Effects of carbon monoxide and heme oxygenase inhibitors in cerebral vessels of rats and mice

Regulation of the Cerebral Circulation During Development

The cerebral microcirculation undergoes dynamic changes in parallel with the development of neurons, glia, and their energy metabolism throughout gestation and postnatally. Cerebral blood flow (CBF), oxygen consumption, and glucose consumption are as low as 20% of adult levels in humans born prematurely but eventually exceed adult levels at ages 3 to 11 years, which coincide with the period of continued brain growth, synapse formation, synapse pruning, and myelination. Neurovascular coupling to sensory activation is present but attenuated at birth. By 2 postnatal months, the increase in CBF often is disproportionately smaller than the increase in oxygen consumption, in contrast to the relative hyperemia seen in adults. Vascular smooth muscle myogenic tone increases in parallel with developmental increases in arterial pressure. CBF autoregulatory response to increased arterial pressure is intact at birth but has a more limited range with arterial hypotension. Hypoxia-induced vasodilation in preterm fetal sheep with low oxygen consumption does not sustain cerebral oxygen transport, but the response becomes better developed for sustaining oxygen transport by term. Nitric oxide tonically inhibits vasomotor tone, and glutamate receptor activation can evoke its release in lambs and piglets. In piglets, astrocyte-derived carbon monoxide plays a central role in vasodilation evoked by glutamate, ADP, and seizures, and prostanoids play a large role in endothelial-dependent and hypercapnic vasodilation. Overall, homeostatic mechanisms of CBF regulation in response to arterial pressure, neuronal activity, carbon dioxide, and oxygenation are present at birth but continue to develop postnatally as neurovascular signaling pathways are dynamically altered and integrated. © 2021 American Physiological Society. Compr Physiol 11:1-62, 2021.

[Cognitive impairment in heart failure: the role of microcirculation abnormalities]

Heart failure is one of the most frequent causes predisposing to cognitive impairment where its prevalence varies from 25 to 80% of cases. In this review, the mechanisms of microcirculatory abnormalities, which play a potential role in the development of cognitive impairment in patients with heart failure, are considered. Understanding of these mechanisms will help in the development of targeted therapy of cardiovascular and cerebrovascular diseases.

Effect of the Hemoxygenase-Carbon Monoxide (HO-CO) System on the Reactivity of Uterine Artery Branches in Rats

First to fourth-order branches of the uterine artery in sexually mature female Wistar rats were studied by biomicroscopy. After administration of a CO donor hemin (60 mM), the diameters of large uterine branches with a well-developed muscle layer markedly increased, while the increase in diameter of small vessels with one often interrupted layer of smooth muscle cells increased insignificantly. Zinc protoporphyrin IX (30 mM) in all cases blocked this effect. However, zinc protoporphyrin IX does not affect NO-mediated reaction of the branches of the uterine artery caused by administration of L-arginine (60 mM), and L-NAME did not significantly affect reactivity of uterine artery branches associated with the hemoxygenase-CO system. In contrast to NO, CO produced less potent and rapid, but more sustained effect. The target for the hemoxygenase-CO system is mainly arteries with developed muscular layer, while the target for the NO synthase-NO is small vessels where endothelium plays a Rdecisive role in the regulation of vasomotor reactions.

Hydrogen Sulfide: A Therapeutic Option in Systemic Sclerosis

Systemic sclerosis (SSc) is a lethal disease that is characterized by auto-immunity, vascular injury, and progressive fibrosis of multiple organ systems. Despite the fact that the exact etiology of SSc remains unknown, oxidative stress has been associated with a large range of SSc-related complications. In addition to the well-known detrimental properties of reactive oxygen species (ROS), gasotransmitters (e.g., nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H₂S)) are also thought to play an important role in SSc. Accordingly, the diverse physiologic actions of NO and CO and their role in SSc have been previously studied. Recently, multiple studies have also shown the importance of the third gasotransmitter H₂S in both vascular physiology and pathophysiology. Interestingly, homocysteine (which is converted into H₂S through the transsulfuration pathway) is often found to be elevated in SSc patients; suggesting defects in the transsulfuration pathway. Hydrogen sulfide, which is known to have several effects, including a strong antioxidant and vasodilator effect, could potentially play a prominent role in the initiation and progression of vasculopathy. A better understanding of the actions of gasotransmitters, like H₂S, in the development of SSc-related vasculopathy, could help to create early interventions to attenuate the disease course. This paper will review the role of H₂S in vascular (patho-)physiology and potential disturbances in SSc. Moreover, current data from experimental animal studies will be reviewed. Lastly, we will evaluate potential interventional strategies.

