Exogenous nitric oxide inhibits proliferation of cultured vascular endothelial cells

CDC-derived extracellular vesicles reprogram inflammatory macrophages to an arginase 1-dependent proangiogenic phenotype

Macrophages play a pivotal role in tissue repair following myocardial infarction (MI). In response to injury, they exist along a spectrum of activation states tightly regulated by their microenvironment. Cardiosphere-derived cells (CDCs) have been shown to mediate cardioprotection via modulation of the macrophage response. Our study was designed to gain mechanistic insight into the role of CDC-derived extracellular vesicles (EVs) in modulating macrophage phenotypes and operant signaling pathways to better understand their potential contribution to immunomodulatory cardioprotection. We found that CDC-derived EVs alter the functional phenotype of macrophages, modifying levels of phagocytosis and efferocytosis without changing viability or proliferation. Interestingly, extracellular vesicles differentially regulate several M1/M2 genes dependent on macrophage activation before EV treatment but consistently upregulate arginase 1 regardless of macrophage origin or polarization state. CDC-derived EVs polarize M1 macrophages to a proangiogenic phenotype dependent on arginase 1 upregulation and independent of VEGF-A. In addition, EV-dependent arginase 1 upregulation downregulates nitric oxide (NO) secretion in activated macrophages. These data suggest a novel urea-cycle-dependent mechanism in macrophages that promotes angiogenesis and provides additional mechanistic insight into the potential contribution of CDC-derived extracellular vesicles in immunomodulatory cardioprotection.NEW & NOTEWORTHY We hypothesized that in the window of therapeutic extracellular vesicle (EV) administration, inflammatory M1 macrophages are likely the primary target of cardiosphere-derived cell (CDC)-derived EVs. The effect of CDC-EVs on this population, however, is currently unknown. In this study, we demonstrate that CDC-derived EVs polarize M1 macrophages to a proangiogenic phenotype dependent on arginase 1 upregulation. These results provide insight into an immunomodulatory mechanism of CDC-EVs in a more physiologically relevant model of post-myocardial infarction (post-MI) macrophage polarization.

Lup-20(29)-en-3β,28-di-yl-nitrooxy acetate affects MCF-7 proliferation through the crosstalk between apoptosis and autophagy in mitochondria

Betulin (BT), a pentacyclic lupine-type triterpenoid natural product, possesses antitumor activity in various types of cancers. However, its clinical development was discouraged due to its low biological activities and poor solubility. We prepared lup-20(29)-en-3β,28-di-yl-nitrooxy acetate (NBT), a derivative of BT, that was chemically modified at position 3 of ring A and C-28 by introducing a NO-releasing moiety. This study mainly explored the mechanism of NBT in treating breast cancer through the crosstalk between apoptosis and autophagy in mitochondria. NBT possessed a potent antiproliferative activity in MCF-7 cells both in vitro and in vivo. Mechanically, NBT affected cell death through the mitochondrial apoptosis pathway and autophagy. NBT induced cell cycle arrest in the G₀/G₁ phase by decreasing the expression of cyclin D1. It also induced mitochondrial apoptosis by increasing the expression of Bax, caspase-9, and poly(ADP-ribose) polymerase and mitochondrial membrane potential loss and leaks of cytochrome c (Cyt C) from mitochondria in MCF-7 cells and decreasing the expression of mitochondrial Bcl-2. We further demonstrated whether chloroquine (CQ), which inhibits the degradation of autophagosome induced by NBT, affects the proliferation of MCF-7 cells compared with NBT. The experiments inferred that the combination of NBT and CQ significantly promoted MCF-7 cell mitochondria to divide and Cyt C to be released from mitochondria to the cytoplasm, resulting in an increased apoptosis rate. The in vivo experiments showed that NBT inhibited the growth of MCF-7 tumor via the apoptosis pathway, and its effect was similar to 5-fluorouracil.

Endothelial nitric oxide synthase: From biochemistry and gene structure to clinical implications of NOS3 polymorphisms

Nitric oxide (NO) is an important vasodilator with a well-established role in cardiovascular homeostasis. While mediator is synthesized from L-arginine by neuronal, endothelial, and inducible nitric oxide synthases (NOS1,NOS3 and NOS2 respectively), NOS3 is the most important isoform for NO formation in the cardiovascular system. NOS3 is a dimeric enzyme whose expression and activity are regulated at transcriptional, posttranscriptional,and posttranslational levels. The NOS3 gene, which encodes NOS3, exhibits a number of polymorphic sites including single nucleotide polymorphisms (SNPs), variable number of tandem repeats (VNTRs), microsatellites, and insertions/deletions. Some NOS3 polymorphisms show functional effects on NOS3 expression or activity, thereby affecting NO formation. Interestingly, many studies have evaluated the effects of functional NOS3 polymorphisms on disease susceptibility and drug responses. Moreover, some studies have investigated how NOS3 haplotypes may impact endogenous NO formation and disease susceptibility. In this article,we carried out a comprehensive review to provide a basic understanding of biochemical mechanisms involved in NOS3 regulation and how genetic variations in NOS3 may translate into relevant clinical and pharmacogenetic implications.

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.

Effect of Blocking of Neuropeptide Y Y2 Receptor on Tumor Angiogenesis and Progression in Normal and Diet-Induced Obese C57BL/6 Mice

BACKGROUND

Obesity is a risk factor for some types of cancers. Angiogenesis is a necessary step in the multistage progression of tumors such as melanoma. Previous studies reported that neuropeptide Y (NPY) regulates angiogenesis by activating the Y2 receptor on endothelial cells. The present study examined the effects of the NPY Y2 receptor antagonist on tumor weight, angiogenesis and serum levels of vascular endothelial growth factor (VEGF), VEGF receptor-1 (VEGF-R1), and nitric oxide (NO).

METHODS

Twenty four male C57BL/6 mice were divided into control and obese groups. The control group was fed a normal diet whereas the obese group was fed a high fat diet. After 16 weeks, 2×10(6) B16F10 melanoma cells were injected subcutaneously into all animals. Half of the control and the obese animals received 1 µM, 100 µL/kg NPY Y2 receptor antagonist (BIIE 0246) intraperitoneally. After two weeks, the animals were sacrificed, and angiogenic factors and tumor weights and angiogenesis were analyzed.

RESULTS

Tumor weight in the obese mice was higher than in the control (p<0.05). Treatment with BIIE 0246 reduced tumor weight in the obese animals (p<0.05), without effect on control group (p>0.05). Administration of an NPY Y2 receptor antagonist decreased tumor angiogenesis (evaluated as capillary density/mm2) and serum VEGF concentration in the obese group without altering serum VEGF-R1 and NO concentrations.

CONCLUSIONS

Blockade of the NPY Y2 receptor suppressed tumor growth in obese mice by affecting tumor angiogenesis. Thus, it seems that NPY and its Y2 receptor antagonist might be new targets in melanoma tumor therapy.

Nitric oxide stimulates matrix synthesis and deposition by adult human aortic smooth muscle cells within three-dimensional cocultures

Vascular diseases are characterized by the over-proliferation and migration of aortic smooth muscle cells (SMCs), and degradation of extracellular matrix (ECM) within the vessel wall, leading to compromise in cell-cell and cell-matrix signaling pathways. Tissue engineering approaches to regulate SMC over-proliferation and enhance healthy ECM synthesis showed promise, but resulted in low crosslinking efficiency. Here, we report the benefits of exogenous nitric oxide (NO) cues, delivered from S-Nitrosoglutathione (GSNO), to cell proliferation and matrix deposition by adult human aortic SMCs (HA-SMCs) within three-dimensional (3D) biomimetic cocultures. A coculture platform with two adjacent, permeable 3D culture chambers was developed to enable paracrine signaling between vascular cells. HA-SMCs were cultured in these chambers within collagen hydrogels, either alone or in the presence of human aortic endothelial cells (HA-ECs) cocultures, and exogenously supplemented with varying GSNO dosages (0-100 nM) for 21 days. Results showed that EC cocultures stimulated SMC proliferation within GSNO-free cultures. With increasing GSNO concentration, HA-SMC proliferation decreased in the presence or absence of EC cocultures, while HA-EC proliferation increased. GSNO (100 nM) significantly enhanced the protein amounts synthesized by HA-SMCs, in the presence or absence of EC cocultures, while lower dosages (1-10 nM) offered marginal benefits. Multi-fold increases in the synthesis and deposition of elastin, glycosaminoglycans, hyaluronic acid, and lysyl oxidase crosslinking enzyme (LOX) were noted at higher GSNO dosages, and coculturing with ECs significantly furthered these trends. Similar increases in TIMP-1 and MMP-9 levels were noted within cocultures with increasing GSNO dosages. Such increases in matrix synthesis correlated with NO-stimulated increases in endothelial nitric oxide synthase (eNOS) and inducible nitric oxide synthase (iNOS) expression within EC and SMC cultures, respectively. Results attest to the benefits of delivering NO cues to suppress SMC proliferation and promote robust ECM synthesis and deposition by adult human SMCs, with significant applications in tissue engineering, biomaterial scaffold development, and drug delivery.

