Nitric oxide (NO) upregulates NO synthase expression in fetal intrapulmonary artery endothelial cells

Endothelial cell-specific loss of eNOS differentially affects endothelial function

The endothelium maintains and regulates vascular homeostasis mainly by balancing interplay between vasorelaxation and vasoconstriction via regulating Nitric Oxide (NO) availability. Endothelial nitric oxide synthase (eNOS) is one of three NOS isoforms that catalyses the synthesis of NO to regulate endothelial function. However, eNOS’s role in the regulation of endothelial function, such as cell proliferation and migration remain unclear. To gain a better understanding, we genetically knocked down eNOS in cultured endothelial cells using sieNOS and evaluated cell proliferation, migration and also tube forming potential in vitro. To our surprise, loss of eNOS significantly induced endothelial cell proliferation, which was associated with significant downregulation of both cell cycle inhibitor p21 and cell proliferation antigen Ki-67. Knockdown of eNOS induced cell migration but inhibited formation of tube-like structures in vitro. Mechanistically, loss of eNOS was associated with activation of MAPK/ERK and inhibition of PI3-K/AKT signaling pathway. On the contrary, pharmacologic inhibition of eNOS by inhibitors L-NAME or L-NMMA, inhibited cell proliferation. Genetic and pharmacologic inhibition of eNOS, both promoted endothelial cell migration but inhibited tube-forming potential. Our findings confirm that eNOS regulate endothelial function by inversely controlling endothelial cell proliferation and migration, and by directly regulating its tube-forming potential. Differential results obtained following pharmacologic versus genetic inhibition of eNOS indicates a more complex mechanism behind eNOS regulation and activity in endothelial cells, warranting further investigation.

Temporal inhibition of mouse mammary gland cancer metastasis by CORM-A1 and DETA/NO combination therapy

Carbon monoxide and nitric oxide are two of the most important vasoprotective mediators. Their downregulation observed during vascular dysfunction, which is associated with cancer progression, leads to uncontrolled platelet activation. Therefore, the aim of our studies was to improve vasoprotection and to decrease platelet activation during progression of mouse mammary gland cancer by concurrent use of CO and NO donors (CORM-A1 and DETA/NO, respectively).

Methods: Mice injected intravenously with 4T1-luc2-tdTomato or orthotopically with 4T1 mouse mammary gland cancer cells were treated with CORM-A1 and DETA/NO. Ex vivo aggregation and activation of platelets were assessed in the blood of healthy donors and breast cancer patients. Moreover, we analyzed the compounds' direct effect on 4T1 mouse and MDA-MB-231 human breast cancer cells proliferation, adhesion and migration in vitro.

Results: We have observed antimetastatic effect of combination therapy, which was only transient in orthotopic model. During early stages of tumor progression concurrent use of CORM-A1 and DETA/NO demonstrated vasoprotective ability (decreased endothelin-1, sICAM and sE-selectin plasma level) and downregulated platelets activation (decreased bound of fibrinogen and vWf to platelets) as well as inhibited EMT process. Combined treatment with CO and NO donors diminished adhesion and migration of breast cancer cells in vitro and inhibited aggregation as well as TGF-β release from breast cancer patients' platelets ex vivo. However, antimetastatic effect was not observed at a later stage of tumor progression which was accompanied by increased platelets activation and endothelial dysfunction related to a decrease of VASP level.

Conclusion: The therapy was shown to have antimetastatic action and resulted in normalization of endothelial metabolism, diminution of platelet activation and inhibition of EMT process. The effect was more prominent during early stages of tumor dissemination. Such treatment could be applied to inhibit metastasis during the first stages of this process.

Pro-steroidogenic and pro-spermatogenic actions of nitric oxide (NO) on the catfish, Clarias batrachus: An in vivo study

In an earlier study we have demonstrated reproductive-stage dependent, cell specific existence of inducible nitric oxide synthase (iNOS) and neuronal nitric oxide synthase (nNOS)/NO system in testis of the catfish, Clarias batrachus. The present study is an extension to examine the role of NO in steroidogenesis and spermatogenesis through in vivo administration of a NO donor, sodium nitroprusside (SNP) and a NOS inhibitor, N-nitro-l-arginine methyl ester (l-NAME) during the quiescence and recrudescence phase of the reproductive cycle of the catfish. Effects of these chemicals were assessed on the gonadosomatic index (GSI), levels of circulating & testicular testosterone, NO, activities of 3β-hydroxysteroid dehydrogenase (3β-HSD), 17β-hydroxysteroid dehydrogenase (17β-HSD) in testis, expression of different NOS isoforms and testicular morphology in relation to spermatogenesis. SNP treatment increased the GSI, testicular and circulating testosterone & NO, activities of testicular 3β-HSD & 17β-HSD, and expression of NOS isoforms. It also increased the area and perimeters of interstitium and seminiferous tubules in the testis. It accelerated the spermatogenesis, as was evident from the large number of spermatids/spermatozoa in seminiferous tubules and very few spermatogonial cells/primary spermatocytes in comparison to the control testis. On the contrary, l-NAME significantly suppressed GSI, testosterone & NO levels in serum and testis, and activities of testicular 3β-HSD & 17β-HSD. It also suppressed the expression of NOSs in testis. Though l-NAME did not alter the spermatogonial mitotic proliferation with the advancement of testicular recrudescence, it halted the progression of spermatogenesis (meiotic division and spermatozoa formation) as was clear from the increase in spermatogonial cells and very few advanced germ cells in the seminiferous tubules in l-NAME treated testis, compared to the control testis. The above noted effects were highly pronounced in the recrudescing catfish. Their effects were very marginal and at a particular dose levels of SNP and l-NAME in the quiescent testis. This study distinctly provides evidence of pro-steroidogenic and pro-spermatogenic role of NO. This study also demonstrates the existence of eNOS in fish testis for the first time. The positive feedback control of expression of all isoform of NOS in testis by NO is also noteworthy.

