase, is likely to exert the same effects as exogenous CO applied to the perfusing medium. In ventricular myocardium preparations exogenous CO also induced shortening of action potential, while zinc protoporphyrin IX produced the opposite effect.

CONCLUSIONS

Thus, endogenous or exogenous carbon monoxide may act as an important regulator of electrical and contractile cardiac activity.

Reactive oxygen species mediate bactericidal killing elicited by carbon monoxide-releasing molecules

CO-releasing molecules (CO-RMs) were previously shown by us to be more potent bactericides than CO gas. This suggests a mechanism of action for CO-RM, which either potentiates the activity of CO or uses another CO-RM-specific effect. We have also reported that CORM-2 induces the expression of genes related to oxidative stress. In the present study we intend to establish whether the generation of reactive oxygen species by CO-RMs may indeed result in the inhibition of bacterial cellular function. We now report that two CO-RMs (CORM-2 and ALF062) stimulate the production of ROS in Escherichia coli, an effect that is abolished by addition of antioxidants. Furthermore, deletion of genes encoding E. coli systems involved in reactive oxygen species scavenging, namely catalases and superoxide dismutases, potentiates the lethality of CORM-2 due to an increase of intracellular ROS content. CORM-2 also induces the expression of the E. coli DNA repair/SOS system recA, and its inactivation enhances toxicity of CORM-2. Moreover, fluorescence microscopy images reveal that CORM-2 causes DNA lesions to bacterial cells. We also demonstrate that cells treated with CORM-2 contain higher levels of free iron arising from destruction of iron-sulfur proteins. Importantly, we show that CO-RMs generate hydroxyl radicals in a cell-free solution, a process that is abolished by scavenging CO. Altogether, we provide a novel insight into the molecular basis of CO-RMs action by showing that their bactericidal properties are linked to cell damage inflicted by the oxidative stress that they are able to generate.

Heme oxygenase-1 overexpression fails to attenuate hypertension when the nitric oxide synthase system is not fully operative

Heme oxygenase (HO) is an enzyme that is involved in numerous secondary actions. One of its products, CO, seems to have an important but unclear role in blood pressure regulation. CO exhibits a vasodilator action through the activation of soluble guanylate cyclase and the subsequent production of cyclic guanosine monophosphate (cGMP). The aim of the present study was to determine whether pathological and pharmacological HO-1 overexpression has any regulatory role on blood pressure in a renovascular model of hypertension. We examined the effect of zinc protoporyphyrin IX (ZnPP-IX) administration, an inhibitor of HO activity, on mean arterial pressure (MAP) and heart rate in sham-operated and aorta-coarcted (AC) rats and its interaction with the nitric oxide synthase (NOS) pathway. Inhibition of HO increased MAP in normotensive rats with and without hemin pretreatment but not in hypertensive rats. Pretreatment with NG-nitro-L-arginine methyl ester blocked the pressor response to ZnPP-IX, suggesting a key role of NOS in the cardiovascular action of HO inhibition. In the same way, AC rats, an experimental model of hypertension with impaired function and low expression of endothelial NOS (eNOS), did not show any cardiovascular response to inhibition or induction of HO. This finding suggests that eNOS was necessary for modulating the CO response in the hypertensive group. In conclusion, the present study suggests that HO regulates blood pressure through CO only when the NOS pathway is fully operative. In addition, chronic HO induction fails to attenuate the hypertensive stage induced by coarctation as a consequence of the impairment of the NOS pathway.

Reactive oxygen species in the regulation of synaptic plasticity and memory

The brain is a metabolically active organ exhibiting high oxygen consumption and robust production of reactive oxygen species (ROS). The large amounts of ROS are kept in check by an elaborate network of antioxidants, which sometimes fail and lead to neuronal oxidative stress. Thus, ROS are typically categorized as neurotoxic molecules and typically exert their detrimental effects via oxidation of essential macromolecules such as enzymes and cytoskeletal proteins. Most importantly, excessive ROS are associated with decreased performance in cognitive function. However, at physiological concentrations, ROS are involved in functional changes necessary for synaptic plasticity and hence, for normal cognitive function. The fine line of role reversal of ROS from good molecules to bad molecules is far from being fully understood. This review focuses on identifying the multiple sources of ROS in the mammalian nervous system and on presenting evidence for the critical and essential role of ROS in synaptic plasticity and memory. The review also shows that the inability to restrain either age- or pathology-related increases in ROS levels leads to opposite, detrimental effects that are involved in impairments in synaptic plasticity and memory function.