sGC-cGMP signaling: target for anticancer therapy

The biologic endogenous production of cGMP was reported in the 1960s and followed by the demonstration of guanylyl cyclase activity and the isoforms of soluble and membrane-bound guanylyl cyclases. During the same period, cGMP specific phosphodiesterases also was discovered. Murad's lab established link between the endothelium derived relaxation factor (EDRF) and elevated cGMP concentration in the vascular system. October 12, 1998, the Nobel Assembly awarded the Nobel Prize in Medicine or Physiology to scientists Robert Furchgott, Louis Ignarro, and Ferid Murad for their discoveries concerning nitric oxide (NO) as a signaling molecule in the cardiovascular system. In contrast with the short research history of the enzymatic synthesis of NO, the introduction of nitrate-containing compounds for medicinal purposes marked its 150th anniversary in 1997. Glyceryl trinitrate (nitroglycerin; GTN) is the first compound of this category. Alfred Nobel (the founder of the Nobel Prize) himself had suffered from angina pectoris and was prescribed nitroglycerin for his chest pain while he refused to take due to the induction of headaches. Almost a century after its first chemical use, research in the nitric oxide and 3',5'-cyclic guanosine monophosphate (NO/cGMP) pathway has dramatically expanded and the role of NO/cGMP in physiology and pathology has been extensively studied. Soluble guanylyl cyclase (sGC) is the receptor for NO. The α1β1 heterodimer is the predominant isoform of sGC that is obligatory for catalytic activity. NO binds to the ferrous (Fe(2+)) heme at histidine 105 of the β1 subunit and leads to an increase in sGC activity and cGMP production of at least 200-fold. In this chapter, we reviewed the studies of sGC-cGMP signaling in cell proliferation; introduced our work of targeting sGC-cGMP signaling for cancer therapy; and explored the role of sGC-cGMP signaling in the chromatin-microenvironment.

Nitric oxide deficiency in pulmonary hypertension: Pathobiology and implications for therapy

Nitric oxide (NO) is a diffusible gas with diverse roles in human physiology and disease. Significant progress in the understanding of its biological effects has taken place in recent years. This has led to a better understanding of the pathobiology of pulmonary hypertension (PH) and the development of new therapies. This article provides an overview of the NO physiology and its role in the pathobiology of lung diseases, particularly PH. We also discuss current and emerging specific treatments that target NO signaling pathways in PH.

Involvement of NOS3 in RA-Induced neural differentiation of human NT2/D1 cells

Nitric oxide (NO) plays a key role in neurogenesis as a regulator of cell proliferation and differentiation. NO is synthesized from the amino acid L-arginine by nitric oxide synthases (NOS1, NOS2, and NOS3), which are encoded by separate genes and display different tissue distributions. We used an in vitro model of RA-induced neural differentiation of NT2 cells to examine which of the three NO-synthesizing enzymes is involved in this process. The results revealed a transient induction of NOS3 (known as the constitutively expressed endothelial nitric oxide synthase; eNOS) during the time course of the RA treatment. The peak of gene expression and the nuclear presence of NOS3 protein coincided with cell cycle exit of NT2-derived neuronal precursors. The subsequent analysis of cytosine methylation and histone H3 acetylation of the human NOS3 5' regulatory sequences indicated that epigenetic modifications, especially upstream of the proximal promoter (-734 to -989, relative to exon 2 TSS at +1), were also taking place. NOS1 was expressed only in the differentiated neurons (NT2-N), whereas NOS2 was not expressed at all in this cellular model. Thus, a burst of NO production, possibly required to inhibit neural cell proliferation, was generated by the transient expression of NOS3. This pattern of gene expression, in turn, required epigenetic remodeling of its regulatory region.

Restoring soluble guanylyl cyclase expression and function blocks the aggressive course of glioma

The NO and cGMP signaling pathways are of broad physiological and pathological significance. We compared the NO/soluble guanylyl cyclase (sGC)/cGMP pathway in human glioma tissues and cell lines with that of healthy control samples and demonstrated that sGC expression is significantly lower in glioma preparations. Our analysis of GEO databases (National Cancer Institute) further revealed a statistically significant reduction of sGC transcript levels in human glioma specimens. On the other hand, the expression levels of particulate (membrane) guanylyl cyclases (pGC) and cGMP-specific phosphodiesterase (PDE) were intact in the glioma cells that we have tested. Pharmacologically manipulating endogenous cGMP generation in glioma cells through either stimulating pGC by ANP/BNP, or blocking PDE by 3-isobutyl-1-methylxanthine/zaprinast caused significant inhibition of proliferation and colony formation of glioma cells. Genetically restoring sGC expression also correlated inversely with glioma cells growth. Orthotopic implantation of glioma cells transfected with an active mutant form of sGC (sGCα1β1(Cys105)) in athymic mice increased the survival time by 4-fold over the control. Histological analysis of xenografts overexpressing α1β1(Cys105) sGC revealed changes in cellular architecture that resemble the morphology of normal cells. In addition, a decrease in angiogenesis contributed to glioma inhibition by sGC/cGMP therapy. Our study proposes the new concept that suppressed expression of sGC, a key enzyme in the NO/cGMP pathway, may be associated with an aggressive course of glioma. The sGC/cGMP signaling-targeted therapy may be a favorable alternative to chemotherapy and radiotherapy for glioma and perhaps other tumors.

Involvement of the nitric oxide-soluble guanylyl cyclase pathway in the oxytocin-mediated differentiation of porcine bone marrow stem cells into cardiomyocytes

Bone marrow stem cells (BMSCs) express cardiac markers in vitro and in vivo upon induction. Cardiomyogenic differentiation of embryonic stem cells induced by oxytocin (OT) involves the nitric oxide (NO)-soluble guanylyl cyclase (sGC) pathway. Also, OT improved cardiomyogenic differentiation of porcine BMSCs (pBMSCs). Here, we document the role of NO pathway in OT-mediated cardiomyogenic differentiation of pBMSCs obtained from bone marrow aspirates of juvenile pigs. Cells were exposed (OT cells) or not (control cells) to OT, in presence or absence of a NO synthase inhibitor (L-NAME) and a sGC inhibitor (ODQ). Gene (RT-PCR) and protein expression (immunocytochemistry) of NOS was up-regulated after OT induction. Exposure of OT cells to L-NAME, ODQ, or both, leaded to a significant reduction in cardiac troponin I transcripts, and protein (Western Blot) expression. For the latter, ODQ looked more performing in inhibition than L-NAME. Expression of cardiac troponin T and myosin heavy chain (immunocytochemistry) was less abundant in OT cells exposed to inhibitors without apparent synergic effect between L-NAME and ODQ. In control cells, protein expression remained low. Moreover, OT-induced cell proliferation, and this effect was counteracted by NOS/sGC inhibitors. Inhibiting NO production and NO effector, sGC, affected the OT-mediated differentiation of pBMSCs, because abundance of cardiac proteins was reduced to levels similar to those observed in control cells. We propose that following treatment with OT, activation of NO pathway directs pBMSCs to a preferential cardiomyogenic phenotype and stimulates cell proliferation.

Design, synthesis and biological investigation of certain pyrazole-3-carboxylic acid derivatives as novel carriers for nitric oxide

Some novel pyrazole-NO hybrid molecules 5a-e, 6, 8 and 10 were prepared through binding of the pyrazole-3-carboxylic acid derivatives with nitric oxide donor moiety like oxime or nitrate ester. The prepared compounds were evaluated for nitric oxide release, antibacterial and anti-inflammatory activities. The organic nitrate 10 exhibited the highest percentage of NO release using Griess diazotization method. Some of the prepared compounds exhibited remarkable antibacterial activity against Escherichia coli C-600, Pseudomonas aeruginosa, Bacillus subitilis and Staphylococcus aureus NCTC 6571 compared to ciprofloxacin. Most of the tested compounds showed significant anti-inflammatory activity compared to indomethacine using carrageenan induced paw edema method. In general, structural modification of compound 2 either to nitrate ester or oxime hybrids showed better anti-inflammatory with less ulcerogenic liability than their corresponding starting intermediates.