Nitric oxide (NO) stimulates steroidogenesis and folliculogenesis in fish

The present study was undertaken to understand the physiological significance of the existence of nitric oxide synthase (NOS)/nitric oxide (NO) system in fish ovary. For this, two doses of NO donor, sodium nitroprusside (SNP, 25 µg and 50 µg) and NOS inhibitor, N-nitro-l-arginine methyl ester (l-NAME, 50 µg and 100 µg)/100 g body weight were administered during the two reproductive phases of reproductive cycle of theClarias batrachus. During the late-quiescence phase, high dose ofl-NAME decreased the NO, testosterone, 17β-estradiol, vitellogenin contents in serum and ovary and activities of 5-ene-3β-hydroxysteroid dehydrogenases (3β-HSD) and 17β-hydroxysteroid dehydrogenases (17β-HSD) in ovary, whereas higher dose of SNP increased these parameters.l-NAME also reduced oocytes-I but increased perinucleolar oocytes in the ovary, whereas SNP treatment increased the number of advanced oocytes (oocytes-I and II) than the perinucleolar oocytes when compared with control ovary. During the mid-recrudescence phase, both doses of SNP increased NO, testosterone, 17β-estradiol and vitellogenin in serum and ovary; however,l-NAME treatment lowered their levels. The activities of ovarian 3β-HSD and 17β-HSD were also stimulated by SNP, butl-NAME suppressed their activities compared to the control. The SNP-treated ovaries were dominated by oocyte-II and III stages, whereasl-NAME-treated ovary revealed more perinucleolar oocytes and oocytes-I and practically no advanced oocytes. Expression of endothelial NOS (eNOS), inducible NOS (iNOS) and neuronal NOS (nNOS) was augmented by the SNP and declined byl-NAME treatments as compared to the control. This study, thus, provides distinct evidence of NO-stimulated steroidogenesis, vitellogenesis and folliculogenesis in fish.

Utility of large-animal models of BPD: chronically ventilated preterm lambs

This paper is focused on unique insights provided by the preterm lamb physiological model of bronchopulmonary dysplasia (BPD). Connections are also made to insights provided by the former preterm baboon model of BPD, as well as to rodent models of lung injury to the immature, postnatal lung. The preterm lamb and baboon models recapitulate the clinical setting of preterm birth and respiratory failure that require prolonged ventilation support for days or weeks with oxygen-rich gas. An advantage of the preterm lamb model is the large size of preterm lambs, which facilitates physiological studies for days or weeks during the evolution of neonatal chronic lung disease (CLD). To this advantage is linked an integrated array of morphological, biochemical, and molecular analyses that are identifying the role of individual genes in the pathogenesis of neonatal CLD. Results indicate that the mode of ventilation, invasive mechanical ventilation vs. less invasive high-frequency nasal ventilation, is related to outcomes. Our approach also includes pharmacological interventions that test causality of specific molecular players, such as vitamin A supplementation in the pathogenesis of neonatal CLD. The new insights that are being gained from our preterm lamb model may have important translational implications about the pathogenesis and treatment of BPD in preterm human infants.

Electrospun nitric oxide releasing bandage with enhanced wound healing

Research has shown that nitric oxide (NO) enhances wound healing. The incorporation of NO into polymers for medical materials and surgical devices has potential benefits for many wound healing applications. In this work, acrylonitrile (AN)-based terpolymers were electrospun to form non-woven sheets of bandage or wound dressing type materials. NO is bound to the polymer backbone via the formation of a diazeniumdiolate group. In a 14 day NO release study, the dressings released 79 μmol NO g(-1) polymer. The NO-loaded dressings were tested for NO release in vivo, which demonstrate upregulation of NO-inducible genes with dressing application compared to empty dressings. Studies were also conducted to evaluate healing progression in wounds with dressing application performed weekly and daily. In two separate studies, excisional wounds were created on the dorsa of 10 mice. Dressings with NO loaded on the fibers or empty controls were applied to the wounds and measurements of the wound area were taken at each dressing change. The data show significantly enhanced healing progression in the wounds with weekly NO application, which is more dramatic with daily application. Further, the application of daily NO bandages results in improved wound vascularity. These data demonstrate the potential for this novel NO-releasing dressing as a valid wound healing therapy.

Endothelial nitric oxide synthase regulates white matter changes via the BDNF/TrkB pathway after stroke in mice

Stroke induced white matter (WM) damage is associated with neurological functional deficits, but the underlying mechanisms are not well understood. In this study, we investigate whether endothelial nitric oxide synthase (eNOS) affects WM-damage post-stroke. Adult male wild-type (WT) and eNOS knockout (eNOS(-/-)) mice were subjected to middle cerebral artery occlusion. Functional evaluation, infarct volume measurement, immunostaining and primary cortical cell culture were performed. To obtain insight into the mechanisms underlying the effects of eNOS(-/-) on WM-damage, measurement of eNOS, brain-derived neurotrophic factor (BDNF) and its receptor TrkB in vivo and in vitro were also performed. No significant differences were detected in the infarction volume, myelin density in the ipsilateral striatal WM-bundles and myelin-based protein expression in the cerebral ischemic border between WT and eNOS(-/-) mice. However, eNOS(-/-) mice showed significantly: 1) decreased functional outcome, concurrent with decreases of total axon density and phosphorylated high-molecular weight neurofilament density in the ipsilateral striatal WM-bundles. Correlation analysis showed that axon density is significantly positive correlated with neurological functional outcome; 2) decreased numbers of oligodendrocytes / oligodendrocyte progenitor cells in the ipsilateral striatum; 3) decreased synaptophysin, BDNF and TrkB expression in the ischemic border compared with WT mice after stroke (n = 12/group, p<0.05). Primary cortical cell culture confirmed that the decrease of neuronal neurite outgrowth in the neurons derived from eNOS(-/-) mice is mediated by the reduction of BDNF/TrkB (n = 6/group, p<0.05). Our data show that eNOS plays a critical role in WM-damage after stroke, and eNOS(-/-)-induced decreases in the BDNF/TrkB pathway may contribute to increased WM-damage, and thereby decrease functional outcome.