Immunolocation of Heme Oxygenases in the Walls of Cerebral Arteries of Various Diameters in Rats

The distribution of two enzymes involved in the formation of carbon monoxide, heme oxygenases 1 and 2, in the pial branches of orders I-V of the middle cerebral artery basin and in intracerebral vessels was studied in adult Wistar rats. Immunohistochemical studies detected hemeoxygenase-2 in the endothelium of the small pial and intracerebral arterioles and in myocytes of pial branches I-III. Heme oxygenase 1, an inducible form of the enzyme, is normally not expressed in the cerebral vessels, but the enzyme is expressed in response to sodium metaarsenite. In this case, heme oxygenase markers are detected in myocytes of pial arteries I-II and in the endothelium of small pial and intracerebral vessels. Sodium meta-arsenite is inessential for immunolocation and quantitative distribution of heme oxygenase 2 in the vessels.

Cardioprotective Effect of Selective Estrogen Receptor Modulator Raloxifene Are Mediated by Heme Oxygenase in Estrogen-Deficient Rat

Estrogens and raloxifene (RAL) have beneficial effects on certain cardiovascular indices in postmenopausal women characterized by estrogen deficiency. Heme oxygenase (HO) activity is increased by 17β-estradiol (E₂) and RAL in estrogen-deficient rat resulting in vasorelaxation mediated by carbon monoxide. We determined the expressions of HO in cardiac and aortic tissues after ovariectomy (OVX) and subsequent RAL or E₂ treatment. We investigated the effects of pharmacological inhibition of HO enzyme on the arginine vasopressin- (AVP-) induced blood pressure in vivo, the epinephrine- and phentolamine-induced electrocardiogram ST segment changes in vivo, and the myeloperoxidase (MPO) enzyme activity. When compared with intact females, OVX decreased the HO-1 and HO-2 expression, aggravated the electrocardiogram signs of heart ischemia and the blood pressure response to AVP, and increased the cardiac MPO. E₂ and RAL are largely protected against these negative impacts induced by OVX. The pharmacological inhibition of HO in E₂- or RAL-treated OVX animals, however, restored the cardiovascular status close to that observed in nontreated OVX animals. The decreased expression of HO enzymes and the changes in blood pressure ischemia susceptibility and inflammatory state in OVX rat can be reverted by the administration of E₂ or RAL partly through its antioxidant and anti-inflammatory roles.

Carbon monoxide inhalation induces headache in a human headache model

Introduction

Carbon monoxide (CO) is an endogenously produced signalling molecule that has a role in nociceptive processing and cerebral vasodilatation. We hypothesized that inhalation of CO would induce headache and vasodilation of cephalic and extracephalic arteries.

Methods

In a randomized, double-blind, placebo-controlled crossover design, 12 healthy volunteers were allocated to inhalation of CO (carboxyhemoglobin 22%) or placebo on two separate days. Headache was scored on a verbal rating scale from 0–10. We recorded mean blood velocity in the middle cerebral artery (VMCA) by transcranial Doppler, diameter of the superficial temporal artery (STA) and radial artery (RA) by high-resolution ultrasonography and facial skin blood flow by laser speckle contrast imaging.

Results

Ten volunteers developed headache after CO compared to six after placebo. The area under the curve for headache (0–12 hours) was increased after CO compared with placebo ( p = 0.021). CO increased VMCA ( p = 0.002) and facial skin blood flow ( p = 0.012), but did not change the diameter of the STA ( p = 0.060) and RA ( p = 0.433).

Conclusion

In conclusion, the study demonstrated that CO caused mild prolonged headache but no arterial dilatation in healthy volunteers. We suggest this may be caused by a combination of hypoxic and direct cellular effects of CO.

Affinin (Spilanthol), Isolated from Heliopsis longipes, Induces Vasodilation via Activation of Gasotransmitters and Prostacyclin Signaling Pathways

Heliopsis longipes roots have been widely used in Mexican traditional medicine to relieve pain, mainly, toothaches. Previous studies have shown that affinin, the major alkamide of these roots, induces potent antinociceptive and anti-inflammatory activities. However, the effect of H. longipes root extracts and affinin on the cardiovascular system have not been investigated so far. In the present study, we demonstrated that the dichloromethane and ethanolic extracts of H. longipes roots, and affinin, isolated from these roots, produce a concentration-dependent vasodilation of rat aorta. Affinin-induced vasorelaxation was partly dependent on the presence of endothelium and was significantly blocked in the presence of inhibitors of NO, H₂S, and CO synthesis (NG-nitro-l-arginine methyl ester (l-NAME), dl-propargylglycine (PAG), and chromium mesoporphyrin (CrMP), respectively); K⁺ channel blockers (glibenclamide (Gli) and tetraethyl ammonium (TEA)), and guanylate cyclase and cyclooxygenase inhibitors (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) and indomethacin (INDO), respectively). Our results demonstrate, for the first time, that affinin induces vasodilation by mechanisms that involve gasotransmitters, and prostacyclin signaling pathways. These findings indicate that this natural alkamide has therapeutic potential in the treatment of cardiovascular diseases.

