Lourdes Sánchez de Miguel

Expression of Constitutive and Inducible Nitric Oxide Synthases in the Vascular Wall of Young and Aging Rats

Two NO synthase (NOS) isoforms have been described in vessels, an endothelial constitutive NOS (eNOS) and an inducible NOS (iNOS). The purpose of the present study was to examine the endothelium-dependent and endothelium-independent hypotensive response in aging rats, analyzing the ability of their vessels to produce NO. The studies were performed in 2 groups of euvolemic, conscious, male Wistar rats: aging rats (n=20, 18 months old) and young rats (n=20, 5 months old). The hypotensive responses to acetylcholine, bradykinin, and sodium nitroprusside were determined. Furthermore, the expression of the NOS isoforms by Western blot and the eNOS and iNOS activities, defined as Ca2+-dependent and Ca2+-independent conversion of [14C]L-arginine into [14C]L-citrulline, respectively, were also determined. In the aging rats, we found an impaired hypotensive response to acetylcholine and bradykinin (2 NO- and endothelium-dependent hypotensive agents) that was accompanied by a preserved hypotensive response to sodium nitroprusside. Aging rats also demonstrated an enhanced sensitivity response to the pressor effect of the L-arginine antagonist L-Nomega-nitro-L-arginine and a reduced vasoconstrictor response to angiotensin II. The inhibition of NO synthesis normalized the pressor effect of angiotensin II in the aging animals. Nitrite plus nitrate plasma levels were increased in aging rats. Furthermore, cGMP content was also higher in the aging vessels. In the aging aortas, the expression of both eNOS and iNOS isoforms was enhanced. However, in aging rats, the activity of the eNOS isoform was markedly reduced, a finding that was accompanied by the presence of iNOS activity. The vessel wall of aging rats showed an enhanced expression of eNOS and iNOS isoforms. However, eNOS activity was reduced in the aging animals. These findings could explain the impaired endothelium-dependent hypotensive response associated with aging.

Estrogen Stimulates Neuronal Nitric Oxide Synthase Protein Expression in Human Neutrophils

Abstract —Recent studies have postulated the contribution of nitric oxide (NO) released by the endothelium to the beneficial effects of estrogen. Despite a neuronal-type NO synthase (nNOS) described in neutrophils, less is known about the effect of estrogen in these cells. The aim of the present study was to analyze the expression of nNOS protein in human neutrophils under different estrogenic conditions. We first analyzed nNOS expression in neutrophils obtained from premenopausal women. During the first 2 days of the follicular phase (low circulating estrogen concentrations), nNOS expression in neutrophils was reduced with respect to that found in neutrophils obtained from the same donors during the ovulatory phase (high circulating estrogen concentrations). Moreover, the expression of nNOS protein in neutrophils obtained from postmenopausal women after transdermal estrogen therapy was markedly enhanced with respect to that observed before the treatment. In vitro incubation of neutrophils derived from men for 6 hours with 17β-estradiol (10−10 to 10−8 mol/L) upregulated the expression of nNOS protein. The 17β-estradiol receptor antagonists, tamoxifen (10−8 mol/L) and ICI 182780 (10−8 mol/L), inhibited the upregulation of nNOS protein induced by 17β-estradiol. The putative functional implication was denoted by a reduced expression of the CD18 antigen on the surface of 17β-estradiol–incubated neutrophils, which was accompanied by a decreased adhesive capacity. Both effects were prevented by an NO antagonist. In conclusion, the in vivo levels of circulating estrogen concentrations seem to be associated with the level of nNOS protein expression in neutrophils from women. Moreover, low doses of 17β-estradiol upregulate nNOS protein expression in neutrophils from men. The increased ability of 17β-estradiol–incubated neutrophils derived from men to produce NO reduced their adhesive properties.

Aspirin-Stimulated Nitric Oxide Production by Neutrophils After Acute Myocardial Ischemia in Rabbits