Shape-engineered vascular endothelial cells: nitric oxide production, cell elasticity, and actin cytoskeletal features

Single cell shape determines cellular functions. Therefore, control of cell shape is of considerable importance for the tissue engineering field. This study was designed to assess the effect of surface-induced shaping of vascular endothelial cells (ECs) on the intracellular nitric oxide (NO) production level, the cell elasticity, and cytoskeletal (CSK) features on shape-engineered ECs (round, 90, 120 microm diameter; spindle-shaped, 20, 30, 40 microm width) prepared on a photolithographically microprocessed surface. Intracellular NO production was measured using a microscopic spectrometer with diaminofluorescein diacetate probe. Cell elasticity and actin CSK features were analyzed through microindentation measurement and fluorescence observations with fluorescence and atomic force microscopy. Results showed that spindle-shaped cells exhibited lower NO production, higher cell stiffness, and denser actin stress fibers than the round and nonrestrictedly cultured control cells. Relations between cell shape with NO production, cell elasticity, and actin CSK features were discussed.

Nitric oxide and cell proliferation

Nitric oxide (NO*) has been proposed to be a physiological modulator of cell proliferation, able to promote in most cases cell cycle arrest. In this review I explore the molecular basis of this mechanism of action. The modulatory action of NO* on the intracellular concentration of cGMP and the machinery directly involved in the control of cell cycle progression, including the expression and activity of diverse cyclins and cyclin-dependent kinases, their physiological inhibitors, and the master transcriptional regulator retinoblastoma protein, will be discussed. The role of NO* in proliferation mediated by tyrosine kinase receptors such as the epidermal growth factor receptor and downstream signalling pathways will also be considered. Finally, the involvement of NO* in proliferative processes relevant for normal development will be outlined.

Proliferation of cerebellar precursor cells is negatively regulated by nitric oxide in newborn rat

The diffusible messenger, nitric oxide plays multiple roles in neuroprotection, neurodegeneration and brain plasticity. Its involvement in neurogenesis has been disputed, on the basis of results on models in vivo and in culture. We report here that pharmacological blockade of nitric oxide production in rat pups resulted, during a restricted time window of the first three postnatal days, in increased cerebellar proliferation rate, as assessed through tritiated thymidine or BrdU incorporation into DNA. This was accompanied by increased expression of Myc, a transcription factor essential for cerebellar development, and of the cell cycle regulating gene, cyclin D1. These effects were mediated downstream by the nitric oxide-dependent second messenger, cGMP. Schedules of pharmacological NO deprivation targeted to later developmental stages (from postnatal day 3 to 7), no longer increased proliferation, probably because of partial escape of the cGMP level from nitric oxide control. Though limited to a brief temporal window, the proliferative effect of neonatal nitric oxide deprivation could be traced into adulthood. Indeed, the number of BrdU-labeled surviving cells, most of which were of neuronal phenotype, was larger in the cerebellum of 60-day-old rats that had been subjected to NO deprivation during the first three postnatal days than in control rats. Experiments on cell cultures from neonatal cerebellum confirmed that nitric oxide deprivation stimulated proliferation of cerebellar precursor cells and that this effect was not additive with the proliferative action of sonic hedgehog peptide. The finding that nitric oxide deprivation during early cerebellar neurogenesis, stimulates a brief increase in cell proliferation may contribute to a better understanding of the controversial role of nitric oxide in brain development.

Role of intracellular Ca2+ and calmodulin/MAP kinase kinase/extracellular signal-regulated protein kinase signalling pathway in the mitogenic and antimitogenic effect of nitric oxide in glia- and neurone-derived cell lines

To elucidate the mechanism of cell growth regulation by nitric oxide (NO) and the role played in it by Ca2+, we studied the relationship among intracellular Ca2+ concentration ([Ca2+]i), mitogen-activated protein kinases [extracellular signal-regulated protein kinase (ERK)] and proliferation in cell lines exposed to different levels of NO. Data showed that NO released by low [(z)-1-[2-aminiethyl]-N-[2-ammonioethyl]amino]diazen-1-ium-1,2diolate (DETA/NO) concentrations (10 microm) determined a gradual, moderate elevation in [Ca2+]i (46.8 +/- 7.2% over controls) which paralleled activation of ERK and potentiation of cell division. Functionally blocking Ca2+ or inhibiting calmodulin or MAP kinase kinase activities prevented ERK activation and antagonized the mitogenic effect of NO. Experimental conditions favouring Ca2+ entry into cells led to increased [Ca2+]i (189.5 +/- 4.8%), ERK activation and cell division. NO potentiated the Ca2+ elevation (358 +/- 16.8%) and ERK activation leading to expression of p21Cip1 and inhibition of cell proliferation. Furthermore, functionally blocking Ca2+ down-regulated ERK activation and reversed the antiproliferative effect of NO. Both the mitogenic and antimitogenic responses induced by NO were mimicked by a cGMP analogue whereas they were completely antagonized by selective cGMP inhibitors. These results demonstrate for the first time that regulation of cell proliferation by low NO levels is cGMP dependent and occurs via the Ca2+/calmodulin/MAP kinase kinase/ERK pathway. In this effect the amplitude of Ca2+ signalling determines the specificity of the proliferative response to NO possibly by modulating the strength of ERK activation. In contrast to the low level, the high levels (50-300 microm) of DETA/NO negatively regulated cell proliferation via a Ca2+-independent mechanism.

Role of nitric oxide in subventricular zone neurogenesis

A possible role of nitric oxide (NO) in adult neurogenesis has been suggested based on anatomical findings showing that subventricular zone (SVZ) neuroblasts are located close to NO-producing cells, and on the known antiproliferative actions of NO in many cell types. Experiments have been performed in rodents with systemic and intracerebroventricular administrations of the NO synthase (NOS) inhibitor L-NAME. NOS inhibition leads to significant increases in the number of proliferating cells in the SVZ and olfactory bulb (OB). NO exerts its cytostatic action preferentially on the cell population expressing nestin but not betaIII-tubulin, which may correspond to the type C cells described in the SVZ. The negative effect of NO on SVZ cell proliferation has also been confirmed in SVZ primary cultures. An inhibition of the tyrosine kinase activity of the epidermal growth factor receptor (EGFR) is described as one of the molecular mechanisms responsible for the antiproliferative effect of NO in SVZ cells. Biochemical data supporting this conclusion has been obtained using the neuroblastoma cell line NB69, which endogenously expresses the EGFR. In these cells, the antimitotic action of NO occurs upon inhibition of the EGFR tyrosine phosphorylation, probably by a direct S-nitrosylation of the receptor. The latest published reports on NO and neurogenesis indicate that NO physiologically participates in the control of adult neurogenesis by modulating the proliferation and fate of the SVZ progenitor cells. These effects might be partially due to a direct inhibition of the EGFR by S-nitrosylation.

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.

Temporal changes of multiple redox couples from proliferation to growth arrest in IEC-6 intestinal epithelial cells

Changes in intracellular redox couples and redox reactive molecules have been implicated in the regulation of a variety of cellular processes, including cell proliferation and growth arrest by contact inhibition. However, the magnitude, direction, and temporal relationship of redox changes to cellular responses are incompletely defined. The present work sought to characterize redox and metabolic changes associated with proliferative stages to contact inhibition of growth in rat IEC-6 intestinal epithelial cells. From the first day of culture until 1 day before confluence, an increase in GSH concentrations and a significant reduction in the redox potential of the GSSG/2GSH couple were observed. These changes were accompanied by a decrease in relative reactive oxygen species (ROS) and nitric oxide (NO) concentrations and oxidation of the redox potential of the NADP(+)/reduced NADP and NAD(+)/NADH couples. Postconfluent cells exhibited a significant decrease in GSH concentrations and a significant oxidation of the GSSG/2GSH couple. When cell proliferation decreased, relative ROS concentrations increased (P < 0.01), whereas NO concentrations remained unchanged, and the NAD(+)/NADH couple became more reduced. Together, these data indicate that the redox potential of distinct couples varies differentially in both magnitude and direction during successive stages of IEC-6 growth. This finding points out the difficulty of defining intracellular redox status at particular stages of cell growth by examining only one redox species. In addition, the data provide a numerical framework for future research of regulatory mechanisms governed by distinct intracellular redox couples.