Restoration of Endothelial Function in Pparα (-/-) Mice by Tempol

Peroxisome proliferator activated receptor alpha (PPARα) is one of the PPAR isoforms belonging to the nuclear hormone receptor superfamily that regulates genes involved in lipid and lipoprotein metabolism. PPARα is present in the vascular wall and is thought to be involved in protection against vascular disease. To determine if PPARα contributes to endothelial function, conduit and cerebral resistance arteries were studied in Pparα^−/− mice using isometric and isobaric tension myography, respectively. Aortic contractions to PGF_2α and constriction of middle cerebral arteries to phenylephrine were not different between wild type (WT) and Pparα^−/−; however, relaxation/dilation to acetylcholine (ACh) was impaired. There was no difference in relaxation between WT and Pparα^−/− aorta to treatment with a nitric oxide (NO) surrogate indicating impairment in endothelial function. Endothelial NO levels as well as NO synthase expression were reduced in Pparα^−/− aortas, while superoxide levels were elevated. Two-week feeding with the reactive oxygen species (ROS) scavenger, tempol, normalized ROS levels and rescued the impaired endothelium-mediated relaxation in Pparα^−/− mice. These results suggest that Pparα^−/− mice have impaired endothelial function caused by decreased NO bioavailability. Therefore, activation of PPARα receptors may be a therapeutic target for maintaining endothelial function and protection against cardiovascular disease.

[Topochemistry of internuclear interneurons in the human brain stem in arterial hypertension]

OBJECTIVE

To study the internuclear interneurons (IN) involved in the metabolism of nitric oxide, hydrogen sulfide and carbon monoxide in the caudal brainstem in healthy people and those with lifetime hypertension.

MATERIAL AND METHODS

The study was performed on postmortem material of 8 healthy men and 19 men, aged 18-44 years, with lifetime arterial hypertension. Immunohistochemistry methods for nNOS, HO-2, CBS and histochemical method for NADPH-diaphorase were used to study IN groups located between the giant and small cell reticular nuclei (IN1), small cell reticular nucleus and the nucleus of the solitary tract (IN2) surrounded by the lateral reticular nucleus (IN3).

RESULTS

IN differ in size, shape, length and structure of sprouts as well as the nature of relationships formed and intensity of immunohistochemical reaction. The intensity of MN response to the high blood pressure depends on the cell size: qualitative and quantitative changes among the most small MN are mild. In contrast, in many major MN, structural changes, a significant reduction in the proportion of these cells, concentration and reaction rate are noted. More significant changes in quantitative indicators are found among nNOS-positive neurons. The reduction in the quantitative indicators depends on the localization of cells. In IN1, where there are many large IN, changes are more pronounced than in IN3 and IN2, which do not contain so many such cells.

CONCLUSION

Central mechanisms of hemodynamic control include, at least, two groups of interneurons: intranuclear and internuclear. However, among the latter, only large IN are responsive to increases in blood pressure that confirms their participation in the regulation of hemodynamics, Small IN maintain a relatively small organization and perform a stable, obviously, integrating function.

Carbon monoxide may be an important molecule in migraine and other headaches

Introduction

Carbon monoxide was previously considered to just be a toxic gas. A wealth of recent information has, however, shown that it is also an important endogenously produced signalling molecule involved in multiple biological processes. Endogenously produced carbon monoxide may thus play an important role in nociceptive processing and in regulation of cerebral arterial tone.

Discussion

Carbon monoxide-induced headache shares many characteristics with migraine and other headaches. The mechanisms whereby carbon monoxide causes headache may include hypoxia, nitric oxide signalling and activation of cyclic guanosine monophosphate pathways. Here, we review the literature about carbon monoxide-induced headache and its possible mechanisms.

Conclusion

We suggest, for the first time, that carbon monoxide may play an important role in the mechanisms of migraine and other headaches.

Characterization of a cellular denitrase activity that reverses nitration of cyclooxygenase

Protein 3-nitrotyrosine (3-NT) formation is frequently regarded as a simple biomarker of disease, an irreversible posttranslational modification that can disrupt protein structure and function. Nevertheless, evidence that protein 3-NT modifications may be site selective and reversible, thus allowing for physiological regulation of protein activity, has begun to emerge. We have previously reported that cyclooxygenase (COX)-1 undergoes heme-dependent nitration of Tyr(385), an internal and catalytically essential residue. In the present study, we demonstrate that nitrated COX-1 undergoes a rapid reversal of nitration by substrate-selective and biologically regulated denitrase activity. Using nitrated COX-1 as a substrate, denitrase activity was validated and quantified by analytic HPLC with electrochemical detection and determined to be constitutively active in murine and human endothelial cells, macrophages, and a variety of tissue samples. Smooth muscle cells, however, contained little denitrase activity. Further characterizing this denitrase activity, we found that it was inhibited by free 3-NT and may be enhanced by endogenous nitric oxide and exogenously administered carbon monoxide. Finally, we describe a purification protocol that results in significant enrichment of a discrete denitrase-containing fraction, which maintains activity throughout the purification process. These findings reveal that nitrated COX-1 is a substrate for a denitrase in cells and tissues, implying that the reciprocal processes of nitration and denitration may modulate bioactive lipid synthesis in the setting of inflammation. In addition, our data reveal that denitration is a controlled process that may have broad importance for regulating cell signaling events in nitric oxide-generating systems during oxidative/nitrosative stress.