Contributions of vascular inflammation in the brainstem for neurogenic hypertension

Essential hypertension is idiopathic although it is accepted as a complex polygenic trait with underlying genetic components, which remain unknown. Our supposition is that primary hypertension involves activation of the sympathetic nervous system. One pivotal region controlling arterial pressure set point is nucleus tractus solitarii (NTS). We recently identified that pro-inflammatory molecules, such as junctional adhesion molecule-1, were over expressed in endothelial cells of the microvasculature supplying the NTS in an animal model of human hypertension (the spontaneously hypertensive rat: SHR) compared to normotensive Wistar Kyoto (WKY) rats. We have also shown endogenous leukocyte accumulation inside capillaries within the NTS of SHR but not WKY rats. Despite the inflammatory state in the NTS of SHR, transcripts of some inflammatory molecules such as chemokine (C-C motif) ligand 5 (Ccl5), and its receptors, chemokine (C-C motif) receptor 1 and 3 were down-regulated in the NTS of SHR compared to WKY rats. This may be compensatory to avoid further strong inflammatory activity. More importantly, we found that down-regulation of Ccl5 in the NTS of SHR may be pro-hypertensive since microinjection of Ccl5 into the NTS of SHR decreased arterial pressure but was less effective in WKY rats. Leukocyte accumulation of the NTS microvasculature may also induce an increase in vascular resistance and hypoperfusion within the NTS; the latter may trigger release of pro-inflammatory molecules which via paracrine signaling may affect central neural cardiovascular activity conducive to neurogenic hypertension. All told, we suggest that vascular inflammation within the brainstem contributes to neurogenic hypertension by multiple pathways.

Mechanism of protection of bystander cells by exogenous carbon monoxide: impaired response to damage signal of radiation-induced bystander effect

A protective effect of exogenous carbon monoxide (CO), generated by CO releasing molecule ticarbonyldichlororuthenium (II) dimer (CORM-2), on the bystander cells from the toxicity of radiation-induced bystander effect (RIBE) was revealed in our previous study. In the present work, a possible mechanism of this CO effect was investigated. The results from medium transfer experiments showed that α-particle irradiated Chinese hamster ovary (CHO) cells would release nitric oxide (NO), which was detected with specific NO fluorescence probe, to induce p53 binding protein 1 (BP1) formation in the cell population receiving the medium, and the release peak was found to be at 1h post irradiation. Treating the irradiated or bystander cells separately with CO (CORM-2) demonstrated that CO was effective in the bystander cells but not the irradiated cells. Measurements of NO production and release with a specific NO fluorescence probe also showed that CO treatment did not affect the production and release of NO by irradiated cells. Protection of CO on cells to peroxynitrite, an oxidizing free radical from NO, suggested that CO might protect bystander cells via impaired response of bystander cells to NO, a RIBE signal in our research system.

Ion channels as target effectors for carbon monoxide

Our understanding of carbon monoxide (CO) as an endogenous signalling molecule has expanded enormously in recent years, to the point where it can now be safely exploited therapeutically. In more recent years, the ability of CO to modulate ion channel activity has added further diversity to its activity. Here, I summarize briefly the established ion channel targets of CO and describe in more detail its actions on two example ion channels (the cardiac L-type Ca(2+) channel and the neuronal delayed rectifier, Kv2.1). The physiological consequences of such modulation are also considered. It is clear that our knowledge of the cellular effects of this gas is incomplete, and further study is required to further understand and so more fully exploit its therapeutic potential.

Carbon monoxide protects against oxidant-induced apoptosis via inhibition of Kv2.1

Oxidative stress induces neuronal apoptosis and is implicated in cerebral ischemia, head trauma, and age-related neurodegenerative diseases. An early step in this process is the loss of intracellular K(+) via K(+) channels, and evidence indicates that K(v)2.1 is of particular importance in this regard, being rapidly inserted into the plasma membrane in response to apoptotic stimuli. An additional feature of neuronal oxidative stress is the up-regulation of the inducible enzyme heme oxygenase-1 (HO-1), which catabolizes heme to generate biliverdin, Fe(2+), and carbon monoxide (CO). CO provides neuronal protection against stresses such as stroke and excitotoxicity, although the underlying mechanisms are not yet elucidated. Here, we demonstrate that CO reversibly inhibits K(v)2.1. Channel inhibition by CO involves reactive oxygen species and protein kinase G activity. Overexpression of K(v)2.1 in HEK293 cells increases their vulnerability to oxidant-induced apoptosis, and this is reversed by CO. In hippocampal neurons, CO selectively inhibits K(v)2.1, reverses the dramatic oxidant-induced increase in K(+) current density, and provides marked protection against oxidant-induced apoptosis. Our results provide a novel mechanism to account for the neuroprotective effects of CO against oxidative apoptosis, which has potential for therapeutic exploitation to provide neuronal protection in situations of oxidative stress.