BACKGROUND In recent studies, it has been hypothesized that the protective anti-ischemic effects of aspirin outweigh the effects of inhibition of platelet thromboxane A2 synthesis. Recently, we have found that the antiaggregating effects of aspirin significantly affect nitric oxide (NO) generation by neutrophils. METHODS AND RESULTS The present study used circulating neutrophils from myocardial ischemic rabbits to assess the effect of aspirin on the circulating neutrophil-derived NO production and, subsequently, on the modulation of platelet activation. Neutrophils were obtained after 60 minutes of coronary artery occlusion followed by 60 minutes of reperfusion. Sham-operated animals were used as controls. The results demonstrated that aspirin stimulated the production of NO by neutrophils obtained from both sham-operated rabbits and rabbits with myocardial ischemia. However, neutrophils isolated from animals with myocardial ischemia showed an enhanced ability to generate NO in the presence of aspirin. As a functional in vitro marker, we observed that neutrophils had a NO-dependent, platelet-antiactivating effect in the presence of aspirin. In the absence of aspirin, ischemic neutrophils did not modify platelet activation, even though they produced increased amounts of NO. An inhibitory role of superoxide anion on the neutrophil-related antiplatelet effect was suggested because superoxide dismutase induced significant platelet inhibition by myocardial ischemic neutrophils in the absence of aspirin. CONCLUSIONS Our results show that myocardial ischemia/reperfusion stimulates production of NO by circulating neutrophils, an effect that was enhanced in the presence of aspirin. These results suggest a novel interpretation of the protective effect of aspirin on myocardial ischemia damage.

Expression of Inducible Nitric Oxide Synthase After Endothelial Denudation of the Rat Carotid Artery Role of Platelets

There is functional evidence suggesting that endothelial denudation stimulates inducible nitric oxide synthase (iNOS) activity in the vascular wall. In vitro studies have shown that iNOS expression in smooth muscle cells is reduced by endothelial cells. In the present study we have analyzed the time course of iNOS protein expression in the arterial wall after in vivo deendothelialization. Endothelial denudation was performed in the left carotid artery of Wistar rats, and the right carotid artery was used as control. Whereas iNOS protein was weakly expressed 6, 24, and 48 hours after endothelial denudation, a marked iNOS expression was found 7, 14, and 30 days after vascular damage. Because platelet adhesion and aggregation occur early after endothelial damage, we studied the role of activated platelets in the negative modulation of iNOS protein expression during the first 2 days after endothelial denudation. Early after in vivo endothelial injury, platelet-depleted rats showed a marked iNOS protein expression in the vascular wall. Similar results were obtained by blocking the platelet glycoprotein (GP) IIb/IIIa. Although iNOS protein is present in the arterial wall several days after endothelial denudation, early after arterial wall injury iNOS protein is weakly expressed. Platelets play a crucial role in preventing iNOS protein expression early after endothelial damage, an effect that can be avoided with GP IIb/IIIa blockers. Although iNOS protein was weakly expressed in vivo in the rat carotid artery wall 6, 24, and 48 hours after balloon endothelial denudation, a marked iNOS expression was found 7, 14, and 30 days after arterial damage. iNOS expression could be increased early after endothelial injury by removing circulating platelets and by an antibody against the GP IIb/IIIa. In conclusion, platelets prevent iNOS protein expression early after endothelial balloon damage, an effect that can be avoided with GP IIb/IIIa blocking agents.

Nitric oxide production by neutrophils obtained from patients during acute coronary syndromes: expression of the nitric oxide synthase isoforms.

OBJECTIVES To analyze the differences in the nitric oxide (NO) forming system between neutrophils obtained from patients during unstable angina (UA) and during acute myocardial infarction (AMI). BACKGROUND Neutrophils are involved in the regulation of thrombus formation through the release of active substances such as NO. Acute myocardial infarction is the result of an occlusive thrombus; unstable angina is attributed to intermittent thrombus formation. METHODS We studied 49 patients admitted to hospital within 24 h after the onset of chest pain: 31 experienced AMI and 18 experienced UA. Acute myocardial infarction was defined as CK greater than two-fold the upper limit of normal value of biochemical laboratory, with CK-MB >10% total CK. Unstable angina was defined as transient ST segment changes without significant increases in CK and CK-MB. RESULTS The amount of NO generated by neutrophils from AMI patients was significantly higher than that generated by neutrophils from UA patients. Neutrophils from UA and AMI patients showed low levels of endothelial-like NO synthase protein expression and a marked expression of the inducible NO synthase (iNOS) isoform. Although neutrophils from patients during acute coronary syndromes generated high amounts of NO, they did not demonstrate an increased ability to stimulate cyclic guanosine monophosphate (cGMP) synthesis in platelets. This lack of activity to release NO by neutrophils from patients during AMI was unrelated to a defect in the platelet cGMP-forming system; sodium nitroprusside, an exogenous NO donor, similarly increased cGMP levels in platelets from AMI patients and healthy donors. CONCLUSIONS Neutrophils from patients during AMI and UA showed an increased production of NO and a marked expression of the iNOS isoform. However, NO released from these neutrophils showed a deficient functionality. These findings could have clinical implications because they show differences in thrombus growth in patients with UA versus patients with AMI.