Ryanodine receptors, calcium signaling, and regulation of vascular tone in the cerebral parenchymal microcirculation

The cerebral blood supply is delivered by a surface network of pial arteries and arterioles from which arise (parenchymal) arterioles that penetrate into the cortex and terminate in a rich capillary bed. The critical regulation of CBF, locally and globally, requires precise vasomotor regulation of the intracerebral microvasculature. This vascular region is anatomically unique as illustrated by the presence of astrocytic processes that envelope almost the entire basolateral surface of PAs. There are, moreover, notable functional differences between pial arteries and PAs. For example, in pial VSMCs, local calcium release events ("calcium sparks") through ryanodine receptor (RyR) channels in SR membrane activate large conductance, calcium-sensitive potassium channels to modulate vascular diameter. In contrast, VSMCs in PAs express functional RyR and BK channels, but under physiological conditions, these channels do not oppose pressure-induced vasoconstriction. Here, we summarize the roles of ryanodine receptors in the parenchymal microvasculature under physiologic and pathologic conditions, and discuss their importance in the control of CBF.

PPARα-Independent Arterial Smooth Muscle Relaxant Effects of PPARα Agonists

We sought to determine direct vascular effects of peroxisome proliferator-activated receptor alpha (PPARα) agonists using isolated mouse aortas and middle cerebral arteries (MCAs). The PPARα agonists GW7647, WY14643, and gemfibrozil acutely relaxed aortas held under isometric tension and dilated pressurized MCAs with the following order of potency: GW7647≫WY14643>gemfibrozil. Responses were endothelium-independent, and the use of PPARα deficient mice demonstrated that responses were also PPARα-independent. Pretreating arteries with high extracellular K⁺ attenuated PPARα agonist-mediated relaxations in the aorta, but not in the MCA. In the aorta, the ATP sensitive potassium (K_ATP) channel blocker glibenclamide also impaired relaxations whereas the other K⁺ channel inhibitors, 4-aminopyridine and Iberiotoxin, had no effect. In aortas, GW7647 and WY14643 elevated cGMP levels by stimulating soluble guanylyl cyclase (sGC), and inhibition of sGC with ODQ blunted relaxations to PPARα agonists. In the MCA, dilations were inhibited by the protein kinase C (PKC) activator, phorbol 12,13-dibutyrate, and also by ODQ. Our results demonstrated acute, nonreceptor-mediated relaxant effects of PPARα agonists on smooth muscle of mouse arteries. Responses to PPARα agonists in the aorta involved K_ATP channels and sGC, whereas in the MCA the PKC and sGC pathways also appeared to contribute to the response.

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.

The content of elements in rainwater and its relation to the frequency of hospitalization for atrial fibrillation in Opole Voivodship, Poland, during 2000-2002

The elemental composition of rainwater is a suitable indirect indicator of the presence of chemical elements in airborne dust. As such, rainwater is considered a suitable monitor for environmental or natural pollution. The yearly content of chemical elements in rainwater may be considered a good indicator for determining the influence of these environmental factors on human body. We decided to investigate the relationship between chemical elements in rainwater and the frequency of hospitalizations for atrial fibrillation (I48, ICD10) on the population of the region of Opole Voivodship, Poland during the years 2000-2002. The voivodship or province has a population of one million and is divided into 12 counties that have between 44,000 and 151,000 inhabitants. We calculated the yearly average number of hospitalizations by reasons of atrial fibrillation per 10,000 inhabitants in particular counties. The average content of the chosen chemical elements in kilograms per hectare per year was calculated for each county individually and the data evaluated by means of Spearman's correlation coefficient. There is a high positive correlation between chromium in rainwater and hospital admissions for atrial fibrillation (r = 0.62) and mild positive correlation with cadmium (r = 0.57), lead (r = 0.57), zinc (r = 0.50), and chloride (r = 0.48). There are no significant differences between male and female patients. The biological activities of these elements, which may include enhanced adrenergic stimulation, remodeling of calcium or other ion channels, or the cytotoxic effects of hexavalent chromium may explain the positive correlations here reported.