Significance of hydrogen sulfide production in the pancreatic β-cell

Hydrogen sulfide (H(2)S) is an important signaling molecule in various mammalian cells and tissues. H(2)S is synthesized from L-cysteine and regulates several cellular and physiological phenomena (vasorelaxation, hormone secretion, and apoptosis) and multicellular events (neuromodulation and inflammatory responses). H(2)S can be produced in pancreatic β-cells by cystathionine β-synthase (CBS) or cystathionine γ-lyase (CSE). H(2)S inhibits insulin release and regulates β-cell survival. We found that glucose stimulation increased CSE expression at transcript and protein levels in mouse pancreatic islets. We also found that H(2)S protects β-cells that were chronically exposed to high glucose from apoptotic cell death. Loss of β-cell mass and failures of β-cell function are important in the pathogenesis and/or progression of diabetes mellitus; therefore, molecular analyses of the mechanisms of H(2)S production and its protective effects on β-cells may lead to new insights into diabetes mellitus.

Heme oxygenase-1 induction enhances cell survival and restores contractility to unvascularized three-dimensional adult cardiomyocyte grafts implanted in vivo

Autologous adult cardiomyocytes are not utilized for heart repair strategies because of their rapid apoptosis after implantation. We examined whether induction of heme oxygenase-1 (HO-1), a mediator of preconditioning, could enhance early postimplant myocyte survival. Three-dimensional 5×5 mm patches of full-thickness adult murine atrial wall, including cardiomyocytes, capillary networks, and extracellular matrix, were cultured with or without HO-1 inducer cobalt protoporphyrin (CoPP), or the HO-1 inhibitor, tin protoporphyrin (SnPP), or both. Patches were then implanted subcutaneously. Freshly procured atrial wall patches implanted without preculturing served as additional controls. By 14 days postimplant, graft cardiomyocyte content was significantly greater in CoPP-treated patches than in either control group (p<0.02). Adult cardiomyocytes did not contract in culture or immediately after implantation. However, by 14 days postimplant, spontaneous contraction had recovered in 47% of CoPP-treated patches, but in only 6% of precultured patches without CoPP, 0% of SnPP-treated patches, and 0% of uncultured patches (p<0.03). CoPP-treated adult cardiomyocyte patches were also observed to remodel spontaneously into endothelial-lined chambers that pumped nonclotting blood. These findings demonstrate that adult cardiomyocytes have more plasticity and capacity for functional recovery than previously recognized and could have application as an autologous cardiomyocyte source for tissue engineering.

Allosteric modulation of ATP-gated P2X receptor channels

Seven mammalian purinergic receptor subunits, denoted P2X1-P2X7, and several spliced forms of these subunits have been cloned. When heterologously expressed, these cDNAs encode ATP-gated non-selective cation channels organized as trimers. All activated receptors produce cell depolarization and promote Ca(2+) influx through their pores and indirectly by activating voltage-gated calcium channels. However, the biophysical and pharmacological properties of these receptors differ considerably, and the majority of these subunits are also capable of forming heterotrimers with other members of the P2X receptor family, which confers further different properties. These channels have three ATP binding domains, presumably located between neighboring subunits, and occupancy of at least two binding sites is needed for their activation. In addition to the orthosteric binding sites for ATP, these receptors have additional allosteric sites that modulate the agonist action at receptors, including sites for trace metals, protons, neurosteroids, reactive oxygen species and phosphoinositides. The allosteric regulation of P2X receptors is frequently receptor-specific and could be a useful tool to identify P2X members in native tissues and their roles in signaling. The focus of this review is on common and receptor-specific allosteric modulation of P2X receptors and the molecular base accounting for allosteric binding sites.

