Relative contribution of eNOS and nNOS to endothelium-dependent vasodilation in the mouse aorta

Molecular biology of atherosclerosis

At least 468 individual genes have been manipulated by molecular methods to study their effects on the initiation, promotion, and progression of atherosclerosis. Most clinicians and many investigators, even in related disciplines, find many of these genes and the related pathways entirely foreign. Medical schools generally do not attempt to incorporate the relevant molecular biology into their curriculum. A number of key signaling pathways are highly relevant to atherogenesis and are presented to provide a context for the gene manipulations summarized herein. The pathways include the following: the insulin receptor (and other receptor tyrosine kinases); Ras and MAPK activation; TNF-α and related family members leading to activation of NF-κB; effects of reactive oxygen species (ROS) on signaling; endothelial adaptations to flow including G protein-coupled receptor (GPCR) and integrin-related signaling; activation of endothelial and other cells by modified lipoproteins; purinergic signaling; control of leukocyte adhesion to endothelium, migration, and further activation; foam cell formation; and macrophage and vascular smooth muscle cell signaling related to proliferation, efferocytosis, and apoptosis. This review is intended primarily as an introduction to these key signaling pathways. They have become the focus of modern atherosclerosis research and will undoubtedly provide a rich resource for future innovation toward intervention and prevention of the number one cause of death in the modern world.

TLR2 activation causes no morbidity or cardiovascular failure, despite excessive systemic nitric oxide production

AIMS

Septic shock is the leading cause of death in intensive care units worldwide, resulting from a progressive systemic inflammatory reaction causing cardiovascular and organ failure. Nitric oxide (NO) is a potent vasodilator and inhibition of NO synthases (NOS) can increase blood pressure in septic shock. However, NOS inhibition does not improve outcome, on the contrary, and certain NO donors may even provide protection. In addition, NOS produce superoxide in case of substrate or cofactor deficiency or oxidation. We hypothesized that excessive systemic iNOS-derived NO production is insufficient to trigger cardiovascular failure and shock.

METHODS AND RESULTS

We found that the systemic injection with various synthetic Toll-like receptor-2 (TLR2), TLR3, or TLR9 agonists triggered systemic NO production identical to that of lipopolysaccharide (LPS) or tumour necrosis factor. In contrast to the latter, however, these agonists did not cause hypothermia or any other signs of discomfort or morbidity, and inflammatory cytokine production was low. TLR2 stimulation with the triacylated lipopeptide Pam3CSK4 not only caused identical NO levels in circulation, but also identical iNOS expression patterns as LPS. Nevertheless, Pam3CSK4 did not cause hypotension, bradycardia, reduced blood flow, or inadequate tissue perfusion in the kidney or the liver.

CONCLUSION

We demonstrate that excessive iNOS-derived NO in circulation is not necessarily linked to concomitant cardiovascular collapse, morbidity, or mortality. As such, our data indicate that the central role of iNOS-derived NO in inflammation-associated cardiovascular failure may be overestimated.

Diabetes confers a vasoprotective role to the neurocompensatory response elicited by carotid balloon injury: consequences on contralateral carotid tone and blood flow

The purpose from this study was to investigate the consequences of sensory neurocompensation to carotid balloon injury in diabetic rats on angiotensin II-induced contraction and basal blood flow in contralateral carotid. Concentration-response curves for angiotensin II and blood flow were obtained in contralateral carotid from non-treated or capsaicin-treated streptozotocin-induced diabetic rats that underwent carotid balloon injury. Diabetes increased angiotensin II-induced contraction and impaired the blood flow in non-operated rat carotid. In diabetic rats, balloon injury led to neointima formation, which reduced the blood flow in ipsilateral carotid. Carotid balloon injury in diabetic rats reduced angiotensin II-induced contraction and restored the blood flow in contralateral carotid when compared to diabetic non-operated rat carotid. Capsaicin inhibited the effects evoked by carotid balloon injury on diabetic rat contralateral carotid. Endothelium removal, PEG-catalase (hydrogen peroxide scavenger) or l-NPA (neuronal nitric oxide synthase, nNOS, inhibitor) increased angiotensin II-induced contraction in contralateral carotid from diabetic operated rats to the levels observed in diabetic non-operated rat carotid. Our findings suggest that carotid balloon injury in diabetic rats elicits a neurocompensation that attenuates the diabetic hyperreactivity to angiotensin II in contralateral carotid by a sensory nerves-dependent mechanism mediated by hydrogen peroxide derived from endothelial nNOS. This sensory mechanism also restored the blood flow in this vessel, compensating the impaired blood flow in diabetic rat ipsilateral carotid. Thus, our major conclusions are that Diabetes confers a vasoprotective significance to the neurocompensation to carotid balloon injury in preventing further damage at carotid cerebral irrigation after angioplasty in diabetic subjects.