Positive feedback regulation of human inducible nitric-oxide synthase expression by Ras protein S-nitrosylation

The production of nitric oxide (NO) by inducible NO synthase (iNOS) regulates many aspects of physiology and pathology. The expression of iNOS needs to be tightly regulated to balance the broad ranging properties of NO. We have investigated the feedback regulation of cytokine-induced iNOS expression by NO in human cells. The pharmacological inhibition of iNOS activity reduced iNOS protein levels in response to cytokine stimulation in a human epithelial cell line (A549 cells) as well as in primary human astrocytes and bronchial epithelial cells. The addition of exogenous NO using a NO donor prevented the reduction in iNOS levels caused by blockade of iNOS activity. Examination of signaling pathways affected by iNOS indicated that NO S-nitrosylated Ras. Transfection of cells with a S-nitrosylation-resistant Ras mutant reduced iNOS protein levels, indicating a role for this Ras modification in the amplification of iNOS levels. Further, the induction of iNOS protein levels correlated with the late activation of the phosphatidylinositol 3-kinase/Akt and mammalian target of rapamycin (mTOR) pathways, and inhibition of these signaling molecules reduced iNOS levels. Altogether, our findings reveal a previously unknown regulatory pathway that amplifies iNOS expression in human cells.

Sildenafil protects against nitric oxide deficiency-related nephrotoxicity in cyclosporine A treated rats

Cyclosporine A (CsA) is the most widely used immunosuppressant in organ transplant surgery and in treatment of autoimmune disease. Nevertheless, animal and clinical studies have demonstrated that nephrotoxicity is the major adverse effect limiting the prolonged CsA therapeutic use. The present study aimed to investigate possible protective effect of sildenafil, a phoshodiestrase-5 inhibitor, on CsA-induced nephrotoxicity and various mechanism(s) underlies this effect. Male Wistar rats were administered CsA (20 mg/kg/day, s.c.) for 21 days alone or in combination with sildenafil (5 mg/kg/day, p.o.). Sildenafil exhibited nephroprotective effects as evidenced by significant decrease in serum creatinine and urea levels, spot urine albumin-creatinine ratio, as well as renal level of malondialdehyde, with a concurrent increase in renal levels of reduced glutathione and nitric oxide along with catalase activity compared to CsA-treated rats. [corrected]. Additionally, immunohistochemical analysis demonstrated that sildenafil treatment markedly reduced inducible nitric oxide synthase, tumor necrosis factor-alpha, and caspase-3 expressions, while expression of endothelial nitric oxide synthase was prominently enhanced. The protective effects of sildenafil were confirmed by renal histopathological examination. Pretreatment with l-nitro-arginine methyl ester (10 mg/kg/day, i.p.), a non-selective nitric oxide synthase inhibitor, reversed the protection afforded by sildenafil. Taken together, the current study highlighted the renoprotective effects of sildenafil against CsA-induced nephrotoxicity in rats, which might be mediated, in part, through nitric oxide pathway as well as antioxidant, anti-inflammatory, and anti-apoptotic activities.

Expression of eNOS in the lungs of neonates with pulmonary hypertension

BACKGROUND

Neonatal hypoxemic respiratory failure (NHRF) is usually associated with reversible persistent pulmonary hypertension (PPHN). Congenital diaphragmatic hernia (CDH), a cause of refractory NHRF, is associated with irreversible pulmonary hypertension. Nitric oxide (NO) generated in the pulmonary vascular endothelium by endothelial nitric oxide synthase (eNOS) plays a pivotal role in perinatal circulatory adaptation.

OBJECTIVE

To compare the expression of eNOS using IHC in postmortem lung tissue from newborns diagnosed clinically with PPHN and CDH.

DESIGN/METHODS

Formalin-fixed lung tissue from infants who died following treatment for PPHN (n=12) or CDH (n=8) and age and gender matched controls who died from non-respiratory causes (Control, n=14) was evaluated for expression and staining intensity (1-4 scale) of eNOS using IHC.

RESULTS

Mean gestational and postnatal age was comparable across groups. Histological evidence of chronic lung disease, pulmonary hypoplasia and pulmonary hypertension were seen more frequently in CDH compared to PPHN and control infants. eNOS expression was increased in arteriolar media of PPHN infants compared to Controls (p=0.027). CDH infants had increased intensity of staining for eNOS in the arteriolar endothelium (p=0.022) compared to control and PPHN infants and in the alveolar lining (p=0.002) compared to Controls.

CONCLUSIONS

Upregulation of eNOS was seen both in infants with CDH and PPHN but was more marked in infants with CDH. These findings may have implications for understanding disease pathophysiology in cases with fatal outcome and development of novel therapies for neonatal pulmonary hypertension.

Superoxide dismutase restores eNOS expression and function in resistance pulmonary arteries from neonatal lambs with persistent pulmonary hypertension

Endothelial nitric oxide (NO) synthase (eNOS) expression and activity are decreased in fetal lambs with persistent pulmonary hypertension (PPHN). We sought to determine the impact of mechanical ventilation with O(2) with or without inhaled NO (iNO) or recombinant human SOD (rhSOD) on eNOS in the ductal ligation model of PPHN. PPHN lambs and age-matched controls were ventilated with 100% O(2) for 24 h alone or combined with 20 ppm iNO continuously or a single dose of rhSOD (5 mg/kg) given intratracheally at delivery. In 1-day spontaneously breathing lambs, eNOS expression in resistance pulmonary arteries increased relative to fetal levels. eNOS expression increased in control lambs ventilated with 100% O(2), but not in PPHN lambs. Addition of iNO or rhSOD increased eNOS expression and decreased generation of reactive oxygen species (ROS) in PPHN lambs relative to those ventilated with 100% O(2) alone. However, only rhSOD restored eNOS function, increased tetrahydrobiopterin (BH(4)), a critical cofactor for eNOS function, and restored GTP cyclohydrolase I expression in isolated vessels and lungs from PPHN lambs. These data suggest that ventilation of PPHN lambs with 100% O(2) increases ROS production, blunts postnatal increases in eNOS expression, and decreases available BH(4) in PPHN lambs. Although the addition of iNO or rhSOD diminished ROS production and increased eNOS expression, only rhSOD improved eNOS function and levels of available BH(4). Thus therapies designed to decrease oxidative stress and restore eNOS coupling, such as rhSOD, may prove useful in the treatment of PPHN in newborn infants.