Mechanical ventilation-induced oxidative stress in the diaphragm: role of heme oxygenase-1

BACKGROUND

Prolonged mechanical ventilation (MV) results in a rapid onset of diaphragmatic atrophy that is primarily due to increased proteolysis. Although MV-induced protease activation can involve several factors, it is clear that oxidative stress is a required signal for protease activation in the diaphragm during prolonged MV. However, the oxidant-producing pathways in the diaphragm that contribute to MV-induced oxidative stress remain unknown. We have demonstrated that prolonged MV results in increased diaphragmatic expression of a key stress-sensitive enzyme, heme oxygenase (HO)-1. Paradoxically, HO-1 can function as either a pro-oxidant or an antioxidant, and the role that HO-1 plays in MV-induced diaphragmatic oxidative stress is unknown. We tested the hypothesis that HO-1 acts as a pro-oxidant in the diaphragm during prolonged MV.

METHODS

To determine whether HO-1 functions as a pro-oxidant or an antioxidant in the diaphragm during MV, we assigned rats into three experimental groups: (1) a control group, (2) a group that received 18 h of MV and saline solution, and (3) a group that received 18 h of MV and was treated with a selective HO-1 inhibitor. Indices of oxidative stress, protease activation, and fiber atrophy were measured in the diaphragm.

RESULTS

Inhibition of HO-1 activity did not prevent or exacerbate MV-induced diaphragmatic oxidative stress (as indicated by biomarkers of oxidative damage). Further, inhibition of HO-1 activity did not influence MV-induced protease activation or myofiber atrophy in the diaphragm.

CONCLUSIONS

Our results indicate that HO-1 is neither a pro-oxidant nor an antioxidant in the diaphragm during MV. Furthermore, our findings reveal that HO-1 does not play an important role in MV-induced protease activation and diaphragmatic atrophy.

Cerebrovascular responses in mice deficient in the potassium channel, TREK-1

We tested the hypothesis that TREK-1, a two-pore domain K channel, is involved with dilations in arteries. Because there are no selective activators or inhibitors of TREK-1, we generated a mouse line deficient in TREK-1. Endothelium-mediated dilations were not different in arteries from wild-type (WT) and TREK-1 knockout (KO) mice. This includes dilations of the middle cerebral artery to ATP, dilations of the basilar artery to ACh, and relaxations of the aorta to carbachol, a cholinergic agonist. The nitric oxide (NO) and endothelium-dependent hyperpolarizing factor components of ATP dilations were identical in the middle cerebral arteries of WT and TREK-1 KO mice. Furthermore, the NO and cyclooxygenase-dependent components were identical in the basilar arteries of the different genotypes. Dilations of the basilar artery to alpha-linolenic acid, an activator of TREK-1, were not affected by the absence of TREK-1. Whole cell currents recorded using patch-clamp techniques were similar in cerebrovascular smooth muscle cells (CVSMCs) from WT and TREK-1 KO mice. alpha-linolenic acid or arachidonic acid increased whole cell currents in CVSMCs from both WT and TREK-1 KO mice. The selective blockers of large-conductance Ca-activated K channels, penitrem A and iberiotoxin, blocked the increased currents elicited by either alpha-linolenic or arachidonic acid. In summary, dilations were similar in arteries from WT and TREK-1 KO mice. There was no sign of TREK-1-like currents in CVSMCs from WT mice, and there were no major differences in currents between the genotypes. We conclude that regulation of arterial diameter is not altered in mice lacking TREK-1.

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.

Frequency of hospitalization for angina pectoris, stroke, and peripheral venous thrombosis and its relationship to elements in rainwater in Opole Voivodship, Poland, during 2000-2002

The content of elements in rainwater is an indirect indicator of its occurrence in air dust. This is sometimes referred to as rain fallout and is investigated in applied environmental pollution monitoring schemes. The annual content of elements in rainwater may be recognized as good index for assessing influence of those environmental factors on human body. The possible relationship between the concentrations of selected elements in rainwater and the frequency of hospitalization by reason of angina pectoris, stroke, and peripheral venous thrombosis was investigated in the Opole Voivodship (Poland) area during the period 2000-2002. There is a relatively high or partly significant correlation between frequency of hospitalization by reason of these conditions and content of lead, cadmium, chromium, zinc, and chloride in rainwater. Significant gender-dependent differences were observed only in peripheral venous thrombosis, where important correlations with lead, cadmium, and chromium were found only in men.