AMP-activated kinase relaxes agonist induced contractions in the mouse aorta via effects on PKC signaling and inhibits NO-induced relaxation

Adenosine monophosphate activated kinase (AMPK), a regulator of cellular metabolism, has been shown to relax arterial smooth muscle via endothelium-dependent and independent mechanisms. We have examined the role of AMPK in different smooth muscles using the activating compound, 5-amino-4-imidazolecarboxamide riboside-1-β-d-ribofuranoside (AICAR). Isolated preparations of mouse aorta, saphenous artery, ileum and urinary bladder were compared. AICAR produced a reversible dose-dependent relaxation in aortic rings pre-incubated with AICAR and activated with phenylephrine. Less prominent relaxation was noted in the other tissues. This difference in sensitivity to AICAR was not due to differences in the expression levels of AMPK α1 mRNA. In the aorta, AICAR had a greater effect on contractions induced by phenylephrine, compared to high-K(+) induced contractions. Contractions of the aorta in response to the protein kinase C activator PDBu were prominently inhibited by AICAR. The AICAR relaxation observed in the aorta was not prevented by the NOS inhibitor L-NAME, Indomethacin or endothelium removal. Nitric oxide (NO) mediated relaxations in aortic preparations induced by acetylcholine or sodium nitroprusside (SNP) were attenuated by AICAR. In conclusion, AMPK induced relaxation of smooth muscle is tissue-dependent and most prominent in large elastic arteries. The smooth muscle relaxation is NO-independent and occurs downstream of PKC activation and is associated with attenuated relaxant responses to NO.

In vivo noninvasive characterization of brown adipose tissue blood flow by contrast ultrasound in mice

BACKGROUND

Interventions to increase brown adipose tissue (BAT) volume and activation are being extensively investigated as therapies to decrease the body weight in obese subjects. Noninvasive methods to monitor these therapies in animal models and humans are rare. We investigated whether contrast ultrasound (CU) performed in mice could detect BAT and measure its activation by monitoring BAT blood flow. After validation, CU was used to study the role of uncoupling protein 1 and nitric oxide synthases in the acute regulation of BAT blood flow.

METHODS AND RESULTS

Blood flow of interscapular BAT was assessed in mice (n=64) with CU by measuring the signal intensity of continuously infused contrast microbubbles. Blood flow of BAT estimated by CU was 0.5±0.1 (mean±SEM) dB/s at baseline and increased 15-fold during BAT stimulation by norepinephrine (1 µg·kg(-1)·min(-1)). Assessment of BAT blood flow using CU was correlated to that performed with fluorescent microspheres (R(2)=0.86, P<0.001). To evaluate whether intact BAT activation is required to increase BAT blood flow, CU was performed in uncoupling protein 1-deficient mice with impaired BAT activation. Norepinephrine infusion induced a smaller increase in BAT blood flow in uncoupling protein 1-deficient mice than in wild-type mice. Finally, we investigated whether nitric oxide synthases played a role in acute norepinephrine-induced changes of BAT blood flow. Genetic and pharmacologic inhibition of nitric oxide synthase 3 attenuated the norepinephrine-induced increase in BAT blood flow.

CONCLUSIONS

These results indicate that CU can detect BAT in mice and estimate BAT blood flow in mice with functional differences in BAT.

Decreased production of neuronal NOS-derived hydrogen peroxide contributes to endothelial dysfunction in atherosclerosis

BACKGROUND AND PURPOSE

Reduced NO availability has been described as a key mechanism responsible for endothelial dysfunction in atherosclerosis. We previously reported that neuronal NOS (nNOS)-derived H(2)O(2) is an important endothelium-derived relaxant factor in the mouse aorta. The role of H(2)O(2) and nNOS in endothelial dysfunction in atherosclerosis remains undetermined. We hypothesized that a decrease in nNOS-derived H(2)O(2) contributes to the impaired vasodilatation in apolipoprotein E-deficient mice (ApoE(-/-)).

EXPERIMENTAL APPROACH

Changes in isometric tension were recorded on a myograph; simultaneously, NO and H(2)O(2) were measured using carbon microsensors. Antisense oligodeoxynucleotides were used to knockdown eNOS and nNOS in vivo. Western blot and confocal microscopy were used to analyse the expression and localization of NOS isoforms.