Protein kinase Cdelta regulates endothelial nitric oxide synthase expression via Akt activation and nitric oxide generation

In this study, we explore the roles of the delta isoform of PKC (PKCdelta) in the regulation of endothelial nitric oxide synthase (eNOS) activity in pulmonary arterial endothelial cells isolated from fetal lambs (FPAECs). Pharmacological inhibition of PKCdelta with either rottlerin or with the peptide, deltaV1-1, acutely attenuated NO production, and this was associated with a decrease in phosphorylation of eNOS at Ser1177 (S1177). The chronic effects of PKCdelta inhibition using either rottlerin or the overexpression of a dominant negative PKCdelta mutant included the downregulation of eNOS gene expression that was manifested by a decrease in both eNOS promoter activity and protein expression after 24 h of treatment. We also found that PKCdelta inhibition blunted Akt activation as observed by a reduction in phosphorylated Akt at position Ser473. Thus, we conclude that PKCdelta is actively involved in the activation of Akt. To determine the effect of Akt on eNOS signaling, we overexpressed a dominant negative mutant of Akt and determined its effect of NO generation, eNOS expression, and phosphorylation of eNOS at S1177. Our results demonstrated that Akt inhibition was associated with decreased NO production that correlated with reduced phosphorylation of eNOS at S1177, and decreased eNOS promoter activity. We next evaluated the effect of endogenously produced NO on eNOS expression by incubating FPAECs with the eNOS inhibitor 2-ethyl-2-thiopseudourea (ETU). ETU significantly inhibited NO production, eNOS promoter activity, and eNOS protein levels. Together, our data indicate involvement of PKCdelta-mediated Akt activation and NO generation in maintaining eNOS expression.

Nitric oxide production in mouse and rat macrophages: A rapid and efficient assay for screening of drugs immunostimulatory effects in human cells

Activation of inducible nitric oxide (NO) synthase (iNOS) and resulting high-output NO release is known to depend on the action of cytokines. We investigated in vitro production of NO by resident peritoneal macrophages from mice and rats, and secretion of cytokines by these cells as well as by human peripheral blood mononuclear cells (PBMC). The cells were cultured in the presence of a selected group of acyclic nucleoside phosphonates that have previously been shown to possess immunobiological potential. Several of the compounds enhanced production of NO in animal macrophages. This activity was associated with stimulatory effects on secretion of cytokines such as TNF-alpha in all mouse and rat macrophages and human PBMC, and IL-10 in mouse and human cells. Statistically highly significant correlation between the range of NO biosynthesis in rodent cells and extent of cytokine stimulation in human PBMC has been observed. It is suggested that the NO assay may be regarded as an efficient, economical and relatively reliable tool in primary screening for intrinsic immunostimulatory activity of compounds in human cell system, at least from the point of view of cytokine secretion.

An inhaled inducible nitric oxide synthase inhibitor reduces damage of Candida-induced acute lung injury

Excessive nitric oxide (NO) generated by inducible nitric oxide synthase (iNOS) aggravates acute lung injury (ALI) by producing peroxynitrite. We previously showed by immunostaining that the expression of iNOS was suppressed by inhalation of N(G)-nitro-L-arginine methyl ester in mice with Candida-induced ALI. This study tested the hypothesis that a novel iNOS inhibitor suppresses not only iNOS expression, but also iNOS messenger RNA (mRNA) production by interrupting a positive feedback loop at the time of NO production in Candida-induced ALI. Mice were pretreated by inhalation of saline or ONO-1714, a selective iNOS inhibitor, and were given an intravenous injection of Candida albicans to induce ALI. After inhalation of 1 mM aerosolized ONO-1714, the nitrite-nitrate concentration in bronchoalveolar lavage fluid (BALF) at 24 h was significantly lower than that after inhalation of saline. Tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) levels and neutrophils in BALF were decreased by inhalation of ONO-1714. Inhalation of ONO-1714 markedly suppressed nitrotyrosine production and inhibited the expression of iNOS mRNA as well as proteins in the lung. Survival was prolonged by inhalation of ONO-1714. We conclude that pretreatment with inhaled ONO-1714 suppresses the production of peroxinitrite and decreases oxidative stress associated with peroxinitrite in Candida-induced ALI.

Effects of repeated in vivo inhalant nitrite exposure on gene expression in mouse liver and lungs

Exposure to inhalant organic nitrites (drugs of abuse commonly known as "poppers") has been reported to enhance tumor growth in mice, but the mechanism is not fully defined. This study examined the effect of repeated in vivo nitrite exposures on gene expression in the mouse liver and lungs using a gene array panel of 94 cancer- and angiogenesis-related genes. Using 2-fold change as a threshold criterion, repeated nitrite exposure was found to alter the expression of 65 and 23 genes in the liver and lungs, respectively. Six genes were significantly upregulated (p<or=0.05), viz., those encoding VEGF, VEGFD (vascular endothelial growth factor A and D, respectively) in the lungs and FGF1, FGF4 (fibroblast growth factor 1 and 4, respectively), Hsp70 (heat shock 70kDa protein 4), and PF4 (platelet factor 4) in the liver. mRNA encoding HO-1 (heme oxygenase-1) and Smad7 were marginally (p=0.057) stimulated in the liver. Follow-up studies in the liver revealed significant nitrite-induced expression of VEGF protein and mRNA. Immuno-staining of liver slices revealed that the increased hepatic VEGF expression resided mainly in hepatocytes. Stimulation of hepatic VEGF expression by ISBN was not different in endothelial nitric oxide synthase (eNOS) knockout vs. wild-type mice. In conclusion, multiple exposures to inhalant nitrite appeared to cause alteration in the expression of a number of genes relating to cancer and angiogenesis, including VEGF. eNOS presence did not appear to be essential for nitrite-induced VEGF expression. These studies demonstrate that in vivo exposure to inhalant nitrites results in changes in the angiogenesis cascade.

Effects of L-arginine on the endogenous angiogenic response in a model of hypercholesterolemia

BACKGROUND

The angiogenic properties of vascular endothelial growth factor and fibroblast growth factor-2 are mediated in part through nitric oxide release, whose availability is decreased in endothelial dysfunction associated with advanced coronary artery disease. We examined the influence of L-arginine supplementation on the endogenous angiogenic response to ischemia in a porcine model of hypercholesterolemia.