Induction of heme oxygenase 1 attenuates placental ischemia-induced hypertension

Recent in vitro studies have reported that heme oxygenase 1 (HO-1) downregulates the angiostatic protein soluble fms-like tyrosine kinase 1 from placental villous explants and that the HO-1 metabolites CO and bilirubin negatively regulate endothelin 1 and reactive oxygen species. Although soluble fms-like tyrosine kinase 1, endothelin 1, and reactive oxygen species have been implicated in the pathophysiology of hypertension during preeclampsia and in response to placental ischemia in pregnant rats, it is unknown whether chronic induction of HO-1 alters the hypertensive response to placental ischemia. The present study examined the hypothesis that HO-1 induction in a rat model of placental ischemia would beneficially affect blood pressure, angiogenic balance, superoxide, and endothelin 1 production in the ischemic placenta. To achieve this goal we examined the effects of cobalt protoporphyrin, an HO-1 inducer, in the reduced uterine perfusion pressure (RUPP) placental ischemia model and in normal pregnant rats. In response to RUPP treatment, mean arterial pressure increases 29 mm Hg (136±7 versus 106±5 mm Hg), which is significantly attenuated by cobalt protoporphyrin (118±5 mm Hg). Although RUPP treatment causes placental soluble fms-like tyrosine kinase 1/vascular endothelial growth factor ratios to alter significantly to an angiostatic balance (1.00±0.10 versus 1.27±0.20), treatment with cobalt protoporphyrin causes a significant shift in the ratio to an angiogenic balance (0.68±0.10). Placental superoxide increased in RUPP (952.5±278.8 versus 243.9±70.5 relative light units/min per milligram) but was significantly attenuated by HO-1 induction (482.7±117.4 relative light units/min per milligram). Also, the preproendothelin message was significantly increased in RUPP, which was prevented by cobalt protoporphyrin. These data indicate that HO-1, or its metabolites, is a potential therapeutic for the treatment of preeclampsia.

Carbon monoxide involved in modulating HCO3- secretion in rat duodenum

We examined the effect of the tricarbonyl-dichlororuthenium (II) dimer (CORM-2), a carbon monoxide (CO) donor, on duodenal HCO(3)(-) secretion in rats and investigated whether endogenous CO produced by heme oxygenase (HO) is involved in the regulation of this secretion. Under urethane anesthesia, a duodenal loop was perfused with saline, and HCO(3)(-) secretion was measured at pH 7.0 using a pH stat method. CORM-2, biliverdin, FeCl(2), or ruthenium (III) chloride hydrate (RuCl(3)) was applied to the loop for 5 min. The mucosal application of CORM-2 dose-dependently increased HCO(3)(-) secretion, whereas neither RuCl(3), FeCl(2), nor biliverdin had an effect. The stimulatory effect was significantly attenuated by indomethacin but not N(G)-nitro-L-arginine methyl ester. The application of CORM-2 increased the mucosal prostaglandin (PG) E(2) content of the duodenum. The acid-induced HCO(3)(-) response was markedly inhibited by indomethacin and Sn(IV) protoporphyrin IX dichloride (SnPP; an inhibitor of HO) but not Cu(II) protoporphyrin dichloride, and the inhibitory effect of SnPP was significantly reversed by pretreatment with hemin, a substrate of HO. Perfusion of the duodenal loop with 100 mM HCl for 2 h caused a few hemorrhagic lesions in the mucosa, and this response was significantly worsened by the prior administration of SnPP and indomethacin. The expression of HO-1 but not HO-2 protein was up-regulated in the duodenum after the acid treatment. These results suggest that CO, generated endogenously or exogenously, stimulates HCO(3)(-) secretion in the duodenum, and this effect is mediated by endogenous PGs. It is assumed that HO/CO plays a role in maintaining the integrity of the duodenal mucosa.

Nitric oxide synthase expression in the medullary respiratory related nuclei and its involvement in CO-mediated central respiratory effects in neonatal rats

The present study was conducted in order to observe the potential participation of the nitric oxide synthase-NO pathway in CO-mediated regulation of respiration of neonatal rats. An immunofluorescent histochemical technique was used to examine the existence of the neuronal nitric oxide synthase, a key enzyme of synthesizing NO, in medullary respiratory nuclei. The rhythmic respiratory-like discharges of hypoglossal rootlets of medullary slices were recorded to test the role of the nitric oxide synthase in CO-mediated respiratory effects. We observed neuronal nitric oxide synthase expressed in the medullary respiratory nuclei in conjunction with CO lengthened expiratory duration, decreased respiratory frequency, and increased inspiratory amplitude. These CO-mediated respiratory effects could be partially eliminated by prior treatment of the slices with Nω-nitro-L-arginine methyl ester, an inhibitor of nitric oxide synthase. The results suggest that nitric oxide synthase-NO pathway might be involved in the CO-mediated central regulation of respiration at the level of medulla oblongata in neonatal rats.