Endostatin induces acute endothelial nitric oxide and prostacyclin release

Chronic exposure to endostatin (ES) blocks endothelial cell (EC) proliferation, and migration and induces EC apoptosis thereby inhibiting angiogenesis. Nitric oxide (NO) and prostacyclin (PGI(2)), in contrast, play important roles in promoting angiogenesis. In this study, we examined the acute effects of ES on endothelial NO and PGI(2) production. Unexpectedly, a cGMP reporter cell assay showed that ES-induced acute endothelial NO release in cultured bovine aortic endothelial cells (BAECs). Enzyme immunoassay showed that ES also induced an acute increase in PGI(2) production in BAECs. These results were confirmed by ex vivo vascular ring studies that showed vascular relaxation in response to ES. Immunoblot analysis showed that ES stimulated acute phosphorylation of endothelial nitric oxide synthase (eNOS) at Ser116, Ser617, Ser635, and Ser1179, and dephosphorylation at Thr497 in BAECs, events associated with eNOS activation. Short-term exposure of EC to ES, therefore, unlike long-term exposure which is anti-angiogenic, may be pro-angiogenic.

Nitroglycerin, a nitric oxide generator attenuates ferric nitrilotriacetate-induced renal oxidative stress, hyperproliferative response and necrosis in ddY mice

Nitric oxide (NO) is a short lived, readily diffusible intracellular messenger molecule associated with multiple organ-specific regulatory functions. In this communication, we elucidate the effect of exogenous NO administration, using nitroglycerin (GTN), on ferric nitrilotriacetate (Fe-NTA)-induced renal oxidative stress, hyperproliferative response and necrosis in ddY mice. Fe-NTA is a known complete renal carcinogen as well as renal and hepatic tumor promoter, which act by generating oxidative stress in the tissues. GTN treatment to ddY mice prior to Fe-NTA administration resulted in a highly significant protection against Fe-NTA-induced renal oxidative stress, hyperproliferative response and necrosis. In oxidative stress protection studies, the decrease in the level of renal glutathione and antioxidant enzyme activities induced by Fe-NTA were significantly reversed by GTN pretreatment in a dose-dependent manner (12-46% recovery, P<0.05-0.001). GTN pretreatment also resulted in a dose-dependent inhibition (24-39% inhibition, P<0.05-0.001) of Fe-NTA-induced lipid peroxidation as measured by TBARS formation in renal tissues. Similarly, in hyperproliferation protection studies, GTN pretreatment showed a strong inhibition of Fe-NTA-induced renal ornithine decarboxylase (ODC) activity (51-57% inhibition, P<0.001) and [3H]thymidine incorporation (43-58% inhibition, P<0.001) into renal DNA. GTN pretreatment almost completely prevented kidney biomolecules from oxidative damage and protected the tissue against the observed histopathological alterations. From this data, it can be concluded that exogenously produced NO from GTN might scavenge reactive oxygen species (ROS) and decreases toxic metabolites of Fe-NTA and thereby inhibiting renal oxidative stress. In addition, exogenously produced NO can also inhibit Fe-NTA-induced hyperproliferative response by down-regulating the activity of ODC and the rate of [3H]thymidine incorporation into renal DNA and could be suggested as another possible clinical application for this NO-donor (GTN, traditionally used as a vasodilator) in oncological medicine.

Role of bradykinin in renoprotective effects by angiotensin II type 1 receptor antagonist in salt-sensitive hypertension

To elucidate whether bradykinin is involved in the renoprotective effect produced by angiotensin II type 1 receptor antagonist (AT1A) in chronic salt-sensitive hypertension, Dahl salt-sensitive rats receiving a high-salt (8%) diet were treated either with an AT1A (candesartan, 1 mg/kg/day), a bradykinin B2 receptor antagonist (BKB2A; FR172357, 30 mg/kg/day) or a combination of AT1A and BKB2A for 7 weeks. None of the treatments changed the markedly increased systolic blood pressure induced by a high-salt diet. However, chronic treatment with AT1A significantly improved the histological hallmarks of renal damage-i.e., glomerular sclerosis and cell proliferation-despite the presence of severe hypertension. This beneficial action of AT1A was abolished by the concomitant administration of BKB2A. In agreement with these histologically based findings, increases in levels of creatinine clearance induced by AT1A were also reversed back to the basal levels when BKB2A was administered in conjunction with AT1A. Furthermore, urinary excretions of nitrate plus nitrite and prostaglandin E2 increased moderately in response to the administration of AT1A alone, but not in combination with BKB2A. Thus, the blockade of bradykinin signaling abrogates the renoprotective actions of the angiotensin II type 1 (AT1) receptor antagonism. Collectively, these data show that when AT1 action is chronically blocked, endogenous bradykinin plays a pivotal role in preventing the progression of glomerular injury in salt-sensitive hypertension.

Cardiac endothelial-myocardial signaling: its role in cardiac growth, contractile performance, and rhythmicity

Experimental work during the past 15 years has demonstrated that endothelial cells in the heart play an obligatory role in regulating and maintaining cardiac function, in particular, at the endocardium and in the myocardial capillaries where endothelial cells directly interact with adjacent cardiomyocytes. The emerging field of targeted gene manipulation has led to the contention that cardiac endothelial-cardiomyocytal interaction is a prerequisite for normal cardiac development and growth. Some of the molecular mechanisms and cellular signals governing this interaction, such as neuregulin, vascular endothelial growth factor, and angiopoietin, continue to maintain phenotype and survival of cardiomyocytes in the adult heart. Cardiac endothelial cells, like vascular endothelial cells, also express and release a variety of auto- and paracrine agents, such as nitric oxide, endothelin, prostaglandin I(2), and angiotensin II, which directly influence cardiac metabolism, growth, contractile performance, and rhythmicity of the adult heart. The synthesis, secretion, and, most importantly, the activities of these endothelium-derived substances in the heart are closely linked, interrelated, and interactive. It may therefore be simplistic to try and define their properties independently from one another. Moreover, in relation specifically to the endocardial endothelium, an active transendothelial physicochemical gradient for various ions, or blood-heart barrier, has been demonstrated. Linkage of this blood-heart barrier to the various other endothelium-mediated signaling pathways or to the putative vascular endothelium-derived hyperpolarizing factors remains to be determined. At the early stages of cardiac failure, all major cardiovascular risk factors may cause cardiac endothelial activation as an adaptive response often followed by cardiac endothelial dysfunction. Because of the interdependency of all endothelial signaling pathways, activation or disturbance of any will necessarily affect the others leading to a disturbance of their normal balance, leading to further progression of cardiac failure.

Induction of KDR expression in bovine arterial endothelial cells by thrombin: involvement of nitric oxide

Thrombin, a multifunctional serine protease, is generated at the site with vascular injuries. It not only participates in the coagulation cascade, but also can induce a lot of events related to cell mitogenesis and migration. In this study, we investigated the effect of thrombin on endothelial cell proliferation induced by vascular endothelial growth factor (VEGF). Thrombin promoted proliferation of cultured bovine carotid endothelial cells in a time- and dose-dependent manner. Moreover, it drastically enhanced the cell growth stimulated by VEGF. This stimulatory effect was reduced by inhibitors of either protein kinase C (PKC) or mitogen-activated protein kinase kinase (MAPKK). Thrombin induced a significant increase in the level of mRNA of the kinase domain-containing receptor (KDR), but not tms-like tyrosine kinase (Flt-1), in a time-dependent manner, which reached the maximum after 24 h of stimulation. This increase coincides well with the KDR protein expression. The luciferase assay showed that thrombin induced an about 7.5-fold increase in the KDR promoter activity compared with the control. This enhanced KDR promoter activity was also abolished by inhibitors of either PKC or MAPKK. The deletion analyses indicated that the region between -115 and -97 (containing Sp1 binding region) within the KDR promoter gene was required for the enhanced KDR expression induced by thrombin and VEGF. Moreover, the nitric oxide synthase (NOS) inhibitor abolished both the accelerated cell proliferation and the increased KDR expression induced by thrombin and VEGF. This inhibition was abrogated by DETA NONOate, a NO donor with long half-life. These findings suggest that thrombin might potentiate the VEGF-induced angiogenic activity through increasing the level of the VEGF receptor KDR, in which production of NO is involved.