METHODS

Eighteen Yucatan pigs were fed either a normal (NORM, n=6) or a high-cholesterol diet, with (CHOL-ARG, n=6) or without (CHOL, n=6) L-arginine (100 mg/kg/day), throughout the experiment. All pigs underwent ameroid constrictor placement on the circumflex artery (LCx). Seven weeks later, endothelium-dependent coronary microvascular responses to fibroblast growth factor-2 and vascular endothelial growth factor were assessed by videomicroscopy. Perfusion was assessed with radioactive microspheres; angiogenesis was evaluated by platelet-endothelial cell adhesion molecule-1 (CD-31) staining. Regional myocardial function was assessed by sonomicrometry. Expression of endothelial nitric oxide synthase and inducible nitric oxide synthase was measured by Western blot analyses.

RESULTS

Pigs from the CHOL group showed significant endothelial dysfunction in the LCx territory. The dysfunction was normalized partially by L-arginine supplementation, which restored the response in the LCx territory to the level of the nonischemic anterior wall. L-arginine supplementation resulted in increases of perfusion, density of capillary endothelial, and level of endothelial nitric oxide synthase in the ischemic region. Despite these findings, no improvement in myocardial regional function was found.

CONCLUSIONS

L-arginine supplementation can partially restore endothelium-dependent vasorelaxation and improve myocardial perfusion in a swine model of chronic myocardial ischemia with hypercholesterolemia-induced endothelial dysfunction. These findings suggest a putative role for L-arginine in combination with growth factor therapy for end-stage coronary artery disease.

Inhaled nitric oxide effects on lung structure and function in chronically ventilated preterm lambs

RATIONALE

Inhaled nitric oxide (iNO) can reverse neonatal pulmonary hypertension and bronchoconstriction and reduce proliferation of cultured arterial and airway smooth muscle cells.

OBJECTIVES

To see if continuous iNO from birth might reduce pulmonary vascular and respiratory tract resistance (PVR, RE) and attenuate growth of arterial and airway smooth muscle in preterm lambs with chronic lung disease.

METHODS

Eight premature lambs received mechanical ventilation for 3 weeks, four with and four without iNO (5-15 ppm). Four term lambs, mechanically ventilated without iNO for 3 weeks, served as additional control animals.

MEASUREMENTS

PVR and RE were measured weekly. After 3 weeks, lung tissue was processed for quantitative image analysis of smooth muscle abundance around small arteries (SMart) and terminal bronchioles (SMtb). Radial alveolar counts were done to assess alveolar number. Endothelial NO synthase (eNOS) protein in arteries and airways was measured by immunoblot analysis.

MAIN RESULTS

At study's end, PVR was similar in iNO-treated and untreated preterm lambs; PVR was less in iNO-treated preterm lambs compared with term control animals. RE in iNO-treated lambs was less than 40% of RE measured in preterm control animals. SMart was similar in iNO-treated and both groups of control lambs; SMtb in lambs given iNO was significantly less (approximately 50%) than in preterm control animals. Radial alveolar counts of iNO-treated lambs were more than twice that of preterm control animals. eNOS was similar in arteries and airways of iNO-treated preterm lambs compared with control term lambs.

CONCLUSIONS

iNO preserves structure and function of airway smooth muscle and enhances alveolar development in preterm lambs with chronic lung disease.

Endothelial alterations during inhaled NO in lambs with pulmonary hypertension: implications for rebound hypertension

Clinically significant increases in pulmonary vascular resistance (PVR) have been noted upon acute withdrawal of inhaled nitric oxide (iNO). Previous studies in the normal pulmonary circulation demonstrate that iNO increases endothelin-1 (ET-1) levels and decreases endogenous nitric oxide synthase (NOS) activity, implicating an endothelial etiology for the increase in resistance upon iNO withdrawal. However, the effect of iNO on endogenous endothelial function in the clinically relevant pulmonary hypertensive circulation is unknown. The objective of this study was to determine the effects of iNO on endogenous NO-cGMP and ET-1 signaling in lambs with preexisting pulmonary hypertension secondary to increased pulmonary blood flow. Eight fetal lambs underwent in utero placement of an aortopulmonary vascular graft (shunt lambs). After delivery (4 wk), the shunt lambs were mechanically ventilated with iNO (40 ppm) for 24 h. After 24 h of inhaled NO, plasma ET-1 levels increased by 34.8% independently of changes in protein levels (P < 0.05). Contrary to findings in normal lambs, total NOS activity did not decrease during iNO. In fact, Western blot analysis demonstrated that tissue endothelial NOS protein levels decreased by 43% such that NOS activity relative to protein levels actually increased during iNO (P < 0.05). In addition, the beta-subunit of soluble guanylate cyclase decreased by 70%, whereas phosphodiesterase 5 levels were unchanged (P < 0.05). Withdrawal of iNO was associated with an acute increase in PVR, which exceeded baseline PVR by 45%, and a decrease in cGMP concentrations to levels that were below baseline. These data suggest that the endothelial response to iNO and the potential mechanisms of rebound pulmonary hypertension are dependent upon the underlying pulmonary vasculature.

Increased expression of nitric oxide synthase in human lung transplants after nitric oxide inhalation

BACKGROUND

The effects of the ischemia-reperfusion process of organ transplantation on nitric oxide (NO) synthase (NOS) in humans are unknown. The effects of NO inhalation on endogenous NOS expression and activity are controversial. The authors hypothesized that NO inhalation may affect ischemia-reperfusion-induced alterations of the endogenous NOS system.

METHODS

The authors performed lung biopsy on patients in a randomized phase II clinical trial of NO inhalation during lung transplantation. After lung implantation, 20 ppm of NO or placebo gas was administered 10 min after the start of reperfusion. Lung tissues were collected from 20 patients (NO, n=9; placebo, n=11) after cold and warm ischemia, 1 hr and 2 hr after reperfusion. The protein levels of NOS isoforms were analyzed by Western blotting and the total NOS activity was measured.

RESULTS

The protein levels of inducible NOS did not change significantly in either of the groups. In contrast, during the 2-hr reperfusion period, constitutive NOS (neuronal NOS [nNOS] and endothelial NOS) tended to decrease in the placebo group, but gradually increased in the NO group. After 2 hr of reperfusion, the nNOS protein in the NO group was significantly higher than that in the placebo group (P <0.05). However, the total NOS activity remained at low levels in both groups.