2,2,2-trichloroethanol activates a nonclassical potassium channel in cerebrovascular smooth muscle and dilates the middle cerebral artery

Trichloroacetaldehyde monohydrate [chloral hydrate (CH)] is a sedative/hypnotic that increases cerebral blood flow (CBF), and its active metabolite 2,2,2-trichloroethanol (TCE) is an agonist for the nonclassical two-pore domain K(+) (K(2P)) channels TREK-1 and TRAAK. We sought to determine whether TCE dilates cerebral arteries in vitro by activating nonclassical K(+) channels. TCE dilated pressurized and perfused rat middle cerebral arteries (MCAs) in a manner consistent with activation of nonclassical K(+) channels. Dilation to TCE was inhibited by elevated external K(+) but not by an inhibitory cocktail (IC) of classical K(+) channel blockers. Patch-clamp electrophysiology revealed that, in the presence of the IC, TCE increased whole-cell currents and hyperpolarized the membrane potential of isolated MCA smooth muscle cells. Heating increased TCE-sensitive currents, indicating that the activated channel was thermosensitive. Immunofluorescence in sections of the rat MCA demonstrated that, like TREK-1, TRAAK is expressed in the smooth muscle of cerebral arteries. Isoflurane did not, however, dilate the MCA, suggesting that TREK-1 was not functional. These data indicate that TCE activated a nonclassical K(+) channel with the characteristics of TRAAK in rat MCA smooth-muscle cells. Stimulation of K(+) channels such as TRAAK in cerebral arteries may therefore explain in part how CH/TCE increases CBF.

Growth-dependent changes in the contribution of carbon monoxide to arteriolar function

BACKGROUND/AIMS

Endothelium-dependent dilation of skeletal muscle arterioles is mediated by unknown factors in very young rats. We assessed the possible contribution of carbon monoxide (CO) to this dilation and to dilation in older animals.

METHODS

The effects of de-endothelialization or various pharmacological inhibitors on responses to CO or endothelium-dependent dilators were studied in gracilis muscle arterioles from rats at 3-4 weeks ('weanlings') and 6-7 weeks ('juveniles').

RESULTS

Exogenous CO constricted, rather than dilated, arterioles from both age groups. This constriction was reduced by endothelial removal or NOS inhibition in juvenile, but not weanling, arterioles. In contrast, this constriction was abolished by K(+) channel inhibition in weanling, but not juvenile, arterioles. The heme precursor delta-aminolevulinic acid constricted juvenile arterioles but did not affect weanling arterioles. The heme oxygenase inhibitor chromium (III) mesoporphyrin IX abolished the endothelium-dependent dilation of juvenile arterioles to simvastatin, and reduced ACh- and simvastatin-induced dilations of weanling arterioles.

CONCLUSION

These findings suggest that relatively high concentrations of exogenous CO can cause constriction by inhibiting endothelium-derived NO in juvenile arterioles and inhibiting K(+) channels in weanling arterioles. Endogenous CO produced at lower concentrations can contribute to endothelium-dependent dilation in both age groups.

Carbon monoxide induces relaxation of human internal thoracic and radial arterial grafts

Carbon monoxide is produced by the degradation of heme by intracellular heme-oxygenase. The aim of our study was to evaluate, in vitro, the vasodilating effect of carbon monoxide and its mechanisms of action on human internal thoracic and radial artery grafts. Segments of human internal thoracic artery and radial artery, obtained from isolated coronary artery bypass surgery patients, were studied in organ chambers. The arterial rings were precontracted with norepinephrine then submitted to carbon monoxide. Inhibitors of nitric oxide synthase and of soluble guanylate cyclase were added to some arterial rings. Carbon monoxide induced significant relaxation in precontracted human internal thoracic artery and radial artery rings. This relaxation was independent of the presence of functional endothelium in internal thoracic artery. Blocking soluble guanylate cyclase partially inhibited this relaxation, while blocking nitric oxide synthase had no effect. Carbon monoxide has a relaxing effect on human internal thoracic artery and radial artery grafts in vitro, partially via cyclic guanylate monophosphate (cGMP) pathway activation. Inducing carbon monoxide production at the cellular level in vivo in human arterial grafts might help prevent vasospasm.

Impaired pressure-induced constriction in mouse middle cerebral arteries of ASIC2 knockout mice

Recent studies from our laboratory demonstrated the importance of mechanosensitive epithelial Na+channel (ENaC) proteins in pressure-induced constriction in renal and cerebral arteries. ENaC proteins are closely related to acid-sensing ion channel 2 (ASIC2), a protein known to be required for normal mechanotransduction in certain sensory neurons. However, the role of the ASIC2 protein in pressure-induced constriction has never been addressed. The goal of the current study was to investigate the role of ASIC2 proteins in pressure-induced, or myogenic, constriction in the mouse middle cerebral arteries (MCAs) from ASIC2 wild-type (+/+), heterozygous (+/−), and null (−/−) mice. Constrictor responses to KCl (20–80 mM) and phenylephrine (10−7–10−4M) were not different among groups. However, vasoconstrictor responses to increases in intraluminal pressure (15–90 mmHg) were impaired in MCAs from ASIC2−/−and+/−mice. At 60 and 90 mmHg, MCAs from ASIC2+/+mice generated 13.7 ± 2.1% and 15.8 ± 2.0% tone and ASIC2−/−mice generated 7.4 ± 2.8% and 12.5 ± 2.4% tone, respectively. Surprisingly, MCAs from ASIC2+/−mice generated 1.2 ± 2.2% and 3.9 ± 1.8% tone at 60 and 90 mmHg. The reason underlying the total loss of myogenic tone in the ASIC2+/−is not clear, although the loss of mechanosensitive β- and γ-ENaC proteins may be a contributing factor. These results demonstrate that normal ASIC2 expression is required for normal pressure-induced constriction in the MCA. Furthermore, ASIC2 may be involved in establishing the basal level of myogenic tone.