Heme oxygenase metabolites inhibit tubuloglomerular feedback in vivo

Tubuloglomerular feedback (TGF) is a renal autoregulatory mechanism that constricts the afferent arteriole in response to increases in distal NaCl. Heme oxygenases (HO-1 and HO-2) release carbon monoxide (CO) and biliverdin, which may help control renal function. We showed in vitro that HO products inhibit TGF; however, we do not know whether this also occurs in vivo or the mechanism(s) involved. We hypothesized that in vivo HO-1 and HO-2 in the nephron inhibit TGF via release of CO and biliverdin. We first performed laser capture microdissection followed by real-time PCR and found that both HO-1 and HO-2 are expressed in the macula densa. We next performed micropuncture experiments in vivo on individual rat nephrons, adding different compounds to the perfusate, and found that an HO inhibitor, stannous mesoporphyrin (SnMP), potentiated TGF (P < 0.05, SnMP vs. control). The CO-releasing molecule (CORM)-3 partially inhibited TGF at 50 μmol/l (P < 0.01, CORM-3 vs. control) and blocked it completely at higher doses. A soluble guanylyl cyclase (sGC) inhibitor, LY83583, blocked the inhibitory effect of CORM-3 on TGF. Biliverdin also partially inhibited TGF (P < 0.01, biliverdin vs. control), most likely attributable to decreased superoxide (O(2)(-)) because biliverdin was rendered ineffective by tempol, a O(2)(-) dismutase mimetic. We concluded that HO-1 and HO-2 in the nephron inhibit TGF by releasing CO and biliverdin. The inhibitory effect of CO on TGF is mediated by the sGC/cGMP signaling pathway, whereas biliverdin probably acts by reducing O(2)(-).

Heme oxygenase inhibition by 1-aryl-2-(1h-imidazol-1-yl/1h-1,2,4-triazol-1-yl)ethanones and their derivatives

Previous studies by our research group have been concerned with the design of selective inhibitors of heme oxygenases (HO-1 and HO-2). The majority of these were based on a four-carbon linkage of an azole, usually an imidazole, and an aromatic moiety. In the present study, we designed and synthesized a series of inhibition candidates containing a shorter linkage between these groups, specifically, a series of 1-aryl-2-(1H-imidazol-1-yl/1H-1,2,4-triazol-1-yl)ethanones and their derivatives. As regards HO-1 inhibition, the aromatic moieties yielding best results were found to be halogen-substituted residues such as 3-bromophenyl, 4-bromophenyl, and 3,4-dichlorophenyl, or hydrocarbon residues such as 2-naphthyl, 4-biphenyl, 4-benzylphenyl, and 4-(2-phenethyl)phenyl. Among the imidazole-ketones, five (36-39, and 44) were found to be very potent (IC(50)<5 muM) toward both isozymes. Relative to the imidazole-ketones, the series of corresponding triazole-ketones showed four compounds (54, 55, 61, and 62) having a selectivity index >50 in favor of HO-1. In the case of the azole-dioxolanes, two of them (80 and 85), each possessing a 2-naphthyl moiety, were found to be particularly potent and selective HO-1 inhibitors. Three non-carbonyl analogues (87, 89, and 91) of 1-(4-chlorophenyl)-2-(1H-imidazol-1-yl)ethanone were found to be good inhibitors of HO-1. For the first time in our studies, two azole-based inhibitors (37 and 39) were found to exhibit a modest selectivity index in favor of HO-2. The present study has revealed additional candidates based on inhibition of heme oxygenases for potentially useful pharmacological and therapeutic applications.

Garlic accelerates red blood cell turnover and splenic erythropoietic gene expression in mice: evidence for erythropoietin-independent erythropoiesis

Garlic (Allium sativum) has been valued in many cultures both for its health effects and as a culinary flavor enhancer. Garlic's chemical complexity is widely thought to be the source of its many health benefits, which include, but are not limited to, anti-platelet, procirculatory, anti-inflammatory, anti-apoptotic, neuro-protective, and anti-cancer effects. While a growing body of scientific evidence strongly upholds the herb's broad and potent capacity to influence health, the common mechanisms underlying these diverse effects remain disjointed and relatively poorly understood. We adopted a phenotype-driven approach to investigate the effects of garlic in a mouse model. We examined RBC indices and morphologies, spleen histochemistry, RBC half-lives and gene expression profiles, followed up by qPCR and immunoblot validation. The RBCs of garlic-fed mice register shorter half-lives than the control. But they have normal blood chemistry and RBC indices. Their spleens manifest increased heme oxygenase 1, higher levels of iron and bilirubin, and presumably higher CO, a pleiotropic gasotransmitter. Heat shock genes and those critical for erythropoiesis are elevated in spleens but not in bone marrow. The garlic-fed mice have lower plasma erythropoietin than the controls, however. Chronic exposure to CO of mice on garlic-free diet was sufficient to cause increased RBC indices but again with a lower plasma erythropoietin level than air-treated controls. Furthermore, dietary garlic supplementation and CO treatment showed additive effects on reducing plasma erythropoietin levels in mice. Thus, garlic consumption not only causes increased energy demand from the faster RBC turnover but also increases the production of CO, which in turn stimulates splenic erythropoiesis by an erythropoietin-independent mechanism, thus completing the sequence of feedback regulation for RBC metabolism. Being a pleiotropic gasotransmitter, CO may be a second messenger for garlic's other physiological effects.