Activation of mitogenic and antimitogenic pathways in cyclically stretched arterial smooth muscle

Biophysical forces regulate vascular smooth muscle cell (VSMC) physiology and evoke vascular remodeling. Two VSMC autocrine molecules, insulin-like growth factor I (IGF-I) and nitric oxide (NO), are implicated in remodeling attributable to VSMC hyperplasia. We investigated the role of in vitro cyclic stretch on rat VSMC IGF-I, NO, and cellular growth. Cyclic stretch (1 Hz at 120% resting length for 48 h) stimulated VSMC proliferation 2.5-fold vs. unstretched cells and was accompanied by a 1.8-fold increase in VSMC IGF-I secretion. Despite activation of this proliferative pathway, cyclic stretch induced inducible (i) nitric oxide synthase (NOS) expression and a twofold increase in NO secretion, a molecule with documented antiproliferative effects. Cytokine treatment enhanced iNOS expression and NO secretion while inhibiting vascular growth by approximately 50% in static cells. Cytokine treatment of stretched VSMC enhanced NO secretion 2.5-fold while inhibiting growth by approximately 80%. Exogenous IGF-I increased NOS activity 1.5-fold and NO secretion 8.5-fold in static cells. In turn, iNOS inhibition increased IGF-I secretion 1.6-fold and enhanced VSMC growth 1.6-fold in stretched cells. An NO donor (sodium nitroprusside) similarly inhibited VSMC proliferation in static (24%) and stretched (50%) VSMC while also inhibiting IGF-I secretion from stretched cells by approximately 35%. Thus cyclic stretch stimulates mitogenic (IGF-I) and antimitogenic (NO) pathways in VSMC. These two molecules regulate each other's secretory rates, providing tight regulation of VSMC proliferation. These data may have profound implications in understanding vascular growth alterations in vascular injury and hypertension.

Prolonged exposure to YC-1 induces apoptosis in adrenomedullary endothelial and chromaffin cells through a cGMP-independent mechanism

YC-1, a benzyl indazole derivative, is an NO-independent direct activator of soluble guanylyl cyclase (sGC), which presents a synergistic action with NO in stimulating cGMP synthesis. These properties have served to suggest YC-1 as an attractive therapeutic agent by permitting the reduction of nitrovasodilator dosage and regulating endogenous cGMP metabolism. Here we studied the effect of prolonged exposure of adrenomedullary endothelial and chromaffin cells to YC-1. We found that YC-1 increased cGMP in the two types of cells and this action was blocked by the sGC inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). Cells underwent apoptotic death in association with increased caspase-3-like activity, DNA fragmentation, cytoskeletal disorganization and changes in membrane permeability after prolonged incubation with YC-1. Caspase-3-like protease activity and DNA fragments in the cytoplasm were increased in a dose-dependent manner by 16 h YC-1 treatment. The specific and cell permeable caspase-3-like protease inhibitor DEVD-CHO effectively inhibited YC-1-mediated caspase-3-like activation and DNA fragmentation. Moreover, YC-1 also induced cell shape changes accompanied by actin filament disorganization and alterations in membrane permeability. Cells incubated for 24h with YC-1 showed damaged membranes by binding to nucleic acid of a dye excluded by the intact plasma membrane of live cells. YC-1 also induced a decrease in the intracellular non-specific esterase activity, another indication of cell toxicity. Apoptotic phenomena were not prevented by the presence of ODQ although it effectively inhibited the YC-1-elicited cGMP increases. These findings indicate that YC-1 induces apoptosis by activating caspase-3-like protease through a mechanism independent of sGC activation.

Nitric oxide donors retard wound healing in cultured rabbit gastric epithelial cell monolayers

Effects of nitric oxide (NO) on gastric wound healing were investigated in primary rabbit gastric epithelial cell cultures. We analyzed the speed of cell migration, proliferation, and apoptosis after creating a round wound on the cell cultures. The monolayers were incubated with or without the NO donor sodium nitroprusside, oxatriazolimine 1,2,3,4-oxatriazolium, 5amino-3-(3,4-dichlorophenylchloride), or the peroxynitrite generator 3-morpholinosydnomine-N-ethylcarbamide. The possible role of cGMP as a second messenger of NO was investigated with 8-bromo-cGMP. The role of O2(-*) was evaluated using diethyldithiocarbamate and pyrogallol. The effects of superoxide dismutase and allopurinol were also investigated. NO inhibited the speed of cell migration and proliferation and induced cell apoptosis in a dose- and time-dependent manner. The effects were augmented with O2(-*) generators and ameliorated by O2-(8) scavengers, whereas cGMP had no significant effect on wound healing. NO donors retard gastric wound healing by inhibiting migration and proliferation and inducing cell apoptosis. These effects do not seem to be mediated via cGMP, but O2(-*). or peroxynitrites may be involved.

Reduced endothelial nitric oxide synthase in lungs of chronically ventilated preterm lambs

Nitric oxide (NO), produced in lung vascular endothelium and airway epithelium, has an important role in regulating smooth muscle cell growth and tone. Chronic lung disease, a frequent complication of premature birth, is characterized by excess abundance, tone, and reactivity of smooth muscle in the pulmonary circulation and conducting airways, leading to increased lung vascular and airway resistance. Whether these structural and functional changes are associated with diminished pulmonary expression of endothelial nitric oxide synthase (eNOS) protein is unknown. Both quantitative immunoblot analysis and semiquantitative immunohistochemistry showed that there was less eNOS protein in the endothelium of small intrapulmonary arteries and epithelium of small airways of preterm lambs that were mechanically ventilated for 3 wk compared with control lambs born at term. No significant differences were detected for other proteins (inducible NOS, alpha-smooth muscle actin, and pancytokeratin). Lung vascular and respiratory tract resistances were greater in the chronically ventilated preterm lambs compared with control term lambs. These results support the notion that decreased eNOS in the pulmonary circulation and respiratory tract of preterm lambs may contribute to the pathophysiology of chronic lung disease.

Inhibitory effects of S-nitrosoglutathione on cell proliferation and DNA synthesis: possible role of glyoxalase I inactivation

We investigated the inhibitory effects of S-nitrosoglutathione (GSNO) on cell proliferation, DNA synthesis and several enzymatic activities using spontaneously immortalized human endothelial cells (ECV304). Proliferation of ECV304 was inhibited by GSNO in a dose-dependent manner (125-1000 microM). DNA synthesis was decreased 2 h after addition of GSNO to cells and was markedly repressed from 20 h after the addition. The activity of ribonucleotide reductase, a rate-limiting enzyme for DNA synthesis, was unchanged in GSNO-treated cells. GSNO inhibited less than 40% of mitochondrial respiration activity, and the membrane potential and cellular levels of ATP were not significantly decreased by GSNO. GSNO had no inhibitory effect on activities of glutathione peroxidase, glutathione S-transferase and glutathione reductase. However, glyoxalase I (Glo I) activity was decreased to 20% of the control level within 60 min, and was consistently repressed during exposure to GSNO for 20 h. A membrane-permeable Glo I inhibitor, S-bromobenzylglutathione diethylester, inhibited proliferation of ECV304 cells, while methylglyoxal (MG), a toxic metabolite generated during glycolysis and a substrate for Glo I, failed to inhibit the cell growth even at 100 microM. Glo I in several mammalian cell lines was inactivated by GSNO with a pI shift. Although we failed to detect accumulation of MG under conditions of Glo I inactivation, these results suggest that the inhibitory effects of GSNO on cell proliferation and DNA synthesis might be at least partly due to inactivation of Glo I.

Lipopolysaccharide-induced cell cycle arrest in macrophages occurs independently of nitric oxide synthase II induction

Lipopolysaccharide (LPS, a Gram-negative bacterium cell wall component) is a potent macrophage activator that inhibits macrophage proliferation and stimulates production of nitric oxide (NO) via NO synthase II (NOSII). We investigated whether NO mediates the LPS-stimulated cell cycle arrest in mouse bone marrow-derived macrophages (BMM). The addition of the NO donor DETA NONOate (200 microM) inhibited BMM proliferation by approx. 80%. However, despite NO being an antimitogen, LPS was as potent at inhibiting proliferation in BMM derived from NOSII-/- mice as from wild-type mice. Consistent with these findings, LPS-induced cell cycle arrest in normal BMM was not reversed by the addition of the NOSII inhibitor S-methylisothiourea. Moreover, in both normal and NOSII-/- BMM, LPS inhibited the expression of cyclin D1, a protein that is essential for proliferation in many cell types. Despite inhibiting proliferation DETA NONOate had no effect on cyclin D1 expression. Our data indicate that while both LPS and NO inhibit BMM proliferation, LPS inhibition of BMM proliferation can occur independently of NOSII induction.