Inhibition of platelet activation in stroke-prone spontaneously hypertensive rats: comparison of losartan, candesartan, and valsartan.

In vitro studies have suggested that losartan interacts with the thromboxane (TxA2)/ prostaglandin H2 (PGH2) receptor in human platelets, reducing TxA2-dependent platelet activation. The aim of this study was to evaluate the effect of different angiotensin II type 1 receptor antagonists in stroke-prone spontaneously hypertensive rats (SHRSP). The level of platelet activation was assessed by determining P-selectin expression in platelets by flow cytometry. The ex vivo adhesion of platelets was also analyzed. The number of platelets that expressed P-selectin in SPSHR was significantly increased (% P-selectin expression: WKY 4 ± 0, 4%; SHRSP 15.5 ± 0, 8% [n = 8], p < 0.05). In SHRSP receiving losartan (20 mg/kg body weight per day) the percentage of platelets expressing P-selectin fell to levels close to that observed in WKY. The number of platelets from SHRSP treated with valsartan and candesartan (20 mg/kg body weight per day for 14 days) that expressed P-selectin was not significantly different from those from untreated SPRHR. Only losartan treatment reduced ex vivo platelet adhesion to a synthetic surface. The antiplatelet effect of losartan does not appear to be related to the level of blood pressure reduction. In ex vivo experiments, losartan significantly reduced the binding of the radiolabeled TxA2 agonist U46619 to platelets obtained from SHRSP in a dose-dependent manner. Treatment with losartan reduced the number of activated platelets in SHRSP independently of its blood pressure effects. TxA2-receptor blockade is proposed as a mechanism by which losartan can prevent platelet activation.

Comparison of in vitro effects of triflusal and acetysalicylic acid on nitric oxide synthesis by human neutrophils

Recent studies have suggested that the protective anti-ischemic effects of acetylsalicylic acid are stronger than the inhibition of platelet thromboxane A2 synthesis. Since ischemic events still occur in acetylsalicylic acid-treated patients, the development of new drugs with more powerful protective effects is needed. We compared the effects of a new platelet antiaggregating drug, 2-acetoxy-4-trifluoromethyl-benzoic acid (triflusal) and of acetylsalicylic acid on the interaction between human neutrophils and platelets, examining the capability of neutrophils to generate nitric oxide (NO). Triflusal, in the presence of neutrophils, showed a greater antiplatelet potency than acetylsalicylic acid to inhibit thrombin-induced platelet activation. Significant stimulation of NO-mediated mechanisms in the presence of acetylsalicylic acid or triflusal was demonstrated by the following findings: (1) increased metabolism of arginine to citrulline, (2) increase of cGMP in the platelet/neutrophil system and (3) the inhibitory action of the L-arginine (L-Arg) competitive analogue, NG-nitro-L-arginine-methyl ester (L-NAME), which was reversed by L-Arg. Triflusal increased the stimulation of NO synthesis by neutrophils more than did of acetylsalicylic acid. The main metabolite of triflusal, 2-hydroxy-4-trifluoromethylbenzoic acid (HTB), alone or in combination with acetylsalicylic acid, did not modify NO production by neutrophils. Therefore, the whole molecule of triflusal is needed to stimulate NO production by neutrophils. Our results show that, in the presence of neutrophils, triflusal exerts an antiplatelet effect greater than that of acetylsalicylic acid, demonstrating a more powerful stimulation of the NO/cGMP system. The present results indicate that it is possible to develop new and more potent acetylsalicylic acid-related antiplatelet drugs for the prevention of the myocardial ischemic/reperfusion processes.

Endothelial Cells Inhibit NO Generation by Vascular Smooth Muscle Cells Role of Transforming Growth Factor-β

Endothelial cell (EC)-released agents are active regulators of vascular smooth muscle cell (VSMC) functions. The first aim of the present work was to analyze the effect of ECs on interleukin-1 beta (IL-1 beta)-induced NO production by SMCs. Bovine aortic ECs (BAECs) and BVSMCs in culture were used for the study. IL-1 beta (0.03 U/L) stimulated nitrite production by BVSMCs. This increase was smaller in the presence of BAECs. This effect was accompanied by reduced expression of inducible NO synthase (iNOS) in BVSMCs coincubated with BAECs, as analyzed by Western blot analysis. The reduction in iNOS protein expression was partially reversed by a polyclonal antibody against transforming growth factor-beta (TGF-beta). Furthermore, we examined the cytotoxic effect of the NO released from BVSMCs on both BAECs and the BVSMCs themselves. Incubation of BAECs with IL-1 beta-prestimulated BVSMCs induced EC toxicity, which was partially inhibited by an inhibitor of NO synthesis, NG-nitro-L-arginine methyl ester, or an inhibitor of iNOS expression, dexamethasone. No cytotoxic effect of IL-1 beta on BVSMCs themselves was detected. ECs modulate iNOS expression in SMCs by mechanisms that include a TGF-beta-dependent pathway. The NO released from SMCs exerts cytotoxic effects on the adjacent endothelium without altering the viability of the SMCs.