Thiol-disulfide redox dependence of heme binding and heme ligand switching in nuclear hormone receptor rev-erb{beta}

Rev-erbβ is a heme-binding nuclear hormone receptor that represses a broad spectrum of target genes involved in regulating metabolism, the circadian cycle, and proinflammatory responses. Here, we demonstrate that a thiol-disulfide redox switch controls the interaction between heme and the ligand-binding domain of Rev-erbβ. The reduced dithiol state of Rev-erbβ binds heme 5-fold more tightly than the oxidized disulfide state. By means of site-directed mutagenesis and by UV-visible and EPR spectroscopy, we also show that the ferric heme of reduced (dithiol) Rev-erbβ can undergo a redox-triggered switch from imidazole/thiol ligation (via His-568 and Cys-384, based on a prior crystal structure) to His/neutral residue ligation upon oxidation to the disulfide form. On the other hand, we find that change in the redox state of iron has no effect on heme binding to the ligand-binding domain of the protein. The low dissociation constant for the complex between Fe(3+)- or Fe(2+)-heme and the reduced dithiol state of the protein (K(d) = ∼ 20 nM) is in the range of the intracellular free heme concentration. We also determined that the Fe(2+)-heme bound to the ligand-binding domain of Rev-erbβ has high affinity for CO (K(d) = 60 nM), which replaces one of the internal ligands when bound. We suggest that this thiol-disulfide redox switch is one mechanism by which oxidative stress is linked to circadian and/or metabolic imbalance. Heme dissociation from Rev-erbβ has been shown to derepress the expression of target genes in response to changes in intracellular redox conditions. We propose that oxidative stress leads to oxidation of cysteine(s), thus releasing heme from Rev-erbβ and altering its transcriptional activity.

New light on the anti-colitic actions of therapeutic aminosalicylates: the role of heme oxygenase

Although a variety of pharmaceutical preparations of aminosalicylate are commonly used in the clinic for the control of inflammatory bowel disease, the mechanisms underlying their therapeutic actions remain unclear. Recent in vivo and in vitro studies have demonstrated that 5-aminosalicylic acid (5-ASA), regarded as the active moiety in aminosalicylate preparations such as sulfasalazine, can induce the heat shock protein, heme oxygenase-1 (HO-1) and up-regulate HO enzyme activity in the colon. As HO-1 can produce endogenous anti-oxidant and anti-inflammatory moieties such as bilirubin and carbon monoxide (CO), these findings suggest a novel mechanism of action for aminosalicylates, acting as anti-colitic agents through the up-regulation of HO-1 enzyme expression and activity.

Exhaled carbon monoxide and risk of metabolic syndrome and cardiovascular disease in the community

BACKGROUND

Endogenous carbon monoxide (CO) at physiological concentrations is cytoprotective, whereas excess levels reflect underlying oxidative stress, inflammation, and vascular pathology and portend adverse clinical sequelae. However, the relation of exhaled CO to metabolic/vascular risk in the community is unknown.

METHODS AND RESULTS

We related exhaled CO, a surrogate measure of blood CO concentration, to the risk of developing new-onset metabolic syndrome and incident cardiovascular disease following 14 943 routine examinations (4139 unique participants; mean age, 46 years, 53% women) in the Framingham Heart Study. Baseline exhaled CO was associated with the presence of cardiometabolic risk factors (including smoking) and prevalent metabolic syndrome (odds ratio, 1.09 per log CO; 95% confidence interval, 1.02 to 1.17; P=0.01). During up to 4 years of follow-up, 1458 participants developed new-onset metabolic syndrome, and 416 experienced a first cardiovascular disease event. Compared with individuals in the lowest quartile of exhaled CO, those in the highest quartile were more likely to develop metabolic syndrome (odds ratio, 1.48; 95% confidence interval, 1.25 to 1.76; P<0.0001) and cardiovascular disease events (hazard ratio, 1.66; 95% confidence interval, 1.14 to 2.40; P=0.008) in multivariable analyses that included adjustment for smoking status.

CONCLUSION

In our community-based sample, higher exhaled CO levels predicted the development of metabolic syndrome and future cardiovascular disease events, underscoring the importance of this endogenous second messenger in the pathogenesis of metabolic and vascular risk.

Endogenous carbon monoxide production in disease

Carbon monoxide (CO) in tissues and cells can originate from inhalation of CO or endogenously. Endogenous production, carboxyhemoglobin (COHb) formation, and exhaled CO levels are influenced by physiological factors, including disease. It is suggested that endogenous CO production can be used as a biomarker for oxidative and inflammatory processes. Also, endogenous CO can contribute to increased body burden of CO, which may both disrupt normal CO signaling cascades and increase the risk of CO toxicity.