MRNA expression on shape-engineered endothelial cells: adhesion molecules ICAM-1 and VCAM-1

This study was designed to assess the effect of cell shape on mRNA expression of two adhesion molecules, intracellular adhesion molecule-1 and vascular adhesion molecule-1, on endothelial cells. Photo-microprocessing using photoreactive poly(ethylene glycol) produced two different patterned-cell adhesive regions on tissue culture dishes: one is a striped region on which adhered cells are highly elongated and aligned along the long axis of the striped pattern, and the other is a circular region on which cells are less spread out and rounded. mRNA expressions, measured by the reverse transcription-polymerase chain reaction technique, revealed higher mRNA expression for intracellular adhesion molecule-1 and lower mRNA expression for vascular adhesion molecule-1 on elongated cells than those on round cells. This indicates that surface-induced cell shape induces changes in the mRNA expression of these molecules. The significance of cell-shape-induced mRNA expression is discussed in conjunction with the experimental results of flow-induced expression at molecular and mRNA levels.

Expression and function of recombinant endothelial nitric oxide synthase in human endothelial cells

Endothelial dysfunction is frequently involved in the pathogenesis of vascular disease. While nitric oxide (NO) inhibits smooth muscle cell proliferation, its effect on endothelial cell proliferation is unclear. The aim of this study was to determine if adenoviral-mediated gene transfer of endothelial NO synthase (eNOS) to human umbilical vein endothelial cells (HUVECs) would result in increased generation of NO and affect endothelial cell proliferation. HUVECs were transduced with adenoviral vectors encoding eNOS (AdeNOS) or beta-galactosidase (Ad beta gal) or exposed to diluent (control). AdeNOS-transduced cells showed increased eNOS expression as detected by Western blot analysis, and increased concentrations of cGMP (control 0.7 +/- 0.1; Ad beta gal 0.9 +/- 0.2; AdeNOS 3.1 +/- 0.5 pmol/mg protein; p < 0.001) and nitrite (control 11.8 +/- 1.2; Ad beta gal 13.3 +/- 1.7; AdeNOS 21.1 +/- 2.2 nmol/mg protein/hour; p < 0.01). DNA synthesis as assessed by [(3)H]thymidine incorporation and cell counts were significantly reduced (by approximately 30%) in AdeNOS-transduced HUVECs. Expression of mitogen-activated protein kinase was also decreased in AdeNOS-transduced cells. This study shows that adenoviral-mediated gene transfer of eNOS to HUVECs inhibits endothelial cell proliferation.

Endogenously produced nitric oxide inhibits endothelial cell growth as demonstrated using novel antisense cell lines

Proliferation of endothelial cells is a vital component of vascular repair and angiogenesis. The endothelial cell mediator, nitric oxide (NO) has been reported both to inhibit and to promote endothelial cell proliferation. In this study we have generated cell lines which constitutively express antisense RNA to a region of inducible nitric oxide synthase (iNOS) from a murine endothelial cell line, sEnd-1. In response to stimulation with lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma) these antisense cells had no detectable RNA for endogenous iNOS, barely detectable iNOS protein and produced 82% less NO than did the control transfected line. Stimulation of the control transfected line caused significant NO production and inhibition of cell growth whereas for the antisense line, producing little NO in response to stimulation, proliferation remained the same as for unstimulated cells. No differences in cell death were observed between unstimulated and LPS/IFN-gamma stimulated cells. The data presented in this study directly demonstrate that NO derived endogenously from iNOS inhibits proliferation of endothelial cells. This approach overcomes problems in other studies where NO donors or non-isoform specific inhibitors of NO synthase have been used.

Ecdysteroid coordinates optic lobe neurogenesis via a nitric oxide signaling pathway

Proliferation of neural precursors in the optic lobe of Manduca sexta is controlled by circulating steroids and by local production of nitric oxide (NO). Diaphorase staining, anti-NO synthase (NOS) immunocytochemistry and the NO-indicator, DAF-2, show that cells throughout the optic anlage contain NOS and produce NO. Signaling via NO inhibits proliferation in the anlage. When exposed to low levels of ecdysteroid, NO production is stimulated and proliferation ceases. When steroid levels are increased, NO production begins to decrease within 15 minutes independent of RNA or protein synthesis and cells rapidly resume proliferation. Resumption of proliferation is not due simply to the removal of NO repression though, but also requires an ecdysteroid stimulatory pathway. The consequence of these opposing pathways is a sharpening of the responsiveness to the steroid, thereby facilitating a tight coordination between development of the different elements of the adult visual system.

Nitric oxide synthase expression, enzyme activity and NO production during angiogenesis in the chick chorioallantoic membrane

In order to elucidate further the role of nitric oxide (NO) as an endogenous antiangiogenic mediator, mRNA expression of inducible nitric oxide synthase (iNOS), enzyme activity and production of NO were determined in the chick chorioallantoic membrane (CAM), an in vivo model of angiogenesis. In this model, maximum angiogenesis is reached between days 9 - 12 of chick embryo development. After that period, vascular density remains constant. Inducible NO synthase (iNOS) mRNA expression, determined by reverse transcriptase polymerase chain reaction (RT - PCR), increased from the 8th day reaching a maximum (70% increase) at days 10 - 11. NO synthase activity, determined as citrulline formation in the presence of calcium, also increased from day 8 reaching a maximum around day 10 (100% increase). Similar results were obtained in the absence of calcium suggesting that the NOS determined was the inducible form. Nitric oxide production, determined as nitrites, increased from day 8 reaching a maximum around day 10 (64% increase) and remaining stable at day 13. Finally, the bacterial lipopolysaccharide LPS (which activates transcriptionally iNOS), inhibited dose dependently angiogenesis in the CAM. These results in connection with previous findings from this laboratory, showing that NO inhibits angiogenesis in the CAM, suggest that increases in iNOS expression, enzyme activity and NO production closely parallel the progression of angiogenesis in the CAM, thus providing an endogenous brake to control this process. British Journal of Pharmacology (2000) 129, 207 - 213

Hypoxia response element of the human vascular endothelial growth factor gene mediates transcriptional regulation by nitric oxide: control of hypoxia-inducible factor-1 activity by nitric oxide

Nitric oxide (NO) regulates production of vascular endothelial growth factor (VEGF) by normal and transformed cells. We demonstrate that NO donors may up-regulate the activity of the human VEGF promoter in normoxic human glioblastoma and hepatoma cells independent of a cyclic guanosine monophosphate–mediated pathway. Deletion and mutation analysis of the VEGF promoter indicates that the NO-responsive cis-elements are the hypoxia-inducible factor-1 (HIF-1) binding site and an adjacent ancillary sequence that is located immediately downstream within the hypoxia-response element (HRE). This work demonstrates that the HRE of this promoter is the primary target of NO. In addition, VEGF gene regulation by NO, as well as by hypoxia, is potentiated by the AP-1 element of the gene. Our study also reveals that NO and hypoxia induce an increase in HIF-1 binding activity and HIF-1 protein levels, both in the nucleus and the whole cell. These results suggest that there are common features of the NO and hypoxic pathways of VEGF induction, while in part, NO mediates gene transcription by a mechanism distinct from hypoxia. This is demonstrated by a difference in sensitivity to guanylate cyclase inhibitors and a different pattern of HIF-1 binding. These results show that there is a primary role for NO in the control of VEGF synthesis and in cell adaptations to hypoxia. (Blood. 2000;95:189-197)

Hypoxia response element of the human vascular endothelial growth factor gene mediates transcriptional regulation by nitric oxide: control of hypoxia-inducible factor-1 activity by nitric oxide

Nitric oxide (NO) regulates production of vascular endothelial growth factor (VEGF) by normal and transformed cells. We demonstrate that NO donors may up-regulate the activity of the human VEGF promoter in normoxic human glioblastoma and hepatoma cells independent of a cyclic guanosine monophosphate–mediated pathway. Deletion and mutation analysis of the VEGF promoter indicates that the NO-responsive cis-elements are the hypoxia-inducible factor-1 (HIF-1) binding site and an adjacent ancillary sequence that is located immediately downstream within the hypoxia-response element (HRE). This work demonstrates that the HRE of this promoter is the primary target of NO. In addition, VEGF gene regulation by NO, as well as by hypoxia, is potentiated by the AP-1 element of the gene. Our study also reveals that NO and hypoxia induce an increase in HIF-1 binding activity and HIF-1 protein levels, both in the nucleus and the whole cell. These results suggest that there are common features of the NO and hypoxic pathways of VEGF induction, while in part, NO mediates gene transcription by a mechanism distinct from hypoxia. This is demonstrated by a difference in sensitivity to guanylate cyclase inhibitors and a different pattern of HIF-1 binding. These results show that there is a primary role for NO in the control of VEGF synthesis and in cell adaptations to hypoxia. (Blood. 2000;95:189-197)