KEY RESULTS

Aortas from ApoE(-/-) mice showed impaired vasodilatation paralleled by decreased NO and H(2)O(2) production. Inhibition of nNOS with L-Arg(NO2) -L-Dbu, knockdown of nNOS and catalase, which decomposes H(2)O(2) into oxygen and water, decreased ACh-induced relaxation by half, produced a small diminution of NO production and abolished H(2)O(2) in wild-type animals, but had no effect in ApoE(-/-) mice. Confocal microscopy showed increased nNOS immunostaining in endothelial cells of ApoE(-/-) mice. However, ACh stimulation of vessels resulted in less phosphorylation on Ser852 in ApoE(-/-) mice.

CONCLUSIONS AND IMPLICATIONS

Our data show that endothelial nNOS-derived H(2)O(2) production is impaired and contributes to endothelial dysfunction in ApoE(-/-) aorta. The present study provides a new mechanism for endothelial dysfunction in atherosclerosis and may represent a novel target to elaborate the therapeutic strategy for vascular atherosclerosis.

Role of reactive oxygen and nitrogen species in the vascular responses to inflammation

Inflammation is a complex and potentially life-threatening condition that involves the participation of a variety of chemical mediators, signaling pathways, and cell types. The microcirculation, which is critical for the initiation and perpetuation of an inflammatory response, exhibits several characteristic functional and structural changes in response to inflammation. These include vasomotor dysfunction (impaired vessel dilation and constriction), the adhesion and transendothelial migration of leukocytes, endothelial barrier dysfunction (increased vascular permeability), blood vessel proliferation (angiogenesis), and enhanced thrombus formation. These diverse responses of the microvasculature largely reflect the endothelial cell dysfunction that accompanies inflammation and the central role of these cells in modulating processes as varied as blood flow regulation, angiogenesis, and thrombogenesis. The importance of endothelial cells in inflammation-induced vascular dysfunction is also predicated on the ability of these cells to produce and respond to reactive oxygen and nitrogen species. Inflammation seems to upset the balance between nitric oxide and superoxide within (and surrounding) endothelial cells, which is necessary for normal vessel function. This review is focused on defining the molecular targets in the vessel wall that interact with reactive oxygen species and nitric oxide to produce the characteristic functional and structural changes that occur in response to inflammation. This analysis of the literature is consistent with the view that reactive oxygen and nitrogen species contribute significantly to the diverse vascular responses in inflammation and supports efforts that are directed at targeting these highly reactive species to maintain normal vascular health in pathological conditions that are associated with acute or chronic inflammation.

Genetic modifiers of cardiovascular phenotype caused by elastin haploinsufficiency act by extrinsic noncomplementation

Elastin haploinsufficiency causes the cardiovascular complications associated with Williams-Beuren syndrome and isolated supravalvular aortic stenosis. Significant variability exists in the vascular pathology in these individuals. Using the Eln(+/-) mouse, we sought to identify the source of this variability. Following outcrossing of C57Bl/6J Eln(+/-), two backgrounds were identified whose cardiovascular parameters deviated significantly from the parental strain. F1 progeny of the C57Bl/6J; Eln(+/-)x129X1/SvJ were more hypertensive and their arteries less compliant. In contrast, Eln(+/-) animals crossed to DBA/2J were protected from the pathologic changes associated with elastin insufficiency. Among the crosses, aortic elastin and collagen content did not correlate with quantitative vasculopathy traits. Quantitative trait locus analysis performed on F2 C57; Eln(+/-)x129 intercrosses identified highly significant peaks on chromosome 1 (LOD 9.7) for systolic blood pressure and on chromosome 9 (LOD 8.7) for aortic diameter. Additional peaks were identified that affect only Eln(+/-), including a region upstream of Eln on chromosome 5 (LOD 4.5). Bioinformatic analysis of the quantitative trait locus peaks revealed several interesting candidates, including Ren1, Ncf1, and Nos1; genes whose functions are unrelated to elastic fiber assembly, but whose effects may synergize with elastin insufficiency to predispose to hypertension and stiffer blood vessels. Real time RT-PCR studies show background-specific increased expression of Ncf1 (a subunit of the NOX2 NAPDH oxidase) that parallel the presence of increased oxidative stress in Eln(+/-) aortas. This finding raises the possibility that polymorphisms in genes affecting the generation of reactive oxygen species alter cardiovascular function in individuals with elastin haploinsufficiency through extrinsic noncomplementation.