Increased myogenic responsiveness of skeletal muscle arterioles with juvenile growth

Previous studies from this laboratory suggest that during juvenile growth, structural changes in the arteriolar network are accompanied by changes in some of the mechanisms responsible for regulation of tissue blood flow. To test the hypothesis that arteriolar myogenic behavior is altered with growth, we studied gracilis muscle arterioles isolated from Sprague-Dawley rats at two ages: 21-28 and 42-49 days. When studied at their respective in vivo pressures, the myogenic index (instantaneous slope of the active pressure-diameter curve) of arterioles from 42-49-day-old rats was more negative than that of arterioles from 21-28-day-old rats, indicating greater myogenic responsiveness. Endothelial denudation, or prostaglandin H(2) (PGH(2))/thromboxane A(2) (TxA(2)) receptor antagonism without denudation, significantly reduced the myogenic responsiveness of arterioles from the older rats over a wide range of pressures but had no consistent effects on the myogenic responsiveness of arterioles from the younger rats. The heme oxygenase inhibitor chromium (III) mesoporphyrin IX chloride had no effect on the myogenic activity of arterioles from either age group. These findings indicate that microvascular growth in young animals is accompanied by an increase in the myogenic behavior of arterioles, possibly because PGH(2) or TxA(2) assumes a role in reinforcing myogenic activity over this period. As a result, the relative contribution of myogenic activity to blood flow regulation in skeletal muscle may increase during rapid juvenile growth.

Cerebroprotective functions of HO-2

The constitutive isoform of heme oxygenase, HO-2, is highly expressed in the brain and in cerebral vessels. HO-2 functions in the brain have been evaluated using pharmacological inhibitors of the enzyme and HO-2 gene deletion in in vivo animal models and in cultured cells (neurons, astrocytes, cerebral vascular endothelial cells). Rapid activation of HO-2 via post-translational modifications without upregulation of HO-2 expression or HO-1 induction coincides with the increase in cerebral blood flow aimed at maintaining brain homeostasis and neuronal survival during seizures, hypoxia, and hypotension. Pharmacological inhibition or gene deletion of brain HO-2 exacerbates oxidative stress induced by seizures, glutamate, and inflammatory cytokines, and causes cerebral vascular injury. Carbon monoxide (CO) and bilirubin, the end products of HO-catalyzed heme degradation, have distinct cytoprotective functions. CO, by binding to a heme prosthetic group, regulates the key components of cell signaling, including BK(Ca) channels, guanylyl cyclase, NADPH oxidase, and the mitochondria respiratory chain. Cerebral vasodilator effects of CO are mediated via activation of BK(Ca) channels and guanylyl cyclase. CO, by inhibiting the major components of endogenous oxidant-generating machinery, NADPH oxidase and the cytochrome C oxidase of the mitochondrial respiratory chain, blocks formation of reactive oxygen species. Bilirubin, via redox cycling with biliverdin, is a potent oxidant scavenger that removes preformed oxidants. Overall, HO-2 has dual housekeeping cerebroprotective functions by maintaining autoregulation of cerebral blood flow aimed at improving neuronal survival in a changing environment, and by providing an effective defense mechanism that blocks oxidant formation and prevents cell death caused by oxidative stress.

Age and species dependence of pial arteriolar responses to topical carbon monoxide in vivo

In newborn pigs, carbon monoxide (CO) contributes to regulation of cerebrovascular circulation. Results from isolated adult cerebral arteries suggest CO may have less dilatory potential in mature animals. However, few data are available on the direct effects of CO on cerebrovascular circulation in vivo except for those from newborn pigs. Therefore, we tested the hypothesis that i) rat cerebral arterioles dilate to CO in vivo and ii) CO-induced cerebrovascular dilatory responses are age dependent in pigs. Also, we examined whether the permissive role of nitric oxide in CO-induced dilation observed in piglets is present in older pigs and rats. Experiments used anesthetized newborn, 7-week-old, and juvenile (3- to 4-month-old) pigs and 3- to 4-month-old rats with closed cranial windows and topical applications of CO and sodium nitroprusside (SNP). Dilations to SNP were not different at different ages in pigs or between pigs and rats. CO produced pial arteriolar dilations in all groups. Dilation to 10(-5) M CO was reduced in juvenile pigs as compared to newborn and 7-week-old pigs, and tended to less at 10(-6) M CO. Dilations of rat pial arterioles to all concentrations were less than those of newborn and 7-week-old pigs, but not different from those of juvenile pig pial arterioles. In newborn and 7-week-old pigs, l-nitro-arginine (LNA) inhibited the dilation to CO, an effect reversed by a constant background of SNP. In contrast, LNA did not reduce dilation to CO in juvenile pigs or rats. In conclusion, rat pial arterioles like those in piglets dilate to CO in vivo, but there are age and species differences with regard to reactivity and interaction with NO.