Nitric oxide donors selectively potentiate thrombin-stimulated p70(S6k) activity and morphological changes in Swiss 3T3 cells

Thrombin stimulates both DNA synthesis and cell morphological changes in Swiss 3T3 cells, although the mechanism of signal coordination leading to these responses is unknown. We report here that nitric oxide (NO) donors selectively enhance thrombin-stimulated p70(S6k) activity by 40-60%, an effect that was sustained for 24 h. Potentiation of p70(S6k) also was observed with cGMP analogues indicating that this effect is mediated by cGMP-activated protein kinase. NO donors also induced morphological changes characterized by spindle-shaped cells in confluent, nondividing cells or by extended protrusions from the trailing edge in subconfluent, polarized cells. NO donors had no significant effects on intracellular Ca(2+) mobilization, DNA synthesis, proliferation, or ERKs 1 and 2 and p90RSK activities, indicating that mitogenic responses and cell division are not altered by NO donors. We conclude that NO donors modulate the morphological changes associated with cellular motility in response to thrombin stimulation through selective enhancement of p70(S6k) activity.

Nitric oxide mediates either proliferation or cell death in cardiomyocytes. Involvement of polyamines

Nitric oxide (NO) is a molecule involved in several signal transduction pathways leading either to proliferation or to cell death. Induction of ornithine decarboxylase (ODC), the key enzyme of polyamine biosynthesis, represents an early event preceding DNA synthesis. In some cell types increased ODC activity seems to be involved in cytotoxic response. We investigated the role of NO and ODC induction on the events linked to cell proliferation or to cell death in cultured chick embryo cardiomyocytes. Exposure of cardiomyocytes to tumor necrosis factor (TNF) and lipopolysaccharide (LPS) caused NO synthase (NOS) and ODC induction as well as increased incorporation of [3H]-thymidine. This last effect was blocked by a NOS inhibitor and was strongly reduced by difluoromethylornithine (DFMO), an irreversible inhibitor of ODC. Sodium nitroprusside (SNP), an exogenous NO donor, inhibited the increases of NOS and ODC activities and abolished the mitogenic effect of TNF and LPS. Moreover, SNP alone caused cell death in a dose dependent manner. The cytotoxicity of SNP was not affected by DFMO while it was prevented by antioxidants. The results suggest that different pathways would mediate the response of cardiomyocytes to NO: they can lead either to ODC induction and DNA synthesis when NO is formed through NOS induction or to growth inhibition and cell death, when NO is supplied as NO donor. Increased polyamine biosynthesis would mediate the proliferative response of NO, while the cytotoxicity of exogenous NO seems to involve some oxidative reactions and to depend on the balance between NO availability and cellular redox mechanisms.

L-arginine metabolites regulate DNA synthesis and nitric oxide synthase activity in cultured human dermal microvascular endothelial cells--potential positive and negative regulators of angiogenesis derived from L-arginine

Human dermal microvascular endothelial cell (HDMVEC) growth and proliferation is important for skin angiogenesis. Our data support the hypothesis that a regulatory switch from an angiogenic to a nonangiogenic stimulus involves a change in l-arginine metabolism from polyamines (PAs) to nitric oxide (NO) and, conversely, a change to an angiogenic stimulus is expected to drive l-arginine metabolism in favor of PA synthesis. Current studies with cultured HDMVECs demonstrated that NO inhibited, whereas the PA putrescine stimulated DNA synthesis. The nitric oxide synthase (NOS) inhibitor NG-nitro l-arginine methyl ester stimulated DNA synthesis with a significant increase from control at 2.5 and 5 mM (p < 0.05); in contrast, the ornithine decarboxylase (ODC) inhibitor alpha-difluoromethyl ornithine (DFMO) inhibited DNA synthesis with a significant decrease from control at 19.65, 29.48, and 39.48 microM (p < 0.05). NO donors sodium nitroprusside dihydrate, S-nitroso-N-penicillamine, and l-hydroxy-2-oxo-3(3-aminopropyl)-3-propyl-triazine all inhibited DNA synthesis. There was a significant increase in NOS activity with DFMO treatment (p < 0.05) and a less pronounced decrease in NOS activity with direct PA treatment. In summary, NO and PAs are important mediators of HDMVEC growth and PAs downregulate NOS activity in these cells. NOS and ODC enzyme products may not only be important components in the regulation of angiogenesis in the skin but they may also regulate their own synthesis via feedback mechanisms.

Melatonin receptors in PC3 human prostate tumor cells

Melatonin, secreted nocturnally by the pineal gland, can bind to human benign prostate epithelial cells and attenuate their growth and viability. In the present study, melatonin binding and responses were explored in the human steroid-independent PC3 prostatic tumor cells. PC3 cells bound 125I-melatonin with low affinity (Kd ca. 0.9 nM) at high as well as low cell density. Melatonin enhanced cGMP and 3H-thymidine incorporation at low, but attenuated them at high cell density. In addition, melatonin inhibited cAMP at low, but augmented it at high cell density. These effects were associated with an increase in cell count at low- but not high-density cultures. Pertussis toxin treatment suppressed 125I-melatonin binding and ablated all the effects of melatonin on 3H-thymidine incorporation, cAMP, and cGMP at both cell densities. Cholera toxin treatment failed to block the effects of melatonin on 3H-thymidine incorporation, but prevented the modulation by melatonin of cAMP at low and cGMP at high cell density. The cGMP analog 8-Br-cGMP, inhibited melatonin's effects on 3H-thymidine incorporation at both cell densities. H89, a protein kinase A inhibitor, prevented melatonin's effects on 3H-thymidine incorporation at low but not high cell density. These results provide the first demonstration of direct interaction of melatonin with hormone-insensitive prostate tumor cells. The melatonin receptors in the PC3 cells are coupled to pertussis toxin-sensitive G proteins to induce cell density-dependent changes in cGMP, cAMP, and cell growth.

Cyclic stretch regulates autocrine IGF-I in vascular smooth muscle cells: implications in vascular hyperplasia

Vascular smooth muscle cells (VSMC) subjected to acute or chronic stretch display enhanced growth rates in vitro and in vivo. Clinical examples of vascular hyperplasia (e.g., systolic hypertension and postinjury restenosis) suggest that local insulin-like growth factor I (IGF-I) expression is enhanced. Therefore, we investigated the role of in vitro cyclic stretch on rat VSMC IGF-I secretion and cellular growth. In serum-free medium, cyclic stretch (1 Hz at 120% resting length for 48 h) stimulated thymidine incorporation approximately 40% above that seen in nonstretched cells. Graded stretch magnitude (100-125% resting length) yielded graded increases in VSMC growth. Exogenous IGF-I increased growth of serum-starved, nonstretched VSMC in a dose-dependent manner, with maximal growth seen with 10(-7) M. IGF-I secretion from stretched cells was 20- to 30-fold greater than from those cells cultured in a static environment. Stretch-induced increases in growth were completely blocked on addition of anti-IGF-I and partially blocked with platelet-derived growth factor (PDGF) antibodies and with a tyrosine kinase inhibitor (tyrphostin-1). Finally, blockade of stretch-activated cation channels with GdCl3 profoundly inhibited stretch-induced growth. We conclude that stretch increases VSMC IGF-I secretion and that such autocrine IGF-I is required for stretch-induced growth. PDGF and stretch-sensitive cation channels are likely additional components of a complex pathway that regulates stretch-induced VSMC seen in systolic hypertension and postinjury restenosis.