Heme oxygenase-1 deficiency leads to alteration of soluble guanylate cyclase redox regulation

Heme oxygenase-1 knockout, H(mox)1(-/-), mice exhibit exacerbated vascular lesions after ischemia-reperfusion and mechanical injury. Surprisingly, we found no studies that reported contractile responses and sensitivity to vasorelaxants in H(mox)1(-/-) mice. The contractile responses [superior mesenteric arteries (SMA), from female H(mox)1(-/-) mice] exhibited increased sensitivity to phenylephrine (p < 0.001). Cumulative addition of acetylcholine relaxed SMA, with the residual contraction remaining 2 times higher in H(mox)1(-/-) mice (p < 0.001). Sodium nitroprusside (SNP, an NO donor) and 3-(5'-hydroxymethyl-2'-furyl)-1-benzyl indazole [YC-1; acts directly on soluble guanylate cyclase (sGC)] led to further relaxation, yet the residual contraction remained 2 to 3 times higher in H(mox)1(-/-) than H(mox)1(+/+) mice (p < 0.001). Branches from H(mox)1(-/-) mesenteric and renal arteries also showed reduced relaxation (p < 0.025). Relaxation of SMA was measured to 4-({(4-carboxybutyl) [2-(5-fluoro-2-{[4'-(trifluoromethyl) biphenyl-4-yl] methoxy}phenyl)ethyl]amino}benzoic acid (BAY 60-2770), which is a more effective activator of oxidized/heme-free sGC; and to 5-cyclopropyl-2-{1-(2-fluoro-benzyl)-1H-pyrazolo[3,4-b]pyridin-3-yl}-pyrimidin-4-ylamine (BAY 41-2272), a more effective stimulator of reduced sGC. H(mox)1(-/-) arteries were 15 times more sensitive to BAY 60-2770 (p < 0.025) than were H(mox)1(+/+) arteries. Pretreatment with 1H-[1,2,4]oxadiazolo[3,4-a]quinoxalin-1-one (ODQ), an oxidizer of sGC, predictably shifted the BAY 60-2770 response of H(mox)1(+/+) to the left (p < 0.01) and BAY 41-2272 response to the right (p < 0.01). ODQ had little effect on the responses of H(mox)1(-/-) arteries, indicating that much of sGC was oxidized/heme-free. Western analyses of sGC in SMA indicated that both α1 and β1 subunit levels were reduced to <50% of H(mox)1(+/+) level (p < 0.025). These findings support the hypothesis that the antioxidant function of H(mox)1 plays a significant role in the maintenance of sGC in a reduced state, which is resistant to degradation and is sensitive to NO. This function may be especially important in reducing vascular damage during ischemia-reperfusion injury.

A tracer analysis study on the redistribution and oxidization of endogenous carbon monoxide in the human body

Past studies have suggested that some carbon monoxide (CO) moves from blood haemoglobin to tissue cells and that mitochondrial cytochrome c oxidase oxidizes CO to carbon dioxide (CO₂). However, no study has demonstrated this redistribution and oxidization of CO under physiological conditions. The objective of this study was to trace the redistribution and oxidization of CO in the human body by detecting ¹³CO₂ production after the inhalation of ¹³CO. In Experiment 1, we asked a healthy subject to inhale 50 ppm ¹³CO gas. In Experiment 2, we circulated heparinized human blood in a cardio-pulmonary bypass circuit and supplied 50 ppm ¹³CO gas to the oxygenator. We sequentially sampled exhaled and output gases and measured the ¹³CO₂/¹²CO₂ ratios. In Experiment 1, the exhaled ¹³CO₂/¹²CO₂ ratio increased significantly between 4 to 31 h of ¹³CO inhalation. In Experiment 2, the output ¹³CO₂/¹²CO₂ ratio showed no significant increase within 36 h of ¹³CO input. Experiment 1 demonstrated the oxidization of CO in the human body under physiological conditions. Experiment 2 confirmed that oxidization does not occur in the circulating blood and indicated the redistribution of CO from blood carboxyhaemoglobin to tissue cells.