Endogenous Angiotensin II Produced by Endothelium Regulates Interleukin-1β–Stimulated Nitric Oxide Generation in Rat Isolated Vessels

The endothelium is a source of several factors that regulate vascular functions. Angiotensin II is one of the main active factors released by the endothelium. The aim of the present work was to analyze the role of angiotensin II released by the endothelium in the regulation of the inducible nitric oxide synthase expression in rat isolated aortic vessels. Interleukin-1beta (0.03 U/L) stimulated nitrite release by the aortic vessels. The nitrite released was less in vessels with endothelium than in deendothelialized aortic segments. This effect was accompanied by a reduced expression of the inducible nitric oxide synthase in the aortic rings with endothelium. Exogenous angiotensin II inhibited IL-1beta-stimulated inducible nitric oxide synthase protein expression in both deendothelialized vessels and those with endothelium, although with reduced ability on the aortic segments with endothelium by a nitric oxide-independent mechanism. In the aortic rings with endothelium, either inhibition of the AT-1 receptor with losartan or blocking of angiotensin II generation with fosinopril enhanced interleukin-1beta-stimulated inducible nitric oxide synthase protein expression. In conclusion, the endothelium decreases inducible nitric oxide synthase expression in the vascular wall. Angiotensin II released from endothelial cells is a main mediator responsible for this inhibition through an AT-1-type receptor-dependent mechanism.

Trombosis y enfermedad coronaria: neutrófilos, óxido nítrico y aspirina

En los ultimos anos, se ha avanzado enormemente en el conocimiento de los mecanismos que regulan la agregacion plaquetaria y la adhesion al endotelio. En concreto, se han estudiado con detalle las interacciones entre plaquetas, celulas endoteliales y neutrofilos. Estas interacciones no solo afectan a las propiedades de estas celulas como promotoras o inhibidoras de la trombosis sino tambien a otros aspectos de la regulacion de la funcion vascular. De esta forma, el fenomeno trombotico se entiende ahora como un fenomeno multicelular donde las interacciones entre plaquetas, neutrofilos y celulas endoteliales regulan el crecimiento del trombo. Asi, se ha demostrado como dos sustancias vasodilatadoras producidas por el endotelio como son la prostaciclina y el oxido nitrico tienen efectos antiagregantes plaquetarios. Es particularmente importante la activacion plaquetaria en procesos de isquemia miocardica y se han desarrollado, por ello, numerosas estrategias farmacologicas para evitar la activacion plaquetaria intravascular. En este sentido, la aspirina sigue siendo uno de los principales farmacos usados para prevenir y reducir la lesion isquemica. El uso corriente de la aspirina suele ser en dosis bajas capaces de disminuir la agregacion plaquetaria in vivo mediante su inhibicion selectiva de la produccion de tromboxano A2 en las plaquetas manteniendo la produccion de prostaciclina en el endotelio. Durante estos ultimos anos, nuestros estudios se han desarrollado sobre la base de que los efectos antiagregantes de la aspirina no solo se explican por los mecanismos descritos anteriormente sino tambien a traves de su accion sobre los neutrofilos. Nuestros estudios in vitro y ex vivo han demostrado que los neutrofilos aumentan los efectos antiagregantes que la aspirina produce sobre las plaquetas. Demostramos que la aspirina estimula la produccion de oxido nitrico de los neutrofilos inhibiendo los efectos agregantes plaquetarios de la trombina, adrenalina y adenosin trifosfato. Por otro lado, se ha estudiado extensamente el papel de los neutrofilos en los acontecimientos isquemicos en los que producen una lesion tisular debido a la liberacion de proteasas, radicales libres del oxigeno y factor de necrosis tumoral-a. En un modelo agudo de isquemia/reperfusion en conejos, hemos demostrado como la aspirina es capaz de aumentar la produccion de oxido nitrico por el neutrofilo proporcionando en este caso un efecto beneficioso de los neutrofilos en el infarto de miocardio. Sin embargo, se necesitan mas estudios para comprobar los mecanismos de accion de la aspirina durante los fenomenos tromboticos y su efecto sobre las diferentes celulas del entorno vascular.