CONCLUSIONS

NO inhalation-induced increase of constitutive NOS proteins indicates the interaction between inhaled NO molecules and lung tissues. However, the activity of these newly synthesized NOS proteins remains suppressed during the ischemia-reperfusion period of lung transplantation.

Endothelial Nitric Oxide Synthase

Advances in our understanding of the molecular mechanisms involved in the constitutive and regulated expression of endothelial nitric oxide synthase (eNOS) mRNA expression present a new level of complexity to the study of endothelial gene regulation in health and disease. Recent studies highlight the contribution of both transcription and RNA stability to net steady-state mRNA levels of eNOS in vascular endothelium, introducing a new paradigm to gene regulation in the injured blood vessel. Constitutive eNOS expression is dependent on basal transcription machinery in the core promoter, involving positive and negative protein–protein and protein–DNA interactions. Chromatin-based mechanisms and epigenetic events also regulate expression of eNOS at the transcriptional level in a cell-restricted fashion. Although constitutively active, important physiological and pathophysiologic stimuli alter eNOS gene transcription rates. For instance, eNOS transcription rates increase in response to lysophosphatidylcholine, shear stress, and TGF-β, among others. Under basal conditions, eNOS mRNA is extremely stable. Surprisingly, posttranscriptional mechanisms have emerged as important regulatory pathways in the observed decreases in eNOS expression in some settings. In models of inflammation, proliferation/injury, oxidized low-density lipoprotein treatment, and hypoxia, eNOS mRNA destabilization plays a significant role in the rapid downregulation of eNOS mRNA levels.

Withdrawal of inhaled nitric oxide from nonresponders after short exposure

INTRODUCTION

Inhaled nitric oxide has been approved by FDA for treatment of hypoxic respiratory failure in term and near-term neonates. The safety of withdrawing NO in patients who fail to respond is a major concern.

OBJECTIVE

To obtain further insight into the safety of withdrawing NO in patients who do not initially respond to this therapy, the charts of patients enrolled at our center in the Neonatal Nitric Oxide Study (NINOS) were reviewed. Oxygenation indices (OI) before, during and after exposure to NO or placebo were compared.

METHODS

The charts of 110 neonates who received NO or placebo within the NINOS trial guidelines from 1995 to 1999 were reviewed. Arterial blood gases of nonresponders before, during and after a 30-minute exposure to different doses of NO or placebo were analyzed.

RESULTS

For both high-dose and 20 ppm nonresponders who received NO, there was no significant change in OI from baseline after withdrawing NO. For patients receiving placebo, there was a significant increase in OI following a 30-minute exposure to placebo.

CONCLUSIONS

NO has been shown to be effective in the treatment of neonatal respiratory failure; however, not all recipients demonstrate clinical improvement. This study showed that withdrawing NO in nonresponders did not cause increased respiratory morbidity when NO exposure was limited to 30 min. Differences between our results and others showing refractory hypoxia after withdrawing NO may be due to different durations of NO exposure and, possibly, its effect on endogenous NO metabolism.

Development of the myogenic response in postnatal intestine: role of PKC

Previous attempts to determine developmental changes in the vascular myogenic response have been confounded by the presence of competing vasoactive stimuli or the use of isolated vessels with markedly different baseline diameters. To circumvent these issues, small mesenteric arteries (diameter approximately 150 microm) from 1- and 10-day-old piglets were studied in vitro under no-flow conditions. In situ studies demonstrated that the intravascular pressure and diameter of these vessels were similar in both age groups, allowing an effective comparison of the myogenic response not obscured by differences in basal diameter. The pressure-diameter relationship was age specific. Thus, although small mesenteric arteries from both age groups demonstrated myogenic constriction in response to stepwise increases in pressure (0 to 100 mmHg, in 20-mmHg increments), the intensity of contraction was significantly greater in vessels from 1-day-old piglets particularly within the pressure range normally experienced by these vessels in situ. Attenuation or activation of PKC with calphostin C or indolactam, respectively, substantially altered the pressure-diameter relationship in 1-, but not 10-day-old arteries; thus calphostin C essentially eliminated the contractile response to pressure elevation in younger subjects, whereas indolactam significantly increased the intensity of the myogenic response and shifted its activation point to a lower pressure range. Immunoblots carried out on protein recovered from these arteries revealed the presence of alpha, beta, epsilon, iota, and lambda; notably, expression of the alpha- and epsilon-isoforms substantially decreased between postnatal days 1 and 10.

The role of endogenous and exogenous nitric oxide on airway function

Coordinated regulation of airway caliber is important for the maintenance of effective ventilation. Therefore, we sought to characterize the role of endogenously released, and exogenously administered, nitric oxide (NO) in mediating airway smooth muscle relaxation during early postnatal life. In both rat pup and piglet models, cholinergically mediated airway contractile responses were diminished by simultaneous release of endogenous NO and cGMP activation in both central airways and peripheral contractile elements. This ability of endogenously released NO to oppose airway constriction may be impaired in response to hyperoxic exposure or in animal models of cystic fibrosis. Additional studies in piglets have shown that exogenously administered NO causes a modest, but significant, reduction in lung resistance, analogous to the decrease in pulmonary vascular resistance induced by inhaled NO. Clinical trials are now underway in preterm infants at risk for chronic neonatal lung injury to determine whether inhaled NO has a beneficial effect on the development of bronchopulmonary dysplasia and whether exogenous NO modulates airway function in such infants.

Physiological mechanisms regulating the expression of endothelial-type NO synthase

Although endothelial nitric oxide synthase (eNOS) is a constitutively expressed enzyme, its expression is regulated by a number of biophysical, biochemical, and hormonal stimuli, both under physiological conditions and in pathology. This review summarizes the recent findings in this field. Shear stress, growth factors (such as transforming growth factor-beta, fibroblast growth factor, vascular endothelial growth factor, and platelet-derived growth factor), hormones (such as estrogens, insulin, angiotensin II, and endothelin 1), and other compounds (such as lysophosphatidylcholine) upregulate eNOS expression. On the other hand, the cytokine tumor necrosis factor-alpha and bacterial lipopolysaccharide downregulate the expression of this enzyme. The growth status of cells, the actin cytoskeleton, and NO itself are also important regulators of eNOS expression. Both transcriptional and posttranscriptional mechanisms are involved in the expressional regulation of eNOS. Different signaling pathways are involved in the regulation of eNOS promoter activity and eNOS mRNA stability. Changes in eNOS expression and activity under pathophysiological conditions and the pharmacological modulation of eNOS expression are subject of a subsequent brief review (part 2) to be published in the next issue of this journal.