Astrocyte-derived CO is a diffusible messenger that mediates glutamate-induced cerebral arteriolar dilation by activating smooth muscle Cell KCa channels

Astrocyte signals can modulate arteriolar tone, contributing to regulation of cerebral blood flow, but specific intercellular communication mechanisms are unclear. Here we used isolated cerebral arteriole myocytes, astrocytes, and brain slices to investigate whether carbon monoxide (CO) generated by the enzyme heme oxygenase (HO) acts as an astrocyte-to-myocyte gasotransmitter in the brain. Glutamate stimulated CO production by astrocytes with intact HO-2, but not those genetically deficient in HO-2. Glutamate activated transient K(Ca) currents and single K(Ca) channels in myocytes that were in contact with astrocytes, but did not affect K(Ca) channel activity in myocytes that were alone. Pretreatment of astrocytes with chromium mesoporphyrin (CrMP), a HO inhibitor, or genetic ablation of HO-2 prevented glutamate-induced activation of myocyte transient K(Ca) currents and K(Ca) channels. Glutamate decreased arteriole myocyte intracellular Ca2+ concentration and dilated brain slice arterioles and this decrease and dilation were blocked by CrMP. Brain slice arteriole dilation to glutamate was also blocked by L-2-alpha aminoadipic acid, a selective astrocyte toxin, and paxilline, a K(Ca) channel blocker. These data indicate that an astrocytic signal, notably HO-2-derived CO, is used by glutamate to stimulate arteriole myocyte K(Ca) channels and dilate cerebral arterioles. Our study explains the astrocyte and HO dependence of glutamatergic functional hyperemia observed in the newborn cerebrovascular circulation in vivo.

Mechanisms involved in the cerebrovascular dilator effects of N-methyl-d-aspartate in cerebral cortex

Glutamate and its synthetic analogues N-methyl-d-aspartate (NMDA), kainate, and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) are potent dilator agents in the cerebral circulation. The close linkage between neural activity-based release and actions of glutamate on neurons and the related decrease in cerebral vascular resistance is a classic example in support of the concept of tight coupling between increased neural activity and cerebral blood flow. However, mechanisms involved in promoting cerebral vasodilator responses to glutamatergic agents are controversial. Here we review the development and current status of this important field of research especially in respect to cerebrovascular responses to NMDA receptor activation.

Carbon monoxide contributes to hypotension-induced cerebrovascular vasodilation in piglets

The gaseous compound carbon monoxide (CO) has been identified as an important endogenous biological messenger in brain and is a major component in regulation of cerebrovascular circulation in newborns. CO is produced endogenously by catabolism of heme to CO, free iron, and biliverdin during enzymatic degradation of heme by heme oxygenase (HO). The present study was designed to test the hypothesis that endogenously produced CO contributes to hypotension-induced vasodilation of cerebral arterioles. Experiments used anesthetized piglets with implanted, closed cranial windows. Topical application of the HO substrate heme-l-lysinate caused dilation of pial arterioles that was blocked by a metal porphyrin inhibitor of HO, chromium mesoporphyrin (CrMP). In normotensive piglets (arterial pressure 64 +/- 4 mmHg), CrMP did not cause vasoconstriction of pial arterioles but rather a transient dilation. Hypotension (50% of basal blood pressure) increased cerebral CO production and dilated pial arterioles from 66 +/- 2 to 92 +/- 7 microm. In hypotensive piglets, topical CrMP or intravenous tin protoporphyrin decreased cerebral CO production and produced pial arteriolar constriction to normotensive diameters. In additional experiments, because prostacyclin and nitric oxide (NO) are also key dilators that can contribute to cerebrovascular dilation, we held their levels constant. NO/prostacyclin clamp was accomplished with continuous, simultaneous application of indomethacin, N(omega)-nitro-l-arginine, and minimal dilatory concentrations of iloprost and sodium nitroprusside. With constant NO and prostacyclin, the transient dilator and prolonged constrictor responses to CrMP of normotensive and hypotensive piglets, respectively, were the same as when NO and prostaglandins were not held constant. These data suggest that endogenously produced CO contributes to cerebrovascular dilation in response to reduced perfusion pressure.