Isolating the segment of the mitochondrial electron transport chain responsible for mitochondrial damage during cardiac ischemia

Ischemia damages the mitochondrial electron transport chain (ETC), mediated in part by damage generated by the mitochondria themselves. Mitochondrial damage resulting from ischemia, in turn, leads to cardiac injury during reperfusion. The goal of the present study was to localize the segment of the ETC that produces the ischemic mitochondrial damage. We tested if blockade of the proximal ETC at complex I differed from blockade distal in the chain at cytochrome oxidase. Isolated rabbit hearts were perfused for 15min followed by 30min stop-flow ischemia at 37 degrees C. Amobarbital (2.5mM) or azide (5mM) was used to block proximal (complex I) or distal (cytochrome oxidase) sites in the ETC. Time control hearts were buffer-perfused for 45min. Subsarcolemmal mitochondria (SSM) and interfibrillar mitochondria (IFM) were isolated. Ischemia decreased cytochrome c content in SSM but not in IFM compared to time control. Blockade of electron transport at complex I preserved the cytochrome c content in SSM. In contrast, blockade of electron transport at cytochrome oxidase with azide did not retain cytochrome c in SSM during ischemia. Since blockade of electron transport at complex III also prevented cytochrome c loss during ischemia, the specific site that elicits mitochondrial damage during ischemia is likely located in the segment between complex III and cytochrome oxidase.

Neferine inhibits angiotensin II-stimulated proliferation in vascular smooth muscle cells through heme oxygenase-1

AIM

To explore the effect of neferine on angiotensin II (Ang II)-induced vascular smooth muscle cell (VSMC) proliferation.

METHODS

Human umbilical vein smooth muscle cells (HUVSMCs) were used. Cell proliferation was determined by using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and flow cytometry analysis. Heme oxygenase (HO)-1 protein expression was tested by Western blot analysis. Extracellular signal-regulated protein kinase 1/2 (ERK1/2) activation was determined by using immunoblotting.

RESULTS

Pre-incubation of HUVSMCs with neferine (0.1, 0.5, 1.0, and 5.0 micromol/L) significantly inhibited Ang II-induced cell proliferation in a concentration-dependent manner and neferine 5.0 micromol/L increased HO-1 expression by 259% compared with control. The antiproliferative effect of neferine was significantly attenuated by coapplication of zinc protoporphyrin IX (ZnPP IX, an HO-1 inhibitor) with neferine. Ang II-enhanced ERK1/2 phosphorylation was markedly reversed by neferine. By inhibiting HO-1 activity with ZnPP IX, the inhibitive effect of neferine on ERK1/2 phosphorylation was significantly attenuated. Cobalt-protoporphyrin (CoPP), an HO-1 inducer, significantly decreased Ang II-induced ERK1/2 phosphorylation and inhibited Ang II-induced cell proliferation. The ERK1/2 pathway inhibitor PD98059 significantly blocked Ang II-enhanced ERK1/2 phosphorylation and inhibited cell proliferation.

CONCLUSION

These findings suggest that neferine can inhibit Ang II-induced HUVSMC proliferation by upregulating HO-1, leading to the at least partial downregulation of ERK1/2 phosphorylation.

Methylene chloride protects against cecal ligation and puncture-induced acute lung injury by modulating inflammatory mediators

Recent studies suggest that exogenously administered CO is beneficial for the resolution of acute pulmonary inflammation. In this study, we assessed the role of CO donor, methylene chloride (MC), on modulation of lung inflammation during sepsis. Acute lung injury in Sprague-Dawley rats was induced by cecal ligation and perforation (CLP). MC (100mg/kg) was intragastrically administered 2h before CLP induction. Lung tissues and lavage samples were isolated for biochemical determinations and histological measurements 10h after CLP operation. In addition, we investigated survival rate with the other 40 rats. Intragastric administration with MC significantly decreased morbidity and mortality of CLP-induced ALI as confirmed by blinded histological changes, myeloperoxidase activity, mortality, and the content of TNF-alpha and IL-10. This protective effect could be abolished by an MC inhibitor, disulfiram. These results suggested that MC has obvious protective effects against CLP-induced ALI in rats. The mechanism of the protective effects partly involves modulating inflammatory mediators.

Hydrogen sulfide and substance P in inflammation

Hydrogen sulfide (H(2)S) plays an important role in cardiovascular, central nervous, and gastrointestinal systems. Being the third gaseous mediator, H(2)S has been shown to act as a vasodilator. In recent times, more and more attention has been paid to the biological functions of H(2)S in inflammation. Substance P is an 11 amino acid neuropeptide that is released from nerve endings in many tissues. Subsequent to its release, substance P binds to neurokinin-1 (NK-1) receptors on the surface of effector cells and, in addition to being a mediator of pain, it plays an important role in many inflammatory states including asthma, immune-complex-mediated lung injury, experimental arthritis, and inflammatory bowel disease. Substance P has been shown to increase microvascular permeability and promote plasma extravasation. Using animal models of inflammation of different etiologies such as acute pancreatitis, sepsis, and burns, studies in our laboratory have recently shown an important role of the pro-inflammatory action of H(2)S and substance P.