17 beta-Estradiol induces a rapid, endothelium-dependent, sex-specific vasodilatation in spontaneous constricted rat arterioles

OBJECTIVE

Our purpose was to resolve the apparent contradiction between the endothelium-dependent and endothelium-independent vasodilator effects of 17 beta-estradiol reported in different studies.

STUDY DESIGN

The inner diameters of isolated pressurized spontaneously constricted muscle arterioles (diameter = 63 microm) from Wistar rats (n = 21) were measured during exposure to 17 beta-estradiol, and the role of the endothelium and the influence of sex were assessed.

RESULTS

A dose-dependent dilatation was observed during exposure to 17 beta-estradiol concentrations from 10(-10) to 10(-4) mol/L. Arterioles of female rats displayed significantly more dilatation than vessels from male rats. The dilatation was significantly less in endothelium-denuded arterioles or after pretreatment with and in the presence of a nitric oxide synthase inhibitor.

CONCLUSIONS

These results provide strong evidence that, in addition to an endothelium-independent effect, 17 beta-estradiol has a dose-dependent, endothelium-mediated, rapid vasodilatory effect on muscle arterioles from the rat, which is stronger in female rats than in male rats.

Intrauterine growth retardation is associated with reduced activity and expression of the cationic amino acid transport systems y+/hCAT-1 and y+/hCAT-2B and lower activity of nitric oxide synthase in human umbilical vein endothelial cells

Intrauterine growth retardation (IUGR) is associated with vascular complications leading to hypoxia and abnormal fetal development. The effect of IUGR on L-arginine transport and nitric oxide (NO) synthesis was investigated in cultures of human umbilical vein endothelial cells (HUVECs). IUGR was associated with membrane depolarization and reduced L-arginine transport (V(max)= 5.8+/-0.2 versus 3.3+/-0.1 pmol/microg protein per minute), with no significant changes in transport affinity (K(m)=159+/-15 versus 137+/-14 micromol/L). L-Arginine transport was trans-stimulated (8- to 9-fold) in cells from normal and IUGR pregnancies. IUGR was associated with reduced production of L-[3H]citrulline from L-[3H] arginine, lower nitrite and intracellular L-arginine, L-citrulline, and cGMP. IUGR decreased hCAT-1 and hCAT-2B mRNA, and increased eNOS mRNA and protein levels. IUGR-associated inhibition of L-arginine transport and NO synthesis, and membrane depolarization were reversed by the NO donor S-nitroso-N-acetyl-L,D-penicillamine. In summary, endothelium from fetuses with IUGR exhibit altered L-arginine transport and NO synthesis (L-arginine/NO pathway), reduced expression and activity of hCAT-1 and hCAT-2B and reduced eNOS activity. Alterations in L-arginine/NO pathway could be critical for the physiological processes involved in the etiology of IUGR in human pregnancies.

Fos and nitric oxide synthase in rat brain with chronic mesostriatal dopamine deficiency: effects of nitroglycerin and hypoxia

We found sustained proto-oncogene c-fos expression in neurons of the lateral and medial neostriatum and suppression of this expression in nitric oxide synthase (NOS)-containing cells within the islands of Calleja after lesions of the dopaminergic mesostriatal system induced by 6-hydroxydopamine. Systemic administration of nitroglycerin (NTG) or mild hypoxia resulted in a decreased of c-fos expression in the dorsolateral part of the denervated neostriatum. However, in other brain structures NTG or mild hypoxia evoked sustained c-fos expression in NOS-containing neurons and in the sources catecholaminergic projections involved in the control of cardiovascular function. We propose that the administration of NTG, an NO donor, or hypoxia partially attenuate the consequences of an excessively increased glutamate level in the denervated neostriatum which are manifest in high level of c-fos expression.

Endothelin-1 and nitric oxide synthase in short rebound reaction to short exposure to inhaled nitric oxide

On withdrawal of inhalation of nitric oxide (INO) administered after lung injury, pulmonary artery pressure (PAP) and arterial oxygen tension (Pa(O(2))) may deteriorate more than before INO (rebound response). In this study, we investigated the possible roles of endothelin (ET)-1 and nitric oxide (NO) synthase (NOS) activity in the short rebound reaction to short-term inhalation of NO. Twenty-six anesthetized mechanically ventilated piglets were given endotoxin infusion. Twelve animals then received INO (30 parts per million) for two 30-min periods. Nine controls were not given NO. Measurements were made of blood gases and hemodynamic parameters, lung tissue ET-1 expression and NOS activity, and plasma ET-1 concentration. INO decreased PAP and increased Pa(O(2)), but INO withdrawal caused a short rebound reaction with an increase in PAP. Lung tissue expression and plasma concentration of ET-1 increased during INO, and plasma ET-1 increased further after its withdrawal. Activity of constitutive NOS decreased during INO, whereas that of inducible NOS was unchanged. Upregulation of ET-1 and downregulation of NOS activity may have influenced the short rebound reaction to short-term INO.

NO regulates LPS-stimulated cyclooxygenase gene expression and activity in pulmonary artery endothelium

We examined whether nitric oxide (NO) inhibits prostanoid synthesis through actions on cyclooxygenase (COX) gene expression and activity. Bovine pulmonary artery endothelial cells were pretreated for 30 min with the NO donors 1 mM S-nitroso-N-acetylpenicillamine (SNAP), 0.5 mM sodium nitroprusside (SNP), or 0.2 microM spermine NONOate; controls included cells pretreated with either 1 mM N-acetyl-D-penicillamine or the NO synthase (NOS) inhibitor 1 mM N(G)-nitro-L-arginine methyl ester with and without addition of lipopolysaccharide (LPS; 0.1 microg/ml) for 8 h. COX-1 and COX-2 gene and protein expression were examined by RT-PCR and Western analysis, respectively; prostanoid measurements were made by gas chromatography-mass spectrometry, and COX activity was studied after a 30-min incubation with 30 microM arachidonic acid. LPS induced COX-2 gene and protein expression and caused an increase in COX activity and an eightfold increase in 6-keto-PGF(1alpha) release. LPS-stimulated COX-2 gene expression was decreased by approximately 50% by the NO donors. In contrast, LPS caused a significant reduction in COX-1 gene expression and treatment with NO donors had little effect. SNAP, SNP, and NONOate significantly suppressed LPS-stimulated COX activity and 6-keto-PGF(1alpha) release. Our data indicate that increased generation of NO attenuates LPS-stimulated COX-2 gene expression and activity, whereas inhibition of endogenous NOS has little effect.