Endothelial nitric oxide-dependent vasorelaxant effect of isotirumalin, a dihydroflavonol from Derris urucu, on the rat aorta

The present work aimed to investigate the vasorelaxant effect of isotirumalin, a dihydroflavonol isolated from Derris urucu (Leguminosae). The vasorelaxant effect of isotirumalin was investigated in the rat aorta, in the presence and in the absence of a functional endothelium. The production of nitric oxide (NO) induced by isotirumalin was measured simultaneously with its vasorelaxation using carbon microsensors. In endothelium-intact aortic rings, isotirumalin induced a concentration-dependent vasodilator effect the concentration required to produce 30% of relaxation (pIC₃₀=4.84±0.24) that was abolished in endothelium-denuded aortic rings or in the presence of Nω-nitro-L-arginine-methyl-ester (L-NAME; 300 µM). In addition, isotirumalin (100 µM) induced a simultaneous and significant increase on NO production, which was blunted in the presence of L-NAME. The present results demonstrate that isotirumalin is a vasodilator in the rat aorta and act by a mechanism dependent on the presence of a functional endothelium and on NO production.

Estradiol attenuates high glucose-induced endothelial nitrotyrosine: role for neuronal nitric oxide synthase

Hyperglycemia in diabetes causes increased oxidative stress in the vascular endothelium with generation of free radicals such as superoxide. Peroxynitrite, a highly reactive species generated from superoxide and nitric oxide (NO), induces proinflammatory tyrosine nitration of intracellular proteins under such conditions. The female sex hormone estrogen appears to exert protective effects on the nondiabetic endothelium. However, several studies show reduced vascular protection in women with diabetes, suggesting alterations in estrogen signaling under high glucose. In this study, we examined the endothelial effects of estrogen under increasing glucose levels, focusing on nitrotyrosine and peroxynitrite. Human umbilical vein endothelial cells were incubated with normal (5.5 mM) or high (15.5 or 30.5 mM) glucose before addition of estradiol (E2, 1 or 10 nM). Selective NO synthase (NOS) inhibitors were used to determine the role of specific NOS isoforms. Addition of E2 significantly reduced high glucose-induced increase in peroxynitrite and consequently, nitrotyrosine. The superoxide levels were unchanged, suggesting effects on NO generation. Inhibition of neuronal NOS (nNOS) reduced high glucose-induced nitrotyrosine, demonstrating a critical role for this enzyme. E2 increased nNOS activity under normal glucose while decreasing it under high glucose as determined by its phosphorylation status. These data show that nNOS contributes to endothelial peroxynitrite and subsequent nitrotyrosine generation under high glucose, which can be attenuated by E2 through nNOS inhibition. The altered regulation of nNOS by E2 under high glucose is a potential therapeutic target in women with diabetes.

Disruption of COX-2 and eNOS does not confer protection from cardiovascular failure in lipopolysaccharide-treated conscious mice and isolated vascular rings

It was hypothesized that a serial stimulation of vascular cyclooxygenase-2 (COX-2) with subsequent activation of endothelial nitric oxide synthase (eNOS) is responsible for decrease in blood pressure, cardiac performance, and vascular reactivity in endotoxemia caused by LPS. The hypothesis was tested in catheterized, conscious, freely moving, wild-type mice and mice (C57BL/6J background) with targeted deletion of COX-2 and eNOS that were given an intravenous LPS bolus (2 mg/kg, 055:B5). In vitro studies were performed on murine aorta rings. LPS caused a concomitant decrease in mean arterial blood pressure (MAP) and heart rate (HR) that was significant after 3 h and was sustained throughout the experiment (8 h). The LPS-induced changes in MAP and HR were not different from control in COX-2(-/-) and eNOS(-/-) mice. A prostacyclin receptor antagonist (BR5064) blocked the hypotensive effect of a prostacyclin agonist (beraprost), but did not attenuate the LPS-induced decrease in MAP and HR. LPS decreased eNOS and neuronal NOS mRNA abundances in several organs, while inducible NOS mRNA was enhanced. In aortic rings, LPS suppressed α(1)-adrenoceptor-mediated vascular tone. Inhibition of COX-2 activity (NS 398), disruption of COX-2, endothelium removal, or eNOS deletion (eNOS(-/-)) did not improve vascular reactivity after LPS, while the NO synthase blockers 1400W and N(G)-nitro-l-arginine methyl ester prevented loss of tone. COX-2 and eNOS activities are not necessary for LPS-induced decreases in blood pressure, heart rate, and vascular reactivity. Inducible NOS activity appears crucial. COX-2 and eNOS are not obvious therapeutic targets for cardiovascular rescue during gram-negative endotoxemic shock.