Human vascular endothelial cells express oxytocin receptors

Pharmacological studies in humans and animals suggest the existence of vascular endothelial vasopressin (AVP)/oxytocin (OT) receptors that mediate a vasodilatory effect. However, the nature of the receptor subtype(s) involved in this vasodilatory response remains controversial, and its coupled intracellular pathways are unknown. Thus, we set out to determine the type and signaling pathways of the AVP/OT receptor(s) expressed in human vascular endothelial cells (ECs). Saturation binding experiments with purified membranes of primary cultures of ECs from human umbilical vein (HUVEC), aorta (HAEC), and pulmonary artery (HPAEC) and [3H]AVP or [3H]OT revealed the existence of specific binding sites with a greater affinity for OT than AVP (Kd = 1.75 vs. 16.58 nM). Competition binding experiments in intact HUVECs (ECV304 cell line) with the AVP antagonist [125I]4-hydroxyphenacetyl-D-Tyr(Me)-Phe-Gln-Asn-Arg-Pro-Arg-NH2 or the OT antagonist [125I]D(CH2)5[O-Me-Tyr-Thr-Orn-Tyr-NH2]vasotocin, and various AVP/OT analogs confirmed the existence of a single class of surface receptors of the classical OT subtype. RT-PCR experiments with total RNA extracted from HUVEC, HAEC, and HPAEC and specific primers for the human V1 vascular, V2 renal, V3 pituitary, and OT receptors amplified the OT receptor sequence only. No new receptor subtype could be amplified when using degenerate primers. DNA sequencing of the coding region of the human EC OT receptor revealed a nucleotide sequence 100% homologous to that of the uterine OT receptor reported previously. Stimulation of ECs by OT produced mobilization of intracellular calcium and the release of nitric oxide that was prevented by chelation of extra- and intracellular calcium. No stimulation of cAMP or PG production was noted. Finally, OT stimulation of ECs led to a calcium- and protein kinase C-dependent cellular proliferation response. Thus, human vascular ECs express OT receptors that are structurally identical to the uterine and mammary OT receptors. These endothelial OT receptors produce a calcium-dependent vasodilatory response via stimulation of the nitric oxide pathway and have a trophic action.

Regression of glomerular injury by kallikrein infusion in Dahl salt-sensitive rats is a bradykinin B2-receptor-mediated event

AIMS

We investigated whether kallikrein infusion attenuates renal injury in Dahl salt-sensitive rats with hypertension and assessed the role of bradykinin-nitric oxide axis in the renal protection using HOE-140, the bradykinin type-2 (B2) receptor specific antagonist.

METHODS

Subdepressor dose of purified rat urinary kallikrein (RUK) (400 ng/day) was continuously infused through the jugular vein by an osmotic mini-pump for 4 weeks in Dahl salt-sensitive (Dahl S) rats fed a high-salt (2% NaCl) diet.

RESULTS

Blood pressure increased in a time-dependent manner in Dahl S rats fed a high-salt diet. The RUK infusion did not influence the elevation of blood pressure in Dahl S rats. However, the RUK infusion significantly decreased urinary protein excretion, and increased glomerular filtration rate, as compared with untreated high-salt Dahl S rats. Morphological investigation disclosed that the RUK infusion significantly attenuated glomerulosclerosis and arterial and tubular injuries in the kidney of hypertensive Dahl S rats. The RUK infusion produced an increase in urinary excretions of nitric oxide and cyclic guanosine monophosphate. In addition, the RUK infusion enhanced the generation of nitric oxide from the kidney slices. The functional and morphological effects of the RUK infusion on the kidney were completely lessened by co-administration of the bradykinin B2-receptor antagonist, HOE-140.

CONCLUSION

Long-term infusion of subdepressor dose of rat urinary kallikrein attenuates functionally and morphologically the progression of renal injury in Dahl rats susceptible to salt-induced hypertension, and that the protection is mediated by stimulation of bradykinin B2 receptor.

NG-hydroxy-L-arginine and nitric oxide inhibit Caco-2 tumor cell proliferation by distinct mechanisms

The objective of this study was to elucidate the role and mechanism of nitric oxide (NO) synthase (NOS) in modulating the growth of the Caco-2 human colon carcinoma cell line. The two novel observations reported here are, first, that NG-hydroxy-L-arginine (NOHA) inhibits Caco-2 tumor cell proliferation, likely by inhibiting arginase activity, and, second, that NO causes cytostasis by mechanisms that might involve inhibition of ornithine decarboxylase (ODC) activity. Both arginase and ODC are enzymes involved in the conversion of arginine to polyamines required for cell proliferation. Cell growth was monitored by cell count, cell protein analysis, and DNA synthesis. NOHA (1-30 microM) and NO in the form of DETA/NO (1-30 microM) inhibited cell proliferation by 30-85%. The cytostatic effect of NOHA was prevented by addition of excess ornithine, putrescine, spermidine, or spermine to cell cultures, whereas the cytostatic effect of NO (DETA/NO) and alpha-difluoromethylornithine (ODC inhibitor) was unaffected by ornithine but was prevented by putrescine, spermidine, or spermine. The cytostatic effect of NOHA appeared to be independent of its conversion to NO, and the effect of NO appeared to be independent of cGMP. NOHA inhibited urea production by Caco-2 cells and inhibited arginase catalytic activity (85% at 3 microM), whereas NO (DEA/NO and SNAP) inhibited ODC activity (>/=60% at 30 microM) without affecting arginase activity. Coculture of Caco-2 cells with lipopolysaccharide/cytokine-activated rat aortic endothelial cells markedly slowed Caco-2 cell proliferation, and this was blocked by NOS inhibitors. These observations that NOHA and NO may inhibit sequential steps in the arginine-polyamine pathway suggest a novel biological role for NOS in the inhibition of cell proliferation of certain tumor cells and possibly other cell types.

Growth regulation of cultured endothelial cells by inflammatory cytokines: mitogenic, anti-proliferative and cytotoxic effects

The inflammatory cytokines tumor necrosis factor-alpha (TNF alpha) and interleukin-1 alpha (IL-1 alpha) have angiogenic properties but generally inhibit cultured endothelial cell (EC) proliferation. Investigations into the growth-regulatory effects of these two agents on a variety of cultured EC types showed that they exert mitogenic, anti-proliferative or cytotoxic effects depending upon cell type and cytokine combinations. The anti-proliferative effect was distinct from cytotoxicity. Nitric oxide (NO) release from EC, examined as a potential mechanism underlying some of these effects, did not appear to mediate the anti-proliferative effects of these cytokines. However, NO also seemed to have a bimodal effect on EC proliferation depending upon whether the NO was endogenous or exogenous. These data underscore the diversity in cytokine and NO effects on cultured EC which, if reproducible in vivo, may be partly responsible for the variable and sometimes contradictory results obtained with regards to the role of inflammatory cytokines and NO on angiogenesis.

Microenvironmental control of gene expression: implications for tumor angiogenesis, progression, and metastasis

Low oxygen tension (hypoxia) is an important prognostic factor in cancer treatment because it affects tumor formation and malignant progression. Many genes governing these complex processes have been found to be oxygen regulated. This article reviews the present knowledge of hypoxia-inducible gene expression and how this affects angiogenesis, progression, and metastasis. Of particular importance are hypoxia-regulated transcription factors because they can modulate expression of countless different genes. Additional genes analyzed in some detail include those encoding angiogenic growth factors, factors controlling blood flow, and those involved in metastasis. Although hypoxia is generally perceived as a hindrance to cancer therapy, it is possibly exploitable because severe oxygen deficiency is tumor specific. Strategies aimed at using the presence of hypoxia in solid tumors include oxygen sensitive chemotherapy and gene therapy.

Endothelial dysfunction in pulmonary arteries of patients with mild COPD

To investigate whether endothelial dysfunction of pulmonary arteries (PA) is present in patients with mild chronic obstructive pulmonary disease (COPD) and to what extent it is related to the morphological abnormalities of PA, we studied 41 patients who underwent lung resection. Patients were divided into the following groups: nonsmokers (n = 7), smokers with normal lung function (n = 13), and COPD (n = 21). Endothelium-dependent relaxation mediated by nitric oxide was evaluated in vitro in PA rings exposed to cumulative concentrations of acetylcholine (ACh) and ADP. Structural abnormalities of PA were assessed morphometrically. PA of COPD patients developed lower maximal relaxation in response to ADP than both nonsmokers and smokers (P < 0.05 each) and a trend to reduced relaxation in response to ACh (P = 0.08). Maximal relaxation to ADP correlated with the degree of airflow obstruction (r = 0.48, P < 0. 01). Morphometrical analysis of PA revealed thicker intimas, especially in small arteries, in both smokers and COPD compared with nonsmokers (P < 0.05 each). We conclude that endothelial dysfunction of PA is already present in patients with mild COPD. In these patients, as well as in smokers with normal lung function, small arteries show thickened intimas, suggesting that tobacco consumption may play a critical role in the pathogenesis of pulmonary vascular abnormalities in COPD.