Nitric oxide donors regulate nitric oxide synthase in bovine pulmonary artery endothelium

This study examined the notion that exogenous generation of nitric oxide (NO) modulates NOS gene expression and activity. Bovine pulmonary artery endothelial cells (BPAEC) were treated with the NO donors, 1 mM SNAP (S-nitroso-N-acetylpenicillamine), 0.5 mM SNP (sodium nitroprusside) or 0.2 microM NONOate (spermine NONOate) in medium 199 containing 2% FBS. Controls included untreated cells and cells exposed to 1 mM NAP (N-acetyl-D-penicillamine). NOS activity was assessed using a fibroblast-reporter cell assay; intracellular Ca2+ concentrations were assessed by Fura-2 microfluorometry; and NO release was measured by chemiluminescence. Constitutive endothelial (e) and inducible (i) NOS gene and protein expression were examined by northern and western blot analysis, respectively. Two hours exposure to either SNAP or NONOate caused a significant elevation in NO release from the endothelial cells (SNAP = 51.4 +/- 5.9; NONOate = 23.8 +/- 4.2; control = 14.5 +/- 2.8 microM); but A23187 (3 microM)-stimulated NO release was attenuated when compared to controls. Treatment with either SNAP or NONOate for 2 h also resulted in a significant increase in NOS activity in endothelial homogenates (SNAP = 23.6 +/- 2.5; NONOate= 29.8 +/- 7.7; control = 14.5 +/- 2.5fmol cGMP/microg per 10(6) cells). Exposure to SNAP and SNP, but not NONOate, for 1 h caused an increase in intracellular calcium. Between 4 and 8 h, SNAP and NONOate caused a 2- to 3-fold increase in eNOS, but not iNOS, gene (P < 0.05) and protein expression. NAP had little effect on either eNOS gene expression, activity or NO production. Our data indicate that exogenous generation of NO leads to a biphasic response in BPAEC, an early increase in intracellular Ca2+, and increases in NOS activity and NO release followed by increased expression of the eNOS gene, but not the iNOS gene. We conclude that eNOS gene expression and activity are regulated by a positive-feedback regulatory action of exogenous NO.

Differential effects of estrogen and progesterone on AT(1) receptor gene expression in vascular smooth muscle cells

BACKGROUND

The beneficial vasoprotective effects of a postmenopausal estrogen replacement therapy may be prevented by a concomitant administration of progestins. To investigate the differential effects of estrogens and progesterone, we examined their influence on AT(1) receptor gene expression in vascular smooth muscle cells (VSMCs).

METHODS AND RESULTS

17beta-Estradiol caused downregulation of AT(1) receptor mRNA expression to 46+/-14%, whereas progesterone led to a significant upregulation to 201+/-29%, as assessed by Northern analysis. Western blots revealed that estrogen induced a downregulation and progesterone an upregulation of the AT(1) receptor protein. Estrogen-induced decrease of AT(1) receptor expression was mediated through activation of estrogen receptors. Nuclear run-on assays revealed that 17beta-estradiol did not alter AT(1) receptor mRNA transcription rate, whereas progesterone caused an enhanced AT(1) receptor mRNA transcription rate. 17beta-Estradiol decreased the AT(1) receptor mRNA half-life from 5 to 2 hours, whereas progesterone induced a stabilization of AT(1) receptor mRNA to a half-life of 10 hours. Preincubation of VSMCs with PD98059, SB203580, herbimycin, wortmannin, or N:(omega)-nitro-L-arginine suggested that 17beta-estradiol caused AT(1) receptor downregulation through nitric oxide-dependent pathways. Progesterone caused AT(1) receptor overexpression via PI(3)-kinase activation. Angiotensin II-induced release of reactive oxygen species was inhibited by estrogens. Progesterone itself enhanced the production of reactive oxygen species.

CONCLUSIONS

Because AT(1) receptor regulation plays a pivotal role in the pathogenesis of hypertension and atherosclerosis, the differential effects of estrogen and progesterone on the expression of this gene may in part explain the potentially counteracting effects of these reproductive hormones on the incidence of postmenopausal cardiovascular diseases.

Nitrite inhalation in rats elevates tissue NOS III expression and alters tyrosine nitration and phosphorylation

Organic nitrites are nitric oxide (NO) donors that are used predominantly as inhalant drugs of abuse and have been shown to have immunomodulating effects. NO donors can modulate NOS activity and expression, thus altering the level of endogenous NO production. NO can react with superoxide (O(*)(2)(-)) to form peroxynitrite (ONOO(-)), which can nitrate tyrosine residues in proteins and alter tyrosine phosphorylation. We investigated the effects of inhaled isobutyl nitrite (ISBN) on NOS expression, tyrosine nitration, and tyrosine phosphorylation in selected organs of rats. Following exposures of 109 and 1517 ppm ISBN for 4 h, the lung, spleen, liver, and kidney were removed and assayed by SDS-PAGE for NOS III (eNOS), NOS II (iNOS), nitrotyrosine (NT)- and phosphotyrosine (PT)-immunoreactive proteins using specific antibodies. ISBN at 1517 ppm, but not 109 ppm, caused an increase in NOS III expression in the liver and kidney, but not in the lung and spleen. No apparent effect on NOS II expression was observed in these organs. The expressions of NT and PT protein bands (30-200 kDa) were increased in the liver and kidney, but not in the lung and spleen. This increase in NT persisted for 24 h post-exposure. Increased NOS III expression in the liver and kidney may promote peroxynitrite formation and contribute to the increase in NT and PT immunoreactivity. ISBN inhalation may thus cause changes in cellular signaling involving tyrosine phosphorylation. These findings may suggest a mechanistic basis for the apparent immunotoxicity associated with nitrite abuse.